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1
Myagkiy, Andrey. "Mineralization of Nickel in saprolitic ore of New Caledonia : Dynamics of metal transfer and modeling of coupled geochemical and hydrodynamic processes." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0277/document.
Abstract:
La Nouvelle-Calédonie détient d’importantes réserves de nickel latéritique et est devenue, en 2017, le cinquième producteur mondial de Ni. Ces dépôts sont habituellement considérés comme résultant d’altération latéritique intense de la péridotite, qui constitue la principale source de nickel. Ainsi, le principal modèle conceptuel de la formation des minerais de nickel latéritique en Nouvelle-Calédonie est un modèle per descensum où la plupart des éléments (Mg, Ni et Si) ont été lessivés depuis la surface, en particulier lors du développement du sol latéritique. Le nickel est ensuite reprécipité, soit dans la goethite de la latérite fine, soit au niveau de la saprolite, sous forme de goethite et de silicates Mg-Ni, dont des talc-like ou kérolite. Les observations minéralogiques et structurales récentes ainsi que les données minières ont cependant mis en évidence de nombreux types d’hétérogénéités dans les concentrations, et la distribution des porteurs de Ni. Comprendre les facteurs la mobilité de cet élément, ses mécanismes de piégeage ainsi que les paramètres chimiques et hydrodynamiques à l’origine de ce piégeage, est essentiel afin de prévoir la distribution du nickel dans les profils latéritiques en Nouvelle-Calédonie, et constitue l’objectif de cette thèse. Ce travail est basé sur le développement (i) d’un modèle 1D s’intéressant en particulier au comportement géochimique du nickel lors de l’altération de l’ophiolite, sa comparaison avec les observations in situ et une compréhension détaillée de la mobilité des éléments traces pendant le processus, et (ii) d’un modèle 2D hydro-géochimique couplé avec l’hydrodynamique complexe des profils latéritiques, améliorant ainsi la connaissance du contrôle structural sur la redistribution et la minéralisation du nickel. Tandis que les simulations 1D permettent de mieux comprendre les aspects chimiques contrôlant les processus de rétention du nickel au sein d’un profil, le modèle 2D se révèle être un outil puissant pour la compréhension de la formation des dépôts locaux les plus riches en nickel. Les résultats du modèle 2D montrent une remobilisation du nickel depuis les horizons supérieurs puis sa reprécipitation sous forme de silicates dans la saprolite. Le nickel remobilisé provient principalement de la zone saprolitique à cause de la dissolution des silicates de nickel formés précédemment ainsi que de l’olivine résiduelle de cette zone. Ce modèle a également révélé que l’horizon latéritique (et en particulier les oxy- hydroxydes de nickel) avait un faible impact dans la remobilisation du nickel. L’infiltration latérale de l’eau contenant le nickel dissout issu des formations surincombantes est à l’origine de la formation des zones les plus riches dans les parties inférieures du profil. Cette redistribution est entièrement contrôlée par l’hydrodynamique locale, la topographie ainsi que l’orientation et la position des fractures. Les modèles présentés permettent d’expliquer les processus de formation des minerais de nickel latéritique saprolitique, améliorant ainsi la compréhension des paramètres contrôlant la mobilité des éléments traces dans un environnement ultramafique. Ceci donne une nouvelle clé de distribution du nickel dans les profils actuels, qui peut devenir un outil pour la prospection minière, et la recherche de nouvelles ressources exploitablesNew Caledonia hosts significant lateritic nickel reserves, and presently became the fifth largest Ni producer in the world. These deposits are generally thought to be closely as- sociated with the intense chemical and mechanical weathering of peridotite bedrock that is a principal source of nickel. Thus, the main ore genesis model for Ni ores in New Caledonia is based on a single per descensum model where most elements (Mg, Ni, and Si) are leached from the surface, particularly, during lateritic soil development. Nickel is then concentrated either in the fine-grained laterite where goethite is the main Ni bearer, the so-called ’lateritic ore’, or below the laterites, in the saprolite level, where nickel occurs as goethite and several types of Mg-Ni silicates, in particular kerolite. Recent mineralogical and structural observations together with mining data have revealed a lot of different types of heterogeneities associated with the distribution and mineralogy of Ni bearing minerals. Therefore, in depth investigations of Ni mobility, its retardation processes along with its governing chemical and hydrodynamic parameters are of big importance for understanding and subsequent prediction of Ni distribution in profiles of New Caledonia. Such an investigation is an objective of the present work. The concept is based on the development of i) a powerful 1D model with particular emphasis on Ni geochemical behavior during ophiolite weathering, its comparison with in situ observations, and detailed understanding of trace elements mobility, and ii) 2D hydro-geochemical model coupled with complex hydrodynamics, that would additionally provide new insight into the structural control on Ni redistribution and mineralization. While the 1D simulations provide a remarkable result for understanding the chemical features that drive Ni retention processes in a profile, 2D model appears to be a powerful tool for understanding how local Ni-enrichments may form. The results of this model show the reactivation of Ni from upper horizons and its concentration in neo-formed silicates in bottom of the saprolite. The reactivated Ni comes mostly from the saprolite horizon due to the redissolution of previously formed Ni-bearing silicates and still persisting in this olivine zone. Modeling has revealed minor contribution of the laterite horizon (Ni-oxi-hydroxides) into the Ni remobilization. The lateral infiltration of water with remobilized Ni from areas such as topographic highs to downstream slope areas leads to the formation of richest deposits in this lower part of profile. The manner of redistribution is fully governed by the topographic slopes, orientation and position of the fractures. Presented models appear to be of importance in attempt of explanation of Ni mineralization processes, revealing the main keys to understanding the control of trace elements mobility in ultramafic environment. The latter gives new insights into the Ni distribution in present day profiles and, therefore, may greatly help in mineral prospecting and forecasting the distribution of future resources
2
Décultot, Léa. "Étude et modélisation du procédé de refusion par plasma d’arc en creuset froid (PAMCHR) d’alliages de titane pour des applications aéronautiques." Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0031.
Abstract:
Le procédé Plasma Arc Melting Cold Hearth Refining (PAMCHR) permet de recycler des chutes de titane afin d’élaborer des alliages de titane de qualité aéronautique. Les travaux de thèse présentés dans ce manuscrit se concentrent sur l’étape d’affinage du procédé. Elle correspond, après fusion de la matière et avant coulée en lingotière, au transport du métal liquide dans un creuset à fond plat en cuivre refroidi à l’eau. L’apport de chaleur du procédé se fait par des torches à plasma, dans un environnement de gaz inerte. Une modélisation tridimensionnelle de l’écoulement thermo-hydrodynamique de l’alliage de titane, a été développée avec pour base le logiciel CFD Ansys-Fluent. L’objectif de cet outil, nommé PAM3D, est d’améliorer notre compréhension du comportement du titane liquide au sein du creuset d’affinage. Un grand nombre de fonctions ont été intégrées au modèle pour décrire, entre autres, les transferts thermique et dynamique entre le jet de plasma et la surface du bain liquide. La compréhension de ces transferts est primordiale à la modélisation du procédé : ils ont pu être obtenus à l’aide d’une série d’essais, réalisés sur un four pilote PAMCHR, et de simulations obtenues par le développement de deux modèles numériques simples. Des résultats de simulations obtenues par cette première version de PAM3D sont confrontés à des mesures prises à partir de fusions expérimentales, et la comparaison est jugée satisfaisante. Cependant, la valeur maximale implémentée dans le modèle de la contrainte pariétale, dû à l’impact de la torche à la surface du bain, semble être sous-estimée. Des simulations complémentaires mettent d’ailleurs en avant le rôle important des forces hydrodynamiques sur le comportement thermique du bain, et en particulier de cette contrainte pariétaleThe recycling of titanium scraps can be achieved using the Plasma Arc Melting Cold Hearth Refining (PAMCHR) process with the aim of producing aeronautical titanium alloy ingots. In this manuscript, the research work focuses on the refining stage of the process where the liquid is transported in a horizontal copper water-cooled crucible. This important step takes place downstream the melting of the charge and upstream the casting of liquid titanium into the ingot mold crucible. Plasma torches are used as heat source of PAMCHR process, which is conducted under an atmosphere of inert gas. A three-dimensional modeling of the thermo-hydrodynamic flow of the titanium alloy has been set up based on Ansys-Fluent CFD software. The purpose of this tool, named PAM3D, is to improve our understanding of the liquid titanium behavior within the refining crucible. A large number of user functions have been integrated into the model to describe, among other mechanisms, the thermal and momentum transferred from the plasma plume to the surface of the liquid bath. The analysis of these transfers is essential for modeling the process. They are obtained by a study coupling melting tests, carried out in a pilot PAMCHR furnace, and numerical modeling. Numerical results, obtained by this first version of PAM3D are compared to experimental measurements, and the agreement is satisfactory. However, the maximum value of the shear stress, due to the impact of the plasma plume on the bath surface, implemented in the model seems to be underestimated. Moreover, complementary simulations highlight the important role of hydrodynamic forces on the thermal behavior of the bath, and in particular of this shear stress
3
Raturi, Sagar. "Energetics and structural aspects of cation-coupled drug transport by NorM multidrug transporters." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/284914.
