Neuroprotective mechanisms of nevirapine and efavirenz in a model of neurodegeneration
- Authors: Zheve, Georgina Teurai
- Date: 2008
- Subjects: HIV infections -- Treatment AIDS (Disease) -- Treatment AIDS dementia complex -- Treatment Nervous system -- Degeneration -- Treatment Melatonin Neurotoxic agents Quinolinic acid
- Language: English
- Type: Thesis , Masters , MPharm
- Identifier: vital:3807 , http://hdl.handle.net/10962/d1003285
- Description: AIDS Dementia Complex (ADC) is a neurodegenerative disorder implicated in HIV-1 infection that is associated with elevated levels of the neurotoxin, quinolinic acid (QA) which causes a cascade of events to occur, leading to the production of reactive oxygen species (ROS), these being ultimately responsible for oxidative neurotoxicity. In clinical studies, Non-nucleoside reverse transcriptase inhibitors (NNRTIs), efavirenz (EFV) and nevirapine (NVP) have been shown to potentially delay the progressive degeneration of neurons, thus reducing the frequency and neurological deficits associated with ADC. Despite these neuroprotective implications, there is still no biochemical data to demonstrate the mechanisms through which these agents offer neuroprotection. The present study aims to elucidate and further characterize the possible antioxidant and neuroprotective mechanisms of NVP and EFV in vitro and in vivo, using QA-induced neurotoxicity as a model. Research has demonstrated that antioxidants and metal chelators have the ability to offer neuroprotection against free radical induced injury and may be beneficial in the prevention or treatment of neurodegeneration. Hence the antioxidant and metal binding properties of these agents were investigated respectively. Inorganic studies, including the 1, 1-diphenyl-2 picrylhydrazyl (DPPH) assay, show that these agents readily scavenge free radicals in vitro, thus postulating the antioxidant property of these agents. The enhancement of superoxide radical generation and iron mediated Fenton reaction by QA is related to lipid peroxidation in biological systems, the extent of which was assayed using the nitroblue tetrazolium and thiobarbituric acid method respectively. Both agents significantly curtail QA-induced lipid peroxidation and potentially scavenge superoxide anions generated by cyanide in vitro. Furthermore, in vivo results demonstrate the ability of NVP and EFV to protect hippocampal neurons against lipid peroxidation induced by QA and superoxide radicals generated as a consequence thereof. The alleviation of QA-induced oxidative stress in vitro possibly occurs through the binding of iron (II) and / or iron (III), and this argument is further strengthened by the ability of EFV and not NVP to reduce iron (II)-induced lipid peroxidation in vitro directly. In addition the ferrozine and electrochemistry assay were used to measure the extent of iron (II) Fe[superscript 2+] and iron (III) Fe[superscript 3+] chelation activity. Both assays demonstrate that these agents bind iron (II) and iron (III), and prevent redox recycling of iron and subsequent complexation of Fe[superscript 2+] with QA which enhances neuronal damage. Both NNRTIs inhibit the endogenous biosynthesis of QA by inhibiting liver tryptophan 2, 3-dioxygenase activity in vivo and subsequently increasing hippocampal serotonin levels. Furthermore, these agents reduce the turnover of hippocampal serotonin to 5-hydroxyindole acetic acid. NVP and not EFV increase 5-hydroxyindole acetic acid and norepinephrine levels in the hippocampus. The results of the pineal indole metabolism study show that NVP increases the synthesis of melatonin, but decreases N-acetylserotonin, 5-hydroxyindole acetic acid and 5-hydroxytryptophol levels. Furthermore, it shows that EFV decreases 5-hydroxyindole acetic acid and melatonin synthesis. Behavioural studies using a Morris water maze show that the post-treatment of rats with NVP and EFV significantly improves QA-induced spatial memory deficits in the hippocampus. This study therefore provides novel information regarding the neuroprotective mechanisms of NVP and EFV. These findings strengthen the argument that these NNRTIs not only have antiviral effects but possess potential neuroprotective properties, which may contribute to the effectiveness of these drugs in the treatment of ADC.
- Full Text:
- Date Issued: 2008
- Authors: Zheve, Georgina Teurai
- Date: 2008
- Subjects: HIV infections -- Treatment AIDS (Disease) -- Treatment AIDS dementia complex -- Treatment Nervous system -- Degeneration -- Treatment Melatonin Neurotoxic agents Quinolinic acid
- Language: English
- Type: Thesis , Masters , MPharm
- Identifier: vital:3807 , http://hdl.handle.net/10962/d1003285
- Description: AIDS Dementia Complex (ADC) is a neurodegenerative disorder implicated in HIV-1 infection that is associated with elevated levels of the neurotoxin, quinolinic acid (QA) which causes a cascade of events to occur, leading to the production of reactive oxygen species (ROS), these being ultimately responsible for oxidative neurotoxicity. In clinical studies, Non-nucleoside reverse transcriptase inhibitors (NNRTIs), efavirenz (EFV) and nevirapine (NVP) have been shown to potentially delay the progressive degeneration of neurons, thus reducing the frequency and neurological deficits associated with ADC. Despite these neuroprotective implications, there is still no biochemical data to demonstrate the mechanisms through which these agents offer neuroprotection. The present study aims to elucidate and further characterize the possible antioxidant and neuroprotective mechanisms of NVP and EFV in vitro and in vivo, using QA-induced neurotoxicity as a model. Research has demonstrated that antioxidants and metal chelators have the ability to offer neuroprotection against free radical induced injury and may be beneficial in the prevention or treatment of neurodegeneration. Hence the antioxidant and metal binding properties of these agents were investigated respectively. Inorganic studies, including the 1, 1-diphenyl-2 picrylhydrazyl (DPPH) assay, show that these agents readily scavenge free radicals in vitro, thus postulating the antioxidant property of these agents. The enhancement of superoxide radical generation and iron mediated Fenton reaction by QA is related to lipid peroxidation in biological systems, the extent of which was assayed using the nitroblue tetrazolium and thiobarbituric acid method respectively. Both agents significantly curtail QA-induced lipid peroxidation and potentially scavenge superoxide anions generated by cyanide in vitro. Furthermore, in vivo results demonstrate the ability of NVP and EFV to protect hippocampal neurons against lipid peroxidation induced by QA and superoxide radicals generated as a consequence thereof. The alleviation of QA-induced oxidative stress in vitro possibly occurs through the binding of iron (II) and / or iron (III), and this argument is further strengthened by the ability of EFV and not NVP to reduce iron (II)-induced lipid peroxidation in vitro directly. In addition the ferrozine and electrochemistry assay were used to measure the extent of iron (II) Fe[superscript 2+] and iron (III) Fe[superscript 3+] chelation activity. Both assays demonstrate that these agents bind iron (II) and iron (III), and prevent redox recycling of iron and subsequent complexation of Fe[superscript 2+] with QA which enhances neuronal damage. Both NNRTIs inhibit the endogenous biosynthesis of QA by inhibiting liver tryptophan 2, 3-dioxygenase activity in vivo and subsequently increasing hippocampal serotonin levels. Furthermore, these agents reduce the turnover of hippocampal serotonin to 5-hydroxyindole acetic acid. NVP and not EFV increase 5-hydroxyindole acetic acid and norepinephrine levels in the hippocampus. The results of the pineal indole metabolism study show that NVP increases the synthesis of melatonin, but decreases N-acetylserotonin, 5-hydroxyindole acetic acid and 5-hydroxytryptophol levels. Furthermore, it shows that EFV decreases 5-hydroxyindole acetic acid and melatonin synthesis. Behavioural studies using a Morris water maze show that the post-treatment of rats with NVP and EFV significantly improves QA-induced spatial memory deficits in the hippocampus. This study therefore provides novel information regarding the neuroprotective mechanisms of NVP and EFV. These findings strengthen the argument that these NNRTIs not only have antiviral effects but possess potential neuroprotective properties, which may contribute to the effectiveness of these drugs in the treatment of ADC.
- Full Text:
- Date Issued: 2008
An adaptive approach for optimized opportunistic routing over Delay Tolerant Mobile Ad hoc Networks
- Authors: Zhao, Xiaogeng
- Date: 2008
- Subjects: Ad hoc networks (Computer networks) Computer network architectures Computer networks Routing protocols (Computer network protocols)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4588 , http://hdl.handle.net/10962/d1004822
- Description: This thesis presents a framework for investigating opportunistic routing in Delay Tolerant Mobile Ad hoc Networks (DTMANETs), and introduces the concept of an Opportunistic Confidence Index (OCI). The OCI enables multiple opportunistic routing protocols to be applied as an adaptive group to improve DTMANET routing reliability, performance, and efficiency. The DTMANET is a recently acknowledged networkarchitecture, which is designed to address the challenging and marginal environments created by adaptive, mobile, and unreliable network node presence. Because of its ad hoc and autonomic nature, routing in a DTMANET is a very challenging problem. The design of routing protocols in such environments, which ensure a high percentage delivery rate (reliability), achieve a reasonable delivery time (performance), and at the same time maintain an acceptable communication overhead (efficiency), is of fundamental consequence to the usefulness of DTMANETs. In recent years, a number of investigations into DTMANET routing have been conducted, resulting in the emergence of a class of routing known as opportunistic routing protocols. Current research into opportunistic routing has exposed opportunities for positive impacts on DTMANET routing. To date, most investigations have concentrated upon one or other of the quality metrics of reliability, performance, or efficiency, while some approaches have pursued a balance of these metrics through assumptions of a high level of global knowledge and/or uniform mobile device behaviours. No prior research that we are aware of has studied the connection between multiple opportunistic elements and their influences upon one another, and none has demonstrated the possibility of modelling and using multiple different opportunistic elements as an adaptive group to aid the routing process in a DTMANET. This thesis investigates OCI opportunities and their viability through the design of an extensible simulation environment, which makes use of methods and techniques such as abstract modelling, opportunistic element simplification and isolation, random attribute generation and assignment, localized knowledge sharing, automated scenario generation, intelligent weight assignment and/or opportunistic element permutation. These methods and techniques are incorporated at both data acquisition and analysis phases. Our results show a significant improvement in all three metric categories. In one of the most applicable scenarios tested, OCI yielded a 31.05% message delivery increase (reliability improvement), 22.18% message delivery time reduction (performance improvement), and 73.64% routing depth decrement (efficiency improvement). We are able to conclude that the OCI approach is feasible across a range of scenarios, and that the use of multiple opportunistic elements to aid decision-making processes in DTMANET environments has value.
- Full Text:
- Date Issued: 2008
- Authors: Zhao, Xiaogeng
- Date: 2008
- Subjects: Ad hoc networks (Computer networks) Computer network architectures Computer networks Routing protocols (Computer network protocols)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4588 , http://hdl.handle.net/10962/d1004822
- Description: This thesis presents a framework for investigating opportunistic routing in Delay Tolerant Mobile Ad hoc Networks (DTMANETs), and introduces the concept of an Opportunistic Confidence Index (OCI). The OCI enables multiple opportunistic routing protocols to be applied as an adaptive group to improve DTMANET routing reliability, performance, and efficiency. The DTMANET is a recently acknowledged networkarchitecture, which is designed to address the challenging and marginal environments created by adaptive, mobile, and unreliable network node presence. Because of its ad hoc and autonomic nature, routing in a DTMANET is a very challenging problem. The design of routing protocols in such environments, which ensure a high percentage delivery rate (reliability), achieve a reasonable delivery time (performance), and at the same time maintain an acceptable communication overhead (efficiency), is of fundamental consequence to the usefulness of DTMANETs. In recent years, a number of investigations into DTMANET routing have been conducted, resulting in the emergence of a class of routing known as opportunistic routing protocols. Current research into opportunistic routing has exposed opportunities for positive impacts on DTMANET routing. To date, most investigations have concentrated upon one or other of the quality metrics of reliability, performance, or efficiency, while some approaches have pursued a balance of these metrics through assumptions of a high level of global knowledge and/or uniform mobile device behaviours. No prior research that we are aware of has studied the connection between multiple opportunistic elements and their influences upon one another, and none has demonstrated the possibility of modelling and using multiple different opportunistic elements as an adaptive group to aid the routing process in a DTMANET. This thesis investigates OCI opportunities and their viability through the design of an extensible simulation environment, which makes use of methods and techniques such as abstract modelling, opportunistic element simplification and isolation, random attribute generation and assignment, localized knowledge sharing, automated scenario generation, intelligent weight assignment and/or opportunistic element permutation. These methods and techniques are incorporated at both data acquisition and analysis phases. Our results show a significant improvement in all three metric categories. In one of the most applicable scenarios tested, OCI yielded a 31.05% message delivery increase (reliability improvement), 22.18% message delivery time reduction (performance improvement), and 73.64% routing depth decrement (efficiency improvement). We are able to conclude that the OCI approach is feasible across a range of scenarios, and that the use of multiple opportunistic elements to aid decision-making processes in DTMANET environments has value.
