Applications of complex functions on problems in Banach algebras
- Authors: Snyman, Jandré Dillon
- Date: 2019
- Subjects: Banach algebras , Functions of several complex variables
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/48643 , vital:41055
- Description: In this dissertation, we provide applications of complex function theory to problems in Banach algebras. We discuss the structure of analytic functions f : D → A, where D is a domain of C and A is a Banach algebra as given by Aupetit in [3]: either the set {λ ∈ D : Sp(f(λ)) is finite} is of capacity zero, or there exists an integer n such that Sp(f(λ)) has exactly n elements, for every λ, except on a closed, discrete set of capacity zero, where the spectrum has at most n−1 elements. This deep result, which describes the structure of Sp(f(λ)) for all λ ∈ D, relies heavily on subharmonic techniques, which are also included in the dissertation. Let A and B be Banach algebras. A linear mapping φ : A → B is called a Jordan homomorphism if and only if φ(xy + yx) = φ(x)φ(y) + φ(y)φ(x) for every x, y ∈ A. This is equivalent to saying that φ(x 2 ) = φ(x) 2 for every x ∈ A. The following problem, due to I. Kaplansky, is still unsolved for the general Banach algebra case: Let A and B be unital Banach algebras and φ : A → B a unital, invertibility preserving linear mapping. Under what conditions of A and B is φ a Jordan homomorphism? The author’s honours project [24] served as an exposition of the GleasonKahane-Żelazko Theorem [7, Theorem 4], which provides an answer to Kaplansky’s problem in the case where B = C. In this dissertation we look at other special cases of Kaplansky’s problem, such as the case where A and B are von Neumann algberas, as solved by Aupetit [4, Theorem 1.3] and remark that his result holds for the more general case where A is any C ∗ -algebra that has the property that every self-adjoint element is the limit of a sequence of linear combinations of orthogonal idempotents in A, and B is a semi-simple Banach algebra. This result relies heavily on complex function theory, spectral theory and holomorphic functional calculus. We also provide detailed expositions of the work of Taylor [27] in which an operator calculus on undounded, closed linear operators is developed, and the work of Allan [1] in which a holomorphic functional calculus is defined for locally convex algebras.
- Full Text:
- Date Issued: 2019
- Authors: Snyman, Jandré Dillon
- Date: 2019
- Subjects: Banach algebras , Functions of several complex variables
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/48643 , vital:41055
- Description: In this dissertation, we provide applications of complex function theory to problems in Banach algebras. We discuss the structure of analytic functions f : D → A, where D is a domain of C and A is a Banach algebra as given by Aupetit in [3]: either the set {λ ∈ D : Sp(f(λ)) is finite} is of capacity zero, or there exists an integer n such that Sp(f(λ)) has exactly n elements, for every λ, except on a closed, discrete set of capacity zero, where the spectrum has at most n−1 elements. This deep result, which describes the structure of Sp(f(λ)) for all λ ∈ D, relies heavily on subharmonic techniques, which are also included in the dissertation. Let A and B be Banach algebras. A linear mapping φ : A → B is called a Jordan homomorphism if and only if φ(xy + yx) = φ(x)φ(y) + φ(y)φ(x) for every x, y ∈ A. This is equivalent to saying that φ(x 2 ) = φ(x) 2 for every x ∈ A. The following problem, due to I. Kaplansky, is still unsolved for the general Banach algebra case: Let A and B be unital Banach algebras and φ : A → B a unital, invertibility preserving linear mapping. Under what conditions of A and B is φ a Jordan homomorphism? The author’s honours project [24] served as an exposition of the GleasonKahane-Żelazko Theorem [7, Theorem 4], which provides an answer to Kaplansky’s problem in the case where B = C. In this dissertation we look at other special cases of Kaplansky’s problem, such as the case where A and B are von Neumann algberas, as solved by Aupetit [4, Theorem 1.3] and remark that his result holds for the more general case where A is any C ∗ -algebra that has the property that every self-adjoint element is the limit of a sequence of linear combinations of orthogonal idempotents in A, and B is a semi-simple Banach algebra. This result relies heavily on complex function theory, spectral theory and holomorphic functional calculus. We also provide detailed expositions of the work of Taylor [27] in which an operator calculus on undounded, closed linear operators is developed, and the work of Allan [1] in which a holomorphic functional calculus is defined for locally convex algebras.
- Full Text:
- Date Issued: 2019
Assessing flood vulnerability in the Nelson Mandela Bay Metro
- Authors: Zuze, Hillary
- Date: 2019
- Subjects: Floods -- South Africa -- Nelson Mandela Bay Municipality , Natural disasters Hazardous geographic environments Hazardous geographic environments -- Risk assessment , Climatic changes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/44224 , vital:37135
- Description: Floods are the most frequent amongst all global natural disasters at present, causing problems such as bridge collapses, fatalities, building damages and traffic delays. Between 1995 and 2015, there were approximately 3062 global flood disasters which accounted for 56% of all declared natural disasters and these affected 2.3 billion people (almost a third of the world’s population at the time) (EMDAT, 2015). The cost of damages for this period incurred for buildings and other infrastructure was at an all-time high of R23.69 (US$1.891) trillion. It is postulated through various studies that the number of urban flood events reported is increasing significantly in comparison to the previous decades (Armah et al., 2010; Lóczy, 2013; Leaning and Guha-Sapir, 2013; EMDAT, 2015; Tanoue et al., 2016; Rogger et al., 2017). Some research has also noted an increase in the number of floods per year, which has ascended to an average of 171 in this decade, from an annual average of 127 in the previous one (Dozier, 2013; Guha Sapir et al., 2016). Sources such as the Centre of Research and Epidemiological Disasters (Guha Sapir et al., 2016) recorded that from 1995 to 2015, globally, millions of homes were vulnerable to weather-related disasters, along with 130,000 health and education facilities. During this period, urban floods accounted for 98% of houses damaged and 99.9% of education and health facilities demolished by a weather-related disaster (Davies, 2017). Flooding is particularly harmful in terms of fatalities in developing countries due to inadequate flood protection and mitigation measures (Di Baldassarre et al., 2010; Dozier, 2013). Some studies attribute the high fatalities in developing countries to the inadequate disaster management strategies implemented to counter the impacts of urban flooding (Egbinola et al., 2015; Pazzi et al., 2016; Mavhura et al., 2017). Other authors have attributed the high fatalities to the sheer number of people residing in areas prone to flooding, which has been the knock-on effect of rapidly expanding cities, overwhelmed government agencies, and a pre-existing political and social system that promotes marginalisation (Collins, 2008; Aboagye, 2012). The occupation of flood-prone areas by settlements, which is a common feature in developing countries, is the major contributor to the fatalities as it involves a degree of risk. Risk is exposure to an undesired event, in this case flooding, and contributes directly to differing levels of vulnerability (Samuels, 2018). Communities have differing perceptions of flood vulnerability because of a combination of factors. These include the magnitude of the flood experienced, the number of people or the value of assets potentially affected by flooding due to location, and the lack of socioeconomic capacity to do anything to alter their vulnerability to a disaster (Hall et al., 2005; Adger, 2006; Birkmann et al., 2013; Rogger et al., 2017). Some communities acknowledge that there are people residing in flood prone areas and take measures to reduce or eliminate the risk through social, political and economic networks. In other cases, communities are able to identify their exposure to flooding but do not have the capacity to reduce the effects (Bouchard et al., 2007; Agbaoye, 2012; Musungu et al., 2012; Siyongwana, Heijne, and Tele et al., 20155).
- Full Text:
- Date Issued: 2019
- Authors: Zuze, Hillary
- Date: 2019
- Subjects: Floods -- South Africa -- Nelson Mandela Bay Municipality , Natural disasters Hazardous geographic environments Hazardous geographic environments -- Risk assessment , Climatic changes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/44224 , vital:37135
- Description: Floods are the most frequent amongst all global natural disasters at present, causing problems such as bridge collapses, fatalities, building damages and traffic delays. Between 1995 and 2015, there were approximately 3062 global flood disasters which accounted for 56% of all declared natural disasters and these affected 2.3 billion people (almost a third of the world’s population at the time) (EMDAT, 2015). The cost of damages for this period incurred for buildings and other infrastructure was at an all-time high of R23.69 (US$1.891) trillion. It is postulated through various studies that the number of urban flood events reported is increasing significantly in comparison to the previous decades (Armah et al., 2010; Lóczy, 2013; Leaning and Guha-Sapir, 2013; EMDAT, 2015; Tanoue et al., 2016; Rogger et al., 2017). Some research has also noted an increase in the number of floods per year, which has ascended to an average of 171 in this decade, from an annual average of 127 in the previous one (Dozier, 2013; Guha Sapir et al., 2016). Sources such as the Centre of Research and Epidemiological Disasters (Guha Sapir et al., 2016) recorded that from 1995 to 2015, globally, millions of homes were vulnerable to weather-related disasters, along with 130,000 health and education facilities. During this period, urban floods accounted for 98% of houses damaged and 99.9% of education and health facilities demolished by a weather-related disaster (Davies, 2017). Flooding is particularly harmful in terms of fatalities in developing countries due to inadequate flood protection and mitigation measures (Di Baldassarre et al., 2010; Dozier, 2013). Some studies attribute the high fatalities in developing countries to the inadequate disaster management strategies implemented to counter the impacts of urban flooding (Egbinola et al., 2015; Pazzi et al., 2016; Mavhura et al., 2017). Other authors have attributed the high fatalities to the sheer number of people residing in areas prone to flooding, which has been the knock-on effect of rapidly expanding cities, overwhelmed government agencies, and a pre-existing political and social system that promotes marginalisation (Collins, 2008; Aboagye, 2012). The occupation of flood-prone areas by settlements, which is a common feature in developing countries, is the major contributor to the fatalities as it involves a degree of risk. Risk is exposure to an undesired event, in this case flooding, and contributes directly to differing levels of vulnerability (Samuels, 2018). Communities have differing perceptions of flood vulnerability because of a combination of factors. These include the magnitude of the flood experienced, the number of people or the value of assets potentially affected by flooding due to location, and the lack of socioeconomic capacity to do anything to alter their vulnerability to a disaster (Hall et al., 2005; Adger, 2006; Birkmann et al., 2013; Rogger et al., 2017). Some communities acknowledge that there are people residing in flood prone areas and take measures to reduce or eliminate the risk through social, political and economic networks. In other cases, communities are able to identify their exposure to flooding but do not have the capacity to reduce the effects (Bouchard et al., 2007; Agbaoye, 2012; Musungu et al., 2012; Siyongwana, Heijne, and Tele et al., 20155).
- Full Text:
- Date Issued: 2019
Assessing in-vivo clearance of colorectal cancer-targeting peptide-functionalized gold nanoparticles
- Authors: Xakaza, Hlumisa Belinda
- Date: 2019
- Subjects: Nanoparticles , Gold Nanotechnology -- Health aspects
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/44323 , vital:37153
- Description: Colorectal cancer (CRC) is a major public health problem. Gold nanoparticles (AuNPs) have been proved as a possible diagnostic tool to target CRC by peptides conjugated to gold nanoparticles (p-AuNP). According to previous reports, AuNPs accumulate in internal organs and have raised serious concerns on toxicity and safety. Understanding their fate in the body and the physiology underlying their clearance is crucial for toxicological evaluation and clinical translations. Six groups of rats were intravenously injected with a single dose of 100μg/kg body weight of citrate-capped (c.c-AuNPs), PEG-coated (PEG-AuNPs), and peptide functionalized gold nanoparticles (p.L-AuNPs, p.C-AuNPs, and p.14-AuNPs), to assess their physiologic clearance over a short-term (over sequential time-points: day 1, 3, 5, 7 and 14) and long-term period (three months). The inductively coupled optical-electron spectrometry (ICP-OES) showed accumulated c.c-AuNPs in the liver tissue. Moreover, a rapid and decreasing pattern of concentration of AuNPs was observed in urine and feces, with total excretion at day 7. Elevated levels of urine urea nitrogen (UUN) and urine creatinine (UCREA) reported an impaired kidney function for the c.c-AuNP group, while H&E staining indicated chronic progressive nephropathy (CPN) in all groups, 3 months post-injection, which is in all probability related to aging. Signs of inflammation were observed in rats treated with c.c-AuNPs, 2 weeks post-injection. The overall findings showed that the clearance of c.c-AuNPs’ clearance is compromised, which can have side-effects, while the excretion profiles of the p-AuNPs were consistent with the reducing long-term retention in the excretory organs. The p-AuNPs were found to be non-toxic and therefore show promise for CRC diagnostics and therapeutic purposes.
