The reactions of ruthenium (ii) polypyridyl complexes
- Authors: Zheng, Sipeng
- Date: 2009
- Subjects: Ruthenium , Ruthenium compounds , Chemical reactions
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10374 , http://hdl.handle.net/10948/1089 , Ruthenium , Ruthenium compounds , Chemical reactions
- Description: Ruthenium (II) polypyridine complexes in general have been extensively studied because of their unique redox and photochemical properties. A typical example of such complexes is tris(2,2’-bipyridyl) ruthenium (II). In this study, this complex was synthesized and then characterized using electronic spectroscopy and cyclic voltammetry. It was also shown that the ruthenium concentration could be accurately determined using ICP-MS. It was found that the complex is very stable in various chemical environments. It was observed from spectrophotometric investigations that persulphate and lead dioxide easily oxidize Ru(bpy)3 2+ to Ru(bpy)3 3+ in the presence of heat and H2SO4, respectively. It was also observed that the oxidation between Ru(bpy)3 2+ and cerium (IV) occurred at approximately 3:2 [Ce(IV)]/[Ru(II)] mole ratio. The resultant Ru(bpy)3 3+ solution was unstable in the presence of light and recovery of Ru(bpy)3 2+ occurred gradually. The regeneration of Ru(bpy)3 2+ from Ru(bpy)3 3+ was found to be a multistep process, which appears to involve the formation of an intermediate species. The following reaction model was found to best explain the kinetic data obtained: Ru(bpy)3 2+ + Ce(IV) → Ru(bpy)3 3+ Ru(bpy)3 3+ → Ru(bpy)3 2+ Ru(bpy)3 3+ → Ru* intermediate Ru* intermediate → Ru(bpy)3 2+ Theoretical rate constants were also calculated for the same process under the experimental conditions. The comparison between the experimental and theoretical results gave good agreement. In addition, the factors that influence the rate of the regeneration of Ru(bpy)3 2+ from Ru(bpy)3 3+ were also discussed.
- Full Text:
- Date Issued: 2009
- Authors: Zheng, Sipeng
- Date: 2009
- Subjects: Ruthenium , Ruthenium compounds , Chemical reactions
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10374 , http://hdl.handle.net/10948/1089 , Ruthenium , Ruthenium compounds , Chemical reactions
- Description: Ruthenium (II) polypyridine complexes in general have been extensively studied because of their unique redox and photochemical properties. A typical example of such complexes is tris(2,2’-bipyridyl) ruthenium (II). In this study, this complex was synthesized and then characterized using electronic spectroscopy and cyclic voltammetry. It was also shown that the ruthenium concentration could be accurately determined using ICP-MS. It was found that the complex is very stable in various chemical environments. It was observed from spectrophotometric investigations that persulphate and lead dioxide easily oxidize Ru(bpy)3 2+ to Ru(bpy)3 3+ in the presence of heat and H2SO4, respectively. It was also observed that the oxidation between Ru(bpy)3 2+ and cerium (IV) occurred at approximately 3:2 [Ce(IV)]/[Ru(II)] mole ratio. The resultant Ru(bpy)3 3+ solution was unstable in the presence of light and recovery of Ru(bpy)3 2+ occurred gradually. The regeneration of Ru(bpy)3 2+ from Ru(bpy)3 3+ was found to be a multistep process, which appears to involve the formation of an intermediate species. The following reaction model was found to best explain the kinetic data obtained: Ru(bpy)3 2+ + Ce(IV) → Ru(bpy)3 3+ Ru(bpy)3 3+ → Ru(bpy)3 2+ Ru(bpy)3 3+ → Ru* intermediate Ru* intermediate → Ru(bpy)3 2+ Theoretical rate constants were also calculated for the same process under the experimental conditions. The comparison between the experimental and theoretical results gave good agreement. In addition, the factors that influence the rate of the regeneration of Ru(bpy)3 2+ from Ru(bpy)3 3+ were also discussed.
- Full Text:
- Date Issued: 2009
The response of the red mangrove rhizophora mucronata lam, to changes in salinity, inundation and light : predictions for future climate change
- Hoppe-Speer, Sabine Clara Lisa
- Authors: Hoppe-Speer, Sabine Clara Lisa
- Date: 2009
- Subjects: Mangrove plants , Climatic changes , Red mangrove
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10616 , http://hdl.handle.net/10948/1249 , Mangrove plants , Climatic changes , Red mangrove
- Description: Mangrove forests are subjected to many environmental factors which influence species distribution, zonation patterns as well as succession. Important driving factors in these forests are salinity, water level fluctuations and available light. This study investigated the response of red mangrove (Rhizophora mucronata Lam.) seedlings to these factors in controlled laboratory experiments. Increase in salinity and prolonged inundation within estuaries are predicted impacts resulting from sea level rise due to climate change. The study investigated the effect of five salinity treatments (0, 8, 18, 35 and 45 ppt) with a semi-diurnal tidal cycle on seedling growth. In a separate experiment the effect of different inundation treatments: no inundation, 3, 6, 9 hour tidal cycles and continuous inundation (24 h) were investigated. Both morphological and physiological responses of R. mucronata seedlings were measured. There was a decrease in growth (plant height, biomass and leaf production) with increasing salinity. Seedlings in the seawater, hypersaline and no inundation treatments showed symptoms of stress, having increased leaf necrosis ("burn marks"). The highest growth occurred in the low salinity (8 ppt) treatment, but the highest photosynthetic performance and stomatal conductance occurred in the freshwater treatment (0 ppt). The typical response of stem elongation with increasing inundation was observed in the 24 hr inundation treatment. In the light and salinity combination study there were ten different treatments of five different light treatments (unshaded, 20 percent, 50 percent, 80 percent and 90 percent shade) combined with two salinity concentrations (18 and 35 ppt). In this study the seedling growth: plant height, biomass, leaf surface area and leaf production were higher in the moderate salinity (18 ppt) treatments compared to the seawater (35 ppt) treatments. Biomass in the 35 ppt experiment decreased with increasing shade as well as in the unshaded treatments. Photosynthetic performance and stomatal conductance were lower for the unshaded treatment in both 18 and 35 ppt salinity compared to all other treatments with the same salinity. This suggests that R. mucronata more shade than sun tolerant, but overall it can be concluded that the species has a broad tolerance range. The results may be relevant in mangrove rehabilitation and predicting responses to climate change. This is important as mangrove ecosystems may adapt to changing sea levels and in order to restore areas it will be necessary to choose the mangrove species which will grow best. The results may also help to increase the protection of existing mangrove habitats.
- Full Text:
- Date Issued: 2009
- Authors: Hoppe-Speer, Sabine Clara Lisa
- Date: 2009
- Subjects: Mangrove plants , Climatic changes , Red mangrove
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10616 , http://hdl.handle.net/10948/1249 , Mangrove plants , Climatic changes , Red mangrove
- Description: Mangrove forests are subjected to many environmental factors which influence species distribution, zonation patterns as well as succession. Important driving factors in these forests are salinity, water level fluctuations and available light. This study investigated the response of red mangrove (Rhizophora mucronata Lam.) seedlings to these factors in controlled laboratory experiments. Increase in salinity and prolonged inundation within estuaries are predicted impacts resulting from sea level rise due to climate change. The study investigated the effect of five salinity treatments (0, 8, 18, 35 and 45 ppt) with a semi-diurnal tidal cycle on seedling growth. In a separate experiment the effect of different inundation treatments: no inundation, 3, 6, 9 hour tidal cycles and continuous inundation (24 h) were investigated. Both morphological and physiological responses of R. mucronata seedlings were measured. There was a decrease in growth (plant height, biomass and leaf production) with increasing salinity. Seedlings in the seawater, hypersaline and no inundation treatments showed symptoms of stress, having increased leaf necrosis ("burn marks"). The highest growth occurred in the low salinity (8 ppt) treatment, but the highest photosynthetic performance and stomatal conductance occurred in the freshwater treatment (0 ppt). The typical response of stem elongation with increasing inundation was observed in the 24 hr inundation treatment. In the light and salinity combination study there were ten different treatments of five different light treatments (unshaded, 20 percent, 50 percent, 80 percent and 90 percent shade) combined with two salinity concentrations (18 and 35 ppt). In this study the seedling growth: plant height, biomass, leaf surface area and leaf production were higher in the moderate salinity (18 ppt) treatments compared to the seawater (35 ppt) treatments. Biomass in the 35 ppt experiment decreased with increasing shade as well as in the unshaded treatments. Photosynthetic performance and stomatal conductance were lower for the unshaded treatment in both 18 and 35 ppt salinity compared to all other treatments with the same salinity. This suggests that R. mucronata more shade than sun tolerant, but overall it can be concluded that the species has a broad tolerance range. The results may be relevant in mangrove rehabilitation and predicting responses to climate change. This is important as mangrove ecosystems may adapt to changing sea levels and in order to restore areas it will be necessary to choose the mangrove species which will grow best. The results may also help to increase the protection of existing mangrove habitats.
- Full Text:
- Date Issued: 2009
The selective dechlorination of poly-chlorophenols
- Authors: Thomas, Maxwell Paul
- Date: 2009
- Subjects: Sewage -- Purification -- Chlorination , Pesticides -- Toxicology , Chlorine -- Toxicology
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:10391 , http://hdl.handle.net/10948/1124 , Sewage -- Purification -- Chlorination , Pesticides -- Toxicology , Chlorine -- Toxicology
- Description: Liquid phase catalytic hydrodechlorinations can provide a convenient and environmentally friendly method for treating organic chlorinated compounds in waste streams generated during the manufacturing of agrochemicals. During such treatment hydrochloric acid is generated as a by-product, which can be easily neutralized employing a base to yield an inorganic salt. This work describes the results obtained during the liquid phase hydrodechlorination of 2,6-dichlorophenol (2,6-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP). The hydrodechlorination of these chlorinated phenolic compounds in a mixture of methanol and water was investigated using supported and unsupported palladium catalysts to yield lower chlorinated phenols or phenol. Various parameters were investigated such as catalyst concentration, ammonium formate concentration, effect of base addition and effect of temperature. During this study two methods of hydrodechlorination were also investigated such as hydride-transfer hydrogenolysis, using ammonium formate, and hydrogenolysis, using dihydrogen. These methods offer a mild treatment in terms of the reaction temperature with temperatures used below 800C. A comparison of the palladium catalyst systems using these methods also showed that Pd/C produced the best results in terms of the hydrodechlorination rate and the selectivity towards phenol. When the ammonium formate method was used, complete hydrodechlorination of both substrates was achieved in 1h of reaction time at a selectivity of 100 percent towards phenol. A comparison of the method using dihydrogen and Pd/C showed that the reaction rate and the selectivity towards phenol during the hydrodechlorination of 2,6-DCP were 87.92 percent and 93.30 percent. Similarly, the reaction rate and selectivity during 2,4,6- TCP hydrodechlorination were 63.77 percent and 70.57 percent. These results were achieved in a reaction time of 3 hours. A high catalyst loading increases the reaction rate at the expense of selectivity, due to the formation of cyclohexanone, formed during further hydrogenation of phenol. The formation of cyclohexanone was limited at high temperatures (ca. 800C) with none detected during the hydrodechlorination of 2,6-DCP and 0.19 percent during the hydrodechlorination of 2,4,6-TCP. Evaluation of the hydrodechlorination parameters showed that the catalytic efficiency of the Pd/C catalysts was inhibited as the reaction proceeded due to the formation of HCl as by-product. A significant increase in the reaction rate was achieved when the reaction was performed in the presence of an inorganic base, which neutralized HCl.
