In this thesis, two rather different types of problems were investigated. The first was a case of anomalous reactivity in the area of carbohydrate synthesis. Hexopyranosides having the galacto configuration (i.e. C-4?OR axial) display very low SN2 reactivities towards anionic nucleophiles, whereas the corresponding gluco-configured C-6 sulfonates (C-4?OR equatorial) react at rates typical of primary centers. The accepted explanation for this difference involves the repulsive interaction of local dipoles in the transition structure of the galacto compound. This interaction is thought to destabilize the transition structure, making this reaction difficult. However, there are numerous inconsistencies in the application of this simple model (cases where the model fails to predict the observed behavior). Thus, a computational project was undertaken to examine six model systems of this type. The energetics and equilibria of the reactants were determined, including solvation. Reaction pathways and kinetics for various displacements were computed. Analyses of the calculated charge densities allowed for evaluation of any electrostatic interactions. This study revealed a number of important factors affecting the rates of reaction, while clearly showing that dipole-dipole interactions are very limited in these systems. The second project was in the related areas of molecular polarizability and vibrational spectroscopy. Descriptive models have been sought relating the structure and connectivity of molecules to their electronic properties. Researchers in the areas of non-linear optics and of conducting polymers require a better understanding of the effects of structural variations on electronic properties. The 4 simplest models of molecular polarizability and its derivatives with respect to molecular vibrations are grossly inadequate. The highest-level calculations are generally reliable but are not applicable to even moderately sized systems. Thus trends in these properties were investigated for a large series of molecules. Calculations were performed at a variety of theoretical levels in order to determine the ranges of predicted behavior. Since these calculations predicted unusual properties in bicyclo-[1.1.1]-pentane, an experimental project was completed on this molecule. The results of Raman scattering intensity experiments on bicyclo-[1.1.1]-pentane allowed for evaluation of the performance of various computational methods. More importantly, it allowed for the confirmation of some qualitative structure/property relationships. / October 2004

In this thesis, two rather different types of problems were investigated. The first was a case of anomalous reactivity in the area of carbohydrate synthesis. Hexopyranosides having the galacto configuration (i.e. C-4?OR axial) display very low SN2 reactivities towards anionic nucleophiles, whereas the corresponding gluco-configured C-6 sulfonates (C-4?OR equatorial) react at rates typical of primary centers. The accepted explanation for this difference involves the repulsive interaction of local dipoles in the transition structure of the galacto compound. This interaction is thought to destabilize the transition structure, making this reaction difficult. However, there are numerous inconsistencies in the application of this simple model (cases where the model fails to predict the observed behavior). Thus, a computational project was undertaken to examine six model systems of this type. The energetics and equilibria of the reactants were determined, including solvation. Reaction pathways and kinetics for various displacements were computed. Analyses of the calculated charge densities allowed for evaluation of any electrostatic interactions. This study revealed a number of important factors affecting the rates of reaction, while clearly showing that dipole-dipole interactions are very limited in these systems. The second project was in the related areas of molecular polarizability and vibrational spectroscopy. Descriptive models have been sought relating the structure and connectivity of molecules to their electronic properties. Researchers in the areas of non-linear optics and of conducting polymers require a better understanding of the effects of structural variations on electronic properties. The 4 simplest models of molecular polarizability and its derivatives with respect to molecular vibrations are grossly inadequate. The highest-level calculations are generally reliable but are not applicable to even moderately sized systems. Thus trends in these properties were investigated for a large series of molecules. Calculations were performed at a variety of theoretical levels in order to determine the ranges of predicted behavior. Since these calculations predicted unusual properties in bicyclo-[1.1.1]-pentane, an experimental project was completed on this molecule. The results of Raman scattering intensity experiments on bicyclo-[1.1.1]-pentane allowed for evaluation of the performance of various computational methods. More importantly, it allowed for the confirmation of some qualitative structure/property relationships.

