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:
- 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:
Colour and sculpture : an investigation into the use of two dimensional media in sculpture
- Authors: Wright, Jeanne
- Date: 1988
- Subjects: Sculpture -- Technique Sculpture -- History Color in art
- Language: English
- Type: Thesis , Masters , MFA
- Identifier: vital:2436 , http://hdl.handle.net/10962/d1004783
- Description: From Introduction: Creative images which are normally called 'art' can be distinguished as either 'plastic' or visual. Both these forms throughout the history of art have relied to a greater or lesser degree on the use of colour. It is my intention to investigate specifically the changing role which colour has played in sculpture - the 'plastic' media of the visual arts and to chart the technical and aesthetic reasons for the use of colour. This investigation will encompass the historical perspective, the material qualities, aesthetic considerations, transitional codes and methods of approach in sociological frameworks and the examination of colour as a metaphysical element in the presentation of three dimensional media.
- Full Text:
- Authors: Wright, Jeanne
- Date: 1988
- Subjects: Sculpture -- Technique Sculpture -- History Color in art
- Language: English
- Type: Thesis , Masters , MFA
- Identifier: vital:2436 , http://hdl.handle.net/10962/d1004783
- Description: From Introduction: Creative images which are normally called 'art' can be distinguished as either 'plastic' or visual. Both these forms throughout the history of art have relied to a greater or lesser degree on the use of colour. It is my intention to investigate specifically the changing role which colour has played in sculpture - the 'plastic' media of the visual arts and to chart the technical and aesthetic reasons for the use of colour. This investigation will encompass the historical perspective, the material qualities, aesthetic considerations, transitional codes and methods of approach in sociological frameworks and the examination of colour as a metaphysical element in the presentation of three dimensional media.
- Full Text:
Concept development in aspects of ecology
- Authors: Webb, Paul
- Date: 1988
- Subjects: Ecology -- Study and teaching
- Language: English
- Type: text , Thesis , Masters , MEd
- Identifier: vital:1354 , http://hdl.handle.net/10962/d1001420
- Description: In this study food webs and a case study are used to investigate concepts which university students and high school pupils hold about ecology and the degree to which concept development has taken place at particular educational levels. The sample was drawn from first year zoology students and biology pupils in standards eight and ten. Present data indicate that students and pupils could solve problems involving the interactions of populations only if they were simple enough to be answered using strategies based on the food chain concept. Very few subjects could succesfully determine all the interacting pathways along which effects may be transmitted within a food web. The ability to determine all the pathways along which the effects of a change in population numbers within a community are spread, and to analyse the possible net manifestation of sometimes conflicting forces, requires a clear understanding of the concept of food web. An immature understanding of the food web concept by the subjects of this study is suggested as, in most cases, they identified alternate pathways within the food web when explicitly asked to do so, but did not apply this strategy when asked to solve problems based on the same principle. The case study also revealed immature ecological concepts. Responses by standard eight pupils indicate that the opportunity exists at this level to develop a clear and mature understanding of the concept of food web, while comparison of data provided by the three age groups suggests that if clear conceptual development regarding food webs does not take place at school, misconceptions are likely to persist among first year university students.
- Full Text:
- Authors: Webb, Paul
- Date: 1988
- Subjects: Ecology -- Study and teaching
- Language: English
- Type: text , Thesis , Masters , MEd
- Identifier: vital:1354 , http://hdl.handle.net/10962/d1001420
- Description: In this study food webs and a case study are used to investigate concepts which university students and high school pupils hold about ecology and the degree to which concept development has taken place at particular educational levels. The sample was drawn from first year zoology students and biology pupils in standards eight and ten. Present data indicate that students and pupils could solve problems involving the interactions of populations only if they were simple enough to be answered using strategies based on the food chain concept. Very few subjects could succesfully determine all the interacting pathways along which effects may be transmitted within a food web. The ability to determine all the pathways along which the effects of a change in population numbers within a community are spread, and to analyse the possible net manifestation of sometimes conflicting forces, requires a clear understanding of the concept of food web. An immature understanding of the food web concept by the subjects of this study is suggested as, in most cases, they identified alternate pathways within the food web when explicitly asked to do so, but did not apply this strategy when asked to solve problems based on the same principle. The case study also revealed immature ecological concepts. Responses by standard eight pupils indicate that the opportunity exists at this level to develop a clear and mature understanding of the concept of food web, while comparison of data provided by the three age groups suggests that if clear conceptual development regarding food webs does not take place at school, misconceptions are likely to persist among first year university students.
- Full Text:
Criminal and civil aspects of bribery
- Authors: Leslie, Andrew Brian
- Date: 1988
- Subjects: Bribery
- Language: English
- Type: Thesis , Masters , LLM
- Identifier: vital:3701 , http://hdl.handle.net/10962/d1004607
- Description: The purpose of this work is to identify legal action which may be taken against parties to bribery in the fields of criminal and civil law. In particular, the element of mens rea is investigated with regard to criminal corruption. On the civil side, the principal, who has been the victim of bribery, has various remedies against the parties to the bribe. These remedies are analysed with special reference to the influence of English law on the South African law in this field. The options open to the principal, where his agent has made a secret profit which does not amount to bribery, are also considered.
- Full Text:
- Authors: Leslie, Andrew Brian
- Date: 1988
- Subjects: Bribery
- Language: English
- Type: Thesis , Masters , LLM
- Identifier: vital:3701 , http://hdl.handle.net/10962/d1004607
- Description: The purpose of this work is to identify legal action which may be taken against parties to bribery in the fields of criminal and civil law. In particular, the element of mens rea is investigated with regard to criminal corruption. On the civil side, the principal, who has been the victim of bribery, has various remedies against the parties to the bribe. These remedies are analysed with special reference to the influence of English law on the South African law in this field. The options open to the principal, where his agent has made a secret profit which does not amount to bribery, are also considered.
