Investigating the English vocabulary needs, exposure, and knowledge of isiXhosa speaking learners for transition from learning to read in the Foundation Phase to reading to learn in the Intermediate Phase : a case study
- Authors: Sibanda, Jabulani
- Date: 2014
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1968 , http://hdl.handle.net/10962/d1011790
- Description: The nature of learners' transition from Grade 3 to Grade 4 has serious and far reaching ramifications for their educational success in the subsequent grades. This is true of the South African education system, as it is for several other education contexts. The challenge that complicates the transition is largely a lexical one. It is with that understanding that the present study aimed to do three things namely: to determine the vocabulary needs of Grade 3 learners for transitioning to Grade 4; to establish the extent to which Grade 3 isiXhosa speaking learners are exposed to, and prepared for, the acquisition of that requisite vocabulary; and to establish the extent of Grade 4 learners' knowledge of that vocabulary at the beginning of the year. The vocabulary needs of Grade 3 learners for the transition to Grade 4 were determined from the Grade 4 subject textbook corpus. Word frequency was the criterion used to determine the usefulness and critical importance of a word for the transition. The AntConc concordance software program was used to generate word frequencies. Words with high frequency across the different subject areas, which were confirmed as high frequent in four other known word lists, were considered as constituting the vocabulary needs of learners at the verge of this significant transition. The extent of learners' preparedness for transitioning to Grade 4 in terms of their vocabulary exposure and vocabulary instruction was determined through teacher interviews, classroom observations, analysis of teacher classroom talk, analysis of the exposure and recycling of high frequent vocabulary in Grade 3 reading materials and classroom print. From these diverse sources, findings point to a paucity in both the exposure and recycling of the requisite vocabulary in these sources of classroom language input. Classroom observations and teacher interviews attest to lack of deliberate vocabulary instruction in the Grade 3 English First Additional Language lessons. The only extensive coverage of the requisite vocabulary was in the Grade 3 reading materials which included Big books, Readers and Workbooks. The Grade 4 learners' knowledge of the 60 high frequency words was tested through nine vocabulary tests, three of which tested their knowledge of word recognition, three tested passive word knowledge and the remaining three tested learners' active word knowledge. All the Grade 4 learners in the ten participating schools (297) were tested. Performance in the tests indicated that Grade 4 learners' knowledge of words requisite for reading to learn was low. That observation was consistent with an analysis of learners' performance per school, per district, per word, per test and per word bands. Tests of word recognition were done better than those of passive word knowledge and active word knowledge. Particularly problematic was test 4 which tested learners' knowledge of definition of words.
- Full Text:
- Date Issued: 2014
- Authors: Sibanda, Jabulani
- Date: 2014
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1968 , http://hdl.handle.net/10962/d1011790
- Description: The nature of learners' transition from Grade 3 to Grade 4 has serious and far reaching ramifications for their educational success in the subsequent grades. This is true of the South African education system, as it is for several other education contexts. The challenge that complicates the transition is largely a lexical one. It is with that understanding that the present study aimed to do three things namely: to determine the vocabulary needs of Grade 3 learners for transitioning to Grade 4; to establish the extent to which Grade 3 isiXhosa speaking learners are exposed to, and prepared for, the acquisition of that requisite vocabulary; and to establish the extent of Grade 4 learners' knowledge of that vocabulary at the beginning of the year. The vocabulary needs of Grade 3 learners for the transition to Grade 4 were determined from the Grade 4 subject textbook corpus. Word frequency was the criterion used to determine the usefulness and critical importance of a word for the transition. The AntConc concordance software program was used to generate word frequencies. Words with high frequency across the different subject areas, which were confirmed as high frequent in four other known word lists, were considered as constituting the vocabulary needs of learners at the verge of this significant transition. The extent of learners' preparedness for transitioning to Grade 4 in terms of their vocabulary exposure and vocabulary instruction was determined through teacher interviews, classroom observations, analysis of teacher classroom talk, analysis of the exposure and recycling of high frequent vocabulary in Grade 3 reading materials and classroom print. From these diverse sources, findings point to a paucity in both the exposure and recycling of the requisite vocabulary in these sources of classroom language input. Classroom observations and teacher interviews attest to lack of deliberate vocabulary instruction in the Grade 3 English First Additional Language lessons. The only extensive coverage of the requisite vocabulary was in the Grade 3 reading materials which included Big books, Readers and Workbooks. The Grade 4 learners' knowledge of the 60 high frequency words was tested through nine vocabulary tests, three of which tested their knowledge of word recognition, three tested passive word knowledge and the remaining three tested learners' active word knowledge. All the Grade 4 learners in the ten participating schools (297) were tested. Performance in the tests indicated that Grade 4 learners' knowledge of words requisite for reading to learn was low. That observation was consistent with an analysis of learners' performance per school, per district, per word, per test and per word bands. Tests of word recognition were done better than those of passive word knowledge and active word knowledge. Particularly problematic was test 4 which tested learners' knowledge of definition of words.
- Full Text:
- Date Issued: 2014
Isolation, purification and partial characterisation of cancer procoagulant from placental amnion-chorion membranes and its role in angiogenesis inflammation and metastasis
- Authors: Krause, Jason
- Date: 2014
- Subjects: Coagulation , Amnion , Chorion , Metastasis , Inflammation , Neovascularization
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10350 , http://hdl.handle.net/10948/d1020897
- Description: Cancer procoagulant (EC 3.4.22.26) is an enzyme that is derived from tumour and foetal tissue, but not normal tissue. It is a direct activator of factor X and has been isolated from amnion-chorion membranes as well as from extracts and cells from human melanoma. The presence of cancer procoagulant has been associated with the malignant phenotype, as well as having a particularly high activity in metastatic cells. Cancer procoagulant activity is elevated in the serum of early stage breast cancer patients and decreased to normal in the advanced stages of the disease. In this study, cancer procoagulant was successfully isolated from amnion-chorion membranes and purified to homogeneity. The molecular weight of cancer procoagulant was determined using SDS-PAGE and was found to be 68 kDa. Cancer procoagulant was delipidated and it was shown that its activity was increased by the presence of lipids in a dose-dependent manner. Recovery of cancer procoagulant after delipidation is poor, consequently, a larger mass of sample is required to obtain sufficient amounts of delipidated material for N-terminal amino acid analysis. The optimum pH of cancer procoagulant was determined to be pH 8 and its optimal temperature was found to be 50°C. Novel synthetic substrates were designed to assay for cancer procoagulant activity. Currently, 2 potential candidates have been identified, namely, PQVR-AMC and AVSQSKP-AMC. Cancer procoagulant-induced expression of cytokines is differently modulated in the less aggressive MCF-7 cell line as compared to the metastatic and more aggressive MDA-MB-231 cell line. There are marked similarities in the inflammatory response produced by cancer procoagulant in hTERT-HDLEC and MDA-MB-231 cells, which are both associated with migratory capacity. Furthermore, cancer procoagulant-induced PDGF-β expression in hTERT-HDLEC and MDA-MB-231 cells could point to involvement of cancer procoagulant in wound healing and metastatic spread, respectively. Cancer procoagulant induced the motility of MDA-MB-231, MCF-7 and hTERT- cells in vitro in a time- and dose-dependent manner. Together, these results suggest that cancer procoagulant plays a role in the migration of breast cancer cells as well as the migration of endothelial cells.
- Full Text:
- Date Issued: 2014
- Authors: Krause, Jason
- Date: 2014
- Subjects: Coagulation , Amnion , Chorion , Metastasis , Inflammation , Neovascularization
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10350 , http://hdl.handle.net/10948/d1020897
- Description: Cancer procoagulant (EC 3.4.22.26) is an enzyme that is derived from tumour and foetal tissue, but not normal tissue. It is a direct activator of factor X and has been isolated from amnion-chorion membranes as well as from extracts and cells from human melanoma. The presence of cancer procoagulant has been associated with the malignant phenotype, as well as having a particularly high activity in metastatic cells. Cancer procoagulant activity is elevated in the serum of early stage breast cancer patients and decreased to normal in the advanced stages of the disease. In this study, cancer procoagulant was successfully isolated from amnion-chorion membranes and purified to homogeneity. The molecular weight of cancer procoagulant was determined using SDS-PAGE and was found to be 68 kDa. Cancer procoagulant was delipidated and it was shown that its activity was increased by the presence of lipids in a dose-dependent manner. Recovery of cancer procoagulant after delipidation is poor, consequently, a larger mass of sample is required to obtain sufficient amounts of delipidated material for N-terminal amino acid analysis. The optimum pH of cancer procoagulant was determined to be pH 8 and its optimal temperature was found to be 50°C. Novel synthetic substrates were designed to assay for cancer procoagulant activity. Currently, 2 potential candidates have been identified, namely, PQVR-AMC and AVSQSKP-AMC. Cancer procoagulant-induced expression of cytokines is differently modulated in the less aggressive MCF-7 cell line as compared to the metastatic and more aggressive MDA-MB-231 cell line. There are marked similarities in the inflammatory response produced by cancer procoagulant in hTERT-HDLEC and MDA-MB-231 cells, which are both associated with migratory capacity. Furthermore, cancer procoagulant-induced PDGF-β expression in hTERT-HDLEC and MDA-MB-231 cells could point to involvement of cancer procoagulant in wound healing and metastatic spread, respectively. Cancer procoagulant induced the motility of MDA-MB-231, MCF-7 and hTERT- cells in vitro in a time- and dose-dependent manner. Together, these results suggest that cancer procoagulant plays a role in the migration of breast cancer cells as well as the migration of endothelial cells.
- Full Text:
- Date Issued: 2014
Knowledge and knowing in the public management and public administration programmes at a comprehensive university
- Authors: Lück, Jacqueline Catherine
- Date: 2014
- Subjects: Knowledge and learning , Public administration -- Study and teaching (Higher) , Knowledge, Sociology of , Learning, Psychology of , Knowledge, Theory of , Educational equalization -- South Africa , Education, Higher -- South Africa , Literacy -- South Africa , Technical institutes -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1326 , http://hdl.handle.net/10962/d1013166
- Description: Knowledge is often tacit and under researched in educational fields. In order for student access to knowledge and its related academic discourses to be facilitated, a deep understanding needs to be gained of the form that this knowledge takes. This study interrogates the ways in which knowledge is constituted in the first year of a Public Management Diploma and a Public Administration Degree at a comprehensive university in South Africa. The study takes a social realist approach that understands reality as fact but sees our knowledge thereof as a social phenomenon. The study was concerned with knowledge structures and knower structures as it argues that these have not been adequately accounted for in the sociology of education research. But this study comes to this concern from a strongly ideological view of student reading and writing. This study calls on a social practices approach that sees literacy as embedded within specific academic discourses, which vary from context to context. It uses this ideological understanding of literacy as the orienting framework for the study of knowledge. The study takes place in a Higher Education mileu that has begun to transform from its divisive past. The transformation brought about new institutional formations such as the comprehensive university, with its mix of vocational, professional and formative programmes and varied emphasis on contextual and conceptual curriculum coherence. Increasingly, the transformation agenda also shifts concern from simply providing physical access to a previously disenfranchised majority to ensuring full participation in the context of high attrition rates in first year and low retention rates. The data was analysed using the Specialisation Codes of Legitimation Code Theory to see what was being specialised in the Diploma and Degree curricula of the Public Management and Administration fields. These fields are characterised in the literature by ongoing tensions about focus, and perceptions of there being a theoretical vacuum and an inability to deal adequately with challenges in the South African public sector. Analysis of lecturer interviews and first-year curriculum documentation showed that both the Public Management Diploma and Public Administration Degree have stronger epistemic relations (ER), with an emphasis on claims to knowledge of the world. The data showed relatively weak social relations (SR), in that there was not the valuing of a particular lens on the world or a specific disposition required for legitimation within this field. The combination of ER+ and SR- indicates that these curricula are Knowledge Codes, where legitimation is through the acquisition of a set of skills and procedures. The programmes were characterised by fairly low-level procedural knowledge, which may point to a workplace-oriented direction that is dominant in the comprehensive university. In keeping with concerns raised in the literature about this field, there was little evidence of theoretical or propositional knowledge in the Public Management Diploma and while the Public Administration Degree had some evidence of this, it was arguably not to the extent expected of a degree as described in the National Qualifications Framework. This study was limited to the first-year of the Diploma and Degree and subsequent years could present different findings. Lecturers showed awareness of student challenges with literacy practices and made concerned attempts through various interventions to address this but they were found to value the surface features of writing practices over personal engagement with the knowledge. Though the expectations of student literacy practices in tests and assignments were aligned to the ways in which knowledge was constructed in the curriculum, there was little evidence of student induction into disciplinary discourses of the field as knowledge was presented as being neutral and student writing primarily took the form of retelling objective facts. The implications of these findings could include student exclusion from higher-level academic discourse, more powerful knowledge in the workplace and, finally, constrain them from becoming producers of knowledge.
- Full Text:
- Date Issued: 2014
- Authors: Lück, Jacqueline Catherine
- Date: 2014
- Subjects: Knowledge and learning , Public administration -- Study and teaching (Higher) , Knowledge, Sociology of , Learning, Psychology of , Knowledge, Theory of , Educational equalization -- South Africa , Education, Higher -- South Africa , Literacy -- South Africa , Technical institutes -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1326 , http://hdl.handle.net/10962/d1013166
- Description: Knowledge is often tacit and under researched in educational fields. In order for student access to knowledge and its related academic discourses to be facilitated, a deep understanding needs to be gained of the form that this knowledge takes. This study interrogates the ways in which knowledge is constituted in the first year of a Public Management Diploma and a Public Administration Degree at a comprehensive university in South Africa. The study takes a social realist approach that understands reality as fact but sees our knowledge thereof as a social phenomenon. The study was concerned with knowledge structures and knower structures as it argues that these have not been adequately accounted for in the sociology of education research. But this study comes to this concern from a strongly ideological view of student reading and writing. This study calls on a social practices approach that sees literacy as embedded within specific academic discourses, which vary from context to context. It uses this ideological understanding of literacy as the orienting framework for the study of knowledge. The study takes place in a Higher Education mileu that has begun to transform from its divisive past. The transformation brought about new institutional formations such as the comprehensive university, with its mix of vocational, professional and formative programmes and varied emphasis on contextual and conceptual curriculum coherence. Increasingly, the transformation agenda also shifts concern from simply providing physical access to a previously disenfranchised majority to ensuring full participation in the context of high attrition rates in first year and low retention rates. The data was analysed using the Specialisation Codes of Legitimation Code Theory to see what was being specialised in the Diploma and Degree curricula of the Public Management and Administration fields. These fields are characterised in the literature by ongoing tensions about focus, and perceptions of there being a theoretical vacuum and an inability to deal adequately with challenges in the South African public sector. Analysis of lecturer interviews and first-year curriculum documentation showed that both the Public Management Diploma and Public Administration Degree have stronger epistemic relations (ER), with an emphasis on claims to knowledge of the world. The data showed relatively weak social relations (SR), in that there was not the valuing of a particular lens on the world or a specific disposition required for legitimation within this field. The combination of ER+ and SR- indicates that these curricula are Knowledge Codes, where legitimation is through the acquisition of a set of skills and procedures. The programmes were characterised by fairly low-level procedural knowledge, which may point to a workplace-oriented direction that is dominant in the comprehensive university. In keeping with concerns raised in the literature about this field, there was little evidence of theoretical or propositional knowledge in the Public Management Diploma and while the Public Administration Degree had some evidence of this, it was arguably not to the extent expected of a degree as described in the National Qualifications Framework. This study was limited to the first-year of the Diploma and Degree and subsequent years could present different findings. Lecturers showed awareness of student challenges with literacy practices and made concerned attempts through various interventions to address this but they were found to value the surface features of writing practices over personal engagement with the knowledge. Though the expectations of student literacy practices in tests and assignments were aligned to the ways in which knowledge was constructed in the curriculum, there was little evidence of student induction into disciplinary discourses of the field as knowledge was presented as being neutral and student writing primarily took the form of retelling objective facts. The implications of these findings could include student exclusion from higher-level academic discourse, more powerful knowledge in the workplace and, finally, constrain them from becoming producers of knowledge.
