Apresentamos os resultados do estudo das não-linearidades ópticas de origem eletrônica de duas moléculas da classe dos oligômeros de anilina: o dímero e o tetrâmero. Foram medidas quatro concentrações de tetrâmero, puras e também dopadas em 33 e 100%; uma de dímero pura e outra dopada em 100%. As soluções foram preparadas usando dimetil-sulfóxido (DMSO) como solvente e a dopagem foi realizada com ácido clorídrico. As amostras foram caracterizadas por medidas de absorção linear e fluorescência antes das medidas não-lineares. Obtivemos os valores da primeira hiperpolarizabilidade (?) para todas as amostras, o índice de refração não-linear (n2) do tetrâmero dopado e não dopado, e a absorção não-linear em função da intensidade e da concentração do tetrâmero. As medidas foram realizadas através das técnicas de Varredura-Z, absorção não-linear e espalhamento Hiper-Rayleigh. Os resultados foram interpretados em termos da comparação entre diferentes estados de dopagem e da variação da seção de choque do estado fundamental para o primeiro excitado. / We report on the study of electronic optical non linearities in two aniline oligomers: dimer and the tetramer. Four tetramer concentrations were measured, pure and also 33 and 100% doped; one of dimer non doped another 100% doped. The solutions were prepared using dimethyl sulfoxide (DMSO) as solvent and the doping was performed with hydrochloric acid. The samples were characterized by measurements of linear absorption and fluorescence. We obtained the values of the first hyperpolarizability (?) for all samples, the non linear index of refraction (n2) for non doped and doped tetramer, and the non linear absorption in function of intensity and concentration of the tetramer. The measurements were accomplished through the techniques of Z-Scan, non linear absorption and Hyper-Rayleigh Scattering. The results were interpreted in terms of the comparison among different doping states and of the variation of cross-section for the transition from ground to the first excited states.

Dans le cadre de la fusion par confinement inertiel, nous présentons une analyse des effets du champ magnétique sur le développement linéaire des instabilités de Richtmyer-Meshkov, en magnétohydrodynamique idéale d’une part, et de Rayleigh-Taylor au front d’ablation, dans les phases d’accélération et de décélération d’autre part.A l’aide d’un code linéaire de perturbation, nos simulations mono mode nous permettent de confirmer, pour l’instabilité de Richtmyer-Meshkov, la stabilisation apportée par la composante du champ magnétique parallèle au vecteur d’onde des perturbations de l’interface, dont l’amplitude oscille au cours du temps. Nous montrons que la prise en compte de la compressibilité n’apporte pas de changements significatifs par rapport au modèle impulsionnel incompressible existant dans la littérature. Dans nos simulations numériques bidimensionnelles, en géométrie plane, de l’instabilité de Rayleigh-Taylor dans la phase d’accélération, nous prenons en compte le phénomène d’auto-génération de champ magnétique induite par cette instabilité. Nous montrons qu’il est possible d’atteindre des valeurs de champ de l’ordre de quelques teslas et que la croissance de l’amplitude des perturbations transite plus rapidement vers un régime de croissance non-linéaire avec, notamment, un développement accru de la troisième harmonique. Nous proposons également une adaptation d’un modèle existant, étudiant l’effet d’anisotropie de conductivité thermique sur le taux de croissance de l’instabilité de Rayleigh-Taylor au front d’ablation, pour tenter de prendre en compte les effets des champs magnétiques auto-générés sur le taux de croissance de l’instabilité de Rayleigh-Taylor. Enfin, dans une étude numérique à deux dimensions, en géométrie cylindrique, nous analysons les effets des champs magnétiques auto-générés par l’instabilité de Rayleigh-Taylor dans la phase de décélération. Cette dernière étude révèle l’apparition de champs magnétiques pouvant atteindre plusieurs milliers de teslas sans pour autant affecter le comportement de l’instabilité de Rayleigh-Taylor. / In the context of inertial confinement fusion we investigate effects of magnetic fields on the development in the linear regime of two hydrodynamic instabilities: Richtmyer-Meshkov instability using ideal magnetohydrodynamics and ablative Rayleigh-Taylor instability in both acceleration and deceleration stages.Direct numerical simulations with a linear perturbation code enable us to confirm the stabilizing effect of the component of the magnetic field along the perturbations wave vector. The amplitude doesn’t grow linearly in time but experiences oscillations instead. The compressibility taken into account in the code does not affect predictions given by an already existing impulsive and incompressible model.As far as Rayleigh-Taylor instability is concerned we study the effects of self-generated magnetic fields that arise from the development of the instability itself. In the acceleration stage we perform two dimensional simulations in planar geometry. We show that magnetic fields of about 1T can be generated and that the instability growth transits more rapidly into nonlinear growth with the enhancement of the development of the third harmonic. We also propose an adaptation of an existing model that aims at studying thermal conductivity anisotropy effects, to take into account the effects of the self-generated magnetic fields on the Rayleigh-Taylor instability growth rate.Finally, in the deceleration stage, we perform two dimensional simulations in cylindrical geometry that take into account self-generation of magnetic fields due to the instability development. It reveals magnetic fields of about several thousands of teslas that are not strong enough though to affect the instability behavior.

