A contribution towards an understanding of the intensive tank culture of an ornamental Cichlid, Aulonocara Baenschi, from Chipoka, Lake Malawi
- Authors: Impson, N D (Neville Dean)
- Date: 1988
- Subjects: Cichlids -- Nysas, Lake , Cichlids -- Nyasa, Lake -- Physiology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5208 , http://hdl.handle.net/10962/d1004596 , Cichlids -- Nysas, Lake , Cichlids -- Nyasa, Lake -- Physiology
- Description: The intensive tank culture of ornamental mouthbrooding cichlids poses several problems which limit their aquaculture potential. This project addressed some of these problems for Aulonocara baenschi. The production of juveniles in 2501 aquaria was accelerated when: a) aquaria were equipped with refuges, b) females of less than 70mm in standard length were used as broodstock, c) mouthbrooding females were replaced with gravid females at seven day intervals, and d) embryos were removed from the mouths of females at replacement times for artificial incubation. Two sex ratios also accelerated juvenile production. The sex ratio (male:females) 1:30 yielded the highest spawning returns per tank, and therefore represented the most effective utilization of aquarium space (a critical consideration for the small-scale culturist). Contrastingly, the sex ratio 1:12 yielded the highest clutch sizes and a high percentage female spawning return, and therefore represented the most effective utilization of broodstock (an important consideration for culturists inhibited by financial constraints or having an abundance of culture vessels). The reproductive behaviour of A. baenschi was described. Emphasis was given to aspects of reproduction of relevance to culture, for example; spawning times and seasons, clutch size and its relationship with female size, age and size of sexes at first spawning, embryo development rate and size of first swimming juveniles. The slow growth rate of juveniles, combined with a late attainment of marketable size (± seven months) was a major limitation affecting the cuIture potential of A. baenschi. Two factors favouring the cuIture of this species was the high survival rate recorded for both adults and juveniles, and the comparatively high prices fetched by fish on domestic wholesale markets (R4,00 per fish). It is recommended that A. baenschi should not be cultured exclusively for the relatively small South African ornamental fish market. A more profitable strategy for domestic culturists should involve a major production effort with A. baenschi and other desirable species of Aulonocara (e.g . A. ethelwynnae; A. hansbaenschi; A. stuartgranti & A. maylandi) for foreign markets (in particular, the U.S.A.; Western Europe & Japan). Not only are these markets massive, but prevailing exchange rates of the Rand with these currencies favour such a strategy.
- Full Text:
- Date Issued: 1988
- Authors: Impson, N D (Neville Dean)
- Date: 1988
- Subjects: Cichlids -- Nysas, Lake , Cichlids -- Nyasa, Lake -- Physiology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5208 , http://hdl.handle.net/10962/d1004596 , Cichlids -- Nysas, Lake , Cichlids -- Nyasa, Lake -- Physiology
- Description: The intensive tank culture of ornamental mouthbrooding cichlids poses several problems which limit their aquaculture potential. This project addressed some of these problems for Aulonocara baenschi. The production of juveniles in 2501 aquaria was accelerated when: a) aquaria were equipped with refuges, b) females of less than 70mm in standard length were used as broodstock, c) mouthbrooding females were replaced with gravid females at seven day intervals, and d) embryos were removed from the mouths of females at replacement times for artificial incubation. Two sex ratios also accelerated juvenile production. The sex ratio (male:females) 1:30 yielded the highest spawning returns per tank, and therefore represented the most effective utilization of aquarium space (a critical consideration for the small-scale culturist). Contrastingly, the sex ratio 1:12 yielded the highest clutch sizes and a high percentage female spawning return, and therefore represented the most effective utilization of broodstock (an important consideration for culturists inhibited by financial constraints or having an abundance of culture vessels). The reproductive behaviour of A. baenschi was described. Emphasis was given to aspects of reproduction of relevance to culture, for example; spawning times and seasons, clutch size and its relationship with female size, age and size of sexes at first spawning, embryo development rate and size of first swimming juveniles. The slow growth rate of juveniles, combined with a late attainment of marketable size (± seven months) was a major limitation affecting the cuIture potential of A. baenschi. Two factors favouring the cuIture of this species was the high survival rate recorded for both adults and juveniles, and the comparatively high prices fetched by fish on domestic wholesale markets (R4,00 per fish). It is recommended that A. baenschi should not be cultured exclusively for the relatively small South African ornamental fish market. A more profitable strategy for domestic culturists should involve a major production effort with A. baenschi and other desirable species of Aulonocara (e.g . A. ethelwynnae; A. hansbaenschi; A. stuartgranti & A. maylandi) for foreign markets (in particular, the U.S.A.; Western Europe & Japan). Not only are these markets massive, but prevailing exchange rates of the Rand with these currencies favour such a strategy.
- Full Text:
- Date Issued: 1988
An integration of reduction and logic for programming languages
- Authors: Wright, David A
- Date: 1988
- Subjects: Logic programming languages , Programming languages (Electronic computers)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4570 , http://hdl.handle.net/10962/d1002035
- Description: A new declarative language is presented which captures the expressibility of both logic programming languages and functional languages. This is achieved by conditional graph rewriting, with full unification as the parameter passing mechanism. The syntax and semantics are described both formally and informally, and examples are offered to support the expressibility claim made above. The language design is of further interest due to its uniformity and the inclusion of a novel mechanism for type inference in the presence of derived type hierarchies
- Full Text:
- Date Issued: 1988
- Authors: Wright, David A
- Date: 1988
- Subjects: Logic programming languages , Programming languages (Electronic computers)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4570 , http://hdl.handle.net/10962/d1002035
- Description: A new declarative language is presented which captures the expressibility of both logic programming languages and functional languages. This is achieved by conditional graph rewriting, with full unification as the parameter passing mechanism. The syntax and semantics are described both formally and informally, and examples are offered to support the expressibility claim made above. The language design is of further interest due to its uniformity and the inclusion of a novel mechanism for type inference in the presence of derived type hierarchies
- Full Text:
- Date Issued: 1988
An investigation of the structure of the Southern Hemisphere radio-meteor streams
- Authors: Roux, David Gerhardus
- Date: 1988
- Subjects: Radio meteorology -- Southern Hemisphere , Solar system
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5448 , http://hdl.handle.net/10962/d1004587 , Radio meteorology -- Southern Hemisphere , Solar system
- Description: Our current knowledge of the Solar System, with a particular emphasis on the systems of interplanetary objects, is reviewed, and the theory of meteors and the reflection of radio waves from meteoric ionization is then discussed. A description of the meteor radar is given and a method of calibrating the antenna beam is developed. The main project comprises two parts: (a) A general survey of the radar echorate for 20 major and minor meteor streams and the sporadic meteor background, conducted from Grahamstown over the period 1986 April to 1988 January, is described. Definite shower activity was observed for all of the major and some of the minor showers. (b) Based on a scheme proposed by previous workers (Morton & Jones), a method of recovering meteor radiant distributions from the distribution of echo directions is developed. We devise a technique of compensating for possible distortions of the resulting radiant maps, which may arise due to the arisotropic antenna beam. This involves a system of echo-weighting. Radiant maps which showed considerably less distortion than those of the above workers were obtained without the weighting procedure. It is concluded that, although the method in its present form introduces spurious features into the maps, the principle is sound and should eventually be refined to produce the desired compensation
- Full Text:
- Date Issued: 1988
- Authors: Roux, David Gerhardus
- Date: 1988
- Subjects: Radio meteorology -- Southern Hemisphere , Solar system
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5448 , http://hdl.handle.net/10962/d1004587 , Radio meteorology -- Southern Hemisphere , Solar system
- Description: Our current knowledge of the Solar System, with a particular emphasis on the systems of interplanetary objects, is reviewed, and the theory of meteors and the reflection of radio waves from meteoric ionization is then discussed. A description of the meteor radar is given and a method of calibrating the antenna beam is developed. The main project comprises two parts: (a) A general survey of the radar echorate for 20 major and minor meteor streams and the sporadic meteor background, conducted from Grahamstown over the period 1986 April to 1988 January, is described. Definite shower activity was observed for all of the major and some of the minor showers. (b) Based on a scheme proposed by previous workers (Morton & Jones), a method of recovering meteor radiant distributions from the distribution of echo directions is developed. We devise a technique of compensating for possible distortions of the resulting radiant maps, which may arise due to the arisotropic antenna beam. This involves a system of echo-weighting. Radiant maps which showed considerably less distortion than those of the above workers were obtained without the weighting procedure. It is concluded that, although the method in its present form introduces spurious features into the maps, the principle is sound and should eventually be refined to produce the desired compensation
- Full Text:
- Date Issued: 1988
Application of high-performance liquid chromatography for the analysis and pharmocokinetics of mephenoxalone
- Authors: Van der Westhuizen, Fiona
- Date: 1988 , 2013-03-06
- Subjects: High performance liquid chromatography , Central nervous system depressants
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3810 , http://hdl.handle.net/10962/d1004385 , High performance liquid chromatography , Central nervous system depressants
- Description: Mephenoxalone is a mild central nervous system depressant with activity resembling that of meprobamate. Since its introduction in 1961 mephenoxalone has been used as an anxiolytic and as a muscle relaxant, although the latter effect is weak. Preliminary studies on the absorption and disposition of mephenoxalone have been conducted in beagle dogs but no pharmacokinetic data from human studies have been reported, except for a single study in which the biotransformation products present in human urine were identified. Methods presently available for the determination of mephenoxalone in biological fluids lack the sensitivity, specificity and precision required for detailed pharmacokinetic studies. In this study, a rapid, sensitive, precise reverse-phase high-performance liquid chromatographic method with ultraviolet detection at 200nm was employed for the determination of mephenoxalone in biological fluids. Serum and urine samples were prepared for chromatographic analysis using simple liquid-liquid extraction techniques. The application of the assay to pharmacokinetic studies in humans is presented. After administration of a single oral dose of 400mg mephenoxalone dispersed in 150ml water to six young, healthy volunteers, the compound was rapidly absorbed with the peak concentration of 8μg/ml occurring after about 1 hour. The elimination half-life was approximately 3 hours. The drug was extensively metabolized with only about 1 percent of the administered dose being excreted unchanged in the urine after 24 hours. The bioavailability of a newly developed mephenoxalone-containing tablet was also investigated. The drug was absorbed more rapidly from the tablet than from the dispersed dose. This was attributed to a shorter in vivo dissolution time on the basis of in vitro tests, but this effect is not expected to be clinically significant. In addition, two human urinary metabolites of mephenoxalone were identified as unconjugated hydroxylated derivatives using thermospray HPLC-mass spectrometry. The plasma protein-binding properties of mephenoxalone were also investigated.