- Full Text:
Defined by wine : a study of sacramentalism in George Herbertʾs poetry
- Authors: Goddard, Kevin Graham
- Date: 1988
- Subjects: Herbert, George, 1593-1633 -- Criticism and interpretation , Christian poetry, English -- History and criticism
- Language: English
- Type: text , Thesis , Masters , MA
- Identifier: vital:2177 , http://hdl.handle.net/10962/d1001828
- Description: This dissertation proposes that George Herbertʾs poetry may profitably be understood as a sacramental means by which the divine is made present in temporal existence. In order to support this claim, the relation between sacramental symbolism and literary symbolism, particularly Herbertʾs, is examined from a number of perspectives. The symbolic meanings suggested by Herbertʾs title (The Temple), and their relation to sacramentalism are considered in the opening chapter. This includes a consideration of some of the background to the analogical thinking prevalent in both the seventeenth-century and Herbert. It is followed in the second chapter by an examination of some of the modern theories about how literary symbolism may relate to sacramental symbolism, a discussion which is followed by a consideration of this dissertation's argument in relation to modern scholarship. The chapter ends with a reading of ʺThe Flowerʺ. The third chapter discusses the poet's attempt to imitate the divine by ʺcopyingʺ both Scripture and Nature, and this includes a consideration of the allegorical and hieroglyphic modes of thought prevalent in the poems. The concern with imitation encourages an examination of the poet's frequent invitation for God actually to assume the poet's role, and this is the subject of the fourth chapter. The argument suggests that the poet's attempt to ʺsacrificeʺ his own writing may be seen in his concern with corporate imagery and corporate (impersonal) structures. The five ʺAfflictionʺ poems are examined as examples of the first, while structures such as synecdoche and metonymy are examined as examples of the second. The final chapter considers aspects of narrative time in the poems, particularly the sense often evoked of the eternal being imminent in the present. This involves a consideration of both liturgical imagery, and what may be called liturgical structures as they can be seen to operate in the poems. Particular examples of the latter are the relation between the liturgical anamnesis and the poems, as well as certain narrative structures that may be called ʺachronisticʺ.
- Full Text:
- Authors: Goddard, Kevin Graham
- Date: 1988
- Subjects: Herbert, George, 1593-1633 -- Criticism and interpretation , Christian poetry, English -- History and criticism
- Language: English
- Type: text , Thesis , Masters , MA
- Identifier: vital:2177 , http://hdl.handle.net/10962/d1001828
- Description: This dissertation proposes that George Herbertʾs poetry may profitably be understood as a sacramental means by which the divine is made present in temporal existence. In order to support this claim, the relation between sacramental symbolism and literary symbolism, particularly Herbertʾs, is examined from a number of perspectives. The symbolic meanings suggested by Herbertʾs title (The Temple), and their relation to sacramentalism are considered in the opening chapter. This includes a consideration of some of the background to the analogical thinking prevalent in both the seventeenth-century and Herbert. It is followed in the second chapter by an examination of some of the modern theories about how literary symbolism may relate to sacramental symbolism, a discussion which is followed by a consideration of this dissertation's argument in relation to modern scholarship. The chapter ends with a reading of ʺThe Flowerʺ. The third chapter discusses the poet's attempt to imitate the divine by ʺcopyingʺ both Scripture and Nature, and this includes a consideration of the allegorical and hieroglyphic modes of thought prevalent in the poems. The concern with imitation encourages an examination of the poet's frequent invitation for God actually to assume the poet's role, and this is the subject of the fourth chapter. The argument suggests that the poet's attempt to ʺsacrificeʺ his own writing may be seen in his concern with corporate imagery and corporate (impersonal) structures. The five ʺAfflictionʺ poems are examined as examples of the first, while structures such as synecdoche and metonymy are examined as examples of the second. The final chapter considers aspects of narrative time in the poems, particularly the sense often evoked of the eternal being imminent in the present. This involves a consideration of both liturgical imagery, and what may be called liturgical structures as they can be seen to operate in the poems. Particular examples of the latter are the relation between the liturgical anamnesis and the poems, as well as certain narrative structures that may be called ʺachronisticʺ.
- Full Text:
Discussing the evidence : small group work in the history class
- Robinson, Andrew Meredith Lewin
- Authors: Robinson, Andrew Meredith Lewin
- Date: 1988
- Subjects: History -- Study and teaching (Secondary) Group work in education
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:1863 , http://hdl.handle.net/10962/d1004588
- Description: This is a small-scale research study on the discovery method of teaching history through the medium of small-group discussion. The study begins with a brief outline of the theoretical background to these topics, as well as of some of the extant research in the field. The class selected for the study is the standard seven class of a boys' high school. After the researcher has instructed the whole standard in an historical area which is unfamiliar to the pupils, twelve groups of three each are selected and withdrawn from the rest of the class, one group at a time. These thirty-six pupils become the "experimental" group; the rest of the pupils become the "control" group . The groups are selected according to different intellectual criteria and presented with stimulus material of one of three kinds, which is intended to aid them in their discourse. Each group is given the same set of three questions to discuss and, without further assistance by the researcher, the discussion takes place. This is recorded on audio-tape. After all the group discussions have been recorded, an assessment test is given to the whole standard, both experimental and control pupils. At the end of the school term a compulsory examination question is inserted in the history examination. The statistical data forthcoming from these assessments are correlated and the results analysed. Meanwhile, transcripts of all the group discussions have been made and these are analysed on a qualitative basis in terms of the groups' intellectual composition and according to the type of stimulus material used, and the results are recorded. The concept of "leaderless" groups is briefly discussed in the light of the dealings of the various groups in the study. The researcher finally feels justified in concluding that small groups are an ideal medium for the handling of evidence- based learning in history. He also has certain observations to make on the performance of groups of mixed (as opposed to homogeneous) ability as well as on the success of certain types of stimulus material towards initiating profitable discussion.
