In this thesis the spark plasma sintering process (SPS) was used to press Mg2Si powder with Ni and Cu slices into alternating layer stacks. These stacks, once cut at an angle, are an artificially anisotropic material. This anisotropy provides transverse thermoelectric properties to the sample. The transverse transport properties were measured along with the individual component transport properties. The SPS process provided malleable samples that gave a power factors of for the Ni/Mg2Si stack and for the Cu/Mg2Si stack. These fall short of the theoretical calculations which would give the power factors as .0254 for the Ni/Mg2Si stack and .211 for the Cu/Mg2Si stack. It is theorized that eddy currents and interface resistances between the layers are the causes for these discrepancies.

Nos últimos anos tem se dado uma evolução muito grande na área industrial de MEMS, e esta se caracteriza por desenvolvimento dos processos de microeletrônica para diminuição de custos e a própria integração de diferentes sistemas que passam a ser muito confiáveis em diferentes aplicações. Motivado pelas tendências de elevar os conhecimentos de processos para obtenção de MEMS, foi proposto um trabalho de corrosão anisotrópica de silício utilizando solução de hidróxido de potássio (KOH) junto com a adição de sais metálicos. O objetivo é comprovar o efeito de compensação cinética da reação e a influência destes metais no caráter anisotrópico e nas taxas de corrosão. Foi analisado o efeito de zinco, alumínio e cobre, e puderam ser observadas alterações nas taxas de corrosão e, conseqüentemente, nas geometrias resultantes no corpo de silício. Com a caracterização dessas mudanças comprovou-se suposições anteriores de que o efeito de compensação cinética encontrado na síntese direta de dimetilclorosilana (DMDCS) e silício, também ocorreria para a corrosão de silício em KOH, pois esses processos obedecem a lei de Arrhenius e tem um comportamento anisotrópico em silício. Os resultados obtidos, graças a um grande detalhamento de todos as etapas de processo e caracterização voltada à tecnologia do silício, comprovaram as suposições teóricas e mostraram como pode ser modificada a taxa de corrosão na anisotropia com a adição de metais em solução. / In the past few years it has been a huge evolution in industrial area of MEMS, and this one is characterized by the development of the processes of microelectronic to reduce cost and to integrate different systems that become very trustful in different applications. It is being done a work in silicon anisotropic etching in Potassium hydroxide (KOH) added with metallic impurities aiming the study of the kinetic compensation effect and the influence of these metals in the anisotropy and in etch rates. It was analyzed the effects of Zinc, Aluminum and Cupper and it could be observed changes in etch rates, and, consequently, in the resulting geometries. After characterization of theses changes it was proved that previous suppositions that the kinetic compensation effects found in direct synthesis of dimethyldichorosilane (DMDCS) and silicon would also occur for silicon anisotropic etching in KOH, due to both reactions follows Arrhenius law and are anisotropic reactions. The obtained results proved the theory suppositions that the etch rate and anisotropy can be modified when adding metals to the solution.

