Québec Université Laval, Bibliothèque 2012

<p>In this work, we study two important themes in the physics of the interacting one-dimensional (1D) electron gas: the transition from one-dimensional to higher dimensional behavior, and the role of inhomogeneity. The interplay between interactions, reduced dimensionality, and inhomogeneity drives a rich variety of phenomena in mesoscopic physics. In 1D, interactions fundamentally alter the nature of the electron gas, and the homogeneous 1D electron gas is described by Luttinger Liquid theory. We use Quantum Monte Carlo methods to study two situations that are beyond Luttinger Liquid theory --- the quantum phase transition from a linear 1D electron system to a quasi-1D zigzag arrangement, and electron localization in quantum point contacts. </p><p>Since the interacting electron gas has fundamentally different behavior in one dimension than in higher dimensions, the transition from 1D to higher dimensional behavior is of both practical and theoretical interest. We study the first stage in such a transition; the quantum phase transition from a 1D linear arrangement of electrons in a quantum wire to a quasi-1D zigzag configuration, and then to a liquid-like phase at higher densities. As the density increases from its lowest values, first, the electrons form a linear Wigner crystal; then, the symmetry about the axis of the wire is broken as the electrons order in a quasi-1D zigzag phase; and, finally, the electrons form a disordered liquid-like phase. We show that the linear to zigzag phase transition occurs even in narrow wires with strong quantum fluctuations, and that it has characteristics which are qualitatively different from the classical transition.</p><p>Experiments in quantum point contacts (QPC's) show an unexplained feature in the conductance known as the ``0.7 Effect''. The presence of the 0.7 effect is an indication of the rich physics present in inhomogeneous systems, and we study electron localization in quantum point contacts to evaluate several different proposed mechanisms for the 0.7 effect. We show that electrons form a Wigner crystal in a 1D constriction; for sharp constriction potentials the localized electrons are separated from the leads by a gap in the density, while for smoother potentials, the Wigner crystal is smoothly connected to the leads. Isolated bound states can also form in smooth constrictions if they are sufficiently long. We thus show that localization can occur in QPC's for a variety of potential shapes and at a variety of electron densities. These results are consistent with the idea that the 0.7 effect and bound states observed in quantum point contacts are two distinct phenomena.</p> / Dissertation

The thesis is concerned with the contact mechanics behaviour of non-conforming solids. The geometry of the solids considered gives rise to various contact configurations, from concentrated contacts with circular and elliptical configuration to those of finite line nature, as well as those of less concentrated form such as circular flat punches. The radii of curvature of mating bodies in contact or impact give rise to these various nonconforming contact configurations and affect their contact characteristics, from those considered as semi-infinite solids in accord with the classical Hertzian theory to those that deviate from it. Furthermore, layered solids have been considered, some with higher elastic modulus than that of the substrate material (such as hard protective coatings) and some with low elastic moduli, often employed as tribological coatings (such as solid lubricants). Other bonded layered solids behave in viscoelastic manner, with creep relaxation behaviour under load, and are often used to dampen structural vibration upon impact. Analytic models have been developed for all these solids to predict their contact and impact behaviour and obtain pressure distribution, footprint shape and deformation under both elastostatic and transient dynamic conditions. Only few solutions for thin bonded layered elastic solids have been reported for elastostatic analysis. The analytical model developed in this thesis is in accord with those reported in the literature and is extended to the case of impact of balls, and employed for a number of practical applications. The elastostatic impact of a roller against a semi-infinite elastic half-space is also treated by analytic means, which has not been reported in literature. Two and three-dimensional finite element models have been developed and compared with all the derived analytic methods, and good agreement found in all cases. The finite element approach used has been made into a generic tool for all the contact configurations, elastic and viscoelastic. The physics of the contact mechanical problems is fully explained by analytic, numerical and supporting experimentation and agreement found between all these approaches to a high level of conformance. This level of agreement, the development of various analytical impact models for layered solids and finite line configuration, and the development of a multi-layered viscoelastic transducer with agreed numerical predictions account for the main contributions to knowledge. There are a significant number of findings within the thesis, but the major findings relate to the protective nature of hard coatings and high modulus bonded layered solids, and the verified viscoelastic behaviour of low elastic modulus compressible thin bonded layers. Most importantly, the thesis has created a rational framework for contact/impact of solids of low contact contiguity.

