Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1985. / Vita. Abstract. Includes bibliographical references (leaves 109-112). Also available via the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 87-91). Also available on the Internet.

During the past decade the production industry has constantly strived to improve performance and cut costs, this has been aided by the development of high performance tools. The advancement of these tools has been accomplished by the application of hard wearing, low friction, coatings. A key process in the production of such coatings is Physical Vapour Deposition (PVD). Interest in such thin films has led to much research effort, both academic and industrial, being devoted to the area. In order that these advancements in technology continue, research into the fundamental aspects of PVD is required. This thesis describes research and experimental studies which have been performed to study the effect of "steering" an electric arc on various aspects of its behaviour. "Steering" of the arc is achieved by applying external magnetic fields which allow the guidance of the path of the arc. Work by earlier authors has aimed to control the arc more fully. The research presented here is based of a novel electromagnetic three coil steering array of cylindrical geometry. With such coils it is possible to vary the field profiles to a greater degree than has been previously achieved, permitting a greater range of steering arrangements/fields to be applied. The research presented is divided into two distinct areas: Firstly a number of experiments were performed to assess the effectiveness of the new steering coils on the motion of the arc. A personal computer was used here along with new arc motion monitoring electronics. This enabled the simultaneous measurement of the orbital transit times and also the degree of travel perpendicular to the steered direction of motion of the arc, as it traversed the surface of the cathode. Such information was then used to produce values for standard deviation of the arc from its steered path, velocity of the arc and a diffusion constant related to the motion of the arc. Such values then allowed evaluation of the stochastic model of arc motion proposed by Care'. Secondly the effect of changes in magnetic field on the production, ejection angle and size of macroparticles(small molten droplets of the cathode material) was studied. This was accomplished by the design, production and usage of new sample holding equipment. This equipment allowed the coating of highly polished samples at a number of angles in relation to the cathode, with all samples being held equidistant from the arc track. Once such samples coatings had been produced they were then analysed using a Scanning Electron Microscope(SEM) to give macroparticle density figures.

Le cadre de cette thèse est la théorie des surfaces minimales dans deux variétés homogènes, R3 et PSL2(R). Dans R3, étant donné un pavage T du plan par des polygones, qui soit invariant par deux translations indépendantes, on construit une famille de surfaces minimales plongées et triplement périodiques qui désingularise T × R. Dans cette perspective, et inspiré par le travail de Martin Traizet, nous ouvrons les nodes d’une surface de Riemann singulière dans le but de coller ensemble des Karcher saddle towers, chacune placée sur un sommet avec ses bouts au long des arrêtes qui se terminent sur ce sommet même. Dans une seconde partie, nous étudions les graphes minimaux dans PSL2(R) et nous fournissons des exemples de surfaces invariantes. Nous obtenons des estimées du gradient pour les solutions de l’équation des surfaces minimales dans l’espace en considération et on étudie le comportement des suites monotones de solutions. Nous concluons par prolonger à PSL2(R) un théorème de Jenkins et Serrin, qui donnent une condition nécessaire et suffisante pour la solvabilité du problème du Dirichlet de l’équation des surfaces minimales dans R3, avec des données infinies sur le bord d’un domaine convexe et borné. / This doctoral thesis deals with minimal surface theory in two homogeneous manifolds, namely, R3 and PSL2(R). In R3, given a tiling T of the plane by straight edge polygons, which is invariant by two independent translations, we construct a family of embedded triply periodic minimal surfaces which desingularizes T ×R. For this purpose, inspired by the work of Martin Traizet, we open the nodes of singular Riemann surfaces to glue together simply periodic Karcher saddle towers, each placed at a vertex of the tiling in such a way that its wings go along the corresponding edges of the tiling ending at that vertex. On the other hand, in PSL2(R) we study minimal graphs and we furnish many invariant examples. We derive gradient estimates for solutions of the minimal surface equation in the underlying space and we study convergence of monotone sequences of solutions. Finally, we extend to PSL2(R) a result of Jenkins and Serrin who provide a necessary and sufficient condition for the solvability of the Dirichlet problem of the minimal surface equation in R3, with infinite data over boundary arcs of a convex bounded region.

