Showing items 1161 - 1180 of 1292

Your selections:

Cost-benefit analysis of land restoration in the Assegaaibos Catchment Area with regard to water yield and tourism benefit

  • Authors: Currie, Bianca
  • Date: 2007
  • Subjects: Reclamation of land -- Economic aspects -- South Africa -- Assegaaibos Catchment Area , Land use -- Environmental aspects -- South Africa -- Assegaaibos Catchment Area
  • Language: English
  • Type: Thesis , Masters , MTech
  • Identifier: vital:10751 , http://hdl.handle.net/10948/726 , Reclamation of land -- Economic aspects -- South Africa -- Assegaaibos Catchment Area , Land use -- Environmental aspects -- South Africa -- Assegaaibos Catchment Area
  • Description: With the emergence of the new field of resource economics, one now has the ability to value and to include natural resources in decision making. This thesis aims to explore the valuation of natural resources by reviewing the economic values, techniques, methods and ecological aspects of restoration. Assegaaibos mountain catchment in the Western Cape Province has been used as a case-study example. A cost-benefit analysis of the restoration of the mountain catchment, in terms of the direct benefits of water and tourism, has been performed. The costs of restoration were observed to see whether they outweighed the benefits (income) derived (water and tourism). The results show that the water and tourism benefits did outweigh the costs of a basic restoration scenario. However, the basic restoration scenario did not fulfil the ecological requirements of the project. The results also illustrated that in the moderate restoration scenario, costs only outweighed the benefits when a three percent discount rate was applied. With the optimistic restoration scenario, costs outweighed benefits only when an eight percent discount rate was used. In the comprehensive restoration scenario, costs were shown to outweigh by far the water and tourism benefits over a thirty-year time frame. However, it should be noted that the deterioration of the environment (accelerated erosion, reinvasion, reduced water quality) was not factored into the costs of failure to rehabilitate.
  • Full Text:
  • Date Issued: 2007

Cytokine properties of CD23 on human Eosinophilic cells

  • Authors: Ferreira, Lauren
  • Date: 2007
  • Subjects: Cytokines , CD23 antigen , Eosinophil
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10333 , http://hdl.handle.net/10948/503 , http://hdl.handle.net/10948/d1012001 , Cytokines , CD23 antigen , Eosinophil
  • Description: CD23, the low affinity IgE receptor, is expressed by various cell types and has numerous functions depending on the form of the protein, its interaction with various ligands and the type of cell involved. CD23 is pivotal in the regulation of IgE, with the soluble form involved in up-regulation, while the membrane bound form is involved in the down-regulation. It is clear why it is believed to be a central molecule in allergic responses, and a therapeutic target for the treatment of allergic disease. In this study a recombinant form of the entire extracellular domain of the protein, exCD23, was produced by PCR cloning and expressed in E. coli. His•Tag™s were introduced onto the C-terminus and N-terminus, respectively, in order to simplify the purification procedure. After renaturation and purification, the recombinant exCD23 bound IgE, indicating its activity. From the IgE binding studies it was established that the position of the tag did not influence the binding. GST•Tagged™ exCD23 was also produced in an attempt to increase the solubility of the recombinant protein, but this proved unsuccessful. Butyrate differentiated EoL-1 cells were treated with the Nterminal His•Tagged™ exCD23, and the protein appeared to suppress the secretion of the constitutively expressed cytokines, especially IL-8 and IFN- , when compared to untreated cells. In addition, treatment of the EoL-1 cells with exCD23 had a significant proliferative effect, but could not induce differentiation of this cell line into mature eosinophilic-like cells.
  • Full Text:
  • Date Issued: 2007

Elephant feeding behaviour and forage offtake implications in the Addo Elephant National Park

  • Authors: Lessing, Joan Susanna
  • Date: 2007
  • Subjects: Elephants -- South Africa -- Addo Elephant National Park , Elephants -- Behavior , Addo Elephant National Park (South Africa) , Mammals -- Behavior
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10712 , http://hdl.handle.net/10948/542 , http://hdl.handle.net/10948/d1012016 , Elephants -- South Africa -- Addo Elephant National Park , Elephants -- Behavior , Addo Elephant National Park (South Africa) , Mammals -- Behavior
  • Description: Elephants, as megaherbivores and keystone species have major impacts, both positive and negative, on ecosystems such as the Subtropical Thicket of the Eastern Cape. The feeding behaviour of elephants was quantified so as to firstly determine the preferred feeding heights of elephants, and secondly to determine if feeding behaviour and impact varies with size and sex. The preferred feeding height was determined with experimental feeding trials. Feeding height, pluck size, foraging rate and the proportion of plant material discarded were used to test for differences between elephants of different sizes and sexes in the Addo Elephant National Park. The influence of plant growth form on sex-specific feeding was also considered. Elephants preferred to feed at the lowest heights. The preferred feeding height was not related to body size. A wide range of feeding heights was recorded including and extending beyond, both the preferred and maximum feeding height of co-existing indigenous browsers. There was no difference in feeding height between the sizes and sexes. In free ranging conditions, all elephants fed at levels above the preferred foraging height when browsing. There was no difference in feeding behaviour between the different sized elephants, or between males and females. Adult elephants however exhibited larger ranges of feeding heights, pluck sizes, foraging rates and intake rates, including the maximum and minimum values. Growth form influenced the feeding of male and female elephants differently. Elephant feeding behaviour appears to limit opportunities for resource partitioning by way of feeding height segregation. Elephants are also capable of dominating the browse resources available to co-existing browsers by removing large amounts of forage at lower heights. The extent of elephant impact seems to be comparable between sizes and sexes, although adults and especially larger males are often able to use foraging opportunities that other elephants can not effectively utilize. Findings suggest that the feeding heights of elephants are determined by forage availability and reflect the diet in terms of browse or grass. The findings can be used, together with browse inventory methods, to determine browse resources available to elephants, and can also be used to develop monitoring tools to assess the impacts of elephants on plants.
  • Full Text:
  • Date Issued: 2007