- Full Text:
- Date Issued: 1988
- Authors: Van der Westhuizen, Fiona
- Date: 1988 , 2013-03-06
- Subjects: High performance liquid chromatography , Central nervous system depressants
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3810 , http://hdl.handle.net/10962/d1004385 , High performance liquid chromatography , Central nervous system depressants
- Description: Mephenoxalone is a mild central nervous system depressant with activity resembling that of meprobamate. Since its introduction in 1961 mephenoxalone has been used as an anxiolytic and as a muscle relaxant, although the latter effect is weak. Preliminary studies on the absorption and disposition of mephenoxalone have been conducted in beagle dogs but no pharmacokinetic data from human studies have been reported, except for a single study in which the biotransformation products present in human urine were identified. Methods presently available for the determination of mephenoxalone in biological fluids lack the sensitivity, specificity and precision required for detailed pharmacokinetic studies. In this study, a rapid, sensitive, precise reverse-phase high-performance liquid chromatographic method with ultraviolet detection at 200nm was employed for the determination of mephenoxalone in biological fluids. Serum and urine samples were prepared for chromatographic analysis using simple liquid-liquid extraction techniques. The application of the assay to pharmacokinetic studies in humans is presented. After administration of a single oral dose of 400mg mephenoxalone dispersed in 150ml water to six young, healthy volunteers, the compound was rapidly absorbed with the peak concentration of 8μg/ml occurring after about 1 hour. The elimination half-life was approximately 3 hours. The drug was extensively metabolized with only about 1 percent of the administered dose being excreted unchanged in the urine after 24 hours. The bioavailability of a newly developed mephenoxalone-containing tablet was also investigated. The drug was absorbed more rapidly from the tablet than from the dispersed dose. This was attributed to a shorter in vivo dissolution time on the basis of in vitro tests, but this effect is not expected to be clinically significant. In addition, two human urinary metabolites of mephenoxalone were identified as unconjugated hydroxylated derivatives using thermospray HPLC-mass spectrometry. The plasma protein-binding properties of mephenoxalone were also investigated.
- Full Text:
- Date Issued: 1988
Aspects of the biology and population dynamics of the geelbek Atractoscion aequidens (Cuvier) (Pisces: Sciaenidae) off the South African coast
- Authors: Griffiths, Marc H
- Date: 1988
- Subjects: Sciaenidae -- South Africa Fish populations -- South Africa Atractoscion Atractoscion -- South Africa -- Ecology Atractoscion -- South Africa -- Physiology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5194 , http://hdl.handle.net/10962/d1001970
- Description: The geelbek Atractoscion aeguidens is an important commercial and recreational linefish species along the South African eastern seaboard . Aspects of its biology and population dynamics were investigated using data collected from various sampling sites along the South African east coast and from catch statistics obtained from both the Sea Fisheries Research Institute (Cape Town), and dealer records. The biological aspects studied included age and growth, reproduction and feeding. It was established that A. aeguidens is a fast growing species with a relatively late age at sexual maturity and a 1:1 sex ratio. Feeding studies revealed that it has become specialized to feed on small pelagic fish. The South African geelbek stock consists of three distinct age related sub-populations, each representing a particular phase in the life cycle. The sub-adults (1-4 yrs) occur in the South West Cape and feed predominantly on anchovy, Engraulis capensis, which they follow, moving inshore in summer and offshore in winter. The adults (5-9 yrs) undergo a seasonal inshore migration to Natal where they spawn in spring. The dynamics of this migration are strongly influenced by the annual movement of their principal prey viz. , Sardinops ocellatus, to that region. As a result the geelbek first arrive in Natal during mid winter. Evidence is also presented to suggest that a significant number of "adolescent " fish (4-5 yrs) undergo limited gonad maturation and a partial migration to at least as far as the South East Cape. Spawning appears to occur offshore. It is postulated that eggs and larvae are transported southwards by the peripheral waters of the Agulhas Current. After spawning the adults probably remain offshore and use the current to aid their return to the South and South West Cape, where they spend summer feeding on the Agulhas Bank. Juveniles (<1 yr) first appear in the South East Cape between January and March. They apparently use this region as a nursery area for almost a year before moving southwards to join the sub-adults in the South West Cape. In the South East Cape, the juveniles feed initially on mysids whereafter they switch to anchovies and pilchards. A preliminary stock assessment using yield per recruit and spawner biomass per recruit models, indicated that despite the current legislation the South African geelbek population is already overexploited. This is largely attributed to high rates of fishing mortality of the migratory adult population. Further management recommendations are therefore proposed. These include a size limit (660 mm FL), derived from an investigation of the interrelationship between natural mortality and somatic growth in a theoretical unexploited cohort, as well as a uniform bag limit for all user groups (5 fish per person per day)
- Full Text:
- Date Issued: 1988
- Authors: Griffiths, Marc H
- Date: 1988
- Subjects: Sciaenidae -- South Africa Fish populations -- South Africa Atractoscion Atractoscion -- South Africa -- Ecology Atractoscion -- South Africa -- Physiology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5194 , http://hdl.handle.net/10962/d1001970
- Description: The geelbek Atractoscion aeguidens is an important commercial and recreational linefish species along the South African eastern seaboard . Aspects of its biology and population dynamics were investigated using data collected from various sampling sites along the South African east coast and from catch statistics obtained from both the Sea Fisheries Research Institute (Cape Town), and dealer records. The biological aspects studied included age and growth, reproduction and feeding. It was established that A. aeguidens is a fast growing species with a relatively late age at sexual maturity and a 1:1 sex ratio. Feeding studies revealed that it has become specialized to feed on small pelagic fish. The South African geelbek stock consists of three distinct age related sub-populations, each representing a particular phase in the life cycle. The sub-adults (1-4 yrs) occur in the South West Cape and feed predominantly on anchovy, Engraulis capensis, which they follow, moving inshore in summer and offshore in winter. The adults (5-9 yrs) undergo a seasonal inshore migration to Natal where they spawn in spring. The dynamics of this migration are strongly influenced by the annual movement of their principal prey viz. , Sardinops ocellatus, to that region. As a result the geelbek first arrive in Natal during mid winter. Evidence is also presented to suggest that a significant number of "adolescent " fish (4-5 yrs) undergo limited gonad maturation and a partial migration to at least as far as the South East Cape. Spawning appears to occur offshore. It is postulated that eggs and larvae are transported southwards by the peripheral waters of the Agulhas Current. After spawning the adults probably remain offshore and use the current to aid their return to the South and South West Cape, where they spend summer feeding on the Agulhas Bank. Juveniles (<1 yr) first appear in the South East Cape between January and March. They apparently use this region as a nursery area for almost a year before moving southwards to join the sub-adults in the South West Cape. In the South East Cape, the juveniles feed initially on mysids whereafter they switch to anchovies and pilchards. A preliminary stock assessment using yield per recruit and spawner biomass per recruit models, indicated that despite the current legislation the South African geelbek population is already overexploited. This is largely attributed to high rates of fishing mortality of the migratory adult population. Further management recommendations are therefore proposed. These include a size limit (660 mm FL), derived from an investigation of the interrelationship between natural mortality and somatic growth in a theoretical unexploited cohort, as well as a uniform bag limit for all user groups (5 fish per person per day)
- Full Text:
- Date Issued: 1988
Aspects of the biology of the musselcracker, Sparodon Durbanensis, and the bronze bream, Pachymetopon grande, (Pisces : Sparidae), with notes on the Eastern Cape recreational rock-angling and spear fisheries
- Authors: Clarke, John Ross
- Date: 1988
- Subjects: Sparidea -- South Africa Sparodon Durbanensis Bream fishing
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5190 , http://hdl.handle.net/10962/d1001966
- Description: The musselcracker, Soarodon durbanensis, and the bronze bream, Pachymetopon arande, are important components of rock-angling and spearfishing catches In the Eastern Cape. Aspects of their biology, including age and growth, reproduction, nursery areas and feeding, were Investigated to provide a basis for the rational exploitation of the resource. Both species are slow-growing and long-lived. Growth in S. durbanensls was described by the von Bertalanffy growth equation: Lt(mm) = 1021.2(1-e⁻°.°⁹°°⁽t ⁻° .⁷°⁹⁾). The von Bertalanffy growth model did not describe the total data set in P. grande, but by excluding the zero and one year old fish the data were described by: Lt(mm) = 461.1(1-e⁻°.¹⁵³⁽t ⁺¹.⁶⁴°⁾). Detailed histological examination of gonadal development showed that S. durbanensis and P. grande are rudimentary hermaphrodites. Both species had restricted breeding seasons which coincided with peak exploitation. Results indicated that both species are group spawners with pelagic eggs. Size at 50% maturity in S. durbanensis and P. grande was determined at 350 and 300mm fork length, respectively, corresponding to ages of 4.5 and 5.5 years. Intertidal pools functioned as nursery areas for S. durbanensis during the first year, whereas subtidal waters were more important for larger juveniles. P. grande juveniles were commonly observed on subtidal weed beds to a depth of 10m. A size-related change in the diet of S. durbanensis was observed. The juveniles were omnivorous, feeding predominantly on gastropods, echinoids and chlorophytes. The adults fed on a variety of large, reef-associated invertebrates. P. grande were omnivorous, with macroalgae being the principal dietary component. This species appears to utilise the storage and extracellular carbohydrates of the macroalgae. Results showed that macroalgal degradation by gut endosymbionts and the utilisation of macroalgal epibionts does not appear to occur in this species. A detailed analysis of catch composition and catch per unit of effort In the Port Elizabeth rock-angling fishery and the Eastern Cape spearfishery emphasised the recreational importance of S. durbanensis and P. grande. The localised distribution, slow growth and late maturation in both species results in their being susceptible to over-exploitation in these size-selective fisheries. Current legislation protecting these fish is discussed in relation to the findings of this study and additional management measures are proposed.
- Full Text:
- Date Issued: 1988
- Authors: Clarke, John Ross
- Date: 1988
- Subjects: Sparidea -- South Africa Sparodon Durbanensis Bream fishing
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5190 , http://hdl.handle.net/10962/d1001966
- Description: The musselcracker, Soarodon durbanensis, and the bronze bream, Pachymetopon arande, are important components of rock-angling and spearfishing catches In the Eastern Cape. Aspects of their biology, including age and growth, reproduction, nursery areas and feeding, were Investigated to provide a basis for the rational exploitation of the resource. Both species are slow-growing and long-lived. Growth in S. durbanensls was described by the von Bertalanffy growth equation: Lt(mm) = 1021.2(1-e⁻°.°⁹°°⁽t ⁻° .⁷°⁹⁾). The von Bertalanffy growth model did not describe the total data set in P. grande, but by excluding the zero and one year old fish the data were described by: Lt(mm) = 461.1(1-e⁻°.¹⁵³⁽t ⁺¹.⁶⁴°⁾). Detailed histological examination of gonadal development showed that S. durbanensis and P. grande are rudimentary hermaphrodites. Both species had restricted breeding seasons which coincided with peak exploitation. Results indicated that both species are group spawners with pelagic eggs. Size at 50% maturity in S. durbanensis and P. grande was determined at 350 and 300mm fork length, respectively, corresponding to ages of 4.5 and 5.5 years. Intertidal pools functioned as nursery areas for S. durbanensis during the first year, whereas subtidal waters were more important for larger juveniles. P. grande juveniles were commonly observed on subtidal weed beds to a depth of 10m. A size-related change in the diet of S. durbanensis was observed. The juveniles were omnivorous, feeding predominantly on gastropods, echinoids and chlorophytes. The adults fed on a variety of large, reef-associated invertebrates. P. grande were omnivorous, with macroalgae being the principal dietary component. This species appears to utilise the storage and extracellular carbohydrates of the macroalgae. Results showed that macroalgal degradation by gut endosymbionts and the utilisation of macroalgal epibionts does not appear to occur in this species. A detailed analysis of catch composition and catch per unit of effort In the Port Elizabeth rock-angling fishery and the Eastern Cape spearfishery emphasised the recreational importance of S. durbanensis and P. grande. The localised distribution, slow growth and late maturation in both species results in their being susceptible to over-exploitation in these size-selective fisheries. Current legislation protecting these fish is discussed in relation to the findings of this study and additional management measures are proposed.
