WorldWideScience

Sample records for response dispersion models

  1. Advances in real-time technology assessment and emergency response: Close-in atmospheric dispersion modeling and exposure estimation

    International Nuclear Information System (INIS)

    Sims, J.; Lee, R.; McCallen, R.; Lawver, B.; Clark, J.; Rueppel, D.; Sullivan, T.

    1992-07-01

    We have developed a stand-alone, real-time emergency response system to assess and predict the offsite dispersion of particulate releases. We have also developed advanced modeling tools that win expand the capability of the emergency response system to predict nearfield dispersion over complex terrain and around buildings

  2. Ensemble atmospheric dispersion modeling for emergency response consequence assessments

    International Nuclear Information System (INIS)

    Addis, R.P.; Buckley, R.L.

    2003-01-01

    models. This provides a better understanding of the atmosphere and plume behavior than would a single model output. Atmospheric models often give the impression of greater accuracy than the science is capable of delivering. The ensemble approach is a powerful way to reassert the concept of having a family of equally valid solutions, while enabling outliers to be identified. The U.S. Department of Energy's Savannah River Technology Center (SRTC) has participated in RTMOD and ENSEMBLE. SRTC uses the Regional Atmospheric Modeling System (RAMS) and Lagrangian Particle Dispersion Model (LPDM) to provide plume forecasts in real-time for the European grid as described in the figure. The NOAA northern hemispheric model, Global Forecast System (a combination of the medium range forecast and aviation forecast models), is used to provide the initial and boundary conditions for RAMS. The model plume forecast data are sent to the ENSEMBLE WEB page in real-time where they may be compared with other model outputs. SRTC has participated in all the ENSEMBLE exercises in real-time. An example of the ensemble output is shown in the figure, which shows an overlay of the SRTC (crosshatched) initial 60-hour forecast for the plume overlaid on an ensemble of 5 other model outputs. The plume shadings show the level of consensus for a minimum threshold, enabling modelers to determine consensus between models and identify possible outliers. The traditional approach to provide atmospheric consequence assessment tools to aid decision-makers in response to a release from a nuclear facility is to provide a plume output from a particular model. However, the non-unique nature of solutions to the non-linear equations that govern the atmosphere, and the sensitivity of such equations to perturbations in the initial and boundary conditions, results in any single model output being simply one of many viable solutions. As such, the traditional approach does a disservice to decision-makers by inferring greater

  3. Atmospheric dispersion modeling: Challenges of the Fukushima Daiichi response

    Energy Technology Data Exchange (ETDEWEB)

    Sugiyama, Gayle [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Nasstrom, John [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Pobanz, Brenda [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Foster, Kevin [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Simpson, Matthew [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Vogt, Phil [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Aluzzi, Fernando [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Homann, Steve [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2012-05-01

    In this research, the U.S. Department of Energy’s (DOE) National Atmospheric Release Advisory Center (NARAC) provided a wide range of predictions and analyses as part of the response to the Fukushima Daiichi Nuclear Power Plant accident including: daily Japanese weather forecasts and atmospheric transport predictions to inform planning for field monitoring operations and to provide U.S. government agencies with ongoing situational awareness of meteorological conditions; estimates of possible dose in Japan based on hypothetical U.S. Nuclear Regulatory Commission scenarios of potential radionuclide releases to support protective action planning for U.S. citizens; predictions of possible plume arrival times and dose levels at U.S. locations; and source estimation and plume model refinement based on atmospheric dispersion modeling and available monitoring data.

  4. The mesoscale dispersion modeling system a simulation tool for development of an emergency response system

    International Nuclear Information System (INIS)

    Uliasz, M.

    1990-01-01

    The mesoscale dispersion modeling system is under continuous development. The included numerical models require further improvements and evaluation against data from meteorological and tracer field experiments. The system can not be directly applied to real time predictions. However, it seems to be a useful simulation tool for solving several problems related to planning the monitoring network and development of the emergency response system for the nuclear power plant located in a coastal area. The modeling system can be also applied to another environmental problems connected with air pollution dispersion in complex terrain. The presented numerical models are designed for the use on personal computers and are relatively fast in comparison with the similar mesoscale models developed on mainframe computers

  5. A set of rapid-response models for pollutant dispersion assessments in southern Spain coastal waters

    International Nuclear Information System (INIS)

    Perianez, R.; Caravaca, F.

    2010-01-01

    Three rapid-response Lagrangian particle-tracking dispersion models have been developed for southern Spain coastal waters. The three domains cover the Gulf of Cadiz (Atlantic Ocean), the Alboran Sea (Mediterranean), and the Strait of Gibraltar with higher spatial resolution. The models are based on different hydrodynamic submodels, which are run in advance. Tides are calculated using a 2D barotropic model in the three cases. Models used to obtain the residual circulation depend on the physical oceanography of each region. Thus, two-layer models are applied to Gibraltar Strait and Alboran Sea and a 3D baroclinic model is used in the Gulf of Cadiz. Results from these models have been compared with observations to validate them and are then used by the particle-tracking models to calculate dispersion. Chemical, radioactive and oil spills may be simulated, incorporating specific processes for each kind of pollutant. Several application examples are provided.

  6. The Dangers of Dispersal of Responsibilities

    Directory of Open Access Journals (Sweden)

    Adriana Schiopoiu Burlea

    2017-05-01

    Full Text Available Taking into account that it is in the nature of the modern corporation that risks are distributed over several agents, we discuss in this paper the organisational behaviour as it results from such dispersal of responsibilities for both the principal and the agent. We explore the hypothesis that dispersal of responsibilities could be the result or a cause of a lack of consensus between the principal and the agent. Our findings suggest that a dispersal of responsibilities has a negative impact on the principal-agent relationship and that it represents a foundation for theoretical and empirical approaches to organisational behaviour. We find that agent perceptions of a dispersal of responsibilities are linked to his/her resistance to the principal’s interests, but this relationship is deeper than was suggested by previous research. However, if the sharing of responsibilities does not run parallel to that, we may have as a result what we call an agency problem.

  7. Resuspension parameters for TRAC dispersion model

    International Nuclear Information System (INIS)

    Langer, G.

    1987-01-01

    Resuspension factors for the wind erosion of soil contaminated with plutonium are necessary to run the Rocky Flats Plant Terrain Responsive Atmospheric Code (TRAC). The model predicts the dispersion and resulting population dose due to accidental plutonium releases

  8. Discrete dispersion models and their Tweedie asymptotics

    DEFF Research Database (Denmark)

    Jørgensen, Bent; Kokonendji, Célestin C.

    2016-01-01

    The paper introduce a class of two-parameter discrete dispersion models, obtained by combining convolution with a factorial tilting operation, similar to exponential dispersion models which combine convolution and exponential tilting. The equidispersed Poisson model has a special place in this ap......The paper introduce a class of two-parameter discrete dispersion models, obtained by combining convolution with a factorial tilting operation, similar to exponential dispersion models which combine convolution and exponential tilting. The equidispersed Poisson model has a special place...... in this approach, whereas several overdispersed discrete distributions, such as the Neyman Type A, Pólya-Aeppli, negative binomial and Poisson-inverse Gaussian, turn out to be Poisson-Tweedie factorial dispersion models with power dispersion functions, analogous to ordinary Tweedie exponential dispersion models...... with power variance functions. Using the factorial cumulant generating function as tool, we introduce a dilation operation as a discrete analogue of scaling, generalizing binomial thinning. The Poisson-Tweedie factorial dispersion models are closed under dilation, which in turn leads to a Poisson...

  9. MESOI, an interactive atmospheric dispersion model for emergency response applications

    International Nuclear Information System (INIS)

    Ramsdell, J.V.; Athey, G.F.; Glantz, C.S.

    1984-01-01

    MESOI is an interactive atmospheric dispersion model that has been developed for use by the U.S. Department of Energy, and the U.S. Nuclear Regulatory Commission in responding to emergencies at nuclear facilities. MESOI uses both straight-line Gaussian plume and Lagrangian trajectory Gaussian puff models to estimate time-integrated ground-level air and surface concentrations. Puff trajectories are determined from temporally and spatially varying horizontal wind fields that are defined in 3 dimensions. Other processes treated in MESOI include dry deposition, wet deposition and radioactive decay

  10. Low Frequency Dispersion Mechanism of Dielectric Response for Oil-paper Insulation Diagnosis

    Institute of Scientific and Technical Information of China (English)

    ZHOU Lijun; LI Xianlang; WU Guangning

    2013-01-01

    Both the real part and imaginary part of complex permittivity approximately have a log-linear frequency dependency at low frequencies,especially at ultra-low frequencies under conditions of different moisture concentrations and temperatures,which is recognized as the low frequency dispersion (LFD).In order to explain this dispersion,a new mechanism of dielectric response of LFD of oil-paper insulation is proposed.A simplified one-dimensional mathematical model of concentration polarization carrier caused by slow migration is developed and solved,which indicates that ion mobility is closely related to the size of gap and the adsorption capacity of cellulose molecular chains to ions.A stochastic statistical model of the carrier mobility induced LFD is also developed.Moreover,actual tests under 50 ℃and 2% moisture content were put forward,as well as simulations with according current waveforms.The simulation results agreed well with the experimental data in that concentration polarization of carriers caused by slow migration is the probable cause of low frequency dispersion ofdielectric response for oil-paper insulation diagnosis.

  11. Modeling the dispersion effects of contractile fibers in smooth muscles

    Science.gov (United States)

    Murtada, Sae-Il; Kroon, Martin; Holzapfel, Gerhard A.

    2010-12-01

    Micro-structurally based models for smooth muscle contraction are crucial for a better understanding of pathological conditions such as atherosclerosis, incontinence and asthma. It is meaningful that models consider the underlying mechanical structure and the biochemical activation. Hence, a simple mechanochemical model is proposed that includes the dispersion of the orientation of smooth muscle myofilaments and that is capable to capture available experimental data on smooth muscle contraction. This allows a refined study of the effects of myofilament dispersion on the smooth muscle contraction. A classical biochemical model is used to describe the cross-bridge interactions with the thin filament in smooth muscles in which calcium-dependent myosin phosphorylation is the only regulatory mechanism. A novel mechanical model considers the dispersion of the contractile fiber orientations in smooth muscle cells by means of a strain-energy function in terms of one dispersion parameter. All model parameters have a biophysical meaning and may be estimated through comparisons with experimental data. The contraction of the middle layer of a carotid artery is studied numerically. Using a tube the relationships between the internal pressure and the stretches are investigated as functions of the dispersion parameter, which implies a strong influence of the orientation of smooth muscle myofilaments on the contraction response. It is straightforward to implement this model in a finite element code to better analyze more complex boundary-value problems.

  12. Atmospheric dispersion modelling over complex terrain at small scale

    Science.gov (United States)

    Nosek, S.; Janour, Z.; Kukacka, L.; Jurcakova, K.; Kellnerova, R.; Gulikova, E.

    2014-03-01

    Previous study concerned of qualitative modelling neutrally stratified flow over open-cut coal mine and important surrounding topography at meso-scale (1:9000) revealed an important area for quantitative modelling of atmospheric dispersion at small-scale (1:3300). The selected area includes a necessary part of the coal mine topography with respect to its future expansion and surrounding populated areas. At this small-scale simultaneous measurement of velocity components and concentrations in specified points of vertical and horizontal planes were performed by two-dimensional Laser Doppler Anemometry (LDA) and Fast-Response Flame Ionization Detector (FFID), respectively. The impact of the complex terrain on passive pollutant dispersion with respect to the prevailing wind direction was observed and the prediction of the air quality at populated areas is discussed. The measured data will be used for comparison with another model taking into account the future coal mine transformation. Thus, the impact of coal mine transformation on pollutant dispersion can be observed.

  13. Utilities for high performance dispersion model PHYSIC

    International Nuclear Information System (INIS)

    Yamazawa, Hiromi

    1992-09-01

    The description and usage of the utilities for the dispersion calculation model PHYSIC were summarized. The model was developed in the study of developing high performance SPEEDI with the purpose of introducing meteorological forecast function into the environmental emergency response system. The procedure of PHYSIC calculation consists of three steps; preparation of relevant files, creation and submission of JCL, and graphic output of results. A user can carry out the above procedure with the help of the Geographical Data Processing Utility, the Model Control Utility, and the Graphic Output Utility. (author)

  14. Fast Running Urban Dispersion Model for Radiological Dispersal Device (RDD) Releases: Model Description and Validation

    Energy Technology Data Exchange (ETDEWEB)

    Gowardhan, Akshay [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). National Atmospheric Release Advisory Center (NARAC); Neuscamman, Stephanie [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). National Atmospheric Release Advisory Center (NARAC); Donetti, John [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). National Atmospheric Release Advisory Center (NARAC); Walker, Hoyt [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). National Atmospheric Release Advisory Center (NARAC); Belles, Rich [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). National Atmospheric Release Advisory Center (NARAC); Eme, Bill [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). National Atmospheric Release Advisory Center (NARAC); Homann, Steven [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). National Atmospheric Release Advisory Center (NARAC); Simpson, Matthew [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). National Atmospheric Release Advisory Center (NARAC); Nasstrom, John [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). National Atmospheric Release Advisory Center (NARAC)

    2017-05-24

    Aeolus is an efficient three-dimensional computational fluid dynamics code based on finite volume method developed for predicting transport and dispersion of contaminants in a complex urban area. It solves the time dependent incompressible Navier-Stokes equation on a regular Cartesian staggered grid using a fractional step method. It also solves a scalar transport equation for temperature and using the Boussinesq approximation. The model also includes a Lagrangian dispersion model for predicting the transport and dispersion of atmospheric contaminants. The model can be run in an efficient Reynolds Average Navier-Stokes (RANS) mode with a run time of several minutes, or a more detailed Large Eddy Simulation (LES) mode with run time of hours for a typical simulation. This report describes the model components, including details on the physics models used in the code, as well as several model validation efforts. Aeolus wind and dispersion predictions are compared to field data from the Joint Urban Field Trials 2003 conducted in Oklahoma City (Allwine et al 2004) including both continuous and instantaneous releases. Newly implemented Aeolus capabilities include a decay chain model and an explosive Radiological Dispersal Device (RDD) source term; these capabilities are described. Aeolus predictions using the buoyant explosive RDD source are validated against two experimental data sets: the Green Field explosive cloud rise experiments conducted in Israel (Sharon et al 2012) and the Full-Scale RDD Field Trials conducted in Canada (Green et al 2016).

  15. Characterisation of dispersion mechanisms in an urban catchment using a deterministic spatially distributed direct hydrograph travel time model

    Science.gov (United States)

    Rossel, F.; Gironas, J. A.

    2012-12-01

    The link between stream network structure and hydrologic response for natural basins has been extensively studied. It is well known that stream network organization and flow dynamics in the reaches combine to shape the hydrologic response of natural basins. Geomorphologic dispersion and hydrodynamic dispersion along with hillslope processes control to a large extent the overall variance of the hydrograph, particularly under the assumption of constant celerity throughout the basin. In addition, a third mechanism referred as to kinematic dispersion becomes relevant when considering spatial variations of celerity. On contrary, the link between the drainage network structure and overall urban terrain, and the hydrologic response in urban catchments has been much less studied. In particular, the characterization of the different dispersion mechanisms within urban areas remains to be better understood. In such areas artificial elements are expected to contribute to the total dispersion due to the variety of geometries and the spatial distribution of imperviousness. This work quantifies the different dispersion mechanisms in an urban catchment, focusing on their relevance and the spatial scales involved. For this purpose we use the Urban Morpho-climatic Instantaneous Unit Hydrograph model, a deterministic spatially distributed direct hydrograph travel time model, which computes travel times in hillslope, pipe, street and channel cells using formulations derived from kinematic wave theory. The model was applied to the Aubeniere catchment, located in Nantes, France. Unlike stochastic models, this deterministic model allows the quantification of dispersion mechanism at the local scale (i.e. the grid-cell). We found that kinematic dispersion is more relevant for small storm events, whereas geomorphologic dispersion becomes more significant for larger storms, as the mean celerity within the catchment increases. In addition, the total dispersion relates to the drainage area in

  16. Dispersion modeling by kinematic simulation: Cloud dispersion model

    International Nuclear Information System (INIS)

    Fung, J C H; Perkins, R J

    2008-01-01

    A new technique has been developed to compute mean and fluctuating concentrations in complex turbulent flows (tidal current near a coast and deep ocean). An initial distribution of material is discretized into any small clouds which are advected by a combination of the mean flow and large scale turbulence. The turbulence can be simulated either by kinematic simulation (KS) or direct numerical simulation. The clouds also diffuse relative to their centroids; the statistics for this are obtained from a separate calculation of the growth of individual clouds in small scale turbulence, generated by KS. The ensemble of discrete clouds is periodically re-discretized, to limit the size of the small clouds and prevent overlapping. The model is illustrated with simulations of dispersion in uniform flow, and the results are compared with analytic, steady state solutions. The aim of this study is to understand how pollutants disperses in a turbulent flow through a numerical simulation of fluid particle motion in a random flow field generated by Fourier modes. Although this homogeneous turbulent is rather a 'simple' flow, it represents a building block toward understanding pollutant dispersion in more complex flow. The results presented here are preliminary in nature, but we expect that similar qualitative results should be observed in a genuine turbulent flow.

  17. Include dispersion in quantum chemical modeling of enzymatic reactions: the case of isoaspartyl dipeptidase.

    Science.gov (United States)

    Zhang, Hai-Mei; Chen, Shi-Lu

    2015-06-09

    The lack of dispersion in the B3LYP functional has been proposed to be the main origin of big errors in quantum chemical modeling of a few enzymes and transition metal complexes. In this work, the essential dispersion effects that affect quantum chemical modeling are investigated. With binuclear zinc isoaspartyl dipeptidase (IAD) as an example, dispersion is included in the modeling of enzymatic reactions by two different procedures, i.e., (i) geometry optimizations followed by single-point calculations of dispersion (approach I) and (ii) the inclusion of dispersion throughout geometry optimization and energy evaluation (approach II). Based on a 169-atom chemical model, the calculations show a qualitative consistency between approaches I and II in energetics and most key geometries, demonstrating that both approaches are available with the latter preferential since both geometry and energy are dispersion-corrected in approach II. When a smaller model without Arg233 (147 atoms) was used, an inconsistency was observed, indicating that the missing dispersion interactions are essentially responsible for determining equilibrium geometries. Other technical issues and mechanistic characteristics of IAD are also discussed, in particular with respect to the effects of Arg233.

  18. An expert system for dispersion model interpretation

    International Nuclear Information System (INIS)

    Skyllingstad, E.D.; Ramsdell, J.V.

    1988-10-01

    A prototype expert system designed to diagnose dispersion model uncertainty is described in this paper with application to a puff transport model. The system obtains qualitative information from the model user and through an expert-derived knowledge base, performs a rating of the current simulation. These results can then be used in combination with dispersion model output for deciding appropriate evacuation measures. Ultimately, the goal of this work is to develop an expert system that may be operated accurately by an individual uneducated in meteorology or dispersion modeling. 5 refs., 3 figs

  19. Improving practical atmospheric dispersion models

    International Nuclear Information System (INIS)

    Hunt, J.C.R.; Hudson, B.; Thomson, D.J.

    1992-01-01

    The new generation of practical atmospheric dispersion model (for short range ≤ 30 km) are based on dispersion science and boundary layer meteorology which have widespread international acceptance. In addition, recent improvements in computer skills and the widespread availability of small powerful computers make it possible to have new regulatory models which are more complex than the previous generation which were based on charts and simple formulae. This paper describes the basis of these models and how they have developed. Such models are needed to satisfy the urgent public demand for sound, justifiable and consistent environmental decisions. For example, it is preferable that the same models are used to simulate dispersion in different industries; in many countries at present different models are used for emissions from nuclear and fossil fuel power stations. The models should not be so simple as to be suspect but neither should they be too complex for widespread use; for example, at public inquiries in Germany, where simple models are mandatory, it is becoming usual to cite the results from highly complex computational models because the simple models are not credible. This paper is written in a schematic style with an emphasis on tables and diagrams. (au) (22 refs.)

  20. Modeling electrical dispersion phenomena in Earth materials

    Directory of Open Access Journals (Sweden)

    D. Patella

    2008-06-01

    Full Text Available It is illustrated that IP phenomena in rocks can be described using conductivity dispersion models deduced as solutions to a 2nd-order linear differential equation describing the motion of a charged particle immersed in an external electrical field. Five dispersion laws are discussed, namely: the non-resonant positive IP model, which leads to the classical Debye-type dispersion law and by extension to the Cole-Cole model, largely used in current practice; the non-resonant negative IP model, which allows negative chargeability values, known in metals at high frequencies, to be explained as an intrinsic physical property of earth materials in specific field cases; the resonant flat, positive or negative IP models, which can explain the presence of peak effects at specific frequencies superimposed on flat, positive or negative dispersion spectra.

  1. A costal dispersion model

    International Nuclear Information System (INIS)

    Rahm, L.; Nyberg, L.; Gidhagen, L.

    1990-01-01

    A dispersion model to be used off costal waters has been developed. The model has been applied to describe the migration of radionuclides in the Baltic sea. A summary of the results is presented here. (K.A.E)

  2. Dispersal kernel estimation: A comparison of empirical and modelled particle dispersion in a coastal marine system

    Science.gov (United States)

    Hrycik, Janelle M.; Chassé, Joël; Ruddick, Barry R.; Taggart, Christopher T.

    2013-11-01

    Early life-stage dispersal influences recruitment and is of significance in explaining the distribution and connectivity of marine species. Motivations for quantifying dispersal range from biodiversity conservation to the design of marine reserves and the mitigation of species invasions. Here we compare estimates of real particle dispersion in a coastal marine environment with similar estimates provided by hydrodynamic modelling. We do so by using a system of magnetically attractive particles (MAPs) and a magnetic-collector array that provides measures of Lagrangian dispersion based on the time-integration of MAPs dispersing through the array. MAPs released as a point source in a coastal marine location dispersed through the collector array over a 5-7 d period. A virtual release and observed (real-time) environmental conditions were used in a high-resolution three-dimensional hydrodynamic model to estimate the dispersal of virtual particles (VPs). The number of MAPs captured throughout the collector array and the number of VPs that passed through each corresponding model location were enumerated and compared. Although VP dispersal reflected several aspects of the observed MAP dispersal, the comparisons demonstrated model sensitivity to the small-scale (random-walk) particle diffusivity parameter (Kp). The one-dimensional dispersal kernel for the MAPs had an e-folding scale estimate in the range of 5.19-11.44 km, while those from the model simulations were comparable at 1.89-6.52 km, and also demonstrated sensitivity to Kp. Variations among comparisons are related to the value of Kp used in modelling and are postulated to be related to MAP losses from the water column and (or) shear dispersion acting on the MAPs; a process that is constrained in the model. Our demonstration indicates a promising new way of 1) quantitatively and empirically estimating the dispersal kernel in aquatic systems, and 2) quantitatively assessing and (or) improving regional hydrodynamic

  3. Atmospheric dispersion models of radioactivity releases

    International Nuclear Information System (INIS)

    Oza, R.B.

    2016-01-01

    In view of the rapid industrialization in recent time, atmospheric dispersion models have become indispensible 'tools' to ensure that the effects of releases are well within the acceptable limits set by the regulatory authority. In the case of radioactive releases from the nuclear facility, though negligible in quantity and many a times not even measurable, it is required to demonstrate the compliance of these releases to the regulatory limits set by the regulatory authority by carrying out radiological impact assessment. During routine operations of nuclear facility, the releases are so low that environmental impact is usually assessed with the help of atmospheric dispersion models as it is difficult to distinguish negligible contribution of nuclear facility to relatively high natural background radiation. The accidental releases from nuclear facility, though with negligible probability of occurrence, cannot be ruled out. In such cases, the atmospheric dispersion models are of great help to emergency planners for deciding the intervention actions to minimize the consequences in public domain and also to workout strategies for the management of situation. In case of accidental conditions, the atmospheric dispersion models are also utilized for the estimation of probable quantities of radionuclides which might have got released to the atmosphere. Thus, atmospheric dispersion models are an essential tool for nuclear facility during routine operation as well as in the case of accidental conditions

  4. Modelling long-distance seed dispersal in heterogeneous landscapes.

    Energy Technology Data Exchange (ETDEWEB)

    Levey, Douglas, J.; Tewlsbury, Joshua, J.; Bolker, Benjamin, M.

    2008-01-01

    1. Long-distance seed dispersal is difficult to measure, yet key to understanding plant population dynamics and community composition. 2. We used a spatially explicit model to predict the distribution of seeds dispersed long distances by birds into habitat patches of different shapes. All patches were the same type of habitat and size, but varied in shape. They occurred in eight experimental landscapes, each with five patches of four different shapes, 150 m apart in a matrix of mature forest. The model was parameterized with smallscale movement data collected from field observations of birds. In a previous study we validated the model by testing its predictions against observed patterns of seed dispersal in real landscapes with the same types and spatial configuration of patches as in the model. 3. Here we apply the model more broadly, examining how patch shape influences the probability of seed deposition by birds into patches, how dispersal kernels (distributions of dispersal distances) vary with patch shape and starting location, and how movement of seeds between patches is affected by patch shape. 4. The model predicts that patches with corridors or other narrow extensions receive higher numbers of seeds than patches without corridors or extensions. This pattern is explained by edgefollowing behaviour of birds. Dispersal distances are generally shorter in heterogeneous landscapes (containing patchy habitat) than in homogeneous landscapes, suggesting that patches divert the movement of seed dispersers, ‘holding’ them long enough to increase the probability of seed defecation in the patches. Dispersal kernels for seeds in homogeneous landscapes were smooth, whereas those in heterogenous landscapes were irregular. In both cases, long-distance (> 150 m) dispersal was surprisingly common, usually comprising approximately 50% of all dispersal events. 5. Synthesis . Landscape heterogeneity has a large influence on patterns of long-distance seed dispersal. Our

  5. Sensitivity of numerical dispersion modeling to explosive source parameters

    International Nuclear Information System (INIS)

    Baskett, R.L.; Cederwall, R.T.

    1991-01-01

    The calculation of downwind concentrations from non-traditional sources, such as explosions, provides unique challenges to dispersion models. The US Department of Energy has assigned the Atmospheric Release Advisory Capability (ARAC) at the Lawrence Livermore National Laboratory (LLNL) the task of estimating the impact of accidental radiological releases to the atmosphere anywhere in the world. Our experience includes responses to over 25 incidents in the past 16 years, and about 150 exercises a year. Examples of responses to explosive accidents include the 1980 Titan 2 missile fuel explosion near Damascus, Arkansas and the hydrogen gas explosion in the 1986 Chernobyl nuclear power plant accident. Based on judgment and experience, we frequently estimate the source geometry and the amount of toxic material aerosolized as well as its particle size distribution. To expedite our real-time response, we developed some automated algorithms and default assumptions about several potential sources. It is useful to know how well these algorithms perform against real-world measurements and how sensitive our dispersion model is to the potential range of input values. In this paper we present the algorithms we use to simulate explosive events, compare these methods with limited field data measurements, and analyze their sensitivity to input parameters. 14 refs., 7 figs., 2 tabs

  6. Working document dispersion models

    International Nuclear Information System (INIS)

    Dop, H. van

    1988-01-01

    This report is a summary of the most important results from June 1985 of the collaboration of the RIVM (Dutch National Institute for Public Health and Environment Hygiene) and KNMI (Royal Dutch Meteorologic Institute) on the domain of dispersion models. It contains a short description of the actual SO x /NO x -model. Furthermore it contains recommendations for modifications of some numerical-mathematical aspects and an impulse to a more complete description of chemical processes in the atmosphere and the (wet) deposition process. A separate chapter is devoted to the preparation of meteorologic data which are relevant for dispersion as well as atmospheric chemistry and deposition. This report serves as working document for the final formulation of a acidifying- and oxidant-model. (H.W.). 69 refs.; 51 figs.; 13 tabs.; 3 schemes

  7. Modelling airborne dispersion of coarse particulate material

    International Nuclear Information System (INIS)

    Apsley, D.D.

    1989-03-01

    Methods of modelling the airborne dispersion and deposition of coarse particulates are presented, with the emphasis on the heavy particles identified as possible constituents of releases from damaged AGR fuel. The first part of this report establishes the physical characteristics of the irradiated particulate in airborne emissions from AGR stations. The second part is less specific and describes procedures for extending current dispersion/deposition models to incorporate a coarse particulate component: the adjustment to plume spread parameters, dispersion from elevated sources and dispersion in conjunction with building effects and plume rise. (author)

  8. Dispersion Models to Forecast Traffic-related Emissions in Urban Areas

    Directory of Open Access Journals (Sweden)

    Davide Scannapieco

    2011-11-01

    Full Text Available Down the centuries, a direct link had been developed between increase in mobility and increase in wealth. On the other hand, air emission of greenhouse gases (GHG due to vehicles equipped with internal combustion engines can be regarded as a negative pressure over the environment. In the coming decades, road transport is likely to remain a significant contributor to air pollution in cities. Many urban trips cover distances of less than 6 km. Since the effectiveness of catalytic converters in the initial minutes of engine operation is small, the average emission per distance driven is very high in urban areas. Also, poorly maintained vehicles that lack exhaust aftertreatment systems are responsible for a major part of pollutant emissions. Therefore in urban areas, where higher concentrations of vehicles can be easily found, air pollution represents a critical issue, being it related with both environment and human health protection: in truth, research in recent decades consistently indicates the adverse effects of outdoor air pollution on human health, and the evidence points to air pollution stemming from transport as an important contributor to these effects. Several institutions (EEA, USEPA, etc. focused their interest in dispersion models because of their potential effectiveness to forecast atmospheric pollution. Furthermore, air micropollutants such as Polycyclic Aromatic Compounds (PAH and Metallic Trace Elements (MTE are traffic-related and although very low concentrations their dispersion is a serious issue. However, dispersion models are usefully implemented to better manage this estimation problem. Nonetheless, policy makers and land managers have to deal with model selection, taking into account that several dispersion models are available, each one of them focused on specific goals (e.g., wind transport of pollutants, land morphology implementation, evaluation of micropollutants transport, etc.; a further aspect to be considered is

  9. Accident consequence assessments with different atmospheric dispersion models

    International Nuclear Information System (INIS)

    Panitz, H.J.

    1989-11-01

    An essential aim of the improvements of the new program system UFOMOD for Accident Consequence Assessments (ACAs) was to substitute the straight-line Gaussian plume model conventionally used in ACA models by more realistic atmospheric dispersion models. To identify improved models which can be applied in ACA codes and to quantify the implications of different dispersion models on the results of an ACA, probabilistic comparative calculations with different atmospheric dispersion models have been performed. The study showed that there are trajectory models available which can be applied in ACAs and that they provide more realistic results of ACAs than straight-line Gaussian models. This led to a completely novel concept of atmospheric dispersion modelling in which two different distance ranges of validity are distinguished: the near range of some ten kilometres distance and the adjacent far range which are assigned to respective trajectory models. (orig.) [de

  10. Modelling of pollution dispersion in atmosphere

    International Nuclear Information System (INIS)

    Borysiewicz, M.; Stankiewicz, R.

    1994-01-01

    The paper contains the review of the mathematical foundation of atmospheric dispersion models. The atmospheric phenomena relevant to atmospheric dispersion model are discussed. In particular the parametrization of processes with time and space scales smaller than numerical grid size, limited by available computer power, is presented. The special attention was devoted to similarity theory and parametrization of boundary layer. The numerical methods are analysed and the drawbacks of the method are presented. (author). 99 refs, 15 figs, 3 tabs

  11. A dispersion modelling system for urban air pollution

    Energy Technology Data Exchange (ETDEWEB)

    Karppinen, A.; Kukkonen, J.; Nordlund, G.; Rantakrans, E.; Valkama, I.

    1998-10-01

    An Urban Dispersion Modelling system UDM-FMI, developed at the Finnish Meteorological Institute is described in the report. The modelling system includes a multiple source Gaussian plume model and a meteorological pre-processing model. The dispersion model is an integrated urban scale model, taking into account of all source categories (point, line, area and volume sources). It includes a treatment of chemical transformation (for NO{sub 2}) wet and dry deposition (for SO{sub 2}) plume rise, downwash phenomena and dispersion of inert particles. The model allows also for the influence of a finite mixing height. The model structure is mainly based on the state-of-the-art methodology. The system also computes statistical parameters from the time series, which can be compared to air quality guidelines. The relevant meteorological parameters for the dispersion model are evaluated using data produced by a meteorological pre-processor. The model is based mainly on the energy budget method. Results of national investigations have been used for evaluating climate-dependent parameters. The model utilises the synoptic meteorological observations, radiation records and aerological sounding observations. The model results include the hourly time series of the relevant atmospheric turbulence 51 refs.

  12. Meteorological uncertainty of atmospheric dispersion model results (MUD)

    International Nuclear Information System (INIS)

    Havskov Soerensen, J.; Amstrup, B.; Feddersen, H.

    2013-08-01

    The MUD project addresses assessment of uncertainties of atmospheric dispersion model predictions, as well as possibilities for optimum presentation to decision makers. Previously, it has not been possible to estimate such uncertainties quantitatively, but merely to calculate the 'most likely' dispersion scenario. However, recent developments in numerical weather prediction (NWP) include probabilistic forecasting techniques, which can be utilised also for long-range atmospheric dispersion models. The ensemble statistical methods developed and applied to NWP models aim at describing the inherent uncertainties of the meteorological model results. These uncertainties stem from e.g. limits in meteorological observations used to initialise meteorological forecast series. By perturbing e.g. the initial state of an NWP model run in agreement with the available observational data, an ensemble of meteorological forecasts is produced from which uncertainties in the various meteorological parameters are estimated, e.g. probabilities for rain. Corresponding ensembles of atmospheric dispersion can now be computed from which uncertainties of predicted radionuclide concentration and deposition patterns can be derived. (Author)

  13. NARAC Dispersion Model Product Integration With RadResponder

    Energy Technology Data Exchange (ETDEWEB)

    Aluzzi, Fernando [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2015-09-30

    Work on enhanced cooperation and interoperability of Nuclear Incident Response Teams (NIRT) is a joint effort between DHS/FEMA, DOE/NNSA and EPA. One such effort was the integration between the RadResponder Network, a resource sponsored by FEMA for the management of radiological data during an emergency, and the National Atmospheric Advisory Center (NARAC), a DOE/NNSA modeling resource whose predictions are used to aid radiological emergency preparedness and response. Working together under a FEMA-sponsored project these two radiological response assets developed a capability to read and display plume model prediction results from the NARAC computer system in the RadResponder software tool. As a result of this effort, RadResponder users have been provided with NARAC modeling predictions of contamination areas, radiological dose levels, and protective action areas (e.g., areas warranting worker protection or sheltering/evacuation) to help guide protective action decisions and field monitoring surveys, and gain key situation awareness following a radiological/nuclear accident or incident (e.g., nuclear power plant accident, radiological dispersal device incident, or improvised nuclear detonation incident). This document describes the details of this integration effort.

  14. Chaotic Lagrangian models for turbulent relative dispersion.

    Science.gov (United States)

    Lacorata, Guglielmo; Vulpiani, Angelo

    2017-04-01

    A deterministic multiscale dynamical system is introduced and discussed as a prototype model for relative dispersion in stationary, homogeneous, and isotropic turbulence. Unlike stochastic diffusion models, here trajectory transport and mixing properties are entirely controlled by Lagrangian chaos. The anomalous "sweeping effect," a known drawback common to kinematic simulations, is removed through the use of quasi-Lagrangian coordinates. Lagrangian dispersion statistics of the model are accurately analyzed by computing the finite-scale Lyapunov exponent (FSLE), which is the optimal measure of the scaling properties of dispersion. FSLE scaling exponents provide a severe test to decide whether model simulations are in agreement with theoretical expectations and/or observation. The results of our numerical experiments cover a wide range of "Reynolds numbers" and show that chaotic deterministic flows can be very efficient, and numerically low-cost, models of turbulent trajectories in stationary, homogeneous, and isotropic conditions. The mathematics of the model is relatively simple, and, in a geophysical context, potential applications may regard small-scale parametrization issues in general circulation models, mixed layer, and/or boundary layer turbulence models as well as Lagrangian predictability studies.

  15. Modeling of atmospheric dispersion of radionuclides

    International Nuclear Information System (INIS)

    Baklouti, Nada

    2010-01-01

    This work is a prediction of atmospheric dispersion of radionuclide from a chronic rejection of the nuclear power generating plant that can be located in one of the Tunisian sites: Skhira or Bizerte. Also it contains a study of acute rejection 'Chernobyl accident' which was the reference for the validation of GENII the code of modeling of atmospheric dispersion.

  16. Lagrangian Stochastic Dispersion Model IMS Model Suite and its Validation against Experimental Data

    International Nuclear Information System (INIS)

    Bartok, J.

    2010-01-01

    The dissertation presents IMS Lagrangian Dispersion Model, which is a 'new generation' Slovak dispersion model of long-range transport, developed by MicroStep-MIS. It solves trajectory equation for a vast number of Lagrangian 'particles' and stochastic equation that simulates the effects of turbulence. Model contains simulation of radioactive decay (full decay chains of more than 300 nuclides), and dry and wet deposition. Model was integrated into IMS Model Suite, a system in which several models and modules can run and cooperate, e.g. LAM model WRF preparing fine resolution meteorological data for dispersion. The main theme of the work is validation of dispersion model against large scale international campaigns CAPTEX and ETEX, which are two of the largest tracer experiments. Validation addressed treatment of missing data, data interpolation into comparable temporal and spatial representation. The best model results were observed for ETEX I, standard results for CAPTEXes and worst results for ETEX II, known in modelling community for its meteorological conditions that can be hardly resolved by models. The IMS Lagrangian Dispersion Model was identified as capable long range dispersion model for slowly- or nonreacting chemicals and radioactive matter. Influence of input data on simulation quality is discussed within the work. Additional modules were prepared according to praxis requirement: a) Recalculation of concentrations of radioactive pollutant into effective doses form inhalation, immersion in the plume and deposition. b) Dispersion of mineral dust was added and tested in desert locality, where wind and soil moisture were firstly analysed and forecast by WRF. The result was qualitatively verified in case study against satellite observations. (author)

  17. Modelling surface radioactive spill dispersion in the Alboran Sea

    International Nuclear Information System (INIS)

    Perianez, R.

    2006-01-01

    The Strait of Gibraltar and the Alboran Sea are the only connection between the Atlantic Ocean and the Mediterranean Sea. Intense shipping activities occur in the area, including transport of waste radionuclides and transit of nuclear submarines. Thus, it is relevant to have a dispersion model that can be used in an emergency situation after an accident, to help the decision-making process. Such dispersion model requires an appropriate description of the physical oceanography of the region of interest, with simulations of tides and residual (average) circulation. In this work, a particle-tracking dispersion model that can be used to simulate the dispersion of radionuclides in the system Strait of Gibraltar-Alboran Sea is described. Tides are simulated using a barotropic model and for the average circulation a reduced-gravity model is applied. This model is able to reproduce the main features of the Alboran circulation (the well known Western Alboran Gyre, WAG, and the coastal circulation mode). The dispersion model is run off-line, using previously computed tidal and residual currents. The contamination patch is simulated by a number of particles whose individual paths are computed; diffusion and decay being modelled using a Monte Carlo method. Radionuclide concentrations may be obtained from the density of particles per water volume unit. Results from the hydrodynamic models have been compared with observations in the area. Several examples of dispersion computations under different wind and circulation conditions are presented

  18. Dispersion bias, dispersion effect, and the aerosol-cloud conundrum

    International Nuclear Information System (INIS)

    Liu Yangang; Daum, Peter H; Guo Huan; Peng Yiran

    2008-01-01

    This work examines the influences of relative dispersion (the ratio of the standard deviation to the mean radius of the cloud droplet size distribution) on cloud albedo and cloud radiative forcing, derives an analytical formulation that accounts explicitly for the contribution from droplet concentration and relative dispersion, and presents a new approach to parameterize relative dispersion in climate models. It is shown that inadequate representation of relative dispersion in climate models leads to an overestimation of cloud albedo, resulting in a negative bias of global mean shortwave cloud radiative forcing that can be comparable to the warming caused by doubling CO 2 in magnitude, and that this dispersion bias is likely near its maximum for ambient clouds. Relative dispersion is empirically expressed as a function of the quotient between cloud liquid water content and droplet concentration (i.e., water per droplet), yielding an analytical formulation for the first aerosol indirect effect. Further analysis of the new expression reveals that the dispersion effect not only offsets the cooling from the Twomey effect, but is also proportional to the Twomey effect in magnitude. These results suggest that unrealistic representation of relative dispersion in cloud parameterization in general, and evaluation of aerosol indirect effects in particular, is at least in part responsible for several outstanding puzzles of the aerosol-cloud conundrum: for example, overestimation of cloud radiative cooling by climate models compared to satellite observations; large uncertainty and discrepancy in estimates of the aerosol indirect effect; and the lack of interhemispheric difference in cloud albedo.

  19. Biophysical models of larval dispersal in the Benguela Current ...

    African Journals Online (AJOL)

    We synthesise and update results from the suite of biophysical, larval-dispersal models developed in the Benguela Current ecosystem. Biophysical models of larval dispersal use outputs of physical hydrodynamic models as inputs to individual-based models in which biological processes acting during the larval life are ...

  20. Meteorological uncertainty of atmospheric dispersion model results (MUD)

    Energy Technology Data Exchange (ETDEWEB)

    Havskov Soerensen, J.; Amstrup, B.; Feddersen, H. [Danish Meteorological Institute, Copenhagen (Denmark)] [and others

    2013-08-15

    The MUD project addresses assessment of uncertainties of atmospheric dispersion model predictions, as well as possibilities for optimum presentation to decision makers. Previously, it has not been possible to estimate such uncertainties quantitatively, but merely to calculate the 'most likely' dispersion scenario. However, recent developments in numerical weather prediction (NWP) include probabilistic forecasting techniques, which can be utilised also for long-range atmospheric dispersion models. The ensemble statistical methods developed and applied to NWP models aim at describing the inherent uncertainties of the meteorological model results. These uncertainties stem from e.g. limits in meteorological observations used to initialise meteorological forecast series. By perturbing e.g. the initial state of an NWP model run in agreement with the available observational data, an ensemble of meteorological forecasts is produced from which uncertainties in the various meteorological parameters are estimated, e.g. probabilities for rain. Corresponding ensembles of atmospheric dispersion can now be computed from which uncertainties of predicted radionuclide concentration and deposition patterns can be derived. (Author)

  1. Dispersive processes in models of regional radionuclide migration. Technical memorandum

    International Nuclear Information System (INIS)

    Evenson, D.E.; Dettinger, M.D.

    1980-05-01

    Three broad areas of concern in the development of aquifer scale transport models will be local scale diffusion and dispersion processes, regional scale dispersion processes, and numerical problems associated with the advection-dispersion equation. Local scale dispersion processes are fairly well understood and accessible to observation. These processes will generally be dominated in large scale systems by regional processes, or macro-dispersion. Macro-dispersion is primarily the result of large scale heterogeneities in aquifer properties. In addition, the effects of many modeling approximations are often included in the process. Because difficulties arise in parameterization of this large scale phenomenon, parameterization should be based on field measurements made at the same scale as the transport process of interest or else partially circumvented through the application of a probabilistic advection model. Other problems associated with numerical transport models include difficulties with conservation of mass, stability, numerical dissipation, overshoot, flexibility, and efficiency. We recommend the random-walk model formulation for Lawrence Livermore Laboratory's purposes as the most flexible, accurate and relatively efficient modeling approach that overcomes these difficulties

  2. Presentation of Austrians recommended dispersion model for tunnel portals

    Energy Technology Data Exchange (ETDEWEB)

    Oettl, D.; Sturm, P.; Almbauer, R. [Inst. for Internal Combustion Engines and Thermodynamics, Graz Univ. of Technology (Austria)

    2004-07-01

    Street tunnels in cities are often suggested as solution to avoid daily congestions but also to prevent residential areas from high noise and air pollution emissions. In case of longitudinal ventilated tunnels high pollution levels may occur in the vicinity of the portals. The dispersion of pollutants from tunnel portals is considered to differ significantly from those of other sources, such as line or point sources. To the best of the authors knowledge, there exist currently two distinct dispersion models, which are especially designed to treat dispersion from tunnel portals. Okamoto et al proposed a diagnostic wind field model, where the dispersion is modelled using a Taylor-Galerkin-Forester filter method. Oettl et al. developed a Lagrangian-type model (GRAL TM 3.5=Graz Lagrangian model Tunnel Module version 3.5), which is briefly described in the next section. (orig.)

  3. Stochastic models for atmospheric dispersion

    DEFF Research Database (Denmark)

    Ditlevsen, Ove Dalager

    2003-01-01

    Simple stochastic differential equation models have been applied by several researchers to describe the dispersion of tracer particles in the planetary atmospheric boundary layer and to form the basis for computer simulations of particle paths. To obtain the drift coefficient, empirical vertical...... positions close to the boundaries. Different rules have been suggested in the literature with justifications based on simulation studies. Herein the relevant stochastic differential equation model is formulated in a particular way. The formulation is based on the marginal transformation of the position...... velocity distributions that depend on height above the ground both with respect to standard deviation and skewness are substituted into the stationary Fokker/Planck equation. The particle position distribution is taken to be uniform *the well/mixed condition( and also a given dispersion coefficient...

  4. Development of local-scale high-resolution atmospheric dispersion model using large-eddy simulation. Part 3: turbulent flow and plume dispersion in building arrays

    Czech Academy of Sciences Publication Activity Database

    Nakayama, H.; Jurčáková, Klára; Nagai, H.

    2013-01-01

    Roč. 50, č. 5 (2013), s. 503-519 ISSN 0022-3131 Institutional support: RVO:61388998 Keywords : local-scale high-resolution dispersion model * nuclear emergency response system * large-eddy simulation * spatially developing turbulent boundary layer flow Subject RIV: DG - Athmosphere Sciences, Meteorology Impact factor: 1.452, year: 2013

  5. A hybrid plume model for local-scale dispersion

    Energy Technology Data Exchange (ETDEWEB)

    Nikmo, J.; Tuovinen, J.P.; Kukkonen, J.; Valkama, I.

    1997-12-31

    The report describes the contribution of the Finnish Meteorological Institute to the project `Dispersion from Strongly Buoyant Sources`, under the `Environment` programme of the European Union. The project addresses the atmospheric dispersion of gases and particles emitted from typical fires in warehouses and chemical stores. In the study only the `passive plume` regime, in which the influence of plume buoyancy is no longer important, is addressed. The mathematical model developed and its numerical testing is discussed. The model is based on atmospheric boundary-layer scaling theory. In the vicinity of the source, Gaussian equations are used in both the horizontal and vertical directions. After a specified transition distance, gradient transfer theory is applied in the vertical direction, while the horizontal dispersion is still assumed to be Gaussian. The dispersion parameters and eddy diffusivity are modelled in a form which facilitates the use of a meteorological pre-processor. Also a new model for the vertical eddy diffusivity (K{sub z}), which is a continuous function of height in the various atmospheric scaling regions is presented. The model includes a treatment of the dry deposition of gases and particulate matter, but wet deposition has been neglected. A numerical solver for the atmospheric diffusion equation (ADE) has been developed. The accuracy of the numerical model was analysed by comparing the model predictions with two analytical solutions of ADE. The numerical deviations of the model predictions from these analytic solutions were less than two per cent for the computational regime. The report gives numerical results for the vertical profiles of the eddy diffusivity and the dispersion parameters, and shows spatial concentration distributions in various atmospheric conditions 39 refs.

  6. Mathematical modeling of disperse two-phase flows

    CERN Document Server

    Morel, Christophe

    2015-01-01

    This book develops the theoretical foundations of disperse two-phase flows, which are characterized by the existence of bubbles, droplets or solid particles finely dispersed in a carrier fluid, which can be a liquid or a gas. Chapters clarify many difficult subjects, including modeling of the interfacial area concentration. Basic knowledge of the subjects treated in this book is essential to practitioners of Computational Fluid Dynamics for two-phase flows in a variety of industrial and environmental settings. The author provides a complete derivation of the basic equations, followed by more advanced subjects like turbulence equations for the two phases (continuous and disperse) and multi-size particulate flow modeling. As well as theoretical material, readers will discover chapters concerned with closure relations and numerical issues. Many physical models are presented, covering key subjects including heat and mass transfers between phases, interfacial forces and fluid particles coalescence and breakup, a...

  7. Modelling solute dispersion in periodic heterogeneous porous media: Model benchmarking against intermediate scale experiments

    Science.gov (United States)

    Majdalani, Samer; Guinot, Vincent; Delenne, Carole; Gebran, Hicham

    2018-06-01

    This paper is devoted to theoretical and experimental investigations of solute dispersion in heterogeneous porous media. Dispersion in heterogenous porous media has been reported to be scale-dependent, a likely indication that the proposed dispersion models are incompletely formulated. A high quality experimental data set of breakthrough curves in periodic model heterogeneous porous media is presented. In contrast with most previously published experiments, the present experiments involve numerous replicates. This allows the statistical variability of experimental data to be accounted for. Several models are benchmarked against the data set: the Fickian-based advection-dispersion, mobile-immobile, multirate, multiple region advection dispersion models, and a newly proposed transport model based on pure advection. A salient property of the latter model is that its solutions exhibit a ballistic behaviour for small times, while tending to the Fickian behaviour for large time scales. Model performance is assessed using a novel objective function accounting for the statistical variability of the experimental data set, while putting equal emphasis on both small and large time scale behaviours. Besides being as accurate as the other models, the new purely advective model has the advantages that (i) it does not exhibit the undesirable effects associated with the usual Fickian operator (namely the infinite solute front propagation speed), and (ii) it allows dispersive transport to be simulated on every heterogeneity scale using scale-independent parameters.

  8. Gold Nanospheres Dispersed Light Responsive Epoxy Vitrimers

    Directory of Open Access Journals (Sweden)

    Zhenhua Wang

    2018-01-01

    Full Text Available Vitrimers represent a new class of smart materials. They are covalently crosslinked like thermosets, yet they can be reprocessed like thermoplastics. The underlying mechanism is the rapid exchange reactions which form new bonds while breaking the old ones. So far, heating is the most widely used stimulus to activate the exchange reaction. Compared to heating, light not only is much more convenient to achieve remote and regional control, but can also offer fast healing. Gold nanospheres are excellent photothermal agents, but they are difficult to disperse into vitrimers as they easily aggregate. In this paper, we use polydopamine to prepare gold nanospheres. The resultant polydopamine-coated gold nanospheres (GNS can be well dispersed into epoxy vitrimers, endowing epoxy vitrimers with light responsivity. The composites can be reshaped permanently and temporarily with light at different intensity. Efficient surface patterning and healing are also demonstrated.

  9. Response surface analysis to improve dispersed crude oil biodegradation

    Energy Technology Data Exchange (ETDEWEB)

    Zahed, Mohammad A.; Aziz, Hamidi A.; Mohajeri, Leila [School of Civil Engineering, Universiti Sains Malaysia, Nibong Tebal, Penang (Malaysia); Isa, Mohamed H. [Civil Engineering Department, Universiti Teknologi PETRONAS, Tronoh, Perak (Malaysia)

    2012-03-15

    In this research, the bioremediation of dispersed crude oil, based on the amount of nitrogen and phosphorus supplementation in the closed system, was optimized by the application of response surface methodology and central composite design. Correlation analysis of the mathematical-regression model demonstrated that a quadratic polynomial model could be used to optimize the hydrocarbon bioremediation (R{sup 2} = 0.9256). Statistical significance was checked by analysis of variance and residual analysis. Natural attenuation was removed by 22.1% of crude oil in 28 days. The highest removal on un-optimized condition of 68.1% were observed by using nitrogen of 20.00 mg/L and phosphorus of 2.00 mg/L in 28 days while optimization process exhibited a crude oil removal of 69.5% via nitrogen of 16.05 mg/L and phosphorus 1.34 mg/L in 27 days therefore optimization can improve biodegradation in shorter time with less nutrient consumption. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  10. Modeling of corium dispersion in DCH accidents

    International Nuclear Information System (INIS)

    Wu, Q.

    1996-01-01

    A model that governs the dispersion process in the direct containment heating (DCH) reactor accident scenario is developed by a stepwise approach. In this model, the whole transient is subdivided into four phases with an isothermal assumption. These are the liquid and gas discharge, the liquid film flow in the cavity before gas blowdown, the liquid and gas flow in the cavity with droplet entrainment, and the liquid transport and re-entrainment in the subcompartment. In each step, the dominant driving mechanisms are identified to construct the governing equations. By combining all the steps together, the corium dispersion information is obtained in detail. The key parameters are predicted quantitatively. These include the fraction of liquid that flows out of the cavity before gas blowdown, the dispersion fraction and the mean droplet diameter in the cavity, the cavity pressure rise due to the liquid friction force, and the dispersion fractions in the containment via different paths. Compared with the data of the 1:10 scale experiments carried out at Purdue University, fairly good agreement is obtained. A stand-alone prediction of the corium dispersion under prototypic Zion reactor conditions is carried out by assuming an isothermal process without chemical reactions. (orig.)

  11. Comparative calculations and validation studies with atmospheric dispersion models

    International Nuclear Information System (INIS)

    Paesler-Sauer, J.

    1986-11-01

    This report presents the results of an intercomparison of different mesoscale dispersion models and measured data of tracer experiments. The types of models taking part in the intercomparison are Gaussian-type, numerical Eulerian, and Lagrangian dispersion models. They are suited for the calculation of the atmospherical transport of radionuclides released from a nuclear installation. For the model intercomparison artificial meteorological situations were defined and corresponding arithmetical problems were formulated. For the purpose of model validation real dispersion situations of tracer experiments were used as input data for model calculations; in these cases calculated and measured time-integrated concentrations close to the ground are compared. Finally a valuation of the models concerning their efficiency in solving the problems is carried out by the aid of objective methods. (orig./HP) [de

  12. Evaluation of the hydrodynamic behaviour of turbulence promoters in parallel plate electrochemical reactors by means of the dispersion model

    International Nuclear Information System (INIS)

    Colli, A.N.; Bisang, J.M.

    2011-01-01

    Highlights: · The type of turbulence promoters has a strong influence on the hydrodynamics. · The dispersion model is appropriate for expanded plastic turbulence promoters. · The dispersion model is appropriate for glass beads turbulence promoters. - Abstract: The hydrodynamic behaviour of electrochemical reactors with parallel plate electrodes is experimentally studied using the stimulus-response method either with an empty reactor or with different turbulence promoters. Theoretical results which are in accordance with the analytical and numerical resolution of the dispersion model for a closed system are compared with the classical relationships of the normalized outlet concentration for open systems and the validity range of the equations is discussed. The experimental results were well correlated with the dispersion model using glass beads or expanded plastic meshes as turbulence promoters, which have shown the most advantageous performance. The Peclet number was higher than 63. The dispersion coefficient was found to increase linearly with flow velocity in these cases.

  13. Offshore and coastal dispersion (OCD) model. Users guide

    International Nuclear Information System (INIS)

    Hanna, S.R.; Schulman, L.L.; Paine, R.J.; Pleim, J.E.

    1984-09-01

    The Offshore and Coastal Dispersion (OCD) model was adapted from the EPA guideline model MPTER to simulate the effect of offshore emissions from point sources in coastal regions. Modifications were made to incorporate overwater plume transport and dispersion as well as changes that occur as the plume crosses the shoreline. Hourly meteorological data are needed from overwater and overland locations. Turbulence intensities are used but are not mandatory. For overwater dispersion, the turbulence intensities are parameterized from boundary-layer similarity relationships if they are not measured. Specifications of emission characteristics and receptor locations are the same as for MPTER; 250 point sources and 180 receptors may be used

  14. Meteorological Uncertainty of atmospheric Dispersion model results (MUD)

    DEFF Research Database (Denmark)

    Havskov Sørensen, Jens; Amstrup, Bjarne; Feddersen, Henrik

    The MUD project addresses assessment of uncertainties of atmospheric dispersion model predictions, as well as optimum presentation to decision makers. Previously, it has not been possible to estimate such uncertainties quantitatively, but merely to calculate the 'most likely' dispersion scenario....

  15. Debris Dispersion Model Using Java 3D

    Science.gov (United States)

    Thirumalainambi, Rajkumar; Bardina, Jorge

    2004-01-01

    This paper describes web based simulation of Shuttle launch operations and debris dispersion. Java 3D graphics provides geometric and visual content with suitable mathematical model and behaviors of Shuttle launch. Because the model is so heterogeneous and interrelated with various factors, 3D graphics combined with physical models provides mechanisms to understand the complexity of launch and range operations. The main focus in the modeling and simulation covers orbital dynamics and range safety. Range safety areas include destruct limit lines, telemetry and tracking and population risk near range. If there is an explosion of Shuttle during launch, debris dispersion is explained. The shuttle launch and range operations in this paper are discussed based on the operations from Kennedy Space Center, Florida, USA.

  16. Review of potential models for UF6 dispersion

    International Nuclear Information System (INIS)

    Sykes, R.I.; Lewellen, W.S.

    1992-07-01

    A survey of existing atmospheric dispersion models has been conducted to determine the most appropriate basis for the development of a model for predicting the consequences of an accidental UF 6 release. The model is required for safety analysis studies and should therefore be computationally efficient. The release of UF 6 involves a number of physical phenomena which make the situation more complicated than passive dispersion of a trace gas. The safety analysis must consider the density variations in the UF 6 cloud, which can be heavier or lighter than the ambient air. The release also involves rapid chemical reactions and associated heat release, which must be modeled. Other Department of Energy storage facilities require a dense gas prediction capability, so the model must be sufficiently general for use with a variety of release scenarios. The special problems associated with UF 6 make it unique, so there are very few models with existing capability for the problem. There are, however, a large number of dense gas dispersion models, some with relevant chemical reaction modeling, that could potentially form the basis of an advanced UF 6 model. We have examined a large selection of possible candidates, and selected 5 models for detailed consideration

  17. Evaluation of uncertainties in selected environmental dispersion models

    International Nuclear Information System (INIS)

    Little, C.A.; Miller, C.W.

    1979-01-01

    Compliance with standards of radiation dose to the general public has necessitated the use of dispersion models to predict radionuclide concentrations in the environment due to releases from nuclear facilities. Because these models are only approximations of reality and because of inherent variations in the input parameters used in these models, their predictions are subject to uncertainty. Quantification of this uncertainty is necessary to assess the adequacy of these models for use in determining compliance with protection standards. This paper characterizes the capabilities of several dispersion models to predict accurately pollutant concentrations in environmental media. Three types of models are discussed: aquatic or surface water transport models, atmospheric transport models, and terrestrial and aquatic food chain models. Using data published primarily by model users, model predictions are compared to observations

  18. Distributed emergency response system to model dispersion and deposition of atmospheric releases

    International Nuclear Information System (INIS)

    Taylor, S.S.

    1985-04-01

    Aging hardware and software and increasing commitments by the Departments of Energy and Defense have led us to develop a new, expanded system to replace the existing Atmospheric Release Advisory Capability (ARAC) system. This distributed, computer-based, emergency response system is used by state and federal agencies to assess the environmental health hazards resulting from an accidental release of radioactive material into the atmosphere. Like its predecessor, the expanded system uses local meteorology (e.g., wind speed and wind direction), as well as terrain information, to simulate the transport and dispersion of the airborne material. The system also calculates deposition and dose and displays them graphically over base maps of the local geography for use by on-site authorities. This paper discusses the limitations of the existing ARAC system. It also discusses the components and functionality of the new system, the technical difficulties encountered and resolved in its design and implementation, and the software methodologies and tools employed in its development

  19. Applications of the PUFF model to forecasts of volcanic clouds dispersal from Etna and Vesuvio

    Science.gov (United States)

    Daniele, P.; Lirer, L.; Petrosino, P.; Spinelli, N.; Peterson, R.

    2009-05-01

    PUFF is a numerical volcanic ash tracking model developed to simulate the behaviour of ash clouds in the atmosphere. The model uses wind field data provided by meteorological models and adds dispersion and sedimentation physics to predict the evolution of the cloud once it reaches thermodynamic equilibrium with the atmosphere. The software is intended for use in emergency response situations during an eruption to quickly forecast the position and trajectory of the ash cloud in the near (˜1-72 h) future. In this paper, we describe the first application of the PUFF model in forecasting volcanic ash dispersion from the Etna and Vesuvio volcanoes. We simulated the daily occurrence of an eruptive event of Etna utilizing ash cloud parameters describing the paroxysm of 22nd July 1998 and wind field data for the 1st September 2005-31st December 2005 time span from the Global Forecast System (GFS) model at the approximate location of the Etna volcano (38N 15E). The results show that volcanic ash particles are dispersed in a range of directions in response to changing wind field at various altitudes and that the ash clouds are mainly dispersed toward the east and southeast, although the exact trajectory is highly variable, and can change within a few hours. We tested the sensitivity of the model to the mean particle grain size and found that an increased concentration of ash particles in the atmosphere results when the mean grain size is decreased. Similarly, a dramatic variation in dispersion results when the logarithmic standard deviation of the particle-size distribution is changed. Additionally, we simulated the occurrence of an eruptive event at both Etna and Vesuvio, using the same parameters describing the initial volcanic plume, and wind field data recorded for 1st September 2005, at approximately 38N 15E for Etna and 41N 14E for Vesuvio. The comparison of the two simulations indicates that identical eruptions occurring at the same time at the two volcanic centres

  20. One-dimensional Analytical Modelling of Floating Seed Dispersal in Tidal Channels

    Science.gov (United States)

    Shi, W.; Purnama, A.; Shao, D.; Cui, B.; Gao, W.

    2017-12-01

    Seed dispersal is a primary factor influencing plant community development, and thus plays a critical role in maintaining wetland ecosystem functioning. However, compared with fluvial seed dispersal of riparian plants, dispersal of saltmarsh plant seeds in tidal channels is much less studied due to its complex behavior, and relevant mathematical modelling is particularly lacking. In this study, we developed a one-dimensional advection-dispersion model to explore the patterns of tidal seed dispersal. Oscillatory tidal current and water depth were assumed to represent the tidal effects. An exponential decay coefficient λ was introduced to account for seed deposition and retention. Analytical solution in integral form was derived using Green's function and further evaluated using numerical integration. The developed model was applied to simulate Spartina densiflora seed dispersal in a tidal channel located at the Mad River Slough in North Humboldt Bay, California, USA, to demonstrate its practical applicability. Model predictions agree satisfactorily with field observation and simulation results from Delft3D numerical model. Sensitivity analyses were also conducted to evaluate the effects of varying calibrated parameters on model predictions. The range of the seed dispersion as well as the distribution of the seed concentration were further analyzed through statistical parameters such as centroid displacement and variance of the seed cloud together with seed concentration contours. Implications of the modelling results on tidal marsh restoration and protection, e.g., revegetation through seed addition, were also discussed through scenario analysis. The developed analytical model provides a useful tool for ecological management of tidal marshes.

  1. LNG vapor dispersion prediction with the DEGADIS dense-gas dispersion model. Topical report, April 1988-July 1990. Documentation

    International Nuclear Information System (INIS)

    Havens, J.; Spicer, T.

    1990-09-01

    The topical report is one of a series on the development of methods for LNG vapor dispersion prediction for regulatory application. The results indicate that the DEGADIS model is superior both phenomenologically and in performance to the Gaussian line source model promulgated in 49 CFR 193 for LNG vapor dispersion simulation. Availability of the DEGADIS model for VAX and IBM-PC formats provides for wider use of the model and greater potential for industry and regulatory acceptance. The acceptance is seen as an important interim objective while research continues on vapor dispersion estimation methods which provide for effects of vapor detention systems, turbulence induced by plant structure, and plant/area topographical features

  2. Mixing height derived from the DMI-HIRLAM NWP model, and used for ETEX dispersion modelling

    Energy Technology Data Exchange (ETDEWEB)

    Soerensen, J.H.; Rasmussen, A. [Danish Meteorological Inst., Copenhagen (Denmark)

    1997-10-01

    For atmospheric dispersion modelling it is of great significance to estimate the mixing height well. Mesoscale and long-range diffusion models using output from numerical weather prediction (NWP) models may well use NWP model profiles of wind, temperature and humidity in computation of the mixing height. This is dynamically consistent, and enables calculation of the mixing height for predicted states of the atmosphere. In autumn 1994, the European Tracer Experiment (ETEX) was carried out with the objective to validate atmospheric dispersion models. The Danish Meteorological Institute (DMI) participates in the model evaluations with the Danish Emergency Response Model of the Atmosphere (DERMA) using NWP model data from the DMI version of the High Resolution Limited Area Model (HIRLAM) as well as from the global model of the European Centre for Medium-Range Weather Forecast (ECMWF). In DERMA, calculation of mixing heights are performed based on a bulk Richardson number approach. Comparing with tracer gas measurements for the first ETEX experiment, a sensitivity study is performed for DERMA. Using DMI-HIRLAM data, the study shows that optimum values of the critical bulk Richardson number in the range 0.15-0.35 are adequate. These results are in agreement with recent mixing height verification studies against radiosonde data. The fairly large range of adequate critical values is a signature of the robustness of the method. Direct verification results against observed missing heights from operational radio-sondes released under the ETEX plume are presented. (au) 10 refs.

  3. Numerical models and their role in emergency response: a perspective on dispersion modeling for emergency preparedness

    International Nuclear Information System (INIS)

    Greenly, G.D.; Dickerson, M.H.

    1983-03-01

    Numerical models on several levels of complexity should be available to the emergency response planner. They are a basic tool but must be used in conjunction with both measurements and experience. When these tools are used in a complimentary fashion they greatly enhance the capability of the consequence manager to respond in an emergency situation. Because each accident or incident develops it's own characteristics and requirements the system must be capable of a flexible response. Interaction and feedback between model results from a suite of models and measurements (including airborne measurements) serve the emergency response planner's spectrum of needs, ranging from planning exercises and emergency precalculations to a real-time emergency response

  4. Dispersion Modeling Using Ensemble Forecasts Compared to ETEX Measurements.

    Science.gov (United States)

    Straume, Anne Grete; N'dri Koffi, Ernest; Nodop, Katrin

    1998-11-01

    Numerous numerical models are developed to predict long-range transport of hazardous air pollution in connection with accidental releases. When evaluating and improving such a model, it is important to detect uncertainties connected to the meteorological input data. A Lagrangian dispersion model, the Severe Nuclear Accident Program, is used here to investigate the effect of errors in the meteorological input data due to analysis error. An ensemble forecast, produced at the European Centre for Medium-Range Weather Forecasts, is then used as model input. The ensemble forecast members are generated by perturbing the initial meteorological fields of the weather forecast. The perturbations are calculated from singular vectors meant to represent possible forecast developments generated by instabilities in the atmospheric flow during the early part of the forecast. The instabilities are generated by errors in the analyzed fields. Puff predictions from the dispersion model, using ensemble forecast input, are compared, and a large spread in the predicted puff evolutions is found. This shows that the quality of the meteorological input data is important for the success of the dispersion model. In order to evaluate the dispersion model, the calculations are compared with measurements from the European Tracer Experiment. The model manages to predict the measured puff evolution concerning shape and time of arrival to a fairly high extent, up to 60 h after the start of the release. The modeled puff is still too narrow in the advection direction.

  5. Modelling surface radioactive spill dispersion in the Alborán Sea.

    Science.gov (United States)

    Periáñez, R

    2006-01-01

    The Strait of Gibraltar and the Alborán Sea are the only connection between the Atlantic Ocean and the Mediterranean Sea. Intense shipping activities occur in the area, including transport of waste radionuclides and transit of nuclear submarines. Thus, it is relevant to have a dispersion model that can be used in an emergency situation after an accident, to help the decision-making process. Such dispersion model requires an appropriate description of the physical oceanography of the region of interest, with simulations of tides and residual (average) circulation. In this work, a particle-tracking dispersion model that can be used to simulate the dispersion of radionuclides in the system Strait of Gibraltar-Alborán Sea is described. Tides are simulated using a barotropic model and for the average circulation a reduced-gravity model is applied. This model is able to reproduce the main features of the Alborán circulation (the well known Western Alborán Gyre, WAG, and the coastal circulation mode). The dispersion model is run off-line, using previously computed tidal and residual currents. The contamination patch is simulated by a number of particles whose individual paths are computed; diffusion and decay being modelled using a Monte Carlo method. Radionuclide concentrations may be obtained from the density of particles per water volume unit. Results from the hydrodynamic models have been compared with observations in the area. Several examples of dispersion computations under different wind and circulation conditions are presented.

  6. Computer modelling of contaminant migration in natural disperse media

    International Nuclear Information System (INIS)

    Kundas, S.P.; Gishkelyuk, I.A.; Khil'ko, O.S.

    2012-01-01

    The theoretical foundations for modeling of the contaminants migration in natural disperses media taking into account interconnected heat and moisture transport are developed. The calculation of mass transfer parameters based on adsorption isotherms of water and thermodynamic equations in the developed mathematical models. The artificial neural networks use to predict migration of contaminants in natural disperse media is proposed. The developed software package is presented and results of practical application of models and software are discussed. (authors)

  7. Essays on pricing dynamics, price dispersion, and nested logit modelling

    Science.gov (United States)

    Verlinda, Jeremy Alan

    The body of this dissertation comprises three standalone essays, presented in three respective chapters. Chapter One explores the possibility that local market power contributes to the asymmetric relationship observed between wholesale costs and retail prices in gasoline markets. I exploit an original data set of weekly gas station prices in Southern California from September 2002 to May 2003, and take advantage of highly detailed station and local market-level characteristics to determine the extent to which spatial differentiation influences price-response asymmetry. I find that brand identity, proximity to rival stations, bundling and advertising, operation type, and local market features and demographics each influence a station's predicted asymmetric relationship between prices and wholesale costs. Chapter Two extends the existing literature on the effect of market structure on price dispersion in airline fares by modeling the effect at the disaggregate ticket level. Whereas past studies rely on aggregate measures of price dispersion such as the Gini coefficient or the standard deviation of fares, this paper estimates the entire empirical distribution of airline fares and documents how the shape of the distribution is determined by market structure. Specifically, I find that monopoly markets favor a wider distribution of fares with more mass in the tails while duopoly and competitive markets exhibit a tighter fare distribution. These findings indicate that the dispersion of airline fares may result from the efforts of airlines to practice second-degree price discrimination. Chapter Three adopts a Bayesian approach to the problem of tree structure specification in nested logit modelling, which requires a heavy computational burden in calculating marginal likelihoods. I compare two different techniques for estimating marginal likelihoods: (1) the Laplace approximation, and (2) reversible jump MCMC. I apply the techniques to both a simulated and a travel mode

  8. An overview of experimental results and dispersion modelling of nanoparticles in the wake of moving vehicles

    International Nuclear Information System (INIS)

    Carpentieri, Matteo; Kumar, Prashant; Robins, Alan

    2011-01-01

    Understanding the transformation of nanoparticles emitted from vehicles is essential for developing appropriate methods for treating fine scale particle dynamics in dispersion models. This article provides an overview of significant research work relevant to modelling the dispersion of pollutants, especially nanoparticles, in the wake of vehicles. Literature on vehicle wakes and nanoparticle dispersion is reviewed, taking into account field measurements, wind tunnel experiments and mathematical approaches. Field measurements and modelling studies highlighted the very short time scales associated with nanoparticle transformations in the first stages after the emission. These transformations strongly interact with the flow and turbulence fields immediately behind the vehicle, hence the need of characterising in detail the mixing processes in the vehicle wake. Very few studies have analysed this interaction and more research is needed to build a basis for model development. A possible approach is proposed and areas of further investigation identified. - Research highlights: → Nanoparticle emissions experience very short transformation time scales. → Vehicle wakes need to be characterised to analyse nanoparticle dispersion. → Fast response measurements of nanoparticle evolution in vehicle wakes are very rare. → Wind tunnel methodologies can be further improved to include nanoparticle dynamics. → A simple mathematical approach has been proposed for future development. - The transformation of nanoparticles and the flow characteristics in both the near and far wake regions must be understood in order to develop mathematical models.

  9. Spatially varying dispersion to model breakthrough curves.

    Science.gov (United States)

    Li, Guangquan

    2011-01-01

    Often the water flowing in a karst conduit is a combination of contaminated water entering at a sinkhole and cleaner water released from the limestone matrix. Transport processes in the conduit are controlled by advection, mixing (dilution and dispersion), and retention-release. In this article, a karst transport model considering advection, spatially varying dispersion, and dilution (from matrix seepage) is developed. Two approximate Green's functions are obtained using transformation of variables, respectively, for the initial-value problem and for the boundary-value problem. A numerical example illustrates that mixing associated with strong spatially varying conduit dispersion can cause strong skewness and long tailing in spring breakthrough curves. Comparison of the predicted breakthrough curve against that measured from a dye-tracing experiment between Ames Sink and Indian Spring, Northwest Florida, shows that the conduit dispersivity can be as large as 400 m. Such a large number is believed to imply strong solute interaction between the conduit and the matrix and/or multiple flow paths in a conduit network. It is concluded that Taylor dispersion is not dominant in transport in a karst conduit, and the complicated retention-release process between mobile- and immobile waters may be described by strong spatially varying conduit dispersion. Copyright © 2010 The Author(s). Journal compilation © 2010 National Ground Water Association.

