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Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-03-23T21:32:45Z No. of bitstreams: 1 JOÃO PAULO DANTAS DE CARVALHO - DISSERTAÇÃO PPGEQ 2015..pdf: 1534561 bytes, checksum: 93959f6eca85fa51565d250b6a984284 (MD5) / Made available in DSpace on 2018-03-23T21:32:45Z (GMT). No. of bitstreams: 1 JOÃO PAULO DANTAS DE CARVALHO - DISSERTAÇÃO PPGEQ 2015..pdf: 1534561 bytes, checksum: 93959f6eca85fa51565d250b6a984284 (MD5) Previous issue date: 2015-11-11 / CNPq / Desde a sua descoberta, em 1864 por Cailletet, a fragilização de metais por hidrogênio, foi sujeito a inúmeras investigações, sendo primeiramente estudado com a injeção de hidrogênio gasoso em metais e ligas. Devanathan e Stachurski (1962) desenvolveram a técnica eletroquímica de permeação de hidrogênio em metais e ligas, tornando o estudo mais prático, esta metodologia se baseia em uma dupla célula eletroquímica dispostas simetricamente onde o metal a ser estudado é inserido entre elas. Uma delas conhecida como célula de carga irá gerar o H2 a ser permeado através do corpo de prova e na outra, conhecida como célula de detecção, o mesmo será oxidado e quantificado seu fluxo. Toda a detecção é realizada potenciostaticamente, mas a geração pode ser realizada por meio galvanostático (método galvanostático-potenciostático), potenciostacamente (método duplo-potenciostático) ou por permeação em circuito aberto em meio ácido, chamado de „PCAA‟. As normas ASTM 148-97 (2003) e ISO 17081 (2004) padronizam os experimentos de permeação eletroquímica de hidrogênio. Como os diferentes métodos são baseados em soluções de contorno diferenciados para solução da segunda lei de Fick, tais normas não levam isto em consideração adotando o cálculo da difusividade do hidrogênio apenas pelo método duplo potenciostático, mesmo para aqueles que estudam o fenômeno, diga-se de passagem, em sua grande maioria, utilizando a metodologia galvanostático-potenciostático. Autores como McBreen et al (1966) e Boes & Zuchner (1972) descrevem o fenômeno de permeação de hidrogênio em metais de forma matemática, a partir da solução da segunda de lei de Fick, estes trabalhos atestam a diferença entre os métodos duplo-potenciostatico e galvanostático-potenciostático, porém nunca foi proposto um modelo que descreva o comportamento do método PCAA. Com isso, o trabalho tem como objetivo elucidar o emprego dos modelos matemáticos para determinação do coeficiente de difusão do hidrogênio em metais através das distintas técnicas eletroquímicas de permeação, utilizando os aços API 5L X70 e X65, além disto procurou-se um modelo matemático para o caso em que a geração de hidrogênio seja realizada pelo método PCAA. Neste trabalho atesta-se que que o uso das equações proposta pela norma, a princípio, subestimam o valor da difusividade. A equação proposta para o método PCAA, apresentou um perfeito ajuste de dados experimentais de permeação. A correlação proposta para o cálculo da difusividade mostrou-se coerente para estimar este parâmetro, não só para o caso PCAA, como também para todos os casos. / Since its discovery in 1864 by Cailletet, hydrogen embrittlement of metals, was subjected to numerous investigations, first being studied with the injection of gaseous hydrogen in metals and alloys. Devanathan and Stachurski (1962) developed the electrochemical technique of hydrogen permeation in metals and alloys, making it the study more practical this methodology is based on a dual symmetrically arranged electrochemical cell where the metal to be studied is inserted between them. One known as load cell will generate H2 to be permeated through the specimen and the other, known as the detection cell, it will be oxidized and its flow quantified. All detection is performed potentiostaticly, but the generation can be performed by galvanostatic (galvanostaticpotentiostatic method), potentiostaticly (double- potentiostatic method), or by hydrogen permeation on acid environment method known as a PCAA. The regulations ASTM 148-97 (2003) and ISO 17081 (2004) standardize the electrochemical hydrogen permeation experiments. How different methods are based on different workarounds for solution of the second Fick's law, such rules do not take this