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Garcia, Ramos Aguilar Felipe. "Mass transport and geometric inequalities." Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/29637.
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In this thesis we will review some recent results of Optimal Mass Transportation emphasizing on the role of displacement interpolation and displacement
convexity. We will show some of its recent applications, specially the ones by Bernard, and Agueh-Ghoussoub-Kang.
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Odell, Anders. "Quantum transport and geometric integration for molecular systems." Doctoral thesis, KTH, Tillämpad materialfysik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-26780.
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Molecular electronics is envisioned as a possible next step in device miniaturization. It is usually taken to mean the design and manufacturing of electronic devices and applications where organic molecules work as the fundamental functioning unit. It involves the measurement and manipulation of electronic response and transport in molecules attached to conducting leads. Organic molecules have the advantages over conventional solid state electronics of inherent small sizes, endless chemical diversity and ambient temperature low cost manufacturing. In this thesis we investigate the switching and conducting properties of photoswitching dithienylethene derivatives. Such molecules change their conformation in solution when acted upon by light. Photochromic molecules are attractive candidates for use in molecular electronics because of the switching between different states with different conducting properties. The possibility of optically controlling the conductance of the molecule attached to conducting leads may lead to new device implementations. The switching reaction is investigated with potential energy calculations for different values of the reaction coordinate between the closed and the open isomer. The electronic and atomic structure calculations are performed with Density Functional Theory (DFT). The potential energy barrier separating the open and closed isomer is investigated, as well as the nature of the excited states involved in the switching. The conducting properties of the molecule inserted between gold, silver and nickel leads is calculated within the Non Equilibrium Green Function theory (NEGF). The molecule is found to be a good conductor in both conformations, with the low-bias current for the closed one being about 20 times larger than that of the open in the case of gold contacts, and over 30 times larger in the case of silver contacts. For the Ni leads the current for the closed isomer is almost 40 times larger than that of the open. Importantly, the current-voltage characteristics away from the linear response is largely determined by molecular orbital re-hybridization in an electric field, in close analogy to what happens for Mn12 molecules. However in the case of dithienylethene attached to Au and Ag such a mechanism is effective also in conditions of strong electronic coupling to the electrodes. In reality these molecules are in constant motion, and the dynamical properties has to be considered. In this thesis such a line of work is initiated. In order to facilitate efficient and stable dynamical simulations of molecular systems the extended Lagrangian formulation of Born-Oppenheimer molecular dynamics have been implemented in two different codes. The extended Lagrangian framework enables the geometric integration of both the nuclear and electronic degrees of freedom. This provides highly efficient simulations that are stable and energy conserving even under incomplete and approximate self-consistent field (SCF) convergence. In the density functional theory code FreeON, different symplectic integrators up to the 6th order have been adapted and optimized. It is shown how the accuracy can be significantly improved compared to a conventional Verlet integration at the same level of computational cost, in particular for the case of very high accuracy requirements. Geometric integration schemes, including a weak dissipation to remove numerical noise, are developed and implemented in the self-consistent tight-binding code LATTE. We find that the inclusion of dissipation in the symplectic integration methods gives an efficient damping of numerical noise or perturbations that otherwise may accumulate from finite arithmetics in a perfect reversible dynamics. The modification of the integration breakes symplecticity and introduces a global energy drift. The systematic driftin energy and the broken symplecticity can be kept arbitrarily small without significant perturbations of the molecular trajectories.QC 20101202
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Teo, Chi-yan Jeffrey. "Geometric phase and spin transport in quantum systems." Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/hkuto/record/B38226571.
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朱詩亮 and Shiliang Zhu. "Geometric phase and quantum transport in mesoscopic systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B3014775X.
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Teo, Chi-yan Jeffrey, and 張智仁. "Geometric phase and spin transport in quantum systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B38226571.
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Zhu, Shiliang. "Geometric phase and quantum transport in mesoscopic systems." Hong Kong : University of Hong Kong, 2001. http://sunzi.lib.hku.hk/hkuto/record.jsp?B22956268.
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Carr, Andrew Newberry. "Geometric Extensions of Neural Processes." BYU ScholarsArchive, 2020. https://scholarsarchive.byu.edu/etd/8394.
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Neural Processes (NPs) are a class of regression models that learn a map from a set of input-output pairs to a distribution over functions. NPs are computationally tractable and provide a number of benefits over traditional nonlinear regression models. Despite these benefits, there are two main domains where NPs fail. This thesis is focused on presenting extensions of the Neural Process to these two areas. The first of these is the extension of Neural Processes graph and network data which we call Graph Neural Processes (GNP). A Graph Neural Process is defined as a Neural Process that operates on graph data. It takes spectral information from the graph Laplacian as inputs and then outputs a distribution over values. We demonstrate Graph Neural Processes in edge value imputation and discuss benefits and drawbacks of the method for other application areas. The second extension of Neural Processes comes in the fundamental training mechanism. NPs are traditionally trained using maximum likelihood, a probabilistic technique. We show that there are desirable classes of problems where NPs fail to learn. We also show that this drawback is solved by using approximations of the Wasserstein distance. We give experimental justification for our method and demonstrate its performance. These Wasserstein Neural Processes (WNPs) maintain the benefits of traditional NPs while being able to approximate new classes of function mappings.
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Naik, Shibabrat. "Geometric Approaches in Phase Space Transport and Partial Control of Escaping Dynamics." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/73364.
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This dissertation presents geometric approaches of understanding chaotic transport in phase space that is fundamental across many disciplines in physical sciences and engineering. This approach is based on analyzing phase space transport using boundaries and regions inside these boundaries in presence of perturbation.
We present a geometric view of defining such boundaries and study the transport that occurs by crossing such phase space structures. The structure in two dimensional non-autonomous system is the codimension 1 stable and unstable manifolds associated with the hyperbolic fixed points. The manifolds separate regions with varied dynamical fates and their time evolution encodes how the initial conditions in a given region of phase space get transported to other regions. In the context of four dimensional autonomous systems, the corresponding structure is the stable and unstable manifolds of unstable periodic orbits which reside in the bottlenecks of energy surface. The total energy and the cylindrical (or tube) manifolds form the necessary and sufficient condition for global transport between regions of phase space.
Furthermore, we adopt the geometric view to define escaping zones for avoiding transition/escape from a potential well using partial control. In this approach, the objective is two fold: finding the minimum control that is required for avoiding escape and obtaining discrete representation called disturbance of continuous noise that is present in physical sciences and engineering. In the former scenario, along with avoiding escape, the control is constrained to be smaller than the disturbance so that it can not exactly cancel out the disturbances.Ph. D.
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Gumede, Sthembiso R. "Translocation of a polymer chain under geometric confinement." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/86630.
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Thesis (MSc)--Stellenbosch University, 2014.ENGLISH ABSTRACT: The advent of the synthesis or manufacturing of controlled structures on submicron scales as well as experimental developments enabling the investigation of physics in speci c biological systems at extremely small length scales underlines the need for dealing with the statistical physics of small systems which are geometrically con ned. A typical example of a system for which physical questions can be answered by means of theoretical modelling is the virus, where polymer genetic material is encapsulated in a protein shell. In this project the role of con nement on polymer chains will be investigated. We investigate how the translocation of polymer from one region to another through a small opening depends on various electrolytic, polymer concentration and wall interaction conditions. This is an extension of the simple, purely entropic, picture in that the interaction terms enter the picture. We employ a variational scheme in deriving our results.
AFRIKAANSE OPSOMMING: Sowel die moontlikheid van beheerbare sintese of vervaardiging van strukture op sub-mikrometer lengteskale asook die koms van eksperimentele metodes vir die ondersoek van biologiese stelsels op baie klein lengteskale onderstreep hoe nodig dit is om die statiestiese sika van klein stelsels met geometriese beperkings te verstaan. 'n Tipiese voorbeeld waar teoretiese metodes vir siese vrae aangewend word is 'n virus, waar die polimeriese genetiese materiaal in 'n proteïen skil beweeg. In die huidge projek word die rol van 'n spesi eke geometriese beperking op polimeerkettings ondersoek. Ons ondersoek hoe die oorplasing van 'n polimeer deur 'n klein opening van een gebied na die ander deur verskillende elektrolietiese, polimeer-konsentrasie en wandinteraksie eienskappe afhang. Dit is 'n uitbreiding van die eenvoudige, volledig entropiese beeld vir oorplasing deurdat wisselwerkings ingesluit word. 'n Variasiebeginsel word aangewend om die resultate af te lei.
