Default in payment, an application of statistical learning techniques
- Authors: Gcakasi, Lulama
- Date: 2020
- Subjects: Credit -- South Africa -- Risk assessment , Risk management -- Statistical methods -- South Africa , Credit -- Management -- Statistical methods , Commercial statistics
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/141547 , vital:37984
- Description: The ability of financial institutions to detect whether a customer will default on their credit card payment is essential for its profitability. To that effect, financial institutions have credit scoring systems in place to be able to estimate the credit risk associated with a customer. Various classification models are used to develop credit scoring systems such as k-nearest neighbours, logistic regression and classification trees. This study aims to assess the performance of different classification models on the prediction of credit card payment default. Credit data is usually of high dimension and as a result dimension reduction techniques, namely principal component analysis and linear discriminant analysis, are used in this study as a means to improve model performance. Two classification models are used, namely neural networks and support vector machines. Model performance is evaluated using accuracy and area under the curve (AUC). The neuarl network classifier performed better than the support vector machine classifier as it produced higher accuracy rates and AUC values. Dimension reduction techniques were not effective in improving model performance but did result in less computationally expensive models.
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- Date Issued: 2020
Conditions constraining and enabling research production in Historically Black Universities in South Africa
- Authors: Muthama, Evelyn
- Date: 2019
- Subjects: Universities and colleges, Black -- South Africa , Universities and colleges -- Research -- South Africa , Education, Higher -- South Africa , Universities and colleges -- South Africa -- History , Black people -- Education -- South Africa -- History , Discrimination in higher education -- South Africa -- History
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/131527 , vital:36591
- Description: The South African higher education system has a highly uneven landscape emerging from its apartheid past. Institutions remain categorised along racial lines within categories known as ‘Historically Black’ and ‘Historically White’ institutions, or alternatively ‘Historically Disadvantaged’ and ‘Historically Advantaged’ universities. Alongside such categorisations, universities fall within three types, which arose from the restructuring of the higher education landscape post-apartheid through a series of mergers: traditional universities, comprehensive universities, and universities of technology. This study which is part of a larger National Research Foundation-funded project looking at institutional differentiation in South Africa, sought to investigate the conditions enabling and constraining production of research in the Historically Black Universities (HBUs). By providing clarity as to the nature of truth and the concept of knowledge underpinning study, Critical Realism ensures that the study moves beyond the experiences and events captured in the data to the identification of causal mechanisms. Archer’s theory of Social Realism is used alongside Critical Realism, both as a meta-theory to provide an account of the social world and as a more substantive theory in the analysis of data. Social Realism entails understanding that the social world emerges in a complex interplay of powers in the domains of structure, culture and agency. Identifying the powers in each of these domains that enabled or constrained research development meant moving beyond suggesting simple causal relationships to ensure that I identified the complexities of the interplay of mechanisms. Data was collected from all seven institutions designated by the Department of Higher Education and Training as HBUs, by online survey, in depth interviews with academics and heads of research, and through the collection of a range of national and institutional documentation. Using analytical dualism, I endeavoured to identify some of the enablements and constraints at play. There were a number of areas of strength in research in the HBUs. There has also been a significant increase in research output over the last decade; however, the study also identified a number of mechanisms that constrained research productivity. The study found that while there were a number of mechanisms that appeared to have causal tendencies across all the institutions, there were a number of very specific institutional differences. There was very little consistency in understanding of the purpose of research as being key to what universities and academics do. The implication of this incoherence in the domain of culture (i.e. beliefs and discourses in Archer’s terms) is that various interventions in the structural domain intended to foster increased research output often had unintended consequences. Unless there are explicit discussions about how and why research is valuable to the institution and to the country there is unlikely to be sustained growth in output. In particular, the data analysis raises concerns about an instrumentalist understanding of research output in the domain of culture. This in part emerged from the lack of a historical culture of research and was found to be complimentary to managerialist discourses. Another key mechanism identified in the analysis was the use of direct incentives to drive research productivity. Such initiatives seemed to be complementary to a more instrumentalist understanding of the purpose of research and thereby to potentially constrain the likelihood of sustained research growth. While many of the participants were in favour of the use of research incentives, it was also evident that this was often problematic because it steered academics towards salami slicing, and other practices focused on quantity as opposed to quality research. Predatory publications, in particular, have emerged as a problem whereby the research does not get read or cited and so it fails to contribute to knowledge dissemination. Another constraint to research production was related to the increased casualisation of academic staff, which has exacerbated difficulties in attracting and retaining staff especially in rural areas. In South Africa, 56% of academics in universities are now hired on a contract basis which constrained the nurturing of an academic identity and the extent of commitment to the university and its particular academic project. In the HBUs, these employment conditions were exacerbated by increased teaching loads as a result of increased number of students (undergraduates and postgraduates) that have not been matched with similar increases in academic staff. There was a nascent discourse of social justice that focused on research as a core driver of knowledge production in some of the HBUs. This is potentially an area of strength for the HBUs especially emerging from their rural position as there was a complementary culture of social concerns. There was evidence that the nexus between research and community engagement could be a strong means of both strengthening institutional identity and increasing research productivity. But unless the nexus is clearly articulated, a systematic process of support is unlikely to emerge. Given the extent to which the rural positioning of HBUs has been acknowledged to constrain research engagement, this finding has a number of positive implications.