into account by adopting the calculation of the hydrogen diffusivity only by the dual voltage method, even for those who study the phenomenon, say passing for the most part, using the galvanostatic-potentiostatic methodology. Authors such as McBreen et al (1966) and Boes & Züchner (1972) describe the hydrogen permeation phenomenon in mathematical form of metal from the solution of the second Fick law, these works attest to the difference between the double-potentiostatic methods and galvanostatic-potentiostatic, but has never proposed a model that describes the behavior of the PCAA method. Thus, the study aims to elucidate the use of mathematical models to determine the hydrogen diffusion coefficient in metals through the different electrochemical techniques permeation using the API 5L steels X70 and X65, in addition sought a mathematical model for the case where the hydrogen generation is performed by the PCAA method. This work testifies that the use of the equations proposed by the standard at first underestimate the value of diffusivity. The equation proposed for the PCAA method, presented a perfect fit experimental permeation data. The proposed correlations for calculating the diffusivity was found to be consistent to estimate this parameter not only to the case PCAA, but also for all cases.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Uma simulação numérica que leva em conta os efeitos de estratificação e mistura escalar (como a temperatura, salinidade ou substância solúvel em água) é necessária para estudar e prever os impactos ambientais que um reservatório de usina hidrelétrica pode produzir. Este trabalho sugere uma metodologia para o estudo de escoamentos ambientais, principalmente aqueles em que o conhecimento da interação entre a estratificação e mistura pode dar noções importantes dos fenômenos que ocorrem. Por esta razão, ferramentas de simulação numérica 3D de escoamento ambiental são desenvolvidas. Um gerador de malha de tetraedros do reservatório e o modelo de turbulência algébrico baseado no número de Richardson são as principais ferramentas desenvolvidas. A principal dificuldade na geração de uma malha de tetraedros de um reservatório é a distribuição não uniforme dos pontos relacionada com a relação desproporcional entre as escalas horizontais e verticais do reservatório. Neste tipo de distribuição de pontos, o algoritmo convencional de geração de malha de tetraedros pode tornar-se instável. Por esta razão, um gerador de malha não estruturada de tetraedros é desenvolvido e a metodologia utilizada para obter elementos conformes é descrita. A geração de malha superficial de triângulos utilizando a triangulação Delaunay e a construção do tetraedros a partir da malha triangular são os principais passos para o gerador de malha. A simulação hidrodinâmica com o modelo de turbulência fornece uma ferramenta útil e computacionalmente viável para fins de engenharia. Além disso, o modelo de turbulência baseado no número de Richardson leva em conta os efeitos da interação entre turbulência e estratificação. O modelo algébrico é o mais simples entre os diversos modelos de turbulência. Mas, fornece resultados realistas com o ajuste de uma pequena quantidade de parâmetros. São incorporados os modelos de viscosidade/difusividade turbulenta para escoamento estratificado. Na aproximação das equações médias de Reynolds e transporte de escalar é utilizando o Método dos Elementos Finitos. Os termos convectivos são aproximados utilizando o método semi-Lagrangeano, e a aproximação espacial é baseada no método de Galerkin. Os resultados computacionais são comparados com os resultados disponíveis na literatura. E, finalmente, a simulação de escoamento em um braço de reservatório é apresentada. / To study and forecast the environmental impacts that a hydroelectric power plant reservoir may produce, a numerical simulation that takes into account the effects of stratification and scalar mixing (such as temperature, salinity or water-soluble substance) is required. This work proposes a methodology for the study of the environmental fluid flow phenomena, mainly for flows in which the knowledge of the interaction between stratification and mixing can give important notions of the phenomena