On the mocvd growth of ZnO
- Authors: Pagni, Olivier Demeno
- Date: 2004
- Subjects: Zinc oxide thin films , Metal organic chemical vapor deposition
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:11075 , http://hdl.handle.net/10948/382 , Zinc oxide thin films , Metal organic chemical vapor deposition
- Description: Zinc oxide (ZnO) is a II-VI semiconductor material that offers tremendous potential as a light emitter in the blue-to-UV range. It has a wurtzite structure, and a direct band gap that can be tuned from 3.0 to 4.0 eV by alloying with Cd or Mg, respectively. In this work, ZnO thin films were grown by metalorganic chemical vapor deposition (MOCVD) on n-Si 2 ° off (100), amorphous glass, n-GaAs (100), and c-plane sapphire substrates. Diethyl zinc (DEZn) and tert-butanol (TBOH) were chosen as precursors. For the first time, Second Harmonic Generation Imaging was applied to the mapping of ZnO epilayers. The images obtained highlighted the polycrystalline character of the thin films, and provided insight as to the growth mode of ZnO on Si. The influence of substrate temperature on the structural properties of the epilayers was investigated by X-ray diffraction and optical microscopy. Grain sizes as high as 54 nm were measured. The optimum temperature range for this system proved to be 450 – 500 °C. The influence of the VI:II ratio during growth on the optical properties of the epilayers was studied by UV-vis-near IR spectroscopy. The lowest Urbach tail E0 parameter was measured for material grown at a VI:II ratio of 18:1. The films’ free electron concentration was shown to decrease by over two orders of magnitude, from 1019 to 1017 cm-3, as the VI:II ratio increased from 10 to 60:1. This decrease in carrier concentration with rising VI:II ratio was paralleled to the surge at 12 K of a photoluminescence (PL) emission band characteristic of p-type ZnO. The band gap energies extracted from room temperature transmission spectra ranged between 3.35 and 3.38 eV, in agreement with the value of 3.35 eV measured by room temperature PL. Moreover, variable temperature PL spectra were recorded between 12 and 298 K on ZnO grown on Si. The 12 K spectrum was dominated by a donor-bound exciton (D°X) at 3.36 eV, while the 298 K scan displayed strong free exciton emission (FX) at 3.29 eV. The width of the D°X band proved to be as narrow as 7 meV. The intensity ratio between the room temperature near-band edge emission and the defect-related green band was as high as 28:1, highlighting the optical quality of the layers deposited in this work. The electrical properties of the thin films were studied by Hall measurements (van der Pauw configuration), and a maximum room temperature mobility of 11 cm2/Vs was recorded. Furthermore, a palladium (Pd) Schottky barrier diode on ZnO was fabricated. The barrier height and ideality factor were calculated from current–voltage measurements to be 0.83 eV and 1.6, respectively. The capacitance–voltage curve of the diode yielded a carrier concentration in the depletion region of 8·1017 cm-3. This study has shown that the optical and electrical properties of ZnO depend strongly on the growth conditions employed. A suitable choice of growth parameters can yield high quality ZnO that may be used for various devices. Keywords: Hall, MOCVD, optical spectroscopy, photoluminescence, Schottky barrier diode, SH Imaging, X-ray diffraction, ZnO.
- Full Text:
- Date Issued: 2004
- Authors: Pagni, Olivier Demeno
- Date: 2004
- Subjects: Zinc oxide thin films , Metal organic chemical vapor deposition
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:11075 , http://hdl.handle.net/10948/382 , Zinc oxide thin films , Metal organic chemical vapor deposition
- Description: Zinc oxide (ZnO) is a II-VI semiconductor material that offers tremendous potential as a light emitter in the blue-to-UV range. It has a wurtzite structure, and a direct band gap that can be tuned from 3.0 to 4.0 eV by alloying with Cd or Mg, respectively. In this work, ZnO thin films were grown by metalorganic chemical vapor deposition (MOCVD) on n-Si 2 ° off (100), amorphous glass, n-GaAs (100), and c-plane sapphire substrates. Diethyl zinc (DEZn) and tert-butanol (TBOH) were chosen as precursors. For the first time, Second Harmonic Generation Imaging was applied to the mapping of ZnO epilayers. The images obtained highlighted the polycrystalline character of the thin films, and provided insight as to the growth mode of ZnO on Si. The influence of substrate temperature on the structural properties of the epilayers was investigated by X-ray diffraction and optical microscopy. Grain sizes as high as 54 nm were measured. The optimum temperature range for this system proved to be 450 – 500 °C. The influence of the VI:II ratio during growth on the optical properties of the epilayers was studied by UV-vis-near IR spectroscopy. The lowest Urbach tail E0 parameter was measured for material grown at a VI:II ratio of 18:1. The films’ free electron concentration was shown to decrease by over two orders of magnitude, from 1019 to 1017 cm-3, as the VI:II ratio increased from 10 to 60:1. This decrease in carrier concentration with rising VI:II ratio was paralleled to the surge at 12 K of a photoluminescence (PL) emission band characteristic of p-type ZnO. The band gap energies extracted from room temperature transmission spectra ranged between 3.35 and 3.38 eV, in agreement with the value of 3.35 eV measured by room temperature PL. Moreover, variable temperature PL spectra were recorded between 12 and 298 K on ZnO grown on Si. The 12 K spectrum was dominated by a donor-bound exciton (D°X) at 3.36 eV, while the 298 K scan displayed strong free exciton emission (FX) at 3.29 eV. The width of the D°X band proved to be as narrow as 7 meV. The intensity ratio between the room temperature near-band edge emission and the defect-related green band was as high as 28:1, highlighting the optical quality of the layers deposited in this work. The electrical properties of the thin films were studied by Hall measurements (van der Pauw configuration), and a maximum room temperature mobility of 11 cm2/Vs was recorded. Furthermore, a palladium (Pd) Schottky barrier diode on ZnO was fabricated. The barrier height and ideality factor were calculated from current–voltage measurements to be 0.83 eV and 1.6, respectively. The capacitance–voltage curve of the diode yielded a carrier concentration in the depletion region of 8·1017 cm-3. This study has shown that the optical and electrical properties of ZnO depend strongly on the growth conditions employed. A suitable choice of growth parameters can yield high quality ZnO that may be used for various devices. Keywords: Hall, MOCVD, optical spectroscopy, photoluminescence, Schottky barrier diode, SH Imaging, X-ray diffraction, ZnO.
- Full Text:
- Date Issued: 2004
One hundred years of botany at Rhodes University
- Authors: Lubke, Roy , Brink, Estelle
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6523 , http://hdl.handle.net/10962/d1005954
- Description: The Botany Department of Rhodes University is located in the historic Schonland Building. An indigenous garden was created in its courtyard, mainly of species of the Eastern Cape province, and its growth in diversity and stature mirrors the changes in the department over the years. Professor Selmar Schonland, the founding father of botany at Rhodes, was also the curator/director of the Albany Museum. Under his leadership, systematics was firmly established as a discipline at Rhodes and research on the flora of the Eastern Cape begun, to be continued to this day. Under professors William Isaac (1949–1951) and Edgar Twyman (1951–1973), plant physiology became an important area of study, and future leaders in physiology at other universities obtained degrees under them. Phycology and aquatic ecology became notable disciplines with Mary Pocock’s world-class work in the 1940s on freshwater and marine algae, which inspired others such as head of department Professor Stanley Seagrief (1958–1986) to develop these studies further. Mycology and microbiology were established as major subdisciplines under Noel Smith (1926–1948) and Twyman through to the 1960s, when the Department of Microbiology was established. Early studies in ecology owe their success to Tony Martin (1947–1956) and the link with the Grahamstown Botanical Research Station, when a sound base for plant ecology in the Eastern Cape was established. Coastal ecology became a major focus in the 1970s, when Roy Lubke and Ted Avis concentrated on dunes and the management of coastal regions. This led to the establishment of the Department of Environmental Science in the 1990s. The expertise of the botany staff in teaching and research in a variety of fields is reflected in the careers of its many students around the world.
