International Nuclear Information System (INIS)
Suh, K.Y.; Todreas, N.E.; Robsenow, W.M.
1987-01-01
An experimental study has been conducted to confirm and validate the predictive models and correlations for low flow frictional pressure loss in vertical rod bundle geometries under natural circulation conditions. An experimental procedure has been developed to measure low magnitude differential pressures under mixed convection conditions in 19 heated rod bare and wire-wrapped assemblies. The proposed model has been found to successfully predict the effects of wire wrapping, power skew, transition from laminar regime, developing and interacting global and local flow redistributions, and rod number on the mixed convection friction loss characteristics of rod bundles
Error characterization of CO2 vertical mixing in the atmospheric transport model WRF-VPRM
Directory of Open Access Journals (Sweden)
U. Karstens
2012-03-01
Full Text Available One of the dominant uncertainties in inverse estimates of regional CO2 surface-atmosphere fluxes is related to model errors in vertical transport within the planetary boundary layer (PBL. In this study we present the results from a synthetic experiment using the atmospheric model WRF-VPRM to realistically simulate transport of CO2 for large parts of the European continent at 10 km spatial resolution. To elucidate the impact of vertical mixing error on modeled CO2 mixing ratios we simulated a month during the growing season (August 2006 with different commonly used parameterizations of the PBL (Mellor-Yamada-Janjić (MYJ and Yonsei-University (YSU scheme. To isolate the effect of transport errors we prescribed the same CO2 surface fluxes for both simulations. Differences in simulated CO2 mixing ratios (model bias were on the order of 3 ppm during daytime with larger values at night. We present a simple method to reduce this bias by 70–80% when the true height of the mixed layer is known.
Modelling turbulent vertical mixing sensitivity using a 1-D version of NEMO
Reffray, G.; Bourdalle-Badie, R.; Calone, C.
2015-01-01
Through two numerical experiments, a 1-D vertical model called NEMO1D was used to investigate physical and numerical turbulent-mixing behaviour. The results show that all the turbulent closures tested (k+l from Blanke and Delecluse, 1993, and two equation models: generic length scale closures from Umlauf and Burchard, 2003) are able to correctly reproduce the classical test of Kato and Phillips (1969) under favourable numerical conditions while some solutions may diverge depending on the degradation of the spatial and time discretization. The performances of turbulence models were then compared with data measured over a 1-year period (mid-2010 to mid-2011) at the PAPA station, located in the North Pacific Ocean. The modelled temperature and salinity were in good agreement with the observations, with a maximum temperature error between -2 and 2 °C during the stratified period (June to October). However, the results also depend on the numerical conditions. The vertical RMSE varied, for different turbulent closures, from 0.1 to 0.3 °C during the stratified period and from 0.03 to 0.15 °C during the homogeneous period. This 1-D configuration at the PAPA station (called PAPA1D) is now available in NEMO as a reference configuration including the input files and atmospheric forcing set described in this paper. Thus, all the results described can be recovered by downloading and launching PAPA1D. The configuration is described on the NEMO site (PAPA">http://www.nemo-ocean.eu/Using-NEMO/Configurations/C1D_PAPA). This package is a good starting point for further investigation of vertical processes.
International Nuclear Information System (INIS)
El-Doma, M.
2001-02-01
The stability of the endemic equilibrium of an SIS age-structured epidemic model of a vertically as well as horizontally transmitted disease is investigated when the force of infection is of proportionate mixing assumption type. We also investigate the uniform weak disease persistence. (author)
Sundfjord, Arild; Ellingsen, Ingrid; Slagstad, Dag; Svendsen, Harald
2008-10-01
Numerical ocean model simulations of the marginal ice zone (MIZ) of the Barents Sea have been made for the years 2003-2005. As part of a project studying carbon cycling in the northern Barents Sea MIZ, the model simulations provide a pre-history and context for interpretation of physical, biological and chemical field data collected during the annual project cruises in this period. Large-scale features as well as the temporal evolution of stratification and vertical mixing, from well-mixed winter conditions to the end of the ice-free season, are described. Modelled ice concentration at the times of the annual project cruises is in agreement with that inferred from satellite data. The simulated seasonal development of mixing and stratification in the MIZ, from winter via the melting period and through the productive summer season, is described. Turbulent mixing forced by tidal currents and wind episodes is examined, and resulting hydrographical conditions and diffusivities are compared with previously published measurements from the project cruises. The vertical and temporal extent to which such variable mixing influences the water column is realistically modelled, but the strength of mixing appears to be inaccurately distributed. Most importantly, differences in modelled and observed water-column stratification are identified. Enhanced near-surface mixing appears to protrude too deeply in the model, and the water column is excessively homogenized below the pycnocline. Experiments with the Mellor-Yamada Level 2.5 turbulence scheme are compared with those from the Richardson number scheme routinely used in the model. Some important differences between the schemes are identified, but both have similar problems with respect to resulting hydrography. Simulations with horizontal grid resolution increased from 4×4 km to 800×800 m allows for processes inducing significantly more energetic frontal mixing at the MIZ edge to be resolved.
A Nonlinear Model of Mix Coil Spring – Rubber for Vertical Suspension of Railway Vehicle
Directory of Open Access Journals (Sweden)
Dumitriu Mădălina
2016-03-01
Full Text Available The paper focuses on a nonlinear model to represent the mechanical behaviour of a mix coil spring - rubber used in the secondary suspension of passenger rail vehicles. The principle of the model relies on overlapping of the forces corresponding to three components - the elastic component, the viscous component and the dry friction component. The model has two sources on non-linearity, in the elastic force and the friction force, respectively. The main attributes of the model are made visible by its response to an imposed displacement-type harmonic excitation. The results thus obtained from the applications of numerical simulation show a series of basic properties of the model, namely the dependence on amplitude and the excitation frequency of the model response, as well as of its stiffness and damping.
Curtis, Jeffrey H.; Riemer, Nicole; West, Matthew
2017-11-01
The PartMC-MOSAIC particle-resolved aerosol model was previously developed to predict the aerosol mixing state as it evolves in the atmosphere. However, the modeling framework was limited to a zero-dimensional box model approach without resolving spatial gradients in aerosol concentrations. This paper presents the development of stochastic particle methods to simulate turbulent diffusion and dry deposition of aerosol particles in a vertical column within the planetary boundary layer. The new model, WRF-PartMC-MOSAIC-SCM, resolves the vertical distribution of aerosol mixing state. We verified the new algorithms with analytical solutions for idealized test cases and illustrate the capabilities with results from a 2-day urban scenario that shows the evolution of black carbon mixing state in a vertical column.
Characterization of vertical mixing in oscillatory vegetated flows
Abdolahpour, M.; Ghisalberti, M.; Lavery, P.; McMahon, K.
2016-02-01
Seagrass meadows are primary producers that provide important ecosystem services, such as improved water quality, sediment stabilisation and trapping and recycling of nutrients. Most of these ecological services are strongly influenced by the vertical exchange of water across the canopy-water interface. That is, vertical mixing is the main hydrodynamic process governing the large-scale ecological and environmental impact of seagrass meadows. The majority of studies into mixing in vegetated flows have focused on steady flow environments whereas many coastal canopies are subjected to oscillatory flows driven by surface waves. It is known that the rate of mass transfer will vary greatly between unidirectional and oscillatory flows, necessitating a specific investigation of mixing in oscillatory canopy flows. In this study, we conducted an extensive laboratory investigation to characterise the rate of vertical mixing through a vertical turbulent diffusivity (Dt,z). This has been done through gauging the evolution of vertical profiles of concentration (C) of a dye sheet injected into a wave-canopy flow. Instantaneous measurement of the variance of the vertical concentration distribution ( allowed the estimation of a vertical turbulent diffusivity (). Two types of model canopies, rigid and flexible, with identical heights and frontal areas, were subjected to a wide and realistic range of wave height and period. The results showed two important mechanisms that dominate vertical mixing under different conditions: a shear layer that forms at the top of the canopy and wake turbulence generated by the stems. By allowing a coupled contribution of wake and shear layer mixing, we present a relationship that can be used to predict the rate of vertical mixing in coastal canopies. The results further showed that the rate of vertical mixing within flexible vegetation was always lower than the corresponding rigid canopy, confirming the impact of plant flexibility on canopy
Wang, Shudong; Jiao, Hong; Jin, Ying; Thum, Yeow Meng
2010-01-01
The vertical scales of large-scale achievement tests created by using item response theory (IRT) models are mostly based on cluster (or correlated) educational data in which students usually are clustered in certain groups or settings (classrooms or schools). While such application directly violated assumption of independent sample of person in…
Topographic enhancement of vertical turbulent mixing in the Southern Ocean
Mashayek, A.; Ferrari, R.; Merrifield, S.; Ledwell, J. R.; St Laurent, L.; Garabato, A. Naveira
2017-03-01
It is an open question whether turbulent mixing across density surfaces is sufficiently large to play a dominant role in closing the deep branch of the ocean meridional overturning circulation. The diapycnal and isopycnal mixing experiment in the Southern Ocean found the turbulent diffusivity inferred from the vertical spreading of a tracer to be an order of magnitude larger than that inferred from the microstructure profiles at the mean tracer depth of 1,500 m in the Drake Passage. Using a high-resolution ocean model, it is shown that the fast vertical spreading of tracer occurs when it comes in contact with mixing hotspots over rough topography. The sparsity of such hotspots is made up for by enhanced tracer residence time in their vicinity due to diffusion toward weak bottom flows. The increased tracer residence time may explain the large vertical fluxes of heat and salt required to close the abyssal circulation.
International Nuclear Information System (INIS)
Li, R.
2012-01-01
The aim of this research dissertation is at studying natural and mixed convections of fluid flows, and to develop and validate numerical schemes for interface tracking in order to treat incompressible and immiscible fluid flows, later. In a first step, an original numerical method, based on Finite Volume discretizations, is developed for modeling low Mach number flows with large temperature gaps. Three physical applications on air flowing through vertical heated parallel plates were investigated. We showed that the optimum spacing corresponding to the peak heat flux transferred from an array of isothermal parallel plates cooled by mixed convection is smaller than those for natural or forced convections when the pressure drop at the outlet keeps constant. We also proved that mixed convection flows resulting from an imposed flow rate may exhibit unexpected physical solutions; alternative model based on prescribed total pressure at inlet and fixed pressure at outlet sections gives more realistic results. For channels heated by heat flux on one wall only, surface radiation tends to suppress the onset of re-circulations at the outlet and to unify the walls temperature. In a second step, the mathematical model coupling the incompressible Navier-Stokes equations and the Level-Set method for interface tracking is derived. Improvements in fluid volume conservation by using high order discretization (ENO-WENO) schemes for the transport equation and variants of the signed distance equation are discussed. (author)
Energy Technology Data Exchange (ETDEWEB)
Rasmussen, A.; Soerensen, J.H.; Nielsen, N.W. [Danish Meteorological Inst., DMI, Copenhagen (Denmark)
1997-10-01
A sensitivity study is performed of vertical profiles from the numerical weather prediction model DMI-HIRLAM (DMI-HIgh Resolution Limited Area Model). The study involves profiles of horizontal wind, temperature and humidity in the lower troposphere up to 2500 meter. Detailed comparisons of analysed as well as forecast profiles are made with measured data from several radio-sonde stations throughout Europe. Methods for estimating the Mixing Height (MH) based on a bulk Richardson number method, the Vogelezang and Holtslag method and parcel methods are also studied. The methods are inter-compared, and MH based on data from DMI-HIRLAM are compared with the corresponding MH based on radiosonde data. For convective conditions the MH estimates are also compared with subjective estimates of the MH. In this paper preliminary results mainly based on data from Jaegersborg (Copenhagen) are presented. Results based on data from 1994-95 show that the resemblance between measured profiles and the DMI-HIRLAM profiles is fairly good in general. Also the estimates of the MH based on DMI-HIRLAM data is in general of nearly the same quality as estimations based on observed data. However, especially in convective conditions there is a tendency by DMI-HIRLAM to underestimate the strength of the mixing and thereby relatively large errors in the estimates of the MH can occur. (au)
International Nuclear Information System (INIS)
Hall, S.H.; Johnson, V.G.; Early, T.O.
1987-11-01
Tritium, 14 C, and 129 I in groundwater samples are used to demonstrate vertical recharge and measure flow velocity in the fractured and faulted Umtanum Ridge-Gable Mountain acticline, within the Columbia River Basalts, at a sampling site about 6 mi northeast of the proposed high-level nuclear waste repository at the Hanford Site, Washington State. Mixing model calculations yield an apparent downward migration rate of 15 to 19 ft/yr through a sequence of aquifers in the Wanapum Basalt that range in depth from 698 to 1373 ft. Estimates of the vertical flow rate in the overlying Saddle Mountains Basalt are somewhat higher. Hydrographs from neighboring wells, hydrostatic heads, pump test data, and the chemical composition of groundwater samples from the sampling well are consistent with interaquifer communication. Some hydrologic evidence from aquifers in this region suggests that, in the past, flow may have been upward. This possible reversal of flow may be associated with water table mounding in the unconfined aquifer, caused by waste disposal activities at the Hanford Site since World War II. 17 refs., 12 figs., 3 tabs
Role of vertical and horizontal mixing in the tape recorder signal near the tropical tropopause
Glanville, Anne A.; Birner, Thomas
2017-03-01
Nearly all air enters the stratosphere through the tropical tropopause layer (TTL). The TTL therefore exerts a control on stratospheric chemistry and climate. The hemispheric meridional overturning (Brewer-Dobson) circulation spreads this TTL influence upward and poleward. Stratospheric water vapor concentrations are set near the tropical tropopause and are nearly conserved in the lowermost stratosphere. The resulting upward propagating tracer transport signal of seasonally varying entry concentrations is known as the tape recorder signal. Here, we study the roles of vertical and horizontal mixing in shaping the tape recorder signal in the tropical lowermost stratosphere, focusing on the 80 hPa level. We analyze the tape recorder signal using data from satellite observations, a reanalysis, and a chemistry-climate model (CCM). By modifying past methods, we are able to capture the seasonal cycle of effective vertical transport velocity in the tropical lowermost stratosphere. Effective vertical transport velocities are found to be multiple times stronger than residual vertical velocities for the reanalysis and the CCM. We also study the tape recorder signal in an idealized 1-D transport model. By performing a parameter sweep, we test a range of different strengths of transport contributions by vertical advection, vertical mixing, and horizontal mixing. By introducing seasonality into the transport strengths, we find that the most successful simulation of the observed tape recorder signal requires vertical mixing at 80 hPa that is multiple times stronger compared to previous estimates in the literature. Vertical mixing is especially important during boreal summer when vertical advection is weak. Simulating the reanalysis tape recorder requires excessive amounts of vertical mixing compared to observations but also to the CCM, which hints at the role of spurious dispersion due to data assimilation. Contrasting the results between pressure and isentropic coordinates
Mixed multilayered vertical heterostructures utilizing strained monolayer WS2
Sheng, Yuewen; Xu, Wenshuo; Wang, Xiaochen; He, Zhengyu; Rong, Youmin; Warner, Jamie H.
2016-01-01
Creating alternating layers of 2D materials forms vertical heterostructures with diverse electronic and opto-electronic properties. Monolayer WS2 grown by chemical vapour deposition can have inherent strain due to interactions with the substrate. The strain modifies the band structure and properties of monolayer WS2 and can be exploited in a wide range of applications. We demonstrate a non-aqueous transfer method for creating vertical stacks of mixed 2D layers containing a strained monolayer of WS2, with Boron Nitride and Graphene. The 2D materials are all grown by CVD, enabling large area vertical heterostructures to be formed. WS2 monolayers grown by CVD directly on Si substrates with SiO2 surface are easily washed off by water and this makes aqueous based transfer methods challenging for creating vertical stacks on the growth substrate. 2D hexagonal Boron Nitride films are used to provide an insulating layer that limits interactions with a top graphene layer and preserve the strong photoluminescence from the WS2. This transfer method is suitable for layer by layer control of 2D material vertical stacks and is shown to be possible for all CVD grown samples, which opens up pathways for the rapid large scale fabrication of vertical heterostructure systems with atomic thickness depth control and large area coverage.Creating alternating layers of 2D materials forms vertical heterostructures with diverse electronic and opto-electronic properties. Monolayer WS2 grown by chemical vapour deposition can have inherent strain due to interactions with the substrate. The strain modifies the band structure and properties of monolayer WS2 and can be exploited in a wide range of applications. We demonstrate a non-aqueous transfer method for creating vertical stacks of mixed 2D layers containing a strained monolayer of WS2, with Boron Nitride and Graphene. The 2D materials are all grown by CVD, enabling large area vertical heterostructures to be formed. WS2 monolayers grown by
Mixed convection flow and heat transfer in a vertical wavy channel ...
African Journals Online (AJOL)
Mixed convection flow and heat transfer in a vertical wavy channel filled with porous and fluid layers is studied analytically. The flow in the porous medium is modeled using Darcy-Brinkman equation. The coupled non-linear partial differential equations describing the conservation of mass, momentum and energy are solved ...
VERTICAL CONTROL OF OVERBITE IN MIXED DENTITION BY TRAINER SYSTEM
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Miroslava Dinkova
2014-11-01
Full Text Available Purpose. The purpose of this study is to follow-up the biometrical and skeletal vertical changes in patients with deep overbite in mixed dentition after a functional orthodontic treatment with Trainer System™ is conducted. Material and Methods. 32 patients (20 girls and 12 boys with deep overbite in mixed dentition were followed-up. An orthodontic treatment with Trainer System™, including Trainer for kids (T4K-blue, T4K-red and Myobrace was conducted. The recommended time for wearing the appliances was 8–12 hours, mostly at the night and 1–2 hours total time during the day. All the patients were photo-documented. Impressions, panoramic radiographs and lateral cephalograms were taken before the beginning of the treatment and at the end of every single step in relation with every change of appliances. Comparative biometrical and cephalometric analyses were made. The data was statistically processed. Results. The comparative biometrical analyses showed reduction of overbite with 2.5–3.5 mm after the end of the orthodontic treatment. 62% of cases showed relapse from 0.5 to 1mm. After the end of the orthodontic treatment an inclination of upper and lower incisors and changes with M/SN, М/F, ANB, SNA, SNB values were established. Conclusions. If untreated during the growing period, deep overbite leads to serious functional disorders, pathologic abrasion and myo-articular problems. Myofunctional Trainer System™ is successfully applied in the management of deep overbite in growing kids with early mixed dentition. The design of appliances helps the right positioning of tongue and jaws, removes bad habits, harmonizes tooth arches, corrects the vertical problems.
Energy Technology Data Exchange (ETDEWEB)
Lee, S; Dimenna, R; Tamburello, D
2011-02-14
height from zero to 10 ft. The sludge has been characterized and modeled as micron-sized solids, typically 1 to 5 microns, at weight fractions as high as 20 to 30 wt%, specific gravities to 1.4, and viscosities up to 64 cp during motion. The sludge is suspended and mixed through the use of submersible slurry jet pumps. To suspend settled sludge, water is added to the tank as a slurry medium and stirred with the jet pump. Although there is considerable technical literature on mixing and solid suspension in agitated tanks, very little literature has been published on jet mixing in a large-scale tank. One of the main objectives in the waste processing is to provide feed of a uniform slurry composition at a certain weight percentage (e.g. typically {approx}13 wt% at SRS) over an extended period of time. In preparation of the sludge for slurrying, several important questions have been raised with regard to sludge suspension and mixing of the solid suspension in the bulk of the tank: (1) How much time is required to prepare a slurry with a uniform solid composition? (2) How long will it take to suspend and mix the sludge for uniform composition in any particular waste tank? (3) What are good mixing indicators to answer the questions concerning sludge mixing stated above in a general fashion applicable to any waste tank/slurry pump geometry and fluid/sludge combination?
Directory of Open Access Journals (Sweden)
Michael Howlett
2017-05-01
Full Text Available Multifaceted problems such as sustainable development typically involve complex arrangements of institutions and instruments and the subject of how best to design and operate such ‘mixes’, ‘bundles’ or ‘portfolios’ of policy tools is an ongoing issue in this area. One aspect of this question is that some mixes are more difficult to design and operate than others. The paper argues that, ceteris paribus, complex policy-making faces substantial risks of failure when horizontal or vertical dimensions of policy-making are not well integrated. The paper outlines a model of policy mix types which highlights the design problems associated with more complex arrangements and presents two case studies of similarly structured mixes in the areas of marine parks in Australia and coastal zone management in Europe—one a failure and the other a successful case of integration—to illustrate how such mixes can be better designed and managed more effectively.
Boyanovsky, Daniel; Chen, Junmou
2017-11-01
Extensions beyond the standard model allow for a gauge singlet scalar to be kinetically coupled with the Higgs. We consider kinetic mixing between a dark scalar gauge singlet nearly degenerate with the Higgs, focusing on the dynamical aspects of the mixing phenomena. The renormalization program is carried out by obtaining the one-loop effective action which yields an effective non-Hermitian Hamiltonian to study the dynamics of mixing. The scalar Higgs becomes a coherent superposition of the mass eigenstates, thus kinetic mixing leads to oscillations and common decay channels in striking similarity with neutral meson mixing. Near degeneracy yields an enhancement of the kinetic coupling. For small kinetic mixing we find that the mass eigenstates feature different lifetimes which result in a wide separation of time scales of evolution along with important coherence aspects from dark scalar-Higgs interference. The wide separation of scales is manifest as displaced decay vertices which could potentially be a telltale experimental signal of kinetic mixing.
Directory of Open Access Journals (Sweden)
S. Dutreuil
2009-05-01
Full Text Available Artificially enhanced vertical mixing has been suggested as a means by which to fertilize the biological pump with subsurface nutrients and thus increase the oceanic CO_{2} sink. We use an ocean general circulation and biogeochemistry model (OGCBM to examine the impact of artificially enhanced vertical mixing on biological productivity and atmospheric CO_{2}, as well as the climatically significant gases nitrous oxide (N_{2}O and dimethyl sulphide (DMS during simulations between 2000 and 2020. Overall, we find a large increase in the amount of organic carbon exported from surface waters, but an overall increase in atmospheric CO_{2} concentrations by 2020. We quantified the individual effect of changes in dissolved inorganic carbon (DIC, alkalinity and biological production on the change in pCO_{2} at characteristic sites and found the increased vertical supply of carbon rich subsurface water to be primarily responsible for the enhanced CO_{2} outgassing, although increased alkalinity and, to a lesser degree, biological production can compensate in some regions. While ocean-atmosphere fluxes of DMS do increase slightly, which might reduce radiative forcing, the oceanic N_{2}O source also expands. Our study has implications for understanding how natural variability in vertical mixing in different ocean regions (such as that observed recently in the Southern Ocean can impact the ocean CO_{2} sink via changes in DIC, alkalinity and carbon export.
Heat Transfer in MHD Mixed Convection Flow of a Ferrofluid along a Vertical Channel.
Directory of Open Access Journals (Sweden)
Aaiza Gul
Full Text Available This study investigated heat transfer in magnetohydrodynamic (MHD mixed convection flow of ferrofluid along a vertical channel. The channel with non-uniform wall temperatures was taken in a vertical direction with transverse magnetic field. Water with nanoparticles of magnetite (Fe3O4 was selected as a conventional base fluid. In addition, non-magnetic (Al2O3 aluminium oxide nanoparticles were also used. Comparison between magnetic and magnetite nanoparticles were also conducted. Fluid motion was originated due to buoyancy force together with applied pressure gradient. The problem was modelled in terms of partial differential equations with physical boundary conditions. Analytical solutions were obtained for velocity and temperature. Graphical results were plotted and discussed. It was found that temperature and velocity of ferrofluids depend strongly on viscosity and thermal conductivity together with magnetic field. The results of the present study when compared concurred with published work.
The effect of wind mixing on the vertical distribution of buoyant plastic debris
Kukulka, T.; Proskurowski, G.; Morét-Ferguson, S.; Meyer, D. W.; Law, K. L.
2012-04-01
Micro-plastic marine debris is widely distributed in vast regions of the subtropical gyres and has emerged as a major open ocean pollutant. The fate and transport of plastic marine debris is governed by poorly understood geophysical processes, such as ocean mixing within the surface boundary layer. Based on profile observations and a one-dimensional column model, we demonstrate that plastic debris is vertically distributed within the upper water column due to wind-driven mixing. These results suggest that total oceanic plastics concentrations are significantly underestimated by traditional surface measurements, requiring a reinterpretation of existing plastic marine debris data sets. A geophysical approach must be taken in order to properly quantify and manage this form of marine pollution.
A vertically resolved model for phytoplankton aggregation
Indian Academy of Sciences (India)
This work presents models of the vertical distribution and flux of phytoplankton aggregates, including changes with time in the ... in the Arabian Sea; it demonstrates that aggregation can be important for deep sedimentation even when its effect on surface ... western parts, deep flux is strongly coupled to the increase in wind ...
Assessing ocean vertical mixing schemes for the study of climate change
Howard, A. M.; Lindo, F.; Fells, J.; Tulsee, V.; Cheng, Y.; Canuto, V.
2014-12-01
Climate change is a burning issue of our time. It is critical to know the consequences of choosing "business as usual" vs. mitigating our emissions for impacts e.g. ecosystem disruption, sea-level rise, floods and droughts. To make predictions we must model realistically each component of the climate system. The ocean must be modeled carefully as it plays a critical role, including transporting heat and storing heat and dissolved carbon dioxide. Modeling the ocean realistically in turn requires physically based parameterizations of key processes in it that cannot be explicitly represented in a global climate model. One such process is vertical mixing. The turbulence group at NASA-GISS has developed a comprehensive new vertical mixing scheme (GISSVM) based on turbulence theory, including surface convection and wind shear, interior waves and double-diffusion, and bottom tides. The GISSVM is tested in stand-alone ocean simulations before being used in coupled climate models. It is also being upgraded to more faithfully represent the physical processes. To help assess mixing schemes, students use data from NASA-GISS to create visualizations and calculate statistics including mean bias and rms differences and correlations of fields. These are created and programmed with MATLAB. Results with the commonly used KPP mixing scheme and the present GISSVM and candidate improved variants of GISSVM will be compared between stand-alone ocean models and coupled models and observations. This project introduces students to modeling of a complex system, an important theme in contemporary science and helps them gain a better appreciation of climate science and a new perspective on it. They also gain familiarity with MATLAB, a widely used tool, and develop skills in writing and understanding programs. Moreover they contribute to the advancement of science by providing information that will help guide the improvement of the GISSVM and hence of ocean and climate models and ultimately our
Lateral Mixing Mechanisms in Vertical and Horizontal Interconnected Subchannel Two-Phase Flows
International Nuclear Information System (INIS)
Gencay, Sarman; Teyssedou, Alberto; Tye, Peter
2002-01-01
A lateral mixing model based on equal volume exchange between two laterally interconnected subchannels is presented. The following mixing mechanisms are taken into account in this model: (a) diversion cross flow, caused by the lateral pressure difference between adjacent subchannels; (b) turbulent void diffusion, which is governed by the lateral void fraction difference between the subchannels; (c) void drift, responsible for the tendency of the vapor phase to drift toward unobstructed regions; and (d) buoyancy drift, which takes into account the effect of gravity in horizontal flows. Experimental two-phase air-water data obtained using two test sections having different geometries and orientations are used to determine the diffusion coefficients required by the mixing model. Under the absence of diversion crossflow, i.e., negligible lateral pressure difference between the subchannels, it is observed that the diffusion coefficient increases with increasing average void fraction in the subchannels. Moreover, for vertical flows turbulent void diffusion seems to be considerably affected by the geometry of the subchannels. For horizontal flows under nonsymmetric inlet void fraction conditions, even though the interconnected subchannels have the same geometry, different turbulent void diffusion and void drift coefficients are required to satisfy the conditions of hydrodynamic equilibrium. In the present study this condition is achieved by introducing a new void drift coefficient expressed as a correction term applied to the turbulent void drift term
Vertical mixing and coherent anticyclones in the ocean: the role of stratification
Directory of Open Access Journals (Sweden)
I. Koszalka
2010-01-01
Full Text Available The role played by wind-forced anticyclones in the vertical transport and mixing at the ocean mesoscale is investigated with a primitive-equation numerical model in an idealized configuration. The focus of this work is to determine how the stratification impacts such transport.
The flows, forced only at the surface by an idealized wind forcing, are predominantly horizontal and, on average, quasigeostrophic. Inside vortex cores and intense filaments, however, the dynamics is strongly ageostrophic.
Mesoscale anticyclones appear as "islands" of increased penetration of wind energy into the ocean interior and they represent the maxima of available potential energy. The amount of available potential energy is directly correlated with the degree of stratification.
The wind energy injected at the surface is transferred at depth through the generation and subsequent straining effect of Vortex Rossby Waves (VRWs, and through near-inertial internal oscillations trapped inside anticyclonic vortices. Both these mechanisms are affected by stratification. Stronger transfer but larger confinement close to the surface is found when the stratification is stronger. For weaker stratification, vertical mixing close to the surface is less intense but below about 150 m attains substantially higher values due to an increased contribution of both VRWs, whose time scale is on the order of few days, and of near-inertial motions, with a time scale of few hours.
Huggenberger, P.; Huber, E.
2014-12-01
Detailed descriptions of the subsurface heterogeneities in coarse fluvial aquifer gravel often lack in concepts to distinguish between the essence and the noise of a permeability structure and the ability to extrapolate site specific hydraulic information at the tens to several hundred meters scale. At this scale the heterogeneity strongly influences the anisotropies of the flow field and the mixing processes in groundwater. However, in many hydrogeological models the complexity of natural systems is oversimplified. Understanding the link between the dynamics of the surface processes of braided-river systems and the resulting subsurface sedimentary structures is the key to characterizing the complexity of horizontal and vertical mixing processes in groundwater. From the different depositional elements of coarse braided-river systems, the largest permeability contrasts can be observed in the scour-fills. Other elements (e.g. different types of gravel sheets) show much smaller variabilities and could be considered as a kind of matrix. Field experiments on the river Tagliamento (Northeast Italy) based on morphological observation and ground-penetrating radar (GPR) surveys, as well as outcrop analyses of gravel pit exposures (Switzerland) allowed us to define the shape, sizes, spatial distribution and preservation potential of scour-fills. In vertical sections (e.g. 2D GPR data, vertical outcrop), the spatial density of remnant erosional bounding surfaces of scours is an indicator for the dynamics of the braided-river system (lateral mobility of the active floodplain, rate of sediment net deposition and spatial distribution of the confluence scours). In case of combined low aggradation rate and low lateral mobility the deposits may be dominated by a complex overprinting of scour-fills. The delineation of the erosional bounding surfaces, that are coherent over the survey area, is based on the identification of angular discontinuities of the reflectors. Fence diagrams
Directory of Open Access Journals (Sweden)
Nobuaki Kimura
2016-10-01
Full Text Available Studying mixing processes in a stratified lake is important for understanding the biological, chemical and physical processes occurring there. Statistical analyses were performed of data from a small, shallow, stratified lake in a subtropical alpine region (Yuan-Yang Lake in Taiwan to determine the predominant physical factors in heavy-rainfall-induced mixing. This study focused on both vertical mixing in the entire water column and surface-layer mixing extending to the upper thermocline. The effects of meteorological driving forces, such as wind, heating/cooling and inflow on vertical mixing and surface layer mixing, were evaluated using the relationships between each driving force and the change in thermal stability between the pre-mixing and mixing periods. For surface layer mixing, a comparison between penetrative convection related to heating/cooling and wind-related friction velocity was conducted for each heavy rainfall event. A heat content parameter measuring thermal potential energy was introduced to further investigate inflow effects (e.g. effects of changes in discharge volume and temperature on vertical mixing during heavy rainfall events. Results show that wind input affected vertical mixing more significantly than did other meteorological forcing factors during storm-dominant events. Indeed, wind energy input in the surface layer was more pronounced than was energy of heating/cooling for surface layer mixing. Furthermore, inflow effect was shown to be crucial during large scale and extreme weather events (i.e. lower air pressure events in the vertical mixing process. Forcing by heating/cooling likely contributes less to mixing because it is likely less dynamic than the wind and inflow inputs with respect to internal response of the lake. In addition, a principal component analysis (PCA modified by partial correlation was performed to verify the results quantitatively. The first and second components, which accounted for more than
Generalized, Linear, and Mixed Models
McCulloch, Charles E; Neuhaus, John M
2011-01-01
An accessible and self-contained introduction to statistical models-now in a modernized new editionGeneralized, Linear, and Mixed Models, Second Edition provides an up-to-date treatment of the essential techniques for developing and applying a wide variety of statistical models. The book presents thorough and unified coverage of the theory behind generalized, linear, and mixed models and highlights their similarities and differences in various construction, application, and computational aspects.A clear introduction to the basic ideas of fixed effects models, random effects models, and mixed m
Shu, Qian; Koo, Bonyoung; Yarwood, Greg; Henderson, Barron H.
2017-12-01
Differences between two air quality modeling systems reveal important uncertainties in model representations of secondary organic aerosol (SOA) fate. Two commonly applied models (CMAQ: Community Multiscale Air Quality; CAMx: Comprehensive Air Quality Model with extensions) predict very different OA concentrations over the eastern U.S., even when using the same source data for emissions and meteorology and the same SOA modeling approach. Both models include an option to output a detailed accounting of how each model process (e.g., chemistry, deposition, etc.) alters the mass of each modeled species, referred to as process analysis. We therefore perform a detailed diagnostic evaluation to quantify simulated tendencies (Gg/hr) of each modeled process affecting both the total model burden (Gg) of semi-volatile organic compounds (SVOC) in the gas (g) and aerosol (a) phases and the vertical structures to identify causes of concentration differences between the two models. Large differences in deposition (CMAQ: 69.2 Gg/d; CAMx: 46.5 Gg/d) contribute to significant OA bias in CMAQ relative to daily averaged ambient concentration measurements. CMAQ's larger deposition results from faster daily average deposition velocities (VD) for both SVOC (g) (VD,cmaq = 2.15 × VD,camx) and aerosols (VD,cmaq = 4.43 × Vd,camx). Higher aerosol deposition velocity would be expected to cause similar biases for inert compounds like elemental carbon (EC), but this was not seen. Daytime low-biases in EC were also simulated in CMAQ as expected but were offset by nighttime high-biases. Nighttime high-biases were a result of overly shallow mixing in CMAQ leading to a higher fraction of EC total atmospheric mass in the first layer (CAMx: 5.1-6.4%; CMAQ: 5.6-6.9%). Because of the opposing daytime and nighttime biases, the apparent daily average bias for EC is reduced. For OA, there are two effects of reduced vertical mixing: SOA and SVOC are concentrated near the surface, but SOA yields are reduced
Deep circulation driven by strong vertical mixing in the Timor Basin
Cuypers, Yannis; Pous, Stephane; Sprintall, Janet; Atmadipoera, Agus; Madec, Gurvan; Molcard, Robert
2017-02-01
The importance of deep mixing in driving the deep part of the overturning circulation has been a long debated question at the global scale. Our observations provide an illustration of this process at the Timor Basin scale of ˜1000 km. Long-term averaged moored velocity data at the Timor western sill suggest that a deep circulation is present in the Timor Basin. An inflow transport of ˜0.15 Sv is observed between 1600 m and the bottom at 1890 m. Since the basin is closed on its eastern side below 1250 m depth, a return flow must be generated above 1600 m with a ˜0.15 Sv outflow. The vertical turbulent diffusivity is inferred from a heat and transport balance at the basin scale and from Thorpe scale analysis. Basin averaged vertical diffusivity is as large as 1 × 10-3 m2 s-1. Observations are compared with regional low-resolution numerical simulations, and the deep observed circulation is only recovered when a strong vertical diffusivity resulting from the parameterization of internal tidal mixing is considered. Furthermore, the deep vertical mixing appears to be strongly dependent on the choice of the internal tide mixing parameterization and also on the prescribed value of the mixing efficiency.
Discriminative Mixed-Membership Models
National Aeronautics and Space Administration — Although mixed-membership models have achieved great success in unsupervised learning, they have not been widely applied to classification problems. In this paper,...
Effect of viscous dissipation on mixed convection flow in a vertical ...
African Journals Online (AJOL)
papers on mixed convection in a parallel-plate vertical channel are available in the literature. Aung and Worku (1986) ..... in electric circuit analysis. This method constructs ... which implies that the concept of differential transform method is derived from Taylor series expansion, although this method is not able to evaluate the ...
Mixed convective heat transfer from a vertical plate embedded in a ...
Indian Academy of Sciences (India)
Home; Journals; Sadhana; Volume 40; Issue 2. Mixed convective heat transfer from a vertical plate embedded in a saturated non-Darcy porous medium with concentration and melting effect. K Hemalatha Peri K Kameswaran M V D N S Madhavi. Mechanical Sciences Volume 40 Issue 2 April 2015 pp 455-465 ...
Abbring, J.H.
2009-01-01
We study mixed hitting-time models, which specify durations as the first time a Levy process (a continuous-time process with stationary and independent increments) crosses a heterogeneous threshold. Such models of substantial interest because they can be reduced from optimal-stopping models with
MixSIAR: advanced stable isotope mixing models in R
Background/Question/Methods The development of stable isotope mixing models has coincided with modeling products (e.g. IsoSource, MixSIR, SIAR), where methodological advances are published in parity with software packages. However, while mixing model theory has recently been ex...
Surface wind mixing in the Regional Ocean Modeling System (ROMS)
Robertson, Robin; Hartlipp, Paul
2017-12-01
Mixing at the ocean surface is key for atmosphere-ocean interactions and the distribution of heat, energy, and gases in the upper ocean. Winds are the primary force for surface mixing. To properly simulate upper ocean dynamics and the flux of these quantities within the upper ocean, models must reproduce mixing in the upper ocean. To evaluate the performance of the Regional Ocean Modeling System (ROMS) in replicating the surface mixing, the results of four different vertical mixing parameterizations were compared against observations, using the surface mixed layer depth, the temperature fields, and observed diffusivities for comparisons. The vertical mixing parameterizations investigated were Mellor- Yamada 2.5 level turbulent closure (MY), Large- McWilliams- Doney Kpp (LMD), Nakanishi- Niino (NN), and the generic length scale (GLS) schemes. This was done for one temperate site in deep water in the Eastern Pacific and three shallow water sites in the Baltic Sea. The model reproduced the surface mixed layer depth reasonably well for all sites; however, the temperature fields were reproduced well for the deep site, but not for the shallow Baltic Sea sites. In the Baltic Sea, the models overmixed the water column after a few days. Vertical temperature diffusivities were higher than those observed and did not show the temporal fluctuations present in the observations. The best performance was by NN and MY; however, MY became unstable in two of the shallow simulations with high winds. The performance of GLS nearly as good as NN and MY. LMD had the poorest performance as it generated temperature diffusivities that were too high and induced too much mixing. Further observational comparisons are needed to evaluate the effects of different stratification and wind conditions and the limitations on the vertical mixing parameterizations.
A Vertical Grid Module for Baroclinic Models of the Atmosphere
Energy Technology Data Exchange (ETDEWEB)
Drake, John B [ORNL
2008-04-01
The vertical grid of an atmospheric model assigns dynamic and thermo- dynamic variables to grid locations. The vertical coordinate is typically not height but one of a class of meteorological variables that vary with atmo- spheric conditions. The grid system is chosen to further numerical approx- imations of the boundary conditions so that the system is terrain following at the surface. Lagrangian vertical coordinates are useful in reducing the numerical errors from advection processes. That the choices will effect the numercial properties and accuracy is explored in this report. A MATLAB class for Lorentz vertical grids is described and applied to the vertical struc- ture equation and baroclinic atmospheric circulation. A generalized meteo- rolgoical coordinate system is developed which can support σ, isentropic θ vertical coordinate, or Lagrangian vertical coordinates. The vertical atmo- spheric column is a MATLAB class that includes the kinematic and ther- modynamic variables along with methods for computing geopoentials and terms relevant to a 3D baroclinc atmospheric model.
Simple suggestions for including vertical physics in oil spill models
International Nuclear Information System (INIS)
D'Asaro, Eric; University of Washington, Seatle, WA
2001-01-01
Current models of oil spills include no vertical physics. They neglect the effect of vertical water motions on the transport and concentration of floating oil. Some simple ways to introduce vertical physics are suggested here. The major suggestion is to routinely measure the density stratification of the upper ocean during oil spills in order to develop a database on the effect of stratification. (Author)
2016-01-01
Over recent years, several alternative relaxed clock models have been proposed in the context of Bayesian dating. These models fall in two distinct categories: uncorrelated and autocorrelated across branches. The choice between these two classes of relaxed clocks is still an open question. More fundamentally, the true process of rate variation may have both long-term trends and short-term fluctuations, suggesting that more sophisticated clock models unfolding over multiple time scales should ultimately be developed. Here, a mixed relaxed clock model is introduced, which can be mechanistically interpreted as a rate variation process undergoing short-term fluctuations on the top of Brownian long-term trends. Statistically, this mixed clock represents an alternative solution to the problem of choosing between autocorrelated and uncorrelated relaxed clocks, by proposing instead to combine their respective merits. Fitting this model on a dataset of 105 placental mammals, using both node-dating and tip-dating approaches, suggests that the two pure clocks, Brownian and white noise, are rejected in favour of a mixed model with approximately equal contributions for its uncorrelated and autocorrelated components. The tip-dating analysis is particularly sensitive to the choice of the relaxed clock model. In this context, the classical pure Brownian relaxed clock appears to be overly rigid, leading to biases in divergence time estimation. By contrast, the use of a mixed clock leads to more recent and more reasonable estimates for the crown ages of placental orders and superorders. Altogether, the mixed clock introduced here represents a first step towards empirically more adequate models of the patterns of rate variation across phylogenetic trees. This article is part of the themed issue ‘Dating species divergences using rocks and clocks’. PMID:27325829
Simon Huston; Derlie Mateo-Babiano
2013-01-01
Purpose - We explore the growth patterns and development trends of vertical mixed use (VMU) developments in a variety of cities. VMUs are defined as structures with two or more revenue producing uses or land use activities on a single site. One view is that sustainable city development requires densification via VMU construction on brown field sites (within the existing inner city footprint). Design/methodology/approach - After a systematic review of the notion of VMU buildings, we conduct a ...
Effect of interannual variation in winter vertical mixing on CH4 dynamics in a subtropical reservoir
Itoh, Masayuki; Kobayashi, Yuki; Chen, Tzong-Yueh; Tokida, Takeshi; Fukui, Manabu; Kojima, Hisaya; Miki, Takeshi; Tayasu, Ichiro; Shiah, Fuh-Kwo; Okuda, Noboru
2015-07-01
Although freshwaters are considered to be substantial natural sources of atmospheric methane (CH4), in situ processes of CH4 production and consumption in freshwater ecosystems are poorly understood, especially in subtropical areas, leading to uncertainties in the estimation of global CH4 emissions. To improve our understanding of physical and biogeochemical factors affecting CH4 dynamics in subtropical lakes, we examined vertical and seasonal profiles of dissolved CH4 and its carbon isotope ratio (δ13C) and conducted incubation experiments to assess CH4 production and oxidation in the deep subtropical Fei-Tsui Reservoir (FTR; Taiwan). The mixing pattern of the FTR is essentially monomixis, but the intensity of winter vertical mixing changes with climatic conditions. In years with incomplete vertical mixing (does not reach the bottom) and subsequent strong thermal stratification resulting in profundal hypoxia, we observed increases in sedimentary CH4 production and thus profundal CH4 storage with the development of reducing conditions. In contrast, in years with strong winter vertical mixing to the bottom of the reservoir, CH4 production was suppressed under NO3--rich conditions, during which denitrifiers have the competitive advantage over methanogens. Diffusive emission from profundal CH4 storage appeared to be negligible due to the efficiency of CH4 oxidation during ascent through methane-oxidizing bacteria (MOB) activity. Most of the profundal CH4 was rapidly oxidized by MOB in both oxic and anoxic layers, as characterized by its carbon isotope signature. In contrast, aerobic CH4 production in the subsurface layer, which may be enhanced under high temperatures in summer, may account for a large portion of atmospheric CH4 emissions from this reservoir. Our CH4 profiling results provide valuable information for future studies predicting CH4 emissions from subtropical lakes with the progress of global warming.
Cluster Correlation in Mixed Models
Gardini, A.; Bonometto, S. A.; Murante, G.; Yepes, G.
2000-10-01
We evaluate the dependence of the cluster correlation length, rc, on the mean intercluster separation, Dc, for three models with critical matter density, vanishing vacuum energy (Λ=0), and COBE normalization: a tilted cold dark matter (tCDM) model (n=0.8) and two blue mixed models with two light massive neutrinos, yielding Ωh=0.26 and 0.14 (MDM1 and MDM2, respectively). All models approach the observational value of σ8 (and hence the observed cluster abundance) and are consistent with the observed abundance of damped Lyα systems. Mixed models have a motivation in recent results of neutrino physics; they also agree with the observed value of the ratio σ8/σ25, yielding the spectral slope parameter Γ, and nicely fit Las Campanas Redshift Survey (LCRS) reconstructed spectra. We use parallel AP3M simulations, performed in a wide box (of side 360 h-1 Mpc) and with high mass and distance resolution, enabling us to build artificial samples of clusters, whose total number and mass range allow us to cover the same Dc interval inspected through Automatic Plate Measuring Facility (APM) and Abell cluster clustering data. We find that the tCDM model performs substantially better than n=1 critical density CDM models. Our main finding, however, is that mixed models provide a surprisingly good fit to cluster clustering data.
Díaz-Astudillo, Macarena; Cáceres, Mario A.; Landaeta, Mauricio F.
2017-09-01
The patterns of abundance, composition, biomass and vertical migration of zooplankton in short-time scales (ADCP device mounted on the hull of a ship were used to obtain vertical profiles of current velocity data and intensity of the backscattered acoustic signal, which was used to study the migratory strategies and to relate the echo intensity with zooplankton biomass. Repeated vertical profiles of temperature, salinity and density were obtained with a CTD instrument to describe the density patterns during both experiments. Zooplankton were sampled every 3 h using a Bongo net to determine abundance, composition and biomass. Migrations were diel in the stratified station, semi-diel in the mixed station, and controlled by light in both locations, with large and significant differences in zooplankton abundance and biomass between day and night samples. No migration pattern associated with the effect of tides was found. The depth of maximum backscatter strength showed differences of approximately 30 m between stations and was deeper in the mixed station. The relation between mean volume backscattering strength (dB) computed from echo intensity and log10 of total dry weight (mg m-3) of zooplankton biomass was moderate but significant in both locations. Biomass estimated from biological samples was higher in the mixed station and determined by euphausiids. Copepods were the most abundant group in both stations. Acoustic methods were a useful technique to understand the detailed patterns of migratory strategies of zooplankton and to help estimate zooplankton biomass and abundance in the inner waters of southern Chile.
CFD simulation of vertical linear motion mixing in anaerobic digester tanks.
Meroney, Robert N; Sheker, Robert E
2014-09-01
Computational fluid dynamics (CFD) was used to simulate the mixing characteristics of a small circular anaerobic digester tank (diameter 6 m) equipped sequentially with 13 different plunger type vertical linear motion mixers and two different type internal draft-tube mixers. Rates of mixing of step injection of tracers were calculated from which active volume (AV) and hydraulic retention time (HRT) could be calculated. Washout characteristics were compared to analytic formulae to estimate any presence of partial mixing, dead volume, short-circuiting, or piston flow. Active volumes were also estimated based on tank regions that exceeded minimum velocity criteria. The mixers were ranked based on an ad hoc criteria related to the ratio of AV to unit power (UP) or AV/UP. The best plunger mixers were found to behave about the same as the conventional draft-tube mixers of similar UP.
A Method for Modeling of Floating Vertical Axis Wind Turbine
DEFF Research Database (Denmark)
Wang, Kai; Hansen, Martin Otto Laver; Moan, Torgeir
2013-01-01
It is of interest to investigate the potential advantages of floating vertical axis wind turbine (FVAWT) due to its economical installation and maintenance. A novel 5MW vertical axis wind turbine concept with a Darrieus rotor mounted on a semi-submersible support structure is proposed in this paper....... In order to assess the technical and economic feasibility of this novel concept, a comprehensive simulation tool for modeling of the floating vertical axis wind turbine is needed. This work presents the development of a coupled method for modeling of the dynamics of a floating vertical axis wind turbine...
Lozovatsky, Iossif; Planella-Morato, Jesus; Shearman, Kipp; Wang, Qing; Fernando, Harindra Joseph S.
2017-06-01
Results of microstructure measurements conducted in October-November of 2015 as a part of the Coupled Air Sea Processes and Electromagnetic Ducting Research (CASPER) project are discussed. The measurements were taken on the North Carolina shelf and across the Gulf Stream front. On the shelf, the oceanic stratification was influenced by highly variable surface salinity and along-bottom advection. Vertical mixing was mostly governed by variable winds. The vertical eddy diffusivity was estimated using the VMP-based dissipation measurements, and the diffusivity values obtained during calm periods and stormy winds were compared. Parameterization of the diffusivity for various mesoscale dynamical conditions is discussed in terms of shear instabilities and internal wave-generated turbulence based on data obtained in deep waters of the Gulf Stream and on the continental slope.
Mixed Convection Heat Transfer on the Outside of a Vertical Cylinder
International Nuclear Information System (INIS)
Bhattacharyya, A.
1965-10-01
An experimental study was made of turbulent heat transfer from a vertical cylinder placed in a square channel. The flow medium was water flowing upwards. Basic differential equations governing the mixed flow heat transfer phenomena in a vertical annulus are presented. A dimensional analysis is done to find the dimensionless variables affecting the relative magnitude of the effect of buoyancy on forced convection heat transfer. Dimensionless equations correlating the experimental data ana incorporating a buoyancy parameter of the form Gr/Re 2 are presented. Reynolds number range covered is 690 to 129,500 and the Rayleigh num- ber range covered is 10 9 to 4.2 x 10 13 . Effect of different length parameters, like hydraulic diameter and distance of the measuring point from the inlet of the test section, on dimensionless equations are studied
Review of Mixed Convection Flow Regime Map of a Vertical pipe
International Nuclear Information System (INIS)
Chae, Myeong-Seon; Chung, Bum-Jin; Kang, Gyeong-Uk
2015-01-01
In a vertical pipe, the natural convective force due to buoyancy acts upward only, but forced convective force can be either upward or downward. This determines buoyancy-aided and buoyancy-opposed flows depending on the direction of forced flow with respect to the buoyancy forces. Furthermore, depending on the exchange mechanism, the flow condition is classified into laminar and turbulent. In laminar mixed convection, buoyancy-aided flow presents enhanced heat transfer compared to the pure forced convection and buoyancy-opposed flow shows impaired heat transfer as the flow velocity affected by the buoyancy forces. However, in turbulent mixed convection, buoyancy-aided flow shows an impairment of the heat transfer rate for small buoyancy, and a gradational enhancement for large buoyancy. In this study, the existing flow regime map on mixed convection in a vertical pipe was reviewed through an analysis of literatures. Using the investigated data and heat transfer correlations, the flow regime map was reconstructed independently, and compared with the existing one. This study reviewed the limitations of the classical mixed convection flow regime map. Using the existing data and heat transfer correlations by Martinelli and Boelter and Watzinger and Johnson, the flow regime map was reconstructed independently. The results revealed that the existing map used the data selectively among the experimental and theoretical results, and a detailed description for lines forming mixed convection and transition regime were not given. And the information about uncertainty analysis and the evidentiary data were given insufficiently. The flow regime map and investigator commonly used the diameter as the characteristic length for both Re and Gr in place of the height of the heated wall, though the buoyancy forces are proportional to the third power of the height of heated wall
2015-09-30
energy that might otherwise radiate downward and drive subsurface mixing over a broader range of depths. As examined in Polton et al. (2008), the...duration or fetch- limited. Both monsoonal rains and diurnal shortwave heat fluxes at O(1) kW/m2 play a large role in modulating vertical mixing in the...mixed layer may marginally impact entrainment of the upper layer by trapping gravity wave energy at the interface between the two well-mixed layers
Directory of Open Access Journals (Sweden)
Freidooni Mehr N.
2012-01-01
Full Text Available In this paper, the semi-analytical/numerical technique known as the homotopy analysis method (HAM is employed to derive solutions for the laminar axisymmetric mixed convection boundary-layer nanofluid flow past a vertical cylinder. The similarity solutions are employed to transform the parabolic partial differential conservation equations into system of nonlinear, coupled ordinary differential equations, subject to appropriate boundary conditions. A comparison has been done to verify the obtained results with the purely numerical results of Grosan and Pop (2011 with excellent correlation achieved. The effects of nanoparticle volume fraction, curvature parameter and mixed convection or buoyancy parameter on the dimensionless velocity and temperature distributions, skin friction and wall temperature gradients are illustrated graphically. HAM is found to demonstrate excellent potential for simulating nanofluid dynamics problems. Applications of the study include materials processing and also thermal enhancement of energy systems.
Estimates of vertical mixings during a Lagrangian experiment off the Galician coast
Lamy, F.; Sherwin, T.; Soetaert, K.E.R.; Herman, P.M.J.; Torres, R.
2001-01-01
An adjoint 1-D model was used to determine vertical diffusivity coefficients from temperature profiles collected within a filament escaping from the Galician coast following an upwelling event. The optimisation scheme ended with relatively high diffusivity values within the thermocline (9 x 10(-1)
CREATING EFFECTIVE MODELS OF VERTICAL INTEGRATED STRUCTURES IN UKRAINE
Directory of Open Access Journals (Sweden)
D. V. Koliesnikov
2011-01-01
Full Text Available The results of scientific research aimed at development of methodology-theoretical mechanisms of building the effective models of vertically-integrated structures are presented. A presence of vertically-integrated structures on natural-monopolistic markets at private and governmental sectors of economy and priority directions of integration are given.
International Nuclear Information System (INIS)
Malvandi, A.; Safaei, M.R.; Kaffash, M.H.; Ganji, D.D.
2015-01-01
In the current study, an MHD mixed convection of alumina/water nanofluid inside a vertical annular pipe is investigated theoretically. The model used for the nanofluid mixture involves Brownian motion and thermophoretic diffusivities in order to take into account the effects of nanoparticle migration. Since the thermophoresis is the main mechanism of the nanoparticle migration, different temperature gradients have been imposed using the asymmetric heating. Considering hydrodynamically and thermally fully developed flow, the governing equations have been reduced to two-point ordinary boundary value differential equations and they have been solved numerically. It is revealed that the imposed thermal asymmetry would change the direction of nanoparticle migration and distorts the velocity, temperature and nanoparticle concentration profiles. Moreover, it is shown that the advantage of nanofluids in heat transfer enhancement is reduced in the presence of a magnetic field. - Highlights: • MHD mixed convection of alumina/water nanofluid inside a vertical annulus. • The effects of nanoparticle migration on rheological and thermophysical characteristics. • The effects of asymmetric heating on nanoparticle migration. • The effects of asymmetric heating on the heat transfer enhancement. • Inclusion of nanoparticles in presence of a magnetic field has a negative effect on performance
Guest, Tristan B.; Hay, Alex E.
2017-01-01
The vertical structure of surface gravity wave-induced pore pressure is investigated within the intertidal zone of a natural, steeply sloping, megatidal, mixed sand-gravel-cobble beach. Results from a coherent vertical array of buried pore pressure sensors are presented in terms of signal phase lag and attenuation as functions of oscillatory forcing frequency and burial depth. Comparison of the observations with the predictions of a theoretical poro-elastic bed response model indicates that the large observed phase lags and attenuation are attributable to interstitial trapped air. In addition to the dependence on entrapped air volume, the pore pressure phase and attenuation are shown to be sensitive to the hydraulic conductivity of the sediment, to the changing mean water depth during the tidal cycle, and to the redistribution/rearrangement of beach face material by energetic wave action during storm events. The latter result indicates that the effects on pore pressure of sediment column disturbance during instrument burial can persist for days to weeks, depending upon wave forcing conditions. Taken together, these results raise serious questions as to the practicality of using pore pressure measurements to estimate the kinematic properties of surface gravity waves on steep, mixed sand-gravel beaches.
Linear mixed models in sensometrics
DEFF Research Database (Denmark)
Kuznetsova, Alexandra
in terms of preferences. In sensory studies the aim is the collection of the data to better describe products and differences of the products according to a number of sensory attributes. Here trained persons, so-called assessors, score the products in terms of different characteristics such as smell, taste...... of this project is to propose a methodology for analyzing more complex models together with tools facilitating the methodology. This was accomplished by contributing to the mixed effects ANOVA modelling in general and specifically applied to sensory and consumer studies through a series of papers and software...... of the importance of different factors. There exists today very little easily available methodology and software which supports consumer studies with both sensory properties and background information related to health benefits, environment and user-friendliness. In close collaboration with the industrial partners...
Directory of Open Access Journals (Sweden)
Nicole L. Jones
2008-06-01
Full Text Available A one-dimensional numerical model that simulates the effects of whitecapping waves was used to investigate the importance of whitecapping waves to vertical mixing at a 3-meter-deep site in Franks Tract in the Sacramento-San Joaquin Delta over an 11-day period. Locally-generated waves of mean period approximately 2 s were generated under strong wind conditions; significant wave heights ranged from 0 to 0.3 m. A surface turbulent kinetic energy flux was used to model whitecapping waves during periods when wind speeds > 5 m s-1 (62% of observations. The surface was modeled as a wind stress log-layer for the remaining 38% of the observations. The model results demonstrated that under moderate wind conditions (5–8 m s-1 at 10 m above water level, and hence moderate wave heights, whitecapping waves provided the dominant source of turbulent kinetic energy to only the top 10% of the water column. Under stronger wind (> 8 m s-1, and hence larger wave conditions, whitecapping waves provided the dominant source of turbulent kinetic energy over a larger portion of the water column; however, this region extended to the bottom half of the water column for only 7% of the observation period. The model results indicated that phytoplankton concentrations close to the bed were unlikely to be affected by the whitecapping of waves, and that the formation of concentration boundary layers due to benthic grazing was unlikely to be disrupted by whitecapping waves. Furthermore, vertical mixing of suspended sediment was unlikely to be affected by whitecapping waves under the conditions experienced during the 11-day experiment. Instead, the bed stress provided by tidal currents was the dominant source of turbulent kinetic energy over the bottom half of the water column for the majority of the 11-day period.
Strawbridge, K. B.
2013-12-01
LIDAR technology is an excellent tool to probe the complex vertical structure of the atmosphere at high spatial and temporal resolution. This provides the critical vertical context for the interpretation of ground-based chemistry measurements, airborne measurements and model verification and validation. In recent years, Environment Canada has designed an autonomous aerosol LIDAR system that can be deployed to remote areas such as the oil sands. Currently two autonomous LIDAR systems are making measurements in the oil sands region, one since December, 2012 and the other since July, 2013. The LIDAR transmitter emits two wavelengths (1064nm and 532nm) and the detector assembly collects four channels (1064nm backscatter, 532nm backscatter and 532nm depolarization, 607 nm nitrogen channel). Aerosol profiles from near ground to 20 km are collected every 10-60 s providing sufficient resolution to probe atmospheric dynamics, mixing and transport. The depolarization channel provides key information in identifying and discriminating the various aerosol layers aloft such as dust, forest fire plumes, industrial plume sources or ice crystals. The vertical resolution of the LIDAR can determine whether industrial plumes remain aloft or mix down to the surface and also provide estimates as to the concentration of the particulate at various altitudes. It operates 24 hours a day, seven days a week except during precipitation events. The system is operated remotely and the data are updated every hour to a website to allow near real-time capability. An intensive measurement campaign will be carried out in August and September of 2013 and will provide coincident airborne and ground-based measurements for the two LIDAR systems. The first results from this field study will be presented as well as some statistics on the frequency and evolution of plume events that were detected by the LIDARs.
Mixed convective magnetohydrodynamic flow in a vertical channel filled with nanofluids
Directory of Open Access Journals (Sweden)
S. Das
2015-06-01
Full Text Available The fully developed mixed convection flow in a vertical channel filled with nanofluids in the presence of a uniform transverse magnetic field has been studied. Closed form solutions for the fluid temperature, velocity and induced magnetic field are obtained for both the buoyancy-aided and -opposed flows. Three different water-based nanofluids containing copper, aluminium oxide and titanium dioxide are taken into consideration. Effects of the pertinent parameters on the nanofluid temperature, velocity, and induced magnetic field as well as the shear stress and the rate of heat transfer at the channel wall are shown in figures and tables followed by a quantitative discussion. It is found that the magnetic field tends to enhance the nanofluid velocity in the channel. The induced magnetic field vanishes in the cental region of the channel. The critical Rayleigh number at onset of instability of flow is strongly dependent on the volume fraction of nanoparticles and the magnetic field.
Lance, Blake W.
Simulations are becoming increasingly popular in science and engineering. One type of simulation is Computation Fluid Dynamics (CFD) that is used when closed forms solutions are impractical. The field of Verification & Validation emerged from the need to assess simulation accuracy as they often contain approximations and calibrations. Validation involves the comparison of experimental data with simulation outputs and is the focus of this work. Errors in simulation predictions may be assessed in this way. Validation requires highly-detailed data and description to accompany these data, and uncertainties are very important. The purpose of this work is to provide highly complete validation data to assess the accuracy of CFD simulations. This aim is fundamentally different from the typical discovery experiments common in research. The measurement of these physics was not necessarily original but performed with modern, high-fidelity methods. Data were tabulated through an online database for direct use in Reynolds-Averaged Navier-Stokes simulations. Detailed instrumentation and documentation were used to make the data more useful for validation. This work fills the validation data gap for steady and transient mixed convection. The physics in this study included mixed convection on a vertical flat plate. Mixed convection is a condition where both forced and natural convection influence fluid momentum and heat transfer phenomena. Flow was forced over a vertical flat plate in a facility built for validation experiments. Thermal and velocity data were acquired for steady and transient flow conditions. The steady case included both buoyancy-aided and buoyancy-opposed mixed convection while the transient case was for buoyancy-opposed flow. The transient was a ramp-down flow transient, and results were ensemble-averaged for improved statistics. Uncertainty quantification was performed on all results with bias and random sources. An independent method of measuring heat flux was
Turbulent mixed convection in vertical and inclined flat channels with aiding flows
Energy Technology Data Exchange (ETDEWEB)
Poskas, P.; Vilemas, J.; Adomaitis, J.E.; Bartkus, G.