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Gregory, Simon. "The geometric correction and registration of airborne line-scanned imagery for temporal thermal studies." Thesis, Aston University, 2001. http://publications.aston.ac.uk/14142/.
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This thesis begins by providing a review of techniques for interpreting the thermal response at the earth's surface acquired using remote sensing technology. Historic limitations in the precision with which imagery acquired from airborne platforms can be geometrically corrected and co-registered has meant that relatively little work has been carried out examining the diurnal variation of surface temperature over wide regions. Although emerging remote sensing systems provide the potential to register temporal image data within satisfactory levels of accuracy, this technology is still not widely available and does not address the issue of historic data sets which cannot be rectified using conventional parametric approaches. In overcoming these problems, the second part of this thesis describes the development of an alternative approach for rectifying airborne line-scanned imagery. The underlying assumption that scan lines within the imagery are straight greatly reduces the number of ground control points required to describe the image geometry. Furthermore, the use of pattern matching procedures to identify geometric disparities between raw line-scanned imagery and corresponding aerial photography enables the correction procedure to be almost fully automated. By reconstructing the raw image data on a truly line-by-line basis, it is possible to register the airborne line-scanned imagery to the aerial photography with an average accuracy of better than one pixel. Providing corresponding aerial photography is available, this approach can be applied in the absence of platform altitude information allowing multi-temporal data sets to be corrected and registered.
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Anduwan, Gabriel A. Y. "Electron transport in semiconductor nanoconstrictons with and without an impurity in the channel." Virtual Press, 1998. http://liblink.bsu.edu/uhtbin/catkey/1115422.
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The development of electronics has been growing at a fast rate in recent years. More and more ideas have been searched and are increasing at a faster rate. However, there is more detail work in the nanolevel or nanostructure yet to be understood. Thus, more and more semiconductor physicists have move to the new field of study in nanostructures. Nanostructures are the future of electronic devices. By understanding nanostructure electronic devices, electronics is the key for the progress of any modern equipment and advancement. This comes about when electronic transport of a nanostructure is thoroughly understood. Thus, future electronic devices can utilize the development of conductance through components having dimensions on the nanometer scale.The objective of the proposed research project is to study electronic transport in a ring with an infinite potential barrier at the center and a modulated external potential in one of the arms. The relative phase between the two paths in this structure can be controlled by applying electrostatic potential in one of the arms. One can compare these types of systems with optical interferometers, where the phase difference between the two arms is controlled by changing the refractive index of one arm through the electro-optic effect. By modulating the potential in one arm of the ring, we will study the interference effect on conductance. The method of finding the conductance of a nanostructure will be using the recursive Green's function method. This includes finding transverse eigenvalues, eigenfunctions, and hopping integrals to determine Green's propagators. A FORTRAN 77 computer program is used for numerical calculations.These remarkable ultra-small and ultra-clean quantum systems are currently achieved due to significant technological advancement in fabrication. For ultra-small quantum devices, the theoretical understanding of device performance must be based on quantum carrier transport of confined electrons and holes in the channel. This theoretical research will lead to the understanding of the effects of geometry and impurities on transport of the carriers in the nanochannels.Department of Physics and Astronomy
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Pegon, Paul. "Transport branché et structures fractales." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS444/document.
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Cette thèse est consacrée à l’étude du transport branché, de problèmes variationnels qui y sont liés et de structures fractales qui peuvent y apparaître. Le problème du transport branché consiste à connecter deux mesures de même masse par le biais d’un réseau en minimisant un certain coût, qui sera pour notre étude proportionnel à mLα afin de déplacer une masse m sur une distance L. Plusieurs modèles continus ont été proposés pour formuler le problème, et on s’intéresse plus particulièrement aux deux grands types de modèles statiques : le modèle Lagrangien et le modèle Eulérien, avec une emphase sur le premier. Après avoir posé proprement les bases de ces modèles, on établit rigoureusement leur équivalence en utilisant une décomposition de Smirnov des mesures vectorielles à divergence mesure. On s’intéresse par la suite à un problème d’optimisation de forme lié au transport branché qui consiste à déterminer les ensembles de volume 1 les plus proches de l’origine au sens du transport branché. On démontre l’existence d’une solution, décrite comme un ensemble de sous-niveau de la fonction paysage, désormais standard en transport branché. La régularité Hölder de la fonction paysage, obtenue ici sans hypothèse de régularité a priori sur la solution considérée, permet d’obtenir une borne supérieure sur la dimension de Minkowski de son bord, qui est non-entière et dont on conjecture qu’elle en est la dimension exacte. Des simulations numériques, basées sur une approximation variationnelle à la Modica-Mortola de la fonctionnelle du transport branché, ont été effectuées dans le but d’étayer cette conjecture. Une dernière partie de la thèse se concentre sur la fonction paysage, essentielle à l’étude de problèmes variationnels faisant intervenir le transport branché en ce sens qu’elle apparaît comme une variation première du coût d’irrigation. Le but est d’étendre sa définition et ses propriétés fondamentales au cas d’une source étendue, ce à quoi l’on parvient dans le cas d’un réseau possédant un système fini de racines, par exemple pour des mesures à supports disjoints. On donne une définition satisfaisante de la fonction paysage dans ce cas, qui vérifie en particulier la propriété de variation première et on démontre sa régularité Hölder sous des hypothèses raisonnables sur les mesures à connecterThis thesis is devoted to the study of branched transport, related variational problems and fractal structures that are likely to arise. The branched transport problem consists in connecting two measures of same mass through a network minimizing a certain cost, which in our study will be proportional to mLα in order to move a mass m over a distance L. Several continuous models have been proposed to formulate this problem, and we focus on the two main static models : the Lagrangian and the Eulerian ones, with an emphasis on the first one. After setting properly the bases for these models, we establish rigorously their equivalence using a Smirnov decomposition of vector measures whose divergence is a measure. Secondly, we study a shape optimization problem related to branched transport which consists in finding the sets of unit volume which are closest to the origin in the sense of branched transport. We prove existence of a solution, described as a sublevel set of the landscape function, now standard in branched transport. The Hölder regularity of the landscape function, obtained here without a priori hypotheses on the considered solution, allows us to obtain an upper bound on the Minkowski dimension of its boundary, which is non-integer and which we conjecture to be its exact dimension. Numerical simulations, based on a variational approximation a la Modica-Mortola of the branched transport functional, have been made to support this conjecture. The last part of the thesis focuses on the landscape function, which is essential to the study of variational problems involving branched transport as it appears as a first variation of the irrigation cost. The goal is to extend its definition and fundamental properties to the case of an extended source, which we achieve in the case of networks with finite root systems, for instance if the measures have disjoint supports. We give a satisfying definition of the landscape function in that case, which satisfies the first variation property and we prove its Hölder regularity under reasonable assumptions on the measures we want to connect
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Ferrari, Luca Alberto Davide. "Approximations par champs de phases pour des problèmes de transport branché." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLX049/document.
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Dans cette thèse, nous concevons des approximations par champ de phase de certains problèmes de Transport Branché. Le Transport Branché est un cadre mathématique pour modéliser des réseaux de distribution offre-demande qui présentent une structure d'arbre. En particulier, le réseau, les usines d'approvisionnement et le lieu de la demande sont modélisés en tant que mesures et le probléme est présenté comme un probléme d'optimisation sous contrainte. Le coût de transport d'une masse m le long d'un bord de longueur L est h(m)xL et le coût total d'un réseau est défini comme la somme de la contribution sur tous ses arcs. Le cas du Transport Branché correspond avec la choix h(m) =|m|^α où α est dans [0,1). La sous-additivité de la fonction cout s'assure que déplacer deux masses conjointement est moins cher que de le faire séparément. Dans ce travail, nous introduisons diverses approximations variationnelles du problème du transport branché. Les fonctionnelles que on vais utiliser sont basées sur une représentation par champ de phase du réseau et sont plus lisses que le problème original, ce qui permet des méthodes d'optimisation numérique efficaces. Nous introduisons une famille des fonctionnelles inspirées par le fonctionnelle de Ambrosio et Tortorelli pour modéliser une fonction de coût h affine dans l'espace R^2. Pour ce cas, nous produisons un résultat complet de Gamma-convergence et nous le corrélons avec une procédure de minimisation alternée pour obtenir des approximations numériques des minimiseurs. Puis nous généralisons cette approche à n'importe quel espace R^n et obtenons un résultat complet de $Gamma$-convergence dans le cas de surfaces k-dimensionnelles avec kIn this thesis we devise phase field approximations of some Branched Transportation problems. Branched Transportation is a mathematical framework for modeling supply-demand distribution networks which exhibit tree like structures. In particular the network, the supply factories and the demand location are modeled as measures and the problem is cast as a constrained optimization problem. The transport cost of a mass m along an edge with length L is h(m)xL and the total cost of a network is defined as the sum of the contribution on all its edges. The branched transportation case consists with the specific choice h(m)=|m|^α where α is a value in [0,1). The sub-additivity of the cost function ensures that transporting two masses jointly is cheaper than doing it separately. In this work we introduce various variational approximations of the branched transport optimization problem. The approximating functionals are based on a phase field representation of the network and are smoother than the original problem which allows for efficient numerical optimization methods. We introduce a family of functionals inspired by the Ambrosio and Tortorelli one to model an affine transport cost functions. This approach is firstly used to study the problem any affine cost function h in the ambient space R^2. For this case we produce a full Gamma-convergence result and correlate it with an alternate minimization procedure to obtain numerical approximations of the minimizers. We then generalize this approach to any ambient space and obtain a full Gamma-convergence result in the case of k-dimensional surfaces. In particular, we obtain a variational approximation of the Plateau problem in any dimension and co-dimension. In the last part of the thesis we propose two models for general concave cost functions. In the first one we introduce a multiphase field approach and recover any piecewise affine cost function. Finally we propose and study a family of functionals allowing to recover in the limit any concave cost function h
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Louet, Jean. "Problèmes de transport optimal avec pénalisation en gradient." Phd thesis, Université Paris Sud - Paris XI, 2014. http://tel.archives-ouvertes.fr/tel-01070163.