  10. Dense-gas dispersion advection-diffusion model

    International Nuclear Information System (INIS)

    Ermak, D.L.

    1992-07-01

    A dense-gas version of the ADPIC particle-in-cell, advection- diffusion model was developed to simulate the atmospheric dispersion of denser-than-air releases. In developing the model, it was assumed that the dense-gas effects could be described in terms of the vertically-averaged thermodynamic properties and the local height of the cloud. The dense-gas effects were treated as a perturbation to the ambient thermodynamic properties (density and temperature), ground level heat flux, turbulence level (diffusivity), and windfield (gravity flow) within the local region of the dense-gas cloud. These perturbations were calculated from conservation of energy and conservation of momentum principles along with the ideal gas law equation of state for a mixture of gases. ADPIC, which is generally run in conjunction with a mass-conserving wind flow model to provide the advection field, contains all the dense-gas modifications within it. This feature provides the versatility of coupling the new dense-gas ADPIC with alternative wind flow models. The new dense-gas ADPIC has been used to simulate the atmospheric dispersion of ground-level, colder-than-ambient, denser-than-air releases and has compared favorably with the results of field-scale experiments

  11. Finite-element time-domain modeling of electromagnetic data in general dispersive medium using adaptive Padé series

    Science.gov (United States)

    Cai, Hongzhu; Hu, Xiangyun; Xiong, Bin; Zhdanov, Michael S.

    2017-12-01

    The induced polarization (IP) method has been widely used in geophysical exploration to identify the chargeable targets such as mineral deposits. The inversion of the IP data requires modeling the IP response of 3D dispersive conductive structures. We have developed an edge-based finite-element time-domain (FETD) modeling method to simulate the electromagnetic (EM) fields in 3D dispersive medium. We solve the vector Helmholtz equation for total electric field using the edge-based finite-element method with an unstructured tetrahedral mesh. We adopt the backward propagation Euler method, which is unconditionally stable, with semi-adaptive time stepping for the time domain discretization. We use the direct solver based on a sparse LU decomposition to solve the system of equations. We consider the Cole-Cole model in order to take into account the frequency-dependent conductivity dispersion. The Cole-Cole conductivity model in frequency domain is expanded using a truncated Padé series with adaptive selection of the center frequency of the series for early and late time. This approach can significantly increase the accuracy of FETD modeling.

  12. Atmospheric dispersion modeling at the Rocky Flats Plant. Progress report, December 1981-December 1985

    International Nuclear Information System (INIS)

    Hodgin, C.R.

    1986-01-01

    The Rocky Flats Plant applies atmospheric dispersion modeling as a tool for Emergency Response, Risk Assessment, and Regulatory Compliance. Extreme variations in terrain around the facility have necessitated the development of an advanced modeling approach. The Terrain-Responsive Atmospheric Code (TRAC) was developed to treat realistically the changing wind, stability, dispersion, and deposition patterns that are experienced in mountainous areas. The result is a detailed picture of dose and deposition patterns associated with postulated or actual releases. A unified approach was taken to modeling needs at Rocky Flats. This produces consistent dose projections for all applications. A Risk Assessment version of TRAC is now operational. A high-speed version of the code is being implemented for Emergency Response, and development of a regulatory version is under way. Public, scientific, and governmental acceptance of TRAC is critical to successful applications at the Rocky Flats Plant. A program of peer review and regulatory approval was initiated to provide a full outside evaluation of our techniques. Full field validation (tracer testing) is key to demonstrating reliability of the TRAC model. A validation study was planned for implementation beginning in early CY-1986. The necessary funding ($500,000) is being sought. Although the TRAC model development and approval program was developed for site-specific needs at the Rocky Flats Plant, potential exists for wider application within the Department of Energy (DOE). The TRAC model can be easily applied at other sites in complex terrain. A coordinated approach to model validation throughout the Albquerque Operations Office (AL) or DOE complexes could prove more cost effective than site-by-site evaluations. Finally, the model approval procedure developed jointly by Rocky Flats and the Environmental Protection Agency (EPA) is general and could be applied to other models or as the basis for a DOE-wide program

  13. Model-based dispersive wave processing: A recursive Bayesian solution

    International Nuclear Information System (INIS)

    Candy, J.V.; Chambers, D.H.

    1999-01-01

    Wave propagation through dispersive media represents a significant problem in many acoustic applications, especially in ocean acoustics, seismology, and nondestructive evaluation. In this paper we propose a propagation model that can easily represent many classes of dispersive waves and proceed to develop the model-based solution to the wave processing problem. It is shown that the underlying wave system is nonlinear and time-variable requiring a recursive processor. Thus the general solution to the model-based dispersive wave enhancement problem is developed using a Bayesian maximum a posteriori (MAP) approach and shown to lead to the recursive, nonlinear extended Kalman filter (EKF) processor. The problem of internal wave estimation is cast within this framework. The specific processor is developed and applied to data synthesized by a sophisticated simulator demonstrating the feasibility of this approach. copyright 1999 Acoustical Society of America.

  14. Toxicity of dispersant application: Biomarkers responses in gills of juvenile golden grey mullet (Liza aurata).

    Science.gov (United States)

    Milinkovitch, Thomas; Godefroy, Joachim; Théron, Michaël; Thomas-Guyon, Hélène

    2011-10-01

    Dispersant use in nearshore areas is likely to increase the exposure of aquatic organisms to petroleum. To measure the toxicity of this controversial response technique, golden grey mullets (Liza aurata) were exposed to mechanically dispersed oil, chemically dispersed oil, dispersant alone in seawater, water-soluble fraction of oil and to seawater as a control treatment. Several biomarkers were assessed in the gills (enzymatic antioxidant activities, glutathione content, lipid peroxidation) and in the gallbladder (polycylic aromatic hydrocarbons metabolites). The significant differences between chemically dispersed oil and water soluble fraction of oil highlight the environmental risk to disperse an oil slick when containment and recovery can be conducted. The lack of significance between chemically and mechanically dispersed oil suggests that dispersant application is no more toxic than the natural dispersion of the oil slick. The results of this study are of interest in order to establish dispersant use policies in nearshore areas. Copyright © 2011 Elsevier Ltd. All rights reserved.

  15. A 'Puff' dispersion model for routine and accidental releases

    International Nuclear Information System (INIS)

    Grsic, Z.; Rajkovic, B.; Milutinovic, P.

    1999-01-01

    A Puff dispersion model for accidental or routine releases is presented. This model was used as a constitutive part of an automatic meteorological station.All measured quantities are continuously displayed on PC monitor in a digital and graphical form, they are averaging every 10 minutes and sending to the civil information center of Belgrade. In the paper simulation of a pollutant plume dispersion from The oil refinery 'Pancevo', on April 18 th 1999 is presented. (author)

  16. Modelling Pollutant Dispersion in a Street Network

    Science.gov (United States)

    Salem, N. Ben; Garbero, V.; Salizzoni, P.; Lamaison, G.; Soulhac, L.

    2015-04-01

    This study constitutes a further step in the analysis of the performances of a street network model to simulate atmospheric pollutant dispersion in urban areas. The model, named SIRANE, is based on the decomposition of the urban atmosphere into two sub-domains: the urban boundary layer, whose dynamics is assumed to be well established, and the urban canopy, represented as a series of interconnected boxes. Parametric laws govern the mass exchanges between the boxes under the assumption that the pollutant dispersion within the canopy can be fully simulated by modelling three main bulk transfer phenomena: channelling along street axes, transfers at street intersections, and vertical exchange between street canyons and the overlying atmosphere. Here, we aim to evaluate the reliability of the parametrizations adopted to simulate these phenomena, by focusing on their possible dependence on the external wind direction. To this end, we test the model against concentration measurements within an idealized urban district whose geometrical layout closely matches the street network represented in SIRANE. The analysis is performed for an urban array with a fixed geometry and a varying wind incidence angle. The results show that the model provides generally good results with the reference parametrizations adopted in SIRANE and that its performances are quite robust for a wide range of the model parameters. This proves the reliability of the street network approach in simulating pollutant dispersion in densely built city districts. The results also show that the model performances may be improved by considering a dependence of the wind fluctuations at street intersections and of the vertical exchange velocity on the direction of the incident wind. This opens the way for further investigations to clarify the dependence of these parameters on wind direction and street aspect ratios.

  17. Operational mesoscale atmospheric dispersion prediction using high performance parallel computing cluster for emergency response

    International Nuclear Information System (INIS)

    Srinivas, C.V.; Venkatesan, R.; Muralidharan, N.V.; Das, Someshwar; Dass, Hari; Eswara Kumar, P.

    2005-08-01

    An operational atmospheric dispersion prediction system is implemented on a cluster super computer for 'Online Emergency Response' for Kalpakkam nuclear site. The numerical system constitutes a parallel version of a nested grid meso-scale meteorological model MM5 coupled to a random walk particle dispersion model FLEXPART. The system provides 48 hour forecast of the local weather and radioactive plume dispersion due to hypothetical air borne releases in a range of 100 km around the site. The parallel code was implemented on different cluster configurations like distributed and shared memory systems. Results of MM5 run time performance for 1-day prediction are reported on all the machines available for testing. A reduction of 5 times in runtime is achieved using 9 dual Xeon nodes (18 physical/36 logical processors) compared to a single node sequential run. Based on the above run time results a cluster computer facility with 9-node Dual Xeon is commissioned at IGCAR for model operation. The run time of a triple nested domain MM5 is about 4 h for 24 h forecast. The system has been operated continuously for a few months and results were ported on the IMSc home page. Initial and periodic boundary condition data for MM5 are provided by NCMRWF, New Delhi. An alternative source is found to be NCEP, USA. These two sources provide the input data to the operational models at different spatial and temporal resolutions and using different assimilation methods. A comparative study on the results of forecast is presented using these two data sources for present operational use. Slight improvement is noticed in rainfall, winds, geopotential heights and the vertical atmospheric structure while using NCEP data probably because of its high spatial and temporal resolution. (author)

  18. Toward a unified description of nonlinearity and frequency dispersion of piezoelectric and dielectric responses in Pb(Zr,Ti)O3

    International Nuclear Information System (INIS)

    Damjanovic, D.; Bharadwaja, S.S.N.; Setter, N.

    2005-01-01

    A phenomenological approach is proposed describing both nonlinearity and frequency dispersion in dielectric and piezoelectric properties of lead zirconate titanate, Pb(Zr,Ti)O 3 (PZT), thin films and ceramics. The approach couples the frequency dependent response in form of the power law, 1/ω β , with the rate-independent nonlinear response described by the Rayleigh law. The main experimental trends are well described by the model

  19. Atmospheric dispersion models help to improve air quality; Los modelos de dispersion atmosferica ayudan a mejorar la calidad del aire

    Energy Technology Data Exchange (ETDEWEB)

    Martin, F.

    2013-07-01

    One of the main challenges of the atmospheric sciences is to reproduce as well as possible the phenomena and processes of pollutants in the atmosphere. To do it, mathematical models based in this case on fluid dynamics and mass and energy conservation equations, equations that govern the atmospheric chemistry, etc., adapted to the spatial scales to be simulated, are developed. The dispersion models simulate the processes of transport, dispersion, chemical transformation and elimination by deposition that air pollutants undergo once they are emitted. Atmospheric dispersion models with their multiple applications have become essential tools for the air quality management. (Author)

  20. A real-time monitoring/emergency response workstation using a 3-D numerical model initialized with SODAR

    International Nuclear Information System (INIS)

    Lawver, B.S.; Sullivan, T.J.; Baskett, R.L.

    1993-01-01

    Many workstation based emergency response dispersion modeling systems provide simple Gaussian models driven by single meteorological tower inputs to estimate the downwind consequences from accidental spills or stack releases. Complex meteorological or terrain settings demand more sophisticated resolution of the three-dimensional structure of the atmosphere to reliably calculate plume dispersion. Mountain valleys and sea breeze flows are two common examples of such settings. To address these complexities, we have implemented the three-dimensional-diagnostic MATHEW mass-adjusted wind field and ADPIC particle-in-cell dispersion models on a workstation for use in real-time emergency response modeling. Both MATHEW and ADPIC have shown their utility in a variety of complex settings over the last 15 years within the Department of Energy's Atmospheric Release Advisory Capability project

  1. Application of air pollution dispersion modeling for source-contribution assessment and model performance evaluation at integrated industrial estate-Pantnagar

    Energy Technology Data Exchange (ETDEWEB)

    Banerjee, T., E-mail: tirthankaronline@gmail.com [Department of Environmental Science, G.B. Pant University of Agriculture and Technology, Pantnagar, U.S. Nagar, Uttarakhand 263 145 (India); Barman, S.C., E-mail: scbarman@yahoo.com [Department of Environmental Monitoring, Indian Institute of Toxicology Research, Post Box No. 80, Mahatma Gandhi Marg, Lucknow-226 001, Uttar Pradesh (India); Srivastava, R.K., E-mail: rajeevsrivastava08@gmail.com [Department of Environmental Science, G.B. Pant University of Agriculture and Technology, Pantnagar, U.S. Nagar, Uttarakhand 263 145 (India)

    2011-04-15

    Source-contribution assessment of ambient NO{sub 2} concentration was performed at Pantnagar, India through simulation of two urban mathematical dispersive models namely Gaussian Finite Line Source Model (GFLSM) and Industrial Source Complex Model (ISCST-3) and model performances were evaluated. Principal approaches were development of comprehensive emission inventory, monitoring of traffic density and regional air quality and conclusively simulation of urban dispersive models. Initially, 18 industries were found responsible for emission of 39.11 kg/h of NO{sub 2} through 43 elevated stacks. Further, vehicular emission potential in terms of NO{sub 2} was computed as 7.1 kg/h. Air quality monitoring delineates an annual average NO{sub 2} concentration of 32.6 {mu}g/m{sup 3}. Finally, GFLSM and ISCST-3 were simulated in conjunction with developed emission inventories and existing meteorological conditions. Models simulation indicated that contribution of NO{sub 2} from industrial and vehicular source was in a range of 45-70% and 9-39%, respectively. Further, statistical analysis revealed satisfactory model performance with an aggregate accuracy of 61.9%. - Research highlights: > Application of dispersion modeling for source-contribution assessment of ambient NO{sub 2}. > Inventorization revealed emission from industry and vehicles was 39.11 and 7.1 kg/h. > GFLSM revealed that vehicular pollution contributes a range of 9.0-38.6%. > Source-contribution of 45-70% was found for industrial emission through ISCST-3. > Aggregate performance of both models shows good agreement with an accuracy of 61.9%. - Development of industrial and vehicular inventory in terms of ambient NO{sub 2} for model simulation at Pantnagar, India and model validation revealed satisfactory outcome.

  2. A model for long-distance dispersal of boll weevils (Coleoptera: Curculionidae)

    Science.gov (United States)

    Westbrook, John K.; Eyster, Ritchie S.; Allen, Charles T.

    2011-07-01

    The boll weevil, Anthonomus grandis (Boheman), has been a major insect pest of cotton production in the US, accounting for yield losses and control costs on the order of several billion US dollars since the introduction of the pest in 1892. Boll weevil eradication programs have eliminated reproducing populations in nearly 94%, and progressed toward eradication within the remaining 6%, of cotton production areas. However, the ability of weevils to disperse and reinfest eradicated zones threatens to undermine the previous investment toward eradication of this pest. In this study, the HYSPLIT atmospheric dispersion model was used to simulate daily wind-aided dispersal of weevils from the Lower Rio Grande Valley (LRGV) of southern Texas and northeastern Mexico. Simulated weevil dispersal was compared with weekly capture of weevils in pheromone traps along highway trap lines between the LRGV and the South Texas / Winter Garden zone of the Texas Boll Weevil Eradication Program. A logistic regression model was fit to the probability of capturing at least one weevil in individual pheromone traps relative to specific values of simulated weevil dispersal, which resulted in 60.4% concordance, 21.3% discordance, and 18.3% ties in estimating captures and non-captures. During the first full year of active eradication with widespread insecticide applications in 2006, the dispersal model accurately estimated 71.8%, erroneously estimated 12.5%, and tied 15.7% of capture and non-capture events. Model simulations provide a temporal risk assessment over large areas of weevil reinfestation resulting from dispersal by prevailing winds. Eradication program managers can use the model risk assessment information to effectively schedule and target enhanced trapping, crop scouting, and insecticide applications.

  3. Evaluation of atmospheric dispersion/consequence models supporting safety analysis

    International Nuclear Information System (INIS)

    O'Kula, K.R.; Lazaro, M.A.; Woodard, K.

    1996-01-01

    Two DOE Working Groups have completed evaluation of accident phenomenology and consequence methodologies used to support DOE facility safety documentation. The independent evaluations each concluded that no one computer model adequately addresses all accident and atmospheric release conditions. MACCS2, MATHEW/ADPIC, TRAC RA/HA, and COSYMA are adequate for most radiological dispersion and consequence needs. ALOHA, DEGADIS, HGSYSTEM, TSCREEN, and SLAB are recommended for chemical dispersion and consequence applications. Additional work is suggested, principally in evaluation of new models, targeting certain models for continued development, training, and establishing a Web page for guidance to safety analysts

  4. A Deformation Model of TRU Metal Dispersion Fuel Rod for HYPER

    International Nuclear Information System (INIS)

    Lee, Byoung Oon; Hwang, Woan; Park, Won S.

    2002-01-01

    Deformation analysis in fuel rod design is essential to assure adequate fuel performance and integrity under irradiation conditions. An in-reactor performance computer code for a dispersion fuel rod is being developed in the conceptual design stage of blanket fuel for HYPER. In this paper, a mechanistic deformation model was developed and the model was installed into the DIMAC program. The model was based on the elasto-plasticity theory and power-law creep theory. The preliminary deformation calculation results for (TRU-Zr)-Zr dispersion fuel predicted by DIMAC were compared with those of silicide dispersion fuel predicted by DIFAIR. It appeared that the deformation levels for (TRU-Zr)-Zr dispersion fuel were relatively higher than those of silicide fuel. Some experimental tests including in-pile and out-pile experiments are needed for verifying the predictive capability of the DIMAC code. An in-reactor performance analysis computer code for blanket fuel is being developed at the conceptual design stage of blanket fuel for HYPER. In this paper, a mechanistic deformation model was developed and the model was installed into the DIMAC program. The model was based on the elasto-plasticity theory and power-law creep theory. The preliminary deformation calculation results for (TRUZr)- Zr dispersion fuel predicted by DIMAC were compared with those of silicide dispersion fuel predicted by DIFAIR. It appears that the deformation by swelling within fuel meat is very large for both fuels, and the major deformation mechanism at cladding is creep. The swelling strain is almost constant within the fuel meat, and is assumed to be zero in the cladding made of HT9. It is estimated that the deformation levels for (TRU-Zr)-Zr dispersion fuel were relatively higher than those of silicide fuel, and the dispersion fuel performance may be limited by swelling. But the predicted volume change of the (TRU-Zr)-Zr dispersion fuel models is about 6.1% at 30 at.% burnup. The value of cladding

  5. Modeling the generation and dispersion of odors from mushroom composting facilities

    International Nuclear Information System (INIS)

    Heinemann, P.; Wahanik, D.

    1998-01-01

    An odor source generation model and an odor dispersion model were developed to predict the local distribution of odors emanating from mushroom composting facilities. The odor source generation model allowed for simulation of various composting wharf configurations and odor source strengths. This model was linked to a Gaussian plume diffusion model that predicted odor dispersion. Dimethyl disulfide production at a rate of 1760 micrograms/h was simulated by the source generation model and six different atmospheric conditions were analyzed to demonstrate the effect of wind speed, atmospheric stability, and source generation on the dispersion of this odor producing compound. Detectable levels of dimethyl disulfide were predicted to range from less than 100 m from the source during very unstable conditions to almost 5000 m during very stable conditions

  6. Lagrangian modelling of dispersion, sedimentation and resuspension processes in marine environments

    International Nuclear Information System (INIS)

    Gidhagen, L.; Rahm, L.; Nyberg, L.

    1989-01-01

    The model is based on a modified Langevin's equation which simulates the turbulent crossflow velocity fluctuations in shear flows. The velocity and turbulence fields used are generated by a 2-dimensional hydrodynamical model including a k-ε turbulence scheme. Since the dispersion model is formulated for only low particle concentrations, it is decoupled from the hydrodynamical model calculations. A great drawback in conventional dispersion modelling is the more or less unavoidable numerical diffusion. The use of a Lagrangian particle model will avoid this effect and the resulting too low concentrations for a given release. One consequence is a more realistic distribution of deposited particles. However, with regard to the overall deposition rates the simulated sedimentation process agrees well with well-established advection/diffusion model formulations. With a modified hydrodynamic model, the dispersion model can directly be applied to stratified 3D simulations. (orig./HP) [de

  7. A model for the dispersion of pollution from a road network

    Energy Technology Data Exchange (ETDEWEB)

    Haerkoenen, J.; Valkonen, E.; Kukkonen, J.; Rantakarans, E.; Lahtinen, K.; Karppinen, A.; Jalkanen, L.

    1996-12-31

    A mathematical model for predicting the dispersion of pollution from a road network, for use in a regulatory context is presented in the report. The model includes an emission model a treatment of the meteorological and background concentration time series, a dispersion model statistical analysis of the computed time series of concentrations and a Windows-based user interface. The dispersion model is based on a partly analytical solution of the Gaussian diffusion equation for a finite dine source. It allows for any wind direction with respect to the road. The dispersion parameters are modelled in a form which facilitates the use of the meteorological preprocessor. The chemical transformation is modelled by using a modified form of the discrete parcel method, developed in this study. The chemistry model contains the basic reactions of nitrogen oxides, oxygen and ozone. An operational model for evaluating the meteorological and background concentration data for the model applications is also presented. The model does not take into account the influence of buildings and inhomogeneous terrain on the dispersion processes. The validity of the mathematical solution presented has been tested against a more detailed numerical model. The overall differences are reasonable, and the solution can be used with confidence in an operational model. The program has been implemented on a personal computer and on a main-frame computer, and in the later case also executed on a Cray C94 supercomputer. The validation of the model against experimental data is reported elsewhere. Testing of the model near a major road Turunvaeylae Finland 1994 showed that the overall agreement of the measured and predicted values for NO{sub x} and NO{sub 2} concentrations was fairly good 30 refs.

  8. Real-time monitoring/emergency response modeling workstation for a tritium facility

    International Nuclear Information System (INIS)

    Lawver, B.S.; Sims, J.M.; Baskett, R.L.

    1993-01-01

    At Lawrence Livermore National Laboratory (LLNL) we have developed a real-time system to monitor two stacks on our tritium handling facility. The monitors transmit the stack data to a workstation, which computes a three-dimensional numerical model of atmospheric dispersion. The workstation also collects surface and upper air data from meteorological towers and a sodar. The complex meteorological and terrain setting in the Livermore Valley demands more sophisticated resolution of the three-dimensional structure of the atmosphere to reliably calculate plume dispersion than afforded by Gaussian models. We experience both mountain valley and sea breeze flows. To address these complexities, we have implemented the three-dimensional diagnostic MATHEW mass-adjusted wind field and ADPIC particle-in-cell dispersion models on the workstation for use in real-time emergency response modeling. Both MATHEW and ADPIC have shown their utility in a variety of complex settings over the last 15 yr within the U.S. Department of Energy's Atmospheric Release Advisory Capability (ARAC) project. Faster workstations and real-time instruments allow utilization of more complex three-dimensional models, which provides a foundation for building a real-time monitoring and emergency response workstation for a tritium facility. The stack monitors are two ion chambers per stack

  9. Modeling compressible multiphase flows with dispersed particles in both dense and dilute regimes

    Science.gov (United States)

    McGrath, T.; St. Clair, J.; Balachandar, S.

    2018-05-01

    Many important explosives and energetics applications involve multiphase formulations employing dispersed particles. While considerable progress has been made toward developing mathematical models and computational methodologies for these flows, significant challenges remain. In this work, we apply a mathematical model for compressible multiphase flows with dispersed particles to existing shock and explosive dispersal problems from the literature. The model is cast in an Eulerian framework, treats all phases as compressible, is hyperbolic, and satisfies the second law of thermodynamics. It directly applies the continuous-phase pressure gradient as a forcing function for particle acceleration and thereby retains relaxed characteristics for the dispersed particle phase that remove the constituent material sound velocity from the eigenvalues. This is consistent with the expected characteristics of dispersed particle phases and can significantly improve the stable time-step size for explicit methods. The model is applied to test cases involving the shock and explosive dispersal of solid particles and compared to data from the literature. Computed results compare well with experimental measurements, providing confidence in the model and computational methods applied.

  10. Dispersion coefficients for coastal regions

    International Nuclear Information System (INIS)

    MacRae, B.L.; Kaleel, R.J.; Shearer, D.L.

    1983-03-01

    The Nuclear Regulatory Commission (NRC) has undertaken an extensive atmospheric dispersion research and measurement program from which it is intended will emerge improved predictive techniques for employment in licensing decisions and for emergency planning and response. Through this program the NRC has conducted field measurement programs over a wide range of geographic and topographic locations, and are using the acquired tracer and meteorological measurements to evaluate existing dispersion models and prediction techniques, and to develop new techniques when necessary

  11. Toxicity of dispersant application: Biomarkers responses in gills of juvenile golden grey mullet (Liza aurata)

    International Nuclear Information System (INIS)

    Milinkovitch, Thomas; Godefroy, Joachim; Theron, Michael; Thomas-Guyon, Helene

    2011-01-01

    Dispersant use in nearshore areas is likely to increase the exposure of aquatic organisms to petroleum. To measure the toxicity of this controversial response technique, golden grey mullets (Liza aurata) were exposed to mechanically dispersed oil, chemically dispersed oil, dispersant alone in seawater, water-soluble fraction of oil and to seawater as a control treatment. Several biomarkers were assessed in the gills (enzymatic antioxidant activities, glutathione content, lipid peroxidation) and in the gallbladder (polycylic aromatic hydrocarbons metabolites). The significant differences between chemically dispersed oil and water soluble fraction of oil highlight the environmental risk to disperse an oil slick when containment and recovery can be conducted. The lack of significance between chemically and mechanically dispersed oil suggests that dispersant application is no more toxic than the natural dispersion of the oil slick. The results of this study are of interest in order to establish dispersant use policies in nearshore areas. - Highlights: → This study simulates and evaluates the toxicity of dispersant use in nearshore area. → Dispersant use toxicity is assessed through biomarkers measurement in a fish species. → Chemical dispersion of an oil slick increases the petroleum toxicity. → Dispersant use does not enhance the toxicity of a mechanically dispersed oil slick. → This work leads to conclusions concerning dispersant use policies in nearshore area. - When the meteorological conditions induce the dispersion of the oil slick (e.g. wave), the application of dispersant does not increase the toxicity of petroleum.

  12. Modelling drivers of mangrove propagule dispersal and restoration of abandoned shrimp farms

    Directory of Open Access Journals (Sweden)

    D. Di Nitto

    2013-07-01

    Full Text Available Propagule dispersal of four mangrove species Rhizophora mucronata, R. apiculata, Ceriops tagal and Avicennia officinalis in the Pambala–Chilaw Lagoon Complex (Sri Lanka was studied by combining a hydrodynamic model with species-specific knowledge on propagule dispersal behaviour. Propagule transport was simulated using a finite-volume advection-diffusion model to investigate the effect of dispersal vectors (tidal flow, freshwater discharge and wind, trapping agents (retention by vegetation and seed characteristics (buoyancy on propagule dispersal patterns. Sensitivity analysis showed that smaller propagules, like the oval-shaped propagules of Avicennia officinalis, dispersed over larger distances and were most sensitive to changing values of retention by mangrove vegetation compared to larger, torpedo-shaped propagules of Rhizophora spp. and C. tagal. Directional propagule dispersal in this semi-enclosed lagoon with a small tidal range was strongly concentrated towards the edges of the lagoon and channels. Short distance dispersal appeared to be the main dispersal strategy for all four studied species, with most of the propagules being retained within the vegetation. Only a small proportion (max. 5% of propagules left the lagoon through a channel connecting the lagoon with the open sea. Wind significantly influenced dispersal distance and direction once propagules entered the lagoon or adjacent channels. Implications of these findings for mangrove restoration were tested by simulating partial removal in the model of dikes around abandoned shrimp ponds to restore tidal hydrology and facilitate natural recolonisation by mangroves. The specific location of dike removal, (with respect to the vicinity of mangroves and independently suitable hydrodynamic flows, was found to significantly affect the resultant quantities and species of inflowing propagules and hence the potential effectiveness of natural regeneration. These results demonstrate the

  13. Comparison of turbulent particle dispersion models in turbulent shear flows

    Directory of Open Access Journals (Sweden)

    S. Laín

    2007-09-01

    Full Text Available This work compares the performance of two Lagrangian turbulent particle dispersion models: the standard model (e.g., that presented in Sommerfeld et al. (1993, in which the fluctuating fluid velocity experienced by the particle is composed of two components, one correlated with the previous time step and a second one randomly sampled from a Wiener process, and the model proposed by Minier and Peirano (2001, which is based on the PDF approach and performs closure at the level of acceleration of the fluid experienced by the particle. Formulation of a Langevin equation model for the increments of fluid velocity seen by the particle allows capturing some underlying physics of particle dispersion in general turbulent flows while keeping the mathematical manipulation of the stochastic model simple, thereby avoiding some pitfalls and simplifying the derivation of macroscopic relations. The performance of both dispersion models is tested in the configurations of grid-generated turbulence (Wells and Stock (1983 experiments, simple shear flow (Hyland et al., 1999 and confined axisymmetric jet flow laden with solids (Hishida and Maeda (1987 experiments.

  14. Numerical models for computation of pollutant-dispersion in the atmosphere

    International Nuclear Information System (INIS)

    Leder, S.M.; Biesemann-Krueger, A.

    1985-04-01

    The report describes some models which are used to compute the concentration of emitted pollutants in the lower atmosphere. A dispersion model, developed at the University of Hamburg, is considered in more detail and treated with two different numerical methods. The convergence of the methods is investigated and a comparison of numerical results and dispersion experiments carried out at the Nuclear Research Center Karlsruhe is given. (orig.) [de

  15. Modelling airborne dispersion for disaster management

    Science.gov (United States)

    Musliman, I. A.; Yohnny, L.

    2017-05-01

    Industrial disasters, like any other disasters, can happen anytime, anywhere and in any form. Airborne industrial disaster is a kind of catastrophic event involving the release of particles such as chemicals and industrial wastes into environment in gaseous form, for instance gas leakages. Unlike solid and liquid materials, gases are often colourless and odourless, the particles are too tiny to be visible to the naked eyes; hence it is difficult to identify the presence of the gases and to tell the dispersion and location of the substance. This study is to develop an application prototype to perform simulation modelling on the gas particles to determine the dispersion of the gas particles and to identify the coverage of the affected area. The prototype adopted Lagrangian Particle Dispersion (LPD) model to calculate the position of the gas particles under the influence of wind and turbulent velocity components, which are the induced wind due to the rotation of the Earth, and Convex Hull algorithm to identify the convex points of the gas cloud to form the polygon of the coverage area. The application performs intersection and overlay analysis over a set of landuse data at Pasir Gudang, Johor industrial and residential area. Results from the analysis would be useful to tell the percentage and extent of the affected area, and are useful for the disaster management to evacuate people from the affected area. The developed application can significantly increase efficiency of emergency handling during a crisis. For example, by using a simulation model, the emergency handling can predict what is going to happen next, so people can be well informed and preparations works can be done earlier and better. Subsequently, this application helps a lot in the decision making process.

  16. Modelling airborne dispersion for disaster management

    International Nuclear Information System (INIS)

    Musliman, I A; Yohnny, L

    2017-01-01

    Industrial disasters, like any other disasters, can happen anytime, anywhere and in any form. Airborne industrial disaster is a kind of catastrophic event involving the release of particles such as chemicals and industrial wastes into environment in gaseous form, for instance gas leakages. Unlike solid and liquid materials, gases are often colourless and odourless, the particles are too tiny to be visible to the naked eyes; hence it is difficult to identify the presence of the gases and to tell the dispersion and location of the substance. This study is to develop an application prototype to perform simulation modelling on the gas particles to determine the dispersion of the gas particles and to identify the coverage of the affected area. The prototype adopted Lagrangian Particle Dispersion (LPD) model to calculate the position of the gas particles under the influence of wind and turbulent velocity components, which are the induced wind due to the rotation of the Earth, and Convex Hull algorithm to identify the convex points of the gas cloud to form the polygon of the coverage area. The application performs intersection and overlay analysis over a set of landuse data at Pasir Gudang, Johor industrial and residential area. Results from the analysis would be useful to tell the percentage and extent of the affected area, and are useful for the disaster management to evacuate people from the affected area. The developed application can significantly increase efficiency of emergency handling during a crisis. For example, by using a simulation model, the emergency handling can predict what is going to happen next, so people can be well informed and preparations works can be done earlier and better. Subsequently, this application helps a lot in the decision making process. (paper)

  17. Impact of atmospheric release in stable night meteorological conditions; can emergency models predict dispersion

    Energy Technology Data Exchange (ETDEWEB)

    Connan, O.; Hebert, D.; Solier, L.; Voiseux, C.; Lamotte, M.; Laguionie, P.; Maro, D.; Thomas, L. [IRSN/PRP-ENV/SERIS/LRC (France)

    2014-07-01

    Atmospheric dispersion of pollutant or radionuclides in stratified meteorological condition, i.e. especially when weather conditions are very stable, mainly at night, is still poorly understood and not well apprehended by the operational atmospheric dispersion models. However, correctly predicting the dispersion of a radioactive plume, and estimating the radiological consequences for the population, following an unplanned atmospheric release of radionuclides are crucial steps in an emergency response. To better understand dispersion in these special weather conditions, IRSN performed a series of 22 air sampling campaigns between 2010 and 2013 in the vicinity of the La Hague nuclear reprocessing plant (AREVA - NC, France), at distances between 200 m and 3000 m from the facility. Krypton-85 ({sup 85}Kr), a b-and g-emitting radionuclide, released during the reprocessing of spent nuclear fuel was used as a non-reactive tracer of radioactive plumes. Experimental campaigns were realized in stability class stable or very stable (E or F according to Pasquill classification) 18 times, and in neutral conditions (D according to Pasquill classification) 4 times. During each campaign, Krypton-85 real time measurement were made to find the plume around the plant, and then integrated samples (30 min) were collected in bag perpendicularly to the assumed wind direction axis. After measurement by gamma spectrometry, we have, when it was possible, estimate the point of impact and the width of the plume. The objective was to estimate the horizontal dispersion (width) of the plume at ground level in function of the distance and be able to calculate atmospheric transfer coefficients. In a second step, objective was to conclude on the use of common model and on their uncertainties. The results will be presented in terms of impact on the near-field. They will be compared with data obtained in previous years in neutral atmospheric conditions, and finally the results will be confronted with

  18. Contrasting germination responses to vegetative canopies experienced in pre- vs. post-dispersal environments

    Science.gov (United States)

    Leverett, Lindsay D.; Auge, Gabriela A.; Bali, Aman; Donohue, Kathleen

    2016-01-01

    Background Seeds adjust their germination based on conditions experienced before and after dispersal. Post-dispersal cues are expected to be more accurate predictors of offspring environments, and thus offspring success, than pre-dispersal cues. Therefore, germination responses to conditions experienced during seed maturation may be expected to be superseded by responses to conditions experienced during seed imbibition. In taxa of disturbed habitats, neighbours frequently reduce the performance of germinants. This leads to the hypotheses that a vegetative canopy will reduce germination in such taxa, and that a vegetative canopy experienced during seed imbibition will over-ride germination responses to a canopy experienced during seed maturation, since it is a more proximal cue of immediate competition. These hypotheses were tested here in Arabidopsis thaliana. Methods Seeds were matured under a simulated canopy (green filter) or white light. Fresh (dormant) seeds were imbibed in the dark, white light or canopy at two temperatures (10 or 22 °C), and germination proportions were recorded. Germination was also recorded in after-ripened (less dormant) seeds that were induced into secondary dormancy and imbibed in the dark at each temperature, either with or without brief exposure to red and far-red light. Key Results Unexpectedly, a maturation canopy expanded the conditions that elicited germination, even as seeds lost and regained dormancy. In contrast, an imbibition canopy impeded or had no effect on germination. Maturation under a canopy did not modify germination responses to red and far-red light. Seed maturation under a canopy masked genetic variation in germination. Conclusions The results challenge the hypothesis that offspring will respond more strongly to their own environment than to that of their parents. The observed relaxation of germination requirements caused by a maturation canopy could be maladaptive for offspring by disrupting germination responses

  19. Landau fluid model for weakly nonlinear dispersive magnetohydrodynamics

    International Nuclear Information System (INIS)

    Passot, T.; Sulem, P. L.

    2005-01-01

    In may astrophysical plasmas such as the solar wind, the terrestrial magnetosphere, or in the interstellar medium at small enough scales, collisions are negligible. When interested in the large-scale dynamics, a hydrodynamic approach is advantageous not only because its numerical simulations is easier than of the full Vlasov-Maxwell equations, but also because it provides a deep understanding of cross-scale nonlinear couplings. It is thus of great interest to construct fluid models that extended the classical magnetohydrodynamic (MHD) equations to collisionless situations. Two ingredients need to be included in such a model to capture the main kinetic effects: finite Larmor radius (FLR) corrections and Landau damping, the only fluid-particle resonance that can affect large scales and can be modeled in a relatively simple way. The Modelization of Landau damping in a fluid formalism is hardly possible in the framework of a systematic asymptotic expansion and was addressed mainly by means of parameter fitting in a linearized setting. We introduced a similar Landau fluid model but, that has the advantage of taking dispersive effects into account. This model properly describes dispersive MHD waves in quasi-parallel propagation. Since, by construction, the system correctly reproduces their linear dynamics, appropriate tests should address the nonlinear regime. In a first case, we show analytically that the weakly nonlinear modulational dynamics of quasi-parallel propagating Alfven waves is well captured. As a second test we consider the parametric decay instability of parallel Alfven waves and show that numerical simulations of the dispersive Landau fluid model lead to results that closely match the outcome of hybrid simulations. (Author)

  20. Difficulties in modeling dispersed-flow film boiling

    International Nuclear Information System (INIS)

    Andreani, M.; Yadigaroglu, G.

    1991-01-01

    Dispersed Flow Film Boiling (DFFB) is characterized by important departures from thermal and velocity equilibrium that make it suitable for modeling with two-fluid models. The fundamental limitations and difficulties imposed by the one-dimensional nature of these models are extensively discussed. The validity of the assumptions and empirical laws used to close the system of conservation equations is critically reviewed, in light of the multidimensional aspects of the problem. Modifications that could improve the physics of the models are identified. (orig.) [de

  1. Bacterial Community Response in Deep Faroe-Shetland Channel Sediments Following Hydrocarbon Entrainment With and Without Dispersant Addition

    Directory of Open Access Journals (Sweden)

    Luis J. Perez Calderon

    2018-05-01

    Full Text Available Deep sea oil exploration is increasing and presents environmental challenges for deep ocean ecosystems. Marine oil spills often result in contamination of sediments with oil; following the Deepwater Horizon (DwH disaster up to 31% of the released oil entrained in the water column was deposited as oily residues on the seabed. Although the aftermath of DwH was studied intensely, lessons learned may not be directly transferable to other deep-sea hydrocarbon exploration areas, such as the Faroe-Shetland Channel (FSC which comprises cold temperatures and a unique hydrodynamic regime. Here, transport of hydrocarbons into deep FSC sediments, subsequent responses in benthic microbial populations and effects of dispersant application on hydrocarbon fate and microbial communities were investigated. Sediments from 1,000 m in the FSC were incubated at 0°C for 71 days after addition of a 20-hydrocarbon component oil-sediment aggregate. Dispersant was added periodically from day 4. An additional set of cores using sterilized and homogenized sediment was analyzed to evaluate the effects of sediment matrix modification on hydrocarbon entrainment. Sediment layers were independently analyzed for hydrocarbon content by gas chromatography with flame ionization detection and modeled with linear mixed effects models. Oil was entrained over 4 cm deep into FSC sediments after 42 days and dispersant effectiveness on hydrocarbon removal from sediment to the water column decreased with time. Sterilizing and homogenizing sediment resulted in hydrocarbon transport over 4 cm into sediments after 7 days. Significant shifts in bacterial populations were observed (DGGE profiling in response to hydrocarbon exposure after 42 days and below 2 cm deep. Dispersant application resulted in an accelerated and modified shift in bacterial communities. Bacterial 16S rRNA gene sequencing of oiled sediments revealed dominance of Colwellia and of Fusibacter when dispersant was applied over

  2. Air Dispersion Modeling for Building 3026C/D Demolition

    Energy Technology Data Exchange (ETDEWEB)

    Ward, Richard C [ORNL; Sjoreen, Andrea L [ORNL; Eckerman, Keith F [ORNL

    2010-06-01

    This report presents estimates of dispersion coefficients and effective dose for potential air dispersion scenarios of uncontrolled releases from Oak Ridge National Laboratory (ORNL) buildings 3026C, 3026D, and 3140 prior to or during the demolition of the 3026 Complex. The Environmental Protection Agency (EPA) AERMOD system1-6 was used to compute these estimates. AERMOD stands for AERMIC Model, where AERMIC is the American Meteorological Society-EPA Regulatory Model Improvement Committee. Five source locations (three in building 3026D and one each in building 3026C and the filter house 3140) and associated source characteristics were determined with the customer. In addition, the area of study was determined and building footprints and intake locations of air-handling systems were obtained. In addition to the air intakes, receptor sites consisting of ground level locations on four polar grids (50 m, 100 m, 200 m, and 500 m) and two intersecting lines of points (50 m separation), corresponding to sidewalks along Central Avenue and Fifth Street. Three years of meteorological data (2006 2008) were used each consisting of three datasets: 1) National Weather Service data; 2) upper air data for the Knoxville-Oak Ridge area; and 3) local weather data from Tower C (10 m, 30 m and 100 m) on the ORNL reservation. Annual average air concentration, highest 1 h average and highest 3 h average air concentrations were computed using AERMOD for the five source locations for the three years of meteorological data. The highest 1 h average air concentrations were converted to dispersion coefficients to characterize the atmospheric dispersion as the customer was interested in the most significant response and the highest 1 h average data reflects the best time-averaged values available from the AERMOD code. Results are presented in tabular and graphical form. The results for dose were obtained using radionuclide activities for each of the buildings provided by the customer.7

  3. A novel ultrawideband FDTD numerical modeling of ground penetrating radar on arbitrary dispersive soils

    NARCIS (Netherlands)

    Mescia, L.; Bia, P.; Caratelli, D.

    2017-01-01

    A novel two-dimensional (2-D) finite-difference timedomain algorithm for modeling ultrawideband pulse propagation in arbitrary dispersive soils is presented. The soil dispersion is modeled by general power law series representation, accounting for multiple higher order dispersive relaxation

  4. Objectives for next generation of practical short-range atmospheric dispersion models

    International Nuclear Information System (INIS)

    Olesen, H.R.; Mikkelsen, T.

    1992-01-01

    The proceedings contains papers from the workshop ''Objectives for Next Generation of Practical Short-Range Atmospheric Dispersion Models''. They deal with two types of models, namely models for regulatory purposes and models for real-time applications. The workshop was the result of an action started in 1991 for increased cooperation and harmonization within atmospheric dispersion modelling. The focus of the workshop was on the management of model development and the definition of model objectives, rather than on detailed model contents. It was the intention to identify actions that can be taken in order to improve the development and use of atmospheric dispersion models. The papers in the proceedings deal with various topics within the broad spectrum of matters related to up-to-date practical models, such as their scientific basis, requirements for model input and output, meteorological preprocessing, standardisation within modelling, electronic information exchange as a potentially useful tool, model evaluation and data bases for model evaluation. In addition to the papers, the proceedings contain summaries of the discussions at the workshop. These summaries point to a number of recommended actions which can be taken in order to improve ''modelling culture''. (AB)

  5. Evaluation of field-collected drifter and subsurface fluorescein dye concentration data and comparisons to high frequency radar surface current mapping data for dispersed oil transport modeling

    Energy Technology Data Exchange (ETDEWEB)

    Payne, J.R. [Payne Environmental Consultants Inc., Encinitas, CA (United States); Terrill, E.; Carter, M.; Otero, M.; Middleton, W.; Chen, A. [Scripps Inst. of Oceanography, La Jolla, CA (United States); French McCay, D.; Mueller, C.; Jayko, K. [Applied Science Associates Inc., Narragansett, RI (United States); Nordhausen, W.; Lewis, R.; Lampinen, M.; Evans, T. [California Dept. of Fish and Game, San Diego, CA (United States). Office of Spill Prevention and Response; Ohlmann, C. [California Univ., Santa Barbara, CA (United States); Via, G.L.; Ruiz-Santana, H.; Maly, M.; Willoughby, B.; Varela, C. [United States Coast Guard Pacific Strike Team, Novato, CA (United States); Lynch, P.; Sanchez, P. [Marine Spill Response Corp., San Diego, CA (United States)

    2007-07-01

    Extensive coastal areas in the United States have been designated as pre-approved zones for dispersant applications in the event of an oil spill. Although the use of dispersants may reduce impacts to wildlife and shoreline habitats, it is recognized that the dispersed oil may cause impacts to organisms in the water column. The State of California Department of Fish and Game Office of Spill Prevention and Response is currently using oil spill fate and transport modeling to address this issue. The purpose is to develop the time and spatial scales, and equipment needs for a formal dispersed oil monitoring plan (DOMP) to document hydrocarbon water column concentrations, potentially exposed zooplankton, and the impact of the oil spills with and without dispersant use. A series of 7 fluorescein dye releases were completed off the coast of San Diego, California in order to test the operational framework for repeated sampling of dispersed oil plumes as outlined in the DOMP. The ability of high-frequency radar to provide surface current input data to oil spill models was also evaluated. The dye concentrations were measured over three spatial dimensions and time in order to verify the model-predicted movement of subsurface dye. Surface current fields at varying depths were also measured and the subsurface dye plume structure was mapped using a GPS coupled towed-fluorometer equipped with pressure sensors. Measurements were compared with data from traditional special monitoring of applied response technology (SMART). The database acquired through this program represents a technical resource that can help physical and chemical oceanographers, modelers, spill response and contingency planners involved in the debate of whether or not to use dispersants to mitigate near shore and open ocean marine oil spills. 14 refs., 2 tabs., 14 figs.

  6. Simulation of atmospheric dispersion of radionuclides using an Eulerian-Lagrangian modelling system.

    Science.gov (United States)

    Basit, Abdul; Espinosa, Francisco; Avila, Ruben; Raza, S; Irfan, N

    2008-12-01

    In this paper we present an atmospheric dispersion scenario for a proposed nuclear power plant in Pakistan involving the hypothetical accidental release of radionuclides. For this, a concept involving a Lagrangian stochastic particle model (LSPM) coupled with an Eulerian regional atmospheric modelling system (RAMS) is used. The atmospheric turbulent dispersion of radionuclides (represented by non-buoyant particles/neutral traces) in the LSPM is modelled by applying non-homogeneous turbulence conditions. The mean wind velocities governed by the topography of the region and the surface fluxes of momentum and heat are calculated by the RAMS code. A moving least squares (MLS) technique is introduced to calculate the concentration of radionuclides at ground level. The numerically calculated vertical profiles of wind velocity and temperature are compared with observed data. The results obtained demonstrate that in regions of complex terrain it is not sufficient to model the atmospheric dispersion of particles using a straight-line Gaussian plume model, and that by utilising a Lagrangian stochastic particle model and regional atmospheric modelling system a much more realistic estimation of the dispersion in such a hypothetical scenario was ascertained. The particle dispersion results for a 12 h ground release show that a triangular area of about 400 km(2) situated in the north-west quadrant of release is under radiological threat. The particle distribution shows that the use of a Gaussian plume model (GPM) in such situations will yield quite misleading results.

  7. Improved atmospheric dispersion modelling in the new program system UFOMOD for accident consequence assessments

    International Nuclear Information System (INIS)

    Panitz, H.J.

    1988-01-01

    An essential aim of the improvements of the new program system UFOMOD for Accident Consequence Assessments (ACAs) was to substitute the straightline Gaussian plume model conventionally used in ACA models by more realistic atmospheric dispersion models. To identify improved models which can be applied in ACA codes and to quantify the implications of different concepts of dispersion modelling on the results of an ACA, probabilistic comparative calculations with different atmospheric dispersion models have been carried out. The study showed that there are trajectory models available which can be applied in ACAs and that these trajectory models provide more realistic results of ACAs than straight-line Gaussian models. This led to a completly novel concept of atmospheric dispersion modelling which distinguish between two different distance ranges of validity: the near range ( 50 km). The two ranges are assigned to respective trajectory models

  8. Modelling of atmospheric dispersion in a complex medium and associated uncertainties

    International Nuclear Information System (INIS)

    Demael, Emmanuel

    2007-01-01

    This research thesis addresses the study of the digital modelling of atmospheric dispersions. It aimed at validating the Mercure-Saturne tool used with a RANS (Reynolds Averaged Navier-Stokes) approach within the frame of an impact study or of an accidental scenario on a nuclear site while taking buildings and ground relief into account, at comparing the Mercure-Saturne model with a more simple and less costly (in terms of computation time) Gaussian tool (the ADMS software, Atmospheric Dispersion Modelling System), and at quantifying uncertainties related to the use of the Mercure-Saturne model. The first part introduces theoretical elements of atmosphere physics and of the atmospheric dispersion in a boundary layer, presents the Gaussian model and the Mercure-Saturne tool and its associated RANS approach. The second part reports the comparison of the Mercure-Saturne model with conventional Gaussian plume models. The third part reports the study of the atmospheric flow and dispersion about the Bugey nuclear site, based on a study performed in a wind tunnel. The fourth part reports the same kind of study for the Flamanville site. The fifth part reports the use of different approaches for the study of uncertainties in the case of the Bugey site: application of the Morris method (a screening method), and of the Monte Carlo method (quantification of the uncertainty and of the sensitivity of each uncertainty source) [fr

  9. Longitudinal dispersion coefficients for numerical modeling of groundwater solute transport in heterogeneous formations

    DEFF Research Database (Denmark)

    Lee, Jonghyun; Rolle, Massimo; Kitanidis, Peter K.

    2018-01-01

    Most recent research on hydrodynamic dispersion in porous media has focused on whole-domain dispersion while other research is largely on laboratory-scale dispersion. This work focuses on the contribution of a single block in a numerical model to dispersion. Variability of fluid velocity and conc...

  10. Advection models of longitudinal dispersion in rivers

    NARCIS (Netherlands)

    Kranenburg, C.

    1996-01-01

    A derivation is presented of a general cross-section averaged model of longitudinal dispersion, which is based on the notion of the advection of tracer particles. Particle displacement length and particle travel time are conceived as stochastic variables, and a joint probability density function is

  11. Modeling of Rayleigh wave dispersion in Iberia

    Directory of Open Access Journals (Sweden)

    José Badal

    2011-01-01

    Full Text Available Phase and group velocities of 15–70 s Rayleigh waves propagating across the Iberian Peninsula have been transformed into local dispersion curves by linear inversion of travel times. The procedure permits that the waveform dispersion to be obtained as a continuous period-dependent velocity function at grid points belonging to the area probed by the waves, thus providing phase- and group-velocity contour maps for several periods within the interval of interest. The regionalization process rests on a homogeneous initial data set in which the number of observations remains almost constant for all periods of reference. Damped least-squares inversion of the local dispersion curves for shear-wave velocity structure is performed to obtain depth-dependent S-wave velocity profiles at the grid points covering the model region. The reliability of the results should improve significantly owing to the use of phase and group velocities simultaneously. On this basis, we have built horizontal depth sections that give an updated view of the seismic velocity structure of the peninsula at lithospheric and upper mantle depths (20–200 km. After averaging all the pure-path S-wave velocities previously determined at each grid point, the velocity-depth models so obtained for major tectonic units allow the comparison between the Hercynian basement and other areas of Mesozoic folding and Tertiary basins.

  12. Calibration of Discrete Random Walk (DRW) Model via G.I Taylor's Dispersion Theory

    Science.gov (United States)

    Javaherchi, Teymour; Aliseda, Alberto

    2012-11-01

    Prediction of particle dispersion in turbulent flows is still an important challenge with many applications to environmental, as well as industrial, fluid mechanics. Several models of dispersion have been developed to predict particle trajectories and their relative velocities, in combination with a RANS-based simulation of the background flow. The interaction of the particles with the velocity fluctuations at different turbulent scales represents a significant difficulty in generalizing the models to the wide range of flows where they are used. We focus our attention on the Discrete Random Walk (DRW) model applied to flow in a channel, particularly to the selection of eddies lifetimes as realizations of a Poisson distribution with a mean value proportional to κ / ɛ . We present a general method to determine the constant of this proportionality by matching the DRW model dispersion predictions for fluid element and particle dispersion to G.I Taylor's classical dispersion theory. This model parameter is critical to the magnitude of predicted dispersion. A case study of its influence on sedimentation of suspended particles in a tidal channel with an array of Marine Hydrokinetic (MHK) turbines highlights the dependency of results on this time scale parameter. Support from US DOE through the Northwest National Marine Renewable Energy Center, a UW-OSU partnership.

  13. A linearized dispersion relation for orthorhombic pseudo-acoustic modeling

    KAUST Repository

    Song, Xiaolei; Alkhalifah, Tariq Ali

    2012-01-01

    Wavefield extrapolation in acoustic orthorhombic anisotropic media suffers from wave-mode coupling and stability limitations in the parameter range. We introduce a linearized form of the dispersion relation for acoustic orthorhombic media to model acoustic wavefields. We apply the lowrank approximation approach to handle the corresponding space-wavenumber mixed-domain operator. Numerical experiments show that the proposed wavefield extrapolator is accurate and practically free of dispersions. Further, there is no coupling of qSv and qP waves, because we use the analytical dispersion relation. No constraints on Thomsen's parameters are required for stability. The linearized expression may provide useful application for parameter estimation in orthorhombic media.

  14. A linearized dispersion relation for orthorhombic pseudo-acoustic modeling

    KAUST Repository

    Song, Xiaolei

    2012-11-04

    Wavefield extrapolation in acoustic orthorhombic anisotropic media suffers from wave-mode coupling and stability limitations in the parameter range. We introduce a linearized form of the dispersion relation for acoustic orthorhombic media to model acoustic wavefields. We apply the lowrank approximation approach to handle the corresponding space-wavenumber mixed-domain operator. Numerical experiments show that the proposed wavefield extrapolator is accurate and practically free of dispersions. Further, there is no coupling of qSv and qP waves, because we use the analytical dispersion relation. No constraints on Thomsen\\'s parameters are required for stability. The linearized expression may provide useful application for parameter estimation in orthorhombic media.

  15. Catchment Dispersion Mechanisms in an Urban Context

    Science.gov (United States)

    Gironas, J. A.; Mejia, A.; Rossel, F.; Rinaldo, A.; Rodriguez, F.

    2014-12-01

    Dispersion mechanisms have been examined in-depth in natural catchments in previous studies. However, these dispersion mechanisms have been studied little in urban catchments, where artificial transport elements and morphological arrangements are expected to modify travel times and mobilize excess rainfall from spatially distributed impervious sites. Thus, these features can modify the variance of the catchment's travel times and hence the total dispersion. This work quantifies the dispersion mechanisms in an urban catchment using the theory of transport by travel times as represented by the Urban Morpho-climatic Instantaneous Unit Hydrograph (U-McIUH) model. This model computes travel times based on kinematic wave theory and accounts explicitly for the path heterogeneities and altered connectivity patterns characteristic of an urban drainage network. The analysis is illustrated using the Aubinière urban catchment (France) as a case study. We found that kinematic dispersion is dominant for small rainfall intensities, whereas geomorphologic dispersion becomes more dominant for larger intensities. The total dispersion scales with the drainage area in a power law fashion. The kinematic dispersion is dominant across spatial scales up to a threshold of approximately 2-3 km2, after which the geomorphologic dispersion becomes more dominant. Overall, overland flow is responsible for most of the dispersion, while conduits tend to counteract the increase of the geomorphologic dispersion with a negative kinematic dispersion. Further studies with other catchments are needed to assess whether the latter is a general feature of urban drainage networks.

  16. Dispersion in the wake of a model industrial complex

    International Nuclear Information System (INIS)

    Hatcher, R.V.; Meroney, R.N.; Peterka, J.A.; Kothari, K.

    1977-06-01

    Models (1:200 scale) of the EOCR reactor building and surrounding silo and tank buildings at the Idaho National Engineering Laboratory, Idaho Falls, Idaho were put into the Meteorological Wind Tunnel at Colorado State University for the purpose of studying the effects of building wakes on dispersion. Flow visualization was done and concentration measurements were taken. The test program consisted of systematic releases from ground, building height, and stack height sources with no appreciable plume rise. The program was repeated for cases of moderately unstable, neutral, moderately stable, and stable conditions in the wind tunnel. Results show that the buildings significantly alter the dispersion patterns and the addition of any extra buildings or slight terrain change in the immediate vicinity of the building has a major effect. In the near wake region the effects of stratification were still evident causing slightly higher concentrations for stable conditions and slightly lower for unstable. Current dispersion models are discussed and evaluated that predict concentrations in the building wake region

  17. Stress response of the black coral Leiopathes glaberrima when exposed to sub-lethal amounts of crude oil and dispersant

    Directory of Open Access Journals (Sweden)

    Dannise V. Ruiz-Ramos

    2017-12-01

    Full Text Available The 2010 Deep Water Horizon oil well failure released billions of gallons of crude oil into the deep Gulf of Mexico, and, combined with chemical dispersants, this oil caused significant coral mortality. However, the mechanisms by which oil and dispersed oil impact deep marine fauna are not well understood. Here, we investigate the effects of oil and dispersed oil on a black coral common in the deep Gulf of Mexico, 'Leiopathes glaberrima. 'This coral occurs in several color morphs that show ecological and genetic differences. We hypothesized that dispersed oil would be more detrimental to coral health than oil alone and that this difference would be detectable in the gene expression response of the colonies even at sub-lethal concentrations. In two experiments, four and six colonies of red and white color morphs were exposed to oil, dispersant, and dispersed oil for a minimum of 96 hours. Visual assessment indicated that indeed dispersant and dispersed oil treatments were more damaging than oil alone, for target concentrations of 25 mg L–1. Decline in health was observed for all treatments, independently of color morphotype, but the decline was faster in the white colonies exposed to dispersant. The responses to the treatments were also investigated by monitoring gene expression after 24 hours of sub-lethal chemical exposure. Coral gene expression differed by chemical stressor. Interestingly, the polycyclic aromatic hydrocarbon biomarker gene, cytochrome P450, was only up-regulated in dispersed oil but not oil alone, suggesting that the dispersant increased the availability of such hydrocarbons in the tissue. The gene expression response was apparent at 24 hours when visual impacts were not (yet detectable. The use of chemical dispersants in oil-spill remediation may cause health declines in deep-water corals and deserves further study.

  18. Numerical simulations of atmospheric dispersion of iodine-131 by different models.

    Directory of Open Access Journals (Sweden)

    Ádám Leelőssy

    Full Text Available Nowadays, several dispersion models are available to simulate the transport processes of air pollutants and toxic substances including radionuclides in the atmosphere. Reliability of atmospheric transport models has been demonstrated in several recent cases from local to global scale; however, very few actual emission data are available to evaluate model results in real-life cases. In this study, the atmospheric dispersion of 131I emitted to the atmosphere during an industrial process was simulated with different models, namely the WRF-Chem Eulerian online coupled model and the HYSPLIT and the RAPTOR Lagrangian models. Although only limited data of 131I detections has been available, the accuracy of modeled plume direction could be evaluated in complex late autumn weather situations. For the studied cases, the general reliability of models has been demonstrated. However, serious uncertainties arise related to low level inversions, above all in case of an emission event on 4 November 2011, when an important wind shear caused a significant difference between simulated and real transport directions. Results underline the importance of prudent interpretation of dispersion model results and the identification of weather conditions with a potential to cause large model errors.

  19. Angular dependent anisotropic terahertz response of vertically aligned multi-walled carbon nanotube arrays with spatial dispersion

    Science.gov (United States)

    Zhou, Yixuan; Yiwen, E.; Xu, Xinlong; Li, Weilong; Wang, Huan; Zhu, Lipeng; Bai, Jintao; Ren, Zhaoyu; Wang, Li

    2016-12-01

    Spatial dispersion effect of aligned carbon nanotubes (CNTs) in the terahertz (THz) region has significance for both theoretical and applied consideration due to the unique intrinsically anisotropic physical properties of CNTs. Herein, we report the angular dependent reflection of p-polarized THz wave from vertically aligned multi-walled CNT arrays in both experiment and theory. The spectra indicate that the reflection depends on the film thickness of vertically aligned CNTs, the incident angle, and the frequency. The calculation model is based on the spatial dispersion effect of aligned CNTs and performed with effective impedance method and the Maxwell-Garnett approximation. The results fit well with the experiment when the thickness of CNT film is thin, which reveals a coherent superposition mechanism of the CNT surface reflection and CNTs/Si interface reflection. For thick CNT films, the CNTs/Si interface response determines the reflection at small incident angles, while the CNTs surface effect dominates at large incident angles. This work investigates the spatial dispersion effect of vertically aligned CNT arrays in the THz region, and paves a way for potential anisotropic THz applications based on CNTs with oblique incidence requirements.

  20. Physical modelling of flow and dispersion over complex terrain

    Science.gov (United States)

    Cermak, J. E.

    1984-09-01

    Atmospheric motion and dispersion over topography characterized by irregular (or regular) hill-valley or mountain-valley distributions are strongly dependent upon three general sets of variables. These are variables that describe topographic geometry, synoptic-scale winds and surface-air temperature distributions. In addition, pollutant concentration distributions also depend upon location and physical characteristics of the pollutant source. Overall fluid-flow complexity and variability from site to site have stimulated the development and use of physical modelling for determination of flow and dispersion in many wind-engineering applications. Models with length scales as small as 1:12,000 have been placed in boundary-layer wind tunnels to study flows in which forced convection by synoptic winds is of primary significance. Flows driven primarily by forces arising from temperature differences (gravitational or free convection) have been investigated by small-scale physical models placed in an isolated space (gravitational convection chamber). Similarity criteria and facilities for both forced and gravitational-convection flow studies are discussed. Forced-convection modelling is illustrated by application to dispersion of air pollutants by unstable flow near a paper mill in the state of Maryland and by stable flow over Point Arguello, California. Gravitational-convection modelling is demonstrated by a study of drainage flow and pollutant transport from a proposed mining operation in the Rocky Mountains of Colorado. Other studies in which field data are available for comparison with model data are reviewed.

  1. Harmonisation within atmospheric dispersion modelling for regulatory purposes. Proceedings. Vol. 2

    International Nuclear Information System (INIS)

    Suppan, P.

    2004-01-01

    Dispersion modelling has proved to be a very effective tool to assess the environmental impact of human activities on air quality already at the early planning stage. Environmental assessments during planning are required by the EU directive 85/337/EEC. Only models can give detailed information on the distribution of pollutants with high spatial and temporal resolution, while they allow the decision-maker to devise a range of scenarios, in which the various processes determining the environmental impact can be easily simulated and changed. In June 1991, the Joint Research Centre of the European Commission started an initiative on the sharing of information and possible harmonisation of new approaches to atmospheric dispersion modelling and model evaluation. This initiative has fostered a series of conferences that have been concerned with improvement of ''modelling culture'' in Europe. The 9 th International Conference on Harmonisation within atmospheric dispersion modelling for regulatory purposes in Garmisch-Partenkirchen, in Germany/ Bavaria, 1-4 June, 2004, will continue the efforts of the previous conferences. The conference has a role as a forum where users and decision-makers can bring their requirements to the attention of scientists. It is also a natural forum for discussing environmental issues related to the European union enlargement process. The scope of this conference is covered by the following topics: Validation and inter-comparison of models: Model evaluation methodology, experiences with implementation of EU directives; regulatory modelling, short distance dispersion modelling, urban scale and street canyon modelling: Meteorology and air quality, mesoscale meteorology and air quality modelling, environmental impact assessment: Air pollution management and decision support systems. (orig.)

  2. Dispersion modeling of selected PAHs in urban air: A new approach combining dispersion model with GIS and passive air sampling

    Czech Academy of Sciences Publication Activity Database

    Sáňka, O.; Melymuk, L.; Čupr, P.; Dvorská, Alice; Klánová, J.

    2014-01-01

    Roč. 90, oct (2014), s. 88-95 ISSN 1352-2310 Institutional support: RVO:67179843 Keywords : passive air sampling * air dispersion modeling * GIS * polycyclic aromatic hydrocarbons * emission inventories Subject RIV: DI - Air Pollution ; Quality Impact factor: 3.281, year: 2014

  3. Dispersal timing and drought history influence the response of bacterioplankton to drying-rewetting stress.

    Science.gov (United States)

    Székely, Anna J; Langenheder, Silke

    2017-08-01

    The extent and frequency of drought episodes is expected to increase in the following decades making it a crucial stress factor for smaller water bodies. However, very little is known about how bacterioplankton is affected by increased evaporation and how these communities reassemble after rewetting. Here, we present results from a microcosm experiment that assessed the effect of drying-rewetting stress on bacterioplankton in the light of the stress history and the rate and timing of dispersal after the rewetting. We found that the drying phase resulted mainly in a change of function, whereas the complete desiccation and rewetting processes strongly affected both composition and function, which were, however, influenced by the initial conditions and stress history of the communities. Effects of dispersal were generally stronger when it occurred at an early stage after the rewetting. At this stage, selective establishment of dispersed bacteria coupled with enhanced compositional and functional recovery was found, whereas effects of dispersal were neutral, that is, predictable by dispersal rates, at later stages. Our studies therefore show that both the stress history and the timing of dispersal are important factors that influence the response of bacterial communities to environmental change and stress events.

  4. radionuclides modelling dispersion of in the atmosphere for continuous discharges and accidental

    International Nuclear Information System (INIS)

    Teyeb, Malika

    2011-01-01

    The study of the dispersion of radionuclides in the atmosphere is the subject of a physical and numerical modeling of the phenomenon of dispersion. This work aims to study the atmospheric dispersion of accidental releases and continuous, from the possible establishment of a nuclear pressurized water reactor in the potential in Bizerte and Skhira.

  5. Removal of Disperse Blue 56 and Disperse Red 135 dyes from aqueous dispersions by modified montmorillonite nanoclay

    Directory of Open Access Journals (Sweden)

    Ahmadishoar Javad

    2017-01-01

    Full Text Available In this study modified montmorillonite was used as an adsorbent for the removal of two selected disperse dyes i.e., Disperse Blue 56 (DB and Disperse Red 135 (DR from dye dispersions. The adsorption equilibrium data of dyes adsorption were investigated by using Nernst, Freundlich and Langmuir isotherm models. The adsorption kinetics was analyzed by using different models including pseudo-first-order, pseudo-second-order, Elovich and Intraparticle diffusion model. The Freundlich isotherm was found to be the most appropriate model for describing the sorption of the dyes on modified nanoclay. The best fit to the experimental results was obtained by using the pseudo-second-order kinetic equation, which satisfactorily described the process of dye adsorption. Although different kinetic models may control the rate of the adsorption process, the results indicated that the main rate limiting step was the intraparticle diffusion. The results showed that the proposed modified montmorillonite could be used as an effective adsorbent for the removal of disperse dyes even from highly concentrated dispersions.

  6. Atmospheric aerosol dispersion models and their applications to environmental risk assessment

    Directory of Open Access Journals (Sweden)

    Andrzej Mazur

    2014-03-01

    Full Text Available Introduction. Numerical models of dispersion of atmospheric pollutants are widely used to forecast the spread of contaminants in the air and to analyze the effects of this phenomenon. The aim of the study is to investigate the possibilities and the quality of diagnosis and prediction of atmospheric transport of aerosols in the air using the dispersion model of atmospheric pollutants, developed at the Institute of Meteorology and Water Management (IMWM in Warsaw. Material and methods. A model of the dispersion of atmospheric pollutants, linked with meteorological models in a diagnostic mode, was used to simulate the transport of the cloud of aerosols released during the crash near the town of Ożydiw (Ukraine and of volcanic ash – during the volcanic eruption of Eyjafjallajökull in Iceland. Results. Possible directions of dispersion of pollutants in the air and its concentration in the atmosphere and deposition to the soil were assessed. The analysis of temporal variability of concentrations of aerosols in the atmosphere confirmed that the model developed at IMWM is an effective tool for diagnosis of air quality in the area of Poland as well as for determination of exposure duration to the aerosol clouds for different weather scenarios. Conclusions. The results are a confirmation of the thesis, that because in the environmental risk assessment, an important element is not only current information on the level of pollution concentrations, but also the time of exposure to pollution and forecast of these elements, and consequently the predicted effects on man or the environment in general; so it is necessary to use forecasting tools, similar to presented application. The dispersion model described in the paper is an operational tool for description, analysis and forecasting of emergency situations in case of emissions of hazardous substances.

  7. Evaluation of hydrodynamic ocean models as a first step in larval dispersal modelling

    Science.gov (United States)

    Vasile, Roxana; Hartmann, Klaas; Hobday, Alistair J.; Oliver, Eric; Tracey, Sean

    2018-01-01

    Larval dispersal modelling, a powerful tool in studying population connectivity and species distribution, requires accurate estimates of the ocean state, on a high-resolution grid in both space (e.g. 0.5-1 km horizontal grid) and time (e.g. hourly outputs), particularly of current velocities and water temperature. These estimates are usually provided by hydrodynamic models based on which larval trajectories and survival are computed. In this study we assessed the accuracy of two hydrodynamic models around Australia - Bluelink ReANalysis (BRAN) and Hybrid Coordinate Ocean Model (HYCOM) - through comparison with empirical data from the Australian National Moorings Network (ANMN). We evaluated the models' predictions of seawater parameters most relevant to larval dispersal - temperature, u and v velocities and current speed and direction - on the continental shelf where spawning and nursery areas for major fishery species are located. The performance of each model in estimating ocean parameters was found to depend on the parameter investigated and to vary from one geographical region to another. Both BRAN and HYCOM models systematically overestimated the mean water temperature, particularly in the top 140 m of water column, with over 2 °C bias at some of the mooring stations. HYCOM model was more accurate than BRAN for water temperature predictions in the Great Australian Bight and along the east coast of Australia. Skill scores between each model and the in situ observations showed lower accuracy in the models' predictions of u and v ocean current velocities compared to water temperature predictions. For both models, the lowest accuracy in predicting ocean current velocities, speed and direction was observed at 200 m depth. Low accuracy of both model predictions was also observed in the top 10 m of the water column. BRAN had more accurate predictions of both u and v velocities in the upper 50 m of water column at all mooring station locations. While HYCOM

  8. The Lagrangian particle dispersion model FLEXPART-WRF VERSION 3.1

    Energy Technology Data Exchange (ETDEWEB)

    Brioude, J.; Arnold, D.; Stohl, A.; Cassiani, M.; Morton, Don; Seibert, P.; Angevine, W. M.; Evan, S.; Dingwell, A.; Fast, Jerome D.; Easter, Richard C.; Pisso, I.; Bukhart, J.; Wotawa, G.

    2013-11-01

    The Lagrangian particle dispersion model FLEXPART was originally designed for cal- culating long-range and mesoscale dispersion of air pollutants from point sources, such as after an accident in a nuclear power plant. In the meantime FLEXPART has evolved into a comprehensive tool for atmospheric transport modeling and analysis at different scales. This multiscale need from the modeler community has encouraged new developments in FLEXPART. In this document, we present a version that works with the Weather Research and Forecasting (WRF) mesoscale meteoro- logical model. Simple procedures on how to run FLEXPART-WRF are presented along with special options and features that differ from its predecessor versions. In addition, test case data, the source code and visualization tools are provided to the reader as supplementary material.

  9. Longitudinal dispersion coefficients for numerical modeling of groundwater solute transport in heterogeneous formations.

    Science.gov (United States)

    Lee, Jonghyun; Rolle, Massimo; Kitanidis, Peter K

    2017-09-15

    Most recent research on hydrodynamic dispersion in porous media has focused on whole-domain dispersion while other research is largely on laboratory-scale dispersion. This work focuses on the contribution of a single block in a numerical model to dispersion. Variability of fluid velocity and concentration within a block is not resolved and the combined spreading effect is approximated using resolved quantities and macroscopic parameters. This applies whether the formation is modeled as homogeneous or discretized into homogeneous blocks but the emphasis here being on the latter. The process of dispersion is typically described through the Fickian model, i.e., the dispersive flux is proportional to the gradient of the resolved concentration, commonly with the Scheidegger parameterization, which is a particular way to compute the dispersion coefficients utilizing dispersivity coefficients. Although such parameterization is by far the most commonly used in solute transport applications, its validity has been questioned. Here, our goal is to investigate the effects of heterogeneity and mass transfer limitations on block-scale longitudinal dispersion and to evaluate under which conditions the Scheidegger parameterization is valid. We compute the relaxation time or memory of the system; changes in time with periods larger than the relaxation time are gradually leading to a condition of local equilibrium under which dispersion is Fickian. The method we use requires the solution of a steady-state advection-dispersion equation, and thus is computationally efficient, and applicable to any heterogeneous hydraulic conductivity K field without requiring statistical or structural assumptions. The method was validated by comparing with other approaches such as the moment analysis and the first order perturbation method. We investigate the impact of heterogeneity, both in degree and structure, on the longitudinal dispersion coefficient and then discuss the role of local dispersion

  10. A summary of recent refinements to the WAKE dispersion model, a component of the HGSYSTEM/UF6 model suite

    International Nuclear Information System (INIS)

    Yambert, M.W.; Lombardi, D.A.; Goode, W.D. Jr.; Bloom, S.G.