1995-09-01
This paper presents an experimental study of turbulent mixed convection heat transfer for aiding flows in a vertical ({phi}=90{degrees}), inclined ({phi}=60{degrees},30{degrees}), and horizontal ({phi}=0{degrees}) flat channels with symmetrical heating and a ratio of height h to width b of about 1:10 and with length about 4 m (x/2h about 44). The study covered Re from 4x10{sup 3} to 5x10{sup 4} and Gr{sub q} from 5x10{sup 7}to 3x10{sup 10}. For the upper wall, a region of impaired heat transfer was found for all angular positions (from vertical to horizontal) and for bottom wall the augmentation of heat transfer in comparison to forced convection was revealed in the region of {phi}=0{degrees}-60{degrees}. Different characteristic buoyancy parameters were found for regions of impaired and enhanced heat transfer. General relations are suggested to predict the heat transfer for fully-developed-flow conditions and different angular positions.
Effect of Induced Magnetic Field on MHD Mixed Convection Flow in Vertical Microchannel
Jha, B. K.; Aina, B.
2017-08-01
The present work presents a theoretical investigation of an MHD mixed convection flow in a vertical microchannel formed by two electrically non-conducting infinite vertical parallel plates. The influence of an induced magnetic field arising due to motion of an electrically conducting fluid is taken into consideration. The governing equations of the motion are a set of simultaneous ordinary differential equations and their exact solutions in dimensionless form have been obtained for the velocity field, the induced magnetic field and the temperature field. The expressions for the induced current density and skin friction have also been obtained. The effects of various non-dimensional parameters such as rarefaction, fluid wall interaction, the Hartmann number and the magnetic Prandtl number on the velocity, the induced magnetic field, the temperature, the induced current density, and skin friction have been presented in a graphical form. It is found that the effect of the Hartmann number and magnetic Prandtl number on the induced current density is found to have a decreasing nature at the central region of the microchannel.
A Study on the Mixed Convection Heat Transfer in a Vertical Cylinder Using Electroplating System
International Nuclear Information System (INIS)
Ko, Bong Jin
2008-02-01
Hydrogen economy has drawn public attentions as a promising future energy source. Hydrogen is a non-petroleum-based, non-toxic, renewable and clean burning energy source. Hydrogen is the secondary energy, which means that it is produced by consuming the first energy such as coal, gas, petroleum etc. This again means that it is clean so long as it is produced by clean methods. One of the promising production methods of hydrogen is to use the heat from an HTGR(High Temperature Gas-cooled Reactor), a next generation nuclear reactor for a safe and reliable operation as well as for efficient and economic generation of energy. The knowledge of detailed heat transfer phenomena in gaseous phase emerges as an important factor for HTGR, where buoyancy effect plays a significant role. Large and expensive test facilities are to be constructed to assess the detailed mixed convection phenomena. However, using analogy concept, heat transfer system can be transformed to mass transfer system and vice versa. If a simple mass transfer system could be devised, and the experimental solution from that system could be obtained, then this could theoretically lead to a solution for a similar heat transfer system. In this study, a copper electroplating system was selected as the mass transfer system. A copper electroplating system with limiting current technique has a good advantage to simulate heat transfer system as mass transfer coefficient, analogous with heat transfer coefficient, can be directly obtained from the information of the bulk concentration and electric current between electrodes. This study simulated the mixed convective heat transfer phenomena in a vertical cylinder using copper electroplating system. The mixed convection phenomenon is observed when the forced and natural convections are of comparable magnitudes in one system. The mixed convection is classified as laminar and turbulent flows depending on the exchange mechanism and also as buoyancy aided and buoyancy
Theoretical Models of Neutrino Mixing Recent Developments
Altarelli, Guido
2009-01-01
The data on neutrino mixing are at present compatible with Tri-Bimaximal (TB) mixing. If one takes this indication seriously then the models that lead to TB mixing in first approximation are particularly interesting and A4 models are prominent in this list. However, the agreement of TB mixing with the data could still be an accident. We discuss a recent model based on S4 where Bimaximal mixing is instead valid at leading order and the large corrections needed to reproduce the data arise from the diagonalization of charged leptons. The value of $\\theta_{13}$ could distinguish between the two alternatives.
Nabwey, Hossam A.; Boumazgour, Mohamed; Rashad, A. M.
2017-07-01
The group method analysis is applied to study the steady mixed convection stagnation-point flow of a non-Newtonian nanofluid towards a vertical stretching surface. The model utilized for the nanofluid incorporates the Brownian motion and thermophoresis effects. Applying the one-parameter transformation group which reduces the number of independent variables by one and thus, the system of governing partial differential equations has been converted to a set of nonlinear ordinary differential equations, and these equations are then computed numerically using the implicit finite-difference scheme. Comparison with previously published studies is executed and the results are found to be in excellent agreement. Results for the velocity, temperature, and the nanoparticle volume fraction profiles as well as the local skin-friction coefficient and local Nusselt number are presented in graphical and tabular forms, and discussed for different values of the governing parameters to show interesting features of the solutions.
Is Convection Sensitive to Model Vertical Resolution and Why?
Xie, S.; Lin, W.; Zhang, G. J.
2017-12-01
Model sensitivity to horizontal resolutions has been studied extensively, whereas model sensitivity to vertical resolution is much less explored. In this study, we use the US Department of Energy (DOE)'s Accelerated Climate Modeling for Energy (ACME) atmosphere model to examine the sensitivity of clouds and precipitation to the increase of vertical resolution of the model. We attempt to understand what results in the behavior change (if any) of convective processes represented by the unified shallow and turbulent scheme named CLUBB (Cloud Layers Unified by Binormals) and the Zhang-McFarlane deep convection scheme in ACME. A short-term hindcast approach is used to isolate parameterization issues from the large-scale circulation. The analysis emphasizes on how the change of vertical resolution could affect precipitation partitioning between convective- and grid-scale as well as the vertical profiles of convection-related quantities such as temperature, humidity, clouds, convective heating and drying, and entrainment and detrainment. The goal is to provide physical insight into potential issues with model convective processes associated with the increase of model vertical resolution. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Mixed models for predictive modeling in actuarial science
Antonio, K.; Zhang, Y.
2012-01-01
We start with a general discussion of mixed (also called multilevel) models and continue with illustrating specific (actuarial) applications of this type of models. Technical details on (linear, generalized, non-linear) mixed models follow: model assumptions, specifications, estimation techniques
Vaughan, Garrett
Open channel raceway bioreactors are a low-cost system used to grow algae for biofuel production. Microalgae have many promises when it comes to renewable energy applications, but many economic hurdles must be overcome to achieve an economic fuel source that is competitive with petroleum-based fuels. One way to make algae more competitive is to improve vertical mixing in algae raceway bioreactors. Previous studies show that mixing may be increased by the addition of mechanisms such as airfoils. The circulation created helps move the algae from the bottom to top surface for necessary photosynthetic exchange. This improvement in light utilization allowed a certain study to achieve 2.2-2.4 times the amount of biomass relative to bioreactors without airfoils. This idea of increasing mixing in open channel raceways has been the focus of the Utah State University (USU) raceway hydraulics group. Computational Fluid Dynamics (CFD), Acoustic Doppler Velocimetry (ADV), and Particle Image Velocimetry (PIV) are all methods used at USU to computationally and experimentally quantify mixing in an open channel raceway. They have also been used to observe the effects of using delta wings (DW) in increasing vertical mixing in the raceway. These efforts showed great potential in the DW in increasing vertical mixing in the open channel bioreactor. However, this research begged the question, does the DW help increase algae growth? Three algae growth experiments comparing growth in a raceway with and without DW were completed. These experiments were successful, yielding an average 27.1% increase in the biomass. The DW appears to be a promising method of increasing algae biomass production. The next important step was to quantify vertical mixing and understand flow patterns due to two DWs side-by-side. Raceway channels are wider as they increase in size; and arrays of DWs will need to be installed to achieve quality mixing throughout the bioreactor. Quality mixing was attained for
The WZNW model on PSU(1, 1 vertical stroke 2)
Energy Technology Data Exchange (ETDEWEB)
Goetz, G. [CEA Centre d' Etudes de Saclay, 91 - Gif-sur-Yvette (France). Service de Physique Theorique; Quella, T. [King' s College London (United Kingdom). Dept. of Mathematics]|[Amsterdam Univ. (Netherlands). KdV Institute for Mathematics; Schomerus, V. [CEA Centre d' Etudes de Saclay, 91 - Gif-sur-Yvette (France). Service de Physique Theorique]|[Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)
2006-10-15
According to the work of Berkovits, Vafa and Witten, the non-linear sigma model on the supergroup PSU(1,1 vertical stroke 2) is the essential building block for string theory on AdS{sub 3}xS{sup 3}xT{sup 4}. Models associated with a non-vanishing value of the RR flux can be obtained through a psu(1,1 vertical stroke 2) invariant marginal deformation of the WZNW model on PSU(1,1 vertical stroke 2). We take this as a motivation to present a manifestly psu(1,1 vertical stroke 2) covariant construction of the model at the Wess-Zumino point, corresponding to a purely NSNS background 3-form flux. At this point the model possesses an enhanced psu(1,1 vertical stroke 2) current algebra symmetry whose representation theory, including explicit character formulas, is developed systematically in the first part of the paper. The space of vertex operators and a free fermion representation for their correlation functions is our main subject in the second part. Contrary to a widespread claim, bosonic and fermionic fields are necessarily coupled to each other. The interaction changes the supersymmetry transformations, with drastic consequences for the multiplets of localized normalizable states in the model. It is only this fact which allows us to decompose the full state space into multiplets of the global supersymmetry. We analyze these decompositions systematically as a preparation for a forthcoming study of the RR deformation. (orig.)
The WZNW model on PSU(1, 1 vertical stroke 2)
International Nuclear Information System (INIS)
Goetz, G.
2006-10-01
According to the work of Berkovits, Vafa and Witten, the non-linear sigma model on the supergroup PSU(1,1 vertical stroke 2) is the essential building block for string theory on AdS 3 xS 3 xT 4 . Models associated with a non-vanishing value of the RR flux can be obtained through a psu(1,1 vertical stroke 2) invariant marginal deformation of the WZNW model on PSU(1,1 vertical stroke 2). We take this as a motivation to present a manifestly psu(1,1 vertical stroke 2) covariant construction of the model at the Wess-Zumino point, corresponding to a purely NSNS background 3-form flux. At this point the model possesses an enhanced psu(1,1 vertical stroke 2) current algebra symmetry whose representation theory, including explicit character formulas, is developed systematically in the first part of the paper. The space of vertex operators and a free fermion representation for their correlation functions is our main subject in the second part. Contrary to a widespread claim, bosonic and fermionic fields are necessarily coupled to each other. The interaction changes the supersymmetry transformations, with drastic consequences for the multiplets of localized normalizable states in the model. It is only this fact which allows us to decompose the full state space into multiplets of the global supersymmetry. We analyze these decompositions systematically as a preparation for a forthcoming study of the RR deformation. (orig.)
Global vertical mass transport by clouds - A two-dimensional model study
International Nuclear Information System (INIS)
Olofsson, Mats
1988-05-01
A two-dimensional global dispersion model, where vertical transport in the troposphere carried out by convective as well as by frontal cloud systems is explicitly treated, is developed from an existing diffusion model. A parameterization scheme for the cloud transport, based on global cloud statistics, is presented. The model has been tested by using Kr-85, Rn-222 and SO 2 as tracers. Comparisons have been made with observed distributions of these tracers, but also with model results without the cloud transport, using eddy diffusion as the primary means of vertical transport. The model results indicate that for trace species with a turnover time of days to weeks, the introduction of cloud-transport gives much more realistic simulations of their vertical distribution. Layers of increased mixing ratio with height, which can be found in real atmosphere, are reproduced in our cloud-transport model profiles, but can never be simulated with a pure eddy diffusion model. The horizontal transport in the model, by advection and eddy diffusion, gives a realistic distribution between the hemispheres of the more long-lived tracers (Kr-85). A combination of vertical transport by convective and frontal cloud systems is shown to improve the model simulations, compared to limiting it to convective transport only. The importance of including cumulus clouds in the convective transport scheme, in addition to the efficient transport by cumulonimbus clouds, is discussed. The model results are shown to be more sensitive to the vertical detrainment distribution profile than to the absolute magnitude of the vertical mass transport. The scavenging processes for SO 2 are parameterized without the introduction of detailed chemistry. An enhanced removal, due to the increased contact with droplets in the in-cloud lifting process, is introduced in the model. (author)
Mixed-mode modelling mixing methodologies for organisational intervention
Clarke, Steve; Lehaney, Brian
2001-01-01
The 1980s and 1990s have seen a growing interest in research and practice in the use of methodologies within problem contexts characterised by a primary focus on technology, human issues, or power. During the last five to ten years, this has given rise to challenges regarding the ability of a single methodology to address all such contexts, and the consequent development of approaches which aim to mix methodologies within a single problem situation. This has been particularly so where the situation has called for a mix of technological (the so-called 'hard') and human centred (so-called 'soft') methods. The approach developed has been termed mixed-mode modelling. The area of mixed-mode modelling is relatively new, with the phrase being coined approximately four years ago by Brian Lehaney in a keynote paper published at the 1996 Annual Conference of the UK Operational Research Society. Mixed-mode modelling, as suggested above, is a new way of considering problem situations faced by organisations. Traditional...
Anatomy teaching: Flexnerian model to contextualized vertical ...
African Journals Online (AJOL)
Abraham Flexner in 1910 established the fundamental model where the subjects of anatomy, physiology, pharmacology, pathology and bacteriology are mastered before the clinical phase of medical training (1). He was clear that this mastery was best achieved by active student learning in the laboratory guided by clinical.
A vertically resolved model for phytoplankton aggregation
Indian Academy of Sciences (India)
Simple experiments demonstrate the effects of aggregation on the timing and depth distribution of primary production and export. A more detailed ecological model is applied to sites in the Arabian Sea; it demonstrates that aggregation can be important for deep sedimentation even when its effect on surface concentrations ...
Comparison of aerodynamic models for Vertical Axis Wind Turbines
Simao Ferreira, C.J.; Aagaard Madsen, H.; Barone, M.; Roscher, B.; Deglaire, P.; Arduin, I.
2014-01-01
Multi-megawatt Vertical Axis Wind Turbines (VAWTs) are experiencing an increased interest for floating offshore applications. However, VAWT development is hindered by the lack of fast, accurate and validated simulation models. This work compares six different numerical models for VAWTS: a multiple
Comparison of aerodynamic models for Vertical Axis Wind Turbines
DEFF Research Database (Denmark)
Ferreira, C. Simão; Aagaard Madsen, Helge; Barone, M.
2014-01-01
Multi-megawatt Vertical Axis Wind Turbines (VAWTs) are experiencing an increased interest for floating offshore applications. However, VAWT development is hindered by the lack of fast, accurate and validated simulation models. This work compares six different numerical models for VAWTS: a multipl...
Vaughan, Garrett
2013-01-01
Open channel raceway bioreactors are a low-cost system used to grow algae for biofuel production. Microalgae have many promises when it comes to renewable energy applications, but many economic hurdles must be overcome to achieve an economic fuel source that is competitive with petroleum-based fuels. One way to make algae more competitive is to improve vertical mixing in algae raceway bioreactors. Previous studies show that mixing may be increased by the addition of mechanisms such as airf...
Use and abuse of mixing models (MixSIAR)
Background/Question/MethodsCharacterizing trophic links in food webs is a fundamental ecological question. In our efforts to quantify energy flow through food webs, ecologists have increasingly used mixing models to analyze biological tracer data, often from stable isotopes. Whil...
Modeling of Aerosol Vertical Profiles Using GIS and Remote Sensing
Directory of Open Access Journals (Sweden)
Kwon Ho Lee
2009-06-01
Full Text Available The use of Geographic Information Systems (GIS and Remote Sensing (RS by climatologists, environmentalists and urban planners for three dimensional modeling and visualization of the landscape is well established. However no previous study has implemented these techniques for 3D modeling of atmospheric aerosols because air quality data is traditionally measured at ground points, or from satellite images, with no vertical dimension. This study presents a prototype for modeling and visualizing aerosol vertical profiles over a 3D urban landscape in Hong Kong. The method uses a newly developed technique for the derivation of aerosol vertical profiles from AERONET sunphotometer measurements and surface visibility data, and links these to a 3D urban model. This permits automated modeling and visualization of aerosol concentrations at different atmospheric levels over the urban landscape in near-real time. Since the GIS platform permits presentation of the aerosol vertical distribution in 3D, it can be related to the built environment of the city. Examples are given of the applications of the model, including diagnosis of the relative contribution of vehicle emissions to pollution levels in the city, based on increased near-surface concentrations around weekday rush-hour times. The ability to model changes in air quality and visibility from ground level to the top of tall buildings is also demonstrated, and this has implications for energy use and environmental policies for the tall mega-cities of the future.
Vertically-integrated Approaches for Carbon Sequestration Modeling
Bandilla, K.; Celia, M. A.; Guo, B.
2015-12-01
Carbon capture and sequestration (CCS) is being considered as an approach to mitigate anthropogenic CO2 emissions from large stationary sources such as coal fired power plants and natural gas processing plants. Computer modeling is an essential tool for site design and operational planning as it allows prediction of the pressure response as well as the migration of both CO2 and brine in the subsurface. Many processes, such as buoyancy, hysteresis, geomechanics and geochemistry, can have important impacts on the system. While all of the processes can be taken into account simultaneously, the resulting models are computationally very expensive and require large numbers of parameters which are often uncertain or unknown. In many cases of practical interest, the computational and data requirements can be reduced by choosing a smaller domain and/or by neglecting or simplifying certain processes. This leads to a series of models with different complexity, ranging from coupled multi-physics, multi-phase three-dimensional models to semi-analytical single-phase models. Under certain conditions the three-dimensional equations can be integrated in the vertical direction, leading to a suite of two-dimensional multi-phase models, termed vertically-integrated models. These models are either solved numerically or simplified further (e.g., assumption of vertical equilibrium) to allow analytical or semi-analytical solutions. This presentation focuses on how different vertically-integrated models have been applied to the simulation of CO2 and brine migration during CCS projects. Several example sites, such as the Illinois Basin and the Wabamun Lake region of the Alberta Basin, are discussed to show how vertically-integrated models can be used to gain understanding of CCS operations.
Spilker, L. J.; Pilorz, S.; Pearl, J.; Altobelli, N.; Wallis, B.; Brooks, S.; Ferrari, C.; Showalter, M.; Flasar, M.
2006-12-01
The Cassini Composite Infrared Spectrometer (CIRS) obtained spatially resolved thermal infrared scans of Saturn's main rings (A, B and C, and Cassini Division) for both the lit and unlit faces of the rings over a variety of phase angles. The scans show ring temperatures decreasing with increasing solar phase angle. The largest ring temperatures are at a phase angle of zero degrees. These temperature differences with phase suggest that Saturn's main rings include a population of ring particles that spin slowly, possibly with a spin period greater than a few hours, given their low thermal inertia. For the B and A rings, the temperature is correlated with optical depth when viewed from the lit face, and anti- correlated when viewed from the unlit face. On the unlit face of the B ring, not only do the lowest temperatures correlate with the largest optical depths, but these temperatures are the same at both low and high phase angles, suggesting that little sunlight is penetrating these regions. The temperature differential from the lit to the unlit side of the rings is a strong, nearly linear, function of optical depth. This is consistent with the expectation that little sunlight penetrates to the dark side of the densest rings, but also suggests that little vertical mixing of ring particles is taking place in the A and B rings. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA and at CEA Saclay supported by the "Programme National de Planetologie".
Linear mixed models for longitudinal data
Molenberghs, Geert
2000-01-01
This paperback edition is a reprint of the 2000 edition. This book provides a comprehensive treatment of linear mixed models for continuous longitudinal data. Next to model formulation, this edition puts major emphasis on exploratory data analysis for all aspects of the model, such as the marginal model, subject-specific profiles, and residual covariance structure. Further, model diagnostics and missing data receive extensive treatment. Sensitivity analysis for incomplete data is given a prominent place. Several variations to the conventional linear mixed model are discussed (a heterogeity model, conditional linear mixed models). This book will be of interest to applied statisticians and biomedical researchers in industry, public health organizations, contract research organizations, and academia. The book is explanatory rather than mathematically rigorous. Most analyses were done with the MIXED procedure of the SAS software package, and many of its features are clearly elucidated. However, some other commerc...
Digital Repository Service at National Institute of Oceanography (India)
Nakamoto, S.; PrasannaKumar, S.; Oberhuber, J.M.; Saito, H.; Muneyama, K.; Frouin, R.
is influenced not only by local vertical mixing but also by horizontal con- vergence of mass and heat, a mixed layer model must consider both full dynamics due to the use of primitive equations and a parameterization for the vertical mass transfer and related... is dynamically determined without such a con- straint. Instantaneous atmospheric elds are inter- polated from the monthly means. Monthly mean climatology of chlorophyll pigment concentrations were obtained from the Coastal Zone Color Scan- ner (CZCS) from...
Directory of Open Access Journals (Sweden)
Marcelo Pablo Hernando
2011-12-01
Full Text Available One of the adaptations whereby phytoplankton can alleviate damage induced by ultraviolet radiation (280-400 nm is the synthesis of mycosporine-like amino acids (MAAs. The synthesis of MAAs was studied after exposure of the Antarctic diatom Thalassiosira sp. isolated from Potter Cove (South Shetland Is., Antarctica to 2 treatments with a solar simulator: surface (Sfix and vertical mixing (Mix irradiance conditions. Light exposure was simulated in daily cycles with maximum irradiance at noon. Only 2 MAAs, Porphyra-334 (82-85% and Shinorine (15-18%, were identified. The concentration of the two compounds increased during experimental light exposure (50-55% and declined in the dark (10-15%. During the light period the synthesis rate of MAAs per unit of chlorophyll a was higher in the Sfix treatment (µ=0.17 h-1 than in the Mix treatment (µ=0.05 h-1. In spite of the higher MAA levels, low cell numbers were observed in the Sfix treatment, suggesting that the algae synthesized photoprotective compounds at the expense of growth. Our results document overlapping effects of both daily light cycles and vertical mixing affecting the synthesis of MAAs. This, and the high thermal dissipation of the ultraviolet B radiation energy (280-320 nm absorbed by these substances, suggest a rapid photoadaptive response of Thalasiossira sp. upon exposure to elevated irradiance in a stratified water column, as well as the complementary role of vertical mixing in photo-protection.
Control and modelling of vertical temperature distribution in greenhouse crops
Kempkes, F.L.K.; Bakker, J.C.; Braak, van de N.J.
1998-01-01
Based on physical transport processes (radiation, convection and latent heat transfer) a model has been developed to describe the vertical temperature distribution of a greenhouse crop. The radiation exchange factors between heating pipes, crop layers, soil and roof were determined as a function of
Vertical-aware click model-based effectiveness metrics
Markov, I.; Kharitonov, E.; Nikulin, V.; Serdyukov, P.; de Rijke, M.; Crestani, F.; Li, J.; Wang, X.S.
2014-01-01
Today's web search systems present users with heterogeneous information coming from sources of different types, also known as verticals. Evaluating such systems is an important but complex task, which is still far from being solved. In this paper we examine the hypothesis that the use of models that
Variable-property effects in laminar aiding and opposing mixed convection of air in vertical tubes
International Nuclear Information System (INIS)
Nesreddine, H.; Galanis, N.; Nguyen, C.T.
1997-01-01
Mixed convection flow in tubes is encountered in many engineering applications, such as solar collectors, nuclear reactors, and compact heat exchangers. Here, a numerical investigation has been conducted in order to determine the effects of variable properties on the flow pattern and heat transfer performances in laminar developing ascending flow with mixed convection for two cases: in case 1 the fluid is heated, and in case 2 it is cooled. Calculations are performed for air at various Grashof numbers with a fixed entrance Reynolds number of 500 using both the Boussinesq approximation (constant-property model) and a variable-property model. In the latter case, the fluid viscosity and thermal conductivity are allowed to vary with absolute temperature according to simple power laws, while the density varies linearly with the temperature, and the heat capacity is assumed to be constant. The comparison between constant- and variable-property models shows a substantial difference in the temperature and velocity fields when the Grashof number |Gr| is increased. The friction factor is seen to be underpredicted by the Boussinesq approximation when the fluid is heated (case 1), while it is overpredicted for the cooling case (case 2). However, the effects on the heat transfer performance remain negligible except for cases with reverse flow. On the whole, the variable-property model predicts flow reversal at lower values of |Gr|, especially for flows with opposing buoyancy forces. The deviation in results is associated to the difference between the fluid bulk and the wall temperature
Comparison of mixed layer models predictions with experimental data
Energy Technology Data Exchange (ETDEWEB)
Faggian, P.; Riva, G.M. [CISE Spa, Divisione Ambiente, Segrate (Italy); Brusasca, G. [ENEL Spa, CRAM, Milano (Italy)
1997-10-01
The temporal evolution of the PBL vertical structure for a North Italian rural site, situated within relatively large agricultural fields and almost flat terrain, has been investigated during the period 22-28 June 1993 by experimental and modellistic point of view. In particular, the results about a sunny day (June 22) and a cloudy day (June 25) are presented in this paper. Three schemes to estimate mixing layer depth have been compared, i.e. Holzworth (1967), Carson (1973) and Gryning-Batchvarova models (1990), which use standard meteorological observations. To estimate their degree of accuracy, model outputs were analyzed considering radio-sounding meteorological profiles and stability atmospheric classification criteria. Besides, the mixed layer depths prediction were compared with the estimated values obtained by a simple box model, whose input requires hourly measures of air concentrations and ground flux of {sup 222}Rn. (LN)
Model Information Exchange System (MIXS).
2013-08-01
Many travel demand forecast models operate at state, regional, and local levels. While they share the same physical network in overlapping geographic areas, they use different and uncoordinated modeling networks. This creates difficulties for models ...
Ray Tracing Modelling of Reflector for Vertical Bifacial Panel
DEFF Research Database (Denmark)
Jakobsen, Michael Linde; Thorsteinsson, Sune; Poulsen, Peter Behrensdorff
2016-01-01
Bifacial solar panels have recently become a new attractive building block for PV systems. In this work we propose a reflector system for a vertical bifacial panel, and use ray tracing modelling to model the performance. Particularly, we investigate the impact of the reflector volume being filled...... with a refractive medium, and shows the refractive medium improves the reflector performance since it directs almost all the light incident on the incoming plane into the PV panel....
Ray Tracing modelling of reflector for vertical bifacial panel
DEFF Research Database (Denmark)
Jakobsen, Michael Linde; Thorsteinsson, Sune; Poulsen, Peter Behrensdorff
2016-01-01
Bifacial solar panels have recently become a new attractive building block for PV systems. In this work we propose a reflector system for a vertical bifacial panel, and use ray tracing modelling to model the performance. Particularly, we investigate the impact of the reflector volume being filled...... with a refractive medium, and shows the refractive medium improves the reflector performance since it directs almost all the light incident on the incoming plane into the PV panel....
Kawaguchi, Yusuke; Takeda, Hiroki
2017-04-01
This study focuses on the mixing processes in the vicinity of surface mixed layer (SML) of the Arctic Ocean. Turbulence activity and vertical heat transfer are quantitatively characterized in the Northwind Abyssal Plain, based on the RV Mirai Arctic cruise, during the transition from late summer to early winter 2014. During the cruise, noticeable storm events were observed, which came over the ship's location and contributed to the deepening of the SML. According to the ship-based microstructure observation, within the SML, the strong wind events produced enhanced dissipation rates of turbulent kinetic energy in the order of magnitude of ɛ = 10-6-10-4W kg-1. On thermal variance dissipation rate, χ increases toward the base of SML, reaching O(10-7) K2 s-1, resulting in vertical heat flux of O(10) W m-2. During the occasional energetic mixing events, the near-surface warm water was transferred downward and penetrated through the SML base, creating a cross-pycnocline high-temperature anomaly (CPHTA) at approximately 20-30 m depth. Near CPHTA, the vertical heat flux was anomalously magnified to O(10-100) W m-2. Following the fixed-point observation, in the regions of marginal and thick ice zones, the SML heat content was monitored using an autonomous drifting buoy, UpTempO. During most of the ice-covered period, the ocean-to-ice turbulent heat flux was dominant, rather than the diapycnal heat transfer across the SML bottom interface.
Mixed convection flow and heat transfer in a vertical wavy channel ...
African Journals Online (AJOL)
user
forced convective flow in a fluid saturated porous medium channel bounded by two vertical parallel plates was presented by. Prathap Kumar ... width of the channel) vertical wavy and parallel flat wall. ...... In view of Eqs. (25) to (28) the boundary and interface conditions as defined in Eqs. (20) and (21) can be split as follows,.
Single-Phase Crossflow Mixing in a Vertical Tube Bundle Geometry : An Experimental Study
Mahmood, A.
2011-01-01
The vertical rod/tube bundle geometry has a wide variety of industrial applications. Typical examples are the core of light water nuclear reactors (LWR) and vertical tube steam generators. In the core of a LWR, primarily coolant flows upward but their also exist a flow in lateral direction, called
Nonlinear Modeling and Analysis of a Vertical Springless Energy Harvester
Directory of Open Access Journals (Sweden)
Abdel-Rahman Eihab
2012-07-01
Full Text Available Harvesting energy from ambient sources has attracted the attention of researchers and scientists over the last few decades. While solar, thermal and wind energies have been exploited over the years, a new type of energy that has emerged in recent years, and is the subject of many research projects, is vibration energy harvesting. In this paper we will describe and analyze a recently proposed vibration energy harvester, namely the “Springless” vibration energy harvester. In this study, we will model and analyze the “Springless” vibration energy harvester in the vertical configuration. The vertically-aligned configuration is used when vibrations are predominantly in the vertical direction. Test results of a prototype model as well as results form a mathematical model describing the behavior of the harvester are presented. Test results show that the “Springless” energy vibration harvester behaves as a softening nonlinear oscillator for excitations above 0:2g with its center frequency shifting to the right. Similar results were obtained using a mathematical model of the underlying impact oscillator.
Modeling of particle mixing in the atmosphere
International Nuclear Information System (INIS)
Zhu, Shupeng
2015-01-01
This thesis presents a newly developed size-composition resolved aerosol model (SCRAM), which is able to simulate the dynamics of externally-mixed particles in the atmosphere, and evaluates its performance in three-dimensional air-quality simulations. The main work is split into four parts. First, the research context of external mixing and aerosol modelling is introduced. Secondly, the development of the SCRAM box model is presented along with validation tests. Each particle composition is defined by the combination of mass-fraction sections of its chemical components or aggregates of components. The three main processes involved in aerosol dynamic (nucleation, coagulation, condensation/ evaporation) are included in SCRAM. The model is first validated by comparisons with published reference solutions for coagulation and condensation/evaporation of internally-mixed particles. The particle mixing state is investigated in a 0-D simulation using data representative of air pollution at a traffic site in Paris. The relative influence on the mixing state of the different aerosol processes and of the algorithm used to model condensation/evaporation (dynamic evolution or bulk equilibrium between particles and gas) is studied. Then, SCRAM is integrated into the Polyphemus air quality platform and used to conduct simulations over Greater Paris during the summer period of 2009. This evaluation showed that SCRAM gives satisfactory results for both PM2.5/PM10 concentrations and aerosol optical depths, as assessed from comparisons to observations. Besides, the model allows us to analyze the particle mixing state, as well as the impact of the mixing state assumption made in the modelling on particle formation, aerosols optical properties, and cloud condensation nuclei activation. Finally, two simulations are conducted during the winter campaign of MEGAPOLI (Megacities: Emissions, urban, regional and Global Atmospheric Pollution and climate effects, and Integrated tools for
Multivariate generalized linear mixed models using R
Berridge, Damon Mark
2011-01-01
Multivariate Generalized Linear Mixed Models Using R presents robust and methodologically sound models for analyzing large and complex data sets, enabling readers to answer increasingly complex research questions. The book applies the principles of modeling to longitudinal data from panel and related studies via the Sabre software package in R. A Unified Framework for a Broad Class of Models The authors first discuss members of the family of generalized linear models, gradually adding complexity to the modeling framework by incorporating random effects. After reviewing the generalized linear model notation, they illustrate a range of random effects models, including three-level, multivariate, endpoint, event history, and state dependence models. They estimate the multivariate generalized linear mixed models (MGLMMs) using either standard or adaptive Gaussian quadrature. The authors also compare two-level fixed and random effects linear models. The appendices contain additional information on quadrature, model...
Statistical Tests for Mixed Linear Models
Khuri, André I; Sinha, Bimal K
2011-01-01
An advanced discussion of linear models with mixed or random effects. In recent years a breakthrough has occurred in our ability to draw inferences from exact and optimum tests of variance component models, generating much research activity that relies on linear models with mixed and random effects. This volume covers the most important research of the past decade as well as the latest developments in hypothesis testing. It compiles all currently available results in the area of exact and optimum tests for variance component models and offers the only comprehensive treatment for these models a
Directory of Open Access Journals (Sweden)
Srinivasacharya D.
2013-01-01
Full Text Available Mixed convection heat and mass transfer along a vertical plate embedded in a power-law fluid saturated Darcy porous medium with Soret and Dufour effects is studied. The governing partial differential equations are transformed into ordinary differential equations using similarity transformations and then solved numerically using shooting method. The effect of Soret and Dufour parameters, power law index and mixed convection parameter on non-dimensional velocity, temperature and concentration fields are discussed. The variation of different parameters on heat and mass transfer rates is presented in tabular form.
International Nuclear Information System (INIS)
Venugopal, G.; Balaji, C.; Venkateshan, S.P.
2010-01-01
This paper reports the results of an experimental investigation to examine the potential of a simple and inexpensive porous insert developed specifically for augmenting heat transfer from the heated wall of a vertical duct under forced flow conditions. The porous insert used in the study consists of a stack of metallic perforated plates filled inside the duct. The characteristic features of the porous medium model on the hydrodynamic and heat transfer behavior have been investigated. The porous medium model developed in the present study shows thermo- hydrodynamic performance similar to those seen in metal foams. A correlation has been developed for predicting the Nusselt number from the geometry under consideration. The key novelty in the present work is the development of a new correlation for the Nusselt number that does not require any information from hydrodynamic studies. Over the range of parameters considered, the largest increase in the average Nusselt number of 4.52 times that for clear flow is observed with a porous material of porosity of 0.85. (authors)
A skeleton model for the MJO with refined vertical structure
Thual, Sulian; Majda, Andrew J.
2016-05-01
The Madden-Julian oscillation (MJO) is the dominant mode of variability in the tropical atmosphere on intraseasonal timescales and planetary spatial scales. The skeleton model is a minimal dynamical model that recovers robustly the most fundamental MJO features of (I) a slow eastward speed of roughly 5 {ms}^{-1}, (II) a peculiar dispersion relation with dω /dk ≈ 0, and (III) a horizontal quadrupole vortex structure. This model depicts the MJO as a neutrally-stable atmospheric wave that involves a simple multiscale interaction between planetary dry dynamics, planetary lower-tropospheric moisture and the planetary envelope of synoptic-scale activity. Here we propose and analyse an extended version of the skeleton model with additional variables accounting for the refined vertical structure of the MJO in nature. The present model reproduces qualitatively the front-to-rear vertical structure of the MJO found in nature, with MJO events marked by a planetary envelope of convective activity transitioning from the congestus to the deep to the stratiform type, in addition to a front-to-rear structure of moisture, winds and temperature. Despite its increased complexity the present model retains several interesting features of the original skeleton model such as a conserved energy and similar linear solutions. We further analyze a model version with a simple stochastic parametrization for the unresolved details of synoptic-scale activity. The stochastic model solutions show intermittent initiation, propagation and shut down of MJO wave trains, as in previous studies, in addition to MJO events with a front-to-rear vertical structure of varying intensity and characteristics from one event to another.
Directory of Open Access Journals (Sweden)
Prasad K.V.
2017-02-01
Full Text Available The effect of thermal radiation and viscous dissipation on a combined free and forced convective flow in a vertical channel is investigated for a fully developed flow regime. Boussinesq and Roseseland approximations are considered in the modeling of the conduction radiation heat transfer with thermal boundary conditions (isothermal-thermal, isoflux-thermal, and isothermal-flux. The coupled nonlinear governing equations are also solved analytically using the Differential Transform Method (DTM and regular perturbation method (PM. The results are analyzed graphically for various governing parameters such as the mixed convection parameter, radiation parameter, Brinkman number and perturbation parameter for equal and different wall temperatures. It is found that the viscous dissipation enhances the flow reversal in the case of a downward flow while it counters the flow in the case of an upward flow. A comparison of the Differential Transform Method (DTM and regular perturbation method (PM methods shows the versatility of the Differential Transform Method (DTM. The skin friction and the wall temperature gradient are presented for different values of the physical parameters and the salient features are analyzed.
Mixed-effects regression models in linguistics
Heylen, Kris; Geeraerts, Dirk
2018-01-01
When data consist of grouped observations or clusters, and there is a risk that measurements within the same group are not independent, group-specific random effects can be added to a regression model in order to account for such within-group associations. Regression models that contain such group-specific random effects are called mixed-effects regression models, or simply mixed models. Mixed models are a versatile tool that can handle both balanced and unbalanced datasets and that can also be applied when several layers of grouping are present in the data; these layers can either be nested or crossed. In linguistics, as in many other fields, the use of mixed models has gained ground rapidly over the last decade. This methodological evolution enables us to build more sophisticated and arguably more realistic models, but, due to its technical complexity, also introduces new challenges. This volume brings together a number of promising new evolutions in the use of mixed models in linguistics, but also addres...
Ill-posedness in modeling mixed sediment river morphodynamics
Chavarrías, Víctor; Stecca, Guglielmo; Blom, Astrid
2018-04-01
In this paper we analyze the Hirano active layer model used in mixed sediment river morphodynamics concerning its ill-posedness. Ill-posedness causes the solution to be unstable to short-wave perturbations. This implies that the solution presents spurious oscillations, the amplitude of which depends on the domain discretization. Ill-posedness not only produces physically unrealistic results but may also cause failure of numerical simulations. By considering a two-fraction sediment mixture we obtain analytical expressions for the mathematical characterization of the model. Using these we show that the ill-posed domain is larger than what was found in previous analyses, not only comprising cases of bed degradation into a substrate finer than the active layer but also in aggradational cases. Furthermore, by analyzing a three-fraction model we observe ill-posedness under conditions of bed degradation into a coarse substrate. We observe that oscillations in the numerical solution of ill-posed simulations grow until the model becomes well-posed, as the spurious mixing of the active layer sediment and substrate sediment acts as a regularization mechanism. Finally we conduct an eigenstructure analysis of a simplified vertically continuous model for mixed sediment for which we show that ill-posedness occurs in a wider range of conditions than the active layer model.
A novel experimental design model for increasing occlusal vertical dimension.
Li, Yan; Zhang, Zhiguang; Wu, Shuyi; Qiao, Yonggang
2010-03-01
This study aimed to establish a rat model of increasing occlusal vertical dimension (iOVD) using a prosthodontic approach. The OVD was increased by bonding a maxillary, bilateral, posterior dental splint with a bearing ball while the occlusal stops that were made on the stone casts adjusted the occlusion and bonded in the mouths of adult Wistar rats (iOVD group); the controls did not receive a splint. Both groups were subdivided after splint insertion: 3 days and 1, 2, 3, or 4 weeks (n = 6/subgroup). The effects of iOVD were evaluated by radiographs, body weight, and histologic diagnosis of tooth and temporomandibular joints. There were no differences in body weights between the 2 groups; occlusal asymmetric dentition abrasions did not occur in the iOVD rats. The occlusal splints caused the remodeling of the periodontal tissue and condylar cartilage. Overall, an iOVD rat model can be constructed using prosthodontic techniques ensuring a balance of bilateral occlusal height. OVD, occlusal vertical dimension; iOVD, increasing occlusal vertical dimension; TMJ, temporomandibular joint; TMD, temporomandibular disorders.
Macayeal, D. R.
1984-01-01
The warmest water below parts of the Ross Ice Shelf resides in the lowest portion of the water column because of its high salinity. Vertical mixing caused by tidal stirring can thus induce ablation by lifting the warm but dense water into contact with the ice shelf. A numerical tidal simulation indicates that vertically well-mixed conditions predominate in the southeastern part of the sub-ice shelf cavity, where the water column thickness is small. Basal melting in this region is expected to be between 0.05 and 0.5 m/yr and will drive a thermohaline circulation having the following characteristics: high salinity shelf water (at - 1.8 C), formed by winter sea ice production in the open Ross Sea, flows along the seabed toward the tidal mixing fronts below the ice shelf; and meltwater (at -2.2 C), produced in the well-mixed region, flows out of the sub-ice shelf cavity along the ice shelf bottom. Sensitivity of this ablation process to climatic change is expected to be small because high salinity shelf water is constrained to have the sea surface freezing temperature.
Ocean bottom pressure modeling for detection of seafloor vertical deformation
Inazu, D.; Hino, R.; Fujimoto, H.
2009-12-01
Detection of seafloor crustal deformation is a difficult problem in marine geodesy. Horizontal displacement of the ocean bottom has been detected with accuracy of several centimeters per year by the GPS/Acoustic positioning of seafloor reference points (Spiess et al. 1998). Meanwhile, bottom pressure observations can record the vertical deformation of seafloor and there have been many challenges to detect vertical seafloor displacement. However, ocean bottom pressure variations are highly dominated by oceanic signals such as tidal and subinertial motions. The tidal and other oceanic variations in bottom pressure records are mostly equivalent to several tens and several centimeters water height anomalies, respectively. Generally, the ocean tide is efficiently corrected. Non-tidal components are required to be accurately removed from the bottom pressure records so that the vertical displacement of less than ten centimeters, the expected amount of displacement caused by slow slip events often observed in several subduction zones, is detected by continuous bottom pressure monitoring. We examine the bottom pressure estimations derived from the Kalman filter and smoother runs of the ECCO (Estimating the Circulation & Climate of the Ocean) product to compare in-situ bottom pressure records. The assimilated bottom pressure moderately represents the seasonal variation, and hardly represents the variation with periods less than a few months. This high frequency variation is mainly explained by the barotropic phenomena induced by meteorological disturbances. Hirose et al. (2001) and Carrère and Lyard (2003) modeled the barotropic ocean motion with the forcing of atmospheric pressure loading and wind over global oceans for the sake of the correction of satellite observations. This study addresses the accurate bottom pressure modeling, which enables us to detect vertical displacement of several centimeters from the in-situ bottom pressure observations. We develop accurate
Modeling vertical loads in pools resulting from fluid injection. [BWR
Energy Technology Data Exchange (ETDEWEB)
Lai, W.; McCauley, E.W.
1978-06-15
Table-top model experiments were performed to investigate pressure suppression pool dynamics effects due to a postulated loss-of-coolant accident (LOCA) for the Peachbottom Mark I boiling water reactor containment system. The results guided subsequent conduct of experiments in the /sup 1///sub 5/-scale facility and provided new insight into the vertical load function (VLF). Model experiments show an oscillatory VLF with the download typically double-spiked followed by a more gradual sinusoidal upload. The load function contains a high frequency oscillation superimposed on a low frequency one; evidence from measurements indicates that the oscillations are initiated by fluid dynamics phenomena.
Modeling vertical loads in pools resulting from fluid injection
International Nuclear Information System (INIS)
Lai, W.; McCauley, E.W.
1978-01-01
Table-top model experiments were performed to investigate pressure suppression pool dynamics effects due to a postulated loss-of-coolant accident (LOCA) for the Peachbottom Mark I boiling water reactor containment system. The results guided subsequent conduct of experiments in the 1 / 5 -scale facility and provided new insight into the vertical load function (VLF). Model experiments show an oscillatory VLF with the download typically double-spiked followed by a more gradual sinusoidal upload. The load function contains a high frequency oscillation superimposed on a low frequency one; evidence from measurements indicates that the oscillations are initiated by fluid dynamics phenomena
Directory of Open Access Journals (Sweden)
K. Ganesh Kumar
2018-03-01
Full Text Available A study on magnetohydrodynamic mixed convection flow of Casson fluid over a vertical plate has been modelled in the presence of Cross diffusion effect and nonlinear thermal radiation. The governing partial differential equations are remodelled into ordinary differential equations by using similarity transformation. The accompanied differential equations are resolved numerically by using Runge–Kutta–Fehlberg forth-fifth order along with shooting method (RKF45 Method. The results of various physical parameters on velocity and temperature profiles are given diagrammatically. The numerical values of the local skin friction coefficient, local Nusselt number and local Sherwood number also are shown in a tabular form. It is found that, effect of Dufour and Soret parameter increases the temperature and concentration component correspondingly. Keywords: Casson fluid, Nonlinear thermal radiation, Magnetic field, Cross diffusion effect, Vertical surface
Mixed models theory and applications with R
Demidenko, Eugene
2013-01-01
Mixed modeling is one of the most promising and exciting areas of statistical analysis, enabling the analysis of nontraditional, clustered data that may come in the form of shapes or images. This book provides in-depth mathematical coverage of mixed models' statistical properties and numerical algorithms, as well as applications such as the analysis of tumor regrowth, shape, and image. The new edition includes significant updating, over 300 exercises, stimulating chapter projects and model simulations, inclusion of R subroutines, and a revised text format. The target audience continues to be g
Cohesive mixed mode fracture modelling and experiments
DEFF Research Database (Denmark)
Walter, Rasmus; Olesen, John Forbes
2008-01-01
A nonlinear mixed mode model originally developed by Wernersson [Wernersson H. Fracture characterization of wood adhesive joints. Report TVSM-1006, Lund University, Division of Structural Mechanics; 1994], based on nonlinear fracture mechanics, is discussed and applied to model interfacial cracking....... An experimental set-up for the assessment of mixed mode interfacial fracture properties is presented, applying a bi-material specimen, half steel and half concrete, with an inclined interface and under uniaxial load. Loading the inclined steel–concrete interface under different angles produces load–crack opening...... curves, which may be interpreted using the nonlinear mixed mode model. The interpretation of test results is carried out in a two step inverse analysis applying numerical optimization tools. It is demonstrated how to perform the inverse analysis, which couples the assumed individual experimental load...
Numerical and physical model study of a vertical slot fishway
Directory of Open Access Journals (Sweden)
Bombač Martin
2014-06-01
Full Text Available This paper presents the results of an experimental and numerical study of a vertical slot fishway (VSF. A 2-D depth-averaged shallow water numerical model PCFLOW2D coupled with three different turbulent models (constant eddy viscosity, Smagorinsky and k - ε was used. A detailed analysis of numerical parameters needed for a correct simulation of the phenomenon was carried out. Besides the velocity field, attention was paid to important hydraulic parameters such as maximum velocity in the slot region and energy dissipation rate ε in order to evaluate the performance of VSF. A scaled physical hydraulic model was built to ensure reliable experimental data for the validation of the numerical model. Simulations of variant configurations of VSF showed that even small changes in geometry can produce more fishfriendly flow characteristics in pools. The present study indicates that the PCFLOW2D program is an appropriate tool to meet the main demands of the VSF design.
Some aspects of estimation of mixing height using vertical sodar records
Energy Technology Data Exchange (ETDEWEB)
Walczewski, J. [Inst. for Meteorology and Water Management, Cracow (Poland)
1997-10-01
The changes of the vertical range of sodar, depending on technical parameters, were illustrated by resulting changes of the height distribution of convective and elevated layers echoes. The extent of the difference`s in vertical range may be compartively large. In analyzed case, the maximal heights of convective plumes recorded at the same site with use of 3 types of sodar, were like 1:1.35:1.96. The relations of mean centers of gravity of frequency distributions were like 1:1.4:2.4. (au)
Chow, A.; Shrivastava, I.; Adams, E. E.
2016-02-01
Environmental impacts from coastal desalination discharges are usually studied in the near field (region within 100 m of the outfall where dilution is caused mainly by discharge momentum) and/or the far field (region 10s of km or more from the outfall where mixing is affected mainly by large scale circulation). Here we consider an "intermediate field" scenario in which brine accumulates in local depressions within 1 km of the outfall, forming "puddles" on an otherwise flat bathymetry. Such puddles are hard to resolve with numerical far field models, but can impact benthic marine life, e.g., by allowing contaminants to accumulate or respiration of organic matter in the sediments to deplete dissolved oxygen. We model the puddle and the overlying water as a two layer system, with a stationary, dense, bottom layer containing diluted brine, and a top layer comprising ambient seawater that moves with the tidal current. Mass exchange between the two layers is modeled using formulations from the literature expressing the rate of entrainment from the bottom to the top layer as a function of Richardson number. Using idealized bathymetry, we investigate the evolution of the brine puddle as a function of the discharge flow rate and density difference relative to ambient, the near field dilution, and periodic tidal velocities. We study the periodic variation of the puddle volume and area, and determine the criteria for which the puddle might completely erode during a portion of the tidal cycle. Additionally we bookkeep the fate of passive tracers (salt, metals, dissolved oxygen) within the puddle, assuming they obey simple (zero or first order) kinetics. Finally we discuss the implications on benthic organisms living in the puddle and their exposures to prolonged periods of excess salinity, heavy metals, and lowered dissolved oxygen levels.
Modeling of Salt Solubilities in Mixed Solvents
DEFF Research Database (Denmark)
Chiavone-Filho, O.; Rasmussen, Peter
2000-01-01
A method to correlate and predict salt solubilities in mixed solvents using a UNIQUAC+Debye-Huckel model is developed. The UNIQUAC equation is applied in a form with temperature-dependent parameters. The Debye-Huckel model is extended to mixed solvents by properly evaluating the dielectric...... constants and the liquid densities of the solvent media. To normalize the activity coefficients, the symmetric convention is adopted. Thermochemical properties of the salt are used to estimate the solubility product. It is shown that the proposed procedure can describe with good accuracy a series of salt...... solubility measurements in aqueous organic solvent mixtures....
Wake Development of a Model Vertical Axis Wind Turbine
Kadum, Hawwa; Friedman, Sasha; Camp, Elizabeth; Cal, Rau'l.
2015-11-01
At the Portland State University wind tunnel facility, an experiment is conducted to observe the downstream development of the wake past a model vertical axis wind turbine (VAWT). The flow domain is composed of streamwise-spanwise planes at mid-height of the VAWT rotor and data is obtained via particle image velocimetry (PIV). The flow field is assessed by analyzing contours of mean velocities and the full Reynolds stress tensor. Furthermore, profiles of the aforementioned quantities and flow parameters are discussed in the context of downstream evolution/flow development.
Modelling the long-term vertical dynamics of salt marshes
Zoccarato, Claudia; Teatini, Pietro
2017-04-01
Salt marshes are vulnerable environments hosting complex interactions between physical and biological processes with a strong influence on the dynamics of the marsh evolution. The estimation and prediction of the elevation of a salt-marsh platform is crucial to forecast the marsh growth or regression under different scenarios considering, for example, the potential climate changes. The long-term vertical dynamics of a salt marsh is predicted with the aid of an original finite-element (FE) numerical model accounting for the marsh accretion and compaction and for the variation rates of the relative sea level rise, i.e., land subsidence of the marsh basement and eustatic rise of the sea level. The accretion term considers the vertical sedimentation of organic and inorganic material over the marsh surface, whereas the compaction reflects the progressive consolidation of the porous medium under the increasing load of the overlying younger deposits. The modelling approach is based on a 2D groundwater flow simulator, which provides the pressure evolution within a compacting/accreting vertical cross-section of the marsh assuming that the groundwater flow obeys the relative Darcy's law, coupled to a 1D vertical geomechanical module following Terzaghi's principle of effective intergranular stress. Soil porosity, permeability, and compressibility may vary with the effective intergranular stress according to empirically based relationships. The model also takes into account the geometric non-linearity arising from the consideration of large solid grain movements by using a Lagrangian approach with an adaptive FE mesh. The element geometry changes in time to follow the deposit consolidation and the element number increases in time to follow the sedimentation of new material. The numerical model is tested on different realistic configurations considering the influence of (i) the spatial distribution of the sedimentation rate in relation to the distance from the marsh margin, (ii
Comparison of aerodynamic models for Vertical Axis Wind Turbines
Simão Ferreira, C.; Aagaard Madsen, H.; Barone, M.; Roscher, B.; Deglaire, P.; Arduin, I.
2014-06-01
Multi-megawatt Vertical Axis Wind Turbines (VAWTs) are experiencing an increased interest for floating offshore applications. However, VAWT development is hindered by the lack of fast, accurate and validated simulation models. This work compares six different numerical models for VAWTS: a multiple streamtube model, a double-multiple streamtube model, the actuator cylinder model, a 2D potential flow panel model, a 3D unsteady lifting line model, and a 2D conformal mapping unsteady vortex model. The comparison covers rotor configurations with two NACA0015 blades, for several tip speed ratios, rotor solidity and fixed pitch angle, included heavily loaded rotors, in inviscid flow. The results show that the streamtube models are inaccurate, and that correct predictions of rotor power and rotor thrust are an effect of error cancellation which only occurs at specific configurations. The other four models, which explicitly model the wake as a system of vorticity, show mostly differences due to the instantaneous or time averaged formulation of the loading and flow, for which further research is needed.
Wang, Fei; Zhang, Yijun; Zheng, Dong; Xu, Liangtao; Zhang, Wenjuan; Meng, Qing
2017-10-01
A three-dimensional charge-discharge numerical model is used, in a semi-idealized mode, to simulate a thunder-storm cell. Characteristics of the graupel microphysics and vertical air motion associated with the lightning initiation are revealed, which could be useful in retrieving charge strength during lightning when no charge-discharge model is available. The results show that the vertical air motion at the lightning initiation sites ( W ini) has a cubic polynomial correlation with the maximum updraft of the storm cell ( W cell-max), with the adjusted regression coefficient R 2 of approximately 0.97. Meanwhile, the graupel mixing ratio at the lightning initiation sites ( q g-ini) has a linear correlation with the maximum graupel mixing ratio of the storm cell ( q g-cell-max) and the initiation height ( z ini), with the coefficients being 0.86 and 0.85, respectively. These linear correlations are more significant during the middle and late stages of lightning activity. A zero-charge zone, namely, the area with very low net charge density between the main positive and negative charge layers, appears above the area of q g-cell-max and below the upper edge of the graupel region, and is found to be an important area for lightning initiation. Inside the zero-charge zone, large electric intensity forms, and the ratio of q ice (ice crystal mixing ratio) to q g (graupel mixing ratio) illustrates an exponential relationship to q g-ini. These relationships provide valuable clues to more accurately locating the high-risk area of lightning initiation in thunderstorms when only dual-polarization radar data or outputs from numerical models without charging/discharging schemes are available. The results can also help understand the environmental conditions at lightning initiation sites.
Mixed convective heat transfer from a vertical plate embedded in a ...
Indian Academy of Sciences (India)
Abstract. The effect of melting and solute dispersion on heat and mass transfer in non-Darcy fluid flow over a vertical surface has been studied numerically in the present article. The flow is assumed to be laminar and steady state. Using similarity transformations, the governing boundary layer equations are transformed into ...
Bifurcation analysis of vertical transmission model with preventive strategy
Directory of Open Access Journals (Sweden)
Gosalamang Ricardo Kelatlhegile
2016-07-01
Full Text Available We formulate and analyze a deterministic mathematical model for the prevention of a disease transmitted horizontally and vertically in a population of varying size. The model incorporates prevention of disease on individuals at birth and adulthood and allows for natural recovery from infection. The main aim of the study is to investigate the impact of a preventive strategy applied at birth and at adulthood in reducing the disease burden. Bifurcation analysis is explored to determine existence conditions for establishment of the epidemic states. The results of the study showed that in addition to the disease-free equilibrium there exist multiple endemic equilibria for the model reproduction number below unity. These results may have serious implications on the design of intervention programs and public health policies. Numerical simulations were carried out to illustrate analytical results.
Linear and Generalized Linear Mixed Models and Their Applications
Jiang, Jiming
2007-01-01
This book covers two major classes of mixed effects models, linear mixed models and generalized linear mixed models, and it presents an up-to-date account of theory and methods in analysis of these models as well as their applications in various fields. The book offers a systematic approach to inference about non-Gaussian linear mixed models. Furthermore, it has included recently developed methods, such as mixed model diagnostics, mixed model selection, and jackknife method in the context of mixed models. The book is aimed at students, researchers and other practitioners who are interested
Solving vertical transport and chemistry in air pollution models
International Nuclear Information System (INIS)
Berkvens, P.J.F.; Botchev, M.A.; Verwer, J.G.; Krol, M.C.; Peters, W.
2000-01-01
For the time integration of stiff transport-chemistry problems from air pollution modelling, standard ODE solvers are not feasible due to the large number of species and the 3D nature. The popular alternative, standard operator splitting, introduces artificial transients for short-lived species. This complicates the chemistry solution, easily causing large errors for such species. In the framework of an operational global air pollution model, we focus on the problem formed by chemistry and vertical transport, which is based on diffusion, cloud-related vertical winds, and wet deposition. Its specific nature leads to full Jacobian matrices, ruling out standard implicit integration. We compare Strang operator splitting with two alternatives: source splitting and an (unsplit) Rosenbrock method with approximate matrix factorization, all having equal computational cost. The comparison is performed with real data. All methods are applied with half-hour time steps, and give good accuracies. Rosenbrock is the most accurate, and source splitting is more accurate than Strang splitting. Splitting errors concentrate in short-lived species sensitive to solar radiation and species with strong emissions and depositions. 30 refs
Mathematical model of Zika virus with vertical transmission
Directory of Open Access Journals (Sweden)
F.B. Agusto
2017-05-01
Full Text Available Zika is a flavivirus transmitted to humans through either the bites of infected Aedes mosquitoes or sexual transmission. Zika has been linked to congenital anomalies such as microcephaly. In this paper, we analyze a new system of ordinary differential equations which incorporates human vertical transmission of Zika virus, the birth of babies with microcephaly and asymptomatically infected individuals. The Zika model is locally and globally asymptotically stable when the basic reproduction number is less than unity. Our model shows that asymptomatic individuals amplify the disease burden in the community, and the most important parameters for ZIKV spread are the death rate of mosquitoes, the mosquito biting rate, the mosquito recruitment rate, and the transmission per contact to mosquitoes and to adult humans. Scenario exploration indicates that personal-protection is a more effective control strategy than mosquito-reduction strategy. It also shows that delaying conception reduces the number of microcephaly cases, although this does little to prevent Zika transmission in the broader community. However, by coupling aggressive vector control and personal protection use, it is possible to reduce both microcephaly and Zika transmission. 2000 Mathematics Subject Classifications: 92B05, 93A30, 93C15. Keywords: Zika virus, Vertical transmission, Microcephaly, Stability, Control
Implementation of Dynamic Smart Decision Model for Vertical Handoff
Sahni, Nidhi
2010-11-01
International Mobile Telecommunications-Advanced (IMT Advanced), better known as 4G is the next level of evolution in the field of wireless communications. 4G Wireless networks enable users to access information anywhere, anytime, with a seamless connection to a wide range of information and services, and receiving a large volume of information, data, pictures, video and thus increasing the demand for High Bandwidth and Signal Strength. The mobility among various networks is achieved through Vertical Handoff. Vertical handoffs refer to the automatic failover from one technology to another in order to maintain communication. The heterogeneous co-existence of access technologies with largely different characteristics creates a decision problem of determining the "best" available network at "best" time for handoff. In this paper, we implemented the proposed Dynamic and Smart Decision model to decide the "best" network interface and "best" time moment to handoff. The proposed model implementation not only demonstrates the individual user needs but also improve the whole system performance i.e. Quality of Service by reducing the unnecessary handoffs and maintain mobility.
A model for the performance of a vertical tube condenser in the presence of noncondensable gases
Energy Technology Data Exchange (ETDEWEB)
Guentay, A.D.S.
1995-09-01
Some proposed vertical tube condensers are designed to operate at high noncondensable fractions, which warrants a simple model to predict their performance. Models developed thus far are usually non self-contained as they require the specification of the wall temperature to predict the local condensation rate. The present model attempts to fill this gap by addressing the secondary side heat transfer as well. Starting with momentum balance which includes the effect of interfacial shear stress, a Nusselt-type algebraic equation is derived for the film thickness as a function of flow and geometry parameters. The heat and mass transfer analogy relations are then invoked to deduce the condensation rate of steam onto the tube wall. Lastly, the heat transfer to the secondary side is modelled to include cooling by forced, free or mixed convection flows. The model is used for parametric simulations to determine the impact on the condenser performance of important factors such as the inlet gas fraction, the mixture inlet flowrate, the total pressure, and the molecular weight of the noncondensable gas. The model performed simulations of some experiments with pure steam and air-steam mixtures flowing down a vertical tube. The model predicts the data quite well.
Starnes, B J; Self, D R
1999-01-01
This article develops two previous research efforts. William J. Winston (1994, 1995) has proposed a set of strategies by which health care organizations can benefit from forging strategic alliances. Raadt and Self (1997) have proposed a classification model of alliances including horizontal, vertical, internal, and osmotic. In the second of two articles, this paper presents a model of vertical, internal, and osmotic alliances. Advantages and disadvantages of each are discussed. Finally, the complete alliance system model is presented.