- Full Text:
- Date Issued: 2009
- Authors: Thomas, Maxwell Paul
- Date: 2009
- Subjects: Sewage -- Purification -- Chlorination , Pesticides -- Toxicology , Chlorine -- Toxicology
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:10391 , http://hdl.handle.net/10948/1124 , Sewage -- Purification -- Chlorination , Pesticides -- Toxicology , Chlorine -- Toxicology
- Description: Liquid phase catalytic hydrodechlorinations can provide a convenient and environmentally friendly method for treating organic chlorinated compounds in waste streams generated during the manufacturing of agrochemicals. During such treatment hydrochloric acid is generated as a by-product, which can be easily neutralized employing a base to yield an inorganic salt. This work describes the results obtained during the liquid phase hydrodechlorination of 2,6-dichlorophenol (2,6-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP). The hydrodechlorination of these chlorinated phenolic compounds in a mixture of methanol and water was investigated using supported and unsupported palladium catalysts to yield lower chlorinated phenols or phenol. Various parameters were investigated such as catalyst concentration, ammonium formate concentration, effect of base addition and effect of temperature. During this study two methods of hydrodechlorination were also investigated such as hydride-transfer hydrogenolysis, using ammonium formate, and hydrogenolysis, using dihydrogen. These methods offer a mild treatment in terms of the reaction temperature with temperatures used below 800C. A comparison of the palladium catalyst systems using these methods also showed that Pd/C produced the best results in terms of the hydrodechlorination rate and the selectivity towards phenol. When the ammonium formate method was used, complete hydrodechlorination of both substrates was achieved in 1h of reaction time at a selectivity of 100 percent towards phenol. A comparison of the method using dihydrogen and Pd/C showed that the reaction rate and the selectivity towards phenol during the hydrodechlorination of 2,6-DCP were 87.92 percent and 93.30 percent. Similarly, the reaction rate and selectivity during 2,4,6- TCP hydrodechlorination were 63.77 percent and 70.57 percent. These results were achieved in a reaction time of 3 hours. A high catalyst loading increases the reaction rate at the expense of selectivity, due to the formation of cyclohexanone, formed during further hydrogenation of phenol. The formation of cyclohexanone was limited at high temperatures (ca. 800C) with none detected during the hydrodechlorination of 2,6-DCP and 0.19 percent during the hydrodechlorination of 2,4,6-TCP. Evaluation of the hydrodechlorination parameters showed that the catalytic efficiency of the Pd/C catalysts was inhibited as the reaction proceeded due to the formation of HCl as by-product. A significant increase in the reaction rate was achieved when the reaction was performed in the presence of an inorganic base, which neutralized HCl.
- Full Text:
- Date Issued: 2009
Warthog as an introduced species in the Eastern Cape
- Authors: Nyafu, Kanyisa
- Date: 2009
- Subjects: Warthog -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10701 , http://hdl.handle.net/10948/1058 , Warthog -- South Africa -- Eastern Cape
- Description: The introduced common warthog, Phacochoerus africanus, in the Eastern Cape is increasing rapidly both in numbers and distribution, despite attempts by landowners to reduce numbers and exclude warthogs. These control attempts are motivated by concerns over the impacts of warthogs, on vegetation, soil and other animal species. This expansion of warthog populations is paradoxical given that a species of warthog occurred historically in this part of the world, apparently at low densities and was wiped out in the mid-1800s. The question therefore arises as to why warthogs are able to overcome population regulation attempts now, and this becomes an invasive species issue as the species now occurring in the Eastern Cape is in fact an introduced species. The objectives of the study were to investigate the status of warthogs as an introduced invasive species in the Eastern Cape by documenting the rate and direction of population expansion, ecological impacts and possible dietary shift of the introduced species, P. africanus compared to the extinct species P. aethiopicus. The research approach adapted here was to test the hypotheses that, (1) the success of P. africanus in the Eastern Cape reflects dietary differences of the two species based on observations of different dental adaptations, as P. africanus has functional incisors, which are absent in P. aethiopicus. Stable carbon isotope analysis of the tooth enamel was used to determine the diet of the two species. (2) Common warthogs are specialized grazers and will impact on a limited range of grass species, this hypothesis was addressed by describing the diet of common warthogs in one site in the Eastern Cape to identify plant species at risk due to invasion by P. africanus, and microhistological faecal analysis was used. (3) Common warthogs have successfully expanded their range in the Eastern Cape since their introduction and are now showing impact, this was addressed by describing the range of expansion of P. africanus in the Eastern Cape, as well as reviewing landowner perceptions of the impacts of warthogs, this was based on questionnaire surveys distributed in the Sundays and the Fish River valleys. The results of the study showed that there are differences in the diet of Cape warthog P. aethiopicus and common warthog P. africanus. The Cape warthog was largely a grazer (86 percent C4 grasses in their diet), while P. africanus is also a grazer (71 percent of C4 grasses in their diet), but with a larger proportion of browse in their diet. These results support the hypothesis that the presence of functional incisors in the common warthog might provide the common warthog with foraging advantages over the Cape warthog. This might be a contributing factor to the success of this invasive species in the Eastern Cape, and might explain the rapid disappearance of Cape warthogs in the 1800s, which coincided with rapid expansion of herds of domestic grazers. A total of twelve grass species are used by common warthogs and are therefore most vulnerable to impacts of this invasive species. Common warthogs are rapidly expanding their range particularly around the Sundays and the Great Fish River valleys and they are perceived by landowners to have impacts on grass cover, soils and fencing. This spread of warthog in the Eastern Cape exhibits characteristics of an invasive species. In light of the findings of this study, it is therefore important that government authorities and other parties concerned recognize that common warthogs are invasive in the Eastern Cape.
- Full Text:
- Date Issued: 2009
- Authors: Nyafu, Kanyisa
- Date: 2009
- Subjects: Warthog -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10701 , http://hdl.handle.net/10948/1058 , Warthog -- South Africa -- Eastern Cape
- Description: The introduced common warthog, Phacochoerus africanus, in the Eastern Cape is increasing rapidly both in numbers and distribution, despite attempts by landowners to reduce numbers and exclude warthogs. These control attempts are motivated by concerns over the impacts of warthogs, on vegetation, soil and other animal species. This expansion of warthog populations is paradoxical given that a species of warthog occurred historically in this part of the world, apparently at low densities and was wiped out in the mid-1800s. The question therefore arises as to why warthogs are able to overcome population regulation attempts now, and this becomes an invasive species issue as the species now occurring in the Eastern Cape is in fact an introduced species. The objectives of the study were to investigate the status of warthogs as an introduced invasive species in the Eastern Cape by documenting the rate and direction of population expansion, ecological impacts and possible dietary shift of the introduced species, P. africanus compared to the extinct species P. aethiopicus. The research approach adapted here was to test the hypotheses that, (1) the success of P. africanus in the Eastern Cape reflects dietary differences of the two species based on observations of different dental adaptations, as P. africanus has functional incisors, which are absent in P. aethiopicus. Stable carbon isotope analysis of the tooth enamel was used to determine the diet of the two species. (2) Common warthogs are specialized grazers and will impact on a limited range of grass species, this hypothesis was addressed by describing the diet of common warthogs in one site in the Eastern Cape to identify plant species at risk due to invasion by P. africanus, and microhistological faecal analysis was used. (3) Common warthogs have successfully expanded their range in the Eastern Cape since their introduction and are now showing impact, this was addressed by describing the range of expansion of P. africanus in the Eastern Cape, as well as reviewing landowner perceptions of the impacts of warthogs, this was based on questionnaire surveys distributed in the Sundays and the Fish River valleys. The results of the study showed that there are differences in the diet of Cape warthog P. aethiopicus and common warthog P. africanus. The Cape warthog was largely a grazer (86 percent C4 grasses in their diet), while P. africanus is also a grazer (71 percent of C4 grasses in their diet), but with a larger proportion of browse in their diet. These results support the hypothesis that the presence of functional incisors in the common warthog might provide the common warthog with foraging advantages over the Cape warthog. This might be a contributing factor to the success of this invasive species in the Eastern Cape, and might explain the rapid disappearance of Cape warthogs in the 1800s, which coincided with rapid expansion of herds of domestic grazers. A total of twelve grass species are used by common warthogs and are therefore most vulnerable to impacts of this invasive species. Common warthogs are rapidly expanding their range particularly around the Sundays and the Great Fish River valleys and they are perceived by landowners to have impacts on grass cover, soils and fencing. This spread of warthog in the Eastern Cape exhibits characteristics of an invasive species. In light of the findings of this study, it is therefore important that government authorities and other parties concerned recognize that common warthogs are invasive in the Eastern Cape.
- Full Text:
- Date Issued: 2009
A hybrid approach to beach erosion mitigation and amenity enhancement, St Francis Bay, South Africa
- Authors: Anderson, Dylan Rory
- Date: 2008
- Subjects: Beach erosion -- South Africa -- St Francis Bay , Shore protection -- South Africa -- St Francis Bay , Restoration ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10611 , http://hdl.handle.net/10948/d1008192 , Beach erosion -- South Africa -- St Francis Bay , Shore protection -- South Africa -- St Francis Bay , Restoration ecology
- Description: The St Francis Bay beach has experienced chronic erosion over the past three decades. This erosion can largely be attributed to the stabilisation of a large coastal dunefield which contributed +/- 80 percent of the sand supply to St Francis Bay. Stabilisation began in 1975 initially using plant cuttings and followed by the development of the Santareme holiday suburb resulting in complete stabilisation by 1985. Effects were felt from the late 1970‟s and since then the beach has retreated at between 0.5 - 3 m.yr-1. Erosion has encroached on beachfront properties since the early 1990‟s, leading to the placement of 3-4 m high unsightly rock revetments along much of the beach. Where properly maintained these structures have proved successful in protecting the properties behind, however exacerbated erosion of areas in front and adjacent to these structures is evident. Currently no dry beach is present at high tide for most of the year, leading to a significant reduction in beach amenity value. Several technical studies to investigate remediation of this beach erosion problem have been conducted since the early 1990‟s. This study includes investigations into the processes and dynamics of the existing environment and evaluation of the effectiveness and impacts of several elements of a hybrid approach to coastal protection and amenity enhancement for St Francis Bay beach. This proposal incorporated: Multi-Purpose Reefs (MPR‟s) offshore, for coastal protection and amenity enhancement in terms of surfing; beach nourishment with sand from the Kromme Estuary and dune rehabilitation with appropriate native sand binding species. Extensive fieldwork and data collection were conducted, this included: a series of bathymetric surveys; diving surveys and a helicopter flight; sediment sampling; beach profiling and deployment of a wave/current meter. Analysis of these data provided a greater understanding of the existing environment and dynamics of St Francis Bay and provided reliable inputs for numerical modelling. Numerical and physical modelling was conducted to assess the existing processes and conduct MPR design testing. In addition calibrated hydrodynamic modelling of the Kromme Estuary was conducted in order to assess the impacts of sand extraction from the large sand banks within the mouth of the Kromme Estuary for use as beach nourishment. Comparison of bathymetric survey data collected by the author in 2005/06 with survey data collected by the South African Navy Hydrographic Office (SANHO) in 1952 suggest a major loss of sand from the bay, with a volume difference of some 8.8 X 106 m3 calculated. Greater losses were measured between 10-15 m water depths, with shallow areas of +/- 5 m water depth, remaining more stable. This can be attributed to the presence of shallow reef and rocky substrate through much of the bay at this depth range. Monthly RTK GPS survey data from September 2006 to September 2007 indicates a total loss of 40 000 m3 over this period with the greatest losses measured along the northern part of the beach. The greatest losses were measured after large long period waves from a southerly to south-easterly direction occurred in conjunction with equinox tides in mid March 2007. Sediment sampling at over 100 locations within the bay indicated a high percentage of reef (26 percent) and fairly consistent grain size in the fine to medium size class throughout much of the beach, bay and large sand bank within the estuary. While the majority of the South African Coast is exposed to the predominant south westerly winds and waves, St Francis Bay‟s orientation means that waves from a south easterly to easterly direction dominate. The results of the detailed numerical modelling of the hydrodynamics agree with previous calculations and modelling results which concluded that strong unidirectional longshore currents occur along the headland due to the oblique angle of wave incidence and the close to parallel angle of wave incidence along the beach leads to weak longshore currents of variable direction. Erosion along St Francis Bay beach is a result of cross-shore erosion due to large waves from a southerly to easterly direction. Detached breakwaters are the most effective form of coastal protection in these environments and MPR‟s offer additional benefits over traditional breakwater structures. Results of empirical calculations and numerical modelling indicate that the MPR‟s will provide effective coastal protection through the processes of wave dissipation, wave rotation, salient formation and alteration of nearshore circulation. Physical modelling results allowed the MPR design to be assessed and refined in terms of surfing amenity enhancement and construction constraints. In addition numerical modelling results indicate that impacts due to the extraction of up to 600 000 m3 of sand from the lower Kromme Estuary result in highly localised velocity reduction, mainly limited to the extraction areas. The calculated rate of sediment influx into the lower Kromme Estuary indicates that limited extraction, in the order of 20 000 – 40 000 m3 per year, should be sustainable in the long term. Sedimentation of the lower estuary over recent years has had negative recreational and ecological impacts, through reduced navigability and water exchange respectively. Therefore both the estuary and beach systems prove to benefit from this approach. Although not investigated in detail as part of this study, evidence from numerous projects worldwide indicates that foredunes help to trap wind-blown sand on the beach and form a buffer to storm erosion, therefore dune rehabilitation with native sand-binding plant species was recommended as the third element of the proposed remediation of St Francis Bay beach.
