Pandey, S.; Rajaram, H.
2014-12-01
The critical zone (CZ) represents a major life-sustaining realm of the terrestrial surface. The processes controlling the development and transformation of the CZ are important to continued health of the planet as human influence continues to grow. The CZ encompasses the shallow subsurface, a region of reaction, unsaturated flow, and transport. Chemical weathering in the subsurface is one of the important processes involved in the formation and functioning of the CZ. We present two case studies of reactive transport modeling to investigate the influence of subsurface heterogeneity and unsaturated flow on chemical weathering processes in the CZ. The model is implemented using the reactive transport code PFLOTRAN. Heterogeneity in subsurface flow is represented using multiple realizations of conductive fracture networks in a hillslope cross-section. The first case study is motivated by observations at the Boulder Creek Critical Zone Observatory (BCCZO) including extensive hydrologic and geochemical datasets. The simulations show that fractures greatly enhance weathering as compared to a homogeneous porous medium. Simulations of north-facing slope hydrology with prolonged snowmelt pulses also increases weathering rates, showing the importance of slope aspect on weathering intensity. Recent work elucidates deteriorating water quality caused by climate change in the CZ of watersheds where acid rock drainage (ARD) occurs. The more complex reactions of ARD require a customized kinetic reaction module with PFLOTRAN. The second case study explores the mechanisms by which changes in hydrologic forcing, air and ground temperatures, and water table elevations influence ARD. For instance, unreacted pyrite exposed by a water table drop was shown to produce a 125% increase in annual pyrite oxidization rate, which provides one explanation for increased ARD.
Modeling impacts of subscale heterogeneities on dispersive solute transport in subsurface systems.
Vishal, Vikrant; Leung, Juliana Y
2015-11-01
Previous works in the literature demonstrated that dispersion increases with heterogeneities and travel distance in heterogeneous reservoirs. However, it remains challenging to quantify the effects of subscale heterogeneities on dispersion. Scale-up of input dispersivity and other reservoir attributes to the transport modeling scale should account for subscale heterogeneity and its variability. A method is proposed to quantify the uncertainties in reservoir attributes and dispersivity introduced by scale-up. A random walk particle tracking (RWPT) method, which is not prone to numerical dispersion, is used for transport modeling. First, to scale-up rock properties including porosity and permeability, volume variance at the transport modeling scale is computed corresponding to a given spatial correlation model; numerous sets of "conditioning data" are sampled from probability distributions whose mean is the block average of the actual measure values and the variance is the variance of block mean. Stochastic simulations are subsequently performed to generate multiple realizations at the transport modeling scale. Next, multiple sub-grid geostatistical realizations depicting detailed fine-scale heterogeneities and of the same physical sizes as the transport modeling grid block are subjected to RWPT simulation. Effective longitudinal and transverse (horizontal) dispersivities in two-dimensional models are determined simultaneously by matching the corresponding breakthrough concentration history for each realization with an equivalent medium consisting of averaged homogeneous rock properties. Aggregating results derived with all realizations, we generate probability distributions of scaled-up dispersivities conditional to particular averaged rock properties, from which values representative of the transport modeling scale are randomly drawn. The method is applied to model a tracer injection process. Results obtained from coarse-scale models, where reservoir properties and
The potential of imaging subsurface heterogeneities by local, natural earthquakes
Nishitsuji, Y.; Doi, I.; Draganov, D.S.
2014-01-01
We have developed a new imaging technique of subsurface heterogeneities that uses Sp-waves from natural earthquakes. This technique can be used as a first screening tool in frontier exploration areas before conventional active exploration. Analyzing Sp-waves from 28 earthquakes (Mj 2.0 to 4.2) recor
The potential of imaging subsurface heterogeneities by local, natural earthquakes
Nishitsuji, Y.; Doi, I.; Draganov, D.S.
2014-01-01
We have developed a new imaging technique of subsurface heterogeneities that uses Sp-waves from natural earthquakes. This technique can be used as a first screening tool in frontier exploration areas before conventional active exploration. Analyzing Sp-waves from 28 earthquakes (Mj 2.0 to 4.2) recor
Identifying Heterogeneities in Subsurface Environment using the Level Set Method
Energy Technology Data Exchange (ETDEWEB)
Lei, Hongzhuan [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Lu, Zhiming [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Vesselinov, Velimir Valentinov [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2016-08-25
These are slides from a presentation on identifying heterogeneities in subsurface environment using the level set method. The slides start with the motivation, then explain Level Set Method (LSM), the algorithms, some examples are given, and finally future work is explained.
The potential of imaging subsurface heterogeneities by local, natural earthquakes
Nishitsuji, Y.; Doi, I.; Draganov, D.S.
2014-01-01
We have developed a new imaging technique of subsurface heterogeneities that uses Sp-waves from natural earthquakes. This technique can be used as a first screening tool in frontier exploration areas before conventional active exploration. Analyzing Sp-waves from 28 earthquakes (Mj 2.0 to 4.2)
Hartmann, Andreas; Gleeson, Tom; Wada, Yoshihide; Wagener, Thorsten
2017-04-01
Karst aquifers in Europe are an important source of fresh water contributing up to half of the total drinking water supply in some countries. Karstic groundwater recharge is one of the most important components of the water balance of karst systems as it feeds the karst aquifers. Presently available large-scale hydrological models do not consider karst heterogeneity adequately. Projections of current and potential future groundwater recharge of Europe's karst aquifers are therefore unclear. In this study we compare simulations of present (1991-2010) and future (2080-2099) recharge using two different models to simulate groundwater recharge processes. One model includes karst processes (subsurface heterogeneity, lateral flow and concentrated recharge), while the other is based on the conceptual understanding of common hydrological systems (homogeneous subsurface, saturation excess overland flow). Both models are driven by the bias-corrected 5 GCMs of the ISI-MIP project (RCP8.5). To further assess sensitivity of groundwater recharge to climate variability, we calculate the elasticity of recharge rates to annual precipitation, temperature and average intensity of rainfall events, which is the median change of recharge that corresponds to the median change of these climate variables within the present and future time period, respectively. Our model comparison shows that karst regions over Europe have enhanced recharge rates with greater inter-annual variability compared to those with more homogenous subsurface properties. Furthermore, the heterogeneous representation shows stronger elasticity concerning climate variability than the homogeneous subsurface representation. This difference tends to increase towards the future. Our results suggest that water management in regions with heterogeneous subsurface can expect a higher water availability than estimated by most of the current large-scale simulations, while measures should be taken to prepare for increasingly
Impact of Subsurface Heterogeneities on nano-Scale Zero Valent Iron Transport
Krol, M. M.; Sleep, B. E.; O'Carroll, D. M.
2011-12-01
Nano-scale zero valent iron (nZVI) has been applied as a remediation technology at sites contaminated with chlorinated compounds and heavy metals. Although laboratory studies have demonstrated high reactivity for the degradation of target contaminants, the success of nZVI in the field has been limited due to poor subsurface mobility. When injected into the subsurface, nZVI tends to aggregate and be retained by subsurface soils. As such nZVI suspensions need to be stabilized for increased mobility. However, even with stabilization, soil heterogeneities can still lead to non-uniform nZVI transport, resulting in poor distribution and consequently decreased degradation of target compounds. Understanding how nZVI transport can be affected by subsurface heterogeneities can aid in improving the technology. This can be done with the use of a numerical model which can simulate nZVI transport. In this study CompSim, a finite difference groundwater model, is used to simulate the movement of nZVI in a two-dimensional domain. CompSim has been shown in previous studies to accurately predict nZVI movement in the subsurface, and is used in this study to examine the impact of soil heterogeneity on nZVI transport. This work also explores the impact of different viscosities of the injected nZVI suspensions (corresponding to different stabilizing polymers) and injection rates on nZVI mobility. Analysis metrics include travel time, travel distance, and average nZVI concentrations. Improving our understanding of the influence of soil heterogeneity on nZVI transport will lead to improved field scale implementation and, potentially, to more effective remediation of contaminated sites.
Heterogeneity and Microeconometrics Modelling
DEFF Research Database (Denmark)
Browning, Martin; Carro, Jesus
Presented at the 2005 Econometric Society World Congress Plenary Session on "Modelling Heterogeneity". We survey the treatment of heterogeneity in applied microeconometrics analyses. There are three themes. First, there is usually much more heterogeneity than empirical researchers allow for. Seco...
Redox heterogeneity of subsurface waters in the Mesoproterozoic ocean.
Sperling, E A; Rooney, A D; Hays, L; Sergeev, V N; Vorob'eva, N G; Sergeeva, N D; Selby, D; Johnston, D T; Knoll, A H
2014-09-01
A substantial body of evidence suggests that subsurface water masses in mid-Proterozoic marine basins were commonly anoxic, either euxinic (sulfidic) or ferruginous (free ferrous iron). To further document redox variations during this interval, a multiproxy geochemical and paleobiological investigation was conducted on the approximately 1000-m-thick Mesoproterozoic (Lower Riphean) Arlan Member of the Kaltasy Formation, central Russia. Iron speciation geochemistry, supported by organic geochemistry, redox-sensitive trace element abundances, and pyrite sulfur isotope values, indicates that basinal calcareous shales of the Arlan Member were deposited beneath an oxygenated water column, and consistent with this interpretation, eukaryotic microfossils are abundant in basinal facies. The Rhenium-Osmium (Re-Os) systematics of the Arlan shales yield depositional ages of 1414±40 and 1427±43 Ma for two horizons near the base of the succession, consistent with previously proposed correlations. The presence of free oxygen in a basinal environment adds an important end member to Proterozoic redox heterogeneity, requiring an explanation in light of previous data from time-equivalent basins. Very low total organic carbon contents in the Arlan Member are perhaps the key--oxic deep waters are more likely (under any level of atmospheric O2) in oligotrophic systems with low export production. Documentation of a full range of redox heterogeneity in subsurface waters and the existence of local redox controls indicate that no single stratigraphic section or basin can adequately capture both the mean redox profile of Proterozoic oceans and its variance at any given point in time.
Evaluation of a Heterogeneity Preserving Inversion Method for Subsurface Unsaturated Flow
Zhang, Y.; Schaap, M. G.; Neuman, S. P.; Guadagnini, A.; Riva, M.
2013-12-01
Natural recharge to groundwater in semi-arid regions is driven by unsaturated flow through an often deep vadose zone. Understanding and modeling such flow requires knowledge of the subsurface heterogeneity of hydraulic properties. It is expensive and labor intensive to measure such properties, making it necessary to rely on other sources of information. Pedotransfer functions (PTFs) constitute cheap and viable tools to estimate hydraulic properties from soil or sediment texture. Due to the predominantly empirical nature of PTFs and the fact that PTFs are often based on data derived from small laboratory samples, biased estimates of hydraulic parameters may be produced that would likely bias modeled field scale deep vadose zone flow. In this work, an inversion framework that treats the subsurface as a composite medium formed by different zones, each associated with spatially heterogeneous hydraulic parameters, is developed to allow (a) preserving the details of the subsurface heterogeneous nature and (b) assuring consistency among hydraulic parameters associated with different regions of the domain. The approach is demonstrated through a field application, which considers the Maricopa site near Phoenix, Arizona. The study site is a 50x50 meter and 15 meter deep vadose zone at which a 28-day constant-rate infiltration experiment was conducted in 2001. Moisture content at the site was measured daily with neutron thermalization at 400 locations during the infiltration period, and at irregular intervals 100 and 200 days prior and after infiltration, respectively. A PTF based on the Rosetta model is applied on the basis of measured spatial distributions of textural and bulk density data to provide initial estimates of the three-dimensional structure of hydraulic properties. Simple linear functions are defined that transform the PTF estimates of soil hydraulic properties values into hydraulic parameters that minimize the objective functions for the domain, while zonation
Kristensen, Andreas H; Poulsen, Tjalfe G; Mortensen, Lars; Moldrup, Per
2010-07-15
Quantifying the spatial variability of factors affecting natural attenuation of hydrocarbons in the unsaturated zone is important to (i) performing a reliable risk assessment and (ii) evaluating the possibility for bioremediation of petroleum-polluted sites. Most studies to date have focused on the shallow unsaturated zone. Based on a data set comprising analysis of about 100 soil samples taken in a 16 m-deep unsaturated zone polluted with volatile petroleum compounds, we statistically and geostatistically analysed values of essential soil properties. The subsurface of the site was highly layered, resulting in an accumulation of pollution within coarse sandy lenses. Air-filled porosity, readily available phosphorous, and the first-order rate constant (k(1)) of benzene obtained from slurry biodegradation experiments were found to depend on geologic sample characterization (P<0.05), while inorganic nitrogen was homogenously distributed across the soil stratigraphy. Semivariogram analysis showed a spatial continuity of 4-8.6 m in the vertical direction, while it was 2-5 times greater in the horizontal direction. Values of k(1) displayed strong spatial autocorrelation. Even so, the soil potential for biodegradation was highly variable, which from autoregressive state-space modeling was partly explained by changes in soil air-filled porosity and gravimetric water content. The results suggest considering biological heterogeneity when evaluating the fate of contaminants in the subsurface.
Masuda, Naoki; Redner, S
2010-01-01
We introduce the heterogeneous voter model (HVM), in which each agent has its own intrinsic rate to change state, reflective of the heterogeneity of real people, and the partisan voter model (PVM), in which each agent has an innate and fixed preference for one of two possible opinion states. For the HVM, the time until consensus is reached is much longer than in the classic voter model. For the PVM in the mean-field limit, a population evolves to a "selfish" state, where each agent tends to be aligned with its internal preference. For finite populations, discrete fluctuations ultimately lead to consensus being reached in a time that scales exponentially with population size.
Characterizing subsurface hydraulic heterogeneity of alluvial fan using riverstage fluctuations
Wang, Yu-Li; Yeh, Tian-Chyi Jim; Wen, Jet-Chau; Huang, Shao-Yang; Zha, Yuanyuan; Tsai, Jui-Pin; Hao, Yonghong; Liang, Yue
2017-04-01
The objective of this study is to demonstrate the ability of riverstage tomography to estimate 2-D spatial distribution of hydraulic diffusivity (D) of Zhuoshui River alluvial fan, Taiwan, using groundwater level data from 65 wells and stream stage data from 5 gauging stations. In order to accomplish this objective, wavelet analysis is first conducted to investigate the temporal characteristics of groundwater level, precipitation, and stream stage. The results of the analysis show that variations of groundwater level and stream stage are highly correlated over seasonal and annual periods while that between precipitation is less significant. Subsequently, spatial cross-correlation between seasonal variations of groundwater level and riverstage data is analyzed. It is found that the correlation contour map reflects the pattern of sediment distribution of the fan. This finding is further substantiated by the cross-correlation analysis using both noisy and noise-free groundwater and riverstage data of a synthetic aquifer, where aquifer heterogeneity is known exactly. The ability of riverstage tomography is then tested with these synthetic data sets to estimate D distribution. Finally, the riverstage tomography is applied to the alluvial fan. The results of the application reveal that the apex and southeast of the alluvial fan are regions with relatively high D and the D values gradually decrease toward the shoreline of the fan. In addition, D at northern alluvial fan is slightly larger than that at southern. These findings are consistent with the geologic evolution of this alluvial fan.
Wolaver, B. D.; Sun, A. Y.; Nicot, J.; Hovorka, S. D.; Nuñez-Lopez, V.; Young, M.
2011-12-01
Numerical simulations of CO2 storage reservoir leakage can be used to assess risks of shallow groundwater aquifer contamination during monitoring network design. Improperly plugged and abandoned wells are well known to represent one of the greatest risks to successful containment at geologic carbon sequestration sites. Casing and cement seal failure of wells penetrating the confining layer may create fast-flow pathways for CO2 and brine migration from the storage reservoir into the shallow subsurface. To protect drinking water aquifers from possible leaks, injection permits require identification of artificial penetrations and evaluation that wells are adequately plugged and abandoned. However, assumptions made during well evaluation may overlook the likelihood of well failure leading to a leak into an aquifer. We present a monitoring approach that provides quick and accurate detection in the event of a leak to an aquifer. Sand and shale facies are classified to simulate aquifer heterogeneity using representative borehole geophysical data from Texas, U.S.A. Gulf Coast Aquifer System wells. Numerical models simulate pressure perturbations in response to a leak to an aquifer overlying a storage reservoir. Candidate monitoring well locations for a possible leak of randomly selected location are chosen from a suite of possible wells based on the detectability of CO2 leakage from the groundwater model. We first show that the locations and magnitudes of leakage can be identified for homogeneous aquifers by using an inversion procedure and pressure observations. We then consider the effects of conceptual model uncertainty, pressure measurement error, and background noise on detectability of leaky wells. While substantial previous work quantified pressure perturbations caused by leaky wells using analytical solutions or simple numerical model configurations, the effects of formation heterogeneity on pressure perturbation and other uncertain factors are not well examined
A Theoretical Study of Subsurface Drainage Model Simulation of ...
African Journals Online (AJOL)
A Theoretical Study of Subsurface Drainage Model Simulation of Drainage Flow and ... of subsurface drain spacing, evapotranspiration and irrigation water quality on ... The study was carried out on a conceptual uniform homogenous irrigated ...
Energy Technology Data Exchange (ETDEWEB)
Umezawa, Osamu [Department of Mechanical Engineering and Materials Science, Yokohama National University 79-5 Tokiwadai, Hodogaya, Yokohama, 240-8501 (Japan); Morita, Motoaki [Department of Mechanical Engineering and Materials Science, Yokohama National University 79-5 Tokiwadai, Hodogaya, Yokohama, 240-8501, Japan and Now Tokyo University of Marine Science and Technology, Koto-ku, Tokyo 135-8533 (Japan); Yuasa, Takayuki [Department of Mechanical Engineering and Materials Science, Yokohama National University 79-5 Tokiwadai, Hodogaya, Yokohama, 240-8501, Japan and Now Nippon Steel and Sumitomo Metal, Kashima, 314-0014 (Japan); Morooka, Satoshi [Department of Mechanical Engineering and Materials Science, Yokohama National University 79-5 Tokiwadai, Hodogaya, Yokohama, 240-8501, Japan and Now Tokyo Metropolitan University, Hino, Tokyo 191-0065 (Japan); Ono, Yoshinori; Yuri, Tetsumi; Ogata, Toshio [National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, 305-0047 (Japan)
2014-01-27
Subsurface crack initiation in high-cycle fatigue has been detected as (0001) transgranular facet in titanium alloys at low temperature. The discussion on the subsurface crack generation was reviewed. Analyses by neutron diffraction and full constraints model under tension mode as well as crystallographic identification of the facet were focused. The accumulated tensile stress along <0001> may be responsible to initial microcracking on (0001) and the crack opening.
Directional Dipole Model for Subsurface Scattering
DEFF Research Database (Denmark)
Frisvad, Jeppe Revall; Hachisuka, Toshiya; Kjeldsen, Thomas Kim
2014-01-01
Rendering translucent materials using Monte Carlo ray tracing is computationally expensive due to a large number of subsurface scattering events. Faster approaches are based on analytical models derived from diffusion theory. While such analytical models are efficient, they miss out on some...... point source diffusion. A ray source corresponds better to the light that refracts through the surface of a translucent material. Using this ray source, we are able to take the direction of the incident light ray and the direction toward the point of emergence into account. We use a dipole construction...... similar to that of the standard dipole model, but we now have positive and negative ray sources with a mirrored pair of directions. Our model is as computationally efficient as existing models while it includes single scattering without relying on a separate Monte Carlo simulation, and the rendered images...
Integrated geomechanical modelling for deep subsurface damage
Wees, J.D. van; Orlic, B.; Zijl, W.; Jongerius, P.; Schreppers, G.J.; Hendriks, M.
2001-01-01
Government, E&P and mining industry increasingly demand fundamental insight and accurate predictions on subsurface and surface deformation and damage due to exploitation of subsurface natural resources, and subsurface storage of energy residues (e.g. CO2). At this moment deformation is difficult to
Aleer, Sam; Adetutu, Eric M; Weber, John; Ball, Andrew S; Juhasz, Albert L
2014-04-01
In situ bioremediation is potentially a cost effective treatment strategy for subsurface soils contaminated with petroleum hydrocarbons, however, limited information is available regarding the impact of soil spatial heterogeneity on bioremediation efficacy. In this study, we assessed issues associated with hydrocarbon biodegradation and soil spatial heterogeneity (samples designated as FTF 1, 5 and 8) from a site in which in situ bioremediation was proposed for hydrocarbon removal. Test pit activities showed similarities in FTF soil profiles with elevated hydrocarbon concentrations detected in all soils at 2 m below ground surface. However, PCR-DGGE-based cluster analysis showed that the bacterial community in FTF 5 (at 2 m) was substantially different (53% dissimilar) and 2-3 fold more diverse than communities in FTF 1 and 8 (with 80% similarity). When hydrocarbon degrading potential was assessed, differences were observed in the extent of (14)C-benzene mineralisation under aerobic conditions with FTF 5 exhibiting the highest hydrocarbon removal potential compared to FTF 1 and 8. Further analysis indicated that the FTF 5 microbial community was substantially different from other FTF samples and dominated by putative hydrocarbon degraders belonging to Pseudomonads, Xanthomonads and Enterobacteria. However, hydrocarbon removal in FTF 5 under anaerobic conditions with nitrate and sulphate electron acceptors was limited suggesting that aerobic conditions were crucial for hydrocarbon removal. This study highlights the importance of assessing available microbial capacity prior to bioremediation and shows that the site's spatial heterogeneity can adversely affect the success of in situ bioremediation unless area-specific optimizations are performed.
Large-scale heterogeneity in Ceres' subsurface: Clues to internal evolution
Raymond, Carol; Ammannito, Eleonora; Castillo-Rogez, Julie; De Sanctis, Maria Cristina; Jaumann, Ralf; Y McSween, Harry; Marchi, Simone; Prettyman, Thomas H.; Russell, Christopher T.; Scully, Jennifer E. C.; Dawn Science Team
2016-10-01
Dawn's observations at Ceres indicate it is volatile-rich body that has undergone ice-rock differentiation and harbored a past subsurface ocean [1]. Gravity data indicate a volatile-rich shell (crust) overlying a denser core of hydrated silicates [2]. Ubiquitous ammoniated phyllosilicates [3] and carbonates [4] on the surface point towards pervasive hydrothermal alteration. The absence of an ice-dominated layer in the subsurface (from ocean freezing) may indicate partial loss of the ice shell by impact-induced sublimation [5], and mixing with the salts and silicate rich material present near the ancient seafloor. Although the surface shows compositional homogeneity, there are variations present, such as bluer material associated with several young craters, and a broad region of brighter material surrounding Dantu and Kerwan craters that is relatively ammonia-rich [6]. This compositionally-distinct region resides in a ~4 km deep basin – Vendemia Planitia – which has been proposed as a cryptic mega impact basin [7]. The smooth morphology and dearth of impact craters in this area, and the lack of large (>400 km) craters on Ceres in general points to an erasure process that could be the result of resurfacing, possibly in combination with viscous relaxation [7]. A similarly bright and smooth crater-free region surrounding the large impact craters Urvara and Yalode also appears spectrally-distinct, again with a relatively ammonia-rich composition. These areas contrast with the Hanami planum highland, which displays rougher topography and hosts localized regions of ammonia-poor composition associated with the brightest surface material. The surface morphology and composition likely reflect instrinsic subsurface heterogeneity due to convective processes, as well as modification by impact processes.[1] Russell et al., Science, 2016 [2] Park et al., Nature, 2016 [3] De Sanctis et al., 2015 10.1038/nature18290 [4] De Sanctis et al., Nature, 2016 [5] Castillo-Rogez et al
Numerical sunspot models - subsurface structure and helioseismic forward modeling (Invited)
Rempel, M.; Birch, A. C.; Braun, D. C.
2009-12-01
The magnetic and thermal subsurface structure of sunspots has been debated for decades. While local helioseismic inversions allow in principle to constrain the subsurface structure of sunspots, a full inversion is still not possible due to the complicated interaction between waves and magnetic field. As an alternative it is possible to address this problem through forward modeling. Over the past few years numerical MHD models of entire sunspots including radiative transfer and a realistic equation of state have become possible. These simulations include p-modes excited by convection and the full interaction of these modes with the magnetic and thermal structure of the sunspot. In this talk I will present recent progress in MHD modeling of sunspots with special emphasis on the thermal and magnetic structure of numerical sunspot models. It turns out that modeled sunspots so far impose rather shallow perturbations to sound and fast mode speeds in the upper most 2 Mm. Nevertheless the seismic signatures are very similar to observed sunspots.
Analyzing and modeling heterogeneous behavior
Lin, Zhiting; Wu, Xiaoqing; He, Dongyue; Zhu, Qiang; Ni, Jixiang
2016-05-01
Recently, it was pointed out that the non-Poisson statistics with heavy tail existed in many scenarios of human behaviors. But most of these studies claimed that power-law characterized diverse aspects of human mobility patterns. In this paper, we suggest that human behavior may not be driven by identical mechanisms and can be modeled as a Semi-Markov Modulated Process. To verify our suggestion and model, we analyzed a total of 1,619,934 records of library visitations (including undergraduate and graduate students). It is found that the distribution of visitation intervals is well fitted with three sections of lines instead of the traditional power law distribution in log-log scale. The results confirm that some human behaviors cannot be simply expressed as power law or any other simple functions. At the same time, we divided the data into groups and extracted period bursty events. Through careful analysis in different groups, we drew a conclusion that aggregate behavior might be composed of heterogeneous behaviors, and even the behaviors of the same type tended to be different in different period. The aggregate behavior is supposed to be formed by "heterogeneous groups". We performed a series of experiments. Simulation results showed that we just needed to set up two states Semi-Markov Modulated Process to construct proper representation of heterogeneous behavior.
Integrated Surface/subsurface flow modeling in PFLOTRAN
Energy Technology Data Exchange (ETDEWEB)
Painter, Scott L [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
2016-10-01
Understanding soil water, groundwater, and shallow surface water dynamics as an integrated hydrological system is critical for understanding the Earth’s critical zone, the thin outer layer at our planet’s surface where vegetation, soil, rock, and gases interact to regulate the environment. Computational tools that take this view of soil moisture and shallow surface flows as a single integrated system are typically referred to as integrated surface/subsurface hydrology models. We extend the open-source, highly parallel, subsurface flow and reactive transport simulator PFLOTRAN to accommodate surface flows. In contrast to most previous implementations, we do not represent a distinct surface system. Instead, the vertical gradient in hydraulic head at the land surface is neglected, which allows the surface flow system to be eliminated and incorporated directly into the subsurface system. This tight coupling approach leads to a robust capability and also greatly simplifies implementation in existing subsurface simulators such as PFLOTRAN. Successful comparisons to independent numerical solutions build confidence in the approximation and implementation. Example simulations of the Walker Branch and East Fork Poplar Creek watersheds near Oak Ridge, Tennessee demonstrate the robustness of the approach in geometrically complex applications. The lack of a robust integrated surface/subsurface hydrology capability had been a barrier to PFLOTRAN’s use in critical zone studies. This work addresses that capability gap, thus enabling PFLOTRAN as a community platform for building integrated models of the critical zone.
Prediction of Geological Subsurfaces Based on Gaussian Random Field Models
Energy Technology Data Exchange (ETDEWEB)
Abrahamsen, Petter
1997-12-31
During the sixties, random functions became practical tools for predicting ore reserves with associated precision measures in the mining industry. This was the start of the geostatistical methods called kriging. These methods are used, for example, in petroleum exploration. This thesis reviews the possibilities for using Gaussian random functions in modelling of geological subsurfaces. It develops methods for including many sources of information and observations for precise prediction of the depth of geological subsurfaces. The simple properties of Gaussian distributions make it possible to calculate optimal predictors in the mean square sense. This is done in a discussion of kriging predictors. These predictors are then extended to deal with several subsurfaces simultaneously. It is shown how additional velocity observations can be used to improve predictions. The use of gradient data and even higher order derivatives are also considered and gradient data are used in an example. 130 refs., 44 figs., 12 tabs.
Modelling oil plumes from subsurface spills.
Lardner, Robin; Zodiatis, George
2017-07-11
An oil plume model to simulate the behavior of oil from spills located at any given depth below the sea surface is presented, following major modifications to a plume model developed earlier by Malačič (2001) and drawing on ideas in a paper by Yapa and Zheng (1997). The paper presents improvements in those models and numerical testing of the various parameters in the plume model. The plume model described in this paper is one of the numerous modules of the well-established MEDSLIK oil spill model. The deep blowout scenario of the MEDEXPOL 2013 oil spill modelling exercise, organized by REMPEC, has been applied using the improved oil plume module of the MEDSLIK model and inter-comparison with results having the oil spill source at the sea surface are discussed. Copyright © 2017 Elsevier Ltd. All rights reserved.
Subsurface stormflow modeling with sensitivity analysis using a Latin-hypercube sampling technique
Energy Technology Data Exchange (ETDEWEB)
Gwo, J.P.; Toran, L.E.; Morris, M.D. [Oak Ridge National Lab., TN (United States); Wilson, G.V. [Univ. of Tennessee, Knoxville, TN (United States). Dept. of Plant and Soil Science
1994-09-01
Subsurface stormflow, because of its dynamic and nonlinear features, has been a very challenging process in both field experiments and modeling studies. The disposal of wastes in subsurface stormflow and vadose zones at Oak Ridge National Laboratory, however, demands more effort to characterize these flow zones and to study their dynamic flow processes. Field data and modeling studies for these flow zones are relatively scarce, and the effect of engineering designs on the flow processes is poorly understood. On the basis of a risk assessment framework and a conceptual model for the Oak Ridge Reservation area, numerical models of a proposed waste disposal site were built, and a Latin-hypercube simulation technique was used to study the uncertainty of model parameters. Four scenarios, with three engineering designs, were simulated, and the effectiveness of the engineering designs was evaluated. Sensitivity analysis of model parameters suggested that hydraulic conductivity was the most influential parameter. However, local heterogeneities may alter flow patterns and result in complex recharge and discharge patterns. Hydraulic conductivity, therefore, may not be used as the only reference for subsurface flow monitoring and engineering operations. Neither of the two engineering designs, capping and French drains, was found to be effective in hydrologically isolating downslope waste trenches. However, pressure head contours indicated that combinations of both designs may prove more effective than either one alone.
Iterative approach to modeling subsurface stormflow based on nonlinear, hillslope-scale physics
Directory of Open Access Journals (Sweden)
J. H. Spaaks
2009-08-01
Full Text Available Soil water transport in small, humid, upland catchments is often dominated by subsurface stormflow. Recent studies of this process suggest that at the plot scale, generation of transient saturation may be governed by threshold behavior, and that transient saturation is a prerequisite for lateral flow. The interaction between these plot scale processes yields complex behavior at the hillslope scale. We argue that this complexity should be incorporated into our models. We take an iterative approach to developing our model, starting with a very simple representation of hillslope rainfall-runoff. Next, we design new virtual experiments with which we test our model, while adding more structural complexity. In this study, we present results from three such development cycles, corresponding to three different hillslope-scale, lumped models. Model_{1} is a linear tank model, which assumes transient saturation to be homogeneously distributed over the hillslope. Model_{2} assumes transient saturation to be heterogeneously distributed over the hillslope, and that the spatial distribution of the saturated zone does not vary with time. Model_{3} assumes that transient saturation is heterogeneous both in space and in time. We found that the homogeneity assumption underlying Model_{1} resulted in hillslope discharge being too steep during the first part of the rising limb, but not steep enough on the second part. Also, peak height was underestimated. The additional complexity in Model_{2} improved the simulations in terms of the fit, but not in terms of the dynamics. The threshold-based Model_{3} captured most of the hydrograph dynamics (Nash-Sutcliffe efficiency of 0.98. After having assessed our models in a lumped setup, we then compared Model_{1} to Model_{3} in a spatially explicit setup, and evaluated what patterns of subsurface flow were possible with model elements of each type. We found
Computer Aided Design Modeling for Heterogeneous Objects
Gupta, Vikas; Tandon, Puneet
2010-01-01
Heterogeneous object design is an active research area in recent years. The conventional CAD modeling approaches only provide geometry and topology of the object, but do not contain any information with regard to the materials of the object and so can not be used for the fabrication of heterogeneous objects (HO) through rapid prototyping. Current research focuses on computer-aided design issues in heterogeneous object design. A new CAD modeling approach is proposed to integrate the material information into geometric regions thus model the material distributions in the heterogeneous object. The gradient references are used to represent the complex geometry heterogeneous objects which have simultaneous geometry intricacies and accurate material distributions. The gradient references helps in flexible manipulability and control to heterogeneous objects, which guarantees the local control over gradient regions of developed heterogeneous objects. A systematic approach on data flow, processing, computer visualizat...
DEFF Research Database (Denmark)
Kristensen, Andreas Houlberg; Poulsen, Tjalfe; Mortensen, Lars;
2010-01-01
on the shallow unsaturated zone. Based on a data set comprising analysis of about 100 soil samples taken in a 16-m-deep unsaturated zone polluted with volatile petroleum compounds, we statistically and geostatistically analyzed values of essential soil properties. The subsurface of the site was highly layered...
Energy Technology Data Exchange (ETDEWEB)
Maxwell, R M; Kollet, S J
2007-08-23
The impact of three-dimensional subsurface heterogeneity on hillslope runoff generated by excess infiltration (so called Hortonian runoff) is examined. A fully-coupled, parallel subsurface overland flow model is used to simulate runoff from an idealized hillslope. Ensembles of correlated, Gaussian random fields of saturated hydraulic conductivity are used to create uncertainty and variability (i.e. structure) due to subsurface heterogeneity. A large number of cases are simulated in a parametric manner with variance of the hydraulic conductivity varied over two orders of magnitude. These cases include rainfall rates above, equal and below the geometric mean of the hydraulic conductivity distribution. These cases are also compared to theoretical considerations of runoff production based on simple assumptions regarding (1) the rainfall rate and the value of hydraulic conductivity in the surface cell using a spatially-indiscriminant approach; and (2) a percolation-theory type approach to incorporate so-called runon. Simulations to test the ergodicity of hydraulic conductivity on hillslope runoff are also performed. Results show three-dimensional features (particularly in the vertical dimension) in the hydraulic conductivity distributions that create shallow perching, which has an important effect on runoff behavior that is fundamentally different in character than previous two dimensional analyses. The simple theories are shown to be very poor predictors of the saturated area that might runoff due to excess infiltration. It is also shown that ergodicity is reached only for a large number of integral scales ({approx}30) and not for cases where the rainfall rate is less than the geometric mean of the saturated hydraulic conductivity.
Deep Soil: Quantifying and Modeling Subsurface Carbon
James, J. N.; Devine, W.; Harrison, R. B.
2014-12-01
Some soil carbon datasets that are spatially rich, such as the USDA Forest Service Inventory and Analysis National Program dataset, sample soil to only 20 cm (8 inches), despite evidence that substantial stores of soil C can be found deeper in the soil profile. The maximum extent of tree rooting is typically many meters deep and provides: direct exchange with the soil solution; redistribution of water from deep horizons toward the surface during times of drought; resources for active microbial communities in deep soil around root channels; and direct carbon inputs through exudates and root turnover. This study examined soil carbon to a depth of 2.5 meters across 22 soils in Pacific Northwest Douglas-fir forests. Excavations at 20 additional sites took place in summer 2014, greatly expanding the spatial coverage and extent of the data set. Forest floor and mineral soil bulk density samples were collected at depths of 0.1, 0.5, 1.0, 1.5, 2.0 and 2.5 meters. Pool estimates from systematic sampling depths shallower than 1.5 m yielded significantly smaller estimates than the total soil stock to 2.5 meters (P<0.01). On average, only 5% of soil C was found in the litter layer, 35% was found below 0.5 meter, and 21% was found below 1.0 meter. Due to the difficulty of excavating and measuring deep soil carbon, a series of nonlinear mixed effect models were fit to the data to predict deep soil carbon stocks given sampling to 1.0 meter. A model using an inverse polynomial function predicted soil carbon to 2.5 meters with -5.6% mean error. The largest errors occurred in Andisols with non-crystalline minerals, which can adsorb large quantities of carbon on mineral surfaces and preserve it from decomposition. An accurate spatial dataset of soil depth to bedrock would be extremely useful to constrain models of the vertical distribution of soil carbon. Efforts to represent carbon in spatial models would benefit from considering the vertical distribution of carbon in soil. Sampling
SeiVis: An interactive visual subsurface modeling application
Hollt, Thomas
2012-12-01
The most important resources to fulfill today’s energy demands are fossil fuels, such as oil and natural gas. When exploiting hydrocarbon reservoirs, a detailed and credible model of the subsurface structures is crucial in order to minimize economic and ecological risks. Creating such a model is an inverse problem: reconstructing structures from measured reflection seismics. The major challenge here is twofold: First, the structures in highly ambiguous seismic data are interpreted in the time domain. Second, a velocity model has to be built from this interpretation to match the model to depth measurements from wells. If it is not possible to obtain a match at all positions, the interpretation has to be updated, going back to the first step. This results in a lengthy back and forth between the different steps, or in an unphysical velocity model in many cases. This paper presents a novel, integrated approach to interactively creating subsurface models from reflection seismics. It integrates the interpretation of the seismic data using an interactive horizon extraction technique based on piecewise global optimization with velocity modeling. Computing and visualizing the effects of changes to the interpretation and velocity model on the depth-converted model on the fly enables an integrated feedback loop that enables a completely new connection of the seismic data in time domain and well data in depth domain. Using a novel joint time/depth visualization, depicting side-by-side views of the original and the resulting depth-converted data, domain experts can directly fit their interpretation in time domain to spatial ground truth data. We have conducted a domain expert evaluation, which illustrates that the presented workflow enables the creation of exact subsurface models much more rapidly than previous approaches. © 2012 IEEE.
A new model for estimating subsurface ice content based on combined electrical and seismic data sets
Directory of Open Access Journals (Sweden)
C. Hauck
2011-06-01
Full Text Available Detailed knowledge of the material properties and internal structures of frozen ground is one of the prerequisites in many permafrost studies. In the absence of direct evidence, such as in-situ borehole measurements, geophysical methods are an increasingly interesting option for obtaining subsurface information on various spatial and temporal scales. The indirect nature of geophysical soundings requires a relation between the measured variables (e.g. electrical resistivity, seismic velocity and the actual subsurface constituents (rock, water, air, ice. In this work, we present a model which provides estimates of the volumetric fractions of these four constituents from tomographic electrical and seismic images. The model is tested using geophysical data sets from two rock glaciers in the Swiss Alps, where ground truth information in form of borehole data is available. First results confirm the applicability of the so-called 4-phase model, which allows to quantify the contributions of ice-, water- and air within permafrost areas as well as detecting solid bedrock. Apart from a similarly thick active layer with enhanced air content for both rock glaciers, the two case studies revealed a heterogeneous distribution of ice and unfrozen water within Muragl rock glacier, where bedrock was detected at depths of 20–25 m, but a comparatively homogeneous ice body with only minor heterogeneities within Murtèl rock glacier.
A new model for quantifying subsurface ice content based on geophysical data sets
Directory of Open Access Journals (Sweden)
C. Hauck
2010-06-01
Full Text Available Detailed knowledge of the material properties and internal structures of frozen ground is one of the prerequisites in many permafrost studies. In the absence of direct evidence, such as in-situ borehole measurements, geophysical methods are an increasingly interesting option for obtaining subsurface information on various spatial and temporal scales. The indirect nature of geophysical soundings requires a relation between the measured variables (e.g. electrical resistivity, seismic velocity and the actual subsurface constituents (rock, water, air, ice. In this work we present a model, which provides estimates of the volumetric fractions of these four phases from tomographic electrical and seismic images. The model is tested using geophysical data sets from two rock glaciers in the Swiss Alps, where ground truth information in form of borehole data is available. First results confirm the applicability of the so-called 4-phase model, which allows to quantify the contributions of ice-, water- and air within permafrost areas as well as detecting the firm bedrock. Apart from a similarly thick active layer with enhanced air content for both rock glaciers, the two case studies revealed a heterogeneous distribution of ice and unfrozen water within rock glacier Muragl, where bedrock was detected at depths of 20–25 m, but a comparatively homogeneous ice body with only minor heterogeneities within rock glacier Murtèl.
Molecular modeling of heterogeneous catalysis
Gislason, Jason Joseph
A novel method for modeling heterogeneous catalysis was developed to further facilitate the understanding of catalytic reactor mechanisms. The method employs molecular dynamics simulations, statistical mechanical, and Unity Bond Index - Quadratic Exponential Potential (UBI-QEP) calculations to calculate the rate constants for reactions on metal surfaces. The primary difficulty of molecular dynamics simulations on metal surfaces has been the lack of reliable reactive potential energy surfaces. We have overcome this through the development of the Normalized Bond Index - Reactive Potential Function (NBI-RPF), which can accurately describe the reaction of adsorbates on metal surfaces. The first calculations of rate constants for a reaction on a metal surface using molecular dynamics simulations are presented. This method is applied to the determination of the mechanism for selective hydrogenation of acetylene in an ethylene rich flow. It was determined that the selectivity for acetylene hydrogenation is attributable to the higher reactivity of acetylene versus ethylene with respect to hydrogenation by molecular hydrogen. It was shown that hydrogen transfer from the carbonaceous layer to acetylene or ethylene is insignificant in the hydrogenation process. Molecular dynamics simulations and molecular mechanics calculations were used to determine the diffusion rate constants for dimethylnaphthalene isomers is mordenite. 2,6-dimethylnaphthalene and 2,7-dimethylnaphthalene were found to have similar diffusion rate constants. Grand canonical Monte Carlo calculations were performed on the competitive adsorption of 2,6-dimethylnaphthalene and 2,7-dimethylnaphthalene in type X zeolites exchanged individually with barium, calcium, potassium, and rubidium ions, calcium exchanged MCM-22, and hydrogen form mordenite (MOR), X zeolite, Y zeolite, hypBEB, ZSM- 12, and MCM-22. These calculations showed that barium exchanged X zeolite was the most selective toward 2
Simplified subsurface modelling: data assimilation and violated model assumptions
Erdal, Daniel; Lange, Natascha; Neuweiler, Insa
2017-04-01
Integrated models are gaining more and more attention in hydrological modelling as they can better represent the interaction between different compartments. Naturally, these models come along with larger numbers of unknowns and requirements on computational resources compared to stand-alone models. If large model domains are to be represented, e.g. on catchment scale, the resolution of the numerical grid needs to be reduced or the model itself needs to be simplified. Both approaches lead to a reduced ability to reproduce the present processes. This lack of model accuracy may be compensated by using data assimilation methods. In these methods observations are used to update the model states, and optionally model parameters as well, in order to reduce the model error induced by the imposed simplifications. What is unclear is whether these methods combined with strongly simplified models result in completely data-driven models or if they can even be used to make adequate predictions of the model state for times when no observations are available. In the current work we consider the combined groundwater and unsaturated zone, which can be modelled in a physically consistent way using 3D-models solving the Richards equation. For use in simple predictions, however, simpler approaches may be considered. The question investigated here is whether a simpler model, in which the groundwater is modelled as a horizontal 2D-model and the unsaturated zones as a few sparse 1D-columns, can be used within an Ensemble Kalman filter to give predictions of groundwater levels and unsaturated fluxes. This is tested under conditions where the feedback between the two model-compartments are large (e.g. shallow groundwater table) and the simplification assumptions are clearly violated. Such a case may be a steep hill-slope or pumping wells, creating lateral fluxes in the unsaturated zone, or strong heterogeneous structures creating unaccounted flows in both the saturated and unsaturated
Theoretical analysis of non-Gaussian heterogeneity effects on subsurface flow and transport
Riva, Monica; Guadagnini, Alberto; Neuman, Shlomo P.
2017-04-01
Much of the stochastic groundwater literature is devoted to the analysis of flow and transport in Gaussian or multi-Gaussian log hydraulic conductivity (or transmissivity) fields, Y(x)=ln\\func K(x) (x being a position vector), characterized by one or (less frequently) a multiplicity of spatial correlation scales. Yet Y and many other variables and their (spatial or temporal) increments, ΔY, are known to be generally non-Gaussian. One common manifestation of non-Gaussianity is that whereas frequency distributions of Y often exhibit mild peaks and light tails, those of increments ΔY are generally symmetric with peaks that grow sharper, and tails that become heavier, as separation scale or lag between pairs of Y values decreases. A statistical model that captures these disparate, scale-dependent distributions of Y and ΔY in a unified and consistent manner has been recently proposed by us. This new "generalized sub-Gaussian (GSG)" model has the form Y(x)=U(x)G(x) where G(x) is (generally, but not necessarily) a multiscale Gaussian random field and U(x) is a nonnegative subordinator independent of G. The purpose of this paper is to explore analytically, in an elementary manner, lead-order effects that non-Gaussian heterogeneity described by the GSG model have on the stochastic description of flow and transport. Recognizing that perturbation expansion of hydraulic conductivity K=eY diverges when Y is sub-Gaussian, we render the expansion convergent by truncating Y's domain of definition. We then demonstrate theoretically and illustrate by way of numerical examples that, as the domain of truncation expands, (a) the variance of truncated Y (denoted by Yt) approaches that of Y and (b) the pdf (and thereby moments) of Yt increments approach those of Y increments and, as a consequence, the variogram of Yt approaches that of Y. This in turn guarantees that perturbing Kt=etY to second order in σYt (the standard deviation of Yt) yields results which approach those we obtain
DEFF Research Database (Denmark)
Kristensen, Andreas Houlberg; Poulsen, Tjalfe; Mortensen, Lars
2010-01-01
Quantifying the spatial variability of factors affecting natural attenuation of hydrocarbons in the unsaturated zone is important to (i) performing a reliable risk assessment and (ii) evaluating the possibility for bioremediation of petroleum-polluted sites. Most studies to date have focused...... on the shallow unsaturated zone. Based on a data set comprising analysis of about 100 soil samples taken in a 16-m-deep unsaturated zone polluted with volatile petroleum compounds, we statistically and geostatistically analyzed values of essential soil properties. The subsurface of the site was highly layered...
Planetary subsurface investigation by 3D visualization model .
Seu, R.; Catallo, C.; Tragni, M.; Abbattista, C.; Cinquepalmi, L.
Subsurface data analysis and visualization represents one of the main aspect in Planetary Observation (i.e. search for water or geological characterization). The data are collected by subsurface sounding radars as instruments on-board of deep space missions. These data are generally represented as 2D radargrams in the perspective of space track and z axes (perpendicular to the subsurface) but without direct correlation to other data acquisition or knowledge on the planet . In many case there are plenty of data from other sensors of the same mission, or other ones, with high continuity in time and in space and specially around the scientific sites of interest (i.e. candidate landing areas or particular scientific interesting sites). The 2D perspective is good to analyse single acquisitions and to perform detailed analysis on the returned echo but are quite useless to compare very large dataset as now are available on many planets and moons of solar system. The best way is to approach the analysis on 3D visualization model generated from the entire stack of data. First of all this approach allows to navigate the subsurface in all directions and analyses different sections and slices or moreover navigate the iso-surfaces respect to a value (or interval). The last one allows to isolate one or more iso-surfaces and remove, in the visualization mode, other data not interesting for the analysis; finally it helps to individuate the underground 3D bodies. Other aspect is the needs to link the on-ground data, as imaging, to the underground one by geographical and context field of view.
Modelling income processes with lots of heterogeneity
DEFF Research Database (Denmark)
Browning, Martin; Ejrnæs, Mette; Alvarez, Javier
2010-01-01
this observable homogeneity, we find more latent heterogeneity than previous investigators. We show that allowance for heterogeneity makes substantial differences to estimates of model parameters and to outcomes of interest. Additionally, we find strong evidence against the hypothesis that any worker has a unit...
Energy Technology Data Exchange (ETDEWEB)
Ali, Melkamu; Ye, Sheng; Li, Hongyi; Huang, Maoyi; Leung, Lai-Yung R.; Fiori, Aldo; Sivapalan, Murugesu
2014-07-19
Subsurface stormflow is an important component of the rainfall-runoff response, especially in steep forested regions. However; its contribution is poorly represented in current generation of land surface hydrological models (LSMs) and catchment-scale rainfall-runoff models. The lack of physical basis of common parameterizations precludes a priori estimation (i.e. without calibration), which is a major drawback for prediction in ungauged basins, or for use in global models. This paper is aimed at deriving physically based parameterizations of the storage-discharge relationship relating to subsurface flow. These parameterizations are derived through a two-step up-scaling procedure: firstly, through simulations with a physically based (Darcian) subsurface flow model for idealized three dimensional rectangular hillslopes, accounting for within-hillslope random heterogeneity of soil hydraulic properties, and secondly, through subsequent up-scaling to the catchment scale by accounting for between-hillslope and within-catchment heterogeneity of topographic features (e.g., slope). These theoretical simulation results produced parameterizations of the storage-discharge relationship in terms of soil hydraulic properties, topographic slope and their heterogeneities, which were consistent with results of previous studies. Yet, regionalization of the resulting storage-discharge relations across 50 actual catchments in eastern United States, and a comparison of the regionalized results with equivalent empirical results obtained on the basis of analysis of observed streamflow recession curves, revealed a systematic inconsistency. It was found that the difference between the theoretical and empirically derived results could be explained, to first order, by climate in the form of climatic aridity index. This suggests a possible codependence of climate, soils, vegetation and topographic properties, and suggests that subsurface flow parameterization needed for ungauged locations must
Optimization of a catchment-scale coupled surface-subsurface hydrological model using pilot points
Danapour, Mehrdis; Stisen, Simon; Lajer Højberg, Anker
2016-04-01
Transient coupled surface-subsurface models are usually complex and contain a large amount of spatio-temporal information. In the traditional calibration approach, model parameters are adjusted against only few spatially aggregated observations of discharge or individual point observations of groundwater head. However, this approach doesn't enable an assessment of spatially explicit predictive model capabilities at the intermediate scale relevant for many applications. The overall objectives of this project is to develop a new model calibration and evaluation framework by combining distributed model parameterization and regularization with new types of objective functions focusing on optimizing spatial patterns rather than individual points or catchment scale features. Inclusion of detailed observed spatial patterns of hydraulic head gradients or relevant information obtained from remote sensing data in the calibration process could allow for a better representation of spatial variability of hydraulic properties. Pilot Points as an alternative to classical parameterization approaches, introduce great flexibility when calibrating heterogeneous systems without neglecting expert knowledge (Doherty, 2003). A highly parameterized optimization of complex distributed hydrological models at catchment scale is challenging due to the computational burden that comes with it. In this study the physically-based coupled surface-subsurface model MIKE SHE is calibrated for the 8,500 km2 area of central Jylland (Denmark) that is characterized by heterogeneous geology and considerable groundwater flow across topographical catchment boundaries. The calibration of the distributed conductivity fields is carried out with a pilot point-based approach, implemented using the PEST parameter estimation tool. To reduce the high number of calibration parameters, PEST's advanced singular value decomposition combined with regularization was utilized and a reduction of the model's complexity was
DEFF Research Database (Denmark)
Kristensen, Andreas Houlberg; Poulsen, Tjalfe; Mortensen, Lars
2010-01-01
Quantifying the spatial variability of factors affecting natural attenuation of hydrocarbons in the unsaturated zone is important to (i) performing a reliable risk assessment and (ii) evaluating the possibility for bioremediation of petroleum-polluted sites. Most studies to date have focused...... on the shallow unsaturated zone. Based on a data set comprising analysis of about 100 soil samples taken in a 16-m-deep unsaturated zone polluted with volatile petroleum compounds, we statistically and geostatistically analyzed values of essential soil properties. The subsurface of the site was highly layered......, resulting in an accumulation of pollution within coarse sandy lenses. Air-filled porosity, readily available phosphorous, and the first-order rate constant (k1) of benzene obtained from slurry biodegradation experiments were found to depend on geologic sample characterization (P
Modelling of deep subsurface for geohazard risk assessment.
Orlic, B.; Eijs, R. van
2002-01-01
Exploitation of subsurface natural resources, and subsurface storage of energy residues, may cause subsurface and surface deformation and damage to property. Deformation is generally difficult to assess and prove, although economical, environmental and societal interests are huge in terms of strain
Modelling of deep subsurface for geohazard risk assessment.
Orlic, B.; Eijs, R. van
2002-01-01
Exploitation of subsurface natural resources, and subsurface storage of energy residues, may cause subsurface and surface deformation and damage to property. Deformation is generally difficult to assess and prove, although economical, environmental and societal interests are huge in terms of strain
Energy Technology Data Exchange (ETDEWEB)
Hamilton, D.S.; Raeuchle, S.K.; Holtz, M.H. [Bureau of Economic Geology, Austin, TX (United States)] [and others
1997-08-01
We applied an integrated geologic, geophysical, and engineering approach devised to identify heterogeneities in the subsurface that might lead to reserve growth opportunities in our analysis of the Oficina Formation at Budare field, Venezuela. The approach involves 4 key steps: (1) Determine geologic reservoir architecture; (2) Investigate trends in reservoir fluid flow; (3) Integrate fluid flow trends with reservoir architecture; and (4) Estimate original oil-in-place, residual oil saturation, and remaining mobile oil, to identify opportunities for reserve growth. There are three main oil-producing reservoirs in the Oficina Formation that were deposited in a bed-load fluvial system, an incised valley-fill, and a barrier-strandplain system. Reservoir continuity is complex because, in addition to lateral facies variability, the major Oficina depositional systems were internally subdivided by high-frequency stratigraphic surfaces. These surfaces define times of intermittent lacustrine and marine flooding events that punctuated the fluvial and marginal marine sedimentation, respectively. Syn and post depositional faulting further disrupted reservoir continuity. Trends in fluid flow established from initial fluid levels, response to recompletion workovers, and pressure depletion data demonstrated barriers to lateral and vertical fluid flow caused by a combination of reservoir facies pinchout, flooding shale markers, and the faults. Considerable reserve growth potential exists at Budare field because the reservoir units are highly compartment by the depositional heterogeneity and structural complexity. Numerous reserve growth opportunities were identified in attics updip of existing production, in untapped or incompletely drained compartments, and in field extensions.
Adaptive Mesh Refinement in Reactive Transport Modeling of Subsurface Environments
Molins, S.; Day, M.; Trebotich, D.; Graves, D. T.
2015-12-01
Adaptive mesh refinement (AMR) is a numerical technique for locally adjusting the resolution of computational grids. AMR makes it possible to superimpose levels of finer grids on the global computational grid in an adaptive manner allowing for more accurate calculations locally. AMR codes rely on the fundamental concept that the solution can be computed in different regions of the domain with different spatial resolutions. AMR codes have been applied to a wide range of problem including (but not limited to): fully compressible hydrodynamics, astrophysical flows, cosmological applications, combustion, blood flow, heat transfer in nuclear reactors, and land ice and atmospheric models for climate. In subsurface applications, in particular, reactive transport modeling, AMR may be particularly useful in accurately capturing concentration gradients (hence, reaction rates) that develop in localized areas of the simulation domain. Accurate evaluation of reaction rates is critical in many subsurface applications. In this contribution, we will discuss recent applications that bring to bear AMR capabilities on reactive transport problems from the pore scale to the flood plain scale.
Modeling subsurface contaminant reactions and transport at the watershed scale
Energy Technology Data Exchange (ETDEWEB)
Gwo, J.P.; Jardine, P.M.; D`Azevedo, E.F. [Oak Ridge National Lab., TN (United States); Wilson, G.V. [Desert Research Inst., Las Vegas, NV (United States). Water Resources Center
1997-12-01
The objectives of this research are: (1) to numerically examine the multiscale effects of physical and chemical mass transfer processes on watershed scale, variably saturated subsurface contaminant transport, and (2) to conduct numerical simulations on watershed scale reactive solute transport and evaluate their implications to uncertainty characterization and cost benefit analysis. Concurrent physical and chemical nonequilibrium caused by inter aggregate gradients of pressure head and solute concentration and intra-aggregate geochemical and microbiological processes, respectively, may arise at various scales and flowpaths. To this date, experimental investigations of these complex processes at watershed scale remain a challenge and numerical studies are often needed for guidance of water resources management and decision making. This research integrates the knowledge bases developed during previous experimental and numerical investigations at a proposed waste disposal site at the Oak Ridge National Laboratory to study the concurrent effects of physical and chemical nonequilibrium. Comparison of numerical results with field data indicates that: (1) multiregion, preferential flow and solute transport exist under partially saturated condition and can be confirmed theoretically, and that (2) mass transfer between pore regions is an important process influencing contaminant movement in the subsurface. Simulations of watershed scale, multi species reactive solute transport suggest that dominance of geochemistry and hydrodynamics may occur simultaneously at different locales and influence the movement of one species relative to another. Execution times on the simulations of the reactive solute transport model also indicate that the model is ready to assist the selection of important parameters for site characterization.
Modeling subsurface contaminant reactions and transport at the watershed scale
Energy Technology Data Exchange (ETDEWEB)
Gwo, J.P.; Jardine, P.M.; D`Azevedo, E.F. [Oak Ridge National Lab., TN (United States); Wilson, G.V. [Desert Research Inst., Las Vegas, NV (United States). Water Resources Center
1997-12-01
The objectives of this research are: (1) to numerically examine the multiscale effects of physical and chemical mass transfer processes on watershed scale, variably saturated subsurface contaminant transport, and (2) to conduct numerical simulations on watershed scale reactive solute transport and evaluate their implications to uncertainty characterization and cost benefit analysis. Concurrent physical and chemical nonequilibrium caused by inter aggregate gradients of pressure head and solute concentration and intra-aggregate geochemical and microbiological processes, respectively, may arise at various scales and flowpaths. To this date, experimental investigations of these complex processes at watershed scale remain a challenge and numerical studies are often needed for guidance of water resources management and decision making. This research integrates the knowledge bases developed during previous experimental and numerical investigations at a proposed waste disposal site at the Oak Ridge National Laboratory to study the concurrent effects of physical and chemical nonequilibrium. Comparison of numerical results with field data indicates that: (1) multiregion, preferential flow and solute transport exist under partially saturated condition and can be confirmed theoretically, and that (2) mass transfer between pore regions is an important process influencing contaminant movement in the subsurface. Simulations of watershed scale, multi species reactive solute transport suggest that dominance of geochemistry and hydrodynamics may occur simultaneously at different locales and influence the movement of one species relative to another. Execution times on the simulations of the reactive solute transport model also indicate that the model is ready to assist the selection of important parameters for site characterization.
Modeling heterogeneous chemical processes on aerosol surface
Institute of Scientific and Technical Information of China (English)
Junjun Deng; Tijian Wang; Li Liu; Fei Jiang
2010-01-01
To explore the possible impact of heterogeneous chemical processes on atmospheric trace components,a coupled box model including gas-phase chemical processes,aerosol thermodynamic equilibrium processes,and heterogeneous chemical processes on the surface of dust,black carbon(BC)and sea salt is set up to simulate the effects of heterogeneous chemistry on the aerosol surface,and analyze the primary factors affecting the heterogeneous processes.Results indicate that heterogeneous chemical processes on the aerosol surface in the atmosphere will affect the concentrations of trace gases such as H2O2,HO2,O3,NO2,NO3,HNO3 and SO2,and aerosols such as SO42-,NO3-and NH4+.Sensitivity tests suggest that the magnitude of the impact of heterogeneous processes strongly depends on aerosol concentration and the surface uptake coefficients used in the box model.However,the impact of temperature on heterogeneous chemical processes is considerably less.The"renoxification"of HNO3 will affect the components of the troposphere such as nitrogen oxide and ozone.
Kumar, Jitendra; Collier, Nathan; Bisht, Gautam; Mills, Richard T.; Thornton, Peter E.; Iversen, Colleen M.; Romanovsky, Vladimir
2016-09-01
Vast carbon stocks stored in permafrost soils of Arctic tundra are under risk of release to the atmosphere under warming climate scenarios. Ice-wedge polygons in the low-gradient polygonal tundra create a complex mosaic of microtopographic features. This microtopography plays a critical role in regulating the fine-scale variability in thermal and hydrological regimes in the polygonal tundra landscape underlain by continuous permafrost. Modeling of thermal regimes of this sensitive ecosystem is essential for understanding the landscape behavior under the current as well as changing climate. We present here an end-to-end effort for high-resolution numerical modeling of thermal hydrology at real-world field sites, utilizing the best available data to characterize and parameterize the models. We develop approaches to model the thermal hydrology of polygonal tundra and apply them at four study sites near Barrow, Alaska, spanning across low to transitional to high-centered polygons, representing a broad polygonal tundra landscape. A multiphase subsurface thermal hydrology model (PFLOTRAN) was developed and applied to study the thermal regimes at four sites. Using a high-resolution lidar digital elevation model (DEM), microtopographic features of the landscape were characterized and represented in the high-resolution model mesh. The best available soil data from field observations and literature were utilized to represent the complex heterogeneous subsurface in the numerical model. Simulation results demonstrate the ability of the developed modeling approach to capture - without recourse to model calibration - several aspects of the complex thermal regimes across the sites, and provide insights into the critical role of polygonal tundra microtopography in regulating the thermal dynamics of the carbon-rich permafrost soils. Areas of significant disagreement between model results and observations highlight the importance of field-based observations of soil thermal and
Reducing uncertainty in calibrating aquifer flow model with multiple scales of heterogeneity.
Zhang, Ye
2014-01-01
Modeling and calibration of natural aquifers with multiple scales of heterogeneity is a challenging task due to limited subsurface access. While computer modeling plays an essential role in aquifer studies, large uncertainty exists in developing a conceptual model of an aquifer and in calibrating the model for decision making. Due to uncertainties such as a lack of understanding of subsurface processes and a lack of techniques to parameterize the subsurface environment (including hydraulic conductivity, source/sink rate, and aquifer boundary conditions), existing aquifer models often suffer nonuniqueness in calibration, leading to poor predictive capability. A robust calibration methodology is needed that can address the simultaneous estimations of aquifer parameters, source/sink, and boundary conditions. In this paper, we propose a multistage and multiscale approach that addresses subsurface heterogeneity at multiple scales, while reducing uncertainty in estimating the model parameters and model boundary conditions. The key to this approach lies in the appropriate development, verification, and synthesis of existing and new techniques of static and dynamic data integration. In particular, based on a given set of observation data, new inversion techniques can be first used to estimate aquifer large-scale effective parameters and smoothed boundary conditions, based on which parameter and boundary condition estimation can be refined at increasing detail using standard or highly parameterized estimation techniques.
Elements of complexity in subsurface modeling, exemplified with three case studies
Freedman, Vicky L.; Truex, Michael J.; Rockhold, Mark L.; Bacon, Diana H.; Freshley, Mark D.; Wellman, Dawn M.
2017-09-01
There are complexity elements to consider when applying subsurface flow and transport models to support environmental analyses. Modelers balance the benefits and costs of modeling along the spectrum of complexity, taking into account the attributes of more simple models (e.g., lower cost, faster execution, easier to explain, less mechanistic) and the attributes of more complex models (higher cost, slower execution, harder to explain, more mechanistic and technically defensible). In this report, modeling complexity is examined with respect to considering this balance. The discussion of modeling complexity is organized into three primary elements: (1) modeling approach, (2) description of process, and (3) description of heterogeneity. Three examples are used to examine these complexity elements. Two of the examples use simulations generated from a complex model to develop simpler models for efficient use in model applications. The first example is designed to support performance evaluation of soil-vapor-extraction remediation in terms of groundwater protection. The second example investigates the importance of simulating different categories of geochemical reactions for carbon sequestration and selecting appropriate simplifications for use in evaluating sequestration scenarios. In the third example, the modeling history for a uranium-contaminated site demonstrates that conservative parameter estimates were inadequate surrogates for complex, critical processes and there is discussion on the selection of more appropriate model complexity for this application. All three examples highlight how complexity considerations are essential to create scientifically defensible models that achieve a balance between model simplification and complexity.
Mathematical modeling of BTX: biotransformation and transport in the subsurface.
Abriola, L M; Chen, Y M
1995-06-01
A two-dimensional compositional model is presented; this model describes the transport and biotransformation of organic contaminants in a variably saturated subsurface environment. Modeled processes included mass exchange between constituent phases (water, air, soil, and organisms), advective and dispersive fluxes in the water phase, diffusive flux in the air phase, and biotransformation and biomass production in the biophase. In this model, solute transfer across air/water and water/solid interfaces is modeled using equilibrium relationships. Rate-limited mass transfer between the water and biophases is described with a linear driving force expression. Microbial degradation and biomass net growth are modeled by Monod-type kinetics. Solute transport and microbial growth equations are solved using an iterative Galerkin finite element method with a variable time-weighting scheme. Coupled biophase mass balance equations for each component are solved with a Newton-Raphson iterative scheme. Model capabilities are illustrated with two-dimensional, cross-sectional simulations of natural bioattenuation. The influence of biotransformation processes on the transport and extent of a toluene plume is examined.