- Full Text:
- Date Issued: 2004
- Authors: Lubke, Roy , Brink, Estelle
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6523 , http://hdl.handle.net/10962/d1005954
- Description: The Botany Department of Rhodes University is located in the historic Schonland Building. An indigenous garden was created in its courtyard, mainly of species of the Eastern Cape province, and its growth in diversity and stature mirrors the changes in the department over the years. Professor Selmar Schonland, the founding father of botany at Rhodes, was also the curator/director of the Albany Museum. Under his leadership, systematics was firmly established as a discipline at Rhodes and research on the flora of the Eastern Cape begun, to be continued to this day. Under professors William Isaac (1949–1951) and Edgar Twyman (1951–1973), plant physiology became an important area of study, and future leaders in physiology at other universities obtained degrees under them. Phycology and aquatic ecology became notable disciplines with Mary Pocock’s world-class work in the 1940s on freshwater and marine algae, which inspired others such as head of department Professor Stanley Seagrief (1958–1986) to develop these studies further. Mycology and microbiology were established as major subdisciplines under Noel Smith (1926–1948) and Twyman through to the 1960s, when the Department of Microbiology was established. Early studies in ecology owe their success to Tony Martin (1947–1956) and the link with the Grahamstown Botanical Research Station, when a sound base for plant ecology in the Eastern Cape was established. Coastal ecology became a major focus in the 1970s, when Roy Lubke and Ted Avis concentrated on dunes and the management of coastal regions. This led to the establishment of the Department of Environmental Science in the 1990s. The expertise of the botany staff in teaching and research in a variety of fields is reflected in the careers of its many students around the world.
- Full Text:
- Date Issued: 2004
Oomashayela phezulu:
- Mazibuko, Nokuthula, Kaschula, Russell H
- Authors: Mazibuko, Nokuthula , Kaschula, Russell H
- Date: 2004
- Language: Zulu
- Type: text , book
- Identifier: http://hdl.handle.net/10962/175323 , vital:42565 , ISBN 9781869284251
- Description: ‘Sam, khawuphole maan, thob'umoya. KungoLwesihlanu namhlanje, sakuba nalo ithuba elininzi ngomso lokuzithethelela ebazalini bethu! Ha, ha, ha!'wagigitheka uBrunette'Thatha nantsi icider, usele!'UBrunette wayonwabile, wayekuthanda futhi ekonwabela ngoku ukusela, kwaye ezi iicider zazingavakali ngathi butywala! Wayeziva efanelekile kwibhulukhwe yakhe ebomvu, ethe nca kuye emzimbeni kakuhle, nehempe awayeyinxibe ngentla ehambelana nayo, nezihlangu ezichophileyo awayezinxibile. Wagqiba kwangexesha ukuphotha iinwele zakhe ngoboya bomsila wehashe, elungele ipati eyayiza kuba ngobo busuku. Yayintle into yokuba abe woluka iinwele zabantu. Ngokwenza njalo wayezenzela.
- Full Text:
- Date Issued: 2004
- Authors: Mazibuko, Nokuthula , Kaschula, Russell H
- Date: 2004
- Language: Zulu
- Type: text , book
- Identifier: http://hdl.handle.net/10962/175323 , vital:42565 , ISBN 9781869284251
- Description: ‘Sam, khawuphole maan, thob'umoya. KungoLwesihlanu namhlanje, sakuba nalo ithuba elininzi ngomso lokuzithethelela ebazalini bethu! Ha, ha, ha!'wagigitheka uBrunette'Thatha nantsi icider, usele!'UBrunette wayonwabile, wayekuthanda futhi ekonwabela ngoku ukusela, kwaye ezi iicider zazingavakali ngathi butywala! Wayeziva efanelekile kwibhulukhwe yakhe ebomvu, ethe nca kuye emzimbeni kakuhle, nehempe awayeyinxibe ngentla ehambelana nayo, nezihlangu ezichophileyo awayezinxibile. Wagqiba kwangexesha ukuphotha iinwele zakhe ngoboya bomsila wehashe, elungele ipati eyayiza kuba ngobo busuku. Yayintle into yokuba abe woluka iinwele zabantu. Ngokwenza njalo wayezenzela.
- Full Text:
- Date Issued: 2004
Optimization of a manufacturing process for atrazine with a focus on waste minimization
- Authors: Mtyopo, Mteteleli Bethwell
- Date: 2004
- Subjects: Waste minimization , Atrazine -- Environmental aspects
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10976 , http://hdl.handle.net/10948/259 , Waste minimization , Atrazine -- Environmental aspects
- Description: Chemical synthesis is not complete without waste treatment. There is no chemical process that does not produce waste. The untreated effluent discharged by chemical industries poses a major environmental concern. This dissertation describes the results of an investigation carried out on the formation of by-products (impurities) during the synthesis of atrazine by neutralization of the reaction mixture during the actual synthesis procedure, and prior to disposal using carbon dioxide or hydrochloric acid. The main objectives for the said investigation were: {u100083} To optimise the reaction parameters to obtain a higher yield and purity of atrazine. {u100083} To evaluate the use of carbon dioxide and hydrochloric acid to neutralise the reaction mixture. {u100083} To study the solids present in the effluent. Synthetic reactions were carried out in the presence of an organic solvent, methyl isobutyl ketone (MIBK). The synthesis of atrazine was optimised in terms of addition sequence and rates of amine reagents and base (proton acceptor) additions by means of bench scale reactions. It was found that addition of a neutralising step (hydrochloric acid or carbon dioxide) to neutralise the basic reaction mixture prior to and after addition of the secondary amine and the base minimizes the formation of by-products. Of particular importance in ensuring high yields and selectivity to the atrazine product was temperature control, pH control, reagent ratios, addition rates and mixing. The latter was important in view of the rapid reaction of amine/NaOH with cyanuric chloride, as well as the possible reaction of mono-i, the reaction intermediate, with IPA in cases of excesses of reagent. Under optimum conditions, an atrazine composition of >97% was achieved where the resultant product was well within stipulated product specifications.
- Full Text:
- Date Issued: 2004
- Authors: Mtyopo, Mteteleli Bethwell
- Date: 2004
- Subjects: Waste minimization , Atrazine -- Environmental aspects
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10976 , http://hdl.handle.net/10948/259 , Waste minimization , Atrazine -- Environmental aspects
- Description: Chemical synthesis is not complete without waste treatment. There is no chemical process that does not produce waste. The untreated effluent discharged by chemical industries poses a major environmental concern. This dissertation describes the results of an investigation carried out on the formation of by-products (impurities) during the synthesis of atrazine by neutralization of the reaction mixture during the actual synthesis procedure, and prior to disposal using carbon dioxide or hydrochloric acid. The main objectives for the said investigation were: {u100083} To optimise the reaction parameters to obtain a higher yield and purity of atrazine. {u100083} To evaluate the use of carbon dioxide and hydrochloric acid to neutralise the reaction mixture. {u100083} To study the solids present in the effluent. Synthetic reactions were carried out in the presence of an organic solvent, methyl isobutyl ketone (MIBK). The synthesis of atrazine was optimised in terms of addition sequence and rates of amine reagents and base (proton acceptor) additions by means of bench scale reactions. It was found that addition of a neutralising step (hydrochloric acid or carbon dioxide) to neutralise the basic reaction mixture prior to and after addition of the secondary amine and the base minimizes the formation of by-products. Of particular importance in ensuring high yields and selectivity to the atrazine product was temperature control, pH control, reagent ratios, addition rates and mixing. The latter was important in view of the rapid reaction of amine/NaOH with cyanuric chloride, as well as the possible reaction of mono-i, the reaction intermediate, with IPA in cases of excesses of reagent. Under optimum conditions, an atrazine composition of >97% was achieved where the resultant product was well within stipulated product specifications.
