Isolation and characterization of a novel thermostable and catalytically efficient laccase from Peniophora sp. strain UD4
- Authors: Jordaan, Justin
- Date: 2005
- Subjects: Enzymes Enzymes -- Industrial applications Peniophora Laccase
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3970 , http://hdl.handle.net/10962/d1004029
- Description: Enzymes are becoming an effective tool in industrial processes, from crude applications such as bioremediation to fine processes such as chirally selective biocatalysis. The ligninolytic enzymes have recently received considerable attention for industrial application due to both their broad substrate range and their ability to degrade the most recalcitrant natural polymer, lignin. This group of enzymes was therefore identified as the target group for this study. Improved enzyme properties are constantly being sought to enhance the range of applications for enzymes. Biodiversity provides a wide variety of enzymes. Several researchers have concentrated on extremophiles as their primary source of superior enzymes, consequently neglecting temperate environments in their search for these enzymes. The relatively neglected fungal biodiversity of South Africa provided an opportunity to test the hypothesis that potentially important industrial enzymes with unusual properties could be isolated from mesophilic basidiomycetous fungi. Subsequent screening of Eastern Cape biodiversity for thermostable ligninolytic enzymes from basidiomycetes resulted in the isolation of a novel laccase enzyme from a basidiomycetous species. This fungus was identified as Peniophora sp. UD4 by phylogenetic analysis of rDNA ITS sequences. Initial studies indicated a superior optimum temperature of 70°C and thermostability, indicated by no loss in activity at 60°C over nine hours. Further characterization of the laccase revealed a broader than usual substrate range through its unusual ability to oxidatively couple DMAB and MBTH. The laccase also exhibited a broad pH oxidation range for ABTS (pH 2 – 6.8), and a relatively high affinity (K_m_ = 0.0123 mM) and catalytic efficiency (63 252 mM^(-1)^s^(-1)^) for ABTS as a substrate. The laccase activity from Peniophora sp. UD4 was shown to be comprised of three isozymes with a molecular weight of 62 kDa and pI’s of 6.33, 6.45 and 6.50. Investigation of the nutrient and physical factors affecting ligninolytic enzyme production and growth of Peniophora sp. UD4 indicated that the wild-type organism was unsuitable for large scale production of the thermostable laccase due to the low levels of laccase production. The thermostable laccase was applied to defouling of ultrafiltration membranes, bioremediation of industrial waste streams, biocatalysis, and biosensor technology as potential applications. Application of the Peniophora sp. UD4 laccase to defouling of membranes used for ultrafiltration of brown water showed large flux recoveries of 31, 21 and 21% after the first three defouling recycles respectively, compared to 3% for the control without immobilized enzyme. The novel laccase showed potential for the bioremediation of industrial waste streams, the most successful being that of bleach plant effluent, where a reduction of 66% of the phenolic load was achieved. Application of the novel laccase to biocatalytic oxidation of ferulic acid and (±)-α-pinene showed higher product yield as compared to oxidation of these compounds by Trametes versicolor laccase in mediated and non-mediated systems. The major products of (±)-α-pinene oxidation were identified as verbenol and trans-sorberol. The Peniophora sp. UD4 laccase was successfully applied to biosensor technology, which benchmarked significantly better than Trametes versicolor laccase for the detection of 4-chlorophenol. The biosensor developed with laccase from UD4 by covalent binding to a glassy carbon electrode exhibited the best combination of sensitivity and stability. This thesis shows that a laccase with superior properties was obtained from a mesophilic South African basidiomycete. The catalytic properties displayed by the novel laccase from Peniophora sp. UD4 all contribute to the increased industrial applicability of laccases, and may be the most industrially feasible enzyme of its class isolated to date.
- Full Text:
- Date Issued: 2005
- Authors: Jordaan, Justin
- Date: 2005
- Subjects: Enzymes Enzymes -- Industrial applications Peniophora Laccase
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3970 , http://hdl.handle.net/10962/d1004029
- Description: Enzymes are becoming an effective tool in industrial processes, from crude applications such as bioremediation to fine processes such as chirally selective biocatalysis. The ligninolytic enzymes have recently received considerable attention for industrial application due to both their broad substrate range and their ability to degrade the most recalcitrant natural polymer, lignin. This group of enzymes was therefore identified as the target group for this study. Improved enzyme properties are constantly being sought to enhance the range of applications for enzymes. Biodiversity provides a wide variety of enzymes. Several researchers have concentrated on extremophiles as their primary source of superior enzymes, consequently neglecting temperate environments in their search for these enzymes. The relatively neglected fungal biodiversity of South Africa provided an opportunity to test the hypothesis that potentially important industrial enzymes with unusual properties could be isolated from mesophilic basidiomycetous fungi. Subsequent screening of Eastern Cape biodiversity for thermostable ligninolytic enzymes from basidiomycetes resulted in the isolation of a novel laccase enzyme from a basidiomycetous species. This fungus was identified as Peniophora sp. UD4 by phylogenetic analysis of rDNA ITS sequences. Initial studies indicated a superior optimum temperature of 70°C and thermostability, indicated by no loss in activity at 60°C over nine hours. Further characterization of the laccase revealed a broader than usual substrate range through its unusual ability to oxidatively couple DMAB and MBTH. The laccase also exhibited a broad pH oxidation range for ABTS (pH 2 – 6.8), and a relatively high affinity (K_m_ = 0.0123 mM) and catalytic efficiency (63 252 mM^(-1)^s^(-1)^) for ABTS as a substrate. The laccase activity from Peniophora sp. UD4 was shown to be comprised of three isozymes with a molecular weight of 62 kDa and pI’s of 6.33, 6.45 and 6.50. Investigation of the nutrient and physical factors affecting ligninolytic enzyme production and growth of Peniophora sp. UD4 indicated that the wild-type organism was unsuitable for large scale production of the thermostable laccase due to the low levels of laccase production. The thermostable laccase was applied to defouling of ultrafiltration membranes, bioremediation of industrial waste streams, biocatalysis, and biosensor technology as potential applications. Application of the Peniophora sp. UD4 laccase to defouling of membranes used for ultrafiltration of brown water showed large flux recoveries of 31, 21 and 21% after the first three defouling recycles respectively, compared to 3% for the control without immobilized enzyme. The novel laccase showed potential for the bioremediation of industrial waste streams, the most successful being that of bleach plant effluent, where a reduction of 66% of the phenolic load was achieved. Application of the novel laccase to biocatalytic oxidation of ferulic acid and (±)-α-pinene showed higher product yield as compared to oxidation of these compounds by Trametes versicolor laccase in mediated and non-mediated systems. The major products of (±)-α-pinene oxidation were identified as verbenol and trans-sorberol. The Peniophora sp. UD4 laccase was successfully applied to biosensor technology, which benchmarked significantly better than Trametes versicolor laccase for the detection of 4-chlorophenol. The biosensor developed with laccase from UD4 by covalent binding to a glassy carbon electrode exhibited the best combination of sensitivity and stability. This thesis shows that a laccase with superior properties was obtained from a mesophilic South African basidiomycete. The catalytic properties displayed by the novel laccase from Peniophora sp. UD4 all contribute to the increased industrial applicability of laccases, and may be the most industrially feasible enzyme of its class isolated to date.
- Full Text:
- Date Issued: 2005
Ligand isotope vibrational spectroscopic and DFT studies of Pt(II) and Cu(I) complexes
- Authors: Medina, Gerardo Juan
- Date: 2005
- Subjects: Ligands Spectrum analysis Vibrational spectra Infrared spectroscopy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4324 , http://hdl.handle.net/10962/d1004982
- Description: Ligand-isotope labelling studies were performed on Zeise’s salt derivatives with pyridine N-oxide and quinoline N-oxide, their perdeuterated and O-18 isotopomers, C₂D₄ and ¹³CO, and the results of the vibrational analyses are reported. The isotopomers are modelled utilizing DFT calculations at the B3LYP level with the 6-31 G** basis set, and a pseudopotential level for the Pt atom. The calculated and observed structure and vibrational spectra correlate well. The crystal structures of [Pt(C₂2H₄)(pyO)Cl₂] and [Pt(CO)(quinO)Br₂] are reported. The frequency for the νPt-O vibration, ambiguously assigned in the literature, is here assigned unequivocally at 400 cm⁻¹. Previously observed, but inadequately described phenomena are addressed: the νN-O vibration in substituted quinoline N-oxides has been assigned previously at significantly different frequencies, depending on the nature of the substituent. This suggests that there is no specific mid-ir band associated with a high N-O character. A suitable explanation is presented for this phenomenon, showing that in low symmetry systems (eg. quinO) the N-O stretch is dispersed among several modes, whereas in high symmetry systems (eg. pyO) only a few limited modes have a high N-O character. A theoretical study of Cu(I) carbonyl compounds with macrocyclic ligands is presented. Local and global HSAB parameters applied to the donor and Cu atoms are used to explain the observed reactivities and the available spectroscopic data. Extended to [Cu(CO){H₂N(CH₂)[subscript n]NH(CH₂)[subscript m] NH₂}] BPh₄ (where n = 2, m = 2, 3 and n =3, m = 3, 4) and their -d₅ and ¹³CO isotopomers, subtle differences obtained experimentally for the CO stretching frequency in this series have been reproduced in the DFT calculations at the B3LYP level, using the 6-31 G* and 6-31 G** basis sets. Several properties (ligand pK[subscript a] values, νCO frequencies, etc.) correlate with some HSAB descriptors. Vibrational analyses are presented of Cu(I) carbonyl Schiff-base derivatives of N-Benzylidene-N’-[2-(benzyilidene-amino)-ethyl]-ethane-1,2-diamine, {2,2N3(C₆H₄R)₂}, and their -d₅ and ¹³CO isotopomers. The crystal structure of [Cu(CO){2,2N3(C₆H₅)₂}]BPh₄ is reported. From geometry optimizations and the HSAB descriptors, spectroscopic trends ([n]Cu-N and [nu]CO) are related to calculated global hardness and the Hammett substituent parameters, and are discussed in terms of σ-donation and π-backbonding of Cu- CO.
- Full Text:
- Date Issued: 2005
- Authors: Medina, Gerardo Juan
- Date: 2005
- Subjects: Ligands Spectrum analysis Vibrational spectra Infrared spectroscopy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4324 , http://hdl.handle.net/10962/d1004982
- Description: Ligand-isotope labelling studies were performed on Zeise’s salt derivatives with pyridine N-oxide and quinoline N-oxide, their perdeuterated and O-18 isotopomers, C₂D₄ and ¹³CO, and the results of the vibrational analyses are reported. The isotopomers are modelled utilizing DFT calculations at the B3LYP level with the 6-31 G** basis set, and a pseudopotential level for the Pt atom. The calculated and observed structure and vibrational spectra correlate well. The crystal structures of [Pt(C₂2H₄)(pyO)Cl₂] and [Pt(CO)(quinO)Br₂] are reported. The frequency for the νPt-O vibration, ambiguously assigned in the literature, is here assigned unequivocally at 400 cm⁻¹. Previously observed, but inadequately described phenomena are addressed: the νN-O vibration in substituted quinoline N-oxides has been assigned previously at significantly different frequencies, depending on the nature of the substituent. This suggests that there is no specific mid-ir band associated with a high N-O character. A suitable explanation is presented for this phenomenon, showing that in low symmetry systems (eg. quinO) the N-O stretch is dispersed among several modes, whereas in high symmetry systems (eg. pyO) only a few limited modes have a high N-O character. A theoretical study of Cu(I) carbonyl compounds with macrocyclic ligands is presented. Local and global HSAB parameters applied to the donor and Cu atoms are used to explain the observed reactivities and the available spectroscopic data. Extended to [Cu(CO){H₂N(CH₂)[subscript n]NH(CH₂)[subscript m] NH₂}] BPh₄ (where n = 2, m = 2, 3 and n =3, m = 3, 4) and their -d₅ and ¹³CO isotopomers, subtle differences obtained experimentally for the CO stretching frequency in this series have been reproduced in the DFT calculations at the B3LYP level, using the 6-31 G* and 6-31 G** basis sets. Several properties (ligand pK[subscript a] values, νCO frequencies, etc.) correlate with some HSAB descriptors. Vibrational analyses are presented of Cu(I) carbonyl Schiff-base derivatives of N-Benzylidene-N’-[2-(benzyilidene-amino)-ethyl]-ethane-1,2-diamine, {2,2N3(C₆H₄R)₂}, and their -d₅ and ¹³CO isotopomers. The crystal structure of [Cu(CO){2,2N3(C₆H₅)₂}]BPh₄ is reported. From geometry optimizations and the HSAB descriptors, spectroscopic trends ([n]Cu-N and [nu]CO) are related to calculated global hardness and the Hammett substituent parameters, and are discussed in terms of σ-donation and π-backbonding of Cu- CO.
- Full Text:
- Date Issued: 2005
Material characterisation of laser formed dual phase steel components
- Authors: Els-Botes, Annelize
- Date: 2005
- Subjects: Steel -- Fatigue , Bending , Lasers , Sheet-steel -- Effect of lasers on
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:9609 , http://hdl.handle.net/10948/176 , Steel -- Fatigue , Bending , Lasers , Sheet-steel -- Effect of lasers on
- Description: The nature and scope of this thesis can be divided into four categories: • FORMING PARAMETERS • Identification of various laser forming parameters in order to produce specimens of similar dimension (radius of curvature). • TEMPERATURE AND MICROSTRUCTURE • To study the effect of maximum temperature reached during the forming operation on the microstructure of the various specimens. • FATIGUE LIFE • Compare the fatigue life of the specimens produced by various laser parameters to that of the original material, and also the fatigue life of mechanical formed specimens. • RESIDUAL STRESS PROFILE Determine if the laser forming process induces detrimental residual stress magnitudes in the specimens. The main objective of this thesis was to gain an understanding of the way in which laser forming affects the fatigue performance and residual stress magnitude / distribution of dual phase steel. Although lasers have been used successfully in various manufacturing processes (welding, cutting, marking, etc.), little information is available on the influence of laser forming on many automotive alloys such as dual phase steel. The first part of the work involved a literature review of the process and factors affecting the laser forming process. It became clear from the literature overview that laser forming of sheet material thicker than 1mm is complex in nature. The variables that can influence the process are complicated and their interaction with each other is not easily controlled. The main parameters that were thus controlled in this study are as follows: • Laser power (P) • Laser head travel speed (v) • Laser beam size (mm) The chapters that follow the literature review, deals with the laser forming process of dual phase steel and the production of fatigue specimens using various laser parameters. It was found that the following laser parameters resulted in specimens with approximately the same radius of curvature: Laser power KW Beam diameter mm Interval spacing % Overlap Scanning velocity m/min Line Energy J/m 5 20 10 50 2,5 2000 3,1 14 10,5 25 2 1550 1,5 7,5 7,5 0 1,2 1250 From the results obtained from fatigue testing specimens produced with the above settings, it is clear that the laser forming process has the potential to be employed as a production stage in the manufacture of wheel centre discs while maintaining adequate fatigue strength. Large beam diameters which cause heat penetration through the thickness of the specimen and hence microstructure breakdown should be avoided, since it was shown that these specimens exhibited impaired mechanical properties than those produced with a smaller laser beam diameter. The microstructural changes observed during the forming process needs to be considered since the mechanical properties of the material changes with a change in microstructure. A dramatic change in microstructure was observed; therefore it is of crucial importance that microstructural evaluation plays an important part in deciding optimum laser parameters for the forming process of ferrous alloys. During residual stress analysis, trends were observed between measurements taken at the same location of the samples; regardless whether measurements were taken on the laser irradiated side or the reverse side of the specimen. The only difference was the magnitude of the relieved residual stress. In most cases the obtained relieved residual stress was much smaller in magnitude than that of the original plate (in the bulk of the material). The surface indicated a slight tensile residual stress for most samples evaluated. A good correlation in distribution profile was obtained between microhardness and relieved residual stress distribution at the ‘middle of sample’ location. This indicates that an increase in hardness indicates an increase in residual stress magnitude for the laser formed specimens. In conclusion, this research has proved that it is possible to deform metal plate of a 3,5mm thickness with a CO2 laser system. The research also established the effect of process parameters on the final product’s shape/bend angle and characterised the effect of the laser forming process on the material’s mechanical properties and structural integrity.
