MOCVD growth and electrical characterisation of InAs thin films
- Authors: Shamba, Precious
- Date: 2007
- Subjects: Metal organic chemical vapor deposition
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10527 , http://hdl.handle.net/10948/706 , Metal organic chemical vapor deposition
- Description: In this work, a systematic study relating the surface morphologies, electrical and structural properties of both doped and undoped InAs and InAsSb epitaxial films grown by metalorganic chemical vapour deposition (MOCVD) was undertaken. A comparative study using TBAs and AsH3 as the group V source in the growth of InAs revealed a considerable improvement, primarily in the electrical properties of InAs grown using TBAs with no significant difference in the surface morphology. InAs layers grown using TBAs, exhibited superior 77 K mobilities of up to 46 000 cm2/Vs, exceeding the best MOCVD data to date. The feasibility of tetraethyl tin (TESn) as an n-type dopant in InAs was to our knowledge investigated for the first time. The incorporation efficiency of this dopant was extensively studied as a function of substrate temperature, V/III ratio, substrate orientation and TESn flow rate. Results from this study show that the doping efficiency is temperature dependent and is not influenced by a variation of the V/III ratio or substrate orientation. Furthermore, Sn doping concentrations could be controlled over 2 orders of magnitude ranging between 2.7 x 1017 and 4.7 x 1019 cm-3 with 77 K mobilities ranging from 12 000 to 1300 cm2/Vs. The electrical properties of zinc doped InAs employing dimethyl zinc (DMZn) as the ptype dopant, were studied as a function of V/III ratio and substrate orientation. The effect of a variation of these parameters on the structural properties and surface morphology of InAs is also reported. The substrate orientation appears to have no influence on the Zn incorporation. An increase in Zn incorporation resulted in a deterioration of both the surface morphology and structural quality of the InAs layers. The incorporation efficiency of DMZn in InAsSb was studied as a function of growth temperature, V/III ratio and DMZn flow rate. A higher Zn incorporation was observed in InAsSb epitaxial layers grown at a lower temperature and V/III ratio as opposed to the layers grown at a higher temperature and V/III ratio. This study also revealed that the use of DMZn caused a dopant memory effect. A two-layer model proposed by Nedoluha and Koch (1952) was used to simulate the Hall measurements of Zn doped InAs and InAsSb in order to correct the shortcomings of conventional Hall measurements in determining the electrical properties exhibited by these materials.
- Full Text:
- Date Issued: 2007
- Authors: Shamba, Precious
- Date: 2007
- Subjects: Metal organic chemical vapor deposition
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10527 , http://hdl.handle.net/10948/706 , Metal organic chemical vapor deposition
- Description: In this work, a systematic study relating the surface morphologies, electrical and structural properties of both doped and undoped InAs and InAsSb epitaxial films grown by metalorganic chemical vapour deposition (MOCVD) was undertaken. A comparative study using TBAs and AsH3 as the group V source in the growth of InAs revealed a considerable improvement, primarily in the electrical properties of InAs grown using TBAs with no significant difference in the surface morphology. InAs layers grown using TBAs, exhibited superior 77 K mobilities of up to 46 000 cm2/Vs, exceeding the best MOCVD data to date. The feasibility of tetraethyl tin (TESn) as an n-type dopant in InAs was to our knowledge investigated for the first time. The incorporation efficiency of this dopant was extensively studied as a function of substrate temperature, V/III ratio, substrate orientation and TESn flow rate. Results from this study show that the doping efficiency is temperature dependent and is not influenced by a variation of the V/III ratio or substrate orientation. Furthermore, Sn doping concentrations could be controlled over 2 orders of magnitude ranging between 2.7 x 1017 and 4.7 x 1019 cm-3 with 77 K mobilities ranging from 12 000 to 1300 cm2/Vs. The electrical properties of zinc doped InAs employing dimethyl zinc (DMZn) as the ptype dopant, were studied as a function of V/III ratio and substrate orientation. The effect of a variation of these parameters on the structural properties and surface morphology of InAs is also reported. The substrate orientation appears to have no influence on the Zn incorporation. An increase in Zn incorporation resulted in a deterioration of both the surface morphology and structural quality of the InAs layers. The incorporation efficiency of DMZn in InAsSb was studied as a function of growth temperature, V/III ratio and DMZn flow rate. A higher Zn incorporation was observed in InAsSb epitaxial layers grown at a lower temperature and V/III ratio as opposed to the layers grown at a higher temperature and V/III ratio. This study also revealed that the use of DMZn caused a dopant memory effect. A two-layer model proposed by Nedoluha and Koch (1952) was used to simulate the Hall measurements of Zn doped InAs and InAsSb in order to correct the shortcomings of conventional Hall measurements in determining the electrical properties exhibited by these materials.
- Full Text:
- Date Issued: 2007
Multi-income level investment in golf estates
- Authors: Ngubeni, Steven Piet
- Date: 2007
- Subjects: Real estate development , Sustainable development -- South Africa , Housing development -- South Africa , Planned communities
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:9694 , http://hdl.handle.net/10948/771 , Real estate development , Sustainable development -- South Africa , Housing development -- South Africa , Planned communities
- Description: The government of South African has stated its intentions to enforce a policy which will compel developers of upmarket residential properties to set aside 20 percent of their upmarket residential developments to accommodate affordable housing. The developers on the other hand, have expressed concerns about this approach. The principal aim of this study and of the research was to investigate the desirability of the concept of multi-income-level investment approach to the development of golf estates. A phenomenological strand of qualitative research method was used in the research. The following formed the focal point of the research: • An investigation into the perceptions of the stakeholders, especially the buyers of up-market properties, about mixed-income-level investments in golf estates. • The potential effect of the implementation of including affordable housing in the development of golf estates • An investigation of the perceived effect on the profitability of investments by the inclusion of affordable housing in golf estate properties. • The extent of the contribution of including affordable housing in golf estate developments to the reduction of the current backlog
- Full Text:
- Date Issued: 2007
- Authors: Ngubeni, Steven Piet
- Date: 2007
- Subjects: Real estate development , Sustainable development -- South Africa , Housing development -- South Africa , Planned communities
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:9694 , http://hdl.handle.net/10948/771 , Real estate development , Sustainable development -- South Africa , Housing development -- South Africa , Planned communities
- Description: The government of South African has stated its intentions to enforce a policy which will compel developers of upmarket residential properties to set aside 20 percent of their upmarket residential developments to accommodate affordable housing. The developers on the other hand, have expressed concerns about this approach. The principal aim of this study and of the research was to investigate the desirability of the concept of multi-income-level investment approach to the development of golf estates. A phenomenological strand of qualitative research method was used in the research. The following formed the focal point of the research: • An investigation into the perceptions of the stakeholders, especially the buyers of up-market properties, about mixed-income-level investments in golf estates. • The potential effect of the implementation of including affordable housing in the development of golf estates • An investigation of the perceived effect on the profitability of investments by the inclusion of affordable housing in golf estate properties. • The extent of the contribution of including affordable housing in golf estate developments to the reduction of the current backlog
- Full Text:
- Date Issued: 2007
Particle precipitation effects on the South African ionosphere
- Authors: Sibanda, Patrick
- Date: 2007
- Subjects: Ionosphere -- South Africa , Precipitation (Chemistry) -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5481 , http://hdl.handle.net/10962/d1005267 , Ionosphere -- South Africa , Precipitation (Chemistry) -- South Africa
- Description: Particle precipitation involves the injection of energetic particles into the ionosphere which could increase the ionisation and conductivity of the upper atmosphere. The goal of this study was to examine the ionospheric response and changes due to particle precipitation in the region over South Africa, using a combination of groundbased and satellite instruments. Particle precipitation events were identified from satellite particle flux measurements of the Defence Meteorological Satellite Program (DMSP). Comprehensive studies were done on the events of 5 April, 2000 and 7 October, 2000. Analysis of the data from the satellite instruments indicates that no particle precipitation was observed over the South African region during these events and that it is unlikely to occur during other such events. To validate the data, methods and tools used in this study, precipitation in the South Atlantic anomaly (SAA) region is used. Satellite ion density measurements revealed that strong density enhancements occurred over the SAA region at satellite altitudes during the precipitation events, but this did not occur in the South African region. The measurements also revealed how the ionisation enhancements in the SAA region correlated with geomagnetic and solar activities. Particle precipitation and convective electric fields are two major magnetospheric energy sources to the upper atmosphere in the auroral and the SAA regions. These increase dramatically during geomagnetic storms and can disturb thermospheric circulation in the atmosphere and alter the rates of production and recombination of the ionised species. Ionosonde observations at Grahamstown, South Africa (33.30S, 26.50E), provided the data to build a picture of the response of the ionosphere over the South African region to particle precipitation during the precipitation events. This analysis showed that, within the confines of the available data, no direct connections between particle precipitation events and disturbances in the ionosphere over this region were revealed.
- Full Text:
- Date Issued: 2007
- Authors: Sibanda, Patrick
- Date: 2007
- Subjects: Ionosphere -- South Africa , Precipitation (Chemistry) -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5481 , http://hdl.handle.net/10962/d1005267 , Ionosphere -- South Africa , Precipitation (Chemistry) -- South Africa
- Description: Particle precipitation involves the injection of energetic particles into the ionosphere which could increase the ionisation and conductivity of the upper atmosphere. The goal of this study was to examine the ionospheric response and changes due to particle precipitation in the region over South Africa, using a combination of groundbased and satellite instruments. Particle precipitation events were identified from satellite particle flux measurements of the Defence Meteorological Satellite Program (DMSP). Comprehensive studies were done on the events of 5 April, 2000 and 7 October, 2000. Analysis of the data from the satellite instruments indicates that no particle precipitation was observed over the South African region during these events and that it is unlikely to occur during other such events. To validate the data, methods and tools used in this study, precipitation in the South Atlantic anomaly (SAA) region is used. Satellite ion density measurements revealed that strong density enhancements occurred over the SAA region at satellite altitudes during the precipitation events, but this did not occur in the South African region. The measurements also revealed how the ionisation enhancements in the SAA region correlated with geomagnetic and solar activities. Particle precipitation and convective electric fields are two major magnetospheric energy sources to the upper atmosphere in the auroral and the SAA regions. These increase dramatically during geomagnetic storms and can disturb thermospheric circulation in the atmosphere and alter the rates of production and recombination of the ionised species. Ionosonde observations at Grahamstown, South Africa (33.30S, 26.50E), provided the data to build a picture of the response of the ionosphere over the South African region to particle precipitation during the precipitation events. This analysis showed that, within the confines of the available data, no direct connections between particle precipitation events and disturbances in the ionosphere over this region were revealed.