Abstract:
NorM multidrug transport proteins belong to the multiple antibiotics and toxins extrusion (MATE) family of secondary active transporters. Members of this family are present across all species including bacteria, plants and humans. In bacteria, their over-expression can lead to antibiotic resistance, whereas in the human body, the transporters can alter the plasma levels of drugs. NorM proteins are therefore relevant for the pharmacokinetic properties of drugs. Previously, NorM from Vibrio cholerae (NorM-VC) was shown to export drug (ethidium) in an antiport reaction that is coupled to the simultaneous uptake of protons and sodium ions down their electrochemical gradients across the plasma membrane. But NorM from Pseudomonas stutzeri (NorM-PS) was shown to transport DAPI by utilising proton cycling exclusively. NorM-VC and NorM-PS share 42% identical amino-acid residues and yet their functions differ in terms of their ion coupling properties. These differences in functionality of two highly homologous proteins provide an excellent opportunity to carry out a comparative study. The work presented in this thesis investigates the energetics of drug transport processes by NorM-VC and NorM-PS and the structural basis for ion-coupled drug transport by NorM-VC. Ethidium efflux assays in intact Lactococcus lactis cells were used to study the effect of the magnitude and composition of the proton- and sodium-motive force on transport activity. Furthermore, ethidium binding assays were used to study partial reactions in drug efflux processes. These biochemical data were supplemented by computational studies and analyses of current protein structures. Based on the observations detailed here, a novel transport model for NorM-VC is proposed, which explains published findings for NorM-VC and other MATE transporters. The model represents a potentially universal mechanism for MATE transporters that can be used to predict further structure-function relationships in this important family of member transporters.
4
Roche, Benoît. "Transport électronique à travers deux dopants, en régime statique et dynamique dans des transistors silicium." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00947330.
Abstract:
Dans cette thèse, nous nous sommes intéressés à l'étude à basse température de dispositifs en silicium de taille nanométrique. Dans ces dispositifs, il est possible de faire passer le courant électrique à travers un nombre réduit de dopants. Nous avons étudié plus spécifiquement le cas de deux dopants en séries, dont les potentiels électrostatiques sont contrôlés indépendamment par deux tensions de grille. En régime de transport électronique statique, il est possible d'effectuer une spectroscopie des niveaux électronique des dopants. On mesure la séparation des deux premiers états de dopants phosphore, qui est proche de 10 meV, alors qu'elle est de 11,7 meV pour des dopants dilués dans un cristal massif. Cette différence s'explique par la proximité des dopants avec une interface avec de l'oxyde de silicium. En régime dynamique, lorsque les niveaux des dopants sont modulés par un signal périodique, on observe qu'un courant est généré par le dispositif. L'évolution du courant en fonction des tensions de grille est simulée en prenant en compte les couplages tunnels du système. À haute fréquence, lorsque l'on observe la quantification d'énergie électromagnétique échangée avec le système, on reproduit le courant mesuré en fonction de l'amplitude du signal appliqué sur les grilles. Cette mesure permet de mettre en évidence la cohérence d'un électron partagé sur deux dopants.
5
Ippisch, Olaf. "Coupled transport in natural porous media." [S.l. : s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=96376022X.
6
Ippisch, Olaf. "Coupled transport in natural porous media." [S.l. : s.n.], 2003. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB10605053.
7
Kronbichler, Martin. "Computational Techniques for Coupled Flow-Transport Problems." Doctoral thesis, Uppsala universitet, Avdelningen för teknisk databehandling, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-162215.
Abstract:
This thesis presents numerical techniques for solving problems of incompressible flow coupled to scalar transport equations using finite element discretizations in space. The two applications considered in this thesis are multi-phase flow, modeled by level set or phase field methods, and planetary mantle convection based on the Boussinesq approximation. A systematic numerical study of approximation errors in evaluating the surface tension in finite element models for two-phase flow is presented. Forces constructed from a gradient in the same discrete function space as used for the pressure are shown to give the best performance. Moreover, two approaches for introducing contact line dynamics into level set methods are proposed. Firstly, a multiscale approach extracts a slip velocity from a micro simulation based on the phase field method and imposes it as a boundary condition in the macro model. This multiscale method is shown to provide an efficient model for the simulation of contact-line driven flow. The second approach combines a level set method based on a smoothed color function with a the phase field method in different parts of the domain. Away from contact lines, the additional information in phase field models is not necessary and it is disabled from the equations by a switch function. An in-depth convergence study is performed in order to quantify the benefits from this combination. Also, the resulting hybrid method is shown to satisfy an a priori energy estimate. For the simulation of mantle convection, an implementation framework based on modern finite element and solver packages is presented. The framework is capable of running on today's large computing clusters with thousands of processors. All parts in the solution chain, from mesh adaptation over assembly to the solution of linear systems, are done in a fully distributed way. These tools are used for a parallel solver that combines higher order time and space discretizations. For treating the convection-dominated temperature equation, an advanced stabilization technique based on an artificial viscosity is used. For more efficient evaluation of finite element operators in iterative methods, a matrix-free implementation built on cell-based quadrature is proposed. We obtain remarkable speedups over sparse matrix-vector products for many finite elements which are of practical interest. Our approach is particularly efficient for systems of differential equations.
8
Mavkov, Bojan. "Control of coupled transport in Tokamak plasmas." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAT004/document.
Abstract:
L'objectif de cette thèse est le développement de nouvelles méthodes d'analyse et de commande pour une classe d'équations aux dérivées partielles couplées permettant de modéliser le transport combiné du flux magnétique et de la pression (produit de la densité et de la température) dans les plasmas tokamak. Le système couplé est représenté par deux équations 1D de diffusion résistive. Dans cette thèse, on a obtenu deux types de modèles: le premier repose sur des principes physiques et le second exploite les données obtenues en utilisant des techniques d'identification des systèmes. La conception de commande est basée sur l'etude en dimension infinie en utilisant l'analyse de Lyapunov. Le contrôle composite est synthétisé en utilisant la théorie des perturbations singulières pour isoler la composante rapide de la composante lente. Tout le travail théorique est implémenté et testé dans des simulations basées sur la physique avancée en utilisant le simulateur de plasma pour les tokamaks DIII-D, ITER et TCVThe objective of this thesis is to propose new methods for analysis and control of partial differential equations that describe the coupling between the transport models of the electron pressure (density multiplied by the temperature) and the magnetic flux in the tokamak plasma. The coupled system is presented by two1D resistive diffusion equations. In this thesis two kinds of control models are obtained. The first is a first-principle driven model and the second one is the data-driven model obtained using system identification techniques. The control design is based on an infinite dimensional setting using Lyapunov analysis. Composite control is designed using singular perturbation theory to divide the fast from the slow component. All the theoretical work is implemented and benchmarked in advanced physics based on simulations using plasma simulator dor DIII-D, ITER and TCV tokamaks
9
Simpson, Brent W. "Genetic investigation of how an ATP hydrolysis cycle is coupled to lipopolysaccharide transport." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1523988371297363.
10
Bouyssier, Julien. "Transports couplés en géométries complexes." Toulouse 3, 2012. http://thesesups.ups-tlse.fr/1929/.
Abstract:
Ces travaux s'intéressent aux questions de transports non stationnaires et de transferts stationnaires de chaleur et de masse par convection-diffusion au sein de géométries complexes. Par complexe, nous entendons d'une part pour le transport que le fluide est convecté au sein d'une cavité de section quelconque lentement variable dans la direction longitudinale, c'est à dire ayant des variations longitudinales grandes devant hauteur et largeur moyennes. Nous considérons d'autre part le transfert au sein de domaines non-axisymétriques dans lesquels sont plongés un ou plusieurs tubes où le fluide porteur s'écoule. Pour ce qui concerne le transfert, ce travail a consisté à montrer comment étendre le principe, valider l'utilisation, et illustrer l'efficacité d'une décomposition en mode de Graetz pour la prédiction des échanges dans des configurations réalistes d'échangeurs. Cette décomposition permet de formuler le problème initial 3D comme un problème aux valeurs propres généralisées en 2D dont la résolution numérique est drastiquement moins coûteuse. Nous généralisons la notion de mode de Graetz à des conditions aux limites latérales quelconques et, en particulier pour le cas d'échangeurs équilibrés où nous avons mis en évidence un nouveau mode linéairement variables dans la direction longitudinale. Nous mettons en oeuvre le calcul de ces modes de Graetz dans le cas de configurations semi-infinies pour traiter, par exemple, des configurations transversalement périodiques (types plancher chauffant) et montrons qu'un faible nombre de modes suffit pour donner une très bonne approximation des transferts. Dans le cas d'échangeurs finis couplé avec des tubes en entrée/sortie, nous montrons comment déterminer les amplitudes des modes de Graetz dans les différents domaines par la minimisation d'une fonctionnelle associée aux conditions d'entrée sorties retenues. Ces modes permettent l'étude paramétrique systématique des champs de température, des flux de chaleurs entre les domaines fluides et solides ainsi que des rendements thermiques d'un échangeur à deux tubes. Nos résultats indiquent que la longueur d'échange caractéristique est gouvernée par le premier mode de Graetz généralisé à grand nombre de Péclet. Nous montrons aussi, en particulier, qu'un échangeur symétrique possède un spectre symétrique, et une évolution amont/aval symétrique. Dans le cas de la dispersion de Taylor, nous avons établi une forme conservative 3D des équations de dispersion de Taylor en géométrie variable généralisant le cas 2D déjà connu. Nous avons ensuite implémenté en éléments finis puis validé numériquement ces équations de dispersion en 2D et 3D. Nous montrons que les variations longitudinales 3D de la cavité peuvent considérablement augmenter la dispersion longitudinaleThis work interest is about stationary transfer and non-stationary transport by convection-diffusion onto complex geometries. For transport issues, complex refers to convection into flattened cavity of arbitrary transverse shape, slowly varying along the longitudinal direction. In the context of transfer, complex refers to non-axisymmetric domains of arbitrary transverse shape along which one or several parallel tubes convect heat or mass. For the transfer problem, this work extends the principle, validates the use, and illustrates the efficiency of Graetz modes decompositions for exchanges prediction in realistic exchangers configurations. This decomposition permits to formulate the initial 3D problem as a generalysed 2D eigenvalue problem, the numerical evaluation of which is drastically reduced. We generalyze Graetz modes solutions for arbitrary applied lateral boundary conditions. In the particular case of balanced exchangers, we bring to the fore a new neutral mode whose longitudinal variations are linear as opposed to classical Graetz modes displaying exponential decay. The numerical computation of those modes for semi-infinite configurations with lateral periodic boundary conditions shows that a few number of those provides a very good approximation for exchanges. In the case of finite exchangers coupled with inlet/oulet tubes, we show how to evaluate the amplitudes of Graetz modes in the various domains (inlet, exchanger, outlet) from functional minimization associated with input/output boundary conditions. The evaluation of these amplitudes permit a systematic parametric study of temperature fields, heat fluxes between fluid and solid, and hot/cold performance of a couple-tube exchanger. Our results indicate that the typical exchange length is governed by the first Graetz mode at large P\'eclet number. We also show that a symmetric exchanger has a symmetric spectrum and a upward/backward symmetric evolution. In the case transport we elaborate theoretically the conservative form of 3D Taylor dispersion equations into variable cavities which generalyzes the framework already known in 2D. We numerically implement these averaged dispersion equations with finite element, and validate in 2D the obtained results. We show that 3D longitudinal variations of a cavity has a strong impact on the longitudinal dispersion
11
Rashid, Mohammad Zunaidur. "ATOMISTIC MODELING OF COUPLED ELECTRON-PHONON TRANSPORT IN NANOSTRUCTURES." OpenSIUC, 2021. https://opensiuc.lib.siu.edu/dissertations/1939.