- Full Text:
- Date Issued: 2005
- Authors: Els-Botes, Annelize
- Date: 2005
- Subjects: Steel -- Fatigue , Bending , Lasers , Sheet-steel -- Effect of lasers on
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:9609 , http://hdl.handle.net/10948/176 , Steel -- Fatigue , Bending , Lasers , Sheet-steel -- Effect of lasers on
- Description: The nature and scope of this thesis can be divided into four categories: • FORMING PARAMETERS • Identification of various laser forming parameters in order to produce specimens of similar dimension (radius of curvature). • TEMPERATURE AND MICROSTRUCTURE • To study the effect of maximum temperature reached during the forming operation on the microstructure of the various specimens. • FATIGUE LIFE • Compare the fatigue life of the specimens produced by various laser parameters to that of the original material, and also the fatigue life of mechanical formed specimens. • RESIDUAL STRESS PROFILE Determine if the laser forming process induces detrimental residual stress magnitudes in the specimens. The main objective of this thesis was to gain an understanding of the way in which laser forming affects the fatigue performance and residual stress magnitude / distribution of dual phase steel. Although lasers have been used successfully in various manufacturing processes (welding, cutting, marking, etc.), little information is available on the influence of laser forming on many automotive alloys such as dual phase steel. The first part of the work involved a literature review of the process and factors affecting the laser forming process. It became clear from the literature overview that laser forming of sheet material thicker than 1mm is complex in nature. The variables that can influence the process are complicated and their interaction with each other is not easily controlled. The main parameters that were thus controlled in this study are as follows: • Laser power (P) • Laser head travel speed (v) • Laser beam size (mm) The chapters that follow the literature review, deals with the laser forming process of dual phase steel and the production of fatigue specimens using various laser parameters. It was found that the following laser parameters resulted in specimens with approximately the same radius of curvature: Laser power KW Beam diameter mm Interval spacing % Overlap Scanning velocity m/min Line Energy J/m 5 20 10 50 2,5 2000 3,1 14 10,5 25 2 1550 1,5 7,5 7,5 0 1,2 1250 From the results obtained from fatigue testing specimens produced with the above settings, it is clear that the laser forming process has the potential to be employed as a production stage in the manufacture of wheel centre discs while maintaining adequate fatigue strength. Large beam diameters which cause heat penetration through the thickness of the specimen and hence microstructure breakdown should be avoided, since it was shown that these specimens exhibited impaired mechanical properties than those produced with a smaller laser beam diameter. The microstructural changes observed during the forming process needs to be considered since the mechanical properties of the material changes with a change in microstructure. A dramatic change in microstructure was observed; therefore it is of crucial importance that microstructural evaluation plays an important part in deciding optimum laser parameters for the forming process of ferrous alloys. During residual stress analysis, trends were observed between measurements taken at the same location of the samples; regardless whether measurements were taken on the laser irradiated side or the reverse side of the specimen. The only difference was the magnitude of the relieved residual stress. In most cases the obtained relieved residual stress was much smaller in magnitude than that of the original plate (in the bulk of the material). The surface indicated a slight tensile residual stress for most samples evaluated. A good correlation in distribution profile was obtained between microhardness and relieved residual stress distribution at the ‘middle of sample’ location. This indicates that an increase in hardness indicates an increase in residual stress magnitude for the laser formed specimens. In conclusion, this research has proved that it is possible to deform metal plate of a 3,5mm thickness with a CO2 laser system. The research also established the effect of process parameters on the final product’s shape/bend angle and characterised the effect of the laser forming process on the material’s mechanical properties and structural integrity.
- Full Text:
- Date Issued: 2005
Metalorganic vapour phase epitaxial growth and characterisation of Sb-based semiconductors
- Authors: Vankova, Viera
- Date: 2005
- Subjects: Compound semiconductors , Epitaxy , Organometallic compounds , Metal organic chemical vapor deposition
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10548 , http://hdl.handle.net/10948/d1019678
- Description: This study focuses on the growth and characterization of epitaxial InAs and InAs1-xSbx. Layers are grown on InAs, GaAs and GaSb substrates by metalorganic vapour phase epitaxy, using trimethylindium, trimethylantimony and arsine as precursors. The growth parameters (V/III ratio, Sb vapour phase compositions) are varied in the temperature range from 500 ºC to 700 ºC, in order to study the influence of these parameters on the structural, optical and electrical properties of the materials. The layers were assessed by X-ray diffraction, electron and optical microscopy, photoluminescence and Hall measurements. Furthermore, the influence of hydrogenation and annealing on the electrical and optical properties of GaSb was investigated. It is shown that the growth temperature and the V/III ratio play a vital role in the resulting surface morphology of homoepitaxial and heteroepitaxial InAs layers. Growth at low temperatures is found to promote three-dimensional growth in both cases, with improvements in the surface morphologies observed for higher growth temperatures. All the investigated epilayers are n-type. It is shown that the electrical properties of heteroepitaxial InAs epilayers are complicated by a competition between bulk conduction and conduction due to a surface accumulation and an interface layer. The low temperature photoluminescence spectra of homoepitaxial InAs are dominated by two transitions. These are identified as band-to-band/excitonic and donor-acceptor recombination. The incorporation efficiency of antimony (Sb) into InAs1-xSbx is dependent on the growth temperature and the V/III ratio. Under the growth conditions used in this study, the incorporation efficiency of Sb is controlled by the thermal stability of the two constituent binaries (i.e. InAs and InSb). Changes in the low temperature photoluminescence spectra are detected with increasing x. From temperature and laser power dependent measurements, the highest energy line is attributed to band-to-band/excitonic recombination, while the peak appearing approximately 15 meV below this line is assigned to donor-acceptor recombination. The origin of an additional “moving” peak observed for higher Sb mole fraction x is tentatively attributed to quasi-donor-acceptor-recombination, arising from increased impurity/defect concentrations and a higher compensation ratio in the material. However, the unusual behaviour of this peak may also be ascribed to the presence of some degree of ordering in InAsSb. The exposure of a semiconductor to a hydrogen plasma usually leads to the passivation of shallow and deep centres, thereby removing their electrical and optical activity. In this study, the passivation and thermal stability of the native acceptor in p-type GaSb is also investigated. It is shown that this acceptor can be passivated, where after improvements in the electrical and optical properties of GaSb are observed. Upon annealing the passivated samples above 300 °C, the acceptor is reactivated.
- Full Text:
- Date Issued: 2005
- Authors: Vankova, Viera
- Date: 2005
- Subjects: Compound semiconductors , Epitaxy , Organometallic compounds , Metal organic chemical vapor deposition
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10548 , http://hdl.handle.net/10948/d1019678
- Description: This study focuses on the growth and characterization of epitaxial InAs and InAs1-xSbx. Layers are grown on InAs, GaAs and GaSb substrates by metalorganic vapour phase epitaxy, using trimethylindium, trimethylantimony and arsine as precursors. The growth parameters (V/III ratio, Sb vapour phase compositions) are varied in the temperature range from 500 ºC to 700 ºC, in order to study the influence of these parameters on the structural, optical and electrical properties of the materials. The layers were assessed by X-ray diffraction, electron and optical microscopy, photoluminescence and Hall measurements. Furthermore, the influence of hydrogenation and annealing on the electrical and optical properties of GaSb was investigated. It is shown that the growth temperature and the V/III ratio play a vital role in the resulting surface morphology of homoepitaxial and heteroepitaxial InAs layers. Growth at low temperatures is found to promote three-dimensional growth in both cases, with improvements in the surface morphologies observed for higher growth temperatures. All the investigated epilayers are n-type. It is shown that the electrical properties of heteroepitaxial InAs epilayers are complicated by a competition between bulk conduction and conduction due to a surface accumulation and an interface layer. The low temperature photoluminescence spectra of homoepitaxial InAs are dominated by two transitions. These are identified as band-to-band/excitonic and donor-acceptor recombination. The incorporation efficiency of antimony (Sb) into InAs1-xSbx is dependent on the growth temperature and the V/III ratio. Under the growth conditions used in this study, the incorporation efficiency of Sb is controlled by the thermal stability of the two constituent binaries (i.e. InAs and InSb). Changes in the low temperature photoluminescence spectra are detected with increasing x. From temperature and laser power dependent measurements, the highest energy line is attributed to band-to-band/excitonic recombination, while the peak appearing approximately 15 meV below this line is assigned to donor-acceptor recombination. The origin of an additional “moving” peak observed for higher Sb mole fraction x is tentatively attributed to quasi-donor-acceptor-recombination, arising from increased impurity/defect concentrations and a higher compensation ratio in the material. However, the unusual behaviour of this peak may also be ascribed to the presence of some degree of ordering in InAsSb. The exposure of a semiconductor to a hydrogen plasma usually leads to the passivation of shallow and deep centres, thereby removing their electrical and optical activity. In this study, the passivation and thermal stability of the native acceptor in p-type GaSb is also investigated. It is shown that this acceptor can be passivated, where after improvements in the electrical and optical properties of GaSb are observed. Upon annealing the passivated samples above 300 °C, the acceptor is reactivated.
- Full Text:
- Date Issued: 2005
Modeling and measurement of torqued procession in radio pulsars
- Authors: Tiplady, Adrian John
- Date: 2005
- Subjects: Pulsars , Radio telescopes , Radio astronomy , Precession , Hartebeeshoek Radio Astronomy Observatory (HartRAO)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5475 , http://hdl.handle.net/10962/d1005260
- Description: The long term isolated pulsar monitoring program, which commenced in 1984 using the 26 m radio telescope at the Hartebeeshoek Radio Astronomy Observatory (HartRAO), has produced high resolution timing residual data over long timespans. This has enabled the analysis of observed spin down behaviour for 27 braking pulsars, most of which have dataspans longer than 14 years. The phenomenology of observed timing residuals of certain pulsars can be explained by pseudo periodic effects such as precession. Analytic and numerical models are developed to study the kinematic and dynamic behaviour of isolated but torqued precessing pulsars. The predicted timing residual behaviour of the models is characterised, and confronted with timing data from selected pulsars. Cyclic variations in the observed timing residuals of PSR B1642-03, PSR B1323-58 and PSR B1557-50 are fitted with a torqued precession model. The phenomenology of the observed timing behaviour of these pulsars can be explained by the precession models, but precise model fitting was not possible. This is not surprising given that the complexity of the pulsar systems is not completely described by the model. The extension of the pulsar monitoring program at HartRAO is used as motivation for the design and development of a new low cost, multi-purpose digital pulsar receiver. The instrument is implemented using a hybrid filterbank architecture, consisting of an analogue frontend and digital backend, to perform incoherent dedispersion. The design of a polyphase filtering system, which will consolidate multiple processing units into a single filtering solution, is discussed for future implementation.
- Full Text:
- Date Issued: 2005
- Authors: Tiplady, Adrian John
- Date: 2005
- Subjects: Pulsars , Radio telescopes , Radio astronomy , Precession , Hartebeeshoek Radio Astronomy Observatory (HartRAO)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5475 , http://hdl.handle.net/10962/d1005260
- Description: The long term isolated pulsar monitoring program, which commenced in 1984 using the 26 m radio telescope at the Hartebeeshoek Radio Astronomy Observatory (HartRAO), has produced high resolution timing residual data over long timespans. This has enabled the analysis of observed spin down behaviour for 27 braking pulsars, most of which have dataspans longer than 14 years. The phenomenology of observed timing residuals of certain pulsars can be explained by pseudo periodic effects such as precession. Analytic and numerical models are developed to study the kinematic and dynamic behaviour of isolated but torqued precessing pulsars. The predicted timing residual behaviour of the models is characterised, and confronted with timing data from selected pulsars. Cyclic variations in the observed timing residuals of PSR B1642-03, PSR B1323-58 and PSR B1557-50 are fitted with a torqued precession model. The phenomenology of the observed timing behaviour of these pulsars can be explained by the precession models, but precise model fitting was not possible. This is not surprising given that the complexity of the pulsar systems is not completely described by the model. The extension of the pulsar monitoring program at HartRAO is used as motivation for the design and development of a new low cost, multi-purpose digital pulsar receiver. The instrument is implemented using a hybrid filterbank architecture, consisting of an analogue frontend and digital backend, to perform incoherent dedispersion. The design of a polyphase filtering system, which will consolidate multiple processing units into a single filtering solution, is discussed for future implementation.
