Grabcuts for image segmentation: a comparative study of clustering techniques
- Authors: Manzi, Nozuko Zuleika
- Date: 2019
- Subjects: Algorithms , Computer graphics
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/14494 , vital:39995
- Description: Image segmentation is the partitioning of a digital image into small segments such as pixels or sets of pixels. It is significant as it allows for the visualization of structures of interest, removing unnecessary information. In addition, image segmentation is used in many fields like, for instance healthcare for image surgery, construction, etc. as it enables structure analysis. Segmentation of images can be computationally expensive especially when a large dataset is used, thus the importance of fast and effective segmentation algorithms is realised. This method is used to locate objects and boundaries (i.e. foreground and background) in images. The aim of this study is to provide a comparison of clustering techniques that would allow the Grabcuts for image segmentation algorithm to be effective and inexpensive. The Grabcuts based method, which is an extension of the graph cut based method, has been instrumental in solving many problems in computer vision i.e. image restoration, image segmentation, object recognition, tracking and analysis. According to Ramirez,et.al [47], the Grabcuts approach is an iterative and minimal user interaction algorithm as it chooses a segmentation by iteratively revising the foreground and background pixels assignments. The method uses min-cut/ max-flow algorithm to segment digital images proposed by Boykov and Jolly [9]. The input of this approach is a digital image with a selected v region of interest (ROI). The ROI is selected using a rectangular bounding box. The pixels inside the bounding box are assigned to the foreground, while the others are assigned to the background. In this study, the Grabcuts for image segmentation algorithm designed by [48] with a Gaussian Mixture Model (GMM) based on the Kmeans and Kmedoids clustering techniques are developed and compared. In addition, the algorithms developed are allowed to run on the Central Processing Unit (CPU) under two scenarios. Scenario 1 involves allowing the Kmeans and Kmedoids clustering techniques to the Squared Euclidean distance measures to calculate the similarities and dissimilarities in pixels in an image. In scenario 2, the Kmeans and Kmedoids clustering techniques will use the City Block distance measure to calculate similarities as well as dissimilarities between pixels in a given image. The same images from the Berkeley Segmentation Dataset and Benchmark 500 were used as input to the algorithms and the number of clusters, K, was varied from 2 to 5. It was observed that the Kmeans clustering technique outperformed the Kmedoids clustering technique under the two scenarios for all the test images with K varied from 2 to 5, in terms of runtime required. In addition, the Kmeans clustering technique obtained more compact and separate clusters under scenario 1, than its counterpart. On the other hand, the Kmedoids obtained more compact and separate clusters than the Kmeans clustering technique under scenario 2. The silhouette validity index favoured the smallest number of clusters for both clustering techniques as it suggested the optimal number of clusters for the Kmeans and Kmedoids clustering techniques under the two scenarios was 2. Although the Kmeans required less computation time than vi its counterpart, the generation of foreground and background took longer for the GMM based on Kmeans than it did for the GMM based on Kmedoids clustering technique. Furthermore, the Grabcuts for image segmentation algorithm with a GMM based on the Kmedoids clustering technique was computationally less expensive than the Grabcuts for image segmentation algorithm with a GMM based on the Kmeans clustering technique. This was observed to be true under both scenario 1 and 2. The Grabcuts for image with the GMM based on the Kmeans clustering techniques obtained slightly better segmentation results when the visual quality is concerned, than its counterpart under the two scenarios considered. On the other hand, the BFscores showed that the Grabcuts for image segmentation algorithm with the GMM based on Kmedoids produces images with higher BF-scores than its counterpart when K was varied from 2 to 5 for most of the test images. In addition, most of the images obtained the majority of their best segmentation results when K=2. This was observed to be true under scenario 1 as well as scenario 2. Therefore, the Kmedoids clustering technique under scenario 2 with K=2 would be the best option for the segmentation of difficult images in BSDS500. This is due to its ability to generate GMMs and segment difficult images more efficiently (i.e. time complexity, higher BF-scores, more under segmented rather than over segmented images, inter alia.) while producing comparable visual segmentation results to those obtained by the Grabcuts for image segmentation: GMM-Kmeans.
- Full Text:
- Date Issued: 2019
- Authors: Manzi, Nozuko Zuleika
- Date: 2019
- Subjects: Algorithms , Computer graphics
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/14494 , vital:39995
- Description: Image segmentation is the partitioning of a digital image into small segments such as pixels or sets of pixels. It is significant as it allows for the visualization of structures of interest, removing unnecessary information. In addition, image segmentation is used in many fields like, for instance healthcare for image surgery, construction, etc. as it enables structure analysis. Segmentation of images can be computationally expensive especially when a large dataset is used, thus the importance of fast and effective segmentation algorithms is realised. This method is used to locate objects and boundaries (i.e. foreground and background) in images. The aim of this study is to provide a comparison of clustering techniques that would allow the Grabcuts for image segmentation algorithm to be effective and inexpensive. The Grabcuts based method, which is an extension of the graph cut based method, has been instrumental in solving many problems in computer vision i.e. image restoration, image segmentation, object recognition, tracking and analysis. According to Ramirez,et.al [47], the Grabcuts approach is an iterative and minimal user interaction algorithm as it chooses a segmentation by iteratively revising the foreground and background pixels assignments. The method uses min-cut/ max-flow algorithm to segment digital images proposed by Boykov and Jolly [9]. The input of this approach is a digital image with a selected v region of interest (ROI). The ROI is selected using a rectangular bounding box. The pixels inside the bounding box are assigned to the foreground, while the others are assigned to the background. In this study, the Grabcuts for image segmentation algorithm designed by [48] with a Gaussian Mixture Model (GMM) based on the Kmeans and Kmedoids clustering techniques are developed and compared. In addition, the algorithms developed are allowed to run on the Central Processing Unit (CPU) under two scenarios. Scenario 1 involves allowing the Kmeans and Kmedoids clustering techniques to the Squared Euclidean distance measures to calculate the similarities and dissimilarities in pixels in an image. In scenario 2, the Kmeans and Kmedoids clustering techniques will use the City Block distance measure to calculate similarities as well as dissimilarities between pixels in a given image. The same images from the Berkeley Segmentation Dataset and Benchmark 500 were used as input to the algorithms and the number of clusters, K, was varied from 2 to 5. It was observed that the Kmeans clustering technique outperformed the Kmedoids clustering technique under the two scenarios for all the test images with K varied from 2 to 5, in terms of runtime required. In addition, the Kmeans clustering technique obtained more compact and separate clusters under scenario 1, than its counterpart. On the other hand, the Kmedoids obtained more compact and separate clusters than the Kmeans clustering technique under scenario 2. The silhouette validity index favoured the smallest number of clusters for both clustering techniques as it suggested the optimal number of clusters for the Kmeans and Kmedoids clustering techniques under the two scenarios was 2. Although the Kmeans required less computation time than vi its counterpart, the generation of foreground and background took longer for the GMM based on Kmeans than it did for the GMM based on Kmedoids clustering technique. Furthermore, the Grabcuts for image segmentation algorithm with a GMM based on the Kmedoids clustering technique was computationally less expensive than the Grabcuts for image segmentation algorithm with a GMM based on the Kmeans clustering technique. This was observed to be true under both scenario 1 and 2. The Grabcuts for image with the GMM based on the Kmeans clustering techniques obtained slightly better segmentation results when the visual quality is concerned, than its counterpart under the two scenarios considered. On the other hand, the BFscores showed that the Grabcuts for image segmentation algorithm with the GMM based on Kmedoids produces images with higher BF-scores than its counterpart when K was varied from 2 to 5 for most of the test images. In addition, most of the images obtained the majority of their best segmentation results when K=2. This was observed to be true under scenario 1 as well as scenario 2. Therefore, the Kmedoids clustering technique under scenario 2 with K=2 would be the best option for the segmentation of difficult images in BSDS500. This is due to its ability to generate GMMs and segment difficult images more efficiently (i.e. time complexity, higher BF-scores, more under segmented rather than over segmented images, inter alia.) while producing comparable visual segmentation results to those obtained by the Grabcuts for image segmentation: GMM-Kmeans.
