Antecedents and outcomes of service encounters in the restaurant industry in Zimbabwe
- Authors: Mukucha, Paul
- Date: 2018
- Subjects: Consumer behavior , Hospitality industry -- Zimbabwe -- Management Management -- Zimbabwe
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/32949 , vital:32479
- Description: This study aimed to determine the antecedents and outcomes of service encounter experiences of patrons in the restaurant industry in Zimbabwe. In addition, the study aimed to test the strength of the relationships between service encounter experiences and the selected antecedents, and outcomes. Service encounter experiences were investigated to contribute to the success of restaurants in Zimbabwe. The study presented literature on the restaurant industry in Zimbabwe. The literature explored the types of restaurant businesses that are operating in Zimbabwe, the contribution of the restaurant industry to the national economy, the attractiveness of the restaurant industry and the market structure of the restaurant industry. The literature also revealed that the restaurant industry immensely contributes to the national economy of Zimbabwe through employment creation and statutory payments. It was further revealed that the restaurant industry in Zimbabwe is attractive because there are little entry and exit barriers, and there is some degree of differentiation of service delivery. The contemporary issues that affect the restaurant industry in Zimbabwe cut across several macro business factors, and were identified as political, economic, social, technological, legal and environmental factors. Theories and literature were considered, and the study extensively presented content related to the postulated relationships among the study’s variables, namely the specified antecedents of service encounter experiences which are the variables service contact levels, ambience factors, service delivery quality, and typology of patrons; and the selected outcomes of service encounter experiences, namely patronage retention, re-patronage retention, and patronage loyalty. A synthesis of how all the study constructs are interrelated, culminating with the proposed conceptual model, were presented. The proposed conceptual model that captures service encounter experiences and its possible antecedents and outcomes, depicted a series of hypotheses. The hypotheses presented were developed by using extant theoretical and empirical literature. The study further presented the research methodology, and the results of this study. This explanatory study followed a quantitative survey research design and 400 restaurant patrons in Zimbabwe were respondents to the study’s questionnaire. Descriptive statistics were calculated. In addition, using exploratory factor analyses results, the conceptual framework was updated, and further inferential statistics were computed. These statistics included a reliability analysis, correlation analysis and regression analyses to statistically test the proposed relationships. The empirical results revealed that all the postulated independent variables, except the variable service contact levels, are positively and significantly related to the patrons’ service encounter experiences. Furthermore, the study revealed that the patrons’ service encounter experiences significantly influence two specified dependent variables namely re-patronage intention and patronage loyalty. Patronage retention, which was one of the hypothesised outcomes of service encounter experiences, was eliminated from the proposed conceptual model during the measurement scale validation phase as almost all of its items loaded onto the patronage loyalty factor. This suggested the absence of a conceptual distinction between patronage retention and patronage loyalty. The study concluded that the levels of the patrons’ service encounter experiences in the restaurant industry in Zimbabwe are high as a result of higher levels of the postulated antecedents such as ambience factors, service delivery quality and typology of patrons. However, the levels of contact in restaurants did not have any significant impact on the patrons’ service encounter experiences. The study also concluded that eliciting pleasant service encounter experiences generates higher levels of re-patronage retention and patronage loyalty. The conclusions generated in this study subsequently led to a number of recommendations for restaurants in Zimbabwe. The study also contributed by either closing or clarifying many research gaps as well as by developing a hypothetical model and measuring instrument. This study was the first to show how ambience factors, service quality delivery and the typology of patrons, based on their personality traits, could positively influence the service encounter experiences of Zimbabwean restaurants’ patrons. Furthermore, the study confirms that in the restaurant industry, the patronage retention construct is conceptually the same as the patronage loyalty construct. Moreover, restaurant businesses must exploit the differences in their patrons’ dispositions in order to enhance service encounter experiences through providing differentiated service offerings.
- Full Text:
- Date Issued: 2018
- Authors: Mukucha, Paul
- Date: 2018
- Subjects: Consumer behavior , Hospitality industry -- Zimbabwe -- Management Management -- Zimbabwe
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/32949 , vital:32479
- Description: This study aimed to determine the antecedents and outcomes of service encounter experiences of patrons in the restaurant industry in Zimbabwe. In addition, the study aimed to test the strength of the relationships between service encounter experiences and the selected antecedents, and outcomes. Service encounter experiences were investigated to contribute to the success of restaurants in Zimbabwe. The study presented literature on the restaurant industry in Zimbabwe. The literature explored the types of restaurant businesses that are operating in Zimbabwe, the contribution of the restaurant industry to the national economy, the attractiveness of the restaurant industry and the market structure of the restaurant industry. The literature also revealed that the restaurant industry immensely contributes to the national economy of Zimbabwe through employment creation and statutory payments. It was further revealed that the restaurant industry in Zimbabwe is attractive because there are little entry and exit barriers, and there is some degree of differentiation of service delivery. The contemporary issues that affect the restaurant industry in Zimbabwe cut across several macro business factors, and were identified as political, economic, social, technological, legal and environmental factors. Theories and literature were considered, and the study extensively presented content related to the postulated relationships among the study’s variables, namely the specified antecedents of service encounter experiences which are the variables service contact levels, ambience factors, service delivery quality, and typology of patrons; and the selected outcomes of service encounter experiences, namely patronage retention, re-patronage retention, and patronage loyalty. A synthesis of how all the study constructs are interrelated, culminating with the proposed conceptual model, were presented. The proposed conceptual model that captures service encounter experiences and its possible antecedents and outcomes, depicted a series of hypotheses. The hypotheses presented were developed by using extant theoretical and empirical literature. The study further presented the research methodology, and the results of this study. This explanatory study followed a quantitative survey research design and 400 restaurant patrons in Zimbabwe were respondents to the study’s questionnaire. Descriptive statistics were calculated. In addition, using exploratory factor analyses results, the conceptual framework was updated, and further inferential statistics were computed. These statistics included a reliability analysis, correlation analysis and regression analyses to statistically test the proposed relationships. The empirical results revealed that all the postulated independent variables, except the variable service contact levels, are positively and significantly related to the patrons’ service encounter experiences. Furthermore, the study revealed that the patrons’ service encounter experiences significantly influence two specified dependent variables namely re-patronage intention and patronage loyalty. Patronage retention, which was one of the hypothesised outcomes of service encounter experiences, was eliminated from the proposed conceptual model during the measurement scale validation phase as almost all of its items loaded onto the patronage loyalty factor. This suggested the absence of a conceptual distinction between patronage retention and patronage loyalty. The study concluded that the levels of the patrons’ service encounter experiences in the restaurant industry in Zimbabwe are high as a result of higher levels of the postulated antecedents such as ambience factors, service delivery quality and typology of patrons. However, the levels of contact in restaurants did not have any significant impact on the patrons’ service encounter experiences. The study also concluded that eliciting pleasant service encounter experiences generates higher levels of re-patronage retention and patronage loyalty. The conclusions generated in this study subsequently led to a number of recommendations for restaurants in Zimbabwe. The study also contributed by either closing or clarifying many research gaps as well as by developing a hypothetical model and measuring instrument. This study was the first to show how ambience factors, service quality delivery and the typology of patrons, based on their personality traits, could positively influence the service encounter experiences of Zimbabwean restaurants’ patrons. Furthermore, the study confirms that in the restaurant industry, the patronage retention construct is conceptually the same as the patronage loyalty construct. Moreover, restaurant businesses must exploit the differences in their patrons’ dispositions in order to enhance service encounter experiences through providing differentiated service offerings.
- Full Text:
- Date Issued: 2018
AP-MOVPE growth and characterisation of GaSb/GaAs quantum dots
- Authors: Tile, Ngcali
- Date: 2018
- Subjects: Quantum theory , Quantum electronics Quantum dots Semiconductors
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/36716 , vital:34047
- Description: GaSb/GaAs quantum dots (QD) were grown by atmospheric pressure (AP) metal-organic vapour phase epitaxy (MOVPE) using triethylgallium (TEGa), tertiarybutylarsine (tBAs) and trimethylantimony (TMSb) as gallium (Ga), arsenic (As) and (Sb) sources, respectively. The effect of AP-MOVPE growth parameters on the formation of GaSb QD structures on GaAs was studied. The formation of small, coherent GaSb dots on GaAs improved with decreasing V/III ratios, which were controlled through changing either the TMSb/TEGa ratio at a constant growth temperature or changing the growth temperature at a constant TMSb/TEGa ratio. The maximum effective V/III ratio for dot formation was 0.175. The dot density was more sensitive to growth time than to source mole fraction in the reactor, since time determines the amount of deposited material. The dot density increased with increasing growth time, while the shape and size of the dots were more sensitive to the source vapour mole fraction, which controls the growth rate. Lower mole fractions resulted in smaller sized dots with a more uniform distribution compared to higher mole fractions. Dome-shaped dots with densities as high as 4×1010 cm-2, average base length of 35 nm and average height of 5 nm were achieved. Capping of GaSb QDs at high temperatures caused flattening and the formation of a thin, inhomogeneous GaSb layer inside GaAs. No obvious QD photoluminescence (PL) peak was detected for these samples. A two stage process for capping the dots (involving growth of a low temperature GaAs cap, followed by a high temperature cap) led to the retention of the dot-like features in/on a wetting layer (WL) of GaSb and distinct PL peaks for both the QDs and WL. An increase in excitation power during PL measurements for this particular sample caused the QD and WL peaks to shift to higher energies. This is attributed to electrostatic band bending, leading to triangular potential wells, typical for type II band alignment between GaAs and strained GaSb. Variable temperature PL measurements showed the decrease in the intensity of the WL peak to be faster than that of the QD peak as the measurement temperature increased. A detailed high resolution transmission electron microscopy analysis was performed to study the morphology and chemical interaction between GaAs and GaSb regions for capped GaSb/GaAs QDs. The capped dots had dimensions similar to those of uncapped dots and had a higher concentration of Sb at their center, with the periphery being intermixed with GaAs. Measurement of lattice strain performed inside these dots revealed the strain to be distributed inhomogenously throughout the dot area. The effect of GaAs host matrix on excitonic behaviour in AP-MOVPE grown GaSb/GaAs quantum dots was investigated. Room temperature (RT) PL emission was achieved from a single layer of quantum dots by controlling the GaAs host matrix growth temperature. These samples were prepared using a GaSb dot growth temperature of 530 °C, followed by growth of a thin GaAs ‘cold’ cap, before depositing the final part of the GaAs capping layer at either 550 °C, 600 °C or 650 °C. PL measurements at 10 K revealed QD emission peaks for all the samples at around 1.1 eV. However, variable temperature PL revealed different thermal quenching rates of the emission, with the rates of quenching reduced with increasing GaAs growth temperature. This was ascribed to reduced defect densities in GaAs grown at higher temperature, which resulted in QD emission even at RT. This RT emission peaked at approximately 1 eV. The hole localisation energy determined for these samples at RT was approximately 470 meV.
- Full Text:
- Date Issued: 2018
- Authors: Tile, Ngcali
- Date: 2018
- Subjects: Quantum theory , Quantum electronics Quantum dots Semiconductors
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/36716 , vital:34047
- Description: GaSb/GaAs quantum dots (QD) were grown by atmospheric pressure (AP) metal-organic vapour phase epitaxy (MOVPE) using triethylgallium (TEGa), tertiarybutylarsine (tBAs) and trimethylantimony (TMSb) as gallium (Ga), arsenic (As) and (Sb) sources, respectively. The effect of AP-MOVPE growth parameters on the formation of GaSb QD structures on GaAs was studied. The formation of small, coherent GaSb dots on GaAs improved with decreasing V/III ratios, which were controlled through changing either the TMSb/TEGa ratio at a constant growth temperature or changing the growth temperature at a constant TMSb/TEGa ratio. The maximum effective V/III ratio for dot formation was 0.175. The dot density was more sensitive to growth time than to source mole fraction in the reactor, since time determines the amount of deposited material. The dot density increased with increasing growth time, while the shape and size of the dots were more sensitive to the source vapour mole fraction, which controls the growth rate. Lower mole fractions resulted in smaller sized dots with a more uniform distribution compared to higher mole fractions. Dome-shaped dots with densities as high as 4×1010 cm-2, average base length of 35 nm and average height of 5 nm were achieved. Capping of GaSb QDs at high temperatures caused flattening and the formation of a thin, inhomogeneous GaSb layer inside GaAs. No obvious QD photoluminescence (PL) peak was detected for these samples. A two stage process for capping the dots (involving growth of a low temperature GaAs cap, followed by a high temperature cap) led to the retention of the dot-like features in/on a wetting layer (WL) of GaSb and distinct PL peaks for both the QDs and WL. An increase in excitation power during PL measurements for this particular sample caused the QD and WL peaks to shift to higher energies. This is attributed to electrostatic band bending, leading to triangular potential wells, typical for type II band alignment between GaAs and strained GaSb. Variable temperature PL measurements showed the decrease in the intensity of the WL peak to be faster than that of the QD peak as the measurement temperature increased. A detailed high resolution transmission electron microscopy analysis was performed to study the morphology and chemical interaction between GaAs and GaSb regions for capped GaSb/GaAs QDs. The capped dots had dimensions similar to those of uncapped dots and had a higher concentration of Sb at their center, with the periphery being intermixed with GaAs. Measurement of lattice strain performed inside these dots revealed the strain to be distributed inhomogenously throughout the dot area. The effect of GaAs host matrix on excitonic behaviour in AP-MOVPE grown GaSb/GaAs quantum dots was investigated. Room temperature (RT) PL emission was achieved from a single layer of quantum dots by controlling the GaAs host matrix growth temperature. These samples were prepared using a GaSb dot growth temperature of 530 °C, followed by growth of a thin GaAs ‘cold’ cap, before depositing the final part of the GaAs capping layer at either 550 °C, 600 °C or 650 °C. PL measurements at 10 K revealed QD emission peaks for all the samples at around 1.1 eV. However, variable temperature PL revealed different thermal quenching rates of the emission, with the rates of quenching reduced with increasing GaAs growth temperature. This was ascribed to reduced defect densities in GaAs grown at higher temperature, which resulted in QD emission even at RT. This RT emission peaked at approximately 1 eV. The hole localisation energy determined for these samples at RT was approximately 470 meV.