    1998-08-01

    The original WAKE dispersion model a component of the HGSYSTEM/UF 6 model suite, is based on Shell Research Ltd.'s HGSYSTEM Version 3.0 and was developed by the US Department of Energy for use in estimating downwind dispersion of materials due to accidental releases from gaseous diffusion plant (GDP) process buildings. The model is applicable to scenarios involving both ground-level and elevated releases into building wake cavities of non-reactive plumes that are either neutrally or positively buoyant. Over the 2-year period since its creation, the WAKE model has been used to perform consequence analyses for Safety Analysis Reports (SARs) associated with gaseous diffusion plants in Portsmouth (PORTS), Paducah (PGDP), and Oak Ridge. These applications have identified the need for additional model capabilities (such as the treatment of complex terrain and time-variant releases) not present in the original utilities which, in turn, has resulted in numerous modifications to these codes as well as the development of additional, stand-alone postprocessing utilities. Consequently, application of the model has become increasingly complex as the number of executable, input, and output files associated with a single model run has steadily grown. In response to these problems, a streamlined version of the WAKE model has been developed which integrates all calculations that are currently performed by the existing WAKE, and the various post-processing utilities. This report summarizes the efforts involved in developing this revised version of the WAKE model

  11. Dispersion Relations for Electroweak Observables in Composite Higgs Models

    CERN Document Server

    Contino, Roberto

    2015-12-14

    We derive dispersion relations for the electroweak oblique observables measured at LEP in the context of $SO(5)/SO(4)$ composite Higgs models. It is shown how these relations can be used and must be modified when modeling the spectral functions through a low-energy effective description of the strong dynamics. The dispersion relation for the parameter $\\epsilon_3$ is then used to estimate the contribution from spin-1 resonances at the 1-loop level. Finally, it is shown that the sign of the contribution to the $\\hat S$ parameter from the lowest-lying spin-1 states is not necessarily positive definite, but depends on the energy scale at which the asymptotic behavior of current correlators is attained.

  12. A real-time monitoring/emergency response modeling workstation for a tritium facility

    International Nuclear Information System (INIS)

    Lawver, B.S.; Sims, J.M.; Baskett, R.L.

    1993-07-01

    At Lawrence Livermore National Laboratory (LLNL) we developed a real-time system to monitor two stacks on our tritium handling facility. The monitors transmit the stack data to a workstation which computes a 3D numerical model of atmospheric dispersion. The workstation also collects surface and upper air data from meteorological towers and a sodar. The complex meteorological and terrain setting in the Livermore Valley demands more sophisticated resolution of the three-dimensional structure of the atmosphere to reliably calculate plume dispersion than afforded by Gaussian models. We experience both mountain valley and sea breeze flows. To address these complexities, we have implemented the three-dimensional diagnostic MATHEW mass-adjusted wind field and ADPIC particle-in-cell dispersion models on the workstation for use in real-time emergency response modeling. Both MATHEW and ADPIC have shown their utility in a variety of complex settings over the last 15 years within the Department of Energy's Atmospheric Release Advisory Capability (ARAC[1,2]) project

  13. [Response surface method optimize of nano-silica solid dispersion technology assistant enzymatic hydrolysis preparation genistein].

    Science.gov (United States)

    Jin, Xin; Zhang, Zhen-Hai; Zhu, Jing; Sun, E; Yu, Dan-Hong; Chen, Xiao-Yun; Liu, Qi-Yuan; Ning, Qing; Jia, Xiao-Bin

    2012-04-01

    This article reports that nano-silica solid dispersion technology was used to raise genistein efficiency through increasing the enzymatic hydrolysis rate. Firstly, genistin-nano-silica solid dispersion was prepared by solvent method. And differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) were used to verify the formation of solid dispersion, then enzymatic hydrolysis of solid dispersion was done by snailase to get genistein. With the conversion of genistein as criteria, single factor experiments were used to study the different factors affecting enzymatic hydrolysis of genistin and its solid dispersion. And then, response surface method was used to optimize of nano-silica solid dispersion technology assistant enzymatic hydrolysis. The optimum condition to get genistein through enzymatic hydrolysis of genistin-nano-silica solid dispersion was pH 7.1, temperature 52.2 degrees C, enzyme concentration 5.0 mg x mL(-1) and reaction time 7 h. Under this condition, the conversion of genistein was (93.47 +/- 2.40)%. Comparing with that without forming the genistin-nano-silica solid dispersion, the conversion increased 2.62 fold. At the same time, the product of hydrolysis was purified to get pure genistein. The method of enzymatic hydrolysis of genistin-nano-silica solid dispersion by snailase to obtain genistein is simple, efficiency and suitable for the modern scale production.

  14. Modeling atmospheric dispersion for reactor accident consequence evaluation

    International Nuclear Information System (INIS)

    Alpert, D.J.; Gudiksen, P.H.; Woodard, K.

    1982-01-01

    Atmospheric dispersion models are a central part of computer codes for the evaluation of potential reactor accident consequences. A variety of ways of treating to varying degrees the many physical processes that can have an impact on the predicted consequences exists. The currently available models are reviewed and their capabilities and limitations, as applied to reactor accident consequence analyses, are discussed

  15. Fuel Performance Modeling of U-Mo Dispersion Fuel: The thermal conductivity of the interaction layers of the irradiated U-Mo dispersion fuel

    Energy Technology Data Exchange (ETDEWEB)

    Mistarhi, Qusai M.; Ryu, Ho Jin [KAIST, Daejeon (Korea, Republic of)

    2016-05-15

    U-Mo/Al dispersion fuel performed well at a low burn-up. However, higher burn-up and higher fission rate irradiation testing showed enhanced fuel meat swelling which was caused by high interaction layer growth and pore formation. The performance of the dispersion type fuel in the irradiation and un-irradiation environment is very important. During the fabrication of the dispersion type fuel an Interaction Layer (IL) is formed due to the inter-diffusion between the U-Mo fuel particles and the Al matrix which is an intermetallic compound (U,Mo)Alx. During irradiation, the IL becomes amorphous causing a further decrease in the thermal conductivity and an increase in the centerline temperature of the fuel meat. Several analytical models and numerical methods were developed to study the performance of the unirradiated U-Mo/Al dispersion fuel. Two analytical models were developed to study the performance of the irradiated U-Mo/Al dispersion fuel. In these models, the thermal conductivity of the IL was assumed to be constant. The properties of the irradiated U-Mo dispersion fuel have been investigated recently by Huber et al. The objective of this study is to develop a correlation for IL thermal conductivity during irradiation as a function of the temperature and fission density from the experimentally measured thermal conductivity of the irradiated U-Mo/Al dispersion fuel. The thermal conductivity of IL during irradiation was calculated from the experimentally measured data and a correlation was developed from the thermal conductivity of IL as a function of T and fission density.

  16. Aquatic dispersion modelling of a tritium plume in Lake Ontario

    International Nuclear Information System (INIS)

    Klukas, M.H.; Moltyaner, G.L.

    1996-05-01

    Approximately 2900 kg of tritiated water, containing 2.3E+15 Bq of tritium, were released to Lake Ontario via the cooling water discharge when a leak developed in a moderator heat exchanger in Unit 1 at the Pickering Nuclear Generating Station (PNGS) on 1992 August 2. The release provided the opportunity to study the dispersion of a tritium plume in the coastal zone of Lake Ontario. Current direction over the two-week period following the release was predominantly parallel to the shore, and elevated tritium concentrations were observed up to 20 km east and 85 km west of the PNGS. Predictions of the tritium plume movement were made using current velocity measurements taken at 8-m depth, 2.5 km offshore from Darlington and using a empirical relationship where alongshore current speed is assumed to be proportional to the alongshore component of the wind speed. The tritium migration was best described using current velocity measurements. The tritium plume dispersion is modelled using the one-dimensional advection-dispersion equation. Transport parameters are the alongshore current speed and longitudinal dispersion coefficient. Longitudinal dispersion coefficients, estimated by fitting the solution of the advection-dispersion equation to measured concentration distance profiles ranged from 3.75 to 10.57 m 2 s -1 . Simulations using the fitted values of the dispersion coefficient were able to describe maximum tritium concentrations measured at water supply plants located within 25 km of Pickering to within a factor of 3. The dispersion coefficient is a function of spatial and temporal variability in current velocity and the fitted dispersion coefficients estimated here may not be suitable for predicting tritium plume dispersion under different current conditions. The sensitivity of the dispersion coefficient to variability in current conditions should be evaluated in further field experiments. (author). 13 refs., 7 tabs., 12 figs

  17. Scaling and modeling in the analysis of dispersive relaxation of ionic materials

    International Nuclear Information System (INIS)

    Macdonald, J. Ross

    2001-01-01

    Problems with scaling of conductive-system experimental M dat # double p rime#(ω) and σ dat prime(ω) data are considered and resolved by dispersive-relaxation-model fitting and comparison. Scaling is attempted for both synthetic and experimental M # double p rime#(ω) data sets. A crucial element in all experimental frequency-response data is the influence of the high-frequency-limiting dipolar-and-vibronic dielectric constant var-epsilon D∞ , often designated var-epsilon ∞ , and not related to ionic transport. It is shown that var-epsilon D∞ precludes scaling of M dat # double p rime#(ω) for ionic materials when the mobile-charge concentration varies. When the effects of var-epsilon D∞ are properly removed from the data, however, such scaling is viable. Only the σprime(ω) and var-epsilon # double p rime#(ω) parts of immittance response are uninfluenced by var-epsilon D∞ . Thus, scaling is possible for experimental σprime(ω) data sets under concentration variation if the shape parameter of a well-fitting model remains constant and if any parts of the response not associated with bulk ionic transport are eliminated. Comparison between the predictions of the original-modulus-formalism (OMF) response model of 1972 - 1973 and a corrected version of it that takes proper account of var-epsilon D∞ , the corrected modulus formalism (CMF), demonstrates that the role played by var-epsilon D∞ (or var-epsilon ∞ ) in the OMF is incorrect. Detailed fitting of data for three different ionic glasses using a Kohlrausch - Williams - Watts response model, the KWW 1 , for OMF and CMF analysis clearly demonstrates that the OMF leads to inconsistent shape-parameter (β 1 ) estimates and the CMF does not. The CMF KWW 1 model is shown to subsume, correct, and generalize the recent disparate scaling/fitting approaches of Sidebottom, Leon, Roling, and Ngai. [copyright] 2001 American Institute of Physics

  18. A model for dispersion of contaminants in the subway environment

    Energy Technology Data Exchange (ETDEWEB)

    Coke, L. R.; Sanchez, J. G.; Policastro, A. J.

    2000-05-03

    Although subway ventilation has been studied extensively, very little has been published on dispersion of contaminants in the subway environment. This paper presents a model that predicts dispersion of contaminants in a complex subway system. It accounts for the combined transient effects of train motion, station airflows, train car air exchange rates, and source release properties. Results are presented for a range of typical subway scenarios. The effects of train piston action and train car air exchange are discussed. The model could also be applied to analyze the environmental impact of hazardous materials releases such as chemical and biological agents.

  19. Absorptive and dispersive optical profiles in fluctuating environments: A stochastic model

    International Nuclear Information System (INIS)

    Paz, J.L.; Mendoza-Garcia, A.; Mastrodomenico, A.

    2011-01-01

    In this study, we determined the absorptive and dispersive optical profiles of a molecular system coupled with a thermal bath. Solvent effects were explicitly considered by modelling the non-radiative interaction with the solute as a random variable. The optical stochastical Bloch equations (OSBE) were solved using a time-ordered cumulant expansion with white noise as a correlation function. We found a solution for the Fourier component of coherence at the third order of perturbation for the nonlinear Four-wave mixing signal and produced analytical expressions for the optical responses of the system. Finally, we examined the behaviour of these properties with respect to the noise parameter, frequency detuning of the dynamic perturbation, and relaxation times.

  20. Meteorological Uncertainty of atmospheric Dispersion model results (MUD)

    DEFF Research Database (Denmark)

    Havskov Sørensen, Jens; Amstrup, Bjarne; Feddersen, Henrik

    The MUD project addresses assessment of uncertainties of atmospheric dispersion model predictions, as well as possibilities for optimum presentation to decision makers. Previously, it has not been possible to estimate such uncertainties quantitatively, but merely to calculate the ‘most likely’ di...

  1. Variational Boussinesq model for strongly nonlinear dispersive waves

    NARCIS (Netherlands)

    Lawrence, C.; Adytia, D.; van Groesen, E.

    2018-01-01

    For wave tank, coastal and oceanic applications, a fully nonlinear Variational Boussinesq model with optimized dispersion is derived and a simple Finite Element implementation is described. Improving a previous weakly nonlinear version, high waves over flat and varying bottom are shown to be

  2. Anomalous behavior in the third harmonic generation z response through dispersion induced shape changes and matching χ(3)

    Science.gov (United States)

    Pillai, Rajesh S.; Brakenhoff, G. J.; Müller, M.

    2006-09-01

    The third harmonic generation (THG) axial response in the vicinity of an interface formed by two isotropic materials of normal dispersion is typically single peaked, with the maximum intensity at the interface position. Here it is shown experimentally that this THG z response may show anomalous behavior—being double peaked with a dip coinciding with the interface position—when the THG contributions from both materials are of similar magnitude. The observed anomalous behavior is explained, using paraxial Gaussian theory, by considering dispersion induced shape changes in the THG z response.

  3. Applications of complex terrain meteorological models to emergency response management

    International Nuclear Information System (INIS)

    Yamada, Tetsuji; Leone, J.M. Jr.; Rao, K.S.; Dickerson, M.H.; Bader, D.C.; Williams, M.D.

    1989-01-01

    The Office of Health and Environmental Research (OHER), US Department of Energy (DOE), has supported the development of mesoscale transport and diffusion and meteorological models for several decades. The model development activities are closely tied to the OHER field measurement program which has generated a large amount of meteorological and tracer gas data that have been used extensively to test and improve both meteorological and dispersion models. This paper briefly discusses the history of the model development activities associated with the OHER atmospheric science program. The discussion will then focus on how results from this program have made their way into the emergency response community in the past, and what activities are presently being pursued to improve real-time emergency response capabilities. Finally, fruitful areas of research for improving real-time emergency response modeling capabilities are suggested. 35 refs., 5 figs

  4. 2-D model for pollutant dispersion at the coastal outfall off Paradip

    Digital Repository Service at National Institute of Oceanography (India)

    Suryanarayana, A.; Babu, M.T.; Vethamony, P.; Gouveia, A.D.

    Simulation of dispersion of the effluent discharge has been carried out using 2-D Model to verify the advection and diffusion of the pollutant patch of the proposed effluent disposal off Paradip, Orissa, India. The simulation of dispersion...

  5. Mechanistic model for dispersion coefficients in bubble column

    CSIR Research Space (South Africa)

    Skosana, PJ

    2015-05-01

    Full Text Available predicts axial and radial dispersion coefficients that are of the same order of magnitude as the reported data. Whereas the model is based on a description of the underlying physical phenomena, its validity and extrapolation is expected to be more reliable...

  6. Implementation of meso-scale radioactive dispersion model for GPU

    Energy Technology Data Exchange (ETDEWEB)

    Sunarko [National Nuclear Energy Agency of Indonesia (BATAN), Jakarta (Indonesia). Nuclear Energy Assessment Center; Suud, Zaki [Bandung Institute of Technology (ITB), Bandung (Indonesia). Physics Dept.

    2017-05-15

    Lagrangian Particle Dispersion Method (LPDM) is applied to model atmospheric dispersion of radioactive material in a meso-scale of a few tens of kilometers for site study purpose. Empirical relationships are used to determine the dispersion coefficient for various atmospheric stabilities. Diagnostic 3-D wind-field is solved based on data from one meteorological station using mass-conservation principle. Particles representing radioactive pollutant are dispersed in the wind-field as a point source. Time-integrated air concentration is calculated using kernel density estimator (KDE) in the lowest layer of the atmosphere. Parallel code is developed for GTX-660Ti GPU with a total of 1 344 scalar processors using CUDA. A test of 1-hour release discovers that linear speedup is achieved starting at 28 800 particles-per-hour (pph) up to about 20 x at 14 4000 pph. Another test simulating 6-hour release with 36 000 pph resulted in a speedup of about 60 x. Statistical analysis reveals that resulting grid doses are nearly identical in both CPU and GPU versions of the code.

  7. A random walk model to simulate the atmospheric dispersion of radionuclide

    Science.gov (United States)

    Zhuo, Jun; Huang, Liuxing; Niu, Shengli; Xie, Honggang; Kuang, Feihong

    2018-01-01

    To investigate the atmospheric dispersion of radionuclide in large-medium scale, a numerical simulation method based on random walk model for radionuclide atmospheric dispersion was established in the paper. The route of radionuclide migration and concentration distribution of radionuclide can be calculated out by using the method with the real-time or historical meteorological fields. In the simulation, a plume of radionuclide is treated as a lot of particles independent of each other. The particles move randomly by the fluctuations of turbulence, and disperse, so as to enlarge the volume of the plume and dilute the concentration of radionuclide. The dispersion of the plume over time is described by the variance of the particles. Through statistical analysis, the relationships between variance of the particles and radionuclide dispersion characteristics can be derived. The main mechanisms considered in the physical model are: (1) advection of radionuclide by mean air motion, (2) mixing of radionuclide by atmospheric turbulence, (3) dry and wet deposition, (4) disintegration. A code named RADES was developed according the method. And then, the European Tracer Experiment (ETEX) in 1994 is simulated by the RADES and FLEXPART codes, the simulation results of the concentration distribution of tracer are in good agreement with the experimental data.

  8. Unstructured Spectral Element Model for Dispersive and Nonlinear Wave Propagation

    DEFF Research Database (Denmark)

    Engsig-Karup, Allan Peter; Eskilsson, Claes; Bigoni, Daniele

    2016-01-01

    We introduce a new stabilized high-order and unstructured numerical model for modeling fully nonlinear and dispersive water waves. The model is based on a nodal spectral element method of arbitrary order in space and a -transformed formulation due to Cai, Langtangen, Nielsen and Tveito (1998). In...

  9. Dispersant Effectiveness, In-Situ Droplet Size Distribution and ...

    Science.gov (United States)

    This report summarizes two projects covered under an Interagency Agreement between the Bureau of Safety and Environmental Enforcement (BSEE) and the U.S. Environmental Protection Agency (EPA) in collaboration with the Bedford Institute of Oceanography, Department of Fisheries and Oceans Canada (BIO DFO), New Jersey Institute of Technology (NJIT) and Dalhousie University. Both projects dovetail together in addressing the ability to differentiate physical from chemical dispersion effectiveness using dispersed oil simulations within a flume tank for improving forensic response monitoring tools. This report is split into separateTasks based upon the two projects funded by BSEE: 1) Dispersant Effectiveness, In-Situ Droplet Size Distribution and Numerical Modeling to Assess Subsurface Dispersant Injection as a Deepwater Blowout Oil Spill Response Option. 2) Evaluation of Oil Fluorescence Characteristics to Improve Forensic Response Tools. This report summarizes 2 collaborative projects funded through an Interagency Agreement with DOI BSEE and a Cooperative Agreement with DFO Canada. BSEE required that the projects be combined into one report as they are both covered under the one Interagency Agreement. Task B (Fluorescence of oils) is an SHC 3.62 FY16 product.

  10. Design, synthesis, and film formation of stimuli-responsive colloidal dispersions containing phospholipids

    Science.gov (United States)

    Lestage, David Jackson

    These studies were undertaken to further understand the design of colloidal dispersions containing bio-active phospholipids (PL) as stabilizing agents and their stimuli-responsive behaviors during film formation. Methyl methacrylate (MMA) and n-butyl acrylate (nBA) dispersions were synthesized using anionic surfactants and PL, and the surface-responsiveness of coalesced films was monitored at the film-air (F-A) and film-substrate (F-S) interfaces after exposure to temperature, UV, pH, ionic strength, and enzymatic stimuli. Using spectroscopic molecular-level probes such as attenuated total reflectance (ATR) and internal reflection IR imaging (IRIRI), these studies show that structural features of PL and surfactants significantly affect stimuli-responsiveness of polymeric films. MMA/nBA homopolymer, blend, copolymer, and core-shell particle coalescence studies indicated that controlled permeability is influenced by particle composition and sodium dioctyl sulfosuccinate (SDOSS) mobility to the F-A interface is enhanced in response to temperature. Utilization of hydrogenated soybean phosphocholine (HSPC) as a co-surfactant with SDOSS resulted in bimodal p-MMA/nBA colloidal particles, and experiments showed that ionic interactions with HSPC inhibit SDOSS mobility. However, the controlled release of individual species is detected in the presence of Ca2+ ionic strength stimuli. Utilizing 1,2-bis(10,12-tricosadiynoyl)- sn-glycero-3-phosphocholine (DCPC), cocklebur-shape particle morphologies were obtained and using transmission electron microscopy (TEM), self-assembled tubules were detected at particle interfaces, but not in the presence of Ca 2+. At altered concentration levels of DCPC, surface localized ionic clusters (SLICs) composed of SDOSS and DCPC form at the F-A and F-S interfaces in response to temperature and ionic strength stimuli. Micelle formation of 1-myristoyl-2-hydroxy-sn-glycero-phosphocholine (MHPC) stabilizes unimodal p-MMA/nBA colloidal particles

  11. User assessment of smoke-dispersion models for wildland biomass burning.

    Science.gov (United States)

    Steve Breyfogle; Sue A. Ferguson

    1996-01-01

    Several smoke-dispersion models, which currently are available for modeling smoke from biomass burns, were evaluated for ease of use, availability of input data, and output data format. The input and output components of all models are listed, and differences in model physics are discussed. Each model was installed and run on a personal computer with a simple-case...

  12. Federal Response Assets for a Radioactive Dispersal Device Incident

    Energy Technology Data Exchange (ETDEWEB)

    Sullivan,T.

    2009-06-30

    If a large scale RDD event where to occur in New York City, the magnitude of the problem would likely exceed the capabilities of City and State to effectively respond to the event. New York State could request Federal Assistance if the United States President has not already made the decision to provide it. The United States Federal Government has a well developed protocol to respond to emergencies. The National Response Framework (NRF) describes the process for responding to all types of emergencies including RDD incidents. Depending on the location and type of event, the NRF involves appropriate Federal Agencies, e.g., Department of Homeland Security (DHS), the Department of Energy (DOE), Environmental Protection Agency (EPA), United States Coast Guard (USCG), Department of Defense (DOD), Department of Justice (DOJ), Department of Agriculture (USDA), and Nuclear Regulatory Commission (NRC). The Federal response to emergencies has been refined and improved over the last thirty years and has been tested on natural disasters (e.g. hurricanes and floods), man-made disasters (oil spills), and terrorist events (9/11). However, the system has never been tested under an actual RDD event. Drills have been conducted with Federal, State, and local agencies to examine the initial (early) phases of such an event (TopOff 2 and TopOff 4). The Planning Guidance for Protection and Recovery Following Radiological Dispersal Device (RDD) and Improvised Nuclear Device (IND) incidents issued by the Department of Homeland Security (DHS) in August 2008 has never been fully tested in an interagency exercise. Recently, another exercise called Empire 09 that was situated in Albany, New York was conducted. Empire 09 consists of 3 different exercises be held in May and June, 2009. The first exercise, May 2009, involved a table top exercise for phase 1 (0-48 hours) of the response to an RDD incident. In early June, a full-scale 3- day exercise was conducted for the mid-phase response (48

  13. Benchmarking of numerical models describing the dispersion of radionuclides in the Arctic Seas

    DEFF Research Database (Denmark)

    Scott, E.M.; Gurbutt, P.; Harms, I.

    1997-01-01

    As part of the International Arctic Seas Assessment Project (IASAP) of the International Atomic Energy Agency (IAEA), a working group was created to model the dispersal and transfer of radionuclides released from radioactive waste disposed of in the Kara Sea. The objectives of this group are: (1......) development of realistic and reliable assessment models for the dispersal of radioactive contaminants both within, and from, the Arctic ocean; and (2) evaluation of the contributions of different transfer mechanisms to contaminant dispersal and hence, ultimately, to the risks to human health and environment...

  14. Real-time dispersion calculation using the Lagrange model LASAT

    International Nuclear Information System (INIS)

    Janicke, L.

    1987-01-01

    The LASAT (Lagrange Simulation of Aerosol Transport) dispersion model demonstrates pollutant transport in the atmosphere by simulating the paths of representative random samples of pollutant particles on the computer as natural as possible. The author demonstrates the generated particle paths and refers to literature for details of the model algorithm. (DG) [de

  15. RANS modeling of scalar dispersion from localized sources within a simplified urban-area model

    Science.gov (United States)

    Rossi, Riccardo; Capra, Stefano; Iaccarino, Gianluca

    2011-11-01

    The dispersion of a passive scalar downstream a localized source within a simplified urban-like geometry is examined by means of RANS scalar flux models. The computations are conducted under conditions of neutral stability and for three different incoming wind directions (0°, 45°, 90°) at a roughness Reynolds number of Ret = 391. A Reynolds stress transport model is used to close the flow governing equations whereas both the standard eddy-diffusivity closure and algebraic flux models are employed to close the transport equation for the passive scalar. The comparison with a DNS database shows improved reliability from algebraic scalar flux models towards predicting both the mean concentration and the plume structure. Since algebraic flux models do not increase substantially the computational effort, the results indicate that the use of tensorial-diffusivity can be promising tool for dispersion simulations for the urban environment.

  16. Modelling and tracer studies of atmospheric dispersion and deposition in regions of complex topography

    International Nuclear Information System (INIS)

    Norden, C.E.

    1981-11-01

    An indium tracer aerosol generating apparatus based on an alcohol/oxygen burner, and an analytical procedure by which filter samples containing tracer material could be analysed quantitatively by means of neutron activation analysis, were developed for use in atmospheric dispersion and deposition studies. A number of series of atmospheric dispersion experiments were conducted in the Richards Bay and Koeberg- Cape Town areas. The results are given, comparing the airbone tracer concentrations measured at ground level with values predicted by means of a numerical model, utilising two to three schemes, varying in sophistication, for calculating the dispersion coefficients. Recommendations are given regarding a dispersion model and dispersion coefficients for regular use in the Koeberg area, and ways for estimating plume trajectories

  17. Low frequency complex dielectric (conductivity) response of dilute clay suspensions: Modeling and experiments.

    Science.gov (United States)

    Hou, Chang-Yu; Feng, Ling; Seleznev, Nikita; Freed, Denise E

    2018-04-11

    In this work, we establish an effective medium model to describe the low-frequency complex dielectric (conductivity) dispersion of dilute clay suspensions. We use previously obtained low-frequency polarization coefficients for a charged oblate spheroidal particle immersed in an electrolyte as the building block for the Maxwell Garnett mixing formula to model the dilute clay suspension. The complex conductivity phase dispersion exhibits a near-resonance peak when the clay grains have a narrow size distribution. The peak frequency is associated with the size distribution as well as the shape of clay grains and is often referred to as the characteristic frequency. In contrast, if the size of the clay grains has a broad distribution, the phase peak is broadened and can disappear into the background of the canonical phase response of the brine. To benchmark our model, the low-frequency dispersion of the complex conductivity of dilute clay suspensions is measured using a four-point impedance measurement, which can be reliably calibrated in the frequency range between 0.1 Hz and 10 kHz. By using a minimal number of fitting parameters when reliable information is available as input for the model and carefully examining the issue of potential over-fitting, we found that our model can be used to fit the measured dispersion of the complex conductivity with reasonable parameters. The good match between the modeled and experimental complex conductivity dispersion allows us to argue that our simplified model captures the essential physics for describing the low-frequency dispersion of the complex conductivity of dilute clay suspensions. Copyright © 2018 Elsevier Inc. All rights reserved.

  18. Air quality dispersion models from energy sources

    International Nuclear Information System (INIS)

    Lazarevska, Ana

    1996-01-01

    Along with the continuing development of new air quality models that cover more complex problems, in the Clean Air Act, legislated by the US Congress, a consistency and standardization of air quality model applications were encouraged. As a result, the Guidelines on Air Quality Models were published, which are regularly reviewed by the Office of Air Quality Planning and Standards, EPA. These guidelines provide a basis for estimating the air quality concentrations used in accessing control strategies as well as defining emission limits. This paper presents a review and analysis of the recent versions of the models: Simple Terrain Stationary Source Model; Complex Terrain Dispersion Model; Ozone,Carbon Monoxide and Nitrogen Dioxide Models; Long Range Transport Model; Other phenomenon Models:Fugitive Dust/Fugitive Emissions, Particulate Matter, Lead, Air Pathway Analyses - Air Toxic as well as Hazardous Waste. 8 refs., 4 tabs., 2 ills

  19. Mathematical modeling of pigment dispersion taking into account the full agglomerate particle size distribution

    DEFF Research Database (Denmark)

    Kiil, Søren

    2017-01-01

    The purpose of this work is to develop a mathematical model that can quantify the dispersion of pigments, with a focus on the mechanical breakage of pigment agglomerates. The underlying physical mechanism was assumed to be surface erosion of spherical pigment agglomerates. The full agglomerate pa.......g., in the development of novel dispersion principles and for analysis of dispersion failures. The general applicability of the model, beyond the three pigments considered, needs to be confirmed....

  20. Meteorological monitoring for dose assessment and emergency response modeling - how much is enough?

    International Nuclear Information System (INIS)

    Glantz, C.S.

    1990-01-01

    Individuals responsible for emergency response or environmental/dose assessment routinely ask if there are enough meteorological data to adequately support their objectives. The answer requires detailed consideration of the intended applications, capabilities of the atmospheric dispersion model data, pollutant release characteristics, terrain in the modeling region, and size and distribution of the human population in the modeling domain. The meteorologist's detailed knowledge of, and experience in, studying atmospheric transport and diffusion can assist in determining the appropriate level of meteorological monitoring

  1. Plutonium explosive dispersal modeling using the MACCS2 computer code

    International Nuclear Information System (INIS)

    Steele, C.M.; Wald, T.L.; Chanin, D.I.

    1998-01-01

    The purpose of this paper is to derive the necessary parameters to be used to establish a defensible methodology to perform explosive dispersal modeling of respirable plutonium using Gaussian methods. A particular code, MACCS2, has been chosen for this modeling effort due to its application of sophisticated meteorological statistical sampling in accordance with the philosophy of Nuclear Regulatory Commission (NRC) Regulatory Guide 1.145, ''Atmospheric Dispersion Models for Potential Accident Consequence Assessments at Nuclear Power Plants''. A second advantage supporting the selection of the MACCS2 code for modeling purposes is that meteorological data sets are readily available at most Department of Energy (DOE) and NRC sites. This particular MACCS2 modeling effort focuses on the calculation of respirable doses and not ground deposition. Once the necessary parameters for the MACCS2 modeling are developed and presented, the model is benchmarked against empirical test data from the Double Tracks shot of project Roller Coaster (Shreve 1965) and applied to a hypothetical plutonium explosive dispersal scenario. Further modeling with the MACCS2 code is performed to determine a defensible method of treating the effects of building structure interaction on the respirable fraction distribution as a function of height. These results are related to the Clean Slate 2 and Clean Slate 3 bunkered shots of Project Roller Coaster. Lastly a method is presented to determine the peak 99.5% sector doses on an irregular site boundary in the manner specified in NRC Regulatory Guide 1.145 (1983). Parametric analyses are performed on the major analytic assumptions in the MACCS2 model to define the potential errors that are possible in using this methodology

  2. Plutonium explosive dispersal modeling using the MACCS2 computer code

    Energy Technology Data Exchange (ETDEWEB)

    Steele, C.M.; Wald, T.L.; Chanin, D.I.

    1998-11-01

    The purpose of this paper is to derive the necessary parameters to be used to establish a defensible methodology to perform explosive dispersal modeling of respirable plutonium using Gaussian methods. A particular code, MACCS2, has been chosen for this modeling effort due to its application of sophisticated meteorological statistical sampling in accordance with the philosophy of Nuclear Regulatory Commission (NRC) Regulatory Guide 1.145, ``Atmospheric Dispersion Models for Potential Accident Consequence Assessments at Nuclear Power Plants``. A second advantage supporting the selection of the MACCS2 code for modeling purposes is that meteorological data sets are readily available at most Department of Energy (DOE) and NRC sites. This particular MACCS2 modeling effort focuses on the calculation of respirable doses and not ground deposition. Once the necessary parameters for the MACCS2 modeling are developed and presented, the model is benchmarked against empirical test data from the Double Tracks shot of project Roller Coaster (Shreve 1965) and applied to a hypothetical plutonium explosive dispersal scenario. Further modeling with the MACCS2 code is performed to determine a defensible method of treating the effects of building structure interaction on the respirable fraction distribution as a function of height. These results are related to the Clean Slate 2 and Clean Slate 3 bunkered shots of Project Roller Coaster. Lastly a method is presented to determine the peak 99.5% sector doses on an irregular site boundary in the manner specified in NRC Regulatory Guide 1.145 (1983). Parametric analyses are performed on the major analytic assumptions in the MACCS2 model to define the potential errors that are possible in using this methodology.

  3. mathematical modelling of atmospheric dispersion of pollutants

    International Nuclear Information System (INIS)

    Mohamed, M.E.

    2002-01-01

    the main objectives of this thesis are dealing with environmental problems adopting mathematical techniques. in this respect, atmospheric dispersion processes have been investigated by improving the analytical models to realize the realistic physical phenomena. to achieve these aims, the skeleton of this work contained both mathematical and environmental topics,performed in six chapters. in chapter one we presented a comprehensive review study of most important informations related to our work such as thermal stability , plume rise, inversion, advection , dispersion of pollutants, gaussian plume models dealing with both radioactive and industrial contaminants. chapter two deals with estimating the decay distance as well as the decay time of either industrial or radioactive airborne pollutant. further, highly turbulent atmosphere has been investigated as a special case in the three main thermal stability classes namely, neutral, stable, and unstable atmosphere. chapter three is concerned with obtaining maximum ground level concentration of air pollutant. the variable effective height of pollutants has been considered throughout the mathematical treatment. as a special case the constancy of effective height has been derived mathematically and the maximum ground level concentration as well as its location have been established

  4. Randomly dispersed particle fuel model in the PSG Monte Carlo neutron transport code

    International Nuclear Information System (INIS)

    Leppaenen, J.

    2007-01-01

    High-temperature gas-cooled reactor fuels are composed of thousands of microscopic fuel particles, randomly dispersed in a graphite matrix. The modelling of such geometry is complicated, especially using continuous-energy Monte Carlo codes, which are unable to apply any deterministic corrections in the calculation. This paper presents the geometry routine developed for modelling randomly dispersed particle fuels using the PSG Monte Carlo reactor physics code. The model is based on the delta-tracking method, and it takes into account the spatial self-shielding effects and the random dispersion of the fuel particles. The calculation routine is validated by comparing the results to reference MCNP4C calculations using uranium and plutonium based fuels. (authors)

  5. Solute transport along a single fracture in a porous rock: a simple analytical solution and its extension for modeling velocity dispersion

    Science.gov (United States)

    Liu, Longcheng; Neretnieks, Ivars; Shahkarami, Pirouz; Meng, Shuo; Moreno, Luis

    2018-02-01

    A simple and robust solution is developed for the problem of solute transport along a single fracture in a porous rock. The solution is referred to as the solution to the single-flow-path model and takes the form of a convolution of two functions. The first function is the probability density function of residence-time distribution of a conservative solute in the fracture-only system as if the rock matrix is impermeable. The second function is the response of the fracture-matrix system to the input source when Fickian-type dispersion is completely neglected; thus, the effects of Fickian-type dispersion and matrix diffusion have been decoupled. It is also found that the solution can be understood in a way in line with the concept of velocity dispersion in fractured rocks. The solution is therefore extended into more general cases to also account for velocity variation between the channels. This leads to a development of the multi-channel model followed by detailed statistical descriptions of channel properties and sensitivity analysis of the model upon changes in the model key parameters. The simulation results obtained by the multi-channel model in this study fairly well agree with what is often observed in field experiments—i.e. the unchanged Peclet number with distance, which cannot be predicted by the classical advection-dispersion equation. In light of the findings from the aforementioned analysis, it is suggested that forced-gradient experiments can result in considerably different estimates of dispersivity compared to what can be found in natural-gradient systems for typical channel widths.

  6. Open Burn/Open Detonation Dispersion Model (OBODM) User's Guide. Volume I. User's Instructions

    National Research Council Canada - National Science Library

    Bjorklund, Jay

    1998-01-01

    ...) of obsolete munitions and solid propellants. OBODM uses loud/plume rise, dispersion, and deposition algorithms taken from existing models for instantaneous and quasi-continuous sources to predict the downwind transport and dispersion...

  7. Application of GIS to modified models of vehicle emission dispersion

    Science.gov (United States)

    Jin, Taosheng; Fu, Lixin

    This paper reports on a preliminary study of the forecast and evaluation of transport-related air pollution dispersion in urban areas. Some modifications of the traditional Gauss dispersion models are provided, and especially a crossroad model is built, which considers the great variation of vehicle emission attributed to different driving patterns at the crossroad. The above models are combined with a self-developed geographic information system (GIS) platform, and a simulative system with graphical interfaces is built. The system aims at visually describing the influences on the urban environment by urban traffic characteristics and therefore gives a reference to the improvement of urban air quality. Due to the introduction of a self-developed GIS platform and a creative crossroad model, the system is more effective, flexible and accurate. Finally, a comparison of the simulated (predicted) and observed hourly concentration is given, which indicates a good simulation.

  8. Estimating sub-surface dispersed oil concentration using acoustic backscatter response.

    Science.gov (United States)

    Fuller, Christopher B; Bonner, James S; Islam, Mohammad S; Page, Cheryl; Ojo, Temitope; Kirkey, William

    2013-05-15

    The recent Deepwater Horizon disaster resulted in a dispersed oil plume at an approximate depth of 1000 m. Several methods were used to characterize this plume with respect to concentration and spatial extent including surface supported sampling and autonomous underwater vehicles with in situ instrument payloads. Additionally, echo sounders were used to track the plume location, demonstrating the potential for remote detection using acoustic backscatter (ABS). This study evaluated use of an Acoustic Doppler Current Profiler (ADCP) to quantitatively detect oil-droplet suspensions from the ABS response in a controlled laboratory setting. Results from this study showed log-linear ABS responses to oil-droplet volume concentration. However, the inability to reproduce ABS response factors suggests the difficultly in developing meaningful calibration factors for quantitative field analysis. Evaluation of theoretical ABS intensity derived from the particle size distribution provided insight regarding method sensitivity in the presence of interfering ambient particles. Copyright © 2013 Elsevier Ltd. All rights reserved.

  9. Uncertainty in dispersion forecasts using meteorological ensembles

    International Nuclear Information System (INIS)

    Chin, H N; Leach, M J

    1999-01-01

    The usefulness of dispersion forecasts depends on proper interpretation of results. Understanding the uncertainty in model predictions and the range of possible outcomes is critical for determining the optimal course of action in response to terrorist attacks. One of the objectives for the Modeling and Prediction initiative is creating tools for emergency planning for special events such as the upcoming the Olympics. Meteorological forecasts hours to days in advance are used to estimate the dispersion at the time of the event. However, there is uncertainty in any meteorological forecast, arising from both errors in the data (both initial conditions and boundary conditions) and from errors in the model. We use ensemble forecasts to estimate the uncertainty in the forecasts and the range of possible outcomes

  10. Stress modeling in colloidal dispersions undergoing non-viscometric flows

    Science.gov (United States)

    Dolata, Benjamin; Zia, Roseanna

    2017-11-01

    We present a theoretical study of the stress tensor for a colloidal dispersion undergoing non-viscometric flow. In such flows, the non-homogeneous suspension stress depends on not only the local average total stresslet-the sum of symmetric first moments of both the hydrodynamic traction and the interparticle force-but also on the average quadrupole, octupole, and higher-order moments. To compute the average moments, we formulate a six dimensional Smoluchowski equation governing the microstructural evolution of a suspension in an arbitrary fluid velocity field. Under the conditions of rheologically slow flow, where the Brownian relaxation of the particles is much faster than the spatiotemporal evolution of the flow, the Smoluchowski equation permits asymptotic solution, revealing a suspension stress that follows a second-order fluid constitutive model. We obtain a reciprocal theorem and utilize it to show that all constitutive parameters of the second-order fluid model may be obtained from two simpler linear-response problems: a suspension undergoing simple shear and a suspension undergoing isotropic expansion. The consequences of relaxing the assumption of rheologically slow flow, including the appearance of memory and microcontinuum behaviors, are discussed.

  11. Dispersant effectiveness in the field on fresh oils and emulsions

    International Nuclear Information System (INIS)

    Lunel, T.; Davies, L.

    1996-01-01

    A detailed data set on the effectiveness of dispersants on fresh oils and emulsions, was presented. The data set could be used to calibrate laboratory dispersant tests and dispersion models so that oil spill response teams would have accurate information to make decisions regarding remediation processes. AEA Technology developed steady state continuous release experiments to provide a data set with quantitative measures of dispersant effectiveness in the field. The Sea Empress incident was closely monitored in order to compare the quantification obtained through field trials. It was noted that the prediction of the percentage of oil dispersed chemically is not the only indication of whether or not to use a dispersant. The important determinant to consider should be the extent to which the natural dispersion process would be enhanced by dispersant application. 17 refs., 5 tabs., 18 figs

  12. A laboratory dispersant effectiveness test which reflects dispersant efficiency in the field

    International Nuclear Information System (INIS)

    Lunel, T.; Wood, P.

    1996-01-01

    Oil dispersion efficiencies of surfactants, from laboratory dispersion tests and field data were compared and calibrated. Data from an oil spill, where dispersants were used as a major part of the response, was analysed. The data was accumulated through the monitoring of the dispersant operation of the Sea Empress spill incident, in which Forties Blend oil was spilled at sea. This detailed data set was used to calibrate existing laboratory dispersant tests, and to devise a new International Dispersant Effectiveness Test. The objective was to create a comprehensive guide to decision making on whether and when to start a dispersant spraying operation. The dispersion efficiencies obtained from the laboratory dispersant tests were compared with field data. Flume tests produced the highest percentage of dispersed oil for all the dispersal tests. However, it was emphasised that the total percentage of oil dispersed should not be the only measure of dispersant effectiveness, since it does not distinguish between the contribution of natural and chemically enhanced dispersion. 9 refs., 1 tab., 9 figs

  13. Dispersion of tracers by the oceanic eddy field modelling programme

    International Nuclear Information System (INIS)

    Richards, K.J.; O'Farrell, S.P.

    1987-01-01

    A numerical model has been developed to study the dispersion of tracers by the oceanic eddy field. The present study is designed to study the dispersion of particles in a mesoscale eddy field produced by the numerical model. Dispersion rates are calculated for flows above three types of topography, a flat bottom, a random collection of hills and a ridge. The presence of topography is found to significantly affect the flow. The effective diffusion coefficient of the flow near the bottom is reduced by 20% for the random topography and 60% for the ridge from that for the flat bottom case. Estimates are given of the number of float years required to obtain a given accuracy for the diffusion coefficient. At the surface a modest number of floats (order 5) are required to obtain a 50% accuracy. However at the bottom, to be within a factor of 2 of the true value for the flows considered requires respectively 26, 42 and 103 float years for the flat, random and ridge cases. (author)

  14. Atmospheric dispersion estimates in the vicinity of buildings

    International Nuclear Information System (INIS)

    Ramsdell, J.V. Jr.; Fosmire, C.J.

    1995-01-01

    A model describing atmospheric dispersion in the vicinity of buildings was developed for the U.S. Nuclear Regulatory Commission (NRC) in the late 1980s. That model has recently undergone additional peer review. The reviewers identified four areas of concern related to the model and its application. This report describes revisions to the model in response to the reviewers concerns. Model revision involved incorporation of explicit treatment of enhanced dispersion at low wind speeds in addition to explicit treatment of enhanced dispersion at high speeds resulting from building wakes. Model parameters are evaluated from turbulence data. Experimental diffusion data from seven reactor sites are used for model evaluation. Compared with models recommended in current NRC guidance to licensees, the revised model is less biased and shows more predictive skill. The revised model is also compared with two non-Gaussian models developed to estimate maximum concentrations in building wakes. The revised model concentration predictions are nearly the same as the predictions of the non-Gaussian models. On the basis of these comparisons of the revised model concentration predictions with experimental data and the predictions of other models, the revised model is found to be an appropriate model for estimating concentrations in the vicinity of buildings

  15. Modelling of pollution dispersion in atmosphere; Modelowanie procesow propagacji skazen w atmosferze

    Energy Technology Data Exchange (ETDEWEB)

    Borysiewicz, M; Stankiewicz, R

    1994-12-31

    The paper contains the review of the mathematical foundation of atmospheric dispersion models. The atmospheric phenomena relevant to atmospheric dispersion model are discussed. In particular the parametrization of processes with time and space scales smaller than numerical grid size, limited by available computer power, is presented. The special attention was devoted to similarity theory and parametrization of boundary layer. The numerical methods are analysed and the drawbacks of the method are presented. (author). 99 refs, 15 figs, 3 tabs.

  16. Viscoelasticity and diffusional properties of colloidal model dispersions

    International Nuclear Information System (INIS)

    Naegele, Gerhard

    2003-01-01

    We examine linear viscoelastic, and translational and rotational diffusion properties of colloidal model dispersions. Theoretical results are discussed, in comparison with experiments, for monodisperse suspensions of charged and neutral colloidal spheres, and for binary dispersions of differently sized tracer and host particles. The theoretical methods employed comprise a mode-coupling scheme for Brownian particles, and a rooted cluster expansion scheme of tracer diffusion with two- and three-body hydrodynamic interactions included. We analyse in particular the validity of various empirical generalized Stokes-Einstein-Debye (SED) relations between the (dynamic) shear viscosity and translational/rotational diffusion coefficients. Some of these generalized SED relations are basic to microrheological measurements aimed at characterizing the viscoelasticity of complex fluids on the basis of the diffusional properties of immersed tracer particles

  17. Viscoelasticity and diffusional properties of colloidal model dispersions

    CERN Document Server

    Naegele, G

    2003-01-01

    We examine linear viscoelastic, and translational and rotational diffusion properties of colloidal model dispersions. Theoretical results are discussed, in comparison with experiments, for monodisperse suspensions of charged and neutral colloidal spheres, and for binary dispersions of differently sized tracer and host particles. The theoretical methods employed comprise a mode-coupling scheme for Brownian particles, and a rooted cluster expansion scheme of tracer diffusion with two- and three-body hydrodynamic interactions included. We analyse in particular the validity of various empirical generalized Stokes-Einstein-Debye (SED) relations between the (dynamic) shear viscosity and translational/rotational diffusion coefficients. Some of these generalized SED relations are basic to microrheological measurements aimed at characterizing the viscoelasticity of complex fluids on the basis of the diffusional properties of immersed tracer particles.

  18. Dispersive versus constant-geometry models of the neutron-208Pb mean field

    International Nuclear Information System (INIS)

    Mahaux, C.; Sartor, R.

    1990-01-01

    Phenomenological optical-model analyses of differential elastic scattering cross sections of neutrons by 208 Pb indicate that the radius of the real part of the potential decreases with increasing energy in the domain 4< E<40 MeV. On the other hand, the experimental total cross section is compatible with a real potential whose radial shape is energy independent. In order to clarify this situation, we compare a 'constant geometry' model whose real part has an energy-independent radial shape with a 'dispersive model' whose real part has an energy-dependent radial shape calculated from the dispersion relation which connects the real and imaginary parts of the field. The following three main features are considered. (i) The junction of the optical-model potential with the shell-model potential at negative energy. (ii) The agreement between the calculated total and differential cross sections and their experimental values. (iii) The extent to which the real part of the optical-model potential can be accurately determined by analyzing the total cross section only. It is concluded that the presently available experimental data support the existence of an energy dependence of the radial shape of the real potential, in keeping with the dispersion relation. A new parametrization of a 'dispersive' mean field is also presented. It does not involve more parameters than the previously published one but takes better account of the physical properties of the spectral functions; it is shown to improve the agreement between predicted and experimental scattering data. (orig.)

  19. Tracer dispersion - experiment and CFD

    International Nuclear Information System (INIS)

    Zitny, R.

    2004-01-01

    Description of tracer distribution by means of dispersion models is a method successfully used in process engineering for fifty years. Application of dispersion models in reactor engineering for characterization of flows in column apparatus, heat exchangers, etc. is summarized and experimental tracer techniques as well as CFD methods for dispersion coefficients evaluation are discussed. Possible extensions of thermal axial dispersion model (ADM) and a core-wall ADM model suitable for description of tracer dispersion in laminar flows are suggested as well as CFD implementation as 1D finite elements. (author)

  20. OSCAR2000 : a multi-component 3-dimensional oil spill contingency and response model

    International Nuclear Information System (INIS)

    Reed, M.; Daling, P.S.; Brakstad, O.G.; Singsaas, I.; Faksness, L.-G.; Hetland, B.; Ekrol, N.

    2000-01-01

    Researchers at SINTEF in Norway have studied the weathering of surface oil. They developed a realistic model to analyze alternative spill response strategies. The model represented the formation and composition of the water-accommodated fraction (WAF) of oil for both treated and untreated oil spills. As many as 25 components, pseudo-components, or metabolites were allowed for the specification of oil. Calculations effected using OSCAR were verified in great detail on numerous occasions. The model made it possible to determine rather realistically the dissolution, transformation, and toxicology of dispersed oil clouds, as well as evaporation, emulsification, and natural dispersion. OSCAR comprised a data-based oil weathering model, a three-dimensional oil trajectory and chemical fates model, an oil spill combat model, exposure models for birds, marine mammals, fish and ichthyoplankton. 17 refs., 1 tab., 11 figs

  1. The use of nonlinear regression analysis for integrating pollutant concentration measurements with atmospheric dispersion modeling for source term estimation

    International Nuclear Information System (INIS)

    Edwards, L.L.; Freis, R.P.; Peters, L.G.; Gudiksen, P.H.; Pitovranov, S.E.

    1993-01-01

    The accuracy associated with assessing the environmental consequences of an accidental release of radioactivity is highly dependent on the knowledge of the source term characteristics, which are generally poorly known. The development of an automated numerical technique that integrates the radiological measurements with atmospheric dispersion modeling for more accurate source term estimation is reported. Often, this process of parameter estimation is performed by an emergency response assessor, who takes an intelligent first guess at the model parameters, then, comparing the model results with whatever measurements are available, makes an intuitive, informed next guess of the model parameters. This process may be repeated any number of times until the assessor feels that the model results are reasonable in terms of the measured observations. A new approach, based on a nonlinear least-squares regression scheme coupled with the existing Atmospheric Release Advisory Capability three-dimensional atmospheric dispersion models, is to supplement the assessor's intuition with automated mathematical methods that do not significantly increase the response time of the existing predictive models. The viability of the approach is evaluated by estimation of the known SF 6 tracer release rates associated with the Mesoscale Atmospheric Transport Studies tracer experiments conducted at the Savannah River Laboratory during 1983. These 19 experiments resulted in 14 successful, separate tracer releases with sampling of the tracer plumes along the cross-plume arc situated ∼30 km from the release site

  2. Improving long-range dispersion predictions with ETEX real-time and a-posteriori model evaluations

    International Nuclear Information System (INIS)

    Desiato, F.

    1997-01-01

    The Italian environmental Protection Agency (ANPA), which is responsible for the evaluation of the consequences of accidental releases into the atmosphere, has participated to both the real-time (phase-1) and a-posteriori (phase-2) ETEX model evaluations. The double benchmark actually constituted an invaluable experience for better understanding the skill and limits of the present long-range dispersion modelling capabilities. In particular, the strong difference between phase-1 and phase-2 model performance emphasised the opportunity to modify, improve or tune a number of specific aspects of the overall simulation. ETEX model runs were carried out with the Lagrangian particle model APOLLO. The meteorological input was constituted by ECMWF fields. Three-hourly average concentrations paired in space and time and time-integrated concentrations were used in the evaluation of the results, based on a set of statistical indexes and concentration contour lines and scatter diagrams

  3. LANDSCAPE MODELING OF CHARACTERISTIC HABITAT SCALES, DISPERSAL, AND CONNECTIVITY FROM THE PERSPECTIVE OF THE ORGANISM

    Science.gov (United States)

    A modeling framework was developed to investigate the interactive effects of life history characteristics and landscape heterogeneity on dispersal success. An individual-based model was used to examine how dispersal between resource patches is affected by four landscape characte...

  4. Dispersion-convolution model for simulating peaks in a flow injection system.

    Science.gov (United States)

    Pai, Su-Cheng; Lai, Yee-Hwong; Chiao, Ling-Yun; Yu, Tiing

    2007-01-12

    A dispersion-convolution model is proposed for simulating peak shapes in a single-line flow injection system. It is based on the assumption that an injected sample plug is expanded due to a "bulk" dispersion mechanism along the length coordinate, and that after traveling over a distance or a period of time, the sample zone will develop into a Gaussian-like distribution. This spatial pattern is further transformed to a temporal coordinate by a convolution process, and finally a temporal peak image is generated. The feasibility of the proposed model has been examined by experiments with various coil lengths, sample sizes and pumping rates. An empirical dispersion coefficient (D*) can be estimated by using the observed peak position, height and area (tp*, h* and At*) from a recorder. An empirical temporal shift (Phi*) can be further approximated by Phi*=D*/u2, which becomes an important parameter in the restoration of experimental peaks. Also, the dispersion coefficient can be expressed as a second-order polynomial function of the pumping rate Q, for which D*(Q)=delta0+delta1Q+delta2Q2. The optimal dispersion occurs at a pumping rate of Qopt=sqrt[delta0/delta2]. This explains the interesting "Nike-swoosh" relationship between the peak height and pumping rate. The excellent coherence of theoretical and experimental peak shapes confirms that the temporal distortion effect is the dominating reason to explain the peak asymmetry in flow injection analysis.

  5. Pollen Forecast and Dispersion Modelling

    Science.gov (United States)

    Costantini, Monica; Di Giuseppe, Fabio; Medaglia, Carlo Maria; Travaglini, Alessandro; Tocci, Raffaella; Brighetti, M. Antonia; Petitta, Marcello

    2014-05-01

    The aim of this study is monitoring, mapping and forecast of pollen distribution for the city of Rome using in-situ measurements of 10 species of common allergenic pollens and measurements of PM10. The production of daily concentration maps, associated to a mobile phone app, are innovative compared to existing dedicated services to people who suffer from respiratory allergies. The dispersal pollen is one of the most well-known causes of allergic disease that is manifested by disorders of the respiratory functions. Allergies are the third leading cause of chronic disease and it is estimated that tens millions of people in Italy suffer from it. Recent works reveal that during the last few years there was a progressive increase of affected subjects, especially in urban areas. This situation may depend: on the ability to transport of pollutants, on the ability to react between pollutants and pollen and from a combination of other irritants, existing in densely populated and polluted urban areas. The methodology used to produce maps is based on in-situ measurements time series relative to 2012, obtained from networks of air quality and pollen stations in the metropolitan area of Rome. The monitoring station aerobiological of University of Rome "Tor Vergata" is located at the Department of Biology. The instrument used to pollen monitoring is a volumetric sampler type Hirst (Hirst 1952), Model 2000 VPPS Lanzoni; the data acquisition is carried out as reported in Standard UNI 11008:2004 - "Qualità dell'aria - Metodo di campionamento e conteggio dei granuli pollinici e delle spore fungine aerodisperse" - the protocol that describes the procedure for measuring of the concentration of pollen grains and fungal spores dispersed into the atmosphere, and reported in the "Manuale di gestione e qualità della R.I.M.A" (Travaglini et. al. 2009). All 10 allergenic pollen are monitored since 1996. At Tor Vergata university is also operating a meteorological station (SP2000, CAE

  6. User manual of nuclide dispersion in phreatic aquifers model

    International Nuclear Information System (INIS)

    Rives, D.E.

    1999-01-01

    The Nuclide Dispersion in Phreatic Aquifers (DRAF) model was developed in the 'Division Estudios Ambientales' of the 'Gerencia de Seguridad Radiologica y Nuclear, Comision Nacional de Energia Atomica' (1991), for the Safety Assessment of Near Surface Radioactive Waste Disposal Facilities. Afterwards, it was modified in several opportunities, adapting it to a number of application conditions. The 'Manual del usuario del codigo DRAF' here presented is a reference document for the use of the last three versions of the code developed for the 'Autoridad Regulatoria Nuclear' between 1995 and 1996. The DRAF model solves the three dimension's solute transport equation for porous media by the finite differences method. It takes into account the advection, dispersion, radioactive decay, and retention in the solid matrix processes, and has multiple possibilities for the source term. There are three versions of the model, two of them for the saturated zone and one for the unsaturated zone. All the versions have been verified in different conditions, and have been applied in exercises of the International Atomic Energy Agency and also in real cases. (author)

  7. A numerical three-dimensional ocean general circulation and radionuclides dispersion model

    International Nuclear Information System (INIS)

    Chartier, M.; Marti, O.

    1988-01-01

    The dispersion of radioactive waste disposed of in the deep-sea or transferred from the atmosphere is a complex hydrodynamic problem concerned by space scales as large as the world ocean. The recent development in the high-speed computers has led to significant progress in ocean modelling and now allows a thorough improvement in the accuracy of the simulations of the nuclides dispersion in the sea. A three-dimensional ocean general circulation model has been recently developed in France for research and engineering purposes. The model solves the primitive equation of the ocean hydrodynamics and the advection-diffusion equation for any dissolved tracer. The code has been fully vectorized and multitasked on 1 to 4 processors of the CRAY-2

  8. Combining a dispersal model with network theory to assess habitat connectivity.

    Science.gov (United States)

    Lookingbill, Todd R; Gardner, Robert H; Ferrari, Joseph R; Keller, Cherry E

    2010-03-01

    Assessing the potential for threatened species to persist and spread within fragmented landscapes requires the identification of core areas that can sustain resident populations and dispersal corridors that can link these core areas with isolated patches of remnant habitat. We developed a set of GIS tools, simulation methods, and network analysis procedures to assess potential landscape connectivity for the Delmarva fox squirrel (DFS; Sciurus niger cinereus), an endangered species inhabiting forested areas on the Delmarva Peninsula, USA. Information on the DFS's life history and dispersal characteristics, together with data on the composition and configuration of land cover on the peninsula, were used as input data for an individual-based model to simulate dispersal patterns of millions of squirrels. Simulation results were then assessed using methods from graph theory, which quantifies habitat attributes associated with local and global connectivity. Several bottlenecks to dispersal were identified that were not apparent from simple distance-based metrics, highlighting specific locations for landscape conservation, restoration, and/or squirrel translocations. Our approach links simulation models, network analysis, and available field data in an efficient and general manner, making these methods useful and appropriate for assessing the movement dynamics of threatened species within landscapes being altered by human and natural disturbances.

  9. Modeling the dispersal of spiny lobster (

    NARCIS (Netherlands)

    Whomersley, P.; van der Molen, J.; Holt, D.; Trundle, C.; Clark, S.; Fletcher, D.

    2018-01-01

    Knowledge of larval dispersal, population dynamics and connectivity in relation to the management and conservation of commercially important species is vital if existing fisheries are to remain sustainable into the future. Larval dispersal of the commercially exploited spiny lobster, Palinurus

  10. Modelling of U-Mo/Al Dispersion fuel fission induced swelling and creep

    Energy Technology Data Exchange (ETDEWEB)

    Jeong, Gwan Yoon; Sohn, Dong Seong [Ulsan National Institute of Science and Technology, Ulsan (Korea, Republic of); Kim, Yeon Soo [Argonne National Laboratory, Argonne (United States)

    2014-05-15

    In a Dispersion fuel which U-Mo particles are dispersed in Al metal matrix, a similar phenomenon forming a bulge region was observed but it is difficult to quantify and construct a model for explaining creep and swelling because of its complex microstructure change during irradiation including interaction layer (IL) and porosity formation. In a Dispersion fuel meat, fission product induces fuel particles swelling and it has to be accommodated by the deformation of the Al matrix and newly formed IL during irradiation. Then, it is reasonable that stress from fuel swelling in the complex structure should be relaxed by local adjustments of particles, Al matrix, and IL. For analysis of U-Mo/Al Dispersion fuel creep, the creep of U-Mo particle, Al matrix, and IL should be considered. Moreover, not only fuel particle swelling and IL growth, but also fuel and Al matrix consumptions due to IL formation are accounted in terms of their volume fraction changes during irradiation. In this work, fuel particles, Al matrix and IL are treated in a way of homogenized constituents: Fuel particles, Al matrix and IL consist of an equivalent meat during irradiation. Meat volume swelling of two representative plates was measured: One (Plate A) was a pure Al matrix with 6g/cc uranium loading, the other (Plate B) a silicon added Al matrix with 8g/cc uranium loading. The meat swelling of calculated as a function of burnup. The meat swelling of calculation and measurement was compared and the creep rate coefficients for Al and IL were estimated by repetitions. Based on assumption that only the continuous phase of Al-IL combined matrix accommodated the stress from fuel particle swelling and it was allowed to have creep deformation, the homogenization modeling was performed. The meat swelling of two U-Mo/Al Dispersion fuel plates was modeled by using homogenization model.

  11. Modelling of U-Mo/Al Dispersion fuel fission induced swelling and creep

    International Nuclear Information System (INIS)

    Jeong, Gwan Yoon; Sohn, Dong Seong; Kim, Yeon Soo

    2014-01-01

    In a Dispersion fuel which U-Mo particles are dispersed in Al metal matrix, a similar phenomenon forming a bulge region was observed but it is difficult to quantify and construct a model for explaining creep and swelling because of its complex microstructure change during irradiation including interaction layer (IL) and porosity formation. In a Dispersion fuel meat, fission product induces fuel particles swelling and it has to be accommodated by the deformation of the Al matrix and newly formed IL during irradiation. Then, it is reasonable that stress from fuel swelling in the complex structure should be relaxed by local adjustments of particles, Al matrix, and IL. For analysis of U-Mo/Al Dispersion fuel creep, the creep of U-Mo particle, Al matrix, and IL should be considered. Moreover, not only fuel particle swelling and IL growth, but also fuel and Al matrix consumptions due to IL formation are accounted in terms of their volume fraction changes during irradiation. In this work, fuel particles, Al matrix and IL are treated in a way of homogenized constituents: Fuel particles, Al matrix and IL consist of an equivalent meat during irradiation. Meat volume swelling of two representative plates was measured: One (Plate A) was a pure Al matrix with 6g/cc uranium loading, the other (Plate B) a silicon added Al matrix with 8g/cc uranium loading. The meat swelling of calculated as a function of burnup. The meat swelling of calculation and measurement was compared and the creep rate coefficients for Al and IL were estimated by repetitions. Based on assumption that only the continuous phase of Al-IL combined matrix accommodated the stress from fuel particle swelling and it was allowed to have creep deformation, the homogenization modeling was performed. The meat swelling of two U-Mo/Al Dispersion fuel plates was modeled by using homogenization model

  12. Harmonisation within atmospheric dispersion modelling for regulatory purposes. Proceedings. Vol. 1

    International Nuclear Information System (INIS)

    Suppan, P.

    2004-01-01

    Dispersion modelling has proved to be a very effective tool to assess the environmental impact of human activities to be a very effective tool to assess the environmental impact of human activities on air quality already at the early planning stage. Environmental assessments during planning are required by the EU directive 85/337/EEC. Only models can give detailed information on the distribution of pollutants with high spatial and temporal resolution, while they allow the decision-maker to devise a range of scenarios, in which the various processes determining the environmental impact can be easily simulated and changed. In June 1991, the Joint Research Centre of the European Commission started an initiative on the sharing of information and possible harmonisation of new approaches to atmospheric disperion modelling and model evaluation. This initiative has fostered a series of conferences that have be concerned with improvement of ''modelling culture'' in Europe. The 9th International Conference on Harmonisation within Atmospheric dispersion Modelling for Regulatory Purposes in Garmisch-Partenkirchen, in Germany/Bavaria, 1-4 June, 2004, will continue the efforts of the previous conferences. The conference has a role as a forum where users and decision-makers can bring their requirements to the attention of scientists. It is also a natural forum for discussing environmental issues related to the European Union enlargement process. The scope of this conference is covered by the following topics: 1. Validation and inter-comparison of models: Model evaluation methodology - 2. Experiences with implementation of EU directives: regulatory modelling - 3. Short distance dispersion modelling - 4. Urban scale and street canyon modelling: Meteorology and air quality - 5. Mesoscale meteorology and air quality modelling - 6. Environmental impact assessment: Air pollution management and decision support systems. (orig.)

  13. Modeling pollutant dispersion within a tornadic thunderstorm

    Energy Technology Data Exchange (ETDEWEB)

    Pepper, D W

    1982-01-01

    A three-dimensional numerical model has been developed to calculate ground-level air concentration and deposition of particles entrained in a tornadic thunderstorm. The rotational characteristics of the tornadic storm are within the larger mesoscale flow of the storm system and transported with the vortex. Turbulence exchange coefficients are based on empirical values. The quasi-Lagrangian method of moments is used to model the transport of concentration within a grid cell volume. Results indicate that updrafts and downdrafts, coupled with scavenging of particles by precipitation, account for most of the material being deposited closer to the site than anticipated. Approximately 5% of the pollutant is dispersed into the stratosphere.

  14. Ultrafine particles dispersion modeling in a street canyon: development and evaluation of a composite lattice Boltzmann model.

    Science.gov (United States)

    Habilomatis, George; Chaloulakou, Archontoula

    2013-10-01

    Recently, a branch of particulate matter research concerns on ultrafine particles found in the urban environment, which originate, to a significant extent, from traffic sources. In urban street canyons, dispersion of ultrafine particles affects pedestrian's short term exposure and resident's long term exposure as well. The aim of the present work is the development and the evaluation of a composite lattice Boltzmann model to study the dispersion of ultrafine particles, in urban street canyon microenvironment. The proposed model has the potential to penetrate into the physics of this complex system. In order to evaluate the model performance against suitable experimental data, ultrafine particles levels have been monitored on an hourly basis for a period of 35 days, in a street canyon, in Athens area. The results of the comparative analysis are quite satisfactory. Furthermore, our modeled results are in a good agreement with the results of other computational and experimental studies. This work is a first attempt to study the dispersion of an air pollutant by application of the lattice Boltzmann method. Copyright © 2013 Elsevier B.V. All rights reserved.

  15. High Resilience of Seed Dispersal Webs Highlighted by the Experimental Removal of the Dominant Disperser.

    Science.gov (United States)

    Timóteo, Sérgio; Ramos, Jaime Albino; Vaughan, Ian Phillip; Memmott, Jane

    2016-04-04

    The pressing need to conserve and restore habitats in the face of ongoing species loss [1, 2] requires a better understanding of what happens to communities when species are lost or reinstated [3, 4]. Theoretical models show that communities are relatively insensitive to species loss [5, 6]; however, they disagree with field manipulations showing a cascade of extinctions [7, 8] and have seldom been tested under field conditions (e.g., [9]). We experimentally removed the most abundant seed-dispersing ant species from seed dispersal networks in a Mediterranean landscape, replicating the experiment in three types of habitat, and then compared these communities to un-manipulated control communities. Removal did not result in large-scale changes in network structure. It revealed extensive structural plasticity of the remaining community, which rearranged itself through rewiring, while maintaining its functionality. The remaining ant species widened their diet breadth in a way that maintained seed dispersal, despite the identity of many interactions changing. The species interaction strength decreased; thus, the importance of each ant species for seed dispersal became more homogeneous, thereby reducing the dependence of seed species on one dominant ant species. Compared to the experimental results, a simulation model that included rewiring considerably overestimated the effect of species loss on network robustness. If community-level species loss models are to be of practical use in ecology or conservation, they need to include behavioral and population responses, and they need to be routinely tested under field conditions; doing this would be to the advantage of both empiricists and theoreticians. Copyright © 2016 Elsevier Ltd. All rights reserved.

  16. ERUPTION TO DOSE: COUPLING A TEPHRA DISPERSAL MODEL WITHIN A PERFORMANCE ASSESSMENT FRAMEWORK

    International Nuclear Information System (INIS)

    G. N. Keating, J. Pelletier

    2005-01-01

    The tephra dispersal model used by the Yucca Mountain Project (YMP) to evaluate the potential consequences of a volcanic eruption through the waste repository must incorporate simplifications in order to function within a large Monte-Carlo style performance assessment framework. That is, the explicit physics of the conduit, vent, and eruption column processes are abstracted to a 2-D, steady-state advection-dispersion model (ASHPLUME) that can be run quickly over thousands of realizations of the overall system model. Given the continuous development of tephra dispersal modeling techniques in the last few years, we evaluated the adequacy of this simplified model for its intended purpose within the YMP total system performance assessment (TSPA) model. We evaluated uncertainties inherent in model simplifications including (1) instantaneous, steady-state vs. unsteady eruption, which affects column height, (2) constant wind conditions, and (3) power-law distribution of the tephra blanket; comparisons were made to other models and published ash distributions. Spatial statistics are useful for evaluating differences in these model output vs. results using more complex wind, column height, and tephra deposition patterns. However, in order to assess the adequacy of the model for its intended use in TSPA, we evaluated the propagation of these uncertainties through FAR, the YMP ash redistribution model, which utilizes ASHPLUME tephra deposition results to calculate the concentration of nuclear waste-contaminated tephra at a dose-receptor population as a result of sedimentary transport and mixing processes on the landscape. Questions we sought to answer include: (1) what conditions of unsteadiness, wind variability, or departure from simplified tephra distribution result in significant effects on waste concentration (related to dose calculated for the receptor population)? (2) What criteria can be established for the adequacy of a tephra dispersal model within the TSPA

  17. Modelling the dispersion of non-conservative radionuclides in tidal waters. Pt. 1: Conceptual and mathematical model

    International Nuclear Information System (INIS)

    Perianez, R.; Abril, J.M.; Garcia-Leon, M.

    1996-01-01

    A 2D four-phase model to study the dispersion of non-conservative radionuclides in tidal waters, in conditions of disequilibrium for ionic exchanges, has been developed. At disequilibrium conditions, ionic exchanges cannot be formulated using distribution coefficients k d . Thus, kinetic transfer coefficients have been used. The model includes ionic exchanges among water and the solid phases (suspended matter and two grain size fractions of sediments), the deposition and resuspension of suspended matter and advective plus diffusive transport. In the second part of this work, which is presented in a separate paper, the model is applied to simulate 226 Ra dispersion, discharged from a fertilizer processing plant, in an estuarine system in the south-west of Spain. (Author)

  18. Dispersed plug flow model for upflow anaerobic sludge bed reactors with focus on granular sludge dynamics

    NARCIS (Netherlands)

    Kalyuzhnyi, S.V.; Fedorovich, V.V.; Lens, P.N.L.

    2006-01-01

    A new approach to model upflow anaerobic sludge bed (UASB)-reactors, referred to as a one-dimensional dispersed plug flow model, was developed. This model focusses on the granular sludge dynamics along the reactor height, based on the balance between dispersion, sedimentation and convection using

  19. A Platoon Dispersion Model Based on a Truncated Normal Distribution of Speed

    Directory of Open Access Journals (Sweden)

    Ming Wei

    2012-01-01

    Full Text Available Understanding platoon dispersion is critical for the coordination of traffic signal control in an urban traffic network. Assuming that platoon speed follows a truncated normal distribution, ranging from minimum speed to maximum speed, this paper develops a piecewise density function that describes platoon dispersion characteristics as the platoon moves from an upstream to a downstream intersection. Based on this density function, the expected number of cars in the platoon that pass the downstream intersection, and the expected number of cars in the platoon that do not pass the downstream point are calculated. To facilitate coordination in a traffic signal control system, dispersion models for the front and the rear of the platoon are also derived. Finally, a numeric computation for the coordination of successive signals is presented to illustrate the validity of the proposed model.

  20. Model Equation for Acoustic Nonlinear Measurement of Dispersive Specimens at High Frequency

    Science.gov (United States)

    Zhang, Dong; Kushibiki, Junichi; Zou, Wei

    2006-10-01

    We present a theoretical model for acoustic nonlinearity measurement of dispersive specimens at high frequency. The nonlinear Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation governs the nonlinear propagation in the SiO2/specimen/SiO2 multi-layer medium. The dispersion effect is considered in a special manner by introducing the frequency-dependant sound velocity in the KZK equation. Simple analytic solutions are derived by applying the superposition technique of Gaussian beams. The solutions are used to correct the diffraction and dispersion effects in the measurement of acoustic nonlinearity of cottonseed oil in the frequency range of 33-96 MHz. Regarding two different ultrasonic devices, the accuracies of the measurements are improved to ±2.0% and ±1.3% in comparison with ±9.8% and ±2.9% obtained from the previous plane wave model.

