A statistical evaluation and analysis of mosquito repellent combination
- Authors: Asquith, Ilse Bernadette
- Date: 2004
- Subjects: Mosquitoes -- Control , Insect baits and repellents
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10422 , http://hdl.handle.net/10948/d1015732
- Description: The present product development project was aimed at studying the synergism and/or antagonism amongst various known insect repellent actives with the view to formulating a multi-active repellent product with improved properties when compared to current single-active commercial products. Advanced statistical methods were used to identify synergism between individual active substances and to define a formulation as close as possible to the “ideal” formulation. Several mosquito repellent samples were prepared and sent to the South African Bureau of Standards (SABS) in Pretoria to test for their efficiency in repelling mosquitoes. From the results of the repellency tests of the various active combinations, three actives were identified that showed promising signs of synergism. These actives were then studied in further detail to determine their optimum combination. In addition, it was shown that when using a natural flavourant as promoter and incorporating a slow-release agent into formulations for aerosols and lotions, a product is obtained that gives comparable levels of efficiency to current commercial products, but at much reduced levels of active loading. Accelerated stability tests performed on the final combination of the three actives used in the final formulation showed no adverse reactions over a three-week study. These tests shall be repeated once the final application form (lotion, aerosol, etc) and product packing have been decided.
- Full Text:
- Date Issued: 2004
- Authors: Asquith, Ilse Bernadette
- Date: 2004
- Subjects: Mosquitoes -- Control , Insect baits and repellents
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10422 , http://hdl.handle.net/10948/d1015732
- Description: The present product development project was aimed at studying the synergism and/or antagonism amongst various known insect repellent actives with the view to formulating a multi-active repellent product with improved properties when compared to current single-active commercial products. Advanced statistical methods were used to identify synergism between individual active substances and to define a formulation as close as possible to the “ideal” formulation. Several mosquito repellent samples were prepared and sent to the South African Bureau of Standards (SABS) in Pretoria to test for their efficiency in repelling mosquitoes. From the results of the repellency tests of the various active combinations, three actives were identified that showed promising signs of synergism. These actives were then studied in further detail to determine their optimum combination. In addition, it was shown that when using a natural flavourant as promoter and incorporating a slow-release agent into formulations for aerosols and lotions, a product is obtained that gives comparable levels of efficiency to current commercial products, but at much reduced levels of active loading. Accelerated stability tests performed on the final combination of the three actives used in the final formulation showed no adverse reactions over a three-week study. These tests shall be repeated once the final application form (lotion, aerosol, etc) and product packing have been decided.
- Full Text:
- Date Issued: 2004
The application of rheological techniques in the characterization of semisolids in the pharmaceutical industry
- Authors: Jaganath, Nelesh
- Date: 2004
- Subjects: Drugs -- Dosage forms , Rheology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10128 , http://hdl.handle.net/10948/380 , Drugs -- Dosage forms , Rheology
- Description: Rheological characterization of pharmaceutical semisolids is of importance as it provides fundamental information required for the assessment of some of the final properties of a product such as viscosity, elasticity, quality and storage stability. The effect of formulation variables on product characteristics such as consistency and correlation of consumer evaluation of consistency can also be attained. (Ramachandran et al., 1999) This study focussed on using rheological techniques to fully characterize the properties of various semisolid formulations being developed or produced at a South African-based generic pharmaceutical company. Various tests were employed to characterize the semisolid dosage forms (creams and ointments), including continuous shear tests such as flow and viscosity curves and yield point measurements, oscillatory tests such as amplitude and frequency sweeps, as well as step and temperature ramp tests. A method to determine justifiable and meaningful viscosity specifications was developed, where excellent reproducibility of results were obtained when compared to the single-point viscosity determinations usually used. An evaluation as to whether rheology can be utilized as an assessment tool for product stability revealed varying results, with the oscillation-frequency sweep test displaying modest predictive capabilities. Observable differences in rheological character were found when evaluating ointment formulations exhibiting deviating quality characteristics. When analysing the effect of varying processing parameters, namely, cooling rate and mixing speed, during the manufacture of a cream, statistically significant rheological differences were obtained, while a thorough characterization of a scale-up procedure was also achieved upon analysis of various rheological properties.
- Full Text:
- Date Issued: 2004
- Authors: Jaganath, Nelesh
- Date: 2004
- Subjects: Drugs -- Dosage forms , Rheology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10128 , http://hdl.handle.net/10948/380 , Drugs -- Dosage forms , Rheology
- Description: Rheological characterization of pharmaceutical semisolids is of importance as it provides fundamental information required for the assessment of some of the final properties of a product such as viscosity, elasticity, quality and storage stability. The effect of formulation variables on product characteristics such as consistency and correlation of consumer evaluation of consistency can also be attained. (Ramachandran et al., 1999) This study focussed on using rheological techniques to fully characterize the properties of various semisolid formulations being developed or produced at a South African-based generic pharmaceutical company. Various tests were employed to characterize the semisolid dosage forms (creams and ointments), including continuous shear tests such as flow and viscosity curves and yield point measurements, oscillatory tests such as amplitude and frequency sweeps, as well as step and temperature ramp tests. A method to determine justifiable and meaningful viscosity specifications was developed, where excellent reproducibility of results were obtained when compared to the single-point viscosity determinations usually used. An evaluation as to whether rheology can be utilized as an assessment tool for product stability revealed varying results, with the oscillation-frequency sweep test displaying modest predictive capabilities. Observable differences in rheological character were found when evaluating ointment formulations exhibiting deviating quality characteristics. When analysing the effect of varying processing parameters, namely, cooling rate and mixing speed, during the manufacture of a cream, statistically significant rheological differences were obtained, while a thorough characterization of a scale-up procedure was also achieved upon analysis of various rheological properties.
- Full Text:
- Date Issued: 2004
An investigation into development of a stable aqeous suspension of Metronidazole Benzoate for oral use
- Authors: Zietsman, Sharon Lynne
- Date: 2005
- Subjects: Metronidazole -- Testing , Excipients -- South Africa -- Testing , Rheology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10158 , http://hdl.handle.net/10948/456 , Metronidazole -- Testing , Excipients -- South Africa -- Testing , Rheology -- South Africa
- Description: Metronidazole is a synthetic, nitroimidazole-derivative antibacterial and antiprotozoal agent (ed. McEvoy, 2001). It has been reported that crystallization occurs in aqueous suspensions of metronidazole benzoate, a bland-tasting prodrug of metronidazole, as a result of conversion from the anhydrous to the monohydrate form, thereby compromising the stability and clinical efficacy of the substance due to the particle size growth (Hoelgaard & Moller, 1983). A generic South African based pharmaceutical company commenced formulation of an aqueous metronidazole benzoate suspension and experienced problems with crystallization that occurred in products stored at 2 to 8 °C. This study aimed to continue development of the product in order to identify a formulation that prevents formation of the hydrate form of metronidazole benzoate and the accompanying crystal growth. A variety of metronidazole benzoate suspensions were manufactured on a laboratory scale using a number of natural and synthetic suspending agents, including magnesium aluminium silicate, povidone K90, xanthan gum and Avicel® RC-591 (microcrystalline cellulose and carboxymethylcellulose sodium), over a range of concentrations. Analytical quantification methods were developed and validated, and the physicochemical properties of the raw material and finished products were fully characterized. Rheological tests were performed in order to characterize the suspension flow properties. Real-time and accelerated stability studies and a temperature cycle study were conducted in accordance with the International Conference on Harmonization (ICH) guidelines. Conversion of metronidazole benzoate to the monohydrate form took place in suspensions containing xanthan gum 0.65 percent m/v under real-time and accelerated storage conditions. The suspensions containing Avicel® RC-591 were found to be physically and chemically stable after the temperature cycle and over the 12-week period whilst stored at 25 ºC / 60 percent RH and 5 ºC. The suspensions were chemically stable whilst stored at 40 ºC / 75 percent RH but showed sedimentation at this accelerated condition. The metronidazole benzoate contained in these products remained in the anhydrous state under all storage conditions and were consequently concluded to be the most stable formulations out of all the products analyzed in the current study. The suspending agent system consisting of microcrystalline cellulose and carboxymethylcellulose sodium thus shows promise in preventing the conversion of metronidazole benzoate from the anhydrate to the monohydrate form, thereby inhibited the subsequent increase in particle size due to crystal growth.
- Full Text:
- Date Issued: 2005
- Authors: Zietsman, Sharon Lynne
- Date: 2005
- Subjects: Metronidazole -- Testing , Excipients -- South Africa -- Testing , Rheology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10158 , http://hdl.handle.net/10948/456 , Metronidazole -- Testing , Excipients -- South Africa -- Testing , Rheology -- South Africa
- Description: Metronidazole is a synthetic, nitroimidazole-derivative antibacterial and antiprotozoal agent (ed. McEvoy, 2001). It has been reported that crystallization occurs in aqueous suspensions of metronidazole benzoate, a bland-tasting prodrug of metronidazole, as a result of conversion from the anhydrous to the monohydrate form, thereby compromising the stability and clinical efficacy of the substance due to the particle size growth (Hoelgaard & Moller, 1983). A generic South African based pharmaceutical company commenced formulation of an aqueous metronidazole benzoate suspension and experienced problems with crystallization that occurred in products stored at 2 to 8 °C. This study aimed to continue development of the product in order to identify a formulation that prevents formation of the hydrate form of metronidazole benzoate and the accompanying crystal growth. A variety of metronidazole benzoate suspensions were manufactured on a laboratory scale using a number of natural and synthetic suspending agents, including magnesium aluminium silicate, povidone K90, xanthan gum and Avicel® RC-591 (microcrystalline cellulose and carboxymethylcellulose sodium), over a range of concentrations. Analytical quantification methods were developed and validated, and the physicochemical properties of the raw material and finished products were fully characterized. Rheological tests were performed in order to characterize the suspension flow properties. Real-time and accelerated stability studies and a temperature cycle study were conducted in accordance with the International Conference on Harmonization (ICH) guidelines. Conversion of metronidazole benzoate to the monohydrate form took place in suspensions containing xanthan gum 0.65 percent m/v under real-time and accelerated storage conditions. The suspensions containing Avicel® RC-591 were found to be physically and chemically stable after the temperature cycle and over the 12-week period whilst stored at 25 ºC / 60 percent RH and 5 ºC. The suspensions were chemically stable whilst stored at 40 ºC / 75 percent RH but showed sedimentation at this accelerated condition. The metronidazole benzoate contained in these products remained in the anhydrous state under all storage conditions and were consequently concluded to be the most stable formulations out of all the products analyzed in the current study. The suspending agent system consisting of microcrystalline cellulose and carboxymethylcellulose sodium thus shows promise in preventing the conversion of metronidazole benzoate from the anhydrate to the monohydrate form, thereby inhibited the subsequent increase in particle size due to crystal growth.
