An investigation of the in vitro anticancer properties of selected platinum compounds
- Authors: Du Plessis-Stoman, Debbie
- Date: 2006
- Subjects: Antineoplastic agents , Platinum compounds , Cancer -- Immunological aspects , Cancer -- Chemotherapy
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10334 , http://hdl.handle.net/10948/498 , http://hdl.handle.net/10948/d1012002 , Antineoplastic agents , Platinum compounds , Cancer -- Immunological aspects , Cancer -- Chemotherapy
- Description: This dissertation mainly deals with some biochemical aspects regarding the efficacy of novel platinum anticancer compounds, as part of a broader study in which both chemistry and biochemistry are involved. Various novel diamine and N-S donor chelate compounds of platinum II and IV have been developed in which factors such as stereochemistry, ligand exchange rate and biocompatibility were considered as additional parameters. In the first order testing, each of these compounds was tested with reference to their “killing” potential by comparing their rate of killing, over a period of 48 hours with those of cisplatin and oxaliplatin. Some 80 compounds were tested in this way. Although only a few could be regarded as equal to or even better than cisplatin and oxaliplatin, the testing of these compounds on cancer cells provided useful knowledge for the further development of novel compounds. Four of the better compounds, namely Y9, Y14, Y16 and Lt16.2 were selected for further studies to obtain more detailed knowledge of their anticancer action, including some flow cytometric studies. In addition to the above, cisplatin resistant cells were produced for each of the three different cell lines tested, namely, HeLa, HT29 and MCF7 cancer cell lines, by intermittent and incremental exposure to cisplatin (all the cell lines tested became resistant to cisplatin). Each of the selected compounds were exposed to the cells in the same manner, in order to attempt the induction of resistance against these compounds in the three cell lines tested (i.e. whether these cells will become resistant to the various compounds). Each of these selected platinum containing compounds were subsequently tested against the “cisplatin resistant” cell lines in order to determine their efficacy against such cells. One such compound could be singled out, since cervical cancer cells (HeLa cells) do not become resistant to it. This behaviour is similar to that of oxaliplatin against cervical cancer and colon cancer (HT29) cells (oxaliplatin is the number one treatment for colon cancer at present). This compound also proved to be more active against cisplatin resistant cell lines. It was found that all the compounds induced apoptosis in the cell lines tested as well as inhibit the DNA cycle at one or more phase. Finally, an effort was made to evaluate the different compounds by comparing them with respect to their properties relating to anticancer action.
- Full Text:
- Date Issued: 2006
- Authors: Du Plessis-Stoman, Debbie
- Date: 2006
- Subjects: Antineoplastic agents , Platinum compounds , Cancer -- Immunological aspects , Cancer -- Chemotherapy
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10334 , http://hdl.handle.net/10948/498 , http://hdl.handle.net/10948/d1012002 , Antineoplastic agents , Platinum compounds , Cancer -- Immunological aspects , Cancer -- Chemotherapy
- Description: This dissertation mainly deals with some biochemical aspects regarding the efficacy of novel platinum anticancer compounds, as part of a broader study in which both chemistry and biochemistry are involved. Various novel diamine and N-S donor chelate compounds of platinum II and IV have been developed in which factors such as stereochemistry, ligand exchange rate and biocompatibility were considered as additional parameters. In the first order testing, each of these compounds was tested with reference to their “killing” potential by comparing their rate of killing, over a period of 48 hours with those of cisplatin and oxaliplatin. Some 80 compounds were tested in this way. Although only a few could be regarded as equal to or even better than cisplatin and oxaliplatin, the testing of these compounds on cancer cells provided useful knowledge for the further development of novel compounds. Four of the better compounds, namely Y9, Y14, Y16 and Lt16.2 were selected for further studies to obtain more detailed knowledge of their anticancer action, including some flow cytometric studies. In addition to the above, cisplatin resistant cells were produced for each of the three different cell lines tested, namely, HeLa, HT29 and MCF7 cancer cell lines, by intermittent and incremental exposure to cisplatin (all the cell lines tested became resistant to cisplatin). Each of the selected compounds were exposed to the cells in the same manner, in order to attempt the induction of resistance against these compounds in the three cell lines tested (i.e. whether these cells will become resistant to the various compounds). Each of these selected platinum containing compounds were subsequently tested against the “cisplatin resistant” cell lines in order to determine their efficacy against such cells. One such compound could be singled out, since cervical cancer cells (HeLa cells) do not become resistant to it. This behaviour is similar to that of oxaliplatin against cervical cancer and colon cancer (HT29) cells (oxaliplatin is the number one treatment for colon cancer at present). This compound also proved to be more active against cisplatin resistant cell lines. It was found that all the compounds induced apoptosis in the cell lines tested as well as inhibit the DNA cycle at one or more phase. Finally, an effort was made to evaluate the different compounds by comparing them with respect to their properties relating to anticancer action.
- Full Text:
- Date Issued: 2006
Cytokine signalling functions of human soluble IgE receptors in peripheral blood mononuclear cells from normal and hyper-allergic individuals and in B-lymphoblastoid and monocytic cell lines
- Authors: Askew, Sandra Lyn
- Date: 2006
- Subjects: Ligands , Cell receptors , Cellular signal transduction
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10305 , http://hdl.handle.net/10948/455 , Ligands , Cell receptors , Cellular signal transduction
- Description: CD23 is a multifunctional receptor/ligand, found in a variety of cell types, such as human peripheral blood mononuclear cells (PBMCs), B-lymphoblastoid cell lines, mast cells and basophils. It is also found on a variety of haematopoietic cell lines. As the low-affinity receptor for immunoglobulin E (IgE), CD23 plays a role in antigen-presentation and macrophage activation. As a surface molecule cleaved from the cell membrane, soluble CD23 (sCD23) can act as an adhesion molecule and a cytokine. Perturbances of such molecular interactions may lead to various diseases such as allergies and other inflammatory diseases. It has been speculated that elevated levels of sCD23 may be used to bind secreted IgE, thus preventing it from binding to membrane CD23 on haematopoietic cells, preventing B cells from being activated into IgE producing cells. Signal transduction by sCD23 is dependent on cell subsets, ligands and co-factors required for its function. sCD23 plays a direct role in inducing tumour necrosis factor alpha (TNFα), interleukin-1 alpha (IL-1α) and interleukin-1 beta (IL-1β) and soluble IL-1 receptor from activated human monocytes and PBMCs in vitro. Recombinant forms of 25 and 37 kDa human sCD23 were produced by polymerase chain reaction (PCR)-cloning into pET23a, a bacterial expression vector. The proteins were expressed and refolded, followed by purification by gel filtration chromatography. The purified proteins were biochemically characterized to ensure purity and biological activity, by observing the binding to human IgE both in enzyme-linked immunosorbant assay (ELISA) and surface plasmon resonance (SPR) spectroscopy. ELISA showed KD values of 7.23 x 10-9M and 8.12 x 10-9M for the 25 and 37 kDa proteins, respectively. These values were significantly lower than that of Hibbert et al., (2005). SPR data obtained for the 25 kDa CD23 was not of reliable quality but SPR for the 33kDa sCD23 showed a KD of 1.18 x 10-7M, close to that of Hibbert et al., (2005), J. Exp. Med, 202: 751-760. To test the therapeutic potential of the recombinant molecule, a B-lymphoblastoid cell line (Raji), a pre-monocytic cell line (U937), and PBMCs from normal and hyper-allergic individuals were used. All cells showed no change in production of cytokines. It is essential to investigate further cytokine functions and production implicated by recombinant forms of sCD23, as well as binding of sCD23 to CD21 and CD11b/c, and in vivo IgE regulation before a conclusion can be drawn as to whether recombinant sCD23 is a potential therapeutic target against allergic disease.
- Full Text:
- Date Issued: 2006
- Authors: Askew, Sandra Lyn
- Date: 2006
- Subjects: Ligands , Cell receptors , Cellular signal transduction
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10305 , http://hdl.handle.net/10948/455 , Ligands , Cell receptors , Cellular signal transduction
- Description: CD23 is a multifunctional receptor/ligand, found in a variety of cell types, such as human peripheral blood mononuclear cells (PBMCs), B-lymphoblastoid cell lines, mast cells and basophils. It is also found on a variety of haematopoietic cell lines. As the low-affinity receptor for immunoglobulin E (IgE), CD23 plays a role in antigen-presentation and macrophage activation. As a surface molecule cleaved from the cell membrane, soluble CD23 (sCD23) can act as an adhesion molecule and a cytokine. Perturbances of such molecular interactions may lead to various diseases such as allergies and other inflammatory diseases. It has been speculated that elevated levels of sCD23 may be used to bind secreted IgE, thus preventing it from binding to membrane CD23 on haematopoietic cells, preventing B cells from being activated into IgE producing cells. Signal transduction by sCD23 is dependent on cell subsets, ligands and co-factors required for its function. sCD23 plays a direct role in inducing tumour necrosis factor alpha (TNFα), interleukin-1 alpha (IL-1α) and interleukin-1 beta (IL-1β) and soluble IL-1 receptor from activated human monocytes and PBMCs in vitro. Recombinant forms of 25 and 37 kDa human sCD23 were produced by polymerase chain reaction (PCR)-cloning into pET23a, a bacterial expression vector. The proteins were expressed and refolded, followed by purification by gel filtration chromatography. The purified proteins were biochemically characterized to ensure purity and biological activity, by observing the binding to human IgE both in enzyme-linked immunosorbant assay (ELISA) and surface plasmon resonance (SPR) spectroscopy. ELISA showed KD values of 7.23 x 10-9M and 8.12 x 10-9M for the 25 and 37 kDa proteins, respectively. These values were significantly lower than that of Hibbert et al., (2005). SPR data obtained for the 25 kDa CD23 was not of reliable quality but SPR for the 33kDa sCD23 showed a KD of 1.18 x 10-7M, close to that of Hibbert et al., (2005), J. Exp. Med, 202: 751-760. To test the therapeutic potential of the recombinant molecule, a B-lymphoblastoid cell line (Raji), a pre-monocytic cell line (U937), and PBMCs from normal and hyper-allergic individuals were used. All cells showed no change in production of cytokines. It is essential to investigate further cytokine functions and production implicated by recombinant forms of sCD23, as well as binding of sCD23 to CD21 and CD11b/c, and in vivo IgE regulation before a conclusion can be drawn as to whether recombinant sCD23 is a potential therapeutic target against allergic disease.
- Full Text:
- Date Issued: 2006
Epitaxial growth and characterisation of CuGaS2
- Authors: Branch, Matthew Stewart
- Date: 2006
- Subjects: Epitaxy , Chalcopyrite , Semiconductors
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10541 , http://hdl.handle.net/10948/438 , http://hdl.handle.net/10948/d1012893 , Epitaxy , Chalcopyrite , Semiconductors
- Description: In this work, the growth and characterisation of the chalcopyrite semiconductor CuGaS2 is presented. The purpose of this study is to gain a better understanding of the defect chemistry of this class of materials through a systematic study relating the structural and optical properties to the composition of thin films grown by metalorganic vapour phase epitaxy. Details associated with the optimisation of the growth process are presented in a format relating the changes in the composition and morphology to variations in the growth process. The structural properties of thin films grown on GaAs(001) substrates are described. A dominance of polycrystalline growth is found to occur for Cu-rich material, whereas near-stoichiometric to Ga-rich material is typified by epitaxial growth. Secondary phases are identified by X-ray diffractometry and Raman spectroscopy for severely non-stoichiometric material. In some cases, the formation of the cubic zincblende and CuPt polytype of CuGaS2 are identified by transmission electron microscopy. It will be shown that changes in the Cu/Ga ratio of the solid strongly influence the photoluminescence response of the layers. Weak excitonic luminescence is observed for both slightly Ga-rich and Cu-rich material. Near stoichiometric layers exhibit luminescence centered at ~2.4 eV. Cu-rich layers are dominated by a line occurring at ~2.1 eV, whereas a different line at ~2.25 eV dominates for Ga-rich layers. A clear picture emerges of the radiative mechanisms dominating for Cu-rich and Ga-rich layers.