- Full Text:
- Date Issued: 2008
A study of the Amathole District Municipality's settlement plan in the light of the land reform and spatial planning measures
- Authors: Zenzile, Mlamli Lennox
- Date: 2008
- Subjects: Land reform -- South Africa -- Eastern Cape , Land tenure -- South Africa -- Eastern Cape , Land settlement -- Government policy -- South Africa -- Eastern Cape , Local government -- South Africa -- Eastern Cape , Municipal government -- South Africa -- Eastern Cape , Land use -- Planning -- South Africa , Restitution -- South Africa -- Eastern Cape , Compensation (Law) -- South Africa -- Eastern Cape , Human rights -- South Africa -- Eastern Cape , Right of property -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , LLM
- Identifier: vital:3700 , http://hdl.handle.net/10962/d1003215 , Land reform -- South Africa -- Eastern Cape , Land tenure -- South Africa -- Eastern Cape , Land settlement -- Government policy -- South Africa -- Eastern Cape , Local government -- South Africa -- Eastern Cape , Municipal government -- South Africa -- Eastern Cape , Land use -- Planning -- South Africa , Restitution -- South Africa -- Eastern Cape , Compensation (Law) -- South Africa -- Eastern Cape , Human rights -- South Africa -- Eastern Cape , Right of property -- South Africa -- Eastern Cape
- Description: This study concerns the analysis of policy, and the statutory and regulatory impact of spatial planning on the land reform programme with emphasis on the land reform settlement plan (LSRP) of the Amathole District Municipality (ADM). There is a brief historical overview of the effect of the policy of spatial segregation in both rural and urban areas of the ADM. This study demonstrates, inter alia, the challenges faced by the ADM in both consolidating and physically integrating communities that were hitherto divided across racial lines. The critical question is whether the ADM has the ability to produce a Spatial Development Framework (SDF), which will be responsive to the needs of the region and serve as a catalyst in reversing the physical distortions caused by the land-planning legislation of the apartheid past. The greatest challenge lies in meeting the developmental aspirations of the Development Facilitation Act, 1995, the Local Government: Municipal Systems Act, 2000 and the National Spatial Development Perspective, 2003. Chapter 1 deals with the purpose, research problem and the method of research, as well as the definition of terms used in this research and literature review. Chapter 2 deals with the evolution of central themes of spatial planning and land reform, spatial development plans and integrated development plans (IDPs), the alignment of Amathole SDF and Eastern Cape Spatial Development Plan and the co-ordination of spatial frameworks. Chapter 3 deals with the composition of the ADM and the evolution of the LRSP, as well as land-tenure reform programmes impacting on the Amathole Municipality region. This chapter analyses the settlement plan against spatial planning legislation, the issue of institutional arrangements and mechanisms of consolidated local planning processes. Chapter 5 deals with the thorny issue of participation of traditional leaders in municipal planning and the government’s land-reform programme. Despite the existence of legislation in this regard, implementation seems to pose some difficulties. This chapter also deals with the co-operative governance framework. Chapter 6 is a concluding chapter dealing with the gaps discovered in the Amathole Municipality in the light of existing legislation. Reference to cases is made to demonstrate the challenges confronting the ADM. One notable aspect is the issue of urban-rural dichotomy and how the two worlds are positioned in their competition for the use of space. It is evident from this research that the post-1994 policy and legislative framework and implementation machinery lacks capacity to change the current form of the apartheid city-planning paradigm, something which impacts immensely on the sustainability of the current human-settlement development programmes. Population dynamics in terms of migration are hugely driven by search for employment opportunities and better services. The efficiency and ability of the municipal spatial evelopment frameworks in directing and dictating the identification of development nodes in its juristic boundary informed by the overarching national policy and legislative framework is key in building a better South Africa.
- Full Text:
- Date Issued: 2008
- Authors: Zenzile, Mlamli Lennox
- Date: 2008
- Subjects: Land reform -- South Africa -- Eastern Cape , Land tenure -- South Africa -- Eastern Cape , Land settlement -- Government policy -- South Africa -- Eastern Cape , Local government -- South Africa -- Eastern Cape , Municipal government -- South Africa -- Eastern Cape , Land use -- Planning -- South Africa , Restitution -- South Africa -- Eastern Cape , Compensation (Law) -- South Africa -- Eastern Cape , Human rights -- South Africa -- Eastern Cape , Right of property -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , LLM
- Identifier: vital:3700 , http://hdl.handle.net/10962/d1003215 , Land reform -- South Africa -- Eastern Cape , Land tenure -- South Africa -- Eastern Cape , Land settlement -- Government policy -- South Africa -- Eastern Cape , Local government -- South Africa -- Eastern Cape , Municipal government -- South Africa -- Eastern Cape , Land use -- Planning -- South Africa , Restitution -- South Africa -- Eastern Cape , Compensation (Law) -- South Africa -- Eastern Cape , Human rights -- South Africa -- Eastern Cape , Right of property -- South Africa -- Eastern Cape
- Description: This study concerns the analysis of policy, and the statutory and regulatory impact of spatial planning on the land reform programme with emphasis on the land reform settlement plan (LSRP) of the Amathole District Municipality (ADM). There is a brief historical overview of the effect of the policy of spatial segregation in both rural and urban areas of the ADM. This study demonstrates, inter alia, the challenges faced by the ADM in both consolidating and physically integrating communities that were hitherto divided across racial lines. The critical question is whether the ADM has the ability to produce a Spatial Development Framework (SDF), which will be responsive to the needs of the region and serve as a catalyst in reversing the physical distortions caused by the land-planning legislation of the apartheid past. The greatest challenge lies in meeting the developmental aspirations of the Development Facilitation Act, 1995, the Local Government: Municipal Systems Act, 2000 and the National Spatial Development Perspective, 2003. Chapter 1 deals with the purpose, research problem and the method of research, as well as the definition of terms used in this research and literature review. Chapter 2 deals with the evolution of central themes of spatial planning and land reform, spatial development plans and integrated development plans (IDPs), the alignment of Amathole SDF and Eastern Cape Spatial Development Plan and the co-ordination of spatial frameworks. Chapter 3 deals with the composition of the ADM and the evolution of the LRSP, as well as land-tenure reform programmes impacting on the Amathole Municipality region. This chapter analyses the settlement plan against spatial planning legislation, the issue of institutional arrangements and mechanisms of consolidated local planning processes. Chapter 5 deals with the thorny issue of participation of traditional leaders in municipal planning and the government’s land-reform programme. Despite the existence of legislation in this regard, implementation seems to pose some difficulties. This chapter also deals with the co-operative governance framework. Chapter 6 is a concluding chapter dealing with the gaps discovered in the Amathole Municipality in the light of existing legislation. Reference to cases is made to demonstrate the challenges confronting the ADM. One notable aspect is the issue of urban-rural dichotomy and how the two worlds are positioned in their competition for the use of space. It is evident from this research that the post-1994 policy and legislative framework and implementation machinery lacks capacity to change the current form of the apartheid city-planning paradigm, something which impacts immensely on the sustainability of the current human-settlement development programmes. Population dynamics in terms of migration are hugely driven by search for employment opportunities and better services. The efficiency and ability of the municipal spatial evelopment frameworks in directing and dictating the identification of development nodes in its juristic boundary informed by the overarching national policy and legislative framework is key in building a better South Africa.
- Full Text:
- Date Issued: 2008
Designing and implementing a new pulsar timer for the Hartebeesthoek Radio Astronomy Observatory
- Authors: Youthed, Andrew David
- Date: 2008
- Subjects: Astronomical observatories , Radio astronomy , Pulsars , Astronomical instruments , Reduced instruction set computers , Random access memory
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5458 , http://hdl.handle.net/10962/d1005243 , Astronomical observatories , Radio astronomy , Pulsars , Astronomical instruments , Reduced instruction set computers , Random access memory
- Description: This thesis outlines the design and implementation of a single channel, dual polarization pulsar timing instrument for the Hartebeesthoek Radio Astronomy Observatory (HartRAO). The new timer is designed to be an improved, temporary replacement for the existing device which has been in operation for over 20 years. The existing device is no longer reliable and is di±cult to maintain. The new pulsar timer is designed to provide improved functional- ity, higher sampling speed, greater pulse resolution, more °exibility and easier maintenance over the existing device. The new device is also designed to keeping changes to the observation system to a minimum until a full de-dispersion timer can be implemented at theobservatory. The design makes use of an 8-bit Reduced Instruction Set Computer (RISC) micro-processor with external Random Access Memory (RAM). The instrument includes an IEEE-488 subsystem for interfacing the pulsar timer to the observation computer system. The microcontroller software is written in assembler code to ensure optimal loop execution speed and deterministic code execution for the system. The design path is discussed and problems encountered during the design process are highlighted. Final testing of the new instrument indicates an improvement in the sam- pling rate of 13.6 times and a significant reduction in 60Hz interference over the existing instrument.
- Full Text:
- Date Issued: 2008
- Authors: Youthed, Andrew David
- Date: 2008
- Subjects: Astronomical observatories , Radio astronomy , Pulsars , Astronomical instruments , Reduced instruction set computers , Random access memory
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5458 , http://hdl.handle.net/10962/d1005243 , Astronomical observatories , Radio astronomy , Pulsars , Astronomical instruments , Reduced instruction set computers , Random access memory
- Description: This thesis outlines the design and implementation of a single channel, dual polarization pulsar timing instrument for the Hartebeesthoek Radio Astronomy Observatory (HartRAO). The new timer is designed to be an improved, temporary replacement for the existing device which has been in operation for over 20 years. The existing device is no longer reliable and is di±cult to maintain. The new pulsar timer is designed to provide improved functional- ity, higher sampling speed, greater pulse resolution, more °exibility and easier maintenance over the existing device. The new device is also designed to keeping changes to the observation system to a minimum until a full de-dispersion timer can be implemented at theobservatory. The design makes use of an 8-bit Reduced Instruction Set Computer (RISC) micro-processor with external Random Access Memory (RAM). The instrument includes an IEEE-488 subsystem for interfacing the pulsar timer to the observation computer system. The microcontroller software is written in assembler code to ensure optimal loop execution speed and deterministic code execution for the system. The design path is discussed and problems encountered during the design process are highlighted. Final testing of the new instrument indicates an improvement in the sam- pling rate of 13.6 times and a significant reduction in 60Hz interference over the existing instrument.