- Full Text:
- Date Issued: 1988
Cleavage of the precursor coat protein of black beetle virus strain w17 in rabbit reticulocyte lysate
- Authors: Blackhurst, Diane Mary
- Date: 1988
- Subjects: Beetles , Insects -- Viruses
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3880 , http://hdl.handle.net/10962/d1001614
- Description: Black beetle virus (BBV) is a bipartite single-stranded RNA virus belonging to the family Nodaviridae. Its host range has been found to be limited to insects. RNA 1, the larger of the two RNA molecules, with a MW of 1,15 x 10⁶ and the smaller RNA 2 with a MW of 0,46 x 10⁶, are both packaged in the same virus particle. The two RNA molecules are translated separately, with RNA 1 coding for protein A of MW 105 x 10³ and RNA 2 coding for protein α of MW 47 x 10³. Protein α is the major capsid protein precursor, which during in vivo maturation is cleaved to form the coat protein β of MW 43 x 10³, and protein γ of MW 5 x 10³. Cell-free translation of BBV (strain W17) mRNA was carried out in rabbit reticulocyte lysates. Protein α was detectable between 0 and 30 minutes after RNA addition. A protein 'β', which was found to co-electrophorese on polyacrylamide gels with authentic β and which was immunoprecipitated by anti-BBV antiserum, was detectable after 30 minutes. Results of this work show that the formation of 'β' could be prevented by the addition of RNase to the lysate, indicating that intact RNA is necessary for α to β cleavage. Arresting protein synthesis by the addition of cycloheximide to the lysate mix did not inhibit the cleavage. The formation of β could also be prevented by cooling the lysate mix to 1°C. Cleavage of α to β still occurred when RNA 2, without the presence of RNA 1, was translated. Therefore the cleavage is not dependent on a translation product of RNA 1. Sedimentation of lysate on sucrose density gradients showed that α to β cleavage was not accompanied by assembly of BBV RNA and protein lnto a viral substructure as has been shown to occur with some viruses, for example certain picornaviruses. Serial dilution of lysate containing α showed that the level of β decreased with increasing dilution, indicating that the cleavage is not mediated by autocatalysis, but by some other unknown factor. Although much work has been carried out on black beetle virus, no work has been published to date concerning α to β cleavage as an indication of assembly in rabbit reticulocyte lysates. Results of these cell-free translation experiments thus indicate that BBV coat protein precursor α, in association with its messenger RNA 2, undergoes a maturation cleavage in the lysate to produce BBV coat protein β. In addition, this cleavage seems to occur without assembly into any intermediate viral structure
- Full Text:
- Date Issued: 1988
- Authors: Blackhurst, Diane Mary
- Date: 1988
- Subjects: Beetles , Insects -- Viruses
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3880 , http://hdl.handle.net/10962/d1001614
- Description: Black beetle virus (BBV) is a bipartite single-stranded RNA virus belonging to the family Nodaviridae. Its host range has been found to be limited to insects. RNA 1, the larger of the two RNA molecules, with a MW of 1,15 x 10⁶ and the smaller RNA 2 with a MW of 0,46 x 10⁶, are both packaged in the same virus particle. The two RNA molecules are translated separately, with RNA 1 coding for protein A of MW 105 x 10³ and RNA 2 coding for protein α of MW 47 x 10³. Protein α is the major capsid protein precursor, which during in vivo maturation is cleaved to form the coat protein β of MW 43 x 10³, and protein γ of MW 5 x 10³. Cell-free translation of BBV (strain W17) mRNA was carried out in rabbit reticulocyte lysates. Protein α was detectable between 0 and 30 minutes after RNA addition. A protein 'β', which was found to co-electrophorese on polyacrylamide gels with authentic β and which was immunoprecipitated by anti-BBV antiserum, was detectable after 30 minutes. Results of this work show that the formation of 'β' could be prevented by the addition of RNase to the lysate, indicating that intact RNA is necessary for α to β cleavage. Arresting protein synthesis by the addition of cycloheximide to the lysate mix did not inhibit the cleavage. The formation of β could also be prevented by cooling the lysate mix to 1°C. Cleavage of α to β still occurred when RNA 2, without the presence of RNA 1, was translated. Therefore the cleavage is not dependent on a translation product of RNA 1. Sedimentation of lysate on sucrose density gradients showed that α to β cleavage was not accompanied by assembly of BBV RNA and protein lnto a viral substructure as has been shown to occur with some viruses, for example certain picornaviruses. Serial dilution of lysate containing α showed that the level of β decreased with increasing dilution, indicating that the cleavage is not mediated by autocatalysis, but by some other unknown factor. Although much work has been carried out on black beetle virus, no work has been published to date concerning α to β cleavage as an indication of assembly in rabbit reticulocyte lysates. Results of these cell-free translation experiments thus indicate that BBV coat protein precursor α, in association with its messenger RNA 2, undergoes a maturation cleavage in the lysate to produce BBV coat protein β. In addition, this cleavage seems to occur without assembly into any intermediate viral structure
- Full Text:
- Date Issued: 1988
Effects of vitamin A on tumour and untransformed cells
- Authors: De Villiers, Diane Lynette
- Date: 1988
- Subjects: Vitamin A , Vitamin A in the body , Cancer -- Prevention
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3881 , http://hdl.handle.net/10962/d1001615
- Description: Vitamin A and its chemical analogues (retinoids) are known to play a role in the maintenance and differentiation of epithelial tissue. Retinoids have been shown to inhibit carcinogenesis in a number of tissues in experimental animals and to inhibit the growth of various untransformed and cancer cell lines in vitro. This study investigated the effect of retinyl acetate supplemented at concentrations of 1 μM, 5 μM, 10 μM and 100 μM to in vitro cultured untransformed LLCMK cells, and transformed BL-6 melanoma and human hepatoma cell lines. A small but non-significant effect of vitamin A addition on the growth of the untransformed cells was observed, while substantial inhibition of proliferation of the two tumour cell lines was found. At the cytotoxic level of 100 μM supplemented vitamin A, all three cell lines showed marked inhibition of growth. This led to an electron microscopy study to examine the ultrastructural effect of the vitamin A addition. At the low non-toxic levels of vitamin A addition (1 - 10 μM), no ultrastructural changes were observed in the untransformed cells. However, at a level of 5 μM and 10 μM vitamin A addition in the tumour cells, an increase in the size of suspected lipid droplets was observed. At the cytotoxic level of 100 μM supplemented vitamin A, large lipid droplets were very apparent, as was much cellular degeneration. This effect was more marked in the tumour cells than in the untransformed cells. The lipid nature of the droplets was confirmed by using the lipid stain, Sudan IV. In order to investigate the effect of added vitamin A at the cell surface level, an ELISA system was used to quantify the level of the cell surface glycoprotein, fibronectin, in the culture media. Vitamin A plays an important role in the production of mature fibronectin by participating in the glycosylation of the molecule. This study showed no major effect of added vitamin A on the release of fibronectin into the culture media. This did not, however, exclude the possibility that the vitamin A was involved in the production and enhanced binding of fibronectin to the cell surface, and was possibly also exerting an effect on the availability of fibronectin receptors. Further studies would, however, be required to substantiate such effects of vitamin A supplementation. No single mechanism of action of vitamin A on tumour cell growth inhibition was identified, but the possibility that at least two mechanisms exist, was suggested
- Full Text:
- Date Issued: 1988
- Authors: De Villiers, Diane Lynette
- Date: 1988
- Subjects: Vitamin A , Vitamin A in the body , Cancer -- Prevention
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3881 , http://hdl.handle.net/10962/d1001615
- Description: Vitamin A and its chemical analogues (retinoids) are known to play a role in the maintenance and differentiation of epithelial tissue. Retinoids have been shown to inhibit carcinogenesis in a number of tissues in experimental animals and to inhibit the growth of various untransformed and cancer cell lines in vitro. This study investigated the effect of retinyl acetate supplemented at concentrations of 1 μM, 5 μM, 10 μM and 100 μM to in vitro cultured untransformed LLCMK cells, and transformed BL-6 melanoma and human hepatoma cell lines. A small but non-significant effect of vitamin A addition on the growth of the untransformed cells was observed, while substantial inhibition of proliferation of the two tumour cell lines was found. At the cytotoxic level of 100 μM supplemented vitamin A, all three cell lines showed marked inhibition of growth. This led to an electron microscopy study to examine the ultrastructural effect of the vitamin A addition. At the low non-toxic levels of vitamin A addition (1 - 10 μM), no ultrastructural changes were observed in the untransformed cells. However, at a level of 5 μM and 10 μM vitamin A addition in the tumour cells, an increase in the size of suspected lipid droplets was observed. At the cytotoxic level of 100 μM supplemented vitamin A, large lipid droplets were very apparent, as was much cellular degeneration. This effect was more marked in the tumour cells than in the untransformed cells. The lipid nature of the droplets was confirmed by using the lipid stain, Sudan IV. In order to investigate the effect of added vitamin A at the cell surface level, an ELISA system was used to quantify the level of the cell surface glycoprotein, fibronectin, in the culture media. Vitamin A plays an important role in the production of mature fibronectin by participating in the glycosylation of the molecule. This study showed no major effect of added vitamin A on the release of fibronectin into the culture media. This did not, however, exclude the possibility that the vitamin A was involved in the production and enhanced binding of fibronectin to the cell surface, and was possibly also exerting an effect on the availability of fibronectin receptors. Further studies would, however, be required to substantiate such effects of vitamin A supplementation. No single mechanism of action of vitamin A on tumour cell growth inhibition was identified, but the possibility that at least two mechanisms exist, was suggested
- Full Text:
- Date Issued: 1988
Environmental requirements for the hatchery rearing of African catfish Clarias Gariepinus (Pisces: Clariidae) larvae and juveniles
- Britz, P J (Peter Jacobus), 1959-
- Authors: Britz, P J (Peter Jacobus), 1959-
- Date: 1988
- Subjects: Catfishes -- Africa , Fish culture , Clariidae , Clarias
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5188 , http://hdl.handle.net/10962/d1001964 , Catfishes -- Africa , Fish culture , Clariidae , Clarias
- Description: Inadequate seed production has historically been a factor limiting the commercial culture of Clarias gariepinus. The need to determine the environmental requirements of larvae was identified, in order to facilitate their successful mass rearing in hatcheries. The effects of key environmental factors on the growth, survival and aspects of the behaviour of C. gariepinus larvae and juveniles were investigated under controlled conditions. A strong emphasis was placed on the interpretation of the observed responses in terms of the natural history of the animal. Larvae were obtained by artificially inducing and spawning feral adult broodfish. Larval growth rates were highest in the temperature range 26-33ºC, with a peak at 30ºC. Survival of larvae was high between 22 and 33ºC. The final temperature preferendum of juveniles, determined in a thermal gradient was 30ºC, and it was concluded that this temperature is probably optimal for most of the physiological processes of the animal. Larvae and juveniles displayed strong negative phototaxis. When reared under different photoperiod regimes, larval growth increased with longer dark periods, however a similar rate of mortality was recorded in all photoperiod treatments. The provision of cover was found to enhance larval growth under conditions of continual light (24L/OD), however under conditions of continual darkness (OL/24D) similar growth rates were recorded regardless of the presence or absence of cover. All growth rates in continual darkness (OL/24D) were higher than those in continual light (24L/OD), regardless of whether cover was provided or not. It was concluded that a OL/24D photoperiod is optimal for larval rearing. At salinities between 0 and 5% similar growth and mortality rates of larvae were recorded. At 7.5 % larval growth and survival rates were lower, and at 10 % all larvae died within 48 hours. The 96h-LCSO for unionised ammonia was found to be 2.3 mg/l. The cytological effects of unionised ammonia were evident as degenerative changes in the gill and liver tissues. In an investigation of tank hygiene, it was found that larval growth and survival rates were highest in tanks not cleaned at all. As the frequency of tank cleaning increased, the growth and survival rates of larvae decreased. When reared at densities ranging from 45-450/1, larval growth was found to be density dependent. A model of hatchery productivity (number larvae of standard size produced/time/vol.) was developed based on the density dependent nature of larval growth. The model predicts that maximum productivity, will be achieved at a rearing density of 1400/1. The high growth and survival rates obtained over a broad range of each environmental parameter investigated serve to explain how larvae survive and grow in their unstable floodplain habitat in nature. The broad environmental tolerances of C. gariepinus are of benefit with respect to the culture of larvae, as successful larval rearing is possible over a fairly wide range of environmental conditions.
