Estimation of a generalist meso-carnivore (black-backed jackal) population from a fenced protected area
- Davidson-Phillips, Samuel Ralph
- Authors: Davidson-Phillips, Samuel Ralph
- Date: 2024-04
- Subjects: Wildlife conservation , Carnivorous animals -- Conservation , Carnivorous animals -- Ecology
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/63698 , vital:73589
- Description: Since 2017, landowners, field guides, and management staff have reported large groups of black-backed jackals (Lupullela mesomelas) (here-forward jackal) in the Welgevonden Game Reserve, Limpopo, South Africa. This is linked with several observations of jackals predating on various ungulate species, potentially leading to unintended consequences on prey populations. These observations combined with an apparent poor survival rate of impala (Aepyceros melampus) and continuous declines in their number led to the perception that jackals could be partly responsible. Several studies have attempted to describe the ecological role of jackals within multiple environments, most of which have proven to be variable and context dependent. Human-modified landscapes along with the fencing of protected areas, may have manipulated the role of jackal within these scenarios. Jackals are wide-ranging and generally not confined by fencing, therefore their population trends possibly fluctuate within these anthropogenic landscapes. Re-introduced apex predators have been shown to facilitate food (provision of carrion) and simultaneously suppress jackal (active killing), this, however, remains difficult to predict. Jackals are classified as facultative cooperative hunters, and the term describes how they hunt in groups opportunistically when suitable resources of prey are available. The indication by several studies that jackals do actively predate rather than only scavenge, illustrates that the species has the potential to cause declines in an ungulate population. It therefore appears erroneous to exclude the species in terms of predator-prey relationships, particularly for land managers of fenced protected areas. The first step to any ecological management is the understanding of population size and trends over time. Unfortunately, little to no reliable methods exist to assess or monitor jackal populations. A popular tool for cryptic and wide-ranging terrestrial carnivores is Spatial Capture Recapture (SCR) models, typically through a camera trap array. These often rely on individual identities and an imperfect detection process to derive a statistical estimate of a given area. Jackals have been assumed to be individually unidentifiable and therefore these methods have largely been excluded. To address this a pilot-targeted camera-trap survey was conducted to improve capture and image quality. Following the role of this procedure, semi-automated software was applied to test the feasibility of individual identifications of captured images. This resulted in a subset of 58 right and left identifiable flank images, compiled from the highest graded images (n = 220) using the open-source Interactive Individual IdentificationSystem Beta Contour 3.0 (I3S Contour). I3S Contour assists users by distinguishing between unique contours on independent flanks without omitting observer effort and ranking. The effectiveness of the identification procedure was evaluated using three software tool trials, namely Computer-aided Annotation, Manual Contour Annotation, and Manual Contour Annotation (MA-2), where MA-2 included additional user-defined meta-data to images. Results showed that jackals could be individually identified from camera trap images and thus opened up the use of previously excluded SCR methodologies. Utilising the jackal database derived from the identification procedures described a total of 28 complete identifications (both flanks matched), 32 left-sided and 36 right-sided captures were used. These were derived from two independent survey periods split between seasonality (Winter & Spring). Two SCR methods were compared, namely, the Spatially Explicit Camera Recapture (SECR) and the newly developed Spatial Presence-Absence (SPA) modelling approach. SECR relies on full individual identification linked to spatial locations to derive spatial parameters to estimate population densities. The SECR methodology has been considered the most precise and was thus used as the benchmark. SPA relies on detections only (i.e., without individual identities), along with informative or uninformative priors. This must be across a spatial array that has detectors close enough to allow for simultaneous detections during each occasion (< 24 hours). Comparisons between these model outputs indicated a high degree of confidence interval overlap; however, SPA had a consistently higher posterior mode density estimate (63-64% higher), where the coefficient of variation between outputs also indicated the SPA having a closer relative precision. The targeted survey results for both model outputs for 2021 did not appear unusually high when compared to other studies. To assess the WGR population size over the long term, opportunistic by-catch data from a nine-year leopard (Panthera pardus) camera survey (Panthera organisation) was utilised. Model outputs from each of the years indicated that population estimates remained relatively stable. This was an unexpected result as the SPA densities did not follow the detection observations. This could be attributed to M not being set high enough (200) and the model reaching the limit, resulting in similar outputs between years. An alternative explanation is where the station spacing is larger than the diameter of the home range, which may reduce spatial correlation. , Thesis (MSc) -- Faculty of Science, School of Natural Resource Science & Management, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Davidson-Phillips, Samuel Ralph
- Date: 2024-04
- Subjects: Wildlife conservation , Carnivorous animals -- Conservation , Carnivorous animals -- Ecology
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/63698 , vital:73589
- Description: Since 2017, landowners, field guides, and management staff have reported large groups of black-backed jackals (Lupullela mesomelas) (here-forward jackal) in the Welgevonden Game Reserve, Limpopo, South Africa. This is linked with several observations of jackals predating on various ungulate species, potentially leading to unintended consequences on prey populations. These observations combined with an apparent poor survival rate of impala (Aepyceros melampus) and continuous declines in their number led to the perception that jackals could be partly responsible. Several studies have attempted to describe the ecological role of jackals within multiple environments, most of which have proven to be variable and context dependent. Human-modified landscapes along with the fencing of protected areas, may have manipulated the role of jackal within these scenarios. Jackals are wide-ranging and generally not confined by fencing, therefore their population trends possibly fluctuate within these anthropogenic landscapes. Re-introduced apex predators have been shown to facilitate food (provision of carrion) and simultaneously suppress jackal (active killing), this, however, remains difficult to predict. Jackals are classified as facultative cooperative hunters, and the term describes how they hunt in groups opportunistically when suitable resources of prey are available. The indication by several studies that jackals do actively predate rather than only scavenge, illustrates that the species has the potential to cause declines in an ungulate population. It therefore appears erroneous to exclude the species in terms of predator-prey relationships, particularly for land managers of fenced protected areas. The first step to any ecological management is the understanding of population size and trends over time. Unfortunately, little to no reliable methods exist to assess or monitor jackal populations. A popular tool for cryptic and wide-ranging terrestrial carnivores is Spatial Capture Recapture (SCR) models, typically through a camera trap array. These often rely on individual identities and an imperfect detection process to derive a statistical estimate of a given area. Jackals have been assumed to be individually unidentifiable and therefore these methods have largely been excluded. To address this a pilot-targeted camera-trap survey was conducted to improve capture and image quality. Following the role of this procedure, semi-automated software was applied to test the feasibility of individual identifications of captured images. This resulted in a subset of 58 right and left identifiable flank images, compiled from the highest graded images (n = 220) using the open-source Interactive Individual IdentificationSystem Beta Contour 3.0 (I3S Contour). I3S Contour assists users by distinguishing between unique contours on independent flanks without omitting observer effort and ranking. The effectiveness of the identification procedure was evaluated using three software tool trials, namely Computer-aided Annotation, Manual Contour Annotation, and Manual Contour Annotation (MA-2), where MA-2 included additional user-defined meta-data to images. Results showed that jackals could be individually identified from camera trap images and thus opened up the use of previously excluded SCR methodologies. Utilising the jackal database derived from the identification procedures described a total of 28 complete identifications (both flanks matched), 32 left-sided and 36 right-sided captures were used. These were derived from two independent survey periods split between seasonality (Winter & Spring). Two SCR methods were compared, namely, the Spatially Explicit Camera Recapture (SECR) and the newly developed Spatial Presence-Absence (SPA) modelling approach. SECR relies on full individual identification linked to spatial locations to derive spatial parameters to estimate population densities. The SECR methodology has been considered the most precise and was thus used as the benchmark. SPA relies on detections only (i.e., without individual identities), along with informative or uninformative priors. This must be across a spatial array that has detectors close enough to allow for simultaneous detections during each occasion (< 24 hours). Comparisons between these model outputs indicated a high degree of confidence interval overlap; however, SPA had a consistently higher posterior mode density estimate (63-64% higher), where the coefficient of variation between outputs also indicated the SPA having a closer relative precision. The targeted survey results for both model outputs for 2021 did not appear unusually high when compared to other studies. To assess the WGR population size over the long term, opportunistic by-catch data from a nine-year leopard (Panthera pardus) camera survey (Panthera organisation) was utilised. Model outputs from each of the years indicated that population estimates remained relatively stable. This was an unexpected result as the SPA densities did not follow the detection observations. This could be attributed to M not being set high enough (200) and the model reaching the limit, resulting in similar outputs between years. An alternative explanation is where the station spacing is larger than the diameter of the home range, which may reduce spatial correlation. , Thesis (MSc) -- Faculty of Science, School of Natural Resource Science & Management, 2024
- Full Text:
- Date Issued: 2024-04
Evaluating elephant, Loxodonta africana, space-use and elephant-linked vegetation change in Liwonde National Park, Malawi
- Authors: Evers, Emma Else Maria
- Date: 2024-04
- Subjects: Elephants -- Nutrition -- Malawi , Ecological heterogeneity , Vegetation and climate
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/63744 , vital:73594
- Description: Heterogeneity, the spatio-temporal variation of abiotic and biotic factors, is a key concept that underpins many ecological phenomena and promotes biodiversity. Ecosystem engineers, such as African savanna elephants (hereafter elephant), Loxodonta africana, are organisms capable of affecting heterogeneity through the creation or modification of habitats. Thus, their impacts can have important consequences for ecosystem biodiversity, both positive and negative. Caughley’s “elephant problem” cautions that confined or compressed, growing elephant populations will inevitably lead to a loss of biodiversity. However, a shift in our understanding of elephants suggests that not all elephant impacts lead to negative biodiversity consequences, as long as there is a heterogeneous spread of elephant impacts that allows for spatio-temporal refuges promoting the persistence of both impact-tolerant and impact-intolerant species. To date, little empirical evidence is available in support of managing elephants under this paradigm and few studies are available that infer the consequences of the distribution of elephant impacts on biodiversity. In addition, most studies use parametric statistics that do not account for scale, spatial autocorrelation, or non-stationarity, leading to a misrepresentation of the underlying processes and patterns of drivers of elephant space-use and the consequences of their impacts on biodiversity. Here, I evaluate spatio-temporal patterns and drivers of elephant space-use, and how the distribution of their impacts affects biodiversity through vegetation changes, using a multi-scaled spatial approach, in Liwonde National Park, Malawi. My study demonstrates that elephant space-use in Liwonde is heterogeneous, leading to spatio-temporal variation in the distribution of their impacts, even in a small, fenced reserve. The importance of the drivers of this heterogeneous space-use varied based on the scale of analysis, water was generally important at larger scales while vegetation quality (indexed by NDVI) was more important at smaller scales. When examined using local models, my results suggest that relationships exhibit non-stationarity, what is important in one area of the park is not necessarily important in other areas. The spatio-temporal variation of the inferred impacts of elephants in Liwonde still allowed for spatio-temporal refuges to be created, no clear linear relationship was found between elephant return intervals and woody species structural and functional diversity (indexed by changes in tree cover and changes in annual regrowth using Normalized Difference Vegetation Index as a measure, respectively) throughout the park. My study provides support for adopting the heterogeneity paradigm for managing elephants and demonstrates that not all elephant impacts result in negative vegetation change. I also demonstrate the crucial implications of accounting for scale, non-stationarity, and spatial autocorrelation to evaluate how animals both respond to, and contribute to, environmental heterogeneity. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Evers, Emma Else Maria
- Date: 2024-04
- Subjects: Elephants -- Nutrition -- Malawi , Ecological heterogeneity , Vegetation and climate
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/63744 , vital:73594
- Description: Heterogeneity, the spatio-temporal variation of abiotic and biotic factors, is a key concept that underpins many ecological phenomena and promotes biodiversity. Ecosystem engineers, such as African savanna elephants (hereafter elephant), Loxodonta africana, are organisms capable of affecting heterogeneity through the creation or modification of habitats. Thus, their impacts can have important consequences for ecosystem biodiversity, both positive and negative. Caughley’s “elephant problem” cautions that confined or compressed, growing elephant populations will inevitably lead to a loss of biodiversity. However, a shift in our understanding of elephants suggests that not all elephant impacts lead to negative biodiversity consequences, as long as there is a heterogeneous spread of elephant impacts that allows for spatio-temporal refuges promoting the persistence of both impact-tolerant and impact-intolerant species. To date, little empirical evidence is available in support of managing elephants under this paradigm and few studies are available that infer the consequences of the distribution of elephant impacts on biodiversity. In addition, most studies use parametric statistics that do not account for scale, spatial autocorrelation, or non-stationarity, leading to a misrepresentation of the underlying processes and patterns of drivers of elephant space-use and the consequences of their impacts on biodiversity. Here, I evaluate spatio-temporal patterns and drivers of elephant space-use, and how the distribution of their impacts affects biodiversity through vegetation changes, using a multi-scaled spatial approach, in Liwonde National Park, Malawi. My study demonstrates that elephant space-use in Liwonde is heterogeneous, leading to spatio-temporal variation in the distribution of their impacts, even in a small, fenced reserve. The importance of the drivers of this heterogeneous space-use varied based on the scale of analysis, water was generally important at larger scales while vegetation quality (indexed by NDVI) was more important at smaller scales. When examined using local models, my results suggest that relationships exhibit non-stationarity, what is important in one area of the park is not necessarily important in other areas. The spatio-temporal variation of the inferred impacts of elephants in Liwonde still allowed for spatio-temporal refuges to be created, no clear linear relationship was found between elephant return intervals and woody species structural and functional diversity (indexed by changes in tree cover and changes in annual regrowth using Normalized Difference Vegetation Index as a measure, respectively) throughout the park. My study provides support for adopting the heterogeneity paradigm for managing elephants and demonstrates that not all elephant impacts result in negative vegetation change. I also demonstrate the crucial implications of accounting for scale, non-stationarity, and spatial autocorrelation to evaluate how animals both respond to, and contribute to, environmental heterogeneity. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
Evaluation of road surface distresses using GPS and GIS techniques: a case study of the City of Johannesburg, South Africa
- Authors: Tsedu, Rinae
- Date: 2024-04
- Subjects: Global Positioning System South Africa -- Johannesburg , Navigation -- Technological innovations , Geographic information systems -- South Africa -- Johannesburg
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64401 , vital:73695
- Description: Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Tsedu, Rinae
- Date: 2024-04
- Subjects: Global Positioning System South Africa -- Johannesburg , Navigation -- Technological innovations , Geographic information systems -- South Africa -- Johannesburg
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64401 , vital:73695
- Description: Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
Exploring the role of herbivory in Albany Subtropical Thicket restoration
- Authors: Hunt, Kristen Louise
- Date: 2024-04
- Subjects: Shrubs -- South Africa , Portulacaria afra -- South Africa , Grasslands -- South Africa , Plant communities -- South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64060 , vital:73647
- Description: This dissertation attempted to investigate the influence of herbivory on the success of thicket restoration, addressing a critical gap in the current knowledge within the restoration initiative. Despite two decades of thicket restoration practices, the role of herbivory in influencing restoration success has been assumed and not yet quantified. This research aimed to observe and identify herbivore species and their interactions that may affect the survival of Portulacaria afra Jacq. material planted in thicket restoration contexts. This research took place on three game farms serving as case studies within the Albany Subtropical Thicket (Eastern Cape, South Africa). Multiple experiments were conducted to assess how the concept of different “natural refugia” might impact herbivore interactions with planted material, incorporating factors such as planting around rainfall, within open and semi-intact vegetation patches, and in proximity to water sources. Trail cameras were used for real-time monitoring of herbivore interactions within planted sites to understand and quantify herbivore interactions with P. afra cuttings and how they may impact plant survival. Results from the trail camera monitoring (Chapter 2) indicate varied herbivore interactions occurring on planted material, with the primary herbivore responsible for these interactions varying among farms. Species interactions were not consistent across farms, and herbivore interactions exhibited spatial and temporal variability. Notably, interactions declined soon after the start of the wet phase when surrounding vegetation could recover, indicating the influences of alternative forage availability on herbivore foraging choices. Different herbivore interactions were identified and quantified through trail camera images, ranging from minor biomass removal (estimated at <5 cm of stem and leaf material) to more detrimental actions such as uprooting and leaf stripping. Consistently, planted P. afra survival rates (Chapter 3) were significantly higher for protected material than those exposed to herbivores, regardless of whether planted in a dry or wet phase. Moreover, when exposed to herbivores, rooted material had significantly higher survival rates than unrooted material, indicating the potential advantage of a well-developed root system in faster recovery after a herbivory event. This research explored the influence of various factors, including rainfall, rooting state, protection, surrounding vegetation, and proximity to water, on P. afra survival and how some of these factors may affect P. afra survival in relation to herbivore interactions (Chapter 3). Significant differences in cutting survival were observed between dry and wet phases, rooted and unrooted material, and material protected vs exposed to herbivores. While survival was not significantly different in experiments involving surrounding vegetation and proximity to water, potential patterns were identified, warranting further investigation. A clipping and defoliation experiment under simulated seasonal conditions emphasised the significance of , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Hunt, Kristen Louise
- Date: 2024-04
- Subjects: Shrubs -- South Africa , Portulacaria afra -- South Africa , Grasslands -- South Africa , Plant communities -- South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64060 , vital:73647
- Description: This dissertation attempted to investigate the influence of herbivory on the success of thicket restoration, addressing a critical gap in the current knowledge within the restoration initiative. Despite two decades of thicket restoration practices, the role of herbivory in influencing restoration success has been assumed and not yet quantified. This research aimed to observe and identify herbivore species and their interactions that may affect the survival of Portulacaria afra Jacq. material planted in thicket restoration contexts. This research took place on three game farms serving as case studies within the Albany Subtropical Thicket (Eastern Cape, South Africa). Multiple experiments were conducted to assess how the concept of different “natural refugia” might impact herbivore interactions with planted material, incorporating factors such as planting around rainfall, within open and semi-intact vegetation patches, and in proximity to water sources. Trail cameras were used for real-time monitoring of herbivore interactions within planted sites to understand and quantify herbivore interactions with P. afra cuttings and how they may impact plant survival. Results from the trail camera monitoring (Chapter 2) indicate varied herbivore interactions occurring on planted material, with the primary herbivore responsible for these interactions varying among farms. Species interactions were not consistent across farms, and herbivore interactions exhibited spatial and temporal variability. Notably, interactions declined soon after the start of the wet phase when surrounding vegetation could recover, indicating the influences of alternative forage availability on herbivore foraging choices. Different herbivore interactions were identified and quantified through trail camera images, ranging from minor biomass removal (estimated at <5 cm of stem and leaf material) to more detrimental actions such as uprooting and leaf stripping. Consistently, planted P. afra survival rates (Chapter 3) were significantly higher for protected material than those exposed to herbivores, regardless of whether planted in a dry or wet phase. Moreover, when exposed to herbivores, rooted material had significantly higher survival rates than unrooted material, indicating the potential advantage of a well-developed root system in faster recovery after a herbivory event. This research explored the influence of various factors, including rainfall, rooting state, protection, surrounding vegetation, and proximity to water, on P. afra survival and how some of these factors may affect P. afra survival in relation to herbivore interactions (Chapter 3). Significant differences in cutting survival were observed between dry and wet phases, rooted and unrooted material, and material protected vs exposed to herbivores. While survival was not significantly different in experiments involving surrounding vegetation and proximity to water, potential patterns were identified, warranting further investigation. A clipping and defoliation experiment under simulated seasonal conditions emphasised the significance of , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
Herpetofaunal diversity and affiliations of the Okavango River Basin, with specific focus on the Angolan headwaters
- Authors: Conradie, Werner
- Date: 2024-04
- Subjects: Water conservation -- Okavango River Delta , Watersheds -- Okavango River -- Angola , Biodiversity -- Angola
- Language: English
- Type: Doctorate theses , text
- Identifier: http://hdl.handle.net/10948/63667 , vital:73576
- Description: Although Africa is reputed to possess some of the richest herpetofaunal diversities in the world, a number of areas remain poorly documented and thus inadequately conserved. One such area in particular is the south-eastern part of Angola. Angola endured a long struggle for independence with a protracted civil war that lasted for nearly three decades, leaving the status of the country’s biodiversity in turmoil. Over the past two decades, Angola has become more accessible for biodiversity surveys, opening up new opportunities to document these previously poorly studied areas and help conserve its biodiversity. South-eastern Angola is the water source of the world-renowned Okavango Delta. However very little is known about the biodiversity, diversity status and conservation significance of the headwaters supplying the largest inland delta in the world. To address this bias in sampling and to investigate the conservation importance of the region, a series of rapid biodiversity surveys of the Angolan Okavango River Basin were conducted between 2012 and 2019. This study contributed over 2150 individual records of amphibians and reptiles, representing 88 reptile and 43 amphibian species. At least 15 species were added to the growing country checklist, with the south-eastern region of Angola now comprising 113 reptile species and 51 amphibian species. Because of this study, the area is now one of the most species-rich and well-studied areas in Angola. This study provided the first genetic data for 26 species, and sequences containing Angolan specimens for the first time were generated for 80 species, of which 23 species have originally been described from Angola. Maximum likelihood and Bayesian inference analyses, supported by species delimitation analyses, were utilised to validate specific species statuses. This allowed for the description of five new species of snake, one gecko and two frogs for Angola. The material further contributed to the description of a new genus of snakes. Numerous undescribed and potentially cryptic species were identified, long-lasting taxonomic issues were resolved, and various taxonomic adjustments were emphasised. Further contributions of the material include assisting in the revision of targeted Angolan amphibian and reptile groups as well as large-scale phylogenetic studies across Africa. , Thesis (PhD) -- Faculty of Science, School of Natural Resource Science & Management, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Conradie, Werner
- Date: 2024-04
- Subjects: Water conservation -- Okavango River Delta , Watersheds -- Okavango River -- Angola , Biodiversity -- Angola
- Language: English
- Type: Doctorate theses , text
- Identifier: http://hdl.handle.net/10948/63667 , vital:73576
- Description: Although Africa is reputed to possess some of the richest herpetofaunal diversities in the world, a number of areas remain poorly documented and thus inadequately conserved. One such area in particular is the south-eastern part of Angola. Angola endured a long struggle for independence with a protracted civil war that lasted for nearly three decades, leaving the status of the country’s biodiversity in turmoil. Over the past two decades, Angola has become more accessible for biodiversity surveys, opening up new opportunities to document these previously poorly studied areas and help conserve its biodiversity. South-eastern Angola is the water source of the world-renowned Okavango Delta. However very little is known about the biodiversity, diversity status and conservation significance of the headwaters supplying the largest inland delta in the world. To address this bias in sampling and to investigate the conservation importance of the region, a series of rapid biodiversity surveys of the Angolan Okavango River Basin were conducted between 2012 and 2019. This study contributed over 2150 individual records of amphibians and reptiles, representing 88 reptile and 43 amphibian species. At least 15 species were added to the growing country checklist, with the south-eastern region of Angola now comprising 113 reptile species and 51 amphibian species. Because of this study, the area is now one of the most species-rich and well-studied areas in Angola. This study provided the first genetic data for 26 species, and sequences containing Angolan specimens for the first time were generated for 80 species, of which 23 species have originally been described from Angola. Maximum likelihood and Bayesian inference analyses, supported by species delimitation analyses, were utilised to validate specific species statuses. This allowed for the description of five new species of snake, one gecko and two frogs for Angola. The material further contributed to the description of a new genus of snakes. Numerous undescribed and potentially cryptic species were identified, long-lasting taxonomic issues were resolved, and various taxonomic adjustments were emphasised. Further contributions of the material include assisting in the revision of targeted Angolan amphibian and reptile groups as well as large-scale phylogenetic studies across Africa. , Thesis (PhD) -- Faculty of Science, School of Natural Resource Science & Management, 2024
- Full Text:
- Date Issued: 2024-04
IL-4/ IL-13 directed microglial activation and differentiation in response to LPS-induced neuroinflammation
- Authors: Ackerdien, Shiraz
- Date: 2024-04
- Subjects: Inflammation , Inflammation -- Treatment , Anti-inflammatory agents
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/63606 , vital:73554
- Description: Microglia activation is a common hallmark of neuroinflammation that occurs during pathogen invasion or lipopolysaccharide (LPS)-induced inflammation. A neuroinflammatory response is elicited by the release of proinflammatory cytokines which stimulates microglia in an autocrine manner to be polarized into classically activated, pro-inflammatory M1 cells. Prolonged exposure to the inflammatory response can have disastrous effects on the central nervous system (CNS). However, microglia can alternatively be polarized into the activated M2 anti-inflammatory phenotype, but the exact molecular mechanism mediating this phenotypic switch remains poorly understood. Studies have shown that interleukin (IL)-4 can induce the M2 phenotype and activate the signal transducer and activator of the transcription 6 (STAT6) signalling pathway that in turn provokes a beneficial Th2 immune response. Since IL-4 and IL-13 share a common IL-4 receptor alpha (IL-4Rα) chain, it is possible that alternative microglia differentiation and its anti-inflammatory action also involve IL-13. This study aimed to investigate how IL-13 and STAT6 signalling orchestrates the microglial response and differentiation associated with LPS-induced inflammation. Furthermore, the molecular mechanisms that relieve LPS-induced neuroinflammation and neural protection through IL-13-enhanced BDNF signalling were also investigated. C8-B4 microglial cells were induced with LPS to exhibit an M1 pro-inflammatory phenotype or stimulated with IL-4 and/or IL-13 to exhibit an M2 anti-inflammatory microglial phenotype. The cell viability following LPS, IL-4, and/ or IL-13 exposure was determined. The LPS-induced neuroinflammatory response and the anti-inflammatory response induced by IL-4 and IL-13 which promotes STAT-6 signalling were determined by measuring TNFα, IL-1β, and BDNF protein concentrations using ELISA assays. The polarising effects of LPS and IL-4/IL-13 cytokines were also examined via changes in the expression of Iba-1, CD206, CD86, and STAT-6 determined by immunofluorescence analysis. These changes were further investigated by quantifying the mRNA transcripts of TNFα, IL-1 β, Arg-1, CD206, IL-4R, and STAT-6 and BDNF using qRT-PCR. , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Ackerdien, Shiraz
- Date: 2024-04
- Subjects: Inflammation , Inflammation -- Treatment , Anti-inflammatory agents
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/63606 , vital:73554
- Description: Microglia activation is a common hallmark of neuroinflammation that occurs during pathogen invasion or lipopolysaccharide (LPS)-induced inflammation. A neuroinflammatory response is elicited by the release of proinflammatory cytokines which stimulates microglia in an autocrine manner to be polarized into classically activated, pro-inflammatory M1 cells. Prolonged exposure to the inflammatory response can have disastrous effects on the central nervous system (CNS). However, microglia can alternatively be polarized into the activated M2 anti-inflammatory phenotype, but the exact molecular mechanism mediating this phenotypic switch remains poorly understood. Studies have shown that interleukin (IL)-4 can induce the M2 phenotype and activate the signal transducer and activator of the transcription 6 (STAT6) signalling pathway that in turn provokes a beneficial Th2 immune response. Since IL-4 and IL-13 share a common IL-4 receptor alpha (IL-4Rα) chain, it is possible that alternative microglia differentiation and its anti-inflammatory action also involve IL-13. This study aimed to investigate how IL-13 and STAT6 signalling orchestrates the microglial response and differentiation associated with LPS-induced inflammation. Furthermore, the molecular mechanisms that relieve LPS-induced neuroinflammation and neural protection through IL-13-enhanced BDNF signalling were also investigated. C8-B4 microglial cells were induced with LPS to exhibit an M1 pro-inflammatory phenotype or stimulated with IL-4 and/or IL-13 to exhibit an M2 anti-inflammatory microglial phenotype. The cell viability following LPS, IL-4, and/ or IL-13 exposure was determined. The LPS-induced neuroinflammatory response and the anti-inflammatory response induced by IL-4 and IL-13 which promotes STAT-6 signalling were determined by measuring TNFα, IL-1β, and BDNF protein concentrations using ELISA assays. The polarising effects of LPS and IL-4/IL-13 cytokines were also examined via changes in the expression of Iba-1, CD206, CD86, and STAT-6 determined by immunofluorescence analysis. These changes were further investigated by quantifying the mRNA transcripts of TNFα, IL-1 β, Arg-1, CD206, IL-4R, and STAT-6 and BDNF using qRT-PCR. , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
Investigating the anti-inflammatory effect of blueberry-AuNP on microglial cells and obese rat brains
- Authors: Ngwato, Anacia
- Date: 2024-04
- Subjects: Anti-inflammatory agents , Brain -- Anatomy , Brain -- Physiology
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64266 , vital:73670
- Description: Nanotoxicology is a field of study that investigates how nanomaterials interact with biological systems. It focuses on understanding the correlation between the physicochemical properties of nanomaterials, such as size and stability, and their potential toxic effects. Gold nanoparticles (AuNPs), for instance, have a variety of applications in the biological sciences. Therefore, there is a great deal of attention given to evaluating their toxicity to ensure their safe and effective use in biological systems. Anti-inflammatory AuNPs have shown to be a desirable application in obesity treatments since obesity is associated with systematic inflammation. Thus, the study aimed to evaluate the anti-inflammatory effect of BE-AuNPs on C8-B4 microglial cell lines and, to validate the results, the grey matter of brain tissue of obese rats treated with BE-AuNPs. Following the synthesis and characterization of BE-AuNPs, C8-B4 microglial cells were treated with the BE-AuNPs and were evaluated through MTT, HRTEM imaging, qPCR, and ROS. LPS was used to activate the cells. Concentration-dependent toxicity of BE-AuNPs and cellular uptake was observed. The qPCR results showed that the BE-AuNPs decreased the LPS-induced inflammation in the cells. The BE-AuNPs were shown to reduce ROS in inflammatory conditions in the cells. Rat brain tissue analysis through qPCR and ROS demonstrated that BE-AuNPs reduce HFD-induced inflammation and had no ROS effects on the brain, respectively. Thus, leading to a conclusion the BE-AuNPs used in this study are anti-inflammatory. , Thesis (MSc) -- Faculty of Science, Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Ngwato, Anacia
- Date: 2024-04
- Subjects: Anti-inflammatory agents , Brain -- Anatomy , Brain -- Physiology
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64266 , vital:73670
- Description: Nanotoxicology is a field of study that investigates how nanomaterials interact with biological systems. It focuses on understanding the correlation between the physicochemical properties of nanomaterials, such as size and stability, and their potential toxic effects. Gold nanoparticles (AuNPs), for instance, have a variety of applications in the biological sciences. Therefore, there is a great deal of attention given to evaluating their toxicity to ensure their safe and effective use in biological systems. Anti-inflammatory AuNPs have shown to be a desirable application in obesity treatments since obesity is associated with systematic inflammation. Thus, the study aimed to evaluate the anti-inflammatory effect of BE-AuNPs on C8-B4 microglial cell lines and, to validate the results, the grey matter of brain tissue of obese rats treated with BE-AuNPs. Following the synthesis and characterization of BE-AuNPs, C8-B4 microglial cells were treated with the BE-AuNPs and were evaluated through MTT, HRTEM imaging, qPCR, and ROS. LPS was used to activate the cells. Concentration-dependent toxicity of BE-AuNPs and cellular uptake was observed. The qPCR results showed that the BE-AuNPs decreased the LPS-induced inflammation in the cells. The BE-AuNPs were shown to reduce ROS in inflammatory conditions in the cells. Rat brain tissue analysis through qPCR and ROS demonstrated that BE-AuNPs reduce HFD-induced inflammation and had no ROS effects on the brain, respectively. Thus, leading to a conclusion the BE-AuNPs used in this study are anti-inflammatory. , Thesis (MSc) -- Faculty of Science, Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
Investigation of four roof-shaped host compounds for their separation potential of mixtures of guest Isomers and related compounds
- Authors: Senekal, Ulrich
- Date: 2024-04
- Subjects: Grignard reagents , Optical isomers -- Analysis , Supramolecular chemistry
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/64368 , vital:73684
- Description: The inclusion ability of four roof-shaped host compounds, namely trans-9,10-dihydro-9,10- ethanoanthracene-11,12-dicarboxylic acid (H1), dimethyl trans-9,10-dihydro-9,10- ethanoanthracene-11,12-dicarboxylate (H2), trans-α,α,α’,α’-tetraphenyl-9,10-dihydro-9,10- ethanoanthracene-11,12-dimethanol (H3) and trans-α,α,α’,α’-tetrakis(4-chlorophenyl)-9,10- dihydro-9,10-ethanoanthracene-11,12-dimethanol (H4), were investigated when presented with numerous guest series (eight in number), including the xylene isomers and ethylbenzene, pyridine and the methylpyridine isomers, structurally related toluene, ethylbenzene and cumene, the dichlorobenzenes, six-membered heterocyclic ring compounds (dioxane, morpholine, piperidine and pyridine), anisole and the methylanisole isomers, anisole and the bromoanisole guests, and phenol and the methoxyphenol isomers. The four host compounds were synthesized via Diels-Alder (H1), esterification (H2) and Grignard addition (H3 and H4) reactions, producing yields of product of up to 93%. The yields for the Grignard reactions were lower, 54 and 37%, for the corresponding procedures using phenylmagnesium bromide or 4-chlorophenylmagnesium bromide. Computational molecular modelling studies were conducted on all four host compounds, and the resultant molecular geometries compared with the apohost (guest-free) crystal structures, when available. The geometries of the lowest energy conformers were in close correlation with the observed host structures as obtained from the apohost crystal structures (unfortunately, H3 and H4 were not able to form adequate quality crystals for SCXRD analyses). Interestingly, H1–H4 displayed intramolecular non-classical C–H∙∙∙O hydrogen bonds, while only H1 and H2 demonstrated intermolecular interactions of this type. H3 and H4 assumed one of two forms depending on the guest that was employed: the “active” form presented a strong intramolecular O–H∙∙∙O hydrogen bond, while the “inactive” form possessed weak π∙∙∙π and O–H∙∙∙π interactions. All of the host compounds were subjected to crystallization experiments from each of the guest species, as well as from mixtures of guests from each series (the guest competition experiments), where 1H-, 13C-NMR spectroscopy, GC-MS and/or GC-FID were used to analyse any resultant solids formed, as applicable. Single crystal X-ray diffraction (SCXRD) experiments were carried out on each single solvent complex produced in this work, where the crystal quality was suitable, while thermal analyses were also employed on these to determine their relative thermal stabilities. During the single-guest crystallization experiments, H4 was found to be remarkable in its inclusion ability, forming complexes with all but p-dichlorobenzene, typically with a 1:1 host:guest (H:G) ratio. H1 was more selective in its inclusion behaviour, not enclathrating cumene, 3-bromoanisole, phenol or the three methoxyphenol isomers (favouring 1:1 or 2:1 H:G ratios where complexation was successful). Interestingly, H1 formed salts when presented with 2- and 3-methylpyridine, and morpholine and piperidine. H2 and H3 were less remarkable in their inclusion ability, furnishing apohost crystals or gels in some experiments (typically a 3:1 H:G ratio was favoured for both when complexation occurred). Of the four roof-shaped host compounds, H1 and H4 displayed enhanced selectivities for certain guest species, showing near-complete affinity for a specific guest compound when presented with a guest mixture. H1 was able to include 100.0 and 98.8% p-dichlorobenzene (p-DCB) (from m-DCB/p-DCB and o-DCB/p-DCB mixtures), 96.6 and 93.6% p-xylene (p-Xy) (from m-Xy/p-Xy and o-Xy/p-Xy), 99.3% 4-methylanisole (4-MA) (from 2-MA/4-MA) and 97.1% 4-bromoanisole (4-BA) (from ANI/2-BA/3-BA/4-BA, where ANI is anisole). Host compound H4 was able to include ≈ 90% of selected meta-substituted guests, while H2 and H3 demonstrated moderate preferences for the guest compounds employed in this work (< 60%). It was concluded that some xylene guest mixtures may be purified using all but H2, whereas only H1 and H2 showed potential in separating the pyridines. All but H2 may also be employed in the separation of selected dichlorobenzene mixtures, while H2 showed potential for the separation of the six-membered heterocyclic guest compounds (dioxane, morpholine, piperidine and pyridine), were these ever required to be separated. Both H1 and H4 exhibited an overwhelming affinity for the methyl- and bromoanisole guest compounds, and this work has shown that these are likely host candidates for the purification of a variety of these guest mixtures through supramolecular strategies. SCXRD analyses showed that H1 experienced intermolecular host···host hydrogen bonding interactions between the carboxylic acid functional groups, while H2 typically demonstrated intermolecular non-classical hydrogen bonds in its complexes, forming sheets of host molecules along the c-axis. H4 preferred the “inactive” form whereas H3 assumed either an “active” or “inactive“ form. Various host···guest interactions such as π∙∙∙π, C–H∙∙∙π, C–O∙∙∙π, hydrogen bonding and other short contacts were responsible for guest retention in the crystal structures. Thermal analyses were conducted on all of the successfully formed complexes. Ton (the guest release onset temperature) and Tp (the temperature at which the guest release was most rapid) were recorded, when possible, while the mass losses associated with the guest release event were compared with those mass losses expected, in most cases. , Thesis (PhD) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Senekal, Ulrich
- Date: 2024-04
- Subjects: Grignard reagents , Optical isomers -- Analysis , Supramolecular chemistry
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/64368 , vital:73684
- Description: The inclusion ability of four roof-shaped host compounds, namely trans-9,10-dihydro-9,10- ethanoanthracene-11,12-dicarboxylic acid (H1), dimethyl trans-9,10-dihydro-9,10- ethanoanthracene-11,12-dicarboxylate (H2), trans-α,α,α’,α’-tetraphenyl-9,10-dihydro-9,10- ethanoanthracene-11,12-dimethanol (H3) and trans-α,α,α’,α’-tetrakis(4-chlorophenyl)-9,10- dihydro-9,10-ethanoanthracene-11,12-dimethanol (H4), were investigated when presented with numerous guest series (eight in number), including the xylene isomers and ethylbenzene, pyridine and the methylpyridine isomers, structurally related toluene, ethylbenzene and cumene, the dichlorobenzenes, six-membered heterocyclic ring compounds (dioxane, morpholine, piperidine and pyridine), anisole and the methylanisole isomers, anisole and the bromoanisole guests, and phenol and the methoxyphenol isomers. The four host compounds were synthesized via Diels-Alder (H1), esterification (H2) and Grignard addition (H3 and H4) reactions, producing yields of product of up to 93%. The yields for the Grignard reactions were lower, 54 and 37%, for the corresponding procedures using phenylmagnesium bromide or 4-chlorophenylmagnesium bromide. Computational molecular modelling studies were conducted on all four host compounds, and the resultant molecular geometries compared with the apohost (guest-free) crystal structures, when available. The geometries of the lowest energy conformers were in close correlation with the observed host structures as obtained from the apohost crystal structures (unfortunately, H3 and H4 were not able to form adequate quality crystals for SCXRD analyses). Interestingly, H1–H4 displayed intramolecular non-classical C–H∙∙∙O hydrogen bonds, while only H1 and H2 demonstrated intermolecular interactions of this type. H3 and H4 assumed one of two forms depending on the guest that was employed: the “active” form presented a strong intramolecular O–H∙∙∙O hydrogen bond, while the “inactive” form possessed weak π∙∙∙π and O–H∙∙∙π interactions. All of the host compounds were subjected to crystallization experiments from each of the guest species, as well as from mixtures of guests from each series (the guest competition experiments), where 1H-, 13C-NMR spectroscopy, GC-MS and/or GC-FID were used to analyse any resultant solids formed, as applicable. Single crystal X-ray diffraction (SCXRD) experiments were carried out on each single solvent complex produced in this work, where the crystal quality was suitable, while thermal analyses were also employed on these to determine their relative thermal stabilities. During the single-guest crystallization experiments, H4 was found to be remarkable in its inclusion ability, forming complexes with all but p-dichlorobenzene, typically with a 1:1 host:guest (H:G) ratio. H1 was more selective in its inclusion behaviour, not enclathrating cumene, 3-bromoanisole, phenol or the three methoxyphenol isomers (favouring 1:1 or 2:1 H:G ratios where complexation was successful). Interestingly, H1 formed salts when presented with 2- and 3-methylpyridine, and morpholine and piperidine. H2 and H3 were less remarkable in their inclusion ability, furnishing apohost crystals or gels in some experiments (typically a 3:1 H:G ratio was favoured for both when complexation occurred). Of the four roof-shaped host compounds, H1 and H4 displayed enhanced selectivities for certain guest species, showing near-complete affinity for a specific guest compound when presented with a guest mixture. H1 was able to include 100.0 and 98.8% p-dichlorobenzene (p-DCB) (from m-DCB/p-DCB and o-DCB/p-DCB mixtures), 96.6 and 93.6% p-xylene (p-Xy) (from m-Xy/p-Xy and o-Xy/p-Xy), 99.3% 4-methylanisole (4-MA) (from 2-MA/4-MA) and 97.1% 4-bromoanisole (4-BA) (from ANI/2-BA/3-BA/4-BA, where ANI is anisole). Host compound H4 was able to include ≈ 90% of selected meta-substituted guests, while H2 and H3 demonstrated moderate preferences for the guest compounds employed in this work (< 60%). It was concluded that some xylene guest mixtures may be purified using all but H2, whereas only H1 and H2 showed potential in separating the pyridines. All but H2 may also be employed in the separation of selected dichlorobenzene mixtures, while H2 showed potential for the separation of the six-membered heterocyclic guest compounds (dioxane, morpholine, piperidine and pyridine), were these ever required to be separated. Both H1 and H4 exhibited an overwhelming affinity for the methyl- and bromoanisole guest compounds, and this work has shown that these are likely host candidates for the purification of a variety of these guest mixtures through supramolecular strategies. SCXRD analyses showed that H1 experienced intermolecular host···host hydrogen bonding interactions between the carboxylic acid functional groups, while H2 typically demonstrated intermolecular non-classical hydrogen bonds in its complexes, forming sheets of host molecules along the c-axis. H4 preferred the “inactive” form whereas H3 assumed either an “active” or “inactive“ form. Various host···guest interactions such as π∙∙∙π, C–H∙∙∙π, C–O∙∙∙π, hydrogen bonding and other short contacts were responsible for guest retention in the crystal structures. Thermal analyses were conducted on all of the successfully formed complexes. Ton (the guest release onset temperature) and Tp (the temperature at which the guest release was most rapid) were recorded, when possible, while the mass losses associated with the guest release event were compared with those mass losses expected, in most cases. , Thesis (PhD) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
Investigation of the host potential of compounds derived from tartaric acid, succinic acid and 1,4-cyclohexanedioic acid
- Authors: Adam, Muhammad Ameen
- Date: 2024-04
- Subjects: Chemical reactions , Chemistry, Organic , Bacteriology
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/63617 , vital:73562
- Description: The present investigation considered the host behaviour of three compounds, namely (+)-(2R,3R)-1,1,4,4-tetraphenylbutane-1,2,3,4-tetraol (H1), 1,1,4,4-tetraphenyl-1,4-butanediol (H2) and cyclohexane-1,4-diylbis(diphenylmethanol) (H3) in various guest mixtures. These host compounds were readily synthesized by means of Grignard addition reactions on the diesters of tartaric acid, succinic acid and 1,4-cyclohexanedioic acid. The guest mixtures included cyclopentanone, cyclohexanone, cycloheptanone and cyclooctanone, γ-butyrolactone, 2-pyrrolidone, N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone, and pyridine, 2-methylpyridine, 3-methylpyridine and 4-methylpyridine. Crystals of (+)-(2R,3R)-1,1,4,4-tetraphenylbutane-1,2,3,4-tetraol (H1) were grown from cyclopentanone (5-ONE), cyclohexanone (6-ONE), cycloheptanone (7-ONE) and cyclooctanone (8-ONE,) producing 1:1 host:guest complexes in each instance. Thermal analysis showed the thermal stabilities of these complexes to be in the order 6-ONE > 7-ONE > 8-ONE > 5-ONE which correlated exactly with results from binary guest/guest competition experiments, where 6-ONE was always preferred by H1, while 5-ONE was consistently disfavoured. Single crystal X-ray diffraction (SCXRD) analyses demonstrated that each guest compound was retained in the crystals by means of a hydrogen bond with an alcohol moiety of the host compound. Furthermore, preferred guests 6- and 7-ONE produced crystals with greater densities than guests less favoured (5- and 8-ONE). A conformational analysis of the guest geometries in the four complexes with H1 revealed that the low energy guest conformers were present. The host selectivity for 6- and 7-ONE was proposed to be due to the improved molecular packing in the crystals of the complexes containing these two guest compounds, observed from their higher crystal densities. Hirshfeld surface analyses were not useful in explaining the preference of H1 for 6-ONE relative to 7-ONE (these types of analyses were not possible for the 5-ONE and 8-ONE-containing inclusion compounds due to the nature and degree of disorder present in the guest molecules). H1 was also crystallized from γ-butyrolactone (GBL), 2-pyrrolidone (NP), N-methyl-2-pyrrolidone (NMP) and N-ethyl-2-pyrrolidone (NEP), and 1H-NMR spectroscopy revealed that all but GBL were included. The host compound was also presented with these guest solvents in various mixtures, and it was observed that NMP was an extremely favoured guest solvent, followed by NEP and NP, with GBL being consistently disfavoured in every experiment. It was therefore shown that in certain instances, H1 may serve as an alternative tool for separating some of these mixtures through host-guest chemistry strategies. The hydrogen bonding motifs present in each of the successfully formed complexes were extensively investigated through SCXRD analysis, as was the thermal behaviour of these complexes. In the latter instance, the peak temperature of the endotherm (from the DSC trace) representing the guest release was greater for the inclusion compound with favoured NMP (145.5 °C) relative to the complexes with NP (139.8 °C) and NEP (120.5 °C). Host compounds H2 and H3 were revealed to have the ability to include each of pyridine (PYR), 2-methylpyridine (2MP), 3-methylpyridine (3MP) and 4-methylpyridine (4MP). H2 displayed selective behaviour for 3MP and 4MP when presented with mixtures of these guest compounds, whilst H3 preferred PYR. In the latter case, this PYR-containing inclusion compound was also the more stable one (the guest release onset temperature was highest, Ton 66.0 °C). It was demonstrated that H2 has the ability to separate very many binary mixtures of these pyridines on a practical platform, since K (the selectivity coefficient) values were 10 or greater in many instances. However, unfortunately, the more difficult-to-separate mixtures containing 3MP and 4MP cannot be purified or separated by employing H2 and supramolecular chemistry strategies. H3 was also shown to be a likely candidate for binary guest separations in very many of the guest solutions considered here, where K was also 10 or greater, and even infinity in many cases. SCXRD demonstrated that 2MP, 3MP and 4MP were retained in the crystals of their complexes by means of classical hydrogen bonds with the host compound. Satisfyingly, this hydrogen bond between 2MP and H2 (3.0213(18) Å) was significantly longer than that between this host compound and both disorder components of 3MP (2.875(2) and 2.825(9) Å) and that between H2 and 4MP (2.8458(13) Å). This observation explains the affinity of H2 for both 3MP and 4MP, and why 2MP was disfavoured. The results of thermal experiments did not wholly concur with observations from the guest/guest competition experiments. Hirshfeld surface analyses were also conducted but were not entirely conclusive with respect to explaining the host selectivity behaviour. In the case of H3, SCXRD analyses revealed that favoured PYR experienced a classical hydrogen bond with the host compound that was statistically significantly shorter (2.795(2) Å, 165°) than those between the other guest compounds and H3. Additionally, this guest compound was the only one to be involved in a (host)C−H···π(guest) interaction (2.91 Å, 139°) and also a non-classical hydrogen bond with the host compound ((host)C−H···N−C(guest), 2.77 Å (144°)). Finally, Hirshfeld surface analyses showed also that preferred PYR experienced a greater percentage of C···H/H···C (33.1%) and H···N/N···H (11.1%) interactions compared with the complexes with 2MP, 3MP and 4MP. However, it is not clear whether these Hirshfeld observations explain the affinity of H3 for PYR. , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Adam, Muhammad Ameen
- Date: 2024-04
- Subjects: Chemical reactions , Chemistry, Organic , Bacteriology
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/63617 , vital:73562
- Description: The present investigation considered the host behaviour of three compounds, namely (+)-(2R,3R)-1,1,4,4-tetraphenylbutane-1,2,3,4-tetraol (H1), 1,1,4,4-tetraphenyl-1,4-butanediol (H2) and cyclohexane-1,4-diylbis(diphenylmethanol) (H3) in various guest mixtures. These host compounds were readily synthesized by means of Grignard addition reactions on the diesters of tartaric acid, succinic acid and 1,4-cyclohexanedioic acid. The guest mixtures included cyclopentanone, cyclohexanone, cycloheptanone and cyclooctanone, γ-butyrolactone, 2-pyrrolidone, N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone, and pyridine, 2-methylpyridine, 3-methylpyridine and 4-methylpyridine. Crystals of (+)-(2R,3R)-1,1,4,4-tetraphenylbutane-1,2,3,4-tetraol (H1) were grown from cyclopentanone (5-ONE), cyclohexanone (6-ONE), cycloheptanone (7-ONE) and cyclooctanone (8-ONE,) producing 1:1 host:guest complexes in each instance. Thermal analysis showed the thermal stabilities of these complexes to be in the order 6-ONE > 7-ONE > 8-ONE > 5-ONE which correlated exactly with results from binary guest/guest competition experiments, where 6-ONE was always preferred by H1, while 5-ONE was consistently disfavoured. Single crystal X-ray diffraction (SCXRD) analyses demonstrated that each guest compound was retained in the crystals by means of a hydrogen bond with an alcohol moiety of the host compound. Furthermore, preferred guests 6- and 7-ONE produced crystals with greater densities than guests less favoured (5- and 8-ONE). A conformational analysis of the guest geometries in the four complexes with H1 revealed that the low energy guest conformers were present. The host selectivity for 6- and 7-ONE was proposed to be due to the improved molecular packing in the crystals of the complexes containing these two guest compounds, observed from their higher crystal densities. Hirshfeld surface analyses were not useful in explaining the preference of H1 for 6-ONE relative to 7-ONE (these types of analyses were not possible for the 5-ONE and 8-ONE-containing inclusion compounds due to the nature and degree of disorder present in the guest molecules). H1 was also crystallized from γ-butyrolactone (GBL), 2-pyrrolidone (NP), N-methyl-2-pyrrolidone (NMP) and N-ethyl-2-pyrrolidone (NEP), and 1H-NMR spectroscopy revealed that all but GBL were included. The host compound was also presented with these guest solvents in various mixtures, and it was observed that NMP was an extremely favoured guest solvent, followed by NEP and NP, with GBL being consistently disfavoured in every experiment. It was therefore shown that in certain instances, H1 may serve as an alternative tool for separating some of these mixtures through host-guest chemistry strategies. The hydrogen bonding motifs present in each of the successfully formed complexes were extensively investigated through SCXRD analysis, as was the thermal behaviour of these complexes. In the latter instance, the peak temperature of the endotherm (from the DSC trace) representing the guest release was greater for the inclusion compound with favoured NMP (145.5 °C) relative to the complexes with NP (139.8 °C) and NEP (120.5 °C). Host compounds H2 and H3 were revealed to have the ability to include each of pyridine (PYR), 2-methylpyridine (2MP), 3-methylpyridine (3MP) and 4-methylpyridine (4MP). H2 displayed selective behaviour for 3MP and 4MP when presented with mixtures of these guest compounds, whilst H3 preferred PYR. In the latter case, this PYR-containing inclusion compound was also the more stable one (the guest release onset temperature was highest, Ton 66.0 °C). It was demonstrated that H2 has the ability to separate very many binary mixtures of these pyridines on a practical platform, since K (the selectivity coefficient) values were 10 or greater in many instances. However, unfortunately, the more difficult-to-separate mixtures containing 3MP and 4MP cannot be purified or separated by employing H2 and supramolecular chemistry strategies. H3 was also shown to be a likely candidate for binary guest separations in very many of the guest solutions considered here, where K was also 10 or greater, and even infinity in many cases. SCXRD demonstrated that 2MP, 3MP and 4MP were retained in the crystals of their complexes by means of classical hydrogen bonds with the host compound. Satisfyingly, this hydrogen bond between 2MP and H2 (3.0213(18) Å) was significantly longer than that between this host compound and both disorder components of 3MP (2.875(2) and 2.825(9) Å) and that between H2 and 4MP (2.8458(13) Å). This observation explains the affinity of H2 for both 3MP and 4MP, and why 2MP was disfavoured. The results of thermal experiments did not wholly concur with observations from the guest/guest competition experiments. Hirshfeld surface analyses were also conducted but were not entirely conclusive with respect to explaining the host selectivity behaviour. In the case of H3, SCXRD analyses revealed that favoured PYR experienced a classical hydrogen bond with the host compound that was statistically significantly shorter (2.795(2) Å, 165°) than those between the other guest compounds and H3. Additionally, this guest compound was the only one to be involved in a (host)C−H···π(guest) interaction (2.91 Å, 139°) and also a non-classical hydrogen bond with the host compound ((host)C−H···N−C(guest), 2.77 Å (144°)). Finally, Hirshfeld surface analyses showed also that preferred PYR experienced a greater percentage of C···H/H···C (33.1%) and H···N/N···H (11.1%) interactions compared with the complexes with 2MP, 3MP and 4MP. However, it is not clear whether these Hirshfeld observations explain the affinity of H3 for PYR. , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
Investigation of the synthesis and characterisation of spiro orthocarbonates and heterocyclic orthocarbonates
- Authors: Cuthbertson, Jarryd Pierre
- Date: 2024-04
- Subjects: Chemistry, Analytic , Analytical chemistry , Chemistry
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/63678 , vital:73578
- Description: A series of mostly asymmetrical spiro orthocarbonates and heterospirocyclic derivatives of orthocarbonic acid was synthesized from 2,2-dichlorobenzodioxole and a number of difunctional reagents. A systematic study of the size of the chelate rings formed around the spirocentric carbon atom was conducted by selecting representative samples of aliphatic and aromatic diols. The feasibility and scope of potential starting materials used was expanded by reacting DCBD successfully with thiols. Molecular structures of these compounds were confirmed using diffraction studies on single crystals. All compounds were analyzed using multinuclear NMR. DFT calculations performed on the compounds allowed for the development of equations that can accurately predict 13C chemical shifts of SOCs. Furthermore, the experimental NMR spectroscopy gave rise to an increment shift system for the 13C NMR shifts allowing for further assignment of carbon atom positions in compounds with multiple possible bonding patterns. , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Cuthbertson, Jarryd Pierre
- Date: 2024-04
- Subjects: Chemistry, Analytic , Analytical chemistry , Chemistry
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/63678 , vital:73578
- Description: A series of mostly asymmetrical spiro orthocarbonates and heterospirocyclic derivatives of orthocarbonic acid was synthesized from 2,2-dichlorobenzodioxole and a number of difunctional reagents. A systematic study of the size of the chelate rings formed around the spirocentric carbon atom was conducted by selecting representative samples of aliphatic and aromatic diols. The feasibility and scope of potential starting materials used was expanded by reacting DCBD successfully with thiols. Molecular structures of these compounds were confirmed using diffraction studies on single crystals. All compounds were analyzed using multinuclear NMR. DFT calculations performed on the compounds allowed for the development of equations that can accurately predict 13C chemical shifts of SOCs. Furthermore, the experimental NMR spectroscopy gave rise to an increment shift system for the 13C NMR shifts allowing for further assignment of carbon atom positions in compounds with multiple possible bonding patterns. , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
Lion and leopard diet and dispersal in human-dominated landscapes
- Authors: Forbes, Ryan Edward
- Date: 2024-04
- Subjects: Carnivora -- South Africa , Carnivorous animals -- Conservation , Carnivorous animals -- Ecology
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/63766 , vital:73596
- Description: Terrestrial carnivore population declines are driven by habitat loss and fragmentation, prey-depletion, persecution, and retaliatory killings. Population strongholds now centre on protected areas, that face increasing human pressure, resulting in population isolation, declining prey populations, and livestock intrusion. I therefore aimed to investigate dispersal and connectivity, and diets of lions (Panthera leo) and leopards (P. pardus) in response to human-use and wildlife density gradients in the Greater Limpopo Transfrontier Conservation Area (GLTCA). Firstly, I investigated dispersal and connectivity for these carnivores across the GLTCA, using single nucleotide polymorphisms. I present evidence that in the prey-depleted Mozambique portion of the GLTCA, lion and leopard dispersal distances are higher compared with the prey-abundant Kruger National Park (KNP). I also provide the first evidence for long-range dispersal in female lions. Despite evidence for connectivity occurring across the GLTCA, I recorded population structuring across the region for both carnivores, likely due to habitat fragmentation by human activities in the Mozambique portion of the GLTCA. I then assessed carnivore diet responses to prey depletion and livestock availability by comparing lion and leopard diets in the prey-abundant/livestock-absent KNP (South Africa), with the prey-depleted/livestock-abundant Limpopo National Park (LNP, Mozambique), using scat analyses. Lions and leopards downshifted their prey size selection in LNP relative to KNP. Despite both carnivores expanding their dietary niche breadths in LNP relative to KNP, diet overlap did not differ between sites. This suggests that even when prey is depleted, lions and leopards can partition food resources, which likely limits competition. Despite cattle (Bos taurus) being the most abundant ungulate in LNP, lions and leopards strongly avoided cattle, supporting the notion that carnivores can perceive the risk of hunting livestock and modulate their foraging behaviour to reduce human-carnivore conflict. Should my findings reflect general patterns in carnivore dispersal and diet responses to human-use and wildlife gradients, then carnivore conservation initiates across their range should focus on prey population rehabilitation, improved livestock husbandry practices, the establishment of effective dispersal corridors and improved human-tolerance towards large carnivores. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Forbes, Ryan Edward
- Date: 2024-04
- Subjects: Carnivora -- South Africa , Carnivorous animals -- Conservation , Carnivorous animals -- Ecology
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/63766 , vital:73596
- Description: Terrestrial carnivore population declines are driven by habitat loss and fragmentation, prey-depletion, persecution, and retaliatory killings. Population strongholds now centre on protected areas, that face increasing human pressure, resulting in population isolation, declining prey populations, and livestock intrusion. I therefore aimed to investigate dispersal and connectivity, and diets of lions (Panthera leo) and leopards (P. pardus) in response to human-use and wildlife density gradients in the Greater Limpopo Transfrontier Conservation Area (GLTCA). Firstly, I investigated dispersal and connectivity for these carnivores across the GLTCA, using single nucleotide polymorphisms. I present evidence that in the prey-depleted Mozambique portion of the GLTCA, lion and leopard dispersal distances are higher compared with the prey-abundant Kruger National Park (KNP). I also provide the first evidence for long-range dispersal in female lions. Despite evidence for connectivity occurring across the GLTCA, I recorded population structuring across the region for both carnivores, likely due to habitat fragmentation by human activities in the Mozambique portion of the GLTCA. I then assessed carnivore diet responses to prey depletion and livestock availability by comparing lion and leopard diets in the prey-abundant/livestock-absent KNP (South Africa), with the prey-depleted/livestock-abundant Limpopo National Park (LNP, Mozambique), using scat analyses. Lions and leopards downshifted their prey size selection in LNP relative to KNP. Despite both carnivores expanding their dietary niche breadths in LNP relative to KNP, diet overlap did not differ between sites. This suggests that even when prey is depleted, lions and leopards can partition food resources, which likely limits competition. Despite cattle (Bos taurus) being the most abundant ungulate in LNP, lions and leopards strongly avoided cattle, supporting the notion that carnivores can perceive the risk of hunting livestock and modulate their foraging behaviour to reduce human-carnivore conflict. Should my findings reflect general patterns in carnivore dispersal and diet responses to human-use and wildlife gradients, then carnivore conservation initiates across their range should focus on prey population rehabilitation, improved livestock husbandry practices, the establishment of effective dispersal corridors and improved human-tolerance towards large carnivores. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
Mathematical modelling of the tumour treatment with chemotherapy
- Authors: Nyaweni, Fundile Sindy
- Date: 2024-04
- Subjects: Mathematical models , Mathematics , Chemotherapy
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64289 , vital:73672
- Description: In this study, a cancer disease model incorporating predator-prey dynamics between immune cells and tumor cells, as well as competition between tumor cells and normal cells, is formulated in an attempt to understand the interaction dynamics that govern the complex interplay within the tumor microenvironment. Mathematical analysis is employed to derive conditions for the boundedness of solutions and to discuss disease thresholds such as the basic reproduction number, R0. Equilibrium points are identified, and stability conditions for the system are derived. Sensitivity analysis is used to assess uncertainties in the parameters of the model, specifically their impact on R0. Numerical simulations are conducted, utilizing the Runge-Kutta scheme to solve the model. Furthermore, optimal control (OC) techniques are applied to examine the role of chemotherapy in enhancing tumor cell elimination and minimizing adverse effects on immune cells and normal cells. The improved model, incorporating normal cells, anticancer drugs, and immune cells, allows for a more comprehensive analysis of the dynamic interactions within the biological system. The optimal control is determined using the forward-backward sweep numerical method. The numerical simulation is carried out in MATLAB to validate and complement the analytical findings. The results indicate that a low concentration of the drug leads to a prolonged period for tumor clearance. Conversely, a higher drug concentration results in quicker tumor clearance, albeit with adverse effects on normal and effector cells. The OC identifies when to stop the treatment once the tumor clears. Furthermore, OC facilitates the regeneration of normal and immune cells beyond treatment, in contrast to a control scenario without optimization. The findings highlight the importance of early detection and careful chemotherapy dosage selection for effective and personalized cancer treatment strategies. , Thesis (MSc) -- Faculty of Science, School Computer Science, Mathematics, Physics and Statistics, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Nyaweni, Fundile Sindy
- Date: 2024-04
- Subjects: Mathematical models , Mathematics , Chemotherapy
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64289 , vital:73672
- Description: In this study, a cancer disease model incorporating predator-prey dynamics between immune cells and tumor cells, as well as competition between tumor cells and normal cells, is formulated in an attempt to understand the interaction dynamics that govern the complex interplay within the tumor microenvironment. Mathematical analysis is employed to derive conditions for the boundedness of solutions and to discuss disease thresholds such as the basic reproduction number, R0. Equilibrium points are identified, and stability conditions for the system are derived. Sensitivity analysis is used to assess uncertainties in the parameters of the model, specifically their impact on R0. Numerical simulations are conducted, utilizing the Runge-Kutta scheme to solve the model. Furthermore, optimal control (OC) techniques are applied to examine the role of chemotherapy in enhancing tumor cell elimination and minimizing adverse effects on immune cells and normal cells. The improved model, incorporating normal cells, anticancer drugs, and immune cells, allows for a more comprehensive analysis of the dynamic interactions within the biological system. The optimal control is determined using the forward-backward sweep numerical method. The numerical simulation is carried out in MATLAB to validate and complement the analytical findings. The results indicate that a low concentration of the drug leads to a prolonged period for tumor clearance. Conversely, a higher drug concentration results in quicker tumor clearance, albeit with adverse effects on normal and effector cells. The OC identifies when to stop the treatment once the tumor clears. Furthermore, OC facilitates the regeneration of normal and immune cells beyond treatment, in contrast to a control scenario without optimization. The findings highlight the importance of early detection and careful chemotherapy dosage selection for effective and personalized cancer treatment strategies. , Thesis (MSc) -- Faculty of Science, School Computer Science, Mathematics, Physics and Statistics, 2024
- Full Text:
- Date Issued: 2024-04
Photocatalytic reduction of CO2 into green fuels on microspherical nanocomposites comprising of CdS, TiO2, ZnFe2O4 semiconductors and heterojunctions
- Authors: Mudau, Rendani Julian
- Date: 2024-04
- Subjects: Heterojunctions , Chemistry, Inorganic , Nanochemistry
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64214 , vital:73665
- Description: Human anthropogenic activities have led to an increase in CO2 levels resulting in global warming. There is a need to reduce CO2 levels in the atmosphere by capturing the gas and converting the captured CO2 into fuels. Photocatalytic conversion of CO2 into valuable products via photoreduction is a promising technique to reduce carbon dioxide using sunlight and water. Redox reactions between CO2 and water using photocatalysts offer an effective method of lowering CO2, which has detrimental effects on the environment. This dissertation reports the synthesis and characterization of five photochemical catalysts comprising of CdS, TiO2, ZnFe2O4 semiconductors and heterojunctions and their use as photocatalysts for the photocatalytic reduction of CO2 into green fuels. Mott−Schottky plot of TiO2, CdS and CdS/TiO2 confirmed the formation of n-type, n-type, and n-n type material respectively. The band gap of TiO2, CdS, and CdS/TiO2 obtained were 3.21,2.24, 2.04 eV, respectively, the combination of TiO2 and CdS resulted in the lowering of band gap energy which is favourable for photocatalytic reduction studies. XRD of TiO2, CdS and CdS/TiO2 provided relevant information about the various phase reflections of the photocatalysts, it also supported reports confirming the increase in crystallite size of TiO2 anatase phase upon calcination. Chemical environment of the various photocatalysts, such as Ti2p1/2, Ti2p3/2, O1s, Cd3d3/2, Cd3d5/2, S2p1/2 and S2p3/2 were observed in TiO2, CdS and CdS/TiO2. BET surface area of TiO2, CdS and CdS/TiO2 was also observed to be 2.9243, 4.0605, and 9.8450 m2g, respectively. Photocatalytic reduction of CO2 resulted in formic acid, formaldehyde, acetic acid, carbon monoxide, ethanol, and methanol after 12 h. Modification of CdS with TiO2 to form CdS/TiO2 produced high yield of formic acid (217.7 μmol/g) compared to CdS (8.7 μmol/g) and TiO2 (122.5 μmol/g). CdS had high yield of formaldehyde (20.4 μmol/g) and ethanol (57.8 μmol/g) compared to TiO2 (12.9, 3.6 μmol/g of formaldehyde and ethanol, respectively) and CdS/TiO2 (19.7 μmol/g and there was no detection of ethanol). TiO2 shows high yield of methanol (145.2 μmol/g) and is the only catalysts that produced carbon monoxide (52.2 μmol/g) compared to CdS (87.8 μmol/g of methanol) and CdS/TiO2 (50.2 μmol/g of methanol). A detailed elucidation of the various products was reported by means of nuclear magnetic resonance (NMR) spectrometer. ZnFe2O4 and CdS/TiO2/ZnFe2O4 were characterized and employed for photocatalytic reduction of CO2 in water. XRD and XPS confirmed the presence Fe (2+) and Fe (3+) in tetrahedral/octahedral and Zn (2+) in tetrahedral on ZnFe2O4 and CdS/TiO2. CdS/TiO2/ZnFe2O4 presented a lowered band gap of 1.98 eV due to the presence of ZnFe2O4 while the band gap of ZnFe2O4 obtained is 1.95 eV. The Mott-Schottky plots confirmed the conduction (2.81 and 2.59 eV) and valence band (–0.86 and –6.1 eV) of ZnFe2O4 and CdS/TiO2/ZnFe2O4 together with their junctions, respectively. ZnFe2O4 and CdS/TiO2/ZnFe2O4 are p-type and p-n type junctions, respectively. Photocatalytic reduction of CO2 under visible light for 12 h using CdS/TiO2/ZnFe2O4 hollow microspheres nanocomposites produced methanol (182.1 μmol/g), formic acid (1.9 μmol/g), formaldehyde (9.5 μmol/g), ethanol (67.1 μmol/g), and oxalic acid (38.9 μmol/g). Amongst the synthesized catalysts, CdS/TiO2/ZnFe2O4 produced high yield of methanol, ethanol, and oxalic acid. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Mudau, Rendani Julian
- Date: 2024-04
- Subjects: Heterojunctions , Chemistry, Inorganic , Nanochemistry
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64214 , vital:73665
- Description: Human anthropogenic activities have led to an increase in CO2 levels resulting in global warming. There is a need to reduce CO2 levels in the atmosphere by capturing the gas and converting the captured CO2 into fuels. Photocatalytic conversion of CO2 into valuable products via photoreduction is a promising technique to reduce carbon dioxide using sunlight and water. Redox reactions between CO2 and water using photocatalysts offer an effective method of lowering CO2, which has detrimental effects on the environment. This dissertation reports the synthesis and characterization of five photochemical catalysts comprising of CdS, TiO2, ZnFe2O4 semiconductors and heterojunctions and their use as photocatalysts for the photocatalytic reduction of CO2 into green fuels. Mott−Schottky plot of TiO2, CdS and CdS/TiO2 confirmed the formation of n-type, n-type, and n-n type material respectively. The band gap of TiO2, CdS, and CdS/TiO2 obtained were 3.21,2.24, 2.04 eV, respectively, the combination of TiO2 and CdS resulted in the lowering of band gap energy which is favourable for photocatalytic reduction studies. XRD of TiO2, CdS and CdS/TiO2 provided relevant information about the various phase reflections of the photocatalysts, it also supported reports confirming the increase in crystallite size of TiO2 anatase phase upon calcination. Chemical environment of the various photocatalysts, such as Ti2p1/2, Ti2p3/2, O1s, Cd3d3/2, Cd3d5/2, S2p1/2 and S2p3/2 were observed in TiO2, CdS and CdS/TiO2. BET surface area of TiO2, CdS and CdS/TiO2 was also observed to be 2.9243, 4.0605, and 9.8450 m2g, respectively. Photocatalytic reduction of CO2 resulted in formic acid, formaldehyde, acetic acid, carbon monoxide, ethanol, and methanol after 12 h. Modification of CdS with TiO2 to form CdS/TiO2 produced high yield of formic acid (217.7 μmol/g) compared to CdS (8.7 μmol/g) and TiO2 (122.5 μmol/g). CdS had high yield of formaldehyde (20.4 μmol/g) and ethanol (57.8 μmol/g) compared to TiO2 (12.9, 3.6 μmol/g of formaldehyde and ethanol, respectively) and CdS/TiO2 (19.7 μmol/g and there was no detection of ethanol). TiO2 shows high yield of methanol (145.2 μmol/g) and is the only catalysts that produced carbon monoxide (52.2 μmol/g) compared to CdS (87.8 μmol/g of methanol) and CdS/TiO2 (50.2 μmol/g of methanol). A detailed elucidation of the various products was reported by means of nuclear magnetic resonance (NMR) spectrometer. ZnFe2O4 and CdS/TiO2/ZnFe2O4 were characterized and employed for photocatalytic reduction of CO2 in water. XRD and XPS confirmed the presence Fe (2+) and Fe (3+) in tetrahedral/octahedral and Zn (2+) in tetrahedral on ZnFe2O4 and CdS/TiO2. CdS/TiO2/ZnFe2O4 presented a lowered band gap of 1.98 eV due to the presence of ZnFe2O4 while the band gap of ZnFe2O4 obtained is 1.95 eV. The Mott-Schottky plots confirmed the conduction (2.81 and 2.59 eV) and valence band (–0.86 and –6.1 eV) of ZnFe2O4 and CdS/TiO2/ZnFe2O4 together with their junctions, respectively. ZnFe2O4 and CdS/TiO2/ZnFe2O4 are p-type and p-n type junctions, respectively. Photocatalytic reduction of CO2 under visible light for 12 h using CdS/TiO2/ZnFe2O4 hollow microspheres nanocomposites produced methanol (182.1 μmol/g), formic acid (1.9 μmol/g), formaldehyde (9.5 μmol/g), ethanol (67.1 μmol/g), and oxalic acid (38.9 μmol/g). Amongst the synthesized catalysts, CdS/TiO2/ZnFe2O4 produced high yield of methanol, ethanol, and oxalic acid. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2024
- Full Text:
- Date Issued: 2024-04
Photoluminescence and electroluminescence imaging of PV devices
- Authors: Roodt, Roelof Petrus
- Date: 2024-04
- Subjects: Photoluminescence , Biosensors
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64333 , vital:73676
- Description: Luminescence imaging has become a particularly useful and valuable tool for the characterisation of photovoltaic devices. This study entailed the design, construction, and optimisation of a system for the electroluminescence (EL) and photoluminescence (PL) imaging of various solar cell devices. The system can perform EL and PL imaging of solar cells of different cell technologies and materials systems, including Si, perovskite, and triple-junction concentrator solar cells. This required appropriate electrical power supplies for carrier injection for EL imaging and optical excitation for PL imaging. The different materials systems also required wavelength appropriate filters for PL imaging. In addition, the system utilized a temperature-controlled sample stage and was placed in a chamber for environmental control and isolation of UV radiation from laboratory. In addition to optimization of imaging conditions, luminescence images need to be optimized to facilitate detailed analysis and the application of appropriate algorithms to extract device parameters and hence generate device parameter images of the devices under investigation. For EL imaging, two power supplies were used to inject current into the solar cells. The reason for the two power supplies is that the first power supply had a current range of ± 1 A and an applied voltage capability of ± 21 V. This was used for the smaller solar cells. It was also convenient to use as the power supply could also measure the injected current and applied voltage and digitally store it with the images. For the larger solar cells, a second power supply was utilized, which could inject current into the samples in the range of ± 12 A at an applied voltage of ± 40 V. To measure the current and voltage of the power supply provided, two digital multimeters were utilized. For acquiring images, the same camera was used for EL and PL imaging. The sensor used in the camera is a silicon CMOS sensor. For PL imaging, four light emitting diode (LED) boards, consisting out of sixty-four LED’s, per board, of four different wavelengths, were used to optically excite the solar cells. The four wavelengths emitted by the LED’s were chosen to match the bandgaps of the different solar cell devices investigated. The LEDs were powered with a multi-channel constant voltage power supply, where the current could be varied. The Si solar cell is a 156 x 156 mm commercial solar cell. The perovskite solar module is a 40 x 40 mm module, which consists out of six cells connected in series. The triple-junction concentrator solar cell has a dimension of 10 x 10 mm which consists of three junctions staked on top of one another. These three layers consist of indium gallium phosphate (InGaP), indium gallium arsenide (InGaAs) and germanium (Ge). To capture EL and PL images of these various solar cell devices, filters of specific wavelengths were placed in front of the camera to isolate the light generated by the different devices. In addition to isolating the luminescence observed from the solar cells, an image correction procedure was adapted from literature, to be applicable to acquiring luminescence images of these various solar cells. As there are a range of factors which influence the quality and clarity of the luminescence images, i.e., chromatic aberration, diffraction, and absorption depth, to name a few, the wavelength dependency of these factors was investigated. This was done by acquiring a point spread function (PSF) for each of these devices and then using these PSF's together with a deconvolution algorithm to correct the luminescence images. The PSF was acquired by fitting a point source emission image to a function that includes exponential and Gaussian terms. The point source image was obtained by placing a black piece of vinyl with a pinhole in it over the solar cell. To communicate with all the various devices and to acquire images at various intensities a LABVIEW program was written. This was used then used to control the power supplies, digital multimeters, camera, and the LED's. This allowed for the user to specify at what points along the current-voltage (I-V) curve data points needed to be measured together with the luminescence images captured. For PL imaging the intensity of the LED's was then also adjusted according to user specified values. The system was utilised to acquire EL images of the Si solar cell, EL and PL images of the perovskite solar cell and EL images of the InGaP and InGaAs layers in the triple-junction concentrator solar cell. With the correction procedure utilised in this study, it was seen that the image quality and clarity improved, compared to the conventional way of capturing luminescence images. These statements are supported by the results obtained for the series resistance maps of the Si solar cell and the perovskite solar module, as the series resistance maps obtained from the corrected luminescence images have less noise and more detail compared to the results from the raw luminescence images. From the EL images captured for the two layers of the triple junction concentrator, it was clear that the intensity profile of the two layers is different, as the intensity for the InGaP layers was that the device had bright edges and darker intensity on the interior where exactly the opposite was observed for the InGaAs layer, having a bright interior and darker edges. This is most likely due to the opto-electric coupling of these layers withing the triple junction solar cell. For the series resistance images obtained for the Si solar cell, it is observed that at lower carrier injection, the series resistance is lower compared to higher carrier injection levels. This result can also be influenced by the increase in cell temperature with the increase in injected carriers. The series resistance maps obtained from the perovskite EL images shows an interesting result. As the perovskite solar cell has degraded, three of the six cells have optically inactive regions, showing lower luminescence intensities. The series resistance of the other three cells are much lower compared to these cells that have inactive regions under low injection conditions. As the injection level increases, it is seen that the series resistance values of five of the six cells become comparable to one another. With regards to the PSF, it was found that using a bandpass filter in front of the lens reduced to amount of spreading observed from a single point source across the detector. Furthermore, there is a strong wavelength dependency in the PSF as the severity increased with increase in the emission wavelength of the solar cells under investigation.In this study an opto-electrical characterisation system was constructed to acquire PL and EL images of various solar cell technologies. In addition to this, a range of factors that influence the quality of these images were investigated and used in the image correction procedure to correct the images for all these cell technologies. It was shown that the correction procedure works for all three of the technologies investigated in this study, and all these factors showed a strong wavelength dependency. These corrected luminescence images together with current-voltage (I-V) data was then used to determine characteristic parameters of a one-diode model of the various PV devices. This was not only achieved, but it also clearly indicated that all the correction procedures need to be considered to obtain a clear and accurate representation of the actual PV device. This has a major influence on the understanding and improvement of these PV devices. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Roodt, Roelof Petrus
- Date: 2024-04
- Subjects: Photoluminescence , Biosensors
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64333 , vital:73676
- Description: Luminescence imaging has become a particularly useful and valuable tool for the characterisation of photovoltaic devices. This study entailed the design, construction, and optimisation of a system for the electroluminescence (EL) and photoluminescence (PL) imaging of various solar cell devices. The system can perform EL and PL imaging of solar cells of different cell technologies and materials systems, including Si, perovskite, and triple-junction concentrator solar cells. This required appropriate electrical power supplies for carrier injection for EL imaging and optical excitation for PL imaging. The different materials systems also required wavelength appropriate filters for PL imaging. In addition, the system utilized a temperature-controlled sample stage and was placed in a chamber for environmental control and isolation of UV radiation from laboratory. In addition to optimization of imaging conditions, luminescence images need to be optimized to facilitate detailed analysis and the application of appropriate algorithms to extract device parameters and hence generate device parameter images of the devices under investigation. For EL imaging, two power supplies were used to inject current into the solar cells. The reason for the two power supplies is that the first power supply had a current range of ± 1 A and an applied voltage capability of ± 21 V. This was used for the smaller solar cells. It was also convenient to use as the power supply could also measure the injected current and applied voltage and digitally store it with the images. For the larger solar cells, a second power supply was utilized, which could inject current into the samples in the range of ± 12 A at an applied voltage of ± 40 V. To measure the current and voltage of the power supply provided, two digital multimeters were utilized. For acquiring images, the same camera was used for EL and PL imaging. The sensor used in the camera is a silicon CMOS sensor. For PL imaging, four light emitting diode (LED) boards, consisting out of sixty-four LED’s, per board, of four different wavelengths, were used to optically excite the solar cells. The four wavelengths emitted by the LED’s were chosen to match the bandgaps of the different solar cell devices investigated. The LEDs were powered with a multi-channel constant voltage power supply, where the current could be varied. The Si solar cell is a 156 x 156 mm commercial solar cell. The perovskite solar module is a 40 x 40 mm module, which consists out of six cells connected in series. The triple-junction concentrator solar cell has a dimension of 10 x 10 mm which consists of three junctions staked on top of one another. These three layers consist of indium gallium phosphate (InGaP), indium gallium arsenide (InGaAs) and germanium (Ge). To capture EL and PL images of these various solar cell devices, filters of specific wavelengths were placed in front of the camera to isolate the light generated by the different devices. In addition to isolating the luminescence observed from the solar cells, an image correction procedure was adapted from literature, to be applicable to acquiring luminescence images of these various solar cells. As there are a range of factors which influence the quality and clarity of the luminescence images, i.e., chromatic aberration, diffraction, and absorption depth, to name a few, the wavelength dependency of these factors was investigated. This was done by acquiring a point spread function (PSF) for each of these devices and then using these PSF's together with a deconvolution algorithm to correct the luminescence images. The PSF was acquired by fitting a point source emission image to a function that includes exponential and Gaussian terms. The point source image was obtained by placing a black piece of vinyl with a pinhole in it over the solar cell. To communicate with all the various devices and to acquire images at various intensities a LABVIEW program was written. This was used then used to control the power supplies, digital multimeters, camera, and the LED's. This allowed for the user to specify at what points along the current-voltage (I-V) curve data points needed to be measured together with the luminescence images captured. For PL imaging the intensity of the LED's was then also adjusted according to user specified values. The system was utilised to acquire EL images of the Si solar cell, EL and PL images of the perovskite solar cell and EL images of the InGaP and InGaAs layers in the triple-junction concentrator solar cell. With the correction procedure utilised in this study, it was seen that the image quality and clarity improved, compared to the conventional way of capturing luminescence images. These statements are supported by the results obtained for the series resistance maps of the Si solar cell and the perovskite solar module, as the series resistance maps obtained from the corrected luminescence images have less noise and more detail compared to the results from the raw luminescence images. From the EL images captured for the two layers of the triple junction concentrator, it was clear that the intensity profile of the two layers is different, as the intensity for the InGaP layers was that the device had bright edges and darker intensity on the interior where exactly the opposite was observed for the InGaAs layer, having a bright interior and darker edges. This is most likely due to the opto-electric coupling of these layers withing the triple junction solar cell. For the series resistance images obtained for the Si solar cell, it is observed that at lower carrier injection, the series resistance is lower compared to higher carrier injection levels. This result can also be influenced by the increase in cell temperature with the increase in injected carriers. The series resistance maps obtained from the perovskite EL images shows an interesting result. As the perovskite solar cell has degraded, three of the six cells have optically inactive regions, showing lower luminescence intensities. The series resistance of the other three cells are much lower compared to these cells that have inactive regions under low injection conditions. As the injection level increases, it is seen that the series resistance values of five of the six cells become comparable to one another. With regards to the PSF, it was found that using a bandpass filter in front of the lens reduced to amount of spreading observed from a single point source across the detector. Furthermore, there is a strong wavelength dependency in the PSF as the severity increased with increase in the emission wavelength of the solar cells under investigation.In this study an opto-electrical characterisation system was constructed to acquire PL and EL images of various solar cell technologies. In addition to this, a range of factors that influence the quality of these images were investigated and used in the image correction procedure to correct the images for all these cell technologies. It was shown that the correction procedure works for all three of the technologies investigated in this study, and all these factors showed a strong wavelength dependency. These corrected luminescence images together with current-voltage (I-V) data was then used to determine characteristic parameters of a one-diode model of the various PV devices. This was not only achieved, but it also clearly indicated that all the correction procedures need to be considered to obtain a clear and accurate representation of the actual PV device. This has a major influence on the understanding and improvement of these PV devices. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2024
- Full Text:
- Date Issued: 2024-04
Preparation and Investigation of coumarin-based chemosensors towards sensing of ions using UV studies in aqueous systems
- Authors: Kotze, Tyla
- Date: 2024-04
- Subjects: Chemistry, Analytic , Water chemistry , Ionic solutions , Aquatic ecology , Geochemistry
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64116 , vital:73654
- Description: Humanity's unrelenting expansion has shown little regard for the environment, and this has resulted in tons of toxic heavy metal cations and anions being released into the environment through industrial, agricultural, electronic, and mining dumping. The release of these toxic heavy metals can cause diseases and sometimes lead to death, especially in third-world countries with low-income that reside in informal settlements, who suffer the most. Furthermore, the release of these toxins eventually finds their way back into the environment through bioaccumulation in fish, plants and animals. Although there is an ever need for the growth of these industries; low-cost, sensitive, selective, and organic-based sensors is a positive step forward in highlighting the need for environmental restoration and remediation, whilst striving to avoid unnecessary disease and death through this development. In this project, coumarin-based chemosensors for the detection of cationic and anionic species in aqueous and organic media are described. This project involves the synthesis of six different coumarin-based ether derivatives (E2-E5) and coumarin-based ester derivatives (H1-H2). FT-IR, 1H NMR and 13C NMR were used to confirm the structures of all sensors. The abilities of these novel compounds as chemosensors for detection of cations and anions were investigated using UV-vis analysis. These compounds displayed a favourable interaction with Fe2+ and Fe3+ ions with an increase in absorbance. Ether derivatives E2-E5 did not display any degree of selectivity or sensitivity towards the chosen anions. It was found that in the presence of FeCl2, sensors H1 and H2 displayed a degree of selectivities and further investigations were therefore carried out. From the titration experiments, the limit of detection, limit of quantification and association constants were determined. Job’s plot analyses were performed to determine the binding ratios, which was supported by Benesi-Hildebrand studies. The binding ratio between the sensors and metal cations during complexation was found to be 1:1. Reversibility studies were carried out using EDTA to determine whether the sensors could be reused. Molecular Modelling studies were used to determine the most preferred binding sites. Lastly, real-life application screenings were also run to determine if the sensors will be able to be used in real-life scenarios. , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Kotze, Tyla
- Date: 2024-04
- Subjects: Chemistry, Analytic , Water chemistry , Ionic solutions , Aquatic ecology , Geochemistry
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64116 , vital:73654
- Description: Humanity's unrelenting expansion has shown little regard for the environment, and this has resulted in tons of toxic heavy metal cations and anions being released into the environment through industrial, agricultural, electronic, and mining dumping. The release of these toxic heavy metals can cause diseases and sometimes lead to death, especially in third-world countries with low-income that reside in informal settlements, who suffer the most. Furthermore, the release of these toxins eventually finds their way back into the environment through bioaccumulation in fish, plants and animals. Although there is an ever need for the growth of these industries; low-cost, sensitive, selective, and organic-based sensors is a positive step forward in highlighting the need for environmental restoration and remediation, whilst striving to avoid unnecessary disease and death through this development. In this project, coumarin-based chemosensors for the detection of cationic and anionic species in aqueous and organic media are described. This project involves the synthesis of six different coumarin-based ether derivatives (E2-E5) and coumarin-based ester derivatives (H1-H2). FT-IR, 1H NMR and 13C NMR were used to confirm the structures of all sensors. The abilities of these novel compounds as chemosensors for detection of cations and anions were investigated using UV-vis analysis. These compounds displayed a favourable interaction with Fe2+ and Fe3+ ions with an increase in absorbance. Ether derivatives E2-E5 did not display any degree of selectivity or sensitivity towards the chosen anions. It was found that in the presence of FeCl2, sensors H1 and H2 displayed a degree of selectivities and further investigations were therefore carried out. From the titration experiments, the limit of detection, limit of quantification and association constants were determined. Job’s plot analyses were performed to determine the binding ratios, which was supported by Benesi-Hildebrand studies. The binding ratio between the sensors and metal cations during complexation was found to be 1:1. Reversibility studies were carried out using EDTA to determine whether the sensors could be reused. Molecular Modelling studies were used to determine the most preferred binding sites. Lastly, real-life application screenings were also run to determine if the sensors will be able to be used in real-life scenarios. , Thesis (MSc) -- Faculty of Science, School of Biomolecular & Chemical Sciences, 2024
- Full Text:
- Date Issued: 2024-04
Quantifying the impact of the spatio-temporal variability of land use/land cover on surface run-off generation and groundwater recharge in the luvuvhu river catchment area as a study area
- Ramuhovhi, Dakalo Ndivhuwo Stella
- Authors: Ramuhovhi, Dakalo Ndivhuwo Stella
- Date: 2024-04
- Subjects: Remote sensing , Geographic information systems , Groundwater flow
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64322 , vital:73675
- Description: Assessing the spatio-temporal dynamics of land use land cover (LULC) change on hydrological response is vital for catchment sustainability and developing proper management strategies. The study aimed to assess the spatiotemporal effects and implications of LULC dynamics on surface runoff in the Luvuvhu River Catchment, Limpopo Province, using the Soil and Water Assessment Tool (SWAT) model. Satellite images of Landsat 5-thematic mapper and Landsat 8 operational land imager for the years 1990 and 2021 were used to explore the characteristics of LULC for this study by adopting the maximum likelihood (ML) supervised classification method. Five LULC classes were classified in this study; namely, water, built-up area, bare surface, dense vegetation, and sparse vegetation. The classification results show good accuracy values in the range of 76% (1990) and 84% (2021) with overall kappa of 63.8% and 72.8% for 1990 and 2021, respectively. For the purpose of this study, integration of geospatial technique and SWAT model were configured to operate at a monthly time interval over a span of 34 years, specifically from 1979 to 2013 to simulate surface runoff. The SWAT simulation process was executed using a digital elevation model, soil, LULC, and weather data. The analysis of LULC for 1990 and 2021 runoff modelling, it was found that, the runoff depth increased gradually from 3249 mm to 5162.5 mm during 1990 and 2021 LULC change, respectively. The R2, ENS, PBIAS, and RSR values for the calibration and the validation were 0.81 and 0.76, and 0.72 and 0.68, 0.64 and 0.58, 0.54 and 0.63 respectively. These values indicate good correlation between the observed and simulated stream flow data Therefore, suitable and timely management measures must be taken by policy decision-makers to enable sustainable development and to protect the catchment’s natural resources in order to reduce the severity of the changes. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Ramuhovhi, Dakalo Ndivhuwo Stella
- Date: 2024-04
- Subjects: Remote sensing , Geographic information systems , Groundwater flow
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64322 , vital:73675
- Description: Assessing the spatio-temporal dynamics of land use land cover (LULC) change on hydrological response is vital for catchment sustainability and developing proper management strategies. The study aimed to assess the spatiotemporal effects and implications of LULC dynamics on surface runoff in the Luvuvhu River Catchment, Limpopo Province, using the Soil and Water Assessment Tool (SWAT) model. Satellite images of Landsat 5-thematic mapper and Landsat 8 operational land imager for the years 1990 and 2021 were used to explore the characteristics of LULC for this study by adopting the maximum likelihood (ML) supervised classification method. Five LULC classes were classified in this study; namely, water, built-up area, bare surface, dense vegetation, and sparse vegetation. The classification results show good accuracy values in the range of 76% (1990) and 84% (2021) with overall kappa of 63.8% and 72.8% for 1990 and 2021, respectively. For the purpose of this study, integration of geospatial technique and SWAT model were configured to operate at a monthly time interval over a span of 34 years, specifically from 1979 to 2013 to simulate surface runoff. The SWAT simulation process was executed using a digital elevation model, soil, LULC, and weather data. The analysis of LULC for 1990 and 2021 runoff modelling, it was found that, the runoff depth increased gradually from 3249 mm to 5162.5 mm during 1990 and 2021 LULC change, respectively. The R2, ENS, PBIAS, and RSR values for the calibration and the validation were 0.81 and 0.76, and 0.72 and 0.68, 0.64 and 0.58, 0.54 and 0.63 respectively. These values indicate good correlation between the observed and simulated stream flow data Therefore, suitable and timely management measures must be taken by policy decision-makers to enable sustainable development and to protect the catchment’s natural resources in order to reduce the severity of the changes. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
Reconstructing the fire history and palaeoenvironment at Thyspunt, Southern Cape Coast, Eastern Cape
- Authors: Ntsondwa, Asithandile
- Date: 2024-04
- Subjects: Paleoecology -- South Africa -- Eastern Cape , Paleoclimatology -- South Africa -- Eastern Cape , Sedimentation analysis
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64277 , vital:73671
- Description: This study aims to comprehensively understand the palaeoenvironments at Thyspunt in the Eastern Cape, a subregion of the Cape Floristic Region, through fire reconstruction and sediment analyses. Given the fire-dependent nature of the dominant vegetation (fynbos) in the area, there is a need for fire reconstructions and an understanding of the broader ecological dynamics within the southern Cape coastal region (SCCR). This research focused on reconstructing the fire regimes using sedimentary micro- and macrocharcoal from a sediment core (TP-1) extracted from the Langefonteinvlei wetland at Thyspunt, covering the last 5000 years. The charcoal fragments were separated into three size classes, with two falling under microcharcoal (size class 1: 10 – 100 μm and size class 2: 100 – 150 μm) and fragments greater than 150 μm representing macrocharcoal. The sedimentary profile of the TP-1 sequence was characterised based on loss on ignition and x-ray fluorescence analyses to provide better insight into the area's geological and geomorphic setting, climate history, and sediment properties. The results from the geochemical data revealed consistently high calcium carbonate composition throughout the sequence with a decrease in concentration at ~2000 cal. yr BP, 1300 cal. yr BP, and from 500 cal. yr BP to recent years. The sediments had relatively high organic content during the last 500 years. The geochemical data also indicate that the sediments are associated with shallow marine and near-shore depositional environments with a sharp increase in fine material at about 4500 cal. yr BP representing a low-energy environment. High fire activities occur around 4000 cal. yr. BP and from 1500 cal. yr BP till present, with former fire activities more likely associated with increased wildfires (driven by climate change) and the latter possibly reflecting human influence at that time. Microcharcoal fragments (size class 1: 10 – 100 μm) had higher concentrations than the other size fragments. This study underpins the importance of a multiproxy study to enrich our understanding of fire histories in Thyspunt and contributes to broader regional insights. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
Reconstructing the fire history and palaeoenvironment at Thyspunt, Southern Cape Coast, Eastern Cape
- Authors: Ntsondwa, Asithandile
- Date: 2024-04
- Subjects: Paleoecology -- South Africa -- Eastern Cape , Paleoclimatology -- South Africa -- Eastern Cape , Sedimentation analysis
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64277 , vital:73671
- Description: This study aims to comprehensively understand the palaeoenvironments at Thyspunt in the Eastern Cape, a subregion of the Cape Floristic Region, through fire reconstruction and sediment analyses. Given the fire-dependent nature of the dominant vegetation (fynbos) in the area, there is a need for fire reconstructions and an understanding of the broader ecological dynamics within the southern Cape coastal region (SCCR). This research focused on reconstructing the fire regimes using sedimentary micro- and macrocharcoal from a sediment core (TP-1) extracted from the Langefonteinvlei wetland at Thyspunt, covering the last 5000 years. The charcoal fragments were separated into three size classes, with two falling under microcharcoal (size class 1: 10 – 100 μm and size class 2: 100 – 150 μm) and fragments greater than 150 μm representing macrocharcoal. The sedimentary profile of the TP-1 sequence was characterised based on loss on ignition and x-ray fluorescence analyses to provide better insight into the area's geological and geomorphic setting, climate history, and sediment properties. The results from the geochemical data revealed consistently high calcium carbonate composition throughout the sequence with a decrease in concentration at ~2000 cal. yr BP, 1300 cal. yr BP, and from 500 cal. yr BP to recent years. The sediments had relatively high organic content during the last 500 years. The geochemical data also indicate that the sediments are associated with shallow marine and near-shore depositional environments with a sharp increase in fine material at about 4500 cal. yr BP representing a low-energy environment. High fire activities occur around 4000 cal. yr. BP and from 1500 cal. yr BP till present, with former fire activities more likely associated with increased wildfires (driven by climate change) and the latter possibly reflecting human influence at that time. Microcharcoal fragments (size class 1: 10 – 100 μm) had higher concentrations than the other size fragments. This study underpins the importance of a multiproxy study to enrich our understanding of fire histories in Thyspunt and contributes to broader regional insights. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
Seagrasses in Mozambique: distribution, people’s perceptions and restoration best practice
- Mabuto, Manuela Elisa Manuel Amone, Hollander, Johan
- Authors: Mabuto, Manuela Elisa Manuel Amone , Hollander, Johan
- Date: 2024-04
- Subjects: Seagrasses -- Mozambique , Seagrasses -- Southern Hemisphere , Coastal zone management -- Mozambique , Restoration ecology -- Mozambique
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/64126 , vital:73655
- Description: This thesis investigated the restoration of seagrass meadows and their associated biodiversity thus contributing to their conservation and to people's well-being. A mixed methods approach was used, and results presented in five chapters. Chapter I is a general introduction to the study outlining relevant information, research objectives and hypotheses. Chapter II investigates coastal community’s perceptions on the role of seagrass ecosystems, local impacts of coastal erosion and the need for seagrass restoration in Mozambique. It showed that there is a high awareness of the studied communities to seagrass importance for their livelihoods. Communities supported restoration and identified community engagement as a fundamental component for a successful implementation of restoration projects in their area. Chapter III conducted a mapping inventory for seagrass using open access data sources and investigated change detection in seagrass extent in southern Mozambique using Satellite imagery. In addition, Unmanned Aerial Vehicles (drones) were used to map seagrass to the species level at Inhaca Island. The results showed that seagrass habitats have been losing extent in recent years mainly in Bairro dos Pescadores at northwest Maputo Bay, due to sedimentation from flooding and inappropriate gleaning / clam collection practices. Around Inhaca Island seagrass extent has changed in response to natural causes and from anthropogenic disturbance near the main village and port area. For the first time for this area drones were used to rapidly and effectively acquire high- resolution data for detailed seagrass mapping and monitoring. The different mapping approaches were critically analyzed, and a way forward discussed. In Chapter IV, two different field experiments were conducted simultaneously. One, mimicked disturbance of meadows in terms of digging to collect clams, a common practice in northeastern Maputo Bay to assess the time of natural recovery and another replanted Zostera capensis using different plug sizes. The results indicated that once anthropogenic impacts are ceased, Z. capensis meadows are restored 12 months after impact exclusion. There was a 75% survival rate for the mechanical plug restoration approach; positive implications for seagrass transplantation projects that are both time consuming and financially costly. It was clear from the study that a combination of both impact exclusion and active restoration is needed for seagrass survival. Chapter V investigated the influence of seagrass restoration on the abundance and diversity of macroinvertebrates. After two years of observations, replanted seagrass areas had not recovered compared to natural established seagrass beds. However, a strong linear relationship existed between the abundance of seagrasses and the quantity of associated macrofauna species. Chapter VI provided recommendations on better ways to perform seagrass restoration and management. The main findings of this thesis provide new knowledge on the mapping of seagrass on a local to a regional scale as well as on better restoration practice of the seagrass Zostera capensis, an IUCN Red List vulnerable species. Communities’ perceptions on seagrass were investigated contributing to an understanding of the socio-ecological conservation and management of these critical and yet threatened ecosystems. , Thesis (PhD) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Mabuto, Manuela Elisa Manuel Amone , Hollander, Johan
- Date: 2024-04
- Subjects: Seagrasses -- Mozambique , Seagrasses -- Southern Hemisphere , Coastal zone management -- Mozambique , Restoration ecology -- Mozambique
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/64126 , vital:73655
- Description: This thesis investigated the restoration of seagrass meadows and their associated biodiversity thus contributing to their conservation and to people's well-being. A mixed methods approach was used, and results presented in five chapters. Chapter I is a general introduction to the study outlining relevant information, research objectives and hypotheses. Chapter II investigates coastal community’s perceptions on the role of seagrass ecosystems, local impacts of coastal erosion and the need for seagrass restoration in Mozambique. It showed that there is a high awareness of the studied communities to seagrass importance for their livelihoods. Communities supported restoration and identified community engagement as a fundamental component for a successful implementation of restoration projects in their area. Chapter III conducted a mapping inventory for seagrass using open access data sources and investigated change detection in seagrass extent in southern Mozambique using Satellite imagery. In addition, Unmanned Aerial Vehicles (drones) were used to map seagrass to the species level at Inhaca Island. The results showed that seagrass habitats have been losing extent in recent years mainly in Bairro dos Pescadores at northwest Maputo Bay, due to sedimentation from flooding and inappropriate gleaning / clam collection practices. Around Inhaca Island seagrass extent has changed in response to natural causes and from anthropogenic disturbance near the main village and port area. For the first time for this area drones were used to rapidly and effectively acquire high- resolution data for detailed seagrass mapping and monitoring. The different mapping approaches were critically analyzed, and a way forward discussed. In Chapter IV, two different field experiments were conducted simultaneously. One, mimicked disturbance of meadows in terms of digging to collect clams, a common practice in northeastern Maputo Bay to assess the time of natural recovery and another replanted Zostera capensis using different plug sizes. The results indicated that once anthropogenic impacts are ceased, Z. capensis meadows are restored 12 months after impact exclusion. There was a 75% survival rate for the mechanical plug restoration approach; positive implications for seagrass transplantation projects that are both time consuming and financially costly. It was clear from the study that a combination of both impact exclusion and active restoration is needed for seagrass survival. Chapter V investigated the influence of seagrass restoration on the abundance and diversity of macroinvertebrates. After two years of observations, replanted seagrass areas had not recovered compared to natural established seagrass beds. However, a strong linear relationship existed between the abundance of seagrasses and the quantity of associated macrofauna species. Chapter VI provided recommendations on better ways to perform seagrass restoration and management. The main findings of this thesis provide new knowledge on the mapping of seagrass on a local to a regional scale as well as on better restoration practice of the seagrass Zostera capensis, an IUCN Red List vulnerable species. Communities’ perceptions on seagrass were investigated contributing to an understanding of the socio-ecological conservation and management of these critical and yet threatened ecosystems. , Thesis (PhD) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
Self-attentive vision in evolutionary robotics
- Authors: Botha, Bouwer
- Date: 2024-04
- Subjects: Evolutionary robotics , Robotics , Neural networks (Computer science)
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/63628 , vital:73566
- Description: The autonomy of a robot refers to its ability to achieve a task in an environment with minimal human supervision. This may require autonomous solutions to be able to perceive their environment to inform their decisions. An inexpensive and highly informative way that robots can perceive the environment is through vision. The autonomy of a robot is reliant on the quality of the robotic controller. These controllers are the software interface between the robot and environment that determine the actions of the robot based on the perceived environment. Controllers are typically created using manual programming techniques, which become progressively more challenging with increasing complexity of both the robot and task. An alternative to manual programming is the use of machine learning techniques such as those used by Evolutionary Robotics (ER). ER is an area of research that investigates the automatic creation of controllers. Instead of manually programming a controller, an Evolutionary Algorithms can be used to evolve the controller through repeated interactions with the task environment. Employing the ER approach on camera-based controllers, however, has presented problems for conventional ER methods. Firstly, existing architectures that are capable of automatically processing images, have a large number of trained parameters. These architectures over-encumber the evolutionary process due to the large search space of possible configurations. Secondly, the evolution of complex controllers needs to be done in simulation, which requires either: (a) the construction of a photo-realistic virtual environment with accurate lighting, texturing and models or (b) potential reduction of the controller capability by simplifying the problem via image preprocessing. Any controller trained in simulation also raises the inherent concern of not being able to transfer to the real world. This study proposes a new technique for the evolution of camera-based controllers in ER, that aims to address the highlighted problems. The use of self-attention is proposed to facilitate the evolution of compact controllers that are able to evolve specialized sets of task-relevant features in unprocessed images by focussing on important image regions. Furthermore, a new neural network-based simulation approach, Generative Neuro-Augmented Vision (GNAV), is proposed to simplify simulation construction. GNAV makes use of random data collected in a simple virtual environment and the real world. A neural network is trained to overcome the visual discrepancies between these two environments. GNAV enables a controller to be trained in a simple simulated environment that appears similar to the real environment, while requiring minimal human supervision. The capabilities of the new technique were demonstrated using a series of real-world navigation tasks based on camera vision. Controllers utilizing the proposed self-attention mechanism were trained using GNAV and transferred to a real camera-equipped robot. The controllers were shown to be able to perform the same tasks in the real world. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Botha, Bouwer
- Date: 2024-04
- Subjects: Evolutionary robotics , Robotics , Neural networks (Computer science)
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/63628 , vital:73566
- Description: The autonomy of a robot refers to its ability to achieve a task in an environment with minimal human supervision. This may require autonomous solutions to be able to perceive their environment to inform their decisions. An inexpensive and highly informative way that robots can perceive the environment is through vision. The autonomy of a robot is reliant on the quality of the robotic controller. These controllers are the software interface between the robot and environment that determine the actions of the robot based on the perceived environment. Controllers are typically created using manual programming techniques, which become progressively more challenging with increasing complexity of both the robot and task. An alternative to manual programming is the use of machine learning techniques such as those used by Evolutionary Robotics (ER). ER is an area of research that investigates the automatic creation of controllers. Instead of manually programming a controller, an Evolutionary Algorithms can be used to evolve the controller through repeated interactions with the task environment. Employing the ER approach on camera-based controllers, however, has presented problems for conventional ER methods. Firstly, existing architectures that are capable of automatically processing images, have a large number of trained parameters. These architectures over-encumber the evolutionary process due to the large search space of possible configurations. Secondly, the evolution of complex controllers needs to be done in simulation, which requires either: (a) the construction of a photo-realistic virtual environment with accurate lighting, texturing and models or (b) potential reduction of the controller capability by simplifying the problem via image preprocessing. Any controller trained in simulation also raises the inherent concern of not being able to transfer to the real world. This study proposes a new technique for the evolution of camera-based controllers in ER, that aims to address the highlighted problems. The use of self-attention is proposed to facilitate the evolution of compact controllers that are able to evolve specialized sets of task-relevant features in unprocessed images by focussing on important image regions. Furthermore, a new neural network-based simulation approach, Generative Neuro-Augmented Vision (GNAV), is proposed to simplify simulation construction. GNAV makes use of random data collected in a simple virtual environment and the real world. A neural network is trained to overcome the visual discrepancies between these two environments. GNAV enables a controller to be trained in a simple simulated environment that appears similar to the real environment, while requiring minimal human supervision. The capabilities of the new technique were demonstrated using a series of real-world navigation tasks based on camera vision. Controllers utilizing the proposed self-attention mechanism were trained using GNAV and transferred to a real camera-equipped robot. The controllers were shown to be able to perform the same tasks in the real world. , Thesis (MSc) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2024
- Full Text:
- Date Issued: 2024-04
Spatiotemporal recharge determination in response to episodic rainfall events within the Central Karoo, South Africa
- Authors: Williams, Aarifah
- Date: 2024-04
- Subjects: Groundwater -- South Africa -- Beaufort West , Groundwater recharge , Hydrogeology
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64459 , vital:73735
- Description: With inadequate and unpredictable rainfall patterns resulting in a mean annual precipitation of 464 mm, South Africa is classified as a water-stressed semi-arid country. Consequently, between 2015 and 2021, the majority of South Africa was confronted with severe drought conditions, with numerous dams running dry across the country. The Beaufort West Municipality is a prime example of the adverse effects of South Africa's inadequate and erratic rainfall patterns. In Beaufort West, a town located within the Central Karoo region of the Western Cape, groundwater is the primary source of water. Since recharge within the region is episodic, occurring irregularly, understanding the dynamics surrounding recharge in the area is essential for achieving sustainable long-term water resource management. This study aimed to gain a better understanding of how the aquifers within the Beaufort West Municipality Well Fields respond to extended periods of drought, extreme episodic precipitation events and excessive abstraction. This study aimed to quantify extreme recharge in the Beaufort West municipal wellfields using the water-table fluctuation (WTF) method. Additionally, it sought to deepen comprehension of the local climate's interaction with groundwater levels, surface water dynamics, and recharge through a 32-year historical data analysis (1990 to 2022) encompassing precipitation, evaporation, and surface water parameters. Findings revealed the complex relationship between precipitation, evaporation, regional geology, and water abstraction, influencing recharge periods, duration, and mechanisms across different regions within the aquifer system. Groundwater levels exhibited rapid declines during droughts due to extensive well field abstraction, but recovery was evident following episodic high precipitation events in 1993, 1996, 2010/2011, and 2019/2020. This comprehensive analysis serves as a valuable foundation for informed water resource management strategies, emphasizing the need for diversified approaches ensure the long-term water security and resilience of the Beaufort West Municipality. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04
- Authors: Williams, Aarifah
- Date: 2024-04
- Subjects: Groundwater -- South Africa -- Beaufort West , Groundwater recharge , Hydrogeology
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/64459 , vital:73735
- Description: With inadequate and unpredictable rainfall patterns resulting in a mean annual precipitation of 464 mm, South Africa is classified as a water-stressed semi-arid country. Consequently, between 2015 and 2021, the majority of South Africa was confronted with severe drought conditions, with numerous dams running dry across the country. The Beaufort West Municipality is a prime example of the adverse effects of South Africa's inadequate and erratic rainfall patterns. In Beaufort West, a town located within the Central Karoo region of the Western Cape, groundwater is the primary source of water. Since recharge within the region is episodic, occurring irregularly, understanding the dynamics surrounding recharge in the area is essential for achieving sustainable long-term water resource management. This study aimed to gain a better understanding of how the aquifers within the Beaufort West Municipality Well Fields respond to extended periods of drought, extreme episodic precipitation events and excessive abstraction. This study aimed to quantify extreme recharge in the Beaufort West municipal wellfields using the water-table fluctuation (WTF) method. Additionally, it sought to deepen comprehension of the local climate's interaction with groundwater levels, surface water dynamics, and recharge through a 32-year historical data analysis (1990 to 2022) encompassing precipitation, evaporation, and surface water parameters. Findings revealed the complex relationship between precipitation, evaporation, regional geology, and water abstraction, influencing recharge periods, duration, and mechanisms across different regions within the aquifer system. Groundwater levels exhibited rapid declines during droughts due to extensive well field abstraction, but recovery was evident following episodic high precipitation events in 1993, 1996, 2010/2011, and 2019/2020. This comprehensive analysis serves as a valuable foundation for informed water resource management strategies, emphasizing the need for diversified approaches ensure the long-term water security and resilience of the Beaufort West Municipality. , Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
- Full Text:
- Date Issued: 2024-04