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Frost, Nageena Kiani. "CFD modelling of fluid flow and contaminant transport in hydrogeological systems". Thesis, University of Greenwich, 2006. http://gala.gre.ac.uk/6171/.
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This study provides an understanding of various aspects of hydrogeological systems modelling and the use of computational techniques to predict and optimise hydrological parameter assessment, anisotropic scaling, macrodispersion and solute flux measurements under unsteady, uniform/non-uniform flow conditions. The incorporated models are structured around multi-physics continuum mechanics analysis to investigate fluid flow and solute transport in hydrogeological systems. The control-volume unstructured mesh configuration, based on cell-centred or vertex-based FV algorithms for CFD and CSM problems is employed. The non-linear material behaviour exhibited by porous soils and the fluid flow evaluation under system stresses is described by elasto-visco-plastic constitutive relationships and the coupling between CFD and CSM processes. The designed simulation models are used to calibrate the flow problems associated with regional groundwater levels estimation, determination of soil hydraulic properties and moisture distribution in dry soils in response to infiltration of compressible or incompressible fluids. For solute transport problems, investigations of spatial distribution of solute species in homogeneous/layered heterogeneous systems are undertaken by accounting for chemical, geochemical and biological reactions caused by particle deposition processes and liquid-solid interactions in natural subsurface systems. The simulated shape and spread of contaminant plume are effectively influenced by the governing transport mechanism for solutes. The attention in leachate is predicted to have a significant role in reducing the level of contaminant concentration and its potential impact on the attainable groundwater resources.
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Muhammad, Sarkawt Hamarahim. "Application of Numerical Modeling to Study River Dynamics: Hydro-Geomorphological Evolution Due to Extreme Events in the Sandy River, Oregon". PDXScholar, 2017. https://pdxscholar.library.pdx.edu/open_access_etds/3478.
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The Sandy River (OR) is a coastal tributary of the Columbia River and has a steep hydroshed 1316 square kilometers which is located on the western side of Mount Hood (elevation range 3 m to 1800 m). The system exhibits highly variable flow: Its average discharge is ~40 m3/s, and the highest recorded discharge was 1739 m3/s in 1964. In this study I model the geomorphic sensitivity of an 1800m reach located the downstream of the former Marmot Dam, which was removed in 2007. The hydro-geomorphic response to major flood has implications for system management and aquatic life.
Studying hydro-geomorphic change requires a systematic approach. Here, I define flows and flood hydrographs for specified return interval based on the observed hydrologic record, and then examine potential hydro-geomorphic changes using a numerical model. A Pearson Type III distribution is used to calculate 100, 75, 50, 25, 10, and 2 year return periods. Extreme event hydrographs are derived by fitting derived and observed flood hydrographs to the gamma distribution curve. Sediment transport and geomorphology are then modeled numerically with Nays2DH, a solver that is part of iRIC software. Because the model is computationally intensive, I model the domain with five different spatial grid resolutions, to find proper grid resolution. The grid resolutions used are 1.5 m, 2 m, 3 m, 4 m, and 5 m. We choose 4 m as optimum grid resolution, based on the convergence of model results. The model is run for extreme event hydrographs with six above return periods. For result visualization and analysis, we focus on flow properties and bed elevation at peak flow and at the end of each event. For both times for each event, important flow and sediment transport parameters are visualized for the entire domain in plane form and eight cross-sections at 200 m intervals. Finally, we divide the geomorphic response into areas of erosion and deposition. Linear regression analyses of mean values of erosion and deposition at peak flow for all extreme events yield R2 of 0.981 for erosion and 0.986 for deposition. The mean erosion and deposition depth at the end of the events is modeled by nonlinear regression with correlation coefficient of 0.965 for erosion and 0.998 for deposition. The regression models provide direct understanding of impacts of different floods on the geomorphic response of the river domain. examination of the model as a whole suggest that the amount of erosion and deposition in the bed and banks is a function of channel geometry, bank and bed geology, riparian area condition and strongly depend on the amount of flow through the channel.
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Guillemoto, Quentin. "Transfert des molécules organiques traces des eaux usées traitées dans un système de Soil Aquifer Treatment (SAT) : application à l’hydrosystème côtier d’Agon-Coutainville". Electronic Thesis or Diss., Sorbonne université, 2022. http://www.theses.fr/2022SORUS510.
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Les pressions sur les eaux souterraines (sècheresses, surexploitations, pollutions…) contribuent à une diminution globale de la disponibilité de la ressource. Les solutions de recharge maitrisée des aquifères (MAR) et de traitement de l’eau par le sol et l’aquifère (SAT) présentent des avantages certains pour une future gestion durable de la qualité et de la quantité des eaux souterraines et notamment par l’utilisation des eaux usées traitées. La préservation de la qualité des eaux souterraines lors de l’introduction de ces eaux dans un système MAR doit être assurée. Une difficulté majeure réside dans la compréhension des processus induits par ces techniques conditionnant la qualité des eaux souterraines, notamment les molécules organiques traces (TrOCs) présentes dans les eaux usées traitées qui font l’objet d’une attention particulière ces dernières années. A ce jour, la compréhension du devenir des TrOCs dans un SAT est très limitée malgré une connaissance croissante des processus régissant leur réactivité (dégradation, sorption). Encore plus rares sont les études qui considèrent le SAT comme partie intégrante d’un hydrosystème naturel, dans lequel la dynamique des écoulements souterrains augmente la complexité du comportement de ces molécules. La méthodologie de la thèse combine l’analyse de données, l’expérimentation et la modélisation mises en œuvre à des échelles spatio-temporelles différentes. Elle est appliquée au site SAT côtier localisé à Agon-Coutainville (Normandie, France) actif depuis plus de 20 ans. L’interprétation des données acquises sur le terrain par des outils géochimiques et d’analyse de séries temporelles établi une première description du comportement d’une sélection de TrOCs dans le SAT. Les résultats à l’échelle du site montrent la diversité de comportement des TrOCs associée à la fois à des facteurs réactifs, opérationnels et hydrodynamiques. Une expérience d’infiltration contrôlée en conditions opérationnelles à l’échelle d’un bassin d’infiltration sur 35 jours est interprétée à l’aide d’outils de modélisation géochimique et analytique du transport réactif (Advection-Dispersion Equation, ADE). Les résultats montrent une atténuation naturelle de 5 TrOCs via le SAT après un temps de résidence moyen de 12 jours par la quantification des coefficients de dégradation du premier ordre (μ) et coefficient de retard (R). A l’échelle pluriannuelle de l’aquifère accueillant le système SAT, un modèle d’écoulement et de transport (MARTHE) est construit afin de quantifier l’influence des facteurs environnementaux (climat, marées, conditions opérationnelles) sur l’hydrosystème côtier quant au devenir des TrOCs. Les résultats du modèle montrent leurs incidences sur les vitesses d’écoulement, la dilution et la réactivité des TrOCs. Une atténuation des concentrations en TrOCs par réactivité est attendue sur les deux-tiers de la surface du SAT lors des 6 mois de l’année les plus secs, alors que sur la surface restante, la dynamique marine locale amène une baisse des concentrations majoritairement par dilution. A l’exutoire naturel de l’aquifère, les temps de résidence moyens simulées s’étalent entre 74 et 489 jours selon la dynamique saisonnière qui pourrait être précisée par des investigations complémentaires concernant les eaux de surface (mer et cours d’eau). Ces travaux apportent une méthodologie innovante pluridisciplinaire intégrant divers outils pour aborder le devenir des TrOCs dans des systèmes SAT à différentes échelles spatiales et temporelles, tout en considérant le comportement hydrodynamique et réactif de tels systèmes. De nombreuses perspectives à ces travaux de thèse s’ouvrent, particulièrement concernant la caractérisation fine de la réactivité des TrOCs dans de tels systèmes en contexte côtier, ou encore le développement d’outils de modélisation hydrodynamique intégrant des processus réactifs mécanistiques, ce qui améliorerait la compréhension du comportement des TrOCs dans ces systèmesPressures on groundwater (droughts, overexploitation, pollution, etc.) contribute to an overall decrease in the availability of the resource. Manages Aquifer Recharge (MAR) and Soil Aquifer Treatment (SAT) have clear advantages for future sustainable quality and quantity management of groundwater, especially through the use of treated wastewater. The preservation of groundwater quality when introducing these so-called unconventional waters into MAR must be ensured. A major difficulty lies in understanding the processes induced by these techniques that affect groundwater quality. These include the Trace Organic Compounds (TrOCs) present in treated wastewater, which have received particular attention in recent years. To date, the understanding of the fate of TrOCs at the scale of a SAT site is very limited despite a growing knowledge of the processes induced (degradation, sorption). Even fewer studies consider the SAT system as an integral part of a natural hydrosystem, in which the dynamics of groundwater flows increase the complexity of the behaviour of these molecules. The methodology of the thesis combines data analysis, experimentation and modelling implemented at different spatio-temporal scales. It was applied to the coastal SAT site located in Agon-Coutainville (Normandy, France) which has been active for more than 20 years. Interpretation of the data acquired in the field using geochemical and time series analysis tools allowed a first description of the behaviour of a selection of TrOCs within a SAT system. The results at the site scale show the diversity of behaviour of TrOCs in the SAT associated with reactive, operational and hydrodynamic factors. A controlled infiltration experiment under operational conditions at the scale of an infiltration basin over 35 days was interpreted using geochemical modelling tools and analytical modelling of reactive transport (Advection-Dispersion Equation, ADE). The results show a natural attenuation of TrOCs from the SAT after an average residence time of 12 days in the SAT by quantifying first-order degradation coefficients (μ) and retardation coefficients (R) for some molecules On the multi-year scale of the aquifer hosting the SAT system, a flow and transport model (MARTHE) was built to quantify the influence of environmental factors (climate, tides, operational conditions) on the coastal hydrosystem with regard to the fate of TrOCs. The results of the model show their impact on flow rates, dilution and reactivity of TrOCs. An attenuation of TrOC concentrations by reactivity is expected over two-thirds of the surface of the SAT during the driest six months of the year, while over the remaining surface, local marine dynamics lead to a decrease in concentrations mainly by dilution. At the natural outlet of the aquifer, the simulated average residence times range from 74 to 489 days depending on the seasonal dynamics, which could be specified by additional investigations concerning the surface water (sea and river). This work provides an innovative multidisciplinary methodology integrating various tools to address the fate of TrOCs in SAT systems at different spatial and temporal scales, while considering the hydrodynamic and reactive behaviour of such systems. Many perspectives to this thesis work are arising, particularly concerning the characterisation of the reactivity of TrOCs in such systems in a coastal context, or the development of hydrodynamic modelling tools integrating more mechanistic reactive processes, which would improve the understanding of the behaviour of TrOCs in these systems
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Ross, James. "Approximate Reasoning in Hydrogeological Modeling". ScholarWorks @ UVM, 2008. http://scholarworks.uvm.edu/graddis/200.