  1. Dispersive Sachdev-Ye-Kitaev model: Band structure and quantum chaos

    Science.gov (United States)

    Zhang, Pengfei

    2017-11-01

    The Sachdev-Ye-Kitaev (SYK) model is a concrete model for a non-Fermi liquid with maximally chaotic behavior in (0 +1 ) dimensions. In order to gain some insights into real materials in higher dimensions where fermions could hop between different sites, here we consider coupling a SYK lattice by constant hopping. We call this the dispersive SYK model. Focusing on (1 +1 ) -dimensional homogeneous hopping, by either tuning the temperature or the relative strength of the random interaction (hopping) and constant hopping, we find a crossover between a dispersive metal to an incoherent metal, where the dynamic exponent z changes from 1 to ∞ . We study the crossover by calculating the spectral function, charge density correlator, and the Lyapunov exponent. We further find the Lyapunov exponent becomes larger when the chemical potential is tuned to approach a van Hove singularity because of the large density of states near the Fermi surface. The effect of the topological nontrivial bands is also discussed.

  2. Validation of the Canadian atmospheric dispersion model for the CANDU reactor complex at Wolsong, Korea

    International Nuclear Information System (INIS)

    Klukas, M.H.; Davis, P.A.

    2000-01-01

    AECL is undertaking the validation of ADDAM, an atmospheric dispersion and dose code based on the Canadian Standards Association model CSA N288.2. The key component of the validation program involves comparison of model predicted and measured vertical and lateral dispersion parameters, effective release height and air concentrations. A wind tunnel study of the dispersion of exhaust gases from the CANDU complex at Wolsong, Korea provides test data for dispersion over uniform and complex terrain. The test data are for distances close enough to the release points to evaluate the model for exclusion area boundaries (EAB) as small as 500 m. Lateral and vertical dispersion is described well for releases over uniform terrain but the model tends to over-predict these parameters for complex terrain. Both plume rise and entrainment are modelled conservatively and the way they are combined in the model produces conservative estimates of the effective release height for low and high wind speeds. Estimates for the medium wind speed case (50-m wind speed, 3.8 ms -1 ) are conservative when the correction for entrainment is made. For the highest ground-level concentrations, those of greatest interest in a safety analysis, 82% of the predictions were within a factor 2 of the observed values. The model can be used with confidence to predict air concentrations of exhaust gases at the Wolsong site for neutral conditions, even for flows over the hills to the west, and is unlikely to substantially under-predict concentrations. (author)

  3. The effect of a tall tower on flow and dispersion through a model urban neighborhood: part 2. Pollutant dispersion.

    Science.gov (United States)

    Brixey, Laurie A; Heist, David K; Richmond-Bryant, Jennifer; Bowker, George E; Perry, Steven G; Wiener, Russell W

    2009-12-01

    This article is the second in a two-paper series presenting results from wind tunnel and computational fluid dynamics (CFD) simulations of flow and dispersion in an idealized model urban neighborhood. Pollutant dispersion results are presented and discussed for a model neighborhood that was characterized by regular city blocks of three-story row houses with a single 12-story tower located at the downwind edge of one of these blocks. The tower had three significant effects on pollutant dispersion in the surrounding street canyons: drawing the plume laterally towards the tower, greatly enhancing the vertical dispersion of the plume in the wake of the tower, and significantly decreasing the residence time of pollutants in the wake of the tower. In the wind tunnel, tracer gas released in the avenue lee of the tower, but several blocks away laterally, was pulled towards the tower and lifted in the wake of the tower. The same lateral movement of the pollutant was seen in the next avenue, which was approximately 2.5 tower heights downwind of the tower. The tower also served to ventilate the street canyon directly in its wake more rapidly than the surrounding areas. This was evidenced by CFD simulations of concentration decay where the residence time of pollutants lee of the 12-story tower was found to be less than half the residence time behind a neighboring three-story building. This same phenomenon of rapid vertical dispersion lee of a tower among an array of smaller buildings was also demonstrated in a separate set of wind tunnel experiments using an array of cubical blocks. A similar decrease in the residence time was observed when the height of one block was increased.

  4. Estimating dispersion from a tornado vortex and mesocyclone

    International Nuclear Information System (INIS)

    Weber, A.H.; Hunter, C.H.

    1996-06-01

    Atmospheric dispersion modeling is required to ensure that a postulated breach in radionuclide storage containers at the Savannah River Site (SRS) from a tornado strike of Fujita-scale intensity F2 or higher will not result in an unacceptable dose to individuals. Fujita-scale tornado descriptions are included in Appendix A of this report. Dispersion models previously used at SRS for estimating dispersion following a tornado strike were developed by D.W. Pepper in 1975 (DP-1387, Dispersion of Small Particles) and H.R. Haynes and D.W. Taylor in 1983 (DPST-82-982, Estimating Doses from Tornado Winds). Research conducted in 1983 on the formation and evolution of tornadic thunderstorms has lead to a more complete understanding of the tornado vortex and associated persistent updraft and downdraft regions within the parent thunderstorm. To ensure that appropriate, contemporary methods are used for safety analysis, the Pepper model and the Haynes and Taylor model were evaluated with respect to current knowledge of circulations within tornadic thunderstorms. Pepper's model is complex numerically but contains most of the desired physical parameterizations. Haynes and Taylor's model is used with the Puff-Plume model (an emergency response model on the Weather INformation and Display System at SRS) and has provisions for radionuclide deposition and rainout. Haynes and Taylor assumed heavy rain following the tornado for a period of ten minutes, followed by a lighter rain for another ten minutes, then no rain for the period when the material is transported to 100 km downwind. However, neither model incorporates the effects of a nearby thunderstorm downdraft

  5. FIREPLUME model for plume dispersion from fires: Application to uranium hexafluoride cylinder fires

    International Nuclear Information System (INIS)

    Brown, D.F.; Dunn, W.E.

    1997-06-01

    This report provides basic documentation of the FIREPLUME model and discusses its application to the prediction of health impacts resulting from releases of uranium hexafluoride (UF 6 ) in fires. The model application outlined in this report was conducted for the Draft Programmatic Environmental Impact Statement for Alternative Strategies for the Long-Term Management and Use of Depleted UF 6 . The FIREPLUME model is an advanced stochastic model for atmospheric plume dispersion that predicts the downwind consequences of a release of toxic materials from an explosion or a fire. The model is based on the nonbuoyant atmospheric dispersion model MCLDM (Monte Carlo Lagrangian Dispersion Model), which has been shown to be consistent with available laboratory and field data. The inclusion of buoyancy and the addition of a postprocessor to evaluate time-varying concentrations lead to the current model. The FIREPLUME model, as applied to fire-related UF 6 cylinder releases, accounts for three phases of release and dispersion. The first phase of release involves the hydraulic rupture of the cylinder due to heating of the UF 6 in the fire. The second phase involves the emission of material into the burning fire, and the third phase involves the emission of material after the fire has died during the cool-down period. The model predicts the downwind concentration of the material as a function of time at any point downwind at or above the ground. All together, five fire-related release scenarios are examined in this report. For each scenario, downwind concentrations of the UF 6 reaction products, uranyl fluoride and hydrogen fluoride, are provided for two meteorological conditions: (1) D stability with a 4-m/s wind speed, and (2) F stability with a 1-m/s wind speed

  6. Modelling electro-active polymers with a dispersion-type anisotropy

    Science.gov (United States)

    Hossain, Mokarram; Steinmann, Paul

    2018-02-01

    We propose a novel constitutive framework for electro-active polymers (EAPs) that can take into account anisotropy with a chain dispersion. To enhance actuation behaviour, particle-filled EAPs become promising candidates nowadays. Recent studies suggest that particle-filled EAPs, which can be cured under an electric field during the manufacturing time, do not necessarily form perfect anisotropic composites, rather they create composites with dispersed chains. Hence in this contribution, an electro-mechanically coupled constitutive model is devised that considers the chain dispersion with a probability distribution function in an integral form. To obtain relevant quantities in discrete form, numerical integration over the unit sphere is utilized. Necessary constitutive equations are derived exploiting the basic laws of thermodynamics that result in a thermodynamically consistent formulation. To demonstrate the performance of the proposed electro-mechanically coupled framework, we analytically solve a non-homogeneous boundary value problem, the extension and inflation of an axisymmetric cylindrical tube under electro-mechanically coupled load. The results capture various electro-mechanical couplings with the formulation proposed for EAP composites.

  7. Generation of shrimp waste-based dispersant for oil spill response.

    Science.gov (United States)

    Zhang, Kedong; Zhang, Baiyu; Song, Xing; Liu, Bo; Jing, Liang; Chen, Bing

    2018-04-01

    In this study, shrimp waste was enzymatically hydrolyzed to generate a green dispersant and the product was tested for crude oil dispersion in seawater. The hydrolysis process was first optimized based on the dispersant effectiveness (DE) of the product. The functional properties of the product were identified including stability, critical micelle concentration, and emulsification activity. Water was confirmed as a good solvent for dispersant generation when compared with three chemical solvents. The effects of salinity, mixing energy, and temperature on the dispersion of the Alaska North Slope (ANS) crude oil were examined. Microtox acute toxicity test was also conducted to evaluate the toxicity of the produced dispersant. In addition, DE of the product on three different types of crude oil, including ANS crude oil, Prudhoe Bay crude oil (PBC), and Arabian Light crude oil (ALC) was compared with that of the Corexit 9500, respectively. The research output could lead to a promising green solution to the oil spill problem and might result in many other environmental applications.

  8. A mean-density model of ionic surfactants for the dispersion of carbon nanotubes in aqueous solutions

    Science.gov (United States)

    Joung, Young Soo

    2018-05-01

    We propose a new analytical model of ionic surfactants used for the dispersion of carbon nanotubes (CNTs) in aqueous solutions. Although ionic surfactants are commonly used to facilitate the dispersion of CNTs in aqueous solutions, understanding the dispersion process is challenging and time-consuming owing to its complexity and nonlinearity. In this work, we develop a mean-density model of ionic surfactants to simplify the calculation of interaction forces between CNTs stabilized by ionic surfactants. Using this model, we can evaluate various interaction forces between the CNTs and ionic surfactants under different conditions. The dispersion mechanism is investigated by estimating the potential of mean force (PMF) as a function of van der Waals forces, electrostatic forces, interfacial tension, and osmotic pressure. To verify the proposed model, we compare the PMFs derived using our method with those derived from molecular dynamics simulations using comparable CNTs and ionic surfactants. Notably, for stable dispersions, the osmotic pressure and interfacial energy are important for long-range and short-range interactions, respectively, in comparison with the effect of electrostatic forces. Our model effectively prescribes specific surfactants and their concentrations to achieve stable aqueous suspensions of CNTs.

  9. Fossil biogeography: a new model to infer dispersal, extinction and sampling from palaeontological data.

    Science.gov (United States)

    Silvestro, Daniele; Zizka, Alexander; Bacon, Christine D; Cascales-Miñana, Borja; Salamin, Nicolas; Antonelli, Alexandre

    2016-04-05

    Methods in historical biogeography have revolutionized our ability to infer the evolution of ancestral geographical ranges from phylogenies of extant taxa, the rates of dispersals, and biotic connectivity among areas. However, extant taxa are likely to provide limited and potentially biased information about past biogeographic processes, due to extinction, asymmetrical dispersals and variable connectivity among areas. Fossil data hold considerable information about past distribution of lineages, but suffer from largely incomplete sampling. Here we present a new dispersal-extinction-sampling (DES) model, which estimates biogeographic parameters using fossil occurrences instead of phylogenetic trees. The model estimates dispersal and extinction rates while explicitly accounting for the incompleteness of the fossil record. Rates can vary between areas and through time, thus providing the opportunity to assess complex scenarios of biogeographic evolution. We implement the DES model in a Bayesian framework and demonstrate through simulations that it can accurately infer all the relevant parameters. We demonstrate the use of our model by analysing the Cenozoic fossil record of land plants and inferring dispersal and extinction rates across Eurasia and North America. Our results show that biogeographic range evolution is not a time-homogeneous process, as assumed in most phylogenetic analyses, but varies through time and between areas. In our empirical assessment, this is shown by the striking predominance of plant dispersals from Eurasia into North America during the Eocene climatic cooling, followed by a shift in the opposite direction, and finally, a balance in biotic interchange since the middle Miocene. We conclude by discussing the potential of fossil-based analyses to test biogeographic hypotheses and improve phylogenetic methods in historical biogeography. © 2016 The Author(s).

  10. Effect of tubing length on the dispersion correction of an arterially sampled input function for kinetic modeling in PET.

    Science.gov (United States)

    O'Doherty, Jim; Chilcott, Anna; Dunn, Joel

    2015-11-01

    Arterial sampling with dispersion correction is routinely performed for kinetic analysis of PET studies. Because of the the advent of PET-MRI systems, non-MR safe instrumentation will be required to be kept outside the scan room, which requires the length of the tubing between the patient and detector to increase, thus worsening the effects of dispersion. We examined the effects of dispersion in idealized radioactive blood studies using various lengths of tubing (1.5, 3, and 4.5 m) and applied a well-known transmission-dispersion model to attempt to correct the resulting traces. A simulation study was also carried out to examine noise characteristics of the model. The model was applied to patient traces using a 1.5 m acquisition tubing and extended to its use at 3 m. Satisfactory dispersion correction of the blood traces was achieved in the 1.5 m line. Predictions on the basis of experimental measurements, numerical simulations and noise analysis of resulting traces show that corrections of blood data can also be achieved using the 3 m tubing. The effects of dispersion could not be corrected for the 4.5 m line by the selected transmission-dispersion model. On the basis of our setup, correction of dispersion in arterial sampling tubing up to 3 m by the transmission-dispersion model can be performed. The model could not dispersion correct data acquired using a 4.5 m arterial tubing.

  11. Uncertainty propagation analysis applied to volcanic ash dispersal at Mt. Etna by using a Lagrangian model

    Science.gov (United States)

    de'Michieli Vitturi, Mattia; Pardini, Federica; Spanu, Antonio; Neri, Augusto; Vittoria Salvetti, Maria

    2015-04-01

    Volcanic ash clouds represent a major hazard for populations living nearby volcanic centers producing a risk for humans and a potential threat to crops, ground infrastructures, and aviation traffic. Lagrangian particle dispersal models are commonly used for tracking ash particles emitted from volcanic plumes and transported under the action of atmospheric wind fields. In this work, we present the results of an uncertainty propagation analysis applied to volcanic ash dispersal from weak plumes with specific focus on the uncertainties related to the grain-size distribution of the mixture. To this aim, the Eulerian fully compressible mesoscale non-hydrostatic model WRF was used to generate the driving wind, representative of the atmospheric conditions occurring during the event of November 24, 2006 at Mt. Etna. Then, the Lagrangian particle model LPAC (de' Michieli Vitturi et al., JGR 2010) was used to simulate the transport of mass particles under the action of atmospheric conditions. The particle motion equations were derived by expressing the Lagrangian particle acceleration as the sum of the forces acting along its trajectory, with drag forces calculated as a function of particle diameter, density, shape and Reynolds number. The simulations were representative of weak plume events of Mt. Etna and aimed to quantify the effect on the dispersal process of the uncertainty in the particle sphericity and in the mean and variance of a log-normal distribution function describing the grain-size of ash particles released from the eruptive column. In order to analyze the sensitivity of particle dispersal to these uncertain parameters with a reasonable number of simulations, and therefore with affordable computational costs, response surfaces in the parameter space were built by using the generalized polynomial chaos technique. The uncertainty analysis allowed to quantify the most probable values, as well as their pdf, of the number of particles as well as of the mean and

  12. Modeling a failure criterion for U-Mo/Al dispersion fuel

    Science.gov (United States)

    Oh, Jae-Yong; Kim, Yeon Soo; Tahk, Young-Wook; Kim, Hyun-Jung; Kong, Eui-Hyun; Yim, Jeong-Sik

    2016-05-01

    The breakaway swelling in U-Mo/Al dispersion fuel is known to be caused by large pore formation enhanced by interaction layer (IL) growth between fuel particles and Al matrix. In this study, a critical IL thickness was defined as a criterion for the formation of a large pore in U-Mo/Al dispersion fuel. Specifically, the critical IL thickness is given when two neighboring fuel particles come into contact with each other in the developed IL. The model was verified using the irradiation data from the RERTR tests and KOMO-4 test. The model application to full-sized sample irradiations such as IRISs, FUTURE, E-FUTURE, and AFIP-1 tests resulted in conservative predictions. The parametric study revealed that the fuel particle size and the homogeneity of the fuel particle distribution are influential for fuel performance.

  13. Modeling a failure criterion for U–Mo/Al dispersion fuel

    Energy Technology Data Exchange (ETDEWEB)

    Oh, Jae-Yong, E-mail: tylor@kaeri.re.kr [Korea Atomic Energy Research Institute, 111, Daedeok-Daero 989 Beon-Gil, Yuseong-Gu, Daejeon 305-353 (Korea, Republic of); Kim, Yeon Soo [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Tahk, Young-Wook; Kim, Hyun-Jung; Kong, Eui-Hyun; Yim, Jeong-Sik [Korea Atomic Energy Research Institute, 111, Daedeok-Daero 989 Beon-Gil, Yuseong-Gu, Daejeon 305-353 (Korea, Republic of)

    2016-05-15

    The breakaway swelling in U–Mo/Al dispersion fuel is known to be caused by large pore formation enhanced by interaction layer (IL) growth between fuel particles and Al matrix. In this study, a critical IL thickness was defined as a criterion for the formation of a large pore in U–Mo/Al dispersion fuel. Specifically, the critical IL thickness is given when two neighboring fuel particles come into contact with each other in the developed IL. The model was verified using the irradiation data from the RERTR tests and KOMO-4 test. The model application to full-sized sample irradiations such as IRISs, FUTURE, E-FUTURE, and AFIP-1 tests resulted in conservative predictions. The parametric study revealed that the fuel particle size and the homogeneity of the fuel particle distribution are influential for fuel performance.

  14. Study of the determination method of the river dispersion coefficient

    International Nuclear Information System (INIS)

    Carvalho, M.A.G. de.

    1982-01-01

    An application of the method introduced by 'Fischer, H.B. - 1968 - Dispersion prediction in natural streams Journal of the Sanitary Engineering Division, ACSE, vol. 94 n 5A5. Proc. Paper 6169 pp 927-943.', for the calculation of the dispersion coefficient, based on Taylor's model is made. The aim is to develop a method which avoids the necessity of having an instantaneous impulse at the entrance section (1st section) of the system being measured. The dispersion coefficient is determined by curve fitting the experimental response in the 2nd secton and that obtained with the model by means of the non-linear least-squares method. The same method is applied with the residence time distribution function. The theoretical differences between these two function and their results are discussed. By adjusting the two model parameters in all these calculations, the dispersion coefficient and the mean velocity are determined, simultaneously. A comparison between the moment's method and Fischer's formulation is also done using the same experimental data. (E.G.) [pt

  15. A model for short and medium range dispersion of radionuclides released to the atmosphere

    International Nuclear Information System (INIS)

    Clarke, R.H.

    1979-09-01

    A Working Group was established to give practical guidance on the estimation of the dispersion of radioactive releases to the atmosphere. The dispersion is estimated in the short and medium range, that is from about 100 m to a few tens of kilometres from the source, and is based upon a Gaussian plume model. A scheme is presented for categorising atmospheric conditions and values of the associated dispersion parameters are given. Typical results are presented for releases in specific meteorological conditions and a scheme is included to allow for durations of release of up to 24 hours. Consideration has also been given to predicting longer term average concentrations, typically annual averages, and results are presented which facilitate site specific calculations. The results of the models are extended to 100 km from the source, but the increasing uncertainty with which results may be predicted beyond a few tens of kilometres from the source is emphasised. Three technical appendices provide some of the rationale behind the decisions made in adopting the various models in the proposed dispersion scheme. (author)

  16. A computer model for dispersed fluid-solid turbulent flows

    International Nuclear Information System (INIS)

    Liu, C.H.; Tulig, T.J.

    1985-01-01

    A computer model is being developed to simulate two-phase turbulent flow phenomena in fluids containing finely dispersed solids. The model is based on a dual-continuum picture of the individual phases and an extension of a two-equation turbulence closure theory. The resulting set of nonlinear partial differential equations are solved using a finite difference procedure with special treatment to promote convergence. The model has been checked against a number of idealized flow problems with known solutions. The authors are currently comparing model predictions with measurements to determine a proper set of turbulence parameters needed for simulating two-phase turbulent flows

  17. Fluctuation Scaling, Calibration of Dispersion, and Detection of Differences.

    Science.gov (United States)

    Holland, Rianne; Rebmann, Roman; Williams, Craig; Hanley, Quentin S

    2017-11-07

    Fluctuation scaling describes the relationship between the mean and standard deviation of a set of measurements. An example is Horwitz scaling, which has been reported from interlaboratory studies. Horwitz and similar studies have reported simple exponential and segmented scaling laws with exponents (α) typically between 0.85 (Horwitz) and 1 when not operating near a detection limit. When approaching a detection limit, the exponents change and approach an apparently Gaussian (α = 0) model. This behavior is often presented as a property of interlaboratory studies, which makes controlled replication to understand the behavior costly to perform. To assess the contribution of instrumentation to larger scale fluctuation scaling, we measured the behavior of two inductively coupled plasma atomic emission spectrometry (ICP-AES) systems, in two laboratories measuring thulium using two emission lines. The standard deviation universally increased with the uncalibrated signal, indicating the system was heteroscedastic. The response from all lines and both instruments was consistent with a single exponential dispersion model having parameters α = 1.09 and β = 0.0035. No evidence of Horwitz scaling was found, and there was no evidence of Poisson noise limiting behavior. The "Gaussian" component was a consequence of background subtraction for all lines and both instruments. The observation of a simple exponential dispersion model in the data allows for the definition of a difference detection limit (DDL) with universal applicability to systems following known dispersion. The DDL is the minimum separation between two points along a dispersion model required to claim they are different according to a particular statistical test. The DDL scales transparently with the mean and works at any location in a response function.

  18. Mixed Platoon Flow Dispersion Model Based on Speed-Truncated Gaussian Mixture Distribution

    Directory of Open Access Journals (Sweden)

    Weitiao Wu

    2013-01-01

    Full Text Available A mixed traffic flow feature is presented on urban arterials in China due to a large amount of buses. Based on field data, a macroscopic mixed platoon flow dispersion model (MPFDM was proposed to simulate the platoon dispersion process along the road section between two adjacent intersections from the flow view. More close to field observation, truncated Gaussian mixture distribution was adopted as the speed density distribution for mixed platoon. Expectation maximum (EM algorithm was used for parameters estimation. The relationship between the arriving flow distribution at downstream intersection and the departing flow distribution at upstream intersection was investigated using the proposed model. Comparison analysis using virtual flow data was performed between the Robertson model and the MPFDM. The results confirmed the validity of the proposed model.

  19. Pollutant dispersion models for issues of air pollution control

    International Nuclear Information System (INIS)

    1985-01-01

    14 papers entered separately into the data base were presented at the meeting for application-oriented dispersion models for issues of air pollution control. These papers focus on fields of application, availability of required input data relevant to emissions and meteorology, performance and accuracy of these methods and their practicability. (orig./PW) [de

  20. Accumulation capacitance frequency dispersion of III-V metal-insulator-semiconductor devices due to disorder induced gap states

    International Nuclear Information System (INIS)

    Galatage, R. V.; Zhernokletov, D. M.; Dong, H.; Brennan, B.; Hinkle, C. L.; Wallace, R. M.; Vogel, E. M.

    2014-01-01

    The origin of the anomalous frequency dispersion in accumulation capacitance of metal-insulator-semiconductor devices on InGaAs and InP substrates is investigated using modeling, electrical characterization, and chemical characterization. A comparison of the border trap model and the disorder induced gap state model for frequency dispersion is performed. The fitting of both models to experimental data indicate that the defects responsible for the measured dispersion are within approximately 0.8 nm of the surface of the crystalline semiconductor. The correlation between the spectroscopically detected bonding states at the dielectric/III-V interface, the interfacial defect density determined using capacitance-voltage, and modeled capacitance-voltage response strongly suggests that these defects are associated with the disruption of the III-V atomic bonding and not border traps associated with bonding defects within the high-k dielectric.

  1. An efficient approach to transient turbulent dispersion modeling by CFD-statistical analysis of a many-puff system

    International Nuclear Information System (INIS)

    Ching, W-H; K H Leung, Michael; Leung, Dennis Y C

    2009-01-01

    Transient turbulent dispersion phenomena can be found in various practical problems, such as the accidental release of toxic chemical vapor and the airborne transmission of infectious droplets. Computational fluid dynamics (CFD) is an effective tool for analyzing such transient dispersion behaviors. However, the transient CFD analysis is often computationally expensive and time consuming. In the present study, a computationally efficient CFD-statistical hybrid modeling method has been developed for studying transient turbulent dispersion. In this method, the source emission is represented by emissions of many infinitesimal puffs. Statistical analysis is performed to obtain first the statistical properties of the puff trajectories and subsequently the most probable distribution of the puff trajectories that represent the macroscopic dispersion behaviors. In two case studies of ambient dispersion, the numerical modeling results obtained agree reasonably well with both experimental measurements and conventional k-ε modeling results published in the literature. More importantly, the proposed many-puff CFD-statistical hybrid modeling method effectively reduces the computational time by two orders of magnitude.

  2. Forecasting the consequences of accidental releases of radionuclides in the atmosphere from ensemble dispersion modelling

    International Nuclear Information System (INIS)

    Galmarini, S.; Bianconi, R.; Bellasio, R.; Graziani, G.

    2001-01-01

    The RTMOD system is presented as a tool for the intercomparison of long-range dispersion models as well as a system for support of decision making. RTMOD is an internet-based procedure that collects the results of more than 20 models used around the world to predict the transport and deposition of radioactive releases in the atmosphere. It allows the real-time acquisition of model results and their intercomparison. Taking advantage of the availability of several model results, the system can also be used as a tool to support decision making in case of emergency. The new concept of ensemble dispersion modelling is introduced which is the basis for the decision-making application of RTMOD. New statistical parameters are presented that allow gathering the results of several models to produce a single dispersion forecast. The devised parameters are presented and tested on the results of RTMOD exercises

  3. Bet-hedging as a complex interaction among developmental instability, environmental heterogeneity, dispersal, and life-history strategy.

    Science.gov (United States)

    Scheiner, Samuel M

    2014-02-01

    One potential evolutionary response to environmental heterogeneity is the production of randomly variable offspring through developmental instability, a type of bet-hedging. I used an individual-based, genetically explicit model to examine the evolution of developmental instability. The model considered both temporal and spatial heterogeneity alone and in combination, the effect of migration pattern (stepping stone vs. island), and life-history strategy. I confirmed that temporal heterogeneity alone requires a threshold amount of variation to select for a substantial amount of developmental instability. For spatial heterogeneity only, the response to selection on developmental instability depended on the life-history strategy and the form and pattern of dispersal with the greatest response for island migration when selection occurred before dispersal. Both spatial and temporal variation alone select for similar amounts of instability, but in combination resulted in substantially more instability than either alone. Local adaptation traded off against bet-hedging, but not in a simple linear fashion. I found higher-order interactions between life-history patterns, dispersal rates, dispersal patterns, and environmental heterogeneity that are not explainable by simple intuition. We need additional modeling efforts to understand these interactions and empirical tests that explicitly account for all of these factors.

  4. Atmospheric Dispersion Simulation for Level 3 PSA at Ulchin Nuclear Site using a PUFF model

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Seung Jun; Han, Seok-Jung; Jeong, Hyojoon; Jang, Seung-Cheol [KAERI, Daejeon (Korea, Republic of)

    2015-05-15

    Air dispersion prediction is a key in the level 3 PSA to predict radiation releases into the environment for preparing an effective strategy for an evacuation as a basis of the emergency preparedness. To predict the atmospheric dispersion accurately, the specific conditions of the radiation release location should be considered. There are various level 3 PSA tools and MACSS2 is one of the widely used level 3 PSA tools in many countries including Korea. Due to the characteristics of environmental conditions in Korea, it should be demonstrated that environmental conditions of Korea nuclear sites can be appropriately illustrated by the tool. In Korea, because all nuclear power plants are located on coasts, sea and land breezes might be a significant factor. The objectives of this work is to simulate the atmospheric dispersion for Ulchin nuclear site in Korea using a PUFF model and to generate the data which can be used for the comparison with that of PLUME model. A nuclear site has own atmospheric dispersion characteristics. Especially in Korea, nuclear sites are located at coasts and it is expected that see and land breeze effects are relatively high. In this work, the atmospheric dispersion at Ulchin nuclear site was simulated to evaluate the effect of see and land breezes in four seasons. In the simulation results, it was observed that the wind direction change with time has a large effect on atmospheric dispersion. If the result of a PLUME model is more conservative than most severe case of a PUFF model, then the PLUME model could be used for Korea nuclear sites in terms of safety assessment.

  5. MODELING DISPERSION FROM CHEMICALS RELEASED AFTER A TRAIN COLLISION IN GRANITEVILLE, SOUTH CAROLINA

    Energy Technology Data Exchange (ETDEWEB)

    Buckley, R; Chuck Hunter, C; Robert Addis, R; Matt Parker, M

    2006-08-07

    The Savannah River National Laboratory's (SRNL) Weather INformation and Display (WIND) System was used to provide meteorological and atmospheric modeling/consequence assessment support to state and local agencies following the collision of two Norfolk Southern freight trains on the morning of January 6, 2005. This collision resulted in the release of several toxic chemicals to the environment, including chlorine. The dense and highly toxic cloud of chlorine gas that formed in the vicinity of the accident was responsible for nine fatalities, and caused injuries to more than five hundred others. Transport model results depicting the forecast path of the ongoing release were made available to emergency managers in the county's Unified Command Center shortly after SRNL received a request for assistance. Support continued over the ensuing two days of the active response. The SRNL also provided weather briefings and transport/consequence assessment model results to responders from South Carolina Department of Health and Environmental Control (SCDHEC), the Savannah River Site's (SRS) Emergency Operations Center (EOC), Department of Energy Headquarters, and hazmat teams dispatched from the SRS. Although model-generated forecast winds used in consequence assessments conducted during the incident were provided at 2-km horizontal grid spacing during the accident response, a high-resolution Regional Atmospheric Modeling System (RAMS, version 4.3.0) simulation was later performed to examine potential influences of local topography on plume migration. The detailed RAMS simulation was used to determine meteorology using multiple grids with an innermost grid spacing of 125 meters. Results from the two simulations are shown to generally agree with meteorological observations at the time; consequently, local topography did not significantly affect wind in the area. Use of a dense gas dispersion model to simulate localized plume behavior using the higher resolution

  6. Atmospheric transport and dispersion modeling for the Hanford Environmental Dose Reconstruction Project

    International Nuclear Information System (INIS)

    Ramsdell, J.V.

    1991-07-01

    Radiation doses that may have resulted from operations at the Hanford Site are being estimated in the Hanford Environmental Dose Reconstruction (HEDR) Project. One of the project subtasks, atmospheric transport, is responsible for estimating the transport, diffusion and deposition of radionuclides released to the atmosphere. This report discusses modeling transport and diffusion in the atmospheric pathway. It is divided into three major sections. The first section of the report presents the atmospheric modeling approach selected following discussion with the Technical Steering Panel that directs the HEDR Project. In addition, the section discusses the selection of the MESOI/MESORAD suite of atmospheric dispersion models that form the basis for initial calculations and future model development. The second section of the report describes alternative modeling approaches that were considered. Emphasis is placed on the family of plume and puff models that are based on Gaussian solution to the diffusion equations. The final portion of the section describes the performance of various models. The third section of the report discusses factors that bear on the selection of an atmospheric transport modeling approach for HEDR. These factors, which include the physical setting of the Hanford Site and the available meteorological data, serve as constraints on model selection. Five appendices are included in the report. 39 refs., 4 figs., 2 tabs

  7. Accounting for Field-Scale Dry Deposition in Backward Lagrangian Stochastic Dispersion Modelling of NH3 Emissions

    Directory of Open Access Journals (Sweden)

    Christoph Häni

    2018-04-01

    Full Text Available A controlled ammonia (NH3 release experiment was performed at a grassland site. The aim was to quantify the effect of dry deposition between the source and the receptors (NH3 measurement locations on emission rate estimates by means of inverse dispersion modelling. NH3 was released for three hours at a constant rate of Q = 6.29 mg s−1 from a grid of 36 orifices spread over an area of 250 m2. The increase in line-integrated NH3 concentration was measured with open-path optical miniDOAS devices at different locations downwind of the artificial source. Using a backward Lagrangian stochastic (bLS dispersion model (bLSmodelR, the fraction of the modelled release rate to the emitted NH3 ( Q bLS / Q was calculated from the measurements of the individual instruments. Q bLS / Q was found to be systematically lower than 1, on average between 0.69 and 0.91, depending on the location of the receptor. We hypothesized that NH3 dry deposition to grass and soil surfaces was the main factor responsible for the observed depletion of NH3 between source and receptor. A dry deposition algorithm based on a deposition velocity approach was included in the bLS modelling. Model deposition velocities were evaluated from a ‘big-leaf’ canopy resistance analogy. Canopy resistances (generally termed R c that provided Q bLS / Q = 1 ranged from 75 to 290 s m−1, showing that surface removal of NH3 by dry deposition can plausibly explain the original underestimation of Q bLS / Q . The inclusion of a dry deposition process in dispersion modelling is crucial for emission estimates, which are based on concentration measurements of depositing tracers downwind of homogeneous area sources or heterogeneously-distributed hot spots, such as, e.g., urine patches on pastures in the case of NH3.

  8. Mechanism for enhanced absorption of a solid dispersion formulation of LY2300559 using the artificial stomach duodenum model.

    Science.gov (United States)

    Polster, Christopher S; Wu, Sy-Juen; Gueorguieva, Ivelina; Sperry, David C

    2015-04-06

    An artificial stomach duodenum (ASD) model has been used to demonstrate the performance difference between two formulations of LY2300559, a low-solubility acidic developmental drug. The two formulations investigated were a conventional high-shear wet granulation (HSWG) formulation and a solid dispersion formulation. A pharmacokinetic study in humans demonstrated the enhanced performance of the solid dispersion formulation relative to the HSWG formulation. The Cmax and AUC of the solid dispersion was 2.6 and 1.9 times greater, respectively, compared to the HSWG formulation. In the ASD, the solid dispersion formulation performance was characterized by three main phases: (1) rapid release in the stomach, creating a supersaturated concentration of drug, (2) precipitation in the stomach, and (3) rapid redissolution of the precipitate in the duodenum to concentration levels that are supersaturated relative to crystalline drug. A series of complementary experiments were employed to describe this performance behavior mechanistically. Imaging experiments with a pH indicating dye showed that local pH gradients from meglumine in the solid dispersion formulation were responsible for creating a high initial supersaturation concentration in the stomach. Upon dissipation of meglumine, the drug precipitated in the stomach as an amorphous solid. Because the precipitated drug is in an amorphous form, it can then rapidly redissolve as it transits to the more neutral environment of the duodenum. This unexpected sequence of physical state changes gives a mechanistic explanation for the enhanced in vivo performance of the solid dispersion formulation relative to the HSWG formulation.

  9. Comparison of results from dispersion models for regulatory purposes based on Gaussian-and Lagrangian-algorithms: an evaluating literature study

    International Nuclear Information System (INIS)

    Walter, H.

    2004-01-01

    Powerful tools to describe atmospheric transport processes for radiation protection can be provided by meteorology; these are atmospheric flow and dispersion models. Concerning dispersion models, Gaussian plume models have been used since a long time to describe atmospheric dispersion processes. Advantages of the Gaussian plume models are short computation time, good validation and broad acceptance worldwide. However, some limitations and their implications on model result interpretation have to be taken into account, as the mathematical derivation of an analytic solution of the equations of motion leads to severe constraints. In order to minimise these constraints, various dispersion models for scientific and regulatory purposes have been developed and applied. Among these the Lagrangian particle models are of special interest, because these models are able to simulate atmospheric transport processes close to reality, e.g. the influence of orography, topography, wind shear and other meteorological phenomena. Within this study, the characteristics and computational results of Gaussian dispersion models as well as of Lagrangian models have been compared and evaluated on the base of numerous papers and reports published in literature. Special emphasis has been laid on the intention that dispersion models should comply with EU requests (Richtlinie 96/29/Euratom, 1996) on a more realistic assessment of the radiation exposure to the population. (orig.)

  10. Solitary excitations in discrete two-dimensional nonlinear Schrodinger models with dispersive dipole-dipole interactions

    DEFF Research Database (Denmark)

    Christiansen, Peter Leth; Gaididei, Yuri Borisovich; Johansson, M.

    1998-01-01

    The dynamics of discrete two-dimensional nonlinear Schrodinger models with long-range dispersive interactions is investigated. In particular, we focus on the cases where the dispersion arises from a dipole-dipole interaction, assuming the dipole moments at each lattice site to be aligned either...

  11. Practical Model for First Hyperpolarizability Dispersion Accounting for Both Homogeneous and Inhomogeneous Broadening Effects.

    Science.gov (United States)

    Campo, Jochen; Wenseleers, Wim; Hales, Joel M; Makarov, Nikolay S; Perry, Joseph W

    2012-08-16

    A practical yet accurate dispersion model for the molecular first hyperpolarizability β is presented, incorporating both homogeneous and inhomogeneous line broadening because these affect the β dispersion differently, even if they are indistinguishable in linear absorption. Consequently, combining the absorption spectrum with one free shape-determining parameter Ginhom, the inhomogeneous line width, turns out to be necessary and sufficient to obtain a reliable description of the β dispersion, requiring no information on the homogeneous (including vibronic) and inhomogeneous line broadening mechanisms involved, providing an ideal model for practical use in extrapolating experimental nonlinear optical (NLO) data. The model is applied to the efficient NLO chromophore picolinium quinodimethane, yielding an excellent fit of the two-photon resonant wavelength-dependent data and a dependable static value β0 = 316 × 10(-30) esu. Furthermore, we show that including a second electronic excited state in the model does yield an improved description of the NLO data at shorter wavelengths but has only limited influence on β0.

  12. Evaluation of a mesoscale dispersion modelling tool during the CAPITOUL experiment

    Science.gov (United States)

    Lac, C.; Bonnardot, F.; Connan, O.; Camail, C.; Maro, D.; Hebert, D.; Rozet, M.; Pergaud, J.

    2008-12-01

    Atmospheric transport and dispersion were investigated during the CAPITOUL campaign using measurements of sulphur hexafluoride (SF6) tracer. Six releases of SF6 tracer were performed (March 9-11 and July 1-3, 2004) in the same suburban area of Toulouse conurbation, during the Intensive Observing Periods (IOP) of CAPITOUL. Concentration data were collected both at ground-level along axes perpendicular to the wind direction (at distances ranging between 280 m and 5000 m from the release point), and above the ground at 100 m and 200 m height using aircraft flights. Meteorological conditions were all associated with daytime anticyclonic conditions with weak winds and convective clear and cloudy boundary layers. A meso-scale dispersion modelling system, PERLE, developed at Meteo-France for environmental emergencies in case of atmospheric accidental release, was evaluated in terms of meteorology and dispersion, for the different tracer experiments, in its operational configuration. PERLE is based on the combination of the non-hydrostatic meso-scale MESO-NH model, running at 2 km horizontal resolution, and the Lagrangian particle model SPRAY. The statistical meteorological evaluation includes two sets of simulations with initialisation from ECMWF or ALADIN. The meteorological day-to-day error statistics show fairly good Meso-NH predictions, in terms of wind speed, wind direction and near-surface temperature. A strong sensitivity to initial fields concerns the surface fluxes, crucial for dispersion, with an excessive drying of the convective boundary layer with ALADIN initial fields, leading to an overprediction of surface sensible heat fluxes. A parameterization of dry and shallow convection according to the Eddy-Diffusivity-Mass-Flux (EDMF) approach (Pergaud et al. 2008) allows an efficient mixing in the Convective Boundary Layer (CBL) and improves significantly the wind fields. A statistical evaluation of the dispersion prediction was then performed and shows a

  13. Strongly coupled dispersed two-phase flows; Ecoulements diphasiques disperses fortement couples

    Energy Technology Data Exchange (ETDEWEB)

    Zun, I.; Lance, M.; Ekiel-Jezewska, M.L.; Petrosyan, A.; Lecoq, N.; Anthore, R.; Bostel, F.; Feuillebois, F.; Nott, P.; Zenit, R.; Hunt, M.L.; Brennen, C.E.; Campbell, C.S.; Tong, P.; Lei, X.; Ackerson, B.J.; Asmolov, E.S.; Abade, G.; da Cunha, F.R.; Lhuillier, D.; Cartellier, A.; Ruzicka, M.C.; Drahos, J.; Thomas, N.H.; Talini, L.; Leblond, J.; Leshansky, A.M.; Lavrenteva, O.M.; Nir, A.; Teshukov, V.; Risso, F.; Ellinsen, K.; Crispel, S.; Dahlkild, A.; Vynnycky, M.; Davila, J.; Matas, J.P.; Guazelli, L.; Morris, J.; Ooms, G.; Poelma, C.; van Wijngaarden, L.; de Vries, A.; Elghobashi, S.; Huilier, D.; Peirano, E.; Minier, J.P.; Gavrilyuk, S.; Saurel, R.; Kashinsky, O.; Randin, V.; Colin, C.; Larue de Tournemine, A.; Roig, V.; Suzanne, C.; Bounhoure, C.; Brunet, Y.; Tanaka, A.T.; Noma, K.; Tsuji, Y.; Pascal-Ribot, S.; Le Gall, F.; Aliseda, A.; Hainaux, F.; Lasheras, J.; Didwania, A.; Costa, A.; Vallerin, W.; Mudde, R.F.; Van Den Akker, H.E.A.; Jaumouillie, P.; Larrarte, F.; Burgisser, A.; Bergantz, G.; Necker, F.; Hartel, C.; Kleiser, L.; Meiburg, E.; Michallet, H.; Mory, M.; Hutter, M.; Markov, A.A.; Dumoulin, F.X.; Suard, S.; Borghi, R.; Hong, M.; Hopfinger, E.; Laforgia, A.; Lawrence, C.J.; Hewitt, G.F.; Osiptsov, A.N.; Tsirkunov, Yu. M.; Volkov, A.N.

    2003-07-01

    This document gathers the abstracts of the Euromech 421 colloquium about strongly coupled dispersed two-phase flows. Behaviors specifically due to the two-phase character of the flow have been categorized as: suspensions, particle-induced agitation, microstructure and screening mechanisms; hydrodynamic interactions, dispersion and phase distribution; turbulence modulation by particles, droplets or bubbles in dense systems; collective effects in dispersed two-phase flows, clustering and phase distribution; large-scale instabilities and gravity driven dispersed flows; strongly coupled two-phase flows involving reacting flows or phase change. Topic l: suspensions particle-induced agitation microstructure and screening mechanisms hydrodynamic interactions between two very close spheres; normal stresses in sheared suspensions; a critical look at the rheological experiments of R.A. Bagnold; non-equilibrium particle configuration in sedimentation; unsteady screening of the long-range hydrodynamic interactions of settling particles; computer simulations of hydrodynamic interactions among a large collection of sedimenting poly-disperse particles; velocity fluctuations in a dilute suspension of rigid spheres sedimenting between vertical plates: the role of boundaries; screening and induced-agitation in dilute uniform bubbly flows at small and moderate particle Reynolds numbers: some experimental results. Topic 2: hydrodynamic interactions, dispersion and phase distribution: hydrodynamic interactions in a bubble array; A 'NMR scattering technique' for the determination of the structure in a dispersion of non-brownian settling particles; segregation and clustering during thermo-capillary migration of bubbles; kinetic modelling of bubbly flows; velocity fluctuations in a homogeneous dilute dispersion of high-Reynolds-number rising bubbles; an attempt to simulate screening effects at moderate particle Reynolds numbers using an hybrid formulation; modelling the two

  14. Contaminant dispersion prediction and source estimation with integrated Gaussian-machine learning network model for point source emission in atmosphere

    International Nuclear Information System (INIS)

    Ma, Denglong; Zhang, Zaoxiao

    2016-01-01

    Highlights: • The intelligent network models were built to predict contaminant gas concentrations. • The improved network models coupled with Gaussian dispersion model were presented. • New model has high efficiency and accuracy for concentration prediction. • New model were applied to indentify the leakage source with satisfied results. - Abstract: Gas dispersion model is important for predicting the gas concentrations when contaminant gas leakage occurs. Intelligent network models such as radial basis function (RBF), back propagation (BP) neural network and support vector machine (SVM) model can be used for gas dispersion prediction. However, the prediction results from these network models with too many inputs based on original monitoring parameters are not in good agreement with the experimental data. Then, a new series of machine learning algorithms (MLA) models combined classic Gaussian model with MLA algorithm has been presented. The prediction results from new models are improved greatly. Among these models, Gaussian-SVM model performs best and its computation time is close to that of classic Gaussian dispersion model. Finally, Gaussian-MLA models were applied to identifying the emission source parameters with the particle swarm optimization (PSO) method. The estimation performance of PSO with Gaussian-MLA is better than that with Gaussian, Lagrangian stochastic (LS) dispersion model and network models based on original monitoring parameters. Hence, the new prediction model based on Gaussian-MLA is potentially a good method to predict contaminant gas dispersion as well as a good forward model in emission source parameters identification problem.

  15. Contaminant dispersion prediction and source estimation with integrated Gaussian-machine learning network model for point source emission in atmosphere

    Energy Technology Data Exchange (ETDEWEB)

    Ma, Denglong [Fuli School of Food Equipment Engineering and Science, Xi’an Jiaotong University, No.28 Xianning West Road, Xi’an 710049 (China); Zhang, Zaoxiao, E-mail: zhangzx@mail.xjtu.edu.cn [State Key Laboratory of Multiphase Flow in Power Engineering, Xi’an Jiaotong University, No.28 Xianning West Road, Xi’an 710049 (China); School of Chemical Engineering and Technology, Xi’an Jiaotong University, No.28 Xianning West Road, Xi’an 710049 (China)

    2016-07-05

    Highlights: • The intelligent network models were built to predict contaminant gas concentrations. • The improved network models coupled with Gaussian dispersion model were presented. • New model has high efficiency and accuracy for concentration prediction. • New model were applied to indentify the leakage source with satisfied results. - Abstract: Gas dispersion model is important for predicting the gas concentrations when contaminant gas leakage occurs. Intelligent network models such as radial basis function (RBF), back propagation (BP) neural network and support vector machine (SVM) model can be used for gas dispersion prediction. However, the prediction results from these network models with too many inputs based on original monitoring parameters are not in good agreement with the experimental data. Then, a new series of machine learning algorithms (MLA) models combined classic Gaussian model with MLA algorithm has been presented. The prediction results from new models are improved greatly. Among these models, Gaussian-SVM model performs best and its computation time is close to that of classic Gaussian dispersion model. Finally, Gaussian-MLA models were applied to identifying the emission source parameters with the particle swarm optimization (PSO) method. The estimation performance of PSO with Gaussian-MLA is better than that with Gaussian, Lagrangian stochastic (LS) dispersion model and network models based on original monitoring parameters. Hence, the new prediction model based on Gaussian-MLA is potentially a good method to predict contaminant gas dispersion as well as a good forward model in emission source parameters identification problem.

  16. Evaluation of field-collected data measuring fluorescein dye movements and dispersion for dispersed oil transport modeling

    Energy Technology Data Exchange (ETDEWEB)

    French McCay, D.; Mueller, C.; Jayko, K.; Longval, B.; Schroeder, M. [Applied Science Associates Inc., Narragansett, RI (United States); Terrill, E.; Carter, M.; Otero, M.; Kim, S.Y. [Scripps Inst. of Oceanography, La Jolla, CA (United States); Nordhausen, W.; Lampinen, M. [California Dept. of Fish and Game, San Diego, CA (United States). Office of Spill Prevention and Response; Payne, J.R. [Payne Environmental Consultants Inc., Encinitas, CA (United States); Ohlmann, C. [California Univ., Santa Barbara, CA (United States)

    2007-07-01

    In the event of on oil spill at sea, the concentration of hydrocarbons in the water column can be evaluated using oil spill fate and transport modeling. Such modeling can also determine the potential exposure to zooplankton, and the impacts of oil spills with and without the use of dispersants. This paper reported on fluorescein dye studies that were conducted off Sand Diego, California to evaluate the ability of transport models to hindcast movement and dispersion of dye using data such as surface currents calculated from high-frequency radar; near surface currents from drifter measurements drogued at several depths; dye concentrations measured by fluorescence; spreading and dye intensity measurements based on aerial photography; and, water density profiles from conductivity-temperature-depth (CTD) casts. This paper presented modeling issues that remain to be addressed, such as the need to resolve small-scale transport processes in order to evaluate effects on water column biota. Since these processes determining current velocities are complex, it is not feasible to include most of the complexities at appropriately small scales in oil spill modeling applications. The difficulty in predicting currents that transport oil components and organisms with a hydrodynamic model application that does not include temporal details in the forcing function was also discussed. This paper demonstrated that the SIMAP spill trajectory model, using the drifter velocities as current input, successfully reproduced trajectories of the dye. The effect of wind drift transporting the surface material faster than the subsurface materials was identified as a spreading mechanism. Therefore, subtraction of the wind drift from the shallower drifter velocities, and inclusion of wind drift in SIMAP would allow those velocities to be used for depths other than those tracked by the drifters. 57 refs., 8 tabs., 17 figs.

  17. Multiple Linear Regression Modeling To Predict the Stability of Polymer-Drug Solid Dispersions: Comparison of the Effects of Polymers and Manufacturing Methods on Solid Dispersion Stability.

    Science.gov (United States)

    Fridgeirsdottir, Gudrun A; Harris, Robert J; Dryden, Ian L; Fischer, Peter M; Roberts, Clive J

    2018-03-29

    Solid dispersions can be a successful way to enhance the bioavailability of poorly soluble drugs. Here 60 solid dispersion formulations were produced using ten chemically diverse, neutral, poorly soluble drugs, three commonly used polymers, and two manufacturing techniques, spray-drying and melt extrusion. Each formulation underwent a six-month stability study at accelerated conditions, 40 °C and 75% relative humidity (RH). Significant differences in times to crystallization (onset of crystallization) were observed between both the different polymers and the two processing methods. Stability from zero days to over one year was observed. The extensive experimental data set obtained from this stability study was used to build multiple linear regression models to correlate physicochemical properties of the active pharmaceutical ingredients (API) with the stability data. The purpose of these models is to indicate which combination of processing method and polymer carrier is most likely to give a stable solid dispersion. Six quantitative mathematical multiple linear regression-based models were produced based on selection of the most influential independent physical and chemical parameters from a set of 33 possible factors, one model for each combination of polymer and processing method, with good predictability of stability. Three general rules are proposed from these models for the formulation development of suitably stable solid dispersions. Namely, increased stability is correlated with increased glass transition temperature ( T g ) of solid dispersions, as well as decreased number of H-bond donors and increased molecular flexibility (such as rotatable bonds and ring count) of the drug molecule.

  18. Development of regional atmospheric dynamic and air pollution models for nuclear emergency response system WSPEEDI

    International Nuclear Information System (INIS)

    Furuno, Akiko; Yamazawa, Hiromi; Lee, Soon-Hwan; Tsujita, Yuichi; Takemiya, Hiroshi; Chino, Masamichi

    2000-01-01

    WSPEEDI (Worldwide version of System for Prediction of Environmental Emergency Dose Information) is a computer-based emergency response system to predict long-range atmospheric dispersion of radionuclides discharged into the atmosphere due to a nuclear accident. WSPEEDI has been applied to several international exercises and real events. Through such experiences, the new version of WSPEEDI aims to employ a combination of an atmospheric dynamic model and a particle random walk model for more accurate predictions. This paper describes these models, improvement of prediction and computational techniques for quick responses. (author)

  19. Model calculating annual mean atmospheric dispersion factor for coastal site of nuclear power plant

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    This paper describes an atmospheric dispersion field experiment performed on the coastal site of nuclear power plant in the east part of China during 1995 to 1996. The three-dimension joint frequency are obtained by hourly observation of wind and temperature on a 100m high tower; the frequency of the “event day of land and sea breezes” are given by observation of surface wind and land and sea breezes; the diffusion parameters are got from measurements of turbulent and wind tunnel simulation test.A new model calculating the annual mean atmospheric dispersion factor for coastal site of nuclear power plant is developed and established.This model considers not only the effect from mixing release and mixed layer but also the effect from the internal boundary layer and variation of diffusion parameters due to the distance from coast.The comparison between results obtained by the new model and current model shows that the ratio of annual mean atmospheric dispersion factor gained by the new model and the current one is about 2.0.

  20. Modeling and preliminary analysis on the temperature profile of the (TRU-Zr)-Zr dispersion fuel rod for HYPER

    International Nuclear Information System (INIS)

    Lee, B. W.; Hwang, W.; Lee, B. S.; Park, W. S.

    2000-01-01

    Either TRU-Zr metal alloy or (TRU-Zr)-Zr dispersion fuel is considered as a blanket fuel for HYPER(Hybrid Power Extraction Reactor). In order to develop the code for dispersion fuel rod performance analysis under steady state condition, the fuel temperature distribution model which is the one of the most important factors in a fuel performance code has been developed in this paper,. This developed model computes the one dimensional radial temperature distribution of a cylindrical fuel rod. The temperature profile results by this model are compared with the temperature distributions of U 3 Si-A1 dispersion fuel and TRU-Zr metal alloy fuel. This model will be installed in performance analysis code for dispersion fuel

  1. PHYSICAL AND NUMERICAL MODELING OF ASD EXHAUST DISPERSION AROUND HOUSES

    Science.gov (United States)

    The report discusses the use of a wind tunnel to physically model the dispersion of exhaust plumes from active soil depressurization (ASD) radon mitigation systems in houses. he testing studied the effects of exhaust location (grade level vs. above the eave), as house height, roo...

  2. Local-scale high-resolution atmospheric dispersion model using large-eddy simulation. LOHDIM-LES

    International Nuclear Information System (INIS)

    Nakayama, Hiromasa; Nagai, Haruyasu

    2016-03-01

    We developed LOcal-scale High-resolution atmospheric DIspersion Model using Large-Eddy Simulation (LOHDIM-LES). This dispersion model is designed based on LES which is effective to reproduce unsteady behaviors of turbulent flows and plume dispersion. The basic equations are the continuity equation, the Navier-Stokes equation, and the scalar conservation equation. Buildings and local terrain variability are resolved by high-resolution grids with a few meters and these turbulent effects are represented by immersed boundary method. In simulating atmospheric turbulence, boundary layer flows are generated by a recycling turbulent inflow technique in a driver region set up at the upstream of the main analysis region. This turbulent inflow data are imposed at the inlet of the main analysis region. By this approach, the LOHDIM-LES can provide detailed information on wind velocities and plume concentration in the investigated area. (author)

  3. Development of numerical dispersion model for radioactive nuclei including resuspension processes

    International Nuclear Information System (INIS)

    Chiba, Masaru; Kurita, Susumu; Sasaki, Hidetaka

    2003-01-01

    Global-scale and local-scale dispersion model are developed combining to global and local scale meteorological forecasting model. By applying this system to another miner constituent such as mineral dust blowing by strong wind in arid region, this system shows very good performance to watch and predict the distribution of it. (author)

  4. Pseudospectral modeling and dispersion analysis of Rayleigh waves in viscoelastic media

    Science.gov (United States)

    Zhang, K.; Luo, Y.; Xia, J.; Chen, C.

    2011-01-01

    Multichannel Analysis of Surface Waves (MASW) is one of the most widely used techniques in environmental and engineering geophysics to determine shear-wave velocities and dynamic properties, which is based on the elastic layered system theory. Wave propagation in the Earth, however, has been recognized as viscoelastic and the propagation of Rayleigh waves presents substantial differences in viscoelastic media as compared with elastic media. Therefore, it is necessary to carry out numerical simulation and dispersion analysis of Rayleigh waves in viscoelastic media to better understand Rayleigh-wave behaviors in the real world. We apply a pseudospectral method to the calculation of the spatial derivatives using a Chebyshev difference operator in the vertical direction and a Fourier difference operator in the horizontal direction based on the velocity-stress elastodynamic equations and relations of linear viscoelastic solids. This approach stretches the spatial discrete grid to have a minimum grid size near the free surface so that high accuracy and resolution are achieved at the free surface, which allows an effective incorporation of the free surface boundary conditions since the Chebyshev method is nonperiodic. We first use an elastic homogeneous half-space model to demonstrate the accuracy of the pseudospectral method comparing with the analytical solution, and verify the correctness of the numerical modeling results for a viscoelastic half-space comparing the phase velocities of Rayleigh wave between the theoretical values and the dispersive image generated by high-resolution linear Radon transform. We then simulate three types of two-layer models to analyze dispersive-energy characteristics for near-surface applications. Results demonstrate that the phase velocity of Rayleigh waves in viscoelastic media is relatively higher than in elastic media and the fundamental mode increases by 10-16% when the frequency is above 10. Hz due to the velocity dispersion of P

  5. Modeling of mesoscale dispersion effect on the piezoresistivity of carbon nanotube-polymer nanocomposites via 3D computational multiscale micromechanics methods

    International Nuclear Information System (INIS)

    Ren, Xiang; Seidel, Gary D; Chaurasia, Adarsh K; Oliva-Avilés, Andrés I; Ku-Herrera, José J; Avilés, Francis

    2015-01-01

    In uniaxial tension and compression experiments, carbon nanotube (CNT)-polymer nanocomposites have demonstrated exceptional mechanical and coupled electrostatic properties in the form of piezoresistivity. In order to better understand the correlation of the piezoresistive response with the CNT dispersion at the mesoscale, a 3D computational multiscale micromechanics model based on finite element analysis is constructed to predict the effective macroscale piezoresistive response of CNT/polymer nanocomposites. The key factors that may contribute to the overall piezoresistive response, i.e. the nanoscale electrical tunneling effect, the inherent CNT piezoresistivity and the CNT mesoscale network effect are incorporated in the model based on a 3D multiscale mechanical–electrostatic coupled code. The results not only explain how different nanoscale mechanisms influence the overall macroscale piezoresistive response through the mesoscale CNT network, but also give reason and provide bounds for the wide range of gauge factors found in the literature offering insight regarding how control of the mesoscale CNT networks can be used to tailor nanocomposite piezoresistive response. (paper)

  6. Dispersive dielectric and conductive effects in 2D resistor-capacitor networks.

    Science.gov (United States)

    Hamou, R F; Macdonald, J R; Tuncer, E

    2009-01-14

    How to predict and better understand the effective properties of disordered material mixtures has been a long-standing problem in different research fields, especially in condensed matter physics. In order to address this subject and achieve a better understanding of the frequency-dependent properties of these systems, a large 2D L × L square structure of resistors and capacitors was used to calculate the immittance response of a network formed by random filling of binary conductor/insulator phases with 1000 Ω resistors and 10 nF capacitors. The effects of percolating clusters on the immittance response were studied statistically through the generation of 10 000 different random network samples at the percolation threshold. The scattering of the imaginary part of the immittance near the dc limit shows a clear separation between the responses of percolating and non-percolating samples, with the gap between their distributions dependent on both network size and applied frequency. These results could be used to monitor connectivity in composite materials. The effects of the content and structure of the percolating path on the nature of the observed dispersion were investigated, with special attention paid to the geometrical fractal concept of the backbone and its influence on the behavior of relaxation-time distributions. For three different resistor-capacitor proportions, the appropriateness of many fitting models was investigated for modeling and analyzing individual resistor-capacitor network dispersed frequency responses using complex-nonlinear-least-squares fitting. Several remarkable new features were identified, including a useful duality relationship and the need for composite fitting models rather than either a simple power law or a single Davidson-Cole one. Good fits of data for fully percolating random networks required two dispersive fitting models in parallel or series, with a cutoff at short times of the distribution of relaxation times of one of

  7. A dynamic approach for the impact of a toxic gas dispersion hazard considering human behaviour and dispersion modelling.

    Science.gov (United States)

    Lovreglio, Ruggiero; Ronchi, Enrico; Maragkos, Georgios; Beji, Tarek; Merci, Bart

    2016-11-15

    The release of toxic gases due to natural/industrial accidents or terrorist attacks in populated areas can have tragic consequences. To prevent and evaluate the effects of these disasters different approaches and modelling tools have been introduced in the literature. These instruments are valuable tools for risk managers doing risk assessment of threatened areas. Despite the significant improvements in hazard assessment in case of toxic gas dispersion, these analyses do not generally include the impact of human behaviour and people movement during emergencies. This work aims at providing an approach which considers both modelling of gas dispersion and evacuation movement in order to improve the accuracy of risk assessment for disasters involving toxic gases. The approach is applied to a hypothetical scenario including a ship releasing Nitrogen dioxide (NO2) on a crowd attending a music festival. The difference between the results obtained with existing static methods (people do not move) and a dynamic approach (people move away from the danger) which considers people movement with different degrees of sophistication (either a simple linear path or more complex behavioural modelling) is discussed. Copyright © 2016 Elsevier B.V. All rights reserved.

  8. Assessment of particle-tracking models for dispersed particle-laden flows implemented in OpenFOAM and ANSYS FLUENT

    Directory of Open Access Journals (Sweden)

    Franziska Greifzu

    2016-01-01

    Full Text Available In the present study two benchmark problems for turbulent dispersed particle-laden flow are investigated with computational fluid dynamics (CFD. How the CFD programs OpenFOAM and ANSYS FLUENT model these flows is tested and compared. The numerical results obtained with Lagrangian–Eulerian (LE point-particle (PP models for Reynolds-averaged Navier–Stokes (RANS simulations of the fluid flow in steady state and transient modes are compared with the experimental data available in the literature. The effect of the dispersion model on the particle motion is investigated in particular, as well as the order of coupling between the continuous carrier phase and the dispersed phase. First, a backward-facing step (BFS case is validated. As a second case, the confined bluff body (CBB is used. The simulated fluid flows correspond well with the experimental data for both test cases. The results for the dispersed solid phase reveal a good accordance between the simulation results and the experiments. It seems that particle dispersion is slightly under-predicted when ANSYS FLUENT is used, whereas the applied solver in OpenFOAM overestimates the dispersion somewhat. Only minor differences between the coupling schemes are detected due to the low volume fractions and mass loadings that are investigated. In the BFS test case the importance of the spatial dimension of the numerical model is demonstrated. Even if it is reasonable to assume a two-dimensional fluid flow structure, it is crucial to simulate the turbulent particle-laden flow with a three-dimensional model since the turbulent dispersion of the particles is three-dimensional.

  9. Pollutant Dispersion Modeling in Natural Streams Using the Transmission Line Matrix Method

    Directory of Open Access Journals (Sweden)

    Safia Meddah

    2015-09-01

    Full Text Available Numerical modeling has become an indispensable tool for solving various physical problems. In this context, we present a model of pollutant dispersion in natural streams for the far field case where dispersion is considered longitudinal and one-dimensional in the flow direction. The Transmission Line Matrix (TLM, which has earned a reputation as powerful and efficient numerical method, is used. The presented one-dimensional TLM model requires a minimum input data and provides a significant gain in computing time. To validate our model, the results are compared with observations and experimental data from the river Severn (UK. The results show a good agreement with experimental data. The model can be used to predict the spatiotemporal evolution of a pollutant in natural streams for effective and rapid decision-making in a case of emergency, such as accidental discharges in a stream with a dynamic similar to that of the river Severn (UK.

  10. Two-Fluid Models for Simulating Dispersed Multiphase Flows-A Review

    Directory of Open Access Journals (Sweden)

    L.X. Zhou

    2009-01-01

    Full Text Available The development of two-fluid models for simulating dispersed multiphase flows (gas-particle, gas-droplet, bubble-liquid, liquid-particle flows by the present author within the last 20 years is systematically reviewed. The two-fluid models based on Reynolds expansion, time averaging and mass-weighed averaging, and also PDF transport equations are described. Different versions of two-phase turbulence models, including the unified second-order moment (USM and k-ε-kp models, the DSM-PDF model, the SOM-MC model, the nonlinear k-e-kp model, and the USM-Θ model for dense gas-particle flows and their application and experimental validation are discussed.

  11. Contributions of chemical exchange to T1ρ dispersion in a tissue model.

    Science.gov (United States)

    Cobb, Jared G; Xie, Jingping; Gore, John C

    2011-12-01

    Variations in T(1ρ) with locking-field strength (T(1ρ) dispersion) may be used to estimate proton exchange rates. We developed a novel approach utilizing the second derivative of the dispersion curve to measure exchange in a model system of cross-linked polyacrylamide gels. These gels were varied in relative composition of comonomers, increasing stiffness, and in pH, modifying exchange rates. Magnetic resonance images were recorded with a spin-locking sequence as described by Sepponen et al. These measurements were fit to a mono-exponential decay function yielding values for T(1ρ) at each locking-field measured. These values were then fit to a model by Chopra et al. for estimating exchange rates. For low stiffness gels, the calculated exchange values increased by a factor of 4 as pH increased, consistent with chemical exchange being the dominant contributor to T(1ρ) dispersion. Interestingly, calculated chemical exchange rates also increased with stiffness, likely due to modified side-chain exchange kinetics as the composition varied. This article demonstrates a new method to assess the structural and chemical effects on T(1ρ) relaxation dispersion with a suitable model. These phenomena may be exploited in an imaging context to emphasize the presence of nuclei of specific exchange rates, rather than chemical shifts. Copyright © 2011 Wiley Periodicals, Inc.

  12. On unitarity of the particle-hole dispersive optical model

    Science.gov (United States)

    Gorelik, M. L.; Shlomo, S.; Tulupov, B. A.; Urin, M. H.

    2018-02-01

    For the recently developed particle-hole dispersive optical model, weak violations of unitarity due to a phenomenological description of the spreading effect are considered. Methods for unitarity restoration are proposed and implemented for the 208Pb nucleus in the description of the energy-averaged isoscalar monopole double transition density and strength functions in a wide excitation energy interval that includes the isoscalar giant monopole resonance and its overtone. To illustrate abilities of the model, direct neutron decay of the mentioned giant resonance is also considered.

  13. Comparison of the local-scale atmospheric dispersion model Cedrat with 85KR measurements

    International Nuclear Information System (INIS)

    Rennesson, M.; Devin, P.; Maro, D.; Fitamant, M.L.; Bouland, P.

    2004-01-01

    An accurate model of atmospheric dispersion of radionuclides over the complex terrain of the La Hague reprocessing plant (North Cotentin, France) has been developed by COGEMA, in partnership with Paris VI University. This model, called CEDRAT 1.0.1 (operational since October 2002), takes into account areas typically outside the validity limits of Gaussian models: relief and building influence, short-distance (beyond 500 m from the release point) and stable atmospheric conditions. The modelling tool is based on an original method: a 2D-meshed model for flow resolution at permanent rate in the prevailing wind direction, and a 3D description of the dispersion phenomena, taking into account wet and dry deposits, at permanent or transitory rate. This leads to an effective compromise between rapidity (45 min on a 6000 nodes grid, with a standard PC), robustness and accuracy, coupled with a user-friendly interface. Primarily the validation process consisted of a comparison with the 3D complex dispersion reference model MERCURE, developed by EDF. Then, MERCURE and CEDRAT results were compared on real release scenario basis, for which actual meteorological conditions and tracer data collected at monitoring stations around the site were known. To enlarge this validation process, a second level of comparison was made in collaboration with a IRSN Cherbourg team, through different field experiments, which provided both ground and elevated level measurements (collected with a captive balloon), for different stability classes of the atmosphere. The plume tracer is krypton 85, an inert gas released from a height of 100 m. Thus, the aim of this paper is to present the original method to describe short distance dispersion over complex terrain and its validation enrichment for stability conditions and areas not yet observed, through wind and cross-wind Atmospheric Transfer Coefficients comparisons, at both ground and elevated levels. (author)

  14. Atmospheric dispersion of radioactive materials

    International Nuclear Information System (INIS)

    Chino, Masamichi

    1988-01-01

    The report describes currently available techniques for predicting the dispersion of accidentally released radioactive materials and techniques for visualization using computer graphics. A simulation study is also made on the dispersion of radioactive materials released from the Chernobyl plant. The simplest models include the Gauss plume model and the puff model, which cannot serve to analyze the effects of the topography, vertical wind shear, temperature inversion layer, etc. Numerical analysis methods using advection and dispersion equations are widely adopted for detailed evaluation of dispersion in an emergency. An objective analysis model or a hydrodynamical model is often used to calculate the air currents which are required to determine the advection. A small system based on the puff model is widely adopted in Europe, where the topography is considered to have only simple effects. A more sophisticated large-sized system is required in nuclear facilities located in an area with more complex topographic features. An emergency system for dispersion calculation should be equipped with a graphic display to serve for quick understanding of the radioactivity distribution. (Nogami, K.)

  15. A vegetation modeling concept for Building and Environmental Aerodynamics wind tunnel tests and its application in pollutant dispersion studies

    International Nuclear Information System (INIS)

    Gromke, Christof

    2011-01-01

    A new vegetation modeling concept for Building and Environmental Aerodynamics wind tunnel investigations was developed. The modeling concept is based on fluid dynamical similarity aspects and allows the small-scale modeling of various kinds of vegetation, e.g. field crops, shrubs, hedges, single trees and forest stands. The applicability of the modeling concept was validated in wind tunnel pollutant dispersion studies. Avenue trees in urban street canyons were modeled and their implications on traffic pollutant dispersion were investigated. The dispersion experiments proved the modeling concept to be practicable for wind tunnel studies and suggested to provide reliable concentration results. Unfavorable effects of trees on pollutant dispersion and natural ventilation in street canyons were revealed. Increased traffic pollutant concentrations were found in comparison to the tree-free reference case. - Highlights: → A concept for aerodynamic modelling of vegetation in small scale wind tunnel studies is presented. → The concept was applied to study pollutant dispersion in urban street canyons with avenue tress. → The wind tunnel studies show that modelling the aerodynamic effects of vegetation is important. → Avenue trees give rise to increased pollutant concentrations in urban street canyons. - Avenue trees in urban street canyons affect the pollutant dispersion and result in increased traffic exhaust concentrations.

  16. Analysis of dispersed frequency response for ionic glasses: influence of electrode and nearly constant loss effects

    International Nuclear Information System (INIS)

    Macdonald, J Ross

    2005-01-01

    Analysis by D L Sidebottom of the dispersive frequency response of the real-part of the conductivity, σ'(ω), for many alkali phosphate and metaphosphate glasses, using a fitting model involving a 'universal dynamic response' power law with an exponent n and a constant-loss term, led to anomalous n behaviour that he explained as arising from variable constriction of the local cation conduction space. In order to obtain adequate fits, he eliminated from the data all low-frequency decreases of σ'(ω) below the dc plateau, ones actually associated with electrode effects. Such a cut-off does not, however, eliminate electrode effects possibly present in the high-frequency part of the data range. The results of the present detailed analysis and fitting of both synthetic data and several of his experimental data sets show unequivocally that his anomalous n behaviour arose from neglecting electrode effects. Their inclusion, with or without data cut-off in the fitting model, leads to the expected high-frequency slope value of n = 2/3 associated with bulk conduction, as required by recently published topological effective-dimension considerations for dielectric relaxation in conductive systems. Further, the effects of the inclusion in a full fitting model of series and possibly parallel complex constant-phase-element contributions, representing electrode and nearly constant loss effects, respectively, have been investigated in detail. Such composite models usually lead to best fitting of either the full or cut-off complex data when they include the semi-universal, topologically based K1 bulk model, one indirectly derived from the assumption of stretched-exponential temporal behaviour

  17. Comparison of marine dispersion model predictions with environmental radionuclide concentrations

    International Nuclear Information System (INIS)

    Johnson, C.E.; McKay, W.A.

    1988-01-01

    The comparison of marine dispersion model results with measurements is an essential part of model development and testing. The results from two residual flow models are compared with seawater concentrations, and in one case with concentrations measured in marine molluscs. For areas with short turnover times, seawater concentrations respond rapidly to variations in discharge rate and marine currents. These variations are difficult to model, and comparison with concentrations in marine animals provides an alternative and complementary technique for model validation with the advantages that the measurements reflect the mean conditions and frequently form a useful time series. (author)

  18. Marine radioactivity studies in the Suez Canal: Modelling hydrodynamics and dispersion

    International Nuclear Information System (INIS)

    Abril, J.M.; Abdel-Aal, M.M.

    1999-01-01

    This paper comprises the work carried out under the IAEA Technical Co-operation Project EGY/07/002. The main goal was to develop a modelling study on the dispersion of radioactive pollution in the Suez Canal

  19. CRUNCH, Dispersion Model for Continuous Dense Vapour Release in Atmosphere

    International Nuclear Information System (INIS)

    Jagger, S.F.