- Full Text:
- Date Issued: 2005
The mining and visualisation of application services data
- Authors: Knoetze, Ronald Morgan
- Date: 2005
- Subjects: Data mining -- South Africa , Computer algorithms , Network performance (Telecommunication) -- Research -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10480 , http://hdl.handle.net/10948/451 , Data mining -- South Africa , Computer algorithms , Network performance (Telecommunication) -- Research -- South Africa
- Description: Many network monitoring tools do not provide sufficiently in-depth and useful reports on network usage, particularly in the domain of application services data. The optimisation of network performance is only possible if the networks are monitored effectively. Techniques that identify patterns of network usage can assist in the successful monitoring of network performance. The main goal of this research was to propose a model to mine and visualise application services data in order to support effective network management. To demonstrate the effectiveness of the model, a prototype, called NetPatterns, was developed using data for the Integrated Tertiary Software (ITS) application service collected by a network monitoring tool on the NMMU South Campus network. Three data mining algorithms for application services data were identified for the proposed model. The data mining algorithms used are classification (decision tree), clustering (K-Means) and association (correlation). Classifying application services data serves to categorise combinations of network attributes to highlight areas of poor network performance. The clustering of network attributes serves to indicate sparse and dense regions within the application services data. Association indicates the existence of any interesting relationships between different network attributes. Three visualisation techniques were selected to visualise the results of the data mining algorithms. The visualisation techniques selected were the organisation chart, bubble chart and scatterplots. Colour and a variety of other visual cues are used to complement the selected visualisation techniques. The effectiveness and usefulness of NetPatterns was determined by means of user testing. The results of the evaluation clearly show that the participants were highly satisfied with the visualisation of network usage presented by NetPatterns. All participants successfully completed the prescribed tasks and indicated that NetPatterns is a useful tool for the analysis of network usage patterns.
- Full Text:
- Date Issued: 2005
- Authors: Knoetze, Ronald Morgan
- Date: 2005
- Subjects: Data mining -- South Africa , Computer algorithms , Network performance (Telecommunication) -- Research -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10480 , http://hdl.handle.net/10948/451 , Data mining -- South Africa , Computer algorithms , Network performance (Telecommunication) -- Research -- South Africa
- Description: Many network monitoring tools do not provide sufficiently in-depth and useful reports on network usage, particularly in the domain of application services data. The optimisation of network performance is only possible if the networks are monitored effectively. Techniques that identify patterns of network usage can assist in the successful monitoring of network performance. The main goal of this research was to propose a model to mine and visualise application services data in order to support effective network management. To demonstrate the effectiveness of the model, a prototype, called NetPatterns, was developed using data for the Integrated Tertiary Software (ITS) application service collected by a network monitoring tool on the NMMU South Campus network. Three data mining algorithms for application services data were identified for the proposed model. The data mining algorithms used are classification (decision tree), clustering (K-Means) and association (correlation). Classifying application services data serves to categorise combinations of network attributes to highlight areas of poor network performance. The clustering of network attributes serves to indicate sparse and dense regions within the application services data. Association indicates the existence of any interesting relationships between different network attributes. Three visualisation techniques were selected to visualise the results of the data mining algorithms. The visualisation techniques selected were the organisation chart, bubble chart and scatterplots. Colour and a variety of other visual cues are used to complement the selected visualisation techniques. The effectiveness and usefulness of NetPatterns was determined by means of user testing. The results of the evaluation clearly show that the participants were highly satisfied with the visualisation of network usage presented by NetPatterns. All participants successfully completed the prescribed tasks and indicated that NetPatterns is a useful tool for the analysis of network usage patterns.
- Full Text:
- Date Issued: 2005
Web usage mining of organisational web sites
- Authors: Oosthuizen, Craig Peter
- Date: 2005
- Subjects: Web usage mining -- South Africa , Internet users -- South Africa , Information visualization
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:9595 , http://hdl.handle.net/10948/399 , Web usage mining -- South Africa , Internet users -- South Africa , Information visualization
- Description: Web Usage Mining (WUM) can be used to determine whether the information architecture of a web site is structured correctly. Existing WUM tools however, do not indicate which web usage mining algorithms are used or provide effective graphical visualisations of the results obtained. WUM techniques can be used to determine typical navigation patterns of the users of organisational web sites. An organisational web site can be described as a site which has a high level of content. The Computer Science & Information Systems (CS&IS) web site at the Nelson Mandela Metropolitan University (NMMU) is an example of such a web site. The process of combining WUM and information visualisation techniques in order to discover useful information about web usage patterns is called visual web mining. The goal of this research is to discuss the development of a WUM model and a prototype, called WebPatterns, which allows the user to effectively visualise web usage patterns of an organisational web site. This will facilitate determining whether the information architecture of the CS&IS web site is structured correctly. The WUM algorithms used in WebPatterns are association rule mining and sequence analysis. The purpose of association rule mining is to discover relationships between different web pages within a web site. Sequence analysis is used to determine the longest time ordered paths that satisfy a user specified minimum frequency. A radial tree layout is used in WebPatterns to visualise the static structure of the organisational web site. The structure of the web site is laid out radially, with the home page in the middle and other pages positioned in circles at various levels around it. Colour and other visual cues are used to show the results of the WUM algorithms. User testing was used to determine the effectiveness and usefulness of WebPatterns for visualising web usage patterns. The results of the user testing clearly show that the participants were highly satisfied with the visual design and information provided by WebPatterns. All the participants also indicated that they would like to use WebPatterns in the future. Analysis of the web usage patterns presented by WebPatterns was used to determine that the information architecture of the CS&IS web site can be restructured to better facilitate information retrieval. Changes to the CS&IS web site web were suggested, included placing embedded hyperlinks on the home page to the frequently accessed sections of the web site.
- Full Text:
- Date Issued: 2005
- Authors: Oosthuizen, Craig Peter
- Date: 2005
- Subjects: Web usage mining -- South Africa , Internet users -- South Africa , Information visualization
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:9595 , http://hdl.handle.net/10948/399 , Web usage mining -- South Africa , Internet users -- South Africa , Information visualization
- Description: Web Usage Mining (WUM) can be used to determine whether the information architecture of a web site is structured correctly. Existing WUM tools however, do not indicate which web usage mining algorithms are used or provide effective graphical visualisations of the results obtained. WUM techniques can be used to determine typical navigation patterns of the users of organisational web sites. An organisational web site can be described as a site which has a high level of content. The Computer Science & Information Systems (CS&IS) web site at the Nelson Mandela Metropolitan University (NMMU) is an example of such a web site. The process of combining WUM and information visualisation techniques in order to discover useful information about web usage patterns is called visual web mining. The goal of this research is to discuss the development of a WUM model and a prototype, called WebPatterns, which allows the user to effectively visualise web usage patterns of an organisational web site. This will facilitate determining whether the information architecture of the CS&IS web site is structured correctly. The WUM algorithms used in WebPatterns are association rule mining and sequence analysis. The purpose of association rule mining is to discover relationships between different web pages within a web site. Sequence analysis is used to determine the longest time ordered paths that satisfy a user specified minimum frequency. A radial tree layout is used in WebPatterns to visualise the static structure of the organisational web site. The structure of the web site is laid out radially, with the home page in the middle and other pages positioned in circles at various levels around it. Colour and other visual cues are used to show the results of the WUM algorithms. User testing was used to determine the effectiveness and usefulness of WebPatterns for visualising web usage patterns. The results of the user testing clearly show that the participants were highly satisfied with the visual design and information provided by WebPatterns. All the participants also indicated that they would like to use WebPatterns in the future. Analysis of the web usage patterns presented by WebPatterns was used to determine that the information architecture of the CS&IS web site can be restructured to better facilitate information retrieval. Changes to the CS&IS web site web were suggested, included placing embedded hyperlinks on the home page to the frequently accessed sections of the web site.