Abstract:
Electronics industry has been developing at a tremendous rate for last five decades and currently is one of the biggest industries in the world. The key to the rapid growth of electronics industry is innovation that made possible the constant scaling of transistors with reduced cost and improved performance. Scaling transistors were simpler at the beginning, but currently as the gate length of transistors has reached few nanometers, different short channel effects have emerged and power density of transistors has also increased drastically, which made further scaling much more challenging. To study electro-thermal transport in these reduced dimensionality devices, continuum models are no longer sufficient. In this work, the electrical and thermal transport properties have been modeled by solving Boltzmann Transport Equation (BTE) for electrons and phonons, respectively, using the Monte Carlo (MC) technique. To solve BTE for the phonons, a coupled Molecular Mechanics-Monte Carlo approach is employed where phonon band-structure is obtained using the atomistic modified Valence Force Field (VFF) model and is coupled with a Monte Carlo Phonon Transport kernel which solves the BTE for phonons. The phonon-phonon scattering is modeled in relaxation time approximation (RTA) using Holland’s formalism. Diffusive boundary scattering for phonons has been modeled using the Beckmann-Kirchhoff (B-K) surface roughness scattering model taking into account the effects of phonon wavelength, incident angles and degree of surface roughness. The effect of rough surface on longitudinal acoustic (LA) and transverse acoustic (TA) phonon branches has been studied with the help of the B-K model and it has been found that, at elevated temperatures, there is less backscattering to the LA branch due to rough surface. Effort has been made then to couple the developed phonon Monte Carlo transport simulator with an electron Monte Carlo transport simulator to study the origin and effects of self-heating in a nanoscale field-effect transistor (FET). In contrast to the widely used continuum model, where Fourier heat diffusion equation is usually solved to describe the thermal transport, the simulator developed in this dissertation treats both the electrons and the phonons at the particle level. Acoustic and intervalley g and f type electron-phonon scattering mechanisms are considered and the resulting local temperature modification has been used to bridge the electron and phonon transport paths. Phonon transport at the oxide-silicon interface has been modeled using the Diffuse Mismatch (DM) model, whereas, the phonons in the oxide have been described using the Debye model and temperature and frequency dependent relaxation time. The simulator is then benchmarked and used to study the electron-phonon transport processes in a FinFET device with a gate length of 18 nm, channel width of 4 nm, and a fin height of 8 nm. Preliminary results show that there can be a current degradation of as high as ~9.56% due to self-heating effect. Also, temperature in the entire channel region could rise due to self-heating. The maximum temperature rise in the channel region is found to be ~30K.
12
Inzoli, Isabella, Signe Kjelstrup, Dick Bedeaux, and Jean-Marc Simon. "The coupled transport of heat and mass across a silicalite surface." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-189575.
13
Larisch, Wolfgang. "4 Coupled compartments – an analytical solution for diffusion and reaction kinetics." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-198373.
14
Jakobsson, Håkan. "Discontinous Galerkin Methods for Coupled Flow and Transport problems." Thesis, Umeå universitet, Institutionen för matematik och matematisk statistik, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-51335.
Abstract:
We investigate the use of discontinuous Galerkin finite element methods in a mul- tiphysics setting involving coupled flow and transport in porous media. We solve an elliptic equation for the fluid pressure using Nitsche’s method and an approxima- tion, Σ, of the exact convection field σ will be constructed by interpolation onto the lowest-order Raviart-Thomas space of functions. We sequentially solve the transport equation, with the convection field Σ, for the fluid saturation by use of the lowest order discontinuous Galerkin method. We also supply numerical evidence of the importance of local conservation in this setting, and furthermore propose a line of argument indicating that if Σ is constructed using conservative fluxes, the modeling error σ − Σ may not have a great impact on the total error in certain quantities of interest.
15
Castleton, I. M. "Electron transport in coupled one- and two-dimensional systems." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597365.
Abstract:
In this dissertation, transport measurements are presented on the coupling between two closely separated two-dimensional electron gases (2DEGs) formed within GaAs/AlGaAs heterostructures. The experiments fall into three main areas. Firstly, the electrical properties of a new type of switching transistor are investigated. A 2DEG is formed at the inverted and non-inverted heterojunction of a wide GaAs/AlGaAs quantum well. With the use of front and back gates, charge is moved from one 2DEG to the other in a manner similar to that proposed theoretically in the Velocity Modulated Transistor (VMT) device concept. In the VMT, switching is obtained through a mobility modulation rather than through a more conventional carrier density modulation, thereby minimising capacitive time delays. By adjusting the grown-in carrier density and mobility of each 2DEG, successful VMT operation is demonstrated, and a mobility modulation of a factor of 125 is achieved. In the second part, the resistance resonance in strongly coupled double 2DEGs is investigated. The size of the resistance resonance in three samples is measured as a function of the 2DEG mobility ratio, and the results are compared with predictions made by classical and quantum transport theories. Quenching of the resistance resonance by an in-plane magnetic field is observed, and the low- and high-field magnetoresistance are explained by considering the field-induced distortions of the Fermi surface. Finally, the transport properties of structures containing double quasi-1D wires are studied. The wires are formed by laterally confining two 2DEGs using a single Schottky split-gate. Ballistic quantisation in units of 2e2/h and 4e2/h is observed in widely spaced, non-interacting wires, while closely spaced wires are used to investigate the effects of wavefunction hybridisation in reduced dimensionality. Variations in the screening of a single quasi-1D wire are revealed by compressibility measurements.
16
Gunduz, Orhan. "Coupled flow and contaminant transport modeling in large watersheds." Diss., Available online, Georgia Institute of Technology, 2004:, 2004. http://etd.gatech.edu/theses/available/etd-04092004-160146/unrestricted/gunduz%5Forhan%5F200405%5Fphd.pdf.
Abstract:
Thesis (Ph. D.)--Civil & Environmental Engineering, Georgia Institute of Technology, 2004.Dr. Paul Work, Committee Member ; Dr. Philip Roberts, Committee Member ; Dr. Mustafa Aral, Committee Chair ; Dr. Terry Sturm, Committee Member ; Dr. Turgay Uzer, Committee Member. Vita. Includes bibliographical references (leaves 442-466).
17
Xie, (Lily) Hong 1965. "Contaminant transport coupled with nonlinear biodegradation and nonlinear sorption." Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/290676.
Abstract:
A coupled process one-dimensional model with two-region transport, two-domain nonlinear sorption, and nonlinear biodegradation is formulated in this research. A numerical code is developed for this complex system with two sets of initial/boundary conditions. The second order upwind method is used to solve PDEs of the system, and the Adam-Bashforth three step method is used to solve ODEs of the system. By nondimensionalizing the governing equations for transport and nonlinear biodegradation, we show that biodegradation is controlled by three characteristic combined factors: the effective maximum specific growth rate, the relative half-saturation constant, and the relative substrate-utilization coefficient. A diagram with type curves was constructed based on the three characteristic factors to show the conditions under which complete and incomplete biodegradation is observed, and the conditions for which the linear, first-order approximation is valid for representing biodegradation. Analytical and numerical approaches were used to study the effect of substrate boundary concentration on biodegradation in a coupled-process system. For a system with fixed biotic and abiotic properties, substrate input concentration could be positively or negatively correlated to the magnitude of substrate degradation, depending on the time scale of the process. The relative scale of substrate concentration and its half-saturation constant is very important for the success and efficiency of bioremediation. It is found that bioremediation can be more efficient for higher concentration contaminant under certain conditions. The impact of biodegradation on solute transport with linear or nonlinear, equilibrium sorption was studied by using moments analysis. Computation results show that linear biodegradation has no impact on spatial moments of transport with linear instantaneous sorption. Conversely, it has an impact when sorption is nonlinear, since nonlinear sorption is enhanced by biodegradation. Nonlinear biodegradation causes preferential non-uniform substrate degradation and, therefore, affects spatial moments of transport with linear or nonlinear sorption. The oxygen constraint decreases the degree of nonlinear biodegradation and increases the degree of preferential degradation, thus it also impacts spatial moments of transport with linear or nonlinear sorption.
18
Bendjebbar, Fatna. "Modélisation hydrodynamique d'une torche à plasma couplée inductivement." Thesis, Clermont-Ferrand 2, 2013. http://www.theses.fr/2013CLF22340/document.
Abstract:
L’objectif de cette thèse était la modélisation numérique de la torche à plasma à couplage inductive. (ICP). Nous avons établi les bases de données nécessaires : composition, propriétés thermodynamiques et de transport appliqués aux mélanges d’argon, d’acide nitrique et d’eau. Le modèle hydrodynamique de la torche ICP (7 spires) considère le plasma à l'équilibre thermodynamique et couple les équations de Navier-Stokes pour décrire l'écoulement du plasma aux équations de Maxwell pour décrire l'évolution du champ électrique et du champ magnétiqueThe purpose of the work was the numerical modeling of the inductive coupling plasma torch. (ICP). We have established the necessary databases: composition, thermodynamic and transport properties applied to argon mixtures of nitric acid and water. The hydrodynamic model of the ICP torch (7 coils) considers the plasma at thermodynamic equilibrium and uses the Navier-Stokes equations to describe the plasma flow and the Maxwell equations to describe the evolution of the electric field and the magnetic field
19
Armstrong, Gillian. "Solute transport and intracellular pH in intestinal epithelial cells." Thesis, University of Newcastle Upon Tyne, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320390.