    1987-01-01

    1 - Description of program or function: The situation modelled is as follows. A dense gas emerges from a source such that it can be considered to emerge through a rectangular area, placed in the vertical plane and perpendicular to the plume direction, which assumes that of the ambient wind. The gas flux at the source, and in every plane perpendicular to the plume direction, is constant in time and a stationary flow field has been attained. For this to apply, the characteristic time of release must be much larger than that for dispersal of the contaminant. The plume can be thought to consist of a number of rectangular elements or 'puffs' emerging from the source at regular time intervals. The model follows the development of these puffs at a series of downwind points. These puffs are immediately assumed to advect with the ambient wind at their half-height. The plume also slumps due to the action of gravity and is allowed to entrain air through its sides and top surface. Spreading of a fluid element is caused by pressure differences across this element and since the pressure gradient in the wind direction is small, the resulting pressure differences and slumping velocities are small also, thus permitting this convenient approximation. Initially, as the plume slumps, its vertical dimension decreases and with it the slumping velocity and advection velocity. Thus the plume advection velocity varies as a function of downwind distance. With the present steady state modelling, and to satisfy continuity constraints, there must be consequent adjustment of plume height. Calculation of this parameter from the volume flux ensures this occurs. As the cloud height begins to grow, the advection velocity increases and the plume height decreases accordingly. With advection downwind, the cloud gains buoyancy by entraining air and, if the cloud is cold, by absorbing heat from the ground. Eventually the plume begins to disperse as would a passive pollutant, through the action of

  20. Modeling of dilute and dense dispersed fluid-particle flow

    Energy Technology Data Exchange (ETDEWEB)

    Laux, Harald

    1998-08-01

    A general two-fluid model is derived and applied in CFD computations to various test cases of important industrial multiphase flows. It is general in the sense of its applicability to dilute and dense dispersed fluid-particle flows. The model is limited to isothermal flow without mass transfer and only one particle phase is described. The instantaneous fluid phase equations, including the phase interaction terms, are derived from a volume averaging technique, and the instantaneous particle phase equations are derived from the kinetic theory of granular material. Whereas the averaging procedure, the treatment of the interaction terms, and the kinetic theory approach have been reported in literature prior to this work the combination of the approaches is new. The resulting equations are derived without ambiguity in the interpretation of the particle phase pressure (equation-of-state of particle phase). The basic modeling for the particle phase is improved in two steps. Because in the basic modeling only stresses due to kinetic and collisional interactions are included, a simple model for an effective viscosity is developed in order to allow also frictional stresses within the particle phase. Moreover, turbulent stresses and turbulent dispersion of particles play often an important role for the transport processes. Therefore in a second step, a two-equation turbulence model for both fluid and particle phase turbulence is derived by applying the phasic average to the instantaneous equations. The resulting k-{epsilon}-k{sup d}-{epsilon}{sup d} model is new. Mathematical closure is attempted such that the resulting set of equations is valid for both dilute arid dense flows. During the development of the closure relations a clear distinction is made between granular or ''viscous'' microscale fluctuations and turbulent macro scale fluctuations (true particle turbulence) within the particle phase. The set of governing equations is discretized by using a finite volume method

  1. Modeling of dilute and dense dispersed fluid-particle flow

    Energy Technology Data Exchange (ETDEWEB)

    Laux, Harald

    1998-08-01

    A general two-fluid model is derived and applied in CFD computations to various test cases of important industrial multiphase flows. It is general in the sense of its applicability to dilute and dense dispersed fluid-particle flows. The model is limited to isothermal flow without mass transfer and only one particle phase is described. The instantaneous fluid phase equations, including the phase interaction terms, are derived from a volume averaging technique, and the instantaneous particle phase equations are derived from the kinetic theory of granular material. Whereas the averaging procedure, the treatment of the interaction terms, and the kinetic theory approach have been reported in literature prior to this work the combination of the approaches is new. The resulting equations are derived without ambiguity in the interpretation of the particle phase pressure (equation-of-state of particle phase). The basic modeling for the particle phase is improved in two steps. Because in the basic modeling only stresses due to kinetic and collisional interactions are included, a simple model for an effective viscosity is developed in order to allow also frictional stresses within the particle phase. Moreover, turbulent stresses and turbulent dispersion of particles play often an important role for the transport processes. Therefore in a second step, a two-equation turbulence model for both fluid and particle phase turbulence is derived by applying the phasic average to the instantaneous equations. The resulting k-{epsilon}-k{sup d}-{epsilon}{sup d} model is new. Mathematical closure is attempted such that the resulting set of equations is valid for both dilute arid dense flows. During the development of the closure relations a clear distinction is made between granular or ''viscous'' microscale fluctuations and turbulent macro scale fluctuations (true particle turbulence) within the particle phase. The set of governing equations is discretized by using a

  2. Modeling Dispersion of Chemical-Biological Agents in Three Dimensional Living Space

    International Nuclear Information System (INIS)

    William S. Winters

    2002-01-01

    This report documents a series of calculations designed to demonstrate Sandia's capability in modeling the dispersal of chemical and biological agents in complex three-dimensional spaces. The transport of particles representing biological agents is modeled in a single room and in several connected rooms. The influence of particle size, particle weight and injection method are studied

  3. Development of a FBR fuel pin bundle deformation analysis code 'BAMBOO' . Development of a dispersion model and its validation

    International Nuclear Information System (INIS)

    Uwaba, Tomoyuki; Ukai, Shigeharu; Asaga, Takeo

    2002-03-01

    Bundle Duct Interaction (BDI) is one of the life limiting factors of a FBR fuel subassembly. Under the BDI condition, the fuel pin dispersion would occur mainly by the deviation of the wire position due to the irradiation. In this study the effect of the dispersion on the bundle deformation was evaluated by using the BAMBOO code and following results were obtained. (1) A new contact analysis model was introduced in BAMBOO code. This model considers the contact condition at the axial position other than the nodal point of the beam element that composes the fuel pin. This improvement made it possible in the bundle deformation analysis to cause fuel pin dispersion due to the deviations of the wire position. (2) This model was validated with the results of the out-of-pile compression test with the wire deviation. The calculated pin-to-duct and pin-to-pin clearances with the dispersion model almost agreed with the test results. Therefore it was confirmed that the BAMBOO code reasonably predicts the bundle deformation with the dispersion. (3) In the dispersion bundle the pin-to-pin clearances widely scattered. And the minimum pin-to-duct clearance increased or decreased depending on the dispersion condition compared to the no-dispersion bundle. This result suggests the possibility that the considerable dispersion would affect the thermal integrity of the bundle. (author)

  4. Traveling waves in a delayed SIR model with nonlocal dispersal and nonlinear incidence

    Science.gov (United States)

    Zhang, Shou-Peng; Yang, Yun-Rui; Zhou, Yong-Hui

    2018-01-01

    This paper is concerned with traveling waves of a delayed SIR model with nonlocal dispersal and a general nonlinear incidence. The existence and nonexistence of traveling waves of the system are established respectively by Schauder's fixed point theorem and two-sided Laplace transform. It is also shown that the spread speed c is influenced by the dispersal rate of the infected individuals and the delay τ.

  5. Modelling larval dispersal dynamics of common sole (Solea solea) along the western Iberian coast

    Science.gov (United States)

    Tanner, Susanne E.; Teles-Machado, Ana; Martinho, Filipe; Peliz, Álvaro; Cabral, Henrique N.

    2017-08-01

    Individual-based coupled physical-biological models have become the standard tool for studying ichthyoplankton dynamics and assessing fish recruitment. Here, common sole (Solea solea L.), a flatfish of high commercial importance in Europe was used to evaluate transport of eggs and larvae and investigate the connectivity between spawning and nursery areas along the western Iberian coast as spatio-temporal variability in dispersal and recruitment patterns can result in very strong or weak year-classes causing large fluctuations in stock size. A three-dimensional particle tracking model coupled to Regional Ocean Modelling System model was used to investigate variability of sole larvae dispersal along the western Iberian coast over a five-year period (2004-2009). A sensitivity analysis evaluating: (1) the importance of diel vertical migrations of larvae and (2) the size of designated recruitment areas was performed. Results suggested that connectivity patterns of sole larvae dispersal and their spatio-temporal variability are influenced by the configuration of the coast with its topographical structures and thus the suitable recruitment area available as well as the wind-driven mesoscale circulation along the Iberian coast.

  6. Applying Dispersive Changes to Lagrangian Particles in Groundwater Transport Models

    Science.gov (United States)

    Konikow, Leonard F.

    2010-01-01

    Method-of-characteristics groundwater transport models require that changes in concentrations computed within an Eulerian framework to account for dispersion be transferred to moving particles used to simulate advective transport. A new algorithm was developed to accomplish this transfer between nodal values and advecting particles more precisely and realistically compared to currently used methods. The new method scales the changes and adjustments of particle concentrations relative to limiting bounds of concentration values determined from the population of adjacent nodal values. The method precludes unrealistic undershoot or overshoot for concentrations of individual particles. In the new method, if dispersion causes cell concentrations to decrease during a time step, those particles in the cell having the highest concentration will decrease the most, and those with the lowest concentration will decrease the least. The converse is true if dispersion is causing concentrations to increase. Furthermore, if the initial concentration on a particle is outside the range of the adjacent nodal values, it will automatically be adjusted in the direction of the acceptable range of values. The new method is inherently mass conservative. ?? US Government 2010.

  7. Parametric laws to model urban pollutant dispersion with a street network approach

    Science.gov (United States)

    Soulhac, L.; Salizzoni, P.; Mejean, P.; Perkins, R. J.

    2013-03-01

    This study discusses the reliability of the street network approach for pollutant dispersion modelling in urban areas. This is essentially based on a box model, with parametric relations that explicitly model the main phenomena that contribute to the street canyon ventilation: the mass exchanges between the street and the atmosphere, the pollutant advection along the street axes and the pollutant transfer at street intersections. In the first part of the paper the focus is on the development of a model for the bulk transfer street/atmosphere, which represents the main ventilation mechanisms for wind direction that are almost perpendicular to the axis of the street. We then discuss the role of the advective transfer along the street axis on its ventilation, depending on the length of the street and the direction of the external wind. Finally we evaluate the performances of a box model integrating parametric exchange laws for these transfer phenomena. To that purpose we compare the prediction of the model to wind tunnel experiments of pollutant dispersion within a street canyon placed in an idealised urban district.

  8. Atmospheric dispersion models for real-time application in the decision support system being developed within the CEC

    International Nuclear Information System (INIS)

    Mikkelsen, T.

    1992-01-01

    A number of Commission of the European Communities member states are presently coordinating their research and development of a ''Real-time On-line DecisiOn Support'' (RODOS) for emergency assistance in the event of nuclear accident. In addition to atmospheric dispersion, the system involves multiple other radiological disciplines. The ability to estimate a specific atmospheric dispersion scenarios in real-time becomes a first-priority task and is of uttermost importance for the subsequent success or failure of such a comprehensive decision support system to guide off-site emergency situations. No single dispersion model is at present able to cover all possible release-types and scales of dispersion. A hierarchy of atmospheric flow and dispersion models is presently being ranked for suitability to real-time calculate air and integrated-air concentrations. Starting at the short-range scale, models are discriminated with respect to principle, adequacy and flexibility, CPU-time constraints, experimental evaluation record, instantaneous or short-time release handling, deposition measures (wet and dry), input and output data flexibility and uncertainty-handling and model-interpretation. Additional features of particular importance are: Robustness in schemes for meteorological preprocessing of meteorological input data, and on-line backfitting and data-assimilation procedures. Models demonstrating practical and operational use, including real-time operational experience, have in this context the highest priority, as opposed to the more sophisticated and theoretical ''development-type'' models. Real-time methods founded on our present knowledge and data concerning flow and dispersion in the atmospheric boundary layer, are of primary interest. (au) (18 refs.)

  9. Modelling the atmospheric dispersion of foot-and-mouth disease virus for emergency preparedness

    DEFF Research Database (Denmark)

    Sørensen, J.H.; Jensen, C.O.; Mikkelsen, T.

    2001-01-01

    A model system for simulating airborne spread of foot-and-mouth disease (FMD) is described. The system includes a virus production model and the local- and mesoscale atmospheric dispersion model RIMPUFF linked to the LINCOM local-scale Row model. LINCOM is used to calculate the sub-grid scale Row...

  10. Detailed source term estimation of the atmospheric release for the Fukushima Daiichi Nuclear Power Station accident by coupling simulations of an atmospheric dispersion model with an improved deposition scheme and oceanic dispersion model

    Energy Technology Data Exchange (ETDEWEB)

    Katata, G.; Chino, M.; Kobayashi, T. [Japan Atomic Energy Agency (JAEA), Ibaraki (Japan); and others

    2015-07-01

    Temporal variations in the amount of radionuclides released into the atmosphere during the Fukushima Daiichi Nuclear Power Station (FNPS1) accident and their atmospheric and marine dispersion are essential to evaluate the environmental impacts and resultant radiological doses to the public. In this paper, we estimate the detailed atmospheric releases during the accident using a reverse estimation method which calculates the release rates of radionuclides by comparing measurements of air concentration of a radionuclide or its dose rate in the environment with the ones calculated by atmospheric and oceanic transport, dispersion and deposition models. The atmospheric and oceanic models used are WSPEEDI-II (Worldwide version of System for Prediction of Environmental Emergency Dose Information) and SEA-GEARN-FDM (Finite difference oceanic dispersion model), both developed by the authors. A sophisticated deposition scheme, which deals with dry and fog-water depositions, cloud condensation nuclei (CCN) activation, and subsequent wet scavenging due to mixed-phase cloud microphysics (in-cloud scavenging) for radioactive iodine gas (I{sub 2} and CH{sub 3}I) and other particles (CsI, Cs, and Te), was incorporated into WSPEEDI-II to improve the surface deposition calculations. The results revealed that the major releases of radionuclides due to the FNPS1 accident occurred in the following periods during March 2011: the afternoon of 12 March due to the wet venting and hydrogen explosion at Unit 1, midnight of 14 March when the SRV (safety relief valve) was opened three times at Unit 2, the morning and night of 15 March, and the morning of 16 March. According to the simulation results, the highest radioactive contamination areas around FNPS1 were created from 15 to 16 March by complicated interactions among rainfall, plume movements, and the temporal variation of release rates. The simulation by WSPEEDI-II using the new source term reproduced the local and regional patterns of

  11. Unconfined Groundwater Dispersion Model On Sand Layers In Coral Island

    OpenAIRE

    Sultan

    2016-01-01

    The research objective is to analyze the sand layer to determine the characteristics of the unconfined groundwater aquifer on coral island and found the dispersion model of unconfined groundwater in the sand layer in the coral island. The method used is direct research in the field, laboratory analysis and secondary data. Observations geological conditions, as well as the measurement and interpretation of geoelectrical potential groundwater models based on the value of the conductivity of gro...

  12. Analytical solution of dispersion relations for the nuclear optical model

    Energy Technology Data Exchange (ETDEWEB)

    VanderKam, J.M. [Center for Communications Research, Thanet Road, Princeton, NJ 08540 (United States); Weisel, G.J. [Triangle Universities Nuclear Laboratory, and Duke University, Box 90308, Durham, NC 27708-0308 (United States); Penn State Altoona, 3000 Ivyside Park, Altoona, PA 16601-3760 (United States); Tornow, W. [Triangle Universities Nuclear Laboratory, and Duke University, Box 90308, Durham, NC 27708-0308 (United States)

    2000-12-01

    Analytical solutions of dispersion integral relations, linking the real and imaginary parts of the nuclear optical model, have been derived. These are displayed for some widely used forms of the volume- and surface-absorptive nuclear potentials. When the analytical solutions are incorporated into the optical-model search code GENOA, replacing a numerical integration, the code runs three and a half to seven times faster, greatly aiding the analysis of direct-reaction, elastic scattering data. (author)

  13. Dispersal behavior correlates with personality of a North American fish

    Institute of Scientific and Technical Information of China (English)

    Josh E.RASMUSSEN; Mark C.BELK

    2012-01-01

    The process of dispersal is determined by the interaction of individual (intrinsic) traits and environmental (extrinsic) factors.Although many studies address and quantify dispersal,few evaluate both intrinsic and extrinsic factors jointly.We test the relative importance of intrinsic traits (exploration tendency and size) and extrinsic factors (population density and habitat quality) on dispersal of a medium-sized western United States minnow,southern lcatherside chub Lepidomeda aliciae.A generalized linear model with a binomial response was used to determine the probability of individuals dispersing one year after tagging.Medium-sized individuals that were more prone to explore novel environments were 10.7 times more likely to be recaptured outside of their original capture area after a year (dispersal) compared to non-explorer individuals of the same size class.Differences between explorer classifications within the small and large size classes were negligible.Open habitat within 50 m upstream also increased the probability of dispersal relative to controls.Relative location within the study reach,and population density were not significantly related to dispersal probabilities of individuals.Our results indicate that understanding ofpersonality may illuminate patterns of dispersal within and among populations [Current Zoology 58 (2):260-270,2012].

  14. Radiation response of vitamin A in aqueous dispersions

    International Nuclear Information System (INIS)

    Bhushan, B.; Kumta, U.S.

    1977-01-01

    The radiation destruction of vitamin A acetate was monitored in isooctane, coconut oil, and aqueous dispersions. The G(-vit. A), i.e., the number of vitamin A molecules destroyed per 100 eV of energy absorbed in lipid solvents and aqueous preparations, increased with the concentrations of vitamin A used. In the freely dissolved state, as in isooctane or coconut oil, the extent of destruction of vitamin A was more or less identical. However, a marked reduction in the radiation destruction of vitamin A was observed in aqueous dispersions at all concentrations except at 1 x 10 -4 M. Incorporation of sugars, starch, and egg albumin in aqueous preparations offered considerable protection to vitamin A from radiation damage which could be discerned even at the lowest concentration (1 x 10 -4 M). The protective influence of aqueous dispersion as noted for vitamin A was also observed for β-carotene, vitamin A alcohol, and ubiquinone-30. The significance of the above findings in radiation processing of foods has been discussed

  15. User's manual for DWNWND: an interactive Gaussian plume atmospheric transport model with eight dispersion parameter options

    International Nuclear Information System (INIS)

    Fields, D.E.; Miller, C.W.

    1980-05-01

    The most commonly used approach for estimating the atmospheric concentration and deposition of material downwind from its point of release is the Gaussian plume atmospheric dispersion model. Two of the critical parameters in this model are sigma/sub y/ and sigma/sub z/, the horizontal and vertical dispersion parameters, respectively. A number of different sets of values for sigma/sub y/ and sigma/sub z/ have been determined empirically for different release heights and meteorological and terrain conditions. The computer code DWNWND, described in this report, is an interactive implementation of the Gaussian plume model. This code allows the user to specify any one of eight different sets of the empirically determined dispersion paramters. Using the selected dispersion paramters, ground-level normalized exposure estimates are made at any specified downwind distance. Computed values may be corrected for plume depletion due to deposition and for plume settling due to gravitational fall. With this interactive code, the user chooses values for ten parameters which define the source, the dispersion and deposition process, and the sampling point. DWNWND is written in FORTRAN for execution on a PDP-10 computer, requiring less than one second of central processor unit time for each simulation

  16. Between-site differences in the scale of dispersal and gene flow in red oak.

    Directory of Open Access Journals (Sweden)

    Emily V Moran

    Full Text Available Nut-bearing trees, including oaks (Quercus spp., are considered to be highly dispersal limited, leading to concerns about their ability to colonize new sites or migrate in response to climate change. However, estimating seed dispersal is challenging in species that are secondarily dispersed by animals, and differences in disperser abundance or behavior could lead to large spatio-temporal variation in dispersal ability. Parentage and dispersal analyses combining genetic and ecological data provide accurate estimates of current dispersal, while spatial genetic structure (SGS can shed light on past patterns of dispersal and establishment.In this study, we estimate seed and pollen dispersal and parentage for two mixed-species red oak populations using a hierarchical bayesian approach. We compare these results to those of a genetic ML parentage model. We also test whether observed patterns of SGS in three size cohorts are consistent with known site history and current dispersal patterns. We find that, while pollen dispersal is extensive at both sites, the scale of seed dispersal differs substantially. Parentage results differ between models due to additional data included in bayesian model and differing genotyping error assumptions, but both indicate between-site dispersal differences. Patterns of SGS in large adults, small adults, and seedlings are consistent with known site history (farmed vs. selectively harvested, and with long-term differences in seed dispersal. This difference is consistent with predator/disperser satiation due to higher acorn production at the low-dispersal site. While this site-to-site variation results in substantial differences in asymptotic spread rates, dispersal for both sites is substantially lower than required to track latitudinal temperature shifts.Animal-dispersed trees can exhibit considerable spatial variation in seed dispersal, although patterns may be surprisingly constant over time. However, even under

  17. Equilibrium Price Dispersion in a Matching Model with Divisible Money

    NARCIS (Netherlands)

    Kamiya, K.; Sato, T.

    2002-01-01

    The main purpose of this paper is to show that, for any given parameter values, an equilibrium with dispersed prices (two-price equilibrium) exists in a simple matching model with divisible money presented by Green and Zhou (1998).We also show that our two-price equilibrium is unique in certain

  18. AERMOD: A DISPERSION MODEL FOR INDUSTRIAL SOURCE APPLICATIONS PART I: GENERAL MODEL FORMULATION AND BOUNDARY LAYER CHARACTERIZATION

    Science.gov (United States)

    The formulations of the AMS/EPA Regulatory Model Improvement Committee's applied air dispersion model (AERMOD) as related to the characterization of the planetary boundary layer are described. This is the first in a series of three articles. Part II describes the formulation of...

  19. DART model for irradiation-induced swelling of dispersion fuel elements including aluminum-fuel interaction

    International Nuclear Information System (INIS)

    Rest, J.; Hofman, G.L.

    1997-01-01

    The Dispersion Analysis Research Tool (DART) contains models for fission-gas-induced fuel swelling, interaction of fuel with the matrix aluminum, for the resultant reaction-product swelling, and for the calculation of the stress gradient within the fuel particle. The effects of an aluminide shell on fuel particle swelling are evaluated. Validation of the model is demonstrated by a comparison of DART calculations of fuel swelling of U 3 SiAl-Al and U 3 Si 2 -Al for various dispersion fuel element designs with the data

  20. Modeling the influence of interaction layer formation on thermal conductivity of U–Mo dispersion fuel

    International Nuclear Information System (INIS)

    Burkes, Douglas E.; Casella, Andrew M.; Huber, Tanja K.

    2015-01-01

    Highlights: • Hsu equation provides best thermal conductivity estimate of U–Mo dispersion fuel. • Simple model considering interaction layer formation was coupled with Hsu equation. • Interaction layer thermal conductivity is not the most important attribute. • Effective thermal conductivity is mostly influenced by interaction layer formation. • Fuel particle distribution also influences the effective thermal conductivity. - Abstract: The Global Threat Reduction Initiative Program continues to develop existing and new test reactor fuels to achieve the maximum attainable uranium loadings to support the conversion of a number of the world’s remaining high-enriched uranium fueled reactors to low-enriched uranium fuel. Currently, the program is focused on assisting with the development and qualification of a fuel design that consists of a uranium–molybdenum (U–Mo) alloy dispersed in an aluminum matrix. Thermal conductivity is an important consideration in determining the operational temperature of the fuel and can be influenced by interaction layer formation between the dispersed phase and matrix, porosity that forms during fabrication of the fuel plates or rods, and upon the concentration of the dispersed phase within the matrix. This paper develops and validates a simple model to study the influence of interaction layer formation, dispersed particle size, and volume fraction of dispersed phase in the matrix on the effective conductivity of the composite. The model shows excellent agreement with results previously presented in the literature. In particular, the thermal conductivity of the interaction layer does not appear to be as important in determining the effective conductivity of the composite, while formation of the interaction layer and subsequent consumption of the matrix reveals a rather significant effect. The effective thermal conductivity of the composite can be influenced by the dispersed particle distribution by minimizing interaction

  1. Marine Radioactivity Studies in the Suez Canal, Part II: Field Experiments and a Modelling Study of Dispersion

    Science.gov (United States)

    Abril, J. M.; Abdel-Aal, M. M.; Al-Gamal, S. A.; Abdel-Hay, F. A.; Zahar, H. M.

    2000-04-01

    In this paper we take advantage of the two field tracing experiments carried out under the IAEA project EGY/07/002, to develop a modelling study on the dispersion of radioactive pollution in the Suez Canal. The experiments were accomplished by using rhodamine B as a tracer, and water samples were measured by luminescence spectrometry. The presence of natural luminescent particles in the canal waters limited the use of some field data. During experiments, water levels, velocities, wind and other physical parameters were recorded to supply appropriate information for the modelling work. From this data set, the hydrodynamics of the studied area has been reasonably described. We apply a 1-D-Gaussian and 2-D modelling approaches to predict the position and the spatial shape of the plume. The use of different formulations for dispersion coefficients is studied. These dispersion coefficients are then applied in a 2-D-hydrodynamic and dispersion model for the Bitter Lake to investigate different scenarios of accidental discharges.

  2. Sea Outfall Design Based on a Stochastic Transport/Dispersion Model

    DEFF Research Database (Denmark)

    Larsen, Torben

    1983-01-01

    /dispersion phenomena can easily be modelled by the stochastic approach without going into advanced methods as finite differences or elements. The advantage of this approach is the simple programming and Iow need of computer memory. The disadvantage could be the need for excessive computing time.......This paper describes a numerical model of the dilution and disappearance of sewage discharged to the coastal zone. The model is based on the Monte Carlo (or random walk) principle. A cloud of particles is released at discrete time steps and the 3-dimensional path of every particle is simulated...

  3. Attenuation and velocity dispersion in the exploration seismic frequency band

    Science.gov (United States)

    Sun, Langqiu

    In an anelastic medium, seismic waves are distorted by attenuation and velocity dispersion, which depend on petrophysical properties of reservoir rocks. The effective attenuation and velocity dispersion is a combination of intrinsic attenuation and apparent attenuation due to scattering, transmission response, and data acquisition system. Velocity dispersion is usually neglected in seismic data processing partly because of insufficient observations in the exploration seismic frequency band. This thesis investigates the methods of measuring velocity dispersion in the exploration seismic frequency band and interprets the velocity dispersion data in terms of petrophysical properties. Broadband, uncorrelated vibrator data are suitable for measuring velocity dispersion in the exploration seismic frequency band, and a broad bandwidth optimizes the observability of velocity dispersion. Four methods of measuring velocity dispersion in uncorrelated vibrator VSP data are investigated, which are the sliding window crosscorrelation (SWCC) method, the instantaneous phase method, the spectral decomposition method, and the cross spectrum method. Among them, the SWCC method is a new method and has satisfactory robustness, accuracy, and efficiency. Using the SWCC method, velocity dispersion is measured in the uncorrelated vibrator VSP data from three areas with different geological settings, i.e., Mallik gas hydrate zone, McArthur River uranium mines, and Outokumpu crystalline rocks. The observed velocity dispersion is fitted to a straight line with respect to log frequency for a constant (frequency-independent) Q value. This provides an alternative method for calculating Q. A constant Q value does not directly link to petrophysical properties. A modeling study is implemented for the Mallik and McArthur River data to interpret the velocity dispersion observations in terms of petrophysical properties. The detailed multi-parameter petrophysical reservoir models are built according to

  4. Micro-meteorological modelling in urban areas: pollutant dispersion and radiative effects modelling

    International Nuclear Information System (INIS)

    Milliez, Maya

    2006-01-01

    Atmospheric pollution and urban climate studies require to take into account the complex processes due to heterogeneity of urban areas and the interaction with the buildings. In order to estimate the impact of buildings on flow and pollutant dispersion, detailed numerical simulations were performed over an idealized urban area, with the three-dimensional model Mercure-Saturne, modelling both concentration means and their fluctuations. To take into account atmospheric radiation in built up areas and the thermal effects of the buildings, we implemented a three-dimensional radiative model adapted to complex geometry. This model, adapted from a scheme used for thermal radiation, solves the radiative transfer equation in a semi-transparent media, using the discrete ordinate method. The new scheme was validated with idealized cases and compared to a complete case. (author) [fr

  5. Parameterizing Urban Canopy Layer transport in an Lagrangian Particle Dispersion Model

    Science.gov (United States)

    Stöckl, Stefan; Rotach, Mathias W.

    2016-04-01

    The percentage of people living in urban areas is rising worldwide, crossed 50% in 2007 and is even higher in developed countries. High population density and numerous sources of air pollution in close proximity can lead to health issues. Therefore it is important to understand the nature of urban pollutant dispersion. In the last decades this field has experienced considerable progress, however the influence of large roughness elements is complex and has as of yet not been completely described. Hence, this work studied urban particle dispersion close to source and ground. It used an existing, steady state, three-dimensional Lagrangian particle dispersion model, which includes Roughness Sublayer parameterizations of turbulence and flow. The model is valid for convective and neutral to stable conditions and uses the kernel method for concentration calculation. As most Lagrangian models, its lower boundary is the zero-plane displacement, which means that roughly the lower two-thirds of the mean building height are not included in the model. This missing layer roughly coincides with the Urban Canopy Layer. An earlier work "traps" particles hitting the lower model boundary for a recirculation period, which is calculated under the assumption of a vortex in skimming flow, before "releasing" them again. The authors hypothesize that improving the lower boundary condition by including Urban Canopy Layer transport could improve model predictions. This was tested herein by not only trapping the particles, but also advecting them with a mean, parameterized flow in the Urban Canopy Layer. Now the model calculates the trapping period based on either recirculation due to vortex motion in skimming flow regimes or vertical velocity if no vortex forms, depending on incidence angle of the wind on a randomly chosen street canyon. The influence of this modification, as well as the model's sensitivity to parameterization constants, was investigated. To reach this goal, the model was

  6. An Empirical Model of Wage Dispersion with Sorting

    DEFF Research Database (Denmark)

    Bagger, Jesper; Lentz, Rasmus

    (submodular). The model is estimated on Danish matched employer-employee data. We find evidence of positive assortative matching. In the estimated equilibrium match distribution, the correlation between worker skill and firm productivity is 0.12. The assortative matching has a substantial impact on wage......This paper studies wage dispersion in an equilibrium on-the-job-search model with endogenous search intensity. Workers differ in their permanent skill level and firms differ with respect to productivity. Positive (negative) sorting results if the match production function is supermodular...... to mismatch by asking how much greater output would be if the estimated population of matches were perfectly positively assorted. In this case, output would increase by 7.7%....

  7. Structural habitat predicts functional dispersal habitat of a large carnivore: how leopards change spots.

    Science.gov (United States)

    Fattebert, Julien; Robinson, Hugh S; Balme, Guy; Slotow, Rob; Hunter, Luke

    2015-10-01

    Natal dispersal promotes inter-population linkage, and is key to spatial distribution of populations. Degradation of suitable landscape structures beyond the specific threshold of an individual's ability to disperse can therefore lead to disruption of functional landscape connectivity and impact metapopulation function. Because it ignores behavioral responses of individuals, structural connectivity is easier to assess than functional connectivity and is often used as a surrogate for landscape connectivity modeling. However using structural resource selection models as surrogate for modeling functional connectivity through dispersal could be erroneous. We tested how well a second-order resource selection function (RSF) models (structural connectivity), based on GPS telemetry data from resident adult leopard (Panthera pardus L.), could predict subadult habitat use during dispersal (functional connectivity). We created eight non-exclusive subsets of the subadult data based on differing definitions of dispersal to assess the predictive ability of our adult-based RSF model extrapolated over a broader landscape. Dispersing leopards used habitats in accordance with adult selection patterns, regardless of the definition of dispersal considered. We demonstrate that, for a wide-ranging apex carnivore, functional connectivity through natal dispersal corresponds to structural connectivity as modeled by a second-order RSF. Mapping of the adult-based habitat classes provides direct visualization of the potential linkages between populations, without the need to model paths between a priori starting and destination points. The use of such landscape scale RSFs may provide insight into predicting suitable dispersal habitat peninsulas in human-dominated landscapes where mitigation of human-wildlife conflict should be focused. We recommend the use of second-order RSFs for landscape conservation planning and propose a similar approach to the conservation of other wide-ranging large

  8. Modelling the observed vertical transport of {sup 7}Be in specific soils with advection dispersion model

    Energy Technology Data Exchange (ETDEWEB)

    Torres Astorga, Romina; Velasco, Hugo; Valladares, Diego L.; Lohaiza, Flavia; Ayub, Jimena Juri; Rizzotto, Marcos [Grupo de Estudios Ambientales. Instituto de Matematica Aplicada San Luis - Universidad Nacional de San Luis - CONICET, San Luis (Argentina)

    2014-07-01

    {sup 7}Be is a short-lived environmental radionuclide, produced in the upper atmosphere by spallation of nitrogen and oxygen by cosmic rays. After of the production by the nuclear reaction, {sup 7}Be diffuses through the atmosphere until it attaches to atmospheric aerosols. Subsequently, it is deposited on the earth surface mainly as wet fallout. The main physical processes which transport {sup 7}Be in soil are diffusion and advection by water. Migration parameters and measurements confirm that sorption is the main physical process, which confines {sup 7}Be concentration to soil surface. The literature data show that in soils, {sup 7}Be is concentrated near the surface (0-2 cm) as it is adsorbed onto clay minerals after its deposition on the soil surface and does not penetrate deeper into soils due to its short half-life. The maximum mass activity density of {sup 7}Be is found at the point of input of the radionuclide, i.e. at the surface of the soil column, showing a exponential distribution profile typical of a purely diffusive transport. Many studies applying the advection dispersion models have been reported in the literature in order to modelling the transport of {sup 137}Cs in soils. On them, the models are used to achieve information of the mechanisms that govern the transport, i. e. the model is used to explain the soil profile of radionuclide. The effective dispersion coefficient and the apparent advection velocity of radionuclide in soil are also obtained by fitting the analytical solution of the model equation to measured depth distributions of the radionuclide. In this work, the advective dispersive transport model with linear sorption is used to analyze the vertical migration process of {sup 7}Be in soils of undisturbed or reference sites. The deposition history is approximated by pulse-like input functions and time dependent analytical solution of equation model is obtained. The values of dispersion coefficient and apparent advection velocity obtained

  9. Wave-equation dispersion inversion

    KAUST Repository

    Li, Jing

    2016-12-08

    We present the theory for wave-equation inversion of dispersion curves, where the misfit function is the sum of the squared differences between the wavenumbers along the predicted and observed dispersion curves. The dispersion curves are obtained from Rayleigh waves recorded by vertical-component geophones. Similar to wave-equation traveltime tomography, the complicated surface wave arrivals in traces are skeletonized as simpler data, namely the picked dispersion curves in the phase-velocity and frequency domains. Solutions to the elastic wave equation and an iterative optimization method are then used to invert these curves for 2-D or 3-D S-wave velocity models. This procedure, denoted as wave-equation dispersion inversion (WD), does not require the assumption of a layered model and is significantly less prone to the cycle-skipping problems of full waveform inversion. The synthetic and field data examples demonstrate that WD can approximately reconstruct the S-wave velocity distributions in laterally heterogeneous media if the dispersion curves can be identified and picked. The WD method is easily extended to anisotropic data and the inversion of dispersion curves associated with Love waves.

  10. Comparison of different passive dispersion models for the simulation of a given release

    International Nuclear Information System (INIS)

    Wendum, D.; Musson-Genon, L.

    1996-01-01

    For internal needs of Electricite de France (dispersion computations of radioactive effluents during nuclear emergency situations, simulations of chemical pollution on the vicinity of thermal power plants), different models of passive dispersion in the atmosphere have been developed at the R and D D. This report presents the comparison of the performances of three such models: DIFTRA (Lagrangian puff model, with operational goal), DIFEUL (three dimensional Eulerian) and DiFPAR (Monte-Carlo particle model). The aim of this intercomparison is to assess the model differences of concentration values computed during an academic release in real meteorological conditions. The obtained results give inter-model differences of the same order as the model vs. experience differences observed during an international model comparison experiment using data of the Chernobyl release, the ATMES exercise. In a future study we plan to compare the results of these models to the results of an international tracer campaign named ETEX95, during which a passive tracer cloud has been followed over Europe. (author). 13 refs., 8 figs

  11. Assessment of the use of dispersants on oil spills in California marine waters

    International Nuclear Information System (INIS)

    Trudel, K.; Ross, S.; Belore, R.; Buffington, S.; Ogawa, C.; Panzer, D.

    2002-01-01

    The technical issues regarding the use of dispersants to clean up oil spills from offshore production sources and transportation sources in California were assessed in this study which examined both operational and environmental issues. The operational issues included the dispersibility of produced and imported oils, along with the capabilities of California response resources to deal with typical spills and limiting environmental impacts to offshore environments. The environmental issues include the risks associated with typical spills and potential net environmental benefit of chemically dispersing oil spills. Most crude oils produced offshore California are heavy and border on the undispersable range, but the imported crudes are somewhat lighter. Modeling has shown that most produced oils and some imported oils emulsify quickly and weather more quickly to the point where they are no longer dispersible. There is a very narrow window of time for chemical dispersions to be used effectively. The net environmental benefit analysis demonstrates that the use of dispersants lessens the total environmental impact of spill scenarios. It was emphasized that it is necessary to act quickly if chemical dispersion is to be effective. Rapid response strategies are needed, including locally based vessel and helicopter spraying systems. 19 refs., 8 tabs., 1 fig

  12. Dispersion, sorption and photodegradation of petroleum hydrocarbons in dispersant-seawater-sediment systems.

    Science.gov (United States)

    Zhao, Xiao; Liu, Wen; Fu, Jie; Cai, Zhengqing; O'Reilly, S E; Zhao, Dongye

    2016-08-15

    This work examined effects of model oil dispersants on dispersion, sorption and photodegradation of petroleum hydrocarbons in simulated marine systems. Three dispersants (Corexit 9500A, Corexit 9527A and SPC 1000) were used to prepare dispersed water accommodated oil (DWAO). While higher doses of dispersants dispersed more n-alkanes and PAHs, Corexit 9500A preferentially dispersed C11-C20 n-alkanes, whereas Corexit 9527A was more favorable for smaller alkanes (C10-C16), and SPC 1000 for C12-C28 n-alkanes. Sorption of petroleum hydrocarbons on sediment was proportional to TPH types/fractions in the DWAOs. Addition of 18mg/L of Corexit 9500A increased sediment uptake of 2-3 ring PAHs, while higher dispersant doses reduced the uptake, due to micelle-enhanced solubilization effects. Both dispersed n-alkanes and PAHs were susceptible to photodegradation under simulated sunlight. For PAHs, both photodegradation and photo-facilitated alkylation were concurrently taking place. The information can facilitate sounder assessment of fate and distribution of dispersed oil hydrocarbons in marine systems. Copyright © 2016 Elsevier Ltd. All rights reserved.

  13. Long-range transmission of pollutants simulated by a two-dimensional pseudospectral dispersion model

    International Nuclear Information System (INIS)

    Prahm, L.P.; Christensen, O.

    1977-01-01

    The pseudospectral dispersion model (Christensen and Prahm, 1976) is adapted for simulation of the long-range transmission of sulphur pollutants in the European region, covering an area of about 4000 km x 4000 km. Regional ''background'' concentrations of sulphur oxides are found to be highly dependent on distant sources and to correlate poorly with local source strength during the considered three- and four-day episodes. The simulation is based on emission data, given in squares of about 50 km x 50 km and on synoptic wind fields derived from observed wind velocities of the 850 mb level and the surface level. The two-dimensional model includes a constant vertical mixing depth. Appropriate values for the deposition and the transformation rates of SO 2 and SO/sup 4 are used. The concentration of pollutants computed from the two-dimensional pseudospectral dispersion model reflects the variable meteorological conditions. Computed concentrations are compared with measurements, giving spatial correlations between 0.4 and 0.8 for more than 400 ground-based 24 h mean values, and a spatial correlation of 0.9 for eight aircraft samples averaged over approx.30 min. A discussion of the influence of different sources of error in the model simulation is given. The high numerical accuracy of the pseudospectral model is combined with a modest consumption of CPU computer time. This study is the first application of the pseudospectral dispersion model which compares computed concentrations with measured field data. The model has possible applications as a tool for assessment of the impact of both national and international emission regulation strategies

  14. Identification and elucidation of anthropogenic source contribution in PM10 pollutant: Insight gain from dispersion and receptor models.

    Science.gov (United States)

    Roy, Debananda; Singh, Gurdeep; Yadav, Pankaj

    2016-10-01

    Source apportionment study of PM 10 (Particulate Matter) in a critically polluted area of Jharia coalfield, India has been carried out using Dispersion model, Principle Component Analysis (PCA) and Chemical Mass Balance (CMB) techniques. Dispersion model Atmospheric Dispersion Model (AERMOD) was introduced to simplify the complexity of sources in Jharia coalfield. PCA and CMB analysis indicates that monitoring stations near the mining area were mainly affected by the emission from open coal mining and its associated activities such as coal transportation, loading and unloading of coal. Mine fire emission also contributed a considerable amount of particulate matters in monitoring stations. Locations in the city area were mostly affected by vehicular, Liquid Petroleum Gas (LPG) & Diesel Generator (DG) set emissions, residential, and commercial activities. The experimental data sampling and their analysis could aid understanding how dispersion based model technique along with receptor model based concept can be strategically used for quantitative analysis of Natural and Anthropogenic sources of PM 10 . Copyright © 2016. Published by Elsevier B.V.

  15. Adjustable rheology of fumed silica dispersion in urethane prepolymers: Composition-dependent sol and gel behaviors and energy-mediated shear responses

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Zhong, E-mail: 11329038@zju.edu.cn; Song, Yihu, E-mail: s-yh0411@zju.edu.cn; Wang, Xiang, E-mail: 11229036@zju.edu.cn; Zheng, Qiang, E-mail: zhengqiang@zju.edu.cn [MOE Key Laboratory of Macromolecule Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027 (China)

    2015-07-15

    Variation of colloidal and interfacial interactions leads to a microstructural diversity in fumed silica dispersions exhibiting absolutely different sol- or gel-like rheological responses. In this study, fumed silicas with different surface areas (200–400 m{sup 2}/g) and surface characteristics (hydrophilic or hydrophobic) are dispersed into moisture-cured polyurethane. The microstructures investigated using transmission electron microscope are associated perfectly with three different rheological behaviors: (i) Sols with well-dispersed silica aggregates, (ii) weak gels with agglomerate-linked networks, and (iii) strong gels with concentrated networks of large agglomerates. Though sols and gels are well distinguished by shear thickening or sustained thinning response through steady shear flow test, it is interesting that the sols and weak gels exhibit a uniform modulus plateau-softening-hardening-softening response with increasing dynamic strain at frequency 10 rad s{sup −1} while the strong gels show a sustained softening beyond the linear regime. Furthermore, the onset of softening and hardening can be normalized: The two softening are isoenergetic at mechanical energies of 0.3 J m{sup −3} and 10 kJ m{sup −3}. On the other hand, the hardening is initiated by a critical strain of 60%. The mechanisms involved in the generation of the sol- and the gel-like dispersions and their structural evolutions during shear are thoroughly clarified in relation to the polyols, the characteristic and content of silica and the curing catalysts.

  16. Science-based response planning guidance for the first 100 minutes of the response to a radiological dispersal device

    International Nuclear Information System (INIS)

    Musolino, S.V.; Harper, F.T.

    2016-01-01

    The first 100 minutes of a response to a radiological dispersal device are critical as this period will set the stage for how the overall response will be executed. First responders will be tasked with multiple activities such as confirming a radiological release, conducting lifesaving rescue operations, issuing protective actions, and beginning characterization of the scene. These activities need to take place as soon as the responders arrive on the scene (the first few minutes). The effectiveness of these early activities will define how well or how poorly the response will be in the emergency phase. The document which is under development provides guidance that can be used for planning an effective response to an RDD that will result in protection of the responders and the members of the public. The information is based on research and results of extensive experiments conducted by the Department of Energy National Laboratories. This guidance provides a realistic estimate of the possible consequences of an RDD detonation and delineates five missions and ten tactics that should be executed by the first responders and local response agencies in the first 100 minutes of a response. The guidance includes recommendations on how to execute the strategy, equipment requirements including personal protective equipment and public messaging

  17. A Monte Carlo simulation study comparing linear regression, beta regression, variable-dispersion beta regression and fractional logit regression at recovering average difference measures in a two sample design.

    Science.gov (United States)

    Meaney, Christopher; Moineddin, Rahim

    2014-01-24

    In biomedical research, response variables are often encountered which have bounded support on the open unit interval--(0,1). Traditionally, researchers have attempted to estimate covariate effects on these types of response data using linear regression. Alternative modelling strategies may include: beta regression, variable-dispersion beta regression, and fractional logit regression models. This study employs a Monte Carlo simulation design to compare the statistical properties of the linear regression model to that of the more novel beta regression, variable-dispersion beta regression, and fractional logit regression models. In the Monte Carlo experiment we assume a simple two sample design. We assume observations are realizations of independent draws from their respective probability models. The randomly simulated draws from the various probability models are chosen to emulate average proportion/percentage/rate differences of pre-specified magnitudes. Following simulation of the experimental data we estimate average proportion/percentage/rate differences. We compare the estimators in terms of bias, variance, type-1 error and power. Estimates of Monte Carlo error associated with these quantities are provided. If response data are beta distributed with constant dispersion parameters across the two samples, then all models are unbiased and have reasonable type-1 error rates and power profiles. If the response data in the two samples have different dispersion parameters, then the simple beta regression model is biased. When the sample size is small (N0 = N1 = 25) linear regression has superior type-1 error rates compared to the other models. Small sample type-1 error rates can be improved in beta regression models using bias correction/reduction methods. In the power experiments, variable-dispersion beta regression and fractional logit regression models have slightly elevated power compared to linear regression models. Similar results were observed if the

  18. Evaluation of three atmospheric dispersion models using tracer release experiment data

    International Nuclear Information System (INIS)

    Daoo, V.J.; Oza, R.B.; Pandit, G.G.; Sadasivan, S.; Venkat Raj, V.

    2004-01-01

    Performance of three atmospheric dispersion models viz: (1) Gaussian Plume Model (GPM), (2) Equi-Distance PUFF Model (EDPUFFM) and (3) Particle Trajectory Model (PTM) is evaluated using field data collected from a tracer (SF 6 ) release experiment. The experiment was conducted within the campus of the Bhabha Atomic Research Centre (BARC), located at Trombay, Mumbai, India. The three models used are currently in operation at the BARC. The first one is a standard, well-documented empirical model while the other two models have been developed at the Bhabha Atomic Research Centre. The PTM is a numerical model while the EDPUFFM is a hybrid model combining both the numerical and analytical techniques. The procedure for evaluation is as per the recommendations of 1980 AMS (American Meteorological Society) workshop on atmospheric dispersion models performance evaluation. In addition, linear regression analysis has also been carried out. The regression analysis reveals that on an average, the EDPUFFM and the GPM predictions are higher by a factor of about 1.5 while the PTM predictions are lower by a factor of about 4. Comparison of various performance measures reveals that the performance of the EDPUFFM is marginally better than that of the GPM while the PTM performance is comparatively poor. The uncertainty factors obtained in this study, especially for higher concentration range ( > 100 ppt) are similar to those obtained in other validation study carried out elsewhere to validate the GPM predictions. However, for lower concentration range and for the conditions after the source is switched off, all the three models perform poorly in predicting the concentration. (author)

  19. DART model for thermal conductivity of U3Si2 aluminum dispersion fuel

    International Nuclear Information System (INIS)

    Rest, J.; Snelgrove, J.L.; Hofman, G.L.

    1995-09-01

    This paper describes the primary physical models that form the basis of the DART model for calculating irradiation-induced changes in the thermal conductivity of aluminium dispersion fuel. DART calculations of fuel swelling, pore closure, and thermal conductivity are compared with measured values

  20. Ultraviolet radiation induces dose-dependent pigment dispersion in crustacean chromatophores.

    Science.gov (United States)

    Gouveia, Glauce Ribeiro; Lopes, Thaís Martins; Neves, Carla Amorim; Nery, Luiz Eduardo Maia; Trindade, Gilma Santos

    2004-10-01

    Pigment dispersion in chromatophores as a response to UV radiation was investigated in two species of crustaceans, the crab Chasmagnathus granulata and the shrimp Palaemonetes argentinus. Eyestalkless crabs and shrimps maintained on either a black or a white background were irradiated with different UV bands. In eyestalkless crabs the significant minimal effective dose inducing pigment dispersion was 0.42 J/cm(2) for UVA and 2.15 J/cm(2) for UVB. Maximal response was achieved with 10.0 J/cm(2) UVA and 8.6 J/cm(2) UVB. UVA was more effective than UVB in inducing pigment dispersion. Soon after UV exposure, melanophores once again reached the initial stage of pigment aggregation after 45 min. Aggregated erythrophores of shrimps adapted to a white background showed significant pigment dispersion with 2.5 J/cm(2) UVA and 0.29 J/cm(2) UVC. Dispersed erythrophores of shrimps adapted to a black background did not show any significant response to UVA, UVB or UVC radiation. UVB did not induce any significant pigment dispersion in shrimps adapted to either a white or a black background. As opposed to the tanning response, which only protects against future UV exposure, the pigment dispersion response could be an important agent protecting against the harmful effects of UV radiation exposure.

  1. Vapor generation rate model for dispersed drop flow

    International Nuclear Information System (INIS)

    Unal, C.; Tuzla, K.; Cokmez-Tuzla, A.F.; Chen, J.C.

    1991-01-01

    A comparison of predictions of existing nonequilibrium post-CHF heat transfer models with the recently obtained rod bundle data has been performed. The models used the experimental conditions and wall temperatures to predict the heat flux and vapor temperatures at the location of interest. No existing model was able to reasonably predict the vapor superheat and the wall heat flux simultaneously. Most of the models, except Chen-Sundaram-Ozkaynak, failed to predict the wall heat flux, while all of the models could not predict the vapor superheat data or trends. A recently developed two-region heat transfer model, the Webb-Chen two-region model, did not give a reasonable prediction of the vapor generation rate in the far field of the CHF point. A new correlation was formulated to predict the vapor generation rate in convective dispersed droplet flow in terms of thermal-hydraulic parameters and thermodynamic properties. A comparison of predictions of the two-region heat transfer model, with the use of a presently developed correlation, with all the existing post-CHF data, including single-tube and rod bundle, showed significant improvements in predicting the vapor superheat and tube wall heat flux trends. (orig.)

  2. Biomass burning aerosol over Romania using dispersion model and Calipso data

    Science.gov (United States)

    Nicolae, Victor; Dandocsi, Alexandru; Marmureanu, Luminita; Talianu, Camelia

    2018-04-01

    The purpose of the study is to analyze the seasonal variability, for the hot and cold seasons, of biomass burning aerosol observed over Romania using forward dispersion calculations based on FLEXPART model. The model was set up to use as input the MODIS fire data with a degree of confidence over 25% after transforming the emitted power in emission rate. The modelled aerosols in this setup was black carbon coated by organics. Distribution in the upper layers were compared to Calipso retrieval.

  3. Hindrance Velocity Model for Phase Segregation in Suspensions of Poly-dispersed Randomly Oriented Spheroids

    Science.gov (United States)

    Faroughi, S. A.; Huber, C.

    2015-12-01

    Crystal settling and bubbles migration in magmas have significant effects on the physical and chemical evolution of magmas. The rate of phase segregation is controlled by the force balance that governs the migration of particles suspended in the melt. The relative velocity of a single particle or bubble in a quiescent infinite fluid (melt) is well characterized; however, the interplay between particles or bubbles in suspensions and emulsions and its effect on their settling/rising velocity remains poorly quantified. We propose a theoretical model for the hindered velocity of non-Brownian emulsions of nondeformable droplets, and suspensions of spherical solid particles in the creeping flow regime. The model is based on three sets of hydrodynamic corrections: two on the drag coefficient experienced by each particle to account for both return flow and Smoluchowski effects and a correction on the mixture rheology to account for nonlocal interactions between particles. The model is then extended for mono-disperse non-spherical solid particles that are randomly oriented. The non-spherical particles are idealized as spheroids and characterized by their aspect ratio. The poly-disperse nature of natural suspensions is then taken into consideration by introducing an effective volume fraction of particles for each class of mono-disperse particles sizes. Our model is tested against new and published experimental data over a wide range of particle volume fraction and viscosity ratios between the constituents of dispersions. We find an excellent agreement between our model and experiments. We also show two significant applications for our model: (1) We demonstrate that hindered settling can increase mineral residence time by up to an order of magnitude in convecting magma chambers. (2) We provide a model to correct for particle interactions in the conventional hydrometer test to estimate the particle size distribution in soils. Our model offers a greatly improved agreement with

  4. Modelling the long-term consequences of a hypothetical dispersal of radioactivity in an urban area including remediation alternatives

    DEFF Research Database (Denmark)

    Thiessen, K.M.; Andersson, Kasper Grann; Batandjieva, B.

    2009-01-01

    The Urban Remediation Working Group of the International Atomic Energy Agency's EMRAS (Environmental Modelling for Radiation Safety) program was organized to address issues of remediation assessment modelling for urban areas contaminated with dispersed radionuclides. The present paper describes...... the second of two modelling exercises. This exercise was based on a hypothetical dispersal of radioactivity in an urban area from a radiological dispersal device, with reference surface contamination at selected sites used as the primary input information. Modelling endpoints for the exercise included...... radionuclide concentrations and external dose rates at specified locations, contributions to the dose rates from individual surfaces, and annual and cumulative external doses to specified reference individuals. Model predictions were performed for a "no action" situation (with no remedial measures...

  5. DART model for thermal conductivity of U3Si2 Aluminum dispersion fuel

    International Nuclear Information System (INIS)

    Rest, J.; Snelgrove, J.L.; Hofman, G.L.

    2004-01-01

    This paper describes the primary physical models that form the basis of the DART model for calculating irradiation-induced changes in the thermal conductivity of aluminum dispersion fuel. DART calculations of fuel swelling, pore closure, and thermal conductivity are compared with measured values. (author)

  6. DFT Modeling of Cross-Linked Polyethylene: Role of Gold Atoms and Dispersion Interactions.

    Science.gov (United States)

    Blaško, Martin; Mach, Pavel; Antušek, Andrej; Urban, Miroslav

    2018-02-08

    Using DFT modeling, we analyze the concerted action of gold atoms and dispersion interactions in cross-linked polyethylene. Our model consists of two oligomer chains (PEn) with 7, 11, 15, 19, or 23 carbon atoms in each oligomer cross-linked with one to three Au atoms through C-Au-C bonds. In structures with a single gold atom the C-Au-C bond is located in the central position of the oligomer. Binding energies (BEs) with respect to two oligomer radical fragments and Au are as high as 362-489 kJ/mol depending on the length of the oligomer chain. When the dispersion contribution in PEn-Au-PEn oligomers is omitted, BE is almost independent of the number of carbon atoms, lying between 293 and 296 kJ/mol. The dispersion energy contributions to BEs in PEn-Au-PEn rise nearly linearly with the number of carbon atoms in the PEn chain. The carbon-carbon distance in the C-Au-C moiety is around 4.1 Å, similar to the bond distance between saturated closed shell chains in the polyethylene crystal. BEs of pure saturated closed shell PEn-PEn oligomers are 51-187 kJ/mol. Both Au atoms and dispersion interactions contribute considerably to the creation of nearly parallel chains of oligomers with reasonably high binding energies.

  7. Improved scheme for parametrization of convection in the Met Office's Numerical Atmospheric-dispersion Modelling Environment (NAME)

    Science.gov (United States)

    Meneguz, Elena; Thomson, David; Witham, Claire; Kusmierczyk-Michulec, Jolanta

    2015-04-01

    NAME is a Lagrangian atmospheric dispersion model used by the Met Office to predict the dispersion of both natural and man-made contaminants in the atmosphere, e.g. volcanic ash, radioactive particles and chemical species. Atmospheric convection is responsible for transport and mixing of air resulting in a large exchange of heat and energy above the boundary layer. Although convection can transport material through the whole troposphere, convective clouds have a small horizontal length scale (of the order of few kilometres). Therefore, for large-scale transport the horizontal scale on which the convection exists is below the global NWP resolution used as input to NAME and convection must be parametrized. Prior to the work presented here, the enhanced vertical mixing generated by non-resolved convection was reproduced by randomly redistributing Lagrangian particles between the cloud base and cloud top with probability equal to 1/25th of the NWP predicted convective cloud fraction. Such a scheme is essentially diffusive and it does not make optimal use of all the information provided by the driving meteorological model. To make up for these shortcomings and make the parametrization more physically based, the convection scheme has been recently revised. The resulting version, presented in this paper, is now based on the balance equation between upward, entrainment and detrainment fluxes. In particular, upward mass fluxes are calculated with empirical formulas derived from Cloud Resolving Models and using the NWP convective precipitation diagnostic as closure. The fluxes are used to estimate how many particles entrain, move upward and detrain. Lastly, the scheme is completed by applying a compensating subsidence flux. The performance of the updated convection scheme is benchmarked against available observational data of passive tracers. In particular, radioxenon is a noble gas that can undergo significant long range transport: this study makes use of observations of

  8. Integration of measurements with atmospheric dispersion models: Source term estimation for dispersal of (239)Pu due to non-nuclear detonation of high explosive

    Science.gov (United States)

    Edwards, L. L.; Harvey, T. F.; Freis, R. P.; Pitovranov, S. E.; Chernokozhin, E. V.

    1992-10-01

    The accuracy associated with assessing the environmental consequences of an accidental release of radioactivity is highly dependent on our knowledge of the source term characteristics and, in the case when the radioactivity is condensed on particles, the particle size distribution, all of which are generally poorly known. This paper reports on the development of a numerical technique that integrates the radiological measurements with atmospheric dispersion modeling. This results in a more accurate particle-size distribution and particle injection height estimation when compared with measurements of high explosive dispersal of (239)Pu. The estimation model is based on a non-linear least squares regression scheme coupled with the ARAC three-dimensional atmospheric dispersion models. The viability of the approach is evaluated by estimation of ADPIC model input parameters such as the ADPIC particle size mean aerodynamic diameter, the geometric standard deviation, and largest size. Additionally we estimate an optimal 'coupling coefficient' between the particles and an explosive cloud rise model. The experimental data are taken from the Clean Slate 1 field experiment conducted during 1963 at the Tonopah Test Range in Nevada. The regression technique optimizes the agreement between the measured and model predicted concentrations of (239)Pu by varying the model input parameters within their respective ranges of uncertainties. The technique generally estimated the measured concentrations within a factor of 1.5, with the worst estimate being within a factor of 5, very good in view of the complexity of the concentration measurements, the uncertainties associated with the meteorological data, and the limitations of the models. The best fit also suggest a smaller mean diameter and a smaller geometric standard deviation on the particle size as well as a slightly weaker particle to cloud coupling than previously reported.

  9. Integration of measurements with atmospheric dispersion models: Source term estimation for dispersal of 239Pu due to non- nuclear detonation of high explosive

    International Nuclear Information System (INIS)

    Edwards, L.L.; Harvey, T.F.; Freis, R.P.; Pitovranov, S.E.; Chernokozhin, E.V.

    1992-10-01

    The accuracy associated with assessing the environmental consequences of an accidental release of radioactivity is highly dependent on our knowledge of the source term characteristics and, in the case when the radioactivity is condensed on particles, the particle size distribution, all of which are generally poorly known. This paper reports on the development of a numerical technique that integrates the radiological measurements with atmospheric dispersion modeling. This results in a more accurate particle-size distribution and particle injection height estimation when compared with measurements of high explosive dispersal of 239 Pu. The estimation model is based on a non-linear least squares regression scheme coupled with the ARAC three-dimensional atmospheric dispersion models. The viability of the approach is evaluated by estimation of ADPIC model input parameters such as the ADPIC particle size mean aerodynamic diameter, the geometric standard deviation, and largest size. Additionally we estimate an optimal ''coupling coefficient'' between the particles and an explosive cloud rise model. The experimental data are taken from the Clean Slate 1 field experiment conducted during 1963 at the Tonopah Test Range in Nevada. The regression technique optimizes the agreement between the measured and model predicted concentrations of 239 Pu by varying the model input parameters within their respective ranges of uncertainties. The technique generally estimated the measured concentrations within a factor of 1.5, with the worst estimate being within a factor of 5, very good in view of the complexity of the concentration measurements, the uncertainties associated with the meteorological data, and the limitations of the models. The best fit also suggest a smaller mean diameter and a smaller geometric standard deviation on the particle size as well as a slightly weaker particle to cloud coupling than previously reported

  10. SPRAYTRAN 1.0 User’s Guide: A GIS-Based Atmospheric Spray Droplet Dispersion Modeling System

    Energy Technology Data Exchange (ETDEWEB)

    Allwine, K Jerry; Rutz, Frederick C.; Droppo, James G.; Rishel, Jeremy P.; Chapman, Elaine G.; Bird, S. L.; Thistle, Harold W.

    2006-09-20

    SPRAY TRANsport (SPRAYTRAN) is a comprehensive dispersion modeling system that is used to simulate the offsite drift of pesticides from spray applications. SPRAYTRAN functions as a console application within Environmental System Research Institute’s ArcMap Geographic Information System (Version 9.x) and integrates the widely-used, U.S. Environmental Protection Agency (EPA)-approved CALifornia PUFF (CALPUFF) dispersion model and model components to simulate longer-range transport and diffusion in variable terrain and spatially/temporally varying meteorological (e.g., wind) fields. Area sources, which are used to define spray blocks in SPRAYTRAN, are initialized using output files generated from a separate aerial-spray-application model called AGDISP (AGricultural DISPersal). The AGDISP model is used for estimating the amount of pesticide deposited to the spray block based on spraying characteristics (e.g., pesticide type, spray nozzles, and aircraft type) and then simulating the near-field (less than 300-m) drift from a single pesticide application. The fraction of pesticide remaining airborne from the AGDISP near-field simulation is then used by SPRAYTRAN for simulating longer-range (greater than 300 m) drift and deposition of the pesticide.

  11. MAFALDA: An early warning modeling tool to forecast volcanic ash dispersal and deposition

    Science.gov (United States)

    Barsotti, S.; Nannipieri, L.; Neri, A.

    2008-12-01

    Forecasting the dispersal of ash from explosive volcanoes is a scientific challenge to modern volcanology. It also represents a fundamental step in mitigating the potential impact of volcanic ash on urban areas and transport routes near explosive volcanoes. To this end we developed a Web-based early warning modeling tool named MAFALDA (Modeling and Forecasting Ash Loading and Dispersal in the Atmosphere) able to quantitatively forecast ash concentrations in the air and on the ground. The main features of MAFALDA are the usage of (1) a dispersal model, named VOL-CALPUFF, that couples the column ascent phase with the ash cloud transport and (2) high-resolution weather forecasting data, the capability to run and merge multiple scenarios, and the Web-based structure of the procedure that makes it suitable as an early warning tool. MAFALDA produces plots for a detailed analysis of ash cloud dynamics and ground deposition, as well as synthetic 2-D maps of areas potentially affected by dangerous concentrations of ash. A first application of MAFALDA to the long-lasting weak plumes produced at Mt. Etna (Italy) is presented. A similar tool can be useful to civil protection authorities and volcanic observatories in reducing the impact of the eruptive events. MAFALDA can be accessed at http://mafalda.pi.ingv.it.

  12. The importance of realistic dispersal models in conservation planning: application of a novel modelling platform to evaluate management scenarios in an Afrotropical biodiversity hotspot.

    Science.gov (United States)

    Aben, Job; Bocedi, Greta; Palmer, Stephen C F; Pellikka, Petri; Strubbe, Diederik; Hallmann, Caspar; Travis, Justin M J; Lens, Luc; Matthysen, Erik

    2016-08-01

    As biodiversity hotspots are often characterized by high human population densities, implementation of conservation management practices that focus only on the protection and enlargement of pristine habitats is potentially unrealistic. An alternative approach to curb species extinction risk involves improving connectivity among existing habitat patches. However, evaluation of spatially explicit management strategies is challenging, as predictive models must account for the process of dispersal, which is difficult in terms of both empirical data collection and modelling.Here, we use a novel, individual-based modelling platform that couples demographic and mechanistic dispersal models to evaluate the effectiveness of realistic management scenarios tailored to conserve forest birds in a highly fragmented biodiversity hotspot. Scenario performance is evaluated based on the spatial population dynamics of a well-studied forest bird species.The largest population increase was predicted to occur under scenarios increasing habitat area. However, the effectiveness was sensitive to spatial planning. Compared to adding one large patch to the habitat network, adding several small patches yielded mixed benefits: although overall population sizes increased, specific newly created patches acted as dispersal sinks, which compromised population persistence in some existing patches. Increasing matrix connectivity by the creation of stepping stones is likely to result in enhanced dispersal success and occupancy of smaller patches. Synthesis and applications . We show that the effectiveness of spatial management is strongly driven by patterns of individual dispersal across landscapes. For species conservation planning, we advocate the use of models that incorporate adequate realism in demography and, particularly, in dispersal behaviours.

  13. Turbulent diffusion modelling for windflow and dispersion analysis

    International Nuclear Information System (INIS)

    Bartzis, J.G.

    1988-01-01

    The need for simple but reliable models for turbulent diffusion for windflow and atmospheric dispersion analysis is a necessity today if one takes into consideration the relatively high demand in computer time and costs for such an analysis, arising mainly from the often large solution domains needed, the terrain complexity and the transient nature of the phenomena. In the accident consequence assessment often there is a need for a relatively large number of cases to be analysed increasing further the computer time and costs. Within the framework of searching for relatively simple and universal eddy viscosity/diffusivity models, a new three dimensional non isotropic model is proposed applicable to any domain complexity and any atmospheric stability conditions. The model utilizes the transport equation for turbulent kinetic energy but introduces a new approach in effective length scale estimation based on the flow global characteristics and local atmospheric stability. The model is discussed in detail and predictions are given for flow field and boundary layer thickness. The results are compared with experimental data with satisfactory results

  14. State of the art atmospheric dispersion modelling. Should the Gaussian plume model still be used?

    Energy Technology Data Exchange (ETDEWEB)

    Richter, Cornelia [Gesellschaft fuer Anlagen- und Reaktorsicherheit (GRS) gGmbH, Koeln (Germany)

    2016-11-15

    For regulatory purposes with respect to licensing and supervision of airborne releases of nuclear installations, the Gaussian plume model is still in use in Germany. However, for complex situations the Gaussian plume model is to be replaced by a Lagrangian particle model. Now the new EU basic safety standards for protection against the dangers arising from exposure to ionising radiation (EU BSS) [1] asks for a realistic assessment of doses to the members of the public from authorised practices. This call for a realistic assessment raises the question whether dispersion modelling with the Gaussian plume model is an adequate approach anymore or whether the use of more complex models is mandatory.

  15. An overview of experimental results and dispersion modelling of nanoparticles in the wake of moving vehicles.

    Science.gov (United States)

    Carpentieri, Matteo; Kumar, Prashant; Robins, Alan

    2011-03-01

    Understanding the transformation of nanoparticles emitted from vehicles is essential for developing appropriate methods for treating fine scale particle dynamics in dispersion models. This article provides an overview of significant research work relevant to modelling the dispersion of pollutants, especially nanoparticles, in the wake of vehicles. Literature on vehicle wakes and nanoparticle dispersion is reviewed, taking into account field measurements, wind tunnel experiments and mathematical approaches. Field measurements and modelling studies highlighted the very short time scales associated with nanoparticle transformations in the first stages after the emission. These transformations strongly interact with the flow and turbulence fields immediately behind the vehicle, hence the need of characterising in detail the mixing processes in the vehicle wake. Very few studies have analysed this interaction and more research is needed to build a basis for model development. A possible approach is proposed and areas of further investigation identified. Copyright © 2010 Elsevier Ltd. All rights reserved.

  16. mc1r Pathway regulation of zebrafish melanosome dispersion

    DEFF Research Database (Denmark)

    Richardson, Jennifer; Lundegaard, Pia Rengtved; Reynolds, Natalie L

    2008-01-01

    Zebrafish rapidly alter their pigmentation in response to environmental changes. For black melanocytes, this change is due to aggregation or dispersion of melanin in the cell. Dispersion and aggregation are controlled by intracellular cyclic adenosine monophosphate (cAMP) levels, which increase...... in mammals, and melanosome dispersal in cold-blood vertebrates, the pathway components are highly conserved. However, it has only been assumed that mc1r mediates melanosome dispersal in fish. Here, using morpholino oligonucleotides designed to knockdown mc1r expression, we find that mc1r morphants are unable...... to disperse melanosomes when grown in dark conditions. We also use chemical modifiers of the cAMP pathway, and find an unexpected response to the specific phosphodiesterase 4 (PDE4) inhibitor, rolipram, in melanosome dispersal. When treated with the drug, melanosomes fail to fully disperse in dark conditions...

  17. A DGTD method for the numerical modeling of the interaction of light with nanometer scale metallic structures taking into account non-local dispersion effects

    Energy Technology Data Exchange (ETDEWEB)

    Schmitt, Nikolai [Inria, 2004 Route des Lucioles, BP 93, 06902 Sophia Antipolis Cedex (France); Technische Universitaet Darmstadt, Institut fuer Theorie Elektromagnetischer Felder (TEMF), Schlossgartenstr. 8, 64289 Darmstadt (Germany); Scheid, Claire [Inria, 2004 Route des Lucioles, BP 93, 06902 Sophia Antipolis Cedex (France); University of Nice – Sophia Antipolis, Mathematics laboratory, Parc Valrose, 06108 Nice, Cedex 02 (France); Lanteri, Stéphane, E-mail: Stephane.Lanteri@inria.fr [Inria, 2004 Route des Lucioles, BP 93, 06902 Sophia Antipolis Cedex (France); Moreau, Antoine [Institut Pascal, Université Blaise Pascal, 24, avenue des Landais, 63171 Aubière Cedex (France); Viquerat, Jonathan [Inria, 2004 Route des Lucioles, BP 93, 06902 Sophia Antipolis Cedex (France)

    2016-07-01

    The interaction of light with metallic nanostructures is increasingly attracting interest because of numerous potential applications. Sub-wavelength metallic structures, when illuminated with a frequency close to the plasma frequency of the metal, present resonances that cause extreme local field enhancements. Exploiting the latter in applications of interest requires a detailed knowledge about the occurring fields which can actually not be obtained analytically. For the latter mentioned reason, numerical tools are thus an absolute necessity. The insight they provide is very often the only way to get a deep enough understanding of the very rich physics at play. For the numerical modeling of light-structure interaction on the nanoscale, the choice of an appropriate material model is a crucial point. Approaches that are adopted in a first instance are based on local (i.e. with no interaction between electrons) dispersive models, e.g. Drude or Drude–Lorentz models. From the mathematical point of view, when a time-domain modeling is considered, these models lead to an additional system of ordinary differential equations coupled to Maxwell's equations. However, recent experiments have shown that the repulsive interaction between electrons inside the metal makes the response of metals intrinsically non-local and that this effect cannot generally be overlooked. Technological achievements have enabled the consideration of metallic structures in a regime where such non-localities have a significant influence on the structures' optical response. This leads to an additional, in general non-linear, system of partial differential equations which is, when coupled to Maxwell's equations, significantly more difficult to treat. Nevertheless, dealing with a linearized non-local dispersion model already opens the route to numerous practical applications of plasmonics. In this work, we present a Discontinuous Galerkin Time-Domain (DGTD) method able to solve the system

  18. Advanced modeling of the size poly-dispersion of boiling flows

    International Nuclear Information System (INIS)

    Ruyer, Pierre; Seiler, Nathalie

    2008-01-01

    Full text of publication follows: This work has been performed within the Institut de Radioprotection et de Surete Nucleaire that leads research programs concerning safety analysis of nuclear power plants. During a LOCA (Loss Of Coolant Accident), in-vessel pressure decreases and temperature increases, leading to the onset of nucleate boiling. The present study focuses on the numerical simulation of the local topology of the boiling flow. There is experimental evidence of a local and statistical large spectra of possible bubble sizes. The relative importance of the correct description of this poly-dispersion in size is due to the dependency of (i) main hydrodynamic forces, like lift, as well as of (ii) transfer area with respect to the individual bubble size. We study the corresponding CFD model in the framework of an ensemble averaged description of the dispersed two-phase flow. The transport equations of the main statistical moment densities of the population size distribution are derived and models for the mass, momentum and heat transfers at the bubble scale as well as for bubble coalescence are achieved. This model introduced within NEPTUNE-CFD code of the NEPTUNE thermal-hydraulic platform, a joint project of CEA, EDF, IRSN and AREVA, has been tested on boiling flows obtained on the DEBORA facility of the CEA at Grenoble. These numerical simulations provide a validation and attest the impact of the proposed model. (authors) [fr

  19. Homogenization of a Directed Dispersal Model for Animal Movement in a Heterogeneous Environment.

    Science.gov (United States)

    Yurk, Brian P

    2016-10-01

    The dispersal patterns of animals moving through heterogeneous environments have important ecological and epidemiological consequences. In this work, we apply the method of homogenization to analyze an advection-diffusion (AD) model of directed movement in a one-dimensional environment in which the scale of the heterogeneity is small relative to the spatial scale of interest. We show that the large (slow) scale behavior is described by a constant-coefficient diffusion equation under certain assumptions about the fast-scale advection velocity, and we determine a formula for the slow-scale diffusion coefficient in terms of the fast-scale parameters. We extend the homogenization result to predict invasion speeds for an advection-diffusion-reaction (ADR) model with directed dispersal. For periodic environments, the homogenization approximation of the solution of the AD model compares favorably with numerical simulations. Invasion speed approximations for the ADR model also compare favorably with numerical simulations when the spatial period is sufficiently small.