- Full Text:
- Date Issued: 2008
- Authors: Anderson, Dylan Rory
- Date: 2008
- Subjects: Beach erosion -- South Africa -- St Francis Bay , Shore protection -- South Africa -- St Francis Bay , Restoration ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10611 , http://hdl.handle.net/10948/d1008192 , Beach erosion -- South Africa -- St Francis Bay , Shore protection -- South Africa -- St Francis Bay , Restoration ecology
- Description: The St Francis Bay beach has experienced chronic erosion over the past three decades. This erosion can largely be attributed to the stabilisation of a large coastal dunefield which contributed +/- 80 percent of the sand supply to St Francis Bay. Stabilisation began in 1975 initially using plant cuttings and followed by the development of the Santareme holiday suburb resulting in complete stabilisation by 1985. Effects were felt from the late 1970‟s and since then the beach has retreated at between 0.5 - 3 m.yr-1. Erosion has encroached on beachfront properties since the early 1990‟s, leading to the placement of 3-4 m high unsightly rock revetments along much of the beach. Where properly maintained these structures have proved successful in protecting the properties behind, however exacerbated erosion of areas in front and adjacent to these structures is evident. Currently no dry beach is present at high tide for most of the year, leading to a significant reduction in beach amenity value. Several technical studies to investigate remediation of this beach erosion problem have been conducted since the early 1990‟s. This study includes investigations into the processes and dynamics of the existing environment and evaluation of the effectiveness and impacts of several elements of a hybrid approach to coastal protection and amenity enhancement for St Francis Bay beach. This proposal incorporated: Multi-Purpose Reefs (MPR‟s) offshore, for coastal protection and amenity enhancement in terms of surfing; beach nourishment with sand from the Kromme Estuary and dune rehabilitation with appropriate native sand binding species. Extensive fieldwork and data collection were conducted, this included: a series of bathymetric surveys; diving surveys and a helicopter flight; sediment sampling; beach profiling and deployment of a wave/current meter. Analysis of these data provided a greater understanding of the existing environment and dynamics of St Francis Bay and provided reliable inputs for numerical modelling. Numerical and physical modelling was conducted to assess the existing processes and conduct MPR design testing. In addition calibrated hydrodynamic modelling of the Kromme Estuary was conducted in order to assess the impacts of sand extraction from the large sand banks within the mouth of the Kromme Estuary for use as beach nourishment. Comparison of bathymetric survey data collected by the author in 2005/06 with survey data collected by the South African Navy Hydrographic Office (SANHO) in 1952 suggest a major loss of sand from the bay, with a volume difference of some 8.8 X 106 m3 calculated. Greater losses were measured between 10-15 m water depths, with shallow areas of +/- 5 m water depth, remaining more stable. This can be attributed to the presence of shallow reef and rocky substrate through much of the bay at this depth range. Monthly RTK GPS survey data from September 2006 to September 2007 indicates a total loss of 40 000 m3 over this period with the greatest losses measured along the northern part of the beach. The greatest losses were measured after large long period waves from a southerly to south-easterly direction occurred in conjunction with equinox tides in mid March 2007. Sediment sampling at over 100 locations within the bay indicated a high percentage of reef (26 percent) and fairly consistent grain size in the fine to medium size class throughout much of the beach, bay and large sand bank within the estuary. While the majority of the South African Coast is exposed to the predominant south westerly winds and waves, St Francis Bay‟s orientation means that waves from a south easterly to easterly direction dominate. The results of the detailed numerical modelling of the hydrodynamics agree with previous calculations and modelling results which concluded that strong unidirectional longshore currents occur along the headland due to the oblique angle of wave incidence and the close to parallel angle of wave incidence along the beach leads to weak longshore currents of variable direction. Erosion along St Francis Bay beach is a result of cross-shore erosion due to large waves from a southerly to easterly direction. Detached breakwaters are the most effective form of coastal protection in these environments and MPR‟s offer additional benefits over traditional breakwater structures. Results of empirical calculations and numerical modelling indicate that the MPR‟s will provide effective coastal protection through the processes of wave dissipation, wave rotation, salient formation and alteration of nearshore circulation. Physical modelling results allowed the MPR design to be assessed and refined in terms of surfing amenity enhancement and construction constraints. In addition numerical modelling results indicate that impacts due to the extraction of up to 600 000 m3 of sand from the lower Kromme Estuary result in highly localised velocity reduction, mainly limited to the extraction areas. The calculated rate of sediment influx into the lower Kromme Estuary indicates that limited extraction, in the order of 20 000 – 40 000 m3 per year, should be sustainable in the long term. Sedimentation of the lower estuary over recent years has had negative recreational and ecological impacts, through reduced navigability and water exchange respectively. Therefore both the estuary and beach systems prove to benefit from this approach. Although not investigated in detail as part of this study, evidence from numerous projects worldwide indicates that foredunes help to trap wind-blown sand on the beach and form a buffer to storm erosion, therefore dune rehabilitation with native sand-binding plant species was recommended as the third element of the proposed remediation of St Francis Bay beach.
- Full Text:
- Date Issued: 2008
Adaptive user interfaces for mobile map-based visualisation
- Authors: Van Tonder, Bradley Paul
- Date: 2008
- Subjects: Cartography , Maps -- Design , Digital mapping , Geographic information systems , User interfaces (Computer systems) -- Design
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10470 , http://hdl.handle.net/10948/866 , Cartography , Maps -- Design , Digital mapping , Geographic information systems , User interfaces (Computer systems) -- Design
- Description: Mobile devices today frequently serve as platforms for the visualisation of map-based data. Despite the obvious advantages, mobile map-based visualisation (MMV) systems are often difficult to design and use. Limited screen space, resource constraints and awkward interaction mechanisms are among the many problems with which designers and users have to contend. Adaptive user interfaces (AUIs), which adapt to the individual user, represent a possible means of addressing the problems of MMV. Adaptive MMV systems are, however, generally designed in an ad-hoc fashion, making the benefits achieved difficult to replicate. In addition, existing models for adaptive MMV systems are either conceptual in nature or only address a subset of the possible input variables and adaptation effects. The primary objective of this research was to develop and evaluate an adaptive MMV system using a model-based approach. The Proteus Model was proposed to support the design of MMV systems which adapt in terms of information, visualisation and user interface in response to the user‟s behaviour, tasks and context. The Proteus Model describes the architectural, interface, data and algorithm design of an adaptive MMV system. A prototype adaptive MMV system, called MediaMaps, was designed and implemented based on the Proteus Model. MediaMaps allows users to capture, location-tag, organise and visualise multimedia on their mobile phones. Information adaptation is performed through the use of an algorithm to assist users in sorting media items into collections based on time and location. Visualisation adaptation is performed by adapting various parameters of the map-based visualisations according to user preferences. Interface adaptation is performed through the use of adaptive lists. An international field study of MediaMaps was conducted in which participants were required to use MediaMaps on their personal mobile phones for a period of three weeks. The results of the field study showed that high levels of accuracy were achieved by both the information and interface adaptations. High levels of user satisfaction were reported, with participants rating all three forms of adaptation as highly useful. The successful implementation of MediaMaps provides practical evidence that the model-based design of adaptive MMV systems is feasible. The positive results of the field study clearly show that the adaptations implemented were highly accurate and that participants found these adaptations to be useful, usable and easy to understand. This research thus provides empirical evidence that the use of AUIs can provide significant benefits for the visualisation of map-based information on mobile devices.
- Full Text:
- Date Issued: 2008
- Authors: Van Tonder, Bradley Paul
- Date: 2008
- Subjects: Cartography , Maps -- Design , Digital mapping , Geographic information systems , User interfaces (Computer systems) -- Design
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10470 , http://hdl.handle.net/10948/866 , Cartography , Maps -- Design , Digital mapping , Geographic information systems , User interfaces (Computer systems) -- Design
- Description: Mobile devices today frequently serve as platforms for the visualisation of map-based data. Despite the obvious advantages, mobile map-based visualisation (MMV) systems are often difficult to design and use. Limited screen space, resource constraints and awkward interaction mechanisms are among the many problems with which designers and users have to contend. Adaptive user interfaces (AUIs), which adapt to the individual user, represent a possible means of addressing the problems of MMV. Adaptive MMV systems are, however, generally designed in an ad-hoc fashion, making the benefits achieved difficult to replicate. In addition, existing models for adaptive MMV systems are either conceptual in nature or only address a subset of the possible input variables and adaptation effects. The primary objective of this research was to develop and evaluate an adaptive MMV system using a model-based approach. The Proteus Model was proposed to support the design of MMV systems which adapt in terms of information, visualisation and user interface in response to the user‟s behaviour, tasks and context. The Proteus Model describes the architectural, interface, data and algorithm design of an adaptive MMV system. A prototype adaptive MMV system, called MediaMaps, was designed and implemented based on the Proteus Model. MediaMaps allows users to capture, location-tag, organise and visualise multimedia on their mobile phones. Information adaptation is performed through the use of an algorithm to assist users in sorting media items into collections based on time and location. Visualisation adaptation is performed by adapting various parameters of the map-based visualisations according to user preferences. Interface adaptation is performed through the use of adaptive lists. An international field study of MediaMaps was conducted in which participants were required to use MediaMaps on their personal mobile phones for a period of three weeks. The results of the field study showed that high levels of accuracy were achieved by both the information and interface adaptations. High levels of user satisfaction were reported, with participants rating all three forms of adaptation as highly useful. The successful implementation of MediaMaps provides practical evidence that the model-based design of adaptive MMV systems is feasible. The positive results of the field study clearly show that the adaptations implemented were highly accurate and that participants found these adaptations to be useful, usable and easy to understand. This research thus provides empirical evidence that the use of AUIs can provide significant benefits for the visualisation of map-based information on mobile devices.