- Full Text:
- Date Issued: 2006
- Authors: Branch, Matthew Stewart
- Date: 2006
- Subjects: Epitaxy , Chalcopyrite , Semiconductors
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10541 , http://hdl.handle.net/10948/438 , http://hdl.handle.net/10948/d1012893 , Epitaxy , Chalcopyrite , Semiconductors
- Description: In this work, the growth and characterisation of the chalcopyrite semiconductor CuGaS2 is presented. The purpose of this study is to gain a better understanding of the defect chemistry of this class of materials through a systematic study relating the structural and optical properties to the composition of thin films grown by metalorganic vapour phase epitaxy. Details associated with the optimisation of the growth process are presented in a format relating the changes in the composition and morphology to variations in the growth process. The structural properties of thin films grown on GaAs(001) substrates are described. A dominance of polycrystalline growth is found to occur for Cu-rich material, whereas near-stoichiometric to Ga-rich material is typified by epitaxial growth. Secondary phases are identified by X-ray diffractometry and Raman spectroscopy for severely non-stoichiometric material. In some cases, the formation of the cubic zincblende and CuPt polytype of CuGaS2 are identified by transmission electron microscopy. It will be shown that changes in the Cu/Ga ratio of the solid strongly influence the photoluminescence response of the layers. Weak excitonic luminescence is observed for both slightly Ga-rich and Cu-rich material. Near stoichiometric layers exhibit luminescence centered at ~2.4 eV. Cu-rich layers are dominated by a line occurring at ~2.1 eV, whereas a different line at ~2.25 eV dominates for Ga-rich layers. A clear picture emerges of the radiative mechanisms dominating for Cu-rich and Ga-rich layers.
- Full Text:
- Date Issued: 2006
Factors influencing species richness, cover and composition of vegetation on Namaqualand quartz fields
- Authors: Van Tonder, Carlo
- Date: 2006
- Subjects: Plant diversity -- South Africa -- Namaqualand , Soil biology -- South Africa -- Namaqualand
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10752 , http://hdl.handle.net/10948/630 , Plant diversity -- South Africa -- Namaqualand , Soil biology -- South Africa -- Namaqualand
- Description: Quartz fields contribute significantly to plant diversity in the Succulent Karoo biome. They are distinctly different from surrounding habitats and have high levels of plant endemism. Biological soil crusts are features of quartz field soils and fulfill a vital function in that they stabilize soils. It is important for managers of nature reserves and agricultural rangelands to know what factors influence quartz field soils and vegetation. Both stakeholders could benefit from new information that would allow for informed decision-making regarding land-use on quartz fields. The present study took place in the Namaqua National Park that contains a significant proportion of the Riethuis-Wallekraal quartz fields phytochorion. The first part of the study aimed to understand whether certain land-use activities potentially destabilize quartz field soils, which might have possible ramifications for associated biological soil crusts and vegetation. It was followed by relating variation in soil stability with species richness, cover and species composition of quartz field vegetation. Overall, positions assumed to be impacted by land-use activities had less stable soils compared to positions assumed not be impacted. Soil stability had a significant influence on species richness and cover but to a lesser degree on species composition. Quartz field vegetation was significantly influenced by soil physical and chemical properties as well as location in the quartz fields landscape. The second part of the study aimed at understanding how species richness of isolated quartz outcrops is related to their size compared to that of a mainland body of quartz outcrops. No clear species-area relationships emerged from the study. There were significant differences between isolated outcrops and mainland outcrops in substrate and vegetation composition. Findings are discussed in relation to Island Biogeography Theory.
- Full Text:
- Date Issued: 2006
- Authors: Van Tonder, Carlo
- Date: 2006
- Subjects: Plant diversity -- South Africa -- Namaqualand , Soil biology -- South Africa -- Namaqualand
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10752 , http://hdl.handle.net/10948/630 , Plant diversity -- South Africa -- Namaqualand , Soil biology -- South Africa -- Namaqualand
- Description: Quartz fields contribute significantly to plant diversity in the Succulent Karoo biome. They are distinctly different from surrounding habitats and have high levels of plant endemism. Biological soil crusts are features of quartz field soils and fulfill a vital function in that they stabilize soils. It is important for managers of nature reserves and agricultural rangelands to know what factors influence quartz field soils and vegetation. Both stakeholders could benefit from new information that would allow for informed decision-making regarding land-use on quartz fields. The present study took place in the Namaqua National Park that contains a significant proportion of the Riethuis-Wallekraal quartz fields phytochorion. The first part of the study aimed to understand whether certain land-use activities potentially destabilize quartz field soils, which might have possible ramifications for associated biological soil crusts and vegetation. It was followed by relating variation in soil stability with species richness, cover and species composition of quartz field vegetation. Overall, positions assumed to be impacted by land-use activities had less stable soils compared to positions assumed not be impacted. Soil stability had a significant influence on species richness and cover but to a lesser degree on species composition. Quartz field vegetation was significantly influenced by soil physical and chemical properties as well as location in the quartz fields landscape. The second part of the study aimed at understanding how species richness of isolated quartz outcrops is related to their size compared to that of a mainland body of quartz outcrops. No clear species-area relationships emerged from the study. There were significant differences between isolated outcrops and mainland outcrops in substrate and vegetation composition. Findings are discussed in relation to Island Biogeography Theory.
- Full Text:
- Date Issued: 2006
Horticultural propagation of the threatened species, Syncarpha revurvata (L.f.)B. Nord
- Authors: Swart, Pierre André
- Date: 2006
- Subjects: Horticultural crops -- Propagation , Plant propagation , Horticulture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10624 , http://hdl.handle.net/10948/613 , Horticultural crops -- Propagation , Plant propagation , Horticulture
- Description: Syncarpha recurvata (L.f.) B. Nord. (Asteraceae, Gnaphalieae) is listed as a vulnerable (intermediate priority) species. The propagation methods of achene germination, stem cuttings, air layering and micropropagation were investigated to obtain an efficient propagation method. Smoke water dilutions of 1:100, 1:50 and 1:10 significantly increased germination, with the 1:100 smoke water dilutions showing the highest germination percentage (22.4 percent). Achenes collected between August and October 2005 showed higher germination and viability than achenes collected between May and July 2006. Fifty percent of the stem cuttings and 32 percent of the airlayered branches rooted. Embryo culture was the only successful culture type out of the four attempted. Two embryos germinated and four became photosynthetic. Two of the germinated embryos also produced callus cells, a medium supplemented with 5 μM IAA may be used to test for a suitable plant regulator for organogenesis or embryogenesis. Syncarpha recurvata plants were also transplanted into pots and 60 percent survived. A growth rate of 1.466 mm y-1 was obtained from total shoot length measurements. In this study, it was found that air-layering branches of transplanted Syncarpha recurvata plants is the most efficient propagation method.
- Full Text:
- Date Issued: 2006
- Authors: Swart, Pierre André
- Date: 2006
- Subjects: Horticultural crops -- Propagation , Plant propagation , Horticulture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10624 , http://hdl.handle.net/10948/613 , Horticultural crops -- Propagation , Plant propagation , Horticulture
- Description: Syncarpha recurvata (L.f.) B. Nord. (Asteraceae, Gnaphalieae) is listed as a vulnerable (intermediate priority) species. The propagation methods of achene germination, stem cuttings, air layering and micropropagation were investigated to obtain an efficient propagation method. Smoke water dilutions of 1:100, 1:50 and 1:10 significantly increased germination, with the 1:100 smoke water dilutions showing the highest germination percentage (22.4 percent). Achenes collected between August and October 2005 showed higher germination and viability than achenes collected between May and July 2006. Fifty percent of the stem cuttings and 32 percent of the airlayered branches rooted. Embryo culture was the only successful culture type out of the four attempted. Two embryos germinated and four became photosynthetic. Two of the germinated embryos also produced callus cells, a medium supplemented with 5 μM IAA may be used to test for a suitable plant regulator for organogenesis or embryogenesis. Syncarpha recurvata plants were also transplanted into pots and 60 percent survived. A growth rate of 1.466 mm y-1 was obtained from total shoot length measurements. In this study, it was found that air-layering branches of transplanted Syncarpha recurvata plants is the most efficient propagation method.
- Full Text:
- Date Issued: 2006
Impacts of impala on subtropical thicket in the Shamwari Game Reserve, Eastern Cape
- Authors: Gerber, Johann
- Date: 2006
- Subjects: Impala -- Feeding and feeds -- South Africa -- Eastern Cape , Impala -- Habitat -- South Africa -- Eastern Cape , Savannas -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10627 , http://hdl.handle.net/10948/509 , http://hdl.handle.net/10948/d1012011 , Impala -- Feeding and feeds -- South Africa -- Eastern Cape , Impala -- Habitat -- South Africa -- Eastern Cape , Savannas -- South Africa -- Eastern Cape
- Description: Subtropical thicket supports a large variety of indigenous browsing herbivores, such as elephants, black rhino, kudu and bushbuck, but impala historically never occurred in the Eastern Cape. The aim of this study was to determine what impacts extralimital impala (Aepyceros melampus) have on subtropical thicket. The thicket of the Shamwari Game Reserve, Eastern Cape, was used for the study. To quantify the effects of impala, feeding behaviour and diet was investigated during summer and winter. Sixteen impala were also enclosed in a camp of subtropical thicket where they would be limited to feedings on thicket. Vegetation composition and structure were monitored for a period of 12 months in the enclosure. Impala followed the expected high percentage graze and a low percentage browse in thicket in summer. However, the expected was not observed during winter: at this time grazing and browsing were equally important. Field collection of feeding behaviour data showed that impala are attracted to fringes of intact bush clumps or degraded thicket. Analysis of the impala diet confirmed this, with a significantly higher percentage graze (48 percent) than browse (22 percent) during summer. However, during winter, diet analysis indicated grazing to be much higher (36 percent) than browsing (6 percent) with the impala temporarily taking advantage of nutritious grasses still present. The enclosed portion of thicket was originally at 80 percent ecological status but it showed significant changes after addition of 16 impala. Animal trails increased in number and in width, resulting in a trampling effect. Grass cover was significantly different inside the enclosure after 12 months compared to outside. The amount of available browse of the enclosed thicket was also significantly different after addition of the impala. It is concluded that impala have a negative effect on thicket, with trampling the most significant effect. Long term monitoring of the effects of extralimital impala in different types of thicket will be required to accurately quantify their direct effects on subtropical thicket in the Eastern Cape. The main aim of this study was to determine the impacts of impala on Thicket. The study showed significant impacts on Thicket as found in Shamwari, and therefore the aim of the study was achieved.
- Full Text:
- Date Issued: 2006
- Authors: Gerber, Johann
- Date: 2006
- Subjects: Impala -- Feeding and feeds -- South Africa -- Eastern Cape , Impala -- Habitat -- South Africa -- Eastern Cape , Savannas -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10627 , http://hdl.handle.net/10948/509 , http://hdl.handle.net/10948/d1012011 , Impala -- Feeding and feeds -- South Africa -- Eastern Cape , Impala -- Habitat -- South Africa -- Eastern Cape , Savannas -- South Africa -- Eastern Cape
- Description: Subtropical thicket supports a large variety of indigenous browsing herbivores, such as elephants, black rhino, kudu and bushbuck, but impala historically never occurred in the Eastern Cape. The aim of this study was to determine what impacts extralimital impala (Aepyceros melampus) have on subtropical thicket. The thicket of the Shamwari Game Reserve, Eastern Cape, was used for the study. To quantify the effects of impala, feeding behaviour and diet was investigated during summer and winter. Sixteen impala were also enclosed in a camp of subtropical thicket where they would be limited to feedings on thicket. Vegetation composition and structure were monitored for a period of 12 months in the enclosure. Impala followed the expected high percentage graze and a low percentage browse in thicket in summer. However, the expected was not observed during winter: at this time grazing and browsing were equally important. Field collection of feeding behaviour data showed that impala are attracted to fringes of intact bush clumps or degraded thicket. Analysis of the impala diet confirmed this, with a significantly higher percentage graze (48 percent) than browse (22 percent) during summer. However, during winter, diet analysis indicated grazing to be much higher (36 percent) than browsing (6 percent) with the impala temporarily taking advantage of nutritious grasses still present. The enclosed portion of thicket was originally at 80 percent ecological status but it showed significant changes after addition of 16 impala. Animal trails increased in number and in width, resulting in a trampling effect. Grass cover was significantly different inside the enclosure after 12 months compared to outside. The amount of available browse of the enclosed thicket was also significantly different after addition of the impala. It is concluded that impala have a negative effect on thicket, with trampling the most significant effect. Long term monitoring of the effects of extralimital impala in different types of thicket will be required to accurately quantify their direct effects on subtropical thicket in the Eastern Cape. The main aim of this study was to determine the impacts of impala on Thicket. The study showed significant impacts on Thicket as found in Shamwari, and therefore the aim of the study was achieved.