that occur. For this, a numerical simulation tool for 3D environmental flow is developed. A tetrahedral mesh generator of the reservoir based on the terrain topology and an algebraic turbulence model based on the Richardson number are the main tools developed. The main difficulty in tetrahedral mesh generation of a reservoir is nonuniform distribution of the points related to the huge ratio between the horizontal and vertical scales of the reservoir. In this type of point distributions, conventional tetrahedron mesh generation algorithm may become unstable. For this reason, a unstructured tetrahedral mesh generator is developed and the methodology used to obtain conforming elements is described. Triangular surface mesh generation using the Delaunay triangulation and the construction of the tetrahedra from the triangular surface mesh are the main steps to the mesh generator. The hydrodynamic simulation of reservoirs with a turbulence model provides a useful tool that is computationally viable for engineering purposes. Furthermore, the turbulence model based on the Richardson number takes into account the effects of interaction between turbulence and stratification. The algebraic model is the simplest among the various models of turbulence, but provides realistic results with the fitting of a small amount of parameters. Eddy-Viscosity/Diffusivity models for stratified turbulent flows models are incorporated. Using the Finite Element Method (FEM) approximation the Reynolds-averaged Navier-Stokes (RANS) and mean scalar transport equations are approximated. The convective terms are discretized employing the Semi-Lagrangian method, and the spatial discretization is based on the Galerkin method. The computational results are compared with the results available in the literature. Finally, the simulation of the flow in a branch of a reservoir is presented.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Uma simulação numérica que leva em conta os efeitos de estratificação e mistura escalar (como a temperatura, salinidade ou substância solúvel em água) é necessária para estudar e prever os impactos ambientais que um reservatório de usina hidrelétrica pode produzir. Este trabalho sugere uma metodologia para o estudo de escoamentos ambientais, principalmente aqueles em que o conhecimento da interação entre a estratificação e mistura pode dar noções importantes dos fenômenos que ocorrem. Por esta razão, ferramentas de simulação numérica 3D de escoamento ambiental são desenvolvidas. Um gerador de malha de tetraedros do reservatório e o modelo de turbulência algébrico baseado no número de Richardson são as principais ferramentas desenvolvidas. A principal dificuldade na geração de uma malha de tetraedros de um reservatório é a distribuição não uniforme dos pontos relacionada com a relação desproporcional entre as escalas horizontais e verticais do reservatório. Neste tipo de distribuição de pontos, o algoritmo convencional de geração de malha de tetraedros pode tornar-se instável. Por esta razão, um gerador de malha não estruturada de tetraedros é desenvolvido e a metodologia utilizada para obter elementos conformes é descrita. A geração de malha superficial de triângulos utilizando a triangulação Delaunay e a construção do tetraedros a partir da malha triangular são os principais passos para o gerador de malha. A simulação hidrodinâmica com o modelo de turbulência fornece uma ferramenta útil e computacionalmente viável para fins de engenharia. Além disso, o modelo de turbulência baseado no número de Richardson leva em conta os efeitos da interação entre turbulência e estratificação. O modelo algébrico é o mais simples entre os diversos modelos de turbulência. Mas, fornece resultados realistas com o ajuste de uma pequena quantidade de parâmetros. São incorporados os modelos de viscosidade/difusividade turbulenta para escoamento estratificado. Na aproximação das equações médias de Reynolds e transporte de escalar é utilizando o Método dos Elementos Finitos. Os termos convectivos são aproximados utilizando o método semi-Lagrangeano, e a aproximação espacial é baseada no método de Galerkin. Os resultados computacionais são comparados com os resultados disponíveis na literatura. E, finalmente, a