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Investigation of four roof-shaped host compounds for their separation potential of mixtures of guest Isomers and related compounds

  • Authors: Senekal, Ulrich
  • Date: 2024-04
  • Subjects: Grignard reagents , Optical isomers -- Analysis , Supramolecular chemistry
  • Language: English
  • Type: Doctoral theses , text
  • Identifier: http://hdl.handle.net/10948/64368 , vital:73684
  • Description: The inclusion ability of four roof-shaped host compounds, namely trans-9,10-dihydro-9,10- ethanoanthracene-11,12-dicarboxylic acid (H1), dimethyl trans-9,10-dihydro-9,10- ethanoanthracene-11,12-dicarboxylate (H2), trans-α,α,α’,α’-tetraphenyl-9,10-dihydro-9,10- ethanoanthracene-11,12-dimethanol (H3) and trans-α,α,α’,α’-tetrakis(4-chlorophenyl)-9,10- dihydro-9,10-ethanoanthracene-11,12-dimethanol (H4), were investigated when presented with numerous guest series (eight in number), including the xylene isomers and ethylbenzene, pyridine and the methylpyridine isomers, structurally related toluene, ethylbenzene and cumene, the dichlorobenzenes, six-membered heterocyclic ring compounds (dioxane, morpholine, piperidine and pyridine), anisole and the methylanisole isomers, anisole and the bromoanisole guests, and phenol and the methoxyphenol isomers. The four host compounds were synthesized via Diels-Alder (H1), esterification (H2) and Grignard addition (H3 and H4) reactions, producing yields of product of up to 93%. The yields for the Grignard reactions were lower, 54 and 37%, for the corresponding procedures using phenylmagnesium bromide or 4-chlorophenylmagnesium bromide. Computational molecular modelling studies were conducted on all four host compounds, and the resultant molecular geometries compared with the apohost (guest-free) crystal structures, when available. The geometries of the lowest energy conformers were in close correlation with the observed host structures as obtained from the apohost crystal structures (unfortunately, H3 and H4 were not able to form adequate quality crystals for SCXRD analyses). Interestingly, H1–H4 displayed intramolecular non-classical C–H∙∙∙O hydrogen bonds, while only H1 and H2 demonstrated intermolecular interactions of this type. H3 and H4 assumed one of two forms depending on the guest that was employed: the “active” form presented a strong intramolecular O–H∙∙∙O hydrogen bond, while the “inactive” form possessed weak π∙∙∙π and O–H∙∙∙π interactions. All of the host compounds were subjected to crystallization experiments from each of the guest species, as well as from mixtures of guests from each series (the guest competition experiments), where 1H-, 13C-NMR spectroscopy, GC-MS and/or GC-FID were used to analyse any resultant solids formed, as applicable. Single crystal X-ray diffraction (SCXRD) experiments were carried out on each single solvent complex produced in this work, where the crystal quality was suitable, while thermal analyses were also employed on these to determine their relative thermal stabilities. During the single-guest crystallization experiments, H4 was found to be remarkable in its inclusion ability, forming complexes with all but p-dichlorobenzene, typically with a 1:1 host:guest (H:G) ratio. H1 was more selective in its inclusion behaviour, not enclathrating cumene, 3-bromoanisole, phenol or the three methoxyphenol isomers (favouring 1:1 or 2:1 H:G ratios where complexation was successful). Interestingly, H1 formed salts when presented with 2- and 3-methylpyridine, and morpholine and piperidine. H2 and H3 were less remarkable in their inclusion ability, furnishing apohost crystals or gels in some experiments (typically a 3:1 H:G ratio was favoured for both when complexation occurred). Of the four roof-shaped host compounds, H1 and H4 displayed enhanced selectivities for certain guest species, showing near-complete affinity for a specific guest compound when presented with a guest mixture. H1 was able to include 100.0 and 98.8% p-dichlorobenzene (p-DCB) (from m-DCB/p-DCB and o-DCB/p-DCB mixtures), 96.6 and 93.6% p-xylene (p-Xy) (from m-Xy/p-Xy and o-Xy/p-Xy), 99.3% 4-methylanisole (4-MA) (from 2-MA/4-MA) and 97.1% 4-bromoanisole (4-BA) (from ANI/2-BA/3-BA/4-BA, where ANI is anisole). Host compound H4 was able to include ≈ 90% of selected meta-substituted guests, while H2 and H3 demonstrated moderate preferences for the guest compounds employed in this work (< 60%). It was concluded that some xylene guest mixtures may be purified using all but H2, whereas only H1 and H2 showed potential in separating the pyridines. All but H2 may also be employed in the separation of selected dichlorobenzene mixtures, while H2 showed potential for the separation of the six-membered heterocyclic guest compounds (dioxane, morpholine, piperidine and pyridine), were these ever required to be separated. Both H1 and H4 exhibited an overwhelming affinity for the methyl- and bromoanisole guest compounds, and this work has shown that these are likely host candidates for the purification of a variety of these guest mixtures through supramolecular strategies. SCXRD analyses showed that H1 experienced intermolecular host···host hydrogen bonding interactions between the carboxylic acid functional groups, while H2 typically demonstrated intermolecular non-classical hydrogen bonds in its complexes, forming sheets of host molecules along the c-axis. H4 preferred the “inactive” form whereas H3 assumed either an “active” or “inactive“ form. Various host···guest interactions such as π∙∙∙π, C–H∙∙∙π, C–O∙∙∙π, hydrogen bonding and other short contacts were responsible for guest retention in the crystal structures. Thermal analyses were conducted on all of the successfully formed complexes. Ton (the guest release onset temperature) and Tp (the temperature at which the guest release was most rapid) were recorded, when possible, while the mass losses associated with the guest release event were compared with those mass losses expected, in most cases. , Thesis (PhD) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
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  • Date Issued: 2024-04

Investigation of the host potential of compounds derived from tartaric acid, succinic acid and 1,4-cyclohexanedioic acid