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Le problème du transport optimal, originellement introduit par Monge au 18ème siècle, consiste à minimiser l'énergie nécessaire au déplacement d'une masse dont la répartition est donnée vers une autre masse dont la répartition est elle aussi donnée; mathématiquement, cela se traduit par : trouver le minimiseur de l'intégrale de c(x,T(x)) (où c est le coût de transport de x vers T(x)) parmi toutes les applications T à mesure image prescrite.Cette thèse est consacrée à l'étude de problèmes variationnels similaires où l'on fait intervenir la matrice jacobienne de la fonction de transport, c'est-à-dire que le coût dépend de trois variables c(x,T(x),DT(x)) ; il s'agit typiquement de rajouter l'intégale de |DT(x)|^2 à la fonctionnelle afin d'obtenir une pénalisation Sobolev. Ce type de problème trouve ses motivations en mécanique des milieux continus, élasticité incompressible ou en analyse de forme et appelle d'un point de vue mathématique une approche totalement différente de celle du problème de transport usuel.Les questions suivantes sont envisagées :- bonne définition du problème, notamment de l'énergie de Dirichlet, via les espaces de Sobolev par rapport à une mesure, et résultats d'existence de minimiseurs ;- caractérisation de ces minimiseurs : optimalité du transport croissant sur la droite réelle, et approche du type équation d'Euler-Lagrange en dimension quelconque ;- sélection d'un minimiseur via une procédure de pénalisation du type Gamma-convergence (l'énergie de Dirichlet est mutipliée par un petit paramètre) lorsque le coût de transport est le coût de Monge donné par la distance, pour lequel l'application de transport optimale n'est pas unique ;- autres approches du problème et perspectives : formulation dynamique du type Benamou-Brenier, et formulation duale similaire à celle de Kantorovitch dans le cas du problème du transport optimal usuel.
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Juknevičiūtė, Lina. "Visuomeninio transporto sustojimų geometrinių parametrų ir apkrovų analizė." Master's thesis, Lithuanian Academic Libraries Network (LABT), 2004. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2004~D_20040625_100049-85282.
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The vehicles of public transport serve big and small places and town for the work quality of public transport that belong to people job and their rest. On purpose to secure safety and good organized traffic, satisfying the requirements of passengers, so the stops of public transport are constructing in respective places.The pavement constructions of public transport (bus and trolleybus) stops are sway under the special loads. So theirs planning and construction demands on keeping particular requirements and regulations.This research work gives the analysis of the effect of geometric parameters of public transport stops on their pavement stability, the analysis of agent loads to pavement constructions of stops in Vilnius city, the strength measurements are accomplished of pavement constructions.In the end of thesis are represented the conclusions and recommendations.
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Tang, Shengjie. "Traffic safety analysis for cyclists at roundabouts, a case study in Norrköping." Thesis, Linköpings universitet, Kommunikations- och transportsystem, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-149424.
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Cyclists as vulnerable road users are oftentimes unprotected with exposed human body, can fall easily and sustain serious injuries when encountered collisions, especially with motorists. At roundabouts, accident reduction rate for cyclists is rather uncertain or sometimes less favorable compared to other road users (e.g. motorists, pedestrians). This thesis focuses on advancing the understanding of traffic safety issues for cyclists at roundabouts by identifying concerns faced by cyclists and evaluating their designs to find out which configuration has high or higher safety level towards cyclists. The research approach adopted in this work includes a wide review of relevant literature on cyclist safety and roundabouts and the implementation of empirical research, the latter was carried out through a Case Study in Norrköping city by obtaining cyclist related accident data from Swedish Traffic Accident Data Acquisition database to identify roundabouts with high cyclist-related accidents in the city assisted with PTV Visum Safety tool and fetching traffic volume from city network model operated by Norrköping Municipality for each identified roundabout. The main findings from this research conclude that single-lane roundabouts with separated cycle paths in high traffic volume setting provide better or higher safety performance for cyclists compared to other roundabout configurations.
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Kloeckner, Benoît. "Géométrie des variétés, des espaces de mesures et des espaces de sous-groupes." Habilitation à diriger des recherches, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00785679.
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Ce mémoire présente des résultats dans trois directions. En géométrie riemannienne, on montre une généralisation de l'inégalité de Günther sur le volume, et en dimension 4 une inégalité isopérimétrique pour les variétés à courbure majorée. En géométrie des espaces de Wasserstein, issus du transport optimal, on montre des résultats plongement et de non-plongement, on calcule des groupes d'isométries, et on étudie la dynamique de l'action sur les mesures des applications dilatantes du cercle. En topologie de Chabauty, on montre que l'espace des sous-groupes fermés de $R^n$ est simplement connexe.
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Albuquerque, Roberta Rodrigues. "Cálculo estocástico e transporte paralelo." [s.n.], 2010. http://repositorio.unicamp.br/jspui/handle/REPOSIP/306333.
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Orientador: Pedro José CatuognoDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Matemática, Estatística e Computação Científica
Made available in DSpace on 2018-08-16T07:50:09Z (GMT). No. of bitstreams: 1 Albuquerque_RobertaRodrigues_M.pdf: 577918 bytes, checksum: 382f6bfc15bbbcfa2efbd32b5ec398e7 (MD5) Previous issue date: 2010
Resumo: Neste trabalho estamos interessados no transporte paralelo da geometria diferencial no contexto do cálculo estocástico. Inicialmente resumimos os pontos fundamentais da geometria riemmaniana como as idéias de conexão, curvatura, transporte paralelo, a identidade de Bochner-Weitenböck e o mapa de desenvolvimento de Cartan, em seguida desenvolvemos alguns resultados da geometria estocástica como a fórmula geométrica de Itô, mas para isto inserimos brevemente a chamada geometria de segunda ordem. Ao final, examinaremos o transporte paralelo estocástico em algumas circunstâncias como no mapa de desenvolvimento estocástico, mapa de rolamento estocástico, construção do movimento Browniano em variedades e ainda com fluxos estocásticos na solução da equação de Stratonovich
Abstract: This dissertation is about the stochastic version of the parallel translation in the differential geometry. In the beginning it provides some basic background to Riemannian geometry, for example, the definiton of conexion, curvature, parallel translation, the Bochner-Weitenböck identity and the Cartan's rolling map theorem. After that, it is to dedicate to development of some results on stochastic geometry as the geometric Itô formula, but to do that it is important to study the second order geometry. In the end, it is essential to give attention to stochastic parallel transport in some environment as the Cartan's rolling map in the stochastic context, stochastic rolling constuctions, Brownian motion on manifolds and the stochastic flow as the solution of the Stratonovich equation
Mestrado
Geometria Estocastica
Mestre em Matemática
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Ford, John T. "Solids transport in complex annular geometries." Thesis, Heriot-Watt University, 1997. http://hdl.handle.net/10399/676.
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Kremer, Friedrich, Martin Treß, Emmanuel U. Mapesa, Wycliffe K. Kipnusu, and Wilhelm Kossack. "Glassy dynamics of polymers in geometrical confinement." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-182180.
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Agliari, Elena, Raffaella Burioni, Davide Cassi, and Franco M. Neri. "Autocatalytic reaction-diffusion processes in restricted geometries." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-192966.