- Full Text:
- Date Issued: 2004
Oral tradition and the creation of late prehistory in Roviana Lagoon, Solomon Islands
- Sheppard, Peter, Walter, Richard, Aswani, Shankar
- Authors: Sheppard, Peter , Walter, Richard , Aswani, Shankar
- Date: 2004
- Subjects: To be catalogued
- Language: English
- Type: text , book
- Identifier: http://hdl.handle.net/10962/439958 , vital:73723 , ISBN 0975047639
- Description: The use of oral tradition or oral history in archaeology is often a contentious issue. In this paper we briefly review methodological issues surrounding the use of such data and follow this with a case study using our research into the last 1,000 years of prehistory in Roviana Lagoon (New Georgia Group, Solomon Islands). We argue that it is not possible to generalize cross-culturally about the historicity of oral tradition/history. However, in the Roviana case, careful use of ethnohistory and archaeology together indicates that:(a) Roviana oral history is linear;(b) there is a close relationship between genealogical age and radiocarbon age; and (c) the modern uses of the oral tradition by Roviana provide a theory of their use in the past. We conclude that the model for the formation of the Roviana Chiefdom which emerges from the working back and forth between archaeology and ethnohistory has much more explanatory power than one based on either source of data by itself.
- Full Text:
- Date Issued: 2004
- Authors: Sheppard, Peter , Walter, Richard , Aswani, Shankar
- Date: 2004
- Subjects: To be catalogued
- Language: English
- Type: text , book
- Identifier: http://hdl.handle.net/10962/439958 , vital:73723 , ISBN 0975047639
- Description: The use of oral tradition or oral history in archaeology is often a contentious issue. In this paper we briefly review methodological issues surrounding the use of such data and follow this with a case study using our research into the last 1,000 years of prehistory in Roviana Lagoon (New Georgia Group, Solomon Islands). We argue that it is not possible to generalize cross-culturally about the historicity of oral tradition/history. However, in the Roviana case, careful use of ethnohistory and archaeology together indicates that:(a) Roviana oral history is linear;(b) there is a close relationship between genealogical age and radiocarbon age; and (c) the modern uses of the oral tradition by Roviana provide a theory of their use in the past. We conclude that the model for the formation of the Roviana Chiefdom which emerges from the working back and forth between archaeology and ethnohistory has much more explanatory power than one based on either source of data by itself.
- Full Text:
- Date Issued: 2004
Over-expression, purification and biochemical characterization of DOXP reductoisomerase and the rational design of novel anti-malarial drugs
- Authors: Tanner, Delia Caroline
- Date: 2004
- Subjects: Malaria -- Prevention , Malaria -- Drug therapy , Antimalarials -- Therapeutic use , Proteins -- Purification , Amino acids -- Analysis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3931 , http://hdl.handle.net/10962/d1003990 , Malaria -- Prevention , Malaria -- Drug therapy , Antimalarials -- Therapeutic use , Proteins -- Purification , Amino acids -- Analysis
- Description: Malaria poses the greatest threat of all parasites to human life. Current vaccines and efficacious drugs are available however their use is limited due to toxicity, emergence of drug resistance, and cost. The discovery of an alternative pathway of isoprenoid biosynthesis, the non-mevalonate pathway, within the malarial parasite has resulted in development of novel anti-malarial drugs. 1-Deoxy-D-xylulose-5-phosphate (DOXP) reductoisomerase, the second enzyme in this pathway, is responsible for the synthesis of 2-C-methyl-D-erythritol 4-phosphate (MEP) in an intramolecular rearrangement step followed by a reduction process involving NADPH as a hydrogen donor and divalent cations as co-factors. Fosmidomycin and FR900098 have been identified as inhibitors of DOXP reductoisomerase. However, they lack clinical efficacy. In this investigation recombinant DOXP reductoisomerase from Escherichia coli (EcDXR) and Plasmodium falciparum (pfDXR) were biochemically characterized as potential targets for inhibition. (His)6-EcDXR was successfully purified using nickel-chelate affinity chromatography with a specific activity of 1.77 μmoles/min/mg and Km value 282 μM. Utilizing multiple sequence alignment, previous structural data predictions and homology modeling approaches, critical active site amino acid residues were identified and their role in the catalytic activity investigated utilizing site-directed mutagenesis techniques. We have shown evidence that suggests that Trp212 and Met214 interact to maintain the active site architecture and hydrophobic interactions necessary for substrate binding, cofactor binding and enzyme activity. Replacement of Trp212 with Tyr, Phe, and Leu reduced specific activity relative to EcDXR. EcDXR(W212F) and EcDXR(W212Y) had an increased Km relative to EcDXR indicative of loss in affinity toward DOXP, whereas EcDXR(W212L) had a lower Km of ~8 μM indicative of increased affinity for DOXP. The W212L substitution possibly removed contacts necessary for full catalytic activity, but could be considered a non-disruptive substitution in that it maintained active site architecture sufficient for DOXP reductoisomerase activity. EcDXR(M214I) had 36-fold reduced enzyme activity relative to EcDXR, while its Km (~8 μM) was found to be lower than that of EcDXR. This suggested that the M214I substitution had maintained (perhaps improved) substrate and active site architecture, but may have perturbed interactions with NADPH. Rational drug design strategies and docking methods have been utilized in the development of furan derivatives as DOXP reductoisomerase inhibitors, and the synthesis of phosphorylated derivatives (5) and (6) has been achieved. Future inhibitor studies using these novel potential DOXP reductoisomerase inhibitors may lead to the development of effective anti-malarial drug candidates.
- Full Text:
- Date Issued: 2004
- Authors: Tanner, Delia Caroline
- Date: 2004
- Subjects: Malaria -- Prevention , Malaria -- Drug therapy , Antimalarials -- Therapeutic use , Proteins -- Purification , Amino acids -- Analysis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3931 , http://hdl.handle.net/10962/d1003990 , Malaria -- Prevention , Malaria -- Drug therapy , Antimalarials -- Therapeutic use , Proteins -- Purification , Amino acids -- Analysis
- Description: Malaria poses the greatest threat of all parasites to human life. Current vaccines and efficacious drugs are available however their use is limited due to toxicity, emergence of drug resistance, and cost. The discovery of an alternative pathway of isoprenoid biosynthesis, the non-mevalonate pathway, within the malarial parasite has resulted in development of novel anti-malarial drugs. 1-Deoxy-D-xylulose-5-phosphate (DOXP) reductoisomerase, the second enzyme in this pathway, is responsible for the synthesis of 2-C-methyl-D-erythritol 4-phosphate (MEP) in an intramolecular rearrangement step followed by a reduction process involving NADPH as a hydrogen donor and divalent cations as co-factors. Fosmidomycin and FR900098 have been identified as inhibitors of DOXP reductoisomerase. However, they lack clinical efficacy. In this investigation recombinant DOXP reductoisomerase from Escherichia coli (EcDXR) and Plasmodium falciparum (pfDXR) were biochemically characterized as potential targets for inhibition. (His)6-EcDXR was successfully purified using nickel-chelate affinity chromatography with a specific activity of 1.77 μmoles/min/mg and Km value 282 μM. Utilizing multiple sequence alignment, previous structural data predictions and homology modeling approaches, critical active site amino acid residues were identified and their role in the catalytic activity investigated utilizing site-directed mutagenesis techniques. We have shown evidence that suggests that Trp212 and Met214 interact to maintain the active site architecture and hydrophobic interactions necessary for substrate binding, cofactor binding and enzyme activity. Replacement of Trp212 with Tyr, Phe, and Leu reduced specific activity relative to EcDXR. EcDXR(W212F) and EcDXR(W212Y) had an increased Km relative to EcDXR indicative of loss in affinity toward DOXP, whereas EcDXR(W212L) had a lower Km of ~8 μM indicative of increased affinity for DOXP. The W212L substitution possibly removed contacts necessary for full catalytic activity, but could be considered a non-disruptive substitution in that it maintained active site architecture sufficient for DOXP reductoisomerase activity. EcDXR(M214I) had 36-fold reduced enzyme activity relative to EcDXR, while its Km (~8 μM) was found to be lower than that of EcDXR. This suggested that the M214I substitution had maintained (perhaps improved) substrate and active site architecture, but may have perturbed interactions with NADPH. Rational drug design strategies and docking methods have been utilized in the development of furan derivatives as DOXP reductoisomerase inhibitors, and the synthesis of phosphorylated derivatives (5) and (6) has been achieved. Future inhibitor studies using these novel potential DOXP reductoisomerase inhibitors may lead to the development of effective anti-malarial drug candidates.