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

A eficiência dos sistemas mecânicos é influenciada diretamente pelo coeficiente de atrito local, sendo este relacionado com os regimes de lubrificação. O coeficiente de atrito pode ser estudado usando o método de elementos finitos (MEF) com a finalidade de substituir ensaios experimentais e reduzir tempo de análise. Esta dissertação teve como objetivo desenvolver uma metodologia para avaliar o coeficiente de atrito em um par tribológico e seu efeito na eficiência por simulação numérica. Para esta modelagem foi definido um sistema composto por um par de engrenagens helicoidais. Em uma primeira análise, foi empregado o programa AVL Excite Power Unit, que utiliza a ferramenta MBD (Multi-Body Dynamic - Dinâmica de Multi-Corpos), possibilitando a simulação da transmissão com seus principais elementos em um modelo 1D, que leva em consideração a teoria da lubrificação elastohidrodinâmica (EHL). Também foi utilizado o programa Abaqus®, da Dassault Systèmes, para a criação de um modelo 3D, que considera o par engrenado e sendo necessário o desenvolvimento de uma subrotina para a aplicação do modelo de lubrificação da literatura. Em todas as simulações foram considerados condições de operação de um banco de provas e três diferentes acabamentos superficiais dos dentes das engrenagens em função do processo de fabricação: fresamento, retificação e polimento. Além da rugosidade, avaliou-se o efeito da velocidade angular nas perdas do sistema. O modelo 3D foi comparado com o modelo 1D e com resultados de eficiência de ensaios de banco de prova. O modelo 3D permitiu avaliar o coeficiente de atrito local na linha de contato do dente engrenado. Maiores velocidades angulares aumentaram a espessura de específica de filme, diminuindo assim o coeficiente de atrito e promovendo uma melhoria na eficiência do sistema. Os menores valores de coeficiente de atrito estão na região do diâmetro primitivo, onde o SRR é nulo. A velocidade angular influenciou mais do que a rugosidade. As análises dos modelos 1D e 3D indicaram que o modelo 1D superestima a eficiência da transmissão, enquanto que o modelo 3D apresentou resultados compatíveis com o banco de provas. / The efficiency of mechanical systems is influenced directly by the local friction coefficient, which is related to the lubrication regimes. The coefficient of friction can be studied using the finite element method (FEM) to replace experimental tests and reduce analysis time. This dissertation had the objective to develop a methodology to evaluate the coefficient of friction in a tribological pair and the effect on the efficiency by numerical simulation. In this model, a system composed of a pair of helical gears was defined. In a first analysis, the AVL Excite Power Unit software was used, which uses the tool MBD (Multi-Body Dynamic), enabling the simulation of the transmission with the main elements in a 1D model, which takes into account the theory of elastohydrodynamic lubrication (EHL). The Abaqus® software was used to create a 3D model, which considers the pair of helical gear and a developed subroutine for application of the literature lubrication model. In all simulations, the conditions of operation of a rig tests and three different surface finishes of the gear teeth were considered, depending on the manufacturing process: milling, grinding and polishing. Besides the roughness, the effect of angular velocity on the losses of the system was evaluated. The 3D model was compared with the 1D model and with the results of rig tests efficiency. The 3D model allowed to evaluate the coefficient of local friction in the contact line of the tooth. Higher angular velocities increased the film specific thickness, thus reducing the coefficient of friction and promoting an improvement in the efficiency of the system. The lowest values of coefficient of friction are in the region of the primitive diameter, there the SRR is zero. The angular velocity influenced more than the roughness. The analyzes of the 1D and 3D models indicated that the 1D model overestimates the transmission efficiency, while the 3D model presented results compatible with the rig tests.