  • Authors: Adam, Muhammad Ameen
  • Date: 2024-04
  • Subjects: Chemical reactions , Chemistry, Organic , Bacteriology
  • Language: English
  • Type: Master's theses , text
  • Identifier: http://hdl.handle.net/10948/63617 , vital:73562
  • Description: The present investigation considered the host behaviour of three compounds, namely (+)-(2R,3R)-1,1,4,4-tetraphenylbutane-1,2,3,4-tetraol (H1), 1,1,4,4-tetraphenyl-1,4-butanediol (H2) and cyclohexane-1,4-diylbis(diphenylmethanol) (H3) in various guest mixtures. These host compounds were readily synthesized by means of Grignard addition reactions on the diesters of tartaric acid, succinic acid and 1,4-cyclohexanedioic acid. The guest mixtures included cyclopentanone, cyclohexanone, cycloheptanone and cyclooctanone, γ-butyrolactone, 2-pyrrolidone, N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone, and pyridine, 2-methylpyridine, 3-methylpyridine and 4-methylpyridine. Crystals of (+)-(2R,3R)-1,1,4,4-tetraphenylbutane-1,2,3,4-tetraol (H1) were grown from cyclopentanone (5-ONE), cyclohexanone (6-ONE), cycloheptanone (7-ONE) and cyclooctanone (8-ONE,) producing 1:1 host:guest complexes in each instance. Thermal analysis showed the thermal stabilities of these complexes to be in the order 6-ONE > 7-ONE > 8-ONE > 5-ONE which correlated exactly with results from binary guest/guest competition experiments, where 6-ONE was always preferred by H1, while 5-ONE was consistently disfavoured. Single crystal X-ray diffraction (SCXRD) analyses demonstrated that each guest compound was retained in the crystals by means of a hydrogen bond with an alcohol moiety of the host compound. Furthermore, preferred guests 6- and 7-ONE produced crystals with greater densities than guests less favoured (5- and 8-ONE). A conformational analysis of the guest geometries in the four complexes with H1 revealed that the low energy guest conformers were present. The host selectivity for 6- and 7-ONE was proposed to be due to the improved molecular packing in the crystals of the complexes containing these two guest compounds, observed from their higher crystal densities. Hirshfeld surface analyses were not useful in explaining the preference of H1 for 6-ONE relative to 7-ONE (these types of analyses were not possible for the 5-ONE and 8-ONE-containing inclusion compounds due to the nature and degree of disorder present in the guest molecules). H1 was also crystallized from γ-butyrolactone (GBL), 2-pyrrolidone (NP), N-methyl-2-pyrrolidone (NMP) and N-ethyl-2-pyrrolidone (NEP), and 1H-NMR spectroscopy revealed that all but GBL were included. The host compound was also presented with these guest solvents in various mixtures, and it was observed that NMP was an extremely favoured guest solvent, followed by NEP and NP, with GBL being consistently disfavoured in every experiment. It was therefore shown that in certain instances, H1 may serve as an alternative tool for separating some of these mixtures through host-guest chemistry strategies. The hydrogen bonding motifs present in each of the successfully formed complexes were extensively investigated through SCXRD analysis, as was the thermal behaviour of these complexes. In the latter instance, the peak temperature of the endotherm (from the DSC trace) representing the guest release was greater for the inclusion compound with favoured NMP (145.5 °C) relative to the complexes with NP (139.8 °C) and NEP (120.5 °C). Host compounds H2 and H3 were revealed to have the ability to include each of pyridine (PYR), 2-methylpyridine (2MP), 3-methylpyridine (3MP) and 4-methylpyridine (4MP). H2 displayed selective behaviour for 3MP and 4MP when presented with mixtures of these guest compounds, whilst H3 preferred PYR. In the latter case, this PYR-containing inclusion compound was also the more stable one (the guest release onset temperature was highest, Ton 66.0 °C). It was demonstrated that H2 has the ability to separate very many binary mixtures of these pyridines on a practical platform, since K (the selectivity coefficient) values were 10 or greater in many instances. However, unfortunately, the more difficult-to-separate mixtures containing 3MP and 4MP cannot be purified or separated by employing H2 and supramolecular chemistry strategies. H3 was also shown to be a likely candidate for binary guest separations in very many of the guest solutions considered here, where K was also 10 or greater, and even infinity in many cases. SCXRD demonstrated that 2MP, 3MP and 4MP were retained in the crystals of their complexes by means of classical hydrogen bonds with the host compound. Satisfyingly, this hydrogen bond between 2MP and H2 (3.0213(18) Å) was significantly longer than that between this host compound and both disorder components of 3MP (2.875(2) and 2.825(9) Å) and that between H2 and 4MP (2.8458(13) Å). This observation explains the affinity of H2 for both 3MP and 4MP, and why 2MP was disfavoured. The results of thermal experiments did not wholly concur with observations from the guest/guest competition experiments. Hirshfeld surface analyses were also conducted but were not entirely conclusive with respect to explaining the host selectivity behaviour. In the case of H3, SCXRD analyses revealed that favoured PYR experienced a classical hydrogen bond with the host compound that was statistically significantly shorter (2.795(2) Å, 165°) than those between the other guest compounds and H3. Additionally, this guest compound was the only one to be involved in a (host)C−H···π(guest) interaction (2.91 Å, 139°) and also a non-classical hydrogen bond with the host compound ((host)C−H···N−C(guest), 2.77 Å (144°)). Finally, Hirshfeld surface analyses showed also that preferred PYR experienced a greater percentage of C···H/H···C (33.1%) and H···N/N···H (11.1%) interactions compared with the complexes with 2MP, 3MP and 4MP. However, it is not clear whether these Hirshfeld observations explain the affinity of H3 for PYR. , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
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  • Date Issued: 2024-04

Investigation of the synthesis and characterisation of spiro orthocarbonates and heterocyclic orthocarbonates

  • Authors: Cuthbertson, Jarryd Pierre
  • Date: 2024-04
  • Subjects: Chemistry, Analytic , Analytical chemistry , Chemistry
  • Language: English
  • Type: Master's theses , text
  • Identifier: http://hdl.handle.net/10948/63678 , vital:73578
  • Description: A series of mostly asymmetrical spiro orthocarbonates and heterospirocyclic derivatives of orthocarbonic acid was synthesized from 2,2-dichlorobenzodioxole and a number of difunctional reagents. A systematic study of the size of the chelate rings formed around the spirocentric carbon atom was conducted by selecting representative samples of aliphatic and aromatic diols. The feasibility and scope of potential starting materials used was expanded by reacting DCBD successfully with thiols. Molecular structures of these compounds were confirmed using diffraction studies on single crystals. All compounds were analyzed using multinuclear NMR. DFT calculations performed on the compounds allowed for the development of equations that can accurately predict 13C chemical shifts of SOCs. Furthermore, the experimental NMR spectroscopy gave rise to an increment shift system for the 13C NMR shifts allowing for further assignment of carbon atom positions in compounds with multiple possible bonding patterns. , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
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  • Date Issued: 2024-04

Learners’ understanding of their linguistic resources as a basis for learning natural sciences

  • Authors: Thorne, Rochelle Eugenia
  • Date: 2024-04
  • Subjects: Linguistic analysis (Linguistics) , Science -- Study and teaching -- Methodology , Science -- Study and teaching (Elementary)
  • Language: English
  • Type: Doctoral theses , text
  • Identifier: http://hdl.handle.net/10948/64049 , vital:73646
  • Description: With eleven official languages, South Africa is known for its multilingual environment. Despite this, the country's educational system heavily favours English and Afrikaans. Despite the varied linguistic backgrounds of learners, English continues to be used as the Language of Learning and Teaching (LoLT), which raises questions regarding fair access to education. Within the context of South Africa's constitution and policy frameworks, particularly the Language in Education Policy (LiEP), this study aims to investigate how group work activities in a Natural Sciences classroom can give learners an opportunity to mobilise their multilingual repertoires. Three formerly Afrikaans-medium high schools in the Northern Areas of Gqeberha, were the sites for this research which focuses on Grade Nine Natural Sciences learners. Through the use of both quantitative and qualitative methods such as questionnaires, classroom observations, and focus groups, the study explores how learners make use of their language resources to navigate science instruction in English. The results contest the idea that languages are distinct entities and show that learners use language interchangeably as a learning tool, a practice known as translanguaging. Group work becomes an important space in which learners exercise agency in language selection, enabling the link of dialogical, multilingual, and cultural responses. Sociocultural theory offers insights into group work relationships and provides the theoretical foundation for understanding how learners use language to understand scientific topics. Building on Gibbons' mode continuum (2003), which maps the shifts in discourse in classroom contexts from every day talk at the “here and now” to more specialized talk, the study also explored an expanded continuum which aimed at clarifying the nuances of language and cognitive progression among learners working in collaborative groups. This study adds to the conversation about language ideologies by recognising the ideologies of inclusion, access and identity which informed learners’ thinking and attitudes to language choice in education. Thus, the study emphasises the importance of a sophisticated comprehension of multilingual repertoires in the classroom. In order to better accommodate the changing linguistic patterns of multilingual learners, the study recommends re-evaluating language policies and encouraging educators to exploit the potential of group work to develop understanding of scientific concepts. , Thesis (DPhil) -- Faculty of Education, School of Post Graduate Education, 2024
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  • Date Issued: 2024-04