A modelagem computacional tem se tornado uma poderosa ferramenta utilizada mundialmente em pesquisas sobre sistemas de comunicação móvel. Em tais sistemas, a modelagem do canal é fator indispensável, pois as características de mobilidade e propagação presentes nesse tipo de sistema são responsáveis por distorções ocorridas sobre o sinal transmitido. O presente trabalho reúne os principais modelos matemáticos e computacionais de canal de comunicação móvel. Realiza-se uma abordagem histórica sobre o assunto, apresentado a natureza do problema do desvanecimento e a forma como foi modelado inicialmente. Por outro lado, apresentam-se modelos recentes, considerados eficazes do ponto de vista matemático e eficientes do ponto de vista computacional. O trabalho traz como contribuição a proposta de um novo modelo de canal com desvanecimento. Os modelos apresentados foram analisados do ponto de vista matemático por meio de suas propriedades estatísticas. Do ponto de vista numérico e computacional a análise se deu por meio de simulações. A principal conclusão obtida mostra que dois modelos com filtragem no domínio da freqüência, sendo um deles o novo modelo proposto, são os mais indicados para simular formas de onda que representem um canal com desvanecimento Rayleigh. Este trabalho tem a pretensão de ser útil para pesquisadores atuantes na área de modelagem e simulação de sistemas atuais de comunicação móvel. / Computational modelling is a powerful and widely used tool for research in mobile communication systems. In such systems, the communication channel modelling is an indispensable factor, because its mobility and propagation characteristics can cause distortion over the transmitted waveform. This work contains the main mathematical and computing communication channel models. A historical cover is provided, which presents the nature of the problem and the initial modelling of the fading phenomenon. On the other hand, recent models are presented, which are mathematically effective and computationally efficient. One contribution of this work is the proposal of a new fading channel computational model, which was suitably tested and validated. The presented models were mathematically analyzed through its statistical properties. From numerical and computational point of view, the models were analyzed through several simulations. The main conclusion, from analytical and simulated results, shows that two models using frequency filtering are the best choice for the generation of multiple uncorrelated Rayleigh fading waveforms, where one of them is the new proposed model. This work can help mobile communications researchers to suitably model the communication channel in a computer simulation.

A modelagem computacional tem se tornado uma poderosa ferramenta utilizada mundialmente em pesquisas sobre sistemas de comunicação móvel. Em tais sistemas, a modelagem do canal é fator indispensável, pois as características de mobilidade e propagação presentes nesse tipo de sistema são responsáveis por distorções ocorridas sobre o sinal transmitido. O presente trabalho reúne os principais modelos matemáticos e computacionais de canal de comunicação móvel. Realiza-se uma abordagem histórica sobre o assunto, apresentado a natureza do problema do desvanecimento e a forma como foi modelado inicialmente. Por outro lado, apresentam-se modelos recentes, considerados eficazes do ponto de vista matemático e eficientes do ponto de vista computacional. O trabalho traz como contribuição a proposta de um novo modelo de canal com desvanecimento. Os modelos apresentados foram analisados do ponto de vista matemático por meio de suas propriedades estatísticas. Do ponto de vista numérico e computacional a análise se deu por meio de simulações. A principal conclusão obtida mostra que dois modelos com filtragem no domínio da freqüência, sendo um deles o novo modelo proposto, são os mais indicados para simular formas de onda que representem um canal com desvanecimento Rayleigh. Este trabalho tem a pretensão de ser útil para pesquisadores atuantes na área de modelagem e simulação de sistemas atuais de comunicação móvel. / Computational modelling is a powerful and widely used tool for research in mobile communication systems. In such systems, the communication channel modelling is an indispensable factor, because its mobility and propagation characteristics can cause distortion over the transmitted waveform. This work contains the main mathematical and computing communication channel models. A historical cover is provided, which presents the nature of the problem and the initial modelling of the fading phenomenon. On the other hand, recent models are presented, which are mathematically effective and computationally efficient. One contribution of this work is the proposal of a new fading channel computational model, which was suitably tested and validated. The presented models were mathematically analyzed through its statistical properties. From numerical and computational point of view, the models were analyzed through several simulations. The main conclusion, from analytical and simulated results, shows that two models using frequency filtering are the best choice for the generation of multiple uncorrelated Rayleigh fading waveforms, where one of them is the new proposed model. This work can help mobile communications researchers to suitably model the communication channel in a computer simulation.