In this thesis, two rather different types of problems were investigated. The first was a case of anomalous reactivity in the area of carbohydrate synthesis. Hexopyranosides having the galacto configuration (i.e. C-4?OR axial) display very low SN2 reactivities towards anionic nucleophiles, whereas the corresponding gluco-configured C-6 sulfonates (C-4?OR equatorial) react at rates typical of primary centers. The accepted explanation for this difference involves the repulsive interaction of local dipoles in the transition structure of the galacto compound. This interaction is thought to destabilize the transition structure, making this reaction difficult. However, there are numerous inconsistencies in the application of this simple model (cases where the model fails to predict the observed behavior). Thus, a computational project was undertaken to examine six model systems of this type. The energetics and equilibria of the reactants were determined, including solvation. Reaction pathways and kinetics for various displacements were computed. Analyses of the calculated charge densities allowed for evaluation of any electrostatic interactions. This study revealed a number of important factors affecting the rates of reaction, while clearly showing that dipole-dipole interactions are very limited in these systems. The second project was in the related areas of molecular polarizability and vibrational spectroscopy. Descriptive models have been sought relating the structure and connectivity of molecules to their electronic properties. Researchers in the areas of non-linear optics and of conducting polymers require a better understanding of the effects of structural variations on electronic properties. The 4 simplest models of molecular polarizability and its derivatives with respect to molecular vibrations are grossly inadequate. The highest-level calculations are generally reliable but are not applicable to even moderately sized systems. Thus trends in these properties were investigated for a large series of molecules. Calculations were performed at a variety of theoretical levels in order to determine the ranges of predicted behavior. Since these calculations predicted unusual properties in bicyclo-[1.1.1]-pentane, an experimental project was completed on this molecule. The results of Raman scattering intensity experiments on bicyclo-[1.1.1]-pentane allowed for evaluation of the performance of various computational methods. More importantly, it allowed for the confirmation of some qualitative structure/property relationships.

Malaria continues to be a significant cause of morbidity and mortality in the developing world with Africa being the most affected. Malaria vector control with chemical insecticides is the primary intervention to curb transmission. However, the success of chemical based interventions is threatened by the escalating development of insecticide resistance in the major anopheline mosquito vectors.

O desenvolvimento de queimadores de baixo NOx é baseado na compreensão da interação entre a cinética química da combustão e o campo do escoamento. Escoamentos rotacionais (swirling flows) são caracterizados pela presença de gradientes de pressão radiais e axiais, e tem sido aplicados como técnica de combustão para a minimização desses poluentes. Neste trabalho é apresentada a modelagem numérica de uma câmara de combustão cilíndrica com queimador dotado com swirler de blocos móveis. O modelo, composto pela equação de continuidade, balanços da quantidade de movimento em três dimensões, o transporte da energia cinética turbulenta e da vorticidade, transporte de espécies químicas e energia, foi implementado numericamente sob a plataforma computacional Fluent. A câmara foi simulada considerando propano combustível e os resultados comparados a dados experimentais de uma câmara cilíndrica operada com GLP. Como principal resultado foi possível identificar a ocorrência da ZCR no escoamento e a influência do número de swirl sobre as características da combustão. / The development of low NOx burners is based on the comprehension of the interaction between combustion kinetics and flow field. Swirling flows are characterized by radial and axial pressure gradients, which improve the recirculation of the hot products into the flame region, and then enhance the combustion efficiency have being proposed as a mean to reduce NOx emissions from these equipment’s. This work presents the numerical modeling of cylindrical combustion chamber equipped with movable blocks burner. The model includes the continuity equation along with the 3D momentum balance equations, the k-ω shear stress transport turbulence model equations, the energy balance and the equations for transport chemical species. Results of the simulation of the swirling reactive flow in the combustion chamber, performed using Fluent CFD package, are validated by comparison with experimental data obtained elsewhere. As a main result, it was possible to identify the occurrence of a CRZ in the flow and to discuss the influence of the swirl number on the combustion characteristics.