- Full Text:
- Date Issued: 2019
Assessing the Contribution of SMMEs to Job creation in the Eastern Cape South Africa
- Authors: Mbambo, William Bongile
- Date: 2018
- Subjects: Business enterprises -- South Africa -- Eastern Cape Job creation -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD ( Public Administration)
- Identifier: http://hdl.handle.net/10353/13675 , vital:39690
- Description: Job creation through support to Small, Medium and Micro Enterprises (SMMEs) is one of the South African government’s priorities in the Eastern Cape Vision 2030 Provincial Development Plan, to overcome the chronic unemployment situation faced by millions of South Africans. The Eastern Cape Province is amongst one of the areas challenged by high levels of unemployment in South Africa. In order to assess whether SMMEs had the capacity to create employment opportunities in the Eastern Cape Province. This study investigate on how SMMEs plans to provide employment opportunities, also examine whether SMMEs has created any employment opportunities thus far in the Eastern Cape Province. The study used David Birch (1979 and 1981) Kerr, Wittenberg and Arrow (2013), theories to assess whether SMMEs had the capacity to create employment opportunities in the Province. The study adopted a mixed methods approach in order to assess SMMEs as a tool for employment creation in its various dimensions. The results of the study reveal that Small, Medium and Micro Enterprises do not necessarily generate substantial employment. Therefore, the study recommends that the government should provide more financial support for SMMEs, organize entrepreneurship workshops, seminars and training workshops, which could improve their business operating skills as well as provide easy access to loans.
- Full Text:
- Date Issued: 2018
- Authors: Mbambo, William Bongile
- Date: 2018
- Subjects: Business enterprises -- South Africa -- Eastern Cape Job creation -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD ( Public Administration)
- Identifier: http://hdl.handle.net/10353/13675 , vital:39690
- Description: Job creation through support to Small, Medium and Micro Enterprises (SMMEs) is one of the South African government’s priorities in the Eastern Cape Vision 2030 Provincial Development Plan, to overcome the chronic unemployment situation faced by millions of South Africans. The Eastern Cape Province is amongst one of the areas challenged by high levels of unemployment in South Africa. In order to assess whether SMMEs had the capacity to create employment opportunities in the Eastern Cape Province. This study investigate on how SMMEs plans to provide employment opportunities, also examine whether SMMEs has created any employment opportunities thus far in the Eastern Cape Province. The study used David Birch (1979 and 1981) Kerr, Wittenberg and Arrow (2013), theories to assess whether SMMEs had the capacity to create employment opportunities in the Province. The study adopted a mixed methods approach in order to assess SMMEs as a tool for employment creation in its various dimensions. The results of the study reveal that Small, Medium and Micro Enterprises do not necessarily generate substantial employment. Therefore, the study recommends that the government should provide more financial support for SMMEs, organize entrepreneurship workshops, seminars and training workshops, which could improve their business operating skills as well as provide easy access to loans.
- Full Text:
- Date Issued: 2018
Exports and economic growth in South Africa
- Authors: Feddersen, Maura
- Date: 2014
- Subjects: Exports -- South Africa Economic development -- South Africa Unemployment -- South Africa Poverty -- South Africa Income distribution -- South Africa Investments -- South Africa Saving and investment -- South Africa South Africa -- Economic conditions South Africa -- Social conditions
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: vital:1087 , http://hdl.handle.net/10962/d1012029
- Description: Various studies conclude that accelerated economic growth and development are necessary in South Africa to make a significant contribution towards reducing high levels of unemployment, inequality and poverty. Moreover, in theories of economic growth the export sector is frequently accorded a special role in encouraging faster economic growth, which is often supported by empirical evidence. Nonetheless, a question that remains unresolved is whether higher export growth leads to higher economic growth in South Africa and what particular role exports may play within the overall economic growth process of the country. This study applies Johansen’s cointegration procedure, impulse response functions, variance decomposition analysis and Granger causality tests to shed light on the channels through which export growth may impact South Africa’s economic growth rate. Quarterly time series data ranging from 1975q1 to 2012q4 is employed in the study’s empirical tests. The empirical results lend support to the idea that the role of exports in the economic growth process fundamentally lies in their ability to encourage investment and capital formation. While export growth supports higher economic growth in the short-run, it does not have the same effect in the long-run. Nonetheless, with export growth supporting faster capital formation in South Africa, and capital formation, in turn, significantly increasing economic growth in the long-run, the impetus to growth stemming from exports has been found to lie in the channel to capital formation. On the basis of the empirical results, not only are exports a critical requirement of higher investment, but they are also anticipated to play a prominent role in lifting the balance of payments constraint that would make investment-led growth possible in the first place. Overall, a strategy of export-led growth that does not explicitly emphasise the export-capital-growth connection is likely to fall short of reflecting the dynamics contained within the exports-growth relationship in South Africa.
- Full Text:
- Date Issued: 2014
- Authors: Feddersen, Maura
- Date: 2014
- Subjects: Exports -- South Africa Economic development -- South Africa Unemployment -- South Africa Poverty -- South Africa Income distribution -- South Africa Investments -- South Africa Saving and investment -- South Africa South Africa -- Economic conditions South Africa -- Social conditions
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: vital:1087 , http://hdl.handle.net/10962/d1012029
- Description: Various studies conclude that accelerated economic growth and development are necessary in South Africa to make a significant contribution towards reducing high levels of unemployment, inequality and poverty. Moreover, in theories of economic growth the export sector is frequently accorded a special role in encouraging faster economic growth, which is often supported by empirical evidence. Nonetheless, a question that remains unresolved is whether higher export growth leads to higher economic growth in South Africa and what particular role exports may play within the overall economic growth process of the country. This study applies Johansen’s cointegration procedure, impulse response functions, variance decomposition analysis and Granger causality tests to shed light on the channels through which export growth may impact South Africa’s economic growth rate. Quarterly time series data ranging from 1975q1 to 2012q4 is employed in the study’s empirical tests. The empirical results lend support to the idea that the role of exports in the economic growth process fundamentally lies in their ability to encourage investment and capital formation. While export growth supports higher economic growth in the short-run, it does not have the same effect in the long-run. Nonetheless, with export growth supporting faster capital formation in South Africa, and capital formation, in turn, significantly increasing economic growth in the long-run, the impetus to growth stemming from exports has been found to lie in the channel to capital formation. On the basis of the empirical results, not only are exports a critical requirement of higher investment, but they are also anticipated to play a prominent role in lifting the balance of payments constraint that would make investment-led growth possible in the first place. Overall, a strategy of export-led growth that does not explicitly emphasise the export-capital-growth connection is likely to fall short of reflecting the dynamics contained within the exports-growth relationship in South Africa.