- Full Text:
- Authors: Robinson, Andrew Meredith Lewin
- Date: 1988
- Subjects: History -- Study and teaching (Secondary) Group work in education
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:1863 , http://hdl.handle.net/10962/d1004588
- Description: This is a small-scale research study on the discovery method of teaching history through the medium of small-group discussion. The study begins with a brief outline of the theoretical background to these topics, as well as of some of the extant research in the field. The class selected for the study is the standard seven class of a boys' high school. After the researcher has instructed the whole standard in an historical area which is unfamiliar to the pupils, twelve groups of three each are selected and withdrawn from the rest of the class, one group at a time. These thirty-six pupils become the "experimental" group; the rest of the pupils become the "control" group . The groups are selected according to different intellectual criteria and presented with stimulus material of one of three kinds, which is intended to aid them in their discourse. Each group is given the same set of three questions to discuss and, without further assistance by the researcher, the discussion takes place. This is recorded on audio-tape. After all the group discussions have been recorded, an assessment test is given to the whole standard, both experimental and control pupils. At the end of the school term a compulsory examination question is inserted in the history examination. The statistical data forthcoming from these assessments are correlated and the results analysed. Meanwhile, transcripts of all the group discussions have been made and these are analysed on a qualitative basis in terms of the groups' intellectual composition and according to the type of stimulus material used, and the results are recorded. The concept of "leaderless" groups is briefly discussed in the light of the dealings of the various groups in the study. The researcher finally feels justified in concluding that small groups are an ideal medium for the handling of evidence- based learning in history. He also has certain observations to make on the performance of groups of mixed (as opposed to homogeneous) ability as well as on the success of certain types of stimulus material towards initiating profitable discussion.
- Full Text:
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:
- 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:
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:
- 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:
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:
- 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:
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:
- 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:
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:
- 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:
History outside the classroom : the use of museums in the teaching of history
- Authors: Rheeder, Willem Lodewikus
- Date: 1988
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:21147 , http://hdl.handle.net/10962/6584
- Description: In the modern technical age in which we live , knowledge of the past is often pushed into the background As a result of this history teaching often becomes an attempt to pump an assortment of arbitrary facts into the minds of scholars by means of 'chalk and talk' methods. Educationists all over the world see this tendency as the major reason for the declining popularity of history as a school subject . In other parts of the world, such as the United States of America and Britain, education departments and teachers have faced this challenge and it seems as if the status of history as a school subject has been retrieved . In the Republic of South Africa the new core syllabuses are geared towards moving away from the earlier restricted emphasis of facts, but there is very little guidance on how teachers are to implement this 'new' approach, which focus more on the "how" of history and on the teaching of historical skills In this thesis museum visits as one of the modes of outdoor education, is studied as a possible additional alternative method of teaching history in South African schools . A study is made of what museums are and of the possible educational values of museum visits. It soon becomes clear that the major beneficial aspect of museum visits could be the acquisition of historical skills such as comprehension, application , analysis , synthesis and evaluation In order to gain insight into the practical implementation of museum visits several groups were observed while visiting the museum, after which two pilot studies were undertaken in the Kaffrarian and South African Missionary Museums with Black standard ten pupils and senior student teachers . Attention is given to aspects of administrative , teacher and pupil preparation the implementation of the visit and the types of follow-up work which could be used. During and after the implementation of the two pilot studies certain characteristic problems were experienced these are : the compilation of worksheets and cultural differences . The most important of language difficulties : It also became clear that education officers at museums find it difficult to cope with the special educational needs of the different visiting groups . For this reason an approach is advocated where the teacher compiles his own worksheet suited to the needs of his specific pupils Guidelines are given as to how pre-planned worksheets could be adapted : how different question-types could be used to compile a worksheet in which skills ascend from the simple to the complex: and how worksheets could be compiled for mixed ability groups. It is hoped that this thesis will lead to renewed interest in the use of the museum in the teaching of history and will serve as guideline for teachers planning to take history "out of its coffin".
- Full Text:
- Authors: Rheeder, Willem Lodewikus
- Date: 1988
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:21147 , http://hdl.handle.net/10962/6584
- Description: In the modern technical age in which we live , knowledge of the past is often pushed into the background As a result of this history teaching often becomes an attempt to pump an assortment of arbitrary facts into the minds of scholars by means of 'chalk and talk' methods. Educationists all over the world see this tendency as the major reason for the declining popularity of history as a school subject . In other parts of the world, such as the United States of America and Britain, education departments and teachers have faced this challenge and it seems as if the status of history as a school subject has been retrieved . In the Republic of South Africa the new core syllabuses are geared towards moving away from the earlier restricted emphasis of facts, but there is very little guidance on how teachers are to implement this 'new' approach, which focus more on the "how" of history and on the teaching of historical skills In this thesis museum visits as one of the modes of outdoor education, is studied as a possible additional alternative method of teaching history in South African schools . A study is made of what museums are and of the possible educational values of museum visits. It soon becomes clear that the major beneficial aspect of museum visits could be the acquisition of historical skills such as comprehension, application , analysis , synthesis and evaluation In order to gain insight into the practical implementation of museum visits several groups were observed while visiting the museum, after which two pilot studies were undertaken in the Kaffrarian and South African Missionary Museums with Black standard ten pupils and senior student teachers . Attention is given to aspects of administrative , teacher and pupil preparation the implementation of the visit and the types of follow-up work which could be used. During and after the implementation of the two pilot studies certain characteristic problems were experienced these are : the compilation of worksheets and cultural differences . The most important of language difficulties : It also became clear that education officers at museums find it difficult to cope with the special educational needs of the different visiting groups . For this reason an approach is advocated where the teacher compiles his own worksheet suited to the needs of his specific pupils Guidelines are given as to how pre-planned worksheets could be adapted : how different question-types could be used to compile a worksheet in which skills ascend from the simple to the complex: and how worksheets could be compiled for mixed ability groups. It is hoped that this thesis will lead to renewed interest in the use of the museum in the teaching of history and will serve as guideline for teachers planning to take history "out of its coffin".
