A compliance framework for IT governance adoption and use by state-owned entities in South Africa
- Authors: Nxozi, Monelo
- Date: 2023-03-31
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/419244 , vital:71628
- Description: Embargoed. Possible release date in early 2025. , Thesis (PhD) -- Faculty of Commerce, Information Systems, 2023
- Full Text:
- Authors: Nxozi, Monelo
- Date: 2023-03-31
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/419244 , vital:71628
- Description: Embargoed. Possible release date in early 2025. , Thesis (PhD) -- Faculty of Commerce, Information Systems, 2023
- Full Text:
A native weevil and an exotic planthopper: investigating potential biological control agents for nymphaea mexicana zuccarini (nymphaeaceae) and its hybrids in South Africa
- Authors: Reid, Megan Kim
- Date: 2023-03-31
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/422554 , vital:71957 , DOI 10.21504/10962/422554
- Description: Nymphaea mexicana Zuccarini (Nymphaeaceae) is an invasive plant originating from southern USA and Mexico that has become problematic in South Africa, invading several water bodies around the country. Manual removal of this plant is very labour intensive and is not cost efficient or effective for long term control, while the use of herbicides is damaging to the environment and expensive. Consequently, this plant is a desirable candidate for biological control, which takes advantage of enemy release of the target weed and aims to re-establish population suppression induced by host specific natural enemies. Initiating biological control requires that several steps are followed to maximise the success of the programme, and the first few of these, including overseas surveys in the native range of the plant, have already been completed. This thesis aimed to continue biological control research for this species to take further steps at effectively managing the plant. Firstly, pre-release surveys in the invaded range are necessary to: determine what factors (including enemy release) contribute to the invasiveness of the target weed; establish a baseline of information to allow for comparison after biological control agents have been released; and identify any insect herbivores that may already be present in the country. The pre-release surveys conducted in this study revealed useful information about N. mexicana invasions in South Africa and provided evidence that enemy release is applicable to this case. However, these studies determined that a native weevil, Bagous longulus Gyllenhal (Coleoptera: Curculionidae), has expanded its host range to include the exotic N. mexicana at three sites, and may thus have potential for management of the species through augmentative releases. The invasion of N. mexicana in South Africa is further complicated by the presence of several Nymphaea hybrids originating from a complex history of horticultural trade. Although previous research has shown that several hybrid groups are present in South Africa, their parentage is not known. As biological control requires the use of host specific insects adapted to overcome the unique chemical and morphological defences utilised by plant species, hybrids are notoriously difficult to manage because they possess intermediate characters inherited from parent species to which natural enemies may not have adapted. Although biological control of hybrids is challenging, other case studies have demonstrated that it is possible to find suitable agents, but the chances of success are increased if putative parents of the hybrids are known so that they can be surveyed for natural enemies. Further molecular studies including possible parents of the Nymphaea hybrids in South Africa were thus carried out in this thesis to focus future surveying efforts. Two main hybrid groups were identified with genetic similarity to two tested putative Nymphaea parents, and this will allow further investigations of these species to improve the chances of successfully managing these hybrid groups. Some of the tested hybrids showed genetic contributions from multiple groups, some of which were unidentified, so it is necessary to prioritise the most problematic hybrids for biological control. With more insight into the genetic makeup of the Nymphaea hybrids in South Africa, investigations into the host specificity of potential biological control agents can be conducted. The ideal biological control agent should have a broad enough host range to impact and survive on both N. mexicana and its hybrids, but without a host range so broad that it would pose risk to native South African species. Host specificity trials are thus necessary to determine the suitability of potential agents. The identification of B. longulus feeding on N. mexicana during pre-release surveys motivated further investigations to determine the natural distribution, field host range, and host specificity of B. longulus in experimentally controlled conditions. Further surveys were therefore conducted at native Nymphaea sites around South Africa in addition to host specificity trials using the native Nymphaea nouchali Burm. f. (Nymphaeaceae), two populations of N. mexicana, and a cultivated hybrid. Results from the surveys and host specificity tests suggest that B. longulus is widely distributed across South Africa, is specific to Nymphaea with no observed preference between N. mexicana and the native N. nouchali, and does not perform well on Nymphaea hybrids. Hence, B. longulus is promising for use in new association biological control through augmentative releases but is not suitable for management of hybrids. In addition to the potential use of the South African B. longulus, it is necessary to conduct host specificity trials for natural enemies from the native range of N. mexicana that were prioritised in previous studies. Megamelus toddi Beamer (Hemiptera: Delphacidae) is one such species that was imported into quarantined laboratory conditions from Florida, USA. Host specificity trials were conducted using the same test plants as described for the studies on B. longulus, in addition to multigeneration trials to determine how long M. toddi could survive on non-target host plants. As with the B. longulus studies, no statistically significant differences in preference were observed between N. mexicana and N. nouchali, but M. toddi could not complete development on the test hybrid, indicating that this species is also unsuitable for the management of Nymphaea hybrids. Despite suboptimal plant health, M. toddi completed development for three generations on the native N. nouchali. This lack of host specificity deems M. toddi unsafe for release in South Africa but highlights the importance of following predefined steps to develop a biological control programme. The concluding chapter of this thesis discusses the aforementioned findings in a broader context by considering the driving forces of plant invasions in general and specifically for N. mexicana in South Africa. Case studies are also consulted to provide insight into how to proceed with managing Nymphaea hybrids in South Africa, while the factors governing host specificity and host range expansion are also discussed and considered in the context of B. longulus and M. toddi. Finally, after a consideration of the limitations of these studies, recommendations are made to continue the development of biological control for N. mexicana in South Africa. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Authors: Reid, Megan Kim
- Date: 2023-03-31
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/422554 , vital:71957 , DOI 10.21504/10962/422554