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The accurate determination of hydraulic conductivity is an important element of successful groundwater flow and transport modeling. However, the exhaustive measurement of this hydrogeological parameter is quite costly and, as a result, unrealistic. Alternatively, relationships between hydraulic conductivity and other hydrogeological variables less costly to measure have been used to estimate this crucial variable whenever needed. Until this point, however, the majority of these relationships have been assumed to be crisp and precise, contrary to what intuition dictates. The research presented herein addresses the imprecision inherent in hydraulic conductivity estimation, framing this process in a fuzzy logic framework. Because traditional hydrogeological practices are not suited to handle fuzzy data, various approaches to incorporating fuzzy data at different steps in the groundwater modeling process have been previously developed. Such approaches have been both redundant and contrary at times, including multiple approaches proposed for both fuzzy kriging and groundwater modeling. This research proposes a consistent rubric for the handling of fuzzy data throughout the entire groundwater modeling process. This entails the estimation of fuzzy data from alternative hydrogeological parameters, the sampling of realizations from fuzzy hydraulic conductivity data, including, most importantly, the appropriate aggregation of expert-provided fuzzy hydraulic conductivity estimates with traditionally-derived hydraulic conductivity measurements, and utilization of this information in the numerical simulation of groundwater flow and transport.
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Orr, A. E. "Hydrogeological influences on the fate and transport of nitrate in groundwater". Thesis, Queen's University Belfast, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.680365.
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Nitrate (N03) contamination is a significant global concern in many agricultural catchments. This research undertook a national scale and a catchment scale to investigate the influence of hydrogeological setting the fate and transport of N03 in agricultural catchments. In this researc statistical analyses of a national database showed that groundwater N03 concentrations are controlled by a combination of factors including the hydrogeological. setting, which incorporates transmissivitY ' and flow path length, landuse pressure, soil type, subsoil thickness and" permeability, groundwater oxidation reduction potential (ORP) conditions. A catchment scale study was undertaken of two study catchments containing contrasting hydrogeological characteristics. In the Nuenna catchment underlain by an Rkd aquifer, point sources are not a significant influence on the water quality in terms of N in the Nuenna River. In the Glen Burn catchment, underlain by a Pl aquifer, point sources have a significant influence on the Glen Burn River water quality. This contribution from sources increases as the groundwater level decreases and discharge from shallow groundwater reduces. Greater storage and persistence of N03 in the Nuenna Rkd aquifer indicate that lag time for a decrease in groundwater N03 concentrations to occur more significant factor in Rkd aquifers. In contrast, lag time is not as significant in the Glen Burn Pl aquifer where N03 concentrations in the shallow bedrock are influenced by groundwater table fluctuations, the presence of preferential pathways through the till and seasonal changes pressure loadings. Denitrification with depth in this aquifer is shown through suitable hydrochemical conditions, an isotopic enrichment ratio 1.8:1 between 015N and 0180 and the presence of bacteria containing the gene. In contrast, hydrochemical, isotopic and microbial analyses have that denitrification is not significant in the Nuenna catchment, but the dominant biogeochemical process is nitrification.
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Matynowski, Eric D. "Groundwater Modeling and Hydrogeological Parameter Estimation: Potomac Aquifer System, SWIFT Research Center". Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/99171.
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The Sustainable Water Interactive for Tomorrow (SWIFT) project in eastern Virginia is a Managed Aquifer Recharge project designed to alleviate the depletion of the Potomac Aquifer System due to unsustainable groundwater withdrawals. At the SWIFT Research Center (SWIFTRC) in Nansemond, VA, a pilot testing well (TW-1) has been implemented to help determine the feasibility of full-scale implementation. The pumping data from TW-1 and observation head data from surrounding monitoring wells (MW) at the SWIFTRC were used to calculate hydrogeological parameters (transmissivity, hydraulic conductivity, specific storage, and storage coefficient). Two sets of data were analyzed from before and after TW-1 was rehabilitated to account for the change in the flow distribution to each screen in TW-1. Comparing the results to past literature, the calculated (Theis and Cooper-Jacob methods) hydraulic conductivity/transmissivity values are within the same order of magnitude. Using borehole logs as well as apparent conductance and resistivity logs, multiple single and multi-layered models for both the upper and middle Potomac aquifers were produced with MODFLOW. Parameter estimation using MODFLOW and PEST and the two sets of observation data resulted in hydrogeological parameters similar to those calculated using Theis and Cooper-Jacob methods. The change in the hydraulic conductivity and specific storage between the pre and post rehabilitation flow distributions is proportional to that change in the flow distribution. For future modeling of the aquifer system, the hydrogeological parameters from the model using the 4/26/19 data set with the post rehabilitation flow distribution is recommended. Drawdown results from a multi-layered MODFLOW model were compared to results using the Theis method using both the Theis-calculated and MODFLOW-PEST modeled hydrogeological parameters. The results were nearly identical except for the Upper Potomac Aquifer (UPA) layer 1, as the model has a large change in aquifer thickness with distance from TW-1 that the Theis-based calculations do not consider. Travel times from the monitoring wells to TW-1 were calculated with the single and multi-layered models pumping 700 GPM from TW-1. Travel times from the SWIFT MW within the UPA sublayers ranged from 204 to 597 days depending on the sublayer, while travel times from the USGS MW within the UPA sublayers ranged from 2,395 to 7,859 days. For the single layer model of the UPA, the travel time from the SWIFT MW to TW-1 was 372 days while the travel time from the USGS MW was 4,839 days. Travel times from the SWIFT MW within the MPA sublayers were 416 and 1,195 days, while travel times from the USGS MW within the MPA sublayers were 4,339 and 11,245 days. For the single layer model of the MPA, the travel time from the SWIFT MW to TW-1 was 743 days while the travel time from the USGS MW was 7,545 days.Master of Science
The Sustainable Water Interactive for Tomorrow (SWIFT) project in eastern Virginia is a project designed to help slow the depletion of the Potomac Aquifer System due to unsustainable groundwater withdrawals. At the SWIFT Research Center (SWIFTRC) in Nansemond, VA, a testing well (TW-1) has been implemented to help determine if the full-scale implementation of the SWIFT project is feasible. The pumping data from TW-1 and observation head data from surrounding monitoring wells (MW) at the SWIFTRC were used to calculate hydrogeological parameters (transmissivity, hydraulic conductivity, specific storage, and storage coefficients). These parameters help describe the behavior of the aquifer system. Two sets of data were analyzed from before and after TW-1 was rehabilitated to account for the change in the flow distribution within TW-1. Comparing the results to past literature, the calculated (using analytical methods, Theis and Cooper-Jacob methods) hydraulic conductivity/transmissivity values are within the same order of magnitude. Using data from the boreholes, multiple single and multi-layered models for both the upper and middle Potomac aquifers were produced with MODFLOW, a groundwater modeling software. Estimating parameters using observation data within MODFLOW resulted in hydrogeological parameters similar to those calculated using the Theis and Cooper-Jacob methods. The change in the hydraulic conductivity and specific storage between the pre and post rehabilitation flow distributions within TW-1 is proportional to that change in the flow distribution. For future modeling of the aquifer system, the hydrogeological parameters from the model using the 4/26/19 (most recent) data set with the post rehabilitation (more current) flow distribution is recommended. Drawdown (decrease in the water table) results from a multi-layered MODFLOW model were compared to results using the Theis method using both the Theis-calculated and MODFLOW modeled hydrogeological parameters. The results were nearly identical except for the Upper Potomac Aquifer (UPA) layer 1, as the model has a large change in aquifer thickness with distance from TW-1 that the Theis-based calculations do not consider. The time it took for a particle of water to travel from the monitoring wells to TW-1 were calculated with the single and multi-layered models pumping 700 GPM from TW-1. Travel times from the SWIFT MW within the UPA sublayers ranged from 204 to 597 days depending on the sublayer, while travel times from the USGS MW within the UPA sublayers ranged from 2,395 to 7,859 days. For the single layer model of the UPA, the travel time from the SWIFT MW to TW-1 was 372 days while the travel time from the USGS MW was 4,839 days. Travel times from the SWIFT MW within the MPA sublayers were 416 and 1,195 days, while travel times from the USGS MW within the MPA sublayers were 4,339 and 11,245 days. For the single layer model of the MPA, the travel time from the SWIFT MW to TW-1 was 743 days while the travel time from the USGS MW was 7,545 days.