simulação de escoamento em um braço de reservatório é apresentada. / To study and forecast the environmental impacts that a hydroelectric power plant reservoir may produce, a numerical simulation that takes into account the effects of stratification and scalar mixing (such as temperature, salinity or water-soluble substance) is required. This work proposes a methodology for the study of the environmental fluid flow phenomena, mainly for flows in which the knowledge of the interaction between stratification and mixing can give important notions of the phenomena that occur. For this, a numerical simulation tool for 3D environmental flow is developed. A tetrahedral mesh generator of the reservoir based on the terrain topology and an algebraic turbulence model based on the Richardson number are the main tools developed. The main difficulty in tetrahedral mesh generation of a reservoir is nonuniform distribution of the points related to the huge ratio between the horizontal and vertical scales of the reservoir. In this type of point distributions, conventional tetrahedron mesh generation algorithm may become unstable. For this reason, a unstructured tetrahedral mesh generator is developed and the methodology used to obtain conforming elements is described. Triangular surface mesh generation using the Delaunay triangulation and the construction of the tetrahedra from the triangular surface mesh are the main steps to the mesh generator. The hydrodynamic simulation of reservoirs with a turbulence model provides a useful tool that is computationally viable for engineering purposes. Furthermore, the turbulence model based on the Richardson number takes into account the effects of interaction between turbulence and stratification. The algebraic model is the simplest among the various models of turbulence, but provides realistic results with the fitting of a small amount of parameters. Eddy-Viscosity/Diffusivity models for stratified turbulent flows models are incorporated. Using the Finite Element Method (FEM) approximation the Reynolds-averaged Navier-Stokes (RANS) and mean scalar transport equations are approximated. The convective terms are discretized employing the Semi-Lagrangian method, and the spatial discretization is based on the Galerkin method. The computational results are compared with the results available in the literature. Finally, the simulation of the flow in a branch of a reservoir is presented.

Du fait de problèmes de santé publique, l’industrie agroalimentaire doit réduire la quantité de sel et de matière grasse dans les aliments, et donc dans les charcuteries. Lors de la fabrication des saucissons secs, une diminution combinée des taux de sel et de matière grasse animale peut se traduire par des problèmes de stabilité microbiologique, des défauts d’arôme et de texture dus à des modifications physicochimiques et biochimiques. Dans ce contexte, les objectifs de cette thèse étaient : (1) d’étudier l’impact d’une réduction directe des teneurs en sel et en matière grasse animale sur les évolutions physicochimiques et biochimiques au sein des produits, (2) d’identifier les composés aromatiques responsables de l’arôme du saucisson sec, ainsi que leurs origines, (3) de développer de nouvelles formulations de saucissons secs à teneurs réduites en sodium et en acides gras saturés, et (4) d’étudier les transferts d’eau et sel et de développer une isotherme de sorption spécifique pour le saucisson sec. L’étude de l’effet d’une réduction directe combinée a mis en évidence la difficulté de fabriquer des saucissons secs à teneurs réduites en sel et en matière grasse animale, sans modifier les évolutions physicochimiques et biochimiques. Une identification des composés volatils odorants de saucissons secs de haut de gamme a permis de montrer que l’aromatisation par l’ail et le poivre noir pouvait être un levier technologique permettant d’améliorer la qualité aromatique des saucissons secs allégés en sel et en matière grasse animale. L’impact de l’aromatisation et d’une substitution partielle combinée du sel par le chlorure de potassium et du gras de bardière de porc par l’huile de tournesol oléique sur les propriétés physicochimiques, les réactions biochimiques et les attributs