- Full Text:
- Date Issued: 2019
Assessing in-vivo clearance of colorectal cancer-targeting peptide-functionalized gold nanoparticles
- Authors: Xakaza, Hlumisa Belinda
- Date: 2019
- Subjects: Nanoparticles , Gold Nanotechnology -- Health aspects
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/44323 , vital:37153
- Description: Colorectal cancer (CRC) is a major public health problem. Gold nanoparticles (AuNPs) have been proved as a possible diagnostic tool to target CRC by peptides conjugated to gold nanoparticles (p-AuNP). According to previous reports, AuNPs accumulate in internal organs and have raised serious concerns on toxicity and safety. Understanding their fate in the body and the physiology underlying their clearance is crucial for toxicological evaluation and clinical translations. Six groups of rats were intravenously injected with a single dose of 100μg/kg body weight of citrate-capped (c.c-AuNPs), PEG-coated (PEG-AuNPs), and peptide functionalized gold nanoparticles (p.L-AuNPs, p.C-AuNPs, and p.14-AuNPs), to assess their physiologic clearance over a short-term (over sequential time-points: day 1, 3, 5, 7 and 14) and long-term period (three months). The inductively coupled optical-electron spectrometry (ICP-OES) showed accumulated c.c-AuNPs in the liver tissue. Moreover, a rapid and decreasing pattern of concentration of AuNPs was observed in urine and feces, with total excretion at day 7. Elevated levels of urine urea nitrogen (UUN) and urine creatinine (UCREA) reported an impaired kidney function for the c.c-AuNP group, while H&E staining indicated chronic progressive nephropathy (CPN) in all groups, 3 months post-injection, which is in all probability related to aging. Signs of inflammation were observed in rats treated with c.c-AuNPs, 2 weeks post-injection. The overall findings showed that the clearance of c.c-AuNPs’ clearance is compromised, which can have side-effects, while the excretion profiles of the p-AuNPs were consistent with the reducing long-term retention in the excretory organs. The p-AuNPs were found to be non-toxic and therefore show promise for CRC diagnostics and therapeutic purposes.
- Full Text:
- Date Issued: 2019
Block copolymer templates for metal oxide nanostructures
- Authors: Talla, Assane
- Date: 2019
- Subjects: Nanotechnology , Nanostructured materials Metal oxide semiconductors
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/43889 , vital:37075
- Description: Recent advances in technology have increased the need for fabrication of devices with feature sizes of tens of nanometers, such as ultra-fine filters or membranes, and high density data storage media, to name a few. For this reason, research is now focused on block copolymer nanolithographic processes, particularly the fabrication of nanoscale templates with domains well below 100 nm. Block copolymers have the tendency to self-organise into various structures, such as lamellae, spheres or cylinders on a nanometer scale. Among these possible configurations, the perpendicular cylindrical structure is most desirable, because it can be used for templates or masks for feature development, in particular, oriented wires or rods. In this work, the aim is to create a nano-mask from a di-block copolymer thin film, for zinc oxide nanorods growth. For this purpose poly (styrene-block-methylmethacrylate) (PS-b-PMMA) was investigated as a potential nano-mask. Samples were characterized using X-ray reflectometry to determine the thicknesses of the PS-b-PMMA thin films, while scanning probe microscopy and scanning electron microscopy was used to investigate the surface morphology of the samples. PS-b-PMMA thin films were produced on a random copolymer (poly (styrene-random-methylmethacrylate) (PS-r-PMMA) coated onto a silicon substrate. The PS-r-PMMA permits a non-preferential interaction between the di-block constituents and the substrate. Thermal annealing in vacuum of PS-b-PMMA on PS-r-PMMA led to perpendicular cylinders of PMMA within a PS matrix in the di-block. The typical thicknesses measured for the di-block copolymer films ranged between 33 nm and 37 nm. During this study, a perpendicular orientation of the di-block components was also produced when PS-b-PMMA was spun onto a layer of zinc oxide nanoparticles and thermally annealed in vacuum. It was shown that the ZnO nanoparticles created a corrugated surface on silicon which induced perpendicular cylinders of PMMA within the PS matrix. This was possible for a specific surface roughness parameter and film thickness. In this case, the typical thickness determined for the di-block copolymer ranged between 33 and 35 nm and the surface roughness parameter was 0.07. For the fabrication of a di-block template or PS nano-mask, the vertically oriented PMMA cylindrical nanodomains in the PS matrix were removed by exposing the film to ultraviolet radiation at an adequate dose, followed successively by washing in acetic acid and de-ionized water. It was shown that ultraviolet exposure is necessary to ensure the degradation of PMMA. A subsequent rinse in glacial acetic acid and DI water of the film exposed to ultraviolet, left an array of ordered nanoscopic pores with sizes ranging between 10 nm and 20 nm. Finally, the growth of ZnO nanorods on the di-block template produced on zinc oxide nanoparticles, was attempted using an aqueous solution based-method, namely chemical bath deposition. The rods did not grow inside the nanopores, probably due to poor capillary action. In additional experiments, the di-block template was removed by toluene (a selective solvent for PS) followed by the growth of ZnO rods on the exposed nanoparticle surface. Vertical and well separated ZnO rods formed on this surface, in places where the underlying seed layer had been attacked by the acetic acid treatment during removal of the PMMA. The observed ZnO rod morphology can be used in applications such as solar cell.
- Full Text:
- Date Issued: 2019
- Authors: Talla, Assane
- Date: 2019
- Subjects: Nanotechnology , Nanostructured materials Metal oxide semiconductors
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/43889 , vital:37075
- Description: Recent advances in technology have increased the need for fabrication of devices with feature sizes of tens of nanometers, such as ultra-fine filters or membranes, and high density data storage media, to name a few. For this reason, research is now focused on block copolymer nanolithographic processes, particularly the fabrication of nanoscale templates with domains well below 100 nm. Block copolymers have the tendency to self-organise into various structures, such as lamellae, spheres or cylinders on a nanometer scale. Among these possible configurations, the perpendicular cylindrical structure is most desirable, because it can be used for templates or masks for feature development, in particular, oriented wires or rods. In this work, the aim is to create a nano-mask from a di-block copolymer thin film, for zinc oxide nanorods growth. For this purpose poly (styrene-block-methylmethacrylate) (PS-b-PMMA) was investigated as a potential nano-mask. Samples were characterized using X-ray reflectometry to determine the thicknesses of the PS-b-PMMA thin films, while scanning probe microscopy and scanning electron microscopy was used to investigate the surface morphology of the samples. PS-b-PMMA thin films were produced on a random copolymer (poly (styrene-random-methylmethacrylate) (PS-r-PMMA) coated onto a silicon substrate. The PS-r-PMMA permits a non-preferential interaction between the di-block constituents and the substrate. Thermal annealing in vacuum of PS-b-PMMA on PS-r-PMMA led to perpendicular cylinders of PMMA within a PS matrix in the di-block. The typical thicknesses measured for the di-block copolymer films ranged between 33 nm and 37 nm. During this study, a perpendicular orientation of the di-block components was also produced when PS-b-PMMA was spun onto a layer of zinc oxide nanoparticles and thermally annealed in vacuum. It was shown that the ZnO nanoparticles created a corrugated surface on silicon which induced perpendicular cylinders of PMMA within the PS matrix. This was possible for a specific surface roughness parameter and film thickness. In this case, the typical thickness determined for the di-block copolymer ranged between 33 and 35 nm and the surface roughness parameter was 0.07. For the fabrication of a di-block template or PS nano-mask, the vertically oriented PMMA cylindrical nanodomains in the PS matrix were removed by exposing the film to ultraviolet radiation at an adequate dose, followed successively by washing in acetic acid and de-ionized water. It was shown that ultraviolet exposure is necessary to ensure the degradation of PMMA. A subsequent rinse in glacial acetic acid and DI water of the film exposed to ultraviolet, left an array of ordered nanoscopic pores with sizes ranging between 10 nm and 20 nm. Finally, the growth of ZnO nanorods on the di-block template produced on zinc oxide nanoparticles, was attempted using an aqueous solution based-method, namely chemical bath deposition. The rods did not grow inside the nanopores, probably due to poor capillary action. In additional experiments, the di-block template was removed by toluene (a selective solvent for PS) followed by the growth of ZnO rods on the exposed nanoparticle surface. Vertical and well separated ZnO rods formed on this surface, in places where the underlying seed layer had been attacked by the acetic acid treatment during removal of the PMMA. The observed ZnO rod morphology can be used in applications such as solar cell.
- Full Text:
- Date Issued: 2019
Bootstrap-based tolerance intervals for photovoltaic energy yield assessments
- Authors: Deyzel, Jani Igna
- Date: 2019
- Subjects: Bootstrap (Statistics) , Mathematical statistics Photovoltaic power systems
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/39469 , vital:35256
- Description: The assessment of the energy yield of a photovoltaic (PV) system is one of the key assessments required by investors and developers. Currently, available methods used for this assessment only provide a point estimate as the final assessment. This study proposes a statistical technique which provides an additional energy yield assessment method by using tolerance intervals. Variance component models are used to better account for the variability present in the daily and hourly energy yields of three different PV modules. A bootstrap-based technique is used to obtain 𝛽-expectation and (𝛼,𝛽) two-sided tolerance intervals. These tolerance intervals provided more information with a content and confidence level for seasonal and yearly time-periods. In addition, the comparisons of the PV modules provide valuable information to investors and developers.
- Full Text:
- Date Issued: 2019
- Authors: Deyzel, Jani Igna
- Date: 2019
- Subjects: Bootstrap (Statistics) , Mathematical statistics Photovoltaic power systems
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/39469 , vital:35256
- Description: The assessment of the energy yield of a photovoltaic (PV) system is one of the key assessments required by investors and developers. Currently, available methods used for this assessment only provide a point estimate as the final assessment. This study proposes a statistical technique which provides an additional energy yield assessment method by using tolerance intervals. Variance component models are used to better account for the variability present in the daily and hourly energy yields of three different PV modules. A bootstrap-based technique is used to obtain 𝛽-expectation and (𝛼,𝛽) two-sided tolerance intervals. These tolerance intervals provided more information with a content and confidence level for seasonal and yearly time-periods. In addition, the comparisons of the PV modules provide valuable information to investors and developers.
- Full Text:
- Date Issued: 2019
Carbon and nutrient storage of the Swartkops Estuary salt marsh and seagrass habitats
- Authors: Els, Jessica
- Date: 2019
- Subjects: Estuarine ecology -- South Africa -- Swartkops River Estuary , Salt marsh ecology -- South Africa -- Swartkops River Estuary Seagrasses -- Ecology Seagrasses -- Conservation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/42196 , vital:36634
- Description: Coastal wetlands play an important role in filtering nutrient contaminants from water bodies and are also effective carbon sinks. These systems are known as blue carbon ecosystems. Blue carbon is defined as the carbon stored and sequestered by coastal vegetated habitats such as seagrasses, salt marsh and mangroves. These habitats are being lost on a global scale due to climate change and other anthropogenic pressures. Quantifying ecosystem services provided by these habitats may lead to better conservation and restoration strategies. Research on this topic has escalated over the past decade but there are no published studies in South Africa. The aim of this study was to quantify the carbon, nitrogen, and phosphorus stocks in the above and below ground tissues of Zostera capensis, Spartina maritima, and Salicornia tegetaria — a seagrass, salt marsh grass, and salt marsh succulent. This was done in both summer and winter to understand the variability of carbon and nutrient storage. The organic carbon stock of the sediment beneath these three species was also quantified. Results showed that S. maritima, S. tegetaria, and Z. capensis stored 16 ± 2.9 Mg C. ha-1, 4.3 ± 0.7 Mg C. ha-1, and 2.1 ± 0.5 Mg C. ha-1 in their respective biomass, and 247 ± 48 Mg C. ha-1, 212 ± 44 Mg C. ha-1, and 224 ± 38 Mg C. ha-1 respectively in the sediment beneath these habitats. This was determined by elemental analysis and the loss on ignition method (LOI). The sediment made up the dominant carbon pool in the estuary and there was very little seasonal variation, however spatial variation was evident. The sediment carbon stocks were similar to the global mean for salt marsh (255 Mg C. ha-1) and greater than the global mean for seagrass (108 Mg C. ha-1). The Swartkops Estuary stored a total (biomass and sediment carbon combined) of 14 094 Mg C in the Z. capensis area of 62 ha, 25 286 Mg C in the S. maritima area of 96 ha, and 5 916 Mg C in the S. tegetaria, covering an area of 27 ha. This is significantly less than what has been found globally in estuaries, but this is largely due to the smaller area cover of these macrophytes. The amount of carbon stored per hectare is much larger in this South African system than in many international studies — possibly due to the high levels of pollution coming into the system. Nitrogen and phosphorus stocks in the plants fluctuated seasonally in relation to the nutrient input to the estuary, with the greatest stocks found in winter in Z. capensis, S. maritima, and S. tegetaria (0.42 ± 0.03 Mg N. ha-1, 1.6 ± 0.13 Mg N. ha-1, and 0.37 ± 0.02 Mg N. ha-1, respectively; and 0.4 ± 0.03 Mg P. ha-1, 1.2 ± 0.10 Mg P. ha-1 in Z. capensis and S. maritima respectively) because nutrient inputs to the system were highest in winter, however the P stocks in S. tegetaria were greatest in summer (0.35 ± 0.04 Mg P. ha-1). The reason for this difference is because of their ability to store phosphorus better than nitrogen and for longer periods of time due to luxury uptake. Salicornia tegetaria N and P stocks were also lower than the other two species, possibly due to its placement along the intertidal gradient, as it is not tidally inundated for as long as the other two species. The Z. capensis and S. maritima at Site 1 showed extremely high amounts of nitrogen in their tissues (105.3 ± 1.6 g kg-1 and 74.91 ± 4.1 g kg-1 respectively). This is due to the area being a depositional site as it was an old oyster farm and experiences little tidal flushing from the sea despite its proximity to the mouth. Nutrient ratios and N: biomass were determined as an indication of nutrient pollution. The N: biomass was low in both seasons in Z. capensis, S. maritima, and S. tegetaria (0.08, 0.02, 0.04 respectively) indicating consistant eutrophic conditions in the estuary. Plant biomass was a better indicator of nutrient pollution than epiphytes which were very low in the Swartkops Estuary and did not prove as a useful indicator of nutrient enrichment. These results can inform local management plans of the ecosystem service potential of these species and how they should be protected for future and current sustainable use as filters for nutrient pollution to keep the water quality in a better state. It also outlines the current state of blue carbon and nutrient stocks in an urban South African estuary.