- Full Text:
- Date Issued: 2005
On the growth and characterisation of AIGaN alloys for optoelectronic applications
- Authors: James, Grant Robert
- Date: 2005
- Subjects: Gallium nitride -- Electric properties , Photoluminescence
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/8824 , vital:26433
- Description: In this study the growth and characterisation of undoped and Si-doped AlxGa1-xN has been performed. The layers were grown using low-pressure metalorganic vapour phase deposition (MOCVD) on sapphire substrates. The optical and electrical properties of the AlxGa1-xN layers were studied using variable temperature Hall effect and photoluminescence measurements. AlxGa1-xN layers were grown over the entire composition range. Room temperature ultraviolet (UV) transmission measurements showed that the material quality was very good for layers with an Al content, x, of 0 _ x _ 0.5. However, the quality of layers of higher composition was seen to rapidly decrease with increasing x. The electrical and optical properties of AlxGa1-xN with x < 0.5 were also good, comparable to those reported on in literature. The study of the Si-doping of AlxGa1-xN was performed in two parts; firstly a series of Al0.23Ga0.77N samples was grown in which the doping level was increased from zero to n _ 3 × 1018 cm-3. A similar, albeit a less rigorous, study was performed for Al0.41Ga0.59N and Al0.5Ga0.5N. A second series of samples was then grown in which the doping level was kept constant, while the Al content was incrementally increased. Room temperature Hall effect measurements performed on Si-doped Al0.23Ga0.77N showed that the electron concentration did not scale linearly with the silane flow, as was the case in GaN. It was also seen that the electron mobility of the layers increased with slight Si-doping, possibly due to an improvement in the crystalline quality and/or a change in the conduction mechanism. It was also found that at higher compositions (x = 0.41 and 0.50) an increase in the doping level resulted in an increase in the mobility. Variable temperature Hall effect and photoluminescence measurements, performed on the Al0.23Ga0.77N samples, revealed a good correlation between the first PL activation energy E1 and the donor activation energy ED, prompting the conclusion that the first PL recombination channel in AlxGa1-xN is due to the delocalisation of excitons bound at neutral Si donors. Furthermore, E1 and ED were seen to decrease with n1/3, as is the case for GaN and other semiconductor materials. It was also observed that strong exciton localisation occurs in slightly Si-doped material, with the amount of localization becoming less at higher doping levels. Possible mechanisms responsible for the second PL recombination channel of activation energy E2 were also proposed. The electrical and optical properties of the second set of AlxGa1-xN samples was then studied. The PL properties of undoped AlxGa1-xN were typical of a homogeneous alloy system, with the increase in the PL FWHM and exciton localisation energies with x following the trend predicted by alloy disorder theory. The variation of the band gap energy with the Al content could not, however, be fitted over the entire composition range using a single bowing parameter. It was proposed that this was due either to an effect of the 9 7 valence band crossover, or due to exciton localisation at alloy disorder and/or impurities. As was the case for GaN and Al0.23Ga0.77N, all undoped material was highly resistive. As was mentioned earlier, the exciton localisation energies increased according to alloy disorder theory in undoped AlxGa1-xN. In the doped samples, however, a large increase in the donor localisation energy was measured for x > 0.3. The possibility that Si could become a DX-centre in AlxGa1-xN was then investigated. However, Hall effect measurements showed that the Si activation energy increased in good agreement with the model of a shallow effective mass state donor, with no sudden increase in ED being observed up to x = 0.4. It was then suggested that the increase in the E1 and E2 activation energies, as well as the exciton localisation energies, could be due to the 9 7 valence band crossover, which occurs at roughly the same composition. However, due to the scarcity of reports on the valence band structure in AlxGa1-xN no conclusions could be made at this stage as to the effect of the 9 7 valence band crossover on the PL properties of AlxGa1-xN.
- Full Text:
- Date Issued: 2005
- Authors: James, Grant Robert
- Date: 2005
- Subjects: Gallium nitride -- Electric properties , Photoluminescence
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/8824 , vital:26433
- Description: In this study the growth and characterisation of undoped and Si-doped AlxGa1-xN has been performed. The layers were grown using low-pressure metalorganic vapour phase deposition (MOCVD) on sapphire substrates. The optical and electrical properties of the AlxGa1-xN layers were studied using variable temperature Hall effect and photoluminescence measurements. AlxGa1-xN layers were grown over the entire composition range. Room temperature ultraviolet (UV) transmission measurements showed that the material quality was very good for layers with an Al content, x, of 0 _ x _ 0.5. However, the quality of layers of higher composition was seen to rapidly decrease with increasing x. The electrical and optical properties of AlxGa1-xN with x < 0.5 were also good, comparable to those reported on in literature. The study of the Si-doping of AlxGa1-xN was performed in two parts; firstly a series of Al0.23Ga0.77N samples was grown in which the doping level was increased from zero to n _ 3 × 1018 cm-3. A similar, albeit a less rigorous, study was performed for Al0.41Ga0.59N and Al0.5Ga0.5N. A second series of samples was then grown in which the doping level was kept constant, while the Al content was incrementally increased. Room temperature Hall effect measurements performed on Si-doped Al0.23Ga0.77N showed that the electron concentration did not scale linearly with the silane flow, as was the case in GaN. It was also seen that the electron mobility of the layers increased with slight Si-doping, possibly due to an improvement in the crystalline quality and/or a change in the conduction mechanism. It was also found that at higher compositions (x = 0.41 and 0.50) an increase in the doping level resulted in an increase in the mobility. Variable temperature Hall effect and photoluminescence measurements, performed on the Al0.23Ga0.77N samples, revealed a good correlation between the first PL activation energy E1 and the donor activation energy ED, prompting the conclusion that the first PL recombination channel in AlxGa1-xN is due to the delocalisation of excitons bound at neutral Si donors. Furthermore, E1 and ED were seen to decrease with n1/3, as is the case for GaN and other semiconductor materials. It was also observed that strong exciton localisation occurs in slightly Si-doped material, with the amount of localization becoming less at higher doping levels. Possible mechanisms responsible for the second PL recombination channel of activation energy E2 were also proposed. The electrical and optical properties of the second set of AlxGa1-xN samples was then studied. The PL properties of undoped AlxGa1-xN were typical of a homogeneous alloy system, with the increase in the PL FWHM and exciton localisation energies with x following the trend predicted by alloy disorder theory. The variation of the band gap energy with the Al content could not, however, be fitted over the entire composition range using a single bowing parameter. It was proposed that this was due either to an effect of the 9 7 valence band crossover, or due to exciton localisation at alloy disorder and/or impurities. As was the case for GaN and Al0.23Ga0.77N, all undoped material was highly resistive. As was mentioned earlier, the exciton localisation energies increased according to alloy disorder theory in undoped AlxGa1-xN. In the doped samples, however, a large increase in the donor localisation energy was measured for x > 0.3. The possibility that Si could become a DX-centre in AlxGa1-xN was then investigated. However, Hall effect measurements showed that the Si activation energy increased in good agreement with the model of a shallow effective mass state donor, with no sudden increase in ED being observed up to x = 0.4. It was then suggested that the increase in the E1 and E2 activation energies, as well as the exciton localisation energies, could be due to the 9 7 valence band crossover, which occurs at roughly the same composition. However, due to the scarcity of reports on the valence band structure in AlxGa1-xN no conclusions could be made at this stage as to the effect of the 9 7 valence band crossover on the PL properties of AlxGa1-xN.
- Full Text:
- Date Issued: 2005
Operationally defining sexual orientation : towards the development of a fundamental measure of adolescent sexual responsiveness variations
- Authors: Heath, Lance Julian
- Date: 2005
- Subjects: Sexual orientation Homosexuality Psychometrics Teenagers--Sexual behavior
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1681 , http://hdl.handle.net/10962/d1003564
- Description: Much published work has pointed to the need for the development of a sound operational definition of sexual orientation in order to enable the research in this area to progress. To contribute to this process the current research set out to develop two measures of sexual orientation and examine their psychometric properties. In order to develop relevant tools historical, conceptual and operational definitions of sexual orientation were critically examined and standard questionnaire development techniques applied. The first scale consisted of 32 items and was administered to a total of 835 adolescents, comprising three sub-groups (189 Grade 11 Scholars, 547 First Year and 99 Third Year Psychology Students). A Cronbach alpha coefficient of 0.85 was calculated indicating that this instrument had very good internal consistency reliability. Similar factors emerged in each of the sample sub-groups when factor analyses were performed suggesting that this instrument has good external and construct validities. These factors each had respectable Cronbach alpha coefficients indicating their own internal consistency. The four factors which consistently emerged were Same Sex Responsiveness, Opposite Sex Responsiveness, Previous Month’s Same Sex Responsiveness and Previous Month’s Opposite Sex Responsiveness. The second scale consisted of 16 items and was administered to 646 adolescents, comprising the latter two sub-groups referred to above. A Cronbach alpha coefficient of 0.82 was calculated indicating that this instrument also had very good internal consistency reliability. Once again similar factors with generally good internal consistency emerged in factor analysis suggesting that this too was a valid instrument. The factors that emerged from the second scale were Same Sex Responsiveness, Unattractive Opposite Sex Responsiveness, Attractive Opposite Sex Responsiveness and Attraction. Future developments, adjustments and applications of the instruments as well as implications for the arena of sexual orientation research are discussed. In the light of the dearth of information with regard to the sexual orientations of South African adolescents the current study also briefly explored and presented the sample’s responses in terms of the dimensions of each questionnaire as well as how each emerging factor related to the demographics (education level, gender, sexual orientation self-label and age) of the sample.
- Full Text:
- Date Issued: 2005
- Authors: Heath, Lance Julian
- Date: 2005
- Subjects: Sexual orientation Homosexuality Psychometrics Teenagers--Sexual behavior
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1681 , http://hdl.handle.net/10962/d1003564
- Description: Much published work has pointed to the need for the development of a sound operational definition of sexual orientation in order to enable the research in this area to progress. To contribute to this process the current research set out to develop two measures of sexual orientation and examine their psychometric properties. In order to develop relevant tools historical, conceptual and operational definitions of sexual orientation were critically examined and standard questionnaire development techniques applied. The first scale consisted of 32 items and was administered to a total of 835 adolescents, comprising three sub-groups (189 Grade 11 Scholars, 547 First Year and 99 Third Year Psychology Students). A Cronbach alpha coefficient of 0.85 was calculated indicating that this instrument had very good internal consistency reliability. Similar factors emerged in each of the sample sub-groups when factor analyses were performed suggesting that this instrument has good external and construct validities. These factors each had respectable Cronbach alpha coefficients indicating their own internal consistency. The four factors which consistently emerged were Same Sex Responsiveness, Opposite Sex Responsiveness, Previous Month’s Same Sex Responsiveness and Previous Month’s Opposite Sex Responsiveness. The second scale consisted of 16 items and was administered to 646 adolescents, comprising the latter two sub-groups referred to above. A Cronbach alpha coefficient of 0.82 was calculated indicating that this instrument also had very good internal consistency reliability. Once again similar factors with generally good internal consistency emerged in factor analysis suggesting that this too was a valid instrument. The factors that emerged from the second scale were Same Sex Responsiveness, Unattractive Opposite Sex Responsiveness, Attractive Opposite Sex Responsiveness and Attraction. Future developments, adjustments and applications of the instruments as well as implications for the arena of sexual orientation research are discussed. In the light of the dearth of information with regard to the sexual orientations of South African adolescents the current study also briefly explored and presented the sample’s responses in terms of the dimensions of each questionnaire as well as how each emerging factor related to the demographics (education level, gender, sexual orientation self-label and age) of the sample.
- Full Text:
- Date Issued: 2005
Photophysical and photochemical studies of non-transition metal phthalocyanine derivatives
- Ogunsipe, Abimbola Olukayode
- Authors: Ogunsipe, Abimbola Olukayode
- Date: 2005
- Subjects: Photochemotherapy Phthalocyanines Spectrum analysis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4445 , http://hdl.handle.net/10962/d1007721
- Description: A detailed photophysicochemical study of some non-transition metal (AI, Zn, Si, Ge, and Sn) metallophthalocyanine (MPc) derivatives is presented. The effects of substituents, central metal ions and solvents on the photophysical and photochemical properties are investigated and rationalized accordingly. The presence of peripheral substituents on the macrocycle enhances the yield of the triplet state. Near infra-red absorptions of the solvents reveal that solvents which absorb around 1100 nm and around 1270 nm, quench the triplet state of the MPc derivative and singlet oxygen, respectively. Although water has a high singlet oxygen quenching effect, the singlet oxygen quantum yield (Φ∆) value for sulphonated zinc phthalocyanine in water is still reasonably high at 0.48, which may provide an explanation for the efficient photosensitization by this molecule in photodynamic studies. The lowering of Φ∆ following protonation of the MPc macrocycle is attributed to the lowering of triplet energy to the level where energy transfer to ground state oxygen is no longer favourable. MPc inclusion complexes with cyclodextrins showed larger Φ∆ values when compared to the complexes before inclusion. Job's plots show that 2:1 and 4:1 (CD:MPc) complexes may be formed. Fluorescence quenching by electron donors and acceptors were analysed by StemVolmer relationship and the results used in determining fluorescence lifetimes of the complexes. Qualitative and quantitative interpretations of the interaction of sulphonated MPcs with bovine serum albumin (BSA) are provided in this thesis. 1:1 adducts were formed with BSA, but the binding feasibilities varied markedly. Spectral, photophysical and photochemical properties of the complexes are altered in the presence of BSA.
- Full Text:
- Date Issued: 2005
- Authors: Ogunsipe, Abimbola Olukayode
- Date: 2005
- Subjects: Photochemotherapy Phthalocyanines Spectrum analysis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4445 , http://hdl.handle.net/10962/d1007721
- Description: A detailed photophysicochemical study of some non-transition metal (AI, Zn, Si, Ge, and Sn) metallophthalocyanine (MPc) derivatives is presented. The effects of substituents, central metal ions and solvents on the photophysical and photochemical properties are investigated and rationalized accordingly. The presence of peripheral substituents on the macrocycle enhances the yield of the triplet state. Near infra-red absorptions of the solvents reveal that solvents which absorb around 1100 nm and around 1270 nm, quench the triplet state of the MPc derivative and singlet oxygen, respectively. Although water has a high singlet oxygen quenching effect, the singlet oxygen quantum yield (Φ∆) value for sulphonated zinc phthalocyanine in water is still reasonably high at 0.48, which may provide an explanation for the efficient photosensitization by this molecule in photodynamic studies. The lowering of Φ∆ following protonation of the MPc macrocycle is attributed to the lowering of triplet energy to the level where energy transfer to ground state oxygen is no longer favourable. MPc inclusion complexes with cyclodextrins showed larger Φ∆ values when compared to the complexes before inclusion. Job's plots show that 2:1 and 4:1 (CD:MPc) complexes may be formed. Fluorescence quenching by electron donors and acceptors were analysed by StemVolmer relationship and the results used in determining fluorescence lifetimes of the complexes. Qualitative and quantitative interpretations of the interaction of sulphonated MPcs with bovine serum albumin (BSA) are provided in this thesis. 1:1 adducts were formed with BSA, but the binding feasibilities varied markedly. Spectral, photophysical and photochemical properties of the complexes are altered in the presence of BSA.