Programming Models for Heterogeneous Multicore Systems
2011-08-08
Badia, F.D. Igual, J. Labarta, R. Mayo and E.S. Quintana- Orti . “An extension of the StarSs Programming Model for Platforms with Multiple GPUs...R. Mayo, J.M. Perez, J. Planas, E.S. Quintana- Orti . “A Proposal to Extend the OpenMP Tasking Model for Heterogeneous Architectures ” LNCS Vol. 5568
Two-temperature model for pulsed-laser-induced subsurface modifications in Si
Verburg, P.C.; Römer, G.R.B.E.; Huis In 'T Veld, A.J.
2014-01-01
We investigated the laser-material interaction during the production of laser-induced subsurface modifications in silicon with a numerical model. Such modifications are of interest for subsurface wafer dicing. To predict the shape of these modifications, a two-temperature model and an optical model
Emerge - A Python environment for the modeling of subsurface transfers
Lopez, S.; Smai, F.; Sochala, P.
2014-12-01
The simulation of subsurface mass and energy transfers often relies on specific codes that were mainly developed using compiled languages which usually ensure computational efficiency at the expense of relatively long development times and relatively rigid software. Even if a very detailed, possibly graphical, user-interface is developed the core numerical aspects are rarely accessible and the smallest modification will always need a compilation step. Thus, user-defined physical laws or alternative numerical schemes may be relatively difficult to use. Over the last decade, Python has emerged as a popular and widely used language in the scientific community. There already exist several libraries for the pre and post-treatment of input and output files for reservoir simulators (e.g. pytough). Development times in Python are considerably reduced compared to compiled languages, and programs can be easily interfaced with libraries written in compiled languages with several comprehensive numerical libraries that provide sequential and parallel solvers (e.g. PETSc, Trilinos…). The core objective of the Emerge project is to explore the possibility to develop a modeling environment in full Python. Consequently, we are developing an open python package with the classes/objects necessary to express, discretize and solve the physical problems encountered in the modeling of subsurface transfers. We heavily relied on Python to have a convenient and concise way of manipulating potentially complex concepts with a few lines of code and a high level of abstraction. Our result aims to be a friendly numerical environment targeting both numerical engineers and physicist or geoscientists with the possibility to quickly specify and handle geometries, arbitrary meshes, spatially or temporally varying properties, PDE formulations, boundary conditions…
Modeling epidemics dynamics on heterogenous networks.
Ben-Zion, Yossi; Cohen, Yahel; Shnerb, Nadav M
2010-05-21
The dynamics of the SIS process on heterogenous networks, where different local communities are connected by airlines, is studied. We suggest a new modeling technique for travelers movement, in which the movement does not affect the demographic parameters characterizing the metapopulation. A solution to the deterministic reaction-diffusion equations that emerges from this model on a general network is presented. A typical example of a heterogenous network, the star structure, is studied in detail both analytically and using agent-based simulations. The interplay between demographic stochasticity, spatial heterogeneity and the infection dynamics is shown to produce some counterintuitive effects. In particular it was found that, while movement always increases the chance of an outbreak, it may decrease the steady-state fraction of sick individuals. The importance of the modeling technique in estimating the outcomes of a vaccination campaign is demonstrated.
Low-Rank Kalman Filtering in Subsurface Contaminant Transport Models
El Gharamti, Mohamad
2010-12-01
Understanding the geology and the hydrology of the subsurface is important to model the fluid flow and the behavior of the contaminant. It is essential to have an accurate knowledge of the movement of the contaminants in the porous media in order to track them and later extract them from the aquifer. A two-dimensional flow model is studied and then applied on a linear contaminant transport model in the same porous medium. Because of possible different sources of uncertainties, the deterministic model by itself cannot give exact estimations for the future contaminant state. Incorporating observations in the model can guide it to the true state. This is usually done using the Kalman filter (KF) when the system is linear and the extended Kalman filter (EKF) when the system is nonlinear. To overcome the high computational cost required by the KF, we use the singular evolutive Kalman filter (SEKF) and the singular evolutive extended Kalman filter (SEEKF) approximations of the KF operating with low-rank covariance matrices. The SEKF can be implemented on large dimensional contaminant problems while the usage of the KF is not possible. Experimental results show that with perfect and imperfect models, the low rank filters can provide as much accurate estimates as the full KF but at much less computational cost. Localization can help the filter analysis as long as there are enough neighborhood data to the point being analyzed. Estimating the permeabilities of the aquifer is successfully tackled using both the EKF and the SEEKF.
Molecular Simulation towards Efficient and Representative Subsurface Reservoirs Modeling
Kadoura, Ahmad
2016-09-01
This dissertation focuses on the application of Monte Carlo (MC) molecular simulation and Molecular Dynamics (MD) in modeling thermodynamics and flow of subsurface reservoir fluids. At first, MC molecular simulation is proposed as a promising method to replace correlations and equations of state in subsurface flow simulators. In order to accelerate MC simulations, a set of early rejection schemes (conservative, hybrid, and non-conservative) in addition to extrapolation methods through reweighting and reconstruction of pre-generated MC Markov chains were developed. Furthermore, an extensive study was conducted to investigate sorption and transport processes of methane, carbon dioxide, water, and their mixtures in the inorganic part of shale using both MC and MD simulations. These simulations covered a wide range of thermodynamic conditions, pore sizes, and fluid compositions shedding light on several interesting findings. For example, the possibility to have more carbon dioxide adsorbed with more preadsorbed water concentrations at relatively large basal spaces. The dissertation is divided into four chapters. The first chapter corresponds to the introductory part where a brief background about molecular simulation and motivations are given. The second chapter is devoted to discuss the theoretical aspects and methodology of the proposed MC speeding up techniques in addition to the corresponding results leading to the successful multi-scale simulation of the compressible single-phase flow scenario. In chapter 3, the results regarding our extensive study on shale gas at laboratory conditions are reported. At the fourth and last chapter, we end the dissertation with few concluding remarks highlighting the key findings and summarizing the future directions.
A stochastic model for tumor heterogeneity
Simone, Giuseppina
2015-01-01
Phenotype variations define heterogeneity of biological and molecular systems, which play a crucial role in several mechanisms. Heterogeneity has been demonstrated in tumor cells. Here, samples from blood of patients affected from colon tumor were analyzed and fished with a microfluidic assay based on galactose active moieties, and incubated, for culturing, in SCID mice. Following the experimental investigation, a model based on Markov theory was implemented and discussed to explain the equilibrium existing between phenotypes of subpopulations of cells sorted using the microfluidic assay. The model in combination with the experimental results had many implications for tumor heterogeneity. It displayed interconversion of phenotypes, as observed after experiments. The interconversion generates of metastatic cells and implies that targeting the CTCs will be not an efficient method to prevent tumor recurrence. Most importantly, understanding the transitions between cell phenotypes in cell population can boost the...
Sculpting Mountains: Interactive Terrain Modeling Based on Subsurface Geology.
Cordonnier, Guillaume; Cani, Marie-Paule; Benes, Bedrich; Braun, Jean; Galin, Eric
2017-03-29
Most mountain ranges are formed by the compression and folding of colliding tectonic plates. Subduction of one plate causes large-scale asymmetry while their layered composition (or stratigraphy) explains the multi-scale folded strata observed on real terrains. We introduce a novel interactive modeling technique to generate visually plausible, large scale terrains that capture these phenomena. Our method draws on both geological knowledge for consistency and on sculpting systems for user interaction. The user is provided hands-on control on the shape and motion of tectonic plates, represented using a new geologically-inspired model for the Earth crust. The model captures their volume preserving and complex folding behaviors under collision, causing mountains to grow. It generates a volumetric uplift map representing the growth rate of subsurface layers. Erosion and uplift movement are jointly simulated to generate the terrain. The stratigraphy allows us to render folded strata on eroded cliffs. We validated the usability of our sculpting interface through a user study, and compare the visual consistency of the earth crust model with geological simulation results and real terrains.
Kantar, Cetin; Demiray, Hilal; Dogan, Nazime Mercan
2011-03-01
Laboratory batch sorption and column experiments were performed to investigate the effects of microbial EPSs isolated from Pseudomonas putida P18, Pseudomonas aeruginosa P16 and Pseudomonas stutzeri P40 on Cr(III) mobility in heterogeneous subsurface soils. Our batch and column results indicate that microbial EPS may have a pronounced effect on Cr(III) sorption and transport behavior depending on system conditions (e.g., pH, type of EPS). While EPS had no effect on Cr(III) sorption at pH<5, it led to a significant decrease in Cr(III) sorption under slightly acidic to alkaline pH range. Column experiments performed at pH 7.9 suggest that, in the presence of EPS, chromium(III) was significantly mobilized relative to non-EPS containing system due to the formation less sorbing and highly soluble Cr-EPS complexes and competition of EPS against Cr for surface sites. A two-site non-electrostatic surface chemical model incorporating a discrete ligand approach for the description of Cr-EPS interactions accurately predicted Cr(III) sorption and transport behavior in the presence of EPS under variable chemical conditions. Our simulations show that an accurate description of Cr(III) transport in the presence of EPS requires incorporation of proton and Cr(III) binding by EPS, EPS binding by soil minerals, Cr(III) binding by soil minerals, and ternary Cr(III)-EPS surface complexes into the transport equations. Although this approach may not accurately describe the actual mechanisms at the molecular level, it can improve our ability to accurately describe the effects of EPS on Cr(III) mobility in subsurface environment relative to the use of distribution coefficients (K(d)).
Canales, I.; Fucugauchi, J. U.; Perez-Cruz, L. L.; Camargo, A. Z.; Perez-Cruz, G.
2011-12-01
Asymmetries in the geophysical signature of Chicxulub crater are being evaluated to investigate on effects of impact angle and trajectory and pre-existing target structural controls for final crater form. Early studies interpreted asymmetries in the gravity anomaly in the offshore sector to propose oblique either northwest- and northeast-directed trajectories. An oblique impact was correlated to the global ejecta distribution and enhanced environmental disturbance. In contrast, recent studies using marine seismic data and computer modeling have shown that crater asymmetries correlate with pre-existing undulations of the Cretaceous continental shelf, suggesting a structural control of target heterogeneities. Documentation of Yucatan subsurface stratigraphy has been limited by lack of outcrops of pre-Paleogene rocks. The extensive cover of platform carbonate rocks has not been affected by faulting or deformation and with no rivers cutting the carbonates, information comes mainly from the drilling programs and geophysical surveys. Here we revisit the subsurface stratigraphy in the crater area from the well log data and cores retrieved in the drilling projects and marine seismic reflection profiles. Other source of information being exploited comes from the impact breccias, which contain a sampling of disrupted target sequences, including crystalline basement and Mesozoic sediments. We analyze gravity and seismic data from the various exploration surveys, including multiple Pemex profiles in the platform and the Chicxulub experiments. Analyses of well log data and seismic profiles identify contacts for Lower Cretaceous, Cretaceous/Jurassic and K/Pg boundaries. Results show that the Cretaceous continental shelf was shallower on the south and southwest than on the east, with emerged areas in Quintana Roo and Belize. Mesozoic and upper Paleozoic sediments show variable thickness, possibly reflecting the crystalline basement regional structure. Paleozoic and Precambrian
Subsurface temperature of the onshore Netherlands: new temperature dataset and modelling
Bonté, D.; Wees, J.-D. van; Verweij, J.M.
2012-01-01
Subsurface temperature is a key parameter for geothermal energy prospection in sedimentary basins. Here, we present the results of a 3D temperature modelling using a thermal-tectonic forward modelling method, calibrated with subsurface temperature measurements in the Netherlands. The first step invo
Virtual Heterogeneous Model Integration Layer
Directory of Open Access Journals (Sweden)
Muhammad Ali Memon
2016-05-01
Full Text Available The classic way of building a software today sim-plistically consists in connecting a piece of code calling a method with the piece of code implementing that method. We consider these piece of code (software systems not calling anything, behaving in a non deterministic way and providing complex sets of services in different domains. In software engineering reusability is the holly grail, and specially the reusability of code from autonomus tools requires powerful compostion/integration mechanisms. These systems are developed by different developers and being modified inceremently. Integrating these autonomous tools generate various conflicts. To deal with these conflicts, current integration mechanisms defines specific set of rules to resolve these conflicts and accompalish integration. Indeed still there is a big chance that changes made by other developers, or they update their changes in order to make them compliant with other developers cancel the updates done by others. The approach presented here claims three contributions in the field of Hetrogeneous Software Integration. First, this approach eliminate the need of conflicts resolving mechanism. Secondly, it provides the mechanism to work in the presence of conflicts without resolving them. Finally, contribution is that the integration mechanism does not affect if either of the system evolves. We do this by introducing an intermediate virtual layer between two systems that introduce a delta models which consist of three parts; viability that share required elements, hiding that hide conflicting elements and aliasing that aliases same concepts in both systems.
Characterization, Modeling, Monitoring and Remediation of Radionuclides in the Subsurface
Nicholson, T. J.; Cady, R.
2009-12-01
NRC sponsors research to identify and assess characterization, modeling, monitoring and remediation methods used to quantify and evaluate radionuclide release and migration in the subsurface. The need for and selection of remediation methods is based on a dose assessment to determine compliance with regulatory criteria. If remediation is warranted, the choice of remediation methods is based upon site- and source-characterization data. This data is integrated in a Conceptual Site Model (CSM). The assumptions and parameterization of the CSM are tested using a program of field tests and confirmatory monitoring. In particular, the features, events and processes in the unsaturated zone where many leaks and spills originate need characterization and confirmatory monitoring. The choice of the remediation method, if warranted, is based upon the confirmed CSM and the monitoring baseline. Remediation strategies being considered are: in situ bioremediation; pump, treat, monitor and release; monitored natural attenuation. Successful remediation strategies include monitoring programs to determine their efficacy. This monitoring is coupled to performance assessment models using performance indicators (PIs). These PIs provide a measurable indication of remediation performance, and are derived from analysis of the CSM and the hydrologic, chemical and microbial functions of the chosen remediation method. Case studies illustrate these observations and provide detailed examples of CSMs and PIs.
Application of tomography seismic for subsurface modeling of Kelud Mountain
Destawan, R.; Bernando, A.; Aziz, M.; Palupi, I. R.
2016-05-01
Kelud is a Quaternary volcano formed by the collision between the Indo-Australian plate with the Eurasian plate, exactly in the south of Java. This volcano is included in stratovolcanoes type explosive eruption characteristics. In order observation of subsurface conditions, performed imaging tomography. The research used data recordings from the 4 point observation in 2007. The data processing started from the initial velocity modeling, ray tracing calculations using the method of bending and tomographic velocity model Vp, Vs and Vp/Vs using inversion techniques delay time. Based on the research activities carried out, were resulted velocity structure models Vp, Vs, Vp/Vs and the hypocenter distribution of volcanic earthquakes occurring in Kelud. Velocity structures of Vp and Vs with variations of negative values between -60 to 0% and the value of Vp / Vs positive indicating the presence of hot fluid Kelud from top to sea level. While the positive values of Vs velocity structure between 0 to 20%, which dominate the east and south peaks interpreted as the rest of the frozen magma from previous volcanic activity.
Modeling Approaches for Describing Microbial Population Heterogeneity
DEFF Research Database (Denmark)
Lencastre Fernandes, Rita
, ethanol and biomass throughout the reactor. This work has proven that the integration of CFD and population balance models, for describing the growth of a microbial population in a spatially heterogeneous reactor, is feasible, and that valuable insight on the interplay between flow and the dynamics......Although microbial populations are typically described by averaged properties, individual cells present a certain degree of variability. Indeed, initially clonal microbial populations develop into heterogeneous populations, even when growing in a homogeneous environment. A heterogeneous microbial......) to predict distributions of certain population properties including particle size, mass or volume, and molecular weight. Similarly, PBM allow for a mathematical description of distributed cell properties within microbial populations. Cell total protein content distributions (a measure of cell mass) have been...
Nousiainen, Riikka; Warsta, Lassi; Turunen, Mika; Huitu, Hanna; Koivusalo, Harri; Pesonen, Liisa
2015-10-01
Effectiveness of a subsurface drainage system decreases with time, leading to a need to restore the drainage efficiency by installing new drain pipes in problem areas. The drainage performance of the resulting system varies spatially and complicates runoff and nutrient load generation within the fields. We presented a method to estimate the drainage performance of a heterogeneous subsurface drainage system by simulating the area with the three-dimensional hydrological FLUSH model. A GIS analysis was used to delineate the surface runoff contributing area in the field. We applied the method to reproduce the water balance and to investigate the effectiveness of a subsurface drainage network of a clayey field located in southern Finland. The subsurface drainage system was originally installed in the area in 1971 and the drainage efficiency was improved in 1995 and 2005 by installing new drains. FLUSH was calibrated against total runoff and drain discharge data from 2010 to 2011 and validated against total runoff in 2012. The model supported quantification of runoff fractions via the three installed drainage networks. Model realisations were produced to investigate the extent of the runoff contributing areas and the effect of the drainage parameters on subsurface drain discharge. The analysis showed that better model performance was achieved when the efficiency of the oldest drainage network (installed in 1971) was decreased. Our analysis method can reveal the drainage system performance but not the reason for the deterioration of the drainage performance. Tillage layer runoff from the field was originally computed by subtracting drain discharge from the total runoff. The drains installed in 1995 bypass the measurement system, which renders the tillage layer runoff calculation procedure invalid after 1995. Therefore, this article suggests use of a local correction coefficient based on the simulations for further research utilizing data from the study area.
Energy Technology Data Exchange (ETDEWEB)
Hammond, Glenn E.; Lichtner, Peter C.; Lu, Chuan
2007-08-01
Numerical modeling has become a critical tool to the Department of Energy for evaluating the environmental impact of alternative energy sources and remediation strategies for legacy waste sites. Unfortunately, the physical and chemical complexity of many sites overwhelms the capabilities of even most “state of the art” groundwater models. Of particular concern are the representation of highly-heterogeneous stratified rock/soil layers in the subsurface and the biological and geochemical interactions of chemical species within multiple fluid phases. Clearly, there is a need for higher-resolution modeling (i.e. more spatial, temporal, and chemical degrees of freedom) and increasingly mechanistic descriptions of subsurface physicochemical processes. We present research being performed in the development of PFLOTRAN, a parallel multiphase flow and multicomponent reactive transport model. Written in Fortran90, PFLOTRAN is founded upon PETSc data structures and solvers and has exhibited impressive strong scalability on up to 4000 processors on the ORNL Cray XT3. We are employing PFLOTRAN in the simulation of uranium transport at the Hanford 300 Area, a contaminated site of major concern to the Department of Energy, the State of Washington, and other government agencies where overly-simplistic historical modeling erroneously predicted decade removal times for uranium by ambient groundwater flow. By leveraging the billions of degrees of freedom available through high-performance computation using tens of thousands of processors, we can better characterize the release of uranium into groundwater and its subsequent transport to the Columbia River, and thereby better understand and evaluate the effectiveness of various proposed remediation strategies.
Modeling vaccination in a heterogeneous metapopulation system
Lachiany, Menachem
2016-09-01
We present here a multicity SIS epidemic model with vaccination. The model describes the dynamics of heterogeneous metapopulations that contain imperfectly vaccinated individuals. The effect of vaccination on heterogeneous multicity models has not been previously studied. We show that under very generic conditions, the epidemic threshold does not depend on the diffusion coefficient of the vaccinated individuals, but it does depend on the diffusion coefficient of the infected population. We then show, using a novel methodology, that the reproduction number is determined by the homogeneous model parameters and by the maximal number of neighbors a city can have, when the diffusion coefficient of the infected population is low. Finally, we present numerical simulations to support the analytical results.
Gomes Hochberg, C.; Furman, A.; Weisbrod, N.
2013-12-01
Reuse of treated wastewater (TWW) for irrigation is one of the solutions to water shortage. Not only it saves water, it also supplies organic matter (OM) and other nutrients to the soil. However, long term application of TWW can affect soil physical and chemical properties. Additionally, substances added via TWW irrigation can accentuate already existent soil heterogeneity, which may impact physical and chemical processes in soils. As more agricultural fields are being irrigated with TWW, it is crucial to understand its implications on soils. The objectives of this research are to investigate: (a) the impact of TWW irrigation on soil heterogeneity, and on hydraulic processes; and (b) the fate of salts and nutrients in the subsurface in soils irrigated with TWW vs. tap water (TP). The experiment is carried out in Lachish farm, Israel. Two trenches were dug and a sensors network of 38 tensiometers, 37 TDRs, 6 redox probes, and 38 thermocouples was installed in high resolution in each cross section (1.5 x 1.5 m). The cross sections are 13 meters apart in a vineyard irrigated for over 10 years with TP and TWW. One cross section is in a TP area while the other is in TWW area. Soil samples were collected according to visually observed heterogeneity of the soil profiles and randomly. Chemical analyses were conducted in both soil and water samples. In addition, infiltration rate, Leaf Area Index (LAI), and harvest yield were determined. For irrigation water analyses, DOM in TWW is higher than TP (average concentrations of 25.9 and 1.4 mg/L, respectively). Soil organic matter is in average 1% higher in soils irrigated with TWW in the first 10 cm, while for lower depths OM content is the same under both treatments. No repellency was detected for either soils (WDPT40%). ESP, EC and pH were higher for TWW soils, but not high enough to be characterized as saline and/or sodic. However, it presented SAR and EC levels of moderate infiltration reduction risk. Infiltration rate was
3D modelling of the shallow subsurface of Zeeland, the Netherlands
Stafleu, J.; Busschers, F.S.; Maljers, D.; Menkovic, A.
2011-01-01
The Geological Survey of the Netherlands aims at building a 3D geological voxel model of the upper 30 m of the subsurface of the Netherlands in order to provide a sound basis for subsurface related questions on, amongst others, groundwater extraction and management, land subsidence studies, aggregat
Simple model to study heterogeneous electrocatalysts
Franco-Junior, Edison; Lopes, Ana Carolina G.; Suffredini, Hugo B.; Homem-de-Mello, Paula
2015-01-01
New electrocatalyst materials have been proposed to increase the performance of fuel cells. Experimental studies show that Pt and Pb metallic and oxide materials are quite efficient in the oxidation of alcohols and small organic molecules such as formic acid in advanced fuel cells. This work proposes a model for studying morphologically heterogeneous catalysts through quantum chemistry methods such as density functional calculations. For testing the model, we have experimentally studied the adsorption of small organic molecules, namely formic acid and methanol, on Pt and Pb electrodes. All methodologies we have tested can be employed for this kind of study, but M06 functional results correlate best with previous simulations of homogeneous catalysts and with experimental data obtained for homogeneous and heterogeneous electrodes. Our model indicates that the presence of a Pt-Pb interface is responsible for higher adsorption energies of these molecules, most likely due to the orientation of the organic molecules that should facilitate the oxidation process.
Site occupancy models with heterogeneous detection probabilities
Royle, J. Andrew
2006-01-01
Models for estimating the probability of occurrence of a species in the presence of imperfect detection are important in many ecological disciplines. In these ?site occupancy? models, the possibility of heterogeneity in detection probabilities among sites must be considered because variation in abundance (and other factors) among sampled sites induces variation in detection probability (p). In this article, I develop occurrence probability models that allow for heterogeneous detection probabilities by considering several common classes of mixture distributions for p. For any mixing distribution, the likelihood has the general form of a zero-inflated binomial mixture for which inference based upon integrated likelihood is straightforward. A recent paper by Link (2003, Biometrics 59, 1123?1130) demonstrates that in closed population models used for estimating population size, different classes of mixture distributions are indistinguishable from data, yet can produce very different inferences about population size. I demonstrate that this problem can also arise in models for estimating site occupancy in the presence of heterogeneous detection probabilities. The implications of this are discussed in the context of an application to avian survey data and the development of animal monitoring programs.
Three-Dimensional Subsurface Flow, Fate and Transport of Microbes and Chemicals (3DFATMIC) Model
This model simulates subsurface flow, fate and transport of contaminants that are undergoing chemical or biological transformations. The model is applicable to transient conditions in both saturated and unsaturated zones.
PDF-based heterogeneous multiscale filtration model.
Gong, Jian; Rutland, Christopher J
2015-04-21
Motivated by modeling of gasoline particulate filters (GPFs), a probability density function (PDF) based heterogeneous multiscale filtration (HMF) model is developed to calculate filtration efficiency of clean particulate filters. A new methodology based on statistical theory and classic filtration theory is developed in the HMF model. Based on the analysis of experimental porosimetry data, a pore size probability density function is introduced to represent heterogeneity and multiscale characteristics of the porous wall. The filtration efficiency of a filter can be calculated as the sum of the contributions of individual collectors. The resulting HMF model overcomes the limitations of classic mean filtration models which rely on tuning of the mean collector size. Sensitivity analysis shows that the HMF model recovers the classical mean model when the pore size variance is very small. The HMF model is validated by fundamental filtration experimental data from different scales of filter samples. The model shows a good agreement with experimental data at various operating conditions. The effects of the microstructure of filters on filtration efficiency as well as the most penetrating particle size are correctly predicted by the model.
Transmission models of tuberculosis in heterogeneous population
Institute of Scientific and Technical Information of China (English)
JIA Zhong-wei; LI Xiao-wen; FENG Dan; CAO Wu-chun
2007-01-01
Objective To review the transmission models of tuberculosis in heterogeneous population.Data sources The data used in this review were adopted mainly from the studies of models of tuberculosis reported from 1995 to 2006.Study selection Relevant literature on transmission models of tuberculosis in heterogeneous populations are referenced.Results Casual/random factors and genetic factors are the main reasons for epidemics of tuberculosis in recent years.Mass public transport is playing the primary role in casually close contact which can facilitate the transmission of tuberculosis. Genetic susceptibility not only varies endemic prevalence levels, but also drastically alters the effects of treatment for tuberculosis patients. Detailed studies further exhibit that casual contact and genetic factor are responsible for over 30%-40% of the total new cases in recent years. The prevalence of tuberculosis could double (from 33% to 60%)if a genetically susceptible phenotype is present in only 30% of the population. And some challenges have emerged along with these exciting results.Conclusions Casual/random contact, public transport and genetic susceptibility are responsible for most new tuberculosis cases and a wide variation in endemic tuberculosis levels between regions. Hence, the transmission model of tuberculosis in a heterogeneous population can provide more clues to underlying mechanism of tuberculosis transmission than in a homogeneous population. However, many challenges remain for us in understanding transmission of disease.
Modeling mechanical response of heterogeneous materials
Pal, Siladitya
developed. It is found that two different material phases (collagens) of mussel byssus thread are optimally distributed along the thread. These applications demonstrate that the presence of heterogeneity in the system demands high computational resources for simulation and modeling. Thus, Higher Dimensional Model Representation (HDMR) based surrogate modeling concept has been proposed to reduce computational complexity. The applicability of such methodology has been demonstrated in failure envelope construction and in multiscale finite element techniques. It is observed that surrogate based model can capture the behavior of complex material systems with sufficient accuracy. The computational algorithms presented in this thesis will further pave the way for accurate prediction of macroscopic deformation behavior of various class of advanced materials from their measurable microstructural features at a reasonable computational cost.
Mathematical analysis of epidemiological models with heterogeneity
Energy Technology Data Exchange (ETDEWEB)
Van Ark, J.W.
1992-01-01
For many diseases in human populations the disease shows dissimilar characteristics in separate subgroups of the population; for example, the probability of disease transmission for gonorrhea or AIDS is much higher from male to female than from female to male. There is reason to construct and analyze epidemiological models which allow this heterogeneity of population, and to use these models to run computer simulations of the disease to predict the incidence and prevalence of the disease. In the models considered here the heterogeneous population is separated into subpopulations whose internal and external interactions are homogeneous in the sense that each person in the population can be assumed to have all average actions for the people of that subpopulation. The first model considered is an SIRS models; i.e., the Susceptible can become Infected, and if so he eventually Recovers with temporary immunity, and after a period of time becomes Susceptible again. Special cases allow for permanent immunity or other variations. This model is analyzed and threshold conditions are given which determine whether the disease dies out or persists. A deterministic model is presented; this model is constructed using difference equations, and it has been used in computer simulations for the AIDS epidemic in the homosexual population in San Francisco. The homogeneous version and the heterogeneous version of the differential-equations and difference-equations versions of the deterministic model are analyzed mathematically. In the analysis, equilibria are identified and threshold conditions are set forth for the disease to die out if the disease is below the threshold so that the disease-free equilibrium is globally asymptotically stable. Above the threshold the disease persists so that the disease-free equilibrium is unstable and there is a unique endemic equilibrium.
Modelling the Heterogeneous Markov Attrition Process .
Directory of Open Access Journals (Sweden)
Jau Yeu Menq
1993-01-01
Full Text Available A model for heterogeneous dynamics combat as a continuos-time Markov process has been studied, and on account of the special form of its infinitesimal generator, recursive algorithms are derived to compute the important characteristics of the combat, such as the combat time distribution, expected value and variance, and the probability of winning and expected survivors. Numerical results are also presented. This approach can also be used to consider initial contact forces of both sides as random variables.
Surface-subsurface integrated modeling is commonly limited by the extent of the surface domain. This limitation requires modelers to define the subsurface boundaries as a function of the surface domain resulting in inaccurate flow and transport simulation at the model boundary. In this study, the SW...
Features and heterogeneities in growing network models
Ferretti, Luca; Yang, Bin; Marmorini, Giacomo; Bianconi, Ginestra
2011-01-01
Many complex networks from the World-Wide-Web to biological networks are growing taking into account the heterogeneous features of the nodes. The feature of a node might be a discrete quantity such as a classification of a URL document as personal page, thematic website, news, blog, search engine, social network, ect. or the classification of a gene in a functional module. Moreover the feature of a node can be a continuous variable such as the position of a node in the embedding space. In order to account for these properties, in this paper we provide a generalization of growing network models with preferential attachment that includes the effect of heterogeneous features of the nodes. The main effect of heterogeneity is the emergence of an "effective fitness" for each class of nodes, determining the rate at which nodes acquire new links. Beyond the degree distribution, in this paper we give a full characterization of the other relevant properties of the model. We evaluate the clustering coefficient and show ...
Features and heterogeneities in growing network models
Ferretti, Luca; Cortelezzi, Michele; Yang, Bin; Marmorini, Giacomo; Bianconi, Ginestra
2012-06-01
Many complex networks from the World Wide Web to biological networks grow taking into account the heterogeneous features of the nodes. The feature of a node might be a discrete quantity such as a classification of a URL document such as personal page, thematic website, news, blog, search engine, social network, etc., or the classification of a gene in a functional module. Moreover the feature of a node can be a continuous variable such as the position of a node in the embedding space. In order to account for these properties, in this paper we provide a generalization of growing network models with preferential attachment that includes the effect of heterogeneous features of the nodes. The main effect of heterogeneity is the emergence of an “effective fitness” for each class of nodes, determining the rate at which nodes acquire new links. The degree distribution exhibits a multiscaling behavior analogous to the the fitness model. This property is robust with respect to variations in the model, as long as links are assigned through effective preferential attachment. Beyond the degree distribution, in this paper we give a full characterization of the other relevant properties of the model. We evaluate the clustering coefficient and show that it disappears for large network size, a property shared with the Barabási-Albert model. Negative degree correlations are also present in this class of models, along with nontrivial mixing patterns among features. We therefore conclude that both small clustering coefficients and disassortative mixing are outcomes of the preferential attachment mechanism in general growing networks.
Vázquez-Suñé, Enric; Ángel Marazuela, Miguel; Velasco, Violeta; Diviu, Marc; Pérez-Estaún, Andrés; Álvarez-Marrón, Joaquina
2016-09-01
The overdevelopment of cities since the industrial revolution has shown the need to incorporate a sound geological knowledge in the management of required subsurface infrastructures and in the assessment of increasingly needed groundwater resources. Additionally, the scarcity of outcrops and the technical difficulty to conduct underground exploration in urban areas highlights the importance of implementing efficient management plans that deal with the legacy of heterogeneous subsurface information. To deal with these difficulties, a methodology has been proposed to integrate all the available spatio-temporal data into a comprehensive spatial database and a set of tools that facilitates the analysis and processing of the existing and newly added data for the city of Barcelona (NE Spain). Here we present the resulting actual subsurface 3-D geological model that incorporates and articulates all the information stored in the database. The methodology applied to Barcelona benefited from a good collaboration between administrative bodies and researchers that enabled the realization of a comprehensive geological database despite logistic difficulties. Currently, the public administration and also private sectors both benefit from the geological understanding acquired in the city of Barcelona, for example, when preparing the hydrogeological models used in groundwater assessment plans. The methodology further facilitates the continuous incorporation of new data in the implementation and sustainable management of urban groundwater, and also contributes to significantly reducing the costs of new infrastructures.
National Oceanic and Atmospheric Administration, Department of Commerce — Surface and sub-surface current model outputs were obtained from researchers at the University of Massachusetts-Boston to examine spatial and temporal current...
Final Report: A Model Management System for Numerical Simulations of Subsurface Processes
Energy Technology Data Exchange (ETDEWEB)
Zachmann, David
2013-10-07
The DOE and several other Federal agencies have committed significant resources to support the development of a large number of mathematical models for studying subsurface science problems such as groundwater flow, fate of contaminants and carbon sequestration, to mention only a few. This project provides new tools to help decision makers and stakeholders in subsurface science related problems to select an appropriate set of simulation models for a given field application.
Dusek, Jaromir; Vogel, Tomas; Dohnal, Michal; Gerke, Horst H.
2012-08-01
In the absence of overland flow, shallow subsurface runoff is one of the most important mechanisms determining hydrological responses of headwater catchments to rainstorms. Subsurface runoff can be triggered by preferential flow of infiltrating water frequently occurring in heterogeneous and structured soils as a basically one-dimensional (1D) vertical process. Any attempt to include effects of preferential flow in hydrological hillslope studies is limited by the fact that the thickness of the permeable soil is mostly small compared to the length of the hillslope. The objective of this study is to describe preferential flow effects on hillslope-scale subsurface runoff by combining a 1D vertical dual-continuum approach with a 1D lateral flow equation. The 1D vertical flow of water in a variably saturated soil is described by a coupled set of Richards' equations and the 1D saturated lateral flow of water on less permeable bedrock by the diffusion wave equation. The numerical solution of the combined model was used to study rainfall-runoff events on the Tomsovska hillslope by comparing simulated runoff with observed trench discharge data. The dual-continuum model generated the observed rapid runoff response, which served as an input for the lateral flow model. The diffusion wave model parameters (i.e., length of the contributing hillslope, effective porosity, and effective hydraulic conductivity) indicate that the hillslope length that contributed to subsurface drainage is relatively short (in the range of 25-50 m). Significant transformation of the 1D vertical inflow signal by lateral flow is expected for longer hillslopes, smaller effective conductivities, and larger effective porosities. The physically-based combined modeling approach allows for a consistent description of both preferential flow in a 1D vertical soil profile and lateral subsurface hillslope flow in the simplest way.
DEFF Research Database (Denmark)
Nielsen, Chris Valentin; Martins, Paulo A. F.; Bay, Niels Oluf
2016-01-01
New equipment for testing asperity deformation at various normal loads and subsurface elongations is presented. Resulting real contact area ratios increase heavily with increasing subsurface expansion due to lowered yield pressure on the asperities when imposing subsurface normal stress parallel ...... for estimating friction in the numerical modelling of metal forming processes....
2014-09-01
Gridded Surface Subsurface Hydrologic Analysis (GSSHA) Hydrology Model by Brian E. Skahill and Charles W. Downer PURPOSE: The purpose of this... Hydrologic Analysis (GSSHA) model. These new capabilities enable the incorporation of soft data, or prior information (i.e., extra observations which...traditional hydrologic simulation models (viz., lumped and semidistributed model structures). Such models have the potential to predict with greater
Modelling Preference Heterogeneity for Theatre Tickets
DEFF Research Database (Denmark)
Baldin, Andrea; Bille, Trine
) and latent class are proposed in order to model ticket purchase behaviour. These models allow us explicitly to take into account consumers' preference heterogeneity with respect to the attributes associated to each ticket alternative In addition, the distribution of the willingness-to-pay (WTP) of choice...... attributes is estimated. Understanding theatre-goers' choice behaviour and WTP for the quality of seat and the day of performance is important to policy makers and theatre managers in adopting different pricing and marketing strategies.......This paper analyzes the behavioural choice for theatre tickets using a rich dataset for 2010-2013 from the sale system of the Royal Danish National Theatre. A consumer who decides to attend a theater production faces multiple sources of price variation that depends on: socio...
Blessent, Daniela; Barco, Janet; Temgoua, André Guy Tranquille; Echeverrri-Ramirez, Oscar
2017-03-01
Numerical results are presented of surface-subsurface water modeling of a natural hillslope located in the Aburrá Valley, in the city of Medellín (Antioquia, Colombia). The integrated finite-element hydrogeological simulator HydroGeoSphere is used to conduct transient variably saturated simulations. The objective is to analyze pore-water pressure and saturation variation at shallow depths, as well as volumes of water infiltrated in the porous medium. These aspects are important in the region of study, which is highly affected by soil movements, especially during the high-rain seasons that occur twice a year. The modeling exercise considers rainfall events that occurred between October and December 2014 and a hillslope that is currently monitored because of soil instability problems. Simulation results show that rainfall temporal variability, mesh resolution, coupling length, and the conceptual model chosen to represent the heterogeneous soil, have a noticeable influence on results, particularly for high rainfall intensities. Results also indicate that surface-subsurface coupled modeling is required to avoid unrealistic increase in hydraulic heads when high rainfall intensities cause top-down saturation of soil. This work is a first effort towards fostering hydrogeological modeling expertise that may support the development of monitoring systems and early landslide warning in a country where the rainy season is often the cause of hydrogeological tragedies associated with landslides, mud flow or debris flow.
Blessent, Daniela; Barco, Janet; Temgoua, André Guy Tranquille; Echeverrri-Ramirez, Oscar
2016-10-01
Numerical results are presented of surface-subsurface water modeling of a natural hillslope located in the Aburrá Valley, in the city of Medellín (Antioquia, Colombia). The integrated finite-element hydrogeological simulator HydroGeoSphere is used to conduct transient variably saturated simulations. The objective is to analyze pore-water pressure and saturation variation at shallow depths, as well as volumes of water infiltrated in the porous medium. These aspects are important in the region of study, which is highly affected by soil movements, especially during the high-rain seasons that occur twice a year. The modeling exercise considers rainfall events that occurred between October and December 2014 and a hillslope that is currently monitored because of soil instability problems. Simulation results show that rainfall temporal variability, mesh resolution, coupling length, and the conceptual model chosen to represent the heterogeneous soil, have a noticeable influence on results, particularly for high rainfall intensities. Results also indicate that surface-subsurface coupled modeling is required to avoid unrealistic increase in hydraulic heads when high rainfall intensities cause top-down saturation of soil. This work is a first effort towards fostering hydrogeological modeling expertise that may support the development of monitoring systems and early landslide warning in a country where the rainy season is often the cause of hydrogeological tragedies associated with landslides, mud flow or debris flow.
Modelling heterogeneous meltwater percolation on the Greenland Ice Sheet
Ligtenberg, S.
2015-12-01
The Greenland Ice Sheet (GrIS) has experienced an increase of surface meltwater production over the last decades, with the latest record set in the summer of 2012. For current and future ice sheet mass balance assessments, it is important to quantify what part of this meltwater reaches the ocean and contributes to sea level change. Meltwater produced at the surface has several options: it can infiltrate the local firn pack, where it is either stored temporarily or refrozen, or it can run off along the surface or via en-glacial drainage systems. In this study, we focus on the first; more specifically, in which manner meltwater percolates the firn column. Over the past years, GrIS research has shown that meltwater does not infiltrate the firn pack homogeneously (i.e. matrix flow), but that inhomogeneities in horizontal firn layers causes preferential flow paths for meltwater (i.e. piping). Although this process has been observed and studied on a few isolated sites, it has never been examined on the entire GrIS. To do so, we use the firn model IMAU-FDM with new parameterizations for preferential flow, impermeable ice lenses and sub-surface runoff. At the surface, IMAU-FDM is forced with realistic climate data from the regional climate model RACMO2.3. The model results are evaluated with temperatures and density measurements from firn cores across the GrIS. By allowing for heterogeneous meltwater percolation, the model is able to store heat and mass much deeper in the firn column. This is, however, in part counteracted by the inclusion of impermeability of ice lenses, which causes part of the meltwater to run off horizontally.
Income distribution: An adaptive heterogeneous model
da Silva, L. C.; de Figueirêdo, P. H.
2014-02-01
In this communication an adaptive process is introduced into a many-agent model for closed economic system in order to establish general features of income distribution. In this new version agents are able to modify their exchange parameter ωi of resources through an adaptive process. The conclusions indicate that assuming an instantaneous learning behavior of all agents a Γ-distribution for income is reproduced while a frozen behavior establishes a Pareto’s distribution for income with an exponent ν=0.94±0.02. A third case occurs when a heterogeneous “inertia” behavior is introduced leading us to a Γ-distribution at the low income regime and a power-law decay for the large income values with an exponent ν=2.05±0.05. This method enables investigation of the resources flux in the economic environment and produces also bounding values for the Gini index comparable with data evidences.
Kalvans, Juris
2013-01-01
Interstellar ices are layers of molecules deposited on !ne dust grains in dark and dense molecular cloud cores. Subsurface ice has been considered in a few astrochemical models, which have shown that it can be of great importance. The aim of this work is to introduce an established subsurface ice description into the state-of-the-art astrochemical model ALCHEMIC. The model has been developed by the Heidelberg astrochemistry group. The result is an up-to-date model for interstellar molecular cloud research with possible application for protoplanetary disks.
3D subsurface modelling reveals the shallow geology of Amsterdam
Schokker, J.; Bakker, M.A.W.; Dubelaar, C.W.; Dambrink, R.M.; Harting, R.
2015-01-01
Amsterdam is situated on the coastal-deltaic plain of the western Netherlands. Its geographical position brought the city prosperity, but also created huge challenges associated with heterogeneous and often adverse ground conditions. This paper explores the geology of Amsterdam to a depth of c. 100
Srinivas, G.; Chowdary, Jasti S.; Gnanaseelan, C.; Prasad, K. V. S. R.; Karmakar, Ananya; Parekh, Anant
2017-05-01
In the present study the association between mean and interannual subsurface temperature bias over the equatorial Indian Ocean (EIO) is investigated during boreal summer (June through September; JJAS) in the National Centers for Environmental Prediction (NCEP) Climate Forecast System (CFSv2) hindcast. Anomalously high subsurface warm bias (greater than 3 °C) over the eastern EIO (EEIO) region is noted in CFSv2 during summer, which is higher compared to other parts of the tropical Indian Ocean. Prominent eastward current bias in the upper 100 m over the EIO region induced by anomalous westerly winds is primarily responsible for subsurface temperature bias. The eastward currents transport warm water to the EEIO and is pushed down to subsurface due to downwelling. Thus biases in both horizontal and vertical currents over the EIO region support subsurface warm bias. The evolution of systematic subsurface warm bias in the model shows strong interannual variability. These maximum subsurface warming episodes over the EEIO are mainly associated with La Niña like forcing. Strong convergence of low level winds over the EEIO and Maritime continent enhanced the westerly wind bias over the EIO during maximum warming years. This low level convergence of wind is induced by the bias in the gradient in the mean sea level pressure with positive bias over western EIO and negative bias over EEIO and parts of western Pacific. Consequently, changes in the atmospheric circulation associated with La Niña like conditions affected the ocean dynamics by modulating the current bias thereby enhancing the subsurface warm bias over the EEIO. It is identified that EEIO subsurface warming is stronger when La Niña co-occurred with negative Indian Ocean Dipole events as compared to La Niña only years in the model. Ocean general circulation model (OGCM) experiments forced with CFSv2 winds clearly support our hypothesis that ocean dynamics influenced by westerly winds bias is primarily
Modeling the Subsurface Evolution of Active Region Flux Tubes
Fan, Y
2009-01-01
I present results from a set of 3D spherical-shell MHD simulations of the buoyant rise of active region flux tubes in the solar interior which put new constraints on the initial twist of the subsurface tubes in order for them to emerge with tilt angles consistent with the observed Joy's law for the mean tilt of solar active regions. Due to the asymmetric stretching of the $\\Omega$-shaped tube by the Coriolis force, a field strength asymmetry develops with the leading side having a greater field strength and thus being more cohesive compared to the following side. Furthermore, the magnetic flux in the leading leg shows more coherent values of local twist $\\alpha \\equiv {\\bf J} \\cdot {\\bf B} / B^2$, whereas the values in the following leg show large fluctuations and are of mixed signs.
3D subsurface geological modeling using GIS, remote sensing, and boreholes data
Kavoura, Katerina; Konstantopoulou, Maria; Kyriou, Aggeliki; Nikolakopoulos, Konstantinos G.; Sabatakakis, Nikolaos; Depountis, Nikolaos
2016-08-01
The current paper presents the combined use of geological-geotechnical insitu data, remote sensing data and GIS techniques for the evaluation of a subsurface geological model. High accuracy Digital Surface Model (DSM), airphotos mosaic and satellite data, with a spatial resolution of 0.5m were used for an othophoto base map compilation of the study area. Geological - geotechnical data obtained from exploratory boreholes and the 1:5000 engineering geological maps were digitized and implemented in a GIS platform for a three - dimensional subsurface model evaluation. The study is located at the North part of Peloponnese along the new national road.
DEFF Research Database (Denmark)
Balling, N.; Poulsen, Søren Erbs; Bording, Thue Sylvester
2015-01-01
equilibrium temperature logging has been carried out in a number of accessible deep boreholes. A regional distribution of subsurface temperatures is obtained by combining measurements and 3D numerical modelling in which the heat equation is solved. Modelling results are constrained by observations in terms....... Information of subsurface temperature distribution originates from direct measurements in boreholes and from indirect theoretical modelling. "Point observations" of varying quality are available as industrially measured "Bottom Hole Temperatures" from deep exploration boreholes and accurate continuous...... of available measured temperatures and observed surface heat flow. Information on subsurface thermal conductivity, which is a critical parameter, is obtained from core measurements and well-log analyses. Interval temperature gradients are found to vary by a factor of three to four across lithologies...
Painter, Scott L.; Coon, Ethan T.; Atchley, Adam L.; Berndt, Markus; Garimella, Rao; Moulton, J. David; Svyatskiy, Daniil; Wilson, Cathy J.
2016-08-01
The need to understand potential climate impacts and feedbacks in Arctic regions has prompted recent interest in modeling of permafrost dynamics in a warming climate. A new fine-scale integrated surface/subsurface thermal hydrology modeling capability is described and demonstrated in proof-of-concept simulations. The new modeling capability combines a surface energy balance model with recently developed three-dimensional subsurface thermal hydrology models and new models for nonisothermal surface water flows and snow distribution in the microtopography. Surface water flows are modeled using the diffusion wave equation extended to include energy transport and phase change of ponded water. Variation of snow depth in the microtopography, physically the result of wind scour, is modeled phenomenologically with a diffusion wave equation. The multiple surface and subsurface processes are implemented by leveraging highly parallel community software. Fully integrated thermal hydrology simulations on the tilted open book catchment, an important test case for integrated surface/subsurface flow modeling, are presented. Fine-scale 100 year projections of the integrated permafrost thermal hydrological system on an ice wedge polygon at Barrow Alaska in a warming climate are also presented. These simulations demonstrate the feasibility of microtopography-resolving, process-rich simulations as a tool to help understand possible future evolution of the carbon-rich Arctic tundra in a warming climate.
Lifetime prediction for the subsurface crack propagation using three-dimensional dynamic FEA model
Yin, Yuan; Chen, Yun-Xia; Liu, Le
2017-03-01
The subsurface crack propagation is one of the major interests for gear system research. The subsurface crack propagation lifetime is the number of cycles remaining for a spall to appear, which can be obtained through either stress intensity factor or accumulated plastic strain analysis. In this paper, the heavy loads are applied to the gear system. When choosing stress intensity factor, the high compressive stress suppresses Mode I stress intensities and severely reduces Mode II stress intensities in the heavily loaded lubricated contacts. Such that, the accumulated plastic strain is selected to calculate the subsurface crack propagation lifetime from the three-dimensional FEA model through ANSYS Workbench transient analysis. The three-dimensional gear FEA dynamic model with the subsurface crack is built through dividing the gears into several small elements. The calculation of the total cycles of the elements is proposed based on the time-varying accumulated plastic strain, which then will be used to calculate the subsurface crack propagation lifetime. During this process, the demonstration from a subsurface crack to a spall can be uncovered. In addition, different sizes of the elements around the subsurface crack are compared in this paper. The influences of the frictional coefficient and external torque on the crack propagation lifetime are also discussed. The results show that the lifetime of crack propagation decreases significantly when the external load T increasing from 100 N m to 150 N m. Given from the distributions of the accumulated plastic strain, the lifetime shares no significant difference when the frictional coefficient f ranging in 0.04-0.06.
Modeling Radicalization Phenomena in Heterogeneous Populations
Galam, Serge
2015-01-01
The phenomenon of radicalization is investigated within an heterogeneous population composed of a core subpopulation, sharing a way of life locally rooted, and a recently immigrated subpopulation of different origins with ways of life which can be partly in conflict with the local one. While core agents are embedded in the country prominent culture and identity, they are not likely to modify their way of life, which make them naturally inflexible about it. On the opposite, the new comers can either decide to live peacefully with the core people adapting their way of life, or to keep strictly on their way and oppose the core population, leading eventually to criminal activities. To study the corresponding dynamics of radicalization we introduce a 3-state agent model with a proportion of inflexible agents and a proportion of flexible ones, which can be either peaceful or opponent. Assuming agents interact via weighted pairs within a Lotka-Volterra like Ordinary Differential Equation framework, the problem is an...
Hokanson, Kelly; Carrera-Hernández, Jaime; Devito, Kevin; Mendoza, Carl
2016-04-01
The Boreal Plains (BP) region of Canada is experiencing high levels of anthropogenic activity and may be susceptible to climate change to various degrees. The BP is characterized by heterogeneous glacial landforms, with large contrasts in storage and transmissivity, which when coupled with wet-dry climate cycles, results in complex groundwater-surface water interactions. Predicting the impacts of land use change, climate change, and the future performance of constructed and reclaimed landscapes is currently not possible due to our limited knowledge regarding the natural variability of water table fluctuations, geochemistry, and salinity across the various glacial landforms in the BP. We compare isotopes, EC, chemistry (DOC, Ca, Mg, SO4) and water table position between a drought (2003) and a wet (2013) year to examine the interactions between climate, landform, and geology on the variation in landscape connectivity and overall salinity distribution. Data were collected from surface waters to a depth of 40 m, along a 50 km transect encompassing pond-wetland-forestland sequences across the major glacial depositional types typical of the BP (coarse textured glaciofluvial outwash, fine textured stagnant ice moraine, and lacustrine clay plain). Within each landform, sites range from isolated local flow systems to large intermediate scale flow systems. High spatial variability of water table fluctuations and salinity illustrate the strong regional controls that climate and geology exerts over scales of groundwater flow between landforms and surface water bodies across the BP, reinforcing the need to link surface water and groundwater processes when developing conceptual models. Additionally, when coupled with a strong, physical hydrogeologic conceptual model, synoptic chemical and isotopic surveys can be used to confirm scales and directions of flow; however, without an understanding of the climatic and geologic influence of the region, such data cannot be used as a
Brogi, Cosimo; Huisman, Johan Alexander; Kaufmann, Manuela Sarah; von Hebel, Christian; van der Kruk, Jan; Vereecken, Harry
2017-04-01
Soil subsurface structures can play a key role in crop performance, especially during water stress periods. Geophysical techniques like electromagnetic induction EMI have been shown to be able of providing information about dominant shallow subsurface features. However, previous work with EMI has typically not reached beyond the field scale. The objective of this study is to use large-scale multi-configuration EMI to characterize patterns of soil structural organization (layering and texture) and the associated impact on crop vegetation at the km2 scale. For this, we carried out an intensive measurement campaign and collected high spatial resolution multi-configuration EMI data on an agricultural area of approx. 1 km2 (102 ha) near Selhausen (North Rhine-Westphalia, Germany) with a maximum depth of investigation of around 2.5 m. We measured using two EMI instruments simultaneously with a total of nine coil configurations. The instruments were placed inside polyethylene sleds that were pulled by an all-terrain-vehicle along parallel lines with a spacing of 2 to 2.5 m. The driving speed was between 5 and 7 km h-1 and we used a 0.2 Hz sampling frequency to obtain an in-line resolution of approximately 0.3 m. The survey area consists of almost 50 different fields managed in different way. The EMI measurements were collected between April and December 2016 within a few days after the harvest of each field. After data acquisition, EMI data were automatically filtered, temperature corrected, and interpolated onto a common grid. The resulting EMI maps allowed us to identify three main areas with different subsurface heterogeneities. The differences between these areas are likely related to the late quaternary geological history (Pleistocene and Holocene) of the area that resulted in spatially variable soil texture and layering, which has a strong impact on spatio-temporal soil water content variability. The high resolution surveys also allowed us to identify small scale
Model Comparison in Subsurface Science: The DECOVALEX and Sim-SEQ Initiatives (Invited)
Birkholzer, J. T.; Mukhopadhyay, S.; Rutqvist, J.; Tsang, C.
2013-12-01
Building predictive model for flow and transport processes in the subsurface is a challenging task, even more so if these processes are coupled to geomechanical and/or geochemical effects. Modelers must take into consideration a multiplicity of length scales, a wide range of time scales, the coupling between processes, different model components, and the spatial variability in the value of most model input parameters (and often limited knowledge about them). Consequently, modelers have to make choices while developing their conceptual models. Such model choices may cause a wide range in the predictions made by different models and different modeling groups, even if each of the underlying simulators has been perfectly verified against appropriate benchmarks. In other words, the modeling activity itself is prone to uncertainty and bias. This uncertainty, referred to here as model selection uncertainty, forms one of the greatest sources of uncertainty for predictive modeling. In this paper, we discuss two examples of model intercomparison exercises that are currently undertaken to better understand model selection uncertainty, elucidate system behavior, inform needs for data collection and better physics parameterizations, and enhance community understanding of capabilities. The first example is the international DECOVALEX project, which was launched in 1992 by a group of countries dealing with modeling issues related to geologic disposal of radioactive waste. DECOVALEX is an acronym for DEvelopment of COupled THM models and their VALidation against Experiments. To date, the project has progressed successfully through five stages, each of which featuring a small number of test cases for model comparison related to coupled thermo-hydro-mechanical (THM) processes in geologic systems. The test cases are proposed and developed by the organizations participating in DECOVALEX; they typically involve results from major field and laboratory experiments. Over the past decades
BACKGROUND: Removal of crop residues for bioenergy production can alter soil hydrologic properties, but there is little information on its impact on transport of herbicides and their degradation products to subsurface drains. The Root Zone Water Quality Model, previously calibrated using measured fl...
A coupled surface/subsurface flow model accounting for air entrapment and air pressure counterflow
DEFF Research Database (Denmark)
Delfs, Jens Olaf; Wang, Wenqing; Kalbacher, Thomas
2013-01-01
This work introduces the soil air system into integrated hydrology by simulating the flow processes and interactions of surface runoff, soil moisture and air in the shallow subsurface. The numerical model is formulated as a coupled system of partial differential equations for hydrostatic (diffusive...
Refsgaard, Jens Christian; Auken, Esben; Bamberg, Charlotte A; Christensen, Britt S B; Clausen, Thomas; Dalgaard, Esben; Effersø, Flemming; Ernstsen, Vibeke; Gertz, Flemming; Hansen, Anne Lausten; He, Xin; Jacobsen, Brian H; Jensen, Karsten Høgh; Jørgensen, Flemming; Jørgensen, Lisbeth Flindt; Koch, Julian; Nilsson, Bertel; Petersen, Christian; De Schepper, Guillaume; Schamper, Cyril; Sørensen, Kurt I; Therrien, Rene; Thirup, Christian; Viezzoli, Andrea
2014-01-15
In order to fulfil the requirements of the EU Water Framework Directive nitrate load from agricultural areas to surface water in Denmark needs to be reduced by about 40%. The regulations imposed until now have been uniform, i.e. the same restrictions for all areas independent of the subsurface conditions. Studies have shown that on a national basis about 2/3 of the nitrate leaching from the root zone is reduced naturally, through denitrification, in the subsurface before reaching the streams. Therefore, it is more cost-effective to identify robust areas, where nitrate leaching through the root zone is reduced in the saturated zone before reaching the streams, and vulnerable areas, where no subsurface reduction takes place, and then only impose regulations/restrictions on the vulnerable areas. Distributed hydrological models can make predictions at grid scale, i.e. at much smaller scale than the entire catchment. However, as distributed models often do not include local scale hydrogeological heterogeneities, they are typically not able to make accurate predictions at scales smaller than they are calibrated. We present a framework for assessing nitrate reduction in the subsurface and for assessing at which spatial scales modelling tools have predictive capabilities. A new instrument has been developed for airborne geophysical measurements, Mini-SkyTEM, dedicated to identifying geological structures and heterogeneities with horizontal and lateral resolutions of 30-50 m and 2m, respectively, in the upper 30 m. The geological heterogeneity and uncertainty are further analysed by use of the geostatistical software TProGS by generating stochastic geological realisations that are soft conditioned against the geophysical data. Finally, the flow paths within the catchment are simulated by use of the MIKE SHE hydrological modelling system for each of the geological models generated by TProGS and the prediction uncertainty is characterised by the variance between the
Quasi-steady-state Model of Subsurface Ice on Mars through Obliquity Variation
Bapst, Jonathan; Wood, S.
2010-10-01
Stability and evolution of subsurface ice is relevant to the understanding of past and current Mars geology and climatology. The effect of subsurface water vapor reaching a diffusive steady-state is considered here. As long as deep water is present (as ancient ice, groundwater, or dehydrating minerals), water vapor will diffuse from the subsurface towards the atmosphere (i.e. the spatial location of lower vapor density) and recondense as ice as it experiences colder temperatures near the surface. This process allows the occurrence of stable subsurface ice at lower latitudes and greater depths than the near-surface ice in equilibrium with atmospheric water vapor. One aspect of our investigation is updating a previous steady-state model from Mellon and Jakosky [1993, 1995] and Mellon et al. [1997] with newer expressions for thermal conductivity and tortuosity. Also considered are the effects of latent heat (i.e. heat of vaporization and condensation) which may have a significant role in this process. Theoretical models of thermal conductivity are especially important as variation in conductivity is based on the ice content in the porous media (e.g. Martian regolith). The model is then applied to a larger scale in determining ice allocation for a hypothetical Martian hemisphere. By changing orbital parameters, such as obliquity, we can see the effects made on the location, depth, and density of ice beneath the Martian surface.
Elsheikh, A. H.
2013-12-01
Calibration of subsurface flow models is an essential step for managing ground water aquifers, designing of contaminant remediation plans, and maximizing recovery from hydrocarbon reservoirs. We investigate an efficient sampling algorithm known as nested sampling (NS), which can simultaneously sample the posterior distribution for uncertainty quantification, and estimate the Bayesian evidence for model selection. Model selection statistics, such as the Bayesian evidence, are needed to choose or assign different weights to different models of different levels of complexities. In this work, we report the first successful application of nested sampling for calibration of several nonlinear subsurface flow problems. The estimated Bayesian evidence by the NS algorithm is used to weight different parameterizations of the subsurface flow models (prior model selection). The results of the numerical evaluation implicitly enforced Occam\\'s razor where simpler models with fewer number of parameters are favored over complex models. The proper level of model complexity was automatically determined based on the information content of the calibration data and the data mismatch of the calibrated model.
Further RAGE modeling of asteroid mitigation: surface and subsurface explosions in porous objects
Energy Technology Data Exchange (ETDEWEB)
Weaver, Robert P [Los Alamos National Laboratory; Plesko, Catherine S [Los Alamos National Laboratory; Dearholt, William R [Los Alamos National Laboratory
2011-01-03
Disruption or mitigation of a potentially hazardous object (PHO) by a high-energy subsurface burst is considered. This is just one possible method of impact-hazard mitigation. We present RAGE hydrocode models of the shock-generated disruption of PHOs by subsurface nuclear bursts using scenario-specific models from realistic RADAR shape models. We will show 2D and 3D models for the disruption by a large energy source at the center of such PHO models ({approx}100 kt-10 Mt) specifically for the shape of the asteroid 25143 Itokawa. We study the effects of non-uniform composition (rubble pile), shallow buried bursts for the optimal depth of burial and porosity.
Bignardi, S.; Mantovani, A.; Abu Zeid, N.
2016-08-01
OpenHVSR is a computer program developed in the Matlab environment, designed for the simultaneous modeling and inversion of large Horizontal-to-Vertical Spectral Ratio (HVSR or H/V) datasets in order to construct 2D/3D subsurface models (topography included). The program is designed to provide a high level of interactive experience to the user and still to be of intuitive use. It implements several effective and established tools already present in the code ModelHVSR by Herak (2008), and many novel features such as: -confidence evaluation on lateral heterogeneity -evaluation of frequency dependent single parameter impact on the misfit function -relaxation of Vp/Vs bounds to allow for water table inclusion -a new cost function formulation which include a slope dependent term for fast matching of peaks, which greatly enhances convergence in case of low quality HVSR curves inversion -capability for the user of editing the subsurface model at any time during the inversion and capability to test the changes before acceptance. In what follows, we shall present many features of the program and we shall show its capabilities on both simulated and real data. We aim to supply a powerful tool to the scientific and professional community capable of handling large sets of HSVR curves, to retrieve the most from their microtremor data within a reduced amount of time and allowing the experienced scientist the necessary flexibility to integrate into the model their own geological knowledge of the sites under investigation. This is especially desirable now that microtremor testing has become routinely used. After testing the code over different datasets, both simulated and real, we finally decided to make it available in an open source format. The program is available by contacting the authors.
Modeling of Mauritius as a Heterogeneous Mantle Plume
Moore, J. C.; White, W. M.; Paul, D.; Duncan, R. A.