- Full Text:
- Date Issued: 2008
Water quality, abalone growth and the potential for integrated mariculture on a South African abalone Haliotis midae L. farm
- Authors: Yearsley, Rowan David
- Date: 2008
- Subjects: Abalones -- South Africa Abalone culture -- South Africa Abalones -- Growth Mariculture -- South Africa Water quality -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5334 , http://hdl.handle.net/10962/d1005180
- Description: Abalone Haliotis midae farming in South Africa is highly intensive, employing pump-ashore, flow-through systems. Despite the known sensitivity of abalone to water quality, there is only a rudimentary understanding of water quality dynamics on South African abalone farms and its effects on abalone production. Furthermore, the potential for reusing the relatively dilute abalone farm effluent to culture other animal species has not been investigated. This study investigated the dynamics of water quality and growth on a South African abalone farm and assessed the suitability of the effluent for the culture of silver kob Argyrosomus inodorus and bloodworm Arenicola loveni loveni. Monitoring of water quality and abalone growth in abalone tanks revealed that oxygen concentrations decreased, while H⁺ ion and free-ammonia (NH₃) concentration increased in a gradient between the inflow and outflow. Abalone growth was positively correlated with oxygen concentration and negatively correlated with free-ammonia and H⁺ ion concentration. The oxygen (O) concentration of the farm influent was dependent upon the influents’ temperature (T) and was described by the relationship O (mg L⁻¹) = 11.244 – 0.208T (r²=0.74). Linear regression analysis of data collected from abalone farm tanks revealed that the concentration of total ammonia at the outflow of abalone tanks (μg TAN L⁻¹) was dependant upon temperature (°C), flow-rate (L s⁻¹ kg⁻¹ H. midae), abalone size (g) and length of time since the tank was last cleaned (d) (n = 125, r² = 0.80). The production of total ammonia (μg TAN s⁻¹ kg⁻¹) was related to temperature, abalone size and days that the tanks remained un-cleaned (n = 125; r² = 0.81). A diurnal cycle of respiration was evident in abalone tanks with higher oxygen consumption and H+ ion production at night. The oxygen concentration of farm effluent was related to temperature, farm biomass and flow rate by means of a linear regression equation (n = 40; r² = 0.69). The results demonstrated the importance of optimising the flow-rate per unit of biomass for various temperatures and sizes of abalone. As abalone size and temperature cannot be controlled under farm conditions, the flow-rate per unit of biomass which the abalone culture system receives will determine the quality of the culture water. The specific growth rate (0.48 ± 0.01 % BW d⁻¹), mortality (1.8 ± 0.5 %), feed conversion ratio (3.0 ± 0.2) and protein efficiency ratio (1.0 ± 0.1) of silver kob kept in either abalone farm effluent or control seawater for 120 days did not differ significantly (t-test, P>0.05). A 90 day growth trial indicated that abalone farm effluent is a suitable culture medium for bloodworm. Bloodworm supplied with control seawater lost weight at 0.19 ± 0.04 % BW d-1, while those given abalone effluent grew at 0.39 ± 0.07 % BW d⁻¹. Mortality was 6 ± 3 % in effluent and 11 ± 8 % in seawater. The bloodworm were efficient at processing solid waste. Abalone farm effluent initially contained 7.7 ± 13 mg L⁻¹ more suspended solids than control seawater, which contained 3.5 ± 0.5 mg L⁻¹, but after passing through bloodworm systems the concentration in abalone effluent was reduced to only 1.4 ± 3.5 mg L⁻¹ above that in control seawater. Therefore, abalone farm effluent could be reused as a culture medium for both silver kob and bloodworm. Future work is needed to investigate aspects of the feasibility of such systems such as growth rates at different sizes and stocking densities.
- Full Text:
- Date Issued: 2008
- Authors: Yearsley, Rowan David
- Date: 2008
- Subjects: Abalones -- South Africa Abalone culture -- South Africa Abalones -- Growth Mariculture -- South Africa Water quality -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5334 , http://hdl.handle.net/10962/d1005180
- Description: Abalone Haliotis midae farming in South Africa is highly intensive, employing pump-ashore, flow-through systems. Despite the known sensitivity of abalone to water quality, there is only a rudimentary understanding of water quality dynamics on South African abalone farms and its effects on abalone production. Furthermore, the potential for reusing the relatively dilute abalone farm effluent to culture other animal species has not been investigated. This study investigated the dynamics of water quality and growth on a South African abalone farm and assessed the suitability of the effluent for the culture of silver kob Argyrosomus inodorus and bloodworm Arenicola loveni loveni. Monitoring of water quality and abalone growth in abalone tanks revealed that oxygen concentrations decreased, while H⁺ ion and free-ammonia (NH₃) concentration increased in a gradient between the inflow and outflow. Abalone growth was positively correlated with oxygen concentration and negatively correlated with free-ammonia and H⁺ ion concentration. The oxygen (O) concentration of the farm influent was dependent upon the influents’ temperature (T) and was described by the relationship O (mg L⁻¹) = 11.244 – 0.208T (r²=0.74). Linear regression analysis of data collected from abalone farm tanks revealed that the concentration of total ammonia at the outflow of abalone tanks (μg TAN L⁻¹) was dependant upon temperature (°C), flow-rate (L s⁻¹ kg⁻¹ H. midae), abalone size (g) and length of time since the tank was last cleaned (d) (n = 125, r² = 0.80). The production of total ammonia (μg TAN s⁻¹ kg⁻¹) was related to temperature, abalone size and days that the tanks remained un-cleaned (n = 125; r² = 0.81). A diurnal cycle of respiration was evident in abalone tanks with higher oxygen consumption and H+ ion production at night. The oxygen concentration of farm effluent was related to temperature, farm biomass and flow rate by means of a linear regression equation (n = 40; r² = 0.69). The results demonstrated the importance of optimising the flow-rate per unit of biomass for various temperatures and sizes of abalone. As abalone size and temperature cannot be controlled under farm conditions, the flow-rate per unit of biomass which the abalone culture system receives will determine the quality of the culture water. The specific growth rate (0.48 ± 0.01 % BW d⁻¹), mortality (1.8 ± 0.5 %), feed conversion ratio (3.0 ± 0.2) and protein efficiency ratio (1.0 ± 0.1) of silver kob kept in either abalone farm effluent or control seawater for 120 days did not differ significantly (t-test, P>0.05). A 90 day growth trial indicated that abalone farm effluent is a suitable culture medium for bloodworm. Bloodworm supplied with control seawater lost weight at 0.19 ± 0.04 % BW d-1, while those given abalone effluent grew at 0.39 ± 0.07 % BW d⁻¹. Mortality was 6 ± 3 % in effluent and 11 ± 8 % in seawater. The bloodworm were efficient at processing solid waste. Abalone farm effluent initially contained 7.7 ± 13 mg L⁻¹ more suspended solids than control seawater, which contained 3.5 ± 0.5 mg L⁻¹, but after passing through bloodworm systems the concentration in abalone effluent was reduced to only 1.4 ± 3.5 mg L⁻¹ above that in control seawater. Therefore, abalone farm effluent could be reused as a culture medium for both silver kob and bloodworm. Future work is needed to investigate aspects of the feasibility of such systems such as growth rates at different sizes and stocking densities.
- Full Text:
- Date Issued: 2008
A study of the existence of equilibrium in mathematical economics
- Authors: Xotyeni, Zukisa Gqabi
- Date: 2008
- Subjects: Equilibrium (Economics) -- Mathematical models , Macroeconomics -- Mathematical models , Economics -- Mathematical models , Welfare economics -- Mathematical models , Lattice theory , Economics, Mathematical
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5418 , http://hdl.handle.net/10962/d1005232 , Equilibrium (Economics) -- Mathematical models , Macroeconomics -- Mathematical models , Economics -- Mathematical models , Welfare economics -- Mathematical models , Lattice theory , Economics, Mathematical
- Description: In this thesis we define and study the existence of an equilibrium situation in which producers maximize their profits relative to the production vectors in their production sets, consumers satisfy their preferences in their consumption sets under certain budget constraint, and for every commodity total demand equals total supply. This competitive equilibrium situation is referred to as the Walrasian equilibrium. The existence of this equilibrium is investigated from a various mathematical points of view. These include microeconomic theory, simplicial spaces, global analysis and lattice theory.
- Full Text:
- Date Issued: 2008
- Authors: Xotyeni, Zukisa Gqabi
- Date: 2008
- Subjects: Equilibrium (Economics) -- Mathematical models , Macroeconomics -- Mathematical models , Economics -- Mathematical models , Welfare economics -- Mathematical models , Lattice theory , Economics, Mathematical
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5418 , http://hdl.handle.net/10962/d1005232 , Equilibrium (Economics) -- Mathematical models , Macroeconomics -- Mathematical models , Economics -- Mathematical models , Welfare economics -- Mathematical models , Lattice theory , Economics, Mathematical
- Description: In this thesis we define and study the existence of an equilibrium situation in which producers maximize their profits relative to the production vectors in their production sets, consumers satisfy their preferences in their consumption sets under certain budget constraint, and for every commodity total demand equals total supply. This competitive equilibrium situation is referred to as the Walrasian equilibrium. The existence of this equilibrium is investigated from a various mathematical points of view. These include microeconomic theory, simplicial spaces, global analysis and lattice theory.
- Full Text:
- Date Issued: 2008
Development of a novel in situ CPRG-based biosensor and bioprobe for monitoring coliform β-D-Galactosidase in water polluted by faecal matter
- Authors: Wutor, Victor Collins
- Date: 2008
- Subjects: Biosensors Molecular probes Enterobacteriaceae Feces -- Microbiology Water -- Pollution -- Environmental aspects Environmental monitoring Chromogenic compounds
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3944 , http://hdl.handle.net/10962/d1004003
- Description: The ultimate objective of this work was to develop a real-time method for detecting and monitoring β-D-galactosidase as a suitable indicator of the potential presence of total coliform bacteria in water environments. Preliminary comparison of the chromogenic substrate, chlorophenol red β-D-galactopyranoside and the fluorogenic substrate, MuGAL, revealed unreliable results with the fluorogenic technique due to interference from compounds commonly found in environmental water samples. Thus, the chromogenic assay was further explored. Hydrolysis of the chromogenic substrate chlorophenol red β-D-galactopyranoside by β-D-galactosidase to yield chlorophenol red was the basis of this assay. Fundamental studies with chlorophenol red β-Dgalactopyranoside showed that β-D-galactosidase occurs extracellularly and in low concentrations in the polluted water environment. A direct correlation between enzyme activity and an increase in environmental water sample volume, as well as enzyme activity with total coliform colony forming unit counts were observed. Spectrophotometric detection was achieved within a maximum period of 24 h with a limit of detection level of 1 colony forming unit 100 ml[superscript -1]. This enzyme also exhibited physical and kinetic properties different from those of the pure commercially available β-D-galactosidase. Cell permeabilisation was not required for releasing enzymes into the extracellular environment. PEG 20 000 offered the best option for concentrating β-D-galactosidase. The source of β-D-galactosidase in the polluted environmental water samples was confirmed as Escherichia coli through SDS-PAGE, tryptic mapping and MALDI-TOF, thus justifying the further use of this method for detecting and/or monitoring total coliforms. Several compounds and metal ions commonly found in environmental water samples (as well as those used in water treatment processes) did have an effect on β-D-galactosidase. All the divalent cations except Mg [superscript 2+], at the concentrations studied, inhibited the relative activity of β-D-galactosidase in both commercial β-D-galactosidase and environmental samples. Immobilisation of chlorophenol red β-D-galactopyranoside onto a solid support material for the development of a strip bioprobe was unsuccessful, even though the nylon support material yielded some positive results. A monthly (seasonal) variation in β-Dgalactosidase activity from the environmental water samples was observed, with the highest activity coinciding with the highest monthly temperatures. Electro-oxidative detection and/or monitoring of chlorophenol red was possible. Chlorophenol red detection was linear over a wide range of concentrations (0.001-0.01 μg ml[superscript -1]). Interference by chlorophenol red β-D-galactopyranoside in the reduction window affected analysis. A range of phthalocyanine metal complexes were studied in an attempt to reduce fouling and/or increase the sensitivity of the biosensor. The selected phthalocyanine metal complexes were generally sensitive to changes in pH with a reduction in sensitivity from acidic pH to alkaline pH. The tetrasulphonated phthalocyanine metal complex of copper was, however, more stable with a minimum change of sensitivity. The phthalocyanine metal complexes were generally stable to changes in temperature. While only two consecutive scans were possible with the unmodified glassy carbon electrode, 77 consecutive scans were performed successfully with the CuPc-modified glassy carbon electrode. Among the phthalocyanine metal complexes studied, the CuPc-modified glassy carbon electrode therefore provided excellent results for the development of a biosensor. The CuPc modified-glassy carbon electrode detected 1 colony forming unit 100 ml[superscript -1] in 15 minutes, while the plain unmodified glassy carbon electrode required 6 hours to detect the equivalent number of colony forming units. CoPc, ZnPc and CuTSPc required 2, 2.25 and 1.75 h, respectively, to detect the same numbers of colony forming units. The CuPcmodified glassy carbon electrode detected 40 colony forming units 100 ml[superscript -1] instantly. In general, a direct correlation between colony forming units and current generated in the sensor was observed (R2=0.92). A higher correlation coefficient of 0.99 for 0-30 coliform colony forming units 100 ml[superscript -1] was determined. Current was detected in some water samples which did not show any colony forming units on the media, probably due to the phenomenon of viable but non-culturable bacteria, which is the major disadvantage encountered in the use of media for detecting indicator microorganisms. This novel biosensor therefore presents a very robust and sensitive technique for the detection and/or monitoring of coliform bacterial activity in water.