Endozoochory in the subtropical thicket: comparing effects of species with different digestive systems on seed fate

  • Authors: Davis, Shavaughn
  • Date: 2007
  • Subjects: Seeds -- Dispersal
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10714 , http://hdl.handle.net/10948/494 , http://hdl.handle.net/10948/d1012018 , Seeds -- Dispersal
  • Description: Endozoochory is an important form of seed dispersal and as such plays a fundamental role in plant population and community ecology. This is especially true in the Subtropical Thicket biome where many plant species are adapted for endozoochory. Endozoochorous seed dispersal is carried out by a wide range of thicket fauna, but changes in the faunal assemblage associated with transformed thicket threatens to disrupt the process of endozoochorous seed dispersal and in turn the regeneration dynamics of thicket plants. Outside of conservation areas, indigenous seed dispersers are often replaced by domestic species, such as goats, which are hypothesized to differ in their seed dispersal efficiencies. The dispersal efficiencies of important thicket seed dispersers that occur in transformed and untransformed thicket were therefore investigated. The influence of gut morphologyphysiology on seed gut passage time, seed mortality and germination in animal species representing different digestive models was measured, as well as the role of black-backed jackal in thicket plant seed dispersal. Black-backed jackal were found to disperse the seeds of few thicket plant species and are therefore not considered important thicket seed dispersers under the climatic conditions prevailing during the study. The average gut passage time of seeds was found to differ significantly between birds and mammals, but not between elephants (hindgut fermentor), goats (ruminant) and pigs (omnivore, foregut fermentor) as was expected considering the differences in their digestive morphology. A significantly shorter gut passage of large seeds compared with small seeds was observed in goats, due to the regurgitation of larger seeds. Seed regurgitation in ruminants may prove to be an important factor contributing to their quality as seed dispersers in transformed thicket. The mortality of seeds was significantly higher in goats than in elephants, probably due to the efficient digestion associated with ruminants. The effect of gut passage on seed germination was not consistent and varied between animal species and across different thicket plant species. It was concluded that seed dispersers that occur in transformed and untransformed thicket differ in their seed dispersal efficiency due, in part, to differences in the nature of their digestive tracts. This has important implications for the process of seed dispersal in thicket, and the rehabilitation of degraded thicket vegetation.
  • Full Text:
  • Date Issued: 2007

Field and laboratory measurements of PMD using interferometric techniques

  • Authors: Mankga, Maphuti Comfort
  • Date: 2007
  • Subjects: Fiber optics , Polarization (Light)
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10531 , http://hdl.handle.net/10948/557 , Fiber optics , Polarization (Light)
  • Description: In this study, the generalized and traditional interferometric techniques (GINTY and TINTY) are used to investigate some of the important aspects of Polarization Mode Dispersion (PMD) phenomenon in optical fibres. Measurements of PMD and chromatic dispersion (CD) are performed on buried optical fibre cable in the Pretoria Telkom’s metropolitan network. The upgradeability of this network was investigated, and it was observed that just over a half of the fibres are upgradeable to 10 Gb.s-1 transmissions. Long-haul aerial network in the Northern Cape was also tested for upgradeability to 10 Gb.s-1. It was found that 41 percent of the fibres tested are upgradeable to 10 Gb.s-1. Long-term monitoring showed that PMD varies rapidly in aerial fibres and, on the other hand, it is relatively stable in buried cables. Investigations on the accuracy of the techniques showed that polarization scrambling is essential for the reduction of the measurements uncertainties. Furthermore, it was observed that TINTY underestimates the single scan PMD distributions. The study on the effect of the change in mode coupling on various fibre configurations was performed, and fibres showed a reduction in PMD after the introduction of mode coupling. Measurements of PMD conducted in the laboratory on cabled fibre with low PMD showed the floor sensitivity of TINTY. Comparison between GINTY and Jones Matrix Eigeanalysis (JME) PMD measurements methods were performed on an emulator, and the results showed a good agreement in the measured PMD.
  • Full Text:
  • Date Issued: 2007

Improving certain high performance properties of natural fibres

  • Authors: Chapple, Stephen Anthony
  • Date: 2007
  • Subjects: Textile chemistry , Fireproofing of fabrics
  • Language: English
  • Type: Thesis , Masters , MTech
  • Identifier: vital:10451 , http://hdl.handle.net/10948/815 , Textile chemistry , Fireproofing of fabrics
  • Description: Cotton possesses many characteristics that make it desirable to the consumer, and this has resulted in its usage in a broad range of products. Cotton, however, is a flammable material that is easily ignited and rapidly consumed. The flame retardant treatment of cotton is, therefore, an important textile process that has received wide attention over many years. There are a number of commercial flame retardant treatments available for cotton, the most common being phosphate-based. These treatments, however, often have drawbacks or have a negative impact on the desirable properties of the fibre and the challenge still exists for designing better flame retardant products and systems that are durable and have limited impact on fibre properties. The study considers the application of the sol-gel as a coating on fabric that was pre-treated with a phosphate-based flame retardant or as a means for applying a phosphate-based flame retardant. Both treatment methods were found to be suitable for imparting flame resistance to the fabric. The effect of various phosphate-based flame retardants on flammability and fabric properties such as colour, handle and strength was investigated and it was shown that a diammonium phosphate and urea combination gave the best flame resistance. In this regard, a flame resistance was achieved with a lower amount of phosphorous than was used in similar conventional treatments. The durability of the coating to rinsing with water and soaping with a detergent was also investigated. It was found that the flame resistance was lost after rinsing or soaping but the prevention of afterglow combustion was retained. It was shown that the preparatory treatment of the fabric influenced the sol-gel coating process and the flammability of the fabric. Mercerisation and bleaching of the fabric increased the “wet pick-up” during the coating process and improved the flame resistance. The influence of various factors was also investigated in further detail. The ratio of the sol-gel components, the delay after coating prior to drying (hang time) and the curing time were investigated using an experimental design. The curing time and the ratio of components in the sol-gel were shown to have the greatest influence on fabric properties and fabric flammability. It was shown that there is a trade-off between the desired high level of fabric flame resistance and preserving the inherent properties of the fabric such as colour, handle and strength.
  • Full Text:
  • Date Issued: 2007