- Full Text:
- Date Issued: 2005
Rainfall variability in Southern Africa, its influences on streamflow variations and its relationships with climatic variations
- Authors: Valimba, Patrick
- Date: 2005
- Subjects: Rain and rainfall -- Africa, Southern Climatic changes -- Africa, Southern Streamflow -- Africa, Southern
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:6030 , http://hdl.handle.net/10962/d1006159
- Description: Hydrological variability involving rainfall and streamflows in southern Africa have been often studied separately or have used cumulative rainfall and streamflow indices. The main objective of this study was to investigate spatio-temporal variations of rainfall, their influences on streamflows and their relationships with climatic variations with emphasis on indices that characterise the hydrological extremes, floods and droughts. It was found that 60-70% of the time when it rains, daily rainfalls are below their long-term averages and daily amounts below 10 mm are the most frequent in southern Africa. Spatially, climatologies of rainfall sub-divided the southern African subcontinent into the dry western/southwestern part and the “humid” eastern and northern part. The daily amounts below 20 mm contribute significantly to annual rainfall amounts in the dry part while all types of daily rainfall exceeding 1 mm have comparable contributions in the humid part. The climatologies indicated the highest likelihood of experiencing intense daily events during the core of the wet seasons with the highest frequencies in central Mozambique and the southern highlands of Tanzania. Interannual variations of rainfall indicated that significant changes had occurred between the late-1940s and early-1980s, particularly in the 1970s. The changes in rainfall were more evident in the number of daily rainfall events than in rainfall amounts, led generally to increasing early summer and decreased late summer rainfall. It was also found that intra-seasonal dry day sequences were an important parameter in the definition of a rainy season’s onset and end in southern Africa apart from rainfall amounts. Interannual variations of the rainy season characteristics (onset, end, duration) followed the variations of rainfall amounts and number of events. The duration of the rainy season was affected by the onset (Tanzania), onset or end (tropical southern Africa - southwestern highlands of Tanzania, Zambia, northern Zimbabwe and central Mozambique) and end (the remaing part of southern Africa). Flow duration curves (FDCs) identified three types of rivers (ephemeral, seasonal and perennial) in southern Africa with ephemeral rivers found mainly in the dry western part of the region. Seasonal streamflow patterns followed those of rainfall while interannual streamflow variations indicated significant changes of mean flows with little evidences of high and low flow regime changes except in Namibia and some parts of northern Zimbabwe. It was, however, not possible to provide strong links between the identified changes in streamflows and those in rainfall. Regarding the influences of climate variability on hydrological variability in southern Africa, rainfall variations in southern Africa were found to be influenced strongly by ENSO and SST in the tropical Indian ocean and moderately by SST in the south Madagascar basin. The influence of ENSO was consistent for all types of daily rainfall and peaks for the light and moderate (< 20 mm) events in the southern part and for the intense events in the northern part. SST in the tropical Indian ocean influence the light and moderate events while SST close to the region influence the heavy events. However, the relationships experienced significant changes in the mid-1950s and in the 1970s. The former changes led to improved associations while the latter deteriorated or reversed the relationships. The influences of climatic variables on streamflows and rainy season characteristics were inferred from the rainfall-streamflow and rainfall-climatic variables relationships.
- Full Text:
- Date Issued: 2005
- Authors: Valimba, Patrick
- Date: 2005
- Subjects: Rain and rainfall -- Africa, Southern Climatic changes -- Africa, Southern Streamflow -- Africa, Southern
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:6030 , http://hdl.handle.net/10962/d1006159
- Description: Hydrological variability involving rainfall and streamflows in southern Africa have been often studied separately or have used cumulative rainfall and streamflow indices. The main objective of this study was to investigate spatio-temporal variations of rainfall, their influences on streamflows and their relationships with climatic variations with emphasis on indices that characterise the hydrological extremes, floods and droughts. It was found that 60-70% of the time when it rains, daily rainfalls are below their long-term averages and daily amounts below 10 mm are the most frequent in southern Africa. Spatially, climatologies of rainfall sub-divided the southern African subcontinent into the dry western/southwestern part and the “humid” eastern and northern part. The daily amounts below 20 mm contribute significantly to annual rainfall amounts in the dry part while all types of daily rainfall exceeding 1 mm have comparable contributions in the humid part. The climatologies indicated the highest likelihood of experiencing intense daily events during the core of the wet seasons with the highest frequencies in central Mozambique and the southern highlands of Tanzania. Interannual variations of rainfall indicated that significant changes had occurred between the late-1940s and early-1980s, particularly in the 1970s. The changes in rainfall were more evident in the number of daily rainfall events than in rainfall amounts, led generally to increasing early summer and decreased late summer rainfall. It was also found that intra-seasonal dry day sequences were an important parameter in the definition of a rainy season’s onset and end in southern Africa apart from rainfall amounts. Interannual variations of the rainy season characteristics (onset, end, duration) followed the variations of rainfall amounts and number of events. The duration of the rainy season was affected by the onset (Tanzania), onset or end (tropical southern Africa - southwestern highlands of Tanzania, Zambia, northern Zimbabwe and central Mozambique) and end (the remaing part of southern Africa). Flow duration curves (FDCs) identified three types of rivers (ephemeral, seasonal and perennial) in southern Africa with ephemeral rivers found mainly in the dry western part of the region. Seasonal streamflow patterns followed those of rainfall while interannual streamflow variations indicated significant changes of mean flows with little evidences of high and low flow regime changes except in Namibia and some parts of northern Zimbabwe. It was, however, not possible to provide strong links between the identified changes in streamflows and those in rainfall. Regarding the influences of climate variability on hydrological variability in southern Africa, rainfall variations in southern Africa were found to be influenced strongly by ENSO and SST in the tropical Indian ocean and moderately by SST in the south Madagascar basin. The influence of ENSO was consistent for all types of daily rainfall and peaks for the light and moderate (< 20 mm) events in the southern part and for the intense events in the northern part. SST in the tropical Indian ocean influence the light and moderate events while SST close to the region influence the heavy events. However, the relationships experienced significant changes in the mid-1950s and in the 1970s. The former changes led to improved associations while the latter deteriorated or reversed the relationships. The influences of climatic variables on streamflows and rainy season characteristics were inferred from the rainfall-streamflow and rainfall-climatic variables relationships.
- Full Text:
- Date Issued: 2005
Re-inventing educational leadership for school and community transformation: learning from the Educational Leadership Management and Development programme of the University of Fort Hare
- Authors: Moyo, George
- Date: 2005
- Subjects: University of Fort Hare. Educational Leadership Management and Development Educational leadership -- South Africa Educational change -- South Africa School management and organization -- South Africa School improvement programs -- South Africa School principals -- South Africa Community and school -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1719 , http://hdl.handle.net/10962/d1003602
- Description: This study explores educational leadership development and social change strategies pioneered by one programme, the Educational Leadership Management and Development (ELMD) programme of the University of Fort Hare. The programme seeks to model a way of doing social and educational transformation through educational leadership development. Conceptually, the model was meant to draw together a number of education stakeholders operating at various levels of the schooling system to undergo the same programme of leadership development. The programme participants, who included district education officials, schools principals, members of school management teams, educators and members of School Governing Bodies, were to enrol as teams. They would work on learning tasks that were both academic and practical in nature, with an emphasis on experiential learning that leads to the creation of district and community networks of partners, development teams or forums and communities of practice, as well as the production and implementation of district and school development plans. Informed by this conceptual position, the study was structured by two underlying questions. First, whether the ELMD was re-inventing educational leadership beyond the traditional focus on principalship towards one that is inclusive of other education stakeholders. Second, how leadership development as a vehicle for social and educational change can be carried out. The research process was guided by a multi-paradigm perspective which drew heavily on the interpretive and critical science orientations. This led to the crafting of research methods that looked for data that would assist in an understanding of what was happening in the programme, as well as what power dynamics were at play and with what consequences for innovation. The evidence emanating from the study suggests a number of possibilities for consideration by future leadership development programme designers. First, the ELMD programme delivery design shows what can be done to draw participants from various levels of the schooling system, district, school and community and teach them educational leadership together in a mode that mobilizes them for change. Second, how social distance separating different levels of the education hierarchy and status consciousness may disappear gradually as people are brought together to work on tasks of mutual concern. Third, after a year of engagement with ELMD ideas and approach, the participants in the programme appeared to have started a journey of selftransformation towards becoming qualitatively different people who saw themselves as teams capable of tackling education and social problems in their schools and communities. These participants had begun to forge working networks, but the extent to which these could be characterized as knowledge ecosystems and communities of practice remains a question to explore. Fourth, that the current higher education accreditation policies and practices do not accommodate innovative learning approaches of the kind that the ELMD is developing. In this regard, the ELMD experienced difficulties in coming up with an assessment policy and practices which meet the academic as well as the practical developmental concerns of the programme. Fifth, programme instrumentalities and mandates that are put in place do not, in themselves, bring about change. The actual change comes about through the actions of human leadership capable of navigating between structural enablers and constraints.
- Full Text:
- Date Issued: 2005
- Authors: Moyo, George
- Date: 2005
- Subjects: University of Fort Hare. Educational Leadership Management and Development Educational leadership -- South Africa Educational change -- South Africa School management and organization -- South Africa School improvement programs -- South Africa School principals -- South Africa Community and school -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1719 , http://hdl.handle.net/10962/d1003602
- Description: This study explores educational leadership development and social change strategies pioneered by one programme, the Educational Leadership Management and Development (ELMD) programme of the University of Fort Hare. The programme seeks to model a way of doing social and educational transformation through educational leadership development. Conceptually, the model was meant to draw together a number of education stakeholders operating at various levels of the schooling system to undergo the same programme of leadership development. The programme participants, who included district education officials, schools principals, members of school management teams, educators and members of School Governing Bodies, were to enrol as teams. They would work on learning tasks that were both academic and practical in nature, with an emphasis on experiential learning that leads to the creation of district and community networks of partners, development teams or forums and communities of practice, as well as the production and implementation of district and school development plans. Informed by this conceptual position, the study was structured by two underlying questions. First, whether the ELMD was re-inventing educational leadership beyond the traditional focus on principalship towards one that is inclusive of other education stakeholders. Second, how leadership development as a vehicle for social and educational change can be carried out. The research process was guided by a multi-paradigm perspective which drew heavily on the interpretive and critical science orientations. This led to the crafting of research methods that looked for data that would assist in an understanding of what was happening in the programme, as well as what power dynamics were at play and with what consequences for innovation. The evidence emanating from the study suggests a number of possibilities for consideration by future leadership development programme designers. First, the ELMD programme delivery design shows what can be done to draw participants from various levels of the schooling system, district, school and community and teach them educational leadership together in a mode that mobilizes them for change. Second, how social distance separating different levels of the education hierarchy and status consciousness may disappear gradually as people are brought together to work on tasks of mutual concern. Third, after a year of engagement with ELMD ideas and approach, the participants in the programme appeared to have started a journey of selftransformation towards becoming qualitatively different people who saw themselves as teams capable of tackling education and social problems in their schools and communities. These participants had begun to forge working networks, but the extent to which these could be characterized as knowledge ecosystems and communities of practice remains a question to explore. Fourth, that the current higher education accreditation policies and practices do not accommodate innovative learning approaches of the kind that the ELMD is developing. In this regard, the ELMD experienced difficulties in coming up with an assessment policy and practices which meet the academic as well as the practical developmental concerns of the programme. Fifth, programme instrumentalities and mandates that are put in place do not, in themselves, bring about change. The actual change comes about through the actions of human leadership capable of navigating between structural enablers and constraints.
- Full Text:
- Date Issued: 2005
Supervision : a Foucaultian exploration of institutional and interpersonal power relations between postgraduate supervisors, their students and the university domain
- Authors: Rau, Asta
- Date: 2005
- Subjects: Foucault, Michel, 1926-1984 -- Methodology Foucault, Michel, 1926-1984 -- Criticism and interpretation Graduate students -- Supervision of Dissertations, Academic
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1786 , http://hdl.handle.net/10962/d1003671
- Description: Supervision is widely acknowledged as influencing the quality of postgraduate theses, and by association, of postgraduates. Despite this, publications on conducting research offer far less guidance on managing the supervision relationship than on the practicalities of producing a thesis. In-depth, qualitative supervision studies are few and fewer still examine power in the supervision relationship. Michel Foucault’s insights are used to explore the question: How do postgraduate supervisors and their Master’s students experience the supervision relationship and how are the dynamics of interpersonal and institutional power implicated in these relationships? Foucault argues that power relations always involve resistances; these function primarily through institutionalized discourses to produce different forms of knowledge, one form of which is identity or subjectivity. Accordingly, power relations are explored in terms of thesis-as-product, person-as-product and the impact of both on the mediation of knowledge in the educational domain. Four institutionalized discourses in the university domain are examined: · Commercial educational management discourse: targets academics through issues of quality assurance, throughput, publication, research productivity and funding. · Anarchic educational leadership discourse: integrates quantum principles with commercial demands, change management strategies and meaningful participation. · Humanistic discourse: favours a pastoral ethic and is person-centered. · Holistic discourse: cultivates ecological sensibility and values the interconnectedness of all aspects of being-in-the-world. Data collected in sixteen semi-structured interviews with three matched supervisor-student pairs selected from the humanities and education faculties of one South African university, are presented as case studies. Data analysis combines grounded theory techniques with selected aspects of Foucault’s methods. A conceptual model is devised to analyse how participants use resistance strategies to interface their autonomy and dependency with their expectations, abilities, and professional and pastoral care. The research yields rich data in which several thematic correlations in interpersonal and institutional power dynamics are grounded. These include: the significance of supervisor-student matching; links between expectations, abilities, the way participants negotiate power and the quality of professional and pastoral care they experience; the benefit of personal affinity to thesis-as-product and person-as-product; and the impact of commercial demands on participants’ power relations. Participants tend to reproduce the discourses in which they are embedded and adopt or adapt aspects of contesting discourses to this end. Potential avenues are identified for improving supervision practice and for further research.
- Full Text:
- Date Issued: 2005
- Authors: Rau, Asta
- Date: 2005
- Subjects: Foucault, Michel, 1926-1984 -- Methodology Foucault, Michel, 1926-1984 -- Criticism and interpretation Graduate students -- Supervision of Dissertations, Academic
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1786 , http://hdl.handle.net/10962/d1003671
- Description: Supervision is widely acknowledged as influencing the quality of postgraduate theses, and by association, of postgraduates. Despite this, publications on conducting research offer far less guidance on managing the supervision relationship than on the practicalities of producing a thesis. In-depth, qualitative supervision studies are few and fewer still examine power in the supervision relationship. Michel Foucault’s insights are used to explore the question: How do postgraduate supervisors and their Master’s students experience the supervision relationship and how are the dynamics of interpersonal and institutional power implicated in these relationships? Foucault argues that power relations always involve resistances; these function primarily through institutionalized discourses to produce different forms of knowledge, one form of which is identity or subjectivity. Accordingly, power relations are explored in terms of thesis-as-product, person-as-product and the impact of both on the mediation of knowledge in the educational domain. Four institutionalized discourses in the university domain are examined: · Commercial educational management discourse: targets academics through issues of quality assurance, throughput, publication, research productivity and funding. · Anarchic educational leadership discourse: integrates quantum principles with commercial demands, change management strategies and meaningful participation. · Humanistic discourse: favours a pastoral ethic and is person-centered. · Holistic discourse: cultivates ecological sensibility and values the interconnectedness of all aspects of being-in-the-world. Data collected in sixteen semi-structured interviews with three matched supervisor-student pairs selected from the humanities and education faculties of one South African university, are presented as case studies. Data analysis combines grounded theory techniques with selected aspects of Foucault’s methods. A conceptual model is devised to analyse how participants use resistance strategies to interface their autonomy and dependency with their expectations, abilities, and professional and pastoral care. The research yields rich data in which several thematic correlations in interpersonal and institutional power dynamics are grounded. These include: the significance of supervisor-student matching; links between expectations, abilities, the way participants negotiate power and the quality of professional and pastoral care they experience; the benefit of personal affinity to thesis-as-product and person-as-product; and the impact of commercial demands on participants’ power relations. Participants tend to reproduce the discourses in which they are embedded and adopt or adapt aspects of contesting discourses to this end. Potential avenues are identified for improving supervision practice and for further research.