- Full Text:
- Date Issued: 2008
Alternative products in the inhibition of te plant pathogen scleroyinia sclerotiorum on potato production
- Authors: Dhliwayo, Tererayi
- Date: 2008
- Subjects: Potatoes -- Diseases and pests
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10587 , http://hdl.handle.net/10948/941 , Potatoes -- Diseases and pests
- Description: White mold caused by Sclerotinia sclerotiorum attacks a wide host range of broad-leafed plants which includes potatoes. Current control is limited to the use of chemicals, but biological control has emerged as an eco-friendly alternative. For the study, 19 bacterial strains and 18 fungal strains obtained from soil samples taken from a potato field naturally infested with the pathogen S. sclerotiorum were tested for the effects on S. sclerotiorum mycelium growth and sclerotia viability in vitro. A total of eight bacterial strains and six fungal strains proved to be effective in the inhibition of S. sclerotiorum mycelium growth on PDA plate using a dual culture technique. These antagonistic microbes were six Bacillus subtilis, Bacillus pumilis, Bacillus marisflavi, Fusarium solani, Fusarium equiseti, Fusarium chlamydosporum, Aspergillus niger, Aspergillus insuetus and Penicillium citrinum. There was a significant difference (p<0.05) in the interaction between S. sclerotiorum mycelium growth and the time after inoculation with a S. sclerotiorum mycelium plug for both bacterial and fungal soil isolates. An additional sclerotia viability test was carried out using four of the eight antagonistic bacteria, and six of the antagonistic fungi. The results showed that two Bacillus species, namely B. pumilis and B. marisflavi can effectively reduce sclerotia viability. The other two bacteria (both B. subtilis), recorded low percentage reduction in sclerotia viability. As for the six antagonistic fungi, the viability test proved to be less effective in determining sclerotia viability. However, the result of this study supports the use of bio-control agents, not only because they are environmentally friendly, but because they are also an effective way of controlling the plant pathogen, S. sclerotiorum.
- Full Text:
- Date Issued: 2008
- Authors: Dhliwayo, Tererayi
- Date: 2008
- Subjects: Potatoes -- Diseases and pests
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10587 , http://hdl.handle.net/10948/941 , Potatoes -- Diseases and pests
- Description: White mold caused by Sclerotinia sclerotiorum attacks a wide host range of broad-leafed plants which includes potatoes. Current control is limited to the use of chemicals, but biological control has emerged as an eco-friendly alternative. For the study, 19 bacterial strains and 18 fungal strains obtained from soil samples taken from a potato field naturally infested with the pathogen S. sclerotiorum were tested for the effects on S. sclerotiorum mycelium growth and sclerotia viability in vitro. A total of eight bacterial strains and six fungal strains proved to be effective in the inhibition of S. sclerotiorum mycelium growth on PDA plate using a dual culture technique. These antagonistic microbes were six Bacillus subtilis, Bacillus pumilis, Bacillus marisflavi, Fusarium solani, Fusarium equiseti, Fusarium chlamydosporum, Aspergillus niger, Aspergillus insuetus and Penicillium citrinum. There was a significant difference (p<0.05) in the interaction between S. sclerotiorum mycelium growth and the time after inoculation with a S. sclerotiorum mycelium plug for both bacterial and fungal soil isolates. An additional sclerotia viability test was carried out using four of the eight antagonistic bacteria, and six of the antagonistic fungi. The results showed that two Bacillus species, namely B. pumilis and B. marisflavi can effectively reduce sclerotia viability. The other two bacteria (both B. subtilis), recorded low percentage reduction in sclerotia viability. As for the six antagonistic fungi, the viability test proved to be less effective in determining sclerotia viability. However, the result of this study supports the use of bio-control agents, not only because they are environmentally friendly, but because they are also an effective way of controlling the plant pathogen, S. sclerotiorum.
- Full Text:
- Date Issued: 2008
An adaptive user interface model for contact centres
- Authors: Jason, Bronwin Anastasia
- Date: 2008
- Subjects: Call centers -- Management , Customer services -- Management , Call centers -- Customer services
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10467 , http://hdl.handle.net/10948/989 , Call centers -- Management , Customer services -- Management , Call centers -- Customer services
- Description: Contact centres (CC), are the primary interaction point between a company and its customers and these are rapidly expanding in terms of both workforce and economic scope. An important challenge for today's CC solutions is to increase the speed at which CCAs retrieve information to answer customer queries. CCAs, however, differ in their ability to respond to these queries and do not interact with the computer user interface (UI) in the same way as they each have different capabilities, experience and expertise. Studies have provided empirical support that user performance can be increased when the computer UI characteristics match the user skill level. Adaptive user interfaces (AUIs) are the key to creating personalised systems. Their sole task is to provide an interface most suitable to users' needs whilst facilitating the users' varying skill levels. The aim of this research was to develop an AUI model for CCs to support and improve the expertise level of CCAs. A literature review of CCs, user expertise, AUIs and existing AUI models resulted in the proposal of an AUI model for CCs. The proposed AUI model was described in terms of its architecture, component-level and interface design. An AUI prototype was developed as a proof-of-concept of the proposed AUI model. A literature review on existing AUI evaluation approaches resulted in an evaluation strategy for the proposed AUI model. The AUI prototype was evaluated according to the evaluation strategy that was identified. User testing incorporating eye-tracking and a post-test questionnaire was used to determine the usefulness and usability of the AUI prototype. Significant results were found with regards to user satisfaction ratings, the learnability of the AUI prototype and its effectiveness. This dissertation makes an important contribution in the design of an AUI model that supports and improves the expertise level of CCAs. The model could be used to assist the development of CC applications incorporating AUIs. Future research is however needed to evaluate the effect of the proposed AUI model in a larger CC environment.
- Full Text:
- Date Issued: 2008
- Authors: Jason, Bronwin Anastasia
- Date: 2008
- Subjects: Call centers -- Management , Customer services -- Management , Call centers -- Customer services
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10467 , http://hdl.handle.net/10948/989 , Call centers -- Management , Customer services -- Management , Call centers -- Customer services
- Description: Contact centres (CC), are the primary interaction point between a company and its customers and these are rapidly expanding in terms of both workforce and economic scope. An important challenge for today's CC solutions is to increase the speed at which CCAs retrieve information to answer customer queries. CCAs, however, differ in their ability to respond to these queries and do not interact with the computer user interface (UI) in the same way as they each have different capabilities, experience and expertise. Studies have provided empirical support that user performance can be increased when the computer UI characteristics match the user skill level. Adaptive user interfaces (AUIs) are the key to creating personalised systems. Their sole task is to provide an interface most suitable to users' needs whilst facilitating the users' varying skill levels. The aim of this research was to develop an AUI model for CCs to support and improve the expertise level of CCAs. A literature review of CCs, user expertise, AUIs and existing AUI models resulted in the proposal of an AUI model for CCs. The proposed AUI model was described in terms of its architecture, component-level and interface design. An AUI prototype was developed as a proof-of-concept of the proposed AUI model. A literature review on existing AUI evaluation approaches resulted in an evaluation strategy for the proposed AUI model. The AUI prototype was evaluated according to the evaluation strategy that was identified. User testing incorporating eye-tracking and a post-test questionnaire was used to determine the usefulness and usability of the AUI prototype. Significant results were found with regards to user satisfaction ratings, the learnability of the AUI prototype and its effectiveness. This dissertation makes an important contribution in the design of an AUI model that supports and improves the expertise level of CCAs. The model could be used to assist the development of CC applications incorporating AUIs. Future research is however needed to evaluate the effect of the proposed AUI model in a larger CC environment.
- Full Text:
- Date Issued: 2008
An overview of the management practices for wool production amongst the communal farmers of the Hewu district in the Eastern Cape Province
- Authors: Makapela, Mbulelo Joseph
- Date: 2008
- Subjects: Sheep industry -- South Africa -- Eastern Cape , Wool industry -- South Africa -- Eastern Cape , Sheep -- South Africa -- Eastern Cape -- Reproduction
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10734 , http://hdl.handle.net/10948/1009 , Sheep industry -- South Africa -- Eastern Cape , Wool industry -- South Africa -- Eastern Cape , Sheep -- South Africa -- Eastern Cape -- Reproduction
- Description: The research was conducted in the Hewu area situated between Queenstown (20 km) and Whittlesea (15km) in the Eastern Cape Province of South Africa. In this area communal farming is practiced. Livestock and livestock products (wool) are the main sources of income. The farmers are mainly farming with Merino and Döhne Merino sheep. The lack of management systems (production, reproduction and management) for communal farmers resulted into ineffective communal farming defining the research problem. The research objectives set were: • To establish production norms for wool sheep. • To establish reproduction norms for wool sheep. • To establish effective management practices for wool sheep farmers. • To examine key constraints of wool sheep farmers. The farmers shear their sheep every 12 months usually in October of every year. The average wool production per sheep is 2.17kg. The clip averages a fineness of 19.1-20 micron. That is far below the wool production of the commercial farmers of the Eastern Cape who are producing between 4kg to 5kg per sheep at an average growing period of 12 months. The lack of proper fencing and camps causes major reproduction problems. The lambing percentage of the ewes is 94.85 percent. The weaning percentage referring to the reproductive efficiency of the mated ewes is only 17.24 percent. The survival rate of the lambs born alive is only 18.18 percent. Reproduction is the biggest problem of communal farms. Effective livestock- and grazing management systems for communal areas are essential for the successful development of farmers on communal grazing areas. Unfortunately the Hewu farmers still have many problems effecting their wool production and the production of lambs.
- Full Text:
- Date Issued: 2008
- Authors: Makapela, Mbulelo Joseph
- Date: 2008
- Subjects: Sheep industry -- South Africa -- Eastern Cape , Wool industry -- South Africa -- Eastern Cape , Sheep -- South Africa -- Eastern Cape -- Reproduction
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10734 , http://hdl.handle.net/10948/1009 , Sheep industry -- South Africa -- Eastern Cape , Wool industry -- South Africa -- Eastern Cape , Sheep -- South Africa -- Eastern Cape -- Reproduction
- Description: The research was conducted in the Hewu area situated between Queenstown (20 km) and Whittlesea (15km) in the Eastern Cape Province of South Africa. In this area communal farming is practiced. Livestock and livestock products (wool) are the main sources of income. The farmers are mainly farming with Merino and Döhne Merino sheep. The lack of management systems (production, reproduction and management) for communal farmers resulted into ineffective communal farming defining the research problem. The research objectives set were: • To establish production norms for wool sheep. • To establish reproduction norms for wool sheep. • To establish effective management practices for wool sheep farmers. • To examine key constraints of wool sheep farmers. The farmers shear their sheep every 12 months usually in October of every year. The average wool production per sheep is 2.17kg. The clip averages a fineness of 19.1-20 micron. That is far below the wool production of the commercial farmers of the Eastern Cape who are producing between 4kg to 5kg per sheep at an average growing period of 12 months. The lack of proper fencing and camps causes major reproduction problems. The lambing percentage of the ewes is 94.85 percent. The weaning percentage referring to the reproductive efficiency of the mated ewes is only 17.24 percent. The survival rate of the lambs born alive is only 18.18 percent. Reproduction is the biggest problem of communal farms. Effective livestock- and grazing management systems for communal areas are essential for the successful development of farmers on communal grazing areas. Unfortunately the Hewu farmers still have many problems effecting their wool production and the production of lambs.