- Full Text:
John Chrysostom's understanding of the Eucharist in its relation to the Christian life
- Authors: Amos, Charles Harry
- Date: 1988
- Subjects: John Chrysostom, Saint, d. 407 , Lord's Supper , Lord's Supper -- Biblical teaching
- Language: English
- Type: Thesis , Masters , MTh
- Identifier: vital:1217 , http://hdl.handle.net/10962/d1001547
- Description: The aim of this thesis is to reveal the intimate relationship between John Chrysostom's Eucharistic theology and the christian life, and that at the Eucharist Man's true being is demonstrated. It investigates Chrysostom's exegetical and oratorical method in order to ascertain how he approached a text and how he delivered his understanding of it. He is a representative of the Antiochene School of Exegesis and his fame as a preacher was a result not so much of his oratorical construction, but of the underlying spiritual unity within the oration. The purpose of all his preaching and exegesis was to evoke a moral response from his hearers. In the consecration of the elements, Chrysostcm displayed a remarkable openness to the varying traditions. He saw reciting the words of institution and invoking the Spirit as effecting consecration. Not only this, but also the moral life of the congregation played its part in effecting consecration. Once the elements had been consecrated, Christ was sacrificed, symbolically and literally, not again but in memory (Greek letters) of the Passion, which thereby becomes a present reality. In Chrysostom's understanding of the real presence he displays yet again an openness to the traditions. Christ is both present symbolically through the elements and literally through the transformation of the elements. The real presence demanded of the communicant a high degree of morality. To approach the Table on which Christ lay demanded a life of virtue, not only from the individual communicant but from the whole community. Those who partook unworthily imitated Judas and shared his fate. The community had to approach the Table in unity. At the Table, however, the community received its unity from Christ, the community became the body of Christ. Through participation and becoming the body of Christ, the community was united with the Godhead . Schism, therefore, was a very serious sin for it tore the body of Christ apart. For Chrysostom, Christ was also present in and intimately united with the poor. The church had to be able to be aware of Christ's presence in the poor and be responsible toward Him. In giving to the poor, the communiicant acknowledged that he/she had received at the Table and also received his/her salvation from Christ through the poor. The whole Eucharistic feast not only fed the christian with spiritual food, but called the communicant away from gross materialism to a life-giving dependance on God. It called the communicant to give to others as he/she had received from Christ.
- Full Text:
- Authors: Amos, Charles Harry
- Date: 1988
- Subjects: John Chrysostom, Saint, d. 407 , Lord's Supper , Lord's Supper -- Biblical teaching
- Language: English
- Type: Thesis , Masters , MTh
- Identifier: vital:1217 , http://hdl.handle.net/10962/d1001547
- Description: The aim of this thesis is to reveal the intimate relationship between John Chrysostom's Eucharistic theology and the christian life, and that at the Eucharist Man's true being is demonstrated. It investigates Chrysostom's exegetical and oratorical method in order to ascertain how he approached a text and how he delivered his understanding of it. He is a representative of the Antiochene School of Exegesis and his fame as a preacher was a result not so much of his oratorical construction, but of the underlying spiritual unity within the oration. The purpose of all his preaching and exegesis was to evoke a moral response from his hearers. In the consecration of the elements, Chrysostcm displayed a remarkable openness to the varying traditions. He saw reciting the words of institution and invoking the Spirit as effecting consecration. Not only this, but also the moral life of the congregation played its part in effecting consecration. Once the elements had been consecrated, Christ was sacrificed, symbolically and literally, not again but in memory (Greek letters) of the Passion, which thereby becomes a present reality. In Chrysostom's understanding of the real presence he displays yet again an openness to the traditions. Christ is both present symbolically through the elements and literally through the transformation of the elements. The real presence demanded of the communicant a high degree of morality. To approach the Table on which Christ lay demanded a life of virtue, not only from the individual communicant but from the whole community. Those who partook unworthily imitated Judas and shared his fate. The community had to approach the Table in unity. At the Table, however, the community received its unity from Christ, the community became the body of Christ. Through participation and becoming the body of Christ, the community was united with the Godhead . Schism, therefore, was a very serious sin for it tore the body of Christ apart. For Chrysostom, Christ was also present in and intimately united with the poor. The church had to be able to be aware of Christ's presence in the poor and be responsible toward Him. In giving to the poor, the communiicant acknowledged that he/she had received at the Table and also received his/her salvation from Christ through the poor. The whole Eucharistic feast not only fed the christian with spiritual food, but called the communicant away from gross materialism to a life-giving dependance on God. It called the communicant to give to others as he/she had received from Christ.