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STEFANIA, GENNARO ALBERTO. "HYDROGEOLOGICAL MODELING TO SUPPORT THE MANAGEMENT OF GROUNDWATER RESOURCES IN ALPINE VALLEYS". Doctoral thesis, Università degli Studi di Milano-Bicocca, 2018. http://hdl.handle.net/10281/199125.
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Il presente progetto di dottorato riguarda lo sviluppo di metodologie e strumenti modellistici a supporto della gestione delle risorse idriche sotterranee da un punto di vista quantitativo e qualitativo. A tale scopo, il progetto ha preso in considerazione gli acquiferi delle valli alpine, i quali rappresentano un particolare contesto idrogeologico in sui le interazioni tra acque sotterranee e superficiali nonché il pompaggio dei pozzi incidono profondamente sul comportamento idraulico delle falde. Inoltre, l'impostazione idrogeologica di questi acquiferi rende le acque sotterranee altamente vulnerabili alla contaminazione da parte delle attività umane.
Il lavoro, sviluppato in collaborazione con ARPA Valle d’Aosta, ha preso in considerazione tre aspetti principali che riguardano la gestione qualitativa e quantitativa dell’acquifero della Piana d'Aosta (Regione Valle d'Aosta, Italia).
Il primo aspetto ha riguardato la modellizzazione tridimensionale dell’acquifero della Piana d’Aosta e delle sue interazione con le acque superficiali. A tale scopo è stato sviluppo un modello numerico per simulare il flusso idrico sotterraneo al fine di identificare e quantificare le relazioni di scambio tra acque sotterranee e acque superficiali e allo stesso tempo valutare l'effetto del pompaggio sulle risorse idriche. Il modello di flusso idrico sotterraneo è stato sviluppato utilizzando MODFLOW2005 accoppiato al più recente pacchetto Stream-Flow routine package (SFR2) per simulare la rete idrica superficiale. Il modello, settato in condizioni stazionarie e transitorie, è stato calibrato mediante una procedura di calibrazione inversa eseguita usando il codice PEST. I risultati del modello hanno permesso di quantificare il bilancio idrogeologico, le interazioni acque sotterranee/superficiali, valutare l’effetto del pompaggio sulle risorse idriche, nonché individuare le aree più idonee per la realizzazione di nuovi pozzi.
Il secondo aspetto ha riguardato la gestione dei dati idrochimici delle acque sotterranee, il quale ha condotto allo sviluppo di un database idrochimica, disponibile online, chiamato TANGCHIM. Tale database idrochimico è stato accoppiato ad un pre-esistente database idrogeologico (TANGRAM) al fine di fornire una piattaforma integrata in grado di gestire, visualizzare e condividere tutti i dati idrogeologici e idrochimici relativi a pozzi e piezometri.
Il terzo argomento ha riguardato l’analisi di un fenomeno d’inquinamento delle acque sotterranee dovuto all’ingresso di percolato proveniente da un sito di discarica presente nella Piana d’Aosta. Questo lavoro è stato suddiviso in due parti principali.
La prima parte ha previsto la definizione di una metodologia generalizzata in grado di supportare gli enti gestori delle acque sotterranee alla definizione del modello concettuale di un sito contaminato (in questo caso una discarica) e, allo steso tempo, calcolare i livelli di guardia ai sensi della direttiva Europea sulle discariche (1999/31/EC). Tale metodologia costituisce complessivamente uno strumento utile per la pianificazione del monitoraggio di siti di discarica situati in aree storicamente impattate da pregresse attività antropiche.
Il secondo obiettivo ha riguardato l’individuazione, all’interno del sito di discarica, delle aree sorgenti attraverso cui il percolato si infiltra nel sottosuolo, contaminando le acque di falda.
L'indagine è stata condotta utilizzando i dati idrochimici e zuccheri artificiali campionati nel marzo 2017, applicando tecniche di statistica multivariata e modelli di trasporto. L’individuazione delle sorgenti si è resa necessaria al fine di migliorare la gestione del sito e progettare un adeguato sistema di bonifica.The present PhD project deals with the development of methodologies and tools in order to support the management of groundwater resources from a quantitative and qualitative point of view. The work deals with a particular hydrogeological context such as the Alpine valleys aquifers, where groundwater/surface water interactions as well the wells pumping have a crucial role in the hydraulic behaviour of groundwater. Moreover, the hydrogeological setting of these aquifers makes groundwater highly vulnerable to the contamination by the human activities. The work involves three main topics concerning specified issues affecting the Alpine valley aquifer of the Aosta Plain (Aosta Valley Region, N Italy). The first topic is related to the modeling of the three-dimensional groundwater flow and its interaction with the surface water. This topic was addressed by the development of a numerical groundwater flow model of the Aosta Plain aquifer in order to identify groundwater/surface-water relationships and evaluate the overall effect of the pumping on water resources. The model was developed using MODFLOW2005 and the more recent Stream-Flow routine package (SFR2) to simulate the surface-water network. An inverse calibration procedure performed by the PEST code was used to obtain the steady-state and transient solutions. The quantification of the hydrogeological budget, the groundwater/surface-water interactions and the effect of well withdrawals on water resources were done using the model results. The second topic deals with the management of groundwater hydrochemical data. This topic was addressed through the development of the online hydrochemical database called TANGCHIM which was joined with an existing hydrogeological database in order to provide an integrated platform able to manage, display and share water quality and quantity data. The third topic takes into account a groundwater pollution related to a landfill site. Within this topic, two main aims were achieved. The first one is related to the definition of a methodology able to support groundwater managers to define the conceptual model of the site and to calculate the trigger levels, a useful tool for monitoring landfill sites located in historical human-impacted areas. The second aim is related to the detection of the sources related to the groundwater contamination affecting the landfill site. The investigation was conducted using hydrochemical parameters and artificial sweeteners, multivariate statistical analysis and transport modeling. The source apportionment analysis was accomplished to distinguish the contribution of different sources of the leachate infiltration in order to improve the management of the landfill site and design a proper remediation system.
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O'Shaughnessy, Vince. "The hydrogeological and contaminant transport properties of fractured Leda clay in eastern Ontario". Thesis, University of Ottawa (Canada), 1993. http://hdl.handle.net/10393/6782.
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The objectives of the study were to investigate the hydraulic, geochemical and solute or contaminant transport properties of the upper fractured zone at four Leda clay deposits in Eastern Ontario. These four sites are known as NRC, Fallowfield, Renfrew and Casselman. Physical conditions and depth of fractures of the Leda subsoil was investigated with the use of boreholes and test pits. Piezometers were installed using a conventional auger method and the double-Shelby method developed at the University of Waterloo. Hydrogeological aspects of the upper twelve metres were analyzed using water level fluctuations and variation profiles, hydraulic head and conductivity profiles. A geochemistry analysis was made by measuring the major ions and tritium concentration distribution in groundwater samples obtained from piezometers. Laboratory tests were performed on five Leda clay samples to determine the effective diffusion coefficients and the retardation factors of the major ions. The results of the study indicated that the upper portion of Leda clay deposits within Eastern Ontario are fractured and hydraulically active. Fractured Leda clay deposits less than 12 metres in depth are highly questionable on their ability to protect any underlying aquifer from surficial or buried contaminants.
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Ismail, Mohd Ashraf bin Mohamad. "Study on hydrogeological modeling and evaluation of groundwater behaviors in fractured rock mass". 京都大学 (Kyoto University), 2010. http://hdl.handle.net/2433/120805.
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Blumstock, Maria Elisabeth. "Spatial organisation of groundwater-surface water interactions in an upland catchment : integrating hydrometric, tracer and modelling approaches". Thesis, University of Aberdeen, 2017. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=233033.