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- Date Issued: 2019
Design and fabrication of components of dye sensitised solar cells
- Authors: Msane, Gugu
- Date: 2019
- Subjects: Dye-sensitized solar cells
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/117106 , vital:34478
- Description: In recent decades there has been increasing global concern about the sustainability of our use of fossil fuels, which has led to increased interest in carbon–free sustainable renewable sources such as solar energy. Dye sensitized solar cells (DSSCs) are a cheap and clean technology that harnesses solar energy efficiently and convert it to electrical energy. A DSSC consists of a transparent working electrode coated with a dye-sensitized mesoporous film of nanocrystalline particles of semiconductor e.g. TiO2, an electrolyte containing a suitable redox couple and a platinized counter electrode. All the components of the DSSCs play vital roles in controlling the performance of the cell. The synergy of these components of the cells also needs to be investigated to optimise their interaction and create efficient and stable DSSCs. The information gathered from this investigation can give insight on how to improve the efficiencies of DSSCs. In this research study the semiconductor, transparent conducting layer and sensitizer were designed, optimized one at a time and their effect on the overall efficiency of the DSSCs studied. In this way it was easy to observe the effect of the individual components on the efficiency of the DSSCs. The conventional DSSCs usually use TiO2 as a semiconductor. In this research TiO2 was doped with cerium (Ce) to enhance its optical properties by reducing the band gap. A series of Ce-doped TiO2 with Ce content ranging from 0.1 to 1 mol % were successfully synthesized by an acid catalyzed sol-gel method, and their performance as the photoanodes of dye-sensitized solar cells (DSSCs) was investigated. Ce doping resulted in a red shift in the absorption of the TiO2 indicating narrowing of the band gap. The band gap first narrowed with increase in concentration of dopant up until 0.9 % dopant concentration. After this optimum doping concentration the band gap widened again. DFT calculations showed that Ce doping introduces Ce4f impurity states located just below the conduction band resulting in band gap narrowing. Ce content (0.9%) doped TiO2 photoanodes improved the performance of DSSCs with a conversion efficiency of 2.11% compared to 0,21% for the one with a pure TiO2 under 1 sun, AM1.5. Graphitised/TiO2 nanocomposites were also used a semiconductor to slow down recombination of electrons and holes in the cells. Electrophoretic deposition (EPD) was used to deposit graphitised/TiO2 nanocomposites onto an FTO electrode for application as photoelectrode in dye-sensitized solar cells (DSSCs). An enhanced power conversion efficiency (PCE) of 2.25% was observed for the 0.5 wt% graphene oxide/TiO2 (GO/TiO2) based DSSC which was higher than that of the conversion efficiency of pure TiO2 nanoparticles (i.e. 0.52%). Graphene oxide led to high migration of photoinduced electrons to the conduction band of the collection electrode and inhibition of charge carriers recombination resulting in enhanced photoconversion efficiency. A GO content above 0.5 % resulted in a reduced transparency leading to a decrease in the PCE. 0.5 wt % GO/0.9 Ce–TiO2 Ce based DSSC showed a slightly enhanced efficiency of 2.45%. 0.5 rGO/TiO2 based DSSCs had a high efficiency than 0.5 rGO/TiO2 due to improved conductivity of rGO nanosheets and suppressed recombination of charge carriers. To cut down DSSC production costs a silver wire network transparent conducting polyethylene electrodes was fabricated and used as an indium tin oxide (ITO) alternative substrates in DSSCs. The transmittance of the AgNW network was 82 % which is comparable to ITO substrates. Titanium oxide (TiO2) films on the AgWN/PET substrates were obtained using the electrophoresis method. These substrates were sensitised and used to fabricate a dye sensitised solar cell. From the measured current–voltage or I-V characteristic under AM1.5 illumination of the formed DSSC using AgWN substrates, an open circuit voltage (VOC) of 0.377 V, a short circuit current (ISC) of 0.0067 mA and a fill factor (FF) 25.7 % with an efficiency of 0.00862 % were obtained from a cell of 0.075 cm2 working area. The stability of the cell improved when a room temperature ionic liquid electrolyte was used. Gold nanofiber transparent electrodes were also prepared by the electrospinning techniques and used as an alternative to indium tin oxides substrates. Transparent conducting gold nanofiber (AuNF) transparent conducting electrodes were fabricated by using a low–cost electrospinning process and used as photoelectrodes for DSSCs. TiO2 