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Martens, Steffen. "Transport of Brownian particles in confined geometries." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2013. http://dx.doi.org/10.18452/16764.
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Ziel dieser Arbeit ist es die Fick-Jacobs Näherung, welche eine genaue Beschreibung zahlreiche Transporteigenschaften von Brownschen Teilchen in räumlich beschränkten Geometrien liefern kann, auf experimentell vorherrschende Gegebenheiten, z.B., sich stark ändernde Geometrien, komplizierte Kraftfelder, Teilchenausdehnung und endliche viskose Reibung, zu erweitern. Dazu wird zuerst die exakte Lösung für die stationäre Wahrscheinlichkeitsdichte mittels Entwicklung in einem geometrischen Parameter, der die Kanalmodulation misst, berechnet. Die höheren Entwicklungsterme ermöglichen die Berechnung von Korrekturen zu den Transportkoeffizienten für sich stark ändernde Geometrien. Ferner kann die Fick-Jacobs Näherung mittels der Entwicklungsmethode auf beliebige Kraftfelder verallgemeinert werden. Am Beispiel des mikrofluidischen Kanals zeigen wir, dass das Zusammenspiel von externen Kräften (skalare Potentiale) und Strömungen (Vektorpotentiale) zur effizienten Trennung von Objekten, mittels des Effektes des hydrodynamisch induzierten entropischen Einsperrens, genutzt werden kann. Da das effiziente Sortieren nach Größe eine der wichtigsten Ziele in der Grundlagenforschung ist, zeigen wir wie die Teilchenausdehnung in die Fick-Jacobs Näherung integriert werden kann. Abschließend wird der Einfluss der Mediumsviskosität auf den Teilchentransport untersucht. Wenn die Zeitskalen separieren, führt adiabatische Eliminierung auch für endliche Reibung zu einer Fick-Jacobs ähnlichen Beschreibung. Diese ist unweigerlich mit Energiegleichverteilung und mit verschwindender Geschwindigkeitskorrelation verbunden. Numerische Simulationen zeigen, dass diese Beschreibung für moderate bis starke Dämpfung und schwache externe Kräfte akkurat ist. Für starke Kräfte wird die angenommene Energiegleichverteilung infolge von Teilchen-Wand Kollisionen verletzt. Dies führt zu einer nichtlinearen Abhängigkeit der Teilchengeschwindigkeit und des effektiven Diffusionskoeffizienten von der Kraftstärke.This work intends to show how experimentally relevant issues such as strong channel corrugation, sophisticated external force fields, particle size, and the solvent''s viscosity can be incorporated into the commonly used Fick-Jacobs approach which provides a powerful tool to capture many properties of Brownian particles'' transport in confined geometries. First, we derive exact solutions of the stationary probability distribution in terms of an expansion parameter specifying the channel corrugation. Thereby, the leading order is equivalent to the Fick-Jacobs approach. By means of higher expansion orders, which become significant for strong channel corrugation, we obtain corrections to the key particle transport quantities. Going one step further, we generalize the Fick-Jacobs approach to the most general forces. As an exemplary application, we consider microfluidic devices in which the interplay of conservative forces and pressure-driven flows (vector potentials) offers a unique opportunity to efficiently separate Brownian particles of the same size using the newly discovered effect of hydrodynamically enforced entropic trapping. Since separation and sorting by size is a main challenge in basic research, we demonstrate that within certain limits the analytic expressions for the key transport quantities, derived for point-like particles, can be applied to extended objects, too. Lastly, we study the impact of the solvent''s viscosity on particle transport. If the time scales separate, adiabatic elimination results in an effective description even for finite damping. The possibility of such description is intimately connected with equipartition and vanishing velocity correlation. Numerical simulations show that this approach is accurate for moderate to strong damping and for weak forces. For strong external forces, equipartition may break down due to reflections at the boundaries. This leads to a non-monotonic dependence of the particle mobility on the force strength.
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Rocha, Edroaldo Lummertz da. "Transporte de fônons em geometrias fractais." reponame:Repositório Institucional da UFSC, 2012. http://repositorio.ufsc.br/xmlui/handle/123456789/93840.
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Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Elétrica, Florianópolis, 2010Made available in DSpace on 2012-10-25T03:54:25Z (GMT). No. of bitstreams: 1 285783.pdf: 7381305 bytes, checksum: e6ab920307eaaac21698854288707f6f (MD5)
O transporte térmico em geometrias fractais é investigado utilizando o formalismo de funções de Green atomísticas. Os fractais considerados são o triângulo de Sierpinski, o Barnsley Fern e a Self-contacting Tree. A densidade de estados total e local, transmissão de fônons e estimativas da condutância térmica são calculadas utilizando o formalismo descrito. Além disso, funções de correlação são utilizadas para analisar os resultados. A influência da desordem nas propriedades de transporte é investigada e observa-se uma transição de estados fractônicos para fonônicos na presença de desordem. Argumenta-se que os fônons gerados podem ser estendidos ou localizados devido às oscilações presentes na condutância térmica em função do nível de desordem. Portanto, observa-se um comportamento distinto daquele esperado pela teoria da localização de Anderson onde as funções de onda associadas as vibrações da rede deveriam apresentar efeitos de localização dependentes da desordem. É observado que para determinados intervalos de desordem os fônons gerados são estendidos. Neste caso, o modelo de Anderson pode não ser o mais indicado para descrever a transição. No entanto, para níveis de desordem onde a dimensão de correlação encontra-se em um regime de dimensão fractal estatística, os resultados obtidos são condizentes com aqueles esperados pelo modelo de Anderson.
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Menezes, Welton Alves de. "Reconstrução intranodal da solução numérica gerada pelo método espectronodal constante para problemas Sn de autovalor em geometria retangular bidimensional." Universidade do Estado do Rio de Janeiro, 2009. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=875.
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Conselho Nacional de Desenvolvimento Científico e TecnológicoNesta dissertação o método espectronodal SD-SGF-CN, cf. spectral diamond spectral Green's function - constant nodal, é utilizado para a determinação dos fluxos angulares médios nas faces dos nodos homogeneizados em domínio heterogêneo. Utilizando esses resultados, desenvolvemos um algoritmo para a reconstrução intranodal da solução numérica visto que, em cálculos de malha grossa, soluções numéricas mais localizadas não são geradas. Resultados numéricos são apresentados para ilustrar a precisão do algoritmo desenvolvido.
In this dissertation the spectral nodal method SD-SGF-CN, cf. spectral diamond spectral Green's function - constant nodal, is used to determine the angular fluxes averaged along the edges of the homogenized nodes in heterogeneous domains. Using these results, we developed an algorithm for the reconstruction of the node-edge average angular fluxes within the nodes of the spatial grid set up on the domain, since more localized numerical solutions are not generated by coarse-mesh numerical methods. Numerical results are presented to illustrate the accuracy of the algorithm we offer.
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Chacón-Acosta, Guillermo, Angel A. García-Chung, and Leonardo Dagdug. "On the geometrical description of effective diffusion in confined environments." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-198069.
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Ralley, Kevin. "Few-photon transport in quasi-one-dimensional geometries." Thesis, University of Birmingham, 2013. http://etheses.bham.ac.uk//id/eprint/4316/.
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An analysis of some aspects of photon transport through cavities and emitters embedded in a one-dimensional geometries is presented. The concept of photon blockade is defined for few-photon states interacting with a single two-level atom and the strength of achievable blockade is calculated in this setting. A brief review of some promising schemes for achieving photon blockade from the literature is also provided. The conflict between linear and nonlinear optical processes is studied for a novel version of the famous Hong-Ou-Mandel effect in a photonic waveguide with a side-coupled two-level emitter.
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Agliari, Elena, Raffaella Burioni, Davide Cassi, and Franco M. Neri. "Autocatalytic reaction-diffusion processes in restricted geometries." Diffusion fundamentals 7 (2007) 1, S. 1-8, 2007. https://ul.qucosa.de/id/qucosa%3A14157.
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Hentschel, Martina. "Mesoscopic wave phenomena in electronic and optical ring structures." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2001. http://nbn-resolving.de/urn:nbn:de:swb:14-1008319980781-38394.
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Gegenstand dieser Arbeit sind Wellenphänomene in mesoskopischen Ringstrukturen. In Teil I der Arbeit befassen wir uns mit spinabhängigem Transport von Elektronen in effektiv eindimensionalen Ringen in Gegenwart inhomogener Magnetfelder. Wir benutzen die exakten Lösungen der Schrödinger-Gleichung im allgemeinen nicht-adiabatischen Fall in einem Transfer-Matrix-Formalismus und untersuchen Auswirkungen von geometrischen Phasen auf den Magnetwiderstand. Für den Spezialfall eines Magnetfeldes in der Ringebene sagen wir einen interessanten Spin-Flip-Effekt vorher, der die Steuerung der Polarisationsrichtung von Elektronen über einen externen Aharonov-Bohm-Fluß erlaubt. Optische mesoskopische Systeme sind Thema von Teil II dieser Arbeit. Wir betrachten zweidimensionale annulare Strukturen, charakterisiert durch unterschiedliche Brechungsindizes, sowohl im klassischen Bild der geometrischen Optik als auch mit Wellenmethoden auf der Grundlage der Maxwellschen Gleichungen. Insbesondere diskutieren wir erstmals eine Streumatrixbeschreibung optischer Mikroresonatoren und wenden sie auf das dielektrische annulare Billard an. Ein Vergleich der Ergebnisse des Wellen- und Strahlenbildes liefert eine gute Übereinstimmung, jedoch sind im Grenzfall großer Wellenlängen von der Ordnung der Systemabmessungen Korrekturen zum Strahlenbild nötig. Wir zeigen am Beispiel von Fresnel-Gesetzen für gekrümmte Oberflächen erstmals, daß der Goos-Hänchen-Effekt diese Korrekturen quantitativ erfaßt. Ausgehend von der Wellenbeschreibung leiten wir neue analytische Formeln für verallgemeinerte Fresnel-Gesetze für beide möglichen Polarisationsrichtungen ab. Die Anwendung des Strahlenbildes erlaubt eine schlüssige Interpretation eines Experiments mit einer quadrupolaren Glasfaser, außerdem schlagen wir Strahlenkonzepte als Grundlage der Konstruktion von Mikrolasern mit maßgeschneiderten Charakteristika vorIn this work we investigate wave phenomena in mesoscopic systems using different theoretical approaches. In Part I, we focus on effectively one-dimensional electronic ring structures and address the phenomenon of geometric phases in spin-dependent electronic transport in the presence of non-uniform magnetic fields. In the general non-adiabatic case, exact solutions of the Schrödinger equation are used in a transfer matrix formalism to compute the transmission probability through the ring. In the magneto-conductance we identify clear signatures of interference effects due to geometric phases, for example in rings where the non-uniform field is created by a central micromagnet. For the special case of an in-plane magnetic field we predict an interesting spin-flip effect that allows one to control the spin polarization of electrons by applying an external Aharonov-Bohm flux. Optical mesoscopic systems are the subject of Part II. We consider two-dimensional annular structures characterized by different refractive indices, and apply classical methods from geometric optics as well as wave concepts based on Maxwell's equations. For the first time, an S-matrix approach is successfully employed in the description of resonances in optical microresonators; in particular we propose the dielectric annular billiard as an attractive model system. Comparing ray and wave pictures, we find general agreement, except for large wavelengths of the order of the system size, where corrections to the ray model are necessary. The Goos-Hänchen effect as an extension of the ray picture is shown to quantitatively account for wave modifications of Fresnel's laws due to curved interfaces. We derive novel analytical expressions for the corrected Fresnel formulas for both polarizations of light. Motivated by the successful ray description, we give a conclusive interpretation of a recent filter experiment on a quadrupolar glass fibre, and suggest novel concepts for microresonator-based lasers
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Garcia-Chung, Angel A., Guillermo Chacón-Acosta, and Leonardo Dagdug. "On the geometrical description of the effective diffusion in confined environments." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-198166.
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Oliveira, Francisco Bruno Souza. "Problema inverso de reconstrução analítica aproximada da solução da equação de transporte de partículas neutras monoenergéticas em geometria unidimensional cartesiana com espalhamento isotrópico." Universidade do Estado do Rio de Janeiro, 2007. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=779.
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Nesta tese mostraremos uma aplicação do método SGF, cf., spectral Greens function, para gerar fluxos angulares nas interfaces dos nodos na formulação de ordenadas discretas (SN) para equação de transporte de partículas neutras em geometria cartesiana unidimensional e a uma velocidade, usando quadraturas de alta ordem. Utilizando o método de malha grossa SGF, primeiramente determinamos as constantes arbitrárias da solução geral analítica das equações SN em cada nodo espacial. Então usamos a fórmula de quadratura angular para estimar uma expressão para o fluxo escalar de nêutrons e substituímos no termo de fonte de espalhamento isotrópico na equação de transporte. Resolvemos analiticamente a equação unidimensional de transporte de nêutrons com a fonte de espalhamento aproximada desta maneira e geramos os valores para o fluxo angular no interior de cada nodo espacial. Como o método SGF gera soluções numéricas de malha grossa completamente livres de erro de truncamento espacial, esperamos que o esquema de reconstrução analítica proposto tenha alta precisão para os fluxos angulares, considerando as condições de continuidade nas interfaces dos nodos do domínio espacial. Esta técnica caracteriza um problema inverso, pois a partir da solução de malha grossa do método SGF, podemos reconstruir o fluxo angular de nêutrons em qualquer ponto do domínio.We offer in this work an application of the SGF method, cf., spectral Greens function, to generate the angular fluxes at the region interfaces of multilayer slabs, using high-order angular quadrature sets in the one-speed discrete ordinates (SN) formulation of the neutral particle transport equation. Using the SGF coarse-mesh numerical solution, we first determine the arbitrary constants of the analytical general solution of the SN equations within each spatial node. Then, we use the angular quadrature formula to estimate the expression of the scalar flux distribution, that we substitute into the isotropic scattering source term of the transport equation. We solve analytically the slab-geometry transport equation, with the scattering source so approximated, in order to generate the angular flux profile within each spatial node. As the SGF method generates coarse-mesh numerical solution, which is completely free from spatial truncation errors, we expect that the offered approximate analytical reconstruction scheme be accurate enough for the localized angular flux distribution, considering the node interface continuity conditions within the domain. This technique is thought of as an inverse problem since from the SGF coarse-mesh nodal solution we are able to reconstruct the angular flux profile at any point inside the domain.
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Silva, Elton Cesar da. "Efeitos da geometria toroidal na atuação de campos helicoidais ressonantes em Tokamaks." Universidade de São Paulo, 2001. http://www.teses.usp.br/teses/disponiveis/43/43131/tde-09102012-151302/.
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Neste trabalho, consideramos os efeitos de um campo magnético ressonante externo sobre o plasma confinado em um tokamak. Este campo magnético pode ser produzido quer por condutores helicoidais ou por um limitador magnético caótico. O principal propósito desse campo magnético ressonante é criar uma região de linhas de força caóticas na borda da coluna de plasma que pode melhorar o confinamento do plasma. O campo magnético de equilíbrio foi obtido resolvendo-se a equação de GRAD-SHAFRANOV em um sistema de coordenadas intrinsecamente toroidal (as coordenadas polares toroidais). Obtivemos o campo magnético, gerado pelos condutores helicoidais, através da solução explícita da equação de LAPLACE no mesmo sistema de coordenadas. A partir desse campo magnético, tomando o termo de mais baixa ordem, obtivemos analiticamente um mapa estroboscópico simplético para um conjunto de anéis limitadores magnéticos caóticos. Calculamos esse mapa estroboscópico simplético usando uma formulação hamiltoniana e adotando a. ação dos limitadores magnéticos caóticos como uma sequência de pulsos do tipo função delta. Com esse mapa estroboscópico simplético, caracterizamos algumas ilhas magnéticas ressonantes e a transição para um regime de caos global através da superposição das mesmas. Usamos esse mapa estroboscópico simplético para estudar o transporte das linhas de força na borda da coluna de plasma. A perda de linhas de força caóticas, que atingem a parede interna do tokamak, segue uma distribuição de POISSON. Calculamos, ainda, o número médio de voltas, ao redor da câmara de vácuo, necessárias para que uma linha de força caótica atinja a parede da câmara.In this work, we have considered the effects of an external resonant magnetic field on the plasma confined in a tokamak. This resonant field can be produced by helical windings or by a chaotic magnetic limiter. The main purpose of this resonant magnetic field is to create a region of chaotic field lines at the edge of the plasma that can improve the confinement of the plasma. The equilibrium tokamak field was obtained by solving the GRAD-SHAFRANOV equation in an intrinsically toroidal coordinate system (the toroidal polar coordinates). We have obtained the magnetic field which has been generated by helical windings through an explicit solution of the LAPCACE equation in the same coordinate system. From this magnetic field, taken in its lowest order, we have analytically obtained a sympletic stroboscopic map for a set of chaotic magnetic limiters. We have calculated this sympletic stroboscopic map by using a Hamiltonian formulation and by supposing the action of the chaotic magnetic limiters as a sequence of delta-function pulses. With this sympletic stroboscopic map we have characterized some resonant magnetic islands and the onset of global chaos through their overlap. We have used this sympletic stroboscopic map in order to study the transport of the field lines at the edge of the plasma. The loss of chaotic field lines that reach the inner wall of the tokamak follows a POISSON distribution. We have also calculated the average number of toroidal turns for a chaotic field line to reach the inner wall of the tokamak.
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Chacón-Acosta, Guillermo, Angel A. García-Chung, and Leonardo Dagdug. "On the geometrical description of effective diffusion in confined environments: On the geometrical description of effective diffusion in confinedenvironments: two-dimensional case." Diffusion fundamentals 24 (2015) 9, S. 1, 2015. https://ul.qucosa.de/id/qucosa%3A14523.
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Grebenkov, Denis S. "Multiple correlation function approach: rigorous results for simple geometries." Diffusion fundamentals 5 (2007) 1, S. 1-34, 2007. https://ul.qucosa.de/id/qucosa%3A14264.
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The multiple correlation function approach is briefly presented and applied to investigate spin-echo signal attenuation due to restricted diffusion in simple geometries (slab, cylinder, and sphere) in the presence of surface relaxation. Exact and explicit
representations for the zeroth and second moments of the total phase accumulated by diffusing spins are derived by using the Laplace transform summation technique. Within the Gaussian phrase approximation, these two moments determine the reference and diffusion-weighted signals, respectively. In the slow-diffusion or short-time regime, the series expansion in half-integer powers of the diffusion coefficient is generalized to arbitrary temporal profile of a linear magnetic field gradient. In the motional-narrowing or long-time regime, it is shown how the presence of surface relaxation modifies the classical Robertson’s relation. Practical consequences of these findings are discussed.
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Garcia-Chung, Angel A., Guillermo Chacón-Acosta, and Leonardo Dagdug. "On the geometrical description of the effective diffusion in confined environments: On the geometrical description of the effective diffusion in confinedenvironments: 3D channels." Diffusion fundamentals 24 (2015) 17, S. 1, 2015. https://ul.qucosa.de/id/qucosa%3A14531.
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DIAS, ARTUR F. "Metodo PsubN para calculos de blindagem em geometria de multiplacas." reponame:Repositório Institucional do IPEN, 1999. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10771.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Xiao, Fanrong, and Sabina Hrabetova. "Monte Carlo simulation study of geometrical factors causing anomalous diffusion in brain extracellular space." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-184822.
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Syed, Asif Ahmed. "Water Transport Terminal." Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/31738.
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This thesis is an attempt in the exploration of an architectural idea of breaking away from a conventional column beam structure.
This idea led to a geometrical form which would be most stable, supported by itself, and also helps mitigate the lateral forces of wind and water in which it would stand. The conical form and scale achieved in the proposal would also help create a landmark to the cityâ s growing skyline.
It also acts as the point of threshold between land and water, providing an opportunity to sense water in a variety of ways.Master of Architecture
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Stech, Pedro Henrique. "Parâmetros do projeto geométrico para trens de passageiros de alta velocidade e longo percurso." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/3/3138/tde-30032012-121739/.
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Este trabalho tem como objetivo principal direcionar a tomada de decisões para a escolha dos diferentes parâmetros que envolvem o alinhamento horizontal e vertical do projeto geométrico ferroviário de trens de alta velocidade (TAV) e de longo percurso, bem como descrever conceitos teóricos para parâmetros de segurança e conforto, baseados em normas internacionais. A pesquisa se desenvolve através de consultas em revistas especializadas, artigos, publicações, normas técnicas e livros. Pela escassez de dados em língua nacional e material bibliográfico desatualizado, as pesquisas se concentram essencialmente em material internacional. Apesar do Brasil ser um dos países em desenvolvimento com maior ascensão no cenário global, tem apresentado, nas últimas décadas, sérios problemas de infra-estrutura devido a uma distribuição desequilibrada na área de transportes, com altíssima concentração no modo rodoviário, com aeroportos e rodovias operando acima da capacidade satisfatória, além de um leque limitado de alternativas de transporte. Devido à falta de investimentos no setor ferroviário, grande parte da malha ferroviária brasileira tornou-se inoperante ou até mesmo inexistente, resultando numa enorme diminuição da mão de obra qualificada e formação acadêmica nesse ramo. Como conseqüência, os estudos relacionados ao projeto ferroviário também foram afetados diretamente. Nesse contexto, é importante que se resgate normas, publicações, especificações técnicas e experiências adotadas em outros países com sólidas tradições ferroviárias, de modo a incorporar em nossa formação acadêmica tais conceitos, como é um dos objetivos dessa dissertação.This dissertation has as main objective to guide in taking decisions for the selection of different parameters which involve the horizontal and vertical railway geometric design of high speed (HST) and long distance trains as well as theoretical concepts for describing security parameters and comfort, based on international standards. The research is developed through consultations in specialized magazines, articles, publications, standards and technical books. Due to the scarcity of data in the national language and outdated library materials, the research focuses primarily on international material. Although Brazil is a developing country with one of the highest rises in the global scene, the country has faced in recent decades serious infrastructure problems due to an uneven distribution in the area of transport, with high concentration in the road, and airports and roads operating above satisfactory capacity, resulted by a limited range of transportation alternatives. Due to the lack of investment in the railway sector, much of the Brazilian railway system became inoperative or even nonexistent, resulting in a tremendous decrease of skilled labor and academic training in this field. As a result, studies related to the railway project have also been directly impacted. In this context, it is important to rescue standards, publications, experiences and technical specifications adopted in other countries with strong tradition in railways in order to incorporate these concepts into our academic formation, which is one of the purposes of this dissertation.
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Cumming, David Robert Sime. "Geometrical effects and semi-classical transport in ballistic electron devices." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.281953.
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Sumiyoshi, Hiroaki. "Geometrical Responses in Topological Materials." 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225387.
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Colgan, Gary. "The study of transport in simple and complex geometries using MRI." Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620507.
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Oliveira, Fernando Rodrígues de. "Solução analítica da equação de multigrupo de cinética de nêutrons em geometria cartesiana e cilíndrica unidimensionais." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2013. http://hdl.handle.net/10183/77922.
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Neste trabalho apresentamos uma solução analítica para a equação de cinética unidimensional de difusão de nêutrons, para o modelo de dois grupos de energia, nas geometrias cartesiana e cilíndrica, pelo método espectral. A ideia básica desta metodologia consiste na expansão da solução para os fluxos de nêutrons rápido e térmico, assim como, a solução para as concentrações de precursores de nêutrons atrasados, em séries de autofunções adequadamente escolhidas para a geometria considerada, ou seja, funções seno para a cartesiana e Bessel para a cilíndrica. Dessa maneira, substituem-se estas expansões na equação de cinética, integrando a equação resultante multiplicada pelas autofunções apropriadas à geometria estudada e, ao usar a propriedade da ortogonalidade, obtemos uma equação diferencial matricial linear de primeira ordem com solução conhecida. Assim, ao lançar mão das autofunções adequadas, mostramos a generalidade desta metodologia para solução deste tipo de problema nas geometrias consideradas. Por fim, apresentamos simulações numéricas e comparações com resultados da literatura para os fluxos de nêutrons e concentrações de nêutrons atrasados.In this work, we report an analytical solution for the kinetic onedimensional neutron di usion equation for the two-group energy model, in cartesian and cylindrical geometry, by the spectral method. The basic idea of the proposed methodology, relies on the expansion of the fast and thermal neutron uxes, as well, the delay neutron precursors concentrations, in a series of eigenfunctions, properly selected for the geometry considered, we mean sine functions for cartesian geometry and Bessel functions for cylindrical geometry. Replacing these expansions in the kinetic equation, taking moments and using the ortogonality property, we come out with a linear rst order matrix di erential equation with a well known solution. Actually, we have shown the generality of the proposed methodology to work out this kind of problem for the geometries considered using properly the eigenfunctions. Finally, we present numerical simulations and comparisons against literature results for the neutron uxes and delayed neutron precursors concentrations.
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Neto, Apiano Ferreira de Morais. "Escoamento de fluidos complexos e transporte de partÃculas em geometrias irregulares." Universidade Federal do CearÃ, 2011. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=5889.
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Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgicoNeste trabalho, foram estudados vÃrios tipos de escoamentos laminares de fluidos incompressÃveis Newtonianos e nÃo-Newtonianos. Isto foi feito atravÃs do estudo da interaÃÃo destes escoamentos com geometrias complexas atravÃs de modelagem computacional e da soluÃÃo numÃrica das equaÃÃes de conservaÃÃo do momento e continuidade de massa. Numa primeira etapa, a modelagem computacional de uma rede de poros foi usada para a gerar padrÃes de agregados granulares resultando de mecanismos de erosÃo-deposiÃÃo de grÃos leves. A geometria da rede de poros foi alterada dinamicamente de acordo com a transferÃncia de momento do escoamento para as partÃculas localizadas em cada vÃrtice da rede de poros. Os resultados mostraram que, para esse processo irreversÃvel, o modelo foi capaz de reproduzir padrÃes tÃpicos de processos de erosÃo bem-conhecidos. Numa segunda etapa, um separador de partÃculas semelhante à estrutura pulmonar foi proposto com base nas propriedades de escoamento em uma estrutura ramificada e nas propriedades de transporte inercial das partÃculas, quantificadas atravÃs do nÃmero de Stokes. Os resultados indicaram que a variaÃÃo dos parÃmetros de construÃÃo da estrutura ramificada leva a um regime eficiente do processo de separaÃÃo em um amplo espectro de valores do nÃmero de Stokes. Por Ãltimo, o escoamento de vÃrios fluidos nÃo-Newtonianos atravÃs de meios porosos desordenados em trÃs-dimensÃes foi estudado. Os resultados mostraram, para fluidos do tipo lei-de-potÃncia, que o escoamento pode ser descrito como uma curva universal se o nÃmero de Reynolds e a permeabilidade hidrÃulica forem redefinidos de maneira apropriada. Fluidos de Bingham tambÃm foram estudados atravÃs do modelo de Herschel-Bulkley. Neste caso, as simulaÃÃes revelaram que as interaÃÃes entre a geometria complexa do espaÃo poroso, as propriedades reolÃgicas do fluido e os efeitos inerciais do escoamento sÃo responsÃveis por uma melhora substancial da permeabilidade hidrÃulica do sistema em valores intermediÃrios do nÃmero de Reynolds.
In this work many types of incompressible laminar Newtonian and Non-Newtonian flows are studied. The interplay of these flows with complex geometries was investigated using computational modeling and numerical solution of the conservation of momentum and mass continuity equations. As a first step, the computational modeling of a network of pores was adopted to reveal the formation patterns caused by the mechanism of erosion-deposition of light grains. The geometry of the pore network was changed dynamically according to the flow momentum transfer for particles located on each vertex of the pore network. The results showed that, for this irreversible processes, the model is capable of reproducing patterns of formation of well-known erosion processes. In a second step, a particle separator inspired on the lung structure was proposed based on the flow properties in a branched structure and transport of inertial particles, quantified in terms of the Stokes number. The results indicated that the variation of construction parameters of the branched structure leads to an efficient design of the separation process in a wide range of values of the Stokes number. Finally, the flow of non-Newtonian fluids through three-dimensional disordered porous media has been studied. The results showed, for power-law fluids that the flow can de described as a universal curve if the Reynolds number and the hydraulic permeability are redefined properly. The flow of Bingham fluids was also studied using the model of Herschel-Bulkley. In this case, the simulations showed that the interaction between the complex geometry of the pore space, the rheological properties of the fluid and the inertial effects of the flow is responsible for a substantial improvement of the hydraulic permeability of the system at intermediate values of the Reynolds number.
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Xiao, Fanrong, and Sabina Hrabetova. "Monte Carlo simulation study of geometrical factors causing anomalous diffusion in brain extracellular space." Diffusion fundamentals 16 (2011) 27, S. 1-2, 2011. https://ul.qucosa.de/id/qucosa%3A13759.
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Ariyaratne, Chanchala. "Design and optimisation of swirl pipes and transition geometries for slurry transport." Thesis, University of Nottingham, 2005. http://eprints.nottingham.ac.uk/11570/.
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This thesis is primarily concerned with the design and optimisation of transition ducts for lobed swirl-inducing pipes. Single-phase swirl-inducing pipe flows were modelled and optimised using Computational Fluid Dynamics (CFD). Optimised pipes were manufactured using rapid prototyping and an experimental investigation examines their effect on settling slurries of different densities. The CFD model was successfully validated by experimental measurements of pressure loss and tangential velocity. An optimum transition geometry was determined for use as an entry and an exit duct with optimised swirl inducing pipe. Transition pipes either before or after the swirl inducing pipe reduced entry and exit pressure losses by providing a gradual transition from circular to lobed cross-section. They also increased induced swirl and reduced swirl decay. CFD simulations with carboxymethyl cellulose (CMC) instead of water as the flow medium indicated that as the viscosity increased, a smaller pitch, thereby a tighter twist, is required in the swirl-inducing pipe to achieve effective swirl induction. Settling slurry experiments showed that swirl induction resulted in better particle distribution and prevented solids dragging along the bottom of the pipe. This suggests reduction in localised erosion and provides an opportunity to operate at lower flow velocities without blockage. Lower velocities mean lower energy costs and further erosion reduction. When transitions were incorporated pressure losses across the swirl inducing pipe were reduced and the length of particle suspension increased. It was proven, by CFD and experimentation, that entry and exit transition should be an integral part of the swirl inducing pipe. This results in an efficient swirl induction which reduces energy costs from high pressure losses that otherwise occur due to sudden changes in flow geometry.
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Rodrigues, Letícia Jenisch. "Cálculo dos fatores de Dancoff com absorção parcial de nêutrons em geometria Cluster pelo método direto." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2007. http://hdl.handle.net/10183/10583.
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Por muitos anos, vários métodos têm sido propostos para a obtenção dos fatores de Dancoff para materiais perfeitamente e parcialmente absorvedores de nêutrons em meios heterogêneos. No presente trabalho, esse fator é definido como a probabilidade que um nêutron emitido a partir de uma superfície de um elemento combustível irá entrar em outro elemento combustível sem sofrer nenhuma colisão no moderador ou no revestimento. A absorção ressonante em arranjos compactos é fortemente influenciada por esse fator, e nos casos mais gerais de células irregulares, os modelos utilizados ainda apresentam diferenças que refletem em cálculos de criticalidade, taxas de conversão e queima. O código WIMS, um dos mais utilizados códigos de gerenciamento de núcleo de reatores nucleares, possuía originalmente uma sub-rotina PIJ utilizada para calcular matrizes de colisão e fatores de Dancoff, para materiais perfeitamente absorvedores (Black Dancoff factors), para células combustíveis, em um determinado grupo de energia utilizando a definição em termos das probabilidades de colisão. O cálculo dessas probabilidades era baseado nas distâncias percorridas pelos nêutrons entre regiões da célula. A malha de integração, sobre a qual as integrações duplas das funções de Bickley eram calculadas por regra trapezoidal simples, era composta por conjuntos de linhas paralelas, igualmente espaçadas radialmente, traçados para cada um dos ângulos azimutais igualmente incrementados em relação a uma direção de referência. Embora rápido, o esquema de cálculo era ineficiente. A malha fixa era independente do tamanho das regiões que compunham célula, de maneira que regiões muito pequenas, muitas vezes eram atravessadas por poucos traços. Uma modificação nessa sub-rotina, atualmente chamada de PIJM, foi implementada de maneira que cada região da célula tivesse uma malha própria, evitando o excesso de traços em algumas regiões e a falta de traços em outras. Outra melhoria foi a modificação da técnica de integração, isto é, as integrais radiais passaram a ser calculadas por quadraturas gaussianas e as angulares por regra trapezoidal estendida, resultando em melhorias significativas nos fatores de Dancoff comprovadas por comparações com resultados precisos existentes na literatura em situações simples. Entretanto, os fatores assim calculados consideravam as regiões combustíveis formadas por materiais perfeitamente absorvedores.O objetivo deste trabalho é obter os fatores de Dancoff, com absorção parcial do combustível, em células cilíndricas a partir de sua definição alternativa, ou seja, a correção na probabilidade de escape do combustível devido às demais varetas combustíveis do meio. Através da modificação da sub-rotina PIJM determina-se esses fatores para cinco posições diferentes de varetas, utilizando-se a célula canadense CANDU–37, obtendo-se resultados satisfatórios em relação aos encontrados na literatura especializada.Accurate analysis of resonance absorption in heterogeneous systems is essential in problems like criticality, breeding ratios and fuel depletion calculations. In compact arrays of fuel rods, resonance absorption is strongly affected by the Dancoff factor, defined in this study as the probability that a neutron emitted from the surface of a fuel element, enters another fuel element without any collision in the moderator or cladding. In fact, in the most practical cases of irregular cells, it is observed that inaccuracies in computing both Grey and Black Dancoff factors, i.e. for partially and perfectly absorbing fuel rods, can lead to considerable errors in the calculated values of such integral quantities. For this reason, much effort has been made in the past decades to further improve the models for calculating Dancoff factors, a task that has been accomplished in connection with the development of faster computers. In the WIMS code, Black Dancoff factors based on the above mentioned collision probability definition are computed in cluster geometry, for each one of the symmetrically distinct fuel pin positions in the cell. Sets of equally-spaced parallel lines are drawn in subroutine PIJ, at a number of discrete equally-incremented azimuthal angles, covering the whole system and forming a mesh over which the in-plane integrations of the Bickley functions are carried out by simple trapezoidal rule, leading to the first-flight collision matrices. Although fast, the method in PIJ is inefficient, since the constructed mesh does not depended on the system details, so that regions of small relative volumes are crossed out by relatively few lines, which affects the convergence of the calculated probabilities. A new routine (PIJM) was then created to incorporate a more efficient integration scheme considering each system region individually, minimizing convergence problems and reducing the number of neutron track lines required in the in-plane integrations for any given accuracy. In this routine, the radial integrations are performed by Gauss´ formula whereas the angular ones are obtained by extended trapezoidal rule. In the present work, PIJM is extended to compute Grey Dancoff factors by the collision probability definition, in two-dimensional cylindrical cells in cluster geometry. Theeffectiveness of the method is accessed by comparing Grey Dancoff factors as calculated by PIJM, with those available in the literature by the Monte Carlo method, for the irregular geometries of the Canadian CANDU37 assembly. Dancoff factors at five symmetrically distinct fuel pin positions are found in very good agreement with the literature results.
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Kremer, Friedrich, Martin Treß, Emmanuel U. Mapesa, Wycliffe K. Kipnusu, and Wilhelm Kossack. "Glassy dynamics of polymers in geometrical confinement: from nanometric layers to single condensed isolated coils." Diffusion fundamentals 20 (2013) 21, S. 1-2, 2013. https://ul.qucosa.de/id/qucosa%3A13584.
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Simch, Márcia Rosales Ribeiro. "Solução LTSn para problemas de transferência radiativa com polarização em geometria plana." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2004. http://hdl.handle.net/10183/5432.
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O método LTSN tem sido utilizado na resolução de uma classe abrangente de problemas de transporte de partículas neutras que são reduzidos a um sistema linear algébrico depois da aplicação da transformada de Laplace. Na maioria dos casos estudados os autovalores associados são reais e simétricos. Para o problema de criticalidade os autovalores associados são reais ou imaginários puros e simétricos, e para o o problema de multigrupo podem aparecer autovalores complexos. O objetivo deste trabalho consiste na generalização da formulação LTSN para problemas de transporte com autovalores complexos. Por esse motivo é focada a solução de um problema radiativo de transporte com polarização em uma placa plana. A solução apresentada fundamenta-se na aplicação da transformada de Laplace ao conjunto de equações SN dos problemas resultantes da decomposição da equação de transferência radiativa com polarização em série de Fourier, seguindo o procedimento de Chandrasekhar. Esse procedimento gera 2L + 2 sistemas lineares de ordem 4N dependentes do parâmetro complexo "s". Aqui, L é o grau de anisotropia e N a ordem de quadratura. A solução desse sistema simbólico é obtida através da aplicação da transformada inversa de Laplace depois da inversão da matriz simbólica pelo método da diagonalização. Para a obtenção das constantes de integração é assumido que os componentes do vetor de Stokes são reais e as matrizes dos autovalores e autovetores são separadas em suas partes real e imaginária. A solução LTSN para autovalores complexos é validada através da comparação da solução para uma placa com espessura unitária, grau de anisotropia L = 13, albedo de espalhamento simples $ = 0:99, coe ciente de re exão de Lambert ¸0 = 0:1 e N = 150, segundo dados da literatura consultada.
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Marona, Diana Vega. "Solução LTSN da equação de transporte em geometria cartesiana unidimensional para c=1." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2007. http://hdl.handle.net/10183/12155.
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Nos últimos anos, o método LTSN - que resolve diversos problemas de transporte em uma placa plana - emergiu de forma contínua em nossa literatura. Porém, não é de nosso conhecimento que se tenha aplicado este método a problemas isotrópicos de transporte de partículas neutras em uma placa plana, quando o parâmetro albedo vale c = 1. Sabemos que para esta situação a equação de transporte unidimensional apresenta dois autovalores que se encontram no infinito. Consequentemente, a formulação LTSN não pode ser aplicada, pois a solução LTSN é utilizada para problemas onde a matriz LTSN é diagonalizável, e isto ocorre quando c 6= 1. Para a resolução destes tipos de problemas, nós modificamos a solução LTSN que aproxima a solução de Case quando o albedo é unitário, combinando de forma adequada a decomposição de Schur e a expansão de Heavside. A convergência provada do Método LTSN permite que determinemos a solução com precisão prescrita. Apresentamos simulações e comparações numéricas com resultados disponíveis na literatura. Por este procedimento, esperamos terminar o estudo da praticabilidade do LTSN para resolver problemas do transporte em uma placa plana.In the last years, the LTSN method - for transport problems in slabgeometry appears frequently in the literature. However, to our knowledge, this method has not been applied to the solution of neutral particle transport problems in a slab with isotropic scattering for c = 1. We know that in this situation the neutron transport equation presents two eigenvalues that coalesce to infinity. Therefore, the LTSN formulation can not be applied to this type of problem, because the LTSN solution is derived for problems in which the LTSN matrix is non-defective, that is for problems with c 6= 1. To solve these types of problems we modify the LTSN solution that approaches the Case solution when the albedo is unitary, combining in an adequate form the Schur decomposition and the Heavside expansion. The convergence of the LTSN method allows us to determine the solution with prescribed accuracy. We present numerical simulations and comparisons with results available in the literature. By this procedure we hope to complete the study of the LTSN formulation to solve transport problems in slab-geometry.
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Leal, Tiago Gaspar. "Simulações LBM de escoamentos em geometrias complexas." Master's thesis, Universidade de Aveiro, 2011. http://hdl.handle.net/10773/8354.
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Mestrado em Engenharia MecânicaO método Lattice Boltzmann (LBM) permite simular escoamentos de fluidos dos mais diversos tipos em boa concordância com a realidade. Para se retirar as devidas conclusões do cálculo executado pelo algoritmo do LBM é necessária a intervenção de uma plataforma que ilustre visualmente os resultados. Nesse sentido o presente trabalho propõe procedimentos que permitam a integração de geometrias complexas num simulador LBM. Para o efeito, adaptou-se um código LBM escrito em MATLAB disponível em literatura aberta. Foram feitas simulações de escoamentos em diversas geometrias integradas, tendo sido levado em conta soluções capazes de melhor representar resultados obtidos. Adicionalmente foram feitos pequenos testes de forma a validar o algoritmo, assim como previsões de permeabilidade de algumas estruturas porosas com soluções analíticas conhecidas. Entre as várias aplicações de engenharia que o procedimento descrito poderá ter, deuse ênfase ao projecto de moldes a serem utilizados na produção de compósitos poliméricos. Como objectivo final e já fora do contexto da presente dissertação, pretende-se, vir a adaptar e a validar o algoritmo em escoamentos de fluido numa matriz (preform) mediante o processo de Moldação por Transferência de Resina (RTM), contribuindo deste modo, para a verificação de quais as condições ideais para uma total impregnação de resina na matriz e por conseguinte assegurar a integridade estrutural da peça.
Lattice Boltzmann Method allows the simulation of a wide range of fluid flows, with results quite consistent with reality. To facilitate the interpretation of the results produced by the LBM simulation and eventually draw the appropriate conclusions is necessary the intervention of a platform that visually illustrates the results. In this regard, this project proposes a procedure which allows the integration of arbitrary geometries in a LBM simulator. For this purpose, an LBM code was adapted; results of simulations for relevant cases are presented in this dissertation. In addition, several tests were done to validate the algorithm used, including permeability prediction in some structures, namely ordered arrangements of spheres. Among many engineering applications, the procedure described may be of particular use in the design of moulds for the production of polymer composites. In fact, the final goal, although outside the context of this dissertation, is to validate the algorithm for fluid flow prediction in preforms used in the Resin Transfer Moulding (RTM) process, thus contributing to the understanding of the impregnation of preform by the resin eventually yielding improved structural integrity.