Thesis (Ph. D.)--University of Virginia, 1997. / Includes bibliographical references (436-463). Also available online through Digital Dissertations.

Made available in DSpace on 2014-06-12T18:02:32Z (GMT). No. of bitstreams: 2 arquivo3968_1.pdf: 494550 bytes, checksum: dc123436c569f80c9bebfbc057d36cbc (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2009 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O objetivo desta dissertação é avaliar e aplicar métodos de análise de influência na análise estatística de formas. A partir do modelo de deleção de casos (CDM) obtem-se uma medida da distância de Cook quando o conjunto de dados tem distribuição Bingham complexa. Mediante simulações de Monte Carlo e o método bootstrap tem-se a estimação da região de confiança para a distância de Cook em diferentes conjuntos de dados com distribuição Bingham complexa. Além disso, é mostrado nesta dissertação que outros métodos para análise de influência podem funcionar em análise de formas. A eficácia da distância de Cook frente aos métodos apresentados é avaliada

Diffusion MRI (dMRI) measurements allow us to infer the microstructural properties of white matter and to reconstruct fiber pathways in-vivo. High angular diffusion imaging (HARDI) allows for the creation of more and more complex local models connecting the microstructure to the measured signal. One of the challenges is the derivation of meaningful metrics describing the underlying structure from the local models. The aim hereby is to increase the specificity of the widely used metric fractional anisotropy (FA) by using the additional information contained within the HARDI data. A local model which is connected directly to the underlying microstructure through the model of a single fiber population is spherical deconvolution. It produces a fiber orientation density function (fODF), which can often be interpreted as superposition of multiple peaks, each associated to one relatively coherent fiber population (bundle). Parameterizing these peaks one is able to disentangle and characterize these bundles. In this work, the fODF peaks are approximated by Bingham distributions, capturing first and second order statistics of the fiber orientations, from which metrics for the parametric quantification of fiber bundles are derived. Meaningful relationships between these measures and the underlying microstructural properties are proposed. The focus lies on metrics derived directly from properties of the Bingham distribution, such as peak length, peak direction, peak spread, integral over the peak, as well as a metric derived from the comparison of the largest peaks, which probes the complexity of the underlying microstructure. These metrics are compared to the conventionally used fractional anisotropy (FA) and it is shown how they may help to increase the specificity of the characterization of microstructural properties. Visualization of the micro-structural arrangement is another application of dMRI. This is done by using tractography to propagate the fiber layout, extracted from the local model, in each voxel. In practice most tractography algorithms use little of the additional information gained from HARDI based local models aside from the reconstructed fiber bundle directions. In this work an approach to tractography based on the Bingham parameterization of the fODF is introduced. For each of the fiber populations present in a voxel the diffusion signal and tensor are computed. Then tensor deflection tractography is performed. This allows incorporating the complete bundle information, performing local interpolation as well as using multiple directions per voxel for generating tracts. Another aspect of this work is the investigation of the spherical harmonic representation which is used most commonly for the fODF by means of the parameters derived from the Bingham distribution fit. Here a strong connection between the approximation errors in the spherical representation of the Dirac delta function and the distribution of crossing angles recovered from the fODF was discovered. The final aspect of this work is the application of the metrics derived from the Bingham fit to a number of fetal datasets for quantifying the brain’s development. This is done by introducing the Gini-coefficient as a metric describing the brain’s age.

