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Generating functions in branching processes and birth and death processes

Generating functions in branching processes and birth and death processes Docrat, Raeesa "If I have seen further, it is by standing upon the shoulders of giants" -Sir Isaac Newton Birth and death processes and branching processes are areas of stochastic processes that can be applied to a multitude of elds and disciplines, such as biology, economics and engineering. In general, the analysis of distributions and moments of these processes are di cult to obtain in explicit form. The use of generating functions makes computation much easier. The dissertation looks at the theory, application and innovation of using generating functions in the analysis of branching and birth and death processes. A dissertation submitted to the Faculty of Science, University of the Witwatersrand, in ful llment of the requirements for the degree of Master of Science. Johannesburg, March 2018.


Synthesis of carbon nano-onions and their application in photovoltaic cells

Synthesis of carbon nano-onions and their application in photovoltaic cells Mongwe, Thomas Hlamalani In this study the synthesis and use of multi-layered and quasi-spherical carbon nano-onions (CNOs) for use as a catalyst in dye-sensitized solar cells (DSSCs) is reported. The synthesis of CNOs was achieved following procedures reported in the literature. Two synthesis methods are reported this study; the catalytic chemical vapour deposition (CCVD) and the flame pyrolysis method (FP). To selectively synthesize CNOs using CCVD, a supported iron catalyst was prepared for the decomposition of acetylene (C2H2), used as carbon source. Sodium chloride was used as a support due to its water solubility advantage. During the CCVD synthesis at 450 °C, mixtures of carbonaceous nanomaterials were observed that included carbon nanofibres. To counter act this problem, the FP method was used and CNOs of high purity were obtained from this method. The FP method is a catalyst free method and in this study clarified butter (Ghee) was used as the carbon source as well as the fuel. The flame produced the soot material (CNOs) effectively. The carbon nanostructured materials produced from both methods were analyzed and characterized using various analytical techniques such as Branauer-Emmett-Teller (BET) analysis, Fourier Transform Infrared (FTIR) spectroscopy, Raman spectroscopy, Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Thermo-Gravimetric Analysis (TGA), Ultra-Violet visible (UV-vis) spectroscopy, and Powder X-ray diffraction (XRD). These techniques revealed that both methods produce CNOs. However, the ones produced from the CCVD method incorporated the metal catalyst and also included carbon nanofibers (CNFs). The CNOs produced were quasi-spherical nanostructured materials with diameters less than 100 nm. Materials produced through FP, were very pure and were synthesized in good yield in gram scaled. The highly pure CNOs from the FP method were successfully doped with nitrogen (post-doped) using gaseous ammonia. Both the doped and undoped CNOs were tested in DSSCs. It was observed that both types of materials are capable of acting as a catalyst for this type of photovoltaic cells. However, the nitrogen doped material had better catalytic behavior compared to the undoped CNOs. This was attributed to the fact that doping CNOs with nitrogen promoted n-type behavior such that electron transportation in the cell was easily promoted. A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfillment for the degree of Master of Science in Chemistry. Johannesburg. April 2018.


Gentrification-induced displacement: a phenomenological study of inner-city residents' experiences in Johannesburg

Gentrification-induced displacement: a phenomenological study of inner-city residents' experiences in Johannesburg Ah Goo, Delia Felecia Stephanie With the evolution and the intensification of gentrification, its once clear-cut ties to displacement have been obscured. Displacement is now often denied and contested in the literature and a number of recent studies have provided quantitative evidence of the limited extent of the phenomenon. Questions have also been raised as to whether low-income residents are in fact displaced and whether gentrification is detrimental to the poor. However, the perspectives of people who have been displaced as a result of gentrification have largely been overlooked in the literature, in part due to the methodological difficulty of tracing displaced people. The aim of this study was to explore and to describe the phenomenon of displacement, from the perspective of individuals who lived and/or worked in a gentrifying area in the inner city of Johannesburg, as well as those who had been excluded or physically displaced by gentrification processes. In response to the call for more qualitative approaches to gentrification, a phenomenological approach was used in order to uncover the experience of displacement. In contrast to research that has highlighted the positive effects of gentrification, displacement was found to be a traumatic experience, which had an impact on the overall well-being of the participants of the study. Poor and marginalised people were rendered homeless, causing a disruption in their everyday life-world. The essence of the phenomenon of displacement was found to be one of great pain and loss, which was still experienced by the participants long after their physical relocation had taken place. As the inner city of Johannesburg transforms, reinvestment policies and strategies should therefore seek to be in the interests of the poor and not only the middle class, particularly since today it is home to people who were once denied the right to live there, due to South Africa’s apartheid policies. A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2018.


Impact of alluvial diamond mining on macroinvertebrate community structure in the lower Vaal River, Northern Cape Province

Impact of alluvial diamond mining on macroinvertebrate community structure in the lower Vaal River, Northern Cape Province Ramollo, Phetole Peter Macroinvertebrates and physico-chemical parameters were assessed at four sites in the lower Vaal River. The primary aim of the study was to determine the impact that alluvial diamond mining activities have on aquatic macroinvertebrate community structure using the South African Scoring System version five (SASS 5), as an index of the river’s ecological status. The macroinvertebrates were sampled using the SASS5 method and the results were analysed together with selected physico-chemical water parameters and Integrated Habitat Assessment. The results indicated that habitat played a major role in the presence of macroinvertebrates. Macroinvertebrate diversity was calculated using the Shannon- Wiener Index. A total of 28,167 macroinvertebrates belonging to 36 families were recorded throughout the sampling seasons. The highest abundance was recorded at Site 4, the most impacted site, but in turn this site had the lowest diversity. Chironomidae was the most abundant family (2,588 individuals) and the least abundant were the Chlorocyphidae and Velidae, each having five individuals. High numbers of taxa were noted amongst the Simuliidae, Corbiculidae, Physidae, and Oligochaeta. Site 4 was the only site where the presence of livestock was seen, and construction trucks were observed driving over the biotopes crossing over banks of the river, further adding pressure on the existing alluvial diamond mining impacts that contributed to low presence of macroinvertebrates. Generally, the alluvial diamond mining activities had severe impacts on the riverbed and changed the river flow regime and water quality. The hypotheses that the water quality of the Vaal River is negatively impacted by the alluvial diamond mining practices, and that the mining activities negatively impacted on macroinvertebrate community structure were supported. A research report submitted to the Faculty of Science, in partial fulfilment of the requirements for the degree of Master of Science in Environmental Sciences in School of Animal, Plant and Environmental Sciences at the University of the Witwatersrand. Johannesburg, 2018.


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