- Full Text:
Lovedale 1930-1955 : the study of a missionary institution in its social, educational and political context
- White, Timothy Raymond Howard
- Authors: White, Timothy Raymond Howard
- Date: 1988
- Subjects: Lovedale Institution , History , South Africa , Education , African people
- Language: English
- Type: text , Thesis , Masters , MA
- Identifier: vital:2527 , http://hdl.handle.net/10962/d1001856
- Description: Lovedale was founded by the Glasgow Missionary Society as an eduational centre for Africans. Education was to be adapted to the lives of the Africans which would be a departure from the English classical tradition. This meant that emphasis was placed on vocational training and that academic education focussed on the study of English rather than the Classics. But the importance of mother-tongue education was also stressed. The missionaries placed emphasis on village education, whereby the African would be taught skills and crafts that would be useful to him in life. Education, they argued, should also aim at character-training and at spreading the Christian message. They also wanted to see co-operation between the Church and the State in the education of the African. Vocational education was designed to create African artisans who would be able to compete with Whites; but it also aimed at emphasizing the importance of industry in building up character. The Lovedale Press illustrates vocational training in progress, dealing with the difficulties that arose when African printers came into competition with Whites. But the missionaries also used the Press to propagate the Christian message and to promote African literature. An ideological rift began to open up between the missions and the new Black political beliefs of the Second World War. This led to the Lovedale Riot which is considered in the broader framework of sociopolitical unrest within the country. After the 1948 Election an ideological rift also developed between the missions and the State. This study concludes by examining the introduction of the Bantu Education Act and the Lovedale response to this. It was felt that although Bantu Education threatened to undermine their educational endeavour, they should nevertheless cooperate with the system in order to save what they had built up.
- Full Text:
- Authors: White, Timothy Raymond Howard
- Date: 1988
- Subjects: Lovedale Institution , History , South Africa , Education , African people
- Language: English
- Type: text , Thesis , Masters , MA
- Identifier: vital:2527 , http://hdl.handle.net/10962/d1001856
- Description: Lovedale was founded by the Glasgow Missionary Society as an eduational centre for Africans. Education was to be adapted to the lives of the Africans which would be a departure from the English classical tradition. This meant that emphasis was placed on vocational training and that academic education focussed on the study of English rather than the Classics. But the importance of mother-tongue education was also stressed. The missionaries placed emphasis on village education, whereby the African would be taught skills and crafts that would be useful to him in life. Education, they argued, should also aim at character-training and at spreading the Christian message. They also wanted to see co-operation between the Church and the State in the education of the African. Vocational education was designed to create African artisans who would be able to compete with Whites; but it also aimed at emphasizing the importance of industry in building up character. The Lovedale Press illustrates vocational training in progress, dealing with the difficulties that arose when African printers came into competition with Whites. But the missionaries also used the Press to propagate the Christian message and to promote African literature. An ideological rift began to open up between the missions and the new Black political beliefs of the Second World War. This led to the Lovedale Riot which is considered in the broader framework of sociopolitical unrest within the country. After the 1948 Election an ideological rift also developed between the missions and the State. This study concludes by examining the introduction of the Bantu Education Act and the Lovedale response to this. It was felt that although Bantu Education threatened to undermine their educational endeavour, they should nevertheless cooperate with the system in order to save what they had built up.
- Full Text:
Men's repression of their emotional life as a counterpart of their oppression of women
- Authors: Hine, Grant Burnett
- Date: 1988
- Subjects: Men -- Psychology , Masculinity , Sex role , Oppression (Psychology) , Stereotype (Psychology)
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:3112 , http://hdl.handle.net/10962/d1004593 , Men -- Psychology , Masculinity , Sex role , Oppression (Psychology) , Stereotype (Psychology)
- Description: Masculinity and femininity are taken for granted as being a natural part of everyday existence forming acceptable images of what it means to be a man and a woman. It is revealed that in conforming to the sexual stereotype of what it means to be masculine and feminine, men's repression of their emotional life forms a counterpart of their oppression of women, for the repression of men's emotional life as a process, manifests itself through the oppression of women. The socioeconomic relations, being exploitative in nature, having been obscured and mystified by masculine and feminine forms of false consciousness, justify the prevalent social circumstances by portraying them as natural and inevitable, thus serving to hide the fact that men and women comprise of both, masculine and feminine characteristics. Disclosing the quality of the experience of men's repression of their emotional life as a counterpart of their oppression of women, through qualitative description and reflection, it is evident that individuality and human social relationships are restricted by the constraints of masculine and feminine stereotypes. It is clearly highlighted, that women help to perpetuate the repression of male emotional life and in turn their own oppression through supporting the successful work, status and power oriented 'macho' male. Through the recognition of the pressures, and a re-evaluation of the masculine role, men will no longer see cause to oppress women and through that there will no longer be a need to repress their own emotional life. There is a need for self-reflection in those individuals and groups restricted by the constraints of masculinity and femininity for the realization of new possibilities of enlightened social action and individuality.