- Full Text:
- Date Issued: 2007
Population structure, growth and recruitment of two exploited infralittoral molluscs (Haliotis midae and Turbo sarmaticus) along the south east coast, South Africa
- Authors: Proudfoot, Lee-Anne
- Date: 2007
- Subjects: Abalones -- South Africa , Abalones -- Growth -- South Africa , Turbinidae -- South Africa , Mollusks -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5744 , http://hdl.handle.net/10962/d1005430 , Abalones -- South Africa , Abalones -- Growth -- South Africa , Turbinidae -- South Africa , Mollusks -- South Africa
- Description: The two most frequently exploited species along the south east coast of South Africa are the gastropods, Haliotis midae (abalone) and Turbo sarmaticus (alikreukel). H. midae is a high valued commercial species, and suffers intense levels of illegal fishing. T. sarmaticus however, has no commercial value but is the preferred food item for impoverished subsistence communities. Owing to the fact that no legal commercial fishery exists for either species along the south coast, very few studies have been undertaken, especially in the heavily exploited infralittoral. Infralittoral size frequency distributions for both species revealed significant variation in density and size among sites of varying exploitation pressure. Densities ranged between 0 – 2.23 m⁻² (H. midae) and 0.03 – 4.93 m⁻² (T. sarmaticus) and maximum shell lengths ranged from 49.4 – 153.5 mm (H. midae) and 28.3 – 104.4 mm (T. sarmaticus). Relatively high densities and large sizes were found in marine reserves and secluded areas, and low densities and small sizes at sites near to large population centres and within the former Ciskei homeland region. Mean size of the largest 10% of the population, total density and sexually mature density were significantly related to exploitation predictors for both species. In addition, densities of H. midae juveniles were significantly related to exploitation predictors, suggesting that recruitment may be suppressed at the most exploited sites. Exploitation of T. sarmaticus tended to be localized with refuge and subtidal populations persisting. H. midae exploitation was however, far more extensive and intense. Growth of H. midae was investigated using three methods; mark-recapture, cohort analysis and growth banding analysis at Kowie Rocks, Port Alfred. The most useful of these methods for determining growth was a new technique described for growth banding analysis; which was validated using cohort analysis and measurements of shells of known age. This technique was less time consuming and labour intensive than previously described methods. Abalone growth was best described by the Schnute (1981) growth function. Systematic geographic variation in growth was observed for 10 sites along the South African coastline. Significant differences in growth among sites existed for animals between 0-4 years (P < 0.0001) and 4-6 years (P < 0.0001), and in the mean maximum sizes attained (P < 0.001). In general, abalone from the south east/east coast were found to have faster growth rates, smaller mean maximum sizes and attained sexual maturity earlier than those along the south west/ west coast. Haliotis midae recruit and juvenile densities were found to differ significantly among sites of varying exploitation pressure (P < 0.0001) and among months for recruit densities (P < 0.001). Exploited sites had low recruit and juvenile densities compared to unexploited sites and peak recruitment occurred during October/ November 2005. Recruit densities were significantly related to infralittoral adult densities during two of the three sampling months (P<0.05), when recruitment was low. No relationship was observed during the period of high recruitment, with all sites receiving high recruit densities. It was concluded that variation in recruit densities was the result of a combination of both density-dependent relationships (i.e. local spawner density and temporal variability in recruitment intensity) and the possible dispersal capabilities of H. midae. In addition, it was concluded that at present recruitment overfishing was not occurring along the south east coast. Post-recruitment mortality rates were variable but relatively constant, with hypothetical percentage survival and density curves revealing high rates and similar mortality curves among sites. Variation in juvenile densities was consequently a result of initial recruit densities and not variation in post-recruitment mortality. T. sarmaticus populations were found to be regionally sustainable and persisted along the south east coast due to adjacent intertidal and subtidal refuge populations. However, H. midae populations are becoming decimated along the south east coast. From the information obtained in this study new management proposals were suggested and discussed, such as closed areas and region-based management fisheries together with stock enhancement. These suggestions may prove to be feasible alternatives to present management strategies.
- Full Text:
- Date Issued: 2007
- Authors: Proudfoot, Lee-Anne
- Date: 2007
- Subjects: Abalones -- South Africa , Abalones -- Growth -- South Africa , Turbinidae -- South Africa , Mollusks -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5744 , http://hdl.handle.net/10962/d1005430 , Abalones -- South Africa , Abalones -- Growth -- South Africa , Turbinidae -- South Africa , Mollusks -- South Africa
- Description: The two most frequently exploited species along the south east coast of South Africa are the gastropods, Haliotis midae (abalone) and Turbo sarmaticus (alikreukel). H. midae is a high valued commercial species, and suffers intense levels of illegal fishing. T. sarmaticus however, has no commercial value but is the preferred food item for impoverished subsistence communities. Owing to the fact that no legal commercial fishery exists for either species along the south coast, very few studies have been undertaken, especially in the heavily exploited infralittoral. Infralittoral size frequency distributions for both species revealed significant variation in density and size among sites of varying exploitation pressure. Densities ranged between 0 – 2.23 m⁻² (H. midae) and 0.03 – 4.93 m⁻² (T. sarmaticus) and maximum shell lengths ranged from 49.4 – 153.5 mm (H. midae) and 28.3 – 104.4 mm (T. sarmaticus). Relatively high densities and large sizes were found in marine reserves and secluded areas, and low densities and small sizes at sites near to large population centres and within the former Ciskei homeland region. Mean size of the largest 10% of the population, total density and sexually mature density were significantly related to exploitation predictors for both species. In addition, densities of H. midae juveniles were significantly related to exploitation predictors, suggesting that recruitment may be suppressed at the most exploited sites. Exploitation of T. sarmaticus tended to be localized with refuge and subtidal populations persisting. H. midae exploitation was however, far more extensive and intense. Growth of H. midae was investigated using three methods; mark-recapture, cohort analysis and growth banding analysis at Kowie Rocks, Port Alfred. The most useful of these methods for determining growth was a new technique described for growth banding analysis; which was validated using cohort analysis and measurements of shells of known age. This technique was less time consuming and labour intensive than previously described methods. Abalone growth was best described by the Schnute (1981) growth function. Systematic geographic variation in growth was observed for 10 sites along the South African coastline. Significant differences in growth among sites existed for animals between 0-4 years (P < 0.0001) and 4-6 years (P < 0.0001), and in the mean maximum sizes attained (P < 0.001). In general, abalone from the south east/east coast were found to have faster growth rates, smaller mean maximum sizes and attained sexual maturity earlier than those along the south west/ west coast. Haliotis midae recruit and juvenile densities were found to differ significantly among sites of varying exploitation pressure (P < 0.0001) and among months for recruit densities (P < 0.001). Exploited sites had low recruit and juvenile densities compared to unexploited sites and peak recruitment occurred during October/ November 2005. Recruit densities were significantly related to infralittoral adult densities during two of the three sampling months (P<0.05), when recruitment was low. No relationship was observed during the period of high recruitment, with all sites receiving high recruit densities. It was concluded that variation in recruit densities was the result of a combination of both density-dependent relationships (i.e. local spawner density and temporal variability in recruitment intensity) and the possible dispersal capabilities of H. midae. In addition, it was concluded that at present recruitment overfishing was not occurring along the south east coast. Post-recruitment mortality rates were variable but relatively constant, with hypothetical percentage survival and density curves revealing high rates and similar mortality curves among sites. Variation in juvenile densities was consequently a result of initial recruit densities and not variation in post-recruitment mortality. T. sarmaticus populations were found to be regionally sustainable and persisted along the south east coast due to adjacent intertidal and subtidal refuge populations. However, H. midae populations are becoming decimated along the south east coast. From the information obtained in this study new management proposals were suggested and discussed, such as closed areas and region-based management fisheries together with stock enhancement. These suggestions may prove to be feasible alternatives to present management strategies.
- Full Text:
- Date Issued: 2007
Pricing exotic options using C++
- Authors: Nhongo, Tawuya D R
- Date: 2007
- Subjects: C++ (Computer program language) , Monte Carlo method , Simulation methods , Options (Finance) -- Mathematical models , Pricing -- Mathematical models
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5577 , http://hdl.handle.net/10962/d1008373 , C++ (Computer program language) , Monte Carlo method , Simulation methods , Options (Finance) -- Mathematical models , Pricing -- Mathematical models
- Description: This document demonstrates the use of the C++ programming language as a simulation tool in the efficient pricing of exotic European options. Extensions to the basic problem of simulation pricing are undertaken including variance reduction by conditional expectation, control and antithetic variates. Ultimately we were able to produce a modularized, easily extend-able program which effectively makes use of Monte Carlo simulation techniques to price lookback, Asian and barrier exotic options. Theories of variance reduction were validated except in cases where we used control variates in combination with the other variance reduction techniques in which case we observed increased variance. Again, the main aim of this half thesis was to produce a C++ program which would produce stable pricings of exotic options.
- Full Text:
- Date Issued: 2007
- Authors: Nhongo, Tawuya D R
- Date: 2007
- Subjects: C++ (Computer program language) , Monte Carlo method , Simulation methods , Options (Finance) -- Mathematical models , Pricing -- Mathematical models
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5577 , http://hdl.handle.net/10962/d1008373 , C++ (Computer program language) , Monte Carlo method , Simulation methods , Options (Finance) -- Mathematical models , Pricing -- Mathematical models
- Description: This document demonstrates the use of the C++ programming language as a simulation tool in the efficient pricing of exotic European options. Extensions to the basic problem of simulation pricing are undertaken including variance reduction by conditional expectation, control and antithetic variates. Ultimately we were able to produce a modularized, easily extend-able program which effectively makes use of Monte Carlo simulation techniques to price lookback, Asian and barrier exotic options. Theories of variance reduction were validated except in cases where we used control variates in combination with the other variance reduction techniques in which case we observed increased variance. Again, the main aim of this half thesis was to produce a C++ program which would produce stable pricings of exotic options.
- Full Text:
- Date Issued: 2007
Rehabilitation of the Orange River Mouth Salt Marsh : seed, wind and sediment characteristics
- Authors: Shaw, Gregory Alan
- Date: 2007
- Subjects: Salt marshes -- Orange River , Rivers -- South Africa -- Environmental aspects , Orange River -- Ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10626 , http://hdl.handle.net/10948/603 , http://hdl.handle.net/10948/d1012010 , Salt marshes -- Orange River , Rivers -- South Africa -- Environmental aspects , Orange River -- Ecology
- Description: The Orange River is an important source of freshwater and like many other wetlands in semi-arid regions, supports various social (Spurgeon, 1998), economic (Spurgeon, 1998; Bornman et al., 2005) and ecological functions. The saltmarsh at the Orange River Mouth has become degraded over time following numerous anthropogenic impacts. As a result the Transboundary RAMSAR site was placed on the Montreux record emphasising the importance for rehabilitation. The potential of the marsh for natural rehabilitation was assessed through three physical factors which were considered to have the most influence on the saltmarsh i.e. 1) sediment 2) water 3) wind. Three sampling areas were chosen to investigate the sediment characteristics of the ORM saltmarsh and the suitability for seed germination and adult survival. Site A was representative of the general marsh area, Site B was thought to have favourable sediment conditions for saltmarsh growth because of the large numbers of seedlings and Site C was prone to inundation by wind blown sediment. The sites were sampled in 2005 (dry conditions) and in 2006 after high rainfall and river flooding. Electrical conductivity (EC) of the sediment throughout the marsh was hypersaline in many instances above the tolerance range for S. pillansii (> 80 mS.cm-1) The freshwater event in 2006 lowered salinity significantly in two of the three sites. Differences in sediment characteristics were also compared for three habitats i.e. driftlines, open sites and under vegetation. Driftlines (C. coronopifolia = 872 seedlings m-2; S. pillansii = 1296 seedlings m-2) and the microhabitat associated with adult plants (C. coronopifolia = 803 seedlings m-2; S. pillansii = 721 seedlings m-2) created favourable conditions for seedling growth, however open unvegetated (C. coronopifolia = 56 seedlings m-2; S. pillansii = 49 seedlings m-2) areas had significantly lower seedling density. Due to the marsh currently being in a desertified state this study aimed to establish whether the remaining vegetation could produce enough seed to revegetate the marsh. Laboratory studies indicated that seeds of both species germinated best in freshwater (0 psu). The germination of S. pillansii seeds was 40 percent at 0 psu compared to 5 percent at 35 psu. After storage under hypersaline conditions (35 psu) C. coronopifolia showed 100 percent seed germination when returned to freshwater whereas storage at 70 psu decreased the viability of S. pillansii seeds. The plants are producing adequate seed that will allow for regrowth and rehabilitation if sediment and groundwater characteristics are suitable for seed germination, seedling growth and adult survival. However the increase in bare areas at the Orange River mouth as a result of salt marsh dieback has increased the available sediment source. The wind blown sediment has covered large areas of the remaining adult salt marsh vegetation, particularly in the northern corner at Site C, causing further die-back.