- Full Text:
- Date Issued: 2006
Metabolic effects brought about by tricyclic antidepressants and the contribution of a medicinal plant in alleviating high fat diet induced insulin resistance in male wistar rats
- Authors: Chadwick, Wayne
- Date: 2006
- Subjects: Rats -- Metabolism , Diabetes -- Research , Medicinal plants -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10329 , http://hdl.handle.net/10948/461 , Rats -- Metabolism , Diabetes -- Research , Medicinal plants -- South Africa
- Description: Type II diabetes is becoming a growing problem in developed countries worldwide. The median age for diagnosis was around sixty, but recent surveys have shown that the entire age distribution curve shifting left. The incidence of type II diabetes is thought to be parallel with the growing rate of obesity associated with an unhealthy western diet. Type II diabetes is an expensive disease to manage, it is for this reason that cheaper medication needs to be investigated in the form of traditional plants, such as Sutherlandia frutescens. Prescription medication, such as tricyclic antidepressants, may also increase body weight thereby playing a role in obesity. The cause of weight gain in such cases may go unrecognized or lead to cessation of the medication with or without the practitioner’s knowledge or approval. It is therefore necessary to investigate the causative agents responsible for the excessive weight gain. Drinking water containing extracts of S. frutescens or metformin was administered to two groups of eleven insulin resistant male Wistar rats. The insulin resistant control group received water without any medication. Rats were sacrificed after 8 weeks allowing for fasting blood glucose, insulin and tissue glycogen content determination. Glucose uptake was also determined using [3H] deoxyglucose. The effect of the medication and the diet on muscle post receptor insulin signaling proteins was determined through Western blots. Liver proteomics was also performed using 2-D electrophoresis. In a separate experiment 26 male Wistar rats were exposed to strepotozotocin toxin, 7 of these rats received intravenous insulin treatment, 7 rats received S. frutescens extract and 7 rats received a combination of both medications, the remaining 5 received no treatment and served as the control. Rats were sacrificed after 6 days allowing for fasting blood glucose, insulin and tissue glycogen content determination. Two groups of 14 male Wistar rats received amitriptyline or trimipramine (common tricyclic antidepressants) in their drinking water, the control group (30 rats) received water without any medication. The rats’ weight and food consumption was monitored throughout the trial and their oxygen consumption was also determined. Rats were sacrificed after 6 weeks or 14 weeks of medicinal compliance allowing for fasting blood glucose, insulin and tissue glycogen content determination. Glucose uptake was also determined using [3H] deoxyglucose. S. frutescens treatment normalized circulating serum insulin levels and significantly increased the rate of glucose clearance. Certain post receptor insulin signaling proteins were also significantly increased relative to the insulin resistant control group. 2-D electrophoresis identified the normalization of protein levels associated with the urea cycle. S. frutescens was also able to, independently; maintain normoglycaemic levels in the strepotozotocin treated group. The tricyclic antidepressants significantly increased blood glucose levels while significantly reducing tissue glycogen levels for both sacrifice periods. Serum insulin remained unchanged while a significant increase in insulin degradation and insulin degrading enzyme levels were found for both antidepressants. S. frutescens shows promise as a low cost antidiabetic medication for future use. Although the antidepressants did not promote weight gain, the increase in blood glucose levels may be cause for concern in patients with a pre-disposition toward developing diabetes.
- Full Text:
- Date Issued: 2006
- Authors: Chadwick, Wayne
- Date: 2006
- Subjects: Rats -- Metabolism , Diabetes -- Research , Medicinal plants -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10329 , http://hdl.handle.net/10948/461 , Rats -- Metabolism , Diabetes -- Research , Medicinal plants -- South Africa
- Description: Type II diabetes is becoming a growing problem in developed countries worldwide. The median age for diagnosis was around sixty, but recent surveys have shown that the entire age distribution curve shifting left. The incidence of type II diabetes is thought to be parallel with the growing rate of obesity associated with an unhealthy western diet. Type II diabetes is an expensive disease to manage, it is for this reason that cheaper medication needs to be investigated in the form of traditional plants, such as Sutherlandia frutescens. Prescription medication, such as tricyclic antidepressants, may also increase body weight thereby playing a role in obesity. The cause of weight gain in such cases may go unrecognized or lead to cessation of the medication with or without the practitioner’s knowledge or approval. It is therefore necessary to investigate the causative agents responsible for the excessive weight gain. Drinking water containing extracts of S. frutescens or metformin was administered to two groups of eleven insulin resistant male Wistar rats. The insulin resistant control group received water without any medication. Rats were sacrificed after 8 weeks allowing for fasting blood glucose, insulin and tissue glycogen content determination. Glucose uptake was also determined using [3H] deoxyglucose. The effect of the medication and the diet on muscle post receptor insulin signaling proteins was determined through Western blots. Liver proteomics was also performed using 2-D electrophoresis. In a separate experiment 26 male Wistar rats were exposed to strepotozotocin toxin, 7 of these rats received intravenous insulin treatment, 7 rats received S. frutescens extract and 7 rats received a combination of both medications, the remaining 5 received no treatment and served as the control. Rats were sacrificed after 6 days allowing for fasting blood glucose, insulin and tissue glycogen content determination. Two groups of 14 male Wistar rats received amitriptyline or trimipramine (common tricyclic antidepressants) in their drinking water, the control group (30 rats) received water without any medication. The rats’ weight and food consumption was monitored throughout the trial and their oxygen consumption was also determined. Rats were sacrificed after 6 weeks or 14 weeks of medicinal compliance allowing for fasting blood glucose, insulin and tissue glycogen content determination. Glucose uptake was also determined using [3H] deoxyglucose. S. frutescens treatment normalized circulating serum insulin levels and significantly increased the rate of glucose clearance. Certain post receptor insulin signaling proteins were also significantly increased relative to the insulin resistant control group. 2-D electrophoresis identified the normalization of protein levels associated with the urea cycle. S. frutescens was also able to, independently; maintain normoglycaemic levels in the strepotozotocin treated group. The tricyclic antidepressants significantly increased blood glucose levels while significantly reducing tissue glycogen levels for both sacrifice periods. Serum insulin remained unchanged while a significant increase in insulin degradation and insulin degrading enzyme levels were found for both antidepressants. S. frutescens shows promise as a low cost antidiabetic medication for future use. Although the antidepressants did not promote weight gain, the increase in blood glucose levels may be cause for concern in patients with a pre-disposition toward developing diabetes.
- Full Text:
- Date Issued: 2006
On the characterisation of copper indium diselenide based photovoltaic devices
- Authors: Thantsha, Nicolas Matome
- Date: 2006
- Subjects: Photovoltaic cells
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10536 , http://hdl.handle.net/10948/443 , Photovoltaic cells
- Description: Photovoltaic (PV) modules based on thin film systems of CuInSe2 (CIS) and its alloys on low cost substrates are promising candidates to meet the long term efficiency, reliability and manufacturing cost goals. The attention to the CIS solar cell technology is because of the high absorption coefficient of the solar cell absorber layer. Solar cells and PV modules are conventionally assessed by measuring the currentvoltage characteristic of the device. This thesis presents an assessment procedure developed capable of assessing the device parameters with reference to I-V measurements. This thesis then characterizes the performance of the CIS based solar cells and modules in conjunction with other PV modules of different technologies such as crystalline Silicon modules by analyzing the light and dark I-V measurements of the devices. The light and dark I-V characteristics of PV devices were investigated and device parameters were extracted from the I-V data. The extraction and interpretation of these device parameters has a variety of important applications. It has been proven that the device parameters can be used for quality control during production and to provide insights into the operation of the PV devices, thereby improving the efficiency of the devices. The assessment comprises light I-V measurements at standard test conditions (STC), irradiance dependence measurements, parasitic series and shunt resistances measurements and the dark I-V measurements of the PV devices. The PV modules assessed comprise different technologies, namely, thin film based modules (CIS and a-Si) and multicrystalline Si and Edged-defined Film-fed Growth Si (EFG-Si). The dark I-V measurements results showed that the EFG-Si module has acceptable shunt (900 W) and series (0.4 W) resistances, thereby leading to the higher power output depicted from the light I-V measurements. The low quality cells of a-Si module were so low that the fill factor was the smallest (43%). In addition, the dark I-V measurements results revealed that CIS modules are less dependent to temperature at high voltages.
- Full Text:
- Date Issued: 2006
- Authors: Thantsha, Nicolas Matome
- Date: 2006
- Subjects: Photovoltaic cells
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10536 , http://hdl.handle.net/10948/443 , Photovoltaic cells
- Description: Photovoltaic (PV) modules based on thin film systems of CuInSe2 (CIS) and its alloys on low cost substrates are promising candidates to meet the long term efficiency, reliability and manufacturing cost goals. The attention to the CIS solar cell technology is because of the high absorption coefficient of the solar cell absorber layer. Solar cells and PV modules are conventionally assessed by measuring the currentvoltage characteristic of the device. This thesis presents an assessment procedure developed capable of assessing the device parameters with reference to I-V measurements. This thesis then characterizes the performance of the CIS based solar cells and modules in conjunction with other PV modules of different technologies such as crystalline Silicon modules by analyzing the light and dark I-V measurements of the devices. The light and dark I-V characteristics of PV devices were investigated and device parameters were extracted from the I-V data. The extraction and interpretation of these device parameters has a variety of important applications. It has been proven that the device parameters can be used for quality control during production and to provide insights into the operation of the PV devices, thereby improving the efficiency of the devices. The assessment comprises light I-V measurements at standard test conditions (STC), irradiance dependence measurements, parasitic series and shunt resistances measurements and the dark I-V measurements of the PV devices. The PV modules assessed comprise different technologies, namely, thin film based modules (CIS and a-Si) and multicrystalline Si and Edged-defined Film-fed Growth Si (EFG-Si). The dark I-V measurements results showed that the EFG-Si module has acceptable shunt (900 W) and series (0.4 W) resistances, thereby leading to the higher power output depicted from the light I-V measurements. The low quality cells of a-Si module were so low that the fill factor was the smallest (43%). In addition, the dark I-V measurements results revealed that CIS modules are less dependent to temperature at high voltages.
- Full Text:
- Date Issued: 2006
Optimisation of an in vitro model for anti-diabetic screening
- Authors: Wilson, Gayle Pamela
- Date: 2006
- Subjects: Hypoglycemic agents , Diabetes -- Treatment -- South Africa , Materia medica, Vegetable -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10308 , http://hdl.handle.net/10948/428 , Hypoglycemic agents , Diabetes -- Treatment -- South Africa , Materia medica, Vegetable -- South Africa
- Description: The need for alternative strategies for the prevention and treatment of diabetes is growing rapidly as type II diabetes is reaching epidemic status in our society. This need was the basis for the creation of this study, as it was necessary to start looking towards medicinal plants as potential antidiabetic treatment and no comprehensive in vitro model existed. In creating a model for determining the effects of alternative traditional medicines as antidiabetic potentiates, it was necessary that two metabolic pathways, namely glucose uptake and insulin secretion, which play a significant role in glucose homeostasis, be at the centre of our investigations. The objective of this project was to optimize the methodology required to screen and ultimately determine the effectiveness of the plant extracts Kankerbos and MRC2003, as antidiabetic potentiates, through observing their effects on glucose utilisation and insulin secretion. If these medicinal plants are going to make a positive contribution to the health of type II diabetic South Africans, then the determination of their efficacy is essential. The cell lines used in this study included 3T3-L1 preadipocytes, Chang liver, C2C12 muscle and INS-1 rat pancreatic cells. Each cell line represents a different in vivo organ that is known to have an influence on glucose homeostasis in our bodies, each with its own unique metabolic pathways and mechanisms of activity, thereby making each one a vital component in the study. The positive controls for the two models were insulin and metformin (glucose utilisation) and glibenclamide (insulin secretion). Insulin was shown to provide a significant increase in the amount of glucose taken up in C2C12 muscle and Chang liver cells for acute conditions. Chronic treatments with metformin provided a significant increase in glucose utilised by Chang liver cells. Glibenclamide was an effective positive control for stimulating insulin secretion by INS-1 cells under acute conditions as there was a significant increase in the amount of insulin secreted. MRC2003 did not show any significant antidiabetic activity. Sutherlandia frutescens (Kankerbos) showed biological activities comparable to some of the more recognized antidiabetic compounds throughout the study. With regards to the glucose utilisation model, Kankerbos was seen to have both acute and chronic effects in different cell lines. In the C2C12 muscle cell line, Kankerbos significantly increased glucose uptake when they were exposed to acute conditions. Kankerbos also had a significant effect on the Chang liver cells as it was observed that under both acute and chronic conditions, this plant extract induced the uptake of glucose into these cells. With respect to the insulin secretion model involving INS-1 cells, no significant effect was seen during acute exposure with Kankerbos treatment. However during chronic exposure, an increase in insulin secretion was initiated by this plant extract. Overall, the results of this study suggest that Kankerbos has a twofold mechanism of action for its glucose-lowering effects. Given that Kankerbos is widely available in South Africa, this study was valuable as it provided an indication that Kankerbos has antidiabetic activities and could possibly be used as an alternative antidiabetic medication.