- Full Text:
- Date Issued: 2019
- Authors: Els, Jessica
- Date: 2019
- Subjects: Estuarine ecology -- South Africa -- Swartkops River Estuary , Salt marsh ecology -- South Africa -- Swartkops River Estuary Seagrasses -- Ecology Seagrasses -- Conservation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/42196 , vital:36634
- Description: Coastal wetlands play an important role in filtering nutrient contaminants from water bodies and are also effective carbon sinks. These systems are known as blue carbon ecosystems. Blue carbon is defined as the carbon stored and sequestered by coastal vegetated habitats such as seagrasses, salt marsh and mangroves. These habitats are being lost on a global scale due to climate change and other anthropogenic pressures. Quantifying ecosystem services provided by these habitats may lead to better conservation and restoration strategies. Research on this topic has escalated over the past decade but there are no published studies in South Africa. The aim of this study was to quantify the carbon, nitrogen, and phosphorus stocks in the above and below ground tissues of Zostera capensis, Spartina maritima, and Salicornia tegetaria — a seagrass, salt marsh grass, and salt marsh succulent. This was done in both summer and winter to understand the variability of carbon and nutrient storage. The organic carbon stock of the sediment beneath these three species was also quantified. Results showed that S. maritima, S. tegetaria, and Z. capensis stored 16 ± 2.9 Mg C. ha-1, 4.3 ± 0.7 Mg C. ha-1, and 2.1 ± 0.5 Mg C. ha-1 in their respective biomass, and 247 ± 48 Mg C. ha-1, 212 ± 44 Mg C. ha-1, and 224 ± 38 Mg C. ha-1 respectively in the sediment beneath these habitats. This was determined by elemental analysis and the loss on ignition method (LOI). The sediment made up the dominant carbon pool in the estuary and there was very little seasonal variation, however spatial variation was evident. The sediment carbon stocks were similar to the global mean for salt marsh (255 Mg C. ha-1) and greater than the global mean for seagrass (108 Mg C. ha-1). The Swartkops Estuary stored a total (biomass and sediment carbon combined) of 14 094 Mg C in the Z. capensis area of 62 ha, 25 286 Mg C in the S. maritima area of 96 ha, and 5 916 Mg C in the S. tegetaria, covering an area of 27 ha. This is significantly less than what has been found globally in estuaries, but this is largely due to the smaller area cover of these macrophytes. The amount of carbon stored per hectare is much larger in this South African system than in many international studies — possibly due to the high levels of pollution coming into the system. Nitrogen and phosphorus stocks in the plants fluctuated seasonally in relation to the nutrient input to the estuary, with the greatest stocks found in winter in Z. capensis, S. maritima, and S. tegetaria (0.42 ± 0.03 Mg N. ha-1, 1.6 ± 0.13 Mg N. ha-1, and 0.37 ± 0.02 Mg N. ha-1, respectively; and 0.4 ± 0.03 Mg P. ha-1, 1.2 ± 0.10 Mg P. ha-1 in Z. capensis and S. maritima respectively) because nutrient inputs to the system were highest in winter, however the P stocks in S. tegetaria were greatest in summer (0.35 ± 0.04 Mg P. ha-1). The reason for this difference is because of their ability to store phosphorus better than nitrogen and for longer periods of time due to luxury uptake. Salicornia tegetaria N and P stocks were also lower than the other two species, possibly due to its placement along the intertidal gradient, as it is not tidally inundated for as long as the other two species. The Z. capensis and S. maritima at Site 1 showed extremely high amounts of nitrogen in their tissues (105.3 ± 1.6 g kg-1 and 74.91 ± 4.1 g kg-1 respectively). This is due to the area being a depositional site as it was an old oyster farm and experiences little tidal flushing from the sea despite its proximity to the mouth. Nutrient ratios and N: biomass were determined as an indication of nutrient pollution. The N: biomass was low in both seasons in Z. capensis, S. maritima, and S. tegetaria (0.08, 0.02, 0.04 respectively) indicating consistant eutrophic conditions in the estuary. Plant biomass was a better indicator of nutrient pollution than epiphytes which were very low in the Swartkops Estuary and did not prove as a useful indicator of nutrient enrichment. These results can inform local management plans of the ecosystem service potential of these species and how they should be protected for future and current sustainable use as filters for nutrient pollution to keep the water quality in a better state. It also outlines the current state of blue carbon and nutrient stocks in an urban South African estuary.
- Full Text:
- Date Issued: 2019
Chacma baboons (papio ursinus) influence zoogeomorphic processes in the Karoo through rock movement
- Authors: Maré, Celesté
- Date: 2019
- Subjects: Geomorphology -- South Africa -- Eastern Cape , Biogeomorphology Geology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/40966 , vital:36278
- Description: Animals sculpt landforms by physically altering the substrate. The field of zoogeomorphology has developed to explicitly consider the role of animals as geomorphic agents. Many digging and burrowing animals are then considered zoogeomorphic agents. While the significance of soil disturbing species is well established, geomorphic impacts are rarely quantified for rock transporting species. Chacma baboons (Papio ursinus, hereafter baboon), a widespread and abundant primate, have the potential to act as a zoogeomorphic agent through their purposeful rock displacement while foraging. With this study I assessed the role of baboons as rock rolling agents by demonstrating that baboons roll rocks to search for and feed on organisms beneath, quantifying the extent of this process, and establishing the preferences of baboons for rock features. Observations from a troop of wild baboons showed that rock rolling is an important component of the daily foraging routine of baboons, and confirmed that baboons roll rocks to feed on the organisms beneath. Baboon rock movement was extensive, with potentially tons of rock material moved across many hectares over one year in some habitats. The distance of this rock movement was influenced by a combination of rock mass, rock shape and the slope of the landscape. Baboons showed clear preferences for the rocks they rolled in terms of shape and size, with rock size being an important driver of baboon rock rolling. With this study I show that the chacma baboon is an important rock moving species, with the potential to impact a range of ecological and geological processes. As such, baboons may serve as a keystone species as they are the only species in this environment to intentionally move rocks in this way. However, because baboons are considered pests and are widely persecuted, their role in zoogeomorphic processes are vulnerable to being lost.
- Full Text:
- Date Issued: 2019
- Authors: Maré, Celesté
- Date: 2019
- Subjects: Geomorphology -- South Africa -- Eastern Cape , Biogeomorphology Geology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/40966 , vital:36278
- Description: Animals sculpt landforms by physically altering the substrate. The field of zoogeomorphology has developed to explicitly consider the role of animals as geomorphic agents. Many digging and burrowing animals are then considered zoogeomorphic agents. While the significance of soil disturbing species is well established, geomorphic impacts are rarely quantified for rock transporting species. Chacma baboons (Papio ursinus, hereafter baboon), a widespread and abundant primate, have the potential to act as a zoogeomorphic agent through their purposeful rock displacement while foraging. With this study I assessed the role of baboons as rock rolling agents by demonstrating that baboons roll rocks to search for and feed on organisms beneath, quantifying the extent of this process, and establishing the preferences of baboons for rock features. Observations from a troop of wild baboons showed that rock rolling is an important component of the daily foraging routine of baboons, and confirmed that baboons roll rocks to feed on the organisms beneath. Baboon rock movement was extensive, with potentially tons of rock material moved across many hectares over one year in some habitats. The distance of this rock movement was influenced by a combination of rock mass, rock shape and the slope of the landscape. Baboons showed clear preferences for the rocks they rolled in terms of shape and size, with rock size being an important driver of baboon rock rolling. With this study I show that the chacma baboon is an important rock moving species, with the potential to impact a range of ecological and geological processes. As such, baboons may serve as a keystone species as they are the only species in this environment to intentionally move rocks in this way. However, because baboons are considered pests and are widely persecuted, their role in zoogeomorphic processes are vulnerable to being lost.
- Full Text:
- Date Issued: 2019
Comparing organic and conventional farming systems in George, South Africa
- Authors: Swanepoel, Marike
- Date: 2019
- Subjects: Organic farming -- South Africa -- George , Sustainable agriculture -- South Africa -- George Agricultural systems -- South Africa -- George
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/43946 , vital:37086
- Description: This study presents some of the findings of a long-term comparative study at the Nelson Mandela University George campus which started in 2014. This research compares the differences in crop yields and soil fertility under conventional and organic farming systems. Although previous research that was conducted will be presented briefly, the main focus of this dissertation is to report on the research results generated during the 2016/17 and 2017/18 cropping seasons. The baseline study (indicator measurements) was done in 2014 and investigated soil fertility before the different farming systems were implemented. The rapid increase in human population threatens food security, especially in developing countries. Climate change together with the degradation of soil and other natural resources due to high-input industrial farming, provide further challenges in terms of agriculture and future food security. Agricultural production in South Africa faces three obstacles: water scarcity, infertile soils and poor institutional support. Therefore, regenerative and sustainable agriculture practices such as organic farming, are increasingly being promoted as an alternative to conventional farming systems in southern Africa. What is the best way of farming? This is the question every farmer is confronted with. Some say organic whilst others say conventional, but how do we determine this? What is the role of crop rotation in pest management, soil fertility and crop yield? So we set up the research to compare the two farming systems so that decisions can be based on sound scientific findings. Results showed a significant increase in the case of the organic yield in season 2016/17 for cabbage and in both seasons (2016/17 & 2017/18) for cowpea and sweet potato, proving that organic farming yields can increase over time. Soil fertility changes from the baseline year (2014) till the end of season 2017/18 were compared. Overall organic farming systems showed very promising results with higher levels of soil pH followed by a significant increase in important soil nutrients (P, K & C) compared to conventional systems. Crop rotation also had positive effects.
- Full Text:
- Date Issued: 2019
- Authors: Swanepoel, Marike
- Date: 2019
- Subjects: Organic farming -- South Africa -- George , Sustainable agriculture -- South Africa -- George Agricultural systems -- South Africa -- George
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/43946 , vital:37086
- Description: This study presents some of the findings of a long-term comparative study at the Nelson Mandela University George campus which started in 2014. This research compares the differences in crop yields and soil fertility under conventional and organic farming systems. Although previous research that was conducted will be presented briefly, the main focus of this dissertation is to report on the research results generated during the 2016/17 and 2017/18 cropping seasons. The baseline study (indicator measurements) was done in 2014 and investigated soil fertility before the different farming systems were implemented. The rapid increase in human population threatens food security, especially in developing countries. Climate change together with the degradation of soil and other natural resources due to high-input industrial farming, provide further challenges in terms of agriculture and future food security. Agricultural production in South Africa faces three obstacles: water scarcity, infertile soils and poor institutional support. Therefore, regenerative and sustainable agriculture practices such as organic farming, are increasingly being promoted as an alternative to conventional farming systems in southern Africa. What is the best way of farming? This is the question every farmer is confronted with. Some say organic whilst others say conventional, but how do we determine this? What is the role of crop rotation in pest management, soil fertility and crop yield? So we set up the research to compare the two farming systems so that decisions can be based on sound scientific findings. Results showed a significant increase in the case of the organic yield in season 2016/17 for cabbage and in both seasons (2016/17 & 2017/18) for cowpea and sweet potato, proving that organic farming yields can increase over time. Soil fertility changes from the baseline year (2014) till the end of season 2017/18 were compared. Overall organic farming systems showed very promising results with higher levels of soil pH followed by a significant increase in important soil nutrients (P, K & C) compared to conventional systems. Crop rotation also had positive effects.