- Full Text:
- Date Issued: 2005
Synthesis and electrocatalytic properties of polymerizable metallophthalocyanines
- Authors: Obirai, Joseph Chinye
- Date: 2005
- Subjects: Phthalocyanines Electrochemistry
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4447 , http://hdl.handle.net/10962/d1007733
- Description: The syntheses, spectral and electrochemical characterization of new family electropolymerizable pyrrole, thiophene and mercaptopyrimidin substituted metallophthalocyanine (MPc) complexes are described. Tetraamino substituted chromium and manganese phthalocyanine complexes were also synthesized and characterized. The spectral and electrochemical results are comparable to literature reports. The complexes formed stable films when deposited on electrode surfaces. The MPc films were formed by electropolymerization, drop-dry method and self-assembling. Nickel hydroxide-like electrodes were formed by electrotransformation of nickel-tetra-4- (pyrrol-1-yl)phenoxy phthalocyanine polymer films to the corresponding PcNi-O-NiPc modified electrodes in alkaline solution. The thiophene, mercaptopyrimidine functionalized MPcs and amino group containing complexes formed good self-assembled monolayers (SAMs) on gold electrode. The electrode modification processes were reproducible. The conductivities of the electrode were dependent on the surface concentrations of the complexes as a function of electropolymerization scan numbers. The electrodes showed good catalytic responses toward L-cysteine, nitrite, nitric oxide (NO), glycine, phenol and its derivative and oxygen. The results also suggest that the presence of thio groups on the ring substituents lowers the oxidation potential of Lcysteine more compared to literature values. The stability of the amperometric responses toward the various analytes is used to diagnose the applicability of the materials for electroanalytical purposes. The limits of detection for L-cysteine, nitrite, NO and glycine were in the range of ~10⁻⁷ to 10⁻⁵ mol dm⁻³.
- Full Text:
- Date Issued: 2005
- Authors: Obirai, Joseph Chinye
- Date: 2005
- Subjects: Phthalocyanines Electrochemistry
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4447 , http://hdl.handle.net/10962/d1007733
- Description: The syntheses, spectral and electrochemical characterization of new family electropolymerizable pyrrole, thiophene and mercaptopyrimidin substituted metallophthalocyanine (MPc) complexes are described. Tetraamino substituted chromium and manganese phthalocyanine complexes were also synthesized and characterized. The spectral and electrochemical results are comparable to literature reports. The complexes formed stable films when deposited on electrode surfaces. The MPc films were formed by electropolymerization, drop-dry method and self-assembling. Nickel hydroxide-like electrodes were formed by electrotransformation of nickel-tetra-4- (pyrrol-1-yl)phenoxy phthalocyanine polymer films to the corresponding PcNi-O-NiPc modified electrodes in alkaline solution. The thiophene, mercaptopyrimidine functionalized MPcs and amino group containing complexes formed good self-assembled monolayers (SAMs) on gold electrode. The electrode modification processes were reproducible. The conductivities of the electrode were dependent on the surface concentrations of the complexes as a function of electropolymerization scan numbers. The electrodes showed good catalytic responses toward L-cysteine, nitrite, nitric oxide (NO), glycine, phenol and its derivative and oxygen. The results also suggest that the presence of thio groups on the ring substituents lowers the oxidation potential of Lcysteine more compared to literature values. The stability of the amperometric responses toward the various analytes is used to diagnose the applicability of the materials for electroanalytical purposes. The limits of detection for L-cysteine, nitrite, NO and glycine were in the range of ~10⁻⁷ to 10⁻⁵ mol dm⁻³.
- Full Text:
- Date Issued: 2005
The anatomy and distribution of the cyperaceae in the Eastern Cape region of South Africa
- Authors: Sonnenberg, Bernd Jürgen
- Date: 2005
- Subjects: Cyperaceae Cyperaceae -- Anatomy Cyperaceae -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4228 , http://hdl.handle.net/10962/d1003797
- Description: The principal objective of this investigation, was to collect the family Cyperaceae and to study their leaf, bract and culm anatomy. The second was to examine the collection for unique structures or forms, whilst a third was to classify the Cyperaceae according to their photosynthetic structures and types. Distribution of the Cyperaceae within the broad region defined as the Eastern Cape would be influenced by rainfall pattern. It was expected that C₃ species would predominate in more mesic environments and habitats, whilst the C₄ species would be found in drier less favourable habitats. Collection within the region (November 1993 to late January 1997), yielded 106 species, totalling some 600 specimens. Both sub-families of the Cyperaceae (Caricoideae and Cyperoideae), eight tribes (Abildgaardieae, Cariceae, Cypereae, Hypotvtreae, Rhynchosporeae, Shoeneae, Sirpeae and Slerieae) and twenty five genera were found to be present. Sixty percent of the species were C₃ and forty percent were C₄. Sixteen new species, which had not been collected within the boundaries of the region previously were also found. Over 43 percent of the species collected had unique anatomical characteristics that appeared to be influenced by habitat and or climate influenced. These are the characters influenced by hydromorphic, mesomorphic and xeromorphic environments. These anatomical characters: Thickness of leaves and bracts; thickness of the adaxial and abaxial epidermis of the leaves and bracts; flush, sunken and raised stomata; presence or absence of bulliform cells; presence and distribution of sclerenchymatous structures; presence or absence of a hypodermis; presence or absence of cavities in the leaves, bracts and culms; mesophyll or ground tissue structure, and the presence or absence of secretary structures. A few noteworthy anatomical characters that are influenced by climate are present in Cladium mariscus subsp. jamaicense (Schoeneae), the Cariceae, the Cypereae and the Sclerieae. Within Cladium mariscus subsp. jamaicense the pseudo-dorsiventral leaves and bracts, as well as the large lamina cavities, containing trans-lamina girders are unique. Papillate epidermal cells are limited to the tribe Cariceae. In the Cypereae many of the species lack bulliform cells and hypodermal layers. In Pycreus cooperi (Cypereae) the vascular bundles of the leaves and bracts, appear to be stacked in rows, that are inter-spaced with lamina cavities. In the Sclerieae the mesophyll structure is specific to the species level. Unique anatomical characteristics were also present in the leaves, bracts and culms of the genus Carpha. In this genus distinctive lateral vascular bundles were present abutting the large bundles and/or midrib bundle. The most distinctive anatomical characteristics that could be used to separate the members of the Cyperaceae were the structures and associated structures related to the photosynthetic pathway. The Eastern Cape Cyperaceae could be divided into three distinct groups based on photosynthetic structure, namely one C₃, a C₄ and a potential C₃-C₄ intermediate group. The C₃ group was found to have non-radiate mesophyll and an outer parenchymatous sheath with small chloroplasts (Cariceae, Cyperaceae [in part], Hypolytreae (Chrysithrix capensis], Rhynchosporeae [R. brownii], Schoeneae, Scirpeae and Sclerieae). The C₄ group has radiate mesophyll and an inner parenchymatous sheath with enlarged chloroplasts (Kranz or PCR sheath). The C₄ species are present in tribes Abildgaardieae, Cypereae (in part) and Rhynchosporeae (R. barrosiana). In the Eastern Cape, a few species with C₃ anatomy have anatomical characteristics that are similar to the species with C₄ anatomy (Cyathocoma hexandra [bracts], Cyperus tennellus var. tennellus [leaves and bracts], Ficinia bulbosa [leaves], F. dura [leaves and bracts], F. lateralis coastal [leaves and bracts], F. oligantha [bracts], F. pingiour [bracts], F. stolonifera [leaves and bracts], F. tribracteata [leaves and bracts], F. zeyheri [leaves and bracts], Isolepis cernua [leaves and bracts], I. costata var. macra [bracts], Schoenus nigricans [leaves], Scirpus nodosus [bracts] and Tetraria cuspidata [leaves and bracts)). The vascular bundles within this intermediate group, fall within the Hattersleyand Watson (1975) minimal cell lateral count and maximal cell distal count criteria for C₄ grass species. However, no biochemical data exists to see whether they are C₃-C₄ intermediates or whether the Hattersley and Watson (1975) C₄ criteria for grasses applies to smaller, or scutiform Cyperaceae or not. Based on the results presented here, five distinct structural forms/types were found to be present in the C₃, C₄ and C₃-C₄ intermediate groups. The C₃ and the potential C₃-C₄ intermediate species may be divided into two types, based on the number of vascular sheaths present. In the first or A-type, vascular bundles are surrounded by two sheaths and in the more dominant B-type, by three. The A-type was found in the Cypereae (Cyperus denudatus and C. textilis) and most of the Scirpeae. B-type anatomy occurred in the Cariceae, Cypereae (c. difformis, C. pulcher, C. sphaerospermus, C. tennellus var. tennellus and P. mundii), Hypolytreae, Rhynchosporeae (R. brownii), Schoeneae, Scirpeae (Bolboschoenus maritimus, Ficinia cinnamomea, F. fascicularis, F. lateralis both, F. pingiour, the genus Fuirena, I. diabolica, I. fluitans, I. prolifera and Schoenoplectus paludicola) and Sclerieae tribes. Based on the vascular sheath structure, the C₄ species could be divided into three groups, namely bulbostyloid, chlorocyperoid and fimbristyloid, where the bulbostyloid structure occurred in Bulbostylis schoenoides. Cyperus (in part), Kyllinga, Mariscus and Pycreus (except P. mundii) had a chlorocyperoid structure. Genera with fimbristyloid structure were recorded in the genera Abildgaardia, Bulbostylis and Fimbristylis. The bulbostyloid type represents a potential a fifth C₄ anatomical type within the C₄ Cyperaceae. As a result of this observation, it is possible that the C₄ syndrome may have evolved five times in the Cyperaceae and not four as previously suggested by Bruhl and Perry (1995) and by Soros and Dengler (2001). The C₃ Cyperaceae species within the Eastern Cape are more dominant in higher elevation habitats the C₄ species, similar to the C₃ grasses. The only C₄ species that occur at high elevations are those with three sheaths. The C₃ and C₄ species within the region occur in similar low rainfall habitat ranges, where the C₄'s are more dominant in xeric habitats on drier soils than the C₃ species, similar to the grasses. Where more C₃ species occur in higher rainfall habitats than the C₄ species. With the exception of the Afromontane Bulbostylis schoenoides and R. barrosiana, the C₄ species similar to the grasses are dominant in high light and temperature habitats with low rainfall, unlike the C₄ Cyperaceae of Japan and America. Only five species occur in the desert like conditions of the Karoo-Namib biome (Cyperus laevigatus, C. rupestris var. rupestris, I. cernua, M. capensis and M. uitenhagensis), which have less than 250mm of rainfall per annum. Only three species are habitat-specific or may be endemic to a specific area within the Eastern Cape, namely A. capensis, Chrysithrix capensis and R. barrosiana. A. capensis in marshes on the Amatole mountains near Alice and Hogsback. C. capensis to the Tstsikamma mountains of the Wite Els Bosch forests. R. barrosiana to the marshlands of the Cape Morgan coastal Nature reserve at Kei Mouth. The anatomical types of the C₃ and more especially C₄ Cyperaceae are not specifically found in a particular rainfall regime or habitat type, which is contrary to the thesis hypothesis. However, the C₃ species are mostly correlated with hydrophytic to mesic habitats, with the exception of Ficinia and the two sheathed species. Ficinia is dominant in mesic grasslands and halophytic habitats. The two sheathed C₃ species are mostly present in halophytic habitats. The C₄ species are also more dominant in mesic to xerophytic grasslands, as expected in the hypothesis. Where only a few species occur in habitats correlated with increasing rainfall and temperature similar to the C₄ Cyperaceae of Japan and America. It may thus be that the development and evolution of the different C₄ anatomical forms (or phylogenetic forms) within the Cyperaceae may have enabled these species to establish themselves in habitats that were alien to their origins. It may be that the ability to regulate photoassimilate and water transport within the Cyperaceae enables their success in a dynamic and unpredictable climate, such as the Eastern Cape. Many of the anatomical characteristics reported in this thesis and its appendices are unique to the tribes, genera and/or species of the Eastern Cape Cyperaceae and thus may be valuable to future taxonomic classifications of the family. The research presented here should provide a good working platform for future, more detailed research on this often forgotten component of the vegetation.
