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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

Hydrogeological characterisation of crystalline basement aquifers within the Limpopo Province, South Africa

Holland, Martin 21 June 2011 (has links)
Geologically complex crystalline aquifers are distributed extensively in Africa and also underlie large parts of the semi-arid Limpopo Province where some of the greatest groundwater needs in South Africa occur. The importance of these basement aquifers makes it vital to identify high yielding hydrogeological zones that can be targeted for water supply, to sustain areas of high population density with few or no alternative water sources. The biggest challenge is to understand the factors that determine the secondary permeability of these weathered-fractured rock aquifers. The focus of this study was therefore to systematically analyse regional factors that may influence borehole yields and aquifer transmissivities. The study covered four distinct geological and morpho-structural domains within the Limpopo Province, covering about 23 500 km2. The borehole dataset compiled for the study consisted of over 8 000 boreholes contained in the Groundwater Resources Information Project (GRIP) Limpopo database of the South African Department of Water Affairs. Approximately 3 000 of these boreholes have been hydraulically tested and the lithology has been recorded in 1 200 cases. A commonly encountered problem of pumping tests analysis in crystalline aquifers is in choosing an appropriate model that best fits the observed drawdown response. In this thesis modern methods are proposed for the analysis of pumping test data in weathered-fractured rock aquifers and highlight the importance of diagnostic plots, especially derivatives, for the detection of flow regimes and the choice of the correct ‘theoretical’ model. Based on the classification no single analytical method can be universally applied to crystalline basement aquifers when considering the analysis of pumping test data. The GRIP borehole dataset was analysed in conjunction with spatial information to identify the relationship of regional factors such as - geology, hydrology, weathering thickness, topography, geomorphology, neo-tectonic stresses, and structural lineaments - on groundwater occurrence. Geology has a clear influence, with boreholes exploiting alluvial aquifers composed of highly permeable material, and certain rock types such as pegmatite, showing generally higher borehole productivities. Favourable borehole locations from a topographical point of view are predictably along rivers and valleys. Other identified favourable groundwater targets are the metamorphic aureoles of younger granite intrusions. Despite the local importance of the regolith as a recharge and storage mechanism for the underlying fractured bedrock, no correlation between borehole yields and depth of weathering was found. The pattern of lineament and dyke orientations in the different morpho-structural domains led to a more complex conceptual model of groundwater occurrence. This model is inconsistent with the predicted regime based on regional stress field data and suggests that local variations have a strong influence on groundwater occurrence. Due to the complex geological history of the area, it is difficult to link open discontinuities to a distinct recent or past tectonic event. It can be concluded that regional stress field data, as in this case, may not account for local, possibly highly significant, stress field variations. The hydrogeological importance of several factors on groundwater occurrence presented in this study can be used as a working reference for future groundwater development programmes. / Thesis (PhD)--University of Pretoria, 2011. / Geology / unrestricted
2