The aims of the present study were to characterize the typical volume (total distance) and intensities (high-speed distance > 75% of maximum speed for weekday practices, Monday through Friday and competitive games on Saturday; compare the daily practice volume and intensities to competitive games to determine if the targeted volume and intensities are achieved as part of the periodized strategies using GPS software; and examine the relationship among total distance, high-speed distance in the prediction of player-load . Thirty NCAA Division I Football players (187.9 ± 5.5 cm; 107.4 ± 24.6 kg) were monitored using GPS receivers with integrated accelerometers during the 13-week regular season during the 2016 season. Separate one-way repeated measures ANOVAs demonstrated that competitive game loads and intensity were significantly different than weekday practices (p-value ≤ 0.05). There were significant differences among weekday practices in terms of overall volume and intensities, however the overall training goals were not met. Stepwise linear regression revealed that total distance is a significant predictor of player load. The results of the present study indicated that total distance, but not high-speed distance, could best be used to describe and track the development of a periodization model for training in Division I Collegiate Football using GPS technologies.

O desenvolvimento de queimadores de baixo NOx é baseado na compreensão da interação entre a cinética química da combustão e o campo do escoamento. Escoamentos rotacionais (swirling flows) são caracterizados pela presença de gradientes de pressão radiais e axiais, e tem sido aplicados como técnica de combustão para a minimização desses poluentes. Neste trabalho é apresentada a modelagem numérica de uma câmara de combustão cilíndrica com queimador dotado com swirler de blocos móveis. O modelo, composto pela equação de continuidade, balanços da quantidade de movimento em três dimensões, o transporte da energia cinética turbulenta e da vorticidade, transporte de espécies químicas e energia, foi implementado numericamente sob a plataforma computacional Fluent. A câmara foi simulada considerando propano combustível e os resultados comparados a dados experimentais de uma câmara cilíndrica operada com GLP. Como principal resultado foi possível identificar a ocorrência da ZCR no escoamento e a influência do número de swirl sobre as características da combustão. / The development of low NOx burners is based on the comprehension of the interaction between combustion kinetics and flow field. Swirling flows are characterized by radial and axial pressure gradients, which improve the recirculation of the hot products into the flame region, and then enhance the combustion efficiency have being proposed as a mean to reduce NOx emissions from these equipment’s. This work presents the numerical modeling of cylindrical combustion chamber equipped with movable blocks burner. The model includes the continuity equation along with the 3D momentum balance equations, the k-ω shear stress transport turbulence model equations, the energy balance and the equations for transport chemical species. Results of the simulation of the swirling reactive flow in the combustion chamber, performed using Fluent CFD package, are validated by comparison with experimental data obtained elsewhere. As a main result, it was possible to identify the occurrence of a CRZ in the flow and to discuss the influence of the swirl number on the combustion characteristics.

O desenvolvimento de queimadores de baixo NOx é baseado na compreensão da interação entre a cinética química da combustão e o campo do escoamento. Escoamentos rotacionais (swirling flows) são caracterizados pela presença de gradientes de pressão radiais e axiais, e tem sido aplicados como técnica de combustão para a minimização desses poluentes. Neste trabalho é apresentada a modelagem numérica de uma câmara de combustão cilíndrica com queimador dotado com swirler de blocos móveis. O modelo, composto pela equação de continuidade, balanços da quantidade de movimento em três dimensões, o transporte da energia cinética turbulenta e da vorticidade, transporte de espécies químicas e energia, foi implementado numericamente sob a plataforma computacional Fluent. A câmara foi simulada considerando propano combustível e os resultados comparados a dados experimentais de uma câmara cilíndrica operada com GLP. Como principal resultado foi possível identificar a ocorrência da ZCR no escoamento e a influência do número de swirl sobre as características da combustão. / The development of low NOx burners is based on the comprehension of the interaction between combustion kinetics and flow field. Swirling flows are characterized by radial and axial pressure gradients, which improve the recirculation of the hot products into the flame region, and then enhance the combustion efficiency have being proposed as a mean to reduce NOx emissions from these equipment’s. This work presents the numerical modeling of cylindrical combustion chamber equipped with movable blocks burner. The model includes the continuity equation along with the 3D momentum balance equations, the k-ω shear stress transport turbulence model equations, the energy balance and the equations for transport chemical species. Results of the simulation of the swirling reactive flow in the combustion chamber, performed using Fluent CFD package, are validated by comparison with experimental data obtained elsewhere. As a main result, it was possible to identify the occurrence of a CRZ in the flow and to discuss the influence of the swirl number on the combustion characteristics.