- Full Text:
- Date Issued: 2018
Beneficiary perceptions regarding farm worker equity share schemes in South Africa
- Authors: Xolo, Siyavuya Nicholas
- Date: 2018
- Subjects: Investments -- South Africa , Investment analysis Land reform -- South Africa Agricultural laborers -- South Africa
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/36323 , vital:33920
- Description: The study aimed to assess beneficiary perceptions regarding farm worker equity share schemes in South Africa. Farm worker equity share schemes started in the early 1990s with the aim of having a special arrangement pertaining to the ownership and operation of a farm between the farmer and the farm workers. This was intended to assist farm workers in not only remaining as farm workers but also to gain ownership of the farm. This could lead to the empowerment of farm workers, better working conditions, improved living standards and their rights to land ownership. Farm worker equity share schemes have been widely reported as having failed to meet their intended objectives, thus, in 2009, the Department of Rural Development and Land Reform initiated a study to assess the implementation of equity share schemes. Although the report was not made public, it reports that out of the 88 equity share schemes at the time, only nine managed to pay dividends ranging from R200 to R2000 per year. As a result, the Department of Rural Development and Land Reform put a moratorium on equity share schemes; this was however removed in 2011. It is against this background that this study was undertaken to assess beneficiaries’ perceptions regarding farm worker equity share schemes in South Africa. A positivistic research paradigm was employed in this study, by means of quantitative research. Secondary data in the form of textbooks, journal articles and Internet sources provided the theoretical framework for this study. Primary data was obtained using the survey method, by means of self-administered structured questionnaires. Convenience and purposive sampling were applied in order to select 20 farms that use equity share schemes. The farms selected for this study were located in the Eastern Cape, Gauteng, Mpumalanga and the Western Cape provinces, covering a variety of farming activities such as citrus fruits, crops, vegetables and wineries. Ideally, a total of 15 farm workers per farm were targeted. However, due to a variation in these farm worker equity share schemes, on some farms less than 15 workers and in others more than 15 workers were selected for the study; this resulted in a total sample size of 341 farm workers. Ten null-hypotheses and a hypothetical model of beneficiary perceptions regarding farm worker equity share schemes were tested. The influence of seven independent variables were tested, these are: stakeholder trust, operational risks, government interventions, two-way communication, farm worker empowerment, training and skills development, and access to resources on farm worker equity share schemes. In addition, the influence of farm worker equity share schemes on three dependent variables, namely, farming performance, sustainability and employee expectations were tested. The Statistica (version 13.2) computer programme was used to analyse the results by means of advanced statistical techniques (such as exploratory factor analysis, regression and correlation analyses) as well as descriptive analysis and frequency distributions. After various statistical procedures, the model was re-specified; some of the variables were then renamed and the hypotheses were adjusted accordingly. The empirical results showed that three key variables to the success of farm worker equity share schemes are stakeholder trust, government interventions and farm owner support. It was determined that these key variables could lead to increased farming performance, farming sustainability and meeting employee expectations. This study provided useful and practical guidelines to farm owners and administrators of equity share schemes, so as to ensure effective strategising that could enhance their competitiveness and long term survival. The findings of this study could inform strategy policy formulation and implementation in the agricultural sector, as pertaining to farm worker equity share schemes. The study used a sound and well-developed research design and methodology, which has been justified and successfully applied to this research; this method can be utilised by other similar studies to conduct empirical research in the field of farm worker equity share schemes. It is envisaged that the results and recommendations of this study could be used to implement effective strategies that could ensure the effective functioning of farm worker equity share schemes in South Africa.
- Full Text:
- Date Issued: 2018
- Authors: Xolo, Siyavuya Nicholas
- Date: 2018
- Subjects: Investments -- South Africa , Investment analysis Land reform -- South Africa Agricultural laborers -- South Africa
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/36323 , vital:33920
- Description: The study aimed to assess beneficiary perceptions regarding farm worker equity share schemes in South Africa. Farm worker equity share schemes started in the early 1990s with the aim of having a special arrangement pertaining to the ownership and operation of a farm between the farmer and the farm workers. This was intended to assist farm workers in not only remaining as farm workers but also to gain ownership of the farm. This could lead to the empowerment of farm workers, better working conditions, improved living standards and their rights to land ownership. Farm worker equity share schemes have been widely reported as having failed to meet their intended objectives, thus, in 2009, the Department of Rural Development and Land Reform initiated a study to assess the implementation of equity share schemes. Although the report was not made public, it reports that out of the 88 equity share schemes at the time, only nine managed to pay dividends ranging from R200 to R2000 per year. As a result, the Department of Rural Development and Land Reform put a moratorium on equity share schemes; this was however removed in 2011. It is against this background that this study was undertaken to assess beneficiaries’ perceptions regarding farm worker equity share schemes in South Africa. A positivistic research paradigm was employed in this study, by means of quantitative research. Secondary data in the form of textbooks, journal articles and Internet sources provided the theoretical framework for this study. Primary data was obtained using the survey method, by means of self-administered structured questionnaires. Convenience and purposive sampling were applied in order to select 20 farms that use equity share schemes. The farms selected for this study were located in the Eastern Cape, Gauteng, Mpumalanga and the Western Cape provinces, covering a variety of farming activities such as citrus fruits, crops, vegetables and wineries. Ideally, a total of 15 farm workers per farm were targeted. However, due to a variation in these farm worker equity share schemes, on some farms less than 15 workers and in others more than 15 workers were selected for the study; this resulted in a total sample size of 341 farm workers. Ten null-hypotheses and a hypothetical model of beneficiary perceptions regarding farm worker equity share schemes were tested. The influence of seven independent variables were tested, these are: stakeholder trust, operational risks, government interventions, two-way communication, farm worker empowerment, training and skills development, and access to resources on farm worker equity share schemes. In addition, the influence of farm worker equity share schemes on three dependent variables, namely, farming performance, sustainability and employee expectations were tested. The Statistica (version 13.2) computer programme was used to analyse the results by means of advanced statistical techniques (such as exploratory factor analysis, regression and correlation analyses) as well as descriptive analysis and frequency distributions. After various statistical procedures, the model was re-specified; some of the variables were then renamed and the hypotheses were adjusted accordingly. The empirical results showed that three key variables to the success of farm worker equity share schemes are stakeholder trust, government interventions and farm owner support. It was determined that these key variables could lead to increased farming performance, farming sustainability and meeting employee expectations. This study provided useful and practical guidelines to farm owners and administrators of equity share schemes, so as to ensure effective strategising that could enhance their competitiveness and long term survival. The findings of this study could inform strategy policy formulation and implementation in the agricultural sector, as pertaining to farm worker equity share schemes. The study used a sound and well-developed research design and methodology, which has been justified and successfully applied to this research; this method can be utilised by other similar studies to conduct empirical research in the field of farm worker equity share schemes. It is envisaged that the results and recommendations of this study could be used to implement effective strategies that could ensure the effective functioning of farm worker equity share schemes in South Africa.
- Full Text:
- Date Issued: 2018
Biological activities of tulbaghia violacea against cryptococcus species
- Authors: Mitradev, Pattoo
- Date: 2018
- Subjects: Violaceae -- Therapeutic use -- South Africa , Anticoagulants (Medicine) , Medicinal plants -- South Africa
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/32772 , vital:32357
- Description: Cryptococcus neoformans and Cryptococcus gattii, which are environmental yeasts, are the etiological agents of cryptococcosis in both immunocompromised and immunocompetent individuals, and account for high mortality and morbidity rates in sub-Saharan Africa. The current antifungal agents used for treatment of cryptococcal infections either target the fungal cell wall (β-(1,3) glucan and chitin) or cell membrane directly or ergosterol biosynthetic pathways or fungal DNA and RNA. Gaps in antifungal therapy include the unavailability and exhorbitant costs of these drugs especially to patients in the developing world. Drug resistance to conventional drugs is also an ever-increasing problem. It is therefore essential to find alternative natural compounds from medicinal plants that are safer, cheaper and more widely available. Tulbaghia violacea, also known as wild garlic, has been used as a traditional remedy in South Africa for the treatment of several ailments. Aqueous and organic extracts of the plant have been demonstrated to have antimicrobial and antifungal activity against several pathogens. However, there is a huge gap in our current knowledge in that the mechanism/s of action/s of these extracts have not been fully investigated. The focus of the current study therefore was to determine whether T. violacea extracts from the roots, rhizome, leaves and tubers exhibited antifungal activity against C. neoformans and C. gattii and to evaluate the ability of the rhizome extract to induce changes in key fungal virulence factors. Three mechanisms (ergosterol, β-(1,3) glucan and chitin production) regulating the antifungal activity of the rhizome extract were also examined. In the current study, phytochemical analysis of aqueous extracts of the roots, leaves, rhizomes and tubers showed that the rhizomes had the highest phenolic, saponin and tannin content when compared to the other plant organs. Fingerprinting by GC-MS revealed identical compounds in the different plant parts with the detection of 4 H Pyran-4-one DDMP (known antifungal), previously unreported in studies on T. violacea. The bulk of the extract comprised of 40% sulphur-containing and 20% furan-containing compounds. The remaining minor compounds comprised of 2x alcohols (13.3%), 1x pyran (6.7%), 1x ketone (6.7%), 1x halogen (6.7%) and 1x acid (6.7%) compounds. The rhizomes also had highest content of 2 methyl methioacetic acid, benzophenone and chloromethyl methylsulfide compared to the other plant parts. The rhizomes were found to be more potent against both pathogenic fungi tested here with an MIC and MFC of 1.25 mg/ml. Nystatin was included as a positive control when determining the MIC’s and MFC’s of the different plant extracts. The antifungal nature of the T. violacea extracts in the current study may be due to the synergistic effects of the sulphide, furan, pyran and ketone compounds present in the extracts, but this still remains to be verified in future studies. An investigation of the effects of an aqueous rhizome extract of T. violacea on Cryptococcus virulence factors showed that phospholipase activity of C. neoformans and C. gattii remained unaffected with increasing sub-lethal doses of the plant extract. There was significant reduction in urease production in both fungi in a dose dependent manner relative to the untreated cultures after 24 hr exposure to the extract. However, urease production reverted to normal after 48 hr post exposure implying that the cultures were able to recover due to temporary inhibition of urease activity. A significant decrease in melanin production was observed in both C. neoformans and C. gattii with increasing sub-inhibitory concentrations of the rhizome extract. Investigation of the effect of the plant extract on the ultrastucture of the fungi via Transmission Electron Microscopy showed the induction of cytomorphological changes in C. neoformans and C. gattii. Changes included thickening of the cell wall, an increase in the number of vacuoles, mitochondrial swelling and occasional detachment of the membrane from the cell wall. These changes suggest the activation of possible defence mechanisms to compensate for the loss of cellular materials or an effort to sequester toxic T. violacea components or toxic intermediates generated from inhibited cellular pathways. The capsule size and architecture remained unaltered in the presence of sub-lethal doses of the rhizome extract. To study the mechanism of action of the rhizome extract on ergosterol biosynthesis, total sterols were extracted and ergosterol, squalene, 2,3-oxidosqualene and lanosterol were quantified using Reverse Phase High Performance Liquid Chromatography. Ergosterol concentration declined in a dose dependent manner for both pathogenic yeasts similar to the positive control terbinafine, while there was a slight accumulation of squalene in C. gattii only. 2,3-oxidosqualene levels accumulated in both fungi relative to the untreated control. Lanosterol production showed an oscillatory trend for the two microorganisms. Together, these findings indicate that the rhizome extract is capable of inhibiting squalene epoxidase and 2,3-oxidosqualene/ lanosterol cyclase causing a decrease in ergosterol production.
- Full Text:
- Date Issued: 2018
- Authors: Mitradev, Pattoo
- Date: 2018
- Subjects: Violaceae -- Therapeutic use -- South Africa , Anticoagulants (Medicine) , Medicinal plants -- South Africa
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/32772 , vital:32357
- Description: Cryptococcus neoformans and Cryptococcus gattii, which are environmental yeasts, are the etiological agents of cryptococcosis in both immunocompromised and immunocompetent individuals, and account for high mortality and morbidity rates in sub-Saharan Africa. The current antifungal agents used for treatment of cryptococcal infections either target the fungal cell wall (β-(1,3) glucan and chitin) or cell membrane directly or ergosterol biosynthetic pathways or fungal DNA and RNA. Gaps in antifungal therapy include the unavailability and exhorbitant costs of these drugs especially to patients in the developing world. Drug resistance to conventional drugs is also an ever-increasing problem. It is therefore essential to find alternative natural compounds from medicinal plants that are safer, cheaper and more widely available. Tulbaghia violacea, also known as wild garlic, has been used as a traditional remedy in South Africa for the treatment of several ailments. Aqueous and organic extracts of the plant have been demonstrated to have antimicrobial and antifungal activity against several pathogens. However, there is a huge gap in our current knowledge in that the mechanism/s of action/s of these extracts have not been fully investigated. The focus of the current study therefore was to determine whether T. violacea extracts from the roots, rhizome, leaves and tubers exhibited antifungal activity against C. neoformans and C. gattii and to evaluate the ability of the rhizome extract to induce changes in key fungal virulence factors. Three mechanisms (ergosterol, β-(1,3) glucan and chitin production) regulating the antifungal activity of the rhizome extract were also examined. In the current study, phytochemical analysis of aqueous extracts of the roots, leaves, rhizomes and tubers showed that the rhizomes had the highest phenolic, saponin and tannin content when compared to the other plant organs. Fingerprinting by GC-MS revealed identical compounds in the different plant parts with the detection of 4 H Pyran-4-one DDMP (known antifungal), previously unreported in studies on T. violacea. The bulk of the extract comprised of 40% sulphur-containing and 20% furan-containing compounds. The remaining minor compounds comprised of 2x alcohols (13.3%), 1x pyran (6.7%), 1x ketone (6.7%), 1x halogen (6.7%) and 1x acid (6.7%) compounds. The rhizomes also had highest content of 2 methyl methioacetic acid, benzophenone and chloromethyl methylsulfide compared to the other plant parts. The rhizomes were found to be more potent against both pathogenic fungi tested here with an MIC and MFC of 1.25 mg/ml. Nystatin was included as a positive control when determining the MIC’s and MFC’s of the different plant extracts. The antifungal nature of the T. violacea extracts in the current study may be due to the synergistic effects of the sulphide, furan, pyran and ketone compounds present in the extracts, but this still remains to be verified in future studies. An investigation of the effects of an aqueous rhizome extract of T. violacea on Cryptococcus virulence factors showed that phospholipase activity of C. neoformans and C. gattii remained unaffected with increasing sub-lethal doses of the plant extract. There was significant reduction in urease production in both fungi in a dose dependent manner relative to the untreated cultures after 24 hr exposure to the extract. However, urease production reverted to normal after 48 hr post exposure implying that the cultures were able to recover due to temporary inhibition of urease activity. A significant decrease in melanin production was observed in both C. neoformans and C. gattii with increasing sub-inhibitory concentrations of the rhizome extract. Investigation of the effect of the plant extract on the ultrastucture of the fungi via Transmission Electron Microscopy showed the induction of cytomorphological changes in C. neoformans and C. gattii. Changes included thickening of the cell wall, an increase in the number of vacuoles, mitochondrial swelling and occasional detachment of the membrane from the cell wall. These changes suggest the activation of possible defence mechanisms to compensate for the loss of cellular materials or an effort to sequester toxic T. violacea components or toxic intermediates generated from inhibited cellular pathways. The capsule size and architecture remained unaltered in the presence of sub-lethal doses of the rhizome extract. To study the mechanism of action of the rhizome extract on ergosterol biosynthesis, total sterols were extracted and ergosterol, squalene, 2,3-oxidosqualene and lanosterol were quantified using Reverse Phase High Performance Liquid Chromatography. Ergosterol concentration declined in a dose dependent manner for both pathogenic yeasts similar to the positive control terbinafine, while there was a slight accumulation of squalene in C. gattii only. 2,3-oxidosqualene levels accumulated in both fungi relative to the untreated control. Lanosterol production showed an oscillatory trend for the two microorganisms. Together, these findings indicate that the rhizome extract is capable of inhibiting squalene epoxidase and 2,3-oxidosqualene/ lanosterol cyclase causing a decrease in ergosterol production.
