A Combined Experimental and Computational Study of Hydridospirophosphorane Ligand Systems Featuring Halogenated Mandelic Acids
- Authors: Maritz, Marius Johann
- Date: 2023-12
- Subjects: Organic compounds -- Synthesis , Heterocyclic compounds , catalysis -- South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/62096 , vital:71911
- Description: The search for new stereoselective catalysts remains important for the isolation of enantiomeric products from racemic mixtures. The need exists for these catalysts to be more efficient, to be more cost effective as well as be stable over time without undergoing changes in molecular structure and selectivity. The purpose of this research project was to experimentally synthesise and characterise asymmetric catalysts for the use in enantioselective synthesis. The catalysts consisted of the main group element phosphorous as central atom, with the phenyl rings of mandelic acid ligands monosubstituted with halogen atoms fluorine, chlorine and bromine in different configurations. Ligand binding resulted in the formation of hydridospirophosphorane structures, from which the molecular properties and binding geometry of these molecules could be explained by the theory of apicophilicity. Characterization was performed by NMR and IR spectroscopy as well as diffraction studies that provided the experimental crystal structures. The structural, energetic and spectroscopy results were compared to the theoretically obtained molecular properties using DFT analysis. Various interand intramolecular interactions that existed between molecules found in crystal packing environments were discussed. Additional properties that were investigated included modelling solvation effects, molecular orbital analysis, Hirshfeld surfaces, orbital and atomic energy and population analysis as well as ESP energy calculations with the optimized crystal structures as input. Molecular overlay comparisons were also performed between the experimental and optimized structures where the effectiveness of various DFT functionals and basis sets could be determined. The method with the best overall cost-to-accuracy ratio was found to be the triple-zeta def2-tzvp basis set with B3LYP functional theory and the addition of Grimme’s dispersion correction. Results indicated differences in crystal packing depending largely on the given halogen atoms present in the substituted phenyl rings, with differences observed in electronegativity and steric effects. One of the crystal systems showed additional interactions with solvent molecules, giving the impression that obtaining crystal void formation was possible. Alterations in the transition state activation energies between the isomers of each molecule were found to be present and supported the theory behind the mechanism of stereochemical induction. The studied compounds were therefore effective in isolating different enantiomeric ligands by means of energy differences between conformers and displayed unique catalytic properties resulting from the phosphorous main group element. The hydridospirophosphoranes conformers responsible for the lowest theoretically calculated activation energy induced crystallization as was seen by diffraction results for all compounds. Even as an intriguing observation, crystallization will largely depend on solubility rather than a specific conformer’s amount in solution. , Thesis (MSc) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-12
- Authors: Maritz, Marius Johann
- Date: 2023-12
- Subjects: Organic compounds -- Synthesis , Heterocyclic compounds , catalysis -- South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/62096 , vital:71911
- Description: The search for new stereoselective catalysts remains important for the isolation of enantiomeric products from racemic mixtures. The need exists for these catalysts to be more efficient, to be more cost effective as well as be stable over time without undergoing changes in molecular structure and selectivity. The purpose of this research project was to experimentally synthesise and characterise asymmetric catalysts for the use in enantioselective synthesis. The catalysts consisted of the main group element phosphorous as central atom, with the phenyl rings of mandelic acid ligands monosubstituted with halogen atoms fluorine, chlorine and bromine in different configurations. Ligand binding resulted in the formation of hydridospirophosphorane structures, from which the molecular properties and binding geometry of these molecules could be explained by the theory of apicophilicity. Characterization was performed by NMR and IR spectroscopy as well as diffraction studies that provided the experimental crystal structures. The structural, energetic and spectroscopy results were compared to the theoretically obtained molecular properties using DFT analysis. Various interand intramolecular interactions that existed between molecules found in crystal packing environments were discussed. Additional properties that were investigated included modelling solvation effects, molecular orbital analysis, Hirshfeld surfaces, orbital and atomic energy and population analysis as well as ESP energy calculations with the optimized crystal structures as input. Molecular overlay comparisons were also performed between the experimental and optimized structures where the effectiveness of various DFT functionals and basis sets could be determined. The method with the best overall cost-to-accuracy ratio was found to be the triple-zeta def2-tzvp basis set with B3LYP functional theory and the addition of Grimme’s dispersion correction. Results indicated differences in crystal packing depending largely on the given halogen atoms present in the substituted phenyl rings, with differences observed in electronegativity and steric effects. One of the crystal systems showed additional interactions with solvent molecules, giving the impression that obtaining crystal void formation was possible. Alterations in the transition state activation energies between the isomers of each molecule were found to be present and supported the theory behind the mechanism of stereochemical induction. The studied compounds were therefore effective in isolating different enantiomeric ligands by means of energy differences between conformers and displayed unique catalytic properties resulting from the phosphorous main group element. The hydridospirophosphoranes conformers responsible for the lowest theoretically calculated activation energy induced crystallization as was seen by diffraction results for all compounds. Even as an intriguing observation, crystallization will largely depend on solubility rather than a specific conformer’s amount in solution. , Thesis (MSc) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-12
An efficient approach for the synthesis of dolutegravir and its analogue exploiting flow chemistry
- Authors: Nqeketo, Sinazo
- Date: 2023-04
- Subjects: HIV (Viruses) – Enzymes –Inhibitors , Antiviral agents -- South Africa
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/${Handle} , vital:70635
- Description: Africa has the highest Human Immunodeficiency Virus (HIV) prevalence in the world and has invested heavily in running its HIV programmes and conducting research of medical significance. Despite efforts in combating this disease the production, distribution, cost, and availability of antiretroviral (ARV) generics remains a major problem as they are imported from China and India. Exploring the recently emerged “enabling technique”, namely flow chemistry in the production of APIs has gained a lot of attention. This study was devoted on exploring the application of flow chemistry on the synthesis of a newly approved anti-HIV drug dolutegravir (DTG); an integrase inhibitor with a high genetic barrier to resistance with a daily dosing scheduled compared to other ARVs and its third-generation inhibitor analogue, cabotegravir. Chapter one covers a comprehensive background and literature review of the HIV epidemic, an introduction of antiretroviral therapy as well as detailed dolutegravir and cabotegravir synthesis. A brief introduction of continuous flow technology with its advantages and disadvantages is discussed in this chapter. The efficient seven-step continuous flow procedure afforded dolutegravir and cabotegravir in improved reaction times and yields compared to the traditional batch procedure was demonstrated. The significant advantage of this flow process includes the reduction of the overall reaction time from step one to step seven, from prolonged 68 hours in batch to 34 minutes. The overall yield of each reaction step improved dramatically upon flow optimization. The yields of the second step (selective ester hydrolysis), fourth step (cyclization) and fifth step (amidation) increased from 64 %, 40 % and 33 % in batch to 98 %, 71 % and 100 % yield by HPLC respectively. Other than improved yields and residence times which was aided advantages of microreactor technology including intensive mixing, the flow process is also much better because it is cost effective. Most importantly, a novel process on the formation of pyridinone intermediate using ion-exchange resin catalysts towards the synthesis of dolutegravir and cabotegravir was described in this study , Thesis (PhD) -- Faculty of Science, School of Biomolecular and Chemical Science, 2023
- Full Text:
- Date Issued: 2023-04
- Authors: Nqeketo, Sinazo
- Date: 2023-04
- Subjects: HIV (Viruses) – Enzymes –Inhibitors , Antiviral agents -- South Africa
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/${Handle} , vital:70635
- Description: Africa has the highest Human Immunodeficiency Virus (HIV) prevalence in the world and has invested heavily in running its HIV programmes and conducting research of medical significance. Despite efforts in combating this disease the production, distribution, cost, and availability of antiretroviral (ARV) generics remains a major problem as they are imported from China and India. Exploring the recently emerged “enabling technique”, namely flow chemistry in the production of APIs has gained a lot of attention. This study was devoted on exploring the application of flow chemistry on the synthesis of a newly approved anti-HIV drug dolutegravir (DTG); an integrase inhibitor with a high genetic barrier to resistance with a daily dosing scheduled compared to other ARVs and its third-generation inhibitor analogue, cabotegravir. Chapter one covers a comprehensive background and literature review of the HIV epidemic, an introduction of antiretroviral therapy as well as detailed dolutegravir and cabotegravir synthesis. A brief introduction of continuous flow technology with its advantages and disadvantages is discussed in this chapter. The efficient seven-step continuous flow procedure afforded dolutegravir and cabotegravir in improved reaction times and yields compared to the traditional batch procedure was demonstrated. The significant advantage of this flow process includes the reduction of the overall reaction time from step one to step seven, from prolonged 68 hours in batch to 34 minutes. The overall yield of each reaction step improved dramatically upon flow optimization. The yields of the second step (selective ester hydrolysis), fourth step (cyclization) and fifth step (amidation) increased from 64 %, 40 % and 33 % in batch to 98 %, 71 % and 100 % yield by HPLC respectively. Other than improved yields and residence times which was aided advantages of microreactor technology including intensive mixing, the flow process is also much better because it is cost effective. Most importantly, a novel process on the formation of pyridinone intermediate using ion-exchange resin catalysts towards the synthesis of dolutegravir and cabotegravir was described in this study , Thesis (PhD) -- Faculty of Science, School of Biomolecular and Chemical Science, 2023
- Full Text:
- Date Issued: 2023-04
An evaluation of the effectiveness of area-based conservation intervention in avoiding biodiversity loss in South Africa
- Authors: Van Straten, Maurice Oswald
- Date: 2023-04
- Subjects: Soil conservation -- South Africa , Livestock farms – South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61132 , vital:69765
- Description: Habitat degradation, livestock farming, crop cultivation, rangeland overutilization and veld mismanagement are among the factors causing biodiversity loss worldwide. Rangelands in arid and semi-arid environments are no exception, as they are under stress from conversion into cropland and pressure from livestock farming. In these arid areas, rainfall is unpredictable and plant recruitment levels low, resulting in veld rehabilitation being a potentially expensive and time-consuming undertaking for landowners. Landowners implement different rehabilitation methods to increase overall vegetation cover and prevent further soil and vegetation degradation. These rehabilitation methods may include the creation of micro-catchments, mulching, brushpacking, ripping, geotextiles, stone cobbling and erosion control fences, individually or in combination with the addition of reseeding, replanting, and use of manure or fertilizer to supplement land rehabilitation. This study investigated the significance of three rehabilitation methods (hollows, brush packing and a combination of these two methods) on water infiltration rates, soil moisture content, and vegetation canopy cover with associated growth form canopy cover over a period of 17 months (March 2021 to August 2022). This study showed that rehabilitation methods implemented had no significant impact on water infiltration rates and vegetation canopy cover. However, rehabilitation methods had a significant impact on soil moisture content. The use of a hollows is recommended when attempting to increase the soil moisture content percentage when performing rehabilitation. Overall vegetation canopy cover is influenced more by seasonal changes than by the rehabilitation methods implemented. This study indicated that the creation of micro-catchments is an effective rehabilitation method to use in an arid area, as it promotes vegetation establishment and growth. , Thesis (MSc) -- Faculty of Science, School of Natural Resource Science and Management , 2023