- Full Text:
- Date Issued: 2008
- Authors: Wutor, Victor Collins
- Date: 2008
- Subjects: Biosensors Molecular probes Enterobacteriaceae Feces -- Microbiology Water -- Pollution -- Environmental aspects Environmental monitoring Chromogenic compounds
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3944 , http://hdl.handle.net/10962/d1004003
- Description: The ultimate objective of this work was to develop a real-time method for detecting and monitoring β-D-galactosidase as a suitable indicator of the potential presence of total coliform bacteria in water environments. Preliminary comparison of the chromogenic substrate, chlorophenol red β-D-galactopyranoside and the fluorogenic substrate, MuGAL, revealed unreliable results with the fluorogenic technique due to interference from compounds commonly found in environmental water samples. Thus, the chromogenic assay was further explored. Hydrolysis of the chromogenic substrate chlorophenol red β-D-galactopyranoside by β-D-galactosidase to yield chlorophenol red was the basis of this assay. Fundamental studies with chlorophenol red β-Dgalactopyranoside showed that β-D-galactosidase occurs extracellularly and in low concentrations in the polluted water environment. A direct correlation between enzyme activity and an increase in environmental water sample volume, as well as enzyme activity with total coliform colony forming unit counts were observed. Spectrophotometric detection was achieved within a maximum period of 24 h with a limit of detection level of 1 colony forming unit 100 ml[superscript -1]. This enzyme also exhibited physical and kinetic properties different from those of the pure commercially available β-D-galactosidase. Cell permeabilisation was not required for releasing enzymes into the extracellular environment. PEG 20 000 offered the best option for concentrating β-D-galactosidase. The source of β-D-galactosidase in the polluted environmental water samples was confirmed as Escherichia coli through SDS-PAGE, tryptic mapping and MALDI-TOF, thus justifying the further use of this method for detecting and/or monitoring total coliforms. Several compounds and metal ions commonly found in environmental water samples (as well as those used in water treatment processes) did have an effect on β-D-galactosidase. All the divalent cations except Mg [superscript 2+], at the concentrations studied, inhibited the relative activity of β-D-galactosidase in both commercial β-D-galactosidase and environmental samples. Immobilisation of chlorophenol red β-D-galactopyranoside onto a solid support material for the development of a strip bioprobe was unsuccessful, even though the nylon support material yielded some positive results. A monthly (seasonal) variation in β-Dgalactosidase activity from the environmental water samples was observed, with the highest activity coinciding with the highest monthly temperatures. Electro-oxidative detection and/or monitoring of chlorophenol red was possible. Chlorophenol red detection was linear over a wide range of concentrations (0.001-0.01 μg ml[superscript -1]). Interference by chlorophenol red β-D-galactopyranoside in the reduction window affected analysis. A range of phthalocyanine metal complexes were studied in an attempt to reduce fouling and/or increase the sensitivity of the biosensor. The selected phthalocyanine metal complexes were generally sensitive to changes in pH with a reduction in sensitivity from acidic pH to alkaline pH. The tetrasulphonated phthalocyanine metal complex of copper was, however, more stable with a minimum change of sensitivity. The phthalocyanine metal complexes were generally stable to changes in temperature. While only two consecutive scans were possible with the unmodified glassy carbon electrode, 77 consecutive scans were performed successfully with the CuPc-modified glassy carbon electrode. Among the phthalocyanine metal complexes studied, the CuPc-modified glassy carbon electrode therefore provided excellent results for the development of a biosensor. The CuPc modified-glassy carbon electrode detected 1 colony forming unit 100 ml[superscript -1] in 15 minutes, while the plain unmodified glassy carbon electrode required 6 hours to detect the equivalent number of colony forming units. CoPc, ZnPc and CuTSPc required 2, 2.25 and 1.75 h, respectively, to detect the same numbers of colony forming units. The CuPcmodified glassy carbon electrode detected 40 colony forming units 100 ml[superscript -1] instantly. In general, a direct correlation between colony forming units and current generated in the sensor was observed (R2=0.92). A higher correlation coefficient of 0.99 for 0-30 coliform colony forming units 100 ml[superscript -1] was determined. Current was detected in some water samples which did not show any colony forming units on the media, probably due to the phenomenon of viable but non-culturable bacteria, which is the major disadvantage encountered in the use of media for detecting indicator microorganisms. This novel biosensor therefore presents a very robust and sensitive technique for the detection and/or monitoring of coliform bacterial activity in water.
- Full Text:
- Date Issued: 2008
The role of discourse in the constitution of radiographic knowledge: a critical realist account
- Authors: Wright, Jennifer Lynne
- Date: 2008
- Subjects: Education, Higher -- South Africa Universities and colleges -- South Africa English language -- Study and teaching (Higher) -- South Africa Language and education Discourse analysis Radiography -- Study and teaching
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1320 , http://hdl.handle.net/10962/d1003953
- Description: The ways in which knowledge is constituted in Higher Education in South Africa today needs to take into account the historical diversity of learners’ academic and literacy competencies. The thesis begins by considering the ways in which, historically, many learners in Higher Education have been under prepared for the challenges of studying complex disciplines through the medium of English, which is often their second or third additional language. It also considers the sometimes inappropriate response of Higher Education to the plight of these learners and the present and potential role of language specialists working in collaboration with disciplinary specialists to support these learners. In this ethnographic research, I use an ontological metatheory, critical realism, as my analytical lens. Critical realism is an appropriate analytical lens for exploring and gaining insight into the possible causal mechanisms that generate the stratified and often inscrutable nature of social reality, including the role of language and discourse in education. I employ a case study design to explore the role of discourse in lecturers and clinical radiographers’ constitution of the knowledge of entry level Radiography learners at the Groote Schuur campus of Cape Peninsula University of Technology (CPUT). Taking discourse as my unit of analysis, I develop a model of knowledge constitution based on a Hallidayan framework (1978). This model comprises two contexts of culture (Higher Education and Health Care) within which are embedded two contexts of situation (the university classroom and a clinical radiography workplace). In these contexts, I focus on how lecturers and clinical radiographers constitute radiographic knowledge through the field, tenor and mode of their discourse. My research sheds light on learners’ construal of various aspects of this process of knowledge constitution, and I consider implications for Radiography teaching and learning. I conclude that, because of the dual contexts in which the learners’ knowledge is constituted, literacy requirements in the two contexts are quite different. For this reason, learners may often be unmotivated to enhance their literacies, particularly in reading and writing; yet, in the interests of the future growth of the profession, the latter will be required of them as practitioners who conduct research and publish. I argue that the real empowerment of Radiography learners thus lies in their lecturers’ agency: there is a need for them to implement certain practices that will shape the learners’ identity, not only as clinical practitioners, but as researchers and writers. In doing this, they will ensure that the learners’ potential is realised and they have the capacity to make meaningful contributions to the growth of the future radiography profession.
- Full Text:
- Date Issued: 2008
- Authors: Wright, Jennifer Lynne
- Date: 2008
- Subjects: Education, Higher -- South Africa Universities and colleges -- South Africa English language -- Study and teaching (Higher) -- South Africa Language and education Discourse analysis Radiography -- Study and teaching
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1320 , http://hdl.handle.net/10962/d1003953
- Description: The ways in which knowledge is constituted in Higher Education in South Africa today needs to take into account the historical diversity of learners’ academic and literacy competencies. The thesis begins by considering the ways in which, historically, many learners in Higher Education have been under prepared for the challenges of studying complex disciplines through the medium of English, which is often their second or third additional language. It also considers the sometimes inappropriate response of Higher Education to the plight of these learners and the present and potential role of language specialists working in collaboration with disciplinary specialists to support these learners. In this ethnographic research, I use an ontological metatheory, critical realism, as my analytical lens. Critical realism is an appropriate analytical lens for exploring and gaining insight into the possible causal mechanisms that generate the stratified and often inscrutable nature of social reality, including the role of language and discourse in education. I employ a case study design to explore the role of discourse in lecturers and clinical radiographers’ constitution of the knowledge of entry level Radiography learners at the Groote Schuur campus of Cape Peninsula University of Technology (CPUT). Taking discourse as my unit of analysis, I develop a model of knowledge constitution based on a Hallidayan framework (1978). This model comprises two contexts of culture (Higher Education and Health Care) within which are embedded two contexts of situation (the university classroom and a clinical radiography workplace). In these contexts, I focus on how lecturers and clinical radiographers constitute radiographic knowledge through the field, tenor and mode of their discourse. My research sheds light on learners’ construal of various aspects of this process of knowledge constitution, and I consider implications for Radiography teaching and learning. I conclude that, because of the dual contexts in which the learners’ knowledge is constituted, literacy requirements in the two contexts are quite different. For this reason, learners may often be unmotivated to enhance their literacies, particularly in reading and writing; yet, in the interests of the future growth of the profession, the latter will be required of them as practitioners who conduct research and publish. I argue that the real empowerment of Radiography learners thus lies in their lecturers’ agency: there is a need for them to implement certain practices that will shape the learners’ identity, not only as clinical practitioners, but as researchers and writers. In doing this, they will ensure that the learners’ potential is realised and they have the capacity to make meaningful contributions to the growth of the future radiography profession.
- Full Text:
- Date Issued: 2008
The effect of restricted environments on selected postural, physiological and perceptual responses
- Authors: Wolfe, Amy
- Date: 2008
- Subjects: Human engineering , Posture , Human mechanics , Work environment , Human beings -- Effect of environment on , Musculoskeletal system -- Wounds and injuries , Industrial safety , Work -- Physiological aspects , Stress (Physiology)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5115 , http://hdl.handle.net/10962/d1005193 , Human engineering , Posture , Human mechanics , Work environment , Human beings -- Effect of environment on , Musculoskeletal system -- Wounds and injuries , Industrial safety , Work -- Physiological aspects , Stress (Physiology)
- Description: Manual lifting tasks are the predominant means of transporting materials in industry with many of these tasks being performed in confined spaces. Research has tended to focus on the biomechanical implications of working in small spaces with a decided lack of information about the physiological and perceptual responses in these environments. This holistic study therefore investigated the manner in which the human operator responded to conditions where the ceiling height was lowered and reach demands increased. Thirty-two young physically active male subjects (age: 21.55yr; stature: 1810mm) were recruited to complete a 2-way repeated measures experiment during which four lifting protocols where different combinations of ceiling height (‘normal’ or reduced to 1460mm in height) and reach demands (400mm or 800mm) were tested. A crude postural analysis was conducted while physiological responses were detailed and continuously monitored. Perceptual responses were also assessed. The tasks with a ‘normal’ ceiling height (mean compression forces: 2615N; mean shearing forces: 388N) and the greatest reach distance (mean compression forces: 3655N; mean shearing forces: 386N) placed individuals under the highest strain. Mean heart rate (HR) responses were significantly lower (p < 0.05) in the URN condition when compared to the RF condition. Furthermore, HR responses were statistically significantly affected by the height of the ceiling and the reach depth. Statistically significant differences (p< 0.05) in mean tidal volume (VT) occurred in the least (URN) and most (RF) restrictive conditions. Statistically significant differences (p < 0.05) in mean VE were evident between URN and URF, between URN and RF and between RN and RF. Ceiling height and reach demands had a statistically significant effect on all respiratory responses. There was a statistically significant difference in mean oxygen consumption (VO2) between the URN and all other conditions, and between the most restricted task (RF) and all other conditions. Both the effect of ceiling height and reach demands had a statistically statistically significant impact on VO2. Respiratory quotient (RQ) was significantly higher when loads were moved over 800mm compared to 400mm yet ceiling height did not have a statistically significant effect on RQ. Mean energy expenditure was significantly higher in the RF condition compared to the two least restrictive conditions (URN and RN). Statistically significant differences in EE were also evident between URN and RN, and between URN and URF. EE was significantly affected by reductions in ceiling height and increases in reach demands. Perceptually, the RF task (mean ‘Central’ RPE of 11) was perceived to place significantly greater cardiorespiratory demands on the operator compared to the URN (CRPE: 10) and RN (CRPE: 10) conditions. Statistically significant differences in perceived musculoskeletal strain only occurred between URN and RF. The effect of reach was perceived to have a statistically significant effect on both cardiovascular and musculoskeletal demands whereas ceiling height only had a statistically significant effect on musculoskeletal demands. The greatest discomfort was experienced in the lower back with the most intense discomfort occurring in the RN condition.