- Full Text:
- Date Issued: 2004
Parasitoids associated with the diamondback moth, Plutella xylostella (L.), in the Eastern Cape, South Africa
- Smith, Tamara J, Villet, Martin H
- Authors: Smith, Tamara J , Villet, Martin H
- Date: 2004
- Subjects: To be catalogued
- Language: English
- Type: text , conference
- Identifier: http://hdl.handle.net/10962/442795 , vital:74034 , ISBN , https://www.cabidigitallibrary.org/doi/full/10.5555/20093098381
- Description: Seasonal fluctuations of diamondback moth and its hymenopteran parasitoids were recorded weekly from April 1997 to November 1999 at four cabbage sites in the Grahamstown area of the Eastern Cape, South Africa. Two sites were commercial farms with active spraying programmes; the others were unsprayed. Infestation levels were highest during spring (September to November) and autumn (March to May), where 100% infestation of plants was reached at times. The highest infestation was found during the spring months, where 12 larvae/plant were found at the unsprayed sites and between 6 and 10 larvae at the sprayed sites. At the unsprayed sites abundance of diamondback moth larvae and parasitoids was high during 1997, but much lower during 1998 and 1999, indicating possible control by the parasitoids. Nine species of parasitoid were recorded from diamondback moth during this period and four (Cotesia plutellae (Kurdjumov) (Hymenoptera: Braconidae), Diadegma mollipla (Holmgren) (Hymenoptera: Ichneumonidae), Diadromus collaris Gravenhorst (Hymenoptera: Ichneumonidae) and Oomyzus sokolowskii (Kurdjumov) (Hymenoptera: Eulophidae)) showed potential as biological control agents. The highest rate of parasitism was found from mid-autumn to the beginning of winter (April to June) and from mid-spring to the beginning of summer (October to December). Percent parasitism varied throughout the year, ranging between 10% and 80%. Parasitism of 100% was observed when moth numbers were low. Different species of parasitoids were found to be dominant at different times of the year.
- Full Text:
- Date Issued: 2004
- Authors: Smith, Tamara J , Villet, Martin H
- Date: 2004
- Subjects: To be catalogued
- Language: English
- Type: text , conference
- Identifier: http://hdl.handle.net/10962/442795 , vital:74034 , ISBN , https://www.cabidigitallibrary.org/doi/full/10.5555/20093098381
- Description: Seasonal fluctuations of diamondback moth and its hymenopteran parasitoids were recorded weekly from April 1997 to November 1999 at four cabbage sites in the Grahamstown area of the Eastern Cape, South Africa. Two sites were commercial farms with active spraying programmes; the others were unsprayed. Infestation levels were highest during spring (September to November) and autumn (March to May), where 100% infestation of plants was reached at times. The highest infestation was found during the spring months, where 12 larvae/plant were found at the unsprayed sites and between 6 and 10 larvae at the sprayed sites. At the unsprayed sites abundance of diamondback moth larvae and parasitoids was high during 1997, but much lower during 1998 and 1999, indicating possible control by the parasitoids. Nine species of parasitoid were recorded from diamondback moth during this period and four (Cotesia plutellae (Kurdjumov) (Hymenoptera: Braconidae), Diadegma mollipla (Holmgren) (Hymenoptera: Ichneumonidae), Diadromus collaris Gravenhorst (Hymenoptera: Ichneumonidae) and Oomyzus sokolowskii (Kurdjumov) (Hymenoptera: Eulophidae)) showed potential as biological control agents. The highest rate of parasitism was found from mid-autumn to the beginning of winter (April to June) and from mid-spring to the beginning of summer (October to December). Percent parasitism varied throughout the year, ranging between 10% and 80%. Parasitism of 100% was observed when moth numbers were low. Different species of parasitoids were found to be dominant at different times of the year.
- Full Text:
- Date Issued: 2004
Particle precipitation effects in the daytime E-region in the South Atlantic Anomaly region
- Authors: Haggard, Raymond
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6794 , http://hdl.handle.net/10962/d1003836
- Description: The behaviour of the normal daytime E-layer over the South Atlantic Anomaly region during 23 days of project ISAAC (29 June to 21 July 1983) has been examined. Enhanced production rates due to precipitated electrons were calculated from the observed data and compared well with the production rates from the mean electron fluxes in the range 0.2–26 keV observed from the satellite Atmosphere Explorer-C during 1973–77, discussed by Gledhill and Hoffman.1 The present study shows that there is evidence of a significant source of extra ionization, in addition to solar ultraviolet and X-radiation, in the South Atlantic Anomaly region.
- Full Text:
- Date Issued: 2004
- Authors: Haggard, Raymond
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6794 , http://hdl.handle.net/10962/d1003836
- Description: The behaviour of the normal daytime E-layer over the South Atlantic Anomaly region during 23 days of project ISAAC (29 June to 21 July 1983) has been examined. Enhanced production rates due to precipitated electrons were calculated from the observed data and compared well with the production rates from the mean electron fluxes in the range 0.2–26 keV observed from the satellite Atmosphere Explorer-C during 1973–77, discussed by Gledhill and Hoffman.1 The present study shows that there is evidence of a significant source of extra ionization, in addition to solar ultraviolet and X-radiation, in the South Atlantic Anomaly region.
- Full Text:
- Date Issued: 2004
Petrology and geochemistry of Early Cretaceous bimodal continental flood volcanism of the NW Etendeka, Namibia Part 1: introduction, mafic lavas and re-evaluation of mantle source components
- Ewart, A, Marsh, Julian S, Milner, Simon C, Duncan, Andrew R, Kamber, B S, Armstrong, R A
- Authors: Ewart, A , Marsh, Julian S , Milner, Simon C , Duncan, Andrew R , Kamber, B S , Armstrong, R A
- Date: 2004
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/150583 , vital:38986 , https://doi.org/10.1093/petrology/egg083
- Description: The bimodal NW Etendeka province is located at the continental end of the Tristan plume trace in coastal Namibia. It comprises a high-Ti (Khumib type) and three low-Ti basalt (Tafelberg, Kuidas and Esmeralda types) suites, with, at stratigraphically higher level, interstratified high-Ti latites (three units) and quartz latites (five units), and one low-Ti quartz latite. Khumib basalts are enriched in high field strength elements and light rare earth elements relative to low-Ti types and exhibit trace element affinities with Tristan da Cunha lavas.
- Full Text: false
- Date Issued: 2004
- Authors: Ewart, A , Marsh, Julian S , Milner, Simon C , Duncan, Andrew R , Kamber, B S , Armstrong, R A
- Date: 2004
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/150583 , vital:38986 , https://doi.org/10.1093/petrology/egg083
- Description: The bimodal NW Etendeka province is located at the continental end of the Tristan plume trace in coastal Namibia. It comprises a high-Ti (Khumib type) and three low-Ti basalt (Tafelberg, Kuidas and Esmeralda types) suites, with, at stratigraphically higher level, interstratified high-Ti latites (three units) and quartz latites (five units), and one low-Ti quartz latite. Khumib basalts are enriched in high field strength elements and light rare earth elements relative to low-Ti types and exhibit trace element affinities with Tristan da Cunha lavas.
- Full Text: false
- Date Issued: 2004
Petrology and geochemistry of early cretaceous bimodal continental flood volcanism of the NW Etendeka, Namibia Part 2: characteristics and petrogenesis of the high-Ti latite and high-Ti and low-Ti voluminous quartz latite eruptives
- Ewart, A, Marsh, Julian S, Milner, Simon C, Duncan, Andrew R, Kamber, B S, Armstrong, R A
- Authors: Ewart, A , Marsh, Julian S , Milner, Simon C , Duncan, Andrew R , Kamber, B S , Armstrong, R A
- Date: 2004
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/150593 , vital:38987 , https://doi.org/10.1093/petrology/egg082
- Description: As a result of their relative concentration towards the respective Atlantic margins, the silicic eruptives of the Paraná (Brazil)–Etendeka large igneous province are disproportionately abundant in the Etendeka of Namibia. The NW Etendeka silicic units, dated at ∼132 Ma, occupy the upper stratigraphic levels of the volcanic sequences, restricted to the coastal zone, and comprise three latites and five quartz latites (QL).