- Full Text:
- Date Issued: 2023-04
- Authors: Van Straten, Maurice Oswald
- Date: 2023-04
- Subjects: Soil conservation -- South Africa , Livestock farms – South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61132 , vital:69765
- Description: Habitat degradation, livestock farming, crop cultivation, rangeland overutilization and veld mismanagement are among the factors causing biodiversity loss worldwide. Rangelands in arid and semi-arid environments are no exception, as they are under stress from conversion into cropland and pressure from livestock farming. In these arid areas, rainfall is unpredictable and plant recruitment levels low, resulting in veld rehabilitation being a potentially expensive and time-consuming undertaking for landowners. Landowners implement different rehabilitation methods to increase overall vegetation cover and prevent further soil and vegetation degradation. These rehabilitation methods may include the creation of micro-catchments, mulching, brushpacking, ripping, geotextiles, stone cobbling and erosion control fences, individually or in combination with the addition of reseeding, replanting, and use of manure or fertilizer to supplement land rehabilitation. This study investigated the significance of three rehabilitation methods (hollows, brush packing and a combination of these two methods) on water infiltration rates, soil moisture content, and vegetation canopy cover with associated growth form canopy cover over a period of 17 months (March 2021 to August 2022). This study showed that rehabilitation methods implemented had no significant impact on water infiltration rates and vegetation canopy cover. However, rehabilitation methods had a significant impact on soil moisture content. The use of a hollows is recommended when attempting to increase the soil moisture content percentage when performing rehabilitation. Overall vegetation canopy cover is influenced more by seasonal changes than by the rehabilitation methods implemented. This study indicated that the creation of micro-catchments is an effective rehabilitation method to use in an arid area, as it promotes vegetation establishment and growth. , Thesis (MSc) -- Faculty of Science, School of Natural Resource Science and Management , 2023
- Full Text:
- Date Issued: 2023-04
An evaluation of the effectiveness of area-based conservation interventions in avoiding biodiversity loss in South Africa
- Authors: Von Staden, Lize
- Date: 2023-04
- Subjects: Environmental policy , Conservation of natural resources -- Government policy -- South Africa
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/61115 , vital:69762
- Description: Counterfactual impact evaluation studies form an important evidence base for the effectiveness of conservation projects, programs, and policies (collectively referred to as conservation interventions). In South Africa, counterfactual impact evaluation methods have rarely been applied to local conservation interventions, and therefore evidence for the effectiveness of key strategic national conservation approaches is lacking. This study evaluated three area-based interventions that together aim to avoid the loss of areas most important for the persistence of biodiversity in the terrestrial realm as evidence towards the effectiveness of South Africa’s landscape approach to biodiversity conservation. The first intervention, South Africa’s National Protected Area Expansion Strategy (NPAES), set ambitious targets to double the extent of South Africa’s protected area network while ensuring that the expansion preferentially occurs in areas of under-represented biodiversity. The strategy was evaluated in terms of its effectiveness in guiding protected area expansion towards more equitable representation of South Africa’s biodiversity through an assessment of changes in indicators of protected area expansion decision-making before and after the implementation of the strategy. The second intervention is the use of maps of biodiversity priorities to guide land use change decisions outside protected areas. Impact was evaluated as avoided loss of Critical Biodiversity Areas (CBAs), which need to remain in a natural condition to meet in situ conservation targets for species, ecosystems, and ecological processes. Avoided loss in CBAs was benchmarked against avoided loss in protected areas, to contextualize the effectiveness of land use planning as a conservation intervention. Lastly, the effectiveness of stricter land use regulations for threatened ecosystems to reduce land conversion pressure on these ecosystems was evaluated. Key findings were that protected areas are highly effective conservation interventions where they can be implemented, but their capacity for conservation impact is limited by severe constraints on strategic expansion. , Thesis (PhD) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text:
- Date Issued: 2023-04
- Authors: Von Staden, Lize
- Date: 2023-04
- Subjects: Environmental policy , Conservation of natural resources -- Government policy -- South Africa
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/61115 , vital:69762
- Description: Counterfactual impact evaluation studies form an important evidence base for the effectiveness of conservation projects, programs, and policies (collectively referred to as conservation interventions). In South Africa, counterfactual impact evaluation methods have rarely been applied to local conservation interventions, and therefore evidence for the effectiveness of key strategic national conservation approaches is lacking. This study evaluated three area-based interventions that together aim to avoid the loss of areas most important for the persistence of biodiversity in the terrestrial realm as evidence towards the effectiveness of South Africa’s landscape approach to biodiversity conservation. The first intervention, South Africa’s National Protected Area Expansion Strategy (NPAES), set ambitious targets to double the extent of South Africa’s protected area network while ensuring that the expansion preferentially occurs in areas of under-represented biodiversity. The strategy was evaluated in terms of its effectiveness in guiding protected area expansion towards more equitable representation of South Africa’s biodiversity through an assessment of changes in indicators of protected area expansion decision-making before and after the implementation of the strategy. The second intervention is the use of maps of biodiversity priorities to guide land use change decisions outside protected areas. Impact was evaluated as avoided loss of Critical Biodiversity Areas (CBAs), which need to remain in a natural condition to meet in situ conservation targets for species, ecosystems, and ecological processes. Avoided loss in CBAs was benchmarked against avoided loss in protected areas, to contextualize the effectiveness of land use planning as a conservation intervention. Lastly, the effectiveness of stricter land use regulations for threatened ecosystems to reduce land conversion pressure on these ecosystems was evaluated. Key findings were that protected areas are highly effective conservation interventions where they can be implemented, but their capacity for conservation impact is limited by severe constraints on strategic expansion. , Thesis (PhD) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text:
- Date Issued: 2023-04
An exploration of the Participatory Guarantee System (PGS) facilitating the growth and certification of small-scale organic farmers: Giyani, Garden Route and Overberg case studies
- Authors: Mashele,N’wa-Jama
- Date: 2023-04
- Subjects: Organic farming – Case studies --South Africa , Organic farming research
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/60741 , vital:66574
- Description: In this study, I evaluated the Participatory Guarantee System (PGS) as a framework to support the growth and certification of small-scale organic farmers. I used the interpretivism and constructivism lenses to understand the PGS from the perspective of members of three PGS groups. The research was qualitative, treating the three PGS groups as case studies. I collected data using focus groups, semi-structured interviews, questionnaires, field notes and observations. The theoretical frameworks that guided the research and data analysis were Socio-ecological Systems (SES) based principles and the Multi-Level-Perspective (MLP) framework. The data were analysed using Atlas.ti content analysis software. The key results were grouped into four themes: capacity; market and logistics; learning process; and disturbance, shock and stress. The theme of ‘capacity’ dealt with the functioning of a PGS, where three categories were identified: group composition and capacity; resource limitations and institutional support; marketing and consumer education. The more diversity in age, education and culture of PGS stakeholders, the better performance and chances of continuity and propagation. PGS has limited capacity partly due to its voluntary nature and infancy. It needs institutional support to grow and be useful for members. Department of Agriculture extension officers knew little about organic farming, thus limiting their engagement and assistance to such farmers. The theme of ‘market and logistics’ looked at the various factors that influence the farmers’ market reach. The perception from the members was that there was minimal consumer awareness about organic agriculture and the PGS. The marketing of organic produce relied largely on the individual farmer’s efforts and ability to search for and secure markets. The theme of the ‘learning process’ was categorised into learning and knowledge exchange. Members of the PGS groups highly regarded the invaluable knowledge shared through farm visits and online platforms, such as their WhatsApp groups. This knowledge improved and informed their farming techniques and led to the growth of v their skill base and experimentation. They viewed the way knowledge was exchanged as non-threatening and highly useful. The fourth theme of ‘disturbance, shock and stress’ dealt with the effects of COVID19. The three groups were all affected by lockdown restrictions (at the time of data collection) and were initially cut off from their usual markets. This led to a loss of income, loss of farm staff and a loss of the desired growth of the farms. The group’s diverse farming practices bolstered their resilience, enabling them to adapt and try alternative marketing strategies. , Thesis (MSc) -- Faculty of Science, School of Natural Resource Management, 2023
- Full Text:
- Date Issued: 2023-04
- Authors: Mashele,N’wa-Jama
- Date: 2023-04
- Subjects: Organic farming – Case studies --South Africa , Organic farming research
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/60741 , vital:66574
- Description: In this study, I evaluated the Participatory Guarantee System (PGS) as a framework to support the growth and certification of small-scale organic farmers. I used the interpretivism and constructivism lenses to understand the PGS from the perspective of members of three PGS groups. The research was qualitative, treating the three PGS groups as case studies. I collected data using focus groups, semi-structured interviews, questionnaires, field notes and observations. The theoretical frameworks that guided the research and data analysis were Socio-ecological Systems (SES) based principles and the Multi-Level-Perspective (MLP) framework. The data were analysed using Atlas.ti content analysis software. The key results were grouped into four themes: capacity; market and logistics; learning process; and disturbance, shock and stress. The theme of ‘capacity’ dealt with the functioning of a PGS, where three categories were identified: group composition and capacity; resource limitations and institutional support; marketing and consumer education. The more diversity in age, education and culture of PGS stakeholders, the better performance and chances of continuity and propagation. PGS has limited capacity partly due to its voluntary nature and infancy. It needs institutional support to grow and be useful for members. Department of Agriculture extension officers knew little about organic farming, thus limiting their engagement and assistance to such farmers. The theme of ‘market and logistics’ looked at the various factors that influence the farmers’ market reach. The perception from the members was that there was minimal consumer awareness about organic agriculture and the PGS. The marketing of organic produce relied largely on the individual farmer’s efforts and ability to search for and secure markets. The theme of the ‘learning process’ was categorised into learning and knowledge exchange. Members of the PGS groups highly regarded the invaluable knowledge shared through farm visits and online platforms, such as their WhatsApp groups. This knowledge improved and informed their farming techniques and led to the growth of v their skill base and experimentation. They viewed the way knowledge was exchanged as non-threatening and highly useful. The fourth theme of ‘disturbance, shock and stress’ dealt with the effects of COVID19. The three groups were all affected by lockdown restrictions (at the time of data collection) and were initially cut off from their usual markets. This led to a loss of income, loss of farm staff and a loss of the desired growth of the farms. The group’s diverse farming practices bolstered their resilience, enabling them to adapt and try alternative marketing strategies. , Thesis (MSc) -- Faculty of Science, School of Natural Resource Management, 2023