- Full Text:
- Date Issued: 2005
- Authors: Sonnenberg, Bernd Jürgen
- Date: 2005
- Subjects: Cyperaceae Cyperaceae -- Anatomy Cyperaceae -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4228 , http://hdl.handle.net/10962/d1003797
- Description: The principal objective of this investigation, was to collect the family Cyperaceae and to study their leaf, bract and culm anatomy. The second was to examine the collection for unique structures or forms, whilst a third was to classify the Cyperaceae according to their photosynthetic structures and types. Distribution of the Cyperaceae within the broad region defined as the Eastern Cape would be influenced by rainfall pattern. It was expected that C₃ species would predominate in more mesic environments and habitats, whilst the C₄ species would be found in drier less favourable habitats. Collection within the region (November 1993 to late January 1997), yielded 106 species, totalling some 600 specimens. Both sub-families of the Cyperaceae (Caricoideae and Cyperoideae), eight tribes (Abildgaardieae, Cariceae, Cypereae, Hypotvtreae, Rhynchosporeae, Shoeneae, Sirpeae and Slerieae) and twenty five genera were found to be present. Sixty percent of the species were C₃ and forty percent were C₄. Sixteen new species, which had not been collected within the boundaries of the region previously were also found. Over 43 percent of the species collected had unique anatomical characteristics that appeared to be influenced by habitat and or climate influenced. These are the characters influenced by hydromorphic, mesomorphic and xeromorphic environments. These anatomical characters: Thickness of leaves and bracts; thickness of the adaxial and abaxial epidermis of the leaves and bracts; flush, sunken and raised stomata; presence or absence of bulliform cells; presence and distribution of sclerenchymatous structures; presence or absence of a hypodermis; presence or absence of cavities in the leaves, bracts and culms; mesophyll or ground tissue structure, and the presence or absence of secretary structures. A few noteworthy anatomical characters that are influenced by climate are present in Cladium mariscus subsp. jamaicense (Schoeneae), the Cariceae, the Cypereae and the Sclerieae. Within Cladium mariscus subsp. jamaicense the pseudo-dorsiventral leaves and bracts, as well as the large lamina cavities, containing trans-lamina girders are unique. Papillate epidermal cells are limited to the tribe Cariceae. In the Cypereae many of the species lack bulliform cells and hypodermal layers. In Pycreus cooperi (Cypereae) the vascular bundles of the leaves and bracts, appear to be stacked in rows, that are inter-spaced with lamina cavities. In the Sclerieae the mesophyll structure is specific to the species level. Unique anatomical characteristics were also present in the leaves, bracts and culms of the genus Carpha. In this genus distinctive lateral vascular bundles were present abutting the large bundles and/or midrib bundle. The most distinctive anatomical characteristics that could be used to separate the members of the Cyperaceae were the structures and associated structures related to the photosynthetic pathway. The Eastern Cape Cyperaceae could be divided into three distinct groups based on photosynthetic structure, namely one C₃, a C₄ and a potential C₃-C₄ intermediate group. The C₃ group was found to have non-radiate mesophyll and an outer parenchymatous sheath with small chloroplasts (Cariceae, Cyperaceae [in part], Hypolytreae (Chrysithrix capensis], Rhynchosporeae [R. brownii], Schoeneae, Scirpeae and Sclerieae). The C₄ group has radiate mesophyll and an inner parenchymatous sheath with enlarged chloroplasts (Kranz or PCR sheath). The C₄ species are present in tribes Abildgaardieae, Cypereae (in part) and Rhynchosporeae (R. barrosiana). In the Eastern Cape, a few species with C₃ anatomy have anatomical characteristics that are similar to the species with C₄ anatomy (Cyathocoma hexandra [bracts], Cyperus tennellus var. tennellus [leaves and bracts], Ficinia bulbosa [leaves], F. dura [leaves and bracts], F. lateralis coastal [leaves and bracts], F. oligantha [bracts], F. pingiour [bracts], F. stolonifera [leaves and bracts], F. tribracteata [leaves and bracts], F. zeyheri [leaves and bracts], Isolepis cernua [leaves and bracts], I. costata var. macra [bracts], Schoenus nigricans [leaves], Scirpus nodosus [bracts] and Tetraria cuspidata [leaves and bracts)). The vascular bundles within this intermediate group, fall within the Hattersleyand Watson (1975) minimal cell lateral count and maximal cell distal count criteria for C₄ grass species. However, no biochemical data exists to see whether they are C₃-C₄ intermediates or whether the Hattersley and Watson (1975) C₄ criteria for grasses applies to smaller, or scutiform Cyperaceae or not. Based on the results presented here, five distinct structural forms/types were found to be present in the C₃, C₄ and C₃-C₄ intermediate groups. The C₃ and the potential C₃-C₄ intermediate species may be divided into two types, based on the number of vascular sheaths present. In the first or A-type, vascular bundles are surrounded by two sheaths and in the more dominant B-type, by three. The A-type was found in the Cypereae (Cyperus denudatus and C. textilis) and most of the Scirpeae. B-type anatomy occurred in the Cariceae, Cypereae (c. difformis, C. pulcher, C. sphaerospermus, C. tennellus var. tennellus and P. mundii), Hypolytreae, Rhynchosporeae (R. brownii), Schoeneae, Scirpeae (Bolboschoenus maritimus, Ficinia cinnamomea, F. fascicularis, F. lateralis both, F. pingiour, the genus Fuirena, I. diabolica, I. fluitans, I. prolifera and Schoenoplectus paludicola) and Sclerieae tribes. Based on the vascular sheath structure, the C₄ species could be divided into three groups, namely bulbostyloid, chlorocyperoid and fimbristyloid, where the bulbostyloid structure occurred in Bulbostylis schoenoides. Cyperus (in part), Kyllinga, Mariscus and Pycreus (except P. mundii) had a chlorocyperoid structure. Genera with fimbristyloid structure were recorded in the genera Abildgaardia, Bulbostylis and Fimbristylis. The bulbostyloid type represents a potential a fifth C₄ anatomical type within the C₄ Cyperaceae. As a result of this observation, it is possible that the C₄ syndrome may have evolved five times in the Cyperaceae and not four as previously suggested by Bruhl and Perry (1995) and by Soros and Dengler (2001). The C₃ Cyperaceae species within the Eastern Cape are more dominant in higher elevation habitats the C₄ species, similar to the C₃ grasses. The only C₄ species that occur at high elevations are those with three sheaths. The C₃ and C₄ species within the region occur in similar low rainfall habitat ranges, where the C₄'s are more dominant in xeric habitats on drier soils than the C₃ species, similar to the grasses. Where more C₃ species occur in higher rainfall habitats than the C₄ species. With the exception of the Afromontane Bulbostylis schoenoides and R. barrosiana, the C₄ species similar to the grasses are dominant in high light and temperature habitats with low rainfall, unlike the C₄ Cyperaceae of Japan and America. Only five species occur in the desert like conditions of the Karoo-Namib biome (Cyperus laevigatus, C. rupestris var. rupestris, I. cernua, M. capensis and M. uitenhagensis), which have less than 250mm of rainfall per annum. Only three species are habitat-specific or may be endemic to a specific area within the Eastern Cape, namely A. capensis, Chrysithrix capensis and R. barrosiana. A. capensis in marshes on the Amatole mountains near Alice and Hogsback. C. capensis to the Tstsikamma mountains of the Wite Els Bosch forests. R. barrosiana to the marshlands of the Cape Morgan coastal Nature reserve at Kei Mouth. The anatomical types of the C₃ and more especially C₄ Cyperaceae are not specifically found in a particular rainfall regime or habitat type, which is contrary to the thesis hypothesis. However, the C₃ species are mostly correlated with hydrophytic to mesic habitats, with the exception of Ficinia and the two sheathed species. Ficinia is dominant in mesic grasslands and halophytic habitats. The two sheathed C₃ species are mostly present in halophytic habitats. The C₄ species are also more dominant in mesic to xerophytic grasslands, as expected in the hypothesis. Where only a few species occur in habitats correlated with increasing rainfall and temperature similar to the C₄ Cyperaceae of Japan and America. It may thus be that the development and evolution of the different C₄ anatomical forms (or phylogenetic forms) within the Cyperaceae may have enabled these species to establish themselves in habitats that were alien to their origins. It may be that the ability to regulate photoassimilate and water transport within the Cyperaceae enables their success in a dynamic and unpredictable climate, such as the Eastern Cape. Many of the anatomical characteristics reported in this thesis and its appendices are unique to the tribes, genera and/or species of the Eastern Cape Cyperaceae and thus may be valuable to future taxonomic classifications of the family. The research presented here should provide a good working platform for future, more detailed research on this often forgotten component of the vegetation.
- Full Text:
- Date Issued: 2005
The assessment and management of bycatch and discards in the South African demersal trawl fishery
- Authors: Walmsley, Sarah Ann
- Date: 2005
- Subjects: Bycatches (Fisheries) Fishery management -- South Africa Fisheries -- South Africa Trawls and trawling -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5228 , http://hdl.handle.net/10962/d1005071
- Description: Over the past few decades it has become recognised that an ecosystem approach is required to manage world fisheries. Management strategies must ensure that non-target (bycatch) as well as target catches are sustainable. To achieve this, detailed commercial catch and biological information is required. The composition of catches made by trawlers operating off the south and west coasts of South Africa was investigated. Distinct fishing areas were identified on each coast, based on target species and fishing depth. Catch composition differed markedly among the areas defined. Although hake Merluccius sp. dominated South Coast catches, a large proportion of the catch was composed of bycatch. On the West Coast, hake dominated catches and this domination increased with increasing depth. On both coasts approximately 90% of the observed nominal catch was processed and landed. Estimates of annual discards suggested that the fishery discarded 38 thousand tons of fish per annum (16% of the nominal trawl catch). The data also indicated that hake discarding, the capture of linefish and the increased targeting of high value species might be cause for concern. Spatial analysis indicated that a variety of factors such as trawling position, catch size and catch composition affects bycatch dynamics. The monkfish Lophius vomerinus is a common bycatch species that has been increasingly targeted by demersal trawlers. This study showed that L. vomerinus is a slow-growing, long-lived species (West Coast males L∞ = 68.50cm TL, t₀ = -1.69yr, K = 0.10yr⁻¹; West Coast females L∞ = 110.23cm TL, t₀ = -1.54yr, K = 0.05yr⁻¹; South Coast sexes combined L∞ = 70.12cm TL, t₀ = - 0.80yr, K = 0.11yr⁻¹), that matures at approximately 6 years of age. These traits could have serious management implications for the species. Per-recruit analysis suggested that the stock might be overexploited, although further investigation is required to confirm this. Solutions were suggested for each of the concerns raised, taking cognisance of the differences observed between the South and West Coasts and the economic dependence of South Coast companies on bycatch. The needs of future research were considered.
- Full Text:
- Date Issued: 2005
- Authors: Walmsley, Sarah Ann
- Date: 2005
- Subjects: Bycatches (Fisheries) Fishery management -- South Africa Fisheries -- South Africa Trawls and trawling -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5228 , http://hdl.handle.net/10962/d1005071
- Description: Over the past few decades it has become recognised that an ecosystem approach is required to manage world fisheries. Management strategies must ensure that non-target (bycatch) as well as target catches are sustainable. To achieve this, detailed commercial catch and biological information is required. The composition of catches made by trawlers operating off the south and west coasts of South Africa was investigated. Distinct fishing areas were identified on each coast, based on target species and fishing depth. Catch composition differed markedly among the areas defined. Although hake Merluccius sp. dominated South Coast catches, a large proportion of the catch was composed of bycatch. On the West Coast, hake dominated catches and this domination increased with increasing depth. On both coasts approximately 90% of the observed nominal catch was processed and landed. Estimates of annual discards suggested that the fishery discarded 38 thousand tons of fish per annum (16% of the nominal trawl catch). The data also indicated that hake discarding, the capture of linefish and the increased targeting of high value species might be cause for concern. Spatial analysis indicated that a variety of factors such as trawling position, catch size and catch composition affects bycatch dynamics. The monkfish Lophius vomerinus is a common bycatch species that has been increasingly targeted by demersal trawlers. This study showed that L. vomerinus is a slow-growing, long-lived species (West Coast males L∞ = 68.50cm TL, t₀ = -1.69yr, K = 0.10yr⁻¹; West Coast females L∞ = 110.23cm TL, t₀ = -1.54yr, K = 0.05yr⁻¹; South Coast sexes combined L∞ = 70.12cm TL, t₀ = - 0.80yr, K = 0.11yr⁻¹), that matures at approximately 6 years of age. These traits could have serious management implications for the species. Per-recruit analysis suggested that the stock might be overexploited, although further investigation is required to confirm this. Solutions were suggested for each of the concerns raised, taking cognisance of the differences observed between the South and West Coasts and the economic dependence of South Coast companies on bycatch. The needs of future research were considered.
- Full Text:
- Date Issued: 2005
The biophysical dynamics of the Lower Shire River Floodplain fisheries in Malawi
- Authors: Chimatiro, Sloans Kalumba
- Date: 2005
- Subjects: Shire River Valley (Malawi and Mozambique) Fisheries -- Malawi
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5243 , http://hdl.handle.net/10962/d1005086
- Description: Fishes of African floodplains typically comprise populations having short life cycles, relatively few age groups, more generalised feeding behaviour, and which experience spawning success that is strongly influenced by abiotic factors such as hydrological regime of the river, climatic seasonality and habitat characteristics. In addition, African river-floodplain ecosystems do not have appropriate predictive models for estimating yield in these ecosystems. While most predictive models developed to date for floodplain fisheries have taken into account morpho-edaphic factors, they have generally excluded climatic factors as a mega-determinant of the variability of floodplain fisheries. The principle aim of this thesis has been to develop a predictive management model that incorporates data on essential biological aspects of the target species, characteristics of the habitat as well as overall climatic factors, and thus allow for adaptive management of the fisheries in a continuously fluctuating floodplain environment. Lower Shire Floodplain (34 ⁰ 45’ – 35 ⁰ E and 16 ⁰ 00’-17 ⁰ 15’ S) in Malawi, one of the major rivers-floodplains in the Zambezi Basin, was used to test this type of model. The major hypothesis tested in this study was that “the dynamics of the fishery of Lower Shire Floodplain are driven by and adapted to the seasonal, but predictable, hydro-climatic regime of the floodplain”. The specific objectives were: to describe the floodplain’s climate and hydrological pattern; to develop a quantitative characterisation of the major habitats of the Lower Shire Floodplain; to assess the fishery in terms of size, gear utilisation, gear selectivity and yield; to assess the biological parameters of the target species, necessary for the management of the fishery; to analyse how water fluctuation in the floodplain affects the recruitment and life history of the two target species; and to develop of a predictive hydro-climatic model to benefit the management of the fisheries. The climate of the floodplain was characterised by low (765 ± 198 mm) and fairly variable (Cv = 27%) rainfall, which largely occurred between December and January. The area was generally humid (mean RH 68%), with mild to hot (25- 33ºC) and variable monthly mean diurnal (12ºC) temperature. Four quarterly hydro-climatic seasons were identified and comprised: Quarter 1 (Jul-Sep) characterised by hot, dry weather with a low flood regime; Quarter 2 (Oct-Dec) hot, windy, wet weather with low-but-rising flood regime; Quarter 3 (Jan-Mar) hot humid, wet weather with the flood regime at peak; and Quarter 4 (Apr-Jun) humid and cool weather with receding flood regime. The annual hydrograph of the floodplain was represented by four categories of flood regime as: low (Jul-Sept), low-but-rising (Oct-Dec), peak (Jan- Mar), and falling (Apr-Jun). The floodplain experienced a water deficit of 95.1 mm.year⁻¹, and it was hypothesised that ground water recharge maintained water in the floodplain the rest of the year. Three major habitats were identified in the floodplain. The river-floodplain, characterised by deep fast-flowing water, sandy substrate and little emergent vegetation; the permanently connected lagoons, were shallow (≤ 2 m) with sandymud bottom and slow flowing water; and the seasonally connected lagoons had slowflowing stagnant water, with comparatively more emergent and floating vegetation. Physicochemical characteristics of the habitats varied significantly with hydroclimatic seasons (one-way ANOVA, p ≤ 0.05), indicating the influence of flood regime, which joined the habitats in a non-equilibrial spatial distribution. Consequently, during receding and low flood regimes river-floodplain and permanently connected lagoons exhibited similar characteristics while all three habitats had similar characteristics during the rising and peak flood regimes. It was, therefore, concluded that in floodplains, habitats shift horizontally and vertically according to the water level. Gill nets, cast nets, long line, and fish traps accounted for 99% of the total count of gears, and hence considered the major fishing sectors. Two principal species in the floodplain were the catfish Clarias gariepinus and the cichlid Oreochromis mossambicus. Length-at-maximum-selectivity (ø) and length-at-50%-sexual-maturity (Lm₅₀) for each of the two species showed that although they were selected into the four fishing sectors at lengths above maturity, maximum selectivity into the long line occurred at a length before maturity for O. mossambicus. In addition, the width of the gamma selectivity function (σ) indicated that a considerable proportion of juveniles of the two species were also selected. Therefore, it was decided that management for the floodplain be centred on controlling over-fishing and preserving the spawner stock, by banning seine and mosquito nets, and closing river-floodplain and permanently connected lagoons to fishing during the low flood regime. There were significant seasonal variations in CPUE, lowest in the low flood, and highest during the peak flood regime. Sectioned otoliths were used to determine the age and growth of the two principal species in the floodplain. Marginal zone analysis revealed that annulus formation in all the species occurred during the period of low air and water temperatures, high evaporation and receding water levels, hence a high rate of desiccation and negative water budget. For O. mossambicus, maximum age reached was 6 years while in C. gariepinus it was 9 years. The 3-parameter von Bertalanffy growth model adequately described growth as lt = 177.6(1-e⁻·⁴⁴⁽t ⁺ ¹·⁴³⁾) mm TL for O. mossambicus and lt = 502.9(1-e⁻°·³¹⁽t ⁺ ¹·⁹²⁾) mm TL for C. gariepinus. Female O. mossambicus reached 50%-sexual-maturity at 109 mm SL, while males matured at 105 mm, and both male and female C. gariepinus reached Lm₅₀ at 249 mm SL. The breeding seasons of both O. mossambicus and Clarias gariepinus were between September and March, with modal peaks in January and November, respectively. The annual total mortality rates (Z) were 0.62 ± 0.18 yr⁻¹ for O. mossambicus and 0.93 ± 0.47 yr⁻¹ for C. gariepinus. The mean empirical estimates of natural mortality (M) were 0.46 yr⁻¹ for O. mossambicus and 0.50 year⁻¹ for C. gariepinus, and fishing mortality (F) was calculated as 0.16 yr⁻¹ for O. mossambicus and 0.43 yr⁻¹ for C. gariepinus. The overall exploitation level (Z/K) was 1.41 for O. mossambicus and 3.01 for C. gariepinus. Given that the Z/K ratio was >1, it was asserted that both O. mossambicus and C. gariepinus were mortality-dominated and fairly heavily exploited. However, potential for sustainable exploitation existed since both species showed signs of resilience due short longevity and high rate of natural mortality. Given the limitation of simple exponential models of fish mortality and growth under the situation of seasonal fluctuation of water levels, a simple predictive hydroclimatic- fisheries model was developed. The model predicted the life-history and production parameters fairly accurately (0.53 ≤ r² ≥ 0.98, p ≤ 0.05), and showed that environmental and biological events in the floodplain significantly (0.43 ≤ r² ≥ 0.91, p ≤ 0.05) followed the periodic function of time (day-of-the-year), hence, strongly seasonal. In addition, the flood-pulse preceded all the major biological events, with predicted phase lags established at 55.6º for peak flood, 157.2º, 260.1º, 334.6º and 341.4º for condition factor for O. mossambicus, recruitment, spawning period for O. mossambicus and C. gariepinus, respectively. Therefore, it was recommended that water obstruction on the Shire River must ensure sufficient water flow during the peak flood and spawning period to allow flooding and inundation of the floodplain in order to create habitat favourable for spawning and feeding as well as improve recruitment.