- Full Text:
- Date Issued: 2006
- Authors: Wilson, Gayle Pamela
- Date: 2006
- Subjects: Hypoglycemic agents , Diabetes -- Treatment -- South Africa , Materia medica, Vegetable -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10308 , http://hdl.handle.net/10948/428 , Hypoglycemic agents , Diabetes -- Treatment -- South Africa , Materia medica, Vegetable -- South Africa
- Description: The need for alternative strategies for the prevention and treatment of diabetes is growing rapidly as type II diabetes is reaching epidemic status in our society. This need was the basis for the creation of this study, as it was necessary to start looking towards medicinal plants as potential antidiabetic treatment and no comprehensive in vitro model existed. In creating a model for determining the effects of alternative traditional medicines as antidiabetic potentiates, it was necessary that two metabolic pathways, namely glucose uptake and insulin secretion, which play a significant role in glucose homeostasis, be at the centre of our investigations. The objective of this project was to optimize the methodology required to screen and ultimately determine the effectiveness of the plant extracts Kankerbos and MRC2003, as antidiabetic potentiates, through observing their effects on glucose utilisation and insulin secretion. If these medicinal plants are going to make a positive contribution to the health of type II diabetic South Africans, then the determination of their efficacy is essential. The cell lines used in this study included 3T3-L1 preadipocytes, Chang liver, C2C12 muscle and INS-1 rat pancreatic cells. Each cell line represents a different in vivo organ that is known to have an influence on glucose homeostasis in our bodies, each with its own unique metabolic pathways and mechanisms of activity, thereby making each one a vital component in the study. The positive controls for the two models were insulin and metformin (glucose utilisation) and glibenclamide (insulin secretion). Insulin was shown to provide a significant increase in the amount of glucose taken up in C2C12 muscle and Chang liver cells for acute conditions. Chronic treatments with metformin provided a significant increase in glucose utilised by Chang liver cells. Glibenclamide was an effective positive control for stimulating insulin secretion by INS-1 cells under acute conditions as there was a significant increase in the amount of insulin secreted. MRC2003 did not show any significant antidiabetic activity. Sutherlandia frutescens (Kankerbos) showed biological activities comparable to some of the more recognized antidiabetic compounds throughout the study. With regards to the glucose utilisation model, Kankerbos was seen to have both acute and chronic effects in different cell lines. In the C2C12 muscle cell line, Kankerbos significantly increased glucose uptake when they were exposed to acute conditions. Kankerbos also had a significant effect on the Chang liver cells as it was observed that under both acute and chronic conditions, this plant extract induced the uptake of glucose into these cells. With respect to the insulin secretion model involving INS-1 cells, no significant effect was seen during acute exposure with Kankerbos treatment. However during chronic exposure, an increase in insulin secretion was initiated by this plant extract. Overall, the results of this study suggest that Kankerbos has a twofold mechanism of action for its glucose-lowering effects. Given that Kankerbos is widely available in South Africa, this study was valuable as it provided an indication that Kankerbos has antidiabetic activities and could possibly be used as an alternative antidiabetic medication.
- Full Text:
- Date Issued: 2006
SL-model for paired comparisons
- Authors: Sjölander, Morné Rowan
- Date: 2006
- Subjects: Paired comparisons (Statistics) , Mathematical statistics
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10574 , http://hdl.handle.net/10948/605 , Paired comparisons (Statistics) , Mathematical statistics
- Description: The method of paired comparisons can be found all the way back to 1860, where Fechner made the first publication in this method, using it for his psychometric investigations [4]. Thurstone formalised the method by providing a mathematical background to it [9-11] and in 1927 the method’s birth took place with his psychometric publications, one being “a law of comparative judgment” [12-14]. The law of comparative judgment is a set of equations relating the proportion of times any stimulus k is judged greater on a given attribute than any other stimulus j to the scales and discriminal dispersions of the two stimuli on the psychological continuum. The amount of research done for discrete models of paired comparisons is not a lot. This study develops a new discrete model, the SL-model for paired comparisons. Paired comparisons data processing in which objects have an upper limit to their scores was also not yet developed, and making such a model is one of the aims of this report. The SLmodel is thus developed in this context; however, the model easily generalises to not necessarily having an upper limit on scores.
- Full Text:
- Date Issued: 2006
- Authors: Sjölander, Morné Rowan
- Date: 2006
- Subjects: Paired comparisons (Statistics) , Mathematical statistics
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10574 , http://hdl.handle.net/10948/605 , Paired comparisons (Statistics) , Mathematical statistics
- Description: The method of paired comparisons can be found all the way back to 1860, where Fechner made the first publication in this method, using it for his psychometric investigations [4]. Thurstone formalised the method by providing a mathematical background to it [9-11] and in 1927 the method’s birth took place with his psychometric publications, one being “a law of comparative judgment” [12-14]. The law of comparative judgment is a set of equations relating the proportion of times any stimulus k is judged greater on a given attribute than any other stimulus j to the scales and discriminal dispersions of the two stimuli on the psychological continuum. The amount of research done for discrete models of paired comparisons is not a lot. This study develops a new discrete model, the SL-model for paired comparisons. Paired comparisons data processing in which objects have an upper limit to their scores was also not yet developed, and making such a model is one of the aims of this report. The SLmodel is thus developed in this context; however, the model easily generalises to not necessarily having an upper limit on scores.
- Full Text:
- Date Issued: 2006
The effect of different slaughter age regimes on the primary and secondary production parameters of Ostriches (Struthio Camelus Domesticus) and the economic consequences of different slaughter ages
- Authors: Bhiya, Clovis Solomon
- Date: 2006
- Subjects: Slaughtering and slaughter-houses -- South Africa , Ostrich farming -- South Africa , Ostriches -- Breeding -- South Africa
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10735 , http://hdl.handle.net/10948/837 , Slaughtering and slaughter-houses -- South Africa , Ostrich farming -- South Africa , Ostriches -- Breeding -- South Africa
- Description: The South African ostrich industry is presently characterised by a drastic decline in the slaughter price of slaughter birds, due to the drop in the price of meat as well as leather. As a result, the economic viability of ostrich farming is severely hampered by these developments, and many generally accepted industry practices have to be reviewed. Among the practices under review is the possibility of slaughtering ostriches at an earlier age than the traditional slaughter age of 12 - 14 months, in order to minimise feed costs and the incidence of damage to the skin. However, little information is available on the effect of the slaughter age on the yield and quality of the economically important end-products. The effect of slaughter age on production and the economic viability of a commercially intensive ostrich production system was consequently evaluated in a completely randomised experimental design involving two batches (n= 81 and n= 94) of ostriches. The experiments took place at Kromme Rhee experimental farm of the Elsenburg Research Centre near Stellenbosch. The birds were subject to experimental treatment at the age of 4 months (n= 81, from May 2004 to March 2005) and 6 months (n= 94, from August 2004 to August 2005) respectively. The ostriches were randomly divided into 10 groups of between 16 and 20 birds per group. Standard production practices, as applied in an intensive ostrich production unit, were implemented. Clean drinking water and self-mixed grower diet (min 15 percent crude protein, 0.68 percent lysine and 11.4 MJ ME per kg feed) and finisher diet (min 14 percent crude protein, 0.55 percent lysine and 9.8 MJ ME per kg feed) were provided ad libitum to the birds. Birds were slaughtered at the ages of 8.5, 10.5, 12.5, 14.5, and 16.5 months respectively. Data on feed intake and yields of cold carcass, crust skin size, skin grade and total feathers was recorded for birds slaughtered at the respective ages. Data was analysed according to the analysis of variances. Values for meat yield, skin size yield and feed intake were predicted by regression analysis based on experimental values. Industry figures and norms were used as proxy for other production inputs and costs. A gross margin type analysis was performed to evaluate the effect of different slaughter ages on the profitability of each production system. There was a positive correlation between age and feed intake (r2= 0.40), slaughter weight (r2= 0.97), cold carcass yield (r2= 0.48), skin surface area (r2= 0.39), skin grade (r2= 0.19) and total yield of feathers (r2= 0.29). The dry skin grade showed deterioration as slaughter age was prolonged. Highly significant differences (P< 0.01) in slaughter weight, cold carcass yield, skin surface area, dry skin grade and total feathers were detected at the different slaughter ages. There were no significant differences (P> 0.05) with respect to gender for slaughter weight, skin surface area and dry skin grade within the different age groups. Males had significantly higher (P< 0.05) cold carcass yield and total feather yield than their female counterparts. From this study it can be concluded that an increase in slaughter age significantly increases feed intake, slaughter weight, cold carcass yield, and skin surface area. It is also clear that an increase in slaughter age can be detrimental to dry skin grade. The relative income contribution of the three main products (skin: meat: feathers) occurred in a ratio of 47:53:0, 52:47:1, 47:50:3, 44:51:5, 39:56:5 at the respective slaughter ages. Total income revealed an increase of 26 percent from 8.5 to 10.5 months slaughtering, an increase of 4 percent between 10.5 and 12.5 months, and an increase of 11 percent between 12.5 and 14.5 months. The income dropped by 0.3 percent between 14.5 and 16.5 months slaughtering. Total costs increased with slaughter age, particularly feed costs which showed an increase (at a decreasing rate) between the different slaughter ages. The margin above specified cost per bird was the highest for birds slaughtered at the age of 10.5 months. The margin above cost showed a steady decline as birds were slaughtered at higher ages. Slaughtering at 16.5 months revealed a negative margin. To compare the effect of differences in time span on different slaughter age regimes, margin above costs for each system over 5 years were discounted to a present value. In this study, with current feed costs and income from end products, slaughtering at 10.5 months revealed the highest present value for the margin above cost. Furthermore, slaughtering at 16.5 months revealed a negative present value on the margin above cost after 5 years. Financial viability calculations are relevant and valid for data obtained in this case study. Financial viability is however case-specific and may vary between producers, depending on their individual management practices, production systems and cost structures. Results from this study may be of significant value to managerial decision-making in the ostrich industry.