- Full Text:
- Date Issued: 2014
Laser bending of commercially pure grade 2 titanium alloy plates: mechanisms analysis and characterisation of mechanical properties
- Authors: Mjali, Kadephi Vuyolwethu
- Date: 2014
- Subjects: Materials -- Mechanical properties , Bending , Titanium-aluminum alloys
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:9642 , http://hdl.handle.net/10948/d1021147
- Description: The processing of materials has become a specialist field and the industry will continue to grow due to rising costs in labour and raw materials which has forced many automotive industry suppliers to invest heavily in this field. In order to be relevant and competitive in today’s industrial world, companies in South Africa are now forced to dedicate billions of rands in profits to research and development. Metals like titanium are finding favour with automotive and aviation companies in pursuit of savings in fuel consumption. This saving is achieved by reducing weight on aircraft and automobiles yet still meeting acceptable and improved structural integrity. In-depth research into the behaviour of various materials under varying loading conditions is therefore essential. The study on the processing of commercially pure grade 2 titanium alloy plates focuses on the development of process parameters for bending the material using a 4kW Nd: YAG laser to an approximate radius of curvature of 120mm. The resulting mechanical properties of laser formed plates are then compared to those obtained from mechanically formed samples. The titanium parent material was used to benchmark the performance of formed samples. The effect of process parameters on the mechanical properties and structural integrity also formed part of this study. To obtain the bending parameters for laser forming, various combinations of processing speeds and laser powers were used. The line energy is dependent on the power and scanning velocity parameters and these are shown in table 1. The laser power, line energy and scanning velocity were the main parameters controlled in this study and the beam diameter remained unchanged. Residual stress analysis, micro-hardness and fatigue life testing were carried out to analyse mechanical properties and the structural integrity of the plate samples. Microstructural analysis was also done to observe changes in the material as a result of the forming processes. From the results it is evident that laser forming is beneficial to the hardness of titanium but detrimental to the fatigue life at higher line energies. Residual stress analysis showed the amount of stress within the study samples increased with each forming operation. This information was vital in the analysis of the fatigue life of titanium. A fatigue life prediction model was developed from this study and it shed some light on the behaviour of titanium in fatigue testing. The model could be used to predict fatigue life when no fatigue data is available for commercially pure grade 2 titanium alloy plates. In conclusion, this study helped establish parameters that could be used to bend titanium while the analysis of mechanical properties showed the limits of working with this alloy.
- Full Text:
- Date Issued: 2014
- Authors: Mjali, Kadephi Vuyolwethu
- Date: 2014
- Subjects: Materials -- Mechanical properties , Bending , Titanium-aluminum alloys
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:9642 , http://hdl.handle.net/10948/d1021147
- Description: The processing of materials has become a specialist field and the industry will continue to grow due to rising costs in labour and raw materials which has forced many automotive industry suppliers to invest heavily in this field. In order to be relevant and competitive in today’s industrial world, companies in South Africa are now forced to dedicate billions of rands in profits to research and development. Metals like titanium are finding favour with automotive and aviation companies in pursuit of savings in fuel consumption. This saving is achieved by reducing weight on aircraft and automobiles yet still meeting acceptable and improved structural integrity. In-depth research into the behaviour of various materials under varying loading conditions is therefore essential. The study on the processing of commercially pure grade 2 titanium alloy plates focuses on the development of process parameters for bending the material using a 4kW Nd: YAG laser to an approximate radius of curvature of 120mm. The resulting mechanical properties of laser formed plates are then compared to those obtained from mechanically formed samples. The titanium parent material was used to benchmark the performance of formed samples. The effect of process parameters on the mechanical properties and structural integrity also formed part of this study. To obtain the bending parameters for laser forming, various combinations of processing speeds and laser powers were used. The line energy is dependent on the power and scanning velocity parameters and these are shown in table 1. The laser power, line energy and scanning velocity were the main parameters controlled in this study and the beam diameter remained unchanged. Residual stress analysis, micro-hardness and fatigue life testing were carried out to analyse mechanical properties and the structural integrity of the plate samples. Microstructural analysis was also done to observe changes in the material as a result of the forming processes. From the results it is evident that laser forming is beneficial to the hardness of titanium but detrimental to the fatigue life at higher line energies. Residual stress analysis showed the amount of stress within the study samples increased with each forming operation. This information was vital in the analysis of the fatigue life of titanium. A fatigue life prediction model was developed from this study and it shed some light on the behaviour of titanium in fatigue testing. The model could be used to predict fatigue life when no fatigue data is available for commercially pure grade 2 titanium alloy plates. In conclusion, this study helped establish parameters that could be used to bend titanium while the analysis of mechanical properties showed the limits of working with this alloy.
- Full Text:
- Date Issued: 2014
Leadership and accountability of ward councillors in South African municipalities: a case study of Buffalo City Metropolitan Municipality
- Authors: Mfene, Primrose Nompendulo
- Date: 2014
- Subjects: Municipal government -- South Africa -- Eastern Cape , Local government -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:8244 , http://hdl.handle.net/10948/d1010954 , Municipal government -- South Africa -- Eastern Cape , Local government -- South Africa -- Eastern Cape
- Description: The aim of the study is to critically examine the leadership and accountability of ward councillors in South African municipalities: A case of Buffalo City Municipality. The theory of communicative action by Jürgen Habermas was used to interpret the manner in which ward councillors are expected to interact with the members of the community when performing their leadership and accountability roles. The study adopted a case study design that assisted in establishing what is required from ward councillors with regard to their leadership and accountability roles in local governance. Qualitative and quantitative data collection instruments were used to collect data. The focus group interviews with ward committee members (n=100) from twenty-five (25) wards identified themes that relate to leadership and accountability constructs. The identified themes were verified in the quantitative phase in which questionnaires were administered to fifty (50) ward councillors. The qualitative data was analysed thematically using NVivo and quantitative data was analysed using MS Excel. Generally, the views of the ward councillors regarding their leadership and accountability were positive. However, their leadership and accountability were largely dependent on their individualised communication skills and emotional intelligence. Hence the study established that unless ward councillors are equipped with skills and knowledge in communication and emotional intelligence respectively, their leadership and accountability roles will not be able to contribute effectively to local governance. Subsequently, the study made a set of recommendations in this regard.
- Full Text:
- Date Issued: 2014
- Authors: Mfene, Primrose Nompendulo
- Date: 2014
- Subjects: Municipal government -- South Africa -- Eastern Cape , Local government -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:8244 , http://hdl.handle.net/10948/d1010954 , Municipal government -- South Africa -- Eastern Cape , Local government -- South Africa -- Eastern Cape
- Description: The aim of the study is to critically examine the leadership and accountability of ward councillors in South African municipalities: A case of Buffalo City Municipality. The theory of communicative action by Jürgen Habermas was used to interpret the manner in which ward councillors are expected to interact with the members of the community when performing their leadership and accountability roles. The study adopted a case study design that assisted in establishing what is required from ward councillors with regard to their leadership and accountability roles in local governance. Qualitative and quantitative data collection instruments were used to collect data. The focus group interviews with ward committee members (n=100) from twenty-five (25) wards identified themes that relate to leadership and accountability constructs. The identified themes were verified in the quantitative phase in which questionnaires were administered to fifty (50) ward councillors. The qualitative data was analysed thematically using NVivo and quantitative data was analysed using MS Excel. Generally, the views of the ward councillors regarding their leadership and accountability were positive. However, their leadership and accountability were largely dependent on their individualised communication skills and emotional intelligence. Hence the study established that unless ward councillors are equipped with skills and knowledge in communication and emotional intelligence respectively, their leadership and accountability roles will not be able to contribute effectively to local governance. Subsequently, the study made a set of recommendations in this regard.
- Full Text:
- Date Issued: 2014
Mechanisms, analysis and characterisation of mechanical properties of laser formed commercially pure grade 2 titanium alloy plates
- Authors: Mjali, Kadephi Vuyolwethu
- Date: 2014
- Subjects: Materials -- Mechanical properties , Bending , Titanium-aluminum alloys
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:9641 , http://hdl.handle.net/10948/d1021083
- Description: The processing of materials has become a specialist field and the industry will continue to grow due to rising costs in labour and raw materials which has forced many automotive industry suppliers to invest heavily in this field. In order to be relevant and competitive in today’s industrial world, companies in South Africa are now forced to dedicate billions of rands in profits to research and development. Metals like titanium are finding favour with automotive and aviation companies in pursuit of savings in fuel consumption. This saving is achieved by reducing weight on aircraft and automobiles yet still meeting acceptable and improved structural integrity. In-depth research into the behaviour of various materials under varying loading conditions is therefore essential. The study on the processing of commercially pure grade 2 titanium alloy plates focuses on the development of process parameters for bending the material using a 4kW Nd: YAG laser to an approximate radius of curvature of 120mm. The resulting mechanical properties of laser formed plates are then compared to those obtained from mechanically formed samples. The titanium parent material was used to benchmark the performance of formed samples. The effect of process parameters on the mechanical properties and structural integrity also formed part of this study. To obtain the bending parameters for laser forming, various combinations of processing speeds and laser powers were used. The line energy is dependent on the power and scanning velocity parameters and these are shown in table 1. The laser power, line energy and scanning velocity were the main parameters controlled in this study and the beam diameter remained unchanged. Residual stress analysis, micro-hardness and fatigue life testing were carried out to analyse mechanical properties and the structural integrity of the plate samples. Microstructural analysis was also done to observe changes in the material as a result of the forming processes. From the results it is evident that laser forming is beneficial to the hardness of titanium but detrimental to the fatigue life at higher line energies. Residual stress analysis showed the amount of stress within the study samples increased with each forming operation. This information was vital in the analysis of the fatigue life of titanium. A fatigue life prediction model was developed from this study and it shed some light on the behaviour of titanium in fatigue testing. The model could be used to predict fatigue life when no fatigue data is available for commercially pure grade 2 titanium alloy plates. In conclusion, this study helped establish parameters that could be used to bend titanium while the analysis of mechanical properties showed the limits of working with this alloy.
- Full Text:
- Date Issued: 2014
- Authors: Mjali, Kadephi Vuyolwethu
- Date: 2014
- Subjects: Materials -- Mechanical properties , Bending , Titanium-aluminum alloys
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:9641 , http://hdl.handle.net/10948/d1021083
- Description: The processing of materials has become a specialist field and the industry will continue to grow due to rising costs in labour and raw materials which has forced many automotive industry suppliers to invest heavily in this field. In order to be relevant and competitive in today’s industrial world, companies in South Africa are now forced to dedicate billions of rands in profits to research and development. Metals like titanium are finding favour with automotive and aviation companies in pursuit of savings in fuel consumption. This saving is achieved by reducing weight on aircraft and automobiles yet still meeting acceptable and improved structural integrity. In-depth research into the behaviour of various materials under varying loading conditions is therefore essential. The study on the processing of commercially pure grade 2 titanium alloy plates focuses on the development of process parameters for bending the material using a 4kW Nd: YAG laser to an approximate radius of curvature of 120mm. The resulting mechanical properties of laser formed plates are then compared to those obtained from mechanically formed samples. The titanium parent material was used to benchmark the performance of formed samples. The effect of process parameters on the mechanical properties and structural integrity also formed part of this study. To obtain the bending parameters for laser forming, various combinations of processing speeds and laser powers were used. The line energy is dependent on the power and scanning velocity parameters and these are shown in table 1. The laser power, line energy and scanning velocity were the main parameters controlled in this study and the beam diameter remained unchanged. Residual stress analysis, micro-hardness and fatigue life testing were carried out to analyse mechanical properties and the structural integrity of the plate samples. Microstructural analysis was also done to observe changes in the material as a result of the forming processes. From the results it is evident that laser forming is beneficial to the hardness of titanium but detrimental to the fatigue life at higher line energies. Residual stress analysis showed the amount of stress within the study samples increased with each forming operation. This information was vital in the analysis of the fatigue life of titanium. A fatigue life prediction model was developed from this study and it shed some light on the behaviour of titanium in fatigue testing. The model could be used to predict fatigue life when no fatigue data is available for commercially pure grade 2 titanium alloy plates. In conclusion, this study helped establish parameters that could be used to bend titanium while the analysis of mechanical properties showed the limits of working with this alloy.