- Full Text:
- Date Issued: 2019
Comparison of mesozooplankton communities at three shallow seamounts in the South West Indian Ocean using size spectrum analysis
- Rasoloarijao, Zo, Huggett, Jenny
- Authors: Rasoloarijao, Zo , Huggett, Jenny
- Date: 2019
- Subjects: Seamounts
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/43012 , vital:36731
- Description: Seamounts influence ocean dynamics and consequently the surrounding ecosystem. Zooplankton communities associated with seamounts may be influenced by various mechanisms related to increased retention,such as Taylor columns and/or enhanced local productivity, leading to increased predation pressure. Through this study we investigated mesozooplankton distribution and community structure in the vicinity of three shallow seamounts in the South West Indian Ocean (SWIO) during September 2016, December 2016 and April/May 2017 at La Pérouse, MadRidge and Walters Shoal respectively. The water-column was profiled at 42 stations using a CTD-F equipped with a L-ADCP and mesozooplankton was sampled with a Bongo net or a Hydrobios Midi MultiNet, both fitted with 200 µm mesh. Walters Shoal had significantly lower mesozooplankton total abundance and biovolume compared to La Perouse and MadRidge. La Perouse and MadRidge showed similar mesozooplankton community structures with steep Normalised Biovolume Size Spectrum (NBSS) slopes, indicating higher productivity and dominance of small organisms, compared to Walters Shoal where the slopes were flatter. Total and per taxon abundances and biovolumes at locations “On” and “Off” the seamount were similar, as was the size diversity for MadRidge and Walter Shoal. None of the environmental parameters tested had a significant effect on variability of the mesozooplankton community structure at the stations overall.
- Full Text:
- Date Issued: 2019
- Authors: Rasoloarijao, Zo , Huggett, Jenny
- Date: 2019
- Subjects: Seamounts
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/43012 , vital:36731
- Description: Seamounts influence ocean dynamics and consequently the surrounding ecosystem. Zooplankton communities associated with seamounts may be influenced by various mechanisms related to increased retention,such as Taylor columns and/or enhanced local productivity, leading to increased predation pressure. Through this study we investigated mesozooplankton distribution and community structure in the vicinity of three shallow seamounts in the South West Indian Ocean (SWIO) during September 2016, December 2016 and April/May 2017 at La Pérouse, MadRidge and Walters Shoal respectively. The water-column was profiled at 42 stations using a CTD-F equipped with a L-ADCP and mesozooplankton was sampled with a Bongo net or a Hydrobios Midi MultiNet, both fitted with 200 µm mesh. Walters Shoal had significantly lower mesozooplankton total abundance and biovolume compared to La Perouse and MadRidge. La Perouse and MadRidge showed similar mesozooplankton community structures with steep Normalised Biovolume Size Spectrum (NBSS) slopes, indicating higher productivity and dominance of small organisms, compared to Walters Shoal where the slopes were flatter. Total and per taxon abundances and biovolumes at locations “On” and “Off” the seamount were similar, as was the size diversity for MadRidge and Walter Shoal. None of the environmental parameters tested had a significant effect on variability of the mesozooplankton community structure at the stations overall.
- Full Text:
- Date Issued: 2019
Critical success factors of South African construction companies
- Authors: Lombard, Daniel
- Date: 2019
- Subjects: Construction industry -- Planning -- South Africa , Construction industry -- Management Construction industry -- South Africa Success in business -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/42229 , vital:36637
- Description: The aim of the study was to identify the driving forces of the South African construction industry for registered cidb Grade 9 companies. The next objective was to identify the critical success factors (CSF) that are required to be used by the forward-looking and pro-active cidb Grade 9 companies. The most important critical success factors were then highlighted to form a core group of CSFs for construction industry. From this core group of CSFs an attempt was then made to identify business strategies that can assist companies in gaining a competitive advantage in the construction industry of South Africa. The research was based on the problem statement from which the sub-questions and hypothesis were derived. The primary data was collected through a mixed method of quantitative and qualitative research. A ontological philosophy was used for the research to effectively collaborate with the mixed method of research used. The approach of the research was a mix of both inductive and deductive, as it pursued to identify the forces and factors dominating the construction industry. The study subsequently determined what business strategies best suit these results. The research questionnaire was distributed between senior managers of grade 9 cidb construction companies and found that the most eminent driving forces of the industry are political and government decision making, as well as economic conditions. The CSFs showed a clear indication of what the respondents perceived as the most important factors. Although there have been many advances in technology and processes over the years, the most important CSF for contractors are still the processes of bidding and tendering and the factors relating to these. The qualitative research portion of the study was an investigation on what business strategies were best related to the key driving forces and most important CSFs. Interviews were held with directors of cidb grade 9 construction companies. The themes that were identified from the analyses of the qualitative data were that business strategies relevant to differentiation, diversification, cost leadership or hybrid were seen as the most effective for construction companies. The bidding and tendering process is not merely the same process that it used to be. Frequent reviews of what the industry is going through have also become a major necessity. The research was limited to companies registered as grade 9 with the Construction Industry Development Board. The research is seen as valued as the construction industry is highly important towards the development of the economy of a country and the impact that it has on communities.
- Full Text:
- Date Issued: 2019
- Authors: Lombard, Daniel
- Date: 2019
- Subjects: Construction industry -- Planning -- South Africa , Construction industry -- Management Construction industry -- South Africa Success in business -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/42229 , vital:36637
- Description: The aim of the study was to identify the driving forces of the South African construction industry for registered cidb Grade 9 companies. The next objective was to identify the critical success factors (CSF) that are required to be used by the forward-looking and pro-active cidb Grade 9 companies. The most important critical success factors were then highlighted to form a core group of CSFs for construction industry. From this core group of CSFs an attempt was then made to identify business strategies that can assist companies in gaining a competitive advantage in the construction industry of South Africa. The research was based on the problem statement from which the sub-questions and hypothesis were derived. The primary data was collected through a mixed method of quantitative and qualitative research. A ontological philosophy was used for the research to effectively collaborate with the mixed method of research used. The approach of the research was a mix of both inductive and deductive, as it pursued to identify the forces and factors dominating the construction industry. The study subsequently determined what business strategies best suit these results. The research questionnaire was distributed between senior managers of grade 9 cidb construction companies and found that the most eminent driving forces of the industry are political and government decision making, as well as economic conditions. The CSFs showed a clear indication of what the respondents perceived as the most important factors. Although there have been many advances in technology and processes over the years, the most important CSF for contractors are still the processes of bidding and tendering and the factors relating to these. The qualitative research portion of the study was an investigation on what business strategies were best related to the key driving forces and most important CSFs. Interviews were held with directors of cidb grade 9 construction companies. The themes that were identified from the analyses of the qualitative data were that business strategies relevant to differentiation, diversification, cost leadership or hybrid were seen as the most effective for construction companies. The bidding and tendering process is not merely the same process that it used to be. Frequent reviews of what the industry is going through have also become a major necessity. The research was limited to companies registered as grade 9 with the Construction Industry Development Board. The research is seen as valued as the construction industry is highly important towards the development of the economy of a country and the impact that it has on communities.
- Full Text:
- Date Issued: 2019
Damage recovery for robot controllers and simulators evolved using bootstrapped neuro-simulation
- Authors: Leonard, Brydon Andrew
- Date: 2019
- Subjects: Robots -- Control systems , Robots -- Programming Robotics Neural networks (Computer science)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/40424 , vital:36164
- Description: Robots are becoming increasingly complex. This has made manually designing the software responsible for controlling these robots (controllers) challenging, leading to the creation of the field of evolutionary robotics (ER). The ER approach aims to automatically evolve robot controllers and morphologies by utilising concepts from biological evolution. ER techniques use evolutionary algorithms (EA) to evolve populations of controllers - a process that requires the evaluation of a large number of controllers. Performing these evaluations on a real-world robot is both infeasibly time-consuming and poses the risk of damage to the robot. Simulators present a solution to the issue by allowing the evaluation of controllers to take place on a virtual robot. Traditional methods of controller evolution in simulation encounter two major issues. Firstly, physics simulators are complex to create and are often very computationally expensive. Secondly, the reality gap is encountered when controllers are evolved in simulators that are unable to simulate the real world well enough due to implications or small inaccuracies in the simulation, which together cause controllers in the simulation to be unable to transfer effectively to reality. Bootstrapped Neuro-Simulation (BNS) is an ER algorithm that aims to address the issues inherent with the use of simulators. The algorithm concurrently creates a simulator and evolves a population of controllers. The process starts with an initially random population of controllers and an untrained simulator neural network (SNN), a type of robot simulator which utilises artificial neural networks (ANNs) to simulate a robot's behaviour. Controllers are then continually selected for evaluation in the real world, and the data from these real-world evaluations is used to train the controller-evaluation SNN. BNS is a relatively new algorithm that has not yet been explored in depth. An investigation was, therefore, conducted into BNS's ability to evolve closed-loop controllers. BNS was successful in evolving such controllers, and various adaptations to the algorithm were investigated for their ability to improve the evolution of closed-loop controllers. In addition, the factors which had the greatest impact on BNS's effectiveness were reported upon. Damage recovery is an area that has been the focus of a great deal of research. This is because the progression of the field of robotics means that robots no longer operate only in the safe environments that they once did. Robots are now put to use in areas as inaccessible as the surface of Mars, where repairs by a human are impossible. Various methods of damage recovery have previously been proposed and evaluated, but none focused on BNS as a method of damage recovery. In this research, it was hypothesised that BNS's constantly learning nature would allow it to recover from damage, as it would continue to use new information about the state of the real robot to evolve new controllers capable of functioning in the damaged robot. BNS was found to possess the hypothesised damage recovery ability. The algorithm's evaluation was carried out through the evolution of controllers for simple navigation and light-following tasks for a wheeled robot, as well as a locomotion task for a complex legged robot. Various adaptations to the algorithm were then evaluated through extensive parameter investigations in simulation, showing varying levels of effectiveness. These results were further confirmed through evaluation of the adaptations and effective parameter values in real-world evaluations on a real robot. Both a simple and more complex robot morphology were investigated.
- Full Text:
- Date Issued: 2019
- Authors: Leonard, Brydon Andrew
- Date: 2019
- Subjects: Robots -- Control systems , Robots -- Programming Robotics Neural networks (Computer science)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/40424 , vital:36164
- Description: Robots are becoming increasingly complex. This has made manually designing the software responsible for controlling these robots (controllers) challenging, leading to the creation of the field of evolutionary robotics (ER). The ER approach aims to automatically evolve robot controllers and morphologies by utilising concepts from biological evolution. ER techniques use evolutionary algorithms (EA) to evolve populations of controllers - a process that requires the evaluation of a large number of controllers. Performing these evaluations on a real-world robot is both infeasibly time-consuming and poses the risk of damage to the robot. Simulators present a solution to the issue by allowing the evaluation of controllers to take place on a virtual robot. Traditional methods of controller evolution in simulation encounter two major issues. Firstly, physics simulators are complex to create and are often very computationally expensive. Secondly, the reality gap is encountered when controllers are evolved in simulators that are unable to simulate the real world well enough due to implications or small inaccuracies in the simulation, which together cause controllers in the simulation to be unable to transfer effectively to reality. Bootstrapped Neuro-Simulation (BNS) is an ER algorithm that aims to address the issues inherent with the use of simulators. The algorithm concurrently creates a simulator and evolves a population of controllers. The process starts with an initially random population of controllers and an untrained simulator neural network (SNN), a type of robot simulator which utilises artificial neural networks (ANNs) to simulate a robot's behaviour. Controllers are then continually selected for evaluation in the real world, and the data from these real-world evaluations is used to train the controller-evaluation SNN. BNS is a relatively new algorithm that has not yet been explored in depth. An investigation was, therefore, conducted into BNS's ability to evolve closed-loop controllers. BNS was successful in evolving such controllers, and various adaptations to the algorithm were investigated for their ability to improve the evolution of closed-loop controllers. In addition, the factors which had the greatest impact on BNS's effectiveness were reported upon. Damage recovery is an area that has been the focus of a great deal of research. This is because the progression of the field of robotics means that robots no longer operate only in the safe environments that they once did. Robots are now put to use in areas as inaccessible as the surface of Mars, where repairs by a human are impossible. Various methods of damage recovery have previously been proposed and evaluated, but none focused on BNS as a method of damage recovery. In this research, it was hypothesised that BNS's constantly learning nature would allow it to recover from damage, as it would continue to use new information about the state of the real robot to evolve new controllers capable of functioning in the damaged robot. BNS was found to possess the hypothesised damage recovery ability. The algorithm's evaluation was carried out through the evolution of controllers for simple navigation and light-following tasks for a wheeled robot, as well as a locomotion task for a complex legged robot. Various adaptations to the algorithm were then evaluated through extensive parameter investigations in simulation, showing varying levels of effectiveness. These results were further confirmed through evaluation of the adaptations and effective parameter values in real-world evaluations on a real robot. Both a simple and more complex robot morphology were investigated.