- Full Text:
- Authors: Hine, Grant Burnett
- Date: 1988
- Subjects: Men -- Psychology , Masculinity , Sex role , Oppression (Psychology) , Stereotype (Psychology)
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:3112 , http://hdl.handle.net/10962/d1004593 , Men -- Psychology , Masculinity , Sex role , Oppression (Psychology) , Stereotype (Psychology)
- Description: Masculinity and femininity are taken for granted as being a natural part of everyday existence forming acceptable images of what it means to be a man and a woman. It is revealed that in conforming to the sexual stereotype of what it means to be masculine and feminine, men's repression of their emotional life forms a counterpart of their oppression of women, for the repression of men's emotional life as a process, manifests itself through the oppression of women. The socioeconomic relations, being exploitative in nature, having been obscured and mystified by masculine and feminine forms of false consciousness, justify the prevalent social circumstances by portraying them as natural and inevitable, thus serving to hide the fact that men and women comprise of both, masculine and feminine characteristics. Disclosing the quality of the experience of men's repression of their emotional life as a counterpart of their oppression of women, through qualitative description and reflection, it is evident that individuality and human social relationships are restricted by the constraints of masculine and feminine stereotypes. It is clearly highlighted, that women help to perpetuate the repression of male emotional life and in turn their own oppression through supporting the successful work, status and power oriented 'macho' male. Through the recognition of the pressures, and a re-evaluation of the masculine role, men will no longer see cause to oppress women and through that there will no longer be a need to repress their own emotional life. There is a need for self-reflection in those individuals and groups restricted by the constraints of masculinity and femininity for the realization of new possibilities of enlightened social action and individuality.
- Full Text:
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:
- 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:
Oor die kortkuns van John Miles
- Authors: De Beer, Marésa
- Date: 1988
- Subjects: Miles, John, 1938- -- Criticism and interpretation
- Language: Afrikaans
- Type: text , Thesis , Masters , MA
- Identifier: vital:3569 , http://hdl.handle.net/10962/d1002092
- Description: This thesis involves intensive analyses of some of the short-short stories in John Miles's Liefs nie op straat nie, in order to reveal the narrative strategies employed in each. In other words, it is geared to "the rules that govern ... textual actualization and, consequently, those rules that govern the way literary discourse functions as communication" (Riffaterre 1983: 158). Subsequently, attention is given to the interrelationship among the texts, the way in which they act upon one another and interact with the title of the volume, in order to establish the function of such relations. The following texts are analysed in consecutive chapters: "Lucy", "Lappies, kan jy my hoor, Lappies?", "Voorgevoel", "Dom Nakkie, my Dom Nakkie" and "Wie het nog Dom Nakkie gesien?", "Hy staan by die deur en hy klop", "Gustav gaan speel", and "Liefs nie op straat nie". In a concluding chapter the implications of the title are discussed with reference to all the texts in the volume, including those not analysed individually. It is concluded that, on the one hand, the expectations raised by the title are ironicized because the title is never "completed" explicitly, and because that which, by implication, should not be seen in public ("op straat"), is specifically situated in the street and scrutinized in close-up. But on the other hand the title also evokes a peculiar mentality present in all the texts, either in the narrators, or in the characters, or in both. The discussion of "Lucy" is focussed mainly on the contrast and interaction between the world of the child and that of the adult and on the way in which this interaction is actualized within the text through the contrast in the experience of time, the use of "mémoire involontaire", "durée" and the contrasts between (and overlapping of) narrative perspective and focalization. In respect of "Lappies, kan jy my hoor, Lappies?" special attention is paid to similarities and contrasts between this text and the traditional suspense story, notably the way in which conventional techniques are employed to create suspense, as well as to generate an entire subtext which eventually "relocates" the text on the niveau of the murderer's psychological dilemma. In discussing "Voorgevoel" emphasis is not placed primarily on what is conveyed by the narrator, but on the way in which his intentions are subverted both by the window pane through which he is looking and by the narration as such. In this way he is foregrounded and revealed as narrator, just as the text is foregrounded and revealed as literature, with the emphasis, in both cases, not only on their defence mechanisms but also on their impotence. "Dom Nakkie, my Dom Nakkie" and "Wie het nog Dom Nakkie gesien?" are grouped together in one chapter in order to illuminate the interaction between the two narratives in the first text, as well as the interaction between the two texts. Ultimately, they may be seen as three narratives juxtaposed through irony and relativism. The "triumph" of the "preferably not in public" mentality, both in the text and in society, is also illustrated by the interaction between the three narratives. In chapter, 5, in which "Hy staan by die deur en hy klop" is discussed, attention is focussed on the ironic function of the Biblical references, the contrast between Jan and the rest of society, and the way in which the "climax" is located within the Iserian "blank" in the text, so that the entire process of decoding is based on a filling in of that "blank" and its implications. "Gustav gaan speel" is based loosely on Barthes's lexia model, in order to determine the signifying process in the text, and also to demonstrate the way in which the text presupposes rereading. In the discussion of the title text it is revealed how the text is centered in the basic dichotomy between the narrator-as-writer and the journalist, and the way in which this polarity is relativized by the text as such. The text is demonstrated to be the credo of the volume as a whole as well as of the fiction of the Seventies in Afrikaans.