2008-12-01
Mauritius Island (20°20' S, 57°30' E) is located in the western Indian Ocean and is the penultimate volcanic island of the Réunion mantle plume. Mauritius has a well-established history of episodic volcanism and erosional hiatus, traditionally characterized by three chemically and temporally distinct eruptive phases: 1) the voluminous shield-building lavas of the Older Series (8.4-5.5 Ma), 2) the Intermediate Series (3.5-1.9 Ma), and 3) the Younger Series (1.0-0.00 Ma; Duncan, unpub. data). Recent collaboration with the Mauritian Water Resource Unit has permitted the study of a series of newly available drill cores, facilitating an advanced subsurface investigation into the evolution of the island. Radiometric dating of deep lava units from these cores has identified the earliest known sample from Mauritius (B18-1; 8.4 Ma) and demonstrated the existence of Intermediate and Younger Series lavas at previously unanticipated depths, some greater than 150 meters. Calculated volumes for the combined post- erosional lavas exceed 35 km3, closely resembling new results for Hawaiian analogues (20-60 km3; Garcia, pers. comm.). While these two post-erosional series remain temporally distinct (a 0.9 M.y. hiatus remains despite new dates), they are indistinguishable in major, trace, and isotopic composition. The shield building Older Series lavas are enriched in incompatible trace elements relative to the post-erosional lavas, an inverse relationship to that observed at both Hawaii (Maui, Oahu, and Kauai) and Tahaa (Societies). In contrast isotope systematics are consistent, with shield building lavas having more enriched isotopic signatures than post-erosional lavas. The observed differences cannot be explained solely by variations in the extent of partial melting and require distinct and heterogeneous sources for the shield and post-erosional lavas. Two magma generation scenarios for a heterogeneous mantle plume with enriched (eclogitic) and depleted (peridotitic
Teaching the geological subsurface with 3D models
Thorpe, Steve; Ward, Emma
2014-05-01
3D geological models have great potential as a resource when teaching geological concepts as it allows the student to visualise and interrogate UK geology. They are especially useful when dealing with the conversion of 2D field, map and GIS outputs into three dimensional geological units, which is a common problem for many students. Today's earth science students use a variety of skills and processes during their learning experience including spatial thinking, image construction, detecting patterns, making predictions and deducing the orientation of themselves. 3D geological models can reinforce spatial thinking strategies and encourage students to think about processes and properties, in turn helping the student to recognise pre-learnt geological principles in the field and to convert what they see at the surface into a picture of what is going on at depth. The British Geological Survey (BGS) has been producing digital 3D geological models for over 10 years. The models produced are revolutionising the working practices, data standards and products of the BGS. Sharing our geoscience information with academia is highlighted throughout the BGS strategy as is instilling practical skills in future geoscience professionals, such as model building and interpretation. In 2009 a project was launched to investigate the potential of the models as a teaching resource. The study included justifying if and how the models help students to learn, how models have been used historically, and how other forms of modelling are being used today. BGS now produce 3D geological models for use by anyone teaching or learning geoscience. They incorporate educational strategies that will develop geospatial skills and alleviate potential problems that some students experience. They are contained within contemporary case studies and show standard geological concepts, structures, sedimentary rocks, cross sections and field techniques. 3D geological models of the Isle of Wight and Ingleborough
3D subsurface temperature model of Europe for geothermal exploration
Limberger, J.; Wees, J.D. van
2014-01-01
For the assessment of geothermal resources in Europe we constructed a digital 3D temperature model of the European crust and sedimentary basins, incorporating publicly available temperature data. Using European crustal thickness models and indirect parameters such as surface heat flow measurements,
3D subsurface temperature model of Europe for geothermal exploration
Limberger, J.; Wees, J.D. van
2014-01-01
For the assessment of geothermal resources in Europe we constructed a digital 3D temperature model of the European crust and sedimentary basins, incorporating publicly available temperature data. Using European crustal thickness models and indirect parameters such as surface heat flow measurements,
Modelling heterogeneous interfaces for solar water splitting
Pham, Tuan Anh; Ping, Yuan; Galli, Giulia
2017-04-01
The generation of hydrogen from water and sunlight offers a promising approach for producing scalable and sustainable carbon-free energy. The key of a successful solar-to-fuel technology is the design of efficient, long-lasting and low-cost photoelectrochemical cells, which are responsible for absorbing sunlight and driving water splitting reactions. To this end, a detailed understanding and control of heterogeneous interfaces between photoabsorbers, electrolytes and catalysts present in photoelectrochemical cells is essential. Here we review recent progress and open challenges in predicting physicochemical properties of heterogeneous interfaces for solar water splitting applications using first-principles-based approaches, and highlights the key role of these calculations in interpreting increasingly complex experiments.
Modelling heterogeneous interfaces for solar water splitting
Energy Technology Data Exchange (ETDEWEB)
Pham, Tuan Anh; Ping, Yuan; Galli, Giulia
2017-01-09
The generation of hydrogen from water and sunlight others a promising approach for producing scalable and sustainable carbon-free energy. The key of a successful solar-to-fuel technology is the design of efficient, long-lasting and low-cost photoelectrochemical cells, which are responsible for absorbing sunlight and driving water splitting reactions. To this end, a detailed understanding and control of heterogeneous interfaces between photoabsorbers, electrolytes and catalysts present in photoelectrochemical cells is essential. Here we review recent progress and open challenges in predicting physicochemical properties of heterogeneous interfaces for solar water splitting applications using first-principles-based approaches, and highlights the key role of these calculations in interpreting increasingly complex experiments.
Jacques, Diederik
2017-04-01
As soil functions are governed by a multitude of interacting hydrological, geochemical and biological processes, simulation tools coupling mathematical models for interacting processes are needed. Coupled reactive transport models are a typical example of such coupled tools mainly focusing on hydrological and geochemical coupling (see e.g. Steefel et al., 2015). Mathematical and numerical complexity for both the tool itself or of the specific conceptual model can increase rapidly. Therefore, numerical verification of such type of models is a prerequisite for guaranteeing reliability and confidence and qualifying simulation tools and approaches for any further model application. In 2011, a first SeSBench -Subsurface Environmental Simulation Benchmarking- workshop was held in Berkeley (USA) followed by four other ones. The objective is to benchmark subsurface environmental simulation models and methods with a current focus on reactive transport processes. The final outcome was a special issue in Computational Geosciences (2015, issue 3 - Reactive transport benchmarks for subsurface environmental simulation) with a collection of 11 benchmarks. Benchmarks, proposed by the participants of the workshops, should be relevant for environmental or geo-engineering applications; the latter were mostly related to radioactive waste disposal issues - excluding benchmarks defined for pure mathematical reasons. Another important feature is the tiered approach within a benchmark with the definition of a single principle problem and different sub problems. The latter typically benchmarked individual or simplified processes (e.g. inert solute transport, simplified geochemical conceptual model) or geometries (e.g. batch or one-dimensional, homogeneous). Finally, three codes should be involved into a benchmark. The SeSBench initiative contributes to confidence building for applying reactive transport codes. Furthermore, it illustrates the use of those type of models for different
FDTD Modeling of Transient Scattering by Subsurface Targets
Institute of Scientific and Technical Information of China (English)
Gong Zhu-qian; Zhu Guo-qiang
2004-01-01
In this paper, a two-dimensional (2-D) finitedifference time-domain method (FDTD) scheme is used to simulate the transient scattering characteristics of buried objects, which are modeled by columns of arbitrary permittivities, conductivities, and sizes. The FDTD soil is modeled by isotropic, homogeneous and lossy media. The standing-trave-ling wave boundary condition (STWBC) that can simplify calculation and save CPU storage is used for modeling physical absorbers inside the FDTD computational domain. Reflection of electromagnetic pulses incident on a layered medium and transient scattering by the ground and an underground air square cylinder are computed. These results verify the validity of the FDTD scheme by comparisons with those shown in some references. Numerical results presented in the final part of this paper are desirable and meaningful, explicitly distinguishing echo waves stemming from the ground and the buried objects.
Bast, Alexander; Meyer, Christine; Meier, Wolfgang; Wilcke, Wolfgang; Lüscher, Peter; Graf, Frank; Gärtner, Holger
2014-05-01
The observation and monitoring of the aboveground plant development is a common practice in eco-engineering to estimate the plant's influence on the stabilization process. In contrast to this aboveground "sphere", the near subsurface is invisible and therefore difficult to address. To get an impression of the near subsurface and to model slope stability, (soil)samples are taken or a soil profile is dug and root traits (e.g., tensile strength) are determined. Other parameters as rooting depth, root length density, root clustering or the type of root in general are also of interest. However, soil samples or soil profiles only provide limited point-by-point data, alter parts of the study site, and are often time-consuming and expensive. The development of plants results a complex spatial and temporal distribution of the root network along a slope. This network causes shear strength variations and hydrological heterogeneities in the near subsurface within short distances. In contrast to the common point data, geophysical methods provide minimally-invasive, spatial and, via a time-lapse approach (monitoring), also temporal information of the near subsurface conditions. Hence, by measuring physical properties of the near subsurface, the root system, i.e. root distribution and rooting depth can be modeled. Furthermore, if a correlation between root traits and the measured physical properties is determined, the corresponding root trait can be estimated. To test this approach we applied electrical resistivity tomography (ERT) in a subalpine catchment in the Prättigau valley/Eastern Swiss Alps. Different ERT-soundings were conducted using varying electrode spacings (5cm, 25cm, 50cm and 100cm), electrode arrays (Wenner and Wenner-Schlummberger) and locations (eco-engineered slopes, stabilized two, three and 17 years ago; two forest stands of different stand densities). Furthermore, we took soil samples along the electrical profiles, and dug out several soil profiles to
Numerical modelling of tooth enamel subsurface lesion formation induced by dental plaque.
Ilie, O; van Turnhout, A G; van Loosdrecht, M C M; Picioreanu, C
2014-01-01
Using a one-dimensional mathematical model that couples tooth demineralisation and remineralisation with metabolic processes occurring in the dental plaque, two mechanisms for subsurface lesion formation were evaluated. It was found that a subsurface lesion can develop only as the result of alternating periods of demineralisation (acid attack during sugar consumption) and remineralisation (resting period) in tooth enamel with uniform mineral composition. It was also shown that a minimum plaque thickness that can induce an enamel lesion exists. The subsurface lesion formation can also be explained by assuming the existence of a fluoride-containing layer at the tooth surface that decreases enamel solubility. A nearly constant thickness of the surface layer was obtained with both proposed mechanisms. Sensitivity analysis showed that surface layer formation is strongly dependent on the length of remineralisation and demineralisation cycles. The restoration period is very important and the numerical simulations support the observation that often consumption of sugars is a key factor in caries formation. The calculated profiles of mineral content in enamel are similar to those observed experimentally. Most probably, both studied mechanisms interact in vivo in the process of caries development, but the simplest explanation for subsurface lesion formation remains the alternation between demineralisation and remineralisation cycles without any pre-imposed gradients.
Subsurface temperatures in Denmark – measurements and modelling
DEFF Research Database (Denmark)
Balling, N.; Poulsen, Søren Erbs; Bording, Thue Sylvester;
2014-01-01
lithologies of different conductivity. Mean geothermal gradients from surface to depths of 1000 to 3000 m are generally between 20 and 30 °C/km. As an example, modelled temperatures for the Gassum geothermal reservoir are shown with temperatures largely between 35 and 90 °C for depths of interest....
LEACHING MODELS FOR SUBSURFACE POLLUTION ASSESSMENT IN AGROECOSYSTEMS
Unrestricted use of pesticides in agriculture threatens ground-water resources and can have adverse ecological impact on the nation's receiving surface waters. In this paper, we develop mass fraction models for exposure assessment and the regulation of agricultural organic chemic...
Coupled modelling of subsurface water flux for an integrated flood risk management
Directory of Open Access Journals (Sweden)
T. Sommer
2009-07-01
Full Text Available Flood events cause significant damage not only on the surface but also underground. Infiltration of surface water into soil, flooding through the urban sewer system and, in consequence, rising groundwater are the main causes of subsurface damage. The modelling of flooding events is an important part of flood risk assessment. The processes of subsurface discharge of infiltrated water necessitate coupled modelling tools of both, surface and subsurface water fluxes. Therefore, codes for surface flooding, for discharge in the sewerage system and for groundwater flow were coupled with each other. A coupling software was used to amalgamate the individual programs in terms of mapping between the different model geometries, time synchronization and data exchange. The coupling of the models was realized on two scales in the Saxon capital of Dresden (Germany. As a result of the coupled modelling it could be shown that surface flooding dominates processes of any flood event. Compared to flood simulations without coupled modelling no substantial changes of the surface inundation area could be determined. Regarding sewerage, the comparison between the influx of groundwater into sewerage and the loading due to infiltration by flood water showed infiltration of surface flood water to be the main reason for sewerage overloading. Concurrent rainfalls can intensify the problem. The infiltration of the sewerage system by rising groundwater contributes only marginally to the loading of the sewerage and the distribution of water by sewerage has only local impacts on groundwater rise. However, the localization of risk areas due to rising groundwater requires the consideration of all components of the subsurface water fluxes. The coupled modelling has shown that high groundwater levels are the result of a multi-causal process that occurs before and during the flood event.
Conceptual Model of Iodine Behavior in the Subsurface at the Hanford Site
Energy Technology Data Exchange (ETDEWEB)
Truex, Michael J. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Lee, Brady D. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Johnson, Christian D. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Qafoku, Nikolla P. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Last, George V. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Lee, Michelle H. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Kaplan, Daniel I. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
2015-09-01
The fate and transport of 129I in the environment and potential remediation technologies are currently being studied as part of environmental remediation activities at the Hanford Site. A conceptual model describing the nature and extent of subsurface contamination, factors that control plume behavior, and factors relevant to potential remediation processes is needed to support environmental remedy decisions. Because 129I is an uncommon contaminant, relevant remediation experience and scientific literature are limited. Thus, the conceptual model also needs to both describe known contaminant and biogeochemical process information and to identify aspects about which additional information needed to effectively support remedy decisions. this document summarizes the conceptual model of iodine behavior relevant to iodine in the subsurface environment at the Hanford site.
Analytical modeling of the subsurface volatile organic vapor concentration in vapor intrusion.
Shen, Rui; Pennell, Kelly G; Suuberg, Eric M
2014-01-01
The inhalation of volatile and semi-volatile organic compounds that intrude from a subsurface contaminant source into indoor air has become the subject of health and safety concerns over the last twenty years. Building subslab and soil gas contaminant vapor concentration sampling have become integral parts of vapor intrusion field investigations. While numerical models can be of use in analyzing field data and in helping understand the subslab and soil gas vapor concentrations, they are not widely used due to the perceived effort in setting them up. In this manuscript, we present a new closed-form analytical expression describing subsurface contaminant vapor concentrations, including subslab vapor concentrations. The expression was derived using Schwarz-Christoffel mapping. Results from this analytical model match well the numerical modeling results. This manuscript also explores the relationship between subslab and exterior soil gas vapor concentrations, and offers insights on what parameters need to receive greater focus in field studies.
A new dynamic model for heterogeneous traffic flow
Tang, T. Q.; Huang, H. J.; Zhao, S. G.; Shang, H. Y.
2009-06-01
Based on the property of heterogeneous traffic flow, we in this Letter present a new car-following model. Applying the relationship between the micro and macro variables, a new dynamic model for heterogeneous traffic flow is obtained. The fundamental diagram and the jam density of the heterogeneous traffic flow consisting of bus and car are studied under three different conditions: (1) without any restrictions, (2) under the action of the traffic control policy that restrains some private cars and (3) using bus to replace the private cars restrained by the traffic control policy. The numerical results show that our model can describe some qualitative properties of the heterogeneous traffic flow consisting of bus and car, which verifies that our model is reasonable.
2016-08-01
ER D C/ CH L TR -1 6 -1 4 Gridded Surface Subsurface Hydrologic Analysis Modeling for Analysis of Flood Design Features at the Picayune...impacting the level of flood protection of adjacent landowners. To ensure the current level of flood protection is maintained, a hydrologic model was...Subsurface Hydrologic Analysis (GSSHA) model was selected for this effort. The GSSHA model simulates fully coupled rainfall distribution, extraction
Zehe, Erwin; Jackisch, Conrad; Rodriguez, Nicolas; Klaus, Julian
2017-04-01
Only a minute amount of global fresh water is stored in the unsaturated zone. Yet this tiny compartment controls soil microbial activity and associated trace gas emissions, transport and transformations of contaminants, plant productivity, runoff generation and groundwater recharge. To date, the processes controlling renewal and age of different fractions of the soil water stock are far from being understood. Current theories and process concepts were largely inferred either from over-simplified laboratory experiments, or non-exhaustive point observations and tracer data in the field. Tracer data provide key but yet integrated information about the distribution of travel times of the tracer molecules to a certain depth or on their travel depth distribution within a given time. We hence are able to observe the "effect" of soil structure i.e. partitioning of infiltrating water between fast preferential and slow flow paths and imperfect subsequent mixing between these flow paths in the subsurface and the related plant water uptake. However, we are not able to study the "cause" - because technologies for in-situ observations of flow, flow path topology and exchange processes at relevant interfaces have up to now not been at hand. In the present study we will make use of a Lagrangian model for subsurface water dynamics to explore how subsurface heterogeneity and mixing among different storage fractions affects residence time distribution in the unsaturated zone in a forward approach. Soil water is represented by particles of constant mass, which travel according to the Itô form of the Fokker Planck equation. The model concept builds on established soil physics by estimating the drift velocity and the diffusion term based on the soil water characteristics. The model has been shown to simulate capillary driven soil moisture dynamics in good accordance with a) the Richards equation and b) observed soil moisture data in different soil. The particle model may furthermore
Jackisch, Conrad; Demand, Dominic; Allroggen, Niklas; Loritz, Ralf; Zehe, Erwin
2017-04-01
In order to discuss hypothesis testing in hydrology, the question of the solid foundation of such tests has to be answered. But how certain are we about our measurements of the components of the water balance and the states and dynamics of the complex systems? What implicit assumptions or bias are already embedded in our perception of the processes? How can we find light in the darkness of heterogeneity? We will contribute examples from experimental findings, modelling approaches and landscape analysis to the discussion. Example soil moisture and the soil continuum: The definition of soil moisture as fraction of water in the porous medium assumes locally well-mixed conditions. Moreover, a unique relation of soil water retention presumes instant local thermodynamic equilibrium in the pore water arrangement. We will show findings from soil moisture responses to precipitation events, from irrigation experiments, and from a model study of initial infiltration velocities. The results highlight, that the implicit assumption relating soil moisture state dynamics with actual soil water flow is biased towards the slow end of the actual velocity distribution and rather blind for preferential flow acting in a very small proportion of the pore space. Moreover, we highlight the assumption of a well-defined continuum during the extrapolation of point-scale measurements and why spatially and temporally continuous observation techniques of soil water states are essential for advancing our understanding and development of subsurface process theories. Example hydraulic conductivity: Hydraulic conductivity lies at the heart of hydrological research and modelling. Its values can range across several orders of magnitude at a single site alone. Yet, we often consider it a crisp, effective parameter. We have conducted measurements of soil hydraulic conductivity in the lab and in the field. Moreover, we assessed infiltration capacity and conducted plot-scale irrigation experiments to
Sensitivity of transpiration to subsurface properties: Exploration with a 1-D model
Vrettas, Michail D.; Fung, Inez Y.
2017-06-01
The amount of moisture transpired by vegetation is critically tied to the moisture supply accessible to the root zone. In a Mediterranean climate, integrated evapotranspiration (ET) is typically greater in the dry summer when there is an uninterrupted period of high insolation. We present a 1-D model to explore the subsurface factors that may sustain ET through the dry season. The model includes a stochastic parameterization of hydraulic conductivity, root water uptake efficiency, and hydraulic redistribution by plant roots. Model experiments vary the precipitation, the magnitude and seasonality of ET demand, as well as rooting profiles and rooting depths of the vegetation. The results show that the amount of subsurface moisture remaining at the end of the wet winter is determined by the competition among abundant precipitation input, fast infiltration, and winter ET demand. The weathered bedrock retains ˜30% of the winter rain and provides a substantial moisture reservoir that may sustain ET of deep-rooted (>8 m) trees through the dry season. A small negative feedback exists in the root zone, where the depletion of moisture by ET decreases hydraulic conductivity and enhances the retention of moisture. Hence, hydraulic redistribution by plant roots is impactful in a dry season, or with a less conductive subsurface. Suggestions for implementing the model in the CESM are discussed.
Modeling heterogeneous unsaturated porous media flow at Yucca Mountain
Energy Technology Data Exchange (ETDEWEB)
Robey, T.H. [Spectra Research Institute, Albuquerque, NM (United States)
1994-12-31
Geologic systems are inherently heterogeneous and this heterogeneity can have a significant impact on unsaturated flow through porous media. Most previous efforts to model groundwater flow through Yucca Mountain have used stratigraphic units with homogeneous properties. However, modeling heterogeneous porous and fractured tuff in a more realistic manner requires numerical methods for generating heterogeneous simulations of the media, scaling of material properties from core scale to computational scale, and flow modeling that allows channeling. The Yucca Mountain test case of the INTRAVAL project is used to test the numerical approaches. Geostatistical methods are used to generate more realistic representations of the stratigraphic units and heterogeneity within units is generated using sampling from property distributions. Scaling problems are reduced using an adaptive grid that minimizes heterogeneity within each flow element. A flow code based on the dual mixed-finite-element method that allows for heterogeneity and channeling is employed. In the Yucca Mountain test case, the simulated volumetric water contents matched the measured values at drill hole USW UZ-16 except in the nonwelded portion of Prow Pass.
Moon, Y.; Park, E.; Song, Y.; Moon, H.
2005-12-01
To build an efficient way of handling potential risk associated with a closed mining site with abandoned waste rock and finely crushed mill tailing, detailed characterization on the site is crucial. Among the items to be characterized, mineral characteristics, particle distribution and surface/groundwater flow relationship, shape existence of heavy metal and discriminating the sulfide mineral oxidation and second minerals formation due to the rain or surface water environment may reveal very important aspects of the contaminated site such as kinds and level of contamination, contaminant generation in the event of precipitations, contaminant reaction/transport in the vadose zone, etc. Guryoung mine site in Korea, which is consistent with the purpose of this research, was selected as a research area. In order to illustrate and describe a geological heterogeneity, three-dimensional Coupled Markov chain (CMC) was used. The sampling site was constructed as elemental data using GPS. The sample's analytic data of physical-chemical-mineralogical aspects and cation exchange capacity were built as the database. The result is following: In oxidation zone (0.43 to 1.00 m), the particle contained more than 10 percent of clayey due to the weathering, and the pH was below 3 by oxidation of pyrite. The presence of jarosite, gypsum and goethite was confirmed. The cation exchange capacity was analyzed greater than 10 meq per 100 mg. In transition zone, sandy contained greater percentage, and its pH was 3 to 5. Metals and heavy metals extracted using 0.1 N HCl had the highest concentration, and pyrite took the greatest percentage. In primary zone, sandy contained the greatest percentage at the top but silt took over as going down. The pH was neutral, 5 to 8. Also calcite was identified as second mineral due to the reduction of primary zone. These results were built as database, and applying CMC, the three-dimensional distribution of tailing was confirmed.
Analytical modeling of the subsurface volatile organic vapor concentration in vapor intrusion
Shen, Rui; Pennell, Kelly G.; Suuberg, Eric M.
2013-01-01
The inhalation of volatile and semi-volatile organic compounds that intrude from a subsurface contaminant source into indoor air has become the subject of health and safety concerns over the last twenty years. Building subslab and soil gas contaminant vapor concentration sampling have become integral parts of vapor intrusion field investigations. While numerical models can be of use in analyzing field data and in helping understand the subslab and soil gas vapor concentrations, they are not w...
Numerical modelling of the transport of trace gases including methane in the subsurface of Mars
Stevens, Adam H.; Patel, Manish R.; Lewis, Stephen R.
2015-04-01
We model the transport of gas through the martian subsurface in order to quantify the timescales of release of a trace gas with a source at depth using a Fickian model of diffusion through a putative martian regolith column. The model is then applied to the case of methane to determine if diffusive transport of gas can explain previous observations of methane in the martian atmosphere. We investigate which parameters in the model have the greatest effect on transport timescales and show that the calculated diffusivity is very sensitive to the pressure profile of the subsurface, but relatively insensitive to the temperature profile, though diffusive transport may be affected by other temperature dependent properties of the subsurface such as the local vapour pressure. Uncertainties in the structure and physical conditions of the martian subsurface also introduce uncertainties in the timescales calculated. It was found that methane may take several hundred thousand Mars-years to diffuse from a source at depth. Purely diffusive transport cannot explain transient release that varies on timescales of less than one martian year from sources such as serpentinization or methanogenic organisms at depths of more than 2 km. However, diffusion of gas released by the destabilisation of methane clathrate hydrates close to the surface, for example caused by transient mass wasting events or erosion, could produce a rapidly varying flux of methane into the atmosphere of more than 10-3 kg m-2 s-1 over a duration of less than half a martian year, consistent with observations of martian methane variability. Seismic events, magmatic intrusions or impacts could also potentially produce similar patterns of release, but are far more complex to simulate.
Wijewardana, Y N S; Shilpadi, A T; Mowjood, M I M; Kawamoto, K; Galagedara, L W
2017-02-01
The assessment of polluted areas and municipal solid waste (MSW) sites using non-destructive geophysical methods is timely and much needed in the field of environmental monitoring and management. The objectives of this study are (i) to evaluate the ground-penetrating radar (GPR) wave responses as a result of different electrical conductivity (EC) in groundwater and (ii) to conduct MSW stratification using a controlled lysimeter and modeling approach. A GPR wave simulation was carried out using GprMax2D software, and the field test was done on two lysimeters that were filled with sand (Lysimeter-1) and MSW (Lysimeter-2). A Pulse EKKO-Pro GPR system with 200- and 500-MHz center frequency antennae was used to collect GPR field data. Amplitudes of GPR-reflected waves (sub-surface reflectors and water table) were studied under different EC levels injected to the water table. Modeling results revealed that the signal strength of the reflected wave decreases with increasing EC levels and the disappearance of the subsurface reflection and wave amplitude reaching zero at higher EC levels (when EC >0.28 S/m). Further, when the EC level was high, the plume thickness did not have a significant effect on the amplitude of the reflected wave. However, it was also found that reflected signal strength decreases with increasing plume thickness at a given EC level. 2D GPR profile images under wet conditions showed stratification of the waste layers and relative thickness, but it was difficult to resolve the waste layers under dry conditions. These results show that the GPR as a non-destructive method with a relatively larger sample volume can be used to identify highly polluted areas with inorganic contaminants in groundwater and waste stratification. The current methods of MSW dumpsite investigation are tedious, destructive, time consuming, costly, and provide only point-scale measurements. However, further research is needed to verify the results under heterogeneous aquifer
Heterogeneous Epidemic Model for Assessing Data Dissemination in Opportunistic Networks
DEFF Research Database (Denmark)
Rozanova, Liudmila; Alekseev, Vadim; Temerev, Alexander
2014-01-01
In this paper we apply a susceptible-infected-susceptible (SIS) epidemic model to analyse data dissemination in opportunistic networks with heterogeneous setting of transmission parameters, as established in author's previous paper? . We obtained the estimation of the final epidemic size assuming...... that amount of data transferred between network nodes possesses a Pareto distribution, implying scale-free properties. In this context, more heterogeneity in susceptibility means the less severe epidemic progression, and, on the contrary, more heterogeneity in infectivity leads to more severe epidemics...
Energy Technology Data Exchange (ETDEWEB)
Refsgaard, Jens Christian, E-mail: jcr@geus.dk [Geological Survey of Denmark and Greenland (GEUS) (Denmark); Auken, Esben [Department of Earth Sciences, Aarhus University (Denmark); Bamberg, Charlotte A. [City of Aarhus (Denmark); Christensen, Britt S.B. [Geological Survey of Denmark and Greenland (GEUS) (Denmark); Clausen, Thomas [DHI, Hørsholm (Denmark); Dalgaard, Esben [Department of Earth Sciences, Aarhus University (Denmark); Effersø, Flemming [SkyTEM Aps, Beder (Denmark); Ernstsen, Vibeke [Geological Survey of Denmark and Greenland (GEUS) (Denmark); Gertz, Flemming [Knowledge Center for Agriculture, Skejby (Denmark); Hansen, Anne Lausten [Department of Geosciences and Natural Resource Management, University of Copenhagen (Denmark); He, Xin [Geological Survey of Denmark and Greenland (GEUS) (Denmark); Jacobsen, Brian H. [Department of Food and Resource Economics, University of Copenhagen (Denmark); Jensen, Karsten Høgh [Department of Geosciences and Natural Resource Management, University of Copenhagen (Denmark); Jørgensen, Flemming; Jørgensen, Lisbeth Flindt [Geological Survey of Denmark and Greenland (GEUS) (Denmark); Koch, Julian [Department of Geosciences and Natural Resource Management, University of Copenhagen (Denmark); Nilsson, Bertel [Geological Survey of Denmark and Greenland (GEUS) (Denmark); Petersen, Christian [City of Odder (Denmark); De Schepper, Guillaume [Université Laval, Québec (Canada); Schamper, Cyril [Department of Earth Sciences, Aarhus University (Denmark); and others
2014-01-01
In order to fulfil the requirements of the EU Water Framework Directive nitrate load from agricultural areas to surface water in Denmark needs to be reduced by about 40%. The regulations imposed until now have been uniform, i.e. the same restrictions for all areas independent of the subsurface conditions. Studies have shown that on a national basis about 2/3 of the nitrate leaching from the root zone is reduced naturally, through denitrification, in the subsurface before reaching the streams. Therefore, it is more cost-effective to identify robust areas, where nitrate leaching through the root zone is reduced in the saturated zone before reaching the streams, and vulnerable areas, where no subsurface reduction takes place, and then only impose regulations/restrictions on the vulnerable areas. Distributed hydrological models can make predictions at grid scale, i.e. at much smaller scale than the entire catchment. However, as distributed models often do not include local scale hydrogeological heterogeneities, they are typically not able to make accurate predictions at scales smaller than they are calibrated. We present a framework for assessing nitrate reduction in the subsurface and for assessing at which spatial scales modelling tools have predictive capabilities. A new instrument has been developed for airborne geophysical measurements, Mini-SkyTEM, dedicated to identifying geological structures and heterogeneities with horizontal and lateral resolutions of 30–50 m and 2 m, respectively, in the upper 30 m. The geological heterogeneity and uncertainty are further analysed by use of the geostatistical software TProGS by generating stochastic geological realisations that are soft conditioned against the geophysical data. Finally, the flow paths within the catchment are simulated by use of the MIKE SHE hydrological modelling system for each of the geological models generated by TProGS and the prediction uncertainty is characterised by the variance between the
Surrogate model based iterative ensemble smoother for subsurface flow data assimilation
Chang, Haibin; Liao, Qinzhuo; Zhang, Dongxiao
2017-02-01
Subsurface geological formation properties often involve some degree of uncertainty. Thus, for most conditions, uncertainty quantification and data assimilation are necessary for predicting subsurface flow. The surrogate model based method is one common type of uncertainty quantification method, in which a surrogate model is constructed for approximating the relationship between model output and model input. Based on the prediction ability, the constructed surrogate model can be utilized for performing data assimilation. In this work, we develop an algorithm for implementing an iterative ensemble smoother (ES) using the surrogate model. We first derive an iterative ES scheme using a regular routine. In order to utilize surrogate models, we then borrow the idea of Chen and Oliver (2013) to modify the Hessian, and further develop an independent parameter based iterative ES formula. Finally, we establish the algorithm for the implementation of iterative ES using surrogate models. Two surrogate models, the PCE surrogate and the interpolation surrogate, are introduced for illustration. The performances of the proposed algorithm are tested by synthetic cases. The results show that satisfactory data assimilation results can be obtained by using surrogate models that have sufficient accuracy.
Heterogeneous Conformism and Wealth Distribution in a Neoclassical Growth Model
Mino, Kazuo; Nakamoto, Yasuhiro
2015-01-01
This paper explores the role of consumption externalities in a neoclassical growth model in which households have heterogeneous preferences. We fi nd that a higher degree of average conformism accelerates the convergence speed of the economy towards the steady state as in the case of homogeneous conformism. Furthermore, we reveal that the wealth inequality expands or shrinks in the case of heterogeneous conformism, while it does not expand but shrinks in the case of homogeneous conformism.
Impact of mineralogical heterogeneity on reactive transport modelling
Liu, Min; Shabaninejad, Mehdi; Mostaghimi, Peyman
2017-07-01
Impact of mineralogical heterogeneity of rocks in reactive modelling is investigated by applying a pore scale model based on the Lattice Boltzmann and Finite Volume Methods. Mass transport, chemical reaction and solid structure modification are included in the model. A two-dimensional mineral map of a sandstone rock is acquired using the imaging technique of QEMSCAN SEM with Energy-Dispersive X-ray Spectroscopy (EDS). The mineralogical heterogeneity is explored by conducting multi-mineral reaction simulations on images containing various minerals. The results are then compared with the prediction of single mineral dissolution modelling. Dissolution patterns and permeability variations of multi-mineral and single mineral reactions are presented. The errors of single mineral reaction modelling are also estimated. Numerical results show that mineralogical heterogeneity can cause significant errors in permeability prediction, if a uniform mineral distribution is assumed. The errors are smaller in high Péclet regimes than in low Péclet regimes in this sample.
Performance Modeling for Heterogeneous Wireless Networks with Multiservice Overflow Traffic
DEFF Research Database (Denmark)
Huang, Qian; Ko, King-Tim; Iversen, Villy Bæk
2009-01-01
Performance modeling is important for the purpose of developing efficient dimensioning tools for large complicated networks. But it is difficult to achieve in heterogeneous wireless networks, where different networks have different statistical characteristics in service and traffic models....... Multiservice loss analysis based on multi-dimensional Markov chain becomes intractable in these networks due to intensive computations required. This paper focuses on performance modeling for heterogeneous wireless networks based on a hierarchical overlay infrastructure. A method based on decomposition...... of the correlated traffic is used to achieve an approximate performance modeling for multiservice in hierarchical heterogeneous wireless networks with overflow traffic. The accuracy of the approximate performance obtained by our proposed modeling is verified by simulations....
Institute of Scientific and Technical Information of China (English)
HE ZhiGuo; WU WeiMing
2009-01-01
This paper presents a physically-based integrated hydrologic model that can simulate the rain-fall-induced 2D surface water flow, 3D variably saturated subsurface flow, upland soil erosion and transport, and contaminant transport in the surface-subsurface system of a watershed.The model couples surface and subsurface flows based on the assumption of continuity conditions of pressure head and exchange flux at the ground, considering infiltration and evapotranspiration.The upland rill/interrill soil erosion and transport are simulated using a non-equilibrium transport model.Con-taminant transport in the integrated surface and subsurface domains is simulated using advec-tion-diffusion equations with mass changes due to sediment sorption and desorption and exchanges between two domains due to infiltration, diffusion, and bed change.The model requires no special treatments at the interface of upland areas and streams and is suitable for wetland areas and agricul-tural watersheds with shallow streams.
Adenekan, A. E.; Patzek, T. W.; Pruess, K.
1993-11-01
A numerical compositional simulator (Multiphase Multicomponent Nonisothermal Organics Transport Simulator (M2NOTS)) has been developed for modeling transient, three-dimensional, nonisothermal, and multiphase transport of multicomponent organic contaminants in the subsurface. The governing equations include (1) advection of all three phases in response to pressure, capillary, and gravity forces; (2) interphase mass transfer that allows every component to partition into each phase present; (3) diffusion; and (4) transport of sensible and latent heat energy. Two other features distinguish M2NOTS from other simulators reported in the groundwater literature: (1) the simulator allows for any number of chemical components and every component is allowed to partition into all fluid phases present, and (2) each phase is allowed to completely disappear from, or appear in, any region of the domain during a simulation. These features are required to model realistic field problems involving transport of mixtures of nonaqueous phase liquid contaminants, and to quantify performance of existing and emerging remediation methods such as vacuum extraction and steam injection.
Equatorial Indian Ocean subsurface current variability in an Ocean General Circulation Model
Gnanaseelan, C.; Deshpande, Aditi
2017-05-01
The variability of subsurface currents in the equatorial Indian Ocean is studied using high resolution Ocean General Circulation Model (OGCM) simulations during 1958-2009. February-March eastward equatorial subsurface current (ESC) shows weak variability whereas strong variability is observed in northern summer and fall ESC. An eastward subsurface current with maximum amplitude in the pycnocline is prominent right from summer to winter during strong Indian Ocean Dipole (IOD) years when air-sea coupling is significant. On the other hand during weak IOD years, both the air-sea coupling and the ESC are weak. This strongly suggests the role of ESC on the strength of IOD. The extension of the ESC to the summer months during the strong IOD years strengthens the oceanic response and supports intensification and maintenance of IODs through modulation of air sea coupling. Although the ESC is triggered by equatorial winds, the coupled air-sea interaction associated with IODs strengthens the ESC to persist for several seasons thereby establishing a positive feedback cycle with the surface. This suggests that the ESC plays a significant role in the coupled processes associated with the evolution and intensification of IOD events by cooling the eastern basin and strengthening thermocline-SST (sea surface temperature) interaction. As the impact of IOD events on Indian summer monsoon is significant only during strong IOD years, understanding and monitoring the evolution of ESC during these years is important for summer monsoon forecasting purposes. There is a westward phase propagation of anomalous subsurface currents which persists for a year during strong IOD years, whereas such persistence or phase propagation is not seen during weak IOD years, supporting the close association between ESC and strength of air sea coupling during strong IOD years. In this study we report the processes which strengthen the IOD events and the air sea coupling associated with IOD. It also unravels
Scroll wave dynamics in a model of the heterogeneous heart
Konovalov, P. V.; Pravdin, S. F.; Solovyova, O. E.; Panfilov, A. V.
2016-07-01
Scroll waves are found in physical, chemical and biological systems and underlie many significant processes including life-threatening cardiac arrhythmias. The theory of scroll waves predicts scroll wave dynamics should be substantially affected by heterogeneity of cardiac tissue together with other factors including shape and anisotropy. In this study, we used our recently developed analytical model of the human ventricle to identify effects of shape, anisotropy, and regional heterogeneity of myocardium on scroll wave dynamics. We found that the main effects of apical-base heterogeneity were an increased scroll wave drift velocity and a shift towards the region of maximum action potential duration. We also found that transmural heterogeneity does not substantially affect scroll wave dynamics and only in extreme cases changes the attractor position.
Energy Technology Data Exchange (ETDEWEB)
Ganusov, Vitaly V [Los Alamos National Laboratory
2008-01-01
Estimation of division and death rates of lymphocytes in different conditions is vital for quantitative understanding of the immune system. Deuterium, in the form of deuterated glucose or heavy water, can be used to measure rates of proliferation and death of lymphocytes in vivo. Inferring these rates from labeling and delabeling curves has been subject to considerable debate with different groups suggesting different mathematical models for that purpose. We show that the three models that are most commonly used are in fact mathematically identical and differ only in their interpretation of the estimated parameters. By extending these previous models, we here propose a more mechanistic approach for the analysis of data from deuterium labeling experiments. We construct a model of 'kinetic heterogeneity' in which the total cell population consists of many sub-populations with different rates of cell turnover. In this model, for a given distribution of the rates of turnover, the predicted fraction of labeled DNA accumulated and lost can be calculated. Our model reproduces several previously made experimental observations, such as a negative correlation between the length of the labeling period and the rate at which labeled DNA is lost after label cessation. We demonstrate the reliability of the new explicit kinetic heterogeneity model by applying it to artificially generated datasets, and illustrate its usefulness by fitting experimental data. In contrast to previous models, the explicit kinetic heterogeneity model (1) provides a mechanistic way of interpreting labeling data; (2) allows for a non-exponential loss of labeled cells during delabeling, and (3) can be used to describe data with variable labeling length.
Energy Technology Data Exchange (ETDEWEB)
Ganusov, Vitaly V [Los Alamos National Laboratory
2008-01-01
Estimation of division and death rates of lymphocytes in different conditions is vital for quantitative understanding of the immune system. Deuterium, in the form of deuterated glucose or heavy water, can be used to measure rates of proliferation and death of lymphocytes in vivo. Inferring these rates from labeling and delabeling curves has been subject to considerable debate with different groups suggesting different mathematical models for that purpose. We show that the three models that are most commonly used are in fact mathematically identical and differ only in their interpretation of the estimated parameters. By extending these previous models, we here propose a more mechanistic approach for the analysis of data from deuterium labeling experiments. We construct a model of 'kinetic heterogeneity' in which the total cell population consists of many sub-populations with different rates of cell turnover. In this model, for a given distribution of the rates of turnover, the predicted fraction of labeled DNA accumulated and lost can be calculated. Our model reproduces several previously made experimental observations, such as a negative correlation between the length of the labeling period and the rate at which labeled DNA is lost after label cessation. We demonstrate the reliability of the new explicit kinetic heterogeneity model by applying it to artificially generated datasets, and illustrate its usefulness by fitting experimental data. In contrast to previous models, the explicit kinetic heterogeneity model (1) provides a mechanistic way of interpreting labeling data; (2) allows for a non-exponential loss of labeled cells during delabeling, and (3) can be used to describe data with variable labeling length.
Upscaling heterogeneity in aquifer reactivity via exposure-time concept: forward model.
Seeboonruang, Uma; Ginn, Timothy R
2006-03-20
Reactive properties of aquifer solid phase materials play an important role in solute fate and transport in the natural subsurface on time scales ranging from years in contaminant remediation to millennia in dynamics of aqueous geochemistry. Quantitative tools for dealing with the impact of natural heterogeneity in solid phase reactivity on solute fate and transport are limited. Here we describe the use of a structural variable to keep track of solute flux exposure to reactive surfaces. With this approach, we develop a non-reactive tracer model that is useful for determining the signature of multi-scale reactive solid heterogeneity in terms of solute flux distributions at the field scale, given realizations of three-dimensional reactive site density fields. First, a governing Eulerian equation for the non-reactive tracer model is determined by an upscaling technique in which it is found that the exposure time of solution to reactive surface areas evolves via both a macroscopic velocity and a macroscopic dispersion in the artificial dimension of exposure time. Second, we focus on the Lagrangian approach in the context of a streamtube ensemble and demonstrate the use of the distribution of solute flux over the exposure time dimension in modeling two-dimensional transport of a solute undergoing simplified linear reversible reactions, in hypothetical conditions following prior laboratory experiments. The distribution of solute flux over exposure time in a given case is a signature of the impact of heterogeneous aquifer reactivity coupled with a particular physical heterogeneity, boundary conditions, and hydraulic gradient. Rigorous application of this approach in a simulation sense is limited here to linear kinetically controlled reactions.
Majority-vote model with heterogeneous agents on square lattice
Lima, F W S
2013-01-01
We study a nonequilibrium model with up-down symmetry and a noise parameter $q$ known as majority-vote model of M.J. Oliveira 1992 with heterogeneous agents on square lattice. By Monte Carlo simulations and finite-size scaling relations the critical exponents $\\beta/\
Doi, Suhail A R; Barendregt, Jan J; Khan, Shahjahan; Thalib, Lukman; Williams, Gail M
2015-11-01
This article examines an improved alternative to the random effects (RE) model for meta-analysis of heterogeneous studies. It is shown that the known issues of underestimation of the statistical error and spuriously overconfident estimates with the RE model can be resolved by the use of an estimator under the fixed effect model assumption with a quasi-likelihood based variance structure - the IVhet model. Extensive simulations confirm that this estimator retains a correct coverage probability and a lower observed variance than the RE model estimator, regardless of heterogeneity. When the proposed IVhet method is applied to the controversial meta-analysis of intravenous magnesium for the prevention of mortality after myocardial infarction, the pooled OR is 1.01 (95% CI 0.71-1.46) which not only favors the larger studies but also indicates more uncertainty around the point estimate. In comparison, under the RE model the pooled OR is 0.71 (95% CI 0.57-0.89) which, given the simulation results, reflects underestimation of the statistical error. Given the compelling evidence generated, we recommend that the IVhet model replace both the FE and RE models. To facilitate this, it has been implemented into free meta-analysis software called MetaXL which can be downloaded from www.epigear.com.
Model and method for optimizing heterogeneous systems
Antamoshkin, O. A.; Antamoshkina, O. A.; Zelenkov, P. V.; Kovalev, I. V.
2016-11-01
Methodology of distributed computing performance boost by reduction of delays number is proposed. Concept of n-dimentional requirements triangle is introduced. Dynamic mathematical model of resource use in distributed computing systems is described.
Modeling Strain Rate Effect for Heterogeneous Brittle Materials
Institute of Scientific and Technical Information of China (English)
MA Guowei; DONG Aiai; LI Jianchun
2006-01-01
Rocks are heterogeneous from the point of microstructure which is of significance to their dynamic failure behavior.Both the compressive and tensile strength of rock-like materials is regarded different from the static strength.The present study adopts smoothed particle hydrodynamics (SPH) which is a virtual particle based meshfree method to investigate strain rate effect for heterogeneous brittle materials.The SPH method is capable of simulating rock fracture,free of the mesh constraint of the traditional FEM and FDM models.A pressure dependent J-H constitutive model involving heterogeneity is employed in the numerical modeling.The results show the compressive strength increases with the increase of strain rate as well as the tensile strength,which is important to the engineering design.
Directory of Open Access Journals (Sweden)
T. J. Bohn
2013-10-01
Full Text Available We used a process-based model to examine the role of spatial heterogeneity of surface and sub-surface water on the carbon budget of the wetlands of the West Siberian Lowland over the period 1948–2010. We found that, while surface heterogeneity (fractional saturated area had little overall effect on estimates of the region's carbon fluxes, sub-surface heterogeneity (spatial variations in water table depth played an important role in both the overall magnitude and spatial distribution of estimates of the region's carbon fluxes. In particular, to reproduce the spatial pattern of CH4 emissions recorded by intensive in situ observations across the domain, in which very little CH4 is emitted north of 60° N, it was necessary to (a account for CH4 emissions from unsaturated wetlands and (b use spatially varying methane model parameters that reduced estimated CH4 emissions in the northern (permafrost half of the domain (and/or account for lower CH4 emissions under inundated conditions. Our results suggest that previous estimates of the response of these wetlands to thawing permafrost may have overestimated future increases in methane emissions in the permafrost zone.
Shiraishi, H.; Sasaka, K.; Hamamoto, H.; Hachinohe, S.; Ishiyama, T.
2011-12-01
Most of Japanese local governments have been estimating whole picture of quake damage under scenario earthquakes to reduce both casualties and physical damage. Saitama prefectural government, which is adjacent to north of Tokyo, have already made the estimation four times since 1970's. This estimation requires precise mathematical models of subsurface structures for calculating ground surface accelerations during massive quakes. The models have been updated with every new research. In the early models, the shallow layers had been created with applying geological layers of typical 241 types to the whole prefecture. On the other hand, in the current models, the shallow layers are created with the results of drilling surveys under public works. This update on the models allows us to estimate the quake damage more precisely in every 250m square throughout the prefecture. However even the current models are not complete yet. Because the drilling surveys have not been done enough in rural areas compared with urban areas. The models of shallow layers in rural areas have therefore been created by interpolating with considering terrains among the locations of drilling surveys. Thereby accuracy of the models depends on that of the interpolations. Against this background authors have examined the accuracy of the models by making comparisons of phase velocity dispersions between observed velocities through spatial autocorrelation (SPAC) technique and calculated velocities from the models. Two types of SPAC arrays with radii of 3m, 30m are deployed and data acquisition time is 30min for each array. The result shows that the subsurface structures of urban areas are well modeled, because both the dispersion curves are almost agreed, furthermore amplitude responses of the models are in good agreement with the responses determined by the results of microtremor survey method (MSM). In contrast, the subsurface structures of rural areas include cases that have not been modeled with
Institute of Scientific and Technical Information of China (English)
TIAN; Xiangjun; XIE; Zhenghui; ZHANG; Shenglei
2006-01-01
Subsurface runoff in a land surface model is usually parameterized as a single-valued function of total storage in a basin aquifer reservoir. This kind of parameterization is often single-valued function of storage-discharge under a steady or "quasi-steady" state, which cannot represent the influence of aquifer recharge on subsurface runoff generation. In this paper, a new subsurface runoff parameterization with water storage and recharge based on the Boussinesq-storage equation is developed. This model is validated by a subsurface flow separation algorithm for an example river basin, which shows that the new model can simulate the subsurface flow reasonably.
Experimental validation of a sub-surface model of solar power for distributed marine sensor systems
Hahn, Gregory G.; Cantin, Heather P.; Shafer, Michael W.
2016-04-01
The capabilities of distributed sensor systems such as marine wildlife telemetry tags could be significantly enhanced through the integration of photovoltaic modules. Photovoltaic cells could be used to supplement the primary batteries for wildlife telemetry tags to allow for extended tag deployments, wherein larger amounts of data could be collected and transmitted in near real time. In this article, we present experimental results used to validate and improve key aspects of our original model for sub-surface solar power. We discuss the test methods and results, comparing analytic predictions to experimental results. In a previous work, we introduced a model for sub-surface solar power that used analytic models and empirical data to predict the solar irradiance available for harvest at any depth under the ocean's surface over the course of a year. This model presented underwater photovoltaic transduction as a viable means of supplementing energy for marine wildlife telemetry tags. The additional data provided by improvements in daily energy budgets would enhance the temporal and spatial comprehension of the host's activities and/or environments. Photovoltaic transduction is one method that has not been widely deployed in the sub-surface marine environments despite widespread use on terrestrial and avian species wildlife tag systems. Until now, the use of photovoltaic cells for underwater energy harvesting has generally been disregarded as a viable energy source in this arena. In addition to marine telemetry systems, photovoltaic energy harvesting systems could also serve as a means of energy supply for autonomous underwater vehicles (AUVs), as well as submersible buoys for oceanographic data collection.
Comparison of multiplicative heterogeneous variance adjustment models for genetic evaluations.
Márkus, Sz; Mäntysaari, E A; Strandén, I; Eriksson, J-Å; Lidauer, M H
2014-06-01
Two heterogeneous variance adjustment methods and two variance models were compared in a simulation study. The method used for heterogeneous variance adjustment in the Nordic test-day model, which is a multiplicative method based on Meuwissen (J. Dairy Sci., 79, 1996, 310), was compared with a restricted multiplicative method where the fixed effects were not scaled. Both methods were tested with two different variance models, one with a herd-year and the other with a herd-year-month random effect. The simulation study was built on two field data sets from Swedish Red dairy cattle herds. For both data sets, 200 herds with test-day observations over a 12-year period were sampled. For one data set, herds were sampled randomly, while for the other, each herd was required to have at least 10 first-calving cows per year. The simulations supported the applicability of both methods and models, but the multiplicative mixed model was more sensitive in the case of small strata sizes. Estimation of variance components for the variance models resulted in different parameter estimates, depending on the applied heterogeneous variance adjustment method and variance model combination. Our analyses showed that the assumption of a first-order autoregressive correlation structure between random-effect levels is reasonable when within-herd heterogeneity is modelled by year classes, but less appropriate for within-herd heterogeneity by month classes. Of the studied alternatives, the multiplicative method and a variance model with a random herd-year effect were found most suitable for the Nordic test-day model for dairy cattle evaluation.
Salinas, P.; Jackson, M.; Pavlidis, D.; Pain, C.; Adam, A.; Xie, Z.; Percival, J. R.
2015-12-01
We present a new, high-order, control-volume-finite-element (CVFE) method with discontinuous representation for pressure and velocity to simulate multiphase flow in heterogeneous porous media. Time is discretized using an adaptive, fully implicit method. Heterogeneous geologic features are represented as volumes bounded by surfaces. Within these volumes, termed geologic domains, the material properties are constant. A given model typically contains numerous such geologic domains. Our approach conserves mass and does not require the use of CVs that span domain boundaries. Computational efficiency is increased by use of dynamic mesh optimization, in which an unstructured mesh adapts in space and time to key solution fields, such as pressure, velocity or saturation, whilst preserving the geometry of the geologic domains. Up-, cross- or down-scaling of material properties during mesh optimization is not required, as the properties are uniform within each geologic domain. We demonstrate that the approach, amongst other features, accurately preserves sharp saturation changes associated with high aspect ratio geologic domains such as fractures and mudstones, allowing efficient simulation of flow in highly heterogeneous models. Moreover, accurate solutions are obtained at significantly lower computational cost than an equivalent fine, fixed mesh and conventional CVFE methods. The use of implicit time integration allows the method to efficiently converge using highly anisotropic meshes without having to reduce the time-step. The work is significant for two key reasons. First, it resolves a long-standing problem associated with the use of classical CVFE methods to model flow in highly heterogeneous porous media, in which CVs span boundaries between domains of contrasting material properties. Second, it reduces computational cost/increases solution accuracy through the use of dynamic mesh optimization and time-stepping with large Courant number.
Modelling Configuration Knowledge in Heterogeneous Product Families
DEFF Research Database (Denmark)
Queva, Matthieu Stéphane Benoit; Männistö, Tomi; Ricci, Laurent
2011-01-01
Product configuration systems play an important role in the development of Mass Customisation. The configuration of complex product families may nowadays involve multiple design disciplines, e.g. hardware, software and services. In this paper, we present a conceptual approach for modelling the va...
Integration of Heterogenous Digital Surface Models
Boesch, R.; Ginzler, C.
2011-08-01
The application of extended digital surface models often reveals, that despite an acceptable global accuracy for a given dataset, the local accuracy of the model can vary in a wide range. For high resolution applications which cover the spatial extent of a whole country, this can be a major drawback. Within the Swiss National Forest Inventory (NFI), two digital surface models are available, one derived from LiDAR point data and the other from aerial images. Automatic photogrammetric image matching with ADS80 aerial infrared images with 25cm and 50cm resolution is used to generate a surface model (ADS-DSM) with 1m resolution covering whole switzerland (approx. 41000 km2). The spatially corresponding LiDAR dataset has a global point density of 0.5 points per m2 and is mainly used in applications as interpolated grid with 2m resolution (LiDAR-DSM). Although both surface models seem to offer a comparable accuracy from a global view, local analysis shows significant differences. Both datasets have been acquired over several years. Concerning LiDAR-DSM, different flight patterns and inconsistent quality control result in a significantly varying point density. The image acquisition of the ADS-DSM is also stretched over several years and the model generation is hampered by clouds, varying illumination and shadow effects. Nevertheless many classification and feature extraction applications requiring high resolution data depend on the local accuracy of the used surface model, therefore precise knowledge of the local data quality is essential. The commercial photogrammetric software NGATE (part of SOCET SET) generates the image based surface model (ADS-DSM) and delivers also a map with figures of merit (FOM) of the matching process for each calculated height pixel. The FOM-map contains matching codes like high slope, excessive shift or low correlation. For the generation of the LiDAR-DSM only first- and last-pulse data was available. Therefore only the point distribution can
Model-based design of horizontal subsurface flow constructed treatment wetlands: a review.
Rousseau, Diederik P L; Vanrolleghem, Peter A; De Pauw, Niels
2004-03-01
The increasing application of constructed wetlands for wastewater treatment coupled with increasingly strict water quality standards is an ever growing incentive for the development of better process design tools. This paper reviews design models for horizontal subsurface flow constructed treatment wetlands, ranging from simple rules of thumb and regression equations, to the well-known first-order k-C* models, Monod-type equations and more complex dynamic, compartmental models. Especially highlighted in this review are the model constraints and parameter uncertainty. A case study has been used to demonstrate the model output variability and to unravel whether or not more complex but also less manageable models offer a significant advantage to the designer.
A time-dependent Mixing Model for PDF Methods in Heterogeneous Aquifers
Schüler, Lennart; Suciu, Nicolae; Knabner, Peter; Attinger, Sabine
2016-04-01
Predicting the transport of groundwater contaminations remains a demanding task, especially with respect to the heterogeneity of the subsurface and the large measurement uncertainties. A risk analysis also includes the quantification of the uncertainty in order to evaluate how accurate the predictions are. Probability density function (PDF) methods are a promising alternative to predicting the transport of solutes in groundwater under uncertainty. They make it possible to derive the evolution equations of the mean concentration and the concentration variance, which can be used as a first measure of uncertainty. A mixing model, also known as a dissipation model, is essential for both methods. Finding a satisfactory mixing model is still an open question and due to the rather elaborate PDF methods, a difficult undertaking. Both the PDF equation and the concentration variance equation depend on the same mixing model. This connection is used to find and test an improved mixing model for the much easier to handle concentration variance. Subsequently, this mixing model is transferred to the PDF equation and tested. The newly proposed mixing model yields significantly improved results for both variance modelling and PDF modelling. The implications of the new mixing model for different kinds of flow conditions are discussed and some comments are made on efficiently handling spatially resolved higher moments.
Numerical analysis and centrifugal modeling of LNAPLs transport in subsurface system
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
The transport of non-aqueous phase liquids (NAPLs) in unsaturated soils and groundwater is an important research topic in geo-environmental engineering. In this paper, the mechanism of light NAPLs (LNAPLs) transport in subsurface system is briefly introduced, and the mass transport equations, fluid flow equations, and the constitutive model of relative permeability - saturation - capillary pressure are discussed. Then the numerical method is introduced to simulate the multiphase flow problems in porous media, and the tempospatial distribution of LNAPLs is obtained. Moreover, different boundary conditions are employed in numerical simulation to investigate its effect on transport behavior. To verify the numerical data, centrifugal tests are conducted to model the LNAPLs migration in unsaturated soils and groundwater. The calculation results are agreeable with the experimental findings of centrifugal modeling, which indicates that LNAPLs from leaking point move downwards due to gravity force, and form a high concentration zone above the capillary fringe, and then spread out laterally along the groundwater table. Some LNAPL enters groundwater system to further migrate. The combination of numerical simulation and centrifuge modeling can be a useful means to study the transport behavior of LNAPLs in subsurface system.
Application of an Orbital GPR Model to Detecting Martian Polar Subsurface Features
Xu, Y.; Cummer, S. A.; Farrell, W. M.
2005-01-01
There are numerous challenges in successfully implementing and interpreting planetary ground penetrating radar (GPR) measurements. Many are due to substantial uncertainties in the target ground parameters and the intervening medium (i.e., the ionosphere). These uncertainties generate a compelling need for meaningful quantitative simulation of the planetary GPR problem. An accurate numerical model would enable realistic numerical GPR simulations using parameter regimes much broader than are possible in laboratory or field experiments. Parameters such as source bandwidth and power, surface and subsurface features, and ionospheric profiles could be rapidly iterated to understand their impact on GPR performance and the reliable interpretation of GPR data.
Modelling subsurface hydrology in Mediterranean regions to investigate spatial and temporal trends
Evans, Cristina M.; Singer, Michael B.; Dritschel, David G.
2016-04-01
Mediterranean environments have highly variable hydrologic regimes characterised by two distinct seasons: cold/wet and warm/dry. Understanding how this climate is expressed in subsurface hydrology is a basis for the effective management of water as a resource. Riparian systems are particularly complex due to the contribution of both infiltrating precipitation and subsurface hyporheic flows. Therefore a more in-depth investigation of subsurface hydrology is required to understand riparian corridors. Numerical models can be used to simulate soil-water distribution and exchange. We have built-on existing theory of flow through porous media to create a physically-based, river- and climate-driven numerical model of hyporheic flow and infiltration/evaporation that predicts the water content at any depth in a soil column and at any distance from the river channel. The model incorporates the Richards equation - describing the vertical infiltration and diffusion of water in porous media - and the Boussinesq equation, which simulates the horizontal evolution of the water-table (hyporheic flow). These equations have been fully coupled to reflect the interplay between the saturated and unsaturated zones. The model produces a daily time-series of water table elevations and vertical soil moisture patterns in the vadose zones to allow us to study the hydrological partitioning and soil-moisture distribution in a given soil profile. We apply this tool to Mediterranean regions over a number of years to explore seasonal and inter-annual hydrological patterns. Two sites along the Rhône River in France with distinct climates allow us to investigate the impact of riverine and climate functioning. In particular we assess the impact of distance from the river channel and exposure to warmer and dryer conditions. Finally, the temporal legacy of extreme events such as floods and droughts is considered within the context of the impact to riparian vegetation. These comparisons will resolve
Adaptive multiresolution modeling of groundwater flow in heterogeneous porous media
Malenica, Luka; Gotovac, Hrvoje; Srzic, Veljko; Andric, Ivo
2016-04-01
Proposed methodology was originally developed by our scientific team in Split who designed multiresolution approach for analyzing flow and transport processes in highly heterogeneous porous media. The main properties of the adaptive Fup multi-resolution approach are: 1) computational capabilities of Fup basis functions with compact support capable to resolve all spatial and temporal scales, 2) multi-resolution presentation of heterogeneity as well as all other input and output variables, 3) accurate, adaptive and efficient strategy and 4) semi-analytical properties which increase our understanding of usually complex flow and transport processes in porous media. The main computational idea behind this approach is to separately find the minimum number of basis functions and resolution levels necessary to describe each flow and transport variable with the desired accuracy on a particular adaptive grid. Therefore, each variable is separately analyzed, and the adaptive and multi-scale nature of the methodology enables not only computational efficiency and accuracy, but it also describes subsurface processes closely related to their understood physical interpretation. The methodology inherently supports a mesh-free procedure, avoiding the classical numerical integration, and yields continuous velocity and flux fields, which is vitally important for flow and transport simulations. In this paper, we will show recent improvements within the proposed methodology. Since "state of the art" multiresolution approach usually uses method of lines and only spatial adaptive procedure, temporal approximation was rarely considered as a multiscale. Therefore, novel adaptive implicit Fup integration scheme is developed, resolving all time scales within each global time step. It means that algorithm uses smaller time steps only in lines where solution changes are intensive. Application of Fup basis functions enables continuous time approximation, simple interpolation calculations across
Modelling Waterfall Retreat in Heterogenous Bedrock
Attal, M.; Hodge, R. A.; Williams, R.; Baynes, E.
2016-12-01
Bedrock rivers are the mediators of environmental change through mountainous landscapes. In response to an increase in uplift rate for example, a "knickpoint" (often materialised as a waterfall) will propagate upstream, separating a domain downstream where the river and its adjacent hillslopes have steepened in response to the change from a "relict" domain upstream which is adjusted to the conditions before the change (Crosby and Whipple 2006). Many studies assume that knickpoint propagation rate scales with drainage area, based on the stream power theory. However, recent studies in a range of locations have found no obvious relationship between knickpoint retreat rate and drainage area, potentially resulting from the stream power law neglecting (i) the influence of sediment on the processes associated with waterfall migration and (ii) thresholds for bedrock detachment (Cook et al. 2013; Mackey et al. 2014; DiBiase et al. 2015; Baynes et al. 2015; Brocard et al. 2016). In this study, we develop a 1D model of waterfall retreat in horizontally bedded bedrock with varying joint spacing. In the model, knickpoint migration is based on two rules: a waterfall will start migrating once the threshold flow depth (a function of knickpoint height and joint spacing) has been exceeded (Lamb and Dietrich 2009), and the migration rate will then be a function of the water-depth-to-waterfall-height ratio, based on experimental results by Baynes (2015). Using a hydrograph based on a Poisson rectangular pulse rainfall simulator (Tucker and Bras 2001), we demonstrate the importance of structure in controlling the speed at which waterfalls migrate but also their number and the length over which they are distributed (Fig. 1). The model is applied to the Jökulsá á Fjöllum, NE Iceland, where rapid migration of waterfalls as a result of discrete events has been identified (Baynes et al. 2015), using new constraints on joint spacing derived from high resolution lidar survey of the gorge
Energy Technology Data Exchange (ETDEWEB)
Elsheikh, Ahmed H., E-mail: aelsheikh@ices.utexas.edu [Institute for Computational Engineering and Sciences (ICES), University of Texas at Austin, TX (United States); Institute of Petroleum Engineering, Heriot-Watt University, Edinburgh EH14 4AS (United Kingdom); Wheeler, Mary F. [Institute for Computational Engineering and Sciences (ICES), University of Texas at Austin, TX (United States); Hoteit, Ibrahim [Department of Earth Sciences and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal (Saudi Arabia)
2014-02-01
A Hybrid Nested Sampling (HNS) algorithm is proposed for efficient Bayesian model calibration and prior model selection. The proposed algorithm combines, Nested Sampling (NS) algorithm, Hybrid Monte Carlo (HMC) sampling and gradient estimation using Stochastic Ensemble Method (SEM). NS is an efficient sampling algorithm that can be used for Bayesian calibration and estimating the Bayesian evidence for prior model selection. Nested sampling has the advantage of computational feasibility. Within the nested sampling algorithm, a constrained sampling step is performed. For this step, we utilize HMC to reduce the correlation between successive sampled states. HMC relies on the gradient of the logarithm of the posterior distribution, which we estimate using a stochastic ensemble method based on an ensemble of directional derivatives. SEM only requires forward model runs and the simulator is then used as a black box and no adjoint code is needed. The developed HNS algorithm is successfully applied for Bayesian calibration and prior model selection of several nonlinear subsurface flow problems.
Adaptive Multiscale Finite Element Method for Subsurface Flow Simulation
Van Esch, J.M.
2010-01-01
Natural geological formations generally show multiscale structural and functional heterogeneity evolving over many orders of magnitude in space and time. In subsurface hydrological simulations the geological model focuses on the structural hierarchy of physical sub units and the flow model addresses
Adaptive Multiscale Finite Element Method for Subsurface Flow Simulation
Van Esch, J.M.
2010-01-01
Natural geological formations generally show multiscale structural and functional heterogeneity evolving over many orders of magnitude in space and time. In subsurface hydrological simulations the geological model focuses on the structural hierarchy of physical sub units and the flow model addresses
Multinomial mixture model with heterogeneous classification probabilities
Holland, M.D.; Gray, B.R.