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This thesis presents studies of the heterogeneous nature of groundwater-surface water (GW-SW) interactions at the hillslope and catchment scale in the 3.2km2 Bruntland Burn, UK. GW fluctuations were measured within three contrasting hydropedological units. Synoptic hydrogeochemical surveys were carried out (major ions, stable isotopes) to capture the increased influence of GW to the stream during a 10year return period drought. The catchment was shown to have highly dynamic GW stores, with each landscape unit translating into different rainfall-runoff processes. Soil characteristics were shown to be the strongest predictors for variability in GW dynamics. Each soil type was characterised by a unique storage-discharge relationship and threshold response with a certain GW level above which lateral flow dominated. On the lower hillslope, predominating lateral flow and little recharge to depth is supported by hydrologically responsive soils. Connectivity between the steeper slopes and the valley bottom, however, needed persistent wet periods to overcome storage thresholds. Here, vertical flow paths recharging deeper GW dominated, with GW levels falling below the soil layer into the underlying drift. It was found that relatively well mixed, near-surface sources of stream flow predominated in wetter conditions, whilst baseflows are variable and reflect a diverse range of GW stores. Geophysics (ERT) and GW level measurements were integrated into MODFLOW-NWT to simulate GW-SW interactions along a representative 2D-hillslope transect. Although only a preliminary model, it was shown that shallow pathways have much shorter residence times, thus maintaining high water tables in the riparian peatlands, than deeper flow paths discharging through the drift and directly into the stream. Largest sources of GW are located within the drift, resulting in complex spatial patterns of runoff generation. This work illustrated the utility of a basic model to predict GW flow paths, highlighting how water and solutes are stored and released in montane headwater catchments.
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Harb, Mohammed. "Quantum transport modeling with GPUs". Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=114417.
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In this thesis, we have developed a parallel GPU accelerated code for carrying out transport calculations within the Non-Equilibrium Green's Function (NEGF) framework using the Tight-Binding (TB) model. We also discuss the theoretical, modelling, and computational issues that arise in this implementation. We demonstrate that a heterogenous implementation with CPUs and GPUs is superior to single processor, multiple processor, and massively parallel CPU-only implementations. The GPU-Matlab Interface (GMI) developed in this work for use in our NEGF-TB code is not application specific and can be used by researchers in any field without previous knowledge of GPU programming or multi-threaded programming. We also demonstrate that GMI competes very well with commercial packages.Finally, we apply our heterogenous NEGF-TB code to the study of electronic transport properties of Si nanowires and nanobeams. We investigate the effect of several kinds of structural defects on the conductance of such devices and demonstrate that our method can handle systems of over 200,000 atoms in a reasonable time scale while using just 1-4 GPUs.Dans cette thèse, nous présentons un logiciel qui effectue des calculs de transport quantique en utilisant conjointement la théorie des fonctions de Green hors équilibre (non equilibrium Green function, NEGF) et le modèle des liens étroits (tight-binding model, TB). Notre logiciel tire avantage du parallélisme inhérent aux algorithmes utilisés en plus d'être accéléré grâce à l'utilisation de processeurs graphiques (GPU). Nous abordons également les problèmes théoriques, géométriques et numériques qui se posent lors de l'implémentation du code NEGF-TB. Nous démontrons ensuite qu'une implémentation hétérogène utilisant des CPU et des GPU est supérieure aux implémentations à processeur unique, à celles à processeurs multiples, et même aux implémentations massivement parallèles n'utilisant que des CPU. Le GPU-Matlab Interface (GMI) présenté dans cette thèse fut développé pour des fins de calculs de transport quantique NEGF-TB. Néanmoins, les capacités de GMI ne se limitent pas à l'utilisation que nous en faisons ici et GMI peut être utilisé par des chercheurs de tous les domaines n'ayant pas de connaissances préalables de la programmation GPU ou de la programmation "multi-thread". Nous démontrons également que GMI compétitionne avantageusement avec des logiciels commerciaux similaires.Enfin, nous utilisons notre logiciel NEGF-TB pour étudier certaines propriétés de transport électronique de nanofils de Si et de Nanobeams. Nous examinons l'effet de plusieurs sortes de lacunes sur la conductance de ces structures et démontrons que notre méthode peut étudier des systèmes de plus de 200 000 atomes en un temps raisonnable en utilisant de un à quatre GPU sur un seul poste de travail.
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Cheng, L. "Dual porosity reactive transport modeling". Thesis, University of Sheffield, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425583.
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El, Kheiashy Karim. "Flow-Transport Modeling and Quantification". ScholarWorks@UNO, 2007. http://scholarworks.uno.edu/td/548.
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Several research investigations have been conducted on the flow and sediment transport over bed forms in alluvial rivers (e.g. mean flow field, turbulence, shear partitioning, bed load transport and bed form geometry). Much of this work was either laboratory studies or small scale field investigations. Recently, advance in technology have improved the way data are collected and analyzed, e.g. flow data, velocity data and detailed bathymetric information that provide greater knowledge about the bed form geometry. Recent advances in computing power have also reduced the computational restrictions on using three dimensional numerical models in modeling flow applications to predict the temporal and spatial changes of flow and sediment environments. The work performed in this research quantified the periodic nature of bed forms types and geometries along the Lower Mississippi river. Correlations were performed relating the hydrodynamics of the river to the bed form types and geometries. The research work showed the inability of hydrostatic numerical modeling systems to accurately predict flow separation at the bed form crest but indicated that these models could reasonably predict the out of phase relationship between the bed form and the water surface profile. Furthermore the hydrostatic models predicted the total bed resistance as adequately as the non-hydrostatic models. It was found that non-hydrostatic models are required to properly simulate flow separation at bed form crests. Models such as MIKE 3 with constant z-level vertical discretization failed to capture the observed boundary layers unless very fine grids are used. A new procedure was developed as a part of this research, in which relations and dependencies between the hydrodynamic resistance and the bed form dimensions relative to the numerical model spatial scale were derived. This procedure can be used to aid in numerical riverine model calibration and to provide a better representation of flow resistance in hydrodynamic modeling codes.
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Cattaneo, L. "CHARACTERIZATION OF THE SUBSURFACE THROUGH JOINT HYDROGEOLOGICAL AND GEOPHYSICAL INVERSION". Doctoral thesis, Università degli Studi di Milano, 2014. http://hdl.handle.net/2434/239175.
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Characterization of the subsurface heterogeneity, monitoring groundwater dynamics, modelling flow and transport in the subsoil are of paramount importance for protection of groundwater quality, design of remediation plans, control of restoration activities. One of the key physical parameters that control groundwater flow and solute transport is hydraulic conductivity. Both hydraulic conductivity and electrical resistivity depend on porosity, water content and textural properties. Moreover, the difficulties of directly and effectively measure hydraulic conductivity makes the possibility of predicting it from geophysical measurements very attractive. Hydrogeophysics provides useful complementary techniques, both for hydrostratigraphic and hydrogeological characterization and for monitoring. It provides a minimally invasive approach to obtaining spatially-continuous data-sets, at a relatively high temporal and spatial sampling density. The general-purpose objective of this work is the development of a modelling tool for the subsurface characterization, in order to improve studies on groundwater flow and contaminant transport, with the specific goal of obtaining a spatial 3D parameter distribution of hydraulic conductivity and electrical resistivity. Such a tool profits from DC geoelectrical and hydraulic collected data, which are used in a joint geophysical and hydrological data inversion, with an approach similar to the Ensemble Kalman Filter.
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Keslin, Jeff Michael. "Modeling energy transport in porcine skin". College Park, Md.: University of Maryland, 2009. http://hdl.handle.net/1903/9197.
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Thesis (M.S.) -- University of Maryland, College Park, 2009.Thesis research directed by: Dept. of Fire Protection Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Kutay, Muhammed Emin. "Modeling moisture transport in asphalt pavements". College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/2911.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2005.Thesis research directed by: Civil Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Guo, Qingchao. "Numerical modeling of suspended sediment transport". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0019/NQ54671.pdf.
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Abel, Markus. "Turbulent flows : transport, analysis and modeling /". Potsdam, 2005. http://www.gbv.de/dms/goettingen/509529178.pdf.
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Khuc, Trong Philipp. "Modeling intracellular transport in Drosophila oocytes". Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708730.
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Mehrabi, M. Reza. "Modeling transport processes in directional solidification". Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/11999.
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Sapper, Erik David. "Multiscale Modeling of Electromagnetic Radiation Transport". Diss., North Dakota State University, 2013. https://hdl.handle.net/10365/26717.
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The transport of electromagnetic radiation is a critical factor in determining many of the advanced features of novel materials, composites, and coatings systems. The radiation interaction with a material's surface, as well as its transport and interaction within the material, both combine to produce the overall electromagnetic signature of that object, which is the root cause of the color and appearance of these materials. Historically, approaches to light scattering behavior prediction focus on either the surface interactions or the bulk interactions, and the models most used today are valid only for certain compatible size and length scales of radiation. As next generation materials become more advanced, and increasingly have formulation components that reside on the nanoscale, a robust, rigorous, yet highly general approach to electromagnetic signature prediction is required. A hybrid, multiscale approach to the computational prediction of light scattering by coatings and composite materials is presented here, where ray tracing and geometric optics formalism tracks individual photons as they enter the material of interest, and finite element solutions to the Maxwell equations are used to generate the radiation interaction result of nanoscale inclusions embedded within the bulk of the material. The approach presented here is highly general in nature; scattering inclusions may be pigments, fibers, nanoparticles, air voids, or heterogeneous phase components. The multiscale approach enables investigation of the electromagnetic signature at various length scales, and predicts spectral reflectance, directional reflectance, and color, among other properties, of various multicomponent systems.Army Research Laboratory, ARL Grant #14518
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Wang, Mengyi S. M. Massachusetts Institute of Technology. "Multiscale computational modeling of nanofluidic transport". Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/128996.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2020Cataloged from student-submitted PDF of thesis.