- Full Text:
- Date Issued: 2007
- Authors: Shaw, Gregory Alan
- Date: 2007
- Subjects: Salt marshes -- Orange River , Rivers -- South Africa -- Environmental aspects , Orange River -- Ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10626 , http://hdl.handle.net/10948/603 , http://hdl.handle.net/10948/d1012010 , Salt marshes -- Orange River , Rivers -- South Africa -- Environmental aspects , Orange River -- Ecology
- Description: The Orange River is an important source of freshwater and like many other wetlands in semi-arid regions, supports various social (Spurgeon, 1998), economic (Spurgeon, 1998; Bornman et al., 2005) and ecological functions. The saltmarsh at the Orange River Mouth has become degraded over time following numerous anthropogenic impacts. As a result the Transboundary RAMSAR site was placed on the Montreux record emphasising the importance for rehabilitation. The potential of the marsh for natural rehabilitation was assessed through three physical factors which were considered to have the most influence on the saltmarsh i.e. 1) sediment 2) water 3) wind. Three sampling areas were chosen to investigate the sediment characteristics of the ORM saltmarsh and the suitability for seed germination and adult survival. Site A was representative of the general marsh area, Site B was thought to have favourable sediment conditions for saltmarsh growth because of the large numbers of seedlings and Site C was prone to inundation by wind blown sediment. The sites were sampled in 2005 (dry conditions) and in 2006 after high rainfall and river flooding. Electrical conductivity (EC) of the sediment throughout the marsh was hypersaline in many instances above the tolerance range for S. pillansii (> 80 mS.cm-1) The freshwater event in 2006 lowered salinity significantly in two of the three sites. Differences in sediment characteristics were also compared for three habitats i.e. driftlines, open sites and under vegetation. Driftlines (C. coronopifolia = 872 seedlings m-2; S. pillansii = 1296 seedlings m-2) and the microhabitat associated with adult plants (C. coronopifolia = 803 seedlings m-2; S. pillansii = 721 seedlings m-2) created favourable conditions for seedling growth, however open unvegetated (C. coronopifolia = 56 seedlings m-2; S. pillansii = 49 seedlings m-2) areas had significantly lower seedling density. Due to the marsh currently being in a desertified state this study aimed to establish whether the remaining vegetation could produce enough seed to revegetate the marsh. Laboratory studies indicated that seeds of both species germinated best in freshwater (0 psu). The germination of S. pillansii seeds was 40 percent at 0 psu compared to 5 percent at 35 psu. After storage under hypersaline conditions (35 psu) C. coronopifolia showed 100 percent seed germination when returned to freshwater whereas storage at 70 psu decreased the viability of S. pillansii seeds. The plants are producing adequate seed that will allow for regrowth and rehabilitation if sediment and groundwater characteristics are suitable for seed germination, seedling growth and adult survival. However the increase in bare areas at the Orange River mouth as a result of salt marsh dieback has increased the available sediment source. The wind blown sediment has covered large areas of the remaining adult salt marsh vegetation, particularly in the northern corner at Site C, causing further die-back.
- Full Text:
- Date Issued: 2007
Reproductive co-existence among five sympatric single-stemmed aloes in the Gamtoos River Valley, Eastern Cape
- Authors: Botes, Christo
- Date: 2007
- Subjects: Aloe -- South Africa -- Gamtoos River Valley , Aloe -- South Africa -- Identification
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10628 , http://hdl.handle.net/10948/481 , Aloe -- South Africa -- Gamtoos River Valley , Aloe -- South Africa -- Identification
- Description: In this study I documented the convergence of five congeneric bird-pollinated plants (Aloe pluridens, A. lineata var. muirii, A. speciosa, A. africana, and A. ferox) into three functional groups based on size, shape, and the arrangements of flowers on the inflorescence, but also nectar rewards, pollen deposition sites on the bird-pollinators, and the degree to which bees play a role in their pollination. Individuals of similar functional groups were divergent in their peak flowering times and limited their degree of flowering overlap further by spatial aggregation and niche separation, within the Thicket of the Gamtoos River Valley. The nectar properties were especially useful in structuring the bird pollinator community, which resulted in greater ethological isolation and hence, greater reproductive assurance in the mixed co-flowering plant communities. Choice array experiments revealed that it was the fine scale aggregation of flowering individuals that ensured that bird-pollinators feed selectively, since when equal choice was available, interspecific visitation increased significantly compared to natural scenarios. Bird behaviour and the ecological intermediateness of one to the species explained its prominence in hybrid combinations. The spatial occurrence of hybrid individuals can be traced back to the energetics of foraging and its influence on bird floral constancy. The pollination ecology of similar South African Aloe species were extrapolated from these and recent findings by various authors, but emphasises the need for a robust natural phylogeny of the Aloaceae in order to draw comprehensive conclusions on the evolutionary radiation of this highly charismatic group.
- Full Text:
- Date Issued: 2007
- Authors: Botes, Christo
- Date: 2007
- Subjects: Aloe -- South Africa -- Gamtoos River Valley , Aloe -- South Africa -- Identification
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10628 , http://hdl.handle.net/10948/481 , Aloe -- South Africa -- Gamtoos River Valley , Aloe -- South Africa -- Identification
- Description: In this study I documented the convergence of five congeneric bird-pollinated plants (Aloe pluridens, A. lineata var. muirii, A. speciosa, A. africana, and A. ferox) into three functional groups based on size, shape, and the arrangements of flowers on the inflorescence, but also nectar rewards, pollen deposition sites on the bird-pollinators, and the degree to which bees play a role in their pollination. Individuals of similar functional groups were divergent in their peak flowering times and limited their degree of flowering overlap further by spatial aggregation and niche separation, within the Thicket of the Gamtoos River Valley. The nectar properties were especially useful in structuring the bird pollinator community, which resulted in greater ethological isolation and hence, greater reproductive assurance in the mixed co-flowering plant communities. Choice array experiments revealed that it was the fine scale aggregation of flowering individuals that ensured that bird-pollinators feed selectively, since when equal choice was available, interspecific visitation increased significantly compared to natural scenarios. Bird behaviour and the ecological intermediateness of one to the species explained its prominence in hybrid combinations. The spatial occurrence of hybrid individuals can be traced back to the energetics of foraging and its influence on bird floral constancy. The pollination ecology of similar South African Aloe species were extrapolated from these and recent findings by various authors, but emphasises the need for a robust natural phylogeny of the Aloaceae in order to draw comprehensive conclusions on the evolutionary radiation of this highly charismatic group.
- Full Text:
- Date Issued: 2007
Rhenium(V)-Imido complexes with potentially multidentate ligands containing the amino group
- Authors: Booysen, Irvin Noel
- Date: 2007
- Subjects: Rhenium , Ligands
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10385 , http://hdl.handle.net/10948/479 , Rhenium , Ligands
- Description: The complex trans-[Re(dab)Cl3(PPh3)2] (H2dab=1,2-diaminobenzene) was prepared from the reaction of trans-[ReOCl3(PPh3)2] with H2dab in ethanol. The ligand dab is coordinated to the rhenium(V) centre through a dianionic imido nitrogen only, in a distorted octahedral coordination geometry around the metal ion. The complex trans-[Re(ada)Cl3(PPh3)2] (H2ada=2-aminodiphenylamine) was prepared from the reaction of trans-[ReOCl3(PPh3)2] with H2ada in acetonitrile. The ligand ada is coordinated to the rhenium(V) centre through a dianionic imido nitrogen only, in a distorted octahedral coordination geometry around the metal ion. Surprisingly, the Re-Cl bond length trans to the Re=N bond is shorter than the two equatorial Re-Cl bond lengths. The reaction of equimolar quantities of cis-[ReO2I(PPh3)2] with 5,6-diamino-1,3- dimethyluracil (H2ddd) in acetonitrile led to the formation of [Re(ddd)(Hddd)I(PPh3)2](ReO4). The X-ray crystal structure shows that the ligand ddd is coordinated monodentately through the doubly deprotonated amino nitrogen and is therefore present as an imide. The chelate Hddd is coordinated bidentately via the neutral amino nitrogen, which is coordinated trans to the imido nitrogen, and the singly deprotonated amido nitrogen, trans to the iodide. The reaction of equimolar quantities of [NH4(ReO4)] with H2ddd in methanol under reflux conditions led to the isolation of [C12H12N6O4] as only product. The [ReO4]- ion is therefore instrumental in the formation of [C12H12N6O4], and since the product contains no rhenium in any oxidation state, the conclusion is that [ReO4]- catalyses the oxidative deamination of H2ddd. The X-ray crystal structure consists of two centrosymmetric, tricyclic rings, comprising a central pyrazine ring and two terminal pyrimidine rings. The reaction of a twofold molar excess of H2apb (H2apb=2-(2-aminophenyl)-1Hbenzimidazole) with trans-[ReO2(py)4]Cl in ethanol gave the green product of the formulation [ReO(Hapb)(apb)] in good yield. The rhenium atom lies in a distorted trigonal-bipyramidal environment. The two imidazole N(2) atoms lie in the apical positions trans to each other, with the oxo-oxygen and two amido N(1) atoms in the trigonal plane. The complex has C2-symmetry. The two amino groups are singly deprotonated and provide a negative charge each, so that they are coordinated as amides. The oxo group provides two negative charges. In order to obtain electroneutrality for the rhenium(V) complex, the two coordinated imidazole nitrogens provide one negative charge. The complex salt trans-[Re(mps)Cl(PPh3)2](ReO4) (H3mps=N-(2-amino-3- methylphenyl)salicylideneimine) was prepared by the reaction of trans- [ReOCl3(PPh3)2] with a twofold molar excess of H3mps. The X-ray crystal structure shows that the trianionic ligand mps acts as a tridentate chelate via the doubly deprotonated amino nitrogen (which is present in trans- [Re(mps)Cl(PPh3)2](ReO4) as an imide), the neutral imino nitrogen and the deprotonated phenolic oxygen. The [ReO4]- anion has approximately regular tetrahedral geometry. Two significant hydrogen bonds are formed between two of the perrhenyl oxygens and the water of crystallization. The six-coordinated complex cis-[Re(mps)Cl2(PPh3)2] was prepared by the reaction of trans-[ReOCl3(PPh3)2] with a twofold molar excess of H3mps in benzene. The Xray crystal structure shows that the mps ligand coordinates as a tridentate chelate via the doubly deprotonated 2-amino nitrogen, the neutral imino nitrogen and the phenolate oxygen. The imide and phenolate oxygen coordinate trans to each other in a distorted octahedral geometry around the rhenium(V) centre, with the two chlorides in cis positions.