Lion and leopard diet and dispersal in human-dominated landscapes

  • Authors: Forbes, Ryan Edward
  • Date: 2024-04
  • Subjects: Carnivora -- South Africa , Carnivorous animals -- Conservation , Carnivorous animals -- Ecology
  • Language: English
  • Type: Master's theses , text
  • Identifier: http://hdl.handle.net/10948/63766 , vital:73596
  • Description: Terrestrial carnivore population declines are driven by habitat loss and fragmentation, prey-depletion, persecution, and retaliatory killings. Population strongholds now centre on protected areas, that face increasing human pressure, resulting in population isolation, declining prey populations, and livestock intrusion. I therefore aimed to investigate dispersal and connectivity, and diets of lions (Panthera leo) and leopards (P. pardus) in response to human-use and wildlife density gradients in the Greater Limpopo Transfrontier Conservation Area (GLTCA). Firstly, I investigated dispersal and connectivity for these carnivores across the GLTCA, using single nucleotide polymorphisms. I present evidence that in the prey-depleted Mozambique portion of the GLTCA, lion and leopard dispersal distances are higher compared with the prey-abundant Kruger National Park (KNP). I also provide the first evidence for long-range dispersal in female lions. Despite evidence for connectivity occurring across the GLTCA, I recorded population structuring across the region for both carnivores, likely due to habitat fragmentation by human activities in the Mozambique portion of the GLTCA. I then assessed carnivore diet responses to prey depletion and livestock availability by comparing lion and leopard diets in the prey-abundant/livestock-absent KNP (South Africa), with the prey-depleted/livestock-abundant Limpopo National Park (LNP, Mozambique), using scat analyses. Lions and leopards downshifted their prey size selection in LNP relative to KNP. Despite both carnivores expanding their dietary niche breadths in LNP relative to KNP, diet overlap did not differ between sites. This suggests that even when prey is depleted, lions and leopards can partition food resources, which likely limits competition. Despite cattle (Bos taurus) being the most abundant ungulate in LNP, lions and leopards strongly avoided cattle, supporting the notion that carnivores can perceive the risk of hunting livestock and modulate their foraging behaviour to reduce human-carnivore conflict. Should my findings reflect general patterns in carnivore dispersal and diet responses to human-use and wildlife gradients, then carnivore conservation initiates across their range should focus on prey population rehabilitation, improved livestock husbandry practices, the establishment of effective dispersal corridors and improved human-tolerance towards large carnivores. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
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  • Date Issued: 2024-04

Local economic development as a catalyst for job creation in Amathole District

  • Authors: Sikuza, Pumeza
  • Date: 2024-04
  • Subjects: Job creation -- South Africa -- Eastern Cape , Employment (Economic theory) , Economic development
  • Language: English
  • Type: Master's theses , text
  • Identifier: http://hdl.handle.net/10948/65423 , vital:74139
  • Description: This study assessed local economic development (LED) as a catalyst for job creation in Amathole District. LED is a mechanism that could be used to reduce the socio-economic difficulties faced by the district. These socio-economic challenges include high levels of poverty, unemployment and inequality. The research study is crucial because its area of focus is situated in the province with the highest official unemployment rate in South Africa. With the rising levels of unemployment, which is rising unabated, there is a likelihood of fundamental challenges being experienced by municipalities inhibiting their ability to fulfil their critical service role effectively. The study seeks to investigate whether the LED strategies implemented by the municipalities in the Amathole District are achieving the objectives of poverty alleviation and job creation. The sample and focus were six local municipalities in the Amathole District and the district municipality. The local municipalities in the district are the Amahlathi Local Municipality, Great Kei Local Municipality, Mbhashe Local Municipality, Mnquma Local Municipality, Ngqushwa Local Municipality and the Amathole District Municipality. Primary data was obtained and assessed through semi-structured questionnaires, and the respondents were asked probing questions. The interviews were typed verbatim, and themes were identified during the analysis and interpretation of the data collected. The relevant secondary data was also assessed and analysed from the annual reports and integrated development plans of the municipalities and were captured into Microsoft Excel for analysis. The study findings conclude that the unemployment rates in the Amathole District municipalities have increased during the period reviewed. It was noted that the upper-bound poverty rates in Amathole District remained unchanged during the reviewed period, but the lower-bound poverty rates increased. It was also noted through the calculation of the coefficient correlation that there is a stronger correlation between unemployment and the lower-bound poverty rate than unemployment and the upper-bound poverty rate. In order to eradicate the challenges of poverty and unemployment increasing despite the LED being implemented, it is recommended that adequate funding be made available, that co-ordination of sector plans be improved, LED be prioritised by municipalities, baseline information be utilised and improved, sustainable employment opportunities be created, and there be robust skills development initiatives in municipalities. , Thesis (MPhil) -- Faculty of Business and Economic Sciences, School of Economics, Development and Tourism, 2024
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  • Date Issued: 2024-04

Local government support for SMMEs in the construction industry to reduce unemployment: the case of Nelson Mandela Bay Municipality

  • Authors: Jiba, Mncedikazi Felicelle
  • Date: 2024-04
  • Subjects: Small business , Construction industry , Unemployment
  • Language: English
  • Type: Master's theses , text
  • Identifier: http://hdl.handle.net/${Handle} , vital:74011
  • Description: Despite government intervention, a significant proportion of businesses fail within the first few years of operation, and the unemployment rate remains high. If local government is assisting SMMEs in construction, it is important to look at whether it is addressing the primary issues of preventing SMMESs in construction from failing. Because the construction industry employs many unskilled workers, it is also negatively impacted by the number of businesses that are closing or going out of business. Purposive sampling, thematic analysis, and a qualitative approach were used in this documentary research. A total of 50 documents that addressed the role of local government in supporting and developing the SMMEs in construction at NMBM were reviewed. The findings of the study indicate that 86% of the documents reviewed indicate that SMMEs in construction to participate in Support Programmes as one of the potential complementary strategies for local government to support the growth of SMMEs in the construction industry and help them create jobs. Furthermore, the results of the study also indicate that 86% of the documents reviewed state late payments as one of the major challenges leading to the failure of the SMMEs in the NMBM construction industry. This research has also proposed a sub section in the finance department at NMBM that to deal with the payment of SMMEs including SMMEs in the construction industry, as a potential change to the current support structure and legislation of local government that are meant to boost the performance of SMMEs in the construction industry and help them accomplish their stated objectives of creating jobs. , Thesis (MPhil) -- Faculty of Business and Economic Sciences, School of Economics, Development and Tourism, 2024
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  • Date Issued: 2024-04