- Description: Nymphaea mexicana Zuccarini (Nymphaeaceae) is an invasive plant originating from southern USA and Mexico that has become problematic in South Africa, invading several water bodies around the country. Manual removal of this plant is very labour intensive and is not cost efficient or effective for long term control, while the use of herbicides is damaging to the environment and expensive. Consequently, this plant is a desirable candidate for biological control, which takes advantage of enemy release of the target weed and aims to re-establish population suppression induced by host specific natural enemies. Initiating biological control requires that several steps are followed to maximise the success of the programme, and the first few of these, including overseas surveys in the native range of the plant, have already been completed. This thesis aimed to continue biological control research for this species to take further steps at effectively managing the plant. Firstly, pre-release surveys in the invaded range are necessary to: determine what factors (including enemy release) contribute to the invasiveness of the target weed; establish a baseline of information to allow for comparison after biological control agents have been released; and identify any insect herbivores that may already be present in the country. The pre-release surveys conducted in this study revealed useful information about N. mexicana invasions in South Africa and provided evidence that enemy release is applicable to this case. However, these studies determined that a native weevil, Bagous longulus Gyllenhal (Coleoptera: Curculionidae), has expanded its host range to include the exotic N. mexicana at three sites, and may thus have potential for management of the species through augmentative releases. The invasion of N. mexicana in South Africa is further complicated by the presence of several Nymphaea hybrids originating from a complex history of horticultural trade. Although previous research has shown that several hybrid groups are present in South Africa, their parentage is not known. As biological control requires the use of host specific insects adapted to overcome the unique chemical and morphological defences utilised by plant species, hybrids are notoriously difficult to manage because they possess intermediate characters inherited from parent species to which natural enemies may not have adapted. Although biological control of hybrids is challenging, other case studies have demonstrated that it is possible to find suitable agents, but the chances of success are increased if putative parents of the hybrids are known so that they can be surveyed for natural enemies. Further molecular studies including possible parents of the Nymphaea hybrids in South Africa were thus carried out in this thesis to focus future surveying efforts. Two main hybrid groups were identified with genetic similarity to two tested putative Nymphaea parents, and this will allow further investigations of these species to improve the chances of successfully managing these hybrid groups. Some of the tested hybrids showed genetic contributions from multiple groups, some of which were unidentified, so it is necessary to prioritise the most problematic hybrids for biological control. With more insight into the genetic makeup of the Nymphaea hybrids in South Africa, investigations into the host specificity of potential biological control agents can be conducted. The ideal biological control agent should have a broad enough host range to impact and survive on both N. mexicana and its hybrids, but without a host range so broad that it would pose risk to native South African species. Host specificity trials are thus necessary to determine the suitability of potential agents. The identification of B. longulus feeding on N. mexicana during pre-release surveys motivated further investigations to determine the natural distribution, field host range, and host specificity of B. longulus in experimentally controlled conditions. Further surveys were therefore conducted at native Nymphaea sites around South Africa in addition to host specificity trials using the native Nymphaea nouchali Burm. f. (Nymphaeaceae), two populations of N. mexicana, and a cultivated hybrid. Results from the surveys and host specificity tests suggest that B. longulus is widely distributed across South Africa, is specific to Nymphaea with no observed preference between N. mexicana and the native N. nouchali, and does not perform well on Nymphaea hybrids. Hence, B. longulus is promising for use in new association biological control through augmentative releases but is not suitable for management of hybrids. In addition to the potential use of the South African B. longulus, it is necessary to conduct host specificity trials for natural enemies from the native range of N. mexicana that were prioritised in previous studies. Megamelus toddi Beamer (Hemiptera: Delphacidae) is one such species that was imported into quarantined laboratory conditions from Florida, USA. Host specificity trials were conducted using the same test plants as described for the studies on B. longulus, in addition to multigeneration trials to determine how long M. toddi could survive on non-target host plants. As with the B. longulus studies, no statistically significant differences in preference were observed between N. mexicana and N. nouchali, but M. toddi could not complete development on the test hybrid, indicating that this species is also unsuitable for the management of Nymphaea hybrids. Despite suboptimal plant health, M. toddi completed development for three generations on the native N. nouchali. This lack of host specificity deems M. toddi unsafe for release in South Africa but highlights the importance of following predefined steps to develop a biological control programme. The concluding chapter of this thesis discusses the aforementioned findings in a broader context by considering the driving forces of plant invasions in general and specifically for N. mexicana in South Africa. Case studies are also consulted to provide insight into how to proceed with managing Nymphaea hybrids in South Africa, while the factors governing host specificity and host range expansion are also discussed and considered in the context of B. longulus and M. toddi. Finally, after a consideration of the limitations of these studies, recommendations are made to continue the development of biological control for N. mexicana in South Africa. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
A statistical study of travelling ionospheric disturbances over the African-European and American sectors
- Authors: Thaganyana, Golekamang Piet
- Date: 2023-03-31
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/422541 , vital:71956 , DOI 10.21504/10962/422543
- Description: This research presents a long-term statistical study of travelling ionospheric disturbances (TIDs) of low- and high-latitude origin over the American and African-European sectors between 2010 and 2018. The TIDs of low latitude origin (hereafter known as poleward TIDs) were studied in both quiet and disturbed conditions, whereas the equatorward TIDs were only studied during quiet conditions. The Kp > 4 and Dst_ -50 nT was used as a criterion for geomagnetic disturbed conditions, while the four geomagnetically quiet days were selected each month based on Kp < 3. Observations of TIDs are made using Global Navigational Satellite Systems (GNSS) total electron content derived data. During quiet conditions, seven and two transhemispheric TIDs were identified over the African-European and American sectors, respectively. The observed TIDs originated from the wintertime hemisphere and propagated into the summertime hemisphere. The horizontal velocity, periods, and horizontal wavelengths of TIDs are in range of cH = 120-274 m/s, 48-80 min and _H = 379-1104 km, respectively. These quiet-time equatorward TIDs have been associated with tertiary gravity waves (GWs) from the dissipation of secondary GWs which are in turn generated from the dissipation of mountain waves (MWs) as a result of excited orographic forcing. The poleward TIDs during geomagnetically quiet conditions over the African and American sectors occur mainly during local daytime. Poleward TIDs were observed mostly in the African-European sector than the American sector. Their horizontal propagation velocities and periods range between 129-280 m/s and 39-70 min over African-European and American sectors. Although the mechanisms responsible for launching quiet-time poleward TIDs have not been established in this study, lower atmospheric processes such as convection systems, sudden stratospheric warming and cold weather fronts may have a role in their generation. During geomagnetic storms in the African sector, almost all poleward TIDs (with the exception of two cases) during the main phase were large-scale with horizontal velocities and periods ranging from 250-503 m/s and 30 min to 2 hours. During recovery phase, poleward TIDs fall under the category of medium scale. In the American sector, the majority of poleward TIDs occurred during the storm's main phase, as opposed to the African-European sector, which experienced a significant number of poleward TIDs during the recovery phase. The periods and horizontal velocities of TIDs range from 45 min-1.5 h and 180-296 m/s during main phase. During the recovery phase, the horizontal velocity and period range from 177-271 m/s and 40-1.5 h, respectively. Overall, it has been shown that statistically, changes in equatorial electrodynamics related to enhanced eastward electric _eld and hence increased equatorial electrojet (vertical E_B drift) correlates highly with the reported poleward TIDs. , Thesis (PhD) -- Faculty of Science, Physics and Electronics, 2023