- Full Text:
- Date Issued: 2007
- Authors: Booysen, Irvin Noel
- Date: 2007
- Subjects: Rhenium , Ligands
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10385 , http://hdl.handle.net/10948/479 , Rhenium , Ligands
- Description: The complex trans-[Re(dab)Cl3(PPh3)2] (H2dab=1,2-diaminobenzene) was prepared from the reaction of trans-[ReOCl3(PPh3)2] with H2dab in ethanol. The ligand dab is coordinated to the rhenium(V) centre through a dianionic imido nitrogen only, in a distorted octahedral coordination geometry around the metal ion. The complex trans-[Re(ada)Cl3(PPh3)2] (H2ada=2-aminodiphenylamine) was prepared from the reaction of trans-[ReOCl3(PPh3)2] with H2ada in acetonitrile. The ligand ada is coordinated to the rhenium(V) centre through a dianionic imido nitrogen only, in a distorted octahedral coordination geometry around the metal ion. Surprisingly, the Re-Cl bond length trans to the Re=N bond is shorter than the two equatorial Re-Cl bond lengths. The reaction of equimolar quantities of cis-[ReO2I(PPh3)2] with 5,6-diamino-1,3- dimethyluracil (H2ddd) in acetonitrile led to the formation of [Re(ddd)(Hddd)I(PPh3)2](ReO4). The X-ray crystal structure shows that the ligand ddd is coordinated monodentately through the doubly deprotonated amino nitrogen and is therefore present as an imide. The chelate Hddd is coordinated bidentately via the neutral amino nitrogen, which is coordinated trans to the imido nitrogen, and the singly deprotonated amido nitrogen, trans to the iodide. The reaction of equimolar quantities of [NH4(ReO4)] with H2ddd in methanol under reflux conditions led to the isolation of [C12H12N6O4] as only product. The [ReO4]- ion is therefore instrumental in the formation of [C12H12N6O4], and since the product contains no rhenium in any oxidation state, the conclusion is that [ReO4]- catalyses the oxidative deamination of H2ddd. The X-ray crystal structure consists of two centrosymmetric, tricyclic rings, comprising a central pyrazine ring and two terminal pyrimidine rings. The reaction of a twofold molar excess of H2apb (H2apb=2-(2-aminophenyl)-1Hbenzimidazole) with trans-[ReO2(py)4]Cl in ethanol gave the green product of the formulation [ReO(Hapb)(apb)] in good yield. The rhenium atom lies in a distorted trigonal-bipyramidal environment. The two imidazole N(2) atoms lie in the apical positions trans to each other, with the oxo-oxygen and two amido N(1) atoms in the trigonal plane. The complex has C2-symmetry. The two amino groups are singly deprotonated and provide a negative charge each, so that they are coordinated as amides. The oxo group provides two negative charges. In order to obtain electroneutrality for the rhenium(V) complex, the two coordinated imidazole nitrogens provide one negative charge. The complex salt trans-[Re(mps)Cl(PPh3)2](ReO4) (H3mps=N-(2-amino-3- methylphenyl)salicylideneimine) was prepared by the reaction of trans- [ReOCl3(PPh3)2] with a twofold molar excess of H3mps. The X-ray crystal structure shows that the trianionic ligand mps acts as a tridentate chelate via the doubly deprotonated amino nitrogen (which is present in trans- [Re(mps)Cl(PPh3)2](ReO4) as an imide), the neutral imino nitrogen and the deprotonated phenolic oxygen. The [ReO4]- anion has approximately regular tetrahedral geometry. Two significant hydrogen bonds are formed between two of the perrhenyl oxygens and the water of crystallization. The six-coordinated complex cis-[Re(mps)Cl2(PPh3)2] was prepared by the reaction of trans-[ReOCl3(PPh3)2] with a twofold molar excess of H3mps in benzene. The Xray crystal structure shows that the mps ligand coordinates as a tridentate chelate via the doubly deprotonated 2-amino nitrogen, the neutral imino nitrogen and the phenolate oxygen. The imide and phenolate oxygen coordinate trans to each other in a distorted octahedral geometry around the rhenium(V) centre, with the two chlorides in cis positions.
- Full Text:
- Date Issued: 2007
Securing media streams in an Asterisk-based environment and evaluating the resulting performance cost
- Authors: Clayton, Bradley
- Date: 2007 , 2007-01-08
- Subjects: Asterisk (Computer file) , Computer networks -- Security measures , Internet telephony -- Security measures
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4647 , http://hdl.handle.net/10962/d1006606 , Asterisk (Computer file) , Computer networks -- Security measures , Internet telephony -- Security measures
- Description: When adding Confidentiality, Integrity and Availability (CIA) to a multi-user VoIP (Voice over IP) system, performance and quality are at risk. The aim of this study is twofold. Firstly, it describes current methods suitable to secure voice streams within a VoIP system and make them available in an Asterisk-based VoIP environment. (Asterisk is a well established, open-source, TDM/VoIP PBX.) Secondly, this study evaluates the performance cost incurred after implementing each security method within the Asterisk-based system, using a special testbed suite, named DRAPA, which was developed expressly for this study. The three security methods implemented and studied were IPSec (Internet Protocol Security), SRTP (Secure Real-time Transport Protocol), and SIAX2 (Secure Inter-Asterisk eXchange 2 protocol). From the experiments, it was found that bandwidth and CPU usage were significantly affected by the addition of CIA. In ranking the three security methods in terms of these two resources, it was found that SRTP incurs the least bandwidth overhead, followed by SIAX2 and then IPSec. Where CPU utilisation is concerned, it was found that SIAX2 incurs the least overhead, followed by IPSec, and then SRTP.
- Full Text:
- Date Issued: 2007
- Authors: Clayton, Bradley
- Date: 2007 , 2007-01-08
- Subjects: Asterisk (Computer file) , Computer networks -- Security measures , Internet telephony -- Security measures
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4647 , http://hdl.handle.net/10962/d1006606 , Asterisk (Computer file) , Computer networks -- Security measures , Internet telephony -- Security measures
- Description: When adding Confidentiality, Integrity and Availability (CIA) to a multi-user VoIP (Voice over IP) system, performance and quality are at risk. The aim of this study is twofold. Firstly, it describes current methods suitable to secure voice streams within a VoIP system and make them available in an Asterisk-based VoIP environment. (Asterisk is a well established, open-source, TDM/VoIP PBX.) Secondly, this study evaluates the performance cost incurred after implementing each security method within the Asterisk-based system, using a special testbed suite, named DRAPA, which was developed expressly for this study. The three security methods implemented and studied were IPSec (Internet Protocol Security), SRTP (Secure Real-time Transport Protocol), and SIAX2 (Secure Inter-Asterisk eXchange 2 protocol). From the experiments, it was found that bandwidth and CPU usage were significantly affected by the addition of CIA. In ranking the three security methods in terms of these two resources, it was found that SRTP incurs the least bandwidth overhead, followed by SIAX2 and then IPSec. Where CPU utilisation is concerned, it was found that SIAX2 incurs the least overhead, followed by IPSec, and then SRTP.
- Full Text:
- Date Issued: 2007
Securing softswitches from malicious attacks
- Authors: Opie, Jake Weyman
- Date: 2007
- Subjects: Internet telephony -- Security measures , Computer networks -- Security measures , Digital telephone systems , Communication -- Technological innovations , Computer network protocols , TCP/IP (Computer network protocol) , Switching theory
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4683 , http://hdl.handle.net/10962/d1007714 , Internet telephony -- Security measures , Computer networks -- Security measures , Digital telephone systems , Communication -- Technological innovations , Computer network protocols , TCP/IP (Computer network protocol) , Switching theory
- Description: Traditionally, real-time communication, such as voice calls, has run on separate, closed networks. Of all the limitations that these networks had, the ability of malicious attacks to cripple communication was not a crucial one. This situation has changed radically now that real-time communication and data have merged to share the same network. The objective of this project is to investigate the securing of softswitches with functionality similar to Private Branch Exchanges (PBX) from malicious attacks. The focus of the project will be a practical investigation of how to secure ILANGA, an ASTERISK-based system under development at Rhodes University. The practical investigation that focuses on ILANGA is based on performing six varied experiments on the different components of ILANGA. Before the six experiments are performed, basic preliminary security measures and the restrictions placed on the access to the database are discussed. The outcomes of these experiments are discussed and the precise reasons why these attacks were either successful or unsuccessful are given. Suggestions of a theoretical nature on how to defend against the successful attacks are also presented.
- Full Text:
- Date Issued: 2007
- Authors: Opie, Jake Weyman
- Date: 2007
- Subjects: Internet telephony -- Security measures , Computer networks -- Security measures , Digital telephone systems , Communication -- Technological innovations , Computer network protocols , TCP/IP (Computer network protocol) , Switching theory
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4683 , http://hdl.handle.net/10962/d1007714 , Internet telephony -- Security measures , Computer networks -- Security measures , Digital telephone systems , Communication -- Technological innovations , Computer network protocols , TCP/IP (Computer network protocol) , Switching theory
- Description: Traditionally, real-time communication, such as voice calls, has run on separate, closed networks. Of all the limitations that these networks had, the ability of malicious attacks to cripple communication was not a crucial one. This situation has changed radically now that real-time communication and data have merged to share the same network. The objective of this project is to investigate the securing of softswitches with functionality similar to Private Branch Exchanges (PBX) from malicious attacks. The focus of the project will be a practical investigation of how to secure ILANGA, an ASTERISK-based system under development at Rhodes University. The practical investigation that focuses on ILANGA is based on performing six varied experiments on the different components of ILANGA. Before the six experiments are performed, basic preliminary security measures and the restrictions placed on the access to the database are discussed. The outcomes of these experiments are discussed and the precise reasons why these attacks were either successful or unsuccessful are given. Suggestions of a theoretical nature on how to defend against the successful attacks are also presented.
- Full Text:
- Date Issued: 2007
Statistical analyses of artificial waterpoints: their effect on the herbaceous and woody structure composition within the Kruger National Park
- Authors: Goodall, Victoria Lucy
- Date: 2007
- Subjects: South African National Parks , Ecology -- Statistical methods , Regression analysis , Log-linear models , Game reserves -- South Africa , Kruger National Park (South Africa)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5570 , http://hdl.handle.net/10962/d1002810 , South African National Parks , Ecology -- Statistical methods , Regression analysis , Log-linear models , Game reserves -- South Africa , Kruger National Park (South Africa)
- Description: The objective of this project is to link the statistical theory used in the ecological sciences with an actual project that was developed for the South African National Parks Scientific Services. It investigates the changes that have occurred in the herbaceous and woody structure due to the closure of artificial waterpoints; including the impacts that elephants and other herbivores have on the vegetation of the Kruger National Park. This project was designed in conjunction with South African National Parks (SANP) Scientific Services and it is a registered project with this department. The results of this project will be submitted to Scientific Services in accordance with the terms and conditions of a SANP research project. A major concern within the KNP is the declining numbers of rare antelope and numerous projects have been developed to investigate possible ways of halting this decline and thus protecting the heterogeneity of the Kruger National Park. Three different datasets were investigated, covering three aspects of vegetation structure and composition within the KNP. The first investigated the changes that have occurred since the N'washitsumbe enclosure in the Far Northern KNP was fenced off from the rest of the park. The results show that over the 40 years since the enclosure was built, changes have occurred which have resulted in a significant difference in the abundance of Increaser 2 and Decreaser grass species between the inside and the outside of the enclosure. Increaser 2 and Decreaser categories are the result of a grass species classification depending on whether the species thrives or is depressed by heavy grazing. The difference in grass species composition and structure between the inside and the outside of the enclosure indicates that the grazing animals within the KNP have influenced the grass composition in a way that favours the dominant animals. This has resulted in a declining roan antelope population - one of the species that is considered as a 'rare antelope'. Many artificial waterpoints (boreholes and dams) have also been closed throughout the KNP in the hope of resulting in a change in vegetation structure and composition in favour of the roan. Veld condition assessment data for 87 boreholes throughout the Park was analyzed to determine whether the veld in the vicinity is beginning to change towards a more Decreaser dominated sward which would favour the roan. The results were analyzed for the different regions of the Park; and they indicate that changes are becoming evident; however, the results are not particularly conclusive, yet. The majority of the boreholes were closed between 1994 and 1998 which means that not a lot of data were available to be analyzed. A similar study conducted in another 10 years time might reveal more meaningful results. However the results are moving in the direction hoped for by the management of the KNP. The results show that the grass composition has a higher proportion of Decreaser grasses since the closure of the waterpoints, and the grass biomass around these areas has also improved. The results were analyzed on an individual basis; and then on a regional basis as the minimal data meant that the individual analyses did not provide any significant results. A third study was then done on the impact that the rapidly increasing elephant population on the vegetation within the Riparian zone along three rivers in the Far Northern region of the KNP. The riparian zone is an important part of the landscape, in terms of providing food for many animals as well as shade. The elephant population has increased substantially since the termination of the culling program and this means that the feeding requirements of the population has increased which could result in severe damage upon the vegetation, as elephants can be very destructive feeders. The results show surprising differences between the three years of data that were analyzed; however the results indicate that the elephants are targeting specific height ranges of trees when feeding; however they do not seem to consistently target specific tree species. This is positive for the diversity of the Riparian zone as this region is very important both ecologically and aesthetically for the tourists who visit the Park.