Les surfaces implicites ont été perçues au cours des années 80, comme une alternative intéressante aux modélisations paramétriques des surfaces (NURBS, etc). Elles sont définies comme l'ensemble des points de même valeur d'un champ potentiel, c'est-à-dire la frontière de deux volumes. Ainsi elles possèdent des propriétés avantageuses dans le cadre de la modélisation géométrique: gestion automatique de la topologie, garantie de manipuler des entités manifold, possibilité de définir des transitions lisses entre des objets se fusionnant. Elles furent cependant délaissées au début des années 2000 en raison des contraintes qu'elles imposent: évaluation et affichage coûteux en temps de calcul, et forme des surfaces difficilement contrôlables. Les contributions de cette thèse proposent des solutions à ces problématiques de la modélisation par surfaces implicites. Il est tout d'abord montré qu'une nouvelle structure d'accélération, combinant les propriétés d'une hiérarchie de volumes englobants et d'un Kd-Tree, permet d'accélérer l'affichage par lancer de rayons d'un grand nombre de surfaces implicites. Il est ainsi possible d'animer en temps réel une surface de type fluide, définie par les points d'isovaleur d'un champ potentiel obtenu par la somme de primitives simples. Les opérateurs simples de composition de surfaces implicites, tels que la somme, permettent d'évaluer rapidement des champs potentiels combinant plusieurs milliers de primitives. Néanmoins, l'apparence organique des surfaces produites est difficile à contrôler. Cette thèse propose un nouveau type d'opérateur de composition, utilisant à la fois les valeurs et les gradients des champs potentiels sources, qui permet d'avoir beaucoup plus de contrôle sur la forme des surfaces produites tout en supprimant les effets indésirables des opérateurs classiques, tels que le gonflement à l'intersection de surfaces ou la fusion de surfaces proches. Enfin il est montré comment ces opérateurs de mélange peuvent être utilisés pour déformer des surfaces de type maillage, animées par un squelette. Nous définissons un champ potentiel par composition de primitives implicites générées aux arêtes du squelette. A chaque déformation du squelette, le champ potentiel est lui aussi déformé par les opérateurs de composition choisis: ces déformations peuvent être reproduites sur le maillage en déplaçant chaque sommet du maillage jusqu'à la surface d'isovaleur correspondante à leur valeur de potentiel initiale. Cette technique permet d'obtenir rapidement des déformations plausibles au niveau des articulations des membres modélisés / Implicit surfaces have been considered during the eightees as a promising alternative to parametric surfaces (NURBS patches, etc...). They are defined as the set of points having the same value of a scalar field, thus spliting the space into two volumes. Their volumetric nature confers them interesting properties for geometric modeling: the topology of objects is handled automatically, geometries are guaranteed to be manifold and they can produce smooth blendings of objects easily. However, they were abandoned at the beginning of the 21st century due to the limitations they impose: they are computationally expensive to evaluate and to display, and the shape of the transition between objects is difficult to control. This thesis proposes new solutions to these problems in implicit surfaces modeling. First of all, it is shown that the use of a new object-partitioning structure, mixing the properties of a bounding volume hierarchy and a Kd-Tree, makes it possible to raytrace a large number of implicit primitives at interactive frame rates. Therefore it allows real time visualization of fluid-like shapes, defined as an isosurface of a potential field computed as the sum of simple primitives. Simple composition operators of implicit surfaces, such as the sum operator, allow a fast computation of a potential field combining thousands of primitives. Nevertheless, the shape of the resulting surfaces is organic and difficult to control. In this thesis, a new kind of composition operators is proposed, which takes both the value and the gradient of the source potential fields as input. These operators give much more control on the shape of the surfaces, and they avoid the classical problems of implicit surfaces composition, such as bulging at the intersection of two primitives or blending of surfaces at a distance. Finally, a new skeleton-based animation technique is presented which reproduces the deformations of some implicit surfaces on a given mesh. We define a potential field as the composition of implicit primitives generated at the bones of the skeleton. Thus each motion of the skeleton will cause distortions in the associated potential field. These distortions can be reproduced on the mesh by moving each of its vertices to the isosurface of the potential field corresponding to their initial potential value. This technique is able to produce rapidly realistic deformations on the limbs of an articulated model of a body