- Full Text: false
- Date Issued: 2004
- Authors: Ewart, A , Marsh, Julian S , Milner, Simon C , Duncan, Andrew R , Kamber, B S , Armstrong, R A
- Date: 2004
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/150593 , vital:38987 , https://doi.org/10.1093/petrology/egg082
- Description: As a result of their relative concentration towards the respective Atlantic margins, the silicic eruptives of the Paraná (Brazil)–Etendeka large igneous province are disproportionately abundant in the Etendeka of Namibia. The NW Etendeka silicic units, dated at ∼132 Ma, occupy the upper stratigraphic levels of the volcanic sequences, restricted to the coastal zone, and comprise three latites and five quartz latites (QL).
- Full Text: false
- Date Issued: 2004
Phenomenology in education : a case study in educational leadership
- Authors: Van der Mescht, Hennie
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6101 , http://hdl.handle.net/10962/d1008665
- Description: [From the introduction]: Overheard during tea at an Education Faculty research design course: “Phenomenology produces interesting and surprising results, but it’s just too much work …” The speaker was a prospective Masters student who had decided against “phenomenological” research, presumably because “it’s just too much work”. Having been deeply involved in phenomenological research myself for some years, I could identify with his reservation. But his first statement is of course equally true: phenomenological research does indeed produce “interesting and surprising results”, as many of my students have found. I should at the outset describe what I mean by phenomenological research more carefully, since, as Schweitzer (2002) has recently pointed out, there is certainly more than one meaning out there. The kind of research I am referring to is not the kind frequently featured in this journal, which Schweitzer (2002) describes as “Husserlian”, but another kind, which he describes as “‘what’s it like for them’ type of studies”. In this paper I present a case for the latter, and consider its appropriateness to the field of education. I argue that this approach to phenomenological research (which Schweitzer refers to as empirical) is a potentially powerful way of making sense of education practitioners’ (and learners’) sense-making, and can lead to startling new insights into the uniquely complex processes of learning, teaching and educational managing and leading.
- Full Text:
- Date Issued: 2004
- Authors: Van der Mescht, Hennie
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6101 , http://hdl.handle.net/10962/d1008665
- Description: [From the introduction]: Overheard during tea at an Education Faculty research design course: “Phenomenology produces interesting and surprising results, but it’s just too much work …” The speaker was a prospective Masters student who had decided against “phenomenological” research, presumably because “it’s just too much work”. Having been deeply involved in phenomenological research myself for some years, I could identify with his reservation. But his first statement is of course equally true: phenomenological research does indeed produce “interesting and surprising results”, as many of my students have found. I should at the outset describe what I mean by phenomenological research more carefully, since, as Schweitzer (2002) has recently pointed out, there is certainly more than one meaning out there. The kind of research I am referring to is not the kind frequently featured in this journal, which Schweitzer (2002) describes as “Husserlian”, but another kind, which he describes as “‘what’s it like for them’ type of studies”. In this paper I present a case for the latter, and consider its appropriateness to the field of education. I argue that this approach to phenomenological research (which Schweitzer refers to as empirical) is a potentially powerful way of making sense of education practitioners’ (and learners’) sense-making, and can lead to startling new insights into the uniquely complex processes of learning, teaching and educational managing and leading.
- Full Text:
- Date Issued: 2004
Phylogeny, biogeography, and the evolution of life-history traits in Leucadendron (Proteaceae)
- Barker, Nigel P, Vanderpoorten, Alain, Morton, Cynthia M, Rourke, John P
- Authors: Barker, Nigel P , Vanderpoorten, Alain , Morton, Cynthia M , Rourke, John P
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6496 , http://hdl.handle.net/10962/d1004491
- Description: Leucadendron is a moderately large genus of Proteaceae almost entirely restricted to the Cape Floristic Region of southern Africa. The genus is unusual in being dioecious and sexually dimorphic. ITS sequence data were obtained from 62 of the 96 currently recognized taxa (85 species and 11 subspecies). Phylogenetic analyses were conducted under Maximum Likelihood and parsimony and resolved nine groups of species with varying degrees of bootstrap support, but relationships between these groups are largely unsupported. The phylogeny conflicts with the current taxonomic arrangement, which is based mainly on fruit morphology. The two sections of the genus, Alatosperma and Leucadendron, and several subsections within these sections, are resolved as non-monophyletic. This means that taxonomically important characters (such as fruit shape) have evolved multiple times, as the species with nutlike fruit (resolved into two of the nine groups) appear to have evolved independently from ancestors with winged fruit. Based on the topology obtained, the life history traits of anemophily, myrmechochory, and re-sprouting have also originated multiple times. Dispersal–Vicariance (DIVA) analysis suggests that the genus had an ancestral area in the Karoo Mountain and Southeastern phytogeographic centres of endemism in the southwestern Cape. , Elsevier
- Full Text:
- Date Issued: 2004
- Authors: Barker, Nigel P , Vanderpoorten, Alain , Morton, Cynthia M , Rourke, John P
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6496 , http://hdl.handle.net/10962/d1004491
- Description: Leucadendron is a moderately large genus of Proteaceae almost entirely restricted to the Cape Floristic Region of southern Africa. The genus is unusual in being dioecious and sexually dimorphic. ITS sequence data were obtained from 62 of the 96 currently recognized taxa (85 species and 11 subspecies). Phylogenetic analyses were conducted under Maximum Likelihood and parsimony and resolved nine groups of species with varying degrees of bootstrap support, but relationships between these groups are largely unsupported. The phylogeny conflicts with the current taxonomic arrangement, which is based mainly on fruit morphology. The two sections of the genus, Alatosperma and Leucadendron, and several subsections within these sections, are resolved as non-monophyletic. This means that taxonomically important characters (such as fruit shape) have evolved multiple times, as the species with nutlike fruit (resolved into two of the nine groups) appear to have evolved independently from ancestors with winged fruit. Based on the topology obtained, the life history traits of anemophily, myrmechochory, and re-sprouting have also originated multiple times. Dispersal–Vicariance (DIVA) analysis suggests that the genus had an ancestral area in the Karoo Mountain and Southeastern phytogeographic centres of endemism in the southwestern Cape. , Elsevier
- Full Text:
- Date Issued: 2004
Pictograms for conveying medicine instructions: comprehension in various South African language groups
- Dowse, Roslind, Ehlers, Martina S
- Authors: Dowse, Roslind , Ehlers, Martina S
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6354 , http://hdl.handle.net/10962/d1006038
- Description: The comprehension of medicine instructions is essential for the safe and effective use of medicines. In cases where low literacy constitutes a possible barrier to understanding written medicine information fully, the inclusion of pictograms may facilitate comprehension. Twenty-three internationally available pictograms and 23 corresponding locally developed images were evaluated in 304 low-literate respondents from eight different South African language groups. Demographic data were collected and an English literacy test was administered to those respondents who had stated that they could read English. Interviewees were shown the 46 pictograms in random order and were asked for their interpretation. Preference for either the international or local version was assessed. Correct interpretation of individual pictograms ranged from 14% to 97%. Images which had been developed locally were more successful in eliciting correct interpretations than those obtained from an international source (USP pictograms). Only 2 of the 23 USP pictograms achieved the 85% criterion of the American National Standards Institute compared with 12 of 23 locally developed counterparts. Local pictograms were preferred over the American ones in all cases. Standard of education had a significant influence on interpretation, whereas no significant differences in interpretation could be attributed to cultural diversity between the African language groups. Almost all respondents (98%) reacted positively to the idea of having pictograms on their medicine labels. The success of the local pictograms highlighted the value of a rigorous and consultative design and test process. Results from one African language group can reliably be extrapolated to other groups in South Africa.