- Full Text:
- Authors: De Beer, Marésa
- Date: 1988
- Subjects: Miles, John, 1938- -- Criticism and interpretation
- Language: Afrikaans
- Type: text , Thesis , Masters , MA
- Identifier: vital:3569 , http://hdl.handle.net/10962/d1002092
- Description: This thesis involves intensive analyses of some of the short-short stories in John Miles's Liefs nie op straat nie, in order to reveal the narrative strategies employed in each. In other words, it is geared to "the rules that govern ... textual actualization and, consequently, those rules that govern the way literary discourse functions as communication" (Riffaterre 1983: 158). Subsequently, attention is given to the interrelationship among the texts, the way in which they act upon one another and interact with the title of the volume, in order to establish the function of such relations. The following texts are analysed in consecutive chapters: "Lucy", "Lappies, kan jy my hoor, Lappies?", "Voorgevoel", "Dom Nakkie, my Dom Nakkie" and "Wie het nog Dom Nakkie gesien?", "Hy staan by die deur en hy klop", "Gustav gaan speel", and "Liefs nie op straat nie". In a concluding chapter the implications of the title are discussed with reference to all the texts in the volume, including those not analysed individually. It is concluded that, on the one hand, the expectations raised by the title are ironicized because the title is never "completed" explicitly, and because that which, by implication, should not be seen in public ("op straat"), is specifically situated in the street and scrutinized in close-up. But on the other hand the title also evokes a peculiar mentality present in all the texts, either in the narrators, or in the characters, or in both. The discussion of "Lucy" is focussed mainly on the contrast and interaction between the world of the child and that of the adult and on the way in which this interaction is actualized within the text through the contrast in the experience of time, the use of "mémoire involontaire", "durée" and the contrasts between (and overlapping of) narrative perspective and focalization. In respect of "Lappies, kan jy my hoor, Lappies?" special attention is paid to similarities and contrasts between this text and the traditional suspense story, notably the way in which conventional techniques are employed to create suspense, as well as to generate an entire subtext which eventually "relocates" the text on the niveau of the murderer's psychological dilemma. In discussing "Voorgevoel" emphasis is not placed primarily on what is conveyed by the narrator, but on the way in which his intentions are subverted both by the window pane through which he is looking and by the narration as such. In this way he is foregrounded and revealed as narrator, just as the text is foregrounded and revealed as literature, with the emphasis, in both cases, not only on their defence mechanisms but also on their impotence. "Dom Nakkie, my Dom Nakkie" and "Wie het nog Dom Nakkie gesien?" are grouped together in one chapter in order to illuminate the interaction between the two narratives in the first text, as well as the interaction between the two texts. Ultimately, they may be seen as three narratives juxtaposed through irony and relativism. The "triumph" of the "preferably not in public" mentality, both in the text and in society, is also illustrated by the interaction between the three narratives. In chapter, 5, in which "Hy staan by die deur en hy klop" is discussed, attention is focussed on the ironic function of the Biblical references, the contrast between Jan and the rest of society, and the way in which the "climax" is located within the Iserian "blank" in the text, so that the entire process of decoding is based on a filling in of that "blank" and its implications. "Gustav gaan speel" is based loosely on Barthes's lexia model, in order to determine the signifying process in the text, and also to demonstrate the way in which the text presupposes rereading. In the discussion of the title text it is revealed how the text is centered in the basic dichotomy between the narrator-as-writer and the journalist, and the way in which this polarity is relativized by the text as such. The text is demonstrated to be the credo of the volume as a whole as well as of the fiction of the Seventies in Afrikaans.
- Full Text:
Organisational structures for effective geography teaching in selected medium and large primary schools
- Authors: Kaschula, Nathaniel Ronald
- Date: 1988
- Subjects: Geography -- Study and teaching (Elementary) -- South Africa Education, Primary -- Research -- South Africa
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:1859 , http://hdl.handle.net/10962/d1004552
- Description: Effective teaching is determined by a host of factors, not least of which is the educational guidance given to the teacher. This guidance should come about through an effecctively designed support structure initiated by the school principal as part of his management strategy. Very little has been written on this topic, particularly with reference to primary schools. In the past, geography teachers were trained, appointed to a school and expected to get on with their teaching. However, present-day teachers, in order to be effective educators, require in-service training. This should occur In a variety of ways and on a continuous basis, because teaching is an on-going business and not a job to be learned once and for always. This thesis investigates the organisational structures that exist for the teaching of geography in selected medium and large primary schools in the Eastern Cape. The author found that principals used either a subject head or standard head model. In large primary schools a subject head model was preferred i.e. a specialist geography teacher was responslble for developing the subject vertically from standard 2 to 5. The opposite was true in medium-sized schools. Principals of these schools preferred to delegate responsibility to a standard head. It was the duty ot the standard head, usually a generalist teacher without specific training in geography, to develop geography horizontally among, for example, all the standard 3 pupils. The role played by key members of a primary schools' instructional leadership team, namely the principal, subject head, and the standard head are examined in detail. The author offers justification why geography should be included In the primary curriculum. It is his contention that geography contributes to a child's general education, develops basic geographical skills, extends general mental abilities and fosters positive attitudes towards other people with whom he shares this world. A management model is proposed for principals, flexible enough for application in all schools. It is designed to ensure that teachers continue growing professionaIIy within the structure of a small group. There is no best way to organise the teaching of geography because each school has its own unique resources which should be optimally utilised in order to bring about learning. The professional development of geography teachers is possible because someone competent in geographical education should assume leadership of the qroup. This will enable ideas to be shared, plans made and strategies implemented in an eftort to improve teacher-competence through an efficiently organised geography department. In the final chapter conclusions are drawn and a recommendatlon is made for primary school principals to Implement an organlsatlonal model for the teaching of geography. A choice may be made from three models, namely a standard head, subject head or a comblnation of both models. It Is within the parameters of one of these structures that the subject can be properly managed, for example, field-trips planned, teaching aids purchased, envlronmental educatlon programmes designed, teaching strategies discussed and examinat(ons set. Thls view is supported by Cawood and GIbbon's (1980) empirical evidence. They found that good educatlonal leadership fosters effective teaching in schools.