sensoriels de saucissons secs, a été étudié. Cette étude a montré le rôle important de l’aromatisation qui agit en introduisant des molécules aromatiques qui rehaussent l’acceptabilité des produits par les consommateurs, en tant qu’exhausteur de la perception du goût salé et aussi, sur les processus fermentaires qui vont conditionner l’aspect et la texture finale du produit. La substitution partielle combinée est une solution efficace pour conserver au mieux la qualité organoleptique des saucissons, en permettant, d’une part, d’éviter les défauts texturaux et sensoriels liés aux modifications physicochimiques, protéolytiques et lipolytiques générés par une réduction directe combinée, et d’autre part, d’améliorer l’arôme du produit en rehaussant les niveaux d’oxydations lipidique et protéique. L’étude des transferts d’eau et de sel a mis en évidence une migration du sel vers le cœur du saucisson, et a permis de déterminer des valeurs de diffusivité apparente de l’eau en surface de ces produits. Il a été montré qu’une forte réduction en matière grasse réduisait la diffusivité de l’eau à la surface du saucisson. Une isotherme de sorption spécifique permettant de prédire l’aw en fonction des teneurs en eau, en lipides et en sel a été construite en adaptant un modèle de Ross établi pour la gélatine salée et grasse. / Because of public health problems, the food industry must lower sodium and animal fat contents in all food products, therefore in cured meat products. During dry-fermented sausage manufacture, a combined reduction both in salt and animal fat contents may induce microbial safety problems and textural and aroma defects due to physical-chemical and biochemical changes. On account of that, this work of thesis aims (1) to investigate the impact of a direct reduction on the salt and animal fat contents on the physical-chemical and biochemical evolutions in the products, (2) to identify the aromatic compounds responsible for the aroma of dry-fermented sausage, and their origins, (3) to develop new nutritionally-improved formulations of dry-fermented sausages with less sodium and saturated fatty acids, and (4) to study the impact of lipid and sodium chloride contents on water transfers in dry-fermented sausages and to build a specific sorption isotherm curve for dry sausages. The study of the effect of a combined direct reduction highlighted the difficulty of manufacturing sodium-reduced fat-reduced dry sausages, without affecting the physical-chemical and biochemical evolutions. Identification of odorous volatile compounds of high quality dry sausages showed that flavouring, especially garlic and black pepper, could be a good solution for improving the aromatic quality of salt-reduced fat-reduced dry-fermented sausages. The impact of flavouring and of a combined salt and animal fat replacement by potassium chloride and oleic sunflower oil, respectively, on physical-chemical properties, biochemical reactions and sensory attributes of dry-fermented sausages was then studied. This specific study showed the crucial role played by flavouring which introduces aromatic molecules that enhance the product acceptability by consumers, which acts as an enhancer of the saltiness perception and which improves the product appearance and texture by boosting the fermentation process. Consequently, the combined partial substitution is an efficient solution to preserve at best the organoleptic quality of the products, allowing, on one hand, avoiding the textural and sensory defects related to physical-chemical, proteolytic and lipolytic modifications induced by a combined direct reduction, and on the other hand, enhancing the product aroma by increasing the levels of lipid and protein oxidations. The study on water and salt transfers highlighted a salt diffusion towards the dry sausage core, and made it possible to determine values of apparent water diffusivity at the sausage surface. We demonstrated that a strong reduction in animal fat content significantly lowered the water diffusivity value at the product surface. A specific sorption isotherm curve based on a modified Ross model was built, allowing dry-fermented sausages water activity to be calculated as a function of water, fat and salt contents.