- Full Text:
- Date Issued: 2014
Mobilising processes of abstraction, experiential learning and representation of traditional ecological knowledge in participatory monitoring of mangroves and fisheries : an approach towards enhancing social learning processes on the eastern coast of Tanzania
- Authors: Sabai, Daniel
- Date: 2014
- Subjects: Traditional ecological knowledge , Environmental education -- Tanzania , Environmental education -- Study and teaching -- Tanzania , Coastal zone management -- Tanzania , Social learning -- Tanzania , Experiential learning -- Tanzania , Mangrove conservation -- Tanzania , Fishery management -- Tanzania
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1979 , http://hdl.handle.net/10962/d1013060
- Description: This study addresses a core problem that was uncovered in records from coastal management monitoring initiatives on the eastern coast of Tanzania associated with the application and use of coastal monitoring indicators developed by external development partners for the coastal zone. These records suggest that local communities, who are key actors in participatory monitoring of coastal and marine resources, face many challenges associated with adapting and applying the said frameworks of indicators and monitoring plans. These indicators tend to be scientifically abstracted and methodologically reified; given prevailing contextual and socio‐cultural realities amongst them. The research project addresses the following key research question: How can processes of abstraction, conceptualisation, and representation of TEK contribute to the development of coastal management indicators that are less reified, more contextually and culturally congruent, and which may potentially be used by resource users in the wider social learning process of detecting trends, threats, changes and conditions of mangrove and fisheries resources? In response to the contextual problem and the research question, the study employs processes of abstraction and experiential learning techniques to unlock knowledge that local communities have, as an input for underlabouring existing scientific indicators on the Eastern coast of Tanzania. The research is constituted as critical realist case study research, involving two communities on the eastern coast of Tanzania, namely the Moa and the Boma communities (in Mkinga coastal district). Overall, the study involved 37 participants in a series of interviews, focus group discussions, and experiential learning processes using visualised data, and an experiential learning intervention workshop, and follow‐ups over a period of 3 years. The study worked with mangroves and fisheries to provide focus to the case study research and to allow for in‐depth engagement with the assumptions and processes associated with indicators development and use. Through the above mentioned data generation processes, critical realist analysis, and experiential learning processes involving abstraction and representation of traditional ecological knowledge held by mangrove restorers and fishers in the study areas, the study uncovers possible challenges of adapting and applying scientific indicators in participatory monitoring of a mangrove ecosystem. Using ampliative modes of inference for data analysis (induction, abduction and retroduction) and a critical realist scientific explanatory framework known as DRRREI(C) (Resolution, Re‐description, Retrodiction, Elimination, Identification, & Correction) the study suggests a new approach that may lead to the development of a framework of indicators that are less reified, more congruent to users (coastal communities), and likely to attract a wider context‐based social learning which favours epistemological access between scientific institutions (universities inclusive), and local communities. It attempts to establish an interface between knowledge that scientific institutions produce and the potential knowledge that exists in local contexts (traditional ecological knowledge), and seeks to widen and improve knowledge sharing and experiential learning practices that may potentially benefit coastal and marine resources in the study area. As mentioned above, the knowledge and abstraction processes related to the indicators development focussed on the mangrove ecosystem and associated fisheries, as engaged in the two participating communities in the eastern coast of Tanzania. The specific findings are therefore limited by the case boundaries, but the methodological process could be replicated and used elsewhere. The study’s contributions are theoretical and methodological, but also social and practice‐centred. The study brings into view the need to consider the contextual relevance of adapted knowledge, the capacity or ability of beneficiaries to adapt and apply scientific models, frameworks or tools, and the potential of local knowledge as an input for enhancing or improving monitoring of mangroves and mangrove‐based fisheries. Finally, the study comes up with a framework of indicators which is regarded by the coastal communities involved in the study as being less reified, more contextually and culturally congruent, and which may potentially be used in detecting environmental trends, threats, changes and conditions of mangrove and fisheries resources, and attract wider social learning processes.
- Full Text:
- Date Issued: 2014
- Authors: Sabai, Daniel
- Date: 2014
- Subjects: Traditional ecological knowledge , Environmental education -- Tanzania , Environmental education -- Study and teaching -- Tanzania , Coastal zone management -- Tanzania , Social learning -- Tanzania , Experiential learning -- Tanzania , Mangrove conservation -- Tanzania , Fishery management -- Tanzania
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1979 , http://hdl.handle.net/10962/d1013060
- Description: This study addresses a core problem that was uncovered in records from coastal management monitoring initiatives on the eastern coast of Tanzania associated with the application and use of coastal monitoring indicators developed by external development partners for the coastal zone. These records suggest that local communities, who are key actors in participatory monitoring of coastal and marine resources, face many challenges associated with adapting and applying the said frameworks of indicators and monitoring plans. These indicators tend to be scientifically abstracted and methodologically reified; given prevailing contextual and socio‐cultural realities amongst them. The research project addresses the following key research question: How can processes of abstraction, conceptualisation, and representation of TEK contribute to the development of coastal management indicators that are less reified, more contextually and culturally congruent, and which may potentially be used by resource users in the wider social learning process of detecting trends, threats, changes and conditions of mangrove and fisheries resources? In response to the contextual problem and the research question, the study employs processes of abstraction and experiential learning techniques to unlock knowledge that local communities have, as an input for underlabouring existing scientific indicators on the Eastern coast of Tanzania. The research is constituted as critical realist case study research, involving two communities on the eastern coast of Tanzania, namely the Moa and the Boma communities (in Mkinga coastal district). Overall, the study involved 37 participants in a series of interviews, focus group discussions, and experiential learning processes using visualised data, and an experiential learning intervention workshop, and follow‐ups over a period of 3 years. The study worked with mangroves and fisheries to provide focus to the case study research and to allow for in‐depth engagement with the assumptions and processes associated with indicators development and use. Through the above mentioned data generation processes, critical realist analysis, and experiential learning processes involving abstraction and representation of traditional ecological knowledge held by mangrove restorers and fishers in the study areas, the study uncovers possible challenges of adapting and applying scientific indicators in participatory monitoring of a mangrove ecosystem. Using ampliative modes of inference for data analysis (induction, abduction and retroduction) and a critical realist scientific explanatory framework known as DRRREI(C) (Resolution, Re‐description, Retrodiction, Elimination, Identification, & Correction) the study suggests a new approach that may lead to the development of a framework of indicators that are less reified, more congruent to users (coastal communities), and likely to attract a wider context‐based social learning which favours epistemological access between scientific institutions (universities inclusive), and local communities. It attempts to establish an interface between knowledge that scientific institutions produce and the potential knowledge that exists in local contexts (traditional ecological knowledge), and seeks to widen and improve knowledge sharing and experiential learning practices that may potentially benefit coastal and marine resources in the study area. As mentioned above, the knowledge and abstraction processes related to the indicators development focussed on the mangrove ecosystem and associated fisheries, as engaged in the two participating communities in the eastern coast of Tanzania. The specific findings are therefore limited by the case boundaries, but the methodological process could be replicated and used elsewhere. The study’s contributions are theoretical and methodological, but also social and practice‐centred. The study brings into view the need to consider the contextual relevance of adapted knowledge, the capacity or ability of beneficiaries to adapt and apply scientific models, frameworks or tools, and the potential of local knowledge as an input for enhancing or improving monitoring of mangroves and mangrove‐based fisheries. Finally, the study comes up with a framework of indicators which is regarded by the coastal communities involved in the study as being less reified, more contextually and culturally congruent, and which may potentially be used in detecting environmental trends, threats, changes and conditions of mangrove and fisheries resources, and attract wider social learning processes.
- Full Text:
- Date Issued: 2014
Modelling the hydrological responses to changes in land use and cover in the Malaba River Catchment, Eastern Uganda
- Authors: Barasa, Bernard
- Date: 2014
- Subjects: Hydrologic models -- Uganda , Runoff -- Uganda
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10670 , http://hdl.handle.net/10948/d1020153
- Description: Hydrological responses vary from one catchment to another, depending on the nature of land use and cover changes. Modelling the hydrological responses to changes in land use and cover at different catchment spatial scales was the major focus of this study. This study assessed the hydrological responses attributed to changes in land use and extreme weather events resulting into increased sediment loading/concentration, rainfall-runoff generation/volume, streamflow fluctuation and modification of the river channel in the Malaba River Catchment, Eastern Uganda. The hydrological responses were assessed using hydrological models (IHACRES, SCS CN, and SHETRAN) to examine the effect of land use on soil physio-chemical properties susceptibility to rainfall-runoff generation and volume, frequency and severity of extreme weather events, changes in streamflow variations, sediment loading/concentration and river channel morphology. The preliminary study results showed that the frequency of extreme weather events reduced from 4-10 to 1-3 years over the catchment. The performance of the IHACRES model with a Nash-Sutcliffe Efficiency (NSE) of 0.89 showed that streamflow comparatively corresponded with the results obtained the drought indices in predicting the recorded events of severe drought (2005) and flood (1997). Changes in land use and cover types showed that the highest change in the gain of land was experienced from the agricultural land use (36.7 percent), and tropical forest (regeneration) (2.2 percent). The biggest losses in land were experienced in the wetlands (24.6 percent) and bushland and thickets (15.3 percent) land cover types. The SHETRAN model calibrated period had a NSE of 0.78 and 0.81 in the validation period showed satisfactory fits between the measured and simulated streamflow. The agricultural land use (crop growing) had a higher influence on the rainfall-runoff generation and increase in the streamflow than the tropical forest, and bushland cover types in the simulated period. Similarly, the curve number model estimated a comparatively higher surface rainfall-runoff volume generated from the agricultural land use (crop growing) (71,740 m3) than in the bushlands and thickets (42,872 m3) from a rainstorm followed by the tropical forest cover type. This was also reflected in the lower rates of saturated hydraulic conductivity from the agricultural land use (crop growing). The study also showed that human-induced sediment loading due to gold mining activities contributed a much higher impact on the concentration of suspended sediments and streamflow than sediments from rainfall-runoff from the sampled streams. The main contributor of human-induced sediments to the Malaba River were Nankuke River (130.6kg/annum), followed by Omanyi River (70.6kg/annum), and Nabewo River (66.8kg/annum). Human-induced sediment loading had a profound impact on the streamflow variations both in the dry and wet seasons from the sampled tributaries. Lastly, in regard to the effect of land use and cover types on the river channel morphology, tree plantation (cohesion=12, angle of internal friction=27) and bushland and thickets (cohesion=14, angle of internal friction=22) cover types had the most stable river banks compared to the wetland and agricultural land use and cover types that exhibited higher levels of sediment concentration.
- Full Text:
- Date Issued: 2014
- Authors: Barasa, Bernard
- Date: 2014
- Subjects: Hydrologic models -- Uganda , Runoff -- Uganda
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10670 , http://hdl.handle.net/10948/d1020153
- Description: Hydrological responses vary from one catchment to another, depending on the nature of land use and cover changes. Modelling the hydrological responses to changes in land use and cover at different catchment spatial scales was the major focus of this study. This study assessed the hydrological responses attributed to changes in land use and extreme weather events resulting into increased sediment loading/concentration, rainfall-runoff generation/volume, streamflow fluctuation and modification of the river channel in the Malaba River Catchment, Eastern Uganda. The hydrological responses were assessed using hydrological models (IHACRES, SCS CN, and SHETRAN) to examine the effect of land use on soil physio-chemical properties susceptibility to rainfall-runoff generation and volume, frequency and severity of extreme weather events, changes in streamflow variations, sediment loading/concentration and river channel morphology. The preliminary study results showed that the frequency of extreme weather events reduced from 4-10 to 1-3 years over the catchment. The performance of the IHACRES model with a Nash-Sutcliffe Efficiency (NSE) of 0.89 showed that streamflow comparatively corresponded with the results obtained the drought indices in predicting the recorded events of severe drought (2005) and flood (1997). Changes in land use and cover types showed that the highest change in the gain of land was experienced from the agricultural land use (36.7 percent), and tropical forest (regeneration) (2.2 percent). The biggest losses in land were experienced in the wetlands (24.6 percent) and bushland and thickets (15.3 percent) land cover types. The SHETRAN model calibrated period had a NSE of 0.78 and 0.81 in the validation period showed satisfactory fits between the measured and simulated streamflow. The agricultural land use (crop growing) had a higher influence on the rainfall-runoff generation and increase in the streamflow than the tropical forest, and bushland cover types in the simulated period. Similarly, the curve number model estimated a comparatively higher surface rainfall-runoff volume generated from the agricultural land use (crop growing) (71,740 m3) than in the bushlands and thickets (42,872 m3) from a rainstorm followed by the tropical forest cover type. This was also reflected in the lower rates of saturated hydraulic conductivity from the agricultural land use (crop growing). The study also showed that human-induced sediment loading due to gold mining activities contributed a much higher impact on the concentration of suspended sediments and streamflow than sediments from rainfall-runoff from the sampled streams. The main contributor of human-induced sediments to the Malaba River were Nankuke River (130.6kg/annum), followed by Omanyi River (70.6kg/annum), and Nabewo River (66.8kg/annum). Human-induced sediment loading had a profound impact on the streamflow variations both in the dry and wet seasons from the sampled tributaries. Lastly, in regard to the effect of land use and cover types on the river channel morphology, tree plantation (cohesion=12, angle of internal friction=27) and bushland and thickets (cohesion=14, angle of internal friction=22) cover types had the most stable river banks compared to the wetland and agricultural land use and cover types that exhibited higher levels of sediment concentration.
- Full Text:
- Date Issued: 2014
Molecular phylogeny, phylogeography and evolutionary adaptation of foraging behaviour amongst sympatric patellid limpets along the southern African shoreline
- Authors: Mmonwa, Kolobe Lucas
- Date: 2014
- Subjects: Limpets -- South Africa -- Adaptation , Limpets -- South Africa -- Ecology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5882 , http://hdl.handle.net/10962/d1013222
- Description: The southern African shoreline is inhabited by a great diversity of patellid limpets of which most are endemic to South Africa. These limpets have evolved foraging mechanisms that partition ecological resources and reduce interspecific competition, resulting in ecological specialists and generalists. The evolution of ecological specialization or generalization remains poorly understood and there is no agreement on how such evolutionary transitions are correlated with levels of genetic diversity. This study investigated evolutionary correlations between territoriality in foraging and genetic structure of southern African patellid limpets (Cymbula and Scutellastra spp.) using stable δ13C and δ15N ratios, mitochondrial and nuclear DNA markers. The outcomes of the study were best rationalized and understood in the context of the scale of analysis in terms of both space and taxonomy. At biogeographic scales and the interspecific level, the stable isotope signatures and genetic structure of these limpets are determined by extrinsic factors such as biogeography and oceanography. However, at the smallest site scales and the intraspecific level, the isotope signatures and genetic diversity of these limpets are significantly correlated to their foraging traits. At large scales, there are no correlations between foraging behaviour and either genetic structure or isotope signature. At smaller scales, territorial Scutellastra foragers display both isotopic enrichment and greater haplotype diversity than congeneric non-territorial foragers. Thus, the isotope signatures and genetic structure of these limpets are determined by intrinsic species-specific response linked to their foraging behaviour. However, this pattern was intriguing as differences between territorial and non-territorial limpets in both isotopic signature and genetic diversity were observed only along the south coast when the same species were compared in other biogeographic regions. The significant interaction effect between foraging behaviour and stable isotope signatures was only observed from the sites within the Agulhas Bank or which are strongly influenced by the Agulhas current. This south enrichment in isotopic ratios is due to the mixing differences between onshore and offshore waters as the Agulhas current moves from east to south. At the generic level, the correlation between foraging behaviour and isotope signatures and genetic structure were particularly profound for Scutellastra species. The molecular phylogeny revealed deep evolutionary divergence between territorial and non-territorial Scutellastra spp. This divergence was concordant with morphological differences in shell shape and radula anatomy between territorial and non-territorial species. A taxonomic review of the scutellastrid spp. is proposed, suggesting possible re-consideration of the genus as two genera characterized by either territoriality or non-territoriality. The divergence between territorial and non-territorial species in both Scutellastra and Cymbula took place approximately in the early Oligocene. Major climatic cooling and decreases in sea level occurred during the Oligocene and this probably exposed much of the lower intertidal zone, increasing new potential habitats and algal availability. The Oligocene exposure of rocky shores and algal abundance in the lower intertidal zone probably elicited resource partitioning amongst these patellid limpets and subsequently, the evolution of territorial and non-territorial species. Analyses of the demographic history of these patellid limpets revealed evidence of post-glacial spatial expansion around the Pleistocene, implying these limpets were at population equilibrium during the dramatic LGM sea temperatures. Thus, these limpets managed to expand their range during dynamic oceanographic oscillations and dramatic sea-level changes in the Pleistocene. This study highlighted the importance of applying ecological traits as a subject to investigate and comprehend the evolutionary ecology of marine herbivores. The foraging traits of these true limpets are reflected in both their stable isotope ratios and genealogy, presumably as an evolutionary consequence of competition.