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Made available in DSpace on 2014-06-11T19:24:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-01-20Bitstream added on 2014-06-13T20:32:14Z : No. of bitstreams: 1 calcada_ftb_me_guara.pdf: 2051959 bytes, checksum: ca1589717e6afa4ab2801767fb3f5869 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / No presente trabalho foi feita a analise quantitativa das superfícies de fratura obtidas através da propagação de trinca em fadiga. As trincas em fadiga são o modo de falha que ocorre por uma carga cíclica e repetida aplicada a um corpo de prova, o que irá causar a nucleação, propagação da trinca até a sua ruptura. Utilizou-se a ferramente da dimensão fractal para analisarmos correlações com a propagação de trincas. Os materiais que foram ensaiados são: liga de alumínio AA7475 e aço 300M, ambos materiais de uso aeronáutico. Foram realizados ensaios de propagação de trinca em fadiga em corpos de prova do tipo C(T) para a obtenção da superfície de fratura para análise. Posteriormente as superfícies foram analisadas em microscopio óptico e em microscópio eletrônico de varredura. Foi realizada a medição da dimensão monofractal (DF), quando a superfície é descrita por um único valor, também os valores de dimensão textural (DT), quando temos macroescalas e a dimensão estrutural (DS), quando temos microescalas. Com os resultados obtidos podemos analisar que o DS é quem melhor representa o comportamento das superfícies de fratura, já que este indica os micromecanismos de fratura presentes. Os valores de DS são menos dispersos na identificação das regiões de fadiga (pré-trinca, propagação estável e propagação instável da trinca),possibilitando a comparação com as imagens obtidas de cada etapa do mecanismo de fratura. Os valores de DT são melhores representados pelas reconstruções em microscópio óptico, pois estas permitem descrição mais precisa da topografia do material, considerando que o DT é característico em macroescalas. Já os valores de DS são melhores descritos em análises de microscopia eletrônica de varredura, já que esta apresenta melhor definição para a observação... / In this paper we make quantitative analysis of fracture surfaces obtained through from fatigue crack propagation. The fatigue cracks are in the mode of failure that occurs for a repetead cycling loading and applied to a specimen, which will cause the nucleation, crack propagation until rupture. We will use the tool of fractal dimension to analyze correlations with the crack propagation. The materials that were tasted are: AA7475 aluminum alloy and 300M steel, both materials for aeronautical use. Tested were performed in fatigue crack propagation inspecimens of type C(T) to obtain the fracture surface for analysis. Subsequently the surfaces were examines in optical microscope and scanning electron microscope. Was performed to measure the monofractal dimension (DF), when the surface is described by a single value, so the textural dimension values (DT), and when we involved macroescale and finally structural dimension (DS) when was presente microscale. With the results we can analyze the DS is who represents the best value for the fractal fracture surface, as this indicates the micromechanics of fracture surfaces. The DS values are less dispersed in the identification of regions of fatigue (pre-crack propagation stable and unstable crack propagation), allowing comparison with the images obtained from each step of the mechanism of fracture. The values of DT are better represented when we do analysis in an optical microscope, because it a achieves the best results of the topography of the material, whereas the DT is characteristic macroscale. The values of DS are best described in the analysis of scanning electron microscopy, since it show better the micromechanics of fracture. So we can say the the DS would be the best representative of the fractal dimension to the analysis of micromechanics of fracture surfaces to their good representation at the microscale