Fases e criticalidade no modelo ashkin - teller de tr?s cores

Piolho, Francisco de Assis Pereira 14 December 2007 (has links)
Made available in DSpace on 2014-12-17T15:14:49Z (GMT). No. of bitstreams: 1 FranciscoAPP.pdf: 1034371 bytes, checksum: b3ff17842c3ee8ab8282b0e829786698 (MD5) Previous issue date: 2007-12-14 / The usual Ashkin-Teller (AT) model is obtained as a superposition of two Ising models coupled through a four-spin interaction term. In two dimension the AT model displays a line of fixed points along which the exponents vary continuously. On this line the model becomes soluble via a mapping onto the Baxter model. Such richness of multicritical behavior led Grest and Widom to introduce the N-color Ashkin-Teller model (N-AT). Those authors made an extensive analysis of the model thus introduced both in the isotropic as well as in the anisotropic cases by several analytical and computational methods. In the present work we define a more general version of the 3-color Ashkin-Teller model by introducing a 6-spin interaction term. We investigate the corresponding symmetry structure presented by our model in conjunction with an analysis of possible phase diagrams obtained by real space renormalization group techniques. The phase diagram are obtained at finite temperature in the region where the ferromagnetic behavior is predominant. Through the use of the transmissivities concepts we obtain the recursion relations in some periodical as well as aperiodic hierarchical lattices. In a first analysis we initially consider the two-color Ashkin-Teller model in order to obtain some results with could be used as a guide to our main purpose. In the anisotropic case the model was previously studied on the Wheatstone bridge by Claudionor Bezerra in his Master Degree dissertation. By using more appropriated computational resources we obtained isomorphic critical surfaces described in Bezerra's work but not properly identified. Besides, we also analyzed the isotropic version in an aperiodic hierarchical lattice, and we showed how the geometric fluctuations are affected by such aperiodicity and its consequences in the corresponding critical behavior. Those analysis were carried out by the use of appropriated definitions of transmissivities. Finally, we considered the modified 3-AT model with a 6-spin couplings. With the inclusion of such term the model becomes more attractive from the symmetry point of view. For some hierarchical lattices we derived general recursion relations in the anisotropic version of the model (3-AAT), from which case we can obtain the corresponding equations for the isotropic version (3-IAT). The 3-IAT was studied extensively in the whole region where the ferromagnetic couplings are dominant. The fixed points and the respective critical exponents were determined. By analyzing the attraction basins of such fixed points we were able to find the three-parameter phase diagram (temperature ? 4-spin coupling ? 6-spin coupling). We could identify fixed points corresponding to the universality class of Ising and 4- and 8-state Potts model. We also obtained a fixed point which seems to be a sort of reminiscence of a 6-state Potts fixed point as well as a possible indication of the existence of a Baxter line. Some unstable fixed points which do not belong to any aforementioned q-state Potts universality class was also found / O modelo Ashkin-Teller (AT) usual consiste na superposi??o de dois modelos de Ising acoplados por um termo de intera??o de quatro spins. Em duas dimens?es o modelo AT apresenta uma linha de pontos fixos com expoentes cr?ticos variando continuamente, sobre a qual ele se torna sol?vel atrav?s de um mapeamento no modelo Baxter. Motivado por esta riqueza de comportamento multicr?tico em duas dimens?es, Grest e Widom introduziram e estudaram o modelo Ashkin-Teller de N cores (AT-N), nas vers?es anisotr?pica (AAT-N) e isotr?pica (IAT-N), atrav?s de v?rios m?todos anal?ticos e computacionais. Neste trabalho apresentamos uma vers?o mais geral do modelo Ashkin-Teller de 3 cores (AT-3) onde e introduzido um acoplamento de 6 spins. Estudamos o modelo atrav?s da an?lise da estrutura de suas simetrias, seguido de an?lises de poss?veis diagramas de fases determinados por t?cnicas de grupo de renormaliza??o no espa?o real. Esses diagramas s?o obtidos em temperatura finita na regi?o onde predomina o comportamento ferromagn?tico. Com o aux?lio do conceito de transmissividade obtemos as rela??es de recorr?ncia em redes hier?rquicas com liga??es peri?dicas e quasi-peri?dicas. Numa an?lise preliminar, consideramos inicialmente o modelo Ashkin-Teller de duas cores, a fim de obter resultados que possam servir de guia ao nosso objetivo principal. No caso anisotr?pico (AAT-2), o modelo foi tratado na Ponte de Wheatstone, conforme j? havia sido estudado por Claudionor Bezerra na sua disserta??o de mestrado. Usando ferramentas computacionais mais adequadas, encontramos superf?cies cr?ticas isomorfas previstas no trabalho citado, mas ainda n?o identificadas explicitamente. Al?m disso, analisamos a vers?o isotr?pica (IAT-2), em uma rede hier?rquica aperi?dica. Mostramos,neste caso, como a aperiodicidade da rede afeta as flutua??es geom?tricas, causando mudan?as no comportamento cr?tico do modelo. Essas an?lises foram feitas utilizando defini??es apropriadas de transmissividade. Em seguida passamos ao estudo do modelo Ashkin-Teller de 3 cores onde, al?m do acoplamento de 4 spins, introduzimos um acoplamento de 6 spins, que torna o modelo mais atraente do ponto de vista das simetrias que ele passa a apresentar. Calculamos rela??es de recorr?ncias gerais para o modelo na vers?o anisotr?pica (AAT-3), de onde podemos obter o caso particular do sistema isotr?pico (IAT-3), em certas redes hier?rquicas. A vers?o IAT-3 do modelo foi estudada detalhadamente na regi?o onde predominam as intera??es ferromagn?ticas. Determinamos os pontos fixos e respectivos expoentes cr?ticos. Analisando as bacias de atra??o desses pontos fixos, conseguimos obter o diagrama de fases tri-dimensional (temperatura ? acoplamento de quatro spins ? acoplamento de seis spins). Identificamos pontos fixos do tipo Ising e de Potts de 4 e de 8 estados, al?m de ind?cios de um ponto fixo reminiscente do Potts de 6 estados e uma possibilidade de uma linha de Baxter. Identificamos tamb?m pontos fixos cr?ticos inst?veis que n?o pertencem a nenhuma classe de universalidade identificada com o modelo de Potts q estados

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