- Full Text:
- Date Issued: 2014
- Authors: Mmonwa, Kolobe Lucas
- Date: 2014
- Subjects: Limpets -- South Africa -- Adaptation , Limpets -- South Africa -- Ecology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5882 , http://hdl.handle.net/10962/d1013222
- Description: The southern African shoreline is inhabited by a great diversity of patellid limpets of which most are endemic to South Africa. These limpets have evolved foraging mechanisms that partition ecological resources and reduce interspecific competition, resulting in ecological specialists and generalists. The evolution of ecological specialization or generalization remains poorly understood and there is no agreement on how such evolutionary transitions are correlated with levels of genetic diversity. This study investigated evolutionary correlations between territoriality in foraging and genetic structure of southern African patellid limpets (Cymbula and Scutellastra spp.) using stable δ13C and δ15N ratios, mitochondrial and nuclear DNA markers. The outcomes of the study were best rationalized and understood in the context of the scale of analysis in terms of both space and taxonomy. At biogeographic scales and the interspecific level, the stable isotope signatures and genetic structure of these limpets are determined by extrinsic factors such as biogeography and oceanography. However, at the smallest site scales and the intraspecific level, the isotope signatures and genetic diversity of these limpets are significantly correlated to their foraging traits. At large scales, there are no correlations between foraging behaviour and either genetic structure or isotope signature. At smaller scales, territorial Scutellastra foragers display both isotopic enrichment and greater haplotype diversity than congeneric non-territorial foragers. Thus, the isotope signatures and genetic structure of these limpets are determined by intrinsic species-specific response linked to their foraging behaviour. However, this pattern was intriguing as differences between territorial and non-territorial limpets in both isotopic signature and genetic diversity were observed only along the south coast when the same species were compared in other biogeographic regions. The significant interaction effect between foraging behaviour and stable isotope signatures was only observed from the sites within the Agulhas Bank or which are strongly influenced by the Agulhas current. This south enrichment in isotopic ratios is due to the mixing differences between onshore and offshore waters as the Agulhas current moves from east to south. At the generic level, the correlation between foraging behaviour and isotope signatures and genetic structure were particularly profound for Scutellastra species. The molecular phylogeny revealed deep evolutionary divergence between territorial and non-territorial Scutellastra spp. This divergence was concordant with morphological differences in shell shape and radula anatomy between territorial and non-territorial species. A taxonomic review of the scutellastrid spp. is proposed, suggesting possible re-consideration of the genus as two genera characterized by either territoriality or non-territoriality. The divergence between territorial and non-territorial species in both Scutellastra and Cymbula took place approximately in the early Oligocene. Major climatic cooling and decreases in sea level occurred during the Oligocene and this probably exposed much of the lower intertidal zone, increasing new potential habitats and algal availability. The Oligocene exposure of rocky shores and algal abundance in the lower intertidal zone probably elicited resource partitioning amongst these patellid limpets and subsequently, the evolution of territorial and non-territorial species. Analyses of the demographic history of these patellid limpets revealed evidence of post-glacial spatial expansion around the Pleistocene, implying these limpets were at population equilibrium during the dramatic LGM sea temperatures. Thus, these limpets managed to expand their range during dynamic oceanographic oscillations and dramatic sea-level changes in the Pleistocene. This study highlighted the importance of applying ecological traits as a subject to investigate and comprehend the evolutionary ecology of marine herbivores. The foraging traits of these true limpets are reflected in both their stable isotope ratios and genealogy, presumably as an evolutionary consequence of competition.
- Full Text:
- Date Issued: 2014
Molecular systematics and antifreeze biology of sub-Antarctic notothenioid fishes
- Authors: Miya, Tshoanelo Portia
- Date: 2014
- Subjects: Nototheniidae , Antifreeze proteins , Nototheniidae -- Classification -- Molecular aspects , Polyacrylamide gel electrophoresis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5388 , http://hdl.handle.net/10962/d1020938
- Description: Fishes of the perciform suborder Notothenioidei are found in Antarctic and sub-Antarctic waters that are separated by the Antarctic Polar Front (APF), with some species being distributed on both sides of this front. In this wide latitudinal range, these fishes are exposed to different temperatures ranging from -2 °C in the High Antarctic regions to 12 °C in the sub-Antarctic regions. To survive in icy Antarctic waters, the Antarctic notothenioid species have evolved antifreeze glycoproteins (AFGPs) that prevent their body fluids from freezing. The findings of past research on the AFGP attributes of several notothenioid species inhabiting ice-free sub-Antarctic environments have presented a complex picture. Furthermore, previous taxonomic studies split widely distributed notothenioids into different species and/or subspecies, with other studies disagreeing with these splits. To understand the response of the sub-Antarctic notothenioids to warmer, ice-free environments, it is necessary to have a good understanding of their antifreeze biology and systematics. Therefore, this study aimed to determine the association, if any, between the antifreeze attributes of sub-Antarctic notothenioid fishes and their taxonomic status. And more...
- Full Text:
- Date Issued: 2014
- Authors: Miya, Tshoanelo Portia
- Date: 2014
- Subjects: Nototheniidae , Antifreeze proteins , Nototheniidae -- Classification -- Molecular aspects , Polyacrylamide gel electrophoresis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5388 , http://hdl.handle.net/10962/d1020938
- Description: Fishes of the perciform suborder Notothenioidei are found in Antarctic and sub-Antarctic waters that are separated by the Antarctic Polar Front (APF), with some species being distributed on both sides of this front. In this wide latitudinal range, these fishes are exposed to different temperatures ranging from -2 °C in the High Antarctic regions to 12 °C in the sub-Antarctic regions. To survive in icy Antarctic waters, the Antarctic notothenioid species have evolved antifreeze glycoproteins (AFGPs) that prevent their body fluids from freezing. The findings of past research on the AFGP attributes of several notothenioid species inhabiting ice-free sub-Antarctic environments have presented a complex picture. Furthermore, previous taxonomic studies split widely distributed notothenioids into different species and/or subspecies, with other studies disagreeing with these splits. To understand the response of the sub-Antarctic notothenioids to warmer, ice-free environments, it is necessary to have a good understanding of their antifreeze biology and systematics. Therefore, this study aimed to determine the association, if any, between the antifreeze attributes of sub-Antarctic notothenioid fishes and their taxonomic status. And more...
- Full Text:
- Date Issued: 2014
Narratives that shape the professional identities of mathematics teachers
- Felix, Clyde Benedict Aurelius
- Authors: Felix, Clyde Benedict Aurelius
- Date: 2014
- Subjects: Mathematics teachers -- South Africa -- Port Elizabeth , Mathematics teachers -- South Africa -- Grahamstown , Mathematics teachers -- Professional relationships , Mathematics teachers -- Training of , Mathematics -- Study and teaching -- South Africa -- Eastern Cape , Education -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1995 , http://hdl.handle.net/10962/d1013547
- Description: The central position in this study is that the professional identities, and consequently the classroom practices, of mathematics teachers are continuously being shaped by their narratives of past and present experiences. The primary research question explores the narratives that shape the professional identities of seven mathematics teachers; and the secondary research question, how their narratives shape their professional identities. Furthermore, the potential implications of this study for the design and implementation of pre-service teacher education programmes and in-service teacher development initiatives are considered. This study is framed by Socioculturalism; a theoretical perspective of human thinking as social in origin and of learning as participation in social practices. Futhermore, in line with Situated Learning Theory, the key theoretical notions are: identity (or learning as becoming); community (or learning as belonging); practice (or learning as doing); and meaning (or learning as experience). Identity is construed here as a conceptual bridge between learning and its cultural settings; and also between the individual and the social. In this study, the identity-shaping narratives of seven mathematics teachers, all purposively sampled from schools in the Port Elizabeth and Grahamstown education districts of the Eastern Cape Province of South Africa, were accessed via a narrative inquiry; followed by a horizontal analysis to identify common patterns or recurring themes in the narratives of all seven participants; and, a vertical analysis of the narratives of four of the participants to determine how their narratives shape their professional identities. Recurring themes that emerged during the horizontal analysis include the influence of: family support; role models; changing work environments; continuous professional development; professional recognition; religion; and, micro-politics. The vertical analysis demonstrated how, through a process of interpreting the narratives and restorying them into a meaningful core narrative; it is possible to gain insights into how personal narratives shape a professional identity. This study highlights the importance of listening to the narratives of mathematics teachers; because their professional identities, and consequently their teaching practices, are continuously being shaped by their narratives. It is anticipated that this research will be of interest and benefit to researchers, policy-makers, and teachers; especially in the area of Mathematics Education, where both narrative inquiry as a research method and research into teachers’ professional identities are relatively new.
- Full Text:
- Date Issued: 2014
- Authors: Felix, Clyde Benedict Aurelius
- Date: 2014
- Subjects: Mathematics teachers -- South Africa -- Port Elizabeth , Mathematics teachers -- South Africa -- Grahamstown , Mathematics teachers -- Professional relationships , Mathematics teachers -- Training of , Mathematics -- Study and teaching -- South Africa -- Eastern Cape , Education -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1995 , http://hdl.handle.net/10962/d1013547
- Description: The central position in this study is that the professional identities, and consequently the classroom practices, of mathematics teachers are continuously being shaped by their narratives of past and present experiences. The primary research question explores the narratives that shape the professional identities of seven mathematics teachers; and the secondary research question, how their narratives shape their professional identities. Furthermore, the potential implications of this study for the design and implementation of pre-service teacher education programmes and in-service teacher development initiatives are considered. This study is framed by Socioculturalism; a theoretical perspective of human thinking as social in origin and of learning as participation in social practices. Futhermore, in line with Situated Learning Theory, the key theoretical notions are: identity (or learning as becoming); community (or learning as belonging); practice (or learning as doing); and meaning (or learning as experience). Identity is construed here as a conceptual bridge between learning and its cultural settings; and also between the individual and the social. In this study, the identity-shaping narratives of seven mathematics teachers, all purposively sampled from schools in the Port Elizabeth and Grahamstown education districts of the Eastern Cape Province of South Africa, were accessed via a narrative inquiry; followed by a horizontal analysis to identify common patterns or recurring themes in the narratives of all seven participants; and, a vertical analysis of the narratives of four of the participants to determine how their narratives shape their professional identities. Recurring themes that emerged during the horizontal analysis include the influence of: family support; role models; changing work environments; continuous professional development; professional recognition; religion; and, micro-politics. The vertical analysis demonstrated how, through a process of interpreting the narratives and restorying them into a meaningful core narrative; it is possible to gain insights into how personal narratives shape a professional identity. This study highlights the importance of listening to the narratives of mathematics teachers; because their professional identities, and consequently their teaching practices, are continuously being shaped by their narratives. It is anticipated that this research will be of interest and benefit to researchers, policy-makers, and teachers; especially in the area of Mathematics Education, where both narrative inquiry as a research method and research into teachers’ professional identities are relatively new.
- Full Text:
- Date Issued: 2014
Nonlinear optical studies of metallophtalocyanines and hemiporphyrazines in solution
- Authors: Britton, Jonathan
- Date: 2014
- Subjects: Phthalocyanines Photochemistry Nanoparticles Nanostructured materials Polymers Quantum dots
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4464 , http://hdl.handle.net/10962/d1011608
- Description: This thesis presents the study of the effects of CdTe-TGA quantum dots (QDs) on optical limiting ability of different phthalocyanine (Pc) complexes (5-12) containing Zn, Ga, In central metals and substituted with benzyloxyphenoxy, phenoxy, tertbutylphenoxy and amino groups in solution and in poly (methyl methacrylate) (PMMA) films. The optical limiting parameters of Pcs were higher for tertbutylphenoxy when compared to benzyloxyphenoxy and phenoxy substituents, in DMSO. Non-peripheral substitution decreased the optical limiting parameters. Third-order susceptibility (Im[χ⁽³⁾]/α) values of Pcs in the absence and presence of CdTe QDs were in the 10⁻¹² to 10⁻¹° esu cm range. Hyperpolarizabilities (γ) ranged from 10⁻³¹ to 10⁻²⁹ esu L for Pc alone or in mixture with QDs. The effect on the optical limiting abilities of twelve embedded phthalocyanines containing In, Ga, Zn and Al as central metals in polymer thin films was also examined. The effect of forming a covalent link zinc tetraamino phthalocyanine (12) with poly (methyl acrylic acid) (PMAA) and Zn (13) and OHAl (14) octacarboxy phthalocyanines to polyethylenimine (PEI) was also studied. The hyperpolarizability of the twelve phthalocyanines in polymer was found to be in the range of 10⁻²⁶ to 10⁻²⁴ esu.L. This is significantly higher than the hyperpolarizabilities of these phthalocyanines in solution. Non-linear optical (NLO) parameters were determined for phthalocyanine complexes containing In, Ga and Zn as central metals when embedded in PMMA polymer in the presence of quantum dots (QDs). The QDs mainly employed were CdTe-TGA (TGA = thioglylcolic acid). Triplet lifetimes increased as k (excited state (σex) to ground state (σg) absorption cross section ratio) values decreased with the addition of the CdTe-TGA to the phthalocyanines. The saturation energy density (Fsat) values were smaller in the films when compared to the solutions. Complex 7 tetrasubstituted with tert-butylphenoxy groups at non-peripheral positions was also studied in the presence of CdS-TGA, CdSe-TGA, fullerenes and single walled carbon nanotubes. There is a general improvement in optical limiting ability of Pc complexes in the presence of nanomaterials (NMs). Degradation studies seem to indicate that placing a phthalocyanine within a polymer thin film may protect it slightly from photo- and thermal degradation. 3(4), 15(16)-Bis-(4 -tert-butyl-phenoxy)-10, 22-diaminohemiporphyrazinato chloroindium hemiporphyrazine was synthesized from 1, 3, 5-triaminobenzene and 4-tert-butyl-phenoxyisoindoline. The structure of the complex was confirmed using mass, nuclear magnetic resonance and infrared spectroscopies. The nonlinear parameters of the compound was also analyzed in dimethylformamide and found to be significantly greater than previously analyzed phthalocyanines.