- Full Text:
- Date Issued: 2014
An exploration of a London Church Congregation's perceptions of homosexuality
- Authors: Beattie, Cora Rebecca
- Date: 2011
- Subjects: Conflict management -- Religious aspects -- Christianity , Interpersonal conflict -- Religious aspects -- Christianity , Church controversies , Homosexuality -- Religious aspects -- Christianity , Homosexuality in the Bible
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:8171 , http://hdl.handle.net/10948/1640 , Conflict management -- Religious aspects -- Christianity , Interpersonal conflict -- Religious aspects -- Christianity , Church controversies , Homosexuality -- Religious aspects -- Christianity , Homosexuality in the Bible
- Description: The following treatise focuses on the ongoing conflict within the church regarding the issue of homosexuality. It is an important issue that has divided both churches and denominations and it continues to cause hurt in both the lives of Christians and non-Christians alike, both straight and gay. The popular position seems to be that the church, and Christians in general, are homophobic and believe that Christianity and homosexuality are not compatible. This research is a case study and focuses on a church in London. The research was carried out to discover whether this position, often portrayed by the media, was true of this church. It also sought to discover whether theories of conflict management and in particular John Burton’s theory of basic human needs could offer insight and alternative approaches in future discussions. The findings of this research offer hope in the situation in that they show this particular church is not homophobic, nor do the majority believe homosexuality and Christianity to be incompatible.
- Full Text:
- Date Issued: 2011
- Authors: Beattie, Cora Rebecca
- Date: 2011
- Subjects: Conflict management -- Religious aspects -- Christianity , Interpersonal conflict -- Religious aspects -- Christianity , Church controversies , Homosexuality -- Religious aspects -- Christianity , Homosexuality in the Bible
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:8171 , http://hdl.handle.net/10948/1640 , Conflict management -- Religious aspects -- Christianity , Interpersonal conflict -- Religious aspects -- Christianity , Church controversies , Homosexuality -- Religious aspects -- Christianity , Homosexuality in the Bible
- Description: The following treatise focuses on the ongoing conflict within the church regarding the issue of homosexuality. It is an important issue that has divided both churches and denominations and it continues to cause hurt in both the lives of Christians and non-Christians alike, both straight and gay. The popular position seems to be that the church, and Christians in general, are homophobic and believe that Christianity and homosexuality are not compatible. This research is a case study and focuses on a church in London. The research was carried out to discover whether this position, often portrayed by the media, was true of this church. It also sought to discover whether theories of conflict management and in particular John Burton’s theory of basic human needs could offer insight and alternative approaches in future discussions. The findings of this research offer hope in the situation in that they show this particular church is not homophobic, nor do the majority believe homosexuality and Christianity to be incompatible.
- Full Text:
- Date Issued: 2011
The nexilitas factor: host-guest relationships in small owner managed commercial accommodation facilities in contemporary South Africa
- Von Lengeling, Volkher Heinrich Christoph
- Authors: Von Lengeling, Volkher Heinrich Christoph
- Date: 2011
- Subjects: Hospitality industry -- South Africa Interpersonal relations Social interaction Liminality Consumer behavior Home-based businesses -- South Africa
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:2093 , http://hdl.handle.net/10962/d1002656
- Description: The commercialization of hospitality established arguably the oldest profession. Historically small commercial hospitality establishments, known as inns in the western world, were of ill repute. Perhaps connected to their reputation, this category of accommodation facility has been seriously neglected as an area of academic inquiry, particularly from the perspective of the host. While there has been a huge growth in the interdisciplinary field of tourism studies in recent decades, little attention has been paid to the role of the host in the host-guest relationship at whatever level of analysis. This thesis seeks to redress the balance. Hospitality is a basic form of social bonding. This type of bonding, where a hierarchy between strangers is implicit (as with hosts and guests), may be termed ‘nexilitas’; nexilitas is a form of social bonding in liminal circumstances. To that extent it is comparable to ‘communitas’ which describes social bonding between equals in certain liminal circumstances. The difference is that nexilitas is a form of bonding between individuals in a complex power relationship. The host controls the hospitality space, but custom also empowers the guest with certain expectations, especially in the commercial context. The thesis identifies the various forms of hospitality – traditional ‘true’ or ‘pure’ hospitality, social hospitality, cultural hospitality and commercial hospitality – and discusses these critically in their historical and cross-cultural contexts, with emphasis on the perspective of the host. The passage of hospitality is then traced through the three phases of preliminality, liminality and post-liminality and discussed along the themes anticipation, arrival and accommodation and finally departure of the guest. While the historical and ethnographic review is mainly based on written histories and the experiences of other anthropologists as guests as well as ethnographers, the passage of hospitality draws on the multi-sited auto-anthropological experiences of the author, both as host and as ethnographer of contemporary South African hosts in small owner-managed commercial hospitality establishments.
- Full Text:
- Date Issued: 2011
- Authors: Von Lengeling, Volkher Heinrich Christoph
- Date: 2011
- Subjects: Hospitality industry -- South Africa Interpersonal relations Social interaction Liminality Consumer behavior Home-based businesses -- South Africa
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:2093 , http://hdl.handle.net/10962/d1002656
- Description: The commercialization of hospitality established arguably the oldest profession. Historically small commercial hospitality establishments, known as inns in the western world, were of ill repute. Perhaps connected to their reputation, this category of accommodation facility has been seriously neglected as an area of academic inquiry, particularly from the perspective of the host. While there has been a huge growth in the interdisciplinary field of tourism studies in recent decades, little attention has been paid to the role of the host in the host-guest relationship at whatever level of analysis. This thesis seeks to redress the balance. Hospitality is a basic form of social bonding. This type of bonding, where a hierarchy between strangers is implicit (as with hosts and guests), may be termed ‘nexilitas’; nexilitas is a form of social bonding in liminal circumstances. To that extent it is comparable to ‘communitas’ which describes social bonding between equals in certain liminal circumstances. The difference is that nexilitas is a form of bonding between individuals in a complex power relationship. The host controls the hospitality space, but custom also empowers the guest with certain expectations, especially in the commercial context. The thesis identifies the various forms of hospitality – traditional ‘true’ or ‘pure’ hospitality, social hospitality, cultural hospitality and commercial hospitality – and discusses these critically in their historical and cross-cultural contexts, with emphasis on the perspective of the host. The passage of hospitality is then traced through the three phases of preliminality, liminality and post-liminality and discussed along the themes anticipation, arrival and accommodation and finally departure of the guest. While the historical and ethnographic review is mainly based on written histories and the experiences of other anthropologists as guests as well as ethnographers, the passage of hospitality draws on the multi-sited auto-anthropological experiences of the author, both as host and as ethnographer of contemporary South African hosts in small owner-managed commercial hospitality establishments.