  20. Chemical dispersants

    NARCIS (Netherlands)

    Rahsepar, Shokouhalsadat; Smit, Martijn P.J.; Murk, Albertinka J.; Rijnaarts, Huub H.M.; Langenhoff, Alette A.M.

    2016-01-01

    Chemical dispersants were used in response to the Deepwater Horizon oil spill in the Gulf of Mexico, both at the sea surface and the wellhead. Their effect on oil biodegradation is unclear, as studies showed both inhibition and enhancement. This study addresses the effect of Corexit on oil

  1. The physiological effects of oil, dispersant and dispersed oil on the bay mussel, Mytilus trossulus, in Arctic/Subarctic conditions.

    Science.gov (United States)

    Counihan, Katrina L

    2018-06-01

    Increasing oil development around Alaska and other Arctic regions elevates the risk for another oil spill. Dispersants are used to mitigate the impact of an oil spill by accelerating natural degradation processes, but the reduced hydrophobicity of dispersed oil may increase its bioavailability to marine organisms. There is limited research on the effect of dispersed oil on cold water species and ecosystems. Therefore, spiked exposure tests were conducted with bay mussels (Mytilus trossulus) in seawater with non-dispersed oil, Corexit 9500 and oil dispersed with different concentrations of Corexit 9500. After three weeks of exposure, acute and chronic physiological impacts were determined. The majority of physiological responses occurred during the first seven days of exposure, with mussels exhibiting significant cytochrome P450 activity, superoxide dismutase activity and heat shock protein levels. Mussels exposed to non-dispersed oil also experienced immune suppression, reduced transcription and higher levels of mortality. After 21 days, mussels in all treatments exhibited evidence of genetic damage, tissue loss and a continued stress response. Bay mussels are useful as indicators of ecosystem health and recovery, and this study was an important step in understanding how non-dispersed oil, dispersant and dispersed oil affect the physiology of this sentinel species in Arctic/subarctic conditions. Copyright © 2018 Elsevier B.V. All rights reserved.

  2. Hydrodynamic dispersion characteristics of lateral inflow into a river tested by a laboratory model

    Directory of Open Access Journals (Sweden)

    P. Y. Chou

    2009-02-01

    Full Text Available Groundwater and river-water have a different composition and interact in and below the riverbed. The riverbed-aquifer flux interactions have received growing interest because of their role in the exchange and transformation of nutrients and pollutants between rivers and the aquifer. In this research our main purpose is to identify the physical processes and characteristics needed for a numerical transport model, which includes the unsaturated recharge zone, the aquifer and the riverbed. In order to investigate such lateral groundwater inflow process, a laboratory J-shaped column experiment was designed. This study determined the transport parameters of the J-shaped column by fitting an analytical solution of the convective-dispersion equation for every flux on individual segments to the observed breakthrough curves of the resident concentration, and by inverse modelling for every flux simultaneously over the entire flow domain. The obtained transport-parameter relation was tested by numerical simulation using HYDRUS 2-D/3-D.

    Four steady-state flux conditions (i.e. 0.5 cm hr−1, 1 cm hr−1, 1.5 cm hr−1 and 2 cm hr−1 were applied, transport parameters including pore water velocity and dispersivity were determined for both unsaturated and saturated sections along the column. Results showed that under saturated conditions the dispersivity was fairly constant and independent of the flux. In contrast, dispersivity under unsaturated conditions was flux dependent and increased at lower flux. For our porous medium the dispersion coefficient related best to the quotient of the pore water velocity divided by the water content. A simulation model of riverbed-aquifer flux interaction should take this into account.

  3. Polarization and switching properties of holographic polymer-dispersed liquid-crystal gratings. I. Theoretical model

    Science.gov (United States)

    Sutherland, Richard L.

    2002-12-01

    Polarization properties and electro-optical switching behavior of holographic polymer-dispersed liquid-crystal (HPDLC) reflection and transmission gratings are studied. A theoretical model is developed that combines anisotropic coupled-wave theory with an elongated liquid-crystal-droplet switching model and includes the effects of a statistical orientational distribution of droplet-symmetry axes. Angle- and polarization-dependent switching behaviors of HPDLC gratings are elucidated, and the effects on dynamic range are described. A new type of electro-optical switching not seen in ordinary polymer-dispersed liquid crystals, to the best of the author's knowledge, is presented and given a physical interpretation. The model provides valuable insight to the physics of these gratings and can be applied to the design of HPDLC holographic optical elements.

  4. Spatial characterization of catchment dispersion mechanisms in an urban context

    Science.gov (United States)

    Rossel, Florian; Gironás, Jorge; Mejía, Alfonso; Rinaldo, Andrea; Rodriguez, Fabrice

    2014-12-01

    Previous studies have examined in-depth the dispersion mechanisms in natural catchments. In contrast, these dispersion mechanisms have been studied little in urban catchments, where artificial transport elements and morphological arrangements are expected to modify travel times and mobilize excess rainfall from spatially distributed impervious sites. This has the ability to modify the variance of the catchment's travel times and hence the total dispersion. This work quantifies the dispersion mechanisms in an urban catchment using the theory of transport by travel times as represented by the Urban Morpho-climatic Instantaneous Unit Hydrograph (U-McIUH) model. The U-McIUH computes travel times based on kinematic wave theory and accounts explicitly for the path heterogeneities and altered connectivity patterns characteristic of an urban drainage network. The analysis is illustrated using the Aubinière urban catchment in France as a case study. We found that kinematic dispersion is dominant for small rainfall intensities, whereas geomorphologic dispersion becomes more dominant for larger intensities. The total dispersion scales with the drainage area in a power law fashion. The kinematic dispersion is dominant across spatial scales up to a threshold of approximately 2-3 km2, after which the geomorphologic dispersion becomes more dominant. Overall, overland flow is responsible for most of the dispersion in the catchment, while conduits tend to counteract the increase of the geomorphologic dispersion with a negative kinematic dispersion. Further study with other catchments is needed to asses if the latter is a general feature of urban drainage networks.

  5. Numerical analysis and modeling of plume meandering in passive scalar dispersion downstream of a wall-mounted cube

    International Nuclear Information System (INIS)

    Rossi, R.; Iaccarino, G.

    2013-01-01

    Highlights: • Scalar dispersion downstream of a wall-mounted cube is examined by DNS and RANS models. • Vortex-shedding and plume meandering are established in the wake of the cube. • Low-frequency modulation is observed in the vortex-shedding and plume meandering. • Counter-gradient transport takes place in the streamwise component of the scalar flux. • Concentration decay and plume spread improved by the unsteady RANS model. -- Abstract: A DNS database is employed to examine the onset of plume meandering downstream of a wall-mounted cube and to address the impact of large-scale unsteadiness in modeling dispersion using the RANS equations. The cube is immersed in a uniform stream where the thin boundary-layer developing over the flat plate is responsible for the onset of vortex-shedding in the wake of the bluff-body. Spectra of velocity and concentration fluctuations exhibit a prominent peak in the energy content at the same frequency, showing that the plume meandering is established by the action of the vortex-shedding. The vortex-shedding and plume meandering display a low-frequency modulation where coherent fluctuations are suppressed at times with a quasi-regular period. The onset of the low-frequency modulation is indicated by a secondary peak in the energy spectrum and confirmed by the autocorrelation of velocity and scalar fluctuations. Unsteady RANS simulations performed with the v 2 − f model are able to detect the onset of the plume meandering and show remarkable improvement of the predicted decay rate and rate of spread of the scalar plume when compared to steady RANS solutions. By computing explicitly the periodic component of velocity and scalar fluctuations, the unsteady v 2 − f model is able to provide a representation of scalar flux components consistent with DNS statistics, where the counter-gradient transport mechanism that takes place in the streamwise component is also captured by URANS results. Nonetheless, the agreement with DNS

  6. Modeling non-Fickian dispersion by use of the velocity PDF on the pore scale

    Science.gov (United States)

    Kooshapur, Sheema; Manhart, Michael

    2015-04-01

    For obtaining a description of reactive flows in porous media, apart from the geometrical complications of resolving the velocities and scalar values, one has to deal with the additional reactive term in the transport equation. An accurate description of the interface of the reacting fluids - which is strongly influenced by dispersion- is essential for resolving this term. In REV-based simulations the reactive term needs to be modeled taking sub-REV fluctuations and possibly non-Fickian dispersion into account. Non-Fickian dispersion has been observed in strongly heterogeneous domains and in early phases of transport. A fully resolved solution of the Navier-Stokes and transport equations which yields a detailed description of the flow properties, dispersion, interfaces of fluids, etc. however, is not practical for domains containing more than a few thousand grains, due to the huge computational effort required. Through Probability Density Function (PDF) based methods, the velocity distribution in the pore space can facilitate the understanding and modelling of non-Fickian dispersion [1,2]. Our aim is to model the transition between non-Fickian and Fickian dispersion in a random sphere pack within the framework of a PDF based transport model proposed by Meyer and Tchelepi [1,3]. They proposed a stochastic transport model where velocity components of tracer particles are represented by a continuous Markovian stochastic process. In addition to [3], we consider the effects of pore scale diffusion and formulate a different stochastic equation for the increments in velocity space from first principles. To assess the terms in this equation, we performed Direct Numerical Simulations (DNS) for solving the Navier-Stokes equation on a random sphere pack. We extracted the PDFs and statistical moments (up to the 4th moment) of the stream-wise velocity, u, and first and second order velocity derivatives both independent and conditioned on velocity. By using this data and

  7. A Generalized turbulent dispersion model for bubbly flow numerical simulation in NEPTUNE-CFD

    Energy Technology Data Exchange (ETDEWEB)

    Laviéville, Jérôme, E-mail: Jerome-marcel.lavieville@edf.fr; Mérigoux, Nicolas, E-mail: nicolas.merigoux@edf.fr; Guingo, Mathieu, E-mail: mathieu.guingo@edf.fr; Baudry, Cyril, E-mail: Cyril.baudry@edf.fr; Mimouni, Stéphane, E-mail: stephane.mimouni@edf.fr

    2017-02-15

    The NEPTUNE-CFD code, based upon an Eulerian multi-fluid model, is developed within the framework of the NEPTUNE project, financially supported by EDF (Electricité de France), CEA (Commissariat à l’Energie Atomique et aux Energies Alternatives), IRSN (Institut de Radioprotection et de Sûreté Nucléaire) and AREVA-NP. NEPTUNE-CFD is mainly focused on Nuclear Safety applications involving two-phase water-steam flows, like two-phase Pressurized Shock (PTS) and Departure from Nucleate Boiling (DNB). Many of these applications involve bubbly flows, particularly, for application to flows in PWR fuel assemblies, including studies related to DNB. Considering a very usual model for interfacial forces acting on bubbles, including drag, virtual mass and lift forces, the turbulent dispersion force is often added to moderate the lift effect in orthogonal directions to the main flow and get the right dispersion shape. This paper presents a formal derivation of this force, considering on the one hand, the fluctuating part of drag and virtual mass, and on the other hand, Turbulent Pressure derivation obtained by comparison between Lagrangian and Eulerian description of bubbles motion. An extension of the Tchen’s theory is used to express the turbulent kinetic energy of bubbles and the two-fluid turbulent covariance tensor in terms of liquid turbulent velocities and time scale. The model obtained by this way, called Generalized Turbulent Dispersion Model (GTD), does not require any user parameter. The model is validated against Liu & Bankoff air-water experiment, Arizona State University (ASU) experiment, DEBORA experiment and Texas A&M University (TAMU) boiling flow experiments.

  8. The usefulness of time-dependent reactor accident consequence modelling for emergency response planning

    International Nuclear Information System (INIS)

    Paretzke, H.G.; Jacob, P.; Mueller, H.; Proehl, G.

    1989-01-01

    After major releases of radionuclides into the atmosphere fast reaction of authorities will be necessary to inform the public of potential consequences and to consider and optimize mitigating actions. These activities require availability of well designed computer models, adequate and fast measurements and prior training of responsible persons. The quantitative assessment models should be capable of taking into account of actual atmospheric dispersion conditions, actual deposition situation (dry, rain, snow, fog), seasonal status of the agriculture, food processing and distribution pathways, etc. In this paper the usefulness of such models will be discussed, their limitations, the relative importance of exposure pathways and a selection of important methods to decrease the activity in food products after an accident. Real-time reactor accident consequence models should be considered as a condition sine qua non for responsible use of nuclear power for electricity production

  9. Stress-dependent permeability and wave dispersion in tight cracked rocks: Experimental validation of simple effective medium models

    Science.gov (United States)

    Sarout, Joel; Cazes, Emilie; Delle Piane, Claudio; Arena, Alessio; Esteban, Lionel

    2017-08-01

    We experimentally assess the impact of microstructure, pore fluid, and frequency on wave velocity, wave dispersion, and permeability in thermally cracked Carrara marble under effective pressure up to 50 MPa. The cracked rock is isotropic, and we observe that (1) P and S wave velocities at 500 kHz and the low-strain (S waves and 9% for P waves at 1 MPa, and (4) wave dispersion virtually vanishes above 30 MPa. Assuming no interactions between the cracks, effective medium theory is used to model the rock's elastic response and its permeability. P and S wave velocity data are jointly inverted to recover the crack density and effective aspect ratio. The permeability data are inverted to recover the cracks' effective radius. These parameters lead to a good agreement between predicted and measured wave velocities, dispersion and permeability up to 50 MPa, and up to a crack density of 0.5. The evolution of the crack parameters suggests that three deformation regimes exist: (1) contact between cracks' surface asperities up to 10 MPa, (2) progressive crack closure between 10 and 30 MPa, and (3) crack closure effectively complete above 30 MPa. The derived crack parameters differ significantly from those obtained by analysis of 2-D electron microscope images of thin sections or 3-D X-ray microtomographic images of millimeter-size specimens.

  10. Instrument Response Modeling and Simulation for the GLAST Burst Monitor

    International Nuclear Information System (INIS)

    Kippen, R. M.; Hoover, A. S.; Wallace, M. S.; Pendleton, G. N.; Meegan, C. A.; Fishman, G. J.; Wilson-Hodge, C. A.; Kouveliotou, C.; Lichti, G. G.; Kienlin, A. von; Steinle, H.; Diehl, R.; Greiner, J.; Preece, R. D.; Connaughton, V.; Briggs, M. S.; Paciesas, W. S.; Bhat, P. N.

    2007-01-01

    The GLAST Burst Monitor (GBM) is designed to provide wide field of view observations of gamma-ray bursts and other fast transient sources in the energy range 10 keV to 30 MeV. The GBM is composed of several unshielded and uncollimated scintillation detectors (twelve NaI and two BGO) that are widely dispersed about the GLAST spacecraft. As a result, reconstructing source locations, energy spectra, and temporal properties from GBM data requires detailed knowledge of the detectors' response to both direct radiation as well as that scattered from the spacecraft and Earth's atmosphere. This full GBM instrument response will be captured in the form of a response function database that is derived from computer modeling and simulation. The simulation system is based on the GEANT4 Monte Carlo radiation transport simulation toolset, and is being extensively validated against calibrated experimental GBM data. We discuss the architecture of the GBM simulation and modeling system and describe how its products will be used for analysis of observed GBM data. Companion papers describe the status of validating the system

  11. A model to predict failure of irradiated U–Mo dispersion fuel

    Energy Technology Data Exchange (ETDEWEB)

    Burkes, Douglas E., E-mail: Douglas.Burkes@pnnl.gov; Senor, David J.; Casella, Andrew M.

    2016-12-15

    Highlights: • Simple model to predict failure of dispersion fuel meat designs. • Evaluated as a function of fabrication parameters and irradiation conditions. • Predictions compare well with experimental measurements of miniature fuel plates. • Interaction layer formation reduces matrix strength and increases temperature. • Si additions to the matrix appear effective only at moderate heat flux and burnup. - Abstract: Numerous global programs are focused on the continued development of existing and new research and test reactor fuels to achieve maximum attainable uranium loadings to support the conversion of a number of the world’s remaining high-enriched uranium fueled reactors to low-enriched uranium fuel. Some of these programs are focused on development and qualification of a fuel design that consists of a uranium–molybdenum (U–Mo) alloy dispersed in an aluminum matrix as one option for reactor conversion. The current paper extends a failure model originally developed for UO{sub 2}-stainless steel dispersion fuels and uses currently available thermal–mechanical property information for the materials of interest in the currently proposed design. A number of fabrication and irradiation parameters were investigated to understand the conditions at which failure of the matrix, classified as onset of pore formation in the matrix, might occur. The results compared well with experimental observations published as part of the Reduced Enrichment for Research and Test Reactors (RERTR)-6 and -7 mini-plate experiments. Fission rate, a function of the {sup 235}U enrichment, appeared to be the most influential parameter in premature failure, mainly as a result of increased interaction layer formation and operational temperature, which coincidentally decreased the strength of the matrix and caused more rapid fission gas production and recoil into the surrounding matrix material. Addition of silicon to the matrix appeared effective at reducing the rate of

  12. A general advection-diffusion model for radioactive substance dispersion released from nuclear power plants

    International Nuclear Information System (INIS)

    Buske, D.

    2011-01-01

    The present contribution focuses on the question of radioactive material dispersion after discharge from a nuclear power plant in the context of micro-meteorology, i.e. an atmospheric dispersion model. The advection-diffusion equation with Fickian closure for the turbulence is solved for the atmospheric boundary layer where the eddy diffusivity coefficients and the wind profile are assumed to be space dependent. The model is solved in closed form using integral transform and spectral theory. Convergence of the solution is discussed in terms of a convergence criterion using a new interpretation of the Cardinal Theorem of Interpolation theory and Parseval's theorem. The solution is compared to other methods and model adequacy is analyzed. Model validation is performed against experimental data from a controlled release of radioactive material at the Itaorna Beach (Angra dos Reis, Rio de Janeiro state, Brazil, 1985). (author)

  13. Some Observational and Modeling Studies of the Atmospheric Boundary Layer at Mississippi Gulf Coast for Air Pollution Dispersion Assessment

    Directory of Open Access Journals (Sweden)

    Anjaneyulu Yerramilli

    2008-12-01

    Full Text Available Coastal atmospheric conditions widely vary from those over inland due to the land-sea interface, temperature contrast and the consequent development of local circulations. In this study a field meteorological experiment was conducted to measure vertical structure of boundary layer during the period 25-29 June, 2007 at three locations Seabee base, Harrison and Wiggins sites in the Mississippi coast. A GPS Sonde along with slow ascent helium balloon and automated weather stations equipped with slow and fast response sensors were used in the experiment. GPS sonde were launched at three specific times (0700 LT, 1300 LT and 1800 LT during the experiment days. The observations indicate shallow boundary layer near the coast which gradually develops inland. The weather research and forecasting (WRF meso-scale atmospheric model and a Lagrangian particle dispersion model (HYSPLIT are used to simulate the lower atmospheric flow and dispersion in a range of 100 km from the coast for 28-30 June, 2007. The simulated meteorological parameters were compared with the experimental observations. The meso-scale model results show significant temporal and spatial variations in the meteorological fields as a result of development of sea breeze flow, its coupling with the large scale flow field and the ensuing alteration in the mixing depth across the coast. Simulated ground-level concentrations of SO2 from four elevated point sources located along the coast indicate diurnal variation and impact of the local sea-land breeze on the direction of the plume. Model concentration levels were highest during the stable morning condition and during the sea-breeze time in the afternoon. The highest concentrations were found up to 40 km inland during sea breeze time. The study illustrates the application of field meteorological observations for the validation of WRF which is coupled to HYSPLIT for dispersion assessment in the coastal region.

  14. A CFD modeling study of the impacts of NO x and VOC emissions on reactive pollutant dispersion in and above a street canyon

    Science.gov (United States)

    Kwak, Kyung-Hwan; Baik, Jong-Jin

    2012-01-01

    A computational fluid dynamics (CFD) model that includes the carbon bond mechanism IV (CBM-IV) is developed and used to investigate reactive pollutant dispersion in and above a street canyon with an aspect ratio of 1. Fourteen emission scenarios of NO x and volatile organic compounds (VOCs) are considered. Dispersion types are classified into NO-type, NO 2-type, and O 3-type dispersion that exhibit concentration maxima at the street bottom, near the center of the street canyon, and above the street canyon, respectively. For the base emission scenario, the number of reactive species is 9 in the NO-type dispersion, 10 in the NO 2-type dispersion, and 15 in the O 3-type dispersion. As the NO x emission level decreases or the VOC emission level increases, some species in the O 3-type dispersion are shifted to the NO 2-type dispersion. The VOC-to-NO x emission ratio is found to be an important factor in determining the transition of dispersion type. In this transition process, OH plays a key role through a radical chain including HO 2, RO, and RO 2. Because of their high OH reactivities, XYL (xylene) and OLE (olefin carbon bond) among VOCs are largely responsible for the transition of dispersion type. The O 3 sensitivity is examined by reducing NO x or VOC emission level by a half. Because the NO titration of O 3 is more pronounced than the NO 2 photolysis and the radical chain process in the street canyon, the O 3 concentration therein is negatively correlated with the NO x emission level and weakly correlated with the VOC emission level. As a result, the street canyon is a negatively NO x-sensitive regime.

  15. Modeling Smoke Plume-Rise and Dispersion from Southern United States Prescribed Burns with Daysmoke

    Science.gov (United States)

    G L Achtemeier; S L Goodrick; Y Liu; F Garcia-Menendez; Y Hu; M. Odman

    2011-01-01

    We present Daysmoke, an empirical-statistical plume rise and dispersion model for simulating smoke from prescribed burns. Prescribed fires are characterized by complex plume structure including multiple-core updrafts which makes modeling with simple plume models difficult. Daysmoke accounts for plume structure in a three-dimensional veering/sheering atmospheric...

  16. Evaluation of regional and local atmospheric dispersion models for the analysis of traffic-related air pollution in urban areas

    Science.gov (United States)

    Fallah-Shorshani, Masoud; Shekarrizfard, Maryam; Hatzopoulou, Marianne

    2017-10-01

    Dispersion of road transport emissions in urban metropolitan areas is typically simulated using Gaussian models that ignore the turbulence and drag induced by buildings, which are especially relevant for areas with dense downtown cores. To consider the effect of buildings, street canyon models are used but often at the level of single urban corridors and small road networks. In this paper, we compare and validate two dispersion models with widely varying algorithms, across a modelling domain consisting of the City of Montreal, Canada accounting for emissions of more 40,000 roads. The first dispersion model is based on flow decomposition into the urban canopy sub-flow as well as overlying airflow. It takes into account the specific height and geometry of buildings along each road. The second model is a Gaussian puff dispersion model, which handles complex terrain and incorporates three-dimensional meteorology, but accounts for buildings only through variations in the initial vertical mixing coefficient. Validation against surface observations indicated that both models under-predicted measured concentrations. Average weekly exposure surfaces derived from both models were found to be reasonably correlated (r = 0.8) although the Gaussian dispersion model tended to underestimate concentrations around the roadways compared to the street canyon model. In addition, both models were used to estimate exposures of a representative sample of the Montreal population composed of 1319 individuals. Large differences were noted whereby exposures derived from the Gaussian puff model were significantly lower than exposures derived from the street canyon model, an expected result considering the concentration of population around roadways. These differences have large implications for the analyses of health effects associated with NO2 exposure.

  17. Frequency dispersion analysis of thin dielectric MOS capacitor in a five-element model

    Science.gov (United States)

    Zhang, Xizhen; Zhang, Sujuan; Zhu, Huichao; Pan, Xiuyu; Cheng, Chuanhui; Yu, Tao; Li, Xiangping; Cheng, Yi; Xing, Guichao; Zhang, Daming; Luo, Xixian; Chen, Baojiu

    2018-02-01

    An Al/ZrO2/IL/n-Si (IL: interface layer) MOS capacitor has been fabricated by metal organic decomposition of ZrO2 and thermal deposition Al. We have measured parallel capacitance (C m) and parallel resistance (R m) versus bias voltage curves (C m, R m-V) at different AC signal frequency (f), and C m, R m-f curves at different bias voltage. The curves of C m, R m-f measurements show obvious frequency dispersion in the range of 100 kHz-2 MHz. The energy band profile shows that a large voltage is applied on the ZrO2 layer and IL at accumulation, which suggests possible dielectric polarization processes by some traps in ZrO2 and IL. C m, R m-f data are used for frequency dispersion analysis. To exclude external frequency dispersion, we have extracted the parameters of C (real MOS capacitance), R p (parallel resistance), C IL (IL capacitance), R IL (IL resistance) and R s (Si resistance) in a five-element model by using a three-frequency method. We have analyzed intrinsic frequency dispersion of C, R p, C IL, R IL and R s by studying the dielectric characteristics and Si surface layer characteristics. At accumulation, the dispersion of C and R p is attributed to dielectric polarization such as dipolar orientation and oxide traps. The serious dispersion of C IL and R IL are relative to other dielectric polarization, such as border traps and fixed oxide traps. The dispersion of R s is mainly attributed to contact capacitance (C c) and contact resistance (R c). At depletion and inversion, the frequency dispersion of C, R p, C IL, R IL, and R s are mainly attributed to the depletion layer capacitance (C D). The interface trap capacitance (C it) and interface trap resistance (R it) are not dominant for the dispersion of C, R p, C IL, R IL, and R s.

  18. Density-Dependent Formulation of Dispersion-Repulsion Interactions in Hybrid Multiscale Quantum/Molecular Mechanics (QM/MM) Models

    DEFF Research Database (Denmark)

    Curutchet, Carles; Cupellini, Lorenzo; Kongsted, Jacob

    2018-01-01

    embedding approaches, respectively, nonelectrostatic dispersion and repulsion interactions are instead commonly described through classical potentials despite their quantum mechanical origin. Here we present an extension of the Tkatchenko-Scheffler semiempirical van der Waals (vdWTS) scheme aimed......Mixed multiscale quantum/molecular mechanics (QM/MM) models are widely used to explore the structure, reactivity, and electronic properties of complex chemical systems. Whereas such models typically include electrostatics and potentially polarization in so-called electrostatic and polarizable...... at describing dispersion and repulsion interactions between quantum and classical regions within a QM/MM polarizable embedding framework. Starting from the vdWTSexpression, we define a dispersion and a repulsion term, both of them density-dependent and consistently based on a Lennard-Jones-like potential. We...

  19. To evaluate the change in release from solid dispersion using sodium lauryl sulfate and model drug sulfathiazole.

    Science.gov (United States)

    Dave, Rutesh H; Patel, Hardikkumar H; Donahue, Edward; Patel, Ashwinkumar D

    2013-10-01

    The solubility of drugs remains one of the most challenging aspects of formulation development. There are numerous ways to improve the solubility of drugs amongst which the most promising strategy is solid dispersion. Different ratios of sulfathiazole: PVP-K29/32: sodium lauryl sulfate (SLS) were prepared (1:1:0.1, 1:1:0.5, 1:1:1) and various methods were employed to characterize the prepared solid dispersions, namely modulated differential scanning calorimeter, X-ray powder diffraction, Fourier Transformed Infrared Spectroscopy and dissolution studies. Lack of crystallinity was observed in internal and external systems suggesting a loss of crystallinity, whereas the physical mixtures showed a characteristic peak of sulfathiazole. In vitro dissolution results clearly showed that the incorporation of a relatively small amount of surfactants (5, 20 or 33% w/w) into a solid dispersion can improve its dissolution rates compared to binary solid dispersion (SD) alone and pure sulfathiazole. In all ratios solid dispersion internal shows a higher dissolution rate compared to a physical mixture and solid dispersion external which suggests that the way that the surfactant is incorporated into the solid dispersion plays an important role in changing the solubility of a drug. The solubilization mechanism is mainly responsible for this higher dissolution rate when we incorporate the SLS in SD.

  20. DIMO, a plant dispersal model

    NARCIS (Netherlands)

    Wamelink, G.W.W.; Jochem, R.; Greft, van der J.G.M.; Franke, J.; Malinowska, A.H.; Geertsema, W.; Prins, A.H.; Ozinga, W.A.; Hoek, van der D.C.J.; Grashof-Bokdam, C.J.

    2014-01-01

    Due to human activities many natural habitats have become isolated. As a result the dispersal of many plant species is hampered. Isolated populations may become extinct and have a lower probability to become reestablished in a natural way. Moreover, plant species may be forced to migrate to new

  1. A Novel A Posteriori Investigation of Scalar Flux Models for Passive Scalar Dispersion in Compressible Boundary Layer Flows

    Science.gov (United States)

    Braman, Kalen; Raman, Venkat

    2011-11-01

    A novel direct numerical simulation (DNS) based a posteriori technique has been developed to investigate scalar transport modeling error. The methodology is used to test Reynolds-averaged Navier-Stokes turbulent scalar flux models for compressible boundary layer flows. Time-averaged DNS velocity and turbulence fields provide the information necessary to evolve the time-averaged scalar transport equation without requiring the use of turbulence modeling. With this technique, passive dispersion of a scalar from a boundary layer surface in a supersonic flow is studied with scalar flux modeling error isolated from any flowfield modeling errors. Several different scalar flux models are used. It is seen that the simple gradient diffusion model overpredicts scalar dispersion, while anisotropic scalar flux models underpredict dispersion. Further, the use of more complex models does not necessarily guarantee an increase in predictive accuracy, indicating that key physics is missing from existing models. Using comparisons of both a priori and a posteriori scalar flux evaluations with DNS data, the main modeling shortcomings are identified. Results will be presented for different boundary layer conditions.

  2. A comprehensive experimental databank for the verification of urban car emission dispersion models

    Energy Technology Data Exchange (ETDEWEB)

    Pavageau, M.; Rafailidis, S.; Schatzmann, M. [Universitaet Hamburg (Germany). Meteorologisches Inst.

    2001-07-01

    A summary presentation is made of representative samples from a comprehensive experimental databank on car exhaust dispersion in urban street canyons. Physical modelling, under neutral stratification conditions, was used to provide visualisation, pollutant concentration and velocity measurements above and inside test canyons amidst surrounding urban roughness. The study extended to two different canyon aspects ratios, in combination with different roof configurations on the surrounding buildings. To serve as a reliable basis for validation and testing of urban pollution dispersion codes, special emphasis was placed in this work on data quality assurance. (Author)

  3. A discontinuous Galerkin approach for conservative modeling of fully nonlinear and weakly dispersive wave transformations

    Science.gov (United States)

    Sharifian, Mohammad Kazem; Kesserwani, Georges; Hassanzadeh, Yousef

    2018-05-01

    This work extends a robust second-order Runge-Kutta Discontinuous Galerkin (RKDG2) method to solve the fully nonlinear and weakly dispersive flows, within a scope to simultaneously address accuracy, conservativeness, cost-efficiency and practical needs. The mathematical model governing such flows is based on a variant form of the Green-Naghdi (GN) equations decomposed as a hyperbolic shallow water system with an elliptic source term. Practical features of relevance (i.e. conservative modeling over irregular terrain with wetting and drying and local slope limiting) have been restored from an RKDG2 solver to the Nonlinear Shallow Water (NSW) equations, alongside new considerations to integrate elliptic source terms (i.e. via a fourth-order local discretization of the topography) and to enable local capturing of breaking waves (i.e. via adding a detector for switching off the dispersive terms). Numerical results are presented, demonstrating the overall capability of the proposed approach in achieving realistic prediction of nearshore wave processes involving both nonlinearity and dispersion effects within a single model.

  4. Recent developments in the applications of the Regional Atmospheric Modeling System (RAMS) for emergency response planning and operational forecasting at the Kennedy Space Center

    International Nuclear Information System (INIS)

    Lyons, W.A.; Tremback, C.J.

    1996-01-01

    The authors will summarize ten years of developing and applying the Regional Atmospheric Modeling System (RAMS) to emergency response and operational dispersion forecasting at the Kennedy Space Center (KSC). RAMS forms the core of two workstation-based operational systems, ERDAS (the Emergency Response Dose Assessment System) and PROWESS (Parallelized RAMS Operational Weather Simulation System) which are undergoing extensive operational testing prior to potential deployment as part of the range forecasting system at KSC. RAMS has been interfaced with HYPACT (the Hybrid Particle and Concentration Transport Model) to produce detailed 3-D dispersion forecasts from a variety of sources including cold spills, routine launch operations, and explosive conflagrations of launch vehicles

  5. Using the /phi/resund experimental data to evaluate the ARAC emergency response models

    International Nuclear Information System (INIS)

    Gudiksen, P.H.; Gryning, S.E.

    1988-07-01

    A series of meteorological and tracer experiments, was conducted during May and June 1984 over the 20-km wide /O/resund strait between Denmark and Sweden for the purpose of studying atmospheric dispersion processes over cold water and warm land surfaces and providing the data needed to evaluate meso-scale models in a coastal environment. In concert with these objectives the data from these experiments have been used as part of a continuing effort to evaluate the capability of the three-dimensional MATHEW/ADPIC (M/A) atmospheric dispersion models to simulate pollutant transport and diffusion characteristics of the atmospheric during a wide variety of meteorological conditions. Since previous studies have focused primarily on M/A model evaluations over rolling and complex terrain at inland sites, the /O/resund experiments provide a unique opportunity to evaluate the models in a coastal environment. The M/A models are used by the Atmospheric Release Advisory Capability (ARAC), developed by the Lawrence Livermore National Laboratory, for performing real-time assessments of the environmental consequences of potential or actual releases of radioactivity into the atmosphere. These assessments include estimation of radiation doses to nearby population centers and of the extent of surface contamination. Model evaluations, using field experimental data such as those generated by the /O/resund experiments, serve as a basis for providing emergency response managers with estimated of the uncertainties associated with accident consequence assessments. This report provides a brief description of the /O/resund experiments, the current understanding of the meteorological processes governing pollutant dispersion over the /O/resund strait, and the results of the M/A model simulations of these experiments. 11 refs., 7 figs., 1 tab

  6. Non-Fickian dispersive transport of strontium in laboratory-scale columns: Modelling and evaluation

    Science.gov (United States)

    Liu, Dongxu; Jivkov, Andrey P.; Wang, Lichun; Si, Gaohua; Yu, Jing

    2017-06-01

    In the context of environmental remediation of contaminated sites and safety assessment of nuclear waste disposal in the near-surface zone, we investigate the leaching and non-Fickian dispersive migration with sorption of strontium (mocking strontium-90) through columns packed with sand and clay. Analysis is based on breakthrough curves (BTCs) from column experiments, which simulated rainfall infiltration and source term release scenario, rather than applying constant tracer solution at the inlet as commonly used. BTCs are re-evaluated and transport parameters are estimated by inverse modelling using two approaches: (1) equilibrium advection-dispersion equation (ADE); and (2) continuous time random walk (CTRW). Firstly, based on a method for calculating leach concentration, the inlet condition with an exponential decay input is identified. Secondly, the results show that approximately 39%-58% of Br- and 16%-49% of Sr2+ are eluted from the columns at the end of the breakthrough experiments. This suggests that trapping mechanisms, including diffusion into immobile zones and attachment of tracer on mineral surfaces, are more pronounced for Sr2+ than for Br-. Thirdly, we demonstrate robustness of CTRW-based truncated power-law (TPL) model in capturing non-Fickian reactive transport with 0 2. The non-Fickian dispersion observed experimentally is explained by variations of local flow field from preferential flow paths due to physical heterogeneities. Particularly, the additional sorption process of strontium on clay minerals contributes to the delay of the peak concentration and the tailing features, which leads to an enhanced non-Fickian transport for strontium. Finally, the ADE and CTRW approaches to environmental modelling are evaluated. It is shown that CTRW with a sorption term can describe non-Fickian dispersive transport of strontium at laboratory scale by identifying appropriate parameters, while the traditional ADE with a retardation factor fails to reproduce

  7. Numerical modeling of disperse material evaporation in axisymmetric thermal plasma reactor

    Directory of Open Access Journals (Sweden)

    Stefanović Predrag Lj.

    2003-01-01

    Full Text Available A numerical 3D Euler-Lagrangian stochastic-deterministic (LSD model of two-phase flow laden with solid particles was developed. The model includes the relevant physical effects, namely phase interaction, panicle dispersion by turbulence, lift forces, particle-particle collisions, particle-wall collisions, heat and mass transfer between phases, melting and evaporation of particles, vapour diffusion in the gas flow. It was applied to simulate the processes in thermal plasma reactors, designed for the production of the ceramic powders. Paper presents results of extensive numerical simulation provided (a to determine critical mechanism of interphase heat and mass transfer in plasma flows, (b to show relative influence of some plasma reactor parameters on solid precursor evaporation efficiency: 1 - inlet plasma temperature, 2 - inlet plasma velocity, 3 - particle initial diameter, 4 - particle injection angle a, and 5 - reactor wall temperature, (c to analyze the possibilities for high evaporation efficiency of different starting solid precursors (Si, Al, Ti, and B2O3 powder, and (d to compare different plasma reactor configurations in conjunction with disperse material evaporation efficiency.

  8. Estimation of the environmental impact of emissions from the La Reina NEC, by atmospheric dispersion modeling

    International Nuclear Information System (INIS)

    Bustamante C, Paula M.; Ortiz R, Marcela A.

    1996-01-01

    Based on a dispersion model, an accidental release of radioactive material to the atmosphere was simulated. To evaluate the consequences of the accidental release it was used the P C COSYMA program (KfK and NRPB). The atmospheric dispersion model was MUSEMET, a segmented Gaussian plume model which requires information on meteorological conditions for a period of one year. This study was carried out to determine the plume's behavior and path, and to define protective actions. The meteorological analysis shows an airflow from the WSW and a channeling flow from the S E at night, due to topographical influences. (author)

  9. Modeling of response, socioeconomic, and natural resource damage costs for hypothetical oil spill scenarios in San Francisco Bay

    International Nuclear Information System (INIS)

    Etkin, D.S.; French McCay, D.; Whittier, N.; Sankaranarayanan, S.; Jennings, J.

    2002-01-01

    A study was conducted to determine the influence of oil type, spill size, response strategy and location factors on oil spill response costs, with particular reference to the cost benefits of the use of dispersants. Modeling has been conducted for a hypothetical oil spill in San Francisco Bay to determine biological impacts, damages to natural resources and response costs. The SIMAP modeling software by the Applied Science Associates was used to model 3 spill sizes (20, 50 and 95 percentile by volume) and 4 types of oil (gasoline, diesel, heavy fuel oil, and crude oil). Response costs, natural resource damages and socioeconomic impact were determined based on spill trajectory and fate. Mechanical recovery-based operations carry higher response costs than dispersant-based operations. Response costs for diesel and gasoline spills make up 20 per cent of the total costs, compared to 43 per cent for crude and heavy fuel oil spills. Damages to natural resources are higher for spills of toxic lighter fuels such as gasoline and diesel because gasoline has a greater impact on the water column with less shoreline oiling, resulting in more damages to natural resources. Heavier oils have a greater impact on shorelines and higher response and socioeconomic costs. Although socioeconomic costs varied by location, they tend to be greater than response costs and natural resource damage costs. Proportions of the different costs were described with reference to various spill factors. Socioeconomic costs are 61, 76, 45 and 53 per cent respectively for gasoline, diesel, crude oil, and heavy fuel oil spills. 27 refs., 23 tabs., 5 figs

  10. Modeling skull's acoustic attenuation and dispersion on photoacoustic signal

    Science.gov (United States)

    Mohammadi, L.; Behnam, H.; Nasiriavanaki, M. R.

    2017-03-01

    Despite the great promising results of a recent new transcranial photoacoustic brain imaging technology, it has been shown that the presence of the skull severely affects the performance of this imaging modality. In this paper, we investigate the effect of skull on generated photoacoustic signals with a mathematical model. The developed model takes into account the frequency dependence attenuation and acoustic dispersion effects occur with the wave reflection and refraction at the skull surface. Numerical simulations based on the developed model are performed for calculating the propagation of photoacoustic waves through the skull. From the simulation results, it was found that the skull-induced distortion becomes very important and the reconstructed image would be strongly distorted without correcting these effects. In this regard, it is anticipated that an accurate quantification and modeling of the skull transmission effects would ultimately allow for skull aberration correction in transcranial photoacoustic brain imaging.

  11. Modeling of high-density U-MO dispersion fuel plate performance

    International Nuclear Information System (INIS)

    Hayes, S.L.; Meyer, M.K.; Hofman, G.L.; Rest, J.; Snelgrove, J.L.

    2002-01-01

    Results from postirradiation examinations (PIE) of highly loaded U-Mo/Al dispersion fuel plates over the past several years have shown that the interaction between the metallic fuel particles and the matrix aluminum can be extensive, reducing the volume of the high-conductivity matrix phase and producing a significant volume of low-conductivity reaction-product phase. This phenomenon results in a significant decrease in fuel meat thermal conductivity during irradiation. PIE has further shown that the fuel-matrix interaction rate is a sensitive function of irradiation temperature. The interplay between fuel temperature and fuel-matrix interaction makes the development of a simple empirical correlation between the two difficult. For this reason a comprehensive thermal model has been developed to calculate temperatures throughout the fuel plate over its lifetime, taking into account the changing volume fractions of fuel, matrix and reaction-product phases within the fuel meat owing to fuel-matrix interaction; this thermal model has been incorporated into the dispersion fuel performance code designated PLATE. Other phenomena important to fuel thermal performance that are also treated in PLATE include: gas generation and swelling in the fuel and reaction-product phases, incorporation of matrix aluminum into solid solution with the unreacted metallic fuel particles, matrix extrusion resulting from fuel swelling, and cladding corrosion. The phenomena modeled also make possible a prediction of fuel plate swelling. This paper presents a description of the models and empirical correlations employed within PLATE as well as validation of code predictions against fuel performance data for U-Mo experimental fuel plates from the RERTR-3 irradiation test. (author)

  12. Comparative Risk Assessment of spill response options for a deepwater oil well blowout: Part 1. Oil spill modeling.

    Science.gov (United States)

    French-McCay, Deborah; Crowley, Deborah; Rowe, Jill J; Bock, Michael; Robinson, Hilary; Wenning, Richard; Walker, Ann Hayward; Joeckel, John; Nedwed, Tim J; Parkerton, Thomas F

    2018-05-31

    Oil spill model simulations of a deepwater blowout in the Gulf of Mexico De Soto Canyon, assuming no intervention and various response options (i.e., subsea dispersant injection SSDI, in addition to mechanical recovery, in-situ burning, and surface dispersant application) were compared. Predicted oil fate, amount and area of surfaced oil, and exposure concentrations in the water column above potential effects thresholds were used as inputs to a Comparative Risk Assessment to identify response strategies that minimize long-term impacts. SSDI reduced human and wildlife exposure to volatile organic compounds; dispersed oil into a large water volume at depth; enhanced biodegradation; and reduced surface water, nearshore and shoreline exposure to floating oil and entrained/dissolved oil in the upper water column. Tradeoffs included increased oil exposures at depth. However, since organisms are less abundant below 200 m, results indicate that overall exposure of valued ecosystem components was minimized by use of SSDI. Copyright © 2018 Elsevier Ltd. All rights reserved.

  13. Equilibrium-eulerian les model for turbulent poly-dispersed particle-laden flow

    KAUST Repository

    Icardi, Matteo; Marchisio, Daniele Luca; Chidambaram, Narayanan; Fox, Rodney O.

    2013-01-01

    An efficient Eulerian method for poly-dispersed particles in turbulent flows is implemented, verified and validated for a channel flow. The approach couples a mixture model with a quadrature-based moment method for the particle size distribution in a LES framework, augmented by an approximate deconvolution method to reconstructs the unfiltered velocity. The particle velocity conditioned on particle size is calculated with an equilibrium model, valid for low Stokes numbers. A population balance equation is solved with the direct quadrature method of moments, that efficiently represents the continuous particle size distribution. In this first study particulate processes are not considered and the capability of the model to properly describe particle transport is investigated for a turbulent channel flow. First, single-phase LES are validated through comparison with DNS. Then predictions for the two-phase system, with particles characterised by Stokes numbers ranging from 0.2 to 5, are compared with Lagrangian DNS in terms of particle velocity and accumulation at the walls. Since this phenomenon (turbophoresis) is driven by turbulent fluctuations and depends strongly on the particle Stokes number, the approximation of the particle size distribution, the choice of the sub-grid scale model and the use of an approximate deconvolution method are important to obtain good results. Our method can be considered as a fast and efficient alternative to classical Lagrangian methods or Eulerian multi-fluid models in which poly-dispersity is usually neglected.

  14. Equilibrium-eulerian les model for turbulent poly-dispersed particle-laden flow

    KAUST Repository

    Icardi, Matteo

    2013-04-01

    An efficient Eulerian method for poly-dispersed particles in turbulent flows is implemented, verified and validated for a channel flow. The approach couples a mixture model with a quadrature-based moment method for the particle size distribution in a LES framework, augmented by an approximate deconvolution method to reconstructs the unfiltered velocity. The particle velocity conditioned on particle size is calculated with an equilibrium model, valid for low Stokes numbers. A population balance equation is solved with the direct quadrature method of moments, that efficiently represents the continuous particle size distribution. In this first study particulate processes are not considered and the capability of the model to properly describe particle transport is investigated for a turbulent channel flow. First, single-phase LES are validated through comparison with DNS. Then predictions for the two-phase system, with particles characterised by Stokes numbers ranging from 0.2 to 5, are compared with Lagrangian DNS in terms of particle velocity and accumulation at the walls. Since this phenomenon (turbophoresis) is driven by turbulent fluctuations and depends strongly on the particle Stokes number, the approximation of the particle size distribution, the choice of the sub-grid scale model and the use of an approximate deconvolution method are important to obtain good results. Our method can be considered as a fast and efficient alternative to classical Lagrangian methods or Eulerian multi-fluid models in which poly-dispersity is usually neglected.

  15. A compressible two-phase model for dispersed particle flows with application from dense to dilute regimes

    Energy Technology Data Exchange (ETDEWEB)

    McGrath, Thomas P., E-mail: thomas.p.mcgrath@navy.mil [Naval Surface Warfare Center Indian Head Explosive Ordnance Disposal Technology Division, 4013 Fowler Rd., Indian Head, Maryland 20640 (United States); St Clair, Jeffrey G. [Naval Surface Warfare Center Indian Head Explosive Ordnance Disposal Technology Division, 4013 Fowler Rd., Indian Head, Maryland 20640 (United States); Department of Mechanical and Aerospace Engineering, University of Florida, 231 MAE-A, P.O. Box 116250, Gainesville, Florida 32611 (United States); Balachandar, S. [Department of Mechanical and Aerospace Engineering, University of Florida, 231 MAE-A, P.O. Box 116250, Gainesville, Florida 32611 (United States)

    2016-05-07

    Multiphase flows are present in many important fields ranging from multiphase explosions to chemical processing. An important subset of multiphase flow applications involves dispersed materials, such as particles, droplets, and bubbles. This work presents an Eulerian–Eulerian model for multiphase flows containing dispersed particles surrounded by a continuous media such as air or water. Following a large body of multiphase literature, the driving force for particle acceleration is modeled as a direct function of both the continuous-phase pressure gradient and the gradient of intergranular stress existing within the particle phase. While the application of these two components of driving force is well accepted in much of the literature, other models exist in which the particle-phase pressure gradient itself drives particle motion. The multiphase model treats all phases as compressible and is derived to ensure adherence to the 2nd Law of Thermodynamics. The governing equations are presented and discussed, and a characteristic analysis shows the model to be hyperbolic, with a degeneracy in the case that the intergranular stress, which is modeled as a configuration pressure, is zero. Finally, results from a two sample problems involving shock-induced particle dispersion are presented. The results agree well with experimental measurements, providing initial confidence in the proposed model.

  16. Dispersion model for airborne particulates inside a building

    International Nuclear Information System (INIS)

    Perkins, W.C.; Stoddard, D.H.

    1985-01-01

    An empirical model has been developed for the spread of airborne radioactive particles after they are released inside a building. The model has been useful in performing safety analyses of actinide materials facilities at the Savannah River Plant (SRP). These facilities employ the multiple-air-zone concept; that is, ventilation air flows from rooms or areas of least radioactive material hazard, through zones of increasing hazard, to a treatment system. A composite of the data for dispersion of airborne activity during 12 actual case incidents at SRP forms the basis for this model. These incidents occurred during approximately 90 plant-years of experience at SRP with the chemical and metallurgical processing of purified neptunium and plutonium after their recovery from irradiated uranium. The model gives ratios of the airborne activity concentrations in rooms and corridors near the site of the release. The multiple-air-zone concept has been applied to many designs of nuclear facilities as a safety feature to limit the spread of airborne activity from a release. The model illustrates the limitations of this concept: it predicts an apparently anomalous behavior of airborne particulates; namely, a small migration against the flow of the ventilation air

  17. Uncoupling the effects of seed predation and seed dispersal by granivorous ants on plant population dynamics.

    Directory of Open Access Journals (Sweden)

    Xavier Arnan

    Full Text Available Secondary seed dispersal is an important plant-animal interaction, which is central to understanding plant population and community dynamics. Very little information is still available on the effects of dispersal on plant demography and, particularly, for ant-seed dispersal interactions. As many other interactions, seed dispersal by animals involves costs (seed predation and benefits (seed dispersal, the balance of which determines the outcome of the interaction. Separate quantification of each of them is essential in order to understand the effects of this interaction. To address this issue, we have successfully separated and analyzed the costs and benefits of seed dispersal by seed-harvesting ants on the plant population dynamics of three shrub species with different traits. To that aim a stochastic, spatially-explicit individually-based simulation model has been implemented based on actual data sets. The results from our simulation model agree with theoretical models of plant response dependent on seed dispersal, for one plant species, and ant-mediated seed predation, for another one. In these cases, model predictions were close to the observed values at field. Nonetheless, these ecological processes did not affect in anyway a third species, for which the model predictions were far from the observed values. This indicates that the balance between costs and benefits associated to secondary seed dispersal is clearly related to specific traits. This study is one of the first works that analyze tradeoffs of secondary seed dispersal on plant population dynamics, by disentangling the effects of related costs and benefits. We suggest analyzing the effects of interactions on population dynamics as opposed to merely analyzing the partners and their interaction strength.

  18. Experimental and Numerical Modelling of CO2 Atmospheric Dispersion in Hazardous Gas Emission Sites.

    Science.gov (United States)

    Gasparini, A.; sainz Gracia, A. S.; Grandia, F.; Bruno, J.

    2015-12-01

    Under stable atmospheric conditions and/or in presence of topographic depressions, CO2 concentrations can reach high values resulting in lethal effect to living organisms. The distribution of denser than air gases released from the underground is governed by gravity, turbulence and dispersion. Once emitted, the gas distribution is initially driven by buoyancy and a gas cloud accumulates on the ground (gravitational phase); with time the density gradient becomes less important due to dispersion or mixing and gas distribution is mainly governed by wind and atmospheric turbulence (passive dispersion phase). Natural analogues provide evidences of the impact of CO2 leakage. Dangerous CO2 concentration in atmosphere related to underground emission have been occasionally reported although the conditions favouring the persistence of such a concentration are barely studied.In this work, the dynamics of CO2 in the atmosphere after ground emission is assessed to quantify their potential risk. Two approaches have been followed: (1) direct measurement of air concentration in a natural emission site, where formation of a "CO2 lake" is common and (2) numerical atmospheric modelling. Two sites with different morphology were studied: (a) the Cañada Real site, a flat terrain in the Volcanic Field of Campo de Calatrava (Spain); (b) the Solforata di Pomezia site, a rough terrain in the Alban Hills Volcanic Region (Italy). The comparison between field data and model calculations reveal that numerical dispersion models are capable of predicting the formation of CO2 accumulation over the ground as a consequence of underground gas emission. Therefore, atmospheric modelling could be included as a valuable methodology in the risk assessment of leakage in natural degassing systems and in CCS projects. Conclusions from this work provide clues on whether leakage may be a real risk for humans and under which conditions this risk needs to be included in the risk assessment.

  19. A mechanistic Eulerian-Lagrangian model for dispersed flow film boiling

    International Nuclear Information System (INIS)

    Andreani, M.; Yadigaroglu, G.

    1991-01-01

    In this paper a new mechanistic model of heat transfer in the dispersed flow regime is presented. The usual assumptions that render most of the available models unsuitable for the analysis of the reflooding phase of the LOCA are discussed, and a two-dimensional time-independent numerical model is developed. The gas temperature field is solved in a fixed-grid (Eulerian) mesh, with the droplets behaving as mass and energy sources. The histories of a large number of computational droplets are followed in a Lagrangian frame, considering evaporation, break-up and interactions with the vapor and with the wall. comparisons of calculated wall and vapor temperatures with experimental data are shown for two reflooding tests

  20. Modeling Solution of Nonlinear Dispersive Partial Differential Equations using the Marker Method

    International Nuclear Information System (INIS)

    Lewandowski, Jerome L.V.

    2005-01-01

    A new method for the solution of nonlinear dispersive partial differential equations is described. The marker method relies on the definition of a convective field associated with the underlying partial differential equation; the information about the approximate solution is associated with the response of an ensemble of markers to this convective field. Some key aspects of the method, such as the selection of the shape function and the initial loading, are discussed in some details

  1. NOx dispersion modelling around roundabout in a small city, example from Hungary

    Science.gov (United States)

    Farkas, Orsolya; Rákai, Anikó; Czáder, Károly; Török, Ákos

    2013-04-01

    The present paper focuses on the modelling of pollutant distribution and dispersion in an urban region that is located in a moderately industrialized town of Hungary, Székesfehérvár, with a population of 100,000. The study area is located close to the city centre, with different housing styles and different building elevations. High-rise buildings with 10 floors to small houses with gardens are found in the modelled area. The roundabout has 5 access roads; three major ones and two minor ones with different geometries and traffic load. The traffic load of the roads was defined by traffic count, while for the meteorological characteristics wind-statistics were created. Additional input parameters were the ground plan and the elevation of buildings. To simulate the airflow and the dispersion of pollutants a Computational Fluid Dynamics code called MISKAM was used. The background concentration was taken from the dataset of a nearby air quality monitoring station. According to vehicle counting the 5 roads of the roundabout have very different loads from 12 vehicles to more than 412 vehicles/hour. Three different grid systems were applied ranging from half million to 5 million cells. The difference in the results related to grid density was also evaluated. Wind speed distribution, wind turbulence and building wake flow patterns were identified by using the model. With the help of the simulation the NOx flow and dispersion of pollutants around the roundabout can be estimated and the critical locations with higher pollution concentration are presented. The results of the modelling can be more generalized and used in the design of the layout, development, traffic-control and environmental aspects of roundabouts located in small urban areas.

  2. Description and validation of ERAD: An atmospheric dispersion model for high explosive detonations

    Energy Technology Data Exchange (ETDEWEB)

    Boughton, B.A.; DeLaurentis, J.M.

    1992-10-01

    The Explosive Release Atmospheric Dispersion (ERAD) model is a three-dimensional numerical simulation of turbulent atmospheric transport and diffusion. An integral plume rise technique is used to provide a description of the physical and thermodynamic properties of the cloud of warm gases formed when the explosive detonates. Particle dispersion is treated as a stochastic process which is simulated using a discrete time Lagrangian Monte Carlo method. The stochastic process approach permits a more fundamental treatment of buoyancy effects, calm winds and spatial variations in meteorological conditions. Computational requirements of the three-dimensional simulation are substantially reduced by using a conceptualization in which each Monte Carlo particle represents a small puff that spreads according to a Gaussian law in the horizontal directions. ERAD was evaluated against dosage and deposition measurements obtained during Operation Roller Coaster. The predicted contour areas average within about 50% of the observations. The validation results confirm the model`s representation of the physical processes.

  3. Modelling the long-term consequences of a hypothetical dispersal of radioactivity in an urban area including remediation alternatives

    International Nuclear Information System (INIS)

    Thiessen, K.M.; Andersson, K.G.; Batandjieva, B.; Cheng, J.-J.; Hwang, W.T.; Kaiser, J.C.; Kamboj, S.; Steiner, M.; Tomas, J.; Trifunovic, D.; Yu, C.

    2009-01-01

    The Urban Remediation Working Group of the International Atomic Energy Agency's EMRAS (Environmental Modelling for Radiation Safety) program was organized to address issues of remediation assessment modelling for urban areas contaminated with dispersed radionuclides. The present paper describes the second of two modelling exercises. This exercise was based on a hypothetical dispersal of radioactivity in an urban area from a radiological dispersal device, with reference surface contamination at selected sites used as the primary input information. Modelling endpoints for the exercise included radionuclide concentrations and external dose rates at specified locations, contributions to the dose rates from individual surfaces, and annual and cumulative external doses to specified reference individuals. Model predictions were performed for a 'no action' situation (with no remedial measures) and for selected countermeasures. The exercise provided an opportunity for comparison of three modelling approaches, as well as a comparison of the predicted effectiveness of various countermeasures in terms of their short-term and long-term effects on predicted doses to humans.

  4. A micromorphic model for monolayer hexagonal boron nitride with determined constitutive constants by phonon dispersions

    International Nuclear Information System (INIS)

    Zhang, Bin; Yang, Gang

    2014-01-01

    A two dimensional (2D) micromorphic model is developed for monolayer hexagonal boron nitride (h-BN). Theoretical expressions of phonon dispersions for 2D crystals are derived based on the simplified governing equations of specialized three dimensional micromorphic crystals. The constitutive constants of governing equations of the h-BN micromorphic model are determined, which is performed by fitting the available phonon dispersions data of experimental measurements and first-principles calculations with our theoretical expressions. The obtained Young’s modulus and Poisson’s ratio of h-BN are comparable with the results of ab initio calculations and inelastic x-ray scattering experiments, thus the constitutive relations of the h-BN model are verified, which also indicates that mechanical properties of monolayer h-BN could be characterized by our 2D micromorphic model

  5. Universal dispersion model for characterization of optical thin films over wide spectral range: Application to magnesium fluoride

    Science.gov (United States)

    Franta, Daniel; Nečas, David; Giglia, Angelo; Franta, Pavel; Ohlídal, Ivan

    2017-11-01

    Optical characterization of magnesium fluoride thin films is performed in a wide spectral range from far infrared to extreme ultraviolet (0.01-45 eV) utilizing the universal dispersion model. Two film defects, i.e. random roughness of the upper boundaries and defect transition layer at lower boundary are taken into account. An extension of universal dispersion model consisting in expressing the excitonic contributions as linear combinations of Gaussian and truncated Lorentzian terms is introduced. The spectral dependencies of the optical constants are presented in a graphical form and by the complete set of dispersion parameters that allows generating tabulated optical constants with required range and step using a simple utility in the newAD2 software package.

  6. Modeling the Dispersal of Spiny Lobster (Palinurus elephas Larvae: Implications for Future Fisheries Management and Conservation Measures

    Directory of Open Access Journals (Sweden)

    Paul Whomersley

    2018-03-01

    Full Text Available Knowledge of larval dispersal, population dynamics and connectivity in relation to the management and conservation of commercially important species is vital if existing fisheries are to remain sustainable into the future. Larval dispersal of the commercially exploited spiny lobster, Palinurus elephas, was modeled from Marine Protected Areas located in the southwest of England for a 16-month period using a General Individuals Transport Model (GITM. The model included physical particle advection based on current fields from a 3D hydrodynamics model and a larval behavior module. Our results demonstrate the overall dispersal patterns of P. elephas larvae and highlight populations capable of self-seeding and those which are seemingly reliant on larvae from more distant populations. The results indicate where further research may be required to fully understand how populations of P. elephas are maintained at regional, national and international scales while providing us with the opportunity to discuss the effectiveness of current approaches to conservation and fisheries management.

  7. Effects of chemical dispersants on oil physical properties and dispersion. Volume 1

    International Nuclear Information System (INIS)

    Khelifa, A.; Fingas, M.; Hollebone, B.P.; Brown, C.E.; Pjontek, D.

    2007-01-01

    Laboratory and field testing have shown that the dispersion of oil spilled in water is influenced by chemical dispersants via the modification of the interfacial properties of the oil, such as oil-brine interfacial tension (IFT). This study focused on new laboratory experiments that measured the effects on the physical properties and dispersion of oil, with particular reference to the effects of chemical dispersants on IFT and oil viscosity and the subsequent effects on oil droplet formation. Experiments were conducted at 15 degrees C using Arabian Medium, Alaska North Slope and South Louisiana crude and Corexit 9500 and Corexit 9527 chemical dispersants. The dispersants were denser than the 3 oils. The effect of IFT reduction on oil dispersion was measured and showed substantial reduction in the size and enhancement of the concentration of oil droplets in the water column. It was shown that the brine-oil IFT associated with the 3 crudes reduced to less than 3.6 mN/m with the application of the chemical dispersants, even at a low dispersant-to-oil ratio (DOR) value of 1:200. The use of chemical dispersants increased the viscosity of the dispersant-oil mixture up to 40 per cent over the neat crude oil. It was shown that for each mixing condition, an optimum value of DOR exists that provides for maximal dispersant effectiveness. The IFT reaches maximum reduction at optimum DOR. It was suggested that oil spill modelling can be improved with further study of IFT reduction with DOR and variations of critical micelle concentration with the type and solubility of chemical dispersant, oil type and oil to water ratio. 13 refs., 3 tabs., 7 figs

  8. NUMERICAL SOLUTION OF STEADY STATE DISPERSION FLOW MODEL FOR LACTOSE-LACTASE HYDROLYSIS WITH DIFFERENT KINETICS IN FIXED BED

    Directory of Open Access Journals (Sweden)

    OLAOSEBIKAN ABIDOYE OLAFADEHAN

    2010-06-01

    Full Text Available A detailed computational procedure for evaluating lactose hydrolysis with immobilized enzyme in a packed bed tubular reactor under dispersion flow conditions is presented. The dispersion flow model for lactose hydrolysis using different kinetics, taking cognizance of external mass transfer resistances, was solved by the method of orthogonal collocation. The reliability of model simulations was tested using experimental data from a laboratory packed bed column, where the -galactosidase of Kluyveromyces fragilis was immobilized on spherical chitosan beads. Comparison of the simulated results with experimental exit conversion shows that the dispersion flow model and using Michaelis-Menten kinetics with competitive product (galactose inhibition are appropriate to interpret the experimental results and simulate the process of lactose hydrolysis in a fixed bed.

  9. Recent developments in the atmospheric dispersion models to be used for regulatory purposes and in risk evaluation

    International Nuclear Information System (INIS)

    Graziani, G.

    1996-01-01

    Climatological models and those most widely used for risk evaluation are generally based on the classification of atmospheric turbulence according to the Pasquill-Gifford categories, and use the Gaussian solution of the dispersion equation. One of their main limitations is that they deal only with continuous or instantaneous (puff) emission. Furthermore, a discretisation in the definition of atmospheric turbulence is performed according to the Pasquill-Gifford categories. This can generate uncertainties, since partial information on the state of the atmosphere at the time of emission can lead to the choice of one category rather than another and consequently to select wrong dispersion parameters. Some of these limits, such as the assumption of flat or slowly varying terrain, and the choice of constant atmospheric conditions during the duration of the release, are intrinsic to the schematization required by these models. Other limitations, such as the finite duration of the emissions and the continuous variation of the physical quantities describing the effect of turbulence on dispersion parameters, can be overcome. This paper describes the possible improvements which can be made in the dispersion models used in regulating emissions in the atmosphere and to calculate the associated risk. In particular the turbulence is based on the definition of some physical quantities varying with continuity which can be easily deduced from simple observations at the meteorological station at release site. It then analyses the application of this approach to a simple dispersion model, which can take into account the finite and non-zero durations of accidental emissions

  10. Dispersion of coupled mode-gap cavities

    NARCIS (Netherlands)

    Lian, Jin; Sokolov, Sergei; Yuce, E.; Combrie, S.; de Rossi, A.; Mosk, Allard

    2015-01-01

    The dispersion of a coupled resonator optical waveguide made of photonic crystal mode-gap cavities is pronouncedly asymmetric. This asymmetry cannot be explained by the standard tight binding model. We show that the fundamental cause of the asymmetric dispersion is the inherent dispersive cavity

  11. Fate of dispersants associated with the deepwater horizon oil spill.

    Science.gov (United States)

    Kujawinski, Elizabeth B; Kido Soule, Melissa C; Valentine, David L; Boysen, Angela K; Longnecker, Krista; Redmond, Molly C

    2011-02-15

    Response actions to the Deepwater Horizon oil spill included the injection of ∼771,000 gallons (2,900,000 L) of chemical dispersant into the flow of oil near the seafloor. Prior to this incident, no deepwater applications of dispersant had been conducted, and thus no data exist on the environmental fate of dispersants in deepwater. We used ultrahigh resolution mass spectrometry and liquid chromatography with tandem mass spectrometry (LC/MS/MS) to identify and quantify one key ingredient of the dispersant, the anionic surfactant DOSS (dioctyl sodium sulfosuccinate), in the Gulf of Mexico deepwater during active flow and again after flow had ceased. Here we show that DOSS was sequestered in deepwater hydrocarbon plumes at 1000-1200 m water depth and did not intermingle with surface dispersant applications. Further, its concentration distribution was consistent with conservative transport and dilution at depth and it persisted up to 300 km from the well, 64 days after deepwater dispersant applications ceased. We conclude that DOSS was selectively associated with the oil and gas phases in the deepwater plume, yet underwent negligible, or slow, rates of biodegradation in the affected waters. These results provide important constraints on accurate modeling of the deepwater plume and critical geochemical contexts for future toxicological studies.

  12. Global atmospheric dispersion modelling after the Fukushima accident

    Energy Technology Data Exchange (ETDEWEB)

    Suh, K.S.; Youm, M.K.; Lee, B.G.; Min, B.I. [Korea Atomic Energy Research Institute (Korea, Republic of); Raul, P. [Universidad de Sevilla (Spain)

    2014-07-01

    A large amount of radioactive material was released to the atmosphere due to the Fukushima nuclear accident in March 2011. The radioactive materials released into the atmosphere were mostly transported to the Pacific Ocean, but some of them were fallen on the surface due to dry and wet depositions in the northwest area from the Fukushima nuclear site. Therefore, northwest part of the nuclear site was seriously contaminated and it was designated with the restricted zone within a radius of 20 ∼ 30 km around the Fukushima nuclear site. In the early phase of the accident from 11 March to 30 March, the radioactive materials were dispersed to an area of the inland and offshore of the nuclear site by the variations of the wind. After the Fukushima accident, the radionuclides were detected through the air monitoring in the many places over the world. The radioactive plume was transported to the east part off the site by the westerly jet stream. It had detected in the North America during March 17-21, in European countries during March 23-24, and in Asia during from March 24 to April 6, 2011. The radioactive materials were overall detected across the northern hemisphere passed by 15 ∼ 20 days after the accident. Three dimensional numerical model was applied to evaluate the dispersion characteristics of the radionuclides released into the air. Simulated results were compared with measurements in many places over the world. Comparative results had good agreements in some places, but they had a little differences in some locations. The difference between the calculations and measurements are due to the meteorological data and relatively coarse resolutions in the model. Some radioactive materials were measured in Philippines, Taiwan, Hon Kong and South Korea during from March 23-28. It inferred that it was directly transported from the Fukushima by the northeastern monsoon winds. This event was well represented in the numerical model. Generally, the simulations had a good

  13. The Whitham approach to dispersive shocks in systems with cubic–quintic nonlinearities

    KAUST Repository

    Crosta, M

    2012-09-12

    By employing a rigorous approach based on the Whitham modulation theory, we investigate dispersive shock waves arising in a high-order nonlinear Schrödinger equation with competing cubic and quintic nonlinear responses. This model finds important applications in both nonlinear optics and Bose–Einstein condensates. Our theory predicts the formation of dispersive shocks with totally controllable properties, encompassing both steering and compression effects. Numerical simulations confirm these results perfectly. Quite remarkably, shock tuning can be achieved in the regime of a very small high order, i.e. quintic, nonlinearity.

  14. The Whitham approach to dispersive shocks in systems with cubic–quintic nonlinearities

    KAUST Repository

    Crosta, M; Trillo, S; Fratalocchi, Andrea

    2012-01-01

    By employing a rigorous approach based on the Whitham modulation theory, we investigate dispersive shock waves arising in a high-order nonlinear Schrödinger equation with competing cubic and quintic nonlinear responses. This model finds important applications in both nonlinear optics and Bose–Einstein condensates. Our theory predicts the formation of dispersive shocks with totally controllable properties, encompassing both steering and compression effects. Numerical simulations confirm these results perfectly. Quite remarkably, shock tuning can be achieved in the regime of a very small high order, i.e. quintic, nonlinearity.

  15. A nonlinear model for frequency dispersion and DC intrinsic parameter extraction for GaN-based HEMT

    Science.gov (United States)

    Nguyen, Tung The-Lam; Kim, Sam-Dong

    2017-11-01

    We propose in this study a practical nonlinear model for the AlGaN/GaN high electron mobility transistors (HEMTs) to extract DC intrinsic transconductance (gmDC), output conductance (gdsDC), and electron mobility from the intrinsic parameter set measured at high frequencies. An excellent agreement in I-V characteristics of the model with a fitting error of 0.11% enables us successfully extract the gmDC, gdsDC, and the total transconductance dispersion. For this model, we also present a reliable analysis scheme wherein the frequency dispersion effect due regional surface states in AlGaN/GaN HEMTs is taken into account under various bias conditions.

  16. Dispersion in cylindrical channels on the laminar flow at low Fourier numbers.

    Science.gov (United States)

    Kucza, Witold; Dąbrowa, Juliusz; Nawara, Katarzyna

    2015-06-30

    A numerical solution of the uniform dispersion model in cylindrical channels at low Fourier numbers is presented. The presented setup allowed to eliminate experimental non-idealities interfering the laminar flow. Double-humped responses measured in a flow injection system with impedance detection agreed with those predicted by theory. Simulated concentration profiles as well as flow injection analysis (FIA) responses show the predictive and descriptive power of the numerical approach. A strong dependence of peak shapes on Fourier numbers, at its low values, makes the approach suitable for determination of diffusion coefficients. In the work, the uniform dispersion model coupled with the Levenberg-Marquardt method of optimization allowed to determine the salt diffusion coefficient for KCl, NaCl, KMnO4 and CuSO4 in water. The determined values (1.83, 1.53, 1.57 and 0.90)×10(-9)m(2)s(-1), respectively, agree well with the literature data. Copyright © 2015 Elsevier B.V. All rights reserved.

  17. Atmospheric Dispersion Models for the Calculation of Environmental Impact: A Comparative Study

    International Nuclear Information System (INIS)

    Caputo, Marcelo; Gimenez, Marcelo; Felicelli, Sergio; Schlamp, Miguel

    2000-01-01

    In this paper some new comparisons are presented between the codes AERMOD, HPDM and HYSPLIT.The first two are Gaussian stationary plume codes and they were developed to calculate environmental impact produced by chemical contaminants.HYSPLIT is a hybrid code because it uses a Lagrangian reference system to describe the transport of a puff center of mass and uses an Eulerian system to describe the dispersion within the puff.The meteorological and topographic data used in the present work were obtained from runs of the prognostic code RAMS, provided by NOAA. The emission was fixed in 0.3 g/s , 284 K and 0 m/s .The surface rough was fixed in 0.1m and flat terrain was considered.In order to analyze separate effects and to go deeper in the comparison, the meteorological data was split into two, depending on the atmospheric stability class (F to B), and the wind direction was fixed to neglect its contribution to the contaminant dispersion.The main contribution of this work is to provide recommendations about the validity range of each code depending on the model used.In the case of Gaussian models the validity range is fixed by the distance in which the atmospheric condition can be consider homogeneous.In the other hand the validity range of HYSPLIT's model is determined by the spatial extension of the meteorological data.The results obtained with the three codes are comparable if the emission is in equilibrium with the environment.This means that the gases were emitted at the same temperature of the medium with zero velocity.There was an important difference between the dispersion parameters used by the Gaussian codes

  18. Assessing vanadium and arsenic exposure of people living near a petrochemical complex with two-stage dispersion models

    International Nuclear Information System (INIS)

    Chio, Chia-Pin; Yuan, Tzu-Hsuen; Shie, Ruei-Hao; Chan, Chang-Chuan

    2014-01-01

    Highlights: • Two-stage dispersion models can estimate exposures to hazardous air pollutants. • Spatial distribution of V levels is derived for sources without known emission rates. • A distance-to-source gradient is found for V levels from a petrochemical complex. • Two-stage dispersion is useful for modeling air pollution in resource-limited areas. - Abstract: The goal of this study is to demonstrate that it is possible to construct a two-stage dispersion model empirically for the purpose of estimating air pollution levels in the vicinity of petrochemical plants. We studied oil refineries and coal-fired power plants in the No. 6 Naphtha Cracking Complex, an area of 2,603-ha situated on the central west coast of Taiwan. The pollutants targeted were vanadium (V) from oil refineries and arsenic (As) from coal-fired power plants. We applied a backward fitting method to determine emission rates of V and As, with 192 PM 10 filters originally collected between 2009 and 2012. Our first-stage model estimated emission rates of V and As (median and 95% confidence intervals at 0.0202 (0.0040–0.1063) and 0.1368 (0.0398–0.4782) g/s, respectively. In our second stage model, the predicted zone-average concentrations showed a strong correlation with V, but a poor correlation with As. Our findings show that two-stage dispersion models are relatively precise for estimating V levels at residents’ addresses near the petrochemical complex, but they did not work as well for As levels. In conclusion, our model-based approach can be widely used for modeling exposure to air pollution from industrial areas in countries with limited resources

  19. A Semi-Analytical Model for Dispersion Modelling Studies in the Atmospheric Boundary Layer

    Science.gov (United States)

    Gupta, A.; Sharan, M.