In vitro testing to investigate the anticoagulant/antithrombotic and antidiabetic biological activity of Leonotis Leonurus

  • Authors: Mnonopi, Nandipha Olivia
  • Date: 2007
  • Subjects: Leonotis leonurus -- Physiological aspects , Medicinal plants -- South Africa , Materia medica, Vegetable -- South Africa , Plant bioactive compounds
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10331 , http://hdl.handle.net/10948/693 , Leonotis leonurus -- Physiological aspects , Medicinal plants -- South Africa , Materia medica, Vegetable -- South Africa , Plant bioactive compounds
  • Description: The rising costs of prescription drugs in the maintenance of personal health and wellbeing have increased the interest in medicinal plants. The World Health Organization estimates that 65 percent-80 percent of the world’s population use traditional medicine as their primary form of health care. In this project the focus has been on the use of Leonotis leonurus extracts as a traditional medicine. The major chemical constituent of this plant is marrubiin, which is a diterpenoid labdane lactone formed from a precursor called premarrubiin. Aqueous and acetone extract (AL and OL extract, respectively) of this plant has been found to have an antithrombotic effect, with IC50 values of 3mg/ml and 6mg/ml, respectively. The extracts also have an effect on fibrinolysis, where the lysis time was decreased by more than 50 percent by the organic extract and standard marrubiin. In whole blood ADP-induced platelet aggregation, the organic extract inhibited aggregation by 68 percent at a final concentration of 138μg/ml (equivalent to 7.2μg/ml marrubiin). Marrubiin has also been screened for antithrombotic/anticoagulant activity; no antithrombotic activity has been observed but it increased the rate of fibrinolysis, by decreasing lysis time by 64 percent and also decreasing fibrin formation. From these findings it can be concluded that marrubiin has a fibrinolytic effect and antiplatelet aggregation effect. In the diabetic studies, in hyperglycemic condition, the OL (10μg/ml) extract and standard marrubiin significantly increased insulin secretion by 200 percent (2-fold) and 400 percent (4-fold), respectively, with respect to the control. The OL extract and standard marrubiin stimulated the release of insulin, the stimulatory index was significantly increased by 450 percent (4.5-fold) and 500 percent (5-fold), respectively, with respect to the control. In the apoptotic studies, in the normoglycemic and hyperglycemic conditions, the OL extract decreased the occurrence of apoptosis, in a dose-dependent manner, with the lower concentrations inducing apoptosis significantly higher than the relevant controls. Standard marrubiin did not have an effect on apoptosis in hyperglycemic condition, but it decreased the occurrence of apoptosis by 200 percent (2-fold) under normoglycemic conditions. The OL extract increased proliferation by 148 percent (1.48- fold) and 155 percent (1.55-fold) in normoglycemic and hyperglycemic conditions, respectively. The same effect was observed for standard marrubiin, where, proliferation was increased by 180 percent (1.8-fold) and 200 percent (2.0-fold) in normoglycemic and hyperglycemic conditions, respectively. RT-PCR displayed that standard marrubiin inhibited the expression of insulin by 50 percent under normoglycemic conditions.
  • Full Text:
  • Date Issued: 2007

Investigating the influences of validation on pharmaceutical manufacturing processes

  • Authors: Muller, Damian Christian
  • Date: 2007
  • Subjects: Pharmaceutical industry -- Quality control , Pharmaceutical technology , Drugs -- Standards
  • Language: English
  • Type: Thesis , Masters , MTech
  • Identifier: vital:10412 , http://hdl.handle.net/10948/566 , Pharmaceutical industry -- Quality control , Pharmaceutical technology , Drugs -- Standards
  • Description: This investigation attempts to examine the influences of validation on pharmaceutical processes especially at a new manufacturing facility that has to meet international requirements, and fulfil a cost effective business strategy. At Aspen Pharmacare, a pharmaceutical organisation, there are two manufacturing facilities situated adjacent to each other, one new and one old. The new facility creates ideal opportunities to supply products to local and international markets. The investigation compares legal requirements from local and international regulatory authorities. Validation and qualification practices as well as the problems encountered during the different phases are discussed. Particular attention is given to the validation approach at the new Aspen facility. Problems and proposed solutions relating to the design review, installation, operational, and performance qualification are discussed. Validation of analytical methods for cleaning analysis, cleaning validation of equipment, and optimisation of some tablet manufacturing processes are described. Statistical evaluations of analytical results are included to find the optimum conditions for integrating new personnel with new processes and equipment. A business model reviews the cost of non-conformances of the enalapril maleate 10 mg tablets manufactured at the two manufacturing facilities. Finally the dissertation proves that validation is not only a regulatory requirement but that it also provides benefits such as adding value to the business, and ultimately reducing the cost of medicines.
  • Full Text:
  • Date Issued: 2007