- Full Text:
- Date Issued: 2011
Corporeal tales : an investigation into narrative form in contemporary South African dance and choreography
- Authors: Parker, Alan Charles
- Date: 2008
- Subjects: Sichel, Adrienne Krouse, Matthew Dance -- South Africa Choreography -- South Africa Choreographers -- South Africa Dance criticism -- South Africa
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:2157 , http://hdl.handle.net/10962/d1007658
- Description: In the years following the fall of Apartheid in South Africa, dance and choreography have undergone considerable transformation. This investigation stems from one observation relative to this change that has been articulated by two of South Africa's most respected dance critics, Adrienne Sichel and Matthew Krouse. Both critics have noted a growing concern for narrative in South African contemporary choreography, coupled with an apparent propensity for narratives of a distinctly personal and 'autobiographical' nature. In Part One: 'Just after the beginning', the proposed preoccupation with narrative in South African contemporary choreography is discussed in light of the relationship between narrative and the notion of personal identity. The use of the performed narrative as a medium to explore questions about identity is offered as one explanation underpinning this increased proclivity, where the interrogation of the form of the danced narrative provides a site for exploration of personal identity. Part Two: 'Somewhere in the middle' interrogates the notion of form through an in-depth discussion of the experimentation with form within theatrical and antitheatrical dance traditions over the last fifty years. Specific works by three selected South African choreographers (Ginslov, Maqoma and Sabbagha) are discussed in terms of their general approach to narrative form. This provides an illustration of some of the approaches to narrative form emergent in contemporary South African choreographic practices. Part Three: 'Nearing the end' offers Acty Tang's Chaste (2007) as a case study to illustrate the practical application of the dance narrative as a means to interrogate questions relating to personal identity. A detailed analysis of Tang's particular approach to forming the narrative of Chaste is conducted, exposing the intertextual, multimedia and multidisciplinary approach to creating the danced narrative.
- Full Text:
- Date Issued: 2008
- Authors: Parker, Alan Charles
- Date: 2008
- Subjects: Sichel, Adrienne Krouse, Matthew Dance -- South Africa Choreography -- South Africa Choreographers -- South Africa Dance criticism -- South Africa
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:2157 , http://hdl.handle.net/10962/d1007658
- Description: In the years following the fall of Apartheid in South Africa, dance and choreography have undergone considerable transformation. This investigation stems from one observation relative to this change that has been articulated by two of South Africa's most respected dance critics, Adrienne Sichel and Matthew Krouse. Both critics have noted a growing concern for narrative in South African contemporary choreography, coupled with an apparent propensity for narratives of a distinctly personal and 'autobiographical' nature. In Part One: 'Just after the beginning', the proposed preoccupation with narrative in South African contemporary choreography is discussed in light of the relationship between narrative and the notion of personal identity. The use of the performed narrative as a medium to explore questions about identity is offered as one explanation underpinning this increased proclivity, where the interrogation of the form of the danced narrative provides a site for exploration of personal identity. Part Two: 'Somewhere in the middle' interrogates the notion of form through an in-depth discussion of the experimentation with form within theatrical and antitheatrical dance traditions over the last fifty years. Specific works by three selected South African choreographers (Ginslov, Maqoma and Sabbagha) are discussed in terms of their general approach to narrative form. This provides an illustration of some of the approaches to narrative form emergent in contemporary South African choreographic practices. Part Three: 'Nearing the end' offers Acty Tang's Chaste (2007) as a case study to illustrate the practical application of the dance narrative as a means to interrogate questions relating to personal identity. A detailed analysis of Tang's particular approach to forming the narrative of Chaste is conducted, exposing the intertextual, multimedia and multidisciplinary approach to creating the danced narrative.
- Full Text:
- Date Issued: 2008
Applications of the Baylis-Hillman reaction in the synthesis of coumarin derivatives
- Authors: Musa, Musiliyu Ayodele
- Date: 2003
- Subjects: Coumarins Heterocyclic compounds -- Derivatives
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4403 , http://hdl.handle.net/10962/d1006705
- Description: The reaction of specially prepared salicylaldehyde benzyl ethers with the activated alkenes, methyl acrylate or acrylonitrile, in the presence of the catalyst, DABCO, has afforded Baylis-Hillman products, which have been subjected to conjugate addition with either piperidine or benzylamine. Hydrogenolysis of these conjugate addition products in the presence of a palladium-on-carbon catalyst has been shown to afford the corresponding 3-substituted coumarins, while treatment of O-benzylated Baylis-Hillman adducts with HCl or HI afforded the corresponding 3-(halomethyl)coumarins directly, in up to 94%. The 3-(halomethyl)coumarins have also been obtained in excellent yields (up to 98%) and even more conveniently, by treating the unprotected Baylis-Hillman products with HCl in a mixture of AcOH and Ac₂O, obtained from tert-butyl acrylate and various salicylaldehydes. The generality of an established route to the synthesis of coumarins via an intramolecular Baylis-Hillman reaction, involving the use of salicylaldehyde acrylate esters in the presence of DABCO, has also been demonstrated. Reactions between the 3-(halomethyl)coumarins and various nitrogen and carbon nucleophiles have been shown to proceed with a high degree of regioselectivity at the exocyclic allylic centre to afford 3-substituted coumarin products. The electronimpact mass spectra of selected coumarin derivatives have been investigated using high-resolution and B/E linked scan data. Fragmentation pathways have been proposed and fragmentation modes associated with different coumarin-containing analogues have been compared. A series of coumarin-containing analogues of ritonavir (a clinically useful HIV-1 protease inhibitor) have been prepared and characterized. The synthetic approach has involved the coupling of coumarin derivatives with a hydroxyethylene dipeptide isostere to afford ritonavir analogues containing coumarin termini. An interactive docking procedure has been used to explore the docking of ritonavir and a coumarincontaining analogue into the enzyme active site.