- Full Text:
- Date Issued: 1988
- Authors: Britz, P J (Peter Jacobus), 1959-
- Date: 1988
- Subjects: Catfishes -- Africa , Fish culture , Clariidae , Clarias
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5188 , http://hdl.handle.net/10962/d1001964 , Catfishes -- Africa , Fish culture , Clariidae , Clarias
- Description: Inadequate seed production has historically been a factor limiting the commercial culture of Clarias gariepinus. The need to determine the environmental requirements of larvae was identified, in order to facilitate their successful mass rearing in hatcheries. The effects of key environmental factors on the growth, survival and aspects of the behaviour of C. gariepinus larvae and juveniles were investigated under controlled conditions. A strong emphasis was placed on the interpretation of the observed responses in terms of the natural history of the animal. Larvae were obtained by artificially inducing and spawning feral adult broodfish. Larval growth rates were highest in the temperature range 26-33ºC, with a peak at 30ºC. Survival of larvae was high between 22 and 33ºC. The final temperature preferendum of juveniles, determined in a thermal gradient was 30ºC, and it was concluded that this temperature is probably optimal for most of the physiological processes of the animal. Larvae and juveniles displayed strong negative phototaxis. When reared under different photoperiod regimes, larval growth increased with longer dark periods, however a similar rate of mortality was recorded in all photoperiod treatments. The provision of cover was found to enhance larval growth under conditions of continual light (24L/OD), however under conditions of continual darkness (OL/24D) similar growth rates were recorded regardless of the presence or absence of cover. All growth rates in continual darkness (OL/24D) were higher than those in continual light (24L/OD), regardless of whether cover was provided or not. It was concluded that a OL/24D photoperiod is optimal for larval rearing. At salinities between 0 and 5% similar growth and mortality rates of larvae were recorded. At 7.5 % larval growth and survival rates were lower, and at 10 % all larvae died within 48 hours. The 96h-LCSO for unionised ammonia was found to be 2.3 mg/l. The cytological effects of unionised ammonia were evident as degenerative changes in the gill and liver tissues. In an investigation of tank hygiene, it was found that larval growth and survival rates were highest in tanks not cleaned at all. As the frequency of tank cleaning increased, the growth and survival rates of larvae decreased. When reared at densities ranging from 45-450/1, larval growth was found to be density dependent. A model of hatchery productivity (number larvae of standard size produced/time/vol.) was developed based on the density dependent nature of larval growth. The model predicts that maximum productivity, will be achieved at a rearing density of 1400/1. The high growth and survival rates obtained over a broad range of each environmental parameter investigated serve to explain how larvae survive and grow in their unstable floodplain habitat in nature. The broad environmental tolerances of C. gariepinus are of benefit with respect to the culture of larvae, as successful larval rearing is possible over a fairly wide range of environmental conditions.
- Full Text:
- Date Issued: 1988
Explanation in rule-based expert systems
- Authors: Carden, Kenneth John
- Date: 1988
- Subjects: Expert systems (Computer science) Ecology -- Research
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4569 , http://hdl.handle.net/10962/d1002034
- Description: The ability of an expert system to explain its reasoning is fundamental to the system's credibility. Explanations become even more vital in systems which use methods of uncertainty propagation. The research documented here describes the development of an explanation sub-system which interfaces with the P.R.O. Expert System Toolkit. This toolkit has been used in the development of three small ecological expert systems. This project has involved adapting the results of research in the field of explanation-generation, to the requirements of the ecologist users. The subsystem contains two major components. The first lists the rules that fired during a consultation. The second component comprises routines responsible for quantifying the effects on the system conclusions of the answers given to questions. These latter routines can be used to perform sensitivity analyses on the answers given. The incorporation of such routines in small expert systems is quite unique
- Full Text:
- Date Issued: 1988
- Authors: Carden, Kenneth John
- Date: 1988
- Subjects: Expert systems (Computer science) Ecology -- Research
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4569 , http://hdl.handle.net/10962/d1002034
- Description: The ability of an expert system to explain its reasoning is fundamental to the system's credibility. Explanations become even more vital in systems which use methods of uncertainty propagation. The research documented here describes the development of an explanation sub-system which interfaces with the P.R.O. Expert System Toolkit. This toolkit has been used in the development of three small ecological expert systems. This project has involved adapting the results of research in the field of explanation-generation, to the requirements of the ecologist users. The subsystem contains two major components. The first lists the rules that fired during a consultation. The second component comprises routines responsible for quantifying the effects on the system conclusions of the answers given to questions. These latter routines can be used to perform sensitivity analyses on the answers given. The incorporation of such routines in small expert systems is quite unique
- Full Text:
- Date Issued: 1988
Feeding by larvae of the American bollworm, Heliothis armigera (Hübner) (Lepidoptera: Noctuidae) on cotton plants
- Van der Walt, Susanna Johanna
- Authors: Van der Walt, Susanna Johanna
- Date: 1988
- Subjects: Cotton -- Diseases and pests , Helicoverpa armigera , Lepidoptera
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5622 , http://hdl.handle.net/10962/d1004386 , Cotton -- Diseases and pests , Helicoverpa armigera , Lepidoptera
- Description: H. armigera larvae are a key stage for pest management in conmercial irrigated cotton crops in South Africa. Effective survey methods for detecting larval populations in the field require an understanding of the biology of the larvae, particularly their feeding habits. Their feeding is central to the development of pest threshold levels for the implementation of integrated control programmes. This applies to routine surveys for the larvae as well as to the damage they cause. Biological characteristics of the larvae are described with the emphasis on the identification of the larval instars, which were consistently five in number in both field and laboratory populations. The distribution of H. armigera larvae on cotton plants in the field was examined, but was found to more or less random; had there been a clear preference for any height zones or compass direction this would have been an obvious avenue for improving the survey methods currently in use. Details of field and laboratory investigations of the selection of feeding sites by the larvae are given. The study confirmed a clear preference by the larvae for cotton buds, flowers and bolls (in the thesis collectively called "fruiting forms"), over leaves. There were indications that the larvae selected flowers more readily than buds or bolls. This "preference", however, is shown to be of no practical value for refining survey methods. Damage levels to cotton due to B. armigera are discussed. Both direct losses and indirect losses due to the abortion of fruiting forms are considered. These criteria are inadequate since they do not take into account the ability of cotton plants to compensate for these losses. It is concluded that this compensation by cotton plants should be taken into account in further studies of the pest status of B. armigera.
- Full Text:
- Date Issued: 1988
- Authors: Van der Walt, Susanna Johanna
- Date: 1988
- Subjects: Cotton -- Diseases and pests , Helicoverpa armigera , Lepidoptera
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5622 , http://hdl.handle.net/10962/d1004386 , Cotton -- Diseases and pests , Helicoverpa armigera , Lepidoptera
- Description: H. armigera larvae are a key stage for pest management in conmercial irrigated cotton crops in South Africa. Effective survey methods for detecting larval populations in the field require an understanding of the biology of the larvae, particularly their feeding habits. Their feeding is central to the development of pest threshold levels for the implementation of integrated control programmes. This applies to routine surveys for the larvae as well as to the damage they cause. Biological characteristics of the larvae are described with the emphasis on the identification of the larval instars, which were consistently five in number in both field and laboratory populations. The distribution of H. armigera larvae on cotton plants in the field was examined, but was found to more or less random; had there been a clear preference for any height zones or compass direction this would have been an obvious avenue for improving the survey methods currently in use. Details of field and laboratory investigations of the selection of feeding sites by the larvae are given. The study confirmed a clear preference by the larvae for cotton buds, flowers and bolls (in the thesis collectively called "fruiting forms"), over leaves. There were indications that the larvae selected flowers more readily than buds or bolls. This "preference", however, is shown to be of no practical value for refining survey methods. Damage levels to cotton due to B. armigera are discussed. Both direct losses and indirect losses due to the abortion of fruiting forms are considered. These criteria are inadequate since they do not take into account the ability of cotton plants to compensate for these losses. It is concluded that this compensation by cotton plants should be taken into account in further studies of the pest status of B. armigera.
- Full Text:
- Date Issued: 1988
Geological control of aquifer properties of the Chuniespoort Group in the Klip River Valley and Natalspruit Basin, Transvaal
- Foster, Michael Benedict John
- Authors: Foster, Michael Benedict John
- Date: 1988 , 2013-03-08
- Subjects: Hydrogeology -- South Africa -- Transvaal , Aquifers -- South Africa -- Transvaal , Water supply -- South Africa -- Transvaal
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4881 , http://hdl.handle.net/10962/d1013338
- Description: The aquifer of the study area occupies an escarpment and low lying limestone plain, and exhibits a Vaal River type karst. The four dolomitic formations present fall into two distinct aquifer forming types; chert poor units and chert rich units. The chert poor units of the Oaktree and Lyttelton Formations were deposited in a subtidal environment and were probably dolomi tised in a migrating schizohaline environment during basin subsidence and shoreline trangression. The chert rich units of the Monte Christo and Eccles Formations were deposited in the shallow subtidal to supratidal zones and the interbedded chert and dolomites may result from minor cyclical marine trangressions and regressions or be a geochemical response to the periodic flooding of freshwater carbonate and flats and tidal deltas. These fundamental geological differences are reflected in correspondingly different development of karst. Transmissive zones in the chert poor units are generally discrete solution features in massive dolomite, 1 m to 2 m thick. Transmissive zones in the chert rich units comprise thick (up to 60 m) and extremely weathered chert with a high void content resulting from the dissolution of carbonate material. The relative importance of various geological features to the development of the karst was assessed using information from two extensive hydrogeological investigations of the area. From the results it bas been concluded that lithostratigraphy, including the occurrence of palaeokarstic horizons, is the major control of aquifer properties. All other geological features are of lesser importance but may nevertheless be associated with enhanced transmissivi ties in any given unit. Faults and lineaments are the structural features most widely associated with highly transmissive zones. The knowledge gained in this study is applicable elsewhere as the principal hydrogeological characteristics of the study area are common to many of the Chuniespoort Group aquifers in the Pretoria - Witwatersrand - Vereeniging Region.