Die fortschreitende Miniaturisierung von elektronischen Systemen begleitet von steigender Leistung und Funktionalität führt zur Erhöhung der Leistungsdichte. Um diesem Trend zu entsprechen, werden neue Entwärmungskonzepte benötigt, die wiederum neuartige Materialien und Materialverbünde fordern. Ein wichtiger Aspekt dieser Arbeit ist deshalb die Konzentration auf die für den Wärmetransport entscheidenden Materialien. Diese Arbeit befasst sich mit der Entwicklung von Methoden für die umfassende thermische Charakterisierung von den verschiedenen Materialien und Materialklassen, die in der Elektronikindustrie verwendet werden. Die Messsysteme wurden so entworfen und entwickelt, dass spezifische Anwendungsbedingungen berücksichtigt werden können, keine aufwändige Probenherstellung notwendig ist und gleichzeitig eine hohe Messgenauigkeit gewährleistet ist. Es wurden vier verschiedene Messsysteme innerhalb dieser Arbeit entwickelt und realisiert, die in ihrer Gesamtheit die Charakterisierung von fast allen Package-Materialien unter gewünschten Randbedingungen ermöglichen. Zahlreiche Materialien und Effekte wurden daraufhin im Rahmen dieser Arbeit mit den entwickelten Messsystemen untersucht und diskutiert. / The continuous miniaturization of electronic systems accompanied by increasing performance and functionality leads to an increase in power density. In order to comply this trend, new heat dissipation concepts are needed which demand new materials and material composites. An important aspect of this work is therefore the concentration on the materials that are decisive for the heat flow. This thesis deals with the development of Methods for comprehensive thermal characterization of the different materials and material classes used in the electronics industry. The measuring systems have been designed and developed in such a way that they enable to take into account specific application conditions, no costly sample preparation is necessary and at the same time high measuring accuracy is ensured. Four different measuring systems were developed and realized within this work, which, in their entirety, enable the characterization of almost all package materials under desired boundary conditions. Based on this, numerous materials and effects were investigated and discussed in the context of this work with the developed measurement systems.

<p>Thorium dioxide (ThO₂) and metallic uranium (alpha-U) represent important alternative nuclear fuels. Investigating the behavior of defects introduced into these materials in an irradiation environment is critical for understanding microstructure evolution and property changes. The objective of this dissertation is to investigate the clustering of point defects in ThO₂ and alpha-U under irradiation, into voids and prismatic dislocation loops as a function of irradiation dose rate and temperature. To achieve this, we have developed a mean-field cluster dynamics (CD) model based on reaction rate theory to predict the evolution of self-interstitial atom (SIA) and vacancy loops in neutron-irradiated alpha-U. Detailed atomistic simulations have been carried out using molecular dynamics (MD) to study the configuration of such loops and compute their energetics, which are essential parameters of the CD model. Bond-boost hyper-MD simulations have been performed to compute the diffusivity of uranium SIA and vacancies, which govern the kinetics of the clustering phenomenon. Another CD model has been demonstrated for proton-irradiated ThO₂, considering the clustering of Th and O SIA and vacancies into SIA loops and voids, respectively, with varying sizes and stoichiometry. The compositions of all SIA loops and voids dictated by crystallography of ThO₂ in its fluorite structure have been presented in their respective cluster composition space (CCS). The CD model solves the density evolution of off-stoichiometric loops and voids, with irradiation, in their respective CCS. MD simulations have been performed to compute the energetics of different clusters in their CCS, as parameters of the CD model. Temperature-accelerated MD simulations have been performed to compute the diffusivity of Th and O point defects, that dictates the kinetics of defect clustering on irradiation. In alpha-U, the CD predictions show an accumulation of small sized vacancy loops and the growth of SIA loops with irradiation dose, which closely fits the reported size distribution of loops in neutron-irradiated alpha-U by Hudson and coworkers. The CD predicted density of defect clusters in proton-irradiated ThO₂, shows the evolution of near-stoichiometric SIA loops in their CCS. The size distribution of SIA loops at high irradiation doses closely corresponds to the transmission electron microscopy (TEM) observations reported in the literature. Also, the CD model did not predict the growth of voids and vacancy clusters, which is consistent with findings in literature. The model was further used to predict the density of sub-nanometric defect clusters and point defects, on low-dose irradiation, that significantly impairs the thermal conductivity of ThO₂. An extensive TEM and CD investigation has also been carried out to study the growth and coarsening of SIA loop and voids during post-irradiation isochronal annealing of ThO₂ at high temperatures.</p>