20
Di, Giulio Eugenio <1986>. "Improvement of photon transport model by including coupled photon-electron transport and kernel refinement." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amsdottorato.unibo.it/6954/1/Eugenio_Di_Giulio_tesi.pdf.
Abstract:
The first part of this work deals with the inverse problem solution in the X-ray spectroscopy field. An original strategy to solve the inverse problem by using the maximum entropy principle is illustrated. It is built the code UMESTRAT, to apply the described strategy in a semiautomatic way. The application of UMESTRAT is shown with a computational example. The second part of this work deals with the improvement of the X-ray Boltzmann model, by studying two radiative interactions neglected in the current photon models. Firstly it is studied the characteristic line emission due to Compton ionization. It is developed a strategy that allows the evaluation of this contribution for the shells K, L and M of all elements with Z from 11 to 92. It is evaluated the single shell Compton/photoelectric ratio as a function of the primary photon energy. It is derived the energy values at which the Compton interaction becomes the prevailing process to produce ionization for the considered shells. Finally it is introduced a new kernel for the XRF from Compton ionization. In a second place it is characterized the bremsstrahlung radiative contribution due the secondary electrons. The bremsstrahlung radiation is characterized in terms of space, angle and energy, for all elements whit Z=1-92 in the energy range 1–150 keV by using the Monte Carlo code PENELOPE. It is demonstrated that bremsstrahlung radiative contribution can be well approximated with an isotropic point photon source. It is created a data library comprising the energetic distributions of bremsstrahlung. It is developed a new bremsstrahlung kernel which allows the introduction of this contribution in the modified Boltzmann equation. An example of application to the simulation of a synchrotron experiment is shown.
21
Di, Giulio Eugenio <1986>. "Improvement of photon transport model by including coupled photon-electron transport and kernel refinement." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amsdottorato.unibo.it/6954/.
Abstract:
The first part of this work deals with the inverse problem solution in the X-ray spectroscopy field. An original strategy to solve the inverse problem by using the maximum entropy principle is illustrated. It is built the code UMESTRAT, to apply the described strategy in a semiautomatic way. The application of UMESTRAT is shown with a computational example. The second part of this work deals with the improvement of the X-ray Boltzmann model, by studying two radiative interactions neglected in the current photon models. Firstly it is studied the characteristic line emission due to Compton ionization. It is developed a strategy that allows the evaluation of this contribution for the shells K, L and M of all elements with Z from 11 to 92. It is evaluated the single shell Compton/photoelectric ratio as a function of the primary photon energy. It is derived the energy values at which the Compton interaction becomes the prevailing process to produce ionization for the considered shells. Finally it is introduced a new kernel for the XRF from Compton ionization. In a second place it is characterized the bremsstrahlung radiative contribution due the secondary electrons. The bremsstrahlung radiation is characterized in terms of space, angle and energy, for all elements whit Z=1-92 in the energy range 1–150 keV by using the Monte Carlo code PENELOPE. It is demonstrated that bremsstrahlung radiative contribution can be well approximated with an isotropic point photon source. It is created a data library comprising the energetic distributions of bremsstrahlung. It is developed a new bremsstrahlung kernel which allows the introduction of this contribution in the modified Boltzmann equation. An example of application to the simulation of a synchrotron experiment is shown.
22
Srinivasan, Venkatraman. "Analytical solutions for sequentially coupled multi-species reactive transport problems." Auburn, Ala., 2007. http://repo.lib.auburn.edu/07M%20Theses/SRINIVASAN_VENKATRAMAN_13.pdf.
Abstract:
Thesis (M.S.)--Auburn University, 2007.Abstract. Vita. "This thesis has produced the following three journal publications: 1) V. Srinivasan, T.P. Clement, and K.K. Lee. "Domenico solution -- Is it valid?", Ground Water, 25(2): 136-146, May 2007 ; 2) V. Srinivasan and T.P. Clement. "Analytical solutions for sequentially coupled reactive transport problems. Part I: Mathematical derivations", submitted May 2007, Advances in Water Resources ; 3) V. Srinivasan and T.P. Clement. "Analytical solutions for sequentially coupled reactive transport problems. Part II: Special cases, implementation and testing", submitted May 2007, Advances in Water Resources." -- From p. v. Includes bibliographic references (ℓ. 91-98)
23
Chang, Eric Kenneth. "Coupled sorption and transport of nonionic surfactants in natural soils." Thesis, Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/21257.
24
Young, Carolyn. "Transport and charge sensing measurements of coupled quantum dot devices." Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=106374.
Abstract:
We study transport and charge sensing measurements of double quantum dots (DQDs). Several proposals have been put forth for DQD-based qubits, making these systems interesting from the perspective of solid-state quantum computation. This thesis discusses three theoretical studies of error-generation in DQD qubit read-out. First, we consider transport measurements and calculate the contribution to the DQD conductance from cotunneling processes involving the virtual occupation of excited states. We present an efficient numerical method, based on the tight-binding formalism, for the calculation of the DQD transmission associated with two-particle cotunneling. We study the effect of electron-electron interactions within the constant interaction picture and, by treating the lead-DQD tunneling exactly, are able to consider the limit of strong coupling. We generate theoretical conductance maps, or stability diagrams, reflecting a wide region of parameter space, allowing us to compare the incidence of cotunneling in a variety of electrostatic regimes. Next, we focus on charge-sensing measurements and study the Heisenberg backaction associated with read out via a capacitively coupled quantum point contact (QPC). We show that the fundamental source of backaction is due to the QPC charge noise, rather than the shot noise. We derive a rigorous lower bound on the magnitude of the charge noise, and calculate the corresponding inelastic rates in a DQD charge qubit. Furthermore, we show that the charge and shot noise backaction mechanisms are in principle distinguishable when the QPC is non-adiabatic. We also apply our results to the case of two-electron DQD spin qubits, where the read out is performed via spin-to-charge conversion, and estimate the corresponding relaxation and dephasing times. Finally, we study an indirect backaction effect associated with read out by a QPC. In our picture, the QPC charge noise serves to locally heat a bath of phonons, driving it out of equilibrium. The phonons then travel to the DQD, where they are resonantly absorbed by the qubit, leading to inelastic transitions that show a distinct periodicity as a function of frequency. Strong oscillations in the DQD occupation have recently been measured experimentally by two independent groups. We show that the coupling between the phonon bath and the QPC can lead to focussing, which enhances the resonant phonon absorption and leads to the striking effect seen in experiment.Nous etudions la mesure de points quantiques doubles (DQDs), specifiquement le transport electronique et la detection de charge. Plusieurs propositions ont ete avancees pour des qubits bases sur les DQDs, qui rend ces systèmes interessants du point de vue du calcul quantique a l'etat solide. Cette these comprend trois etudes theoriques au sujet de la generation d'erreurs lors de la mesure des qubits DQD. Premierement, nous considerons les mesures de transport, et calculons la contribution a la conductance DQD des processus cotunneling impliquant l'occupation virtuelle des etats excites. Nous presentons une methode numerique efficace, basee sur le formalisme tight-binding, pour le calcul de la transmission DQD associee avec le cotunneling a deux electrons. Nous etudions l'effet des interactions electron-electron dans un modele d'interaction constante et, en traitant la puissance de tunnel entre les QDs exactement, examinons la limite de couplage fort. Nous generons des cartes de conductance theoriques qui refletent une vaste region de l'espace des parametres, et qui nous permettent de comparer l'incidence de cotunneling dans une variete de regimes electrostatiques. Ensuite, nous concentrons sur des mesures de detection de charge, et etudions le backaction Heisenberg associee a la mesure par un contact de point quantique (QPC). Nous montrons que la source fondamentale de backaction est du au bruit de charge du QPC, plutot que le bruit de courant. Nous formulons une borne inferieure rigoureuse pour l'ampleur du bruit de charge, et calculons les taux correspondants aux transitions inelastiques dans un qubit de charge DQD. Par ailleurs, nous montrons que les mecanismes de backaction associes avec le bruit de charge et de courrant, respectivement, peuvent en principe etre distingues quand le QPC est non-adiabatique. Nous appliquons egalement nos resultats au cas de qubits de spin, ou il y a deux electrons dans le DQD et la mesure est effectuee par la conversion entre spin et charge, et estimons les temps de relaxation et de decoherence correspondants.Finalement, nous etudions un effet backaction indirect associe a la lecture par un QPC. Dans notre modele, le bruit de charge du QPC sert a chauffer localement un bain de phonons, ce qui le conduit hors de l'equilibre. Ensuite, les phonons voyagent du QPC au DQD, ou ils sont absorbes de maniere resonante par le qubit, conduisant des transitions inelastiques. Ces transitions montrent une periodicite distincte en fonction de la frequence. De fortes oscillations dans l'occupation du DQD ont recemment ete mesurees experimentalement par deux groupes independants. Nous montrons que le couplage entre le bain de phonons et la charge du QPC peut conduire les phonons a concentrer, ce qui ameliore l'absorption de phonons resonants et produit l'effet vu au laboratoire.
25
Rjagopal, Ramasubramaniam. "Correlated single electron transport in capacitively coupled tunnel junction arrays /." view abstract or download file of text, 1999. http://wwwlib.umi.com/cr/uoregon/fullcit?p9957570.
Abstract:
Thesis (Ph. D.)--University of Oregon, 1999.Typescript. Includes vita and abstract. Includes bibliographical references (leaves 95-97). Also available for download via the World Wide Web; free to University of Oregon users. Address:http://wwwlib.umi.com/cr/uoregon/fullcit?p9957570.