- Full Text:
- Date Issued: 2014
- Authors: Britton, Jonathan
- Date: 2014
- Subjects: Phthalocyanines Photochemistry Nanoparticles Nanostructured materials Polymers Quantum dots
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4464 , http://hdl.handle.net/10962/d1011608
- Description: This thesis presents the study of the effects of CdTe-TGA quantum dots (QDs) on optical limiting ability of different phthalocyanine (Pc) complexes (5-12) containing Zn, Ga, In central metals and substituted with benzyloxyphenoxy, phenoxy, tertbutylphenoxy and amino groups in solution and in poly (methyl methacrylate) (PMMA) films. The optical limiting parameters of Pcs were higher for tertbutylphenoxy when compared to benzyloxyphenoxy and phenoxy substituents, in DMSO. Non-peripheral substitution decreased the optical limiting parameters. Third-order susceptibility (Im[χ⁽³⁾]/α) values of Pcs in the absence and presence of CdTe QDs were in the 10⁻¹² to 10⁻¹° esu cm range. Hyperpolarizabilities (γ) ranged from 10⁻³¹ to 10⁻²⁹ esu L for Pc alone or in mixture with QDs. The effect on the optical limiting abilities of twelve embedded phthalocyanines containing In, Ga, Zn and Al as central metals in polymer thin films was also examined. The effect of forming a covalent link zinc tetraamino phthalocyanine (12) with poly (methyl acrylic acid) (PMAA) and Zn (13) and OHAl (14) octacarboxy phthalocyanines to polyethylenimine (PEI) was also studied. The hyperpolarizability of the twelve phthalocyanines in polymer was found to be in the range of 10⁻²⁶ to 10⁻²⁴ esu.L. This is significantly higher than the hyperpolarizabilities of these phthalocyanines in solution. Non-linear optical (NLO) parameters were determined for phthalocyanine complexes containing In, Ga and Zn as central metals when embedded in PMMA polymer in the presence of quantum dots (QDs). The QDs mainly employed were CdTe-TGA (TGA = thioglylcolic acid). Triplet lifetimes increased as k (excited state (σex) to ground state (σg) absorption cross section ratio) values decreased with the addition of the CdTe-TGA to the phthalocyanines. The saturation energy density (Fsat) values were smaller in the films when compared to the solutions. Complex 7 tetrasubstituted with tert-butylphenoxy groups at non-peripheral positions was also studied in the presence of CdS-TGA, CdSe-TGA, fullerenes and single walled carbon nanotubes. There is a general improvement in optical limiting ability of Pc complexes in the presence of nanomaterials (NMs). Degradation studies seem to indicate that placing a phthalocyanine within a polymer thin film may protect it slightly from photo- and thermal degradation. 3(4), 15(16)-Bis-(4 -tert-butyl-phenoxy)-10, 22-diaminohemiporphyrazinato chloroindium hemiporphyrazine was synthesized from 1, 3, 5-triaminobenzene and 4-tert-butyl-phenoxyisoindoline. The structure of the complex was confirmed using mass, nuclear magnetic resonance and infrared spectroscopies. The nonlinear parameters of the compound was also analyzed in dimethylformamide and found to be significantly greater than previously analyzed phthalocyanines.
- Full Text:
- Date Issued: 2014
On the electrical characterisation of bulk and epitaxial n-type Te doped GaSb
- Authors: Murape, Davison Munyaradzi
- Date: 2014
- Subjects: Gallium arsenide semiconductors , Electronics
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10554 , http://hdl.handle.net/10948/d1020763
- Description: Since the development of the transistor in the Bell Telephone Laboratories in 1948 [78], the semiconductor industry has transformed the world we live in. It is difficult to picture a world without the modern day cutting edge technology. Imagine performing every day functions without “trivial” devices such as computers, cell phones or microwave ovens. The ability to tailor the band gaps of various binary, ternary and quaternary semiconductor systems has opened up a whole new spectrum of potential purpose designed devices [27]. This thesis focuses on the electronic properties of gallium (III) antimonide (V). The antimonides, in general, have the smallest band gap and highest electron mobility of the III-V compound semiconductors and are well suited for long wavelength emission and detection as well as high frequency switching device applications. Furthermore, III-V ternaries and quaternaries, such as (AlGaIn)(AsSb), lattice matched to gallium antimonide (GaSb) are considered serious competitors for HgCdTe and PbSe in long-wavelength infrared (LWIR) and very long-wavelength infrared (VLWIR) technology [4, 10, 11]. Epitaxial material systems based on GaSb are suitable for a wide range of applications such as missile and surveillance systems and a host of other military and civil applications. In addition, an assortment of devices on InAs, GaSb, and AlSb, including resonant tunnelling devices, infrared detectors and mid-infrared semiconductor lasers have been demonstrated [14, 15]. Furthermore, antimonide based devices could potentially reduce optical fibre power loss by a few orders of magnitude, as their implementation can lead to use of non-silica based optical fibres that minimise Raleigh scatter related power loss [8]. GaSb related technology faces a number of challenges. A significant amount of effort is required to exploit the potential it offers. GaSb oxidises readily in the ambient, resulting in the formation of a native oxide layer as well as deposits of elemental antimony (Sb) at the oxide/substrate interface therefore it has poor surface electronic properties resulting from high surface state densities[4, 17, 18]. As grown GaSb is characterised by a high density of surface states of which many are classified as non-radiative (Auger) recombination centres. The elemental Sb layer constitutes an unwanted conduction path parallel to the active surface region [17]. The potential that GaSb and GaSb-based strained layer superlattices offer as successors to the current generation of LWIR and VLWIR optoelectronic materials has therefore been largely impeded [4]. Furthermore, processing steps in device fabrication leads to an unintentionally damaged GaSb surface exacerbating the situation. Any efforts to engineer devices of superior quality on GaSb have to address these and more material specific problems [19]. This study attempts to contribute towards an improved understanding of the structural and electrical properties of the near surface region of Te-doped bulk (100) and MOVPE grown epitaxial Te doped n- GaSb. The main focus of this study is to develop means to de-oxidise and stabilize the highly reactive GaSb surface and to develop diode structures to demonstrate the improved interface characteristics and use related current–voltage (I-V) measurements to quantify the surface state density before and after treatment. These devices were also used to probe the near surface region for electrically active deep level defects that often act as non-radiative recombination centers. Au, Pd and Al were used as metals to establish a metal semiconductor barrier and subsequent depletion region. Sulphur based chemicals, ([(NH4)2S / (NH4)2SO4] + S), not previously reported for the treatment of (100) n-GaSb surfaces, and the commonly used passivants Na2S:9H2O and (NH4)2S were compared by assessing the electrical and structural properties both before and after treatment. The effect of treatment on the electrical response of the material was determined using current-voltage, capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) measurements, while the surface morphology and composition were studied by SEM, AES and XPS.
- Full Text:
- Date Issued: 2014
- Authors: Murape, Davison Munyaradzi
- Date: 2014
- Subjects: Gallium arsenide semiconductors , Electronics
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10554 , http://hdl.handle.net/10948/d1020763
- Description: Since the development of the transistor in the Bell Telephone Laboratories in 1948 [78], the semiconductor industry has transformed the world we live in. It is difficult to picture a world without the modern day cutting edge technology. Imagine performing every day functions without “trivial” devices such as computers, cell phones or microwave ovens. The ability to tailor the band gaps of various binary, ternary and quaternary semiconductor systems has opened up a whole new spectrum of potential purpose designed devices [27]. This thesis focuses on the electronic properties of gallium (III) antimonide (V). The antimonides, in general, have the smallest band gap and highest electron mobility of the III-V compound semiconductors and are well suited for long wavelength emission and detection as well as high frequency switching device applications. Furthermore, III-V ternaries and quaternaries, such as (AlGaIn)(AsSb), lattice matched to gallium antimonide (GaSb) are considered serious competitors for HgCdTe and PbSe in long-wavelength infrared (LWIR) and very long-wavelength infrared (VLWIR) technology [4, 10, 11]. Epitaxial material systems based on GaSb are suitable for a wide range of applications such as missile and surveillance systems and a host of other military and civil applications. In addition, an assortment of devices on InAs, GaSb, and AlSb, including resonant tunnelling devices, infrared detectors and mid-infrared semiconductor lasers have been demonstrated [14, 15]. Furthermore, antimonide based devices could potentially reduce optical fibre power loss by a few orders of magnitude, as their implementation can lead to use of non-silica based optical fibres that minimise Raleigh scatter related power loss [8]. GaSb related technology faces a number of challenges. A significant amount of effort is required to exploit the potential it offers. GaSb oxidises readily in the ambient, resulting in the formation of a native oxide layer as well as deposits of elemental antimony (Sb) at the oxide/substrate interface therefore it has poor surface electronic properties resulting from high surface state densities[4, 17, 18]. As grown GaSb is characterised by a high density of surface states of which many are classified as non-radiative (Auger) recombination centres. The elemental Sb layer constitutes an unwanted conduction path parallel to the active surface region [17]. The potential that GaSb and GaSb-based strained layer superlattices offer as successors to the current generation of LWIR and VLWIR optoelectronic materials has therefore been largely impeded [4]. Furthermore, processing steps in device fabrication leads to an unintentionally damaged GaSb surface exacerbating the situation. Any efforts to engineer devices of superior quality on GaSb have to address these and more material specific problems [19]. This study attempts to contribute towards an improved understanding of the structural and electrical properties of the near surface region of Te-doped bulk (100) and MOVPE grown epitaxial Te doped n- GaSb. The main focus of this study is to develop means to de-oxidise and stabilize the highly reactive GaSb surface and to develop diode structures to demonstrate the improved interface characteristics and use related current–voltage (I-V) measurements to quantify the surface state density before and after treatment. These devices were also used to probe the near surface region for electrically active deep level defects that often act as non-radiative recombination centers. Au, Pd and Al were used as metals to establish a metal semiconductor barrier and subsequent depletion region. Sulphur based chemicals, ([(NH4)2S / (NH4)2SO4] + S), not previously reported for the treatment of (100) n-GaSb surfaces, and the commonly used passivants Na2S:9H2O and (NH4)2S were compared by assessing the electrical and structural properties both before and after treatment. The effect of treatment on the electrical response of the material was determined using current-voltage, capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) measurements, while the surface morphology and composition were studied by SEM, AES and XPS.
- Full Text:
- Date Issued: 2014
Oxidative desulfurization of fuel oils-catalytic oxidation and adsorptive removal of organosulfur compounds
- Authors: Ogunlaja, Adeniyi Sunday
- Date: 2014
- Subjects: Organosulfur compounds , Organosulfur compounds -- Oxidation , Organosulfur compounds -- Absorption and adsorption , Petroleum as fuel , Catalysis , Imprinted polymers , Molecular imprinting , Nanofibers , Electrospinning
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4498 , http://hdl.handle.net/10962/d1013152
- Description: The syntheses and evaluation of oxidovanadium(IV) complexes as catalysts for the oxidation of refractory organosulfur compounds in fuels is presented. The sulfones produced from the oxidation reaction were removed from fuel oils by employing molecularly imprinted polymers (MIPs). The oxidovanadium(IV) homogeneous catalyst, [V ͥ ͮ O(sal-HBPD)], as well as its heterogeneous polymer supported derivatives, poly[V ͥ ͮ O(sal-AHBPD)] and poly[V ͥ ͮ O(allylSB-co-EGDMA)], were synthesized and fully characterized by elemental analysis, FTIR, UV-Vis, XPS, AFM, SEM, BET and single crystal XRD for [V ͥ ͮ O(sal-HBPD)]. The MIPs were also characterized by elemental analysis, FTIR, SEM, EDX and BET. The catalyzed oxidation of fuel oil model sulfur compounds, thiophene (TH), benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT), was conducted under batch and continuous flow processes at 40°C by using tert-butylhydroperoxide (t-BuOOH) as oxidant. The continuous flow oxidation process presented the highest overall conversions and very high selectivity for sulfones. Maximum oxidation conversions of 71%, 89%, 99% and 88% was achieved for TH, BT, DBT and 4,6-DMDBT respectively when poly[V ͥ ͮ O(allylSB-co-EGDMA)] was employed at a flow-rate of 1 mL/h with over 90% sulfone selectivity. The process was further applied to the oxidation of hydro-treated diesel containing 385 ± 4.6 ppm of sulfur (mainly dibenzothiophene and dibenzothiophene derivatives), and this resulted to a high sulfur oxidation yield (> 99%), thus producing polar sulfones which are extractible by polar solid phase extractants. Adsorption of the polar sulfone compounds was carried-out by employing MIPs which were fabricated through the formation of recognition sites complementary to oxidized sulfur-containing compounds (sulfones) on electrospun polybenzimidazole (PBI) nanofibers, cross-linked chitosan microspheres and electrospun chitosan nanofibers. Adsorption of benzothiophene sulfone (BTO₂), dibenzothiophene sulfone (DBTO₂) and 4,6-dimethyldibenzothiophene sulfone (4,6-DMDBTO₂) on the various molecularly imprinted adsorbents presented a Freundlich (multi-layered) adsorption isotherm which indicated interaction of adsorbed organosulfur compounds. Maximum adsorption observed for BTO₂, DBTO₂ and 4,6-DMDBTO₂ respectively was 8.5 ± 0.6 mg/g, 7.0 ± 0.5 mg/g and 6.6 ± 0.7 mg/g when imprinted chitosan nanofibers were employed, 4.9 ± 0.5 mg/g, 4.2 ± 0.7 mg/g and 3.9 ± 0.6 mg/g on molecularly imprinted chitosan microspheres, and 28.5 ± 0.4 mg/g, 29.8 ± 2.2 mg/g and 20.1 ± 1.4 mg/g on molecularly imprinted PBI nanofibers. Application of electrospun chitosan nanofibers on oxidized hydro-treated diesel presented a sulfur removal capacity of 84%, leaving 62 ± 3.2 ppm S in the fuel, while imprinted PBI electrospun nanofibers displayed excellent sulfur removal, keeping sulfur in the fuel after the oxidation/adsorption below the determined limit of detection (LOD), which is 2.4 ppm S. The high level of sulfur removal displayed by imprinted PBI nanofibers was ascribed to hydrogen bonding effects, and π-π stacking between aromatic sulfone compounds and the benzimidazole ring which were confirmed by chemical modelling with density functional theory (DFT) as well as the imprinting effect. The home-made pressurized hot water extraction (PHWE) system was applied for extraction/desorption of sulfone compounds adsorbed on the PBI nanofibers at a flow rate of 1 mL/min and at 150°C with an applied pressure of 30 bars. Application of molecularly imprinted PBI nanofibers for the desulfurization of oxidized hydro-treated fuel showed potential for use in refining industries to reach ultra-low sulfur fuel level, which falls below the 10 ppm sulfur limit which is mandated by the environmental protection agency (EPA) from 2015.