- Full Text:
- Date Issued: 2005
A comparison framework for server virtualisation systems a case study
- Authors: Van Tonder, Martin Stephen
- Date: 2006
- Subjects: Virtual computer systems -- South Africa Case studies , Virtual storage (Computer science) -- South Africa Case studies
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10481 , http://hdl.handle.net/10948/439 , http://hdl.handle.net/10948/d1012009 , Virtual computer systems -- South Africa Case studies , Virtual storage (Computer science) -- South Africa Case studies
- Description: Recent years have seen a revival of interest in virtualisation research. Although this term has been used to refer to various systems, the focus of this research is on systems which partition a single physical server into multiple virtual servers. It is difficult for researchers and practitioners to get a clear picture of the state of the art in server virtualisation. This is due in part to the large number of systems available. Another reason is that information about virtualisation systems lacks structure, and is dispersed among multiple sources. Practitioners, such as data centre managers and systems administrators, may be familiar with virtualisation systems from a specific vendor, but generally lack a broader view of the field. This makes it difficult to make informed decisions when selecting these systems. Researchers and vendors who are developing virtualisation systems also lack a standard framework for identifying the strengths and weaknesses of their systems, compared to competing systems. It is also time-consuming for researchers who are new to the field to learn about current virtualisation systems. The purpose of this research was to develop a framework to solve these problems. The objectives of the research correspond to the applications of the framework. These include conducting comparative evaluations of server virtualisation systems, identifying strengths and weaknesses of particular virtualisation systems, specifying virtualisation system requirements to facilitate system selection, and gathering information about current virtualisation systems in a structured form. These four objectives were satisfied. The design of this framework was also guided by six framework design principles. These principles, or secondary objectives, were also met. The framework was developed based on an extensive literature study of data centres, virtualisation and current virtualisation systems. Criteria were selected through an inductive process. The feasibility of conducting evaluations using the framework was demonstrated by means of literature-based evaluations, and a practical case study. The use of the framework to facilitate virtualisation system selection was also demonstrated by means of a case study featuring the NMMU Telkom CoE data centre. This framework has a number of practical applications, ranging from the facilitation of decision-making to identifying areas for improvement in current virtualisation systems. The information resulting from evaluations using the framework is also a valuable resource for researchers who are new to the field. The literature study which forms the theoretical foundation of this work is particularly useful in this regard. A future extension to this work would be to develop a decision support system based on the framework. Another possibility is to make the framework, and evaluations, available on-line as a resource for data center managers, vendors and researchers. This would also enable other researchers to provide additional feedback, enabling the framework to be further refined
- Full Text:
- Date Issued: 2006
- Authors: Van Tonder, Martin Stephen
- Date: 2006
- Subjects: Virtual computer systems -- South Africa Case studies , Virtual storage (Computer science) -- South Africa Case studies
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10481 , http://hdl.handle.net/10948/439 , http://hdl.handle.net/10948/d1012009 , Virtual computer systems -- South Africa Case studies , Virtual storage (Computer science) -- South Africa Case studies
- Description: Recent years have seen a revival of interest in virtualisation research. Although this term has been used to refer to various systems, the focus of this research is on systems which partition a single physical server into multiple virtual servers. It is difficult for researchers and practitioners to get a clear picture of the state of the art in server virtualisation. This is due in part to the large number of systems available. Another reason is that information about virtualisation systems lacks structure, and is dispersed among multiple sources. Practitioners, such as data centre managers and systems administrators, may be familiar with virtualisation systems from a specific vendor, but generally lack a broader view of the field. This makes it difficult to make informed decisions when selecting these systems. Researchers and vendors who are developing virtualisation systems also lack a standard framework for identifying the strengths and weaknesses of their systems, compared to competing systems. It is also time-consuming for researchers who are new to the field to learn about current virtualisation systems. The purpose of this research was to develop a framework to solve these problems. The objectives of the research correspond to the applications of the framework. These include conducting comparative evaluations of server virtualisation systems, identifying strengths and weaknesses of particular virtualisation systems, specifying virtualisation system requirements to facilitate system selection, and gathering information about current virtualisation systems in a structured form. These four objectives were satisfied. The design of this framework was also guided by six framework design principles. These principles, or secondary objectives, were also met. The framework was developed based on an extensive literature study of data centres, virtualisation and current virtualisation systems. Criteria were selected through an inductive process. The feasibility of conducting evaluations using the framework was demonstrated by means of literature-based evaluations, and a practical case study. The use of the framework to facilitate virtualisation system selection was also demonstrated by means of a case study featuring the NMMU Telkom CoE data centre. This framework has a number of practical applications, ranging from the facilitation of decision-making to identifying areas for improvement in current virtualisation systems. The information resulting from evaluations using the framework is also a valuable resource for researchers who are new to the field. The literature study which forms the theoretical foundation of this work is particularly useful in this regard. A future extension to this work would be to develop a decision support system based on the framework. Another possibility is to make the framework, and evaluations, available on-line as a resource for data center managers, vendors and researchers. This would also enable other researchers to provide additional feedback, enabling the framework to be further refined
- Full Text:
- Date Issued: 2006
A Hall-effect study of as-grown and hydrogenerated n-type ZnO layers grown by MOCVD
- Somhlahlo, Nomabali Nelisiwe
- Authors: Somhlahlo, Nomabali Nelisiwe
- Date: 2006
- Subjects: Hall effect , Electric currents
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10535 , http://hdl.handle.net/10948/444 , http://hdl.handle.net/10948/d1012014 , Hall effect , Electric currents
- Description: A series of as-grown ZnO layers have been electrically characterised by the temperature dependent (20 – 300 K) Hall-effect technique. The ZnO layers were grown by metal organic chemical vapour deposition (MOCVD) on glass substrates under various growth conditions. The temperature dependent Hall-effect technique produced mobility and carrier concentration measurements. These measurements were found to be reproducible and reliable. The carrier concentration data for the layers was fitted by the charge balance equation to accurately determine the donor level and corresponding donor concentration as well as the acceptor concentration for each sample. The measured donor levels were found to vary from sample to sample and there is evidence from the results that the variations are related to the differing growth conditions of the layers. The mobility data was also fitted to establish the dominant electron scattering mechanisms in the layers. The dominant scattering mechanisms were found to vary from sample to sample. For most of the layers studied, the dominant scattering mechanism was found to be both the ionised impurity scattering at low temperatures (20 – 100 K) and grain boundary scattering at higher temperatures (100 – 300 K). The effects of exposing the ZnO layers to hydrogen plasma were also investigated by the temperature dependent Hall-effect technique. Findings indicate that hydrogen is readily incorporated in ZnO, leading always to an increased carrier concentration. It was further noted that incorporating hydrogen into ZnO in some layers increased the mobility while in other layers it caused a decrease in the mobility. The hydrogenated samples were subsequently annealed at 600 °C for 1 hour in argon ambient resulting in the carrier concentration reducing to its original value. This effect is attributed to hydrogen diffusing out of ZnO.
- Full Text:
- Date Issued: 2006
- Authors: Somhlahlo, Nomabali Nelisiwe
- Date: 2006
- Subjects: Hall effect , Electric currents
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10535 , http://hdl.handle.net/10948/444 , http://hdl.handle.net/10948/d1012014 , Hall effect , Electric currents
- Description: A series of as-grown ZnO layers have been electrically characterised by the temperature dependent (20 – 300 K) Hall-effect technique. The ZnO layers were grown by metal organic chemical vapour deposition (MOCVD) on glass substrates under various growth conditions. The temperature dependent Hall-effect technique produced mobility and carrier concentration measurements. These measurements were found to be reproducible and reliable. The carrier concentration data for the layers was fitted by the charge balance equation to accurately determine the donor level and corresponding donor concentration as well as the acceptor concentration for each sample. The measured donor levels were found to vary from sample to sample and there is evidence from the results that the variations are related to the differing growth conditions of the layers. The mobility data was also fitted to establish the dominant electron scattering mechanisms in the layers. The dominant scattering mechanisms were found to vary from sample to sample. For most of the layers studied, the dominant scattering mechanism was found to be both the ionised impurity scattering at low temperatures (20 – 100 K) and grain boundary scattering at higher temperatures (100 – 300 K). The effects of exposing the ZnO layers to hydrogen plasma were also investigated by the temperature dependent Hall-effect technique. Findings indicate that hydrogen is readily incorporated in ZnO, leading always to an increased carrier concentration. It was further noted that incorporating hydrogen into ZnO in some layers increased the mobility while in other layers it caused a decrease in the mobility. The hydrogenated samples were subsequently annealed at 600 °C for 1 hour in argon ambient resulting in the carrier concentration reducing to its original value. This effect is attributed to hydrogen diffusing out of ZnO.
- Full Text:
- Date Issued: 2006
A model for information architecture of government web sites in Southern Africa
- Authors: Bernardo, Tomás
- Date: 2006
- Subjects: Information storage and retrieval systems , Web sites -- Design , Government information -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10479 , http://hdl.handle.net/10948/459 , Information storage and retrieval systems , Web sites -- Design , Government information -- South Africa
- Description: The main purpose of this research is to investigate the Information Architecture (IA) of government web sites in Southern Africa. The government web sites of Mozambique and South Africa were selected for the purpose of this research. A further aim of this research was to derive a model for the IA of government web sites. The model was based on IA components and guidelines as well as on web site components and E-government requirements. The IA guidelines in the model were derived from general design guidelines and guidelines for government web sites. The IA guidelines in the proposed model were used to conduct an analytical and empirical evaluation of the selected sites. The selection of the sites was based on similarities in the Information and Communication Technology (ICT) strategies and policies, the annual Internet growth rates, the Internet user profiles and the Egovernment initiatives in both countries. Differences between the sites also contributed to their selection. Mozambique is one of the least developed countries in the world, while South Africa is one of the most developed countries in Africa. Heuristic evaluation was used for the analytical evaluation while questionnaires and user testing were used for the empirical evaluation. Some of the usability problems identified in the heuristic evaluation, such as incorrect organisation of information and navigation issues, were also identified in the empirical evaluation, confirming to the existence of these usability problems. The results of this research show that the IA of government web sites has an impact on user performance and satisfaction and that the proposed model can be used to design and evaluate the IA of government web sites in Southern Africa.
- Full Text:
- Date Issued: 2006
- Authors: Bernardo, Tomás
- Date: 2006
- Subjects: Information storage and retrieval systems , Web sites -- Design , Government information -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10479 , http://hdl.handle.net/10948/459 , Information storage and retrieval systems , Web sites -- Design , Government information -- South Africa
- Description: The main purpose of this research is to investigate the Information Architecture (IA) of government web sites in Southern Africa. The government web sites of Mozambique and South Africa were selected for the purpose of this research. A further aim of this research was to derive a model for the IA of government web sites. The model was based on IA components and guidelines as well as on web site components and E-government requirements. The IA guidelines in the model were derived from general design guidelines and guidelines for government web sites. The IA guidelines in the proposed model were used to conduct an analytical and empirical evaluation of the selected sites. The selection of the sites was based on similarities in the Information and Communication Technology (ICT) strategies and policies, the annual Internet growth rates, the Internet user profiles and the Egovernment initiatives in both countries. Differences between the sites also contributed to their selection. Mozambique is one of the least developed countries in the world, while South Africa is one of the most developed countries in Africa. Heuristic evaluation was used for the analytical evaluation while questionnaires and user testing were used for the empirical evaluation. Some of the usability problems identified in the heuristic evaluation, such as incorrect organisation of information and navigation issues, were also identified in the empirical evaluation, confirming to the existence of these usability problems. The results of this research show that the IA of government web sites has an impact on user performance and satisfaction and that the proposed model can be used to design and evaluate the IA of government web sites in Southern Africa.
- Full Text:
- Date Issued: 2006
A raman spectroscopy study of semiconducting thin films
- Authors: Goosen, William Edward
- Date: 2006
- Subjects: Raman spectroscopy , Semiconductor films , Thin films
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10514 , http://hdl.handle.net/10948/426 , Raman spectroscopy , Semiconductor films , Thin films
- Description: A home-built Raman system, utilizing a pseudo-backscattering geometry, was built in the Physics Department at the Nelson Mandela Metropolitan University (NMMU). The system was then used to analyse a variety of bulk and thin film semiconducting materials currently being studied in the Physics Department. Silicon wafers were exposed to hydrogen plasma. Raman analysis of hydrogen induced platelets (HIPs), resulting from hydrogen plasma treatment of silicon, is reported. ZnO layers were deposited on glass, GaAs, Si, sapphire and SiC-Si substrates by metalorganic chemical vapour deposition (MOCVD) in the Physics Department at the NMMU. It was found that the ZnO layers grown by MOCVD all exhibited a strong E2 (high) phonon mode that dominated the Raman spectra. Furthermore, the spectra lacked the A1 (LO) phonon mode which is usually associated with the O-vacancy, the Zn-interstitial, or complexes of the two, indicating that the layers were all of good quality. The influence of depositing the ZnO thin film on a 3 mm thick SiC layer was also investigated and compared with the deposition of ZnO on Si substrate, in order to reduce the lattice mismatch between ZnO and the Si substrate. The possible shift of the Raman peaks due to the residual strain in the film, if present, could not be resolved. Characterization of GaN and AlxGa1-xN produced by MOCVD at the CRHEA laboratory of the CNRS in Valbonne, France is reported. A sharp peak at 567 cm-1 corresponding to the E2 (high) mode of GaN broadens and shifts to higher wavenumbers as the aluminium content of the AlxGa1-xN is increased. The shift is accompanied by a decrease in the intensity and a broadening of this peak. The broadening was attributed to a general decrease in the quality of the layers which accompanies increased aluminium content in AlxGa1-xN.