2011-01-01
Royle and Link (Ecology 86(9):2505-2512, 2005) proposed an analytical method that allowed estimation of multinomial distribution parameters and classification probabilities from categorical data measured with error. While useful, we demonstrate algebraically and by simulations that this method yields biased multinomial parameter estimates when the probabilities of correct category classifications vary among sampling units. We address this shortcoming by treating these probabilities as logit-normal random variables within a Bayesian framework. We use Markov chain Monte Carlo to compute Bayes estimates from a simulated sample from the posterior distribution. Based on simulations, this elaborated Royle-Link model yields nearly unbiased estimates of multinomial and correct classification probability estimates when classification probabilities are allowed to vary according to the normal distribution on the logit scale or according to the Beta distribution. The method is illustrated using categorical submersed aquatic vegetation data. ?? 2010 Springer Science+Business Media, LLC.
Directory of Open Access Journals (Sweden)
M. Bergvall
2011-07-01
Full Text Available Few studies have been carried out that cover the entire transport process of pesticides, from application at the soil surface, through subsurface transport, to contamination of drinking water in esker aquifers. In formerly glaciated regions, such as Scandinavia, many of the most important groundwater resources are situated in glaciofluvial eskers. The purpose of the present study was to model and identify significant processes that govern subsurface transport of pesticides in extensive glaciofluvial and littoral sediments. To simulate the transport processes, we coupled a vadose zone model at soil profile scale to a regional groundwater flow model. The model was applied to a municipal drinking-water aquifer, contaminated with the pesticide-metabolite BAM (2,6-dichlorobenzoamide. At regional scale, with the combination of a ten-meter-deep vadose zone and coarse texture, the observed concentrations could be described by the model without assuming preferential flow. A sensitivity analysis revealed that hydraulic conductivity in the aquifer and infiltration rate accounted for almost half of the model uncertainty. The calibrated model was applied to optimize the location of extraction wells for remediation, which were used to validate the predictive modeling. Running a worst-case scenario, the model showed that the establishment of two remediation wells would clean the aquifer in four years, compared to nine years without them. Further development of the model would require additional field measurements in order to improve the description of macrodispersion in deep, sandy vadose zones. We also suggest that future research should focus on characterization of the variability of hydraulic conductivity and its effect on contaminant transport in eskers.
Energy Technology Data Exchange (ETDEWEB)
Boerresen, Knut Arne
1996-12-31
Hydrocarbon recovery from subsurface reservoirs has become increasingly dependent on advanced recovery techniques that require improved understanding of the physics of fluid flow within and across geological units including small-scale heterogeneities and fractures. In this thesis, impacts from heterogeneities on local fluid flow are studied experimentally by means of imaging techniques to visualize fluid flow in two dimensions during flooding of larger reservoir models. Part 1 reflects the multi-disciplinary collaboration, by briefly introducing the relevant geology, the literature on experiments on fluid flow in bedded structures, and outlining the applied numerical simulator and imaging techniques applied to visualize fluid flow. The second part contains a synopsis of displacement experiments in naturally laminated sandstones and in crossbed laboratory models, and of the impact from incipient shear fractures on oil recovery. The detailed results obtained from the experiments and simulations are described in six papers, all included. 215 refs., 108 figs., 16 tabs.
Detection of unobserved heterogeneity with growth mixture models
Jost Reinecke; Luca Mariotti
2009-01-01
Latent growth curve models as structural equation models are extensively discussedin various research fields (Duncan et al., 2006). Recent methodological and statisticalextension are focused on the consideration of unobserved heterogeneity in empiricaldata. Muth´en extended the classical structural equation approach by mixture components,i. e. categorical latent classes (Muth´en 2002, 2004, 2007).The paper will discuss applications of growth mixture models with data from oneof the first panel...
Heterogeneous Speed Profiles in Discrete Models for Pedestrian Simulation
Bandini, Stefania; Crociani, Luca; Vizzari, Giuseppe
2014-01-01
Discrete pedestrian simulation models are viable alternatives to particle based approaches based on a continuous spatial representation. The effects of discretisation, however, also imply some difficulties in modelling certain phenomena that can be observed in reality. This paper focuses on the possibility to manage heterogeneity in the walking speed of the simulated population of pedestrians by modifying an existing multi-agent model extending the floor field approach. Whereas some discrete ...
Integrated geomechanical modelling at TNO for assessement of deep subsurface risks
Orlic, B.; Fokker, P.; Zijl, W.; Scheffers, B.
2001-01-01
Public authorities, E & P and the mining industry increasingly demand fundamental insight and accurate predictions on subsurface and surface deformation and damage due to exploitation of subsurface natural resources, and subsurface storage of energy residues (e.g. CO2). At this moment deformation is
Overview of research and development in subsurface fate and transport modeling
Energy Technology Data Exchange (ETDEWEB)
Sullivan, T.M. [Brookhaven National Lab., Upton, NY (United States); Chehata, M. [Science Applications Internationa Corp. (United States)
1995-05-01
The US Department of Energy is responsible for the remediation of over 450 different subsurface-contaminated sites. Contaminant plumes at these sites range in volume from several to millions of cubic yards. The concentration of contaminants also ranges over several orders of magnitude. Contaminants include hazardous wastes such as heavy metals and organic chemicals, radioactive waste including tritium, uranium, and thorium, and mixed waste, which is a combination of hazardous and radioactive wastes. The physical form of the contaminants includes solutes, nonaqueous phase liquids (NAPLs), and vapor phase contaminants such as volatilized organic chemicals and radon. The subject of contaminant fate and transport modeling is multi-disciplinary, involving hydrology, geology, microbiology, chemistry, applied mathematics, computer science, and other areas of expertise. It is an issue of great significance in the United States and around the world. As such, many organizations have substantial programs in this area. In gathering data to prepare this report, a survey was performed of research and development work that is funded by US government agencies to improve the understanding and mechanistic modeling of processes that control contaminant movement through subsurface systems. Government agencies which fund programs that contain fate and transport modeling components include the Environmental Protection Agency, Nuclear Regulatory Commission, Department of Agriculture, Department of Energy, National Science Foundation, Department of Defense, United States Geological Survey, and National Institutes of Health.
Overview of research and development in subsurface fate and transport modeling
Energy Technology Data Exchange (ETDEWEB)
Sullivan, T.M. [Brookhaven National Lab., Upton, NY (United States); Chehata, M. [Science Applications Internationa Corp. (United States)
1995-05-01
The US Department of Energy is responsible for the remediation of over 450 different subsurface-contaminated sites. Contaminant plumes at these sites range in volume from several to millions of cubic yards. The concentration of contaminants also ranges over several orders of magnitude. Contaminants include hazardous wastes such as heavy metals and organic chemicals, radioactive waste including tritium, uranium, and thorium, and mixed waste, which is a combination of hazardous and radioactive wastes. The physical form of the contaminants includes solutes, nonaqueous phase liquids (NAPLs), and vapor phase contaminants such as volatilized organic chemicals and radon. The subject of contaminant fate and transport modeling is multi-disciplinary, involving hydrology, geology, microbiology, chemistry, applied mathematics, computer science, and other areas of expertise. It is an issue of great significance in the United States and around the world. As such, many organizations have substantial programs in this area. In gathering data to prepare this report, a survey was performed of research and development work that is funded by US government agencies to improve the understanding and mechanistic modeling of processes that control contaminant movement through subsurface systems. Government agencies which fund programs that contain fate and transport modeling components include the Environmental Protection Agency, Nuclear Regulatory Commission, Department of Agriculture, Department of Energy, National Science Foundation, Department of Defense, United States Geological Survey, and National Institutes of Health.
Directory of Open Access Journals (Sweden)
M. Bergvall
2011-02-01
Full Text Available Few studies have been carried out that cover the entire transport process of pesticides, from application at the soil surface, through subsurface transport, to contamination of drinking water in esker aquifers. In formerly glaciated areas, such as Scandinavia, many of the most important groundwater resources are situated in glaciofluvial eskers. The purpose of the present study was to model and identify significant processes that govern subsurface transport of pesticides in extensive glaciofluvial and littoral sediments. To simulate the transport processes, we coupled a vadose zone model at the point scale to a regional groundwater flow model. The model was applied to a municipal drinking-water aquifer, contaminated with the pesticide-metabolite BAM (2,6-dichlorobenzoamide. A sensitivity analysis revealed that hydraulic conductivity and infiltration rate accounted for almost half of the model uncertainty. For a ten-meter-deep vadose zone of coarse texture, macropore flow was found to be of minor importance for contaminant transport. The calibrated model was applied to optimize the location of extraction wells for remediation, which were used to verify the predictive modeling. Running a worst-case scenario, the model showed that the establishment of two remediation wells would clean the aquifer in four years, compared to nine years without them. Further development of the model would require additional field measurements to assess the importance of macropore flow in deep, sandy aquifers. We also suggest that future research should focus on characterization of the variability of hydraulic conductivity and its effect on contaminant transport in eskers.
A heterogeneous model for heat transfer in packed beds
Wijngaarden, R.J.; Westerterp, K.R.
1993-01-01
If transient heat transfer occurs in a packed bed or a reaction is carried out on the pellets, the heterogeneity of the bed is essential because of the heat flow between pellets and gas. Global heat parameters for the packed bed, such as λeff and αw, are usually derived from homogeneous models. Ther
Reformulation of Rothermel's wildland fire behaviour model for heterogeneous fuelbeds.
David V. Sandberg; Cynthia L. Riccardi; Mark D. Schaaf
2007-01-01
Abstract: The Fuel Characteristic Classification System (FCCS) includes equations that calculate energy release and one-dimensional spread rate in quasi-steady-state fires in heterogeneous but spatially uniform wildland fuelbeds, using a reformulation of the widely used Rothermel fire spread model. This reformulation provides an automated means to predict fire behavior...
A multiscale modeling study for the natural convection mass transfer in a subsurface aquifer
Alam, Jahrul M
2013-01-01
Quantitative and realistic computer simulations of mass transfer associated with CO2 disposal in subsurface aquifers is a challenging endeavor. This article has proposed a novel and efficient multiscale modeling framework, and has examined its potential to study the pen- etrative mass transfer in a CO2 plume that migrates in an aquifer. Nu- merical simulations indicate that the migration of the injected CO2 enhances the vorticity generation, and the dissolution of CO2 has a strong effect on the natural convection mass transfer. The vorticity decays with the increase of the porosity. The time scale of the vertical migration of a CO2 plume is strongly dependent on the rate of CO2 dissolution. Comparisons confirm the near optimal performance of the proposed multiscale model. These primary results with an idealized computational model of the CO2 migration in an aquifer brings the potential of the proposed multiscale model to the field of heat and mass transfer in the geoscience.
Directory of Open Access Journals (Sweden)
Guenter Langergraber
2016-12-01
Full Text Available To date, only few process-based models for subsurface flow treatment wetlands have been developed. For modelling a treatment wetland, these models have to comprise a number of sub-models to describe water flow, pollutant transport, pollutant transformation and degradation, effects of wetland plants, and transport and deposition of suspended particulate matter. The two most advanced models are the HYDRUS Wetland Module and BIO-PORE. These two models are briefly described. This paper shows typical simulation results for vertical flow wetlands and discusses experiences and challenges using process-based wetland models in relation to the sub-models describing the most important wetland processes. It can be demonstrated that existing simulation tools can be applied for simulating processes in treatment wetlands. Most important for achieving a good match between measured and simulated pollutant concentrations is a good calibration of the water flow and transport models. Only after these calibrations have been made and the effect of the influent fractionation on simulation results has been considered, should changing the parameters of the biokinetic models be taken into account. Modelling the effects of wetland plants is possible and has to be considered when important. Up to now, models describing clogging are the least established models among the sub-models required for a complete wetland model and thus further development and research is required.
Zhuang, Kai; Izallalen, Mounir; Mouser, Paula; Richter, Hanno; Risso, Carla; Mahadevan, Radhakrishnan; Lovley, Derek R
2011-02-01
The advent of rapid complete genome sequencing, and the potential to capture this information in genome-scale metabolic models, provide the possibility of comprehensively modeling microbial community interactions. For example, Rhodoferax and Geobacter species are acetate-oxidizing Fe(III)-reducers that compete in anoxic subsurface environments and this competition may have an influence on the in situ bioremediation of uranium-contaminated groundwater. Therefore, genome-scale models of Geobacter sulfurreducens and Rhodoferax ferrireducens were used to evaluate how Geobacter and Rhodoferax species might compete under diverse conditions found in a uranium-contaminated aquifer in Rifle, CO. The model predicted that at the low rates of acetate flux expected under natural conditions at the site, Rhodoferax will outcompete Geobacter as long as sufficient ammonium is available. The model also predicted that when high concentrations of acetate are added during in situ bioremediation, Geobacter species would predominate, consistent with field-scale observations. This can be attributed to the higher expected growth yields of Rhodoferax and the ability of Geobacter to fix nitrogen. The modeling predicted relative proportions of Geobacter and Rhodoferax in geochemically distinct zones of the Rifle site that were comparable to those that were previously documented with molecular techniques. The model also predicted that under nitrogen fixation, higher carbon and electron fluxes would be diverted toward respiration rather than biomass formation in Geobacter, providing a potential explanation for enhanced in situ U(VI) reduction in low-ammonium zones. These results show that genome-scale modeling can be a useful tool for predicting microbial interactions in subsurface environments and shows promise for designing bioremediation strategies.
Liggett, Jessica E.; Knowling, Matthew J.; Werner, Adrian D.; Simmons, Craig T.
2013-07-01
In physically based catchment hydrology models, dynamic surface-subsurface interactions are often represented using the surface conductance (SC) coupling approach. Guidance on SC parameterisation within block-centred codes is limited, and common practice is to express the SC coefficient as the quotient of the vertical saturated hydraulic conductivity and the half-cell thickness of the uppermost layer. This study evaluates the implementation of the SC approach utilising a popular block-centred, surface-subsurface hydrology model (MODHMS) to simulate one-dimensional infiltration experiments under Hortonian conditions. Results show that defining the SC coefficient based on a half-cell thickness of the uppermost subsurface cell inhibits accurate prediction of infiltration rates (qe) and the time to initiate surface runoff (tro) for the adopted rainfall-runoff scenario. Increasing the SC coefficient independently of the grid allows for accurate simulation of qe, but not tro. The addition of a thin layer at the surface is shown to improve model accuracy substantially, such that qe and tro approach those obtained using an equivalent mesh-centred model (i.e. where the surface and upper subsurface nodes are coincident). Whilst the addition of a single thin layer in block-centred codes allows improved prediction of surface-subsurface interaction, it does not provide a surrogate for fine discretisation throughout the subsurface that is necessary for accurate simulation of unsaturated zone flow. This study offers guidance on the implementation of the SC approach in a block-centred code and demonstrates the importance of systematic testing of parameters (that are otherwise calibrated) in physically based surface-subsurface hydrology models.
Dean, D. W.; Illangasekare, T. H.; Turner, A.; Russell, T. F.
2004-12-01
Modeling of the complex behavior of DNAPLs in naturally heterogeneous subsurface formations poses many challenges. Even though considerable progress have been made in developing improved numerical schemes to solve the governing partial differential equations, most of these methods still rely on deterministic description of the processes. This research explores the use of stochastic differential equations to model multiphase flow in heterogeneous aquifers, specifically the flow of DNAPLs in saturated soils. The models developed are evaluated using experimental data generated in two-dimensional test systems. A fundamental assumption used in the model formulation is that the movement of a fluid particle in each phase is described by a stochastic process and that the positions of all fluid particles over time are governed by a specific law. It is this law, which we seek to determine. The approach results in a nonlinear stochastic differential equation describing the position of the non-wetting phase fluid particle. The nonlinearity in the stochastic differential equation arises because both the drift and diffusion coefficients depend on the volumetric fraction of the phase, which in turn depends on the position of the fluid particles in the problem domain. The concept of a fluid particle is central to the development of the proposed model. Expressions for both saturation and volumetric fraction are developed using this concept of fluid particle. Darcy's law and the continuity equation are used to derive a Fokker-Planck equation governing flow. The Ito calculus is then applied to derive a stochastic differential equation(SDE) for the non-wetting phase. This SDE has both drift and diffusion terms which depend on the volumetric fraction of the non-wetting phase. Standard stochastic theories based on the Ito calculus and the Wiener process and the equivalent Fokker-Planck PDE's are typically used to model diffusion processes. However, these models, in their usual form
An iterative stochastic ensemble method for parameter estimation of subsurface flow models
Elsheikh, Ahmed H.
2013-06-01
Parameter estimation for subsurface flow models is an essential step for maximizing the value of numerical simulations for future prediction and the development of effective control strategies. We propose the iterative stochastic ensemble method (ISEM) as a general method for parameter estimation based on stochastic estimation of gradients using an ensemble of directional derivatives. ISEM eliminates the need for adjoint coding and deals with the numerical simulator as a blackbox. The proposed method employs directional derivatives within a Gauss-Newton iteration. The update equation in ISEM resembles the update step in ensemble Kalman filter, however the inverse of the output covariance matrix in ISEM is regularized using standard truncated singular value decomposition or Tikhonov regularization. We also investigate the performance of a set of shrinkage based covariance estimators within ISEM. The proposed method is successfully applied on several nonlinear parameter estimation problems for subsurface flow models. The efficiency of the proposed algorithm is demonstrated by the small size of utilized ensembles and in terms of error convergence rates. © 2013 Elsevier Inc.
Energy Technology Data Exchange (ETDEWEB)
Ye, Sheng; Li, Hongyi; Huang, Maoyi; Ali, Melkamu; Leng, Guoyong; Leung, Lai-Yung R.; Wang, Shaowen; Sivapalan, Murugesu
2014-07-21
Subsurface stormflow is an important component of the rainfall–runoff response, especially in steep terrain. Its contribution to total runoff is, however, poorly represented in the current generation of land surface models. The lack of physical basis of these common parameterizations precludes a priori estimation of the stormflow (i.e. without calibration), which is a major drawback for prediction in ungauged basins, or for use in global land surface models. This paper is aimed at deriving regionalized parameterizations of the storage–discharge relationship relating to subsurface stormflow from a top–down empirical data analysis of streamflow recession curves extracted from 50 eastern United States catchments. Detailed regression analyses were performed between parameters of the empirical storage–discharge relationships and the controlling climate, soil and topographic characteristics. The regression analyses performed on empirical recession curves at catchment scale indicated that the coefficient of the power-law form storage–discharge relationship is closely related to the catchment hydrologic characteristics, which is consistent with the hydraulic theory derived mainly at the hillslope scale. As for the exponent, besides the role of field scale soil hydraulic properties as suggested by hydraulic theory, it is found to be more strongly affected by climate (aridity) at the catchment scale. At a fundamental level these results point to the need for more detailed exploration of the co-dependence of soil, vegetation and topography with climate.
A "mental models" approach to the communication of subsurface hydrology and hazards
Gibson, Hazel; Stewart, Iain S.; Pahl, Sabine; Stokes, Alison
2016-05-01
Communicating information about geological and hydrological hazards relies on appropriately worded communications targeted at the needs of the audience. But what are these needs, and how does the geoscientist discern them? This paper adopts a psychological "mental models" approach to assess the public perception of the geological subsurface, presenting the results of attitudinal studies and surveys in three communities in the south-west of England. The findings reveal important preconceptions and misconceptions regarding the impact of hydrological systems and hazards on the geological subsurface, notably in terms of the persistent conceptualisation of underground rivers and the inferred relations between flooding and human activity. The study demonstrates how such mental models can provide geoscientists with empirical, detailed and generalised data of perceptions surrounding an issue, as well reveal unexpected outliers in perception that they may not have considered relevant, but which nevertheless may locally influence communication. Using this approach, geoscientists can develop information messages that more directly engage local concerns and create open engagement pathways based on dialogue, which in turn allow both geoscience "experts" and local "non-experts" to come together and understand each other more effectively.
Gorbatikov, A. V.; Montesinos, F. G.; Arnoso, J.; Stepanova, M. Yu; Benavent, M.; Tsukanov, A. A.
2013-07-01
To study the deep structure of El Hierro Island, Canarian Archipelago, we have used a microseismic sounding method (MSM) based on the fact that heterogeneities of the Earth's crust disturb the spectrum of the low-frequency microseismic field in their vicinity. So, at the Earth's surface, the spectral amplitudes of definite frequency f above the high-velocity heterogeneities are decreasing, and above the low-velocity ones they are increasing. Moreover, the frequency f is connected with the depth of a heterogeneity H and the velocity of the fundamental mode of Rayleigh waves V R( f) through the relation H ≈ 0.4 V R( f)/ f. From these relations, the MSM lets us model the subsurface structure in a 3D context by inverting the amplitude-frequency spatial distribution of the microseismic field of low frequency. The validity of the method is shown through of numerical simulations and previous applications with known or verified solutions. This MSM is now used to invert the microseismic data registered in El Hierro Island. The obtained subsurface model reveals two large intrusive bodies beneath the island. Joint interpretation of microseismic and gravimetric data and their comparison with the available geological studies relate the central-eastern intrusive body to the early stage of the island formation. With respect to the western intrusive body, at the depths of 15-25 km, an area with lowest seismic velocities is identified, where we suggest that a modern magmatic reservoir is located. This reservoir could be associated with the recent submarine eruption in October 2011 and the accompanying seismic swarm, which started in July 2011. Several correlations between the shallowest structures identified by the gravity and MSM approaches are also found. Besides the numerical simulation and previous studies of this method, the correlation between gravity results, the MSM model, the geological information and the possible explanation of the features of the seismic swarm through
Formal heterogeneous system modeling with SystemC
DEFF Research Database (Denmark)
Niaki, Seyed Hosein Attarzadeh; Jakobsen, Mikkel Koefoed; Sulonen, Tero;
2012-01-01
Electronic System Level (ESL) design of embedded systems proposes raising the abstraction level of the design entry to cope with the increasing complexity of such systems. To exploit the benefits of ESL, design languages should allow specification of models which are a) heterogeneous, to describe...... different aspects of systems; b) formally defined, for application of analysis and synthesis methods; c) executable, to enable early detection of specification; and d) parallel, to exploit the multi- and many-core platforms for simulation and implementation. We present a modeling library on top of System......C, targeting heterogeneous embedded system design, based on four models of computation. The library has a formal basis where all elements are well defined and lead in construction of analyzable models. The semantics of communication and computation are implemented by the library, which allows the designer...
Finite mixture varying coefficient models for analyzing longitudinal heterogenous data.
Lu, Zhaohua; Song, Xinyuan
2012-03-15
This paper aims to develop a mixture model to study heterogeneous longitudinal data on the treatment effect of heroin use from a California Civil Addict Program. Each component of the mixture is characterized by a varying coefficient mixed effect model. We use the Bayesian P-splines approach to approximate the varying coefficient functions. We develop Markov chain Monte Carlo algorithms to estimate the smooth functions, unknown parameters, and latent variables in the model. We use modified deviance information criterion to determine the number of components in the mixture. A simulation study demonstrates that the modified deviance information criterion selects the correct number of components and the estimation of unknown quantities is accurate. We apply the proposed model to the heroin treatment study. Furthermore, we identify heterogeneous longitudinal patterns.
Averaging principle for second-order approximation of heterogeneous models with homogeneous models.
Fibich, Gadi; Gavious, Arieh; Solan, Eilon
2012-11-27
Typically, models with a heterogeneous property are considerably harder to analyze than the corresponding homogeneous models, in which the heterogeneous property is replaced by its average value. In this study we show that any outcome of a heterogeneous model that satisfies the two properties of differentiability and symmetry is O(ε(2)) equivalent to the outcome of the corresponding homogeneous model, where ε is the level of heterogeneity. We then use this averaging principle to obtain new results in queuing theory, game theory (auctions), and social networks (marketing).
Hydraulic fracturing fluid migration in the subsurface: A review and expanded modeling results
Birdsell, Daniel T.; Rajaram, Harihar; Dempsey, David; Viswanathan, Hari S.
2015-09-01
Understanding the transport of hydraulic fracturing (HF) fluid that is injected into the deep subsurface for shale gas extraction is important to ensure that shallow drinking water aquifers are not contaminated. Topographically driven flow, overpressured shale reservoirs, permeable pathways such as faults or leaky wellbores, the increased formation pressure due to HF fluid injection, and the density contrast of the HF fluid to the surrounding brine can encourage upward HF fluid migration. In contrast, the very low shale permeability and capillary imbibition of water into partially saturated shale may sequester much of the HF fluid, and well production will remove HF fluid from the subsurface. We review the literature on important aspects of HF fluid migration. Single-phase flow and transport simulations are performed to quantify how much HF fluid is removed via the wellbore with flowback and produced water, how much reaches overlying aquifers, and how much is permanently sequestered by capillary imbibition, which is treated as a sink term based on a semianalytical, one-dimensional solution for two-phase flow. These simulations include all of the important aspects of HF fluid migration identified in the literature review and are performed in five stages to faithfully represent the typical operation of a hydraulically fractured well. No fracturing fluid reaches the aquifer without a permeable pathway. In the presence of a permeable pathway, 10 times more fracturing fluid reaches the aquifer if well production and capillary imbibition are not included in the model.
Application of screening model for assessing subsurface NAPL contamination and remediation
Energy Technology Data Exchange (ETDEWEB)
MacFarlane, S.; Shiu, W.Y. [Univ. of Toronto, Ontario (Canada); Mackay, D. [Trent Univ., Peterborough, Ontario (Canada)
1997-12-31
To select the most appropriate technique for remediating non-aqueous phase liquids (NAPL)-contaminated sites a full understanding is required of the characteristics of the site, the contaminant, and the effectiveness of the remedial measure. A screening model has been developed (MacFarlane and Mackay, in press) for evaluating the partitioning of components of NAPLs present in the subsurface environment and for providing order of magnitude estimates of the effectiveness, in terms of recovery time, of a variety of remedial technologies including water and solvent flushing, air and steam stripping, and enhanced degradation. The model calculations employ the fugacity concept which is found to simplify and clarify the calculations. Two types of calculations are employed in the screening assessment. Level 1 fugacity calculations are simple multimedia equilibrium calculations that deduce how a chemical partitions between media or phases in a defined environment. Level 2 fugacity calculations account for or quantify losses of chemical being conveyed out of the environment by advective flows in phases such as air or water or by degradation by chemical or biochemical reactions. The screening model was originally applied to an existing fractured bedrock site in Smithville, Ontario which is contaminated with a NAPL containing polychlorinated biphenyls, trichlorobenzene, and trichloroethylene. In this paper, the model approach is illustrated for vinyl chloride which may be present at the site due to biochemical reactions occurring in the subsurface. It is their aim to show that this approach can provide screening level insights into the behavior and remediation of NAPLs and can serve as a first step and justification towards more detailed modeling.
Kerschke, Dorit; Schilling, Maik; Simon, Andreas; Wächter, Joachim
2014-05-01
application enables an intuitive navigation through all available information and allows the visualization of geological maps (2D), seismic transects (2D/3D), wells (2D/3D), and the 3D-model. These achievements will alleviate spatial and geological data management within the German State Geological Offices and foster the interoperability of heterogeneous systems. It will provide guidance to a systematic subsurface management across system, domain and administrative boundaries on the basis of a federated spatial data infrastructure, and include the public in the decision processes (e-Governance). Yet, the interoperability of the systems has to be strongly propelled forward through agreements on standards that need to be decided upon in responsible committees. The project B3D is funded with resources from the European Fund for Regional Development (EFRE).
Heterogeneous models place the root of the placental mammal phylogeny.
Morgan, Claire C; Foster, Peter G; Webb, Andrew E; Pisani, Davide; McInerney, James O; O'Connell, Mary J
2013-09-01
Heterogeneity among life traits in mammals has resulted in considerable phylogenetic conflict, particularly concerning the position of the placental root. Layered upon this are gene- and lineage-specific variation in amino acid substitution rates and compositional biases. Life trait variations that may impact upon mutational rates are longevity, metabolic rate, body size, and germ line generation time. Over the past 12 years, three main conflicting hypotheses have emerged for the placement of the placental root. These hypotheses place the Atlantogenata (common ancestor of Xenarthra plus Afrotheria), the Afrotheria, or the Xenarthra as the sister group to all other placental mammals. Model adequacy is critical for accurate tree reconstruction and by failing to account for these compositional and character exchange heterogeneities across the tree and data set, previous studies have not provided a strongly supported hypothesis for the placental root. For the first time, models that accommodate both tree and data set heterogeneity have been applied to mammal data. Here, we show the impact of accurate model assignment and the importance of data sets in accommodating model parameters while maintaining the power to reject competing hypotheses. Through these sophisticated methods, we demonstrate the importance of model adequacy, data set power and provide strong support for the Atlantogenata over other competing hypotheses for the position of the placental root.
Clustered iterative stochastic ensemble method for multi-modal calibration of subsurface flow models
Elsheikh, Ahmed H.
2013-05-01
A novel multi-modal parameter estimation algorithm is introduced. Parameter estimation is an ill-posed inverse problem that might admit many different solutions. This is attributed to the limited amount of measured data used to constrain the inverse problem. The proposed multi-modal model calibration algorithm uses an iterative stochastic ensemble method (ISEM) for parameter estimation. ISEM employs an ensemble of directional derivatives within a Gauss-Newton iteration for nonlinear parameter estimation. ISEM is augmented with a clustering step based on k-means algorithm to form sub-ensembles. These sub-ensembles are used to explore different parts of the search space. Clusters are updated at regular intervals of the algorithm to allow merging of close clusters approaching the same local minima. Numerical testing demonstrates the potential of the proposed algorithm in dealing with multi-modal nonlinear parameter estimation for subsurface flow models. © 2013 Elsevier B.V.
Temperature dependence of heterogeneous nucleation: Extension of the Fletcher model
McGraw, Robert; Winkler, Paul; Wagner, Paul
2015-04-01
Recently there have been several cases reported where the critical saturation ratio for onset of heterogeneous nucleation increases with nucleation temperature (positive slope dependence). This behavior contrasts with the behavior observed in homogeneous nucleation, where a decreasing critical saturation ratio with increasing nucleation temperature (negative slope dependence) seems universal. For this reason the positive slope dependence is referred to as anomalous. Negative slope dependence is found in heterogeneous nucleation as well, but because so few temperature-dependent measurements have been reported, it is not presently clear which slope condition (positive or negative) will become more frequent. Especially interesting is the case of water vapor condensation on silver nanoparticles [Kupc et al., AS&T 47: i-iv, 2013] where the critical saturation ratio for heterogeneous nucleation onset passes through a maximum, at about 278K, with higher (lower) temperatures showing the usual (anomalous) temperature dependence. In the present study we develop an extension of Fletcher's classical, capillarity-based, model of heterogeneous nucleation that explicitly resolves the roles of surface energy and surface entropy in determining temperature dependence. Application of the second nucleation theorem, which relates temperature dependence of nucleation rate to cluster energy, yields both necessary and sufficient conditions for anomalous temperature behavior in the extended Fletcher model. In particular it is found that an increasing contact angle with temperature is a necessary, but not sufficient, condition for anomalous temperature dependence to occur. Methods for inferring microscopic contact angle and its temperature dependence from heterogeneous nucleation probability measurements are discussed in light of the new theory.
The value of "black-box" neural network modeling in subsurface flow prediction
Paleologos, E.; Skitzi, I.; Katsifarakis, K.
2012-04-01
In several hydrologic cases the complexity of the processes involved tied in with the uncertainty in the subsurface geologic environment, geometries, and boundary conditions cannot be addressed by constitutive relationships, either in a deterministic or a stochastic framework. "Black-box" models are used routinely in surface hydrologic predictions, but in subsurface hydrology there is still a tendency to rely on physical descriptions, even in problems where the geometry, the medium, the processes, the boundary conditions are largely unknown. Subsurface flow in karstic environments exemplifies all the above complexities and uncertainties rendering the use of physical models impractical. The current study uses neural networks to exemplify that "black-box" models can provide useful predictions even in the absence of physical process descriptions. Daily discharges of two springs lying in a karstic environment were simulated for a period of two and a half years with the use of a multi-layer perceptron back-propagation neural network. Missing discharge values were supplemented by assuming linear relationships during base flow conditions, thus extending the length of the data record during the network's training phase and improving its performance. The time lag between precipitation and spring discharge differed significantly for the two springs indicating that in karstic environments hydraulic behavior is dominated, even within a few hundred meters, by local conditions. Optimum training results were attained with a Levenberg-Marquardt algorithm resulting in a network architecture consisting of two input layer neurons, four hidden layer neurons, and one output layer neuron, the spring's discharge. The neural network's predictions captured the behavior for both springs and followed very closely the discontinuities in the discharge time series. Under/over-estimation of observed discharges for the two springs remained below 3%, with the exception of a few local maxima where
Modelling heat transfer in heterogeneous media using fractional calculus.
Sierociuk, Dominik; Dzielinski, Andrzej; Sarwas, Grzegorz; Petras, Ivo; Podlubny, Igor; Skovranek, Tomas
2013-05-13
This paper presents the results of modelling the heat transfer process in heterogeneous media with the assumption that part of the heat flux is dispersed in the air around the beam. The heat transfer process in a solid material (beam) can be described by an integer order partial differential equation. However, in heterogeneous media, it can be described by a sub- or hyperdiffusion equation which results in a fractional order partial differential equation. Taking into consideration that part of the heat flux is dispersed into the neighbouring environment we additionally modify the main relation between heat flux and the temperature, and we obtain in this case the heat transfer equation in a new form. This leads to the transfer function that describes the dependency between the heat flux at the beginning of the beam and the temperature at a given distance. This article also presents the experimental results of modelling real plant in the frequency domain based on the obtained transfer function.
A Unified Access Model for Interconnecting Heterogeneous Wireless Networks
2015-05-01
with each other via a central controller. The 2 access technologies used were 802.11 ( WiFi ) and a Carrier-Sense Multiple Access (CSMA) protocol ...wireless subnets could communicate with each other. 3. Results and Discussion Using the 3-VM LTE/ WiFi configuration, we placed a User Datagram Protocol ...control plane protocols . A network model that can abstract disparate MAC layers in heterogeneous networks and interconnect them using a unified and
Jago-on, Karen Ann Bianet; Kaneko, Shinji; Fujikura, Ryo; Fujiwara, Akimasa; Imai, Tsuyoshi; Matsumoto, Toru; Zhang, Junyi; Tanikawa, Hiroki; Tanaka, Katsuya; Lee, Backjin; Taniguchi, Makoto
2009-04-15
This paper synthesizes existing information and knowledge on subsurface environments to understand the major cause and effect relationships of subsurface environmental issues by using the DPSIR (Driving force-Pressure-Status-Impact-Response) approach as the framework of analysis. Description is given to the major subsurface environmental issues common among the selected Asian cities (Bangkok, Jakarta, Manila, Osaka, Seoul, Taipei and Tokyo), such as excessive groundwater abstraction, land subsidence and groundwater contamination. The DPSIR framework is used to analyze the issues and problems of subsurface in key stages and suggestions are made for additional indicators to improve our description of the stages of urban development for the future.
Shrestha, R. R.; Rode, M.
2008-12-01
Concentration of reactive chemicals has different chemical signatures in baseflow and surface runoff. Previous studies on nitrate export from a catchment indicate that the transport processes are driven by subsurface flow. Therefore nitrate signature can be used for understanding the event and pre-event contributions to streamflow and surface-subsurface flow interactions. The study uses flow and nitrate concentration time series data for understanding the relationship between these two variables. Unsupervised artificial neural network based learning method called self organizing map is used for the identification of clusters in the datasets. Based on the cluster results, five different pattern in the datasets are identified which correspond to (i) baseflow, (ii) subsurface flow increase, (iii) surface runoff increase, (iv) surface runoff recession, and (v) subsurface flow decrease regions. The cluster results in combination with a hydrologic model are used for discharge separation. For this purpose, a multi-objective optimization tool NSGA-II is used, where violation of cluster results is used as one of the objective functions. The results show that the use of cluster results as supplementary information for the calibration of a hydrologic model gives a plausible simulation of subsurface flow as well total runoff at the catchment outlet. The study is undertaken using data from the Weida catchment in the North-Eastern Germany, which is a sub-catchment of the Weisse Elster river in the Elbe river basin.
Wienhöfer, J.; Zehe, E.
2012-04-01
Rapid lateral flow processes via preferential flow paths are widely accepted to play a key role for rainfall-runoff response in temperate humid headwater catchments. A quantitative description of these processes, however, is still a major challenge in hydrological research, not least because detailed information about the architecture of subsurface flow paths are often impossible to obtain at a natural site without disturbing the system. Our study combines physically based modelling and field observations with the objective to better understand how flow network configurations influence the hydrological response of hillslopes. The system under investigation is a forested hillslope with a small perennial spring at the study area Heumöser, a headwater catchment of the Dornbirnerach in Vorarlberg, Austria. In-situ points measurements of field-saturated hydraulic conductivity and dye staining experiments at the plot scale revealed that shrinkage cracks and biogenic macropores function as preferential flow paths in the fine-textured soils of the study area, and these preferential flow structures were active in fast subsurface transport of artificial tracers at the hillslope scale. For modelling of water and solute transport, we followed the approach of implementing preferential flow paths as spatially explicit structures of high hydraulic conductivity and low retention within the 2D process-based model CATFLOW. Many potential configurations of the flow path network were generated as realisations of a stochastic process informed by macropore characteristics derived from the plot scale observations. Together with different realisations of soil hydraulic parameters, this approach results in a Monte Carlo study. The model setups were used for short-term simulation of a sprinkling and tracer experiment, and the results were evaluated against measured discharges and tracer breakthrough curves. Although both criteria were taken for model evaluation, still several model setups
Dual states estimation of a subsurface flow-transport coupled model using ensemble Kalman filtering
El Gharamti, Mohamad
2013-10-01
Modeling the spread of subsurface contaminants requires coupling a groundwater flow model with a contaminant transport model. Such coupling may provide accurate estimates of future subsurface hydrologic states if essential flow and contaminant data are assimilated in the model. Assuming perfect flow, an ensemble Kalman filter (EnKF) can be used for direct data assimilation into the transport model. This is, however, a crude assumption as flow models can be subject to many sources of uncertainty. If the flow is not accurately simulated, contaminant predictions will likely be inaccurate even after successive Kalman updates of the contaminant model with the data. The problem is better handled when both flow and contaminant states are concurrently estimated using the traditional joint state augmentation approach. In this paper, we introduce a dual estimation strategy for data assimilation into a one-way coupled system by treating the flow and the contaminant models separately while intertwining a pair of distinct EnKFs, one for each model. The presented strategy only deals with the estimation of state variables but it can also be used for state and parameter estimation problems. This EnKF-based dual state-state estimation procedure presents a number of novel features: (i) it allows for simultaneous estimation of both flow and contaminant states in parallel; (ii) it provides a time consistent sequential updating scheme between the two models (first flow, then transport); (iii) it simplifies the implementation of the filtering system; and (iv) it yields more stable and accurate solutions than does the standard joint approach. We conducted synthetic numerical experiments based on various time stepping and observation strategies to evaluate the dual EnKF approach and compare its performance with the joint state augmentation approach. Experimental results show that on average, the dual strategy could reduce the estimation error of the coupled states by 15% compared with the
A cellular automata model of epidemics of a heterogeneous susceptibility
Institute of Scientific and Technical Information of China (English)
Jin Zhen; Liu Quan-Xing
2006-01-01
In this paper we present a model with spatial heterogeneity based on cellular automata (CA). In the model we consider the relevant heterogeneity of host (susceptible) mixing and the natural birth rate. We divide the susceptible population into three groups according to the immunity of each individual based on the classical susceptible-infectedremoved (SIR) epidemic models, and consider the spread of an infectious disease transmitted by direct contact among humans and vectors that have not an incubation period to become infectious. We test the local stability and instability of the disease-free equilibrium by the spectrum radii of Jacobian. The simulation shows that the structure of the nearest neighbour size of the cell (or the degree of the scale-free networks) plays a very important role in the spread properties of infectious disease. The positive equilibrium of the infections versus the neighbour size follows the third power law if an endemic equilibrium point exists. Finally, we analyse the feature of the infection waves for the homogeneity and heterogeneous cases respectively.
Energy Technology Data Exchange (ETDEWEB)
C Kantar; H Demiray; N Dogan; C Dodge
2011-12-31
Chromium (III) binding by exopolymeric substances (EPS) isolated from Pseudomonas putida P18, Pseudomonas aeruginosa P16 and Pseudomonas stutzeri P40 strains were investigated by the determination of conditional stability constants and the concentration of functional groups using the ion-exchange experiments and potentiometric titrations. Spectroscopic (EXAFS) analysis was also used to obtain information on the nature of Cr(III) binding with EPS functional groups. The data from ion-exchange experiments and potentiometric titrations were evaluated using a non-electrostatic discrete ligand approach. The modeling results show that the acid/base properties of EPSs can be best characterized by invoking four different types of acid functional groups with arbitrarily assigned pK{sub a} values of 4, 6, 8 and 10. The analysis of ion-exchange data using the discrete ligand approach suggests that while the Cr binding by EPS from P. aeruginosa can be successfully described based on a reaction stoichiometry of 1:2 between Cr(III) and HL{sub 2} monoprotic ligands, the accurate description of Cr binding by EPSs extracted from P. putida and P. stutzeri requires postulation of 1:1 Cr(III)-ligand complexes with HL{sub 2} and HL{sub 3} monoprotic ligands, respectively. These results indicate that the carboxyl and/or phosphoric acid sites contribute to Cr(III) binding by microbial EPS, as also confirmed by EXAFS analysis performed in the current study. Overall, this study highlights the need for incorporation of Cr-EPS interactions into transport and speciation models to more accurately assess microbial Cr(VI) reduction and chromium transport in subsurface systems, including microbial reactive treatment barriers.
Energy Technology Data Exchange (ETDEWEB)
Kantar, C.; Dodge, C.; Demiray, H.; Dogan, N.M.
2011-01-26
Chromium (III) binding by exopolymeric substances (EPS) isolated from Pseudomonas putida P18, Pseudomonas aeruginosa P16 and Pseudomonas stutzeri P40 strains were investigated by the determination of conditional stability constants and the concentration of functional groups using the ion-exchange experiments and potentiometric titrations. Spectroscopic (EXAFS) analysis was also used to obtain information on the nature of Cr(III) binding with EPS functional groups. The data from ion-exchange experiments and potentiometric titrations were evaluated using a non-electrostatic discrete ligand approach. The modeling results show that the acid/base properties of EPSs can be best characterized by invoking four different types of acid functional groups with arbitrarily assigned pK{sub a} values of 4, 6, 8 and 10. The analysis of ion-exchange data using the discrete ligand approach suggests that while the Cr binding by EPS from P. aeruginosa can be successfully described based on a reaction stoichiometry of 1:2 between Cr(III) and HL{sub 2} monoprotic ligands, the accurate description of Cr binding by EPSs extracted from P. putida and P. stutzeri requires postulation of 1:1 Cr(III)-ligand complexes with HL{sub 2} and HL{sub 3} monoprotic ligands, respectively. These results indicate that the carboxyl and/or phosphoric acid sites contribute to Cr(III) binding by microbial EPS, as also confirmed by EXAFS analysis performed in the current study. Overall, this study highlights the need for incorporation of Cr-EPS interactions into transport and speciation models to more accurately assess microbial Cr(VI) reduction and chromium transport in subsurface systems, including microbial reactive treatment barriers.
Kantar, Cetin; Demiray, Hilal; Dogan, Nazime Mercan; Dodge, Cleveland J
2011-03-01
Chromium (III) binding by exopolymeric substances (EPS) isolated from Pseudomonas putida P18, Pseudomonas aeruginosa P16 and Pseudomonas stutzeri P40 strains were investigated by the determination of conditional stability constants and the concentration of functional groups using the ion-exchange experiments and potentiometric titrations. Spectroscopic (EXAFS) analysis was also used to obtain information on the nature of Cr(III) binding with EPS functional groups. The data from ion-exchange experiments and potentiometric titrations were evaluated using a non-electrostatic discrete ligand approach. The modeling results show that the acid/base properties of EPSs can be best characterized by invoking four different types of acid functional groups with arbitrarily assigned pK(a) values of 4, 6, 8 and 10. The analysis of ion-exchange data using the discrete ligand approach suggests that while the Cr binding by EPS from P. aeruginosa can be successfully described based on a reaction stoichiometry of 1:2 between Cr(III) and HL(2) monoprotic ligands, the accurate description of Cr binding by EPSs extracted from P. putida and P. stutzeri requires postulation of 1:1 Cr(III)-ligand complexes with HL(2) and HL(3) monoprotic ligands, respectively. These results indicate that the carboxyl and/or phosphoric acid sites contribute to Cr(III) binding by microbial EPS, as also confirmed by EXAFS analysis performed in the current study. Overall, this study highlights the need for incorporation of Cr-EPS interactions into transport and speciation models to more accurately assess microbial Cr(VI) reduction and chromium transport in subsurface systems, including microbial reactive treatment barriers.
Brunetti, Carlotta; Linde, Niklas; Vrugt, Jasper A.
2017-04-01
Geophysical data can help to discriminate among multiple competing subsurface hypotheses (conceptual models). Here, we explore the merits of Bayesian model selection in hydrogeophysics using crosshole ground-penetrating radar data from the South Oyster Bacterial Transport Site in Virginia, USA. Implementation of Bayesian model selection requires computation of the marginal likelihood of the measured data, or evidence, for each conceptual model being used. In this paper, we compare three different evidence estimators, including (1) the brute force Monte Carlo method, (2) the Laplace-Metropolis method, and (3) the numerical integration method proposed by Volpi et al. (2016). The three types of subsurface models that we consider differ in their treatment of the porosity distribution and use (a) horizontal layering with fixed layer thicknesses, (b) vertical layering with fixed layer thicknesses and (c) a multi-Gaussian field. Our results demonstrate that all three estimators provide equivalent results in low parameter dimensions, yet in higher dimensions the brute force Monte Carlo method is inefficient. The isotropic multi-Gaussian model is most supported by the travel time data with Bayes factors that are larger than 10100 compared to conceptual models that assume horizontal or vertical layering of the porosity field.
Davison, Jason H.; Hwang, Hyoun-Tae; Sudicky, Edward A.; Lin, John C.
2015-12-01
Human activities amplified by climate change pose a significant threat to the sustainability of water resources. Coupled climate-hydrologic simulations commonly predict these threats by combining shallow 1-D land surface models (LSMs) with traditional 2-D and 3-D hydrology models. However, these coupled models limit the moisture and energy-feedback dynamics to the shallow near-surface. This paper presents a novel analysis by applying an integrated variably-saturated subsurface/surface hydrology and heat transport model, HydroGeoSphere (HGS), as a land surface model (LSM). Furthermore, this article demonstrates the coupling of HGS to a simple 0-D atmospheric boundary layer (ABL) model. We then applied our coupled HGS-ABL model to three separate test cases and reproduced the strong correlation between the atmospheric energy balance to the depth of the groundwater table. From our simulations, we found that conventional LSMs may overestimate surface temperatures for extended drought periods because they underestimate the heat storage in the groundwater zone. Our final test case of the atmospheric response to drought conditions illustrated that deeper roots buffered the atmosphere better than shallow roots by maintaining higher latent heat fluxes, lower sensible heat fluxes, and lower surface and atmospheric temperatures.
A coupled surface/subsurface flow model accounting for air entrapment and air pressure counterflow
DEFF Research Database (Denmark)
Delfs, Jens Olaf; Wang, Wenqing; Kalbacher, Thomas
2013-01-01
This work introduces the soil air system into integrated hydrology by simulating the flow processes and interactions of surface runoff, soil moisture and air in the shallow subsurface. The numerical model is formulated as a coupled system of partial differential equations for hydrostatic (diffusive...... algorithm, leakances operate as a valve for gas pressure in a liquid-covered porous medium facilitating the simulation of air out-break events through the land surface. General criteria are stated to guarantee stability in a sequential iterative coupling algorithm and, in addition, for leakances to control...... the mass exchange between compartments. A benchmark test, which is based on a classic experimental data set on infiltration excess (Horton) overland flow, identified a feedback mechanism between surface runoff and soil air pressures. Our study suggests that air compression in soils amplifies surface runoff...
Design and Implementation of “Many Parallel Task” Hybrid Subsurface Model
Energy Technology Data Exchange (ETDEWEB)
Agarwal, Khushbu; Chase, Jared M.; Schuchardt, Karen L.; Scheibe, Timothy D.; Palmer, Bruce J.; Elsethagen, Todd O.
2011-11-01
Continuum scale models have been used to study subsurface flow, transport, and reactions for many years. Recently, pore scale models, which operate at scales of individual soil grains, have been developed to more accurately model pore scale phenomena, such as precipitation, that may not be well represented at the continuum scale. However, particle-based models become prohibitively expensive for modeling realistic domains. Instead, we are developing a hybrid model that simulates the full domain at continuum scale and applies the pore model only to areas of high reactivity. The hybrid model uses a dimension reduction approach to formulate the mathematical exchange of information across scales. Since the location, size, and number of pore regions in the model varies, an adaptive Pore Generator is being implemented to define pore regions at each iteration. A fourth code will provide data transformation from the pore scale back to the continuum scale. These components are coupled into a single hybrid model using the SWIFT workflow system. Our hybrid model workflow simulates a kinetic controlled mixing reaction in which multiple pore-scale simulations occur for every continuum scale timestep. Each pore-scale simulation is itself parallel, thus exhibiting multi-level parallelism. Our workflow manages these multiple parallel tasks simultaneously, with the number of tasks changing across iterations. It also supports dynamic allocation of job resources and visualization processing at each iteration. We discuss the design, implementation and challenges associated with building a scalable, Many Parallel Task, hybrid model to run efficiently on thousands to tens of thousands of processors.
Personalized heterogeneous deformable model for fast volumetric registration.
Si, Weixin; Liao, Xiangyun; Wang, Qiong; Heng, Pheng Ann
2017-02-20
Biomechanical deformable volumetric registration can help improve safety of surgical interventions by ensuring the operations are extremely precise. However, this technique has been limited by the accuracy and the computational efficiency of patient-specific modeling. This study presents a tissue-tissue coupling strategy based on penalty method to model the heterogeneous behavior of deformable body, and estimate the personalized tissue-tissue coupling parameters in a data-driven way. Moreover, considering that the computational efficiency of biomechanical model is highly dependent on the mechanical resolution, a practical coarse-to-fine scheme is proposed to increase runtime efficiency. Particularly, a detail enrichment database is established in an offline fashion to represent the mapping relationship between the deformation results of high-resolution hexahedral mesh extracted from the raw medical data and a newly constructed low-resolution hexahedral mesh. At runtime, the mechanical behavior of human organ under interactions is simulated with this low-resolution hexahedral mesh, then the microstructures are synthesized in virtue of the detail enrichment database. The proposed method is validated by volumetric registration in an abdominal phantom compression experiments. Our personalized heterogeneous deformable model can well describe the coupling effects between different tissues of the phantom. Compared with high-resolution heterogeneous deformable model, the low-resolution deformable model with our detail enrichment database can achieve 9.4× faster, and the average target registration error is 3.42 mm, which demonstrates that the proposed method shows better volumetric registration performance than state-of-the-art. Our framework can well balance the precision and efficiency, and has great potential to be adopted in the practical augmented reality image-guided robotic systems.
Macheras, Panos
2016-01-01
The state of the art in Biopharmaceutics, Pharmacokinetics, and Pharmacodynamics Modeling is presented in this new second edition book. It shows how advanced physical and mathematical methods can expand classical models in order to cover heterogeneous drug-biological processes and therapeutic effects in the body. The book is divided into four parts; the first deals with the fundamental principles of fractals, diffusion and nonlinear dynamics; the second with drug dissolution, release, and absorption; the third with epirical, compartmental, and stochastic pharmacokinetic models, with two new chapters, one on fractional pharmacokinetics and one on bioequivalence; and the fourth mainly with classical and nonclassical aspects of pharmacodynamics. The classical models that have relevance and application to these sciences are also considered throughout. This second edition has new information on reaction limited models of dissolution, non binary biopharmaceutic classification system, time varying models, and interf...
Elsheikh, Ahmed H.
2014-02-01
A Hybrid Nested Sampling (HNS) algorithm is proposed for efficient Bayesian model calibration and prior model selection. The proposed algorithm combines, Nested Sampling (NS) algorithm, Hybrid Monte Carlo (HMC) sampling and gradient estimation using Stochastic Ensemble Method (SEM). NS is an efficient sampling algorithm that can be used for Bayesian calibration and estimating the Bayesian evidence for prior model selection. Nested sampling has the advantage of computational feasibility. Within the nested sampling algorithm, a constrained sampling step is performed. For this step, we utilize HMC to reduce the correlation between successive sampled states. HMC relies on the gradient of the logarithm of the posterior distribution, which we estimate using a stochastic ensemble method based on an ensemble of directional derivatives. SEM only requires forward model runs and the simulator is then used as a black box and no adjoint code is needed. The developed HNS algorithm is successfully applied for Bayesian calibration and prior model selection of several nonlinear subsurface flow problems. © 2013 Elsevier Inc.
Modeling and analysis of sub-surface leakage current in nano-MOSFET under cutoff regime
Swami, Yashu; Rai, Sanjeev
2017-02-01
The high leakage current in nano-meter regimes is becoming a significant portion of power dissipation in nano-MOSFET circuits as threshold voltage, channel length, and gate oxide thickness are scaled down to nano-meter range. Precise leakage current valuation and meticulous modeling of the same at nano-meter technology scale is an increasingly a critical work in designing the low power nano-MOSFET circuits. We present a specific compact model for sub-threshold regime leakage current in bulk driven nano-MOSFETs. The proposed logical model is instigated and executed into the latest updated PTM bulk nano-MOSFET model and is found to be in decent accord with technology-CAD simulation data. This paper also reviews various transistor intrinsic leakage mechanisms for nano-MOSFET exclusively in weak inversion, like drain-induced barricade lowering (DIBL), gate-induced drain leakage (GIDL), gate oxide tunneling (GOT) leakage etc. The root cause of the sub-surface leakage current is mainly due to the nano-scale short channel length causing source-drain coupling even in sub-threshold domain. Consequences leading to carriers triumphing the barricade between the source and drain. The enhanced model effectively considers the following parameter dependence in the account for better-quality value-added results like drain-to-source bias (VDS), gate-to-source bias (VGS), channel length (LG), source/drain junction depth (Xj), bulk doping concentration (NBULK), and operating temperature (Top).
Sarjan, Achmad Fajar Narotama; Niasari, Sintia Windhi
2017-07-01
There are some of geothermal prospects around Java Island. One of them are located in Telomoyo Volcano area, Magelang, Central Java. The existence of hot spring manifestations in Telomoyo Volcano area shows the presence of geothermal system. The upflow zone of this geothermal system was formed in the caldera of Telomoyo Volcano area, while the outflow zone was formed around Candi Umbul. In addition, from the geological map shows a geological structure assumed as a normal fault with southwest-northeast orientation that was caused by the volcanic activity. The aim of this research is to give a brief introduction about subsurface resistivity beneath Telomoyo Volcano area using 1-D magnetotelluric forward model. Thus, we can determine the possibility of data that will obtained during the acquisition process based on the geological model that was made. The apparent resistivity, phase, and period values were obtained from the forward modeling process. The result from this study is a 1-D resistivity section with synthetics curves of each geothermal model. In each model the presence of clay cap characterized by a low resistivity layer. A layer below the clay cap with a medium resistivity value interpreted as the reservoir of this geothermal system. The heat source of this geothermal area is characterized by a low resistivity that is located at depth 4000-5500m. This study is still in progress to acquire the exact values of resistivity from each layer from the field data acquisition in Telomoyo Volcano area, Magelang.
Fracture surfaces of heterogeneous materials: A 2D solvable model
Katzav, E.; Adda-Bedia, M.; Derrida, B.
2007-05-01
Using an elastostatic description of crack growth based on the Griffith criterion and the principle of local symmetry, we present a stochastic model describing the propagation of a crack tip in a 2D heterogeneous brittle material. The model ensures the stability of straight cracks and allows for the study of the roughening of fracture surfaces. When neglecting the effect of the nonsingular stress, the problem becomes exactly solvable and yields analytic predictions for the power spectrum of the paths. This result suggests an alternative to the conventional power law analysis often used in the analysis of experimental data.
Hierarchical Policy Model for Managing Heterogeneous Security Systems
Lee, Dong-Young; Kim, Minsoo
2007-12-01
The integrated security management becomes increasingly complex as security manager must take heterogeneous security systems, different networking technologies, and distributed applications into consideration. The task of managing these security systems and applications depends on various systems and vender specific issues. In this paper, we present a hierarchical policy model which are derived from the conceptual policy, and specify means to enforce this behavior. The hierarchical policy model consist of five levels which are conceptual policy level, goal-oriented policy level, target policy level, process policy level and low-level policy.
El-Amin, Mohamed
2011-05-15
Injection of CO2 in hydrocarbon reservoir has double benefit. On the one hand, it is a profitable method due to issues related to global warming, and on the other hand it is an effective mechanism to enhance hydrocarbon recovery. Such injection associates complex processes involving, e.g., solute transport of dissolved materials, in addition to local changes in density of the phases. Also, increasing carbon dioxide injection may cause a structural deformation of the medium, so it is important to include such effect into the model. The structural deformation modelling in carbon sequestration is important to evaluate the medium stability to avoid CO2 leakage to the atmosphere. On the other hand, geologic formation of the medium is usually heterogeneous and consists of several layers of different permeability. In this work we conduct numerical simulation of two-phase flow in a heterogeneous porous medium domain with dissolved solute transport as well as structural deformation effects. The solute transport of the dissolved component is described by concentration equation. The structural deformation for geomechanics is derived from a general local differential balance equation with neglecting the local mass balance of solid phase and the inertial force term. The flux continuity condition is used at interfaces between different permeability layers of the heterogeneous medium. We analyze the vertical migration of a CO2 plume injected into a 2D layered reservoir. Analysis of distribution of flow field components such as saturation, pressures, velocities, and CO2 concentration are presented.
Jin, Q.; Zheng, Z.; Zhu, C.
2006-12-01
Microorganisms in nature conserve energy by catalyzing various geochemical reactions. To build a quantitative relationship between geochemical conditions and metabolic rates, we propose a bioenergetics-kinetics coupled modeling approach. This approach describes microbial community as a metabolic network, i.e., fermenting microbes degrade organic substrates while aerobic respirer, nitrate reducer, metal reducer, sulfate reducer, and methanogen consume the fermentation products. It quantifies the control of substrate availability and biological energy conservation on the metabolic rates using thermodynamically consistent rate laws. We applied this simulation approach to study the progress of microbial metabolism during a field biostimulation experiment conducted in Oak Ridge, Tennessee. In the experiment, ethanol was injected into a monitoring well and groundwater was sampled to monitor changes in the chemistry. With time, concentrations of ethanol and SO42- decreased while those of NH4+, Fe2+, and Mn2+ increased. The simulation results fitted well to the observation, indicating simultaneous ethanol degradation and terminal electron accepting processes. The rates of aerobic respiration and denitrification were mainly controlled by substrate concentrations while those of ethanol degradation, sulfate reduction, and methanogenesis were controlled dominantly by the energy availability. The simulation results suggested two different microbial growth statuses in the subsurface. For the functional groups with significant growth, variations with time in substrate concentrations demonstrated a typical S curve. For the groups without significant growth, initial decreases in substrate concentrations were linear with time. Injecting substrates followed by monitoring environmental chemistry therefore provides a convenient approach to characterize microbial growth in the subsurface where methods for direct observation are currently unavailable. This research was funded by the
Premaratne, Pavithra Dhanuka
Disruption and fragmentation of an asteroid using nuclear explosive devices (NEDs) is a highly complex yet a practical solution to mitigating the impact threat of asteroids with short warning time. A Hypervelocity Asteroid Intercept Vehicle (HAIV) concept, developed at the Asteroid Deflection Research Center (ADRC), consists of a primary vehicle that acts as kinetic impactor and a secondary vehicle that houses NEDs. The kinetic impactor (lead vehicle) strikes the asteroid creating a crater. The secondary vehicle will immediately enter the crater and detonate its nuclear payload creating a blast wave powerful enough to fragment the asteroid. The nuclear subsurface explosion modeling and hydrodynamic simulation has been a challenging research goal that paves the way an array of mission critical information. A mesh-free hydrodynamic simulation method, Smoothed Particle Hydrodynamics (SPH) was utilized to obtain both qualitative and quantitative solutions for explosion efficiency. Commercial fluid dynamics packages such as AUTODYN along with the in-house GPU accelerated SPH algorithms were used to validate and optimize high-energy explosion dynamics for a variety of test cases. Energy coupling from the NED to the target body was also examined to determine the effectiveness of nuclear subsurface explosions. Success of a disruption mission also depends on the survivability of the nuclear payload when the secondary vehicle approaches the newly formed crater at a velocity of 10 km/s or higher. The vehicle may come into contact with debris ejecting the crater which required the conceptual development of a Whipple shield. As the vehicle closes on the crater, its skin may also experience extreme temperatures due to heat radiated from the crater bottom. In order to address this thermal problem, a simple metallic thermal shield design was implemented utilizing a radiative heat transfer algorithm and nodal solutions obtained from hydrodynamic simulations.
Kempka, Thomas; Nakaten, Benjamin; De Lucia, Marco; Nakaten, Natalie; Otto, Christopher; Pohl, Maik; Tillner, Elena; Kühn, Michael
2016-04-01
Utilization of the geological subsurface for production and storage of hydrocarbons, chemical energy and heat as well as for waste disposal requires the quantification and mitigation of environmental impacts as well as the improvement of georesources utilization in terms of efficiency and sustainability. The development of tools for coupled process simulations is essential to tackle these challenges, since reliable assessments are only feasible by integrative numerical computations. Coupled processes at reservoir to regional scale determine the behaviour of reservoirs, faults and caprocks, generally demanding for complex 3D geological models to be considered besides available monitoring and experimenting data in coupled numerical simulations. We have been developing a flexible numerical simulation framework that provides efficient workflows for integrating the required data and software packages to carry out coupled process simulations considering, e.g., multiphase fluid flow, geomechanics, geochemistry and heat. Simulation results are stored in structured data formats to allow for an integrated 3D visualization and result interpretation as well as data archiving and its provision to collaborators. The main benefits in using the flexible simulation framework are the integration of data geological and grid data from any third party software package as well as data export to generic 3D visualization tools and archiving formats. The coupling of the required process simulators in time and space is feasible, while different spatial dimensions in the coupled simulations can be integrated, e.g., 0D batch with 3D dynamic simulations. User interaction is established via high-level programming languages, while computational efficiency is achieved by using low-level programming languages. We present three case studies on the assessment of geological subsurface utilization based on different process coupling approaches and numerical simulations.
Becker, M. D.; Wang, Y.; Pennell, K. D.; Abriola, L. M.