- Full Text:
- Authors: Thaganyana, Golekamang Piet
- Date: 2023-03-31
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/422541 , vital:71956 , DOI 10.21504/10962/422543
- Description: This research presents a long-term statistical study of travelling ionospheric disturbances (TIDs) of low- and high-latitude origin over the American and African-European sectors between 2010 and 2018. The TIDs of low latitude origin (hereafter known as poleward TIDs) were studied in both quiet and disturbed conditions, whereas the equatorward TIDs were only studied during quiet conditions. The Kp > 4 and Dst_ -50 nT was used as a criterion for geomagnetic disturbed conditions, while the four geomagnetically quiet days were selected each month based on Kp < 3. Observations of TIDs are made using Global Navigational Satellite Systems (GNSS) total electron content derived data. During quiet conditions, seven and two transhemispheric TIDs were identified over the African-European and American sectors, respectively. The observed TIDs originated from the wintertime hemisphere and propagated into the summertime hemisphere. The horizontal velocity, periods, and horizontal wavelengths of TIDs are in range of cH = 120-274 m/s, 48-80 min and _H = 379-1104 km, respectively. These quiet-time equatorward TIDs have been associated with tertiary gravity waves (GWs) from the dissipation of secondary GWs which are in turn generated from the dissipation of mountain waves (MWs) as a result of excited orographic forcing. The poleward TIDs during geomagnetically quiet conditions over the African and American sectors occur mainly during local daytime. Poleward TIDs were observed mostly in the African-European sector than the American sector. Their horizontal propagation velocities and periods range between 129-280 m/s and 39-70 min over African-European and American sectors. Although the mechanisms responsible for launching quiet-time poleward TIDs have not been established in this study, lower atmospheric processes such as convection systems, sudden stratospheric warming and cold weather fronts may have a role in their generation. During geomagnetic storms in the African sector, almost all poleward TIDs (with the exception of two cases) during the main phase were large-scale with horizontal velocities and periods ranging from 250-503 m/s and 30 min to 2 hours. During recovery phase, poleward TIDs fall under the category of medium scale. In the American sector, the majority of poleward TIDs occurred during the storm's main phase, as opposed to the African-European sector, which experienced a significant number of poleward TIDs during the recovery phase. The periods and horizontal velocities of TIDs range from 45 min-1.5 h and 180-296 m/s during main phase. During the recovery phase, the horizontal velocity and period range from 177-271 m/s and 40-1.5 h, respectively. Overall, it has been shown that statistically, changes in equatorial electrodynamics related to enhanced eastward electric _eld and hence increased equatorial electrojet (vertical E_B drift) correlates highly with the reported poleward TIDs. , Thesis (PhD) -- Faculty of Science, Physics and Electronics, 2023
- Full Text:
Characterization of Trypanosoma brucei Sti1 and its interactions with Trypanosoma brucei Hsp83 and human Hsp90
- Authors: Jamabo, Miebaka
- Date: 2023-03-31
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/422629 , vital:71963 , DOI 10.21504/10962/422629
- Description: Neglected tropical diseases continue to pose global concern due to their impact on health and socio-economic status of developing countries in sub-Saharan Africa. African trypanosomiasis is one of the neglected tropical diseases caused by the kinetoplastid flagellate parasite Trypanosoma brucei (T. brucei). The disease is fatal if untreated and the toolbox to combat the disease has been plagued with many difficulties such as drug resistance, toxic chemotherapeutics, and cumbersome drug delivery processes. In recent years, the disease has received attention from organizations such as the Drugs for Neglected Diseases initiative (DNDi) in partnership with WHO as well as academia and industry to provide alternatives to the existing drugs as part of a targeted approach to eliminate human African trypanosomiasis by 2030. The life cycle of the T. brucei parasite requires that it transitions between a cold-blooded vector (the tsetse fly) and a human host. To survive this extreme environmental change and maintain its infectious cycle, the parasite has evolved an arsenal of tools which include a strong immune evasion technique and a robust molecular chaperone system. Heat shock protein 90 (Hsp90) is one of the most abundant eukaryotic molecular chaperones that has been extensively studied in many organisms. It is indispensable for maintaining proteostasis in some organisms and its inhibition is currently being explored as a drug target for cancer and other parasitic diseases. In T. brucei, cytosolic Hsp90 is specifically referred to as Hsp83 due to variations in the sizes amongst different orthologues. Hsp90 is present in high levels in all stages of the T. brucei cell cycle both constitutively and on exposure to stress. To function in the cell, Hsp90 is dependent on co-chaperones, one of which can be found in most organisms, namely, the stress-inducible protein 1 (Sti1). The Hsp90-Sti1 interaction was shown to be crucial for growth in the intracellular kinetoplastid parasite, Leishmania donovani. However, this partnership has not been explored in the extracellular parasite T. brucei. To analyse the interaction of Hsp90 with Sti1 in T. brucei, this study combined in silico, in vitro and in vivo tools. In silico analyses of the Hsp90 complement in T. brucei revealed the presence of twelve putative Hsp90 genes, ten of which code for the cytosolic protein and are arranged in tandem in a head to tail fashion on the same chromosome. One gene each was found for the mitochondrial and ER paralogues of Hsp90, similar to all other species analysed. Eight putative co-chaperones specific to T. brucei were also discovered: six tetratricopeptide repeat domain (TPR) containing co-chaperones and two non-TPR containing co-chaperones. Structural and evolutionary analysis also confirmed that the domains were conserved across the species analysed. T. brucei Sti1 (TbSti1), T. brucei cytosolic Hsp90 (TbHsp83) and human cytosolic Hsp90 (hHsp90) were heterologously overproduced in E. coli and purified using nickel affinity chromatography. With specific antibodies, the expression and localization of the proteins were confirmed. TbSti1 showed strong affinity to the Hsp90s in the nanomolar range, with higher affinity for hHsp90 compared to TbHsp83. TbHsp83 and hHsp90 showed typical chaperone properties by suppressing the aggregation of thermolabile substrate MDH at equimolar concentrations and both chaperones had potent ATP hydrolysis activity. TbSti1, on the other hand, showed no MDH suppression activity and did not affect the ATP hydrolysis activity of TbHsp83 or hHsp90. Ex-vivo experiments using HeLa CRISPR Hop knockout (KO) human cell lines transfected with pcDNA3.1(+)HA-TbSti1 revealed TbSti1 also localized to the cytoplasm. The transfected cells showed a distinct fibroblast-like morphology which was different from the circular morphology seen in the Hop KO untransfected and wild type untransfected cells. Finally, co-immunoprecipitation studies revealed that TbSti1 co-immunoprecipitated with hHsp90. These results show the first characterization of the TbHsp83-TbSti1 partnership in T. brucei. The strong association between both proteins suggests a functional role for this partnership in T. brucei and could provide an updated context for understanding Trypanosome brucei biology. , Thesis (PhD) -- Faculty of Science, Biotechnology and Innovation Centre, 2023
- Full Text:
- Authors: Jamabo, Miebaka
- Date: 2023-03-31
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/422629 , vital:71963 , DOI 10.21504/10962/422629