Mathematical modelling of the tumour treatment with chemotherapy

  • Authors: Nyaweni, Fundile Sindy
  • Date: 2024-04
  • Subjects: Mathematical models , Mathematics , Chemotherapy
  • Language: English
  • Type: Master's theses , text
  • Identifier: http://hdl.handle.net/10948/64289 , vital:73672
  • Description: In this study, a cancer disease model incorporating predator-prey dynamics between immune cells and tumor cells, as well as competition between tumor cells and normal cells, is formulated in an attempt to understand the interaction dynamics that govern the complex interplay within the tumor microenvironment. Mathematical analysis is employed to derive conditions for the boundedness of solutions and to discuss disease thresholds such as the basic reproduction number, R0. Equilibrium points are identified, and stability conditions for the system are derived. Sensitivity analysis is used to assess uncertainties in the parameters of the model, specifically their impact on R0. Numerical simulations are conducted, utilizing the Runge-Kutta scheme to solve the model. Furthermore, optimal control (OC) techniques are applied to examine the role of chemotherapy in enhancing tumor cell elimination and minimizing adverse effects on immune cells and normal cells. The improved model, incorporating normal cells, anticancer drugs, and immune cells, allows for a more comprehensive analysis of the dynamic interactions within the biological system. The optimal control is determined using the forward-backward sweep numerical method. The numerical simulation is carried out in MATLAB to validate and complement the analytical findings. The results indicate that a low concentration of the drug leads to a prolonged period for tumor clearance. Conversely, a higher drug concentration results in quicker tumor clearance, albeit with adverse effects on normal and effector cells. The OC identifies when to stop the treatment once the tumor clears. Furthermore, OC facilitates the regeneration of normal and immune cells beyond treatment, in contrast to a control scenario without optimization. The findings highlight the importance of early detection and careful chemotherapy dosage selection for effective and personalized cancer treatment strategies. , Thesis (MSc) -- Faculty of Science, School Computer Science, Mathematics, Physics and Statistics, 2024
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  • Date Issued: 2024-04

Micro-insurance and rural micro-enterprises in the North West Province of South Africa

  • Authors: Molefe, Samuel Seabelo
  • Date: 2024-04
  • Subjects: Insurance -- South Africa -- North West Province , Small business -- South Africa -- North West Province , Business enterprises -- Insurance
  • Language: English
  • Type: Doctoral theses , text
  • Identifier: http://hdl.handle.net/10948/65208 , vital:74049
  • Description: The Provision of micro-insurance in developing countries' rural areas is quite important, but not without its share of challenges. Among those challenges are logistics and demand. Several problems experienced by developing countries, including moral hazards, adverse selection, correlated risks, high transaction costs, and lack of data, negatively impacting access to insurance, were identified. Other researchers are, however, hard at work trying to come up with solutions to address those challenges. The selective coverage by insurance providers leaves a large segment of the world’s poor population in the hundred poorest countries with limited or no access to micro-insurance. North West province of South Africa, was identified as one of the top four rural provinces, with a higher percentage of people living in poverty. The province was selected for the study, with the purpose of determining the relationship between micro-insurance and micro-enterprises. The study followed a mixed methodology design, with pragmatism as a research paradigm. The research instruments used were interviews focus group discussions (18 participants), and survey questionnaires (112 respondents). Data was collected using concurrent triangulated mixed methods from both strands, qualitative and quantitative were analyzed, and the results were merged and corroborated. The main finding is that micro-entrepreneurs do not have business micro-insurance and would be willing to have one if it existed. What emerged from other findings is that there is a positive relationship between trust and willingness to purchase insurance, as well as a positive relationship between risk and insurance demand. Furthermore, there are negative relationships between shocks and insurance demand, demand and prevalence, and the inclusion and demand for insurance. This is contrary to what is in literature. There is further, evidence of more dependence on funeral and death benefits, other than on investment and savings micro-insurance policies. This study recommended that there should be a national policy in place to address challenges experienced by micro-entrepreneurs in terms of access to insurance. Also, potential micro-insurance service providers deserve leniency through the lowering of entry barriers such as capital adequacy requirements. Furthermore, the issue of illegal or unregistered service providers must be addressed to protect consumers. It was also recommended that more awareness be created through tribal administrations, by micro-insurance regulators and service providers, to promote inclusion among micro-entrepreneurs and other rural low-income earners in general. In conclusion, it is envisaged that this exploration will lead to an applicable model that can assist insurance service providers and other stakeholders in coming up with innovative micro-insurance product packages. , Thesis (DPhil) -- Faculty of Business and Economic Sciences, School of Economics, Development and Tourism, 2024
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  • Date Issued: 2024-04

Mindsets of change agents for development: a case study of the Sundays River Valley, Eastern Cape

  • Authors: Bezuidenhout, Theo Gerhardus
  • Date: 2024-04
  • Subjects: Social change , Sustainable development -- South Africa , Well-being , Economic development -- Social aspects
  • Language: English
  • Type: Master's theses , text
  • Identifier: http://hdl.handle.net/10948/64874 , vital:73937
  • Description: Societal development in underdeveloped areas is a process of enhancing and improving the quality of life in communities, with a focus on meeting their social, economic, environmental, and political needs. Despite ideological efforts and growing interest in movements, mobilisations and communities promoting social change, little research has been done on the mindsets of change agents. Margaret Archer’s (1988), Morphogenetic Approach to social development has been used in this case as a theoretical framework emphasising that social change and development occur through interactions between individuals and their social environments. This approach focusses on the importance of feedback loops, where changes in the environment and the reactions of individuals to these changes both influence and are influenced by one another. Through reflective learning, semistructured interviews and document analysis, the dissertation explored research questions concerning different perspectives of change agents in the Sundays River Valley. The theories examined provide options of theoretical frameworks which can be used to assess and evaluate the work and role of change agents to participate in societal development. This is important in the Sundays River Valley context as, up to now, there has been no shortage or lack of development plans and policies for the area. Rather, what has been absent is the theoretical frameworks to provide the context and meaning for change agents to participate in societal development and occupy their role in the various development plans and policies. Collaborative development and participation acknowledge that solving complex social problems requires the efforts of multiple organisations, individuals, and generations. To enable societal development requires social trust and cooperation of multiple stakeholders, including government, community members, businesses, development agencies, non-governmental organisations and educational institutions. , Thesis (MA) -- Faculty of Business and Economic Sciences, School of Economics, Development and Tourism , 2024
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  • Date Issued: 2024-04

Minimum sentencing disparities in the criminal justice system

  • Authors: Minnaar, Evolia Geraldine
  • Date: 2024-04
  • Subjects: Sentences (Criminal procedure) , Sentencing disparities , Criminal Law Amendment Act
  • Language: English
  • Type: Master's theses , text
  • Identifier: http://hdl.handle.net/10948/66229 , vital:74444
  • Description: In South Africa, judicial officers have wide discretionary authority with regard to both the type of and the severity of the sentence. Sentencing is a particularly challenging part of the criminal justice process. It is challenging, because South Africa's sentencing system does not have uniform sentencing guidelines that can assist presiding officers in exercising their judicial discretion in the sentencing process. Nor does South Africa have a Sentencing Council to establish sentencing guidelines. Parliament adopted the Criminal Law Amendment Act, which provides for mandatory minimum sentences for certain serious and violent offences. One of the legislation's intended objectives was to advance consistency and avoid disparities in sentencing. The legislation has limited, but not eliminated the court's discretion. A deviation or an escape clause is provided to sentencing courts to depart from the prescribed minimum sentence. If a sentencing court is satisfied that substantial and compelling circumstances exist, departure is justified and a lesser sentence should be imposed. Legislature does not define the phrase "substantial and compelling circumstances". Nor does legislature provide guidance, regarding what the phrase constitutes and does not constitute. Thus, courts have to exercise their judicial discretion when imposing sentences. When interpreting the phrase substantial and compelling circumstances, the courts generally consider that the legislature prescribed minimum sentences as the sentences that should ordinarily be imposed for serious offences. The courts further consider that the legislature aimed to ensure a severe, standardised and consistent response from the courts. Thus, courts should not depart from the prescribed minimum sentence for lightly and flimsy reasons. Further, the traditional mitigating and aggravating factors should still be considered in sentencing. Additionally, if the court considers that the prescribed sentence will be unjust, the court has to depart from the prescribed sentence and impose a lesser sentence. The courts, however, interpret the abovementioned principles inconsistently. This is attributed to the legislature's failure to provide clear, uniform and adequate guidelines to the courts. Disparities in sentencing still permeate South Africa's sentencing system, which creates a challenge to achieve consistency in sentencing. The conclusion of this research is that there is still dissatisfaction with sentencing among the public and sentenced prisoners. Another conclusion of this research is that the legislation has exacerbated prison overcrowding. A further conclusion in this research is that the legislation has not achieved one of its fundamental objectives, namely advancing consistency and avoiding disparities in sentencing. Comparative research is also done in order to see how South Africa's system can be developed and/or improved. , Thesis (LMM) -- Faculty of Law, Department of Criminal and Procedural Law, 2024
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  • Date Issued: 2024-04