- Full Text:
- Date Issued: 2008
- Authors: Wolfe, Amy
- Date: 2008
- Subjects: Human engineering , Posture , Human mechanics , Work environment , Human beings -- Effect of environment on , Musculoskeletal system -- Wounds and injuries , Industrial safety , Work -- Physiological aspects , Stress (Physiology)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5115 , http://hdl.handle.net/10962/d1005193 , Human engineering , Posture , Human mechanics , Work environment , Human beings -- Effect of environment on , Musculoskeletal system -- Wounds and injuries , Industrial safety , Work -- Physiological aspects , Stress (Physiology)
- Description: Manual lifting tasks are the predominant means of transporting materials in industry with many of these tasks being performed in confined spaces. Research has tended to focus on the biomechanical implications of working in small spaces with a decided lack of information about the physiological and perceptual responses in these environments. This holistic study therefore investigated the manner in which the human operator responded to conditions where the ceiling height was lowered and reach demands increased. Thirty-two young physically active male subjects (age: 21.55yr; stature: 1810mm) were recruited to complete a 2-way repeated measures experiment during which four lifting protocols where different combinations of ceiling height (‘normal’ or reduced to 1460mm in height) and reach demands (400mm or 800mm) were tested. A crude postural analysis was conducted while physiological responses were detailed and continuously monitored. Perceptual responses were also assessed. The tasks with a ‘normal’ ceiling height (mean compression forces: 2615N; mean shearing forces: 388N) and the greatest reach distance (mean compression forces: 3655N; mean shearing forces: 386N) placed individuals under the highest strain. Mean heart rate (HR) responses were significantly lower (p < 0.05) in the URN condition when compared to the RF condition. Furthermore, HR responses were statistically significantly affected by the height of the ceiling and the reach depth. Statistically significant differences (p< 0.05) in mean tidal volume (VT) occurred in the least (URN) and most (RF) restrictive conditions. Statistically significant differences (p < 0.05) in mean VE were evident between URN and URF, between URN and RF and between RN and RF. Ceiling height and reach demands had a statistically significant effect on all respiratory responses. There was a statistically significant difference in mean oxygen consumption (VO2) between the URN and all other conditions, and between the most restricted task (RF) and all other conditions. Both the effect of ceiling height and reach demands had a statistically statistically significant impact on VO2. Respiratory quotient (RQ) was significantly higher when loads were moved over 800mm compared to 400mm yet ceiling height did not have a statistically significant effect on RQ. Mean energy expenditure was significantly higher in the RF condition compared to the two least restrictive conditions (URN and RN). Statistically significant differences in EE were also evident between URN and RN, and between URN and URF. EE was significantly affected by reductions in ceiling height and increases in reach demands. Perceptually, the RF task (mean ‘Central’ RPE of 11) was perceived to place significantly greater cardiorespiratory demands on the operator compared to the URN (CRPE: 10) and RN (CRPE: 10) conditions. Statistically significant differences in perceived musculoskeletal strain only occurred between URN and RF. The effect of reach was perceived to have a statistically significant effect on both cardiovascular and musculoskeletal demands whereas ceiling height only had a statistically significant effect on musculoskeletal demands. The greatest discomfort was experienced in the lower back with the most intense discomfort occurring in the RN condition.
- Full Text:
- Date Issued: 2008
Barriers and drivers to the implementation of the "clean development mechanism" within the Nelson Mandela Bay Municipality: a case study
- Authors: Wilson, Craig Michael
- Date: 2008
- Subjects: Nelson Mandela Metropolitan Municipality (Eastern Cape, South Africa) Local government -- South Africa -- Eastern Cape -- Case studies Climatic changes -- South Africa -- Eastern Cape -- Case studies Greenhouse gases -- Environmental aspects -- South Africa -- Eastern Cape -- Case studies Environmental economics -- South Africa -- Eastern Cape -- Case studies Greenhouse effect, Atmospheric Global warming
- Language: English
- Type: Thesis , Masters , MBA
- Identifier: vital:731 , http://hdl.handle.net/10962/d1003851
- Description: The global threat of climate change is one of the most crucial environmental issues facing the world in modern times. In response to this threat, international governments have drafted the Kyoto Protocol which included the Clean Development Mechanism (CDM). The CDM is a scheme which invited developing countries, like South Africa, to become involved in climate change mitigation projects. While South Africa has been identified as an attractive host country for CDM projects, research has revealed that it lags behind other developing countries in this regard. This study provides a theoretical background to the CDM and grounds the subject within the field of Environmental Economics. Following a literature review of factors that could influence the involvement of a municipality in CDM projects, this thesis undertook a case study of the barriers and drivers to CDM implementation within the Nelson Mandela Bay Municipality (NMBM). Use was made of semi-structured interviews, where a questionnaire was used to guide the researcher’s interview process. Five NMBM officers, who were likely to have been involved with CDM project implementation, were interviewed. Data collected was analyzed using a coding technique and was compared and contrasted to the literature in a process of explanation building. It was possible to elicit 14 factors that acted as CDM-barriers; seven that acted as CDM-drivers; and 10 that were required to change within the NMBM to encourage greater CDM involvement. Of the barriers, lack of awareness, poor political will and lack of funding emerged as the most inhibiting. Of the CDM-drivers, the potential financial benefits; ownership of infrastructure capable of producing carbon assets; and technology transfer emerged as the factors most likely to promote CDM involvement. With regards the factors that require change, it emerged that a positive response would result from a proactive stance by National Government on the CDM; the use of Public-Private-Partnerships to facilitate CDM projects; and improved communication and capacity building within the NMBM and the Nelson Mandela Bay business community. The main recommendation offered to the NMBM was for it to draft a Sustainable Development Policy as well as a formal sustainable development strategy to drive a coherent and consolidated approach to the Municipality’s involvement with CDM projects. Further, it was proposed that the NMBM should, lobby National Government for it to promulgate enabling legislation and a framework which would encourage CDM investment in South Africa; and engage with local business to promote the active involvement of the Nelson Mandela Bay with the implementation of CDM projects. Keywords: Global Warming, Kyoto Protocol, Clean Development Mechanism, Sustainable Development, Environmental Economics, Public Sector, Nelson Mandela Bay Municipality.
- Full Text:
- Date Issued: 2008
- Authors: Wilson, Craig Michael
- Date: 2008
- Subjects: Nelson Mandela Metropolitan Municipality (Eastern Cape, South Africa) Local government -- South Africa -- Eastern Cape -- Case studies Climatic changes -- South Africa -- Eastern Cape -- Case studies Greenhouse gases -- Environmental aspects -- South Africa -- Eastern Cape -- Case studies Environmental economics -- South Africa -- Eastern Cape -- Case studies Greenhouse effect, Atmospheric Global warming
- Language: English
- Type: Thesis , Masters , MBA
- Identifier: vital:731 , http://hdl.handle.net/10962/d1003851
- Description: The global threat of climate change is one of the most crucial environmental issues facing the world in modern times. In response to this threat, international governments have drafted the Kyoto Protocol which included the Clean Development Mechanism (CDM). The CDM is a scheme which invited developing countries, like South Africa, to become involved in climate change mitigation projects. While South Africa has been identified as an attractive host country for CDM projects, research has revealed that it lags behind other developing countries in this regard. This study provides a theoretical background to the CDM and grounds the subject within the field of Environmental Economics. Following a literature review of factors that could influence the involvement of a municipality in CDM projects, this thesis undertook a case study of the barriers and drivers to CDM implementation within the Nelson Mandela Bay Municipality (NMBM). Use was made of semi-structured interviews, where a questionnaire was used to guide the researcher’s interview process. Five NMBM officers, who were likely to have been involved with CDM project implementation, were interviewed. Data collected was analyzed using a coding technique and was compared and contrasted to the literature in a process of explanation building. It was possible to elicit 14 factors that acted as CDM-barriers; seven that acted as CDM-drivers; and 10 that were required to change within the NMBM to encourage greater CDM involvement. Of the barriers, lack of awareness, poor political will and lack of funding emerged as the most inhibiting. Of the CDM-drivers, the potential financial benefits; ownership of infrastructure capable of producing carbon assets; and technology transfer emerged as the factors most likely to promote CDM involvement. With regards the factors that require change, it emerged that a positive response would result from a proactive stance by National Government on the CDM; the use of Public-Private-Partnerships to facilitate CDM projects; and improved communication and capacity building within the NMBM and the Nelson Mandela Bay business community. The main recommendation offered to the NMBM was for it to draft a Sustainable Development Policy as well as a formal sustainable development strategy to drive a coherent and consolidated approach to the Municipality’s involvement with CDM projects. Further, it was proposed that the NMBM should, lobby National Government for it to promulgate enabling legislation and a framework which would encourage CDM investment in South Africa; and engage with local business to promote the active involvement of the Nelson Mandela Bay with the implementation of CDM projects. Keywords: Global Warming, Kyoto Protocol, Clean Development Mechanism, Sustainable Development, Environmental Economics, Public Sector, Nelson Mandela Bay Municipality.
- Full Text:
- Date Issued: 2008
Interest rate risk management : a case study of GBS Mutual Bank
- Authors: Williamson, Gareth Alan
- Date: 2008
- Subjects: GBS Mutual Bank , Interest rates -- Case studies , Interest rate risk -- Case studies , Risk management -- Case studies , Financial risk -- Case studies , Banks and banking -- Case studies
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: vital:986 , http://hdl.handle.net/10962/d1002720 , GBS Mutual Bank , Interest rates -- Case studies , Interest rate risk -- Case studies , Risk management -- Case studies , Financial risk -- Case studies , Banks and banking -- Case studies
- Description: Banks play a pivotal role in the economic growth and development of countries, primarily through the diversification of risk for both themselves and other economic agents. Interest rate risk is regarded as one of the most prominent financial risks faced by a bank. A large portion of private banks’ revenue stems from net interest income that is generated from the difference between various assets and liabilities that are held on the balance sheet. Fluctuations in the interest rate can alter a bank’s interest income and value, making interest rate risk management vital to its success. The asset and liability committee of a bank is the internal committee charged with the duty of managing the bank’s interest rate risk exposure through the use of various hedging strategies and instruments. This thesis uses a case study methodology to analyse GBS Mutual Bank interest rate risk management. Its specific business circumstances, balance sheet structure and the market conditions over a specified period are used to comment on the practicality of a variety of balance sheet positioning strategies and derivative hedging instruments. The thesis also provides recommendations for the bank’s asset and liability committee in terms of its functions and organisation. It is elucidated that the most practical balance sheet hedging strategies are a volume strategy and immunisation, while the most practical derivative hedging instruments are interest rate futures and interest rate collars. It is found that the bank has a well functioning asset and liability committee whose only encumbrance to its functionality is the inadequacy of the informational technology used to measure, control and manage its interest rate risk position. This thesis concludes by summarising the practicality of the various interest rate risk hedging alternatives available to the GBS Mutual Bank. Implementing a particular strategy or instrument depends, of course, on its asset and liability committee’s decision.
- Full Text:
- Date Issued: 2008
- Authors: Williamson, Gareth Alan
- Date: 2008
- Subjects: GBS Mutual Bank , Interest rates -- Case studies , Interest rate risk -- Case studies , Risk management -- Case studies , Financial risk -- Case studies , Banks and banking -- Case studies
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: vital:986 , http://hdl.handle.net/10962/d1002720 , GBS Mutual Bank , Interest rates -- Case studies , Interest rate risk -- Case studies , Risk management -- Case studies , Financial risk -- Case studies , Banks and banking -- Case studies
- Description: Banks play a pivotal role in the economic growth and development of countries, primarily through the diversification of risk for both themselves and other economic agents. Interest rate risk is regarded as one of the most prominent financial risks faced by a bank. A large portion of private banks’ revenue stems from net interest income that is generated from the difference between various assets and liabilities that are held on the balance sheet. Fluctuations in the interest rate can alter a bank’s interest income and value, making interest rate risk management vital to its success. The asset and liability committee of a bank is the internal committee charged with the duty of managing the bank’s interest rate risk exposure through the use of various hedging strategies and instruments. This thesis uses a case study methodology to analyse GBS Mutual Bank interest rate risk management. Its specific business circumstances, balance sheet structure and the market conditions over a specified period are used to comment on the practicality of a variety of balance sheet positioning strategies and derivative hedging instruments. The thesis also provides recommendations for the bank’s asset and liability committee in terms of its functions and organisation. It is elucidated that the most practical balance sheet hedging strategies are a volume strategy and immunisation, while the most practical derivative hedging instruments are interest rate futures and interest rate collars. It is found that the bank has a well functioning asset and liability committee whose only encumbrance to its functionality is the inadequacy of the informational technology used to measure, control and manage its interest rate risk position. This thesis concludes by summarising the practicality of the various interest rate risk hedging alternatives available to the GBS Mutual Bank. Implementing a particular strategy or instrument depends, of course, on its asset and liability committee’s decision.