- Full Text:
- Date Issued: 2008
Analysis of the extended defects in 3C-SiC
- Authors: Olivier, Ezra Jacobus
- Date: 2008
- Subjects: Crystals -- Defects , Crystallography , Silicon carbide
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10525 , http://hdl.handle.net/10948/730 , Crystals -- Defects , Crystallography , Silicon carbide
- Description: The dissertation focuses on the analysis of the extended defects present in as-grown and proton bombarded β-SiC (annealed and unannealed) grown by chemical vapour deposition (CVD) on (001) Si. The proton irradiation was done to a dose of 2.8 × 1016 protons/cm2 and the annealing took place at 1300°C and 1600°C for 1hr. The main techniques used for the analysis were transmission electron microscopy (TEM) and high resolution TEM (HRTEM). From the diffraction study of the material the phase of the SiC was confirmed to be the cubic beta phase with the zinc-blende structure. The main defects found in the β- SiC were stacking faults (SFs) with their associated partial dislocations and microtwins. The SFs were uniformly distributed throughout the foil. The SFs were identified as having a fault vector of the type 1/3 <111> with bonding partial dislocations of the type 1/6 <121> by using image simulation. The SFs were also found to be predominantly extrinsic in nature by using HRTEM analysis of SFs viewed edge-on. Also both bright and dar-field images of SFs on inclined planes exhibited symmetrical and complementary fringe contrast images. This is a result of the anomalous absorption ratio of SiC lying between that of Si and diamond. The analysis of the annealed and unannealed irradiated β-SiC yielded no evidence of radiation damage or change in the crystal structure of the β-SiC. This confirmed that β-SiC is a radiation resistant material. The critical proton dose for the creation of small dislocation loops seems to be higher than for other compound semiconductors with the zinc-blende structure.
- Full Text:
- Date Issued: 2008
- Authors: Olivier, Ezra Jacobus
- Date: 2008
- Subjects: Crystals -- Defects , Crystallography , Silicon carbide
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10525 , http://hdl.handle.net/10948/730 , Crystals -- Defects , Crystallography , Silicon carbide
- Description: The dissertation focuses on the analysis of the extended defects present in as-grown and proton bombarded β-SiC (annealed and unannealed) grown by chemical vapour deposition (CVD) on (001) Si. The proton irradiation was done to a dose of 2.8 × 1016 protons/cm2 and the annealing took place at 1300°C and 1600°C for 1hr. The main techniques used for the analysis were transmission electron microscopy (TEM) and high resolution TEM (HRTEM). From the diffraction study of the material the phase of the SiC was confirmed to be the cubic beta phase with the zinc-blende structure. The main defects found in the β- SiC were stacking faults (SFs) with their associated partial dislocations and microtwins. The SFs were uniformly distributed throughout the foil. The SFs were identified as having a fault vector of the type 1/3 <111> with bonding partial dislocations of the type 1/6 <121> by using image simulation. The SFs were also found to be predominantly extrinsic in nature by using HRTEM analysis of SFs viewed edge-on. Also both bright and dar-field images of SFs on inclined planes exhibited symmetrical and complementary fringe contrast images. This is a result of the anomalous absorption ratio of SiC lying between that of Si and diamond. The analysis of the annealed and unannealed irradiated β-SiC yielded no evidence of radiation damage or change in the crystal structure of the β-SiC. This confirmed that β-SiC is a radiation resistant material. The critical proton dose for the creation of small dislocation loops seems to be higher than for other compound semiconductors with the zinc-blende structure.
- Full Text:
- Date Issued: 2008
Aspects of the breeding biology of the African penguin on Bird Island, Algoa Bay
- Authors: Ralph, Mark Shaun
- Date: 2008
- Subjects: Penguins -- South Africa -- Conservation , Penguins -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10716 , http://hdl.handle.net/10948/840 , Penguins -- South Africa -- Conservation , Penguins -- South Africa
- Description: It is important to the survival of the Africa Penguin (Spheniscus demersus) population that breeding at the nest site is successful and that large numbers of chicks are fledged into the breeding population. Nest distribution on Bird Island is not random and locality preferences for breeding exist. Although it seems that sufficient area exists on Bird Island for penguin nests, it can hardly be considered as suitable to optimise breeding. During prolonged heat conditions, breeders relocated to nest sites that were sheltered. Nests that were below ground in burrows was the only habitat that did not suffer nest desertion whilst all the other habitat types (including those that were sheltered) experienced 2-3 fold declines in nest numbers. Nests density and the selection of suitable nest sites are significantly influenced by the stage of breeding that the majority of birds are in, yet nests that are shaded, well-ventilated and protected seem to be the most preferred sites for breeding. Adults that attempt to breed are considered then to be in a healthy condition and will usually lay a double clutch (Randell 1983). The frequency of double clutches being laid during the peak breeding attempt was significantly higher compared to the replacement one. Breeding failure was fairly similar to breeding success during the incubation stage for nests with double clutches however, was substantially higher in single clutches. The growth rate of chicks was best fit to the von Bertalanffy growth curve in 90 percent of the cases. The overall growth rate of chicks from double broods was faster than from single broods, however was not significant. A-chicks maitain a high growth rate until they fledged. Yet, the sibling B-chick recorded the lowest growth rate of the successfully fledged chicks and up to until day 30 recorded a similar weight to those chicks that failed to fledge. Contrary to findings of Randall (1983), chicks from single broods delayed fledging, recorded lowest overall growth rates and experienced the greatest weight loss of all groups, yet fledged successfully. In order for chicks to fledge successfully, they needed to obtain a weight of 1060 g before day 30.5 in their growth cycles to avoid death due to startvation later on. Single chicks that are raised from a double cluth, fledged more other than chicks raised from a single clutch. Unfit or ill-adapted breeders that are marginal in the capabilities of raising offspring, already manifest in a small clutch size and offspring unable to obtain adequate weights during the initial stages of growth.
- Full Text:
- Date Issued: 2008
- Authors: Ralph, Mark Shaun
- Date: 2008
- Subjects: Penguins -- South Africa -- Conservation , Penguins -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10716 , http://hdl.handle.net/10948/840 , Penguins -- South Africa -- Conservation , Penguins -- South Africa
- Description: It is important to the survival of the Africa Penguin (Spheniscus demersus) population that breeding at the nest site is successful and that large numbers of chicks are fledged into the breeding population. Nest distribution on Bird Island is not random and locality preferences for breeding exist. Although it seems that sufficient area exists on Bird Island for penguin nests, it can hardly be considered as suitable to optimise breeding. During prolonged heat conditions, breeders relocated to nest sites that were sheltered. Nests that were below ground in burrows was the only habitat that did not suffer nest desertion whilst all the other habitat types (including those that were sheltered) experienced 2-3 fold declines in nest numbers. Nests density and the selection of suitable nest sites are significantly influenced by the stage of breeding that the majority of birds are in, yet nests that are shaded, well-ventilated and protected seem to be the most preferred sites for breeding. Adults that attempt to breed are considered then to be in a healthy condition and will usually lay a double clutch (Randell 1983). The frequency of double clutches being laid during the peak breeding attempt was significantly higher compared to the replacement one. Breeding failure was fairly similar to breeding success during the incubation stage for nests with double clutches however, was substantially higher in single clutches. The growth rate of chicks was best fit to the von Bertalanffy growth curve in 90 percent of the cases. The overall growth rate of chicks from double broods was faster than from single broods, however was not significant. A-chicks maitain a high growth rate until they fledged. Yet, the sibling B-chick recorded the lowest growth rate of the successfully fledged chicks and up to until day 30 recorded a similar weight to those chicks that failed to fledge. Contrary to findings of Randall (1983), chicks from single broods delayed fledging, recorded lowest overall growth rates and experienced the greatest weight loss of all groups, yet fledged successfully. In order for chicks to fledge successfully, they needed to obtain a weight of 1060 g before day 30.5 in their growth cycles to avoid death due to startvation later on. Single chicks that are raised from a double cluth, fledged more other than chicks raised from a single clutch. Unfit or ill-adapted breeders that are marginal in the capabilities of raising offspring, already manifest in a small clutch size and offspring unable to obtain adequate weights during the initial stages of growth.
- Full Text:
- Date Issued: 2008
Characterization of polarization dependent loss in optical fibres and optical components in the presence of polarization mode dispersion
- Authors: Pelaelo, Gaoboelwe
- Date: 2008
- Subjects: Fiber optics , Polarization (Light)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10528 , http://hdl.handle.net/10948/695 , Fiber optics , Polarization (Light)
- Description: In this study, the Jones matrix eigenanalysis (JME), optical spectrum analyzer (OSA) and polarization scrambling methods were used to investigate polarization dependent loss (PDL) in the presence of polarization mode dispersion (PMD) in optical components and fibres. The PDL measurements were conducted both in the laboratory and in the field. For field measurements, a buried link (28.8 km) and an aerial fibre (7.1 km) were extensively studied. The findings obtained from these studies are very important for network operators who must assess the impact of PDL on the network reliability. The three different PDL measurement methods (JME, OSA and polarization scrambling) were compared and their PDL values were found to agree very well at the selected wavelength of 1550 nm. Concatenation of PDL components showed that as expected, PDL increase as the number of PDL components were added. The interactions between PMD and PDL measurements were analyzed. A PMD/PDL emulator was constructed. We observed that PMD decreased while PDL increased. The PMD decrease was a result of the PMD vector cancellation enhanced by the randomly distributed mode coupling angles while PDL increase was a result of each PM fibre segments contributing to the overall global PDL. It was observed that the presence of PMD in a link containing PDL, results in PDL being wavelength dependent and this resulted in the extraction of the PMD information from the PDL data. PDL was found to be Maxwellian distributed when considering low values of PMD. High PMD values resulted in the PDL distribution deviating from Maxwellian. Long-term PDL and PMD (average DGD) measurements indicated that the PDL and PMD varied slowly with time and wavelength for both the laboratory and field measurements. It was observed that the BER increase as both PDL and PMD increased for simulated optical link.
- Full Text:
- Date Issued: 2008
- Authors: Pelaelo, Gaoboelwe
- Date: 2008
- Subjects: Fiber optics , Polarization (Light)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10528 , http://hdl.handle.net/10948/695 , Fiber optics , Polarization (Light)
- Description: In this study, the Jones matrix eigenanalysis (JME), optical spectrum analyzer (OSA) and polarization scrambling methods were used to investigate polarization dependent loss (PDL) in the presence of polarization mode dispersion (PMD) in optical components and fibres. The PDL measurements were conducted both in the laboratory and in the field. For field measurements, a buried link (28.8 km) and an aerial fibre (7.1 km) were extensively studied. The findings obtained from these studies are very important for network operators who must assess the impact of PDL on the network reliability. The three different PDL measurement methods (JME, OSA and polarization scrambling) were compared and their PDL values were found to agree very well at the selected wavelength of 1550 nm. Concatenation of PDL components showed that as expected, PDL increase as the number of PDL components were added. The interactions between PMD and PDL measurements were analyzed. A PMD/PDL emulator was constructed. We observed that PMD decreased while PDL increased. The PMD decrease was a result of the PMD vector cancellation enhanced by the randomly distributed mode coupling angles while PDL increase was a result of each PM fibre segments contributing to the overall global PDL. It was observed that the presence of PMD in a link containing PDL, results in PDL being wavelength dependent and this resulted in the extraction of the PMD information from the PDL data. PDL was found to be Maxwellian distributed when considering low values of PMD. High PMD values resulted in the PDL distribution deviating from Maxwellian. Long-term PDL and PMD (average DGD) measurements indicated that the PDL and PMD varied slowly with time and wavelength for both the laboratory and field measurements. It was observed that the BER increase as both PDL and PMD increased for simulated optical link.