- Full Text:
- Date Issued: 2004
- Authors: Dowse, Roslind , Ehlers, Martina S
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6354 , http://hdl.handle.net/10962/d1006038
- Description: The comprehension of medicine instructions is essential for the safe and effective use of medicines. In cases where low literacy constitutes a possible barrier to understanding written medicine information fully, the inclusion of pictograms may facilitate comprehension. Twenty-three internationally available pictograms and 23 corresponding locally developed images were evaluated in 304 low-literate respondents from eight different South African language groups. Demographic data were collected and an English literacy test was administered to those respondents who had stated that they could read English. Interviewees were shown the 46 pictograms in random order and were asked for their interpretation. Preference for either the international or local version was assessed. Correct interpretation of individual pictograms ranged from 14% to 97%. Images which had been developed locally were more successful in eliciting correct interpretations than those obtained from an international source (USP pictograms). Only 2 of the 23 USP pictograms achieved the 85% criterion of the American National Standards Institute compared with 12 of 23 locally developed counterparts. Local pictograms were preferred over the American ones in all cases. Standard of education had a significant influence on interpretation, whereas no significant differences in interpretation could be attributed to cultural diversity between the African language groups. Almost all respondents (98%) reacted positively to the idea of having pictograms on their medicine labels. The success of the local pictograms highlighted the value of a rigorous and consultative design and test process. Results from one African language group can reliably be extrapolated to other groups in South Africa.
- Full Text:
- Date Issued: 2004
Politics, latent and overt, in Hill of Fools
- Authors: Wright, Laurence
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:7064 , http://hdl.handle.net/10962/d1007430
- Description: [From the text]: R. L. Peteni’s novel Hill of Fools (1976) is a work that benefits greatly when Collingwood’s maxim is observed. The author’s family history and the circumstances surrounding the book’s publication add a dimension of political and social meaning which its surface deliberately occludes. Perhaps more importantly, while the story can readily be enjoyed, the quality of sensibility behind the work is not readily accessed without understanding some of the socio-political background.
- Full Text:
- Date Issued: 2004
- Authors: Wright, Laurence
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:7064 , http://hdl.handle.net/10962/d1007430
- Description: [From the text]: R. L. Peteni’s novel Hill of Fools (1976) is a work that benefits greatly when Collingwood’s maxim is observed. The author’s family history and the circumstances surrounding the book’s publication add a dimension of political and social meaning which its surface deliberately occludes. Perhaps more importantly, while the story can readily be enjoyed, the quality of sensibility behind the work is not readily accessed without understanding some of the socio-political background.
- Full Text:
- Date Issued: 2004
Pollination biology of Bergeranthus multiceps (Aizoaceae) with preliminary observations of repeated flower opening and closure
- Peter, Craig I, Dold, Anthony P, Barker, Nigel P, Ripley, Bradford S
- Authors: Peter, Craig I , Dold, Anthony P , Barker, Nigel P , Ripley, Bradford S
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6529 , http://hdl.handle.net/10962/d1005970
- Description: Little is known about pollination of the Aizoaceae (Mesembryanthemaceae). There are sparse reports of generalist pollination in the family by a variety of insects (predominantly bees). Furthermore, most species are self-incompatible in cultivation. In this study, observations were made on two populations of Bergeranthus multiceps (Salm-Dyck) Schwantes growing in the Eastern Cape province of South Africa. Insects visiting the flowers were collected and examined for pollen. While 79 individual insects (in 24 genera representing 14 families and four orders) were collected visiting the flowers, the majority (43 individuals) were female Allodapula variegata bees (Apidae, subfamily Xylocopinae, tribe Allodapini)collecting pollen. All other bee visitors were also female, suggesting pollen collection as the primary activity at the flowers. The protandrous flowers were found to be self-incompatible, pointing to the importance of bee-mediated xenogamy in this species. The flowers of B. multiceps are bright yellow in the human visual spectrum. In addition, the petals of this species reflect ultraviolet light. In contrast, the yellow anthers absorb UV. Flower opening and closing is common in the Aizoaceae. Interestingly, in B. multiceps flowers open at about 15:30 and remain open for approximately three hours before closing again in the late afternoon. These afternoon flower opening events were found to be closely correlated to ambient temperatures above 23°C, relative humidity lower than 50% and vapour pressure deficit below 1.05 kPa measured from as early as 09:00 on the days when flowers opened.
- Full Text:
- Date Issued: 2004
- Authors: Peter, Craig I , Dold, Anthony P , Barker, Nigel P , Ripley, Bradford S
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6529 , http://hdl.handle.net/10962/d1005970
- Description: Little is known about pollination of the Aizoaceae (Mesembryanthemaceae). There are sparse reports of generalist pollination in the family by a variety of insects (predominantly bees). Furthermore, most species are self-incompatible in cultivation. In this study, observations were made on two populations of Bergeranthus multiceps (Salm-Dyck) Schwantes growing in the Eastern Cape province of South Africa. Insects visiting the flowers were collected and examined for pollen. While 79 individual insects (in 24 genera representing 14 families and four orders) were collected visiting the flowers, the majority (43 individuals) were female Allodapula variegata bees (Apidae, subfamily Xylocopinae, tribe Allodapini)collecting pollen. All other bee visitors were also female, suggesting pollen collection as the primary activity at the flowers. The protandrous flowers were found to be self-incompatible, pointing to the importance of bee-mediated xenogamy in this species. The flowers of B. multiceps are bright yellow in the human visual spectrum. In addition, the petals of this species reflect ultraviolet light. In contrast, the yellow anthers absorb UV. Flower opening and closing is common in the Aizoaceae. Interestingly, in B. multiceps flowers open at about 15:30 and remain open for approximately three hours before closing again in the late afternoon. These afternoon flower opening events were found to be closely correlated to ambient temperatures above 23°C, relative humidity lower than 50% and vapour pressure deficit below 1.05 kPa measured from as early as 09:00 on the days when flowers opened.
- Full Text:
- Date Issued: 2004
Praxis-based assignments for professional development in the Rhodes University/Swaziland Participatory Course in Environmental Education : the case of assignment four
- Authors: Motsa, Elizabeth Matfobhi
- Date: 2004
- Subjects: Rhodes University / Swaziland Participatory Course in Environmental Education Environmental education -- Swaziland Environmental education -- Study and teaching -- Swaziland
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:1710 , http://hdl.handle.net/10962/d1003593
- Description: The aim of this study was to find out how praxis is fostered in professional development processes, through the assignment four of the Rhodes University / Swaziland Participatory course in Environmental Education (referred to as the Swaziland course), in the Swaziland context. The research aimed at exploring instances of praxis in assignment four development processes and in implementing the assignment ‘product’ in the field of participants’ practice at their schools. The research is intended to improve practice in professional development in the Swaziland course, and in the SADC region more broadly, although the case study does not assume generalisability. The study employed a naturalistic research methodology, involving the development of an interpretive case study to aid understanding of social phenomena in the natural setting. It is influenced by the belief that knowledge is socially constructed and the assumption that meanings are generated and shared through language. The research methods involved observing interactions in the course processes during tutorials sessions and I compiled a course processes profile. I also analyzed copies of assignment four products of two course participants, and observed them using their assignment ‘products’ in their workplaces. Using this data, I generated two ‘constructions’ of the two course participants’ experiences of praxis-based assignment work in the Swaziland course. I also interviewed two course tutors. Data was analysed with an intention to understand actions and interactions relating to praxis-based assignment work. Two ‘layers’ of data analysis were undertaken, to deepen understanding of the phenomenon studied. Through this research I have learnt that though assignment processes enable praxis basedlearning, there are problems encountered in participants’ field of practice due to power relations and participants articulation of the relationship between theory and practice. These, and other structural factors impinge on reflexive agency in the context of both educational and environmental praxis. The structures in the school system frustrate reflexive agency in environmental teaching and learning, and socio-political and socio-economic structures also constrain environmental praxis, hence false consciousness prevails. Given the above situation I recommend further research into the relationship between environmental and educational praxis in environmental education and further research into reflexive agency in environmental education contexts.