La caractérisation non destructive de l’adhérence des structures du type couche sur substrat est un enjeu industriel et académique important. Ce type d’échantillon est en effet utilisé pour de nombreuses applications et sa durée de vie dépend en grande partie de la qualité d’adhérence des films au substrat. Celle-ci modifie sensiblement le comportement dispersif des ondes acoustiques de surface se propageant dans de ce type de structure. Pour générer et détecter ces ondes, un dispositif Ultrasons-Laser a été privilégié. Dans un premier temps, nous avons cherché à contourner les difficultés d’interprétation rencontrées habituellement dans le contrôle de l’adhérence par ondes acoustiques de surface. Les variations d’épaisseur de la couche peuvent en effet avoir une influence sur la dispersion des ondes comparable à celle due à l’adhérence. Pour ce faire, des films polymères dont l’épaisseur est quasi-constante sont employés et apposés sur un substrat en aluminium. Ces films possèdent en plus la propriété d’être transparents. Cela permet de focaliser l’impulsion laser générant les ondes acoustiques à travers le film, directement à la surface du substrat et de placer ainsi la source acoustique à l’interface film-substrat. L’influence de la position de la source sur le comportement dispersif des ondes acoustiques de surface et par conséquent sur le contrôle de la qualité d’adhérence est alors étudiée expérimentalement ainsi qu’au travers de simulations par éléments finis. Finalement, une caractérisation de l’adhérence de différents échantillons est effectuée grâce aux courbes de dispersion obtenues à l’aide de la méthode Matrix-Pencil appliquée aux résultats expérimentaux. En utilisant un algorithme d’inversion, les raideurs d’interface caractéristiques de l’adhérence des échantillons analysés sont estimées. / The non-destructive characterization of the adhesion of layer-on-substrate structures is an important issue in industrial and academic domains. This type of sample is indeed used for many applications and its lifetime depends mainly on the adhesion of the film to the substrate. This one changes significantly the dispersive behavior of the surface acoustic waves. To generate and detect these waves, a Laser-Ultrasonics setup has been used. First, we are looking to bypass the interpretation difficulties usually encountered in the control of adhesion by surface acoustic waves. Indeed, the layer thickness variations influence the dispersion of the waves in a similar way to the adhesion. Consequently, the polymer films used have a quasi-constant thickness and they are deposited directly on an aluminum substrate. In addition, these films are also transparent. It allows us to generate directly the acoustic waves on the substrate surface, at the interface between the film and the substrate, by focusing the laser pulse through the film. In this way, the influence of the source location on the dispersive behavior of the surface acoustic waves and thus on the adhesion quality control may be studied experimentally and by using finite element simulations. Finally, a characterization of the adhesion of several samples is performed using the dispersion curves obtained applying the Matrix-Pencil method to the experimental results. An inversion algorithm allows us to estimate the interfacial stiffnesses corresponding to the adhesion of the samples.

No description available.