- Full Text:
- Date Issued: 2008
Characterization of polarization effects on deployed aerial optical fibre in South Africa
- Authors: Mudau, Azwitamisi Eric
- Date: 2008
- Subjects: Polarization (Light) , Fiber optics
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10521 , http://hdl.handle.net/10948/1060 , Polarization (Light) , Fiber optics
- Description: In this study, two polarization effects, namely the state of polarization (SOP) and polarization mode dispersion (PMD) in optical fibre cable are investigated. The change in polarization effects introduces errors in optical fibre communication system. We find that the SOP drifts slowly in buried cables, and rapidly in aerial cables. This is because buried cables are located in a static environment, whereas aerial cables are exposed directly to a dynamic environment. The SOP change in aerial cable shows significant correlation with its environment (the global radiation, temperature and wind). The autocorrelation function (ACF) was not performed in buried cable, since they do not satisfy the ACF assumption, whereas in aerial cable it is found that the ACF of the SOP decorrelates quite quickly during the day. The 50 percent decorrelation time during the day and night are 9.6 and 30.4 minutes, respectively. During the day the properties of the optical fibre change rapidly as a result of the rapidly changing environmental conditions, whereas at night the environmental conditions change relatively slowly. Fast Fourier Transform (FFT) of the SOP fluctuations show discrete peaks, which corresponds to the wind induced vibrational frequency of the cable. The PMD fluctuations for undeployed and deployed aerial optical fibre cable are monitored using the generalized interferometric technique (GINTY). It is found that the PMD measured with polarization scrambling is more scattered but more reliable than the PMD measured without polarization scrambling. This is because the PMD obtained with polarization scrambling is averaged over different input and output (I/O) SOP pairs. For deployed aerial cable, it is found that the PMD measured without polarization scrambling fluctuates rapidly during high wind speed conditions. Furthermore, there is a correlation between the measured PMD and the change in temperature. It is found that the change in temperature has a stronger influence than the wind on the PMD of the optical fibre link.
- Full Text:
- Date Issued: 2008
- Authors: Mudau, Azwitamisi Eric
- Date: 2008
- Subjects: Polarization (Light) , Fiber optics
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10521 , http://hdl.handle.net/10948/1060 , Polarization (Light) , Fiber optics
- Description: In this study, two polarization effects, namely the state of polarization (SOP) and polarization mode dispersion (PMD) in optical fibre cable are investigated. The change in polarization effects introduces errors in optical fibre communication system. We find that the SOP drifts slowly in buried cables, and rapidly in aerial cables. This is because buried cables are located in a static environment, whereas aerial cables are exposed directly to a dynamic environment. The SOP change in aerial cable shows significant correlation with its environment (the global radiation, temperature and wind). The autocorrelation function (ACF) was not performed in buried cable, since they do not satisfy the ACF assumption, whereas in aerial cable it is found that the ACF of the SOP decorrelates quite quickly during the day. The 50 percent decorrelation time during the day and night are 9.6 and 30.4 minutes, respectively. During the day the properties of the optical fibre change rapidly as a result of the rapidly changing environmental conditions, whereas at night the environmental conditions change relatively slowly. Fast Fourier Transform (FFT) of the SOP fluctuations show discrete peaks, which corresponds to the wind induced vibrational frequency of the cable. The PMD fluctuations for undeployed and deployed aerial optical fibre cable are monitored using the generalized interferometric technique (GINTY). It is found that the PMD measured with polarization scrambling is more scattered but more reliable than the PMD measured without polarization scrambling. This is because the PMD obtained with polarization scrambling is averaged over different input and output (I/O) SOP pairs. For deployed aerial cable, it is found that the PMD measured without polarization scrambling fluctuates rapidly during high wind speed conditions. Furthermore, there is a correlation between the measured PMD and the change in temperature. It is found that the change in temperature has a stronger influence than the wind on the PMD of the optical fibre link.
- Full Text:
- Date Issued: 2008
Constructing confidence intervals for polarization mode dispersion
- Authors: Erlank, Warrick
- Date: 2008
- Subjects: Fiber optics , Polarization (Light)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10571 , http://hdl.handle.net/10948/951 , Fiber optics , Polarization (Light)
- Description: Polarization mode dispersion (PMD) causes significant impairment in high bit-rate optical telecommunications systems. Knowledge of a fibre’s PMD mean value, and the relevant confidence interval, is essential for determining a fibre’s maximum allowable bit-rate. Various methods of confidence interval construction for time series data were tested in this dissertation using simulation. These included the autocovariance-matrix methods as suggested by Box and Jenkins, as well as the more practical and simpler batch means methods. Some of these methods were shown to be significantly better than the standard method of calculating confidence intervals for non time series data. The best of the tested methods were used on actual PMD data. The effect of using polarization scramblers was also tested.
- Full Text:
- Date Issued: 2008
- Authors: Erlank, Warrick
- Date: 2008
- Subjects: Fiber optics , Polarization (Light)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10571 , http://hdl.handle.net/10948/951 , Fiber optics , Polarization (Light)
- Description: Polarization mode dispersion (PMD) causes significant impairment in high bit-rate optical telecommunications systems. Knowledge of a fibre’s PMD mean value, and the relevant confidence interval, is essential for determining a fibre’s maximum allowable bit-rate. Various methods of confidence interval construction for time series data were tested in this dissertation using simulation. These included the autocovariance-matrix methods as suggested by Box and Jenkins, as well as the more practical and simpler batch means methods. Some of these methods were shown to be significantly better than the standard method of calculating confidence intervals for non time series data. The best of the tested methods were used on actual PMD data. The effect of using polarization scramblers was also tested.
- Full Text:
- Date Issued: 2008
Development of platinum metal specific separating agents
- Authors: Jonck, Heine
- Date: 2008
- Subjects: Platinum , Platinum -- Separation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10401 , http://hdl.handle.net/10948/712 , Platinum , Platinum -- Separation
- Description: In this dissertation, the aim was to develop a platinum specific resin to be utilized for the early removal of platinum from the industrial feed solution. Efforts were therefore directed towards the syntheses of silica based resins, with active centra, designed for platinum. The large chlorometallate ions present in the feed stream, were characterized in terms of physical parameters relevant to phase distribution, namely distortability (RD), charge density, softness (σ) etc. Matching cations for each of the types were investigated. In order to attempt the design of platinum specific resins, different structural amines were used to aminate the silicone precursor and to subsequently fix these onto the silica framework. Two different solvents namely alcohol and dmf were used in this process, resulting in two sets of resins, with different properties. The design was based on previous experience with these ions, with reference to their behaviour towards different types of cations. The platinum species, PtCl6 2- and PtCl4 2-, as well as the most important contaminants in the feed stream, were typified, bearing in mind size, charge, charge density and distortability. Different types of cationic centra, having differences in charge density, stereochemical crowding and extent of hydrophobicity, were synthesized and tested-both as solvent extractants (where possible) and silica based resins. The results indicated that, partly screened secondary ammonium cationic resin species, which could be regarded as “intermediate”, proved to be satisfactory both in their high percentage extraction for PtCl4 2- and rejection of contaminants like chlororhodates, chloroiridates(III) and FeCl4 -. It was however necessary, to work at a redox potential, where iridium(IV) in the form of IrCl6 2-, was absent. Various 2-aminoalkane resins were prepared, with variation in the length of alkane group and synthesised by the two different solvents. The latter resulted in two sets of resins with not only differing compactness, but also having significantly different properties with reference to platinum specificity, HCl effect and stripping potential. The 2-aminobutane and 2-aminoheptane resins in particular, proved to be very satisfactory platinum specific resins, both with respect to selectivity, platinum capacity and stripping potential. The various physical parameters could be applied to identify the chemical behaviour of anions and assist in the development of anion specificity for the relevant species.
- Full Text:
- Date Issued: 2008
- Authors: Jonck, Heine
- Date: 2008
- Subjects: Platinum , Platinum -- Separation
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10401 , http://hdl.handle.net/10948/712 , Platinum , Platinum -- Separation
- Description: In this dissertation, the aim was to develop a platinum specific resin to be utilized for the early removal of platinum from the industrial feed solution. Efforts were therefore directed towards the syntheses of silica based resins, with active centra, designed for platinum. The large chlorometallate ions present in the feed stream, were characterized in terms of physical parameters relevant to phase distribution, namely distortability (RD), charge density, softness (σ) etc. Matching cations for each of the types were investigated. In order to attempt the design of platinum specific resins, different structural amines were used to aminate the silicone precursor and to subsequently fix these onto the silica framework. Two different solvents namely alcohol and dmf were used in this process, resulting in two sets of resins, with different properties. The design was based on previous experience with these ions, with reference to their behaviour towards different types of cations. The platinum species, PtCl6 2- and PtCl4 2-, as well as the most important contaminants in the feed stream, were typified, bearing in mind size, charge, charge density and distortability. Different types of cationic centra, having differences in charge density, stereochemical crowding and extent of hydrophobicity, were synthesized and tested-both as solvent extractants (where possible) and silica based resins. The results indicated that, partly screened secondary ammonium cationic resin species, which could be regarded as “intermediate”, proved to be satisfactory both in their high percentage extraction for PtCl4 2- and rejection of contaminants like chlororhodates, chloroiridates(III) and FeCl4 -. It was however necessary, to work at a redox potential, where iridium(IV) in the form of IrCl6 2-, was absent. Various 2-aminoalkane resins were prepared, with variation in the length of alkane group and synthesised by the two different solvents. The latter resulted in two sets of resins with not only differing compactness, but also having significantly different properties with reference to platinum specificity, HCl effect and stripping potential. The 2-aminobutane and 2-aminoheptane resins in particular, proved to be very satisfactory platinum specific resins, both with respect to selectivity, platinum capacity and stripping potential. The various physical parameters could be applied to identify the chemical behaviour of anions and assist in the development of anion specificity for the relevant species.
- Full Text:
- Date Issued: 2008
Diet and feeding effects of introduced giraffe in the Eastern Cape
- Authors: Jacobs, Evert Philippus
- Date: 2008
- Subjects: Giraffe -- Food -- South Africa -- Eastern Cape , Giraffe -- Ecology -- South Africa -- Eastern Cape , Animal-plant relationships -- South Africa -- Eastern Cape , Introduced mammals -- Ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10703 , http://hdl.handle.net/10948/964 , Giraffe -- Food -- South Africa -- Eastern Cape , Giraffe -- Ecology -- South Africa -- Eastern Cape , Animal-plant relationships -- South Africa -- Eastern Cape , Introduced mammals -- Ecology -- South Africa -- Eastern Cape
- Description: This study presents the results of a study on introduced giraffe diet and feeding effects within the Eastern Cape Province of South Africa. Five sites were selected over a moisture gradient from the mesic east to the arid west of the Eastern Cape to describe giraffe diet and provide baseline data for feeding effect experiments. At each site faecal samples were collected seasonally and diet composition determined by microhistological analysis. Plant species availability was measured using the point intersect method in order to compare plant availability to plant consumption to determine diet preferences. Giraffe diet across the sites showed a unimodal response to rainfall by utilising fewer species in drier areas where plant availability is low and increasing the number of species consumed as the rainfall increases. In higher rainfall areas, giraffe reduced the number of plant species fed upon because of the high availability of important species that reduces the need for a varied diet. Across all sites, plant availability was dominated by woody plant species (more than 90 percent at each site). A total of 57 plants species were recorded as being eaten across the five sites. Several PDI (Principle Diet Items) plant species (Acacia karroo, Schotia afra, Pappea capensis and Euclea undulata) were eaten across sites. Over all the sites, significantly preferred species were Asparagus striatus, Schotia latifolia, Asparagus suaveolens, Commelina benghalensis, Viscum rotundifolium, and Acacia cyclops. Acacia karroo, Schotia afra, Pappea capensis, Rhus crenata, A. tetracantha, and Grewia robusta were utilised in proportion to their availability. Euclea undulata, Rhus longispina and Putterlickia pyracantha were avoided. Feeding effects were tested by erecting exclosures around trees, covering one half of each tree. Ten trees were selected for these manipulative experiments which ran from September 2003 to February 2005. The number of branches, number of leaves, branch orders, branch diameter, branch length, leaf length and leaf width were measured for ten samples per side (enclosed vs. exposed) and analysed using a Wilcoxon matched pairs test and tested for effect size using Cohen’s d. Although no significant differences were detected between the sides measured, the effect size indicated differences in all measurements between sides ranging from low to moderate. Leaf length was greater on the outside of exclosures and showed a moderate difference between the sides in terms of the d-value with the p-value (0.059) tending towards significance. Although leaf width was higher on the inside of exclosures, it only showed a moderate difference for d with no statistical significance. Leaf area was higher on the inside of exclosures and tended to significance (p = 0.059) and similarly the d value indicated moderate differences between the sides in terms of effect size. Similarly branch length was higher on the inside of exclosures although not significantly, the p-value (0.07) approached significance. The effect size for branch length also showed a moderate difference between the sides. The number of branches and the number of leaves showed no statistical differences between the sides although the p-value (0.059) for the number of branches, as well as number of leaves (p = 0.07) approached significance. For both these variables, effect size showed a moderate difference. Giraffe showed diversity in their diet selection across sites but mainly fed upon available species. Some preferred species were however less available and this preference could possibly result in increased pressure on the selected plant species Exclosure experiments showed no significant differences in leaf and shoot characteristics although all measurements showed differences in terms of effect size meriting further investigation. It is concluded that giraffe impact on sites may be reduced if populations are properly managed however, high densities of giraffe could lead to similar vegetation impacts as observed in other areas where giraffe have been introduced and potentially change vegetation structure and plant community composition.