- Full Text:
- Date Issued: 2003
- Authors: Musa, Musiliyu Ayodele
- Date: 2003
- Subjects: Coumarins Heterocyclic compounds -- Derivatives
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4403 , http://hdl.handle.net/10962/d1006705
- Description: The reaction of specially prepared salicylaldehyde benzyl ethers with the activated alkenes, methyl acrylate or acrylonitrile, in the presence of the catalyst, DABCO, has afforded Baylis-Hillman products, which have been subjected to conjugate addition with either piperidine or benzylamine. Hydrogenolysis of these conjugate addition products in the presence of a palladium-on-carbon catalyst has been shown to afford the corresponding 3-substituted coumarins, while treatment of O-benzylated Baylis-Hillman adducts with HCl or HI afforded the corresponding 3-(halomethyl)coumarins directly, in up to 94%. The 3-(halomethyl)coumarins have also been obtained in excellent yields (up to 98%) and even more conveniently, by treating the unprotected Baylis-Hillman products with HCl in a mixture of AcOH and Ac₂O, obtained from tert-butyl acrylate and various salicylaldehydes. The generality of an established route to the synthesis of coumarins via an intramolecular Baylis-Hillman reaction, involving the use of salicylaldehyde acrylate esters in the presence of DABCO, has also been demonstrated. Reactions between the 3-(halomethyl)coumarins and various nitrogen and carbon nucleophiles have been shown to proceed with a high degree of regioselectivity at the exocyclic allylic centre to afford 3-substituted coumarin products. The electronimpact mass spectra of selected coumarin derivatives have been investigated using high-resolution and B/E linked scan data. Fragmentation pathways have been proposed and fragmentation modes associated with different coumarin-containing analogues have been compared. A series of coumarin-containing analogues of ritonavir (a clinically useful HIV-1 protease inhibitor) have been prepared and characterized. The synthetic approach has involved the coupling of coumarin derivatives with a hydroxyethylene dipeptide isostere to afford ritonavir analogues containing coumarin termini. An interactive docking procedure has been used to explore the docking of ritonavir and a coumarincontaining analogue into the enzyme active site.
- Full Text:
- Date Issued: 2003
Development and characterisation of a membrane gradostat bioreactor for the bioremediation of aromatic pollutants using white rot fungi
- Authors: Leukes, Winston D
- Date: 1999
- Subjects: Aromatic compounds Pollutants Fungi Bioremediation Industrial microbiology Biotechnology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4032 , http://hdl.handle.net/10962/d1004092
- Description: Bioremediation of aromatic pollutants using the ligninolytic enzymes of the white rot fungi has been thoroughly researched and has been shown to have considerable potential for industrial application. However, little success in scale-up and industrialisation of this technology has been attained due to problems associated with the continuous production of the pollutant-degrading enzymes using conventional bioreactor systems. The low productivities reported result from the incompatibility of conventional submerged culture reactor techniques with the physiological requirements of these fungi which have evolved on a solid-air interface, viz. wood. The enzymes are also produced only during the stationary phase of growth and can therefore be regarded as secondary metabolites. This study reports the conceptualisation, characterisation and evaluation of a novel bioreactor system as a solution to the continuous production of idiophasic pollutant degrading enzymes by the white rot fungus Phanerochaete chlysosporium. The reactor concept evolved from observation of these fungi in their native state, i. e. the metabolism of lignocellulosic material and involves the immobilisation of the organism onto a capillary ultrafiltration membrane. Nutrient gradients established across the biofilm, an inherent characteristic of fixed bed perfusion reactors, are exploited to provide both nutrient rich and nutrient poor zones across the biofilm. This allows growth or primary metabolism in the nutrient rich zone, pushing older biomass into the nutrient poor zone where secondary metabolism is induced by nutrient starvation. In effect, this represents a transformation of the events of a batch culture from a temporal to a spatial domain, allowing continuous production of secondary metabolites over time. Direct contact of the outer part of the biofilm with an air stream simulated the solid-air interface of the native state of the fungus. In order to facilitate the practical application of the membrane gradostat reactor (MGR) concept, conventional capillary membranes and membrane bioreactor modules were first evaluated. These were found to be unsuitable for application of the MGR concept. However, critical analysis of the shortcomings of the conventional systems resulted in the formulation of a set of design criteria for the development of a suitable membrane and module. These design criteria were satisfied by the development of a novel capillary membrane for membrane bioreactors, as well as a transverse flow membrane module, which is a novel approach in membrane bioreactor configuration. For the physiological characterisation of the MGR concept, a single fibre bioreactor unit was designed, which allowed destructive sampling of the biofilm for analysis. Using this system, it was shown that distinct morphological zones could be observed radially across the mature biofilm obtained through MGR operation. That these morphotypes do represent the temporal events of a typical batch culture in a spatial domain was confirmed by following the morphological changes occurring during batch culture of the immobilised fungus where the onset of primary and secondary metabolic conditions were manipulated through control of the nutrient supply. The different morphotypes were correlated to distinct growth phases by comparison of the morphology to the secretion of known enzymatic markers for secondary metabolism, viz. succinate dehydrogenase and cytochrome C oxidoreductase. Detailed structure-function analysis of the biofilm using transmission electron microscopy and adapted enzyme cytochemical staining techniques showed that the biofilm appeared to operate as a co-ordinated unit, with primary and secondary metabolism apparently linked in one thallus through nutrient translocation. This study provided new insights into the physiology of P. chrysosp,o rium and a detailed descriptive model was formulated which correlates well to existing models of wood degradation by the white rot fungi (WRF). Evaluation of the process on a laboratory scale using a novel transverse flow membrane bioreactor showed that a volumetric productivity of 1916 U.L.⁻¹day⁻¹ for manganese peroxidase, one of the pollutant degrading enzymes, could be attained, corresponding to a final concentration of 2 361 U.L.⁻¹ This may be compared to the best reported system (Moreira el at. 1997), where a volumetric productivity of 202 U.L.⁻¹day⁻¹was achieved with a final concentration of 250 U.L.⁻¹ However, MGR productivity is yet to be subjected to rigorous optimisation studies. The process could be operated continuously for 60 days. However, peak productivity could not be maintained for long periods. This was found to be due to physical phenomena relating to the fluid dynamics of the system which caused fluid flow maldistribution, which would have to be resolved through engineering analysis. In evaluation of the MGR concept for aromatic pollutant removal, in this case ρ- cresol, from growth medium, good performance was also achieved. The VmaxKm calculated by linear regression for the MGR was 0.8 (R² = 0.93), which compared favourably to that reported by Lewandowski et al. (1990), who obtained a Vmax/Km of 0.34 for a packed bed reactor treating chlorophenol. It was concluded that the MGR showed suitable potential to warrant further development, and that the descriptive characterisation of the biofilm physiology provided a sufficient basis for process analysis once engineering aspects ofthe system could be resolved.