- Full Text:
- Date Issued: 2014
- Authors: Ogunlaja, Adeniyi Sunday
- Date: 2014
- Subjects: Organosulfur compounds , Organosulfur compounds -- Oxidation , Organosulfur compounds -- Absorption and adsorption , Petroleum as fuel , Catalysis , Imprinted polymers , Molecular imprinting , Nanofibers , Electrospinning
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4498 , http://hdl.handle.net/10962/d1013152
- Description: The syntheses and evaluation of oxidovanadium(IV) complexes as catalysts for the oxidation of refractory organosulfur compounds in fuels is presented. The sulfones produced from the oxidation reaction were removed from fuel oils by employing molecularly imprinted polymers (MIPs). The oxidovanadium(IV) homogeneous catalyst, [V ͥ ͮ O(sal-HBPD)], as well as its heterogeneous polymer supported derivatives, poly[V ͥ ͮ O(sal-AHBPD)] and poly[V ͥ ͮ O(allylSB-co-EGDMA)], were synthesized and fully characterized by elemental analysis, FTIR, UV-Vis, XPS, AFM, SEM, BET and single crystal XRD for [V ͥ ͮ O(sal-HBPD)]. The MIPs were also characterized by elemental analysis, FTIR, SEM, EDX and BET. The catalyzed oxidation of fuel oil model sulfur compounds, thiophene (TH), benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT), was conducted under batch and continuous flow processes at 40°C by using tert-butylhydroperoxide (t-BuOOH) as oxidant. The continuous flow oxidation process presented the highest overall conversions and very high selectivity for sulfones. Maximum oxidation conversions of 71%, 89%, 99% and 88% was achieved for TH, BT, DBT and 4,6-DMDBT respectively when poly[V ͥ ͮ O(allylSB-co-EGDMA)] was employed at a flow-rate of 1 mL/h with over 90% sulfone selectivity. The process was further applied to the oxidation of hydro-treated diesel containing 385 ± 4.6 ppm of sulfur (mainly dibenzothiophene and dibenzothiophene derivatives), and this resulted to a high sulfur oxidation yield (> 99%), thus producing polar sulfones which are extractible by polar solid phase extractants. Adsorption of the polar sulfone compounds was carried-out by employing MIPs which were fabricated through the formation of recognition sites complementary to oxidized sulfur-containing compounds (sulfones) on electrospun polybenzimidazole (PBI) nanofibers, cross-linked chitosan microspheres and electrospun chitosan nanofibers. Adsorption of benzothiophene sulfone (BTO₂), dibenzothiophene sulfone (DBTO₂) and 4,6-dimethyldibenzothiophene sulfone (4,6-DMDBTO₂) on the various molecularly imprinted adsorbents presented a Freundlich (multi-layered) adsorption isotherm which indicated interaction of adsorbed organosulfur compounds. Maximum adsorption observed for BTO₂, DBTO₂ and 4,6-DMDBTO₂ respectively was 8.5 ± 0.6 mg/g, 7.0 ± 0.5 mg/g and 6.6 ± 0.7 mg/g when imprinted chitosan nanofibers were employed, 4.9 ± 0.5 mg/g, 4.2 ± 0.7 mg/g and 3.9 ± 0.6 mg/g on molecularly imprinted chitosan microspheres, and 28.5 ± 0.4 mg/g, 29.8 ± 2.2 mg/g and 20.1 ± 1.4 mg/g on molecularly imprinted PBI nanofibers. Application of electrospun chitosan nanofibers on oxidized hydro-treated diesel presented a sulfur removal capacity of 84%, leaving 62 ± 3.2 ppm S in the fuel, while imprinted PBI electrospun nanofibers displayed excellent sulfur removal, keeping sulfur in the fuel after the oxidation/adsorption below the determined limit of detection (LOD), which is 2.4 ppm S. The high level of sulfur removal displayed by imprinted PBI nanofibers was ascribed to hydrogen bonding effects, and π-π stacking between aromatic sulfone compounds and the benzimidazole ring which were confirmed by chemical modelling with density functional theory (DFT) as well as the imprinting effect. The home-made pressurized hot water extraction (PHWE) system was applied for extraction/desorption of sulfone compounds adsorbed on the PBI nanofibers at a flow rate of 1 mL/min and at 150°C with an applied pressure of 30 bars. Application of molecularly imprinted PBI nanofibers for the desulfurization of oxidized hydro-treated fuel showed potential for use in refining industries to reach ultra-low sulfur fuel level, which falls below the 10 ppm sulfur limit which is mandated by the environmental protection agency (EPA) from 2015.
- Full Text:
- Date Issued: 2014
Patterns and drivers of benthic macrofouna to support systematic conservation planning for marine unconsolidated sediment ecosystems
- Authors: Karenyi, Natasha
- Date: 2014
- Subjects: Marine sediments -- Microbiology , Biotic communities , Ecosystem management , Conservation of natural resources
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10355 , http://hdl.handle.net/10948/d1020989
- Description: Marine unconsolidated sediments constitute the largest ecosystems on earth in terms of spatial coverage, but there are still critical gaps in the science required to support conservation and ecosystem-based management. This is mainly due to the inaccessibility of these ecosystems in wave-exposed environments or deeper waters and the difficulty in observing biota in their three-dimensional sedimentary habitat. Currently, the physical driving processes of intertidal unconsolidated sediment ecosystems are much better understood than those of the subtidal ecosystems. However, these ecosystems are linked through water and sediment movement. This thesis, therefore, considers the continuum of unconsolidated sediment ecosystems across the entire continental shelf (i.e. intertidal to the shelf edge). The aim of this thesis was two-fold; (i) to advance the foundational understanding of biodiversity patterns and driving processes in unconsolidated sediment habitats, and (ii) to apply this knowledge in the development of a systematic conservation plan for marine unconsolidated sediment ecosystems. The South African west coast continental shelf was used as a case study in order to represent Eastern boundary upwelling regions. This study sought to investigate biodiversity patterns in macro-infaunal communities and determine their driving processes for incorporation into habitat classifications and the development of a habitat map. Systematic conservation plans require a map of biodiversity patterns and processes, and quantitative conservation targets to ensure representation of all biodiversity features including habitats.in marine protected areas. This thesis provided these key elements by classifying the unconsolidated sediment habitats and determining habitat-specific evidence-based conservation targets to support conservation of these important ecosystems. The application of these elements was then demonstrated in a systematic conservation plan for the unconsolidated sediment ecosystems of the South African west coast. Diversity patterns were examined using physical and macro-infauna data, ranging from the beach to the shelf edge (0-412 m). These data were analysed to develop two different habitat classifications, namely seascapes derived from geophysical and biophysical data, and biotopes derived from the combination of macro-infaunal and physical data. Multivariate analyses of 13 physical variables identified eight seascapes for the unconsolidated sediment samples from 48 sites on the South African west coast. These were based on depth, slope, sediment type, and upwelling-related processes (i.e. maximum chlorophyll concentration, sediment organic carbon content and austral summer bottom oxygen concentration). Latitude and bottom temperature were not considered major drivers of seascapes on the west coast because latitude closely reflected changes in upwelling-related processes and the temperature range was narrow across the shelf. This study revealed that productivity, a biophysical variable not usually included in geo-physical habitat classifications, played a significant role in the definition of seascapes on the South African west coast. It is therefore recommended that productivity be included in future seascape classifications to improve the utility of these classifications particularly in areas of variable productivity. Seascapes should, however, be tested against biological data to improve the understanding of key physical drivers of communities in unconsolidated sediment ecosystems. Macro-infaunal community distributions were determined along with their physical drivers for the unconsolidated sediments of the South African west coast. A total of 44 828 individuals from 469 taxa were identified from 48 sites representing 46.2 m2 of seafloor. Seven distinct macro-infaunal communities were defined through multivariate analyses and their key characteristic and distinguishing species were identified. These communities reflected five depth zones across the shelf, namely beach, inner shelf (10-42 m), middle shelf (60-142 m), outer shelf (150-357 m) and shelf edge (348-412 m). The processes driving the community structure of these depth zones were postulated to be tides, wave turbulence, seasonal hypoxia, habitat stability and homogeneity, and internal tides and/or shelf break upwelling, with drivers listed in order of increasing influence with depth. The middle shelf was further separated into three distinct communities based on sediment type, sediment organic carbon content and frequency of hypoxia. Variations in water turbulence, sediment grain size, upwelling-related variables and riverine sediment input were identified as the likely primary drivers of macro-infaunal community patterns. This chapter culminated in the development of a biotope classification based on the combination of macro-infaunal communities and their physical habitats (i.e. biotopes). South Africa has developed an expert-derived National Marine and Coastal Habitat (SANMC) Classification System which is used as a biodiversity surrogate in ecosystem assessment and spatial planning. This thesis tested the validity of this classification and the data derived Seascape classification against macro-infauna species abundance and biomass data in an effort to determine how well the different classifications represent macro-infaunal diversity of the west coast. These two classifications were also compared to the Biotope classification which combines macro-infaunal communities with their physical habitats. A canonical analysis of principle coordinates (CAP) was utilised to test the success with which each sample was allocated to the relevant habitat type in each classification. The total allocation success for each classification was used as a measure of effectiveness in terms of representing biodiversity patterns. Both classifications had similar allocation successes of 89-92 percent and 92-94 percent for the Seascape and National Habitat Classification respectively, but either over- or under-classified the macrofauna communities. The Biotope classification had the highest allocation success (98 percent), therefore it is the most accurate reflection of the macrofauna biodiversity patterns on the west coast. A key finding of this study was the increasing accuracy of classifications from physically- to expert- to biologically-derived habitat classifications. In this thesis, the Biotope classification was deemed the best representative of biodiversity patterns and was therefore used to produce the Biotope map for use in spatial assessment and planning. The distinct depth patterns that emerged in both the Seascape and Biotope classifications highlighted the need for further investigation of the relationship between depth and biodiversity. Despite variability in macro-infaunal communities, a general unifying pattern in biodiversity across the shelf was sought. Three relationships between depth and species richness have been described in the literature; namely a unimodal pattern, a positively linear relationship with depth, and no relationship between depth and species richness. These hypotheses were tested on the west coast. Two different species richness metrics were utilised to test the depth-diversity relationship, namely observed species density (spp.0.2m-2) and estimated species richness (spp.site-1). Observed species density increased from the beach to the shelf edge (350 m), then decreased to 412 m. The decline may have been due to difficulty in detecting species at greater depths as a result of sampling challenges. The inclusion of an innovative extrapolative method for estimating species richness (the capture-recapture heterogeneity model) within the Bayesian statistical framework mitigated the effects of species detection heterogeneity and revealed that species richness actually increased continuously across the shelf from beach to shelf edge. Thus the general relationship between depth and species richness is positively linear on the west coast of South Africa The new macro-infauna dataset and biotope map provided the opportunity to develop the first habitat-specific evidence-based conservation targets for unconsolidated sediments of the west coast. Species-Area Relationship (SAR) based conservation targets were developed for the biotopes using a modification of the generally accepted methodology. The accepted methodology has three steps (i) the estimation of total species richness for each habitat using the Bootstrap asymptotic estimator, (ii) the calculation of the slope of the species area curve (i.e. the z-value), and (iii) the calculation of targets representing 80 percent of the species. The inclusion of an innovative extrapolative species richness estimator, the Multi-species Site Occupancy Model (MSOM) provided better species richness estimation than the more conventional bootstrap species richness estimator, even though both are based on species accumulation. The MSOM, applied in the Bayesian statistical framework takes detectability of a species into account.