- Full Text:
- Date Issued: 2008
An investigation of the educational aspirations of high school female learners
- Authors: Willemse, Anneley
- Date: 2008
- Subjects: Women -- Education Student aspirations Vocational interests High school students Sex discrimination in education Sex differences in education Teenage girls -- Education
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:1833 , http://hdl.handle.net/10962/d1004301
- Description: Researchers hold numerous perceptions of the educational aspirations and future career choices of teenage girls. Studies argue that factors such as the curriculum, teachers' and parents' attitudes, the impact of HIV/AIDS, and teenage pregnancy, influence girls' future educational and occupational hopes and dreams either positively or negatively. Other researchers claim that learners' career choice is limited by their potential and school performance. The existing literature also suggests that girls have lower self-esteem and levels of achievement than boys. This research seeks to gain insight into high school girls' perceived academic and vocational prospects. The research was carried out in an interpretive paradigm. Six secondary school female learners from one school participated in the study. Semistructured interviews were the core method of data collection, supplemented by questionnaires and a focus group interview. As teenagers, the girls were expected to already have started to think about their future hopes and dreams. The findings revealed that all the girls seemed to experience school as a place where they could acquire knowledge about what they needed to make them autonomous and successful in adult life. For them, their parents remained their major significant others. They regarded fear of poverty as a major factor motivating them to achieve their educational and vocational aspirations. Peer pressure appeared not to be a major determinant of these girls' successes in school. The girls believed that there is a relationship between their academic performance and their future vocational choice. In addition, the girls did not see boys as a threat to their climbing the ladder of success.
- Full Text:
- Date Issued: 2008
- Authors: Willemse, Anneley
- Date: 2008
- Subjects: Women -- Education Student aspirations Vocational interests High school students Sex discrimination in education Sex differences in education Teenage girls -- Education
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:1833 , http://hdl.handle.net/10962/d1004301
- Description: Researchers hold numerous perceptions of the educational aspirations and future career choices of teenage girls. Studies argue that factors such as the curriculum, teachers' and parents' attitudes, the impact of HIV/AIDS, and teenage pregnancy, influence girls' future educational and occupational hopes and dreams either positively or negatively. Other researchers claim that learners' career choice is limited by their potential and school performance. The existing literature also suggests that girls have lower self-esteem and levels of achievement than boys. This research seeks to gain insight into high school girls' perceived academic and vocational prospects. The research was carried out in an interpretive paradigm. Six secondary school female learners from one school participated in the study. Semistructured interviews were the core method of data collection, supplemented by questionnaires and a focus group interview. As teenagers, the girls were expected to already have started to think about their future hopes and dreams. The findings revealed that all the girls seemed to experience school as a place where they could acquire knowledge about what they needed to make them autonomous and successful in adult life. For them, their parents remained their major significant others. They regarded fear of poverty as a major factor motivating them to achieve their educational and vocational aspirations. Peer pressure appeared not to be a major determinant of these girls' successes in school. The girls believed that there is a relationship between their academic performance and their future vocational choice. In addition, the girls did not see boys as a threat to their climbing the ladder of success.
- Full Text:
- Date Issued: 2008
An exploratory study of Rhodes students' attitudes and perceptions towards HIV/Aids
- Authors: Weston, Robyn
- Date: 2008
- Subjects: Rhodes University -- Students Rhodes University -- Students -- Attitudes Counseling in higher education AIDS (Disease) -- Prevention -- South Africa HIV infections -- South Africa AIDS (Disease) -- Study and teaching -- South Africa HIV infections -- Study and teaching -- South Africa HIV infections -- Diagnosis -- South Africa
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:3095 , http://hdl.handle.net/10962/d1003294
- Description: The present study explores Rhodes students' perceptions and attitudes towards HIV/Aids issues. This study focuses on risk behaviour, stigmatisation, social perceptions and voluntary counselling and HIV testing (VCT). There is a lack of research on student attitudes, knowledge and behaviour at Rhodes University. It was therefore deemed pertinent to research this topic in that context. It was envisaged that the study would provide insights to be used in the formulation of improved strategies for HIV/Aids programs and education, ultimately impacting on the exponential increase of the pandemic in the Southern African region. A sample of six hundred and seventy five Rhodes University undergraduates completed a survey and its findings were interpreted in terms of relevant literature. A mixed methods approach using qualitative and quantitative methods was used. A focus group consisting of seven post-graduate students informed the development of the survey along with relevant literature. Four departments from the faculties of Commerce, Humanities, Science and Law were randomly sampled for the survey phase. Statistica was used to calculate descriptive statistics while the chi-square statistic was applied to examine the relationships between the variables. The findings show that the majority of students have high intention levels in planning to use preventative behaviour. However, in practise, this may not be the case. Many students feel that they belong to high or medium risk groups, as opposed to the low-risk groups. In terms of motivation levels, only sixty three percent of students are highly motivated to protect themselves from HIV/Aids and one third of respondents felt that they could not ask their partner to accompany them for an HIV/Aids test. In addition, students who had received VCT were more likely to be positive about the counselling process.
- Full Text:
- Date Issued: 2008
- Authors: Weston, Robyn
- Date: 2008
- Subjects: Rhodes University -- Students Rhodes University -- Students -- Attitudes Counseling in higher education AIDS (Disease) -- Prevention -- South Africa HIV infections -- South Africa AIDS (Disease) -- Study and teaching -- South Africa HIV infections -- Study and teaching -- South Africa HIV infections -- Diagnosis -- South Africa
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:3095 , http://hdl.handle.net/10962/d1003294
- Description: The present study explores Rhodes students' perceptions and attitudes towards HIV/Aids issues. This study focuses on risk behaviour, stigmatisation, social perceptions and voluntary counselling and HIV testing (VCT). There is a lack of research on student attitudes, knowledge and behaviour at Rhodes University. It was therefore deemed pertinent to research this topic in that context. It was envisaged that the study would provide insights to be used in the formulation of improved strategies for HIV/Aids programs and education, ultimately impacting on the exponential increase of the pandemic in the Southern African region. A sample of six hundred and seventy five Rhodes University undergraduates completed a survey and its findings were interpreted in terms of relevant literature. A mixed methods approach using qualitative and quantitative methods was used. A focus group consisting of seven post-graduate students informed the development of the survey along with relevant literature. Four departments from the faculties of Commerce, Humanities, Science and Law were randomly sampled for the survey phase. Statistica was used to calculate descriptive statistics while the chi-square statistic was applied to examine the relationships between the variables. The findings show that the majority of students have high intention levels in planning to use preventative behaviour. However, in practise, this may not be the case. Many students feel that they belong to high or medium risk groups, as opposed to the low-risk groups. In terms of motivation levels, only sixty three percent of students are highly motivated to protect themselves from HIV/Aids and one third of respondents felt that they could not ask their partner to accompany them for an HIV/Aids test. In addition, students who had received VCT were more likely to be positive about the counselling process.
- Full Text:
- Date Issued: 2008
The tax implications of non-resident sportspersons performing and earning an income in South Africa
- Authors: Wessels, Jacques
- Date: 2008
- Subjects: South African Revenue Service , Sports -- Taxation -- Law and legislation -- South Africa , Taxation -- Law and legislation -- South Africa , Income tax -- Law and legislation -- South Africa , Income tax -- Foreign income , Income tax -- South Africa -- Foreign income , Withholding tax -- Law and legislation -- South Africa
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: vital:893 , http://hdl.handle.net/10962/d1003719 , South African Revenue Service , Sports -- Taxation -- Law and legislation -- South Africa , Taxation -- Law and legislation -- South Africa , Income tax -- Law and legislation -- South Africa , Income tax -- Foreign income , Income tax -- South Africa -- Foreign income , Withholding tax -- Law and legislation -- South Africa
- Description: As the number of non-resident sports persons competing in South Africa increases so does the need to tax them more effectively. It was for this reason that the South African legislature decided to insert Part IlIA into the Income Tax Act which regulates the taxation of non-resident sports persons in South Africa. The new tax on foreign sports persons, which came into effect during August 2006, is a withholding tax placing the onus upon the organizer of the event to withhold the tax portion of the payment to the non-resident sportsperson and pay it over to the revenue services. The rate of taxation has been set at 15 percent on all amounts received by or accruing to a foreign sportsperson. The question which the research addressed is whether this new tax will prove to be an effective tax, both from the point of view of its equity and the administration of the tax. In order to determine the impact of the new tax, it was compared to similar taxes implemented in the United Kingdom and Australia and also to other withholding taxes levied in South Africa. The new tax was also measured against a theoretical model for effectiveness, compared to the pre-August 2006 situation and to the taxation of resident sportsmen and women, using hypothetical examples. The major shortcomings of the new withholding tax are the uncertainty with regard to the intention of the legislature on matters such as the taxation of capital income versus revenue income, the question whether payments to support staff are included in the ambit of the new tax, the taxation of the award of assets in lieu of cash payments and the definition of a resident. A further area of concern is that the rate of taxation of 15 percent appears to be too low and creates horizontal inequity between the taxation of resident and non-resident sports persons. The new tax on non-resident sports persons may have its shortcomings but, depending upon the administrative and support structures put in place to deal with it, will be an effective tax. The rate at which the tax is levied could result in a less tax being collected than before but, with the reduced administrative cost of tax collection, the effective/statutory ratio of the tax could well be much higher than it was. This is a new tax in South Africa and certain initial problems are inevitable and will undoubtedly be solved as the administrators gain experience and as the case law governing this tax develops. , KMBT_363
- Full Text:
- Date Issued: 2008
- Authors: Wessels, Jacques
- Date: 2008
- Subjects: South African Revenue Service , Sports -- Taxation -- Law and legislation -- South Africa , Taxation -- Law and legislation -- South Africa , Income tax -- Law and legislation -- South Africa , Income tax -- Foreign income , Income tax -- South Africa -- Foreign income , Withholding tax -- Law and legislation -- South Africa
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: vital:893 , http://hdl.handle.net/10962/d1003719 , South African Revenue Service , Sports -- Taxation -- Law and legislation -- South Africa , Taxation -- Law and legislation -- South Africa , Income tax -- Law and legislation -- South Africa , Income tax -- Foreign income , Income tax -- South Africa -- Foreign income , Withholding tax -- Law and legislation -- South Africa
- Description: As the number of non-resident sports persons competing in South Africa increases so does the need to tax them more effectively. It was for this reason that the South African legislature decided to insert Part IlIA into the Income Tax Act which regulates the taxation of non-resident sports persons in South Africa. The new tax on foreign sports persons, which came into effect during August 2006, is a withholding tax placing the onus upon the organizer of the event to withhold the tax portion of the payment to the non-resident sportsperson and pay it over to the revenue services. The rate of taxation has been set at 15 percent on all amounts received by or accruing to a foreign sportsperson. The question which the research addressed is whether this new tax will prove to be an effective tax, both from the point of view of its equity and the administration of the tax. In order to determine the impact of the new tax, it was compared to similar taxes implemented in the United Kingdom and Australia and also to other withholding taxes levied in South Africa. The new tax was also measured against a theoretical model for effectiveness, compared to the pre-August 2006 situation and to the taxation of resident sportsmen and women, using hypothetical examples. The major shortcomings of the new withholding tax are the uncertainty with regard to the intention of the legislature on matters such as the taxation of capital income versus revenue income, the question whether payments to support staff are included in the ambit of the new tax, the taxation of the award of assets in lieu of cash payments and the definition of a resident. A further area of concern is that the rate of taxation of 15 percent appears to be too low and creates horizontal inequity between the taxation of resident and non-resident sports persons. The new tax on non-resident sports persons may have its shortcomings but, depending upon the administrative and support structures put in place to deal with it, will be an effective tax. The rate at which the tax is levied could result in a less tax being collected than before but, with the reduced administrative cost of tax collection, the effective/statutory ratio of the tax could well be much higher than it was. This is a new tax in South Africa and certain initial problems are inevitable and will undoubtedly be solved as the administrators gain experience and as the case law governing this tax develops. , KMBT_363
- Full Text:
- Date Issued: 2008
Studies in marine diterpene chemistry
- Van Wyk, Albert Wynand Wincke
- Authors: Van Wyk, Albert Wynand Wincke
- Date: 2008
- Subjects: Natural products Diterpenes Mollusks Marine metabolites Chemical oceanography
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4354 , http://hdl.handle.net/10962/d1005019
- Description: This thesis comprises both a natural product investigation and a synthetic component. The natural product investigations are presented in Chapters Two and Three. In Chapter Two the isolation and spectroscopic identification of the new isocopalane diterpene 12S,13R,14Sisocopalan- 13-ol-12,14-diacetate (2.1) and two known 3-(14S)-isocopal-12-ene-15-oyl-1- acetyl-sn-glycerol (2.2) and 3-(14S)-isocopal-12-ene-15-oyl-2-acetyl-sn-glycerol (2.3) from a single, large, unidentified sub-Antarctic nudibranch, collected near Marion Island, approximately 2000 km south of Cape Town are described. Chapter Three discusses the isolation, spectroscopic structure elucidation and anti-oesophageal cancer activity (3.1-3.4 only) of two known labdane diterpenes 6β,7α-diacetoxylabda-8,13E-dien-15-ol (3.1) and 2α,6β,7α-triacetoxylabda-8,13E-dien-15-ol (3.2) and one new 6β,7α,15-triacetoxylabda 8,13E-diene (3.3), as well as new 3α,11-dihydroxy-9,11-seco-cholest-4,7-dien-6,9-dione (3.4) and cholest 7-en-3,5,7-triol (3.5) from the endemic pulmonate mollusc, Trimusculus costatus. The absolute configuration of 3.2, and hence 3.1 and 3.3 (from biogenetic arguments) was determined through X-ray diffraction of a single crystal of the camphanate ester of 3.2. The absolute configuration of the secondary hydroxyl at C-3 of 3.4 was established using the Modified Mosher’s method. The synthetic component of the thesis commences in Chapter Four with the semi-synthesis of labdane diterpene nitriles 9α-cyano-15,16-epoxy-7β-hydroxylabda-13(16),14-dien-6-one (4.1), 9α-cyano-15,16-epoxy-7-hydroxylabda-7,13(16),14-trien-6-one (4.2) and 9α-cyano-15,16- epoxy-6β,7β dihydroxylabda-13(16),14-diene (4.3) from the terrestrial labdane diterpene, hispanolone (4.4). This work is an extension of previous synthetic studies directed towards the synthesis of T. costatus metabolites. Diterpenes 4.1-4.3 exhibited in planta activity against the economically important crop pathogens, Magnaporthea grisea and Puccinia recondita. Chapter Five describes the successful semi-synthesis of two isomeric marine molluscan labdane diterpene aldehyde metabolites, labd-13E-ene-8β-ol-15-al (5.1) and labd-13Z-ene- 8β-ol-15-al (5.2) from the commercially available, terrestrial plant derived, labdane diterpene manool (5.3). Diterpenes 5.1 and 5.2, originally isolated from the Mediterranean nudibranch,Pleurobranchaea meckelii and selected diterpenes arising from this synthesis were evaluated for their activity against an oesophageal cancer cell line (WHCO1). Chapter Six further develops the research discussed in Chapter Five, where ethyl 17-norabiet-13(15)-E-en-8β-ol- 16-oate (5.49) and ethyl 17-norabiet-13(15)-Z-en-8β-ol-16-oate (5.50) were first semisynthesized serendipitously. Based on their structural relationship to naturally occurring tricyclic diterpenes with anti-plasmodial activity, tricyclic diterpenes, 17-norpimaran-13α- ethoxy-8,16-olactone (6.6), 17-norisopimar-15-ene-8β,13β-diol (6.7), 17-norisopimarane- 8β,16-diol (6.8) and 17-norabiet-13(15)-ene-8β,16-diol (6.9) were semi-synthesized from the terrestrial labdane diterpene, 5.3, and critically evaluated for their antimalarial potential from parasite inhibition and haemolytic studies.