En partant d'une problématique industrielle correspondant à la naissance de fissures lors de l'excavation d'un tunnel dans un matériau argileux, nous proposons de nous intéresser à un sujet plus large qui est celui de la nucléation d'une fissure de dimension macroscopique. Ainsi, des résultats généraux et théoriques sont établis tout au long de ce mémoire. Ces derniers sont toutefois utilisés pour proposer une interprétation aux faciès de fissuration observés lors de l'excavation de galeries de stockage à grandeur profondeur. Dans un premier temps, un modèle géométrique idéalisé pour des fissures est justifié. Cette étude préalable permet à la fois d'acter la nature fermée des fissures susceptibles de nucléer ainsi que d'utiliser le critère mixte en statuant sur le bienfondé d'une étude bidimensionnelle équivalente. En précisant la notion de longueur de nucléation stable et en s'inspirant des outils classiques de la mécanique linéaire de la rupture, nous établissons dans un second temps notre propre critère de nucléation. Pour ce faire, nous proposons, grâce à des modélisations micromécaniques, de revisiter l'approche thermodynamique usuelle dans un cadre adiabatique afin d'être davantage en accord avec la brutalité du phénomène étudié. Par la suite, nous mettons aux points différentes méthodes permettant d'utiliser le critère suggéré. Enfin, le critère est mis en œuvre dans le cadre de la problématique industrielle initiale pour essayer de donner une justification à l'anisotropie des géométries des fissures observées, et ce, en prenant en compte les différentes directions de forage de l'ouvrage. Dans un deuxième temps, nous proposons de nous intéresser, de manière plus prospective, aux problématiques liées aux modèles locaux d'endommagement. Une attention particulière est accordée à la notion de stabilité des états d'équilibre. Ainsi, une adaptation du critère de Hill est proposée et des différences quantitatives sont soulignées lorsqu'un cadre adiabatique, nous paraissant plus justifié, est pris en compte. Enfin, le problème de la localisation de l'endommagement dans un problème unidimensionnel est abordé / Starting from an industrial issue that is cracks onset when excavating a tunnel, this work aims at giving new insights into a more general problematic which is the initiation of macroscopic cracks. Thus, general and theoretical results are established. Nevertheless, they are applied in order to give some explanations to the excavation-induced fractures observed around the deep geological repository. To begin with, an idealised geometrical model is detailed and justified. Thanks to this preliminary work, we establish that the cracks that should be taken into account are closed ones. In addition we show that it's possible for small cracks length to work on an equivalent bidimensionnal problem. This last result allows us to apply the mixed criteria. After giving the definition of a stable crack initiation length we define our own criteria to predict cracks onset. In order to do so and in order to be more in adequacy with the caracter brutal of a crack initiation, we offer through a micromecanic modelisation to deploy the usual thermodynamic approach in an adiabatic context. Different methods to compute the key quantity which is the incremental energy released rate are then built. Finally, the criteria is applied to give some justifications to the anisotropic geometry of the excavation-induced fractures. In a second part of this work, we focuse on the problematics tied to the local damage models. For instance, the notion of stability for an equilibrium state is discussed. Hill's stability critera is adapted to damage problems. Once again, it seems that an adiabatic context is more suited and the differences implied are emphasized. To conclude, we offer to investigate the localisation issue in one dimensionnal problems

Unbound granular materials are generally used in road pavements as base and subbase layers. The granular materials provide load distribution through aggregate contacts to a level that can help the subgrade to withstand the applied loads. Several research studies have shown that unbound pavement layers exhibit anisotropic properties. Anisotropy is caused by the preferred orientation of aggregates and compaction forces. The result is unbound pavement layers that have higher stiffness in the vertical direction than in the horizontal direction. This behavior is not accounted for in the design and analysis procedures included in the proposed AASHTO 2002 design guide. One of the objectives of this study is to conduct a comparative analysis of flexible pavement response using different models for unbound pavement layers: linear isotropic, nonlinear isotropic, linear anisotropic and nonlinear anisotropic. Pavement response is computed using a finite element program. The computations from nonlinear isotropic and anisotropic models of unbound layers are compared to the AASHO field experimental measurements. The second objective is to analyze the influence of using isotropic and anisotropic properties for the pavement layers on the performance of flexible pavements calculated using the AASHTO 2002 models. Finally, a comprehensive sensitivity analysis of the proposed AASHTO 2002 performance models to the properties of the unbound pavement layers is conducted. The sensitivity analysis includes different types of base materials, base layer thicknesses, hot mix asphalt type and thickness, environmental conditions, and subgrade materials.

Diffusion can be classified as either normal or anomalous. A variety of experimental systems are evaluated to classify diffusion. Potential regressions and step size distributions are analysed. Nor-mal diffusion holds except where flocculation takes place, or where concentrations of cationic starches are high or with cationic starches and latex together. In these cases, subdiffusion takes place. Furthermore, limiting values are used to calculate diffusion coefficients. Diffusion of non-spherical particles is covered as well, here tested on microcrystalline cellulose.