- Full Text:
- Date Issued: 2018
Black South African men’s adjustment to divorce: a divorce-stress-adjustment model
- Muchena, Kudakwashe Christopher
- Authors: Muchena, Kudakwashe Christopher
- Date: 2018
- Subjects: Divorce -- Psychological aspects , Social psychology Men -- Psychology
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/50121 , vital:42048
- Description: The decision to divorce marks a turning point for each individual involved. It can be viewed as more than just a legal process. From a psychological perspective, it does not matter who initiated the divorce, it always comes with emotional ramifications for all those involved. Statistically there is a high rate of divorce in South Africa and there have been significant shifts in trends over time. However, black South African men’s experience of, action in, and adjustment to divorce has been relatively neglected in the divorce research, yet it is important for understanding contemporary social arrangements and processes, as well as for broadening the understanding of black South African men’s lives. How black South African men describe their situations and respond to marital dissolution may point to their positions in the gender-structured community and to how they interpret the nature of social practice, marriages, divorce and their position in society. The present study aimed at exploring black South African men’s experience of, and adjustment to, divorce. More specifically, the study developed a divorce-stress-adjustment model for divorced black South African men. The theoretical framework underpinning this study was that of Symbolic Interactionism that was complemented and enhanced by Erikson’s Psychosocial Theory, focusing specifically on identity development in adulthood. This was a qualitative study using an Interpretative Phenomenological Analysis (IPA) as both the research design and data analytic theory and process. The eight participants were volunteers who were recruited purposively. In accordance with IPA guidelines, data for the study was collected using biographical questionnaires and semi-structured interviews. The emerging themes were grouped into four superordinate themes, that is, pre-divorce experiences, experiencing divorce, adjustment process and post-divorce experience. Each superordinate theme had corresponding subordinate themes and subthemes. The themes were then used to develop the divorce-stress adjustment model indicating that the experience of divorce is an interconnected process. Weed’s recommendations for interpretative synthesis of interview data were used.
- Full Text:
- Date Issued: 2018
- Authors: Muchena, Kudakwashe Christopher
- Date: 2018
- Subjects: Divorce -- Psychological aspects , Social psychology Men -- Psychology
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/50121 , vital:42048
- Description: The decision to divorce marks a turning point for each individual involved. It can be viewed as more than just a legal process. From a psychological perspective, it does not matter who initiated the divorce, it always comes with emotional ramifications for all those involved. Statistically there is a high rate of divorce in South Africa and there have been significant shifts in trends over time. However, black South African men’s experience of, action in, and adjustment to divorce has been relatively neglected in the divorce research, yet it is important for understanding contemporary social arrangements and processes, as well as for broadening the understanding of black South African men’s lives. How black South African men describe their situations and respond to marital dissolution may point to their positions in the gender-structured community and to how they interpret the nature of social practice, marriages, divorce and their position in society. The present study aimed at exploring black South African men’s experience of, and adjustment to, divorce. More specifically, the study developed a divorce-stress-adjustment model for divorced black South African men. The theoretical framework underpinning this study was that of Symbolic Interactionism that was complemented and enhanced by Erikson’s Psychosocial Theory, focusing specifically on identity development in adulthood. This was a qualitative study using an Interpretative Phenomenological Analysis (IPA) as both the research design and data analytic theory and process. The eight participants were volunteers who were recruited purposively. In accordance with IPA guidelines, data for the study was collected using biographical questionnaires and semi-structured interviews. The emerging themes were grouped into four superordinate themes, that is, pre-divorce experiences, experiencing divorce, adjustment process and post-divorce experience. Each superordinate theme had corresponding subordinate themes and subthemes. The themes were then used to develop the divorce-stress adjustment model indicating that the experience of divorce is an interconnected process. Weed’s recommendations for interpretative synthesis of interview data were used.
- Full Text:
- Date Issued: 2018
Black South African men’s adjustment to divorce: a divorce-stress-adjustment model
- Muchena, Christopher Kudakwashe
- Authors: Muchena, Christopher Kudakwashe
- Date: 2018
- Subjects: Divorced men -- Psychological aspects , Adjustment (Psychology)
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/17933 , vital:28543
- Description: The decision to divorce marks a turning point for each individual involved. It can be viewed as more than just a legal process. From a psychological perspective, it does not matter who initiated the divorce, it always comes with emotional ramifications for all those involved. Statistically there is a high rate of divorce in South Africa and there have been significant shifts in trends over time. However, black South African men’s experience of, action in, and adjustment to divorce has been relatively neglected in the divorce research, yet it is important for understanding contemporary social arrangements and processes, as well as for broadening the understanding of black South African men’s lives. How black South African men describe their situations and respond to marital dissolution may point to their positions in the gender-structured community and to how they interpret the nature of social practice, marriages, divorce and their position in society. The present study aimed at exploring black South African men’s experience of, and adjustment to, divorce. More specifically, the study developed a divorce-stress-adjustment model for divorced black South African men. The theoretical framework underpinning this study was that of Symbolic Interactionism that was complemented and enhanced by Erikson’s Psychosocial Theory, focusing specifically on identity development in adulthood. This was a qualitative study using an Interpretative Phenomenological Analysis (IPA) as both the research design and data analytic theory and process. The eight participants were volunteers who were recruited purposively. In accordance with IPA guidelines, data for the study was collected using biographical questionnaires and semi-structured interviews. The emerging themes were grouped into four superordinate themes, that is, pre-divorce experiences, experiencing divorce, adjustment process and post-divorce experience. Each superordinate theme had corresponding subordinate themes and subthemes. The themes were then used to develop the divorce-stress-adjustment model indicating that the experience of divorce is an interconnected process. Weed’s recommendations for interpretative synthesis of interview data were used.
- Full Text:
- Date Issued: 2018
- Authors: Muchena, Christopher Kudakwashe
- Date: 2018
- Subjects: Divorced men -- Psychological aspects , Adjustment (Psychology)
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/17933 , vital:28543
- Description: The decision to divorce marks a turning point for each individual involved. It can be viewed as more than just a legal process. From a psychological perspective, it does not matter who initiated the divorce, it always comes with emotional ramifications for all those involved. Statistically there is a high rate of divorce in South Africa and there have been significant shifts in trends over time. However, black South African men’s experience of, action in, and adjustment to divorce has been relatively neglected in the divorce research, yet it is important for understanding contemporary social arrangements and processes, as well as for broadening the understanding of black South African men’s lives. How black South African men describe their situations and respond to marital dissolution may point to their positions in the gender-structured community and to how they interpret the nature of social practice, marriages, divorce and their position in society. The present study aimed at exploring black South African men’s experience of, and adjustment to, divorce. More specifically, the study developed a divorce-stress-adjustment model for divorced black South African men. The theoretical framework underpinning this study was that of Symbolic Interactionism that was complemented and enhanced by Erikson’s Psychosocial Theory, focusing specifically on identity development in adulthood. This was a qualitative study using an Interpretative Phenomenological Analysis (IPA) as both the research design and data analytic theory and process. The eight participants were volunteers who were recruited purposively. In accordance with IPA guidelines, data for the study was collected using biographical questionnaires and semi-structured interviews. The emerging themes were grouped into four superordinate themes, that is, pre-divorce experiences, experiencing divorce, adjustment process and post-divorce experience. Each superordinate theme had corresponding subordinate themes and subthemes. The themes were then used to develop the divorce-stress-adjustment model indicating that the experience of divorce is an interconnected process. Weed’s recommendations for interpretative synthesis of interview data were used.
- Full Text:
- Date Issued: 2018
Black women’s narratives of womanhood: before and after hysterectomy
- Kota-Nyati, Phumeza Patricia
- Authors: Kota-Nyati, Phumeza Patricia
- Date: 2018
- Subjects: Hysterectomy -- psychological aspects , Women -- psychological aspects Gender identity Intersectionality (Sociology)
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/29995 , vital:30807
- Description: The removal of the uterus, medically referred to as a hysterectomy, is a permanent and irreversible procedure that potentially results in a number of immediate and significant effects. Performing a hysterectomy is at times the only medical option to a long and traumatic history of pelvic pains and surgeries. The decision to undergo this very costly, painful, and life-changing procedure can have an influence on the way women view themselves. Women’s narratives of womanhood before and after hysterectomy need to be understood within the context of women’s socially constructed identities. Gendered identity has been closely linked to genital and/or reproductive organs and the removal of these organs may influence the way women and societies define womanhood.The interpretive paradigm of constructionism with a narrative inquiry design was used as the lens to examine the women’s experiences. In-depth interviews were analysed through thematic analysis. The findings of this research revealed negative experiences resulting from severe symptoms before hysterectomy, exposed multi-layered structures of power and dominance during treatment, and indicated positive outcomes of hysterectomy. The findings should inform medical and allied practitioners regarding hysterectomy as a treatment option and add to the theoretical debate on the relationships between hysterectomy, womanhood, and identity.
- Full Text:
- Date Issued: 2018
- Authors: Kota-Nyati, Phumeza Patricia
- Date: 2018
- Subjects: Hysterectomy -- psychological aspects , Women -- psychological aspects Gender identity Intersectionality (Sociology)
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/29995 , vital:30807
- Description: The removal of the uterus, medically referred to as a hysterectomy, is a permanent and irreversible procedure that potentially results in a number of immediate and significant effects. Performing a hysterectomy is at times the only medical option to a long and traumatic history of pelvic pains and surgeries. The decision to undergo this very costly, painful, and life-changing procedure can have an influence on the way women view themselves. Women’s narratives of womanhood before and after hysterectomy need to be understood within the context of women’s socially constructed identities. Gendered identity has been closely linked to genital and/or reproductive organs and the removal of these organs may influence the way women and societies define womanhood.The interpretive paradigm of constructionism with a narrative inquiry design was used as the lens to examine the women’s experiences. In-depth interviews were analysed through thematic analysis. The findings of this research revealed negative experiences resulting from severe symptoms before hysterectomy, exposed multi-layered structures of power and dominance during treatment, and indicated positive outcomes of hysterectomy. The findings should inform medical and allied practitioners regarding hysterectomy as a treatment option and add to the theoretical debate on the relationships between hysterectomy, womanhood, and identity.
- Full Text:
- Date Issued: 2018
Characterization and ecology of selected micro-estuaries and micro-outlets in the Eastern Cape province, South Africa
- Authors: Magoro, Mandla Leon
- Date: 2018
- Subjects: Estuarine ecology -- South Africa -- Eastern Cape , Estuaries -- Management Estuaries -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/31644 , vital:31640
- Description: South Africa has more than 200 Temporarily Open/Closed Estuaries (TOCEs) along its approximately 3000 km coastline. In addition, there are approximately 200 micro-estuaries and micro-outlets on the subcontinent, many of which share some of the characteristics with TOCEs but differ in that they are supplied by localised coastal stream catchments with a more limited supply of freshwater and less connectivity to the marine environment. Between 2015 and 2016, this study endeavoured to investigate the physico-chemical properties, microalgal dynamics as well as the seasonal species abundance and composition of aquatic invertebrates and fishes in four micro-estuaries and four micro-outlets along the warm-temperate section of the Eastern Cape coast. The micro-outlets were dominated by oligohaline or freshwater conditions, while the micro-estuaries were mostly mesohaline. Microalgal biomass in these systems was influenced by temperature, nutrient conditions and light availability. Chironomidae and Ephemeroptera dominated benthic macro-invertebrate communities in the micro-outlets, while Amphipoda and Mysida were most dominant in micro-estuaries. Copepoda and Amphipoda dominated the zooplankton assemblages in both system types. Nekton communities in micro-outlets were dominated by juvenile Myxus capensis and tadpoles (mostly Xenopus laevis), while Oreochromis mossambicus, Gilchristella aestuaria, M. capensis and Mugil cephalus were the four most common species in the micro-estuaries. Seasonal variations in physico-chemical parameters and community composition of both the nekton and invertebrates were recorded during this study. Micro-estuaries and micro-outlets exhibited relatively lower diversity and abundances of biota than TOCEs. Furthermore, the micro-estuaries have a low estuarine function when compared to TOCEs, while the micro-outlets have very limited estuarine characteristics and were dominated by freshwater biota. The micro-systems are smaller in size and contain lower proportions of estuary-associated taxa when compared to larger estuarine systems such as TOCEs and permanently open estuaries. The results of this study confirm that there are distinctions between the biota of iv the two micro-system types, thus making biotic assemblages, together with physico-chemical parameters, a viable tool for differentiating between micro-estuaries and micro-outlets. This study represents the first investigation into the ecological functioning of micro-estuaries and micro-outlets. As a whole, micro-systems serve as nursery areas for freshwater-associated invertebrate taxa. Due to their limited periods of stability, micro-estuaries serve as intermediate nursery areas for 0+ juveniles of estuary-associated marine fish which, after less than a year, then migrate to larger estuarine systems located nearby. The small catchment size and short period of stability in these systems heightens their level of sensitivity to water flow alterations through dams, direct water abstraction, afforestation and watercourse diversion, while their lower buffering capacity makes them more susceptible to pollution and nutrient inputs from intensive agricultural activities and urban expansion.