Cette thèse propose une approche pour générer un mouvement corps complet avec contacts non coplanaires, permettant à un robot de se déplacer dans un environnement, de manipuler des objets complexes ou de collaborer avec différents agents. Les méthodes développées dans cette thèse tentent de prendre en compte une grande variété de robots, de l'humanoïde au manipulateur à base fixe en passant par les objets sous actionnés. En premier lieu, nous abordons le problème du choix des positions des points de contacts qu'un robot sous-actionné doit prendre pour se déplacer dans l'environnement. Nous calculons, en un seul problème d'optimisation non-linéaire, une séquence de postures qui satisfait une séquence de contacts donnés. Cette formulation permet de trouver la position des contacts optimale, car le choix de la position d'un contact d'une posture va prendre en compte les postures précédentes et suivantes. Elle permet aussi d'effectuer des tâches pour certaines postures qui prendront en compte l'aspect prioritaire du déplacement. Nous introduisons ensuite une méthode de génération de mouvement qui, en se basant sur la programmation quadratique, permet de résoudre le problème de géométrie inverse et de la dynamique inverse pour un robot à base fixe ou mobile, tout en satisfaisant des contraintes d'égalités et d'inégalités.Cette génération de mouvement est assez rapide pour fonctionner à la vitesse de la boucle de contrôle des robotsHRP2-10 et HRP4, et peut donc être utilisé en temps réel. À l'aide d'une machine à état, nous transformons la séquence de postures calculée à priori en une série de tâches à effectuer par le générateur de mouvement, ce qui permet à notre robot de se déplacer dans un environnement complexe. Nous étendons alors notre méthode de génération de mouvement pour calculer la commande d'un nombre arbitraire de robots. Cette extension nous permet de gérer des tâches de manipulation d'objets complexes, de collaboration entre plusieurs agents et de mouvement dans un environnement dynamique. Nous pouvons aussi spécifier directement les tâches dans le repère de l'objet manipulé pour faciliter l'élaboration de notre consigne. Dans l'optique de valider cette méthode sur un robot réel, nous formulons le problème d'estimation des paramètres inertiels d'un objet manipulé grâce à l'algèbre vectorielle spatiale. Finalement, nous validons nos travaux sur les robots HRP2-10 et HRP4. Sur le premier robot, nous validons la génération de posture et la génération de mouvement mono-robot sur le scénario demonté d'une échelle verticale aux normes industrielles. La manipulation d'objets et l'estimation des paramètres inertiels sont validées par la suite sur le robot HRP4. / This PhD proposes a whole body motion generation approach with non coplanar contacts that allowsa robot to move in an environment, manipulate complex objects or collaborate with differentagents.Methods developed in this PhD try to manage many kinds of robots, from the humanoid to thefixed base manipulator and also handling underactuated objects.Firstly, we address the problem contacts positioning that an underactuated robot should taketo move in its environment.We compute in one non-linear optimization problem a sequence of postures that fulfill aninputed contact list. This formulation allows to find the optimal contact placement regardingprevious and next stances. It also allows to execute a task for some posture while taking into accountthe priority of the motion.Next, we introduce a motion generation method that uses quadratic programming to solveinverse kinematics and dynamics problems for a fixed or mobile base robot under equality andinequality constraints.This motion generation is fast enough to fit the HRP2-10 and HRP4 control loop andcan be used in real-time.With a finite state machine we turn the posture sequence into a list of tasks that should beexecuted by the motion generation to allow a robot to move in a complex environment.We extend this motion generation scheme to compute the motion of an arbitrary number of robots.This extension allows us to manage complex object manipulation tasks, multi-agent collaboration andmotion in a dynamic environment. We can also specify a task in the manipulated object frameto ease motion design.To validate this method on a real robot, we formulate inertial parametersestimation of manipulated objects with spatial vector algebra.Finally, we validate our works on the HRP2-10 and HRP4 robot. On the first one,we validate the posture and mono-robot motion generation on a scenario where the robot climbs anindustry standard vertical ladder.On the second one, we validate object manipulation and inertial parameters estimation.