    2017-12-01

    The severe impact of harmful air pollutants has always been a cause of concern for a wide variety of air quality analysis. The analytical models based on the solution of the advection-diffusion equation have been the first and remain the convenient way for modeling air pollutant dispersion as it is easy to handle the dispersion parameters and related physics in it. A mathematical model describing the crosswind integrated concentration is presented. The analytical solution to the resulting advection-diffusion equation is limited to a constant and simple profiles of eddy diffusivity and wind speed. In practice, the wind speed depends on the vertical height above the ground and eddy diffusivity profiles on the downwind distance from the source as well as the vertical height. In the present model, a method of eigen-function expansion is used to solve the resulting partial differential equation with the appropriate boundary conditions. This leads to a system of first order ordinary differential equations with a coefficient matrix depending on the downwind distance. The solution of this system, in general, can be expressed in terms of Peano-baker series which is not easy to compute, particularly when the coefficient matrix becomes non-commutative (Martin et al., 1967). An approach based on Taylor's series expansion is introduced to find the numerical solution of first order system. The method is applied to various profiles of wind speed and eddy diffusivities. The solution computed from the proposed methodology is found to be efficient and accurate in comparison to those available in the literature. The performance of the model is evaluated with the diffusion datasets from Copenhagen (Gryning et al., 1987) and Hanford (Doran et al., 1985). In addition, the proposed method is used to deduce three dimensional concentrations by considering the Gaussian distribution in crosswind direction, which is also evaluated with diffusion data corresponding to a continuous point source.

  20. Dispersion relations in the noncommutative φ3 and Wess-Zumino model in the Yang-Feldman formalism

    International Nuclear Information System (INIS)

    Doescher, C.; Zahn, J.

    2006-05-01

    We study dispersion relations in the noncommutative φ 3 and Wess-Zumino model in the Yang-Feldman formalism at one-loop order. Non-planar graphs lead to a distortion of the dispersion relation. We find that this effect is small if the scale of noncommutativity is identified with the Planck scale and parameters typical for a Higgs field are employed. (Orig.)

  1. Density-Dependent Formulation of Dispersion-Repulsion Interactions in Hybrid Multiscale Quantum/Molecular Mechanics (QM/MM) Models.

    Science.gov (United States)

    Curutchet, Carles; Cupellini, Lorenzo; Kongsted, Jacob; Corni, Stefano; Frediani, Luca; Steindal, Arnfinn Hykkerud; Guido, Ciro A; Scalmani, Giovanni; Mennucci, Benedetta

    2018-03-13

    Mixed multiscale quantum/molecular mechanics (QM/MM) models are widely used to explore the structure, reactivity, and electronic properties of complex chemical systems. Whereas such models typically include electrostatics and potentially polarization in so-called electrostatic and polarizable embedding approaches, respectively, nonelectrostatic dispersion and repulsion interactions are instead commonly described through classical potentials despite their quantum mechanical origin. Here we present an extension of the Tkatchenko-Scheffler semiempirical van der Waals (vdW TS ) scheme aimed at describing dispersion and repulsion interactions between quantum and classical regions within a QM/MM polarizable embedding framework. Starting from the vdW TS expression, we define a dispersion and a repulsion term, both of them density-dependent and consistently based on a Lennard-Jones-like potential. We explore transferable atom type-based parametrization strategies for the MM parameters, based on either vdW TS calculations performed on isolated fragments or on a direct estimation of the parameters from atomic polarizabilities taken from a polarizable force field. We investigate the performance of the implementation by computing self-consistent interaction energies for the S22 benchmark set, designed to represent typical noncovalent interactions in biological systems, in both equilibrium and out-of-equilibrium geometries. Overall, our results suggest that the present implementation is a promising strategy to include dispersion and repulsion in multiscale QM/MM models incorporating their explicit dependence on the electronic density.

  2. Discontinuous Galerkin Time-Domain Modeling of Graphene Nano-Ribbon Incorporating the Spatial Dispersion Effects

    KAUST Repository

    Li, Ping; Jiang, Li Jun; Bagci, Hakan

    2018-01-01

    It is well known that graphene demonstrates spatial dispersion properties, i.e., its conductivity is nonlocal and a function of spectral wave number (momentum operator) q. In this paper, to account for effects of spatial dispersion on transmission of high speed signals along graphene nano-ribbon (GNR) interconnects, a discontinuous Galerkin time-domain (DGTD) algorithm is proposed. The atomically-thick GNR is modeled using a nonlocal transparent surface impedance boundary condition (SIBC) incorporated into the DGTD scheme. Since the conductivity is a complicated function of q (and one cannot find an analytical Fourier transform pair between q and spatial differential operators), an exact time domain SIBC model cannot be derived. To overcome this problem, the conductivity is approximated by its Taylor series in spectral domain under low-q assumption. This approach permits expressing the time domain SIBC in the form of a second-order partial differential equation (PDE) in current density and electric field intensity. To permit easy incorporation of this PDE with the DGTD algorithm, three auxiliary variables, which degenerate the second-order (temporal and spatial) differential operators to first-order ones, are introduced. Regarding to the temporal dispersion effects, the auxiliary differential equation (ADE) method is utilized to eliminates the expensive temporal convolutions. To demonstrate the applicability of the proposed scheme, numerical results, which involve characterization of spatial dispersion effects on the transfer impedance matrix of GNR interconnects, are presented.

  3. Discontinuous Galerkin Time-Domain Modeling of Graphene Nano-Ribbon Incorporating the Spatial Dispersion Effects

    KAUST Repository

    Li, Ping

    2018-04-13

    It is well known that graphene demonstrates spatial dispersion properties, i.e., its conductivity is nonlocal and a function of spectral wave number (momentum operator) q. In this paper, to account for effects of spatial dispersion on transmission of high speed signals along graphene nano-ribbon (GNR) interconnects, a discontinuous Galerkin time-domain (DGTD) algorithm is proposed. The atomically-thick GNR is modeled using a nonlocal transparent surface impedance boundary condition (SIBC) incorporated into the DGTD scheme. Since the conductivity is a complicated function of q (and one cannot find an analytical Fourier transform pair between q and spatial differential operators), an exact time domain SIBC model cannot be derived. To overcome this problem, the conductivity is approximated by its Taylor series in spectral domain under low-q assumption. This approach permits expressing the time domain SIBC in the form of a second-order partial differential equation (PDE) in current density and electric field intensity. To permit easy incorporation of this PDE with the DGTD algorithm, three auxiliary variables, which degenerate the second-order (temporal and spatial) differential operators to first-order ones, are introduced. Regarding to the temporal dispersion effects, the auxiliary differential equation (ADE) method is utilized to eliminates the expensive temporal convolutions. To demonstrate the applicability of the proposed scheme, numerical results, which involve characterization of spatial dispersion effects on the transfer impedance matrix of GNR interconnects, are presented.

  4. Comparison of numerical models for calculating dispersion from accidental releases of pollutants

    Energy Technology Data Exchange (ETDEWEB)

    Pepper, D W [Savannah River Lab., Aiken, SC; Cooper, R E; Baker, A J

    1982-01-01

    A modular, data-based system approach has been developed to facilitate computational simulation of multi-dimensional pollutant dispersion in atmospheric, steam, estuary, and groundwater applications. This system is used to assess effects of accidental releases of pollutants to the environment. Model sophistication ranges from simple statistical to complex three-dimensional numerical methods. The system used specifies desired degree of model sophistication from a terminal. The model used depends on the particular type of problem being solved, and on a basis of merit related to computer cost. The results of prediction for several model problems are presented.

  5. Development and application of dispersive soft ferrite models for time-domain simulation

    International Nuclear Information System (INIS)

    DeFord, J.F.; Kamin, G.; Craig, G.D.; Walling, L.

    1992-01-01

    Ferrite has a variety of applications in accelerator components, and the capability to model this magnetic material in the time domain is an important adjunct to currently available accelerator modeling tool. We describe in this report a material model we have developed for the magnetic characteristics of PE11BL, the ferrite found in the ETA-II (Experimental Test Accelerator-II) induction module. This model, which includes the important magnetic dispersion effects found in most soft ferrites, has been implemented in 1-D and 2-D finite-difference time-domain (FDTD) electromagnetic simulators, and comparisons with analytic and experimental results are presented

  6. Modelling of marine radionuclide dispersion in IAEA MODARIA program: Lessons learnt from the Baltic Sea and Fukushima scenarios

    Energy Technology Data Exchange (ETDEWEB)

    Periáñez, R., E-mail: rperianez@us.es [Dpt Física Aplicada I, ETSIA, Universidad de Sevilla, Ctra Utrera km 1, 41013-Sevilla (Spain); Bezhenar, R. [Ukrainian Center of Environmental and Water Projects, Glushkov av., 42, Kiev 03187 (Ukraine); Brovchenko, I. [Institute of Mathematical Machine and System Problems, Glushkov av., 42, Kiev 03187 (Ukraine); Duffa, C. [Institut de Radioprotection et de Sûreté Nucléaire, BP 330, 83507 La Seyne sur Mer (France); Iosjpe, M. [Norwegian Radiation Protection Authority, Grini næringspark 13, NO-1332, Østerås (Norway); Jung, K.T. [Korea Institute of Ocean Science and Technology, 787 Hean-ro, Sangnok-gu, Ansan-si, Gyeonggi-do, 426-744 (Korea, Republic of); Kobayashi, T. [Japan Atomic Energy Agency, 2-4 Shirakata Shirane, Tokai, Ibaraki 319-1195 (Japan); Lamego, F. [Instituto de Engenheria Nuclear, Rua Hélio de Almeida 75, Ilha do Fundão, CEP 21941-906 Rio de Janeiro (Brazil); Maderich, V. [Institute of Mathematical Machine and System Problems, Glushkov av., 42, Kiev 03187 (Ukraine); Min, B.I. [Korea Atomic Energy Research Institute, Daedeok-Daero 989-111, Yuseong-Gu, Daejeon (Korea, Republic of); Nies, H. [Bundesamt fuer Seeschifffahrt und Hydrographie, Bernhard-Nocht-Str. 78, 20359 Hamburg (Germany); Osvath, I. [International Atomic Energy Agency Environment Laboratories, 4a Quai Antoine 1er, MC-98000 (Monaco); Outola, I. [Radiation and Nuclear Safety Authority, Laippatie 4, 00880 Helsinki (Finland); Psaltaki, M. [National Technical University of Athens, Iroon Polytexneiou 9, 15780 Zografou (Greece); and others

    2016-11-01

    State-of-the art dispersion models were applied to simulate {sup 137}Cs dispersion from Chernobyl nuclear power plant disaster fallout in the Baltic Sea and from Fukushima Daiichi nuclear plant releases in the Pacific Ocean after the 2011 tsunami. Models were of different nature, from box to full three-dimensional models, and included water/sediment interactions. Agreement between models was very good in the Baltic. In the case of Fukushima, results from models could be considered to be in acceptable agreement only after a model harmonization process consisting of using exactly the same forcing (water circulation and parameters) in all models. It was found that the dynamics of the considered system (magnitude and variability of currents) was essential in obtaining a good agreement between models. The difficulties in developing operative models for decision-making support in these dynamic environments were highlighted. Three stages which should be considered after an emergency, each of them requiring specific modelling approaches, have been defined. They are the emergency, the post-emergency and the long-term phases. - Highlights: • Models applied to simulate {sup 137}Cs marine dispersion after nuclear accidents. • Not good agreement initially found in highly dynamic environments. • Difficulties in developing models for decision making after emergencies highlighted.

  7. Derivation of simplified basic equations of gas-liquid two-phase dispersed flow based on two-fluid model

    International Nuclear Information System (INIS)

    Kataoka, Isao; Tomiyama, Akio

    2004-01-01

    The simplified and physically reasonable basic equations for the gas-liquid dispersed flow were developed based on some appropriate assumptions and the treatment of dispersed phase as isothermal rigid particles. Based on the local instant formulation of mass, momentum and energy conservation of the dispersed flow, time-averaged equations were obtained assuming that physical quantities in the dispersed phase are uniform. These assumptions are approximately valid when phase change rate and/or chemical reaction rate are not so large at gas-liquid interface and there is no heat generation in within the dispersed phase. Detailed discussions were made on the characteristics of obtained basic equations and physical meanings of terms consisting the basic equations. It is shown that, in the derived averaged momentum equation, the terms of pressure gradient and viscous momentum diffusion do not appear and, in the energy equation, the term of molecular thermal diffusion heat flux does not appear. These characteristics of the derived equations were shown to be very consistent concerning the physical interpretation of the gas-liquid dispersed flow. Furthermore, the obtained basic equations are consistent with experiments for the dispersed flow where most of averaged physical quantities are obtained assuming that the distributions of those are uniform within the dispersed phase. Investigation was made on the problem whether the obtained basic equations are well-posed or ill-posed for the initial value problem. The eigenvalues of the simplified mass and momentum equations are calculated for basic equations obtained here and previous two-fluid basic equations with one pressure model. Well-posedness and ill-posedness are judged whether the eigenvalues are real or imaginary. The result indicated the newly developed basic equations always constitute the well-posed initial value problem while the previous two-fluid basic equations based on one pressure model constitutes ill

  8. Validation of a two-dimensional pollutant dispersion model in an isolated street canyon

    Energy Technology Data Exchange (ETDEWEB)

    Chan, T.L.; Dong, G.; Leung, C.W.; Cheung, C.S. [The Hong Kong Polytechnic University, Kowloon (Hong Kong). Research Centre for Combustion and Pollution Control, Department of Mechanical Engineering; Hung, W.T. [The Hong Kong Polytechnic University, Kowloon (Hong Kong). Department of Civil and Structural Engineering

    2002-07-01

    A two-dimensional numerical model based on Reynolds-averaged Navier-Stokes equations coupled with a series of standard, Renormalization Group (RNG) and realizable k-{epsilon} turbulence models was developed to simulate the fluid-flow development and pollutant dispersion within an isolated street canyon using the FLUENT code. In the present study, the validation of the numerical model was evaluated using an extensive experimental database obtained from the atmospheric boundary layer wind tunnel at the Meteorological Institute of Hamburg University, Germany (J. Wind Eng. Ind. Aerodyn. 62 (1996) 37). Among the studied turbulence models, the RNG k-{epsilon} turbulence model was found to be the most optimum turbulence model coupled with the two-dimensional street canyon model developed in the present study. Both the calculated and measured dimensionless pollutant concentrations have been shown to be less dependent on the variation of wind speed and source strength conditions for the studied street canyon aspect ratio of the B/H=1 case. However, the street canyon configuration has significant influence on the pollutant dispersion. The wider street and lower height of the buildings are favorable to pollutant dilution within the street canyon. The fluid-flow development has demonstrated that the rotative vortex or vortices generated within the urban street canyon can transport the pollutants from a line source to the wall surfaces of the buildings. (author)

  9. Coexistence for an Almost Periodic Predator-Prey Model with Intermittent Predation Driven by Discontinuous Prey Dispersal

    Directory of Open Access Journals (Sweden)

    Yantao Luo

    2017-01-01

    Full Text Available An almost periodic predator-prey model with intermittent predation and prey discontinuous dispersal is studied in this paper, which differs from the classical continuous and impulsive dispersal predator-prey models. The intermittent predation behavior of the predator species only happens in the channels between two patches where the discontinuous migration movement of the prey species occurs. Using analytic approaches and comparison theorems of the impulsive differential equations, sufficient criteria on the boundedness, permanence, and coexistence for this system are established. Finally, numerical simulations demonstrate that, for an intermittent predator-prey model, both the intermittent predation and intrinsic growth rates of the prey and predator species can greatly impact the permanence, extinction, and coexistence of the population.

  10. Reactimeter dispersion equation

    OpenAIRE

    A.G. Yuferov

    2016-01-01

    The aim of this work is to derive and analyze a reactimeter metrological model in the form of the dispersion equation which connects reactimeter input/output signal dispersions with superimposed random noise at the inlet. It is proposed to standardize the reactimeter equation form, presenting the main reactimeter computing unit by a convolution equation. Hence, the reactimeter metrological characteristics are completely determined by this unit hardware function which represents a transient re...

  11. Probability density function shape sensitivity in the statistical modeling of turbulent particle dispersion

    Science.gov (United States)

    Litchford, Ron J.; Jeng, San-Mou

    1992-01-01

    The performance of a recently introduced statistical transport model for turbulent particle dispersion is studied here for rigid particles injected into a round turbulent jet. Both uniform and isosceles triangle pdfs are used. The statistical sensitivity to parcel pdf shape is demonstrated.

  12. Assimilating concentration observations for transport and dispersion modeling in a meandering wind field

    Science.gov (United States)

    Haupt, Sue Ellen; Beyer-Lout, Anke; Long, Kerrie J.; Young, George S.

    Assimilating concentration data into an atmospheric transport and dispersion model can provide information to improve downwind concentration forecasts. The forecast model is typically a one-way coupled set of equations: the meteorological equations impact the concentration, but the concentration does not generally affect the meteorological field. Thus, indirect methods of using concentration data to influence the meteorological variables are required. The problem studied here involves a simple wind field forcing Gaussian dispersion. Two methods of assimilating concentration data to infer the wind direction are demonstrated. The first method is Lagrangian in nature and treats the puff as an entity using feature extraction coupled with nudging. The second method is an Eulerian field approach akin to traditional variational approaches, but minimizes the error by using a genetic algorithm (GA) to directly optimize the match between observations and predictions. Both methods show success at inferring the wind field. The GA-variational method, however, is more accurate but requires more computational time. Dynamic assimilation of a continuous release modeled by a Gaussian plume is also demonstrated using the genetic algorithm approach.

  13. Enhanced air dispersion modelling at a typical Chinese nuclear power plant site: Coupling RIMPUFF with two advanced diagnostic wind models.

    Science.gov (United States)

    Liu, Yun; Li, Hong; Sun, Sida; Fang, Sheng

    2017-09-01

    An enhanced air dispersion modelling scheme is proposed to cope with the building layout and complex terrain of a typical Chinese nuclear power plant (NPP) site. In this modelling, the California Meteorological Model (CALMET) and the Stationary Wind Fit and Turbulence (SWIFT) are coupled with the Risø Mesoscale PUFF model (RIMPUFF) for refined wind field calculation. The near-field diffusion coefficient correction scheme of the Atmospheric Relative Concentrations in the Building Wakes Computer Code (ARCON96) is adopted to characterize dispersion in building arrays. The proposed method is evaluated by a wind tunnel experiment that replicates the typical Chinese NPP site. For both wind speed/direction and air concentration, the enhanced modelling predictions agree well with the observations. The fraction of the predictions within a factor of 2 and 5 of observations exceeds 55% and 82% respectively in the building area and the complex terrain area. This demonstrates the feasibility of the new enhanced modelling for typical Chinese NPP sites. Copyright © 2017 Elsevier Ltd. All rights reserved.

  14. Performance assessment of Large Eddy Simulation (LES) for modeling dispersion in an urban street canyon with tree planting

    NARCIS (Netherlands)

    Moonen, P.; Gromke, C.B.; Dorer, V.

    2013-01-01

    The potential of a Large Eddy Simulation (LES) model to reliably predict near-field pollutant dispersion is assessed. To that extent, detailed time-resolved numerical simulations of coupled flow and dispersion are conducted for a street canyon with tree planting. Different crown porosities are

  15. Progress in urban dispersion studies

    DEFF Research Database (Denmark)

    Batchvarova, E.; Gryning, Sven-Erik

    2006-01-01

    The present Study addresses recent achievements in better representation Of the urban area structure in meteorology and dispersion parameterisations. The setup and Main Outcome of several recent dispersion experiments in Urban areas and their use in model validation are discussed. The maximum con...

  16. Surfactant-assisted dispersion of carbon nanotubes: mechanism of stabilization and biocompatibility of the surfactant

    Science.gov (United States)

    Singh, Raman Preet; Jain, Sanyog; Ramarao, Poduri

    2013-10-01

    Nanoparticles (NPs) are thermodynamically unstable system and tend to aggregate to reduce free energy. The aggregation property of NPs results in inhomogeneous exposure of cells to NPs resulting in variable cellular responses. Several types of surfactants are used to stabilize NP dispersions and obtain homogenous dispersions. However, the effects of these surfactants, per se, on cellular responses are not completely known. The present study investigated the application of Pluronic F68 (PF68) for obtaining stable dispersion of NPs using carbon nanotubes as model NPs. PF68-stabilized NP suspensions are stable for long durations and do not show signs of aggregation or settling during storage or after autoclaving. The polyethylene oxide blocks in PF68 provide steric hindrance between adjacent NPs leading to stable NP dispersions. Further, PF68 is biocompatible in nature and does not affect integrity of mitochondria, lysosomes, DNA, and nuclei. Also, PF68 neither induce free radical or cytokine production nor does it interfere with cellular uptake mechanisms. The results of the present study suggest that PF68-assisted dispersion of NPs produced suspensions, which are stable after autoclaving. Further, PF68 does not interfere with normal physiological functions suggesting its application in nanomedicine and nanotoxicity evaluation.

  17. Surfactant-assisted dispersion of carbon nanotubes: mechanism of stabilization and biocompatibility of the surfactant

    International Nuclear Information System (INIS)

    Singh, Raman Preet; Jain, Sanyog; Ramarao, Poduri

    2013-01-01

    Nanoparticles (NPs) are thermodynamically unstable system and tend to aggregate to reduce free energy. The aggregation property of NPs results in inhomogeneous exposure of cells to NPs resulting in variable cellular responses. Several types of surfactants are used to stabilize NP dispersions and obtain homogenous dispersions. However, the effects of these surfactants, per se, on cellular responses are not completely known. The present study investigated the application of Pluronic F68 (PF68) for obtaining stable dispersion of NPs using carbon nanotubes as model NPs. PF68-stabilized NP suspensions are stable for long durations and do not show signs of aggregation or settling during storage or after autoclaving. The polyethylene oxide blocks in PF68 provide steric hindrance between adjacent NPs leading to stable NP dispersions. Further, PF68 is biocompatible in nature and does not affect integrity of mitochondria, lysosomes, DNA, and nuclei. Also, PF68 neither induce free radical or cytokine production nor does it interfere with cellular uptake mechanisms. The results of the present study suggest that PF68-assisted dispersion of NPs produced suspensions, which are stable after autoclaving. Further, PF68 does not interfere with normal physiological functions suggesting its application in nanomedicine and nanotoxicity evaluation

  18. Surfactant-assisted dispersion of carbon nanotubes: mechanism of stabilization and biocompatibility of the surfactant

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Raman Preet, E-mail: ramanpreetsingh@hotmail.com [Evalueserve SEZ (Gurgaon) Pvt. Ltd. (India); Jain, Sanyog [National Institute of Pharmaceutical Education and Research, Centre for Pharmaceutical Nanotechnology, Department of Pharmaceutics (India); Ramarao, Poduri, E-mail: ramaraop@yahoo.com [Central University of Punjab, School of Basic and Applied Sciences (India)

    2013-10-15

    Nanoparticles (NPs) are thermodynamically unstable system and tend to aggregate to reduce free energy. The aggregation property of NPs results in inhomogeneous exposure of cells to NPs resulting in variable cellular responses. Several types of surfactants are used to stabilize NP dispersions and obtain homogenous dispersions. However, the effects of these surfactants, per se, on cellular responses are not completely known. The present study investigated the application of Pluronic F68 (PF68) for obtaining stable dispersion of NPs using carbon nanotubes as model NPs. PF68-stabilized NP suspensions are stable for long durations and do not show signs of aggregation or settling during storage or after autoclaving. The polyethylene oxide blocks in PF68 provide steric hindrance between adjacent NPs leading to stable NP dispersions. Further, PF68 is biocompatible in nature and does not affect integrity of mitochondria, lysosomes, DNA, and nuclei. Also, PF68 neither induce free radical or cytokine production nor does it interfere with cellular uptake mechanisms. The results of the present study suggest that PF68-assisted dispersion of NPs produced suspensions, which are stable after autoclaving. Further, PF68 does not interfere with normal physiological functions suggesting its application in nanomedicine and nanotoxicity evaluation.

  19. The Dynamics of M15: Observations of the Velocity Dispersion Profile and Fokker-Planck Models

    Science.gov (United States)

    Dull, J. D.; Cohn, H. N.; Lugger, P. M.; Murphy, B. W.; Seitzer, P. O.; Callanan, P. J.; Rutten, R. G. M.; Charles, P. A.

    1997-05-01

    We report a new measurement of the velocity dispersion profile within 1' (3 pc) of the center of the globular cluster M15 (NGC 7078), using long-slit spectra from the 4.2 m William Herschel Telescope at La Palma Observatory. We obtained spatially resolved spectra for a total of 23 slit positions during two observing runs. During each run, a set of parallel slit positions was used to map out the central region of the cluster; the position angle used during the second run was orthogonal to that used for the first. The spectra are centered in wavelength near the Ca II infrared triplet at 8650 Å, with a spectral range of about 450 Å. We determined radial velocities by cross-correlation techniques for 131 cluster members. A total of 32 stars were observed more than once. Internal and external comparisons indicate a velocity accuracy of about 4 km s-1. The velocity dispersion profile rises from about σ = 7.2 +/- 1.4 km s-1 near 1' from the center of the cluster to σ = 13.9 +/- 1.8 km s-1 at 20". Inside of 20", the dispersion remains approximately constant at about 10.2 +/- 1.4 km s-1 with no evidence for a sharp rise near the center. This last result stands in contrast with that of Peterson, Seitzer, & Cudworth who found a central velocity dispersion of 25 +/- 7 km s-1, based on a line-broadening measurement. Our velocity dispersion profile is in good agreement with those determined in the recent studies of Gebhardt et al. and Dubath & Meylan. We have developed a new set of Fokker-Planck models and have fitted these to the surface brightness and velocity dispersion profiles of M15. We also use the two measured millisecond pulsar accelerations as constraints. The best-fitting model has a mass function slope of x = 0.9 (where 1.35 is the slope of the Salpeter mass function) and a total mass of 4.9 × 105 M⊙. This model contains approximately 104 neutron stars (3% of the total mass), the majority of which lie within 6" (0.2 pc) of the cluster center. Since the

  20. Sensitivity analysis of the near-road dispersion model RLINE - An evaluation at Detroit, Michigan

    Science.gov (United States)

    Milando, Chad W.; Batterman, Stuart A.

    2018-05-01

    The development of accurate and appropriate exposure metrics for health effect studies of traffic-related air pollutants (TRAPs) remains challenging and important given that traffic has become the dominant urban exposure source and that exposure estimates can affect estimates of associated health risk. Exposure estimates obtained using dispersion models can overcome many of the limitations of monitoring data, and such estimates have been used in several recent health studies. This study examines the sensitivity of exposure estimates produced by dispersion models to meteorological, emission and traffic allocation inputs, focusing on applications to health studies examining near-road exposures to TRAP. Daily average concentrations of CO and NOx predicted using the Research Line source model (RLINE) and a spatially and temporally resolved mobile source emissions inventory are compared to ambient measurements at near-road monitoring sites in Detroit, MI, and are used to assess the potential for exposure measurement error in cohort and population-based studies. Sensitivity of exposure estimates is assessed by comparing nominal and alternative model inputs using statistical performance evaluation metrics and three sets of receptors. The analysis shows considerable sensitivity to meteorological inputs; generally the best performance was obtained using data specific to each monitoring site. An updated emission factor database provided some improvement, particularly at near-road sites, while the use of site-specific diurnal traffic allocations did not improve performance compared to simpler default profiles. Overall, this study highlights the need for appropriate inputs, especially meteorological inputs, to dispersion models aimed at estimating near-road concentrations of TRAPs. It also highlights the potential for systematic biases that might affect analyses that use concentration predictions as exposure measures in health studies.

  1. Modelling of pollen dispersion in the atmosphere: evaluation with a continuous 1β+1δ lidar

    Science.gov (United States)

    Sicard, Michaël; Izquierdo, Rebeca; Jorba, Oriol; Alarcón, Marta; Belmonte, Jordina; Comerón, Adolfo; De Linares, Concepción; Baldasano, José Maria

    2018-04-01

    Pollen allergenicity plays an important role on human health and wellness. It is thus of large public interest to increase our knowledge of pollen grain behavior in the atmosphere (source, emission, processes involved during their transport, etc.) at fine temporal and spatial scales. First simulations with the Barcelona Supercomputing Center NMMB/BSC-CTM model of Platanus and Pinus dispersion in the atmosphere were performed during a 5-day pollination event observed in Barcelona, Spain, between 27 - 31 March, 2015. The simulations are compared to vertical profiles measured with the continuous Barcelona Micro Pulse Lidar system. First results show that the vertical distribution is well reproduced by the model in shape, but not in intensity, the model largely underestimating in the afternoon. Guidelines are proposed to improve the dispersion of airborne pollen by numerical prediction models.

  2. Behavioral tradeoffs when dispersing across a patchy landscape.

    Science.gov (United States)

    Patrick A. Zollner; Steven L. Lima

    2005-01-01

    A better understanding of the behavior of dispersing animals will assist in determining the factors that limit their success and ultimately help improve the way dispersal is incorporated into population models. To that end, we used a simulation model to investigate three questions about behavioral tradeoffs that dispersing animals might face: (i) speed of movement...

  3. Dispersion model for airborne radioactive particulates inside a process building

    International Nuclear Information System (INIS)

    Perkins, W.C.; Stoddard, D.H.

    1984-02-01

    An empirical model, predicting the spread of airborne radioactive particles after they are released inside a building, has been developed. The basis for this model is a composite of data for dispersion of airborne activity recorded during 12 case incidents. These incidents occurred at the Savannah River Plant (SRP) during approximately 90 plant-years of experience with the chemical and metallurgical processing of purified neptunium and plutonium. The model illustrates that the multiple-air-zone concept, used in the designs of many nuclear facilities, can be an efficient safety feature to limit the spread of airborne activity from a release. This study also provides some insight into an apparently anomalous behavior of airborne particulates, namely, their migration against the prevailing flow of ventilation air. 2 references, 12 figures, 4 tables

  4. Peer review CALMET/CALPUFF dispersion modelling analysis : Proposed Duke Point generation facility Georgia Strait Crossing pipeline

    International Nuclear Information System (INIS)

    2002-01-01

    A peer review of the air quality dispersion modeling analysis for the proposed gas-fired plant at Duke Point in the vicinity of Nanaimo, British Columbia was required, and SENES Consultants Limited (SENES) was commissioned to perform it. British Columbia Hydro had requested that Levelton Engineering Ltd. prepare an air quality impact assessment, and it was submitted to be included in Vancouver Island Generation Project (VIGP) permit application. This permit application was for the Joint Panel Review of the Georgia Strait Crossing Pipeline (GSX) Project and the British Columbia Environmental Assessment Office. The CALMET/CALPUFF Modelling System had been used by Levelton to conduct the air quality dispersion modelling analysis. Copies of the input and output files that had been used for the conduct of the modelling analysis were provided to SENES. The ability for SENES to reproduce the modelling results that had been published in the GSX application represented the first step in the peer review. This was accomplished by running the files received from Levelton into the CALMET/CALPUFF models. A detailed review of the methodology selected by Levelton during the conduct of the dispersion modelling analysis was then initiated by SENES. Some deficiencies were identified by SENES, despite concurrence with the overall conceptual approach adopted by Levelton. The deficiencies concerned meteorological data; startup, partial load and upset conditions; pollutant emissions; health risk assessment; cumulative impact on ambient particulate matter 10 concentrations; and collateral environmental impacts. refs., 2 tabs., 21 figs

  5. Numerical modeling of flow and pollutant dispersion in street canyons with tree planting

    NARCIS (Netherlands)

    Balczó, M.; Gromke, C.B.; Ruck, B.

    2009-01-01

    Numerical simulations of the impact of tree planting on airflow and traffic pollutant dispersion in urban street canyons have been performed using the commercial CFD (Computational Fluid Dynamics) code MISKAM. A k-e turbulence model including additional terms for the treatment of vegetation, has

  6. Spatially-varying surface roughness and ground-level air quality in an operational dispersion model

    International Nuclear Information System (INIS)

    Barnes, M.J.; Brade, T.K.; MacKenzie, A.R.; Whyatt, J.D.; Carruthers, D.J.; Stocker, J.; Cai, X.; Hewitt, C.N.

    2014-01-01

    Urban form controls the overall aerodynamic roughness of a city, and hence plays a significant role in how air flow interacts with the urban landscape. This paper reports improved model performance resulting from the introduction of variable surface roughness in the operational air-quality model ADMS-Urban (v3.1). We then assess to what extent pollutant concentrations can be reduced solely through local reductions in roughness. The model results suggest that reducing surface roughness in a city centre can increase ground-level pollutant concentrations, both locally in the area of reduced roughness and downwind of that area. The unexpected simulation of increased ground-level pollutant concentrations implies that this type of modelling should be used with caution for urban planning and design studies looking at ventilation of pollution. We expect the results from this study to be relevant for all atmospheric dispersion models with urban-surface parameterisations based on roughness. -- Highlights: • Spatially variable roughness improved performance of an operational model. • Scenario modelling explored effect of reduced roughness on air pollution. • Reducing surface roughness can increase modelled ground-level pollution. • Damped vertical mixing outweighs increased horizontal advection in model study. • Result should hold for any model with a land-surface coupling based on roughness. -- Spatially varying roughness improves model simulations of urban air pollutant dispersion. Reducing roughness does not always decrease ground-level pollution concentrations

  7. Measurement of Chromatic Dispersion using the Baseband Radio-Frequency Response of a Phase-Modulated Analog Optical Link Employing a Reference Fiber

    National Research Council Canada - National Science Library

    McKinney, Jason D; Diehl, John

    2007-01-01

    In this work we demonstrate a new technique for measuring the chromatic dispersion of an optical fiber using the baseband RF response of a phase-modulated analog optical link in concert with a well...

  8. Validation and comparison of dispersion models of RTARC DSS

    International Nuclear Information System (INIS)

    Duran, J.; Pospisil, M.

    2004-01-01

    RTARC DSS (Real Time Accident Release Consequences - Decision Support System) is a computer code developed at the VUJE Trnava, Inc. (Stubna, M. et al, 1993). The code calculations include atmospheric transport and diffusion, dose assessment, evaluation and displaying of the affected zones, evaluation of the early health effects, concentration and dose rate time dependence in the selected sites etc. The simulation of the protective measures (sheltering, iodine administration) is involved. The aim of this paper is to present the process of validation of the RTARC dispersion models. RTARC includes models for calculations of release for very short (Method Monte Carlo - MEMOC), short (Gaussian Straight-Line Model) and long distances (Puff Trajectory Model - PTM). Validation of the code RTARC was performed using the results of comparisons and experiments summarized in the Table 1.: 1. Experiments and comparisons in the process of validation of the system RTARC - experiments or comparison - distance - model. Wind tunnel experiments (Universitaet der Bundeswehr, Muenchen) - Area of NPP - Method Monte Carlo. INEL (Idaho National Engineering Laboratory) - short/medium - Gaussian model and multi tracer atmospheric experiment - distances - PTM. Model Validation Kit - short distances - Gaussian model. STEP II.b 'Realistic Case Studies' - long distances - PTM. ENSEMBLE comparison - long distances - PTM (orig.)

  9. Application of data assimilation to improve the forecasting capability of an atmospheric dispersion model for a radioactive plume

    International Nuclear Information System (INIS)

    Jeong, H.J.; Han, M.H.; Hwang, W.T.; Kim, E.H.

    2008-01-01

    Modeling an atmospheric dispersion of a radioactive plume plays an influential role in assessing the environmental impacts caused by nuclear accidents. The performance of data assimilation techniques combined with Gaussian model outputs and measurements to improve forecasting abilities are investigated in this study. Tracer dispersion experiments are performed to produce field data by assuming a radiological emergency. Adaptive neuro-fuzzy inference system (ANFIS) and linear regression filter are considered to assimilate the Gaussian model outputs with measurements. ANFIS is trained so that the model outputs are likely to be more accurate for the experimental data. Linear regression filter is designed to assimilate measurements similar to the ANFIS. It is confirmed that ANFIS could be an appropriate method for an improvement of the forecasting capability of an atmospheric dispersion model in the case of a radiological emergency, judging from the higher correlation coefficients between the measured and the assimilated ones rather than a linear regression filter. This kind of data assimilation method could support a decision-making system when deciding on the best available countermeasures for public health from among emergency preparedness alternatives

  10. Progress on Numerical Modeling of the Dispersion of Ceramic Nanoparticles During Ultrasonic Processing and Solidification of Al-Based Nanocomposites

    Science.gov (United States)

    Zhang, Daojie; Nastac, Laurentiu

    2016-12-01

    In present study, 6061- and A356-based nano-composites are fabricated by using the ultrasonic stirring technology (UST) in a coreless induction furnace. SiC nanoparticles are used as the reinforcement. Nanoparticles are added into the molten metal and then dispersed by ultrasonic cavitation and acoustic streaming assisted by electromagnetic stirring. The applied UST parameters in the current experiments are used to validate a recently developed magneto-hydro-dynamics (MHD) model, which is capable of modeling the cavitation and nanoparticle dispersion during UST processing. The MHD model accounts for turbulent fluid flow, heat transfer and solidification, and electromagnetic field, as well as the complex interaction between the nanoparticles and both the molten and solidified alloys by using ANSYS Maxwell and ANSYS Fluent. Molecular dynamics (MD) simulations are conducted to analyze the complex interactions between the nanoparticle and the liquid/solid interface. The current modeling results demonstrate that a strong flow can disperse the nanoparticles relatively well during molten metal and solidification processes. MD simulation results prove that ultrafine particles (10 nm) will be engulfed by the solidification front instead of being pushed, which is beneficial for nano-dispersion.

  11. Blackbody emission from light interacting with an effective moving dispersive medium.

    Science.gov (United States)

    Petev, M; Westerberg, N; Moss, D; Rubino, E; Rimoldi, C; Cacciatori, S L; Belgiorno, F; Faccio, D

    2013-07-26

    Intense laser pulses excite a nonlinear polarization response that may create an effective flowing medium and, under appropriate conditions, a blocking horizon for light. Here, we analyze in detail the interaction of light with such laser-induced flowing media, fully accounting for the medium dispersion properties. An analytical model based on a first Born approximation is found to be in excellent agreement with numerical simulations based on Maxwell's equations and shows that when a blocking horizon is formed, the stimulated medium scatters light with a blackbody emission spectrum. Based on these results, diamond is proposed as a promising candidate medium for future studies of Hawking emission from artificial, dispersive horizons.

  12. A collection of mathematical models for dispersion in surface water and groundwater

    International Nuclear Information System (INIS)

    Codell, R.B.; Key, K.T.; Whelan, G.

    1982-06-01

    This report represents a collection of some of the manual procedures and simple computer programs used by the Hydrologic Engineering Section of the Division of Engineering, Office of Nuclear Reactor Regulation, for computing the fate of routinely or accidentally released radionuclides in surface water and groundwater. All models are straightforward simulations of dispersion with constant coefficients in simple geometries

  13. Measuring high-frequency responses of an electro-optic phase modulator based on dispersion induced phase modulation to intensity modulation conversion

    Science.gov (United States)

    Zhang, Shangjian; Wang, Heng; Wang, Yani; Zou, Xinhai; Zhang, Yali; Liu, Shuang; Liu, Yong

    2014-11-01

    We investigate the phase modulation to intensity modulation conversion in dispersive fibers for measuring frequency responses of electro-optic phase modulators, and demonstrate two typical measurements with cascade path and fold-back path. The measured results achieve an uncertainty of less than 2.8% within 20 GHz. Our measurements show stable and repeatable results because the optical carrier and its phase-modulated sidebands are affected by the same fiber impairments. The proposed method requires only dispersive fibers and works without any small-signal assumption, which is applicable for swept frequency measurement at different driving levels and operating wavelengths.

  14. Validation of dispersion model of RTARC-DSS based on ''KIT'' field experiments

    International Nuclear Information System (INIS)

    Duran, J.

    2000-01-01

    The aim of this study is to present the performance of the Gaussian dispersion model RTARC-DSS (Real Time Accident Release Consequences - Decision Support System) at the 'Kit' field experiments. The Model Validation Kit is a collection of three experimental data sets from Kincaid, Copenhagen, Lillestrom and supplementary Indianopolis experimental campaigns accompanied by software for model evaluation. The validation of the model has been performed on the basis of the maximum arc-wise concentrations using the Bootstrap resampling procedure the variation of the model residuals. Validation was performed for the short-range distances (about 1 - 10 km, maximum for Kincaid data set - 50 km from source). Model evaluation procedure and amount of relative over- or under-prediction are discussed and compared with the model. (author)

  15. Ductility Enhancement of Molybdenum Phase by Nano-sizedd Oxide Dispersions

    Energy Technology Data Exchange (ETDEWEB)

    Bruce Kang

    2008-07-31

    The present research is focused on ductility enhancement of molybdenum (Mo) alloys by adding nano-sized oxide particles to the alloy system. The research approach includes: (1) determination of microscopic mechanisms responsible for the macroscopic ductility enhancement effects through atomistic modeling of the metal-ceramic interface; (2) subsequent computer simulation-aided optimization of composition and nanoparticle size of the dispersion for improved performance; (3) synthesis and characterization of nanoparticle dispersion following the guidance from atomistic computational modeling analyses (e.g., by processing a small sample of Mo alloy for evaluation); and (4) experimental testing of the mechanical properties to determine optimal ductility enhancement.Through atomistic modeling and electronic structure analysis using full-potential linearized muffin-tin orbital (FP-LMTO) techniques, research to date has been performed on a number of selected chromium (Cr) systems containing nitrogen (N) and/or magnesium oxide (MgO) impurities. The emphasis has been on determining the properties of the valence electrons and the characteristics of the chemical bonds they formed. It was found that the brittle/ductile behavior of this transitional metal system is controlled by the relative population of valence charges: bonds formed by s valence electrons yield metallic, ductile behavior, whereas bonds formed by d valence electrons lead to covalent, brittle behavior. The presence of valence bands from impurities also affects the metal bonding, thereby explaining the detrimental and beneficial effects induced by the inclusion of N impurities and MgO dispersions. These understandings are useful for optimizing ductility enhancement effects on the dispersion materials.

  16. Metapopulation extinction risk: dispersal's duplicity.

    Science.gov (United States)

    Higgins, Kevin

    2009-09-01

    Metapopulation extinction risk is the probability that all local populations are simultaneously extinct during a fixed time frame. Dispersal may reduce a metapopulation's extinction risk by raising its average per-capita growth rate. By contrast, dispersal may raise a metapopulation's extinction risk by reducing its average population density. Which effect prevails is controlled by habitat fragmentation. Dispersal in mildly fragmented habitat reduces a metapopulation's extinction risk by raising its average per-capita growth rate without causing any appreciable drop in its average population density. By contrast, dispersal in severely fragmented habitat raises a metapopulation's extinction risk because the rise in its average per-capita growth rate is more than offset by the decline in its average population density. The metapopulation model used here shows several other interesting phenomena. Dispersal in sufficiently fragmented habitat reduces a metapopulation's extinction risk to that of a constant environment. Dispersal between habitat fragments reduces a metapopulation's extinction risk insofar as local environments are asynchronous. Grouped dispersal raises the effective habitat fragmentation level. Dispersal search barriers raise metapopulation extinction risk. Nonuniform dispersal may reduce the effective fraction of suitable habitat fragments below the extinction threshold. Nonuniform dispersal may make demographic stochasticity a more potent metapopulation extinction force than environmental stochasticity.

  17. MESOILT2, a Lagrangian trajectory climatological dispersion model

    International Nuclear Information System (INIS)

    Ramsdell, J.V. Jr.; Burk, K.W.

    1991-03-01

    The objective of the Hanford Environmental Dose Reconstruction (HEDR) Project is to estimate the radiation dose that individuals could have received as a result of emissions from nuclear operations at the Hanford Site. An independent Technical Steering Panel (TSP) directs the project, which is conducted by the Pacific Northwest Laboratory (PNL). The TSP directed PNL to demonstrate that its recommended approach for dose reconstruction is technically feasible and practical. This demonstration was Phase 1 of the project. This report is specifically concerned with the approach that PNL recommends for dealing with the atmospheric pathway. The TSP established a model domain for the atmospheric pathway for Phase 1 that includes 10 counties in Washington and Oregon and covers several thousand square miles. It is unrealistic to assume that atmospheric models which estimate transport and diffusion based on the meteorological conditions near the point of release of material at the time of release are adequate for a region this large. As a result, PNL recommended use of a Lagrangian trajectory, puff dispersion model for the Phase I study. This report describes the MESOILT2 computer code and the atmospheric transport, diffusion, deposition, and depletion models used in Phase I. The contents of the report include a technical description of the models, a user's guide for the codes, and descriptions of the individual code elements. 53 refs., 17 figs., 5 tabs

  18. Advances and Problems in Mathematical Modelling of Dispersion of ...

    African Journals Online (AJOL)

    Most expressions for dispersion of pollutants have failed to give accurate predictions in both channel and natural stream flows. This paper outlines the basic concepts on which the fundamental dispersion equations have been derived. Some of the advances on these equations are examined and their deficiencies pointed ...

  19. Dispersion of radionuclides in the European north-western seas: observations and modelling

    International Nuclear Information System (INIS)

    Bailly du Bois, Pascal

    2013-01-01

    In this report for an Accreditation to supervise research (HDR), the author reports the use over 30 years by the Cherbourg-Octeville IRSN Laboratory of artificial radionuclides in solution in sea water as oceanographic markers. Such measurements on radio-markers which are soluble in sea water, enabled a better knowledge of dissolved substance displacements in north-western seas of Europe, notably the Channel, the North Sea, the Celtic Sea, and the Irish Sea. The author reports researches which aimed at studying the dispersion of radionuclides in seawater and their use as water mass markers, at validating hydrodynamic models of dispersion at different time-space scales, at the understanding and simulation of the sedimentary transport, and at studying the transfer to living species. These different topics give the document its structure [fr

  20. Modeling emerald ash borer dispersal using percolation theory: estimating the rate of range expansion in a fragmented landscape

    Science.gov (United States)

    Robin A. J. Taylor; Daniel A. Herms; Louis R. Iverson

    2008-01-01

    The dispersal of organisms is rarely random, although diffusion processes can be useful models for movement in approximately homogeneous environments. However, the environments through which all organisms disperse are far from uniform at all scales. The emerald ash borer (EAB), Agrilus planipennis, is obligate on ash (Fraxinus spp...

  1. Mesoscale atmospheric modeling of accidental toxic and radioactive releases for emergency response at SRS

    International Nuclear Information System (INIS)

    O'Steen, B.L.; Fast, J.D.

    1992-01-01

    In August of 1991, the Environmental Transport Group (ETG) began the development of an advanced Emergency Response (ER) system based upon the Colorado State University Regional Atmospheric Modeling System 1 (RAMS). This model simulates the three-dimensional, time-dependent, flow field and thermodynamic structure of the planetary boundary layer (PBL). A companion Lagrangian Particle Dispersion Model 2 (LPDM) simulates contaminant transport based on the flow and turbulence fields generated by RAMS. The current report describes progress to date on this project in the areas of data development, data assimilation, and operational (real-time) procedures. In particular, a diagnostic capability for simulating contaminant transport is demonstrated

  2. Radiation environmental real-time monitoring and dispersion modeling

    International Nuclear Information System (INIS)

    Kovacik, A.; Bartokova, I.; Omelka, J.; Melicherova, T.

    2014-01-01

    The system of real-time radiation monitoring provided by MicroStep-MIS is a turn-key solution for measurement, acquisition, processing, reporting, archiving and displaying of various radiation data. At the level of measurements, the monitoring stations can be equipped with various devices from radiation probes, measuring the actual ambient gamma dose rate, to fully automated aerosol monitors, returning analysis results of natural and manmade radionuclides concentrations in the air. Using data gathered by our radiation probes RPSG-05 integrated into monitoring network of Crisis Management of the Slovak Republic and into monitoring network of Slovak Hydrometeorological Institute, we demonstrate its reliability and long-term stability of measurements. Data from RPSG-05 probes and GammaTracer probes, both of these types are used in the SHI network, are compared. The sensitivity of RPSG-05 is documented on data where changes of dose rate are caused by precipitation. Qualities of RPSG-05 probe are illustrated also on example of its use in radiation monitoring network in the United Arab Emirates. A more detailed information about radioactivity of the atmosphere can be obtained by using spectrometric detectors (e.g. scintillation detectors) which, besides gamma dose rate values, offer also a possibility to identify different radionuclides. However, this possibility is limited by technical parameters of detector like energetic resolution and detection efficiency in given geometry of measurement. A clearer information with less doubts can be obtained from aerosol monitors with a built-in silicon detector of alpha and beta particles and with an electrically cooled HPGe detector dedicated for gamma-ray spectrometry, which is performed during the sampling. Data from a complex radiation monitoring network can be used, together with meteorological data, in radiation dispersion model by MicroStep-MIS. This model serves for simulation of atmospheric propagation of radionuclides

  3. Dispersed oil decreases the ability of a model fish (Dicentrarchus labrax) to cope with hydrostatic pressure.

    Science.gov (United States)

    Dussauze, Matthieu; Pichavant-Rafini, Karine; Belhomme, Marc; Buzzacott, Peter; Privat, Killian; Le Floch, Stéphane; Lemaire, Philippe; Theron, Michaël

    2017-01-01

    Data on the biological impact of oil dispersion in deep-sea environment are scarce. Hence, the aim of this study was to evaluate the potential interest of a pressure challenge as a new experimental approach for the assessment of consequences of chemically dispersed oil, followed by a high hydrostatic pressure challenge. This work was conducted on a model fish: juvenile Dicentrarchus labrax. Seabass were exposed for 48 h to dispersant alone (nominal concentration (NC) = 4 mg L -1 ), mechanically dispersed oil (NC = 80 mg L -1 ), two chemically dispersed types of oil (NC = 50 and 80 mg L -1 with a dispersant/oil ratio of 1/20), or kept in clean seawater. Fish were then exposed for 30 min at a simulated depth of 1350 m, corresponding to pressure of 136 absolute atmospheres (ATA). The probability of fish exhibiting normal activity after the pressure challenge significantly increased from 0.40 to 0.55 when they were exposed to the dispersant but decreased to 0.26 and 0.11 in the case of chemical dispersion of oil (at 50 and 80 mg L -1 , respectively). The chemical dispersion at 80 mg L -1 also induced an increase in probability of death after the pressure challenge (from 0.08 to 0.26). This study clearly demonstrates the ability of a pressure challenge test to give evidence of the effects of a contaminant on the capacity of fish to face hydrostatic pressure. It opens new perspectives on the analysis of the biological impact of chemical dispersion of oil at depth, especially on marine species performing vertical migrations.

  4. Estimate of dispersion in an unsaturated aquifer

    Science.gov (United States)

    Stephenson, D.; De Jesus, A. S. M.

    1985-10-01

    The Nuclear Development Corporation of South Africa (Pty) Ltd. (NUCOR) is constructing a low-level radioactive waste disposal site near Springbok in Namaqualand, an arid region to the west of South Africa. A groundwater model was developed which required site-specific data and this work describes procedures developed to assess the dispersivity of the soil in the vicinity of the proposed site. Preliminary laboratory tests, carried out using a sodium chloride solution, indicated the order of magnitude of the dispersivity for saturated soil at various levels. This enabled site tests to be designed. The site tests were done by injecting a pulse of scandium-46 into a hole and monitoring the displacement of the radioactive cloud as it moved down under gravity and spread laterally. A mathematical model was developed to predict the behaviour of the cloud and calibration of the model yielded vertical and horizontal dispersivities. The dispersion of radioactivity at the cloud front was assumed to occur in unsaturated medium while the continuously injected water behind the radioactivity was assumed to disperse in a saturated medium. Thus monitoring the concentration of both yielded approximate values for the effective dispersivities in unsaturated and saturated media.

  5. Dispersion of radioactive materials in air and water

    International Nuclear Information System (INIS)

    Tolksdorf, P.; Meurin, G.

    1976-01-01

    A review of current analytical methods for treating the dispersion of radioactive material in air and water is given. It is shown that suitable calculational models, based on experiments, exist for the dispersion in air. By contrast, the analysis of the dispersion of radioactive material in water still depends on the evaluation of experiments with site-specific models. (orig.) [de

  6. Dispersion properties of photonic crystal fibres

    DEFF Research Database (Denmark)

    Bjarklev, Anders Overgaard; Broeng, Jes; Dridi, Kim

    1998-01-01

    Approximate dispersion and bending properties of all-silica two-dimensional photonic crystal fibres are characterised by the combination of an effective-index model and classical analysis tools for optical fibres. We believe for the first time to have predicted the dispersion properties of photonic...... crystal fibres. The results strongly indicate that these fibres have potential applications as dispersion managing components...

  7. A one-dimensional semi-empirical model considering transition boiling effect for dispersed flow film boiling

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yu-Jou [Institute of Nuclear Engineering and Science, National Tsing Hua University, Hsinchu 30013, Taiwan, ROC (China); Pan, Chin, E-mail: cpan@ess.nthu.edu.tw [Institute of Nuclear Engineering and Science, National Tsing Hua University, Hsinchu 30013, Taiwan, ROC (China); Department of Engineering and System Science, National Tsing Hua University, Hsinchu 30013, Taiwan, ROC (China); Low Carbon Energy Research Center, National Tsing Hua University, Hsinchu 30013, Taiwan, ROC (China)

    2017-05-15

    Highlights: • Seven heat transfer mechanisms are studied numerically by the model. • A semi-empirical method is proposed to account for the transition boiling effect. • The parametric effects on the heat transfer mechanisms are investigated. • The thermal non-equilibrium phenomenon between vapor and droplets is investigated. - Abstract: The objective of this paper is to develop a one-dimensional semi-empirical model for the dispersed flow film boiling considering transition boiling effects. The proposed model consists of conservation equations, i.e., vapor mass, vapor energy, droplet mass and droplet momentum conservation, and a set of closure relations to address the interactions among wall, vapor and droplets. The results show that the transition boiling effect is of vital importance in the dispersed flow film boiling regime, since the flowing situation in the downstream would be influenced by the conditions in the upstream. In addition, the present paper, through evaluating the vapor temperature and the amount of heat transferred to droplets, investigates the thermal non-equilibrium phenomenon under different flowing conditions. Comparison of the wall temperature predictions with the 1394 experimental data in the literature, the present model ranging from system pressure of 30–140 bar, heat flux of 204–1837 kW/m{sup 2} and mass flux of 380–5180 kg/m{sup 2} s, shows very good agreement with RMS of 8.80% and standard deviation of 8.81%. Moreover, the model well depicts the thermal non-equilibrium phenomenon for the dispersed flow film boiling.

  8. Modeling the Dispersibility of Single Walled Carbon Nanotubes in Organic Solvents by Quantitative Structure-Activity Relationship Approach

    Science.gov (United States)

    Yilmaz, Hayriye; Rasulev, Bakhtiyor; Leszczynski, Jerzy

    2015-01-01

    The knowledge of physico-chemical properties of carbon nanotubes, including behavior in organic solvents is very important for design, manufacturing and utilizing of their counterparts with improved properties. In the present study a quantitative structure-activity/property relationship (QSAR/QSPR) approach was applied to predict the dispersibility of single walled carbon nanotubes (SWNTs) in various organic solvents. A number of additive descriptors and quantum-chemical descriptors were calculated and utilized to build QSAR models. The best predictability is shown by a 4-variable model. The model showed statistically good results (R2training = 0.797, Q2 = 0.665, R2test = 0.807), with high internal and external correlation coefficients. Presence of the X0Av descriptor and its negative term suggest that small size solvents have better SWCNTs solubility. Mass weighted descriptor ATS6m also indicates that heavier solvents (and small in size) most probably are better solvents for SWCNTs. The presence of the Dipole Z descriptor indicates that higher polarizability of the solvent molecule increases the solubility. The developed model and contributed descriptors can help to understand the mechanism of the dispersion process and predictorganic solvents that improve the dispersibility of SWNTs. PMID:28347035

  9. Modeling the Dispersibility of Single Walled Carbon Nanotubes in Organic Solvents by Quantitative Structure-Activity Relationship Approach

    Directory of Open Access Journals (Sweden)

    Hayriye Yilmaz

    2015-05-01

    Full Text Available The knowledge of physico-chemical properties of carbon nanotubes, including behavior in organic solvents is very important for design, manufacturing and utilizing of their counterparts with improved properties. In the present study a quantitative structure-activity/property relationship (QSAR/QSPR approach was applied to predict the dispersibility of single walled carbon nanotubes (SWNTs in various organic solvents. A number of additive descriptors and quantum-chemical descriptors were calculated and utilized to build QSAR models. The best predictability is shown by a 4-variable model. The model showed statistically good results (R2training = 0.797, Q2 = 0.665, R2test = 0.807, with high internal and external correlation coefficients. Presence of the X0Av descriptor and its negative term suggest that small size solvents have better SWCNTs solubility. Mass weighted descriptor ATS6m also indicates that heavier solvents (and small in size most probably are better solvents for SWCNTs. The presence of the Dipole Z descriptor indicates that higher polarizability of the solvent molecule increases the solubility. The developed model and contributed descriptors can help to understand the mechanism of the dispersion process and predictorganic solvents that improve the dispersibility of SWNTs.

  10. Dispersal and metapopulation stability

    Directory of Open Access Journals (Sweden)

    Shaopeng Wang

    2015-10-01

    Full Text Available Metapopulation dynamics are jointly regulated by local and spatial factors. These factors may affect the dynamics of local populations and of the entire metapopulation differently. Previous studies have shown that dispersal can stabilize local populations; however, as dispersal also tends to increase spatial synchrony, its net effect on metapopulation stability has been controversial. Here we present a simple metapopulation model to study how dispersal, in interaction with other spatial and local processes, affects the temporal variability of metapopulations in a stochastic environment. Our results show that in homogeneous metapopulations, the local stabilizing and spatial synchronizing effects of dispersal cancel each other out, such that dispersal has no effect on metapopulation variability. This result is robust to moderate heterogeneities in local and spatial parameters. When local and spatial dynamics exhibit high heterogeneities, however, dispersal can either stabilize or destabilize metapopulation dynamics through various mechanisms. Our findings have important theoretical and practical implications. We show that dispersal functions as a form of spatial intraspecific mutualism in metapopulation dynamics and that its effect on metapopulation stability is opposite to that of interspecific competition on local community stability. Our results also suggest that conservation corridors should be designed with appreciation of spatial heterogeneities in population dynamics in order to maximize metapopulation stability.

  11. Development of a Dispersal Model for Balsam Woolly Adelgid, Adelges piceae Ratzeburg (Hemiptera: Adelgidae, to Facilitate Landscape-Level Management Planning

    Directory of Open Access Journals (Sweden)

    L. W. Lass

    2014-01-01

    Full Text Available The balsam woolly adelgid (Adelges piceae Ratzeburg attacks subalpine fir (Abies lasiocarpa (Hook. Nutt. in eastern Washington, Oregon, and northern Idaho. Historical balsam woolly adelgid distributions present an opportunity to understand climatic factors that influence the species’ distribution at a landscape scale. The distribution data allows for creation of predictive models that detail the likelihood of occurrence and associated geographic data allow modeling of species dispersal. Predictive variables linked to the distribution of the hosts and to abiotic environmental conditions were utilized to create a spatial probability model of occurrence. Balsam woolly adelgid predominantly disperses by wind, and hence, both wind speed and wind direction were used to create a dispersal probability model. Results from wind dispersal modeling suggested that two-thirds of the new infestations were due to July and August wind direction and speed. Average July winds ranged from 0.5 to 3.27 m/s, flowing south westerly, and August winds ranged from 0.43 to 1.55 m/s, flowing north easterly. Land managers can use the results of the predictive model to better understand where current infestations are likely to expand. Prediction of where the balsam woolly adelgid might move allows managers to adjust actions to respond to future insect movement and establishment.

  12. Calculation of Longitudinal Dispersion Coefficient and Modeling the Pollution Transmission in Rivers (Case studies: Severn and Narew Rivers

    Directory of Open Access Journals (Sweden)

    A. Parsaie

    2017-01-01

    empirical formulas and artificial intelligent techniques have been proposed. In this study LDC is calculated for the Severn River and Narew River and some selected empirical formulas have been assessed to calculate the LDC. Dispersion Routing Method: As mentioned previously, calculating the LDC is more important, so firstly, the longitudinal dispersion was calculated from the concentration profile by Dispersion Routing Method (DRM. Using the DRM included the four stage.1-considering of initial value for LDC .2-calculating the concentration profile at the downstream station by using the upstream concentration profile and LDC.3- Performing a comparison between the calculated profile and measured profile.4- if the calculating profile is not a suitable cover, the measured profile of the process will be repeated until the calculated profile shows a good covering on the measured profile. Numerical Method: The ADE includes two different parts advection and dispersion. The pure advection term is related to transmission modeling without any dispersing and the dispersion term is related to the dispersion without any transmission. To discrete the ADE the finite volume method was used. According to physical properties of these two terms and the recommendation of researchers a suitable scheme should be considered for numerical solution of ADE terms. Among the finite volume schemes, the quickest scheme was selected to discrete the advection term, because of this scheme has suitable ability to model the pure advection term. The quickest scheme is an explicit scheme and the stability condition should be considered. To discrete the dispersion term, the central implicit scheme was selected. This scheme is unconditionally stable. Results and Discussion: The results of longitudinal dispersion coefficient for the Severn River and Narew River were calculated using the DRM method and empirical formulas. The results of LDC calculation showed that the minimum and maximum values for the Severn River

  13. Finite-difference modeling and dispersion analysis of high-frequency love waves for near-surface applications

    Science.gov (United States)

    Luo, Y.; Xia, J.; Xu, Y.; Zeng, C.; Liu, J.

    2010-01-01

    Love-wave propagation has been a topic of interest to crustal, earthquake, and engineering seismologists for many years because it is independent of Poisson's ratio and more sensitive to shear (S)-wave velocity changes and layer thickness changes than are Rayleigh waves. It is well known that Love-wave generation requires the existence of a low S-wave velocity layer in a multilayered earth model. In order to study numerically the propagation of Love waves in a layered earth model and dispersion characteristics for near-surface applications, we simulate high-frequency (>5 Hz) Love waves by the staggered-grid finite-difference (FD) method. The air-earth boundary (the shear stress above the free surface) is treated using the stress-imaging technique. We use a two-layer model to demonstrate the accuracy of the staggered-grid modeling scheme. We also simulate four-layer models including a low-velocity layer (LVL) or a high-velocity layer (HVL) to analyze dispersive energy characteristics for near-surface applications. Results demonstrate that: (1) the staggered-grid FD code and stress-imaging technique are suitable for treating the free-surface boundary conditions for Love-wave modeling, (2) Love-wave inversion should be treated with extra care when a LVL exists because of a lack of LVL information in dispersions aggravating uncertainties in the inversion procedure, and (3) energy of high modes in a low-frequency range is very weak, so that it is difficult to estimate the cutoff frequency accurately, and "mode-crossing" occurs between the second higher and third higher modes when a HVL exists. ?? 2010 Birkh??user / Springer Basel AG.

  14. Improved Meteorological Input for Atmospheric Release Decision support Systems and an Integrated LES Modeling System for Atmospheric Dispersion of Toxic Agents: Homeland Security Applications

    Energy Technology Data Exchange (ETDEWEB)

    Arnold, E; Simpson, M; Larsen, S; Gash, J; Aluzzi, F; Lundquist, J; Sugiyama, G

    2010-04-26

    When hazardous material is accidently or intentionally released into the atmosphere, emergency response organizations look to decision support systems (DSSs) to translate contaminant information provided by atmospheric models into effective decisions to protect the public and emergency responders and to mitigate subsequent consequences. The Department of Homeland Security (DHS)-led Interagency Modeling and Atmospheric Assessment Center (IMAAC) is one of the primary DSSs utilized by emergency management organizations. IMAAC is responsible for providing 'a single piont for the coordination and dissemination of Federal dispersion modeling and hazard prediction products that represent the Federal position' during actual or potential incidents under the National Response Plan. The Department of Energy's (DOE) National Atmospheric Release Advisory Center (NARAC), locatec at the Lawrence Livermore National Laboratory (LLNL), serves as the primary operations center of the IMAAC. A key component of atmospheric release decision support systems is meteorological information - models and data of winds, turbulence, and other atmospheric boundary-layer parameters. The accuracy of contaminant predictions is strongly dependent on the quality of this information. Therefore, the effectiveness of DSSs can be enhanced by improving the meteorological options available to drive atmospheric transport and fate models. The overall goal of this project was to develop and evaluate new meteorological modeling capabilities for DSSs based on the use of NASA Earth-science data sets in order to enhance the atmospheric-hazard information provided to emergency managers and responders. The final report describes the LLNL contributions to this multi-institutional effort. LLNL developed an approach to utilize NCAR meteorological predictions using NASA MODIS data for the New York City (NYC) region and demonstrated the potential impact of the use of different data sources and data

  15. Integrating individual movement behaviour into dispersal functions.

    Science.gov (United States)

    Heinz, Simone K; Wissel, Christian; Conradt, Larissa; Frank, Karin

    2007-04-21

    Dispersal functions are an important tool for integrating dispersal into complex models of population and metapopulation dynamics. Most approaches in the literature are very simple, with the dispersal functions containing only one or two parameters which summarise all the effects of movement behaviour as for example different movement patterns or different perceptual abilities. The summarising nature of these parameters makes assessing the effect of one particular behavioural aspect difficult. We present a way of integrating movement behavioural parameters into a particular dispersal function in a simple way. Using a spatial individual-based simulation model for simulating different movement behaviours, we derive fitting functions for the functional relationship between the parameters of the dispersal function and several details of movement behaviour. This is done for three different movement patterns (loops, Archimedean spirals, random walk). Additionally, we provide measures which characterise the shape of the dispersal function and are interpretable in terms of landscape connectivity. This allows an ecological interpretation of the relationships found.

  16. Numerical predictions of particle dispersed two-phase flows, using the LSD and SSF models

    International Nuclear Information System (INIS)

    Avila, R.; Cervantes de Gortari, J.; Universidad Nacional Autonoma de Mexico, Mexico City. Facultad de Ingenieria)

    1988-01-01

    A modified version of a numerical scheme which is suitable to predict parabolic dispersed two-phase flow, is presented. The original version of this scheme was used to predict the test cases discussed during the 3rd workshop on TPF predictions in Belgrade, 1986. In this paper, two particle dispersion models are included which use the Lagrangian approach predicting test case 1 and 3 of the 4th workshop. For the prediction of test case 1 the Lagrangian Stochastic Deterministic model (LSD) is used providing acceptable good results of mean and turbulent quantities for both solid and gas phases; however, the computed void fraction distribution is not in agreement with the measurements at locations away from the inlet, especially near the walls. Test case 3 is predicted using both the LSD and the Stochastic Separated Flow (SSF) models. It was found that the effects of turbulence modulation are large when the LSD model is used, whereas the particles have a negligible influence on the continuous phase if the SSF model is utilized for the computations. Predictions of gas phase properties based on both models agree well with measurements; however, the agreement between calculated and measured solid phase properties is less satisfactory. (orig.)

  17. Wave equation dispersion inversion using a difference approximation to the dispersion-curve misfit gradient

    KAUST Repository

    Zhang, Zhendong

    2016-07-26

    We present a surface-wave inversion method that inverts for the S-wave velocity from the Rayleigh wave dispersion curve using a difference approximation to the gradient of the misfit function. We call this wave equation inversion of skeletonized surface waves because the skeletonized dispersion curve for the fundamental-mode Rayleigh wave is inverted using finite-difference solutions to the multi-dimensional elastic wave equation. The best match between the predicted and observed dispersion curves provides the optimal S-wave velocity model. Our method can invert for lateral velocity variations and also can mitigate the local minimum problem in full waveform inversion with a reasonable computation cost for simple models. Results with synthetic and field data illustrate the benefits and limitations of this method. © 2016 Elsevier B.V.

  18. Modeling blast waves, gas and particles dispersion in urban and hilly ground areas

    International Nuclear Information System (INIS)

    Hank, S.; Saurel, R.; Le Metayer, O.; Lapebie, E.

    2014-01-01

    The numerical simulation of shock and blast waves as well as particles dispersion in highly heterogeneous media such as cities, urban places, industrial plants and part of countries is addressed. Examples of phenomena under study are chemical gas products dispersion from damaged vessels, gas dispersion in urban places under explosion conditions, shock wave propagation in urban environment. A three-dimensional simulation multiphase flow code (HI2LO) is developed in this aim. To simplify the consideration of complex geometries, a heterogeneous discrete formulation is developed. When dealing with large scale domains, such as countries, the topography is considered with the help of elevation data. Meteorological conditions are also considered, in particular regarding complex temperature and wind profiles. Heat and mass transfers on sub-scale objects, such as buildings, trees and other obstacles are considered as well. Particles motion is addressed through a new turbulence model involving a single parameter to describe accurately plumes. Validations against experiments in basic situations are presented as well as examples of industrial and environmental computations. (authors)

  19. A study of the physical factors affecting air pollution dispersion in Helwan

    International Nuclear Information System (INIS)

    Megahed, A.A.

    1992-01-01

    Air pollution is considered as one of the most important environmental problems facing the humanity. Cement industry, usually, is responsible for building high levels of pollutants. The present research focused on the study of air pollution control of cement industry using mathematical modeling. A mathematical dispersion model was developed based on Gaussian distribution where the dispersion parameters increase with increasing atmospheric turbulence. The Gaussian equation takes in consideration the effect of emission rates. stack height, buoyant plume rise, weather and meteorological parameters. The model was tested for different stack heights, wind speeds. And atmospheric stability classes. Maximum ground level concentration of cement pollutants were measured in different locations of Helwan, south Cairo around the cement factories. Analysis of results shows that the ground level of pollutants concentrations are inversely proportional to wind speed and atmospheric stability classes. Stack height also affects the behaviour of deposition of cement particulates. The model results show satisfactory agreement with the measured concentrations. 6 figs

  20. A semiparametric negative binomial generalized linear model for modeling over-dispersed count data with a heavy tail: Characteristics and applications to crash data.

    Science.gov (United States)

    Shirazi, Mohammadali; Lord, Dominique; Dhavala, Soma Sekhar; Geedipally, Srinivas Reddy

    2016-06-01

    Crash data can often be characterized by over-dispersion, heavy (long) tail and many observations with the value zero. Over the last few years, a small number of researchers have started developing and applying novel and innovative multi-parameter models to analyze such data. These multi-parameter models have been proposed for overcoming the limitations of the traditional negative binomial (NB) model, which cannot handle this kind of data efficiently. The research documented in this paper continues the work related to multi-parameter models. The objective of this paper is to document the development and application of a flexible NB generalized linear model with randomly distributed mixed effects characterized by the Dirichlet process (NB-DP) to model crash data. The objective of the study was accomplished using two datasets. The new model was compared to the NB and the recently introduced model based on the mixture of the NB and Lindley (NB-L) distributions. Overall, the research study shows that the NB-DP model offers a better performance than the NB model once data are over-dispersed and have a heavy tail. The NB-DP performed better than the NB-L when the dataset has a heavy tail, but a smaller percentage of zeros. However, both models performed similarly when the dataset contained a large amount of zeros. In addition to a greater flexibility, the NB-DP provides a clustering by-product that allows the safety analyst to better understand the characteristics of the data, such as the identification of outliers and sources of dispersion. Copyright © 2016 Elsevier Ltd. All rights reserved.

  1. Quorum sensing and density-dependent dispersal in an aquatic model system.

    Directory of Open Access Journals (Sweden)

    Simon Fellous

    Full Text Available Many organisms use cues to decide whether to disperse or not, especially those related to the composition of their environment. Dispersal hence sometimes depends on population density, which can be important for the dynamics and evolution of sub-divided populations. But very little is known about the factors that organisms use to inform their dispersal decision. We investigated the cues underlying density-dependent dispersal in inter-connected microcosms of the freshwater protozoan Paramecium caudatum. In two experiments, we manipulated (i the number of cells per microcosm and (ii the origin of their culture medium (supernatant from high- or low-density populations. We found a negative relationship between population density and rates of dispersal, suggesting the use of physical cues. There was no significant effect of culture medium origin on dispersal and thus no support for chemical cues usage. These results suggest that the perception of density - and as a result, the decision to disperse - in this organism can be based on physical factors. This type of quorum sensing may be an adaptation optimizing small scale monitoring of the environment and swarm formation in open water.