- Full Text:
- Date Issued: 2006
- Authors: Goosen, William Edward
- Date: 2006
- Subjects: Raman spectroscopy , Semiconductor films , Thin films
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10514 , http://hdl.handle.net/10948/426 , Raman spectroscopy , Semiconductor films , Thin films
- Description: A home-built Raman system, utilizing a pseudo-backscattering geometry, was built in the Physics Department at the Nelson Mandela Metropolitan University (NMMU). The system was then used to analyse a variety of bulk and thin film semiconducting materials currently being studied in the Physics Department. Silicon wafers were exposed to hydrogen plasma. Raman analysis of hydrogen induced platelets (HIPs), resulting from hydrogen plasma treatment of silicon, is reported. ZnO layers were deposited on glass, GaAs, Si, sapphire and SiC-Si substrates by metalorganic chemical vapour deposition (MOCVD) in the Physics Department at the NMMU. It was found that the ZnO layers grown by MOCVD all exhibited a strong E2 (high) phonon mode that dominated the Raman spectra. Furthermore, the spectra lacked the A1 (LO) phonon mode which is usually associated with the O-vacancy, the Zn-interstitial, or complexes of the two, indicating that the layers were all of good quality. The influence of depositing the ZnO thin film on a 3 mm thick SiC layer was also investigated and compared with the deposition of ZnO on Si substrate, in order to reduce the lattice mismatch between ZnO and the Si substrate. The possible shift of the Raman peaks due to the residual strain in the film, if present, could not be resolved. Characterization of GaN and AlxGa1-xN produced by MOCVD at the CRHEA laboratory of the CNRS in Valbonne, France is reported. A sharp peak at 567 cm-1 corresponding to the E2 (high) mode of GaN broadens and shifts to higher wavenumbers as the aluminium content of the AlxGa1-xN is increased. The shift is accompanied by a decrease in the intensity and a broadening of this peak. The broadening was attributed to a general decrease in the quality of the layers which accompanies increased aluminium content in AlxGa1-xN.
- Full Text:
- Date Issued: 2006
A structural study of Witteberg group rocks (Cape supergroup) in the Cape fold belt, Steytlerville district, Eastern Cape
- Authors: Brunsdon, Gideon
- Date: 2006
- Subjects: Geology, Structural|zSouth Africa|zEastern Cape , Faults (Geology)|zSouth Africa|zEastern Cape , Folds (Geology)|zSouth Africa|zEastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10666 , http://hdl.handle.net/10948/d1019682
- Description: A structural study of Witteberg Group Rocks was conducted along the Soutkloof River, approximately 14 km east of Steytlerville, Eastern Cape Province of South Africa. Here a north to south geotraverse was studied in an attempt at unravelling the structural geology of the rocks belonging to the Upper Devonian to Lower Carboniferous Witteberg Group (Upper Cape Supergroup). These rocks are mostly arenaceous and include quartzite, sandstone, siltstone and shale which have been folded, faulted and metamorphosed. Thrust, normal and strike-slip faulting occur in the area. Shallow south-dipping low-angle thrust fault planes are displaced by steep south-dipping thrust planes and subordinate north-dipping backthrusts. Displacement along thrust planes is predominantly northwards. Steeply dipping thrust fault planes are often reactivated as east-west striking normal faults. Strike-slip faulting postdates all observed structural features and displaces normal and thrust fault planes. Open to tight folds are present and are mostly northvergent and often steepened or truncated by steep south-dipping thrust fault planes. South-vergent folds are related to backthrusting and post-fold faulting. The study has revealed that the current geological map and the local stratigraphy were compiled without recognising major structural features such as thrust, normal and strike-slip faulting and their (the map and currently accepted stratigraphy) validity are therefore questioned. The presence of extensive faulting suggests that the conventional stratigraphic interpretation of the Witteberg Group should be revised.
- Full Text:
- Date Issued: 2006
- Authors: Brunsdon, Gideon
- Date: 2006
- Subjects: Geology, Structural|zSouth Africa|zEastern Cape , Faults (Geology)|zSouth Africa|zEastern Cape , Folds (Geology)|zSouth Africa|zEastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10666 , http://hdl.handle.net/10948/d1019682
- Description: A structural study of Witteberg Group Rocks was conducted along the Soutkloof River, approximately 14 km east of Steytlerville, Eastern Cape Province of South Africa. Here a north to south geotraverse was studied in an attempt at unravelling the structural geology of the rocks belonging to the Upper Devonian to Lower Carboniferous Witteberg Group (Upper Cape Supergroup). These rocks are mostly arenaceous and include quartzite, sandstone, siltstone and shale which have been folded, faulted and metamorphosed. Thrust, normal and strike-slip faulting occur in the area. Shallow south-dipping low-angle thrust fault planes are displaced by steep south-dipping thrust planes and subordinate north-dipping backthrusts. Displacement along thrust planes is predominantly northwards. Steeply dipping thrust fault planes are often reactivated as east-west striking normal faults. Strike-slip faulting postdates all observed structural features and displaces normal and thrust fault planes. Open to tight folds are present and are mostly northvergent and often steepened or truncated by steep south-dipping thrust fault planes. South-vergent folds are related to backthrusting and post-fold faulting. The study has revealed that the current geological map and the local stratigraphy were compiled without recognising major structural features such as thrust, normal and strike-slip faulting and their (the map and currently accepted stratigraphy) validity are therefore questioned. The presence of extensive faulting suggests that the conventional stratigraphic interpretation of the Witteberg Group should be revised.
- Full Text:
- Date Issued: 2006
An investigation of the in vitro anticancer properties of selected platinum compounds
- Authors: Du Plessis-Stoman, Debbie
- Date: 2006
- Subjects: Antineoplastic agents , Platinum compounds , Cancer -- Immunological aspects , Cancer -- Chemotherapy
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10334 , http://hdl.handle.net/10948/498 , http://hdl.handle.net/10948/d1012002 , Antineoplastic agents , Platinum compounds , Cancer -- Immunological aspects , Cancer -- Chemotherapy
- Description: This dissertation mainly deals with some biochemical aspects regarding the efficacy of novel platinum anticancer compounds, as part of a broader study in which both chemistry and biochemistry are involved. Various novel diamine and N-S donor chelate compounds of platinum II and IV have been developed in which factors such as stereochemistry, ligand exchange rate and biocompatibility were considered as additional parameters. In the first order testing, each of these compounds was tested with reference to their “killing” potential by comparing their rate of killing, over a period of 48 hours with those of cisplatin and oxaliplatin. Some 80 compounds were tested in this way. Although only a few could be regarded as equal to or even better than cisplatin and oxaliplatin, the testing of these compounds on cancer cells provided useful knowledge for the further development of novel compounds. Four of the better compounds, namely Y9, Y14, Y16 and Lt16.2 were selected for further studies to obtain more detailed knowledge of their anticancer action, including some flow cytometric studies. In addition to the above, cisplatin resistant cells were produced for each of the three different cell lines tested, namely, HeLa, HT29 and MCF7 cancer cell lines, by intermittent and incremental exposure to cisplatin (all the cell lines tested became resistant to cisplatin). Each of the selected compounds were exposed to the cells in the same manner, in order to attempt the induction of resistance against these compounds in the three cell lines tested (i.e. whether these cells will become resistant to the various compounds). Each of these selected platinum containing compounds were subsequently tested against the “cisplatin resistant” cell lines in order to determine their efficacy against such cells. One such compound could be singled out, since cervical cancer cells (HeLa cells) do not become resistant to it. This behaviour is similar to that of oxaliplatin against cervical cancer and colon cancer (HT29) cells (oxaliplatin is the number one treatment for colon cancer at present). This compound also proved to be more active against cisplatin resistant cell lines. It was found that all the compounds induced apoptosis in the cell lines tested as well as inhibit the DNA cycle at one or more phase. Finally, an effort was made to evaluate the different compounds by comparing them with respect to their properties relating to anticancer action.
- Full Text:
- Date Issued: 2006
- Authors: Du Plessis-Stoman, Debbie
- Date: 2006
- Subjects: Antineoplastic agents , Platinum compounds , Cancer -- Immunological aspects , Cancer -- Chemotherapy
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10334 , http://hdl.handle.net/10948/498 , http://hdl.handle.net/10948/d1012002 , Antineoplastic agents , Platinum compounds , Cancer -- Immunological aspects , Cancer -- Chemotherapy
- Description: This dissertation mainly deals with some biochemical aspects regarding the efficacy of novel platinum anticancer compounds, as part of a broader study in which both chemistry and biochemistry are involved. Various novel diamine and N-S donor chelate compounds of platinum II and IV have been developed in which factors such as stereochemistry, ligand exchange rate and biocompatibility were considered as additional parameters. In the first order testing, each of these compounds was tested with reference to their “killing” potential by comparing their rate of killing, over a period of 48 hours with those of cisplatin and oxaliplatin. Some 80 compounds were tested in this way. Although only a few could be regarded as equal to or even better than cisplatin and oxaliplatin, the testing of these compounds on cancer cells provided useful knowledge for the further development of novel compounds. Four of the better compounds, namely Y9, Y14, Y16 and Lt16.2 were selected for further studies to obtain more detailed knowledge of their anticancer action, including some flow cytometric studies. In addition to the above, cisplatin resistant cells were produced for each of the three different cell lines tested, namely, HeLa, HT29 and MCF7 cancer cell lines, by intermittent and incremental exposure to cisplatin (all the cell lines tested became resistant to cisplatin). Each of the selected compounds were exposed to the cells in the same manner, in order to attempt the induction of resistance against these compounds in the three cell lines tested (i.e. whether these cells will become resistant to the various compounds). Each of these selected platinum containing compounds were subsequently tested against the “cisplatin resistant” cell lines in order to determine their efficacy against such cells. One such compound could be singled out, since cervical cancer cells (HeLa cells) do not become resistant to it. This behaviour is similar to that of oxaliplatin against cervical cancer and colon cancer (HT29) cells (oxaliplatin is the number one treatment for colon cancer at present). This compound also proved to be more active against cisplatin resistant cell lines. It was found that all the compounds induced apoptosis in the cell lines tested as well as inhibit the DNA cycle at one or more phase. Finally, an effort was made to evaluate the different compounds by comparing them with respect to their properties relating to anticancer action.