- Full Text:
- Date Issued: 1999
- Authors: Leukes, Winston D
- Date: 1999
- Subjects: Aromatic compounds Pollutants Fungi Bioremediation Industrial microbiology Biotechnology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4032 , http://hdl.handle.net/10962/d1004092
- Description: Bioremediation of aromatic pollutants using the ligninolytic enzymes of the white rot fungi has been thoroughly researched and has been shown to have considerable potential for industrial application. However, little success in scale-up and industrialisation of this technology has been attained due to problems associated with the continuous production of the pollutant-degrading enzymes using conventional bioreactor systems. The low productivities reported result from the incompatibility of conventional submerged culture reactor techniques with the physiological requirements of these fungi which have evolved on a solid-air interface, viz. wood. The enzymes are also produced only during the stationary phase of growth and can therefore be regarded as secondary metabolites. This study reports the conceptualisation, characterisation and evaluation of a novel bioreactor system as a solution to the continuous production of idiophasic pollutant degrading enzymes by the white rot fungus Phanerochaete chlysosporium. The reactor concept evolved from observation of these fungi in their native state, i. e. the metabolism of lignocellulosic material and involves the immobilisation of the organism onto a capillary ultrafiltration membrane. Nutrient gradients established across the biofilm, an inherent characteristic of fixed bed perfusion reactors, are exploited to provide both nutrient rich and nutrient poor zones across the biofilm. This allows growth or primary metabolism in the nutrient rich zone, pushing older biomass into the nutrient poor zone where secondary metabolism is induced by nutrient starvation. In effect, this represents a transformation of the events of a batch culture from a temporal to a spatial domain, allowing continuous production of secondary metabolites over time. Direct contact of the outer part of the biofilm with an air stream simulated the solid-air interface of the native state of the fungus. In order to facilitate the practical application of the membrane gradostat reactor (MGR) concept, conventional capillary membranes and membrane bioreactor modules were first evaluated. These were found to be unsuitable for application of the MGR concept. However, critical analysis of the shortcomings of the conventional systems resulted in the formulation of a set of design criteria for the development of a suitable membrane and module. These design criteria were satisfied by the development of a novel capillary membrane for membrane bioreactors, as well as a transverse flow membrane module, which is a novel approach in membrane bioreactor configuration. For the physiological characterisation of the MGR concept, a single fibre bioreactor unit was designed, which allowed destructive sampling of the biofilm for analysis. Using this system, it was shown that distinct morphological zones could be observed radially across the mature biofilm obtained through MGR operation. That these morphotypes do represent the temporal events of a typical batch culture in a spatial domain was confirmed by following the morphological changes occurring during batch culture of the immobilised fungus where the onset of primary and secondary metabolic conditions were manipulated through control of the nutrient supply. The different morphotypes were correlated to distinct growth phases by comparison of the morphology to the secretion of known enzymatic markers for secondary metabolism, viz. succinate dehydrogenase and cytochrome C oxidoreductase. Detailed structure-function analysis of the biofilm using transmission electron microscopy and adapted enzyme cytochemical staining techniques showed that the biofilm appeared to operate as a co-ordinated unit, with primary and secondary metabolism apparently linked in one thallus through nutrient translocation. This study provided new insights into the physiology of P. chrysosp,o rium and a detailed descriptive model was formulated which correlates well to existing models of wood degradation by the white rot fungi (WRF). Evaluation of the process on a laboratory scale using a novel transverse flow membrane bioreactor showed that a volumetric productivity of 1916 U.L.⁻¹day⁻¹ for manganese peroxidase, one of the pollutant degrading enzymes, could be attained, corresponding to a final concentration of 2 361 U.L.⁻¹ This may be compared to the best reported system (Moreira el at. 1997), where a volumetric productivity of 202 U.L.⁻¹day⁻¹was achieved with a final concentration of 250 U.L.⁻¹ However, MGR productivity is yet to be subjected to rigorous optimisation studies. The process could be operated continuously for 60 days. However, peak productivity could not be maintained for long periods. This was found to be due to physical phenomena relating to the fluid dynamics of the system which caused fluid flow maldistribution, which would have to be resolved through engineering analysis. In evaluation of the MGR concept for aromatic pollutant removal, in this case ρ- cresol, from growth medium, good performance was also achieved. The VmaxKm calculated by linear regression for the MGR was 0.8 (R² = 0.93), which compared favourably to that reported by Lewandowski et al. (1990), who obtained a Vmax/Km of 0.34 for a packed bed reactor treating chlorophenol. It was concluded that the MGR showed suitable potential to warrant further development, and that the descriptive characterisation of the biofilm physiology provided a sufficient basis for process analysis once engineering aspects ofthe system could be resolved.
- Full Text:
- Date Issued: 1999
The petrology of the Merensky cyclic unit and associated rocks and their significance in the evolution of the Western Bushveld Complex
- Authors: Kruger, Floris Johan
- Date: 1984
- Subjects: Petrology -- Africa, Southern Petrofabric analysis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5006 , http://hdl.handle.net/10962/d1005636
- Description: A brief review of the various models proposed to account for the Bushveld Complex shows that there are two main hypotheses. These are the Multiple Intrusion hypothesis and the In Situ Crystallization hypothesis. The latter also allows for multiple additions to the crystallizing magma, and several variants involving the number of these inputs , their composition, volume and timing have been proposed. To facilitate description and investigation of the study section, the stratigraphic nomenclature of this part of the Rustenberg Layered Suite is revised and clarified. It is proposed that the boundary between the Critical Zone and Main Zone be placed at the base of the Merensky cyclic unit, and thus the whole of the Merensky and Bastard cyclic units are included in the Main Zone. Furthermore, the extremely confused terminology for smaller units within the Merensky and Bastard cyclic units is resolved by discarding the term Reef as a formal term and substituting lithological terms such as Merensky pegmatoid, Merensky pyroxenite, Bastard pyroxenite and Merensky mottled anorthosite etc. It is recommended that the term Reef be retained as an informal term to designate the mineralized horizon which may be mined, regardless of lithology. The term "pegmatoid" is restricted to stratiform or lensoid masses of coarse grained feldspathic pyroxenite or harzburgite which are part of the layered sequence. The transgressive vertical pipe-like, coarse-grained ultramafic "iron-rich bodies are termed "ultramafic pegmatites ". The main features of the Merensky and Bastard cyclic units are the regular chemical and mineralogical changes that occur with respect to stratigraphic height in these units. In the Merensky cyclic unit there is a smooth iron enrichment in the orthopyroxenes upward in the succession and a transition from pyroxenite at the base to mottled anorthosite at the top of the unit. The Bastard cyclic unit is broadly similar to the Merensky cyclic unit. A variety of textures and chemical features are in disequilibrium in some samples but not in others, and great complexity is evident wh en individual samples are studied in detail. The initial ⁸⁷Sr/⁸⁶Sr ratios of plagioclase separates and whole rocks from the study section show a distinct step-like increase in the Merensky cyclic unit to .70806 at the base of the, Merensky cyclic unit to .70806 at the base of the Bastard cyclic unit. In contrast , samples from below the Merensky cyclic unit have a constant initial Sr-isotopic ratio, as do the samples from the Bastard cyclic unit. These isotopic and chemical data, and available published geologic relationships suggest that a major new influx of basic magma occurred after the Footwall unit was deposited and that this mixed with the residual magma in the chamber and then precipitated the Merensky and Bastard cyclic units. The crystal settling theory as outlined by Wager and Brown (1968) fails to account for the chemical and stratigraphic variations observed in the study section. The theory of bottom crystallization, initially proposed by Jackson (1961), more adequately explains the features observed. Applying a model outlined by Irvine (1980a & b), it has been established from chemical data, that the Merensky cyclic unit crystallized from a magma layer with a thickness roughly equivalent to the average thickness of the cyclic unit itself (±10m). A similar exercise on the Bastard unit was not possible. The formation of the Footwall unit is still enigmatic. Infiltration metasomatism and sintering can modify the petrographic and chemical characteristics of rocks and minerals after deposition at the liquidus stage. During the solidification of the crystal mush a separate vapour phase may form in the crystal mush, which could move up through the crystal pile. This process may ultimately be responsible for the generation of potholes and pegmatoidal horizons, such as the Merensky pegmatoid. The upward increase in the initial ⁸⁷Sr/⁸⁶Sr ratio within the Merensky cyclic unit is strong evidence that infiltration metasomatism has played an important part in the generation of the Merensky cyclic unit. This process, coupled with fluid enrichment, may also result in the formation of pegmatoid layers. Sintering appears to have been a common process in the mottled anorthosites of the study section and may have severely reduced the amount of trapped interstitial liquid in these rocks.