- Full Text:
- Date Issued: 2019
Determination of social, environmental and economic benefits for community participation in forestry in Mpumalanga, South Africa
- Long, Leo Searle, Chirwa, Paxie
- Authors: Long, Leo Searle , Chirwa, Paxie
- Date: 2019
- Subjects: Forests and forestry -- South Africa -- Mpumalanga
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/34339 , vital:33307
- Description: Rural communities living adjacent to commercial forestry operations are often affected by numerous negative social issues such as poverty, unemployment, poor healthcare, and limited infrastructure, amongst others. In excess of 61% of forestry land managed by the state owned SAFCOL SOC Ltd is under land claim, as part of the Restitution of Land Rights Act (Act 22 of 1994). It is therefore necessary for forest companies to seek active means of engaging and partnering with these communities through a participatory forest management (PFM) approach. This study explored the sustainable (social, environmental and economic), benefits of such an approach as perceived (experienced) by these local rural communities, and specifically land claimants. The study was conducted in communities adjacent to SAFCOL plantations in the Mpumalanga Province of South Africa. Data were collected between May and June 2017 by means of a structured questionnaire. Surveys were conducted on 46 households within the identified communities so as to verify and evaluate perceived benefits in terms of forest products, ecosystem services and amenities/services/infrastructure provided by SAFCOL and the broader forest industry. The results indicated that these communities recognize and obtain numerous social, environmental and economic benefits from the forest including Non-Timber Forest Products (NTFPs) such as firewood; forest provisioning ecosystem services (FPESs) such as improved water quality; and more metaphysical benefits such as access to gravesites and the protection of traditions and customs. These benefits have the ability to improve the social well-being, economic independence, and the quality of environmental services obtained by the associated communities. It was however found that the utilization of these benefits was widely differentiated according to gender and land claimant status. Whilst males and females largely benefitted equally, there was a distinct benefit preference between genders for different NTFPs. For example males showed preference for the collection of building material, bush meat and for livestock husbandry, whilst females showed preference for the collection of firewood, medicinal plants and fruit, amongst others. Similarly, it was found that overall, non-land claimants benefited more than land claimants. Reasons for this are primarily due to the increased distance with which the land claimants live from the forest resource when compared to non-land claimants. The empirical value of the data produced through this study will be invaluable in negotiations with the land claimant communities on land settlement agreements, joint venture proposals, including Participatory Forest Management, and future land tenure. Through such inclusivity and vested interest in the sustainable management of the forests, corporate risk is reduced and community/land claimant relationships are reinforced. Such Participatory Forest Management arrangements are key to ensuring the longevity and resilience to the forest sector post-transfer of claimed land.
- Full Text:
- Date Issued: 2019
- Authors: Long, Leo Searle , Chirwa, Paxie
- Date: 2019
- Subjects: Forests and forestry -- South Africa -- Mpumalanga
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/34339 , vital:33307
- Description: Rural communities living adjacent to commercial forestry operations are often affected by numerous negative social issues such as poverty, unemployment, poor healthcare, and limited infrastructure, amongst others. In excess of 61% of forestry land managed by the state owned SAFCOL SOC Ltd is under land claim, as part of the Restitution of Land Rights Act (Act 22 of 1994). It is therefore necessary for forest companies to seek active means of engaging and partnering with these communities through a participatory forest management (PFM) approach. This study explored the sustainable (social, environmental and economic), benefits of such an approach as perceived (experienced) by these local rural communities, and specifically land claimants. The study was conducted in communities adjacent to SAFCOL plantations in the Mpumalanga Province of South Africa. Data were collected between May and June 2017 by means of a structured questionnaire. Surveys were conducted on 46 households within the identified communities so as to verify and evaluate perceived benefits in terms of forest products, ecosystem services and amenities/services/infrastructure provided by SAFCOL and the broader forest industry. The results indicated that these communities recognize and obtain numerous social, environmental and economic benefits from the forest including Non-Timber Forest Products (NTFPs) such as firewood; forest provisioning ecosystem services (FPESs) such as improved water quality; and more metaphysical benefits such as access to gravesites and the protection of traditions and customs. These benefits have the ability to improve the social well-being, economic independence, and the quality of environmental services obtained by the associated communities. It was however found that the utilization of these benefits was widely differentiated according to gender and land claimant status. Whilst males and females largely benefitted equally, there was a distinct benefit preference between genders for different NTFPs. For example males showed preference for the collection of building material, bush meat and for livestock husbandry, whilst females showed preference for the collection of firewood, medicinal plants and fruit, amongst others. Similarly, it was found that overall, non-land claimants benefited more than land claimants. Reasons for this are primarily due to the increased distance with which the land claimants live from the forest resource when compared to non-land claimants. The empirical value of the data produced through this study will be invaluable in negotiations with the land claimant communities on land settlement agreements, joint venture proposals, including Participatory Forest Management, and future land tenure. Through such inclusivity and vested interest in the sustainable management of the forests, corporate risk is reduced and community/land claimant relationships are reinforced. Such Participatory Forest Management arrangements are key to ensuring the longevity and resilience to the forest sector post-transfer of claimed land.
- Full Text:
- Date Issued: 2019
Developing ocean particle tracking tools for cross-disciplinary oceanic research with applications in the Agulhas current region
- Hart-Davis, Michael Geofrey, Backeberg, Björn C
- Authors: Hart-Davis, Michael Geofrey , Backeberg, Björn C
- Date: 2019
- Subjects: Ocean currents , Ocean currents -- Measurement Oceanography Oceanography -- Research -- South Atlantic Ocean
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/42308 , vital:36644
- Description: Lagrangian ocean analysis is a powerful way to study ocean processes from in-situ observations and numerical model simulations. As numerical modelling capabilities develop and physical mechanisms of the ocean are better understood, the importance of particle trajectory modelling continues to increase. Therefore, developing cross-disciplinary particle trajectory model applications for the Greater Agulhas System is highly relevant due to its potential contribution to scientific studies and operational applications. This thesis presents the results of developing particle trajectory model applications in the Greater Agulhas System towards better understanding the physical mechanisms that drive ocean processes in the region. The model is used in three applications that demonstrate their cross-disciplinary potential. These applications include a search and rescue scenario, the study of ocean dynamics and the study of the fate of juvenile turtles. Introducing spatially and temporally varying stochastic motion to account for the processes not resolved in the ocean surface current products, as well as including more appropriate boundary conditions, were shown to improve the accuracy of virtual drifters in representing the trajectory of a real surface drifter. Next, implementing the spatially and temporally varying stochastic motion in the particle trajectory model and applying it to a search and rescue scenario of a capsized catamaran revealed that including both winds and surface ocean currents in the particle trajectory model allowed for an improved prediction of the capsized vessel’s trajectory. By comparing a pair of real surface drifters with the particle trajectory model and analysing high resolution sea surface temperature (SST) fields it was shown that the formation of an eddy on the Agulhas Plateau combined with the weakening of the core current velocity resulted in enhanced eddycurrent interactions facilitating the separation of the real surface drifter-pair as they passed through this region. Lastly, the particle trajectory model was used to study the importance of including active swimming characteristic when studying the fate of juvenile turtles. It was found that including active swimming resulted in a change in the distribution of juvenile turtles and, therefore, needs to be included to provide a proper understanding of the fate of juvenile turtles in the ocean. With further development and refinement of the particle trajectory model, Lagrangian ocean analysis has the potential to provide valuable information towards improving our understanding of physical and biological ocean processes at a range of spatial and temporal scales with potential operational oceanography applications.
- Full Text:
- Date Issued: 2019
- Authors: Hart-Davis, Michael Geofrey , Backeberg, Björn C
- Date: 2019
- Subjects: Ocean currents , Ocean currents -- Measurement Oceanography Oceanography -- Research -- South Atlantic Ocean
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/42308 , vital:36644
- Description: Lagrangian ocean analysis is a powerful way to study ocean processes from in-situ observations and numerical model simulations. As numerical modelling capabilities develop and physical mechanisms of the ocean are better understood, the importance of particle trajectory modelling continues to increase. Therefore, developing cross-disciplinary particle trajectory model applications for the Greater Agulhas System is highly relevant due to its potential contribution to scientific studies and operational applications. This thesis presents the results of developing particle trajectory model applications in the Greater Agulhas System towards better understanding the physical mechanisms that drive ocean processes in the region. The model is used in three applications that demonstrate their cross-disciplinary potential. These applications include a search and rescue scenario, the study of ocean dynamics and the study of the fate of juvenile turtles. Introducing spatially and temporally varying stochastic motion to account for the processes not resolved in the ocean surface current products, as well as including more appropriate boundary conditions, were shown to improve the accuracy of virtual drifters in representing the trajectory of a real surface drifter. Next, implementing the spatially and temporally varying stochastic motion in the particle trajectory model and applying it to a search and rescue scenario of a capsized catamaran revealed that including both winds and surface ocean currents in the particle trajectory model allowed for an improved prediction of the capsized vessel’s trajectory. By comparing a pair of real surface drifters with the particle trajectory model and analysing high resolution sea surface temperature (SST) fields it was shown that the formation of an eddy on the Agulhas Plateau combined with the weakening of the core current velocity resulted in enhanced eddycurrent interactions facilitating the separation of the real surface drifter-pair as they passed through this region. Lastly, the particle trajectory model was used to study the importance of including active swimming characteristic when studying the fate of juvenile turtles. It was found that including active swimming resulted in a change in the distribution of juvenile turtles and, therefore, needs to be included to provide a proper understanding of the fate of juvenile turtles in the ocean. With further development and refinement of the particle trajectory model, Lagrangian ocean analysis has the potential to provide valuable information towards improving our understanding of physical and biological ocean processes at a range of spatial and temporal scales with potential operational oceanography applications.
- Full Text:
- Date Issued: 2019
Development of a nystatin-loaded micellar system for oral mucoadhesion
- Authors: Sarpong, Nancy Owusu Akyere
- Date: 2019
- Subjects: Medical microbiology , HIV infections -- Treatment Clinical pharmacology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/43556 , vital:36918
- Description: Oropharyngeal Candidiasis (OPC) is an opportunistic fungal infection that affects mostly infants and immunocompromised patients. In recent years, the disease has been on the rise due to an increased life span, the HIV pandemic and the increased use of broad spectrum antibiotics. OPC may be treated using a nystatin suspension, which is not as effective as it could be due to the mechanism by which the suspension is applied to the affected tissue. This research aims to improve the effectiveness of nystatin, for the treatment of OPC, by proposing a nystatin loaded micellar system incorporated into a mucoadhesive system for drug delivery. This will ensure that nystatin is gradually released from the film, thus increasing retention time of nystatin at the affected area. In this study, a mixture design was developed, which was used to determine the most appropriate solvent system for nystatin solubilization. Optimisation of the micelle formulation was achieved by using the central composite rational design (CCRD). The two factors that were taken into consideration were the temperature of the hydration medium (water) and the length of time the micellar solution was exposed to the temperature environment of the rotary evaporator. The responses that were investigated were the mean particle size, mean polydispersity index (PDI), mean zeta potential, change in mean particle size and change in mean PDI. The optimal micelle formulation was characterised for size, stability, morphology and drug encapsulation efficiency. The micelles were found to be spherical and stable with an acceptable size range. However, their drug encapsulation efficiency was low. The mucoadhesive film was formulated and characterised for physical characteristics, pliability, percentage swelling index and drug release profile. The film was found to be highly pliable and evenly distributed with a smooth surface; no bumps or bubbles were visible. The film was able to swell to up to 550 %. In vitro studies showed that nystatin was gradually released from the film.
- Full Text:
- Date Issued: 2019
- Authors: Sarpong, Nancy Owusu Akyere
- Date: 2019
- Subjects: Medical microbiology , HIV infections -- Treatment Clinical pharmacology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/43556 , vital:36918
- Description: Oropharyngeal Candidiasis (OPC) is an opportunistic fungal infection that affects mostly infants and immunocompromised patients. In recent years, the disease has been on the rise due to an increased life span, the HIV pandemic and the increased use of broad spectrum antibiotics. OPC may be treated using a nystatin suspension, which is not as effective as it could be due to the mechanism by which the suspension is applied to the affected tissue. This research aims to improve the effectiveness of nystatin, for the treatment of OPC, by proposing a nystatin loaded micellar system incorporated into a mucoadhesive system for drug delivery. This will ensure that nystatin is gradually released from the film, thus increasing retention time of nystatin at the affected area. In this study, a mixture design was developed, which was used to determine the most appropriate solvent system for nystatin solubilization. Optimisation of the micelle formulation was achieved by using the central composite rational design (CCRD). The two factors that were taken into consideration were the temperature of the hydration medium (water) and the length of time the micellar solution was exposed to the temperature environment of the rotary evaporator. The responses that were investigated were the mean particle size, mean polydispersity index (PDI), mean zeta potential, change in mean particle size and change in mean PDI. The optimal micelle formulation was characterised for size, stability, morphology and drug encapsulation efficiency. The micelles were found to be spherical and stable with an acceptable size range. However, their drug encapsulation efficiency was low. The mucoadhesive film was formulated and characterised for physical characteristics, pliability, percentage swelling index and drug release profile. The film was found to be highly pliable and evenly distributed with a smooth surface; no bumps or bubbles were visible. The film was able to swell to up to 550 %. In vitro studies showed that nystatin was gradually released from the film.