- Full Text:
- Date Issued: 2006
Cytokine signalling functions of human soluble IgE receptors in peripheral blood mononuclear cells from normal and hyper-allergic individuals and in B-lymphoblastoid and monocytic cell lines
- Authors: Askew, Sandra Lyn
- Date: 2006
- Subjects: Ligands , Cell receptors , Cellular signal transduction
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10305 , http://hdl.handle.net/10948/455 , Ligands , Cell receptors , Cellular signal transduction
- Description: CD23 is a multifunctional receptor/ligand, found in a variety of cell types, such as human peripheral blood mononuclear cells (PBMCs), B-lymphoblastoid cell lines, mast cells and basophils. It is also found on a variety of haematopoietic cell lines. As the low-affinity receptor for immunoglobulin E (IgE), CD23 plays a role in antigen-presentation and macrophage activation. As a surface molecule cleaved from the cell membrane, soluble CD23 (sCD23) can act as an adhesion molecule and a cytokine. Perturbances of such molecular interactions may lead to various diseases such as allergies and other inflammatory diseases. It has been speculated that elevated levels of sCD23 may be used to bind secreted IgE, thus preventing it from binding to membrane CD23 on haematopoietic cells, preventing B cells from being activated into IgE producing cells. Signal transduction by sCD23 is dependent on cell subsets, ligands and co-factors required for its function. sCD23 plays a direct role in inducing tumour necrosis factor alpha (TNFα), interleukin-1 alpha (IL-1α) and interleukin-1 beta (IL-1β) and soluble IL-1 receptor from activated human monocytes and PBMCs in vitro. Recombinant forms of 25 and 37 kDa human sCD23 were produced by polymerase chain reaction (PCR)-cloning into pET23a, a bacterial expression vector. The proteins were expressed and refolded, followed by purification by gel filtration chromatography. The purified proteins were biochemically characterized to ensure purity and biological activity, by observing the binding to human IgE both in enzyme-linked immunosorbant assay (ELISA) and surface plasmon resonance (SPR) spectroscopy. ELISA showed KD values of 7.23 x 10-9M and 8.12 x 10-9M for the 25 and 37 kDa proteins, respectively. These values were significantly lower than that of Hibbert et al., (2005). SPR data obtained for the 25 kDa CD23 was not of reliable quality but SPR for the 33kDa sCD23 showed a KD of 1.18 x 10-7M, close to that of Hibbert et al., (2005), J. Exp. Med, 202: 751-760. To test the therapeutic potential of the recombinant molecule, a B-lymphoblastoid cell line (Raji), a pre-monocytic cell line (U937), and PBMCs from normal and hyper-allergic individuals were used. All cells showed no change in production of cytokines. It is essential to investigate further cytokine functions and production implicated by recombinant forms of sCD23, as well as binding of sCD23 to CD21 and CD11b/c, and in vivo IgE regulation before a conclusion can be drawn as to whether recombinant sCD23 is a potential therapeutic target against allergic disease.
- Full Text:
- Date Issued: 2006
- Authors: Askew, Sandra Lyn
- Date: 2006
- Subjects: Ligands , Cell receptors , Cellular signal transduction
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10305 , http://hdl.handle.net/10948/455 , Ligands , Cell receptors , Cellular signal transduction
- Description: CD23 is a multifunctional receptor/ligand, found in a variety of cell types, such as human peripheral blood mononuclear cells (PBMCs), B-lymphoblastoid cell lines, mast cells and basophils. It is also found on a variety of haematopoietic cell lines. As the low-affinity receptor for immunoglobulin E (IgE), CD23 plays a role in antigen-presentation and macrophage activation. As a surface molecule cleaved from the cell membrane, soluble CD23 (sCD23) can act as an adhesion molecule and a cytokine. Perturbances of such molecular interactions may lead to various diseases such as allergies and other inflammatory diseases. It has been speculated that elevated levels of sCD23 may be used to bind secreted IgE, thus preventing it from binding to membrane CD23 on haematopoietic cells, preventing B cells from being activated into IgE producing cells. Signal transduction by sCD23 is dependent on cell subsets, ligands and co-factors required for its function. sCD23 plays a direct role in inducing tumour necrosis factor alpha (TNFα), interleukin-1 alpha (IL-1α) and interleukin-1 beta (IL-1β) and soluble IL-1 receptor from activated human monocytes and PBMCs in vitro. Recombinant forms of 25 and 37 kDa human sCD23 were produced by polymerase chain reaction (PCR)-cloning into pET23a, a bacterial expression vector. The proteins were expressed and refolded, followed by purification by gel filtration chromatography. The purified proteins were biochemically characterized to ensure purity and biological activity, by observing the binding to human IgE both in enzyme-linked immunosorbant assay (ELISA) and surface plasmon resonance (SPR) spectroscopy. ELISA showed KD values of 7.23 x 10-9M and 8.12 x 10-9M for the 25 and 37 kDa proteins, respectively. These values were significantly lower than that of Hibbert et al., (2005). SPR data obtained for the 25 kDa CD23 was not of reliable quality but SPR for the 33kDa sCD23 showed a KD of 1.18 x 10-7M, close to that of Hibbert et al., (2005), J. Exp. Med, 202: 751-760. To test the therapeutic potential of the recombinant molecule, a B-lymphoblastoid cell line (Raji), a pre-monocytic cell line (U937), and PBMCs from normal and hyper-allergic individuals were used. All cells showed no change in production of cytokines. It is essential to investigate further cytokine functions and production implicated by recombinant forms of sCD23, as well as binding of sCD23 to CD21 and CD11b/c, and in vivo IgE regulation before a conclusion can be drawn as to whether recombinant sCD23 is a potential therapeutic target against allergic disease.
- Full Text:
- Date Issued: 2006
Designing for maintenance
- Authors: Syce, Melvin
- Date: 2006
- Subjects: Buildings -- Maintenance -- South Africa , Buildings -- Protection -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:9670 , http://hdl.handle.net/10948/440 , http://hdl.handle.net/10948/d1011924 , Buildings -- Maintenance -- South Africa , Buildings -- Protection -- South Africa
- Description: This treatise is a study of the methodology and the thought processes followed when buildings are designed, in order to determine to what extent, if any, designers consider the need for buildings to be maintained long after they walk off site and part with the project. The concept of taking future maintenance requirements into account as part of the design process is referred to as “designing for maintenance” (DFM). It can be assumed that, from a professional perspective, designers must keep the client’s needs in mind when designing. Facilities managers face the challenge of balancing a budget with maintaining a functional building – a dream building would be a maintenance-free building. Armed with the knowledge of DFM it is hoped that future buildings will be designed in a manner that will facilitate maintenance, thereby achieving significant savings on the life cycle costing of buildings. Buys (2004) suggests that designers should adopt a more open-minded approach toward maintenance during the design stages of buildings. Maintenance, with reference to access, methods, material and funding, could benefit from this approach, with a positive effect on the life cycle costing of a building. In order of priority when starting a building project, the design process is at the top of the list. Because this process happens right at the outset of a project, it is important to address the level of maintenance awareness that goes into designing, at this stage. The research concludes that one of the methods which could have a permanent effect on designers’ awareness of DFM would be to include it in the subjects taught at schools where designers are trained. This idea was discussed with a number of lecturers in this field and they were all in favour of this approach. There is a perception that built environment practitioners and professionals such as architects and contractors in the various fields related to the built environment, often engage in their particular task as if they exist in isolation from the project as a whole and from the rest of the project team. However, it is becoming increasingly evident that all built environment aspects are interwoven and interlinked, and that all are part of a larger context. With reference to the built environment as a whole, no action or element exists in isolation from a larger web of activity. The challenge, to nurture within students an awareness of the range and interconnectedness of elements and processes that contribute to the holistic idea, rests with the educators in the design fields, because it is clear that the final impact of any project relies to a large extent on what was specified by the designers in terms of materials and construction methods. The impact of the world’s six billion inhabitants on the environment is clearly a critical issue but does little to influence the actions of most design professionals. Documented experiences should serve as valuable tools to guide designers towards making more educated decisions on building design. Built environment professionals should educate themselves about the range of issues involved in the analysis, design and production of the built environment and the interaction between these factors.
- Full Text:
- Date Issued: 2006
- Authors: Syce, Melvin
- Date: 2006
- Subjects: Buildings -- Maintenance -- South Africa , Buildings -- Protection -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:9670 , http://hdl.handle.net/10948/440 , http://hdl.handle.net/10948/d1011924 , Buildings -- Maintenance -- South Africa , Buildings -- Protection -- South Africa
- Description: This treatise is a study of the methodology and the thought processes followed when buildings are designed, in order to determine to what extent, if any, designers consider the need for buildings to be maintained long after they walk off site and part with the project. The concept of taking future maintenance requirements into account as part of the design process is referred to as “designing for maintenance” (DFM). It can be assumed that, from a professional perspective, designers must keep the client’s needs in mind when designing. Facilities managers face the challenge of balancing a budget with maintaining a functional building – a dream building would be a maintenance-free building. Armed with the knowledge of DFM it is hoped that future buildings will be designed in a manner that will facilitate maintenance, thereby achieving significant savings on the life cycle costing of buildings. Buys (2004) suggests that designers should adopt a more open-minded approach toward maintenance during the design stages of buildings. Maintenance, with reference to access, methods, material and funding, could benefit from this approach, with a positive effect on the life cycle costing of a building. In order of priority when starting a building project, the design process is at the top of the list. Because this process happens right at the outset of a project, it is important to address the level of maintenance awareness that goes into designing, at this stage. The research concludes that one of the methods which could have a permanent effect on designers’ awareness of DFM would be to include it in the subjects taught at schools where designers are trained. This idea was discussed with a number of lecturers in this field and they were all in favour of this approach. There is a perception that built environment practitioners and professionals such as architects and contractors in the various fields related to the built environment, often engage in their particular task as if they exist in isolation from the project as a whole and from the rest of the project team. However, it is becoming increasingly evident that all built environment aspects are interwoven and interlinked, and that all are part of a larger context. With reference to the built environment as a whole, no action or element exists in isolation from a larger web of activity. The challenge, to nurture within students an awareness of the range and interconnectedness of elements and processes that contribute to the holistic idea, rests with the educators in the design fields, because it is clear that the final impact of any project relies to a large extent on what was specified by the designers in terms of materials and construction methods. The impact of the world’s six billion inhabitants on the environment is clearly a critical issue but does little to influence the actions of most design professionals. Documented experiences should serve as valuable tools to guide designers towards making more educated decisions on building design. Built environment professionals should educate themselves about the range of issues involved in the analysis, design and production of the built environment and the interaction between these factors.