- Description: Neglected tropical diseases continue to pose global concern due to their impact on health and socio-economic status of developing countries in sub-Saharan Africa. African trypanosomiasis is one of the neglected tropical diseases caused by the kinetoplastid flagellate parasite Trypanosoma brucei (T. brucei). The disease is fatal if untreated and the toolbox to combat the disease has been plagued with many difficulties such as drug resistance, toxic chemotherapeutics, and cumbersome drug delivery processes. In recent years, the disease has received attention from organizations such as the Drugs for Neglected Diseases initiative (DNDi) in partnership with WHO as well as academia and industry to provide alternatives to the existing drugs as part of a targeted approach to eliminate human African trypanosomiasis by 2030. The life cycle of the T. brucei parasite requires that it transitions between a cold-blooded vector (the tsetse fly) and a human host. To survive this extreme environmental change and maintain its infectious cycle, the parasite has evolved an arsenal of tools which include a strong immune evasion technique and a robust molecular chaperone system. Heat shock protein 90 (Hsp90) is one of the most abundant eukaryotic molecular chaperones that has been extensively studied in many organisms. It is indispensable for maintaining proteostasis in some organisms and its inhibition is currently being explored as a drug target for cancer and other parasitic diseases. In T. brucei, cytosolic Hsp90 is specifically referred to as Hsp83 due to variations in the sizes amongst different orthologues. Hsp90 is present in high levels in all stages of the T. brucei cell cycle both constitutively and on exposure to stress. To function in the cell, Hsp90 is dependent on co-chaperones, one of which can be found in most organisms, namely, the stress-inducible protein 1 (Sti1). The Hsp90-Sti1 interaction was shown to be crucial for growth in the intracellular kinetoplastid parasite, Leishmania donovani. However, this partnership has not been explored in the extracellular parasite T. brucei. To analyse the interaction of Hsp90 with Sti1 in T. brucei, this study combined in silico, in vitro and in vivo tools. In silico analyses of the Hsp90 complement in T. brucei revealed the presence of twelve putative Hsp90 genes, ten of which code for the cytosolic protein and are arranged in tandem in a head to tail fashion on the same chromosome. One gene each was found for the mitochondrial and ER paralogues of Hsp90, similar to all other species analysed. Eight putative co-chaperones specific to T. brucei were also discovered: six tetratricopeptide repeat domain (TPR) containing co-chaperones and two non-TPR containing co-chaperones. Structural and evolutionary analysis also confirmed that the domains were conserved across the species analysed. T. brucei Sti1 (TbSti1), T. brucei cytosolic Hsp90 (TbHsp83) and human cytosolic Hsp90 (hHsp90) were heterologously overproduced in E. coli and purified using nickel affinity chromatography. With specific antibodies, the expression and localization of the proteins were confirmed. TbSti1 showed strong affinity to the Hsp90s in the nanomolar range, with higher affinity for hHsp90 compared to TbHsp83. TbHsp83 and hHsp90 showed typical chaperone properties by suppressing the aggregation of thermolabile substrate MDH at equimolar concentrations and both chaperones had potent ATP hydrolysis activity. TbSti1, on the other hand, showed no MDH suppression activity and did not affect the ATP hydrolysis activity of TbHsp83 or hHsp90. Ex-vivo experiments using HeLa CRISPR Hop knockout (KO) human cell lines transfected with pcDNA3.1(+)HA-TbSti1 revealed TbSti1 also localized to the cytoplasm. The transfected cells showed a distinct fibroblast-like morphology which was different from the circular morphology seen in the Hop KO untransfected and wild type untransfected cells. Finally, co-immunoprecipitation studies revealed that TbSti1 co-immunoprecipitated with hHsp90. These results show the first characterization of the TbHsp83-TbSti1 partnership in T. brucei. The strong association between both proteins suggests a functional role for this partnership in T. brucei and could provide an updated context for understanding Trypanosome brucei biology. , Thesis (PhD) -- Faculty of Science, Biotechnology and Innovation Centre, 2023
- Full Text:
Economically important cephalopods of southern Angola, with a focus on the artisanal jig fishery
- Vázquez Morán, Chénelle Lesley
- Authors: Vázquez Morán, Chénelle Lesley
- Date: 2023-03-31
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/422529 , vital:71955 , DOI 10.21504/10962/422529
- Description: The global decline in marine finfish stocks has been met with a concomitant expansion of fisheries for cephalopods. Despite the increase in the exploitation and commercialization of cephalopods, there is a dearth of scientific information for over 90% of the extant species and this is even more marked in the developing world. Angolan capture fisheries production noted a tenfold increase in cephalopod landings between 1994 and 2003. One of the important fisheries is a cephalopod directed jig fishery that targets the squid Loligo reynaudii and the cuttlefish Sepia vermiculata in southern Angola, however, there is a complete lack of socio-ecological information available for this fishery. Hence the aim of this thesis was to provide basic biological and demographic information on L. reynaudii and S. vermiculata distributed off the coast of southern Angola, assess the importance and dependence of local artisanal fishers on these two species and examine the current management strategies and policies in the region This study found that the artisanal cephalopod jig fishery is critical for the livelihoods of the coastal communities of southern Angola, particularly due to the limited alternative income generating opportunities available. The cephalopod jig fishery is highly labour intensive, with fishers spending a considerable amount of time per day, drifting over known fishing grounds. Catch composition of the artisanal jig fishery indicated that squid is the dominant species within the fishery, in terms of numerical abundance and weight. The productivity and progression of the fishery is hampered by a number of ecological, socio-economic and governance constraints, as highlighted by socio-economic surveys conducted with local squid fishers. Such constraints include, but are not limited to declining catches, increased negative interactions with seals, increased inter-sector competition, lack of infrastructure, poor quality fishing equipment as well as a lack of communication and support from government officials. To examine aspects of the biology and demography of L. reynaudii, whole specimens were collected monthly, from the two primary fishing areas in southern Angola; Namibe and Tombua, during two main sampling periods, June 2008 – May 2009 (Period 1) and June 2014 – May 2015 (Period 2). Male L. reynaudii were found to be significantly larger in size and weight than females, however both the average and maximum dorsal mantle length (DML) decreased between sampling periods. Length-at-50% maturity was larger for male L. reynaudii (170.47 mm DML – 1st period, 165.44 mm DML – 2nd period) than female L. reynaudii (114.71 mm DML – 1st period, 109.43 mm DML – 2nd period). Gonadosomatic indices (GSI) varied significantly during month and season for both sexes. Peak GSI coincided with a low catches in the artisanal jig fishery suggesting that the population may undergo a spawning migration away from fishing grounds, during late spring and summer. The theory of a seasonal spawning migration is further supported in this study by the low abundance of juvenile and sub-adult L, reynaudii collected during the study, along with the inability to detect egg beds in known fishing grounds. Stomach content analysis indicated that teleosts were the most important dietary item (66.3% F of the stomach contents). Trachurus capensis and Engraulis encrasicolus are both highly abundant small pelagic fishes in the cold nutrient rich waters of the Benguela Current and dominated the diet of sampled squid during autumn and winter months. It is likely that the prevalence of large, adult squid off the coast of Angola, as observed within the current study, may be ascribed to the suitable environmental conditions and the abundance of suitable prey. The results from the current study indicate that the southern Angolan subpopulation reveals similarities to that of the West Coast subpopulation of squid in South Africa, with regards to demographics and reproductive characteristics. It is likely that the population in southern Angola is an extension of the South African subpopulation of L. reynaudii on the western extremities. To examine the basic population biology and ecology of S. vermiculata off southern Angola whole specimens were collected from the fishery between December 2014 and April 2015. Morphological results