L’agrégation érythrocytaire est le principal facteur responsable des propriétés non newtoniennes sanguines pour des conditions d’écoulement à faible cisaillement. Lorsque les globules rouges s’agrègent, ils forment des rouleaux et des structures tridimensionnelles enchevêtrées qui font passer la viscosité sanguine de quelques mPa.s à une centaine de mPa.s. Cette organisation microstructurale érythrocytaire est maintenue par des liens inter-globulaires de faible énergie, lesquels sont brisés par une augmentation du cisaillement. Ces propriétés macroscopiques sont bien connues. Toutefois, les liens étiologiques entre ces propriétés rhéologiques générales et leurs effets pathophysiologiques demeurent difficiles à évaluer in vivo puisque les propriétés sanguines sont dynamiques et fortement tributaires des conditions d’écoulement. Ainsi, à partir de propriétés rhéologiques mesurées in vitro dans des conditions contrôlées, il devient difficile d’extrapoler leurs valeurs dans un environnement physiologique. Or, les thrombophlébites se développent systématiquement en des loci particuliers du système cardiovasculaire. D’autre part, plusieurs études cliniques ont établi que des conditions hémorhéologiques perturbées constituent des facteurs de risque de thrombose veineuse mais leurs contributions étiologiques demeurent hypothétiques ou corrélatives. En conséquence, un outil de caractérisation hémorhéologique applicable in vivo et in situ devrait permettre de mieux cerner et comprendre ces implications. Les ultrasons, qui se propagent dans les tissus biologiques, sont sensibles à l’agrégation érythrocytaire. De nature non invasive, l’imagerie ultrasonore permet de caractériser in vivo et in situ la microstructure sanguine dans des conditions d’écoulements physiologiques. Les signaux ultrasonores rétrodiffusés portent une information sur la microstructure sanguine reflétant directement les perturbations hémorhéologiques locales. Une cartographie in vivo de l’agrégation érythrocytaire, unique aux ultrasons, devrait permettre d’investiguer les implications étiologiques de l’hémorhéologie dans la maladie thrombotique vasculaire. Cette thèse complète une série de travaux effectués au Laboratoire de Biorhéologie et d’Ultrasonographie Médicale (LBUM) du centre de recherche du Centre hospitalier de l’Université de Montréal portant sur la rétrodiffusion ultrasonore érythrocytaire et menant à une application in vivo de la méthode. Elle se situe à la suite de travaux de modélisation qui ont mis en évidence la pertinence d’un modèle particulaire tenant compte de la densité des globules rouges, de la section de rétrodiffusion unitaire d’un globule et du facteur de structure. Ce modèle permet d’établir le lien entre la microstructure sanguine et le spectre fréquentiel du coefficient de rétrodiffusion ultrasonore. Une approximation au second ordre en fréquence du facteur de structure est proposée dans ces travaux pour décrire la microstructure sanguine. Cette approche est tout d’abord présentée et validée dans un champ d’écoulement cisaillé homogène. Une extension de la méthode en 2D permet ensuite la cartographie des propriétés structurelles sanguines en écoulement tubulaire par des images paramétriques qui mettent en évidence le caractère temporel de l’agrégation et la sensibilité ultrasonore à ces phénomènes. Une extrapolation menant à une relation entre la taille des agrégats érythrocytaires et la viscosité sanguine permet l’établissement de cartes de viscosité locales. Enfin, il est démontré, à l’aide d’un modèle animal, qu’une augmentation subite de l’agrégation érythrocytaire provoque la formation d’un thrombus veineux. Le niveau d’agrégation, la présence du thrombus et les variations du débit ont été caractérisés, dans cette étude, par imagerie ultrasonore. Nos résultats suggèrent que des paramètres hémorhéologiques, préférablement mesurés in vivo et in situ, devraient faire partie du profil de risque thrombotique. / The aggregation of erythrocytes is the main determinant of blood non Newtonian behaviour under low shearing flow conditions. When red blood cells (RBCs) aggregate, they form « rouleaux » and complex tridimensional structures that increase blood viscosity from a few mPa.s to a hundred mPa.s. The reversible RBC aggregation phenomenon is attributed to weak adhesive links between erythrocytes that are readily broken by increasing flow shearing. Blood bulk rheological properties have been comprehensively studied. However, the in vivo physiological impacts of abnormal clustering of RBCs are more difficult to assess. Clinical studies have identified altered hemorheology as a risk factor for thrombosis, but a clear etiological relationship between abnormal aggregation and thrombosis has not yet been established, in part because clinical conclusions were derived from correlative findings. It is to