No alto rio Uruguai, pesquisas arqueológicas são realizadas desde 1950 e apontam a importância desse rio para os povoamentos pré-históricos. A variabilidade artefatual arqueológica encontrada nessa região, como ocorreu para outras áreas brasileiras, foi inicialmente organizada em fases e tradições, no âmbito da Ecologia Cultural. Nas últimas décadas, as pesquisas têm levantado novas informações sobre os caçadores-coletores relacionados à tradição Umbu e seus sistemas técnicos, que ocuparam a região na passagem Pleistoceno-Holoceno e sobre as sociedades ceramistas, Guarani e Itararé-Taquara, que colonizaram o alto Uruguai no último milênio. Com esta pesquisa, procuro trazer novos elementos sobre os contatos culturais estabelecidos entre as sociedades de agricultores ceramistas Guarani e Itararé-Taquara, que ocuparam a Volta do Uvá (alto rio Uruguai), durante o Holoceno tardio. O contato cultural é entendido aqui não somente como mecanismo de intercâmbio de bens já manufaturados, mas também de métodos e técnicas para elaborar a cerâmica. As análises tecnológicas e estilísticas realizadas nos conjuntos cerâmicos Guarani e Itararé-Taquara, evidenciam duas tradições culturais bem diferenciadas que, mesmo ocupando a região num mesmo bloco espaço-temporal, parecem ter tido um baixo grau de interação cultural, ao menos no que se refere aos conjuntos cerâmicos. / In the region Alto Uruguai River, archeological research have been deveolped since 1950 and reinforce the importance of that river for the pre-historical people. The archeological artifactual variability found in that region, as it had occurred to other Brazilian areas, was initially organized in phases and traditions, according to Cultural Ecology field. Over the last decades, research has been raising new information about the collector-hunters related to Umbu tradition and their technical systems, which had occupied the region in the passage Pleistocene-Holocene and about the ceramist societies, Guarani and Itararé-Taquara, which colonized the region Alto Uruguai in the last millennium. By doing this research, it is aimed to suggest new elements on the cultural contacts established beteween the agricultural ceramist societies Guarani and Itararé-Taquara, that occupied the Volta do Uvá (Alto Uruguai River), during Late Holocene. The cultural contact is understood hereby, not only as mecanism for interchange of manufactured goods, but also methods and techniques to elaborate the ceramic. The technological and stylistic analysis performed in the ceramic sets Guarani and Itararé-Taquara, left evident two of the cultural traditions differenciated, which even occupying the region in the same space-time block, they seem to have had a low degree of cultural interaction, at least related to ceramic sets.

Du fait de la complexité des processus de spéciation, l'étude des relations évolutives entre espèces nécessite une approche intégrative. Nous avons combiné croisements expérimentaux et études moléculaires (séquençage mitochondrial et RAD-seq) pour étudier les relations évolutives entre espèces indigènes et introduites du genre Ciona, en Europe. Nous avons examiné deux mécanismes post-zygotiques restant à explorer pour expliquer l'absence d'introgression de C. robusta et C. intestinalis dans leur zone de sympatrie en Manche : 1) la contre-sélection des hybrides par l'environnement (température et salinité) et 2) des incompatibilités de type Dobzhansky-Muller (DMIs). L'absence de dépression hybride (étudiée chez 725 hybrides F1) nous a conduit à rejeter le premier mécanisme. Le second a été exploré grâce à l'étude de sept familles double-hybrides ou issues de rétrocroisements, analysées par RAD-seq. Une stérilité sur la fonction mâle des hybrides F1 et d'importantes distorsions de ségrégation sont en faveur de la présence de DMIs. Nous avons étendu notre étude à d'autres espèces du genre Ciona. Les principaux résultats, notamment soutenus par une approche phylogénomique (7 taxons - 89 individus), sont : 1) la remise en cause du statut d'espèce de C. roulei par rapport