- Full Text:
- Date Issued: 2004
- Authors: Motsa, Elizabeth Matfobhi
- Date: 2004
- Subjects: Rhodes University / Swaziland Participatory Course in Environmental Education Environmental education -- Swaziland Environmental education -- Study and teaching -- Swaziland
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:1710 , http://hdl.handle.net/10962/d1003593
- Description: The aim of this study was to find out how praxis is fostered in professional development processes, through the assignment four of the Rhodes University / Swaziland Participatory course in Environmental Education (referred to as the Swaziland course), in the Swaziland context. The research aimed at exploring instances of praxis in assignment four development processes and in implementing the assignment ‘product’ in the field of participants’ practice at their schools. The research is intended to improve practice in professional development in the Swaziland course, and in the SADC region more broadly, although the case study does not assume generalisability. The study employed a naturalistic research methodology, involving the development of an interpretive case study to aid understanding of social phenomena in the natural setting. It is influenced by the belief that knowledge is socially constructed and the assumption that meanings are generated and shared through language. The research methods involved observing interactions in the course processes during tutorials sessions and I compiled a course processes profile. I also analyzed copies of assignment four products of two course participants, and observed them using their assignment ‘products’ in their workplaces. Using this data, I generated two ‘constructions’ of the two course participants’ experiences of praxis-based assignment work in the Swaziland course. I also interviewed two course tutors. Data was analysed with an intention to understand actions and interactions relating to praxis-based assignment work. Two ‘layers’ of data analysis were undertaken, to deepen understanding of the phenomenon studied. Through this research I have learnt that though assignment processes enable praxis basedlearning, there are problems encountered in participants’ field of practice due to power relations and participants articulation of the relationship between theory and practice. These, and other structural factors impinge on reflexive agency in the context of both educational and environmental praxis. The structures in the school system frustrate reflexive agency in environmental teaching and learning, and socio-political and socio-economic structures also constrain environmental praxis, hence false consciousness prevails. Given the above situation I recommend further research into the relationship between environmental and educational praxis in environmental education and further research into reflexive agency in environmental education contexts.
- Full Text:
- Date Issued: 2004
Pre-emigration reflections : Afrikaans speakers moving to New Zealand
- De Klerk, Vivian A, Barkhuizen, Gary P
- Authors: De Klerk, Vivian A , Barkhuizen, Gary P
- Date: 2004
- Language: English
- Type: Article , text
- Identifier: vital:6138 , http://hdl.handle.net/10962/d1011590
- Description: This article reports on the pre-emigration reflections of 15 Afrikaans speakers, all of whom were in the final stages of preparing to emigrate to New Zealand. The study explores the linguistic histories of the participants, their attitudes to their mother tongue (Afrikaans) and to English, and their views on South Africa's language policy and how it has influenced their decisions to leave the country. The paper also offers a view on possible long-term linguistic outcomes for these families.
- Full Text:
- Date Issued: 2004
- Authors: De Klerk, Vivian A , Barkhuizen, Gary P
- Date: 2004
- Language: English
- Type: Article , text
- Identifier: vital:6138 , http://hdl.handle.net/10962/d1011590
- Description: This article reports on the pre-emigration reflections of 15 Afrikaans speakers, all of whom were in the final stages of preparing to emigrate to New Zealand. The study explores the linguistic histories of the participants, their attitudes to their mother tongue (Afrikaans) and to English, and their views on South Africa's language policy and how it has influenced their decisions to leave the country. The paper also offers a view on possible long-term linguistic outcomes for these families.
- Full Text:
- Date Issued: 2004
Price discovery, price behaviour, and efficiency of selected grain commodities traded on the agricultural products division of the JSE securities exchange
- Authors: Viljoen, Christo
- Date: 2004
- Subjects: Johannesburg Stock Exchange Stock exchanges -- South Africa International economic relations Primary commodities -- South Africa Grain trade -- South Africa Financial futures -- South Africa Price regulation -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:952 , http://hdl.handle.net/10962/d1002686
- Description: Agricultural commodity derivatives were first introduced in South Africa in 1996 after the deregulation of the former marketing system. In the context of its proposed functions, namely price discovery and risk management, the question arose as to whether the futures market developed over time to performed its role efficiently. According to the Efficient Markets Hypothesis (EMH) an efficient market is one that accurately incorporates all information available at any point in time. The purpose of the research was to address the issue of price discovery efficiency, firstly, focusing on the weak-form methodology. Secondly, considering the behaviour of futures prices over time, the study addressed the concern of anomalies in daily returns – phenomena contradictory to the EMH by implication. Thirdly, as a means of defining the sources of inefficiency, the role of scheduled public information and its impact on futures prices was examined. Therefore, the primary objective of the research was to investigate and identify the main components of agricultural futures market inefficiency within the unique price formation structure of South African grain markets. The assessment of this problem is important in terms of evaluating the growth and development of the futures market for different grain commodities to date. The Exchange needs to review rules and regulations on a frequent basis in order to ensure proper functioning at all times especially in the case of a relatively new and fast growing market. The study contributed to the knowledge of understanding the price adjustment process and its implications for market efficiency in the context of the three grain markets considered. The weak-form efficiency was tested using a co-integration based model. Analysing daily spot and futures prices of white maize, yellow maize, and wheat, results indicated that all three markets were efficient and unbiased. Non-parametric tests revealed the significant presence of day-of-the-week and turn-of-the-month effects in the futures returns of the three commodities. Further non-parametric analyses suggested a high degree of uncertainty in futures returns around scheduled agricultural and macroeconomic information release dates also contributing significantly to the identified anomalies. It was concluded that (1) the markets’ ability to anticipate the contents of future information to be released, (2) the current skewed size distribution of broking members, (3) the significant role of the R/$ exchange rate in the price formation process of South African grains and, therefore, (4) the relationship to and influence of the broader economy enhanced the return effects (anomalies) creating opportunity for profitable arbitrage. This conclusion was mainly attributed to South Africa’s status as a price-taker in the world grain complex as well as the relatively short existence of the local agricultural futures markets.
- Full Text:
- Date Issued: 2004
- Authors: Viljoen, Christo
- Date: 2004
- Subjects: Johannesburg Stock Exchange Stock exchanges -- South Africa International economic relations Primary commodities -- South Africa Grain trade -- South Africa Financial futures -- South Africa Price regulation -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:952 , http://hdl.handle.net/10962/d1002686
- Description: Agricultural commodity derivatives were first introduced in South Africa in 1996 after the deregulation of the former marketing system. In the context of its proposed functions, namely price discovery and risk management, the question arose as to whether the futures market developed over time to performed its role efficiently. According to the Efficient Markets Hypothesis (EMH) an efficient market is one that accurately incorporates all information available at any point in time. The purpose of the research was to address the issue of price discovery efficiency, firstly, focusing on the weak-form methodology. Secondly, considering the behaviour of futures prices over time, the study addressed the concern of anomalies in daily returns – phenomena contradictory to the EMH by implication. Thirdly, as a means of defining the sources of inefficiency, the role of scheduled public information and its impact on futures prices was examined. Therefore, the primary objective of the research was to investigate and identify the main components of agricultural futures market inefficiency within the unique price formation structure of South African grain markets. The assessment of this problem is important in terms of evaluating the growth and development of the futures market for different grain commodities to date. The Exchange needs to review rules and regulations on a frequent basis in order to ensure proper functioning at all times especially in the case of a relatively new and fast growing market. The study contributed to the knowledge of understanding the price adjustment process and its implications for market efficiency in the context of the three grain markets considered. The weak-form efficiency was tested using a co-integration based model. Analysing daily spot and futures prices of white maize, yellow maize, and wheat, results indicated that all three markets were efficient and unbiased. Non-parametric tests revealed the significant presence of day-of-the-week and turn-of-the-month effects in the futures returns of the three commodities. Further non-parametric analyses suggested a high degree of uncertainty in futures returns around scheduled agricultural and macroeconomic information release dates also contributing significantly to the identified anomalies. It was concluded that (1) the markets’ ability to anticipate the contents of future information to be released, (2) the current skewed size distribution of broking members, (3) the significant role of the R/$ exchange rate in the price formation process of South African grains and, therefore, (4) the relationship to and influence of the broader economy enhanced the return effects (anomalies) creating opportunity for profitable arbitrage. This conclusion was mainly attributed to South Africa’s status as a price-taker in the world grain complex as well as the relatively short existence of the local agricultural futures markets.