26
Ripplinger, Scott. "Development of a Coupled Fluid and Colloidall Particle Transport Model." DigitalCommons@USU, 2013. https://digitalcommons.usu.edu/etd/2041.
Abstract:
A colloidal system usually refers to when very small particles are suspended within a solution. The study of these systems encompasses a variety of cases including bacteria in ground water, blood cells and platelets in blood plasma, and river silt transport. Taking a look at these kinds of systems using computer simulation can provide a great deal of insight into how they work. Most approaches to date do not look at the details of the system, however, and are specific to given system. In this study a program called OpenFOAM is used as a basis to build a computer simulation tool that is flexible and that provides a detailed look at what is happening with all of the particles within the colloidal solution. This code is run through a series of tests to verify its usefulness.
27
Larisch, Wolfgang. "4 Coupled compartments – an analytical solution for diffusion and reaction kinetics." Diffusion fundamentals 24 (2015) 32, S. 1, 2015. https://ul.qucosa.de/id/qucosa%3A13497.
28
Lefevre, Benoit. "La soutenabilité environnementale des transports urbains dans les villes du sud : Le couple « transport – usage des sols » au cœur des dynamiques urbaines." Paris, ENMP, 2007. http://pastel.paristech.org/3538/01/BLEFEVRE_THESEFINALE_DEF.pdf.
Abstract:
L’objectif de cette thèse est d’explorer si, compte tenu des dynamiques démographiques et des faibles capacités financières, les technologies accessibles aux villes du Sud sont aptes à infléchir significativement les trajectoires des consommations énergétiques et des émissions de CO2 liées aux transports urbains. Le chapitre 1 récapitule ce que nous savons aujourd’hui des déterminants des consommations énergétiques liées aux transports urbains et des évolutions récentes de ces déterminants. Le chapitre 2 discute les solutions envisageables dans les politiques de transport et d’usage des sols pour placer les villes du Sud sur des trajectoires soutenables de développement. Ces conclusions nous conduisent à examiner les interactions entre le système de transport et le système d’usage des sols sur une ville particulière, Bogota (Colombie). Le chapitre 3 analyse le fonctionnement du couple « transport – usage des sols » au cœur des dynamiques urbaines sur le temps long, depuis la fondation de Bogota jusqu’à la fin du XXème siècle. Le chapitre 4 étudie les effets d’une infrastructure de transport, le Bus Rapid Transit (BRT) TransMilenio, sur les marchés foncier et immobiliers, la structure urbaine et la matrice Origine-Destination des déplacements. Le chapitre 5 évalue les outils de prospective capables de simuler différentes combinaisons des leviers d’action dont disposent les aménageurs urbains et sélectionne un modèle intégré existant (TRANUS), auquel est adossé un module de quantification des consommations énergétiques et des émissions de CO2 (Signature Energétique des Transports Urbains, SETU). Le chapitre 6 teste à l’aide de TRANUS-SETU la capacité des politiques de transport et d’urbanisme à infléchir les trajectoires de consommations énergétiques liées aux transports urbains sur le cas de Bangalore (Inde)The objective of this PhD dissertation is to explore if, in view of rapid demographic growth and limited financial capacities, the technologies accessible to poor cities can decrease trajectories of energy consumption and CO2 emissions due to urban transportation. Chapter 1 reviews what we already know of the determinants involved, and their recent evolutions. Chapter 2 analyzes conceivable transport and land-use solutions that would allow southern cities to attain sustainable development trajectories. The conclusions drawn from the first two chapters led us to analyze the interactions between the transport system and land-use system on a particular city, Bogota (Colombia). Chapter 3 studies the functional relations in the “Transport – Land Use” couple and its impact on urban space structuring processes in the long term, from the foundation of Bogota to the end of the 20th century. Chapter 4 focus on the impact of a new transportation infrastructure – the TransMilenio Bus Rapid Transit (BRT) – on real-estate and housing markets, on urban structure and the Origin-Destination trip matrix. Chapter 5 reviews the existing prospective tools able to simulate various combinations of realistic policies, and to measure their consequences on the levels of energy consumption and CO2 emissions related to urban transportation. The integrated urban “Transport – Land Use” model, TRANUS, is chosen and completed with a module of of energy consumption and CO2 emissions quantification, called “Energy Signature of Urban Transportation” (SETU). Chapter 6 tests the capacity of these combinations of policies to affect the trajectories of the energy consumption of urban transportation through the application of TRANUS-SETU on a case study, Bangalore (India)
29
Siqueira, Maicon Zaniboni. "Anisotropic shear viscosity and critical behavior of non-hydrodynamic quasinormal modes in strongly coupled plasmas." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-16082017-161531/.
Abstract:
In this thesis we use the holographic gauge/gravity duality to study two different aspects of strongly coupled non-Abelian plasmas. In the first topic we study the effects of strong (Abelian) magnetic fields on the transport coefficients of a strongly coupled non-Abelian plasma. Due to the spatial anisotropy created by the magnetic field, the most general viscosity tensor of a magnetized plasma has 5 shear viscosity coefficients and 2 bulk viscosities. We use the holographic correspondence for a strongly coupled N=4 Supersymmetric Yang-Mills (SYM) plasma to evaluate the shear viscosity perpendicular to the magnetic field and the shear viscosity parallel to the field. In the presence of a magnetic field, the shear viscosity perpendicular to the field saturates the Kovtun-Son-Starinets viscosity bound while in the direction parallel to the field the bound is violated. The second topic investigated in this thesis is motivated by the study of the near equilibrium behavior of strongly interacting non-Abelian plasmas that display a critical point in their phase diagram. We focus on the spectra of non-hydrodynamic quasinormal modes of a strongly coupled N=4 SYM plasma in the presence of a chemical potential, which displays a critical point in equilibrium. Except close to the critical point, we observe that by increasing the chemical potential one generally increases the damping rate of the quasinormal modes, which leads to a reduction of the characteristic equilibration times in the dual strongly coupled plasma. However, as one approaches the critical point the typical equilibration time increases though its derivative with respect to the chemical potential diverges with an exponent equal to -1/2. We also find a purely imaginary non-hydrodynamical mode in the vector diffusion channel at nonzero chemical potential which dictates the equilibration time in this channel near the critical point.Nessa tese usamos a dualidade holográfica calibre/gravidade para estudar dois aspectos diferentes de plasmas não-Abelianos fortemente acoplados. No primeiro tópico estudamos os efeitos de campos magnéticos (Abelianos) intensos sobre o coeficientes de transporte de um plasma não-Abeliano fortemente acoplado. Devido à anisotropia espacial criada pelo campo magnético, o tensor de viscosidade mais geral de um plasma magnetizado deve possuir 5 coeficientes de viscosidade de cisalhamento e 2 de viscosidade volumétrica. Usamos a correspondência holográfica para um plasma N=4 Supersimétrico de Yang-Mills (SYM) fortemente acoplado para calcular a viscosidade de cisalhamento perpendicular ao campo magnético e a viscosidade de cisalhamento paralela ao campo. Na presença do campo magnético, a viscosidade de cisalhamento perpendicular ao campo satura o limite viscoso de Kovtun-Son-Starinets enquanto que na direção paralela ao campo o limite é violado. O segundo tópico investigado nessa tese é motivado pelo estudo do comportamento próximo ao equilíbrio de plasmas não-Abelianos fortemente interagentes que exibem um ponto crítico em seus diagramas de fase. Focamos no espectro dos modos quasinormais não-hidrodinâmicos de um plasma N=4 SYM fortemente acoplado na presença de um potencial químico, que exibe um ponto crítico no equilíbrio. Exceto próximo ao ponto crítico, observamos que ao aumentar o potencial químico geralmente se intensifica a taxa de amortecimento dos modos quasinormais, que levam à redução dos tempos de equilibração característicos do plasma dual fortemente acoplado. Entretanto, aproximando-se do ponto crítico o tempo de equilibração típico aumenta embora sua derivada em relação ao potencial químico diverge com um expoente igual à -1/2. Encontramos também um modo não-hidrodinâmico puramente imaginário no canal de difusão vetorial com potencial químico não-nulo que dita o tempo de equilibração neste canal próximo do ponto crítico.
30
He, Hongtao. "Vertical transport properties of weakly-coupled Ac-driven GaAs/AlAs superlattices /." View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202006%20HE.
31
Breider, Thomas James. "Coupled halogen-sulfur-aerosol modelling in a 3D chemical transport model." Thesis, University of Leeds, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.535692.
32
Ippisch, Olaf [Verfasser]. "Coupled Transport in Natural Porous Media (2. rev. Ed.) / Olaf Ippisch." Heidelberg : Universitätsbibliothek Heidelberg, 2003. http://d-nb.info/1185583955/34.
33
Mouchliadis, Leonidas. "Transport and coherence properties of indirect excitions in coupled quantum wells." Thesis, Cardiff University, 2008. http://orca.cf.ac.uk/54724/.
Abstract:
This dissertation consists of a theoretical investigation into the transport and coherence properties of indirect excitons in coupled quantum wells (QWs) at helium temperatures. The motion of excitons along the quantum well plane is described through a quantum diffusion equation and the possibility of excitonic cloud formation is studied both due to the natural potential fluctuations and externally applied confining potentials. The photoluminescence (PL) of decaying excitons is used as a probe for their properties such as concentration, effective temperature and optical lifetime. The exciton thermalisation from an initial high energy to the lattice temperature is achieved within their lifetime due to a very effective coupling between the exciton states and a continuum of phonon states, a direct consequence of the relaxation of momentum conservation along the growth direction of a QW. Moreover, the natural spatial separation between electrons and holes prevents their recombination, resulting in long lifetimes. The dynamics of the system of excitons in optically-induced traps is also studied and the numerical solution of the quantum diffusion equation provides an insight into the extremely fast loading times of the trap with a highly degenerate exciton gas. The hierarchy of timescales in such a trap allows for the creation of a cold and dense gas confined within the trap, opening a new route towards the long sought Bose-Einstein Condensation (BEC) in solid state. Finally the issue of exciton spatial coherence is studied and an analytic expression for the coherence function, i.e., the measure of the coherence in a system, is derived. A direct comparison with large coherence lengths recently observed in systems of quantum well excitons and microcavity polaritons is attempted and interesting conclusions are drawn regarding the build up of spontaneous coherence in these systems.