à C. intestinalis (probablement deux lignées allopatriques), 2) les premières données montrant la forte divergence évolutive de C. edwardsi avec les autres Ciona spp. et 3) la présence de variabilité génétique et/ou d'introgression chez C. intestinalis type C et type D. Ces résultats ouvrent d'intéressantes perspectives de recherches dont des études populationnelles des espèces présentes en Méditerranée. / Speciation is a complex process. Evolutionary relationships between close species thus required an integrative approach. We combined experimental crosses and molecular data (mitochondrial and RAD-tag sequencing) to investigate evolutionary relationships between native and non-indigenous species of the genus Ciona nowadays found in Europe. We studied two post-zygotic mechanisms, still to be examined, to explain the lack of introgression between C. robusta and C. intestinalis in their sympatric range –i.e. the English Channel: i) selection against hybrids, by the environment (here temperature and salinity) and ii) Dobzhansky-Muller incompatibilities (DMIs). The absence of outbreeding depression (over 725 F1-hybrids) makes unlikely the first mechanism. The second has been investigated with seven families of F2-hybrids and backcrosses, all studied with RAD-tag sequences. Male sterility on F1-hybrids and many segregation distortions are in favor of presence of DMIs. We then expanded our study to other Ciona species. The main outcomes, supported by a phylogenomic approach (7 taxa - 89 individuals) are: 1) a needed reappraisal of the species status of C. roulei and C. intestinalis, which are most likely two allopatric lineages of a same species (as defined by biological and phylogenetic species concepts), 2) the first data showing that C. edwardsi is strongly evolutionary divergent from the other Ciona species and 3) the presence of unexpected genetic variability and/or introgression in C. intestinalis type C and D. All together these results open new research perspectives, in particular based on population studies of the species nowadays found in the Mediterranean Sea.

Cette thèse s’intéresse aux contacts de langues présents dans la formation des enseignants de français langue étrangère. Depuis quelques années, l’enseignement des langues étrangères se répand au Mexique. En 2009, 22 licences formaient des enseignants de langues, sans compter les institutions privées, et ce chiffre continue d’évoluer. Les étudiants y débutent leur contact avec le français avec certains imaginaires sociaux, issus de deux siècles de colonisation et de traditions culturelles nées des contacts de langues. Ainsi, plusieurs images restent ancrées dans l’imaginaire collectif, notamment celles de Malinche, et certaines idées sur l’altérité perdurent, suscitant des postures enseignantes particulières. À partir des imaginaires des langues et des locuteurs, nous analyserons les rapports de pouvoir existant dans le contact de langues en cours de français. Prenant en compte cet héritage comme un écran socio-culturel de perception de l’autre, notre étude repose sur les témoignages des enseignants et apprenants mexicains en licence de langues et en master de didactique du français, qui racontent leurs parcours linguistiques et leurs expériences lors des formations. / The main subject is the contact between languages present in the formation of French as a Foreign Language teachers. Globalization has fostered that teaching foreign languages, particularly French, spreads throughout Mexico. However, Mexican students have their first contact with the French language permeated by certain social imaginaries. Over time, the imaginaries -particularly those related to Malinche- have had a significant role. The different imaginaries surrounding foreign languages and their speakers bring back old conceptions and behaviours while interaction with the other and when we speak another language. Imaginaries also serve to analyse power relationships between languages. Thus, heritage can be considered a socio-cultural screen that shapes our perception of otherness.