Slag transport models for vertical and horizontal surfaces. [SLGTR code
Energy Technology Data Exchange (ETDEWEB)
Chow, L S.H.; Johnson, T R
1978-01-01
In a coal-fired MHD system, all downstream component surfaces that are exposed to combustion gases will be covered by a solid, liquid, or solid-liquid film of slag, seed, or a mixture of the two, the specific nature of the film depending on the physical properties of the slag and seed and on local conditions. An analysis was made of a partly-liquid slag film flowing on a cooled vertical or horizontal wall of a large duct, through which passed slag-laden combustion gases. The model is applicable to the high-temperature steam generators in the downstream system of an MHD power plant and was used in calculations for a radiant-boiler concept similar to that in the 1000-MWe Gilbert-STD Baseline Plant study and also for units large enough for 230 and 8 lb/s (104.3 and 3.5 kg/s) of combustion gas. The qualitative trends of the results are similar for both vertical and horizontal surfaces. The results show the effects of the slag film, slag properties, and gas emissivity on the heat flux to the steam tubes. The slag film does not reduce the rate of heat transfer in proportion to its surface temperature, because most of the heat is radiated from the gas and particles suspended in it to the slag surface.
A Lagrangian mixing frequency model for transported PDF modeling
Turkeri, Hasret; Zhao, Xinyu
2017-11-01
In this study, a Lagrangian mixing frequency model is proposed for molecular mixing models within the framework of transported probability density function (PDF) methods. The model is based on the dissipations of mixture fraction and progress variables obtained from Lagrangian particles in PDF methods. The new model is proposed as a remedy to the difficulty in choosing the optimal model constant parameters when using conventional mixing frequency models. The model is implemented in combination with the Interaction by exchange with the mean (IEM) mixing model. The performance of the new model is examined by performing simulations of Sandia Flame D and the turbulent premixed flame from the Cambridge stratified flame series. The simulations are performed using the pdfFOAM solver which is a LES/PDF solver developed entirely in OpenFOAM. A 16-species reduced mechanism is used to represent methane/air combustion, and in situ adaptive tabulation is employed to accelerate the finite-rate chemistry calculations. The results are compared with experimental measurements as well as with the results obtained using conventional mixing frequency models. Dynamic mixing frequencies are predicted using the new model without solving additional transport equations, and good agreement with experimental data is observed.
Directory of Open Access Journals (Sweden)
Wenrui Huang
2010-03-01
Full Text Available This paper presents an improvement of the Mellor and Yamada's 2nd order turbulence model in the Princeton Ocean Model (POM for better predictions of vertical stratifications of salinity in estuaries. The model was evaluated in the strongly stratified estuary, Apalachicola River, Florida, USA. The three-dimensional hydrodynamic model was applied to study the stratified flow and salinity intrusion in the estuary in response to tide, wind, and buoyancy forces. Model tests indicate that model predictions over estimate the stratification when using the default turbulent parameters. Analytic studies of density-induced and wind-induced flows indicate that accurate estimation of vertical eddy viscosity plays an important role in describing vertical profiles. Initial model revision experiments show that the traditional approach of modifying empirical constants in the turbulence model leads to numerical instability. In order to improve the performance of the turbulence model while maintaining numerical stability, a stratification factor was introduced to allow adjustment of the vertical turbulent eddy viscosity and diffusivity. Sensitivity studies indicate that the stratification factor, ranging from 1.0 to 1.2, does not cause numerical instability in Apalachicola River. Model simulations show that increasing the turbulent eddy viscosity by a stratification factor of 1.12 results in an optimal agreement between model predictions and observations in the case study presented in this study. Using the proposed stratification factor provides a useful way for coastal modelers to improve the turbulence model performance in predicting vertical turbulent mixing in stratified estuaries and coastal waters.
International Nuclear Information System (INIS)
Hernandez, E.A.
2007-01-01
The effect of UV radiation on two Antarctic marine bacterial strains (UVps and UVvi) was studied in the water column of Potter Cove (South Shetland, Antarctica). Quartz flasks were filled with the bacterial suspensions and exposed to solar radiation at 0 m, 1 m and 3 m depth. Assays using flasks exposed to direct solar radiation and others using flasks covered with/by interferential filters which discriminate between UVA and UVB, were performed. In other assays, a vertical mixing of 4 m/h was simulated. Both strains showed a significant decrease in viability (expressed as colony - forming units) when exposed to a surface UVB dose of 8.4 kJ m -2 . Studies with interferential filters showed a significant decrease at 0 and 1 m depth under both UV treatments. The UVps strain appeared to be more sensitive to UVB than to UVA. Damage produced by UVB was attenuated by the vertical mixing when the surface UVB dose was 4.8 kJ m -2 . This effect was not observed when surface UVB dose was 7.7 kJ m -2 . These results show that the negative effect caused by UVB radiation on the bacterio plankton would be significant only in the first meter of water column of the Antarctic coastal waters with high levels of suspended particulate material. (author) [es
Mixed convective heat transfer from a vertical plate embedded in a ...
Indian Academy of Sciences (India)
In problems dealing with porous media, the effect of melting, radiation is important in indus- tries and technologies. The applications are found in situation such as geothermal systems, heating and cooling chamber, fossil fuel combustion, energy processes and Astro-physical flows. The effects of non-Darcy mixed convection ...
Mixed convective heat transfer from a vertical plate embedded in a ...
Indian Academy of Sciences (India)
thermal radiaiton in a non-Darcy porous medium. J. Porous Media 8(5): 1–9. Prasad B D C N and Hemalatha K 2010 Non-Darcy mixed convection with thermal dispersion-Radiation in a saturated porous medium. The Open Transport Phenomena J. 2: 109–115. Sparrow E M, Patankar S V and Ramadhyani S 1977 Analysis ...
Understanding and Improving Ocean Mixing Parameterizations for modeling Climate Change
Howard, A. M.; Fells, J.; Clarke, J.; Cheng, Y.; Canuto, V.; Dubovikov, M. S.
2017-12-01
Climate is vital. Earth is only habitable due to the atmosphere&oceans' distribution of energy. Our Greenhouse Gas emissions shift overall the balance between absorbed and emitted radiation causing Global Warming. How much of these emissions are stored in the ocean vs. entering the atmosphere to cause warming and how the extra heat is distributed depends on atmosphere&ocean dynamics, which we must understand to know risks of both progressive Climate Change and Climate Variability which affect us all in many ways including extreme weather, floods, droughts, sea-level rise and ecosystem disruption. Citizens must be informed to make decisions such as "business as usual" vs. mitigating emissions to avert catastrophe. Simulations of Climate Change provide needed knowledge but in turn need reliable parameterizations of key physical processes, including ocean mixing, which greatly impacts transport&storage of heat and dissolved CO2. The turbulence group at NASA-GISS seeks to use physical theory to improve parameterizations of ocean mixing, including smallscale convective, shear driven, double diffusive, internal wave and tidal driven vertical mixing, as well as mixing by submesoscale eddies, and lateral mixing along isopycnals by mesoscale eddies. Medgar Evers undergraduates aid NASA research while learning climate science and developing computer&math skills. We write our own programs in MATLAB and FORTRAN to visualize and process output of ocean simulations including producing statistics to help judge impacts of different parameterizations on fidelity in reproducing realistic temperatures&salinities, diffusivities and turbulent power. The results can help upgrade the parameterizations. Students are introduced to complex system modeling and gain deeper appreciation of climate science and programming skills, while furthering climate science. We are incorporating climate projects into the Medgar Evers college curriculum. The PI is both a member of the turbulence group at
International Nuclear Information System (INIS)
Harris, M.K.
1999-01-01
Groundwater modeling scenarios were performed to support the Corrective Measures Study and Interim Action Plan for the southwest plume of the Burial Ground Complex/Mixed Waste Management Facility. The modeling scenarios were designed to provide data for an economic analysis of alternatives, and subsequently evaluate the effectiveness of the selected remedial technologies for tritium reduction to Fourmile Branch. Modeling scenarios assessed include no action, vertical barriers, pump, treat, and reinject; and vertical recirculation wells
Scrutiny of mixed convection flow of a nanofluid in a vertical channel
Directory of Open Access Journals (Sweden)
M. Fakour
2014-11-01
Full Text Available The laminar fully developed nanofluid flow and heat transfer in a vertical channel are investigated. By means of a new set of similarity variables, the governing equations are reduced to a set of three coupled equations with an unknown constant, which are solved along with the corresponding boundary conditions and the mass flux conservation relation by the homotopy perturbation method (HPM. We have tried to show reliability and performance of the present method compared with the numerical method (Runge–Kutta fourth-rate to solve this problem. The effects of the Grashof number (Gr, Prandtl number (Pr and Reynolds number (Re on the nanofluid flows are then investigated successively. The effects of the Brownian motion parameter (Nb, the thermophoresis parameter (Nt, and the Lewis number (Le on the temperature and nanoparticle concentration distributions are discussed. The current analysis shows that the nanoparticles can improve the heat transfer characteristics significantly for this flow problem.
A multi-model analysis of vertical ozone profiles
Jonson, J. E.; Stohl, A.; Fiore, A. M.; Hess, P.; Szopa, S.; Wild, O.; Zeng, G.; Dentener, F. J.; Lupu, A.; Schultz, M. G.; Duncan, B. N.; Sudo, K.; Wind, P.; Schulz, M.; Marmer, E.; Cuvelier, C.; Keating, T.; Zuber, A.; Valdebenito, A.; Dorokhov, V.; de Backer, H.; Davies, J.; Chen, G. H.; Johnson, B.; Tarasick, D. W.; Stübi, R.; Newchurch, M. J.; von der Gathen, P.; Steinbrecht, W.; Claude, H.
2010-06-01
A multi-model study of the long-range transport of ozone and its precursors from major anthropogenic source regions was coordinated by the Task Force on Hemispheric Transport of Air Pollution (TF HTAP) under the Convention on Long-range Transboundary Air Pollution (LRTAP). Vertical profiles of ozone at 12-h intervals from 2001 are available from twelve of the models contributing to this study and are compared here with observed profiles from ozonesondes. The contributions from each major source region are analysed for selected sondes, and this analysis is supplemented by retroplume calculations using the FLEXPART Lagrangian particle dispersion model to provide insight into the origin of ozone transport events and the cause of differences between the models and observations. In the boundary layer ozone levels are in general strongly affected by regional sources and sinks. With a considerably longer lifetime in the free troposphere, ozone here is to a much larger extent affected by processes on a larger scale such as intercontinental transport and exchange with the stratosphere. Such individual events are difficult to trace over several days or weeks of transport. This may explain why statistical relationships between models and ozonesonde measurements are far less satisfactory than shown in previous studies for surface measurements at all seasons. The lowest bias between model-calculated ozone profiles and the ozonesonde measurements is seen in the winter and autumn months. Following the increase in photochemical activity in the spring and summer months, the spread in model results increases, and the agreement between ozonesonde measurements and the individual models deteriorates further. At selected sites calculated contributions to ozone levels in the free troposphere from intercontinental transport are shown. Intercontinental transport is identified based on differences in model calculations with unperturbed emissions and emissions reduced by 20% by region
A multi-model analysis of vertical ozone profiles
Directory of Open Access Journals (Sweden)
J. E. Jonson
2010-06-01
Full Text Available A multi-model study of the long-range transport of ozone and its precursors from major anthropogenic source regions was coordinated by the Task Force on Hemispheric Transport of Air Pollution (TF HTAP under the Convention on Long-range Transboundary Air Pollution (LRTAP. Vertical profiles of ozone at 12-h intervals from 2001 are available from twelve of the models contributing to this study and are compared here with observed profiles from ozonesondes. The contributions from each major source region are analysed for selected sondes, and this analysis is supplemented by retroplume calculations using the FLEXPART Lagrangian particle dispersion model to provide insight into the origin of ozone transport events and the cause of differences between the models and observations.
In the boundary layer ozone levels are in general strongly affected by regional sources and sinks. With a considerably longer lifetime in the free troposphere, ozone here is to a much larger extent affected by processes on a larger scale such as intercontinental transport and exchange with the stratosphere. Such individual events are difficult to trace over several days or weeks of transport. This may explain why statistical relationships between models and ozonesonde measurements are far less satisfactory than shown in previous studies for surface measurements at all seasons. The lowest bias between model-calculated ozone profiles and the ozonesonde measurements is seen in the winter and autumn months. Following the increase in photochemical activity in the spring and summer months, the spread in model results increases, and the agreement between ozonesonde measurements and the individual models deteriorates further.
At selected sites calculated contributions to ozone levels in the free troposphere from intercontinental transport are shown. Intercontinental transport is identified based on differences in model calculations with unperturbed emissions and
Bracco, Annalisa; Choi, Jun; Kurian, Jaison; Chang, Ping
2018-02-01
A set of nine regional ocean model simulations at various horizontal (from 1 to 9 km) and vertical (from 25 to 150 layers) resolutions with different vertical mixing parameterizations is carried out to examine the transport and mixing of a passive tracer released near the ocean bottom over the continental slope in the northern Gulf of Mexico. The release location is in proximity to the Deepwater Horizon oil well that ruptured in April 2010. Horizontal and diapycnal diffusivities are calculated and their dependence on the model set-up and on the representation of mesoscale and submesoscale circulations is discussed. Horizontal and vertical resolutions play a comparable role in determining the modeled horizontal diffusivities. Vertical resolution is key to a proper representation of passive tracer propagation and - in the case of the Gulf of Mexico - contributes to both confining the tracer along the continental slope and limiting its vertical spreading. The choice of the tracer advection scheme is also important, with positive definiteness in the tracer concentration being achieved at the price of spurious mixing across density surfaces. In all cases, however, the diapycnal mixing coefficient derived from the model simulations overestimates the observed value, indicating an area where model improvement is needed.
International Nuclear Information System (INIS)
Miyano, Hiroshi; Narabayashi, Tadashi
2011-01-01
Mechanical seal for nuclear reactor coolant recirculation pump must purge the cold water supply from the outside. The cold purge water is flowing into the hot water zone in the pump through a narrow gap between pump shaft and casing over. On the mixing region of the cold purge water and hot water in the narrow gap, the random level temperature fluctuation occurs on the structural metal surface of casing cover and pump shaft. Then it could lead to cyclic thermal stress and fatigue damage. The experiments and analysis have done, made clear the mechanism of generation of temperature fluctuations. Also, it was studied how to measure the structure of the mixing zone temperature control and how to prevent the occurrence of a large temperature fluctuation. In addition, it is proposed the method of evaluating a random temperature fluctuation by using the envelope curve and its fatigue by OOR counting to applying to the evaluation of the similar random fluid temperature fluctuation problems. (author)
Vertical repositioning accuracy of magnetic mounting systems on 4 articulator models.
Lee, Wonsup; Kwon, Ho-Beom
2018-03-01
Research of the ability of a cast mounted on an articulator on maintaining the identical position of a cast mounted on an articulator after repeated repositioning is lacking, despite the possible effects this may have on the occlusion of a mounted cast. The purpose of this in vitro study was to verify and compare the vertical repositioning accuracy of 4 different, commercially available articulator magnetic mounting plate systems. Four articulators and their associated magnetic mounting plates were selected for the study. These were the Artex AR articulator (Amann Girrbach AG), the Denar Mark II articulator (Whip Mix Corp), the Kavo Protar Evo articulator (Kavo Dental GmbH), and the SAM3 articulator (SAM Präzisionstechnik GmbH). Three new magnetic mounting plates were prepared for each articulator system. The repositioning accuracy of each mounting plate was evaluated by comparing the standard deviation of the vertical distances measured between the mounting plate and a laser displacement sensor. The lower arm of the articulator was secured, and the vertical distance was measured by positioning the laser displacement sensor positioned vertically above the mounting plate. Once the vertical distance was measured, the mounting plate was detached from the articulator and reattached manually to prepare for the next measurement. This procedure was repeated 30 times for each of the 3 magnetic mounting plates. Data were analyzed by ANOVA for 2-stage nested design and the Levene test (α=.05). Significant differences were detected among articulator systems and between magnetic mounting plates of the same type. The standard deviations of the measurements made with the Artex AR articulator, Denar Mark II articulator, Kavo Protar Evo articulator, and SAM3 articulator were 0.0027, 0.0308, 0.0214, and 0.0215 mm, respectively. Thus, the repositioning accuracy could be ranked in the order as follows: Artex AR, Kavo Protar Evo, SAM3, and Denar Mark II. The position of the
Mixed convection flow due to a vertical plate in the presence of heat source and chemical reaction
Directory of Open Access Journals (Sweden)
Rajeswari Seshadri
2016-06-01
Full Text Available In this paper, the hydromagnetic heat and mass transfer by mixed convection flow due to a vertical flat plate is considered for analysis. The governing equations are solved both analytically and numerically. The analytical solutions are obtained using the Homotopy Analysis Method (HAM while the numerical solutions are computed using Keller–Box method (K–B. Convergence of the Homotopy solutions for the governing non-dimensional equations are derived. A detailed error analysis is done to compute the average squared residual errors for flow, temperature and concentration. The optimal values of the convergence control parameter are computed for velocity and temperature. This study includes the effects of various parameters such as magnetic parameter, Grashof number, chemical reaction parameter, heat source parameter and Biot number on skin friction, heat and mass transfer rates as well on velocity, temperature and concentration profiles. Comparison of the HAM and K–B methods shows a very good agreement.
Directory of Open Access Journals (Sweden)
Norfifah Bachok
Full Text Available The steady boundary layer flow of a viscous and incompressible fluid over a moving vertical flat plate in an external moving fluid with viscous dissipation is theoretically investigated. Using appropriate similarity variables, the governing system of partial differential equations is transformed into a system of ordinary (similarity differential equations, which is then solved numerically using a Maple software. Results for the skin friction or shear stress coefficient, local Nusselt number, velocity and temperature profiles are presented for different values of the governing parameters. It is found that the set of the similarity equations has unique solutions, dual solutions or no solutions, depending on the values of the mixed convection parameter, the velocity ratio parameter and the Eckert number. The Eckert number significantly affects the surface shear stress as well as the heat transfer rate at the surface.
Mixed convective low flow pressure drop in vertical rod assemblies - II. Experimental validation
International Nuclear Information System (INIS)
Suh, K.Y.; Todreas, N.E.; Rohsenow, W.M.
1987-01-01
A predictive theory has been developed for the rod bundle frictional pressure drop characteristics under natural circulation conditions on the basis of the intra-assembly and intra-subchannel flow redistribution due to buoyancy for a wide spectrum of radial power profiles and for the geometric arrangements of practical design interest. Both the individual subchannel correlations and overall bundle design correlation have been formulated as the products of the buoyancy multipliers and the isothermal friction factors at the same Reynolds numbers. Two types of subchannel friction factors have been obtained: the standard one to be used with spatial average density and the modified one to be used with bulk mean density. A correlating procedure has been proposed to assess the local, global and skew buoyancy effects. The effects of interacting subchannel flows, developing mixed convective flow, wire wrapping, radial power skew and transition from laminar flow regime have been taken into account
Ganesh Kumar, K.; Archana, M.; Gireesha, B. J.; Krishanamurthy, M. R.; Rudraswamy, N. G.
2018-03-01
A study on magnetohydrodynamic mixed convection flow of Casson fluid over a vertical plate has been modelled in the presence of Cross diffusion effect and nonlinear thermal radiation. The governing partial differential equations are remodelled into ordinary differential equations by using similarity transformation. The accompanied differential equations are resolved numerically by using Runge-Kutta-Fehlberg forth-fifth order along with shooting method (RKF45 Method). The results of various physical parameters on velocity and temperature profiles are given diagrammatically. The numerical values of the local skin friction coefficient, local Nusselt number and local Sherwood number also are shown in a tabular form. It is found that, effect of Dufour and Soret parameter increases the temperature and concentration component correspondingly.
Exact solutions in a model of vertical gas migration
Energy Technology Data Exchange (ETDEWEB)
Silin, Dmitriy B.; Patzek, Tad W.; Benson, Sally M.
2006-06-27
This work is motivated by the growing interest in injectingcarbon dioxide into deep geological formations as a means of avoidingatmospheric emissions of carbon dioxide and consequent global warming.One of the key questions regarding the feasibility of this technology isthe potential rate of leakage out of the primary storage formation. Weseek exact solutions in a model of gas flow driven by a combination ofbuoyancy, viscous and capillary forces. Different combinations of theseforces and characteristic length scales of the processes lead todifferent time scaling and different types of solutions. In the case of athin, tight seal, where the impact of gravity is negligible relative tocapillary and viscous forces, a Ryzhik-type solution implies square-rootof time scaling of plume propagation velocity. In the general case, a gasplume has two stable zones, which can be described by travelling-wavesolutions. The theoretical maximum of the velocity of plume migrationprovides a conservative estimate for the time of vertical migration.Although the top of the plume has low gas saturation, it propagates witha velocity close to the theoretical maximum. The bottom of the plumeflows significantly more slowly at a higher gas saturation. Due to localheterogeneities, the plume can break into parts. Individual plumes alsocan coalesce and from larger plumes. The analytical results are appliedto studying carbon dioxide flow caused by leaks from deep geologicalformations used for CO2 storage. The results are also applicable formodeling flow of natural gas leaking from seasonal gas storage, or formodeling of secondary hydrocarbon migration.
Mixing rates and vertical heat fluxes north of Svalbard from Arctic winter to spring
Meyer, Amelie; Fer, Ilker; Sundfjord, Arild; Peterson, Algot K.
2017-06-01
Mixing and heat flux rates collected in the Eurasian Basin north of Svalbard during the N-ICE2015 drift expedition are presented. The observations cover the deep Nansen Basin, the Svalbard continental slope, and the shallow Yermak Plateau from winter to summer. Mean quiescent winter heat flux values in the Nansen Basin are 2 W m-2 at the ice-ocean interface, 3 W m-2 in the pycnocline, and 1 W m-2 below the pycnocline. Large heat fluxes exceeding 300 W m-2 are observed in the late spring close to the surface over the Yermak Plateau. The data consisting of 588 microstructure profiles and 50 days of high-resolution under-ice turbulence measurements are used to quantify the impact of several forcing factors on turbulent dissipation and heat flux rates. Wind forcing increases turbulent dissipation seven times in the upper 50 m, and doubles heat fluxes at the ice-ocean interface. The presence of warm Atlantic Water close to the surface increases the temperature gradient in the water column, leading to enhanced heat flux rates within the pycnocline. Steep topography consistently enhances dissipation rates by a factor of four and episodically increases heat flux at depth. It is, however, the combination of storms and shallow Atlantic Water that leads to the highest heat flux rates observed: ice-ocean interface heat fluxes average 100 W m-2 during peak events and are associated with rapid basal sea ice melt, reaching 25 cm/d.
Directory of Open Access Journals (Sweden)
Darbhasayanam Srinivasacharya
2016-06-01
Full Text Available This paper investigates the influence of thermophoresis on mixed convection heat and mass transfer flow over a vertical wavy surface in a porous medium with variable properties, namely variable viscosity and variable thermal conductivity. The effect of wavy surface is incorporated into non-dimensional equations by using suitable transformations and then transformed into non-linear ordinary differential equations by employing the similarity transformations and then solved numerically. The transport process of flow, heat and mass transfer in the boundary layer for aiding and opposing flow cases is discussed. The structure of flow, temperature and concentration fields in the Darcy porous media are more pronounced by complex interactions among variable viscosity, variable thermal conductivity, mixed convective parameter, thermophoresis and amplitude of the wavy surface. Increasing thermophoresis parameter enhances velocity profile, concentration distribution and Sherwood number while reduces Nusselt number. As increase in variable viscosity, temperature and concentration distributions are enhanced while velocity profile, Nusselt number and Sherwood numbers are reduced. This study finds applications in aerosol Technology, space technology and processes involving high temperatures.
International Nuclear Information System (INIS)
Choi, T.
1985-01-01
An external forced-, free-, and mixed convection heat transfer, with opposing buoyant and inertial forces from heated vertical cylinders, was experimentally and numerically investigated. A Mach-Zehnder interferometer was used for the experiment, and a discretization method with Patankar's algorithm SIMPLER was used for the numerical analysis. The mixed-convection behavior which appears during the transition from downward forced flow to free convection was simulated by quasi-unsteady state conditions. Forced downward flow is commonly used in gas-cooled nuclear reactors. The results of this study have a bearing on gas-cooled reactor safety. The transition was characterized by five distinctive heat and flow regimes. They are free-, suppressed-, vortex-, unsteady-, and forced-convection regimes. Local and average heat transfer coefficients were determined at forced flow rates from 30 to 130 cm/sec., over a temperature difference of 85 to 130 K with heater diameters of 12.7, 19.05, and 25.4 mm
Lee, Keunjong; Matsuno, Takeshi; Endoh, Takahiro; Ishizaka, Joji; Zhu, Yuanli; Takeda, Shigenobu; Sukigara, Chiho
2017-07-01
In summer, Changjiang Diluted Water (CDW) expands over the shelf region of the northern East China Sea. Dilution of the low salinity water could be caused by vertical mixing through the halocline. Vertical mixing through the pycnocline can transport not only saline water, but also high nutrient water from deeper layers to the surface euphotic zone. It is therefore very important to quantitatively evaluate the vertical mixing to understand the process of primary production in the CDW region. We conducted extensive measurements in the region during the period 2009-2011. Detailed investigations of the relative relationship between the subsurface chlorophyll maximum (SCM) and the nitracline suggested that there were two patterns relating to the N/P ratio. Comparing the depths of the nitracline and SCM, it was found that the SCM was usually located from 20 to 40 m and just above the nitracline, where the N/P ratio within the nitracline was below 15, whereas it was located from 10 to 30 m and within the nitracline, where the N/P ratio was above 20. The large value of the N/P ratio in the latter case suggests the influence of CDW. Turbulence measurements showed that the vertical flux of nutrients with vertical mixing was large (small) where the N/P ratio was small (large). A comparison with a time series of primary production revealed a consistency with the pattern of snapshot measurements, suggesting that the nutrient supply from the lower layer contributes considerably to the maintenance of SCM.
Boll, Christina; Leppin, Julian Sebastian; Schömann, Klaus
2016-01-01
Overeducation potentially signals a productivity loss. With Socio-Economic Panel data from 1984 to 2011 we identify drivers of educational mismatch for East and West medium and highly educated Germans. Addressing measurement error, state dependence and unobserved heterogeneity, we run dynamic mixed multinomial logit models for three different…
Multiple model adaptive control with mixing
Kuipers, Matthew
Despite the remarkable theoretical accomplishments and successful applications of adaptive control, the field is not sufficiently mature to solve challenging control problems requiring strict performance and safety guarantees. Towards addressing these issues, a novel deterministic multiple-model adaptive control approach called adaptive mixing control is proposed. In this approach, adaptation comes from a high-level system called the supervisor that mixes into feedback a number of candidate controllers, each finely-tuned to a subset of the parameter space. The mixing signal, the supervisor's output, is generated by estimating the unknown parameters and, at every instant of time, calculating the contribution level of each candidate controller based on certainty equivalence. The proposed architecture provides two characteristics relevant to solving stringent, performance-driven applications. First, the full-suite of linear time invariant control tools is available. A disadvantage of conventional adaptive control is its restriction to utilizing only those control laws whose solutions can be feasibly computed in real-time, such as model reference and pole-placement type controllers. Because its candidate controllers are computed off line, the proposed approach suffers no such restriction. Second, the supervisor's output is smooth and does not necessarily depend on explicit a priori knowledge of the disturbance model. These characteristics can lead to improved performance by avoiding the unnecessary switching and chattering behaviors associated with some other multiple adaptive control approaches. The stability and robustness properties of the adaptive scheme are analyzed. It is shown that the mean-square regulation error is of the order of the modeling error. And when the parameter estimate converges to its true value, which is guaranteed if a persistence of excitation condition is satisfied, the adaptive closed-loop system converges exponentially fast to a closed
Mixed models in cerebral ischemia study
Directory of Open Access Journals (Sweden)
Matheus Henrique Dal Molin Ribeiro
2016-06-01
Full Text Available The data modeling from longitudinal studies stands out in the current scientific scenario, especially in the areas of health and biological sciences, which induces a correlation between measurements for the same observed unit. Thus, the modeling of the intra-individual dependency is required through the choice of a covariance structure that is able to receive and accommodate the sample variability. However, the lack of methodology for correlated data analysis may result in an increased occurrence of type I or type II errors and underestimate/overestimate the standard errors of the model estimates. In the present study, a Gaussian mixed model was adopted for the variable response latency of an experiment investigating the memory deficits in animals subjected to cerebral ischemia when treated with fish oil (FO. The model parameters estimation was based on maximum likelihood methods. Based on the restricted likelihood ratio test and information criteria, the autoregressive covariance matrix was adopted for errors. The diagnostic analyses for the model were satisfactory, since basic assumptions and results obtained corroborate with biological evidence; that is, the effectiveness of the FO treatment to alleviate the cognitive effects caused by cerebral ischemia was found.
Directory of Open Access Journals (Sweden)
Bram Setyadji
2016-03-01
Full Text Available Understanding the vertical distribution of large pelagic fish, swordfish in particular, could improve our knowledge on its fisheries strategy, management and resource conservation. However the methods often require expensive tools and resources, which probably most scientists from the development countries couldn’t afford. Thus developing model on the diel vertical movement behavior of swordfish using number of hook between float (HBF and complete-set temperature and depth recorder (TDR data could be an alternative. In general context, capture depth distributions are a good indicator of the natural depth distribution of the fish if the entire depth range of the species is targeted by longline gear. The proposed sinusoidal model suggested that swordfish showed a diel pattern in depth distribution, marked by remained in the surface and mixed layer waters at night and dived into deeper waters during the day. Keywords: swordfish, behavior, HBF, TDR, sinusoidal model
Extended model for Richtmyer-Meshkov mix
Energy Technology Data Exchange (ETDEWEB)
Mikaelian, K O
2009-11-18
We examine four Richtmyer-Meshkov (RM) experiments on shock-generated turbulent mix and find them to be in good agreement with our earlier simple model in which the growth rate h of the mixing layer following a shock or reshock is constant and given by 2{alpha}A{Delta}v, independent of initial conditions h{sub 0}. Here A is the Atwood number ({rho}{sub B}-{rho}{sub A})/({rho}{sub B} + {rho}{sub A}), {rho}{sub A,B} are the densities of the two fluids, {Delta}V is the jump in velocity induced by the shock or reshock, and {alpha} is the constant measured in Rayleigh-Taylor (RT) experiments: {alpha}{sup bubble} {approx} 0.05-0.07, {alpha}{sup spike} {approx} (1.8-2.5){alpha}{sup bubble} for A {approx} 0.7-1.0. In the extended model the growth rate beings to day after a time t*, when h = h*, slowing down from h = h{sub 0} + 2{alpha}A{Delta}vt to h {approx} t{sup {theta}} behavior, with {theta}{sup bubble} {approx} 0.25 and {theta}{sup spike} {approx} 0.36 for A {approx} 0.7. They ascribe this change-over to loss of memory of the direction of the shock or reshock, signaling transition from highly directional to isotropic turbulence. In the simplest extension of the model h*/h{sub 0} is independent of {Delta}v and depends only on A. They find that h*/h{sub 0} {approx} 2.5-3.5 for A {approx} 0.7-1.0.
Validation of mixing heights derived from the operational NWP models at the German weather service
Energy Technology Data Exchange (ETDEWEB)
Fay, B.; Schrodin, R.; Jacobsen, I. [Deutscher Wetterdienst, Offenbach (Germany); Engelbart, D. [Deutscher Wetterdienst, Meteorol. Observ. Lindenberg (Germany)
1997-10-01
NWP models incorporate an ever-increasing number of observations via four-dimensional data assimilation and are capable of providing comprehensive information about the atmosphere both in space and time. They describe not only near surface parameters but also the vertical structure of the atmosphere. They operate daily, are well verified and successfully used as meteorological pre-processors in large-scale dispersion modelling. Applications like ozone forecasts, emission or power plant control calculations require highly resolved, reliable, and routine values of the temporal evolution of the mixing height (MH) which is a critical parameter in determining the mixing and transformation of substances and the resulting pollution levels near the ground. The purpose of development at the German Weather Service is a straightforward mixing height scheme that uses only parameters derived from NWP model variables and thus automatically provides spatial and temporal fields of mixing heights on an operational basis. An universal parameter to describe stability is the Richardson number Ri. Compared to the usual diagnostic or rate equations, the Ri number concept of determining mixing heights has the advantage of using not only surface layer parameters but also regarding the vertical structure of the boundary layer resolved in the NWP models. (au)
On the SU(2 vertical stroke 1) WZNW model and its statistical mechanics applications
Energy Technology Data Exchange (ETDEWEB)
Saleur, H. [CEA Centre d' Etudes de Saclay, 91 - Gif-sur-Yvette (France). Service de Physique Theorique]|[University of Southern California, Los Angeles, CA (United States). Dept. of Physics; Schomerus, V. [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)
2006-11-15
Motivated by a careful analysis of the Laplacian on the supergroup SU(2 vertical stroke 1) we formulate a proposal for the state space of the SU(2 vertical stroke 1) WZNW model. We then use properties of sl(2 vertical stroke 1) characters to compute the partition function of the theory. In the special case of level k=1 the latter is found to agree with the properly regularized partition function for the continuum limit of the integrable sl(2 vertical stroke 1)3- anti 3 super-spin chain. Some general conclusions applicable to other WZNW models (in particular the case k=-1/2) are also drawn. (orig.)
Bergado, D. T.; Long, P. V.; Chaiyaput, S.; Balasubramaniam, A. S.
2018-04-01
Soft ground improvement techniques have become most practical and popular methods to increase soil strength, soil stiffness and reduce soil compressibility including the soft Bangkok clay. This paper focuses on comparative performances of prefabricated vertical drain (PVD) using surcharge, vacuum and heat preloading as well as the cement-admixed clay of Deep Cement Mixing (DCM) and Stiffened DCM (SDCM) methods. The Vacuum-PVD can increase the horizontal coefficient of consolidation, Ch, resulting in faster rate of settlement at the same magnitudes of settlement compared to Conventional PVD. Several field methods of applying vacuum preloading are also compared. Moreover, the Thermal PVD and Thermal Vacuum PVD can increase further the coefficient of horizontal consolidation, Ch, with the associated reduction of kh/ks values by reducing the drainage retardation effects in the smear zone around the PVD which resulted in faster rates of consolidation and higher magnitudes of settlements. Furthermore, the equivalent smear effect due to non-uniform consolidation is also discussed in addition to the smear due to the mechanical installation of PVDs. In addition, a new kind of reinforced deep mixing method, namely Stiffened Deep Cement Mixing (SDCM) pile is introduced to improve the flexural resistance, improve the field quality control, and prevent unexpected failures of the Deep Cement Mixing (DCM) pile. The SDCM pile consists of DCM pile reinforced with the insertion of precast reinforced concrete (RC) core. The full scale test embankment on soft clay improved by SDCM and DCM piles was also analysed. Numerical simulations using the 3D PLAXIS Foundation finite element software have been done to understand the behavior of SDCM and DCM piles. The simulation results indicated that the surface settlements decreased with increasing lengths of the RC cores, and, at lesser extent, increasing sectional areas of the RC cores in the SDCM piles. In addition, the lateral movements
Randelhoff, Achim; Sundfjord, Arild
2018-04-01
The future of Arctic marine ecosystems has received increasing attention in recent years as the extent of the sea ice cover is dwindling. Although the Pacific and Atlantic inflows both import huge quantities of nutrients and plankton, they feed into the Arctic Ocean in quite diverse regions. The strongly stratified Pacific sector has a historically heavy ice cover, a shallow shelf and dominant upwelling-favourable winds, while the Atlantic sector is weakly stratified, with a dynamic ice edge and a complex bathymetry. We argue that shelf break upwelling is likely not a universal but rather a regional, albeit recurring, feature of the new Arctic. It is the regional oceanography that decides its importance through a range of diverse factors such as stratification, bathymetry and wind forcing. Teasing apart their individual contributions in different regions can only be achieved by spatially resolved time series and dedicated modelling efforts. The Northern Barents Sea shelf is an example of a region where shelf break upwelling likely does not play a dominant role, in contrast to the shallower shelves north of Alaska where ample evidence for its importance has already accumulated. Still, other factors can contribute to marked future increases in biological productivity along the Arctic shelf break. A warming inflow of nutrient-rich Atlantic Water feeds plankton at the same time as it melts the sea ice, permitting increased photosynthesis. Concurrent changes in sea ice cover and zooplankton communities advected with the boundary currents make for a complex mosaic of regulating factors that do not allow for Arctic-wide generalizations.
Directory of Open Access Journals (Sweden)
A. Randelhoff
2018-04-01
Full Text Available The future of Arctic marine ecosystems has received increasing attention in recent years as the extent of the sea ice cover is dwindling. Although the Pacific and Atlantic inflows both import huge quantities of nutrients and plankton, they feed into the Arctic Ocean in quite diverse regions. The strongly stratified Pacific sector has a historically heavy ice cover, a shallow shelf and dominant upwelling-favourable winds, while the Atlantic sector is weakly stratified, with a dynamic ice edge and a complex bathymetry. We argue that shelf break upwelling is likely not a universal but rather a regional, albeit recurring, feature of the new Arctic. It is the regional oceanography that decides its importance through a range of diverse factors such as stratification, bathymetry and wind forcing. Teasing apart their individual contributions in different regions can only be achieved by spatially resolved time series and dedicated modelling efforts. The Northern Barents Sea shelf is an example of a region where shelf break upwelling likely does not play a dominant role, in contrast to the shallower shelves north of Alaska where ample evidence for its importance has already accumulated. Still, other factors can contribute to marked future increases in biological productivity along the Arctic shelf break. A warming inflow of nutrient-rich Atlantic Water feeds plankton at the same time as it melts the sea ice, permitting increased photosynthesis. Concurrent changes in sea ice cover and zooplankton communities advected with the boundary currents make for a complex mosaic of regulating factors that do not allow for Arctic-wide generalizations.
International Nuclear Information System (INIS)
Mohammed, Hussein A.
2008-01-01
Laminar mixed convection heat transfer for assisted and opposed air flows in the entrance region of a vertical circular tube with the using of a uniform wall heat flux boundary condition has been experimentally investigated. The experimental setup was designed for determining the effect of flow direction and the effect of tube inclination on the surface temperature, local and average Nusselt numbers with Reynolds number ranged from 400 to 1600 and Grashof number from 2.0 x 10 5 to 6.2 x 10 6 . It was found that the circumferential surface temperature along the dimensionless tube length for opposed flow would be higher than that both of assisted flow and horizontal tube [Mohammed HA, Salman YK. Experimental investigation of combined convection heat transfer for thermally developing flow in a horizontal circular cylinder. Appl Therm Eng 2007;27(8-9):1522-33] due to the stronger free convective currents within the cross-section. The Nusselt number values would be lower for opposed flow than that for assisted flow. It was inferred that the behaviour of Nu x for opposed flow to be strongly dependent on the combination of Re and Gr numbers. Empirical equations expressing the average Nusselt numbers in terms of Grashof and Reynolds numbers were proposed for both assisted and opposed flow cases. The average heat transfer results were compared with previous literature and showed similar trend and satisfactory agreement
Energy Technology Data Exchange (ETDEWEB)
Lok, Y.Y. [Center for Academic Services, Kolej Universiti Teknikal Kebangsaan Malaysia, 75450 Ayer Keroh, Melaka (Malaysia); Amin, N. [Department of Mathematics, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor (Malaysia); Pop, I. [Faculty of Mathematics, University of Cluj, R-3400 Cluj, CP 253 (Romania)
2006-12-15
The unsteady mixed convection boundary-layer flow of a micro-polar fluid near the region of the stagnation point on a double-infinite vertical flat plate is studied. It is assumed that the unsteadiness is caused by the impulsive motion of the free stream velocity and by sudden increase or sudden decrease in the surface temperature from the uniform ambient temperature. The problem is reduced to a system of non-dimensional partial differential equations, which is solved numerically using the Keller-box method. This method may present well-behaved solutions for the transient (small time) solution and those of the steady-state flow (large time) solution. It was found that there is a smooth transition from the small-time solution (initial unsteady-state flow) to the large-time solution (final steady-state flow). Further, it is shown that for both assisting and opposing cases and a fixed value of the Prandtl number, the reduced steady-state skin friction and the steady-state heat transfer from the wall (or Nusselt number) decrease with the increase of the material parameter. On the other hand, it is shown that with the increase of the Prandtl number and a fixed value of the material parameter, the reduced steady-state skin friction decreases when the flow is assisting and it increases when the flow is opposing. (author)
García, Francisca C.
2015-07-17
The ’cytometric diversity’ of phytoplankton communities has been studied based on single-cell properties, but the applicability of this method to characterize bacterioplankton has been unexplored. Here, we analysed seasonal changes in cytometric diversity of marine bacterioplankton along a decadal time-series at three coastal stations in the Southern Bay of Biscay. Shannon-Weaver diversity estimates and Bray-Curtis similarities obtained by cytometric and molecular (16S rRNA tag sequencing) methods were significantly correlated in samples from a 3.5-year monthly time-series. Both methods showed a consistent cyclical pattern in the diversity of surface bacterial communities with maximal values in winter. The analysis of the highly resolved flow cytometry time-series across the vertical profile showed that water column mixing was a key factor explaining the seasonal changes in bacterial composition and the winter increase in bacterial diversity in coastal surface waters. Due to its low cost and short processing time as compared to genetic methods, the cytometric diversity approach represents a useful complementary tool in the macroecology of aquatic microbes.
A Pseudo-Vertical Equilibrium Model for Slow Gravity Drainage Dynamics
Becker, Beatrix; Guo, Bo; Bandilla, Karl; Celia, Michael A.; Flemisch, Bernd; Helmig, Rainer
2017-12-01
Vertical equilibrium (VE) models are computationally efficient and have been widely used for modeling fluid migration in the subsurface. However, they rely on the assumption of instant gravity segregation of the two fluid phases which may not be valid especially for systems that have very slow drainage at low wetting phase saturations. In these cases, the time scale for the wetting phase to reach vertical equilibrium can be several orders of magnitude larger than the time scale of interest, rendering conventional VE models unsuitable. Here we present a pseudo-VE model that relaxes the assumption of instant segregation of the two fluid phases by applying a pseudo-residual saturation inside the plume of the injected fluid that declines over time due to slow vertical drainage. This pseudo-VE model is cast in a multiscale framework for vertically integrated models with the vertical drainage solved as a fine-scale problem. Two types of fine-scale models are developed for the vertical drainage, which lead to two pseudo-VE models. Comparisons with a conventional VE model and a full multidimensional model show that the pseudo-VE models have much wider applicability than the conventional VE model while maintaining the computational benefit of the conventional VE model.
A Note on the Identifiability of Generalized Linear Mixed Models
DEFF Research Database (Denmark)
Labouriau, Rodrigo
2014-01-01
I present here a simple proof that, under general regularity conditions, the standard parametrization of generalized linear mixed model is identifiable. The proof is based on the assumptions of generalized linear mixed models on the first and second order moments and some general mild regularity ...... conditions, and, therefore, is extensible to quasi-likelihood based generalized linear models. In particular, binomial and Poisson mixed models with dispersion parameter are identifiable when equipped with the standard parametrization...
Madadi-Kandjani, E.; Fox, R. O.; Passalacqua, A.
2017-06-01
An extended quadrature method of moments using the β kernel density function (β -EQMOM) is used to approximate solutions to the evolution equation for univariate and bivariate composition probability distribution functions (PDFs) of a passive scalar for binary and ternary mixing. The key element of interest is the molecular mixing term, which is described using the Fokker-Planck (FP) molecular mixing model. The direct numerical simulations (DNSs) of Eswaran and Pope ["Direct numerical simulations of the turbulent mixing of a passive scalar," Phys. Fluids 31, 506 (1988)] and the amplitude mapping closure (AMC) of Pope ["Mapping closures for turbulent mixing and reaction," Theor. Comput. Fluid Dyn. 2, 255 (1991)] are taken as reference solutions to establish the accuracy of the FP model in the case of binary mixing. The DNSs of Juneja and Pope ["A DNS study of turbulent mixing of two passive scalars," Phys. Fluids 8, 2161 (1996)] are used to validate the results obtained for ternary mixing. Simulations are performed with both the conditional scalar dissipation rate (CSDR) proposed by Fox [Computational Methods for Turbulent Reacting Flows (Cambridge University Press, 2003)] and the CSDR from AMC, with the scalar dissipation rate provided as input and obtained from the DNS. Using scalar moments up to fourth order, the ability of the FP model to capture the evolution of the shape of the PDF, important in turbulent mixing problems, is demonstrated. Compared to the widely used assumed β -PDF model [S. S. Girimaji, "Assumed β-pdf model for turbulent mixing: Validation and extension to multiple scalar mixing," Combust. Sci. Technol. 78, 177 (1991)], the β -EQMOM solution to the FP model more accurately describes the initial mixing process with a relatively small increase in computational cost.
Vertical discretization with finite elements for a global hydrostatic model on the cubed sphere
Yi, Tae-Hyeong; Park, Ja-Rin
2017-06-01
A formulation of Galerkin finite element with basis-spline functions on a hybrid sigma-pressure coordinate is presented to discretize the vertical terms of global Eulerian hydrostatic equations employed in a numerical weather prediction system, which is horizontally discretized with high-order spectral elements on a cubed sphere grid. This replaces the vertical discretization of conventional central finite difference that is first-order accurate in non-uniform grids and causes numerical instability in advection-dominant flows. Therefore, a model remains in the framework of Galerkin finite elements for both the horizontal and vertical spatial terms. The basis-spline functions, obtained from the de-Boor algorithm, are employed to derive both the vertical derivative and integral operators, since Eulerian advection terms are involved. These operators are used to discretize the vertical terms of the prognostic and diagnostic equations. To verify the vertical discretization schemes and compare their performance, various two- and three-dimensional idealized cases and a hindcast case with full physics are performed in terms of accuracy and stability. It was shown that the vertical finite element with the cubic basis-spline function is more accurate and stable than that of the vertical finite difference, as indicated by faster residual convergence, fewer statistical errors, and reduction in computational mode. This leads to the general conclusion that the overall performance of a global hydrostatic model might be significantly improved with the vertical finite element.
Vertical Integration of Biochemistry and Clinical Medicine Using a Near-Peer Learning Model
Gallan, Alexander J.; Offner, Gwynneth D.; Symes, Karen
2016-01-01
Vertical integration has been extensively implemented across medical school curricula but has not been widely attempted in the field of biochemistry. We describe a novel curricular innovation in which a near-peer learning model was used to implement vertical integration in our medical school biochemistry course. Senior medical students developed…
The Sensitivity of Value-Added Modeling to the Creation of a Vertical Score Scale
Briggs, Derek C.; Weeks, Jonathan P.
2009-01-01
The purpose of this study was to evaluate the sensitivity of growth and value-added modeling to the way an underlying vertical score scale has been created. Longitudinal item-level data were analyzed with both student- and school-level identifiers for the entire state of Colorado between 2003 and 2006. Eight different vertical scales were…
Hsu, Yung-Ting; Al-Hezaimi, Khalid; Galindo-Moreno, Pablo; O'Valle, Francisco; Al-Rasheed, Abdulaziz; Wang, Hom-Lay
2017-09-01
Vertical bone augmentation (VBA) remains unpredictable and challenging for most clinicians. This study aims to compare hard tissue outcomes of VBA, with and without recombinant human bone morphogenetic protein (rhBMP)-2, under space-making titanium mesh in a canine model. Eleven male beagle dogs were used in the study. Experimental ridge defects were created to form atrophic ridges. VBA was performed via guided bone regeneration using titanium mesh and allografts. In experimental hemimandibles, rhBMP-2/absorbable collagen sponge was well mixed with allografts prior to procedures, whereas a control buffer was applied within controls. Dogs were euthanized after a 4-month healing period. Clinical and radiographic examinations were performed to assess ridge dimensional changes. In addition, specimens were used for microcomputed tomography (micro-CT) assessment and histologic analysis. Membrane exposure was found on five of 11 (45.5%) rhBMP-2-treated sites, whereas it was found on nine of 11 (81.8%) non-rhBMP-2-treated sites. Within 4 months of healing, rhBMP-2-treated sites showed better radiographic bone density, greater defect fill, and significantly more bone gain in ridge height (P 0.05). Under light microscope, predominant lamellar patterns were found in the specimen obtained from rhBMP-2 sites. With inherent limitations of the canine model and the concern of such a demanding surgical technique, current findings suggest that the presence of rhBMP-2 in a composite graft allows an increase of vertical gain, with formation of ectopic bone over the titanium mesh in comparison with non-rhBMP-2 sites.
RESEARCH AND MODEL DEVELOPMENT OF DRILLING AND BLASTING TECHNOLOGY PENETRATIONS OF VERTICAL SHAFTS
Directory of Open Access Journals (Sweden)
O. I. Rubleva
2007-10-01
Full Text Available The model of destruction of rocks by explosion in vertical shafts is presented. On its basis the most important parameters of technical-and-economical indices of the drilling-and-blasting technology are calculated.
Three-dimensional models of conventional and vertical junction laser-photovoltaic energy converters
Heinbockel, John H.; Walker, Gilbert H.
1988-01-01
Three-dimensional models of both conventional planar junction and vertical junction photovoltaic energy converters have been constructed. The models are a set of linear partial differential equations and take into account many photoconverter design parameters. The model is applied to Si photoconverters; however, the model may be used with other semiconductors. When used with a Nd laser, the conversion efficiency of the Si vertical junction photoconverter is 47 percent, whereas the efficiency for the conventional planar Si photoconverter is only 17 percent. A parametric study of the Si vertical junction photoconverter is then done in order to describe the optimum converter for use with the 1.06-micron Nd laser. The efficiency of this optimized vertical junction converter is 44 percent at 1 kW/sq cm.
National Research Council Canada - National Science Library
Barron, Charlie N; Kara, A. B; Martin, Paul J; Rhodes, Robert C; Smedstad, Lucy F
2006-01-01
.... NCOM is a baroclinic, hydrostatic, Boussinesq, free-surface ocean model that allows its vertical coordinate to consist of sigma coordinates for the upper layers and z-levels below a user-specified depth...
Structure constants of the OSP(1 vertical stroke 2) WZNW model
Energy Technology Data Exchange (ETDEWEB)
Hikida, Y.; Schomerus, V.
2007-11-15
We propose exact formulas for the 2- and 3-point functions of the WZNW model on the non-compact supergroup OSP(1 vertical stroke 2). Using the path integral approach that was recently developed in arXiv:0706.1030 we show how local correlation functions in the OSP(p vertical stroke 2) WZNW models can be obtained from those of N=p supersymmetric Liouville field theory for p=1,2. We then employ known results on correlators in N=1 Liouville theory to determine the structure constants of the OSP(1 vertical stroke 2) theory. (orig.)
Mioche, Guillaume; Jourdan, Olivier; Delanoë, Julien; Gourbeyre, Christophe; Febvre, Guy; Dupuy, Régis; Monier, Marie; Szczap, Frédéric; Schwarzenboeck, Alfons; Gayet, Jean-François
2017-10-01
This study aims to characterize the microphysical and optical properties of ice crystals and supercooled liquid droplets within low-level Arctic mixed-phase clouds (MPCs). We compiled and analyzed cloud in situ measurements from four airborne spring campaigns (representing 18 flights and 71 vertical profiles in MPCs) over the Greenland and Norwegian seas mainly in the vicinity of the Svalbard archipelago. Cloud phase discrimination and representative vertical profiles of the number, size, mass and shape of ice crystals and liquid droplets are established. The results show that the liquid phase dominates the upper part of the MPCs. High concentrations (120 cm-3 on average) of small droplets (mean values of 15 µm), with an averaged liquid water content (LWC) of 0.2 g m-3 are measured at cloud top. The ice phase dominates the microphysical properties in the lower part of the cloud and beneath it in the precipitation region (mean values of 100 µm, 3 L-1 and 0.025 g m-3 for diameter, particle concentration and ice water content (IWC), respectively). The analysis of the ice crystal morphology shows that the majority of ice particles are irregularly shaped or rimed particles; the prevailing regular habits found are stellars and plates. We hypothesize that riming and diffusional growth processes, including the Wegener-Bergeron-Findeisen (WBF) mechanism, are the main growth mechanisms involved in the observed MPCs. The impact of larger-scale meteorological conditions on the vertical profiles of MPC properties was also investigated. Large values of LWC and high concentration of smaller droplets are possibly linked to polluted situations and air mass origins from the south, which can lead to very low values of ice crystal size and IWC. On the contrary, clean situations with low temperatures exhibit larger values of ice crystal size and IWC. Several parameterizations relevant for remote sensing or modeling studies are also determined, such as IWC (and LWC) - extinction
Modeling Dynamic Effects of the Marketing Mix on Market Shares
D. Fok (Dennis); R. Paap (Richard); Ph.H.B.F. Franses (Philip Hans)
2003-01-01
textabstractTo comprehend the competitive structure of a market, it is important to understand the short-run and long-run effects of the marketing mix on market shares. A useful model to link market shares with marketing-mix variables, like price and promotion, is the market share attraction model.
Applied model for the growth of the daytime mixed layer
DEFF Research Database (Denmark)
Batchvarova, E.; Gryning, Sven-Erik
1991-01-01
A slab model is proposed for developing the height of the mixed layer capped by stable air aloft. The model equations are closed by relating the consumption of energy (potential and kinetic) at the top of the mixed layer to the production of convective and mechanical turbulent kinetic energy with...
An Optimization Model Development for Laterized-Concrete Mix ...
African Journals Online (AJOL)
An Optimization Model Development for Laterized-Concrete Mix Proportioning in Building Constructions. ... Nigerian Journal of Technology ... In this study, a mathematical model was developed and was used to optimize the mix proportion that will produce the maximum strength of laterized concrete using Scheffe's simplex ...
Modeling the vertical soil organic matter profile using Bayesian parameter estimation
Directory of Open Access Journals (Sweden)
M. C. Braakhekke
2013-01-01
Full Text Available The vertical distribution of soil organic matter (SOM in the profile may constitute an important factor for soil carbon cycling. However, the formation of the SOM profile is currently poorly understood due to equifinality, caused by the entanglement of several processes: input from roots, mixing due to bioturbation, and organic matter leaching. In this study we quantified the contribution of these three processes using Bayesian parameter estimation for the mechanistic SOM profile model SOMPROF. Based on organic carbon measurements, 13 parameters related to decomposition and transport of organic matter were estimated for two temperate forest soils: an Arenosol with a mor humus form (Loobos, the Netherlands, and a Cambisol with mull-type humus (Hainich, Germany. Furthermore, the use of the radioisotope ^{210}Pb_{ex} as tracer for vertical SOM transport was studied. For Loobos, the calibration results demonstrate the importance of organic matter transport with the liquid phase for shaping the vertical SOM profile, while the effects of bioturbation are generally negligible. These results are in good agreement with expectations given in situ conditions. For Hainich, the calibration offered three distinct explanations for the observations (three modes in the posterior distribution. With the addition of ^{210}Pb_{ex} data and prior knowledge, as well as additional information about in situ conditions, we were able to identify the most likely explanation, which indicated that root litter input is a dominant process for the SOM profile. For both sites the organic matter appears to comprise mainly adsorbed but potentially leachable material, pointing to the importance of organo-mineral interactions. Furthermore, organic matter in the mineral soil appears to be mainly derived from root litter, supporting previous studies that highlighted the importance of root input for soil carbon sequestration. The ^{210 }
International Nuclear Information System (INIS)
Oulaid, Othmane; Benhamou, Brahim; Galanis, Nicolas
2010-01-01
This paper, deals with a numerical study of the effects of buoyancy forces on an upward, steady state, laminar flow of humid air in a vertical parallel-plate channel. The plates are wetted by a thin liquid water film and maintained at a constant temperature which is lower than that of the air entering the channel. A 2D fully elliptical model, associated with the Boussinesq assumption, is used to take into account axial diffusion. The solution of this mathematical model is based on the finite volume method and the velocity-pressure coupling is handled by the SIMPLER algorithm. Numerical results show that buoyancy forces have a significant effect on the hydrodynamic, thermal and mass fraction fields. Additionally, these forces induce flow reversal for high air temperatures and mass fractions at the channel entrance. It is established that heat transfer associated with phase change is, sometimes, more significant than sensible heat transfer. Furthermore, this importance depends on the mass fraction gradient. The conditions for the existence of flow reversal are presented in charts and analytical expressions specifying the critical thermal Grashof number as a function of the Reynolds number for different values of the solutal Grashof number and different aspect ratios of the channel.
An efficient Lagrangian stochastic model of vertical dispersion in the convective boundary layer
Franzese, Pasquale; Luhar, Ashok K.; Borgas, Michael S.
We consider the one-dimensional case of vertical dispersion in the convective boundary layer (CBL) assuming that the turbulence field is stationary and horizontally homogeneous. The dispersion process is simulated by following Lagrangian trajectories of many independent tracer particles in the turbulent flow field, leading to a prediction of the mean concentration. The particle acceleration is determined using a stochastic differential equation, assuming that the joint evolution of the particle velocity and position is a Markov process. The equation consists of a deterministic term and a random term. While the formulation is standard, attention has been focused in recent years on various ways of calculating the deterministic term using the well-mixed condition incorporating the Fokker-Planck equation. Here we propose a simple parameterisation for the deterministic acceleration term by approximating it as a quadratic function of velocity. Such a function is shown to represent well the acceleration under moderate velocity skewness conditions observed in the CBL. The coefficients in the quadratic form are determined in terms of given turbulence statistics by directly integrating the Fokker-Planck equation. An advantage of this approach is that, unlike in existing Lagrangian stochastic models for the CBL, the use of the turbulence statistics up to the fourth order can be made without assuming any predefined form for the probability distribution function (PDF) of the velocity. The main strength of the model, however, lies in its simplicity and computational efficiency. The dispersion results obtained from the new model are compared with existing laboratory data as well as with those obtained from a more complex Lagrangian model in which the deterministic acceleration term is based on a bi-Gaussian velocity PDF. The comparison shows that the new model performs well.
Directory of Open Access Journals (Sweden)
D. Srinivasacharya
2016-01-01
Full Text Available Mixed convection heat and mass transfer along a vertical plate embedded in a power-law fluid saturated Darcy porous medium with chemical reaction and radiation effects is studied. The governing partial differential equations are transformed into ordinary differential equations using similarity transformations and then solved numerically using shooting method. A parametric study of the physical parameters involved in the problem is conducted and a representative set of numerical results is illustrated graphically.
Practical likelihood analysis for spatial generalized linear mixed models
DEFF Research Database (Denmark)
Bonat, W. H.; Ribeiro, Paulo Justiniano
2016-01-01
, respectively, examples of binomial and count datasets modeled by spatial generalized linear mixed models. Our results show that the Laplace approximation provides similar estimates to Markov Chain Monte Carlo likelihood, Monte Carlo expectation maximization, and modified Laplace approximation. Some advantages...
Holladay, Jennifer
2009-01-01
Since 2002, Teaching Tolerance's Mix It Up at Lunch Day program has helped millions of students cross social boundaries and create more inclusive school communities. Its goal is to create a safe, purposeful opportunity for students to break down the patterns of social self-segregation that too often plague schools. Research conducted in 2006 by…
Molecular Thermodynamic Modeling of Mixed Solvent Solubility
DEFF Research Database (Denmark)
Ellegaard, Martin Dela; Abildskov, Jens; O’Connell, John P.
2010-01-01
A method based on statistical mechanical fluctuation solution theory for composition derivatives of activity coefficients is employed for estimating dilute solubilities of 11 solid pharmaceutical solutes in nearly 70 mixed aqueous and nonaqueous solvent systems. The solvent mixtures range from ne...
A multifluid mix model with material strength effects
Energy Technology Data Exchange (ETDEWEB)
Chang, C. H. [Los Alamos National Laboratory; Scannapieco, A. J. [Los Alamos National Laboratory
2012-04-23
We present a new multifluid mix model. Its features include material strength effects and pressure and temperature nonequilibrium between mixing materials. It is applicable to both interpenetration and demixing of immiscible fluids and diffusion of miscible fluids. The presented model exhibits the appropriate smooth transition in mathematical form as the mixture evolves from multiphase to molecular mixing, extending its applicability to the intermediate stages in which both types of mixing are present. Virtual mass force and momentum exchange have been generalized for heterogeneous multimaterial mixtures. The compression work has been extended so that the resulting species energy equations are consistent with the pressure force and material strength.
Reliability assessment of competing risks with generalized mixed shock models
International Nuclear Information System (INIS)
Rafiee, Koosha; Feng, Qianmei; Coit, David W.
2017-01-01
This paper investigates reliability modeling for systems subject to dependent competing risks considering the impact from a new generalized mixed shock model. Two dependent competing risks are soft failure due to a degradation process, and hard failure due to random shocks. The shock process contains fatal shocks that can cause hard failure instantaneously, and nonfatal shocks that impact the system in three different ways: 1) damaging the unit by immediately increasing the degradation level, 2) speeding up the deterioration by accelerating the degradation rate, and 3) weakening the unit strength by reducing the hard failure threshold. While the first impact from nonfatal shocks comes from each individual shock, the other two impacts are realized when the condition for a new generalized mixed shock model is satisfied. Unlike most existing mixed shock models that consider a combination of two shock patterns, our new generalized mixed shock model includes three classic shock patterns. According to the proposed generalized mixed shock model, the degradation rate and the hard failure threshold can simultaneously shift multiple times, whenever the condition for one of these three shock patterns is satisfied. An example using micro-electro-mechanical systems devices illustrates the effectiveness of the proposed approach with sensitivity analysis. - Highlights: • A rich reliability model for systems subject to dependent failures is proposed. • The degradation rate and the hard failure threshold can shift simultaneously. • The shift is triggered by a new generalized mixed shock model. • The shift can occur multiple times under the generalized mixed shock model.