- Full Text:
- Date Issued: 2019
Development of silver-based polyaniline nanocomposite for electrochemical oxidation and detection of organosulfur compounds
- Authors: Shoba, Siyabonga
- Date: 2019
- Subjects: Polyethylene -- Analysis , Composite materials Nanocomposites (Materials)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/43600 , vital:36928
- Description: Human activities such as combustion of fossil fuels through automobiles, factories and electricity generation using coal results in major productions of sulfur dioxide to the atmosphere. The sulfur dioxide gas chemically reacts with other substances (i.e. water and oxygen) in the atmosphere and produces acidic pollutants. These acidic pollutants exist in both wet and dry form and before they are deposited on the earth’s surface, they can travel long distances carried by the wind. They are deposited in a wet form as rain, snow, fog and sleet and in a dry form as gases or particles. This has led to the mandated 10 ppm S in fuel by the environmental protection agency (EPA). Electrochemical desulfurization (ECDS) has been reported as an innovative technique for removing sulfur via redox processes. ECDS technique is a low costs process as no catalysts and oxidant are involved and it is a green technology (environmental benignity), thus making the process more economical than conventional hydrodesulfurization (HDS) technologies. Modification of electrodes for electrochemistry as well as electrodeposition of metal nanoparticles offers interesting electrochemical activities due to their reduced size and high surface area to volume ratio. Electrochemical oxidation of benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) was analysed in acetonitrile using carbon electrodes modified with silver (Ag)-polyaniline (PAni) based nanocomposites (GCE/PAni/Ag and GCE/Ag). The PAni, PAni/Ag composites were characterized using spectroscopic (FT-IR, XRD, XPS) and microscopic (SEM and TEM) techniques. SEM confirmed that the synthesized PAni and PAni/Ag presented an amorphous granular morphology with the aggregation of small irregular particle sizes. Cyclic voltammetry of BT, DBT and 4,6-DMDBT on the modified glassy carbon (GCE) electrode show chemically irreversible anodic peaks which corresponds to electron transfer of sulfur to form sulfoxide and lastly sulfone containing compounds. The overall conversion yield of DBT and 4,6-DMDBT to respective sulfones increased as water content increases. Products were characterized by means of gas chromatograph coupled to mass spectrometer (GC-MS), 1H and 13C NMR. Similarly, silver-modified Glassy Carbon (GCE) electrode was used for the electrochemical detection of benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) in the presence of naphthalene (NP) and carbazole (CR). The electrochemical response of BT, DBT and 4,6-DMDBT on the modified electrode was determined using Differential Pulse Voltammetry (DPV) in acetonitrile. The electrochemical behaviour of BT, DBT and 4,6-DMDBT showed that the modified electrode exhibited excellent oxidation electro-catalytic activity. The dynamic range for the organosulfur compounds determination was from 1 to 11 ppm with detection limits (LOD) of 0.60 ppmS, 0.41 ppmS and 0.21 ppmS for BT, DBT and 4,6-DMDBT, respectively. Electrochemical sensor showed excellent selectivity of the compounds in the presence of interfering compounds such as naphthalene, carbazole and thiourea over the studied range of concentrations. The prepared electrode exhibited satisfactory reusability and stability after four successive measurement. It has been demonstrated in this study that modified glassy carbon (GCE) electrode (GCE/PAni/Ag) can be successfully used for the assay of sulfur containing compounds such as BT, DBT and 4, 6-DMDBT in petroleum samples.
- Full Text:
- Date Issued: 2019
- Authors: Shoba, Siyabonga
- Date: 2019
- Subjects: Polyethylene -- Analysis , Composite materials Nanocomposites (Materials)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/43600 , vital:36928
- Description: Human activities such as combustion of fossil fuels through automobiles, factories and electricity generation using coal results in major productions of sulfur dioxide to the atmosphere. The sulfur dioxide gas chemically reacts with other substances (i.e. water and oxygen) in the atmosphere and produces acidic pollutants. These acidic pollutants exist in both wet and dry form and before they are deposited on the earth’s surface, they can travel long distances carried by the wind. They are deposited in a wet form as rain, snow, fog and sleet and in a dry form as gases or particles. This has led to the mandated 10 ppm S in fuel by the environmental protection agency (EPA). Electrochemical desulfurization (ECDS) has been reported as an innovative technique for removing sulfur via redox processes. ECDS technique is a low costs process as no catalysts and oxidant are involved and it is a green technology (environmental benignity), thus making the process more economical than conventional hydrodesulfurization (HDS) technologies. Modification of electrodes for electrochemistry as well as electrodeposition of metal nanoparticles offers interesting electrochemical activities due to their reduced size and high surface area to volume ratio. Electrochemical oxidation of benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) was analysed in acetonitrile using carbon electrodes modified with silver (Ag)-polyaniline (PAni) based nanocomposites (GCE/PAni/Ag and GCE/Ag). The PAni, PAni/Ag composites were characterized using spectroscopic (FT-IR, XRD, XPS) and microscopic (SEM and TEM) techniques. SEM confirmed that the synthesized PAni and PAni/Ag presented an amorphous granular morphology with the aggregation of small irregular particle sizes. Cyclic voltammetry of BT, DBT and 4,6-DMDBT on the modified glassy carbon (GCE) electrode show chemically irreversible anodic peaks which corresponds to electron transfer of sulfur to form sulfoxide and lastly sulfone containing compounds. The overall conversion yield of DBT and 4,6-DMDBT to respective sulfones increased as water content increases. Products were characterized by means of gas chromatograph coupled to mass spectrometer (GC-MS), 1H and 13C NMR. Similarly, silver-modified Glassy Carbon (GCE) electrode was used for the electrochemical detection of benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) in the presence of naphthalene (NP) and carbazole (CR). The electrochemical response of BT, DBT and 4,6-DMDBT on the modified electrode was determined using Differential Pulse Voltammetry (DPV) in acetonitrile. The electrochemical behaviour of BT, DBT and 4,6-DMDBT showed that the modified electrode exhibited excellent oxidation electro-catalytic activity. The dynamic range for the organosulfur compounds determination was from 1 to 11 ppm with detection limits (LOD) of 0.60 ppmS, 0.41 ppmS and 0.21 ppmS for BT, DBT and 4,6-DMDBT, respectively. Electrochemical sensor showed excellent selectivity of the compounds in the presence of interfering compounds such as naphthalene, carbazole and thiourea over the studied range of concentrations. The prepared electrode exhibited satisfactory reusability and stability after four successive measurement. It has been demonstrated in this study that modified glassy carbon (GCE) electrode (GCE/PAni/Ag) can be successfully used for the assay of sulfur containing compounds such as BT, DBT and 4, 6-DMDBT in petroleum samples.
- Full Text:
- Date Issued: 2019
Devulcanisation of truck tyre tread vulcanisates in supercritical carbon dioxide using diphenyl disulphide and 2,2- dithiobis(benzothiazole)
- Mabuto, Briswell, Ogunlanja, A
- Authors: Mabuto, Briswell , Ogunlanja, A
- Date: 2019
- Subjects: Vulcanization , Polymeric composites Rubber Carbon dioxide -- Thermal properties Environmental chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/40702 , vital:36224
- Description: A lot of work has been done in the recycling industry in an effort to increase the amount of reclaimed rubber used in new tyre formulations. The major drawback has been inferior physical and mechanical properties of reclaimed/virgin rubber blends in comparison to the virgin rubber material. Deterioration in these properties has been identified to be a result of chain degradation during reclamation processes as well as presence of crosslinks in the final reclaim product. Devulcanisation techniques have gained precedence due to the relatively improved properties of devulcanised/virgin rubber blends. The concept of devulcanisation is to reverse vulcanisation, resulting in total or partial cleavage of crosslinks. In this way, chain degradation is minimised while crosslink scission is maximised, thereby resulting in good quality devulcanised rubber. However, due to the persistence of chain degradation and crosslinks during devulcanisation processes, a very limited number of reports have claimed success in achieving this goal. Therefore there is still the need to develop a devulcanisation method that ensures improved quality and productivity of devulcanised rubber. Typical truck tyre tread vulcanisates were used for optimisation of time, temperature, heating rate, pressure and amount of devulcanising agent while monitoring percentage devulcanisation in supercritical carbon dioxide medium. Optimisation of the devulcanisation conditions was done by employing a twolevel central composite design in the isothermal and non-isothermal heating stages. This was followed by a single factor analysis of devulcanisation conditions in the non-isothermal stage. The effect of the presence of carbon black was investigated by comparing the percentage devulcanisation of carbon black filled and unfilled samples. The results show that supercritical carbon dioxide is an effective medium of devulcanisation using diphenyl disulphide (DD) and 2,2-dithiobis(benzothiazole) (MBTS). The relatively higher degree of devulcanisation observed during the non-isothermal stage compared to the isothermal stage, led to a shift of focus to non-isothermal devulcanisation. Temperature and time were found to have a significant antagonistic effect on the percentage devulcanisation, while changes in pressure above critical point and mass of devulcanising agent showed no effect on percentage devulcanisation. The heating rate was determined by the set-point, of which 180 ℃ set-point temperature resulted in desirable degree of devulcanisation for both DD and MBTS. 76.18 ± 5.50 % devulcanisation in 5 minutes at 102 ℃ was observed for DD whilst 70.92 ± 4.10 % devulcanisation in 4 minutes at 97 ℃ was observed for MBTS. Changes in pressure above critical point and mass of devulcanising agent used in devulcanisation showed no significant effect in the percentage devulcanisation and so they were kept constant at 80 bars and 1.00 % v (of weight of rubber sample) devulcanisation agent, respectively. The presence of carbon black was found to have an effect on the degree of devulcanisation; 87.95 % and 81.33 % devulcanisation was observed for unfilled samples devulcanised using DD and MBTS respectively. Thermogravimetric analysis of the natural rubber/styrene butadiene rubber (NR/SBR respectively) relative composition of devulcanisates indicated uneven devulcanisation when using DD, whereas MBTS did not show any form of preference. DD showed preference for NR devulcanisation over SBR. Further analysis of the sol and gel fractions were performed using; Differential Scanning Calorimetry, Fourier Transform Infrared Spectroscopy, Gel Permeation Chromatography and Gas Chromatography coupled with Mass Spectroscopy. Application of the optimised conditions to devulcanise ground tyre rubber (GTR) resulted in relatively lower degrees of devulcanisation for both DD and MBTS; 41.22 ± 4.22 and 22.41 ± 1.97 respectively. The differences in the degree of devulcanisation of the laboratory prepared vulcanisates and the GTR was determined to be due to sample differences; i.e. sample constituents, particle dimensions and crosslink network (crosslink distribution in particular).