- Full Text:
- Date Issued: 2008
- Authors: Jacobs, Evert Philippus
- Date: 2008
- Subjects: Giraffe -- Food -- South Africa -- Eastern Cape , Giraffe -- Ecology -- South Africa -- Eastern Cape , Animal-plant relationships -- South Africa -- Eastern Cape , Introduced mammals -- Ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10703 , http://hdl.handle.net/10948/964 , Giraffe -- Food -- South Africa -- Eastern Cape , Giraffe -- Ecology -- South Africa -- Eastern Cape , Animal-plant relationships -- South Africa -- Eastern Cape , Introduced mammals -- Ecology -- South Africa -- Eastern Cape
- Description: This study presents the results of a study on introduced giraffe diet and feeding effects within the Eastern Cape Province of South Africa. Five sites were selected over a moisture gradient from the mesic east to the arid west of the Eastern Cape to describe giraffe diet and provide baseline data for feeding effect experiments. At each site faecal samples were collected seasonally and diet composition determined by microhistological analysis. Plant species availability was measured using the point intersect method in order to compare plant availability to plant consumption to determine diet preferences. Giraffe diet across the sites showed a unimodal response to rainfall by utilising fewer species in drier areas where plant availability is low and increasing the number of species consumed as the rainfall increases. In higher rainfall areas, giraffe reduced the number of plant species fed upon because of the high availability of important species that reduces the need for a varied diet. Across all sites, plant availability was dominated by woody plant species (more than 90 percent at each site). A total of 57 plants species were recorded as being eaten across the five sites. Several PDI (Principle Diet Items) plant species (Acacia karroo, Schotia afra, Pappea capensis and Euclea undulata) were eaten across sites. Over all the sites, significantly preferred species were Asparagus striatus, Schotia latifolia, Asparagus suaveolens, Commelina benghalensis, Viscum rotundifolium, and Acacia cyclops. Acacia karroo, Schotia afra, Pappea capensis, Rhus crenata, A. tetracantha, and Grewia robusta were utilised in proportion to their availability. Euclea undulata, Rhus longispina and Putterlickia pyracantha were avoided. Feeding effects were tested by erecting exclosures around trees, covering one half of each tree. Ten trees were selected for these manipulative experiments which ran from September 2003 to February 2005. The number of branches, number of leaves, branch orders, branch diameter, branch length, leaf length and leaf width were measured for ten samples per side (enclosed vs. exposed) and analysed using a Wilcoxon matched pairs test and tested for effect size using Cohen’s d. Although no significant differences were detected between the sides measured, the effect size indicated differences in all measurements between sides ranging from low to moderate. Leaf length was greater on the outside of exclosures and showed a moderate difference between the sides in terms of the d-value with the p-value (0.059) tending towards significance. Although leaf width was higher on the inside of exclosures, it only showed a moderate difference for d with no statistical significance. Leaf area was higher on the inside of exclosures and tended to significance (p = 0.059) and similarly the d value indicated moderate differences between the sides in terms of effect size. Similarly branch length was higher on the inside of exclosures although not significantly, the p-value (0.07) approached significance. The effect size for branch length also showed a moderate difference between the sides. The number of branches and the number of leaves showed no statistical differences between the sides although the p-value (0.059) for the number of branches, as well as number of leaves (p = 0.07) approached significance. For both these variables, effect size showed a moderate difference. Giraffe showed diversity in their diet selection across sites but mainly fed upon available species. Some preferred species were however less available and this preference could possibly result in increased pressure on the selected plant species Exclosure experiments showed no significant differences in leaf and shoot characteristics although all measurements showed differences in terms of effect size meriting further investigation. It is concluded that giraffe impact on sites may be reduced if populations are properly managed however, high densities of giraffe could lead to similar vegetation impacts as observed in other areas where giraffe have been introduced and potentially change vegetation structure and plant community composition.
- Full Text:
- Date Issued: 2008
Equiprime near-rings
- Authors: Mogae, Kabelo
- Date: 2008
- Subjects: Near-rings
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10505 , http://hdl.handle.net/10948/1028 , Near-rings
- Description: Prior to 1990, the only well known ideal-hereditary Kurosh-Amitsur radicals in the variety of zero-symmetric near-rings were the Jacobson type radicals Iv(N) , where ∨∈{2,3} and the Brown-McCoy radical. In 1990, Booth, Groenewald and Veldsman introduced the concept of an equiprime near-ring which leads to an ideal-hereditary Kurosh-Amitsur radical in N∘. The concept of an equiprime near-ring generalizes the concept of a prime ring to near-rings. Although the search for more ideal-hereditary radicals of near-rings was apparently the original motivation for the introduction of equiprime near-rings, it became clear that these near-rings are interesting in their own right. It is our aim in this treatise to give an exposition of the many interesting properties of equiprime near-rings. We begin with a brief reminder of near-ring rudiments; giving basic definitions and elementary results which are necessary for understanding and development of subsequent chapters. With the basics out of the way, our main task begins with a consideration of equiprime, strongly and completely equiprime left ideals. It is noted that any zero-symmetric near-ring can be embedded in an equiprime near-ring. Moreover, the class of equiprime near-rings is shown to be hereditary. Open questions arising out of the study of equiprime near-rings are highlighted along the way. In Chapter 3 we consider well known examples of near-rings and determine when such near-rings are equiprime. This provides more insight into the nature of equiprime near-rings and is a fertile ground for the birth of examples and counterexamples which may be used to close or solve some open question within the literature. We also prove some results which generalize some results of Booth and Hall [10] and Veldsman [29]. These results have not been previously presented elsewhere to the best of our knowledge. vii In Chapter 4, the equiprime near-rings are shown to yield an ideal-hereditary radical in N∘. It is shown that a special radical theory can be built on the equiprime nearrings in much the same way prime rings are used in ring theory to define special radical classes of rings.
- Full Text:
- Date Issued: 2008
- Authors: Mogae, Kabelo
- Date: 2008
- Subjects: Near-rings
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10505 , http://hdl.handle.net/10948/1028 , Near-rings
- Description: Prior to 1990, the only well known ideal-hereditary Kurosh-Amitsur radicals in the variety of zero-symmetric near-rings were the Jacobson type radicals Iv(N) , where ∨∈{2,3} and the Brown-McCoy radical. In 1990, Booth, Groenewald and Veldsman introduced the concept of an equiprime near-ring which leads to an ideal-hereditary Kurosh-Amitsur radical in N∘. The concept of an equiprime near-ring generalizes the concept of a prime ring to near-rings. Although the search for more ideal-hereditary radicals of near-rings was apparently the original motivation for the introduction of equiprime near-rings, it became clear that these near-rings are interesting in their own right. It is our aim in this treatise to give an exposition of the many interesting properties of equiprime near-rings. We begin with a brief reminder of near-ring rudiments; giving basic definitions and elementary results which are necessary for understanding and development of subsequent chapters. With the basics out of the way, our main task begins with a consideration of equiprime, strongly and completely equiprime left ideals. It is noted that any zero-symmetric near-ring can be embedded in an equiprime near-ring. Moreover, the class of equiprime near-rings is shown to be hereditary. Open questions arising out of the study of equiprime near-rings are highlighted along the way. In Chapter 3 we consider well known examples of near-rings and determine when such near-rings are equiprime. This provides more insight into the nature of equiprime near-rings and is a fertile ground for the birth of examples and counterexamples which may be used to close or solve some open question within the literature. We also prove some results which generalize some results of Booth and Hall [10] and Veldsman [29]. These results have not been previously presented elsewhere to the best of our knowledge. vii In Chapter 4, the equiprime near-rings are shown to yield an ideal-hereditary radical in N∘. It is shown that a special radical theory can be built on the equiprime nearrings in much the same way prime rings are used in ring theory to define special radical classes of rings.
- Full Text:
- Date Issued: 2008
Faktore wat die oorlewing van volstruiskuikens (Struthio Camelus) verhoog
- Authors: Janse Van Vuuren, Maryke
- Date: 2008
- Subjects: Ostrich farming -- South Africa , Ostriches -- Breeding -- South Africa
- Language: Afrikaans
- Type: Thesis , Masters , MTech
- Identifier: vital:10588 , http://hdl.handle.net/10948/848 , Ostrich farming -- South Africa , Ostriches -- Breeding -- South Africa
- Description: Hierdie verhandeling is ‘n samestelling van verskeie studies, elk opgeskryf in die formaat en styl soos vereis deur die Suid-Afrikaanse Vereeniging vir Diereproduksie (South African Society of Animal Science). Hoofstuk 1 is ‘n literatuurstudie bestaande uit ‘n algemene inleiding wat agtergrond oor die studie verskaf en sluit die probleemstelling in, naamlik die swak oorlewing van volstruiskuikens wat onder kunsmatige toestande grootgemaak word. Hoofstukke 2, 3, 4 en 5 bestaan uit die eerste vier studies, waartydens sekere bestuurs-aspekte, wat moontlik oorlewing van volstruiskuikens kan verbeter (nl: populasiedigtheid, tipe vloer-oppervlak, die aanwending van broeipare en die aanwending van peetouers), ondersoek is. Hoofstukke 6, 7, 8 & 9 handel oor studies wat gerig is om voeding meer aanloklik te maak vir volstruiskuikens teneinde voedselinname te stimuleer en sodoende produksie en oorlewing te verbeter (nl: verskaffing van groenvoer, geur van voer, kleur van voer en beligting van voer). Die laaste hoofstuk bestaan uit ‘n algemene gevolgtrekking en aanbevelings. Alhoewel daar gepoog is om herhaling in hoofstukke te beperk, was dit onmoontlik om herhaling van sekere gedeeltes van hoofstukke te voorkom.