Includes bibliographical references (pages 56-61).
Water scarcity is one of the largest global challenges, affecting two-thirds of the world population. Water desalination and purification technologies, such as novel membrane processes and materials, are in great demand to produce clean water from contaminated sources or the sea. However, the lack of fundamental understanding of structure-property-performance has hindered the advancement of these techniques. In this study, we address this critical knowledge gap by adapting multiscale computational modeling to better understand the mechanisms of intrinsic molecular interaction in nanofluidic applications. We performed ab initio molecular dynamics to study the nanoscale solvation behavior of selected ions on finite graphene models. The degree of charge transfer between ion and water, and the effect of defects on dynamics and solvation has been investigated. Furthermore, a quantum mechanics/molecular mechanics (QM/MM) model for the accurate description of free energy changes in ion adsorption process has been developed. Lastly, we combined classical molecular dynamics and density functional theory (DFT) to elucidate the dielectric-driven mechanism of ionization behavior in nanoporous polyamide films. We seek to utilize this knowledge for the design of next-generation membranes for separation and water purification.
by Mengyi Wang.
S.M.
S.M. Massachusetts Institute of Technology, Department of Materials Science and Engineering
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Saunders, Michael G. "Electrodynamical Modeling for Light Transport Simulation". Digital Commons @ East Tennessee State University, 2017. https://dc.etsu.edu/honors/373.
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Modernity in the computer graphics community is characterized by a burgeoning interest in physically based rendering techniques. That is to say that mathematical reasoning from first principles is widely preferred to ad hoc, approximate reasoning in blind pursuit of photorealism. Thereby, the purpose of our research is to investigate the efficacy of explicit electrodynamical modeling by means of the generalized Jones vector given by Azzam [1] and the generalized Jones matrix given by Ortega-Quijano & Arce-Diego [2] in the context of stochastic light transport simulation for computer graphics. To augment the status quo path tracing framework with such a modeling technique would permit a plethora of complex optical effects—including dispersion, birefringence, dichroism, and thin film interference, and the physical optical elements associated with these effects—to become naturally supported, fully integrated features in physically based rendering software.
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Reimann, Peter, Andreas Meyer, Thomas Töws i Sebastian Getfert. "Modeling DNA-translocation through nanopores". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-179409.
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Huisinga, Torsten. "Internet Data Transport - From the Perspective of Discrete Mass Transport Modeling". Gerhard-Mercator-Universitaet Duisburg, 2006. http://www.ub.uni-duisburg.de/ETD-db/theses/available/duett-04212006-081607/.
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In recent years a new class of one-dimensional cellular automata (CA) models has attracted much attention. These so-called mass transport models can be characterized as nonequilibrium stochastic processes. In the presented thesis a new model of this class, the Asymmetric Multi Occupation Process (AMOP) is considered. This CA model was first introduced with open boundary conditions to simulate Internet data transport. It is defined on a one-dimensional lattice equipped with buffers of finite size that can be occupied by at most B particles. The local dynamics are implemented by the totally asymmetric shift of discrete mass variables respectively particles under consideration of hard-core repulsion and parallel dynamics. In the first part of this work the AMOP with periodic boundary conditions is investigated by means of numerical as well as analytical considerations. Regarding deterministic model dynamics the influence of finite buffer and system sizes onto the fundamental diagram (FD), i.e., flow-density relation is analyzed. Furthermore, for stochastic movement the FDs obtained by numerical simulations are compared with analytical results derived by Mean-Field (MF) approaches and a 2-cluster approximation. In the second part the AMOP with open boundary conditions is investigated in the context of boundary induced phase transitions. In case of deterministic bulk dynamics an analytical exact representation of the system inflow as well as the outflow is presented in dependence of the buffer size. As a result the deterministic phase diagram derived by numerical simulations could be verified by analytical considerations. Regarding stochastic particle movement the phase diagram is obtained by Monte Carlo simulations. In both cases it is shown that the jammed phase is strongly enlarged for increasing buffer sizes. Finally, in the third part of this thesis the influence of interacting boundaries on the model dynamics is analyzed. Therefore, a new fall back inflow strategy is introduced in order to stabilize high flow states and thus prevent the system from a complete jamming. Precisely, the inflow is determined by the state of the last site of the system. As a result the phase diagrams of the deterministic and the stochastic model obtained by means of numerical simulations are presented. Two new phases could be identified a free-flow as well as a jammed phase both characterized by a striped microscopic pattern. Especially in the arising striped jammed regime system flow and mean velocity are drastically enlarged compared to generic inflow strategies. Here, the fall back strategy is capable to prevent the system from a complete jamming. Thus, the introduced inflow procedure represents an effective strategy for establishing reliable connections.
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Seto, Haruki. "Two-Dimensional Transport Modeling of Tokamak Plasmas". 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/188588.
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Ladha, Nuruddin B. "Modeling solute transport in soils from Ataratiri". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0007/MQ45524.pdf.
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Perez-Bidegain, Mario. "Modeling phosphorus transport using the WEPP model". [Ames, Iowa : Iowa State University], 2007.
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Tafazoli, Sara. "Modeling pesticide fate and transport in soils". Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=79746.
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The work presented in this thesis represents a contribution to the area of modeling of the transport and fate of herbicides applied to cropped fields, and was part of a larger research effort geared towards better management of herbicides. The main objective of this thesis was to develop a graphical user interface (GUI) for PESTFADE, a process-based mathematical model of pesticide transport and degradation, and to provide documentation for the execution of PESTFADE. The model simulates changes in pesticide concentration at different depths in the soil, based on relevant physical, chemical, biological and meteorological factors. PESTFADE is considered to be one of the most comprehensive models of its kind. However, it was, until now, difficult to implement due to absence of a user manual and graphical interface suitable for exploitation in a Windows environment. The author developed the GUI in Visual Basic, created macros to facilitate certain calculations, rewrote the original FORTRAN 77 code and then validated the updated version against field data obtained from an experimental site (Eugene Whelan Farm, Woodslea, Ontario). A preliminary development of an artificial neural network (ANN) to perform the same simulation implicitly, with fewer input parameters and less computational time, was also done.The thesis describes PESTFADE and the GUI, gives guidelines for implementing the package, and presents the results of the field validation of the revised version. During this work, the author discovered that there were problems in the parts of the code dealing with sorption phenomena. This can be solved by conventional kinetics or by Gamble kinetics.
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Abou, Nahra Joumana. "Modeling phosphorus transport in soil and water". Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=102946.
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The main objective of this project was to investigate and model phosphorus (P) transport in soil column studies. A model named HYDRUS-NICA was developed, by coupling a hydrological and transport model (HYDRUS-1D model) with an aqueous chemical model (non-ideal competitive adsorption - NICA), to improve the predictions of P transport in soil and water. The HYDRUS-NICA model was developed by replacing the non-linear empirical (Freundlich and Langmuir) equations of the HYDRUS-1D model with the NICA model equations. The numerical accuracy of the HYDRUS-NICA model was then evaluated by comparing the relative errors produced by the HYDRUS-NICA and HYDRUS-1D models. The results showed that the numerical schemes of the HYDRUS-NICA code are stable.The ability of the NICA model to describe phosphate (PO4) adsorption to soil particles was tested using soils collected from agricultural fields in southern Quebec. The surface charge and PO4 adsorption capacity of these soils were measured. Results were used to estimate the NICA model parameters using a non-linear fitting function. The NICA model accurately described the surface charge of these soils and the PO4 adsorption processes.
The HYDRUS-1D model was applied to simulate water flow and PO4 transport in re-constructed soil column experiments. The HYDRUS-1D model was calibrated based on physical and chemical parameters that were estimated from different experiments. Overall, the HYDRUS-1D model successfully simulated the water flow in the columns; however, it overestimated the final adsorbed PO4 concentrations in the soil. The discrepancies in the results suggested that the HYDRUS-1D model could not account for the differences in the soil structure found in the columns, or that the Freundlich isotherm could not adequately describe PO4 adsorption.
The HYDRUS-NICA model was calibrated and validated with results from re-packed column experiments. The simulated results were then compared with results obtained by the HYDRUS-1D model. The overall goodness-of-fit for the HYDRUS-1D model simulations was classified as poor. The HYDRUS-NICA model improved significantly the prediction of PO4 transport, with the coefficient of modeling efficiency values being close to unity, and the coefficient of residual mass values being close to zero. The HYDRUS-NICA model can be used as a tool to improve the prediction of PO4 transport at the field scale.
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Mesones, Aurich Laura. "Modeling microorganism transport in riverbank filtration systems". Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=18661.