  2. Development of scheme for predicting atmospheric dispersion of radionuclides during nuclear emergency by using atmospheric dynamic model

    Energy Technology Data Exchange (ETDEWEB)

    Nagai, Haruyasu; Chino, Masamichi; Yamazawa, Hiromi (Japan Atomic Energy Research Inst., Tokyo (Japan))

    1999-07-01

    The meteorological forecast models are critically important for the accuracy of predicting the atmospheric dispersion of radionuclides discharged into atmosphere during nuclear emergencies. Thus, this paper describes a new scheme for predicting environmental impacts due to accidental release of radionuclides by using an atmospheric dynamic model PHYSIC. The advantages of introducing PHYSIC are, (1) three-dimensional local meteorological forecasts can be conducted, (2) synoptic meteorological changes can be considered by inputting grid data of synoptic forecasts from Japan Meteorological Agency to PHYSIC as initial and boundary conditions, (3) forecasts can be improved by nudging method using local meteorological observations, and (4) atmospheric dispersion model can consider the variation of the mixed layer. (author)

  3. Development of scheme for predicting atmospheric dispersion of radionuclides during nuclear emergency by using atmospheric dynamic model

    International Nuclear Information System (INIS)

    Nagai, Haruyasu; Chino, Masamichi; Yamazawa, Hiromi

    1999-01-01

    The meteorological forecast models are critically important for the accuracy of predicting the atmospheric dispersion of radionuclides discharged into atmosphere during nuclear emergencies. Thus, this paper describes a new scheme for predicting environmental impacts due to accidental release of radionuclides by using an atmospheric dynamic model PHYSIC. The advantages of introducing PHYSIC are, (1) three-dimensional local meteorological forecasts can be conducted, (2) synoptic meteorological changes can be considered by inputting grid data of synoptic forecasts from Japan Meteorological Agency to PHYSIC as initial and boundary conditions, (3) forecasts can be improved by nudging method using local meteorological observations, and (4) atmospheric dispersion model can consider the variation of the mixed layer. (author)

  4. Circulation and microplastic dispersion in the Chiemsee (Germany) investigated with numerical modeling.

    Science.gov (United States)

    Marcello Falcieri, Francesco; Laforsch, Christian; Piehl, Sarah; Ricchi, Antonio; Atwood, Elizabeth C.; Carniel, Sandro; Sclavo, Mauro

    2017-04-01

    The Chiemsee (measuring about 80 km2 and a maximum depth of 73 m) is a NATURA 2000 site and one of the major German lakes and plays a significant environmental role for the region. Moreover it is an important touristic destination, making its beaches and water quality highly valuable from a socio-economical viewpoint. As for most inland European aquatic environments, the Chiemsee was recently found to be contaminated by microplastic (i.e. plastic fragments smaller than 0.5 mm). Two main microplastics sources were identified in the Chiemsee: riverine inputs, and degradation of litter from touristic beaches. Hence, it is of interest to study lake circulation and the resulting microplastic dispersion from these sources in order to support activities to achieve a good environmental status. Here we present the first attempt to characterize the hydrodynamic processes of the Chiemsee with a high resolution 3D implementation of the Regional Ocean Modeling System (ROMS). The simulations were forced with observed riverine inputs and modeled atmospherical fields computed with a local implementation of the Weather Research and Forecasting (WRF) model. Modeling results provide a first insight into the Chiemsee circulation system and contribute to understanding the dispersion pathways of microplastic particles from different sources. Furthermore, results can be used to highlight coastlines with higher risk of microplastic accumulation, identified using a set of Lagrangian simulations. The work was partially supported by the CNR Short Term Mobility grant.

  5. A model for evaluating dispersed outdoor recreation use estimation

    Science.gov (United States)

    Stanley J. Zarnoch; Donald B. K. English; Susan M. Kocis

    2004-01-01

    An outdoor recreation use simulator (ORUS) has been developed to simulate dispersed recreation survey data similar to that collected by the National Visitor Use Monitoring (NVUM) Project's survey of the national forests of the U.S.A. Statistical distributions are used to represent the various behaviors of recreationists during their visit to a dispersed area. The...

  6. Source strength and dispersion of CO2 releases from high-pressure pipelines: CFD model using real gas equation of state

    International Nuclear Information System (INIS)

    Liu, Xiong; Godbole, Ajit; Lu, Cheng; Michal, Guillaume; Venton, Philip

    2014-01-01

    Highlights: • Validated CFD models for decompression and dispersion of CO 2 releases from pipelines. • Incorporation of real gas EOS into CFD code for source strength estimation. • Demonstration of better performance of SST k–ω turbulence model for jet flow. • Demonstration of better performance of real gas EOS compared to ideal gas EOS. • Demonstration of superiority of CFD models over a commercial risk assessment package. - Abstract: Transportation of CO 2 in high-pressure pipelines forms a crucial link in the ever-increasing application of Carbon Capture and Storage (CCS) technologies. An unplanned release of CO 2 from a pipeline presents a risk to human and animal populations and the environment. Therefore it is very important to develop a deeper understanding of the atmospheric dispersion of CO 2 before the deployment of CO 2 pipelines, to allow the appropriate safety precautions to be taken. This paper presents a two-stage Computational Fluid Dynamics (CFD) study developed (1) to estimate the source strength, and (2) to simulate the subsequent dispersion of CO 2 in the atmosphere, using the source strength estimated in stage (1). The Peng–Robinson (PR) EOS was incorporated into the CFD code. This enabled accurate modelling of the CO 2 jet to achieve more precise source strength estimates. The two-stage simulation approach also resulted in a reduction in the overall computing time. The CFD models were validated against experimental results from the British Petroleum (BP) CO 2 dispersion trials, and also against results produced by the risk management package Phast. Compared with the measurements, the CFD simulation results showed good agreement in both source strength and dispersion profile predictions. Furthermore, the effect of release direction on the dispersion was studied. The presented research provides a viable method for the assessment of risks associated with CCS

  7. Multiphysics Simulations of Entrained Flow Gasification. Part I: Validating the Nonreacting Flow Solver and the Particle Turbulent Dispersion Model

    KAUST Repository

    Kumar, Mayank

    2012-01-19

    In this two-part paper, we describe the construction, validation, and application of a multiscale model of entrained flow gasification. The accuracy of the model is demonstrated by (1) rigorously constructing and validating the key constituent submodels against relevant canonical test cases from the literature and (2) validating the integrated model against experimental data from laboratory scale and commercial scale gasifiers. In part I, the flow solver and particle turbulent dispersion models are validated against experimental data from nonswirling flow and swirling flow test cases in an axisymmetric sudden expansion geometry and a two-phase flow test case in a cylindrical bluff body geometry. Results show that while the large eddy simulation (LES) performs best among all tested models in predicting both swirling and nonswirling flows, the shear stress transport (SST) k-ω model is the best choice among the commonly used Reynolds-averaged Navier-Stokes (RANS) models. The particle turbulent dispersion model is accurate enough in predicting particle trajectories in complex turbulent flows when the underlying turbulent flow is well predicted. Moreover, a commonly used modeling constant in the particle dispersion model is optimized on the basis of comparisons with particle-phase experimental data for the two-phase flow bluff body case. © 2011 American Chemical Society.

  8. The comparative effects of oil dispersants and oil/dispersant conjugates on germination of the marine macroalga Phyllospora comosa (Fucales: Phaeophyta)

    International Nuclear Information System (INIS)

    Burridge, T.R.; Shir, M.-A.

    1995-01-01

    Germination inhibition of the marine macrophyte Phyllospora comosa was utilized as a sub-lethal end-point to assess and compare the effects of four oil dispersants and dispersed diesel fuel and crude oil combinations. Inhibition of germination by the water-soluble fraction of diesel fuel increased following the addition of each of the dispersants; the nominal 48-h EC 50 concentration of diesel fuel declined from 6800 to approximately 400 μl 1 -1 nominal for each dispersed combination. This contrasted with crude oil, where the addition of two dispersants resulted in an enhanced germination rate and an increase in nominal EC 50 concentrations from 130 μl 1 -1 for the undispersed crude to 4000 and 2500 μl 1 -1 . The results indicate that, while germination inhibition of P. comosa may be enhanced by the chemical dispersal of oil response varies with type of both oil and oil dispersant. (author)

  9. Study of neutron shell structure of even-even 40-56Ca isotopes by the dispersive optical model

    International Nuclear Information System (INIS)

    Bespalova, O.V.; Boboshin, I.N.; Varlamov, V.V.; Ermakova, T.A.; Ishkhanov, B.S.; Romanovskij, E.A.; Spasskaya, T.I.; Timokhina, T.P.

    2005-01-01

    The single-particle energies and occupation probabilities of the bound neutron states in 40,42,44,46,48 Ca isotopes were obtained by the joint evaluation of the stripping and pick-up reaction data. The results were analyzed by the dispersive optical model and a good agreement was achieved. The dispersive optical potential was extrapolated to unstable 50,52,54,56 Ca nuclei. The calculated single-particle energies of the bound neutron states in unstable Ca isotopes were compared with the nuclear shell-model calculations, which predicted new magic number N = 34 for nuclei with Z = 20 [ru

  10. A CFD model for pollutant dispersion in rivers

    Directory of Open Access Journals (Sweden)

    Modenesi K.

    2004-01-01

    Full Text Available Studies have shown that humankind will experience a water shortage in the coming decades. It is therefore paramount to develop new techniques and models with a view to minimizing the impact of pollution. It is important to predict the environmental impact of new emissions in rivers, especially during periods of drought. Computational fluid dynamics (CFD has proved to be an invaluable tool to develop models able to analyze in detail particle dispersion in rivers. However, since these models generate grids with thousands (even millions of points to evaluate velocities and concentrations, they still require powerful machines. In this context, this work contributes by presenting a new three-dimensional model based on CFD techniques specifically developed to be fast, providing a significant improvement in performance. It is able to generate predictions in a couple of hours for a one-thousand-meter long section of river using Pentium IV computers. Commercial CFD packages would require weeks to solve the same problem. Another innovation inb this work is that a half channel with a constant elliptical cross section represents the river, so the Navier Stokes equations were derived for the elliptical system. Experimental data were obtained from REPLAN (PETROBRAS refining unit on the Atibaia River in São Paulo, Brazil. The results show good agreement with experimental data.

  11. Annular dispersed flow analysis model by Lagrangian method and liquid film cell method

    International Nuclear Information System (INIS)

    Matsuura, K.; Kuchinishi, M.; Kataoka, I.; Serizawa, A.

    2003-01-01

    A new annular dispersed flow analysis model was developed. In this model, both droplet behavior and liquid film behavior were simultaneously analyzed. Droplet behavior in turbulent flow was analyzed by the Lagrangian method with refined stochastic model. On the other hand, liquid film behavior was simulated by the boundary condition of moving rough wall and liquid film cell model, which was used to estimate liquid film flow rate. The height of moving rough wall was estimated by disturbance wave height correlation. In each liquid film cell, liquid film flow rate was calculated by considering droplet deposition and entrainment flow rate. Droplet deposition flow rate was calculated by Lagrangian method and entrainment flow rate was calculated by entrainment correlation. For the verification of moving rough wall model, turbulent flow analysis results under the annular flow condition were compared with the experimental data. Agreement between analysis results and experimental results were fairly good. Furthermore annular dispersed flow experiments were analyzed, in order to verify droplet behavior model and the liquid film cell model. The experimental results of radial distribution of droplet mass flux were compared with analysis results. The agreement was good under low liquid flow rate condition and poor under high liquid flow rate condition. But by modifying entrainment rate correlation, the agreement become good even under high liquid flow rate. This means that basic analysis method of droplet and liquid film behavior was right. In future work, verification calculation should be carried out under different experimental condition and entrainment ratio correlation also should be corrected

  12. Dispersion model computations of urban air pollution in Espoo, Finland

    Energy Technology Data Exchange (ETDEWEB)

    Valkonen, E.; Haerkoenen, J.; Kukkonen, J.; Rantakrans, E.; Jalkanen, L.

    1997-12-31

    This report presents the numerical results of air quality studies of the city of Espoo in southern Finland. This city is one of the four cities in the Helsinki metropolitan area, having a total population of 850 000. A thorough emission inventory was made of both mobile and stationary sources in the Helsinki metropolitan area. The atmospheric dispersion was evaluated using an urban dispersion modelling system, including a Gaussian multiple-source plume model and a meteorological pre-processing model. The hourly time series of CO, NO{sub 2} and SO{sub 2} concentrations were predicted, using the emissions and meteorological data for the year 1990. The predicted results show a clear decrease in the yearly mean concentrations from southeast to northwest. This is due in part to the denser traffic in the southern parts of Espoo, and in part to pollution from the neighbouring cities of Helsinki and Vantaa, located east of Espoo. The statistical concentration parameters found for Espoo were lower than the old national air quality guidelines (1984); however, some occurrences of above-threshold values were found for NO{sub 2} in terms of the new guidelines (1996). The contribution of traffic to the total concentrations varies spatially from 30 to 90 % for NO{sub 2} from 1 to 65 % for SO{sub 2} while for CO it is nearly 100 %. The concentrations database will be further utilised to analyse the influence of urban air pollution on the health of children attending selected day nurseries in Espoo. The results of this study can also be applied in traffic and city planning. In future work the results will also be compared with data from the urban measurement network of the Helsinki Metropolitan Area Council. (orig.) 19 refs.

  13. Comparison of gridded versus observation data to initialize ARAC dispersion models for the Algeciras, Spain steel mill CS-137 release

    International Nuclear Information System (INIS)

    Aluzzi, F J; Pace, J C; Pobanz, B M; Vogt, P J

    1999-01-01

    On May 30, 1998 scrap metal containing radioactive Cesium-137 (Cs-137) was accidentally melted in a furnace at the Acerinox steel mill in Algeciras, Spain. Cs-137 was released from the mill's smokestack, and spread across the western Mediterranean Sea to France and Italy and beyond. The first indication of the release was radiation levels up to 1000 times background reported by Swiss, French, and Italian authorities during the following two weeks. Initially no elevated radiation levels were detected over Spain. A release of hazardous material to the atmosphere is the type of situation the Atmospheric Release Advisory Capability (ARAC) emergency response organization was designed to address. The amount and exact time of the release were unknown, though the incident was thought to have taken place during the last week in May. Using air concentration measurements supplied by colleagues of ARAC in Spain, France, Switzerland, Italy, Sweden, Russia and the European Union, ARAC meteorologists estimated the magnitude and timing of the release (Vogt, 1999). Correctly locating the downwind footprint is the most important goal of emergency response modeling. In this study, we compare predicted results for the Algeciras event based on four wind data sources: (1) US Navy Operational Global Atmospheric Prediction System (NOGAPS) data alone, (2) surface and upper air observations alone, (3) NOGAPS data together with surface and upper air observations, and (4) forecasts from ARAC's in-house execution of the U.S. Navy Operational Regional Atmospheric Prediction System (NORAPS) (without surface or upper air observations). We compare the resulting dispersion predictions from ARAC's diagnostic dispersion modeling system to the measurements supplied by our European colleagues to determine which data source produced the best results

  14. STELLAR MASS DEPENDENT DISK DISPERSAL

    International Nuclear Information System (INIS)

    Kennedy, Grant M.; Kenyon, Scott J.

    2009-01-01

    We use published optical spectral and infrared (IR) excess data from nine young clusters and associations to study the stellar mass dependent dispersal of circumstellar disks. All clusters older than ∼3 Myr show a decrease in disk fraction with increasing stellar mass for solar to higher mass stars. This result is significant at about the 1σ level in each cluster. For the complete set of clusters we reject the null hypothesis-that solar and intermediate-mass stars lose their disks at the same rate-with 95%-99.9% confidence. To interpret this behavior, we investigate the impact of grain growth, binary companions, and photoevaporation on the evolution of disk signatures. Changes in grain growth timescales at fixed disk temperature may explain why early-type stars with IR excesses appear to evolve faster than their later-type counterparts. Little evidence that binary companions affect disk evolution suggests that photoevaporation is the more likely mechanism for disk dispersal. A simple photoevaporation model provides a good fit to the observed disk fractions for solar and intermediate-mass stars. Although the current mass-dependent disk dispersal signal is not strong, larger and more complete samples of clusters with ages of 3-5 Myr can improve the significance and provide better tests of theoretical models. In addition, the orbits of extra-solar planets can constrain models of disk dispersal and migration. We suggest that the signature of stellar mass dependent disk dispersal due to photoevaporation may be present in the orbits of observed extra-solar planets. Planets orbiting hosts more massive than ∼1.6 M sun may have larger orbits because the disks in which they formed were dispersed before they could migrate.

  15. Operational evaluation of the RLINE dispersion model for studies of traffic-related air pollutants

    Science.gov (United States)

    Milando, Chad W.; Batterman, Stuart A.

    2018-06-01

    Exposure to traffic-related air pollutants (TRAP) remains a key public health issue, and improved exposure measures are needed to support health impact and epidemiologic studies and inform regulatory responses. The recently developed Research LINE source model (RLINE), a Gaussian line source dispersion model, has been used in several epidemiologic studies of TRAP exposure, but evaluations of RLINE's performance in such applications have been limited. This study provides an operational evaluation of RLINE in which predictions of NOx, CO and PM2.5 are compared to observations at air quality monitoring stations located near high traffic roads in Detroit, MI. For CO and NOx, model performance was best at sites close to major roads, during downwind conditions, during weekdays, and during certain seasons. For PM2.5, the ability to discern local and particularly the traffic-related portion was limited, a result of high background levels, the sparseness of the monitoring network, and large uncertainties for certain processes (e.g., formation of secondary aerosols) and non-mobile sources (e.g., area, fugitive). Overall, RLINE's performance in near-road environments suggests its usefulness for estimating spatially- and temporally-resolved exposures. The study highlights considerations relevant to health impact and epidemiologic applications, including the importance of selecting appropriate pollutants, using appropriate monitoring approaches, considering prevailing wind directions during study design, and accounting for uncertainty.

  16. A Stochastic Model for the Landing Dispersion of Hazard Detection and Avoidance Capable Flight Systems

    Science.gov (United States)

    Witte, L.

    2014-06-01

    To support landing site assessments for HDA-capable flight systems and to facilitate trade studies between the potential HDA architectures versus the yielded probability of safe landing a stochastic landing dispersion model has been developed.

  17. Dispersed flow film boiling

    International Nuclear Information System (INIS)

    Andreani, M.; Yadigaroglu, G.

    1989-12-01

    Dispersed flow film boiling is the heat transfer regime that occurs at high void fractions in a heated channel. The way this transfer mode is modelled in the NRC computer codes (RELAP5 and TRAC) and the validity of the assumption and empirical correlations used is discussed. An extensive review of the theoretical and experimental work related with heat transfer to highly dispersed mixtures reveals the basic deficiencies of these models: the investigation refers mostly to the typical conditions of low rate bottom reflooding, since the simulation of this physical situation by the computer codes has often showed poor results. The alternative models that are available in the literature are reviewed, and their merits and limits are highlighted. The modification that could improve the physics of the models implemented in the codes are identified. (author) 13 figs., 123 refs

  18. Integrating a street-canyon model with a regional Gaussian dispersion model for improved characterisation of near-road air pollution

    Science.gov (United States)

    Fallah-Shorshani, Masoud; Shekarrizfard, Maryam; Hatzopoulou, Marianne

    2017-03-01

    The development and use of dispersion models that simulate traffic-related air pollution in urban areas has risen significantly in support of air pollution exposure research. In order to accurately estimate population exposure, it is important to generate concentration surfaces that take into account near-road concentrations as well as the transport of pollutants throughout an urban region. In this paper, an integrated modelling chain was developed to simulate ambient Nitrogen Dioxide (NO2) in a dense urban neighbourhood while taking into account traffic emissions, the regional background, and the transport of pollutants within the urban canopy. For this purpose, we developed a hybrid configuration including 1) a street canyon model, which simulates pollutant transfer along streets and intersections, taking into account the geometry of buildings and other obstacles, and 2) a Gaussian puff model, which resolves the transport of contaminants at the top of the urban canopy and accounts for regional meteorology. Each dispersion model was validated against measured concentrations and compared against the hybrid configuration. Our results demonstrate that the hybrid approach significantly improves the output of each model on its own. An underestimation appears clearly for the Gaussian model and street-canyon model compared to observed data. This is due to ignoring the building effect by the Gaussian model and undermining the contribution of other roads by the canyon model. The hybrid approach reduced the RMSE (of observed vs. predicted concentrations) by 16%-25% compared to each model on its own, and increased FAC2 (fraction of predictions within a factor of two of the observations) by 10%-34%.

  19. Development of an analytical Lagrangian model for passive scalar dispersion in low-wind speed meandering conditions

    Science.gov (United States)

    Stefanello, M. B.; Degrazia, G. A.; Mortarini, L.; Buligon, L.; Maldaner, S.; Carvalho, J. C.; Acevedo, O. C.; Martins, L. G. N.; Anfossi, D.; Buriol, C.; Roberti, D.

    2018-02-01

    Describing the effects of wind meandering motions on the dispersion of scalars is a challenging task, since this type of flow represents a physical state characterized by multiple scales. In this study, a Lagrangian stochastic diffusion model is derived to describe scalar transport during the horizontal wind meandering phenomenon that occurs within a planetary boundary layer. The model is derived from the linearization of the Langevin equation, and it employs a heuristic functional form that represents the autocorrelation function of meandering motion. The new solutions, which describe the longitudinal and lateral wind components, were used to simulate tracer experiments that were performed in low-wind speed conditions. The results of the comparison indicate that the new model can effectively reproduce the observed concentrations of the contaminants, and therefore, it can satisfactorily describe enhanced dispersion effects due to the presence of meandering.

  20. Invariant Theory for Dispersed Transverse Isotropy: An Efficient Means for Modeling Fiber Splay

    Science.gov (United States)

    Freed, alan D.; Einstein, Daniel R.; Vesely, Ivan

    2004-01-01

    Most soft tissues possess an oriented architecture of collagen fiber bundles, conferring both anisotropy and nonlinearity to their elastic behavior. Transverse isotropy has often been assumed for a subset of these tissues that have a single macroscopically-identifiable preferred fiber direction. Micro-structural studies, however, suggest that, in some tissues, collagen fibers are approximately normally distributed about a mean preferred fiber direction. Structural constitutive equations that account for this dispersion of fibers have been shown to capture the mechanical complexity of these tissues quite well. Such descriptions, however, are computationally cumbersome for two-dimensional (2D) fiber distributions, let alone for fully three-dimensional (3D) fiber populations. In this paper, we develop a new constitutive law for such tissues, based on a novel invariant theory for dispersed transverse isotropy. The invariant theory is based on a novel closed-form splay invariant that can easily handle 3D fiber populations, and that only requires a single parameter in the 2D case. The model is polyconvex and fits biaxial data for aortic valve tissue as accurately as the standard structural model. Modification of the fiber stress-strain law requires no re-formulation of the constitutive tangent matrix, making the model flexible for different types of soft tissues. Most importantly, the model is computationally expedient in a finite-element analysis.

  1. Clay squirt: Local flow dispersion in shale-bearing sandstones

    DEFF Research Database (Denmark)

    Sørensen, Morten Kanne; Fabricius, Ida Lykke

    2017-01-01

    Dispersion of elastic-wave velocity is common in sandstone and larger in shaly sandstone than in clean sandstone. Dispersion in fluid-saturated shaly sandstone often exceeds the level expected from the stress-dependent elastic moduli of dry sandstone. The large dispersion has been coined clay...... squirt and is proposed to originate from a pressure gradient between the clay microporosity and the effective porosity. We have formulated a simple model that quantifies the clay-squirt effect on bulk moduli of sandstone with homogeneously distributed shale laminae or dispersed shale. The model...... predictions were compared with the literature data. For sandstones with dispersed shale, agreement was found, whereas other sandstones have larger fluid-saturated bulk modulus, possibly due to partially load-bearing shales or heterogeneous shale distribution. The data that agree with the clay-squirt model...

  2. Revisiting the advection-dispersion model - Testing an alternative

    International Nuclear Information System (INIS)

    Neretnieks, I.

    2001-01-01

    Some of the basic assumptions of the Advection-Dispersion model, AD-model, are revisited. That model assumes a continuous mixing along the flowpath similar to Fickian diffusion. This implies that there is a constant dispersion length irrespective of observation distance. This is contrary to most field observations. The properties of an alternative model based on the assumption that individual water packages can retain their identity over long distances are investigated. The latter model is called the Multi-Channel model, MChM. Inherent in the latter model is that if the waters in the different pathways are collected and mixed, the 'dispersion length' is proportional to observation distance. Using diffusion theory it is investigated over which distances or contact times, adjacent water packages will keep their identity. It is found that for a contact time of 10 hours, two streams, each wider than 6 mm, that flow side by side, will not have lost their identity. For 1000 hours contact time the minimum width is 6 cm. The MChM and AD-models were found to have very similar Residence Time Distributions, RTD, for Peclet numbers larger than 3. A generalised relation between flowrate and residence time is developed, including the so-called cubic law and constant aperture assumptions. Using the generalised relation, surprisingly it is found that for a system that has the same average flow volume and average flowrate the form of the RTD curves are the same irrespective of the form of the relation. Both models are also compared for a system where there is strong interaction of the solute with the rock matrix. In this case it is assumed that the solute can diffuse into and out of the fracture walls and also to sorb on the micro-fractures of the matrix. The so-called Flow Wetted Surface, FWS, between the flowing water in the fracture and the rock is a key entity in such systems. It is found that the AD-model predicts much later arrivals and lower concentrations than does the MCh-model

  3. Optimisation of Oil Spill Dispersants on Weathered Oils. A New Approach Using Experimental Design and Multivariate Data Analysis

    Energy Technology Data Exchange (ETDEWEB)

    Brandvik, Per Johan

    1997-12-31

    This thesis describes how laboratory experiments combined with numerical modelling were used to predict weathering of an oil slick at different environmental conditions (temperature, wind etc.). It also applies laboratory test methods to screen dispersant effectiveness under different temperatures and salinities. A new approach is developed for dispersant optimization based on statistical design and multivariate analysis; this resulted in a new dispersant with low toxicity and high effectiveness on a broad selection of oil types. The thesis illustrates the potential of dispersant used as an operational response method on oil spills by discussing three different oil spill scenarios and compares the effect of using dispersants to using mechanical recovery and to doing nothing. Some recommendations that may increase the effectiveness of the Norwegian oil spill contingency are also given. 172 refs., 65 figs., 9 tabs.

  4. Dispersion of effluents in the atmosphere; Dispersion des effluents dans l`atmosphere

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1999-12-31

    This conference day was organized by the `convection` section of the French association of thermal engineers with the support of the environment and energy mastery agency (ADEME). This book of proceedings contains 10 papers entitled: `physical modeling of atmospheric dispersion in wind tunnels. Some industrial examples`; `modeling of the noxious effects of a fire on the environment of an industrial site: importance of thermal engineering related hypotheses`; `atmospheric diffusion of a noxious cloud: fast evaluation method of safety areas around refrigerating installations that use ammonia`; `modeling of atmospheric flows in urban areas in order to study the dispersion of pollutants`; `use of a dispersion parameter to characterize the evolution of a diffusion process downstream of a linear source of passive contaminant placed inside a turbulent boundary layer`; `elements of reflexion around the development of an analytical methodology applied to the elaboration of measurement strategies of air quality in ambient and outdoor atmospheres around industrial sites`; `state-of-the-art about treatment techniques for VOC-rich gaseous effluents`; `characteristics of the time variation of the atmospheric pollution in the Paris region and visualization of its space distribution`; `mass-spectrometry for the measurement of atmospheric pollutants`; `volume variations in natural convection turbulence`. (J.S.)

  5. Dispersion of effluents in the atmosphere; Dispersion des effluents dans l`atmosphere

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1998-12-31

    This conference day was organized by the `convection` section of the French association of thermal engineers with the support of the environment and energy mastery agency (ADEME). This book of proceedings contains 10 papers entitled: `physical modeling of atmospheric dispersion in wind tunnels. Some industrial examples`; `modeling of the noxious effects of a fire on the environment of an industrial site: importance of thermal engineering related hypotheses`; `atmospheric diffusion of a noxious cloud: fast evaluation method of safety areas around refrigerating installations that use ammonia`; `modeling of atmospheric flows in urban areas in order to study the dispersion of pollutants`; `use of a dispersion parameter to characterize the evolution of a diffusion process downstream of a linear source of passive contaminant placed inside a turbulent boundary layer`; `elements of reflexion around the development of an analytical methodology applied to the elaboration of measurement strategies of air quality in ambient and outdoor atmospheres around industrial sites`; `state-of-the-art about treatment techniques for VOC-rich gaseous effluents`; `characteristics of the time variation of the atmospheric pollution in the Paris region and visualization of its space distribution`; `mass-spectrometry for the measurement of atmospheric pollutants`; `volume variations in natural convection turbulence`. (J.S.)

  6. Real-time modeling of complex atmospheric releases in urban areas

    International Nuclear Information System (INIS)

    Baskett, R.L.; Ellis, J.S.; Sullivan, T.J.

    1994-08-01

    If a nuclear installation in or near an urban area has a venting, fire, or explosion, airborne radioactivity becomes the major concern. Dispersion models are the immediate tool for estimating the dose and contamination. Responses in urban areas depend on knowledge of the amount of the release, representative meteorological data, and the ability of the dispersion model to simulate the complex flows as modified by terrain or local wind conditions. A centralized dispersion modeling system can produce realistic assessments of radiological accidents anywhere in a country within several minutes if it is computer-automated. The system requires source-term, terrain, mapping and dose-factor databases, real-time meteorological data acquisition, three-dimensional atmospheric transport and dispersion models, and experienced staff. Experience with past responses in urban areas by the Atmospheric Release Advisory Capability (ARAC) program at Lawrence Livermore National Laboratory illustrate the challenges for three-dimensional dispersion models

  7. Real-time modelling of complex atmospheric releases in urban areas

    International Nuclear Information System (INIS)

    Baskett, R.L.; Ellis, J.S.; Sullivan, T.J.

    2000-01-01

    If a nuclear installation in or near an urban area has a venting, fire, or explosion, airborne radioactivity becomes the major concern. Dispersion models are the immediate tool for estimating the dose and contamination. Responses in urban areas depend on knowledge of the amount of the release, representative meteorological data, and the ability of the dispersion model to simulate the complex flows as modified by terrain or local wind conditions. A centralised dispersion modelling system can produce realistic assessments of radiological accidents anywhere in a country within several minutes if it is computer-automated. The system requires source-term, terrain, mapping and dose-factor databases, real-time meteorological data acquisition, three-dimensional atmospheric transport and dispersion models, and experienced staff. Experience with past responses in urban areas by the Atmospheric Release Advisory Capability (ARAC) program at Lawrence Livermore National Laboratory illustrate the challenges for three-dimensional dispersion models. (author)

  8. Addendum: ``The Dynamics of M15: Observations of the Velocity Dispersion Profile and Fokker-Planck Models'' (ApJ, 481, 267 [1997])

    Science.gov (United States)

    Dull, J. D.; Cohn, H. N.; Lugger, P. M.; Murphy, B. W.; Seitzer, P. O.; Callanan, P. J.; Rutten, R. G. M.; Charles, P. A.

    2003-03-01

    Figures 9, 10, and 12 of D97. We take responsibility for the errors in the original versions of these figures and regret any confusion that these may have caused. We also present an expanded version of Figure 6, which extends the radial scale to both smaller and larger values, in order to show the full run of the velocity dispersion profile. The profile of the intermediate-phase model of D97 is in good agreement with the HST-STIS velocity dispersion profile presented by Gerssen et al. (2002). In particular, the central value of ~14 km s-1, predicted by this model, nicely coincides with their findings. We note that three independent studies have now demonstrated that there is a dense, central concentration of dark mass in M15, by use of three alternative methods: Fokker-Planck simulations (D97), GRAPE-6 simulations (Baumgardt et al. 2003), and Jeans equation modeling (Gerssen et al. 2002, 2003). The dark mass is proposed to consist of neutron stars and massive white dwarfs, in the former two studies, versus a central black hole in the latter. Irrespective of these different interpretations of the nature of the dark mass, its presence now appears to be well established on dynamical grounds.

  9. Use of dispersion modelling for Environmental Impact Assessment of biological air pollution from composting: Progress, problems and prospects.

    Science.gov (United States)

    Douglas, P; Hayes, E T; Williams, W B; Tyrrel, S F; Kinnersley, R P; Walsh, K; O'Driscoll, M; Longhurst, P J; Pollard, S J T; Drew, G H

    2017-12-01

    With the increase in composting asa sustainable waste management option, biological air pollution (bioaerosols) from composting facilities have become a cause of increasing concern due to their potential health impacts. Estimating community exposure to bioaerosols is problematic due to limitations in current monitoring methods. Atmospheric dispersion modelling can be used to estimate exposure concentrations, however several issues arise from the lack of appropriate bioaerosol data to use as inputs into models, and the complexity of the emission sources at composting facilities. This paper analyses current progress in using dispersion models for bioaerosols, examines the remaining problems and provides recommendations for future prospects in this area. A key finding is the urgent need for guidance for model users to ensure consistent bioaerosol modelling practices. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

  10. MESOI, an interactive atmospheric dispersion model for emergency response applications

    International Nuclear Information System (INIS)

    Ramsdell, J.V.; Athey, G.F.; Glantz, C.S.

    1983-12-01

    MESOI is an interactive atmospheric despersion model that has been developed for use by the US Department of Energy, and the US Nuclear Regulatory Commission in responding to emergencies at nuclear facilities. MESOI uses both straight-line Gaussian plume and Lagrangian trajectory Gaussian puff models to estimate time-integrated ground-level air and surface concentrations. Puff trajectories are determined from temporally and spatially varying horizontal wind fields that are defined in 3 dimensions. Other processes treated in MESOI include dry deposition, wet deposition and radioactive decay. 9 references

  11. Mesoscopic dispersion of colloidal agglomerate in a complex fluid modelled by a hybrid fluid-particle model.

    Science.gov (United States)

    Dzwinel, Witold; Yuen, David A

    2002-03-15

    The dispersion of the agglomerating fluid process involving colloids has been investigated at the mesoscale level by a discrete particle approach--the hybrid fluid-particle model (FPM). Dynamical processes occurring in the granulation of colloidal agglomerate in solvents are severely influenced by coupling between the dispersed microstructures and the global flow. On the mesoscale this coupling is further exacerbated by thermal fluctuations, particle-particle interactions between colloidal beds, and hydrodynamic interactions between colloidal beds and the solvent. Using the method of FPM, we have tackled the problem of dispersion of a colloidal slab being accelerated in a long box filled with a fluid. Our results show that the average size of the agglomerated fragments decreases with increasing shearing rate gamma, according to the power law A x gamma(k), where k is around 2. For larger values of gamma, the mean size of the agglomerate S(avg) increases slowly with gamma from the collisions between the aggregates and the longitudinal stretching induced by the flow. The proportionality constant A increases exponentially with the scaling factor of the attractive forces acting between the colloidal particles. The value of A shows a rather weak dependence on the solvent viscosity. But A increases proportionally with the scaling factor of the colloid-solvent dissipative interactions. Similar type of dependence can be found for the mixing induced by Rayleigh-Taylor instabilities involving the colloidal agglomerate and the solvent. Three types of fragmentation structures can be identified, which are called rupture, erosion, and shatter. They generate very complex structures with multiresolution character. The aggregation of colloidal beds is formed by the collisions between aggregates, which are influenced by the flow or by the cohesive forces for small dispersion energies. These results may be applied to enhance our understanding concerning the nonlinear complex

  12. A real case simulation of the air-borne effluent dispersion on a typical summer day under CDA scenario for PFBR using an advanced meteorological and dispersion model

    International Nuclear Information System (INIS)

    Srinivas, C.V; Venkatesan, R.; Bagavath Singh, A.; Somayaji, K.M.

    2003-11-01

    Environmental concentrations and radioactive doses within and beyond the site boundary for the CDA situation of PFBR have been estimated using an Advanced Radiological Impact Prediction system for a real atmospheric situation on a typical summer day in the month of May 2003. The system consists of a meso-scale atmospheric prognostic model MM5 coupled with a random walk Lagrangian particle dispersion model FLEXPART for the simulation of transport, diffusion and deposition of radio nuclides. The details of the modeling system, its capabilities and various features are presented. The model has been validated for the simulated coastal atmospheric features of land-sea breeze, development of TIBL etc., with site and regional meteorological observations from IMD. Analysis of the dose distribution in a situation that corresponds to the atmospheric conditions on the chosen day shows that the doses for CDA through different pathways are 8 times less than the earlier estimations made according to regulatory requirements using the Gaussian Plume Model (GPM) approach. However for stack releases a higher dose than was reported earlier occurred beyond the site boundary at 2-4 km range under stable and fumigation conditions. The doses due to stack releases under these conditions maintained almost the same value in 3 to 10 km range and decreased there after. Deposition velocities computed from radionuclide species, wind speed, surface properties were 2 orders lower than the values used earlier and hence gave more realistic estimates of ground deposited activity. The study has enabled to simulate the more complex meteorological situation that actually is present at the site of interest and the associated spatial distribution of radiological impact around Kalpakkam. In order to draw meaningful conclusion that can be compared with regulatory estimates future study would be undertaken to simulate the dispersion under extreme meteorological situations which could possibly be worse than

  13. Dispersion prognosis and consequences in the environment in emergency management context. A Nordic harmonization effort 1991-94

    International Nuclear Information System (INIS)

    Tveten, U.

    1998-01-01

    Neighbour countries have often chosen different atmospheric dispersion prognosis models for use in emergency situations. In a Nordic project in the Nordic Nuclear Safety Research Programme a worldwide survey of long-range atmospheric dispersion models was carried out. On the basis of this survey, each of the meteorological institutes of Denmark, Finland and Norway chose systems upon which future development would be based. The Swedish Meteorological and Hydrological Institute had already developed a model. These and some other available models were subsequently utilised in Nordic 'functional' emergency exercises. The exercises also served as program intercomparison exercises, whereby some programming errors were actually discovered. The exercises also revealed that the currently used graphical presentations of the results may be difficult to understand properly in an emergency situation. The authorities responsible for emergency preparedness use the predictions from the atmospheric dispersion models to evaluate radiation doses to the population. In order to provide decision makers with more readily accessible information, a computerised 'handbook' containing all pertinent information has therefore been developed. (R.P.)

  14. Dispersion of tracers by the oceanic eddy field modelling programme

    International Nuclear Information System (INIS)

    Richards, K.J.

    1986-01-01

    A numerical model has been developed to study the dispersion of tracers by the oceanic eddy field. The study is designed to investigate the horizontal and vertical structure of the eddies and how this structure is influenced by the bottom topography. It is found that hills and valleys have a strong effect on the eddies above them. The flow close to the bottom has a tendency to be steered by the height contours. The surface and bottom flows become decorrelated and the vertical variation of the kinetic energy of the eddies is increased with higher topographic features. (author)

  15. A nonlocal application of the dispersive optical model to 208Pb

    Science.gov (United States)

    Keim, M. A.; Mahzoon, M. H.; Atkinson, M. C.; Charity, R. J.; Dickhoff, W. H.

    2017-09-01

    A nonlocal application of the dispersive optical model to neutrons and protons in 208Pb is presented. A nucleon self-energy is described by parametrized real and imaginary parts connected through a dispersion relation. This parametrization includes nonlocal Hartree-Fock and local Coulomb and spin-orbit real terms, and nonlocal volume and surface and local spin-orbit imaginary terms. A simple Gaussian nonlocality is employed, and appropriate asymmetry parameters are included to describe the N-Z dependence of the nucleus. These parameters are constrained by fitting to experimental data, including particle numbers, energy levels, the charge density, elastic-scattering angular distributions, reaction cross sections, and the neutron total reaction cross section. From the resulting nucleon self-energy, the neutron matter distribution and neutron skin are deduced. This work was supported by the US Department of Energy, Division of Nuclear Physics under Grant DE-FG02-87ER-40316, the US National Science Foundation under Grants PHY-1304242 and PHY-1613362, and the Washington University Office of Undergraduate Research.

  16. Modeling solid-fuel dispersal during slow loss-of-flow-type transients

    International Nuclear Information System (INIS)

    DiMelfi, R.J.; Fenske, G.R.

    1981-01-01

    The dispersal, under certain accident conditions, of solid particles of fast-reactor fuel is examined in this paper. In particular, we explore the possibility that solid-fuel fragmentation and dispersal can be driven by expanding fission gas, during a slow LOF-type accident. The consequences of fragmentation are studied in terms of the size and speed of dispersed particles, and the overall quantity of fuel moved. (orig.)

  17. Biomonitoring of airborne particulate matter emitted from a cement plant and comparison with dispersion modelling results

    Science.gov (United States)

    Abril, Gabriela A.; Wannaz, Eduardo D.; Mateos, Ana C.; Pignata, María L.

    2014-01-01

    The influence of a cement plant that incinerates industrial waste on the air quality of a region in the province of Córdoba, Argentina, was assessed by means of biomonitoring studies (effects of immission) and atmospheric dispersion (effects of emission) of PM10 with the application of the ISC3 model (Industrial Source Complex) developed by the USEPA (Environmental Protection Agency). For the biomonitoring studies, samples from the epiphyte plant Tillandsia capillaris Ruíz & Pav. f. capillaris were transplanted to the vicinities of the cement plant in order to determine the physiological damage and heavy metal accumulation (Ca, Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb). For the application of the ISC3 model, point and area sources from the cement plant were considered to obtain average PM10 concentration results from the biomonitoring exposure period. This model permitted it to be determined that the emissions from the cement plant (point and area sources) were confined to the vicinities, without significant dispersion in the study area. This was also observed in the biomonitoring study, which identified Ca, Cd and Pb, pH and electric conductivity (EC) as biomarkers of this cement plant. Vehicular traffic emissions and soil re-suspension could be observed in the biomonitors, giving a more complete scenario. In this study, biomonitoring studies along with the application of atmospheric dispersion models, allowed the atmospheric pollution to be assessed in more detail.

  18. SEARCH: Spatially Explicit Animal Response to Composition of Habitat.

    Science.gov (United States)

    Pauli, Benjamin P; McCann, Nicholas P; Zollner, Patrick A; Cummings, Robert; Gilbert, Jonathan H; Gustafson, Eric J

    2013-01-01

    Complex decisions dramatically affect animal dispersal and space use. Dispersing individuals respond to a combination of fine-scale environmental stimuli and internal attributes. Individual-based modeling offers a valuable approach for the investigation of such interactions because it combines the heterogeneity of animal behaviors with spatial detail. Most individual-based models (IBMs), however, vastly oversimplify animal behavior and such behavioral minimalism diminishes the value of these models. We present program SEARCH (Spatially Explicit Animal Response to Composition of Habitat), a spatially explicit, individual-based, population model of animal dispersal through realistic landscapes. SEARCH uses values in Geographic Information System (GIS) maps to apply rules that animals follow during dispersal, thus allowing virtual animals to respond to fine-scale features of the landscape and maintain a detailed memory of areas sensed during movement. SEARCH also incorporates temporally dynamic landscapes so that the environment to which virtual animals respond can change during the course of a simulation. Animals in SEARCH are behaviorally dynamic and able to respond to stimuli based upon their individual experiences. Therefore, SEARCH is able to model behavioral traits of dispersing animals at fine scales and with many dynamic aspects. Such added complexity allows investigation of unique ecological questions. To illustrate SEARCH's capabilities, we simulated case studies using three mammals. We examined the impact of seasonally variable food resources on the weight distribution of dispersing raccoons (Procyon lotor), the effect of temporally dynamic mortality pressure in combination with various levels of behavioral responsiveness in eastern chipmunks (Tamias striatus), and the impact of behavioral plasticity and home range selection on disperser mortality and weight change in virtual American martens (Martes americana). These simulations highlight the relevance of

  19. Cross-Sectional Dispersion of Firm Valuations and Expected Stock Returns

    OpenAIRE

    Jiang, Danling

    2008-01-01

    This paper develops two competing hypotheses for the relation between the cross-sectional standard deviation of logarithmic firm fundamental-to-price ratios (``dispersion'') and expected aggregate returns. In models with fully rational beliefs, greater dispersion indicates greater risk and higher expected aggregate returns. In models with investor overconfidence, greater dispersion indicates greater mispricing and lower expected aggregate returns. Consistent with the behavioral models, the re...

  20. Convergence monitoring of Markov chains generated for inverse tracking of unknown model parameters in atmospheric dispersion

    International Nuclear Information System (INIS)

    Kim, Joo Yeon; Ryu, Hyung Joon; Jung, Gyu Hwan; Lee, Jai Ki

    2011-01-01

    The dependency within the sequential realizations in the generated Markov chains and their reliabilities are monitored by introducing the autocorrelation and the potential scale reduction factor (PSRF) by model parameters in the atmospheric dispersion. These two diagnostics have been applied for the posterior quantities of the release point and the release rate inferred through the inverse tracking of unknown model parameters for the Yonggwang atmospheric tracer experiment in Korea. The autocorrelations of model parameters are decreasing to low values approaching to zero with increase of lag, resulted in decrease of the dependencies within the two sequential realizations. Their PSRFs are reduced to within 1.2 and the adequate simulation number recognized from these results. From these two convergence diagnostics, the validation of Markov chains generated have been ensured and PSRF then is especially suggested as the efficient tool for convergence monitoring for the source reconstruction in atmospheric dispersion. (author)

  1. Fused silica thermal conductivity dispersion at high temperature

    International Nuclear Information System (INIS)

    Bouchut, P.; Decruppe, D.; Delrive, L.

    2004-01-01

    A continuous CO 2 laser is focused to locally anneal small fused silica spots. A noncontact radiometry diagnostic enables us to follow surface temperature variation that occurs from site to site. A 'steady state' dispersion of surface temperature is observed across our sample. We show that nonhomogeneous silica thermal conductivity, above 1000 K is responsible for this temperature dispersion

  2. Optimization of the piezoelectric response of 0–3 composites: a modeling approach

    International Nuclear Information System (INIS)

    Chambion, B; Goujon, L; Badie, L; Mugnier, Y; Barthod, C; Galez, C; Wiebel, S; Venet, C

    2011-01-01

    Finite element modeling is used in this study to optimize the electromechanical behavior of 0–3 composites according to the material properties of their constituents. Our modeling approach considers an 'extended' 2D representative volume element (RVE) with randomly dispersed piezoelectric particles. A variable distribution of their polarization axes is also implemented because a full periodic arrangement of fillers and a unique poling orientation are unrealistic in practice. Comparisons with a simpler RVE and with an analytical model based on the Mori–Tanaka approach are performed as a function of the particle concentration for the elastic, dielectric and piezoelectric homogenized properties. An optimization of the piezoelectric response of 0–3 composites according to material considerations is then computed, allowing it to be shown that the piezoelectric strain coefficient is not the only relevant parameter and that lead-free piezoelectric fillers such as LiNbO 3 and ZnO are competitive alternatives. Finally, the piezoelectric responses of 0–3 composites with different filler arrangements are quantitatively compared to 1–3 composites and to the corresponding bulk material

  3. Evaluation and modeling of the eutectic composition of various drug-polyethylene glycol solid dispersions.

    Science.gov (United States)

    Baird, Jared A; Taylor, Lynne S

    2011-06-01

    The purpose of this study was to gain a better understanding of which factors contribute to the eutectic composition of drug-polyethylene glycol (PEG) blends and to compare experimental values with predictions from the semi-empirical model developed by Lacoulonche et al. Eutectic compositions of various drug-PEG 3350 solid dispersions were predicted, assuming athermal mixing, and compared to experimentally determined eutectic points. The presence or absence of specific interactions between the drug and PEG 3350 were investigated using Fourier transform infrared (FT-IR) spectroscopy. The eutectic composition for haloperidol-PEG and loratadine-PEG solid dispersions was accurately predicted using the model, while predictions for aceclofenac-PEG and chlorpropamide-PEG were very different from those experimentally observed. Deviations in the model prediction from ideal behavior for the systems evaluated were confirmed to be due to the presence of specific interactions between the drug and polymer, as demonstrated by IR spectroscopy. Detailed analysis showed that the eutectic composition prediction from the model is interdependent on the crystal lattice energy of the drug compound (evaluated from the melting temperature and the heat of fusion) as well as the nature of the drug-polymer interactions. In conclusion, for compounds with melting points less than 200°C, the model is ideally suited for predicting the eutectic composition of systems where there is an absence of drug-polymer interactions.

  4. Dispersive shock mediated resonant radiations in defocused nonlinear medium

    Science.gov (United States)

    Bose, Surajit; Chattopadhyay, Rik; Bhadra, Shyamal Kumar

    2018-04-01

    We report the evolution of resonant radiation (RR) in a self-defocused nonlinear medium with two zero dispersion wavelengths. RR is generated from dispersive shock wave (DSW) front when the pump pulse is in non-solitonic regime close to first zero dispersion wavelength (ZDW). DSW is responsible for pulse splitting resulting in the generation of blue solitons when leading edge of the pump pulse hits the first ZDW. DSW also generates a red shifted dispersive wave (DW) in the presence of higher order dispersion coefficients. Further, DSW through cross-phase modulation with red shifted dispersive wave (DW) excites a localized radiation. The presence of zero nonlinearity point in the system restricts red-shift of RR and enhances the red shifting of DW. It also helps in the formation of DSW at shorter distance and squeezes the solitonic region beyond second zero dispersion point. Predicted results indicate that the spectral evolution depends on the product of Kerr nonlinearity and group velocity dispersion.

  5. Radiological impact from spanish coal power plants.2.- Dispersion model for deconcentration calculations

    International Nuclear Information System (INIS)

    Alvarez, M.C.; Garzon, L.

    1990-01-01

    In this paper a practical dispersion model is presented, which permits to calculate, in Spain, the concentration of natural radionuclides released to the atmosphere from coal power plants. To apply the model it is necessary to know the following data: emission rates, dry deposition velocity, scavenging coefficient, mixing layer height, together with climatological frequency data relating to wind speed and wind direction (to determinate trajectories from a given source) in the areas examined. Meteorological data can be obtained from meteorological stations across Spain. (Author)

  6. Skull's acoustic attenuation and dispersion modeling on photoacoustic signal

    Science.gov (United States)

    Mohammadi, Leila; Behnam, Hamid; Tavakkoli, Jahan; Nasiriavanaki, Mohammadreza

    2018-02-01

    Despite the promising results of the recent novel transcranial photoacoustic (PA) brain imaging technology, it has been demonstrated that the presence of the skull severely affects the performance of this imaging modality. We theoretically investigate the effects of acoustic heterogeneity induced by skull on the PA signals generated from single particles, with firstly developing a mathematical model for this phenomenon and then explore experimental validation of the results. The model takes into account the frequency dependent attenuation and dispersion effects occur with wave reflection, refraction and mode conversion at the skull surfaces. Numerical simulations based on the developed model are performed for calculating the propagation of photoacoustic waves through the skull. The results show a strong agreement between simulation and ex-vivo study. The findings are as follow: The thickness of the skull is the most PA signal deteriorating factor that affects both its amplitude (attenuation) and phase (distortion). Also we demonstrated that, when the depth of target region is low and it is comparable to the skull thickness, however, the skull-induced distortion becomes increasingly severe and the reconstructed image would be strongly distorted without correcting these effects. It is anticipated that an accurate quantification and modeling of the skull transmission effects would ultimately allow for aberration correction in transcranial PA brain imaging.

  7. Mate-finding as an overlooked critical determinant of dispersal variation in sexually-reproducing animals.

    Science.gov (United States)

    Gilroy, James J; Lockwood, Julie L

    2012-01-01

    Dispersal is a critically important process in ecology, but robust predictive models of animal dispersal remain elusive. We identify a potentially ubiquitous component of variation in animal dispersal that has been largely overlooked until now: the influence of mate encounters on settlement probability. We use an individual-based model to simulate dispersal in sexually-reproducing organisms that follow a simple set of movement rules based on conspecific encounters, within an environment lacking spatial habitat heterogeneity. We show that dispersal distances vary dramatically with fluctuations in population density in such a model, even in the absence of variation in dispersive traits between individuals. In a simple random-walk model with promiscuous mating, dispersal distributions become increasingly 'fat-tailed' at low population densities due to the increasing scarcity of mates. Similar variation arises in models incorporating territoriality. In a model with polygynous mating, we show that patterns of sex-biased dispersal can even be reversed across a gradient of population density, despite underlying dispersal mechanisms remaining unchanged. We show that some widespread dispersal patterns found in nature (e.g. fat tailed distributions) can arise as a result of demographic variability in the absence of heterogeneity in dispersive traits across the population. This implies that models in which individual dispersal distances are considered to be fixed traits might be unrealistic, as dispersal distances vary widely under a single dispersal mechanism when settlement is influenced by mate encounters. Mechanistic models offer a promising means of advancing our understanding of dispersal in sexually-reproducing organisms.

  8. Serum Proteins Enhance Dispersion Stability and Influence the Cytotoxicity and Dosimetry of ZnO Nanoparticles in Suspension and Adherent Cancer Cell Models

    Science.gov (United States)

    Anders, Catherine B.; Chess, Jordan J.; Wingett, Denise G.; Punnoose, Alex

    2015-11-01

    Agglomeration and sedimentation of nanoparticles (NPs) within biological solutions is a major limitation in their use in many downstream applications. It has been proposed that serum proteins associate with the NP surface to form a protein corona that limits agglomeration and sedimentation. Here, we investigate the effect of fetal bovine serum (FBS) proteins on the dispersion stability, dosimetry, and NP-induced cytotoxicity of cationic zinc oxide nanoparticles (nZnO) synthesized via forced hydrolysis with a core size of 10 nm. Two different in vitro cell culture models, suspension and adherent, were evaluated by comparing a phosphate buffered saline (PBS) nZnO dispersion (nZnO/PBS) and an FBS-stabilized PBS nZnO dispersion (nZnO - FBS/PBS). Surface interactions of FBS on nZnO were analyzed via spectroscopic and optical techniques. Fourier transformed infrared spectroscopy (FTIR) confirmed the adsorption of negatively charged protein components on the cationic nZnO surface through the disappearance of surfaced-adsorbed carboxyl functional groups and the subsequent detection of vibrational modes associated with the protein backbone of FBS-associated proteins. Further confirmation of these interactions was noted in the isoelectric point shift of the nZnO from the characteristic pH of 9.5 to a pH of 6.1. In nZnO - FBS/PBS dispersions, the FBS reduced agglomeration and sedimentation behaviors to impart long-term improvements (>24 h) to the nZnO dispersion stability. Furthermore, mathematical dosimetry models indicate that nZnO - FBS/PBS dispersions had consistent NP deposition patterns over time unlike unstable nZnO/PBS dispersions. In suspension cell models, the stable nZnO - FBS/PBS dispersion resulted in a ~33 % increase in the NP-induced cytotoxicity for both Jurkat leukemic and Hut-78 lymphoma cancer cells. In contrast, the nZnO - FBS/PBS dispersion resulted in 49 and 71 % reductions in the cytotoxicity observed towards the adherent breast (T-47D) and prostate

  9. Serum Proteins Enhance Dispersion Stability and Influence the Cytotoxicity and Dosimetry of ZnO Nanoparticles in Suspension and Adherent Cancer Cell Models.

    Science.gov (United States)

    Anders, Catherine B; Chess, Jordan J; Wingett, Denise G; Punnoose, Alex

    2015-12-01

    Agglomeration and sedimentation of nanoparticles (NPs) within biological solutions is a major limitation in their use in many downstream applications. It has been proposed that serum proteins associate with the NP surface to form a protein corona that limits agglomeration and sedimentation. Here, we investigate the effect of fetal bovine serum (FBS) proteins on the dispersion stability, dosimetry, and NP-induced cytotoxicity of cationic zinc oxide nanoparticles (nZnO) synthesized via forced hydrolysis with a core size of 10 nm. Two different in vitro cell culture models, suspension and adherent, were evaluated by comparing a phosphate buffered saline (PBS) nZnO dispersion (nZnO/PBS) and an FBS-stabilized PBS nZnO dispersion (nZnO - FBS/PBS). Surface interactions of FBS on nZnO were analyzed via spectroscopic and optical techniques. Fourier transformed infrared spectroscopy (FTIR) confirmed the adsorption of negatively charged protein components on the cationic nZnO surface through the disappearance of surfaced-adsorbed carboxyl functional groups and the subsequent detection of vibrational modes associated with the protein backbone of FBS-associated proteins. Further confirmation of these interactions was noted in the isoelectric point shift of the nZnO from the characteristic pH of 9.5 to a pH of 6.1. In nZnO - FBS/PBS dispersions, the FBS reduced agglomeration and sedimentation behaviors to impart long-term improvements (>24 h) to the nZnO dispersion stability. Furthermore, mathematical dosimetry models indicate that nZnO - FBS/PBS dispersions had consistent NP deposition patterns over time unlike unstable nZnO/PBS dispersions. In suspension cell models, the stable nZnO - FBS/PBS dispersion resulted in a ~33 % increase in the NP-induced cytotoxicity for both Jurkat leukemic and Hut-78 lymphoma cancer cells. In contrast, the nZnO - FBS/PBS dispersion resulted in 49 and 71 % reductions in the cytotoxicity observed towards the adherent breast (T-47D) and prostate

  10. Taylor dispersion of nanoparticles

    Science.gov (United States)

    Balog, Sandor; Urban, Dominic A.; Milosevic, Ana M.; Crippa, Federica; Rothen-Rutishauser, Barbara; Petri-Fink, Alke

    2017-08-01

    The ability to detect and accurately characterize particles is required by many fields of nanotechnology, including materials science, nanotoxicology, and nanomedicine. Among the most relevant physicochemical properties of nanoparticles, size and the related surface-to-volume ratio are fundamental ones. Taylor dispersion combines three independent phenomena to determine particle size: optical extinction, translational diffusion, and sheer-enhanced dispersion of nanoparticles subjected to a steady laminar flow. The interplay of these defines the apparent size. Considering that particles in fact are never truly uniform nor monodisperse, we rigorously address particle polydispersity and calculate the apparent particle size measured by Taylor dispersion analysis. We conducted case studies addressing aqueous suspensions of model particles and large-scale-produced "industrial" particles of both academic and commercial interest of various core materials and sizes, ranging from 15 to 100 nm. A comparison with particle sizes determined by transmission electron microscopy confirms that our approach is model-independent, non-parametric, and of general validity that provides an accurate account of size polydispersity—independently on the shape of the size distribution and without any assumption required a priori.

  11. Dispersal networks for enhancing bacterial degradation in heterogeneous environments

    International Nuclear Information System (INIS)

    Banitz, Thomas; Wick, Lukas Y.; Fetzer, Ingo; Frank, Karin; Harms, Hauke; Johst, Karin

    2011-01-01

    Successful biodegradation of organic soil pollutants depends on their bioavailability to catabolically active microorganisms. In particular, environmental heterogeneities often limit bacterial access to pollutants. Experimental and modelling studies revealed that fungal networks can facilitate bacterial dispersal and may thereby improve pollutant bioavailability. Here, we investigate the influence of such bacterial dispersal networks on biodegradation performance under spatially heterogeneous abiotic conditions using a process-based simulation model. To match typical situations in polluted soils, two types of abiotic conditions are studied: heterogeneous bacterial dispersal conditions and heterogeneous initial resource distributions. The model predicts that networks facilitating bacterial dispersal can enhance biodegradation performance for a wide range of these conditions. Additionally, the time horizon over which this performance is assessed and the network's spatial configuration are key factors determining the degree of biodegradation improvement. Our results support the idea of stimulating the establishment of fungal mycelia for enhanced bioremediation of polluted soils. - Highlights: → Bacterial dispersal networks can considerably improve biodegradation performance. → They facilitate bacterial access to dispersal-limited areas and remote resources. → Abiotic conditions, time horizon and network structure govern the improvements. → Stimulating the establishment of fungal mycelia promises enhanced soil remediation. - Simulation modelling demonstrates that fungus-mediated bacterial dispersal can considerably improve the bioavailability of organic pollutants under spatially heterogeneous abiotic conditions typical for water-unsaturated soils.

  12. Dispersal networks for enhancing bacterial degradation in heterogeneous environments

    Energy Technology Data Exchange (ETDEWEB)

    Banitz, Thomas, E-mail: thomas.banitz@ufz.de [Department of Ecological Modelling, UFZ - Helmholtz Centre for Environmental Research, Permoserstr. 15, 04318 Leipzig (Germany); Wick, Lukas Y.; Fetzer, Ingo [Department of Environmental Microbiology, UFZ - Helmholtz Centre for Environmental Research, Permoserstr. 15, 04318 Leipzig (Germany); Frank, Karin [Department of Ecological Modelling, UFZ - Helmholtz Centre for Environmental Research, Permoserstr. 15, 04318 Leipzig (Germany); Harms, Hauke [Department of Environmental Microbiology, UFZ - Helmholtz Centre for Environmental Research, Permoserstr. 15, 04318 Leipzig (Germany); Johst, Karin [Department of Ecological Modelling, UFZ - Helmholtz Centre for Environmental Research, Permoserstr. 15, 04318 Leipzig (Germany)

    2011-10-15

    Successful biodegradation of organic soil pollutants depends on their bioavailability to catabolically active microorganisms. In particular, environmental heterogeneities often limit bacterial access to pollutants. Experimental and modelling studies revealed that fungal networks can facilitate bacterial dispersal and may thereby improve pollutant bioavailability. Here, we investigate the influence of such bacterial dispersal networks on biodegradation performance under spatially heterogeneous abiotic conditions using a process-based simulation model. To match typical situations in polluted soils, two types of abiotic conditions are studied: heterogeneous bacterial dispersal conditions and heterogeneous initial resource distributions. The model predicts that networks facilitating bacterial dispersal can enhance biodegradation performance for a wide range of these conditions. Additionally, the time horizon over which this performance is assessed and the network's spatial configuration are key factors determining the degree of biodegradation improvement. Our results support the idea of stimulating the establishment of fungal mycelia for enhanced bioremediation of polluted soils. - Highlights: > Bacterial dispersal networks can considerably improve biodegradation performance. > They facilitate bacterial access to dispersal-limited areas and remote resources. > Abiotic conditions, time horizon and network structure govern the improvements. > Stimulating the establishment of fungal mycelia promises enhanced soil remediation. - Simulation modelling demonstrates that fungus-mediated bacterial dispersal can considerably improve the bioavailability of organic pollutants under spatially heterogeneous abiotic conditions typical for water-unsaturated soils.

  13. Determination of uptake of dispersed oil in the copepod Calanus finmarchicus

    International Nuclear Information System (INIS)

    Melbye, A.G.; Altin, D.; Frost, T.

    2001-01-01

    Many research programs in Norway have focused on the acute toxic effects of oils on zooplankton. Oil companies and those responsible for pollution control strive to develop predictive models for the fate and behaviour of seawater discharges from offshore activities. The models include transport, acute toxic effects, uptake and biodegradation, and accumulation in the food chain. Exposure studies have been conducted using both static tests and continuous flow tests. This paper presented a study in which the biological uptake of dispersed oil in the copepod Calanus finmarchicus was examined using a specially designed flow-through system with an oil dispersion generator. The oil used in the exposure studies was a base oil product from TotalFina that had a very low concentration of water-soluble components, and had very low acute toxicity towards the test organism. The oil was dispersed to a size range of 1 to 10μm. The test species actively filters water for particles in the size range less than 10 to 50 μm. Exposure of the oil dispersion at an average concentration of 600 μg/L gave increasing bioaccumulation from 7 to 14 days, and the calculated bioaccumulation factor was found to be in the range of 200-800. Solvent washing of a duplicate sample of zooplankton at 14 days indicated that a significant portion of the hydrocarbon is absorbed to the surface of the organisms. 14 refs., 4 tabs., 5 figs

  14. Defaunation leads to interaction deficits, not interaction compensation, in an island seed dispersal network.

    Science.gov (United States)

    Fricke, Evan C; Tewksbury, Joshua J; Rogers, Haldre S

    2018-01-01

    Following defaunation, the loss of interactions with mutualists such as pollinators or seed dispersers may be compensated through increased interactions with remaining mutualists, ameliorating the negative cascading impacts on biodiversity. Alternatively, remaining mutualists may respond to altered competition by reducing the breadth or intensity of their interactions, exacerbating negative impacts on biodiversity. Despite the importance of these responses for our understanding of the dynamics of mutualistic networks and their response to global change, the mechanism and magnitude of interaction compensation within real mutualistic networks remains largely unknown. We examined differences in mutualistic interactions between frugivores and fruiting plants in two island ecosystems possessing an intact or disrupted seed dispersal network. We determined how changes in the abundance and behavior of remaining seed dispersers either increased mutualistic interactions (contributing to "interaction compensation") or decreased interactions (causing an "interaction deficit") in the disrupted network. We found a "rich-get-richer" response in the disrupted network, where remaining frugivores favored the plant species with highest interaction frequency, a dynamic that worsened the interaction deficit among plant species with low interaction frequency. Only one of five plant species experienced compensation and the other four had significant interaction deficits, with interaction frequencies 56-95% lower in the disrupted network. These results do not provide support for the strong compensating mechanisms assumed in theoretical network models, suggesting that existing network models underestimate the prevalence of cascading mutualism disruption after defaunation. This work supports a mutualist biodiversity-ecosystem functioning relationship, highlighting the importance of mutualist diversity for sustaining diverse and resilient ecosystems. © 2017 John Wiley & Sons Ltd.

  15. Fused deposition modelling of sodium caseinate dispersions

    NARCIS (Netherlands)

    Schutyser, M.A.I.; Houlder, S.; Wit, de Martin; Buijsse, C.A.P.; Alting, A.C.

    2018-01-01

    Only recently, researchers have started experimenting with 3D printing of foods. The aim of this study was to investigate 3D printed objects from sodium caseinate dispersions, exhibiting reversible gelation behaviour. Gelation and dispensing behaviour were explored and structures of different

  16. A new percolation model for composite solid electrolytes and dispersed ionic conductors

    Science.gov (United States)

    Risyad Hasyim, Muhammad; Lanagan, Michael T.

    2018-02-01

    Composite solid electrolytes (CSEs) including conductor/insulator composites known as dispersed ionic conductors (DICs) have motivated the development of novel percolation models that describe their conductivity. Despite the long history, existing models lack in one or more key areas: (1) rigorous foundation for their physical theory, (2) explanation for non-universal conductor-insulator transition, (3) classification of DICs, and (4) extension to frequency-domain. This work describes a frequency-domain effective medium approximation (EMA) of a bond percolation model for CSEs. The EMA is derived entirely from Maxwell’s equations and contains basic microstructure parameters. The model was applied successfully to several composite systems from literature. Simulations and fitting of literature data address these key areas and illustrate the interplay between space charge layer properties and bulk microstructure.

  17. Role of EPS, Dispersant and Nutrients on the Microbial Response and MOS Formation in the Subarctic Northeast Atlantic

    Directory of Open Access Journals (Sweden)

    Tony Gutierrez

    2017-04-01

    Full Text Available In this study we report the formation of marine oil snow (MOS, its associated microbial community, the factors influencing its formation, and the microbial response to crude oil in surface waters of the Faroe-Shetland Channel (FSC. The FSC is a subarctic region that is hydrodynamically complex located in the northeast Atlantic where oil extraction is currently occurring and where exploration is likely to expand into its deeper waters (>500 m. A major oil spill in this region may mirror the aftermath that ensued following the Deepwater Horizon (DWH blowout in the Gulf of Mexico, where the massive influx of Macondo crude oil triggered the formation of copious quantities of rapidly sinking MOS and successional blooms of opportunistic oil-degrading bacteria. In laboratory experiments, we simulated environmental conditions in sea surface waters of the FSC using water collected from this site during the winter of 2015. We demonstrated that the presence of dispersant triggers the formation of MOS, and that nutrient amendments magnify this. Illumina MiSeq sequencing revealed the enrichment on MOS of associated oil-degrading (Cycloclasticus, Thalassolituus, Marinobacter and EPS-producing (Halomonas, Pseudoalteromonas, Alteromonas bacteria, and included major representation by Psychrobacter and Cobetia with putative oil-degrading/EPS-producing qualities. The formation of marine snow, in the absence of crude oil and dispersant, in seawater amended with nutrients alone indicated that the de novo synthesis of bacterial EPS is a key factor in MOS formation, and the glycoprotein composition of the MOS aggregates confirmed that its amorphous biopolymeric matrix was of microbial (likely bacterial origin. The presence of dispersants and crude oil with/without nutrients resulted in distinct microbial responses marked by intermittent, and in some cases short-lived, blooms of opportunistic heterotrophs, principally obligate hydrocarbonoclastic (Alcanivorax

  18. Industrial point source CO2 emission strength estimation with aircraft measurements and dispersion modelling.

    Science.gov (United States)

    Carotenuto, Federico; Gualtieri, Giovanni; Miglietta, Franco; Riccio, Angelo; Toscano, Piero; Wohlfahrt, Georg; Gioli, Beniamino

    2018-02-22

    CO 2 remains the greenhouse gas that contributes most to anthropogenic global warming, and the evaluation of its emissions is of major interest to both research and regulatory purposes. Emission inventories generally provide quite reliable estimates of CO 2 emissions. However, because of intrinsic uncertainties associated with these estimates, it is of great importance to validate emission inventories against independent estimates. This paper describes an integrated approach combining aircraft measurements and a puff dispersion modelling framework by considering a CO 2 industrial point source, located in Biganos, France. CO 2 density measurements were obtained by applying the mass balance method, while CO 2 emission estimates were derived by implementing the CALMET/CALPUFF model chain. For the latter, three meteorological initializations were used: (i) WRF-modelled outputs initialized by ECMWF reanalyses; (ii) WRF-modelled outputs initialized by CFSR reanalyses and (iii) local in situ observations. Governmental inventorial data were used as reference for all applications. The strengths and weaknesses of the different approaches and how they affect emission estimation uncertainty were investigated. The mass balance based on aircraft measurements was quite succesful in capturing the point source emission strength (at worst with a 16% bias), while the accuracy of the dispersion modelling, markedly when using ECMWF initialization through the WRF model, was only slightly lower (estimation with an 18% bias). The analysis will help in highlighting some methodological best practices that can be used as guidelines for future experiments.

  19. Evaluating realized seed dispersal across fragmented tropical landscapes: a two-fold approach using parentage analysis and the neighbourhood model.

    Science.gov (United States)

    Ismail, Sascha A; Ghazoul, Jaboury; Ravikanth, Gudasalamani; Kushalappa, Cheppudira G; Uma Shaanker, Ramanan; Kettle, Chris J

    2017-05-01

    Despite the importance of seed dispersal for survival of plant species in fragmented landscapes, data on seed dispersal at landscape scales remain sparse. Effective seed dispersal among fragments determines recolonization and plant species persistence in such landscapes. We present the first large-scale (216-km 2 ) direct estimates of realized seed dispersal of a high-value timber tree (Dysoxylum malabaricum) across an agro-forest landscape in the Western Ghats, India. Based upon an exhaustive inventory of adult trees and a sample of 488 seedlings all genotyped at 10 microsatellite loci, we estimated realized seed dispersal using parentage analysis and the neighbourhood model. Our estimates found that most realized seed dispersal was within 200 m, which is insufficient to effectively bridge the distances between forest patches. We conclude that using mobility of putative animal dispersers can be misleading when estimating tropical tree species vulnerability to habitat fragmentation. This raises serious concerns about the potential of many tropical trees to recolonize isolated forest patches where high-value tree species have already been removed. © 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.

  20. Dispersion modeling of accidental releases of toxic gases - Comparison of the models and their utility for the fire brigades.

    Science.gov (United States)

    Stenzel, S.; Baumann-Stanzer, K.

    2009-04-01

    Dispersion modeling of accidental releases of toxic gases - Comparison of the models and their utility for the fire brigades. Sirma Stenzel, Kathrin Baumann-Stanzer In the case of accidental release of hazardous gases in the atmosphere, the emergency responders need a reliable and fast tool to assess the possible consequences and apply the optimal countermeasures. For hazard prediction and simulation of the hazard zones a number of air dispersion models are available. The most model packages (commercial or free of charge) include a chemical database, an intuitive graphical user interface (GUI) and automated graphical output for display the results, they are easy to use and can operate fast and effective during stress situations. The models are designed especially for analyzing different accidental toxic release scenarios ("worst-case scenarios"), preparing emergency response plans and optimal countermeasures as well as for real-time risk assessment and management. There are also possibilities for model direct coupling to automatic meteorological stations, in order to avoid uncertainties in the model output due to insufficient or incorrect meteorological data. Another key problem in coping with accidental toxic release is the relative width spectrum of regulations and values, like IDLH, ERPG, AEGL, MAK etc. and the different criteria for their application. Since the particulate emergency responders and organizations require for their purposes unequal regulations and values, it is quite difficult to predict the individual hazard areas. There are a quite number of research studies and investigations coping with the problem, anyway the end decision is up to the authorities. The research project RETOMOD (reference scenarios calculations for toxic gas releases - model systems and their utility for the fire brigade) was conducted by the Central Institute for Meteorology and Geodynamics (ZAMG) in cooperation with the Vienna fire brigade, OMV Refining & Marketing GmbH and