[pt] A Equação da Difusividade Hidráulica Não-Linear (EDHN) modela o escoamento monofásico de fluidos em meios porosos levando em conta a variação das propriedades da rocha e do fluido presente no interior de seus poros. Normalmente, a solução adimensional da linha-fonte pD(rD, tD) para escoamento de líquidos é encontrada por meio do uso da transformada de Laplace ou transformação de Boltzmann, o qual, o perfil transiente de pressões em coordenadas cartesianas é descrito pela função erro complementar erfc(xD, yD, tD) e, em coordenadas cilíndricas pela função integral exponencial Ei(rD, tD). Este trabalho propõe a solução analítica pelo método de expansão assíntotica de primeira ordem em séries, para solução de alguns problemas de escoamento de petróleo em meios porosos com permeabilidade dependente da pressão de poros e termo fonte. A solução geral será implementada no software Matlab (marca registrada) e a calibração do modelo matemático será realizada comparandose a solução obtida neste trabalho com a solução calculada por meio de um simulador de fluxo óleo em meios porosos denominado IMEX (marca registrada) , amplamente usado na indústria de petróleo e em pesquisas científicas e que usa o método de diferenças finitas. A solução geral da equação diferencial é dada pela soma da solução para escoamento de líquidos com permeabilidade constante e o termo de primeira ordem da expansão assintótica, composto pela não linearidade devido à variação de permeabilidade. O efeito da variação instantânea de permeabilidade em função da pressão de poros é claramente demonstrado nos gráficos diagnósticos e especializados apresentados. / [en] The Nonlinear Hydraulic Diffusivity Equation (NHDE) models the singlephase flow of fluids in porous media considering the variation in the properties of the rock and the fluid present inside its pores. Normally, the dimensionless linear solution for the flow of oil is performed using the Laplace and Fourier transform or Boltzmann transformation and provides the unsteady pressure profile in Cartesian coordinates given by complementary error function erfc(xD, yD, tD) and in cylindrical coordinates described by the exponential integral function Ei(rD, tD). This work develops a new analytical model based on an integro-differential solution to predict the formation mechanical damage caused by the permeability loss during the well-reservoir life-cycle for several oil flow problems. The appropriate Green s function (GF) to solve NHDE for each well-reservoir setting approached in this thesis is used. The general solution is implemented in the Matlab (trademark) and the mathematical model calibration will be carried out by comparing the solution obtained in this work to the porous media finite difference oil flow simulator named IMEX (trademark). The general solution of the NHDE is computed by the sum of the linear solution (constant permeability) and the first order term of the asymptotic series expansion, composed of the nonlinear effect of the permeability loss. The instantaneous permeability loss effect is clearly noticed in the diagnostic and specialized plots.

Much study has been carried out to determine the properties of Lamellar Graphite Iron (LGI) or grey iron and their relations to factors such as the cooling rate, the dendrite morphology, the pouring temperature, and so on. However, there hasn’t been much comprehensive study on the properties of LGI outside the generally used and accepted composition, with 1 to 3% Silicon. The scope of this study is to measure and evaluate the thermal conductivity and tensile strength of LGI, for a higher concentration of  Si and different carbon contents. The concentration of Si aimed for was 4% but the concentration obtained after spectroscopy was between 4.1% to 4.15%. There are two hypereutectic, one near-eutectic and three hypoeutectic samples considered and these six chemical compositions were cast under different cooling conditions . The cooling time has been varied by providing different molds of 30mm, 55mm, and 80mm diameter cylinders respectively, for all the six sample compositions. The microstructure analysis carried out studies the segregation of Si, the graphite morphology, primary austenite morphology. These factors are then compared to the thermal and tensile behavior measured in this study. It can be observed that the thermal conductivity studied in the present work has a direct correlation for a higher Si content and tends to be greater than the thermal conductivity values observed from other studies with lower content Of Si. However, the conductivity shows an inverse relation with the cooling rate and is maximum for the samples with the lowest cooling rate. The tensile strength, on the other hand, seems to have a lower value than that observed in previous studies for LGI with 1 to 3% Si, but shows a direct correlation with the cooling rate. The mean area fraction of dendrites obtained and the mean interdendritic hydraulic diameter is also measured and their influence on the properties are also studied. The addition of more Si has greatly favored the thermal behavior positively but has also reduced the tensile strength.