- Full Text:
- Date Issued: 2023-04
An investigation of alternative separation strategies for common chemical mixtures by means of host-guest chemistry protocols with host compounds N,N′- bis(5-phenyl-5-dibenzo[a,d]cycloheptenyl)ethylenediamine and N,N’-bis(5-phenyl-10,11- dihydro-5-dibenzo[a,d]cycloheptenyl)ethylenediamine
- Authors: Barton, Danica Brione
- Date: 2023-04
- Subjects: Ethylenediaminetetraacetic acid -- South Africa , Enzymes –Analysis
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61176 , vital:69791
- Description: In this work, the selectivity behaviour of two host compounds, namely N,N’-bis(5-phenyl-5- ibenzo[a,d]cycloheptenyl)ethylenediamine (H1) and N,N’-bis(5-phenyl-10,11-dihydro-5- ibenzo[a,d]cycloheptenyl)ethylenediamine (H2), was assessed in mixtures of difficult-toseparate compounds, including the xylenes and ethylbenzene, pyridine and methylpyridines, and anisole and methylanisoles. These host compounds were synthesized using Grignard addition reactions with phenylmagnesium bromide on dibenzo[a,d]cyclohepten-5-one and 10,11- dihydrodibenzo[a,d]cyclohepten-5-one, respectively. The resultant alcohols were treated with perchloric acid to form the corresponding perchlorate salts, which were then reacted with ethylenediamine to afford the required H1 and H2 host compounds. Yields were 95 ad 52% for this final step in each case. An investigation of the conformations, both from experiment (using single crystal X-ray diffractometry (SCXRD) on the apohost compound) and computational calculations was undertaken. Unfortunately, H1 always crystallized out as a powder unless this host compound formed a complex with a guest species, and so could not be subjected to SCXRD analysis as apohost alone. However, a single crystal structure for apohost H2 was successfully obtained and compared with computational data from a previous investigation. It was observed that the conformation of apohost H2 compared favourably with that of the lowest energy conformer from that work. In single solvent recrystallization experiments with o-, m-, p-xylene (o-Xy, m-Xy, p-Xy) and ethylbenzene (EB), both H1 and H2 formed complexes with only one of the four guest species, namely p-Xy and o-Xy, respectively. The host:guest (H:G) ratios were 1:1 for both of these complexes. In the equimolar guest/guest competition experiments, inclusion complexes only formed when p-Xy or o-Xy, respectively, were present in the mixtures; if p-Xy (for experiments with H1) or o-Xy (H2) was absent from these mixtures, only apohost was recovered from the glass vessels. Three selectivity profiles were constructed for each of these host compounds, in which each one was recrystallized from binary mixed guests in various proportions. These demonstrated an overwhelming preference of H1 for p-Xy and H2 for o-Xy, which concurred with the results from the equimolar experiments. Thermal analysis using H1∙p-Xy revealed that this complex was unstable at ambient conditions, while SCXRD explained this observation: this complex may be defined as a true clathrate since no host‧‧‧guest interactions were identified at all, and the guest was retained in the complex by means of steric factors alone. Furthermore, the guest molecules resided in wide open channels that may have facilitated the guest release process. H2∙o-Xy, on the other hand, was stable at room temperature, and the guest release event only commenced at 69.7 °C (Ton). This too was explained by SCXRD analyses in that interactions between host and guest species were observed in this case. Additionally, the guest molecules were housed in discrete cages, which made their escape more challenging compared with p-Xy in H1∙p-Xy. It was concluded that, in this guest series, both of the host compounds would be effective as separatory tools employing host-guest chemistry protocols due to their remarkable selectivities for p-Xy (H1) and o-Xy (H2). , Thesis (MSc) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-04
- Authors: Barton, Danica Brione
- Date: 2023-04
- Subjects: Ethylenediaminetetraacetic acid -- South Africa , Enzymes –Analysis
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61176 , vital:69791
- Description: In this work, the selectivity behaviour of two host compounds, namely N,N’-bis(5-phenyl-5- ibenzo[a,d]cycloheptenyl)ethylenediamine (H1) and N,N’-bis(5-phenyl-10,11-dihydro-5- ibenzo[a,d]cycloheptenyl)ethylenediamine (H2), was assessed in mixtures of difficult-toseparate compounds, including the xylenes and ethylbenzene, pyridine and methylpyridines, and anisole and methylanisoles. These host compounds were synthesized using Grignard addition reactions with phenylmagnesium bromide on dibenzo[a,d]cyclohepten-5-one and 10,11- dihydrodibenzo[a,d]cyclohepten-5-one, respectively. The resultant alcohols were treated with perchloric acid to form the corresponding perchlorate salts, which were then reacted with ethylenediamine to afford the required H1 and H2 host compounds. Yields were 95 ad 52% for this final step in each case. An investigation of the conformations, both from experiment (using single crystal X-ray diffractometry (SCXRD) on the apohost compound) and computational calculations was undertaken. Unfortunately, H1 always crystallized out as a powder unless this host compound formed a complex with a guest species, and so could not be subjected to SCXRD analysis as apohost alone. However, a single crystal structure for apohost H2 was successfully obtained and compared with computational data from a previous investigation. It was observed that the conformation of apohost H2 compared favourably with that of the lowest energy conformer from that work. In single solvent recrystallization experiments with o-, m-, p-xylene (o-Xy, m-Xy, p-Xy) and ethylbenzene (EB), both H1 and H2 formed complexes with only one of the four guest species, namely p-Xy and o-Xy, respectively. The host:guest (H:G) ratios were 1:1 for both of these complexes. In the equimolar guest/guest competition experiments, inclusion complexes only formed when p-Xy or o-Xy, respectively, were present in the mixtures; if p-Xy (for experiments with H1) or o-Xy (H2) was absent from these mixtures, only apohost was recovered from the glass vessels. Three selectivity profiles were constructed for each of these host compounds, in which each one was recrystallized from binary mixed guests in various proportions. These demonstrated an overwhelming preference of H1 for p-Xy and H2 for o-Xy, which concurred with the results from the equimolar experiments. Thermal analysis using H1∙p-Xy revealed that this complex was unstable at ambient conditions, while SCXRD explained this observation: this complex may be defined as a true clathrate since no host‧‧‧guest interactions were identified at all, and the guest was retained in the complex by means of steric factors alone. Furthermore, the guest molecules resided in wide open channels that may have facilitated the guest release process. H2∙o-Xy, on the other hand, was stable at room temperature, and the guest release event only commenced at 69.7 °C (Ton). This too was explained by SCXRD analyses in that interactions between host and guest species were observed in this case. Additionally, the guest molecules were housed in discrete cages, which made their escape more challenging compared with p-Xy in H1∙p-Xy. It was concluded that, in this guest series, both of the host compounds would be effective as separatory tools employing host-guest chemistry protocols due to their remarkable selectivities for p-Xy (H1) and o-Xy (H2). , Thesis (MSc) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-04
Assessing diatom community composition and structure in palaeosediments of a southern Cape coastal wetland
- Authors: Sepato, Tshiamo Tsholofelo
- Date: 2023-04
- Subjects: Diatoms --South Africa – Southern Cape , Paleoecology , Marine algae --South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61258 , vital:69847
- Description: Palaeoenvironmental studies are important as they aid in reconstructing histories of past landscapes and provide key long-term information for the conservation and management of ecosystems. The southern Cape coast is a focus area for palaeoenvironmental research due to its high botanical and climatic importance. A three-metre sediment core was retrieved from Whale Rock wetland (Plettenberg Bay, southern Cape Coast) and spanned ~8000 years – a large proportion of the Holocene epoch. Diatom data preserved in palaeosediments of the Whale Rock wetland are presented within this study. A total of 48 diatom species was identified. Based on the multivariate statistical analysis, the diatom assemblages were divided into three zones: Zone WR-1-A (~7200 – 6450 cal yr BP); Zone WR-1- B (~6450 – 6250 cal yr BP) and Zone WR-1-C (~250 cal yr BP – to present). Two diatom preservation hiatus periods were observed at ~8000 – 7200 cal yr BP and ~6400 – 230 cal yr BP. The results indicated that benthic diatom species were significantly dominant throughout the Whale Rock record. The diatom evidence revealed that the Whale Rock wetland system freshened over time as diatom species identified in Zone WR-1-A and Zone WR-1- B indicated marine influences whereas Zone WR-1-C displayed a dominance of species that thrive in freshwater conditions. A transitional phase occurred at ~6400 cal yr BP where abrupt changes began prior to the significant ~6400 – 230 cal yr BP diatom preservation hiatus period. Principal Component Analysis showed that salinity was the main environmental driver of change impacting the species abundance and diversity of diatom communities within the wetland system throughout the Holocene. When compared with regional palaeoenvironmental and palaeolimnological data, it is evident that several other wetland systems moved from a marine/brackish favoured system to a freshwater system with the transitional phase occurring at different periods within the Holocene. This study indicated that diatoms are powerful biological proxies of environmental change. It is recommended that the site be revisited to investigate further the hiatus phases to further explore the lack of diatom preservation for these periods and to also contribute more palaeoenvironmental proxy evidence as well as modern hydrological information. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2022
- Full Text:
- Date Issued: 2023-04
- Authors: Sepato, Tshiamo Tsholofelo
- Date: 2023-04
- Subjects: Diatoms --South Africa – Southern Cape , Paleoecology , Marine algae --South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61258 , vital:69847
- Description: Palaeoenvironmental studies are important as they aid in reconstructing histories of past landscapes and provide key long-term information for the conservation and management of ecosystems. The southern Cape coast is a focus area for palaeoenvironmental research due to its high botanical and climatic importance. A three-metre sediment core was retrieved from Whale Rock wetland (Plettenberg Bay, southern Cape Coast) and spanned ~8000 years – a large proportion of the Holocene epoch. Diatom data preserved in palaeosediments of the Whale Rock wetland are presented within this study. A total of 48 diatom species was identified. Based on the multivariate statistical analysis, the diatom assemblages were divided into three zones: Zone WR-1-A (~7200 – 6450 cal yr BP); Zone WR-1- B (~6450 – 6250 cal yr BP) and Zone WR-1-C (~250 cal yr BP – to present). Two diatom preservation hiatus periods were observed at ~8000 – 7200 cal yr BP and ~6400 – 230 cal yr BP. The results indicated that benthic diatom species were significantly dominant throughout the Whale Rock record. The diatom evidence revealed that the Whale Rock wetland system freshened over time as diatom species identified in Zone WR-1-A and Zone WR-1- B indicated marine influences whereas Zone WR-1-C displayed a dominance of species that thrive in freshwater conditions. A transitional phase occurred at ~6400 cal yr BP where abrupt changes began prior to the significant ~6400 – 230 cal yr BP diatom preservation hiatus period. Principal Component Analysis showed that salinity was the main environmental driver of change impacting the species abundance and diversity of diatom communities within the wetland system throughout the Holocene. When compared with regional palaeoenvironmental and palaeolimnological data, it is evident that several other wetland systems moved from a marine/brackish favoured system to a freshwater system with the transitional phase occurring at different periods within the Holocene. This study indicated that diatoms are powerful biological proxies of environmental change. It is recommended that the site be revisited to investigate further the hiatus phases to further explore the lack of diatom preservation for these periods and to also contribute more palaeoenvironmental proxy evidence as well as modern hydrological information. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2022