Vertical Vibration Model for Unsteady Lubrication in Rolls-Strip Interface of Cold Rolling Mills
Directory of Open Access Journals (Sweden)
Xu Yang
2012-01-01
Full Text Available According to the vertical vibration phenomena existing in cold rolling mills, the unsteady lubrication mechanism in roll gap and its influence to rolling stability was chosen as the case for analysis. On the basis of rolling theory, lubrication and friction theory, and mechanic vibration theory, the vertical vibration model for unsteady lubrication in rolls-strip interface was presented. The Geometry model of roll gap, the unsteady lubrication model of roller-strip working interface, the distribution model of normal rolling stress and friction stress, and the rolling vertical structure model were taken into account. Based on the rolling equipment and process parameters of aluminium mill, the rolling force curve and dynamic response of working roll displacement variation was simulated on Matlab/Simulink platform. A comparison with actual production data shows the validity of this vibration model.
Podglajen, A.; Pfister, L.; Jensen, E. J.; Alexander, M. J.; Karcher, B.; Randel, W. J.; Bui, T. V.; Dean-Day, J. M.
2016-12-01
The El Niño-driven fire season in Indonesia, 2015, is recorded to have the most severe fire emissions since NASA's Earth Observation System (EOS) satellites started making observations of tropospheric pollutants from space. Carbon monoxide (CO), one of the major pollutants emitted during the fire season, has direct impacts on chemistry in the troposphere as a precursor to ozone O3 and carbon dioxide (CO2) and through interactions with the hydroxyl radical (OH) that increase the lifetime of methane (CH4). The relatively long chemical lifetime of CO (weeks to months) enables long-range transport as well as vertical transport into the upper troposphere and lower stratosphere (UTLS) region. In this study, measurements of CO from the Terra/MOPITT (Measurement of Pollution in the Troposphere) and Aura/MLS (Microwave Limb Sounder) are used to characterize the global impact of high CO emitted during the 2015 Indonesian fire season. The MOPITT and MLS instruments together provide a powerful tool for exploring global distributions of CO with overlap in the UTLS region. Simulations of CO from the Community Atmosphere Model with Chemistry (CAM-chem) are used to better understand transport pathways of CO from the surface into the lower stratosphere. We find that high concentrations of CO from the September-October 2015 Indonesian fires persisted in the UTLS throughout 2016, much longer than previous years with significant fire emissions.
Modeling study on axial wetting length of meniscus in vertical rectangular microgrooves
International Nuclear Information System (INIS)
Nie, Xuelei; Hu, Xuegong; Tang, Dawei
2013-01-01
In this work, the traditional model for predicting axial wetting length of meniscus in vertical microgrooves is introduced firstly. The traditional model may cause inaccurate results in predicting wetting length in vertical microgrooves because of the assumption of round meniscus in cross sections of microgrooves and the way of calculating curvature. In order to develop this model and make it more accurate, a revised micro-PIV system is built to test the meniscus shapes in cross sections of vertical and horizontal microgrooves, and the experimental results prove that the real shapes of meniscus are parabolic other than round. The fitting formulas of meniscus shapes are obtained with software Origin 7.5. Based on experimental results and fitting formulas, the traditional model is revised by changing the way to calculate curvature. In the modified model, the curvature for calculating axial wetting length of meniscus equals average curvature of meniscus in cross section of vertical microgrooves minus the average curvature of meniscus in cross section of horizontal microgrooves. It is proved that the modified model can predict the wetting length in vertical microgrooves better than the original model. The average difference between experiment and modified model is 2.5% while that between experiment and traditional model is 174.2%. The disadvantage of the modified model is that using the new model to predict wetting length needs to know the real shapes of meniscus in vertical and horizontal microgrooves. -- Highlights: ► An experimental system is designed to test the shapes of meniscus in microgrooves. ► The real shapes of meniscus in microgrooves are obtained for first time. ► The shapes of meniscus in microgrooves is compared and analyzed. ► The model for predicting wetting length of meniscus in microgrooves is developed
Ramzan, Muhammad; Bilal, Muhammad
2015-01-01
The aim of present paper is to study the series solution of time dependent MHD second grade incompressible nanofluid towards a stretching sheet. The effects of mixed convection and thermal radiation are also taken into account. Because of nanofluid model, effects Brownian motion and thermophoresis are encountered. The resulting nonlinear momentum, heat and concentration equations are simplified using appropriate transformations. Series solutions have been obtained for velocity, temperature and nanoparticle fraction profiles using Homotopy Analysis Method (HAM). Convergence of the acquired solution is discussed critically. Behavior of velocity, temperature and concentration profiles on the prominent parameters is depicted and argued graphically. It is observed that temperature and concentration profiles show similar behavior for thermophoresis parameter Νt but opposite tendency is noted in case of Brownian motion parameter Νb. It is further analyzed that suction parameter S and Hartman number Μ depict decreasing behavior on velocity profile.
Directory of Open Access Journals (Sweden)
Muhammad Ramzan
Full Text Available The aim of present paper is to study the series solution of time dependent MHD second grade incompressible nanofluid towards a stretching sheet. The effects of mixed convection and thermal radiation are also taken into account. Because of nanofluid model, effects Brownian motion and thermophoresis are encountered. The resulting nonlinear momentum, heat and concentration equations are simplified using appropriate transformations. Series solutions have been obtained for velocity, temperature and nanoparticle fraction profiles using Homotopy Analysis Method (HAM. Convergence of the acquired solution is discussed critically. Behavior of velocity, temperature and concentration profiles on the prominent parameters is depicted and argued graphically. It is observed that temperature and concentration profiles show similar behavior for thermophoresis parameter Νt but opposite tendency is noted in case of Brownian motion parameter Νb. It is further analyzed that suction parameter S and Hartman number Μ depict decreasing behavior on velocity profile.
Study on vertical seismic response model of BWR-type reactor building
International Nuclear Information System (INIS)
Konno, T.; Motohashi, S.; Izumi, M.; Iizuka, S.
1993-01-01
A study on advanced seismic design for LWR has been carried out by the Nuclear Power Engineering Corporation (NUPEC), under the sponsorship of the Ministry of International Trade and Industry (MITI) of Japan. As a part of the study, it has been investigated to construct an accurate analytical model of reactor buildings for a seismic response analysis, which can reasonably represent dynamic characteristics of the building. In Japan, vibration models of reactor buildings for horizontal ground motion have been studied and examined through many simulation analyses for forced vibration tests and earthquake observations of actual buildings. And now it is possible to establish a reliable horizontal vibration model on the basis of multi-lumped mass and spring model. However, vertical vibration models have not been so much studied as horizontal models, due to less observed data for vertical motions. In this paper, the vertical seismic response models of a BWR-type reactor building including soil-structure interaction effect are numerically studied, by comparing the dynamic characteristics of (1) three dimensional finite element model, (2) multi-stick lumped mass model with a flexible base-mat, (3) multi-stick lumped mass model with a rigid base-mat and (4) single-stick lumped mass model. In particular, the BWR-type reactor building has the long span truss roof which is considered to be one of the critical members to vertical excitation. The modelings of the roof trusses are also studied
Wagman, Benjamin M.
2014-05-04
Uncertainty in wind forcing has long hampered direct tests of ocean model output against observations for the purpose of refining the boundary layer K-Profile Parameterization (KPP) of oceanic vertical mixing. Considered here is a short-term metric that could be sensitive to the ways in which the KPP directly affects the adjustment of sea surface temperatures for a given change in wind stress. In particular a metric is developed based on the lagged correlation between the 2–6 day filtered wind stress and sea surface temperature. The metric is normalized by estimated observational and model uncertainties such that the significance of differences may be assessed. For this purpose multiple wind reanalysis products and their blended combinations were used to represent the range of forcing uncertainty, while perturbed KPP parameter model runs explore the sensitivity of the metric to the parameterization of vertical mixing. The correlation metric is sensitive to perturbations to most KPP parameters, in ways that accord with expectations, although only a few parameters show a sensitivity on the same order as the sensitivity to switching between wind products. This suggests that uncertainties in wind forcing continue to be a significant limitation for applying direct observational tests of KPP physics. Moreover, model correlations are biased high, suggesting that the model lacks or does not resolve sources of variability on the 2–6 day time scale.
Model for radial gas fraction profiles in vertical pipe flow
International Nuclear Information System (INIS)
Lucas, D.; Krepper, E.; Prasser, H.M.
2001-01-01
A one-dimensional model is presented, which predicts the radial volume fraction profiles from a given bubble size distribution. It bases on the assumption of an equilibrium of the forces acting on a bubble perpendicularly to the flow path (non drag forces). For the prediction of the flow pattern this model could be used within an procedure together with appropriate models for local bubble coalescence and break-up. (orig.)
Bayesian Option Pricing Using Mixed Normal Heteroskedasticity Models
DEFF Research Database (Denmark)
Rombouts, Jeroen V.K.; Stentoft, Lars Peter
While stochastic volatility models improve on the option pricing error when compared to the Black-Scholes-Merton model, mispricings remain. This paper uses mixed normal heteroskedasticity models to price options. Our model allows for significant negative skewness and time varying higher order mom...... to a benchmark model in terms of dollar losses and the ability to explain the smirk in implied volatilities....
High Resolution Modeling of the Orographically Forced Vertical Motion on the Island of Oahu
Robinson, T. E., Jr.; Businger, S.
2014-12-01
The weather on Oahu is dictated in large part by the orographic forcing by the Ko'olau Mountain range. Using a high-resolution vertical motion diagnostic model with 0.0005° grid spacing, vertical wind speeds are calculated over the island. The model initialization is done with uniform 10 m s-1 winds, with the wind direction gradually varied. The results show that increased vertical motion occurs for winds from 145° in the valleys along the south shore of Oahu and the Waianae Mountains. For northeast trade winds, the Ko'oalu Range ridgeline produces a maximum vertical motion enhancement. As the winds become more northerly, easterly, or southerly, the geometry of the orography increases in importance and preferential locations of upward motion are observed. Comparing the winds from 145° and 25°, the concave headwall structures of the Ko'olaus are shown to play a critical role in the vertical motion. The southerly wind causes enhanced vertical motion along the southern facing arms of the headwalls, and the northerly winds have an identical effect on the northern facing arms. These results are not limited to when the wind is perpendicular to the ridgeline. By forcing the model with sounding winds taken during the Hawaiian Educational Radar Opportunity, the results are consistent with rain showers occurring over the mountains down shear from locations of strongest updrafts.
An enhanced fire hazard assessment model and validation experiments for vertical cable trays
Energy Technology Data Exchange (ETDEWEB)
Li, Lu [Sate Key Laboratory of Fire Science, University of Science and Technology of China, Hefei 230027 (China); Huang, Xianjia, E-mail: huangxianjia@gziit.ac.cn [Joint Laboratory of Fire Safety in Nuclear Power Plants, Institute of Industry Technology Guangzhou & Chinese Academy of Sciences, Guangzhou 511458 (China); Bi, Kun; Liu, Xiaoshuang [China Nuclear Power Design Co., Ltd., Shenzhen 518045 (China)
2016-05-15
Highlights: • An enhanced model was developed for vertical cable fire hazard assessment in NPP. • The validated experiments on vertical cable tray fires were conducted. • The capability of the model for cable tray with different cable spacing were tested. - Abstract: The model, referred to as FLASH-CAT (Flame Spread over Horizontal Cable Trays), was developed to estimate the heat release rate for vertical cable tray fire. The focus of this work is to investigate the application of an enhanced model to the single vertical cable tray fires with different cable spacing. The experiments on vertical cable tray fires with three typical cable spacing were conducted. The histories of mass loss rate and flame length were recorded during the cable fire. From the experimental results, it is found that the space between cable lines intensifies the cable combustion and accelerates the flame spread. The predictions by the enhanced model show good agreements with the experimental data. At the same time, it is shown that the enhanced model is capable of predicting the different behaviors of cable fires with different cable spacing by adjusting the flame spread speed only.
Computer modeling of jet mixing in INEL waste tanks
International Nuclear Information System (INIS)
Meyer, P.A.
1994-01-01
The objective of this study is to examine the feasibility of using submerged jet mixing pumps to mobilize and suspend settled sludge materials in INEL High Level Radioactive Waste Tanks. Scenarios include removing the heel (a shallow liquid and sludge layer remaining after tank emptying processes) and mobilizing and suspending solids in full or partially full tanks. The approach used was to (1) briefly review jet mixing theory, (2) review erosion literature in order to identify and estimate important sludge characterization parameters (3) perform computer modeling of submerged liquid mixing jets in INEL tank geometries, (4) develop analytical models from which pump operating conditions and mixing times can be estimated, and (5) analyze model results to determine overall feasibility of using jet mixing pumps and make design recommendations
Multiobjective Fuzzy Mixed Assembly Line Sequencing Optimization Model
Tahriri, Farzad; Zawiah Md Dawal, Siti; Taha, Zahari
2014-01-01
It can be deduced from previous studies that there exists a research gap in assembly line sequencing optimization model for mixed-model production lines. In particular, there is a lack of studies which focus on the integration between job shop and assembly lines using fuzzy techniques. Hence, this paper is aimed at addressing the multiobjective mixed-model assembly line sequencing problem by integrating job shop and assembly production lines for factories with modular layouts. The primary go...
International Nuclear Information System (INIS)
Welser-Sherrill, L.; Mancini, R. C.; Haynes, D. A.; Haan, S. W.; Koch, J. A.; Izumi, N.; Tommasini, R.; Golovkin, I. E.; MacFarlane, J. J.; Radha, P. B.; Delettrez, J. A.; Regan, S. P.; Smalyuk, V. A.
2007-01-01
The presence of shell mix in inertial confinement fusion implosion cores is an important characteristic. Mixing in this experimental regime is primarily due to hydrodynamic instabilities, such as Rayleigh-Taylor and Richtmyer-Meshkov, which can affect implosion dynamics. Two independent theoretical mix models, Youngs' model and the Haan saturation model, were used to estimate the level of Rayleigh-Taylor mixing in a series of indirect drive experiments. The models were used to predict the radial width of the region containing mixed fuel and shell materials. The results for Rayleigh-Taylor mixing provided by Youngs' model are considered to be a lower bound for the mix width, while those generated by Haan's model incorporate more experimental characteristics and consequently have larger mix widths. These results are compared with an independent experimental analysis, which infers a larger mix width based on all instabilities and effects captured in the experimental data
Schumann, Ulrich; Mayer, Bernhard
2017-11-01
Earth's surface temperature sensitivity to radiative forcing (RF) by contrail cirrus and the related RF efficacy relative to CO2 are investigated in a one-dimensional idealized model of the atmosphere. The model includes energy transport by shortwave (SW) and longwave (LW) radiation and by mixing in an otherwise fixed reference atmosphere (no other feedbacks). Mixing includes convective adjustment and turbulent diffusion, where the latter is related to the vertical component of mixing by large-scale eddies. The conceptual study shows that the surface temperature sensitivity to given contrail RF depends strongly on the timescales of energy transport by mixing and radiation. The timescales are derived for steady layered heating (ghost forcing) and for a transient contrail cirrus case. The radiative timescales are shortest at the surface and shorter in the troposphere than in the mid-stratosphere. Without mixing, a large part of the energy induced into the upper troposphere by radiation due to contrails or similar disturbances gets lost to space before it can contribute to surface warming. Because of the different radiative forcing at the surface and at top of atmosphere (TOA) and different radiative heating rate profiles in the troposphere, the local surface temperature sensitivity to stratosphere-adjusted RF is larger for SW than for LW contrail forcing. Without mixing, the surface energy budget is more important for surface warming than the TOA budget. Hence, surface warming by contrails is smaller than suggested by the net RF at TOA. For zero mixing, cooling by contrails cannot be excluded. This may in part explain low efficacy values for contrails found in previous global circulation model studies. Possible implications of this study are discussed. Since the results of this study are model dependent, they should be tested with a comprehensive climate model in the future.
Directory of Open Access Journals (Sweden)
U. Schumann
2017-11-01
Full Text Available Earth's surface temperature sensitivity to radiative forcing (RF by contrail cirrus and the related RF efficacy relative to CO2 are investigated in a one-dimensional idealized model of the atmosphere. The model includes energy transport by shortwave (SW and longwave (LW radiation and by mixing in an otherwise fixed reference atmosphere (no other feedbacks. Mixing includes convective adjustment and turbulent diffusion, where the latter is related to the vertical component of mixing by large-scale eddies. The conceptual study shows that the surface temperature sensitivity to given contrail RF depends strongly on the timescales of energy transport by mixing and radiation. The timescales are derived for steady layered heating (ghost forcing and for a transient contrail cirrus case. The radiative timescales are shortest at the surface and shorter in the troposphere than in the mid-stratosphere. Without mixing, a large part of the energy induced into the upper troposphere by radiation due to contrails or similar disturbances gets lost to space before it can contribute to surface warming. Because of the different radiative forcing at the surface and at top of atmosphere (TOA and different radiative heating rate profiles in the troposphere, the local surface temperature sensitivity to stratosphere-adjusted RF is larger for SW than for LW contrail forcing. Without mixing, the surface energy budget is more important for surface warming than the TOA budget. Hence, surface warming by contrails is smaller than suggested by the net RF at TOA. For zero mixing, cooling by contrails cannot be excluded. This may in part explain low efficacy values for contrails found in previous global circulation model studies. Possible implications of this study are discussed. Since the results of this study are model dependent, they should be tested with a comprehensive climate model in the future.
Mixed finite elements for global tide models.
Cotter, Colin J; Kirby, Robert C
2016-01-01
We study mixed finite element methods for the linearized rotating shallow water equations with linear drag and forcing terms. By means of a strong energy estimate for an equivalent second-order formulation for the linearized momentum, we prove long-time stability of the system without energy accumulation-the geotryptic state. A priori error estimates for the linearized momentum and free surface elevation are given in [Formula: see text] as well as for the time derivative and divergence of the linearized momentum. Numerical results confirm the theoretical results regarding both energy damping and convergence rates.
Modeling Vertical Plasma Flows in Solar Filament Barbs
Litvinenko, Y.
2003-12-01
Speeds of observed flows in quiescent solar filaments are typically much less than the local Alfvén speed. This is why the flows in filament barbs can be modeled by perturbing a local magnetostatic solution describing the balance between the Lorentz force, gravity, and gas pressure in a barb. Similarly, large-scale filament flows can be treated as adiabatically slow deformations of a force-free magnetic equilibrium that describes the global structure of a filament. This approach reconciles current theoretical models with the puzzling observational result that some of the flows appear to be neither aligned with the magnetic field nor controlled by gravity.
Profile construction in experimental choice designs for mixed logit models
Sandor, Z; Wedel, M
2002-01-01
A computationally attractive model for the analysis of conjoint choice experiments is the mixed multinomial logit model, a multinomial logit model in which it is assumed that the coefficients follow a (normal) distribution across subjects. This model offers the advantage over the standard
International Nuclear Information System (INIS)
Weiler, K.H.
1979-01-01
Vertical profiles of NO were measured at midlatitudes by means of a balloonborne payload using the chemiluminescent principle. A newly developed pressure dependent turbofan enables sufficient main flow even under near vacuum conditions, as low as 3 mb a flight duration of 20 hours. The data are continuously transmitted via a PCM-system to the ground station. The whole instrument was sealed prior to the flight and opened above the clouds by telecommand in order to avoid contamination by water vapour. Extensive laboratory and in situ calibration procedures led for the first time to overall errors of less than +-5% for the midday mean value between 3 to 10 mb and +- 25% at 150 mb. The resolving power is better than 20 pptsub(v) (10 -11 ) depending on the actual temperature, maniflow, and pressure. At about 25 mb, the reduction in NO with the setting of the sun was observed. A very slow decrease in the mixing ratio was found, which agrees with measurements of other workers but not with present model predictions. The mixing ratio between 7 and 10 mb was between 3 and 4 ppbsub(v) (10 -9 ). The minimum mixing ratio of about 0.07 ppbsub(v) was observed at about 60 mb. Also a hysteresis between ascent and descent was observed. It is concluded that the different diurnal variations of NO are strongly dependent on vertical exchange processes, scattering processes, and the surface albedo. (orig.) [de
Modelling vertical uniform contact stress of heavy vehicle tyres
CSIR Research Space (South Africa)
Steenkamp, Anton J
2016-07-01
Full Text Available The field of tyre dynamics is a relatively new, but highly complex field of engineering. The testing and modelling of various tyres in order to determine stress distributions of tyres on the road surface, under varying conditions, remains a relevant...
Modelling the tides and their impacts on the vertical stratification ...
African Journals Online (AJOL)
The Sofala Bank, a wide shelf located along the central coast of Mozambique, hosts tides with high amplitudes. The Regional Ocean Modelling System (ROMS) was used to analyse the tidal currents on the bank and to investigate their effects on the stratification and generation of tidal fronts. During spring tides, barotropic ...
Solving vertical transport and chemistry in air pollution models
P.J.F. Berkvens (Patrick); M.A. Botchev; J.G. Verwer (Jan); M.C. Krol; W. Peters
2000-01-01
textabstractFor the time integration of stiff transport-chemistry problems from air pollution modelling, standard ODE solvers are not feasible due to the large number of species and the 3D nature. The popular alternative, standard operator splitting, introduces artificial transients for short-lived
Solving Vertical Transport and Chemistry in Air Pollution Models.
Berkvens, P.J.F.; Bochev, Mikhail A.; Verwer, J.G.; Krol, M.C.; Peters, W.
For the time integration of stiff transport-chemistry problems from air pollution modelling, standard ODE solvers are not feasible due to the large number of species and the 3D nature. The popular alternative, standard operator splitting, introduces artificial transients for short-lived species.
Solving vertical transport and chemistry in air pollution models
Berkvens, P.J.F.; Bochev, M.A.; Krol, M.C.; Peters, W.; Verwer, J.G.; Chock, David P.; Carmichael, Gregory R.; Brick, Patricia
2002-01-01
For the time integration of stiff transport-chemistry problems from air pollution modelling, standard ODE solvers are not feasible due to the large number of species and the 3D nature. The popular alternative, standard operator splitting, introduces artificial transients for short-lived species.
TransCom model simulations of methane: Comparison of vertical profiles with aircraft measurements
Saito, R.; Patra, P.K.; Sweeney, C.; Machida, T.; Krol, M.C.; Houweling, S.; Bousquet, P.; Agusti-Panareda, A.; Belikov, D.; Bergmann, D.; Bian, H.S.; Cameron-Smith, P.; Chipperfield, M.P.; Fortems-Cheiney, A.; Fraser, A.; Gatti, L.V.; Gloor, E.; Hess, P.; Kawa, S.R.; Law, R.M.; Locatelli, R.; Loh, Z.; Maksyutov, S.; Meng, L.; Miller, J.B.; Palmer, P.I.; Prinn, R.G.; Rigby, M.; Wilson, C.
2013-01-01
To assess horizontal and vertical transports of methane (CH4) concentrations at different heights within the troposphere, we analyzed simulations by 12 chemistry transport models (CTMs) that participated in the TransCom-CH4 intercomparison experiment. Model results are compared with aircraft
Gravitational attraction of a vertical pyramid model of flat top-and ...
Indian Academy of Sciences (India)
bottom and sloping sides with a depth-wise linear density variation. However, he was unable to derive a complete analytical expression for its gravity effect. Keywords. Gravity effect; vertical pyramid model with flat top-and-bottom; parabolic density variation; gravity forward modelling. J. Earth Syst. Sci. 124, No. 8, December ...
Performance of HSPA Vertical Sectorization System under Semi-Deterministic Propagation Model
DEFF Research Database (Denmark)
Nguyen, Huan Cong; Makinen, Jarmo; Stoermer, Wolfgang
2013-01-01
The performance of the Vertical Sectorization (VS) system has been evaluated previously using an empirical propagation model and a regular network layout. In this paper, our aim is to investigate the gain of the VS system under a more realistic scenario. A semi-deterministic path loss model run o...
Ruin Probabilities in the Mixed Claim Frequency Risk Models
Directory of Open Access Journals (Sweden)
Zhao Xiaoqin
2014-01-01
Full Text Available We consider two mixed claim frequency risk models. Some important probabilistic properties are obtained by probability-theory methods. Some important results about ruin probabilities are obtained by martingale approach.
Mixing model with multi-particle interactions for Lagrangian simulations of turbulent mixing
Energy Technology Data Exchange (ETDEWEB)
Watanabe, T., E-mail: watanabe.tomoaki@c.nagoya-u.jp; Nagata, K. [Department of Aerospace Engineering, Nagoya University, Nagoya (Japan)
2016-08-15
We report on the numerical study of the mixing volume model (MVM) for molecular diffusion in Lagrangian simulations of turbulent mixing problems. The MVM is based on the multi-particle interaction in a finite volume (mixing volume). A priori test of the MVM, based on the direct numerical simulations of planar jets, is conducted in the turbulent region and the interfacial layer between the turbulent and non-turbulent fluids. The results show that the MVM predicts well the mean effects of the molecular diffusion under various numerical and flow parameters. The number of the mixing particles should be large for predicting a value of the molecular diffusion term positively correlated to the exact value. The size of the mixing volume relative to the Kolmogorov scale η is important in the performance of the MVM. The scalar transfer across the turbulent/non-turbulent interface is well captured by the MVM especially with the small mixing volume. Furthermore, the MVM with multiple mixing particles is tested in the hybrid implicit large-eddy-simulation/Lagrangian-particle-simulation (LES–LPS) of the planar jet with the characteristic length of the mixing volume of O(100η). Despite the large mixing volume, the MVM works well and decays the scalar variance in a rate close to the reference LES. The statistics in the LPS are very robust to the number of the particles used in the simulations and the computational grid size of the LES. Both in the turbulent core region and the intermittent region, the LPS predicts a scalar field well correlated to the LES.
Markov and mixed models with applications
DEFF Research Database (Denmark)
Mortensen, Stig Bousgaard
the individual in almost any thinkable way. This project focuses on measuring the eects on sleep in both humans and animals. The sleep process is usually analyzed by categorizing small time segments into a number of sleep states and this can be modelled using a Markov process. For this purpose new methods...... for non-parametric estimation of Markov processes are proposed to give a detailed description of the sleep process during the night. Statistically the Markov models considered for sleep states are closely related to the PK models based on SDEs as both models share the Markov property. When the models...
The Stochastic Ising Model with the Mixed Boundary Conditions
Directory of Open Access Journals (Sweden)
Wang Jun
2009-01-01
Full Text Available Abstract We estimate the spectral gap of the two-dimensional stochastic Ising model for four classes of mixed boundary conditions. On a finite square, in the absence of an external field, two-sided estimates on the spectral gap for the first class of (weak positive boundary conditions are given. Further, at inverse temperatures , we will show lower bounds of the spectral gap of the Ising model for the other three classes mixed boundary conditions.
Modelling mixed forest growth : a review of models for forest management
Porte, A.; Bartelink, H.H.
2002-01-01
Most forests today are multi-specific and heterogeneous forests (`mixed forests'). However, forest modelling has been focusing on mono-specific stands for a long time, only recently have models been developed for mixed forests. Previous reviews of mixed forest modelling were restricted to certain
Actuarial statistics with generalized linear mixed models
Antonio, K.; Beirlant, J.
2007-01-01
Over the last decade the use of generalized linear models (GLMs) in actuarial statistics has received a lot of attention, starting from the actuarial illustrations in the standard text by McCullagh and Nelder [McCullagh, P., Nelder, J.A., 1989. Generalized linear models. In: Monographs on Statistics
Incorporating vehicle mix in stimulus-response car-following models
Directory of Open Access Journals (Sweden)
Saidi Siuhi
2016-06-01
Full Text Available The objective of this paper is to incorporate vehicle mix in stimulus-response car-following models. Separate models were estimated for acceleration and deceleration responses to account for vehicle mix via both movement state and vehicle type. For each model, three sub-models were developed for different pairs of following vehicles including “automobile following automobile,” “automobile following truck,” and “truck following automobile.” The estimated model parameters were then validated against other data from a similar region and roadway. The results indicated that drivers' behaviors were significantly different among the different pairs of following vehicles. Also the magnitude of the estimated parameters depends on the type of vehicle being driven and/or followed. These results demonstrated the need to use separate models depending on movement state and vehicle type. The differences in parameter estimates confirmed in this paper highlight traffic safety and operational issues of mixed traffic operation on a single lane. The findings of this paper can assist transportation professionals to improve traffic simulation models used to evaluate the impact of different strategies on ameliorate safety and performance of highways. In addition, driver response time lag estimates can be used in roadway design to calculate important design parameters such as stopping sight distance on horizontal and vertical curves for both automobiles and trucks.
Constitutive mixed mode model for cracks in concrete
DEFF Research Database (Denmark)
Jacobsen, J.S.; Poulsen, P.N.; Olesen, J.F.
2013-01-01
The scope of the paper is to set up a constitutive mixed mode model for cracks in concrete. The model is formulated at macro level and includes the most important micro scale effects. An associated plasticity model inspired by the modified Cam clay model is established. The hardening parameters...... are based on the standard Mode I tensile softening response and the response for Mode I crushing. The roughness of the crack is included through a topographic description of the crack surface. The constitutive behavior is based on the integration of local contributions. The local mixed mode ratio...... is determined from the topographic information and the constitutive model is thereby purely mechanically based. Using the actual topographic description the model is validated against experimental results for mixed mode crack openings....
Bleck, Rainer; Bao, Jian-Wen; Benjamin, Stanley G.; Brown, John M.; Fiorino, Michael; Henderson, Thomas B.; Lee, Jin-Luen; MacDonald, Alexander E.; Madden, Paul; Middlecoff, Jacques;
2015-01-01
A hydrostatic global weather prediction model based on an icosahedral horizontal grid and a hybrid terrain following/ isentropic vertical coordinate is described. The model is an extension to three spatial dimensions of a previously developed, icosahedral, shallow-water model featuring user-selectable horizontal resolution and employing indirect addressing techniques. The vertical grid is adaptive to maximize the portion of the atmosphere mapped into the isentropic coordinate subdomain. The model, best described as a stacked shallow-water model, is being tested extensively on real-time medium-range forecasts to ready it for possible inclusion in operational multimodel ensembles for medium-range to seasonal prediction.
Nonlinear mixed-effects modeling: individualization and prediction.
Olofsen, Erik; Dinges, David F; Van Dongen, Hans P A
2004-03-01
The development of biomathematical models for the prediction of fatigue and performance relies on statistical techniques to analyze experimental data and model simulations. Statistical models of empirical data have adjustable parameters with a priori unknown values. Interindividual variability in estimates of those values requires a form of smoothing. This traditionally consists of averaging observations across subjects, or fitting a model to the data of individual subjects first and subsequently averaging the parameter estimates. However, the standard errors of the parameter estimates are assessed inaccurately by such averaging methods. The reason is that intra- and inter-individual variabilities are intertwined. They can be separated by mixed-effects modeling in which model predictions are not only determined by fixed effects (usually constant parameters or functions of time) but also by random effects, describing the sampling of subject-specific parameter values from probability distributions. By estimating the parameters of the distributions of the random effects, mixed-effects models can describe experimental observations involving multiple subjects properly (i.e., yielding correct estimates of the standard errors) and parsimoniously (i.e., estimating no more parameters than necessary). Using a Bayesian approach, mixed-effects models can be "individualized" as observations are acquired that capture the unique characteristics of the individual at hand. Mixed-effects models, therefore, have unique advantages in research on human neurobehavioral functions, which frequently show large inter-individual differences. To illustrate this we analyzed laboratory neurobehavioral performance data acquired during sleep deprivation, using a nonlinear mixed-effects model. The results serve to demonstrate the usefulness of mixed-effects modeling for data-driven development of individualized predictive models of fatigue and performance.
modelling of far modelling of far-field mixing o field mixing o ambient
African Journals Online (AJOL)
User
quality[3]. Although many studies have addressed biochemical analysis of the polluted water. 8067349981. FIELD MIXING OF INDUSTRIAL. FIELD MIXING OF INDUSTRIAL EFFLUENT PLUM ... and also ascertain the extent of its effect from discharge location to downs .... control and concluded by drawing attention to the.
Bilinear Mixed Effects Models for Dyadic Data
National Research Council Canada - National Science Library
Hoff, Peter D
2003-01-01
.... Such an effect, along with standard linear fixed and random effects, is incorporated into a generalized linear model, and a Markov chain Monte Carlo algorithm is provided for Bayesian estimation and inference...
Modeling Dynamic Effects of the Marketing Mix on Market Shares
Fok, Dennis; Paap, Richard; Franses, Philip Hans
2003-01-01
textabstractTo comprehend the competitive structure of a market, it is important to understand the short-run and long-run effects of the marketing mix on market shares. A useful model to link market shares with marketing-mix variables, like price and promotion, is the market share attraction model. In this paper we put forward a representation of the attraction model, which allows for explicitly disentangling long-run from short-run effects. Our model also contains a second level, in which th...
Multivariate Survival Mixed Models for Genetic Analysis of Longevity Traits
DEFF Research Database (Denmark)
Pimentel Maia, Rafael; Madsen, Per; Labouriau, Rodrigo
2013-01-01
A class of multivariate mixed survival models for continuous and discrete time with a complex covariance structure is introduced in a context of quantitative genetic applications. The methods introduced can be used in many applications in quantitative genetics although the discussion presented....... The discrete time models used are multivariate variants of the discrete relative risk models. These models allow for regular parametric likelihood-based inference by exploring a coincidence of their likelihood functions and the likelihood functions of suitably defined multivariate generalized linear mixed...
Directory of Open Access Journals (Sweden)
David I Forrester
2014-09-01
Full Text Available Background Forest ecosystem functioning is strongly influenced by the absorption of photosynthetically active radiation (APAR, and therefore, accurate predictions of APAR are critical for many process-based forest growth models. The Lambert-Beer law can be applied to estimate APAR for simple homogeneous canopies composed of one layer, one species, and no canopy gaps. However, the vertical and horizontal structure of forest canopies is rarely homogeneous. Detailed tree-level models can account for this heterogeneity but these often have high input and computational demands and work on finer temporal and spatial resolutions than required by stand-level growth models. The aim of this study was to test a stand-level light absorption model that can estimate APAR by individual species in mixed-species and multi-layered stands with any degree of canopy openness including open-grown trees to closed canopies. Methods The stand-level model was compared with a detailed tree-level model that has already been tested in mixed-species stands using empirical data. Both models were parameterised for five different forests, including a wide range of species compositions, species proportions, stand densities, crown architectures and canopy structures. Results The stand-level model performed well in all stands except in the stand where extinction coefficients were unusually variable and it appears unlikely that APAR could be predicted in such stands using (tree- or stand-level models that do not allow individuals of a given species to have different extinction coefficients, leaf-area density or analogous parameters. Conclusion This model is parameterised with species-specific information about extinction coefficients and mean crown length, diameter, height and leaf area. It could be used to examine light dynamics in complex canopies and in stand-level growth models.
Kipling, Zak; Stier, Philip; Johnson, Colin E.; Mann, Graham W.; Bellouin, Nicolas; Bauer, Susanne E.; Bergman, Tommi; Chin, Mian; Diehl, Thomas; Ghan, Steven J.;
2016-01-01
The vertical profile of aerosol is important for its radiative effects, but weakly constrained by observations on the global scale, and highly variable among different models. To investigate the controlling factors in one particular model, we investigate the effects of individual processes in HadGEM3-UKCA and compare the resulting diversity of aerosol vertical profiles with the inter-model diversity from the AeroCom Phase II control experiment. In this way we show that (in this model at least) the vertical profile is controlled by a relatively small number of processes, although these vary among aerosol components and particle sizes. We also show that sufficiently coarse variations in these processes can produce a similar diversity to that among different models in terms of the global-mean profile and, to a lesser extent, the zonal-mean vertical position. However, there are features of certain models' profiles that cannot be reproduced, suggesting the influence of further structural differences between models. In HadGEM3-UKCA, convective transport is found to be very important in controlling the vertical profile of all aerosol components by mass. In-cloud scavenging is very important for all except mineral dust. Growth by condensation is important for sulfate and carbonaceous aerosol (along with aqueous oxidation for the former and ageing by soluble material for the latter). The vertical extent of biomass-burning emissions into the free troposphere is also important for the profile of carbonaceous aerosol. Boundary-layer mixing plays a dominant role for sea salt and mineral dust, which are emitted only from the surface. Dry deposition and below-cloud scavenging are important for the profile of mineral dust only. In this model, the microphysical processes of nucleation, condensation and coagulation dominate the vertical profile of the smallest particles by number (e.g. total CN >3 nm), while the profiles of larger particles (e.g. CN>100 nm) are controlled by the
Study on particle deposition in vertical square ventilation duct flows by different models
International Nuclear Information System (INIS)
Zhang Jinping; Li Angui
2008-01-01
A proper representation of the air flow in a ventilation duct is crucial for adequate prediction of the deposition velocity of particles. In this paper, the mean turbulent air flow fields are predicted by two different numerical models (the Reynolds stress transport model (RSM) and the realizable k-εmodel). Contours of mean streamwise velocity deduced from the k-ε model are compared with those obtained from the Reynolds stress transport model. Dimensionless deposition velocities of particles in downward and upward ventilation duct flows are also compared based on the flow fields presented by the two different numerical models. Trajectories of the particles are tracked using a one way coupling Lagrangian eddy-particle interaction model. Thousands of individual particles are released in the represented flow, and dimensionless deposition velocities are evaluated for the vertical walls in fully developed smooth vertical downward and upward square duct flows generated by the RSM and realizable k-ε model. The effects of particle diameter, dimensionless relaxation time, flow direction and air speed in vertical upward and downward square duct flows on the particle deposition velocities are discussed. The effects of lift and gravity on the particle deposition velocities are evaluated in vertical flows presented by the RSM. It is shown that the particle deposition velocities based on the RSM and realizable k-εmodel have subtle differences. The flow direction and the lift force significantly affect the particle deposition velocities in vertical duct flows. The simulation results are compared with earlier experimental data and the numerical results for fully developed duct flows. It is shown that the deposition velocities predicted are in agreement with the experimental data and the numerical results
Isothermal coarse mixing: experimental and CFD modelling
International Nuclear Information System (INIS)
Gilbertson, M.A.; Kenning, D.B.R.; Hall, R.W.
1992-01-01
A plane, two-dimensional flow apparatus has been built which uses a jet of solid 6mm diameter balls to model a jet of molten drops falling into a tank of water to study premixing prior to a vapour explosion. Preliminary experiments with unheated stainless steel balls are here compared with computational fluid dynamics (CFD) calculations by the code CHYMES. (6 figures) (Author)
A new approach to model mixed hydrates
Czech Academy of Sciences Publication Activity Database
Hielscher, S.; Vinš, Václav; Jäger, A.; Hrubý, Jan; Breitkopf, C.; Span, R.
2018-01-01
Roč. 459, March (2018), s. 170-185 ISSN 0378-3812 R&D Projects: GA ČR(CZ) GA17-08218S Institutional support: RVO:61388998 Keywords : gas hydrate * mixture * modeling Subject RIV: BJ - Thermodynamics Impact factor: 2.473, year: 2016 https://www. science direct.com/ science /article/pii/S0378381217304983
International Nuclear Information System (INIS)
Hua Ting-Ting; Guo Yu-Feng; Yu Ying; Jian Tong; Yao Jia-Fei; Sheu Gene
2013-01-01
By solving the 2D Poisson's equation, analytical models are proposed to calculate the surface potential and electric field distributions of lateral power devices with arbitrary vertical doping profiles. The vertical and the lateral breakdown voltages are formulized to quantify the breakdown characteristic in completely-depleted and partially-depleted cases. A new reduced surface field (RESURF) criterion which can be used in various drift doping profiles is further derived for obtaining the optimal trade-off between the breakdown voltage and the on-resistance. Based on these models and the numerical simulation, the electric field modulation mechanism and the breakdown characteristics of lateral power devices are investigated in detail for the uniform, linear, Gaussian, and some discrete doping profiles along the vertical direction in the drift region. Then, the mentioned vertical doping profiles of these devices with the same geometric parameters are optimized, and the results show that the optimal breakdown voltages and the effective drift doping concentrations of these devices are identical, which are equal to those of the uniform-doped device, respectively. The analytical results of these proposed models are in good agreement with the numerical results and the previous experimental results, confirming the validity of the models presented here. (interdisciplinary physics and related areas of science and technology)
Creating a benchmark of vertical axis wind turbines in dynamic stall for validating numerical models
DEFF Research Database (Denmark)
Castelein, D.; Ragni, D.; Tescione, G.
2015-01-01
An experimental campaign using Particle Image Velocimetry (2C-PIV) technique has been conducted on a H-type Vertical Axis Wind Turbine (VAWT) to create a benchmark for validating and comparing numerical models. The turbine is operated at tip speed ratios (TSR) of 4.5 and 2, at an average chord-ba...
Reliability Based Optimal Design of Vertical Breakwaters Modelled as a Series System Failure
DEFF Research Database (Denmark)
Christiani, E.; Burcharth, H. F.; Sørensen, John Dalsgaard
1996-01-01
Reliability based design of monolithic vertical breakwaters is considered. Probabilistic models of important failure modes such as sliding and rupture failure in the rubble mound and the subsoil are described. Characterisation of the relevant stochastic parameters are presented, and relevant design...... variables are identified and an optimal system reliability formulation is presented. An illustrative example is given....
Vertical Integration of Geographic Information Sciences: A Recruitment Model for GIS Education
Yu, Jaehyung; Huynh, Niem Tu; McGehee, Thomas Lee
2011-01-01
An innovative vertical integration model for recruiting to GIS education was introduced and tested following four driving forces: curriculum development, GIS presentations, institutional collaboration, and faculty training. Curriculum development was a useful approach to recruitment, student credit hour generation, and retention-rate improvement.…
Stability analysis of a general age-dependent vaccination model of a vertically transmitted disease
International Nuclear Information System (INIS)
El Doma, M.
1995-07-01
An SIR epidemic model of a general age-dependent vaccination of a vertically as well as horizontally transmitted disease is investigated when the population is in steady state and the fertility, mortality and removal rates depends on age. We determine the steady states and examine their stabilities. (author). 24 refs
Gravitational attraction of a vertical pyramid model of flat top-and ...
Indian Academy of Sciences (India)
Home; Journals; Journal of Earth System Science; Volume 124; Issue 8. Gravitational attraction of a vertical pyramid model of flat top-and-bottom with depth-wise parabolic density variation. Anand P Gokula Rambhatla G Sastry. Volume 124 Issue 8 December 2015 pp 1735-1744 ...
Directory of Open Access Journals (Sweden)
J. Callies
2012-01-01
Full Text Available A simple model of the thermohaline circulation (THC is formulated, with the objective to represent explicitly the geostrophic force balance of the basinwide THC. The model comprises advective-diffusive density balances in two meridional-vertical planes located at the eastern and the western walls of a hemispheric sector basin. Boundary mixing constrains vertical motion to lateral boundary layers along these walls. Interior, along-boundary, and zonally integrated meridional flows are in thermal-wind balance. Rossby waves and the absence of interior mixing render isopycnals zonally flat except near the western boundary, constraining meridional flow to the western boundary layer. The model is forced by a prescribed meridional surface density profile.
This two-plane model reproduces both steady-state density and steady-state THC structures of a primitive-equation model. The solution shows narrow deep sinking at the eastern high latitudes, distributed upwelling at both boundaries, and a western boundary current with poleward surface and equatorward deep flow. The overturning strength has a 2/3-power-law dependence on vertical diffusivity and a 1/3-power-law dependence on the imposed meridional surface density difference. Convective mixing plays an essential role in the two-plane model, ensuring that deep sinking is located at high latitudes. This role of convective mixing is consistent with that in three-dimensional models and marks a sharp contrast with previous two-dimensional models.
Overall, the two-plane model reproduces crucial features of the THC as simulated in simple-geometry three-dimensional models. At the same time, the model self-consistently makes quantitative a conceptual picture of the three-dimensional THC that hitherto has been expressed either purely qualitatively or not self-consistently.
Stochastic model of Rayleigh-Taylor turbulent mixing
International Nuclear Information System (INIS)
Abarzhi, S.I.; Cadjan, M.; Fedotov, S.
2007-01-01
We propose a stochastic model to describe the random character of the dissipation process in Rayleigh-Taylor turbulent mixing. The parameter alpha, used conventionally to characterize the mixing growth-rate, is not a universal constant and is very sensitive to the statistical properties of the dissipation. The ratio between the rates of momentum loss and momentum gain is the statistic invariant and a robust parameter to diagnose with or without turbulent diffusion accounted for
Vertically-Integrated Dual-Continuum Models for CO2 Injection in Fractured Aquifers
Tao, Y.; Guo, B.; Bandilla, K.; Celia, M. A.
2017-12-01
Injection of CO2 into a saline aquifer leads to a two-phase flow system, with supercritical CO2 and brine being the two fluid phases. Various modeling approaches, including fully three-dimensional (3D) models and vertical-equilibrium (VE) models, have been used to study the system. Almost all of that work has focused on unfractured formations. 3D models solve the governing equations in three dimensions and are applicable to generic geological formations. VE models assume rapid and complete buoyant segregation of the two fluid phases, resulting in vertical pressure equilibrium and allowing integration of the governing equations in the vertical dimension. This reduction in dimensionality makes VE models computationally more efficient, but the associated assumptions restrict the applicability of VE model to formations with moderate to high permeability. In this presentation, we extend the VE and 3D models for CO2 injection in fractured aquifers. This is done in the context of dual-continuum modeling, where the fractured formation is modeled as an overlap of two continuous domains, one representing the fractures and the other representing the rock matrix. Both domains are treated as porous media continua and can be modeled by either a VE or a 3D formulation. The transfer of fluid mass between rock matrix and fractures is represented by a mass transfer function connecting the two domains. We have developed a computational model that combines the VE and 3D models, where we use the VE model in the fractures, which typically have high permeability, and the 3D model in the less permeable rock matrix. A new mass transfer function is derived, which couples the VE and 3D models. The coupled VE-3D model can simulate CO2 injection and migration in fractured aquifers. Results from this model compare well with a full-3D model in which both the fractures and rock matrix are modeled with 3D models, with the hybrid VE-3D model having significantly reduced computational cost. In
Vertical Instability in EAST: Comparison of Model Predictions with Experimental Results
International Nuclear Information System (INIS)
Qian Jinping; Wan Baonian; Shen Biao; Xiao Bingjia; Sun Youwen; Shi Yuejiang; Lin Shiyao; Li Jiangang; Gong Xianzu
2008-01-01
Growth rates of the axisymmetric mode in elongated plasmas in the experimental advanced superconducting tokamak (EAST) are measured with zero feedback gains and then compared with numerically calculated growth rates for the reconstructed shapes. The comparison is made after loss of vertical position control. The open-loop growth rates were scanned with the number of vessel eigenmodes, which up to 20 is enough to make the growth rates settled. The agreement between the growth rates measured experimentally and the growth rates determined numerically is good. The results show that a linear RZIP model is essentially good enough for the vertical position feedback control.
Multiobjective Fuzzy Mixed Assembly Line Sequencing Optimization Model
Directory of Open Access Journals (Sweden)
Farzad Tahriri
2014-01-01
Full Text Available It can be deduced from previous studies that there exists a research gap in assembly line sequencing optimization model for mixed-model production lines. In particular, there is a lack of studies which focus on the integration between job shop and assembly lines using fuzzy techniques. Hence, this paper is aimed at addressing the multiobjective mixed-model assembly line sequencing problem by integrating job shop and assembly production lines for factories with modular layouts. The primary goal is to minimize the make-span, setup time, and cost simultaneously in mixed-model assembly lines. Such conflicting goals arise when switching between different products. A genetic algorithm (GA approach is used to solve this problem, in which trapezoidal fuzzy numbers are implemented for variables such as operation and travelling time in order to generate results with higher accuracy and representative of real-case data.
Linear mixed models a practical guide using statistical software
West, Brady T; Galecki, Andrzej T
2006-01-01
Simplifying the often confusing array of software programs for fitting linear mixed models (LMMs), Linear Mixed Models: A Practical Guide Using Statistical Software provides a basic introduction to primary concepts, notation, software implementation, model interpretation, and visualization of clustered and longitudinal data. This easy-to-navigate reference details the use of procedures for fitting LMMs in five popular statistical software packages: SAS, SPSS, Stata, R/S-plus, and HLM. The authors introduce basic theoretical concepts, present a heuristic approach to fitting LMMs based on bo
Directory of Open Access Journals (Sweden)
Shiqian Nie
2017-01-01
Full Text Available The fractional advection-diffusion equation (fADE model is a new approach to describe the vertical distribution of suspended sediment concentration in steady turbulent flow. However, the advantages and parameter definition of the fADE model in describing the sediment suspension distribution are still unclear. To address this knowledge gap, this study first reviews seven models, including the fADE model, for the vertical distribution of suspended sediment concentration in steady turbulent flow. The fADE model, among others, describes both Fickian and non-Fickian diffusive characteristics of suspended sediment, while the other six models assume that the vertical diffusion of suspended sediment follows Fick’s first law. Second, this study explores the sensitivity of the fractional index of the fADE model to the variation of particle sizes and sediment settling velocities, based on experimental data collected from the literatures. Finally, empirical formulas are developed to relate the fractional derivative order to particle size and sediment settling velocity. These formulas offer river engineers a substitutive way to estimate the fractional derivative order in the fADE model.
International Nuclear Information System (INIS)
Meng Xinzhu; Jiao Jianjun; Chen Lansun
2009-01-01
Since the investigation of impulsive delay differential equations is beginning, the literature on delay epidemic models with pulse vaccination is not extensive. In this paper, we propose a new SEIRS epidemic disease model with two profitless delays and vertical transmission, and analyze the dynamics behaviors of the model under pulse vaccination. Using the discrete dynamical system determined by the stroboscopic map, we obtain a 'infection-free' periodic solution, further, show that the 'infection-free' periodic solution is globally attractive when some parameters of the model are under appropriate conditions. Using a new modeling method, we obtain sufficient condition for the permanence of the epidemic model with pulse vaccination. We show that time delays, pulse vaccination and vertical transmission can bring different effects on the dynamics behaviors of the model by numerical analysis. Our results also show the delays are 'profitless'. In this paper, the main feature is to introduce two discrete time delays, vertical transmission and impulse into SEIRS epidemic model and to give pulse vaccination strategies.
Teaching the Mixed Model Design: A Flowchart to Facilitate Understanding.
Mills, Jamie D.
2005-01-01
The Mixed Model (MM) design, sometimes known as a Split-Plot design, is very popular in educational research. This model can be used to examine the effects of several independent variables on a dependent variable and it offers a more powerful alternative to the completely randomized design. The MM design considers both a between-subjects factor,…
Papadopoulos, Chris; Tabatabai, Habib; Buechel, Craig
2005-05-01
Tuned Liquid Dampers (TLD) are used to limit horizontal vibrations in structures, and offer practical alternatives to Tuned Mass Dampers (TMD). However, to our knowledge, liquid damping systems have not been developed to reduce vertical vibrations. In this work, we develop a model for a Vertical Motion Liquid Damper (VMLD), idealized as a discrete, two degree of freedom system. One degree of freedom represents the 'target' structure that is to be damped, and the other represents the approximate, one-dimensional motion of a liquid in a U-shaped tube. Internal losses due to the fluid oscillation serve to limit and control motions of the target structure. The U-shaped tube has a flexible joint such that one vertical portion and the horizontal portion of the tube remain fixed, and the remaining vertical portion of the tube is affixed to the vibrating structure, allowing the liquid to become excited. The equations of motion are derived using Lagrange's Equations, and are integrated using Runge-Kutta algorithms that are available in Matlab. An experimental model was built in the laboratory, consisting of a mass attached to the end of a cantilevered beam (corresponding to the target structure), and a U-tube made from PVC pipe. The various damping and stiffness parameters of the system were calibrated independently based on experimental data. Measured data from the experimental model show reasonable agreement with numerical simulations.
Underwater glider observations and modeling of an abrupt mixing event in the upper ocean
Ruiz, S.; Renault, L.; Garau, B.; Tintoré, J.
2012-04-01
An abrupt mixing event in the upper ocean is investigated in the Northwestern Mediterranean Sea using gliders, a new ocean monitoring technology, combined with regional atmospheric model outputs and mooring data. Intense winds (up to 20 m s-1) and buoyancy forcing during December 2009 induced strong vertical mixing of the upper ocean layer in the Balearic Sea. High-resolution data from a coastal glider reveal a surface cooling of near 2 ° C and the deepening of the Mixed Layer Depth (MLD) by more than 40 meters in the center of the basin. Comparisons between glider and ship-emulated sections of hydrographic profiles show that the glider data make visible the small-scale spatial variability of the MLD. The heat content released to the atmosphere by the upper ocean during this mixing event exceeds 1000 W m-2. A simulation from the Weather Research and Forecasting model reports values consistent with these observations. Additionally the atmospheric numerical simulation shows the development and evolution of a cyclone located south of the Balearic Islands. This cyclone is likely to be responsible for the wind intensification and the consequent air-sea energy exchanges that occurred in the study area during this period.
Fluid mixing in stratified gravity currents: the Prandtl mixing length.
Odier, P; Chen, J; Rivera, M K; Ecke, R E
2009-04-03
Shear-induced vertical mixing in a stratified flow is a key ingredient of thermohaline circulation. We experimentally determine the vertical flux of momentum and density of a forced gravity current using high-resolution velocity and density measurements. A constant eddy-viscosity model provides a poor description of the physics of mixing, but a Prandtl mixing length model relating momentum and density fluxes to mean velocity and density gradients works well. For the average gradient Richardson number Ri(g) approximately 0.08 and a Taylor Reynolds number Re(lambda) approximately 100, the mixing lengths are fairly constant, about the same magnitude, comparable to the turbulent shear length.
Mathematical modelling of mixing in gas stirred ladles
International Nuclear Information System (INIS)
Ramirez-Argaez, M. A.; Tapia, J.; Espinoza, J.; Alcantar, E.
2006-01-01
In this work injection of air into a water physical model of an industrial steel ladle was mathematically simulated. Calculations were developed based on a multiphase Eulerian fluid flow model involving principles of conservation of mass, momentum and chemical species on both phases in order to predict turbulent flow patterns and mixing times in both centric and eccentric injections. Mixing phenomena was addressed by injecting a tracer centric and eccentric injections. Mixing phenomena was addressed by injecting a tracer and it was analyzed the effect of the gas flow rate, injector position, number of injectors and geometry of the ladle on the mixing time. It was concluded that the optimum injection conditions is using a single injector at 2/3 of the radius with high gas flow rates. It is shown that incrementing the number of injectors is detrimental on mixing. Finally, quantitative correlations of mixing time as a function of gas flow rate, position of the injectors, geometry of the ladle and mass of liquid were obtained. (Author)
The salinity effect in a mixed layer ocean model
Miller, J. R.
1976-01-01
A model of the thermally mixed layer in the upper ocean as developed by Kraus and Turner and extended by Denman is further extended to investigate the effects of salinity. In the tropical and subtropical Atlantic Ocean rapid increases in salinity occur at the bottom of a uniformly mixed surface layer. The most significant effects produced by the inclusion of salinity are the reduction of the deepening rate and the corresponding change in the heating characteristics of the mixed layer. If the net surface heating is positive, but small, salinity effects must be included to determine whether the mixed layer temperature will increase or decrease. Precipitation over tropical oceans leads to the development of a shallow stable layer accompanied by a decrease in the temperature and salinity at the sea surface.
Modeling and Analysis of Mixed Synchronous/Asynchronous Systems
Driscoll, Kevin R.; Madl. Gabor; Hall, Brendan
2012-01-01
Practical safety-critical distributed systems must integrate safety critical and non-critical data in a common platform. Safety critical systems almost always consist of isochronous components that have synchronous or asynchronous interface with other components. Many of these systems also support a mix of synchronous and asynchronous interfaces. This report presents a study on the modeling and analysis of asynchronous, synchronous, and mixed synchronous/asynchronous systems. We build on the SAE Architecture Analysis and Design Language (AADL) to capture architectures for analysis. We present preliminary work targeted to capture mixed low- and high-criticality data, as well as real-time properties in a common Model of Computation (MoC). An abstract, but representative, test specimen system was created as the system to be modeled.
Mixed waste treatment model: Basis and analysis
International Nuclear Information System (INIS)
Palmer, B.A.
1995-09-01
The Department of Energy's Programmatic Environmental Impact Statement (PEIS) required treatment system capacities for risk and cost calculation. Los Alamos was tasked with providing these capacities to the PEIS team. This involved understanding the Department of Energy (DOE) Complex waste, making the necessary changes to correct for problems, categorizing the waste for treatment, and determining the treatment system requirements. The treatment system requirements depended on the incoming waste, which varied for each PEIS case. The treatment system requirements also depended on the type of treatment that was desired. Because different groups contributing to the PEIS needed specific types of results, we provided the treatment system requirements in a variety of forms. In total, some 40 data files were created for the TRU cases, and for the MLLW case, there were 105 separate data files. Each data file represents one treatment case consisting of the selected waste from various sites, a selected treatment system, and the reporting requirements for such a case. The treatment system requirements in their most basic form are the treatment process rates for unit operations in the desired treatment system, based on a 10-year working life and 20-year accumulation of the waste. These results were reported in cubic meters and for the MLLW case, in kilograms as well. The treatment system model consisted of unit operations that are linked together. Each unit operation's function depended on the input waste streams, waste matrix, and contaminants. Each unit operation outputs one or more waste streams whose matrix, contaminants, and volume/mass may have changed as a result of the treatment. These output streams are then routed to the appropriate unit operation for additional treatment until the output waste stream meets the treatment requirements for disposal. The total waste for each unit operation was calculated as well as the waste for each matrix treated by the unit
Directory of Open Access Journals (Sweden)
Nanying Shentu
2014-08-01
Full Text Available Due to invisibility and complexity of the underground displacement monitoring, there exit few practical monitoring sensors capable of monitoring the underground horizontal and vertical displacements simultaneously. A novel electromagnetic underground displacement sensor able to monitor both the horizontal and the vertical displacements was proposed in our previous studies and abbreviated as the H-V type sensor. Through comprehensive application of Hall sensing mechanism analysis, 3D magnetic field distribution solution to the permanent magnet, and multidimensional numerical integration method, a model called the Equivalent Magnetic Charge-Numerical Integration Model (EMC-NI is presented in this paper and serves as the H-V type sensor’s Hall voltage measurement model. This model can quantitatively evaluate the complicated relationship among the sensor’s Hall voltage output, its measuring parameters (underground horizontal displacement, vertical displacement and tilt angle at different depth within the monitored soil rock mass and morphological parameters (geometry, shape and property parameters for the sensor units. Comprehensive studies and comparisons have conducted between the experimentally measured and EMC-NI modeled Hall voltage under counterpart conditions, through which not only the model’s modeling effectiveness and calculation accuracy are objectively evaluated, but also some valuable theoretical support is provided for the sensor’ sensing properties evaluation, design optimization, and subsequent study of displacement parameter inversion approach.
Three-dimensional modelling of leachate recirculation using vertical wells in bioreactor landfills.
Feng, Shi-Jin; Chen, Zheng-Wei; Cao, Ben-Yi
2016-12-01
Bioreactor landfills use leachate recirculation to enhance the biodegradation of municipal solid waste and accelerate landfill stabilisation, which can provide significant environmental and economic benefits. Vertical wells are operated as a major method for leachate recirculation systems. The objectives of this article are to analyse the leachate migration in bioreactor landfills using vertical wells and to offer theoretical basis for the design of leachate recirculation systems. A three-dimensional numerical model was built using FLAC-3D, and this model can consider the saturated and unsaturated flow of leachate within anisotropic waste to reflect the actual conditions. First, main influence factors of leachate migration were analysed, including the vertical well height, hydraulic conductivity, and anisotropic coefficient, in a single-well recirculation system. Then, the effects of different configurations of a group-well system were studied and the optimal well spacing was obtained. Some key design parameters (e.g. the recirculation flow rate, volume of impact zone, radius of impact zone and time to reach steady state) were also evaluated. The results show that the hydraulic conductivity has a great impact on the optimal height of vertical wells and uniform configuration is the best option in terms of both volume of impact zone and time to reach steady state. © The Author(s) 2016.
Computer modeling of ORNL storage tank sludge mobilization and mixing
Energy Technology Data Exchange (ETDEWEB)
Terrones, G.; Eyler, L.L.
1993-09-01
This report presents and analyzes the results of the computer modeling of mixing and mobilization of sludge in horizontal, cylindrical storage tanks using submerged liquid jets. The computer modeling uses the TEMPEST computational fluid dynamics computer program. The horizontal, cylindrical storage tank configuration is similar to the Melton Valley Storage Tanks (MVST) at Oak Ridge National (ORNL). The MVST tank contents exhibit non-homogeneous, non-Newtonian rheology characteristics. The eventual goals of the simulations are to determine under what conditions sludge mobilization using submerged liquid jets is feasible in tanks of this configuration, and to estimate mixing times required to approach homogeneity of the contents of the tanks.
Computer modeling of ORNL storage tank sludge mobilization and mixing
International Nuclear Information System (INIS)
Terrones, G.; Eyler, L.L.