Modelling offsite construction to control hazards and direct cost of accidents

  • Authors: Simukonda, Wakisa Tulombolombo
  • Date: 2024-04
  • Subjects: Construction industry -- Accidents , Construction industry -- Risk management , Building -- Safety measures
  • Language: English
  • Type: Doctotal theses , text
  • Identifier: http://hdl.handle.net/10948/64818 , vital:73923
  • Description: The construction industry contributes significantly to the growth of developed and emerging economies. The industry contributes a sizeable proportion of Gross Domestic Product and Gross National Product. However, the poor safety performance of the industry and its consequential socio-economic impact threatens the industry’s significant contributions. It is for this reason that off-site construction has been identified as a sine qua non for addressing poor safety performance. The application of design for manufacture and assembly and lean techniques in the manufacture and assembly processes of off-site construction is suggested to minimise safety hazards in construction. The research was conducted to establish the relevant design for manufacture and assembly and lean techniques for addressing safety hazards in off-site construction and to develop a conceptual model of off-site construction for controlling hazards and direct costs of accidents to protect people and profits in construction. A preliminary conceptual model of off-site construction was initially devised based on a literature review and later refined into a developed conceptual model of off-site construction using findings from the qualitative phase of the study. The confirmation of the relationships and concepts presented in the developed conceptual model of off-site construction was based on the findings from quantitative data. The quantitative data were analysed using the Statistical Package for Social Science (SPSS) Version 26. Within SPSS, descriptive and inferential statistics were used to examine the relationships between off-site construction methods and safety issues, while Cronbach’s alpha was used to measure the validity of the findings. Based on the findings of the study, significant safety benefits of off-site construction methods of design for manufacture and assembly and lean techniques were identified. The benefits relate to the elimination of safety hazards including lack of personal protective equipment, work at height, poor work methods, poor house-keeping and lack of training and experience. Furthermore, the research findings indicated that implementing design for manufacture and assembly and lean practices limits direct costs of accidents, including costs expended on wages and medical bills. The positive outcomes of applying design for manufacture and assembly and lean techniques include better project management and working conditions, improved quality, minimised construction waste, and increased productivity. Factors impeding application of design for manufacture and assembly and lean techniques within contracting organisations include lack of stakeholder collaboration, a conservative mind-set towards traditional construction, lack of preferential policies and expensive logistics. These challenges can be addressed by promoting awareness of off-site construction methods, capacity-building, establishing a robust local supply chain and the involvement of government in creating an enabling political and legal environment, among others. Based on the research, an integrated conceptual model of off-site construction was developed for using off-site construction to control hazards and direct costs of accidents to protect people and profits in construction. In essence, the model can be used to identify design for manufacture and assembly and lean practices applicable in off-site construction projects to control potential safety hazards and risks. Identification and application of appropriate design for manufacture and assembly and lean practices, while addressing safety challenges, would result in the elimination of safety hazards and direct costs associated with the occurrence of accidents. Consequently, prevention of accidents would ensure the safety and health of people in construction, while the reduction of direct costs of accidents would improve the profitability margins of contracting organisations. Based on the study, recommendations are made for wider adoption of off-site construction as a modern construction method, and application of design for manufacture and assembly and lean techniques in off-site construction as strategic, industry and national, initiatives for improving safety in the construction industry. , Thesis (DPhil) -- Faculty ofEngineering, the Built Environment, and Technology, School of Built Environment and Civil Engineering, 2024
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  • Date Issued: 2024-04

Multi-purpose community centres as catalysts for socio-economic development in Eastern Cape province, South Africa

  • Authors: Gobe, Cynthia Bongiwe Ntombikayise
  • Date: 2024-04
  • Subjects: Community centers -- South Africa , Buildings -- Environmental engineering -- South Africa , Sustainable construction -- Economic aspects , Infrastructure (Economics) -- South Africa Sustainable development
  • Language: English
  • Type: Doctoral theses , text
  • Identifier: http://hdl.handle.net/10948/64533 , vital:73747
  • Description: The central issue facing African society, especially underdeveloped countries is that most of the population lives below the poverty line, experiences high levels of unemployment and unsustainable livelihoods. The poor and marginalised groups in many communities are deprived access to infrastructure and socio-economic amenities, this includes accessibility to government services, information, and developmental opportunities. The development of Multi-purpose Community Centres (MPCCs) is viewed as a value-adding solution to several challenges facing unequal societies, such as inadequate infrastructure, remote settlement patterns, poor access to basic services, poor access to technology, poor access to information, increased unemployment rate, increased poverty rate, and many others. The study examines the socio-economic impact of MPCCs on municipalities of the Eastern Cape Province in South Africa and explores how these centres, as built environment outputs can become a stimulus for sustainable livelihoods in urban, rural, and peri-urban human settlements, including informal settlements. The study falls under implementation evaluation research methodologies which assesses whether a programme has been adequately implemented before making inference on its effectiveness. Anchored in a Social Constructivism knowledge paradigm and leaning on a Systems and Development Theories, the study adopted a Mixed Method Research approach. In view of the data required document reviews, field observations, interviews and questionnaire surveys were employed. The research findings revealed that despite the delivery of MPCCs by the Department of Human Settlements, these centers have not provided much socio-economic opportunities to members of the communities where they are built. The MPCCs under study are facing many challenges that render them ineffective to fulfill their mandate of improving the lives of residents. The study yielded an inclusive and responsive human settlements development model for the creation of well-functioning socio-economic impactful MPCCs within existing and forth-coming housing projects and informal settlements. , Thesis (DPhil) -- Faculty of Engineering, the Built Environment, and Technology, School of Built Environment and Civil Engineering, 2024
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  • Date Issued: 2024-04

Numerical modelling of power law constants established through impression and micro-Uniaxial creep methods for service exposed A234WPB steel