note that cardiovascular diseases such as deep venous thrombosis generally occur at specific locations within the vascular bed, suggesting a hemodynamic contribution to the development of this disease. Consequently, it is postulated that in vivo hemorheological characterization may help shed some light on the role of RBC hyper-aggregation on cardiovascular disorders. Ultrasound imaging, a non-invasive method relying on the propagation of mechanical waves within biological tissues, is sensitive to RBC aggregation. Indeed, the study of backscattered waves allows characterizing blood microstructure in vivo and in situ under physiological flow conditions. The work described in this thesis is based on prior simulation studies, performed at the Laboratory of Biorheology and Medical Ultrasonics of the University of Montreal Hospital Research Center, in which the backscattering of ultrasound from aggregating RBCs was modeled by considering a particle scattering strategy. In this approach, each RBC is a weak ultrasound scatterer (Born assumption) and the backscattering coefficient is modeled as the product of the RBC number density, the RBC backscattering cross section and a structure factor. This model relates variations in the backscattering coefficient to the RBC spatial organisation through the structure factor, which is the only parameter that changes during the aggregation process. A second order expansion in frequency of the structure factor was used to describe blood microstructure in terms of a packing factor W and an ensemble averaged aggregate diameter D. The model was first presented and validated by considering a homogenous shear flow condition using three broadband mono-element transducers. It was then extended in 2D to allow computation of parametric images in tube flow. An extrapolation based on the assumption that viscosity is related to the level of aggregation was used to compute local viscosity maps. Finally, a last contribution was the demonstration that a sudden increase in aggregation tendency directly promoted the formation of venous thrombosis in an experimental animal model. In that study, RBC aggregation, thrombus formation and flow variations were monitored longitudinally for two weeks using ultrasound. The results reported in this thesis suggest that rheological parameters on RBC clustering, ideally assessed in vivo and in situ, should be included in thrombosis risk profiling.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This work researches on free and forced vibrations of a double beam coupled system. The system is regarded as two Euler-Bernoulli beams which are parallel, have the same length, are simply supported and are connected through a viscoelastic layer. Natural frequencies and their mode shapes, also called eigenfunctions, of the coupled system are obtained through a uniform beam methodology which uses the free dynamical basis to represent the solution of the the modal equation. This study uses modal analysis and block matrix formulation, while the dynamical basis used to represent the modal solution is obtained from the dynamical solution of a fourth order differential equation whose coefficients are just those of the original problem. The natural frequencies and mode shapes of the undamped system are determined for several values of beam parameters. For the damped case, damping ratios of each beam and also of the viscoelastic layer (which characterizes the coupling the system) are considered. The forced response is represented using matrix impulse response, which is the solution of an initial value problem with impulsive initial conditions. / Neste trabalho é realizado um estudo sobre vibrações livres e forçadas de um sistema de dupla viga acoplado. O sistema é composto por duas vigas do tipo Euler-Bernoulli, paralelas, de mesmo comprimento, simplesmente apoiadas e conectadas por uma camada viscoelástica. São obtidas as frequências naturais e os modos de vibração ou autofunções do sistema acoplado utilizando uma metodologia para vigas uniformes, que usa a base dinâmica para escrever a solução da equação modal. O estudo é realizado através da análise modal e de uma formulação matricial em blocos, e a base dinâmica usada para escrever a solução da equação modal é gerada pela solução dinâmica de uma equação diferencial de quarta ordem cujos coeficientes são os mesmos do problema considerado. As frequências naturais e os modos de vibração para o sistema não amortecido são determinados para vários valores dos parâmetros da viga. Para o caso amortecido, consideramos o amortecimento individual em cada viga e o amortecimento que compõe a camada viscoelástica o qual caracteriza o acoplamento no sistema. A resposta forçada do sistema é escrita em função da resposta impulso matricial que é solução de um problema de valor inicial com condições iniciais impulsivas.