This thesis will present the synthesis, characterization and magnetic measurements of lanthanide complexes with varying nuclearities (Ln, Ln2, Ln3 and Ln4). EuIII, GdIII, TbIII, DyIII, HoIII and YbIII have been selected as the metal centers. Eight polydentate Schiff-base ligands have been synthesized with N- and mostly O-based coordination environments which chelate 7-, 8- or 9-coordinate lanthanide ions. The molecular structures were characterized by single crystal X-ray crystallography and the magnetic properties were measured using a SQUID magnetometer. Each chapter consists of crystal structures and magnetic measurements for complexes with the same nuclearity. There are eight DyIII SMMs in this thesis which are discrete molecules that act as magnets below a certain temperature called their blocking temperature. This phenomenon results from an appreciable spin ground state (S) as well as negative uni-axial anisotropy (D), both present in lanthanide ions owing to their f electron shell, generating an effective energy barrier for the reversal of the magnetization (Ueff). The ab initio calculations are also included for the SMMs with high anisotropic energy barriers to understand the mechanisms of slow magnetic relaxation in these systems.

Traditional tribology is based on the surface with random micro structures due to limitations of manufacturing technology. The modern manufacturing technology now promises to fabricate surfaces with regular micro structures (or asperities). The word asperity refers to a single physical entity on the surface of a material, contributing to a concept called roughness in traditional tribology. Regular asperity surfaces imply that all asperities on the surface of a material have the same shape and size, and a deterministic distribution over the surface. The emergence of regular asperity surfaces will have a transformative impact to the discipline of tribology.<p> The overall objective of this thesis is to study how the regular asperity would affect the tribological behavior. Specifically, this thesis develops a computational model to demonstrate and characterize the effect of the surface with regular anisotropic asperities (RAA) on the directional friction behavior when the surface is in a fully lubricated state. By directional friction, it is meant that friction force changes its magnitude with the change of the relative motion direction. By anisotropic asperity, it is meant that the geometry of the asperity is not symmetrical along the motion direction.<p> This thesis presents a detailed development of the computational model by employing computational fluid dynamics (CFD) techniques. In particular, the model takes the Navier-Stokes (NS) equation as a governing equation and the Half-Sommerfeld Condition (HSC) to represent fluid behavior in the cavitation region; as such the model is named NS-HSC for short. Verification of the NS-HSC model is conducted with the information available in literature. A theory is proposed to explain the relationship between directional friction behavior and specific RAA structures. The thesis concludes: (1) the NS-HSC model is more accurate than the existing model in the literature and can be used to predict directional friction behavior and to design RAA surfaces, and (2) the proposed theory is excellent consistent with the NS-HSC model and thus useful to analysis and design of RAA surfaces for directional friction.<p> The major contributions of this thesis are: (1) the first model in the field of tribology to predict the directional friction behavior for RAA surfaces under a fully lubricated status, (2) the first investigation, in the field of CFD, into combining the NS and HSC for modeling a laminar flow with cavitation, and (3) the first theory in the field of tribology for directional friction on fully lubricated RAA surfaces.

Traditional tribology is based on the surface with random micro structures due to limitations of manufacturing technology. The modern manufacturing technology now promises to fabricate surfaces with regular micro structures (or asperities). The word asperity refers to a single physical entity on the surface of a material, contributing to a concept called roughness in traditional tribology. Regular asperity surfaces imply that all asperities on the surface of a material have the same shape and size, and a deterministic distribution over the surface. The emergence of regular asperity surfaces will have a transformative impact to the discipline of tribology.<p> The overall objective of this thesis is to study how the regular asperity would affect the tribological behavior. Specifically, this thesis develops a computational model to demonstrate and characterize the effect of the surface with regular anisotropic asperities (RAA) on the directional friction behavior when the surface is in a fully lubricated state. By directional friction, it is meant that friction force changes its magnitude with the change of the relative motion direction. By anisotropic asperity, it is meant that the geometry of the asperity is not symmetrical along the motion direction.<p> This thesis presents a detailed development of the computational model by employing computational fluid dynamics (CFD) techniques. In particular, the model takes the Navier-Stokes (NS) equation as a governing equation and the Half-Sommerfeld Condition (HSC) to represent fluid behavior in the cavitation region; as such the model is named NS-HSC for short. Verification of the NS-HSC model is conducted with the information available in literature. A theory is proposed to explain the relationship between directional friction behavior and specific RAA structures. The thesis concludes: (1) the NS-HSC model is more accurate than the existing model in the literature and can be used to predict directional friction behavior and to design RAA surfaces, and (2) the proposed theory is excellent consistent with the NS-HSC model and thus useful to analysis and design of RAA surfaces for directional friction.<p> The major contributions of this thesis are: (1) the first model in the field of tribology to predict the directional friction behavior for RAA surfaces under a fully lubricated status, (2) the first investigation, in the field of CFD, into combining the NS and HSC for modeling a laminar flow with cavitation, and (3) the first theory in the field of tribology for directional friction on fully lubricated RAA surfaces.