2011-12-01
As the manufacture and use of nanomaterials become more prevalent, the development of mathematical models capable of predicting nanomaterial transport and retention in subsurface systems is crucial to assessing their environmental fate. To enhance aqueous solubility, nanoparticle production often involves the use of a surfactant or other stabilizing agent. The presence of stabilizing agents, whether natural or synthetic, could significantly influence nanoparticle mobility and fate in the subsurface. In this study, quantum dot (QD) mobility experiments were performed in columns packed with three size fractions of Ottawa sand (d50 = 125, 165, and 335 μm) at two different pore-water velocities (0.8 m/d and 7.6 m/d). The QDs synthesized for these experiments consisted of a CdSe core embedded in a CdZnS shell with a poly(acrylic acid)-octylamine (PAA) coating to promote suspension stability. The QDs were negatively charged (measured zeta potential ca. -35 mV) with a hydrodynamic diameter of approximately 30 nm. Experimental observations consistently revealed low amounts of QD deposition near the column inlet, results that were inconsistent with expectations based upon clean bed filtration theory. This phenomenon was hypothesized to be related to competitive adsorption of residual aqueous PAA to the sand surface. A systematic modeling approach was undertaken to explore mechanisms controlling the transport and deposition of QDs in the presence of competitively adsorbing aqueous PAA. The model incorporated a coupled system of equations governing the fate and transport of both nanoparticles and chemical additives. QD retention was described using a modification of a traditional clean bed filtration governing equation that assumes irreversible first-order attachment and incorporates a maximum or limiting retention capacity. Simultaneous transport and adsorption of PAA were modeled using a traditional advection-dispersion-reaction equation that incorporates a first
Yoo, Jin Woo
In my 1st essay, the study explores Pennsylvania residents. willingness to pay for development of renewable energy technologies such as solar power, wind power, biomass electricity, and other renewable energy using a choice experiment method. Principle component analysis identified 3 independent attitude components that affect the variation of preference, a desire for renewable energy and environmental quality and concern over cost. The results show that urban residents have a higher desire for environmental quality and concern less about cost than rural residents and consequently have a higher willingness to pay to increase renewable energy production. The results of sub-sample analysis show that a representative respondent in rural (urban) Pennsylvania is willing to pay 3.8(5.9) and 4.1(5.7)/month for increasing the share of Pennsylvania electricity generated from wind power and other renewable energy by 1 percent point, respectively. Mean WTP for solar and biomass electricity was not significantly different from zero. In my second essay, heterogeneity of individual WTP for various renewable energy technologies is investigated using several different variants of the multinomial logit model: a simple MNL with interaction terms, a latent class choice model, a random parameter mixed logit choice model, and a random parameter-latent class choice model. The results of all models consistently show that respondents. preference for individual renewable technology is heterogeneous, but the degree of heterogeneity differs for different renewable technologies. In general, the random parameter logit model with interactions and a hybrid random parameter logit-latent class model fit better than other models and better capture respondents. heterogeneity of preference for renewable energy. The impact of the land under agricultural conservation easement (ACE) contract on the values of nearby residential properties is investigated using housing sales data in two Pennsylvania
Directory of Open Access Journals (Sweden)
Alexander J Probst
Full Text Available Earth harbors an enormous portion of subsurface microbial life, whose microbiome flux across geographical locations remains mainly unexplored due to difficult access to samples. Here, we investigated the microbiome relatedness of subsurface biofilms of two sulfidic springs in southeast Germany that have similar physical and chemical parameters and are fed by one deep groundwater current. Due to their unique hydrogeological setting these springs provide accessible windows to subsurface biofilms dominated by the same uncultivated archaeal species, called SM1 Euryarchaeon. Comparative analysis of infrared imaging spectra demonstrated great variations in archaeal membrane composition between biofilms of the two springs, suggesting different SM1 euryarchaeal strains of the same species at both aquifer outlets. This strain variation was supported by ultrastructural and metagenomic analyses of the archaeal biofilms, which included intergenic spacer region sequencing of the rRNA gene operon. At 16S rRNA gene level, PhyloChip G3 DNA microarray detected similar biofilm communities for archaea, but site-specific communities for bacteria. Both biofilms showed an enrichment of different deltaproteobacterial operational taxonomic units, whose families were, however, congruent as were their lipid spectra. Consequently, the function of the major proportion of the bacteriome appeared to be conserved across the geographic locations studied, which was confirmed by dsrB-directed quantitative PCR. Consequently, microbiome differences of these subsurface biofilms exist at subtle nuances for archaea (strain level variation and at higher taxonomic levels for predominant bacteria without a substantial perturbation in bacteriome function. The results of this communication provide deep insight into the dynamics of subsurface microbial life and warrant its future investigation with regard to metabolic and genomic analyses.
Macheras, Panos
2006-01-01
The state of the art in Biopharmaceutics, Pharmacokinetics, and Pharmacodynamics Modeling is presented in this book. It shows how advanced physical and mathematical methods can expand classical models in order to cover heterogeneous drug-biological processes and therapeutic effects in the body. The book is divided into four parts; the first deals with the fundamental principles of fractals, diffusion and nonlinear dynamics; the second with drug dissolution, release, and absorption; the third with empirical, compartmental, and stochastic pharmacokinetic models, and the fourth mainly with nonclassical aspects of pharmacodynamics. The classical models that have relevance and application to these sciences are also considered throughout. Many examples are used to illustrate the intrinsic complexity of drug administration related phenomena in the human, justifying the use of advanced modeling methods. This timely and useful book will appeal to graduate students and researchers in pharmacology, pharmaceutical scienc...
Modeling meander morphodynamics over self-formed heterogeneous floodplains
Bogoni, Manuel; Putti, Mario; Lanzoni, Stefano
2017-06-01
This work addresses the signatures embedded in the planform geometry of meandering rivers consequent to the formation of floodplain heterogeneities as the river bends migrate. Two geomorphic features are specifically considered: scroll bars produced by lateral accretion of point bars at convex banks and oxbow lake fills consequent to neck cutoffs. The sedimentary architecture of these geomorphic units depends on the type and amount of sediment, and controls bank erodibility as the river impinges on them, favoring or contrasting the river migration. The geometry of numerically generated planforms obtained for different scenarios of floodplain heterogeneity is compared to that of natural meandering paths. Half meander metrics and spatial distribution of channel curvatures are used to disclose the complexity embedded in meandering geometry. Fourier Analysis, Principal Component Analysis, Singular Spectrum Analysis and Multivariate Singular Spectrum Analysis are used to emphasize the subtle but crucial differences which may emerge between apparently similar configurations. A closer similarity between observed and simulated planforms is attained when fully coupling flow and sediment dynamics (fully-coupled models) and when considering self-formed heterogeneities that are less erodible than the surrounding floodplain.
Directory of Open Access Journals (Sweden)
C. Lanni
2012-03-01
Full Text Available Topographic index-based hydrological models have gained wide use to describe the hydrological control on the triggering of rainfall-induced shallow landslides at the catchment scale. A common assumption in these models is that a spatially continuous water table occurs simultaneously at any point across the catchment. However, during a rainfall event isolated patches of subsurface saturation form above an impeding layer and hydrological connectivity of these patches is a necessary condition for lateral flow initiation at a point on the hillslope.
Here, a new hydrological model is presented, which allows to account for the concept of hydrological connectivity while keeping the simplicity of the topographic index approach. A dynamic topographic index is used to describe the transient lateral flow that is established at a hillslope element when the rainfall amount exceeds a threshold value allowing for (a development of a perched water table above an impeding layer, (b hydrological connectivity between the hillslope element and its own upslope contributing area. A spatially variable soil depth is the main control of hydrological connectivity in the model. The hydrological model is coupled with the infinite slope stability model, and with a scaling model for the rainfall frequency-duration relationship to determine the return period of the critical rainfall needed to cause instability on three catchments located in the Italian Alps. The results show the good ability of our model in predicting observed shallow landslides. The model is finally used to determine local rainfall intensity-duration thresholds that may lead to shallow landslide initiation.
Energy Technology Data Exchange (ETDEWEB)
Lovley, Derek R.
2012-10-31
This project successfully accomplished its goal of coupling genome-scale metabolic models with hydrological and geochemical models to predict the activity of subsurface microorganisms during uranium bioremediation. Furthermore, it was demonstrated how this modeling approach can be used to develop new strategies to optimize bioremediation. The approach of coupling genome-scale metabolic models with reactive transport modeling is now well enough established that it has been adopted by other DOE investigators studying uranium bioremediation. Furthermore, the basic principles developed during our studies will be applicable to much broader investigations of microbial activities, not only for other types of bioremediation, but microbial metabolism in diversity of environments. This approach has the potential to make an important contribution to predicting the impact of environmental perturbations on the cycling of carbon and other biogeochemical cycles.
Recovery Act: Web-based CO{sub 2} Subsurface Modeling
Energy Technology Data Exchange (ETDEWEB)
Paolini, Christopher; Castillo, Jose
2012-11-30
The Web-based CO{sub 2} Subsurface Modeling project focused primarily on extending an existing text-only, command-line driven, isothermal and isobaric, geochemical reaction-transport simulation code, developed and donated by Sienna Geodynamics, into an easier-to-use Web-based application for simulating long-term storage of CO{sub 2} in geologic reservoirs. The Web-based interface developed through this project, publically accessible via URL http://symc.sdsu.edu/, enables rapid prototyping of CO{sub 2} injection scenarios and allows students without advanced knowledge of geochemistry to setup a typical sequestration scenario, invoke a simulation, analyze results, and then vary one or more problem parameters and quickly re-run a simulation to answer what-if questions. symc.sdsu.edu has 2x12 core AMD Opteron™ 6174 2.20GHz processors and 16GB RAM. The Web-based application was used to develop a new computational science course at San Diego State University, COMP 670: Numerical Simulation of CO{sub 2} Sequestration, which was taught during the fall semester of 2012. The purpose of the class was to introduce graduate students to Carbon Capture, Use and Storage (CCUS) through numerical modeling and simulation, and to teach students how to interpret simulation results to make predictions about long-term CO{sub 2} storage capacity in deep brine reservoirs. In addition to the training and education component of the project, significant software development efforts took place. Two computational science doctoral and one geological science masters student, under the direction of the PIs, extended the original code developed by Sienna Geodynamics, named Sym.8. New capabilities were added to Sym.8 to simulate non-isothermal and non-isobaric flows of charged aqueous solutes in porous media, in addition to incorporating HPC support into the code for execution on many-core XSEDE clusters. A successful outcome of this project was the funding and training of three new computational
Lithospheric Architecture, Heterogenities, Instabilities, Melting - insight form numerical modelling
Gorczyk, Weronika; Hobbs, Bruce; Ord, Alison; Gessner, Klaus; Gerya, Taras V.
2010-05-01
The seismological structure of the Earth's lithosphere is identified to be strongly heterogeneous in terms of thermal and rheological structures. Lithospheric discontinuities (sharp changes in the thermal and/or compositional structure) are thought to be long lived and are mostly correlated with major tectonic boundaries that commonly have been reactivated and which subsequently are the foci of magma intrusion and major mineralization. Resent studies have shown that mantle metasomatism is also controlled by such boundaries. This paper explores the control that lithospheric heterogeneity exerts on the thermal and chemical evolution during deformation subsequent to the development of the heterogeneity. We explore the behaviour of the rheological heterogeneous lithosphere in a compressional regime. The occurrence of such variations may be caused for instance by amalgamation of micro-continents such as is thought to be characteristic of the Yilgarn, Western Australia or South Africa. Theses micro-continents, due to diverse histories may be characterised by various thermal and rheological structures. The models are simplistic but illustrate the basic principles. The code used in this study is based on a conservative finite-difference, multi-grid, marker in cell method. Devolatilisation reactions and melting can affect the physical properties of rocks and are incorporated in a self-consistent manner. We use a petrological-thermomechanical modelling approach with all rock properties including mechanical properties calculated in the Lagrangian scheme for rock markers at every time step based on Gibbs free energy minimization as a function of the local pressure, temperature and rock composition. The results illustrate that initial structural complexity is necessary for and has a dramatic effect on fault and development, the growth of deep basins, core complex formation, melting and devolatilisation within the lithosphere. The horizontal and vertical variation in plastic
Senthilkumar, M.; Elango, L.
2011-06-01
Groundwater modelling is widely used as a management tool to understand the behaviour of aquifer systems under different hydrological stresses, whether induced naturally or by humans. The objective of this study was to assess the effect of a subsurface barrier on groundwater flow in the Palar River basin, Tamil Nadu, southern India. Groundwater is supplied to a nearby nuclear power plant and groundwater also supplies irrigation, industrial and domestic needs. In order to meet the increasing demand for groundwater for the nuclear power station, a subsurface barrier/dam was proposed across Palar River to increase the groundwater heads and to minimise the subsurface discharge of groundwater into the sea. The groundwater model used in this study predicted that groundwater levels would increase by about 0.1-0.3 m extending out a distance of about 1.5-2 km from the upstream side of the barrier, while on the downstream side, the groundwater head would lower by about 0.1-0.2 m. The model also predicted that with the subsurface barrier in place the additional groundwater requirement of approximately 13,600 m3/day (3 million gallons (UK)/day) can be met with minimum decline in regional groundwater head.
Roningen, J. M.; Eylander, J. B.
2014-12-01
Groundwater use and management is subject to economic, legal, technical, and informational constraints and incentives at a variety of spatial and temporal scales. Planned and de facto management practices influenced by tax structures, legal frameworks, and agricultural and trade policies that vary at the country scale may have medium- and long-term effects on the ability of a region to support current and projected agricultural and industrial development. USACE is working to explore and develop global-scale, physically-based frameworks to serve as a baseline for hydrologic policy comparisons and consequence assessment, and such frameworks must include a reasonable representation of groundwater systems. To this end, we demonstrate the effects of different subsurface parameterizations, scaling, and meteorological forcings on surface and subsurface components of the Catchment Land Surface Model Fortuna v2.5 (Koster et al. 2000). We use the Land Information System 7 (Kumar et al. 2006) to process model runs using meteorological components of the Air Force Weather Agency's AGRMET forcing data from 2006 through 2011. Seasonal patterns and trends are examined in areas of the Upper Nile basin, northern China, and the Mississippi Valley. We also discuss the relevance of the model's representation of the catchment deficit with respect to local hydrogeologic structures.
A General Paradigm of Modeling Three-Dimensional Subsurface Water Quality
Zhang, F.; Yeh, G.
2004-12-01
This paper presents the model development of reactive chemical transport in subsurface water systems. Through the decomposition of the system of species transport equations via Gauss-Jordan column reduction of the reaction network, fast reactions and slow reactions are decoupled, which enables robust numerical integrations. Species reactive transport equations are transformed into two sets: algebraic equations (either mass action equations or users¡_ specified) of equilibrium variables and reactive transport equations of kinetic variables. As a result, the model uses kinetic-variables instead of biogeochemical species as primary dependent variables, which reduces the number of transport equations and simplifies reaction terms in these equations. In order to improve the efficiency and robustness of the computation, five options are provided to solve the advection-dispersion transport equations. They are Finite Element Method (FEM) Applied to the Conservative Form of Transport Equations, FEM Applied to the Advective Form of Transport Equations, Modified Lagrangian-Eulerian (LE) approach, LE approach with FEM Applied to the Conservative Form of Transport Equations for Upstream Flux Boundary, and LE approach with FEM Applied to the Advective Form of Transport Equations for Upstream Flux Boundary. Three chemical strategies are employed to deal with the reaction terms. They are Fully-implicit scheme, Mixed Predictor-corrector and Operator-splitting method, and Operator-splitting approach. Three example problems are employed to demonstrate the robustness of the numerical simulations and the design capability of the model.
Energy Technology Data Exchange (ETDEWEB)
Kaplan, D.; et. al
2010-01-11
The uncertainty associated with the sorption coefficient, or K{sub d} value, is one of the key uncertainties in estimating risk associated with burying low-level nuclear waste in the subsurface. The objective of this study was to measure >648 K{sub d} values and provide a measure of the range and distribution (normal or log-normal) of radionuclide K{sub d} values appropriate for the E-Area disposal site, within the Savannah River Site, near Aiken South Carolina. The 95% confidence level for the mean K{sub d} was twice the mean in the Aquifer Zone (18-30.5 m depth), equal to the mean for the Upper Vadose Zone (3.3-10 m depth), and half the mean for the Lower Vadose Zone (3.10-18 m depth). The distribution of K{sub d} values was log normal in the Upper Vadose Zone and Aquifer Zone, and normal in the Lower Vadose Zone. To our knowledge, this is the first report of natural radionuclide Kd variability in the literature. Using ranges and distribution coefficients that are specific to the hydrostratigraphic unit improved model accuracy and reduced model uncertainty. Unfortunately, extension of these conclusions to other sites is likely not appropriate given that each site has its own sources of hydrogeological variability. However, this study provides one of the first examples of the development stochastic ranges and distributions of K{sub d} values for a hydrological unit for stochastic modeling.
Tunçsiper, B; Ayaz, S C; Akça, L
2006-01-01
With the aim of protecting drinking water sources in rural regions, pilot-scale subsurface water flow (SSF) and free water surface flow (FWS) constructed wetland systems were evaluated for removal efficiencies of nitrogenous pollutants in tertiary stage treated wastewaters (effluent from the Pasaköy biological nutrient removal plant). Five different hydraulic application rates and emergent (Canna, Cyperus, Typhia sp., Phragmites sp., Juncus, Poaceae, Paspalum and Iris) and floating (Pistia, Salvina and Lemna) plant species were assayed. The average annual NH4-N, NO3-N and organic-N treatment efficiencies were 81, 40 and 74% in SSFs and 76, 59 and 75% in FWSs, respectively. Two types of the models (first-order plug flow and multiple regression) were tried to estimate the system performances. Nitrification, denitrification and ammonification rate constants (k20) values in SSF and FWS systems were 0.898 d-1 and 0.541 d(-1), 0.486 d(-1) and 0.502 d(-1), 0.986 d(-1) and 0.908, respectively. Results show that the first-order plug flow model clearly estimates slightly higher or lower values than observed when compared with the other model.
Institute of Scientific and Technical Information of China (English)
Wang Chao; Wang Pei-fang; Li Yong
2003-01-01
A composite modeling approach was presented for simulating the three-dimensional (3-D) subsurface transport of dissolved contaminants with transformation products. The approach was based on vertical infiltration and contaminant transport in the unsaturated zone and 3-D groundwater flow and contaminant migration in the saturated zone. Moisture movement and groundwater flow were considered to be steady, but contaminant transport was treated as continuous and transient. The transformed unsaturated zone and saturated zone transport equations were solved numerically with different techniques. The model contains a 3-D solution to flow and transport in the saturated zone, as well as two-dimensional solutions to vertical cross-sectional and areal scenarios. In order to verify the composite modeling, extensive experiments were conducted in two large-scale variable-slope soil tanks of 1200cm in length, 150cm in width and 150cm in height. Sand soil was filled in the tank as the porous media. The solutions of KBr or NH4C1 were introduced into each soil tank from 80×37cm2 area sources located on the top of the porous medium. Results from numerical simulations were compared with the data from tests. Predicted results are in good agreement with the experimental data.
Heterogeneous individuals' behavioral biases model and numerical simulation
Institute of Scientific and Technical Information of China (English)
ZHANG Da-yong; LIANG Guo-wei
2010-01-01
A model of the relationships between individual cognitive biases and individual decision-making based on the analysis of cognitive biases of bonded rationality individual,has been established in this paper by introducing a set of new variables callod overconfidence coefficient and attribution bias coefficient to the sentiment model.The irrational expectation and irrational risk aversion as two inseparable aspects of bonded rationality are expressed in an unified model,and a method of measuring individual cognitive biases is proposed,which overcomes the shortcomings of traditional normative models that can not describe the differences of behaviors among heterogeneous individuals.As a result,numerical simulations show that individual cognitive risk is a positive interaction with overconfidence coefficient,and a negative interaction with attribution bias coefficient.
A heterogeneous model for gas transport in carbon molecular sieves.
Ding, L P; Yuan, Y X; Farooq, S; Bhatia, S K
2005-01-18
A dual resistance model with distribution of either barrier or pore diffusional activation energy is proposed in this work for gas transport in carbon molecular sieve (CMS) micropores. This is a novel approach in which the equilibrium is homogeneous, but the kinetics is heterogeneous. The model seems to provide a possible explanation for the concentration dependence of the thermodynamically corrected barrier and pore diffusion coefficients observed in previous studies from this laboratory on gas diffusion in CMS. The energy distribution is assumed to follow the gamma distribution function. It is shown that the energy distribution model can fully capture the behavior described by the empirical model established in earlier studies to account for the concentration dependence of thermodynamically corrected barrier and pore diffusion coefficients. A methodology is proposed for extracting energy distribution parameters, and it is further shown that the extracted energy distribution parameters can effectively predict integral uptake and column breakthrough profiles over a wide range of operating pressures.
Zheng, Fei; Gao, Yanwei; Sun, Yuanyuan; Shi, Xiaoqing; Xu, Hongxia; Wu, Jichun
2015-12-01
Understanding the migration of dense non-aqueous phase liquids (DNAPLs) in complex subsurface systems is important for evaluating contamination source zones and designing remediation schemes after spill events. Six sandbox experiments were performed to explore the individual effect of flow velocity, and the combined effect of flow velocity and layered lenses on a DNAPL (PCE) migration in porous media. DNAPL saturation was measured using a light transmission system, and saturation distribution was quantified by spatial moments. The experimental results show that large flow velocity significantly promotes lateral and vertical migration of the low-viscosity DNAPL, while when layered lenses exist, the infiltration rate decreases and horizontal spread increases. Migration processes were numerically simulated, and the modelling results tested against experimental results. Furthermore, migration of DNAPLs with different viscosities was simulated to explore the combined effects of flow velocity and geological heterogeneity. Simulation results show that enhanced heterogeneity makes low-viscosity DNAPLs migrate along preferential pathways, resulting in irregular DNAPL morphology. Layered lenses combined with heterogeneity complicate the effect of flow velocity on the migration of low-viscosity DNAPLs by changing percolation paths. Results also demonstrate that flow velocity exhibits relatively little influence on the migration of medium/high-viscosity DNAPLs, which is predominantly controlled by viscosity and heterogeneity. Enhanced heterogeneity has a larger effect on migration behavior. Findings indicate that the migration paths and position of the source zone could change significantly, due to the combined effect of groundwater flow velocity and geological heterogeneity; thus, comprehensive hydrogeological investigation is needed to characterize the source zone.
Bernardes, Paulo; Pereira, Bruno; Alves, Mafalda; Fontes, Luís; Sousa, Andreia; Martins, Manuela; Magalhães, Fernanda; Pimenta, Mário
2017-04-01
Braga is one of the oldest cities of the Iberian NW and as of so, the research team's studying the city's historical core for the past 40 years is often confronted with the unpredictability factor laying beneath an urban site with such a long construction history. In fact, Braga keeps redesigning its urban structure over itself on for the past 2000 years, leaving us with a research object filled with an impressive set of construction footprints from the various planning decisions that were taken in the city along its historical path. Aiming for a predicting understanding of the subsoil, we have used near surface geophysics as an effort of minimizing the areas of intervention for traditional archaeological survey techniques. The Seminário de Santiago integrated geophysical survey is an example of the difficulties of interpreting geophysical models in very complex subsurface scenarios. This geophysical survey was planned in order to aid the requalification project being designed for this set of historical buildings, that are estimated to date back to the 16h century, and that were built over one of the main urban arteries of both roman and medieval layers of Braga. We have used both GPR as well as ERT methods for the geophysical survey, but for the purpose of this article, we will focus in the use of the ERT alone. For the interpretation of the geophysical models we've cross-referenced the dense knowledge existing over the building's construction phases with the complex geophysical data collected, using mathematical processing and volume-based visualization techniques, resorting to the use of Res2Inv©, Paraview© and Voxler® software's. At the same time we tried to pinpoint the noise caused by the past 30 year's infrastructural interventions regarding the replacement of the building's water and sanitation systems and for which we had no design plants, regardless of its recent occurring. The deep impact of this replacement actions revealed by the archaeological
Simulation of Subsurface Multiphase Contaminant Extraction Using a Bioslurping Well Model
Energy Technology Data Exchange (ETDEWEB)
Matos de Souza, Michelle; Oostrom, Mart; White, Mark D.; Cardoso da Silva, Gerson; Barbosa, Maria Claudia
2016-07-12
Subsurface simulation of multiphase extraction from wells is notoriously difficult. Explicit representation of well geometry requires small grid resolution, potentially leading to large computational demands. To reduce the problem dimensionality, multiphase extraction is mostly modeled using vertically-averaged approaches. In this paper, a multiphase well model approach is presented as an alternative to simplify the application. The well model, a multiphase extension of the classic Peaceman model, has been implemented in the STOMP simulator. The numerical solution approach accounts for local conditions and gradients in the exchange of fluids between the well and the aquifer. Advantages of this well model implementation include the option to simulate the effects of well characteristics and operation. Simulations were conducted investigating the effects of extraction location, applied vacuum pressure, and a number of hydraulic properties. The obtained results were all consistent and logical. A major outcome of the test simulations is that, in contrast with common recommendations to extract from either the gas-NAPL or the NAPL-aqueous phase interface, the optimum extraction location should be in between these two levels. The new model implementation was also used to simulate extraction at a field site in Brazil. The simulation shows a good match with the field data, suggesting that the new STOMP well module may correctly represent oil removal. The field simulations depend on the quality of the site conceptual model, including the porous media and contaminant properties and the boundary and extraction conditions adopted. The new module may potentially be used to design field applications and analyze extraction data.
Reactive transport modeling of subsurface arsenic removal systems in rural Bangladesh.
Rahman, M M; Bakker, M; Patty, C H L; Hassan, Z; Röling, W F M; Ahmed, K M; van Breukelen, B M
2015-12-15
Subsurface Arsenic Removal (SAR) is a technique for in-situ removal of arsenic from groundwater. Extracted groundwater is aerated and re-injected into an anoxic aquifer, where the oxygen in the injected water reacts with ferrous iron in the aquifer to form hydrous ferric oxide (HFO). Subsequent extraction of groundwater contains temporarily lower As concentrations, because As sorbs onto the HFO. Injection, storage, and extraction together is called a cycle. A reactive transport model (RTM) was developed in PHREEQC to determine the hydrogeochemical processes responsible for As (im)mobilization during experimental SAR operation performed in Bangladesh. Oxidation of Fe(II) and As(III) were modeled using kinetic-rate expressions. Cation exchange, precipitation of HFO, and surface complexation, were modeled as equilibrium processes. A best set of surface complexation reactions and corresponding equilibrium constants was adopted from previous studies to simulate all 20 cycles of a SAR experiment. The model gives a reasonable match with observed concentrations of different elements in the extracted water (e.g., the r(2) value of As was 0.59 or higher). As concentrations in the extracted water are governed by four major processes. First, As concentration decreases in response to the elevated pH of injection water and likewise increases when native neutral pH groundwater flows in. Second, the sorption capacity for As increases due to the gradual buildup of HFO. Third, As sorption is enhanced by preferential removal of As(V). Fourth, competitive sorption of Si limits the capacity of freshly precipitated HFO for As sorption. Transferability of the developed reactive transport model was demonstrated through successful application of the model, without further calibration, to two additional SAR sites in Bangladesh. This gives confidence that the model could be useful to assess potential SAR performance at locations in Bangladesh based on local hydrogeochemical conditions.
Bayesian modelling of compositional heterogeneity in molecular phylogenetics.
Heaps, Sarah E; Nye, Tom M W; Boys, Richard J; Williams, Tom A; Embley, T Martin
2014-10-01
In molecular phylogenetics, standard models of sequence evolution generally assume that sequence composition remains constant over evolutionary time. However, this assumption is violated in many datasets which show substantial heterogeneity in sequence composition across taxa. We propose a model which allows compositional heterogeneity across branches, and formulate the model in a Bayesian framework. Specifically, the root and each branch of the tree is associated with its own composition vector whilst a global matrix of exchangeability parameters applies everywhere on the tree. We encourage borrowing of strength between branches by developing two possible priors for the composition vectors: one in which information can be exchanged equally amongst all branches of the tree and another in which more information is exchanged between neighbouring branches than between distant branches. We also propose a Markov chain Monte Carlo (MCMC) algorithm for posterior inference which uses data augmentation of substitutional histories to yield a simple complete data likelihood function that factorises over branches and allows Gibbs updates for most parameters. Standard phylogenetic models are not informative about the root position. Therefore a significant advantage of the proposed model is that it allows inference about rooted trees. The position of the root is fundamental to the biological interpretation of trees, both for polarising trait evolution and for establishing the order of divergence among lineages. Furthermore, unlike some other related models from the literature, inference in the model we propose can be carried out through a simple MCMC scheme which does not require problematic dimension-changing moves. We investigate the performance of the model and priors in analyses of two alignments for which there is strong biological opinion about the tree topology and root position.
Monodisperse Platinum and Rhodium Nanoparticles as Model Heterogeneous Catalysts
Energy Technology Data Exchange (ETDEWEB)
Grass, Michael Edward [Univ. of California, Berkeley, CA (United States)
2008-09-01
Model heterogeneous catalysts have been synthesized and studied to better understand how the surface structure of noble metal nanoparticles affects catalytic performance. In this project, monodisperse rhodium and platinum nanoparticles of controlled size and shape have been synthesized by solution phase polyol reduction, stabilized by polyvinylpyrrolidone (PVP). Model catalysts have been developed using these nanoparticles by two methods: synthesis of mesoporous silica (SBA-15) in the presence of nanoparticles (nanoparticle encapsulation, NE) to form a composite of metal nanoparticles supported on SBA-15 and by deposition of the particles onto a silicon wafer using Langmuir-Blodgett (LB) monolayer deposition. The particle shapes were analyzed by transmission electron microscopy (TEM) and high resolution TEM (HRTEM) and the sizes were determined by TEM, X-ray diffraction (XRD), and in the case of NE samples, room temperature H_{2} and CO adsorption isotherms. Catalytic studies were carried out in homebuilt gas-phase reactors. For the nanoparticles supported on SBA-15, the catalysts are in powder form and were studied using the homebuilt systems as plug-flow reactors. In the case of nanoparticles deposited on silicon wafers, the same systems were operated as batch reactors. This dissertation has focused on the synthesis, characterization, and reaction studies of model noble metal heterogeneous catalysts. Careful control of particle size and shape has been accomplished though solution phase synthesis of Pt and Rh nanoparticles in order to elucidate further structure-reactivity relationships in noble metal catalysis.
Modelling long-distance seed dispersal in heterogeneous landscapes.
Energy Technology Data Exchange (ETDEWEB)
Levey, Douglas, J.; Tewlsbury, Joshua, J.; Bolker, Benjamin, M.
2008-01-01
1. Long-distance seed dispersal is difficult to measure, yet key to understanding plant population dynamics and community composition. 2. We used a spatially explicit model to predict the distribution of seeds dispersed long distances by birds into habitat patches of different shapes. All patches were the same type of habitat and size, but varied in shape. They occurred in eight experimental landscapes, each with five patches of four different shapes, 150 m apart in a matrix of mature forest. The model was parameterized with smallscale movement data collected from field observations of birds. In a previous study we validated the model by testing its predictions against observed patterns of seed dispersal in real landscapes with the same types and spatial configuration of patches as in the model. 3. Here we apply the model more broadly, examining how patch shape influences the probability of seed deposition by birds into patches, how dispersal kernels (distributions of dispersal distances) vary with patch shape and starting location, and how movement of seeds between patches is affected by patch shape. 4. The model predicts that patches with corridors or other narrow extensions receive higher numbers of seeds than patches without corridors or extensions. This pattern is explained by edgefollowing behaviour of birds. Dispersal distances are generally shorter in heterogeneous landscapes (containing patchy habitat) than in homogeneous landscapes, suggesting that patches divert the movement of seed dispersers, ‘holding’ them long enough to increase the probability of seed defecation in the patches. Dispersal kernels for seeds in homogeneous landscapes were smooth, whereas those in heterogenous landscapes were irregular. In both cases, long-distance (> 150 m) dispersal was surprisingly common, usually comprising approximately 50% of all dispersal events. 5. Synthesis . Landscape heterogeneity has a large influence on patterns of long-distance seed dispersal. Our
Heterogeneous traffic flow modelling using second-order macroscopic continuum model
Mohan, Ranju; Ramadurai, Gitakrishnan
2017-01-01
Modelling heterogeneous traffic flow lacking in lane discipline is one of the emerging research areas in the past few years. The two main challenges in modelling are: capturing the effect of varying size of vehicles, and the lack in lane discipline, both of which together lead to the 'gap filling' behaviour of vehicles. The same section length of the road can be occupied by different types of vehicles at the same time, and the conventional measure of traffic concentration, density (vehicles per lane per unit length), is not a good measure for heterogeneous traffic modelling. First aim of this paper is to have a parsimonious model of heterogeneous traffic that can capture the unique phenomena of gap filling. Second aim is to emphasize the suitability of higher-order models for modelling heterogeneous traffic. Third, the paper aims to suggest area occupancy as concentration measure of heterogeneous traffic lacking in lane discipline. The above mentioned two main challenges of heterogeneous traffic flow are addressed by extending an existing second-order continuum model of traffic flow, using area occupancy for traffic concentration instead of density. The extended model is calibrated and validated with field data from an arterial road in Chennai city, and the results are compared with those from few existing generalized multi-class models.
Elsheikh, Ahmed H.
2014-02-01
An efficient Bayesian calibration method based on the nested sampling (NS) algorithm and non-intrusive polynomial chaos method is presented. Nested sampling is a Bayesian sampling algorithm that builds a discrete representation of the posterior distributions by iteratively re-focusing a set of samples to high likelihood regions. NS allows representing the posterior probability density function (PDF) with a smaller number of samples and reduces the curse of dimensionality effects. The main difficulty of the NS algorithm is in the constrained sampling step which is commonly performed using a random walk Markov Chain Monte-Carlo (MCMC) algorithm. In this work, we perform a two-stage sampling using a polynomial chaos response surface to filter out rejected samples in the Markov Chain Monte-Carlo method. The combined use of nested sampling and the two-stage MCMC based on approximate response surfaces provides significant computational gains in terms of the number of simulation runs. The proposed algorithm is applied for calibration and model selection of subsurface flow models. © 2013.
A steady-state saturation model to determine the subsurface travel time (STT in complex hillslopes
Directory of Open Access Journals (Sweden)
T. Sabzevari
2010-06-01
Full Text Available The travel time of subsurface flow in complex hillslopes (hillslopes with different plan shape and profile curvature is an important parameter in predicting the subsurface flow in catchments. This time depends on the hillslopes geometry (plan shape and profile curvature, soil properties and climate conditions. The saturation capacity of hillslopes affect the travel time of subsurface flow. The saturation capacity, and subsurface travel time of compound hillslopes depend on parameters such as soil depth, porosity, soil hydraulic conductivity, plan shape (convergent, parallel or divergent, hillslope length, profile curvature (concave, straight or convex and recharge rate to the groundwater table. An equation for calculating subsurface travel time for all complex hillslopes was presented. This equation is a function of the saturation zone length (SZL on the surface. Saturation zone length of the complex hillslopes was calculated numerically by using the hillslope-storage kinematic wave equation for subsurface flow, so an analytical equation was presented for calculating the saturation zone length of the straight hillslopes and all plan shapes geometries. Based on our results, the convergent hillslopes become saturated very soon and they showed longer SZL with shorter travel time compared to the parallel and divergent ones. The subsurface average flow rate in convergent hillslopes is much less than the divergent ones in the steady state conditions. Concerning to subsurface travel time, convex hillslopes have more travel time in comparison to straight and concave hillslopes. The convex hillslopes exhibit more average flow rate than concave hillslopes and their saturation capacity is very low. Finally, the effects of recharge rate variations, average bedrock slope and soil depth on saturation zone extension were investigated.
Using multilevel models to quantify heterogeneity in resource selection
Wagner, T.; Diefenbach, D.R.; Christensen, S.A.; Norton, A.S.
2011-01-01
Models of resource selection are being used increasingly to predict or model the effects of management actions rather than simply quantifying habitat selection. Multilevel, or hierarchical, models are an increasingly popular method to analyze animal resource selection because they impose a relatively weak stochastic constraint to model heterogeneity in habitat use and also account for unequal sample sizes among individuals. However, few studies have used multilevel models to model coefficients as a function of predictors that may influence habitat use at different scales or quantify differences in resource selection among groups. We used an example with white-tailed deer (Odocoileus virginianus) to illustrate how to model resource use as a function of distance to road that varies among deer by road density at the home range scale. We found that deer avoidance of roads decreased as road density increased. Also, we used multilevel models with sika deer (Cervus nippon) and white-tailed deer to examine whether resource selection differed between species. We failed to detect differences in resource use between these two species and showed how information-theoretic and graphical measures can be used to assess how resource use may have differed. Multilevel models can improve our understanding of how resource selection varies among individuals and provides an objective, quantifiable approach to assess differences or changes in resource selection. ?? The Wildlife Society, 2011.
Energy Technology Data Exchange (ETDEWEB)
Foxall, William [Univ. of California, Berkeley, CA (United States)
1992-11-01
Crystal fault zones exhibit spatially heterogeneous slip behavior at all scales, slip being partitioned between stable frictional sliding, or fault creep, and unstable earthquake rupture. An understanding the mechanisms underlying slip segmentation is fundamental to research into fault dynamics and the physics of earthquake generation. This thesis investigates the influence that large-scale along-strike heterogeneity in fault zone lithology has on slip segmentation. Large-scale transitions from the stable block sliding of the Central 4D Creeping Section of the San Andreas, fault to the locked 1906 and 1857 earthquake segments takes place along the Loma Prieta and Parkfield sections of the fault, respectively, the transitions being accomplished in part by the generation of earthquakes in the magnitude range 6 (Parkfield) to 7 (Loma Prieta). Information on sub-surface lithology interpreted from the Loma Prieta and Parkfield three-dimensional crustal velocity models computed by Michelini (1991) is integrated with information on slip behavior provided by the distributions of earthquakes located using, the three-dimensional models and by surface creep data to study the relationships between large-scale lithological heterogeneity and slip segmentation along these two sections of the fault zone.
Modeling and comparative study of fluid velocities in heterogeneous rocks
Hingerl, Ferdinand F.; Romanenko, Konstantin; Pini, Ronny; Balcom, Bruce; Benson, Sally
2013-04-01
Detailed knowledge of the distribution of effective porosity and fluid velocities in heterogeneous rock samples is crucial for understanding and predicting spatially resolved fluid residence times and kinetic reaction rates of fluid-rock interactions. The applicability of conventional MRI techniques to sedimentary rocks is limited by internal magnetic field gradients and short spin relaxation times. The approach developed at the UNB MRI Centre combines the 13-interval Alternating-Pulsed-Gradient Stimulated-Echo (APGSTE) scheme and three-dimensional Single Point Ramped Imaging with T1 Enhancement (SPRITE). These methods were designed to reduce the errors due to effects of background gradients and fast transverse relaxation. SPRITE is largely immune to time-evolution effects resulting from background gradients, paramagnetic impurities and chemical shift. Using these techniques quantitative 3D porosity maps as well as single-phase fluid velocity fields in sandstone core samples were measured. Using a new Magnetic Resonance Imaging technique developed at the MRI Centre at UNB, we created 3D maps of porosity distributions as well as single-phase fluid velocity distributions of sandstone rock samples. Then, we evaluated the applicability of the Kozeny-Carman relationship for modeling measured fluid velocity distributions in sandstones samples showing meso-scale heterogeneities using two different modeling approaches. The MRI maps were used as reference points for the modeling approaches. For the first modeling approach, we applied the Kozeny-Carman relationship to the porosity distributions and computed respective permeability maps, which in turn provided input for a CFD simulation - using the Stanford CFD code GPRS - to compute averaged velocity maps. The latter were then compared to the measured velocity maps. For the second approach, the measured velocity distributions were used as input for inversely computing permeabilities using the GPRS CFD code. The computed
Mutual information model for link prediction in heterogeneous complex networks
Shakibian, Hadi; Moghadam Charkari, Nasrollah
2017-01-01
Recently, a number of meta-path based similarity indices like PathSim, HeteSim, and random walk have been proposed for link prediction in heterogeneous complex networks. However, these indices suffer from two major drawbacks. Firstly, they are primarily dependent on the connectivity degrees of node pairs without considering the further information provided by the given meta-path. Secondly, most of them are required to use a single and usually symmetric meta-path in advance. Hence, employing a set of different meta-paths is not straightforward. To tackle with these problems, we propose a mutual information model for link prediction in heterogeneous complex networks. The proposed model, called as Meta-path based Mutual Information Index (MMI), introduces meta-path based link entropy to estimate the link likelihood and could be carried on a set of available meta-paths. This estimation measures the amount of information through the paths instead of measuring the amount of connectivity between the node pairs. The experimental results on a Bibliography network show that the MMI obtains high prediction accuracy compared with other popular similarity indices. PMID:28344326
Trumbo, S. K.; Palacios, S. L.; Zimmerman, R. C.; Kudela, R. M.
2012-12-01
Macrocystis pyrifera, giant kelp, is a major primary producer of the California coastal ocean that provides habitat for marine species through the formation of massive kelp beds. The estimation of primary productivity of these kelp beds is essential for a complete understanding of their health and of the biogeochemistry of the region. Current methods involve either the application of a proportionality constant to remotely sensed biomass or in situ frond density measurements. The purpose of this research was to improve upon conventional primary productivity estimates by developing a model which takes into account the spectral differences among juvenile, mature, and senescent tissues as well as the photosynthetic contributions of subsurface kelp. A modified version of a seagrass productivity model (Zimmerman 2006) was used to quantify carbon fixation. Inputs included estimates of the underwater light field as computed by solving the radiative transfer equation (with the Hydrolight(TM) software package) and biological parameters obtained from the literature. It was found that mature kelp is the most efficient primary producer, especially in light-limited environments, due to increased light absorptance. It was also found that incoming light attenuates below useful levels for photosynthesis more rapidly than has been previously accounted for in productivity estimates, with productivity dropping below half maximum at approximately 0.75 m. As a case study for comparison with the biomass method, the model was applied to Isla Vista kelp bed in Santa Barbara, using area estimates from the MODIS-ASTER Simulator (MASTER). A graphical user-interface was developed for users to provide inputs to run the kelp productivity model under varying conditions. Accurately quantifying kelp productivity is essential for understanding its interaction with offshore ecosystems as well as its contribution to the coastal carbon cycle.
Kazumba, Shija; Gillerman, Leonid; DeMalach, Yoel; Oron, Gideon
2010-01-01
Scarcity of fresh high-quality water has heightened the importance of wastewater reuse primarily in dry regions together with improving its efficient use by implementing the Subsurface Drip Irrigation (SDI) method. Sustainable effluent reuse combines soil and plant aspects, along with the maintainability of the application system. In this study, field experiments were conducted for two years on the commercial farm of Revivim and Mashabay-Sade farm (RMF) southeast of the City of Beer-Sheva, Israel. The purpose was to examine the response of alfalfa (Medicago sativa) as a perennial model crop to secondary domestic effluent application by means of a SDI system as compared with conventional overhead sprinkler irrigation. Emitters were installed at different depths and spacing. Similar amounts of effluent were applied to all plots during the experimental period. The results indicated that in all SDI treatments, the alfalfa yields were 11% to 25% higher than the ones obtained under sprinkler irrigated plots, besides the one in which the drip laterals were 200 cm apart. The average Water Use Efficiency (WUE) was better in all SDI treatments in comparison with the sprinkler irrigated plots. An economic assessment reveals the dependence of the net profit on the emitters' installation geometry, combined with the return for alfalfa in the market.
Institute of Scientific and Technical Information of China (English)
FAN Liwei; Hai Reti; WANG Wenxing; LU Zexiang; YANG Zhiming
2008-01-01
A subsurface flow wetland (SSFW) was simulated using a commercial computational fluid dynamic (CFD) code. The constructed media was simulated using porous media and the liquid resident time distribution (RTD) in the SSFW was obtained using the particle trajectory model. The effect of wetland configuration and operating conditions on the hydraulic performance of the SSFW were investigated. The results indicated that the hydraulic performance of the SSFW was predominantly affected by the wetland configuration. The hydraulic efficiency of the SSFW with an inlet at the middle edge of the upper media was 0.584 and the best among the SSFWs with an inlet at the top, the middle, and the bottom edge of the upper media. The constructed media affected the hydraulic performance by the ratio (K) of the upper and lower media resistance. The selection of appropriate media resistance in the protection layer can improve the hydraulic efficiency. When the viscous resistance coefficient of the media in the protection layer changed from 2.315×105 to 1.200×108, the hydraulic efficiency of the SSFW increased from 0.301 to 0.751. However, the effect of operating conditions on the hydraulic efficiency of the SSFW was slight.
An optimization model to design and manage subsurface drip irrigation system for alfalfa
Kandelous, M.; Kamai, T.; Vrugt, J. A.; Simunek, J.; Hanson, B.; Hopmans, J. W.
2010-12-01
Subsurface drip irrigation (SDI) is one of the most efficient and cost-effective methods for watering alfalfa plants. Lateral installation depth and distance, emitter discharge, and irrigation time and frequency of SDI, in addition to soil and climatic conditions affect alfalfa’s root water uptake and yield. Here we use a multi-objective optimization approach to find optimal SDI strategies. Our approach uses the AMALGAM evolutionary search method, in combination with the HYDRUS-2D unsaturated flow model to maximize water uptake by alfalfa’s plant roots, and minimize loss of irrigation and drainage water to the atmosphere or groundwater. We use a variety of different objective functions to analyze SDI. These criteria include the lateral installation depth and distance, the lateral discharge, irrigation duration, and irrigation frequency. Our framework includes explicit recognition of the soil moisture status during the simulation period to make sure that the top soil is dry for harvesting during the growing season. Initial results show a wide spectrum of optimized SDI strategies for different root distributions, soil textures and climate conditions. The developed tool should be useful in helping farmers optimize their irrigation strategy and design.
Mesoscopic model of temporal and spatial heterogeneity in aging colloids
DEFF Research Database (Denmark)
Becker, Nikolaj; Sibani, Paolo; Boettcher, Stefan
2014-01-01
We develop a simple and effective description of the dynamics of dense hard sphere colloids in the aging regime deep in the glassy phase. Our description complements the many efforts to understand the onset of jamming in low density colloids, whose dynamics is still time-homogeneous. Based...... on a small set of principles, our model provides emergent dynamic heterogeneity, reproduces the known results for dense hard sphere colloids and makes detailed, experimentally-testable predictions for canonical observables in glassy dynamics. In particular, we reproduce the shape of the intermediate...... scattering function and particle mean-square displacements for jammed colloidal systems, and we predict a growth for the peak of the χ4 mobility correlation function that is logarithmic in waiting-time. At the same time, our model suggests a novel unified description for the irreversible aging dynamics...
Modeling and Analysis of New Products Diffusion on Heterogeneous Networks
Directory of Open Access Journals (Sweden)
Shuping Li
2014-01-01
Full Text Available We present a heterogeneous networks model with the awareness stage and the decision-making stage to explain the process of new products diffusion. If mass media is neglected in the decision-making stage, there is a threshold whether the innovation diffusion is successful or not, or else it is proved that the network model has at least one positive equilibrium. For networks with the power-law degree distribution, numerical simulations confirm analytical results, and also at the same time, by numerical analysis of the influence of the network structure and persuasive advertisements on the density of adopters, we give two different products propagation strategies for two classes of nodes in scale-free networks.
Stylized facts from a threshold-based heterogeneous agent model
Cross, R; Lamba, H; Seaman, T
2006-01-01
A class of heterogeneous agent models is investigated where investors switch trading position whenever their motivation to do so exceeds some critical threshold. These motivations can be psychological in nature or reflect behaviour suggested by the efficient market hypothesis (EMH). By introducing different propensities into a baseline model that displays EMH behaviour, one can attempt to isolate their effects upon the market dynamics. The simulation results indicate that the introduction of a herding propensity results in excess kurtosis and power-law decay consistent with those observed in actual return distributions, but not in significant long-term volatility correlations. Possible alternatives for introducing such long-term volatility correlations are then identified and discussed.
Stylized facts from a threshold-based heterogeneous agent model
Cross, R.; Grinfeld, M.; Lamba, H.; Seaman, T.
2007-05-01
A class of heterogeneous agent models is investigated where investors switch trading position whenever their motivation to do so exceeds some critical threshold. These motivations can be psychological in nature or reflect behaviour suggested by the efficient market hypothesis (EMH). By introducing different propensities into a baseline model that displays EMH behaviour, one can attempt to isolate their effects upon the market dynamics. The simulation results indicate that the introduction of a herding propensity results in excess kurtosis and power-law decay consistent with those observed in actual return distributions, but not in significant long-term volatility correlations. Possible alternatives for introducing such long-term volatility correlations are then identified and discussed.
Modeling the heterogeneous intestinal absorption of propiverine extended-release.
Weiss, Michael; Sermsappasuk, Pakawadee; Siegmund, Werner
2015-08-30
Propiverine is a widely used antimuscarinic drug with bioavailability that is limited by intestinal first-pass extraction. To study the apparent heterogeneity in intestinal first-pass extraction, we performed a population analysis of oral concentration-time data measured after administration of an extended-release formulation of propiverine in ten healthy subjects. Using an inverse Gaussian function as input model, the assumption that the systemically available fraction increases as a sigmoidal function of time considerably improved the fit. The step-like increase in this fraction at time t=3.7h predicted by the model suggests that propiverine is predominantly absorbed in colon. A nearly perfect correlation was found between the estimates of bioavailability and mean dissolution time. Copyright © 2015 Elsevier B.V. All rights reserved.
Heterogeneous anisotropic complex structure gradual model and constitutive relation
Institute of Scientific and Technical Information of China (English)
李永; 宋健; 张志民
2003-01-01
Four new gradually delaminate models of the three-dimensional macro-/mesoscopic structure and delamination of the heterogeneous anisotropic composite (HAC) are set up by conducting research into its structure and performance. A general theory, which demonstrates the three-dimensional constitutive relation of the macro-/mesoscopic performance of this structure is further developed. The macroscopic expression of HAC is presented in terms of a Tanigawa delaminate homogeneous equivalent approach, the mesoscopic problems are analysed utilizing Eshelby-Mori-Tanaka theory, with the introduction of the representative volume elements of monolayer single unit cell and interlaminar double unit cells.According to the gradual continuity of the structure as a whole, great attention is given to the modelling and research of the interlaminar macroscopic and mesoscopic problems of HAC structure. Comparison with the existing solutions is made through calculation of typical cases.
National Research Council Canada - National Science Library
Downer, Charles
2003-01-01
This document is a primer for use of the Watershed Modeling System (WMS) interface with the physically based, distributed-parameter hydrologic model Gridded Surface Subsurface Hydrologic Analysis (GSSHA...
Modeling flow in a pressure-sensitive, heterogeneous medium
Energy Technology Data Exchange (ETDEWEB)
Vasco, Donald W.; Minkoff, Susan E.
2009-06-01
Using an asymptotic methodology, including an expansion in inverse powers of {radical}{omega}, where {omega} is the frequency, we derive a solution for flow in a medium with pressure dependent properties. The solution is valid for a heterogeneous medium with smoothly varying properties. That is, the scale length of the heterogeneity must be significantly larger then the scale length over which the pressure increases from it initial value to its peak value. The resulting asymptotic expression is similar in form to the solution for pressure in a medium in which the flow properties are not functions of pressure. Both the expression for pseudo-phase, which is related to the 'travel time' of the transient pressure disturbance, and the expression for pressure amplitude contain modifications due to the pressure dependence of the medium. We apply the method to synthetic and observed pressure variations in a deforming medium. In the synthetic test we model one-dimensional propagation in a pressure-dependent medium. Comparisons with both an analytic self-similar solution and the results of a numerical simulation indicate general agreement. Furthermore, we are able to match pressure variations observed during a pulse test at the Coaraze Laboratory site in France.
Samsó, Roger; García, Joan; Molle, Pascal; Forquet, Nicolas
2016-01-01
Horizontal subsurface Flow Constructed Wetlands (HF CWs) are biofilters planted with aquatic macrophytes within which wastewater is treated mostly through contact with bacterial biofilms. The high concentrations of organic carbon and nutrients being transported leads to high bacterial biomass production, which decreases the flow capacity of the porous material (bioclogging). In severe bioclogging scenarios, overland flow may take place, reducing overall treatment performance. In this work we developed a mathematical model using COMSOL Multiphysics™ and MATLAB(®) to simulate bioclogging effects in HF CWs. Variably saturated subsurface flow and overland flow were described using the Richards equation. To simplify the inherent complexity of the processes involved in bioclogging development, only one bacterial group was considered, and its growth was described using a Monod equation. Bioclogging effects on the hydrodynamics were taken into account by using a conceptual model that affects the value of Mualem's unsaturated relative permeability. Simulation results with and without bioclogging were compared to showcase the impact of this process on the overall functioning of CWs. The two scenarios rendered visually different bacteria distributions, flow and transport patterns, showing the necessity of including bioclogging effects on CWs models. This work represents one of the few studies available on bioclogging in variably saturated conditions, and the presented model allows simulating the interaction between overland and subsurface flow occurring in most HF CWs. Hence, this work gets us a step closer to being able to describe CWs functioning in an integrated way using mathematical models. Copyright © 2015 Elsevier Ltd. All rights reserved.
Hoon, Stephen R.; Felde, Vincent J. M. N. L.; Drahorad, Sylvie L.; Felix-Henningsen, Peter
2015-04-01
Soil penetrometers are used routinely to determine the shear strength of soils and deformable sediments both at the surface and throughout a depth profile in disciplines as diverse as soil science, agriculture, geoengineering and alpine avalanche-safety (e.g. Grunwald et al. 2001, Van Herwijnen et al. 2009). Generically, penetrometers comprise two principal components: An advancing probe, and a transducer; the latter to measure the pressure or force required to cause the probe to penetrate or advance through the soil or sediment. The force transducer employed to determine the pressure can range, for example, from a simple mechanical spring gauge to an automatically data-logged electronic transducer. Automated computer control of the penetrometer step size and probe advance rate enables precise measurements to be made down to a resolution of 10's of microns, (e.g. the automated electronic micropenetrometer (EMP) described by Drahorad 2012). Here we discuss the determination, modelling and interpretation of biologically crusted dryland soil sub-surface structures using automated micropenetrometry. We outline a model enabling the interpretation of depth dependent penetration resistance (PR) profiles and their spatial differentials using the model equations, σ {}(z) ={}σ c0{}+Σ 1n[σ n{}(z){}+anz + bnz2] and dσ /dz = Σ 1n[dσ n(z) /dz{} {}+{}Frn(z)] where σ c0 and σ n are the plastic deformation stresses for the surface and nth soil structure (e.g. soil crust, layer, horizon or void) respectively, and Frn(z)dz is the frictional work done per unit volume by sliding the penetrometer rod an incremental distance, dz, through the nth layer. Both σ n(z) and Frn(z) are related to soil structure. They determine the form of σ {}(z){} measured by the EMP transducer. The model enables pores (regions of zero deformation stress) to be distinguished from changes in layer structure or probe friction. We have applied this method to both artificial calibration soils in the
Intercomparison of Multiscale Modeling Approaches in Simulating Subsurface Flow and Transport
Yang, X.; Mehmani, Y.; Barajas-Solano, D. A.; Song, H. S.; Balhoff, M.; Tartakovsky, A. M.; Scheibe, T. D.
2016-12-01
Hybrid multiscale simulations that couple models across scales are critical to advance predictions of the larger system behavior using understanding of fundamental processes. In the current study, three hybrid multiscale methods are intercompared: multiscale loose-coupling method, multiscale finite volume (MsFV) method and multiscale mortar method. The loose-coupling method enables a parallel workflow structure based on the Swift scripting environment that manages the complex process of executing coupled micro- and macro-scale models without being intrusive to the at-scale simulators. The MsFV method applies microscale and macroscale models over overlapping subdomains of the modeling domain and enforces continuity of concentration and transport fluxes between models via restriction and prolongation operators. The mortar method is a non-overlapping domain decomposition approach capable of coupling all permutations of pore- and continuum-scale models with each other. In doing so, Lagrange multipliers are used at interfaces shared between the subdomains so as to establish continuity of species/fluid mass flux. Subdomain computations can be performed either concurrently or non-concurrently depending on the algorithm used. All the above methods have been proven to be accurate and efficient in studying flow and transport in porous media. However, there has not been any field-scale applications and benchmarking among various hybrid multiscale approaches. To address this challenge, we apply all three hybrid multiscale methods to simulate water flow and transport in a conceptualized 2D modeling domain of the hyporheic zone, where strong interactions between groundwater and surface water exist across multiple scales. In all three multiscale methods, fine-scale simulations are applied to a thin layer of riverbed alluvial sediments while the macroscopic simulations are used for the larger subsurface aquifer domain. Different numerical coupling methods are then applied between
Modelling Cryovolcanism Due to Subsurface Ocean Freezing on Pluto and Charon
Conrad, J. W.; Nimmo, F.; Singer, K. N.
2016-12-01
The New Horizons spacecraft identified various possible cryovolcanic features on the surfaces of both Pluto and Charon [1]. However, there are major differences between the cryovolcanism on Pluto and Charon. Pluto has two mound-flanked depressions which are possibly cryovolcanic [2], while Charon's putative cryovolcanism is more widespread within its smooth southern plains. If Pluto or Charon have (or had) subsurface oceans, slow refreezing of these oceans would lead to extensional surface tectonics [3,4] and pressurization of the ocean [5]. Sufficiently large pressurization can overcome the overburden pressure and cause an eruption. We applied thermal evolution models based on [3] to determine likely freezing scenarios. Eruptions on Charon are possible under most conditions, and occur after tens of kilometers of freezing of an ice shell initially 100 km thick. This would produce an areal extensional strain of 1%. The implied globally-averaged thickness of erupted material is a few hundred meters and the critical crack width for propagation through the entire ice shell [6] is about half a meter for all eruption scenarios. Eruptions on Pluto require probably unrealistic freezing scenarios, because of the larger body size and higher overburden pressure. We conclude that ocean freezing is a possible source of cryovolcanism on Charon and may explain the smooth plains in its southern hemisphere [1]. Pluto, on the other hand, requires more complex models to explain the putative cryovolcanic features on its surface. [1] Moore et al., Science 351 (2016): 1284-1293. [2] Singer et al., LPSC 47 (2016): 2276 [3] Robuchon and Nimmo, Icarus 216 (2011): 426-439. [4] Hammond et al., GRL 43 (2016). [5] Manga and Wang, GRL 34 (2007). [6] Porco et al., The Astronomical Journal 148 (2014): 45.
Nixon, Zachary; Michel, Jacqueline
2015-04-07
To better understand the distribution of remaining lingering subsurface oil residues from the Exxon Valdez oil spill (EVOS) along the shorelines of Prince William Sound (PWS), AK, we revised previous modeling efforts to allow spatially explicit predictions of the distribution of subsurface oil. We used a set of pooled field data and predictor variables stored as Geographic Information Systems (GIS) data to generate calibrated boosted tree models predicting the encounter probability of different categories of subsurface oil. The models demonstrated excellent predictive performance as evaluated by cross-validated performance statistics. While the average encounter probabilities at most shoreline locations are low across western PWS, clusters of shoreline locations with elevated encounter probabilities remain in the northern parts of the PWS, as well as more isolated locations. These results can be applied to estimate the location and amount of remaining oil, evaluate potential ongoing impacts, and guide remediation. This is the first application of quantitative machine-learning based modeling techniques in estimating the likelihood of ongoing, long-term shoreline oil persistence after a major oil spill.
Load-Aware Modeling and Analysis of Heterogeneous Cellular Networks
Dhillon, Harpreet S; Andrews, Jeffrey G
2012-01-01
Random spatial models are attractive for modeling heterogeneous cellular networks (HCNs) due to their realism, tractability, and scalability. A major limitation of such models to date in the context of HCNs is the neglect of network traffic and load: all base stations (BSs) have typically been assumed to always be transmitting. Small cells in particular will have a lighter load than macrocells, and so their contribution to the network interference may be significantly overstated in a fully loaded model. This paper incorporates a flexible notion of BS load by introducing a new idea of conditionally thinning the interference field. For a $K$-tier HCN where BSs across tiers differ in terms of transmit power, supported data rate, deployment density, and now load, we derive the coverage probability for a typical mobile, which connects to the strongest BS signal. Conditioned on this connection, the interfering BSs of the $i^{th}$ tier are assumed to transmit independently with probability $p_i$, which models the lo...
Middleware Based Model of Heterogeneous Systems for SCADA Distributed Applications
Directory of Open Access Journals (Sweden)
UNGUREAN, I.
2010-05-01
Full Text Available Infrastructure underlying the distributed information systems is heterogeneous and very complex. Middleware allows the development of distributed information systems, without knowing the functioning details of an infrastructure, by its abstracting. An essential issue on designing such systems is represented by choosing the middleware technologies. An architectural model of a SCADA system based on middleware is proposed in this paper. This system is formed of servers that centralize data and clients, which receive information from a server, thus allowing the chart displaying of such information. All these components own a specific functionality and can exchange information, by means of a middleware bus. A middleware bus signifies a software bus, where more middleware technologies can coexist.
Modeling saltwater intrusion in highly heterogeneous coastal aquifers
Safi, Amir; El-Fadel, Mutasem; Doummar, Joanna; Abou Najm, Majdi; Alameddine, Ibrahim
2016-04-01
In this study, a 3D variable-density flow and solute transport model SEAWAT was used to examine the impact of macroscopic variation in a soil matrix on widening or narrowing the thickness of the saltwater-freshwater mixing zone. Located along the Eastern Mediterranean (Beirut), the pilot aquifer consists of karstified limestone of Cretaceous age overlain by Upper Tertiary and Quaternary unconsolidated deposits. The model used the advanced pilot-points parameterization coupled with PEST to characterize spatial heterogeneity. Historically simulated water levels were relied upon to reduce potential numerical instabilities induced by insensitive parameters in transient calibration. The latter demonstrated a high degree of heterogeneity in the middle parts of the aquifer and along western coastlines with specification of a high hydraulic conductivity and low storativity in fault networks. The response of the aquifer to seasonal stresses such as climate cycles, pumping rates and recharge rates was manifested as high fluctuations in potentiometric surface due to potential fast flow pathways along faults. The final distribution of saltwater intrusion supports two mechanisms 1) lateral encroachment of recent seawater into the western zone of the aquifer which is of most concern due to high horizontal hydraulic conductivity in the wave direction and 2) upconing in the northwest and southwest of the aquifer due to large vertical hydraulic conductivities that tend to exacerbate the vertical movement of salinity. Acknowledgments This study is part of a program on climate change and seawater intrusion along the Eastern Mediterranean funded by the International Development Research Center (IDRC) of Canada at the American University of Beirut (AUB). Special thanks are extended to Dr. Charlotte Macalister at IDRC for her support and feedback in implementing this program.
Rodriguez-Escales, Paula; Sanchez-Vila, Xavier
2016-04-01
The degradation of low adsorptive SMX in subsurface porous media is spatially and temporally variable. It depends on various environmental factors such as in situ redox potential, availability of nutrients, local soil characteristics, and temperature. Its degradation is better under anoxic conditions and by co-metabolism processes. In this work, we first develop a conceptual model of degradation of SMX under different redox conditions (denitrification and iron reducing conditions), characterizing the metabolite formation in each condition, and second, we construct a mathematical model that allows reproducing different experiments of SMX degradation reported in the literature. The model was validated using the experimental data from Barbieri et al. (2012), Nödler et al. (2012) and Mohatt et al. (2011). The model reproduces the reversible degradation of SMX under the presence of nitrous acid as an intermediate product of denitrification (it is the conjugate acid of nitrite), as well as, the metabolite formation (4-nitro-SMX and desamino SMX). In those experiments degradation was mediated by the transient formation of a diazonium cation, which was considered responsible of the substitution of the amine radical by a nitro radical, forming the 4-nitro-SMX. On the other hand, both the diazonium compound and the methanol present in the experiment produced a deamination in the SMX, producing desamino-SMX. The formation of these metabolites was unstable and they were retransformed to SMX. Concerning the iron conditions, SMX was degraded due to the oxidation of iron (Fe2+), which was previously oxidized from goethite due to the degradation of a pool of labile organic carbon. As the oxidation of iron occurred on the goethite surface, the best model to reproduce the SMX reduction was a power law rate. Our work is an attempt to properly formulate the degradation process of an emerging compound considering the real degradation mechanisms, rather than using an upscaled black
Titi, Yopiter Lukas Alexander; Minarto, Eko
2017-01-01
The interpretation and three-dimensional modeling of the subsurface structure of the volcano arc of the Flores island based on the gravity data analysis have been done. This research is aimed for modeling subsurface structure utilized a secondary data of complete Bouguer anomaly gravity data obtained from Bureau Gravimetric International (BGI) using Grablox and Bloxer software. The modeling construction was performed by inversion technique applying the method of Singular Value Decomposition (SVD) and Occam inversion. The result indicates that Subsurface structure of the volcano area of the Flores island consists of sandstone, breccia and andesite have density value ranging from 2,42 g/cm3 to 2,62 g/cm3 and basaltic and lava have density values ranging from 2,65 g/cm3 to 3,24 g/cm3. The most dominating rocks in the study area are basaltic rocks have 2.73 g/cm3 point of average density. The existence of magma chamber in the volcanic arc of Flores island was estimated at a depth of 6 km.
Main, C E; Yool, A; Holliday, N P; Popova, E E; Jones, D O B; Ruhl, H A
2017-01-15
Little is known about the fate of subsurface hydrocarbon plumes from deep-sea oil well blowouts and their effects on processes and communities. As deepwater drilling expands in the Faroe-Shetland Channel (FSC), oil well blowouts are a possibility, and the unusual ocean circulation of this region presents challenges to understanding possible subsurface oil pathways in the event of a spill. Here, an ocean general circulation model was used with a particle tracking algorithm to assess temporal variability of the oil-plume distribution from a deep-sea oil well blowout in the FSC. The drift of particles was first tracked for one year following release. Then, ambient model temperatures were used to simulate temperature-mediated biodegradation, truncating the trajectories of particles accordingly. Release depth of the modeled subsurface plumes affected both their direction of transport and distance travelled from their release location, and there was considerable interannual variability in transport. Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.