- Full Text:
- Date Issued: 2008
- Authors: Janse Van Vuuren, Maryke
- Date: 2008
- Subjects: Ostrich farming -- South Africa , Ostriches -- Breeding -- South Africa
- Language: Afrikaans
- Type: Thesis , Masters , MTech
- Identifier: vital:10588 , http://hdl.handle.net/10948/848 , Ostrich farming -- South Africa , Ostriches -- Breeding -- South Africa
- Description: Hierdie verhandeling is ‘n samestelling van verskeie studies, elk opgeskryf in die formaat en styl soos vereis deur die Suid-Afrikaanse Vereeniging vir Diereproduksie (South African Society of Animal Science). Hoofstuk 1 is ‘n literatuurstudie bestaande uit ‘n algemene inleiding wat agtergrond oor die studie verskaf en sluit die probleemstelling in, naamlik die swak oorlewing van volstruiskuikens wat onder kunsmatige toestande grootgemaak word. Hoofstukke 2, 3, 4 en 5 bestaan uit die eerste vier studies, waartydens sekere bestuurs-aspekte, wat moontlik oorlewing van volstruiskuikens kan verbeter (nl: populasiedigtheid, tipe vloer-oppervlak, die aanwending van broeipare en die aanwending van peetouers), ondersoek is. Hoofstukke 6, 7, 8 & 9 handel oor studies wat gerig is om voeding meer aanloklik te maak vir volstruiskuikens teneinde voedselinname te stimuleer en sodoende produksie en oorlewing te verbeter (nl: verskaffing van groenvoer, geur van voer, kleur van voer en beligting van voer). Die laaste hoofstuk bestaan uit ‘n algemene gevolgtrekking en aanbevelings. Alhoewel daar gepoog is om herhaling in hoofstukke te beperk, was dit onmoontlik om herhaling van sekere gedeeltes van hoofstukke te voorkom.
- Full Text:
- Date Issued: 2008
Geographic variation in the susceptibility of false colding Moth, Thaumatotibia Leucotreta, populations to a granulovirus (CrleGV-SA)
- Authors: Opoku-Debrah, John Kwadwo
- Date: 2008
- Subjects: Cryptophlebia leucotreta , Cryptophlebia leucotreta -- Control , Pests -- Biological control , Citrus -- Diseases and pests
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10586 , http://hdl.handle.net/10948/984 , Cryptophlebia leucotreta , Cryptophlebia leucotreta -- Control , Pests -- Biological control , Citrus -- Diseases and pests
- Description: The false codling moth (FCM), Thaumatotibia (=Cryptophlebia) leucotreta (Meyrick) (Lepidoptera: Tortricidae) is a serious pest of citrus and other crops in Sub-Saharan Africa. The introduction of the Cryptophlebia leucotreta granulovirus (CrleGV-SA) Cryptogran and Cryptex (biopesticides) has proven to be very effective in the control of FCM. However, markedly lower susceptibility of some codling moth (CM), Cydia pomonella (L.) populations to Cydia pomonella granulovirus (CpGV-M), another granulovirus product used in the control of CM’s in Europe have been reported. Genetic differences between FCM populations in South Africa have also been established. It is therefore possible that differences in the susceptibility of these geographically distinct FCM populations to CrleGV-SA might also exist. To investigate this phenomenon, a benchmark for pathogenecity was established. In continuation of previous work with Cryptogran against the 1st and 5th instar FCM larvae, dose-response relationships were established for all five larval instars of FCM. In surface dose-response bioassays, the LC50 values for the 2nd, 3rd and 4th instars were calculated to be 4.516 x 104, 1.662 x 105 and 2.205 x 106 occlusion bodies (OBs)/ml, respectively. The LC90 values for the 2nd, 3rd and 4th instars were calculated to be 4.287 x 106, 9.992 x 106 and 1.661 x 108 OBs/ml, respectively. Susceptibility to CrleGV-SA was found to decline with larval stage and increase with time of exposure. The protocol was used in guiding bioassays with field collected FCM larvae. Laboratory assays conducted with Cryptogran (at 1.661 x 108 OBs/ml) against field collected FCM larvae from Addo, Kirkwood, Citrusdal and Clanwilliam as well as a standard laboratory colony, showed a significant difference in pathogenecity in only one case. This significant difference was observed between 5th instars from the Addo colony and 5th instars from the other populations. Four geographically distinct FCM colonies from Addo, Citrusdal, Marble Hall and Nelspruit were also established. Since Cryptogran and Cryptex are always targeted against 1st instar FCM larvae in the field, further comparative laboratory assays were conducted with the Addo colony and an old laboratory colony. Cryptogran was significantly more pathogenic than Cryptex against both the Addo and the old colony. However, a high level of heterogeneity was observed in responses within each population.
- Full Text:
- Date Issued: 2008
- Authors: Opoku-Debrah, John Kwadwo
- Date: 2008
- Subjects: Cryptophlebia leucotreta , Cryptophlebia leucotreta -- Control , Pests -- Biological control , Citrus -- Diseases and pests
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10586 , http://hdl.handle.net/10948/984 , Cryptophlebia leucotreta , Cryptophlebia leucotreta -- Control , Pests -- Biological control , Citrus -- Diseases and pests
- Description: The false codling moth (FCM), Thaumatotibia (=Cryptophlebia) leucotreta (Meyrick) (Lepidoptera: Tortricidae) is a serious pest of citrus and other crops in Sub-Saharan Africa. The introduction of the Cryptophlebia leucotreta granulovirus (CrleGV-SA) Cryptogran and Cryptex (biopesticides) has proven to be very effective in the control of FCM. However, markedly lower susceptibility of some codling moth (CM), Cydia pomonella (L.) populations to Cydia pomonella granulovirus (CpGV-M), another granulovirus product used in the control of CM’s in Europe have been reported. Genetic differences between FCM populations in South Africa have also been established. It is therefore possible that differences in the susceptibility of these geographically distinct FCM populations to CrleGV-SA might also exist. To investigate this phenomenon, a benchmark for pathogenecity was established. In continuation of previous work with Cryptogran against the 1st and 5th instar FCM larvae, dose-response relationships were established for all five larval instars of FCM. In surface dose-response bioassays, the LC50 values for the 2nd, 3rd and 4th instars were calculated to be 4.516 x 104, 1.662 x 105 and 2.205 x 106 occlusion bodies (OBs)/ml, respectively. The LC90 values for the 2nd, 3rd and 4th instars were calculated to be 4.287 x 106, 9.992 x 106 and 1.661 x 108 OBs/ml, respectively. Susceptibility to CrleGV-SA was found to decline with larval stage and increase with time of exposure. The protocol was used in guiding bioassays with field collected FCM larvae. Laboratory assays conducted with Cryptogran (at 1.661 x 108 OBs/ml) against field collected FCM larvae from Addo, Kirkwood, Citrusdal and Clanwilliam as well as a standard laboratory colony, showed a significant difference in pathogenecity in only one case. This significant difference was observed between 5th instars from the Addo colony and 5th instars from the other populations. Four geographically distinct FCM colonies from Addo, Citrusdal, Marble Hall and Nelspruit were also established. Since Cryptogran and Cryptex are always targeted against 1st instar FCM larvae in the field, further comparative laboratory assays were conducted with the Addo colony and an old laboratory colony. Cryptogran was significantly more pathogenic than Cryptex against both the Addo and the old colony. However, a high level of heterogeneity was observed in responses within each population.
- Full Text:
- Date Issued: 2008
Growth of the South African abalone (Haliotis Midae) on three diets, under commercial conditions
- Authors: Makhande, Emmanuel Denis
- Date: 2008
- Subjects: Haliotis midae -- South Africa , Abalone culture -- South Africa , Abalones -- Nutrition -- South Africa , Abalones -- Physiology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10706 , http://hdl.handle.net/10948/755 , Haliotis midae -- South Africa , Abalone culture -- South Africa , Abalones -- Nutrition -- South Africa , Abalones -- Physiology -- South Africa
- Description: Haliotis midae is the cornerstone of the South African abalone fishery. For more than a decade, the wild abalone stock of South Africa has suffered decline due to over-exploitation and illegal activities such as poaching. Prior to 1970, no regulations were in place concerning the annual landings. As a result the fishery was exploited as if it were an infinite resource. It is this initial uncontrolled harvesting (regardless of age) and poaching that has driven the abalone resource decline. Due to the slow growth rate exhibited by abalone as a species, natural replenishment of wild stock following exploitation and poaching was far below the rate of exploitation of this resource. Studies on the growth of abalone have mainly been conducted under laboratory conditions. The purpose of this study was to measure the growth of abalone, fed different diets, under commercial culture conditions. Three food types were used namely; commercial pellets, seaweed (Ulva spp.) and dried kelp bars (Ecklonia maxima). Four diets were obtained from the three food types namely; combination of commercial pellets and seaweed (Diet A), commercial pellets only (Diet B), seaweed only (Diet C) and dried kelp bars only (Diet D). The food types used in this study represent both artificial (Commercial pellets) and natural feeds (seaweed and kelp) used in commercial abalone culture. The growth of two cohorts (40-50 mm and 50-60 mm) was followed over a 426 day period, with data for the first 183 days being used for statistical analysis to determine performance of a given diet. The best growth rates were found in abalone fed Diet A (40-50 mm: 2.64 mm.month-1; 50-60 mm 2.78: mm.month-1) and B (40-50 mm: 2.20 mm.month-1; 50-60 mm: 2.35: mm.month-1). These (Diets A and B) gave higher growth rates when compared to Diets C and D (natural diets), whose growth rates ranged between 0.50 mm.month-1 and 1.71 mm.month-1 for both cohorts. Also observed in this study was that, the mixture of formulated diet and seaweed gave better growth than formulated diet given exclusively.
- Full Text:
- Date Issued: 2008
- Authors: Makhande, Emmanuel Denis
- Date: 2008
- Subjects: Haliotis midae -- South Africa , Abalone culture -- South Africa , Abalones -- Nutrition -- South Africa , Abalones -- Physiology -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10706 , http://hdl.handle.net/10948/755 , Haliotis midae -- South Africa , Abalone culture -- South Africa , Abalones -- Nutrition -- South Africa , Abalones -- Physiology -- South Africa
- Description: Haliotis midae is the cornerstone of the South African abalone fishery. For more than a decade, the wild abalone stock of South Africa has suffered decline due to over-exploitation and illegal activities such as poaching. Prior to 1970, no regulations were in place concerning the annual landings. As a result the fishery was exploited as if it were an infinite resource. It is this initial uncontrolled harvesting (regardless of age) and poaching that has driven the abalone resource decline. Due to the slow growth rate exhibited by abalone as a species, natural replenishment of wild stock following exploitation and poaching was far below the rate of exploitation of this resource. Studies on the growth of abalone have mainly been conducted under laboratory conditions. The purpose of this study was to measure the growth of abalone, fed different diets, under commercial culture conditions. Three food types were used namely; commercial pellets, seaweed (Ulva spp.) and dried kelp bars (Ecklonia maxima). Four diets were obtained from the three food types namely; combination of commercial pellets and seaweed (Diet A), commercial pellets only (Diet B), seaweed only (Diet C) and dried kelp bars only (Diet D). The food types used in this study represent both artificial (Commercial pellets) and natural feeds (seaweed and kelp) used in commercial abalone culture. The growth of two cohorts (40-50 mm and 50-60 mm) was followed over a 426 day period, with data for the first 183 days being used for statistical analysis to determine performance of a given diet. The best growth rates were found in abalone fed Diet A (40-50 mm: 2.64 mm.month-1; 50-60 mm 2.78: mm.month-1) and B (40-50 mm: 2.20 mm.month-1; 50-60 mm: 2.35: mm.month-1). These (Diets A and B) gave higher growth rates when compared to Diets C and D (natural diets), whose growth rates ranged between 0.50 mm.month-1 and 1.71 mm.month-1 for both cohorts. Also observed in this study was that, the mixture of formulated diet and seaweed gave better growth than formulated diet given exclusively.
- Full Text:
- Date Issued: 2008