- Full Text:
- Date Issued: 2023-04
Assessing the Role of Women on Small-Scale Agribusiness at Wincanton Estate in Kariega, South Africa
- Authors: Zalwango, Joanita
- Date: 2023-04
- Subjects: Leadership in women , Women in agriculture --Eastern Cape – Kariega , Climate change -- Kariega
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61054 , vital:69690
- Description: Agricultural development is a prerequisite for most economies to grow. Agricultural activities are key to food security and sustaining livelihoods globally. Within the African continent, more women are employed in agriculture and agribusiness activities than other sectors. As main contributors to the labour force in the agricultural sector, women get involved in many agricultural and agribusiness activities to sustain their families. With over 60% of women in Sub–Saharan Africa involved in agriculture, there is need to explore and assess the role they play in promoting agribusiness with special focus on Kariega, in South Africa. The identified participants in the study, as self-employed farmers, participate in agribusiness, thereby creating employment opportunities whilst generating personal incomes. Several benefits to female involvement in agribusiness were identified, including the ability to sustain families, stable cash flow, and empowerment. Several challenges were identified, including adequate capital, inaccessibility to private land, droughts, water scarcity, climate change effects and stigmatisation. Through a feminist qualitative methodology, the study utilised semi- structured interviews to collect data from 10 women involved in agribusiness around Kariega, Nelson Mandela Bay. Themes from the findings are analysed to highlight the important role played by women toward agribusiness, their achievements, government and private sector role and the hinderances still faced by these women in agricultural cooperatives. Discussion from the analysis included a framework of recommendations, for policy makers, development practitioners and future researchers. The study found that all stakeholders involved in the agricultural sector should work together for sustainable agricultural development and sustainable development goals to be achieved. Sustainability among women farmers can be achieved by (a) Increasing government intervention and support (b) Climate smart agriculture practices (c) Overcoming stigmatisation (d) Encouraging and involving the youth (e) Diversification and integration of farm businesses and (f) Using contract farming. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text: false
- Date Issued: 2023-04
Assessing the Role of Women on Small-Scale Agribusiness at Wincanton Estate in Kariega, South Africa
- Authors: Zalwango, Joanita
- Date: 2023-04
- Subjects: Leadership in women , Women in agriculture --Eastern Cape – Kariega , Climate change -- Kariega
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61054 , vital:69690
- Description: Agricultural development is a prerequisite for most economies to grow. Agricultural activities are key to food security and sustaining livelihoods globally. Within the African continent, more women are employed in agriculture and agribusiness activities than other sectors. As main contributors to the labour force in the agricultural sector, women get involved in many agricultural and agribusiness activities to sustain their families. With over 60% of women in Sub–Saharan Africa involved in agriculture, there is need to explore and assess the role they play in promoting agribusiness with special focus on Kariega, in South Africa. The identified participants in the study, as self-employed farmers, participate in agribusiness, thereby creating employment opportunities whilst generating personal incomes. Several benefits to female involvement in agribusiness were identified, including the ability to sustain families, stable cash flow, and empowerment. Several challenges were identified, including adequate capital, inaccessibility to private land, droughts, water scarcity, climate change effects and stigmatisation. Through a feminist qualitative methodology, the study utilised semi- structured interviews to collect data from 10 women involved in agribusiness around Kariega, Nelson Mandela Bay. Themes from the findings are analysed to highlight the important role played by women toward agribusiness, their achievements, government and private sector role and the hinderances still faced by these women in agricultural cooperatives. Discussion from the analysis included a framework of recommendations, for policy makers, development practitioners and future researchers. The study found that all stakeholders involved in the agricultural sector should work together for sustainable agricultural development and sustainable development goals to be achieved. Sustainability among women farmers can be achieved by (a) Increasing government intervention and support (b) Climate smart agriculture practices (c) Overcoming stigmatisation (d) Encouraging and involving the youth (e) Diversification and integration of farm businesses and (f) Using contract farming. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text: false
- Date Issued: 2023-04
Continuous flow synthesis of a key intermediate towards the antidiabetic drug repaglinide
- Authors: Williams, Arushan
- Date: 2023-04
- Subjects: Diabetes -- Miscellanea -- South Africa , Diabetes –Treatment
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61064 , vital:69715
- Description: Across the world, diabetes is one of the leading causes of deaths attributed to noncommunicable diseases (NCDs). In Africa, a huge proportion of African countries’ annual healthcare budgets are consumed by diabetes (7 %) with many already experiencing healthcare budget deficits. The prevalence of diabetes is rapidly growing and threatens the economic productivity and livelihood of many families within the region. The world leaders have invested heavily in reducing the pandemic by focusing on increasing the availability of affordable essential medicines in developing countries. The majority of diabetes cases are due to type 2 diabetes (90 %) and may be treated using oral hypoglycaemic drugs (OHDs). Repaglinide (REP) is a non-sulfonylurea insulin secretagogue (meglitinide) with greater HbA1c reduction than metformin in newly onset type 2 diabetic patients, however due to the high price of REP outside Asia, cheaper and less effective OHDs are prescribed to patients. Many of the reported synthetic routes towards REP utilize a key intermediate, 2-(3-ethoxy-4- iethoxycarbonyl)phenyl)acetic acid. The key intermediate contributes significantly to the price of REP as many of the intermediate’s synthetic routes suffer from long reaction times, low yields and industrial complex approaches. Therefore, this has prompted us to investigate an efficient process towards the synthesis of 2-(3-ethoxy-4-(ethoxycarbonyl)phenyl)acetic acid using multiple continuous flow systems. , Thesis (MSc) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-04
- Authors: Williams, Arushan
- Date: 2023-04
- Subjects: Diabetes -- Miscellanea -- South Africa , Diabetes –Treatment
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61064 , vital:69715
- Description: Across the world, diabetes is one of the leading causes of deaths attributed to noncommunicable diseases (NCDs). In Africa, a huge proportion of African countries’ annual healthcare budgets are consumed by diabetes (7 %) with many already experiencing healthcare budget deficits. The prevalence of diabetes is rapidly growing and threatens the economic productivity and livelihood of many families within the region. The world leaders have invested heavily in reducing the pandemic by focusing on increasing the availability of affordable essential medicines in developing countries. The majority of diabetes cases are due to type 2 diabetes (90 %) and may be treated using oral hypoglycaemic drugs (OHDs). Repaglinide (REP) is a non-sulfonylurea insulin secretagogue (meglitinide) with greater HbA1c reduction than metformin in newly onset type 2 diabetic patients, however due to the high price of REP outside Asia, cheaper and less effective OHDs are prescribed to patients. Many of the reported synthetic routes towards REP utilize a key intermediate, 2-(3-ethoxy-4- iethoxycarbonyl)phenyl)acetic acid. The key intermediate contributes significantly to the price of REP as many of the intermediate’s synthetic routes suffer from long reaction times, low yields and industrial complex approaches. Therefore, this has prompted us to investigate an efficient process towards the synthesis of 2-(3-ethoxy-4-(ethoxycarbonyl)phenyl)acetic acid using multiple continuous flow systems. , Thesis (MSc) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-04
Costs and consequences at the population-environment-development interface in St Francis Bay: exploring the linkages of a complex system
- Authors: Pringle, Geena
- Date: 2023-04
- Subjects: Population -- Environmental aspects , Population --Statistics , Loliginidae -- South Africa -- st francis bay
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61294 , vital:70065
- Description: Coastal zones the world over are particularly attractive for the development of human settlements. Naturally, this trend frequently results in human induced disturbances of sensitive ecosystems, often resulting in dramatic and unintended consequences. The South African coastline is no stranger to this phenomenon. Dynamics at the population-environment-development interface in the coastal zone often presents affected communities and institutions with complex challenges. An infamous case along the South African coastline is the settlement of St Francis Bay, the focus of this dissertation. St Francis Bay was established as a holiday village around sixty years ago and its economy is today firmly dependent on the fragile bond and reciprocal relationship between the tourist trade and the integrity of sandy beaches. The dissertation, against this background and drawing from complex systems theory, explores the links between human activity and the biophysical environment and the ominous costs and consequences that are produced at the local population-environment-development interface. Domains that are considered within the nexus of relevant aspects include the wind-driven sediment bypass system across the local headland; climate change; the local economy; social wellbeing, inequality and social justice; as well urban planning and political governance. The desktop study applied to St Francis Bay made use of Geographic Information Systems and statistical information to form the basis of the methodological approach in this dissertation. The Population-Environment-Development nexus was formed as a result. The results illustrate how critical levels of beach erosion are connected amidst an intricate reciprocal nexus to these and other aspects. It demonstrates that the sustainability of the settlement hinges on the understanding of such linkages and underscores the relevance of the methodological approach that is applied. The sustainability of the environment and the resulting impact on the quality of life of the human population remains a challenge for future generations as well as governance systems. By acknowledging and understanding the complexity that exists in coastal zones allows for future research on the topic to be explored and enable key role players to proactively intervene to benefit the population and the environment. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text:
- Date Issued: 2023-04
- Authors: Pringle, Geena
- Date: 2023-04
- Subjects: Population -- Environmental aspects , Population --Statistics , Loliginidae -- South Africa -- st francis bay
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61294 , vital:70065