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Groundwater flow and microorganism (Cryptosporidium parvum, Escherichia coli and MS2) transport was simulated for a Riverbank Filtration (RBF) System in the Rio Grande de Manati region of Puerto Rico. MODFLOW 2000, a 3D saturated flow model, was used to simulate groundwater flow from the river to the wells in the riverbank. RT3D, a multi-species reactive model, was used to simulate microorganism transport. Both models required several parameters: (i) hydro-geological parameters were taken from previous research done in the study area, (ii) transport parameters (attachment coefficient and linear partitioning coefficient) were estimated based on sticking efficiency values reported in the literature. Colloid Filtration Theory was used for the estimation of the transport parameters. From the estimated parameters it was determined that microorganisms would show greater mass transfer from the aqueous to the solid phase at lower porosities. A 3-D grid was built to represent the study area. Groundwater flow output from MODFLOW 2000 showed a discrepancy of only 0.08% between inflow and outflow. MODFLOW 2000 generated inflow and outflow values matched values obtained in an earlier study at the same site, using MODFLOW 96. This indicated that the model's mass balance calculations were very good. RT3D used the flow results, obtained with MODFLOW 2000, to build the transport model. The river water microorganism load was set to a constant level of 100 microorganisms/L. On the basis of a 1000-days' simulation for C. parvum and E. coli, it was shown that the RBF system could provide safer water to the Rio Grande de Manati region. However, the virus analogue MS2 would reach the well after 900 days. Simulations also demonstrated that C. parvum's removal would be more effective, compared to that of E. coli or MS2. Four different scenarios — varying aquifer porosity, pumping rates, number of wells, and intermittent pumping — were simulated to evaluate theiL'écoulement d'eaux souterraines et le transport de microorganismes (Cryptosporidium parvum, Escherichia coli and MS2) furent simulés pour un système de filtration de berge (FDB) situé dans la région de Manati de Rio Grande, au Porto Rico. Le modèle tridimensionnel d'écoulement en milieu saturé MODFLOW servit à simuler le ruissellement souterrain allant de la rivière vers des puits creusés dans la berge. RT3D, un modèle réactif plurispécifique servit à simuler le transport de microorganismes. Ensemble, les deux modèles exigèrent plusieurs paramètres: (i) les paramètres hydrogéologiques provinrent d'une étude précédente au même site, (ii) les paramètres de transport (coefficients d'attachement et de partitionnement linéaire) furent basés sur des valeurs d'efficacité d'adhésion rapportées dans la littérature. La théorie de filtration des colloïdes servit a l'évaluation des paramètres de transport. À partir de ces paramètres on peut prévoir qu'à des porosités moins élevées les microorganismes montreront un transfert de masse plus élevée entre la phase aqueuse et solide. Une grille tridimensionnelle fut établie pour représenter le secteur d'étude. Avec MODFLOW 2000, une différence de 0.08% exista entre l'apport et la sortie d'eaux de ruissellement souterraines. Les apports et sorties d'eau prédites par MODFLOW 2000 concordèrent très bien avec ceux obtenus lors d'une étude préalable au même site, indiquant l'exactitude des calculs de bilan massique du modèle. RT3D fonda son modèle de transport sur les valeurs de ruissellement souterrain calculé par MODFLOW. La charge microbienne de l'eau riveraine fut établie à un niveau constant de 100 microorganismes/L d'eau. Une simulation de 1000 jours pour C. parvum and E. coli, montra qu'un système FDB pouvait fournir une eau plus saine à région de Rio Grande de Manati. Cependant, l'analogue de virus, MS2, se rendrait au puits après 900 jours. Les simulations démo
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Zhou, Mingyan, Ke Wu, James E. Kilduff i Georges Belfort. "Modeling organic molecule transport through nanofiltration membranes". Diffusion fundamentals 16 (2011) 37, S. 1-2, 2011. https://ul.qucosa.de/id/qucosa%3A13772.
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Webster, Gregory Daniel. "Modeling of Ethanol Metabolism and Transdermal Transport". Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/33456.
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Approximately 14,500 people were killed in traffic crashes where the driver was legally intoxicated in 2005, constituting 33% of all traffic fatalities that year. While social efforts to reduce the number of traffic fatalities have shown to be moderately successful, alcohol has remained a factor in 40% of all traffic deaths over the past decade. Transdermal ethanol detection is a promising method that could prevent drunk driving if integrated into an ignition interlock system; potentially preventing 90 million drunk driving trips a year in the US. However, experimental data from previous research has shown significant time delays between alcohol ingestion and detection at the skin which makes real time estimation of blood alcohol concentration via skin measurement difficult. Using a validated model we studied the effects that body weight, metabolic rate and ethanol dose had on the time lag between the blood alcohol concentration and transdermal alcohol concentration. The dose of alcohol ingested was found to have the most significant effect on the skin alcohol lag time. Additionally, custom transdermal ethanol sensors were designed and fabricated and a pilot study on human subjects was conducted to determine if inexpensive transdermal ethanol sensors could be used to detect alcohol in drivers.Master of Science
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Gao, Yue. "Modeling of Drug Transport in Biological Systems". The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1316452154.
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Bennett, Mark R. "Modeling nitrogen transport with the ANSWERS model". Thesis, This resource online, 1997. http://scholar.lib.vt.edu/theses/available/etd-08222008-063218/.
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Zhou, Mingyan, Ke Wu, James E. Kilduff i Georges Belfort. "Modeling organic molecule transport through nanofiltration membranes". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-184966.
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Li, Shimin. "Modeling biocolloid transport in saturated porous media". Diss., The University of Arizona, 1993. http://hdl.handle.net/10150/186407.
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A forced-gradient experiment of virus and carboxylated microsphere transport was carried out at a two-well system in saturated aquifer at Borden, Ontario. The purpose of experiment was to qualitatively and quantitatively investigate bacteriophage transport relative to that of a conservative solute in porous media. A simplified plane radial advection dispersion equation coupled with reversible first-order and equilibrium mass transfer was found to be adequate to simulate the attachment and transport process. For simulating detachment and transport, all rate parameters were varied with time up/down (depending on the parameter) to reflect the changes in pH of groundwater with time from 7.4 to 8.4 then back to 7.4. Both constant and scale-dependent dispersivity were used in the modeling of the transport process. Time-moment analysis of the conservative-tracer breakthrough curves produced dispersivity values of 0.1-0.6 m, close to the macrodispersivity of 0.6 m obtained using a stochastic model to describe a previous larger-scale experiment at the site. The multiple-peak feature of all the breakthrough curves suggests that the aquifer heterogeneity may be more important than local dispersion in affecting the appearance of both electrical conductivity and phage breakthrough curves. Strack's model was found quite well to describe the hydraulic head profile during the whole period of experiment if proper values for transmissivity and cone radius are chosen. Virus traveled at least a few meters in the experiment, but virus concentrations at observation points 1-m to 2-m away were a small fraction of those injected. Though clearly not an equilibrium process, retardation involving a dynamic steady state between attachment and detachment is nevertheless a major determinant of transport versus retention of virus.
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Deleuze, Yannick. "Modeling and simulation of transport during acupuncture". Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066372/document.
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L’objectif de cette thèse est d’appréhender la complexité des mécanismes biologiques de l’acupuncture afin de construire un modèle mathématique multi-échelle. Ce modèle est étudié théoriquement et numériquement. L’acupuncture est une des plus vielles pratiques de l’histoire de la médecine et une partie intégrante de la médecine traditionnelle chinoise. Dans sa pratique la plus classique, une ou plusieurs aiguilles sont placées à des endroits spécifiques, nommés points d’acupuncture. L’aiguille est ensuite manipulée en utilisant des mouvements de rotation et de translation de façon à stimuler le point d’acupuncture. Les effets cliniques de l’acupuncture pourraient être le résultat d’effet de cascades de réactions produites par les interactions entre l’hypoderme et les systèmes nerveux, endocrinien et immunitaire. Le travail présenté s’articule sur la modélisation de l’insertion d’une aiguille dans le tissu conjonctif de l’hypoderme. Un modèle d’écoulement en milieu poreux du liquide interstitiel de l’hypoderme a permis d’étudier numériquement les composantes de contrainte qui agissent sur les récepteurs à la surface des cellules du tissu et notamment des mastocytes.Un modèle mathématique de la réponse chimiotactique des mastocytes à une contrainte physique créée par le traitement d’acupuncture est développé. Ce modèle prend en compte les mécanismes de signalisation cellulaire. La contrainte physique induit la libération rapide et continue, grâce au recrutement chimotactique de mastocytes, d’attractants et de médiateurs chimiques. Le modèle est basé sur le modèle de chimiotaxie de type Keller-SegelThe objective of this thesis is to comprehend the complexity of the underlying basis of acupuncture. Acupuncture needling is investigated in order to establish a multiscale model that takes into account the complexity of biology but is mathematically simple enough to run simulations.Acupuncture is one of the oldest practices in the history of medicine and is the core of Traditional Chinese Medicine. Once needles are inserted in the right locations, called acupoints, they are manipulated via manual needling to stimulate the acupoint. The physiological reactions of acupuncture needling lead to therapeutic effects which can be explained by a series of interactions between the skin and the nervous, the endocrine, and the immune systems.In the present work, the thrusting and lifting of an acupuncture needle inserted in subcutaneous connective tissue is modeled. A porous media model is used to run simulations and compute the pressure and shear stress affecting the organization of fibers and of isolated cells in their matrix. A mathematical model was conceived to take into account cell signaling. There is ample evidence that needle manipulation in acupuncture can cause degranulation of mastocytes directly through a physical stress to occur. Activated mastocytes rapidly release granules containing chemical mediators. These chemical mediators play a key role recruiting mastocytes in their environment and are known to affect the excitability of nerve endings as well as local microcirculation permeability and size for the appropriate transfer of long-term acting endocrine signals. The process is sustained by the recruitment of mastocytes through chemotaxis
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Luca, Liliana. "Hydrodynamic modeling of electron transport in graphene". Doctoral thesis, Università di Catania, 2019. http://hdl.handle.net/10761/4103.