- Full Text:
- Date Issued: 1984
- Authors: Kruger, Floris Johan
- Date: 1984
- Subjects: Petrology -- Africa, Southern Petrofabric analysis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5006 , http://hdl.handle.net/10962/d1005636
- Description: A brief review of the various models proposed to account for the Bushveld Complex shows that there are two main hypotheses. These are the Multiple Intrusion hypothesis and the In Situ Crystallization hypothesis. The latter also allows for multiple additions to the crystallizing magma, and several variants involving the number of these inputs , their composition, volume and timing have been proposed. To facilitate description and investigation of the study section, the stratigraphic nomenclature of this part of the Rustenberg Layered Suite is revised and clarified. It is proposed that the boundary between the Critical Zone and Main Zone be placed at the base of the Merensky cyclic unit, and thus the whole of the Merensky and Bastard cyclic units are included in the Main Zone. Furthermore, the extremely confused terminology for smaller units within the Merensky and Bastard cyclic units is resolved by discarding the term Reef as a formal term and substituting lithological terms such as Merensky pegmatoid, Merensky pyroxenite, Bastard pyroxenite and Merensky mottled anorthosite etc. It is recommended that the term Reef be retained as an informal term to designate the mineralized horizon which may be mined, regardless of lithology. The term "pegmatoid" is restricted to stratiform or lensoid masses of coarse grained feldspathic pyroxenite or harzburgite which are part of the layered sequence. The transgressive vertical pipe-like, coarse-grained ultramafic "iron-rich bodies are termed "ultramafic pegmatites ". The main features of the Merensky and Bastard cyclic units are the regular chemical and mineralogical changes that occur with respect to stratigraphic height in these units. In the Merensky cyclic unit there is a smooth iron enrichment in the orthopyroxenes upward in the succession and a transition from pyroxenite at the base to mottled anorthosite at the top of the unit. The Bastard cyclic unit is broadly similar to the Merensky cyclic unit. A variety of textures and chemical features are in disequilibrium in some samples but not in others, and great complexity is evident wh en individual samples are studied in detail. The initial ⁸⁷Sr/⁸⁶Sr ratios of plagioclase separates and whole rocks from the study section show a distinct step-like increase in the Merensky cyclic unit to .70806 at the base of the, Merensky cyclic unit to .70806 at the base of the Bastard cyclic unit. In contrast , samples from below the Merensky cyclic unit have a constant initial Sr-isotopic ratio, as do the samples from the Bastard cyclic unit. These isotopic and chemical data, and available published geologic relationships suggest that a major new influx of basic magma occurred after the Footwall unit was deposited and that this mixed with the residual magma in the chamber and then precipitated the Merensky and Bastard cyclic units. The crystal settling theory as outlined by Wager and Brown (1968) fails to account for the chemical and stratigraphic variations observed in the study section. The theory of bottom crystallization, initially proposed by Jackson (1961), more adequately explains the features observed. Applying a model outlined by Irvine (1980a & b), it has been established from chemical data, that the Merensky cyclic unit crystallized from a magma layer with a thickness roughly equivalent to the average thickness of the cyclic unit itself (±10m). A similar exercise on the Bastard unit was not possible. The formation of the Footwall unit is still enigmatic. Infiltration metasomatism and sintering can modify the petrographic and chemical characteristics of rocks and minerals after deposition at the liquidus stage. During the solidification of the crystal mush a separate vapour phase may form in the crystal mush, which could move up through the crystal pile. This process may ultimately be responsible for the generation of potholes and pegmatoidal horizons, such as the Merensky pegmatoid. The upward increase in the initial ⁸⁷Sr/⁸⁶Sr ratio within the Merensky cyclic unit is strong evidence that infiltration metasomatism has played an important part in the generation of the Merensky cyclic unit. This process, coupled with fluid enrichment, may also result in the formation of pegmatoid layers. Sintering appears to have been a common process in the mottled anorthosites of the study section and may have severely reduced the amount of trapped interstitial liquid in these rocks.
- Full Text:
- Date Issued: 1984
Bacteriophage growth on stationary phase achromabacter strains
- Authors: Robb, Susan Mary
- Date: 1980
- Subjects: Bacteriophages , Strains and stresses
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4125 , http://hdl.handle.net/10962/d1014131
- Description: Achromobacter w.t. and strain 14 both support phage α3a growth in stationary phase, but unlike the w.t. strain, exponential phase cultures of strain 14 block phage development. A standard method was developed for determining phage growth in stationary phase cultures. Lyophilised cells were used to eliminate variations due to the unstable phenotype of Achromobacter strain 14 cells. Phage α3a growth in stationary phase was characterized by a long and variable latent period of 6 to 9 h and an increased burst size of 709 p.f.u. per cell as compared with 153 p.f.u. per cell in exponential wild type cells. During the latent period the infected cells were very sensitive to changes in growth conditions and in particular, dilution. Pre-conditioning of the bacterial cells by allowing them to stand for 24 h after shaking for 3 days was an important aspect of the stationary phase phage growth system. Cells which had been allowed to stand retained the ability to be infected and to support phage growth for at least 16 days. Shaking cultures gradually lost the ability to support phage growth but the phage could persist in the host cell for 10 days until removal from shaking when the lytic cycle could proceed after allowing the cultures to stand. In comparison the latent period and burst size in Achromobacter w.t. stationary phase cells were reduced to less than 2 h and less than 200 respectively. Stationary phase cultures differed physiologically and morphologically depending on the aeration conditions. In comparison with non-aerated standing cultures, vigorously aerated cultures showed a decrease in viability, RNA synthesis, membrane transport, intracellular ATP levels, UV resistance and heat resistance but had markedly higher protein synthesis levels. Aerated cells were small non-motile rods which did not support phage growth. They developed into large motile rods under conditions of limited aeration and were able to propagate phage. It was proposed that changes in the host control mechanisms for macromolecular synthesis may be instrumental in either blocking or permitting phage development. A spontaneous mutant of Achromobacter strain 14 (14x) which liberated phage and was resistant to superinfection was isolated. The phage-host relationship was unstable and similar to the phage carrier state. The liberated phage were able to grow in exponential strain 14 cells. It was proposed that strain 14 was a defective lysogen and that an immunity phase shift model may account for the differential phage growth in exponential and stationary phase cells. Host transcriptional control appears to be implicated in control of phage development in exponential and stationary phase cells. Achromobacter Lp only supported phage in exponential phase but a rifampicin resistant mutant of this strain was able to propagate phage in stationary phase. In vitro RNA synthesis assays showed that the rifampicin resistance was caused by an alteration in the RNA polymerase. Preliminary experiments to determine intracellular phage macromolecular synthesis were carried out using exponential Achromobacter w.t. cells which had been irradiated with UV prior to infection. In irradiated cells, infection with phage resulted in stimulation of DNA synthesis but no stimulation of protein synthesis. Phage production was drastically reduced in cells which had been treated with very low UV doses. It was proposed that α3a development may rely heavily on host cell functions which are destroyed by UV. Achromobacter mutants with defective leucine transport systems were isolated. Mutants which lost the leucine uptake system completely were totally resistant to phage infection and were unable to adsorb phage α3a. This is the first report to implicate an amino-acid transport system in phage adsorption.