indicate clear sexual dimorphism in soft part characteristics, cuttlebone and beak morphometry. Length-at-50% maturity was smaller in male S. vermiculata (217.53 mm DML) than female S. vermiculata (231.13 mm DML), although these differences were not significant. Stomach content analysis indicated that S. vermiculata predominantly fed on teleost species which were found within 64.5% of stomachs. Teleosts were more dominant in the diet of male S. vermiculata (78.6% F) than female S. vermiculata (53.0% F), which ate a more varied diet including crustaceans (41.2% F) and cephalopods (17.7% F). Availability and abundance of cuttlefish in Namibe indicates that the species may undergo a spatio-temporal shift in distribution, with majority of the artisanal catches of S. vermiculata occurring during summer months. The results from the current study highlights the fisheries potential of L. reynaudii and S. vermiculata and the dependence of artisanal fishers in southern Angola on cephalopods, and more specifically squid. The development of sustainable fisheries management strategies for the artisanal cephalopod jig fishery is critical, particularly as the global exploitation of cephalopods continues to increase with declining finfish populations. Failure to implement management strategies may remove this critical economic safety net for vulnerable coastal communities which have little alternative livelihood opportunities. Ongoing ecological research, a co-management approach and an increased consideration of local ecological knowledge will assist in designing appropriate management plans for the southern Angolan cephalopod jig fishery. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2023
- Full Text:
- Authors: Vázquez Morán, Chénelle Lesley
- Date: 2023-03-31
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/422529 , vital:71955 , DOI 10.21504/10962/422529
- Description: The global decline in marine finfish stocks has been met with a concomitant expansion of fisheries for cephalopods. Despite the increase in the exploitation and commercialization of cephalopods, there is a dearth of scientific information for over 90% of the extant species and this is even more marked in the developing world. Angolan capture fisheries production noted a tenfold increase in cephalopod landings between 1994 and 2003. One of the important fisheries is a cephalopod directed jig fishery that targets the squid Loligo reynaudii and the cuttlefish Sepia vermiculata in southern Angola, however, there is a complete lack of socio-ecological information available for this fishery. Hence the aim of this thesis was to provide basic biological and demographic information on L. reynaudii and S. vermiculata distributed off the coast of southern Angola, assess the importance and dependence of local artisanal fishers on these two species and examine the current management strategies and policies in the region This study found that the artisanal cephalopod jig fishery is critical for the livelihoods of the coastal communities of southern Angola, particularly due to the limited alternative income generating opportunities available. The cephalopod jig fishery is highly labour intensive, with fishers spending a considerable amount of time per day, drifting over known fishing grounds. Catch composition of the artisanal jig fishery indicated that squid is the dominant species within the fishery, in terms of numerical abundance and weight. The productivity and progression of the fishery is hampered by a number of ecological, socio-economic and governance constraints, as highlighted by socio-economic surveys conducted with local squid fishers. Such constraints include, but are not limited to declining catches, increased negative interactions with seals, increased inter-sector competition, lack of infrastructure, poor quality fishing equipment as well as a lack of communication and support from government officials. To examine aspects of the biology and demography of L. reynaudii, whole specimens were collected monthly, from the two primary fishing areas in southern Angola; Namibe and Tombua, during two main sampling periods, June 2008 – May 2009 (Period 1) and June 2014 – May 2015 (Period 2). Male L. reynaudii were found to be significantly larger in size and weight than females, however both the average and maximum dorsal mantle length (DML) decreased between sampling periods. Length-at-50% maturity was larger for male L. reynaudii (170.47 mm DML – 1st period, 165.44 mm DML – 2nd period) than female L. reynaudii (114.71 mm DML – 1st period, 109.43 mm DML – 2nd period). Gonadosomatic indices (GSI) varied significantly during month and season for both sexes. Peak GSI coincided with a low catches in the artisanal jig fishery suggesting that the population may undergo a spawning migration away from fishing grounds, during late spring and summer. The theory of a seasonal spawning migration is further supported in this study by the low abundance of juvenile and sub-adult L, reynaudii collected during the study, along with the inability to detect egg beds in known fishing grounds. Stomach content analysis indicated that teleosts were the most important dietary item (66.3% F of the stomach contents). Trachurus capensis and Engraulis encrasicolus are both highly abundant small pelagic fishes in the cold nutrient rich waters of the Benguela Current and dominated the diet of sampled squid during autumn and winter months. It is likely that the prevalence of large, adult squid off the coast of Angola, as observed within the current study, may be ascribed to the suitable environmental conditions and the abundance of suitable prey. The results from the current study indicate that the southern Angolan subpopulation reveals similarities to that of the West Coast subpopulation of squid in South Africa, with regards to demographics and reproductive characteristics. It is likely that the population in southern Angola is an extension of the South African subpopulation of L. reynaudii on the western extremities. To examine the basic population biology and ecology of S. vermiculata off southern Angola whole specimens were collected from the fishery between December 2014 and April 2015. Morphological results indicate clear sexual dimorphism in soft part characteristics, cuttlebone and beak morphometry. Length-at-50% maturity was smaller in male S. vermiculata (217.53 mm DML) than female S. vermiculata (231.13 mm DML), although these differences were not significant. Stomach content analysis indicated that S. vermiculata predominantly fed on teleost species which were found within 64.5% of stomachs. Teleosts were more dominant in the diet of male S. vermiculata (78.6% F) than female S. vermiculata (53.0% F), which ate a more varied diet including crustaceans (41.2% F) and cephalopods (17.7% F). Availability and abundance of cuttlefish in Namibe indicates that the species may undergo a spatio-temporal shift in distribution, with majority of the artisanal catches of S. vermiculata occurring during summer months. The results from the current study highlights the fisheries potential of L. reynaudii and S. vermiculata and the dependence of artisanal fishers in southern Angola on cephalopods, and more specifically squid. The development of sustainable fisheries management strategies for the artisanal cephalopod jig fishery is critical, particularly as the global exploitation of cephalopods continues to increase with declining finfish populations. Failure to implement management strategies may remove this critical economic safety net for vulnerable coastal communities which have little alternative livelihood opportunities. Ongoing ecological research, a co-management approach and an increased consideration of local ecological knowledge will assist in designing appropriate management plans for the southern Angolan cephalopod jig fishery. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2023
- Full Text:
Evaluation of the effectiveness of small aperture network telescopes as IBR data sources
- Authors: Chindipha, Stones Dalitso
- Date: 2023-03-31
- Subjects: Computer networks Monitoring , Computer networks Security measures , Computer bootstrapping , Time-series analysis , Regression analysis , Mathematical models
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/366264 , vital:65849 , DOI https://doi.org/10.21504/10962/366264