  • Authors: Tembo, Blessed
  • Date: 2024-04
  • Subjects: Number theory , Numerical analysis , Mechanical engineering
  • Language: English
  • Type: Master's theses , text
  • Identifier: http://hdl.handle.net/10948/64852 , vital:73931
  • Description: Continuous monitoring of creep life in materials operating at high temperatures and pressures is imperative to prevent catastrophic failures and ensure timely replacement of worn-out components in industrial plants. Small-scale creep testing methodologies offer a valuable means of assessing material creep life while preserving structural integrity. Motivated by the need for reliable methods in creep life assessment, this study aimed to investigate the creep properties of A234WPB material subjected to service conditions using Impression creep and micro-uniaxial creep testing techniques. The research questions focused on establishing power law constants through small-scale creep testing, validating these constants using numerical modelling, and assessing their practical implementation in predicting material creep life. Samples extracted from service-exposed A234WPB steel alloy underwent step-load impression creep tests and step-temperature micro-uniaxial creep tests to derive the power law creep equation. The determined stress exponent of 3.967 indicated that dislocation creep was the dominant creep-controlling mechanism at 520 °C. A numerical model, utilizing the established power law constants, demonstrated a strong correlation with experimental findings in steady-state creep rates. Furthermore, the conventional Monkman-Grant approach was employed to predict the remaining life of the service-exposed material using impression creep data. The predicted remaining life aligned with the scatter band of uniaxial rupture life on a Larson-Miller plot, highlighting the practical utility of impression creep and micro-uniaxial creep testing techniques in assessing creep life. This study contributes to the advancement of small-scale creep testing methods and underscores their potential for practical implementation in industrial settings, thereby enhancing the reliability and safety of high-temperature and high-pressure operations. , Thesis (MEng) -- Faculty of Engineering, the Built Environment, and Technology, School of Engineering, 2024
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  • Date Issued: 2024-04

Optimisation of laser welding for thin-walled Ti6Al4V glider pressure hull

  • Authors: Nel, Matthew Ryan
  • Date: 2024-04
  • Subjects: Laser welding , Welding , Mechanical engineering
  • Language: English
  • Type: Master's theses , text
  • Identifier: http://hdl.handle.net/10948/64739 , vital:73882
  • Description: Laser welding is a type of fusion welding process characterised by deep penetration, low heat input and high welding speed. This dissertation investigates the suitability of this process for the fabrication of an underwater glider buoyancy engine from thin Ti6Al4V alloy sheet. Areas of interest include the effect of process parameters on weld microstructure, static properties (microhardness, tensile and bend tests) and dynamic properties (fatigue tests). The effect of welding speed and laser defocusing were evaluated considering experimental matrices consisting of four different travel speeds and three defocus distances. These were narrowed down to three travel speeds and a single defocus distance, resulting in a final test matrix delivering three different heat inputs. Thereafter, the effect of heat input on static and dynamic properties was investigated. Vickers microhardness tests were carried out to predict weld response during tensile testing, with the expectation being that harder welds would offload more strain. This was confirmed using digital image correlation, which allowed for virtual measurement and visualisation of strain offloading. Bend tests were carried out on parent and welded samples to confirm whether Ti6Al4V could be formed to the correct geometry. Forming Ti6Al4V into a U-shape was the first consideration, since dynamic testing required samples of this geometry with longitudinal weld orientation. A two-stage forming methodology was developed from these experiments. Formed samples were subjected to fatigue tests in a custom designed fatigue platform for testing weld orientation as it would appear in the final component. Prediction of the welded buoyancy engine life was the goal behind these tests. Fracture surfaces were analysed to gain understanding of where crack initiation and final fracture occurred. Porosity served as the primary cause for crack initiation in failed samples. Pore distribution was heaviest in low-heat weldments and decreased with increasing heat input, while pore size increased with increasing heat input. This resulted in medium-heat weldments exhibiting superior performance to that of low- and high-heat ones. It was concluded that the laser welding process is able to produce weldments of sufficient integrity in thin Ti6Al4V sheet-formed components intended for use in glider buoyancy engines. , Thesis (MEng) -- Faculty of Engineering, the Built Environment and Technology, School of Engineering, 2024
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  • Date Issued: 2024-04

Optimisation techniques to improve the drive efficiency of a mobile ventilator platform

  • Authors: Imran, Mohammed Zaahid
  • Date: 2024-04
  • Subjects: Artificial respiration , Respirators (Medical equipment) , Topology , Medical instruments and apparatus -- Design and construction
  • Language: English
  • Type: Master's theses , text
  • Identifier: http://hdl.handle.net/10948/64555 , vital:73749
  • Description: COVID-19 pandemic has underscored the indispensable role of mechanical ventilators in providing critical respiratory support to patients. This research has focused on the imperative task of optimising the articulation system of the ventilator, designed to enhance its efficiency, with particular emphasis on improving the volume displacement from the ambu bag. Several optimisation methods were explored, including generative design (GD), Design of Experiments (DOE), Shape optimisation, and topology optimisation. The study also highlights the significance of additive manufacturing and material testing in developing ventilator components. The study delves into the intricate development and fine-tuning of the ventilator setup, emphasising its pivotal role in delivering life-sustaining respiratory aid. The ventilator’s core mechanisms, featuring a two-pusher arm system powered by a servo motor, was engineered intricately to apply precise pressure on the ambu bag. The research underscores the importance of optimising both the pusher arm and pressure plates to improve air displacement within the system. A significant challenge addressed in this research was the excessive strain on the servo motor owing to the demands of the articulation system. The research employed strategies such as shape optimisation and topology optimisation to reduce the stress on the articulation system while increasing the air displacement and thus reducing the pusher arm displacement on the ventilator. The research methodology included stages such as setting performance benchmarks, calibration, and verification to ensure precision and reliability; shape optimisation for maximum efficiency; and topology optimisation for superior structural performance and reduced weight. These interconnected stages were instrumental in the comprehensive development and enhancement of the ventilator system, ensuring its effectiveness and dependability in delivering lifesaving respiratory support.This research extensively examined sensor reliability and performance through verification tests and calibrations, highlighting the precision of the servo motor and the suitability of the 5-Amps current sensor for monitoring servo motor current without additional calibration. Optimisation efforts aimed to enhance the ventilators performance by relocating the pusher arm to the bag’s centre, resulting in improved volume displacement efficiency by 7.78 % and a 25.35 % reduction in current consumption. Shape optimisation, especially with curvature-based pressure plates, increased volume displacement by 84.47 % reaching an optimal configuration outputting 1475.73 ml of volume per compression. Understanding the forces through strain gauges and FEA facilitated topology optimisation, the MAXSTIFFDS15 configuration demonstrated promising results by reducing component weight and achieving significant energy savings of 45.04 %, potentially reducing long-term costs. , Thesis (MEng) -- Faculty of Engineering, the Built Environment, and Technology, School of Engineering, 2024
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  • Date Issued: 2024-04

Organisational citizenship behaviour (OCB) in the South African transport state-owned enterprises