- Full Text:
- Date Issued: 1988
- Authors: Foster, Michael Benedict John
- Date: 1988 , 2013-03-08
- Subjects: Hydrogeology -- South Africa -- Transvaal , Aquifers -- South Africa -- Transvaal , Water supply -- South Africa -- Transvaal
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4881 , http://hdl.handle.net/10962/d1013338
- Description: The aquifer of the study area occupies an escarpment and low lying limestone plain, and exhibits a Vaal River type karst. The four dolomitic formations present fall into two distinct aquifer forming types; chert poor units and chert rich units. The chert poor units of the Oaktree and Lyttelton Formations were deposited in a subtidal environment and were probably dolomi tised in a migrating schizohaline environment during basin subsidence and shoreline trangression. The chert rich units of the Monte Christo and Eccles Formations were deposited in the shallow subtidal to supratidal zones and the interbedded chert and dolomites may result from minor cyclical marine trangressions and regressions or be a geochemical response to the periodic flooding of freshwater carbonate and flats and tidal deltas. These fundamental geological differences are reflected in correspondingly different development of karst. Transmissive zones in the chert poor units are generally discrete solution features in massive dolomite, 1 m to 2 m thick. Transmissive zones in the chert rich units comprise thick (up to 60 m) and extremely weathered chert with a high void content resulting from the dissolution of carbonate material. The relative importance of various geological features to the development of the karst was assessed using information from two extensive hydrogeological investigations of the area. From the results it bas been concluded that lithostratigraphy, including the occurrence of palaeokarstic horizons, is the major control of aquifer properties. All other geological features are of lesser importance but may nevertheless be associated with enhanced transmissivi ties in any given unit. Faults and lineaments are the structural features most widely associated with highly transmissive zones. The knowledge gained in this study is applicable elsewhere as the principal hydrogeological characteristics of the study area are common to many of the Chuniespoort Group aquifers in the Pretoria - Witwatersrand - Vereeniging Region.
- Full Text:
- Date Issued: 1988
On a class of pseudo-differential operators in IRⁿ
- Authors: Matjila, D M
- Date: 1988
- Subjects: Pseudodifferential operators Operator theory
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5392 , http://hdl.handle.net/10962/d1001981
- Description: The class of pseudo-differential operators with symbols from Sm (superscript) po̧̧ (subscipt)(Ωx IRⁿ) has been extensively studied.The main assumption which characterises this class of symbols is that a(x,Ȩ) є Sm (superscript)po̧̧ (subscipt)(Ωx IRⁿ) should have a polynomial growth in the Ȩ variable only. The x-variable is controlled on compact subsets of Ω. A polynomial growth in both the x and Ȩ variables on a C°°(lR²ⁿ) function a(x,Ȩ) gives rise to a different class of symbols and a corresponding class of operators. In this work, such symbols and the action of the operators on the functional spaces S(lRⁿ) , S'(lRⁿ) and the Sobolev spaces Qs (superscript) (lRⁿ) (s є lRⁿ) are studied. A study of the calculus (i.e. transposes, adjoints and compositions) and the functional analysis of these operators is done with special attention to L-boundedness and compactness. The class of hypoelliptic pseudo-differential operators in IRⁿ is introduced as a subclass of those considered earlier.These operators possess the property that they allow a pseudo- inverse or parametrix. In conclusion. the spectral theory of these operators is considered. Since a general spectral theory would be beyond the scope of this work, only some special cases of the pseudo-differential operators in IRⁿ are considered. A few applications of this spectral theory are discussed
- Full Text:
- Date Issued: 1988
- Authors: Matjila, D M
- Date: 1988
- Subjects: Pseudodifferential operators Operator theory
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5392 , http://hdl.handle.net/10962/d1001981
- Description: The class of pseudo-differential operators with symbols from Sm (superscript) po̧̧ (subscipt)(Ωx IRⁿ) has been extensively studied.The main assumption which characterises this class of symbols is that a(x,Ȩ) є Sm (superscript)po̧̧ (subscipt)(Ωx IRⁿ) should have a polynomial growth in the Ȩ variable only. The x-variable is controlled on compact subsets of Ω. A polynomial growth in both the x and Ȩ variables on a C°°(lR²ⁿ) function a(x,Ȩ) gives rise to a different class of symbols and a corresponding class of operators. In this work, such symbols and the action of the operators on the functional spaces S(lRⁿ) , S'(lRⁿ) and the Sobolev spaces Qs (superscript) (lRⁿ) (s є lRⁿ) are studied. A study of the calculus (i.e. transposes, adjoints and compositions) and the functional analysis of these operators is done with special attention to L-boundedness and compactness. The class of hypoelliptic pseudo-differential operators in IRⁿ is introduced as a subclass of those considered earlier.These operators possess the property that they allow a pseudo- inverse or parametrix. In conclusion. the spectral theory of these operators is considered. Since a general spectral theory would be beyond the scope of this work, only some special cases of the pseudo-differential operators in IRⁿ are considered. A few applications of this spectral theory are discussed
- Full Text:
- Date Issued: 1988
Petrology and geochemistry of the lower group chromitites and host rocks on the farm Zandspruit 168 JP, Western Bushveld Complex
- Authors: Botha, Michael James
- Date: 1988
- Subjects: Petrology -- Africa, Southern , Geochemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4905 , http://hdl.handle.net/10962/d1001565
- Description: The eight Lower Group chromitite layers of the Ruighoek Pyroxenite in the area west of the Pilanesberg (LGl - LG7), on the farm Zandspruit 168 JP, were sampled in borehole cores drilled through the succession. The stratigraphic succession faIls within Cameron's (980) units B to E of the Critical Zone. The lowermost layer of the Lower Group, the LG 1 chromitite, is located some 440 metres below the MG 2 (Middle Group) chromitite layer, above which the first appearance of cumulus plagioclase in the Complex is seen. By convention, this horizon is designated the top of the Ruighoek Pyroxenite in the Western Bushveld Complex. Homogeneous units of chromite-bearing orthopyroxenite (bronzitite), exhibiting inconspicuous layering defined in terms of variations in orthopyroxene grain-size host all but one of the Lower Group layers; the LG 4 chromitite layer is exposed within an olivine-rich subunit 23 metres in thickness (C₃ subunit). The cumulative thickness of chromitite is 2,92 metres or 0,8 per cent of the studied section, which is 381 metres in thickness. Minimum and maximum thicknesses of the LGl - LG7 layers exposed in drill core are 17 and 81 centimetres, respectively, with minor chromitite layers ranging between 2 and 5 centimetres in thickness. Weighted mean Cr₂0₃ contents of units B to E vary between 1,17 and 3,22 per cent, with the latter estimate representative of the D₂ subunit which hosts the LG 6 chromitite layer. The LG 6 is correlated with the Steelpoort layer of the Eastern Bushveld Complex, and varies between 76 and 81 centimetres in thickness under a large portion of the farm Zandspruit. An undisturbed succession striking N15°E and dipping 12 - 15°E is depicted within the studied area, which is bounded on the eastern side by the north-striking Frank fault. Major folding of the layered succession is evident to the north of the area, where the layering adjacent to the trace of the fault dips 35° to the southwest. Particular attention is paid in the present study to (a) the nature of chromitite layers and their host rocks, (b) the contrast between the mineral chemistry of weakly disseminated chromite and grains within massive ore layers, (c) concentrations of Cr, V, Ni, Co, Sc and Ti in orthopyroxene in relation to stratigraphic height, and levels of Sr, Ba and Zr associated with hypothetically pure, intercumulus plagioclase feldspar, and (d) possible mechanisms which induce crystallization of chromitite layers containing 50 per cent Cr₂0₃ from magma with a Cr content of less than 1 000 ppm. Electron microprobe studies of chromite in relation to mineralogical and textural environment clearly reveal that (a) the proportions of Cr and Al cations are linked to paragenesis: higher Al/Cr ratios characterize olivine-bearing domains, whereas grains intergrown with plagioclase feldspar exhibit low AI/Cr ratios, and (b) Al contents rise with a decline in Mg/(Mg + Fe²⁺) from high values to a value of 0,450, then decrease with a further decline in Mg/(Mg + Fe²⁺). The paragenetically later trend is emphasized in a large population of chromite grains which escaped early encapsulation in orthopyroxene crystals and continued to grow in the environment of intercumulus plagioclase. Within-and between-sample compositional variation of grains in silicate-rich domains is modelled in terms of in situ growth increments, diffusive homogenization of zonal structures, and residence time within interstitial melt. Fractionation trends, as measured by Mg/(Mg + Fe²⁺) ratios in whole-rock and/or microprobe studies of orthopyroxene, are reversed in relation to stratigraphic height towards the top of the B unit and in the overlying C unit. These data are supported, for example, by lower vanadium contents and higher Ni/Sc ratios in hypothetically pure orthopyroxene. Small olivine crystals in chromite-rich domains are enriched in Ni relative to coarse-grained olivine in adjacent dunite: a feature attributed to early isolation of primocrysts from magma in the former case, and in situ equilibration between olivine crystals and Ni-depleted residual melt in the latter case . Similarly, rising Ni contents and Mg/(Mg + Fe²⁺) ratios of orthopyroxene with increasing stratigraphic height in the footwall of the LG 6 chromitite layer, linked to a progressive decline in orthopyroxene grain-size, are effects which may arise out of early separation of interstitial melt from orthopyroxene cumulates. A model is thus proposed which (a) links the thickness of chromitite layers to the vertical separation between successive layers or the thickness of fine-grained orthopyroxenite in the footwall, (b) ascribes copious nucleation of chromite to liquid mixing of this footwall derived, Cr - depleted contaminant with influxes of hot, primitive magma, and (c) tenders the notion that the present modal proportion of mesostasis in the footwall of a chromitite layer serves as a reciprocal measure of the volume of fractionated exudate
- Full Text:
- Date Issued: 1988
- Authors: Botha, Michael James
- Date: 1988
- Subjects: Petrology -- Africa, Southern , Geochemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4905 , http://hdl.handle.net/10962/d1001565