- Full Text:
- Date Issued: 2005
- Authors: Chimatiro, Sloans Kalumba
- Date: 2005
- Subjects: Shire River Valley (Malawi and Mozambique) Fisheries -- Malawi
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5243 , http://hdl.handle.net/10962/d1005086
- Description: Fishes of African floodplains typically comprise populations having short life cycles, relatively few age groups, more generalised feeding behaviour, and which experience spawning success that is strongly influenced by abiotic factors such as hydrological regime of the river, climatic seasonality and habitat characteristics. In addition, African river-floodplain ecosystems do not have appropriate predictive models for estimating yield in these ecosystems. While most predictive models developed to date for floodplain fisheries have taken into account morpho-edaphic factors, they have generally excluded climatic factors as a mega-determinant of the variability of floodplain fisheries. The principle aim of this thesis has been to develop a predictive management model that incorporates data on essential biological aspects of the target species, characteristics of the habitat as well as overall climatic factors, and thus allow for adaptive management of the fisheries in a continuously fluctuating floodplain environment. Lower Shire Floodplain (34 ⁰ 45’ – 35 ⁰ E and 16 ⁰ 00’-17 ⁰ 15’ S) in Malawi, one of the major rivers-floodplains in the Zambezi Basin, was used to test this type of model. The major hypothesis tested in this study was that “the dynamics of the fishery of Lower Shire Floodplain are driven by and adapted to the seasonal, but predictable, hydro-climatic regime of the floodplain”. The specific objectives were: to describe the floodplain’s climate and hydrological pattern; to develop a quantitative characterisation of the major habitats of the Lower Shire Floodplain; to assess the fishery in terms of size, gear utilisation, gear selectivity and yield; to assess the biological parameters of the target species, necessary for the management of the fishery; to analyse how water fluctuation in the floodplain affects the recruitment and life history of the two target species; and to develop of a predictive hydro-climatic model to benefit the management of the fisheries. The climate of the floodplain was characterised by low (765 ± 198 mm) and fairly variable (Cv = 27%) rainfall, which largely occurred between December and January. The area was generally humid (mean RH 68%), with mild to hot (25- 33ºC) and variable monthly mean diurnal (12ºC) temperature. Four quarterly hydro-climatic seasons were identified and comprised: Quarter 1 (Jul-Sep) characterised by hot, dry weather with a low flood regime; Quarter 2 (Oct-Dec) hot, windy, wet weather with low-but-rising flood regime; Quarter 3 (Jan-Mar) hot humid, wet weather with the flood regime at peak; and Quarter 4 (Apr-Jun) humid and cool weather with receding flood regime. The annual hydrograph of the floodplain was represented by four categories of flood regime as: low (Jul-Sept), low-but-rising (Oct-Dec), peak (Jan- Mar), and falling (Apr-Jun). The floodplain experienced a water deficit of 95.1 mm.year⁻¹, and it was hypothesised that ground water recharge maintained water in the floodplain the rest of the year. Three major habitats were identified in the floodplain. The river-floodplain, characterised by deep fast-flowing water, sandy substrate and little emergent vegetation; the permanently connected lagoons, were shallow (≤ 2 m) with sandymud bottom and slow flowing water; and the seasonally connected lagoons had slowflowing stagnant water, with comparatively more emergent and floating vegetation. Physicochemical characteristics of the habitats varied significantly with hydroclimatic seasons (one-way ANOVA, p ≤ 0.05), indicating the influence of flood regime, which joined the habitats in a non-equilibrial spatial distribution. Consequently, during receding and low flood regimes river-floodplain and permanently connected lagoons exhibited similar characteristics while all three habitats had similar characteristics during the rising and peak flood regimes. It was, therefore, concluded that in floodplains, habitats shift horizontally and vertically according to the water level. Gill nets, cast nets, long line, and fish traps accounted for 99% of the total count of gears, and hence considered the major fishing sectors. Two principal species in the floodplain were the catfish Clarias gariepinus and the cichlid Oreochromis mossambicus. Length-at-maximum-selectivity (ø) and length-at-50%-sexual-maturity (Lm₅₀) for each of the two species showed that although they were selected into the four fishing sectors at lengths above maturity, maximum selectivity into the long line occurred at a length before maturity for O. mossambicus. In addition, the width of the gamma selectivity function (σ) indicated that a considerable proportion of juveniles of the two species were also selected. Therefore, it was decided that management for the floodplain be centred on controlling over-fishing and preserving the spawner stock, by banning seine and mosquito nets, and closing river-floodplain and permanently connected lagoons to fishing during the low flood regime. There were significant seasonal variations in CPUE, lowest in the low flood, and highest during the peak flood regime. Sectioned otoliths were used to determine the age and growth of the two principal species in the floodplain. Marginal zone analysis revealed that annulus formation in all the species occurred during the period of low air and water temperatures, high evaporation and receding water levels, hence a high rate of desiccation and negative water budget. For O. mossambicus, maximum age reached was 6 years while in C. gariepinus it was 9 years. The 3-parameter von Bertalanffy growth model adequately described growth as lt = 177.6(1-e⁻·⁴⁴⁽t ⁺ ¹·⁴³⁾) mm TL for O. mossambicus and lt = 502.9(1-e⁻°·³¹⁽t ⁺ ¹·⁹²⁾) mm TL for C. gariepinus. Female O. mossambicus reached 50%-sexual-maturity at 109 mm SL, while males matured at 105 mm, and both male and female C. gariepinus reached Lm₅₀ at 249 mm SL. The breeding seasons of both O. mossambicus and Clarias gariepinus were between September and March, with modal peaks in January and November, respectively. The annual total mortality rates (Z) were 0.62 ± 0.18 yr⁻¹ for O. mossambicus and 0.93 ± 0.47 yr⁻¹ for C. gariepinus. The mean empirical estimates of natural mortality (M) were 0.46 yr⁻¹ for O. mossambicus and 0.50 year⁻¹ for C. gariepinus, and fishing mortality (F) was calculated as 0.16 yr⁻¹ for O. mossambicus and 0.43 yr⁻¹ for C. gariepinus. The overall exploitation level (Z/K) was 1.41 for O. mossambicus and 3.01 for C. gariepinus. Given that the Z/K ratio was >1, it was asserted that both O. mossambicus and C. gariepinus were mortality-dominated and fairly heavily exploited. However, potential for sustainable exploitation existed since both species showed signs of resilience due short longevity and high rate of natural mortality. Given the limitation of simple exponential models of fish mortality and growth under the situation of seasonal fluctuation of water levels, a simple predictive hydroclimatic- fisheries model was developed. The model predicted the life-history and production parameters fairly accurately (0.53 ≤ r² ≥ 0.98, p ≤ 0.05), and showed that environmental and biological events in the floodplain significantly (0.43 ≤ r² ≥ 0.91, p ≤ 0.05) followed the periodic function of time (day-of-the-year), hence, strongly seasonal. In addition, the flood-pulse preceded all the major biological events, with predicted phase lags established at 55.6º for peak flood, 157.2º, 260.1º, 334.6º and 341.4º for condition factor for O. mossambicus, recruitment, spawning period for O. mossambicus and C. gariepinus, respectively. Therefore, it was recommended that water obstruction on the Shire River must ensure sufficient water flow during the peak flood and spawning period to allow flooding and inundation of the floodplain in order to create habitat favourable for spawning and feeding as well as improve recruitment.
- Full Text:
- Date Issued: 2005
The degradation of lignocellulose in a biologically-generated sulphidic environment
- Authors: Roman, Henry James
- Date: 2005
- Subjects: Lignocellulose Sulfides Lignin Lignocellulose -- Biodegradation Mines and mineral resources -- Waste disposal Acid mine drainage
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3997 , http://hdl.handle.net/10962/d1004057
- Description: South Africa is renowned for its mining industry. The period over which the polluted waters from the existing and abandoned mines will require treatment has driven research into the development of passive treatment systems. These waters are characterised by a low pH, high concentrations of heavy metals, high levels of sulphate salts and low concentrations of organic material. The biological treatment of these waters has been a subject of increasing focus as an alternative to physicochemical treatment. The utilisation of lignocellulose as a carbon source has been restricted by the amount of reducing equivalents available within the lignocellulose matrix. After a few months of near 100% sulphate reduction, it was found that although there was a large fraction of lignin and cellulose remaining, sulphate reduction was reduced to less than 20%. The present study demonstrated that lignocellulose can be utilised as a carbon source for sulphate reduction. It was established that lignocellulose degradation was enhanced under biosulphidogenic conditions and that lignin could be degraded by a sulphate reducing microbial consortium. It was established using lignin model compounds synthesized in our laboratory, that the bonds within the lignin polymer can be cleaved within the sulphidic environment. The presence of cellulolytic enzymes, using CMCase as a marker enzyme, was detected within the sulphate reducing microbial consortium. Based on the results obtained a descriptive model was formulated for the degradation of lignocellulose under biosulphidogenic conditions. It was determined that the initial reduction in sulphate observed using lignocellulose as a carbon source was due to the easily extractable components. The degradation of which resulted in the production of sulphide, which aided in the degradation of lignin, allowing greater access to cellulose. Once the easily extractable material is exhausted, the cycle is halted, unless the sulphide production can be maintained. This is the focus of an ongoing project, testing the hypothesis that an easy to assimilate carbon source added after exhaustion of the easily extractable material, can maintain the sulphide production.
- Full Text:
- Date Issued: 2005
- Authors: Roman, Henry James
- Date: 2005
- Subjects: Lignocellulose Sulfides Lignin Lignocellulose -- Biodegradation Mines and mineral resources -- Waste disposal Acid mine drainage
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3997 , http://hdl.handle.net/10962/d1004057
- Description: South Africa is renowned for its mining industry. The period over which the polluted waters from the existing and abandoned mines will require treatment has driven research into the development of passive treatment systems. These waters are characterised by a low pH, high concentrations of heavy metals, high levels of sulphate salts and low concentrations of organic material. The biological treatment of these waters has been a subject of increasing focus as an alternative to physicochemical treatment. The utilisation of lignocellulose as a carbon source has been restricted by the amount of reducing equivalents available within the lignocellulose matrix. After a few months of near 100% sulphate reduction, it was found that although there was a large fraction of lignin and cellulose remaining, sulphate reduction was reduced to less than 20%. The present study demonstrated that lignocellulose can be utilised as a carbon source for sulphate reduction. It was established that lignocellulose degradation was enhanced under biosulphidogenic conditions and that lignin could be degraded by a sulphate reducing microbial consortium. It was established using lignin model compounds synthesized in our laboratory, that the bonds within the lignin polymer can be cleaved within the sulphidic environment. The presence of cellulolytic enzymes, using CMCase as a marker enzyme, was detected within the sulphate reducing microbial consortium. Based on the results obtained a descriptive model was formulated for the degradation of lignocellulose under biosulphidogenic conditions. It was determined that the initial reduction in sulphate observed using lignocellulose as a carbon source was due to the easily extractable components. The degradation of which resulted in the production of sulphide, which aided in the degradation of lignin, allowing greater access to cellulose. Once the easily extractable material is exhausted, the cycle is halted, unless the sulphide production can be maintained. This is the focus of an ongoing project, testing the hypothesis that an easy to assimilate carbon source added after exhaustion of the easily extractable material, can maintain the sulphide production.
- Full Text:
- Date Issued: 2005
The design and evaluation of a short-term group psychotherapy model for survivors of a first myocardial infarction
- Authors: Frewen, Sharon H
- Date: 2005
- Subjects: Health -- Psychological aspects , Medicine and psychology , Coronary heart disease -- Psychological aspects , Type A behavior , Stress (Psychology)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3247 , http://hdl.handle.net/10962/d1015041
- Description: There is extensive evidence that the rehabilitation of individuals with coronary heart disease needs to include psychological components to complement the exercise and dietary recommendations that are normally provided. However, psychological aspects have not been integrated into medical care in South Africa to any significant degree. Psychological interventions overseas have included the modification of the Type A behaviour pattern, stress management, cognitive restructuring, relaxation techniques, improved communication skills, the identification and expression of emotions, and emotional support. The aim of the present study was to design a short-term group intervention which incorporated these aspects and which included an exploration of the mind-body experience post infarct. In addition, the intervention aimed to increase participants' awareness of the compensatory dynamics of the Type A behaviour pattern. The intervention was tailored to South African conditions and was evaluated by means of a multiple case study design. The intervention was delivered to a group of nine coronary heart disease patients which included six survivors of myocardial infarction, the remaining participants having undergone a by-pass operation. Data included weekly feedback sheets evaluating each session, repeated measures on the Profile of Mood States, the Jenkins Activity Survey, a Spouse Rating Scale and extensive qualitative data on each participant including tape recordings of each session and data collected from a series of interviews before, during and after the programme. The feedback sheets and recordings of the sessions were used as a basis for recommendations for revising the content and structure of the programme for future use. Case narratives were written for three of the participants and provided an in-depth look at how and why individual changes did or did not occur in response to the intervention. In addition, the case narratives revealed the role played by the compensatory dynamics of the Type A behaviour pattern in complicating rehabilitation for survivors of myocardial infarction. Two participants were offered a series of individual sessions at 18-month follow-up and the material from these sessions was also used to aid in the interpretation of the data. The content of the 18-month follow-up sessions provided evidence for the importance of conducting a developmental analysis of the origins of low self-esteem and insecurity that maintain and drive the Type A behaviour pattern. In these sessions, this analysis provided the basis for a brief focused psychodynamic psychotherapy that facilitated marked changes that had not been achieved in the 12-week structured group intervention. It is recommended that future research investigate the use of brief psychodynamic psychotherapy on an individual basis as a complement to a group intervention focusing on psycho-education, building social support and management of problematic emotions in everyday situations.