Indian Academy of Sciences (India)
Rajeev Ranjan Kumar; D V Ramana; R N Singh
2012-10-01
Near-subsurface temperatures have signatures of climate change. Thermal models of subsurface have been constructed by prescribing time dependent Dirichlet type boundary condition wherein the temperature at the soil surface is prescribed and depth distribution of temperature is obtained. In this formulation it is not possible to include the relationship between air temperatures and the temperature of soil surface. However, if one uses a Robin type boundary condition, a transfer coefficient relates the air and soil surface temperatures which helps to determine both the temperature at the surface and at depth given near surface air temperatures. This coefficient is a function of meteorological conditions and is readily available. We have developed such a thermal model of near subsurface region which includes both heat conduction and advection due to groundwater flows and have presented numerical results for changes in the temperature–depth profiles for different values of transfer coefficient and groundwater flux. There are significant changes in temperature and depth profiles due to changes in the transfer coefficient and groundwater flux. The analytical model will find applications in the interpretation of the borehole geothermal data to extract both climate and groundwater flow signals.
Modeling Heterogeneous Variance-Covariance Components in Two-Level Models
Leckie, George; French, Robert; Charlton, Chris; Browne, William
2014-01-01
Applications of multilevel models to continuous outcomes nearly always assume constant residual variance and constant random effects variances and covariances. However, modeling heterogeneity of variance can prove a useful indicator of model misspecification, and in some educational and behavioral studies, it may even be of direct substantive…
Model of coupled gas flow and deformation process in heterogeneous coal seams and its application
Institute of Scientific and Technical Information of China (English)
ZHANG Chun-hui; ZHAO Quan-sheng; YU Yong-jiang
2011-01-01
The heterogeneity of coal was studied by mechanical tests. Probability plots of experimental data show that the mechanical parameters of heterogeneous coal follow a Weibull distribution. Based on elasto-plastic mechanics and gas dynamics, the model of coupled gas flow and deformation process of heterogeneous coal was presented and the effects of heterogeneity of coal on gas flow and failure of coal were investigated. Major findings include: The effect of the heterogeneity of coal on gas flow and mechanical failure of coal can be considered by the model in this paper. Failure of coal has a great effect on gas flow.
A detailed model for simulation of catchment scale subsurface hydrologic processes
Paniconi, Claudio; Wood, Eric F.
1993-01-01
A catchment scale numerical model is developed based on the three-dimensional transient Richards equation describing fluid flow in variably saturated porous media. The model is designed to take advantage of digital elevation data bases and of information extracted from these data bases by topographic analysis. The practical application of the model is demonstrated in simulations of a small subcatchment of the Konza Prairie reserve near Manhattan, Kansas. In a preliminary investigation of computational issues related to model resolution, we obtain satisfactory numerical results using large aspect ratios, suggesting that horizontal grid dimensions may not be unreasonably constrained by the typically much smaller vertical length scale of a catchment and by vertical discretization requirements. Additional tests are needed to examine the effects of numerical constraints and parameter heterogeneity in determining acceptable grid aspect ratios. In other simulations we attempt to match the observed streamflow response of the catchment, and we point out the small contribution of the streamflow component to the overall water balance of the catchment.
Interpretation and modeling of a subsurface injection test, 200 East Area, Hanford, Washington
Energy Technology Data Exchange (ETDEWEB)
Smoot, J.L. [Pacific Northwest Lab., Richland, WA (United States); Lu, A.H. [Westinghouse Hanford Co., Richland, WA (United States)
1994-11-01
A tracer experiment was conducted in 1980 and 1981 in the unsaturated zone in the southeast portion of the Hanford 200 East Area near the Plutonium-Uranium Extraction (PUREX) facility. The field design consisted of a central injection well with 32 monitoring wells within an 8-m radius. Water containing radioactive and other tracers was injected weekly during the experiment. The unique features of the experiment were the documented control of the inputs, the experiment`s three-dimensional nature, the in-situ measurement of radioactive tracers, and the use of multiple injections. The spacing of the test wells provided reasonable lag distribution for spatial correlation analysis. Preliminary analyses indicated spatial correlation on the order of 400 to 500 cm in the vertical direction. Previous researchers found that two-dimensional axisymmetric modeling of moisture content generally underpredicts lateral spreading and overpredicts vertical movement of the injected water. Incorporation of anisotropic hydraulic properties resulted in the best model predictions. Three-dimensional modeling incorporated the geologic heterogeneity of discontinuous layers and lenses of sediment apparent in the site geology. Model results were compared statistically with measured experimental data and indicate reasonably good agreement with vertical and lateral field moisture distributions.
Bayesian Uncertainty Quantification for Subsurface Inversion Using a Multiscale Hierarchical Model
Mondal, Anirban
2014-07-03
We consider a Bayesian approach to nonlinear inverse problems in which the unknown quantity is a random field (spatial or temporal). The Bayesian approach contains a natural mechanism for regularization in the form of prior information, can incorporate information from heterogeneous sources and provide a quantitative assessment of uncertainty in the inverse solution. The Bayesian setting casts the inverse solution as a posterior probability distribution over the model parameters. The Karhunen-Loeve expansion is used for dimension reduction of the random field. Furthermore, we use a hierarchical Bayes model to inject multiscale data in the modeling framework. In this Bayesian framework, we show that this inverse problem is well-posed by proving that the posterior measure is Lipschitz continuous with respect to the data in total variation norm. Computational challenges in this construction arise from the need for repeated evaluations of the forward model (e.g., in the context of MCMC) and are compounded by high dimensionality of the posterior. We develop two-stage reversible jump MCMC that has the ability to screen the bad proposals in the first inexpensive stage. Numerical results are presented by analyzing simulated as well as real data from hydrocarbon reservoir. This article has supplementary material available online. © 2014 American Statistical Association and the American Society for Quality.
Heterogeneous nucleation of ice on model carbon surfaces
Molinero, V.; Lupi, L.; Hudait, A.
2014-12-01
Carbonaceous particles account for 10% of the particulate matter in the atmosphere. The experimental investigation of heterogeneous freezing of water droplets by carbonaceous particles reveals widespread ice freezing temperatures. The origin of the soot and its oxidation and aging modulate its ice nucleation ability, however, it is not known which structural and chemical characteristics of soot account for the variability in ice nucleation efficiency. We find that atomically flat carbon surfaces promote heterogeneous nucleation of ice, while molecularly rough surfaces with the same hydrophobicity do not. We investigate a large set of graphitic surfaces of various dimensions and radii of curvature consistent with those of soot in experiments, and find that variations in nanostructures alone could account for the spread in the freezing temperatures of ice on soot in experiments. A characterization of the nanostructure of soot is needed to predict its ice nucleation efficiency. Atmospheric oxidation and aging of soot modulates its ice nucleation ability. It has been suggested that an increase in the ice nucleation ability of aged soot results from an increase in the hydrophilicity of the surfaces upon oxidation. Oxidation, however, also impacts the nanostructure of soot, making it difficult to assess the separate effects of soot nanostructure and hydrophilicity in experiments. We investigate the effect of changes in hydrophilicity of model graphitic surfaces on the freezing temperature of ice. Our results indicate that the hydrophilicity of the surface is not in general a good predictor of ice nucleation ability. We find a correlation between the ability of a surface to promote nucleation of ice and the layering of liquid water at the surface. The results of this work suggest that ordering of liquid water in contact with the surface plays an important role in the heterogeneous ice nucleation mechanism. References: L. Lupi, A. Hudait and V. Molinero, J. Am. Chem. Soc
Heterogeneous Nuclear Reactor Models for Optimal Xenon Control.
Gondal, Ishtiaq Ahmad
Nuclear reactors are generally modeled as homogeneous mixtures of fuel, control, and other materials while in reality they are heterogeneous-homogeneous configurations comprised of fuel and control rods along with other materials. Similarly, for space-time studies of a nuclear reactor, homogeneous, usually one-group diffusion theory, models are used, and the system equations are solved by either nodal or modal expansion approximations. Study of xenon-induced problems has also been carried out using similar models and with the help of dynamic programming or classical calculus of variations or the minimum principle. In this study a thermal nuclear reactor is modeled as a two-dimensional lattice of fuel and control rods placed in an infinite-moderator in plane geometry. The two-group diffusion theory approximation is used for neutron transport. Space -time neutron balance equations are written for two groups and reduced to one space-time algebraic equation by using the two-dimensional Fourier transform. This equation is written at all fuel and control rod locations. Iodine -xenon and promethium-samarium dynamic equations are also written at fuel rod locations only. These equations are then linearized about an equilibrium point which is determined from the steady-state form of the original nonlinear system equations. After studying poisonless criticality, with and without control, and the stability of the open-loop system and after checking its controllability, a performance criterion is defined for the xenon-induced spatial flux oscillation problem in the form of a functional to be minimized. Linear -quadratic optimal control theory is then applied to solve the problem. To perform a variety of different additional useful studies, this formulation has potential for various extensions and variations; for example, different geometry of the problem, with possible extension to three dimensions, heterogeneous -homogeneous formulation to include, for example, homogeneously
Decision Support for Test Trench Location Selection with 3D Semantic Subsurface Utility Models
Racz, Paulina; Syfuss, Lars; Schultz, Carl; van Buiten, Marinus; olde Scholtenhuis, Léon Luc; Vahdatikhaki, Faridaddin; Doree, Andries G.; Lin, Ken-Yu; El-Gohary, Nora; Tang, Pingbo
Subsurface utility construction work often involves repositioning of, and working between, existing buried networks. While the amount of utilities in modern cities grows, excavation work becomes more prone to incidents. To prevent such incidents, excavation workers request existing 2D utility maps,
Wasch, L.J.; Koenen, M.; Wollenweber, J.; Tambach, T.J.
2015-01-01
To ensure the safety of a CO 2 storage site and containment of CO 2 in the subsurface, the integrity of wellbore materials must be maintained. Field and laboratory studies have shown CO 2 -induced reactivity of wellbore cement, but these results have to be extrapolated to the extended time span of C
Subsurface Gas Flow and Ice Grain Acceleration within Enceladus and Europa Fissures: 2D DSMC Models
Tucker, O. J.; Combi, M. R.; Tenishev, V.
2014-12-01
The ejection of material from geysers is a ubiquitous occurrence on outer solar system bodies. Water vapor plumes have been observed emanating from the southern hemispheres of Enceladus and Europa (Hansen et al. 2011, Roth et al. 2014), and N2plumes carrying ice and ark particles on Triton (Soderblom et al. 2009). The gas and ice grain distributions in the Enceladus plume depend on the subsurface gas properties and the geometry of the fissures e.g., (Schmidt et al. 2008, Ingersoll et al. 2010). Of course the fissures can have complex geometries due to tidal stresses, melting, freezing etc., but directly sampled and inferred gas and grain properties for the plume (source rate, bulk velocity, terminal grain velocity) can be used to provide a basis to constrain characteristic dimensions of vent width and depth. We used a 2-dimensional Direct Simulation Monte Carlo (DSMC) technique to model venting from both axi-symmetric canyons with widths ~2 km and narrow jets with widths ~15-40 m. For all of our vent geometries, considered the water vapor source rates (1027 - 1028 s-1) and bulk gas velocities (~330 - 670 m/s) obtained at the surface were consistent with inferred values obtained by fits of the data for the plume densities (1026 - 1028 s-1, 250 - 1000 m/s) respectively. However, when using the resulting DSMC gas distribution for the canyon geometries to integrate the trajectories of ice grains we found it insufficient to accelerate submicron ice grains to Enceladus' escape speed. On the other hand, the gas distributions in the jet like vents accelerated grains > 10 μm significantly above Enceladus' escape speed. It has been suggested that micron-sized grains are ejected from the vents with speeds comparable to the Enceladus escape speed. Here we report on these results including comparisons to results obtained from 1D models as well as discuss the implications of our plume model results. We also show preliminary results for similar considerations applied to Europa
Energy Technology Data Exchange (ETDEWEB)
Yasukawa, K. [Geological Survey of Japan, Tsukuba (Japan); Mogi, T. [Kyushu University, Fukuoka (Japan). Faculty of Engineering
1998-02-01
Self-Potential (SP) anomaly at the ground surface caused by subsurface fluid flow is numerically calculated for two-dimensional models using a simulation code PTSP to investigate the topographic effects on the SP profile. The result shows that the negative SP anomaly generally seen in higher elevation can be explained as a result of topographic effects on the near surface fluid flow system for cases of homogeneous earth. However, heterogeneous permeability distribution possibly changes the fluid flow pattern and its derived SP profile. Heterogeneity in electrical resistivity and cross-coupling conductivity also affects on the SP pattern, causing the shift of peak anomaly location. Therefore, a numerical approach applying hydrogeological and physical property distributions is invaluable for detailed interpretation of SP survey data. 19 refs., 8 figs.
Assessing clustering strategies for Gaussian mixture filtering a subsurface contaminant model
Liu, Bo
2016-02-03
An ensemble-based Gaussian mixture (GM) filtering framework is studied in this paper in term of its dependence on the choice of the clustering method to construct the GM. In this approach, a number of particles sampled from the posterior distribution are first integrated forward with the dynamical model for forecasting. A GM representation of the forecast distribution is then constructed from the forecast particles. Once an observation becomes available, the forecast GM is updated according to Bayes’ rule. This leads to (i) a Kalman filter-like update of the particles, and (ii) a Particle filter-like update of their weights, generalizing the ensemble Kalman filter update to non-Gaussian distributions. We focus on investigating the impact of the clustering strategy on the behavior of the filter. Three different clustering methods for constructing the prior GM are considered: (i) a standard kernel density estimation, (ii) clustering with a specified mixture component size, and (iii) adaptive clustering (with a variable GM size). Numerical experiments are performed using a two-dimensional reactive contaminant transport model in which the contaminant concentration and the heterogenous hydraulic conductivity fields are estimated within a confined aquifer using solute concentration data. The experimental results suggest that the performance of the GM filter is sensitive to the choice of the GM model. In particular, increasing the size of the GM does not necessarily result in improved performances. In this respect, the best results are obtained with the proposed adaptive clustering scheme.
Energy Technology Data Exchange (ETDEWEB)
Gwo, J.P.; Jardine, P.M. [Oak Ridge National Lab., TN (United States); Yeh, G.T. [Pennsylvania State Univ., University Park, PA (United States) Department of Civil and Environmental Engineering; Wilson, G.V. [Tennessee Univ., Knoxville, TN (United States). Dept. of Plant and Soil Science
1995-04-01
Matrix diffusion, a diffusive mass transfer process,in the structured soils and geologic units at ORNL, is believe to be an important subsurface mass transfer mechanism; it may affect off-site movement of radioactive wastes and remediation of waste disposal sites by locally exchanging wastes between soil/rock matrix and macropores/fractures. Advective mass transfer also contributes to waste movement but is largely neglected by researchers. This report presents the first documented 2-D multiregion solute transport code (MURT) that incorporates not only diffusive but also advective mass transfer and can be applied to heterogeneous porous media under transient flow conditions. In this report, theoretical background is reviewed and the derivation of multiregion solute transport equations is presented. Similar to MURF (Gwo et al. 1994), a multiregion subsurface flow code, multiplepore domains as suggested by previous investigators (eg, Wilson and Luxmoore 1988) can be implemented in MURT. Transient or steady-state flow fields of the pore domains can be either calculated by MURF or by modelers. The mass transfer process is briefly discussed through a three-pore-region multiregion solute transport mechanism. Mass transfer equations that describe mass flux across pore region interfaces are also presented and parameters needed to calculate mass transfer coefficients detailed. Three applications of MURT (tracer injection problem, sensitivity analysis of advective and diffusive mass transfer, hillslope ponding infiltration and secondary source problem) were simulated and results discussed. Program structure of MURT and functions of MURT subroutiness are discussed so that users can adapt the code; guides for input data preparation are provided in appendices.
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
This paper presents a physically-based integrated hydrologic model that can simulate the rain-fall-induced 2D surface water flow, 3D variably saturated subsurface flow, upland soil erosion and transport, and contaminant transport in the surface-subsurface system of a watershed. The model couples surface and subsurface flows based on the assumption of continuity conditions of pressure head and exchange flux at the ground, considering infiltration and evapotranspiration. The upland rill/interrill soil erosion and transport are simulated using a non-equilibrium transport model. Contaminant transport in the integrated surface and subsurface domains is simulated using advection-diffusion equations with mass changes due to sediment sorption and desorption and exchanges between two domains due to infiltration, diffusion, and bed change. The model requires no special treatments at the interface of upland areas and streams and is suitable for wetland areas and agricultural watersheds with shallow streams.
Thin inclusion approach for modelling of heterogeneous conducting materials
Energy Technology Data Exchange (ETDEWEB)
Lavrov, Nikolay [Davenport University, 4801 Oakman Boulevard, Dearborn, MI 48126 (United States); Smirnova, Alevtina; Gorgun, Haluk; Sammes, Nigel [University of Connecticut, Department of Materials Science and Engineering, Connecticut Global Fuel Center, 44 Weaver Road, Unit 5233, Storrs, CT 06269 (United States)
2006-04-21
Experimental data show that heterogeneous nanostructure of solid oxide and polymer electrolyte fuel cells could be approximated as an infinite set of fiber-like or penny-shaped inclusions in a continuous medium. Inclusions can be arranged in a cluster mode and regular or random order. In the newly proposed theoretical model of nanostructured material, the most attention is paid to the small aspect ratio of structural elements as well as to some model problems of electrostatics. The proposed integral equation for electric potential caused by the charge distributed over the single circular or elliptic cylindrical conductor of finite length, as a single unit of a nanostructured material, has been asymptotically simplified for the small aspect ratio and solved numerically. The result demonstrates that surface density changes slightly in the middle part of the thin domain and has boundary layers localized near the edges. It is anticipated, that contribution of boundary layer solution to the surface density is significant and cannot be governed by classic equation for smooth linear charge. The role of the cross-section shape is also investigated. Proposed approach is sufficiently simple, robust and allows extension to either regular or irregular system of various inclusions. This approach can be used for the development of the system of conducting inclusions, which are commonly present in nanostructured materials used for solid oxide and polymer electrolyte fuel cell (PEMFC) materials. (author)
Predicting lower mantle heterogeneity from 4-D Earth models
Flament, Nicolas; Williams, Simon; Müller, Dietmar; Gurnis, Michael; Bower, Dan J.
2016-04-01
basal layer ˜ 4% denser than ambient mantle. Increasing convective vigour (Ra ≈ 5 x 108) or decreasing the density of the basal layer decreases both the accuracy and sensitivity of the predicted lower mantle structure. References: D. J. Bower, M. Gurnis, N. Flament, Assimilating lithosphere and slab history in 4-D Earth models. Phys. Earth Planet. Inter. 238, 8-22 (2015). V. Lekic, S. Cottaar, A. Dziewonski, B. Romanowicz, Cluster analysis of global lower mantle tomography: A new class of structure and implications for chemical heterogeneity. Earth Planet. Sci. Lett. 357, 68-77 (2012).
Digital Geological Model (DGM): a 3D raster model of the subsurface of the Netherlands
Gunnink, J.L.; Maljers, D.; Gessel, S.F. van; Menkovic, A.; Hummelman, H.J.
2013-01-01
A 3D geological raster model has been constructed of the onshore of the Netherlands. The model displays geological units for the upper 500 m in 3D in an internally consistent way. The units are based on the lithostratigraphical classification of the Netherlands. This classification is used to interp
Indian Academy of Sciences (India)
M Berlin; M Vasudevan; G Suresh Kumar; Indumathi M Nambi
2015-04-01
The vertical transport of petroleum hydrocarbons from a surface spill through an unsaturated subsurface system is of major concern in assessing the vulnerability of groundwater contamination. A realistic representation on fate and transport of volatile organic compounds at different periods after spill is quite challenging due to the variation in the source behaviour at the surface of spill as well as the variation in the hydrodynamic parameters and the associated inter-phase partitioning coefficients within the subsurface. In the present study, a one dimensional numerical model is developed to simulate the transport of benzene in an unsaturated subsurface system considering the effect of volatilization, dissolution, adsorption and microbial degradation of benzene for (i) constant continuous source, (ii) continuous decaying source, and (iii) residual source. The numerical results suggest that volatilization is the important sink for contaminant removal considering the soil air migration within the unsaturated zone. It is also observed that the coupled effect of dissolution and volatilization is important for the decaying source at the surface immediately after the spill, whereas rate-limited dissolution from residually entrapped source is responsible for the extended contamination towards later period.
Energy Technology Data Exchange (ETDEWEB)
Sokrut, Nikolay; Werner, Kent; Holmen, Johan [Golder Associates AB, Uppsala (Sweden)
2007-01-15
Since 2002, the Swedish Nuclear Fuel and Waste Management Co (SKB) performs site investigations in the Simpevarp area, for the siting of a deep geological repository for spent nuclear fuel. The site descriptive modelling includes conceptual and quantitative modelling of surface-subsurface water interactions, which are key inputs to safety assessment and environmental impact assessment. Such modelling is important also for planning of continued site investigations. In this report, the distributed hydrological model ECOFLOW is applied to the Laxemar subarea to test the ability of the model to simulate surface water and near-surface groundwater flow, and to illustrate ECOFLOW's advantages and drawbacks. The ECOFLOW model area is generally characterised by large areas of exposed or shallow bedrock. The ECOFLOW modelling results are compared to previous results produced by MIKE SHE-MIKE 11 and PCRaster-POLFLOW, in order to check whether non-calibrated surface and subsurface water flows computed by ECOFLOW are consistent with these previous results. The analyses include quantification and comparison of inflow and outflow terms of the water balance, as well as analyses of groundwater recharge-discharge patterns. ECOFLOW is used to simulate a one-year non calibrated period, considering seven catchments (including three areas with direct runoff to the sea) within the Laxemar subarea. The modelling results show the ability of the model to produce reasonable results for a model domain including both porous media (Quaternary deposits) and discontinuous media (bedrock). The results demonstrate notable differences in the specific discharge between the considered catchments, with specific discharge values in the range 157-212 mm/year; the lowest value (the Lake Frisksjoen catchment) may however be erroneous due to numerical instability in the model. Overall, these results agree with specific discharge values computed by MIKE SHE-MIKE 11 and PCRaster-POLFLOW (190 and 128
Stevens, Adam H.; Patel, Manish R.; Lewis, Stephen R.
2017-01-01
We calculate transport timescales of martian methane and investigate the effect of potential release mechanisms into the atmosphere using a numerical model that includes both Fickian and Knudsen diffusion. The incorporation of Knudsen diffusion, which improves on a Fickian description of transport given the low permeability of the martian regolith, means that transport timescales from sources collocated with a putative martian water table are very long, up to several million martian years. Transport timescales also mean that any temporally varying source process, even in the shallow subsurface, would not result in a significant, observable variation in atmospheric methane concentration since changes resulting from small variations in flux would be rapidly obscured by atmospheric transport. This means that a short-lived 'plume' of methane, as detected by Mumma et al. (2009) and Webster et al. (2014), cannot be reconciled with diffusive transport from any reasonable depth and instead must invoke alternative processes such as fracturing or convective plumes. It is shown that transport through the martian regolith will cause a significant change in the isotopic composition of the gas, meaning that methane release from depth will produce an isotopic signature in the atmosphere that could be significantly different than the source composition. The deeper the source, the greater the change, and the change in methane composition in both δ13C and δD approaches -1000 ‰ for sources at a depth greater than around 1 km. This means that signatures of specific sources, in particular the methane produced by biogenesis that is generally depleted in 13CH4 and CH3D, could be obscured. We find that an abiogenic source of methane could therefore display an isotopic fractionation consistent with that expected for biogenic source processes if the source was at sufficient depth. The only unambiguous inference that can be made from measurements of methane isotopes alone is a measured
Church, Jonathan R.
New condensed matter metrologies are being used to probe ever smaller length scales. In support of the diverse field of materials research synchrotron based spectroscopies provide sub-micron spatial resolutions and a breadth of photon wavelengths for scientific studies. For electronic materials the thinnest layers in a complementary metal-oxide-semiconductor (CMOS) device have been reduced to just a few nanometers. This raises concerns for layer uniformity, complete surface coverage, and interfacial quality. Deposition processes like chemical vapor deposition (CVD) and atomic layer deposition (ALD) have been shown to deposit the needed high-quality films for the requisite thicknesses. However, new materials beget new chemistries and, unfortunately, unwanted side-reactions and by-products. CVD/ALD tools and chemical precursors provided by our collaborators at Air Liquide utilized these new chemistries and films were deposited for which novel spectroscopic characterization methods were used. The second portion of the thesis focuses on fading and decomposing paint pigments in iconic artworks. Efforts have been directed towards understanding the micro-environments causing degradation. Hard X-ray photoelectron spectroscopy (HAXPES) and variable kinetic energy X-ray photoelectron spectroscopy (VKE-XPS) are advanced XPS techniques capable of elucidating both chemical environments and electronic band structures in sub-surface regions of electronic materials. HAXPES has been used to study the electronic band structure in a typical CMOS structure; it will be shown that unexpected band alignments are associated with the presence of electronic charges near a buried interface. Additionally, a computational modeling algorithm, Bayes-Sim, was developed to reconstruct compositional depth profiles (CDP) using VKE-XPS data sets; a subset algorithm also reconstructs CDP from angle-resolved XPS data. Reconstructed CDP produced by Bayes-Sim were most strongly correlated to the real
Energy Technology Data Exchange (ETDEWEB)
Moller, Nancy; Weare J. H.
2008-05-29
Successful exploitation of the vast amount of heat stored beneath the earth’s surface in hydrothermal and fluid-limited, low permeability geothermal resources would greatly expand the Nation’s domestic energy inventory and thereby promote a more secure energy supply, a stronger economy and a cleaner environment. However, a major factor limiting the expanded development of current hydrothermal resources as well as the production of enhanced geothermal systems (EGS) is insufficient knowledge about the chemical processes controlling subsurface fluid flow. With funding from past grants from the DOE geothermal program and other agencies, we successfully developed advanced equation of state (EOS) and simulation technologies that accurately describe the chemistry of geothermal reservoirs and energy production processes via their free energies for wide XTP ranges. Using the specific interaction equations of Pitzer, we showed that our TEQUIL chemical models can correctly simulate behavior (e.g., mineral scaling and saturation ratios, gas break out, brine mixing effects, down hole temperatures and fluid chemical composition, spent brine incompatibilities) within the compositional range (Na-K-Ca-Cl-SO4-CO3-H2O-SiO2-CO2(g)) and temperature range (T < 350°C) associated with many current geothermal energy production sites that produce brines with temperatures below the critical point of water. The goal of research carried out under DOE grant DE-FG36-04GO14300 (10/1/2004-12/31/2007) was to expand the compositional range of our Pitzer-based TEQUIL fluid/rock interaction models to include the important aluminum and silica interactions (T < 350°C). Aluminum is the third most abundant element in the earth’s crust; and, as a constituent of aluminosilicate minerals, it is found in two thirds of the minerals in the earth’s crust. The ability to accurately characterize effects of temperature, fluid mixing and interactions between major rock-forming minerals and hydrothermal and
El Gharamti, Mohamad
2014-02-01
The accuracy of groundwater flow and transport model predictions highly depends on our knowledge of subsurface physical parameters. Assimilation of contaminant concentration data from shallow dug wells could help improving model behavior, eventually resulting in better forecasts. In this paper, we propose a joint state-parameter estimation scheme which efficiently integrates a low-rank extended Kalman filtering technique, namely the Singular Evolutive Extended Kalman (SEEK) filter, with the prominent complex-step method (CSM). The SEEK filter avoids the prohibitive computational burden of the Extended Kalman filter by updating the forecast along the directions of error growth only, called filter correction directions. CSM is used within the SEEK filter to efficiently compute model derivatives with respect to the state and parameters along the filter correction directions. CSM is derived using complex Taylor expansion and is second order accurate. It is proven to guarantee accurate gradient computations with zero numerical round-off errors, but requires complexifying the numerical code. We perform twin-experiments to test the performance of the CSM-based SEEK for estimating the state and parameters of a subsurface contaminant transport model. We compare the efficiency and the accuracy of the proposed scheme with two standard finite difference-based SEEK filters as well as with the ensemble Kalman filter (EnKF). Assimilation results suggest that the use of the CSM in the context of the SEEK filter may provide up to 80% more accurate solutions when compared to standard finite difference schemes and is competitive with the EnKF, even providing more accurate results in certain situations. We analyze the results based on two different observation strategies. We also discuss the complexification of the numerical code and show that this could be efficiently implemented in the context of subsurface flow models. © 2013 Elsevier B.V.
Shokri, Ali; Bardsley, William Earl
2016-06-01
Hydrological and hydrogeological investigation of drained land is a complex and integrated procedure. The scale of drainage studies may vary from a high-resolution small scale project through to comprehensive catchment or regional scale investigations. This wide range of scales and integrated system behaviour poses a significant challenge for the development of suitable drainage models. Toward meeting these requirements, a fully distributed coupled surface-subsurface flow model titled DrainFlow has been developed and is described. DrainFlow includes both the diffusive wave equation for surface flow components (overland flow, open drain, tile drain) and Richard's equation for saturated/unsaturated zones. To overcome the non-linearity problem created from switching between wet and dry boundaries, a smooth transitioning technique is introduced to buffer the model at tile drains and at interfaces between surface and subsurface flow boundaries. This gives a continuous transition between Dirichlet and Neumann boundary conditions. DrainFlow is tested against five well-known integrated surface-subsurface flow benchmarks. DrainFlow as applied to some synthetic drainage study examples is quite flexible for changing all or part of the model dimensions as required by problem complexity, problem scale, and data availability. This flexibility enables DrainFlow to be modified to allow for changes in both scale and boundary conditions, as often encountered in real-world drainage studies. Compared to existing drainage models, DrainFlow has the advantage of estimating actual infiltration directly from the partial differential form of Richard's equation rather than through analytical or empirical infiltration approaches like the Green and Ampt equation.
Digital Repository Service at National Institute of Oceanography (India)
Loveson, V.J.; Gujar, A.R.
data over an area under study. The gap between sample locations are to be either simulated or manipulated through various statistical methods. Under such conditions, mapping of the area may not yield the reality of the subsurface features in between... continuous profiles along with 200 MHz antenna and measuring wheel. Some times for confirmation, 400 MHz antenna was also used. GPR system was initialized in the field so that the ground reality, related to geo-electrical conditions of the field...
Heterogeneity Confounds Establishment of "a" Model Microbial Strain.
Keller, Nancy P
2017-02-21
Aspergillus fumigatus is a ubiquitous environmental mold and the leading cause of diverse human diseases ranging from allergenic bronchopulmonary aspergillosis (ABPA) to invasive pulmonary aspergillosis (IPA). Experimental investigations of the biology and virulence of this opportunistic pathogen have historically used a few type strains; however, it is increasingly observed with this fungus that heterogeneity among isolates potentially confounds the use of these reference isolates. Illustrating this point, Kowalski et al. (mBio 7:e01515-16, 2016, https://doi.org/10.1128/mBio.01515-16) demonstrated that variation in 16 environmental and clinical isolates of A. fumigatus correlated virulence with fitness in low oxygen, whereas Fuller et al. (mBio 7:e01517-16, 2016, https://doi.org/10.1128/mBio.01517-16) showed wide variation in light responses at a physiological and protein functionality level in 15 A. fumigatus isolates. In both studies, two commonly used type strains, Af293 and CEA10, displayed significant differences in physiological responses to abiotic stimuli and virulence in a murine model of IPA.
Heterogeneous SIS model for directed networks and optimal immunization
Ottaviano, Stefania; Bonaccorsi, Stefano
2016-01-01
We investigate the influence of a contact network structure over the spread of epidemics in an heterogeneous population. Basically the epidemics spreads over a directed weighted graph. We describe the epidemic process as a continuous-time individual-based susceptible-infected-susceptible (SIS) model using a first-order mean-field approximation. First we consider a network without a specific topology, investigating the epidemic threshold and the stability properties of the system. Then we analyze the case of a community network, relying on the graph-theoretical notion of equitable partition, and using a lower-dimensional dynamical system in order to individuate the epidemic threshold. Moreover we prove that the positive steady-state of the original system, that appears above the threshold, can be computed by this lower-dimensional system. In the second part of the paper we treat the important issue of the infectious disease control. Taking into account the connectivity of the network, we provide a cost-optimal...
Sensor management for multiple target tracking with heterogeneous sensor models
Williams, Jason L.; Fisher, John W., III; Willsky, Alan S.
2006-05-01
Modern sensors are able to rapidly change mode of operation and steer between physically separated objects. While control of such sensors over a rolling planning horizon can be formulated as a dynamic program, the optimal solution is inevitably intractable. In this paper, we consider the control problem under a restricted family of policies and show that the essential sensor control trade-offs are still captured. The advantage of this approach is that one can obtain the optimal policy within the restricted class in a tractable fashion, in this case by using the auction algorithm. The approach is well-suited for problems in which a single sensor (or group of sensors) is being used to track many targets using a heterogeneous sensor model, i.e., where the quality of observations varies with object state, such as due to obscuration. Our algorithm efficiently weighs the rewards achievable by observing each target at each time to find the best sensor plan within the restricted set. We extend this approach using a roll-out algorithm, to handle additional cases such as when observations take different amounts of time to complete.
Fernández-Remolar, David C.; Gómez, Felipe; Prieto-Ballesteros, Olga; Schelble, Rachel T.; Rodríguez, Nuria; Amiols, Ricardo
2008-02-01
Chemolithotrophic communities that colonize subsurface habitats have great relevance for the astrobiological exploration of our Solar System. We hypothesize that the chemical and thermal stabilization of an environment through microbial activity could make a given planetary region habitable. The MARTE project ground-truth drilling campaigns that sampled cryptic subsurface microbial communities in the basement of the Ro Tinto headwaters have shown that acidic surficial habitats are the result of the microbial oxidation of pyritic ores. The oxidation process is exothermic and releases heat under both aerobic and anaerobic conditions. These microbial communities can maintain the subsurface habitat temperature through storage heat if the subsurface temperature does not exceed their maximum growth temperature. In the acidic solutions of the Ro Tinto, ferric iron acts as an effective buffer for controlling water pH. Under anaerobic conditions, ferric iron is the oxidant used by microbes to decompose pyrite through the production of sulfate, ferrous iron, and protons. The integration between the physical and chemical processes mediated by microorganisms with those driven by the local geology and hydrology have led us to hypothesize that thermal and chemical regulation mechanisms exist in this environment and that these homeostatic mechanisms could play an essential role in creating habitable areas for other types of microorganisms. Therefore, searching for the physicochemical expression of extinct and extant homeostatic mechanisms through physical and chemical anomalies in the Mars crust (i.e., local thermal gradient or high concentration of unusual products such as ferric sulfates precipitated out from acidic solutions produced by hypothetical microbial communities) could be a first step in the search for biological traces of a putative extant or extinct Mars biosphere.
A modelling approach for the heterogeneous oxidation of elastomers
Herzig, A.; Sekerakova, L.; Johlitz, M.; Lion, A.
2017-04-01
The influence of oxygen on elastomers, known as oxidation, is one of the most important ageing processes and becomes more and more important for nowadays applications. The interaction with thermal effects as well as antioxidants makes oxidation of polymers a complex process. Based on the polymer chosen and environmental conditions, the ageing processes may behave completely different. In a lot of cases the influence of oxygen is limited to the surface layer of the samples, commonly referred to as diffusion-limited oxidation. For the lifetime prediction of elastomer components, it is essential to have detailed knowledge about the absorption and diffusion behaviour of oxygen molecules during thermo-oxidative ageing and how they react with the elastomer. Experimental investigations on industrially used elastomeric materials are executed in order to develop and fit models, which shall be capable of predicting the permeation and consumption of oxygen as well as changes in the mechanical properties. The latter are of prime importance for technical applications of rubber components. Oxidation does not occur homogeneously over the entire elastomeric component. Hence, material models which include ageing effects have to be amplified in order to consider heterogeneous ageing, which highly depends on the ageing temperature. The influence of elevated temperatures upon accelerated ageing has to be critically analysed, and influences on the permeation and diffusion coefficient have to be taken into account. This work presents phenomenological models which describe the oxygen uptake and the diffusion into elastomers based on an improved understanding of ongoing chemical processes and diffusion limiting modifications. On the one side, oxygen uptake is modelled by means of Henry's law in which solubility is a function of the temperature as well as the ageing progress. The latter is an irreversible process and described by an inner differential evolution equation. On the other side
A modelling approach for the heterogeneous oxidation of elastomers
Herzig, A.; Sekerakova, L.; Johlitz, M.; Lion, A.
2017-09-01
The influence of oxygen on elastomers, known as oxidation, is one of the most important ageing processes and becomes more and more important for nowadays applications. The interaction with thermal effects as well as antioxidants makes oxidation of polymers a complex process. Based on the polymer chosen and environmental conditions, the ageing processes may behave completely different. In a lot of cases the influence of oxygen is limited to the surface layer of the samples, commonly referred to as diffusion-limited oxidation. For the lifetime prediction of elastomer components, it is essential to have detailed knowledge about the absorption and diffusion behaviour of oxygen molecules during thermo-oxidative ageing and how they react with the elastomer. Experimental investigations on industrially used elastomeric materials are executed in order to develop and fit models, which shall be capable of predicting the permeation and consumption of oxygen as well as changes in the mechanical properties. The latter are of prime importance for technical applications of rubber components. Oxidation does not occur homogeneously over the entire elastomeric component. Hence, material models which include ageing effects have to be amplified in order to consider heterogeneous ageing, which highly depends on the ageing temperature. The influence of elevated temperatures upon accelerated ageing has to be critically analysed, and influences on the permeation and diffusion coefficient have to be taken into account. This work presents phenomenological models which describe the oxygen uptake and the diffusion into elastomers based on an improved understanding of ongoing chemical processes and diffusion limiting modifications. On the one side, oxygen uptake is modelled by means of Henry's law in which solubility is a function of the temperature as well as the ageing progress. The latter is an irreversible process and described by an inner differential evolution equation. On the other side
Lee, Jonghyun; Yoon, Hongkyu; Kitanidis, Peter K.; Werth, Charles J.; Valocchi, Albert J.
2016-07-01
Characterizing subsurface properties is crucial for reliable and cost-effective groundwater supply management and contaminant remediation. With recent advances in sensor technology, large volumes of hydrogeophysical and geochemical data can be obtained to achieve high-resolution images of subsurface properties. However, characterization with such a large amount of information requires prohibitive computational costs associated with "big data" processing and numerous large-scale numerical simulations. To tackle such difficulties, the principal component geostatistical approach (PCGA) has been proposed as a "Jacobian-free" inversion method that requires much smaller forward simulation runs for each iteration than the number of unknown parameters and measurements needed in the traditional inversion methods. PCGA can be conveniently linked to any multiphysics simulation software with independent parallel executions. In this paper, we extend PCGA to handle a large number of measurements (e.g., 106 or more) by constructing a fast preconditioner whose computational cost scales linearly with the data size. For illustration, we characterize the heterogeneous hydraulic conductivity (K) distribution in a laboratory-scale 3-D sand box using about 6 million transient tracer concentration measurements obtained using magnetic resonance imaging. Since each individual observation has little information on the K distribution, the data were compressed by the zeroth temporal moment of breakthrough curves, which is equivalent to the mean travel time under the experimental setting. Only about 2000 forward simulations in total were required to obtain the best estimate with corresponding estimation uncertainty, and the estimated K field captured key patterns of the original packing design, showing the efficiency and effectiveness of the proposed method.
Institute of Scientific and Technical Information of China (English)
QIN Peihua; XIE Zhenghui; YUAN Xing
2013-01-01
To improve the capability of numerical modeling of climate-groundwater interactions,a groundwater component and new surface/subsurface runoff schemes were incorporated into the regional climate model RegCM3,renamed RegCM3_Hydro.20-year simulations from both models were used to investigate the effects of groundwater dynamics and surface/subsurface runoff parameterizations on regional climate over seven river basins in China.A comparison of results shows that RegCM3_Hydro reduced the positive biases of annual and summer (June,July,August) precipitation over six river basins,while it slightly increased the bias over the Huaihe River Basin in eastern China.RegCM3_Hydro also reduced the cold bias of surface air temperature from RegCM3 across years,especially for the Haihe and the Huaihe river basins,with significant bias reductions of 0.80℃ and 0.88℃,respectively.The spatial distribution and seasonal variations of water table depth were also well captured.With the new surface and subsurface runoff schemes,RegCM3_Hydro increased annual surface runoff by 0.11-0.62 mm d-1 over the seven basins.Though previous studies found that incorporating a groundwater component tends to increase soil moisture due to the consideration of upward groundwater recharge,our present work shows that the modified runoff schemes cause less infiltration,which outweigh the recharge from groundwater and result in drier soil,and consequently cause less latent heat and more sensible heat over most of the basins.
Mira, Andrés; Veroslavsky, Gerardo; Rossello, Eduardo; Vives, Luis; Rodríguez, Leticia
2015-10-01
From the integration results of geological and geophysical data, a subsurface geological model of the Corrientes province (Argentina) that allows visualizing its deep geological structure and how it affected the Guaraní Aquifer System (GAS) is presented. 44 boreholes, 21 geophysical surveys and 1366 depth data from a Bouguer gravity anomaly model have been used. The model was built from five layers easily distinguishable in the regional subsurface: basement, pre-GAS sediments (Paleozoic), GAS sediments (Triassic-Lower Cretaceous), basalts (Serra Geral Group, Lower Cretaceous) and post basaltic sediments. The resulting geometry shows a basement with a structural high, the Dorsal Asunción-Rio Grande, where the GAS and the basaltic layer are thinner and the Mesozoic sediments rise near the surface. It is an area prone to local recharge and regional discharge of the GAS and it is in line with the latest piezometry and groundwater chemical analysis. Furthermore, two important depocenters have been identified, Corrientes and Curuzú structural high blocks, with at least 3500 m of sedimentary and volcano-sedimentary deposits that suggest the existence of significant pre-carboniferous sediment units associated to ancient extensional structures of the early Paleozoic. The proposed model allows defining a lithostratigraphic column of Corrientes and gives new criteria to redraw the southwest limit of the GAS.
Scheibe, T. D.; Mahadevan, R.; Fang, Y.; Garg, S.; Long, P. E.; Lovley, D. M.
2008-12-01
Several field and laboratory experiments have demonstrated that the growth and activity of iron-reducing bacteria can be stimulated in many subsurface environments by amendment of groundwater with a soluble electron donor. Under strong iron-reducing conditions, these organisms mediate reactions that can impact a wide range of subsurface contaminants including chlorinated hydrocarbons, metals, and radionuclides. Therefore there is strong interest in in-situ bioremediation as a potential technology for cleanup of contaminated aquifers. To evaluate and design bioremediation systems, as well as to evaluate the viability of monitored natural attenuation as an alternative, quantitative models of biogeochemically reactive transport are needed. To date, most such models represent microbial activity in terms of kinetic rate (e.g., Monod- type) formulations. Such models do not account for fundamental changes in microbial functionality (such as utilization of alternative respiratory pathways) that occur as the result of spatial and temporal variations in the geochemical environment experienced by microorganisms. Constraint-based genome-scale in silico models of microbial metabolism present an alternative to simplified rate formulations that provide flexibility to account for changes in microbial function in response to local geochemical conditions. We have developed and applied a methodology for coupling a constraint-based in silico model of Geobacter sulfurreducens with a conventional model of groundwater flow, transport, and geochemical reaction. Two uses of the in silico model are tested: 1) incorporation of modified microbial growth yield coefficients based on the in silico model, and 2) variation of reaction rates in a reactive transport model based on in silico modeling of a range of local geochemical conditions. Preliminary results from this integrated model will be presented.
Heterogeneous kinetic modeling of the catalytic conversion of cycloparaffins
Al-Sabawi, Mustafa N.
catalytic conversions respectively, are reported. Using these data, heterogeneous kinetic models accounting for intracrystallite molecular transport, adsorption and thermal and catalytic cracking of both cycloparaffin reactants are established. Results show that undesirable hydrogen transfer reactions are more pronounced and selectively favoured against other reactions at lower reaction temperatures, while the desirable ring-opening and cracking reactions predominate at the higher reaction temperatures. Moreover, results of the present work show that while crystallite size may have an effect on the overall conversion in some situations, there is a definite effect on the selectivity of products obtained during the cracking of MCH and decalin and the cracking of MCH in a mixture with co-reactants such as 1,3,5-triisopropylbenzene. Keywords. cycloparaffins, naphthenes, fluid catalytic cracking, kinetic modeling, Y-zeolites, diffusion, adsorption, ring-opening, hydrogen transfer, catalyst selectivity.
Wang, Bo; Bauer, Sebastian
2016-04-01
Geological models are the prerequisite of exploring possible use of the subsurface and evaluating induced impacts. Subsurface geological models often show strong complexity in geometry and hydraulic connectivity because of their heterogeneous nature. In order to model that complexity, the corner point grid approach has been applied by geologists for decades. The corner point grid utilizes a set of hexahedral blocks to represent geological formations. Due to the appearance of eroded geological layers, some edges of those blocks may be collapsed and the blocks thus degenerate. This leads to the inconsistency and the impossibility of using the corner point grid directly with a finite element based simulator. Therefore, in this study, we introduce a workflow for transferring heterogeneous geological models to consistent finite element models. In the corner point grid, the hexahedral blocks without collapsed edges are converted to hexahedral elements directly. But if they degenerate, each block is divided into prism, pyramid and tetrahedral elements based on individual degenerated situation. This approach consistently converts any degenerated corner point grid to a consistent hybrid finite element mesh. Along with the above converting scheme, the corresponding heterogeneous geological data, e.g. permeability and porosity, can be transferred as well. Moreover, well trajectories designed in the corner point grid can be resampled to the nodes in the finite element mesh, which represents the location for source terms along the well path. As a proof of concept, we implement the workflow in the framework of transferring models from Petrel to the finite element OpenGeoSys simulator. As application scenario we choose a deep geothermal reservoir operation in the North German Basin. A well doublet is defined in a saline aquifer in the Rhaetian formation, which has a depth of roughly 4000 m. The geometric model shows all kinds of degenerated blocks due to eroded layers and the
A heterogeneous boundedly rational expectation model for housing market
Institute of Scientific and Technical Information of China (English)
Andrew Y. T. LEUNG; Jia-na XU; Wing Shum TSUI
2009-01-01
This research aims to test the housing price dynamics when considering heterogeneous boundedly rational expectations such as naive expectation, adaptive expectation and biased belief. The housing market is investigated as an evolutionary system with heterogeneous and competing expectations. The results show that the dynamics of the expected housing price varies substantially when heterogeneous expectations are considered together with some other endogenous factors. Simulation results explain some stylized phenomena such as equilibrium or oscillation, convergence or divergence, and over-shooting or under-shooting. Furthermore, the results suggest that variation of the proportion of groups of agents is basically dependent on the selected strategies. It also indicates that control policies should be chosen carefully in consistence with a unique real estate market during a unique period since certain parameter portfolio may increase or suppress oscillation.
Modeling of Bandwidth Aggregation over Heterogeneous Wireless Access Networks
DEFF Research Database (Denmark)
Popovska Avramova, Andrijana; Dittmann, Lars
2012-01-01
Motivated by the multihomming capability of the mobile devices and the fact that the heterogeneous wireless access networks overlap in coverage, mobile operators are looking for solutions that will benefit by simultaneous use of the available multiple access interfaces. Multipath or multilink...... transfer deals with the problem on how to effectively aggregate the bandwidth by simultaneous usage of heterogeneous networks that a host is attached to in order to improve the throughput. This paper deals with a simulation based analysis of bandwidth aggregation techniques and their impact on higher layer...
DEFF Research Database (Denmark)
Huang, Qian; Huang, Yue-Cai; Ko, King-Tim;
2011-01-01
dimensioning and planning. This paper investigates the computationally efficient loss performance modeling for multiservice in hierarchical heterogeneous wireless networks. A speed-sensitive call admission control (CAC) scheme is considered in our model to assign overflowed calls to appropriate tiers...
Accounting for heterogeneity of public lands in hedonic property models
Charlotte Ham; Patricia A. Champ; John B. Loomis; Robin M. Reich
2012-01-01
Open space lands, national forests in particular, are usually treated as homogeneous entities in hedonic price studies. Failure to account for the heterogeneous nature of public open spaces may result in inappropriate inferences about the benefits of proximate location to such lands. In this study the hedonic price method is used to estimate the marginal values for...
Post-seismic relaxation theory on laterally heterogeneous viscoelastic model
Pollitz, F.F.
2003-01-01
Investigation was carried out into the problem of relaxation of a laterally heterogeneous viscoelastic Earth following an impulsive moment release event. The formal solution utilizes a semi-analytic solution for post-seismic deformation on a laterally homogeneous Earth constructed from viscoelastic normal modes, followed by application of mode coupling theory to derive the response on the aspherical Earth. The solution is constructed in the Laplace transform domain using the correspondence principle and is valid for any linear constitutive relationship between stress and strain. The specific implementation described in this paper is a semi-analytic discretization method which assumes isotropic elastic structure and a Maxwell constitutive relation. It accounts for viscoelastic-gravitational coupling under lateral variations in elastic parameters and viscosity. For a given viscoelastic structure and minimum wavelength scale, the computational effort involved with the numerical algorithm is proportional to the volume of the laterally heterogeneous region. Examples are presented of the calculation of post-seismic relaxation with a shallow, laterally heterogeneous volume following synthetic impulsive seismic events, and they illustrate the potentially large effect of regional 3-D heterogeneities on regional deformation patterns.
Cross-layer Modelling for Heterogeneous MPSoCs
DEFF Research Database (Denmark)
Madsen, Jan
2005-01-01
One of the challenges of designing a heterogeneous multiprocessor SoC is to find the right partitioning of the application onto the platform architecture. The right partitioning is dependent on the characteristics of the processors and the network connecting them, as well as the application. We p...
Comment on Hoffman and Rovine (2007): SPSS MIXED can estimate models with heterogeneous variances.
Weaver, Bruce; Black, Ryan A
2015-06-01
Hoffman and Rovine (Behavior Research Methods, 39:101-117, 2007) have provided a very nice overview of how multilevel models can be useful to experimental psychologists. They included two illustrative examples and provided both SAS and SPSS commands for estimating the models they reported. However, upon examining the SPSS syntax for the models reported in their Table 3, we found no syntax for models 2B and 3B, both of which have heterogeneous error variances. Instead, there is syntax that estimates similar models with homogeneous error variances and a comment stating that SPSS does not allow heterogeneous errors. But that is not correct. We provide SPSS MIXED commands to estimate models 2B and 3B with heterogeneous error variances and obtain results nearly identical to those reported by Hoffman and Rovine in their Table 3. Therefore, contrary to the comment in Hoffman and Rovine's syntax file, SPSS MIXED can estimate models with heterogeneous error variances.
Negara, Ardiansyah
2015-05-01
Anisotropy of hydraulic properties of the subsurface geologic formations is an essential feature that has been established as a consequence of the different geologic processes that undergo during the longer geologic time scale. With respect to subsurface reservoirs, in many cases, anisotropy plays significant role in dictating the direction of flow that becomes no longer dependent only on driving forces like the pressure gradient and gravity but also on the principal directions of anisotropy. Therefore, there has been a great deal of motivation to consider anisotropy into the subsurface flow and transport models. In this dissertation, we present subsurface flow modeling in single and dual continuum anisotropic porous media, which include the single-phase groundwater flow coupled with the solute transport in anisotropic porous media, the two-phase flow with gravity effect in anisotropic porous media, and the natural gas flow in anisotropic shale reservoirs. We have employed the multipoint flux approximation (MPFA) method to handle anisotropy in the flow model. The MPFA method is designed to provide correct discretization of the flow equations for general orientation of the principal directions of the permeability tensor. The implementation of MPFA method is combined with the experimenting pressure field approach, a newly developed technique that enables the solution of the global problem breaks down into the solution of multitude of local problems. The numerical results of the study demonstrate the significant effects of anisotropy of the subsurface formations. For the single-phase groundwater flow coupled with the solute transport modeling in anisotropic porous media, the results shows the strong impact of anisotropy on the pressure field and the migration of the solute concentration. For the two-phase flow modeling with gravity effect in anisotropic porous media, it is observed that the buoyancy-driven flow, which emerges due to the density differences between the
Intelligent Mobility Management Model for Heterogeneous Wireless Networks
Directory of Open Access Journals (Sweden)
Sanjeev Prakash
2015-12-01
Full Text Available Growing consumer demands for access of communication services in a ubiquitous environment is a driving force behind the development of new technologies. The rapid development in communication technology permits the end users to access heterogeneous wireless networks to utilize the swerve range of data rate service “anywhere any time”. These forces to technology developers to integrate different wireless access technologies which is known as fourth generation (4G. It is become possible to reduce the size of mobile nodes (MNs with manifold network interfaces and development in IP-based applications. 4G mobile/wireless computing and communication heterogeneous environment consist of various access technologies that differ in bandwidth, network conditions, service type, latency and cost. A major challenge of the 4G wireless network is seamless vertical handoff across the heterogeneous wireless access network as the users are roaming in the heterogeneous wireless network environment. Today communication devices are portable and equipped with manifold interfaces and are capable to roam seamlessly among the various access technology networks for maintaining the network connectivity, since no single-interface technology provides ubiquitous coverage and quality-of-service (QoS. This paper reports a mobile agent based heterogeneous wireless network management system. In this system agent’s decision focuses on multi parameter system (MPS. This system works on the parameters- network delay, received signal strength, network latency and study of the collected information about adjoining network cells viz., accessible channel. System is simulated and a comparative study is also made. From results it is observed that system improves the performance of wireless network.
Energy Technology Data Exchange (ETDEWEB)
Wohleber, X
1997-11-17
The TIBERE Model is a neutron leakage method based on B{sub 1} heterogeneous transport equation resolution. In this work, we have studied the influence of the reflection mode at the boundary of the assembly. In particular the White boundary condition has been implemented in the APOLLO2 neutron transport code. We have compared the two TIBERE kinds of boundary conditions (specular and white) with the classical B{sub 1} homogeneous leakage method in the modelling of some reactors. We have remarked the better capability of the TIBERE Model to compute voided assemblies. The white boundary condition is also able to compute a completely voided assembly and, besides, wins a factor 10 in CPU time in comparison with the specular boundary condition. These two heterogenous leakage formalisms have been tested on a partially voided experiment and have shown that the TIBERE Model can compute this kind of situation with a greater precision than the classical B{sub 1} homogeneous leakage method, and with a shorter computational time. (author)
Energy Technology Data Exchange (ETDEWEB)
Wohleber, X
1997-11-17
The TIBERE Model is a neutron leakage method based on B{sub 1} heterogeneous transport equation resolution. In this work, we have studied the influence of the reflection mode at the boundary of the assembly. In particular the White boundary condition has been implemented in the APOLLO2 neutron transport code. We have compared the two TIBERE kinds of boundary conditions (specular and white) with the classical B{sub 1} homogeneous leakage method in the modelling of some reactors. We have remarked the better capability of the TIBERE Model to compute voided assemblies. The white boundary condition is also able to compute a completely voided assembly and, besides, wins a factor 10 in CPU time in comparison with the specular boundary condition. These two heterogenous leakage formalisms have been tested on a partially voided experiment and have shown that the TIBERE Model can compute this kind of situation with a greater precision than the classical B{sub 1} homogeneous leakage method, and with a shorter computational time. (author)
Warsta, L.; Turunen, M.; Koivusalo, H. J.; Paasonen-Kivekäs, M.; Karvonen, T.; Taskinen, A.
2012-12-01
Simulation of hydrological processes for the purposes of agricultural water management and protection in boreal environment requires description of winter time processes, including heat transport, soil freezing and thawing, and snow accumulation and melt. Finland is located north of the latitude of 60 degrees and has one third to one fourth of the total agricultural land area (2.3 milj. ha) on clay soils (> 30% of clay). Most of the clayey fields are subsurface drained to provide efficient drainage and to enable heavy machines to operate on the fields as soon as possible after the spring snowmelt. Generation of drainflow and surface runoff in cultivated fields leads to nutrient and sediment load, which forms the major share of the total load reaching surface waters at the national level. Water, suspended sediment, and soluble nutrients on clayey field surface are conveyed through the soil profile to the subsurface drains via macropore pathways as the clayey soil matrix is almost impermeable. The objective of the study was to develop the missing winter related processes into the FLUSH model, including soil heat transport, snow pack simulation and the effects of soil freezing and thawing on the soil hydraulic conductivity. FLUSH is an open source (MIT license), distributed, process-based model designed to simulate surface runoff and drainflow in clayey, subsurface drained agricultural fields. 2-D overland flow is described with the diffuse wave approximation of the Saint Venant equations and 3-D subsurface flow with a dual-permeability model. Both macropores and soil matrix are simulated with the Richards equation. Soil heat transport is described with a modified 3-D convection-diffusion equation. Runoff and groundwater data was available from different periods from January 1994 to April 1999 measured in a clayey, subsurface drained field section (3.6 ha) in southern Finland. Soil temperature data was collected in two locations (to a depth of 0.8 m) next to the
Sainath, Kamalesh
2015-01-01
We propose a full-wave pseudo-analytical numerical electromagnetic (EM) algorithm to model subsurface induction sensors, traversing planar-layered geological formations of arbitrary EM material anisotropy and loss, which are used, for example, in the exploration of hydrocarbon reserves. Unlike past pseudo-analytical planar-layered modeling algorithms that impose parallelism between the formation's bed junctions however, our method involves judicious employment of Transformation Optics techniques to address challenges related to modeling arbitrarily-oriented, relative slope (i.e., tilting) between said junctions. The algorithm exhibits this flexibility, both with respect to anisotropy in the formation layers as well as junction tilting, via employing special planar slabs that coat each "flattened" (i.e., originally tilted) planar interface, locally redirecting the incident wave within the coating slabs to cause wave fronts to interact with the flattened interfaces as if they were still tilted with a specific, ...
Computational modeling of heterogeneous reactive materials at the mesoscale
Baer, M. R.
2000-04-01
The mesoscopic processes of consolidation, deformation and reaction of shocked porous energetic materials are studied using shock physics analysis of impact on a collection of discrete "crystals." Highly resolved three-dimensional CTH simulations indicate that rapid deformation occurs at material contact points causing large amplitude fluctuations of stress states with wavelengths of the order of several particle diameters. Localization of energy produces "hot-spots" due to shock focusing and plastic work near internal boundaries as material flows into interstitial regions. Numerical experiments indicate that "hot-spots" are strongly influenced by multiple crystal interactions. Chemical reaction processes also produce multiple wave structures associated with particle distribution effects. This study provides new insights into the micromechanical behavior of heterogeneous energetic materials strongly suggesting that initiation and sustained reaction of shocked heterogeneous materials involves states distinctly different from single jump state descriptions.
Modeling Heterogeneity in Networks using Uncertainty Quantification Tools
Rajendran, Karthikeyan; Siettos, Constantinos I; Laing, Carlo R; Kevrekidis, Ioannis G
2015-01-01
Using the dynamics of information propagation on a network as our illustrative example, we present and discuss a systematic approach to quantifying heterogeneity and its propagation that borrows established tools from Uncertainty Quantification. The crucial assumption underlying this mathematical and computational "technology transfer" is that the evolving states of the nodes in a network quickly become correlated with the corresponding node "identities": features of the nodes imparted by the network structure (e.g. the node degree, the node clustering coefficient). The node dynamics thus depend on heterogeneous (rather than uncertain) parameters, whose distribution over the network results from the network structure. Knowing these distributions allows us to obtain an efficient coarse-grained representation of the network state in terms of the expansion coefficients in suitable orthogonal polynomials. This representation is closely related to mathematical/computational tools for uncertainty quantification (th...
Intelligent Mobility Management Model for Heterogeneous Wireless Networks
Sanjeev Prakash; R. B. Patel; Jain, V.K.
2015-01-01
Growing consumer demands for access of communication services in a ubiquitous environment is a driving force behind the development of new technologies. The rapid development in communication technology permits the end users to access heterogeneous wireless networks to utilize the swerve range of data rate service “anywhere any time”. These forces to technology developers to integrate different wireless access technologies which is known as fourth generation (4G). It is become possible to red...
Establishment of a novel cellular model for myxofibrosarcoma heterogeneity
Lohberger, Birgit; Stuendl, Nicole; Leithner, Andreas; Rinner, Beate; Sauer, Stefan; Kashofer, Karl; Liegl-Atzwanger, Bernadette
2017-01-01
Human cancers frequently display substantial intra-tumoural heterogeneity in virtually all distinguishable phenotypic features, such as cellular morphology, gene expression, and metastatic potential. In order to investigate tumour heterogeneity in myxofibrosarcoma, we established a novel myxofibrosarcoma cell line with two well defined sub-clones named MUG-Myx2a and MUG-Myx2b. The parental tumour tissue and both MUG-Myx2 cell lines showed the same STR profile. The fact that MUG-Myx2a showed higher proliferation activity, faster migration and enhanced tumourigenicity was of particular interest. NGS mutation analysis revealed corresponding mutations in the FGFR3, KIT, KDR and TP53 genes. In contrast, the MUG-Myx2a cell lines showed an additional PTEN mutation. Analysis of CNV uncovered a highly aberrant karyotype with frequent losses and gains in the tumour sample. The two MUG-Myx2 cell lines share several CNV features of the tumour tissue, while some CNVs are present only in the two cell lines. Furthermore, certain CNV gains and losses that are exclusive to either MUG-Myx2a or MUG-Myx2b, distinguish the two cell lines. As it is currently not possible to purchase two different sarcoma cell lines derived from the same patient, the novel myxofibrosarcoma cell lines MUG-Myx2a and MUG-Myx2b will be useful tools to study pathogenesis, tumour heterogeneity and treatment options. PMID:28304377
Randomly-fluctuating heterogeneous continuum model of a ballasted railway track
de Abreu Corrêa, Lucio; Quezada, Juan Carlos; Cottereau, Régis; d'Aguiar, Sofia Costa; Voivret, Charles
2017-07-01
This paper proposes a description of a granular medium as a stochastic heterogeneous continuum medium. The heterogeneity of the material properties field recreates the heterogeneous stress field in a granular medium. The stochastic approach means that only statistical information, easily available, is required to construct the model. The heterogeneous continuum model is Calibrated with respect to discrete simulations of a set of railway ballast samples. As they are continuum-based, the equilibrium equations can be solved on a large scale using a parallel implementation of an explicit time discretization scheme for the Finite Element Method. Simulations representative of the influence on the environment of the passage of a train on a ballasted railway track clearly show the influence of the heterogeneity. These simulations seem to correlate well with previously unexplained overly damped measurements in the free field.
Pawar, R.; Dash, Z.; Sakaki, T.; Plampin, M. R.; Lassen, R. N.; Illangasekare, T. H.; Zyvoloski, G.
2011-12-01
One of the concerns related to geologic CO2 sequestration is potential leakage of CO2 and its subsequent migration to shallow groundwater resources leading to geochemical impacts. Developing approaches to monitor CO2 migration in shallow aquifer and mitigate leakage impacts will require improving our understanding of gas phase formation and multi-phase flow subsequent to CO2 leakage in shallow aquifers. We are utilizing an integrated approach combining laboratory experiments and numerical simulations to characterize the multi-phase flow of CO2 in shallow aquifers. The laboratory experiments involve a series of highly controlled experiments in which CO2 dissolved water is injected in homogeneous and heterogeneous soil columns and tanks. The experimental results are used to study the effects of soil properties, temperature, pressure gradients and heterogeneities on gas formation and migration. We utilize the Finite Element Heat and Mass (FEHM) simulator (Zyvoloski et al, 2010) to numerically model the experimental results. The numerical models capture the physics of CO2 exsolution, multi-phase fluid flow as well as sand heterogeneity. Experimental observations of pressure, temperature and gas saturations are used to develop and constrain conceptual models for CO2 gas-phase formation and multi-phase CO2 flow in porous media. This talk will provide details of development of conceptual models based on experimental observation, development of numerical models for laboratory experiments and modelling results.