- Full Text:
- Date Issued: 2006
Horticultural propagation of the threatened species, Syncarpha revurvata (L.f.)B. Nord
- Authors: Swart, Pierre André
- Date: 2006
- Subjects: Horticultural crops -- Propagation , Plant propagation , Horticulture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10624 , http://hdl.handle.net/10948/613 , Horticultural crops -- Propagation , Plant propagation , Horticulture
- Description: Syncarpha recurvata (L.f.) B. Nord. (Asteraceae, Gnaphalieae) is listed as a vulnerable (intermediate priority) species. The propagation methods of achene germination, stem cuttings, air layering and micropropagation were investigated to obtain an efficient propagation method. Smoke water dilutions of 1:100, 1:50 and 1:10 significantly increased germination, with the 1:100 smoke water dilutions showing the highest germination percentage (22.4 percent). Achenes collected between August and October 2005 showed higher germination and viability than achenes collected between May and July 2006. Fifty percent of the stem cuttings and 32 percent of the airlayered branches rooted. Embryo culture was the only successful culture type out of the four attempted. Two embryos germinated and four became photosynthetic. Two of the germinated embryos also produced callus cells, a medium supplemented with 5 μM IAA may be used to test for a suitable plant regulator for organogenesis or embryogenesis. Syncarpha recurvata plants were also transplanted into pots and 60 percent survived. A growth rate of 1.466 mm y-1 was obtained from total shoot length measurements. In this study, it was found that air-layering branches of transplanted Syncarpha recurvata plants is the most efficient propagation method.
- Full Text:
- Date Issued: 2006
- Authors: Swart, Pierre André
- Date: 2006
- Subjects: Horticultural crops -- Propagation , Plant propagation , Horticulture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10624 , http://hdl.handle.net/10948/613 , Horticultural crops -- Propagation , Plant propagation , Horticulture
- Description: Syncarpha recurvata (L.f.) B. Nord. (Asteraceae, Gnaphalieae) is listed as a vulnerable (intermediate priority) species. The propagation methods of achene germination, stem cuttings, air layering and micropropagation were investigated to obtain an efficient propagation method. Smoke water dilutions of 1:100, 1:50 and 1:10 significantly increased germination, with the 1:100 smoke water dilutions showing the highest germination percentage (22.4 percent). Achenes collected between August and October 2005 showed higher germination and viability than achenes collected between May and July 2006. Fifty percent of the stem cuttings and 32 percent of the airlayered branches rooted. Embryo culture was the only successful culture type out of the four attempted. Two embryos germinated and four became photosynthetic. Two of the germinated embryos also produced callus cells, a medium supplemented with 5 μM IAA may be used to test for a suitable plant regulator for organogenesis or embryogenesis. Syncarpha recurvata plants were also transplanted into pots and 60 percent survived. A growth rate of 1.466 mm y-1 was obtained from total shoot length measurements. In this study, it was found that air-layering branches of transplanted Syncarpha recurvata plants is the most efficient propagation method.
- Full Text:
- Date Issued: 2006
Impacts of impala on subtropical thicket in the Shamwari Game Reserve, Eastern Cape
- Authors: Gerber, Johann
- Date: 2006
- Subjects: Impala -- Feeding and feeds -- South Africa -- Eastern Cape , Impala -- Habitat -- South Africa -- Eastern Cape , Savannas -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10627 , http://hdl.handle.net/10948/509 , http://hdl.handle.net/10948/d1012011 , Impala -- Feeding and feeds -- South Africa -- Eastern Cape , Impala -- Habitat -- South Africa -- Eastern Cape , Savannas -- South Africa -- Eastern Cape
- Description: Subtropical thicket supports a large variety of indigenous browsing herbivores, such as elephants, black rhino, kudu and bushbuck, but impala historically never occurred in the Eastern Cape. The aim of this study was to determine what impacts extralimital impala (Aepyceros melampus) have on subtropical thicket. The thicket of the Shamwari Game Reserve, Eastern Cape, was used for the study. To quantify the effects of impala, feeding behaviour and diet was investigated during summer and winter. Sixteen impala were also enclosed in a camp of subtropical thicket where they would be limited to feedings on thicket. Vegetation composition and structure were monitored for a period of 12 months in the enclosure. Impala followed the expected high percentage graze and a low percentage browse in thicket in summer. However, the expected was not observed during winter: at this time grazing and browsing were equally important. Field collection of feeding behaviour data showed that impala are attracted to fringes of intact bush clumps or degraded thicket. Analysis of the impala diet confirmed this, with a significantly higher percentage graze (48 percent) than browse (22 percent) during summer. However, during winter, diet analysis indicated grazing to be much higher (36 percent) than browsing (6 percent) with the impala temporarily taking advantage of nutritious grasses still present. The enclosed portion of thicket was originally at 80 percent ecological status but it showed significant changes after addition of 16 impala. Animal trails increased in number and in width, resulting in a trampling effect. Grass cover was significantly different inside the enclosure after 12 months compared to outside. The amount of available browse of the enclosed thicket was also significantly different after addition of the impala. It is concluded that impala have a negative effect on thicket, with trampling the most significant effect. Long term monitoring of the effects of extralimital impala in different types of thicket will be required to accurately quantify their direct effects on subtropical thicket in the Eastern Cape. The main aim of this study was to determine the impacts of impala on Thicket. The study showed significant impacts on Thicket as found in Shamwari, and therefore the aim of the study was achieved.
- Full Text:
- Date Issued: 2006
- Authors: Gerber, Johann
- Date: 2006
- Subjects: Impala -- Feeding and feeds -- South Africa -- Eastern Cape , Impala -- Habitat -- South Africa -- Eastern Cape , Savannas -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10627 , http://hdl.handle.net/10948/509 , http://hdl.handle.net/10948/d1012011 , Impala -- Feeding and feeds -- South Africa -- Eastern Cape , Impala -- Habitat -- South Africa -- Eastern Cape , Savannas -- South Africa -- Eastern Cape
- Description: Subtropical thicket supports a large variety of indigenous browsing herbivores, such as elephants, black rhino, kudu and bushbuck, but impala historically never occurred in the Eastern Cape. The aim of this study was to determine what impacts extralimital impala (Aepyceros melampus) have on subtropical thicket. The thicket of the Shamwari Game Reserve, Eastern Cape, was used for the study. To quantify the effects of impala, feeding behaviour and diet was investigated during summer and winter. Sixteen impala were also enclosed in a camp of subtropical thicket where they would be limited to feedings on thicket. Vegetation composition and structure were monitored for a period of 12 months in the enclosure. Impala followed the expected high percentage graze and a low percentage browse in thicket in summer. However, the expected was not observed during winter: at this time grazing and browsing were equally important. Field collection of feeding behaviour data showed that impala are attracted to fringes of intact bush clumps or degraded thicket. Analysis of the impala diet confirmed this, with a significantly higher percentage graze (48 percent) than browse (22 percent) during summer. However, during winter, diet analysis indicated grazing to be much higher (36 percent) than browsing (6 percent) with the impala temporarily taking advantage of nutritious grasses still present. The enclosed portion of thicket was originally at 80 percent ecological status but it showed significant changes after addition of 16 impala. Animal trails increased in number and in width, resulting in a trampling effect. Grass cover was significantly different inside the enclosure after 12 months compared to outside. The amount of available browse of the enclosed thicket was also significantly different after addition of the impala. It is concluded that impala have a negative effect on thicket, with trampling the most significant effect. Long term monitoring of the effects of extralimital impala in different types of thicket will be required to accurately quantify their direct effects on subtropical thicket in the Eastern Cape. The main aim of this study was to determine the impacts of impala on Thicket. The study showed significant impacts on Thicket as found in Shamwari, and therefore the aim of the study was achieved.
- Full Text:
- Date Issued: 2006
On the characterisation of copper indium diselenide based photovoltaic devices
- Authors: Thantsha, Nicolas Matome
- Date: 2006
- Subjects: Photovoltaic cells
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10536 , http://hdl.handle.net/10948/443 , Photovoltaic cells
- Description: Photovoltaic (PV) modules based on thin film systems of CuInSe2 (CIS) and its alloys on low cost substrates are promising candidates to meet the long term efficiency, reliability and manufacturing cost goals. The attention to the CIS solar cell technology is because of the high absorption coefficient of the solar cell absorber layer. Solar cells and PV modules are conventionally assessed by measuring the currentvoltage characteristic of the device. This thesis presents an assessment procedure developed capable of assessing the device parameters with reference to I-V measurements. This thesis then characterizes the performance of the CIS based solar cells and modules in conjunction with other PV modules of different technologies such as crystalline Silicon modules by analyzing the light and dark I-V measurements of the devices. The light and dark I-V characteristics of PV devices were investigated and device parameters were extracted from the I-V data. The extraction and interpretation of these device parameters has a variety of important applications. It has been proven that the device parameters can be used for quality control during production and to provide insights into the operation of the PV devices, thereby improving the efficiency of the devices. The assessment comprises light I-V measurements at standard test conditions (STC), irradiance dependence measurements, parasitic series and shunt resistances measurements and the dark I-V measurements of the PV devices. The PV modules assessed comprise different technologies, namely, thin film based modules (CIS and a-Si) and multicrystalline Si and Edged-defined Film-fed Growth Si (EFG-Si). The dark I-V measurements results showed that the EFG-Si module has acceptable shunt (900 W) and series (0.4 W) resistances, thereby leading to the higher power output depicted from the light I-V measurements. The low quality cells of a-Si module were so low that the fill factor was the smallest (43%). In addition, the dark I-V measurements results revealed that CIS modules are less dependent to temperature at high voltages.
- Full Text:
- Date Issued: 2006
- Authors: Thantsha, Nicolas Matome
- Date: 2006
- Subjects: Photovoltaic cells
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10536 , http://hdl.handle.net/10948/443 , Photovoltaic cells
- Description: Photovoltaic (PV) modules based on thin film systems of CuInSe2 (CIS) and its alloys on low cost substrates are promising candidates to meet the long term efficiency, reliability and manufacturing cost goals. The attention to the CIS solar cell technology is because of the high absorption coefficient of the solar cell absorber layer. Solar cells and PV modules are conventionally assessed by measuring the currentvoltage characteristic of the device. This thesis presents an assessment procedure developed capable of assessing the device parameters with reference to I-V measurements. This thesis then characterizes the performance of the CIS based solar cells and modules in conjunction with other PV modules of different technologies such as crystalline Silicon modules by analyzing the light and dark I-V measurements of the devices. The light and dark I-V characteristics of PV devices were investigated and device parameters were extracted from the I-V data. The extraction and interpretation of these device parameters has a variety of important applications. It has been proven that the device parameters can be used for quality control during production and to provide insights into the operation of the PV devices, thereby improving the efficiency of the devices. The assessment comprises light I-V measurements at standard test conditions (STC), irradiance dependence measurements, parasitic series and shunt resistances measurements and the dark I-V measurements of the PV devices. The PV modules assessed comprise different technologies, namely, thin film based modules (CIS and a-Si) and multicrystalline Si and Edged-defined Film-fed Growth Si (EFG-Si). The dark I-V measurements results showed that the EFG-Si module has acceptable shunt (900 W) and series (0.4 W) resistances, thereby leading to the higher power output depicted from the light I-V measurements. The low quality cells of a-Si module were so low that the fill factor was the smallest (43%). In addition, the dark I-V measurements results revealed that CIS modules are less dependent to temperature at high voltages.