  • Authors: Calvert, Candice
  • Date: 2024-04
  • Subjects: Organizational behavior -- South Africa , Government business enterprises -- South Africa , Government ownership -- South Africa
  • Language: English
  • Type: Doctoral theses , text
  • Identifier: http://hdl.handle.net/10948/64896 , vital:73944
  • Description: The transport sector is critically important for economic growth and sustainability of a country and therefore requires carefully crafted strategical policies aimed at social enhancements. Employees who are employed in the major South African transport sector’s State-Owned Enterprises (SOEs) carry the responsibility of providing quality and effective services, thus, they are executing the mandate of the National Department of Transport (NDoT). Therefore, their willingness to contribute positively to the goals of the sector, is critically important. Extra-roles and positive behaviours displayed by employees ensure that organisations gain competitive advantage over competitors. These special behaviours are documented in literature as organisational citizenship behaviours (OCB). OCB is referred to as voluntary positive behaviours displayed by employees, which benefit the organisation and improve the overall performance of employees and the organisation but are not recognised by the reward system of the organisation. The scarcity of literature pertaining to OCB in SOEs and in particular, the transport sector globally indicates that OCB is not entrenched in organisational cultures in this sector. The primary objective of this study is to investigate the views of management and employees regarding the influential factors and the outcomes of OCB in South Africa’s major SOEs in the transport sector. A hypothetical model and a questionnaire were developed to establish the influential factors of OCB and its outcomes on the performance of South Africa’s major transport SOEs. Eight independent variables (leadership styles, organisational culture, management support, personal importance, transparency, job autonomy, employee trust and organisational commitment), the intervening variable (organisational citizenship behaviour) and the dependent variables (employee performance and employee retention) were investigated. Primary data was collected by means of electronic questionnaires, which were distributed to five provinces via a QuestionPro link that was emailed to the contact person nominated by the HR department of the two major transport SOEs. Hard copies of the questionnaire were also physically distributed to prospective participants by the researcher. Non-probability sampling was used, specifically convenience sampling technique. The study targeted 500 respondents and 318 questionnaires were usable which amounts to a response rate of 64%. The reliability of the measuring instrument was determined by means of Cronbach’s alpha coefficient and the construct validity was tested using exploratory factor analysis (EFA). Content validity for the measuring instrument was validated by experts in the fields of organisational behaviour and change management, prior to the distribution of the questionnaire to participants. EFA, descriptive statistics, multiple regression analysis and correlation analysis were determined. A STATISTICA computer programme 14.0 was used. The results of the study showed that OCB, which was tested as a seven-dimensional construct, namely, altruism, sportsmanship, loyalty, individual initiative, civic virtue, courtesy, and self-development, was perceived by respondents as two constructs, namely, OCB-selflessness (OCB-S) (altruism, sportsmanship, individual initiative, courtesy and self-development) and OCB-reliability (OCB-R) (civic virtue and loyalty). The empirical results revealed that personal importance is significantly related to OCB-S, but is not significantly related to OCB-R. Furthermore, the findings showed that transparency is not significantly related to OCB-S, however, there is a significant positive relationship between transparency and OCB-R. It was also found that job autonomy is not significantly related to OCB-S, and has a significant negative relationship with OCB-R. In addition, the research findings showed that employee trust and organisational commitment are significantly related to both OCB-S and OCB-R. OCB-S and OCB-R were found to be significantly related to employee performance and employee retention. This study contributed to the body of knowledge in the fields of organisational behaviour and human resources. Furthermore, the study will contribute to policy makers and management within the transport sector of South Africa and globally in order to develop policies and devise strategies to combat negative workplace environments, stimulate service delivery, and improve the competitive advantage of the organisation and the economic sustainability in the transport sector globally, through employee performance and employee retention. , Thesis (DBA) -- Faculty of Business and Economic Sciences, Business School, 2024
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  • Date Issued: 2024-04

Out of place: an analysis of place as a contributor to the complexities of my “coloured” identity in Malabar, Gqeberha

  • Authors: Flowers, Victoria
  • Date: 2024-04
  • Subjects: Colored people (South Africa) -- Race identity , Ethnicity in art -- South Africa -- Port Elizabeth , Modernism (Art)
  • Language: English
  • Type: Master's theses , text
  • Identifier: http://hdl.handle.net/10948/62780 , vital:72954
  • Description: Coloured identity has been a historical point of contestation in South Africa because Colouredness is assumed as “an inbred quality that arises automatically from miscegenation while instrumentalists share the essentialist premise that coloured identity is something negative and undesirable but blame it on the racism and the exploitative practices of the ruling white minority” (Adhikari, 2009: 15). This archaic belief attributed to racial mixture has now become redundant, due to the emergence of new hybridised Coloured identities that factor other ethnic and cultural groups as well as internal and external elements into their conception. The role of Place in the formation of Coloured identities is at the core of this fine arts based enquiry. This study is located in Malabar, Gqeberha which was established after the forced removals onset by the Group Areas Act of 1950 and the displacement of residents from South End. Additionally, it considers specific locations significant in their linkages to hybridised peoples, and how the place and individuals have been influenced by historical legacies of colonisation and apartheid. These are examined to consider their function in contextualising contemporary lived experiences of Coloured identity within the community of Malabar and its effect on artistic practice through autoethnographic research. Through this autoethnographic and reflexive study and the accompanying empirical research process, I critically examine and explore my Coloured identity as part of being-in-the-world (Heidegger, 1962). This ‘being’ is multifaceted as a result of the significance of Place in South Africa and how it has shaped my perception of how and where I have a sense of being and belonging. , Thesis (MA) -- Faculty of Humanities, School Visual and Performing Arts, 2023
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  • Date Issued: 2024-04

Photocatalytic reduction of CO2 into green fuels on microspherical nanocomposites comprising of CdS, TiO2, ZnFe2O4 semiconductors and heterojunctions

  • Authors: Mudau, Rendani Julian
  • Date: 2024-04
  • Subjects: Heterojunctions , Chemistry, Inorganic , Nanochemistry
  • Language: English
  • Type: Master's theses , text
  • Identifier: http://hdl.handle.net/10948/64214 , vital:73665
  • Description: Human anthropogenic activities have led to an increase in CO2 levels resulting in global warming. There is a need to reduce CO2 levels in the atmosphere by capturing the gas and converting the captured CO2 into fuels. Photocatalytic conversion of CO2 into valuable products via photoreduction is a promising technique to reduce carbon dioxide using sunlight and water. Redox reactions between CO2 and water using photocatalysts offer an effective method of lowering CO2, which has detrimental effects on the environment. This dissertation reports the synthesis and characterization of five photochemical catalysts comprising of CdS, TiO2, ZnFe2O4 semiconductors and heterojunctions and their use as photocatalysts for the photocatalytic reduction of CO2 into green fuels. Mott−Schottky plot of TiO2, CdS and CdS/TiO2 confirmed the formation of n-type, n-type, and n-n type material respectively. The band gap of TiO2, CdS, and CdS/TiO2 obtained were 3.21,2.24, 2.04 eV, respectively, the combination of TiO2 and CdS resulted in the lowering of band gap energy which is favourable for photocatalytic reduction studies. XRD of TiO2, CdS and CdS/TiO2 provided relevant information about the various phase reflections of the photocatalysts, it also supported reports confirming the increase in crystallite size of TiO2 anatase phase upon calcination. Chemical environment of the various photocatalysts, such as Ti2p1/2, Ti2p3/2, O1s, Cd3d3/2, Cd3d5/2, S2p1/2 and S2p3/2 were observed in TiO2, CdS and CdS/TiO2. BET surface area of TiO2, CdS and CdS/TiO2 was also observed to be 2.9243, 4.0605, and 9.8450 m2g, respectively. Photocatalytic reduction of CO2 resulted in formic acid, formaldehyde, acetic acid, carbon monoxide, ethanol, and methanol after 12 h. Modification of CdS with TiO2 to form CdS/TiO2 produced high yield of formic acid (217.7 μmol/g) compared to CdS (8.7 μmol/g) and TiO2 (122.5 μmol/g). CdS had high yield of formaldehyde (20.4 μmol/g) and ethanol (57.8 μmol/g) compared to TiO2 (12.9, 3.6 μmol/g of formaldehyde and ethanol, respectively) and CdS/TiO2 (19.7 μmol/g and there was no detection of ethanol). TiO2 shows high yield of methanol (145.2 μmol/g) and is the only catalysts that produced carbon monoxide (52.2 μmol/g) compared to CdS (87.8 μmol/g of methanol) and CdS/TiO2 (50.2 μmol/g of methanol). A detailed elucidation of the various products was reported by means of nuclear magnetic resonance (NMR) spectrometer. ZnFe2O4 and CdS/TiO2/ZnFe2O4 were characterized and employed for photocatalytic reduction of CO2 in water. XRD and XPS confirmed the presence Fe (2+) and Fe (3+) in tetrahedral/octahedral and Zn (2+) in tetrahedral on ZnFe2O4 and CdS/TiO2. CdS/TiO2/ZnFe2O4 presented a lowered band gap of 1.98 eV due to the presence of ZnFe2O4 while the band gap of ZnFe2O4 obtained is 1.95 eV. The Mott-Schottky plots confirmed the conduction (2.81 and 2.59 eV) and valence band (–0.86 and –6.1 eV) of ZnFe2O4 and CdS/TiO2/ZnFe2O4 together with their junctions, respectively. ZnFe2O4 and CdS/TiO2/ZnFe2O4 are p-type and p-n type junctions, respectively. Photocatalytic reduction of CO2 under visible light for 12 h using CdS/TiO2/ZnFe2O4 hollow microspheres nanocomposites produced methanol (182.1 μmol/g), formic acid (1.9 μmol/g), formaldehyde (9.5 μmol/g), ethanol (67.1 μmol/g), and oxalic acid (38.9 μmol/g). Amongst the synthesized catalysts, CdS/TiO2/ZnFe2O4 produced high yield of methanol, ethanol, and oxalic acid. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2024
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  • Date Issued: 2024-04