- Description: The use of network telescopes to collect unsolicited network traffic by monitoring unallocated address space has been in existence for over two decades. Past research has shown that there is a lot of activity happening in this unallocated space that needs monitoring as it carries threat intelligence data that has proven to be very useful in the security field. Prior to the emergence of the Internet of Things (IoT), commercialisation of IP addresses and widespread of mobile devices, there was a large pool of IPv4 addresses and thus reserving IPv4 addresses to be used for monitoring unsolicited activities going in the unallocated space was not a problem. Now, preservation of such IPv4 addresses just for monitoring is increasingly difficult as there is not enough free addresses in the IPv4 address space to be used for just monitoring. This is the case because such monitoring is seen as a ’non-productive’ use of the IP addresses. This research addresses the problem brought forth by this IPv4 address space exhaustion in relation to Internet Background Radiation (IBR) monitoring. In order to address the research questions, this research developed four mathematical models: Absolute Mean Accuracy Percentage Score (AMAPS), Symmetric Absolute Mean Accuracy Percentage Score (SAMAPS), Standardised Mean Absolute Error (SMAE), and Standardised Mean Absolute Scaled Error (SMASE). These models are used to evaluate the research objectives and quantify the variations that exist between different samples. The sample sizes represent different lens sizes of the telescopes. The study has brought to light a time series plot that shows the expected proportion of unique source IP addresses collected over time. The study also imputed data using the smaller /24 IPv4 net-block subnets to regenerate the missing data points using bootstrapping to create confidence intervals (CI). The findings from the simulated data supports the findings computed from the models. The CI offers a boost to decision making. Through a series of experiments with monthly and quarterly datasets, the study proposed a 95% - 99% confidence level to be used. It was known that large network telescopes collect more threat intelligence data than small-sized network telescopes, however, no study, to the best of our knowledge, has ever quantified such a knowledge gap. With the findings from the study, small-sized network telescope users can now use their network telescopes with full knowledge of gap that exists in the data collected between different network telescopes. , Thesis (PhD) -- Faculty of Science, Computer Science, 2023
- Full Text:
- Authors: Chindipha, Stones Dalitso
- Date: 2023-03-31
- Subjects: Computer networks Monitoring , Computer networks Security measures , Computer bootstrapping , Time-series analysis , Regression analysis , Mathematical models
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/366264 , vital:65849 , DOI https://doi.org/10.21504/10962/366264
- Description: The use of network telescopes to collect unsolicited network traffic by monitoring unallocated address space has been in existence for over two decades. Past research has shown that there is a lot of activity happening in this unallocated space that needs monitoring as it carries threat intelligence data that has proven to be very useful in the security field. Prior to the emergence of the Internet of Things (IoT), commercialisation of IP addresses and widespread of mobile devices, there was a large pool of IPv4 addresses and thus reserving IPv4 addresses to be used for monitoring unsolicited activities going in the unallocated space was not a problem. Now, preservation of such IPv4 addresses just for monitoring is increasingly difficult as there is not enough free addresses in the IPv4 address space to be used for just monitoring. This is the case because such monitoring is seen as a ’non-productive’ use of the IP addresses. This research addresses the problem brought forth by this IPv4 address space exhaustion in relation to Internet Background Radiation (IBR) monitoring. In order to address the research questions, this research developed four mathematical models: Absolute Mean Accuracy Percentage Score (AMAPS), Symmetric Absolute Mean Accuracy Percentage Score (SAMAPS), Standardised Mean Absolute Error (SMAE), and Standardised Mean Absolute Scaled Error (SMASE). These models are used to evaluate the research objectives and quantify the variations that exist between different samples. The sample sizes represent different lens sizes of the telescopes. The study has brought to light a time series plot that shows the expected proportion of unique source IP addresses collected over time. The study also imputed data using the smaller /24 IPv4 net-block subnets to regenerate the missing data points using bootstrapping to create confidence intervals (CI). The findings from the simulated data supports the findings computed from the models. The CI offers a boost to decision making. Through a series of experiments with monthly and quarterly datasets, the study proposed a 95% - 99% confidence level to be used. It was known that large network telescopes collect more threat intelligence data than small-sized network telescopes, however, no study, to the best of our knowledge, has ever quantified such a knowledge gap. With the findings from the study, small-sized network telescope users can now use their network telescopes with full knowledge of gap that exists in the data collected between different network telescopes. , Thesis (PhD) -- Faculty of Science, Computer Science, 2023
- Full Text:
Phytoplankton communities provide insight into ecosystem functioning of the Agulhas Current system
- Authors: Gibb, Ross-Lynne Alida
- Date: 2023-03-31
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/422646 , vital:71965
- Description: Access restricted. Embargoed until 2025. , Thesis (PhD) -- Faculty of Science, Biochemistry and Microbiology, 2023
- Full Text:
- Authors: Gibb, Ross-Lynne Alida
- Date: 2023-03-31
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/422646 , vital:71965
- Description: Access restricted. Embargoed until 2025. , Thesis (PhD) -- Faculty of Science, Biochemistry and Microbiology, 2023
- Full Text:
Rapid Synthesis of Thiol-Co-Capped CdTe/CdSe/ZnSe Multi-Core-Shell QDs and Their Encapsulation in Liposomes and Chitosan Nanoparticles; Comparative Bio-compatibility Studies Using Hela and Vero Cells
- Authors: Daramola, Olamide Abiodun
- Date: 2023-03-31
- Subjects: Chitosan , Chitosan nanoparticles , Quantum dots , Liposomes , Toxicity , Cadmium telluride , Cadmium selenide , Zinc selenide
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/422617 , vital:71962 , DOI 10.21504/10962/422617
- Description: The common method that has been used to reduce the toxicity posed to living cells by CdTe Quantum Dots (QDs) is through the synthesis of CdTe multi-core-shells nanoparticles. In this process, the surface of CdTe QDs is usually coated by less toxic ZnS or ZnSe shells. This heterostructure compound does not only reduce the toxicity of CdTe QDs but can also be used in applications such as deep tissue imaging. The heterostructures can be in numerous forms such as CdTe/CdSe/ZnSe or CdTe/CdSe/ZnS or CdTe/CdS/ZnS multi-core-shell QDs. However, the drawbacks attributed to the fabrication of these compounds is long synthesis times (6- 24 h) in achieving the highest wavelength emission maxima. Others are the use of toxic reagents and poor reproducibility of synthesized materials. An additional problem is that the ZnSe or ZnS coating is insufficient to completely protect the highly toxic Cd metal from escaping into immediate solution. This limits their use in biochemistry and with living systems. Liposomes and biopolymers such as chitosan are known to be environmentally friendly compounds that have been used in various studies as delivery systems for QDs and model drugs for drug delivery applications. They are generally non-toxic and highly bio-compatible. In this study, the rapid synthesis of thiol-co-capped CdTe/CdSe/ZnSe multi-core-shell QDs with a maximum reaction time of 35 mins, gave reliable QDs with emission maxima at 625 nm. The multi-core-shell QDs were encapsulated in two different bio-compatible environments, namely liposome and chitosan nanoparticles (CNP) at 14 different formulations (F) for liposome and 12 different formulations for CNP. Cytotoxicity and florescence imaging studies using HeLa and Vero cells, were used to investigate the improved bio-compatibility. Various characterization techniques were used to elucidate the optical properties, morphology and physico-chemical properties of the QDs and nanocomposites. Two of the best formulations, QD-liposome vesicles (LVs)-F12 and QD-CNP-F9 (with chitosan), demonstrated high loading efficiencies of 42 ± 6 % and 59 ± 5 %, respectively. While the plain CdTe QDs showed high toxicity, some of the encapsulated materials, QD-LVs-F1 and F12, depicted no-toxicity against the cells (IC50 > 0.5 mg/ml). The QDs also retained most of their fluorescence and properties and could easily be tracked in cells and visualized around the nucleus, indicating the successful internalization of the QDs in the cytosol. These results shows that encapsulation of CdTe multi-core-shell QDs in liposomes produce better bio-compatibility compared to multi-core-shell QDs and better than CNP coating. These particles therefore show good promise in cell-labelling, drug delivery studies. Their core-shell nanoparticles have also shown good behavior in enhancing the memory of a device which is based on some recent collaborated works. , Thesis (PhD) -- Faculty of Science, Chemistry, 2023