Orientador: Adler Guilherme Viadana / Banca: Archimedes Perez Filho / Banca: Francisco Sérgio Bernardes Ladeira / Resumo: O propósito da presente dissertação consiste na determinação de unidades de paisagem para o município de São Thomé das Letras (MG), no estudo da evolução morfológica da área e na apreciação de aspectos morfotectônicos. O cumprimento dos objetivos estipulados demandou uma série de dispositivos analíticos que se coadunaram para a interpretação da fisiologia da paisagem e para o discernimento de diferentes unidades paisagísticas representadas em documento cartográfico de síntese. O estudo da evolução morfológica demandou a avaliação de elementos do quadro genético-evolutivo regional como meio para o entendimento dos processos operantes em âmbito local. A pesquisa focalizou a ocorrência e posicionamento de diferentes superfícies de erosão na área de estudo, diferenciando remanescentes relacionados à Superfície Sul-Americana, do Terciário Inferior, de modelados de dissecação mais recentes, de idade plio-pleistocência. A esta etapa se somou, com ênfase, estudos interessados na evolução morfológica levada a efeito durante o Quaternário em consonância com as oscilações climáticas que marca o referido período, o que se deu por meio do estudo de processos de pedimentação recente e dos depósitos correlatos, da avaliação da cobertura vegetal atual e dos fenômenos cársticos operantes, também sendo estimada a evolução do relevo com enfoque na estrutura, que confere tipicidade apalachiana para a morfologia local e regional. No tocante aos aspectos morfotectônicos, a pesquisa se valeu da análise do relevo e da drenagem, enfando os fenômenos neotectônicos com base na identificação de feições morfológicas indicativas (shutter ridges, capturas, migração lateral de cursos dágua, canais fluviais com trechos excessivamente retilíneos, etc.) e na identificação e interpretação dos principais lineamentos. Os estudos morfotectônicos... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The aim of this present dissertation consists in the determination of landscape unity for the town of São Thomé das Letras (MG), in the study of the area morphological evolution and appreciation of morphotectonic aspects. The fulfilment of stipulated purpose demanded a serie of analytical device that were gathered for the comprehention of landscape phisiology as well as the understanding of different landscape unities represented in graphic-chart document of synthesis. The study of morphological evolution demanded the evaluation of components the regional genetic-evolutive chart as so as to understand the operating process in local range. The research focused the occurence and status of different erosion surface in the studied area, differenciating remainders related to Superfície Sul-Americana of low Terciary, of latest dissection molded, of plio-pleistocene age. To such stage, with emphasis, was added studies interested in the morphological evolution effectuatedduring the Quaternary in consonance with climatic fluctuations that mark the referred era, which happened by means of process study of recent pedimentation and correlated deposits from evaluation of current vegetal covering and operating carstic phenomenon, also evolution of relief beig estimated focusing the structure, that grants appalachian tipicality to regional and local morphology. Regarding the morphotectonic aspects, the research turned to the relief analisis and drainage emphasizing the neotectonic phenomena based on identification of indicative morphological features (shutter ridges, captures, water-course lateral migration, river channel with excessively right-lined streches, etc.) and identification and interpretation of main lineages. The morphotectonic studies were subsidized by measuring the geomorphic rate useful for estimating neotectonic effects, notoriously the asymmetry Factor of Drainage Basins... (Complete abstract click electronic access below) / Mestre

Neste trabalho será demonstrada uma versão dos teoremas de Hilbert Liebmann para superfícies em S² x R e H² x R, que são teoremas de existência e unicidade de superfícies completas com curvatura Gaussiana constante nesses ambientes. Como parte da demonstração, a saber a existência, será apresentada uma classificação das superfícies de revolução completas com curvatura Gaussiana constante em torno de um eixo qualquer, em S² x R e em torno de um eixo lorentziano, em H² x R. / In this work it will be proved a version of Hilbert and Liebmann theorems for surfaces in S² X R and H² X R, wich are theorems about existence and uniqueness of complete surfaces with constant Gaussian curvature in those ambients. As part of the proof, namely the existence, it will be presented a classication of complete revolution surfaces with constant Gaussian curvature around any axis in S² X R and around a Lorentzian axis in H² X R.