- Description: The eight Lower Group chromitite layers of the Ruighoek Pyroxenite in the area west of the Pilanesberg (LGl - LG7), on the farm Zandspruit 168 JP, were sampled in borehole cores drilled through the succession. The stratigraphic succession faIls within Cameron's (980) units B to E of the Critical Zone. The lowermost layer of the Lower Group, the LG 1 chromitite, is located some 440 metres below the MG 2 (Middle Group) chromitite layer, above which the first appearance of cumulus plagioclase in the Complex is seen. By convention, this horizon is designated the top of the Ruighoek Pyroxenite in the Western Bushveld Complex. Homogeneous units of chromite-bearing orthopyroxenite (bronzitite), exhibiting inconspicuous layering defined in terms of variations in orthopyroxene grain-size host all but one of the Lower Group layers; the LG 4 chromitite layer is exposed within an olivine-rich subunit 23 metres in thickness (C₃ subunit). The cumulative thickness of chromitite is 2,92 metres or 0,8 per cent of the studied section, which is 381 metres in thickness. Minimum and maximum thicknesses of the LGl - LG7 layers exposed in drill core are 17 and 81 centimetres, respectively, with minor chromitite layers ranging between 2 and 5 centimetres in thickness. Weighted mean Cr₂0₃ contents of units B to E vary between 1,17 and 3,22 per cent, with the latter estimate representative of the D₂ subunit which hosts the LG 6 chromitite layer. The LG 6 is correlated with the Steelpoort layer of the Eastern Bushveld Complex, and varies between 76 and 81 centimetres in thickness under a large portion of the farm Zandspruit. An undisturbed succession striking N15°E and dipping 12 - 15°E is depicted within the studied area, which is bounded on the eastern side by the north-striking Frank fault. Major folding of the layered succession is evident to the north of the area, where the layering adjacent to the trace of the fault dips 35° to the southwest. Particular attention is paid in the present study to (a) the nature of chromitite layers and their host rocks, (b) the contrast between the mineral chemistry of weakly disseminated chromite and grains within massive ore layers, (c) concentrations of Cr, V, Ni, Co, Sc and Ti in orthopyroxene in relation to stratigraphic height, and levels of Sr, Ba and Zr associated with hypothetically pure, intercumulus plagioclase feldspar, and (d) possible mechanisms which induce crystallization of chromitite layers containing 50 per cent Cr₂0₃ from magma with a Cr content of less than 1 000 ppm. Electron microprobe studies of chromite in relation to mineralogical and textural environment clearly reveal that (a) the proportions of Cr and Al cations are linked to paragenesis: higher Al/Cr ratios characterize olivine-bearing domains, whereas grains intergrown with plagioclase feldspar exhibit low AI/Cr ratios, and (b) Al contents rise with a decline in Mg/(Mg + Fe²⁺) from high values to a value of 0,450, then decrease with a further decline in Mg/(Mg + Fe²⁺). The paragenetically later trend is emphasized in a large population of chromite grains which escaped early encapsulation in orthopyroxene crystals and continued to grow in the environment of intercumulus plagioclase. Within-and between-sample compositional variation of grains in silicate-rich domains is modelled in terms of in situ growth increments, diffusive homogenization of zonal structures, and residence time within interstitial melt. Fractionation trends, as measured by Mg/(Mg + Fe²⁺) ratios in whole-rock and/or microprobe studies of orthopyroxene, are reversed in relation to stratigraphic height towards the top of the B unit and in the overlying C unit. These data are supported, for example, by lower vanadium contents and higher Ni/Sc ratios in hypothetically pure orthopyroxene. Small olivine crystals in chromite-rich domains are enriched in Ni relative to coarse-grained olivine in adjacent dunite: a feature attributed to early isolation of primocrysts from magma in the former case, and in situ equilibration between olivine crystals and Ni-depleted residual melt in the latter case . Similarly, rising Ni contents and Mg/(Mg + Fe²⁺) ratios of orthopyroxene with increasing stratigraphic height in the footwall of the LG 6 chromitite layer, linked to a progressive decline in orthopyroxene grain-size, are effects which may arise out of early separation of interstitial melt from orthopyroxene cumulates. A model is thus proposed which (a) links the thickness of chromitite layers to the vertical separation between successive layers or the thickness of fine-grained orthopyroxenite in the footwall, (b) ascribes copious nucleation of chromite to liquid mixing of this footwall derived, Cr - depleted contaminant with influxes of hot, primitive magma, and (c) tenders the notion that the present modal proportion of mesostasis in the footwall of a chromitite layer serves as a reciprocal measure of the volume of fractionated exudate
- Full Text:
- Date Issued: 1988
Phenylpropanolamine : analytical and pharmacokinetic studies using high-performance liquid chromatography
- Authors: Scherzinger, Sabine Hilda
- Date: 1988
- Subjects: Phenylpropanolamine , Pharmacokinetics , High performance liquid chromatography
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: vital:3811 , http://hdl.handle.net/10962/d1004528
- Description: Phenylpropanolamine (PPA), a synthetic sympathomimetic amine structurally related to ephedrine has been widely used over t he past 40 years as a nasal decongestant and appetite suppressant. It has been the focus of much controversy concerning the efficacy of the drug in its use as an anorectic agent, and due to the side effects caused by the higher doses of PPA required for appetite suppression. Although extensively used, there is little information concerning the determination of PPA in biological fluids and on the pharmacokinetics of this drug. An adaptation of a published high-performance liquid chromatographic (HPLC) assay for PPA in serum and urine using U.V. detection at 210 nm is presented. PPA was separated in the reversed phase mode. The method has a limit of sensitivity of 5.0 ng/mL and 10.0 ng/mL in serum and urine respectively. Serum concentration data following a single 25 mg dose of phenylpropanolamine in human volunteers demonstrate the application of the analytical method for bioavailability and pharmacokinetic studies. After the administration of 25 mg, 50 mg or 100 mg PPA.HCl solutions to 5 human volunteers, a dose proportionality study demonstrated that PPA appears to exhibit linear kinetics. Linear one body compartment kinetics were assumed and the wagner-Nelson method used to transform in vivo serum data to absorption plots. The serum data were fitted to a model using nonlinear regression techniques to characterize the pharmacokinetic processes of PPA. The absorption of phenylpropanolamine appears to be discontinuous and the drug seems to favour a two body compartment model. The pharmacokinetic parameters obtained from a steady state study using multiple dosing of PPA.HCl solutions compared with those found from previous studies after the administration of sustained-release formulations. A plasma protein binding study using equilibrium dialysis demonstrated that PPA is not highly protein bound in the blood.
- Full Text:
- Date Issued: 1988
- Authors: Scherzinger, Sabine Hilda
- Date: 1988
- Subjects: Phenylpropanolamine , Pharmacokinetics , High performance liquid chromatography
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: vital:3811 , http://hdl.handle.net/10962/d1004528
- Description: Phenylpropanolamine (PPA), a synthetic sympathomimetic amine structurally related to ephedrine has been widely used over t he past 40 years as a nasal decongestant and appetite suppressant. It has been the focus of much controversy concerning the efficacy of the drug in its use as an anorectic agent, and due to the side effects caused by the higher doses of PPA required for appetite suppression. Although extensively used, there is little information concerning the determination of PPA in biological fluids and on the pharmacokinetics of this drug. An adaptation of a published high-performance liquid chromatographic (HPLC) assay for PPA in serum and urine using U.V. detection at 210 nm is presented. PPA was separated in the reversed phase mode. The method has a limit of sensitivity of 5.0 ng/mL and 10.0 ng/mL in serum and urine respectively. Serum concentration data following a single 25 mg dose of phenylpropanolamine in human volunteers demonstrate the application of the analytical method for bioavailability and pharmacokinetic studies. After the administration of 25 mg, 50 mg or 100 mg PPA.HCl solutions to 5 human volunteers, a dose proportionality study demonstrated that PPA appears to exhibit linear kinetics. Linear one body compartment kinetics were assumed and the wagner-Nelson method used to transform in vivo serum data to absorption plots. The serum data were fitted to a model using nonlinear regression techniques to characterize the pharmacokinetic processes of PPA. The absorption of phenylpropanolamine appears to be discontinuous and the drug seems to favour a two body compartment model. The pharmacokinetic parameters obtained from a steady state study using multiple dosing of PPA.HCl solutions compared with those found from previous studies after the administration of sustained-release formulations. A plasma protein binding study using equilibrium dialysis demonstrated that PPA is not highly protein bound in the blood.
- Full Text:
- Date Issued: 1988
Polymerized serum albumin beads for use as slow-release adjuvants
- Martin, Michelle Elizabeth Denny
- Authors: Martin, Michelle Elizabeth Denny
- Date: 1988
- Subjects: Serum albumin , Antigens , Vaccines
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3879 , http://hdl.handle.net/10962/d1001613
- Description: Experimental vaccines have been made by covalently bonding virus particles into polymerized rabbit serum albumin beads. Using Nodamura virus as a model antigen, these model vaccines induced specific humoral antibody production, comparable with that achieved using Freund's adjuvants. Virus specific antibodies were also induced when Nodamura virus was covalently attached to the bead surface using different crosslinkers. However, when poliovirus type 2 (Sabin strain) was polymerized into beads, the levels of neutralizing antibodies were insignificant compared with control aqueous vaccines. The synthetic immunostimulator, muramyl dipeptide, was included with bead vaccines in an attempt to potentiate the immune response. Immunostimulation is achieved by a slow release of antigen coinciding with the gradual breakdown of bead structure.
- Full Text:
- Date Issued: 1988
- Authors: Martin, Michelle Elizabeth Denny
- Date: 1988
- Subjects: Serum albumin , Antigens , Vaccines
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3879 , http://hdl.handle.net/10962/d1001613
- Description: Experimental vaccines have been made by covalently bonding virus particles into polymerized rabbit serum albumin beads. Using Nodamura virus as a model antigen, these model vaccines induced specific humoral antibody production, comparable with that achieved using Freund's adjuvants. Virus specific antibodies were also induced when Nodamura virus was covalently attached to the bead surface using different crosslinkers. However, when poliovirus type 2 (Sabin strain) was polymerized into beads, the levels of neutralizing antibodies were insignificant compared with control aqueous vaccines. The synthetic immunostimulator, muramyl dipeptide, was included with bead vaccines in an attempt to potentiate the immune response. Immunostimulation is achieved by a slow release of antigen coinciding with the gradual breakdown of bead structure.