- Full Text:
- Date Issued: 2014
- Authors: Karenyi, Natasha
- Date: 2014
- Subjects: Marine sediments -- Microbiology , Biotic communities , Ecosystem management , Conservation of natural resources
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10355 , http://hdl.handle.net/10948/d1020989
- Description: Marine unconsolidated sediments constitute the largest ecosystems on earth in terms of spatial coverage, but there are still critical gaps in the science required to support conservation and ecosystem-based management. This is mainly due to the inaccessibility of these ecosystems in wave-exposed environments or deeper waters and the difficulty in observing biota in their three-dimensional sedimentary habitat. Currently, the physical driving processes of intertidal unconsolidated sediment ecosystems are much better understood than those of the subtidal ecosystems. However, these ecosystems are linked through water and sediment movement. This thesis, therefore, considers the continuum of unconsolidated sediment ecosystems across the entire continental shelf (i.e. intertidal to the shelf edge). The aim of this thesis was two-fold; (i) to advance the foundational understanding of biodiversity patterns and driving processes in unconsolidated sediment habitats, and (ii) to apply this knowledge in the development of a systematic conservation plan for marine unconsolidated sediment ecosystems. The South African west coast continental shelf was used as a case study in order to represent Eastern boundary upwelling regions. This study sought to investigate biodiversity patterns in macro-infaunal communities and determine their driving processes for incorporation into habitat classifications and the development of a habitat map. Systematic conservation plans require a map of biodiversity patterns and processes, and quantitative conservation targets to ensure representation of all biodiversity features including habitats.in marine protected areas. This thesis provided these key elements by classifying the unconsolidated sediment habitats and determining habitat-specific evidence-based conservation targets to support conservation of these important ecosystems. The application of these elements was then demonstrated in a systematic conservation plan for the unconsolidated sediment ecosystems of the South African west coast. Diversity patterns were examined using physical and macro-infauna data, ranging from the beach to the shelf edge (0-412 m). These data were analysed to develop two different habitat classifications, namely seascapes derived from geophysical and biophysical data, and biotopes derived from the combination of macro-infaunal and physical data. Multivariate analyses of 13 physical variables identified eight seascapes for the unconsolidated sediment samples from 48 sites on the South African west coast. These were based on depth, slope, sediment type, and upwelling-related processes (i.e. maximum chlorophyll concentration, sediment organic carbon content and austral summer bottom oxygen concentration). Latitude and bottom temperature were not considered major drivers of seascapes on the west coast because latitude closely reflected changes in upwelling-related processes and the temperature range was narrow across the shelf. This study revealed that productivity, a biophysical variable not usually included in geo-physical habitat classifications, played a significant role in the definition of seascapes on the South African west coast. It is therefore recommended that productivity be included in future seascape classifications to improve the utility of these classifications particularly in areas of variable productivity. Seascapes should, however, be tested against biological data to improve the understanding of key physical drivers of communities in unconsolidated sediment ecosystems. Macro-infaunal community distributions were determined along with their physical drivers for the unconsolidated sediments of the South African west coast. A total of 44 828 individuals from 469 taxa were identified from 48 sites representing 46.2 m2 of seafloor. Seven distinct macro-infaunal communities were defined through multivariate analyses and their key characteristic and distinguishing species were identified. These communities reflected five depth zones across the shelf, namely beach, inner shelf (10-42 m), middle shelf (60-142 m), outer shelf (150-357 m) and shelf edge (348-412 m). The processes driving the community structure of these depth zones were postulated to be tides, wave turbulence, seasonal hypoxia, habitat stability and homogeneity, and internal tides and/or shelf break upwelling, with drivers listed in order of increasing influence with depth. The middle shelf was further separated into three distinct communities based on sediment type, sediment organic carbon content and frequency of hypoxia. Variations in water turbulence, sediment grain size, upwelling-related variables and riverine sediment input were identified as the likely primary drivers of macro-infaunal community patterns. This chapter culminated in the development of a biotope classification based on the combination of macro-infaunal communities and their physical habitats (i.e. biotopes). South Africa has developed an expert-derived National Marine and Coastal Habitat (SANMC) Classification System which is used as a biodiversity surrogate in ecosystem assessment and spatial planning. This thesis tested the validity of this classification and the data derived Seascape classification against macro-infauna species abundance and biomass data in an effort to determine how well the different classifications represent macro-infaunal diversity of the west coast. These two classifications were also compared to the Biotope classification which combines macro-infaunal communities with their physical habitats. A canonical analysis of principle coordinates (CAP) was utilised to test the success with which each sample was allocated to the relevant habitat type in each classification. The total allocation success for each classification was used as a measure of effectiveness in terms of representing biodiversity patterns. Both classifications had similar allocation successes of 89-92 percent and 92-94 percent for the Seascape and National Habitat Classification respectively, but either over- or under-classified the macrofauna communities. The Biotope classification had the highest allocation success (98 percent), therefore it is the most accurate reflection of the macrofauna biodiversity patterns on the west coast. A key finding of this study was the increasing accuracy of classifications from physically- to expert- to biologically-derived habitat classifications. In this thesis, the Biotope classification was deemed the best representative of biodiversity patterns and was therefore used to produce the Biotope map for use in spatial assessment and planning. The distinct depth patterns that emerged in both the Seascape and Biotope classifications highlighted the need for further investigation of the relationship between depth and biodiversity. Despite variability in macro-infaunal communities, a general unifying pattern in biodiversity across the shelf was sought. Three relationships between depth and species richness have been described in the literature; namely a unimodal pattern, a positively linear relationship with depth, and no relationship between depth and species richness. These hypotheses were tested on the west coast. Two different species richness metrics were utilised to test the depth-diversity relationship, namely observed species density (spp.0.2m-2) and estimated species richness (spp.site-1). Observed species density increased from the beach to the shelf edge (350 m), then decreased to 412 m. The decline may have been due to difficulty in detecting species at greater depths as a result of sampling challenges. The inclusion of an innovative extrapolative method for estimating species richness (the capture-recapture heterogeneity model) within the Bayesian statistical framework mitigated the effects of species detection heterogeneity and revealed that species richness actually increased continuously across the shelf from beach to shelf edge. Thus the general relationship between depth and species richness is positively linear on the west coast of South Africa The new macro-infauna dataset and biotope map provided the opportunity to develop the first habitat-specific evidence-based conservation targets for unconsolidated sediments of the west coast. Species-Area Relationship (SAR) based conservation targets were developed for the biotopes using a modification of the generally accepted methodology. The accepted methodology has three steps (i) the estimation of total species richness for each habitat using the Bootstrap asymptotic estimator, (ii) the calculation of the slope of the species area curve (i.e. the z-value), and (iii) the calculation of targets representing 80 percent of the species. The inclusion of an innovative extrapolative species richness estimator, the Multi-species Site Occupancy Model (MSOM) provided better species richness estimation than the more conventional bootstrap species richness estimator, even though both are based on species accumulation. The MSOM, applied in the Bayesian statistical framework takes detectability of a species into account.
- Full Text:
- Date Issued: 2014
Perceived value creation in technology-based entrepreneurial businesses
- Van den Heever, Thomas Stanley
- Authors: Van den Heever, Thomas Stanley
- Date: 2014
- Subjects: New business enterprises , Entrepreneurship , Technological innovations -- Management
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:9329 , http://hdl.handle.net/10948/d1021047
- Description: Small entrepreneurial businesses are widely regarded as important contributors to the economic well-being of countries all over the world as they create value for both the entrepreneur and the economy in which they operate. The value creation process in these businesses often differs from what commonly happens in larger established businesses. Resources available to the entrepreneur are normally much more restricted and decisions are often based on limited information. This thesis focuses on the value that is created by technology-based entrepreneurial businesses, the leveraging of limited resources and the decision-making orientation they adopt during this process. Given the importance of technology-based entrepreneurial businesses in contributing to economic growth and job creation in most global economies, as well as the limited previous research conducted amongst these businesses, the purpose of this study was to identify the human and social capital factors influencing value creation in technology-based entrepreneurial businesses. With this purpose in mind, the primary objective was to identify, investigate and empirically test the relationships between the various identified factors and Perceived value creation in technology-based entrepreneurial businesses, taking into account their decision-making orientation, as well as the uncertain environment under which they operate. This study uses the Resource-Based View of the business as the basis of its theoretical orientation. The literature review revealed five main categories of constructs, namely Knowledge and skills, Experience, Networks, Decision-making orientation and Perceived environmental uncertainty influencing the dependent variable Perceived value creation in technology-based entrepreneurial businesses. Knowledge and skills, Experience and Networks were identified as independent variables while Decision-making orientation was identified as the mediating variable and Perceived environmental uncertainty as the moderating variable. Six demographic variables (type of industry, age of business, number of employees, age of entrepreneur, academic qualifications of entrepreneur and the number of previous businesses started by the entrepreneur) were also identified as potential influencing factors. Various hypotheses were formulated to be tested during the empirical investigation. Each construct was clearly defined and then operationalised. Operationalisation was done by using reliable and valid items sourced from tested measuring instruments used in previous studies, as well as a number of self-generated items based on secondary sources. A structured questionnaire was made available to respondents identified by means of the convenience snowball sampling technique, and the data collected from 313 usable questionnaires was subjected to various statistical analyses. An Exploratory Factor Analyses (EFA) was conducted which confirmed the different variables, and Cronbach-alpha coefficients were calculated to confirm the reliability of the measuring instrument. Structural Equation Modelling (SEM) was the main statistical procedure used to test the significance of the relationships hypothesised between the various independent, mediating, moderating and dependent variables. A number of different models were tested, and the results discussed and explained. The main finding of the study was that technology-based entrepreneurial business can create financial and non-financial value by adopting a decision-making orientation in the business of co-creating the future with other stakeholders. The most important human and social capital factors that influence the decision-making orientation of these businesses are Knowledge and skills, Unstructured networks and Structured networks. The main limitations of the study were firstly the convenience snowball sampling technique used to collect responses, secondly the dependence of reporting on organisation issues by individuals, and thirdly the limited number of influencing factors included in the models. Future research should address these limitations, and could include qualitative analyses. This study has added to the empirical body of knowledge on entrepreneurship research by investigating a particularly important segment of the literature, namely technology-based entrepreneurial businesses. By identifying and developing various models that outline the most significant factors that influence perceived value creation in technology-based entrepreneurial businesses, this study offers recommendations and suggestions for managing these businesses in such a way as to improve the creation of financial and non-financial value in them. It further provides recommendations for business teaching programmes to enhance curriculums by focusing on alternatives to the format of formal business planning.
- Full Text:
- Date Issued: 2014
- Authors: Van den Heever, Thomas Stanley
- Date: 2014
- Subjects: New business enterprises , Entrepreneurship , Technological innovations -- Management
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:9329 , http://hdl.handle.net/10948/d1021047
- Description: Small entrepreneurial businesses are widely regarded as important contributors to the economic well-being of countries all over the world as they create value for both the entrepreneur and the economy in which they operate. The value creation process in these businesses often differs from what commonly happens in larger established businesses. Resources available to the entrepreneur are normally much more restricted and decisions are often based on limited information. This thesis focuses on the value that is created by technology-based entrepreneurial businesses, the leveraging of limited resources and the decision-making orientation they adopt during this process. Given the importance of technology-based entrepreneurial businesses in contributing to economic growth and job creation in most global economies, as well as the limited previous research conducted amongst these businesses, the purpose of this study was to identify the human and social capital factors influencing value creation in technology-based entrepreneurial businesses. With this purpose in mind, the primary objective was to identify, investigate and empirically test the relationships between the various identified factors and Perceived value creation in technology-based entrepreneurial businesses, taking into account their decision-making orientation, as well as the uncertain environment under which they operate. This study uses the Resource-Based View of the business as the basis of its theoretical orientation. The literature review revealed five main categories of constructs, namely Knowledge and skills, Experience, Networks, Decision-making orientation and Perceived environmental uncertainty influencing the dependent variable Perceived value creation in technology-based entrepreneurial businesses. Knowledge and skills, Experience and Networks were identified as independent variables while Decision-making orientation was identified as the mediating variable and Perceived environmental uncertainty as the moderating variable. Six demographic variables (type of industry, age of business, number of employees, age of entrepreneur, academic qualifications of entrepreneur and the number of previous businesses started by the entrepreneur) were also identified as potential influencing factors. Various hypotheses were formulated to be tested during the empirical investigation. Each construct was clearly defined and then operationalised. Operationalisation was done by using reliable and valid items sourced from tested measuring instruments used in previous studies, as well as a number of self-generated items based on secondary sources. A structured questionnaire was made available to respondents identified by means of the convenience snowball sampling technique, and the data collected from 313 usable questionnaires was subjected to various statistical analyses. An Exploratory Factor Analyses (EFA) was conducted which confirmed the different variables, and Cronbach-alpha coefficients were calculated to confirm the reliability of the measuring instrument. Structural Equation Modelling (SEM) was the main statistical procedure used to test the significance of the relationships hypothesised between the various independent, mediating, moderating and dependent variables. A number of different models were tested, and the results discussed and explained. The main finding of the study was that technology-based entrepreneurial business can create financial and non-financial value by adopting a decision-making orientation in the business of co-creating the future with other stakeholders. The most important human and social capital factors that influence the decision-making orientation of these businesses are Knowledge and skills, Unstructured networks and Structured networks. The main limitations of the study were firstly the convenience snowball sampling technique used to collect responses, secondly the dependence of reporting on organisation issues by individuals, and thirdly the limited number of influencing factors included in the models. Future research should address these limitations, and could include qualitative analyses. This study has added to the empirical body of knowledge on entrepreneurship research by investigating a particularly important segment of the literature, namely technology-based entrepreneurial businesses. By identifying and developing various models that outline the most significant factors that influence perceived value creation in technology-based entrepreneurial businesses, this study offers recommendations and suggestions for managing these businesses in such a way as to improve the creation of financial and non-financial value in them. It further provides recommendations for business teaching programmes to enhance curriculums by focusing on alternatives to the format of formal business planning.
- Full Text:
- Date Issued: 2014
Political party institutionalization : a case study of Kenya
- Mutizwa-Mangiza, Shingai Price
- Authors: Mutizwa-Mangiza, Shingai Price
- Date: 2014
- Subjects: Kenya -- Politics and government , Political parties -- Kenya , Kenya -- History , Kenya -- Colonial influence
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:2881 , http://hdl.handle.net/10962/d1013258
- Description: This thesis explores the nature and extent of political party institutionalization in Kenya. More specifically, it focuses on the four dimensions of party institutionalization, namely organizational systemness, value-infusion, decisional autonomy and reification. The study itself is largely located within the historical-institutionalist school of thought, with particular emphasis on the path dependency strand of this theoretical framework. However, the study also employs a political economy approach. It recognizes that the development trajectory of party politics in Kenya did not evolve in a vacuum but within a particular historical-institutional and political-economic context. The thesis advances the notion that those current low levels of party institutionalization that are evident in almost all parties, and the relatively peripheral role that they have in Kenya's governance can be traced to Kenya's colonial and post-colonial political history, the resource poor environment and the onset of globalization.
- Full Text:
- Date Issued: 2014
- Authors: Mutizwa-Mangiza, Shingai Price
- Date: 2014
- Subjects: Kenya -- Politics and government , Political parties -- Kenya , Kenya -- History , Kenya -- Colonial influence
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:2881 , http://hdl.handle.net/10962/d1013258
- Description: This thesis explores the nature and extent of political party institutionalization in Kenya. More specifically, it focuses on the four dimensions of party institutionalization, namely organizational systemness, value-infusion, decisional autonomy and reification. The study itself is largely located within the historical-institutionalist school of thought, with particular emphasis on the path dependency strand of this theoretical framework. However, the study also employs a political economy approach. It recognizes that the development trajectory of party politics in Kenya did not evolve in a vacuum but within a particular historical-institutional and political-economic context. The thesis advances the notion that those current low levels of party institutionalization that are evident in almost all parties, and the relatively peripheral role that they have in Kenya's governance can be traced to Kenya's colonial and post-colonial political history, the resource poor environment and the onset of globalization.
- Full Text:
- Date Issued: 2014
Purification and characterization of TbHsp70.c, a novel Hsp70 from Trypanosoma brucei
- Authors: Burger, Adélle
- Date: 2014
- Subjects: African trypanosomiasis -- Research Heat shock proteins -- Research Trypanosoma brucei -- Research Mycobacterial diseases -- Research -- Africa Parasitic diseases -- Africa -- Prevention Parasites -- Physiology Developing countries -- Economic conditions
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4105 , http://hdl.handle.net/10962/d1011618
- Description: One of Africa’s neglected tropical diseases, African Trypanosomiasis, is not only fatal but also has a crippling impact on economic development. Heat shock proteins play a wide range of roles in the cell and they are required to assist the parasite as it moves from a cold blooded insect vector to a warm blooded mammalian host. The expression of heat shock proteins increases during these heat shock conditions, and this is considered to play a role in differentiation of these vector-borne parasites. Heat shock protein 70 (Hsp70) is an important molecular chaperone that is involved in protein homeostasis, Hsp40 acts as a co-chaperone and stimulates its intrinsically weak ATPase activity. In silico analysis of the T. brucei genome has revealed the existence of 12 Hsp70 proteins and 65 Hsp40 proteins to date. A novel Hsp70, TbHsp70.c, was recently identified in T. brucei. Different from the prototypical Hsp70, TbHsp70.c contains an acidic substrate binding domain and lacks the C-terminal EEVD motif. By implication the substrate range and mechanism by which the substrates are recognized may be novel. The ability of a Type I Hsp40, Tbj2, to function as a co-chaperone of TbHsp70.c was investigated. The main objective of this study was to biochemically characterize TbHsp70.c and its partnership with Tbj2 to further enhance our knowledge of parasite biology. TbHsp70.c and Tbj2 were heterologously expressed and purified and both proteins displayed chaperone activities in their ability to suppress aggregation of thermolabile MDH. TbHsp70.c also suppressed aggregation of rhodanese. ATPase assays revealed that the ATPase activity of TbHsp70.c was stimulated by Tbj2. The targeted inhibition of the function of heat shock proteins is emerging as a tool to combat disease. The small molecule modulators quercetin and methylene blue are known to inhibit the ATPase activity of Hsp70. However, methylene blue did not significantly inhibit the ATPase activity of TbHsp70.c; while quercetin, did inhibit the ATPase activity. In vivo heat stress experiments indicated an up-regulation of the expression levels of TbHsp70.c. RNA interference studies showed partial knockdown of TbHsp70.c with no detrimental effect on the parasite. Fluorescence microscopy studies of TbHsp70.c showed a probable cytoplasmic subcellular localization. In this study both TbHsp70.c and Tbj2 demonstrated chaperone activity and Tbj2 possibly functions as a co-chaperone of TbHsp70.c.