Ionic liquids as media for electro-organic synthesis

  • Authors: Kruger, Elna
  • Date: 2007
  • Subjects: Ionic solutions , Inorganic compounds -- Synthesis , Electrochemistry
  • Language: English
  • Type: Thesis , Masters , MTech
  • Identifier: vital:10413 , http://hdl.handle.net/10948/538 , Ionic solutions , Inorganic compounds -- Synthesis , Electrochemistry
  • Description: The IL’s used in this study were either synthesized or commercially available. Preparation of the IL’s involved 2 step processes: firstly the heating of distilled 1-methylimidazole with distilled 1-chlorobutane under reflux to obtain 1-butyl-3- methylimidazolium chloride; secondly, the metathesis reaction of sodium tetrafluoroborate with 1-butyl-3-methylimidazolium chloride to obtain 1-butyl-3- methylimidazolium tetrafluoroborate. The addition of sodium tetrafluoroborate, sodium hexafluorophosphate and lithium trifluoromethane sulfonamide with 1-butyl-3-methylimidazolium chloride produced good yields of 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide respectively. The IL’s are hygroscopic and must be stored under a nitrogen atmosphere. The IL’s were analyzed using 1H and 13C NMR analysis with CDCl3 as solvent. The physical and chemical properties of these IL’s were compared to commercial products. The physical and chemical properties compared well to reference values from the literature. The physical properties measured include the density, conductivity and electrochemical window. The electrochemical window is dependant primarily on the resistance of the cation to reduction and the resistance of the anion to oxidation. The electrochemical windows of the IL’s were very similar to the reference windows obtained from literature and it can be seen that some IL’s have a slightly lower window which can be due to water present. Water content in the IL’s was determined with the use of a Karl Fischer titrator, with Hydranal 5 Composite as titrant and HPLC grade methanol as the base. The concentration of halide in the IL’s was determined with a Perkin-Elmer ICP-MS.
  • Full Text:
  • Date Issued: 2007

Isolation of bioactive metabolites with activity against HIV-1 target proteins from extracts of Sutherlandia frutescens and Lobostemon trigonus

  • Authors: Dambuza, Ntokozo Shirley
  • Date: 2007
  • Subjects: Medicinal plants -- Africa, Southern , HIV infections -- Alternative treatment -- Africa, Southern , Plant bioactive compounds
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10335 , http://hdl.handle.net/10948/492 , http://hdl.handle.net/10948/d1012003 , Medicinal plants -- Africa, Southern , HIV infections -- Alternative treatment -- Africa, Southern , Plant bioactive compounds
  • Description: Acquired Immunodeficiency Syndrome (AIDS) is a human disease caused by the human immunodeficiency virus type 1 (HIV-1) and it is one of the biggest social, economic and health challenges in the world. The Joint United Nations Programme on HIV/AIDS (UNAIDS) and World Health Organization (WHO) estimated that between 33.4 to 46.0 million people around the world were living with HIV/AIDS in December 2005 and the highest estimates are in the Sub-Saharan Africa (around 25 million). In more developed countries a combined antiretroviral therapy called highly active antiretroviral therapy (HAART) is used, which results in reduced progression to AIDS in most patients. Despite the beneficial effects of HAART, significant side effects are experienced by treated patients. In addition, most infected people live in countries where the treatment is very expensive or, in many cases, not available at all. These people therefore rely on medicinal plants for health care. In this study, aqueous extracts from Sutherlandia frutescens and Lobostemon trigonus were screened for potential anti-HIV activities in a series of in vitro enzymatic assays, including reverse transcriptase, HIV-1 protease and glycohydrolases. Two extracts of Sutherlandia leaves (SFL-1 and SFL-2) were prepared that inhibited HIV reverse transcriptase and a Lobostemon leaf extract (LTL) was shown to also inhibit this enzyme. All extracts were assayed at 1.25mg/ml. Tannin content was determined for all active extracts using a tannic acid assay. SFL-1 and SFL-2 were found to contain about 6 percent and 7 percent tannins, respectively, and LTL contained 31% tannins by weight. Tannins were removed using polyamide columns and three fractions were collected for each. The extracts were also fractionated with Sephadex G-25, Amberlite IR 120 and Dowex 1-X8 as size exclusion, cation exchange and anion exchange, respectively. Extracts were also fractionated by preparative thin layer chromatography where two compounds were separated from S. frutescens extract with high activity against reverse transcriptase while showing insignificant inhibition towards other enzymes tested. SFL-BFW-10 and SFL-WEF-7 inhibited reverse transcriptase by almost 100 percent and the IC50 values calculated for these compounds were 0.34 and 0.23mg/ml, respectively. Cytotoxicity of these compounds was evaluated on Chang liver cells and peripheral blood mononuclear cells (PBMCs). None of these compounds showed any significant inhibition of cell proliferation. The purity of these compounds could not be confirmed because there was insufficient material to use in the techniques required to show purity and identification. Therefore, TLC was used to determine the nature of these compounds. SFL-BFW-10 was identified as an organic acid and SFL-WEF-7 was identified as flavonoid.
  • Full Text:
  • Date Issued: 2007

Micellar-enhanced ultrafiltration of palladium and platinum anions

  • Authors: Gwicana, Sakumzi
  • Date: 2007
  • Subjects: Micelles , Ultrafiltration , Palladium catalysts
  • Language: English
  • Type: Thesis , Masters , MTech
  • Identifier: vital:10414 , http://hdl.handle.net/10948/518 , Micelles , Ultrafiltration , Palladium catalysts
  • Description: The project was concerned with studying the capability of a micellar-enhanced ultrafiltration system (MEUF) to remove platinum group metal ions namely Pt (lV) and Pd (ll) chloro anions from aqueous industrial waste effluents. South Africa has the world’s largest reserves of platinum group metals (PGMs) and other valuable metals such as manganese, chrome ores, titanium minerals etc. which are required for new automotive and other technologies, including fuel cells, catalytic converters and lighter components. The consistent loss with the industrial waste stream and the toxicological effects of these precious metals led to the need to develop new and effective methods to recover them from industrial waste effluents. With such a wide variety of fields where these PGMs are used and the failure of the traditional techniques namely sedimentation, fermentation etc. to effectively reduce or recover these highly toxic and precious metal ions prior to discharging industrial waste effluents, it is necessary to explore other techniques such as membrane technology that can be used to recover these valuable species from industrial waste streams. The present study involved the use of a cationic surfactant, viz cetylpyridinium chloride, which was introduced into an aqueous solution containing palladium and platinum metal anions. The surfactant forms charged micelles above a certain critical concentration value. The metal anions adsorb onto the available oppositely charged sites on the micelle surfaces and are then able to be retained by a suitable membrane. Hollow fibre ultrafiltration membranes with the MWCO of +/- 10 kD and +/-30nm pore size were used as a filter component in this study. For this MEUF system to be effective, it was vital that the anionic metal ion species adsorbed sufficiently onto the available oppositely charged sites of the micelles and that the micelles were retained efficiently by the membrane. Results obtained during the investigation made it possible to make certain predictions about the micellisation process. It was also found that, it was not only the metal ion: surfactant (M:S) ratio that was critical, but the presence of other electrolytes in the aqueous stream proved to have a huge impact on the capability of the MEUF system. Findings of this research study showed that the MEUF system using cetylpyridinium chloride (CPC) can be used to recover or retain Pt (lV) and Pd (ll) anions from industrial waste effluents. It was also found that PtCl6 2-, due to its greater adsorption capabilities onto the micelle surface than PdCl4 2- or PdCl3(H2O)-, was preferentially retained in neutral medium. This may be exploited as a possible means of separating the two metal ions. The developed system offers the following advantages over some traditional and current methods: simplified unit operation line flow process, smaller amounts of chemical usage and no solid toxic sludge to be disposed of. Applications of this work could be of vital importance in catalytic converter recycling, especially in Port Elizabeth where extensive automobile parts manufacturing occurs.
  • Full Text:
  • Date Issued: 2007