Esta tese é composta por três ensaios sobre o mercado de trabalho brasileiro, cada um correspondendo a um capítulo. O primeiro ensaio identifica se há uma relação entre doenças cardiovasculares e salários no Brasil com base nos dados da Pesquisa Nacional de Saúde 2013. Utilizaram-se os métodos de regressão quantílica incondicional e de decomposição para quantis por meio de funções de influência. Os resultados das regressões indicaram que, para os trabalhadores nos primeiros decis de renda as perdas salariais podem ser significativas. Para os homens, a incidência de doenças cardiovasculares pode reduzir os salários entre 0,90% e 14,80%; para as mulheres, entre 1,20% e 18%. A decomposição mostrou que homens e mulheres valorizam atributos distintos para o cômputo de seus salários e que os cuidados preventivos de saúde ajudam a explicar a menor incidência de doenças cardiovasculares no caso das mulheres. Os homens, por seu turno, apresentam maior demanda por serviços médicos em idades mais avançadas, o que é corroborado pela estimativa negativa da idade sobre o efeito atribuível às características próprias. O segundo ensaio analisa a relação entre (i) o ciclo econômico e o uso de contatos pessoais para obter emprego por meio de um modelo com parâmetros variantes no tempo; e (ii) a relação entre o uso de contatos pessoais para obter emprego e os salários utilizando-se regressão quantílica. Para tanto, foram empregados os microdados da Pesquisa Mensal de Emprego entre 2002 e 2015. As estimativas indicam que o uso de contatos pessoais tornou-se menos anticíclico ao longo do tempo Em geral, eles mostram que há mais evidências de uma relação de mudança lenta entre contatos pessoais e o ciclo econômico ao longo do tempo, em vez de uma quebra repentina e discreta. Observa-se que as diferenças salariais entre trabalhadores que usam contatos pessoais versus trabalhadores que usam outros canais desaparecem. As evidências apontam que os trabalhadores recorrem a contatos pessoais devido à avaliação de características de trabalho não pecuniárias. Por fim, o terceiro ensaio faz uma análise dos retornos do empreendedorismo feminino no Brasil para o período 1992-2015. Para tanto, faz uso dos microdados da Pesquisa Nacional por Amostra de Domicílios e uma análise de regressão que incluiu os efeitos idade, período e coorte. Os resultados implicam que as mudanças que são próprias do perfil etário assumem um papel de destaque na evolução dos rendimentos das mulheres que atuam por conta própria e para as empregadoras informais (aquelas com no máximo cinco empregados). O efeito coorte permitiu um acréscimo de renda às autônomas, por meio da abertura e criação de novas oportunidades a esse segmento de mulheres. Contudo, não apresentou nenhuma correlação com os ganhos monetários das empregadoras, sugerindo a existência de “barreiras” para esse grupo. Os efeitos de curto prazo associados às flutuações econômicas tendem a ser contracíclicos, de forma geral, até 2005 e posteriormente são pró-cíclcos. / This thesis is composed of three essays on the Brazilian labor market, each one corresponding to a chapter. The first essay identifies whether there is a relationship between cardiovascular diseases and wages in Brazil based on data from the National Health Survey 2013. The unconditional quantile regression and the quantile-regression based decomposition methods were used, which are based on influence functions. The results of the regressions indicated that, for workers in the first decile of income, wage losses can be significant. For men, the incidence of cardiovascular diseases can reduce wages between 0.90% and 14.80%; for women, between 1.20% and 18%. The decomposition showed that men and women value different attributes for the computation of their wages and that preventive health care helps explain the lower incidence of cardiovascular diseases in the case of women. Men, in turn, have greater demand for medical services at more advanced ages, which is corroborated by the negative age estimate. The second essay analyzes the relationship between (i) business cycle and use of personal contacts to obtain job, and (ii) use of personal contacts to obtain job and wages. To do so, we used the microdata of the Monthly Employment Survey between 2002 and 2015. Time-varying parameter estimates indicate that the relationship between business cycle and use of personal contacts became less countercyclical over time. In general, they show that there is more evidence of a slow changing relationship between personal contacts and the business cycle over time rather than a sudden and discrete one Using quantile regressions, we observed that, controlling for similar observable characteristics, and including unobserved heterogeneity, wage differences between workers using personal contacts versus workers using others channels disappear. The evidences seems to indicate that workers resort to personal contacts because of valuation of non-pecuniary job characteristics. Finally, the third essay analyzes the wage dynamics of women entrepreneurs in Brazil for the 1992-2015 period. To do so, we use the microdata from the National Household Sample Survey. The method consists of a regression analysis that included the effects age, period and cohort. The results suggest that changes in the age play an important role in the evolution of the income of the self-employed and informal employers. The cohort effect allowed an increase in income to the self-employed, through the opening and creation of new opportunities for this segment. However, it did not show any correlation with employers’ monetary gains, suggesting the existence of “barriers” to this group. The short-term effects associated with economic fluctuations tend to be countercyclical, generally up to 2005, and later pro-cyclical.