- Full Text:
- Date Issued: 2018
- Authors: Magoro, Mandla Leon
- Date: 2018
- Subjects: Estuarine ecology -- South Africa -- Eastern Cape , Estuaries -- Management Estuaries -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/31644 , vital:31640
- Description: South Africa has more than 200 Temporarily Open/Closed Estuaries (TOCEs) along its approximately 3000 km coastline. In addition, there are approximately 200 micro-estuaries and micro-outlets on the subcontinent, many of which share some of the characteristics with TOCEs but differ in that they are supplied by localised coastal stream catchments with a more limited supply of freshwater and less connectivity to the marine environment. Between 2015 and 2016, this study endeavoured to investigate the physico-chemical properties, microalgal dynamics as well as the seasonal species abundance and composition of aquatic invertebrates and fishes in four micro-estuaries and four micro-outlets along the warm-temperate section of the Eastern Cape coast. The micro-outlets were dominated by oligohaline or freshwater conditions, while the micro-estuaries were mostly mesohaline. Microalgal biomass in these systems was influenced by temperature, nutrient conditions and light availability. Chironomidae and Ephemeroptera dominated benthic macro-invertebrate communities in the micro-outlets, while Amphipoda and Mysida were most dominant in micro-estuaries. Copepoda and Amphipoda dominated the zooplankton assemblages in both system types. Nekton communities in micro-outlets were dominated by juvenile Myxus capensis and tadpoles (mostly Xenopus laevis), while Oreochromis mossambicus, Gilchristella aestuaria, M. capensis and Mugil cephalus were the four most common species in the micro-estuaries. Seasonal variations in physico-chemical parameters and community composition of both the nekton and invertebrates were recorded during this study. Micro-estuaries and micro-outlets exhibited relatively lower diversity and abundances of biota than TOCEs. Furthermore, the micro-estuaries have a low estuarine function when compared to TOCEs, while the micro-outlets have very limited estuarine characteristics and were dominated by freshwater biota. The micro-systems are smaller in size and contain lower proportions of estuary-associated taxa when compared to larger estuarine systems such as TOCEs and permanently open estuaries. The results of this study confirm that there are distinctions between the biota of iv the two micro-system types, thus making biotic assemblages, together with physico-chemical parameters, a viable tool for differentiating between micro-estuaries and micro-outlets. This study represents the first investigation into the ecological functioning of micro-estuaries and micro-outlets. As a whole, micro-systems serve as nursery areas for freshwater-associated invertebrate taxa. Due to their limited periods of stability, micro-estuaries serve as intermediate nursery areas for 0+ juveniles of estuary-associated marine fish which, after less than a year, then migrate to larger estuarine systems located nearby. The small catchment size and short period of stability in these systems heightens their level of sensitivity to water flow alterations through dams, direct water abstraction, afforestation and watercourse diversion, while their lower buffering capacity makes them more susceptible to pollution and nutrient inputs from intensive agricultural activities and urban expansion.
- Full Text:
- Date Issued: 2018
Compensation for distribution of timing and reference signals over optical fibre networks for telescope arrays
- Authors: Wassin, Shukree
- Date: 2018
- Subjects: Fiber optics , Optical communications Very large array telescopes Optical fiber detectors
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/36425 , vital:33941
- Description: Significant advancements and developments have been made in optical frequency standards, in recent years. In order to verify the accuracy and preciseness of the disseminated RF signal, it is essential to compare its stability with the standards provided in literature as well as by metrology institutes. However, conventional frequency comparison techniques via satellites have extremely inferior stability qualities. As a result, the need for an alternative ultra-high precision RF transfer method presented itself. Highly accurate and precise frequency dissemination across optical fiber has proved a leading contender and a possible solution. When compared to conventional data transfer media, optical fiber has proven to be more superior and yields lower transmission errors and is immune to radio frequency interference. A further quality of optical fibre is that its transmission distance can be extended to greater degree than the traditional coaxial cable due to its low loss property. This thesis deals with the compensation of phase noise in single mode optical fibre. Phase noise degrades the performance and stability of the RF signal as well as the optical carrier frequency across long-haul optical networks. This work begins by experimentally demonstrating a unique and novel way for measuring the round-trip optical fibre latency times. The technique is based on all optical wavelength conversion using a stable PPS injection signal. The result highlighted the importance for active phase error compensation along a fibre link. Various computer simulations were used to study the influence of temperature fluctuation on the optical fibre. The first ever error signals generated at NMU was experimentally demonstrated. Results illustrated that, by minimizing the error voltage the phase difference between the transmitted and reference signals were reduced to zero. Performance analysis testing of the VCSEL phase correction actuator showed that majority of the dither iterations that induced the phase compensation took approximately 0.15 s. Residual frequency instabilities of 3.39791 x 10-12 at 1 s and 8.14848 x 10-12 at 103 s was measured when the 26 km G.655 fibre link was running freely. Experimental results further showed that the relative frequency stabilities measured at 1 s and 103 s were 4.43902 x 10-12 and 1.62055 x 10-13 during active compensation, respectively. The novel work presented in this thesis is exciting since the VCSEL is used as the optical source as well as the phase correction actuator. The benefits of such a device is that is reduces system costs and complexities.
- Full Text:
- Date Issued: 2018
- Authors: Wassin, Shukree
- Date: 2018
- Subjects: Fiber optics , Optical communications Very large array telescopes Optical fiber detectors
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/36425 , vital:33941
- Description: Significant advancements and developments have been made in optical frequency standards, in recent years. In order to verify the accuracy and preciseness of the disseminated RF signal, it is essential to compare its stability with the standards provided in literature as well as by metrology institutes. However, conventional frequency comparison techniques via satellites have extremely inferior stability qualities. As a result, the need for an alternative ultra-high precision RF transfer method presented itself. Highly accurate and precise frequency dissemination across optical fiber has proved a leading contender and a possible solution. When compared to conventional data transfer media, optical fiber has proven to be more superior and yields lower transmission errors and is immune to radio frequency interference. A further quality of optical fibre is that its transmission distance can be extended to greater degree than the traditional coaxial cable due to its low loss property. This thesis deals with the compensation of phase noise in single mode optical fibre. Phase noise degrades the performance and stability of the RF signal as well as the optical carrier frequency across long-haul optical networks. This work begins by experimentally demonstrating a unique and novel way for measuring the round-trip optical fibre latency times. The technique is based on all optical wavelength conversion using a stable PPS injection signal. The result highlighted the importance for active phase error compensation along a fibre link. Various computer simulations were used to study the influence of temperature fluctuation on the optical fibre. The first ever error signals generated at NMU was experimentally demonstrated. Results illustrated that, by minimizing the error voltage the phase difference between the transmitted and reference signals were reduced to zero. Performance analysis testing of the VCSEL phase correction actuator showed that majority of the dither iterations that induced the phase compensation took approximately 0.15 s. Residual frequency instabilities of 3.39791 x 10-12 at 1 s and 8.14848 x 10-12 at 103 s was measured when the 26 km G.655 fibre link was running freely. Experimental results further showed that the relative frequency stabilities measured at 1 s and 103 s were 4.43902 x 10-12 and 1.62055 x 10-13 during active compensation, respectively. The novel work presented in this thesis is exciting since the VCSEL is used as the optical source as well as the phase correction actuator. The benefits of such a device is that is reduces system costs and complexities.
- Full Text:
- Date Issued: 2018
Design of a dedicated IFT microcontroller
- Authors: Himunzowa, Grayson
- Date: 2018
- Subjects: Feedback control systems , Automatic control , Engineering design -- Data processing
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/30017 , vital:30809
- Description: The design of a Dedicated IFT Microcontroller originated from the successful implementation of the Iterative Feedback Tuning (IFT) technique into the Digital Signal Processor microcontroller (DSP56F807C) at the University of Cape Town in 2006. However, implementation of the IFT technique on a general-purpose microcontroller is neither optimal, nor a cost-effective exercise, as most of the microcontroller peripherals remain unused, and drain energy for doing nothing. In addition, microcontrollers and DSPs are software-driven devices whose nature is sequential in executing algorithms, and hence have a significant effect on the bandwidth of the closed-loop control. To mitigate the said problem, the design of a Dedicated IFT Microcontroller is proposed in this thesis. To accomplish this goal, the preliminary task was to explore the IFT theory and its applications, followed by a review of the literature on FPGA design methodology for industrial control systems, Microcontroller design principles, and FPGA theory and trends. Furthermore, a survey of electronic design automation (EDA) tools and other application software was also conducted. After the literature review, the IFT was investigated exhaustively by applying it to three types of plants, namely: a DC motor, an oscillatory plant, and an unstable plant. Each of these plants were tested using three types of initial controllers, namely heavilydamped, critically damped and under-damped initial controllers. The plants were also tested by varying the amplitude of the reference signal, followed by using a single-step signal of constant amplitude of one volt. The intention of exploring all of these possibilities was meant to firmly expose the IFT boundaries of applicability, so that the final product would not be vulnerable to unnecessary post-production discoveries. The design methodology adopted in this research was a popular hierarchical and modular top-down procedure, which is an array of abstraction levels that are detailed as: system level, behavioural level, Register-Transfer Level (RTL) and Gate level. At system level, the Dedicated IFT Microcontroller was defined. Thereafter, at behavioural level, the design was simulated using VHDL, created by porting the LabView IFT code to the Xilinx EDA tool. At the RTL, the synthesisable VHDL code utilising fixed-point number representation was written. The compiled bit file was downloaded onto National Instruments (NI) Digital Electronics FPGA Board featuring iii the Spartan 3 series FPGA. This was tested, using a method known as simulation in the hardware. The key contribution of this thesis is the experimental validation of the IFT technique on FPGA hardware as it has never been published before, the work described in chapter four and five. The other contribution is the analysis of 1DOF IFT technique in terms of limitations of applicability for correct implementation, which is the main work of chapter three. This work could be used to explore other computational methods, like the use of floating-point number representation for high resolution and accuracy in numerical computations. Another avenue that could be exploited is Xilinx's recent Vivado methodology, which has the capacity for traditional programming languages like C or C++, as these have in-built floating-point number capability. Finally, out of this work, two papers have already been published by Springer and IEEE Xplore Publishers, and a journal paper has also been written for publication in the Control Systems Technology journal.
- Full Text:
- Date Issued: 2018
- Authors: Himunzowa, Grayson
- Date: 2018
- Subjects: Feedback control systems , Automatic control , Engineering design -- Data processing
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/30017 , vital:30809
- Description: The design of a Dedicated IFT Microcontroller originated from the successful implementation of the Iterative Feedback Tuning (IFT) technique into the Digital Signal Processor microcontroller (DSP56F807C) at the University of Cape Town in 2006. However, implementation of the IFT technique on a general-purpose microcontroller is neither optimal, nor a cost-effective exercise, as most of the microcontroller peripherals remain unused, and drain energy for doing nothing. In addition, microcontrollers and DSPs are software-driven devices whose nature is sequential in executing algorithms, and hence have a significant effect on the bandwidth of the closed-loop control. To mitigate the said problem, the design of a Dedicated IFT Microcontroller is proposed in this thesis. To accomplish this goal, the preliminary task was to explore the IFT theory and its applications, followed by a review of the literature on FPGA design methodology for industrial control systems, Microcontroller design principles, and FPGA theory and trends. Furthermore, a survey of electronic design automation (EDA) tools and other application software was also conducted. After the literature review, the IFT was investigated exhaustively by applying it to three types of plants, namely: a DC motor, an oscillatory plant, and an unstable plant. Each of these plants were tested using three types of initial controllers, namely heavilydamped, critically damped and under-damped initial controllers. The plants were also tested by varying the amplitude of the reference signal, followed by using a single-step signal of constant amplitude of one volt. The intention of exploring all of these possibilities was meant to firmly expose the IFT boundaries of applicability, so that the final product would not be vulnerable to unnecessary post-production discoveries. The design methodology adopted in this research was a popular hierarchical and modular top-down procedure, which is an array of abstraction levels that are detailed as: system level, behavioural level, Register-Transfer Level (RTL) and Gate level. At system level, the Dedicated IFT Microcontroller was defined. Thereafter, at behavioural level, the design was simulated using VHDL, created by porting the LabView IFT code to the Xilinx EDA tool. At the RTL, the synthesisable VHDL code utilising fixed-point number representation was written. The compiled bit file was downloaded onto National Instruments (NI) Digital Electronics FPGA Board featuring iii the Spartan 3 series FPGA. This was tested, using a method known as simulation in the hardware. The key contribution of this thesis is the experimental validation of the IFT technique on FPGA hardware as it has never been published before, the work described in chapter four and five. The other contribution is the analysis of 1DOF IFT technique in terms of limitations of applicability for correct implementation, which is the main work of chapter three. This work could be used to explore other computational methods, like the use of floating-point number representation for high resolution and accuracy in numerical computations. Another avenue that could be exploited is Xilinx's recent Vivado methodology, which has the capacity for traditional programming languages like C or C++, as these have in-built floating-point number capability. Finally, out of this work, two papers have already been published by Springer and IEEE Xplore Publishers, and a journal paper has also been written for publication in the Control Systems Technology journal.