- Full Text:
- Date Issued: 2019
- Authors: Mabuto, Briswell , Ogunlanja, A
- Date: 2019
- Subjects: Vulcanization , Polymeric composites Rubber Carbon dioxide -- Thermal properties Environmental chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/40702 , vital:36224
- Description: A lot of work has been done in the recycling industry in an effort to increase the amount of reclaimed rubber used in new tyre formulations. The major drawback has been inferior physical and mechanical properties of reclaimed/virgin rubber blends in comparison to the virgin rubber material. Deterioration in these properties has been identified to be a result of chain degradation during reclamation processes as well as presence of crosslinks in the final reclaim product. Devulcanisation techniques have gained precedence due to the relatively improved properties of devulcanised/virgin rubber blends. The concept of devulcanisation is to reverse vulcanisation, resulting in total or partial cleavage of crosslinks. In this way, chain degradation is minimised while crosslink scission is maximised, thereby resulting in good quality devulcanised rubber. However, due to the persistence of chain degradation and crosslinks during devulcanisation processes, a very limited number of reports have claimed success in achieving this goal. Therefore there is still the need to develop a devulcanisation method that ensures improved quality and productivity of devulcanised rubber. Typical truck tyre tread vulcanisates were used for optimisation of time, temperature, heating rate, pressure and amount of devulcanising agent while monitoring percentage devulcanisation in supercritical carbon dioxide medium. Optimisation of the devulcanisation conditions was done by employing a twolevel central composite design in the isothermal and non-isothermal heating stages. This was followed by a single factor analysis of devulcanisation conditions in the non-isothermal stage. The effect of the presence of carbon black was investigated by comparing the percentage devulcanisation of carbon black filled and unfilled samples. The results show that supercritical carbon dioxide is an effective medium of devulcanisation using diphenyl disulphide (DD) and 2,2-dithiobis(benzothiazole) (MBTS). The relatively higher degree of devulcanisation observed during the non-isothermal stage compared to the isothermal stage, led to a shift of focus to non-isothermal devulcanisation. Temperature and time were found to have a significant antagonistic effect on the percentage devulcanisation, while changes in pressure above critical point and mass of devulcanising agent showed no effect on percentage devulcanisation. The heating rate was determined by the set-point, of which 180 ℃ set-point temperature resulted in desirable degree of devulcanisation for both DD and MBTS. 76.18 ± 5.50 % devulcanisation in 5 minutes at 102 ℃ was observed for DD whilst 70.92 ± 4.10 % devulcanisation in 4 minutes at 97 ℃ was observed for MBTS. Changes in pressure above critical point and mass of devulcanising agent used in devulcanisation showed no significant effect in the percentage devulcanisation and so they were kept constant at 80 bars and 1.00 % v (of weight of rubber sample) devulcanisation agent, respectively. The presence of carbon black was found to have an effect on the degree of devulcanisation; 87.95 % and 81.33 % devulcanisation was observed for unfilled samples devulcanised using DD and MBTS respectively. Thermogravimetric analysis of the natural rubber/styrene butadiene rubber (NR/SBR respectively) relative composition of devulcanisates indicated uneven devulcanisation when using DD, whereas MBTS did not show any form of preference. DD showed preference for NR devulcanisation over SBR. Further analysis of the sol and gel fractions were performed using; Differential Scanning Calorimetry, Fourier Transform Infrared Spectroscopy, Gel Permeation Chromatography and Gas Chromatography coupled with Mass Spectroscopy. Application of the optimised conditions to devulcanise ground tyre rubber (GTR) resulted in relatively lower degrees of devulcanisation for both DD and MBTS; 41.22 ± 4.22 and 22.41 ± 1.97 respectively. The differences in the degree of devulcanisation of the laboratory prepared vulcanisates and the GTR was determined to be due to sample differences; i.e. sample constituents, particle dimensions and crosslink network (crosslink distribution in particular).
- Full Text:
- Date Issued: 2019
Effect of single-walled carbon nanotubes on various properties of reclaimed rubber/natural rubber blends
- Authors: Gumede, Jabulani Innocent
- Date: 2019
- Subjects: Carbon nanotubes , Nanotubes Nanostructured materials Polymers
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/39675 , vital:35347
- Description: Mechanical and thermal processes are the preferred methods used to reclaim rubber from waste tyres. However, these methods produce reclaimed rubber (RR) with poor quality and lowered properties compared to virgin rubber. As a result, RR is commonly blended with virgin natural rubber (NR) in order to enhance its quality and properties to widen its application scope. The use of RR in the production of new rubber products is however limited to only about 1-10%. This is because the amounts of RR above this percentage negatively affect the properties of the resultant RR/NR blends. Researchers have used various conventional and nonconventional fillers such as carbon black and maize stalk fibres, respectively, in an attempt to enhance the properties of RR/NR blends. One main disadvantage with the use of these fillers is the need for high quantities to achieve desired properties. Several researchers have therefore focused on developing other reinforcing fillers. The fillers that have recently attracted a lot of attention of the present researchers include single-walled carbon nanotubes (SWCNTs), which are very small tubes solely made up of carbon molecules. This is because SWCNTs offer many impressive properties, and even small quantity of these nanofillers is sufficient to achieve desired properties due to their small size, large surface area and high aspect ratio. The main challenge with the use of SWCNTs however is getting them to disperse well in the rubber matrix. Therefore, their surface is either modified and then mixed with rubber or a dispersant is used to disperse them in the rubber matrix, forming a masterbatch. The common nanomaterial masterbatch product for applications in rubber is the TUBALLTM RUBBER (TR), which is a masterbatch product consisting of 1 wt. % TUBALL™ SWCNTs dispersed, using 1.5 wt.% sulfonol as a dispersant, in 97.5 wt.% NR (from latex Taytex FA). This product is a versatile masterbatch designed to enhance the mechanical, chemical, electrical and thermal properties of rubbers since it contains SWCNTs. However, the performance of this product has not been explored in the cases where recycled/reclaimed rubber is used. The main aim of this project was therefore to explore the effect of SWCNTs (via using TR) in the formulations of RR/virgin NR blends. This project was divided into two parts; (i) optimisation of SWCNTs based on tensile properties of specific formulations of compounds. These compounds were prepared by mixing various amounts of TR and NR using a Banbury internal mixer and two-roll mill. (ii) the effect of the addition of SWCNTs from the optimum SWCNTs/NR masterbatch compound on curing, mechanical, aging, dynamic mechanical and thermal properties of RR/NR blends was studied. Curing properties explored include minimum torque (ML), maximum torque (MH), scorch time (ts0.5), curing time (t90) and cure rate. Mechanical properties studied are tensile strength, modulus at 100%, 200%, 300% and 500% elongation, elongation at break, hardness and resilience. Dynamic mechanical properties include stiffness, storage modulus (E'), loss modulus (E''), loss tangent delta (tanδ) and glass transition temperature (Tg). Thermal degradation (stability) was studied by means of thermogravimetric analysis (TGA) for analysing the effect of SWCNTs inclusion on RR/NR blends. The optimum SWCNTs/NR masterbatch compound contained 0.1 wt. % of SWCNTs. The results obtained for various properties indicate that SWCNTs from the optimum SWCNTs/NR masterbatch compound enhanced the curing, mechanical, aging and dynamic mechanical properties of RR/NR blends with lower RR loading. Thermal properties of RR/NR blends were found to be unaffected by the addition of SWCNTs. However, owing to their impressive properties, the use of SWCNTs as nanofillers in RR/NR blends have the greatest potential for extending the applications of RR/NR blends.
- Full Text:
- Date Issued: 2019
- Authors: Gumede, Jabulani Innocent
- Date: 2019
- Subjects: Carbon nanotubes , Nanotubes Nanostructured materials Polymers
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/39675 , vital:35347
- Description: Mechanical and thermal processes are the preferred methods used to reclaim rubber from waste tyres. However, these methods produce reclaimed rubber (RR) with poor quality and lowered properties compared to virgin rubber. As a result, RR is commonly blended with virgin natural rubber (NR) in order to enhance its quality and properties to widen its application scope. The use of RR in the production of new rubber products is however limited to only about 1-10%. This is because the amounts of RR above this percentage negatively affect the properties of the resultant RR/NR blends. Researchers have used various conventional and nonconventional fillers such as carbon black and maize stalk fibres, respectively, in an attempt to enhance the properties of RR/NR blends. One main disadvantage with the use of these fillers is the need for high quantities to achieve desired properties. Several researchers have therefore focused on developing other reinforcing fillers. The fillers that have recently attracted a lot of attention of the present researchers include single-walled carbon nanotubes (SWCNTs), which are very small tubes solely made up of carbon molecules. This is because SWCNTs offer many impressive properties, and even small quantity of these nanofillers is sufficient to achieve desired properties due to their small size, large surface area and high aspect ratio. The main challenge with the use of SWCNTs however is getting them to disperse well in the rubber matrix. Therefore, their surface is either modified and then mixed with rubber or a dispersant is used to disperse them in the rubber matrix, forming a masterbatch. The common nanomaterial masterbatch product for applications in rubber is the TUBALLTM RUBBER (TR), which is a masterbatch product consisting of 1 wt. % TUBALL™ SWCNTs dispersed, using 1.5 wt.% sulfonol as a dispersant, in 97.5 wt.% NR (from latex Taytex FA). This product is a versatile masterbatch designed to enhance the mechanical, chemical, electrical and thermal properties of rubbers since it contains SWCNTs. However, the performance of this product has not been explored in the cases where recycled/reclaimed rubber is used. The main aim of this project was therefore to explore the effect of SWCNTs (via using TR) in the formulations of RR/virgin NR blends. This project was divided into two parts; (i) optimisation of SWCNTs based on tensile properties of specific formulations of compounds. These compounds were prepared by mixing various amounts of TR and NR using a Banbury internal mixer and two-roll mill. (ii) the effect of the addition of SWCNTs from the optimum SWCNTs/NR masterbatch compound on curing, mechanical, aging, dynamic mechanical and thermal properties of RR/NR blends was studied. Curing properties explored include minimum torque (ML), maximum torque (MH), scorch time (ts0.5), curing time (t90) and cure rate. Mechanical properties studied are tensile strength, modulus at 100%, 200%, 300% and 500% elongation, elongation at break, hardness and resilience. Dynamic mechanical properties include stiffness, storage modulus (E'), loss modulus (E''), loss tangent delta (tanδ) and glass transition temperature (Tg). Thermal degradation (stability) was studied by means of thermogravimetric analysis (TGA) for analysing the effect of SWCNTs inclusion on RR/NR blends. The optimum SWCNTs/NR masterbatch compound contained 0.1 wt. % of SWCNTs. The results obtained for various properties indicate that SWCNTs from the optimum SWCNTs/NR masterbatch compound enhanced the curing, mechanical, aging and dynamic mechanical properties of RR/NR blends with lower RR loading. Thermal properties of RR/NR blends were found to be unaffected by the addition of SWCNTs. However, owing to their impressive properties, the use of SWCNTs as nanofillers in RR/NR blends have the greatest potential for extending the applications of RR/NR blends.
- Full Text:
- Date Issued: 2019
Epibenthic biodiversity, habitat characterisation and anthropogenic pressure mapping of unconsolidated sediment habitats in Algoa Bay, South Africa
- Authors: Truter, Hannah Jessie
- Date: 2019
- Subjects: Aquatic ecology , Marine sciences Conservation biology Ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/43812 , vital:37049
- Description: Implementation of an ecosystem-based management approach for marine systems requires a comprehensive understanding of the biophysical marine environment and the cumulative human impacts at different spatio-temporal scales. In Algoa Bay, South Africa, this study describes the epibenthic communities occurring in unconsolidated marine habitats. It further investigates the potential abiotic factors that influence their distribution and abundance, compares epibenthic communities with existing habitat information and evaluates the protection status of the marine environment in the Bay. Seabed imagery, covering a total area of 171.4m², and sediment samples were collected from 13 stations from which 106 epibenthic species were identified. Multivariate analyses revealed two statistically distinct communities that did not align with the Algoa Bay benthic habitat types defined in the current National Biodiversity Assessment (NBA, 2012). Further assessment indicated that community differences were driven by the presence of rock substrate. A range of abiotic factors were tested against the epibenthic communities to explore patterns and identify potential drivers. The combination of abiotic factors depth, mean grain size, mean bottom temperature and mean bottom current explained 55% fitted variation in epibenthic data. The degree of long-term variability in several of these parameters were likewise identified as explanatory variables, including bottom temperature, current speed and dissolved oxygen. The link between abiotic factors and the epibenthic communities observed indicate that these variables can act as surrogates for habitat mapping in the future. The existing and proposed Marine Protected Area (MPA) in conjunction with the NBA 2012 habitat types does well in protecting the majority of habitats in the Bay, however there remain habitats that lack protection. Utilising the benthic communities and potential drivers identified in this study, the proposed MPA boundary delineations should be somewhat altered to include missing habitat types.
- Full Text:
- Date Issued: 2019
- Authors: Truter, Hannah Jessie
- Date: 2019
- Subjects: Aquatic ecology , Marine sciences Conservation biology Ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/43812 , vital:37049
- Description: Implementation of an ecosystem-based management approach for marine systems requires a comprehensive understanding of the biophysical marine environment and the cumulative human impacts at different spatio-temporal scales. In Algoa Bay, South Africa, this study describes the epibenthic communities occurring in unconsolidated marine habitats. It further investigates the potential abiotic factors that influence their distribution and abundance, compares epibenthic communities with existing habitat information and evaluates the protection status of the marine environment in the Bay. Seabed imagery, covering a total area of 171.4m², and sediment samples were collected from 13 stations from which 106 epibenthic species were identified. Multivariate analyses revealed two statistically distinct communities that did not align with the Algoa Bay benthic habitat types defined in the current National Biodiversity Assessment (NBA, 2012). Further assessment indicated that community differences were driven by the presence of rock substrate. A range of abiotic factors were tested against the epibenthic communities to explore patterns and identify potential drivers. The combination of abiotic factors depth, mean grain size, mean bottom temperature and mean bottom current explained 55% fitted variation in epibenthic data. The degree of long-term variability in several of these parameters were likewise identified as explanatory variables, including bottom temperature, current speed and dissolved oxygen. The link between abiotic factors and the epibenthic communities observed indicate that these variables can act as surrogates for habitat mapping in the future. The existing and proposed Marine Protected Area (MPA) in conjunction with the NBA 2012 habitat types does well in protecting the majority of habitats in the Bay, however there remain habitats that lack protection. Utilising the benthic communities and potential drivers identified in this study, the proposed MPA boundary delineations should be somewhat altered to include missing habitat types.