1993-09-01
This report presents and analyzes the results of the computer modeling of mixing and mobilization of sludge in horizontal, cylindrical storage tanks using submerged liquid jets. The computer modeling uses the TEMPEST computational fluid dynamics computer program. The horizontal, cylindrical storage tank configuration is similar to the Melton Valley Storage Tanks (MVST) at Oak Ridge National (ORNL). The MVST tank contents exhibit non-homogeneous, non-Newtonian rheology characteristics. The eventual goals of the simulations are to determine under what conditions sludge mobilization using submerged liquid jets is feasible in tanks of this configuration, and to estimate mixing times required to approach homogeneity of the contents of the tanks
Ott, Lesley E.
2010-02-18
A three-dimensional (3-D) cloud-scale chemical transport model that includes a parameterized source of lightning NOx on the basis of observed flash rates has been used to simulate six midlatitude and subtropical thunderstorms observed during four field projects. Production per intracloud (PIC) and cloud-to-ground (PCG) flash is estimated by assuming various values of PIC and PCG for each storm and determining which production scenario yields NOx mixing ratios that compare most favorably with in-cloud aircraft observations. We obtain a mean PCG value of 500 moles NO (7 kg N) per flash. The results of this analysis also suggest that on average, PIC may be nearly equal to PCG, which is contrary to the common assumption that intracloud flashes are significantly less productive of NO than are cloud-to-ground flashes. This study also presents vertical profiles of the mass of lightning NOx after convection based on 3-D cloud-scale model simulations. The results suggest that following convection, a large percentage of lightning NOx remains in the middle and upper troposphere where it originated, while only a small percentage is found near the surface. The results of this work differ from profiles calculated from 2-D cloud-scale model simulations with a simpler lightning parameterization that were peaked near the surface and in the upper troposphere (referred to as a “C-shaped” profile). The new model results (a backward C-shaped profile) suggest that chemical transport models that assume a C-shaped vertical profile of lightning NOx mass may place too much mass near the surface and too little in the middle troposphere.
Advective mixing in a nondivergent barotropic hurricane model
Directory of Open Access Journals (Sweden)
B. Rutherford
2010-01-01
Full Text Available This paper studies Lagrangian mixing in a two-dimensional barotropic model for hurricane-like vortices. Since such flows show high shearing in the radial direction, particle separation across shear-lines is diagnosed through a Lagrangian field, referred to as R-field, that measures trajectory separation orthogonal to the Lagrangian velocity. The shear-lines are identified with the level-contours of another Lagrangian field, referred to as S-field, that measures the average shear-strength along a trajectory. Other fields used for model diagnostics are the Lagrangian field of finite-time Lyapunov exponents (FTLE-field, the Eulerian Q-field, and the angular velocity field. Because of the high shearing, the FTLE-field is not a suitable indicator for advective mixing, and in particular does not exhibit ridges marking the location of finite-time stable and unstable manifolds. The FTLE-field is similar in structure to the radial derivative of the angular velocity. In contrast, persisting ridges and valleys can be clearly recognized in the R-field, and their propagation speed indicates that transport across shear-lines is caused by Rossby waves. A radial mixing rate derived from the R-field gives a time-dependent measure of flux across the shear-lines. On the other hand, a measured mixing rate across the shear-lines, which counts trajectory crossings, confirms the results from the R-field mixing rate, and shows high mixing in the eyewall region after the formation of a polygonal eyewall, which continues until the vortex breaks down. The location of the R-field ridges elucidates the role of radial mixing for the interaction and breakdown of the mesovortices shown by the model.
Numerical modeling and preliminary validation of drag-based vertical axis wind turbine
Directory of Open Access Journals (Sweden)
Krysiński Tomasz
2015-03-01
Full Text Available The main purpose of this article is to verify and validate the mathematical description of the airflow around a wind turbine with vertical axis of rotation, which could be considered as representative for this type of devices. Mathematical modeling of the airflow around wind turbines in particular those with the vertical axis is a problematic matter due to the complex nature of this highly swirled flow. Moreover, it is turbulent flow accompanied by a rotation of the rotor and the dynamic boundary layer separation. In such conditions, the key aspects of the mathematical model are accurate turbulence description, definition of circular motion as well as accompanying effects like centrifugal force or the Coriolis force and parameters of spatial and temporal discretization. The paper presents the impact of the different simulation parameters on the obtained results of the wind turbine simulation. Analysed models have been validated against experimental data published in the literature.
Development and Evaluation of an Aerodynamic Model for a Novel Vertical Axis Wind Turbine Concept
Directory of Open Access Journals (Sweden)
Andrew Shires
2013-05-01
Full Text Available There has been a resurgence of interest in the development of vertical axis wind turbines which have several inherent attributes that offer some advantages for offshore operations, particularly their scalability and low over-turning moments with better accessibility to drivetrain components. This paper describes an aerodynamic performance model for vertical axis wind turbines specifically developed for the design of a novel offshore V-shaped rotor with multiple aerodynamic surfaces. The model is based on the Double-Multiple Streamtube method and includes a number of developments for alternative complex rotor shapes. The paper compares predicted results with measured field data for five different turbines with both curved and straight blades and rated powers in the range 100–500 kW. Based on these comparisons, the paper proposes modifications to the Gormont dynamic stall model that gives improved predictions of rotor power for the turbines considered.
Directory of Open Access Journals (Sweden)
Pau Baya
2011-05-01
Full Text Available Remenat (Catalan (Mixed, "revoltillo" (Scrambled in Spanish, is a dish which, in Catalunya, consists of a beaten egg cooked with vegetables or other ingredients, normally prawns or asparagus. It is delicious. Scrambled refers to the action of mixing the beaten egg with other ingredients in a pan, normally using a wooden spoon Thought is frequently an amalgam of past ideas put through a spinner and rhythmically shaken around like a cocktail until a uniform and dense paste is made. This malleable product, rather like a cake mixture can be deformed pulling it out, rolling it around, adapting its shape to the commands of one’s hands or the tool which is being used on it. In the piece Mixed, the contortion of the wood seeks to reproduce the plasticity of this slow heavy movement. Each piece lays itself on the next piece consecutively like a tongue of incandescent lava slowly advancing but with unstoppable inertia.
Energy Technology Data Exchange (ETDEWEB)
Allanach, B.C. [University of Cambridge, Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, Cambridge (United Kingdom); Badziak, Marcin [University of Warsaw, Institute of Theoretical Physics, Faculty of Physics, Warsaw (Poland); University of California, Department of Physics, Berkeley, CA (United States); University of California, Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA (United States); Cottin, Giovanna [University of Cambridge, Cavendish Laboratory, Cambridge (United Kingdom); Desai, Nishita [Institut fuer Theoretische Physik, Heidelberg (Germany); Hugonie, Cyril [LUPM, UMR 5299, CNRS, Universite de Montpellier, Montpellier (France); Ziegler, Robert [Sorbonne Universites, UPMC Univ Paris 06, UMR 7589, LPTHE, Paris (France); CNRS, UMR 7589, LPTHE, Paris (France)
2016-09-15
We study the LHC phenomenology of the next-to-minimal model of gauge-mediated supersymmetry breaking, both for Run I and Run II. The Higgs phenomenology of the model is consistent with observations: a 125 GeV standard model-like Higgs which mixes with singlet-like state of mass around 90 GeV that provides a 2σ excess at LEP II. The model possesses regions of parameter space where a longer-lived lightest neutralino decays in the detector into a gravitino and a b-jet pair or a tau pair resulting in potential displaced vertex signatures. We investigate current bounds on sparticle masses and the discovery potential of the model, both via conventional searches and via searches for displaced vertices. The searches based on promptly decaying sparticles currently give a lower limit on the gluino mass 1080 GeV and could be sensitive up to 1900 GeV with 100 fb{sup -1}, whereas the current displaced vertex searches cannot probe this model due to b-quarks in the final state. We show how the displaced vertex cuts might be relaxed in order to improve signal efficiency, while simultaneously applied prompt cuts reduce background, resulting in a much better sensitivity than either strategy alone and motivating a fully fledged experimental study. (orig.)
International Nuclear Information System (INIS)
Hernando, Marcelo P.; Ferreyra, Gustavo A.
2004-01-01
Full text: The reduction of the Antarctic stratospheric ozone resulted in significant increases in ultraviolet B radiation (UVBR, 280-320 nm) reaching the surface of the ocean. A series of laboratory and field experiments were conducted at Potter Cove (25 de Mayo Is., South Shetland Is., Antarctica) to study the effects of UVBR on photosynthesis of a typical Antarctic bloom forming diatom (Thalassiosira sp.) in fixed and moving incubations. There were three irradiance treatments: PART (with only photosynthetic active radiation, PAR, 400- 700 nm), UVAT (with PAR and ultraviolet A radiation, UVAR, 320-400 nm) and UVBT (with PAR, UVAR and UVBR). The three treatments were incubated in the field and laboratory with a solar simulator (SOLSI) in fixed frames at 0.5 and 5 m depth (S fix and B fix , respectively), while for the moving incubations were done within 6 h cycles (Mix). Considering the field and laboratory pooled data, results suggest an overall 45-50 % photosynthesis inhibition of S fix incubations in relation with Mix ones. During SOLSI experiments no significant differences were found between irradiance treatments under normal and medium ozone concentrations. Under low ozone conditions, a 40 % reduction in photosynthesis was observed in the UVBT for S fix . In contrast, no significant differences were observed between the irradiance treatments for Mix. Field experiment showed results similar to the laboratory ones, but in this case not only S fix but Mix incubations presented a significant reduction in photosynthesis under low ozone. The differences between laboratory and field experiments are discussed in terms of the relative significance of UVBR dose and dose rate on both types of experiments. (author)
Durán, C.; Medina-Sánchez, J. M.; Herrera, G.; Villar-Argaiz, M.; Villafañe, V. E.; Helbling, E. W.; Carrillo, P.
2014-05-01
As a consequence of global change, modifications in the interaction among abiotic stressors on aquatic ecosystems have been predicted. Among other factors, UVR transparency, nutrient inputs and shallower epilimnetic layers could alter the trophic links in the microbial food web. Currently, there are some evidences of higher sensitiveness of aquatic microbial organisms to UVR in opaque lakes. Our aim was to assess the interactive direct and indirect effects of UVR (through the excretion of organic carbon - EOC - by algae), mixing regime and nutrient input on bacterial metabolism. We performed in situ short-term experiments under the following treatments: full sunlight (UVR + PAR, >280 nm) vs. UVR exclusion (PAR only, >400 nm); ambient vs. nutrient addition (phosphorus (P; 30 μg PL-1) and nitrogen (N; up to final N : P molar ratio of 31)); and static vs. mixed regime. The experiments were conducted in three high-mountain lakes of Spain: Enol [LE], Las Yeguas [LY] and La Caldera [LC] which had contrasting UVR transparency characteristics (opaque (LE) vs. clear lakes (LY and LC)). Under ambient nutrient conditions and static regimes, UVR exerted a stimulatory effect on heterotrophic bacterial production (HBP) in the opaque lake but not in the clear ones. Under UVR, vertical mixing and nutrient addition HBP values were lower than under the static and ambient nutrient conditions, and the stimulatory effect that UVR exerted on HBP in the opaque lake disappeared. By contrast, vertical mixing and nutrient addition increased HBP values in the clear lakes, highlighting for a photoinhibitory effect of UVR on HBP. Mixed regime and nutrient addition resulted in negative effects of UVR on HBP more in the opaque than in the clear lakes. Moreover, in the opaque lake, bacterial respiration (BR) increased and EOC did not support the bacterial carbon demand (BCD). In contrast, bacterial metabolic costs did not increase in the clear lakes and the increased nutrient availability even
Hydrodynamic and diffusive mixing in ICF implosion modeling
Ames, Alexander; Weber, Chris; Cook, Andy
2017-11-01
Inertial confinement fusion requires efficient spherical compression of a deuterium-tritium gas mixture by a shock-driven implosion. The performance of the implosion is limited by several phenomena, including differential acceleration of deuterium and tritium ions, and mixing due to the Richtmyer-Meshkov and Rayleigh-Taylor instabilities. The MIRANDA radiation hydrodynamics code at LLNL has recently incorporated multi-species diffusion and multi-group radiation transport models. This enables modeling of the impact of diffusive mixing on the fuel, as well as investigation of ablative Rayleigh-Taylor instability growth and resultant hydrodynamic mixing using single-group and multiple-group radiation drives. Work performed under the auspices of the U.S. D.O.E. by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344.
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
Brughelli, Matt; Cronin, John
2008-01-01
Human running can be modelled as either a spring-mass model or multiple springs in series. A force is required to stretch or compress the spring, and thus stiffness, the variable of interest in this paper, can be calculated from the ratio of this force to the change in spring length. Given the link between force and length change, muscle stiffness and mechanical stiffness have been areas of interest to researchers, clinicians, and strength and conditioning practitioners for many years. This review focuses on mechanical stiffness, and in particular, vertical, leg and joint stiffness, since these are the only stiffness types that have been directly calculated during human running. It has been established that as running velocity increases from slow-to-moderate values, leg stiffness remains constant while both vertical stiffness and joint stiffness increase. However, no studies have calculated vertical, leg or joint stiffness over a range of slow-to-moderate values to maximum values in an athletic population. Therefore, the effects of faster running velocities on stiffness are relatively unexplored. Furthermore, no experimental research has examined the effects of training on vertical, leg or joint stiffness and the subsequent effects on running performance. Various methods of training (Olympic style weightlifting, heavy resistance training, plyometrics, eccentric strength training) have shown to be effective at improving running performance. However, the effects of these training methods on vertical, leg and joint stiffness are unknown. As a result, the true importance of stiffness to running performance remains unexplored, and the best practice for changing stiffness to optimize running performance is speculative at best. It is our hope that a better understanding of stiffness, and the influence of running speed on stiffness, will lead to greater interest and an increase in experimental research in this area.
Asgharzadeh, M. F.; Hashemi, H.; von Frese, R. RB
2018-01-01
Forward modeling is the basis of gravitational anomaly inversion that is widely applied to map subsurface mass variations. This study uses numerical least-squares Gauss-Legendre quadrature (GLQ) integration to evaluate the gravitational potential, anomaly and gradient components of the vertical cylindrical prism element. These results, in turn, may be integrated to accurately model the complete gravitational effects of fluid bearing rock formations and other vertical cylinder-like geological bodies with arbitrary variations in shape and density. Comparing the GLQ gravitational effects of uniform density, vertical circular cylinders against the effects calculated by a number of other methods illustrates the veracity of the GLQ modeling method and the accuracy limitations of the other methods. Geological examples include modeling the gravitational effects of a formation washout to help map azimuthal variations of the formation's bulk densities around the borehole wall. As another application, the gravitational effects of a seismically and gravimetrically imaged salt dome within the Laurentian Basin are evaluated for the velocity, density and geometric properties of the Basin's sedimentary formations.
Delta-tilde interpretation of standard linear mixed model results
DEFF Research Database (Denmark)
Brockhoff, Per Bruun; Amorim, Isabel de Sousa; Kuznetsova, Alexandra
2016-01-01
data set and compared to actual d-prime calculations based on Thurstonian regression modeling through the ordinal package. For more challenging cases we offer a generic "plug-in" implementation of a version of the method as part of the R-package SensMixed. We discuss and clarify the bias mechanisms...
The 4s web-marketing mix model
Constantinides, Efthymios
2002-01-01
This paper reviews the criticism on the 4Ps Marketing Mix framework, the most popular tool of traditional marketing management, and categorizes the main objections of using the model as the foundation of physical marketing. It argues that applying the traditional approach, based on the 4Ps paradigm,
Sensitivity Analysis of Mixed Models for Incomplete Longitudinal Data
Xu, Shu; Blozis, Shelley A.
2011-01-01
Mixed models are used for the analysis of data measured over time to study population-level change and individual differences in change characteristics. Linear and nonlinear functions may be used to describe a longitudinal response, individuals need not be observed at the same time points, and missing data, assumed to be missing at random (MAR),…
Multivariate Survival Mixed Models for Genetic Analysis of Longevity Traits
DEFF Research Database (Denmark)
Pimentel Maia, Rafael; Madsen, Per; Labouriau, Rodrigo
2014-01-01
A class of multivariate mixed survival models for continuous and discrete time with a complex covariance structure is introduced in a context of quantitative genetic applications. The methods introduced can be used in many applications in quantitative genetics although the discussion presented co...
Metabolic modeling of mixed substrate uptake for polyhydroxyalkanoate (PHA) production
Jiang, Y.; Hebly, M.; Kleerebezem, R.; Muyzer, G.; van Loosdrecht, M.C.M.
2011-01-01
Polyhydroxyalkanoate (PHA) production by mixed microbial communities can be established in a two-stage process, consisting of a microbial enrichment step and a PHA accumulation step. In this study, a mathematical model was constructed for evaluating the influence of the carbon substrate composition
Identification of Mixed Causal-Noncausal Models in Finite Samples
Hecq, Alain; Lieb, Lenard; Telg, Sean
2016-01-01
Gouriéroux and Zakoïan (2013) propose to use noncausal models to parsimoniously capture nonlinear features often observed in financial time series and in particular bubble phenomena. In order to distinguish causal autoregressive processes from purely noncausal or mixed causal-noncausal ones, one has
Confidence Intervals for Assessing Heterogeneity in Generalized Linear Mixed Models
Wagler, Amy E.
2014-01-01
Generalized linear mixed models are frequently applied to data with clustered categorical outcomes. The effect of clustering on the response is often difficult to practically assess partly because it is reported on a scale on which comparisons with regression parameters are difficult to make. This article proposes confidence intervals for…
ON THE ESTIMATION AND PREDICTION IN MIXED LINEAR MODELS
Directory of Open Access Journals (Sweden)
LÓPEZ L.A.
1998-01-01
Full Text Available Beginning with the classical Gauss-Markov Linear Model for mixed effects and using the technique of the Lagrange multipliers to obtain an alternative method for the estimation of linear predictors. A structural method is also discussed in order to obtain the variance and covariance matrixes and their inverses.
COMBINING SOURCES IN STABLE ISOTOPE MIXING MODELS: ALTERNATIVE METHODS
Stable isotope mixing models are often used to quantify source contributions to a mixture. Examples include pollution source identification; trophic web studies; analysis of water sources for soils, plants, or water bodies; and many others. A common problem is having too many s...
Mathematically modelling the power requirement for a vertical shaft mowing machine
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Jorge Simón Pérez de Corcho Fuentes
2008-09-01
Full Text Available This work describes a mathematical model for determining the power demand for a vertical shaft mowing machine, particularly taking into account the influence of speed on cutting power, which is different from that of other models of mowers. The influence of the apparatus’ rotation and translation speeds was simulated in determining power demand. The results showed that no chan-ges in cutting power were produced by varying the knives’ angular speed (if translation speed was constant, while cutting power became increased if translation speed was increased. Variations in angular speed, however, influenced other parameters deter-mining total power demand. Determining this vertical shaft mower’s cutting pattern led to obtaining good crop stubble quality at the mower’s lower rotation speed, hence reducing total energy requirements.
Directory of Open Access Journals (Sweden)
Wang Ruifei
2017-12-01
Full Text Available The mathematical model of coupled flow and geomechanics for a vertical fractured well in tight gas reservoirs was established. The analytical modeling of unidirectional flow and radial flow was achieved by Laplace transforms and integral transforms. The results show that uncoupled flow would lead to an overestimate in performance of a vertical fractured well, especially in the later stage. The production rate decreases with elastic modulus because porosity and permeability decrease accordingly. Drawdown pressure should be optimized to lower the impact of coupled flow and geomechanics as a result of permeability decreasing. Production rate increases with fracture half-length significantly in the initial stage and becomes stable gradually. This study could provide a theoretical basis for effective development of tight gas reservoirs.
Wang, Ruifei; Gao, Xuhua; Song, Hongqing; Shang, Xinchun
2017-12-01
The mathematical model of coupled flow and geomechanics for a vertical fractured well in tight gas reservoirs was established. The analytical modeling of unidirectional flow and radial flow was achieved by Laplace transforms and integral transforms. The results show that uncoupled flow would lead to an overestimate in performance of a vertical fractured well, especially in the later stage. The production rate decreases with elastic modulus because porosity and permeability decrease accordingly. Drawdown pressure should be optimized to lower the impact of coupled flow and geomechanics as a result of permeability decreasing. Production rate increases with fracture half-length significantly in the initial stage and becomes stable gradually. This study could provide a theoretical basis for effective development of tight gas reservoirs.
DEFF Research Database (Denmark)
Nielsen, Jørgen Ulff-Møller; Hansen, Jørgen Drud
This paper examines the effects of trade barriers on quality levels in a duopoly model for two countries with one producer in each country. The products are both vertically and horizontally differentiated. In absence of quality regulation, the two producers determine prices and quality levels...... product. On the unregulated markets, integration increases welfare in both countries if they are almost of similar size. However, if the countries are very asymmetrical with respect to size, market integration may harm welfare in the large country. Welfare effects by introduction of minimum quality...... standards are also ambiguous depending on the parameters of the model. Keywords: Vertical product differentiation; horizontal product differentiation; market integration; duopoly; minimum quality standard. JEL: F12, F13, F14....
Mathematical modelling of thermal and flow processes in vertical ground heat exchangers
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Pater Sebastian
2017-12-01
Full Text Available The main task of mathematical modelling of thermal and flow processes in vertical ground heat exchanger (BHE-Borehole Heat Exchanger is to determine the unit of borehole depth heat flux obtainable or transferred during the operation of the installation. This assignment is indirectly associated with finding the circulating fluid temperature flowing out from the U-tube at a given inlet temperature of fluid in respect to other operational parameters of the installation.
Analysis of a general age-dependent vaccination model for a vertically transmitted disease
International Nuclear Information System (INIS)
El Doma, M.
1995-05-01
A SIR epidemic model of a general age-dependent vaccination for a vertically as well as horizontally transmitted disease is investigated when the total population is time dependent, and fertility, mortality and removal rates depend on age. We establish the existence and the uniqueness of the solution and obtain the asymptotic behaviour for the solution. For the steady state solution a critical vaccination coverage which will eventually eradicate the disease is determined. (author). 18 refs
Experimental Study of a Reference Model Vertical-Axis Cross-Flow Turbine
Bachant, Peter; Wosnik, Martin; Gunawan, Budi; Neary, Vincent S.
2016-01-01
The mechanical power, total rotor drag, and near-wake velocity of a 1:6 scale model (1.075 m diameter) of the US Department of Energy?s Reference Model vertical-axis cross-flow turbine were measured experimentally in a towing tank, to provide a comprehensive open dataset for validating numerical models. Performance was measured for a range of tip speed ratios and at multiple Reynolds numbers by varying the rotor?s angular velocity and tow carriage speed, respectively. A peak power coefficient...
A Co-Opetitive Automated Negotiation Model for Vertical Allied Enterprises Teams and Stakeholders
Directory of Open Access Journals (Sweden)
Taiguang Gao
2018-04-01
Full Text Available Upstream and downstream of supply chain enterprises often form a tactic vertical alliance to enhance their operational efficiency and maintain their competitive edges in the market. Hence, it is critical for an alliance to collaborate over their internal resources and resolve the profit conflicts among members, so that the functionality required by stakeholders can be fulfilled. As an effective solution, automated negotiation for the vertical allied enterprises team and stakeholder will sufficiently make use of emerging team advantages and significantly reduce the profit conflicts in teams with grouping decisions rather than unilateral decisions by some leader. In this paper, an automated negotiation model is designed to describe both the collaborative game process among the team members and the competitive negotiation process between the allied team and the stakeholder. Considering the co-competitiveness of the vertical allied team, the designed model helps the team members making decision for their own sake, and the team counter-offers for the ongoing negotiation are generated with non-cooperative game process, where the profit derived from negotiation result is distributed with Shapley value method according to contribution or importance contributed by each team member. Finally, a case study is given to testify the effectiveness of the designed model.
Modelling the relationship between water level and vertical displacements on the Yamula Dam, Turkey
Directory of Open Access Journals (Sweden)
T. Bayrak
2007-01-01
Full Text Available Monitoring deformation pattern of dams is often one of the most effective ways to understand their safety status. The main objective of the study is to find the extent to which rising reservoir level affects the mechanism of deformation of The Yamula Dam under certain change in the reservoir level conditions during to the first filling period. Three different deformation analysis techniques, namely static, kinematic and dynamic, were used to analyze four geodetic monitoring records consisting of vertical displacements of nine object points established on the Dam and six reference points surrounding of it, to see whether the rising reservoir level have a role in the vertical deformations during the first filling period. The largest vertical displacements were in the middle of the dam. There is an apparent linear relationship between the dam subsidence and the reservoir level. A dynamic deformation model was developed to model this situation. The model infers a causative relationship between the reservoir level and the dam deformations. The analysis of the results determines the degree of the correlation between the change in the reservoir level and the observed structural deformation of the dam.
The Functional Model Approach to the Consulting for Vertically - Integrated Construction Group
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Pimenova Anna
2016-01-01
Full Text Available Managerial decision making in the framework of functional modeling of the consulting process have a direct effect on other business - processes of vertically - integrated group of construction companies. As a result, the experience of consulting companies tends to be used for the making managerial solutions. Consultancy is known as one of the most complicated types of buisiness process. It requires a huge and deep examines and researches of targeting area, therefore need to be provided with special methodology, included internal standards of the consulting companies. Correct methodological support, planning process and implementation of managerial solutions should be based on the survey of the direct and inverse connections and interdependence of all group’s business – processes. Functional - process modeling of the vertically - integrated construction group could be considered as an instrument of examination and analysis of the issue how the managerial solution impact on the business-process for the construction group functioning. The main result of the research is the formalized process-oriented model – prototype of the business - processes of vertically - integrated group of construction companies.
Fluctuations in a mixed IS-LM business cycle model
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Hamad Talibi Alaoui
2008-09-01
Full Text Available In the present paper, we extend a delayed IS-LM business cycle model by introducing an additional advance (anticipated capital stock in the investment function. The resulting model is represented in terms of mixed differential equations. For the deviating argument $au$ (advance and delay being a bifurcation parameter we investigate the local stability and the local Hopf bifurcation. Also some numerical simulations are given to support the theoretical analysis.
Configuration mixing in the sdg interacting boson model
Energy Technology Data Exchange (ETDEWEB)
Bouldjedri, A [Department of Physics, Faculty of Science, University of Batna, Avenue Boukhelouf M El Hadi, 05000 Batna (Algeria); Van Isacker, P [GANIL, BP 55027, F-14076 Caen cedex 5 (France); Zerguine, S [Department of Physics, Faculty of Science, University of Batna, Avenue Boukhelouf M El Hadi, 05000 Batna (Algeria)
2005-11-01
A wavefunction analysis of the strong-coupling limits of the sdg interacting boson model is presented. The analysis is carried out for two-boson states and allows us to characterize the boson configuration mixing in the different limits. Based on these results and those of a shell-model analysis of the sdg IBM, qualitative conclusions are drawn about the range of applicability of each limit.
Directory of Open Access Journals (Sweden)
Paolo CORDELLA
2003-09-01
Full Text Available The identification of the factors and mechanisms determining a particular lake’s typology is crucial for the correct interpretation of trophic evolution. Nutrient concentrations are not the only properties which determine the trophic characteristics of lakes; others, such as morphometry, hydrology and climatic conditions, also have a major influence on the development of algal biomass and species composition. Large, deep lakes belong to a well defined typology. Their trophic status depends not only on algal nutrient loads, but also on the extent of the spring vertical mixing and renewal time. These factors are closely interrelated, for the actual renewal time approaches the theoretical renewal time only during the complete overturn. This paper compares the influence of different circulation patterns on the trophic status of two deep subalpine lakes with contrasting mixing characteristics. Lake Garda is the largest lake in Italy (S=368 km2, V=49 km3, Zmax=350 m. It is characterised by irregular circulation events (oligomixis; during the 1990s, complete homogenisation of the water column occurred in 1991 and 1999-2000. The years between these episodes showed an increase of hypolimnetic temperatures and a progressive vertical stratification of nutrients. Full overturn episodes were characterised by a sudden decrease of temperature and complete homogenisation of the chemical and physical variables along the water column, with a corresponding increase of nutrients and algal biomasses at the surface. In contrast, the last mixing involving the deepest waters in Lake Iseo (S= 60,9 km2, V=7,6 km3, Zmax=251 m occurred at the beginning of the 1980s, after which the reduced water renewal and the high trophic level resulted in a marked decrease in oxygen concentrations and in the establishment of conditions of anoxia during the 1990s. At present the lake is meromictic. In 1999 and 2000, when a complete overturn was observed in lakes Maggiore and Como as
Vorrath, Maria-Elena; Lahajnar, Niko; Fischer, Gerhard; Libuku, Viktor Miti; Schmidt, Martin; Emeis, Kay-Christian
2018-04-01
Marine particle fluxes from high productive coastal upwelling systems return upwelled CO2 and nutrients to the deep ocean and sediments and have a substantial impact on the global carbon cycle. This study examines relations between production regimes on the shelf and over the continental margin of the Benguela Upwelling System (BUS) in the SE Atlantic Ocean. Data of composition and timing of vertical particle flux come from sediment trap time series (deployed intermittently between 1988 and 2014) in the regions Walvis Ridge, Walvis Bay, Luederitz and Orange River. We compare their seasonal variability to modelled patterns of chlorophyll concentrations in a 3-D ecosystem model. Both modelled seasonal chlorophyll a standing stocks and sampled particle flux patterns are highly correspondent with a bimodal seasonal cycle offshore the BUS. The material in the particle flux in offshore traps is dominantly carbonate (40-70%), and flux peaks in offshore particle flux originate from two independent events: in austral autumn thermocline shoaling and vertical mixing are decoupled from coastal upwelling, while fluxes in spring coincide with the upwelling season, indicated by slightly elevated biogenic opal values at some locations. Coastal particle fluxes are characterized by a trimodal pattern and are dominated by biogenic opal (22-35%) and organic matter (30-60%). The distinct seasonality in observed fluxes on the shelf is caused by high variability in production, sinking behaviour, wind stress, and hydrodynamic processes. We speculate that global warming will increase ocean stratification and alter coastal upwelling, so that consequences for primary production and particle flux in the BUS are inevitable.
Bouma, Harmen W.; Goldengorin, Boris; Lagakos, S; Perlovsky, L; Jha, M; Covaci, B; Zaharim, A; Mastorakis, N
2009-01-01
In this paper a Boolean Linear Programming (BLP) model is presented for the single machine scheduling problem 1 vertical bar pmtn; p(j) = 2;r(j)vertical bar Sigma w(j)C(j). The problem is a special case of the open problem 1 vertical bar pmtn; p(j) = p; r(j)vertical bar Sigma wj(g)C(j). We show that
Eluru, Naveen; Chakour, Vincent; Chamberlain, Morgan; Miranda-Moreno, Luis F
2013-10-01
Vehicle operating speed measured on roadways is a critical component for a host of analysis in the transportation field including transportation safety, traffic flow modeling, roadway geometric design, vehicle emissions modeling, and road user route decisions. The current research effort contributes to the literature on examining vehicle speed on urban roads methodologically and substantively. In terms of methodology, we formulate a new econometric model framework for examining speed profiles. The proposed model is an ordered response formulation of a fractional split model. The ordered nature of the speed variable allows us to propose an ordered variant of the fractional split model in the literature. The proposed formulation allows us to model the proportion of vehicles traveling in each speed interval for the entire segment of roadway. We extend the model to allow the influence of exogenous variables to vary across the population. Further, we develop a panel mixed version of the fractional split model to account for the influence of site-specific unobserved effects. The paper contributes substantively by estimating the proposed model using a unique dataset from Montreal consisting of weekly speed data (collected in hourly intervals) for about 50 local roads and 70 arterial roads. We estimate separate models for local roads and arterial roads. The model estimation exercise considers a whole host of variables including geometric design attributes, roadway attributes, traffic characteristics and environmental factors. The model results highlight the role of various street characteristics including number of lanes, presence of parking, presence of sidewalks, vertical grade, and bicycle route on vehicle speed proportions. The results also highlight the presence of site-specific unobserved effects influencing the speed distribution. The parameters from the modeling exercise are validated using a hold-out sample not considered for model estimation. The results indicate
Energy Technology Data Exchange (ETDEWEB)
Maupu, V.; Laurence, D. [Electricite de France (EDF), 78 - Chatou (France). Lab. National d`Hydraulique; Boudjemadi, E.; Le Quere, P. [Centre National de la Recherche Scientifique (CNRS), 91 - Orsay (France)
1996-12-31
Natural turbulent convection in a differentially heated infinite vertical slot is computed with a mixed finite differences/Fourier code. At a Rayleigh number of 10{sup 5}, in the case without mean stratification, periodic perturbations from the laminar solution develop and transition to a fully turbulent flow occurs. From then on, a database of one-point statistics is presented: mean velocity and temperature, Reynolds stress components, turbulent heat fluxes and variance of temperature, but also budgets of second moment equations. This database is then used for testing of a second moment closure based on the Launder-Reece-Rodi model on an elliptic relaxation for near wall effects on pressure redistribution. This level of modelling is required by the presence of counter gradient fluxes, which cannot be accounted for eddy viscosity and eddy diffusivity assumptions. Furthermore, an algebraic third order moment closure was found necessary because of counter gradient turbulent transport terms which appear to mainly originate from the mean velocity and temperature gradient terms usually neglected in conventional transport models, such as the standard Daly-Harlow or Hanjalic-Launder models. (authors). 18 refs.
International Nuclear Information System (INIS)
Maupu, V.; Laurence, D.
1996-01-01
Natural turbulent convection in a differentially heated infinite vertical slot is computed with a mixed finite differences/Fourier code. At a Rayleigh number of 10 5 , in the case without mean stratification, periodic perturbations from the laminar solution develop and transition to a fully turbulent flow occurs. From then on, a database of one-point statistics is presented: mean velocity and temperature, Reynolds stress components, turbulent heat fluxes and variance of temperature, but also budgets of second moment equations. This database is then used for testing of a second moment closure based on the Launder-Reece-Rodi model on an elliptic relaxation for near wall effects on pressure redistribution. This level of modelling is required by the presence of counter gradient fluxes, which cannot be accounted for eddy viscosity and eddy diffusivity assumptions. Furthermore, an algebraic third order moment closure was found necessary because of counter gradient turbulent transport terms which appear to mainly originate from the mean velocity and temperature gradient terms usually neglected in conventional transport models, such as the standard Daly-Harlow or Hanjalic-Launder models. (authors)
Handbook of mixed membership models and their applications
Airoldi, Edoardo M; Erosheva, Elena A; Fienberg, Stephen E
2014-01-01
In response to scientific needs for more diverse and structured explanations of statistical data, researchers have discovered how to model individual data points as belonging to multiple groups. Handbook of Mixed Membership Models and Their Applications shows you how to use these flexible modeling tools to uncover hidden patterns in modern high-dimensional multivariate data. It explores the use of the models in various application settings, including survey data, population genetics, text analysis, image processing and annotation, and molecular biology.Through examples using real data sets, yo
Modelling the development of mixing height in near equatorial region
Energy Technology Data Exchange (ETDEWEB)
Samah, A.A. [Univ. of Malaya, Air Pollution Research Unit, Kuala Lumpur (Malaysia)
1997-10-01
Most current air pollution models were developed for mid-latitude conditions and as such many of the empirical parameters used were based on observations taken in the mid-latitude boundary layer which is physically different from that of the equatorial boundary layer. In the equatorial boundary layer the Coriolis parameter f is small or zero and moisture plays a more important role in the control of stability and the surface energy balance. Therefore air pollution models such as the OMLMULTI or the ADMS which were basically developed for mid-latitude conditions must be applied with some caution and would need some adaptation to properly simulate the properties of equatorial boundary layer. This work elucidates some of the problems of modelling the evolution of mixing height in the equatorial region. The mixing height estimates were compared with routine observations taken during a severe air pollution episodes in Malaysia. (au)
Directory of Open Access Journals (Sweden)
R. E. Sheehan
2004-09-01
Full Text Available UHF scintillation measurements of zonal ionospheric drifts have been conducted at Ancon, Peru since 1994 using antennas spaced in the magnetic east-west direction to cross-correlate geo-synchronous satellite signals. An empirical model of average drift over a wide range of Kp and solar flux conditions was constructed from successive two-dimensional fits of drift vs. the parameters and day of year. The model exhibits the typical local time trend of maximum eastward velocity in the early evening with a gradual decrease and reversal in the early morning hours. As expected, velocities at all hours increase with the solar flux and decrease with Kp activity. It was also found that vertical drifts could contribute to the variability of drift measurements to the east of Ancon at a low elevation angle. The vertical drift at the ionospheric intersection to the east can be estimated when combined with nearly overhead observations at Ancon or a similar spaced-antenna site at Antofagasta, Chile. Comparisons on five days with nearly simultaneous measurements of vertical drift by the Julia radar at Jicamarca, Peru show varying agreement with the spaced-antenna estimates. Statistical results from 1997 to 2001 generally agree with radar and satellite studies.
Numerical modeling of two-phase binary fluid mixing using mixed finite elements
Sun, Shuyu
2012-07-27
Diffusion coefficients of dense gases in liquids can be measured by considering two-phase binary nonequilibrium fluid mixing in a closed cell with a fixed volume. This process is based on convection and diffusion in each phase. Numerical simulation of the mixing often requires accurate algorithms. In this paper, we design two efficient numerical methods for simulating the mixing of two-phase binary fluids in one-dimensional, highly permeable media. Mathematical model for isothermal compositional two-phase flow in porous media is established based on Darcy\\'s law, material balance, local thermodynamic equilibrium for the phases, and diffusion across the phases. The time-lag and operator-splitting techniques are used to decompose each convection-diffusion equation into two steps: diffusion step and convection step. The Mixed finite element (MFE) method is used for diffusion equation because it can achieve a high-order and stable approximation of both the scalar variable and the diffusive fluxes across grid-cell interfaces. We employ the characteristic finite element method with moving mesh to track the liquid-gas interface. Based on the above schemes, we propose two methods: single-domain and two-domain methods. The main difference between two methods is that the two-domain method utilizes the assumption of sharp interface between two fluid phases, while the single-domain method allows fractional saturation level. Two-domain method treats the gas domain and the liquid domain separately. Because liquid-gas interface moves with time, the two-domain method needs work with a moving mesh. On the other hand, the single-domain method allows the use of a fixed mesh. We derive the formulas to compute the diffusive flux for MFE in both methods. The single-domain method is extended to multiple dimensions. Numerical results indicate that both methods can accurately describe the evolution of the pressure and liquid level. © 2012 Springer Science+Business Media B.V.
International Nuclear Information System (INIS)
Hu Xia-Rong; Lü Rui
2014-01-01
In this paper, an analytical model for the vertical electric field distribution and optimization of a high voltage-reduced bulk field (REBULF) lateral double-diffused metal—oxide-semiconductor (LDMOS) transistor is presented. The dependences of the breakdown voltage on the buried n-layer depth, thickness, and doping concentration are discussed in detail. The REBULF criterion and the optimal vertical electric field distribution condition are derived on the basis of the optimization of the electric field distribution. The breakdown voltage of the REBULF LDMOS transistor is always higher than that of a single reduced surface field (RESURF) LDMOS transistor, and both analytical and numerical results show that it is better to make a thick n-layer buried deep into the p-substrate. (interdisciplinary physics and related areas of science and technology)
Tests of 40 mm SSC dipole model magnets with vertically split yokes
International Nuclear Information System (INIS)
Koska, W.; Bossert, R.; Coulter, K.J.; Delchamps, S.; Gourlay, S.; Kinney, W.; Jaffery, T.S.; Lamm, M.J.; Strait, J.; Wake, M.
1991-05-01
Several 1 meter long, 40 mm aperture model SSC dipole magnets with vertically split yokes have been built and tested at Fermilab. In addition to the yoke design, these magnets were used to evaluate several variants of the collet clamps which apply prestress to the magnet ends. The magnets were instrumented with voltage taps for quench localization and strain gage based devices for measuring stresses, forces and deflections resulting from cooldown and excitation. Test were carried out in a vertical dewar at temperatures from 3.8 degree K to 4.4 degree K. The quench and mechanical behavior of these magnets will be presented and magnetic field measurements will be shown. A comparison with an earlier series of magnets with horizontally split yokes will be made. 7 refs., 4 figs., 1 tab
Chen, Hsiang-Chun; Wehrly, Thomas E
2015-02-20
The classic concordance correlation coefficient measures the agreement between two variables. In recent studies, concordance correlation coefficients have been generalized to deal with responses from a distribution from the exponential family using the univariate generalized linear mixed model. Multivariate data arise when responses on the same unit are measured repeatedly by several methods. The relationship among these responses is often of interest. In clustered mixed data, the correlation could be present between repeated measurements either within the same observer or between different methods on the same subjects. Indices for measuring such association are needed. This study proposes a series of indices, namely, intra-correlation, inter-correlation, and total correlation coefficients to measure the correlation under various circumstances in a multivariate generalized linear model, especially for joint modeling of clustered count and continuous outcomes. The proposed indices are natural extensions of the concordance correlation coefficient. We demonstrate the methodology with simulation studies. A case example of osteoarthritis study is provided to illustrate the use of these proposed indices. Copyright © 2014 John Wiley & Sons, Ltd.
A marketing mix model for a complex and turbulent environment
Directory of Open Access Journals (Sweden)
R. B. Mason
2007-12-01
Full Text Available Purpose: This paper is based on the proposition that the choice of marketing tactics is determined, or at least significantly influenced, by the nature of the companys external environment. It aims to illustrate the type of marketing mix tactics that are suggested for a complex and turbulent environment when marketing and the environment are viewed through a chaos and complexity theory lens. Design/Methodology/Approach: Since chaos and complexity theories are proposed as a good means of understanding the dynamics of complex and turbulent markets, a comprehensive review and analysis of literature on the marketing mix and marketing tactics from a chaos and complexity viewpoint was conducted. From this literature review, a marketing mix model was conceptualised. Findings: A marketing mix model considered appropriate for success in complex and turbulent environments was developed. In such environments, the literature suggests destabilising marketing activities are more effective, whereas stabilising type activities are more effective in simple, stable environments. Therefore the model proposes predominantly destabilising type tactics as appropriate for a complex and turbulent environment such as is currently being experienced in South Africa. Implications: This paper is of benefit to marketers by emphasising a new way to consider the future marketing activities of their companies. How this model can assist marketers and suggestions for research to develop and apply this model are provided. It is hoped that the model suggested will form the basis of empirical research to test its applicability in the turbulent South African environment. Originality/Value: Since businesses and markets are complex adaptive systems, using complexity theory to understand how to cope in complex, turbulent environments is necessary, but has not been widely researched. In fact, most chaos and complexity theory work in marketing has concentrated on marketing strategy, with
A two-fluid model for vertical flow applied to CO2 injection wells
DEFF Research Database (Denmark)
Linga, Gaute; Lund, Halvor
2016-01-01
to thermal stresses and subsequent loss of well integrity, and it is therefore crucial to employ models that can predict this accurately. In this work, we present a model for vertical well flow that includes both two-phase flow and heat conduction. The flow is described by a two-fluid model, where mass...... robust transition from two-phase to single-phase flow than the previous formulation. The model predicts which flow regimes are present downhole, and calculates friction and heat transfer depending on this. Moreover, the flow model is coupled with a heat conduction model for the layers that comprise......Flow of CO2 in wells is associated with substantial variations in thermophysical properties downhole, due to the coupled transient processes involved: complex flow patterns, density changes, phase transitions, and heat transfer to and from surroundings. Large temperature variations can lead...
Soil-Pile Interaction in the Pile Vertical Vibration Based on Fictitious Soil-Pile Model
Directory of Open Access Journals (Sweden)
Guodong Deng
2014-01-01
Full Text Available By introducing the fictitious soil-pile model, the soil-pile interaction in the pile vertical vibration is investigated. Firstly, assuming the surrounding soil of pile to be viscoelastic material and considering its vertical wave effect, the governing equations of soil-pile system subjected to arbitrary harmonic dynamic force are founded based on the Euler-Bernoulli rod theory. Secondly, the analytical solution of velocity response in frequency domain and its corresponding semianalytical solution of velocity response in time domain are derived by means of Laplace transform technique and separation of variables technique. Based on the obtained solutions, the influence of parameters of pile end soil on the dynamic response is studied in detail for different designing parameters of pile. Lastly, the fictitious soil-pile model and other pile end soil supporting models are compared. It is shown that the dynamic response obtained by the fictitious soil-pile model is among the dynamic responses obtained by other existing models if there are appropriate material parameters and thickness of pile end soil for the fictitious soil-pile model.
Superstring sigma models from spin chains: the SU(1,1 vertical bar 1) case
International Nuclear Information System (INIS)
Bellucci, S.; Casteill, P.-Y.; Morales, J.F.
2005-01-01
We derive the coherent state representation of the integrable spin chain Hamiltonian with non-compact supersymmetry group G=SU(1,1 vertical bar 1). By passing to the continuous limit, we find a spin chain sigma model describing a string moving on the supercoset G/H, H being the stabilizer group. The action is written in a manifestly G-invariant form in terms of the Cartan forms and the string coordinates in the supercoset. The spin chain sigma model is shown to agree with that following from the Green-Schwarz action describing two-charged string spinning on AdS 5 xS 5
Numerical Modeling of Scour at the Head of a Vertical-Wall Breakwater in Waves
Baykal, C.; Balcı, H. B.; Sumer, B. M.; Fuhrman, D. R.
2017-12-01
This study presents a 3D numerical modeling study on the flow and scour at the head of a vertical-wall breakwater in regular waves. The numerical model utilized in the study is based on that given by Jacobsen (2011). The present model has been applied successfully to the scour and backfilling beneath submarine pipelines by Fuhrman et al. (2014), and around a vertical cylindrical pile mounted on a horizontal plane sediment bed by Baykal et al. (2015, 2017). The model is composed of two main modules. The first module is the hydrodynamic model where Reynolds Averaged Navier Stokes (RANS) equations are solved with a k-ω turbulence closure. The second module is the morphologic model which comprises five sub-modules, namely; bed load, suspended load, sand slide, bed evolution and 3D mesh motion. The model is constructed in open-source CFD toolbox OpenFOAM. In this study, the model is applied to experimental data sets of Sumer and Fredsoe (1997) on the scour around a vertical-wall breakwater with a circular round head. Here, it is given the preliminary results of bed evolution of Test-8 of Sumer and Fredsoe (1997) in which a vertical-wall breakwater head with a width of B=140 mm is subjected to oscillatory flow with Tw=2.0 s and maximum orbital velocity at the bed Um=22cm/s, resulting in a Keulegan-Carpenter number, KC=3.14, close to KC experienced in real-life situations (KC = O(1)). The grain size is d=0.17 mm. The Shields parameter in the test case is given as θc=0.11, larger than the critical value for the initiation of motion implying that the scour is in the live-bed regime. The computational domain used in the simulations has the following dimensions: Length, l=40B, Width, w=20B, and Height, h=2B. The total number of cells is O(105) in the simulations. The scoured bed profile computed at the end of 3 periods of oscillatory flow of Test-8 is given in the figure below. The color scale in the figure is given for the ratio of bed elevation to the width of breakwater
Measurements and Models for Hazardous chemical and Mixed Wastes
Energy Technology Data Exchange (ETDEWEB)
Laurel A. Watts; Cynthia D. Holcomb; Stephanie L. Outcalt; Beverly Louie; Michael E. Mullins; Tony N. Rogers
2002-08-21
Mixed solvent aqueous waste of various chemical compositions constitutes a significant fraction of the total waste produced by industry in the United States. Not only does the chemical process industry create large quantities of aqueous waste, but the majority of the waste inventory at the DOE sites previously used for nuclear weapons production is mixed solvent aqueous waste. In addition, large quantities of waste are expected to be generated in the clean-up of those sites. In order to effectively treat, safely handle, and properly dispose of these wastes, accurate and comprehensive knowledge of basic thermophysical properties is essential. The goal of this work is to develop a phase equilibrium model for mixed solvent aqueous solutions containing salts. An equation of state was sought for these mixtures that (a) would require a minimum of adjustable parameters and (b) could be obtained from a available data or data that were easily measured. A model was developed to predict vapor composition and pressure given the liquid composition and temperature. It is based on the Peng-Robinson equation of state, adapted to include non-volatile and salt components. The model itself is capable of predicting the vapor-liquid equilibria of a wide variety of systems composed of water, organic solvents, salts, nonvolatile solutes, and acids or bases. The representative system o water + acetone + 2-propanol + NaNo3 was selected to test and verify the model. Vapor-liquid equilibrium and phase density measurements were performed for this system and its constituent binaries.
A mixed-effects multinomial logistic regression model.
Hedeker, Donald
2003-05-15
A mixed-effects multinomial logistic regression model is described for analysis of clustered or longitudinal nominal or ordinal response data. The model is parameterized to allow flexibility in the choice of contrasts used to represent comparisons across the response categories. Estimation is achieved using a maximum marginal likelihood (MML) solution that uses quadrature to numerically integrate over the distribution of random effects. An analysis of a psychiatric data set, in which homeless adults with serious mental illness are repeatedly classified in terms of their living arrangement, is used to illustrate features of the model. Copyright 2003 by John Wiley & Sons, Ltd.
OPTIMAL MODEL OF FUNCTIONING OF OLERICULTURE: VERTICAL INTEGRATION, AGRICULTURAL FILIERES, CLUSTERS
Directory of Open Access Journals (Sweden)
Y. B. Mindlin
2016-01-01
Full Text Available The goal of the present paper is to identify the optimal strategy of development of the Russian olericulture in order to substitute imported products and to build up logistic and transport infrastructure. Existing problems of the Russian olericulture are described. It is demonstrated that these problems can be solved on the basis of big integrated structures. Formation of these structures can be based on hierarchical (vertical integration or networking (agricultural filieres or clusters models. A comparative analysis of these models of development of olericulture is made. Advantages and inconveniences of each model are described. It is demonstrated that sustainable development of the Russian olericulture can be insured only by a combination of hierarchical and networking tools. Vertical integration will help to reach quick increase of production, while networking models are necessary for inclusion of small producers into production chains, development of product range and development of supporting industries. Networking models are also necessary for social tasks. It means that the optimal strategy of development of the Russian olericulture should be based on a combination of networking and hierarchical tools. This combination is necessary for agricultural corporation as well as for the Russian olericulture in general.
Mixing in Long Cylinder by a Stratified Jet: Laboratory Modeling and Theory
Nath, C.; Voropayev, S. I.; Fernando, H. J. S.
2011-11-01
The evolution of buoyant turbulent jets released into a low aspect ratio (width/height) cavity filled with a homogeneous fluid was investigated experimentally. The motivation was to understand mixing process in U.S. Strategic Petroleum Reserves (SPR), where crude oil is stored in salt caverns of aspect ratio approximately 0.1. During maintenance, degassed oil is introduced as a jet from the top of the caverns while denser gas-laden crude oil is pumped out from the bottom. The focus was on mixing, formation and development of density layer as well as the time for replenishing oil in the container to an acceptable level of vapor pressure (gas concentration). Basing on the results of experiments a theoretical model was advanced which permits to calculate the vertical density distributions in cavern as a function of time and other external parameters. Satisfactory agreement between theory and measurements was demonstrated. The results obtained could be extrapolated to SPR flow mixing situations and help to improve the efficiency of expensive oil cavern refilling. This research is supported by the Sandia National Laboratories.
The 4s web-marketing mix model
Constantinides, Efthymios
2002-01-01
This paper reviews the criticism on the 4Ps Marketing Mix framework, the most popular tool of traditional marketing management, and categorizes the main objections of using the model as the foundation of physical marketing. It argues that applying the traditional approach, based on the 4Ps paradigm, is also a poor choice in the case of virtual marketing and identifies two main limitations of the framework in online environments: the drastically diminished role of the Ps and the lack of any st...
Estimation and Inference for Very Large Linear Mixed Effects Models
Gao, K.; Owen, A. B.
2016-01-01
Linear mixed models with large imbalanced crossed random effects structures pose severe computational problems for maximum likelihood estimation and for Bayesian analysis. The costs can grow as fast as $N^{3/2}$ when there are N observations. Such problems arise in any setting where the underlying factors satisfy a many to many relationship (instead of a nested one) and in electronic commerce applications, the N can be quite large. Methods that do not account for the correlation structure can...
Numerical Modeling of the Vertical Heat Transport Through the Diffusive Layer of the Arctic Ocean
2013-03-01
transport through thermohaline staircases in the Arctic region. Results revealed that vertical fluxes exceeded those of extant “four-thirds flux...vertical heat flux, thermohaline staircase 15. NUMBER OF PAGES 73 16. PRICE CODE 17. SECURITY CLASSIFICATION OF REPORT Unclassified 18...DNS) were conducted to assess the vertical heat transport through thermohaline staircases in the Arctic region. Results revealed that vertical
Modeling the ascent of sounding balloons: derivation of the vertical air motion
Directory of Open Access Journals (Sweden)
A. Gallice
2011-10-01
Full Text Available A new model to describe the ascent of sounding balloons in the troposphere and lower stratosphere (up to ∼30–35 km altitude is presented. Contrary to previous models, detailed account is taken of both the variation of the drag coefficient with altitude and the heat imbalance between the balloon and the atmosphere. To compensate for the lack of data on the drag coefficient of sounding balloons, a reference curve for the relationship between drag coefficient and Reynolds number is derived from a dataset of flights launched during the Lindenberg Upper Air Methods Intercomparisons (LUAMI campaign. The transfer of heat from the surrounding air into the balloon is accounted for by solving the radial heat diffusion equation inside the balloon. In its present state, the model does not account for solar radiation, i.e. it is only able to describe the ascent of balloons during the night. It could however be adapted to also represent daytime soundings, with solar radiation modeled as a diffusive process. The potential applications of the model include the forecast of the trajectory of sounding balloons, which can be used to increase the accuracy of the match technique, and the derivation of the air vertical velocity. The latter is obtained by subtracting the ascent rate of the balloon in still air calculated by the model from the actual ascent rate. This technique is shown to provide an approximation for the vertical air motion with an uncertainty error of 0.5 m s^{−1} in the troposphere and 0.2 m s^{−1} in the stratosphere. An example of extraction of the air vertical velocity is provided in this paper. We show that the air vertical velocities derived from the balloon soundings in this paper are in general agreement with small-scale atmospheric velocity fluctuations related to gravity waves, mechanical turbulence, or other small-scale air motions measured during the SUCCESS campaign (Subsonic Aircraft: Contrail and Cloud Effects
Modelling of NSTX hot vertical displacement events using M 3 D -C 1
Pfefferlé, D.; Ferraro, N.; Jardin, S. C.; Krebs, I.; Bhattacharjee, A.
2018-05-01
The main results of an intense vertical displacement event (VDE) modelling activity using the implicit 3D extended MHD code M3D-C1 are presented. A pair of nonlinear 3D simulations are performed using realistic transport coefficients based on the reconstruction of a so-called NSTX frozen VDE where the feedback control was purposely switched off to trigger a vertical instability. The vertical drift phase is solved assuming axisymmetry until the plasma contacts the first wall, at which point the intricate evolution of the plasma, decaying to large extent in force-balance with induced halo/wall currents, is carefully resolved via 3D nonlinear simulations. The faster 2D nonlinear runs allow to assess the sensitivity of the simulations to parameter changes. In the limit of perfectly conducting wall, the expected linear relation between vertical growth rate and wall resistivity is recovered. For intermediate wall resistivities, the halo region contributes to slowing the plasma down, and the characteristic VDE time depends on the choice of halo temperature. The evolution of the current quench and the onset of 3D halo/eddy currents are diagnosed in detail. The 3D simulations highlight a rich structure of toroidal modes, penetrating inwards from edge to core and cascading from high-n to low-n mode numbers. The break-up of flux-surfaces results in a progressive stochastisation of field-lines precipitating the thermalisation of the plasma with the wall. The plasma current then decays rapidly, inducing large currents in the halo region and the wall. Analysis of normal currents flowing in and out of the divertor plate reveals rich time-varying patterns.
Study on system dynamics of evolutionary mix-game models
Gou, Chengling; Guo, Xiaoqian; Chen, Fang
2008-11-01
Mix-game model is ameliorated from an agent-based MG model, which is used to simulate the real financial market. Different from MG, there are two groups of agents in Mix-game: Group 1 plays a majority game and Group 2 plays a minority game. These two groups of agents have different bounded abilities to deal with historical information and to count their own performance. In this paper, we modify Mix-game model by assigning the evolution abilities to agents: if the winning rates of agents are smaller than a threshold, they will copy the best strategies the other agent has; and agents will repeat such evolution at certain time intervals. Through simulations this paper finds: (1) the average winning rates of agents in Group 1 and the mean volatilities increase with the increases of the thresholds of Group 1; (2) the average winning rates of both groups decrease but the mean volatilities of system increase with the increase of the thresholds of Group 2; (3) the thresholds of Group 2 have greater impact on system dynamics than the thresholds of Group 1; (4) the characteristics of system dynamics under different time intervals of strategy change are similar to each other qualitatively, but they are different quantitatively; (5) As the time interval of strategy change increases from 1 to 20, the system behaves more and more stable and the performances of agents in both groups become better also.
A mechanistic model of heat transfer for gas-liquid flow in vertical wellbore annuli.
Yin, Bang-Tang; Li, Xiang-Fang; Liu, Gang
2018-01-01
The most prominent aspect of multiphase flow is the variation in the physical distribution of the phases in the flow conduit known as the flow pattern. Several different flow patterns can exist under different flow conditions which have significant effects on liquid holdup, pressure gradient and heat transfer. Gas-liquid two-phase flow in an annulus can be found in a variety of practical situations. In high rate oil and gas production, it may be beneficial to flow fluids vertically through the annulus configuration between well tubing and casing. The flow patterns in annuli are different from pipe flow. There are both casing and tubing liquid films in slug flow and annular flow in the annulus. Multiphase heat transfer depends on the hydrodynamic behavior of the flow. There are very limited research results that can be found in the open literature for multiphase heat transfer in wellbore annuli. A mechanistic model of multiphase heat transfer is developed for different flow patterns of upward gas-liquid flow in vertical annuli. The required local flow parameters are predicted by use of the hydraulic model of steady-state multiphase flow in wellbore annuli recently developed by Yin et al. The modified heat-transfer model for single gas or liquid flow is verified by comparison with Manabe's experimental results. For different flow patterns, it is compared with modified unified Zhang et al. model based on representative diameters.
A Computation Fluid Dynamic Model for Gas Lift Process Simulation in a Vertical Oil Well
Directory of Open Access Journals (Sweden)
Kadivar Arash
2017-03-01
Full Text Available Continuous gas-lift in a typical oil well was simulated using computational fluid dynamic (CFD technique. A multi fluid model based on the momentum transfer between liquid and gas bubbles was employed to simulate two-phase flow in a vertical pipe. The accuracy of the model was investigated through comparison of numerical predictions with experimental data. The model then was used to study the dynamic behaviour of the two-phase flow around injection point in details. The predictions by the model were compared with other empirical correlations, as well. To obtain an optimum condition of gas-lift, the influence of the effective parameters including the quantity of injected gas, tubing diameter and bubble size distribution were investigated. The results revealed that increasing tubing diameter, the injected gas rate and decreasing bubble diameter improve gas-lift performance.
A Computation Fluid Dynamic Model for Gas Lift Process Simulation in a Vertical Oil Well
Kadivar, Arash; Lay, Ebrahim Nemati
2017-03-01
Continuous gas-lift in a typical oil well was simulated using computational fluid dynamic (CFD) technique. A multi fluid model based on the momentum transfer between liquid and gas bubbles was employed to simulate two-phase flow in a vertical pipe. The accuracy of the model was investigated through comparison of numerical predictions with experimental data. The model then was used to study the dynamic behaviour of the two-phase flow around injection point in details. The predictions by the model were compared with other empirical correlations, as well. To obtain an optimum condition of gas-lift, the influence of the effective parameters including the quantity of injected gas, tubing diameter and bubble size distribution were investigated. The results revealed that increasing tubing diameter, the injected gas rate and decreasing bubble diameter improve gas-lift performance.
Integration of MATLAB Simulink(Registered Trademark) Models with the Vertical Motion Simulator
Lewis, Emily K.; Vuong, Nghia D.
2012-01-01
This paper describes the integration of MATLAB Simulink(Registered TradeMark) models into the Vertical Motion Simulator (VMS) at NASA Ames Research Center. The VMS is a high-fidelity, large motion flight simulator that is capable of simulating a variety of aerospace vehicles. Integrating MATLAB Simulink models into the VMS needed to retain the development flexibility of the MATLAB environment and allow rapid deployment of model changes. The process developed at the VMS was used successfully in a number of recent simulation experiments. This accomplishment demonstrated that the model integrity was preserved, while working within the hard real-time run environment of the VMS architecture, and maintaining the unique flexibility of the VMS to meet diverse research requirements.
A Linear Mixed-Effects Model of Wireless Spectrum Occupancy
Directory of Open Access Journals (Sweden)
Pagadarai Srikanth
2010-01-01
Full Text Available We provide regression analysis-based statistical models to explain the usage of wireless spectrum across four mid-size US cities in four frequency bands. Specifically, the variations in spectrum occupancy across space, time, and frequency are investigated and compared between different sites within the city as well as with other cities. By applying the mixed-effects models, several conclusions are drawn that give the occupancy percentage and the ON time duration of the licensed signal transmission as a function of several predictor variables.