- Full Text:
- Date Issued: 2018
Development and evaluation of the coach-athlete relationship enhancement intervention
- Authors: Kuit, Wim
- Date: 2018
- Subjects: Interpersonal relations , Coaching (Athletics) -- Psychological aspects Sports -- Psychological aspects
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/22508 , vital:29989
- Description: An expanding body of sport psychology theory and research has highlighted the central role of the coach-athlete relationship (CAR) in the performance, satisfaction and well-being of coaches as well as athletes. Models have been developed that identify the key dimensions of CAR quality and the interpersonal behaviour that maintains it, but there remains a need for interventions that support coaches and athletes to optimise their interpersonal skills. This can be done by harnessing recent advances in personality theory which emphasise a more holistic and developmental view of the person and provide a basis for greater mutual understanding and adaptive interpersonal behaviour change in the CAR. The aims of this study were to develop the Coach-Athlete Relationship Enhancement (CARE) intervention through an integration of the Enneagram personality typology with current models of the CAR, and then to evaluate the impact of the CARE intervention on CAR quality. Sixty-two university-level athletes and their nine coaches participated in the study. Quantitative and qualitative results indicate that the CARE intervention significantly enhanced CAR quality, including direct and meta-perceptions of closeness, commitment and complementarity, as well as co-orientation. Intervention outcomes included enhanced mutual understanding in the CAR, enhanced self-awareness, enhanced team relationships, and adaptive interpersonal behaviour change. These outcomes were associated with a shared awareness between coaches and athletes of their Enneagram personality type traits and motivations. Coach-athlete relationship quality was further enhanced by re-constructing coaches’ and athletes’ personal narratives based on self-descriptions of Enneagram type strengths, and a redefinition of individuals’ core motivations to incorporate adaptive interpersonal behaviour change.
- Full Text:
- Date Issued: 2018
- Authors: Kuit, Wim
- Date: 2018
- Subjects: Interpersonal relations , Coaching (Athletics) -- Psychological aspects Sports -- Psychological aspects
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/22508 , vital:29989
- Description: An expanding body of sport psychology theory and research has highlighted the central role of the coach-athlete relationship (CAR) in the performance, satisfaction and well-being of coaches as well as athletes. Models have been developed that identify the key dimensions of CAR quality and the interpersonal behaviour that maintains it, but there remains a need for interventions that support coaches and athletes to optimise their interpersonal skills. This can be done by harnessing recent advances in personality theory which emphasise a more holistic and developmental view of the person and provide a basis for greater mutual understanding and adaptive interpersonal behaviour change in the CAR. The aims of this study were to develop the Coach-Athlete Relationship Enhancement (CARE) intervention through an integration of the Enneagram personality typology with current models of the CAR, and then to evaluate the impact of the CARE intervention on CAR quality. Sixty-two university-level athletes and their nine coaches participated in the study. Quantitative and qualitative results indicate that the CARE intervention significantly enhanced CAR quality, including direct and meta-perceptions of closeness, commitment and complementarity, as well as co-orientation. Intervention outcomes included enhanced mutual understanding in the CAR, enhanced self-awareness, enhanced team relationships, and adaptive interpersonal behaviour change. These outcomes were associated with a shared awareness between coaches and athletes of their Enneagram personality type traits and motivations. Coach-athlete relationship quality was further enhanced by re-constructing coaches’ and athletes’ personal narratives based on self-descriptions of Enneagram type strengths, and a redefinition of individuals’ core motivations to incorporate adaptive interpersonal behaviour change.
- Full Text:
- Date Issued: 2018
Development of a community pharmacy experiential learning programme in a South African context: a design research approach
- Kritiotis, Lia Costas, Thesis Advisor
- Authors: Kritiotis, Lia Costas , Thesis Advisor
- Date: 2018
- Subjects: Pharmacists -- Training of , Experintial training , Community development -- South Africa
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/17481 , vital:28353
- Description: Application of the design research approach to devise, develop and optimise an experiential learning programme and adaptation of the Volunteer Functions Inventory (VFI) to understand community pharmacists’ motives, are unique contributions to the global pharmacy education setting. This study generated new theory, in the form of substantive and procedural claims (design principles) regarding experiential learning programmes and preceptor and student motivation in a South African pharmacy educational context, which can be added to the existing international landscape and more importantly, plant the foundational seeds of insight that can be utilised as guiding tools by other South African pharmacy faculties.
- Full Text:
- Date Issued: 2018
- Authors: Kritiotis, Lia Costas , Thesis Advisor
- Date: 2018
- Subjects: Pharmacists -- Training of , Experintial training , Community development -- South Africa
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/17481 , vital:28353
- Description: Application of the design research approach to devise, develop and optimise an experiential learning programme and adaptation of the Volunteer Functions Inventory (VFI) to understand community pharmacists’ motives, are unique contributions to the global pharmacy education setting. This study generated new theory, in the form of substantive and procedural claims (design principles) regarding experiential learning programmes and preceptor and student motivation in a South African pharmacy educational context, which can be added to the existing international landscape and more importantly, plant the foundational seeds of insight that can be utilised as guiding tools by other South African pharmacy faculties.
- Full Text:
- Date Issued: 2018
Development of high capacity lithium-manganese-rich cathode materials xLi2MnO3•(1-x)LiMn0.5Ni0.5O2 for lithium ion batteries
- Authors: Rapulenyane, Nomasonto
- Date: 2018
- Subjects: Lithium ion batteries , Electrochemistry Lithium cells
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/34766 , vital:33442
- Description: In this study, a facile synthesis method was developed to produce layered-layered cathode materials with the formula xLi2MnO3•(1-x)LiMO2 (M= Ni and Mn) referred to as lithium-manganese-rich materials for lithium ion batteries. The prepared materials displayed high capacity ≥200 mAh/g at a current density of 20 mA/g in the voltage range of 2.0 V to 4.8 V. In particular the cathode material prepared at pH 10.0 delivered a high initial discharge capacity of 266 mAh/g at 20 mA/g current density and maintained a discharge capacity ≥220 mAh/g at 50 mA/g after 50 cycles. The synthesis method was used to further investigate the effect of lithium ratio in the layered-layered material. Li1+xMn0.6Ni0.2O2, x= 0.2, 0.25, 0.3 and 0.4 cathode materials were produced respectively. The BET surface area analysis results showed that Li1.3Mn0.6Ni0.2O2 material had comparatively higher surface area to the other cathode materials and also delivered good electrochemical results. XPS showed that the cation distribution is affected by the increase in lithium ratio, the Mn4+ percentages decreased significantly with an increase in lithium ratio. All materials peaks deconvoluted into two peaks namely Mn4+ and Mn3+, Li1.3Mn0.6Ni0.2O2 had the highest percentages of the stable Mn4+ 70.8%. Further investigation focused on the effect of the sintering temperature on the structure and the electrochemical performance of Li1+xMn0.6Ni0.2O2, x= 0.25, 0.3 and 0.4 cathode materials. X-ray diffraction showed the same patterns for all cathode materials sintered at 700˚C, 800˚C and 900˚C. Rietveld refined results however, showed that the increase in the sintering temperature, results in a decrease in the Li2MnO3 component percentage in the layered structures. Scanning electron microscopy images further proved that the particle size increases with increasing temperature. The charge–discharge tests of coin cells demonstrated that the materials sintered at 800˚C delivered higher discharge capacities above 200 mAh/g at 20 mA/g current density when compared to the materials made at the lower temperatures. Lastly the cathode material prepared at pH 10.0 was further evaluated in a cell using lithium titanate oxide Li4Ti5O12 as anode material. The cells delivered an initial discharge capacity of 213 mAh/g at 20 mA/g within a voltage range 3.3V-0.5V. The coin cells developed in this work delivered good cycling performance.
- Full Text:
- Date Issued: 2018
- Authors: Rapulenyane, Nomasonto
- Date: 2018
- Subjects: Lithium ion batteries , Electrochemistry Lithium cells
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/34766 , vital:33442
- Description: In this study, a facile synthesis method was developed to produce layered-layered cathode materials with the formula xLi2MnO3•(1-x)LiMO2 (M= Ni and Mn) referred to as lithium-manganese-rich materials for lithium ion batteries. The prepared materials displayed high capacity ≥200 mAh/g at a current density of 20 mA/g in the voltage range of 2.0 V to 4.8 V. In particular the cathode material prepared at pH 10.0 delivered a high initial discharge capacity of 266 mAh/g at 20 mA/g current density and maintained a discharge capacity ≥220 mAh/g at 50 mA/g after 50 cycles. The synthesis method was used to further investigate the effect of lithium ratio in the layered-layered material. Li1+xMn0.6Ni0.2O2, x= 0.2, 0.25, 0.3 and 0.4 cathode materials were produced respectively. The BET surface area analysis results showed that Li1.3Mn0.6Ni0.2O2 material had comparatively higher surface area to the other cathode materials and also delivered good electrochemical results. XPS showed that the cation distribution is affected by the increase in lithium ratio, the Mn4+ percentages decreased significantly with an increase in lithium ratio. All materials peaks deconvoluted into two peaks namely Mn4+ and Mn3+, Li1.3Mn0.6Ni0.2O2 had the highest percentages of the stable Mn4+ 70.8%. Further investigation focused on the effect of the sintering temperature on the structure and the electrochemical performance of Li1+xMn0.6Ni0.2O2, x= 0.25, 0.3 and 0.4 cathode materials. X-ray diffraction showed the same patterns for all cathode materials sintered at 700˚C, 800˚C and 900˚C. Rietveld refined results however, showed that the increase in the sintering temperature, results in a decrease in the Li2MnO3 component percentage in the layered structures. Scanning electron microscopy images further proved that the particle size increases with increasing temperature. The charge–discharge tests of coin cells demonstrated that the materials sintered at 800˚C delivered higher discharge capacities above 200 mAh/g at 20 mA/g current density when compared to the materials made at the lower temperatures. Lastly the cathode material prepared at pH 10.0 was further evaluated in a cell using lithium titanate oxide Li4Ti5O12 as anode material. The cells delivered an initial discharge capacity of 213 mAh/g at 20 mA/g within a voltage range 3.3V-0.5V. The coin cells developed in this work delivered good cycling performance.
- Full Text:
- Date Issued: 2018
Development of InSb/GaSb quantum dots by MOVPE
- Authors: Ahia, Chinedu Christian
- Date: 2018
- Subjects: Semiconductors , Quantum electronics Organometallic compounds
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/23382 , vital:30537
- Description: There has been an increasing interest in the modification of semiconductor band structures through the reduction of their dimensions, which simultaneously increases the band gap energy of the material and gives rise to flexibility in device properties. Advances in III-V antimony (Sb) based semiconductor fabrication have triggered the quest for extension of the emission/absorption wavelength range of this family of compounds for optoelectronic devices operating in the mid-infrared region of the electromagnetic spectrum. An interesting material system for mid-infrared (MIR) applications is indium antimonide (InSb) quantum dots (QDs) within a gallium antimonide (GaSb) matrix. However, its band alignment and emission wavelength has been the subject of some interest and controversy over the years. This study focuses on the development of InSb/GaSb QDs by metal organic vapour phase epitaxy (MOVPE). The samples were grown on different substrates using various growth parameters in order to vary the size, density and aspect ratio of the dots. Interfacial growth interruptions while flowing various source precursors through the reactor were investigated in order to influence the chemical termination of the surface, and hence the resulting strain in the structures. The samples were characterized using photoluminescence spectroscopy, scanning probe microscopy, scanning electron microscopy, X-ray diffraction and transmission electron microscopy. Likewise, the band alignment, energy levels, and carrier wave functions of the samples in this work were modelled theoretically using the nextnanomat software (version 3.1.0.0). A comparison of growth on two different GaSb substrates [(100) 2° off towards <111>B ± 0.1ᵒ and (111) ± 0.1ᵒ] using similar growth conditions yielded a higher dot density on the (100) substrate compared to the (111) substrate. This was attributed to the presence of terraces/atomic steps induced by the misorientation on the (100) substrate, which invariably gives rise to increased adsorption and an enhanced sticking coefficient of adatoms. Studies on the influence of a buffer layer on the morphology of uncapped dots showed that the shape and size of the dots are sensitive to the thickness of the buffer layer. In some case a corrugated buffer surface resulted, which introduced order in the arrangement of the dots, which formed preferentially inside the troughs. An increase in the V/III ratio from 1.0 to 3.0 was found to reduce the areal density of the QDs, while an analysis of the diameter histograms showed a narrowing of the size distribution with an increase in V/III ratio. The larger size distribution at low V/III was ascribed to the increase in indium species and the increased indium adatom migration length. This leads to increased dot density and nucleation sites, and thus triggers an increase in the conversion of tiny QDs into thermodynamically more suitable larger dots via coalescence. However, as the V/III ratio increased, the number of indium adatoms available for growth on the surface reduced, which automatically led to a decrease in the migration length of indium species which is unfavourable for the production of nucleation sites and to a decrease in dot density. Low growth rates were found to be beneficial for the growth of a high density (~5×1010cm-2) of QDs. Photoluminescence (PL) analysis of the capped samples at low temperature (~10 K), using an excitation power of 2 mW, showed a PL peak at ∼732 meV. Upon an increase in laser power to 120 mW, a blue shift of ∼ 8 meV was noticed. This emission typically persisted up to 60–70 K. An increase in the number of InSb QD-layers, was observed to cause an increase in the luminescence spectral line width and a long-wavelength shift of the PL lines, together with an enhancement in the strength of the PL emission. However, high resolution transmission electron microscopy (HRTEM) of the capped dots revealed the formation of an InGaSb quantum well-like structure, ∼10 nm thick, which was responsible for the PL signal mentioned above. The absence of QDs in the capped sample was attributed to inter-diffusion of Ga and In during the deposition of the cap layer, giving rise to a quantum well (QW) instead of the intended QDs. The presence of threading dislocations and stacking faults were also observed in the TEM micrographs of the samples containing multilayers, which can account for the fast quenching of the PL emission with increasing temperature from these samples. Theoretical simulations of the band alignment, wave functions and energy levels were in good agreement with the data collected from the PL spectra of the samples.
- Full Text:
- Date Issued: 2018
- Authors: Ahia, Chinedu Christian
- Date: 2018
- Subjects: Semiconductors , Quantum electronics Organometallic compounds
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/23382 , vital:30537
- Description: There has been an increasing interest in the modification of semiconductor band structures through the reduction of their dimensions, which simultaneously increases the band gap energy of the material and gives rise to flexibility in device properties. Advances in III-V antimony (Sb) based semiconductor fabrication have triggered the quest for extension of the emission/absorption wavelength range of this family of compounds for optoelectronic devices operating in the mid-infrared region of the electromagnetic spectrum. An interesting material system for mid-infrared (MIR) applications is indium antimonide (InSb) quantum dots (QDs) within a gallium antimonide (GaSb) matrix. However, its band alignment and emission wavelength has been the subject of some interest and controversy over the years. This study focuses on the development of InSb/GaSb QDs by metal organic vapour phase epitaxy (MOVPE). The samples were grown on different substrates using various growth parameters in order to vary the size, density and aspect ratio of the dots. Interfacial growth interruptions while flowing various source precursors through the reactor were investigated in order to influence the chemical termination of the surface, and hence the resulting strain in the structures. The samples were characterized using photoluminescence spectroscopy, scanning probe microscopy, scanning electron microscopy, X-ray diffraction and transmission electron microscopy. Likewise, the band alignment, energy levels, and carrier wave functions of the samples in this work were modelled theoretically using the nextnanomat software (version 3.1.0.0). A comparison of growth on two different GaSb substrates [(100) 2° off towards <111>B ± 0.1ᵒ and (111) ± 0.1ᵒ] using similar growth conditions yielded a higher dot density on the (100) substrate compared to the (111) substrate. This was attributed to the presence of terraces/atomic steps induced by the misorientation on the (100) substrate, which invariably gives rise to increased adsorption and an enhanced sticking coefficient of adatoms. Studies on the influence of a buffer layer on the morphology of uncapped dots showed that the shape and size of the dots are sensitive to the thickness of the buffer layer. In some case a corrugated buffer surface resulted, which introduced order in the arrangement of the dots, which formed preferentially inside the troughs. An increase in the V/III ratio from 1.0 to 3.0 was found to reduce the areal density of the QDs, while an analysis of the diameter histograms showed a narrowing of the size distribution with an increase in V/III ratio. The larger size distribution at low V/III was ascribed to the increase in indium species and the increased indium adatom migration length. This leads to increased dot density and nucleation sites, and thus triggers an increase in the conversion of tiny QDs into thermodynamically more suitable larger dots via coalescence. However, as the V/III ratio increased, the number of indium adatoms available for growth on the surface reduced, which automatically led to a decrease in the migration length of indium species which is unfavourable for the production of nucleation sites and to a decrease in dot density. Low growth rates were found to be beneficial for the growth of a high density (~5×1010cm-2) of QDs. Photoluminescence (PL) analysis of the capped samples at low temperature (~10 K), using an excitation power of 2 mW, showed a PL peak at ∼732 meV. Upon an increase in laser power to 120 mW, a blue shift of ∼ 8 meV was noticed. This emission typically persisted up to 60–70 K. An increase in the number of InSb QD-layers, was observed to cause an increase in the luminescence spectral line width and a long-wavelength shift of the PL lines, together with an enhancement in the strength of the PL emission. However, high resolution transmission electron microscopy (HRTEM) of the capped dots revealed the formation of an InGaSb quantum well-like structure, ∼10 nm thick, which was responsible for the PL signal mentioned above. The absence of QDs in the capped sample was attributed to inter-diffusion of Ga and In during the deposition of the cap layer, giving rise to a quantum well (QW) instead of the intended QDs. The presence of threading dislocations and stacking faults were also observed in the TEM micrographs of the samples containing multilayers, which can account for the fast quenching of the PL emission with increasing temperature from these samples. Theoretical simulations of the band alignment, wave functions and energy levels were in good agreement with the data collected from the PL spectra of the samples.
- Full Text:
- Date Issued: 2018
Dimensions of a memorable experience within a marine tourism context
- Authors: Jonas, Altouise Glowdean
- Date: 2018
- Subjects: Customer relations -- Management , Customer relations Relationship marketing Tourism -- Environmental aspects Coastal zone management -- Environmental aspects
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/30540 , vital:30958
- Description: Worldwide, businesses are operating in an environment which is continuously changing, forcing them to adapt their strategies in order to remain competitive. Two changes were of particular importance to this study. Firstly, businesses are faced with an increasing demand from consumers for experiences as opposed to products and services. Secondly, consumers are demanding experiences that are not just ordinary, but are unique and memorable. As one of the largest and most diverse industries globally, tourism offers a multitude of tourist activities. Marine tourism is one of the oldest, most popular and fastest developing types of tourism globally. Marine tourism has also become popular in South Africa. This popularity might be attributed to the country’s expansive coastline and to it being home to one of the most diverse marine systems in the world. Marine tourism makes significant contributions to South Africa’s economy. More benefits can be derived from this lucrative type of tourism if attention is given to the design and provision of marine tourism experiences that go beyond average experiences, and become memorable experiences. The reason for conducting this research was to provide the South African tourism industry, and marine tourism operators in particular, with information which might assist them in designing and staging memorable experiences. Such memorable experiences could result in a competitive advantage and enable the operators to attract more customers, which in turn, will benefit the individual operators, the industry as a whole, and ultimately, the South African economy. The study focused on three marine tourism activities, namely; shark-diving, visits to marine protected areas and whale-watching. Eight dimensions, namely; Delight, Hedonism, Involvement, Knowledge, Meaningfulness, Novelty, Refreshment and Social-Interaction were identified as prospective dimensions of a memorable experience within a marine tourism context. v The study employed purposive, convenience and snowball sampling to identify potential respondents. Primary data was collected by means of an online survey and paper-based self-administered questionnaires. Four hundred and forty-four useable responses were received. The results of the empirical study showed a positive correlation between all the dimensions and memorable experience for each of the three activities and for all the activities combined. A second order factor analysis showed that the eight dimensions loaded onto two factors. The resulting factors were named as the Affective Domain (consisting of Hedonism, Refreshment, Delight and Involvement) and the Cognitive Domain (consisting of Knowledge, Social- Interaction, Meaningfulness and Novelty). A positive relationship was found between the Affective Domain and Memorable Experience and also between the Cognitive Domain and Memorable Experience. The Cognitive domain showed a stronger relationship with Memorable Experience than what the Affective Domain did, for all the activities combined. The memorability of an experience in the case of all three activities combined can, firstly, be improved by Involvement. This is closely followed by the following dimensions in the Affective Domain; Delight, Hedonism and Refreshment. Under the Cognitive Domain the factor which is most important for improving memorability of all the activities combined is Meaningfulness, followed by Knowledge, Novelty and Social-Interaction. Finally, structural equation modelling confirmed a model representing the eight experience dimensions (Delight, Hedonism, Involvement, Knowledge, Meaningfulness, Novelty, Refreshment and Social-Interaction) and identified the relationships between the dimensions and Memorable Experience. This study makes four important contributions. Firstly, it contributes to the under-researched topic of marine tourism in South Africa. Secondly, it adds to the literature on memorable tourism experiences, specifically memorable marine tourism experiences and provides a measurement instrument and framework for further research. Thirdly, the study identifies and confirms that ‘delight’ is an important dimension of a memorable marine tourism experience. vi Lastly, a model was developed which can be used by marine tourism operators to enhance their strategies, operations and facilities which will enable operators to achieve a sustainable competitive advantage.
- Full Text:
- Date Issued: 2018
- Authors: Jonas, Altouise Glowdean
- Date: 2018
- Subjects: Customer relations -- Management , Customer relations Relationship marketing Tourism -- Environmental aspects Coastal zone management -- Environmental aspects
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/30540 , vital:30958
- Description: Worldwide, businesses are operating in an environment which is continuously changing, forcing them to adapt their strategies in order to remain competitive. Two changes were of particular importance to this study. Firstly, businesses are faced with an increasing demand from consumers for experiences as opposed to products and services. Secondly, consumers are demanding experiences that are not just ordinary, but are unique and memorable. As one of the largest and most diverse industries globally, tourism offers a multitude of tourist activities. Marine tourism is one of the oldest, most popular and fastest developing types of tourism globally. Marine tourism has also become popular in South Africa. This popularity might be attributed to the country’s expansive coastline and to it being home to one of the most diverse marine systems in the world. Marine tourism makes significant contributions to South Africa’s economy. More benefits can be derived from this lucrative type of tourism if attention is given to the design and provision of marine tourism experiences that go beyond average experiences, and become memorable experiences. The reason for conducting this research was to provide the South African tourism industry, and marine tourism operators in particular, with information which might assist them in designing and staging memorable experiences. Such memorable experiences could result in a competitive advantage and enable the operators to attract more customers, which in turn, will benefit the individual operators, the industry as a whole, and ultimately, the South African economy. The study focused on three marine tourism activities, namely; shark-diving, visits to marine protected areas and whale-watching. Eight dimensions, namely; Delight, Hedonism, Involvement, Knowledge, Meaningfulness, Novelty, Refreshment and Social-Interaction were identified as prospective dimensions of a memorable experience within a marine tourism context. v The study employed purposive, convenience and snowball sampling to identify potential respondents. Primary data was collected by means of an online survey and paper-based self-administered questionnaires. Four hundred and forty-four useable responses were received. The results of the empirical study showed a positive correlation between all the dimensions and memorable experience for each of the three activities and for all the activities combined. A second order factor analysis showed that the eight dimensions loaded onto two factors. The resulting factors were named as the Affective Domain (consisting of Hedonism, Refreshment, Delight and Involvement) and the Cognitive Domain (consisting of Knowledge, Social- Interaction, Meaningfulness and Novelty). A positive relationship was found between the Affective Domain and Memorable Experience and also between the Cognitive Domain and Memorable Experience. The Cognitive domain showed a stronger relationship with Memorable Experience than what the Affective Domain did, for all the activities combined. The memorability of an experience in the case of all three activities combined can, firstly, be improved by Involvement. This is closely followed by the following dimensions in the Affective Domain; Delight, Hedonism and Refreshment. Under the Cognitive Domain the factor which is most important for improving memorability of all the activities combined is Meaningfulness, followed by Knowledge, Novelty and Social-Interaction. Finally, structural equation modelling confirmed a model representing the eight experience dimensions (Delight, Hedonism, Involvement, Knowledge, Meaningfulness, Novelty, Refreshment and Social-Interaction) and identified the relationships between the dimensions and Memorable Experience. This study makes four important contributions. Firstly, it contributes to the under-researched topic of marine tourism in South Africa. Secondly, it adds to the literature on memorable tourism experiences, specifically memorable marine tourism experiences and provides a measurement instrument and framework for further research. Thirdly, the study identifies and confirms that ‘delight’ is an important dimension of a memorable marine tourism experience. vi Lastly, a model was developed which can be used by marine tourism operators to enhance their strategies, operations and facilities which will enable operators to achieve a sustainable competitive advantage.
- Full Text:
- Date Issued: 2018
Evaluating the impact of energy policies on sustainable development in South Africa
- Authors: Julius, Ibitoye Oyebanji
- Date: 2018
- Subjects: Energy policy -- South Africa , Sustainable development -- South Africa Renewable energy sources -- South Africa Sustainable living -- South Africa
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/30440 , vital:30944
- Description: The unachieved targets of the Millennium Development Goals (MDGs) at the end of 2015 by some developing countries including South Africa, lead to the evolution of the Sustainable Development Goals (SDGs). Ensuring access to sustainable, affordable, and modern energy is one of the 17 SDGs that the countries are expected to achieve before the end of 2030. Green growth is an important strategy for attaining this goal and a pathway to achieving the other goals. Therefore, an empirical study of the impact of energy policies on sustainable development is pertinent. Despite the importance of such research, there exists a gap in the literature relating to green growth and sustainable development from the SDGs point of view. This study fills the existing lacuna by developing an intertemporal holistic model which allows a study of the impact of energy policies on sustainable development in relation to the SDGs. Specifically, this thesis employs the Autoregressive Distributed Lag (ARDL) and Toda-Yamamoto approaches to analyse the long-run relationship and direction of causality respectively between green growth policies and sustainable development in South Africa from 1984 to 2016. This research provides insights into the importance of green growth for factors such as deforestation, fuel exports, energy imports and agricultural development, thus adding to the existing literature on the impact of renewable energy on a country’s social, environmental and economic conditions. Results from the analysis of the long-run relationship between green growth and macroeconomic variables, indicate a positive unidirectional relationship between changes in green growth policies and gross capital formation. This finding suggests that adopting green growth policies leads to increased investments. In contrast, green growth was found to have a negative effect on national income (gross domestic product). However, the Granger causality tests do not establish causality between these variables. Although green growth policies stimulate investments, high start-up costs associated with the implementation of these policies may mean that the resultant higher investments are yet to be translated to higher income levels in the South African economy. The findings indicate a boost in the South African balance of payment within the study period iv iv as evidenced by the positive long-run relationship between green growth policies and fuel exports. Additionally, the results indicate that green growth energy policies have assisted in improving the resilience to international oil price shocks as shown in the negative and significant long-run relationship between green growth and energy imports. With regard to environmental variables, results suggest a substitutability effect between green growth policies and the consumption of non-renewable energy. However, no evidence is found on the impact of green growth policies on the levels of deforestation and carbon dioxide(CO2) emissions, as well as natural resource depletion. In relation to the social variables, adoption of green growth policies was found to lead to improved educational quality, with causality running in both directions. This finding supports the feedback hypothesis. Similarly, green growth policies had a positive impact on agricultural development, again with causality established in both directions. The outcome of the long-run relationship between green energy consumption and unemployment shows that the green growth policies is yet to have a significant impact on unemployment reduction in South Africa. Green growth also has an insignificant and indirect relationship with GDP per capita; this result was affirmed by the absence of causality between GDP per capita and green energy consumption. This research not only makes contributions to the literature on the relevance of green growth policies for achieving economic, social and environmental sustainability, it also suggests possible policy implications which highlight the need for adoption and continued implementation of green growth policies in developing countries such as South Africa.
- Full Text:
- Date Issued: 2018
- Authors: Julius, Ibitoye Oyebanji
- Date: 2018
- Subjects: Energy policy -- South Africa , Sustainable development -- South Africa Renewable energy sources -- South Africa Sustainable living -- South Africa
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/30440 , vital:30944
- Description: The unachieved targets of the Millennium Development Goals (MDGs) at the end of 2015 by some developing countries including South Africa, lead to the evolution of the Sustainable Development Goals (SDGs). Ensuring access to sustainable, affordable, and modern energy is one of the 17 SDGs that the countries are expected to achieve before the end of 2030. Green growth is an important strategy for attaining this goal and a pathway to achieving the other goals. Therefore, an empirical study of the impact of energy policies on sustainable development is pertinent. Despite the importance of such research, there exists a gap in the literature relating to green growth and sustainable development from the SDGs point of view. This study fills the existing lacuna by developing an intertemporal holistic model which allows a study of the impact of energy policies on sustainable development in relation to the SDGs. Specifically, this thesis employs the Autoregressive Distributed Lag (ARDL) and Toda-Yamamoto approaches to analyse the long-run relationship and direction of causality respectively between green growth policies and sustainable development in South Africa from 1984 to 2016. This research provides insights into the importance of green growth for factors such as deforestation, fuel exports, energy imports and agricultural development, thus adding to the existing literature on the impact of renewable energy on a country’s social, environmental and economic conditions. Results from the analysis of the long-run relationship between green growth and macroeconomic variables, indicate a positive unidirectional relationship between changes in green growth policies and gross capital formation. This finding suggests that adopting green growth policies leads to increased investments. In contrast, green growth was found to have a negative effect on national income (gross domestic product). However, the Granger causality tests do not establish causality between these variables. Although green growth policies stimulate investments, high start-up costs associated with the implementation of these policies may mean that the resultant higher investments are yet to be translated to higher income levels in the South African economy. The findings indicate a boost in the South African balance of payment within the study period iv iv as evidenced by the positive long-run relationship between green growth policies and fuel exports. Additionally, the results indicate that green growth energy policies have assisted in improving the resilience to international oil price shocks as shown in the negative and significant long-run relationship between green growth and energy imports. With regard to environmental variables, results suggest a substitutability effect between green growth policies and the consumption of non-renewable energy. However, no evidence is found on the impact of green growth policies on the levels of deforestation and carbon dioxide(CO2) emissions, as well as natural resource depletion. In relation to the social variables, adoption of green growth policies was found to lead to improved educational quality, with causality running in both directions. This finding supports the feedback hypothesis. Similarly, green growth policies had a positive impact on agricultural development, again with causality established in both directions. The outcome of the long-run relationship between green energy consumption and unemployment shows that the green growth policies is yet to have a significant impact on unemployment reduction in South Africa. Green growth also has an insignificant and indirect relationship with GDP per capita; this result was affirmed by the absence of causality between GDP per capita and green energy consumption. This research not only makes contributions to the literature on the relevance of green growth policies for achieving economic, social and environmental sustainability, it also suggests possible policy implications which highlight the need for adoption and continued implementation of green growth policies in developing countries such as South Africa.
- Full Text:
- Date Issued: 2018
Exploring lecturer preparedness to apply a critical approach to curriculum implementation: a case study
- Authors: Sathorar, Heloise Helena
- Date: 2018
- Subjects: Teacher participation in curriculum planning
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/31786 , vital:31828
- Description: This study sought to investigate lecturer preparedness to apply a critical approach to curriculum implementation and to establish their willingness or unwillingness to engage as transformative intellectuals with their students and to apply a problem-posing education in their classrooms. The study investigated lecturers’ critical pedagogy dispositions as well as their orientations towards applying a critical approach to curriculum implementation. A comprehensive literature review was done regarding the concept critical pedagogy, its tenets and principles as well as what it entails to apply a critical approach to curriculum implementation. In particular the literature review highlighted the responsibilities of a transformative intellectual as well as the requirements of applying a problem-posing education. The study was conducted through a constructivist lens and theoretically framed by referring to specific critical pedagogy concepts. The study is located in the interpretive paradigm and a qualitative research approach was followed. In particular, an instrumental case study analysis was used as research method. The sample consisted of 20 permanently employed lecturers from the School for Initial Teacher Education in the Faculty of Education at Nelson Mandela University who volunteered to participate in an online investigation regarding their critical pedagogy dispositions as well as their orientations towards applying a critical approach to curriculum implementation. The findings of the study revealed that lecturers generally have a positive disposition towards critical pedagogy as well as towards the application of a critical approach to curriculum implementation. Despite this positive picture there were pockets of resistance towards critical pedagogy and the application of a critical approach to curriculum implementation. Finally, the study proposes a critical approach model that could be employed to enhance lecturer preparedness to apply a critical approach in their classes.
- Full Text:
- Date Issued: 2018
- Authors: Sathorar, Heloise Helena
- Date: 2018
- Subjects: Teacher participation in curriculum planning
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/31786 , vital:31828
- Description: This study sought to investigate lecturer preparedness to apply a critical approach to curriculum implementation and to establish their willingness or unwillingness to engage as transformative intellectuals with their students and to apply a problem-posing education in their classrooms. The study investigated lecturers’ critical pedagogy dispositions as well as their orientations towards applying a critical approach to curriculum implementation. A comprehensive literature review was done regarding the concept critical pedagogy, its tenets and principles as well as what it entails to apply a critical approach to curriculum implementation. In particular the literature review highlighted the responsibilities of a transformative intellectual as well as the requirements of applying a problem-posing education. The study was conducted through a constructivist lens and theoretically framed by referring to specific critical pedagogy concepts. The study is located in the interpretive paradigm and a qualitative research approach was followed. In particular, an instrumental case study analysis was used as research method. The sample consisted of 20 permanently employed lecturers from the School for Initial Teacher Education in the Faculty of Education at Nelson Mandela University who volunteered to participate in an online investigation regarding their critical pedagogy dispositions as well as their orientations towards applying a critical approach to curriculum implementation. The findings of the study revealed that lecturers generally have a positive disposition towards critical pedagogy as well as towards the application of a critical approach to curriculum implementation. Despite this positive picture there were pockets of resistance towards critical pedagogy and the application of a critical approach to curriculum implementation. Finally, the study proposes a critical approach model that could be employed to enhance lecturer preparedness to apply a critical approach in their classes.
- Full Text:
- Date Issued: 2018
Factors affecting effective ecological restoration of Portulacaria afra (spekboom)-rich subtropical thicket and aboveground carbon endpoint projections
- Van der Vyver, Marius Lodewyk
- Authors: Van der Vyver, Marius Lodewyk
- Date: 2018
- Subjects: Restoration ecology , Plant conservation -- South Africa Portulacaria afra -- South Africa Shrubs -- South Africa
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/23250 , vital:30468
- Description: Among the requirements to achieve effective ecological restoration on a landscape scale are a scientific underpinning, strong adaptive management and the setting of realistic endpoints. Efficacy and success depend on a complex interplay of factors of both local and regional influence. Biome-wide restoration experiments are rare, but valuable for evaluating efficacy of different protocols according to local context. The Thicket-wide Plot (TWP) experiment was initiated by the Subtropical Thicket Restoration Programme to inform landscape-scale ecological restoration of degraded Portulacaria afra (spekboom)-rich Subtropical Thicket. Thirteen different planting treatments of Portulacaria afra (spekboom) truncheons were planted as replicated rows on 0.25 ha fenced plots across the distribution range of spekboom-rich thicket habitat to better establish effective restoration protocols. I used a rule-based learning ensemble algorithm to evaluate 60 different predictors that potentially impact effective restoration, covering a range of climatic, topographic, edaphic, ecological and management related factors observed at 227 of these TWP plots. Percentage survivorship and aboveground biomass carbon sequestration rate (ABCsr) were taken as proxies for efficacy derived from subsequent monitoring data gathered 2 - 5 years after establishment, and a new allometric model I developed for spekboom. I found herbivory and identification of target habitat the two most important predictors of restoration efficacy, both well within the control of the practitioner. Highest survivorship and ABCsr were associated with larger truncheons planted deeper. The only exception to this pattern was found amongst the two smallest size truncheon categories. The application of external rooting hormone or watering treatment to truncheons were found of no significance to effective restoration, while all the pruned treatments were, in association with lesser planting depth, found to be significantly less effective than untreated truncheons planted deeper. When the restoration protocol is optimal (largest truncheons planted deepest in target habitats and protected from herbivory), my results show higher annual carbon sequestration rates (1.46 - 3.7 t C ha−1 yr−1 in aboveground biomass) than most older restoration sites that have been identified as benchmarks of success. In order to project ABC endpoints, I generated 40 new species-specific allometric models and used them to estimate biomass and carbon of intact and degraded stands on five sites spread out across the region. The highest AGC for stands in both intact and degraded states were estimated at 42.96 t Cha−1 and 12.98 t C ha−1 respectively, and the lowest at 26.32 t C ha−1 and 2.52 t C ha−1. Large canopy dominant (LCD) species contributed the largest AGC portion at three intact stands. The second largest portion was recorded for spekboom. The difference between paired stands on each sample site ranged between 23.8 and 32.8 t C ha−1, which provide a realistic target for biome-wide restoration that, when adopted together with current protocols, may be reached within three decades of inception.
- Full Text:
- Date Issued: 2018
- Authors: Van der Vyver, Marius Lodewyk
- Date: 2018
- Subjects: Restoration ecology , Plant conservation -- South Africa Portulacaria afra -- South Africa Shrubs -- South Africa
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/23250 , vital:30468
- Description: Among the requirements to achieve effective ecological restoration on a landscape scale are a scientific underpinning, strong adaptive management and the setting of realistic endpoints. Efficacy and success depend on a complex interplay of factors of both local and regional influence. Biome-wide restoration experiments are rare, but valuable for evaluating efficacy of different protocols according to local context. The Thicket-wide Plot (TWP) experiment was initiated by the Subtropical Thicket Restoration Programme to inform landscape-scale ecological restoration of degraded Portulacaria afra (spekboom)-rich Subtropical Thicket. Thirteen different planting treatments of Portulacaria afra (spekboom) truncheons were planted as replicated rows on 0.25 ha fenced plots across the distribution range of spekboom-rich thicket habitat to better establish effective restoration protocols. I used a rule-based learning ensemble algorithm to evaluate 60 different predictors that potentially impact effective restoration, covering a range of climatic, topographic, edaphic, ecological and management related factors observed at 227 of these TWP plots. Percentage survivorship and aboveground biomass carbon sequestration rate (ABCsr) were taken as proxies for efficacy derived from subsequent monitoring data gathered 2 - 5 years after establishment, and a new allometric model I developed for spekboom. I found herbivory and identification of target habitat the two most important predictors of restoration efficacy, both well within the control of the practitioner. Highest survivorship and ABCsr were associated with larger truncheons planted deeper. The only exception to this pattern was found amongst the two smallest size truncheon categories. The application of external rooting hormone or watering treatment to truncheons were found of no significance to effective restoration, while all the pruned treatments were, in association with lesser planting depth, found to be significantly less effective than untreated truncheons planted deeper. When the restoration protocol is optimal (largest truncheons planted deepest in target habitats and protected from herbivory), my results show higher annual carbon sequestration rates (1.46 - 3.7 t C ha−1 yr−1 in aboveground biomass) than most older restoration sites that have been identified as benchmarks of success. In order to project ABC endpoints, I generated 40 new species-specific allometric models and used them to estimate biomass and carbon of intact and degraded stands on five sites spread out across the region. The highest AGC for stands in both intact and degraded states were estimated at 42.96 t Cha−1 and 12.98 t C ha−1 respectively, and the lowest at 26.32 t C ha−1 and 2.52 t C ha−1. Large canopy dominant (LCD) species contributed the largest AGC portion at three intact stands. The second largest portion was recorded for spekboom. The difference between paired stands on each sample site ranged between 23.8 and 32.8 t C ha−1, which provide a realistic target for biome-wide restoration that, when adopted together with current protocols, may be reached within three decades of inception.
- Full Text:
- Date Issued: 2018
Habitat use of important juvenile fish species in temperate Earnestine nursery areas with notes on feeding ecology and historical shifts to assist with conservation planning, South Africa
- Authors: Nel, Larize
- Date: 2018
- Subjects: Mariculture -- South Africa , Fishes -- Ecology -- South Africa Fishes -- Food -- South Africa
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/32904 , vital:32396
- Description: Estuaries are among the most productive ecosystems worldwide as they provide important refuge and feeding areas for the juveniles of many marine species, many of which have recreational importance. The use of these nursery areas by juvenile fishes in South Africa are in need of further investigation and many critical areas such as shallow water creeks and vegetated habitats remain understudied. By using mixed-methods, estuarine fish assemblages were assessed in five permanently open estuaries in the Eastern Cape Province of South Africa. A total of 81 428 comprising 24 families and 40 species of fishes were sampled by means of a 50 m seine net (12 mm mesh) along the length of these systems that comprised of six equidistant sites during the summer recruitment period (October - December) of 2014 and 2015. A higher catch per unit effort (CPUE) was recorded in 2014 (68 875) compared to the following year where a decline of approximately 82% was observed in the catch (12 553) for all estuaries except the Kromme Estuary. Catches were mainly dominated by the marine estuarine dependent sparid, Rhabdosargus holubi and the solely estuarine clupeid, Gilchristella aestuaria. Species compositions and catch abundance with regards to historical catches showed that the abundance of many marine estuarine dependent juveniles as well as important recreational species have declined within these systems and are mainly attributed to marine overfishing and the exploitation of undersized individuals in estuarine nurseries. Juvenile fishes that occur in these estuaries utilize a range of vegetated habitats ranging from salt marsh creeks, Zostera capensis beds, Spartina maritima and previously unexplored Phragmites australis areas. Sampling was achieved by using passive, double-winged, six-hooped fyke nets, 1 mm mesh size that was secured in placed on the nocturnal flood tide at each inundated vegetated and adjacent unvegetated habitat types. Higher catches were frequently recorded in vegetated areas for solely estuarine and marine estuarine dependent species and supports evidence of plasticity within these habitats. In general, the previously unstudied reed, P. australis showed the highest species richness and abundance of juvenile fishes overall, followed by, Z. capensis and the intertidal salt marsh species, S. maritima. These findings relate to many international trends on the value of vegetated areas as refugia for young fishes in estuaries. Fishes were also showing evidence of feeding and sheltering in these areas. By using conventional stomach contents and stable isotope methods (δ13C and δ15N signatures) on the abundant R. holubi in previously selected vegetation sites, it was clear that this species has a significant reliance on any of these habitats as their diets was largely comprised of a mixture of epiphytic algae and aquatic macrophytes. In addition, the diet of larger individuals (>80 mm) showed a greater component of invertebrates in previously unexplored habitats, which proves their omnivorous diet related to ontogenetic niche use. Knowledge of fine-scale habitat use by fishes is essential for conservation planning as exclusion zones can be optimised to limit anthropogenic influence on nursery use patterns in fishes. The availability of shallow water habitats (<60 cm) was assessed as an additional driver to explain the species diversity and richness of juvenile fishes within the lower reaches. These habitats are known as important nursery habitats providing numerous marine and estuarine spawned fishes with adequate refuge and food supply. This shallow water volume was measured by means of a two-man kayak using both the spring high and low tides in the lower reaches of these systems to assess juvenile assemblages. It was clear from the results that aquatic vegetation significantly adds to the volume of these areas and as a result, much greater fish density and species richness were observed. Generalized additive models showed that marine spawned species were particularly reliant on the availability of this shallow water along with submerged vegetation and additional environmental variables. The presence of structurally submerged vegetation typically characterized within shallow estuarine waters is commonly believed to reduce predation risk resulting in elevated densities of biota. Based on the current stock status and percentage of pristine breeding stock, five fish species classified as collapsed/overexploited was consistently found within these systems with an additional 14 species currently classified as exploited/vulnerable. Based on the current species richness and diversity, available habitat cover and knowledge regarding important recreational species, priority areas that require some form of legal protection in order to meet potential biodiversity targets, could be identified. It is a legal requirement in South Africa that all estuaries require management plans that should be based on good knowledge of priority habitats for fauna and flora. The identification of estuarine protected areas is seen as a mechanism for protecting a representative sample of the biodiversity accompanied by a complete range of environmental gradients and habitat types at a reasonable scale in order to maximize the protection of estuarine species.