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Semi-classical hydrodynamic models for charge transport in graphene have been presented. They are deduced as moment equations of the semiclassical Boltzmann equation with the needed closure relations obtained by resorting to the Maximum Entropy Principle. The models differ in the choice of the moments to assume as basic field variables. Both linear and nonlinear closure relations are analyzed. The validity of all the semi-classical models presented is assessed by comparing the mean values of energy and velocity with those obtained from the direct solutions of the Boltzmann equation in the simple case of suspended monolayer graphene. It has been found that it is crucial to include- among the field variables- the deviatoric part of the stress tensor to maintain a good accuracy in a wider range of applied electric fields. Moreover apparently the results confirm that the nonlinearity is not critical for accuracy.
Then, to take into account quantum phenomena, in the last part of this work a quantum hydrodynamic model for charge transport in graphene is derived from a moment expansion of the Wigner-Boltzmann equation. The needed closure relations are obtained by adding to the semiclassical ones quantum corrections based on the equilibrium Wigner function. The latter is obtained from the Bloch equation by taking into account the appropriate energy band of graphene. Furthermore, quantum energy-transport and drift-diffusion models have been formally derived from the quantum hydrodynamic equations in the long time asymptotic limit. In analogy with the semiclassical case we are confident that the energy-transport and drift-diffusion models have mathematical properties which allow an easier numerical treatment.
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PROIETTI, ZACCARIA Remo. "Modeling of quantum transport in open systems". Doctoral thesis, Politecnico di Torino, 2003. http://hdl.handle.net/11583/2637772.
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Whereas classical transport physics is based on the concept of a probability distribution which is defined over the phase space of the system, the concept of a phase-space distribution function in the quantum formulation of transport is difficult, since the non-commutation of the
position and momentum operators (the Heisenberg uncertainty principle) precludes the precise specification of a point in phase space. However, within the formulation of quantum mechanics, various formalisms based on density matrices, Wigner functions, Feynman path integrals and Green’s functions have been developed. These embrace the quantum nature of transport; moreover, in recent years, each technique has been utilized to address key aspects of quantum transport in semiconductors. At present, there is no unifying, user-friendly approach to quantum transport in semiconductors. Density matrices, and the associated Wigner function approach, Green’s functions, and Feynman path integrals all have their application and computational strength and weakness, and all their are equivalent representations of the quantum nature of transport. In the present work the density-matrix and Wigner-function formalisms will be employed. This choice is due to the fact that the “open system problem” that here is faced, is better managed using such an approach; Indeed the density-matrix formalism is
extremely useful to show the degree of quantum coherence of the system under investigations while the Wigner-function picture is the ideal instrument to describe real-space quantum devices. Such a choice will be better understood looking in more detail to the problem of open
systems, i.e., systems with open spatial boundaries. The most interesting products of micro- and nanoelectronics technology are systems that operate far from equilibrium. A closer inspection of a few examples of such systems reveals that they are generally open, in the sense that they exchange matter with their environment. The present work is aimed at developing a fully microscopic theory to describe open quantum systems starting from the so-called Semiconductor Bloch equations, namely the equations that describe the coherent versus incoherent dynamics of a closed quantum system. In the context of the present work, an open system is a system that exchange locally particles with its
environment. Moreover, we wish to focus upon its far-from-equilibrium behaviour, and thus the specific definition of open system will be further restricted to describe a system coupled to at least two separate particle reservoirs, so that a non-equilibrium state may be created and
maintained. To specify such a system we must regard it as occupying a finite region of space, and thus the exchange of particles must consist of a current flowing through the system surface which is taken to be the boundary of the system. Our aim is to analyse in detail the problem of openness in the present sense with also the possibility to consider energy-relaxation and dephasing processes within the device active
region. More specifically, our analysis will allow us to point out and overcome some basic limitations of the conventional Wigner-function formalism; this will be accomplished by introducing a Generalized Weyl-Wigner approach, able to remove such anomalies, thus
recovering typical results of partially phenomenological models. In this context we shall propose a theoretical scheme where the boundary conditions are described via a source term, i.e., a term representing the particles entering the simulated region from its spatial boundaries. In
particular, we shall propose and demonstrate two fully equivalent theoretical models able to describe adequately an open quantum device: the first one is characterized by a non-diagonal source term (i.e., coherent source) while the second one is characterized by a diagonal source term.
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Serov, Alexander S. "Modeling Oxygen Transport in the Human Placenta". Palaiseau, Ecole polytechnique, 2015. https://theses.hal.science/tel-01205237/document.
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L’efficacité de fonctionnement du placenta humain joue un rôle crucial dans la santé du nouveau-né. L’objectif principal de cette thèse est de développer un modèle mathématique de l’échange des gaz respiratoires au sein du placenta humain, afin d’améliorer la compréhension de la relation entre la structure et la fonction de cet organe. En exploitant la structure détaillée du placenta fournie par les méthodes d’histologie placentaire, nous construisons un modèle 3D du transport d’oxygène dans le placenta en prolongeant la géométrie des coupes histologiques 2D le long de la troisième dimension. Ce modèle est capable de prendre en compte simultanément la diffusion et la convection de l’oxygène dans l’espace intervillaire. Dans la première partie de la thèse, l’équation de diffusion-convection qui détermine l’échange d’oxygène est résolue numériquement pour diverses valeurs de densités de villosités à l’intérieur du placentone. Ces calculs fournissent une estimation de l’absorption d’oxygène d’un placentone pour une densité arbitraire de villosités, et permettent de mettre en évidence l’existence d’une densité optimale de villosités maximisant l’absorption d’oxygène. Cette optimalité peut être vue comme le résultat d’un équilibre entre l’arrivée d’oxygène par le flux entrant du sang maternel et l’absorption à la surface des villosités. À l’étape suivante, l’on s’affranchit de l’hypothèse d’une forme circulaire des villosités, et l’on propose une solution analytique approchée de l’équation de la diffusion-convection. Il est ensuite démontré que deux caractéristiques géométriques – la densité de villosités et le rayon efficace de villosités – suffisent à prédire l’absorption fœtale d’oxygène dans une géométrie donnée. La théorie identifie également deux combinaisons de paramètres physiologiques qui déterminent l’absorption d’oxygène : (i) le flux entrant maximal d’oxygène dans un placentone, et (ii) le nombre de Damköhler défini comme le rapport entre le temps de passage du sang maternel dans l’espace intervillaire et un temps caractéristique d’extraction d’oxygène dans une coupe transversale du modèle. Des formules analytiques permettant de calculer l’absorption d’oxygène d’une façon simple et efficace en sont déduites, et deux diagrammes d’efficacité du transport d’oxygène dans une coupe arbitraire de placenta sont tracés. La théorie analytique propose également une méthode permettant d’exploiter les résultats d’expériences sur la perfusion artificielle du placenta par un sang ne contenant pas d’hémoglobine, afin de prédire l’efficacité de transfert en intégrant cette fois l’interaction entre l’oxygène et l’hémoglobine. Au final, nous présentons une méthode d’analyse de grandes coupes histologiques de placenta humain, dans le but de mesurer de façon automatique les aires, les périmètres et la morphologie des régions de villosités, de l’espace intervillaire et des capillaires fœtaux. Ces données peuvent ensuite être introduites dans le modèle afin d’estimer l’efficacité du placenta. La méthode est appliquée à 25 coupes placentaires provenant de 22 grossesses saines et de 3 grossesses pathologiques. La combinaison des données obtenues avec les diagrammes d’efficacité montre que toutes les valeurs mesurées de la densité de villosités se retrouvent en écart relatif à moins de 10% de la valeur optimale. En revanche, l’efficacité globale correspond à une valeur assez basse (autour de 30–40 %). Dans l’avenir, le modèle présenté peut constituer la base d’un outil fiable de l’évaluation de l’efficacité d’échange d’oxygène au sein du placenta humain à partir de mesures histologiques post partum, ou, à plus long terme, à partir de mesures non-invasives in uteroThe efficient functioning of the human placenta is crucial for the favorable outcome of the pregnancy. This thesis aims at developing a mathematical model of respiratory gas exchange in the human placenta, which would improve our understanding of the relation between the structure and the function of the organ. Taking advantage of the precise 2D placental structure provided by the placental histology, we construct a 3D model of oxygen transport in the placenta by extending 2D histological cross-sections along the third dimension. The model simultaneously accounts for both diffusion and convention of oxygen in the intervillous space and allows us to predict the oxygen uptake of a placentone. In the first part of the thesis, the diffusion-convection equation governing oxygen exchange is numerically solved for different densities of circular fetal villi in a placentone. These calculations provide estimations of the oxygen uptake of a placentone with an arbitrary villi density and demonstrate the existence of an optimal villi density maximizing the uptake. This optimality is explained as a trade-off between the incoming oxygen flow and the absorbing villous surface. As a next step, the assumption of circular villi is relaxed and an approximate analytical solution is proposed for the diffusion-convection equation. It is shown that only two geometrical characteristics — the villi density and the effective villi radius — are required to predict the fetal oxygen uptake. Two combinations of physiological parameters that determine oxygen uptake in a given placenta are also identified: (i) the maximal oxygen inflow of a placentone, and (ii) the Damköhler number defined as the ratio of the transit time of the maternal blood through the intervillous space to a characteristic oxygen extraction time in a cross-section. Analytical formulas for fast and simple calculation of oxygen uptake are derived, and two diagrams of oxygen transport efficiency in an arbitrary placental cross-section are provided. The theory also suggests a method of how the results of artificial placenta perfusion experiments performed with no-hemoglobin blood can be recalculated to account for oxygen-hemoglobin dissociation. Finally, an automatic image analysis method is developed allowing one to analyze large histological human placenta cross-sections and to determine areas, perimeters and shapes of villous, intervillous space and fetal capillary compartments. These data can then be used as input data for the model. This method is applied to 25 cross-sections from 22 healthy and 3 pathological pregnancies. By combination of the obtained data with the described efficiency diagrams, it is demonstrated that the villi density of a healthy human placenta lies within 10% of the optimal value. The overall geometry efficiency of a healthy placenta was found to be rather low (around 30–40 %). In a perspective, the presented model can constitute the base of a reliable tool of assessment of oxygen exchange efficiency in the human placenta from histological measurements post partum, or, in a longer term, from non-invasive in utero measurements
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Demontis, Pierfranco, Federico G. Pazzona i Giuseppe B. Suffritti. "Cellular automata modeling of diffusion under confinement". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-193309.