- Full Text:
- Date Issued: 2006
Optimisation of an in vitro model for anti-diabetic screening
- Authors: Wilson, Gayle Pamela
- Date: 2006
- Subjects: Hypoglycemic agents , Diabetes -- Treatment -- South Africa , Materia medica, Vegetable -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10308 , http://hdl.handle.net/10948/428 , Hypoglycemic agents , Diabetes -- Treatment -- South Africa , Materia medica, Vegetable -- South Africa
- Description: The need for alternative strategies for the prevention and treatment of diabetes is growing rapidly as type II diabetes is reaching epidemic status in our society. This need was the basis for the creation of this study, as it was necessary to start looking towards medicinal plants as potential antidiabetic treatment and no comprehensive in vitro model existed. In creating a model for determining the effects of alternative traditional medicines as antidiabetic potentiates, it was necessary that two metabolic pathways, namely glucose uptake and insulin secretion, which play a significant role in glucose homeostasis, be at the centre of our investigations. The objective of this project was to optimize the methodology required to screen and ultimately determine the effectiveness of the plant extracts Kankerbos and MRC2003, as antidiabetic potentiates, through observing their effects on glucose utilisation and insulin secretion. If these medicinal plants are going to make a positive contribution to the health of type II diabetic South Africans, then the determination of their efficacy is essential. The cell lines used in this study included 3T3-L1 preadipocytes, Chang liver, C2C12 muscle and INS-1 rat pancreatic cells. Each cell line represents a different in vivo organ that is known to have an influence on glucose homeostasis in our bodies, each with its own unique metabolic pathways and mechanisms of activity, thereby making each one a vital component in the study. The positive controls for the two models were insulin and metformin (glucose utilisation) and glibenclamide (insulin secretion). Insulin was shown to provide a significant increase in the amount of glucose taken up in C2C12 muscle and Chang liver cells for acute conditions. Chronic treatments with metformin provided a significant increase in glucose utilised by Chang liver cells. Glibenclamide was an effective positive control for stimulating insulin secretion by INS-1 cells under acute conditions as there was a significant increase in the amount of insulin secreted. MRC2003 did not show any significant antidiabetic activity. Sutherlandia frutescens (Kankerbos) showed biological activities comparable to some of the more recognized antidiabetic compounds throughout the study. With regards to the glucose utilisation model, Kankerbos was seen to have both acute and chronic effects in different cell lines. In the C2C12 muscle cell line, Kankerbos significantly increased glucose uptake when they were exposed to acute conditions. Kankerbos also had a significant effect on the Chang liver cells as it was observed that under both acute and chronic conditions, this plant extract induced the uptake of glucose into these cells. With respect to the insulin secretion model involving INS-1 cells, no significant effect was seen during acute exposure with Kankerbos treatment. However during chronic exposure, an increase in insulin secretion was initiated by this plant extract. Overall, the results of this study suggest that Kankerbos has a twofold mechanism of action for its glucose-lowering effects. Given that Kankerbos is widely available in South Africa, this study was valuable as it provided an indication that Kankerbos has antidiabetic activities and could possibly be used as an alternative antidiabetic medication.
- Full Text:
- Date Issued: 2006
- Authors: Wilson, Gayle Pamela
- Date: 2006
- Subjects: Hypoglycemic agents , Diabetes -- Treatment -- South Africa , Materia medica, Vegetable -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10308 , http://hdl.handle.net/10948/428 , Hypoglycemic agents , Diabetes -- Treatment -- South Africa , Materia medica, Vegetable -- South Africa
- Description: The need for alternative strategies for the prevention and treatment of diabetes is growing rapidly as type II diabetes is reaching epidemic status in our society. This need was the basis for the creation of this study, as it was necessary to start looking towards medicinal plants as potential antidiabetic treatment and no comprehensive in vitro model existed. In creating a model for determining the effects of alternative traditional medicines as antidiabetic potentiates, it was necessary that two metabolic pathways, namely glucose uptake and insulin secretion, which play a significant role in glucose homeostasis, be at the centre of our investigations. The objective of this project was to optimize the methodology required to screen and ultimately determine the effectiveness of the plant extracts Kankerbos and MRC2003, as antidiabetic potentiates, through observing their effects on glucose utilisation and insulin secretion. If these medicinal plants are going to make a positive contribution to the health of type II diabetic South Africans, then the determination of their efficacy is essential. The cell lines used in this study included 3T3-L1 preadipocytes, Chang liver, C2C12 muscle and INS-1 rat pancreatic cells. Each cell line represents a different in vivo organ that is known to have an influence on glucose homeostasis in our bodies, each with its own unique metabolic pathways and mechanisms of activity, thereby making each one a vital component in the study. The positive controls for the two models were insulin and metformin (glucose utilisation) and glibenclamide (insulin secretion). Insulin was shown to provide a significant increase in the amount of glucose taken up in C2C12 muscle and Chang liver cells for acute conditions. Chronic treatments with metformin provided a significant increase in glucose utilised by Chang liver cells. Glibenclamide was an effective positive control for stimulating insulin secretion by INS-1 cells under acute conditions as there was a significant increase in the amount of insulin secreted. MRC2003 did not show any significant antidiabetic activity. Sutherlandia frutescens (Kankerbos) showed biological activities comparable to some of the more recognized antidiabetic compounds throughout the study. With regards to the glucose utilisation model, Kankerbos was seen to have both acute and chronic effects in different cell lines. In the C2C12 muscle cell line, Kankerbos significantly increased glucose uptake when they were exposed to acute conditions. Kankerbos also had a significant effect on the Chang liver cells as it was observed that under both acute and chronic conditions, this plant extract induced the uptake of glucose into these cells. With respect to the insulin secretion model involving INS-1 cells, no significant effect was seen during acute exposure with Kankerbos treatment. However during chronic exposure, an increase in insulin secretion was initiated by this plant extract. Overall, the results of this study suggest that Kankerbos has a twofold mechanism of action for its glucose-lowering effects. Given that Kankerbos is widely available in South Africa, this study was valuable as it provided an indication that Kankerbos has antidiabetic activities and could possibly be used as an alternative antidiabetic medication.
- Full Text:
- Date Issued: 2006
SL-model for paired comparisons
- Authors: Sjölander, Morné Rowan
- Date: 2006
- Subjects: Paired comparisons (Statistics) , Mathematical statistics
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10574 , http://hdl.handle.net/10948/605 , Paired comparisons (Statistics) , Mathematical statistics
- Description: The method of paired comparisons can be found all the way back to 1860, where Fechner made the first publication in this method, using it for his psychometric investigations [4]. Thurstone formalised the method by providing a mathematical background to it [9-11] and in 1927 the method’s birth took place with his psychometric publications, one being “a law of comparative judgment” [12-14]. The law of comparative judgment is a set of equations relating the proportion of times any stimulus k is judged greater on a given attribute than any other stimulus j to the scales and discriminal dispersions of the two stimuli on the psychological continuum. The amount of research done for discrete models of paired comparisons is not a lot. This study develops a new discrete model, the SL-model for paired comparisons. Paired comparisons data processing in which objects have an upper limit to their scores was also not yet developed, and making such a model is one of the aims of this report. The SLmodel is thus developed in this context; however, the model easily generalises to not necessarily having an upper limit on scores.
- Full Text:
- Date Issued: 2006
- Authors: Sjölander, Morné Rowan
- Date: 2006
- Subjects: Paired comparisons (Statistics) , Mathematical statistics
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10574 , http://hdl.handle.net/10948/605 , Paired comparisons (Statistics) , Mathematical statistics
- Description: The method of paired comparisons can be found all the way back to 1860, where Fechner made the first publication in this method, using it for his psychometric investigations [4]. Thurstone formalised the method by providing a mathematical background to it [9-11] and in 1927 the method’s birth took place with his psychometric publications, one being “a law of comparative judgment” [12-14]. The law of comparative judgment is a set of equations relating the proportion of times any stimulus k is judged greater on a given attribute than any other stimulus j to the scales and discriminal dispersions of the two stimuli on the psychological continuum. The amount of research done for discrete models of paired comparisons is not a lot. This study develops a new discrete model, the SL-model for paired comparisons. Paired comparisons data processing in which objects have an upper limit to their scores was also not yet developed, and making such a model is one of the aims of this report. The SLmodel is thus developed in this context; however, the model easily generalises to not necessarily having an upper limit on scores.
- Full Text:
- Date Issued: 2006
The women's health initiative study: impact on the prescribing of hormone replacement therapy in a defined South African population
- Authors: Hanly, Teia
- Date: 2006
- Subjects: Women -- Health and hygiene -- South Africa , Women's health services -- South Africa , Menopause -- Hormone therapy -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10156 , http://hdl.handle.net/10948/519 , http://hdl.handle.net/10948/d1011713 , Women -- Health and hygiene -- South Africa , Women's health services -- South Africa , Menopause -- Hormone therapy -- South Africa
- Description: Context: The Women’s Health Initiative (WHI) study, published in July 2002, had a significant impact on the prescribing of hormone replacement therapy (HRT). The controversy surrounding the findings, however, has led to much uncertainty regarding the prescription of HRT. Aims and Objectives: The aim of this study is to determine both the initial and the continued impact of the WHI study on the prescribing of HRT in a defined South African population and to determine whether HRT was appropriately individualised based on recommendations published subsequent to the WHI study. Setting: Claims data from a Managed Healthcare Organisation (MHO) that administers for a number of medical aid schemes in South Africa. Method: A retrospective drug utilisation review (DUR) was conducted to identify HRT-related prescribing patterns in the defined populations. The time-frame of the dataset included January 2002, to assess prescribing patterns prior to the publication of the WHI study, January 2003 to determine the initial impact of the WHI study, and January 2005 to assess the continued impact. An extensive, additional dataset of all the HRT users in the defined populations was utilised to conduct a sub-group analysis and determine whether HRT had been appropriately individualised. Key Findings: The percentage of patients in the dataset using HRT decreased from 30.05 percent in January 2002 to 28.30 percent in January 2003 and to 23.24 percent in January 2005, with the latter decrease reaching statistical significance. Although sex hormones and modulators (G03) of the genital system were the most frequently prescribed drug class in all three years of the study period, the prescribing frequency decreased significantly from 10.40 percent in January 2002 to 9.32 percent in January 2003 and 7.44 percent in January 2005. The most noteworthy change in the prescribing of HRT was a 3.95 percent decrease in the prescribing of conjugated equine estrogen (CEE), with a corresponding 2.53 percent increase in the prescribing of estradiol between January 2002 and January 2003. However, less pronounced changes were observed in the prescribing frequencies of other types of HRT, including medroxyprogesterone and estrogen (the HRT type investigated in the estrogen plus progestin phase of the WHI study). Patients initiating HRT post-WHI publication were generally found to be in the younger menopausal age categories (40 to 49 years). These patients were more likely to have been initiated on HRT types other than those investigated in the WHI study and were at a higher risk for disease states for which HRT use is beneficial, such as osteoporosis. Patients discontinuing HRT post-WHI publication were generally found to be in the older menopausal age categories (60 to 69 years), were more likely to have been combined HRT users (although not necessarily the type investigated in the WHI study) and were at a higher risk for disease states for which HRT use is considered harmful or has an uncertain effect, such as diseases affecting the cardiovascular system. Conclusion: It can be concluded that the WHI study did have an impact on the prescribing of HRT in the defined South African population of this study, but that the impact was considerably less than the impact reported in global studies. It was also determined that HRT was appropriately individualised according to recommendations made subsequent to publication of the WHI study.