- Description: Coastal zones the world over are particularly attractive for the development of human settlements. Naturally, this trend frequently results in human induced disturbances of sensitive ecosystems, often resulting in dramatic and unintended consequences. The South African coastline is no stranger to this phenomenon. Dynamics at the population-environment-development interface in the coastal zone often presents affected communities and institutions with complex challenges. An infamous case along the South African coastline is the settlement of St Francis Bay, the focus of this dissertation. St Francis Bay was established as a holiday village around sixty years ago and its economy is today firmly dependent on the fragile bond and reciprocal relationship between the tourist trade and the integrity of sandy beaches. The dissertation, against this background and drawing from complex systems theory, explores the links between human activity and the biophysical environment and the ominous costs and consequences that are produced at the local population-environment-development interface. Domains that are considered within the nexus of relevant aspects include the wind-driven sediment bypass system across the local headland; climate change; the local economy; social wellbeing, inequality and social justice; as well urban planning and political governance. The desktop study applied to St Francis Bay made use of Geographic Information Systems and statistical information to form the basis of the methodological approach in this dissertation. The Population-Environment-Development nexus was formed as a result. The results illustrate how critical levels of beach erosion are connected amidst an intricate reciprocal nexus to these and other aspects. It demonstrates that the sustainability of the settlement hinges on the understanding of such linkages and underscores the relevance of the methodological approach that is applied. The sustainability of the environment and the resulting impact on the quality of life of the human population remains a challenge for future generations as well as governance systems. By acknowledging and understanding the complexity that exists in coastal zones allows for future research on the topic to be explored and enable key role players to proactively intervene to benefit the population and the environment. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text:
- Date Issued: 2023-04
Distinguishing elephant induced thicket degradation and climate related factors in Addo Elephant National Park, Eastern Cape, South Africa
- Authors: Mapheto, Tlhologelo James
- Date: 2023-04
- Subjects: Elephant – Behaviour -- South Africa -- Addo Elephant National Park , Wildlife conservation -- South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/60753 , vital:66741
- Description: The Addo Elephant National Park (AENP) is an ecologically sensitive environment where the increase in elephant population, especially in a changing climate is a recipe for landscape degradation and biodiversity loss. The Park is situated in the drought prone Eastern Cape Province, however, the effects of drought on thicket vegetation is less understood. This study aimed to distinguish elephant-induced thicket degradation from the effects of climatic factors, using remote sensing, GIS, and statistical techniques. To characterise and map vegetation conditions of the reserve temporal series Landsat imagery (n = 22) from 1998 to 2018 were analysed. Vegetation states were determined using Normalised Difference Vegetation Index (NDVI) derived from the growing season of the study period. Using supervised per-pixel image classification technique, the NDVI values characterized into distinct land cover classes viz (1) Intact Thicket, (2) Transformed Thicket, (3) Degraded Thicket, (4) Bare Ground and (6) Water Bodies. Post-classification change detection and landscape fragmentation analysis was performed. Climatic data were obtained from existing weather stations and raster surface of accumulated rainfall and mean maximum temperature were developed using the Inverse Distance Weighting (IDW). Time series analysis was implemented on the NDVI and climatic condition data by plotting annual measures to indicate variable trends. Temporal trend analysis was performed on the NDVI data using the nonparametric Mann-Kendall trend analysis test to indicate thicket vegetation condition improvement and general degradation. The Residual Trend (RESTREND) approach was employed to remove the effect of rainfall on vegetation productivity. This involved using the Ordinary Least Square regression functionality in ArcMap to compute the relationship between ∑NDVI and accumulated rainfall for every pixel for the study period. The products of the regression were assessed using Pearson’s Correlation (r) at a significance level of 90% (p-value ≤ 0.1) to distinguish strong relationships. Overlay analysis was performed, using the NDVI trend slope and the correlation coefficient (r) raster surfaces, to model vegetation dynamics influenced by elephant activities. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text:
- Date Issued: 2023-04
- Authors: Mapheto, Tlhologelo James
- Date: 2023-04
- Subjects: Elephant – Behaviour -- South Africa -- Addo Elephant National Park , Wildlife conservation -- South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/60753 , vital:66741
- Description: The Addo Elephant National Park (AENP) is an ecologically sensitive environment where the increase in elephant population, especially in a changing climate is a recipe for landscape degradation and biodiversity loss. The Park is situated in the drought prone Eastern Cape Province, however, the effects of drought on thicket vegetation is less understood. This study aimed to distinguish elephant-induced thicket degradation from the effects of climatic factors, using remote sensing, GIS, and statistical techniques. To characterise and map vegetation conditions of the reserve temporal series Landsat imagery (n = 22) from 1998 to 2018 were analysed. Vegetation states were determined using Normalised Difference Vegetation Index (NDVI) derived from the growing season of the study period. Using supervised per-pixel image classification technique, the NDVI values characterized into distinct land cover classes viz (1) Intact Thicket, (2) Transformed Thicket, (3) Degraded Thicket, (4) Bare Ground and (6) Water Bodies. Post-classification change detection and landscape fragmentation analysis was performed. Climatic data were obtained from existing weather stations and raster surface of accumulated rainfall and mean maximum temperature were developed using the Inverse Distance Weighting (IDW). Time series analysis was implemented on the NDVI and climatic condition data by plotting annual measures to indicate variable trends. Temporal trend analysis was performed on the NDVI data using the nonparametric Mann-Kendall trend analysis test to indicate thicket vegetation condition improvement and general degradation. The Residual Trend (RESTREND) approach was employed to remove the effect of rainfall on vegetation productivity. This involved using the Ordinary Least Square regression functionality in ArcMap to compute the relationship between ∑NDVI and accumulated rainfall for every pixel for the study period. The products of the regression were assessed using Pearson’s Correlation (r) at a significance level of 90% (p-value ≤ 0.1) to distinguish strong relationships. Overlay analysis was performed, using the NDVI trend slope and the correlation coefficient (r) raster surfaces, to model vegetation dynamics influenced by elephant activities. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text:
- Date Issued: 2023-04
Effect of livestock management and services to ecosystems on rangeland health and resilience in the NamaKaroo
- Authors: Boshoff, Mishak
- Date: 2023-04
- Subjects: Livestock – Management --South Africa—Karoo , Range ecology
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/60611 , vital:66017
- Description: Rangelands offer great opportunities for mutualisms between nature conservation and economic productivity if positive feedback loops can be identified and described. The effects of different livestock management practices are controversial. This research examined the effect of different grazing intensities on soil health using springtails (Collembola) and ants (Formicidae) as bioindicators, combined with soil and vegetation variables. The relationship between rangeland managers and rangeland ecosystems, particularly with regard to feedback loops between land care and economic production, was also investigated. Bioindicator samples were collected at different treatments of livestock grazing intensity and a questionnaire was submitted to 65 rangeland managers in the semi-arid Nama-Karoo biome of South Africa. In most cases we found no significant relationship between grazing intensity and Collembola and ant community composition, vegetation variables, and soil variables. The few significant relationships we found were contradictory in their implications for the effect of high intensity grazing on soil health. The results suggested that differences in livestock management are relatively unimportant for soil health, at least in semi-arid systems under conditions immediately following a drought. The questionnaire yielded results on outline of management practices, basis of management decisions, consequences of monitoring veld to inform management decisions, and indicators of successful management. Respondents characterized by higher ecological fluency focused on livestock production when making management decisions, stocked at higher densities, and monitored the rangeland ecosystem to inform their decisions. For monitoring the ecosystem, they used bioindicators such as diversity of biota, successional stage, and ecologically important functional groups. We concluded that the development of ecological knowledge in rangeland managers enables the establishment of feedback loops between ecosystem services and services to ecosystems, which are desirable for economic productivity and nature conservation. Development of relevant ecological knowledge and management techniques should be based on forums and dialogue among rangeland managers, developing distributed cognition and resilience in the community of rangeland managers. , Thesis (MSc) -- Faculty of Science, School Natural Resource Science and Management, 2023
- Full Text:
- Date Issued: 2023-04
- Authors: Boshoff, Mishak
- Date: 2023-04
- Subjects: Livestock – Management --South Africa—Karoo , Range ecology
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/60611 , vital:66017
- Description: Rangelands offer great opportunities for mutualisms between nature conservation and economic productivity if positive feedback loops can be identified and described. The effects of different livestock management practices are controversial. This research examined the effect of different grazing intensities on soil health using springtails (Collembola) and ants (Formicidae) as bioindicators, combined with soil and vegetation variables. The relationship between rangeland managers and rangeland ecosystems, particularly with regard to feedback loops between land care and economic production, was also investigated. Bioindicator samples were collected at different treatments of livestock grazing intensity and a questionnaire was submitted to 65 rangeland managers in the semi-arid Nama-Karoo biome of South Africa. In most cases we found no significant relationship between grazing intensity and Collembola and ant community composition, vegetation variables, and soil variables. The few significant relationships we found were contradictory in their implications for the effect of high intensity grazing on soil health. The results suggested that differences in livestock management are relatively unimportant for soil health, at least in semi-arid systems under conditions immediately following a drought. The questionnaire yielded results on outline of management practices, basis of management decisions, consequences of monitoring veld to inform management decisions, and indicators of successful management. Respondents characterized by higher ecological fluency focused on livestock production when making management decisions, stocked at higher densities, and monitored the rangeland ecosystem to inform their decisions. For monitoring the ecosystem, they used bioindicators such as diversity of biota, successional stage, and ecologically important functional groups. We concluded that the development of ecological knowledge in rangeland managers enables the establishment of feedback loops between ecosystem services and services to ecosystems, which are desirable for economic productivity and nature conservation. Development of relevant ecological knowledge and management techniques should be based on forums and dialogue among rangeland managers, developing distributed cognition and resilience in the community of rangeland managers. , Thesis (MSc) -- Faculty of Science, School Natural Resource Science and Management, 2023
- Full Text:
- Date Issued: 2023-04
Evaluation of the toxicity of secondary metabolites in Solanum incanum L. to advance community knowledge
- Authors: Zivanayi, William
- Date: 2023-04
- Subjects: Solanum -- Zimbabwe , Pesticides -- Toxicology , Medicinal plants
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/61018 , vital:69686