Made available in DSpace on 2014-12-17T14:08:36Z (GMT). No. of bitstreams: 1 NisarRO.pdf: 2584049 bytes, checksum: f18a00826204d450659ba7d3316e358e (MD5) Previous issue date: 2009-05-08 / Among the many types of noise observed in seismic land acquisition there is one produced by surface waves called Ground Roll that is a particular type of Rayleigh wave which characteristics are high amplitude, low frequency and low velocity (generating a cone with high dip). Ground roll contaminates the relevant signals and can mask the relevant information, carried by waves scattered in deeper regions of the geological layers. In this thesis, we will present a method that attenuates the ground roll. The technique consists in to decompose the seismogram in a basis of curvelet functions that are localized in time, in frequency, and also, incorporate an angular orientation. These characteristics allow to construct a curvelet filter that takes in consideration the localization of denoise in scales, times and angles in the seismogram. The method was tested with real data and the results were very good / Dentre os diversos tipos de ru?dos existentes nos dados s?smicos terrestres est? o Ru?do de Rolamento Superficial tamb?m conhecido como ground roll que ? um tipo particular de ondas de Rayleigh com amplitude forte, freq??ncia baixa e velocidade baixa que gera um cone de grande mergulho no sismograma. O ru?do de rolamento superficial contamina os sinais relevantes e pode mascarar a informa??o desejada, trazidas por ondas espalhadas em regi?es mais profundas das camadas geol?gicas. Nesta disserta??o ser? apresentada uma ferramenta que atenua o ru?do de rolamento superficial baseada na transformada curvelet. A t?cnica consiste em decompor o sismograma em uma base de fun??es curvelets as quais s?o localizadas no tempo e na freq??ncia, al?m de incorporarem uma orienta??o angular. Tais caracter?sticas permitem a constru??o de um filtro curvelet que leva em considera??o a localiza??o do ru?do em escalas, limiares de corte dos coeficientes curvelets e dos ?ngulos no sismograma. O m?todo foi testado com dados reais e os resultados obtidos foram muito bons

Fundação Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro / Em suma, esta tese propõe uma metodologia de acompanhamento de interfaces móveis que baseia-se no método dos conjuntos de nível aqui chamado de método das curvas de nível, uma denominação baseada nas aplicações em que as interfaces são representadas por curvas acoplado a uma implementação semi-Lagrangeana, para problemas em meios porosos. Embora esta técnica possa, em princípio, ser aplicada a qualquer problema físico que apresente uma interface móvel, nesta tese são focados escoamentos em meios porosos consolidados e saturados por um ou dois fluidos imiscíveis e incompressíveis. Adicionalmente, um método iterativo paralelizável para a resolução de sistemas de equações lineares definidos em redes, que podem ser reduzidos à forma das equações fundamentais de equilíbrio, é empregado na determinação dos campos de velocidade associados aos escoamentos em meios porosos. O cenário semi-Lagrangeano acoplado ao método das curvas de nível é comparado com a implementação utilizando o bem conhecido esquema up-wind. Um exaustivo estudo realizado revela a superioridade da metodologia proposta frente à concorrente utilizando o up-wind. Finalmente, o método das curvas de nível com implementação semi-Lagrangeana (método semi-Lagrangeano das curvas de nível), e o método iterativo para a determinação do campo de velocidades são aplicados no estudo de problemas transientes em meios porosos que apresentam instabilidades dos tipos Saffman-Taylor e Rayleigh-Taylor. Este estudo envolve uma análise de estabilidade linear, a introdução de diversas perturbações trigonométricas na interface e a sua evolução não-linear. / Briefy, this thesis proposes a method for capturing moving interfaces based on the level set method coupled to a Semi-Lagrangian implementation for problems in porous media. Although this method could, in principle, be applied to any physical problem with moving interfaces, we foccus, in this thesis, on flows inside a consolidated porous media saturated by one or two imiscible and incompressible fluids. Besides, a parallelizable iterative method for solving linear systems defined on a network that can be reduced to the fundamental equilibrium equations, is employed to determine the velocity field associated with the flow in a porous medium. The semi-Lagrangian scheme coupled with the level set method is compared with the well-known implementation with the up-wind scheme. An exhaustive study is performed and reveals the superiority of the proposed scheme in relation to the competing one using the up-wind method. Finally, the level set method with semi-Lagrangian implementation and the iterative method for determining the velocity field are applied to the study of transient problems in porous media which present Saffman-Taylor and Rayleigh-Taylor instabilities. This study involves the application of a linear stability analysis, the introduction of several trigonometric perturbations to the interface and its non-linear evolution.