- Full Text:
- Date Issued: 2007
- Authors: Goodall, Victoria Lucy
- Date: 2007
- Subjects: South African National Parks , Ecology -- Statistical methods , Regression analysis , Log-linear models , Game reserves -- South Africa , Kruger National Park (South Africa)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5570 , http://hdl.handle.net/10962/d1002810 , South African National Parks , Ecology -- Statistical methods , Regression analysis , Log-linear models , Game reserves -- South Africa , Kruger National Park (South Africa)
- Description: The objective of this project is to link the statistical theory used in the ecological sciences with an actual project that was developed for the South African National Parks Scientific Services. It investigates the changes that have occurred in the herbaceous and woody structure due to the closure of artificial waterpoints; including the impacts that elephants and other herbivores have on the vegetation of the Kruger National Park. This project was designed in conjunction with South African National Parks (SANP) Scientific Services and it is a registered project with this department. The results of this project will be submitted to Scientific Services in accordance with the terms and conditions of a SANP research project. A major concern within the KNP is the declining numbers of rare antelope and numerous projects have been developed to investigate possible ways of halting this decline and thus protecting the heterogeneity of the Kruger National Park. Three different datasets were investigated, covering three aspects of vegetation structure and composition within the KNP. The first investigated the changes that have occurred since the N'washitsumbe enclosure in the Far Northern KNP was fenced off from the rest of the park. The results show that over the 40 years since the enclosure was built, changes have occurred which have resulted in a significant difference in the abundance of Increaser 2 and Decreaser grass species between the inside and the outside of the enclosure. Increaser 2 and Decreaser categories are the result of a grass species classification depending on whether the species thrives or is depressed by heavy grazing. The difference in grass species composition and structure between the inside and the outside of the enclosure indicates that the grazing animals within the KNP have influenced the grass composition in a way that favours the dominant animals. This has resulted in a declining roan antelope population - one of the species that is considered as a 'rare antelope'. Many artificial waterpoints (boreholes and dams) have also been closed throughout the KNP in the hope of resulting in a change in vegetation structure and composition in favour of the roan. Veld condition assessment data for 87 boreholes throughout the Park was analyzed to determine whether the veld in the vicinity is beginning to change towards a more Decreaser dominated sward which would favour the roan. The results were analyzed for the different regions of the Park; and they indicate that changes are becoming evident; however, the results are not particularly conclusive, yet. The majority of the boreholes were closed between 1994 and 1998 which means that not a lot of data were available to be analyzed. A similar study conducted in another 10 years time might reveal more meaningful results. However the results are moving in the direction hoped for by the management of the KNP. The results show that the grass composition has a higher proportion of Decreaser grasses since the closure of the waterpoints, and the grass biomass around these areas has also improved. The results were analyzed on an individual basis; and then on a regional basis as the minimal data meant that the individual analyses did not provide any significant results. A third study was then done on the impact that the rapidly increasing elephant population on the vegetation within the Riparian zone along three rivers in the Far Northern region of the KNP. The riparian zone is an important part of the landscape, in terms of providing food for many animals as well as shade. The elephant population has increased substantially since the termination of the culling program and this means that the feeding requirements of the population has increased which could result in severe damage upon the vegetation, as elephants can be very destructive feeders. The results show surprising differences between the three years of data that were analyzed; however the results indicate that the elephants are targeting specific height ranges of trees when feeding; however they do not seem to consistently target specific tree species. This is positive for the diversity of the Riparian zone as this region is very important both ecologically and aesthetically for the tourists who visit the Park.
- Full Text:
- Date Issued: 2007
Studies towards the development of novel multidentate ligands
- Authors: Magqi, Nceba
- Date: 2007
- Subjects: Density functionals , Ligands , Ligands -- Design , Ligands -- Analysis , Camphor
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4358 , http://hdl.handle.net/10962/d1005023 , Density functionals , Ligands , Ligands -- Design , Ligands -- Analysis , Camphor
- Description: In this study, attention has been given to the design and synthesis of novel multidentate ligands for use in the construction of ruthenium-based metathesis catalysts, and their chelating potential has been explored by computer modelling at the Density Functional Theory (DFT) level. Both Kemp’s triacid (1,3,5-trimethyl-1,3,5-cyclohexanetricarboxylic acid) and D-(+)-camphor have been investigated as molecular scaffolds for the development of such ligands. However selective elaboration of the functional groups in Kemp’s triacid proved difficult to achieve, and the research has focused on the development of camphor derivatives. The synthesis of the camphor-based ligands has involved C-8 functionalisation and ring-opening of the bicyclic system to afford tridentate products. The formation of 9-iodocamphorquinone bis(ethylene ketal) together with the desired product, the 8-iodo isomer, has been confirmed by single crystal X-ray analysis of both compounds. Formation of the 9-iodo analogue has provided new insights into the intramolecular rearrangement of camphor skeleton, and the mechanistic implications have been assessed by coset analysis. Attempts to effect nucleophilic displacement of the 8-halogeno groups by nucleophilic donor moieties proved unexpectedly difficult and, coupled with the susceptibility of the carbonyl groups to nucleophilic attack, has led to the formation of novel tricyclic products, viz., 1,6-dimethyl-3-(2-pyridylamino)-4-oxatricyclo[4.3.0.0[superscript 3,7]]-2-nonanone and 6,7-dimethyl-3-(2-pyridylamino)-4-oxatricyclo -[4.3.0.0[superscript 3,7]]-2-nonanone. However the diphenylphosphine group was successfully introduced at C-8 and oxidative ring-opening of the camphor skeleton has afforded the tridentate ligands, 2-(diphenylphosphinoylmethyl)-1,2-dimethyl-1,3-cyclopentanedicarboxylic acid and 2-(diphenylphosphinoylmethyl)-1,3-bis(hydroxymethyl)1,2-dimethylcyclopentane. One- and two-dimensional NMR and, where appropriate, high-resolution MS methods have been used to characterise the products. Three [superscript 13]C NMR chemical shift prediction programmes, viz., ChemWindow and the MODGRAPH neural network and HOSE (Hierachially Ordered Spherical description of Environment), have been applied to representative compounds to assess their efficacy. While the predicted shifts correlated reasonably well with the experimental data, they proved to be insufficiently accurate to differentiate the isomeric systems examined.
- Full Text:
- Date Issued: 2007
- Authors: Magqi, Nceba
- Date: 2007
- Subjects: Density functionals , Ligands , Ligands -- Design , Ligands -- Analysis , Camphor
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4358 , http://hdl.handle.net/10962/d1005023 , Density functionals , Ligands , Ligands -- Design , Ligands -- Analysis , Camphor
- Description: In this study, attention has been given to the design and synthesis of novel multidentate ligands for use in the construction of ruthenium-based metathesis catalysts, and their chelating potential has been explored by computer modelling at the Density Functional Theory (DFT) level. Both Kemp’s triacid (1,3,5-trimethyl-1,3,5-cyclohexanetricarboxylic acid) and D-(+)-camphor have been investigated as molecular scaffolds for the development of such ligands. However selective elaboration of the functional groups in Kemp’s triacid proved difficult to achieve, and the research has focused on the development of camphor derivatives. The synthesis of the camphor-based ligands has involved C-8 functionalisation and ring-opening of the bicyclic system to afford tridentate products. The formation of 9-iodocamphorquinone bis(ethylene ketal) together with the desired product, the 8-iodo isomer, has been confirmed by single crystal X-ray analysis of both compounds. Formation of the 9-iodo analogue has provided new insights into the intramolecular rearrangement of camphor skeleton, and the mechanistic implications have been assessed by coset analysis. Attempts to effect nucleophilic displacement of the 8-halogeno groups by nucleophilic donor moieties proved unexpectedly difficult and, coupled with the susceptibility of the carbonyl groups to nucleophilic attack, has led to the formation of novel tricyclic products, viz., 1,6-dimethyl-3-(2-pyridylamino)-4-oxatricyclo[4.3.0.0[superscript 3,7]]-2-nonanone and 6,7-dimethyl-3-(2-pyridylamino)-4-oxatricyclo -[4.3.0.0[superscript 3,7]]-2-nonanone. However the diphenylphosphine group was successfully introduced at C-8 and oxidative ring-opening of the camphor skeleton has afforded the tridentate ligands, 2-(diphenylphosphinoylmethyl)-1,2-dimethyl-1,3-cyclopentanedicarboxylic acid and 2-(diphenylphosphinoylmethyl)-1,3-bis(hydroxymethyl)1,2-dimethylcyclopentane. One- and two-dimensional NMR and, where appropriate, high-resolution MS methods have been used to characterise the products. Three [superscript 13]C NMR chemical shift prediction programmes, viz., ChemWindow and the MODGRAPH neural network and HOSE (Hierachially Ordered Spherical description of Environment), have been applied to representative compounds to assess their efficacy. While the predicted shifts correlated reasonably well with the experimental data, they proved to be insufficiently accurate to differentiate the isomeric systems examined.
- Full Text:
- Date Issued: 2007
Study of metallophthalocyanines attached onto pre-modified gold surfaces
- Authors: Mashazi, Philani Nkosinathi
- Date: 2007
- Subjects: Phthalocyanines , Electrochemistry , Electrodes, Enzyme , Glucose -- Measurement
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4361 , http://hdl.handle.net/10962/d1005026 , Phthalocyanines , Electrochemistry , Electrodes, Enzyme , Glucose -- Measurement
- Description: Tetra-carboxy acid chloride phthalocyanine complexes of cobalt, iron and manganese were synthesized and characterized using spectroscopic and electrochemical techniques. These complexes were fabricated as thin films on gold electrode following a covalent immobilization and self-assembling methods. Surface electrochemical and spectroscopic characterization showed that these complexes are surface-confined species. The characterization using spectroscopic and electrochemical methods confirmed the formation of thiol and MPc SAMs on gold electrode. The electrocatalytic behaviour of the SAM modified gold electrodes was studied for the detection of L-cysteine and hydrogen peroxide. The limits of detection (LoD) for Lcysteine were of the orders of 10[superscript -7] mol.L[superscript -1] for all the MPc complexes studied and the LoD for hydrogen peroxide at cobalt phthalocyanine modified gold electrode was of the orders of 10[superscript -7]mol.L[superscript -1] for both electrocatalytic oxidation and reduction. The modification process for gold electrodes was reproducible and showed good stability, if stored in pH 4 phosphate buffer solutions and can be used over a long period of time. The cobalt phthalocyanine modified gold electrode was also investigated for the fabrication of glucose oxidase (GOx)-based biosensor and as an electron mediator between the enzyme and gold electrode. The behaviour of the enzyme modified gold electrode towards the detection of glucose was studied and the results gave a limit of detection of the orders of 10[superscript -6] mol.L[superscript -1] with low binding constant (4.8 mM) of enzyme (GOx) to substrate (glucose) referred to as Michaelis-Menten constant. The practical applications, i.e. the real sample analysis and interference studies, for the enzyme modified gold electrodes were investigated. These studies showed that the enzyme electrode is valuable and can be used for glucose detection.