was deposited on these electrodes by using an electrospray method. DSSC using AuNF as transparent electrodes had a power efficiency of 0.52%, compared to devices made with FTO electrodes (1.48%). DSSCs. Versatile dyes with increased spectral response, stability and suppressed recombination of holes and electrons were synthesised and used as a sensitizers for DSSCs. The boron dipyrrin (BODIPY) chromophore was combined with a carboxy coumarin moiety to create donor–acceptor (dyad) system dyes. Regenerative dyad dyes were formed through covalently linking a porphyrin chromophore to a manganese(II) ion through bridging ligands. These chromophores and also porphyrin and BODIPY dyes were used as sensitisers for DSSCs. The regenerative dye based DSSCs showed a photoconversion efficiency of 4.09% which was higher than the efficiency of the parent porphyrin (2.57%). The enhanced efficiency was attributed to the manganese bypridine cluster in the ZnTPP–Mn bpy supramolecule which acted as an electron donor to the photo-oxidized porphyrin continuously regenerating the porphyrin and preventing its decay.
- Full Text:
- Date Issued: 2019
The mutual embodiment of landscape and livelihoods: an environmental history of Nqabara
- Authors: De Klerk, Henning
- Date: 2007
- Subjects: Land reform -- South Africa -- Eastern Cape , Human ecology -- South Africa -- Eastern Cape , Human beings -- Effect of environment on -- South Africa -- Eastern Cape , Land use -- Environmental aspects -- South Africa -- Eastern Cape , Landscapes -- Social aspects -- South Africa -- Eastern Cape , Landscape ecology -- South Africa -- Eastern Cape , Land use, Rural -- South Africa -- Eastern Cape , Rural development -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4750 , http://hdl.handle.net/10962/d1007054 , Land reform -- South Africa -- Eastern Cape , Human ecology -- South Africa -- Eastern Cape , Human beings -- Effect of environment on -- South Africa -- Eastern Cape , Land use -- Environmental aspects -- South Africa -- Eastern Cape , Landscapes -- Social aspects -- South Africa -- Eastern Cape , Landscape ecology -- South Africa -- Eastern Cape , Land use, Rural -- South Africa -- Eastern Cape , Rural development -- South Africa -- Eastern Cape
- Description: This thesis presents a history of the landscape of Nqabara, an administrative area in a rural and coastal area of the Eastern Cape Province, South Africa. In the process of investigating landscape history, the inquiry engages with a range of data sources from diverging discursive contexts, including data from ethnographic fieldwork, from the consultation of archival documents and historical reports as well as from comparative historic and ethnographic research, necessitating a critical consideration of the epistemological contexts of data production and the dialogue between researcher and data. Furthermore, in its aim to move beyond historical description towards explanation, the study interrogates the dualist ontological conceptualisations of nature and culture, society and ecology, object and meaning upon which are built three dominant conceptual frameworks concerned with human-environment relationships: social-ecological systems theory, transdisciplinary landscape studies and political ecology. Drawing primarily upon the works of James Gibson, Anthony Giddens and Tim Ingold, an ontological foundation is developed to guide the enquiry and move towards an alternative understanding of the relationship of people’s livelihoods with respect to the landscape in which it is lived, which I call here the praxisembodiment perspective. This ontology takes the situated patterns of action of a situated agent-in-its-environment as its point of departure and proceeds to develop a framework explaining how relations among the patterns of action of different agents-in-their-environment, emerge in structures that simultaneously enable and constrain future action. The foundation is thereby provided for a monist understanding of how landscape and social structure emerge simultaneously from the complex intersection of patterns of actions and interactions of agents in their environment. This framework calls for an understanding of time, space and scale, not as independent variables influencing process and action, but as emergent properties arising from the patterns of actions of situated agents. Finally the alternative ontology is applied to the history of landscape and livelihoods of people of Nqabara. It is concluded that an appropriate understanding and explanation of the critical transformations in the landscape as well as in social institutions, should be sought through analysis of the complex ways in which patterns of action of multiple spatial and temporal rhythms and between multiple agents in an environment, intersect and resonate.