- Description: The effects of pests and the need to produce adequate food have influenced small-scale farmers in disadvantaged communities to adopt and utilise natural plant pesticides to improve harvests in many Southern African Development Communities. However, the phytochemistry associated with these indigenous plants’ pesticide activity still needs to be explored. The lack of evidence of scientific knowledge of the plant species has caused a lot of health issues among the users of indigenous plant pesticides. Solanum incanum is among the plants utilised to control cabbage aphids in Mkoba village, Zimbabwe. Solanum species are known for their steroidal compounds which comprise glycoalkaloids and saponins. This study evaluated the knowledge, opinions, and attitudes of the vegetable peasant farming community in Gweru regarding their use of the indigenous plant (S. incanum) as a pesticide. The study also reported the phytochemical profiling, structural characterisation of the isolated compounds, and biological and pesticidal activity evaluation of phytochemicals isolated from S. incanum. A descriptive survey was carried out to assess the knowledge, attitude, and practices of a conveniently sampled group of vegetable farmers in Mkoba village who use S. incanum as a pesticide. Forty-nine respondents comprised of 19 males and 30 females of ages ranging from 15 to above 60 years took part in the study by answering an open and closed-ended questionnaire. The survey revealed that parents and neighbours were instrumental in disseminating pesticidal information in the community. Brassica napus were the most grown.vegetable and vulnerable to cabbage aphids. Mixed opinions amongst the respondents varied regarding the health and environmental impact of S. incanum as a pesticide. Seventy-five percent (75%) of the respondents supported the use of S. incanum as a pesticide whilst 25% claimed that the use of S. incanum was the source of the health problems experienced in the community. The survey demonstrated that (45)91% of the farmers displayed poor practices regarding the disposal of empty pesticide containers and the use of personal protective clothing. The most prevalent symptoms in the community were skin rash, nausea, headache, and poor vision and these symptoms were common in the age group 30 to 60 years. , Thesis (PhD) -- Faculty of Science, School of biomolecular and Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-04
- Authors: Zivanayi, William
- Date: 2023-04
- Subjects: Solanum -- Zimbabwe , Pesticides -- Toxicology , Medicinal plants
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/61018 , vital:69686
- Description: The effects of pests and the need to produce adequate food have influenced small-scale farmers in disadvantaged communities to adopt and utilise natural plant pesticides to improve harvests in many Southern African Development Communities. However, the phytochemistry associated with these indigenous plants’ pesticide activity still needs to be explored. The lack of evidence of scientific knowledge of the plant species has caused a lot of health issues among the users of indigenous plant pesticides. Solanum incanum is among the plants utilised to control cabbage aphids in Mkoba village, Zimbabwe. Solanum species are known for their steroidal compounds which comprise glycoalkaloids and saponins. This study evaluated the knowledge, opinions, and attitudes of the vegetable peasant farming community in Gweru regarding their use of the indigenous plant (S. incanum) as a pesticide. The study also reported the phytochemical profiling, structural characterisation of the isolated compounds, and biological and pesticidal activity evaluation of phytochemicals isolated from S. incanum. A descriptive survey was carried out to assess the knowledge, attitude, and practices of a conveniently sampled group of vegetable farmers in Mkoba village who use S. incanum as a pesticide. Forty-nine respondents comprised of 19 males and 30 females of ages ranging from 15 to above 60 years took part in the study by answering an open and closed-ended questionnaire. The survey revealed that parents and neighbours were instrumental in disseminating pesticidal information in the community. Brassica napus were the most grown.vegetable and vulnerable to cabbage aphids. Mixed opinions amongst the respondents varied regarding the health and environmental impact of S. incanum as a pesticide. Seventy-five percent (75%) of the respondents supported the use of S. incanum as a pesticide whilst 25% claimed that the use of S. incanum was the source of the health problems experienced in the community. The survey demonstrated that (45)91% of the farmers displayed poor practices regarding the disposal of empty pesticide containers and the use of personal protective clothing. The most prevalent symptoms in the community were skin rash, nausea, headache, and poor vision and these symptoms were common in the age group 30 to 60 years. , Thesis (PhD) -- Faculty of Science, School of biomolecular and Chemical Sciences, 2023
- Full Text:
- Date Issued: 2023-04
Factors affecting pinniped skull morphology
- Authors: Penaluna, Julia Elizabeth
- Date: 2023-04
- Subjects: hybridisation -- South Africa , Sexual dimorphism (Animals) , Craniology
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61306 , vital:70077
- Description: Morphologies have evolved due to trade-offs between competing selective pressures. This is especially true for the skull. Not only does it contain the brain and the organs that are responsible for sensory function, but it is also contains components that play important roles in feeding, breathing, balance, defence, aggression and communication. The pinnipeds, a group of species that has evolved from terrestrial origins and became adapted to the marine environment, are under numerous selective pressures within the marine environment. These species have had to evolve in order to capture and process food underwater, and to dive. In addition, they are also characterised by substantial sexual size dimorphism in some species. Pinnipeds also make use of numerous marine and haul-out habitats with varying characteristics and complexity. Hybridisation has been recorded among pinnipeds, resulting in the production of hybrid offspring with characteristics that are different to their parent species. The aim of the study was to investigate the effect of these life history characteristics on skull and mandible morphology of pinniped species using three dimensional geometric morphometrics. To achieve this, 43 skull and 15 mandible 3D landmarks were collected using a Microscribe G2X digitizer with 0.2mm accuracy, on the skull and mandibles of 17 species of pinnipeds across three families, and one hybrid species. In total, 96 specimens across these species were examined. Data on the different life history characteristics of each species were collected from the literature. These data were plotted onto the PCA results in order to create and visually compare minimum convex polygons for each life history category. The results found that phylogeny, feeding strategy and sexual dimorphism were the most important factors in explaining differences in pinniped skull and mandible shape and size. may have resulted in these changes. Similarly, the inclusion of more species, covering a broader range of life histories may be beneficial. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text:
- Date Issued: 2023-04
- Authors: Penaluna, Julia Elizabeth
- Date: 2023-04
- Subjects: hybridisation -- South Africa , Sexual dimorphism (Animals) , Craniology
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61306 , vital:70077
- Description: Morphologies have evolved due to trade-offs between competing selective pressures. This is especially true for the skull. Not only does it contain the brain and the organs that are responsible for sensory function, but it is also contains components that play important roles in feeding, breathing, balance, defence, aggression and communication. The pinnipeds, a group of species that has evolved from terrestrial origins and became adapted to the marine environment, are under numerous selective pressures within the marine environment. These species have had to evolve in order to capture and process food underwater, and to dive. In addition, they are also characterised by substantial sexual size dimorphism in some species. Pinnipeds also make use of numerous marine and haul-out habitats with varying characteristics and complexity. Hybridisation has been recorded among pinnipeds, resulting in the production of hybrid offspring with characteristics that are different to their parent species. The aim of the study was to investigate the effect of these life history characteristics on skull and mandible morphology of pinniped species using three dimensional geometric morphometrics. To achieve this, 43 skull and 15 mandible 3D landmarks were collected using a Microscribe G2X digitizer with 0.2mm accuracy, on the skull and mandibles of 17 species of pinnipeds across three families, and one hybrid species. In total, 96 specimens across these species were examined. Data on the different life history characteristics of each species were collected from the literature. These data were plotted onto the PCA results in order to create and visually compare minimum convex polygons for each life history category. The results found that phylogeny, feeding strategy and sexual dimorphism were the most important factors in explaining differences in pinniped skull and mandible shape and size. may have resulted in these changes. Similarly, the inclusion of more species, covering a broader range of life histories may be beneficial. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text:
- Date Issued: 2023-04
Interactive visualisation of electricity usage in smart environments
- Ngwenya, Moreblessing Tafadzwa
- Authors: Ngwenya, Moreblessing Tafadzwa
- Date: 2023-04
- Subjects: Smart environment -- south Africa , Application software -- Development , Intelligent buildings
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61477 , vital:70687
- Description: Saving electricity is a trending topic due to the electricity challenges that are being faced globally. Smart environments are environments that are equipped with physical objects, which include computers, sensors, actuators, smartphones, and wearable devices interconnected together through the Internet of Things. The Internet of Things provides a network to achieve communication, and computation abilities to provide individuals with smart services anytime, and anywhere. Rapid developments in information technology have increased the number of smart appliances being used, leading to increased electricity usage. Devices and appliances in Smart Environments continue to consume electricity even when not in use, because of the standby function. The problems arise as the electricity consumption of the standby function accumulates to large amounts. Effective communication through visualisation of the electricity consumption in a Smart Environment provides a viable solution to reducing the consumption of electricity. This research aimed to design and developed a visualisation system that successfully communicates electricity consumption to the user using a variety of visualisation techniques. The Design Science Research Methodology was used to address the research questions and was used to iteratively design and develop an energy usage visualisation system. The visualisation system was created for the Smart Lab at the Nelson Mandela University's Department of Computing Sciences. A usability study was conducted to assess the usability and efficacy of the system. The system was found to be usable and effective in communicating power usage to potential customers, since the participants were able to complete the tasks in a short amount of time. The positive results show that visualisation can aid in communicating electricity usage to customers, resulting in a possible reduction in electricity consumption and improved decision-making. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2023
- Full Text:
- Date Issued: 2023-04
- Authors: Ngwenya, Moreblessing Tafadzwa
- Date: 2023-04
- Subjects: Smart environment -- south Africa , Application software -- Development , Intelligent buildings
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61477 , vital:70687
- Description: Saving electricity is a trending topic due to the electricity challenges that are being faced globally. Smart environments are environments that are equipped with physical objects, which include computers, sensors, actuators, smartphones, and wearable devices interconnected together through the Internet of Things. The Internet of Things provides a network to achieve communication, and computation abilities to provide individuals with smart services anytime, and anywhere. Rapid developments in information technology have increased the number of smart appliances being used, leading to increased electricity usage. Devices and appliances in Smart Environments continue to consume electricity even when not in use, because of the standby function. The problems arise as the electricity consumption of the standby function accumulates to large amounts. Effective communication through visualisation of the electricity consumption in a Smart Environment provides a viable solution to reducing the consumption of electricity. This research aimed to design and developed a visualisation system that successfully communicates electricity consumption to the user using a variety of visualisation techniques. The Design Science Research Methodology was used to address the research questions and was used to iteratively design and develop an energy usage visualisation system. The visualisation system was created for the Smart Lab at the Nelson Mandela University's Department of Computing Sciences. A usability study was conducted to assess the usability and efficacy of the system. The system was found to be usable and effective in communicating power usage to potential customers, since the participants were able to complete the tasks in a short amount of time. The positive results show that visualisation can aid in communicating electricity usage to customers, resulting in a possible reduction in electricity consumption and improved decision-making. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2023
- Full Text:
- Date Issued: 2023-04
Investigating the role of UAVs and convolutional neural networks in the identification of invasive plant species in the Albany Thicket
- Authors: Wesson, Frank Cameron
- Date: 2023-04
- Subjects: Drone aircraft -- Control systems , Drone -- South Africa , Albany Thicket -- South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61097 , vital:69755
- Description: The study aimed to determine whether plant species could be classified by using high resolution aerial imagery and a convolutional neural network (CNN). The full capabilities of a CNN were examined including testing whether the platform could be used for land cover and the evaluation of land change over time. A drone or unmanned aerial vehicle (UAV) was used to collect the aerial data of the study area, and 45 subplots were used for the image analysis. The CNN was coded and operated in RStudio, and digitised data from the input imagery were used as training and validation data by the programme to learn features. Four classifications were performed using various quantities of input data to access the performance of the neural network. In addition, tests were performed to understand whether the CNN could be used as a land cover and land change detection tool. Accuracy assessments were done on the results to test reliability and accuracy. The best-performing classification achieved an average user and producer accuracy of above 90%, while the overall accuracy was 93%, and the kappa coefficient score was 0.86. The CNN was also able to predict the land coverage area of Opuntia to be within 4% of the ground truthing data area. A change in land cover over time was detected by the programme after the manual clearing of the invasive plant had been undertaken. This research has determined that the use of a CNN in remote sensing is a very powerful tool for supervised image classifications and that it can be used for monitoring land cover by accurately estimating the spatial distribution of plant species and by monitoring the species' growth or decline over time. A CNN could also be used as a tool for landowners to prove that they are making efforts to clear invasive species from their land. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text:
- Date Issued: 2023-04
- Authors: Wesson, Frank Cameron
- Date: 2023-04
- Subjects: Drone aircraft -- Control systems , Drone -- South Africa , Albany Thicket -- South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61097 , vital:69755
- Description: The study aimed to determine whether plant species could be classified by using high resolution aerial imagery and a convolutional neural network (CNN). The full capabilities of a CNN were examined including testing whether the platform could be used for land cover and the evaluation of land change over time. A drone or unmanned aerial vehicle (UAV) was used to collect the aerial data of the study area, and 45 subplots were used for the image analysis. The CNN was coded and operated in RStudio, and digitised data from the input imagery were used as training and validation data by the programme to learn features. Four classifications were performed using various quantities of input data to access the performance of the neural network. In addition, tests were performed to understand whether the CNN could be used as a land cover and land change detection tool. Accuracy assessments were done on the results to test reliability and accuracy. The best-performing classification achieved an average user and producer accuracy of above 90%, while the overall accuracy was 93%, and the kappa coefficient score was 0.86. The CNN was also able to predict the land coverage area of Opuntia to be within 4% of the ground truthing data area. A change in land cover over time was detected by the programme after the manual clearing of the invasive plant had been undertaken. This research has determined that the use of a CNN in remote sensing is a very powerful tool for supervised image classifications and that it can be used for monitoring land cover by accurately estimating the spatial distribution of plant species and by monitoring the species' growth or decline over time. A CNN could also be used as a tool for landowners to prove that they are making efforts to clear invasive species from their land. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text:
- Date Issued: 2023-04
Investigating thermoregulatory responses of rhabdomys pumilio at high wet-bulb temperatures
- Authors: Hartley, Oliver
- Date: 2023-04
- Subjects: Heat stress physiology , Small mammal thermoregulation -- South Africa , Climate change - Wet-bulb temperature
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/60873 , vital:68916
- Description: As the Anthropocene continues to be characterised by ever rising temperature highs, increasingly sporadic and extreme climatic events, and their accompanying mass mortality events, climate scientists now warn that the continued climate destabilisation may for the first time in recorded history prevent terrestrial homeothermic endotherms from being able to thermoregulate. Having evolved to maintain body temperatures (Tbs) well above their ambient (Ta) conditions, these endotherms have evolved a suite of adaptations to a colder environment to allow for homeothermic thermoregulation to occur. However, by the same vein, having evolved in a colder climate to stay warm also has led to a reduced capacity to prevent heat stress when temperature conditions are elevated. In absence of behavioural counter measures, the only physiological means available to thermoregulation to prevent such heat stress is that of evaporative water loss (EWL). If still inefficient, the endotherm will risk becoming hyperthermic. Literature has established that excessive heat exposure or reduced evaporative cooling capacities strain or retard thermoregulatory processes. If an endotherm experiences severe heat exposure, the rate at which passive heating is experienced will increase. Should an endotherm be in a humid environment, evaporative cooling efficiency is reduced. As a result, these two abiotic factors are therefore known to contribute towards heat storage, and therefore thermal stress. However, should both factors occur in the same environment, the heat stress effects are compounded, creating an environment dangerous for thermoregulating endotherms. For this reason, authors have emphasised that future wet-bulb (Tw) conditions may pose a penultimate threat to thermoregulating endotherms. Being a measure of coldest temperature attainable as a result of evaporative cooling, Tw has been proposed to represent a lower temperature thermal limit to endothermic thermoregulation. Once reaching a 2°C differential below an endotherms Tb (Tb – Tw = 2˚C), Tw is believed to impede the evaporative cooling process and, consequentially, commit endotherms to becoming hyperthermic. Considering that most mammals defend constant Tbs within the range of predicted Tw maxima increases that future Tw conditions may pose a significant threat to mammalian thermoregulation. However, to date, despite being well supported in the literature, ii empirical investigations into how extreme Tw conditions will affect endothermic thermoregulation are scant. Therefore, understanding of the proposed inhibitory nature of extreme Tw conditions is lacking. Considering that such conditions are to have a profound effect of endothermic survival, this dearth in understanding could prove fatal. As such, this thesis sought to provide evidence on how extreme Tw conditions may affect thermoregulatory processes in homeothermic endotherms. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text:
- Date Issued: 2023-04
- Authors: Hartley, Oliver
- Date: 2023-04
- Subjects: Heat stress physiology , Small mammal thermoregulation -- South Africa , Climate change - Wet-bulb temperature
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/60873 , vital:68916
- Description: As the Anthropocene continues to be characterised by ever rising temperature highs, increasingly sporadic and extreme climatic events, and their accompanying mass mortality events, climate scientists now warn that the continued climate destabilisation may for the first time in recorded history prevent terrestrial homeothermic endotherms from being able to thermoregulate. Having evolved to maintain body temperatures (Tbs) well above their ambient (Ta) conditions, these endotherms have evolved a suite of adaptations to a colder environment to allow for homeothermic thermoregulation to occur. However, by the same vein, having evolved in a colder climate to stay warm also has led to a reduced capacity to prevent heat stress when temperature conditions are elevated. In absence of behavioural counter measures, the only physiological means available to thermoregulation to prevent such heat stress is that of evaporative water loss (EWL). If still inefficient, the endotherm will risk becoming hyperthermic. Literature has established that excessive heat exposure or reduced evaporative cooling capacities strain or retard thermoregulatory processes. If an endotherm experiences severe heat exposure, the rate at which passive heating is experienced will increase. Should an endotherm be in a humid environment, evaporative cooling efficiency is reduced. As a result, these two abiotic factors are therefore known to contribute towards heat storage, and therefore thermal stress. However, should both factors occur in the same environment, the heat stress effects are compounded, creating an environment dangerous for thermoregulating endotherms. For this reason, authors have emphasised that future wet-bulb (Tw) conditions may pose a penultimate threat to thermoregulating endotherms. Being a measure of coldest temperature attainable as a result of evaporative cooling, Tw has been proposed to represent a lower temperature thermal limit to endothermic thermoregulation. Once reaching a 2°C differential below an endotherms Tb (Tb – Tw = 2˚C), Tw is believed to impede the evaporative cooling process and, consequentially, commit endotherms to becoming hyperthermic. Considering that most mammals defend constant Tbs within the range of predicted Tw maxima increases that future Tw conditions may pose a significant threat to mammalian thermoregulation. However, to date, despite being well supported in the literature, ii empirical investigations into how extreme Tw conditions will affect endothermic thermoregulation are scant. Therefore, understanding of the proposed inhibitory nature of extreme Tw conditions is lacking. Considering that such conditions are to have a profound effect of endothermic survival, this dearth in understanding could prove fatal. As such, this thesis sought to provide evidence on how extreme Tw conditions may affect thermoregulatory processes in homeothermic endotherms. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2023
- Full Text:
- Date Issued: 2023-04
Isolation, characterization and functionalization of cellulose fibres derived from the waste pineapple leaf fibres by hydrolysis to produce cellulose acetate
- Authors: Seyisi, Thulethu
- Date: 2023-04
- Subjects: Nonwoven fabrics -- Technological innovations , Pineapple fiber -- South Africa , Fibrous composites
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61248 , vital:69844
- Description: This thesis forms part of the Nelson Mandela University biomass and nanotechnology project, which aims at using agricultural waste for many applications, including biomedical applications, water treatment, and agricultural films. Pineapple leaf fiber (PALF) is one of the natural fibers with the highest cellulose content (about 80%), and they produce about 2.5–3.3% of the weight of green leaves. However, the other parts of the pineapple fruit, such as the leaves and crown, are still treated as waste due to a lack of understanding of the benefits and risks of these parts of the pineapple fruit. The transformation of PALF as a renewable and abundantly available natural residue into cellulose fibers (CFs) will reduce the waste accumulated in the atmosphere, and it will add value to the cultivation of pineapple. In the biomedical industry, CF is very promising in terms of drug delivery. Cellulose acetate is a remarkable biomaterial extensively used in biomedical applications due to its properties such as being non-toxic, non-irritant, biodegradable, heat resistant, and less hygroscopic. In this research, the isolation, functionalization, and characterization of cellulose from PALFs were conducted. The PALFs were dried and ground into small particles before being alkali treated with sodium hydroxide to remove the non-cellulosic components. Moreover, the remaining lignin in the residue was removed using sodium chlorite and acetic acid; this process is known as the bleaching process. The bleaching process resulted in white CFs, which was an indication of the successful removal of the non-cellulosic material. The obtained CFs were further functionalized using acetic acid, acetic anhydride, and sulfuric acid, and this reaction is known as the acetylation reaction. Subsequently, both treated, untreated, and functionalized CFs were characterised using the following instruments: FTIR, SEM, SPM, TGA, XRD, and XPS. In the FTIR data of raw PALFs, the following functional groups were more pronounced: C-O, C=C-O, and C=O, whereas peak C-O-C disappeared and peak CH2, C-O, were less pronounced. These FTIR results confirmed the successful removal of non-cellulosic components. The SEM and SPM images visually suggested the partial removal of hemicellulose and lignin from the raw PALFs after the chemical treatment, which are the cementing materials around the fiber bundles. The TGA studies revealed good thermal stability for the isolated CFs from PALFs. The XRD diffractograms of the PALFs showed a cellulose I crystal pattern where the peaks were located at angular positions (2θ) of around 18°, 26°, and 41°. Lastly, after the functionalization of CFs, the cellulose structure remained intact (not damaged); instead, the newly ix introduced functional groups (the acetyl group) were attached at the ends of the cellulose structure. These results are therefore confirmation of the successful removal of non-cellulose material from the PALFs after the chemical treatment. , Thesis (MSc) -- Faculty of Science, School of Natural Resource Science and Management, 2023
- Full Text:
- Date Issued: 2023-04
- Authors: Seyisi, Thulethu
- Date: 2023-04
- Subjects: Nonwoven fabrics -- Technological innovations , Pineapple fiber -- South Africa , Fibrous composites
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61248 , vital:69844
- Description: This thesis forms part of the Nelson Mandela University biomass and nanotechnology project, which aims at using agricultural waste for many applications, including biomedical applications, water treatment, and agricultural films. Pineapple leaf fiber (PALF) is one of the natural fibers with the highest cellulose content (about 80%), and they produce about 2.5–3.3% of the weight of green leaves. However, the other parts of the pineapple fruit, such as the leaves and crown, are still treated as waste due to a lack of understanding of the benefits and risks of these parts of the pineapple fruit. The transformation of PALF as a renewable and abundantly available natural residue into cellulose fibers (CFs) will reduce the waste accumulated in the atmosphere, and it will add value to the cultivation of pineapple. In the biomedical industry, CF is very promising in terms of drug delivery. Cellulose acetate is a remarkable biomaterial extensively used in biomedical applications due to its properties such as being non-toxic, non-irritant, biodegradable, heat resistant, and less hygroscopic. In this research, the isolation, functionalization, and characterization of cellulose from PALFs were conducted. The PALFs were dried and ground into small particles before being alkali treated with sodium hydroxide to remove the non-cellulosic components. Moreover, the remaining lignin in the residue was removed using sodium chlorite and acetic acid; this process is known as the bleaching process. The bleaching process resulted in white CFs, which was an indication of the successful removal of the non-cellulosic material. The obtained CFs were further functionalized using acetic acid, acetic anhydride, and sulfuric acid, and this reaction is known as the acetylation reaction. Subsequently, both treated, untreated, and functionalized CFs were characterised using the following instruments: FTIR, SEM, SPM, TGA, XRD, and XPS. In the FTIR data of raw PALFs, the following functional groups were more pronounced: C-O, C=C-O, and C=O, whereas peak C-O-C disappeared and peak CH2, C-O, were less pronounced. These FTIR results confirmed the successful removal of non-cellulosic components. The SEM and SPM images visually suggested the partial removal of hemicellulose and lignin from the raw PALFs after the chemical treatment, which are the cementing materials around the fiber bundles. The TGA studies revealed good thermal stability for the isolated CFs from PALFs. The XRD diffractograms of the PALFs showed a cellulose I crystal pattern where the peaks were located at angular positions (2θ) of around 18°, 26°, and 41°. Lastly, after the functionalization of CFs, the cellulose structure remained intact (not damaged); instead, the newly ix introduced functional groups (the acetyl group) were attached at the ends of the cellulose structure. These results are therefore confirmation of the successful removal of non-cellulose material from the PALFs after the chemical treatment. , Thesis (MSc) -- Faculty of Science, School of Natural Resource Science and Management, 2023
- Full Text:
- Date Issued: 2023-04
Microstructural based creep life assessment of 1CrMov Turbine rotor steels after long-term service
- Nyembe, Hlanganani Siphelele
- Authors: Nyembe, Hlanganani Siphelele
- Date: 2023-04
- Subjects: Materials – Creep –South Africa , Steel -- Creep
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/61380 , vital:70622
- Description: Creep-resistant 1CrMoV steels are used for high-pressure turbine rotors in fossil fuel power stations operating at steam temperatures up to 565 °C in the creep regime. The upper bainitic microstructure of 1CrMoV rotors changes when exposed to high temperature service over long periods. The aim of this study was to relate these microstructural changes for service exposed 1CrMoV rotor steels to the remaining creep life as determined using existing methods. Analytical electron microscopy was used to quantitatively study the microstructural evolution of service-exposed 1CrMoV steel rotors. 1CrMoV rotor steel samples were characterised in the initial state, and three long-term (272 h to 300 kh) service exposed states. Detailed microstructural investigations were conducted to analyse the cavities; bainitic laths and packets; dislocations; carbide phases and their size, population, composition. The creep life fractions were estimated using conventional life assessment methods based on creep cavitation and hardness. The creep life fraction consumed of the rotors, estimated based on the creep cavities and hardness data, ranged from ~0.5 to 1. Electron backscattered diffraction (EBSD) was used to analyse the bainitic packets, laths, misorientations, and dislocations, which showed that the bainitic lath surface area to volume (SV) correlated with service time. The precipitates were extracted from the Fe-matrix using extraction replication and were further investigated using transmission Kikuchi diffraction (TKD), scanning transmission electron microscopy (STEM), selected area electron diffraction (SAED), and energy dispersive spectroscopy (EDS). STEM-EDS and TKD identified M3C, MC, M2C, M7C3, and M23C6 (M = Fe, Cr, Mo, V, Mn) in the 1CrMoV steels. STEM-EDS measurements revealed that Fe/Cr ratios in M3C decreased from 4.5 (initial state) to 2.5 (>272 kh). The Fe/Cr and Fe/Mo ratios in overall carbides decreased from 5 and 10 (initial state) to 1 and 2 (>272 kh), respectively. The TKD analysis indicated that the relative phase proportion of M2C and M7C3 carbides, relative to the total extracted carbides, is positively correlated with service exposure. These microstructural features correlate with the creep life fraction consumed and could potentially be used as another indicator of the remnant creep life. , Thesis (PhD) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics. 2023
- Full Text:
- Date Issued: 2023-04
- Authors: Nyembe, Hlanganani Siphelele
- Date: 2023-04
- Subjects: Materials – Creep –South Africa , Steel -- Creep
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/61380 , vital:70622
- Description: Creep-resistant 1CrMoV steels are used for high-pressure turbine rotors in fossil fuel power stations operating at steam temperatures up to 565 °C in the creep regime. The upper bainitic microstructure of 1CrMoV rotors changes when exposed to high temperature service over long periods. The aim of this study was to relate these microstructural changes for service exposed 1CrMoV rotor steels to the remaining creep life as determined using existing methods. Analytical electron microscopy was used to quantitatively study the microstructural evolution of service-exposed 1CrMoV steel rotors. 1CrMoV rotor steel samples were characterised in the initial state, and three long-term (272 h to 300 kh) service exposed states. Detailed microstructural investigations were conducted to analyse the cavities; bainitic laths and packets; dislocations; carbide phases and their size, population, composition. The creep life fractions were estimated using conventional life assessment methods based on creep cavitation and hardness. The creep life fraction consumed of the rotors, estimated based on the creep cavities and hardness data, ranged from ~0.5 to 1. Electron backscattered diffraction (EBSD) was used to analyse the bainitic packets, laths, misorientations, and dislocations, which showed that the bainitic lath surface area to volume (SV) correlated with service time. The precipitates were extracted from the Fe-matrix using extraction replication and were further investigated using transmission Kikuchi diffraction (TKD), scanning transmission electron microscopy (STEM), selected area electron diffraction (SAED), and energy dispersive spectroscopy (EDS). STEM-EDS and TKD identified M3C, MC, M2C, M7C3, and M23C6 (M = Fe, Cr, Mo, V, Mn) in the 1CrMoV steels. STEM-EDS measurements revealed that Fe/Cr ratios in M3C decreased from 4.5 (initial state) to 2.5 (>272 kh). The Fe/Cr and Fe/Mo ratios in overall carbides decreased from 5 and 10 (initial state) to 1 and 2 (>272 kh), respectively. The TKD analysis indicated that the relative phase proportion of M2C and M7C3 carbides, relative to the total extracted carbides, is positively correlated with service exposure. These microstructural features correlate with the creep life fraction consumed and could potentially be used as another indicator of the remnant creep life. , Thesis (PhD) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics. 2023
- Full Text:
- Date Issued: 2023-04
Modelling the dynamics of Breast Cancer disease with hormone therapy and surgery controls
- Ngalo, Akhona Sunshine, Mbava,Willard
- Authors: Ngalo, Akhona Sunshine , Mbava,Willard
- Date: 2023-04
- Subjects: Cancer -- Molecular aspects , Breast cancer -- South Africa , Hormone therapy
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61487 , vital:70688
- Description: In this study, we discussed a mathematical model that incorporates important interactions between normal cells, tumor cells, immune cells, and estrogen. The mathematical model was revised to include two control measures; namely surgery and hormone therapy to minimize the number of tumor cells. The model was mathematically analyzed with the premise that the two control measures are positive constants. Locally and globally analyses were performed using a variety of analytical methods to investigate the stability of the breast cancer model. Furthermore, an optimal control problem was formulated and used to determine the best strategy for reducing the number of tumor cells by incorporating hormone therapy and surgery, based on the well-known Pontryagin’s Maximum Principle. The numerical results indicates combining both optimal control measures (surgery and hormone therapy) simultaneously is more efficacious than using single control measure separately in decreasing the number of tumor cells. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2023
- Full Text:
- Date Issued: 2023-04
- Authors: Ngalo, Akhona Sunshine , Mbava,Willard
- Date: 2023-04
- Subjects: Cancer -- Molecular aspects , Breast cancer -- South Africa , Hormone therapy
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/61487 , vital:70688
- Description: In this study, we discussed a mathematical model that incorporates important interactions between normal cells, tumor cells, immune cells, and estrogen. The mathematical model was revised to include two control measures; namely surgery and hormone therapy to minimize the number of tumor cells. The model was mathematically analyzed with the premise that the two control measures are positive constants. Locally and globally analyses were performed using a variety of analytical methods to investigate the stability of the breast cancer model. Furthermore, an optimal control problem was formulated and used to determine the best strategy for reducing the number of tumor cells by incorporating hormone therapy and surgery, based on the well-known Pontryagin’s Maximum Principle. The numerical results indicates combining both optimal control measures (surgery and hormone therapy) simultaneously is more efficacious than using single control measure separately in decreasing the number of tumor cells. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2023
- Full Text:
- Date Issued: 2023-04