MOCVD growth and electrical characterisation of InAs thin films

  • Authors: Shamba, Precious
  • Date: 2007
  • Subjects: Metal organic chemical vapor deposition
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10527 , http://hdl.handle.net/10948/706 , Metal organic chemical vapor deposition
  • Description: In this work, a systematic study relating the surface morphologies, electrical and structural properties of both doped and undoped InAs and InAsSb epitaxial films grown by metalorganic chemical vapour deposition (MOCVD) was undertaken. A comparative study using TBAs and AsH3 as the group V source in the growth of InAs revealed a considerable improvement, primarily in the electrical properties of InAs grown using TBAs with no significant difference in the surface morphology. InAs layers grown using TBAs, exhibited superior 77 K mobilities of up to 46 000 cm2/Vs, exceeding the best MOCVD data to date. The feasibility of tetraethyl tin (TESn) as an n-type dopant in InAs was to our knowledge investigated for the first time. The incorporation efficiency of this dopant was extensively studied as a function of substrate temperature, V/III ratio, substrate orientation and TESn flow rate. Results from this study show that the doping efficiency is temperature dependent and is not influenced by a variation of the V/III ratio or substrate orientation. Furthermore, Sn doping concentrations could be controlled over 2 orders of magnitude ranging between 2.7 x 1017 and 4.7 x 1019 cm-3 with 77 K mobilities ranging from 12 000 to 1300 cm2/Vs. The electrical properties of zinc doped InAs employing dimethyl zinc (DMZn) as the ptype dopant, were studied as a function of V/III ratio and substrate orientation. The effect of a variation of these parameters on the structural properties and surface morphology of InAs is also reported. The substrate orientation appears to have no influence on the Zn incorporation. An increase in Zn incorporation resulted in a deterioration of both the surface morphology and structural quality of the InAs layers. The incorporation efficiency of DMZn in InAsSb was studied as a function of growth temperature, V/III ratio and DMZn flow rate. A higher Zn incorporation was observed in InAsSb epitaxial layers grown at a lower temperature and V/III ratio as opposed to the layers grown at a higher temperature and V/III ratio. This study also revealed that the use of DMZn caused a dopant memory effect. A two-layer model proposed by Nedoluha and Koch (1952) was used to simulate the Hall measurements of Zn doped InAs and InAsSb in order to correct the shortcomings of conventional Hall measurements in determining the electrical properties exhibited by these materials.
  • Full Text:
  • Date Issued: 2007

On the characterization of photovoltaic devices for concentrator purposes

  • Authors: Vorster, Frederick Jacobus
  • Date: 2007
  • Subjects: Photovoltaic cells , Image processing , Solar cells
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: vital:10530 , http://hdl.handle.net/10948/639 , Photovoltaic cells , Image processing , Solar cells
  • Description: This study originated from an evaluation of the performance of a commercially available high concentration point focus concentrator PV system. The effect of module design flaws was studied by using current-voltage (I-V) curves obtained from each module in the array. The position of reverse bias steps revealed the severity of mismatch in a string of series-connected cells. By understanding the effects of the various types of mismatch, power losses and damage to the solar cells resulting from hot spot formation can be minimized and several recommendations for improving the basic performance of similar systems were made. Concern over the extent and type of defect failure of the concentrator photovoltaic (CPV) cells prompted an investigation into the use of a light beam induced current (LBIC) technique to investigate the spatial distribution of defects. An overview of current and developing LBIC techniques revealed that the original standard LBIC techniques have found widespread application, and that far-reaching and important developments of the technique have taken place over the years. These developments are driven by natural progression as well as the availability of newly developed advanced measurement equipment. Several techniques such as Lock-in hermography and the use of infrared cameras have developed as complementary techniques to advanced LBIC techniques. As an accurate contactless evaluation tool that is able to image spatially distributed defects in cell material, the basis of this method seemed promising for the evaluation of concentrator cells.
  • Full Text:
  • Date Issued: 2007