- Full Text:
- Date Issued: 2007
- Authors: Mashazi, Philani Nkosinathi
- Date: 2007
- Subjects: Phthalocyanines , Electrochemistry , Electrodes, Enzyme , Glucose -- Measurement
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4361 , http://hdl.handle.net/10962/d1005026 , Phthalocyanines , Electrochemistry , Electrodes, Enzyme , Glucose -- Measurement
- Description: Tetra-carboxy acid chloride phthalocyanine complexes of cobalt, iron and manganese were synthesized and characterized using spectroscopic and electrochemical techniques. These complexes were fabricated as thin films on gold electrode following a covalent immobilization and self-assembling methods. Surface electrochemical and spectroscopic characterization showed that these complexes are surface-confined species. The characterization using spectroscopic and electrochemical methods confirmed the formation of thiol and MPc SAMs on gold electrode. The electrocatalytic behaviour of the SAM modified gold electrodes was studied for the detection of L-cysteine and hydrogen peroxide. The limits of detection (LoD) for Lcysteine were of the orders of 10[superscript -7] mol.L[superscript -1] for all the MPc complexes studied and the LoD for hydrogen peroxide at cobalt phthalocyanine modified gold electrode was of the orders of 10[superscript -7]mol.L[superscript -1] for both electrocatalytic oxidation and reduction. The modification process for gold electrodes was reproducible and showed good stability, if stored in pH 4 phosphate buffer solutions and can be used over a long period of time. The cobalt phthalocyanine modified gold electrode was also investigated for the fabrication of glucose oxidase (GOx)-based biosensor and as an electron mediator between the enzyme and gold electrode. The behaviour of the enzyme modified gold electrode towards the detection of glucose was studied and the results gave a limit of detection of the orders of 10[superscript -6] mol.L[superscript -1] with low binding constant (4.8 mM) of enzyme (GOx) to substrate (glucose) referred to as Michaelis-Menten constant. The practical applications, i.e. the real sample analysis and interference studies, for the enzyme modified gold electrodes were investigated. These studies showed that the enzyme electrode is valuable and can be used for glucose detection.
- Full Text:
- Date Issued: 2007
Synthesis and characterization of symmetrical and unsymmetrical ferrocenyl ligands for use in the preparation of Redox Active Ruthenium Alkylidene Complexes
- Authors: Saku, Duduetsang
- Date: 2007
- Subjects: Ferrocene , Ligands , Asymmetric synthesis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10403 , http://hdl.handle.net/10948/701 , Ferrocene , Ligands , Asymmetric synthesis
- Description: Oxidation of a ferrocenyl group in conjugation to another metal centre can alter the electron density at that metal centre and lead to a change in overall reactivity of a complex. Herein, the synthesis and characterization of redox active symmetrical and unsymmetrical ferrocenylalkene derivatives is described. A change in the standard redox potential of ferrocene (465 mV), to more positive potentials in vinylferrocene 1 (478 mV) and 4-phenylvinylferrocene 3 (499 mV), showed how manipulation of a redox potential can be effected on the ferrocenyl moiety by just using conjugation effects. A shift by +13 mV is observed in 1 and this potential more than doubled in 3 (+34 mV). Ferrocenylderived ruthenium alkylidene complexes were also prepared in a cross metathesis of 1 and 3 with Grubbs’ 1 (676.5 mV) to give complexes Ferrocenylidenebis( tricyclohexylphosphine)dichlororuthenium 14, 4-ferrocenylphenylidene-bis (tricyclohexylphosphine)dichlororuthenium 15 respectively. The extent of the electronic communication between the ferrocenyl group and the ruthenium centre was then estimated by looking at the positive or negative redox potential shifts of 14 and 15 as a result of 1 and 3. A large positive potential shift by 180 mV in 14 indicated that there was a strong electronic communication between the two metal centres, while the smaller, yet significant positive potential shift by 89.5 mV in 15 showed 3 to have a lesser effect on the ruthenium centre. Compounds 14 and 15 were tested in a Ring Closing Metathesis (RCM) of diethyldiallylmalonate showed enhanced reactivity.
- Full Text:
- Date Issued: 2007
- Authors: Saku, Duduetsang
- Date: 2007
- Subjects: Ferrocene , Ligands , Asymmetric synthesis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10403 , http://hdl.handle.net/10948/701 , Ferrocene , Ligands , Asymmetric synthesis
- Description: Oxidation of a ferrocenyl group in conjugation to another metal centre can alter the electron density at that metal centre and lead to a change in overall reactivity of a complex. Herein, the synthesis and characterization of redox active symmetrical and unsymmetrical ferrocenylalkene derivatives is described. A change in the standard redox potential of ferrocene (465 mV), to more positive potentials in vinylferrocene 1 (478 mV) and 4-phenylvinylferrocene 3 (499 mV), showed how manipulation of a redox potential can be effected on the ferrocenyl moiety by just using conjugation effects. A shift by +13 mV is observed in 1 and this potential more than doubled in 3 (+34 mV). Ferrocenylderived ruthenium alkylidene complexes were also prepared in a cross metathesis of 1 and 3 with Grubbs’ 1 (676.5 mV) to give complexes Ferrocenylidenebis( tricyclohexylphosphine)dichlororuthenium 14, 4-ferrocenylphenylidene-bis (tricyclohexylphosphine)dichlororuthenium 15 respectively. The extent of the electronic communication between the ferrocenyl group and the ruthenium centre was then estimated by looking at the positive or negative redox potential shifts of 14 and 15 as a result of 1 and 3. A large positive potential shift by 180 mV in 14 indicated that there was a strong electronic communication between the two metal centres, while the smaller, yet significant positive potential shift by 89.5 mV in 15 showed 3 to have a lesser effect on the ruthenium centre. Compounds 14 and 15 were tested in a Ring Closing Metathesis (RCM) of diethyldiallylmalonate showed enhanced reactivity.
- Full Text:
- Date Issued: 2007
Synthesis of novel coumarin derivatives as potential inhibitors of HIV-1 protease
- Authors: Rose, Nathan Rolf
- Date: 2007 , 2013-07-01
- Subjects: Coumarins , Protease Inhibitors , Heterocyclic compounds -- Derivatives , HIV infections -- Treatment
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4430 , http://hdl.handle.net/10962/d1007220 , Coumarins , Protease Inhibitors , Heterocyclic compounds -- Derivatives , HIV infections -- Treatment
- Description: This research has focused on the development of novel coumann derivatives containing peptide-like side chains as potential HIV-1 protease inhibitors. The reaction of various salicylaldehyde derivatives with tert-butyl acrylate In the presence of 1,4- diazabicyclo[2.2.2]octane (DABCO) has afforded a series of Baylis-Hillman adducts in moderate yield. Cyclisation of the adducts in the presence of HCI afforded the corresponding 3-(chloromethyl)coumarin derivatives, which have been reacted with various amine hydrochlorides in the presence of Proton Sponge® to afford a series of novel 3- (aminomethyl)coumarin derivatives, which were fully characterised by NMR and HRMS methods. Various approaches to the introduction of hydroxyl or amino groups at the C-4 position of coumarin and the 3-(chloromethyl)coumarin derivatives have been explored; these have included dihydroxylation of the coumarin double bond, and the synthesis of 4- benzylaminocoumarin derivatives as potential intermediates. The Vilsmeier-Haack and Mannich reactions have also been investigated as possible methods of introducing the desired peptide-like functionality. Computer modelling of selected structures has indicated that some of the novel 3- (aminomethyl)coumarin derivatives may exhibit activity as inhibitors of HIV-1 protease. The planned enzyme inhibition assays were unfortunately precluded by the aqueous insolubility of the selected compounds. Three ¹³C NMR chemical shift algorithms, viz., Modgraph Neural Network, Modgraph HOSE and Chern Window, have been applied to selected compounds prepared in this study. The Modgraph Neural Network algorithm was found, in all cases, to provide the most accurate correlations with the experimentally-determined chemical shifts. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
- Date Issued: 2007
- Authors: Rose, Nathan Rolf
- Date: 2007 , 2013-07-01
- Subjects: Coumarins , Protease Inhibitors , Heterocyclic compounds -- Derivatives , HIV infections -- Treatment
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4430 , http://hdl.handle.net/10962/d1007220 , Coumarins , Protease Inhibitors , Heterocyclic compounds -- Derivatives , HIV infections -- Treatment
- Description: This research has focused on the development of novel coumann derivatives containing peptide-like side chains as potential HIV-1 protease inhibitors. The reaction of various salicylaldehyde derivatives with tert-butyl acrylate In the presence of 1,4- diazabicyclo[2.2.2]octane (DABCO) has afforded a series of Baylis-Hillman adducts in moderate yield. Cyclisation of the adducts in the presence of HCI afforded the corresponding 3-(chloromethyl)coumarin derivatives, which have been reacted with various amine hydrochlorides in the presence of Proton Sponge® to afford a series of novel 3- (aminomethyl)coumarin derivatives, which were fully characterised by NMR and HRMS methods. Various approaches to the introduction of hydroxyl or amino groups at the C-4 position of coumarin and the 3-(chloromethyl)coumarin derivatives have been explored; these have included dihydroxylation of the coumarin double bond, and the synthesis of 4- benzylaminocoumarin derivatives as potential intermediates. The Vilsmeier-Haack and Mannich reactions have also been investigated as possible methods of introducing the desired peptide-like functionality. Computer modelling of selected structures has indicated that some of the novel 3- (aminomethyl)coumarin derivatives may exhibit activity as inhibitors of HIV-1 protease. The planned enzyme inhibition assays were unfortunately precluded by the aqueous insolubility of the selected compounds. Three ¹³C NMR chemical shift algorithms, viz., Modgraph Neural Network, Modgraph HOSE and Chern Window, have been applied to selected compounds prepared in this study. The Modgraph Neural Network algorithm was found, in all cases, to provide the most accurate correlations with the experimentally-determined chemical shifts. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
- Date Issued: 2007
Synthesis of triprenylated toluquinone and toluhydroquinone metabolites from a marine-derived Penicillium fungus
- Authors: Scheepers, Brent Ashley
- Date: 2007
- Subjects: Penicillium , Antineoplastic agents , Marine fungi , Quinone
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4373 , http://hdl.handle.net/10962/d1005038 , Penicillium , Antineoplastic agents , Marine fungi , Quinone
- Description: This project forms part of a collaborative effort between the marine natural products chemists at Rhodes University and the medical biochemists at the University of Cape Town’s School of Medicine. Our UCT collaborators tested the cytotoxicity of a group of toluhydroquinones and toluquinones (9-15) against the oesophageal cancer cell line WHCO1 and revealed that the triprenylated toluhydroquinone 11 and it’s oxidised analogue 12 were the most active. This thesis presents an investigation into the role of the polyprenyl side-chain in the cytotoxicity of compound 11 and it’s oxidised analogue 12 by synthesizing and testing the cytotoxicity of simplified analogues of this compound. The synthesis of the two ortho-prenylated toluhydroquinone analogues 5-methyl-2-[(2'E,6'E)-3',7' -dimethyl-2',6'-octadienyl]-1,4-benzenediol (19) and 5-methyl-2-[(2'E,6'E)-3',7',11'-trimethyl-2',6',10'-dodecatrienyl]-1,4-benzenediol (21) and their two ortho-prenylated toluquinone analogues, 5-methyl-2-[(2'E,6'E)-3',7'-dimethyl-2',6'-octadienyl]-2,5-cyclohexadiene-1,4-dione (20) and 5-methyl-2-[(2'E,6'E)-3',7',11'-trimethyl-2',6',10'-dodecatrienyl]-2,5-cyclohexadiene-1,4-dione (22) is described. Our initial attempts to couple geranyl bromide, farnesyl bromide and farnesal to the aromatic precursors m-cresol and 1,4-dimethoxy-2-methylbenzene using directed ortho-prenylation and phenoxide carbon-alkylation were unsuccessful. The four target analogues were eventually synthesized via the initial metal halogen exchange reaction between 1-bromo-2,5-dimethoxy-4-methylbenzene and geranyl bromide/farnesyl bromide using n-BuLi and TMEDA in ditheyl ether at 0 °C to yield 92 and 104 respectively in moderate yield. The demethylation of both compounds preceded smoothly using AgO giving the target analogues 20 and 22 in good yield (approx. 90 %). The reduction of quinones 20 and 22 with sodium dithionite gave 19 and 21 in quantitative yield. The synthesis reported here is the first regioselective synthesis of these compounds. The anti-oesophageal cancer activity of 19-22 and two commercially available non-prenylated analogues 17 and 18 were tested against WHCO1. The conclusion drawn from the anti-oesophageal cancer study was that the polyprenyl side-chain plays a negligable role in the cytotoxicity of compounds such as 11 and 9 against the oesophageal cancer cell line WHCO1.