- Full Text:
- Date Issued: 1988
The biology of Acia lineatifrons (Naude) (Homoptera : Cicadellidae) on grapevines in the Western Cape
- Authors: Marais, Elleunorah
- Date: 1988
- Subjects: Homoptera
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5597 , http://hdl.handle.net/10962/d1002047
- Description: The leafhopper, Acia lineatifrons (Naude) was identified as a pest on grapevines near Tulbagh in 1978 and has since been reported on grapevines all over the South Western Cape. A. lineatifrons causes browning of the leaves which often results in the shedding of the discoloured leaves. Heavy defoliation before harvest can result in sunburn damage to the grapes, whilst premature leaf loss after harvest adversely affects the ripening of the canes and the accumulation of reserves. This project was aimed at obtaining basic information on the biology and population dynamics of A. lineatifrons as well as to identify priorities for future research. This information is needed to develop a reliable crop-linked predictive model, methods for monitoring pest populations as well as to develop efficient short- and long-term control measures and pest management strategies. The life cycle of A. lineatifrons was studied in the laboratory. At 26°C the mean incubation period of the eggs was nine to eleven days, the mean developmental period for the five nymphal instars was 15 days and the minimum pre-oviposition period five to ten days. This adds up to a mean generation time of 29 to 36 days at 26°C. At 20°C the mean nymphal development period was 25 days, confirming the strong influence of temperature on the development rate. Fecundity was determined in the laboratory as the number of nymphs produced per female. The mean of 8,5 nymphs per female recorded at 26°C is very low compared to that of other leafhopper species (see Appendix 2). The low fecundity measured was most likely due to sub-optimal environmental conditions in the laboratory, a reduction in the suitability of the host plant under these conditions and handling of the females. The seasonal occurrence of A. lineatifrons on grapevines was studied over three seasons. It was found that the leafhoppers overwinter in the adult stage on indigenous Rubus spp, and that they enter the vineyard from the end of October until the beginning of November. Peak populations occurred between the middle of February and the end of March after which the population declined steadily towards the end of the season as the vine leaves were shed. The sex ratio of the overwintering population on R. chrysocarpus was heavily female biased, possibly due to differential mortality of the sexes. During the growing season the sex ratio was slightly male biased and reached equality on several occasions, both on the Rubus and on the grapevines. The movement of A. lineatifrons between the Rubus and the grapevines was investigated, but no evidence of a directional migration from the Rubus to the grapevines was found. Furthermore, no evidence was found to indicate that morphologically distinct short- and long-distance fliers, as found in Cicadulina species by Rose (1972b), exist in the A. lineatifrons population. Host preference tests also showed that adult leafhoppers apparently have no significant preference for grapevines to Rubus or vice versa. It seems, therefore, that the leafhoppers' move onto the grapevines at the beginning of the growing season is not prompted by a host preference. Chaboussou (1971) suggested that certain organic fungicides may cause leafhopper outbreaks because they affect the suitability of the vines as host plants and alter leafhopper fecundity. The effect of Mikal-M (active ingredient Fosetyl AL/Mancozeb), a systemic dithiocarbanate fungicide, on A. lineatifrons was investigated. Laboratory experiments showed no significant effect on fecundity and leaf analysis of potted vines treated with Mikal-M indicated no significant difference in total leaf nitrogen compared to untreated control plants. However, the field experiment on the effect of Mikal-M on the population build-up of the leafhopper showed that significantly more leafhoppers occurred on the vines treated with Mikal-M than on those treated with a conventional inorganic fungicide, copper oxychloride. In view of the far-reaching implications this can have on the viticultural industry, further research on the effects of organic fungicides on leafhopper populations is recommended to confirm the generality of these results so that recommendations regarding the use of these fungicides may be made. The question as to why A. lineatifrons became a pest only recently was raised. Three possibilities were considered, namely (1) that A. lineatifrons is a species of tropical origin which moved down the continent and became established in the Western Cape only recently, (2) that is has been in the Western Cape at least as long as the grapevines, but required prolonged exposure to establish itself on the new host and (3) that is has been on the vines for some time, but was noticed only recently when outbreaks occurred. These outbreaks could have been caused by the introduction of organic fungicides or the depletion of natural enemies by insecticides used to control other insects in the vineyards. Due to the lack of evidence this question could not be answered conclusively. Other research priorities that were established are the development of methods for damage assessment and monitoring of leafhopper populations, determining if A. lineatifrons can transmit grapevine virusses, the development of an economic threshold level and the identification of natural enemies of A. lineatifrons to enable the development of efficient pest management strategies (Summary, p. 63-65)
- Full Text:
- Date Issued: 1988
- Authors: Marais, Elleunorah
- Date: 1988
- Subjects: Homoptera
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5597 , http://hdl.handle.net/10962/d1002047
- Description: The leafhopper, Acia lineatifrons (Naude) was identified as a pest on grapevines near Tulbagh in 1978 and has since been reported on grapevines all over the South Western Cape. A. lineatifrons causes browning of the leaves which often results in the shedding of the discoloured leaves. Heavy defoliation before harvest can result in sunburn damage to the grapes, whilst premature leaf loss after harvest adversely affects the ripening of the canes and the accumulation of reserves. This project was aimed at obtaining basic information on the biology and population dynamics of A. lineatifrons as well as to identify priorities for future research. This information is needed to develop a reliable crop-linked predictive model, methods for monitoring pest populations as well as to develop efficient short- and long-term control measures and pest management strategies. The life cycle of A. lineatifrons was studied in the laboratory. At 26°C the mean incubation period of the eggs was nine to eleven days, the mean developmental period for the five nymphal instars was 15 days and the minimum pre-oviposition period five to ten days. This adds up to a mean generation time of 29 to 36 days at 26°C. At 20°C the mean nymphal development period was 25 days, confirming the strong influence of temperature on the development rate. Fecundity was determined in the laboratory as the number of nymphs produced per female. The mean of 8,5 nymphs per female recorded at 26°C is very low compared to that of other leafhopper species (see Appendix 2). The low fecundity measured was most likely due to sub-optimal environmental conditions in the laboratory, a reduction in the suitability of the host plant under these conditions and handling of the females. The seasonal occurrence of A. lineatifrons on grapevines was studied over three seasons. It was found that the leafhoppers overwinter in the adult stage on indigenous Rubus spp, and that they enter the vineyard from the end of October until the beginning of November. Peak populations occurred between the middle of February and the end of March after which the population declined steadily towards the end of the season as the vine leaves were shed. The sex ratio of the overwintering population on R. chrysocarpus was heavily female biased, possibly due to differential mortality of the sexes. During the growing season the sex ratio was slightly male biased and reached equality on several occasions, both on the Rubus and on the grapevines. The movement of A. lineatifrons between the Rubus and the grapevines was investigated, but no evidence of a directional migration from the Rubus to the grapevines was found. Furthermore, no evidence was found to indicate that morphologically distinct short- and long-distance fliers, as found in Cicadulina species by Rose (1972b), exist in the A. lineatifrons population. Host preference tests also showed that adult leafhoppers apparently have no significant preference for grapevines to Rubus or vice versa. It seems, therefore, that the leafhoppers' move onto the grapevines at the beginning of the growing season is not prompted by a host preference. Chaboussou (1971) suggested that certain organic fungicides may cause leafhopper outbreaks because they affect the suitability of the vines as host plants and alter leafhopper fecundity. The effect of Mikal-M (active ingredient Fosetyl AL/Mancozeb), a systemic dithiocarbanate fungicide, on A. lineatifrons was investigated. Laboratory experiments showed no significant effect on fecundity and leaf analysis of potted vines treated with Mikal-M indicated no significant difference in total leaf nitrogen compared to untreated control plants. However, the field experiment on the effect of Mikal-M on the population build-up of the leafhopper showed that significantly more leafhoppers occurred on the vines treated with Mikal-M than on those treated with a conventional inorganic fungicide, copper oxychloride. In view of the far-reaching implications this can have on the viticultural industry, further research on the effects of organic fungicides on leafhopper populations is recommended to confirm the generality of these results so that recommendations regarding the use of these fungicides may be made. The question as to why A. lineatifrons became a pest only recently was raised. Three possibilities were considered, namely (1) that A. lineatifrons is a species of tropical origin which moved down the continent and became established in the Western Cape only recently, (2) that is has been in the Western Cape at least as long as the grapevines, but required prolonged exposure to establish itself on the new host and (3) that is has been on the vines for some time, but was noticed only recently when outbreaks occurred. These outbreaks could have been caused by the introduction of organic fungicides or the depletion of natural enemies by insecticides used to control other insects in the vineyards. Due to the lack of evidence this question could not be answered conclusively. Other research priorities that were established are the development of methods for damage assessment and monitoring of leafhopper populations, determining if A. lineatifrons can transmit grapevine virusses, the development of an economic threshold level and the identification of natural enemies of A. lineatifrons to enable the development of efficient pest management strategies (Summary, p. 63-65)
- Full Text:
- Date Issued: 1988
The effect of elevated temperature on the nutrient requirements of rainbow trout, Salmo gairdneri (Pisces : Salmonidae) and the development of "least cost" feeds for trout production in South Africa
- Authors: McEwan, Anthony Graham
- Date: 1988
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:21150 , http://hdl.handle.net/10962/6606
- Description: A review of trout metabolism, ingested energetic pathways, essential dietary nutrient requirements and the effect of water temperature on trout physiology identified the need to determine the effect of elevated temperatures (>18oC) on the nutrient requirements of rainbow trout. This review led to the hypothesis that as the temperature exceeds the optimum the growth potential of trout decreases with a theoretical concomitant decrease in the protein requirement. However, the increased metabolic rates of the fish should be reflected by an increased demand for lipids. The experiments designed to test this hypothesis revealed that at temperatures in excess of 18 oC the protein requirement for small (4.5g) and larger (>25g) juvenile rainbow trout are 40 and 35% respectively. This represents a decrease of 10% for the small juveniles and no change for larger juveniles compared to their requirements at optimum temperatures. The lipid requirements for the small as well as the larger juveniles increased by approximately 5 percent, to between 20 and 23 percent, compared to the requirement at optimum temperatures. Consequently the hypothesis was accepted. A review of practical diet formulation is presented along with a description of the experiments conducted to test several "least cost" diets under South African conditions. Recommendations that winter and summer diets be formulated and that the trout producers manufacture their own feeds are made. The most appropriate diet formulated and tested effected a 21 to 29.9 percent saving compared to the currently available feeds in South Africa.
- Full Text:
- Date Issued: 1988
- Authors: McEwan, Anthony Graham
- Date: 1988
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:21150 , http://hdl.handle.net/10962/6606
- Description: A review of trout metabolism, ingested energetic pathways, essential dietary nutrient requirements and the effect of water temperature on trout physiology identified the need to determine the effect of elevated temperatures (>18oC) on the nutrient requirements of rainbow trout. This review led to the hypothesis that as the temperature exceeds the optimum the growth potential of trout decreases with a theoretical concomitant decrease in the protein requirement. However, the increased metabolic rates of the fish should be reflected by an increased demand for lipids. The experiments designed to test this hypothesis revealed that at temperatures in excess of 18 oC the protein requirement for small (4.5g) and larger (>25g) juvenile rainbow trout are 40 and 35% respectively. This represents a decrease of 10% for the small juveniles and no change for larger juveniles compared to their requirements at optimum temperatures. The lipid requirements for the small as well as the larger juveniles increased by approximately 5 percent, to between 20 and 23 percent, compared to the requirement at optimum temperatures. Consequently the hypothesis was accepted. A review of practical diet formulation is presented along with a description of the experiments conducted to test several "least cost" diets under South African conditions. Recommendations that winter and summer diets be formulated and that the trout producers manufacture their own feeds are made. The most appropriate diet formulated and tested effected a 21 to 29.9 percent saving compared to the currently available feeds in South Africa.