34
Cherubini, Yvonne. "Influence of faults on the 3D coupled fluid and heat transport." Phd thesis, Universität Potsdam, 2013. http://opus.kobv.de/ubp/volltexte/2014/6975/.
Abstract:
Da geologische Störungen können als Grundwasserleiter, -Barrieren oder als gemischte leitende /stauende Fluidsysteme wirken. Aufgrund dessen können Störungen maßgeblich den Grundwasserfluss im Untergrund beeinflussen, welcher deutliche Veränderungen des tiefen thermischen Feldes bewirken kann. Grundwasserdynamik und Temperaturveränderungen sind wiederum entscheidende Faktoren für die Exploration geothermischer Energie.
Diese Studie untersuchte den Einfluss von Störungen auf das Fluidsystem und das thermische Feld im Untergrund. Sie erforschte die physikalischen Prozesse, welche das Fluidverhalten und die Temperaturverteilung in Störungen und in den umgebenden Gesteinen. Dazu wurden 3D Finite Elemente Simulationen des gekoppelten Fluid und Wärmetransports für synthetische sowie reale Modelszenarien auf unterschiedlichen Skalen durchgeführt.
Um den Einfluss einer schräg einfallenden Störung systematisch durch die schrittweise Veränderung der hydraulischen Öffnungsweite und der Permeabilität, zu untersuchen, wurde ein klein-skaliges synthetisches Modell entwickelt. Ein inverser linearer Zusammenhang wurde festgestellt, welcher zeigt, dass sich die Fluidgeschwindigkeit in der Störung jeweils um ~1e-01 m/s verringert, wenn die Öffnungsweite der Störung um jeweils eine Magnitude vergrößert wird. Ein hoher Permeabilitätskontrast zwischen Störung und umgebender Matrix begünstigt die Fluidadvektion hin zur Störung und führt zu ausgeprägten Druck- und Temperaturveränderungen innerhalb und um die Störung herum. Bei geringem Permeabilitätskontrast zwischen Störung und umgebendem Gestein findet hingegen kein Fluidfluss in der Störung statt, wobei das hydrostatische Druck- sowie das Temperaturfeld unverändert bleiben.
Auf Grundlage der synthetischen Modellierungsergebnisse wurde der Einfluss von Störungen auf einer größeren Skala anhand eines komplexeren (realen) geologischen Systems analysiert. Dabei handelt es sich um ein 3D Modell des Geothermiestandortes Groß Schönebeck, der ca. 40 km nördlich von Berlin liegt.
Die Integration von einer permeablen und drei impermeablen Hauptstörungen, zeigte unterschiedlich starke Einflüsse auf Fluidzirkulation, Temperatur – und Druckfeld. Die modellierte konvektive Zirkulation in der permeablen Störung verändert das thermische Feld stark (bis zu 15 K). In den gering durchlässigen Störungen wird die Wärme ausschließlich durch Diffusion geleitet. Der konduktive Wärmetransport beeinflusst das thermische Feld nicht, bewirkt jedoch lokale Veränderungen des hydrostatischen Druckfeldes.
Um den Einfluss großer Störungszonen mit kilometerweitem vertikalen Versatz auf das geothermische Feld der Beckenskala zu untersuchen, wurden gekoppelte Fluid- und Wärmetransportsimulationen für ein 3D Strukturmodell des Gebietes Brandenburg durchgeführt (Noack et al. 2010; 2013). Bezüglich der Störungspermeabilität wurden verschiedene geologische Szenarien modelliert, von denen zwei Endgliedermodelle ausgewertet wurden.
Die Ergebnisse zeigten, dass die undurchlässigen Störungen den Fluidfluss nur lokal beeinflussen. Da sie als hydraulische Barrieren wirken, wird der Fluidfluss mir sehr geringen Geschwindigkeiten entlang der Störungen innerhalb eines Bereichs von ~ 1 km auf jeder Seite umgelenkt. Die modellierten lokalen Veränderungen des Grundwasserzirkulationssystems haben keinen beobachtbaren Effekt auf das Temperaturfeld.
Hingegen erzeugen permeable Störungszonen eine ausgeprägte thermische Signatur innerhalb eines Einflussbereichs von ~ 2.4-8.8 km in -1000 m Tiefe und ~6-12 km in -3000 m Tiefe. Diese thermische Signatur, in der sich kältere und wärmere Temperaturbereiche abwechseln, wird durch auf- und abwärts gerichteten Fluidfluss innerhalb der Störung verursacht, der grundsätzlich durch existierende Gradienten in der hydraulischen Druckhöhe angetrieben wird.
Alle Studien haben gezeigt, dass Störungen einen beachtlichen Einfluss auf den Fluid-, und Wärmefluss haben. Es stellte sich heraus, dass die Permeabilität in der Störung und in den umgebenden geologischen Schichten so wie der spezifische geologische Rahmen entscheidende Faktoren in der Ausbildung verschiedener Wärmetransportmechanismen sind, die sich in Störungen entwickeln können.
Die von permeablen Störungen verursachten Temperaturveränderungen können lokal, jedoch groß sein, genauso wie die durch hydraulisch leitende und nichtleitende Störungen hervorgerufenen Veränderungen des Fluidystems.
Letztlich haben die Simulationen für die unterschiedlich skalierten Modelle gezeigt, dass die Ergebnisse sich nicht aufeinander übertragen lassen und dass es notwendig ist, jeden geologischen Rahmen hinsichtlich Konfiguration und Größenskala gesondert zu betrachten.
Abschließend hat diese Studie demonstriert, dass die Betrachtung von Störungen in 3D Finiten Elementen Modellen für die Simulation von gekoppeltem Fluid- und Wärmetransport auf unterschiedlichen Skalen möglich ist. Da diese Art von numerischen Simulationen sowohl die geologische Struktur des Untergrunds sowie die im Erdinnern ablaufenden physikalischen Prozesse integriert, können sie einen wertvollen Beitrag leisten, indem sie Feld- und Laborgestützte Untersuchungen vervollständigen.Faults can act as conduits, barriers or mixed conduit/barrier systems to fluid flow. Therefore, faults may significantly influence fluid flow regimes operating in the subsurface, possibly resulting in distinct variations of the deep thermal field. Both, flow dynamics and temperature changes are in turn crucial factors that need to be taken into account for geothermal energy exploration. This study investigated the influence of faults on the subsurface fluid system and thermal field and explored the processes controlling fluid behavior and thermal distribution both within host rocks and faults. For this purpose, 3D finite element simulations of coupled fluid and heat transport have been carried out, both for synthetic and real-case model scenarios on different scales. A small-scale synthetic model was developed to systematically assess the impact of an inclined fault by changing gradually its hydraulic width and its permeability within the simulations. An observed linear inverse relationship revealed that changing the fault width by one order of magnitude results in a fluid velocity decrease (~1e-01 m/s) within the fault. A high permeability contrast between fault and matrix favors fluid advection into the fault and leads to pronounced pressure and temperature changes in and around the same domain. When the permeability contrast between fault domain and host rock is low, however, no fluid flow is observed in the fault, thus resulting in undisturbed hydrostatic pressure and temperature fields. On the basis of these synthetic fault modelling results, the influence of faults on a larger scale have been analyzed within a more complex (real-case) geological setting,- a 3D model of the geothermal site Groß Schönebeck
located ~40 km north of Berlin. The integration of one permeable and three impermeable major faults, resulted in distinct changes observed in the local fluid circulation, thermal and pressure field. Modelled convective circulation within the permeable fault decisively modifies the thermal field (up to 15 K). Within the low permeable faults, heat is transferred only by conduction, inducing no thermal imprint but local deviations of the hydrostatic pressure field. To investigate the impact of major fault zones on the basin-scale geothermal field, coupled fluid and heat transport simulations have been conducted for a 3D structural model for Brandenburg region (Noack et al. 2010; 2013). Different geological scenarios in terms of modelled fault permeability have been carried out of which two end member models are analyzed. The results showed that tight fault zones affect the flow field locally. Acting as hydraulic barriers, fluid flow is deviated with very low velocities along them within a range of ~ 1 km on either sides. The modelled local changes in the groundwater circulation system have no considerable effect on the temperature field. By contrast, permeable fault zones induce a pronounced signature on the thermal field extending over a distance of ~ 2.4-8.8 km at -1000 m depth and ~6-12 km at -3000 m depth. This thermal signature, characterized by alternating cooler and hotter temperature domains, is controlled by up- and downward directed flow within the fault domain, principally driven by existing hydraulic head gradients. All studies demonstrated that faults have a considerable impact on the fluid and heat flow. The permeability in faults and surrounding geological layers as well as the specific geological setting turned out to be crucial factors in controlling the different kinds of heat transfer mechanisms that may evolve in faults. Temperature variations caused by permeable faults may be local but significant as well as changes in fluid dynamics by both conduits and barriers. Thus, the results demonstrated the importance to consider faults in geothermal energy exploration. In the final analysis, the simulations for the small-, regional- and basin-scale models showed that the outcomes cannot be transferred by upscaling and that it is necessary to consider each geological setting separately with respect to its configuration and scale dimension. In summary, this study demonstrated that the consideration of faults in 3D finite element models for coupled fluid and heat transport simulations on different scales is feasible. As these type of numerical simulations integrate both, the structural setting of the subsurface and the physical processes controlling subsurface transport, the outcomes of this thesis may provide positive contributions in that they valuably complement field- and laboratory-based investigations.
35
Dmytruk, Olesia. "Quantum transport in a correlated nanostructure coupled to a microwave cavity." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS335/document.