- Full Text:
- Date Issued: 2007
- Authors: Scheepers, Brent Ashley
- Date: 2007
- Subjects: Penicillium , Antineoplastic agents , Marine fungi , Quinone
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4373 , http://hdl.handle.net/10962/d1005038 , Penicillium , Antineoplastic agents , Marine fungi , Quinone
- Description: This project forms part of a collaborative effort between the marine natural products chemists at Rhodes University and the medical biochemists at the University of Cape Town’s School of Medicine. Our UCT collaborators tested the cytotoxicity of a group of toluhydroquinones and toluquinones (9-15) against the oesophageal cancer cell line WHCO1 and revealed that the triprenylated toluhydroquinone 11 and it’s oxidised analogue 12 were the most active. This thesis presents an investigation into the role of the polyprenyl side-chain in the cytotoxicity of compound 11 and it’s oxidised analogue 12 by synthesizing and testing the cytotoxicity of simplified analogues of this compound. The synthesis of the two ortho-prenylated toluhydroquinone analogues 5-methyl-2-[(2'E,6'E)-3',7' -dimethyl-2',6'-octadienyl]-1,4-benzenediol (19) and 5-methyl-2-[(2'E,6'E)-3',7',11'-trimethyl-2',6',10'-dodecatrienyl]-1,4-benzenediol (21) and their two ortho-prenylated toluquinone analogues, 5-methyl-2-[(2'E,6'E)-3',7'-dimethyl-2',6'-octadienyl]-2,5-cyclohexadiene-1,4-dione (20) and 5-methyl-2-[(2'E,6'E)-3',7',11'-trimethyl-2',6',10'-dodecatrienyl]-2,5-cyclohexadiene-1,4-dione (22) is described. Our initial attempts to couple geranyl bromide, farnesyl bromide and farnesal to the aromatic precursors m-cresol and 1,4-dimethoxy-2-methylbenzene using directed ortho-prenylation and phenoxide carbon-alkylation were unsuccessful. The four target analogues were eventually synthesized via the initial metal halogen exchange reaction between 1-bromo-2,5-dimethoxy-4-methylbenzene and geranyl bromide/farnesyl bromide using n-BuLi and TMEDA in ditheyl ether at 0 °C to yield 92 and 104 respectively in moderate yield. The demethylation of both compounds preceded smoothly using AgO giving the target analogues 20 and 22 in good yield (approx. 90 %). The reduction of quinones 20 and 22 with sodium dithionite gave 19 and 21 in quantitative yield. The synthesis reported here is the first regioselective synthesis of these compounds. The anti-oesophageal cancer activity of 19-22 and two commercially available non-prenylated analogues 17 and 18 were tested against WHCO1. The conclusion drawn from the anti-oesophageal cancer study was that the polyprenyl side-chain plays a negligable role in the cytotoxicity of compounds such as 11 and 9 against the oesophageal cancer cell line WHCO1.
- Full Text:
- Date Issued: 2007
The community structure and feeding ecology of the ichthyofauna in the Mngazana and Mngazi estuaries, Port St. Johns, South Africa
- Authors: Grant, Walter Lawrence
- Date: 2007
- Subjects: Estuarine fishes -- South Africa -- Eastern Cape , Fish communities -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10713 , http://hdl.handle.net/10948/513 , http://hdl.handle.net/10948/d1012017 , Estuarine fishes -- South Africa -- Eastern Cape , Fish communities -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape
- Description: The Mngazana and Mngazi estuaries are situated just south of Port St. Johns close to the biogeographical boundary between the warm temperate and subtropical zones along the east coast of Southern Africa. The Mngazana estuary is a permanently open estuary with three species of mangrove. The Mngazi estuary is a temporarily open/closed system. The ichthyofauna was sampled with seine nets and gillnets during June 2005, August 2005, November 2005, February 2006 and April 2006. The fish community structure was significantly different between the two estuaries with the differences being especially noticeable in the larger fish sampled with gillnets. There were significant differences in the fish community sampled with the seine net on both spatial and temporal scales in both of the estuaries. Certain warm temperate species were less abundant and certain subtropical species were more abundant at the Mngazana estuary than they were during a study conducted in 1975. Stomach content analysis revealed that most species had similar diets in the two estuaries with the only differences occurring among benthic feeding species. The diet of sub-adult piscivores comprised of a large proportion of penaeid prawns while the juveniles feed mainly on mysids. The zooplanktivorous fish feed mainly on copepods and mysids with the proportions varying between the species. Benthic feeding fishes showed the greatest variability in diet with plant material, detritus, crabs and copepods being the main food sources. Stable isotopes revealed that particulate organic matter and microphytobenthos were the most important carbon sources to fish in the Mngazi estuary. In the Mngazana estuary a combination of mangrove material, detritus, particulate organic matter and Zostera material were the most important carbon sources. The importance of each of these sources did, however, vary greatly between the different trophic guilds of the fish in the Mngazana estuary. The distribution of certain fish species was investigated in relation to physical parameters (temperature, salinity, turbidity and depth) and biological parameters (prey and predators) in the environment. It was found that most small fish (< 100 mm SL) were strongly correlated with turbidity where-as they showed weak correlations with their prey. Sub-adult piscivores fell into two groups, i.e. those that could tolerate turbid water and those that were only found in clear water. The group that also occurred in turbid water showed very strong correlations with their prey but the clear water group did not. It would appear that the small and thus vulnerable fish seemed to occur in areas that offered them protection rather than areas where their food supply is most abundant, where-as the piscivores were more influenced by prey distribution, as long as the physical conditions were tolerable to them.
- Full Text:
- Date Issued: 2007
- Authors: Grant, Walter Lawrence
- Date: 2007
- Subjects: Estuarine fishes -- South Africa -- Eastern Cape , Fish communities -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10713 , http://hdl.handle.net/10948/513 , http://hdl.handle.net/10948/d1012017 , Estuarine fishes -- South Africa -- Eastern Cape , Fish communities -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape
- Description: The Mngazana and Mngazi estuaries are situated just south of Port St. Johns close to the biogeographical boundary between the warm temperate and subtropical zones along the east coast of Southern Africa. The Mngazana estuary is a permanently open estuary with three species of mangrove. The Mngazi estuary is a temporarily open/closed system. The ichthyofauna was sampled with seine nets and gillnets during June 2005, August 2005, November 2005, February 2006 and April 2006. The fish community structure was significantly different between the two estuaries with the differences being especially noticeable in the larger fish sampled with gillnets. There were significant differences in the fish community sampled with the seine net on both spatial and temporal scales in both of the estuaries. Certain warm temperate species were less abundant and certain subtropical species were more abundant at the Mngazana estuary than they were during a study conducted in 1975. Stomach content analysis revealed that most species had similar diets in the two estuaries with the only differences occurring among benthic feeding species. The diet of sub-adult piscivores comprised of a large proportion of penaeid prawns while the juveniles feed mainly on mysids. The zooplanktivorous fish feed mainly on copepods and mysids with the proportions varying between the species. Benthic feeding fishes showed the greatest variability in diet with plant material, detritus, crabs and copepods being the main food sources. Stable isotopes revealed that particulate organic matter and microphytobenthos were the most important carbon sources to fish in the Mngazi estuary. In the Mngazana estuary a combination of mangrove material, detritus, particulate organic matter and Zostera material were the most important carbon sources. The importance of each of these sources did, however, vary greatly between the different trophic guilds of the fish in the Mngazana estuary. The distribution of certain fish species was investigated in relation to physical parameters (temperature, salinity, turbidity and depth) and biological parameters (prey and predators) in the environment. It was found that most small fish (< 100 mm SL) were strongly correlated with turbidity where-as they showed weak correlations with their prey. Sub-adult piscivores fell into two groups, i.e. those that could tolerate turbid water and those that were only found in clear water. The group that also occurred in turbid water showed very strong correlations with their prey but the clear water group did not. It would appear that the small and thus vulnerable fish seemed to occur in areas that offered them protection rather than areas where their food supply is most abundant, where-as the piscivores were more influenced by prey distribution, as long as the physical conditions were tolerable to them.
- Full Text:
- Date Issued: 2007
The design and assessment of an integrated municipal waste beneficiation facility : towards improved sewage sludge management in developing countries
- Authors: Keirungi, Juliana
- Date: 2007
- Subjects: Sewage -- Purification -- South Africa -- Eastern Cape , Sewage sludge -- South Africa -- Eastern Cape -- Management , Water quality management -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4755 , http://hdl.handle.net/10962/d1007138 , Sewage -- Purification -- South Africa -- Eastern Cape , Sewage sludge -- South Africa -- Eastern Cape -- Management , Water quality management -- South Africa -- Eastern Cape
- Description: This research aimed to firstly confirm the hypothesis that the current management of sewage sludge generated during the treatment of wastewater in the Eastern Cape Province of South Africa is poor and, as such, this material poses a threat to local environmental and human health. Secondly, through a rational design approach, the current research also aimed to design and assess the suitability of a novel integrated process incorporating appropriate technologies for improved sewage sludge management. The lack of an appropriate tool for the assessment of the integrated process necessitated the development of an appropriate technology assessment (TA) methodology based on environmental, technical, social and economic criteria. A combination of informal participatory methods such as semi-structured interviews and formal research methods including questionnaires, risk assessment exercises and laboratory analyses were used. Based on the above it was estimated that 116 tons dry sludge were generated in the province per day and that the concentration of heavy metals present in the sludge was generally within the limits for reuse on agricultural land. Furthermore the sludge from all sample sewage treatment works (STWs) was found to be free of any detectable pathogens. Despite the above, a preliminary risk assessment and chemical analysis revealed that existing sludge management practices at sample STWs posed a threat to the environment, particularly to water resources and exacerbated the problems associated with the discharge of poorly treated municipal wastewater. The root causes of the poor sludge management were considered to be a lack of non-regulatory incentives and financial resources. Highly integrated ecologically engineered systems were thought to offer a solution to the dual problem of poor sludge management and municipal effluent treatment, while providing necessary economic incentives. To facilitate the design of a system appropriate to local conditions, it was necessary to first develop a rational design methodology, which incorporated a detailed TA step. The result of the design process was an Integrated Waste Beneficiation Facility (IWBF) that incorporated a number of process units comprised of appropriate technologies including composting, vermicomposting, algal ponding technology and aquaculture. A detailed TA indicated that the benefits of the proposed IWBF would, at the majority of sample sites, outweigh the potential negative impacts and it was thus recommended that investigations should continue on pilot-scale facilities. Furthermore, although the proposed TA based on four sustainability criteria categories was thought to provide a more accurate assessment of the true sustainability of a technology, the acquisition of information was problematic highlighting the need to re-think current TA methodologies and to address associated constraints allowing the tool to be used and fully comprehensive.