- Full Text:
- Date Issued: 2006
- Authors: Bhiya, Clovis Solomon
- Date: 2006
- Subjects: Slaughtering and slaughter-houses -- South Africa , Ostrich farming -- South Africa , Ostriches -- Breeding -- South Africa
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10735 , http://hdl.handle.net/10948/837 , Slaughtering and slaughter-houses -- South Africa , Ostrich farming -- South Africa , Ostriches -- Breeding -- South Africa
- Description: The South African ostrich industry is presently characterised by a drastic decline in the slaughter price of slaughter birds, due to the drop in the price of meat as well as leather. As a result, the economic viability of ostrich farming is severely hampered by these developments, and many generally accepted industry practices have to be reviewed. Among the practices under review is the possibility of slaughtering ostriches at an earlier age than the traditional slaughter age of 12 - 14 months, in order to minimise feed costs and the incidence of damage to the skin. However, little information is available on the effect of the slaughter age on the yield and quality of the economically important end-products. The effect of slaughter age on production and the economic viability of a commercially intensive ostrich production system was consequently evaluated in a completely randomised experimental design involving two batches (n= 81 and n= 94) of ostriches. The experiments took place at Kromme Rhee experimental farm of the Elsenburg Research Centre near Stellenbosch. The birds were subject to experimental treatment at the age of 4 months (n= 81, from May 2004 to March 2005) and 6 months (n= 94, from August 2004 to August 2005) respectively. The ostriches were randomly divided into 10 groups of between 16 and 20 birds per group. Standard production practices, as applied in an intensive ostrich production unit, were implemented. Clean drinking water and self-mixed grower diet (min 15 percent crude protein, 0.68 percent lysine and 11.4 MJ ME per kg feed) and finisher diet (min 14 percent crude protein, 0.55 percent lysine and 9.8 MJ ME per kg feed) were provided ad libitum to the birds. Birds were slaughtered at the ages of 8.5, 10.5, 12.5, 14.5, and 16.5 months respectively. Data on feed intake and yields of cold carcass, crust skin size, skin grade and total feathers was recorded for birds slaughtered at the respective ages. Data was analysed according to the analysis of variances. Values for meat yield, skin size yield and feed intake were predicted by regression analysis based on experimental values. Industry figures and norms were used as proxy for other production inputs and costs. A gross margin type analysis was performed to evaluate the effect of different slaughter ages on the profitability of each production system. There was a positive correlation between age and feed intake (r2= 0.40), slaughter weight (r2= 0.97), cold carcass yield (r2= 0.48), skin surface area (r2= 0.39), skin grade (r2= 0.19) and total yield of feathers (r2= 0.29). The dry skin grade showed deterioration as slaughter age was prolonged. Highly significant differences (P< 0.01) in slaughter weight, cold carcass yield, skin surface area, dry skin grade and total feathers were detected at the different slaughter ages. There were no significant differences (P> 0.05) with respect to gender for slaughter weight, skin surface area and dry skin grade within the different age groups. Males had significantly higher (P< 0.05) cold carcass yield and total feather yield than their female counterparts. From this study it can be concluded that an increase in slaughter age significantly increases feed intake, slaughter weight, cold carcass yield, and skin surface area. It is also clear that an increase in slaughter age can be detrimental to dry skin grade. The relative income contribution of the three main products (skin: meat: feathers) occurred in a ratio of 47:53:0, 52:47:1, 47:50:3, 44:51:5, 39:56:5 at the respective slaughter ages. Total income revealed an increase of 26 percent from 8.5 to 10.5 months slaughtering, an increase of 4 percent between 10.5 and 12.5 months, and an increase of 11 percent between 12.5 and 14.5 months. The income dropped by 0.3 percent between 14.5 and 16.5 months slaughtering. Total costs increased with slaughter age, particularly feed costs which showed an increase (at a decreasing rate) between the different slaughter ages. The margin above specified cost per bird was the highest for birds slaughtered at the age of 10.5 months. The margin above cost showed a steady decline as birds were slaughtered at higher ages. Slaughtering at 16.5 months revealed a negative margin. To compare the effect of differences in time span on different slaughter age regimes, margin above costs for each system over 5 years were discounted to a present value. In this study, with current feed costs and income from end products, slaughtering at 10.5 months revealed the highest present value for the margin above cost. Furthermore, slaughtering at 16.5 months revealed a negative present value on the margin above cost after 5 years. Financial viability calculations are relevant and valid for data obtained in this case study. Financial viability is however case-specific and may vary between producers, depending on their individual management practices, production systems and cost structures. Results from this study may be of significant value to managerial decision-making in the ostrich industry.
- Full Text:
- Date Issued: 2006
Volhoubaarheid van die kommersiële benutting van inheemse dekriet (Thamnochortus insignis) in die Suid-Kaap
- Authors: Horn, Johan Andries Muller
- Date: 2006
- Subjects: Fynbos -- Harvesting -- South Africa , Thatched roofs -- South Africa
- Language: Afrikaans
- Type: Thesis , Masters , MTech
- Identifier: vital:10591 , http://hdl.handle.net/10948/836 , http://hdl.handle.net/10948/d1012882 , Fynbos -- Harvesting -- South Africa , Thatched roofs -- South Africa
- Description: Thamnochortus insignis (Albertinia thatching reed) is a restio specie which is endemic in the narrow (20 km wide) coastal dune veld, from the Gouritz River in the east to the Breede River in the west (120 km). The area within this belt, where this reed is the dominant restio, covers 65 500 hectares. The culms of the reed is harvested as a natural product from the veld and used as thatch on roofs of houses. The traditional use has been as roofing material in Cape Dutch architecture. At this time, thatch roofs are regarded as a luxury commodity and are used in prestigious residential areas and also eco-friendly housing developments. The first section of the research project was based on a Delphi technique questionnaire completed first by 37 and secondly by 10 stakeholders in the industry. This group of growers, contract harvesters, crop agents and thatchers represented 80 percent percent of the estimated 2005 harvest and 87 percent of the estimated farm gate crop value. The thatching reed industry is the main agricultural enterprise situated in the coastal dune veld of the Southern Cape, i.e. 55 percent of total Gross Product Value generated by the survey respondents. The second section is based on an analysis of experimental harvest plots (50 m2), selected at random (4 replications per site) in the 2 x 3 different production systems, i.e. traditional harvest from natural veld, harvest from veld which had been subjected to mechanical injury ("sleep") and harvest from established orchard-type lands. Harvest data was collected at each site in terms of the following components, i.e. number of harvestable tussocks, circumference of tussocks and number of reed bundles (minimum circumference 210 mm, minimum length 1,2 m). The gross income per site was calculated on the basis of R1,80 per bundle (2006-price level). Economic analysis (Gross Margin above selected costs) indicates that plant density (reed tussocks/ha) is a critical factor, in order to offset the establishment cost of R2 100/ha in established lands, which is not incurred in the other two production systems. Economic returns from the first planted lands (2 100 and 2 900 plants/ha) averaged R7 666/ha against R8 781/ha for the mechanical-injury plants. However, at a density of 5 000 plants/ha, the projected Gross Margin increases to R15 765/ha. The use of mechanicalinjury and natural vegetation production systems both interfere with biodiversity and raise major concerns with regard to sustainability of the sensitive coastal dune fynbos. ANOVA-analysis of the data indicates a highly significant difference (p = 0,01) for all sites and production systems. Statistical analysis of averages indicates that mechanical injury treatment results in a significant increase in the number of tussocks, when compared to established and natural veld, respectively. The variance in the circumference of tussocks was greatest in natural veld (55 to 71 percent) and mechanical injury (54 to 61 percent). Tussocks harvested from established plantings reflected the least level of variance (28 to 38 percent). The larger reed tussocks in the established lands produced more bundles of marketable reed (8 200/ha) than the mechanical-injury (7 625/ha) and natural veld (3 450/ha) respectively. Establishment of T. insignis plantlets in an "orchard" system at spacings of 2 m x 1 m on previous winter cereal lands or old pastures, is shown to meet all the requirements within a sustainable production system, i.e. viability, productivity, environmental-friendly, risk management and social acceptance. Furthermore, the quality of the yield was in line with the proposed grading standard for thatching reed, i.e. minimum circumference 210 mm, minimum length 1,2 m and less than 6,5 percent grey culm content.
- Full Text:
- Date Issued: 2006
- Authors: Horn, Johan Andries Muller
- Date: 2006
- Subjects: Fynbos -- Harvesting -- South Africa , Thatched roofs -- South Africa
- Language: Afrikaans
- Type: Thesis , Masters , MTech
- Identifier: vital:10591 , http://hdl.handle.net/10948/836 , http://hdl.handle.net/10948/d1012882 , Fynbos -- Harvesting -- South Africa , Thatched roofs -- South Africa
- Description: Thamnochortus insignis (Albertinia thatching reed) is a restio specie which is endemic in the narrow (20 km wide) coastal dune veld, from the Gouritz River in the east to the Breede River in the west (120 km). The area within this belt, where this reed is the dominant restio, covers 65 500 hectares. The culms of the reed is harvested as a natural product from the veld and used as thatch on roofs of houses. The traditional use has been as roofing material in Cape Dutch architecture. At this time, thatch roofs are regarded as a luxury commodity and are used in prestigious residential areas and also eco-friendly housing developments. The first section of the research project was based on a Delphi technique questionnaire completed first by 37 and secondly by 10 stakeholders in the industry. This group of growers, contract harvesters, crop agents and thatchers represented 80 percent percent of the estimated 2005 harvest and 87 percent of the estimated farm gate crop value. The thatching reed industry is the main agricultural enterprise situated in the coastal dune veld of the Southern Cape, i.e. 55 percent of total Gross Product Value generated by the survey respondents. The second section is based on an analysis of experimental harvest plots (50 m2), selected at random (4 replications per site) in the 2 x 3 different production systems, i.e. traditional harvest from natural veld, harvest from veld which had been subjected to mechanical injury ("sleep") and harvest from established orchard-type lands. Harvest data was collected at each site in terms of the following components, i.e. number of harvestable tussocks, circumference of tussocks and number of reed bundles (minimum circumference 210 mm, minimum length 1,2 m). The gross income per site was calculated on the basis of R1,80 per bundle (2006-price level). Economic analysis (Gross Margin above selected costs) indicates that plant density (reed tussocks/ha) is a critical factor, in order to offset the establishment cost of R2 100/ha in established lands, which is not incurred in the other two production systems. Economic returns from the first planted lands (2 100 and 2 900 plants/ha) averaged R7 666/ha against R8 781/ha for the mechanical-injury plants. However, at a density of 5 000 plants/ha, the projected Gross Margin increases to R15 765/ha. The use of mechanicalinjury and natural vegetation production systems both interfere with biodiversity and raise major concerns with regard to sustainability of the sensitive coastal dune fynbos. ANOVA-analysis of the data indicates a highly significant difference (p = 0,01) for all sites and production systems. Statistical analysis of averages indicates that mechanical injury treatment results in a significant increase in the number of tussocks, when compared to established and natural veld, respectively. The variance in the circumference of tussocks was greatest in natural veld (55 to 71 percent) and mechanical injury (54 to 61 percent). Tussocks harvested from established plantings reflected the least level of variance (28 to 38 percent). The larger reed tussocks in the established lands produced more bundles of marketable reed (8 200/ha) than the mechanical-injury (7 625/ha) and natural veld (3 450/ha) respectively. Establishment of T. insignis plantlets in an "orchard" system at spacings of 2 m x 1 m on previous winter cereal lands or old pastures, is shown to meet all the requirements within a sustainable production system, i.e. viability, productivity, environmental-friendly, risk management and social acceptance. Furthermore, the quality of the yield was in line with the proposed grading standard for thatching reed, i.e. minimum circumference 210 mm, minimum length 1,2 m and less than 6,5 percent grey culm content.
- Full Text:
- Date Issued: 2006
A comparison between the game and hunting industries in KwaZulu-Natal and the Eastern Cape
- Authors: Kobus, Louann
- Date: 2007
- Subjects: Big game hunting -- South Africa -- KwaZulu-Natal , Big game hunting -- South Africa -- Eastern Cape , Hunting -- South Africa -- KwaZulu-Natal , Hunting -- South Africa -- Eastern Cape , Game farms -- South Africa -- KwaZulu-Natal , Game farms -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10590 , http://hdl.handle.net/10948/534 , http://hdl.handle.net/10948/d1011724 , Big game hunting -- South Africa -- KwaZulu-Natal , Big game hunting -- South Africa -- Eastern Cape , Hunting -- South Africa -- KwaZulu-Natal , Hunting -- South Africa -- Eastern Cape , Game farms -- South Africa -- KwaZulu-Natal , Game farms -- South Africa -- Eastern Cape
- Description: The objectives of this research, were to investigate the characteristics and develop a profile of the game and hunting industries of KwaZulu-Natal, and to undertake a comparison between the game and hunting industries in KwaZulu-Natal and the Eastern Cape. The comparative part of this study was completed using results obtained from a study done in 2002 in the Eastern Cape (van Niekerk, 2002). The main farming activities in KwaZulu-Natal are large livestock production and sugar cane production. In recent years, private landowners in KwaZulu-Natal have undergone a transition from livestock production to game ranching due to the problems faced and the cost implications of the HIV epidemic, stock theft, difficulties faced with changes in the labour laws and the increasing number of land claims against farmers. Although the game and hunting industries are relatively young industries in KwaZulu-Natal they contribute significantly to the economy of the province. Not only is greater conservation of the biodiversity more effective in game ranching but it is also proving to yield great economic returns. The increase in game ranching in recent years is namely due to the monetary value placed on wildlife, the increased value in ecotourism and its value as an earner of foreign exchange, less dependency on unskilled labour than that of livestock farming and lower rates of animal loss through theft compared to that of livestock farming. In KwaZulu-Natal game numbers indicate that impala have the greatest population amongst the respondents, followed by nyala, blesbok, common reedbuck, kudu and blue wildebeest, whilst other game species occur in smaller numbers. Respondents in KwaZulu-Natal indicate that nyala is the largest economic earner for them followed by buffalo, whereas in the Eastern Cape (2002), kudu and springbok provide the greatest income for the province. In KwaZulu-Natal income generated from hunting is second to that of live game sales compared to the Eastern Cape (2002) where hunting is the most important form of game utilisation in terms of income generated. At the time of this study, respondents in KwaZulu-Natal reported an income of R 15 382 397 generated from live sales and R 13 561 459 from hunting. These respondents also indicated that the total value of game utilised annually was in excess of R 30 million. Although game utilisation is occurring on a sustainable basis, there is room for greater utilisation of some game species which, if undertaken correctly, can increase the revenue for the province significantly and also contribute positively to further sustainability of the game populations. KwaZulu-Natal’s competitive advantage is derived from the fact that there is an abundance of game on the ranches, quality trophy animals are available, the number of game species available for hunting and quality of service rendered to hunters by the professional hunters and ranch owners. This study has clearly shown that there is a need for further investigation into the game and hunting industries in KwaZulu-Natal.