On the microstructure and physical properties of hot pressed (Hf, Ti) C

  • Authors: Heiligers, Christiané
  • Date: 2007
  • Subjects: Transition metal carbides
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: vital:10532 , http://hdl.handle.net/10948/523 , http://hdl.handle.net/10948/d1011722 , Transition metal carbides
  • Description: The microstructure and physical properties of hot pressed (Hf, Ti) C have been investigated with the aim of producing a cutting tool material with similar hardness to that of WC-Co and TiC-based cermets. Sintered samples were hot pressed from HfC0.7 and TiC0.9 powders using powder metallurgical techniques and the processing cycle was optimized for this system. Ni was used as a binder in selected samples and C black was added to compensate for sub-stoichiometry and to aid in the reduction of oxides formed during milling. Microstructural analyses were performed by scanning and transmission electron microscopy (SEM and TEM) and the composition was determined from X-ray diffraction (XRD) and energy dispersive X-ray spectrometry (EDS). The physical properties measured are density and Vickers hardness, and the indentation fracture toughness was determined using the Shetty formula. The fundamental interactions between HfC, TiC and Ni during hot pressing were investigated and the results obtained used to explain the microstructure that develops in samples made from powder mixtures. The interactions studied are the inter-diffusion of HfC and TiC through the solid state, and the dissolution and re-precipitation rate of the carbides in a liquid Ni binder. EDS analysis revealed that the rate at which Ti diffuses into HfC is higher than the rate at which Hf diffuses into TiC. Upper limits to the diffusion coefficients for these processes are determined and show that solid solution carbides will form from HfC + TiC powder mixtures at 2000 ºC in 1 hour if the average powder particle size is less than 5 μm. The diffusion rates decrease with a decrease in hot pressing temperature but mass transport between the phases can be enhanced by addition of a metallic binder. TEM and EDS analysis shows that Ni wets TiC more efficiently than HfC and that the solubility of TiC in Ni is also higher than that of HfC. The grain size of the carbide phases increases with an increase in the rate at which they dissolve into and re-precipitate from the liquid binder. The crystal structure of the binder phase depends on the concentration of Ti and Hf that remain in the binder after cooling and the carbide phase in which the binder is embedded. Analysis of TEM electron diffraction patterns show that the binder phase consists of cubic solid solutions as well as intermetallic and cubic phases in which atomic ordering is observed.
  • Full Text:
  • Date Issued: 2007

Prime near-ring modules and their links with the generalised group near-ring

  • Authors: Juglal, Shaanraj
  • Date: 2007
  • Subjects: Near-rings
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: vital:10507 , http://hdl.handle.net/10948/714 , Near-rings
  • Description: In view of the facts that the definition of a ring led to the definition of a near- ring, the definition of a ring module led to the definition of a near-ring module, prime rings resulted in investigations with respect to primeness in near-rings, one is naturally inclined to attempt to define the notion of a group near-ring seeing that the group ring had already been defined and investigated into by, interalia, Groenewald in [7] . However, in trying to define the group near-ring along the same lines as the group ring was defined, it was found that the resulting multiplication was, in general, not associative in the near-ring case due to the lack of one distributive property. In 1976, Meldrum [19] achieved success in defining the group near-ring. How- ever, in his definition, only distributively generated near-rings were considered and the distributive generators played a vital role in the construction. In 1989, Le Riche, Meldrum and van der Walt [17], adopted a similar approach to that which led to a successful and fruitful definition of matrix near-rings, and defined the group near-ring in a more general sense. In particular, they defined R[G], the group near-ring of a group G over a near-ring R, as a subnear-ring of M(RG), the near-ring of all mappings of the group RG into itself. More recently, Groenewald and Lee [14], further generalised the definition of R[G] to R[S : M], the generalised semigroup near-ring of a semigroup S over any faithful R-module M. Again, the natural thing to do would be to extend the results obtained for R[G] to R[S : M], and this they achieved with much success.
  • Full Text:
  • Date Issued: 2007

Rehabilitation of the Orange River Mouth Salt Marsh : seed, wind and sediment characteristics

  • Authors: Shaw, Gregory Alan
  • Date: 2007
  • Subjects: Salt marshes -- Orange River , Rivers -- South Africa -- Environmental aspects , Orange River -- Ecology
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10626 , http://hdl.handle.net/10948/603 , http://hdl.handle.net/10948/d1012010 , Salt marshes -- Orange River , Rivers -- South Africa -- Environmental aspects , Orange River -- Ecology
  • Description: The Orange River is an important source of freshwater and like many other wetlands in semi-arid regions, supports various social (Spurgeon, 1998), economic (Spurgeon, 1998; Bornman et al., 2005) and ecological functions. The saltmarsh at the Orange River Mouth has become degraded over time following numerous anthropogenic impacts. As a result the Transboundary RAMSAR site was placed on the Montreux record emphasising the importance for rehabilitation. The potential of the marsh for natural rehabilitation was assessed through three physical factors which were considered to have the most influence on the saltmarsh i.e. 1) sediment 2) water 3) wind. Three sampling areas were chosen to investigate the sediment characteristics of the ORM saltmarsh and the suitability for seed germination and adult survival. Site A was representative of the general marsh area, Site B was thought to have favourable sediment conditions for saltmarsh growth because of the large numbers of seedlings and Site C was prone to inundation by wind blown sediment. The sites were sampled in 2005 (dry conditions) and in 2006 after high rainfall and river flooding. Electrical conductivity (EC) of the sediment throughout the marsh was hypersaline in many instances above the tolerance range for S. pillansii (> 80 mS.cm-1) The freshwater event in 2006 lowered salinity significantly in two of the three sites. Differences in sediment characteristics were also compared for three habitats i.e. driftlines, open sites and under vegetation. Driftlines (C. coronopifolia = 872 seedlings m-2; S. pillansii = 1296 seedlings m-2) and the microhabitat associated with adult plants (C. coronopifolia = 803 seedlings m-2; S. pillansii = 721 seedlings m-2) created favourable conditions for seedling growth, however open unvegetated (C. coronopifolia = 56 seedlings m-2; S. pillansii = 49 seedlings m-2) areas had significantly lower seedling density. Due to the marsh currently being in a desertified state this study aimed to establish whether the remaining vegetation could produce enough seed to revegetate the marsh. Laboratory studies indicated that seeds of both species germinated best in freshwater (0 psu). The germination of S. pillansii seeds was 40 percent at 0 psu compared to 5 percent at 35 psu. After storage under hypersaline conditions (35 psu) C. coronopifolia showed 100 percent seed germination when returned to freshwater whereas storage at 70 psu decreased the viability of S. pillansii seeds. The plants are producing adequate seed that will allow for regrowth and rehabilitation if sediment and groundwater characteristics are suitable for seed germination, seedling growth and adult survival. However the increase in bare areas at the Orange River mouth as a result of salt marsh dieback has increased the available sediment source. The wind blown sediment has covered large areas of the remaining adult salt marsh vegetation, particularly in the northern corner at Site C, causing further die-back.
  • Full Text:
  • Date Issued: 2007