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Myshlyavtsev, Alexander V., i Marta D. Myshlyavtseva. "Modeling of surface diffusion for stepped surfaces". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-193477.
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Nicholson, Charles. "Modeling brain extracellular space from diffusion data". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-194167.
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The extracellular space (ECS) of the brain is a thin region surrounding each cell that is filled with a medium resembling cerebrospinal fluid and an unknown amount of extracellular matrix. The ECS is difficult to study but diffusion measurements based on a point-source diffusion paradigm have begun to reveal the complex structure of this region. Despite the complexity, a modified version of Fick’s classical diffusion equation incorporating parameters for volume fraction and tortuosity has been shown to be valid. Using real-time iontophoresis and the small molecule tetramethylammonium, the volume fraction of typical brain tissue has been determined to be 0.2, i.e. 20% of the brain is ECS and the typical tortuosity is 1.6, which means that a small molecule has an effective diffusion coefficient that is 2.6 less than in free solution. Monte Carlo modeling, however, shows that a simple ensemble of convex cells, each surrounded by a uniform ECS cannot generate a tortuosity greater than 1.225. Further modeling suggests that the discrepancy between experiments and theory may be accounted for by the existence of dead-space microdomains in the ECS; a viscous extracellular matrix might also play a role. Diffusion measurements with integrative optical imaging of fluorescent macromolecules and quantum dots show that tortuosity is increased with macromolecular size and analysis based on the theory of restricted diffusion in pores suggests that the width of the ECS is in the range 38-64 nm.
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Pongsaksawad, Wanida. "Numerical modeling of interface dynamics and transport phenomena in transport-limited electrolysis processes". Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/36209.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 111-117).
Electrochemical reactions in materials and processes induce morphological instability on the cathode, which can lead to porous deposits or system failure. The growth of the protrusion is a complex phenomenon which involves chemical, electrical, and momentum driving forces in the system. Thus, it is important to understand the effect of electrochemistry in phase boundary evolution in order to optimize the performance of such processes. This thesis contributes to predicting and controlling such interface instability phenomena by developing a computational model that captures them. Successful application of the model to emerging metal extraction processes demonstrates its usefulness. A phase field model of electrochemical interface is developed for transport-limited electrolysis with rapid charge redistribution. This new Cahn-Hillard phase field formulation includes a model electrostatic free energy term, which captures the behavior of the diffuse interface under the applied electric field, in addition to transport by free energy gradient and convection. The model agrees with published stability criterion for a solid cathode. When the electrodes and electrolyte are low-viscosity fluids, flow stabilizes the interface.
(cont.) A new stability criterion for metal reduction in a liquid-liquid system is derived and agrees well with the model results. Next, the phase field model is extended for a ternary system to model titanium reduction in a supported electrolyte system. The model can simulate phase boundaries migration depending on the composition of the electrolyte and also electronically mediated reactions. Finally, Solid Oxide Membrane Electrolytic Smelting with Rotating Cathode (SOMERC), an emerging technology to electrolytically reduce titanium oxide from molten salt, is investigated. In the SOMERC process, rotational flow is introduced to create shear force that is expected to stabilize the interface. Computational fluid dynamics models of rotational flow are carried out to estimate the relationship between cathode rotational speed, shear strain rate, and boundary layer thicknesses. The phase field model presented in this thesis can be applied to any electrochemical reduction processes that are in the mass-transport controlled regime. Stability criteria and detailed morphology in two and three dimensions can be explored.
by Wanida Pongsaksawad.
Ph.D.
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Lee, Si-Yong. "Heterogeneity and transport : geostatistical modeling, non-Fickian transport, and efficiency of remediation methods /". For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2004. http://uclibs.org/PID/11984.
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Kamali-Zare, Padideh, i Charles Nicholson. "Modeling Ca 2+ diffusion in brain extracellular space". Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-182570.
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Long, Wen. "Boussinesq modeling of waves, currents and sediment transport". Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 14.61 Mb., 350 p, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:3221137.
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Campos, Wellington. "Mechanistic modeling of cuttings transport in directional wells /". Access abstract and link to full text, 1995. http://0-wwwlib.umi.com.library.utulsa.edu/dissertations/fullcit/9527819.
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Smeu, Manuel. "Quantum transport modeling of atomic nanostructures on silicon". Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=107818.
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Surface effects can adversely influence the performance of a nanoelectronic device,but may also lead to new functionality. The focus of this thesis is to theoreticallystudy the role of surfaces in nanoelectronics. Our theoretical analysis is from atomicfirst principles achieved by combining density functional theory with the Keldyshnonequilibrium Green's function approach. This technique allows for all atoms in asystem to be treated on an equal footing without any phenomenological parameters.The first part of the thesis considers conduction through a molecule with no substrateto illustrate the sort of system typically modeled in transport calculations. Two Auelectrodes are bridged by a substituted benzenediamine molecule (R = CH3, NH2,OH) where an H atom is removed to form a radical that may behave as a spin filter,depending on the R group. Next is considered a π–stacked line of ethylbenzenemolecules on the Si(100) surface, where the Si atoms are explicitly included in thecalculation. Although the molecules conduct electrons at certain energies, a channeloccurs through the substrate, which can dominate the conductance. The use ofsubstituent groups to modulate the electron transport properties of such wires is alsoinvestigated, showing that the conductance of the molecular wire could be tuned todominate over the substrate. Finally, the conductance of the Si(111)–7 × 7 metallicsurface is studied. Inspired by experiments suggesting that atomic steps reduce thesurface conductance, the atomic structure and transport properties of such steps areexamined, revealing that dimer atom buckling along the step edges is the primaryculprit since it leads to an opening of a local band gap at the step.Les effets de surface peuvent affecter la performance d'un dispositif nanoélectronique, mais peuvent aussi conduire à de nouvelles fonctionnalités. L'objectif de cette thèse est d'effectuer une étude théorique sur le rôle des surfaces en nanoélectronique. Notre analyse, de type premiers principes atomiques, est effectuée en combinant la théorie de la fonctionnelle de la densité avec les fonctions de Green hors-équilibre. Cette technique permet de traiter tous les atomes de manière égale sans utiliser de paramètres phénoménologiques. La première partie de cette thèse considère la conduction à travers une molécule sans substrat, afin d'illustrer le genre de systèmes typiquement modélisés dans les calculs de transport. Deux électrodes en Au sont mises en contactavec une molécule benzènediamine substituée (R = CH3, NH2, OH), où un atome H est retiré pour former un radical qui peut se comporter comme un filtre de spin, dépendant du groupe R. Ensuite, nous nous concentrons sur une ligne formée d'éthylbenzènes empilées–π sur la surface de Si(100), où les atomes de silicium sont explicitement inclus dans le calcul. Quoique les molécules permettent le transport d'électronsà certaines énergies, un canal se forme à travers le substrat qui peut dominer la conductance. Nous étudions aussi comment certains substituants peuvent moduler les propriétés de transport électronique de ces fils moléculaires. Nous trouvons que la conductance du fil moléculaire peut être modifiée pour dominer l'effet du substrat.Enfin, la conductance de la surface métallique Si(111)–7 × 7 est analysée. Dans lebut d'expliquer théoriquement les expériences suggérant que les marches atomiques réduisent la conductance de la surface, la structure atomique et les propriétés de transport de ces marches ont été examinées. Les résultats révèlent que c'est la déformation atomique des dimères le long des marches qui cause ce phénomène, en raison de la formation d'une bande interdite localisée proche de la marche.