- Full Text:
- Date Issued: 2007
- Authors: Kobus, Louann
- Date: 2007
- Subjects: Big game hunting -- South Africa -- KwaZulu-Natal , Big game hunting -- South Africa -- Eastern Cape , Hunting -- South Africa -- KwaZulu-Natal , Hunting -- South Africa -- Eastern Cape , Game farms -- South Africa -- KwaZulu-Natal , Game farms -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10590 , http://hdl.handle.net/10948/534 , http://hdl.handle.net/10948/d1011724 , Big game hunting -- South Africa -- KwaZulu-Natal , Big game hunting -- South Africa -- Eastern Cape , Hunting -- South Africa -- KwaZulu-Natal , Hunting -- South Africa -- Eastern Cape , Game farms -- South Africa -- KwaZulu-Natal , Game farms -- South Africa -- Eastern Cape
- Description: The objectives of this research, were to investigate the characteristics and develop a profile of the game and hunting industries of KwaZulu-Natal, and to undertake a comparison between the game and hunting industries in KwaZulu-Natal and the Eastern Cape. The comparative part of this study was completed using results obtained from a study done in 2002 in the Eastern Cape (van Niekerk, 2002). The main farming activities in KwaZulu-Natal are large livestock production and sugar cane production. In recent years, private landowners in KwaZulu-Natal have undergone a transition from livestock production to game ranching due to the problems faced and the cost implications of the HIV epidemic, stock theft, difficulties faced with changes in the labour laws and the increasing number of land claims against farmers. Although the game and hunting industries are relatively young industries in KwaZulu-Natal they contribute significantly to the economy of the province. Not only is greater conservation of the biodiversity more effective in game ranching but it is also proving to yield great economic returns. The increase in game ranching in recent years is namely due to the monetary value placed on wildlife, the increased value in ecotourism and its value as an earner of foreign exchange, less dependency on unskilled labour than that of livestock farming and lower rates of animal loss through theft compared to that of livestock farming. In KwaZulu-Natal game numbers indicate that impala have the greatest population amongst the respondents, followed by nyala, blesbok, common reedbuck, kudu and blue wildebeest, whilst other game species occur in smaller numbers. Respondents in KwaZulu-Natal indicate that nyala is the largest economic earner for them followed by buffalo, whereas in the Eastern Cape (2002), kudu and springbok provide the greatest income for the province. In KwaZulu-Natal income generated from hunting is second to that of live game sales compared to the Eastern Cape (2002) where hunting is the most important form of game utilisation in terms of income generated. At the time of this study, respondents in KwaZulu-Natal reported an income of R 15 382 397 generated from live sales and R 13 561 459 from hunting. These respondents also indicated that the total value of game utilised annually was in excess of R 30 million. Although game utilisation is occurring on a sustainable basis, there is room for greater utilisation of some game species which, if undertaken correctly, can increase the revenue for the province significantly and also contribute positively to further sustainability of the game populations. KwaZulu-Natal’s competitive advantage is derived from the fact that there is an abundance of game on the ranches, quality trophy animals are available, the number of game species available for hunting and quality of service rendered to hunters by the professional hunters and ranch owners. This study has clearly shown that there is a need for further investigation into the game and hunting industries in KwaZulu-Natal.
- Full Text:
- Date Issued: 2007
A comparison of the vulcanisation of Polyisoprene by a range of Thiuram Diulfides
- Authors: Van Rooyen, Jason Leigh
- Date: 2007
- Subjects: Vulcanization , Vulcanization accelerators
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10399 , http://hdl.handle.net/10948/733 , Vulcanization , Vulcanization accelerators
- Description: This study was initiated in an attempt to investigate dithiocarbamic acid accelerated sulfur vulcanisation. This was, however, found impossible due to the innate instability of dithiocarbamic acids. The focus of the study was then shifted toward thiuram disulfide accelerated sulfur vulcanisation, with emphasis being placed on a rate comparison. Three groups of accelerators were investigated, namely the aromatic, linear aliphatic and cyclic aliphatic thiuram disulfide adducts. The analysis methods that were employed were conventional rubber (cis-1,4-polyisoprene) techniques coupled to model (squalene) compound investigations. The data that was collected consisted of rheometrical torque vs. time data in the rubber system while the data obtained in the model compound study consisted of sulfur and accelerator concentration data as determined by means of high performance liquid chromatography (HPLC). The aromatic accelerators were synthesised in our labs by means of an addition reaction between the aromatic amine and CS2 in basic medium and subsequent oxidation with K3Fe(CN)6, all in a 1:1 molar ratio. The reaction yield was low due to the instability of the dithiocarbamate intermediates and a sluggish oxidation reaction. In the rate constant determination a first order mathematical approach was used for the rubber system as crosslinking is considered to roughly obey first order kinetics. The model compound data was also found to more accurately fit the first order rate law, with an initial slopes method also being applied to the system to determine secondary rate constants and relative rates for the system. The determination of vulcanisation rate constants in the cis-1,4-polyisoprene system was a success, while the rate data determined by means of the squalene model was more related to the rate of accelerator and sulfur consumption as opposed to the rate of crosslinking as is the case with the rubber rate data. The sulfur first order rate data mirrored the rate data derived from the rubber system more closely than the corresponding accelerator rate data, the relative rate data determined by means of initial slopes method, proved that the homolytic cleavage of thiuram disulfides and the subsequent formation of accelerator polysulfides were not limiting steps. This is seen in the similar relative rate data derived from both the raw sulfur and accelerator data in systems that exhibit vastly different vulcanisation rates. Squalene was deemed a suitable model for the cis-1,4-polyisoprene system, although one should consider the extent of charring and solution effects in the individual systems to account for possible incongruities that may be observed between the rubber and simulated system. The lack of agreement between the rubber and model compound rate constant data lies in the fact that the rate of crosslinking is not simplistically related to the rate at which accelerator and sulfur is consumed, this being especially true for the rate at which the accelerator is consumed. Thus the discussion over the acceleratory rates in the various accelerator systems was limited to observations made in the rubber system, with the model compound data was used exclusively to elucidate mechanistic processes. It was discovered that the groups of accelerators examined, namely linear, cyclic and aromatic thiuram disulfide adducts, produced vastly varied rate data. The aromatic thiuram disulfide adducts had only a slight acceleratory effect on the rate of vulcanisation as compared to the unaccelerated sulfur system. The morpholine adduct had a moderately larger rate of acceleration followed by tetramethyl and tetrethylthiuram disulfide, with N’N-dicyclopentamethylenethiuram disulfide having the fastest rate of acceleration.
- Full Text:
- Date Issued: 2007
- Authors: Van Rooyen, Jason Leigh
- Date: 2007
- Subjects: Vulcanization , Vulcanization accelerators
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10399 , http://hdl.handle.net/10948/733 , Vulcanization , Vulcanization accelerators
- Description: This study was initiated in an attempt to investigate dithiocarbamic acid accelerated sulfur vulcanisation. This was, however, found impossible due to the innate instability of dithiocarbamic acids. The focus of the study was then shifted toward thiuram disulfide accelerated sulfur vulcanisation, with emphasis being placed on a rate comparison. Three groups of accelerators were investigated, namely the aromatic, linear aliphatic and cyclic aliphatic thiuram disulfide adducts. The analysis methods that were employed were conventional rubber (cis-1,4-polyisoprene) techniques coupled to model (squalene) compound investigations. The data that was collected consisted of rheometrical torque vs. time data in the rubber system while the data obtained in the model compound study consisted of sulfur and accelerator concentration data as determined by means of high performance liquid chromatography (HPLC). The aromatic accelerators were synthesised in our labs by means of an addition reaction between the aromatic amine and CS2 in basic medium and subsequent oxidation with K3Fe(CN)6, all in a 1:1 molar ratio. The reaction yield was low due to the instability of the dithiocarbamate intermediates and a sluggish oxidation reaction. In the rate constant determination a first order mathematical approach was used for the rubber system as crosslinking is considered to roughly obey first order kinetics. The model compound data was also found to more accurately fit the first order rate law, with an initial slopes method also being applied to the system to determine secondary rate constants and relative rates for the system. The determination of vulcanisation rate constants in the cis-1,4-polyisoprene system was a success, while the rate data determined by means of the squalene model was more related to the rate of accelerator and sulfur consumption as opposed to the rate of crosslinking as is the case with the rubber rate data. The sulfur first order rate data mirrored the rate data derived from the rubber system more closely than the corresponding accelerator rate data, the relative rate data determined by means of initial slopes method, proved that the homolytic cleavage of thiuram disulfides and the subsequent formation of accelerator polysulfides were not limiting steps. This is seen in the similar relative rate data derived from both the raw sulfur and accelerator data in systems that exhibit vastly different vulcanisation rates. Squalene was deemed a suitable model for the cis-1,4-polyisoprene system, although one should consider the extent of charring and solution effects in the individual systems to account for possible incongruities that may be observed between the rubber and simulated system. The lack of agreement between the rubber and model compound rate constant data lies in the fact that the rate of crosslinking is not simplistically related to the rate at which accelerator and sulfur is consumed, this being especially true for the rate at which the accelerator is consumed. Thus the discussion over the acceleratory rates in the various accelerator systems was limited to observations made in the rubber system, with the model compound data was used exclusively to elucidate mechanistic processes. It was discovered that the groups of accelerators examined, namely linear, cyclic and aromatic thiuram disulfide adducts, produced vastly varied rate data. The aromatic thiuram disulfide adducts had only a slight acceleratory effect on the rate of vulcanisation as compared to the unaccelerated sulfur system. The morpholine adduct had a moderately larger rate of acceleration followed by tetramethyl and tetrethylthiuram disulfide, with N’N-dicyclopentamethylenethiuram disulfide having the fastest rate of acceleration.
- Full Text:
- Date Issued: 2007
A model for adaptive multimodal mobile notification
- Authors: Brander, William
- Date: 2007
- Subjects: Mobile computing , Context-aware computing
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10473 , http://hdl.handle.net/10948/699 , Mobile computing , Context-aware computing
- Description: Information is useless unless it is used whilst still applicable. Having a system that notifies the user of important messages using the most appropriate medium and device will benefit users that rely on time critical information. There are several existing systems and models for mobile notification as well as for adaptive mobile notification using context awareness. Current models and systems are typically designed for a specific set of mobile devices, modes and services. Communication however, can take place in many different modes, across many different devices and may originate from many different sources. The aim of this research was to develop a model for adaptive mobile notification using context awareness. An extensive literature study was performed into existing models for adaptive mobile notification systems using context awareness. The literature study identified several potential models but no way to evaluate and compare the models. A set of requirements to evaluate these models was developed and the models were evaluated against these criteria. The model satisfying the most requirements was adapted so as to satisfy the remaining criteria. The proposed model is extensible in terms of the modes, devices and notification sources supported. The proposed model determines the importance of a message, the appropriate device and mode (or modes) of communication based on the user‘s context, and alerts the user of the message using these modes. A prototype was developed as a proof-of-concept of the proposed model and evaluated by conducting an extensive field study. The field study highlighted the fact that most users did not choose the most suitable mode for the context during their initial subscription to the service. The field study also showed that more research needs to be done on an appropriate filtering mechanism for notifications. Users found that the notifications became intrusive and less useful the longer they used them.