- Full Text:
- Date Issued: 2018
- Authors: Nel, Larize
- Date: 2018
- Subjects: Mariculture -- South Africa , Fishes -- Ecology -- South Africa Fishes -- Food -- South Africa
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/32904 , vital:32396
- Description: Estuaries are among the most productive ecosystems worldwide as they provide important refuge and feeding areas for the juveniles of many marine species, many of which have recreational importance. The use of these nursery areas by juvenile fishes in South Africa are in need of further investigation and many critical areas such as shallow water creeks and vegetated habitats remain understudied. By using mixed-methods, estuarine fish assemblages were assessed in five permanently open estuaries in the Eastern Cape Province of South Africa. A total of 81 428 comprising 24 families and 40 species of fishes were sampled by means of a 50 m seine net (12 mm mesh) along the length of these systems that comprised of six equidistant sites during the summer recruitment period (October - December) of 2014 and 2015. A higher catch per unit effort (CPUE) was recorded in 2014 (68 875) compared to the following year where a decline of approximately 82% was observed in the catch (12 553) for all estuaries except the Kromme Estuary. Catches were mainly dominated by the marine estuarine dependent sparid, Rhabdosargus holubi and the solely estuarine clupeid, Gilchristella aestuaria. Species compositions and catch abundance with regards to historical catches showed that the abundance of many marine estuarine dependent juveniles as well as important recreational species have declined within these systems and are mainly attributed to marine overfishing and the exploitation of undersized individuals in estuarine nurseries. Juvenile fishes that occur in these estuaries utilize a range of vegetated habitats ranging from salt marsh creeks, Zostera capensis beds, Spartina maritima and previously unexplored Phragmites australis areas. Sampling was achieved by using passive, double-winged, six-hooped fyke nets, 1 mm mesh size that was secured in placed on the nocturnal flood tide at each inundated vegetated and adjacent unvegetated habitat types. Higher catches were frequently recorded in vegetated areas for solely estuarine and marine estuarine dependent species and supports evidence of plasticity within these habitats. In general, the previously unstudied reed, P. australis showed the highest species richness and abundance of juvenile fishes overall, followed by, Z. capensis and the intertidal salt marsh species, S. maritima. These findings relate to many international trends on the value of vegetated areas as refugia for young fishes in estuaries. Fishes were also showing evidence of feeding and sheltering in these areas. By using conventional stomach contents and stable isotope methods (δ13C and δ15N signatures) on the abundant R. holubi in previously selected vegetation sites, it was clear that this species has a significant reliance on any of these habitats as their diets was largely comprised of a mixture of epiphytic algae and aquatic macrophytes. In addition, the diet of larger individuals (>80 mm) showed a greater component of invertebrates in previously unexplored habitats, which proves their omnivorous diet related to ontogenetic niche use. Knowledge of fine-scale habitat use by fishes is essential for conservation planning as exclusion zones can be optimised to limit anthropogenic influence on nursery use patterns in fishes. The availability of shallow water habitats (<60 cm) was assessed as an additional driver to explain the species diversity and richness of juvenile fishes within the lower reaches. These habitats are known as important nursery habitats providing numerous marine and estuarine spawned fishes with adequate refuge and food supply. This shallow water volume was measured by means of a two-man kayak using both the spring high and low tides in the lower reaches of these systems to assess juvenile assemblages. It was clear from the results that aquatic vegetation significantly adds to the volume of these areas and as a result, much greater fish density and species richness were observed. Generalized additive models showed that marine spawned species were particularly reliant on the availability of this shallow water along with submerged vegetation and additional environmental variables. The presence of structurally submerged vegetation typically characterized within shallow estuarine waters is commonly believed to reduce predation risk resulting in elevated densities of biota. Based on the current stock status and percentage of pristine breeding stock, five fish species classified as collapsed/overexploited was consistently found within these systems with an additional 14 species currently classified as exploited/vulnerable. Based on the current species richness and diversity, available habitat cover and knowledge regarding important recreational species, priority areas that require some form of legal protection in order to meet potential biodiversity targets, could be identified. It is a legal requirement in South Africa that all estuaries require management plans that should be based on good knowledge of priority habitats for fauna and flora. The identification of estuarine protected areas is seen as a mechanism for protecting a representative sample of the biodiversity accompanied by a complete range of environmental gradients and habitat types at a reasonable scale in order to maximize the protection of estuarine species.
- Full Text:
- Date Issued: 2018
In vivo toxicological evaluation of peptide conjugated gold nanoparticles for potential application in colorectal cancer diagnosis
- Authors: Adewale, Olusola Bolaji
- Date: 2018
- Subjects: Nanostructured materials -- Toxicology , Colon (Anatomy) -- Cancer Rectum -- Cancer
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/50133 , vital:42050
- Description: Colorectal cancer (CRC) is among the leading cause of cancer-related deaths in South Africa and worldwide. Efforts are being made at finding improved diagnostic tools, as early detection (before metastasis) is a major factor in CRC treatment. Colonoscopy is the most reliable detection method, but is a specialised and expensive procedure, which is invasive, not readily available and not patient-friendly. There is a risk of developing interval cancers, as colonoscopies are performed every 10 years after the age of 40. The development of non-invasive, cost efficient and readily available diagnostic tools to CRC, which can be performed at more regular intervals, using tumour-targeting molecular imaging agents, is of urgent attention. Gold nanoparticles (AuNPs) possess several physicochemical properties, including ease of synthesis, biocompatibility, and the ability to be conjugated by ligands or biomolecules such as polyethylene glycol (PEG) and peptides for improved stability, tissue targeting and selectivity. These factors potentiate the role in biomedical applications, including cancer theranostics. Conjugation of AuNPs with a targeting molecule (e.g. antibody or peptide) is directed against cancer cell receptors. The peptides, p.C, p.L, and p.14, bind to CRC cells in vitro. Conjugation of AuNPs with these peptides should be investigated for CRC diagnosis in vivo, as it is hypothesised to allow examinations at shorter intervals through imaging techniques. This could reduce the risk of interval cancers, but before developing this novel tool, in vivo toxicity evaluations are essential. This study was therefore aimed at investigating the short- and long-term toxicological effects of a single intravenous injection of peptides (p.C, p.L, and p.14) conjugated to AuNPs in a healthy rat model. Citrate-capped AuNPs were synthesised by the citrate-reduction method, and conjugated with each peptide (biotinylated) using a combination of PEG (99% PEG-OH and 1% PEG-biotin) as a stabilising agent and linker, via biotin-streptavidin interaction. Healthy male Wistar rats were intravenously injected with 14 nm citrate-AuNPs, PEG-, p.C-PEG, p.L-PEG, and p.14-PEG-AuNPs (100 μg/kg body weight), and the control rats were injected with phosphate buffered saline. The animals were monitored for behavioural, physiological, biochemical, haematological and histological changes, as well as inflammatory responses. Phase 1 rats were sacrificed 2 weeks post-injection to determine the immediate or acute toxicity of the AuNPs, while phase 2 animals were sacrificed 12 weeks post-injection, to investigate the delayed or persistence toxicity of the AuNPs. Results revealed no significant toxicities with the citrate, PEG-, p.C-PEG and p.14-PEG-AuNPs over 12 weeks post-exposure, as evidenced by biochemical assays such as serum marker enzymes, liver and kidney function markers, and cholestatic indicators; haematological parameters; oxidative stress markers; and histopathological examinations. P.L-PEG-AuNPs, however, caused significant toxicity (p<0.05) to rats, as evidenced by increased relative liver weight, increased malondialdehyde levels, and total white blood cell counts 2 weeks post-exposure when compared to the control group. This was, however, reversed during the 12 weeks post-exposure. Further, there were no evidence of inflammatory responses, using pro-inflammatory markers including phospho interleukin 18 (IL-18) and interferon-γ (IFN-γ), as indicated by immunohistochemical staining of the liver, spleen, kidney and colon of rats 2 weeks post-injection of AuNPs. Citrate, PEG-, p.C-PEG, and p.14-PEG-AuNPs did not induce immediate, acute or persistent toxicity, while p.L-PEG-AuNPs induced a transient acute toxicity. It can be concluded that 14 nm spherical citrate-AuNPs at 100 μg/kg body weight is a good candidate for biomedical applications, and as a suitable carrier for diagnostic and/or therapeutic molecules. Combination of 99% PEG-OH and 1% PEG-biotin is an appropriate option for stabilising AuNPs in biological environment, and conjugating secondary diagnostic or therapeutic biomolecules or agents to citrate-capped AuNPs. Peptide-conjugated AuNPs are suitable for the development into a diagnostic tool for CRC in vivo.
- Full Text:
- Date Issued: 2018
- Authors: Adewale, Olusola Bolaji
- Date: 2018
- Subjects: Nanostructured materials -- Toxicology , Colon (Anatomy) -- Cancer Rectum -- Cancer
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/50133 , vital:42050
- Description: Colorectal cancer (CRC) is among the leading cause of cancer-related deaths in South Africa and worldwide. Efforts are being made at finding improved diagnostic tools, as early detection (before metastasis) is a major factor in CRC treatment. Colonoscopy is the most reliable detection method, but is a specialised and expensive procedure, which is invasive, not readily available and not patient-friendly. There is a risk of developing interval cancers, as colonoscopies are performed every 10 years after the age of 40. The development of non-invasive, cost efficient and readily available diagnostic tools to CRC, which can be performed at more regular intervals, using tumour-targeting molecular imaging agents, is of urgent attention. Gold nanoparticles (AuNPs) possess several physicochemical properties, including ease of synthesis, biocompatibility, and the ability to be conjugated by ligands or biomolecules such as polyethylene glycol (PEG) and peptides for improved stability, tissue targeting and selectivity. These factors potentiate the role in biomedical applications, including cancer theranostics. Conjugation of AuNPs with a targeting molecule (e.g. antibody or peptide) is directed against cancer cell receptors. The peptides, p.C, p.L, and p.14, bind to CRC cells in vitro. Conjugation of AuNPs with these peptides should be investigated for CRC diagnosis in vivo, as it is hypothesised to allow examinations at shorter intervals through imaging techniques. This could reduce the risk of interval cancers, but before developing this novel tool, in vivo toxicity evaluations are essential. This study was therefore aimed at investigating the short- and long-term toxicological effects of a single intravenous injection of peptides (p.C, p.L, and p.14) conjugated to AuNPs in a healthy rat model. Citrate-capped AuNPs were synthesised by the citrate-reduction method, and conjugated with each peptide (biotinylated) using a combination of PEG (99% PEG-OH and 1% PEG-biotin) as a stabilising agent and linker, via biotin-streptavidin interaction. Healthy male Wistar rats were intravenously injected with 14 nm citrate-AuNPs, PEG-, p.C-PEG, p.L-PEG, and p.14-PEG-AuNPs (100 μg/kg body weight), and the control rats were injected with phosphate buffered saline. The animals were monitored for behavioural, physiological, biochemical, haematological and histological changes, as well as inflammatory responses. Phase 1 rats were sacrificed 2 weeks post-injection to determine the immediate or acute toxicity of the AuNPs, while phase 2 animals were sacrificed 12 weeks post-injection, to investigate the delayed or persistence toxicity of the AuNPs. Results revealed no significant toxicities with the citrate, PEG-, p.C-PEG and p.14-PEG-AuNPs over 12 weeks post-exposure, as evidenced by biochemical assays such as serum marker enzymes, liver and kidney function markers, and cholestatic indicators; haematological parameters; oxidative stress markers; and histopathological examinations. P.L-PEG-AuNPs, however, caused significant toxicity (p<0.05) to rats, as evidenced by increased relative liver weight, increased malondialdehyde levels, and total white blood cell counts 2 weeks post-exposure when compared to the control group. This was, however, reversed during the 12 weeks post-exposure. Further, there were no evidence of inflammatory responses, using pro-inflammatory markers including phospho interleukin 18 (IL-18) and interferon-γ (IFN-γ), as indicated by immunohistochemical staining of the liver, spleen, kidney and colon of rats 2 weeks post-injection of AuNPs. Citrate, PEG-, p.C-PEG, and p.14-PEG-AuNPs did not induce immediate, acute or persistent toxicity, while p.L-PEG-AuNPs induced a transient acute toxicity. It can be concluded that 14 nm spherical citrate-AuNPs at 100 μg/kg body weight is a good candidate for biomedical applications, and as a suitable carrier for diagnostic and/or therapeutic molecules. Combination of 99% PEG-OH and 1% PEG-biotin is an appropriate option for stabilising AuNPs in biological environment, and conjugating secondary diagnostic or therapeutic biomolecules or agents to citrate-capped AuNPs. Peptide-conjugated AuNPs are suitable for the development into a diagnostic tool for CRC in vivo.
- Full Text:
- Date Issued: 2018