A Mixture Innovation Heterogeneous Autoregressive Model for Structural Breaks and Long Memory
DEFF Research Database (Denmark)
Nonejad, Nima
We propose a flexible model to describe nonlinearities and long-range dependence in time series dynamics. Our model is an extension of the heterogeneous autoregressive model. Structural breaks occur through mixture distributions in state innovations of linear Gaussian state space models. Monte Ca...... forecasts compared to any single model specification. It provides further improvements when we average over nonlinear specifications....
Ala-aho, Pertti; Soulsby, Chris; Wang, Hailong; Tetzlaff, Doerthe
2017-04-01
Understanding the role of groundwater for runoff generation in headwater catchments is a challenge in hydrology, particularly so in data-scarce areas. Fully-integrated surface-subsurface modelling has shown potential in increasing process understanding for runoff generation, but high data requirements and difficulties in model calibration are typically assumed to preclude their use in catchment-scale studies. We used a fully integrated surface-subsurface hydrological simulator to enhance groundwater-related process understanding in a headwater catchment with a rich background in empirical data. To set up the model we used minimal data that could be reasonably expected to exist for any experimental catchment. A novel aspect of our approach was in using simplified model parameterisation and including parameters from all model domains (surface, subsurface, evapotranspiration) in automated model calibration. Calibration aimed not only to improve model fit, but also to test the information content of the observations (streamflow, remotely sensed evapotranspiration, median groundwater level) used in calibration objective functions. We identified sensitive parameters in all model domains (subsurface, surface, evapotranspiration), demonstrating that model calibration should be inclusive of parameters from these different model domains. Incorporating groundwater data in calibration objectives improved the model fit for groundwater levels, but simulations did not reproduce well the remotely sensed evapotranspiration time series even after calibration. Spatially explicit model output improved our understanding of how groundwater functions in maintaining streamflow generation primarily via saturation excess overland flow. Steady groundwater inputs created saturated conditions in the valley bottom riparian peatlands, leading to overland flow even during dry periods. Groundwater on the hillslopes was more dynamic in its response to rainfall, acting to expand the saturated area
Controlling Subsurface Fractures and Fluid Flow: A Basic Research Agenda
Energy Technology Data Exchange (ETDEWEB)
Pyrak-Nolte, Laura J [Purdue Univ., West Lafayette, IN (United States); DePaolo, Donald J. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States); Pietraß, Tanja [USDOE Office of Science, Washington, DC (United States)
2015-05-22
. In response, the Office of Science, through its Office of Basic Energy Science (BES), convened a roundtable consisting of 15 national lab, university and industry geoscience experts to brainstorm basic research areas that underpin the SubTER goals but are currently underrepresented in the BES research portfolio. Held in Germantown, Maryland on May 22, 2015, the round-table participants developed a basic research agenda that is detailed in this report. Highlights include the following: -A grand challenge calling for advanced imaging of stress and geological processes to help understand how stresses and chemical substances are distributed in the subsurface—knowledge that is critical to all aspects of subsurface engineering; -A priority research direction aimed at achieving control of fluid flow through fractured media; -A priority research direction aimed at better understanding how mechanical and geochemical perturbations to subsurface rock systems are coupled through fluid and mineral interactions; -A priority research direction aimed at studying the structure, permeability, reactivity and other properties of nanoporous rocks, like shale, which have become critical energy materials and exhibit important hallmarks of mesoscale materials; -A cross-cutting theme that would accelerate development of advanced computational methods to describe heterogeneous time-dependent geologic systems that could, among other potential benefits, provide new and vastly improved models of hydraulic fracturing and its environmental impacts; -A cross-cutting theme that would lead to the creation of “geo-architected materials” with controlled repeatable heterogeneity and structure that can be tested under a variety of thermal, hydraulic, chemical and mechanical conditions relevant to subsurface systems; -A cross-cutting theme calling for new laboratory studies on both natural and geo-architected subsurface materials that deploy advanced high-resolution 3D imaging and chemical analysis
Wang, Neng; Xia, Shuman
2017-01-01
A combined modeling and experimental effort is made in this work to examine the cohesive fracture mechanisms of heterogeneous elastic solids. A two-phase laminated composite, which mimics the key microstructural features of many tough engineering and biological materials, is selected as a model material system. Theoretical and finite element analyses with cohesive zone modeling are performed to study the effective fracture resistance of the heterogeneous material associated with unstable crack propagation and arrest. A crack-tip-position controlled algorithm is implemented in the finite element analysis to overcome the inherent instability issues resulting from crack pinning and depinning at local heterogeneities. Systematic parametric studies are carried out to investigate the effects of various material and geometrical parameters, including the modulus mismatch ratio, phase volume fraction, cohesive zone size, and cohesive law shape. Concurrently, a novel stereolithography-based three-dimensional (3D) printing system is developed and used for fabricating heterogeneous test specimens with well-controlled structural and material properties. Fracture testing of the specimens is performed using the tapered double-cantilever beam (TDCB) test method. With optimal material and geometrical parameters, heterogeneous TDCB specimens are shown to exhibit enhanced effective fracture energy and effective fracture toughness than their homogeneous counterparts, which is in good agreement with the modeling predictions. The integrative computational and experimental study presented here provides a fundamental mechanistic understanding of the fracture mechanisms in brittle heterogeneous materials and sheds light on the rational design of tough materials through patterned heterogeneities.
Stochastic modeling for reliability shocks, burn-in and heterogeneous populations
Finkelstein, Maxim
2013-01-01
Focusing on shocks modeling, burn-in and heterogeneous populations, Stochastic Modeling for Reliability naturally combines these three topics in the unified stochastic framework and presents numerous practical examples that illustrate recent theoretical findings of the authors. The populations of manufactured items in industry are usually heterogeneous. However, the conventional reliability analysis is performed under the implicit assumption of homogeneity, which can result in distortion of the corresponding reliability indices and various misconceptions. Stochastic Modeling for Reliability fills this gap and presents the basics and further developments of reliability theory for heterogeneous populations. Specifically, the authors consider burn-in as a method of elimination of ‘weak’ items from heterogeneous populations. The real life objects are operating in a changing environment. One of the ways to model an impact of this environment is via the external shocks occurring in accordance with some stocha...
A Multianalyzer Machine Learning Model for Marine Heterogeneous Data Schema Mapping
Directory of Open Access Journals (Sweden)
Wang Yan
2014-01-01
Full Text Available The main challenges that marine heterogeneous data integration faces are the problem of accurate schema mapping between heterogeneous data sources. In order to improve the schema mapping efficiency and get more accurate learning results, this paper proposes a heterogeneous data schema mapping method basing on multianalyzer machine learning model. The multianalyzer analysis the learning results comprehensively, and a fuzzy comprehensive evaluation system is introduced for output results’ evaluation and multi factor quantitative judging. Finally, the data mapping comparison experiment on the East China Sea observing data confirms the effectiveness of the model and shows multianalyzer’s obvious improvement of mapping error rate.
A Cellular Automaton Model for Heterogeneous and Incosistent Driver Behavior in Urban Traffic
Institute of Scientific and Technical Information of China (English)
LIUMing-Zhe; ZHAO Shi-Bo; WANG Rui-Li
2012-01-01
In this paper a cellular automaton model is proposed to describe driver behavior at a single-lane urban roundabout. Driver behavior has been considered as heterogeneous and inconsistent. Most traffic papers in the literature just discussed heterogeneous driver behavior, to our best knowledge. Two truncated Caussian distributions are used to model heterogeneous and inconsistent driver behavior, respectively. The physical meanings of two truncated distributions are indicated. This method may help enhance a better understanding of driver behavior at roundabout traffic, and even possibly provide references for roundabout design and management.
Cross-layer Modelling for Heterogeneous MPSoCs
DEFF Research Database (Denmark)
Madsen, Jan
2005-01-01
One of the challenges of designing a heterogeneous multiprocessor SoC is to find the right partitioning of the application onto the platform architecture. The right partitioning is dependent on the characteristics of the processors and the network connecting them, as well as the application. We...... of different mappings of tasks to processors (software or hardware) including memory usage, and effects of RTOS selection, including scheduling, synchronization and resource allocation policies. In this presentation we focus on the programmer’s view illustrated through a design space exploration of a multi...
A MODEL OF HETEROGENEOUS DISTRIBUTED SYSTEM FOR FOREIGN EXCHANGE PORTFOLIO ANALYSIS
Dragutin Kermek; Neven Vrček; Tomislav Jakupić
2006-01-01
The paper investigates the design of heterogeneous distributed system for foreign exchange portfolio analysis. The proposed model includes few separated and dislocated but connected parts through distributed mechanisms. Making system distributed brings new perspectives to performance busting where software based load balancer gets very important role. Desired system should spread over multiple, heterogeneous platforms in order to fulfil open platform goal. Building such a model incorporates d...
GEOSSAV: a simulation tool for subsurface applications
Regli, Christian; Rosenthaler, Lukas; Huggenberger, Peter
2004-04-01
Geostatistical Environment fOr Subsurface Simulation And Visualization (GEOSSAV) is a tool for the integration of hard and soft data into stochastic simulation and visualization of distributions of geological structures and hydrogeological properties in the subsurface. GEOSSAV, as an interface to selected geostatistical modules (bicalib, gamv, vargplt, and sisim) from the Geostatistical Software LIBrary, GSLIB (GSLIB: Geostatistical Software Library and User's Guide, 2nd Edition, Oxford University Press, Oxford, 1998, 369pp), can be used for data analysis, variogram computation of regularly or irregularly spaced data, and sequential indicator simulation of subsurface heterogeneities. Sequential indicator simulation, based on various kriging techniques (simple, ordinary, and Bayesian), is suitable for the simulation of continuous variables such as hydraulic conductivity of an aquifer or chemical concentrations at a contaminated site, and categorical variables which indicate the presence or absence of a particular lithofacies. The software integration platform and development environment of GEOSSAV is Tool command language (Tcl) with its graphical user interface, Toolkit (Tk), and a number of Tcl/Tk extensions. The standard Open Graphics Library application programming interface is used for rendering three-dimensional (3D) data distributions and for slicing perpendicular to the main coordinate axis. Export options for finite-difference groundwater models allow either files that characterize single model layers (which are saved in ASCII matrix format) or files that characterize the complete 3D flow model setup for MODFLOW-based groundwater simulation systems (which are saved in block-centered flow package files (User's documentation for MODFLOW-96, an update to the US Geological Survey modular finite-difference ground-water flow model, Geological Survey Open-File Report 96-485, Reston, VA, 1996, 56pp)). GEOSSAV can be used whenever stochastic solutions are preferred
Boosting iterative stochastic ensemble method for nonlinear calibration of subsurface flow models
Elsheikh, Ahmed H.
2013-06-01
A novel parameter estimation algorithm is proposed. The inverse problem is formulated as a sequential data integration problem in which Gaussian process regression (GPR) is used to integrate the prior knowledge (static data). The search space is further parameterized using Karhunen-Loève expansion to build a set of basis functions that spans the search space. Optimal weights of the reduced basis functions are estimated by an iterative stochastic ensemble method (ISEM). ISEM employs directional derivatives within a Gauss-Newton iteration for efficient gradient estimation. The resulting update equation relies on the inverse of the output covariance matrix which is rank deficient.In the proposed algorithm we use an iterative regularization based on the ℓ2 Boosting algorithm. ℓ2 Boosting iteratively fits the residual and the amount of regularization is controlled by the number of iterations. A termination criteria based on Akaike information criterion (AIC) is utilized. This regularization method is very attractive in terms of performance and simplicity of implementation. The proposed algorithm combining ISEM and ℓ2 Boosting is evaluated on several nonlinear subsurface flow parameter estimation problems. The efficiency of the proposed algorithm is demonstrated by the small size of utilized ensembles and in terms of error convergence rates. © 2013 Elsevier B.V.
Elsheikh, Ahmed H.
2013-06-01
We introduce a nonlinear orthogonal matching pursuit (NOMP) for sparse calibration of subsurface flow models. Sparse calibration is a challenging problem as the unknowns are both the non-zero components of the solution and their associated weights. NOMP is a greedy algorithm that discovers at each iteration the most correlated basis function with the residual from a large pool of basis functions. The discovered basis (aka support) is augmented across the nonlinear iterations. Once a set of basis functions are selected, the solution is obtained by applying Tikhonov regularization. The proposed algorithm relies on stochastically approximated gradient using an iterative stochastic ensemble method (ISEM). In the current study, the search space is parameterized using an overcomplete dictionary of basis functions built using the K-SVD algorithm. The proposed algorithm is the first ensemble based algorithm that tackels the sparse nonlinear parameter estimation problem. © 2013 Elsevier Ltd.
Bucci, Vanni; Majed, Nehreen; Hellweger, Ferdi L; Gu, April Z
2012-03-20
A number of agent-based models (ABMs) for biological wastewater treatment processes have been developed, but their skill in predicting heterogeneity of intracellular storage states has not been tested against observations due to the lack of analytical methods for measuring single-cell intracellular properties. Further, several mechanisms can produce and maintain heterogeneity (e.g., different histories, uneven division) and their relative importance has not been explored. This article presents an ABM for the enhanced biological phosphorus removal (EBPR) treatment process that resolves heterogeneity in three intracellular polymer storage compounds (i.e., polyphosphate, polyhydroxybutyrate, and glycogen) in three functional microbial populations (i.e., polyphosphate-accumulating, glycogen-accumulating, and ordinary heterotrophic organisms). Model predicted distributions were compared to those based on single-cell estimates obtained using a Raman microscopy method for a laboratory-scale sequencing batch reactor (SBR) system. The model can reproduce many features of the observed heterogeneity. Two methods for introducing heterogeneity were evaluated. First, biological variability in individual cell behavior was simulated by randomizing model parameters (e.g., maximum acetate uptake rate) at division. This method produced the best fit to the data. An optimization algorithm was used to determine the best variability (i.e., coefficient of variance) for each parameter, which suggests large variability in acetate uptake. Second, biological variability in individual cell states was simulated by randomizing state variables (e.g., internal nutrient) at division, which was not able to maintain heterogeneity because the memory in the internal states is too short. These results demonstrate the ability of ABM to predict heterogeneity and provide insights into the factors that contribute to it. Comparison of the ABM with an equivalent population-level model illustrates the effect
Nitrate reduction in geologically heterogeneous catchments
DEFF Research Database (Denmark)
Refsgaard, Jens Christian; Auken, Esben; Bamberg, C.A.
2014-01-01
In order to fulfil the requirements of the EU Water Framework Directive nitrate load from agricultural areas to surface water in Denmark needs to be reduced by about 40%. The regulations imposed until now have been uniform, i.e. the same restrictions for all areas independent of the subsurface...... conditions. Studies have shown that on a national basis about 2/3 of the nitrate leaching from the root zone is reduced naturally, through denitrification, in the subsurface before reaching the streams. Therefore, it is more cost-effective to identify robust areas, where nitrate leaching through the root...... the entire catchment. However, as distributed models often do not include local scale hydrogeological heterogeneities, they are typically not able to make accurate predictions at scales smaller than they are calibrated. We present a framework for assessing nitrate reduction in the subsurface...
Revealing spatially heterogeneous relaxation in a model nanocomposite
Cheng, Shiwang; Carrillo, Jan-Michael Y; Bocharova, Vera; Sumpter, Bobby G; Schweizer, Kenneth S; Sokolov, Alexei P
2015-01-01
The detailed nature of spatially heterogeneous dynamics of glycerol-silica nanocomposites is unraveled by combining dielectric spectroscopy with atomistic simulation and statistical mechanical theory. Analysis of the spatial mobility gradient shows no 'glassy' layer, but the alpha relaxation time near the nanoparticle grows with cooling faster than the alpha relaxation time in the bulk, and is ~ 20 times longer at low temperatures. The interfacial layer thickness increases from ~ 1.8 nm at higher temperatures to ~ 3.5 nm upon cooling to near Tg. A real space microscopic description of the mobility gradient is constructed by synergistically combining high temperature atomistic simulation with theory. Our analysis suggests that the interfacial slowing down arises mainly due to an increase of the local cage scale barrier for activated hopping induced by enhanced packing and densification near the nanoparticle surface. The theory is employed to predict how local surface densification can be manipulated to control...
Unobserved Heterogeneity in the Binary Logit Model with Cross-Sectional Data and Short Panels
DEFF Research Database (Denmark)
Holm, Anders; Jæger, Mads Meier; Pedersen, Morten
This paper proposes a new approach to dealing with unobserved heterogeneity in applied research using the binary logit model with cross-sectional data and short panels. Unobserved heterogeneity is particularly important in non-linear regression models such as the binary logit model because, unlike...... in linear regression models, estimates of the effects of observed independent variables are biased even when omitted independent variables are uncorrelated with the observed independent variables. We propose an extension of the binary logit model based on a finite mixture approach in which we conceptualize...
Zacharof, A I; Butler, A P
2004-01-01
A mathematical model simulating the hydrological and biochemical processes occurring in landfilled waste is presented and demonstrated. The model combines biochemical and hydrological models into an integrated representation of the landfill environment. Waste decomposition is modelled using traditional biochemical waste decomposition pathways combined with a simplified methodology for representing the rate of decomposition. Water flow through the waste is represented using a statistical velocity model capable of representing the effects of waste heterogeneity on leachate flow through the waste. Given the limitations in data capture from landfill sites, significant emphasis is placed on improving parameter identification and reducing parameter requirements. A sensitivity analysis is performed, highlighting the model's response to changes in input variables. A model test run is also presented, demonstrating the model capabilities. A parameter perturbation model sensitivity analysis was also performed. This has been able to show that although the model is sensitive to certain key parameters, its overall intuitive response provides a good basis for making reasonable predictions of the future state of the landfill system. Finally, due to the high uncertainty associated with landfill data, a tool for handling input data uncertainty is incorporated in the model's structure. It is concluded that the model can be used as a reasonable tool for modelling landfill processes and that further work should be undertaken to assess the model's performance.
Collignon, Bertrand; Halloy, José
2015-01-01
Collective motion is one of the most ubiquitous behaviours displayed by social organisms and has led to the development of numerous models. Recent advances in the understanding of sensory system and information processing by animals impel to revise classical assumptions made in decisional algorithms. In this context, we present a new model describing the three dimensional visual sensory system of fish that adjust their trajectory according to their perception field. Furthermore, we introduce a new stochastic process based on a probability distribution function to move in targeted directions rather than on a summation of influential vectors as it is classically assumed by most models. We show that this model can spontaneously transits from consensus to choice. In parallel, we present experimental results of zebrafish (alone or in group of 10) swimming in both homogeneous and heterogeneous environments. We use these experimental data to set the parameter values of our model and show that this perception-based a...
Long-range Ising model for credit portfolios with heterogeneous credit exposures
Kato, Kensuke
2016-11-01
We propose the finite-size long-range Ising model as a model for heterogeneous credit portfolios held by a financial institution in the view of econophysics. The model expresses the heterogeneity of the default probability and the default correlation by dividing a credit portfolio into multiple sectors characterized by credit rating and industry. The model also expresses the heterogeneity of the credit exposure, which is difficult to evaluate analytically, by applying the replica exchange Monte Carlo method to numerically calculate the loss distribution. To analyze the characteristics of the loss distribution for credit portfolios with heterogeneous credit exposures, we apply this model to various credit portfolios and evaluate credit risk. As a result, we show that the tail of the loss distribution calculated by this model has characteristics that are different from the tail of the loss distribution of the standard models used in credit risk modeling. We also show that there is a possibility of different evaluations of credit risk according to the pattern of heterogeneity.
An Improved Model for Computing-Intensive Tasks on Heterogeneous Workstations
Institute of Scientific and Technical Information of China (English)
邬延辉; 陆鑫达
2004-01-01
An improved algorithm, which solves cooperative concurrent computing tasks using the idle cycles of a number of high performance heterogeneous workstations interconnected through a high-speed network, was proposed. In order to get better parallel computation performance, this paper gave a model and an algorithm of task scheduling among heterogeneous workstations, in which the costs of loading data, computing, communication and collecting results are considered. Using this efficient algorithm, an optimal subset of heterogeneous workstations with the shortest parallel executing time of tasks can be selected.
Gosses, M. J.; Wöhling, Th.; Moore, C. R.; Dann, R.; Scott, D. M.; Close, M.
2012-04-01
-specific prediction target under consideration. Therefore, the worth of individual observation locations may differ for different prediction targets. Our evaluation is based on predictions of lowland stream discharge resulting from changes in land use and irrigation in the upper Central Plains catchment. In our analysis, we adopt the model predictive uncertainty analysis method by Moore and Doherty (2005) which accounts for contributions from both measurement errors and uncertain structural heterogeneity. The method is robust and efficient due to a linearity assumption in the governing equations and readily implemented for application in the model-independent parameter estimation and uncertainty analysis toolkit PEST (Doherty, 2010). The proposed methods can be applied not only for the evaluation of monitoring networks, but also for the optimization of networks, to compare alternative monitoring strategies, as well as to identify best cost-benefit monitoring design even prior to any data acquisition.
Lowell, R. P.; Houghton, J. L.; Farough, A.; Craft, K. L.; Larson, B. I.; Meile, C. D.
2015-09-01
We describe a variety of one- and two-dimensional mathematical modeling approaches to characterizing diffuse flow circulation at mid-ocean ridge hydrothermal systems. The goal is to estimate the potential extent of the sub-seafloor microbial biosphere based on subsurface contours of the 120 °C isotherm as determined from the various models. The models suggest that the sub-seafloor depth for microbial life may range from less than 1 m in some places to the thickness of crustal layer 2A of ∼ 500 m in others. This depth depends primarily on how diffuse flow is driven. The 120 °C isotherm tends to be much deeper if diffuse flow is induced as boundary layer flow near high-temperature plumes, than if it results from conductive cooling or mixing near the seafloor. Because the heat flow alone may not allow identification of the flow regime in the subsurface, we highlight the use of chemical tracers as an additional constraint that sheds light into the flow and reaction patterns associated with vents. We use thermodynamic modeling, which connects the temperature of the diffuse fluid to its chemical composition. As the temperature-composition relationships differ for mixing versus conductive heating and cooling, the fluid geochemistry can shed light on subsurface transport. Using methane as an example, the geochemical models indicate subsurface microbial methane production and consumption in different regions of the vent field near EPR 9 °50‧ N.
Energy Technology Data Exchange (ETDEWEB)
Oostrom, Mart; Thorne, Paul D.; Zhang, Z. F.; Last, George V.; Truex, Michael J.
2008-12-17
Three-dimensional simulations considered migration of dense, nonaqueous phase liquid (DNAPL) consisting of CT and co disposed organics in the subsurface as a function of the properties and distribution of subsurface sediments and of the properties and disposal history of the waste. Simulations of CT migration were conducted using the Water-Oil-Air mode of Subsurface Transport Over Multiple Phases (STOMP) simulator. A large-scale model was configured to model CT and waste water discharge from the major CT and waste-water disposal sites.
Process Integration, data management, and visualization framework for subsurface sciences
Energy Technology Data Exchange (ETDEWEB)
Schuchardt, Karen L.; Black, Gary D.; Chase, Jared M.; Elsethagen, Todd O.; Sun, Lisong
2007-08-23
Applying subsurface simulation codes to understand heterogeneous flow and transport problems is a complex process potentially involving multiple models, multiple scales, and spanning multiple scientific disciplines. For each model used, the process may involve steps such as changing the model, acquiring and preparing input data sources, configuring the model, executing the model on a remote supercomputer, validating the results, and performing calibration and sensitivity analysis all before predictive modeling can be applied to important environmental remediation problems. This process involves many tools, scripts and data sources usually shared only though informal channels. Additionally, the process contains many sub-processes that are repeated frequently and could be automated and shared. Finally, keeping records of the models, processes, and correlation between inputs and outputs is currently manual, time consuming and error prone. We are developing a software framework that integrates a workflow execution environment, shared data repository, and analysis and visualization tools to support development and use of new hybrid subsurface simulation codes. We are taking advantage of recent advances in scientific process automation using the Kepler system and advances in data services based on content management. Extensibility and flexibility are underlying design considerations to support the constantly changing set of tools, scripts, and models available. We describe the architecture and components of this system with early examples of applying it to a continuum subsurface model.
Holloway, Jean E.; Rudy, Ashley C. A.; Lamoureux, Scott F.; Treitz, Paul M.
2017-06-01
Warming of the Arctic in recent years has led to changes in the active layer and uppermost permafrost. In particular, thick active layer formation results in more frequent thaw of the ice-rich transient layer. This addition of moisture, as well as infiltration from late season precipitation, results in high pore-water pressures (PWPs) at the base of the active layer and can potentially result in landscape degradation. To predict areas that have the potential for subsurface pressurization, we use susceptibility maps generated using a generalized additive model (GAM). As model response variables, we used active layer detachments (ALDs) and mud ejections (MEs), both formed by high PWP conditions at the Cape Bounty Arctic Watershed Observatory, Melville Island, Canada. As explanatory variables, we used the terrain characteristics elevation, slope, distance to water, topographic position index (TPI), potential incoming solar radiation (PISR), distance to water, normalized difference vegetation index (NDVI; ME model only), geology, and topographic wetness index (TWI). ALDs and MEs were accurately modelled in terms of susceptibility to disturbance across the study area. The susceptibility models demonstrate that ALDs are most probable on hill slopes with gradual to steep slopes and relatively low PISR, whereas MEs are associated with higher elevation areas, lower slope angles, and areas relatively far from water. Based on these results, this method identifies areas that may be sensitive to high PWPs and helps improve our understanding of geomorphic sensitivity to permafrost degradation.
Directory of Open Access Journals (Sweden)
C. Lanni
2012-11-01
Full Text Available Topographic index-based hydrological models have gained wide use to describe the hydrological control on the triggering of rainfall-induced shallow landslides at the catchment scale. A common assumption in these models is that a spatially continuous water table occurs simultaneously across the catchment. However, during a rainfall event isolated patches of subsurface saturation form above an impeding layer and their hydrological connectivity is a necessary condition for lateral flow initiation at a point on the hillslope.
Here, a new hydrological model is presented, which allows us to account for the concept of hydrological connectivity while keeping the simplicity of the topographic index approach. A dynamic topographic index is used to describe the transient lateral flow that is established at a hillslope element when the rainfall amount exceeds a threshold value allowing for (a development of a perched water table above an impeding layer, and (b hydrological connectivity between the hillslope element and its own upslope contributing area. A spatially variable soil depth is the main control of hydrological connectivity in the model. The hydrological model is coupled with the infinite slope stability model and with a scaling model for the rainfall frequency–duration relationship to determine the return period of the critical rainfall needed to cause instability on three catchments located in the Italian Alps, where a survey of soil depth spatial distribution is available. The model is compared with a quasi-dynamic model in which the dynamic nature of the hydrological connectivity is neglected. The results show a better performance of the new model in predicting observed shallow landslides, implying that soil depth spatial variability and connectivity bear a significant control on shallow landsliding.
Spatial heterogeneity in hedonic house price models : The case of Austria
Helbich, M.; Brunauer, W.; Vaz, E.; Nijkamp, P.
2014-01-01
Modelling spatial heterogeneity (SH) is a controversial subject in real estate economics. Single-family-home prices in Austria are explored to investigate the capability of global and locally weighted hedonic models. Even if regional indicators are not fully capable to model SH and technical amendme
Evaluating 3-D and 1-D mathematical models for mass transport in heterogeneous biofilms
DEFF Research Database (Denmark)
Morgenroth, Eberhard Friedrich; Eberl, H.; van Loosdrecht, M. C. M.
2000-01-01
Results from a three dimensional model for heterogeneous biofilms including the numerical solution of hydrodynamics were compared to simplified one dimensional models. A one dimensional model with a variable diffusion coefficient over the thickness of the biofilm was well suited to approximate av...... in a growing biofilm and in a mushroom type biofilm assuming different modes of detachment....
A multiple time-scale model for TCP bandwidth sharing under user heterogeneity
Abendroth, D.; Berg, J.L. van den; Mandjes, M.
2005-01-01
Building on the vast body of existing TCP models, we develop a novel versatile model that explicitly captures user heterogeneity, and takes into consideration dynamics at both the packet level and the flow level. It is described how the resulting multiple time-scale model can be numerically evaluate
Evaluating 3-D and 1-D mathematical models for mass transport in heterogeneous biofilms
DEFF Research Database (Denmark)
Morgenroth, Eberhard Friedrich; Eberl, H.; van Loosdrecht, M. C. M.
2000-01-01
Results from a three dimensional model for heterogeneous biofilms including the numerical solution of hydrodynamics were compared to simplified one dimensional models. A one dimensional model with a variable diffusion coefficient over the thickness of the biofilm was well suited to approximate av...... in a growing biofilm and in a mushroom type biofilm assuming different modes of detachment....
Coarse mesh transport theory model for heterogeneous systems
Ilas, Danut
To improve fuel utilization, recent reactor cores have become substantially more heterogeneous. In these cores, use of variable fuel enrichments and strong absorbers lead to high neutron flux gradients, which may limit the accuracy (validity) of diffusion theory based methods. In fact, the diffusion equation itself may become a poor approximation of the Boltzmann equation, the exact equation that describes the neutron flux. Therefore, numerical methods to solve the transport equation efficiently over a large heterogeneous region (such as a reactor core) are very desirable in case where the diffusion approximation breaks down. Presently, the only methods capable of computing the power (flux) distributions very accurately throughout a large system such as a nuclear reactor core are the Monte-Carlo or the fine-mesh transport theory methods. Both these methods suffer from the long computational time which makes them useless for routine core calculations. Starting from a variational principle that admits trial functions that can be discontinuous at coarse mesh (assembly) interfaces, we propose a method to solve the transport equation on a spatial grid made up of meshes as large as the size of a fuel assembly. The variational principle is derived for the most general case, but further methods are developed for one-dimensional geometry with the angular variable treated by discrete ordinates. The method uses the finite element approach for the space variable with basis functions precomputed for each element to obtain an algebraic linear system of equations. The eigenvalue of this system is the multiplication constant and the eigenvector represents the incoming angular fluxes for each coarse mesh. The latter allows the reconstruction of the fine mesh solution (angular flux) throughout the domain of interest when used with the basis functions (surface Green's function) for each coarse mesh. The method requires no homogenization procedure that can be a serious source of
Institute of Scientific and Technical Information of China (English)
李沁; 宋新山; 陆化杰; 严登华
2012-01-01
Series of simulated horizontal subsurface-flow constructed wetlands using different sized glass beads (4-9,8-12,11-17 mm) as wetland filter media were established to investigate the effect of heterogeneous porous media on the hydraulic efficiency of the wetland. Flow through the filter bed was visualized by injecting dyed fluid into the water-saturated model. The hydraulic parameters such as hydraulic retention time, effective volume fraction and hy draulic efficiency were detected using chloride tracer. The flow patterns were also analyzed. Results showed that the dyed fluid in different experiment apparatus presented different flow pattern. In the simulated constructed wetland filled with small grain size glass beads (4-9 mm) , the dyed fluid from top inlet to bottom outlet had the highest effec tive volume, means the constructed wetland had the highest space utilization ratio, effective volume ratio and dye flow distribution area, the dyed fluid was in arc shape around the corner, and the dead area was the smallest. When the di ameter of glass beads ranged 4-9 mm, the mean retention time of wetland and its distribution divergence was 0. 437 8 h and 0. 052 5, the effective volume ratio and hydraulic efficiency of wetland was 0. 495 7 and 0. 469 6 respectively. With increasing the diameter of glass beads, the mean retention time was shortened, the distribution divergence of mean retention time was increased and the effective volume ratio and hydraulic efficiency were decreased. Reasonable distribution of hydraulic retention time could increase the effective volume ratio of wetland, namely the wetland had larger effective volume for sewage migration, which was benefit for the sufficient connection of pollutants, substrate and microbes in substrate, so as to improve the removal efficient of pollutants.%对比以不同粒径(4～9、8～12、11～17 mm)非均质多孔介质(玻璃珠)作为基质的水平潜流人工湿地(以有机玻璃板材模拟)的水力效率
Moghadas, D.; André, F.; Vereecken, H.; Lambot, S.
2009-04-01
Water is a vital resource for human needs, agriculture, sanitation and industrial supply. The knowledge of soil water dynamics and solute transport is essential in agricultural and environmental engineering as it controls plant growth, hydrological processes, and the contamination of surface and subsurface water. Increased irrigation efficiency has also an important role for water conservation, reducing drainage and mitigating some of the water pollution and soil salinity. Geophysical methods are effective techniques for monitoring the vadose zone. In particular, electromagnetic induction (EMI) can provide in a non-invasive way important information about the soil electrical properties at the field scale, which are mainly correlated to important variables such as soil water content, salinity, and texture. EMI is based on the radiation of a VLF EM wave into the soil. Depending on its electrical conductivity, Foucault currents are generated and produce a secondary EM field which is then recorded by the EMI system. Advanced techniques for EMI data interpretation resort to inverse modeling. Yet, a major gap in current knowledge is the limited accuracy of the forward model used for describing the EMI-subsurface system, usually relying on strongly simplifying assumptions. We present a new low frequency EMI method based on Vector Network Analyzer (VNA) technology and advanced forward modeling using a linear system of complex transfer functions for describing the EMI loop antenna and a three-dimensional solution of Maxwell's equations for wave propagation in multilayered media. VNA permits simple, international standard calibration of the EMI system. We derived a Green's function for the zero-offset, off-ground horizontal loop antenna and also proposed an optimal integration path for faster evaluation of the spatial-domain Green's function from its spectral counterpart. This new integration path shows fewer oscillations compared with the real path and permits to avoid the
Uncertainty estimation in one-dimensional heat transport model for heterogeneous porous medium.
Chang, Ching-Min; Yeh, Hund-Der
2014-01-01
In many practical applications, the rates for ground water recharge and discharge are determined based on the analytical solution developed by Bredehoeft and Papadopulos (1965) to the one-dimensional steady-state heat transport equation. Groundwater flow processes are affected by the heterogeneity of subsurface systems; yet, the details of which cannot be anticipated precisely. There exists a great deal of uncertainty (variability) associated with the application of Bredehoeft and Papadopulos' solution (1965) to the field-scale heat transport problems. However, the quantification of uncertainty involved in such application has so far not been addressed, which is the objective of this wok. In addition, the influence of the statistical properties of log hydraulic conductivity field on the variability in temperature field in a heterogeneous aquifer is also investigated. The results of the analysis demonstrate that the variability (or uncertainty) in the temperature field increases with the correlation scale of the log hydraulic conductivity covariance function and the variability of temperature field also depends positively on the position.
Modeling two-dimensional water flow and bromide transport in a heterogeneous lignitic mine soil
Energy Technology Data Exchange (ETDEWEB)
Buczko, U.; Gerke, H.H. [Brandenburg University of Technology, Cottbus (Germany)
2006-02-15
Water and solute fluxes in lignitic mine soils and in many other soils are often highly heterogeneous. Here, heterogeneity reflects dumping-induced inclined structures and embedded heterogeneous distributions of sediment mixtures and of lignitic fragments. Such two-scale heterogeneity effects may be analyzed through the application of two-dimensional models for calculating water and solute fluxes. The objective of this study was to gain more insight to what extent spatial heterogeneity of soil hydraulic parameters contributes to preferential flow at a lignitic mine soil. The simulations pertained to the 'Barenbrucker Hohe' site in Germany where previously water fluxes and applied tracers had been monitored with a cell lysimeter, and from where a soil block had been excavated for detailed two-dimensional characterization of the hydraulic parameters using pedotransfer functions. Based on those previous studies, scenarios with different distributions of hydraulic parameters were simulated. The results show that spatial variability of hydraulic parameters alone can hardly explain the observed flow patterns. The observed preferential flow at the site was probably caused by additional factors such as hydrophobicity, the presence of root channels, anisotropy in the hydraulic conductivity, and heterogeneous root distributions. To study the relative importance of these other factors by applying two-dimensional flow models to such sites, the experimental database must be improved. Single-continuum model approaches may be insufficient for such sites.
Revealing spatially heterogeneous relaxation in a model nanocomposite
Energy Technology Data Exchange (ETDEWEB)
Cheng, Shiwang; Bocharova, Vera [Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Mirigian, Stephen; Schweizer, Kenneth S. [Department of Materials Science and Chemistry, Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801 (United States); Carrillo, Jan-Michael Y.; Sumpter, Bobby G. [Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Sokolov, Alexei P., E-mail: sokolov@utk.edu [Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Department of Chemistry, Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996 (United States)
2015-11-21
The detailed nature of spatially heterogeneous dynamics of glycerol-silica nanocomposites is unraveled by combining dielectric spectroscopy with atomistic simulation and statistical mechanical theory. Analysis of the spatial mobility gradient shows no “glassy” layer, but the α-relaxation time near the nanoparticle grows with cooling faster than the α-relaxation time in the bulk and is ∼20 times longer at low temperatures. The interfacial layer thickness increases from ∼1.8 nm at higher temperatures to ∼3.5 nm upon cooling to near bulk T{sub g}. A real space microscopic description of the mobility gradient is constructed by synergistically combining high temperature atomistic simulation with theory. Our analysis suggests that the interfacial slowing down arises mainly due to an increase of the local cage scale barrier for activated hopping induced by enhanced packing and densification near the nanoparticle surface. The theory is employed to predict how local surface densification can be manipulated to control layer dynamics and shear rigidity over a wide temperature range.
Inductive Model Generation for Text Classification Using a Bipartite Heterogeneous Network
Institute of Scientific and Technical Information of China (English)
Rafael Geraldeli Rossi; Alneu de Andrade Lopes; Thiago de Paulo Faleiros; Solange Oliveira Rezende
2014-01-01
Algorithms for numeric data classification have been applied for text classification. Usually the vector space model is used to represent text collections. The characteristics of this representation such as sparsity and high dimensionality sometimes impair the quality of general-purpose classifiers. Networks can be used to represent text collections, avoiding the high sparsity and allowing to model relationships among different objects that compose a text collection. Such network-based representations can improve the quality of the classification results. One of the simplest ways to represent textual collections by a network is through a bipartite heterogeneous network, which is composed of objects that represent the documents connected to objects that represent the terms. Heterogeneous bipartite networks do not require computation of similarities or relations among the objects and can be used to model any type of text collection. Due to the advantages of representing text collections through bipartite heterogeneous networks, in this article we present a text classifier which builds a classification model using the structure of a bipartite heterogeneous network. Such an algorithm, referred to as IMBHN (Inductive Model Based on Bipartite Heterogeneous Network), induces a classification model assigning weights to ob jects that represent the terms for each class of the text collection. An empirical evaluation using a large amount of text collections from different domains shows that the proposed IMBHN algorithm produces significantly better results than k-NN, C4.5, SVM, and Naive Bayes algorithms.
Matching Heterogenous Open Innovation Strategies with Business Model Dimensions
Saebi, Tina; Foss, Nicolai Juul
2014-01-01
Research on open innovation suggests that companies benefit differentially from adopting open innovation strategies; however, it is unclear why this is so. One possible explanation is that companies' business models are not attuned to open strategies. Accordingly, we propose a contingency model of open business models by systematically linking open innovation strategies to core business model dimensions, notably the content, structure, and governance of transactions. We further illustrate a c...
Stafleu, Jan; Busschers, Freek; Tanabe, Susumu
2016-04-01
The Tokyo Lowland is situated in a Neogene sedimentary basin near the triple junction of the North American, Pacific, and Philippine tectonic plates. The basin is filled with Neogene and Quaternary sediments up to a thickness of 3 km. In the upper 70 m of the basin, thick sequences of soft Holocene sediments occur which are assumed to have played a key role in the spatial variation of damage intensity during the 1923 Kanto earthquake (Magnitude 7.9 to 8.3). Historical records show this earthquake destroyed large parts of the Tokyo urban area which in that time was largely made up by wooden houses. Although the epicentre was 70 km to the southwest of Tokyo, severe damage occurred north of the city centre, presumably due to ground motion amplification in the soft Holocene sediments in the shallow subsurface. In order to assess the presumed relation between the damage pattern of the 1923 earthquake and the occurrence of soft Holocene sediments in the shallow subsurface, we constructed a 3D geological voxel model of the central part of the Tokyo Lowland. The model was constructed using a methodology originally developed for the lowlands of the Netherlands. The modelling workflow basically consists of three steps. First, some 10,000 borehole descriptions (gathered for geomechanical purposes), were subdivided into geological units that have uniform sediment characteristics, using both lithological and geomechanical (N-value) criteria. Second, 2D bounding surfaces were constructed, representing tops and bases of the geological units. These surfaces were used to place each voxel (100 by 100 by 1 m) within the correct geological unit. The N-values and lithological units in the borehole descriptions were subsequently used to perform a 3D stochastic interpolation of N-value and lithological class within each geological unit. Using a vertical voxel stack analysis, we were able to create a map showing the accumulated thickness of soft muds in the Holocene succession. A
Directory of Open Access Journals (Sweden)
C. L. Tague
2012-07-01
Full Text Available Hydrologic models are one of the core tools used to project how water resources may change under a warming climate. These models are typically applied over a range of scales, from headwater streams to higher order rivers, and for a variety of purposes, such as evaluating changes to aquatic habitat or reservoir operation. Most hydrologic models require streamflow data to calibrate subsurface drainage parameters. In many cases, long-term gage records may not be available for calibration, particularly when assessments are focused on low order stream reaches. Consequently, hydrologic modeling of climate change impacts is often performed in the absence of sufficient data to fully parameterize these hydrologic models. In this paper, we assess a geologic-based strategy for assigning drainage parameters. We examine the performance of this modeling strategy for the McKenzie River watershed in the US Oregon Cascades, a region where previous work has demonstrated sharp contrasts in hydrology based primarily on geological differences between the High and Western Cascades. Based on calibration and verification using existing streamflow data, we demonstrate that: (1 a set of streams ranging from 1st to 3rd order within the Western Cascade geologic region can share the same drainage parameter set, and (2 streams from the High Cascade geologic region, however, require a distinctive parameter set. Further, we show that a watershed comprised of a mixture of High and Western Cascade geology can be modeled without additional calibration by transferring parameters from these distinctive High and Western Cascade end-member parameter sets. Using this geologically-based parameter transfer scheme, our model predictions for all watersheds capture dominant historic streamflow patterns, and are sufficiently accurate to resolve geo-climatic differences in how these different watersheds are likely to respond to simple warming scenarios.
Directory of Open Access Journals (Sweden)
C. L. Tague
2013-01-01
Full Text Available Hydrologic models are one of the core tools used to project how water resources may change under a warming climate. These models are typically applied over a range of scales, from headwater streams to higher order rivers, and for a variety of purposes, such as evaluating changes to aquatic habitat or reservoir operation. Most hydrologic models require streamflow data to calibrate subsurface drainage parameters. In many cases, long-term gage records may not be available for calibration, particularly when assessments are focused on low-order stream reaches. Consequently, hydrologic modeling of climate change impacts is often performed in the absence of sufficient data to fully parameterize these hydrologic models. In this paper, we assess a geologic-based strategy for assigning drainage parameters. We examine the performance of this modeling strategy for the McKenzie River watershed in the US Oregon Cascades, a region where previous work has demonstrated sharp contrasts in hydrology based primarily on geological differences between the High and Western Cascades. Based on calibration and verification using existing streamflow data, we demonstrate that: (1 a set of streams ranging from 1st to 3rd order within the Western Cascade geologic region can share the same drainage parameter set, while (2 streams from the High Cascade geologic region require a different parameter set. Further, we show that a watershed comprised of a mixture of High and Western Cascade geologies can be modeled without additional calibration by transferring parameters from these distinctive High and Western Cascade end-member parameter sets. More generally, we show that by defining a set of end-member parameters that reflect different geologic classes, we can more efficiently apply a hydrologic model over a geologically complex landscape and resolve geo-climatic differences in how different watersheds are likely to respond to simple warming scenarios.
ITE CHARACTERIZATION TO SUPPORT CONCEPTUAL MODEL DEVELOPMENT FOR SUBSURFACE RADIONUCLIDE TRANSPORT
Remediation of radionuclide contaminants in ground water often begins with the development of conceptual and analytical models that guide our understanding of the processes controlling radionuclide transport. The reliability of these models is often predicated on the collection o...
Geng, Xiaolong; Boufadel, Michel C.; Cui, Fangda
2017-08-01
A numerical study was undertaken to investigate subsurface release and fate of benzene and toluene in a tidally influenced beach. The simulations were conducted by using a numerical model BIOMARUN, which coupled a multi-Monod kinetic model BIOB to a density-dependent variably saturated groundwater flow model MARUN. The fate and transport of the contaminant plume were characterized by computing its centroid trajectory, spreading area and percentage of biodegradation in beach saturated and unsaturated zone, respectively. Key factors likely affecting this process were investigated, including tide amplitude, capillarity and hydraulic conductivity. It was found that aerobic biodegradation was the major fate of the contaminant plume in the beach. Tidal action twisted the centroid of the contaminant plume during its migration in the beach, which increased the residence time of the plume in the beach. High tidal range significantly altered the spatial distribution of the contaminant biodegradation in the beach. In contrast, the capillary fringe had impacts on the percentage of benzene biodegraded in the saturated and unsaturated zone of the beach. The increase in capillary fringe enhanced the percentage of the contaminant biodegraded in the unsaturated zone, up to 40%, which is comparable to that in the saturated zone. Hydraulic conductivity seemed to have large impacts on the biodegradation rate of the contaminant in the beach. Higher hydraulic conductivity induced faster contaminant biodegradation in the beach.
Martin, Johannie; Dumont, Dany; Tremblay, Jean-Éric
2013-11-01
Previous comprehensive investigations of the Canadian Arctic revealed that subsurface chlorophyll maxima (SCM) are widespread and long-lived structures that can contribute significantly to daily primary production in the water column. However, estimating the annual contribution of SCM to production with in situ or remote-sensing approaches is challenging in the high Arctic. For this reason and to estimate the impacts of fluctuating or changing environmental conditions on SCM, a numerical approach combining a turbulence model and an ecosystem model was implemented for the coastal Beaufort Sea. An ensemble analysis of simulations suggested that SCM contribute 65-90% of total annual primary production and that this proportion is weakly affected by ice regime, winter nitrogen (N) concentration, parameter values determining phytoplankton growth and decay or the physical forcing imposed, all varying within realistic values. Due to the persistent association between the SCM and the shallow nitracline, the pelagic ecosystem of the coastal Beaufort Sea is apparently characterized by a high ratio of new to total production, contrasting with the common assumption that oligotrophic systems are predominantly supported by recycled N and regenerated production. This study demonstrated that the use of a simple model in combination with in situ data leads to novel insights into biogeochemical processes that are otherwise very difficult to measure and track.
Multi-Volume CAD Modeling for Heterogeneous Object Design and Fabrication
Institute of Scientific and Technical Information of China (English)
SUN Wei
2000-01-01
he current computer-aided technologies in design and product development, the evolution of CAD modeling, and a framework of multi-volume CAD modeling system for heterogeneous object design and fabrication are presented in this paper.The multi-volume CAD modeling system is presented based on nonmanifold topological elements. Material identifications are defined as design attributes introduced along with geometric and topological information at the design stage. Extended Euler operation and reasoning Boolean operations for merging and extraction are executed according to the associated material identifications in the developed multi-volume modeling system for heterogeneous object.An application example and a pseudo-processing algorithm for prototyping of heterogeneous structure through solid free-form fabrication are also described.1
Performance Analysis of Heterogeneous Data Centers in Cloud Computing Using a Complex Queuing Model
Directory of Open Access Journals (Sweden)
Wei-Hua Bai
2015-01-01
Full Text Available Performance evaluation of modern cloud data centers has attracted considerable research attention among both cloud providers and cloud customers. In this paper, we investigate the heterogeneity of modern data centers and the service process used in these heterogeneous data centers. Using queuing theory, we construct a complex queuing model composed of two concatenated queuing systems and present this as an analytical model for evaluating the performance of heterogeneous data centers. Based on this complex queuing model, we analyze the mean response time, the mean waiting time, and other important performance indicators. We also conduct simulation experiments to confirm the validity of the complex queuing model. We further conduct numerical experiments to demonstrate that the traffic intensity (or utilization of each execution server, as well as the configuration of server clusters, in a heterogeneous data center will impact the performance of the system. Our results indicate that our analytical model is effective in accurately estimating the performance of the heterogeneous data center.
The effect of ignoring individual heterogeneity in Weibull log-normal sire frailty models
DEFF Research Database (Denmark)
Damgaard, Lars Holm; Korsgaard, Inge Riis; Simonsen, J;
2006-01-01
The objective of this study was, by means of simulation, to quantify the effect of ignoring individual heterogeneity in Weibull sire frailty models on parameter estimates and to address the consequences for genetic inferences. Three simulation studies were evaluated, which included 3 levels...... the software Survival Kit for the incomplete sire model. For the incomplete sire model, the Monte Carlo and Survival Kit parameter estimates were similar. This study established that when unobserved individual heterogeneity was ignored, the parameter estimates that included sire effects were biased toward zero...
Discrete time duration models with group-level heterogeneity
DEFF Research Database (Denmark)
Frederiksen, Anders; Honoré, Bo; Hu, Loujia
2007-01-01
Dynamic discrete choice panel data models have received a great deal of attention. In those models, the dynamics is usually handled by including the lagged outcome as an explanatory variable. In this paper we consider an alternative model in which the dynamics is handled by using the duration...... in the current state as a covariate. We propose estimators that allow for group-specific effect in parametric and semiparametric versions of the model. The proposed method is illustrated by an empirical analysis of job durations allowing for firm-level effects....
Aerodynamic Modeling with Heterogeneous Data Assimilation and Uncertainty Quantification Project
National Aeronautics and Space Administration — Clear Science Corp. proposes to develop an aerodynamic modeling tool that assimilates data from different sources and facilitates uncertainty quantification. The...
Cihan, A.; Birkholzer, J. T.; Zhou, Q.; Trevisan, L.; Illangasekare, T. H.; Rodriguez, D.; Sakaki, T.
2011-12-01
Heterogeneities at multiple scales influence migration and trapping of geologically sequestrated CO2 during injection and post-injection periods. Understanding of small-scale processes is crucial to device upscaling methodologies for incorporating them into macroscopic-scale models. The upscaled models are in turn used to get insights into the complex field-scale processes involved in the migration of supercritical CO2. Theoretical research based on numerical model analysis presented in this study focuses on capillary entrapment in homogeneous and heterogeneous small-scale and intermediate-scale laboratory experiments with surrogate fluids, presented in a companion presentation (Treviso et al., 2011). An improved understanding of pore-scale and larger scale processes on capillary entrapment may be achieved by combining pore-scale and macroscopic-scale modeling approaches. Capillarity controlled entrapped non-wetting phase saturation in macroscopic-scale models is generally either provided as an input parameter after laboratory scale measurements or estimated empirically. A particle trajectory modeling approach with pore-scale physics included is used to gain insights to development of physically-based models for the capillary entrapment in homogeneous and heterogeneous systems. The particle trajectory modeling generates functional relationships between phase saturation, entrapped phase saturation, hydraulic properties of the medium, and velocity of injected phase, which eventually are planned to be used for developing macroscopic scale models of capillary entrapment. The predictions of entrapped fluid saturation from the particle trajectory model are verified with measurements from the small scale experimental test systems. Macroscopic two-phase flow modeling approach with existing and modified constitutive models is tested by comparisons with both small-scale and intermediate-scale experimental results. T2VOC module based on TOUGH2 is used to simulate two
Sensitivity analysis of fine sediment models using heterogeneous data
Kamel, A. M. Yousif; Bhattacharya, B.; El Serafy, G. Y.; van Kessel, T.; Solomatine, D. P.
2012-04-01
Sediments play an important role in many aquatic systems. Their transportation and deposition has significant implication on morphology, navigability and water quality. Understanding the dynamics of sediment transportation in time and space is therefore important in drawing interventions and making management decisions. This research is related to the fine sediment dynamics in the Dutch coastal zone, which is subject to human interference through constructions, fishing, navigation, sand mining, etc. These activities do affect the natural flow of sediments and sometimes lead to environmental concerns or affect the siltation rates in harbours and fairways. Numerical models are widely used in studying fine sediment processes. Accuracy of numerical models depends upon the estimation of model parameters through calibration. Studying the model uncertainty related to these parameters is important in improving the spatio-temporal prediction of suspended particulate matter (SPM) concentrations, and determining the limits of their accuracy. This research deals with the analysis of a 3D numerical model of North Sea covering the Dutch coast using the Delft3D modelling tool (developed at Deltares, The Netherlands). The methodology in this research was divided into three main phases. The first phase focused on analysing the performance of the numerical model in simulating SPM concentrations near the Dutch coast by comparing the model predictions with SPM concentrations estimated from NASA's MODIS sensors at different time scales. The second phase focused on carrying out a sensitivity analysis of model parameters. Four model parameters were identified for the uncertainty and sensitivity analysis: the sedimentation velocity, the critical shear stress above which re-suspension occurs, the shields shear stress for re-suspension pick-up, and the re-suspension pick-up factor. By adopting different values of these parameters the numerical model was run and a comparison between the
Modelling biological invasions: species traits, species interactions, and habitat heterogeneity.
Cannas, Sergio A; Marco, Diana E; Páez, Sergio A
2003-05-01
In this paper we explore the integration of different factors to understand, predict and control ecological invasions, through a general cellular automaton model especially developed. The model includes life history traits of several species in a modular structure interacting multiple cellular automata. We performed simulations using field values corresponding to the exotic Gleditsia triacanthos and native co-dominant trees in a montane area. Presence of G. triacanthos juvenile bank was a determinant condition for invasion success. Main parameters influencing invasion velocity were mean seed dispersal distance and minimum reproductive age. Seed production had a small influence on the invasion velocity. Velocities predicted by the model agreed well with estimations from field data. Values of population density predicted matched field values closely. The modular structure of the model, the explicit interaction between the invader and the native species, and the simplicity of parameters and transition rules are novel features of the model.
Hydrocarbons Heterogeneous Pyrolysis: Experiments and Modeling for Scramjet Thermal Management
Bouchez, Marc; Visez, Nicolas; Herbinet, Olivier; Fournet, René; Marquaire, Paul-Marie
2009-01-01
The last years saw a renewal of interest for hypersonic research in general and regenerative cooling specifically, with a large increase of the number of dedicated facilities and technical studies. In order to quantify the heat transfer in the cooled structures and the composition of the cracked fuel entering the combustor, an accurate model of the thermal decomposition of the fuel is required. This model should be able to predict the fuel chemical composition and physical properties for a broad range of pressures, temperatures and cooling geometries. For this purpose, an experimental and modeling study of the thermal decomposition of generic molecules (long-chain or polycyclic alkanes) that could be good surrogates of real fuels, has been started at the DCPR laboratory located in Nancy (France). This successful effort leads to several versions of a complete kinetic model. These models do not assume any effect from the material that constitutes the cooling channel. A specific experimental study was performed ...
The effect of ignoring individual heterogeneity in Weibull log-normal sire frailty models.
Damgaard, L H; Korsgaard, I R; Simonsen, J; Dalsgaard, O; Andersen, A H
2006-06-01
The objective of this study was, by means of simulation, to quantify the effect of ignoring individual heterogeneity in Weibull sire frailty models on parameter estimates and to address the consequences for genetic inferences. Three simulation studies were evaluated, which included 3 levels of individual heterogeneity combined with 4 levels of censoring (0, 25, 50, or 75%). Data were simulated according to balanced half-sib designs using Weibull log-normal animal frailty models with a normally distributed residual effect on the log-frailty scale. The 12 data sets were analyzed with 2 models: the sire model, equivalent to the animal model used to generate the data (complete sire model), and a corresponding model in which individual heterogeneity in log-frailty was neglected (incomplete sire model). Parameter estimates were obtained from a Bayesian analysis using Gibbs sampling, and also from the software Survival Kit for the incomplete sire model. For the incomplete sire model, the Monte Carlo and Survival Kit parameter estimates were similar. This study established that when unobserved individual heterogeneity was ignored, the parameter estimates that included sire effects were biased toward zero by an amount that depended in magnitude on the level of censoring and the size of the ignored individual heterogeneity. Despite the biased parameter estimates, the ranking of sires, measured by the rank correlations between true and estimated sire effects, was unaffected. In comparison, parameter estimates obtained using complete sire models were consistent with the true values used to simulate the data. Thus, in this study, several issues of concern were demonstrated for the incomplete sire model.
2008-01-01
Using NAFTA's effect on Mexico's exports as a natural experiment, this paper conducts an empirical analysis on the explanatory power of the two strands of heterogeneous firms trade models: the heterogeneous firms trade (HFT) model and the quality heterogeneous firms trade (QHFT) model. The paper first discusses the common prediction of the two models on new goods' exports and on the contrasting prediction on unit price evolution. An empirical analysis shows a strong supportive evidence on the...
Heterogeneity, quality, and reputation in an adaptive recommendation model
Cimini, Giulio; Zhou, Tao; Wei, Dong; Zhang, Yi-Cheng
2010-01-01
Recommender systems help people cope with the problem of information overload. A recently proposed adaptive news recommender model [Medo et al., 2009] is based on epidemic-like spreading of news in a social network. By means of agent-based simulations we study a "good get richer" feature of the model and determine which attributes are necessary for a user to play a leading role in the network. We further investigate the filtering efficiency of the model as well as its robustness against malicious and spamming behaviour. We show that incorporating user reputation in the recommendation process can substantially improve the outcome.
Chang, H.H.; van Marrewijk, C.
2012-01-01
This paper presents a model aim to reconcile the discrepancy between the theoretical and empirical depiction of the productivity distribution. The Melitz (2003) while being able to reflect on the asymmetric selection of heterogeneous firms in trade, the model strictly truncate the least productive f
E. Korkmaz (Evsen)
2014-01-01
markdownabstract__Abstract__ Recent years have seen many advances in quantitative models in the marketing literature. Even though these advances enable model building for a better understanding of customer purchase behavior and customer heterogeneity such that firms develop optimal targeting and pr
E. Korkmaz (Evsen)
2014-01-01
markdownabstract__Abstract__ Recent years have seen many advances in quantitative models in the marketing literature. Even though these advances enable model building for a better understanding of customer purchase behavior and customer heterogeneity such that firms develop optimal targeting and
Heterogeneity in Wage Setting Behavior in a New-Keynesian Model
Eijffinger, S.C.W.; Grajales Olarte, A.; Uras, R.B.
2015-01-01
In this paper we estimate a New-Keynesian DSGE model with heterogeneity in price and wage setting behavior. In a recent study, Coibion and Gorodnichenko (2011) develop a DSGE model, in which firms follow four different types of price setting schemes: sticky prices, sticky information, rule of thumb,
Directory of Open Access Journals (Sweden)
Jikai Liu
2015-12-01
Full Text Available Conventionally, heterogeneous object modeling methods paid limited attention to the concurrent modeling of geometry design and material composition distribution. Procedural method was normally employed to generate the geometry first and then determine the heterogeneous material distribution, which ignores the mutual influence. Additionally, limited capability has been established about irregular material composition distribution modeling with strong local discontinuities. This article overcomes these limitations by developing the computer-aided design–computer-aided engineering associative feature-based heterogeneous object modeling method. Level set functions are applied to model the geometry within computer-aided design module, which enables complex geometry modeling. Finite element mesh is applied to store the local material compositions within computer-aided engineering module, which allows any local discontinuities. Then, the associative feature concept builds the correspondence relationship between these modules. Additionally, the level set geometry and material optimization method are developed to concurrently generate the geometry and material information which fills the contents of the computer-aided design–computer-aided engineering associative feature model. Micro-geometry is investigated as well, instead of only the local material composition. A few cases are studied to prove the effectiveness of this new heterogeneous object modeling method.
Normal linear models with genetically structured residual variance heterogeneity: a case study
DEFF Research Database (Denmark)
Sorensen, Daniel; Waagepetersen, Rasmus Plenge
2003-01-01
Normal mixed models with different levels of heterogeneity in the residual variance are fitted to pig litter size data. Exploratory analysis and model assessment is based on examination of various posterior predictive distributions. Comparisons based on Bayes factors and related criteria favour...
DEFF Research Database (Denmark)
Malaguerra, Flavio; Chambon, Julie Claire Claudia; Albrechtsen, Hans-Jørgen;
2010-01-01
organic matter / electron donors, presence of specific biomass, etc. Here we develop a new fully-kinetic biogeochemical reactive model able to simulate chlorinated solvents degradation as well as production and consumption of molecular hydrogen. The model is validated using batch experiment data...... and global sensitivity analysis is performed....
Subsurface transport modeling of the Savannah River and Yucca Mountain Sites
Energy Technology Data Exchange (ETDEWEB)
Dunlap, B.E.; Pepper, D.W. [Univ. of Nevada, Las Vegas, NV (United States); Stephenson, D.E. [Westinghouse Res. Tech. Center, Aiken, SC (United States)
1994-12-31
An adaptive two-dimensional finite element method is used to model groundwater flow and contaminant transport in variably saturated porous media. The model is applied to known groundwater contamination at the Savannah River Site, which consists of multiple ground strata. A simulation of the proposed Yucca Mountain Repository Site is also executed to assess potential burial of radioactive waste.
Bridging the Semantic Gap Between Heterogeneous Modeling Formalisms and FMI
2014-04-25
FMUs Synchronous Data Flow (SDF) [11] is a dataflow model where a set of actors execute asynchronously and communicate via FIFO queues of (a-priori...concurrency with FIFO queue based communication that SDF is based on, and the somewhat synchronous model that FMI uses, based on persistent signals as...an output FIFO queue, denoted Q o A. FB has a state variable holding an input FIFO queue, denoted QiB , and another state variable holding an output
Modeling seismic wave propagation in heterogeneous medium using overlap domain pseudospectral method
Institute of Scientific and Technical Information of China (English)
YAN Jiu-peng; WANG Yan-bin
2008-01-01
Pseudospectral method is an efficient and high accuracy numerical method for simulating seismic wave propagation in heterogeneous earth medium. Since its derivative operator is global, this method is commonly considered not suitable for parallel computation. In this paper, we introduce the parallel overlap domain decomposition scheme and give a parallel pseudospectral method implemented on distributed memory PC cluster system for modeling seismic wave propagation in heterogeneous medium. In this parallel method, the medium is decomposed into several subdomains and the wave equations are solved in each subdomain simultaneously. The solutions in each subdomain are connected through the transferring at the overlapped region. Using 2D models, we compared the parallel and traditional pseudospectral method, analyzed the accuracy of the parallel method. The results show that the parallel method can efficiently reduce computation time for the same accuracy as the traditional method. This method could be applied to large scale modeling of seismic wave propagation in 3D heterogeneous medium.
An agent-based model for queue formation of powered two-wheelers in heterogeneous traffic
Lee, Tzu-Chang; Wong, K. I.
2016-11-01
This paper presents an agent-based model (ABM) for simulating the queue formation of powered two-wheelers (PTWs) in heterogeneous traffic at a signalized intersection. The main novelty is that the proposed interaction rule describing the position choice behavior of PTWs when queuing in heterogeneous traffic can capture the stochastic nature of the decision making process. The interaction rule is formulated as a multinomial logit model, which is calibrated by using a microscopic traffic trajectory dataset obtained from video footage. The ABM is validated against the survey data for the vehicular trajectory patterns, queuing patterns, queue lengths, and discharge rates. The results demonstrate that the proposed model is capable of replicating the observed queue formation process for heterogeneous traffic.
Voecks, G. E.
1983-01-01
Insufficient theoretical definition of heterogeneous catalysts is the major difficulty confronting industrial suppliers who seek catalyst systems which are more active, selective, and stable than those currently available. In contrast, progress was made in tailoring homogeneous catalysts to specific reactions because more is known about the reaction intermediates promoted and/or stabilized by these catalysts during the course of reaction. However, modeling heterogeneous catalysts on a microscopic scale requires compiling and verifying complex information on reaction intermediates and pathways. This can be achieved by adapting homogeneous catalyzed reaction intermediate species, applying theoretical quantum chemistry and computer technology, and developing a better understanding of heterogeneous catalyst system environments. Research in microscopic reaction modeling is now at a stage where computer modeling, supported by physical experimental verification, could provide information about the dynamics of the reactions that will lead to designing supported catalysts with improved selectivity and stability.