- Full Text:
- Date Issued: 1988
The establishment of a Lidar facility at Rhodes University
- Grant, Richard Peter James Seton
- Authors: Grant, Richard Peter James Seton
- Date: 1988
- Subjects: Optical radar , LIDAR , Receiver , Transmitter , Photon counting electronics , Aerosol scattering , Temperature profiles , Stratosphere
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5445 , http://hdl.handle.net/10962/d1001998
- Description: LIDAR is the optical equivalent of RADAR. A LIDAR facility has been established at Rhodes University using a flashlamp-pumped dye laser as the transmitter and a photomultiplier tube at the focus of a searchlight mirror as the receiver. The setting up of the receiver and transmitter as well as the design and construction of the photon counting electronics is described. The LIDAR has been used to measure aerosol scattering ratios and temperature profiles in the stratosphere and these results are presented with the algorithms and software used to reduce the data. Finally some recommendations are made for future work
- Full Text:
- Date Issued: 1988
- Authors: Grant, Richard Peter James Seton
- Date: 1988
- Subjects: Optical radar , LIDAR , Receiver , Transmitter , Photon counting electronics , Aerosol scattering , Temperature profiles , Stratosphere
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5445 , http://hdl.handle.net/10962/d1001998
- Description: LIDAR is the optical equivalent of RADAR. A LIDAR facility has been established at Rhodes University using a flashlamp-pumped dye laser as the transmitter and a photomultiplier tube at the focus of a searchlight mirror as the receiver. The setting up of the receiver and transmitter as well as the design and construction of the photon counting electronics is described. The LIDAR has been used to measure aerosol scattering ratios and temperature profiles in the stratosphere and these results are presented with the algorithms and software used to reduce the data. Finally some recommendations are made for future work
- Full Text:
- Date Issued: 1988
The geology and metallogeny of the Otavi mountain land, Damara orogen, SWA/Namibia, with particular reference to the Berg Aukas Zn-Pb-V deposit a model of ore genesis
- Authors: Misiewicz, Julian Edward
- Date: 1988
- Subjects: Geology -- Namibia -- Damaraland , Ore deposits -- Namibia , Orogeny , Metallogeny , Geodynamics
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4959 , http://hdl.handle.net/10962/d1005571 , Geology -- Namibia -- Damaraland , Ore deposits -- Namibia , Orogeny , Metallogeny , Geodynamics
- Description: The Olavi Mountain Land is a 10 000 km2 mineral province located at the eastern extremity of the exposed Northern Platform of the Damara Pan African orogenic belt. The Olavi Mountain Land is tbe most important mineral province on the Northern Platform. Exploitation of tbe Cu-Pb-Zn-V province has been on-going since the possession of the territory by the German colonial authority in 1890. Production has been mostly from four mines which in order of importance are Tsumeb, Kombat, Berg Aukas and Abeoab. A second mineral province on the Northern Platform located in the west is centred on Sesfontein where as yet only insignificant mineralization has been noted. Besides these localities, the Northern Platform is conspicuously devoid of notable mineralization. The aim of this thesis has been to document tbe Berg Aukas deposit, an important end-member type of mineralization in the Otavi Mountain Land. The basic premise bas been to show tbat the derivation and localization of the mineralization is a consequence of two broad controls which can be simply summarised as features of the basement and of the carbonate sequences. The geodynamic evolution of the Damara Belt commenced with intra-continental rifting approximately 900 Ma ago. Rift grabens trending north-east were filled by the Nosib Group which comprises mostly clastic lithologies but also some volcanics. The earliest and largest rift is referred to as the Northern Rift. Separation of the Congo, Kalahari, and proto-South American cratons resulted in rifting and rapid downwarping so that an encroaching sea and an Olavi Group carbonate shelf developed along the northern margin of the Northern Rift. Significantly, the carbonates only covered the Northern Rift in the area of the Otavi Mountain Land where a basinal dome, referred to as the Grootfontein Basement High, marked the basin edge. In the west, the carbonates covered the less important Sesfonfein Rift, and it is only in these two areas where Nosib sequences underlie the carbonate platform. Carbonate sedimentation was interrupted by a major period of crustal readjustment and the deposition of an extensive mixtite throughout the geosynclinal Swakop Trough and Northern Platform. This is referred to as the Chuos Formation and subdivides the Olavi Group into a lower Abenab and an upper Tsumeb Subgroup. Reversal of spreading led to plate collision and subduction of tbe Kalahari craton beneath the Congo craton. It was accompanied by orogenesis which resulted in F1 folding of the Northern Platform into a series of north-easterly trending intermontane basins into which a molasse sequence known as the Mulden Group was unconformably deposited. Following this major north-south deformation mild east-west compression initiated F2 folding and the formation of doubly plunging synclines. The Berg Aukas Syncline represents a primary depositional basin which was subsequently folded. The original basin was formed by late Nosib rifting wben spreading caused the Swakop geosynclinal Trough to form. Carbonates of the basal Berg Aukas Formation were deposited in a lagoonal setting typified by reef and fore-reef facies witb peri-platform conditions. Rapid subsidence caused these sediments to be overlain by deep water carbonates of the Gauss Formation. Two styles of mineralization known as the Tsumeb-type and Berg Aukas-type are stratigraphically, isotopically, and mineralogically distinct. The Tsumeb-type is a cupriferous variety of discordant bodies confined to the upper sequences beneath the Mulden unconformity. The Berg Aukas-type is a Zn-Pb variety confined to tbe basal unconformity. The Berg Aukas deposit comprises three ore bodies known as the Northern Ore Horizon, the Central Ore Body, and the Hanging Wall Ore Body. Sphalerite and galena constitute the bypogene ore. Willemite, smithsonite, cerussite, and descloizite are important supergene ores. A review of genetic models concludes that a magmatic origin initially proposed for tbe Tsumeb deposit is entirely rejected and a basin dewatering model in line with Mississippi Valley-type deposits is proposed. The syntectonic nature of mineralization at Berg Aukas and elsewhere in the Otavi Mountain Land indicates that orogenesis encouraged dewatering and leaching of metals from a broad mineralizing front along the margin of the Swakop Trough. These were transported by acidic saline brines which migrated along the clastic aquifers and structural conduits provided by the Northern Rift. Fluid inclusion studies indicate that the hydrothermal fluids at Berg Aukas were very saline (23% TDS) and were transported at temperatures ranging between 92° to 210°C. Hydrothermal fluids which mineralized Berg AukaS-type deposits migrated along the basal unconformity towards the basement high and were responsible for hydrothermally altering the basement granites and gabbros and the Nosib clastic rocks. Tsumeb-type deposits resulted by migration of fluids through the carbonate pile and along north-easterly trending basement geofractures. As a consequence of variation in transport, the Berg Aukas-type and Tsumeb-type fluids leached different sources and therefore derived mineralogically and isotopically seperable characteristics. The localization of the Berg Aukas ores was controlled by the carbonate stratigraphy and structure. Hydrothermal karsting and ore deposition took place on the contact between Massive Grey and Light Grey Dolostones which represents a permeability contrast. The movement of the hydrothermal fluids was controlled by north-south trending vertical fractures caused by F2 folding which resulted in a peric1inal structure. Hydrothermal karsting was accompanied by ca1citic, dolomitic and silicic alteration. The heated acidic fluids initiated solution collapse and a variety of breccia types. Supergene processes resulted in oxidation and upgrading of the ore. Vanadium derived indirectly from gabbros in the basement complex were transported as calcium metavanadate complexes and deposited on contact with the oxidizing base metal sulphides.
- Full Text:
- Date Issued: 1988
- Authors: Misiewicz, Julian Edward
- Date: 1988
- Subjects: Geology -- Namibia -- Damaraland , Ore deposits -- Namibia , Orogeny , Metallogeny , Geodynamics
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4959 , http://hdl.handle.net/10962/d1005571 , Geology -- Namibia -- Damaraland , Ore deposits -- Namibia , Orogeny , Metallogeny , Geodynamics
- Description: The Olavi Mountain Land is a 10 000 km2 mineral province located at the eastern extremity of the exposed Northern Platform of the Damara Pan African orogenic belt. The Olavi Mountain Land is tbe most important mineral province on the Northern Platform. Exploitation of tbe Cu-Pb-Zn-V province has been on-going since the possession of the territory by the German colonial authority in 1890. Production has been mostly from four mines which in order of importance are Tsumeb, Kombat, Berg Aukas and Abeoab. A second mineral province on the Northern Platform located in the west is centred on Sesfontein where as yet only insignificant mineralization has been noted. Besides these localities, the Northern Platform is conspicuously devoid of notable mineralization. The aim of this thesis has been to document tbe Berg Aukas deposit, an important end-member type of mineralization in the Otavi Mountain Land. The basic premise bas been to show tbat the derivation and localization of the mineralization is a consequence of two broad controls which can be simply summarised as features of the basement and of the carbonate sequences. The geodynamic evolution of the Damara Belt commenced with intra-continental rifting approximately 900 Ma ago. Rift grabens trending north-east were filled by the Nosib Group which comprises mostly clastic lithologies but also some volcanics. The earliest and largest rift is referred to as the Northern Rift. Separation of the Congo, Kalahari, and proto-South American cratons resulted in rifting and rapid downwarping so that an encroaching sea and an Olavi Group carbonate shelf developed along the northern margin of the Northern Rift. Significantly, the carbonates only covered the Northern Rift in the area of the Otavi Mountain Land where a basinal dome, referred to as the Grootfontein Basement High, marked the basin edge. In the west, the carbonates covered the less important Sesfonfein Rift, and it is only in these two areas where Nosib sequences underlie the carbonate platform. Carbonate sedimentation was interrupted by a major period of crustal readjustment and the deposition of an extensive mixtite throughout the geosynclinal Swakop Trough and Northern Platform. This is referred to as the Chuos Formation and subdivides the Olavi Group into a lower Abenab and an upper Tsumeb Subgroup. Reversal of spreading led to plate collision and subduction of tbe Kalahari craton beneath the Congo craton. It was accompanied by orogenesis which resulted in F1 folding of the Northern Platform into a series of north-easterly trending intermontane basins into which a molasse sequence known as the Mulden Group was unconformably deposited. Following this major north-south deformation mild east-west compression initiated F2 folding and the formation of doubly plunging synclines. The Berg Aukas Syncline represents a primary depositional basin which was subsequently folded. The original basin was formed by late Nosib rifting wben spreading caused the Swakop geosynclinal Trough to form. Carbonates of the basal Berg Aukas Formation were deposited in a lagoonal setting typified by reef and fore-reef facies witb peri-platform conditions. Rapid subsidence caused these sediments to be overlain by deep water carbonates of the Gauss Formation. Two styles of mineralization known as the Tsumeb-type and Berg Aukas-type are stratigraphically, isotopically, and mineralogically distinct. The Tsumeb-type is a cupriferous variety of discordant bodies confined to the upper sequences beneath the Mulden unconformity. The Berg Aukas-type is a Zn-Pb variety confined to tbe basal unconformity. The Berg Aukas deposit comprises three ore bodies known as the Northern Ore Horizon, the Central Ore Body, and the Hanging Wall Ore Body. Sphalerite and galena constitute the bypogene ore. Willemite, smithsonite, cerussite, and descloizite are important supergene ores. A review of genetic models concludes that a magmatic origin initially proposed for tbe Tsumeb deposit is entirely rejected and a basin dewatering model in line with Mississippi Valley-type deposits is proposed. The syntectonic nature of mineralization at Berg Aukas and elsewhere in the Otavi Mountain Land indicates that orogenesis encouraged dewatering and leaching of metals from a broad mineralizing front along the margin of the Swakop Trough. These were transported by acidic saline brines which migrated along the clastic aquifers and structural conduits provided by the Northern Rift. Fluid inclusion studies indicate that the hydrothermal fluids at Berg Aukas were very saline (23% TDS) and were transported at temperatures ranging between 92° to 210°C. Hydrothermal fluids which mineralized Berg AukaS-type deposits migrated along the basal unconformity towards the basement high and were responsible for hydrothermally altering the basement granites and gabbros and the Nosib clastic rocks. Tsumeb-type deposits resulted by migration of fluids through the carbonate pile and along north-easterly trending basement geofractures. As a consequence of variation in transport, the Berg Aukas-type and Tsumeb-type fluids leached different sources and therefore derived mineralogically and isotopically seperable characteristics. The localization of the Berg Aukas ores was controlled by the carbonate stratigraphy and structure. Hydrothermal karsting and ore deposition took place on the contact between Massive Grey and Light Grey Dolostones which represents a permeability contrast. The movement of the hydrothermal fluids was controlled by north-south trending vertical fractures caused by F2 folding which resulted in a peric1inal structure. Hydrothermal karsting was accompanied by ca1citic, dolomitic and silicic alteration. The heated acidic fluids initiated solution collapse and a variety of breccia types. Supergene processes resulted in oxidation and upgrading of the ore. Vanadium derived indirectly from gabbros in the basement complex were transported as calcium metavanadate complexes and deposited on contact with the oxidizing base metal sulphides.
- Full Text:
- Date Issued: 1988