- Full Text:
- Date Issued: 1980
- Authors: Robb, Susan Mary
- Date: 1980
- Subjects: Bacteriophages , Strains and stresses
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4125 , http://hdl.handle.net/10962/d1014131
- Description: Achromobacter w.t. and strain 14 both support phage α3a growth in stationary phase, but unlike the w.t. strain, exponential phase cultures of strain 14 block phage development. A standard method was developed for determining phage growth in stationary phase cultures. Lyophilised cells were used to eliminate variations due to the unstable phenotype of Achromobacter strain 14 cells. Phage α3a growth in stationary phase was characterized by a long and variable latent period of 6 to 9 h and an increased burst size of 709 p.f.u. per cell as compared with 153 p.f.u. per cell in exponential wild type cells. During the latent period the infected cells were very sensitive to changes in growth conditions and in particular, dilution. Pre-conditioning of the bacterial cells by allowing them to stand for 24 h after shaking for 3 days was an important aspect of the stationary phase phage growth system. Cells which had been allowed to stand retained the ability to be infected and to support phage growth for at least 16 days. Shaking cultures gradually lost the ability to support phage growth but the phage could persist in the host cell for 10 days until removal from shaking when the lytic cycle could proceed after allowing the cultures to stand. In comparison the latent period and burst size in Achromobacter w.t. stationary phase cells were reduced to less than 2 h and less than 200 respectively. Stationary phase cultures differed physiologically and morphologically depending on the aeration conditions. In comparison with non-aerated standing cultures, vigorously aerated cultures showed a decrease in viability, RNA synthesis, membrane transport, intracellular ATP levels, UV resistance and heat resistance but had markedly higher protein synthesis levels. Aerated cells were small non-motile rods which did not support phage growth. They developed into large motile rods under conditions of limited aeration and were able to propagate phage. It was proposed that changes in the host control mechanisms for macromolecular synthesis may be instrumental in either blocking or permitting phage development. A spontaneous mutant of Achromobacter strain 14 (14x) which liberated phage and was resistant to superinfection was isolated. The phage-host relationship was unstable and similar to the phage carrier state. The liberated phage were able to grow in exponential strain 14 cells. It was proposed that strain 14 was a defective lysogen and that an immunity phase shift model may account for the differential phage growth in exponential and stationary phase cells. Host transcriptional control appears to be implicated in control of phage development in exponential and stationary phase cells. Achromobacter Lp only supported phage in exponential phase but a rifampicin resistant mutant of this strain was able to propagate phage in stationary phase. In vitro RNA synthesis assays showed that the rifampicin resistance was caused by an alteration in the RNA polymerase. Preliminary experiments to determine intracellular phage macromolecular synthesis were carried out using exponential Achromobacter w.t. cells which had been irradiated with UV prior to infection. In irradiated cells, infection with phage resulted in stimulation of DNA synthesis but no stimulation of protein synthesis. Phage production was drastically reduced in cells which had been treated with very low UV doses. It was proposed that α3a development may rely heavily on host cell functions which are destroyed by UV. Achromobacter mutants with defective leucine transport systems were isolated. Mutants which lost the leucine uptake system completely were totally resistant to phage infection and were unable to adsorb phage α3a. This is the first report to implicate an amino-acid transport system in phage adsorption.
- Full Text:
- Date Issued: 1980
Peer-group leadership in schools
- Authors: Bandey, Michael John
- Date: 1972
- Subjects: Leadership School discipline -- South Africa -- Cape of Good Hope School management and organization -- South Africa -- Cape of Good Hope Personality assessment of youth -- South Africa -- Cape of Good Hope
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:1927 , http://hdl.handle.net/10962/d1007588
- Description: For a number of years I have wondered why many of the prefects of some of the Grahamstown Schools have not become leaders in the particular sphere into which they chose to go after school. More than one head prefect that I have known has appeared to fade into anonymity after apparently leading his peers at school. I wondered if this was perhaps because at school he was not really a leader but simply an efficient policeman. Conversely, people who were not prefects at school often appeared as leaders in their chosen post-school careers. It seemed as if for some reason the prefect system at the schools concerned did not appreciably aid many pupils to develop their leadership potential or the selection procedures were inefficient. On investigating further I became more and. more interested in this topic until eventually, on discovering that the Rhodes University Education Department had a set of leadership scores, (calculated from a personality test) I undertook this investigation.
- Full Text:
- Date Issued: 1972
- Authors: Bandey, Michael John
- Date: 1972
- Subjects: Leadership School discipline -- South Africa -- Cape of Good Hope School management and organization -- South Africa -- Cape of Good Hope Personality assessment of youth -- South Africa -- Cape of Good Hope
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:1927 , http://hdl.handle.net/10962/d1007588
- Description: For a number of years I have wondered why many of the prefects of some of the Grahamstown Schools have not become leaders in the particular sphere into which they chose to go after school. More than one head prefect that I have known has appeared to fade into anonymity after apparently leading his peers at school. I wondered if this was perhaps because at school he was not really a leader but simply an efficient policeman. Conversely, people who were not prefects at school often appeared as leaders in their chosen post-school careers. It seemed as if for some reason the prefect system at the schools concerned did not appreciably aid many pupils to develop their leadership potential or the selection procedures were inefficient. On investigating further I became more and. more interested in this topic until eventually, on discovering that the Rhodes University Education Department had a set of leadership scores, (calculated from a personality test) I undertook this investigation.
- Full Text:
- Date Issued: 1972
- «
- ‹
- 1
- ›
- »