Efficient mixed integer programming models for family scheduling problems
Directory of Open Access Journals (Sweden)
Meng-Ye Lin
Full Text Available This paper proposes several mixed integer programming models which incorporate optimal sequence properties into the models, to solve single machine family scheduling problems. The objectives are total weighted completion time and maximum lateness, respectively. Experiment results indicate that there are remarkable improvements in computational efficiency when optimal sequence properties are included in the models. For the total weighted completion time problems, the best model solves all of the problems up to 30-jobs within 5 s, all 50-job problems within 4 min and about 1/3 of the 75-job to 100-job problems within 1 h. For maximum lateness problems, the best model solves almost all the problems up to 30-jobs within 11 min and around half of the 50-job to 100-job problems within 1 h. Keywords: Family scheduling, Sequence independent setup, Total weighted completion time, Maximum lateness
Mixed Portmanteau Test for Diagnostic Checking of Time Series Models
Directory of Open Access Journals (Sweden)
Sohail Chand
2014-01-01
Full Text Available Model criticism is an important stage of model building and thus goodness of fit tests provides a set of tools for diagnostic checking of the fitted model. Several tests are suggested in literature for diagnostic checking. These tests use autocorrelation or partial autocorrelation in the residuals to criticize the adequacy of fitted model. The main idea underlying these portmanteau tests is to identify if there is any dependence structure which is yet unexplained by the fitted model. In this paper, we suggest mixed portmanteau tests based on autocorrelation and partial autocorrelation functions of the residuals. We derived the asymptotic distribution of the mixture test and studied its size and power using Monte Carlo simulations.
Modeling and measurement of the motion of the DIII-D vacuum vessel during vertical instabilities
International Nuclear Information System (INIS)
Reis, E.; Blevins, R.D.; Jensen, T.H.; Luxon, J.L.; Petersen, P.I.; Strait, E.J.
1991-11-01
The motions of the D3-D vacuum vessel during vertical instabilities of elongated plasmas have been measured and studied over the past five years. The currents flowing in the vessel wall and the plasma scrapeoff layer were also measured and correlated to a physics model. These results provide a time history load distribution on the vessel which were input to a dynamic analysis for correlation to the measured motions. The structural model of the vessel using the loads developed from the measured vessel currents showed that the calculated displacement history correlated well with the measured values. The dynamic analysis provides a good estimate of the stresses and the maximum allowable deflection of the vessel. In addition, the vessel motions produce acoustic emissions at 21 Hertz that are sufficiently loud to be felt as well as heard by the D3-D operators. Time history measurements of the sounds were correlated to the vessel displacements. An analytical model of an oscillating sphere provided a reasonable correlation to the amplitude of the measured sounds. The correlation of the theoretical and measured vessel currents, the dynamic measurements and analysis, and the acoustic measurements and analysis show that: (1) The physics model can predict vessel forces for selected values of plasma resistivity. The model also predicts poloidal and toroidal wall currents which agree with measured values; (2) The force-time history from the above model, used in conjunction with an axisymmetric structural model of the vessel, predicts vessel motions which agree well with measured values; (3) The above results, input to a simple acoustic model predicts the magnitude of sounds emitted from the vessel during disruptions which agree with acoustic measurements; (4) Correlation of measured vessel motions with structural analysis shows that a maximum vertical motion of the vessel up to 0.24 in will not overstress the vessel or its supports. 11 refs., 10 figs., 1 tab
Disease control of delay SEIR model with nonlinear incidence rate and vertical transmission.
Cheng, Yan; Pan, Qiuhui; He, Mingfeng
2013-01-01
The aim of this paper is to develop two delayed SEIR epidemic models with nonlinear incidence rate, continuous treatment, and impulsive vaccination for a class of epidemic with latent period and vertical transition. For continuous treatment, we obtain a basic reproductive number ℜ0 and prove the global stability by using the Lyapunov functional method. We obtain two thresholds ℜ* and ℜ∗ for impulsive vaccination and prove that if ℜ* 1, then the disease is permanent by using the comparison theorem of impulsive differential equation. Numerical simulations indicate that pulse vaccination strategy or a longer latent period will make the population size infected by a disease decrease.
Two-phase flow dynamics in a model steam generator under vertical acceleration oscillation field
International Nuclear Information System (INIS)
Ishida, T.; Teshima, N.; Sakurai, S.
1992-01-01
The influence of periodically varying acceleration on hydrodynamic response has been studied experimentally using an experimental rig which models a marine reactor subject to vertical motion. The effect on the primary loop is small, but the effect on the secondary loop is large. The variables of the secondary loop, such as circulation flow rate and water level, oscillate with acceleration. The variation of gains in frequency response is analysed. The variations of flow in the secondary loop and in the downcome water level, increase in proportion to the acceleration. The effect of the flow resistance in the secondary loop on the two-phase flow dynamics is clarified. (7 figures) (Author)
Final Report of the Grant: ''Vertical Transport and Mixing in Complex Terrain Airsheds''
Energy Technology Data Exchange (ETDEWEB)
Fernando, Joseph Harindra [Arizona State Univ., Tempe, AZ (United States); Anderson, James [Arizona State Univ., Tempe, AZ (United States); Boyer, Don [Arizona State Univ., Tempe, AZ (United States); Berman, Neil [Arizona State Univ., Tempe, AZ (United States)
2004-12-29
Stable stratification associated with nocturnal thermal circulation in areas of complex terrain leads to interesting and important phenomena that govern local meteorology and contaminant dispersion. Given that most urban areas are in complex topography, understanding and prediction of such phenomena are of immediate practical importance. This project dealt with theoretical, laboratory, numerical and field experimental studies aimed at understanding stratified flow and turbulence phenomena in urban areas, with particular emphasis on flow, turbulence and contaminant transport and diffusion in such flows. A myriad of new results were obtained and some of these results were used to improve the predictive capabilities of the models.
Microstructure - based continuum damage model for Asphalt mixes
International Nuclear Information System (INIS)
Tashman, Laith; Masad, Eyad; Zbib, Hussein; Kaloush, Kamil
2002-01-01
Full text.Hot mix asphalt (HMA) is a complex composite material that consists of different sizes of aggregates, asphalt binder and air voids. One of the most important failures in asphalt pavements is caused by permanent deformation under high service temperature. An HMA with high resistance to permanent deformation work-hardens under repeated loading with accumulating strain. However, HMA that is susceptible to permanenr deformation develop microcracks under repeated loading, which softens the mix and leads ao an increase in the rate of accumulated strain. Most of macroscopic response of HMA, assume isotropic material properties and do not account for the microscopic behavior. This study develops a viscoplastic constitutive model for asphalt mixtures that incorporates microstructure parameters. The model is based on Perzyna's elasto-viscoplastic theory. The viscous flow function is extended to reflect the microstructure anisotropy. In addition, a damage parameter is included in the model to reflect the initiation adn propagation of cracks. The model's parameters are obtained using image analysis procedures, static creep tests and strength tests. The model is used to describe the behavior of number of mixtures with known field performance
Productivity Analysis of Volume Fractured Vertical Well Model in Tight Oil Reservoirs
Directory of Open Access Journals (Sweden)
Jiahang Wang
2017-01-01
Full Text Available This paper presents a semianalytical model to simulate the productivity of a volume fractured vertical well in tight oil reservoirs. In the proposed model, the reservoir is a composite system which contains two regions. The inner region is described as formation with finite conductivity hydraulic fracture network and the flow in fracture is assumed to be linear, while the outer region is simulated by the classical Warren-Root model where radial flow is applied. The transient rate is calculated, and flow patterns and characteristic flowing periods caused by volume fractured vertical well are analyzed. Combining the calculated results with actual production data at the decline stage shows a good fitting performance. Finally, the effects of some sensitive parameters on the type curves are also analyzed extensively. The results demonstrate that the effect of fracture length is more obvious than that of fracture conductivity on improving production in tight oil reservoirs. When the length and conductivity of main fracture are constant, the contribution of stimulated reservoir volume (SRV to the cumulative oil production is not obvious. When the SRV is constant, the length of fracture should also be increased so as to improve the fracture penetration and well production.
Mixing characteristics of sludge simulant in a model anaerobic digester.
Low, Siew Cheng; Eshtiaghi, Nicky; Slatter, Paul; Baudez, Jean-Christophe; Parthasarathy, Rajarathinam
2016-03-01
This study aims to investigate the mixing characteristics of a transparent sludge simulant in a mechanically agitated model digester using flow visualisation technique. Video images of the flow patterns were obtained by recording the progress of an acid-base reaction and analysed to determine the active and inactive volumes as a function of time. The doughnut-shaped inactive region formed above and below the impeller in low concentration simulant decreases in size with time and disappears finally. The 'cavern' shaped active mixing region formed around the impeller in simulant solutions with higher concentrations increases with increasing agitation time and reaches a steady state equilibrium size, which is a function of specific power input. These results indicate that the active volume is jointly determined by simulant rheology and specific power input. A mathematical correlation is proposed to estimate the active volume as a function of simulant concentration in terms of yield Reynolds number.
Box-Cox Mixed Logit Model for Travel Behavior Analysis
Orro, Alfonso; Novales, Margarita; Benitez, Francisco G.
2010-09-01
To represent the behavior of travelers when they are deciding how they are going to get to their destination, discrete choice models, based on the random utility theory, have become one of the most widely used tools. The field in which these models were developed was halfway between econometrics and transport engineering, although the latter now constitutes one of their principal areas of application. In the transport field, they have mainly been applied to mode choice, but also to the selection of destination, route, and other important decisions such as the vehicle ownership. In usual practice, the most frequently employed discrete choice models implement a fixed coefficient utility function that is linear in the parameters. The principal aim of this paper is to present the viability of specifying utility functions with random coefficients that are nonlinear in the parameters, in applications of discrete choice models to transport. Nonlinear specifications in the parameters were present in discrete choice theory at its outset, although they have seldom been used in practice until recently. The specification of random coefficients, however, began with the probit and the hedonic models in the 1970s, and, after a period of apparent little practical interest, has burgeoned into a field of intense activity in recent years with the new generation of mixed logit models. In this communication, we present a Box-Cox mixed logit model, original of the authors. It includes the estimation of the Box-Cox exponents in addition to the parameters of the random coefficients distribution. Probability of choose an alternative is an integral that will be calculated by simulation. The estimation of the model is carried out by maximizing the simulated log-likelihood of a sample of observed individual choices between alternatives. The differences between the predictions yielded by models that are inconsistent with real behavior have been studied with simulation experiments.
International Nuclear Information System (INIS)
Boudjemadi, R.
1996-03-01
The main objectives of this thesis are the direct numerical simulation of natural convection in a vertical differentially heated slot and the improvements of second-order turbulence modelling. A three-dimensional direct numerical simulation code has been developed in order to gain a better understanding of turbulence properties in natural convection flows. This code has been validated in several physical configurations: non-stratified natural convection flows (conduction solution), stratified natural convection flows (double boundary layer solution), transitional and turbulent Poiseuille flows. For the conduction solution, the turbulent regime was reached at a Rayleigh number of 1*10 5 and 5.4*10 5 . A detailed analysis of these results has revealed the principal qualities of the available models but has also pointed our their shortcomings. This data base has been used in order to improve the triple correlations transport models and to select the turbulent time scales suitable for such flows. (author). 122 refs., figs., tabs., 4 appends
Model tests of wind turbine with a vertical axis of rotation type Lenz 2
Zwierzchowski, Jaroslaw; Laski, Pawel Andrzej; Blasiak, Slawomir; Takosoglu, Jakub Emanuel; Pietrala, Dawid Sebastian; Bracha, Gabriel Filip; Nowakowski, Lukasz
A building design of vertical axis wind turbines (VAWT) was presented in the article. The construction and operating principle of a wind turbine were described therein. Two VAWT turbine models were compared, i.a. Darrieus and Lenz2, taking their strengths and weaknesses into consideration. 3D solid models of turbine components were presented with the use of SolidWorks software. Using CFD methods, the air flow on two aerodynamic fins, symmetrical and asymmetrical, at different angles of attack were tested. On the basis of flow simulation conducted in FlowSimulation, an asymmetrical fin was chosen as the one showing greater load bearing capacities. Due to the uncertainty of trouble-free operation of Darrieus turbine on construction elements creating the basis thereof, a 3D model of Lenz2 turbine was constructed, which is more reliable and makes turbine self-start possible. On the basis of the research, components were designed and technical docu mentation was compiled.
Directory of Open Access Journals (Sweden)
L. Zhang
2013-07-01
Full Text Available Atmospheric mineral dust particles exert significant direct radiative forcings and are important drivers of climate and climate change. We used the GEOS-Chem global three-dimensional chemical transport model (CTM coupled with the Fu-Liou-Gu (FLG radiative transfer model (RTM to investigate the dust radiative forcing and heating rate based on different vertical profiles for April 2006. We attempt to actually quantify the sensitivities of radiative forcing to dust vertical profiles, especially the discrepancies between using realistic and climatological vertical profiles. In these calculations, dust emissions were constrained by observations of aerosol optical depth (AOD. The coupled calculations utilizing a more realistic dust vertical profile simulated by GEOS-Chem minimize the physical inconsistencies between 3-D CTM aerosol fields and the RTM. The use of GEOS-Chem simulated vertical profile of dust extinction, as opposed to the FLG prescribed vertical profile, leads to greater and more spatially heterogeneous changes in the estimated radiative forcing and heating rate produced by dust. Both changes can be attributed to a different vertical structure between dust and non-dust source regions. Values of the dust vertically resolved AOD per grid level (VRAOD are much larger in the middle troposphere, though smaller at the surface when the GEOS-Chem simulated vertical profile is used, which leads to a much stronger heating rate in the middle troposphere. Compared to the FLG vertical profile, the use of GEOS-Chem vertical profile reduces the solar radiative forcing at the top of atmosphere (TOA by approximately 0.2–0.25 W m−2 over the African and Asian dust source regions. While the Infrared (IR radiative forcing decreases 0.2 W m−2 over African dust belt, it increases 0.06 W m−2 over the Asian dust belt when the GEOS-Chem vertical profile is used. Differences in the solar radiative forcing at the surface between the use of the GEOS-Chem and
A local mixing model for deuterium replacement in solids
International Nuclear Information System (INIS)
Doyle, B.L.; Brice, D.K.; Wampler, W.R.
1980-01-01
A new model for hydrogen isotope exchange by ion implantation has been developed. The basic difference between the present approach and previous work is that the depth distribution of the implanted species is included. The outstanding feature of this local mixing model is that the only adjustable parameter is the saturation hydrogen concentration which is specific to the target material and dependent only on temperature. The model is shown to give excellent agreement both with new data on H/D exchange in the low Z coating materials VB 2 , TiC, TiB 2 , and B reported here and with previously reported data on stainless steel. The saturation hydrogen concentrations used to fit these data were 0.15, 0.25, 0.15, 0.45, and 1.00 times atomic density respectively. This model should be useful in predicting the recycling behavior of hydrogen isotopes in tokamak limiter and wall materials. (author)
Subgrid models for mass and thermal diffusion in turbulent mixing
Energy Technology Data Exchange (ETDEWEB)
Sharp, David H [Los Alamos National Laboratory; Lim, Hyunkyung [STONY BROOK UNIV; Li, Xiao - Lin [STONY BROOK UNIV; Gilmm, James G [STONY BROOK UNIV
2008-01-01
We are concerned with the chaotic flow fields of turbulent mixing. Chaotic flow is found in an extreme form in multiply shocked Richtmyer-Meshkov unstable flows. The goal of a converged simulation for this problem is twofold: to obtain converged solutions for macro solution features, such as the trajectories of the principal shock waves, mixing zone edges, and mean densities and velocities within each phase, and also for such micro solution features as the joint probability distributions of the temperature and species concentration. We introduce parameterized subgrid models of mass and thermal diffusion, to define large eddy simulations (LES) that replicate the micro features observed in the direct numerical simulation (DNS). The Schmidt numbers and Prandtl numbers are chosen to represent typical liquid, gas and plasma parameter values. Our main result is to explore the variation of the Schmidt, Prandtl and Reynolds numbers by three orders of magnitude, and the mesh by a factor of 8 per linear dimension (up to 3200 cells per dimension), to allow exploration of both DNS and LES regimes and verification of the simulations for both macro and micro observables. We find mesh convergence for key properties describing the molecular level of mixing, including chemical reaction rates between the distinct fluid species. We find results nearly independent of Reynolds number for Re 300, 6000, 600K . Methodologically, the results are also new. In common with the shock capturing community, we allow and maintain sharp solution gradients, and we enhance these gradients through use of front tracking. In common with the turbulence modeling community, we include subgrid scale models with no adjustable parameters for LES. To the authors' knowledge, these two methodologies have not been previously combined. In contrast to both of these methodologies, our use of Front Tracking, with DNS or LES resolution of the momentum equation at or near the Kolmogorov scale, but without
Negative binomial mixed models for analyzing microbiome count data.
Zhang, Xinyan; Mallick, Himel; Tang, Zaixiang; Zhang, Lei; Cui, Xiangqin; Benson, Andrew K; Yi, Nengjun
2017-01-03
Recent advances in next-generation sequencing (NGS) technology enable researchers to collect a large volume of metagenomic sequencing data. These data provide valuable resources for investigating interactions between the microbiome and host environmental/clinical factors. In addition to the well-known properties of microbiome count measurements, for example, varied total sequence reads across samples, over-dispersion and zero-inflation, microbiome studies usually collect samples with hierarchical structures, which introduce correlation among the samples and thus further complicate the analysis and interpretation of microbiome count data. In this article, we propose negative binomial mixed models (NBMMs) for detecting the association between the microbiome and host environmental/clinical factors for correlated microbiome count data. Although having not dealt with zero-inflation, the proposed mixed-effects models account for correlation among the samples by incorporating random effects into the commonly used fixed-effects negative binomial model, and can efficiently handle over-dispersion and varying total reads. We have developed a flexible and efficient IWLS (Iterative Weighted Least Squares) algorithm to fit the proposed NBMMs by taking advantage of the standard procedure for fitting the linear mixed models. We evaluate and demonstrate the proposed method via extensive simulation studies and the application to mouse gut microbiome data. The results show that the proposed method has desirable properties and outperform the previously used methods in terms of both empirical power and Type I error. The method has been incorporated into the freely available R package BhGLM ( http://www.ssg.uab.edu/bhglm/ and http://github.com/abbyyan3/BhGLM ), providing a useful tool for analyzing microbiome data.
Measurement and Model for Hazardous Chemical and Mixed Waste
Energy Technology Data Exchange (ETDEWEB)
Michael E. Mullins; Tony N. Rogers; Stephanie L. Outcalt; Beverly Louie; Laurel A. Watts; Cynthia D. Holcomb
2002-07-30
Mixed solvent aqueous waste of various chemical compositions constitutes a significant fraction of the total waste produced by industry in the United States. Not only does the chemical process industry create large quantities of aqueous waste, but the majority of the waste inventory at the Department of Energy (DOE) sites previously used for nuclear weapons production is mixed solvent aqueous waste. In addition, large quantities of waste are expected to be generated in the clean-up of those sites. In order to effectively treat, safely handle, and properly dispose of these wastes, accurate and comprehensive knowledge of basic thermophysical properties is essential. The goal of this work is to develop a phase equilibrium model for mixed solvent aqueous solutions containing salts. An equation of state was sought for these mixtures that (a) would require a minimum of adjustable parameters and (b) could be obtained from a available data or data that were easily measured. A model was developed to predict vapor composition and pressure given the liquid composition and temperature. It is based on the Peng-Robinson equation of state, adapted to include non-volatile and salt components. The model itself is capable of predicting the vapor-liquid equilibria of a wide variety of systems composed of water, organic solvents, salts, nonvolatile solutes, and acids or bases. The representative system of water + acetone + 2-propanol + NaNO3 was selected to test and verify the model. Vapor-liquid equilibrium and phase density measurements were performed for this system and its constituent binaries.
Linear mixed models a practical guide using statistical software
West, Brady T; Galecki, Andrzej T
2014-01-01
Highly recommended by JASA, Technometrics, and other journals, the first edition of this bestseller showed how to easily perform complex linear mixed model (LMM) analyses via a variety of software programs. Linear Mixed Models: A Practical Guide Using Statistical Software, Second Edition continues to lead readers step by step through the process of fitting LMMs. This second edition covers additional topics on the application of LMMs that are valuable for data analysts in all fields. It also updates the case studies using the latest versions of the software procedures and provides up-to-date information on the options and features of the software procedures available for fitting LMMs in SAS, SPSS, Stata, R/S-plus, and HLM.New to the Second Edition A new chapter on models with crossed random effects that uses a case study to illustrate software procedures capable of fitting these models Power analysis methods for longitudinal and clustered study designs, including software options for power analyses and suggest...
Generalized linear mixed model for segregation distortion analysis.
Zhan, Haimao; Xu, Shizhong
2011-11-11
Segregation distortion is a phenomenon that the observed genotypic frequencies of a locus fall outside the expected Mendelian segregation ratio. The main cause of segregation distortion is viability selection on linked marker loci. These viability selection loci can be mapped using genome-wide marker information. We developed a generalized linear mixed model (GLMM) under the liability model to jointly map all viability selection loci of the genome. Using a hierarchical generalized linear mixed model, we can handle the number of loci several times larger than the sample size. We used a dataset from an F(2) mouse family derived from the cross of two inbred lines to test the model and detected a major segregation distortion locus contributing 75% of the variance of the underlying liability. Replicated simulation experiments confirm that the power of viability locus detection is high and the false positive rate is low. Not only can the method be used to detect segregation distortion loci, but also used for mapping quantitative trait loci of disease traits using case only data in humans and selected populations in plants and animals.
Modelling rainfall amounts using mixed-gamma model for Kuantan district
Zakaria, Roslinazairimah; Moslim, Nor Hafizah
2017-05-01
An efficient design of flood mitigation and construction of crop growth models depend upon good understanding of the rainfall process and characteristics. Gamma distribution is usually used to model nonzero rainfall amounts. In this study, the mixed-gamma model is applied to accommodate both zero and nonzero rainfall amounts. The mixed-gamma model presented is for the independent case. The formulae of mean and variance are derived for the sum of two and three independent mixed-gamma variables, respectively. Firstly, the gamma distribution is used to model the nonzero rainfall amounts and the parameters of the distribution (shape and scale) are estimated using the maximum likelihood estimation method. Then, the mixed-gamma model is defined for both zero and nonzero rainfall amounts simultaneously. The formulae of mean and variance for the sum of two and three independent mixed-gamma variables derived are tested using the monthly rainfall amounts from rainfall stations within Kuantan district in Pahang Malaysia. Based on the Kolmogorov-Smirnov goodness of fit test, the results demonstrate that the descriptive statistics of the observed sum of rainfall amounts is not significantly different at 5% significance level from the generated sum of independent mixed-gamma variables. The methodology and formulae demonstrated can be applied to find the sum of more than three independent mixed-gamma variables.
Li, Xiaofan; Sui, C.-H.; Lau, K-M.; Adamec, D.
1999-01-01
A two-dimensional coupled ocean-cloud resolving atmosphere model is used to investigate possible roles of convective scale ocean disturbances induced by atmospheric precipitation on ocean mixed-layer heat and salt budgets. The model couples a cloud resolving model with an embedded mixed layer-ocean circulation model. Five experiment are performed under imposed large-scale atmospheric forcing in terms of vertical velocity derived from the TOGA COARE observations during a selected seven-day period. The dominant variability of mixed-layer temperature and salinity are simulated by the coupled model with imposed large-scale forcing. The mixed-layer temperatures in the coupled experiments with 1-D and 2-D ocean models show similar variations when salinity effects are not included. When salinity effects are included, however, differences in the domain-mean mixed-layer salinity and temperature between coupled experiments with 1-D and 2-D ocean models could be as large as 0.3 PSU and 0.4 C respectively. Without fresh water effects, the nocturnal heat loss over ocean surface causes deep mixed layers and weak cooling rates so that the nocturnal mixed-layer temperatures tend to be horizontally-uniform. The fresh water flux, however, causes shallow mixed layers over convective areas while the nocturnal heat loss causes deep mixed layer over convection-free areas so that the mixed-layer temperatures have large horizontal fluctuations. Furthermore, fresh water flux exhibits larger spatial fluctuations than surface heat flux because heavy rainfall occurs over convective areas embedded in broad non-convective or clear areas, whereas diurnal signals over whole model areas yield high spatial correlation of surface heat flux. As a result, mixed-layer salinities contribute more to the density differences than do mixed-layer temperatures.
Mona, Lucia; Benedetti, Angela; D'Amico, Giuseppe; Myhre, Cathrine Lund; Schulz, Michael; Wandinger, Ulla; Laj, Paolo; Pappalardo, Gelsomina
2016-04-01
The ACTRIS-2 project, funded by Horizon 2020, addresses the scope of integrating state-of-the-art European ground-based stations for long term observations of aerosols, clouds and short lived gases, capitalizing on the work of FP7-ACTRIS. It aims at achieving the construction of a user-oriented RI, unique in the EU-RI landscape for providing 4-D integrated high-quality data from near-surface to high altitude (vertical profiles and total-column) which are relevant to climate and air-quality research. ACTRIS-2 develops and implements, in a large network of stations in Europe and beyond, observational protocols that permit the harmonization of collected data and their dissemination. ACTRIS secures provision and dissemination of a unique set of data and data-products that would not otherwise be available with the same level of quality and standardization. This results from a 10-year plus effort in constructing a research infrastructure capable of responding to community needs and requirements, and has been engaged since the start of the FP5 EU commission program. ACTRIS ensures compliance with reporting requirements (timing, format, traceability) defined by the major global observing networks. EARLINET (European Aerosol research Lidar NETwork), the aerosol vertical profiling component of ACTRIS, is providing since May 2000 vertical profiles of aerosol extinction and backscatter over Europe. A new structure of the EARLINET database has been designed in a more user oriented approach reporting new data products which are more effective for specific uses of different communities. In particular, a new era is starting with the Copernicus program during which the aerosol vertical profiling capability will be fundamental for assimilation and validation purposes. The new data products have been designed thanks to a strong link with EARLINET data users, first of all modeling and satellite communities, established since the beginning of EARLINET and re-enforced within ACTRIS2
Mixed layer depth calculation in deep convection regions in ocean numerical models
Courtois, Peggy; Hu, Xianmin; Pennelly, Clark; Spence, Paul; Myers, Paul G.
2017-12-01
Mixed Layer Depths (MLDs) diagnosed by conventional numerical models are generally based on a density difference with the surface (e.g., 0.01 kg.m-3). However, the temperature-salinity compensation and the lack of vertical resolution contribute to over-estimated MLD, especially in regions of deep convection. In the present work, we examined the diagnostic MLD, associated with the deep convection of the Labrador Sea Water (LSW), calculated with a simple density difference criterion. The over-estimated MLD led us to develop a new tool, based on an observational approach, to recalculate MLD from model output. We used an eddy-permitting, 1/12° regional configuration of the Nucleus for European Modelling of the Ocean (NEMO) to test and discuss our newly defined MLD. We compared our new MLD with that from observations, and we showed a major improvement with our new algorithm. To show the new MLD is not dependent on a single model and its horizontal resolution, we extended our analysis to include 1/4° eddy-permitting simulations, and simulations using the Modular Ocean Model (MOM) model.
De Biase, C.
2012-01-01
Vertical flow filters (unplanted) and vertical flow constructed wetlands (planted), simple and inexpensive technologies to treat effectively volatile organic compounds (VOCs) contaminated water, consist of containers filled with granular material which is intermittently fed with contaminated water.
Damping beam displacements through phase mixing: an illustrative model
International Nuclear Information System (INIS)
Barletta, W.A.; Briggs, R.J.
1983-01-01
We develop a simple model of a beam transported in a hard wall channel (an idealized very-high-order magnetic-multipole channel). The extremely anharmonic nature of the potential leads to damping of coherent transverse displacements of the beam via phase mixing. For the case of small uniform displacements of the beam we can write down by inspection the analytical form of the motion of the beam centroid. The same technique allows us to evaluate the effects of focussing and scattering elements in the transport channel upon the damping of the transverse motion of the beam
Stochastic Mixing Model with Power Law Decay of Variance
Fedotov, S.; Ihme, M.; Pitsch, H.
2003-01-01
Here we present a simple stochastic mixing model based on the law of large numbers (LLN). The reason why the LLN is involved in our formulation of the mixing problem is that the random conserved scalar c = c(t,x(t)) appears to behave as a sample mean. It converges to the mean value mu, while the variance sigma(sup 2)(sub c) (t) decays approximately as t(exp -1). Since the variance of the scalar decays faster than a sample mean (typically is greater than unity), we will introduce some non-linear modifications into the corresponding pdf-equation. The main idea is to develop a robust model which is independent from restrictive assumptions about the shape of the pdf. The remainder of this paper is organized as follows. In Section 2 we derive the integral equation from a stochastic difference equation describing the evolution of the pdf of a passive scalar in time. The stochastic difference equation introduces an exchange rate gamma(sub n) which we model in a first step as a deterministic function. In a second step, we generalize gamma(sub n) as a stochastic variable taking fluctuations in the inhomogeneous environment into account. In Section 3 we solve the non-linear integral equation numerically and analyze the influence of the different parameters on the decay rate. The paper finishes with a conclusion.
Modeling of speed distribution for mixed bicycle traffic flow
Directory of Open Access Journals (Sweden)
Cheng Xu
2015-11-01
Full Text Available Speed is a fundamental measure of traffic performance for highway systems. There were lots of results for the speed characteristics of motorized vehicles. In this article, we studied the speed distribution for mixed bicycle traffic which was ignored in the past. Field speed data were collected from Hangzhou, China, under different survey sites, traffic conditions, and percentages of electric bicycle. The statistics results of field data show that the total mean speed of electric bicycles is 17.09 km/h, 3.63 km/h faster and 27.0% higher than that of regular bicycles. Normal, log-normal, gamma, and Weibull distribution models were used for testing speed data. The results of goodness-of-fit hypothesis tests imply that the log-normal and Weibull model can fit the field data very well. Then, the relationships between mean speed and electric bicycle proportions were proposed using linear regression models, and the mean speed for purely electric bicycles or regular bicycles can be obtained. The findings of this article will provide effective help for the safety and traffic management of mixed bicycle traffic.
Directory of Open Access Journals (Sweden)
B. Mahanthesh
2016-03-01
Full Text Available The problem of conjugate effects of heat and mass transfer over a moving/stationary vertical plate has been studied under the influence of applied magnetic field, thermal radiation, internal heat generation/absorption and first order chemical reaction. The fluid is assumed to be electrically conducting water based Cu-nanofluid. The Tiwari and Das model is used to model the nanofluid, whereas Rosseland approximation is used for thermal radiation effect. Unified closed form solutions are obtained for the governing equations using Laplace transform method. The velocity, temperature and concentration profiles are expressed graphically for different flow pertinent parameters. The physical quantities of engineering interest such as skin friction, Nusselt number and Sherwood number are also computed. The obtained analytical solutions satisfy all imposed initial and boundary conditions and they can be reduced to known previous results in some limiting cases. It is found that, by varying nanoparticle volume fraction, the flow and heat transfer characteristics could be controlled.
Numerical modelling of isothermal gas-liquid two-phase bubbly flow in vertical pipes
International Nuclear Information System (INIS)
Yamoah, S.
2014-07-01
In order to qualify CFD codes for accurate numerical predictions of transient evolution of flow regimes in a vertical gas-liquid two-phase flow, suitable closure models are needed. The current study focuses on detailed numerical investigation of the interfacial driving force models and assessment of two population balance model approaches viz. the MUltiple-Size-Group (MUSIG) and one-group Interfacial Area Transport Equation (lATE) using the two-fluid modelling approach. Numerical predictions of five primitive variables: gas volume fraction, interfacial area concentration, Sauter mean bubble diameter, gas velocity and liquid velocity; have been validated against experimental data of Monros et al., (2013). Three specific objectives have been completed in this study. Firstly, under the assumption of mono-disperse bubbles, a consistent set of interfacial force models have been investigated. The effect of drag, lift, wall lubrication and turbulent dispersion forces has been assessed. New parameters have been introduced in the wall lubrication force models of Antal et al., (1991) and Frank et al., (2004, 2008) as well as implementing additional drag coefficient models using CFX Expression Language (CEl). The Tomiyama, (1998) lift coefficient model has been modified in this study. In general, the predictions from the sets of interfacial force models yielded satisfactory agreement with the experimental data. A set of Grace drag coefficient model, Tomiyama lift coefficient model, Antal wall force model, and Favre averaged turbulent dispersion force were found to provide the best agreement with the experimental data. Secondly, a model validation study to assess the performance of existing coalescence and breakup models of the MUSIG model in simulating bubbly flow in vertical configuration has been conducted. The breakup model of Luo and Svendsen, (1996) and coalescence model of Prince and Blanch, (1990) have been implemented. Detailed analysis has been performed for the wall
Directory of Open Access Journals (Sweden)
Davide Papini
2010-01-01
Different condenser tube arrangements have been developed for applications to the next generation NPPs. The two most used configurations, namely, horizontal and vertical tube condensers, are thoroughly investigated in this paper. Several thermal-hydraulic features were explored, being the analysis mainly devoted to the description of the best-estimate correlations and models for heat transfer coefficient prediction. In spite of a more critical behaviour concerning thermal expansion issues, vertical tube condensers offer remarkably better thermal-hydraulic performances. An experimental validation of the vertical tube correlations is provided by PERSEO facility (SIET labs, Piacenza, showing a fairly good agreement.
A Note on Recurring Misconceptions When Fitting Nonlinear Mixed Models.
Harring, Jeffrey R; Blozis, Shelley A
2016-01-01
Nonlinear mixed-effects (NLME) models are used when analyzing continuous repeated measures data taken on each of a number of individuals where the focus is on characteristics of complex, nonlinear individual change. Challenges with fitting NLME models and interpreting analytic results have been well documented in the statistical literature. However, parameter estimates as well as fitted functions from NLME analyses in recent articles have been misinterpreted, suggesting the need for clarification of these issues before these misconceptions become fact. These misconceptions arise from the choice of popular estimation algorithms, namely, the first-order linearization method (FO) and Gaussian-Hermite quadrature (GHQ) methods, and how these choices necessarily lead to population-average (PA) or subject-specific (SS) interpretations of model parameters, respectively. These estimation approaches also affect the fitted function for the typical individual, the lack-of-fit of individuals' predicted trajectories, and vice versa.
Chaos in the Mixed Even-Spin Models
Chen, Wei-Kuo
2014-06-01
We consider a disordered system obtained by coupling two mixed even-spin models together. The chaos problem is concerned with the behavior of the coupled system when the external parameters in the two models, such as, temperature, disorder, or external field, are slightly different. It is conjectured that the overlap between two independently sampled spin configurations from, respectively, the Gibbs measures of the two models is essentially concentrated around a constant under the coupled Gibbs measure. Using the extended Guerra replica symmetry breaking bound together with a recent development of controlling the overlap using the Ghirlanda-Guerra identities as well as a new family of identities, we present rigorous results on chaos in temperature. In addition, chaos in disorder and in external field are addressed.
Directory of Open Access Journals (Sweden)
E. Solazzo
2013-06-01
Full Text Available This study is conducted in the framework of the Air Quality Modelling Evaluation International Initiative (AQMEII and aims at the operational evaluation of an ensemble of 12 regional-scale chemical transport models used to predict air quality over the North American (NA and European (EU continents for 2006. The modelled concentrations of ozone and CO, along with the meteorological fields of wind speed (WS and direction (WD, temperature (T, and relative humidity (RH, are compared against high-quality in-flight measurements collected by instrumented commercial aircraft as part of the Measurements of OZone, water vapour, carbon monoxide and nitrogen oxides by Airbus In-service airCraft (MOZAIC programme. The evaluation is carried out for five model domains positioned around four major airports in NA (Portland, Philadelphia, Atlanta, and Dallas and one in Europe (Frankfurt, from the surface to 8.5 km. We compare mean vertical profiles of modelled and measured variables for all airports to compute error and variability statistics, perform analysis of altitudinal error correlation, and examine the seasonal error distribution for ozone, including an estimation of the bias introduced by the lateral boundary conditions (BCs. The results indicate that model performance is highly dependent on the variable, location, season, and height (e.g. surface, planetary boundary layer (PBL or free troposphere being analysed. While model performance for T is satisfactory at all sites (correlation coefficient in excess of 0.90 and fractional bias ≤ 0.01 K, WS is not replicated as well within the PBL (exhibiting a positive bias in the first 100 m and also underestimating observed variability, while above 1000 m, the model performance improves (correlation coefficient often above 0.9. The WD at NA airports is found to be biased in the PBL, primarily due to an overestimation of westerly winds. RH is modelled well within the PBL, but in the free troposphere large
Directory of Open Access Journals (Sweden)
I. Fer
2008-05-01
Full Text Available Storfjorden in the Svalbard Archipelago is a sill-fjord that produces significant volumes of dense, brine-enriched shelf water through ice formation. The dense water produced in the fjord overflows the sill and can reach deep into the Fram Strait. For conditions corresponding to a moderate ice production year, the pathway of the overflow, its descent and evolving water mass properties due to mixing are investigated for the first time using a high resolution 3-D numerical model. An idealized modeling approach forced by a typical annual cycle of buoyancy forcing due to ice production is chosen in a terrain-following vertical co-ordinate. Comparison with observational data, including hydrography, fine resolution current measurements and direct turbulence measurements using a microstructure profiler, gives confidence on the model performance. The model eddy diffusivity profiles contrasted to those inferred from the turbulence measurements give confidence on the skill of the Mellor Yamada scheme in representing sub-grid scale mixing for the Storfjorden overflow, and probably for gravity current modeling, in general. The Storfjorden overflow is characterized by low Froude number dynamics except at the shelf break where the plume narrows, accelerates with speed reaching 0.6 m s^{−1}, yielding local Froude number in excess of unity. The volume flux of the plume increases by five-fold from the sill to downstream of the shelf-break. Rotational hydraulic control is not applicable for transport estimates at the sill using upstream basin information. To the leading order, geostrophy establishes the lateral slope of the plume interface at the sill. This allows for a transport estimate that is consistent with the model results by evaluating a weir relation at the sill.
Impact of capillary hysteresis and trapping on vertically integrated models for CO2 storage
Doster, F.; Nordbotten, J. M.; Celia, M. A.
2013-12-01
Vertically integrated models are frequently applied to study subsurface flow related to CO2 storage scenarios in saline aquifers. In this paper, we study the impact of capillary-pressure hysteresis and CO2 trapping on the integrated constitutive parameter functions. Our results show that for the initial drainage and a subsequent imbibition, trapping is the dominant contributor to hysteresis in integrated models. We also find that for advective processes like injection and plume migration in a sloped aquifer the correct treatment of the hysteretic nature of the capillary fringe is likely of secondary importance. However, for diffusive/dispersive processes such as a redistribution of the CO2 plume due to buoyancy and capillary forces, the hysteretic nature of the capillary fringe may significantly impact the final distribution of the fluids and the timescale of the redistribution.
Modeling of steady motion and vertical-plane dynamics of a tunnel hull
Directory of Open Access Journals (Sweden)
Chaney Christopher S.
2014-06-01
Full Text Available High-speed marine vehicles can take advantage of aerodynamically supported platforms or air wings to increase maximum speed or transportation efficiency. However, this also results in increased complexity of boat dynamics, especially in the presence of waves and wind gusts. In this study, a mathematical model based on the fully unsteady aerodynamic extreme-ground-effect theory and the hydrodynamic added-mass strip theory is applied for simulating vertical-plane motions of a tunnel hull in a disturbed environment, as well as determining its steady states in calm conditions. Calculated responses of the boat to wind gusts and surface waves are demonstrated. The present model can be used as a supplementary method for preliminary estimations of performance of aerodynamically assisted marine craft.
Mathematical modelling of the viable epidermis: impact of cell shape and vertical arrangement
Wittum, Rebecca
2017-12-07
In-silico methods are valuable tools for understanding the barrier function of the skin. The key benefit is that mathematical modelling allows the interplay between cell shape and function to be elucidated. This study focuses on the viable (living) epidermis. For this region, previous works suggested a diffusion model and an approximation of the cells by hexagonal prisms. The work at hand extends this in three ways. First, the extracellular space is treated with full spatial resolution. This induces a decrease of permeability by about 10%. Second, cells of tetrakaidecahedral shape are considered, in addition to the original hexagonal prisms. For both cell types, the resulting membrane permeabilities are compared. Third, for the first time, the influence of cell stacking in the vertical direction is considered. This is particularly important for the stratum granulosum, where tight junctions are present.
A two-dimensional analytical model of vapor intrusion involving vertical heterogeneity
Yao, Yijun; Verginelli, Iason; Suuberg, Eric M.
2017-05-01
In this work, we present an analytical chlorinated vapor intrusion (CVI) model that can estimate source-to-indoor air concentration attenuation by simulating two-dimensional (2-D) vapor concentration profile in vertically heterogeneous soils overlying a homogenous vapor source. The analytical solution describing the 2-D soil gas transport was obtained by applying a modified Schwarz-Christoffel mapping method. A partial field validation showed that the developed model provides results (especially in terms of indoor emission rates) in line with the measured data from a case involving a building overlying a layered soil. In further testing, it was found that the new analytical model can very closely replicate the results of three-dimensional (3-D) numerical models at steady state in scenarios involving layered soils overlying homogenous groundwater sources. By contrast, by adopting a two-layer approach (capillary fringe and vadose zone) as employed in the EPA implementation of the Johnson and Ettinger model, the spatially and temporally averaged indoor concentrations in the case of groundwater sources can be higher than the ones estimated by the numerical model up to two orders of magnitude. In short, the model proposed in this work can represent an easy-to-use tool that can simulate the subsurface soil gas concentration in layered soils overlying a homogenous vapor source while keeping the simplicity of an analytical approach that requires much less computational effort.
Modelling and critical analysis of bubbly flows of dilute nanofluids in a vertical tube
Energy Technology Data Exchange (ETDEWEB)
Li, Xiangdong; Yuan, Yang [School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, PO Box 71, Bundoora, VIC 3083 (Australia); Tu, Jiyuan, E-mail: jiyuan.tu@rmit.edu.au [School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, PO Box 71, Bundoora, VIC 3083 (Australia); Key Laboratory of Ministry of Education for Advanced Reactor Engineering and Safety, Institute of Nuclear and New Energy Technology, Tsinghua University, PO Box 1021, Beijing 100086 (China)
2016-04-15
Highlights: • The classic two-fluid model needs improvement for nanofluid bubbly flows. • The nanoparticle self-assembly changes the interfacial behaviours of bubbles. • Key job is to reformulate the interfacial transfer terms. - Abstract: The bubbly flows of air–nanofluid and air–water in a vertical tube were numerically simulated using the two-fluid model. Comparison of the numerical results against the experimental data of Park and Chang (2011) demonstrated that the classic two-fluid model, although agreed well with the air–water data, was not applicable to the air–nanofluid bubbly flow. It was suggested that in a bubbly flow system, the existence of interfaces allows the spontaneous formation of a thin layer of nanoparticle assembly at the interfaces, which significantly changes the interfacial behaviours of the air bubbles and the roles of the interfacial forces. As the conservation equations of the classic two-fluid model are still applicable to nanofluids, the mechanisms underlying the modified interfacial behaviours need to be carefully taken into account when modelling air–nanofluid bubbly flows. Thus, one of the key tasks when modelling bubbly flows of air–nanofluid using the two-fluid model is to reformulate the interfacial transfer terms according to the interfacial behaviour modifications induced by nanoparticles.
A two-dimensional analytical model of vapor intrusion involving vertical heterogeneity.
Yao, Yijun; Verginelli, Iason; Suuberg, Eric M
2017-05-01
In this work, we present an analytical chlorinated vapor intrusion (CVI) model that can estimate source-to-indoor air concentration attenuation by simulating two-dimensional (2-D) vapor concentration profile in vertically heterogeneous soils overlying a homogenous vapor source. The analytical solution describing the 2-D soil gas transport was obtained by applying a modified Schwarz-Christoffel mapping method. A partial field validation showed that the developed model provides results (especially in terms of indoor emission rates) in line with the measured data from a case involving a building overlying a layered soil. In further testing, it was found that the new analytical model can very closely replicate the results of three-dimensional (3-D) numerical models at steady state in scenarios involving layered soils overlying homogenous groundwater sources. By contrast, by adopting a two-layer approach (capillary fringe and vadose zone) as employed in the EPA implementation of the Johnson and Ettinger model, the spatially and temporally averaged indoor concentrations in the case of groundwater sources can be higher than the ones estimated by the numerical model up to two orders of magnitude. In short, the model proposed in this work can represent an easy-to-use tool that can simulate the subsurface soil gas concentration in layered soils overlying a homogenous vapor source while keeping the simplicity of an analytical approach that requires much less computational effort.
Gandolfi, Ilaria; Curci, Gabriele; Falasca, Serena; Ferrero, Luca
2017-04-01
Analysis and high resolution modelling of black carbon vertical profiles measured over three Italian valleys Ilaria Gandolfi1,2, Gabriele Curci1,2, Serena Falasca1,2, Luca Ferrero3 1 Department of Physical and Chemical Sciences, University of L'Aquila, L'Aquila, Italy 2 Center of Excellence CETEMPS, University of L'Aquila, L'Aquila, Italy 3 POLARIS Research Centre, Department of Earth and Environmental Sciences, University of Milano-Bicocca, Piazza della Scienza 1, 20126, Milan, Italy Last decades were characterized by a growing interest in aerosols: mainly for their effect on human health and on the energy balance of solar and planetary radiation, thus their role in climate change. In this study, we analyze the evolution of vertical profile of black carbon (BC) through tethered balloon observations and chemistry-transport modelling. Black carbon is regarded as the second most important anthropogenic climate forcing agent and its concentration varies significantly depending on the altitude and the sources on the territory. In winter of 2010 University Of Milan Bicocca conducted three intensive measurements campaigns over three Italian basin valleys (Terni, Po Valley, Passiria Valley). The choice of the valleys was made taking into consideration the orography and the river basin structure. The measurement campaign was based on a helium-filled tethered balloon, on which the instrumentation for the analysis has been mounted; the instrumentation consisted on a meteorological station, an OPC, a cascade impactor and a micro-Aethalometer. Subsequently, at University of L'Aquila simulations were produced to help interpretation of these vertical aerosol profiles (mass, composition and distribution) and related optical properties (scattering, absorption) using a chemistry-transport model (WRF-CHIMERE) at high horizontal resolution (1 km). The analysis focused primarily on the calculation of the heating rate and of the Direct Radiative Effect (DRE), and on the analysis of the
Zhou, Bowen; Xue, Ming; Zhu, Kefeng
2017-04-01
Compared to the representation of vertical turbulent mixing through various PBL schemes, the treatment of horizontal turbulence mixing in the boundary layer within mesoscale models, with O(10) km horizontal grid spacing, has received much less attention. In mesoscale models, subgrid-scale horizontal fluxes most often adopt the gradient-diffusion assumption. The horizontal mixing coefficients are usually set to a constant, or through the 2D Smagorinsky formulation, or in some cases based on the 1.5-order turbulence kinetic energy (TKE) closure. In this work, horizontal turbulent mixing parameterizations using physically based characteristic velocity and length scales are proposed for the convective boundary layer based on analysis of a well-resolved, wide-domain large-eddy simulation (LES). The proposed schemes involve different levels of sophistication. The first two schemes can be used together with first-order PBL schemes, while the third uses TKE to define its characteristic velocity scale and can be used together with TKE-based higher-order PBL schemes. The current horizontal mixing formulations are also assessed a priori through the filtered LES results to illustrate their limitations. The proposed parameterizations are tested a posteriori in idealized simulations of turbulent dispersion of a passive scalar. Comparisons show improved horizontal dispersion by the proposed schemes, and further demonstrate the weakness of the current schemes.
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.
Genome-wide selection by mixed model ridge regression and extensions based on geostatistical models.
Schulz-Streeck, Torben; Piepho, Hans-Peter
2010-03-31
The success of genome-wide selection (GS) approaches will depend crucially on the availability of efficient and easy-to-use computational tools. Therefore, approaches that can be implemented using mixed models hold particular promise and deserve detailed study. A particular class of mixed models suitable for GS is given by geostatistical mixed models, when genetic distance is treated analogously to spatial distance in geostatistics. We consider various spatial mixed models for use in GS. The analyses presented for the QTL-MAS 2009 dataset pay particular attention to the modelling of residual errors as well as of polygenetic effects. It is shown that geostatistical models are viable alternatives to ridge regression, one of the common approaches to GS. Correlations between genome-wide estimated breeding values and true breeding values were between 0.879 and 0.889. In the example considered, we did not find a large effect of the residual error variance modelling, largely because error variances were very small. A variance components model reflecting the pedigree of the crosses did not provide an improved fit. We conclude that geostatistical models deserve further study as a tool to GS that is easily implemented in a mixed model package.
B0-bar B0 mixing in supergravity models
International Nuclear Information System (INIS)
Park, G.T.; Kang, S.K.
1996-01-01
We consider the supersymmetric contributions to B 0 d -bar B 0 d mixing in the supergravity (SUGRA) models, which arise from box diagrams where charginos and up-type squarks or charged Higgs bosons and up-type quarks are exchanged. We have calculated R, which is defined to be the ratio between the minimal supersymmetric standard model (MSSM) contributions to x d and the standard model one. By choosing a particular set of Cabibbo-Kobayashi-Maskawa parameters allowed by the present data along with the present experimental data on x d and ε, which lead to 0.7 approx-lt R approx-lt 1.4 in the MSSM, we have demonstrated an indication of possible constraints on m χ 1 ± and tanβ in the SUGRA models. As a result, for m t (m t )=170 GeV and μ>0, we obtain m χ 1 ± approx-gt 112 GeV for tanβ=2 in the no-scale SU(5)xU(1) SUGRA model and m χ 1 ± approx-gt 107(66) GeV for tanβ=2(4) in the dilaton SU(5)xU(1) SUGRA model. In the minimal SU(5) SUGRA model, however, we find no constraint from R. It will be very interesting for one to see what values for R the future experimental data would prefer. copyright 1996 The American Physical Society
On the One-Dimensional Modeling of Vertical Upward Bubbly Flow
Directory of Open Access Journals (Sweden)
C. Peña-Monferrer
2018-01-01
Full Text Available The one-dimensional two-fluid model approach has been traditionally used in thermal-hydraulics codes for the analysis of transients and accidents in water–cooled nuclear power plants. This paper investigates the performance of RELAP5/MOD3 predicting vertical upward bubbly flow at low velocity conditions. For bubbly flow and vertical pipes, this code applies the drift-velocity approach, showing important discrepancies with the experiments compared. Then, we use a classical formulation of the drag coefficient approach to evaluate the performance of both approaches. This is based on the critical Weber criteria and includes several assumptions for the calculation of the interfacial area and bubble size that are evaluated in this work. A more accurate drag coefficient approach is proposed and implemented in RELAP5/MOD3. Instead of using the Weber criteria, the bubble size distribution is directly considered. This allows the calculation of the interfacial area directly from the definition of Sauter mean diameter of a distribution. The results show that only the proposed approach was able to predict all the flow characteristics, in particular the bubble size and interfacial area concentration. Finally, the computational results are analyzed and validated with cross-section area average measurements of void fraction, dispersed phase velocity, bubble size, and interfacial area concentration.
Tu, Chia-Ying; Tseng, Wan-Ling; Kuo, Pei-Hsuan; Lan, Yung-Yao; Tsuang, Ben-Jei; Hsu, Huang-Hsiung
2017-04-01
Precipitation in Taiwan area is significantly influenced by MJO (Madden-Julian Oscillation) in the boreal winter. This study is therefore conducted by toggling the MJO prediction and simulation with a unique model structure. The one-dimensional TKE (Turbulence Kinetic Energy) type ocean model SIT (Snow, Ice, Thermocline) with refined vertical resolution near surface is able to resolve cool skin, as well as diurnal warm layer. SIT can simulate accurate SST and hence give precise air-sea interaction. By coupling SIT with ECHAM5 (MPI-Meteorology), CAM5 (NCAR) and HiRAM (GFDL), the MJO simulations in 20-yrs climate integrations conducted by three SIT-coupled AGCMs are significant improved comparing to those driven by prescribed SST. The horizontal resolutions in ECHAM5, CAM5 and HiRAM are 2-deg., 1-deg and 0.5-deg., respectively. This suggests that the improvement of MJO simulation by coupling SIT is AGCM-resolution independent. This study further utilizes HiRAM coupled SIT to evaluate its MJO forecast skill. HiRAM has been recognized as one of the best model for seasonal forecasts of hurricane/typhoon activity (Zhao et al., 2009; Chen & Lin, 2011; 2013), but was not as successful in MJO forecast. The preliminary result of the HiRAM-SIT experiment during DYNAMO period shows improved success in MJO forecast. These improvements of MJO prediction and simulation in both hindcast experiments and climate integrations are mainly from better-simulated SST diurnal cycle and diurnal amplitude, which is contributed by the refined vertical resolution near ocean surface in SIT. Keywords: MJO Predictability, DYNAMO
Goodness-of-fit tests in mixed models
Claeskens, Gerda
2009-05-12
Mixed models, with both random and fixed effects, are most often estimated on the assumption that the random effects are normally distributed. In this paper we propose several formal tests of the hypothesis that the random effects and/or errors are normally distributed. Most of the proposed methods can be extended to generalized linear models where tests for non-normal distributions are of interest. Our tests are nonparametric in the sense that they are designed to detect virtually any alternative to normality. In case of rejection of the null hypothesis, the nonparametric estimation method that is used to construct a test provides an estimator of the alternative distribution. © 2009 Sociedad de Estadística e Investigación Operativa.
Functional Nonlinear Mixed Effects Models For Longitudinal Image Data
Luo, Xinchao; Zhu, Lixing; Kong, Linglong; Zhu, Hongtu
2015-01-01
Motivated by studying large-scale longitudinal image data, we propose a novel functional nonlinear mixed effects modeling (FN-MEM) framework to model the nonlinear spatial-temporal growth patterns of brain structure and function and their association with covariates of interest (e.g., time or diagnostic status). Our FNMEM explicitly quantifies a random nonlinear association map of individual trajectories. We develop an efficient estimation method to estimate the nonlinear growth function and the covariance operator of the spatial-temporal process. We propose a global test and a simultaneous confidence band for some specific growth patterns. We conduct Monte Carlo simulation to examine the finite-sample performance of the proposed procedures. We apply FNMEM to investigate the spatial-temporal dynamics of white-matter fiber skeletons in a national database for autism research. Our FNMEM may provide a valuable tool for charting the developmental trajectories of various neuropsychiatric and neurodegenerative disorders. PMID:26213453
Local Stability of AIDS Epidemic Model Through Treatment and Vertical Transmission with Time Delay
Novi W, Cascarilla; Lestari, Dwi
2016-02-01
This study aims to explain stability of the spread of AIDS through treatment and vertical transmission model. Human with HIV need a time to positively suffer AIDS. The existence of a time, human with HIV until positively suffer AIDS can be delayed for a time so that the model acquired is the model with time delay. The model form is a nonlinear differential equation with time delay, SIPTA (susceptible-infected-pre AIDS-treatment-AIDS). Based on SIPTA model analysis results the disease free equilibrium point and the endemic equilibrium point. The disease free equilibrium point with and without time delay are local asymptotically stable if the basic reproduction number is less than one. The endemic equilibrium point will be local asymptotically stable if the time delay is less than the critical value of delay, unstable if the time delay is more than the critical value of delay, and bifurcation occurs if the time delay is equal to the critical value of delay.
Modeling containment of large wildfires using generalized linear mixed-model analysis
Mark Finney; Isaac C. Grenfell; Charles W. McHugh
2009-01-01
Billions of dollars are spent annually in the United States to contain large wildland fires, but the factors contributing to suppression success remain poorly understood. We used a regression model (generalized linear mixed-model) to model containment probability of individual fires, assuming that containment was a repeated-measures problem (fixed effect) and...
Linear models for sound from supersonic reacting mixing layers
Chary, P. Shivakanth; Samanta, Arnab
2016-12-01
We perform a linearized reduced-order modeling of the aeroacoustic sound sources in supersonic reacting mixing layers to explore their sensitivities to some of the flow parameters in radiating sound. Specifically, we investigate the role of outer modes as the effective flow compressibility is raised, when some of these are expected to dominate over the traditional Kelvin-Helmholtz (K-H) -type central mode. Although the outer modes are known to be of lesser importance in the near-field mixing, how these radiate to the far-field is uncertain, on which we focus. On keeping the flow compressibility fixed, the outer modes are realized via biasing the respective mean densities of the fast (oxidizer) or slow (fuel) side. Here the mean flows are laminar solutions of two-dimensional compressible boundary layers with an imposed composite (turbulent) spreading rate, which we show to significantly alter the growth of instability waves by saturating them earlier, similar to in nonlinear calculations, achieved here via solving the linear parabolized stability equations. As the flow parameters are varied, instability of the slow modes is shown to be more sensitive to heat release, potentially exceeding equivalent central modes, as these modes yield relatively compact sound sources with lesser spreading of the mixing layer, when compared to the corresponding fast modes. In contrast, the radiated sound seems to be relatively unaffected when the mixture equivalence ratio is varied, except for a lean mixture which is shown to yield a pronounced effect on the slow mode radiation by reducing its modal growth.
Energy Technology Data Exchange (ETDEWEB)
Brazil, Tayra Rodrigues; Neves, Marcele Florencio das; Marciano, Fernanda Roberta; Lobo, Anderson Oliveira, E-mail: aolobo@univap.br [Universidade do Vale do Paraiba (UniVap), Sao Jose dos Campos, SP (Brazil). Lab. de Nanotecnologia Biomedica; Regiani, Inacio [Instituto Tecnologico de Aeronautica (ITA), Sao Jose dos Campos, SP (Brazil)
2013-11-01
For the first time, the growth mechanism of biominerals formed on plate-like nanohydroxyapatite (nHAp) electrodeposited on superhydrophilic vertically aligned multi-walled carbon nanotubes (VAMWCNT-O{sub 2} ) is presented and a model for the specific growth preference is discussed. VAMWCNT-O{sub 2} films were obtained by microwave-assisted chemical vapor deposition method and functionalized by oxygen plasma. nHAp/VAMWCNT-O{sub 2} nanocomposites were fabricated with a direct electrodeposition of the thin nHAp films onto the VAMWCNT-O{sub 2} films. The biomineralized 'scaffolds' were obtained by soaking nHAp/VAMWCNT-O{sub 2} in simulated body fluid for 7, 14 and 21 days. Results show that the carboxyl functional groups directly attached onto VAMWCNT tips after oxygen plasma treatment were essential for the acceleration of the OH- formation and the deposition of plate-like nHAp crystals (author)
Modelling natural convection in a heated vertical channel for room ventilation
International Nuclear Information System (INIS)
Rodrigues, A.M.; Canha da Piedade, A.; Lahellec, A.; Grandpeix, J.Y.
2000-01-01
Solar-air collectors installed on the south-facing walls of school buildings have been tried out in Portugal as a passive means of improving indoor air quality without prejudice to thermal comfort requirements. A numerical investigation of the behaviour of these systems, typified as vertical channels opened at both ends, is presented for typical geometries and outdoor conditions. The study is carried out with natural convection and assumes that the induced flow is turbulent and two-dimensional. The fully averaged equations of motion and energy, added to a two-equation turbulence model, are discretized and solved following the concepts of TEF (Transfer Evolution Formalism) using a finite volume method. Flow and temperature fields are produced and results presented in terms of temperature and velocity distributions at the exit section of the duct. These enable a better understanding of the developing flow and can be helpful in the design phase of this type of system. (author)
DEFF Research Database (Denmark)
Hansen, Jørgen Drud; Nielsen, Jørgen Ulff-Møller
2006-01-01
This paper examines the effects of trade barriers on quality levels in a duopoly model for two countries with one producer in each country. The products are both vertically and horizontally differentiated. In absence of quality regulation, the two producers determine prices and quality levels...... product. On the unregulated markets, integration increases welfare in both countries if they are almost of similar size. However, if the countries are very asymmetrical with respect to size, market integration may harm welfare in the large country. Welfare effects by introduction of minimum quality...... in a two stage game. The firms choose the quality level in the first game, and their prices in the second game. The Nash equilibrium illustrates that the producer in the large country produces a higher quality than the producer in the small country. However, a reduction of the trade barrier twists...
Detection of Fraudulent Transactions Through a Generalized Mixed Linear Models
Directory of Open Access Journals (Sweden)
Jackelyne Gómez–Restrepo
2012-12-01
Full Text Available The detection of bank frauds is a topic which many financial sector companieshave invested time and resources into. However, finding patterns inthe methodologies used to commit fraud in banks is a job that primarily involvesintimate knowledge of customer behavior, with the idea of isolatingthose transactions which do not correspond to what the client usually does.Thus, the solutions proposed in literature tend to focus on identifying outliersor groups, but fail to analyse each client or forecast fraud. This paperevaluates the implementation of a generalized linear model to detect fraud.With this model, unlike conventional methods, we consider the heterogeneityof customers. We not only generate a global model, but also a model for eachcustomer which describes the behavior of each one according to their transactionalhistory and previously detected fraudulent transactions. In particular,a mixed logistic model is used to estimate the probability that a transactionis fraudulent, using information that has been taken by the banking systemsin different moments of time.
A gas flow model for layered landfills with vertical extraction wells.