[pt] Como parte da linha de pesquisa na área de estimulação de poços de petróleo, foi montado um viscosímetro tubular para análise das características de comportamento reológico de um fluido de fraturamento hidráulico (HPGUAR), dotado de dispositivo para preparação do fluido . Os dados experimentais obtidos foram tratados analiticamente segundo dois tipos de equações constitutivas: as do Modelo de Ostwald, amplamente utilizadas pelos pesquisadores da área de Engenharia de Petróleo, e as do Modelo de Bingham. Pela avaliação dos resultados obtidos, pode-se concluir que parecem ocorrer evidências de que o Modelo de Bingham possa ser mais adequado, por retratar de forma mais independente as contribuições isoladas do atrito viscoso e da componente gerada pela viscosidade plástica, na análise teológica do HPGUAR. Sugere-se que investigações mais detalhadas devam ser conduzidas, posto que eventualmente poderiam ser bastante úteis no esclarecimento da pendência existente nos resultados experimentais obtidos por diversos autores consultados. / [en] In order to contribute in the investigation of the stimulation operation of an oil reservoir was built a tubular viscometer to determine the rheological properties of a hydraulic fracturing fluid (HPGUAR). This test rig included a system to prepare the hydraulic fracturing fluid. The experimental results were modelled according to two types of constitutive equations: the Ostwald Model one, widely used in the Petroleum Engineers field, and the Bingham Model one. An evaluation of the experimental results suggests that the Bingham Model should be more adequate than the other one, specifically when it shows the contribuition from the viscous friction and from the plastic viscosity independently, in the determination of the rheological properties of the HPGUAR. More detailed investigations must be carried out, although they should be very usefull in better explaning the differeces obtained among several investigators.

Ingeniero Civil Matemático / El primer objetivo de este trabajo es desarrollar un algoritmo que resuelva la EDP asociada al modelo de Bingham, en un dominio particular, una canaleta. La dificultad se centra en que este modelo introduce una no linealidad al problema. Como segundo objetivo, una vez obtenido este algoritmo, se quiere validar usando mediciones obtenidas mediantes experimentos sobre fluidos que se cree se comportan como el modelo de Bingham indica. Con esto en mente, se estudia el modelo de Bingham y problemas asociados equivalentes en formulación débil. Esto permite concluir características de las soluciones y también encontrar un algoritmo, que nace de la formulación del problema como punto silla. El algoritmo resuelve la no linealidad de las ecuaciones de Cauchy mediante una simplificación nacida de la geometría especial de las canaletas, y la no linealidad de Bingham mediante un astuto algoritmo iterativo debido a Glowinski, que resuelve en cada paso un problema lineal. Se utilizó Matlab para el desarrollo de los algoritmos puesto que debemos utilizar matrices y operaciones de matrices de forma repetida, y Matlab está optimizado para ello. Una vez obtenido un algoritmo, se usan los datos de la tésis de Jorge Martínez, para validar el modelo, y reobtener algunos datos intrínsecos del fluido, a saber, su tensión de fluencia $\tau$ y su viscosidad $\mu$ y compararlos con las versiones obtenidas experimentalmente. Esto se hace mediante una minimización de cuadrados de la diferencia entre datos locales de la velocidad y la solución obtenida por el algoritmo.

The present work deals with the development of a direct simulation strategy for solving the motion of spherical particles in non-Newtonian liquids. The purely viscous (non-elastic) non-Newtonian liquids are described by Bingham and thixotropy models. Validation of the strategy is performed for single phase (lid driven cavity flow) and two phase flows (sphere sedimentation). Lid driven cavity flow results illustrate the flow evolution of thixotropic liquid and subtle differences between thixotropic rheology and pseudo Bingham rheology. Single sphere sedimentation in Bingham liquid is shown to be influenced by the yield stress of the liquid. Time-dependent properties such as aging prominently affect the settling of a sphere in thixotropic liquid. The hydrodynamic interactions between two spheres are also studied at low and moderate Reynolds numbers. In thixotropic liquid, an intriguing phenomenon is observed where the separation distance between the spheres first increases and then rapidly decreases. / Chemical Engineering

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Thesis (M.A.)--University of Wisconsin--Madison, 1967. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

This paper will be confined to the northern portion of the range though it might be noted that the topographical descriptions of the Bingham district apply in a general way to the southern district also. The northern Oquirrhs contain a number of sizeable canyons running either east or west from a central ridge seven thousand to eight thousand feet in altitude. Bingham Canyon, one of the largest of these, is located on the eastern slope of the range and drains into Salt Lake Valley.