- Full Text:
- Date Issued: 2007
- Authors: Brander, William
- Date: 2007
- Subjects: Mobile computing , Context-aware computing
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10473 , http://hdl.handle.net/10948/699 , Mobile computing , Context-aware computing
- Description: Information is useless unless it is used whilst still applicable. Having a system that notifies the user of important messages using the most appropriate medium and device will benefit users that rely on time critical information. There are several existing systems and models for mobile notification as well as for adaptive mobile notification using context awareness. Current models and systems are typically designed for a specific set of mobile devices, modes and services. Communication however, can take place in many different modes, across many different devices and may originate from many different sources. The aim of this research was to develop a model for adaptive mobile notification using context awareness. An extensive literature study was performed into existing models for adaptive mobile notification systems using context awareness. The literature study identified several potential models but no way to evaluate and compare the models. A set of requirements to evaluate these models was developed and the models were evaluated against these criteria. The model satisfying the most requirements was adapted so as to satisfy the remaining criteria. The proposed model is extensible in terms of the modes, devices and notification sources supported. The proposed model determines the importance of a message, the appropriate device and mode (or modes) of communication based on the user‘s context, and alerts the user of the message using these modes. A prototype was developed as a proof-of-concept of the proposed model and evaluated by conducting an extensive field study. The field study highlighted the fact that most users did not choose the most suitable mode for the context during their initial subscription to the service. The field study also showed that more research needs to be done on an appropriate filtering mechanism for notifications. Users found that the notifications became intrusive and less useful the longer they used them.
- Full Text:
- Date Issued: 2007
An analysis of the influence of phosphorus poisoning on the exhaust emission after treatement systems of light-duty diesel vehicles
- Authors: Toral del Rio, Maria Isabel
- Date: 2007
- Subjects: Diesel motor -- Alternative fuels , Automobiles -- Pollution control devices , Automobiles -- Motors -- Exhaust gas , Motor fuels
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10405 , http://hdl.handle.net/10948/697 , Diesel motor -- Alternative fuels , Automobiles -- Pollution control devices , Automobiles -- Motors -- Exhaust gas , Motor fuels
- Description: Climate change has become a discussion topic of exponentially increasing urgency and importance amoung world leaders of all disciplines. These changes are brought about by the emission of so-called Greenhouse gases from various human activities. The primary cause of CO2 emissions is the burning of the Earth’s supply of nonrenewable natural fossil fuels like coal, oil and natural gas. The world first agreed on the prevention of “dangerous” climatic changes at the Earth Summit in 1992. The Kyoto Protocol of 1997 was the first step toward protection of the atmosphere and prescribes restrictions on emission pollutants. Since then the vehicle gas emissions are being controlled by means of different gas emissions norms, like the European Union Norm in Europe. The automotive manufacturers and suppliers are collectively working on reducing overall vehicle emissions. They are focusing on several different emission limiting possibilities, for example improved engine design, special fuel development and exhaust gas treatment systems. The exhaust gas treatment process requires continuous controlling and management of the exhaust gas emissions while driving a vehicle. Certain factors such as high emission temperatures have a negative influence on the life span of these systems. Their functionality and durability is also known to be reduced by the presence of chemical poisoning species like sulphur, phosphorus, zinc and calcium. The chemical poisoning species are produced during combustion of fuel and engine oil. They are therefore contained in the exhaust emissions and can poison the catalyst when passing over it. Phosphorous poisoning is particularly problematic and should be reduced considerably. This study involves the investigation of the phosphorous poisoning process and aims to provide clarity regarding the influences of different fuel and oil compositions on the severity of the process. Engine oil and biodiesel are two major sources of phosphorous poisoning. The phosphorus contained in biodiesel fuel is a natural component and can be minimized during the refining procedure. In contrast to others studies, the biodiesel fuel used during this project was SME (Soya Methyl Ester) with a 20% biodiesel content. This choice of fuel was made because of the increasingly important role that this type of biodiesel is playing in the European market and the future tendency to increase the percentage of biodiesel in the mixture with standard diesel fuel. The phosphorus contained in engine oil is a necessary additive to retain the antioxidant and anti-wear properties of the oil. This study examined the poisoning influences from the most commonly used phosphorus containing oil additive, Zinc Dithiophosphates (ZDDP), as well as a Zn-free, phosphorus containing anti-wear oil additive. This formulation provides information about the phosphorus poisoning process as caused by the engine oil in the absence of Zn in the oil additives. The results show how the phosphorus content in biodiesel fuel affects the functionality of the exhaust gas treatment systems and the importance of reducing the permitted content of phosphorus contained in the fuel. Reducing the phosphorus content in the fuel will conserve the functionality of the exhaust gas treatment systems during their operational life and thereby protect the environmental from emission pollutants. It also provides insight into the differences in the poisoning processes when the phosphorus deposited on the catalyst comes from biodiesel fuel and when it comes from the engine oil. Finally the results also illustrate the influence of different phosphorous forms contained in engine oil additives on the catalyst poisoning process. This information could be used for the development of new oil additive formulations.
- Full Text:
- Date Issued: 2007
- Authors: Toral del Rio, Maria Isabel
- Date: 2007
- Subjects: Diesel motor -- Alternative fuels , Automobiles -- Pollution control devices , Automobiles -- Motors -- Exhaust gas , Motor fuels
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10405 , http://hdl.handle.net/10948/697 , Diesel motor -- Alternative fuels , Automobiles -- Pollution control devices , Automobiles -- Motors -- Exhaust gas , Motor fuels
- Description: Climate change has become a discussion topic of exponentially increasing urgency and importance amoung world leaders of all disciplines. These changes are brought about by the emission of so-called Greenhouse gases from various human activities. The primary cause of CO2 emissions is the burning of the Earth’s supply of nonrenewable natural fossil fuels like coal, oil and natural gas. The world first agreed on the prevention of “dangerous” climatic changes at the Earth Summit in 1992. The Kyoto Protocol of 1997 was the first step toward protection of the atmosphere and prescribes restrictions on emission pollutants. Since then the vehicle gas emissions are being controlled by means of different gas emissions norms, like the European Union Norm in Europe. The automotive manufacturers and suppliers are collectively working on reducing overall vehicle emissions. They are focusing on several different emission limiting possibilities, for example improved engine design, special fuel development and exhaust gas treatment systems. The exhaust gas treatment process requires continuous controlling and management of the exhaust gas emissions while driving a vehicle. Certain factors such as high emission temperatures have a negative influence on the life span of these systems. Their functionality and durability is also known to be reduced by the presence of chemical poisoning species like sulphur, phosphorus, zinc and calcium. The chemical poisoning species are produced during combustion of fuel and engine oil. They are therefore contained in the exhaust emissions and can poison the catalyst when passing over it. Phosphorous poisoning is particularly problematic and should be reduced considerably. This study involves the investigation of the phosphorous poisoning process and aims to provide clarity regarding the influences of different fuel and oil compositions on the severity of the process. Engine oil and biodiesel are two major sources of phosphorous poisoning. The phosphorus contained in biodiesel fuel is a natural component and can be minimized during the refining procedure. In contrast to others studies, the biodiesel fuel used during this project was SME (Soya Methyl Ester) with a 20% biodiesel content. This choice of fuel was made because of the increasingly important role that this type of biodiesel is playing in the European market and the future tendency to increase the percentage of biodiesel in the mixture with standard diesel fuel. The phosphorus contained in engine oil is a necessary additive to retain the antioxidant and anti-wear properties of the oil. This study examined the poisoning influences from the most commonly used phosphorus containing oil additive, Zinc Dithiophosphates (ZDDP), as well as a Zn-free, phosphorus containing anti-wear oil additive. This formulation provides information about the phosphorus poisoning process as caused by the engine oil in the absence of Zn in the oil additives. The results show how the phosphorus content in biodiesel fuel affects the functionality of the exhaust gas treatment systems and the importance of reducing the permitted content of phosphorus contained in the fuel. Reducing the phosphorus content in the fuel will conserve the functionality of the exhaust gas treatment systems during their operational life and thereby protect the environmental from emission pollutants. It also provides insight into the differences in the poisoning processes when the phosphorus deposited on the catalyst comes from biodiesel fuel and when it comes from the engine oil. Finally the results also illustrate the influence of different phosphorous forms contained in engine oil additives on the catalyst poisoning process. This information could be used for the development of new oil additive formulations.
- Full Text:
- Date Issued: 2007
An assessment of habitat suitability of the proposed Tyefu community game reserve in Ngqushwa (fomerly Peddie) district, Eastern Cape
- Authors: Mamfengu, Phozisa Faith
- Date: 2007
- Subjects: Game farms -- South Africa -- Eastern Cape -- Management , Habitat (Ecology) , Eastern Cape (South Africa) -- Social conditions
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10653 , http://hdl.handle.net/10948/736 , Game farms -- South Africa -- Eastern Cape -- Management , Habitat (Ecology) , Eastern Cape (South Africa) -- Social conditions
- Description: Land use forms such as cultivation and livestock farming have become less productive and unsustainable in the Tyefu communal villages of Ngqushwa (Formerly Peddie) district, Eastern Cape, South Africa. This is manifest in abandoned and severely degraded cultivation fields as well as transformed vegetation, making it difficult to earn a land based livelihood. Against the backdrop of severe land degradation and poverty levels in these communal villages, game farming has been recommended as an ecologically, economically and socially sustainable form of land use. Tyefu Community Reserve is a project, recommended by the Subtropical Thicket Ecosystem Project (STEP) backed by the Department of Environment Affairs and Tourism (DEAT), for hunting and venison selling. The proposed area has been fenced and animals to be stocked in the reserve have been requested on a loan basis. Such an undertaking requires an understanding of the abundance and condition of vegetation, terrain parameters, and an assessment of potential wildlife species, as well as the carrying capacity of the recommended reserve as a habitat. With the aid of orthophoto maps, Subtropical Thicket Ecosystem Planning (STEP) shapefiles, ASTER satellite imagery and a High Resolution Digital Camera Image, vegetation types were mapped and their condition was assessed. A Digital Elevation Model (DEM) of the area was used to extract terrain parameters such as slope and aspect. The carrying capacity of the proposed reserve was determined using a model originally developed by Boshoff et al. (2001) for estimating potential wildlife and abundance. The proposed reserve is predominantly covered by dense thicket as compared to the adjacent Tyefu communal villages where thicket has been severely degraded. The prominent topographic characteristics such as slope reveal an escarpment ringing the proposed reserve with gentle slopes towards the centre. Slope direction has also influenced the distribution of vegetation in the proposed reserve, as the moist south facing slopes tend to have a greater proportion of dense thicket as opposed to the warm north facing slopes. Vegetation types and topography of the reserve can provide suitable habitat to a variety of wildlife species and are likely to influence the distribution of mammals in the proposed reserve. The carrying capacity model developed has been useful in determining potential species that can be supported by the reserve, and estimating their abundance. Given the small size of the proposed community reserve (about 1800ha), it has been recommended that it should be stretched to link up with the existing Great Fish River Game Complex. It will then fit within the framework as envisaged by STEP (2004), in the form of Fish River Biodiversity Initiative, a conservation corridor bordering the Great Fish River.
- Full Text:
- Date Issued: 2007
- Authors: Mamfengu, Phozisa Faith
- Date: 2007
- Subjects: Game farms -- South Africa -- Eastern Cape -- Management , Habitat (Ecology) , Eastern Cape (South Africa) -- Social conditions
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10653 , http://hdl.handle.net/10948/736 , Game farms -- South Africa -- Eastern Cape -- Management , Habitat (Ecology) , Eastern Cape (South Africa) -- Social conditions
- Description: Land use forms such as cultivation and livestock farming have become less productive and unsustainable in the Tyefu communal villages of Ngqushwa (Formerly Peddie) district, Eastern Cape, South Africa. This is manifest in abandoned and severely degraded cultivation fields as well as transformed vegetation, making it difficult to earn a land based livelihood. Against the backdrop of severe land degradation and poverty levels in these communal villages, game farming has been recommended as an ecologically, economically and socially sustainable form of land use. Tyefu Community Reserve is a project, recommended by the Subtropical Thicket Ecosystem Project (STEP) backed by the Department of Environment Affairs and Tourism (DEAT), for hunting and venison selling. The proposed area has been fenced and animals to be stocked in the reserve have been requested on a loan basis. Such an undertaking requires an understanding of the abundance and condition of vegetation, terrain parameters, and an assessment of potential wildlife species, as well as the carrying capacity of the recommended reserve as a habitat. With the aid of orthophoto maps, Subtropical Thicket Ecosystem Planning (STEP) shapefiles, ASTER satellite imagery and a High Resolution Digital Camera Image, vegetation types were mapped and their condition was assessed. A Digital Elevation Model (DEM) of the area was used to extract terrain parameters such as slope and aspect. The carrying capacity of the proposed reserve was determined using a model originally developed by Boshoff et al. (2001) for estimating potential wildlife and abundance. The proposed reserve is predominantly covered by dense thicket as compared to the adjacent Tyefu communal villages where thicket has been severely degraded. The prominent topographic characteristics such as slope reveal an escarpment ringing the proposed reserve with gentle slopes towards the centre. Slope direction has also influenced the distribution of vegetation in the proposed reserve, as the moist south facing slopes tend to have a greater proportion of dense thicket as opposed to the warm north facing slopes. Vegetation types and topography of the reserve can provide suitable habitat to a variety of wildlife species and are likely to influence the distribution of mammals in the proposed reserve. The carrying capacity model developed has been useful in determining potential species that can be supported by the reserve, and estimating their abundance. Given the small size of the proposed community reserve (about 1800ha), it has been recommended that it should be stretched to link up with the existing Great Fish River Game Complex. It will then fit within the framework as envisaged by STEP (2004), in the form of Fish River Biodiversity Initiative, a conservation corridor bordering the Great Fish River.