Abstract:
Dans cette thèse, nous étudions d’un point de vue théorique les propriétés physiques de nanostructures couplées à des cavités micro-ondes. L’électrodynamique quantique (QED) en cavité en présence d’une boîte quantique s’est révélée être une technique expérimentale puissante, permettant d'étudier cette dernière par des mesures photoniques en plus des mesures de transport électronique conventionnelles. Dans cette thèse, nous proposons d'utiliser le champ micro-ondes de la cavité afin d’extraire des informations supplémentaires sur les propriétés des conducteurs quantiques : le coefficient de transmission optique est directement lié à la susceptibilité électronique de ces conducteurs quantiques. Nous appliquons ce cadre général à différents systèmes mésoscopiques couplés à une cavité supraconductrice micro-ondes comme une jonction tunnel, une boîte quantique couplée à des réservoirs, un fil topologique et un anneau supraconducteur. La QED en cavité peut être utilisée pour sonder, par l'intermédiaire de mesures photoniques, la dépendance en fréquence de l’admittance du puits quantique couplé à la cavité micro-ondes. En ce qui concerne le fil topologique, nous avons montré que la cavité permet de caractériser la transition de phase topologique, l'émergence de fermions de Majorana, ainsi que la parité de l'état fondamental. Pour l'anneau supraconducteur, nous étudions par l'intermédiaire de la réponse optique de la cavité l’effet Josephson et le passage à l'effet Josephson fractionnaire, qui est associé à l'apparition de fermions de Majorana dans le système. Le cadre théorique proposé dans cette permet de sonder de manière non-invasive un large éventail de nanostructures, des boîtes quantiques aux supraconducteurs topologiques. En outre, il donne de nouvelles informations sur les propriétés de ces conducteurs quantiques, informations non accessibles via des expériences de transportIn this thesis, we study theoretically various physical properties of nanostructures that are coupledto microwave cavities. Cavity quantum electrodynamics (QED) with a quantum dot has been proven to be a powerful experimental technique that allows to study the latter by photonic measurements in addition to electronic transport measurements. In this thesis, we propose to use the cavity microwave field to extract additional information on the properties of quantum conductors: optical transmission coefficient gives direct access to electronic susceptibilities of these quantum conductors. We apply this general framework to different mesoscopic systems coupled to a superconducting microwave cavity, such as a tunnel junction, a quantum dot coupled to the leads, a topological wire and a superconducting ring. Cavity QED can be used to probe the finite frequency admittance of the quantum dot coupled to the microwave cavity via photonic measurements. Concerning the topological wire, we found that the cavity allows for determining the topological phase transition, the emergence of Majorana fermions, and also the parity of the ground state. For the superconducting ring, we propose to study the Josephson effect and the transition from the latter to the fractional Josephson effect, which is associated with the emergence of the Majorana fermions in the system, via the optical response of the cavity. The proposed framework allows to probe a broad range of nanostructures, including quantum dots and topological superconductors, in a non-invasive manner. Furthermore, it gives new information on the properties of these quantum conductors, which was not available in transport experiments
36
Sharma, Preeti. "Coupled electrokinetic fluxes in a single nanochannel for energy conversion." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAY100/document.
Abstract:
Les phénomènes électrocinétiques couplés au sein d'un nanocanal sont d'intérêt pour la conversion d'énergie et la production d'électricité reposant sur le mélange contrôlé d'eau douce et d'eau salée aussi appelée "énergie bleue". L'origine des phénomènes est lié à l'interaction avec des parois chargées et au transport d'ions au sein de ce qu'on nomme les couches de Debye. Ce travail vise à une meilleure compréhension de la physique et des phénomènes de transport dans ces couches dans le cadre de solutions confinées dans des nanocanaux.Une instrumentation spécifique a été développée pendant la thèse pour étudier les mécanismes qui gouvernent ces flux couplés. L'idée est de caractériser simultanément le transport de masse et le courant électrique au sein d'un nanocanal soumis à une différence de salinité de pression ou de tension électrique. Ce travail est divisé en trois parties.Dans la première partie, est décrite une cellule conçue pour la mesure et le contrôle de courant et tension électrique en présence de différence de pression ou de salinité au bornes d'un nanopores. L'utilisation de la cellule est illustrer dans le cas d'une membrane nanoporeuse de nafion.La seconde partie est focalisée sur une méthode simple de préparation d'un nanocanal directement connectable à un dispositif macroscopique. Le nanocanal, d'un micromètre de long, présente une géométrie conique, d'angle ajustable, et des extrémités équipées d'électrode déposées par pulvérisation cathodique.La troisième partie, concerne le développement d'une méthode pour la mesure directe de débit jusqu'à 10 pL/min s'écoulant au sein d'un nanocanal. Cette méthode combinée à une caractérisation électrique, pourra être utilisée, en présence de gradient de pression, de tension ou de salinité pour mesurer le débit et le courant électrique au sein d'un nanocanal de manière simultanée et indépendanteCoupled electrokinetic phenomena within nanochannel are of interest for energy harvestingand production of electricity based on the controlled mixing of river water with sea water known as "blue energy". The origin of the phenomena is related to interaction with charged walls and transport of ions within the so called Debye layer. This work aims at a better understanding of the physics and transport phenomena in this layer associated with solution confined in nanochannel.A specific instrumentation has been developed during this thesis to study the mechanisms governing coupled nanofluics fluxes. The idea is to characterize simultaneously the mass transport within the nanochannel and the electrical current driven through the nanochannel by the application of either salinity difference , pressure difference or voltage difference across the channel. The thesis is divided into three parts.In the first part, a custom made flow cell and experimental conditions to control and measure various fluxes is presented. The capability of cell to measure current or voltage under applied pressure or salinity gradient is presented taking the benefit of commercial nanoporous Nafion membrane.The second part is focused on an easy way of preparation of nanochannel sample in the form of single chip, in which nanochannel is interfaced to micro and macroscopic world. A well-controlled, 1.4µm long nanochannel of conical geometry with a maximum aspect ratio of 10 is fabricated. The minimum apex size of nanochannel achieved here is 50 nm which is about 30 times less than the length of channel. The presence of electrode directly at the interface of nano to micro cavity allow to perform electrical characterization of nanochannel with high precision.The third part of the thesis is devoted to the development of a method for the direct measurement of flow rate as low as 10 pL/min across a single nanochannel. This measurement approach combined with electrical measurement, could be used, in presence of pressure, voltage or salinity gradient, to measure the flow rate and the electrical current across a single nanochannel simultaneously and independently
37
Gatfield, Kelly. "Functional characterisation of mammalian Hâº-coupled amino acid transporters." Thesis, University of Newcastle Upon Tyne, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438398.
38
Kruse, Carola. "Regularity and approximation of a hyperbolic-elliptic coupled problem." Thesis, Brunel University, 2010. http://bura.brunel.ac.uk/handle/2438/5253.
Abstract:
In this thesis, we investigate the regularity and approximation of a hyperbolic-elliptic coupled problem. In particular, we consider the Poisson and the transport equation where both are assigned nonhomogeneous Dirichlet boundary conditions. The coupling of the two problems is executed as follows. The right hand side function of the Poisson equation is the solution ρ of the transport equation whereas the gradient field E = −∇u, with u being solution of the Poisson problem, is the convective field for the transport equation. The analysis is done throughout on a nonconvex, not simply connected domain that is supposed to be homeomorph to an annular domain. In the first part of this thesis, we will focus on the existence and uniqueness of a classical solution to this highly nonlinear problem using the framework of Hölder continuous functions. Herein, we distinguish between a time dependent and time independent formulation. In both cases, we investigate the streamline functions defined by the convective field E. These are used in the time dependent case to derive an operator equation whose fixed point is the streamline function to the gradient of the classical solution u. In the time independent setting, we formulate explicitly the solution operators L for the Poisson and T for the transport equation and show with a fixed point argument the existence and uniqueness of a classical solution (u,ρ). The second part of this thesis deals with the approximation of the coupled problem in Sobolev spaces. First, we show that the nonlinear transport equation can be formulated equivalently as variational inequality and analyse its Galerkin finite element discretization. Due to the nonlinearity of the coupled problem, it is necessary to use iterative solvers. We will introduce the staggered algorithm which is an iterative method solving alternating the Poisson and transport equation until convergence is obtained. Assuming that LοT is a contraction in the Sobolev space H1(Ω), we will investigate the convergence of the discrete staggered algorithm and obtain an error estimate. Subsequently, we present numerical results in two and three dimensions. Beside the staggered algorithm, we will introduce other iterative solvers that are based on linearizing the coupled problem by Newton’s method. We illustrate that all iterative solvers converge satisfactorily to the solution (u, ρ).
39
Offidani, Manuel. "Coupled charge-spin transport and spin-orbit phenomena in 2D Dirac materials." Thesis, University of York, 2018. http://etheses.whiterose.ac.uk/22769/.