L'un des problèmes fondamentaux de l'imagerie cardiaque par résonance magnétique du tenseur de diffusion (IRM-TD) est sa faible résolution spatiale, à cause des limitations matérielles des scanners IRM actuels. L'objectif principal de ce travail de thèse est de développer de nouvelles approches pour améliorer la résolution des données d'IRM-TD afin de mieux représenter l'architecture myocardique du coeur humain et de la comparer avec des résultats issus d'autres techniques d'investigation telles que l'imagerie par lumière polarisée. Dans ce cadre, le travail porte sur trois parties principales. La première concerne le développement d'une nouvelle approche pour l'interpolation des champs de vecteurs propres principaux issus de l'IRM-TD cardiaque humaine. Cette approche consiste d'abord à supprimer les vecteurs corrompus par le bruit au lieu de débruiter de manière uniforme le champ entier de vecteurs, et ensuite à interpoler le champ de vecteurs en utilisant la modèle Thin-Plate-Spline (TPS) afin d'exploiter la corrélation entre les composantes du vecteur. La deuxième partie concerne une nouvelle famille de méthodes d'interpolation pour les champs de tenseurs, basée soit sur les angles d'Euler soit sur le quaternion. Ces méthodes exploitent les caractéristiques du tenseur et préservent les paramètres de tenseurs, tels que le déterminant du tenseur, l'anisotropie fractionnelle (FA) et la diffusivité moyenne (MD). En outre, cette partie compare les principales approches d'interpolation au niveau des images pondérées en diffusion et des champs de tenseurs, et les résultats montrent qu'il serait préférable d'effectuer l'interpolation des données d'IRM-TD au niveau des champs de tenseurs. La troisième partie étudie le changement des paramètres MD et FA après un infarctus du myocarde chez les cochons, et l'influence des méthodes d'interpolation sur ces paramètres dans la zone infarctus et la zone distante. Les résultats montrent que la zone infarctus présente une diminution significative de FA et une augmentation significative de MD, comparée avec la zone distante, et que les méthodes d'interpolations du tenseur ont plus d'influence sur FA que sur MD, ce qui suggère que l'interprétation de ces paramètres cliniques après l'interpolation doive être prise avec précaution. / One of fundamental problems in human cardiac diffusion tensor magnetic resonance imaging (DT-MRI) is its poor spatial resolution, due to the hardware limitations of MRI scanners. The main purpose of this PhD work is to develop new approaches to improving the resolution of cardiac DT-MRI data in order to better understand the myocardial architecture of the heart and compare it with results issues from other investigation techniques such as polarized light imaging. Within this framework, the present work is composed of three main parts. The first part concerns a new approach to interpolating primary eigenvector fields from human cardiac DT-MRI using Thin Plate Spline (TPS) model. This approach removes the noise-corrupted vectors rather than denoising the whole vector field in a uniform manner, and uses TPS model in order to exploit the correlation between vector components during interpolation. The second part is dealt with a new category of feature-based methods for diffusion tensor field interpolation using either Euler angles or quaternion. These feature-based methods well preserve tensor parameters, such as tensor determinant, fractional anisotropy (FA) and mean diffusivity (MD) values. In this part are also compared the main interpolation approaches at the level of diffusion weighted images and tensor fields. The results show that the interpolation of DT-MRI data should be performed at the level of tensor fields. The last part investigates changes in MD and FA after myocardial infarction in porcine hearts, and the influence of diffusion tensor interpolation methods on FA and MD in both infarction and remote region. It is found that the infarction region showed significantly decreased FA and increased MD than the remote region, and that diffusion tensor interpolations have more significant influence on FA than on MD, which suggests that precaution should be taken when performing the clinical analysis based on the parameters after diffusion tensor interpolations.