- Full Text:
- Authors: Kaschula, Nathaniel Ronald
- Date: 1988
- Subjects: Geography -- Study and teaching (Elementary) -- South Africa Education, Primary -- Research -- South Africa
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:1859 , http://hdl.handle.net/10962/d1004552
- Description: Effective teaching is determined by a host of factors, not least of which is the educational guidance given to the teacher. This guidance should come about through an effecctively designed support structure initiated by the school principal as part of his management strategy. Very little has been written on this topic, particularly with reference to primary schools. In the past, geography teachers were trained, appointed to a school and expected to get on with their teaching. However, present-day teachers, in order to be effective educators, require in-service training. This should occur In a variety of ways and on a continuous basis, because teaching is an on-going business and not a job to be learned once and for always. This thesis investigates the organisational structures that exist for the teaching of geography in selected medium and large primary schools in the Eastern Cape. The author found that principals used either a subject head or standard head model. In large primary schools a subject head model was preferred i.e. a specialist geography teacher was responslble for developing the subject vertically from standard 2 to 5. The opposite was true in medium-sized schools. Principals of these schools preferred to delegate responsibility to a standard head. It was the duty ot the standard head, usually a generalist teacher without specific training in geography, to develop geography horizontally among, for example, all the standard 3 pupils. The role played by key members of a primary schools' instructional leadership team, namely the principal, subject head, and the standard head are examined in detail. The author offers justification why geography should be included In the primary curriculum. It is his contention that geography contributes to a child's general education, develops basic geographical skills, extends general mental abilities and fosters positive attitudes towards other people with whom he shares this world. A management model is proposed for principals, flexible enough for application in all schools. It is designed to ensure that teachers continue growing professionaIIy within the structure of a small group. There is no best way to organise the teaching of geography because each school has its own unique resources which should be optimally utilised in order to bring about learning. The professional development of geography teachers is possible because someone competent in geographical education should assume leadership of the qroup. This will enable ideas to be shared, plans made and strategies implemented in an eftort to improve teacher-competence through an efficiently organised geography department. In the final chapter conclusions are drawn and a recommendatlon is made for primary school principals to Implement an organlsatlonal model for the teaching of geography. A choice may be made from three models, namely a standard head, subject head or a comblnation of both models. It Is within the parameters of one of these structures that the subject can be properly managed, for example, field-trips planned, teaching aids purchased, envlronmental educatlon programmes designed, teaching strategies discussed and examinat(ons set. Thls view is supported by Cawood and GIbbon's (1980) empirical evidence. They found that good educatlonal leadership fosters effective teaching in schools.
- Full Text:
Perceptions of, and attitudes towards, varieties of English in the Cape Peninsula, with particular reference to the ʾcoloured communityʾ
- Authors: Wood, Tahir Muhammed
- Date: 1988
- Subjects: English language -- South Africa -- Cape of Good Hope , English language -- Variation , Sociolinguistics -- South Africa
- Language: English
- Type: text , Thesis , Masters , MA
- Identifier: vital:2336 , http://hdl.handle.net/10962/d1002018
- Description: This study set out to analyse the concept of the ʾcoloured communityʾ and to describe the linguistic phenomena associated with it. It was found that the community was characterized by division and an overt rejection of 'coloured' identity. A satisfactory definition of the community could only be arrived at by exploring social psychological and anthropological concepts, particularly that of the social network, and a covert identification was postulated. This in turn was used to explain the linguistic phenomena which were found to be associated with the community. The latter included a vernacular dialect consisting of non-standard Afrikaans blended with English, as well as a stratification of particular items in the English spoken by community members . This stratification was analysed in terms of the social distribution of the items, enabling comparisons to be made with the English spoken by ʾwhitesʾ. A fieldwork study was embarked on with the intention of discovering the nature of the perceptions of, and attitudes towards, the idiolects of certain speakers. These idiolects were considered to be typical and representative of the forms of English normally encountered in the Cape Peninsula, and were described in terms of the co-occurrences of linguistic items which they contained. Tape recordings of the speech of this group of speakers were presented in a series of controlled experiments to subjects from various class and community backgrounds who were required to respond by completing questionnaires. It was found that those lects which contained items and co-occurrences of items peculiar to 'coloured' speakers were associated with lower status than those containing items and co-occurrences of items peculiar to 'white' speakers. Attitudes towards speakers were found to be more complex and depended upon the styles and paralanguage behaviours of the speakers, as well as accent, and also the psychological dispositions of the subjects who participated
- Full Text:
- Authors: Wood, Tahir Muhammed
- Date: 1988
- Subjects: English language -- South Africa -- Cape of Good Hope , English language -- Variation , Sociolinguistics -- South Africa
- Language: English
- Type: text , Thesis , Masters , MA
- Identifier: vital:2336 , http://hdl.handle.net/10962/d1002018
- Description: This study set out to analyse the concept of the ʾcoloured communityʾ and to describe the linguistic phenomena associated with it. It was found that the community was characterized by division and an overt rejection of 'coloured' identity. A satisfactory definition of the community could only be arrived at by exploring social psychological and anthropological concepts, particularly that of the social network, and a covert identification was postulated. This in turn was used to explain the linguistic phenomena which were found to be associated with the community. The latter included a vernacular dialect consisting of non-standard Afrikaans blended with English, as well as a stratification of particular items in the English spoken by community members . This stratification was analysed in terms of the social distribution of the items, enabling comparisons to be made with the English spoken by ʾwhitesʾ. A fieldwork study was embarked on with the intention of discovering the nature of the perceptions of, and attitudes towards, the idiolects of certain speakers. These idiolects were considered to be typical and representative of the forms of English normally encountered in the Cape Peninsula, and were described in terms of the co-occurrences of linguistic items which they contained. Tape recordings of the speech of this group of speakers were presented in a series of controlled experiments to subjects from various class and community backgrounds who were required to respond by completing questionnaires. It was found that those lects which contained items and co-occurrences of items peculiar to 'coloured' speakers were associated with lower status than those containing items and co-occurrences of items peculiar to 'white' speakers. Attitudes towards speakers were found to be more complex and depended upon the styles and paralanguage behaviours of the speakers, as well as accent, and also the psychological dispositions of the subjects who participated
- Full Text:
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:
- 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: