Bush clumps as indicators of thresholds of change in Arid Thicket mosaic piospheres
- Authors: Schmidt, Anton George
- Date: 2017
- Subjects: Biodiversity conservation Ecological processes
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/20811 , vital:29403
- Description: In the literature, Arid Thicket transformation by domestic meso-herbivores is purported to follow a state-and-transition model, whereby the ecosystem is initially resilient to herbivory until some threshold is crossed, where after there is a rapid shift to a new alternative stable state. My study represents a first attempt to verify this hypothesis by searching for evidence of stable ecosystem states separated by structural, functional and degradation thresholds in Pruim-Spekboomveld, a variation of Arid Thicket found in the southern Cape of South Africa. In this variation, thicket bush clumps ranging in size from approximately 1 m2 to 100 m2 are interspersed in a matrix of Succulent Karoo vegetation. I correlate structural and functional attributes of the thicket bush clumps and the soil environment beneath them (indicators of ecosystem function) to distance from artificial watering points in four piosphere treatments that have had a different rangeland management history. I mostly fit linear, exponential and sigmoid regression models to my data and use Akaike’s Information Criterion to select the best fitting model. When analysing data on changes in the variation of vegetation production with distance from water using the Normalized Difference Vegetation Index, I additionally fit Generalized Additive Models to the data to take into account more complex predicted patterns of change. Furthermore, I compare the end regions of my data in the piosphere treatments to each other and to similar data collected in a transformed and untransformed reference site. I use both the pattern and extent of transformation within and between the treatments and the reference sites, to verify the existence of stable states and structural, functional and degradation thresholds. I also subject my entire dataset to multivariate analysis using ordination and permutation procedures, in an attempt to corroborate my results from the univariate analysis and to assess the response of bush clump community composition to herbivory. My results indicate that at the scale of a bush clump, a threshold reduction in species richness, functional type diversity, succulent shrub redundancy and cover, palatable shrub cover and bush clump leaf mass below 1.5 m occurs in regions intensively used by domestic meso-herbivores. Furthermore, at the landscape scale there is a threshold reduction in canopy tree cover and bush clump density. In addition to these structural threshold changes, results from a Landscape Function Analysis indicate that soil nutrient cycling, soil water infiltration and soil stability thresholds are crossed at the landscape scale. The soil nutrient cycling threshold is affirmed by soil chemical analyses which indicate that the most rested treatment in the study area has low carbon and nitrogen levels. Furthermore, the keystone species, Portulacaria afra, is unable to re-establish itself in any of the treatments. High pH and potassium levels in all the treatments, relative to the untransformed reference site, indicate that Portulacaria afra (which prefers moderate soil conditions) is unlikely to re-establish in the study area. This finding suggests that all my treatments have crossed a degradation threshold and therefore represent an alternative stable state to the untransformed reference site. My multivariate analysis supports this finding and further indicates that the sampling zones within 25 m of the watering points in the most utilized treatments have crossed a second degradation threshold. This finding is supported by my results that indicate that structural and function thresholds (related to the size, density and ability of bush clumps to capture and retain soil resources) have been crossed. Furthermore, excessively high concentrations of base cations in these sampling zones, relative to the untransformed reference site, affirm the crossing of a degradation threshold. My results on the changes in the variation of vegetation production with distance from water using the Normalized Difference Vegetation Index, support the growing body of evidence in the literature that suggests that increases in the variance of ecosystem processes and services are important indicators of impending ecological thresholds. In general, my findings support the prediction in the literature that domestic meso-herbivore induced transformation of Arid Mosaic Thicket will follow a state-andtransition model.
- Full Text:
- Date Issued: 2017
- Authors: Schmidt, Anton George
- Date: 2017
- Subjects: Biodiversity conservation Ecological processes
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/20811 , vital:29403
- Description: In the literature, Arid Thicket transformation by domestic meso-herbivores is purported to follow a state-and-transition model, whereby the ecosystem is initially resilient to herbivory until some threshold is crossed, where after there is a rapid shift to a new alternative stable state. My study represents a first attempt to verify this hypothesis by searching for evidence of stable ecosystem states separated by structural, functional and degradation thresholds in Pruim-Spekboomveld, a variation of Arid Thicket found in the southern Cape of South Africa. In this variation, thicket bush clumps ranging in size from approximately 1 m2 to 100 m2 are interspersed in a matrix of Succulent Karoo vegetation. I correlate structural and functional attributes of the thicket bush clumps and the soil environment beneath them (indicators of ecosystem function) to distance from artificial watering points in four piosphere treatments that have had a different rangeland management history. I mostly fit linear, exponential and sigmoid regression models to my data and use Akaike’s Information Criterion to select the best fitting model. When analysing data on changes in the variation of vegetation production with distance from water using the Normalized Difference Vegetation Index, I additionally fit Generalized Additive Models to the data to take into account more complex predicted patterns of change. Furthermore, I compare the end regions of my data in the piosphere treatments to each other and to similar data collected in a transformed and untransformed reference site. I use both the pattern and extent of transformation within and between the treatments and the reference sites, to verify the existence of stable states and structural, functional and degradation thresholds. I also subject my entire dataset to multivariate analysis using ordination and permutation procedures, in an attempt to corroborate my results from the univariate analysis and to assess the response of bush clump community composition to herbivory. My results indicate that at the scale of a bush clump, a threshold reduction in species richness, functional type diversity, succulent shrub redundancy and cover, palatable shrub cover and bush clump leaf mass below 1.5 m occurs in regions intensively used by domestic meso-herbivores. Furthermore, at the landscape scale there is a threshold reduction in canopy tree cover and bush clump density. In addition to these structural threshold changes, results from a Landscape Function Analysis indicate that soil nutrient cycling, soil water infiltration and soil stability thresholds are crossed at the landscape scale. The soil nutrient cycling threshold is affirmed by soil chemical analyses which indicate that the most rested treatment in the study area has low carbon and nitrogen levels. Furthermore, the keystone species, Portulacaria afra, is unable to re-establish itself in any of the treatments. High pH and potassium levels in all the treatments, relative to the untransformed reference site, indicate that Portulacaria afra (which prefers moderate soil conditions) is unlikely to re-establish in the study area. This finding suggests that all my treatments have crossed a degradation threshold and therefore represent an alternative stable state to the untransformed reference site. My multivariate analysis supports this finding and further indicates that the sampling zones within 25 m of the watering points in the most utilized treatments have crossed a second degradation threshold. This finding is supported by my results that indicate that structural and function thresholds (related to the size, density and ability of bush clumps to capture and retain soil resources) have been crossed. Furthermore, excessively high concentrations of base cations in these sampling zones, relative to the untransformed reference site, affirm the crossing of a degradation threshold. My results on the changes in the variation of vegetation production with distance from water using the Normalized Difference Vegetation Index, support the growing body of evidence in the literature that suggests that increases in the variance of ecosystem processes and services are important indicators of impending ecological thresholds. In general, my findings support the prediction in the literature that domestic meso-herbivore induced transformation of Arid Mosaic Thicket will follow a state-andtransition model.
- Full Text:
- Date Issued: 2017
Cape gannets in contrasting environments: ehaviour, demographics and indicators of environmental change
- Authors: Ryklief, Rabiah
- Date: 2017
- Subjects: Endemic birds -- South Africa Marine pollution -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/21167 , vital:29452
- Description: Marine communities represent biological networks, where physical and chemical changes in the marine environment can influence the physiology and behaviour of marine organisms. Stochastic marine conditions can alter key biological interactions and thus, influence the mechanisms that underpin population demography and phenotypic plasticity. Marine top predators, such as seabirds, are often controlled by bottom-up processes and their ability to cope with variable ocean conditions lies in their physiological and behavioural response to such perturbations. Seabirds are central-place foragers during the breeding season making them particularly vulnerable to environmental fluctuations as they face constrains associated with reproductive effort in addition to self-maintenance. The Cape gannet Morus capensis is a medium-sized pelagic seabird that is endemic to southern Africa. The Cape gannet has experienced considerable change in population distribution and abundance over the past 50 years. These changes have been linked to a combination of fishing pressure and climate-mediated regime shifts of their preferred prey, i.e. sardine Sardinops sagax and anchovy ngraulis encrasicolus. Historically, Malgas Island was the largest Cape gannet colony in South Africa. However, it is now in a state of population decline, despite its occurrence within one of the most productive upwelling systems in the world, the Benguela Current. At present, Bird Island is the largest Cape gannet colony and has recently stabilised, despite regular immigration of gannets from the west coast. Furthermore, Bird Island lies within the Agulhas bioregion and is subject to low levels of productivity from the nutrient-poor Agulhas current. Malgas and Bird islands are the two most populous of the six extant Cape gannet colonies. Birds at these colonies provided a natural experiment due to the contrasting population trajectories and environmental conditions at their colonies. The foraging ecology and behaviour of Cape gannets were studied during the breeding season to assess the mechanistic links connecting climate and fisheries to population demography. Cape gannets displayed considerable inter-annual variation in foraging effort and distribution across a five-year period. This highlights the importance of long-term datasets to contextualise the degree of natural variation within a species, as well as considerations for conservation management. For the first time, oceanographic variables such as sea surface temperature and chlorophyll-a, indices that reflect marine productivity, were used to predict Cape gannet foraging distribution. Furthermore, Cape gannets at Bird Island had an energy budget deficit in a year when foraging effort was much higher in comparison to what was observed at Malgas Island. This in turn was linked to the first identification of nutritional stress in a Sulid species. Reasons for this include a combination of higher intra-specific competition in conjunction with a lower energetic content of referential prey species at Bird Island. Foraging effort showed more variability at Malgas Island in comparison to Bird Island, likely due to Malgas Island gannets often taking two short foraging trips a day, whereas Bird Island gannets often spent the night at sea. Some degree of phenotypic plasticity was evidenced by substantial variations across breeding seasons and ocean basins in foraging effort and behaviour.
- Full Text:
- Date Issued: 2017
- Authors: Ryklief, Rabiah
- Date: 2017
- Subjects: Endemic birds -- South Africa Marine pollution -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/21167 , vital:29452
- Description: Marine communities represent biological networks, where physical and chemical changes in the marine environment can influence the physiology and behaviour of marine organisms. Stochastic marine conditions can alter key biological interactions and thus, influence the mechanisms that underpin population demography and phenotypic plasticity. Marine top predators, such as seabirds, are often controlled by bottom-up processes and their ability to cope with variable ocean conditions lies in their physiological and behavioural response to such perturbations. Seabirds are central-place foragers during the breeding season making them particularly vulnerable to environmental fluctuations as they face constrains associated with reproductive effort in addition to self-maintenance. The Cape gannet Morus capensis is a medium-sized pelagic seabird that is endemic to southern Africa. The Cape gannet has experienced considerable change in population distribution and abundance over the past 50 years. These changes have been linked to a combination of fishing pressure and climate-mediated regime shifts of their preferred prey, i.e. sardine Sardinops sagax and anchovy ngraulis encrasicolus. Historically, Malgas Island was the largest Cape gannet colony in South Africa. However, it is now in a state of population decline, despite its occurrence within one of the most productive upwelling systems in the world, the Benguela Current. At present, Bird Island is the largest Cape gannet colony and has recently stabilised, despite regular immigration of gannets from the west coast. Furthermore, Bird Island lies within the Agulhas bioregion and is subject to low levels of productivity from the nutrient-poor Agulhas current. Malgas and Bird islands are the two most populous of the six extant Cape gannet colonies. Birds at these colonies provided a natural experiment due to the contrasting population trajectories and environmental conditions at their colonies. The foraging ecology and behaviour of Cape gannets were studied during the breeding season to assess the mechanistic links connecting climate and fisheries to population demography. Cape gannets displayed considerable inter-annual variation in foraging effort and distribution across a five-year period. This highlights the importance of long-term datasets to contextualise the degree of natural variation within a species, as well as considerations for conservation management. For the first time, oceanographic variables such as sea surface temperature and chlorophyll-a, indices that reflect marine productivity, were used to predict Cape gannet foraging distribution. Furthermore, Cape gannets at Bird Island had an energy budget deficit in a year when foraging effort was much higher in comparison to what was observed at Malgas Island. This in turn was linked to the first identification of nutritional stress in a Sulid species. Reasons for this include a combination of higher intra-specific competition in conjunction with a lower energetic content of referential prey species at Bird Island. Foraging effort showed more variability at Malgas Island in comparison to Bird Island, likely due to Malgas Island gannets often taking two short foraging trips a day, whereas Bird Island gannets often spent the night at sea. Some degree of phenotypic plasticity was evidenced by substantial variations across breeding seasons and ocean basins in foraging effort and behaviour.
- Full Text:
- Date Issued: 2017
Characterisation of photovoltaic devices using large area light beam induced current measurements
- Okullo, Michael, Van Dyk, Ernes, Okullo, W
- Authors: Okullo, Michael , Van Dyk, Ernes , Okullo, W
- Date: 2017
- Subjects: Photovoltaic cells Photovoltaic power generation
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/20526 , vital:29314
- Description: Photovoltaic (PV) modules are made by connecting PV cells in series in order to generate a reasonable voltage that can be used for any productive work. Inaccuracy in cell sorting during crystalline silicon module construction, or non-uniform deposition of PV material and laser scribing during thin _lm module construction, may introduce current mismatch in the module. Current mismatch is a consequence of connecting module cells which have non-identical electrical characteristics. When current mismatch occurs in a module, it is the cell generating the lowest current that determines the module output current and this leads to a decrease in the output power and lifespan of the module. Investigation of current uniformity and the different current reducing features in PV modules, which are potential sources of current mismatch, is therefore critical in optimising the performance of PV modules. In this study, a large area light beam induced current (LA-LBIC) measurement system was developed. This non-destructive technique was used to characterise crystalline silicon PV modules (mono-crystalline and multi-crystalline), thin _lm PV modules (amorphous silicon and copper indium diselenide) and a combined concentrator photovoltaic (CPV) module. A light source mounted onto a motorised x-y scanning stage was used to illuminate a PV module, or the Fresnel lens of a CPV module, point-by-point, while measuring the module output current. The measured current was mapped as a function of position and presented as an LBIC image. The point-illuminated circuit model of a PV module was designed and used to explain the variation in current between and within module cells in the LA-LBIC maps. Application of the model to crystalline silicon modules attributes the variation in photo-generated current between cells mainly to current mismatch between series connected cells. Current variation within cells is attributed to individual cell shunts. In the thin _lm modules, the model attributes the variation in photo-generated current mainly to differences in local cell shunts and series resistances originating from the scribing procedure during cell formation in the manufacturing process. In the PV modules studied, variation in photo-generated current was found to exist both between and within cells. The variation was more pronounced between cells than within cells. Module point I-V curves at different points of the module were measured in order to extract short circuit current, to quantify the variations between and within cells. A striation ring defect, causing a drop in short circuit current of 38%, was detected in the mono-crystalline module. Investigation of the striation ring defect indicated that the defect is active in the bulk (p-type) but inactive in the top (n-type) layer. Further characterisation of the defect revealed that a higher percentage loss in short circuit current occurs at lower light intensities. In the multi-crystalline silicon module, cracks were detected and found to electrically isolate the module cells into two parts, causing them to operate in parallel and consequently introducing current mismatch in the module. The I-V curve of the module at standard test condition (STC) revealed a step below the knee, which is a manifestation of current mismatch in the module. High currents, as a consequence of diffuse reflection, leading to multiple reflections by the top glass were also observed at localised points on the bus bar and cell separations. In the a-Si module, the variation in photo-current within some cells, was found to be substantial. In the copper indium diselenide (CIS) module, an electrical disconnection across the module cells was identified. A disconnection in the form of a triangular shape was also identified in this module, which completely disconnected the front contact of this area from the module. This unique disconnection feature caused current in the module to follow in a reverse direction when the light spot was incident within the boundary of the disconnection. Scans performed under different forward voltage biases were useful in identifying severely shunted module cells. A severely shunted cell was found to generate a higher photo-current than a good cell at the same forward bias voltage. This unique observation was explored further using point-illuminated module I-V measurements, and was found to be due to the crossing over of the I-V curves of the two cells. In order to explore the relationship between cell photo-current and cell shunt resistance, a method to determine the shunt resistances of the cells in an encapsulated module was devised. The method involves measuring the I-V curves of a fully illuminated module and a partially illuminated module when one of its cells is shaded and the I-V curves used to determine the short circuit current and the shunt resistance of the shaded cell. A strong correlation was found to exist between the short circuit current of the shaded cell and the cell shunt resistance, as well as between the short circuit current of the shaded cell and dark LBIC. The LA-LBIC technique was further applied to characterise a combine CPV module. Results showed that the Fresnel lens facets close to the centre generate a higher photo-current at the receiver than those towards the edges. The reduced photo-current towards the edges was attributed to losses due to di_raction, dielectric reflection and internal re_ection. About 65% of the area of the Fresnel lenses were found to be e_ective in light collection in terms of the photo-current generated at the receiver. Abrasions and scratches on the Fresnel lenses were identi_ed as some of the current limiting features in a CPV module. The LA-LBIC technique used in this study has demonstrated the potential to investigate current mismatch, current limiting and current enhancing features in PV modules. The capacity to further characterise current limiting features in order to investigate their effects on photo-current under different wavelengths and light intensities was also demonstrated. Extending the LA-LBIC technique to characterise a combined CPV module is a great achievement of this work.
- Full Text:
- Date Issued: 2017
- Authors: Okullo, Michael , Van Dyk, Ernes , Okullo, W
- Date: 2017
- Subjects: Photovoltaic cells Photovoltaic power generation
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/20526 , vital:29314
- Description: Photovoltaic (PV) modules are made by connecting PV cells in series in order to generate a reasonable voltage that can be used for any productive work. Inaccuracy in cell sorting during crystalline silicon module construction, or non-uniform deposition of PV material and laser scribing during thin _lm module construction, may introduce current mismatch in the module. Current mismatch is a consequence of connecting module cells which have non-identical electrical characteristics. When current mismatch occurs in a module, it is the cell generating the lowest current that determines the module output current and this leads to a decrease in the output power and lifespan of the module. Investigation of current uniformity and the different current reducing features in PV modules, which are potential sources of current mismatch, is therefore critical in optimising the performance of PV modules. In this study, a large area light beam induced current (LA-LBIC) measurement system was developed. This non-destructive technique was used to characterise crystalline silicon PV modules (mono-crystalline and multi-crystalline), thin _lm PV modules (amorphous silicon and copper indium diselenide) and a combined concentrator photovoltaic (CPV) module. A light source mounted onto a motorised x-y scanning stage was used to illuminate a PV module, or the Fresnel lens of a CPV module, point-by-point, while measuring the module output current. The measured current was mapped as a function of position and presented as an LBIC image. The point-illuminated circuit model of a PV module was designed and used to explain the variation in current between and within module cells in the LA-LBIC maps. Application of the model to crystalline silicon modules attributes the variation in photo-generated current between cells mainly to current mismatch between series connected cells. Current variation within cells is attributed to individual cell shunts. In the thin _lm modules, the model attributes the variation in photo-generated current mainly to differences in local cell shunts and series resistances originating from the scribing procedure during cell formation in the manufacturing process. In the PV modules studied, variation in photo-generated current was found to exist both between and within cells. The variation was more pronounced between cells than within cells. Module point I-V curves at different points of the module were measured in order to extract short circuit current, to quantify the variations between and within cells. A striation ring defect, causing a drop in short circuit current of 38%, was detected in the mono-crystalline module. Investigation of the striation ring defect indicated that the defect is active in the bulk (p-type) but inactive in the top (n-type) layer. Further characterisation of the defect revealed that a higher percentage loss in short circuit current occurs at lower light intensities. In the multi-crystalline silicon module, cracks were detected and found to electrically isolate the module cells into two parts, causing them to operate in parallel and consequently introducing current mismatch in the module. The I-V curve of the module at standard test condition (STC) revealed a step below the knee, which is a manifestation of current mismatch in the module. High currents, as a consequence of diffuse reflection, leading to multiple reflections by the top glass were also observed at localised points on the bus bar and cell separations. In the a-Si module, the variation in photo-current within some cells, was found to be substantial. In the copper indium diselenide (CIS) module, an electrical disconnection across the module cells was identified. A disconnection in the form of a triangular shape was also identified in this module, which completely disconnected the front contact of this area from the module. This unique disconnection feature caused current in the module to follow in a reverse direction when the light spot was incident within the boundary of the disconnection. Scans performed under different forward voltage biases were useful in identifying severely shunted module cells. A severely shunted cell was found to generate a higher photo-current than a good cell at the same forward bias voltage. This unique observation was explored further using point-illuminated module I-V measurements, and was found to be due to the crossing over of the I-V curves of the two cells. In order to explore the relationship between cell photo-current and cell shunt resistance, a method to determine the shunt resistances of the cells in an encapsulated module was devised. The method involves measuring the I-V curves of a fully illuminated module and a partially illuminated module when one of its cells is shaded and the I-V curves used to determine the short circuit current and the shunt resistance of the shaded cell. A strong correlation was found to exist between the short circuit current of the shaded cell and the cell shunt resistance, as well as between the short circuit current of the shaded cell and dark LBIC. The LA-LBIC technique was further applied to characterise a combine CPV module. Results showed that the Fresnel lens facets close to the centre generate a higher photo-current at the receiver than those towards the edges. The reduced photo-current towards the edges was attributed to losses due to di_raction, dielectric reflection and internal re_ection. About 65% of the area of the Fresnel lenses were found to be e_ective in light collection in terms of the photo-current generated at the receiver. Abrasions and scratches on the Fresnel lenses were identi_ed as some of the current limiting features in a CPV module. The LA-LBIC technique used in this study has demonstrated the potential to investigate current mismatch, current limiting and current enhancing features in PV modules. The capacity to further characterise current limiting features in order to investigate their effects on photo-current under different wavelengths and light intensities was also demonstrated. Extending the LA-LBIC technique to characterise a combined CPV module is a great achievement of this work.
- Full Text:
- Date Issued: 2017
Characterization of a glycated gelatin model to explore the therapeutic properties of macrofungi in diabetic wound healing: an in vitro study
- Authors: Pringle, Nadine Alex
- Date: 2017
- Subjects: Diabetes -- Animal models Chronic diseases -- Age factors
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/11992 , vital:27017
- Description: Diabetic wounds frequently undergo impaired and prolonged wound healing due to a multitude of factors including hypoxia, impaired angiogenesis, hyperglycaemia, formation of ROS and AGEs, and infection - all of which may lead to cellular dysfunction. To date, however, treatment options for individuals suffering from impaired diabetic wound healing are limited, non-specific, and generally unsuccessful. The search for new and effective treatment strategies is severely hampered by the availability of adequately characterized screening models which comprehensively mimic the complexity of the diabetic wound healing process. In order to explore natural products as potential therapeutics to treat diabetic wounds and to encourage more research on this topic, this study sought out to develop and characterize a more convenient and cost effective in vitro screening assay which mimics the effects of protein glycation on the healing process of diabetic wounds. As proof of principal, this model was subsequently used to screen the potential of five wild mushroom species (P. tinctorius, R. capensis, B. badius, P. ostreatus and G. lucidum) as suitable diabetic wound healing therapies. The glycated gelatin model developed during this study was found to suitably mimic the diabetic state as it successfully simulated the major cellular dysfunctions in macrophages (NO production, phagocytosis, macrophage polarization, NF-ĸB translocation and COX-2 expression) and fibroblasts (proliferation and migration) documented during diabetic wound healing. Together these findings provide confidence that the model may serve as a valuable tool to study the poorly understood mechanisms which characterize cellular dysfunction in response to AGE accumulation and also to aid the identification of novel therapeutic agents to treat this pathology. Screening a number of mushroom extracts revealed that the ethanol extracts of R. capensis and P. ostreatus had the greatest potential for attenuating chronic inflammation due to their ability to promote macrophage phagocytosis, increased M2 activation (R. capensis) and decreased M1 activation (P. ostreatus) as well as reduced COX-2 expression while the water extract of G. lucidum proved to be the most promising candidate for stimulating fibroplasia as it was the most successful at promoting both fibroblast proliferation and migration. Different mushroom species were thus shown to promote different stages of the wound healing process providing sufficient evidence to support further studies related to the use of macrofungi as therapeutic agents in the search for more cost-effective and efficient treatment strategies for impaired diabetic wound healing.
- Full Text:
- Date Issued: 2017
- Authors: Pringle, Nadine Alex
- Date: 2017
- Subjects: Diabetes -- Animal models Chronic diseases -- Age factors
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/11992 , vital:27017
- Description: Diabetic wounds frequently undergo impaired and prolonged wound healing due to a multitude of factors including hypoxia, impaired angiogenesis, hyperglycaemia, formation of ROS and AGEs, and infection - all of which may lead to cellular dysfunction. To date, however, treatment options for individuals suffering from impaired diabetic wound healing are limited, non-specific, and generally unsuccessful. The search for new and effective treatment strategies is severely hampered by the availability of adequately characterized screening models which comprehensively mimic the complexity of the diabetic wound healing process. In order to explore natural products as potential therapeutics to treat diabetic wounds and to encourage more research on this topic, this study sought out to develop and characterize a more convenient and cost effective in vitro screening assay which mimics the effects of protein glycation on the healing process of diabetic wounds. As proof of principal, this model was subsequently used to screen the potential of five wild mushroom species (P. tinctorius, R. capensis, B. badius, P. ostreatus and G. lucidum) as suitable diabetic wound healing therapies. The glycated gelatin model developed during this study was found to suitably mimic the diabetic state as it successfully simulated the major cellular dysfunctions in macrophages (NO production, phagocytosis, macrophage polarization, NF-ĸB translocation and COX-2 expression) and fibroblasts (proliferation and migration) documented during diabetic wound healing. Together these findings provide confidence that the model may serve as a valuable tool to study the poorly understood mechanisms which characterize cellular dysfunction in response to AGE accumulation and also to aid the identification of novel therapeutic agents to treat this pathology. Screening a number of mushroom extracts revealed that the ethanol extracts of R. capensis and P. ostreatus had the greatest potential for attenuating chronic inflammation due to their ability to promote macrophage phagocytosis, increased M2 activation (R. capensis) and decreased M1 activation (P. ostreatus) as well as reduced COX-2 expression while the water extract of G. lucidum proved to be the most promising candidate for stimulating fibroplasia as it was the most successful at promoting both fibroblast proliferation and migration. Different mushroom species were thus shown to promote different stages of the wound healing process providing sufficient evidence to support further studies related to the use of macrofungi as therapeutic agents in the search for more cost-effective and efficient treatment strategies for impaired diabetic wound healing.
- Full Text:
- Date Issued: 2017
Community structure and trophic relations in marine tufa stromatolite pools of the Eastern Cape
- Authors: Rishworth, Gavin Midgley
- Date: 2017
- Subjects: Bioturbation -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/7116 , vital:21236
- Description: Microbialites were the dominant life-form of most shallow oceans during the Precambrian. These structures are formed by the deposition of calcium carbonate by cyanobacteria as well as the binding and trapping of sediment by these and other microalgae. In modern environments they are scarce due to several factors, including grazing pressures by metazoans, altered calcium carbonate saturation states of seawater and competition with macroalgae. The recent discovery of an extensive network of actively accreting layered microbialites (stromatolites) along the South African coastline is potentially informative from this perspective. These stromatolites form within the peritidal zone, at the interface of groundwater seepage and periodic marine incursion, forming pools trapped by the accreting fabric. The aim of this thesis was to characterise the ecosystem dynamics of a representative selection of the South African locations. During a comprehensive monthly assessment over an annual cycle, as well as for additional seasonal collections, physico-chemical measurements were monitored together with biological components such as benthic and pelagic microalgae as well as the invertebrate fauna inhabiting the stromatolite pools. These components were then assessed in terms of the potential physical and biological drivers which might explain patterns of variability. Finally, to link all of the ecosystem components, a food-web analysis was conducted, to determine the trophic linkages and, importantly, the reliance by the various consumer organisms on the stromatolite material as a food resource. Results show that the stromatolite pools are driven by a regular interplay between freshwater and marine salinity states, this being determined by tidal amplitude and ocean storm cycles. Furthermore, marine incursion represents the primary source of phosphorus for the stromatolite pools, while available nitrogen is consistently provided by the freshwater inlet stream at each site. This results in an optimum zone of primary biomass within the main stromatolite pool supported by nutrient conditions, while the shifts in salinity state occurring over a weekly tidal schedule likely exclude organisms and macrophytes that are not halotolerant. This is reflected in the benthic microalgae that form the stromatolite accretions in that they are primarily driven by salinity conditions, in addition to seasonal patterns. Interestingly, the variable nutrient conditions, both between sites and temporally, did not contribute as an important driver of the benthic microalgae but did significantly relate to the pelagic microalgae (phytoplankton). This, together with the higher biomass of benthic microalgae compared to its pelagic counterpart, suggests that the stromatolite pools are a benthic-driven system. The short duration of water retention within the stromatolite pools as a result of the constant freshwater inflow, likely also precludes nutrient build-up and favours the benthic, sessile ecosystem component, especially the stromatolite-forming microalgae. In terms of the metazoan infauna, the South African stromatolite pools support a persistent assemblage. This might be surprising given the apparently destructive influence of grazing and burrowing animals on microbial mats in terms of restricting the formation of layered accretions. However, metazoans that burrow within the stromatolite fabric were observed to coexist with clear, layered accretions. This supports the observations in some other modern microbialite habitats to suggest that metazoan disruption is clearly not the only or primary factor responsible for modern microbialite scarcity. When assessing the possible drivers of the metazoan community occupying the stromatolite matrix, both salinity patterns and resource conditions in terms of nutrient supply and macroalgal cover were consistently best related to infaunal abundance and presence/absence. This further demonstrates the role of salinity conditions in terms of providing a habitat that is restrictive to most metazoan organisms, while also suggesting that the metazoans are responding to macroalgal rather than the stromatolite microalgal conditions. To further develop this observation, the results from the stable isotope work clearly reflect a dominance of pool macroalgae in the diets of invertebrate consumers, with little to no stromatolite material consumed. This suggests that there is limited apparent destructive grazing influence by the metazoans on the stromatolite matrix, in addition to the burrowing bioturbation mentioned previously. Furthermore, the metazoan grazers may be indirectly benefitting the stromatolites by restricting macroalgal biomass, which might otherwise outcompete its microalgal counterpart. This study provides a valuable understanding of benthic-driven peritidal stromatolite ecosystems, and also, from a geological perspective of past stromatolite habitats, suggests some of the mechanisms as to why metazoans may be able to coexist with layered microbialites. Given the threats to similar habitats globally, especially in terms of water resources, management measures necessary to ensure stromatolite persistence in modern environments such as these are proposed. The possible ecological role of peritidal stromatolite habitats within the broader environment, as well as recommendations for future work, is also contextualised.
- Full Text:
- Date Issued: 2017
- Authors: Rishworth, Gavin Midgley
- Date: 2017
- Subjects: Bioturbation -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/7116 , vital:21236
- Description: Microbialites were the dominant life-form of most shallow oceans during the Precambrian. These structures are formed by the deposition of calcium carbonate by cyanobacteria as well as the binding and trapping of sediment by these and other microalgae. In modern environments they are scarce due to several factors, including grazing pressures by metazoans, altered calcium carbonate saturation states of seawater and competition with macroalgae. The recent discovery of an extensive network of actively accreting layered microbialites (stromatolites) along the South African coastline is potentially informative from this perspective. These stromatolites form within the peritidal zone, at the interface of groundwater seepage and periodic marine incursion, forming pools trapped by the accreting fabric. The aim of this thesis was to characterise the ecosystem dynamics of a representative selection of the South African locations. During a comprehensive monthly assessment over an annual cycle, as well as for additional seasonal collections, physico-chemical measurements were monitored together with biological components such as benthic and pelagic microalgae as well as the invertebrate fauna inhabiting the stromatolite pools. These components were then assessed in terms of the potential physical and biological drivers which might explain patterns of variability. Finally, to link all of the ecosystem components, a food-web analysis was conducted, to determine the trophic linkages and, importantly, the reliance by the various consumer organisms on the stromatolite material as a food resource. Results show that the stromatolite pools are driven by a regular interplay between freshwater and marine salinity states, this being determined by tidal amplitude and ocean storm cycles. Furthermore, marine incursion represents the primary source of phosphorus for the stromatolite pools, while available nitrogen is consistently provided by the freshwater inlet stream at each site. This results in an optimum zone of primary biomass within the main stromatolite pool supported by nutrient conditions, while the shifts in salinity state occurring over a weekly tidal schedule likely exclude organisms and macrophytes that are not halotolerant. This is reflected in the benthic microalgae that form the stromatolite accretions in that they are primarily driven by salinity conditions, in addition to seasonal patterns. Interestingly, the variable nutrient conditions, both between sites and temporally, did not contribute as an important driver of the benthic microalgae but did significantly relate to the pelagic microalgae (phytoplankton). This, together with the higher biomass of benthic microalgae compared to its pelagic counterpart, suggests that the stromatolite pools are a benthic-driven system. The short duration of water retention within the stromatolite pools as a result of the constant freshwater inflow, likely also precludes nutrient build-up and favours the benthic, sessile ecosystem component, especially the stromatolite-forming microalgae. In terms of the metazoan infauna, the South African stromatolite pools support a persistent assemblage. This might be surprising given the apparently destructive influence of grazing and burrowing animals on microbial mats in terms of restricting the formation of layered accretions. However, metazoans that burrow within the stromatolite fabric were observed to coexist with clear, layered accretions. This supports the observations in some other modern microbialite habitats to suggest that metazoan disruption is clearly not the only or primary factor responsible for modern microbialite scarcity. When assessing the possible drivers of the metazoan community occupying the stromatolite matrix, both salinity patterns and resource conditions in terms of nutrient supply and macroalgal cover were consistently best related to infaunal abundance and presence/absence. This further demonstrates the role of salinity conditions in terms of providing a habitat that is restrictive to most metazoan organisms, while also suggesting that the metazoans are responding to macroalgal rather than the stromatolite microalgal conditions. To further develop this observation, the results from the stable isotope work clearly reflect a dominance of pool macroalgae in the diets of invertebrate consumers, with little to no stromatolite material consumed. This suggests that there is limited apparent destructive grazing influence by the metazoans on the stromatolite matrix, in addition to the burrowing bioturbation mentioned previously. Furthermore, the metazoan grazers may be indirectly benefitting the stromatolites by restricting macroalgal biomass, which might otherwise outcompete its microalgal counterpart. This study provides a valuable understanding of benthic-driven peritidal stromatolite ecosystems, and also, from a geological perspective of past stromatolite habitats, suggests some of the mechanisms as to why metazoans may be able to coexist with layered microbialites. Given the threats to similar habitats globally, especially in terms of water resources, management measures necessary to ensure stromatolite persistence in modern environments such as these are proposed. The possible ecological role of peritidal stromatolite habitats within the broader environment, as well as recommendations for future work, is also contextualised.
- Full Text:
- Date Issued: 2017
Comparative performance of natural and synthetic fibre nonwoven geotextiles
- Tshifularo, Cyrus Alushavhiwi
- Authors: Tshifularo, Cyrus Alushavhiwi
- Date: 2017
- Subjects: Geotextiles Textile fabrics , Textile fibers -- Testing Textile industry -- Quality control
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/21362 , vital:29504
- Description: The aim of this work was to establish a range of suitable process parameters which can be utilized to produce needlepunched nonwoven fabrics for geotextile applications. Nonwoven fabrics were produced from 100% PP, a blend of 50/50% PP/kenaf and 100% kenaf fibres. The depths of needle penetration of 4, 7 and 10 mm, stroke frequencies of 250, 350 and 450 strokes/min and mass per unit area of 300, 600 and 900 g/m2 were utilized for producing the fabrics, on a Dilo loom. The effect of depth of needle penetration, stroke frequency and mass per unit area on the fabric properties, namely, tensile strength, puncture resistance, pore size, water permeability and transmissivity were analysed. In addition, the effect of chemicals, namely, 10% ammonium hydroxide (NH4OH), 10% sodium chloride (NaCl) and 3% sulphuric acid (H2SO4) solutions on degradation of the fabric was also studied. The results have shown that density, thickness and nominal weight of the needlepunched nonwoven fabrics were related to each other and they were influenced by stroke frequency, depth of needle penetration and feed rate of the needlepunching process. The increase in nominal weight of the fabrics also increases thickness and density of the fabrics. The tensile strength and puncture resistance of the fabrics increased with the increases in stroke frequency, depth of needle penetration and fabric mass per unit area. However, lower tensile strength and puncture resistance were achieved in the fabrics produced at lower stroke frequency, lower depth of needle penetration and lower mass per unit area. Bigger pores were resulted in the fabrics produced at lower stroke frequency, lower depth of needle penetration and lower mass per unit area, however, pore size decreased with increases in stroke frequency, depth of needle penetration and mass per unit area. Water permeability depends on the pore size, properties of the fibres, stroke frequency, depth of needle penetration and mass per unit area. Higher tensile strength and higher puncture resistance were achieved in the needlepunched nonwoven fabrics produced from 100% PP fibres, therefore, they are suitable for some load-bearing geotextile applications, such as reinforcement and separation. However, higher water permeability was achieved in the fabrics produced from 100% kenaf fibres, therefore, they are ideal for geotextile applications where good water permeability is required. Higher values for transmissivity were obtained in the fabrics produced from a blend of 50/50% PP/kenaf fibres, therefore they are suitable for drainage applications. The fabrics produced from a blend of 50/50% PP/kenaf fibres achieved better values of tensile strength, puncture resistance, pore size and water permeability in comparison to that produced from 100% PP and 100% kenaf fibres. However, better tensile strength and puncture resistance were achieved in the fabrics produced from 100% PP fibres and bigger pore size and higher water permeability were achieved in the fabrics produced from 100% kenaf fibres. Therefore, it can be suggested that the nonwoven fabrics produced from a blend of 50/50% PP/kenaf fibres can fulfil almost all requirements of geotextile applications, such as, filtration, separation, reinforcement and drainage. The fabrics produced from 100% PP fibres were not damaged or deteriorated when treated with all the three chemicals due to chemical inertness of polypropylene. However, the fabrics produced from a blend of 50/50% PP/kenaf and 100% kenaf fibres were damaged and deteriorated when treated with H2SO4.
- Full Text:
- Date Issued: 2017
- Authors: Tshifularo, Cyrus Alushavhiwi
- Date: 2017
- Subjects: Geotextiles Textile fabrics , Textile fibers -- Testing Textile industry -- Quality control
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/21362 , vital:29504
- Description: The aim of this work was to establish a range of suitable process parameters which can be utilized to produce needlepunched nonwoven fabrics for geotextile applications. Nonwoven fabrics were produced from 100% PP, a blend of 50/50% PP/kenaf and 100% kenaf fibres. The depths of needle penetration of 4, 7 and 10 mm, stroke frequencies of 250, 350 and 450 strokes/min and mass per unit area of 300, 600 and 900 g/m2 were utilized for producing the fabrics, on a Dilo loom. The effect of depth of needle penetration, stroke frequency and mass per unit area on the fabric properties, namely, tensile strength, puncture resistance, pore size, water permeability and transmissivity were analysed. In addition, the effect of chemicals, namely, 10% ammonium hydroxide (NH4OH), 10% sodium chloride (NaCl) and 3% sulphuric acid (H2SO4) solutions on degradation of the fabric was also studied. The results have shown that density, thickness and nominal weight of the needlepunched nonwoven fabrics were related to each other and they were influenced by stroke frequency, depth of needle penetration and feed rate of the needlepunching process. The increase in nominal weight of the fabrics also increases thickness and density of the fabrics. The tensile strength and puncture resistance of the fabrics increased with the increases in stroke frequency, depth of needle penetration and fabric mass per unit area. However, lower tensile strength and puncture resistance were achieved in the fabrics produced at lower stroke frequency, lower depth of needle penetration and lower mass per unit area. Bigger pores were resulted in the fabrics produced at lower stroke frequency, lower depth of needle penetration and lower mass per unit area, however, pore size decreased with increases in stroke frequency, depth of needle penetration and mass per unit area. Water permeability depends on the pore size, properties of the fibres, stroke frequency, depth of needle penetration and mass per unit area. Higher tensile strength and higher puncture resistance were achieved in the needlepunched nonwoven fabrics produced from 100% PP fibres, therefore, they are suitable for some load-bearing geotextile applications, such as reinforcement and separation. However, higher water permeability was achieved in the fabrics produced from 100% kenaf fibres, therefore, they are ideal for geotextile applications where good water permeability is required. Higher values for transmissivity were obtained in the fabrics produced from a blend of 50/50% PP/kenaf fibres, therefore they are suitable for drainage applications. The fabrics produced from a blend of 50/50% PP/kenaf fibres achieved better values of tensile strength, puncture resistance, pore size and water permeability in comparison to that produced from 100% PP and 100% kenaf fibres. However, better tensile strength and puncture resistance were achieved in the fabrics produced from 100% PP fibres and bigger pore size and higher water permeability were achieved in the fabrics produced from 100% kenaf fibres. Therefore, it can be suggested that the nonwoven fabrics produced from a blend of 50/50% PP/kenaf fibres can fulfil almost all requirements of geotextile applications, such as, filtration, separation, reinforcement and drainage. The fabrics produced from 100% PP fibres were not damaged or deteriorated when treated with all the three chemicals due to chemical inertness of polypropylene. However, the fabrics produced from a blend of 50/50% PP/kenaf and 100% kenaf fibres were damaged and deteriorated when treated with H2SO4.
- Full Text:
- Date Issued: 2017
Development of a liposomal acyclovir mucoadhesive film
- Authors: Nalungwe, Sarah
- Date: 2017
- Subjects: Clinical pharmacology , Liposomes Nanomedicine
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/14212 , vital:27451
- Description: Acyclovir is a synthetic purine nucleoside analogue with in vitro and in vivo inhibitory activity against herpes simplex virus types 1 (HSV-1), 2 (HSV-2), and varicella-zoster virus (VZV). The efficacy of oral acyclovir is limited as a result of its low bioavailability (15-30%) as it is poorly water soluble and therefore requires a frequent dosing regimen. When orally administered, peak plasma concentration occurs after 1.5–2.5 hours, while its elimination half-life is approximately 2-3 hours. Acyclovir displays poor solubility in water and in lipid bilayers, which leads to poor drug levels at target sites after oral, local, or parenteral administration. In order to improve this lack of solubility, novel amphiphilic derivatives have been designed to form nanoparticles, which allow for the efficient encapsulation of this hydrophobic antiviral agent. Reformulation of drugs in liposomes has provided an opportunity to enhance the therapeutic indices of various agents mainly via alteration of their bio-distribution. Liposomal drug delivery systems have received considerable attention due to their immense advantages which include, effective encapsulation of both small and large molecules that have a wide range of hydrophobicity levels and pKa values, prolonging and targeting release of therapeutic agents by modification of liposomal surface and also minimising clinical drug dose thus reducing toxicity effects. Liposomes exhibit a number of special biological characteristics, including specific interactions with biological membranes and various cells, hence, liposomes are used as biocompatible carriers to improve delivery properties across mucus membranes. Mucoadhesive dosage forms may be designed to enable prolonged retention at the site of application, providing a controlled rate of drug release for improved therapeutic outcome. The aim of this study was to develop an acyclovir liposomal mucoadhesive film by actively encapsulating acyclovir into liposomes and preparing a mucoadhesive film to optimise delivery of acyclovir liposomes at target sites. To actively encapsulate acyclovir and prepare the acyclovir-containing liposomes, a comprehensive statistical methodology was used in optimising the liposome formulation to encapsulate acyclovir. Central composite design was used as the response surface methodology statistical tool to design and develop an optimised method for active encapsulation of acyclovir into liposomes. The predicted optimised encapsulation parameters were incubation temperature of 60 °C and incubation time of 45 minutes. The mean percentage encapsulation calculated was 27.72%. The overall average size of the liposomes was 99.5 nm with a narrow distribution polydispersity index of 0.105 and were physically characterised as small unilamellar vesicles which possessed an average zeta potential of -45.6 mV. High Performance Liquid Chromatography (HPLC) was used to analyse and determine acyclovir drug content in the liposomes and drug release pattern from the mucoadhesive film. Polyvinyl-pyrrolidone (PVP) and Polyethylene glycol (PEG) were used in the preparation of mucoadhesive film, in which the acyclovir encapsulated liposomes were incorporated. The average amount of acyclovir drug content quantified to be in 4 cm2 of the mucoadhesive film was 36.8543 μg. The average tensile strength of the mucoadhesive film was determined to be 3.06 N/mm2 with an elongation percentage of 4.54%. The toughness of the film was 71.50 N.mm and the force required to rupture film was 16.49 N. The work and maximum force required to detach the mucoadhesive film from the glass side was 2.58 N.mm and 11615.32 mN, respectively. A Franz diffusion cell was used to perform acyclovir drug release studies from the mucoadhesive film and a commercial brand of acyclovir cream (Acitop®). Percentage acyclovir drug release from the film and cream was plotted against time using Sigmaplot® software version 13 following First order, Peppas, Hixon and Crowell, Higuchi (Square Root Time) and Bakers and Lonsdale mathematical models. The mucoadhesive film acyclovir attained the highest correlation coefficient r2 of 0.9879 following the Baker & Lonsdale mathematical model which describes controlled drug release from spherical matrices hence fits the model as the acyclovir is encapsulated in liposomes which are incorporated in the polymer mucoadhesive film. And the acyclovir cream (Acitop®) attained the highest correlation coefficient r2 of 0.9944 following the Peppas mathematical model. The Peppas model has been used to describe drug release from various release dosage forms when there is more than one type of dosage release or when release mechanism is not well known. One assumption of this model is that drug release occurs in one dimension, which is a suitable release profile for the cream as it is absorbed through the skin in one dimension when applied topically. There was significant difference between the drug release data for the mucoadhesive film and the acyclovir cream (Acitop®). A physically stable mucoadhesive film containing acyclovir-loaded liposomes was developed.
- Full Text:
- Date Issued: 2017
- Authors: Nalungwe, Sarah
- Date: 2017
- Subjects: Clinical pharmacology , Liposomes Nanomedicine
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/14212 , vital:27451
- Description: Acyclovir is a synthetic purine nucleoside analogue with in vitro and in vivo inhibitory activity against herpes simplex virus types 1 (HSV-1), 2 (HSV-2), and varicella-zoster virus (VZV). The efficacy of oral acyclovir is limited as a result of its low bioavailability (15-30%) as it is poorly water soluble and therefore requires a frequent dosing regimen. When orally administered, peak plasma concentration occurs after 1.5–2.5 hours, while its elimination half-life is approximately 2-3 hours. Acyclovir displays poor solubility in water and in lipid bilayers, which leads to poor drug levels at target sites after oral, local, or parenteral administration. In order to improve this lack of solubility, novel amphiphilic derivatives have been designed to form nanoparticles, which allow for the efficient encapsulation of this hydrophobic antiviral agent. Reformulation of drugs in liposomes has provided an opportunity to enhance the therapeutic indices of various agents mainly via alteration of their bio-distribution. Liposomal drug delivery systems have received considerable attention due to their immense advantages which include, effective encapsulation of both small and large molecules that have a wide range of hydrophobicity levels and pKa values, prolonging and targeting release of therapeutic agents by modification of liposomal surface and also minimising clinical drug dose thus reducing toxicity effects. Liposomes exhibit a number of special biological characteristics, including specific interactions with biological membranes and various cells, hence, liposomes are used as biocompatible carriers to improve delivery properties across mucus membranes. Mucoadhesive dosage forms may be designed to enable prolonged retention at the site of application, providing a controlled rate of drug release for improved therapeutic outcome. The aim of this study was to develop an acyclovir liposomal mucoadhesive film by actively encapsulating acyclovir into liposomes and preparing a mucoadhesive film to optimise delivery of acyclovir liposomes at target sites. To actively encapsulate acyclovir and prepare the acyclovir-containing liposomes, a comprehensive statistical methodology was used in optimising the liposome formulation to encapsulate acyclovir. Central composite design was used as the response surface methodology statistical tool to design and develop an optimised method for active encapsulation of acyclovir into liposomes. The predicted optimised encapsulation parameters were incubation temperature of 60 °C and incubation time of 45 minutes. The mean percentage encapsulation calculated was 27.72%. The overall average size of the liposomes was 99.5 nm with a narrow distribution polydispersity index of 0.105 and were physically characterised as small unilamellar vesicles which possessed an average zeta potential of -45.6 mV. High Performance Liquid Chromatography (HPLC) was used to analyse and determine acyclovir drug content in the liposomes and drug release pattern from the mucoadhesive film. Polyvinyl-pyrrolidone (PVP) and Polyethylene glycol (PEG) were used in the preparation of mucoadhesive film, in which the acyclovir encapsulated liposomes were incorporated. The average amount of acyclovir drug content quantified to be in 4 cm2 of the mucoadhesive film was 36.8543 μg. The average tensile strength of the mucoadhesive film was determined to be 3.06 N/mm2 with an elongation percentage of 4.54%. The toughness of the film was 71.50 N.mm and the force required to rupture film was 16.49 N. The work and maximum force required to detach the mucoadhesive film from the glass side was 2.58 N.mm and 11615.32 mN, respectively. A Franz diffusion cell was used to perform acyclovir drug release studies from the mucoadhesive film and a commercial brand of acyclovir cream (Acitop®). Percentage acyclovir drug release from the film and cream was plotted against time using Sigmaplot® software version 13 following First order, Peppas, Hixon and Crowell, Higuchi (Square Root Time) and Bakers and Lonsdale mathematical models. The mucoadhesive film acyclovir attained the highest correlation coefficient r2 of 0.9879 following the Baker & Lonsdale mathematical model which describes controlled drug release from spherical matrices hence fits the model as the acyclovir is encapsulated in liposomes which are incorporated in the polymer mucoadhesive film. And the acyclovir cream (Acitop®) attained the highest correlation coefficient r2 of 0.9944 following the Peppas mathematical model. The Peppas model has been used to describe drug release from various release dosage forms when there is more than one type of dosage release or when release mechanism is not well known. One assumption of this model is that drug release occurs in one dimension, which is a suitable release profile for the cream as it is absorbed through the skin in one dimension when applied topically. There was significant difference between the drug release data for the mucoadhesive film and the acyclovir cream (Acitop®). A physically stable mucoadhesive film containing acyclovir-loaded liposomes was developed.
- Full Text:
- Date Issued: 2017
Devulcanization of model compounds by a variety of diphenyldisulfides
- Authors: Boyce, Annemè
- Date: 2017
- Subjects: Rubber -- Recycling Rubber, Reclaimed , Rubber -- Standards -- South Africa Rubber -- Research Chromatographic analysis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/14730 , vital:27834
- Description: Improvements to the properties of recycled rubber, by developing a more selective breakdown process, is an important issue and a global challenge. Devulcanization is the most promising way to achieve this. It is a process which aims to totally or partially cleave monosulfidic (C-S-C), disulfidic (C-S-S-C) and polysulfidic (C-Sx-C) crosslinks of vulcanized rubber. In this study, the devulcanization of sulfur-vulcanized natural rubber with a variety of diphenyldisulfides has been studied using 2,3-dimethyl-2-butene and squalene as model compounds, vulcanized by sulfur and 2-bisbenzothiazole-2,2’-disulfide. 2-aminodiphenyldisulfide; 4-amino-diphenyldisulfide; bis(2-benzamido-)diphenyldisulfide and 2,2’-bithiosalicylic acid were used as aromatic disulfides devulcanization agents. Thermal analysis was used to investigate interactions between various combinations of curatives in the vulcanization systems in the absence of model compounds. Thermogravimetric analysis was used to detect mass changes during vulcanization and whether the samples decompose/evaporate so as not to contaminate differential scanning calorimetry instrumentation. Differential scanning calorimetry was used to investigate reactions occurring between curatives. Comparison of reversing and non-reversing signals in modulated experiments are suggestive of reactions between devulcanization agents and sulfur, and accelerators Vulcanization of the model compounds were performed in 10m evacuated sealed glass ampoules placed in an oil bath at 160 °C and agitated for the duration of vulcanization. After 60 min the ampoules were removed and quenched. These were then devulcanized by exposure to a devulcanization agent in a sealed ampoule at 180 for 60 min. Crosslinked 2,3-dimethyl-2-butene species were isolated and analysed by reversed phase high performance liquid chromatography. Particular attention was paid to changes in the number of sulfur atoms in the crosslinks. Results indicate that of the devulcanization agents tested 4-amino-diphenyldisulfide was the most effective. No detrimental effect on devulcanization efficiency was caused by the substitution of a basic amino group with an acidic carboxylic acid group Gel permeation chromatography was performed on devulcanized squalene crosslinks using a tetrahydrofuran eluent. GPC investigations with squalene were less effective than HPLC experiments with 2,3-dimethyl-2-butene at evaluating the relative efficiency of individual devulcanization agents. Results were, however, consistent with 4-amino-diphenyldisulfide again being the most efficient devulcanization agent.
- Full Text:
- Date Issued: 2017
- Authors: Boyce, Annemè
- Date: 2017
- Subjects: Rubber -- Recycling Rubber, Reclaimed , Rubber -- Standards -- South Africa Rubber -- Research Chromatographic analysis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/14730 , vital:27834
- Description: Improvements to the properties of recycled rubber, by developing a more selective breakdown process, is an important issue and a global challenge. Devulcanization is the most promising way to achieve this. It is a process which aims to totally or partially cleave monosulfidic (C-S-C), disulfidic (C-S-S-C) and polysulfidic (C-Sx-C) crosslinks of vulcanized rubber. In this study, the devulcanization of sulfur-vulcanized natural rubber with a variety of diphenyldisulfides has been studied using 2,3-dimethyl-2-butene and squalene as model compounds, vulcanized by sulfur and 2-bisbenzothiazole-2,2’-disulfide. 2-aminodiphenyldisulfide; 4-amino-diphenyldisulfide; bis(2-benzamido-)diphenyldisulfide and 2,2’-bithiosalicylic acid were used as aromatic disulfides devulcanization agents. Thermal analysis was used to investigate interactions between various combinations of curatives in the vulcanization systems in the absence of model compounds. Thermogravimetric analysis was used to detect mass changes during vulcanization and whether the samples decompose/evaporate so as not to contaminate differential scanning calorimetry instrumentation. Differential scanning calorimetry was used to investigate reactions occurring between curatives. Comparison of reversing and non-reversing signals in modulated experiments are suggestive of reactions between devulcanization agents and sulfur, and accelerators Vulcanization of the model compounds were performed in 10m evacuated sealed glass ampoules placed in an oil bath at 160 °C and agitated for the duration of vulcanization. After 60 min the ampoules were removed and quenched. These were then devulcanized by exposure to a devulcanization agent in a sealed ampoule at 180 for 60 min. Crosslinked 2,3-dimethyl-2-butene species were isolated and analysed by reversed phase high performance liquid chromatography. Particular attention was paid to changes in the number of sulfur atoms in the crosslinks. Results indicate that of the devulcanization agents tested 4-amino-diphenyldisulfide was the most effective. No detrimental effect on devulcanization efficiency was caused by the substitution of a basic amino group with an acidic carboxylic acid group Gel permeation chromatography was performed on devulcanized squalene crosslinks using a tetrahydrofuran eluent. GPC investigations with squalene were less effective than HPLC experiments with 2,3-dimethyl-2-butene at evaluating the relative efficiency of individual devulcanization agents. Results were, however, consistent with 4-amino-diphenyldisulfide again being the most efficient devulcanization agent.
- Full Text:
- Date Issued: 2017
Dinoflagellate communities in Algoa Bay: abundance and dynamics
- Authors: Van Zyl, Hendrik Francois
- Date: 2017
- Subjects: Marine microbiology , Microbiology Marine biology -- Indian Ocean
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/21218 , vital:29457
- Description: The contribution of dinoflagellates to the phytoplankton of Algoa Bay is largely unknown. This study aimed to address this, but additionally considered seasonal and spatial variation in the dinoflagellate communities of Algoa Bay. Phytoplankton abundance and the inorganic nutrients ammonium, total oxidized nitrogen, soluble reactive phosphorus and silicate were analysed. Diatoms dominated the phytoplankton community in most samples, with dinoflagellates only occasionally dominating the community. No seasonality could be detected in dinoflagellate abundance. Furthermore, no significant spatial patterns could be distinguished in dinoflagellate abundance, with the only exception being that the Port Elizabeth harbour waters contained significantly fewer dinoflagellate cells than the younger Ngqura harbour. Total phytoplankton abundance was correlated with inorganic nitrogen concentrations, but this was due to diatoms – dinoflagellate abundance did not correlate significantly with any nutrient measured. Both the common, historically bloom-forming Noctiluca scintilans, as well as the recently red tide-forming Lingulodinium polyhedra were recorded during the study, the latter almost exclusively from the harbours, which can be considered repositories of these toxic and harmful algal cells. The findings suggest that dinoflagellates in Algoa Bay are a robust phytoplankton group able to survive, and often thrive, in wide range of environmental conditions.
- Full Text:
- Date Issued: 2017
- Authors: Van Zyl, Hendrik Francois
- Date: 2017
- Subjects: Marine microbiology , Microbiology Marine biology -- Indian Ocean
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/21218 , vital:29457
- Description: The contribution of dinoflagellates to the phytoplankton of Algoa Bay is largely unknown. This study aimed to address this, but additionally considered seasonal and spatial variation in the dinoflagellate communities of Algoa Bay. Phytoplankton abundance and the inorganic nutrients ammonium, total oxidized nitrogen, soluble reactive phosphorus and silicate were analysed. Diatoms dominated the phytoplankton community in most samples, with dinoflagellates only occasionally dominating the community. No seasonality could be detected in dinoflagellate abundance. Furthermore, no significant spatial patterns could be distinguished in dinoflagellate abundance, with the only exception being that the Port Elizabeth harbour waters contained significantly fewer dinoflagellate cells than the younger Ngqura harbour. Total phytoplankton abundance was correlated with inorganic nitrogen concentrations, but this was due to diatoms – dinoflagellate abundance did not correlate significantly with any nutrient measured. Both the common, historically bloom-forming Noctiluca scintilans, as well as the recently red tide-forming Lingulodinium polyhedra were recorded during the study, the latter almost exclusively from the harbours, which can be considered repositories of these toxic and harmful algal cells. The findings suggest that dinoflagellates in Algoa Bay are a robust phytoplankton group able to survive, and often thrive, in wide range of environmental conditions.
- Full Text:
- Date Issued: 2017
Ecology of key cerithioidean gastropods in the mangroves of the iSimangaliso Wetland Park, KwaZulu-Natal South Africa
- Authors: Raw, Jacqueline Leoni
- Date: 2017
- Subjects: Gastropoda -- South Africa -- KwaZulu-Natal Mangrove ecology -- South Africa -- KwaZulu-Natal
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/11942 , vital:27009
- Description: Gastropods are one of the most diverse species groups in mangrove habitats, however, many of their specific roles in relation to ecological patterns and processes are currently largely unknown. The overall aim of this research project was to provide basic ecological information for key gastropod species from subtropical mangroves within a protected area. South African mangroves cover relatively small areas and are restricted to estuaries, these habitats therefore present unique opportunities and challenges to the species that occur in them. Three gastropod species, Terebralia palustris, Cerithidea decollata, and Melanoides tuberculata, all occur at their natural southernmost range limit within South Africa and were selected based on their prominence and occurrence in mangrove habitats of the iSimangaliso Wetland Park, a UNESCO World Heritage Site. Trophic linkages and resource partitioning, resource utilization rates, and ecological resilience were investigated respectively using: 1) a stable isotope (δ15N and δ13C) approach; 2) an experimental approach to quantify feeding dynamics (ingestion rate, consumption/digestion efficiency and grazing impact); and 3) a mixed-effects modelling approach to relate population responses to environmental variables. The diet of T. palustris was seasonally variable and a number of sources were incorporated by different sized snails, but their grazing impact on microphytobenthos was not significant. The results also indicated an ontogenetic shift in the dietary niche for T. palustris through robust partitioning of resources between different size classes. The diets of C. decollata and M. tuberculata were dominated by different primary resources as a function of where they occurred in the mangroves. Melanoides tuberculata consumed a wide variety of primary resources, a typical trait of an opportunistic generalist species. The ingestion rate of M. tuberculata was not dependent on the availability of microphytobenthos, and was highest when conditions were oligotrophic. The resilience of C. decollata was related to the tree-climbing behaviour of this species and its occurrence was best explained by sediment conductivity. These responses were considered in conjunction to what has previously been reported on the resilience of the mangrove trees. The results of this research project have provided new basic ecological information for all three gastropod species in this data-deficient subtropical region. This information can potentially be used in comparative studies for these species in other regions or in broader scale ecological studies. Terebralia palustris has recently experienced a range contraction along the South African coastline. This research project has shown that the diet of this species is highly variable and that food limitation and competition for resources should be considered as potential drivers of the local decline. Cerithidea decollata has in contrast expanded its distributional range in this region. This research project has shown that this species has a generalist diet and exhibits traits in relation to tolerance that are expected to have facilitated its expansion into temperate saltmarsh habitats that occur in dynamic estuaries. Melanoides tuberculata is a globally invasive species, and as South African populations are within its native range, ecological information from this region is valuable as it can be used to investigate the potential ecological effects following introduction into new habitats beyond the native range. Biological drivers have a significant impact on mangrove ecosystem functioning, particularly in relation to recycling and the retention of organic carbon generated through primary productivity. Understanding the ecological linkages that maintain ecological functioning and stability is therefore an important step towards conserving and sustainably managing threatened ecosystems such as mangrove forests.
- Full Text:
- Date Issued: 2017
- Authors: Raw, Jacqueline Leoni
- Date: 2017
- Subjects: Gastropoda -- South Africa -- KwaZulu-Natal Mangrove ecology -- South Africa -- KwaZulu-Natal
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/11942 , vital:27009
- Description: Gastropods are one of the most diverse species groups in mangrove habitats, however, many of their specific roles in relation to ecological patterns and processes are currently largely unknown. The overall aim of this research project was to provide basic ecological information for key gastropod species from subtropical mangroves within a protected area. South African mangroves cover relatively small areas and are restricted to estuaries, these habitats therefore present unique opportunities and challenges to the species that occur in them. Three gastropod species, Terebralia palustris, Cerithidea decollata, and Melanoides tuberculata, all occur at their natural southernmost range limit within South Africa and were selected based on their prominence and occurrence in mangrove habitats of the iSimangaliso Wetland Park, a UNESCO World Heritage Site. Trophic linkages and resource partitioning, resource utilization rates, and ecological resilience were investigated respectively using: 1) a stable isotope (δ15N and δ13C) approach; 2) an experimental approach to quantify feeding dynamics (ingestion rate, consumption/digestion efficiency and grazing impact); and 3) a mixed-effects modelling approach to relate population responses to environmental variables. The diet of T. palustris was seasonally variable and a number of sources were incorporated by different sized snails, but their grazing impact on microphytobenthos was not significant. The results also indicated an ontogenetic shift in the dietary niche for T. palustris through robust partitioning of resources between different size classes. The diets of C. decollata and M. tuberculata were dominated by different primary resources as a function of where they occurred in the mangroves. Melanoides tuberculata consumed a wide variety of primary resources, a typical trait of an opportunistic generalist species. The ingestion rate of M. tuberculata was not dependent on the availability of microphytobenthos, and was highest when conditions were oligotrophic. The resilience of C. decollata was related to the tree-climbing behaviour of this species and its occurrence was best explained by sediment conductivity. These responses were considered in conjunction to what has previously been reported on the resilience of the mangrove trees. The results of this research project have provided new basic ecological information for all three gastropod species in this data-deficient subtropical region. This information can potentially be used in comparative studies for these species in other regions or in broader scale ecological studies. Terebralia palustris has recently experienced a range contraction along the South African coastline. This research project has shown that the diet of this species is highly variable and that food limitation and competition for resources should be considered as potential drivers of the local decline. Cerithidea decollata has in contrast expanded its distributional range in this region. This research project has shown that this species has a generalist diet and exhibits traits in relation to tolerance that are expected to have facilitated its expansion into temperate saltmarsh habitats that occur in dynamic estuaries. Melanoides tuberculata is a globally invasive species, and as South African populations are within its native range, ecological information from this region is valuable as it can be used to investigate the potential ecological effects following introduction into new habitats beyond the native range. Biological drivers have a significant impact on mangrove ecosystem functioning, particularly in relation to recycling and the retention of organic carbon generated through primary productivity. Understanding the ecological linkages that maintain ecological functioning and stability is therefore an important step towards conserving and sustainably managing threatened ecosystems such as mangrove forests.
- Full Text:
- Date Issued: 2017
Ecophysiology and nutrient uptake mechanisms facilitating the prolonged bloom persistence by Cyanothece sp. in Lake St Lucia, South Africa
- Authors: Du Plooy, Schalk Jacobus
- Date: 2017
- Subjects: Cyanobacterial blooms , Cyanobacteria -- Physiology , Cyanobacteria
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/7344 , vital:21324
- Description: Cyanobacterial blooms are becoming more frequent worldwide, with possible negative effects on human health. The effects of climate change and eutrophication have been associated with persistent cyanobacterial blooms becoming more frequent. Altered water characteristics, salinity in particular, influence ecosystem dynamics that may lead to conditions conducive to cyanobacterial blooms. The occurrence of an 18-month long Cyanothece sp. bloom (the longest for any cyanobacterium recorded so far worldwide and the first of the genus) from June 2009 to December 2010 in Africa’s largest estuarine lake, St Lucia, highlighted the susceptibility of ecosystems to anthropogenic alterations. This study investigated the long-term survival and physiological adaptations of Cyanothece sp. to various and dynamic environmental conditions that contributed towards its bloom persistence. The main findings are the high salinities at which Cyanothece sp. could perform important physiological processes such as N uptake, N2 fixation and photosynthesis. Nutrient uptake (both nitrogen and phosphorus) was observed over the full experimental salinity range (0-300) while N2 fixation was only observed up to a salinity of 120. Nutrient uptake rates significantly decreased at this threshold salinity of 120. Interestingly, photosystem II activity was not observed in Cyanothece sp. during this study, but photosystem I activity was robust. Salinity had a minor influence on electron transport rates by photosystem I, high temperature (> 30°C) did however increase electron transport rates. Rapid responses to hypo-osmotic shock (i.e. osmotic downshift during freshening events) by Cyanothece sp. cells also helped minimize cell rupture due to high turgor pressure. Zooplankton abundance within the St Lucia system was negatively correlated with salinity, while grazing experiments indicated that the typical estuarine zooplankton species are able to graze on Cyanothece sp. cells. Therefore, the disappearance of zooplankton at salinities above 60 must have been an important factor in the bloom persistence. Apart from the ecological factors that were at play in St Lucia during the bloom period, the persistence of the Cyanothece sp. bloom can be attributed to the robust nature of their nutrient uptake, nitrogen fixation and photosynthetic systems to maintain activity despite extreme hypersalinity levels.
- Full Text:
- Date Issued: 2017
- Authors: Du Plooy, Schalk Jacobus
- Date: 2017
- Subjects: Cyanobacterial blooms , Cyanobacteria -- Physiology , Cyanobacteria
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/7344 , vital:21324
- Description: Cyanobacterial blooms are becoming more frequent worldwide, with possible negative effects on human health. The effects of climate change and eutrophication have been associated with persistent cyanobacterial blooms becoming more frequent. Altered water characteristics, salinity in particular, influence ecosystem dynamics that may lead to conditions conducive to cyanobacterial blooms. The occurrence of an 18-month long Cyanothece sp. bloom (the longest for any cyanobacterium recorded so far worldwide and the first of the genus) from June 2009 to December 2010 in Africa’s largest estuarine lake, St Lucia, highlighted the susceptibility of ecosystems to anthropogenic alterations. This study investigated the long-term survival and physiological adaptations of Cyanothece sp. to various and dynamic environmental conditions that contributed towards its bloom persistence. The main findings are the high salinities at which Cyanothece sp. could perform important physiological processes such as N uptake, N2 fixation and photosynthesis. Nutrient uptake (both nitrogen and phosphorus) was observed over the full experimental salinity range (0-300) while N2 fixation was only observed up to a salinity of 120. Nutrient uptake rates significantly decreased at this threshold salinity of 120. Interestingly, photosystem II activity was not observed in Cyanothece sp. during this study, but photosystem I activity was robust. Salinity had a minor influence on electron transport rates by photosystem I, high temperature (> 30°C) did however increase electron transport rates. Rapid responses to hypo-osmotic shock (i.e. osmotic downshift during freshening events) by Cyanothece sp. cells also helped minimize cell rupture due to high turgor pressure. Zooplankton abundance within the St Lucia system was negatively correlated with salinity, while grazing experiments indicated that the typical estuarine zooplankton species are able to graze on Cyanothece sp. cells. Therefore, the disappearance of zooplankton at salinities above 60 must have been an important factor in the bloom persistence. Apart from the ecological factors that were at play in St Lucia during the bloom period, the persistence of the Cyanothece sp. bloom can be attributed to the robust nature of their nutrient uptake, nitrogen fixation and photosynthetic systems to maintain activity despite extreme hypersalinity levels.
- Full Text:
- Date Issued: 2017
Effect of graphitization on the static mechanical properties of service exposed ASTM A516 Gr. 65 steam pipe metal
- Authors: Du Preez, Christiaan
- Date: 2017
- Subjects: Graphitization Steam-pipes -- Mechanical properties
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/22277 , vital:29933
- Description: The focus of this research project is to establish what effect graphitization has on the static mechanical properties of service exposed ASTM A516 Grade 65 steam pipe material, which operated for prolonged periods above 425 ̊C. The research study was conducted on three graphitized service exposed steam pipe weldment samples and on a newly welded and post weld heat treated sample with graphitized service exposed steam pipe material. Macro samples were removed from each of the samples at two positions and these were evaluated with regard to graphite nodule size, nearest neighbour spacing and % planar graphitization in the parent pipe and HAZ regions on either side of the welds. It was found on all of the service exposed samples that the graphite nodules of the HAZ regions have a smaller median nodule size, smaller median nearest neighbour spacing and increased % planar graphitization in comparison to the parent pipe material. The service expose parent pipe material on either side of the weldments of the respective samples was chemically analyzed. This was done with the focus being on the deoxidizing element content (Si and Al) of the respective parent pipe regions and to what extent these elements influenced the development of planar graphitization in these regions. No correlation could be identified between the level of deoxidizing elements and the levels of % planar graphitization in the parent pipe material. Tensile and Charpy impact samples were removed from the respective service exposed samples parent material on either side of the weld and from the HAZ regions on the side with the highest levels of planar graphitization. These samples were tested and the yield and ultimate tensile strength and Charpy impact toughness of the respective samples were then evaluated to establish how these static mechanical properties were influenced by the % planar graphitization. The yield and ultimate tensile strength of the service exposed material did not show a statistically significant correlation with the % planar graphitization. The Charpy impact toughness results did however show a statistically significant negative correlation towards the % planar graphitization. This was clearly evident from the results of the HAZ regions of the service exposed weldments (Samples A-C) which had the highest levels of % planar graphitization and the lowest impact toughness, while the newly welded and post weld heat treated Sample D had no planar graphitization outside the HAZ and the highest impact toughness. This research project not only investigated how planar graphitization affects the static mechanical properties of service exposed pipe material, it also investigated on a microstructural basis, how planar graphitization nucleates and grows. The microstructural investigation showed that the free carbon required for the development of planar graphitization originated from the regions outside the HAZ, which were formed when the pearlite bands were dissolved during the welding of the steam pipe. The heat input from the welding sensitized this region for the development of planar graphitization, probably due to the formation of a “carbon-rich” matrix due to the partial dissolution of the cementite precipitates. All the carbide precipitates in this region consisted of M3C. aluminium-rich precipitates were found inside newly nucleated graphite nodules, indicating its role as a possible heterogeneous nucleation site. Growth of newly formed graphite nodules showed a preference towards high-angle grain boundaries and regions with dislocations for the initial growth stages of the graphite nodules. The microstructure of the region outside the HAZ of the newly introduced seam weld on the service exposed steam pipe material (with graphitization), was also investigated using advanced electron microscopy methods and it yielded no evidence of the development of planar graphitization.
- Full Text:
- Date Issued: 2017
- Authors: Du Preez, Christiaan
- Date: 2017
- Subjects: Graphitization Steam-pipes -- Mechanical properties
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/22277 , vital:29933
- Description: The focus of this research project is to establish what effect graphitization has on the static mechanical properties of service exposed ASTM A516 Grade 65 steam pipe material, which operated for prolonged periods above 425 ̊C. The research study was conducted on three graphitized service exposed steam pipe weldment samples and on a newly welded and post weld heat treated sample with graphitized service exposed steam pipe material. Macro samples were removed from each of the samples at two positions and these were evaluated with regard to graphite nodule size, nearest neighbour spacing and % planar graphitization in the parent pipe and HAZ regions on either side of the welds. It was found on all of the service exposed samples that the graphite nodules of the HAZ regions have a smaller median nodule size, smaller median nearest neighbour spacing and increased % planar graphitization in comparison to the parent pipe material. The service expose parent pipe material on either side of the weldments of the respective samples was chemically analyzed. This was done with the focus being on the deoxidizing element content (Si and Al) of the respective parent pipe regions and to what extent these elements influenced the development of planar graphitization in these regions. No correlation could be identified between the level of deoxidizing elements and the levels of % planar graphitization in the parent pipe material. Tensile and Charpy impact samples were removed from the respective service exposed samples parent material on either side of the weld and from the HAZ regions on the side with the highest levels of planar graphitization. These samples were tested and the yield and ultimate tensile strength and Charpy impact toughness of the respective samples were then evaluated to establish how these static mechanical properties were influenced by the % planar graphitization. The yield and ultimate tensile strength of the service exposed material did not show a statistically significant correlation with the % planar graphitization. The Charpy impact toughness results did however show a statistically significant negative correlation towards the % planar graphitization. This was clearly evident from the results of the HAZ regions of the service exposed weldments (Samples A-C) which had the highest levels of % planar graphitization and the lowest impact toughness, while the newly welded and post weld heat treated Sample D had no planar graphitization outside the HAZ and the highest impact toughness. This research project not only investigated how planar graphitization affects the static mechanical properties of service exposed pipe material, it also investigated on a microstructural basis, how planar graphitization nucleates and grows. The microstructural investigation showed that the free carbon required for the development of planar graphitization originated from the regions outside the HAZ, which were formed when the pearlite bands were dissolved during the welding of the steam pipe. The heat input from the welding sensitized this region for the development of planar graphitization, probably due to the formation of a “carbon-rich” matrix due to the partial dissolution of the cementite precipitates. All the carbide precipitates in this region consisted of M3C. aluminium-rich precipitates were found inside newly nucleated graphite nodules, indicating its role as a possible heterogeneous nucleation site. Growth of newly formed graphite nodules showed a preference towards high-angle grain boundaries and regions with dislocations for the initial growth stages of the graphite nodules. The microstructure of the region outside the HAZ of the newly introduced seam weld on the service exposed steam pipe material (with graphitization), was also investigated using advanced electron microscopy methods and it yielded no evidence of the development of planar graphitization.
- Full Text:
- Date Issued: 2017
Efficiency evaluation of South African water service provision
- Authors: Brettenny, Warren James
- Date: 2017
- Subjects: Water-supply -- South Africa Municipal water supply -- South Africa , Municipal water supply -- South Africa -- Management Benchmarking (Management) -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/14741 , vital:27835
- Description: In recent years South Africa has experienced numerous service delivery protests. These protests are a result of the lack of delivery of basic services such as water and sanitation (amongst others). To address this, local governments have taken part in benchmarking initiatives (National Benchmarking Initiative, Municipal Benchmarking Initiative) and regulation programmes (BlueDrop,GreenDrop) in an effort to improve the quality of potable water and sanitation services. The latter of these focuses on the quality of the water services delivered and neither focus on the efficiency with which this delivery is achieved. This study uses both nonparametric (data envelopment analysis) aswell as parametric (stochastic frontier) methods to assess the efficiency of water service provision in South Africa over a six year period from 2005 to 2010. Subsequently, the method which is most suited for use in the South African context is proposed. In addition, this study demonstrates how these methods can be used to determine the effectiveness of benchmarking initiatives, namely the National Benchmarking Initiative, in improving the efficiency of water service provision. Furthermore, additional insight into the selection ofm in them out of n bootstrap procedure for efficiency evaluations is established through a simulation study. The inclusion of efficiency evaluations into South African benchmarking initiatives provides new and important insight into the standard of water service delivery. As such, the techniques used in this study illustrate how efficiency analysis can enhance benchmarking initiatives in South Africa.
- Full Text:
- Date Issued: 2017
- Authors: Brettenny, Warren James
- Date: 2017
- Subjects: Water-supply -- South Africa Municipal water supply -- South Africa , Municipal water supply -- South Africa -- Management Benchmarking (Management) -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/14741 , vital:27835
- Description: In recent years South Africa has experienced numerous service delivery protests. These protests are a result of the lack of delivery of basic services such as water and sanitation (amongst others). To address this, local governments have taken part in benchmarking initiatives (National Benchmarking Initiative, Municipal Benchmarking Initiative) and regulation programmes (BlueDrop,GreenDrop) in an effort to improve the quality of potable water and sanitation services. The latter of these focuses on the quality of the water services delivered and neither focus on the efficiency with which this delivery is achieved. This study uses both nonparametric (data envelopment analysis) aswell as parametric (stochastic frontier) methods to assess the efficiency of water service provision in South Africa over a six year period from 2005 to 2010. Subsequently, the method which is most suited for use in the South African context is proposed. In addition, this study demonstrates how these methods can be used to determine the effectiveness of benchmarking initiatives, namely the National Benchmarking Initiative, in improving the efficiency of water service provision. Furthermore, additional insight into the selection ofm in them out of n bootstrap procedure for efficiency evaluations is established through a simulation study. The inclusion of efficiency evaluations into South African benchmarking initiatives provides new and important insight into the standard of water service delivery. As such, the techniques used in this study illustrate how efficiency analysis can enhance benchmarking initiatives in South Africa.
- Full Text:
- Date Issued: 2017
Electrostatic discharge and roughness modelling in diamond turning of contact lenses
- Authors: Kopi, Fundiswa
- Date: 2017
- Subjects: Diamond turning Contact lenses
- Language: English
- Type: Thesis , Masters , MEng
- Identifier: http://hdl.handle.net/10948/18783 , vital:28723
- Description: With the increased application of ultra-high precision machining of polymers and the limited research in single point diamond turning (SPDT) of contact lens polymers, it became imperative to gather understanding on the production of contact lenses using the above-mentioned technology. A limiting factor in SPDT of polymers is wear of the diamond tool, resulting into poor surface finish due to unintended charges generated as a result of the contact/rubbing action between the cutting tool and the cut material. Central Composite Design (CCD) Face Centred experimental design was developed and applied to the SPDT of ONSI-56 and Polymethly methacrylate (PMMA) contact lens buttons. An electrostatic sensor coupled to a computer monitored the electrostatic discharge generated and a profilometer measured the surface roughness. The Response Surface Method (RSM) was utilised during the development of predictive models for both the surface roughness and the electrostatic discharge generated, to deduce the effects of cutting parameters during machining. The cutting speed and the feed rate deemed as the influential parameters on the surface roughness and electrostatic discharge, for both materials. The depth of cut induced more charge generation for PMMA. Predictive models were successfully developed and they were aimed at creating a database a guide to the SPDT of contact lens polymers.
- Full Text:
- Date Issued: 2017
- Authors: Kopi, Fundiswa
- Date: 2017
- Subjects: Diamond turning Contact lenses
- Language: English
- Type: Thesis , Masters , MEng
- Identifier: http://hdl.handle.net/10948/18783 , vital:28723
- Description: With the increased application of ultra-high precision machining of polymers and the limited research in single point diamond turning (SPDT) of contact lens polymers, it became imperative to gather understanding on the production of contact lenses using the above-mentioned technology. A limiting factor in SPDT of polymers is wear of the diamond tool, resulting into poor surface finish due to unintended charges generated as a result of the contact/rubbing action between the cutting tool and the cut material. Central Composite Design (CCD) Face Centred experimental design was developed and applied to the SPDT of ONSI-56 and Polymethly methacrylate (PMMA) contact lens buttons. An electrostatic sensor coupled to a computer monitored the electrostatic discharge generated and a profilometer measured the surface roughness. The Response Surface Method (RSM) was utilised during the development of predictive models for both the surface roughness and the electrostatic discharge generated, to deduce the effects of cutting parameters during machining. The cutting speed and the feed rate deemed as the influential parameters on the surface roughness and electrostatic discharge, for both materials. The depth of cut induced more charge generation for PMMA. Predictive models were successfully developed and they were aimed at creating a database a guide to the SPDT of contact lens polymers.
- Full Text:
- Date Issued: 2017
Elephant space use and impacts on vegetation in response to habitat expansion in succulent thicket
- Lochner, Christiaan Stefanus
- Authors: Lochner, Christiaan Stefanus
- Date: 2017
- Subjects: Grasses -- South Africa -- Addo Elephant National Park , Vegetation mapping -- South Africa -- Addo Elephant National Park Nature conservation -- South Africa -- Addo Elephant National Park Ecology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/18597 , vital:28687
- Description: Elephant alter vegetation composition and structure, and at high densities biodiversity declines. While habitat expansion is one of several tools proposed to mitigate such effects, its effectiveness remains untested. Despite previous incremental expansions of the Addo Main Camp section of the Addo Elephant National Park to reduce the impacts of elephant on vulnerable Succulent Thicket habitats, significant declines in plant species richness, density and biomass were recorded. During 2010 the addition of the Colchester section effectively doubled the area (120 km2 to 230 km2) available to elephant, presumably releasing browsing intensity in the Addo Main Camp section, hence allowing for the regeneration (through growth and resprouting) of the vulnerable canopy shrubs (a key functional guild). I aim to test this hypothesis. I use space use data from before and after expansion to track the distribution of elephant utilization across the park. Additionally, I use data collected between 2008 and 2015 on shrub composition and structure and the structure of individual canopy species, to illustrate the long-term trends in elephant impact. I firstly show that although elephants shift a proportion of their utilization distribution into novel habitat, they continue to show a strong preference for the Addo Main Camp section, with its higher water availability yet heavier utilized vegetation. I also illustrate that within 5 years of the expansion, effects on the canopy shrub community declined, presumably by spreading impacts to novel areas. Specifically, I show that vegetation composition and structure (volume and density) remained stable during this period. While these results indicate that range expansion might be a viable tool to mitigate the impact of elephant on vegetation composition and structure, at least in the short-term, the consequences for ecological functioning remain to be measured. In the long-term, I predict that attempts to use range expansion as a management tool may fail if implemented without limiting population numbers and controlling the distribution of local densities (e.g. by managing surface water availability).
- Full Text:
- Date Issued: 2017
- Authors: Lochner, Christiaan Stefanus
- Date: 2017
- Subjects: Grasses -- South Africa -- Addo Elephant National Park , Vegetation mapping -- South Africa -- Addo Elephant National Park Nature conservation -- South Africa -- Addo Elephant National Park Ecology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/18597 , vital:28687
- Description: Elephant alter vegetation composition and structure, and at high densities biodiversity declines. While habitat expansion is one of several tools proposed to mitigate such effects, its effectiveness remains untested. Despite previous incremental expansions of the Addo Main Camp section of the Addo Elephant National Park to reduce the impacts of elephant on vulnerable Succulent Thicket habitats, significant declines in plant species richness, density and biomass were recorded. During 2010 the addition of the Colchester section effectively doubled the area (120 km2 to 230 km2) available to elephant, presumably releasing browsing intensity in the Addo Main Camp section, hence allowing for the regeneration (through growth and resprouting) of the vulnerable canopy shrubs (a key functional guild). I aim to test this hypothesis. I use space use data from before and after expansion to track the distribution of elephant utilization across the park. Additionally, I use data collected between 2008 and 2015 on shrub composition and structure and the structure of individual canopy species, to illustrate the long-term trends in elephant impact. I firstly show that although elephants shift a proportion of their utilization distribution into novel habitat, they continue to show a strong preference for the Addo Main Camp section, with its higher water availability yet heavier utilized vegetation. I also illustrate that within 5 years of the expansion, effects on the canopy shrub community declined, presumably by spreading impacts to novel areas. Specifically, I show that vegetation composition and structure (volume and density) remained stable during this period. While these results indicate that range expansion might be a viable tool to mitigate the impact of elephant on vegetation composition and structure, at least in the short-term, the consequences for ecological functioning remain to be measured. In the long-term, I predict that attempts to use range expansion as a management tool may fail if implemented without limiting population numbers and controlling the distribution of local densities (e.g. by managing surface water availability).
- Full Text:
- Date Issued: 2017
Evaluating the importance of mangroves as fish nurseries in selected warm temperate South African estuaries
- Authors: Muller, Cuen
- Date: 2017
- Subjects: Mangrove ecology -- South Africa Mangrove fisheries -- South Africa , Estuarine ecology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/12080 , vital:27029
- Description: The value of mangrove habitats as fish nurseries was assessed by comparing communities of early stage and juvenile fishes between estuaries with and without mangroves. Early stage fishes were sampled using boat-based plankton towing while juveniles were sampled by seine netting. Sampling took place at five sites spaced 1 km apart starting near the estuary mouth in four estuaries along the temperate coastline of the Eastern Cape Province of South Africa. Four estuaries were selected based on shared similarities which included catchment area, estuarine area and shared habitats barring the presence of mangroves which occupied the river margins of two systems. Results revealed that early stage and juvenile fish communities (both marine- and estuary-spawned) were similar between systems with and without mangrove habitats. Differences in fish communities among estuaries were rather attributed to axial salinity gradients associated with greater freshwater input, while season and temperature produced significant variances in fish densities with Generalised Additive Models revealing responses of communities to these variables. A common estuarine-dependent fish, Rhabdosargus holubi (Family Sparidae), was further investigated to determine habitat use, residency and dietary patterns in different mangrove habitats. High habitat residency in this species was revealed during a short-term tagging study using Visible Implant Elastomer tags and long-term isotope analysis in juveniles sampled from two contrasting mangrove habitats. A wider feeding niche was observed in an eelgrass-red mangrove connected habitat when compared with more exposed white mangrove areas. Low dependence on mangrove habitats in temperate estuaries is likely due to their tidally dominated inundation and limited refuge potential due to smaller area coverage by mangroves in temperate estuaries. Relatively lower primary productivity in warm temperate mangrove areas, relative to their tropical counterparts, provides no significant feeding advantage or refuge opportunities relative to other available habitats in these estuaries. Warm temperate estuaries, which are both spatially and temporally highly variable, instead host species which are habitat generalists, able to capitalise on these highly dynamic environments.
- Full Text:
- Date Issued: 2017
- Authors: Muller, Cuen
- Date: 2017
- Subjects: Mangrove ecology -- South Africa Mangrove fisheries -- South Africa , Estuarine ecology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/12080 , vital:27029
- Description: The value of mangrove habitats as fish nurseries was assessed by comparing communities of early stage and juvenile fishes between estuaries with and without mangroves. Early stage fishes were sampled using boat-based plankton towing while juveniles were sampled by seine netting. Sampling took place at five sites spaced 1 km apart starting near the estuary mouth in four estuaries along the temperate coastline of the Eastern Cape Province of South Africa. Four estuaries were selected based on shared similarities which included catchment area, estuarine area and shared habitats barring the presence of mangroves which occupied the river margins of two systems. Results revealed that early stage and juvenile fish communities (both marine- and estuary-spawned) were similar between systems with and without mangrove habitats. Differences in fish communities among estuaries were rather attributed to axial salinity gradients associated with greater freshwater input, while season and temperature produced significant variances in fish densities with Generalised Additive Models revealing responses of communities to these variables. A common estuarine-dependent fish, Rhabdosargus holubi (Family Sparidae), was further investigated to determine habitat use, residency and dietary patterns in different mangrove habitats. High habitat residency in this species was revealed during a short-term tagging study using Visible Implant Elastomer tags and long-term isotope analysis in juveniles sampled from two contrasting mangrove habitats. A wider feeding niche was observed in an eelgrass-red mangrove connected habitat when compared with more exposed white mangrove areas. Low dependence on mangrove habitats in temperate estuaries is likely due to their tidally dominated inundation and limited refuge potential due to smaller area coverage by mangroves in temperate estuaries. Relatively lower primary productivity in warm temperate mangrove areas, relative to their tropical counterparts, provides no significant feeding advantage or refuge opportunities relative to other available habitats in these estuaries. Warm temperate estuaries, which are both spatially and temporally highly variable, instead host species which are habitat generalists, able to capitalise on these highly dynamic environments.
- Full Text:
- Date Issued: 2017
Evaluation of near infrared reflectance (NIR) spectroscopy to determine the nutrient composition of raw materials and compound ostrich feeds
- Swart, Etheresia, Lehmann-Maritz, Maryna
- Authors: Swart, Etheresia , Lehmann-Maritz, Maryna
- Date: 2017
- Subjects: Near infrared spectroscopy , Animal nutrition , Animal feeding
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/13779 , vital:27307
- Description: The chemical analysis of feed samples can be time consuming and expensive. The use of near infrared reflectance (NIR) spectroscopy was evaluated in a range of studies as a rapid technique to predict the chemical constituents in feedstuffs and compound ostrich feeds. The prediction of accurate results by NIR spectroscopy relies heavily upon obtaining a calibration set which represents the variation in the main population, accurate laboratory analyses and the application of the best mathematical procedures. This research project was designed to meet five objectives: The first objective was to determine the feasibility of using near infrared reflectance (NIR) spectroscopy to predict dry matter, ash, crude protein, crude fibre, oil content, and fatty acids such as palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1) and linoleic acid (C18:2) in sunflower seed meal. The second objective was to develop calibration models to predict the dry matter, crude protein and oil content in milled canola seed, compared to whole canola seeds. The third objective was to investigate the feasibility of using NIR spectroscopy to predict the dry matter, ash, crude protein, crude fibre and oil content in milled lupin seeds, compared to whole lupin seeds. The fourth objective was to describe the development of near infrared reflectance (NIR) spectroscopy calibration equations for the prediction of chemical composition and amino acid content from different populations of alfalfa hay (Medicago sativa L.). The last objective was to determine the potential of NIR spectroscopy to predict the dry matter, ash, crude protein, crude fibre, ether extract, acid detergent fibre (ADF), neutral detergent fibre (NDF), calcium, phosphorus, in vitro organic matter digestibility (IVOMD) and amino acids such as lysine, methionine, threonine and arginine in compound ostrich feed samples. The results of this study indicate that NIR spectroscopy calibrations in sunflower seed meal are only applicable in sunflower breeding programmes for a fast screening as it was not suitable for prediction purposes. Screening of sunflower seeds by NIR spectroscopy represents a rapid, simple and cost effective alternative that is a great utility for users who need to analyse a large number of samples. Calibrations developed for crude protein and oil content in milled canola seeds proved to be better than calibrations for whole canola seeds. Although the results indicated that calibrations were better for milled canola seeds, it indicated values that were typical of equations suitable for screening purposes to select samples for more detailed chemical analysis. According to calibration statistics obtained for crude protein, crude fibre and oil content in whole lupin seeds, there is no need to grind the seeds to scan the meal as similarly accurate results were obtained by analysing whole seeds. Screening of whole lupin seeds by NIR spectroscopy represents a rapid, simple and cost effective alternative that may be of great utility for users who need to analyse a large number of samples with no sample preparation. The calibration and validation statistics obtained in the study to test the potential of NIR spectroscopy to predict the chemical composition and amino acid contents in alfalfa hay, showed the accuracy was too low for routine analysis, although NIR spectroscopy could be used as a screening tool. Further research needs to be done to improve the accuracy of the NIR spectroscopy analysis, including more samples from different cultivars and years. In the study to examine the possibility of using NIR spectroscopy to predict the chemical composition of compound ostrich feeds, the results indicated that NIR spectroscopy is a suitable tool for a rapid and reliable prediction of the crude protein, crude fibre, ether extract, IVOMD, ADF and NDF in compound ostrich feeds. Calibrations can be improved for amino acids if a larger sample pool is used to develop the calibrations. These studies indicated that NIR spectroscopy can be a rapid and successful tool for the prediction of the nutritive value up to certain amino acid contents of feedstuffs and compound ostrich feeds.
- Full Text:
- Date Issued: 2017
- Authors: Swart, Etheresia , Lehmann-Maritz, Maryna
- Date: 2017
- Subjects: Near infrared spectroscopy , Animal nutrition , Animal feeding
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/13779 , vital:27307
- Description: The chemical analysis of feed samples can be time consuming and expensive. The use of near infrared reflectance (NIR) spectroscopy was evaluated in a range of studies as a rapid technique to predict the chemical constituents in feedstuffs and compound ostrich feeds. The prediction of accurate results by NIR spectroscopy relies heavily upon obtaining a calibration set which represents the variation in the main population, accurate laboratory analyses and the application of the best mathematical procedures. This research project was designed to meet five objectives: The first objective was to determine the feasibility of using near infrared reflectance (NIR) spectroscopy to predict dry matter, ash, crude protein, crude fibre, oil content, and fatty acids such as palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1) and linoleic acid (C18:2) in sunflower seed meal. The second objective was to develop calibration models to predict the dry matter, crude protein and oil content in milled canola seed, compared to whole canola seeds. The third objective was to investigate the feasibility of using NIR spectroscopy to predict the dry matter, ash, crude protein, crude fibre and oil content in milled lupin seeds, compared to whole lupin seeds. The fourth objective was to describe the development of near infrared reflectance (NIR) spectroscopy calibration equations for the prediction of chemical composition and amino acid content from different populations of alfalfa hay (Medicago sativa L.). The last objective was to determine the potential of NIR spectroscopy to predict the dry matter, ash, crude protein, crude fibre, ether extract, acid detergent fibre (ADF), neutral detergent fibre (NDF), calcium, phosphorus, in vitro organic matter digestibility (IVOMD) and amino acids such as lysine, methionine, threonine and arginine in compound ostrich feed samples. The results of this study indicate that NIR spectroscopy calibrations in sunflower seed meal are only applicable in sunflower breeding programmes for a fast screening as it was not suitable for prediction purposes. Screening of sunflower seeds by NIR spectroscopy represents a rapid, simple and cost effective alternative that is a great utility for users who need to analyse a large number of samples. Calibrations developed for crude protein and oil content in milled canola seeds proved to be better than calibrations for whole canola seeds. Although the results indicated that calibrations were better for milled canola seeds, it indicated values that were typical of equations suitable for screening purposes to select samples for more detailed chemical analysis. According to calibration statistics obtained for crude protein, crude fibre and oil content in whole lupin seeds, there is no need to grind the seeds to scan the meal as similarly accurate results were obtained by analysing whole seeds. Screening of whole lupin seeds by NIR spectroscopy represents a rapid, simple and cost effective alternative that may be of great utility for users who need to analyse a large number of samples with no sample preparation. The calibration and validation statistics obtained in the study to test the potential of NIR spectroscopy to predict the chemical composition and amino acid contents in alfalfa hay, showed the accuracy was too low for routine analysis, although NIR spectroscopy could be used as a screening tool. Further research needs to be done to improve the accuracy of the NIR spectroscopy analysis, including more samples from different cultivars and years. In the study to examine the possibility of using NIR spectroscopy to predict the chemical composition of compound ostrich feeds, the results indicated that NIR spectroscopy is a suitable tool for a rapid and reliable prediction of the crude protein, crude fibre, ether extract, IVOMD, ADF and NDF in compound ostrich feeds. Calibrations can be improved for amino acids if a larger sample pool is used to develop the calibrations. These studies indicated that NIR spectroscopy can be a rapid and successful tool for the prediction of the nutritive value up to certain amino acid contents of feedstuffs and compound ostrich feeds.
- Full Text:
- Date Issued: 2017
Exploring acyl azides chemistry in continuous flow systems
- Authors: Sagandira, Cloudius Ray
- Date: 2017
- Subjects: Organic compounds -- Synthesis Flow chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/12065 , vital:27028
- Description: Organic azides are important in the synthesis of many target molecules of great use in fine chemical and pharmaceutical production. The use of this class of compounds is however limited due to their hazardous nature and many safety concerns, as they are highly exothermic. Micro reactors can handle exotherms extremely well, due to the inherent high surface area to volume ratio, unlike the conventional batch process. This dissertation therefore aims to investigate the safe application of micro reactors in acyl azide chemistry.With this in mind, Chapter 1 provides a comprehensive background on organic azides, reaction calorimetric studies, flow chemistry technology (micro reactors) and their theoretical advantages. This chapter also discusses the preparation of organic azides in continuous flow systems and scaling up in continuous flow systems. Chapter 2 illustrates and discusses multivariate optimisation of benzoyl azide synthesis as a model reaction, synthesis of other acyl azides using the model reaction optimised conditions and multistep synthesis of carbamates, amides and amines in continuous flow systems via the Curtius rearrangement of benzoyl azide formed in situ from benzoyl chloride and sodium azide. The chapter also discusses process hazards analysis and evaluation of benzoyl azide synthesis and decomposition using calorimetric studies. It also investigates and discusses the effects of different mixing regimes and channel sizes on scale up. Chapter 3 has comprehensive experimental details for the whole dissertation with Chapter 4 providing the concluding remarks and future work recommendations.
- Full Text:
- Date Issued: 2017
- Authors: Sagandira, Cloudius Ray
- Date: 2017
- Subjects: Organic compounds -- Synthesis Flow chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/12065 , vital:27028
- Description: Organic azides are important in the synthesis of many target molecules of great use in fine chemical and pharmaceutical production. The use of this class of compounds is however limited due to their hazardous nature and many safety concerns, as they are highly exothermic. Micro reactors can handle exotherms extremely well, due to the inherent high surface area to volume ratio, unlike the conventional batch process. This dissertation therefore aims to investigate the safe application of micro reactors in acyl azide chemistry.With this in mind, Chapter 1 provides a comprehensive background on organic azides, reaction calorimetric studies, flow chemistry technology (micro reactors) and their theoretical advantages. This chapter also discusses the preparation of organic azides in continuous flow systems and scaling up in continuous flow systems. Chapter 2 illustrates and discusses multivariate optimisation of benzoyl azide synthesis as a model reaction, synthesis of other acyl azides using the model reaction optimised conditions and multistep synthesis of carbamates, amides and amines in continuous flow systems via the Curtius rearrangement of benzoyl azide formed in situ from benzoyl chloride and sodium azide. The chapter also discusses process hazards analysis and evaluation of benzoyl azide synthesis and decomposition using calorimetric studies. It also investigates and discusses the effects of different mixing regimes and channel sizes on scale up. Chapter 3 has comprehensive experimental details for the whole dissertation with Chapter 4 providing the concluding remarks and future work recommendations.
- Full Text:
- Date Issued: 2017
Exploring feeding ecology and population growth rate responses of ungulates in Southern African arid biomes
- Authors: Vermeulen, Mika Margaret
- Date: 2017
- Subjects: Ungulates -- South Africa Arid regions -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/15237 , vital:28189
- Description: Limited resources, extreme temperatures and predators are some of the stresses that are faced by ungulates in arid biomes. Understanding how these stressors influence ungulate feeding ecology and population growth rates is important for managers, as these could influence the persistence of ungulates in protected areas. An understanding of these stressors is especially relevant given the significant population declines in ungulate species globally. The Nama Karoo biome and the arid Savanna, an arid form of the Savanna biome, are both arid, but have distinct rainfall seasonality and vegetation structure and represent unique characteristics that need to be properly considered in their own regard. The literature on African ungulate feeding ecology covers a range of species and biomes from southern and east Africa, however, very little is known about ungulate dietary preferences in the Nama Karoo. Unexplained population declines in springbok (Antidorcas marsupialis) and red hartebeest (Alcelaphus buselaphus caama) have occurred at local scales across the Nama Karoo and the arid Savanna, most notably springbok population declines at the Karoo National Park (Karoo NP). This study sought to improve the understanding of ungulate feeding ecology and population growth rate responses in two arid biomes of South Africa. To achieve this, ungulate dietary composition was characterised, in terms of the proportional seasonal contribution of C4 and C3 plant forms, of a range of ungulates in the Nama Karoo, at the Karoo NP and the arid Savanna, at the Tswalu Kalahari Reserve (Tswalu KR), using stable carbon isotope analysis. Fresh faecal samples of ungulate species were collected from both the biomes during the dry, early wet and late wet seasons. Species were categorised per biome into feeding guilds and the effects of season, biome and the interaction thereof on the diets of the ungulate species explored. Furthermore, the findings were interpreted against what is known about diets of the respective species elsewhere in southern and east Africa. Secondly, trends in ungulate population growth rates were assessed within the Karoo NP and the Tswalu KR over the past 12 and14 years respectively. Furthermore, the variables influencing ungulate population growth rates (and generality of trends), with emphasis on ungulate biomass and rainfall, were explored at biome and species level. Population size data were obtained from annual aerial censuses for the period 2002-2015 and used to calculate annual growth rates and biomass for each ungulate species. The contribution of C4 forage to the diets of ungulate species in the arid Savanna was generally higher than in the Nama Karoo,in line with greater relative abundance of C4 grasses in the former. During winter (dry season) C3 intake was higher in the Nama Karoo than in the arid Savanna, reflecting C3 plant growth (C3 grasses and shrubs) and rainfall during winter in the Nama Karoo. Mean population growth rates during the study period were negative in some of the threatened species considered, i.e. mountain reedbuck (Redunca fulvorufula fulvorufula), tsessebe (Damaliscus lunatus lunatus) and Hartmann’s mountain zebra (Equus zebra hartmannae). No evidence for negative density dependent regulation (~intra-/interspecific competition) of ungulate population growth rates was found, whereas bottom up (~rainfall) and positive density dependent (~biomass of the species under investigation) regulatory mechanisms were most influential. The rainfall and biomass variables influenced the population growth rates of smaller ungulate species more than those of larger bodied ungulate species. Knowledge of ungulate diets will enable managers of protected areas to better understand how climate change, and resultant changes in relative abundances of plant growth forms, will influence specific ungulate species. The finding that increased population biomass positively influenced certain ungulate species’ growth rates has potential implications for management intervention as ungulate biomass is a variable that can be manipulated in protected areas. The reinforcement of existing mountain reedbuck, springbok and red hartebeest populations, specifically, at the Karoo NP and the Tswalu KR may counter their current negative growth rates in these two protected areas. Finally, the influence of protected area size and fencing, on ungulate vulnerability to predators (~top down) and forage quality (~bottom up) mechanisms in arid biomes needs to be further explored.
- Full Text:
- Date Issued: 2017
- Authors: Vermeulen, Mika Margaret
- Date: 2017
- Subjects: Ungulates -- South Africa Arid regions -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/15237 , vital:28189
- Description: Limited resources, extreme temperatures and predators are some of the stresses that are faced by ungulates in arid biomes. Understanding how these stressors influence ungulate feeding ecology and population growth rates is important for managers, as these could influence the persistence of ungulates in protected areas. An understanding of these stressors is especially relevant given the significant population declines in ungulate species globally. The Nama Karoo biome and the arid Savanna, an arid form of the Savanna biome, are both arid, but have distinct rainfall seasonality and vegetation structure and represent unique characteristics that need to be properly considered in their own regard. The literature on African ungulate feeding ecology covers a range of species and biomes from southern and east Africa, however, very little is known about ungulate dietary preferences in the Nama Karoo. Unexplained population declines in springbok (Antidorcas marsupialis) and red hartebeest (Alcelaphus buselaphus caama) have occurred at local scales across the Nama Karoo and the arid Savanna, most notably springbok population declines at the Karoo National Park (Karoo NP). This study sought to improve the understanding of ungulate feeding ecology and population growth rate responses in two arid biomes of South Africa. To achieve this, ungulate dietary composition was characterised, in terms of the proportional seasonal contribution of C4 and C3 plant forms, of a range of ungulates in the Nama Karoo, at the Karoo NP and the arid Savanna, at the Tswalu Kalahari Reserve (Tswalu KR), using stable carbon isotope analysis. Fresh faecal samples of ungulate species were collected from both the biomes during the dry, early wet and late wet seasons. Species were categorised per biome into feeding guilds and the effects of season, biome and the interaction thereof on the diets of the ungulate species explored. Furthermore, the findings were interpreted against what is known about diets of the respective species elsewhere in southern and east Africa. Secondly, trends in ungulate population growth rates were assessed within the Karoo NP and the Tswalu KR over the past 12 and14 years respectively. Furthermore, the variables influencing ungulate population growth rates (and generality of trends), with emphasis on ungulate biomass and rainfall, were explored at biome and species level. Population size data were obtained from annual aerial censuses for the period 2002-2015 and used to calculate annual growth rates and biomass for each ungulate species. The contribution of C4 forage to the diets of ungulate species in the arid Savanna was generally higher than in the Nama Karoo,in line with greater relative abundance of C4 grasses in the former. During winter (dry season) C3 intake was higher in the Nama Karoo than in the arid Savanna, reflecting C3 plant growth (C3 grasses and shrubs) and rainfall during winter in the Nama Karoo. Mean population growth rates during the study period were negative in some of the threatened species considered, i.e. mountain reedbuck (Redunca fulvorufula fulvorufula), tsessebe (Damaliscus lunatus lunatus) and Hartmann’s mountain zebra (Equus zebra hartmannae). No evidence for negative density dependent regulation (~intra-/interspecific competition) of ungulate population growth rates was found, whereas bottom up (~rainfall) and positive density dependent (~biomass of the species under investigation) regulatory mechanisms were most influential. The rainfall and biomass variables influenced the population growth rates of smaller ungulate species more than those of larger bodied ungulate species. Knowledge of ungulate diets will enable managers of protected areas to better understand how climate change, and resultant changes in relative abundances of plant growth forms, will influence specific ungulate species. The finding that increased population biomass positively influenced certain ungulate species’ growth rates has potential implications for management intervention as ungulate biomass is a variable that can be manipulated in protected areas. The reinforcement of existing mountain reedbuck, springbok and red hartebeest populations, specifically, at the Karoo NP and the Tswalu KR may counter their current negative growth rates in these two protected areas. Finally, the influence of protected area size and fencing, on ungulate vulnerability to predators (~top down) and forage quality (~bottom up) mechanisms in arid biomes needs to be further explored.
- Full Text:
- Date Issued: 2017
Farmers’ perception on factors influencing small-scale vegetable production at Tsengiwe village, South Africa
- Authors: Gqibityala, Akhona
- Date: 2017
- Subjects: Farmers -- South Africa -- Eastern Cape Farms, Small -- South Africa -- Eastern Cape , Vegetable gardening -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/15281 , vital:28210
- Description: Food security and self-sufficiency in the rural areas has been and remains a major concern for the South African government. The study aimed to investigate farmer’s perception of factors influencing small-scale vegetable production in Tsengiwe village in the Eastern Cape. The research focus was on the following aspects that may have an influence on small-scale vegetable production: socio-economic factors, production and resource deficiencies and the impact of indigenous leafy vegetables. The researcher conducted several demonstration workshops during the field work. The pilot studies and community engagements were essential to extract knowledge systems embedded in the cultural traditions of indigenous or local communities. The action research was part of the reflective process of broadminded problem solving led by researcher and community. The research approach used a triangulation research method to extract information, whereby both quantitative and qualitative research was used to ensure greater accuracy. The main data collection was obtained from interviews with small-scale farming households in the Tsengiwe area. The study revealed that households were dependent on elderly female pensioners to source food and water. These women received most of their income from social grants and were mainly responsible for all farming activities in the households. Most households attempted to produce vegetables, although food security and self-sufficiency through own production was rarely achieved.Other perceived farming challenges included: lack of market accessibility, irrigation infrastructure, drought, financial limitations and soil degradation. Indigenous leafy vegetables were found to play a nutritional role in times of food shortage and not as much for their medicinal value. The study recommended the following interventions: Support for the elderly women in development and production practices, interventions to address factors affecting vegetable production, improving soil structure, working towards food self-sufficiency, moving away from dependence on mechanisation in rural farming.
- Full Text:
- Date Issued: 2017
- Authors: Gqibityala, Akhona
- Date: 2017
- Subjects: Farmers -- South Africa -- Eastern Cape Farms, Small -- South Africa -- Eastern Cape , Vegetable gardening -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/15281 , vital:28210
- Description: Food security and self-sufficiency in the rural areas has been and remains a major concern for the South African government. The study aimed to investigate farmer’s perception of factors influencing small-scale vegetable production in Tsengiwe village in the Eastern Cape. The research focus was on the following aspects that may have an influence on small-scale vegetable production: socio-economic factors, production and resource deficiencies and the impact of indigenous leafy vegetables. The researcher conducted several demonstration workshops during the field work. The pilot studies and community engagements were essential to extract knowledge systems embedded in the cultural traditions of indigenous or local communities. The action research was part of the reflective process of broadminded problem solving led by researcher and community. The research approach used a triangulation research method to extract information, whereby both quantitative and qualitative research was used to ensure greater accuracy. The main data collection was obtained from interviews with small-scale farming households in the Tsengiwe area. The study revealed that households were dependent on elderly female pensioners to source food and water. These women received most of their income from social grants and were mainly responsible for all farming activities in the households. Most households attempted to produce vegetables, although food security and self-sufficiency through own production was rarely achieved.Other perceived farming challenges included: lack of market accessibility, irrigation infrastructure, drought, financial limitations and soil degradation. Indigenous leafy vegetables were found to play a nutritional role in times of food shortage and not as much for their medicinal value. The study recommended the following interventions: Support for the elderly women in development and production practices, interventions to address factors affecting vegetable production, improving soil structure, working towards food self-sufficiency, moving away from dependence on mechanisation in rural farming.
- Full Text:
- Date Issued: 2017