Reproductive co-existence among five sympatric single-stemmed aloes in the Gamtoos River Valley, Eastern Cape

  • Authors: Botes, Christo
  • Date: 2007
  • Subjects: Aloe -- South Africa -- Gamtoos River Valley , Aloe -- South Africa -- Identification
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10628 , http://hdl.handle.net/10948/481 , Aloe -- South Africa -- Gamtoos River Valley , Aloe -- South Africa -- Identification
  • Description: In this study I documented the convergence of five congeneric bird-pollinated plants (Aloe pluridens, A. lineata var. muirii, A. speciosa, A. africana, and A. ferox) into three functional groups based on size, shape, and the arrangements of flowers on the inflorescence, but also nectar rewards, pollen deposition sites on the bird-pollinators, and the degree to which bees play a role in their pollination. Individuals of similar functional groups were divergent in their peak flowering times and limited their degree of flowering overlap further by spatial aggregation and niche separation, within the Thicket of the Gamtoos River Valley. The nectar properties were especially useful in structuring the bird pollinator community, which resulted in greater ethological isolation and hence, greater reproductive assurance in the mixed co-flowering plant communities. Choice array experiments revealed that it was the fine scale aggregation of flowering individuals that ensured that bird-pollinators feed selectively, since when equal choice was available, interspecific visitation increased significantly compared to natural scenarios. Bird behaviour and the ecological intermediateness of one to the species explained its prominence in hybrid combinations. The spatial occurrence of hybrid individuals can be traced back to the energetics of foraging and its influence on bird floral constancy. The pollination ecology of similar South African Aloe species were extrapolated from these and recent findings by various authors, but emphasises the need for a robust natural phylogeny of the Aloaceae in order to draw comprehensive conclusions on the evolutionary radiation of this highly charismatic group.
  • Full Text:
  • Date Issued: 2007

Rhenium(V)-Imido complexes with potentially multidentate ligands containing the amino group

  • Authors: Booysen, Irvin Noel
  • Date: 2007
  • Subjects: Rhenium , Ligands
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10385 , http://hdl.handle.net/10948/479 , Rhenium , Ligands
  • Description: The complex trans-[Re(dab)Cl3(PPh3)2] (H2dab=1,2-diaminobenzene) was prepared from the reaction of trans-[ReOCl3(PPh3)2] with H2dab in ethanol. The ligand dab is coordinated to the rhenium(V) centre through a dianionic imido nitrogen only, in a distorted octahedral coordination geometry around the metal ion. The complex trans-[Re(ada)Cl3(PPh3)2] (H2ada=2-aminodiphenylamine) was prepared from the reaction of trans-[ReOCl3(PPh3)2] with H2ada in acetonitrile. The ligand ada is coordinated to the rhenium(V) centre through a dianionic imido nitrogen only, in a distorted octahedral coordination geometry around the metal ion. Surprisingly, the Re-Cl bond length trans to the Re=N bond is shorter than the two equatorial Re-Cl bond lengths. The reaction of equimolar quantities of cis-[ReO2I(PPh3)2] with 5,6-diamino-1,3- dimethyluracil (H2ddd) in acetonitrile led to the formation of [Re(ddd)(Hddd)I(PPh3)2](ReO4). The X-ray crystal structure shows that the ligand ddd is coordinated monodentately through the doubly deprotonated amino nitrogen and is therefore present as an imide. The chelate Hddd is coordinated bidentately via the neutral amino nitrogen, which is coordinated trans to the imido nitrogen, and the singly deprotonated amido nitrogen, trans to the iodide. The reaction of equimolar quantities of [NH4(ReO4)] with H2ddd in methanol under reflux conditions led to the isolation of [C12H12N6O4] as only product. The [ReO4]- ion is therefore instrumental in the formation of [C12H12N6O4], and since the product contains no rhenium in any oxidation state, the conclusion is that [ReO4]- catalyses the oxidative deamination of H2ddd. The X-ray crystal structure consists of two centrosymmetric, tricyclic rings, comprising a central pyrazine ring and two terminal pyrimidine rings. The reaction of a twofold molar excess of H2apb (H2apb=2-(2-aminophenyl)-1Hbenzimidazole) with trans-[ReO2(py)4]Cl in ethanol gave the green product of the formulation [ReO(Hapb)(apb)] in good yield. The rhenium atom lies in a distorted trigonal-bipyramidal environment. The two imidazole N(2) atoms lie in the apical positions trans to each other, with the oxo-oxygen and two amido N(1) atoms in the trigonal plane. The complex has C2-symmetry. The two amino groups are singly deprotonated and provide a negative charge each, so that they are coordinated as amides. The oxo group provides two negative charges. In order to obtain electroneutrality for the rhenium(V) complex, the two coordinated imidazole nitrogens provide one negative charge. The complex salt trans-[Re(mps)Cl(PPh3)2](ReO4) (H3mps=N-(2-amino-3- methylphenyl)salicylideneimine) was prepared by the reaction of trans- [ReOCl3(PPh3)2] with a twofold molar excess of H3mps. The X-ray crystal structure shows that the trianionic ligand mps acts as a tridentate chelate via the doubly deprotonated amino nitrogen (which is present in trans- [Re(mps)Cl(PPh3)2](ReO4) as an imide), the neutral imino nitrogen and the deprotonated phenolic oxygen. The [ReO4]- anion has approximately regular tetrahedral geometry. Two significant hydrogen bonds are formed between two of the perrhenyl oxygens and the water of crystallization. The six-coordinated complex cis-[Re(mps)Cl2(PPh3)2] was prepared by the reaction of trans-[ReOCl3(PPh3)2] with a twofold molar excess of H3mps in benzene. The Xray crystal structure shows that the mps ligand coordinates as a tridentate chelate via the doubly deprotonated 2-amino nitrogen, the neutral imino nitrogen and the phenolate oxygen. The imide and phenolate oxygen coordinate trans to each other in a distorted octahedral geometry around the rhenium(V) centre, with the two chlorides in cis positions.
  • Full Text:
  • Date Issued: 2007