- Full Text:
- Date Issued: 2005
- Authors: Frewen, Sharon H
- Date: 2005
- Subjects: Health -- Psychological aspects , Medicine and psychology , Coronary heart disease -- Psychological aspects , Type A behavior , Stress (Psychology)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3247 , http://hdl.handle.net/10962/d1015041
- Description: There is extensive evidence that the rehabilitation of individuals with coronary heart disease needs to include psychological components to complement the exercise and dietary recommendations that are normally provided. However, psychological aspects have not been integrated into medical care in South Africa to any significant degree. Psychological interventions overseas have included the modification of the Type A behaviour pattern, stress management, cognitive restructuring, relaxation techniques, improved communication skills, the identification and expression of emotions, and emotional support. The aim of the present study was to design a short-term group intervention which incorporated these aspects and which included an exploration of the mind-body experience post infarct. In addition, the intervention aimed to increase participants' awareness of the compensatory dynamics of the Type A behaviour pattern. The intervention was tailored to South African conditions and was evaluated by means of a multiple case study design. The intervention was delivered to a group of nine coronary heart disease patients which included six survivors of myocardial infarction, the remaining participants having undergone a by-pass operation. Data included weekly feedback sheets evaluating each session, repeated measures on the Profile of Mood States, the Jenkins Activity Survey, a Spouse Rating Scale and extensive qualitative data on each participant including tape recordings of each session and data collected from a series of interviews before, during and after the programme. The feedback sheets and recordings of the sessions were used as a basis for recommendations for revising the content and structure of the programme for future use. Case narratives were written for three of the participants and provided an in-depth look at how and why individual changes did or did not occur in response to the intervention. In addition, the case narratives revealed the role played by the compensatory dynamics of the Type A behaviour pattern in complicating rehabilitation for survivors of myocardial infarction. Two participants were offered a series of individual sessions at 18-month follow-up and the material from these sessions was also used to aid in the interpretation of the data. The content of the 18-month follow-up sessions provided evidence for the importance of conducting a developmental analysis of the origins of low self-esteem and insecurity that maintain and drive the Type A behaviour pattern. In these sessions, this analysis provided the basis for a brief focused psychodynamic psychotherapy that facilitated marked changes that had not been achieved in the 12-week structured group intervention. It is recommended that future research investigate the use of brief psychodynamic psychotherapy on an individual basis as a complement to a group intervention focusing on psycho-education, building social support and management of problematic emotions in everyday situations.
- Full Text:
- Date Issued: 2005
The development of a cultural family business model of good governance for Greek family businesses in South Africa
- Adendorff, Christian Michael
- Authors: Adendorff, Christian Michael
- Date: 2005
- Subjects: Family-owned business enterprises -- South Africa Greeks -- South Africa Greeks -- South Africa -- Social life and customs Corporate governance -- South Africa South Africa -- Economic conditions
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1163 , http://hdl.handle.net/10962/d1002779
- Description: Never in the history of the South African nation has the entrepreneurial spirit been more alive. Since the opening of international doors, after the 1994 elections, South Africa has experienced the explosive growth of transnational entrepreneurship. An enduring aspect of the explosion of such economic activity is the need for "good governance" and the need for governance education in South Africa and the rest of the continent has never been greater. The size of the family business component of the South Aftican economy suggests that it is the predominant way of doing business in South Africa. Of importance to this study is the estimate that approximately 95 % of all Greek businesses in South Africa can be classified as family businesses. The sustainability of Greek family businesses requires that they maintain good governance practices that are economically and environmentally acceptable to all stakeholders. It also requires that the next generation of Greek entrepreneurs balance good governance for the businesses as well as for the family. The primary objective of this study was to identify and explore the internal factors that influence and determine good governance to ensure the survival, growth and sustainability of Greek family businesses in South Africa. The secondary research objectives pertained to the underlying dimensions of good governance and required an exploration of the different governance concerns in relation to specific South African Greek behaviour and characteristics. A theoretical model of good governance factors was proposed and tested using Structural Equation Modeling. The study found that perceived good governance in a South African Greek family business context needs to be measured in terms of three factors, namely risk control, the internal regulatory environment and the protection of the stakeholders' interest. The study dealt further with the secondary sources effecting governance for South African businesses and was based on the latest report by the King Commission. An important finding is that the cross cultural aspect of family business governance must now be considered when conducting such research as more and more emphasis is placed on the good governance of all businesses.
- Full Text:
- Date Issued: 2005
- Authors: Adendorff, Christian Michael
- Date: 2005
- Subjects: Family-owned business enterprises -- South Africa Greeks -- South Africa Greeks -- South Africa -- Social life and customs Corporate governance -- South Africa South Africa -- Economic conditions
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1163 , http://hdl.handle.net/10962/d1002779
- Description: Never in the history of the South African nation has the entrepreneurial spirit been more alive. Since the opening of international doors, after the 1994 elections, South Africa has experienced the explosive growth of transnational entrepreneurship. An enduring aspect of the explosion of such economic activity is the need for "good governance" and the need for governance education in South Africa and the rest of the continent has never been greater. The size of the family business component of the South Aftican economy suggests that it is the predominant way of doing business in South Africa. Of importance to this study is the estimate that approximately 95 % of all Greek businesses in South Africa can be classified as family businesses. The sustainability of Greek family businesses requires that they maintain good governance practices that are economically and environmentally acceptable to all stakeholders. It also requires that the next generation of Greek entrepreneurs balance good governance for the businesses as well as for the family. The primary objective of this study was to identify and explore the internal factors that influence and determine good governance to ensure the survival, growth and sustainability of Greek family businesses in South Africa. The secondary research objectives pertained to the underlying dimensions of good governance and required an exploration of the different governance concerns in relation to specific South African Greek behaviour and characteristics. A theoretical model of good governance factors was proposed and tested using Structural Equation Modeling. The study found that perceived good governance in a South African Greek family business context needs to be measured in terms of three factors, namely risk control, the internal regulatory environment and the protection of the stakeholders' interest. The study dealt further with the secondary sources effecting governance for South African businesses and was based on the latest report by the King Commission. An important finding is that the cross cultural aspect of family business governance must now be considered when conducting such research as more and more emphasis is placed on the good governance of all businesses.
- Full Text:
- Date Issued: 2005
The development of an electrochemical process for the production of para-substituted di-hydroxy benzenes
- Authors: Rautenbach, Daniel
- Date: 2005
- Subjects: Phenol , Benzene
- Language: English
- Type: Thesis , Doctoral , DTech (Science)
- Identifier: vital:10367 , http://hdl.handle.net/10948/159 , Phenol , Benzene
- Description: The project was concerned with the investigation of the electrochemical oxidation of various phenols, and to develop a viable reaction system for the production of the respective hydroquinones. Current production routes utilizing phenol as starting material have the limitations of using large amounts of acids, having to be stopped at low conversions and producing a mixture of the hydroquinones and catechols. Of the possible routes to the respective hydroquinones from the various phenols, the electrochemical oxidation of these phenols offers commercial and environmental advantages and hence formed the theme of the investigation. The synthetic possibilities proved to be more prevalent in a system when the electrochemical oxidation of these phenols was performed in an aqueous medium utilizing an organic co-solvent. Results obtained during this investigation made it possible to make certain predications about the mechanism taking place. This was found to depend on the anode material used for the oxidation. The results showed that the process developed for the electrochemical oxidation of these phenols, yields mainly the para-isomers of the respective hydroquinones and benzoquinones in good yields and selectivities, with fair current efficiencies and good mass balances at high conversions. For example: * Phenol (batch) 8 F: 345% current efficiency, 70% hydroquinone, 6% catechol, 9% benzoquinone, 9% phenol and 94 mass balance. * 2-Tert-butylphenol (flow) 10 F: 37% current efficiency, 65% hydroquinone, 33% benzoquinone, 2% phenol and 100% mass balance. * 2,6-Di-tert-butylphenol (flow) 11 F: 23% current efficiency, 92 % hydroquinone, 6% benzoquinone, 1% phenol and 99% mass balance. The developed electrochemical oxidation system offers the following advantages over previous and current methods: simplified isolation and extraction procedures, smaller amounts of acid usage, reasonably selective synthesis of the para-isomer and a less corrosive system all at high conversions.
- Full Text:
- Date Issued: 2005
- Authors: Rautenbach, Daniel
- Date: 2005
- Subjects: Phenol , Benzene
- Language: English
- Type: Thesis , Doctoral , DTech (Science)
- Identifier: vital:10367 , http://hdl.handle.net/10948/159 , Phenol , Benzene
- Description: The project was concerned with the investigation of the electrochemical oxidation of various phenols, and to develop a viable reaction system for the production of the respective hydroquinones. Current production routes utilizing phenol as starting material have the limitations of using large amounts of acids, having to be stopped at low conversions and producing a mixture of the hydroquinones and catechols. Of the possible routes to the respective hydroquinones from the various phenols, the electrochemical oxidation of these phenols offers commercial and environmental advantages and hence formed the theme of the investigation. The synthetic possibilities proved to be more prevalent in a system when the electrochemical oxidation of these phenols was performed in an aqueous medium utilizing an organic co-solvent. Results obtained during this investigation made it possible to make certain predications about the mechanism taking place. This was found to depend on the anode material used for the oxidation. The results showed that the process developed for the electrochemical oxidation of these phenols, yields mainly the para-isomers of the respective hydroquinones and benzoquinones in good yields and selectivities, with fair current efficiencies and good mass balances at high conversions. For example: * Phenol (batch) 8 F: 345% current efficiency, 70% hydroquinone, 6% catechol, 9% benzoquinone, 9% phenol and 94 mass balance. * 2-Tert-butylphenol (flow) 10 F: 37% current efficiency, 65% hydroquinone, 33% benzoquinone, 2% phenol and 100% mass balance. * 2,6-Di-tert-butylphenol (flow) 11 F: 23% current efficiency, 92 % hydroquinone, 6% benzoquinone, 1% phenol and 99% mass balance. The developed electrochemical oxidation system offers the following advantages over previous and current methods: simplified isolation and extraction procedures, smaller amounts of acid usage, reasonably selective synthesis of the para-isomer and a less corrosive system all at high conversions.
- Full Text:
- Date Issued: 2005
The development of best practice guidelines for the contingency management of health-related absenteeism in the motor manufacturing industry
- Authors: Werner, Amanda
- Date: 2005
- Subjects: Sick leave , Absenteeism (Labor) , Contingency theory (Management) , Automobile industry and trade -- South Africa
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:9379 , http://hdl.handle.net/10948/160 , Sick leave , Absenteeism (Labor) , Contingency theory (Management) , Automobile industry and trade -- South Africa
- Description: The research problem in this study was to identify best practices for the contingency management of health-related absenteeism. To achieve this goal, the following actions were taken: A literature study was conducted to identify the scope and impact of health-related absenteeism on organisations and the legal parameters within which health-related absenteeism should be managed. A literature study was also conducted to identify strategies to prevent and reduce health-related absenteeism and strategies to ensure the continuous provision of products and services in periods of high absenteeism. The theoretical study focused on the management of absenteeism, wellness, ill-health/mental problems and HIV/AIDS, as well as contingency strategies aimed at maintaining production and service provision. iii The findings from the literature study were integrated into a model of best practices for the contingency management of health-related absenteeism. This model was used as a basis for the development of a survey questionnaire to determine whether senior human resources practitioners, occupational health practitioners or line managers, who were responsible for the management of health-related absenteeism in organisations, agreed with the best practice guidelines developed in the study. The survey was conducted in the motor and motor component industry in the Nelson Mandela Metropolitan Municipality and Buffalo City Metropole. The empirical results from the study showed a strong concurrence with the best practices guidelines developed in the study, with the exception of the strategies aimed at maintaining undisrupted production and service provision during periods of high absenteeism. In particular, disagreement was shown with regard to alternative work arrangements such as flexible work-hours, a compressed workweek, telecommuting and job-sharing. Absenteeism, in general, is an issue that organisations are challenged with on a daily basis. The proliferation of various diseases, specifically HIV/AIDS, is contributing to this problem. An integrated and strategic approach is required to deal effectively and constructively with the immediate and expected future impact of health-related issues on absenteeism. Organisations could use the best practices guidelines, identified in this study, as a mechanism to benchmark how well they manage health-related absenteeism
- Full Text:
- Date Issued: 2005
- Authors: Werner, Amanda
- Date: 2005
- Subjects: Sick leave , Absenteeism (Labor) , Contingency theory (Management) , Automobile industry and trade -- South Africa
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:9379 , http://hdl.handle.net/10948/160 , Sick leave , Absenteeism (Labor) , Contingency theory (Management) , Automobile industry and trade -- South Africa
- Description: The research problem in this study was to identify best practices for the contingency management of health-related absenteeism. To achieve this goal, the following actions were taken: A literature study was conducted to identify the scope and impact of health-related absenteeism on organisations and the legal parameters within which health-related absenteeism should be managed. A literature study was also conducted to identify strategies to prevent and reduce health-related absenteeism and strategies to ensure the continuous provision of products and services in periods of high absenteeism. The theoretical study focused on the management of absenteeism, wellness, ill-health/mental problems and HIV/AIDS, as well as contingency strategies aimed at maintaining production and service provision. iii The findings from the literature study were integrated into a model of best practices for the contingency management of health-related absenteeism. This model was used as a basis for the development of a survey questionnaire to determine whether senior human resources practitioners, occupational health practitioners or line managers, who were responsible for the management of health-related absenteeism in organisations, agreed with the best practice guidelines developed in the study. The survey was conducted in the motor and motor component industry in the Nelson Mandela Metropolitan Municipality and Buffalo City Metropole. The empirical results from the study showed a strong concurrence with the best practices guidelines developed in the study, with the exception of the strategies aimed at maintaining undisrupted production and service provision during periods of high absenteeism. In particular, disagreement was shown with regard to alternative work arrangements such as flexible work-hours, a compressed workweek, telecommuting and job-sharing. Absenteeism, in general, is an issue that organisations are challenged with on a daily basis. The proliferation of various diseases, specifically HIV/AIDS, is contributing to this problem. An integrated and strategic approach is required to deal effectively and constructively with the immediate and expected future impact of health-related issues on absenteeism. Organisations could use the best practices guidelines, identified in this study, as a mechanism to benchmark how well they manage health-related absenteeism
- Full Text:
- Date Issued: 2005