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- Date Issued: 2007
Phenylpropanolamine : analytical and pharmacokinetic studies using high-performance liquid chromatography
- Authors: Scherzinger, Sabine Hilda
- Date: 1988
- Subjects: Phenylpropanolamine , Pharmacokinetics , High performance liquid chromatography
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: vital:3811 , http://hdl.handle.net/10962/d1004528
- Description: Phenylpropanolamine (PPA), a synthetic sympathomimetic amine structurally related to ephedrine has been widely used over t he past 40 years as a nasal decongestant and appetite suppressant. It has been the focus of much controversy concerning the efficacy of the drug in its use as an anorectic agent, and due to the side effects caused by the higher doses of PPA required for appetite suppression. Although extensively used, there is little information concerning the determination of PPA in biological fluids and on the pharmacokinetics of this drug. An adaptation of a published high-performance liquid chromatographic (HPLC) assay for PPA in serum and urine using U.V. detection at 210 nm is presented. PPA was separated in the reversed phase mode. The method has a limit of sensitivity of 5.0 ng/mL and 10.0 ng/mL in serum and urine respectively. Serum concentration data following a single 25 mg dose of phenylpropanolamine in human volunteers demonstrate the application of the analytical method for bioavailability and pharmacokinetic studies. After the administration of 25 mg, 50 mg or 100 mg PPA.HCl solutions to 5 human volunteers, a dose proportionality study demonstrated that PPA appears to exhibit linear kinetics. Linear one body compartment kinetics were assumed and the wagner-Nelson method used to transform in vivo serum data to absorption plots. The serum data were fitted to a model using nonlinear regression techniques to characterize the pharmacokinetic processes of PPA. The absorption of phenylpropanolamine appears to be discontinuous and the drug seems to favour a two body compartment model. The pharmacokinetic parameters obtained from a steady state study using multiple dosing of PPA.HCl solutions compared with those found from previous studies after the administration of sustained-release formulations. A plasma protein binding study using equilibrium dialysis demonstrated that PPA is not highly protein bound in the blood.
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- Date Issued: 1988
Geology of part of the central Damara belt around the Tumas River, South West Africa
- Authors: Bunting, F J L
- Date: 1978
- Subjects: Geology -- Namibia -- Damaraland , Geology, Stratigraphic -- Namibia , Geology -- Namibia -- Tumas River Watershed , Geology -- Namibia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5049 , http://hdl.handle.net/10962/d1009957 , Geology -- Namibia -- Damaraland , Geology, Stratigraphic -- Namibia , Geology -- Namibia -- Tumas River Watershed , Geology -- Namibia
- Description: The investigation covering 1500 square kilometres within the central granite zone of the Damara belt, South West Africa, revealed Pre - Damara (Abbabis) basement unconformably overlain by metasediments of the Damara Supergroup. The term Leeukop member is proposed for basal metaconglomerates of the Nosib Group that immediately overlie the basement augen-gneisses. Augen-gneiss clasts are present within the Leeukop metaconglomerates. The Damara orogeny has only partly affected the Abbabis rocks of the Tumas River Inlier but further to the west the Husab suite of red granites and granite-gneisses, as field and geochemical evidence suggest, were derived syntectonically during the Damara orogeny by reactivation of the pre- Damara basement. Rõssing alaskitic granites represent late stage melts, that were also derived from Pre- Damara basement rocks during orogenesis, which accumulated post-tectonically in structural traps at the base of the Khomas Subgroup. Salem granitoids are present in synclinal structures associated with metasediments of the Khomas Subgroup and syntectonic derivation by anatexis during the Damara orogeny is suggested. In the east the differentiated Gawib granitoid stock was emplaced post- tectonically through basement rocks into the Damara metasediments. A deep seated origin is indicated by high crystallisation temperatures (>8500°) obtained from quarternary Qz-An-Ab-Or- H₂0 plots. The metamorphic grade increases westwards from medium grade to high grade. In the east, the metapelites contain andalusite, and coexisting muscovite and quartz. This indicates that temperatures of 6000° at 3,5- 4 kb pressure were attained. In the west, coexisting wollastonite and anorthite in the Khan gneisses indicate pressure- temperature conditions of 720° at 4,5-5 kb. Two tectonic events were responsible for the regional structure. An early F₁ episode produced east- west oriented overturned folds and was followed by an intense F₂ episode of isoclinal folding which is responsible for the dominant northeast - southwest regional fabric. The interference of these folds in the proximity of the underlying basement produced the complex dome and basin structures seen in the central and western parts of the area. An F₃ episode of minor importance was also recognized. The presence of continental basement rocks in this central part of the Damara belt is evidence for formation of the orogen by in-situ deformation rather than continental collision.
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- Date Issued: 1978