- Full Text:
- Date Issued: 2008
- Authors: Van Wyk, Albert Wynand Wincke
- Date: 2008
- Subjects: Natural products Diterpenes Mollusks Marine metabolites Chemical oceanography
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4354 , http://hdl.handle.net/10962/d1005019
- Description: This thesis comprises both a natural product investigation and a synthetic component. The natural product investigations are presented in Chapters Two and Three. In Chapter Two the isolation and spectroscopic identification of the new isocopalane diterpene 12S,13R,14Sisocopalan- 13-ol-12,14-diacetate (2.1) and two known 3-(14S)-isocopal-12-ene-15-oyl-1- acetyl-sn-glycerol (2.2) and 3-(14S)-isocopal-12-ene-15-oyl-2-acetyl-sn-glycerol (2.3) from a single, large, unidentified sub-Antarctic nudibranch, collected near Marion Island, approximately 2000 km south of Cape Town are described. Chapter Three discusses the isolation, spectroscopic structure elucidation and anti-oesophageal cancer activity (3.1-3.4 only) of two known labdane diterpenes 6β,7α-diacetoxylabda-8,13E-dien-15-ol (3.1) and 2α,6β,7α-triacetoxylabda-8,13E-dien-15-ol (3.2) and one new 6β,7α,15-triacetoxylabda 8,13E-diene (3.3), as well as new 3α,11-dihydroxy-9,11-seco-cholest-4,7-dien-6,9-dione (3.4) and cholest 7-en-3,5,7-triol (3.5) from the endemic pulmonate mollusc, Trimusculus costatus. The absolute configuration of 3.2, and hence 3.1 and 3.3 (from biogenetic arguments) was determined through X-ray diffraction of a single crystal of the camphanate ester of 3.2. The absolute configuration of the secondary hydroxyl at C-3 of 3.4 was established using the Modified Mosher’s method. The synthetic component of the thesis commences in Chapter Four with the semi-synthesis of labdane diterpene nitriles 9α-cyano-15,16-epoxy-7β-hydroxylabda-13(16),14-dien-6-one (4.1), 9α-cyano-15,16-epoxy-7-hydroxylabda-7,13(16),14-trien-6-one (4.2) and 9α-cyano-15,16- epoxy-6β,7β dihydroxylabda-13(16),14-diene (4.3) from the terrestrial labdane diterpene, hispanolone (4.4). This work is an extension of previous synthetic studies directed towards the synthesis of T. costatus metabolites. Diterpenes 4.1-4.3 exhibited in planta activity against the economically important crop pathogens, Magnaporthea grisea and Puccinia recondita. Chapter Five describes the successful semi-synthesis of two isomeric marine molluscan labdane diterpene aldehyde metabolites, labd-13E-ene-8β-ol-15-al (5.1) and labd-13Z-ene- 8β-ol-15-al (5.2) from the commercially available, terrestrial plant derived, labdane diterpene manool (5.3). Diterpenes 5.1 and 5.2, originally isolated from the Mediterranean nudibranch,Pleurobranchaea meckelii and selected diterpenes arising from this synthesis were evaluated for their activity against an oesophageal cancer cell line (WHCO1). Chapter Six further develops the research discussed in Chapter Five, where ethyl 17-norabiet-13(15)-E-en-8β-ol- 16-oate (5.49) and ethyl 17-norabiet-13(15)-Z-en-8β-ol-16-oate (5.50) were first semisynthesized serendipitously. Based on their structural relationship to naturally occurring tricyclic diterpenes with anti-plasmodial activity, tricyclic diterpenes, 17-norpimaran-13α- ethoxy-8,16-olactone (6.6), 17-norisopimar-15-ene-8β,13β-diol (6.7), 17-norisopimarane- 8β,16-diol (6.8) and 17-norabiet-13(15)-ene-8β,16-diol (6.9) were semi-synthesized from the terrestrial labdane diterpene, 5.3, and critically evaluated for their antimalarial potential from parasite inhibition and haemolytic studies.
- Full Text:
- Date Issued: 2008
WISC-IV performance of South African grade 7 English and Xhosa speaking children with advantaged versus disadvantaged education
- Authors: Van Tonder, Phia
- Date: 2008
- Subjects: Wechsler Intelligence Scale for Children Intelligence tests -- South Africa Educational tests and measurements -- South Africa Psychological tests -- Cross-cultural studies Educational psychology -- South Africa Language and languages -- Ability testing Educational evaluation -- South Africa Education, Elementary -- South Africa
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:3098 , http://hdl.handle.net/10962/d1003920
- Description: Research reveals that the level as well as the quality of education plays a role in the determination of an individual's intellectual capacity. Substantial differences in quality of education for black and white individuals were experienced in South Africa due to Apartheid. Compared to the traditionally white Private and Model C schools, Township/ DET schools had limited resources, as well as a separate syllabus and examination system, a situation that has not improved substantially since democratisation in 1994. Research on black South African adults with the WAIS-III has confirmed significant influences on IQ in association with exposure to either such advantaged (Private/Model C) schooling, or disadvantaged (Township/DET) schooling. However to date there has been no published research on the use of the Wechsler intelligence tests on a black South African child population similarly stratified for quality of education. Therefore, for the purposes of this study, the latest Wechsler Intelligence Scale for Children (WISC-IV) was administered to a sample of 36 Grade 7 learners between the ages of 12-13 (mean 13.01 years), stratified for quality of education to form three comparative groups. Data analyses revealed significant differences on the WISC-IV Factor Indices and Full Scale IQ with the English speaking Private/Model C school group performing the best, followed by the Xhosa speaking Private/ Model C school group, and the Xhosa speaking Township/ DET school group performing the worst. This continuum of lowering is understood to occur abreast of a continuum of decreased exposure to relatively advantaged education. These normative indications are considered to have vital implications for the use of the WISC-IV in the South African cross-cultural situation where vastly differential educational opportunities continue to exist.
- Full Text:
- Date Issued: 2008
- Authors: Van Tonder, Phia
- Date: 2008
- Subjects: Wechsler Intelligence Scale for Children Intelligence tests -- South Africa Educational tests and measurements -- South Africa Psychological tests -- Cross-cultural studies Educational psychology -- South Africa Language and languages -- Ability testing Educational evaluation -- South Africa Education, Elementary -- South Africa
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:3098 , http://hdl.handle.net/10962/d1003920
- Description: Research reveals that the level as well as the quality of education plays a role in the determination of an individual's intellectual capacity. Substantial differences in quality of education for black and white individuals were experienced in South Africa due to Apartheid. Compared to the traditionally white Private and Model C schools, Township/ DET schools had limited resources, as well as a separate syllabus and examination system, a situation that has not improved substantially since democratisation in 1994. Research on black South African adults with the WAIS-III has confirmed significant influences on IQ in association with exposure to either such advantaged (Private/Model C) schooling, or disadvantaged (Township/DET) schooling. However to date there has been no published research on the use of the Wechsler intelligence tests on a black South African child population similarly stratified for quality of education. Therefore, for the purposes of this study, the latest Wechsler Intelligence Scale for Children (WISC-IV) was administered to a sample of 36 Grade 7 learners between the ages of 12-13 (mean 13.01 years), stratified for quality of education to form three comparative groups. Data analyses revealed significant differences on the WISC-IV Factor Indices and Full Scale IQ with the English speaking Private/Model C school group performing the best, followed by the Xhosa speaking Private/ Model C school group, and the Xhosa speaking Township/ DET school group performing the worst. This continuum of lowering is understood to occur abreast of a continuum of decreased exposure to relatively advantaged education. These normative indications are considered to have vital implications for the use of the WISC-IV in the South African cross-cultural situation where vastly differential educational opportunities continue to exist.
- Full Text:
- Date Issued: 2008
The influence of organisational culture on organisational commitment at a selected local municipality
- Van Stuyvesant Meijen, Jolise
- Authors: Van Stuyvesant Meijen, Jolise
- Date: 2008
- Subjects: Local government -- South Africa , Corporate culture -- South Africa , Organizational change -- South Africa , Municipal services -- South Africa , Employee loyalty
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: vital:1172 , http://hdl.handle.net/10962/d1002788
- Description: Since 2000, local municipalities have been through a process of transformation which amalgamated a number of smaller local municipalities into larger municipalities. The amalgamation of a number of municipalities brings together an array of people, and therefore a myriad of organisational cultures are combined. The organisational culture of an organisation has an effect on the organisational commitment of its employees. A fit between the organisational culture and the employees will increase the organisational commitment of those employees and contribute towards improved service delivery. A survey conducted in South Africa indicated that the local municipalities have been delivering poor standards of service to the community; therefore there is a need to increase the service delivery within local municipalities. The importance of looking at the organisational commitment of a local municipality is because if there is commitment within the organisation, then employees will identify with their organisation and its goals, and will deliver the service more effectively and efficiently. Therefore, increasing the service delivery of local municipalities can be achieved through diagnosing the organisational commitment and organisational culture of employees within the selected municipality. The primary objective of this research was therefore to diagnose the relationship between organisational culture and the organisational commitment of employees at the selected municipality. In order to achieve this objective, a survey was conducted to canvas the opinions of respondents (N = 148) from the selected local municipality regarding their perceptions of the existing organisational culture, their preferences regarding the organisational culture within the selected municipality, and finally the organisational commitment. The main findings of this research conducted at a selected municipality can be summarised as follows: The dominant existing organisational culture is the power culture, while the dominant preferred organisational culture is the support culture; There is an organisational culture gap between the existing and preferred organisational cultures at the selected municipality; The dominant organisational commitment within the selected municipality is normative commitment; The findings pertaining to the relationship between organisational culture and organisational commitment of employees within the selected municipality can be stated as follows: The existing organisational cultures have significant effects on the organisational commitment of employees; The preferred organisational cultures do not have significant effects on the organisational commitment of employees; and The organisational culture gap does not have a significant effect on the organisational commitment of employees; The findings pertaining to the relationship between the biographical variables and the existing and preferred organisational culture, organisational commitment and the organisational culture gap can be stated as follows: There is no significant relationship between biographical variables and the existing organisational culture; There are significant relationships between the biographical variables, namely the departments in which respondents work, and the education level of respondents, and the preferred organisational culture; There are significant relationships between the biographical variables and organisational commitment; and The average organisational culture gap scores of the organisational culture scales for the biographical variables are significantly different. It can be concluded that organisational culture has a significant effect on the organisational commitment of employees within the selected municipality and therefore can affect the service delivery of the selected municipality.