Modelling Spread of Oncolytic Viruses in Heterogeneous Cell Populations
Ellis, Michael; Dobrovolny, Hana
2014-03-01
One of the most promising areas in current cancer research and treatment is the use of viruses to attack cancer cells. A number of oncolytic viruses have been identified to date that possess the ability to destroy or neutralize cancer cells while inflicting minimal damage upon healthy cells. Formulation of predictive models that correctly describe the evolution of infected tumor systems is critical to the successful application of oncolytic virus therapy. A number of different models have been proposed for analysis of the oncolytic virus-infected tumor system, with approaches ranging from traditional coupled differential equations such as the Lotka-Volterra predator-prey models, to contemporary modeling frameworks based on neural networks and cellular automata. Existing models are focused on tumor cells and the effects of virus infection, and offer the potential for improvement by including effects upon normal cells. We have recently extended the traditional framework to a 2-cell model addressing the full cellular system including tumor cells, normal cells, and the impacts of viral infection upon both populations. Analysis of the new framework reveals complex interaction between the populations and potential inability to simultaneously eliminate the virus and tumor populations.
Directory of Open Access Journals (Sweden)
Spyridon Liakas
2017-08-01
Full Text Available The particulate discrete element method (DEM can be employed to capture the response of rock, provided that appropriate bonding models are used to cement the particles to each other. Simulations of laboratory tests are important to establish the extent to which those models can capture realistic rock behaviors. Hitherto the focus in such comparison studies has either been on homogeneous specimens or use of two-dimensional (2D models. In situ rock formations are often heterogeneous, thus exploring the ability of this type of models to capture heterogeneous material behavior is important to facilitate their use in design analysis. In situ stress states are basically three-dimensional (3D, and therefore it is important to develop 3D models for this purpose. This paper revisits an earlier experimental study on heterogeneous specimens, of which the relative proportions of weaker material (siltstone and stronger, harder material (sandstone were varied in a controlled manner. Using a 3D DEM model with the parallel bond model, virtual heterogeneous specimens were created. The overall responses in terms of variations in strength and stiffness with different percentages of weaker material (siltstone were shown to agree with the experimental observations. There was also a good qualitative agreement in the failure patterns observed in the experiments and the simulations, suggesting that the DEM data enabled analysis of the initiation of localizations and micro fractures in the specimens.
Aji Hapsoro, Cahyo; Purqon, Acep; Srigutomo, Wahyu
2017-07-01
2-D Time Domain Electromagnetic (TDEM) has been successfully conducted to illustrate the value of Electric field distribution under the Earth surface. Electric field compared by magnetic field is used to analyze resistivity and resistivity is one of physical properties which very important to determine the reservoir potential area of geothermal systems as one of renewable energy. In this modeling we used Time Domain Electromagnetic method because it can solve EM field interaction problem with complex geometry and to analyze transient problems. TDEM methods used to model the value of electric and magnetic fields as a function of the time combined with the function of distance and depth. The result of this modeling is Electric field intensity value which is capable to describe the structure of the Earth’s subsurface. The result of this modeling can be applied to describe the Earths subsurface resistivity values to determine the reservoir potential of geothermal systems.
Metapopulation epidemic models with heterogeneous mixing and travel behaviour
Apolloni, Andrea; Ramasco, Jose' J; Jensen, Pablo; Colizza, Vittoria
2014-01-01
The complex interplay between population movements in space and non-homogeneous mixing patterns have so far hindered the fundamental understanding of the conditions for spatial invasion through a general theoretical framework. To address this issue, we present an analytical modelling approach taking into account such interplay under general conditions of mobility and interactions, in the simplifying assumption of two population classes. We describe a spatially structured population with non-homogeneous mixing and travel behaviour through a multi-host stochastic epidemic metapopulation model. Different population partitions, mixing patterns and mobility structures are considered, along with a specific application for the study of the role of age partition in the early spread of the 2009 H1N1 pandemic influenza. We provide a complete mathematical formulation of the model and derive a semi-analytical expression of the threshold condition for global invasion of an emerging infectious disease in the metapopulation...
Chloride Migration in Heterogeneous Soil - 2. Stohastic Modeling
DEFF Research Database (Denmark)
Destouni, Geogia; Sassner, Mona; Jensen, Karsten Høgh
1994-01-01
The observed statistics of chloride breakthrough presented by Sassner et al. (this issue) were compared with predictions of a stochastic-advective modeling approach. The stochastic-advective model based on the observed spatial distribution of flow rates and on transport parameters consistent...... for providing useful predictions of both field scale solute transport and the associated prediction uncertainty. In contrast, accurate estimation of the statistics of solute advection at the scale of interest for the transport problem is necessary....... with parameter values obtained from local breakthrough curves (BTCs) agreed well with the observations. Alternative models that agreed well with the local BTCs failed to predict the large-scale BTC with realistic parameter values. The results support the assumption that compared to advection variability, local...
Three-dimensional bioremediation modeling in heterogeneous porous media
Energy Technology Data Exchange (ETDEWEB)
Wheeler, M.F. [Rice Univ., Houston, TX (United States). Dept. of Mathematical Sciences; Roberson, K.R. [Pacific Northwest Lab., Richland, WA (United States); Chilakapati, A. [Rice Univ., Houston, TX (United States). Dept. of Chemical Engineering
1992-06-01
Recently Price University and Pacific Northwest Laboratory (PNL) have begun a collaborative research effort that involves laboratory, field, and simulation work directed toward validating remediation strategies, including both natural and in situ bioremediation at US Department of Energy (DOE) sites such as Hanford. Because of chemical, biological, geologic and physical complexities of modeling these DOE sites, one of the major simulation goals of the project is to formulate and implement accurate and efficient (parallel) algorithms for modeling multiphase/multicomponent mow and reactive transport. In this paper we first describe the physical problem that needs to be modeled. Because of the emergence of concurrent supercomputing, we propose accurate numerical algorithms that are based on operator-splitting in time and domain decomposition iterative techniques. In particular reference is made to the biodegradation of carbon tetrachloride.
A duopoly model with heterogeneous congestion-sensitive customers.
M.R.H. Mandjes; J. Timmer
2007-01-01
Abstract This paper analyzes a model with two firms (providers), and two classes of customers. These customers classes are characterized by their attitude towards ‘congestion’ (caused by other customers using the same resources); a firm is selected on the basis of both the prices charged by the firm
A duopoly model with heterogeneous congestion-sensitive customers
Mandjes, M.R.H.; Timmer, J.B.
2003-01-01
This paper analyzes a model with multiple firms (providers), and two classes of customers. These customers classes are characterized by their attitude towards `congestion' (caused by other customers using the same resources); a firm is selected on the basis of both the prices charged by the firms, a
Stochastic models of solute transport in highly heterogeneous geologic media
Energy Technology Data Exchange (ETDEWEB)
Semenov, V.N.; Korotkin, I.A.; Pruess, K.; Goloviznin, V.M.; Sorokovikova, O.S.
2009-09-15
A stochastic model of anomalous diffusion was developed in which transport occurs by random motion of Brownian particles, described by distribution functions of random displacements with heavy (power-law) tails. One variant of an effective algorithm for random function generation with a power-law asymptotic and arbitrary factor of asymmetry is proposed that is based on the Gnedenko-Levy limit theorem and makes it possible to reproduce all known Levy {alpha}-stable fractal processes. A two-dimensional stochastic random walk algorithm has been developed that approximates anomalous diffusion with streamline-dependent and space-dependent parameters. The motivation for introducing such a type of dispersion model is the observed fact that tracers in natural aquifers spread at different super-Fickian rates in different directions. For this and other important cases, stochastic random walk models are the only known way to solve the so-called multiscaling fractional order diffusion equation with space-dependent parameters. Some comparisons of model results and field experiments are presented.
Heterogeneity and aggregation in a financial accelerator model
Assenza, T.; Delli Gatti, D.; Gallegati, M.
2007-01-01
In this paper we present a macroeconomic model in which changes in the variance (and higher moments of the distribution) of firm's financial conditions - i.e. "distributive shocks" - are bound to play a crucial role in the determination of output fluctuations. Firms differ by degree of financial rob
Pregnancy-induced hypertension in a rat heterogeneity model.
J.W.M. Hutten
1988-01-01
textabstractThis thesis presents an approach to develop pregnancy-induced hypertension (PIH) in animals by means of an immunologic model. Hypertensive pregnancy disorders in man may be considered a clinical expression of maladaptation in pregnancy. Maladaptation disease develops early in
DEFF Research Database (Denmark)
Fuchs, Sven; Balling, Niels
2016-01-01
The subsurface temperature field and the geothermal conditions in sedimentary basins are frequently examined by using numerical thermal models. For those models, detailed knowledge of rock thermal properties are paramount for a reliable parameterization of layer properties and boundary conditions...... against known observed temperatures of good quality. Results clearly show that the use of location-specific well-log derived rock thermal properties and the integration of laterally varying input data (reflecting changes of lithofacies) significantly improves the temperature prediction...
Maladen, Ryan D.; Ding, Yang; Umbanhowar, Paul B.; Kamor, Adam; Goldman, Daniel I.
2011-01-01
We integrate biological experiment, empirical theory, numerical simulation and a physical model to reveal principles of undulatory locomotion in granular media. High-speed X-ray imaging of the sandfish lizard, Scincus scincus, in 3 mm glass particles shows that it swims within the medium without using its limbs by propagating a single-period travelling sinusoidal wave down its body, resulting in a wave efficiency, η, the ratio of its average forward speed to the wave speed, of approximately 0.5. A resistive force theory (RFT) that balances granular thrust and drag forces along the body predicts η close to the observed value. We test this prediction against two other more detailed modelling approaches: a numerical model of the sandfish coupled to a discrete particle simulation of the granular medium, and an undulatory robot that swims within granular media. Using these models and analytical solutions of the RFT, we vary the ratio of undulation amplitude to wavelength (A/λ) and demonstrate an optimal condition for sand-swimming, which for a given A results from the competition between η and λ. The RFT, in agreement with the simulated and physical models, predicts that for a single-period sinusoidal wave, maximal speed occurs for A/λ ≈ 0.2, the same kinematics used by the sandfish. PMID:21378020
El Gharamti, Mohamad
2012-04-01
Accurate knowledge of the movement of contaminants in porous media is essential to track their trajectory and later extract them from the aquifer. A two-dimensional flow model is implemented and then applied on a linear contaminant transport model in the same porous medium. Because of different sources of uncertainties, this coupled model might not be able to accurately track the contaminant state. Incorporating observations through the process of data assimilation can guide the model toward the true trajectory of the system. The Kalman filter (KF), or its nonlinear invariants, can be used to tackle this problem. To overcome the prohibitive computational cost of the KF, the singular evolutive Kalman filter (SEKF) and the singular fixed Kalman filter (SFKF) are used, which are variants of the KF operating with low-rank covariance matrices. Experimental results suggest that under perfect and imperfect model setups, the low-rank filters can provide estimates as accurate as the full KF but at much lower computational effort. Low-rank filters are demonstrated to significantly reduce the computational effort of the KF to almost 3%. © 2012 American Society of Civil Engineers.
DEFF Research Database (Denmark)
Moura, Scott; Ruiz, Victor; Bendtsen, Jan Dimon
2013-01-01
This paper focuses on developing a partial differential equation (PDE)-based model and parameter identification scheme for heterogeneous populations of thermostatically controlled loads (TCLs). First, a coupled two-state hyperbolic PDE model for homogenous TCL populations is derived. This model...... is extended to heterogeneous populations by including a diffusive term, which provides an elegant PDE control-oriented model. Second, a novel parameter identification scheme is derived for the PDE model structure, which utilizes only boundary measurements and aggregated power measurements. Simulation results...... against a Monte Carlo model of a large TCL population demonstrate the usefulness of the approach. The proposed model and parameter identification scheme provide system critical information for advanced demand side management control systems....
Gas phase metal cluster model systems for heterogeneous catalysis.
Lang, Sandra M; Bernhardt, Thorsten M
2012-07-14
Since the advent of intense cluster sources, physical and chemical properties of isolated metal clusters are an active field of research. In particular, gas phase metal clusters represent ideal model systems to gain molecular level insight into the energetics and kinetics of metal-mediated catalytic reactions. Here we summarize experimental reactivity studies as well as investigations of thermal catalytic reaction cycles on small gas phase metal clusters, mostly in relation to the surprising catalytic activity of nanoscale gold particles. A particular emphasis is put on the importance of conceptual insights gained through the study of gas phase model systems. Based on these concepts future perspectives are formulated in terms of variation and optimization of catalytic materials e.g. by utilization of bimetals and metal oxides. Furthermore, the future potential of bio-inspired catalytic material systems are highlighted and technical developments are discussed.
Reactor modeling in heterogeneous photocatalysis: toxicity and biodegradability assessment.
Satuf, M L; José, S; Paggi, J C; Brandi, R J; Cassano, A E; Alfano, O M
2010-01-01
Photocatalysis employing titanium dioxide is a useful method to degrade a wide variety of organic and inorganic pollutants from water and air. However, the application of this advanced oxidation process at industrial scale requires the development of mathematical models to design and scale-up photocatalytic reactors. In the present work, intrinsic kinetic expressions previously obtained in a laboratory reactor are employed to predict the performance of a bench scale reactor of different configuration and operating conditions. 4-Chlorophenol was chosen as the model pollutant. The toxicity and biodegradability of the irradiated mixture in the bench photoreactor was also assessed. Good agreement was found between simulation and experimental data. The root mean square error of the estimations was 9.9%. The photocatalytic process clearly enhances the biodegradability of the reacting mixture, and the initial toxicity of the pollutant was significantly reduced by the treatment.
A Unified Model Explaining Heterogeneous Ziegler-Natta Catalysis
Credendino, Raffaele
2015-08-12
We propose a model for MgCl2 supported Ziegler-Natta catalysts capable to reconcile the discrepancies emerged in the last 20 years, when experimental data were tried to be rationalized by molecular models. We show that step defects on the neglected but thermodynamically more stable (104) facet of MgCl2 can lead to sites for strong TiCl4 adsorption. The corresponding Ti-active site is stereoeselective, and its stereoselectivity can be enhanced by coordination of Al-alkyls or Lewis bases in the close proximity. The surface energy of the step defected (104) MgCl2 facet is clearly lower than that of the well accepted (110) facet.
Directory of Open Access Journals (Sweden)
Mohamad Ridwan
2014-12-01
Full Text Available Jakarta is located on a thick sedimentary layer that potentially has a very high seismic wave amplification. However, the available information concerning the subsurface model and bedrock depth is insufficient for a seismic hazard analysis. In this study, a microtremor array method was applied to estimate the geometry and S-wave velocity of the sedimentary layer. The spatial autocorrelation (SPAC method was applied to estimate the dispersion curve, while the S-wave velocity was estimated using a genetic algorithm approach. The analysis of the 1D and 2D S-wave velocity profiles shows that along a north-south line, the sedimentary layer is thicker towards the north. It has a positive correlation with a geological cross section derived from a borehole down to a depth of about 300 m. The SPT data from the BMKG site were used to verify the 1D S-wave velocity profile. They show a good agreement. The microtremor analysis reached the engineering bedrock in a range from 359 to 608 m as depicted by a cross section in the north-south direction. The site class was also estimated at each site, based on the average S-wave velocity until 30 m depth. The sites UI to ISTN belong to class D (medium soil, while BMKG and ANCL belong to class E (soft soil.
Karra, S.; Painter, S. L.; Lichtner, P. C.
2014-10-01
Degradation of near-surface permafrost due to changes in the climate is expected to impact the hydrological, ecological and biogeochemical responses of the Arctic tundra. From a hydrological perspective, it is important to understand the movement of the various phases of water (gas, liquid and ice) during the freezing and thawing of near-surface soils. We present a new non-isothermal, single-component (water), three-phase formulation that treats air as an inactive component. This single component model works well and produces similar results to a more complete and computationally demanding two-component (air, water) formulation, and is able to reproduce results of previously published laboratory experiments. A proof-of-concept implementation in the massively parallel subsurface flow and reactive transport code PFLOTRAN is summarized, and parallel performance of that implementation is demonstrated. When water vapor diffusion is considered, a large effect on soil moisture dynamics is seen, which is due to dependence of thermal conductivity on ice content. A large three-dimensional simulation (with around 6 million degrees of freedom) of seasonal freezing and thawing is also presented.
Altered Micro-RNA Degradation Promotes Tumor Heterogeneity: A Result from Boolean Network Modeling.
Wu, Yunyi; Krueger, Gerhard R F; Wang, Guanyu
2016-02-01
Cancer heterogeneity may reflect differential dynamical outcomes of the regulatory network encompassing biomolecules at both transcriptional and post-transcriptional levels. In other words, differential gene-expression profiles may correspond to different stable steady states of a mathematical model for simulation of biomolecular networks. To test this hypothesis, we simplified a regulatory network that is important for soft-tissue sarcoma metastasis and heterogeneity, comprising of transcription factors, micro-RNAs, and signaling components of the NOTCH pathway. We then used a Boolean network model to simulate the dynamics of this network, and particularly investigated the consequences of differential miRNA degradation modes. We found that efficient miRNA degradation is crucial for sustaining a homogenous and healthy phenotype, while defective miRNA degradation may lead to multiple stable steady states and ultimately to carcinogenesis and heterogeneity. Copyright© 2016 International Institute of Anticancer Research (Dr. John G. Delinassios), All rights reserved.
Energy Technology Data Exchange (ETDEWEB)
Das, Sumanta; Maroli, Amit; Singh, Sudhanshu S.; Stannard, Tyler; Xiao, Xianghui; Chawla, Nikhilesh; Neithalath, Narayanan
2016-06-01
This paper presents a microstructure-guided modeling approach to predict the effective elastic response of heterogeneous materials, and demonstrates its application toward two highly heterogeneous, uncon- ventional structural binders, i.e., iron carbonate and fly ash geopolymer. Microstructural information from synchrotron X-ray tomography (XRT) and intrinsic elastic properties of component solid phases from statistical nanoindentation are used as the primary inputs. The virtual periodic 3D microstructure reconstructed using XRT, along with periodic boundary conditions is used as a basis for strain- controlled numerical simulation scheme in the linear elastic range to predict the elastic modulus as well as the stresses in the microstructural phases. The elastic modulus of the composite material predicted from the microstructure-based constitutive modeling approach correlates very well with experimental measurements for both the materials considered. This technique efficiently links the microstructure to mechanical properties of interest and helps develop material design guidelines for novel heterogeneous composites
Haws, Nathan W; Ball, William P; Bouwer, Edward J
2007-01-01
Low permeability regions in which solute movement is governed by diffusion reduce the availability of pollutants for remediation and can function as long-term sources of groundwater contamination. The inherent difficulty in understanding mass transfer from these regions of sequestered contamination is further complicated by unknown solute distributions within the low-permeability regions (sequestering regions). When models are calibrated to reproduce temporal histories of solute release from a sequestering region (desorption), the fitted parameter values are used to infer the physical or chemical characteristics of the media; however, the calibrated parameters also reflect the case-specific initial conditions (i.e., the solute distribution within the sequestering region domain at the onset of desorption). This phenomenon is demonstrated using model simulations of solute diffusion from hypothetical solids with characteristics similar to those of the well studied Borden, Ontario aquifer system. Solute release from the solids is simulated using a batch diffusion model under different initial solute distributions within the solids. The results of these model simulations are used to calibrate parameters of a multiple first-order rate desorption model (MRM) to illustrate how the fitted MRM parameters increase or decrease depending on the initial "aging" of the solids. Further numerical simulations are conducted for a one-dimensional flow system under steady-state and variable-rate hydraulic flushing. These simulations show that although aging reduces desorptive mass flux during early stages of flushing, aged sites have greater desorptive mass flux (greater solute availability) than "freshly" contaminated media during the later stages of remediation. Overall, the results demonstrate why the physicochemical meaning of observed desorption rates cannot be accurately deduced without first understanding the initial solute distribution within the media.
Energy Technology Data Exchange (ETDEWEB)
Streile, G.P.; Simmons, C.S.
1986-09-01
Theoretical and computer modeling capability for assessing the subsurface movement and fate of organic contaminants in groundwater was examined. Hence, this study is particularly concerned with energy-related, organic compounds that could enter a subsurface environment and move as components of a liquid phase separate from groundwater. The migration of organic chemicals that exist in an aqueous dissolved state is certainly a part of this more general scenario. However, modeling of the transport of chemicals in aqueous solution has already been the subject of several reviews. Hence, this study emphasizes the multiphase scenario. This study was initiated to focus on the important physicochemical processes that control the behavior of organic substances in groundwater systems, to evaluate the theory describing these processes, and to search for and evaluate computer codes that implement models that correctly conceptualize the problem situation. This study is not a code inventory, and no effort was made to identify every available code capable of representing a particular process.
To Model Chemical Reactivity in Heterogeneous Emulsions, Think Homogeneous Microemulsions.
Bravo-Díaz, Carlos; Romsted, Laurence Stuart; Liu, Changyao; Losada-Barreiro, Sonia; Pastoriza-Gallego, Maria José; Gao, Xiang; Gu, Qing; Krishnan, Gunaseelan; Sánchez-Paz, Verónica; Zhang, Yongliang; Dar, Aijaz Ahmad
2015-08-25
Two important and unsolved problems in the food industry and also fundamental questions in colloid chemistry are how to measure molecular distributions, especially antioxidants (AOs), and how to model chemical reactivity, including AO efficiency in opaque emulsions. The key to understanding reactivity in organized surfactant media is that reaction mechanisms are consistent with a discrete structures-separate continuous regions duality. Aggregate structures in emulsions are determined by highly cooperative but weak organizing forces that allow reactants to diffuse at rates approaching their diffusion-controlled limit. Reactant distributions for slow thermal bimolecular reactions are in dynamic equilibrium, and their distributions are proportional to their relative solubilities in the oil, interfacial, and aqueous regions. Our chemical kinetic method is grounded in thermodynamics and combines a pseudophase model with methods for monitoring the reactions of AOs with a hydrophobic arenediazonium ion probe in opaque emulsions. We introduce (a) the logic and basic assumptions of the pseudophase model used to define the distributions of AOs among the oil, interfacial, and aqueous regions in microemulsions and emulsions and (b) the dye derivatization and linear sweep voltammetry methods for monitoring the rates of reaction in opaque emulsions. Our results show that this approach provides a unique, versatile, and robust method for obtaining quantitative estimates of AO partition coefficients or partition constants and distributions and interfacial rate constants in emulsions. The examples provided illustrate the effects of various emulsion properties on AO distributions such as oil hydrophobicity, emulsifier structure and HLB, temperature, droplet size, surfactant charge, and acidity on reactant distributions. Finally, we show that the chemical kinetic method provides a natural explanation for the cut-off effect, a maximum followed by a sharp reduction in AO efficiency with
Recommended Parameter Values for INEEL Subsurface Disposal Area Source Release Modeling
Energy Technology Data Exchange (ETDEWEB)
Riley, Robert G.; Lopresti, Charles A.
2004-06-23
The purpose of this report is to summarize 1) associated information and values for key release model parameters (i.e., best estimate, minimum and maximum) obtained where possible from published experimental data, 2) a structure for selection of sensitivity tests cases that can be used to identify test cases, and 3) recommended test cases for selected contaminants of potential concern to assess remedy effectiveness against a no-treatment base case.
Modeling Subsurface Storm and Tile Drain Systems in GSSHA with SUPERLINK
2014-09-01
represents a major advancement in U.S. Army Corps of Engineers urban and agricultural hydrologic modeling capability. A SUPERLINK network consists of a...Management 48: 207–224. Cunge, J. A., F. M. Holly, and A. Verwey, 1980. Practical aspects of computational river hydraulics. London: Pittman Advanced ...drains. In Drainage for Agriculture, Mongraph No. 17, ed. J. van Schilfgaarde, 245–270. Madison WI: American Society of Agronomy . ERDC/CHL TR-14-11 30
Multi-Robot Systems for Subsurface Planetary Exploration Project
National Aeronautics and Space Administration — The proposed innovation is a heterogeneous multi-robot team developed as a platform for effective subsurface planetary exploration. State-of-art robotic exploration...
The use of mixed logit models to reflect heterogeneity in capture-recapture studies.
Coull, B A; Agresti, A
1999-03-01
We examine issues in estimating population size N with capture-recapture models when there is variable catchability among subjects. We focus on a logistic-normal mixed model, for which the logit of the probability of capture is an additive function of a random subject and a fixed sampling occasion parameter. When the probability of capture is small or the degree of heterogeneity is large, the log-likelihood surface is relatively flat and it is difficult to obtain much information about N. We also discuss a latent class model and a log-linear model that account for heterogeneity and show that the log-linear model has greater scope. Models assuming homogeneity provide much narrower intervals for N but are usually highly overly optimistic, the actual coverage probability being much lower than the nominal level.
Niedermeier, Dennis; Ervens, Barbara; Clauss, Tina; Voigtländer, Jens; Wex, Heike; Hartmann, Susan; Stratmann, Frank
2014-01-01
In a recent study, the Soccer ball model (SBM) was introduced for modeling and/or parameterizing heterogeneous ice nucleation processes. The model applies classical nucleation theory. It allows for a consistent description of both apparently singular and stochastic ice nucleation behavior, by distributing contact angles over the nucleation sites of a particle population assuming a Gaussian probability density function. The original SBM utilizes the Monte Carlo technique, which hampers its usage in atmospheric models, as fairly time-consuming calculations must be performed to obtain statistically significant results. Thus, we have developed a simplified and computationally more efficient version of the SBM. We successfully used the new SBM to parameterize experimental nucleation data of, e.g., bacterial ice nucleation. Both SBMs give identical results; however, the new model is computationally less expensive as confirmed by cloud parcel simulations. Therefore, it is a suitable tool for describing heterogeneous ice nucleation processes in atmospheric models.
Subsurface storage of freshwater in South Florida; a digital model analysis of recoverability
Merritt, Michael L.
1985-01-01
As part of a study of the feasibility of recovering freshwater injected and stored underground in south Florida, a digital solute-transport model was used to investigate the relation of recovery efficiency to the variety of hydrogeologic conditions that could prevail in brackish artesian aquifers and to a variety of management alternatives. The analyses employed a modeling approach in which the control for sensitivity testing was a hypothetical aquifer considered representative of permeable zones in south Florida that might be used for storage of freshwater. Parameter variations in the tests represented possible variations in aquifer conditions in the area. The applicability of the analyses to south Florida limestone aquifers required the assumption that flow nonuniformities in those aquifers are small on the scale of volumes of water likely to be injected, and that their effect could be represented as hydrodynamic dispersion. Generally, it was shown that a loss of recovery efficiency is caused by (1) processes causing mixing of injected freshwater with native saline water (hydrodynamic dispersion), (2) processes causing the more or less irreversible displacement of the injected freshwater with respect to the well (buoyancy stratification, background hydraulic gradients, and interlayer dispersion), or (3) processes causing injection and withdrawal flow patterns to be dissimilar (directionally biased well-bore plugging, and dissimilar injection and withdrawal schedules in multiple-well systems). Other results indicated that recovery efficiency improves considerably with successive cycles, providing that each recovery phase ends when the chloride concentration of withdrawn water exceeds established criteria for potability (usually 250 milligrams per liter), and that freshwater injected into highly permeable or highly saline aquifers (such as the 'boulder zone') would buoy rapidly. Many hydrologic conditions were posed for model analysis. To have obtained comparable
North, Elizabeth W.; Adams, E. Eric; Thessen, Anne E.; Schlag, Zachary; He, Ruoying; Socolofsky, Scott A.; Masutani, Stephen M.; Peckham, Scott D.
2015-02-01
A better understanding of oil droplet formation, degradation, and dispersal in deep waters is needed to enhance prediction of the fate and transport of subsurface oil spills. This research evaluates the influence of initial droplet size and rates of biodegradation on the subsurface transport of oil droplets, specifically those from the Deepwater Horizon oil spill. A three-dimensional coupled model was employed with components that included analytical multiphase plume, hydrodynamic and Lagrangian models. Oil droplet biodegradation was simulated based on first order decay rates of alkanes. The initial diameter of droplets (10-300 μm) spanned a range of sizes expected from dispersant-treated oil. Results indicate that model predictions are sensitive to biodegradation processes, with depth distributions deepening by hundreds of meters, horizontal distributions decreasing by hundreds to thousands of kilometers, and mass decreasing by 92-99% when biodegradation is applied compared to simulations without biodegradation. In addition, there are two- to four-fold changes in the area of the seafloor contacted by oil droplets among scenarios with different biodegradation rates. The spatial distributions of hydrocarbons predicted by the model with biodegradation are similar to those observed in the sediment and water column, although the model predicts hydrocarbons to the northeast and east of the well where no observations were made. This study indicates that improvement in knowledge of droplet sizes and biodegradation processes is important for accurate prediction of subsurface oil spills.
Agent-based modeling of lane discipline in heterogeneous traffic
Dailisan, Damian N.; Lim, May T.
2016-09-01
Designating lanes for different vehicle types is ideal road safety-wise. Practical considerations, however, require road sharing. Using a modified Nagel-Schreckenberg cellular automata model for two vehicle types (cars and motorcycles), we analyzed the interplay of lane discipline, lane changing, and vehicle density. In the absence of lane changing, the transition between free flow and congested states occurs at a higher vehicle (road occupation) density when the ratio of cars to motorcycles is increased. When lane changing is allowed, the smaller motorcycles tend to fill in unused spaces, until the point when the wider cars effectively block their way at high vehicle densities. When the condition of lane discipline is not imposed, i.e. staying wholly within lane boundaries is not required, further improvement in throughput becomes possible at the cost of required driver attentiveness.
Process integration, data management, and visualization framework for subsurface sciences
Energy Technology Data Exchange (ETDEWEB)
Schuchardt, K L; Black, G D; Chase, J M; Elsethagen, T O; Sun, L [Pacific Northwest National Laboratory, PO Box 999 Richland, WA 99320 (United States)
2007-07-15
Applying subsurface simulation codes to understand heterogeneous flow and transport problems is a complex process potentially involving multiple models, multiple scales, and spanning multiple scientific disciplines. A typical end-to-end process involves many tools, scripts and data sources usually shared only though informal channels. Additionally, the process contains many sub-processes that are repeated frequently and could be automated and shared. Finally, keeping records of the models, processes, and correlation between inputs and outputs is currently manual, time consuming and error prone. We are developing a software framework that integrates a workflow execution environment, shared data repository, and analysis and visualization tools to support development and use of new hybrid subsurface simulation codes. We are taking advantage of recent advances in scientific process automation using the Kepler system and advances in data services based on content management. Extensibility and flexibility are key underlying design considerations to support the constantly changing set of tools, scripts, and models available. We describe the architecture and components of this system with early examples of applying it to a continuum subsurface model.
Chaos and Control of Game Model Based on Heterogeneous Expectations in Electric Power Triopoly
Directory of Open Access Journals (Sweden)
Weizhuo Ji
2009-01-01
Full Text Available A dynamic repeated game model has been established based on heterogeneous expectations in electric power triopoly. Theoretical analysis and numerical simulation show the complexity of this model; suppose that the producers make decisions with naive expectation and bounded rationality. The straight-line stabilization chaos control method was successfully applied to the dynamic repeated game model. The results have important practical value for the producers in the electric power oligopoly.
Comolli, Alessandro; Hakoun, Vivien; Dentz, Marco
2017-04-01
Achieving the understanding of the process of solute transport in heterogeneous porous media is of crucial importance for several environmental and social purposes, ranging from aquifers contamination and remediation, to risk assessment in nuclear waste repositories. The complexity of this aim is mainly ascribable to the heterogeneity of natural media, which can be observed at all the scales of interest, from pore scale to catchment scale. In fact, the intrinsic heterogeneity of porous media is responsible for the arising of the well-known non-Fickian footprints of transport, including heavy-tailed breakthrough curves, non-Gaussian spatial density profiles and the non-linear growth of the mean squared displacement. Several studies investigated the processes through which heterogeneity impacts the transport properties, which include local modifications to the advective-dispersive motion of solutes, mass exchanges between some mobile and immobile phases (e.g. sorption/desorption reactions or diffusion into solid matrix) and spatial correlation of the flow field. In the last decades, the continuous time random walk (CTRW) model has often been used to describe solute transport in heterogenous conditions and to quantify the impact of point heterogeneity, spatial correlation and mass transfer on the average transport properties [1]. Open issues regarding this approach are the possibility to relate measurable properties of the medium to the parameters of the model, as well as its capability to provide predictive information. In a recent work [2] the authors have shed new light on understanding the relationship between Lagrangian and Eulerian dynamics as well as on their evolution from arbitrary initial conditions. On the basis of these results, we derive a CTRW model for the description of Darcy-scale transport in d-dimensional media characterized by spatially random permeability fields. The CTRW approach models particle velocities as a spatial Markov process, which is
Modeling dynamics of mutants in heterogeneous stem cell niche
Shahriyari, L.; Mahdipour-Shirayeh, A.
2017-02-01
Studying the stem cell (SC) niche architecture is a crucial step for investigating the process of oncogenesis and obtaining an effective stem cell therapy for various cancers. Recently, it has been observed that there are two groups of SCs in the SC niche collaborating with each other to maintain tissue homeostasis: border stem cells (BSCs), which are responsible in controlling the number of non-stem cells as well as stem cells, and central stem cells (CeSCs), which regulate the SC niche. Here, we develop a bi-compartmental stochastic model for the SC niche to study the spread of mutants within the niche. The analytic calculations and numeric simulations, which are in perfect agreement, reveal that in order to delay the spread of mutants in the SC niche, a small but non-zero number of SC proliferations must occur in the CeSC compartment. Moreover, the migration of BSCs to CeSCs delays the spread of mutants. Furthermore, the fixation probability of mutants in the SC niche is independent of types of SC division as long as all SCs do not divide fully asymmetrically. Additionally, the progeny of CeSCs have a much higher chance than the progeny of BSCs to take over the entire niche.
Ala-aho, Pertti; Soulsby, Chris; Wang, Hailong; Tetzlaff, Doerthe
2016-04-01
We use above-ground hydrological fluxes (streamflow and evapotranspiration (ET)) to calibrate an integrated hydrological simulator for a headwater catchment located in the Scottish highlands. Our study explores the feasibility of simulating spatially distributed catchment response in a physically based framework whilst having only preliminary data about the subsurface hydrological parameters. Furthermore we investigate the added value of insitu ET data in the calibration process. Transient simulations are performed with a fully integrated surface-subsurface hydrological model HydroGeoSphere and calibration of model parameters is done in PEST framework. In the first calibration step only the stream hydrograph is included using the original time series alongside with log-transformed hydrograph and weekly flow volumes in the objective function. ET is estimated with energy balance technique using above canopy temperatures, humidity and net radiation measured within the catchment. In the second calibration step, the ET time series are introduced in the calibration objective function. Parameter identifiability along with uncertainty in the model output will be examined as a part of the model calibration for both calibration steps. Furthermore, the post-calibration model will allow us to simulate spatially distributed hydrological fluxes and to distinguish between different water sources that make up the stream hydrograph using the hydraulic mixing-cell method. Preliminary simulations have shown that transient and spatially distributed surface water, subsurface water and evaporative fluxes of a headwater catchment can be reproduced in integrated modelling framework using only above-ground hydrological data in model calibration. We hypothesize that the evapotranspiration dataset informs the catchment water budget and water transmission rates and is therefore useful in constraining subsurface hydraulic parameters, such as hydraulic conductivities, which are typically
Arora, B.; Spycher, N.; Steefel, C. I.; King, E.; Conrad, M. E.
2015-12-01
Biogeochemical hotspots and hot moments are known to account for a high percentage of carbon and nutrient cycling within flood plain environments. To quantify the impact of these hotspots and hot moments on the carbon cycle, a 2D reactive transport model was developed for the saturated-unsaturated zone of a flood plain site in Rifle, CO. Previous studies have identified naturally reduced zones (NRZs) in the saturated zone of the Rifle site to be hotspots and important regions for subsurface biogeochemical cycling. Wavelet analysis of geochemical concentrations at the site suggested that hydrologic and temperature variations are hot moments and exert an important control on biogeochemical conditions in the Rifle aquifer. Here, we describe the development of a reactive transport model that couples hydrologic and biogeochemical processes to microbial functional distributions inferred from site-specific 'omic' data. The model includes microbial contributions from heterotrophic and chemolithoautotrophic processes. We use Monod based formulations to represent biomass formation and consider energy partitioning between catabolic and anabolic processes. We use this model to explore community emergence at the Rifle site and further constrain the extent and rates of nutrient uptake as well as abiotic and biotic reactions using stable carbon isotopes. Results from 2D model simulations with only abiotic reactions predict lower CO2 partial pressures in the unsaturated zone and severely underpredict (~200%) carbon fluxes to the river compared to simulations with chemolithoautotrophic pathways. δ13C-CO2 profiles also point to biotic sources for the locally observed high CO2 concentrations above NRZs. Results further indicate that groundwater carbon fluxes from the Rifle site to the river are underestimated by almost 180% (to 3.3 g m-2 d-1) when temperature fluctuations are ignored in the simulations. Preliminary results demonstrate the emergence of denitrifiers at specific depths
On the Modeling and Analysis of Heterogeneous Radio Access Networks using a Poisson Cluster Process
DEFF Research Database (Denmark)
Suryaprakash, Vinay; Møller, Jesper; Fettweis, Gerhard P.
Future mobile networks are visualized as networks that consist of more than one type of base station to cope with rising user demands. Such networks are referred to as heterogeneous networks. There have been various attempts at modeling and optimization of such networks using spatial point proces...
Evaluation of Forest Fire Burn Model of Reaction Kinetics of Heterogeneous Explosives
1988-05-01
34Phenomenological Model of Shock Initiation in Heterogeneous Explosives," Phys. Fluids , Vol. 23 (1980), p. 2382. 10. C. M. Tarver and J. 0. Hallquist...Library) I Radford rmy Amnition Plant 2 Rock sland Arsenal avy 4sson office (MMT) (1) Tbrary (sUW-ADM-P) (1) 1 whtes Saeds Nissile Range (STUU-AD-L
Sommer, W.T.
2015-01-01
Modelling and monitoring of Aquifer Thermal Energy Storage Impacts of heterogeneity, thermal interference and bioremediation Wijbrand Sommer
PhD thesis, Wageningen University, Wageningen, NL (2015)
ISBN 978-94-6257-294-2 Abstract Aquifer thermal energy storage (ATES) is
Boundedly rational learning and heterogeneous trading strategies with hybrid neuro-fuzzy models
Bekiros, S.D.
2009-01-01
The present study deals with heterogeneous learning rules in speculative markets where heuristic strategies reflect the rules-of-thumb of boundedly rational investors. The major challenge for "chartists" is the development of new models that would enhance forecasting ability particularly for time
Fibroblast heterogeneity and its implications for engineering organotypic skin models in vitro.
Sriram, Gopu; Bigliardi, Paul Lorenz; Bigliardi-Qi, Mei
2015-11-01
Advances in cell culture methods, multidisciplinary research, clinical need to replace lost skin tissues and regulatory need to replace animal models with alternative test methods has led to development of three dimensional models of human skin. In general, these in vitro models of skin consist of keratinocytes cultured over fibroblast-populated dermal matrices. Accumulating evidences indicate that mesenchyme-derived signals are essential for epidermal morphogenesis, homeostasis and differentiation. Various studies show that fibroblasts isolated from different tissues in the body are dynamic in nature and are morphologically and functionally heterogeneous subpopulations. Further, these differences seem to be dictated by the local biological and physical microenvironment the fibroblasts reside resulting in "positional identity or memory". Furthermore, the heterogeneity among the fibroblasts play a critical role in scarless wound healing and complete restoration of native tissue architecture in fetus and oral mucosa; and excessive scar formation in diseased states like keloids and hypertrophic scars. In this review, we summarize current concepts about the heterogeneity among fibroblasts and their role in various wound healing environments. Further, we contemplate how the insights on fibroblast heterogeneity could be applied for the development of next generation organotypic skin models.
Boundedly rational learning and heterogeneous trading strategies with hybrid neuro-fuzzy models
S.D. Bekiros
2009-01-01
The present study deals with heterogeneous learning rules in speculative markets where heuristic strategies reflect the rules-of-thumb of boundedly rational investors. The major challenge for "chartists" is the development of new models that would enhance forecasting ability particularly for time se
Sommer, W.T.
2015-01-01
Modelling and monitoring of Aquifer Thermal Energy Storage Impacts of heterogeneity, thermal interference and bioremediation Wijbrand Sommer
PhD thesis, Wageningen University, Wageningen, NL (2015)
ISBN 978-94-6257-294-2 Abstract Aquifer thermal energy storage (ATES) is
DEFF Research Database (Denmark)
Stjernholm, M.; Poslad, S.; Zuo, L.;
2004-01-01
The Environmental Data Exchange Network for Inland Water (EDEN-IW) project's main aim is to develop a system for making disparate and heterogeneous databases of Inland Water quality more accessible to users. The core technology is based upon a combination of: ontological model to represent a Sema...
A comparison of methods for representing random taste heterogeneity in discrete choice models
DEFF Research Database (Denmark)
Fosgerau, Mogens; Hess, Stephane
2009-01-01
This paper reports the findings of a systematic study using Monte Carlo experiments and a real dataset aimed at comparing the performance of various ways of specifying random taste heterogeneity in a discrete choice model. Specifically, the analysis compares the performance of two recent advanced...
Cheng, Qing; Lu, Xin; Wu, Joseph T.; Liu, Zhong; Huang, Jincai
2016-01-01
Guangdong experienced the largest dengue epidemic in recent history. In 2014, the number of dengue cases was the highest in the previous 10 years and comprised more than 90% of all cases. In order to analyze heterogeneous transmission of dengue, a multivariate time series model decomposing dengue risk additively into endemic, autoregressive and spatiotemporal components was used to model dengue transmission. Moreover, random effects were introduced in the model to deal with heterogeneous dengue transmission and incidence levels and power law approach was embedded into the model to account for spatial interaction. There was little spatial variation in the autoregressive component. In contrast, for the endemic component, there was a pronounced heterogeneity between the Pearl River Delta area and the remaining districts. For the spatiotemporal component, there was considerable heterogeneity across districts with highest values in some western and eastern department. The results showed that the patterns driving dengue transmission were found by using clustering analysis. And endemic component contribution seems to be important in the Pearl River Delta area, where the incidence is high (95 per 100,000), while areas with relatively low incidence (4 per 100,000) are highly dependent on spatiotemporal spread and local autoregression. PMID:27666657
Topcuoglu, B. D.; Stewart, L. C.; Butterfield, D. A.; Huber, J. A.; Holden, J. F.
2016-12-01
Approximately 1 giga ton (Gt, 1015 g) of CH4 is formed globally per year from H2, CO2 and acetate through methanogenesis, largely by methanogens growing in syntrophic association with anaerobic microbes that hydrolyze and ferment biopolymers. However, our understanding of methanogenesis in hydrothermal regions of the subseafloor and potential syntrophic methanogenesis at thermophilic temperatures (i.e., >50°C) is nascent. In this study, the growth of natural assemblages of thermophilic methanogens from Axial Seamount was primarily limited by H2 availability. Heterotrophs supported thermophilic methanogenesis by H2 syntrophy in microcosm incubations of hydrothermal fluids at 55°C and 80°C supplemented with tryptone only. Based on 16S rRNA gene sequencing, only heterotrophic archaea that produce H2, H2-consuming methanogens, and sulfate reducing archaea were found in 80°C tryptone microcosms from Marker 113 vent. No bacteria were found. In 55°C tryptone microcosms, sequences were found from H2-producing bacteria and H2-consuming methanogens and sulfate-reducing bacteria. In order to model the impact of H2 syntrophy at hyperthemophilic temperatures, a co-culture was established consisting of the H2-producing hyperthermophilic heterotroph Thermococcus paralvinellae and a H2-consuming hyperthermophilic methanogen Methanocaldococcus bathoardescens. When grown alone in a chemostat, the growth rates and steady-state cell concentrations of T. paralvinellae decreased significantly when a high H2 (70 µM) background was present. H2 inhibition was ameliorated by the production of formate, but in silico modeling suggests less energetic yield for the cells. H2 syntrophy relieved H2 inhibition for both the heterotroph and the methanogenic partners. The results demonstrate that thermophilic H2 syntrophy can support methanogenesis within natural microbial assemblages and may be an important alternative energy source for thermophilic autotrophs in marine geothermal environments.
Coarse Grained Modeling of The Interface BetweenWater and Heterogeneous Surfaces
Energy Technology Data Exchange (ETDEWEB)
Willard, Adam; Chandler, David
2008-06-23
Using coarse grained models we investigate the behavior of water adjacent to an extended hydrophobic surface peppered with various fractions of hydrophilic patches of different sizes. We study the spatial dependence of the mean interface height, the solvent density fluctuations related to drying the patchy substrate, and the spatial dependence of interfacial fluctuations. We find that adding small uniform attractive interactions between the substrate and solvent cause the mean position of the interface to be very close to the substrate. Nevertheless, the interfacial fluctuations are large and spatially heterogeneous in response to the underlying patchy substrate. We discuss the implications of these findings to the assembly of heterogeneous surfaces.
Energy Technology Data Exchange (ETDEWEB)
Luscher, Darby J.
2010-04-01
All materials are heterogeneous at various scales of observation. The influence of material heterogeneity on nonuniform response and microstructure evolution can have profound impact on continuum thermomechanical response at macroscopic “engineering” scales. In many cases, it is necessary to treat this behavior as a multiscale process thus integrating the physical understanding of material behavior at various physical (length and time) scales in order to more accurately predict the thermomechanical response of materials as their microstructure evolves. The intent of the dissertation is to provide a formal framework for multiscale hierarchical homogenization to be used in developing constitutive models.
Scaling of cluster heterogeneity in the two-dimensional Potts model.
Lv, Jian-Ping; Yang, Xianqing; Deng, Youjin
2012-08-01
Cluster heterogeneity, the number of clusters of mutually distinct sizes, has been recently studied for explosive percolation and standard percolation [H. K. Lee et al., Phys. Rev. E 84, 020101(R) (2011); J. D. Noh et al., Phys. Rev. E 84, 010101(R) (2011)]. In this work we study the scaling of various quantities related with cluster heterogeneity in a broader context of two-dimensional q-state Potts model. We predict, via an analytic approach, the critical exponents for most of the measured quantities, and confirm these predications for various q values using extensive Monte Carlo simulations.
Reactive transport modeling in the subsurface environment with OGS-IPhreeqc
He, Wenkui; Beyer, Christof; Fleckenstein, Jan; Jang, Eunseon; Kalbacher, Thomas; Naumov, Dimitri; Shao, Haibing; Wang, Wenqing; Kolditz, Olaf
2015-04-01
Worldwide, sustainable water resource management becomes an increasingly challenging task due to the growth of population and extensive applications of fertilizer in agriculture. Moreover, climate change causes further stresses to both water quantity and quality. Reactive transport modeling in the coupled soil-aquifer system is a viable approach to assess the impacts of different land use and groundwater exploitation scenarios on the water resources. However, the application of this approach is usually limited in spatial scale and to simplified geochemical systems due to the huge computational expense involved. Such computational expense is not only caused by solving the high non-linearity of the initial boundary value problems of water flow in the unsaturated zone numerically with rather fine spatial and temporal discretization for the correct mass balance and numerical stability, but also by the intensive computational task of quantifying geochemical reactions. In the present study, a flexible and efficient tool for large scale reactive transport modeling in variably saturated porous media and its applications are presented. The open source scientific software OpenGeoSys (OGS) is coupled with the IPhreeqc module of the geochemical solver PHREEQC. The new coupling approach makes full use of advantages from both codes: OGS provides a flexible choice of different numerical approaches for simulation of water flow in the vadose zone such as the pressure-based or mixed forms of Richards equation; whereas the IPhreeqc module leads to a simplification of data storage and its communication with OGS, which greatly facilitates the coupling and code updating. Moreover, a parallelization scheme with MPI (Message Passing Interface) is applied, in which the computational task of water flow and mass transport is partitioned through domain decomposition, whereas the efficient parallelization of geochemical reactions is achieved by smart allocation of computational workload over
Indian Academy of Sciences (India)
M Vasudevan; G Suresh Kumar; Indumathi M Nambi
2014-12-01
Characterization of aquifers contaminated by petroleum hydrocarbons is limited by the use of dissolution mass transfer correlations developed for single compounds without considering the effects of the mass transfer limitations in presence of other components. A one-dimensional implicit numerical model is developed for the coupled mass transfer and transport processes and the results are analysed using existing mass transfer correlations for better understanding of the single and multicomponent dissolution processes. Themass transfer coefficient in the multicomponent system is found to be more nonlinear and extending with changing slope, unlike the exponential reduction for single compound system. During the initial phase, the dissolution rate of a soluble compound is very high due to the high concentration gradient, and as dissolution progresses, its effective solubility decreases with change in mole fraction. At higher pore volumes, the mole fractions of lower solubility fractions increase which can result in higher effective solubility. The kinetics of interphase mass transfer by dissolution and sorption is favoured by coupled biodegradation. However, mass transfer limitation for more soluble compounds under the conditions of low residual saturation and low mole fraction is observed to be due to low dissolution rate coefficient rather than decreasing concentration gradient.
Directory of Open Access Journals (Sweden)
L. Chow
2017-08-01
Full Text Available The digitization and abstraction of existing buildings into building information models requires the translation of heterogeneous datasets that may include CAD, technical reports, historic texts, archival drawings, terrestrial laser scanning, and photogrammetry into model elements. In this paper, we discuss a project undertaken by the Carleton Immersive Media Studio (CIMS that explored the synthesis of heterogeneous datasets for the development of a building information model (BIM for one of Canada’s most significant heritage assets – the Centre Block of the Parliament Hill National Historic Site. The scope of the project included the development of an as-found model of the century-old, six-story building in anticipation of specific model uses for an extensive rehabilitation program. The as-found Centre Block model was developed in Revit using primarily point cloud data from terrestrial laser scanning. The data was captured by CIMS in partnership with Heritage Conservation Services (HCS, Public Services and Procurement Canada (PSPC, using a Leica C10 and P40 (exterior and large interior spaces and a Faro Focus (small to mid-sized interior spaces. Secondary sources such as archival drawings, photographs, and technical reports were referenced in cases where point cloud data was not available. As a result of working with heterogeneous data sets, a verification system was introduced in order to communicate to model users/viewers the source of information for each building element within the model.
Sarkar, S; Mukherjee, K; Ray, A; Srivastav, A; Wettergren, T A
2012-08-01
This paper presents the qualitative nature of communication network operations as abstraction of typical thermodynamic parameters (e.g., order parameter, temperature, and pressure). Specifically, statistical mechanics-inspired models of critical phenomena (e.g., phase transitions and size scaling) for heterogeneous packet transmission are developed in terms of multiple intensive parameters, namely, the external packet load on the network system and the packet transmission probabilities of heterogeneous packet types. Network phase diagrams are constructed based on these traffic parameters, and decision and control strategies are formulated for heterogeneous packet transmission in the network system. In this context, decision functions and control objectives are derived in closed forms, and the pertinent results of test and validation on a simulated network system are presented.
The Role of Heterogeneous Chemistry of Volatile ORganic Compounds: A Modeling and Laboratory Study
Energy Technology Data Exchange (ETDEWEB)
Gregory R. Carmichael; Vicki H. Grassian
2007-03-01
Overview The outputs of this research have been reported annually via the RIMS system. This report serves as an update and final report. The focus of our DOE BES funded project is on the importance of heterogeneous reactions in the troposphere. The primary objectives of our study were to: (i) Evaluate the extent to which heterogeneous chemistry affects the photochemical oxidant cycle, particularly, sources and sinks of tropospheric ozone; and (ii) Conduct laboratory studies on heterogeneous reactions involving NOy, O3 and VOCs on aerosol surfaces. These objectives were pursued through a multidisciplinary approach that combines modeling and laboratory components as discussed in more detail below. In addition, in response to the reconfiguring of the Atmospheric Science Program to focus on aerosol radiative forcing of climate, we also began to investigate the radiative properties of atmospheric aerosol.
Geologically based model of heterogeneous hydraulic conductivity in an alluvial setting
Fogg, Graham E.; Noyes, Charles D.; Carle, Steven F.
Information on sediment texture and spatial continuity are inherent to sedimentary depositional facies descriptions, which are therefore potentially good predictors of spatially varying hydraulic conductivity (K). Analysis of complex alluvial heterogeneity in Livermore Valley, California, USA, using relatively abundant core descriptions and field pumping-test data, demonstrates a depositional-facies approach to characterization of subsurface heterogeneity. Conventional textural classifications of the core show a poor correlation with K; however, further refinement of the textural classifications into channel, levee, debris-flow, and flood-plain depositional facies reveals a systematic framework for spatial modeling of K. This geologic framework shows that most of the system is composed of very low-K flood-plain materials, and that the K measurements predominantly represent the other, higher-K facies. Joint interpretation of both the K and geologic data shows that spatial distribution of K in this system could not be adequately modeled without geologic data and analysis. Furthermore, it appears that K should not be assumed to be log-normally distributed, except perhaps within each facies. Markov chain modeling of transition probability, representing spatial correlation within and among the facies, captures the relevant geologic features while highlighting a new approach for statistical characterization of hydrofacies spatial variability. The presence of fining-upward facies sequences, cross correlation between facies, as well as other geologic attributes captured by the Markov chains provoke questions about the suitability of conventional geostatistical approaches based on variograms or covariances for modeling geologic heterogeneity. Résumé Les informations sur la texture des sédiments et leur continuité spatiale font partie des descriptions de faciès sédimentaires de dépôt. Par conséquent, ces descriptions sont d'excellents prédicteurs potentiels des
Atomic structure of graphene supported heterogeneous model catalysts
Energy Technology Data Exchange (ETDEWEB)
Franz, Dirk
2017-04-15
Graphene on Ir(111) forms a moire structure with well defined nucleation centres. Therefore it can be utilized to create hexagonal metal cluster lattices with outstanding structural quality. At diffraction experiments these 2D surface lattices cause a coherent superposition of the moire cell structure factor, so that the measured signal intensity scales with the square of coherently scattering unit cells. This artificial signal enhancement enables the opportunity for X-ray diffraction to determine the atomic structure of small nano-objects, which are hardly accessible with any experimental technique. The uniform environment of every metal cluster makes the described metal cluster lattices on graphene/Ir(111) an attractive model system for the investigation of catalytic, magnetic and quantum size properties of ultra-small nano-objects. In this context the use of x-rays provides a maximum of flexibility concerning the possible sample environments (vacuum, selected gases, liquids, sample temperature) and allows in-situ/operando measurements. In the framework of the present thesis the structure of different metal clusters grown by physical vapor deposition in an UHV environment and after gas exposure have been investigated. On the one hand the obtained results will explore many aspects of the atomic structure of these small metal clusters and on the other hand the presented results will proof the capabilities of the described technique (SXRD on cluster lattices). For iridium, platinum, iridium/palladium and platinum/rhodium the growth on graphene/Ir(111) of epitaxial, crystalline clusters with an ordered hexagonal lattice arrangement has been confirmed using SXRD. The clusters nucleate at the hcp sites of the moire cell and bind via rehybridization of the carbon atoms (sp{sup 2} → sp{sup 3}) to the Ir(111) substrate. This causes small displacements of the substrate atoms, which is revealed by the diffraction experiments. All metal clusters exhibit a fcc structure
Kukacka, Jiri; Barunik, Jozef
2013-12-01
The main aim of this work is to incorporate selected findings from behavioural finance into a Heterogeneous Agent Model using the Brock and Hommes (1998) [34] framework. Behavioural patterns are injected into an asset pricing framework through the so-called ‘Break Point Date’, which allows us to examine their direct impact. In particular, we analyse the dynamics of the model around the behavioural break. Price behaviour of 30 Dow Jones Industrial Average constituents covering five particularly turbulent US stock market periods reveals interesting patterns in this aspect. To replicate it, we apply numerical analysis using the Heterogeneous Agent Model extended with the selected findings from behavioural finance: herding, overconfidence, and market sentiment. We show that these behavioural breaks can be well modelled via the Heterogeneous Agent Model framework and they extend the original model considerably. Various modifications lead to significantly different results and model with behavioural breaks is also able to partially replicate price behaviour found in the data during turbulent stock market periods.
Drzewiecki, Wojciech
2016-12-01
In this work nine non-linear regression models were compared for sub-pixel impervious surface area mapping from Landsat images. The comparison was done in three study areas both for accuracy of imperviousness coverage evaluation in individual points in time and accuracy of imperviousness change assessment. The performance of individual machine learning algorithms (Cubist, Random Forest, stochastic gradient boosting of regression trees, k-nearest neighbors regression, random k-nearest neighbors regression, Multivariate Adaptive Regression Splines, averaged neural networks, and support vector machines with polynomial and radial kernels) was also compared with the performance of heterogeneous model ensembles constructed from the best models trained using particular techniques. The results proved that in case of sub-pixel evaluation the most accurate prediction of change may not necessarily be based on the most accurate individual assessments. When single methods are considered, based on obtained results Cubist algorithm may be advised for Landsat based mapping of imperviousness for single dates. However, Random Forest may be endorsed when the most reliable evaluation of imperviousness change is the primary goal. It gave lower accuracies for individual assessments, but better prediction of change due to more correlated errors of individual predictions. Heterogeneous model ensembles performed for individual time points assessments at least as well as the best individual models. In case of imperviousness change assessment the ensembles always outperformed single model approaches. It means that it is possible to improve the accuracy of sub-pixel imperviousness change assessment using ensembles of heterogeneous non-linear regression models.
Yue, S. S.; Wen, Y. N.; Lv, G. N.; Hu, D.
2013-10-01
In recent years, the increasing development of cloud computing technologies laid critical foundation for efficiently solving complicated geographic issues. However, it is still difficult to realize the cooperative operation of massive heterogeneous geographical models. Traditional cloud architecture is apt to provide centralized solution to end users, while all the required resources are often offered by large enterprises or special agencies. Thus, it's a closed framework from the perspective of resource utilization. Solving comprehensive geographic issues requires integrating multifarious heterogeneous geographical models and data. In this case, an open computing platform is in need, with which the model owners can package and deploy their models into cloud conveniently, while model users can search, access and utilize those models with cloud facility. Based on this concept, the open cloud service strategies for the sharing of heterogeneous geographic analysis models is studied in this article. The key technology: unified cloud interface strategy, sharing platform based on cloud service, and computing platform based on cloud service are discussed in detail, and related experiments are conducted for further verification.
Campbell, Stuart G; Hatfield, P Chris; Campbell, Kenneth S
2011-09-01
A skeletal muscle fiber that is stimulated to contract and then stretched from L₁ to L₂ produces more force after the initial transient decays than if it is stimulated at L₂. This behavior has been well studied experimentally, and is known as residual force enhancement. The underlying mechanism remains controversial. We hypothesized that residual force enhancement could reflect mechanical interactions between heterogeneous half-sarcomeres. To test this hypothesis, we subjected a computational model of interacting heterogeneous half-sarcomeres to the same activation and stretch protocols that produce residual force enhancement in real preparations. Following a transient period of elevated force associated with active stretching, the model predicted a slowly decaying force enhancement lasting >30 seconds after stretch. Enhancement was on the order of 13% above isometric tension at the post-stretch muscle length, which agrees well with experimental measurements. Force enhancement in the model was proportional to stretch magnitude but did not depend strongly on the velocity of stretch, also in agreement with experiments. Even small variability in the strength of half-sarcomeres (2.1% standard deviation, normally distributed) was sufficient to produce a 5% force enhancement over isometric tension. Analysis of the model suggests that heterogeneity in half-sarcomeres leads to residual force enhancement by storing strain energy introduced during active stretch in distributions of bound cross-bridges. Complex interactions between the heterogeneous half-sarcomeres then dissipate this stored energy at a rate much slower than isolated cross-bridges would cycle. Given the variations in half-sarcomere length that have been observed in real muscle preparations and the stochastic variability inherent in all biological systems, half-sarcomere heterogeneity cannot be excluded as a contributing source of residual force enhancement.
Directory of Open Access Journals (Sweden)
Lijuan Cui
2016-11-01
Full Text Available We monitored the water quality and hydrological conditions of a horizontal subsurface constructed wetland (HSSF-CW in Beijing, China, for two years. We simulated the area-based constant and the temperature coefficient with the first-order kinetic model. We examined the relationships between the nitrogen (N removal rate, N load, seasonal variations in the N removal rate, and environmental factors—such as the area-based constant, temperature, and dissolved oxygen (DO. The effluent ammonia (NH4+-N and nitrate (NO3−-N concentrations were significantly lower than the influent concentrations (p < 0.01, n = 38. The NO3−-N load was significantly correlated with the removal rate (R2 = 0.96, p < 0.01, but the NH4+-N load was not correlated with the removal rate (R2 = 0.02, p > 0.01. The area-based constants of NO3−-N and NH4+-N at 20 °C were 27 ± 26 (mean ± SD and 14 ± 10 m∙year−1, respectively. The temperature coefficients for NO3−-N and NH4+-N were estimated at 1.004 and 0.960, respectively. The area-based constants for NO3−-N and NH4+-N were not correlated with temperature (p > 0.01. The NO3−-N area-based constant was correlated with the corresponding load (R2 = 0.96, p < 0.01. The NH4+-N area rate was correlated with DO (R2 = 0.69, p < 0.01, suggesting that the factors that influenced the N removal rate in this wetland met Liebig’s law of the minimum.
Trehan, Sumeet; Durlofsky, Louis J.
2016-12-01
A new reduced-order model based on trajectory piecewise quadratic (TPWQ) approximations and proper orthogonal decomposition (POD) is introduced and applied for subsurface oil-water flow simulation. The method extends existing techniques based on trajectory piecewise linear (TPWL) approximations by incorporating second-derivative terms into the reduced-order treatment. Both the linear and quadratic reduced-order methods, referred to as POD-TPWL and POD-TPWQ, entail the representation of new solutions as expansions around previously simulated high-fidelity (full-order) training solutions, along with POD-based projection into a low-dimensional space. POD-TPWQ entails significantly more offline preprocessing than POD-TPWL as it requires generating and projecting several third-order (Hessian-type) terms. The POD-TPWQ method is implemented for two-dimensional systems. Extensive numerical results demonstrate that it provides consistently better accuracy than POD-TPWL, with speedups of about two orders of magnitude relative to high-fidelity simulations for the problems considered. We demonstrate that POD-TPWQ can be used as an error estimator for POD-TPWL, which motivates the development of a trust-region-based optimization framework. This procedure uses POD-TPWL for fast function evaluations and a POD-TPWQ error estimator to determine when retraining, which entails a high-fidelity simulation, is required. Optimization results for an oil-water problem demonstrate the substantial speedups that can be achieved relative to optimizations based on high-fidelity simulation.
Modeling, Empirics and Policy Implications of Firm Heterogeneity in International Trade
Akgul, Zeynep
2015-01-01
Computable General Equilibrium (CGE) models are essential computational tools for trade policy analysis. While traditional CGE models based on the Armington assumption of national product differentiation have been successfully applied to various policy scenarios, they also have significant limitations in explaining the firm-level information prevalent in the recent international trade literature. The pioneering work of Melitz (2003) has provided a firm heterogeneity theory that can help addre...
General model for studying the feasibility of heterogeneous extractive batch distillation
Hegely, Laszlo; Gerbaud, Vincent; Lang, Peter
2014-01-01
International audience; By extending our former model for batch heteroazeotropic distillation, a general model is developed for the batch heterogeneous extractive distillation. An entrainer-rich and an entrainer-lean phase are present in the decanter, where the holdup of both phases can be reduced, kept constant, or increased, thanks to batch operation mode. Any fraction of both phases can be refluxed or withdrawn as distillate. The entrainer is fed continuously either onto one of the plates ...
Modeling and validation of directional reflectance for heterogeneous agro-forestry scenarios
Yelu, Z.; Jing, L.; Qinhuo, L.; Huete, A. R.
2015-12-01
Landscape heterogeneity is a common natural phenomenon but is seldom considered in current radiative transfer models for predicting the surface reflectance. This paper developed an explicit analytical Radiative Transfer model for heterogeneous Agro-Forestry scenarios (RTAF) by dividing the scenario into non-boundary regions and boundary regions. The scattering contribution of the non-boundary regions that are treated as homogeneous canopies can be estimated from the SAILH model, whereas that of the boundary regions with lengths, widths, canopy heights, and orientations of the field patches, is calculated based on the bidirectional gap probability by considering the interactions and mutual shadowing effects among different patches. The hot spot factor is extended for