Unbound granular materials are generally used in road pavements as base and subbase layers. The granular materials provide load distribution through aggregate contacts to a level that can help the subgrade to withstand the applied loads. Several research studies have shown that unbound pavement layers exhibit anisotropic properties. Anisotropy is caused by the preferred orientation of aggregates and compaction forces. The result is unbound pavement layers that have higher stiffness in the vertical direction than in the horizontal direction. This behavior is not accounted for in the design and analysis procedures included in the proposed AASHTO 2002 design guide. One of the objectives of this study is to conduct a comparative analysis of flexible pavement response using different models for unbound pavement layers: linear isotropic, nonlinear isotropic, linear anisotropic and nonlinear anisotropic. Pavement response is computed using a finite element program. The computations from nonlinear isotropic and anisotropic models of unbound layers are compared to the AASHO field experimental measurements. The second objective is to analyze the influence of using isotropic and anisotropic properties for the pavement layers on the performance of flexible pavements calculated using the AASHTO 2002 models. Finally, a comprehensive sensitivity analysis of the proposed AASHTO 2002 performance models to the properties of the unbound pavement layers is conducted. The sensitivity analysis includes different types of base materials, base layer thicknesses, hot mix asphalt type and thickness, environmental conditions, and subgrade materials.

Many materials and biological systems in nature are suspensions composed of disks, such as clay, asphaltenes, and red blood cells. Despite their natural abundance and wide industrial application, disks are least studied compared to spheres and rods, due to the lack of model systems. In our research, disks at micro-scale were mass-produced with unprecedented uniformity in size and shape, and unique flexibility in the control of lateral size, lateral size polydispersity, shape, and aspect ratio (ξ = diameter/thickness). This dissertation focuses on two main areas: the study of the discotic colloidal liquid crystal phase transitions and the application of disk-like colloidal systems as Pickering emulsion and Pickering foam stabilizers. First, we engineered two discotic colloidal systems made from organic and inorganic materials. The former is made of α-eicosene, which is an alkene of 20 carbons. The latter is composed of nano-sheets from exfoliated zirconium phosphate (α-ZrP). Both discotic systems were used to experimentally investigate the liquid crystalline phase transitions (Isotropic-Nematic, Isotropic-Cubic and Isotropic-Columnar). Also, the nematic crystalline phase was studied in detail by embedding it in a translucent and thermo-sensitive hydrogel. This was possible since nematic textures could be formed instantly by ZrP nano-sheets due to their high diameter-thickness ratio. Second, we developed Pickering emulsions and Pickering foams stabilized by high-aspect-ratio nano-sheets. We have also demonstrated for the first time the fabrication of the thinnest amphiphilic Janus and Gemini nano-sheets, which are either surface- or edge-modified plates with a thickness at atomic scale. These nano-sheets were obtained by exfoliating α-ZrP crystals grafted with a coupling agent of hydrophobic molecules on their edges and outer surfaces. Extending this work, we studied crucial fundamental mechanisms that allow Pickering interfacial stabilization, including the effect on the adsorption properties of particle aspect ratio, concentration, and hydrophobicity. Our study is of great interest in the scientific community due to the difficulty in generating a discotic colloidal system of controllable parameters.