Abstract:
The advent of 2D layered materials, boasting high-crystal quality and rich electronic properties, has provided a unique arena for exploring exotic condensed-matter phenomena, including the emergence of ultra-relativistic Dirac fermions in graphene, topological insulating phases in WS_{2}, long-lived excitons in group-VI dichalcogenides and unconventional superconductivity in twisted bilayer graphene. The enhancement of spin-orbit effects in heterointerfaces, built from the vertical stacking of different 2D layers, is recently attracting much attention. A series of crucial experiments have demonstrated the induction of strong spin-orbit effects in graphene sheets proximity-coupled to group-VI dichalcogenides. Owing to a combination of room-temperature spin transport over long distances and gate-tunable spin orbit interactions, such systems hold great promise for all-electrical generation and manipulation of spin currents, which is key to the realisation of the next generation of spintronics devices. To fully unlock the potential of 2D Dirac materials for spintronics, these recent experimental findings call for the formulation of a solid theoretical framework which can underpin them, but also-and more importantly-predict novel phenomena. This thesis aims to develop the foundations of such a framework, with a focus on spin dynamics and coupled charge-spin transport in 2D Dirac materials with strong proximity-induced interactions. A number of key results are established. We show that charge-to-spin interconversion in 2D Dirac materials can be understood in terms of exact symmetry relations (Ward identities). Depending on the specific spin-orbit interactions present in a 2D Dirac system, the symmetry relations dictate the relative contributions of the so-called spin-Hall effect (SHE) and inverse spin Galvanic effect (ISGE). In particular, for materials with interfacial breaking of mirror symmetry and unbroken (broken) sublattice symmetry, the SHE contribution is suppressed (sizable), whereas the ISGE contribution stays typically large and robust in both scenarios. The extrinsic SHE has its origin in a peculiar skew scattering mechanism-emerging from the non-coplanar spin texture of spin-orbit-coupled Dirac bands-and can be tuned by a gate voltage. We propose a diagrammatic approach to obtain the coupled charge/spin diffusion equations, as well as the spin relaxation times and the charge-to-spin interconversion rates. We supplement this study with a density matrix-based approach, allowing one to gain more insight into the delicate competition of the various energy scales present in realistic systems, and to calculate the spin relaxation time anisotropy of experimental relevance. Finally, we examine ferromagnetic 2D Dirac materials, through a unified theory of charge carrier transport combining semiclassical and fully-quantum mechanical approaches. We identify an experimental signature that characterises the crossover from the nonquantised anomalous Hall effect to the topologically-nontrivial quantum anomalous Hall effect, which can help future experimental efforts to unlock this fascinating quantum state of matter with Dirac fermions.
40
Beggs, Bruce Cameron. "Optical charge injection into a gallium arsenide acoustic charge transport device." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/26681.
Abstract:
There is a need for monolithic devices capable of spatial resolution in imaging and ionizing radiation detection. In this thesis, a GaAs acoustic charge transport device (ACT) was studied for this purpose. A new method of charge injection has been demonstrated for the ACT. Using near-infrared optical pulses incident through thin semi-transparent chromium windows, electron-hole-pairs were separated by the electric field in a depleted n-type channel region of the device. For light penetration less than the depth of the electron potential minimum, and for small injection levels, calculations indicated that electrons and holes were separated at their saturation velocities. Holes moving toward the surface of the substrate could recombine with electrons at an evaporated Schottky metal plate. Electrons moving toward the channel centre were bunched and transported by the electric field coupled to a <110> propagating surface acoustic wave (SAW) on (100) cut GaAs. Quantum efficiency, defined as the number of electrons collected at the output per incident photon on the GaAs surface, was greater than 9% at an optical wavelength of 730 nm. When compensation was made for the loss and
reflection due to the chromium windows, the quantum efficiency was in excess of 24%. Charge transfer efficiency was greater than 0.992 with the ACT clocked at 360 MHz. The demonstrated optical injection technique may be of use in future ACT imaging devices.Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate
41
Jevons, Mark Paul. "Expression and function of proton-coupled transporters in the mammalian intestine." Thesis, University of Newcastle Upon Tyne, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.531738.
42
Anderson, Catriona M. H. "Intestinal proton-coupled amino acid and dipeptide transporters : function and regulation." Thesis, University of Newcastle Upon Tyne, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398999.
43
Danzer, Jörg. "Surfactant transport and coupled transport of polycyclic aromatic hydrocarbons (PAHs) and surfactants in natural aquifer material - laboratory experiments." Tübingen : Universität Tübingen, 2005. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB12103792.
44
Shaffer, Nathaniel R. "Theory of collisional transport in ultracold neutral plasmas." Diss., University of Iowa, 2018. https://ir.uiowa.edu/etd/6638.
Abstract:
Ultracold neutral plasmas (UNP) are laboratory plasmas formed by the photoionization of a magneto-optically trapped and cooled gas. Because of their unusually low temperatures, UNPs are an example of a strongly coupled plasma, meaning that the potential energy of Coulomb interactions between particles is comparable to or greater than their thermal kinetic energy. In the field of strongly coupled plasmas, which also includes dense plasmas found in astrophysics and inertial confinement fusion experiments, there is a pressing need to better understand the collisional transport of matter, momentum, and energy between electrons and ions. The main result of this thesis is to demonstrate the existence of a new physical effect that significantly influences the electron-ion collision rates of strongly coupled plasmas. The essence of the effect is that the electron-ion collision rate depends explicitly on the sign of the colliding charges. This runs counter to both traditional plasma kinetic theory and modern extensions to strong coupling, all of which predict collision rates that do not depend on the sign of the electron-ion interaction. The effect is similar to a phenomenon observed charged-particle stopping known as the Barkas effect.
The existence of the Barkas effect in the electron-ion collision rate of strongly coupled plasmas is first demonstrated using molecular dynamics (MD) simulations. A non-equilibrium simulation methodology is developed to extract the electron-ion collision frequency from the relaxation of an induced electron drift velocity. The simulations are carefully designed to ensure that the relaxation process can be modeled with a constant relaxation rate, which facilitates comparison with theoretical predictions developed later in the thesis. The Barkas effect becomes apparent when these simulations are repeated with positrons in place of electrons. It is seen that the positron-ion collision rate is always lower than the equivalent electron-ion one, and that this charge-sign asymmetry widens rapidly with increasing electron (or positron) coupling strength.
It is hypothesized that the observed Barkas effect can be explained by accounting for plasma screening in the kinematics of binary electron-ion collisions. This is the main tenet of Effective Potential Theory (EPT), which assumes transport occurs through binary collisions governed by the potential of mean force. In order to apply EPT to electron-ion transport in UNPs, several new theoretical developments are made. First, it is demonstrated that EPT is able to accurately predict near-equilibrium transport in ionic mixtures as compared with equilibrium MD simulations. Next, a previously proposed model for the potentials of mean force in two-temperature positron-ion plasma is validated using a new two-thermostat MD methodology. Finally, EPT is applied to electron-ion transport in UNPs using a semi-analytic mapping between a two-component plasma and a screened one-component plasma system, which alleviates numerical difficulties in the theory associated with attractive interactions. The EPT predictions for the electron-ion and positron-ion relaxation rates are in excellent agreement with the MD simulations over the range of coupling strengths attained in present-day UNP experiments. EPT is thus shown to be the first transport theory for strongly coupled plasmas that accounts for the close-interaction physics that give rise to the Barkas effect in electron-ion transport.
45
Park, HyeongKae. "Coupled Space-Angle Adaptivity and Goal-Oriented Error Control for Radiation Transport Calculations." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/13944.
Abstract:
This research is concerned with the self-adaptive numerical solution of the neutral particle radiation transport problem. Radiation transport is an extremely challenging computational problem since the governing equation is seven-dimensional (3 in space, 2 in direction, 1 in energy, and 1 in time) with a high degree of coupling between these variables. If not careful, this relatively large number of independent variables when discretized can potentially lead to sets of linear equations of intractable size. Though parallel computing has allowed the solution of very large problems, available computational resources will always be finite due to the fact that ever more sophisticated multiphysics models are being demanded by industry. There is thus the pressing requirement to optimize the discretizations so as to minimize the effort and maximize the accuracy.
One way to achieve this goal is through adaptive phase-space refinement. Unfortunately, the quality of discretization (and its solution) is, in general, not known a priori; accurate error estimates can only be attained via the a posteriori error analysis. In particular, in the context of the finite element method, the a posteriori error analysis provides a rigorous error bound. The main difficulty in applying a well-established a posteriori error analysis and subsequent adaptive refinement in the context of radiation transport is the strong coupling between spatial and angular variables. This research attempts to address this issue within the context of the second-order, even-parity form of the transport equation discretized with the finite-element spherical harmonics method.
The objective of this thesis is to develop a posteriori error analysis in a coupled space-angle framework and an efficient adaptive algorithm. Moreover, the mesh refinement strategy which is tuned for minimizing the error in the target engineering output has been developed by employing the dual argument of the problem. This numerical framework has been implemented in the general-purpose neutral particle code EVENT for assessment.
46
Graf, Thomas. "Modeling coupled thermohaline flow and reactive solute transport in discretely-fractured porous media." Thesis, Québec : Université Laval, 2005. http://www.theses.ulaval.ca/2005/23197/23197.pdf.
47
Chen, Rong. "Coupled electrochemical and heat/mass transport characteristics in passive direct methanol fuel cells /." View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?MECH%202007%20CHEN.
48
Härtle, Rainer [Verfasser], and Michael [Akademischer Betreuer] Thoss. "Vibrationally Coupled Electron Transport through Single-Molecule Junctions / Rainer Härtle. Betreuer: Michael Thoss." Erlangen : Universitätsbibliothek der Universität Erlangen-Nürnberg, 2012. http://d-nb.info/1023597462/34.
49
Stewart, Andrew Kenneth. "Intracellular pH regulation associated with proton-coupled dipeptide transport in mouse small intestine." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298321.
50
Link, Percy Anne. "Improving parameterization of scalar transport through vegetation in a coupled ecosystem-atmosphere model." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/43884.
Abstract:
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2008.Includes bibliographical references (p. 90-93).
Several regional-scale ecosystem models currently parameterize subcanopy scalar transport using a rough-wall boundary eddy diffusivity formulation. This formulation predicts unreasonably high soil evaporation beneath tall, dense forests and low soil evaporation beneath short, sparse grass. This study investigates alternative formulations by reviewing literature on flow and scalar transport in canopies, taking field measurements of subcanopy latent heat flux, and testing alternative model formulations in constrained numerical experiments. A field campaign was conducted in a dense rainforest in Luquillo National Forest, Puerto Rico, to measure wind and fluxes with eddy covariance devices. Wind velocities and fluxes of latent heat, sensible heat, and momentum were found to be much smaller below the canopy than above it. Modeling experiments tested a mixing-layer-based formulation of eddy diffusivity and a soil evaporation cutoff based on vortex penetration depth. The vortex penetration cutoff was found to be the most physically accurate and computationally simple option, and this study recommends that ecosystem and land-surface models adopt this formulation for subcanopy scalar transport.
by Percy Anne Link.
M.Eng.