- Full Text:
- Date Issued: 2008
- Authors: Van Stuyvesant Meijen, Jolise
- Date: 2008
- Subjects: Local government -- South Africa , Corporate culture -- South Africa , Organizational change -- South Africa , Municipal services -- South Africa , Employee loyalty
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: vital:1172 , http://hdl.handle.net/10962/d1002788
- Description: Since 2000, local municipalities have been through a process of transformation which amalgamated a number of smaller local municipalities into larger municipalities. The amalgamation of a number of municipalities brings together an array of people, and therefore a myriad of organisational cultures are combined. The organisational culture of an organisation has an effect on the organisational commitment of its employees. A fit between the organisational culture and the employees will increase the organisational commitment of those employees and contribute towards improved service delivery. A survey conducted in South Africa indicated that the local municipalities have been delivering poor standards of service to the community; therefore there is a need to increase the service delivery within local municipalities. The importance of looking at the organisational commitment of a local municipality is because if there is commitment within the organisation, then employees will identify with their organisation and its goals, and will deliver the service more effectively and efficiently. Therefore, increasing the service delivery of local municipalities can be achieved through diagnosing the organisational commitment and organisational culture of employees within the selected municipality. The primary objective of this research was therefore to diagnose the relationship between organisational culture and the organisational commitment of employees at the selected municipality. In order to achieve this objective, a survey was conducted to canvas the opinions of respondents (N = 148) from the selected local municipality regarding their perceptions of the existing organisational culture, their preferences regarding the organisational culture within the selected municipality, and finally the organisational commitment. The main findings of this research conducted at a selected municipality can be summarised as follows: The dominant existing organisational culture is the power culture, while the dominant preferred organisational culture is the support culture; There is an organisational culture gap between the existing and preferred organisational cultures at the selected municipality; The dominant organisational commitment within the selected municipality is normative commitment; The findings pertaining to the relationship between organisational culture and organisational commitment of employees within the selected municipality can be stated as follows: The existing organisational cultures have significant effects on the organisational commitment of employees; The preferred organisational cultures do not have significant effects on the organisational commitment of employees; and The organisational culture gap does not have a significant effect on the organisational commitment of employees; The findings pertaining to the relationship between the biographical variables and the existing and preferred organisational culture, organisational commitment and the organisational culture gap can be stated as follows: There is no significant relationship between biographical variables and the existing organisational culture; There are significant relationships between the biographical variables, namely the departments in which respondents work, and the education level of respondents, and the preferred organisational culture; There are significant relationships between the biographical variables and organisational commitment; and The average organisational culture gap scores of the organisational culture scales for the biographical variables are significantly different. It can be concluded that organisational culture has a significant effect on the organisational commitment of employees within the selected municipality and therefore can affect the service delivery of the selected municipality.
- Full Text:
- Date Issued: 2008
Newsroom convergence at the Mail & Guardian: a case study
- Authors: Van Noort, Elvira Esmeralda
- Date: 2008
- Subjects: Mail & Guardian Convergence (Telecommunication) Journalism -- Management -- South Africa Mass media -- Management -- South Africa Journalism -- Technological innovations -- South Africa Online journalism -- South Africa Broadcast journalism -- South Africa Mass media -- Ownership Digital media -- South Africa
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:3490 , http://hdl.handle.net/10962/d1002945
- Description: This case study researches newsroom convergence as a process at the Mail & Guardian newspaper and their online edition the Mail & Guardian Online. It focuses on the reporters’ and editors’ attitudes towards newsroom convergence and on cultural resistance against change; one of the major challenges in the process. With structured interviews, observations and questionnaires it was analysed that communication problems between the newsrooms, different production cycles and time management issues are other prominent difficulties. The case study furthermore provides a snapshot of the convergence phenomenon as a process in a particular South African news organisation. The outcomes could not only assist other news companies with convergence plans but also be used as a pilot study for further research on converged newsrooms in South Africa.
- Full Text:
- Date Issued: 2008
- Authors: Van Noort, Elvira Esmeralda
- Date: 2008
- Subjects: Mail & Guardian Convergence (Telecommunication) Journalism -- Management -- South Africa Mass media -- Management -- South Africa Journalism -- Technological innovations -- South Africa Online journalism -- South Africa Broadcast journalism -- South Africa Mass media -- Ownership Digital media -- South Africa
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:3490 , http://hdl.handle.net/10962/d1002945
- Description: This case study researches newsroom convergence as a process at the Mail & Guardian newspaper and their online edition the Mail & Guardian Online. It focuses on the reporters’ and editors’ attitudes towards newsroom convergence and on cultural resistance against change; one of the major challenges in the process. With structured interviews, observations and questionnaires it was analysed that communication problems between the newsrooms, different production cycles and time management issues are other prominent difficulties. The case study furthermore provides a snapshot of the convergence phenomenon as a process in a particular South African news organisation. The outcomes could not only assist other news companies with convergence plans but also be used as a pilot study for further research on converged newsrooms in South Africa.
- Full Text:
- Date Issued: 2008
A comparison of WISC-IV test performance for Afrikaans, English and Xhosa speaking South African grade 7 learners
- Authors: Van der Merwe, Adele
- Date: 2008
- Subjects: Wechsler Intelligence Scale for Children Wechsler Adult Intelligence Scale Intelligence tests -- South Africa Psychological tests -- Cross-cultural studies Educational tests and measurements -- South Africa Educational psychology -- South Africa Language and languages -- Ability testing Educational evaluation -- South Africa Education, Elementary -- South Africa
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:3076 , http://hdl.handle.net/10962/d1002585
- Description: his study builds on South African cross-cultural research which demonstrated the importance of careful stratification of multicultural/multilingual normative samples for quality of education in respect of English and African language (predominantly Xhosa) speaking adults and children tested with the WAIS-III and WISC-IV, respectively. The aim of the present study was to produce an expanded set of preliminary comparative norms on the WISC-IV for white and coloured Afrikaans, white English and black Xhosa speaking Grade 7 children, aged 12 to 13 years, stratified for advantaged versus disadvantaged education. The results of this study replicate the findings of the prior South African cross-cultural studies in respect of quality of education, as groups with advantaged private/former Model C schooling outperformed those with disadvantaged former DET or HOR township schooling. Furthermore, a downward continuum of WISC-IV IQ test performance emerged as follows: 1) white English advantaged (high average), 2) white Afrikaans advantaged and black Xhosa advantaged (average), 3) coloured Afrikaans advantaged (below average), 4) black Xhosa disadvantaged (borderline), and 5) coloured Afrikaans disadvantaged (extremely low). The present study has demonstrated that while language and ethnic variables reveal subtle effects on IQ test performance, quality of education has the most significant effect – impacting significantly on verbal performance with this effect replicated in respect of the FSIQ. Therefore caution should be exercised in interpreting test results of individuals from different language/ethnic groups, and in particular those with disadvantaged schooling, as preliminary data suggest that these individuals achieve scores which are 20 – 35 points lower than the UK standardisation.
- Full Text:
- Date Issued: 2008
- Authors: Van der Merwe, Adele
- Date: 2008
- Subjects: Wechsler Intelligence Scale for Children Wechsler Adult Intelligence Scale Intelligence tests -- South Africa Psychological tests -- Cross-cultural studies Educational tests and measurements -- South Africa Educational psychology -- South Africa Language and languages -- Ability testing Educational evaluation -- South Africa Education, Elementary -- South Africa
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:3076 , http://hdl.handle.net/10962/d1002585
- Description: his study builds on South African cross-cultural research which demonstrated the importance of careful stratification of multicultural/multilingual normative samples for quality of education in respect of English and African language (predominantly Xhosa) speaking adults and children tested with the WAIS-III and WISC-IV, respectively. The aim of the present study was to produce an expanded set of preliminary comparative norms on the WISC-IV for white and coloured Afrikaans, white English and black Xhosa speaking Grade 7 children, aged 12 to 13 years, stratified for advantaged versus disadvantaged education. The results of this study replicate the findings of the prior South African cross-cultural studies in respect of quality of education, as groups with advantaged private/former Model C schooling outperformed those with disadvantaged former DET or HOR township schooling. Furthermore, a downward continuum of WISC-IV IQ test performance emerged as follows: 1) white English advantaged (high average), 2) white Afrikaans advantaged and black Xhosa advantaged (average), 3) coloured Afrikaans advantaged (below average), 4) black Xhosa disadvantaged (borderline), and 5) coloured Afrikaans disadvantaged (extremely low). The present study has demonstrated that while language and ethnic variables reveal subtle effects on IQ test performance, quality of education has the most significant effect – impacting significantly on verbal performance with this effect replicated in respect of the FSIQ. Therefore caution should be exercised in interpreting test results of individuals from different language/ethnic groups, and in particular those with disadvantaged schooling, as preliminary data suggest that these individuals achieve scores which are 20 – 35 points lower than the UK standardisation.
- Full Text:
- Date Issued: 2008
Prototyping a peer-to-peer session initiation protocol user agent
- Authors: Tsietsi, Mosiuoa Jeremia
- Date: 2008 , 2008-03-10
- Subjects: Computer networks , Computer network protocols -- Standards , Data transmission systems -- Standards , Peer-to-peer architecture (Computer networks) , Computer network architectures
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4646 , http://hdl.handle.net/10962/d1006603 , Computer networks , Computer network protocols -- Standards , Data transmission systems -- Standards , Peer-to-peer architecture (Computer networks) , Computer network architectures
- Description: The Session Initiation Protocol (SIP) has in recent years become a popular protocol for the exchange of text, voice and video over IP networks. This thesis proposes the use of a class of structured peer to peer protocols - commonly known as Distributed Hash Tables (DHTs) - to provide a SIP overlay with services such as end-point location management and message relay, in the absence of traditional, centralised resources such as SIP proxies and registrars. A peer-to-peer layer named OverCord, which allows the interaction with any specific DHT protocol via the use of appropriate plug-ins, was designed, implemented and tested. This layer was then incorporated into a SIP user agent distributed by NIST (National Institute of Standards and Technology, USA). The modified user agent is capable of reliably establishing text, audio and video communication with similarly modified agents (peers) as well as conventional, centralized SIP overlays.
- Full Text:
- Date Issued: 2008
- Authors: Tsietsi, Mosiuoa Jeremia
- Date: 2008 , 2008-03-10
- Subjects: Computer networks , Computer network protocols -- Standards , Data transmission systems -- Standards , Peer-to-peer architecture (Computer networks) , Computer network architectures
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4646 , http://hdl.handle.net/10962/d1006603 , Computer networks , Computer network protocols -- Standards , Data transmission systems -- Standards , Peer-to-peer architecture (Computer networks) , Computer network architectures
- Description: The Session Initiation Protocol (SIP) has in recent years become a popular protocol for the exchange of text, voice and video over IP networks. This thesis proposes the use of a class of structured peer to peer protocols - commonly known as Distributed Hash Tables (DHTs) - to provide a SIP overlay with services such as end-point location management and message relay, in the absence of traditional, centralised resources such as SIP proxies and registrars. A peer-to-peer layer named OverCord, which allows the interaction with any specific DHT protocol via the use of appropriate plug-ins, was designed, implemented and tested. This layer was then incorporated into a SIP user agent distributed by NIST (National Institute of Standards and Technology, USA). The modified user agent is capable of reliably establishing text, audio and video communication with similarly modified agents (peers) as well as conventional, centralized SIP overlays.
- Full Text:
- Date Issued: 2008