Feng, Shi-Jin; Zheng, Qi-Teng; Xie, Hai-Jian
2017-08-01
This paper developed a two-dimensional axisymmetric analytical model for layered landfills with vertical wells. The model uses a horizontal layered structure to describe the waste non-homogeneity with depth in gas generation, permeability and temperature. The governing equations in the cylindrical coordinate system were transformed to dimensionless forms and solved using a method of eigenfunction expansion. After verification, the effects of different well boundary conditions and gas extraction systems on recovery efficiency were investigated. A dimensionless double-layer system, consisting of a cover and a waste layer, was also explored. The results show that a constant vacuum pressure boundary condition can be enough to describe a perforated pipe surrounded by drainage gravel with a reasonable value of well radius, such as half the radius of gravel fill. Also, the 7 independent variables (one marked with an asterisk is dimensionless) of a double-layer system can be integrated into 3 dimensionless ones: Cover permeability K v1 ∗ /(Vertical gas permeability of waste K v2 ∗ ×Cover thickness h 1 ∗ ),-Vacuum pressure p w ×P atm K v2 ∗ /(μR g T 2 ×Gas generation rate of waste s 2 ) and ln(Well radius r w ∗ )/(Anisotropy degree of waste k 2 ∗ ). The integration is based on the inherent mechanism of this flow system with certain simplification. The effects of these variables are then quantitatively characterized for a better understanding of gas recovery efficiency. Same recovery efficiency can be achieved with different variable combinations. For example, increasing h 1 ∗ (such as doubling it) has the same effect with decreasing K v1 ∗ (such as halving it). Along with the reduction of variables by half, the integration can facilitate the preliminary design, and is a small but important advance in the consideration of MSW non-homogeneity. Copyright © 2017 Elsevier Ltd. All rights reserved.
Directory of Open Access Journals (Sweden)
Flávia Marisa Prado Saldanha-Corrêa
2004-12-01
Full Text Available The vertical mixing between South Atlantic Central Water (SACW and Coastal Water (CW was simulated through microcosm experiments using the autochthonous phytoplankton community (fraction 20°C and oligotrophic. The phytoplankton growth potential of SACW, CW and an equivalent mixture of both (SACW+CW was compared, under 100, 30 and 10% of sunlight, at surface seawater temperature, in winter and summer conditions. Results demonstrate the importance of SACW as a natural eutrophication agent for the mixing layer, allowing the occurrence of new production by nutrient input, and also as a biological seeder through the development of its autochthonous phytoplankton community when it reaches the euphotic zone. The time lag for phytoplankton development during winter was around 4-5 days, against 1-2 days in summer. The hypothesis of physiological differences between surface and bottom phytoplankton populations from a deep (80 m and thermally homogeneous water column (common winter feature was also tested through the microcosm experiments. Results obtained clearly demonstrate that bottom water presented higher phytoplankton growth potential than the surface one.A mistura vertical entre a Água Central do Atlântico Sul (ACAS e a Água Costeira (AC foi simulada através de experimentos tipo microcosmos, com o fitoplâncton autóctone (fração 20°C e oligotrófica. O potencial trófico dessas águas e de uma mistura equivalente de ambas (ACAS+AC foi comparado a 100, 30 e 10% da luz solar, sob temperatura da água do mar na superfície, em condições de inverno e verão. Os resultados demonstram a importância da ACAS como agente fertilizador da camada de mistura tanto por introduzir nutrientes, favorecendo a ocorrência de produção nova, como pelo incremento da biomassa fitoplanctônica autóctone ao atingir a zona eufótica. A fase de adaptação observada no inverno foi de 4-5 dias enquanto no verão foi de 1-2 dias. A hipótese da existência de
Modeling of Cd(II) sorption on mixed oxide
International Nuclear Information System (INIS)
Waseem, M.; Mustafa, S.; Naeem, A.; Shah, K.H.; Hussain, S.Y.; Safdar, M.
2011-01-01
Mixed oxide of iron and silicon (0.75 M Fe(OH)3:0.25 M SiO/sub 2/) was synthesized and characterized by various techniques like surface area analysis, point of zero charge (PZC), energy dispersive X-rays (EDX) spectroscopy, Thermogravimetric and differential thermal analysis (TG-DTA), Fourier transform infrared spectroscopy (FTIR) and X-rays diffraction (XRD) analysis. The uptake of Cd/sup 2+/ ions on mixed oxide increased with pH, temperature and metal ion concentration. Sorption data have been interpreted in terms of both Langmuir and Freundlich models. The Xm values at pH 7 are found to be almost twice as compared to pH 5. The values of both DH and DS were found to be positive indicating that the sorption process was endothermic and accompanied by the dehydration of Cd/sup 2+/. Further, the negative value of DG confirms the spontaneity of the reaction. The ion exchange mechanism was suggested to take place for each Cd/sup 2+/ ions at pH 5, whereas ion exchange was found coupled with non specific adsorption of metal cations at pH 7. (author)
Efficient material flow in mixed model assembly lines.
Alnahhal, Mohammed; Noche, Bernd
2013-01-01
In this study, material flow from decentralized supermarkets to stations in mixed model assembly lines using tow (tugger) trains is investigated. Train routing, scheduling, and loading problems are investigated in parallel to minimize the number of trains, variability in loading and in routes lengths, and line-side inventory holding costs. The general framework for solving these problems in parallel contains analytical equations, Dynamic Programming (DP), and Mixed Integer Programming (MIP). Matlab in conjunction with LP-solve software was used to formulate the problem. An example was presented to explain the idea. Results which were obtained in very short CPU time showed the effect of using time buffer among routes on the feasible space and on the optimal solution. Results also showed the effect of the objective, concerning reducing the variability in loading, on the results of routing, scheduling, and loading. Moreover, results showed the importance of considering the maximum line-side inventory beside the capacity of the train in the same time in finding the optimal solution.
Modeling, Fabrication, and Analysis of Vertical Conduction Gallium Nitride Fin MOSFET
Tahhan, Maher Bishara
Gallium Nitride has seen much interest in the field of electronics due to its large bandgap and high mobility. In the field of power electronics, this combination leads to a low on-resistance for a given breakdown voltage. To take full advantage of this, vertical conduction transistors in GaN can give high breakdown voltages independent of chip area, leading to transistors with nominally low on resistance with high breakdown at a low cost. Acknowledging this, a vertical transistor design is presented with a small footprint area. This design utilizes a fin structure as a double gated insulated MESFET with electrons flowing from the top of the fin downward. The transistor's characteristics and design is initially explored via simulation and modelling. In this modelling, it is found that the narrow dimension of the fin must be sub-micron to allow for the device to be turned off with no leakage current and have a positive threshold voltage. Several process modules are developed and integrated to fabricate the device. A smooth vertical etch leaving low damage to the surfaces is demonstrated and characterized, preventing micromasking during the GaN dry etch. Methods of removing damage from the dry etch are tested, including regrowth and wet etching. Several hard masks were developed to be used in conjunction with this GaN etch for various requirements of the process, such as material constraints and self-aligning a metal contact. Multiple techniques are tested to deposit and pattern the gate oxide and metal to ensure good contact with the channel without causing unwanted shorts. To achieve small fin dimensions, a self-aligned transistor process flow is presented allowing for smaller critical dimensions at increased fabrication tolerances by avoiding the use of lithographic steps that require alignments to very high accuracy. In the case of the device design presented, the fins are lithographically defined at the limit of i-line stepper system. From this single
Mburu, Gitau; Iorpenda, Kate; Muwanga, Fred
2012-07-11
Efforts to prevent vertical transmission of HIV have gained momentum globally since the launch of the "Global plan towards the elimination of new HIV infections among children by 2015 and keeping their mothers alive", reflecting the growing consensus that we now have low-cost, efficacious interventions that promise to end vertical transmission of HIV. Uganda is one of the 22 focus countries in the global plan and one of the 10 countries with the highest need for prevention of vertical transmission globally. In the context of current shortfalls in the prevention of vertical HIV transmission, this paper presents the results of the Networks project, a community mobilisation model implemented by the International HIV/AIDS Alliance in Uganda, and draws out the theoretical foundations and promising community mobilization practices relevant to prevention of vertical transmission. A retrospective review of the Network project's activities, documentation and evaluation was performed. The Networks project, through community mobilisation and greater involvement of people living with HIV, reached an estimated 1.3 million people with at least one health service. By clustering 750 groups of people living with HIV into larger coalitions, the project supported existing groups to amalgamate their collective strengths and skills in outreach, referral and literacy activities; and improved reach and coverage of HIV services through strengthened linkages with healthcare facilities. Our analysis of the Networks model shows that it could contribute to the prevention of vertical transmission of HIV as a replicable and sustainable community mobilisation approach. In particular, the Networks model increased the uptake of decentralized interventions for preventing vertical transmission through community referrals; promoted male involvement through peer sensitisation; and linked communities to advocacy channels for advancing maternal health and prevention of vertical HIV transmission. BY
Modeling the North American vertical datum of 1988 errors in the conterminous United States
Li, X.
2018-02-01
A large systematic difference (ranging from -20 cm to +130 cm) was found between NAVD 88 (North AmericanVertical Datum of 1988) and the pure gravimetric geoid models. This difference not only makes it very difficult to augment the local geoid model by directly using the vast NAVD 88 network with state-of-the-art technologies recently developed in geodesy, but also limits the ability of researchers to effectively demonstrate the geoid model improvements on the NAVD 88 network. Here, both conventional regression analyses based on various predefined basis functions such as polynomials, B-splines, and Legendre functions and the Latent Variable Analysis (LVA) such as the Factor Analysis (FA) are used to analyze the systematic difference. Besides giving a mathematical model, the regression results do not reveal a great deal about the physical reasons that caused the large differences in NAVD 88, which may be of interest to various researchers. Furthermore, there is still a significant amount of no-Gaussian signals left in the residuals of the conventional regression models. On the other side, the FA method not only provides a better not of the data, but also offers possible explanations of the error sources. Without requiring extra hypothesis tests on the model coefficients, the results from FA are more efficient in terms of capturing the systematic difference. Furthermore, without using a covariance model, a novel interpolating method based on the relationship between the loading matrix and the factor scores is developed for predictive purposes. The prediction error analysis shows that about 3-7 cm precision is expected in NAVD 88 after removing the systematic difference.
Modeling the North American vertical datum of 1988 errors in the conterminous United States
Directory of Open Access Journals (Sweden)
Li X.
2018-01-01
Full Text Available A large systematic difference (ranging from −20 cm to +130 cm was found between NAVD 88 (North AmericanVertical Datum of 1988 and the pure gravimetric geoid models. This difference not only makes it very difficult to augment the local geoid model by directly using the vast NAVD 88 network with state-of-the-art technologies recently developed in geodesy, but also limits the ability of researchers to effectively demonstrate the geoid model improvements on the NAVD 88 network. Here, both conventional regression analyses based on various predefined basis functions such as polynomials, B-splines, and Legendre functions and the Latent Variable Analysis (LVA such as the Factor Analysis (FA are used to analyze the systematic difference. Besides giving a mathematical model, the regression results do not reveal a great deal about the physical reasons that caused the large differences in NAVD 88, which may be of interest to various researchers. Furthermore, there is still a significant amount of no-Gaussian signals left in the residuals of the conventional regression models. On the other side, the FA method not only provides a better not of the data, but also offers possible explanations of the error sources. Without requiring extra hypothesis tests on the model coefficients, the results from FA are more efficient in terms of capturing the systematic difference. Furthermore, without using a covariance model, a novel interpolating method based on the relationship between the loading matrix and the factor scores is developed for predictive purposes. The prediction error analysis shows that about 3-7 cm precision is expected in NAVD 88 after removing the systematic difference.
Linking effort and fishing mortality in a mixed fisheries model
DEFF Research Database (Denmark)
Thøgersen, Thomas Talund; Hoff, Ayoe; Frost, Hans Staby
2012-01-01
Since the implementation of the Common Fisheries Policy of the European Union in 1983, the management of EU fisheries has been enormously challenging. The abundance of many fish stocks has declined because too much fishing capacity has been utilised on healthy fish stocks. Today, this decline...... in fish stocks has led to overcapacity in many fisheries, leading to incentives for overfishing. Recent research has shown that the allocation of effort among fleets can play an important role in mitigating overfishing when the targeting covers a range of species (multi-species—i.e., so-called mixed...... fisheries), while simultaneously optimising the overall economic performance of the fleets. The so-called FcubEcon model, in particular, has elucidated both the biologically and economically optimal method for allocating catches—and thus effort—between fishing fleets, while ensuring that the quotas...
Directory of Open Access Journals (Sweden)
Cascaval Dan
2004-01-01
Full Text Available The mixing time for bioreactors depends mainly on the rheoiogicai properties of the broths, the biomass concentration and morphology, mixing system characteristics and fermentation conditions. For quantifying the influence of these factors on the mixing efficiency for stirred bioreactors, aerated broths of bacteria (P. shermanii, yeasts (S. cerevisiae and fungi (P. chrysogenum, free mycelia and mycelial aggregates of different concentrations have been investigated using a laboratory bioreactor with a double turbine impeller. The experimental data indicated that the influence of the rotation speed, aeration rate and stirrer positions on the mixing intensity strongly differ from one system to another and must be correlated with the microorganism characteristics, namely: the biomass concentration and morphology. Moreover, compared with non-aerated broths, variations of the mixing time with the considered parameters are very different, due to the complex flow mechanism of gas-liquid dispersions. By means of the experimental data and using a multiregression analysis method some mathematical correlations for the mixing time of the general form: tm = a1*Cx2+a2*Cx+a3*IgVa+a4-N2+a5-N+a6/a7*L2+a8*L+a9 were established. The proposed equations offer good agreement with the experiments, the average deviation being ±6.7% - ±9.4 and are adequate for the flow regime Re < 25,000.
Genotype x environment interaction in cowpea by mixed models
Directory of Open Access Journals (Sweden)
Leonardo Castelo Branco Carvalho
Full Text Available ABSTRACT Several methods have been proposed to measure effects of genotype × environment interaction (G×E on various traits of interest of plant species, such as grain yield. Among these methods, mixed models using the Restricted Maximum Likelihood (REML-Best Linear Unbiased Prediction (BLUP procedure with random genotype effects have been reported as advantageous, since they allow the obtaining of actual genotypic values for cultivation and use. The objective of this work was to evaluate the response of grain yield to different locations and years, and the effects of G×E on the performance of cowpea genotypes by the methodology of mixed models. Twenty genotypes were evaluated under rainfed conditions in 47 locations in 2010, 2011 and 2012 using randomized block design. After joint analysis, the genotypes adaptability and stability patterns within and between years were tested by the Harmonic Mean of Relative Performance of Genetic Values (HMRPGV statistics. The analysis within the years showed highly significant effects of the genotype × location interaction in all the years evaluated. The results of the joint analysis presented highly significant effects (. ≤0.01 of the genotype, and triple interaction (genotype × location × year (. ≤0.001, denoting a strong effect of the G×E on the genotype performances. The HMRPGV analysis was adequate to identify superior genotypes, highlighting the MNC02-676F-3, MNC03-737F-5-1, MNC03-737F-5-9, BRS-Tumucumaque, and BRS-Guariba as the genotypes with best stability and highest grain yield. The selection of these genotypes resulted in a new average yield (1,402 kg ha-1 which is higher than that obtained by selection based only on the phenotype (1,230 kg ha-1.
van Beek, G; Beeking, F F
1995-07-01
1. The vertical temperature profile in a broiler house depends on several factors: ground temperature, heat production by the birds, heating of litter by resting birds, stratification and radiation, microbial heat production in the litter, moisture loss from litter and natural convection around the birds. The effect on the vertical temperature profile is calculated for each factor and the effects are finally combined to estimate vertical temperature distribution. 2. The vertical temperature profile in a commercial broiler house depends on the age of the birds. Influential factors for young broilers are ground temperature and stratification. For older broilers, influential factors are floor construction and ground-water table, heat production of broilers and litter, the behaviour of the broilers and air circulation in the house. 3. Temperatures in the living zone can differ appreciably, by a maximum of about 4 degrees C, from mean house temperature. 4. The velocity of air induced by the heat production of the broilers is about 5 cm/s. This provides good air mixing in the living zone.
Leray, S.; de Dreuzy, J.-R.; Bour, O.; Bresciani, E.
2013-02-01
SummaryGroundwater resources in crystalline rock are typically associated with the weathered zone and regional sub-vertical faults that are well connected to the surface. However, some sub-horizontal and shallowly dipping fractured zones can also be highly-productive aquifers. In this paper, numerical simulations of a conceptual hydrogeological model show that the flow to such strongly transmissive fractured zones is controlled by their transmissivity or by their deepening structure. While leakage through the overlying rock units is generally the limiting factor, recharge always occurs at least close to the outcrop of the fractured zone where the overlying rock is thinner and guarantees the availability of some groundwater. At small dip angles, recharge extends spatially and the flow within the fractured zone may even become the limiting factor when the hydraulic conductivity of the overlying rock is not less than two orders of magnitude smaller than the fractured zone transmissivity. This is precisely the case of the Plœmeur aquifer (Brittany, France) located in a crystalline rock geologic setting, where groundwater in a shallowly dipping fractured zone is used as the source of water supply for a nearby city of 20,000 people. Simulation results show that the fractured zones may represent potential aquifers under a large variety of hydrogeological conditions. Aquifers in shallowly dipping structures differ strongly from those located in regional sub-vertical fault zones in terms of flow patterns, and thus supposedly in terms of management of the groundwater resource. They are more local than regional in scale, and consequently do not require regional fracture connectivity. The leakage through the overlying rock unit enhances water quality. Finally, we argue that the potential widespread occurrence of these alternative and possibly less accessible resources should promote the development of appropriate identification methods.
Hernández-Pajares, Manuel; Roma-Dollase, David; Krankowski, Andrzej; García-Rigo, Alberto; Orús-Pérez, Raül
2017-12-01
A summary of the main concepts on global ionospheric map(s) [hereinafter GIM(s)] of vertical total electron content (VTEC), with special emphasis on their assessment, is presented in this paper. It is based on the experience accumulated during almost two decades of collaborative work in the context of the international global navigation satellite systems (GNSS) service (IGS) ionosphere working group. A representative comparison of the two main assessments of ionospheric electron content models (VTEC-altimeter and difference of Slant TEC, based on independent global positioning system data GPS, dSTEC-GPS) is performed. It is based on 26 GPS receivers worldwide distributed and mostly placed on islands, from the last quarter of 2010 to the end of 2016. The consistency between dSTEC-GPS and VTEC-altimeter assessments for one of the most accurate IGS GIMs (the tomographic-kriging GIM `UQRG' computed by UPC) is shown. Typical error RMS values of 2 TECU for VTEC-altimeter and 0.5 TECU for dSTEC-GPS assessments are found. And, as expected by following a simple random model, there is a significant correlation between both RMS and specially relative errors, mainly evident when large enough number of observations per pass is considered. The authors expect that this manuscript will be useful for new analysis contributor centres and in general for the scientific and technical community interested in simple and truly external ways of validating electron content models of the ionosphere.
Computational fluid dynamics modeling of mixed convection flows in buildings enclosures
Energy Technology Data Exchange (ETDEWEB)
Kayne, Alexander; Agarwal, Ramesh K. [Department of Mechanical Engineering and Materials Science, Washington University, St. Louis, MO 63130 (United States)
2013-07-01
In recent years Computational Fluid Dynamics (CFD) simulations are increasingly used to model the air circulation and temperature environment inside the rooms of residential and office buildings to gain insight into the relative energy consumptions of various HVAC systems for cooling/heating for climate control and thermal comfort. This requires accurate simulation of turbulent flow and heat transfer for various types of ventilation systems using the Reynolds-Averaged Navier-Stokes (RANS) equations of fluid dynamics. Large Eddy Simulation (LES) or Direct Numerical Simulation (DNS) of Navier-Stokes equations is computationally intensive and expensive for simulations of this kind. As a result, vast majority of CFD simulations employ RANS equations in conjunction with a turbulence model. In order to assess the modeling requirements (mesh, numerical algorithm, turbulence model etc.) for accurate simulations, it is critical to validate the calculations against the experimental data. For this purpose, we use three well known benchmark validation cases, one for natural convection in 2D closed vertical cavity, second for forced convection in a 2D rectangular cavity and the third for mixed convection in a 2D square cavity. The simulations are performed on a number of meshes of different density using a number of turbulence models. It is found that k-epsilon two-equation turbulence model with a second-order algorithm on a reasonable mesh gives the best results. This information is then used to determine the modeling requirements (mesh, numerical algorithm, turbulence model etc.) for flows in 3D enclosures with different ventilation systems. In particular two cases are considered for which the experimental data is available. These cases are (1) air flow and heat transfer in a naturally ventilated room and (2) airflow and temperature distribution in an atrium. Good agreement with the experimental data and computations of other investigators is obtained.
Cooper, Richard J; Krueger, Tobias; Hiscock, Kevin M; Rawlins, Barry G
2014-11-01
Mixing models have become increasingly common tools for apportioning fluvial sediment load to various sediment sources across catchments using a wide variety of Bayesian and frequentist modeling approaches. In this study, we demonstrate how different model setups can impact upon resulting source apportionment estimates in a Bayesian framework via a one-factor-at-a-time (OFAT) sensitivity analysis. We formulate 13 versions of a mixing model, each with different error assumptions and model structural choices, and apply them to sediment geochemistry data from the River Blackwater, Norfolk, UK, to apportion suspended particulate matter (SPM) contributions from three sources (arable topsoils, road verges, and subsurface material) under base flow conditions between August 2012 and August 2013. Whilst all 13 models estimate subsurface sources to be the largest contributor of SPM (median ∼76%), comparison of apportionment estimates reveal varying degrees of sensitivity to changing priors, inclusion of covariance terms, incorporation of time-variant distributions, and methods of proportion characterization. We also demonstrate differences in apportionment results between a full and an empirical Bayesian setup, and between a Bayesian and a frequentist optimization approach. This OFAT sensitivity analysis reveals that mixing model structural choices and error assumptions can significantly impact upon sediment source apportionment results, with estimated median contributions in this study varying by up to 21% between model versions. Users of mixing models are therefore strongly advised to carefully consider and justify their choice of model structure prior to conducting sediment source apportionment investigations. An OFAT sensitivity analysis of sediment fingerprinting mixing models is conductedBayesian models display high sensitivity to error assumptions and structural choicesSource apportionment results differ between Bayesian and frequentist approaches.
Wallingford, Gregory; Joshi, Nikita; Callagy, Patrice; Stone, Jamie; Brown, Ian; Shen, Sam
2017-11-20
ED overcrowding is an issue that is affecting every emergency department and every hospital. The inability to maintain patient flow into and out of the emergency department paralyzes the ability to provide effective and timely patient care. Many solutions have been proposed on how to mitigate the effects of ED overcrowding. Solutions involve either hospital-wide initiatives or ED-based solutions. In this article, the authors seek to describe and provide metrics for a patient flow methodology that targets ESI 3 patients in a vertical flow model. In the Stanford Emergency Department, a vertical flow model was created from existing ED space by removing fold-down horizontal stretchers and replacing them with multiple chairs that allowed for assessment and medical management in an upright sitting position. The model was launched and sustained through frequent interdisciplinary huddles, detailed inclusion and exclusion criteria, scripted text on how to promote the flow model to patients, and close analytics of metrics. Metrics for success included patient length of stay (LOS) for those triaged to the vertical flow area compared with ESI 3 patients triaged to the traditional emergency department as a comparison group. The secondary outcome is the total number of patients seen in the vertical flow area. This was a 6-month-September 2014, to February 2015-retrospective pre- and postintervention study that examined LOS as a marker for effective launch and implementation of a vertical patient workflow model. The patients triaged to the vertical flow area in the study period tended to be younger than in the control period (43 years versus 52 years, P = 0.00). There was a significant decrease in our primary end point: the total LOS for ESI 3 patients triaged to the vertical flow area (270 minutes versus 384 minutes, P = 0.00). Implementation of a vertical patient flow strategy can decrease LOS for the vertical ESI 3 patients based upon the inclusion and exclusion criteria
Faraway, Julian J
2005-01-01
Linear models are central to the practice of statistics and form the foundation of a vast range of statistical methodologies. Julian J. Faraway''s critically acclaimed Linear Models with R examined regression and analysis of variance, demonstrated the different methods available, and showed in which situations each one applies. Following in those footsteps, Extending the Linear Model with R surveys the techniques that grow from the regression model, presenting three extensions to that framework: generalized linear models (GLMs), mixed effect models, and nonparametric regression models. The author''s treatment is thoroughly modern and covers topics that include GLM diagnostics, generalized linear mixed models, trees, and even the use of neural networks in statistics. To demonstrate the interplay of theory and practice, throughout the book the author weaves the use of the R software environment to analyze the data of real examples, providing all of the R commands necessary to reproduce the analyses. All of the ...
Spatial Linear Mixed Models with Covariate Measurement Errors.
Li, Yi; Tang, Haicheng; Lin, Xihong
2009-01-01
Spatial data with covariate measurement errors have been commonly observed in public health studies. Existing work mainly concentrates on parameter estimation using Gibbs sampling, and no work has been conducted to understand and quantify the theoretical impact of ignoring measurement error on spatial data analysis in the form of the asymptotic biases in regression coefficients and variance components when measurement error is ignored. Plausible implementations, from frequentist perspectives, of maximum likelihood estimation in spatial covariate measurement error models are also elusive. In this paper, we propose a new class of linear mixed models for spatial data in the presence of covariate measurement errors. We show that the naive estimators of the regression coefficients are attenuated while the naive estimators of the variance components are inflated, if measurement error is ignored. We further develop a structural modeling approach to obtaining the maximum likelihood estimator by accounting for the measurement error. We study the large sample properties of the proposed maximum likelihood estimator, and propose an EM algorithm to draw inference. All the asymptotic properties are shown under the increasing-domain asymptotic framework. We illustrate the method by analyzing the Scottish lip cancer data, and evaluate its performance through a simulation study, all of which elucidate the importance of adjusting for covariate measurement errors.
International Nuclear Information System (INIS)
Nihan Onder; Alberto Teyssedou; Danila Roubtsov
2005-01-01
Full text of publication follows: In CANDU reactors the fuel channels are connected to inlet and outlet headers by feeder-pipes that consist of vertical and horizontal legs. In some feeders, orifices are installed for flow adjustment. During a postulated Loss of Coolant Accidents, the emergency cooling water injected into the inlet and outlet headers enters the fuel channels through the feeder pipes. Steam produced in the feeders and in the fuel channels may flow in the direction opposite to that of the water, thereby creating vertical to horizontal Counter-Current Flow (CCF). The rate at which the cooling water enters the fuel channel may be substantially limited by the flooding phenomena that entrains the water in the same direction as the steam flow. Steam flowing in the direction opposite to the cooling water can bring about the formation of slug flow. Long slugs of liquid moving at relatively high speed are transported back towards the headers by the steam. This phenomenon substantially reduces the amount of cooling water that can reach the reactor core. We conducted CCF experiments using a vertical-to-horizontal test section connected by 90 deg. elbows, with an orifice installed in the horizontal leg. Four different orifices were used to carry out the experiments. We have observed that soliton-type waves generated close to the elbow propagate in the horizontal leg towards the orifice, where a partial reflection takes place. Without an orifice, the soliton waves are reflected from the second elbow. The reflected waves move in the opposite direction to that of the incident wave. Since soliton-type waves are periodically generated, the incident and reflected waves interfere at some place in the horizontal leg. If the amplitude of the interference wave is high enough, the bridging of the tubes occur, which generates the slugs. During the experiments the water and air flow rates, pressures and void fraction distributions were measured. The slug propagation
MM 99.58 Physical modelling of Hammerhead forging, Vertical and Lateral load history
DEFF Research Database (Denmark)
Arentoft, Mogens; Eriksen, Morten; Wanheim, Tarras
1999-01-01
The present report presents a laboratory setup with hammerhead forging, where the vertical and lateral force history is obtained under different process conditions......The present report presents a laboratory setup with hammerhead forging, where the vertical and lateral force history is obtained under different process conditions...
Directory of Open Access Journals (Sweden)
Yanwei Fan
2018-01-01
Full Text Available Vertical line source irrigation is a water-saving irrigation method for enhancing direct water and nutrient delivery to the root zone, reducing soil evaporation and improving water and nutrient use efficiency. To identify its influencing factors, we performed computer simulations using the HYDRUS-2D software. The results indicate that for a given soil, the line source seepage area, but not the initial soil water content and buried depth, has a significant effect on the cumulative infiltration. We thus proposed a simplified method, taking into account the seepage area for predicting the cumulative infiltration based on the Philip model. Finally, we evaluated the accuracy of the simplified method using experimental data and found the cumulative infiltrations predicted by the simplified method were in very good agreement with the observed values, showing a low mean average error of 0.028–0.480 L, a root mean square error of 0.043–0.908 L, a percentage bias of 0.321–0.900 and a large Nash-Sutcliffe coefficient close to 1.0 (NSE ≥ 0.995. The results indicate that this simplified infiltration model, for which the only emitter parameter required is the seepage area, could provide a valuable and practical tool for irrigation design.
Chong, Song Hun
2016-08-09
Geosystems often experience numerous loading cycles. Plastic strain accumulation during repetitive mechanical loads can lead to shear shakedown or continued shear ratcheting; in all cases, volumetric strains diminish as the specimen evolves towards terminal density. Previously suggested models and new functions are identified to fit plastic strain accumulation data. All accumulation models are formulated to capture terminal density (volumetric strain) and either shakedown or ratcheting (shear strain). Repetitive vertical loading tests under zero lateral strain conditions are conducted using three different sands packed at initially low and high densities. Test results show that plastic strain accumulation for all sands and density conditions can be captured in the same dimensionless plot defined in terms of the initial relative density, terminal density, and ratio between the amplitude of the repetitive load and the initial static load. This observation allows us to advance a simple but robust procedure to estimate the maximum one-dimensional settlement that a foundation could experience if subjected to repetitive loads. © 2016, Canadian Science Publishing. All rights reserved.
A constraint programming model for mixed model type 2 assembly line balancing problem
Directory of Open Access Journals (Sweden)
Hacı Mehmet Alağaş
2016-08-01
Full Text Available This paper presents a new constraint programming model for mixed-model assembly line balancing problem. The proposed model minimizes the cycle time for a given number of stations. The proposed model is tested with literature problems and its performance is evaluated by comparing to mathematical model. Best obtained solution and elapsed CPU time are used as performance criteria. The experimental results show that the proposed constraint programming model performs well and can be used as an alternative modeling technique to solve the problem.
International Nuclear Information System (INIS)
Yang Tianxing; Ye Xiang; Huang Lei; Xie Yiqun; Ke Sanhuang
2012-01-01
Highlights: ► We simulate the reversible vertical single-atom manipulations on several metal surfaces. ► We propose a method to predict whether a reversible vertical single-atom manipulation can be successful on several metal surfaces. ► A 3-dimensional Ni nanocluster is assembled on the Ni(1 1 1) surface using a Ni trimer-apex tip. - Abstract: We propose a theoretical model to show that pulling up an adatom from an atomic step requires a weaker force than from the flat surfaces of Al(0 0 1), Ni(1 1 1), Pt(1 1 0) and Au(1 1 0). Single adatom in the atomic step can be extracted vertically by a trimer-apex tip while can be released to the flat surface. This reversible vertical manipulation can then be used to fabricate a supported three-dimensional (3D) nanostructure on the Ni(1 1 1) surface. The present modeling can be used to predict whether the reversible vertical single-atom manipulation and thus the assembling of 3D nanostructures can be achieved on a metal surface.
Car Delay Model near Bus Stops with Mixed Traffic Flow
Directory of Open Access Journals (Sweden)
Yang Xiaobao
2013-01-01
Full Text Available This paper proposes a model for estimating car delays at bus stops under mixed traffic using probability theory and queuing theory. The roadway is divided to serve motorized and nonmotorized traffic streams. Bus stops are located on the nonmotorized lanes. When buses dwell at the stop, they block the bicycles. Thus, two conflict points between car stream and other traffic stream are identified. The first conflict point occurs as bicycles merge to the motorized lane to avoid waiting behind the stopping buses. The second occurs as buses merge back to the motorized lane. The average car delay is estimated as the sum of the average delay at these two conflict points and the delay resulting from following the slower bicycles that merged into the motorized lane. Data are collected to calibrate and validate the developed model from one site in Beijing. The sensitivity of car delay to various operation conditions is examined. The results show that both bus stream and bicycle stream have significant effects on car delay. At bus volumes above 200 vehicles per hour, the curbside stop design is not appropriate because of the long car delays. It can be replaced by the bus bay design.
Multi-scale friction modeling for sheet metal forming: the mixed lubrication regime
Hol, J.; Meinders, Vincent T.; Geijselaers, Hubertus J.M.; van den Boogaard, Antonius H.
2015-01-01
A mixed lubrication friction model is presented to accurately account for friction in sheet metal forming FE sim-ulations. The advanced friction model comprises a coupling between a hydrodynamic friction model and a boundary lubrication friction model, based on the lubricant ﬁlm thickness. Mixed
Towards developing a general framework for modelling vertical migration in zooplankton.
Morozov, Andrew Yu; Kuzenkov, Oleg A
2016-09-21
Diel vertical migration (DVM) of zooplankton is a widespread phenomenon in both oceans and lakes, and is generally considered to be the largest synchronized movement of biomass on Earth. Most existing mathematical models of DVM are based on the assumption that animals maximize a certain criterion such as the expected reproductive value, the venturous revenue, the ratio of energy gain/mortality or some predator avoidance function when choosing their instantaneous depth. The major shortcoming of this general point of view is that the predicted DVM may be strongly affected by a subjective choice of a particular optimization criterion. Here we argue that the optimal strategy of DVM can be unambiguously obtained as an outcome of selection in the underlying equations of genotype/traits frequency dynamics. Using this general paradigm, we explore the optimal strategy for the migration across different depths by zooplankton grazers throughout the day. To illustrate our ideas we consider four generic DVM models, each making different assumptions on the population dynamics of zooplankton, and demonstrate that in each model we need to maximize a particular functional to find the optimal strategy. Surprisingly, patterns of DVM obtained for different models greatly differ in terms of their parameters dependence. We then show that the infinite dimensional trait space of different zooplankton trajectories can be projected onto a low dimensional space of generalized parameters and the genotype evolution dynamics can be easily followed using this low-dimensional space. Using this space of generalized parameters we explore the influence of mutagenesis on evolution of DVM, and we show that strong mutagenesis allows the coexistence of an infinitely large number of strategies whereas for weak mutagenesis the selection results in the extinction of most strategies, with the surviving strategies all staying close to the optimal strategy in the corresponding mutagenesis-free system
Constraining Early Cenozoic exhumation of the British Isles with vertical profile modelling
Doepke, Daniel; Cogné, Nathan; Chew, David
2016-04-01
Despite decades of research is the Early Cenozoic exhumation history of Ireland and Britain still poorly understood and subject to contentious debate (e.g., Davis et al., 2012 and subsequent comments). One reason for this debate is the difficultly of constraining the evolution of onshore parts of the British Isles in both time and space. The paucity of Mesozoic and Cenozoic onshore outcrops makes direct analysis of this time span difficult. Furthermore, Ireland and Britain are situated at a passive margin, where the amount of post-rift exhumation is generally very low. Classical thermochronological tools are therefore near the edge of their resolution and make precise dating of post-rift cooling events challenging. In this study we used the established apatite fission track and (U-Th-Sm)/He techniques, but took advantage of the vertical profile approach of Gallagher et al. (2005) implemented in the QTQt modelling package (Gallagher, 2012), to better constrain the thermal histories. This method allowed us to define the geographical extent of a Late Cretaceous - Early Tertiary cooling event and to show that it was centered around the Irish Sea. Thus, we argue that this cooling event is linked to the underplating of hot material below the crust centered on the Irish Sea (Jones et al., 2002; Al-Kindi et al., 2003), and demonstrate that such conclusion would have been harder, if not impossible, to draw by modelling the samples individually without the use of the vertical profile approach. References Al-Kindi, S., White, N., Sinha, M., England, R., and Tiley, R., 2003, Crustal trace of a hot convective sheet: Geology, v. 31, no. 3, p. 207-210. Davis, M.W., White, N.J., Priestley, K.F., Baptie, B.J., and Tilmann, F.J., 2012, Crustal structure of the British Isles and its epeirogenic consequences: Geophysical Journal International, v. 190, no. 2, p. 705-725. Jones, S.M., White, N., Clarke, B.J., Rowley, E., and Gallagher, K., 2002, Present and past influence of the Iceland
Directory of Open Access Journals (Sweden)
Z. Kipling
2016-02-01
Full Text Available The vertical profile of aerosol is important for its radiative effects, but weakly constrained by observations on the global scale, and highly variable among different models. To investigate the controlling factors in one particular model, we investigate the effects of individual processes in HadGEM3–UKCA and compare the resulting diversity of aerosol vertical profiles with the inter-model diversity from the AeroCom Phase II control experiment. In this way we show that (in this model at least the vertical profile is controlled by a relatively small number of processes, although these vary among aerosol components and particle sizes. We also show that sufficiently coarse variations in these processes can produce a similar diversity to that among different models in terms of the global-mean profile and, to a lesser extent, the zonal-mean vertical position. However, there are features of certain models' profiles that cannot be reproduced, suggesting the influence of further structural differences between models. In HadGEM3–UKCA, convective transport is found to be very important in controlling the vertical profile of all aerosol components by mass. In-cloud scavenging is very important for all except mineral dust. Growth by condensation is important for sulfate and carbonaceous aerosol (along with aqueous oxidation for the former and ageing by soluble material for the latter. The vertical extent of biomass-burning emissions into the free troposphere is also important for the profile of carbonaceous aerosol. Boundary-layer mixing plays a dominant role for sea salt and mineral dust, which are emitted only from the surface. Dry deposition and below-cloud scavenging are important for the profile of mineral dust only. In this model, the microphysical processes of nucleation, condensation and coagulation dominate the vertical profile of the smallest particles by number (e.g. total CN > 3 nm, while the profiles of larger particles (e.g. CN
Numerical modelling of the atmospheric mixing-layer diurnal evolution
International Nuclear Information System (INIS)
Molnary, L. de.
1990-03-01
This paper introduce a numeric procedure to determine the temporal evolution of the height, potential temperature and mixing ratio in the atmospheric mixing layer. The time and spatial derivatives were evaluated via forward in time scheme to predict the local evolution of the mixing-layer parameters, and a forward in time, upstream in space scheme to predict the evolution of the mixing-layer over a flat region with a one-dimensional advection component. The surface turbulent fluxes of sensible and latent heat were expressed using a simple sine wave that is function of the hour day and kind of the surface (water or country). (author) [pt
Oxygen reduction kinetics on mixed conducting SOFC model cathodes
Energy Technology Data Exchange (ETDEWEB)
Baumann, F.S.
2006-07-01
The kinetics of the oxygen reduction reaction at the surface of mixed conducting solid oxide fuel cell (SOFC) cathodes is one of the main limiting factors to the performance of these promising systems. For ''realistic'' porous electrodes, however, it is usually very difficult to separate the influence of different resistive processes. Therefore, a suitable, geometrically well-defined model system was used in this work to enable an unambiguous distinction of individual electrochemical processes by means of impedance spectroscopy. The electrochemical measurements were performed on dense thin film microelectrodes, prepared by PLD and photolithography, of mixed conducting perovskite-type materials. The first part of the thesis consists of an extensive impedance spectroscopic investigation of La0.6Sr0.4Co0.8Fe0.2O3 (LSCF) microelectrodes. An equivalent circuit was identified that describes the electrochemical properties of the model electrodes appropriately and enables an unambiguous interpretation of the measured impedance spectra. Hence, the dependencies of individual electrochemical processes such as the surface exchange reaction on a wide range of experimental parameters including temperature, dc bias and oxygen partial pressure could be studied. As a result, a comprehensive set of experimental data has been obtained, which was previously not available for a mixed conducting model system. In the course of the experiments on the dc bias dependence of the electrochemical processes a new and surprising effect was discovered: It could be shown that a short but strong dc polarisation of a LSCF microelectrode at high temperature improves its electrochemical performance with respect to the oxygen reduction reaction drastically. The electrochemical resistance associated with the oxygen surface exchange reaction, initially the dominant contribution to the total electrode resistance, can be reduced by two orders of magnitude. This &apos
Generalized Degrees of Freedom and Adaptive Model Selection in Linear Mixed-Effects Models.
Zhang, Bo; Shen, Xiaotong; Mumford, Sunni L
2012-03-01
Linear mixed-effects models involve fixed effects, random effects and covariance structure, which require model selection to simplify a model and to enhance its interpretability and predictability. In this article, we develop, in the context of linear mixed-effects models, the generalized degrees of freedom and an adaptive model selection procedure defined by a data-driven model complexity penalty. Numerically, the procedure performs well against its competitors not only in selecting fixed effects but in selecting random effects and covariance structure as well. Theoretically, asymptotic optimality of the proposed methodology is established over a class of information criteria. The proposed methodology is applied to the BioCycle study, to determine predictors of hormone levels among premenopausal women and to assess variation in hormone levels both between and within women across the menstrual cycle.
Metabolic modelling of polyhydroxyalkanoate copolymers production by mixed microbial cultures
Directory of Open Access Journals (Sweden)
Reis Maria AM
2008-07-01
Full Text Available Abstract Background This paper presents a metabolic model describing the production of polyhydroxyalkanoate (PHA copolymers in mixed microbial cultures, using mixtures of acetic and propionic acid as carbon source material. Material and energetic balances were established on the basis of previously elucidated metabolic pathways. Equations were derived for the theoretical yields for cell growth and PHA production on mixtures of acetic and propionic acid as functions of the oxidative phosphorylation efficiency, P/O ratio. The oxidative phosphorylation efficiency was estimated from rate measurements, which in turn allowed the estimation of the theoretical yield coefficients. Results The model was validated with experimental data collected in a sequencing batch reactor (SBR operated under varying feeding conditions: feeding of acetic and propionic acid separately (control experiments, and the feeding of acetic and propionic acid simultaneously. Two different feast and famine culture enrichment strategies were studied: (i either with acetate or (ii with propionate as carbon source material. Metabolic flux analysis (MFA was performed for the different feeding conditions and culture enrichment strategies. Flux balance analysis (FBA was used to calculate optimal feeding scenarios for high quality PHA polymers production, where it was found that a suitable polymer would be obtained when acetate is fed in excess and the feeding rate of propionate is limited to ~0.17 C-mol/(C-mol.h. The results were compared with published pure culture metabolic studies. Conclusion Acetate was more conducive toward the enrichment of a microbial culture with higher PHA storage fluxes and yields as compared to propionate. The P/O ratio was not only influenced by the selected microbial culture, but also by the carbon substrate fed to each culture, where higher P/O ratio values were consistently observed for acetate than propionate. MFA studies suggest that when mixtures of
Prediction of stock markets by the evolutionary mix-game model
Chen, Fang; Gou, Chengling; Guo, Xiaoqian; Gao, Jieping
2008-06-01
This paper presents the efforts of using the evolutionary mix-game model, which is a modified form of the agent-based mix-game model, to predict financial time series. Here, we have carried out three methods to improve the original mix-game model by adding the abilities of strategy evolution to agents, and then applying the new model referred to as the evolutionary mix-game model to forecast the Shanghai Stock Exchange Composite Index. The results show that these modifications can improve the accuracy of prediction greatly when proper parameters are chosen.
Log-normal frailty models fitted as Poisson generalized linear mixed models.
Hirsch, Katharina; Wienke, Andreas; Kuss, Oliver
2016-12-01
The equivalence of a survival model with a piecewise constant baseline hazard function and a Poisson regression model has been known since decades. As shown in recent studies, this equivalence carries over to clustered survival data: A frailty model with a log-normal frailty term can be interpreted and estimated as a generalized linear mixed model with a binary response, a Poisson likelihood, and a specific offset. Proceeding this way, statistical theory and software for generalized linear mixed models are readily available for fitting frailty models. This gain in flexibility comes at the small price of (1) having to fix the number of pieces for the baseline hazard in advance and (2) having to "explode" the data set by the number of pieces. In this paper we extend the simulations of former studies by using a more realistic baseline hazard (Gompertz) and by comparing the model under consideration with competing models. Furthermore, the SAS macro %PCFrailty is introduced to apply the Poisson generalized linear mixed approach to frailty models. The simulations show good results for the shared frailty model. Our new %PCFrailty macro provides proper estimates, especially in case of 4 events per piece. The suggested Poisson generalized linear mixed approach for log-normal frailty models based on the %PCFrailty macro provides several advantages in the analysis of clustered survival data with respect to more flexible modelling of fixed and random effects, exact (in the sense of non-approximate) maximum likelihood estimation, and standard errors and different types of confidence intervals for all variance parameters. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.
Vertical propagation of baroclinic Kelvin waves along the west coast of India
Digital Repository Service at National Institute of Oceanography (India)
Nethery, D.; Shankar, D.
, this paper is intended to provide the motivation for studying the vertical propagation of coastal Kelvin waves with a general circulation model, allowing the influence of density variations, basin geometry, and mixing processes to be examined...
Modelling of the vertical migration process of phosphogypsum components in the soil profile
Directory of Open Access Journals (Sweden)
Chernysh Ye. Yu.
2017-12-01
Full Text Available This paper focuses on the study of the process of vertical migration of phosphogypsum components according to the soil profile. The qualitative and quantitative identification of main biogenic elements (phosphorus, sulphur, calcium etc and heavy metals in lysimetric solutions from various horizons while getting on the surface of soil solutions containing phosphogypsum components is carried out by means of designed laboratory and experimental complex. The mineral hard soil fraction is also analysed. According to the results of the X-ray diffractometrical researches, the carbonates with heavy metals in their structure, caused by the ion-exchange with Са2+, were found in the mineral structure of the illuvial horizon soil samples. The results of experimental modeling indicate significant changes in the chemical parameters of groundwater, which are obtained by passing water with phosphogypsum particles on a model soil profile, which makes it easy to track the input data. In the upper part of the profile after 1 000 hours and for the first speed of the infiltration process, the constant moisture level was 25,6%, after the second speed of infiltration, it rose to 29.1 %. Noted that the highest concentration of biogenic elements (calcium, sulfur, potassium was found in lysimetric solutions obtained from the humus and eluvial horizons. In addition, it is determined that iron is present up to 5 %, nickel – within the range of 1–3 %, and copper – up to 1 %. It should be noted that the biochemical transformations of silicon influence the fractional distribution of heavy metals, which can be fixed by sorption-sedimentation mechanisms in silica, oligo and polysilicon compounds, as well as in crystalline lattice structures of clay minerals, quartz, etc. The model of soil and geochemical situation was formed according to the soil profile under the influence of the phosphogypsum within the three-dimensional surface, developed with the help of the
Digital Repository Service at National Institute of Oceanography (India)
AnilKumar, N.; Singbal, S.Y.S.
The vertical advection-diffusion model proposed by Craig has been applied to the study of CO sub(2) and O sub(2) profiles in Central Arabian Sea. Distributions of total CO Sub(2) and O sub(2) are explained better by expressions involving exponential...
International Nuclear Information System (INIS)
Soroko, L.M.
2001-01-01
The first test model of the optical microscope which produces the in focus image of the whole vertical particle track without depth scanning is described. The in focus image of the object consisting of the linear array of the point-like elements was obtained. A comparison with primary out of focus image of such an object has been made
Vertical Accuracy Assessment of ZY-3 Digital Surface Model Using Icesat/glas Laser Altimeter Data
Li, G.; Tang, X.; Yuan, X.; Zhou, P.; Hu, F.
2017-05-01
The Ziyuan-3 (ZY-3) satellite, as the first civilian high resolution surveying and mapping satellite in China, has a very important role in national 1 : 50,000 stereo mapping project. High accuracy digital surface Model (DSMs) can be generated from the three line-array images of ZY-3, and ZY-3 DSMs of China can be produced without using any ground control points (GCPs) by selecting SRTM (Shuttle Radar Topography Mission) and ICESat/GLAS (Ice, Cloud, and land Elevation Satellite, Geo-science Laser Altimeter System) as the datum reference in the Satellite Surveying and Mapping Application Center, which is the key institute that manages and distributes ZY-3 products. To conduct the vertical accuracy evaluation of ZY-3 DSMs of China, three representative regions were chosen and the results were compared to ICESat/GLAS data. The experimental results demonstrated that the root mean square error (RMSE) elevation accuracy of the ZY-3 DSMs was better than 5.0 m, and it even reached to less than 2.5 m in the second region of eastern China. While this work presents preliminary results, it is an important reference for expanding the application of ZY-3 satellite imagery to widespread regions. And the satellite laser altimetry data can be used as referenced data for wide-area DSM evaluation.
Directory of Open Access Journals (Sweden)
Lisha Zhao
2016-01-01
Full Text Available An analytical model has been developed for quantitative evaluation of vertical sweep efficiency based on heterogeneous multilayer reservoirs. By applying the Buckley-Leverett displacement mechanism, a theoretical relationship is deduced to describe dynamic changes of the front of water injection, water saturation of producing well, and swept volume during waterflooding under the condition of constant pressure, which substitutes for the condition of constant rate in the traditional way. Then, this method of calculating sweep efficiency is applied from single layer to multilayers, which can be used to accurately calculate the sweep efficiency of heterogeneous reservoirs and evaluate the degree of waterflooding in multilayer reservoirs. In the case study, the water frontal position, water cut, volumetric sweep efficiency, and oil recovery are compared between commingled injection and zonal injection by applying the derived equations. The results are verified by numerical simulators, respectively. It is shown that zonal injection works better than commingled injection in respect of sweep efficiency and oil recovery and has a longer period of water free production.
Lawson, William J.; Shirey, Kristin; Spann, Redin A.; Zamarripa, C. Austin; Hosler, Jonathan P.; Grayson, Bernadette E.
2016-01-01
Objective Though females are the most common recipients of weight loss surgeries for the amelioration of the comorbidities of obesity, few studies have addressed the efficacy of these procedures with specific attention to reproductive stage. Here we ask in a rodent model of vertical sleeve gastrectomy (VSG) whether improvements to metabolic health are realized in females having received surgical menopause. Specifically we were interested in knowing whether rats made menopausal through surgical means would exhibit persistent hepatic steatosis as reported in previously pregnant, freely-cycling female VSG rats or if it is resolved as reported in male VSG rats. Methods All the rats first received ovariectomy (OVX) and then were placed on high fat diet (HFD) prior to either sham or VSG surgery (N = 12, 9) and then were monitored for resolution of obesity-related comorbidities. Results VSG was sufficient to reduce weight and adiposity in OVX females in comparison to Obese rats (P change in insulin sensitivity. Both circulating (P < 0.01) and hepatic triglyceride (P < 0.01) levels were also reduced after VSG. Liver integrity was improved in OVX-VSG in comparison to OVX-Obese as reflected by reduced aspartate aminotransferase (AST) levels (P < 0.05). The ability of mitochondria to generate ATP was maintained and an increase in complex IV may decrease the production of mitochondrial ROS. Conclusions Taken together, VSG in ovariectomized animals experience many positive benefits including the resolution of hepatic steatosis that persists in reproductively-intact female rats after VSG. PMID:27801704
Modeling Microalgae Productivity in Industrial-Scale Vertical Flat Panel Photobioreactors.
Endres, Christian Hermann; Roth, Arne; Brück, Thomas Bartholomaeus
2018-03-29
Potentially achievable biomass yields are a decisive performance indicator for the economic viability of mass cultivation of microalgae. In this study, a computer model has been developed and applied to estimate the productivity of microalgae for large-scale outdoor cultivation in vertical flat panel photobioreactors. Algae growth is determined based on simulations of the reactor temperature and light distribution. Site-specific weather and irradiation data are used for annual yield estimations in six climate zones. Shading and reflections between opposing panels and between panels and the ground are dynamically computed based on the reactor geometry and the position of the sun. The results indicate that thin panels (≤ 0.05 m) are best suited for the assumed cell density of 2 g L -1 and that reactor panels should face in north-south direction. Panel spacings of 0.4 - 0.75 m appear most suitable for commercial applications. Under these preconditions, yields of around 10 kg m -2 a -1 are possible for most locations in the U.S. Only in hot climates significantly lower yields have to be expected, as extreme reactor temperatures limit overall productivity.
VERTICAL ACCURACY ASSESSMENT OF ZY-3 DIGITAL SURFACE MODEL USING ICESAT/GLAS LASER ALTIMETER DATA
Directory of Open Access Journals (Sweden)
G. Li
2017-05-01
Full Text Available The Ziyuan-3 (ZY-3 satellite, as the first civilian high resolution surveying and mapping satellite in China, has a very important role in national 1 : 50,000 stereo mapping project. High accuracy digital surface Model (DSMs can be generated from the three line-array images of ZY-3, and ZY-3 DSMs of China can be produced without using any ground control points (GCPs by selecting SRTM (Shuttle Radar Topography Mission and ICESat/GLAS (Ice, Cloud, and land Elevation Satellite, Geo-science Laser Altimeter System as the datum reference in the Satellite Surveying and Mapping Application Center, which is the key institute that manages and distributes ZY-3 products. To conduct the vertical accuracy evaluation of ZY-3 DSMs of China, three representative regions were chosen and the results were compared to ICESat/GLAS data. The experimental results demonstrated that the root mean square error (RMSE elevation accuracy of the ZY-3 DSMs was better than 5.0 m, and it even reached to less than 2.5 m in the second region of eastern China. While this work presents preliminary results, it is an important reference for expanding the application of ZY-3 satellite imagery to widespread regions. And the satellite laser altimetry data can be used as referenced data for wide-area DSM evaluation.
Rensink, Arend; Gorrieri, Roberto
We investigate criteria to relate specifications and implementations belonging to conceptually different abstraction levels, and propose vertical bisimulation as a candidate relation for this purpose. Vertical bisimulation is indexed by a function mapping abstract actions onto concrete processes,
International Nuclear Information System (INIS)
Bunn, Derek W.; Martoccia, Maria; Ochoa, Patricia; Kim, Haein; Ahn, Nam-Sung; Yoon, Yong-Beom
2010-01-01
An agent-based simulation model is developed using computational learning to investigate the impact of vertical integration between electricity generators and retailers on market power in a competitive wholesale market setting. It is observed that if partial vertical integration creates some market foreclosure, whether this leads to an increase or decrease in market power is situation specific. A detailed application to the Korean market structure reveals this to be the case. We find that in various cases, whilst vertical integration generally reduces spot prices, it can increase or decrease the market power of other market generators, depending upon the market share and the technology segment of the market, which is integrated, as well as the market concentrations before and after the integration.
Directory of Open Access Journals (Sweden)
Yan Zhu
2016-05-01
Full Text Available Due to the high nonlinearity of the three-dimensional (3-D unsaturated-saturated water flow equation, using a fully 3-D numerical model is computationally expensive for large scale applications. A new unsaturated-saturated water flow model is developed in this paper based on the vertical/horizontal splitting (VHS concept to split the 3-D unsaturated-saturated Richards’ equation into a two-dimensional (2-D horizontal equation and a one-dimensional (1-D vertical equation. The horizontal plane of average head gradient in the triangular prism element is derived to split the 3-D equation into the 2-D equation. The lateral flow in the horizontal plane of average head gradient represented by the 2-D equation is then calculated by the water balance method. The 1-D vertical equation is discretized by the finite difference method. The two equations are solved simultaneously by coupling them into a unified nonlinear system with a single matrix. Three synthetic cases are used to evaluate the developed model code by comparing the modeling results with those of Hydrus1D, SWMS2D and FEFLOW. We further apply the model to regional-scale modeling to simulate groundwater table fluctuations for assessing the model applicability in complex conditions. The proposed modeling method is found to be accurate with respect to measurements.
Nanying Shentu; Guohua Qiu; Xiong Li; Renyuan Tong; Qing Li
2014-01-01
Due to invisibility and complexity of the underground displacement monitoring, there exit few practical monitoring sensors capable of monitoring the underground horizontal and vertical displacements simultaneously. A novel electromagnetic underground displacement sensor able to monitor both the horizontal and the vertical displacements was proposed in our previous studies and abbreviated as the H-V type sensor. Through comprehensive application of Hall sensing mechanism analysis, 3D magnetic ...
Czech Academy of Sciences Publication Activity Database
Jordanova, P.; Dušek, Jiří; Stehlík, M.
2013-01-01
Roč. 128, OCT 15 (2013), s. 124-134 ISSN 0169-7439 R&D Projects: GA ČR(CZ) GAP504/11/1151; GA MŠk(CZ) ED1.1.00/02.0073 Institutional support: RVO:67179843 Keywords : environmental chemistry * ebullition of methane * mixed poisson processes * renewal process * pareto distribution * moving average process * robust statistics * sedge–grass marsh Subject RIV: EH - Ecology, Behaviour Impact factor: 2.381, year: 2013
Digital Repository Service at National Institute of Oceanography (India)
Nakamoto, S.; PrasannaKumar, S.; Oberhuber, J.M.; Saito, H.; Muneyama, K.
and supported by quasi-steady upwelling. Remotely sensed chlorophyll pigment concentrations from the Coastal Zone Color Scanner (CZCS) are used to investigate the chlorophyll modulation of ocean mixed layer thermodynamics in a bulk mixed-layer model, embedded...
From linear to generalized linear mixed models: A case study in repeated measures
Compared to traditional linear mixed models, generalized linear mixed models (GLMMs) can offer better correspondence between response variables and explanatory models, yielding more efficient estimates and tests in the analysis of data from designed experiments. Using proportion data from a designed...
Estimating marginal properties of quantitative real-time PCR data using nonlinear mixed models
DEFF Research Database (Denmark)
Gerhard, Daniel; Bremer, Melanie; Ritz, Christian
2014-01-01
A unified modeling framework based on a set of nonlinear mixed models is proposed for flexible modeling of gene expression in real-time PCR experiments. Focus is on estimating the marginal or population-based derived parameters: cycle thresholds and ΔΔc(t), but retaining the conditional mixed mod...
Viswanathan, Sharadha; Pope, Stephen B.
2007-11-01
Probability density function (PDF) calculations are reported for the dispersion from line sources in isotropic turbulence. These flows pose a significant challenge to statistical models, because the scalar length scale (of the initial plume) is much smaller than the turbulence integral scale. The PDF calculations are based on a new near-neighbor implementation of the interaction by exchange with the conditional mean (IECM) mixing model. The calculations are compared to the experimental data of Warhaft (1984) on single and pairs of line sources, and with the previous calculations of Sawford (2004). This establishes the accuracy of the new implementation of IECM. An array of line sources is also considered with comparison to the experimental data of Warhaft & Lumley (1978), which show the dependence of the scalar variance decay rate on the array spacing relative to the turbulence integral scale. The near-neighbor implementation is applicable to other local mixing models, as arise, for example, in multiple mapping conditioning (Klimenko & Pope 2003). In the particle method used to solve the modeled PDF equation, the near-neighbor implementation results in a particle's mixing with just one or two near neighbors (in the relevant space), and hence maximizes the localness of mixing.
International Nuclear Information System (INIS)
Guerra Aristizabal, Jose Julian; Grosso Vargas, Jorge Luis
2005-01-01
Recently it has been proposed the incorporation of horizontal well technologies in thermal EOR processes like the in situ combustion process (ISC). This has taken to the conception of new recovery mechanisms named here as segregated in-situ combustion processes, which are conventional in-situ combustion process with a segregated flow component. Top/Down combustion, Combustion Override Split-production Horizontal-well and Toe-to-Heel Air Injection are three of these processes, which incorporate horizontal producers and gravity drainage phenomena. When applied to thick reservoirs a process of this nature could be reasonably modeled under concepts of conventional in-situ combustion and Crestal Gas injection, especially for heavy oils mobile at reservoir conditions. A process of this nature has been studied through an analytic model conceived for the particular conditions of the Castilla field, a homogeneous thick anticline structure containing high mobility heavy oil, which seems to be an excellent candidate for the application of these technologies
DEFF Research Database (Denmark)
Holst, René; Jørgensen, Bent
2015-01-01
The paper proposes a versatile class of multiplicative generalized linear longitudinal mixed models (GLLMM) with additive dispersion components, based on explicit modelling of the covariance structure. The class incorporates a longitudinal structure into the random effects models and retains...
Directory of Open Access Journals (Sweden)
Syed Imran A. Shah
2012-01-01
Full Text Available There are two classes of mixing sensitive reactions: competitive-consecutive and competitive-parallel. The yield of desired product from these coupled reactions depends on how fast the reactants are brought together. Recent experimental results have suggested that the mixing effect may depend strongly on the stoichiometry of the reactions. To investigate this, a 1D, dimensionless, reaction-diffusion model at the micromixing scale was developed. Assuming constant mass concentration and mass diffusivities, systems of PDE's were derived on a mass fraction basis for both types of reactions. Two dimensionless reaction rate ratios and a single general Damköhler number emerged from the analysis. The resulting dimensionless equations were used to investigate the effects of mixing, reaction rate ratio, and reaction stoichiometry. As expected, decreasing either the striation thickness or the dimensionless rate ratio maximizes yield, the reaction stoichiometry has a considerable effect on yield, and all three variables interact strongly.