Photoluminescence and electroluminescence imaging of PV devices

  • Authors: Roodt, Roelof Petrus
  • Date: 2024-04
  • Subjects: Photoluminescence , Biosensors
  • Language: English
  • Type: Master's theses , text
  • Identifier: http://hdl.handle.net/10948/64333 , vital:73676
  • Description: Luminescence imaging has become a particularly useful and valuable tool for the characterisation of photovoltaic devices. This study entailed the design, construction, and optimisation of a system for the electroluminescence (EL) and photoluminescence (PL) imaging of various solar cell devices. The system can perform EL and PL imaging of solar cells of different cell technologies and materials systems, including Si, perovskite, and triple-junction concentrator solar cells. This required appropriate electrical power supplies for carrier injection for EL imaging and optical excitation for PL imaging. The different materials systems also required wavelength appropriate filters for PL imaging. In addition, the system utilized a temperature-controlled sample stage and was placed in a chamber for environmental control and isolation of UV radiation from laboratory. In addition to optimization of imaging conditions, luminescence images need to be optimized to facilitate detailed analysis and the application of appropriate algorithms to extract device parameters and hence generate device parameter images of the devices under investigation. For EL imaging, two power supplies were used to inject current into the solar cells. The reason for the two power supplies is that the first power supply had a current range of ± 1 A and an applied voltage capability of ± 21 V. This was used for the smaller solar cells. It was also convenient to use as the power supply could also measure the injected current and applied voltage and digitally store it with the images. For the larger solar cells, a second power supply was utilized, which could inject current into the samples in the range of ± 12 A at an applied voltage of ± 40 V. To measure the current and voltage of the power supply provided, two digital multimeters were utilized. For acquiring images, the same camera was used for EL and PL imaging. The sensor used in the camera is a silicon CMOS sensor. For PL imaging, four light emitting diode (LED) boards, consisting out of sixty-four LED’s, per board, of four different wavelengths, were used to optically excite the solar cells. The four wavelengths emitted by the LED’s were chosen to match the bandgaps of the different solar cell devices investigated. The LEDs were powered with a multi-channel constant voltage power supply, where the current could be varied. The Si solar cell is a 156 x 156 mm commercial solar cell. The perovskite solar module is a 40 x 40 mm module, which consists out of six cells connected in series. The triple-junction concentrator solar cell has a dimension of 10 x 10 mm which consists of three junctions staked on top of one another. These three layers consist of indium gallium phosphate (InGaP), indium gallium arsenide (InGaAs) and germanium (Ge). To capture EL and PL images of these various solar cell devices, filters of specific wavelengths were placed in front of the camera to isolate the light generated by the different devices. In addition to isolating the luminescence observed from the solar cells, an image correction procedure was adapted from literature, to be applicable to acquiring luminescence images of these various solar cells. As there are a range of factors which influence the quality and clarity of the luminescence images, i.e., chromatic aberration, diffraction, and absorption depth, to name a few, the wavelength dependency of these factors was investigated. This was done by acquiring a point spread function (PSF) for each of these devices and then using these PSF's together with a deconvolution algorithm to correct the luminescence images. The PSF was acquired by fitting a point source emission image to a function that includes exponential and Gaussian terms. The point source image was obtained by placing a black piece of vinyl with a pinhole in it over the solar cell. To communicate with all the various devices and to acquire images at various intensities a LABVIEW program was written. This was used then used to control the power supplies, digital multimeters, camera, and the LED's. This allowed for the user to specify at what points along the current-voltage (I-V) curve data points needed to be measured together with the luminescence images captured. For PL imaging the intensity of the LED's was then also adjusted according to user specified values. The system was utilised to acquire EL images of the Si solar cell, EL and PL images of the perovskite solar cell and EL images of the InGaP and InGaAs layers in the triple-junction concentrator solar cell. With the correction procedure utilised in this study, it was seen that the image quality and clarity improved, compared to the conventional way of capturing luminescence images. These statements are supported by the results obtained for the series resistance maps of the Si solar cell and the perovskite solar module, as the series resistance maps obtained from the corrected luminescence images have less noise and more detail compared to the results from the raw luminescence images. From the EL images captured for the two layers of the triple junction concentrator, it was clear that the intensity profile of the two layers is different, as the intensity for the InGaP layers was that the device had bright edges and darker intensity on the interior where exactly the opposite was observed for the InGaAs layer, having a bright interior and darker edges. This is most likely due to the opto-electric coupling of these layers withing the triple junction solar cell. For the series resistance images obtained for the Si solar cell, it is observed that at lower carrier injection, the series resistance is lower compared to higher carrier injection levels. This result can also be influenced by the increase in cell temperature with the increase in injected carriers. The series resistance maps obtained from the perovskite EL images shows an interesting result. As the perovskite solar cell has degraded, three of the six cells have optically inactive regions, showing lower luminescence intensities. The series resistance of the other three cells are much lower compared to these cells that have inactive regions under low injection conditions. As the injection level increases, it is seen that the series resistance values of five of the six cells become comparable to one another. With regards to the PSF, it was found that using a bandpass filter in front of the lens reduced to amount of spreading observed from a single point source across the detector. Furthermore, there is a strong wavelength dependency in the PSF as the severity increased with increase in the emission wavelength of the solar cells under investigation.In this study an opto-electrical characterisation system was constructed to acquire PL and EL images of various solar cell technologies. In addition to this, a range of factors that influence the quality of these images were investigated and used in the image correction procedure to correct the images for all these cell technologies. It was shown that the correction procedure works for all three of the technologies investigated in this study, and all these factors showed a strong wavelength dependency. These corrected luminescence images together with current-voltage (I-V) data was then used to determine characteristic parameters of a one-diode model of the various PV devices. This was not only achieved, but it also clearly indicated that all the correction procedures need to be considered to obtain a clear and accurate representation of the actual PV device. This has a major influence on the understanding and improvement of these PV devices. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2024
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  • Date Issued: 2024-04
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