- Full Text:
- Date Issued: 2004
Probing learners' conceptual understanding of oxidation and reduction (redox) reactions : a case study
- Authors: Addam, Billey Bright
- Date: 2004
- Subjects: Competency based education -- South Africa Oxidation-reduction reaction -- Study and teaching Science -- Study and teaching -- South Africa
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:1409 , http://hdl.handle.net/10962/d1002950
- Description: The new political dispensation in South Africa has seen a lot of changes taking place. The democratic wind, which has been blowing in all spheres of the political arena, could not leave out Education. This has led to the transformation in education and the revision of the curriculum guided by the Outcomes-Based Education philosophy (OBE). Thus, require education authorities as well as educators to look at education more comprehensively. The challenge posed to educators now is to develop tools and strategies that will make learning accessible to as many learners as possible and to teach for understanding and construction of knowledge. The principal objective of this study was to investigate the important role the learner's prior knowledge plays and the use of different tools and strategies in stimulating conceptual understanding and construction of knowledge of redox reactions. This was done using learners' own investigations, practical activities, teaching settings and a workshop. The findings show that the learners lacked organized and structured prior knowledge. Learners could not integrate prior experience with new experience. The main issue seems to be the failure of learners to relate classroom experience to everyday redox phenomena. Possible reasons are discussed with some implications for teaching redox. The study further postulates that to assist learners to develop conceptual understanding of redox reactions, different tools and strategies should be employed and teaching made relevant to real-life situations. In so doing, redox concepts would not be abstract to learners.
- Full Text:
- Date Issued: 2004
- Authors: Addam, Billey Bright
- Date: 2004
- Subjects: Competency based education -- South Africa Oxidation-reduction reaction -- Study and teaching Science -- Study and teaching -- South Africa
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:1409 , http://hdl.handle.net/10962/d1002950
- Description: The new political dispensation in South Africa has seen a lot of changes taking place. The democratic wind, which has been blowing in all spheres of the political arena, could not leave out Education. This has led to the transformation in education and the revision of the curriculum guided by the Outcomes-Based Education philosophy (OBE). Thus, require education authorities as well as educators to look at education more comprehensively. The challenge posed to educators now is to develop tools and strategies that will make learning accessible to as many learners as possible and to teach for understanding and construction of knowledge. The principal objective of this study was to investigate the important role the learner's prior knowledge plays and the use of different tools and strategies in stimulating conceptual understanding and construction of knowledge of redox reactions. This was done using learners' own investigations, practical activities, teaching settings and a workshop. The findings show that the learners lacked organized and structured prior knowledge. Learners could not integrate prior experience with new experience. The main issue seems to be the failure of learners to relate classroom experience to everyday redox phenomena. Possible reasons are discussed with some implications for teaching redox. The study further postulates that to assist learners to develop conceptual understanding of redox reactions, different tools and strategies should be employed and teaching made relevant to real-life situations. In so doing, redox concepts would not be abstract to learners.
- Full Text:
- Date Issued: 2004
Processes that influence the experiences of children living with mothers that have HIV: two case studies
- Authors: Castelletto, Simona
- Date: 2004
- Subjects: AIDS (Disease) in women , AIDS (Disease) -- Social aspects -- South Africa , HIV infections -- Social aspects -- South Africa , Mothers and daughters -- Social aspects , Mothers and sons -- Social aspects , AIDS (Disease) in children -- Social aspects -- South Africa
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:3166 , http://hdl.handle.net/10962/d1007728 , AIDS (Disease) in women , AIDS (Disease) -- Social aspects -- South Africa , HIV infections -- Social aspects -- South Africa , Mothers and daughters -- Social aspects , Mothers and sons -- Social aspects , AIDS (Disease) in children -- Social aspects -- South Africa
- Description: Maternal HIV-infection is considered to be a threat to the psychosocial development of AIDS-affected children. In South Africa, AIDS-affected children may be particularly vulnerable due to the unprecedented effects of the HIV/AIDS epidemic on the breakdown of family and community resources in already disadvantaged communities. The aim of this study was to explore the contextualised experiences of two children living with mothers who have HIV by conducting two case studies. Mother-child dyads were recruited from local HIV/AIDS centres and informed consent was obtained. The mothers were in the minor symptomatic phase of HIV-infection and the children were uninfected and aged between 10 and 12 years. Through semi-structured interviewing, the mothers provided background and contextual information about the children. Play techniques were used in the child interviews to encourage the introduction and exploration of issues salient to the children. Play facilitated engagement around sensitive and potentially anxiety-provoking material. A key issue for the children was their concerns about the anticipated deaths of their mothers. The children held misconceptions about the transmission of HIV/ AIDS. They feared HIV/AIDS and expected that others would have negative perceptions of them. Family processes such as secrecy and avoidance around HIV/AIDS-related issues were understood to perpetuate the children's fears and false beliefs in a broader community context that stigmatised HIV/AIDS. It was argued that the mothers' shame over HIV-infection and their need to protect their relationship with their children compromised their ability to communicate openly with their children and to offer them meaningful emotional support. Limited parental involvement was identified as the key contextual process that engendered vulnerability in the children, as they were isolated within and beyond the family. Recommendations to address the processes that engendered vulnerability in the children are discussed.
- Full Text:
- Date Issued: 2004
- Authors: Castelletto, Simona
- Date: 2004
- Subjects: AIDS (Disease) in women , AIDS (Disease) -- Social aspects -- South Africa , HIV infections -- Social aspects -- South Africa , Mothers and daughters -- Social aspects , Mothers and sons -- Social aspects , AIDS (Disease) in children -- Social aspects -- South Africa
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:3166 , http://hdl.handle.net/10962/d1007728 , AIDS (Disease) in women , AIDS (Disease) -- Social aspects -- South Africa , HIV infections -- Social aspects -- South Africa , Mothers and daughters -- Social aspects , Mothers and sons -- Social aspects , AIDS (Disease) in children -- Social aspects -- South Africa
- Description: Maternal HIV-infection is considered to be a threat to the psychosocial development of AIDS-affected children. In South Africa, AIDS-affected children may be particularly vulnerable due to the unprecedented effects of the HIV/AIDS epidemic on the breakdown of family and community resources in already disadvantaged communities. The aim of this study was to explore the contextualised experiences of two children living with mothers who have HIV by conducting two case studies. Mother-child dyads were recruited from local HIV/AIDS centres and informed consent was obtained. The mothers were in the minor symptomatic phase of HIV-infection and the children were uninfected and aged between 10 and 12 years. Through semi-structured interviewing, the mothers provided background and contextual information about the children. Play techniques were used in the child interviews to encourage the introduction and exploration of issues salient to the children. Play facilitated engagement around sensitive and potentially anxiety-provoking material. A key issue for the children was their concerns about the anticipated deaths of their mothers. The children held misconceptions about the transmission of HIV/ AIDS. They feared HIV/AIDS and expected that others would have negative perceptions of them. Family processes such as secrecy and avoidance around HIV/AIDS-related issues were understood to perpetuate the children's fears and false beliefs in a broader community context that stigmatised HIV/AIDS. It was argued that the mothers' shame over HIV-infection and their need to protect their relationship with their children compromised their ability to communicate openly with their children and to offer them meaningful emotional support. Limited parental involvement was identified as the key contextual process that engendered vulnerability in the children, as they were isolated within and beyond the family. Recommendations to address the processes that engendered vulnerability in the children are discussed.
- Full Text:
- Date Issued: 2004