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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Bias correction and change measurement in spatio-temporal data

Hodge, Miriam Christine January 2012 (has links)
A simplistic view of a dataset is that it is collection of numbers. In fact data are much more than that and all data are collected at a set place and time. Often either the location, or the time, is fixed within the dataset and one or both are disregarded. When the place and time of the collection are incorporated into the analysis, the result is a spatio-temporal model. Spatio-temporal data are the focus of this thesis. The majority of the datasets used are radio tracking studies of animals where the objective is to measure the habitat use. Observations are made over a long period of time and a large area. The largest dataset analysed tracks over a hundred animals, in an area larger than 40 square miles, for multiple years. In this context understanding the spatio-temporal relationships between observations is essential. Even data that do not have an obvious spatial component can benefit from spatio-temporal analysis. For example, the data presented on volatility in the stock market do not have an obvious spatial component. The spatial component is the location in the market, not a physical location. Two different methods for measuring and correcting bias are presented. One method relies on direct modelling of the underlying process being observed. The underlying process is animal movement. A model for animal movement is constructed and used to estimate the missing observations that are thought to be the cause of the bias. The second method does not model the animal movement, but instead relies on a Bayesian Hierarchical Model with some simple assumptions. A long running estimation is used to calculate the most likely result without ever directly estimating the underlying equations. In the second section of the thesis two methods for measuring change from shifts in both spatial and temporal location are presented. The methods, Large Diffeomorphic Deformation Metric Mapping (LDDMM) and Diffeomorphic Demons (DD), were originally developed for anatomical data and are adapted here for nonparametric regression surfaces. These are the first applications of LDDMM and DD outside of computational anatomy.
2

[pt] DESENVOLVIMENTO DE UM SISTEMA DE MEDIÇÃO DE VARIAÇÃO DE VOLUME TOTAL DE AMOSTRAS TRIAXIAIS NÃOSATURADAS E AVALIAÇÃO DO EFEITO DE PROCESSOS DE SATURAÇÃO NO COMPORTAMENTO DE SOLOS SAPROLÍTICOS / [en] DEVELOPMENT OF A TOTAL VOLUME CHANGE MEASURING SYSTEM FOR UNSATURATED TRIAXIAL SAMPLES AND EVALUATION OF THE EFFECT OF SATURATION PROCEDURES ON THE BEHAVIOUR OF SAPROLITIC SOILS

19 November 2021 (has links)
[pt] Esta pesquisa apresenta um estudo sobre a influência de técnicas de saturação, empregadas em laboratórios comerciais e de pesquisa, no comportamento tensão-deformação-resistência de solos residuais quando submetidos a ensaios de compressão triaxial tipo CIU. Os solos avaliados são provenientes de litologias distintas e apresentam diferenças na composição mineralógica, grau de intemperismo e estrutura. Um dos solos pertence ao perfil de alteração de uma rocha alcalina encontrada no município de Tanguá-RJ. Os demais solos são oriundos das feições melanocrática e leucocrática de um migmatito da baixada fluminense (Duque de Caxias-RJ). A variação de volume total dos corpos de prova durante a saturação foi monitorada em alguns ensaios para auxiliar na interpretação dos resultados. Para tanto, foi desenvolvida uma câmara triaxial dupla com sistema de medida de variação de volume total de fácil montagem e custo reduzido, cujas características técnicas são competitivas com as existentes no mercado. O método de saturação que consiste na percolação de água por meio de sucção com baixa tensão confinante seguida de aumento contínuo e simultâneo de tensões (saturação automática) mostrou ser o mais adequado para o solo residual de rocha alcalina, que apresenta estrutura frágil, sem agentes cimentantes e com elevado índice de vazios. Já o solo residual de migmatito (feição melanocrática), que apresenta agentes cimentantes e elevada tensão de cedência, é menos susceptível à técnica de saturação, tendo seu comportamento afetado apenas pelo emprego da técnica de incremento único de contrapressão. / [en] This research presents a study on the influence of saturation procedures, used in commercial and research laboratories, on the stress-strain-strength behavior of residual soils when subjected to CIU triaxial tests. The selected soils are derived from different lithologies and show differences in mineralogical composition, structure and weathering degree. One of them belongs to the weathering profile of an alkaline rock located at the city of Tanguá-RJ. The others are the result of weathering processes on melanocratic and leucocratic features of a migmatite from Duque de Caxias, in Rio de Janeiro Metropolitan Area. Variation of the total volume of the test specimens was monitored during the saturation process in some tests to assess the influence of this procedure on the soil structure. For this purpose, it was developed a double-walled triaxial cell with a system based on the measurement of variation of the volume of the fluid filling the inner cell. The equipment has competitive technical features, besides the low cost and easy to assemble. The saturation technique based on percolating water by suction with a low cell pressure followed by continuous and simultaneous increase of backpressure (automatic saturation) was the most suitable method for the residual soil from the alkaline rock, which presents a weakly cemented structure, without bonding, and high voids ratio. However, the residual soil from the migmatite rock (melanocratic feature), which has strong cementation and high yielding stress, shown to be less susceptible to the saturation procedures, having its behavior affected only by the saturation technique of elevation of backpressure in just onestage.

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