- Full Text:
- Authors: Daramola, Olamide Abiodun
- Date: 2023-03-31
- Subjects: Chitosan , Chitosan nanoparticles , Quantum dots , Liposomes , Toxicity , Cadmium telluride , Cadmium selenide , Zinc selenide
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/422617 , vital:71962 , DOI 10.21504/10962/422617
- Description: The common method that has been used to reduce the toxicity posed to living cells by CdTe Quantum Dots (QDs) is through the synthesis of CdTe multi-core-shells nanoparticles. In this process, the surface of CdTe QDs is usually coated by less toxic ZnS or ZnSe shells. This heterostructure compound does not only reduce the toxicity of CdTe QDs but can also be used in applications such as deep tissue imaging. The heterostructures can be in numerous forms such as CdTe/CdSe/ZnSe or CdTe/CdSe/ZnS or CdTe/CdS/ZnS multi-core-shell QDs. However, the drawbacks attributed to the fabrication of these compounds is long synthesis times (6- 24 h) in achieving the highest wavelength emission maxima. Others are the use of toxic reagents and poor reproducibility of synthesized materials. An additional problem is that the ZnSe or ZnS coating is insufficient to completely protect the highly toxic Cd metal from escaping into immediate solution. This limits their use in biochemistry and with living systems. Liposomes and biopolymers such as chitosan are known to be environmentally friendly compounds that have been used in various studies as delivery systems for QDs and model drugs for drug delivery applications. They are generally non-toxic and highly bio-compatible. In this study, the rapid synthesis of thiol-co-capped CdTe/CdSe/ZnSe multi-core-shell QDs with a maximum reaction time of 35 mins, gave reliable QDs with emission maxima at 625 nm. The multi-core-shell QDs were encapsulated in two different bio-compatible environments, namely liposome and chitosan nanoparticles (CNP) at 14 different formulations (F) for liposome and 12 different formulations for CNP. Cytotoxicity and florescence imaging studies using HeLa and Vero cells, were used to investigate the improved bio-compatibility. Various characterization techniques were used to elucidate the optical properties, morphology and physico-chemical properties of the QDs and nanocomposites. Two of the best formulations, QD-liposome vesicles (LVs)-F12 and QD-CNP-F9 (with chitosan), demonstrated high loading efficiencies of 42 ± 6 % and 59 ± 5 %, respectively. While the plain CdTe QDs showed high toxicity, some of the encapsulated materials, QD-LVs-F1 and F12, depicted no-toxicity against the cells (IC50 > 0.5 mg/ml). The QDs also retained most of their fluorescence and properties and could easily be tracked in cells and visualized around the nucleus, indicating the successful internalization of the QDs in the cytosol. These results shows that encapsulation of CdTe multi-core-shell QDs in liposomes produce better bio-compatibility compared to multi-core-shell QDs and better than CNP coating. These particles therefore show good promise in cell-labelling, drug delivery studies. Their core-shell nanoparticles have also shown good behavior in enhancing the memory of a device which is based on some recent collaborated works. , Thesis (PhD) -- Faculty of Science, Chemistry, 2023
- Full Text:
South African supratidal microbialites: prokaryote communities, metabolic capabilities, and biogeochemical processes
- Authors: Isemonger, Eric William
- Date: 2023-03-31
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/422641 , vital:71964
- Description: Access restricted. Embargoed until 2025. , Thesis (PhD) -- Faculty of Science, Biochemistry and Microbiology, 2023
- Full Text:
- Authors: Isemonger, Eric William
- Date: 2023-03-31
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/422641 , vital:71964
- Description: Access restricted. Embargoed until 2025. , Thesis (PhD) -- Faculty of Science, Biochemistry and Microbiology, 2023
- Full Text:
The development of ionic zinc(II) phthalocyanines for sono-photodynamic combination therapy of cervical and breast cancer
- Authors: Nene, Lindokuhle Cindy
- Date: 2023-03-31
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/422565 , vital:71958 , DOI 10.21504/10962/422565
- Description: This study focuses on the development of the sono-photodynamic combination therapy (SPDT) activity of phthalocyanines (Pcs) on the cervical and breast cancer cell lines in vitro. The SPDT technique utilizes ultrasound in combination with light to elicit cytotoxic effects for cancer eradication. In this work, a selection of tetra-peripherally substituted Zn(II) cationic and zwitterionic Pcs were prepared. The photophysical parameters of the Pcs were determined including their fluorescence behaviours and efficiency of the triplet excited state population. The effects of the ultrasonic parameters (frequencies (MHz) and power (W.cm-2)) on the stability of the Pcs were evaluated. Four parameters were evaluated: Par I (1 MHz: 1 W.cm-2), Par II (1 MHz: 2 W.cm-2), Par III (3 MHz: 1 W.cm-2) and Par IV (3 MHz: 2 W.cm-2). The stability of the Pcs reduced with the increase in the ultrasonic power (for Par II and Par IV). The Par I showed the least degradation compared to the other parameters and was therefore used for the SPDT treatments. The sonodynamic (SDT), photodynamic (PDT) therapy activities of the Pcs were studied and compared to their SPDT efficacies. The Pcs showed reactive oxygen species generation during the SDT, PDT and SPDT treatments. For the SDT and SPDT, singlet oxygen (1O2) and hydroxyl radicals (•OH) were detected. For PDT, only the 1O2 were detected. The cell cytotoxicity studies for the Pcs showed relatively higher therapeutic efficacies for the SDT treatments compared to the PDT treatments, where the SPDT showed higher therapeutic efficacies compared to both the SDT and PDT monotreatments on both the cell lines in vitro. Overall, the combination treatments were better compared to the monotreatments. The activities of the Pcs were compared by their differences in structures, including the type of R-group, type of quaternizing agent and type of nanoparticle conjugates. , Thesis (PhD) -- Faculty of Science, Chemistry, 2023
- Full Text:
- Authors: Nene, Lindokuhle Cindy
- Date: 2023-03-31
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/422565 , vital:71958 , DOI 10.21504/10962/422565
- Description: This study focuses on the development of the sono-photodynamic combination therapy (SPDT) activity of phthalocyanines (Pcs) on the cervical and breast cancer cell lines in vitro. The SPDT technique utilizes ultrasound in combination with light to elicit cytotoxic effects for cancer eradication. In this work, a selection of tetra-peripherally substituted Zn(II) cationic and zwitterionic Pcs were prepared. The photophysical parameters of the Pcs were determined including their fluorescence behaviours and efficiency of the triplet excited state population. The effects of the ultrasonic parameters (frequencies (MHz) and power (W.cm-2)) on the stability of the Pcs were evaluated. Four parameters were evaluated: Par I (1 MHz: 1 W.cm-2), Par II (1 MHz: 2 W.cm-2), Par III (3 MHz: 1 W.cm-2) and Par IV (3 MHz: 2 W.cm-2). The stability of the Pcs reduced with the increase in the ultrasonic power (for Par II and Par IV). The Par I showed the least degradation compared to the other parameters and was therefore used for the SPDT treatments. The sonodynamic (SDT), photodynamic (PDT) therapy activities of the Pcs were studied and compared to their SPDT efficacies. The Pcs showed reactive oxygen species generation during the SDT, PDT and SPDT treatments. For the SDT and SPDT, singlet oxygen (1O2) and hydroxyl radicals (•OH) were detected. For PDT, only the 1O2 were detected. The cell cytotoxicity studies for the Pcs showed relatively higher therapeutic efficacies for the SDT treatments compared to the PDT treatments, where the SPDT showed higher therapeutic efficacies compared to both the SDT and PDT monotreatments on both the cell lines in vitro. Overall, the combination treatments were better compared to the monotreatments. The activities of the Pcs were compared by their differences in structures, including the type of R-group, type of quaternizing agent and type of nanoparticle conjugates. , Thesis (PhD) -- Faculty of Science, Chemistry, 2023