Synthesis and characterization of symmetrical and unsymmetrical ferrocenyl ligands for use in the preparation of Redox Active Ruthenium Alkylidene Complexes

  • Authors: Saku, Duduetsang
  • Date: 2007
  • Subjects: Ferrocene , Ligands , Asymmetric synthesis
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:10403 , http://hdl.handle.net/10948/701 , Ferrocene , Ligands , Asymmetric synthesis
  • Description: Oxidation of a ferrocenyl group in conjugation to another metal centre can alter the electron density at that metal centre and lead to a change in overall reactivity of a complex. Herein, the synthesis and characterization of redox active symmetrical and unsymmetrical ferrocenylalkene derivatives is described. A change in the standard redox potential of ferrocene (465 mV), to more positive potentials in vinylferrocene 1 (478 mV) and 4-phenylvinylferrocene 3 (499 mV), showed how manipulation of a redox potential can be effected on the ferrocenyl moiety by just using conjugation effects. A shift by +13 mV is observed in 1 and this potential more than doubled in 3 (+34 mV). Ferrocenylderived ruthenium alkylidene complexes were also prepared in a cross metathesis of 1 and 3 with Grubbs’ 1 (676.5 mV) to give complexes Ferrocenylidenebis( tricyclohexylphosphine)dichlororuthenium 14, 4-ferrocenylphenylidene-bis (tricyclohexylphosphine)dichlororuthenium 15 respectively. The extent of the electronic communication between the ferrocenyl group and the ruthenium centre was then estimated by looking at the positive or negative redox potential shifts of 14 and 15 as a result of 1 and 3. A large positive potential shift by 180 mV in 14 indicated that there was a strong electronic communication between the two metal centres, while the smaller, yet significant positive potential shift by 89.5 mV in 15 showed 3 to have a lesser effect on the ruthenium centre. Compounds 14 and 15 were tested in a Ring Closing Metathesis (RCM) of diethyldiallylmalonate showed enhanced reactivity.
  • Full Text:
  • Date Issued: 2007

Synthesis of P-Methane-3,8-Diol

  • Authors: Mpuhlu, Batsho
  • Date: 2007
  • Subjects: Insect baits and repellents
  • Language: English
  • Type: Thesis , Masters , MTech
  • Identifier: vital:10411 , http://hdl.handle.net/10948/570 , http://hdl.handle.net/10948/d1011717 , Insect baits and repellents
  • Description: The synthesis of para-menthane-3,8-diol in a batch reactor was investigated in some detail with the view to evaluate the potential of producing said p-menthane- 3,8-diol in a continuous-flow reactor from the results obtained from the batch process. The methodology used as base for this investigation was a published procedure by Takasago of Japan. The Takasago-method produced 92.3 percent Yield for the product para-menthane-3,8-diol, and 2.7 percent Yield of the by-product, acetal. The objective for this investigation was to produce a minimum p-menthane-3,8- diol content of 97.0 percent and a maximum content of 3.0 percent for the by-product acetal. The batch production process was evaluated in detail using statistical experimental design methodologies. Three process variables, namely catalyst loading, organic/aqueous phase ratio and reaction temperature were selected for the study. The experimental method was based on the Takasago procedure, however the substrate was added as a single slug as opposed to gradual addition method and the reaction period was reduced to 30 minutes. Apart from statistical analysis, mechanistic aspects were also used to interpret the following results. Using a central composite design, three response models (one for the conversion of citronellal, p-menthane-3,8-diol and acetal formation) were determined. An analysis of the response surfaces indicated that, to increase the citronellal conversion all three variables should be increased. To increase the amount of pmenthane- 3,8-diol, the reaction temperature and acid concentration should be increased, but the Aq/org ratio should be decreased as the acid catalyst concentration is increased. To minimize the amount of acetals formed during the reaction, the Aq/org ratio should be decreased; temperature and acid concentration can be decreased or increased. The reaction mechanism suggested that p-menthane-3,8-diol may be formed along two pathways: One pathway directly forms p-menthane-3,8-diol, whilst the second pathway forms the isopulegol first, then proceeds to form product by hydrolysis. The acetal is formed as result of the reaction between unreacted citronellal and p-menthane-3,8-diol. From the design experiments it was suggested that reaction time can be reduced to 8 minutes at reaction temperatures between, 80-85 0C The product and acetal were isolated by simple vacuum evaporation of the low boiling citronellal and isopulegol. Results from recycling the catalyst phase were similar to those of the initial process. The results of this investigation has clearly shown that with a proper understanding of the effect of process variables on the performance of the batch synthesis route, the conversion of this traditionally batch (actually semi-batch) process into a continuous process is quite feasible provided that suitable equipment is available. The most important features required for such equipment would be: Intense mixing throughout the reaction zone so as to maximise the surface area between the two immiscible phases, hence the rate of mass transfer between the two phases; and the ability to run reactions above the boiling point of water. Plans for the further study of the process are already well underway and sections of static mixing tubes have been acquired to build a continuous lab scale tubular reactor that would be capable of providing the level of mixing required.
  • Full Text:
  • Date Issued: 2007
  • Disclaimer
  • Privacy
  • Copyright
  • Contact