Modernization of vertical Pelton turbines with the help of CFD and model testing
Mack, Reiner; Gola, Bartlomiej; Smertnig, Martin; Wittwer, Bernhard; Meusburger, Peter
2014-03-01
The modernization of water turbines bears a high potential of increasing the already installed hydropower capacity. In many projects the existing waterways allow a substantial increase of the available flow capacity and with it the energy output. But also the upgrading onto a state of the art hydraulic, mechanical and electrical design will increase the available power considerably after the rehabilitation. The two phase nature of the flow in Pelton turbines requires for the hydraulic refurbishment special care in the application of the available design methods. Where the flow in the high pressure section of the turbine is mainly of one phase nature, CFD has been used as a standard tool for many years. Also the jet quality, and with it the exploration of the source of flow disturbances that cause poor free surface quality can be investigated with CFD. The interaction of the jet with the buckets of the runner is also examined by means of CFD. However, its accuracy with respect to hydraulic efficiency is, because of the two phase flow and the transient flow process, in very few cases good enough for a reliable and accurate prediction of absolute numbers. The optimization of hydraulic bucket profiles is therefore always checked with measurements in homologous scaled model turbines. A similar situation exists for the housing flow after the water is discharged from the runner. Here also CFD techniques are available to explore the general mechanisms. However, due to the two phase flow nature, where only a very small space is filled with moving water, the experimental setup in a model turbine is always the final proof for optimizations of housing inserts and modifications. The hydraulic design of a modernization project for a power station equipped with vertical Pelton turbines of two different designs is described in the proposed paper. It will be shown, how CFD is applied to determine the losses in the high pressure section and how these results are combined with the
Modernization of vertical Pelton turbines with the help of CFD and model testing
International Nuclear Information System (INIS)
Mack, Reiner; Gola, Bartlomiej; Smertnig, Martin; Wittwer, Bernhard; Meusburger, Peter
2014-01-01
The modernization of water turbines bears a high potential of increasing the already installed hydropower capacity. In many projects the existing waterways allow a substantial increase of the available flow capacity and with it the energy output. But also the upgrading onto a state of the art hydraulic, mechanical and electrical design will increase the available power considerably after the rehabilitation. The two phase nature of the flow in Pelton turbines requires for the hydraulic refurbishment special care in the application of the available design methods. Where the flow in the high pressure section of the turbine is mainly of one phase nature, CFD has been used as a standard tool for many years. Also the jet quality, and with it the exploration of the source of flow disturbances that cause poor free surface quality can be investigated with CFD. The interaction of the jet with the buckets of the runner is also examined by means of CFD. However, its accuracy with respect to hydraulic efficiency is, because of the two phase flow and the transient flow process, in very few cases good enough for a reliable and accurate prediction of absolute numbers. The optimization of hydraulic bucket profiles is therefore always checked with measurements in homologous scaled model turbines. A similar situation exists for the housing flow after the water is discharged from the runner. Here also CFD techniques are available to explore the general mechanisms. However, due to the two phase flow nature, where only a very small space is filled with moving water, the experimental setup in a model turbine is always the final proof for optimizations of housing inserts and modifications. The hydraulic design of a modernization project for a power station equipped with vertical Pelton turbines of two different designs is described in the proposed paper. It will be shown, how CFD is applied to determine the losses in the high pressure section and how these results are combined with the
Directory of Open Access Journals (Sweden)
An Nam Hyun
2014-03-01
Full Text Available In this study, an experimental investigation has been made of the applicability of outer-layer vertical blades to real ship model. After first devised by Hutchins and Choi (2003, the outer-layer vertical blades demonstrated its effectiveness in reducing total drag of flat plate (Park et al., 2011 with maximum drag reduction of 9.6%. With a view to assessing the effect in the flow around a ship, the arrays of outer-layer vertical blades have been installed onto the side bottom and flat bottom of a 300k KVLCC model. A series of towing tank test has been carried out to investigate resistance (CTM reduction efficiency and improvement of stern wake distribution with varying geometric parameters of the blades array. The installation of vertical blades led to the CTM reduction of 2.15~2.76% near the service speed. The nominal wake fraction was affected marginally by the blades array and the axial velocity distribution tended to be more uniform by the blades array.
Directory of Open Access Journals (Sweden)
Nam Hyun An
2014-03-01
Full Text Available In this study, an experimental investigation has been made of the applicability of outer-layer vertical blades to real ship model. After first devised by Hutchins and Choi (2003, the outer-layer vertical blades demonstrated its effectiveness in reducing total drag of flat plate (Park et al., 2011 with maximum drag reduction of 9.6%. With a view to assessing the effect in the flow around a ship, the arrays of outer-layer vertical blades have been installed onto the side bottom and flat bottom of a 300k KVLCC model. A series of towing tank test has been carried out to investigate resistance (CTM reduction efficiency and improvement of stern wake distribution with varying geometric parameters of the blades array. The installation of vertical blades led to the CTM reduction of 2.15∼2.76% near the service speed. The nominal wake fraction was affected marginally by the blades array and the axial velocity distribution tended to be more uniform by the blades array.
Directory of Open Access Journals (Sweden)
Eduardo González-Ferreiro
Full Text Available The fuel complex variables canopy bulk density and canopy base height are often used to predict crown fire initiation and spread. Direct measurement of these variables is impractical, and they are usually estimated indirectly by modelling. Recent advances in predicting crown fire behaviour require accurate estimates of the complete vertical distribution of canopy fuels. The objectives of the present study were to model the vertical profile of available canopy fuel in pine stands by using data from the Spanish national forest inventory plus low-density airborne laser scanning (ALS metrics. In a first step, the vertical distribution of the canopy fuel load was modelled using the Weibull probability density function. In a second step, two different systems of models were fitted to estimate the canopy variables defining the vertical distributions; the first system related these variables to stand variables obtained in a field inventory, and the second system related the canopy variables to airborne laser scanning metrics. The models of each system were fitted simultaneously to compensate the effects of the inherent cross-model correlation between the canopy variables. Heteroscedasticity was also analyzed, but no correction in the fitting process was necessary. The estimated canopy fuel load profiles from field variables explained 84% and 86% of the variation in canopy fuel load for maritime pine and radiata pine respectively; whereas the estimated canopy fuel load profiles from ALS metrics explained 52% and 49% of the variation for the same species. The proposed models can be used to assess the effectiveness of different forest management alternatives for reducing crown fire hazard.
The Vineyard Yeast Microbiome, a Mixed Model Microbial Map
Setati, Mathabatha Evodia; Jacobson, Daniel; Andong, Ursula-Claire; Bauer, Florian
2012-01-01
Vineyards harbour a wide variety of microorganisms that play a pivotal role in pre- and post-harvest grape quality and will contribute significantly to the final aromatic properties of wine. The aim of the current study was to investigate the spatial distribution of microbial communities within and between individual vineyard management units. For the first time in such a study, we applied the Theory of Sampling (TOS) to sample gapes from adjacent and well established commercial vineyards within the same terroir unit and from several sampling points within each individual vineyard. Cultivation-based and molecular data sets were generated to capture the spatial heterogeneity in microbial populations within and between vineyards and analysed with novel mixed-model networks, which combine sample correlations and microbial community distribution probabilities. The data demonstrate that farming systems have a significant impact on fungal diversity but more importantly that there is significant species heterogeneity between samples in the same vineyard. Cultivation-based methods confirmed that while the same oxidative yeast species dominated in all vineyards, the least treated vineyard displayed significantly higher species richness, including many yeasts with biocontrol potential. The cultivatable yeast population was not fully representative of the more complex populations seen with molecular methods, and only the molecular data allowed discrimination amongst farming practices with multivariate and network analysis methods. Importantly, yeast species distribution is subject to significant intra-vineyard spatial fluctuations and the frequently reported heterogeneity of tank samples of grapes harvested from single vineyards at the same stage of ripeness might therefore, at least in part, be due to the differing microbiota in different sections of the vineyard. PMID:23300721
Komatsu, K; Abe, Y; Yoshioka, T; Ishimura, H; Ebihara, A; Suda, H
2014-01-01
The purpose of this study was to evaluate the accuracy of diagnosing vertical root fractures (VRFs) by comparing the volume of bone defects in VRFs with those in non-VRFs on reconstructed three-dimensional (3D) models (TDMs) using CBCT. 32 maxillary pre-molars and anterior teeth with radiolucent areas were evaluated on pre-operative CBCT images. Of the 32 teeth, 16 had a fractured root (VRF group) and 16 had a non-fractured root (non-VRF group). The radiolucent area of each tooth was traced in each dimension [mesiodistal, buccolingual and horizontal (the apicoincisal aspect)] by two observers, and 3D images were reconstructed with the Amira(®) software (Visage Imaging Inc., Richmond, Australia). The volume, V, of the TDM was divided into the coronal side and the periapical side at the horizontal slice through the apical foramen, and v was defined as the volume of the coronal side. The values of v/V were calculated for all cases. The Mann-Whitney U test was used to compare values between the VRF group and the non-VRF group (p < 0.05). A receiver operating characteristic (ROC) curve was constructed to select the optimal cut-point. There was a statistically significant difference in the value of v/V between the two groups (p < 0.05). With a cut-point derived from the ROC curve, and the sensitivity, specificity and accuracy of predicting the VRFs were 1.00, 0.75 and 0.88, respectively. Lesions resulting from VRFs can be distinguished from those of non-VRFs on 3D CBCT images with a high degree of accuracy, based on their different 3D shapes.
Ott, Lesley; Pickering, Kenneth; Stenchikov, Georgiy; Allen, Dale; DeCaria, Alex; Ridley, Brian; Lin, Ruei-Fong; Lang, Steve; Tao, Wei-Kuo
2009-01-01
A 3-D cloud scale chemical transport model that includes a parameterized source of lightning NO(x), based on observed flash rates has been used to simulate six midlatitude and subtropical thunderstorms observed during four field projects. Production per intracloud (P(sub IC) and cloud-to-ground (P(sub CG)) flash is estimated by assuming various values of P(sub IC) and P(sub CG) for each storm and determining which production scenario yields NO(x) mixing ratios that compare most favorably with in-cloud aircraft observations. We obtain a mean P(sub CG) value of 500 moles NO (7 kg N) per flash. The results of this analysis also suggest that on average, P(sub IC) may be nearly equal to P(sub CG), which is contrary to the common assumption that intracloud flashes are significantly less productive of NO than are cloud-to-ground flashes. This study also presents vertical profiles of the mass of lightning NO(x), after convection based on 3-D cloud-scale model simulations. The results suggest that following convection, a large percentage of lightning NO(x), remains in the middle and upper troposphere where it originated, while only a small percentage is found near the surface. The results of this work differ from profiles calculated from 2-D cloud-scale model simulations with a simpler lightning parameterization that were peaked near the surface and in the upper troposphere (referred to as a "C-shaped" profile). The new model results (a backward C-shaped profile) suggest that chemical transport models that assume a C-shaped vertical profile of lightning NO(x) mass may place too much mass neat the surface and too little in the middle troposphere.
Smith, C.; Pound, K. S.; Jones, M. H.; Schmitt, L.; Campbell, K.
2005-12-01
Students often have difficulty understanding and visualizing the role that relative sea-level change plays in controlling vertical and lateral facies changes; they also struggle with explanations of regional facies patterns and changes as sea-level dependant. This interactive, dynamic, in-class model has been developed to build their understanding both of this topic, and of the nature of predictive scientific models. The model can be used as a follow-up to field observations, or to pre-teach concepts. The model assumes a land-ocean transect that is divided into 5 sedimentary settings. Each setting in the land-ocean transect is associated with sediment grain size that decreases basinward; the most basinward component is carbonate. In the model, seven 10-cm diameter see-through tubes are set up to represent `cores' spread along the land-ocean transect. Brightly-colored plastic beads are used to represent sediment deposited in each of the sedimentary settings. At the start, the position of the shoreline (sea level) is fixed between the fluvial (tube 2) and beach (tube 3) sediments. Students then deposit beads that represent their sediment type in the each tube. Other students control the sea-level marker, which can be raised or lowered, and students with the sediment (beads) move shoreward or basinward accordingly, and deposit their sediments (beads) in the appropriate tube. This produces a simple visual record (tubes with layers of distinctly colored beads) that show the idealized sedimentary consequences of relative sea-level change. After large-scale patterns in facies changes have been demonstrated and discussed, students can manipulate variables such as supply and rate. Students can fill a basin using a sequence of events they determine, and other student groups can interpret their cores. The learning and approach of this model can be extended to include real sediment (gravel, sand, silt, mud) deposited in cardboard tubes that are then opened and treated as cores
Lund, M. T.; Samset, B. H.; Skeie, R. B.; Berntsen, T.
2017-12-01
Several recent studies have used observations from the HIPPO flight campaigns to constrain the modeled vertical distribution of black carbon (BC) over the Pacific. Results indicate a relatively linear relationship between global-mean atmospheric BC residence time, or lifetime, and bias in current models. A lifetime of less than 5 days is necessary for models to reasonably reproduce these observations. This is shorter than what many global models predict, which will in turn affect their estimates of BC climate impacts. Here we use the chemistry-transport model OsloCTM to examine whether this relationship between global BC lifetime and model skill also holds for a broader a set of flight campaigns from 2009-2013 covering both remote marine and continental regions at a range of latitudes. We perform four sets of simulations with varying scavenging efficiency to obtain a spread in the modeled global BC lifetime and calculate the model error and bias for each campaign and region. Vertical BC profiles are constructed using an online flight simulator, as well by averaging and interpolating monthly mean model output, allowing us to quantify sampling errors arising when measurements are compared with model output at different spatial and temporal resolutions. Using the OsloCTM coupled with a microphysical aerosol parameterization, we investigate the sensitivity of modeled BC vertical distribution to uncertainties in the aerosol aging and scavenging processes in more detail. From this, we can quantify how model uncertainties in the BC life cycle propagate into uncertainties in its climate impacts. For most campaigns and regions, a short global-mean BC lifetime corresponds with the lowest model error and bias. On an aggregated level, sampling errors appear to be small, but larger differences are seen in individual regions. However, we also find that model-measurement discrepancies in BC vertical profiles cannot be uniquely attributed to uncertainties in a single process or
Miccio, Joseph; Parikh, Shruti; Marinaro, Xavier; Prasad, Atulya; McClain, Steven; Singer, Adam J; Clark, Richard A F
2016-03-01
relevant criterion standard, temperature minima at 2 days after burn was found to be the most sensitive and specific test. FLIR imaging is a fast and simple tool that has been shown to predict burn wound outcome in a porcine vertical injury progression model. Data showed that more severe burn wounds get cooler between 1 and 2 days after burn. We found four analytic methods of FLIR images that were predictive of burn progression at 1 and 2 days after burn; however, temperature minima 2 days after burn appeared to be the best predictive test for injury progression to a full-thickness burn. Although these results must be validated in clinical studies, FLIR imaging has the potential to aid clinicians in assessing burn severity and thereby assisting in burn wound management. Copyright © 2015 Elsevier Ltd and ISBI. All rights reserved.
Moreaux, G.; Lemoine, F. G.; Argus, D. F.; Santamaría-Gómez, A.; Willis, P.; Soudarin, L.; Gravelle, M.; Ferrage, P.
2016-10-01
In the context of the 2014 realization of the International Terrestrial Reference Frame, the International DORIS (Doppler Orbitography Radiopositioning Integrated by Satellite) Service (IDS) has delivered to the IERS a set of 1140 weekly SINEX files including station coordinates and Earth orientation parameters, covering the time period from 1993.0 to 2015.0. From this set of weekly SINEX files, the IDS combination centre estimated a cumulative DORIS position and velocity solution to obtain mean horizontal and vertical motion of 160 stations at 71 DORIS sites. The main objective of this study is to validate the velocities of the DORIS sites by comparison with external models or time-series. Horizontal velocities are compared with two recent global plate models (GEODVEL 2010 and NNR-MORVEL56). Prior to the comparisons, DORIS horizontal velocities were corrected for Global Isostatic Adjustment from the ICE-6G (VM5a) model. For more than half of the sites, the DORIS horizontal velocities differ from the global plate models by less than 2-3 mm yr-1. For five of the sites (Arequipa, Dionysos/Gavdos, Manila and Santiago) with horizontal velocity differences with respect to these models larger than 10 mm yr-1, comparisons with GNSS estimates show the veracity of the DORIS motions. Vertical motions from the DORIS cumulative solution are compared with the vertical velocities derived from the latest GPS cumulative solution over the time span 1995.0-2014.0 from the University of La Rochelle solution at 31 co-located DORIS-GPS sites. These two sets of vertical velocities show a correlation coefficient of 0.83. Vertical differences are larger than 2 mm yr-1 at 23 percent of the sites. At Thule, the disagreement is explained by fine-tuned DORIS discontinuities in line with the mass variations of outlet glaciers. Furthermore, the time evolution of the vertical time-series from the DORIS station in Thule show similar trends to the GRACE equivalent water height.
DEFF Research Database (Denmark)
Brockhoff, Per Bruun; Schlich, Pascal; Skovgaard, Ib
2015-01-01
Scale range differences between individual assessors will often constitute a non-trivial part of the assessor-by-product interaction in sensory profile data (Brockhoff, 2003, 1998; Brockhoff and Skovgaard, 1994). We suggest a new mixed model ANOVA analysis approach, the Mixed Assessor Model (MAM...
Item Purification in Differential Item Functioning Using Generalized Linear Mixed Models
Liu, Qian
2011-01-01
For this dissertation, four item purification procedures were implemented onto the generalized linear mixed model for differential item functioning (DIF) analysis, and the performance of these item purification procedures was investigated through a series of simulations. Among the four procedures, forward and generalized linear mixed model (GLMM)…
An applied model for the height of the daytime mixed layer and the entrainment zone
DEFF Research Database (Denmark)
Batchvarova, E.; Gryning, Sven-Erik
1994-01-01
A model is presented for the height of the mixed layer and the depth of the entrainment zone under near-neutral and unstable atmospheric conditions. It is based on the zero-order mixed layer height model of Batchvarova and Gryning (1991) and the parameterization of the entrainment zone depth prop...
Energy Technology Data Exchange (ETDEWEB)
Ibragimov, Ranis N.; Tartakovsky, Alexandre M.
2014-10-29
Efficiency of mixing, resulting from the reflection of an internal wave field imposed on the oscillatory background flow with a three-dimensional bottom topography, is investigated using a linear approximation. The radiating wave field is associated with the spectrum of the linear model, which consists of those mode numbers n and slope values α, for which the solution represents the internal waves of frequencies ω = nω0 radiating upwrad of the topography, where ω0 is the fundamental frequency at which internal waves are generated at the topography. The effects of the bottom topography and the earth’s rotation on the spectrum is analyzed analytically and numerically in the vicinity of the critical slope, which is a slope with the same angle to the horizontal as the internal wave characteristic. In this notation, θ is latitude, f is the Coriolis parameter and N is the buoyancy frequency, which is assumed to be a constant, which corresponds to the uniform stratification.
Retout, Sylvie; Comets, Emmanuelle; Bazzoli, Caroline; Mentré, France
2009-01-01
International audience; We address the problem of design optimization using cost functions in nonlinear mixed effects models with multiple responses. We focus on the relative feasibility of the optimized designs, in term of sampling times and of number of subjects. To do that, we extend the Fedorov–Wynn algorithm—a dedicated design optimization algorithm—to include a cost function that penalizes less feasible designs as well as to take into account multiple responses. We apply this extension ...
Shentu, Nanying; Zhang, Hongjian; Li, Qing; Zhou, Hongliang; Tong, Renyuan; Li, Xiong
2012-01-01
Deep displacement observation is one basic means of landslide dynamic study and early warning monitoring and a key part of engineering geological investigation. In our previous work, we proposed a novel electromagnetic induction-based deep displacement sensor (I-type) to predict deep horizontal displacement and a theoretical model called equation-based equivalent loop approach (EELA) to describe its sensing characters. However in many landslide and related geological engineering cases, both horizontal displacement and vertical displacement vary apparently and dynamically so both may require monitoring. In this study, a II-type deep displacement sensor is designed by revising our I-type sensor to simultaneously monitor the deep horizontal displacement and vertical displacement variations at different depths within a sliding mass. Meanwhile, a new theoretical modeling called the numerical integration-based equivalent loop approach (NIELA) has been proposed to quantitatively depict II-type sensors' mutual inductance properties with respect to predicted horizontal displacements and vertical displacements. After detailed examinations and comparative studies between measured mutual inductance voltage, NIELA-based mutual inductance and EELA-based mutual inductance, NIELA has verified to be an effective and quite accurate analytic model for characterization of II-type sensors. The NIELA model is widely applicable for II-type sensors' monitoring on all kinds of landslides and other related geohazards with satisfactory estimation accuracy and calculation efficiency.
Directory of Open Access Journals (Sweden)
Xiong Li
2011-12-01
Full Text Available Deep displacement observation is one basic means of landslide dynamic study and early warning monitoring and a key part of engineering geological investigation. In our previous work, we proposed a novel electromagnetic induction-based deep displacement sensor (I-type to predict deep horizontal displacement and a theoretical model called equation-based equivalent loop approach (EELA to describe its sensing characters. However in many landslide and related geological engineering cases, both horizontal displacement and vertical displacement vary apparently and dynamically so both may require monitoring. In this study, a II-type deep displacement sensor is designed by revising our I-type sensor to simultaneously monitor the deep horizontal displacement and vertical displacement variations at different depths within a sliding mass. Meanwhile, a new theoretical modeling called the numerical integration-based equivalent loop approach (NIELA has been proposed to quantitatively depict II-type sensors’ mutual inductance properties with respect to predicted horizontal displacements and vertical displacements. After detailed examinations and comparative studies between measured mutual inductance voltage, NIELA-based mutual inductance and EELA-based mutual inductance, NIELA has verified to be an effective and quite accurate analytic model for characterization of II-type sensors. The NIELA model is widely applicable for II-type sensors’ monitoring on all kinds of landslides and other related geohazards with satisfactory estimation accuracy and calculation efficiency.
Directory of Open Access Journals (Sweden)
Hua Li
2014-01-01
Full Text Available The Effective Heat Source (EHS and Effective Momentum Source (EMS models have been proposed to predict the development of thermal stratification and mixing during a steam injection into a large pool of water. These effective models are implemented in GOTHIC software and validated against the POOLEX STB-20 and STB-21 tests and the PPOOLEX MIX-01 test. First, the EHS model is validated against STB-20 test which shows the development of thermal stratification. Different numerical schemes and grid resolutions have been tested. A 48×114 grid with second order scheme is sufficient to capture the vertical temperature distribution in the pool. Next, the EHS and EMS models are validated against STB-21 test. Effective momentum is estimated based on the water level oscillations in the blowdown pipe. An effective momentum selected within the experimental measurement uncertainty can reproduce the mixing details. Finally, the EHS-EMS models are validated against MIX-01 test which has improved space and time resolution of temperature measurements inside the blowdown pipe. Excellent agreement in averaged pool temperature and water level in the pool between the experiment and simulation has been achieved. The development of thermal stratification in the pool is also well captured in the simulation as well as the thermal behavior of the pool during the mixing phase.
Implementation of a flaw model to the fracturing around a vertical shaft
CSIR Research Space (South Africa)
Van de Steen, B
2003-04-01
Full Text Available -scale excavations. The simulated fracture pattern around a vertical shaft is compared to the fracturing around a shaft at a depth of 3400 m. The simulations suggest that wedge-shaped zones, called dog-ears, a reformed by a progressive splitting-like failure...
De Biase, C.; Carminati, A.; Oswald, S.E.; Thullner, M.
2013-01-01
Vertical flow systems filled with porous medium have been shown to efficiently remove volatile organic contaminants (VOCs) from contaminated groundwater. To apply this semi-natural remediation strategy it is however necessary to distinguish between removal due to biodegradation and due to volatile
The photobehaviour of Daphnia spp. as a model to explain diel vertical migration in zooplankton
Ringelberg, J.
1999-01-01
Many pelagic animal species in the marine environment and in lakes migrate to deeper water layers before sunrise and return around sunset. The amplitude of these diel vertical migrations (DVM) varies from several hundreds of metres in the oceans to approx. 5-20 m in lakes. DVM can be studied from a
Optimal foraging and diel vertical migration in a life history model
DEFF Research Database (Denmark)
Sainmont, Julie; Andersen, Ken Haste; Visser, Andre
Zooplankton such as copepods are known to perform diel vertical migration, avoiding the food rich surface during bright hours to avoid visual predator when they are most dangerous, and returning to the surface to feed at night. The resolution of this foraging behaviour requires fine time scale...
Grajeda, Laura M; Ivanescu, Andrada; Saito, Mayuko; Crainiceanu, Ciprian; Jaganath, Devan; Gilman, Robert H; Crabtree, Jean E; Kelleher, Dermott; Cabrera, Lilia; Cama, Vitaliano; Checkley, William
2016-01-01
Childhood growth is a cornerstone of pediatric research. Statistical models need to consider individual trajectories to adequately describe growth outcomes. Specifically, well-defined longitudinal models are essential to characterize both population and subject-specific growth. Linear mixed-effect models with cubic regression splines can account for the nonlinearity of growth curves and provide reasonable estimators of population and subject-specific growth, velocity and acceleration. We provide a stepwise approach that builds from simple to complex models, and account for the intrinsic complexity of the data. We start with standard cubic splines regression models and build up to a model that includes subject-specific random intercepts and slopes and residual autocorrelation. We then compared cubic regression splines vis-à-vis linear piecewise splines, and with varying number of knots and positions. Statistical code is provided to ensure reproducibility and improve dissemination of methods. Models are applied to longitudinal height measurements in a cohort of 215 Peruvian children followed from birth until their fourth year of life. Unexplained variability, as measured by the variance of the regression model, was reduced from 7.34 when using ordinary least squares to 0.81 (p linear mixed-effect models with random slopes and a first order continuous autoregressive error term. There was substantial heterogeneity in both the intercept (p linear regression equation for both estimation and prediction of population- and individual-level growth in height. We show that cubic regression splines are superior to linear regression splines for the case of a small number of knots in both estimation and prediction with the full linear mixed effect model (AIC 19,352 vs. 19,598, respectively). While the regression parameters are more complex to interpret in the former, we argue that inference for any problem depends more on the estimated curve or differences in curves rather
International Nuclear Information System (INIS)
Andrews, M.J.
1992-01-01
A simple experiment has been used to quantitatively investigate turbulent mixing at an unstable interface when the interface is subject to a large two-dimensional disturbance. The introduction of a small amplitude long wavelength does little to alter the early time development of a planar mixed region, but at late times causes a large overturning motion that tends to thin the planar mixed region and accelerate the overall mixing process. Data have been collected from the experiment by way of image analysis of experimental photographs. These data serve as a source of information for the development of a open-quotes two-fluidclose quotes model of the mixing process. A open-quotes two-fluidclose quotes model has been developed to describe the turbulent mixing by Rayleigh-Taylor instabilities of the two different density fluids investigated in the experimental study above. A one-dimensional model was employed for the planar mixing experiments; here attention is focused on the development of a physically plausible equation to describe the length-scale development within the mixed region. The one-dimensional model was then extended to two-dimensions for the overturning experiments, and terms are added to account for thinning of the mixing region at late times. Data collected from the experiments are used to validate the model and to determine several model constants. The two-fluid model successfully simulates the experimental results and is recommended for further application to turbulent mixing processes in buoyant environments
DEFF Research Database (Denmark)
Tornøe, Christoffer Wenzel; Agersø, Henrik; Madsen, Henrik
2004-01-01
equation (ODE) solver package odesolve and the non-Linear mixed effects package NLME thereby enabling the analysis of complicated systems of ODEs by non-linear mixed-effects modelling. The pharmacokinetics of the anti-asthmatic drug theophylline is used to illustrate the applicability of the nlme......The standard software for non-linear mixed-effect analysis of pharmacokinetic/phar-macodynamic (PK/PD) data is NONMEM while the non-linear mixed-effects package NLME is an alternative as tong as the models are fairly simple. We present the nlmeODE package which combines the ordinary differential...
Directory of Open Access Journals (Sweden)
Wei Gong Wei-Chyung Wang
2007-01-01
Full Text Available We used the State University of New York at Albany (SUNYA regional climate model to study the effect of cloud vertical distribution in affecting the surface energy balance of the East Asia summer monsoon (EASM. Simulations were conducted for the summers of 1988 and 1989, during which large contrast in the intra-seasonal cloud radiative forcing (CRF was observed at the top of the atmosphere.
Venda Oliveira, P.J.; Cruz, R.F.P.M.L.; Lemos, L.J.L.; Almeida e Sousa, J.N.V.
2015-01-01
This work compares the field measurements of a non-symmetric embankment built on a Portuguese soft soil improved with prefabricated vertical drains (PVDs), with the numerical predictions of a 3D modelling where the PVDs are simulated according to the field flow conditions. The change in the permeability with the void ratio and the effect of the smear zone are also included in the numerical analysis. The numerical predictions are compared with the field data in terms of settlement, horizontal ...
CFD modeling of thermal mixing in a T-junction geometry using LES model
Energy Technology Data Exchange (ETDEWEB)
Ayhan, Hueseyin, E-mail: huseyinayhan@hacettepe.edu.tr [Hacettepe University, Department of Nuclear Engineering, Beytepe, Ankara 06800 (Turkey); Soekmen, Cemal Niyazi, E-mail: cemalniyazi.sokmen@hacettepe.edu.tr [Hacettepe University, Department of Nuclear Engineering, Beytepe, Ankara 06800 (Turkey)
2012-12-15
Highlights: Black-Right-Pointing-Pointer CFD simulations of temperature and velocity fluctuations for thermal mixing cases in T-junction are performed. Black-Right-Pointing-Pointer It is found that the frequency range of 2-5 Hz contains most of the energy; therefore, may cause thermal fatigue. Black-Right-Pointing-Pointer This study shows that RANS based calculations fail to predict a realistic mixing between the fluids. Black-Right-Pointing-Pointer LES model can predict instantaneous turbulence behavior. - Abstract: Turbulent mixing of fluids at different temperatures can lead to temperature fluctuations at the pipe material. These fluctuations, or thermal striping, inducing cyclical thermal stresses and resulting thermal fatigue, may cause unexpected failure of pipe material. Therefore, an accurate characterization of temperature fluctuations is important in order to estimate the lifetime of pipe material. Thermal fatigue of the coolant circuits of nuclear power plants is one of the major issues in nuclear safety. To investigate thermal fatigue damage, the OECD/NEA has recently organized a blind benchmark study including some of results of present work for prediction of temperature and velocity fluctuations performing a thermal mixing experiment in a T-junction. This paper aims to estimate the frequency of velocity and temperature fluctuations in the mixing region using Computational Fluid Dynamics (CFD). Reynolds Averaged Navier-Stokes and Large Eddy Simulation (LES) models were used to simulate turbulence. CFD results were compared with the available experimental results. Predicted LES results, even in coarse mesh, were found to be in well-agreement with the experimental results in terms of amplitude and frequency of temperature and velocity fluctuations. Analysis of the temperature fluctuations and the power spectrum densities (PSD) at the locations having the strongest temperature fluctuations in the tee junction shows that the frequency range of 2-5 Hz
Models of vertical coordination consistent with the development of bio-energetics
Directory of Open Access Journals (Sweden)
Gianluca Nardone
Full Text Available To foster the development of the biomasses for solid fuel it is fundamental to build up a strategy at a local level in which co-exists farms as well as industrial farms. To such aim, it is necessary to implement an effective vertical coordination between the stakeholders with the definition of a contract that prevents opportunistic behaviors and guarantees the industrial investments of constant supplies over the time. Starting from a project that foresees a biomasses power plant in the south of Italy, this study reflects on the payments to fix in an eventual contract in such a way to maintain the fidelity of the farmers. These one have a greater flexibility since they can choose the most convenient crop. Therefore, their fidelity can be obtained tying the contractual payments to the price of the main alternative crop to the energetic one. The results of the study seem to indicate the opportunity to fix a purchase price of the raw materials linked to the one of durum wheat that is the most widespread crop in the territory and the one that depends more on a volatile market. Using the data of the District 12 of the province of Foggia Water Consortium with an area of 11.300 hectares (instead of the 20.000 demanded in the proposal, it has been possible to organize approximately 600 enterprises in five cluster, each of them identified by a representative farm. With a model of linear programming, we have run different simulations taking into account the possibility to grow sorghum in different ways. Through an aggregation process, it has been calculated that farmers may find it convenient to supply the energetic crop at a price of 50 €/t when the price of durum wheat is 150 €/t. Anyway, this price is lower than the one offered by firm that is planning to build the power plant. Moreover, it has been identified a strong correlation between the price of the durum wheat and the price that makes convenient for the farmers to grow the sorghum. When the
Models of vertical coordination consistent with the development of bio-energetics
Directory of Open Access Journals (Sweden)
Rosaria Viscecchia
2011-02-01
Full Text Available To foster the development of the biomasses for solid fuel it is fundamental to build up a strategy at a local level in which co-exists farms as well as industrial farms. To such aim, it is necessary to implement an effective vertical coordination between the stakeholders with the definition of a contract that prevents opportunistic behaviors and guarantees the industrial investments of constant supplies over the time. Starting from a project that foresees a biomasses power plant in the south of Italy, this study reflects on the payments to fix in an eventual contract in such a way to maintain the fidelity of the farmers. These one have a greater flexibility since they can choose the most convenient crop. Therefore, their fidelity can be obtained tying the contractual payments to the price of the main alternative crop to the energetic one. The results of the study seem to indicate the opportunity to fix a purchase price of the raw materials linked to the one of durum wheat that is the most widespread crop in the territory and the one that depends more on a volatile market. Using the data of the District 12 of the province of Foggia Water Consortium with an area of 11.300 hectares (instead of the 20.000 demanded in the proposal, it has been possible to organize approximately 600 enterprises in five cluster, each of them identified by a representative farm. With a model of linear programming, we have run different simulations taking into account the possibility to grow sorghum in different ways. Through an aggregation process, it has been calculated that farmers may find it convenient to supply the energetic crop at a price of 50 €/t when the price of durum wheat is 150 €/t. Anyway, this price is lower than the one offered by firm that is planning to build the power plant. Moreover, it has been identified a strong correlation between the price of the durum wheat and the price that makes convenient for the farmers to grow the sorghum. When the
Modeling Temporal Behavior in Large Networks: A Dynamic Mixed-Membership Model
Energy Technology Data Exchange (ETDEWEB)
Rossi, R; Gallagher, B; Neville, J; Henderson, K
2011-11-11
Given a large time-evolving network, how can we model and characterize the temporal behaviors of individual nodes (and network states)? How can we model the behavioral transition patterns of nodes? We propose a temporal behavior model that captures the 'roles' of nodes in the graph and how they evolve over time. The proposed dynamic behavioral mixed-membership model (DBMM) is scalable, fully automatic (no user-defined parameters), non-parametric/data-driven (no specific functional form or parameterization), interpretable (identifies explainable patterns), and flexible (applicable to dynamic and streaming networks). Moreover, the interpretable behavioral roles are generalizable, computationally efficient, and natively supports attributes. We applied our model for (a) identifying patterns and trends of nodes and network states based on the temporal behavior, (b) predicting future structural changes, and (c) detecting unusual temporal behavior transitions. We use eight large real-world datasets from different time-evolving settings (dynamic and streaming). In particular, we model the evolving mixed-memberships and the corresponding behavioral transitions of Twitter, Facebook, IP-Traces, Email (University), Internet AS, Enron, Reality, and IMDB. The experiments demonstrate the scalability, flexibility, and effectiveness of our model for identifying interesting patterns, detecting unusual structural transitions, and predicting the future structural changes of the network and individual nodes.
Profiling water vapor mixing ratios in Finland by means of a Raman lidar, a satellite and a model
Filioglou, Maria; Nikandrova, Anna; Niemelä, Sami; Baars, Holger; Mielonen, Tero; Leskinen, Ari; Brus, David; Romakkaniemi, Sami; Giannakaki, Elina; Komppula, Mika
2017-11-01
We present tropospheric water vapor profiles measured with a Raman lidar during three field campaigns held in Finland. Co-located radio soundings are available throughout the period for the calibration of the lidar signals. We investigate the possibility of calibrating the lidar water vapor profiles in the absence of co-existing on-site soundings using water vapor profiles from the combined Advanced InfraRed Sounder (AIRS) and the Advanced Microwave Sounding Unit (AMSU) satellite product; the Aire Limitée Adaptation dynamique Développement INternational and High Resolution Limited Area Model (ALADIN/HIRLAM) numerical weather prediction (NWP) system, and the nearest radio sounding station located 100 km away from the lidar site (only for the permanent location of the lidar). The uncertainties of the calibration factor derived from the soundings, the satellite and the model data are instruments/model for the period of the campaigns. A good agreement is observed for all comparisons with relative errors that do not exceed 50 % up to 8 km altitude in most cases. A 4-year seasonal analysis of vertical water vapor is also presented for the Kuopio site in Finland. During winter months, the air in Kuopio is dry (1.15±0.40 g kg-1); during summer it is wet (5.54±1.02 g kg-1); and at other times, the air is in an intermediate state. These are averaged values over the lowest 2 km in the atmosphere. Above that height a quick decrease in water vapor mixing ratios is observed, except during summer months where favorable atmospheric conditions enable higher mixing ratio values at higher altitudes. Lastly, the seasonal change in disagreement between the lidar and the model has been studied. The analysis showed that, on average, the model underestimates water vapor mixing ratios at high altitudes during spring and summer.
Yokoyama, T.; Ajith, K. K.; Yamamoto, M.; Niranjan, K.
2017-12-01
Equatorial plasma bubble (EPB) is a well-known phenomenon in the equatorial ionospheric F region. As it causes severe scintillation in the amplitude and phase of radio signals, it is important to understand and forecast the occurrence of EPBs from a space weather point of view. The development of EPBs is presently believed as an evolution of the generalized Rayleigh-Taylor instability. We have already developed a 3D high-resolution bubble (HIRB) model with a grid spacing of as small as 1 km and presented nonlinear growth of EPBs which shows very turbulent internal structures such as bifurcation and pinching. As EPBs have field-aligned structures, the latitude range that is affected by EPBs depends on the apex altitude of EPBs over the dip equator. However, it was not easy to observe the apex altitude and vertical rise velocity of EPBs. Equatorial Atmosphere Radar (EAR) in Indonesia is capable of steering radar beams quickly so that the growth phase of EPBs can be captured clearly. The vertical rise velocities of the EPBs observed around the midnight hours are significantly smaller compared to those observed in postsunset hours. Further, the vertical growth of the EPBs around midnight hours ceases at relatively lower altitudes, whereas the majority of EPBs at postsunset hours found to have grown beyond the maximum detectable altitude of the EAR. The HIRB model with varying background conditions are employed to investigate the possible factors that control the vertical rise velocity and maximum attainable altitudes of EPBs. The estimated rise velocities from EAR observations at both postsunset and midnight hours are, in general, consistent with the nonlinear evolution of EPBs from the HIRB model.
Modeling accuracy as a function of response time with the generalized linear mixed effects model.
Davidson, D J; Martin, A E
2013-09-01
In psycholinguistic studies using error rates as a response measure, response times (RT) are most often analyzed independently of the error rate, although it is widely recognized that they are related. In this paper we present a mixed effects logistic regression model for the error rate that uses RT as a trial-level fixed- and random-effect regression input. Production data from a translation-recall experiment are analyzed as an example. Several model comparisons reveal that RT improves the fit of the regression model for the error rate. Two simulation studies then show how the mixed effects regression model can identify individual participants for whom (a) faster responses are more accurate, (b) faster responses are less accurate, or (c) there is no relation between speed and accuracy. These results show that this type of model can serve as a useful adjunct to traditional techniques, allowing psycholinguistic researchers to examine more closely the relationship between RT and accuracy in individual subjects and better account for the variability which may be present, as well as a preliminary step to more advanced RT-accuracy modeling. Copyright © 2013 Elsevier B.V. All rights reserved.
Mixed Higher Order Variational Model for Image Recovery
Directory of Open Access Journals (Sweden)
Pengfei Liu
2014-01-01
Full Text Available A novel mixed higher order regularizer involving the first and second degree image derivatives is proposed in this paper. Using spectral decomposition, we reformulate the new regularizer as a weighted L1-L2 mixed norm of image derivatives. Due to the equivalent formulation of the proposed regularizer, an efficient fast projected gradient algorithm combined with monotone fast iterative shrinkage thresholding, called, FPG-MFISTA, is designed to solve the resulting variational image recovery problems under majorization-minimization framework. Finally, we demonstrate the effectiveness of the proposed regularization scheme by the experimental comparisons with total variation (TV scheme, nonlocal TV scheme, and current second degree methods. Specifically, the proposed approach achieves better results than related state-of-the-art methods in terms of peak signal to ratio (PSNR and restoration quality.
Model of Vertical Resistivity Distribution of Rock Layers in Jeneberang Watershed
Muhammad Altin Massinai, Muhammad; Syamsuddin, Syamsuddin; Makhrani, Makhrani
2010-01-01
Daerah Aliran Sungai (DAS) or Watershed is the accumulation of material from Jeneberang debris avalanche of Mount Bawakaraeng. The Resistivity material from several types of rock settling needs to be identified by using the geoelectric geophysical studies. Geoelectrical resistivity method used in this study aims to map the vertical layers of rock in the upstream and downstream of Jeneberang watershed. The results shows that resistivity values in the upstream of Jeneberang water...
Improving Mixed-phase Cloud Parameterization in Climate Model with the ACRF Measurements
Energy Technology Data Exchange (ETDEWEB)
Wang, Zhien [Univ. of Wyoming, Laramie, WY (United States)
2016-12-13
Mixed-phase cloud microphysical and dynamical processes are still poorly understood, and their representation in GCMs is a major source of uncertainties in overall cloud feedback in GCMs. Thus improving mixed-phase cloud parameterizations in climate models is critical to reducing the climate forecast uncertainties. This study aims at providing improved knowledge of mixed-phase cloud properties from the long-term ACRF observations and improving mixed-phase clouds simulations in the NCAR Community Atmosphere Model version 5 (CAM5). The key accomplishments are: 1) An improved retrieval algorithm was developed to provide liquid droplet concentration for drizzling or mixed-phase stratiform clouds. 2) A new ice concentration retrieval algorithm for stratiform mixed-phase clouds was developed. 3) A strong seasonal aerosol impact on ice generation in Arctic mixed-phase clouds was identified, which is mainly attributed to the high dust occurrence during the spring season. 4) A suite of multi-senor algorithms was applied to long-term ARM observations at the Barrow site to provide a complete dataset (LWC and effective radius profile for liquid phase, and IWC, Dge profiles and ice concentration for ice phase) to characterize Arctic stratiform mixed-phase clouds. This multi-year stratiform mixed-phase cloud dataset provides necessary information to study related processes, evaluate model stratiform mixed-phase cloud simulations, and improve model stratiform mixed-phase cloud parameterization. 5). A new in situ data analysis method was developed to quantify liquid mass partition in convective mixed-phase clouds. For the first time, we reliably compared liquid mass partitions in stratiform and convective mixed-phase clouds. Due to the different dynamics in stratiform and convective mixed-phase clouds, the temperature dependencies of liquid mass partitions are significantly different due to much higher ice concentrations in convective mixed phase clouds. 6) Systematic evaluations
Reliability in the Power System Modeled in a Multi- Stage Stochastic Mixed Integer Programming Model
DEFF Research Database (Denmark)
Simonsen Nielsen, Michael Pascal
Contributions from this article are that it takes the characteristics of the power system into account at different stages, which gives a more realistic presentation of the welfare aspects to be gained by an optimal operation/ dispatch of the power system. This article is utilizing a Multi......-Stage Stochastic Mixed Integer Programming Model that handles uncertainty in a flexible and practical way. The method applied relies on state-of-the-art modeling within this field, but the method applied in this article is extended by using decomposition....
de Maturana, Evangelina López; de los Campos, Gustavo; Wu, Xiao-Lin; Gianola, Daniel; Weigel, Kent A; Rosa, Guilherme J M
2010-01-25
The use of structural equation models for the analysis of recursive and simultaneous relationships between phenotypes has become more popular recently. The aim of this paper is to illustrate how these models can be applied in animal breeding to achieve parameterizations of different levels of complexity and, more specifically, to model phenotypic recursion between three calving traits: gestation length (GL), calving difficulty (CD) and stillbirth (SB). All recursive models considered here postulate heterogeneous recursive relationships between GL and liabilities to CD and SB, and between liability to CD and liability to SB, depending on categories of GL phenotype. Four models were compared in terms of goodness of fit and predictive ability: 1) standard mixed model (SMM), a model with unstructured (co)variance matrices; 2) recursive mixed model 1 (RMM1), assuming that residual correlations are due to the recursive relationships between phenotypes; 3) RMM2, assuming that correlations between residuals and contemporary groups are due to recursive relationships between phenotypes; and 4) RMM3, postulating that the correlations between genetic effects, contemporary groups and residuals are due to recursive relationships between phenotypes. For all the RMM considered, the estimates of the structural coefficients were similar. Results revealed a nonlinear relationship between GL and the liabilities both to CD and to SB, and a linear relationship between the liabilities to CD and SB.Differences in terms of goodness of fit and predictive ability of the models considered were negligible, suggesting that RMM3 is plausible. The applications examined in this study suggest the plausibility of a nonlinear recursive effect from GL onto CD and SB. Also, the fact that the most restrictive model RMM3, which assumes that the only cause of correlation is phenotypic recursion, performs as well as the others indicates that the phenotypic recursion may be an important cause of the
Hughes, E. J.; Krotkov, N. A.; daSilva, A.; Gorkavyi, N.
2015-12-01
The explosive eruption of Chile's Calbuco volcano on April 22nd-23rd produced large volcanic ash and sulfur dioxide clouds that were observed by satellites for over a week. The volcanic clouds were reported to have spanned a large range of altitudes, from 12 km to greater than 20 km. This is confirmed by the vertical profiles of aerosols observed by the NPP/OMPS Limb Profiler, which have a frequency and sensitivity allowing for a thorough look into the evolving vertical structure of the volcanic clouds. The volcanic cloud aerosol signature in the OMPS Limb profiles can be better understood by comparing them to simulations of the volcanic sulfate aerosols, and volcanic ash of various particle sizes. UV and IR satellite observations from the first few days of the eruption are used to constrain the initial source parameters that describe the volcanic eruption (eruption time, duration, mass emitted, injection altitude). The GEOS-5/GOCART model uses these initial source parameters to simulate the transport, deposition, and chemical conversion processes within the volcanic clouds. OMPS limb observations taken during the first days after the eruption provide numerous detailed vertical profiles of the volcanic clouds. The OMPS Limb Aerosol Scattering Index profiles are compared to the GEOS-5/GOCART simulations of sulfate aerosols and volcanic ash to show: the complex vertical structure of the volcanic plumes, the extended presence of aerosols in the volcanic clouds well after the eruption, and how OMPS Limb profiles can be used to constrain different volcanic aerosols in the GEOS-5/GOCART model simulations.
Czech Academy of Sciences Publication Activity Database
Brabec, Marek; Konár, Ondřej; Pelikán, Emil; Malý, Marek
2008-01-01
Roč. 24, č. 4 (2008), s. 659-678 ISSN 0169-2070 R&D Projects: GA AV ČR 1ET400300513 Institutional research plan: CEZ:AV0Z10300504 Keywords : individual gas consumption * nonlinear mixed effects model * ARIMAX * ARX * generalized linear mixed model * conditional modeling Subject RIV: JE - Non-nuclear Energetics, Energy Consumption ; Use Impact factor: 1.685, year: 2008
DEFF Research Database (Denmark)
Draxl, Caroline; Hahmann, Andrea N.; Pena Diaz, Alfredo
2014-01-01
with different PBL parameterizations at one coastal site over western Denmark. The evaluation focuses on determining which PBL parameterization performs best for wind energy forecasting, and presenting a validation methodology that takes into account wind speed at different heights. Winds speeds at heights...... regarding wind energy at these levels partly depends on the formulation and implementation of planetary boundary layer (PBL) parameterizations in these models. This study evaluates wind speeds and vertical wind shears simulated by theWeather Research and Forecasting model using seven sets of simulations...
A Hamiltonian Approach to Fault Isolation in a Planar Vertical Take–Off and Landing Aircraft Model
Directory of Open Access Journals (Sweden)
Rodriguez-Alfaro Luis H.
2015-03-01
Full Text Available The problem of fault detection and isolation in a class of nonlinear systems having a Hamiltonian representation is considered. In particular, a model of a planar vertical take-off and landing aircraft with sensor and actuator faults is studied. A Hamiltonian representation is derived from an Euler-Lagrange representation of the system model considered. In this form, nonlinear decoupling is applied in order to obtain subsystems with (as much as possible specific fault sensitivity properties. The resulting decoupled subsystem is represented as a Hamiltonian system and observer-based residual generators are designed. The results are presented through simulations to show the effectiveness of the proposed approach.
Mathematical, physical and numerical principles essential for models of turbulent mixing
Energy Technology Data Exchange (ETDEWEB)
Sharp, David Howland [Los Alamos National Laboratory; Lim, Hyunkyung [STONY BROOK UNIV; Yu, Yan [STONY BROOK UNIV; Glimm, James G [STONY BROOK UNIV
2009-01-01
We propose mathematical, physical and numerical principles which are important for the modeling of turbulent mixing, especially the classical and well studied Rayleigh-Taylor and Richtmyer-Meshkov instabilities which involve acceleration driven mixing of a fluid discontinuity layer, by a steady accerleration or an impulsive force.
Jin, Meibing; Deal, Clara; Maslowski, Wieslaw; Matrai, Patricia; Roberts, Andrew; Osinski, Robert; Lee, Younjoo J.; Frants, Marina; Elliott, Scott; Jeffery, Nicole; Hunke, Elizabeth; Wang, Shanlin
2018-01-01
The current coarse-resolution global Community Earth System Model (CESM) can reproduce major and large-scale patterns but is still missing some key biogeochemical features in the Arctic Ocean, e.g., low surface nutrients in the Canada Basin. We incorporated the CESM Version 1 ocean biogeochemical code into the Regional Arctic System Model (RASM) and coupled it with a sea-ice algal module to investigate model limitations. Four ice-ocean hindcast cases are compared with various observations: two in a global 1° (40˜60 km in the Arctic) grid: G1deg and G1deg-OLD with/without new sea-ice processes incorporated; two on RASM's 1/12° (˜9 km) grid R9km and R9km-NB with/without a subgrid scale brine rejection parameterization which improves ocean vertical mixing under sea ice. Higher-resolution and new sea-ice processes contributed to lower model errors in sea-ice extent, ice thickness, and ice algae. In the Bering Sea shelf, only higher resolution contributed to lower model errors in salinity, nitrate (NO3), and chlorophyll-a (Chl-a). In the Arctic Basin, model errors in mixed layer depth (MLD) were reduced 36% by brine rejection parameterization, 20% by new sea-ice processes, and 6% by higher resolution. The NO3 concentration biases were caused by both MLD bias and coarse resolution, because of excessive horizontal mixing of high NO3 from the Chukchi Sea into the Canada Basin in coarse resolution models. R9km showed improvements over G1deg on NO3, but not on Chl-a, likely due to light limitation under snow and ice cover in the Arctic Basin.
Bayes factor between Student t and Gaussian mixed models within an animal breeding context
Directory of Open Access Journals (Sweden)
García-Cortés Luis
2008-07-01
Full Text Available Abstract The implementation of Student t mixed models in animal breeding has been suggested as a useful statistical tool to effectively mute the impact of preferential treatment or other sources of outliers in field data. Nevertheless, these additional sources of variation are undeclared and we do not know whether a Student t mixed model is required or if a standard, and less parameterized, Gaussian mixed model would be sufficient to serve the intended purpose. Within this context, our aim was to develop the Bayes factor between two nested models that only differed in a bounded variable in order to easily compare a Student t and a Gaussian mixed model. It is important to highlight that the Student t density converges to a Gaussian process when degrees of freedom tend to infinity. The twomodels can then be viewed as nested models that differ in terms of degrees of freedom. The Bayes factor can be easily calculated from the output of a Markov chain Monte Carlo sampling of the complex model (Student t mixed model. The performance of this Bayes factor was tested under simulation and on a real dataset, using the deviation information criterion (DIC as the standard reference criterion. The two statistical tools showed similar trends along the parameter space, although the Bayes factor appeared to be the more conservative. There was considerable evidence favoring the Student t mixed model for data sets simulated under Student t processes with limited degrees of freedom, and moderate advantages associated with using the Gaussian mixed model when working with datasets simulated with 50 or more degrees of freedom. For the analysis of real data (weight of Pietrain pigs at six months, both the Bayes factor and DIC slightly favored the Student t mixed model, with there being a reduced incidence of outlier individuals in this population.
Directory of Open Access Journals (Sweden)
Mostafa A. A. Mahmoud
2007-01-01
Full Text Available In the present study, an analysis is carried out to study the variable viscosity and chemical reaction effects on the flow, heat, and mass transfer characteristics in a viscous fluid over a semi-infinite vertical porous plate. The governing boundary layer equations are written into a dimensionless form by similarity transformations. The transformed coupled nonlinear ordinary differential equations are solved numerically by using the shooting method. The effects of different parameters on the dimensionless velocity, temperature, and concentration profiles are shown graphically. In addition, tabulated results for the local skin-friction coefficient, the local Nusselt number, and the local Sherwood number are presented and discussed.
Directory of Open Access Journals (Sweden)
Pierre Tchakoua
2016-10-01
Full Text Available The complex and unsteady aerodynamics of vertical axis wind turbines (VAWTs pose significant challenges for simulation tools. Recently, significant research efforts have focused on the development of new methods for analysing and optimising the aerodynamic performance of VAWTs. This paper presents an electric circuit model for Darrieus-type vertical axis wind turbine (DT-VAWT rotors. The novel Tchakoua model is based on the mechanical description given by the Paraschivoiu double-multiple streamtube model using a mechanical‑electrical analogy. Model simulations were conducted using MATLAB for a three-bladed rotor architecture, characterized by a NACA0012 profile, an average Reynolds number of 40,000 for the blade and a tip speed ratio of 5. The results obtained show strong agreement with findings from both aerodynamic and computational fluid dynamics (CFD models in the literature.
Semi-analytical model of the axial movements of an oil-well drillstring in vertical wellbores
Hovda, Sigve
2018-03-01
A lumped element model for the axial movement of an oil-well drillstring is presented. In this paper, the model is restricted to vertical holes, where damping is due to skin friction from time dependent Newtonian annular Couette-Poiseuille flow. The drillstring is constructed of pipes with different diameters and the diameter of the hole varies as a function of depth. Under these assumptions, the axial movement anywhere in the drillstring is basically a convolution between the axial movement on the top and a semi-analytical function that is derived in this paper. Expressions are given for transfer functions for downhole movements and pressures (surge and swab). In a vertical drilling situation, the motion is clearly underdamped, even when the hole is tight. The semi-analytical model illuminates various factors that are shown to be important for describing downhole pressure and motion. In particular the effect of added mass, the steady state viscous forces, the Basset viscous forces and the distribution of pipe sizes in the hole. The latter have non-neglectable impacts on where the resonant frequencies are located, how much they are amplified and what happens to the downhole pressure. Together with statistical power spectra of ocean wave patterns and the response amplitude operators for a floating structure, this model illustrates design concerns related to heave motion and how fast one can run the drillstring into the hole. Moreover, because of the computational simplicity of computing the convolution, the model is well suited for a real-time implementation.
Gonzales, Matthew J; Sturgeon, Gregory; Krishnamurthy, Adarsh; Hake, Johan; Jonas, René; Stark, Paul; Rappel, Wouter-Jan; Narayan, Sanjiv M; Zhang, Yongjie; Segars, W Paul; McCulloch, Andrew D
2013-07-01
High-order cubic Hermite finite elements have been valuable in modeling cardiac geometry, fiber orientations, biomechanics, and electrophysiology, but their use in solving three-dimensional problems has been limited to ventricular models with simple topologies. Here, we utilized a subdivision surface scheme and derived a generalization of the "local-to-global" derivative mapping scheme of cubic Hermite finite elements to construct bicubic and tricubic Hermite models of the human atria with extraordinary vertices from computed tomography images of a patient with atrial fibrillation. To an accuracy of 0.6 mm, we were able to capture the left atrial geometry with only 142 bicubic Hermite finite elements, and the right atrial geometry with only 90. The left and right atrial bicubic Hermite meshes were G1 continuous everywhere except in the one-neighborhood of extraordinary vertices, where the mean dot products of normals at adjacent elements were 0.928 and 0.925. We also constructed two biatrial tricubic Hermite models and defined fiber orientation fields in agreement with diagrammatic data from the literature using only 42 angle parameters. The meshes all have good quality metrics, uniform element sizes, and elements with aspect ratios near unity, and are shared with the public. These new methods will allow for more compact and efficient patient-specific models of human atrial and whole heart physiology. Copyright © 2013 Elsevier B.V. All rights reserved.
Leoni, B.; Garibaldi, L.; Gulati, R.D.
2014-01-01
Lake Iseo is a deep meromictic lake located in Italy. During the past 20 years (1993–2013), the lake has experienced complete mixing of the water column only in spring 2005 and 2006. The full overturn episodes in these 2 years resulted in an increase in nutrients in both years, but an increase in
Drikvandi, Reza
2017-06-01
Nonlinear mixed-effects models are frequently used for pharmacokinetic data analysis, and they account for inter-subject variability in pharmacokinetic parameters by incorporating subject-specific random effects into the model. The random effects are often assumed to follow a (multivariate) normal distribution. However, many articles have shown that misspecifying the random-effects distribution can introduce bias in the estimates of parameters and affect inferences about the random effects themselves, such as estimation of the inter-subject variability. Because random effects are unobservable latent variables, it is difficult to assess their distribution. In a recent paper we developed a diagnostic tool based on the so-called gradient function to assess the random-effects distribution in mixed models. There we evaluated the gradient function for generalized liner mixed models and in the presence of a single random effect. However, assessing the random-effects distribution in nonlinear mixed-effects models is more challenging, especially when multiple random effects are present, and therefore the results from linear and generalized linear mixed models may not be valid for such nonlinear models. In this paper, we further investigate the gradient function and evaluate its performance for such nonlinear mixed-effects models which are common in pharmacokinetics and pharmacodynamics. We use simulations as well as real data from an intensive pharmacokinetic study to illustrate the proposed diagnostic tool.
Directory of Open Access Journals (Sweden)
Eduard Dyachuk
2015-10-01
Full Text Available Cyclic blade motion during operation of vertical axis wind turbines (VAWTs imposes challenges on the simulations models of the aerodynamics of VAWTs. A two-dimensional vortex model is validated against the new experimental data on a 12-kW straight-bladed VAWT, which is operated at an open site. The results on the normal force on one blade are analyzed. The model is assessed against the measured data in the wide range of tip speed ratios: from 1.8 to 4.6. The predicted results within one revolution have a similar shape and magnitude as the measured data, though the model does not reproduce every detail of the experimental data. The present model can be used when dimensioning the turbine for maximum loads.
Review and comparison of bi-fluid interpenetration mixing models
International Nuclear Information System (INIS)
Enaux, C.
2006-01-01
Today, there is a lot of bi-fluid models with two different speeds: Baer-Nunziato models; Godunov-Romensky models. coupled Euler's equations, and so on. In this report, one compares the most used models in the fields of physics and mathematics while basing this study on the literature. From the point of view of physics. for each model. one reviews: -) the type of mixture considered and modeling assumptions, -) the technique of construction, -) some properties like the respect of thermodynamical principles, the respect of the Galilean invariance principle, or the equilibrium conservation. From the point of view of mathematics, for each model, one looks at: -) the possibility of writing the equations in conservative form, -) hyperbolicity, -) the existence of a mathematical entropy. Finally, a unified review of the models is proposed. It is shown that under certain closing assumptions or for certain flow types. some of the models become equivalent. (author)
Energy Technology Data Exchange (ETDEWEB)
Araujo, Gregorio da Cruz; Szpigel, Pedro [Petroleo Brasileiro S.A. (PETROBRAS), Rio de Janeiro, RJ (Brazil)
2012-07-01
The recent spin-offs of Marathon (2011) and ConocoPhillips (2012), as well as other breakups between the upstream and downstream segments announced by the smaller oil companies during the past year, raised questions about one of the main and oldest paradigms of oil industry: the vertical integration. Corporate spin-off is not a new phenomenon in the industry in general, but only very recently has got prominence in the oil industry. The objective of this paper is to analyze the factors that motivate corporate restructuring in the oil industry, leading to strategic decisions that strengthen the vertical integration or that lead to break the value chain. The key point is whether there will be contagion among majors due to the movement of CononoPhillips, starting a new trend in the industry, or whether the restructuring already done will be only restricted to the specific needs of certain oil companies. (author)
Gundersen, Kenneth; Kvaløy, Jan Terje; Eftestøl, Trygve; Kramer-Johansen, Jo
2015-10-15
For patients undergoing cardiopulmonary resuscitation (CPR) and being in a shockable rhythm, the coarseness of the electrocardiogram (ECG) signal is an indicator of the state of the patient. In the current work, we show how mixed effects stochastic differential equations (SDE) models, commonly used in pharmacokinetic and pharmacodynamic modelling, can be used to model the relationship between CPR quality measurements and ECG coarseness. This is a novel application of mixed effects SDE models to a setting quite different from previous applications of such models and where using such models nicely solves many of the challenges involved in analysing the available data. Copyright © 2015 John Wiley & Sons, Ltd.
Directory of Open Access Journals (Sweden)
Laura M. Grajeda
2016-01-01
Full Text Available Abstract Background Childhood growth is a cornerstone of pediatric research. Statistical models need to consider individual trajectories to adequately describe growth outcomes. Specifically, well-defined longitudinal models are essential to characterize both population and subject-specific growth. Linear mixed-effect models with cubic regression splines can account for the nonlinearity of growth curves and provide reasonable estimators of population and subject-specific growth, velocity and acceleration. Methods We provide a stepwise approach that builds from simple to complex models, and account for the intrinsic complexity of the data. We start with standard cubic splines regression models and build up to a model that includes subject-specific random intercepts and slopes and residual autocorrelation. We then compared cubic regression splines vis-à-vis linear piecewise splines, and with varying number of knots and positions. Statistical code is provided to ensure reproducibility and improve dissemination of methods. Models are applied to longitudinal height measurements in a cohort of 215 Peruvian children followed from birth until their fourth year of life. Results Unexplained variability, as measured by the variance of the regression model, was reduced from 7.34 when using ordinary least squares to 0.81 (p < 0.001 when using a linear mixed-effect models with random slopes and a first order continuous autoregressive error term. There was substantial heterogeneity in both the intercept (p < 0.001 and slopes (p < 0.001 of the individual growth trajectories. We also identified important serial correlation within the structure of the data (ρ = 0.66; 95 % CI 0.64 to 0.68; p < 0.001, which we modeled with a first order continuous autoregressive error term as evidenced by the variogram of the residuals and by a lack of association among residuals. The final model provides a parametric linear regression equation for both estimation and