- Full Text:
The role of optimism bias in susceptibility to phishing attacks in a financial services organisation
- Authors: Owen, Morné
- Date: 2023-03-31
- Subjects: Mixed methods research , Phishing , Optimism bias , Information security , Information storage and retrieval systems Financial services industry , Risk perception
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/419257 , vital:71629 , DOI 10.21504/10962/419257
- Description: Researchers looking for ways to change the insecure behaviour that results in successful phishing have considered multiple possible reasons for such behaviour. Therefore, the purpose of this study is to understand the role of optimism bias (OB – defined as a cognitive bias), which characterises overly optimistic or unrealistic individuals, in order to ensure secure behaviour. Research is considered that has focused on issues such as personality traits, trust, attitude and information security awareness training (ISAT). We used a mixed methods design to investigate OB behaviour, building on a recontextualised version of the theory of planned behaviour to evaluate the influence that OB has on phishing susceptibility. To model the data, an analysis was performed on 226 survey responses (systematic random sampling method) from the employees of a financial services organisation using partial least squares (PLS) path modelling. To evaluate OB behaviour, we conducted an experiment consisting of three ISAT sessions and three simulated phishing attacks. After each phishing experiment, we conducted interviews to gain a better understanding of why people succumbed to the attacks. It was subsequently found that overly optimistic individuals are inclined to behave insecurely, while factors such as attitude and trust significantly influence the intention to behave securely. Our contribution to practice is to enhance the effectiveness of ISAT by identifying and addressing the OB weakness to deliver a more successful training outcome. Our contribution to theory enriches the Information Systems literature by evaluating the effect of a cognitive bias on phishing susceptibility and, through research, offering a contextual explanation of the resultant behaviour. , Thesis (PhD) -- Faculty of Commerce, Information Systems, 2023 , Navorsers op soek na ‘n antwoord om onveilige gedrag te verander wat lei na uitvissing het verskeie moontlike redes oorweeg vir sulke gedrag. Daarom is die doel van hierdie verhandeling om die rol van optimistiese vooroordeel (OB - gedefinieer as 'n kognitiewe vooroordeel) te verstaan, wat te optimistiese of onrealistiese individue kenmerk om veilige gedrag te verseker. Navorsing was oorweeg wat gefokus het op kwessies soos persoonlikheidseienskappe, vertroue, gesindheid en inligtingsekuriteitsbewustheidsopleiding (ISAT). Die navorser het gemengde metodes gebruik om OB-gedrag te ondersoek. Daar was voortgebou op 'n gerekontekstualiseerde weergawe van die theory of planned behaviour om die invloed wat OB op uitvissing-vatbaarheid het, te evalueer. Om die data te modelleer, is 'n analise gedoen waar 226 opname antwoorde verkry is van 'n finansiële dienste organisasie en is partial least squares (PLS) path modelling gebruik. Om OB-gedrag te evalueer, het ons 'n eksperiment uitgevoer wat bestaan uit drie ISAT-sessies en drie gesimuleerde uitvissing-aanvalle. Na elke uitvissing-eksperiment het ons onderhoude gevoer om 'n beter begrip te kry waarom mense aan die aanvalle geswig het. Te optimistiese individue is geneig om onveilig op te tree, terwyl faktore soos gesindheid en vertroue die voorneme om veilig op te tree, aansienlik beïnvloed het. Die studie se bydrae tot die praktyk is om die doeltreffendheid van ISAT te verbeter deur die OBswakheid te identifiseer en aan te spreek om 'n meer suksesvolle opleidingsuitkoms te lewer. Verder verryk die studie die Inligtingstelsels-literatuur deur die effek van 'n kognitiewe vooroordeel op uitvissing-vatbaarheid te evalueer en deur navorsing bied dit 'n kontekstuele verduideliking van die gevolglike gedrag.
- Full Text:
The role of optimism bias in susceptibility to phishing attacks in a financial services organisation
- Authors: Owen, Morné
- Date: 2023-03-31
- Subjects: Mixed methods research , Phishing , Optimism bias , Information security , Information storage and retrieval systems Financial services industry , Risk perception
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/419257 , vital:71629 , DOI 10.21504/10962/419257
- Description: Researchers looking for ways to change the insecure behaviour that results in successful phishing have considered multiple possible reasons for such behaviour. Therefore, the purpose of this study is to understand the role of optimism bias (OB – defined as a cognitive bias), which characterises overly optimistic or unrealistic individuals, in order to ensure secure behaviour. Research is considered that has focused on issues such as personality traits, trust, attitude and information security awareness training (ISAT). We used a mixed methods design to investigate OB behaviour, building on a recontextualised version of the theory of planned behaviour to evaluate the influence that OB has on phishing susceptibility. To model the data, an analysis was performed on 226 survey responses (systematic random sampling method) from the employees of a financial services organisation using partial least squares (PLS) path modelling. To evaluate OB behaviour, we conducted an experiment consisting of three ISAT sessions and three simulated phishing attacks. After each phishing experiment, we conducted interviews to gain a better understanding of why people succumbed to the attacks. It was subsequently found that overly optimistic individuals are inclined to behave insecurely, while factors such as attitude and trust significantly influence the intention to behave securely. Our contribution to practice is to enhance the effectiveness of ISAT by identifying and addressing the OB weakness to deliver a more successful training outcome. Our contribution to theory enriches the Information Systems literature by evaluating the effect of a cognitive bias on phishing susceptibility and, through research, offering a contextual explanation of the resultant behaviour. , Thesis (PhD) -- Faculty of Commerce, Information Systems, 2023 , Navorsers op soek na ‘n antwoord om onveilige gedrag te verander wat lei na uitvissing het verskeie moontlike redes oorweeg vir sulke gedrag. Daarom is die doel van hierdie verhandeling om die rol van optimistiese vooroordeel (OB - gedefinieer as 'n kognitiewe vooroordeel) te verstaan, wat te optimistiese of onrealistiese individue kenmerk om veilige gedrag te verseker. Navorsing was oorweeg wat gefokus het op kwessies soos persoonlikheidseienskappe, vertroue, gesindheid en inligtingsekuriteitsbewustheidsopleiding (ISAT). Die navorser het gemengde metodes gebruik om OB-gedrag te ondersoek. Daar was voortgebou op 'n gerekontekstualiseerde weergawe van die theory of planned behaviour om die invloed wat OB op uitvissing-vatbaarheid het, te evalueer. Om die data te modelleer, is 'n analise gedoen waar 226 opname antwoorde verkry is van 'n finansiële dienste organisasie en is partial least squares (PLS) path modelling gebruik. Om OB-gedrag te evalueer, het ons 'n eksperiment uitgevoer wat bestaan uit drie ISAT-sessies en drie gesimuleerde uitvissing-aanvalle. Na elke uitvissing-eksperiment het ons onderhoude gevoer om 'n beter begrip te kry waarom mense aan die aanvalle geswig het. Te optimistiese individue is geneig om onveilig op te tree, terwyl faktore soos gesindheid en vertroue die voorneme om veilig op te tree, aansienlik beïnvloed het. Die studie se bydrae tot die praktyk is om die doeltreffendheid van ISAT te verbeter deur die OBswakheid te identifiseer en aan te spreek om 'n meer suksesvolle opleidingsuitkoms te lewer. Verder verryk die studie die Inligtingstelsels-literatuur deur die effek van 'n kognitiewe vooroordeel op uitvissing-vatbaarheid te evalueer en deur navorsing bied dit 'n kontekstuele verduideliking van die gevolglike gedrag.
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