- Full Text:
- Date Issued: 2007
An intelligent user interface model for contact centre operations
- Authors: Singh, Akash
- Date: 2007
- Subjects: User interfaces (Computer systems) , Human-computer interaction , Mobile computing , Customer services -- Management , Call centers -- Customer services
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10475 , http://hdl.handle.net/10948/d1011399 , User interfaces (Computer systems) , Human-computer interaction , Mobile computing , Customer services -- Management , Call centers -- Customer services
- Description: Contact Centres (CCs) are at the forefront of interaction between an organisation and its customers. Currently, 17 percent of all inbound calls are not resolved on the first call by the first agent attending to that call. This is due to the inability of the contact centre agents (CCAs) to diagnose customer queries and find adequate solutions in an effective and efficient manner. The aim of this research is to develop an intelligent user interface (IUI) model to support and improve CC operations. A literature review of existing IUI architectures, modelbased design and existing CC software together with a field study of CCs has resulted in the design of an IUI model for CCs. The proposed IUI model is described in terms of its architecture, component-level design and interface design. An IUI prototype has been developed as a proof of concept of the proposed IUI model. The IUI prototype was evaluated in order to determine to what extent it supports problem identification and query resolution. User testing, incorporating the use of eye tracking and a post-test questionnaire, was used in order to determine the usability and usefulness of the prototype. The results of this evaluation show that the users were highly satisfied with the task support and query resolution assistance provided by the IUI prototype. This research resulted in the design of an IUI model for the domain of CCs. This model can be used to assist the development of CC applications incorporating IUIs. Use of the proposed IUI model is expected to support and enhance the effectiveness and efficiency of CC operations. Further research is needed to conduct a longitudinal study to determine the impact of IUIs in the CC domain.
- Full Text:
- Date Issued: 2007
- Authors: Singh, Akash
- Date: 2007
- Subjects: User interfaces (Computer systems) , Human-computer interaction , Mobile computing , Customer services -- Management , Call centers -- Customer services
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10475 , http://hdl.handle.net/10948/d1011399 , User interfaces (Computer systems) , Human-computer interaction , Mobile computing , Customer services -- Management , Call centers -- Customer services
- Description: Contact Centres (CCs) are at the forefront of interaction between an organisation and its customers. Currently, 17 percent of all inbound calls are not resolved on the first call by the first agent attending to that call. This is due to the inability of the contact centre agents (CCAs) to diagnose customer queries and find adequate solutions in an effective and efficient manner. The aim of this research is to develop an intelligent user interface (IUI) model to support and improve CC operations. A literature review of existing IUI architectures, modelbased design and existing CC software together with a field study of CCs has resulted in the design of an IUI model for CCs. The proposed IUI model is described in terms of its architecture, component-level design and interface design. An IUI prototype has been developed as a proof of concept of the proposed IUI model. The IUI prototype was evaluated in order to determine to what extent it supports problem identification and query resolution. User testing, incorporating the use of eye tracking and a post-test questionnaire, was used in order to determine the usability and usefulness of the prototype. The results of this evaluation show that the users were highly satisfied with the task support and query resolution assistance provided by the IUI prototype. This research resulted in the design of an IUI model for the domain of CCs. This model can be used to assist the development of CC applications incorporating IUIs. Use of the proposed IUI model is expected to support and enhance the effectiveness and efficiency of CC operations. Further research is needed to conduct a longitudinal study to determine the impact of IUIs in the CC domain.
- Full Text:
- Date Issued: 2007
An investigation into the learnability of object-oriented case tools for computing education
- Authors: Scholtz, Brenda Mary
- Date: 2007
- Subjects: Computer science -- Study and teaching , Object-oriented programming (Computer science) , ACSES (Computer system)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10476 , http://hdl.handle.net/10948/694 , Computer science -- Study and teaching , Object-oriented programming (Computer science) , ACSES (Computer system)
- Description: The use of Computer Aided Software Engineering (CASE) tools for teaching object-oriented systems analysis and design (OOSAD) has many potential benefits, but there are also several problems associated with the usage of these tools. A large portion of these problems relate to the usability and learnability of these tools. Learnability is one of the most important attributes of usability and refers to the capability of the system to enable the user to learn its application. The main research question that this study aims to address is “How can the learnability of OO CASE tools for computing education in South Africa be evaluated?”. In order to answer this question several frameworks for evaluating CASE tool usability and learnability were investigated. One of these frameworks, as proposed by Senapathi, was selected as being the most appropriate for evaluating CASE tool learnability for computing education. This framework maintains that the learnability of a CASE tool is dependent on context of use factors such as the tool used, as well as user characteristics such as gender. The primary aim of this research was thus to validate Senapathi's framework for CASE tool learnability in a South African context. A secondary aim of the research was to extend the implementation of the framework in order to enable the comparison of two CASE tools and to support the inclusion of other user characteristics. An experiment was performed at the Nelson Mandela Metropolitan University (NMMU) in 2006. The participants recruited for this experiment were second year computing students at NMMU. During this experiment, the learnability of two OO CASE tools, namely IBM's Rational Software Modeller and Microsoft's Visio, was evaluated and compared. The quantitative and qualitative results supported Senapathi's results and showed that her framework could be used to evaluate CASE tool learnability and could be adapted to evaluate two CASE tools. The results also showed that the majority of the participants rated the learnability of Microsoft Visio higher for both tasks and that the main reasons participants preferred Visio was due to its simplicity, familiarity and recoverability.
- Full Text:
- Date Issued: 2007
- Authors: Scholtz, Brenda Mary
- Date: 2007
- Subjects: Computer science -- Study and teaching , Object-oriented programming (Computer science) , ACSES (Computer system)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10476 , http://hdl.handle.net/10948/694 , Computer science -- Study and teaching , Object-oriented programming (Computer science) , ACSES (Computer system)
- Description: The use of Computer Aided Software Engineering (CASE) tools for teaching object-oriented systems analysis and design (OOSAD) has many potential benefits, but there are also several problems associated with the usage of these tools. A large portion of these problems relate to the usability and learnability of these tools. Learnability is one of the most important attributes of usability and refers to the capability of the system to enable the user to learn its application. The main research question that this study aims to address is “How can the learnability of OO CASE tools for computing education in South Africa be evaluated?”. In order to answer this question several frameworks for evaluating CASE tool usability and learnability were investigated. One of these frameworks, as proposed by Senapathi, was selected as being the most appropriate for evaluating CASE tool learnability for computing education. This framework maintains that the learnability of a CASE tool is dependent on context of use factors such as the tool used, as well as user characteristics such as gender. The primary aim of this research was thus to validate Senapathi's framework for CASE tool learnability in a South African context. A secondary aim of the research was to extend the implementation of the framework in order to enable the comparison of two CASE tools and to support the inclusion of other user characteristics. An experiment was performed at the Nelson Mandela Metropolitan University (NMMU) in 2006. The participants recruited for this experiment were second year computing students at NMMU. During this experiment, the learnability of two OO CASE tools, namely IBM's Rational Software Modeller and Microsoft's Visio, was evaluated and compared. The quantitative and qualitative results supported Senapathi's results and showed that her framework could be used to evaluate CASE tool learnability and could be adapted to evaluate two CASE tools. The results also showed that the majority of the participants rated the learnability of Microsoft Visio higher for both tasks and that the main reasons participants preferred Visio was due to its simplicity, familiarity and recoverability.
- Full Text:
- Date Issued: 2007
An investigation into the parameters affecting the stability of Dithane
- Authors: Williams, Nadia
- Date: 2007
- Subjects: Fungicides , Dithane
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10407 , http://hdl.handle.net/10948/645 , Fungicides , Dithane
- Description: Plant diseases caused by fungi are the number one cause of crop loss worldwide. The application of a fungicide which is a toxic substance applied either to prevent the growth of, or to kill fungi is one of the methods by which plant diseases are controlled. Ethylenebisdithiocarbamate fungicides are a group of surface acting fungicides which control a broad spectrum of fungi and their associated plant diseases. Mancozeb, also commonly known as Dithane, falls under the polymeric Dithiocarbamate fungicides which have several sites of toxicity to the fungal cell. The use of Mancozeb as a fungicide is increasing worldwide due to the advantages of low acute toxicity, low production and short environmental persistence. However, it has one major disadvantage, namely its lack of oxidative stability under ambient conditions. One of the objectives of this study was to characterize the Dithane samples supplied by Dow AgroSciences in terms of their active ingredient, metal and stabilizer content, and to study the thermal decomposition behaviour of Dithane. An attempt was made to correlate the active ingredient analyses with the TGA and DSC results to establish whether the thermal stability and active ingredient content of Dithane could be simultaneously determined by thermal analysis. This approach offered the attractive advantage of shorter analysis times thus allowing the elimination of the more tedious analytical methods employed by Dow AgroSciences. Furthermore, Fourier Transform infra-red characterization of Dithane samples and metal complexes containing HMT, Mn and/or Zn was carried out in order to identify the presence of functional groups and to gain some insight into the nature of the bonding of HMT, sulfate and water. A study of the nature of the bands in the FTIR spectra of these complexes was able to highlight the nature of the bonding but could not give confirmation of the structures of these complexes. In addition to this, the amount of HMT present in the said complexes was determined by the FTIR using the standard addition method. A final objective of the study was to investigate the reconstitution of Dithane by investigating the influence of the addition order of the various constituents on the stability of the final product. The addition order was found to have a definite influence on the thermal stability of the final product as well as on the percentage of fixed HMT in the product, and the kinetics of the Mn/Zn exchange.
- Full Text:
- Date Issued: 2007
- Authors: Williams, Nadia
- Date: 2007
- Subjects: Fungicides , Dithane
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10407 , http://hdl.handle.net/10948/645 , Fungicides , Dithane
- Description: Plant diseases caused by fungi are the number one cause of crop loss worldwide. The application of a fungicide which is a toxic substance applied either to prevent the growth of, or to kill fungi is one of the methods by which plant diseases are controlled. Ethylenebisdithiocarbamate fungicides are a group of surface acting fungicides which control a broad spectrum of fungi and their associated plant diseases. Mancozeb, also commonly known as Dithane, falls under the polymeric Dithiocarbamate fungicides which have several sites of toxicity to the fungal cell. The use of Mancozeb as a fungicide is increasing worldwide due to the advantages of low acute toxicity, low production and short environmental persistence. However, it has one major disadvantage, namely its lack of oxidative stability under ambient conditions. One of the objectives of this study was to characterize the Dithane samples supplied by Dow AgroSciences in terms of their active ingredient, metal and stabilizer content, and to study the thermal decomposition behaviour of Dithane. An attempt was made to correlate the active ingredient analyses with the TGA and DSC results to establish whether the thermal stability and active ingredient content of Dithane could be simultaneously determined by thermal analysis. This approach offered the attractive advantage of shorter analysis times thus allowing the elimination of the more tedious analytical methods employed by Dow AgroSciences. Furthermore, Fourier Transform infra-red characterization of Dithane samples and metal complexes containing HMT, Mn and/or Zn was carried out in order to identify the presence of functional groups and to gain some insight into the nature of the bonding of HMT, sulfate and water. A study of the nature of the bands in the FTIR spectra of these complexes was able to highlight the nature of the bonding but could not give confirmation of the structures of these complexes. In addition to this, the amount of HMT present in the said complexes was determined by the FTIR using the standard addition method. A final objective of the study was to investigate the reconstitution of Dithane by investigating the influence of the addition order of the various constituents on the stability of the final product. The addition order was found to have a definite influence on the thermal stability of the final product as well as on the percentage of fixed HMT in the product, and the kinetics of the Mn/Zn exchange.
- Full Text:
- Date Issued: 2007