- Full Text:
- Date Issued: 2006
- Authors: Hanly, Teia
- Date: 2006
- Subjects: Women -- Health and hygiene -- South Africa , Women's health services -- South Africa , Menopause -- Hormone therapy -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10156 , http://hdl.handle.net/10948/519 , http://hdl.handle.net/10948/d1011713 , Women -- Health and hygiene -- South Africa , Women's health services -- South Africa , Menopause -- Hormone therapy -- South Africa
- Description: Context: The Women’s Health Initiative (WHI) study, published in July 2002, had a significant impact on the prescribing of hormone replacement therapy (HRT). The controversy surrounding the findings, however, has led to much uncertainty regarding the prescription of HRT. Aims and Objectives: The aim of this study is to determine both the initial and the continued impact of the WHI study on the prescribing of HRT in a defined South African population and to determine whether HRT was appropriately individualised based on recommendations published subsequent to the WHI study. Setting: Claims data from a Managed Healthcare Organisation (MHO) that administers for a number of medical aid schemes in South Africa. Method: A retrospective drug utilisation review (DUR) was conducted to identify HRT-related prescribing patterns in the defined populations. The time-frame of the dataset included January 2002, to assess prescribing patterns prior to the publication of the WHI study, January 2003 to determine the initial impact of the WHI study, and January 2005 to assess the continued impact. An extensive, additional dataset of all the HRT users in the defined populations was utilised to conduct a sub-group analysis and determine whether HRT had been appropriately individualised. Key Findings: The percentage of patients in the dataset using HRT decreased from 30.05 percent in January 2002 to 28.30 percent in January 2003 and to 23.24 percent in January 2005, with the latter decrease reaching statistical significance. Although sex hormones and modulators (G03) of the genital system were the most frequently prescribed drug class in all three years of the study period, the prescribing frequency decreased significantly from 10.40 percent in January 2002 to 9.32 percent in January 2003 and 7.44 percent in January 2005. The most noteworthy change in the prescribing of HRT was a 3.95 percent decrease in the prescribing of conjugated equine estrogen (CEE), with a corresponding 2.53 percent increase in the prescribing of estradiol between January 2002 and January 2003. However, less pronounced changes were observed in the prescribing frequencies of other types of HRT, including medroxyprogesterone and estrogen (the HRT type investigated in the estrogen plus progestin phase of the WHI study). Patients initiating HRT post-WHI publication were generally found to be in the younger menopausal age categories (40 to 49 years). These patients were more likely to have been initiated on HRT types other than those investigated in the WHI study and were at a higher risk for disease states for which HRT use is beneficial, such as osteoporosis. Patients discontinuing HRT post-WHI publication were generally found to be in the older menopausal age categories (60 to 69 years), were more likely to have been combined HRT users (although not necessarily the type investigated in the WHI study) and were at a higher risk for disease states for which HRT use is considered harmful or has an uncertain effect, such as diseases affecting the cardiovascular system. Conclusion: It can be concluded that the WHI study did have an impact on the prescribing of HRT in the defined South African population of this study, but that the impact was considerably less than the impact reported in global studies. It was also determined that HRT was appropriately individualised according to recommendations made subsequent to publication of the WHI study.
- Full Text:
- Date Issued: 2006
A comparison of the vulcanisation of Polyisoprene by a range of Thiuram Diulfides
- Authors: Van Rooyen, Jason Leigh
- Date: 2007
- Subjects: Vulcanization , Vulcanization accelerators
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10399 , http://hdl.handle.net/10948/733 , Vulcanization , Vulcanization accelerators
- Description: This study was initiated in an attempt to investigate dithiocarbamic acid accelerated sulfur vulcanisation. This was, however, found impossible due to the innate instability of dithiocarbamic acids. The focus of the study was then shifted toward thiuram disulfide accelerated sulfur vulcanisation, with emphasis being placed on a rate comparison. Three groups of accelerators were investigated, namely the aromatic, linear aliphatic and cyclic aliphatic thiuram disulfide adducts. The analysis methods that were employed were conventional rubber (cis-1,4-polyisoprene) techniques coupled to model (squalene) compound investigations. The data that was collected consisted of rheometrical torque vs. time data in the rubber system while the data obtained in the model compound study consisted of sulfur and accelerator concentration data as determined by means of high performance liquid chromatography (HPLC). The aromatic accelerators were synthesised in our labs by means of an addition reaction between the aromatic amine and CS2 in basic medium and subsequent oxidation with K3Fe(CN)6, all in a 1:1 molar ratio. The reaction yield was low due to the instability of the dithiocarbamate intermediates and a sluggish oxidation reaction. In the rate constant determination a first order mathematical approach was used for the rubber system as crosslinking is considered to roughly obey first order kinetics. The model compound data was also found to more accurately fit the first order rate law, with an initial slopes method also being applied to the system to determine secondary rate constants and relative rates for the system. The determination of vulcanisation rate constants in the cis-1,4-polyisoprene system was a success, while the rate data determined by means of the squalene model was more related to the rate of accelerator and sulfur consumption as opposed to the rate of crosslinking as is the case with the rubber rate data. The sulfur first order rate data mirrored the rate data derived from the rubber system more closely than the corresponding accelerator rate data, the relative rate data determined by means of initial slopes method, proved that the homolytic cleavage of thiuram disulfides and the subsequent formation of accelerator polysulfides were not limiting steps. This is seen in the similar relative rate data derived from both the raw sulfur and accelerator data in systems that exhibit vastly different vulcanisation rates. Squalene was deemed a suitable model for the cis-1,4-polyisoprene system, although one should consider the extent of charring and solution effects in the individual systems to account for possible incongruities that may be observed between the rubber and simulated system. The lack of agreement between the rubber and model compound rate constant data lies in the fact that the rate of crosslinking is not simplistically related to the rate at which accelerator and sulfur is consumed, this being especially true for the rate at which the accelerator is consumed. Thus the discussion over the acceleratory rates in the various accelerator systems was limited to observations made in the rubber system, with the model compound data was used exclusively to elucidate mechanistic processes. It was discovered that the groups of accelerators examined, namely linear, cyclic and aromatic thiuram disulfide adducts, produced vastly varied rate data. The aromatic thiuram disulfide adducts had only a slight acceleratory effect on the rate of vulcanisation as compared to the unaccelerated sulfur system. The morpholine adduct had a moderately larger rate of acceleration followed by tetramethyl and tetrethylthiuram disulfide, with N’N-dicyclopentamethylenethiuram disulfide having the fastest rate of acceleration.
- Full Text:
- Date Issued: 2007
- Authors: Van Rooyen, Jason Leigh
- Date: 2007
- Subjects: Vulcanization , Vulcanization accelerators
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10399 , http://hdl.handle.net/10948/733 , Vulcanization , Vulcanization accelerators
- Description: This study was initiated in an attempt to investigate dithiocarbamic acid accelerated sulfur vulcanisation. This was, however, found impossible due to the innate instability of dithiocarbamic acids. The focus of the study was then shifted toward thiuram disulfide accelerated sulfur vulcanisation, with emphasis being placed on a rate comparison. Three groups of accelerators were investigated, namely the aromatic, linear aliphatic and cyclic aliphatic thiuram disulfide adducts. The analysis methods that were employed were conventional rubber (cis-1,4-polyisoprene) techniques coupled to model (squalene) compound investigations. The data that was collected consisted of rheometrical torque vs. time data in the rubber system while the data obtained in the model compound study consisted of sulfur and accelerator concentration data as determined by means of high performance liquid chromatography (HPLC). The aromatic accelerators were synthesised in our labs by means of an addition reaction between the aromatic amine and CS2 in basic medium and subsequent oxidation with K3Fe(CN)6, all in a 1:1 molar ratio. The reaction yield was low due to the instability of the dithiocarbamate intermediates and a sluggish oxidation reaction. In the rate constant determination a first order mathematical approach was used for the rubber system as crosslinking is considered to roughly obey first order kinetics. The model compound data was also found to more accurately fit the first order rate law, with an initial slopes method also being applied to the system to determine secondary rate constants and relative rates for the system. The determination of vulcanisation rate constants in the cis-1,4-polyisoprene system was a success, while the rate data determined by means of the squalene model was more related to the rate of accelerator and sulfur consumption as opposed to the rate of crosslinking as is the case with the rubber rate data. The sulfur first order rate data mirrored the rate data derived from the rubber system more closely than the corresponding accelerator rate data, the relative rate data determined by means of initial slopes method, proved that the homolytic cleavage of thiuram disulfides and the subsequent formation of accelerator polysulfides were not limiting steps. This is seen in the similar relative rate data derived from both the raw sulfur and accelerator data in systems that exhibit vastly different vulcanisation rates. Squalene was deemed a suitable model for the cis-1,4-polyisoprene system, although one should consider the extent of charring and solution effects in the individual systems to account for possible incongruities that may be observed between the rubber and simulated system. The lack of agreement between the rubber and model compound rate constant data lies in the fact that the rate of crosslinking is not simplistically related to the rate at which accelerator and sulfur is consumed, this being especially true for the rate at which the accelerator is consumed. Thus the discussion over the acceleratory rates in the various accelerator systems was limited to observations made in the rubber system, with the model compound data was used exclusively to elucidate mechanistic processes. It was discovered that the groups of accelerators examined, namely linear, cyclic and aromatic thiuram disulfide adducts, produced vastly varied rate data. The aromatic thiuram disulfide adducts had only a slight acceleratory effect on the rate of vulcanisation as compared to the unaccelerated sulfur system. The morpholine adduct had a moderately larger rate of acceleration followed by tetramethyl and tetrethylthiuram disulfide, with N’N-dicyclopentamethylenethiuram disulfide having the fastest rate of acceleration.
- Full Text:
- Date Issued: 2007