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The ability to model ground-state properties in density function theory (DFT) is a ected by the theoretical treatment of the electrons and the numerical approach to the theory. The electron-electron interaction energy is approximated by exchange- correlation (XC) functionals which are functions of the electron density. Popular functionals include the localized density approximation (LDA) or one of many gen- eralized gradient approximations (GGA). The numerical approaches used are the core-electron approximating pseudopotential (PsP) or the more accurate all-electron (AE) method. We test whether PsP calculations for some new GGA's can accurately reproduce AE values for cohesive energy, lattice constant, and bulk modulus for six- teen solids. We compare our PsP results to AE results for several XC functionals and gauge the quality of functionals by comparison to experiment. This allows us to determine which errors are caused by functionals and which are caused by PsP's.

Thesis (M.S.)--University of Wisconsin, 1965. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves [55-59]).

A new geophysical method was developed to satisfy a need for in-situ density measurements. Various situations, such as a gravity dam wall requires that density measurements should be done without damage to the structure. The sample volume should also not be that large in order to be sensitive enough for variations. This method measures the in-situ density of the weathered layer and other man made structures, using seismic waves in three directions. The seismic waves utilized are P-waves and S-waves. It is however surface waves that are treated like body waves because they do not separate at this shallow depth. These waves are very sensitive to the attenuation factor, which is in turn sensitive to certain physical properties of the propagation medium. This factor is utilsed when the multi layer problem is encountered. The maximum depth of exploration is 2-5m and depends solely on the seismic skin depth. This method utilises a large base plate. The source is a large sledge hammer and shots are done at each side of the base plate. Different dominant frequencies are identified and used to calculate the densities of the layers associated with that specific frequency. The velocities of the subsurface are determined by small seismic refraction surveys. The method will find application mainly in the civil and engineering geology fields. The main application will be to determine subsurface densities and small movement elasticity modulli for engineers to aid in obtaining adequate design parameters. Case studies on three different geologic environments are presented. The results indicate that this method will be useful, although certain modifications are recommended to make this method even faster and more user friendly. / Thesis (PhD)--University of Pretoria, 2007. / Geology / unrestricted

Understanding regulation of wild animal populations is important in ecological investigations and applied wildlife management. Progress in understanding regulatory processes has been hindered by a long-running debate over the role of density-dependent and density-independent variables in population regulation. Population regulation of exploited species is of particular interest because harvest theory is predicated on assumptions of density-dependent feedback. However, for many exploited species, the functional relationships and mechanisms of population regulation via density dependence are not quantified (e.g., Northern bobwhite (Colinus virginianus). Compounding this task is the lack of a mechanistic understanding of the influence of density-independent factors in population regulation. The overall goal of this dissertation is to investigate the roles of density-dependent and density-independent processes in bobwhite populations. Bobwhites are an excellent species to investigate the role and influence of density-dependent and density-independent factors due to their unique life history, wherein they can exhibit density dependence in survival, reproduction, or both. I provide support for the concomitant influence of density-dependent and density-independent processes operating to regulate bobwhite populations. My results support the importance of food and cover and the additive influence of density-dependent and density-independent factors on bobwhite annual survival. I also report evidence for the differential effects of covariates on survival phases. My results represent the first evidence of support for the Tub and Tap hypotheses on bobwhite survival. I also quantify a density-dependent effect on bobwhite recruitment. Collectively, these results provide new evidence for understanding the role of internal and external factors in bobwhite populations.

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published_or_final_version / Physics / Doctoral / Doctor of Philosophy

published_or_final_version / Physics / Master / Master of Philosophy

published_or_final_version / abstract / Mechanical Engineering / Master / Master of Philosophy