- Full Text:
- Date Issued: 2019
Examining the influence of extrinsic factors on herbivore assemblage composition in a southern African savanna
- Young, Cyanne, Smithwick, Erica
- Authors: Young, Cyanne , Smithwick, Erica
- Date: 2019
- Subjects: Herbivores -- Ecology , Ungulates -- Ecology Mammal populations -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/44334 , vital:37154
- Description: Globally, herbivore populations have become threatened by the effects of a growing human population. This has resulted in over-hunting, habitat encroachment, fragmentation and degradation and competition leading to the replacement of wild herbivore populations with livestock. African herbivores, in particular, have experienced a severe decline in abundance and distribution, and vast conservation management efforts are underway to preserve herbivore populations and promote their growth. However, conservation management efforts sometimes have unintended consequences on the abundance and distribution of herbivores as a result of the complex interactions they have with their ecosystem. The aim of this study was to: 1) examine the drivers of herbivore distribution at the Satara section of Kruger National Park (hereafter ‘KNP’) at a landscape scale, to determine assemblage composition under the constraints of different environmental attributes; and 2) examine feeding selection by grazing herbivores of different morpho-physiological characteristics at a patch scale of differing environmental attributes. To achieve this, thirty-six experimental plots were established at three distances from water at Satara, and manipulated by mowing, mowing and fertilising or fertilising only over the course of a year, to account for seasonal effects. Each plot was fitted with a camera trap which ran for five weeks in each sampling season, and the data collected focussed on eleven herbivore species of differing body size, digestive strategy and feeding preference. These species were selected due to their abundance at Satara, and their representation of a variety of morpho-physiological characteristics. To achieve both aims, generalised linear models were used to determine the probability of occurrence of a functional type (for aim 1- Chapter 3), and individual species (for aim 2- Chapter 4). To construct the generalised linear models for Chapter 3, hypotheses about species’ relative distribution and abundance were developed through a literature review of forage and water availability constraints on feeding preference and body size of herbivore biomass at a landscape scale. I expected strong seasonal relationships between vegetation biomass and quality, and biomass of water-dependent herbivores with increasing distance to water. My analyses of herbivore distribution across the region confirmed broad-scale descriptions of interactions between forage requirements and water availability, across a set of species which differ in functional traits, at a landscape scale. In Chapter 4, trends in probability of occurrence by seven grazing herbivore species were determined using camera trap data at a patch scale. My results showed that season was a major determinant of species distribution, especially those which are not obligate grazers or feed exclusively in the 0.5 km to 2 km zone from water. I found that most selective feeding occurred in the late wet season when water would be more evenly distributed across the landscape and forage resources close to water would have had the chance to recover from depletion as a result of dry season use. The collective efforts of this study show that distance from water was a critical determinant of herbivore distribution across the landscape, and that forage utilisation by small mixed-feeders and large grazers in particular, altered significantly across seasons. This has important implications for the provision of artificial water, given that foraging pressure is increased closer to water. Landscape heterogeneity needs to be maintained through efficient water provision, to allow areas of forage reserve to maintained in the dry season, where species are constrained by water availability and forage quality and quantity.
- Full Text:
- Date Issued: 2019
- Authors: Young, Cyanne , Smithwick, Erica
- Date: 2019
- Subjects: Herbivores -- Ecology , Ungulates -- Ecology Mammal populations -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/44334 , vital:37154
- Description: Globally, herbivore populations have become threatened by the effects of a growing human population. This has resulted in over-hunting, habitat encroachment, fragmentation and degradation and competition leading to the replacement of wild herbivore populations with livestock. African herbivores, in particular, have experienced a severe decline in abundance and distribution, and vast conservation management efforts are underway to preserve herbivore populations and promote their growth. However, conservation management efforts sometimes have unintended consequences on the abundance and distribution of herbivores as a result of the complex interactions they have with their ecosystem. The aim of this study was to: 1) examine the drivers of herbivore distribution at the Satara section of Kruger National Park (hereafter ‘KNP’) at a landscape scale, to determine assemblage composition under the constraints of different environmental attributes; and 2) examine feeding selection by grazing herbivores of different morpho-physiological characteristics at a patch scale of differing environmental attributes. To achieve this, thirty-six experimental plots were established at three distances from water at Satara, and manipulated by mowing, mowing and fertilising or fertilising only over the course of a year, to account for seasonal effects. Each plot was fitted with a camera trap which ran for five weeks in each sampling season, and the data collected focussed on eleven herbivore species of differing body size, digestive strategy and feeding preference. These species were selected due to their abundance at Satara, and their representation of a variety of morpho-physiological characteristics. To achieve both aims, generalised linear models were used to determine the probability of occurrence of a functional type (for aim 1- Chapter 3), and individual species (for aim 2- Chapter 4). To construct the generalised linear models for Chapter 3, hypotheses about species’ relative distribution and abundance were developed through a literature review of forage and water availability constraints on feeding preference and body size of herbivore biomass at a landscape scale. I expected strong seasonal relationships between vegetation biomass and quality, and biomass of water-dependent herbivores with increasing distance to water. My analyses of herbivore distribution across the region confirmed broad-scale descriptions of interactions between forage requirements and water availability, across a set of species which differ in functional traits, at a landscape scale. In Chapter 4, trends in probability of occurrence by seven grazing herbivore species were determined using camera trap data at a patch scale. My results showed that season was a major determinant of species distribution, especially those which are not obligate grazers or feed exclusively in the 0.5 km to 2 km zone from water. I found that most selective feeding occurred in the late wet season when water would be more evenly distributed across the landscape and forage resources close to water would have had the chance to recover from depletion as a result of dry season use. The collective efforts of this study show that distance from water was a critical determinant of herbivore distribution across the landscape, and that forage utilisation by small mixed-feeders and large grazers in particular, altered significantly across seasons. This has important implications for the provision of artificial water, given that foraging pressure is increased closer to water. Landscape heterogeneity needs to be maintained through efficient water provision, to allow areas of forage reserve to maintained in the dry season, where species are constrained by water availability and forage quality and quantity.
- Full Text:
- Date Issued: 2019
Exploring the influence of management practice on mesopredator and herbivore occupancy and interactions
- Authors: Winterton, Deborah Jean
- Date: 2019
- Subjects: Herbivores -- Habitat -- Conservation , Herbivores -- Habitat Herbivores -- Conservation Herbivores -- Ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/44368 , vital:37159
- Description: Ecological studies need to consider ecological interactions between species and their environment across trophic levels. This complexity not only makes the study of ecology very challenging but it also means that ecosystems are vulnerable to change as a disruption at any of the levels could result in cascading effects through the hierarchy. This sensitivity to change makes it especially important to understand ecosystem function as this is needed for effective and adaptive conservation management. A key way in which humans drive and change ecosystem function is through land use and associated management practice. A primary objective of many protected areas is restoration of natural function through re-introduction of large ungulates, which are often fenced and small, thus requiring intensive management that can influence ecosystem function. This is true of the West Coast National Park (the park). Small antelope abundance, and associated drivers, in the contractual Postberg section of the park have been a long-term management question. Postberg is a small (1800 ha) fenced and isolated section of the park which was historically used for agriculture (livestock grazing and some cultivation) and later large wild ungulate species were re-introduced and kept at high densities. The perception of a lower abundance of small antelope has been attributed to predation by a mesopredator (Caracal caracal), however interspecific competition and habitat quality is also known to influence species abundance. Therefore, I aimed to explore the potential mechanisms of small antelope occurrence in the region and how this might differ across three sites with different management practices. Using 18 camera traps, I documented the occurrence of small, medium and large ungulates and caracal. My study spanned across three areas that each represented different forms of management practice with regards to fencing, and stocking rates of managed ungulate species. I made use of single-season, single-species occupancy models in R to assess occupancy of small antelope and caracal and I used the abundance induced heterogeneity model to estimate abundance of managed ungulates. I employed the single-season, two-species occupancy model in PRESENCE to explore species co-occurrence and interactions. Activity patterns and temporal overlap between managed ungulates, small antelope and caracal were assessed using the overlap and activity packages in R. Vegetation height appears to be an important driver of common duiker occupancy. Fallow lands were strongly favoured by managed ungulates suggesting that they may be utilising these patches for foraging. Small antelope occupancy was highest outside of the park and caracal detections were lowest outside of the park. The low detection of caracal across all areas, along with the known diet of caracals, suggests that predation is not likely the driver of small antelope occurrence. Our data suggest that co-occurrence between small antelope and managed ungulates is high and that these sympatric species have probably partitioned food resources. I found that small antelope were mostly crepuscular, managed ungulates more diurnal while caracal were primarily nocturnal. There was a high overlap between small antelope and managed ungulate activity while overlap between caracal and small antelope indicates some temporal partitioning. Overall I found some effects of inter-specific interactions at the local scale. There was, however, no consistent pattern across the areas which, in line with literature, suggests large scale ecological trends are difficult to detect at local scales. Due to the heterogeneity of the region’s vegetation, coupled with the small size of the biome and extensive fragmentation by land use, there are few areas which adequately represent the biome to test how large ungulates would utilise the area at a large scale. This has important implications for the management of small protected areas in the region who are mandated to restore these areas to their historical and natural function. The ability of conservation managers to meet objectives of restoring parks to their historical function, and maintaining these systems as such, may be questioned if our protected areas are not meeting the spatial requirements of re-introduced species.
- Full Text:
- Date Issued: 2019
- Authors: Winterton, Deborah Jean
- Date: 2019
- Subjects: Herbivores -- Habitat -- Conservation , Herbivores -- Habitat Herbivores -- Conservation Herbivores -- Ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/44368 , vital:37159
- Description: Ecological studies need to consider ecological interactions between species and their environment across trophic levels. This complexity not only makes the study of ecology very challenging but it also means that ecosystems are vulnerable to change as a disruption at any of the levels could result in cascading effects through the hierarchy. This sensitivity to change makes it especially important to understand ecosystem function as this is needed for effective and adaptive conservation management. A key way in which humans drive and change ecosystem function is through land use and associated management practice. A primary objective of many protected areas is restoration of natural function through re-introduction of large ungulates, which are often fenced and small, thus requiring intensive management that can influence ecosystem function. This is true of the West Coast National Park (the park). Small antelope abundance, and associated drivers, in the contractual Postberg section of the park have been a long-term management question. Postberg is a small (1800 ha) fenced and isolated section of the park which was historically used for agriculture (livestock grazing and some cultivation) and later large wild ungulate species were re-introduced and kept at high densities. The perception of a lower abundance of small antelope has been attributed to predation by a mesopredator (Caracal caracal), however interspecific competition and habitat quality is also known to influence species abundance. Therefore, I aimed to explore the potential mechanisms of small antelope occurrence in the region and how this might differ across three sites with different management practices. Using 18 camera traps, I documented the occurrence of small, medium and large ungulates and caracal. My study spanned across three areas that each represented different forms of management practice with regards to fencing, and stocking rates of managed ungulate species. I made use of single-season, single-species occupancy models in R to assess occupancy of small antelope and caracal and I used the abundance induced heterogeneity model to estimate abundance of managed ungulates. I employed the single-season, two-species occupancy model in PRESENCE to explore species co-occurrence and interactions. Activity patterns and temporal overlap between managed ungulates, small antelope and caracal were assessed using the overlap and activity packages in R. Vegetation height appears to be an important driver of common duiker occupancy. Fallow lands were strongly favoured by managed ungulates suggesting that they may be utilising these patches for foraging. Small antelope occupancy was highest outside of the park and caracal detections were lowest outside of the park. The low detection of caracal across all areas, along with the known diet of caracals, suggests that predation is not likely the driver of small antelope occurrence. Our data suggest that co-occurrence between small antelope and managed ungulates is high and that these sympatric species have probably partitioned food resources. I found that small antelope were mostly crepuscular, managed ungulates more diurnal while caracal were primarily nocturnal. There was a high overlap between small antelope and managed ungulate activity while overlap between caracal and small antelope indicates some temporal partitioning. Overall I found some effects of inter-specific interactions at the local scale. There was, however, no consistent pattern across the areas which, in line with literature, suggests large scale ecological trends are difficult to detect at local scales. Due to the heterogeneity of the region’s vegetation, coupled with the small size of the biome and extensive fragmentation by land use, there are few areas which adequately represent the biome to test how large ungulates would utilise the area at a large scale. This has important implications for the management of small protected areas in the region who are mandated to restore these areas to their historical and natural function. The ability of conservation managers to meet objectives of restoring parks to their historical function, and maintaining these systems as such, may be questioned if our protected areas are not meeting the spatial requirements of re-introduced species.
- Full Text:
- Date Issued: 2019