Biological indicators measure components of the biota and are used to give general information about complex ecosystems in which they occur, playing key roles in conservation planning and management. This study illustrates the impact of habitat change by factors that are extrinsic to the habitats in question and the importance of spider responses in aiding management decisions. The spider responses illustrated existence of environmental change and represent responses of other biota. The conclusions drawn from this study have important management implications for protected areas with grazing herbivores and occurrence of alien invasive plants. Grazed sites showed the highest abundance, diversity and species richness, while ungrazed had the lowest. The implications from this study are that no grazing has negative implications on lower trophic levels, whereas grazing seems to result in favourable conditions for optimal abundance, diversity and species richness. The higher abundance, diversity and species richness associated with grazed sites could result from increased ground cover, greater variation in habitat structure, increased plant diversity and enhanced soil/plant nutrient concentrations. But, ungrazed sites in turn become more monotonous and provide less habitat diversity. However, the characteristic species for each grazing intensity level demonstrates the difficulty in making generalizations for management even for closely related species. The results further opposed the assumption that grazing lawns are a result of overgrazing and thus highly undesirable. This grassland type in comparison to tall bunch grassland displayed the highest spider diversity and species richness. This evidence further supports the conclusion that grazing lawns are steady state communities of their own and not a sub-set of any other grassland type. Therefore, veld management decisions that eradicate grazing lawns are negative for the park as the fauna and flora associated with this grassland type will be lost, leading to cascading effects. Additionally, this study illustrated that habitat modification by invasion of invasive alien plant species has detrimental consequences for the endemic fauna. C. odorata invasion results in a monotonous habitat structure. Consequently, structural heterogeneity is a primary determinant for spider diversity as opposed to abundance of prey, because plant height and architecture drive spider colonization. Therefore, removal of alien invasive weeds results in returning a system to close approximation of its condition prior to disturbance with both structure and function recreated. Assemblage patterns can be selected as endpoints to measure the ecological rehabilitation; thus, the non-significant differences in assemblage patterns of the control versus cleared sites imply that the system is rehabilitating with clearing without further management intervention. This study adds to the limited information on the implications of grazing intensities, grassland types, short and long-term invasion and clearing of an alien invasive plant on spider communities. Copyright / Dissertation (MSc)--University of Pretoria, 2008. / Animal and Wildlife Sciences / unrestricted

<p>Since the first description of Si nanocrystals, research in this field has gone through raid progress and potential applications of Si nanocrystals have been established. There are several methods applicable to the fabrication of Si nanocrystals with one of the most used being ion implantation followed by thermal annealing. Two types of thermal annealing are available for use: furnace annealing (FA) for several hours, normally in an N₂ atmosphere; and rapid thermal annealing (RTA) for a short time (less than a few minutes), again in an inert atmosphere such as N₂. The formation of the nanocrystals then proceeds with decomposition, segregation, diffusion, nucleation, aggregation, growth and crystallization. This formation requires temperatures in excess of 1000^o C such that noticeable photoluminescence may be observed. This thesis explores the fabrication of Si nanocrystals using the McMaster ion implanter and subsequent RTA. The implantation conditions required to form luminescent nanocrystals are determined. For example, for an implantation energy of 10 KeV a minimum dose of 1.5 10¹⁶ ions cm^-2 is required. The relationship between luminescent intensity and post-implantation annealing is also explored. An optimum annealing temperature of 1100^oC is found. For the first time to the author’s knowledge, a study of the effects of thin film thickness on luminescent intensity is conducted. The major conclusions of this thesis are i) a specific thickness of oxide layer has the maximum PL for a fixed implantation energy and implantation dose, ii) PL intensity is inversely proportional with measuring temperature., iii) the type of oxidation process has a large effect on PL intensity.</p> / Master of Applied Science (MASc)