- Full Text:
- Date Issued: 2014
- Authors: Burger, Adélle
- Date: 2014
- Subjects: African trypanosomiasis -- Research Heat shock proteins -- Research Trypanosoma brucei -- Research Mycobacterial diseases -- Research -- Africa Parasitic diseases -- Africa -- Prevention Parasites -- Physiology Developing countries -- Economic conditions
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4105 , http://hdl.handle.net/10962/d1011618
- Description: One of Africa’s neglected tropical diseases, African Trypanosomiasis, is not only fatal but also has a crippling impact on economic development. Heat shock proteins play a wide range of roles in the cell and they are required to assist the parasite as it moves from a cold blooded insect vector to a warm blooded mammalian host. The expression of heat shock proteins increases during these heat shock conditions, and this is considered to play a role in differentiation of these vector-borne parasites. Heat shock protein 70 (Hsp70) is an important molecular chaperone that is involved in protein homeostasis, Hsp40 acts as a co-chaperone and stimulates its intrinsically weak ATPase activity. In silico analysis of the T. brucei genome has revealed the existence of 12 Hsp70 proteins and 65 Hsp40 proteins to date. A novel Hsp70, TbHsp70.c, was recently identified in T. brucei. Different from the prototypical Hsp70, TbHsp70.c contains an acidic substrate binding domain and lacks the C-terminal EEVD motif. By implication the substrate range and mechanism by which the substrates are recognized may be novel. The ability of a Type I Hsp40, Tbj2, to function as a co-chaperone of TbHsp70.c was investigated. The main objective of this study was to biochemically characterize TbHsp70.c and its partnership with Tbj2 to further enhance our knowledge of parasite biology. TbHsp70.c and Tbj2 were heterologously expressed and purified and both proteins displayed chaperone activities in their ability to suppress aggregation of thermolabile MDH. TbHsp70.c also suppressed aggregation of rhodanese. ATPase assays revealed that the ATPase activity of TbHsp70.c was stimulated by Tbj2. The targeted inhibition of the function of heat shock proteins is emerging as a tool to combat disease. The small molecule modulators quercetin and methylene blue are known to inhibit the ATPase activity of Hsp70. However, methylene blue did not significantly inhibit the ATPase activity of TbHsp70.c; while quercetin, did inhibit the ATPase activity. In vivo heat stress experiments indicated an up-regulation of the expression levels of TbHsp70.c. RNA interference studies showed partial knockdown of TbHsp70.c with no detrimental effect on the parasite. Fluorescence microscopy studies of TbHsp70.c showed a probable cytoplasmic subcellular localization. In this study both TbHsp70.c and Tbj2 demonstrated chaperone activity and Tbj2 possibly functions as a co-chaperone of TbHsp70.c.
- Full Text:
- Date Issued: 2014
Separation of rhodium (III) and iridium (IV) using functional polymeric materials
- Authors: Majavu, Avela
- Date: 2014
- Subjects: Rhodium -- Separation , Iridium -- Separation
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/6576 , vital:21116
- Description: Poly(vinylbenzylchloride) (PVBC) nanofibers were fabricated by the electrospinning process. The Merrifield micropheres, silica microsparticles and PVBC nanofibers were functionalised with different quaternary diammonium groups derived from ethylenediamine (EDA), tetramethylenediamine (TMDA), hexamethylenediamine (HMDA), 1,8-diaminooctane (OMDA), 1,10-diaminodecane (DMDA) and 1,12-diaminododecane (DDMDA) and investigated for separation of [RhCl5(H2O)]2- and [IrCl6]2-. The sorbent materials were characterised by means of FTIR, XPS, SEM, BET surface area, thermogravimetric analysis and elemental analysis, and characterization results showed that the functionalization of the sorbent materials was successful. Batch equilibrium studies were carried out to assess the efficiency of these different anion exchangers using single metal aqueous solutions. The adsorption isotherms and kinetics of both [RhCl5(H2O)]2- and [IrCl6]2- adsorption onto the sorbent materials are presented. The isothermal batch adsorption studies fitted the Freundlich model indicating heterogeneous surface adsorption. The Freundlich isotherm confirmed multilayer adsorption and the Freundlich constant (kf) displayed the following ascending order for nanofibers (F-QUAT EDA, F-QUAT TMDA, F-QUAT HMDA, F-QUAT OMDA and F-QUAT DMDA), silica microparticles (Si-QUAT EDA, Si-QUAT TMDA, Si-QUAT HMDA, Si-QUAT OMDA and Si-QUAT DMDA) and microspheres (B-QUAT EDA, B-QUAT TMDA, B-QUAT HMDA, B-QUAT OMDA and B-QUAT DMDA) and a decrease in kf for F-QUAT DDMDA, Si-QUAT DDMDA and B-QUAT DDMDA has been observed. The pseudo second-order model was found to be the best fit to describe the adsorption kinetics of both metal ions complexes onto all the sorbent materials. K2 value in pseudo second-order kinetics showed that the rate constant for adsorption of [IrCl6]2- onto nanofibers was larger than for silica microparticles and Merrifield microspheres. Column sorption of [IrCl6]2- and [RhCl5(H2O)]2- was carried out and the loading capacities of [IrCl6]2- were obtained, and they showed dependence on the length of the methylene spacer between the two diammonium centres. [RhCl5(H2O)]2- was not adsorbed by the sorbent materials while [IrCl6]2- was loaded onto the column. The highest iridium loading capacities for all the sorbent materials for the diamines with decylene spacer, and were found to be 32.94 mg/g, 29.35 mg/g, and 27.09 mg/g for F-QUAT DMDA, Si-QUAT DMDA and B-QUAT DMDA respectively. It was also observed on the derivatives of DMDA supported on nanofibers that F-QUAT ethyl loading capacity for iridium (19.89 mg/g) reduced which may be due to the electron-donating nature of the ethyl group and the increase of hydrophobicity whereas F-QUAT benzyl loading capacity (244.64 mg/g) increased dramatically due to increase in the size of the cation which lowers the positive charge density of the quaternary diammonium center. The charge delocalizing ability of the benzyl group resulted in the best interaction of the diammonium group derived from this quaternizing agent, yielding the highest loading capacity for [IrCl6]2-. Reusability was conducted and the results showed that the all the sorbent materials can be used repeatedly without decreasing their adsorption capacity significantly. The neat diammonium salts were also synthesized and interacted with the chorido metal complex anions to form ion-pairs which were then studied for their solubility. The synthesis of the quaternary salts was rather challenging and resulted in some interesting species when impurities of the iodide form of the salts were present in the process of converting them to the iodide form. Some of these include I52+, which was confirmed preliminarily by X-ray structural analysis, potentiometry and cyclic voltammetry. Molecular modeling studies were also conducted to explain the interaction of the chlorido anions with the cationic diammonium centres, and to quantify these interactions by thermodynamic parameters, partial charge calculations, dipole moments and electrostatic potentials, and there was good agreement between theory and experiment. This thesis presents iridium-specific materials that could be applied in solutions of secondary PMGs sources containing rhodium and iridium as well as in feed solutions from ore processing.
- Full Text:
- Date Issued: 2014
- Authors: Majavu, Avela
- Date: 2014
- Subjects: Rhodium -- Separation , Iridium -- Separation
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/6576 , vital:21116
- Description: Poly(vinylbenzylchloride) (PVBC) nanofibers were fabricated by the electrospinning process. The Merrifield micropheres, silica microsparticles and PVBC nanofibers were functionalised with different quaternary diammonium groups derived from ethylenediamine (EDA), tetramethylenediamine (TMDA), hexamethylenediamine (HMDA), 1,8-diaminooctane (OMDA), 1,10-diaminodecane (DMDA) and 1,12-diaminododecane (DDMDA) and investigated for separation of [RhCl5(H2O)]2- and [IrCl6]2-. The sorbent materials were characterised by means of FTIR, XPS, SEM, BET surface area, thermogravimetric analysis and elemental analysis, and characterization results showed that the functionalization of the sorbent materials was successful. Batch equilibrium studies were carried out to assess the efficiency of these different anion exchangers using single metal aqueous solutions. The adsorption isotherms and kinetics of both [RhCl5(H2O)]2- and [IrCl6]2- adsorption onto the sorbent materials are presented. The isothermal batch adsorption studies fitted the Freundlich model indicating heterogeneous surface adsorption. The Freundlich isotherm confirmed multilayer adsorption and the Freundlich constant (kf) displayed the following ascending order for nanofibers (F-QUAT EDA, F-QUAT TMDA, F-QUAT HMDA, F-QUAT OMDA and F-QUAT DMDA), silica microparticles (Si-QUAT EDA, Si-QUAT TMDA, Si-QUAT HMDA, Si-QUAT OMDA and Si-QUAT DMDA) and microspheres (B-QUAT EDA, B-QUAT TMDA, B-QUAT HMDA, B-QUAT OMDA and B-QUAT DMDA) and a decrease in kf for F-QUAT DDMDA, Si-QUAT DDMDA and B-QUAT DDMDA has been observed. The pseudo second-order model was found to be the best fit to describe the adsorption kinetics of both metal ions complexes onto all the sorbent materials. K2 value in pseudo second-order kinetics showed that the rate constant for adsorption of [IrCl6]2- onto nanofibers was larger than for silica microparticles and Merrifield microspheres. Column sorption of [IrCl6]2- and [RhCl5(H2O)]2- was carried out and the loading capacities of [IrCl6]2- were obtained, and they showed dependence on the length of the methylene spacer between the two diammonium centres. [RhCl5(H2O)]2- was not adsorbed by the sorbent materials while [IrCl6]2- was loaded onto the column. The highest iridium loading capacities for all the sorbent materials for the diamines with decylene spacer, and were found to be 32.94 mg/g, 29.35 mg/g, and 27.09 mg/g for F-QUAT DMDA, Si-QUAT DMDA and B-QUAT DMDA respectively. It was also observed on the derivatives of DMDA supported on nanofibers that F-QUAT ethyl loading capacity for iridium (19.89 mg/g) reduced which may be due to the electron-donating nature of the ethyl group and the increase of hydrophobicity whereas F-QUAT benzyl loading capacity (244.64 mg/g) increased dramatically due to increase in the size of the cation which lowers the positive charge density of the quaternary diammonium center. The charge delocalizing ability of the benzyl group resulted in the best interaction of the diammonium group derived from this quaternizing agent, yielding the highest loading capacity for [IrCl6]2-. Reusability was conducted and the results showed that the all the sorbent materials can be used repeatedly without decreasing their adsorption capacity significantly. The neat diammonium salts were also synthesized and interacted with the chorido metal complex anions to form ion-pairs which were then studied for their solubility. The synthesis of the quaternary salts was rather challenging and resulted in some interesting species when impurities of the iodide form of the salts were present in the process of converting them to the iodide form. Some of these include I52+, which was confirmed preliminarily by X-ray structural analysis, potentiometry and cyclic voltammetry. Molecular modeling studies were also conducted to explain the interaction of the chlorido anions with the cationic diammonium centres, and to quantify these interactions by thermodynamic parameters, partial charge calculations, dipole moments and electrostatic potentials, and there was good agreement between theory and experiment. This thesis presents iridium-specific materials that could be applied in solutions of secondary PMGs sources containing rhodium and iridium as well as in feed solutions from ore processing.
- Full Text:
- Date Issued: 2014
Some general convergence theorems on fixed points
- Authors: Panicker, Rekha Manoj
- Date: 2014
- Subjects: Fixed point theory , Convergence , Coincidence theory (Mathematics)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5426 , http://hdl.handle.net/10962/d1013112
- Description: In this thesis, we first obtain coincidence and common fixed point theorems for a pair of generalized non-expansive type mappings in a normed space. Then we discuss two types of convergence theorems, namely, the convergence of Mann iteration procedures and the convergence and stability of fixed points. In addition, we discuss the viscosity approximations generated by (ψ ,ϕ)-weakly contractive mappings and a sequence of non-expansive mappings and then establish Browder and Halpern type convergence theorems on Banach spaces. With regard to iteration procedures, we obtain a result on the convergence of Mann iteration for generalized non-expansive type mappings in a Banach space which satisfies Opial's condition. And, in the case of stability of fixed points, we obtain a number of stability results for the sequence of (ψ,ϕ)- weakly contractive mappings and the sequence of their corresponding fixed points in metric and 2-metric spaces. We also present a generalization of Fraser and Nadler type stability theorems in 2-metric spaces involving a sequence of metrics.
- Full Text:
- Date Issued: 2014
- Authors: Panicker, Rekha Manoj
- Date: 2014
- Subjects: Fixed point theory , Convergence , Coincidence theory (Mathematics)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5426 , http://hdl.handle.net/10962/d1013112
- Description: In this thesis, we first obtain coincidence and common fixed point theorems for a pair of generalized non-expansive type mappings in a normed space. Then we discuss two types of convergence theorems, namely, the convergence of Mann iteration procedures and the convergence and stability of fixed points. In addition, we discuss the viscosity approximations generated by (ψ ,ϕ)-weakly contractive mappings and a sequence of non-expansive mappings and then establish Browder and Halpern type convergence theorems on Banach spaces. With regard to iteration procedures, we obtain a result on the convergence of Mann iteration for generalized non-expansive type mappings in a Banach space which satisfies Opial's condition. And, in the case of stability of fixed points, we obtain a number of stability results for the sequence of (ψ,ϕ)- weakly contractive mappings and the sequence of their corresponding fixed points in metric and 2-metric spaces. We also present a generalization of Fraser and Nadler type stability theorems in 2-metric spaces involving a sequence of metrics.
- Full Text:
- Date Issued: 2014