Neste trabalho, nossa principal motivação foi o entendimento da dinâmica de pacotes de onda em isolantes topológicos 2D. Como excitações de carga se movem nesses materiais? De que maneira essas trajetórias dependem das condições iniciais, e de que forma as condições de contorno influenciam nessa dinâmica? Essas foram algumas das perguntas que guiaram nosso trabalho. Através de simulações computacionais, estudamos o movimento de pacotes de onda gaussianos em poços quânticos de HgTe/CdTe. O comportamento de isolante topológico para essa heteroestrutura foi prevista teoricamente no importante trabalho de Bernevig et al. (Science, vol. 314, no. 5806, 2006) e confirmada experimentalmente por König et al. (Science, vol. 318, no. 5851, 2007). Estudando-se a evolução temporal desse sistema, foi possível observar trajetórias que dependem de forma evidente, não apenas da orientação de spin, mas também da orientação de um pseudo-spin proveniente do modelo BHZ. Em sistemas com condições de contorno periódicas em ambas as dimensões e sem a aplicação de campos externos, foram observadas trajetórias com formato de espiral, acompanhadas por um \"side-jump\" dependente da direção do spin e do pseudo-spin. Em especial, para o caso em que o pseudo-spin está inicialmente orientado na direção-z, as trajetórias espiraladas foram subtituidas por um padrão do tipo \"zitterbewegung\" dependente de um potencial de \"bias\". Para sistemas confinados com bordas impenetráveis, observou-se a formação de estados de borda helicais característicos de isolantes topológicos. / In this work, our main motivation was the understanding about the dynamics of wave packets in 2D topological insulators. How charge excitations move throughout theses materials? In what way their trajectories depend on the initial conditions, and how boundary conditions change this dynamics? These were some of the questions that have guided us in our work. Using numerical simulations, we have studied the movement of gaussian wave packets in HgTe/CdTe quantum wells. The topological insulator behavior for this heterostructure was theoretically predicted on the important work conducted in 2006 by Bernevig et al. (Science, vol. 314, n. 5806, 2006), and experimentally confirmed by König et al. (Science, vol. 318, no. 5851, 2007) a year later. Studing the time evolution of this system, was possible to observe trajectories that depend evidently, not only from the spin projection, but also from the pseudospin orientation coming from the BHZ model. From simulations with periodic boundary conditions in both of the two dimensions, and without the application of any external fields, we observed spiral trajectories accompanied by a spin and pseudospin dependent side-jump. Especially, for the case in which the pseudospin was iniatially oriented in \"z\" direction, the spiral trajectories were replaced by a pattern of the type \"zitterbewegung\" dependent of a bias potential. For the confined systems with barriers of hardwall type, was observed the formation of helical edge states, that is the fingerprint of topological insulators.

La thèse, composée de trois parties, est consacrée à des problèmes physiques différents reliés à la Théorie Conforme des Champs (CFT) bidimensionnelle. La première partie s'intéresse aux propriétés de transport hors d'équilibre à travers une jonction de fils quantiques. Trois modèles y sont étudiés. Le premier décrit les fils par un champs bosonique libre compactifié vu comme la bosonisation du liquide de Luttinger d'électrons. La jonction des fils est modélisée par une condition limite assurant la diffusion non triviale des charges entre les fils. Associant la quantification canonique et l'intégrale fonctionnelle, on calcule exactement les fonctions de corrélation des courants dans l'état d'équilibre du modèle, mais aussi dans un état stationnaire hors d'équilibre, ainsi que la statistique complète de comptage pour les transferts de charge et d'énergie entre les fils maintenus en températures et potentiels différents. Les deux autres modèles d'une jonction de fils quantiques sont basés sur la théorie de Wess-Zumino-Witten (WZW). Dans le premier, la jonction est décrite par une "brane cyclique" et dans le deuxième, par une "brane coset". Les résultats dans le premier cas sont aussi complets que pour le champ libre, mais les charges y sont entièrement transmises d'un fils au suivant. Dans le deuxième cas, la diffusion des charges n'est pas triviale, mais le modèle se révèle difficile à résoudre. La deuxième partie de la thèse étudie les anomalies globales de jauge dans les modèles "coset" de CFT réalisés comme la théorie WZW jaugée. La classifications (presque) complète de telles anomalies, lesquelles rendent certains modèles coset inconsistants, est présentée. Elle emploie la classification des sous-algèbres des algèbres de Lie simples due à Dynkin. Finalement, la troisième partie de la thèse décrit la construction géométrique d'indice des familles d'opérateurs unitaires obtenues des projecteurs sur les bandes de valence d'un isolant topologique bidimensionnel invariant par renversement du temps. L'indice construit est relié d'un côté à la racine carrée de l'amplitude de Wess-Zumino d'une telle famille, et, de l'autre, il reproduit l'invariant de Kane-Mele de l'isolant. La dernière identification exige un argument complexe qui exploite une nouvelle anomalie de jauge pour les modèles WZW à bord. Les trois parties de la thèse emploient des outils géométriques de CFT assez semblables, permettant d'obtenir toute une série des résultats originaux. Cette unité de méthode, ainsi que le thème des anomalies, constituent le trait d'union entre les différents composants du manuscrit. / The thesis, consisting of three parts, is focusing on different physical problems that are related to two dimensional Conformal Field Theory (CFT).The first part deals with nonequilibrium transport properties across a junction of quantum wires. Three models are studied. The first one describes the wires by a free compactified bosonic field, seen as the bosonization of the Luttinger liquid of electrons. The junction of the wires is modeled by a boundary condition that ensures nontrivial scattering of the charges between the wires. Combining canonical quantization and functional integral, we compute exactly the current correlation functions in equilibrium, but also in a nonequilibrium stationary state, as well as the full counting statistics of charge and energy between the wires set at different temperatures and potentials. The two other models of quantum wire junction are based on Wess-Zumino-Witten theory (WZW). In the first one, the junction is described by a “cyclic brane” and in the second, by a “coset brane”. The results in the first case are as complete as for the free field, but the charges are fully transmitted from one wire to the next one. In the second case, the scattering is nontrivial, but the model turns out to be difficult to solve.The second part of the thesis studies the global gauge anomalies in “coset” models of CFT, realized as gauged WZW theories. The (almost) complete classification of such anomalies, that lead to some inconsistent coset models, is presented. It is based on Dynkin classification of subalgebras of simple Lie algebras.Finally, the third part of the thesis describes the geometric construction of index from unitary operator families obtained from valence band projectors of a two-dimensional time-reversal invariant topological insulator. The index is related on one hand to the square root of the Wess-Zumino amplitude of such a family, and, on the other hand, it reproduces the Kane-Mele invariant of the insulator. The last identification requires a nontrivial argument that uses a new gauge anomaly of WZW models with boundary.The three parts of the thesis use similar geometrical tool of CFT, that permits to obtain several original results. The unity in the method, as well as the topic of anomalies, builds a bridge between the different components of the manuscript.

Este trabalho visa ao estudo da aplicação da madeira de reflorestamento, da espécie Pinas Taeda, impregnada com resina poliuretana derivada do óleo de mamona, como um novo material para a fabricação de isoladores elétricos híbridos. Esta pesquisa possui um grande apelo ecológico, pois o compósito madeira-resina poliuretana é derivado de madeira de reflorestamento e óleo de mamona. Estudos com cruzetas de madeira mostraram que este material apresenta excelente desempenho em ensaios de Nível Básico de Isolamento (NBI). A madeira apresenta boas características elétricas quando seca e também algumas boas propriedades mecânicas, como a tenacidade que minimiza os estragos causados pelo vandalismo, um dos grandes problemas do setor. A resina poliuretana atribui hidroscopicidade à madeira e proteção contra os ataques de agentes biológicos, além de melhorar suas propriedades mecânicas e elétricas. O processo para a impregnação de resina na madeira foi inovador, devido à utilização de vácuo tanto para o processamento da resina quanto para a impregnação; a pressão atmosférica expulsa o ar da resina, tornando-a mais homogênea, e força-a a preencher as cavidades da madeira. / This work aims at the study of the application of reforestation wood, of Pinus Taeda species, impregnated with polyurethane resin derived from the castor-oil plant as a new product for the manufacture of hybrid electric insulators. This research possesses a great ecological appeal, as the wood-polyurethane resin composite derived from reforestation wood and castor-oil plant. Studies with wood squares have shown this material presents excellent performance in assays of Basic Level of Isolation (NEI). The wood shows good electric characteristics when dried and also some good mechanical properties, as tenacity, which minimizes the vandalism damage, one of the great problems in this sector. The polyurethane resin attributes hydrocospicity to the wood and protection against the attack of biological agents, improving its mechanical and electrical properties. An innovative process was used for the impregnation of the wood with resin, utilizing vacuum for both processing impregnation of the resin. The atmospheric pressure expels the air out of the resin, which becomes more homogeneous, and obliges it to fill the cavities of the wood.

Este trabalho visa ao estudo da aplicação da madeira de reflorestamento, da espécie Pinas Taeda, impregnada com resina poliuretana derivada do óleo de mamona, como um novo material para a fabricação de isoladores elétricos híbridos. Esta pesquisa possui um grande apelo ecológico, pois o compósito madeira-resina poliuretana é derivado de madeira de reflorestamento e óleo de mamona. Estudos com cruzetas de madeira mostraram que este material apresenta excelente desempenho em ensaios de Nível Básico de Isolamento (NBI). A madeira apresenta boas características elétricas quando seca e também algumas boas propriedades mecânicas, como a tenacidade que minimiza os estragos causados pelo vandalismo, um dos grandes problemas do setor. A resina poliuretana atribui hidroscopicidade à madeira e proteção contra os ataques de agentes biológicos, além de melhorar suas propriedades mecânicas e elétricas. O processo para a impregnação de resina na madeira foi inovador, devido à utilização de vácuo tanto para o processamento da resina quanto para a impregnação; a pressão atmosférica expulsa o ar da resina, tornando-a mais homogênea, e força-a a preencher as cavidades da madeira. / This work aims at the study of the application of reforestation wood, of Pinus Taeda species, impregnated with polyurethane resin derived from the castor-oil plant as a new product for the manufacture of hybrid electric insulators. This research possesses a great ecological appeal, as the wood-polyurethane resin composite derived from reforestation wood and castor-oil plant. Studies with wood squares have shown this material presents excellent performance in assays of Basic Level of Isolation (NEI). The wood shows good electric characteristics when dried and also some good mechanical properties, as tenacity, which minimizes the vandalism damage, one of the great problems in this sector. The polyurethane resin attributes hydrocospicity to the wood and protection against the attack of biological agents, improving its mechanical and electrical properties. An innovative process was used for the impregnation of the wood with resin, utilizing vacuum for both processing impregnation of the resin. The atmospheric pressure expels the air out of the resin, which becomes more homogeneous, and obliges it to fill the cavities of the wood.

L’objectif de cette thèse est d’élaborer de nouveaux (super)isolants thermiques à partir de silices nanostructurées telles que les Silices Mésoporeuses Organisées et les phyllosilicates. Dans un premier temps, il s’agissait d’élaborer les matériaux en contrôlant les paramètres clé de synthèse, puis de les caractériser en évaluant notamment les propriétés thermiques. Les matériaux étudiés sont des micro- et nanoparticules de silice mésoporeuse d’une part, synthétisées avec des porosités intra- et interparticulaires contrôlées, et des phyllosilicates naturels et synthétiques d’autre part. Dans un deuxième temps, différents traitements post-synthèse ont été réalisés sur ces matériaux pour améliorer significativement leurs propriétés physico-chimiques –en particulier les propriétés d’isolation thermique– et leurs performances mécaniques. Par la suite, dans le cadre de l’étude des phyllosilicates modifiés, des composites peu denses phyllosilicates/polymères et phyllosilicates/tensioactifs intercalés et/ou exfoliés ont été élaborés afin d’améliorer les propriétés obtenues et de réaliser une mise en forme de ces matériaux. Les conductivités thermiques ont été déterminées sur l’ensemble des matériaux utilisés. / This thesis aims at developing new thermal (super)insulators from nanostructured silicas such as Organized Mesoporous Silicas and phyllosilicates. First, new materials were created controlling the key-parameters of the synthesis ; these materials were then finely characterized and especially their thermal properties. On one hand, studied materials are mesoporous silica micro- and nanoparticles synthesized with controlled intra- and interparticular porosities, and on the other hand natural and synthetic phyllosilicates. Then post-synthesis treatments were applied to enhance significantly thermal and mechanical performances of the products. In a further step, in the case of the treated phyllosilicates, low-density phyllosilicates/polymers composites and intercalated and/or delaminated phyllosilicates/surfactant composites were synthesized to improve the properties that were obtained and to process the materials. Thermal conductivity was determined for all the samples.

Thesis (PhD)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: The main aim of this research programme was to compare the relative performance of different insulator materials used in South Africa when subjected to a severe marine pollution environment. A test programme and procedure, test facility and instrumentation were established. Some novel instrumentation and monitoring equipment were developed and built specifically for this research programme, supported by data analysing software programs. In order to compare material performance only, all non-material design variables between the test insulators had to be removed (e.g. creepage distance, connecting length, inter-shed spacing, profile, etc.). To achieve this some of the test insulators had to be specially manufactured. Leakage current, electrical discharge activity, climatic and environmental data was collected successfully over a one-year test period, starting with new test insulators. The peak and energy values of the leakage current were identified as the two main parameters needed to describe the leakage current activity on the test insulators. A correlation was found between the climatic and environmental data and the leakage current data, and it was found that the leakage current can be determined successfully from some of the climatic and environmental parameters monitored by using multiple regression techniques. Surface conductivity and energy were found to be the best parameters to show the maximum and continuous interaction of the insulator material surface with the electrolytic pollution layer. A natural ageing and pollution test procedure was developed, which has become a South African standard and is gaining international acceptance. A model and hypothesis are proposed to describe the electrical discharge activity that takes place on the test insulators and explain the difference in leakage current performance of the various materials. Keywords: Insulator, Pollution, High Voltage, Leakage current, Material performance. / AFRIKAANSE OPSOMMING: Die hoofdoel van hierdie navorsingsprogram was om die relatiewe prestasie van verskillende isolatormateriale wat in Suid-Afrika gebruik word te vergelyk in 'n swaar besoedelde marine omgewing. 'n Toetsprogram en prosedure, toets fasiliteit en instrumentasie is gevestig. 'n Paar nuwe instrumente en moniteer toerusting is ontwikkel en gebou spesifiek vir hierdie navorsingsprogram, gesteun deur data analise sagteware programme. Ten einde slegs materiaalprestasie te vergelyk, moes alle nie-materiaal ontwerpsveranderlikes tussen die toetsisolators verwyder word (bv. kruipafstand, konnekteer lengte, tussen-skerm spasiëring, profiel, ens.). Om dit reg te kry moes sommige van die toetsisolators spesiaal vervaardig word. Lekstroom, elektriese ontladingsaktiwiteit, klimaat en omgewingsdata is suksesvol versameloor 'n een-jaar toetsperiode, beginnende met nuwe toets isolators. Die piek en energie waardes van die lekstroom is identifiseer as die twee hoof parameters wat nodig is om die lekstroomaktiwiteit op die toetsisolators te beskryf. 'n Korrelasie is gevind tussen die klimaat- en omgewingsdata en die lekstroom data, en dit is gevind dat die lekstroom data suksesvol bepaal kan word van sekere van die klimaat- en omgewingsparameters wat gemoniteer is deur veelvoudige regressie tegnieke te gebruik. Oppervlakskonduktiwiteit en energie is gevind die beste parameters te wees om die maksimum en kontinue interaksie van die isolatormateriaaloppervlak met die elektrolitiese besoedelingslaag aan te toon. 'n Natuurlike veroudering en besoedeling toetsprosedure is ontwikkel, wat 'n Suid-Afrikaanse standaard geword het en besig is om internastionale aanvaarding te wen. 'n Model en hipotese word voorgestelom die elektriese ontladingsaktiwiteit wat op die toetsisolators plaasvind te beskryf en om die verskil in lekstroomprestasie van die verskeie materiale te verduidelik. S/eufelwoorde: Isolator, Besoedeling, Hoog Spanning, Leek stroom, Materiaal prestasie.

Memoire (M. Sc. A.)-- Universite du Quebec a Chicoutimi, 1984. / Bibliographie: f. 109-114. Document électronique également accessible en format PDF. CaQCU

Mémoire (M. Sc.A.)-- Université du Québec à Chicoutimi, 1985. / Bibliogr.: f. [94]-99. Document électronique également accessible en format PDF. CaQCU

Mémoire (M.Eng.)--Université du Québec à Chicoutimi, 1996. / Document électronique également accessible en format PDF. CaQCU

Mémoire (M.Eng.)--Université du Québec à Chicoutimi, 1996. / Document électronique également accessible en format PDF. CaQCU