- Full Text:
- Date Issued: 2007
- Authors: Keirungi, Juliana
- Date: 2007
- Subjects: Sewage -- Purification -- South Africa -- Eastern Cape , Sewage sludge -- South Africa -- Eastern Cape -- Management , Water quality management -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4755 , http://hdl.handle.net/10962/d1007138 , Sewage -- Purification -- South Africa -- Eastern Cape , Sewage sludge -- South Africa -- Eastern Cape -- Management , Water quality management -- South Africa -- Eastern Cape
- Description: This research aimed to firstly confirm the hypothesis that the current management of sewage sludge generated during the treatment of wastewater in the Eastern Cape Province of South Africa is poor and, as such, this material poses a threat to local environmental and human health. Secondly, through a rational design approach, the current research also aimed to design and assess the suitability of a novel integrated process incorporating appropriate technologies for improved sewage sludge management. The lack of an appropriate tool for the assessment of the integrated process necessitated the development of an appropriate technology assessment (TA) methodology based on environmental, technical, social and economic criteria. A combination of informal participatory methods such as semi-structured interviews and formal research methods including questionnaires, risk assessment exercises and laboratory analyses were used. Based on the above it was estimated that 116 tons dry sludge were generated in the province per day and that the concentration of heavy metals present in the sludge was generally within the limits for reuse on agricultural land. Furthermore the sludge from all sample sewage treatment works (STWs) was found to be free of any detectable pathogens. Despite the above, a preliminary risk assessment and chemical analysis revealed that existing sludge management practices at sample STWs posed a threat to the environment, particularly to water resources and exacerbated the problems associated with the discharge of poorly treated municipal wastewater. The root causes of the poor sludge management were considered to be a lack of non-regulatory incentives and financial resources. Highly integrated ecologically engineered systems were thought to offer a solution to the dual problem of poor sludge management and municipal effluent treatment, while providing necessary economic incentives. To facilitate the design of a system appropriate to local conditions, it was necessary to first develop a rational design methodology, which incorporated a detailed TA step. The result of the design process was an Integrated Waste Beneficiation Facility (IWBF) that incorporated a number of process units comprised of appropriate technologies including composting, vermicomposting, algal ponding technology and aquaculture. A detailed TA indicated that the benefits of the proposed IWBF would, at the majority of sample sites, outweigh the potential negative impacts and it was thus recommended that investigations should continue on pilot-scale facilities. Furthermore, although the proposed TA based on four sustainability criteria categories was thought to provide a more accurate assessment of the true sustainability of a technology, the acquisition of information was problematic highlighting the need to re-think current TA methodologies and to address associated constraints allowing the tool to be used and fully comprehensive.
- Full Text:
- Date Issued: 2007
The effect of elephants (Loxodonta africana, Blumenbach, 1797) on Xeric Succulent Thicket
- Authors: Knott, Edward Joseph
- Date: 2007
- Subjects: Addo Elephant National Park (South Africa) , African elephant , Elephants -- South Africa -- Eastern Cape , Elephants -- Nutrition -- South Africa -- Eastern Cape , Elephants -- Ecology -- South Africa -- Eastern Cape , Elephants -- Behavior -- South Africa -- Eastern Cape , Succulent plants -- South Africa -- Eastern Cape , Woody plants -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5674 , http://hdl.handle.net/10962/d1005359 , Addo Elephant National Park (South Africa) , African elephant , Elephants -- South Africa -- Eastern Cape , Elephants -- Nutrition -- South Africa -- Eastern Cape , Elephants -- Ecology -- South Africa -- Eastern Cape , Elephants -- Behavior -- South Africa -- Eastern Cape , Succulent plants -- South Africa -- Eastern Cape , Woody plants -- South Africa -- Eastern Cape
- Description: This study looks at the impact of elephant feeding on the Xeric Succulent Thicket component of Eastern Cape Subtropical Thicket (ECST) in Addo Elephant National Park (AENP). Observations of elephant feeding were carried out and vegetation transects were surveyed for impact of elephant feeding. The results indicated that the Nyati elephants spent the majority of their time grazing (nearly 90%), particularly the cow-young herds, and especially when the herd gathered in larger numbers. Browsing events were concentrated on Acacia karroo (81%) and there was no significant difference between the sexes in their preference for this species. Despite being subjected to most of the browsing, the majority of A. karroo trees were undamaged and the effect of elephants was generally light. It appears unlikely that, three years after re-introduction to Nyati, the elephants have had an effect on community structure of the vegetation. Surveys were conducted on stands of the alien invasive weed prickly pear Opuntia ficus-indica, and it was recorded that elephants in Nyati have had a dramatic effect on prickly pear, utilising all adult plants assessed and destroying 70% of them. This level of destruction in such a short period of time suggests that prickly pear is a highly favoured species. The results from the present study suggest that elephants can play a role in the control of prickly pear. Results are discussed in terms of elephants as both megaherbivores and keystone species, and as agents of intermediate disturbance.
- Full Text:
- Date Issued: 2007
- Authors: Knott, Edward Joseph
- Date: 2007
- Subjects: Addo Elephant National Park (South Africa) , African elephant , Elephants -- South Africa -- Eastern Cape , Elephants -- Nutrition -- South Africa -- Eastern Cape , Elephants -- Ecology -- South Africa -- Eastern Cape , Elephants -- Behavior -- South Africa -- Eastern Cape , Succulent plants -- South Africa -- Eastern Cape , Woody plants -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5674 , http://hdl.handle.net/10962/d1005359 , Addo Elephant National Park (South Africa) , African elephant , Elephants -- South Africa -- Eastern Cape , Elephants -- Nutrition -- South Africa -- Eastern Cape , Elephants -- Ecology -- South Africa -- Eastern Cape , Elephants -- Behavior -- South Africa -- Eastern Cape , Succulent plants -- South Africa -- Eastern Cape , Woody plants -- South Africa -- Eastern Cape
- Description: This study looks at the impact of elephant feeding on the Xeric Succulent Thicket component of Eastern Cape Subtropical Thicket (ECST) in Addo Elephant National Park (AENP). Observations of elephant feeding were carried out and vegetation transects were surveyed for impact of elephant feeding. The results indicated that the Nyati elephants spent the majority of their time grazing (nearly 90%), particularly the cow-young herds, and especially when the herd gathered in larger numbers. Browsing events were concentrated on Acacia karroo (81%) and there was no significant difference between the sexes in their preference for this species. Despite being subjected to most of the browsing, the majority of A. karroo trees were undamaged and the effect of elephants was generally light. It appears unlikely that, three years after re-introduction to Nyati, the elephants have had an effect on community structure of the vegetation. Surveys were conducted on stands of the alien invasive weed prickly pear Opuntia ficus-indica, and it was recorded that elephants in Nyati have had a dramatic effect on prickly pear, utilising all adult plants assessed and destroying 70% of them. This level of destruction in such a short period of time suggests that prickly pear is a highly favoured species. The results from the present study suggest that elephants can play a role in the control of prickly pear. Results are discussed in terms of elephants as both megaherbivores and keystone species, and as agents of intermediate disturbance.
- Full Text:
- Date Issued: 2007
The effect of geography, cultivation and harvest technique on the umckalin concentration and growth of pelargonium sidoides (Geraniaceae)
- Authors: White, Andrew Graeme
- Date: 2007
- Subjects: Pelargoniums , Geraniaceae , Botany -- South Africa -- Eastern Cape , Traditional medicine -- South Africa -- Eastern Cape , Medicinal plants -- South Africa -- Eastern Cape , Coumarins
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4234 , http://hdl.handle.net/10962/d1003803 , Pelargoniums , Geraniaceae , Botany -- South Africa -- Eastern Cape , Traditional medicine -- South Africa -- Eastern Cape , Medicinal plants -- South Africa -- Eastern Cape , Coumarins
- Description: Pelargonium sidoides DC. (Geraniaceae) root extracts are used in the Eastern Cape Province of South Africa as a traditional medicine for the treatment of respiratory tract and gastro-intestinal infections. Ethanolic extracts are used globally as herbal treatments for bronchitis, asthma and as an immune system booster. Despite documented exploitation of wild populations by illegal harvesters, this species has not been awarded a protected status. The high level of harvest in the years preceding this study prompted this investigation of the prospects for sustainable root harvest through wild harvest and greenhouse cultivation. A novel method was developed for the purification of umckalin, a bioactive constituent in root extracts, such that the root umckalin concentrations of wild and cultivated plants could be quantified by HPLC. As part of the cultivation experiments, the concentration of umckalin in roots was measured for plants across part of the species’ distribution range in the Eastern Cape Province. This survey revealed that root umckalin concentrations were inversely related to the average annual rainfall of the collection site (r² = 0.94, p = 0.007) and directly related to soil pH (r² = 0.97, p = 0.002). Thus, the possibility of inducing high umckalin concentrations in greenhouse-cultivated plants was investigated by subjecting plants to rapid and prolonged water stress treatments. Two leaf applied hormone treatments (cytokinin and gibberellin) and a root competition treatment with a fast growing annual (Conyza albida) were also investigated based on the potential function of umckalin in P. sidoides plants. These five treatments did not significantly affect root umckalin concentrations compared to well-watered controls. The results of further experiments suggested that umckalin production may have been influenced by the geographical origin and genetics of plants rather than environmental variation. Following wild harvest experiments, the regrowth of replanted shoots from which a standard proportion of the root was harvested showed that water availability affected shoot survival but not root regrowth rate. Regrowth rates were low, questioning the viability of wild harvest. In contrast, greenhouse cultivated plants showed ca. six times greater growth rates, supporting the cultivation of roots to supply future market demand.
- Full Text:
- Date Issued: 2007
- Authors: White, Andrew Graeme
- Date: 2007
- Subjects: Pelargoniums , Geraniaceae , Botany -- South Africa -- Eastern Cape , Traditional medicine -- South Africa -- Eastern Cape , Medicinal plants -- South Africa -- Eastern Cape , Coumarins
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4234 , http://hdl.handle.net/10962/d1003803 , Pelargoniums , Geraniaceae , Botany -- South Africa -- Eastern Cape , Traditional medicine -- South Africa -- Eastern Cape , Medicinal plants -- South Africa -- Eastern Cape , Coumarins
- Description: Pelargonium sidoides DC. (Geraniaceae) root extracts are used in the Eastern Cape Province of South Africa as a traditional medicine for the treatment of respiratory tract and gastro-intestinal infections. Ethanolic extracts are used globally as herbal treatments for bronchitis, asthma and as an immune system booster. Despite documented exploitation of wild populations by illegal harvesters, this species has not been awarded a protected status. The high level of harvest in the years preceding this study prompted this investigation of the prospects for sustainable root harvest through wild harvest and greenhouse cultivation. A novel method was developed for the purification of umckalin, a bioactive constituent in root extracts, such that the root umckalin concentrations of wild and cultivated plants could be quantified by HPLC. As part of the cultivation experiments, the concentration of umckalin in roots was measured for plants across part of the species’ distribution range in the Eastern Cape Province. This survey revealed that root umckalin concentrations were inversely related to the average annual rainfall of the collection site (r² = 0.94, p = 0.007) and directly related to soil pH (r² = 0.97, p = 0.002). Thus, the possibility of inducing high umckalin concentrations in greenhouse-cultivated plants was investigated by subjecting plants to rapid and prolonged water stress treatments. Two leaf applied hormone treatments (cytokinin and gibberellin) and a root competition treatment with a fast growing annual (Conyza albida) were also investigated based on the potential function of umckalin in P. sidoides plants. These five treatments did not significantly affect root umckalin concentrations compared to well-watered controls. The results of further experiments suggested that umckalin production may have been influenced by the geographical origin and genetics of plants rather than environmental variation. Following wild harvest experiments, the regrowth of replanted shoots from which a standard proportion of the root was harvested showed that water availability affected shoot survival but not root regrowth rate. Regrowth rates were low, questioning the viability of wild harvest. In contrast, greenhouse cultivated plants showed ca. six times greater growth rates, supporting the cultivation of roots to supply future market demand.
- Full Text:
- Date Issued: 2007