A combination of a stationary and non-stationary model to predict corporate failure in South Africa
- Authors: Court, Philip Wathen
- Date: 1994
- Subjects: Bankruptcy -- South Africa Business planning -- South Africa Business failures -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1183 , http://hdl.handle.net/10962/d1002800
- Description: Business failure should be of concern in most industralised countries and the importance of accurately evaluating the phenomenon from a management and investment point of view is enormous. Were it possible to predict failure with a certain degree of confidence, steps could be taken to rectify the situation and the benefit would accrue to all of the stakeholders in the macroenvironment. In essence, the profitability of a business is influenced by two sets of variables. In the first instance, it is influenced by a variety of internal (microeconomic) variables which are firm- specific and which management is generally able to control. A further distinction in this regard may be made between the financial and non-financial variables. In the second instance, it is generally accepted that profitability will be influenced by a number of external (macroeconomic) variables which are generally beyond the control of management. In the main, however, the profitability of the firm is generally determined by a combination of both sets of factors. To date, a great deal of research has been undertaken in an attempt to establish a reliable model which may be used to predict failure. This has mainly been confined to the microeconomic variables which can be used to predict failure and attempts have been made to isolate either a single financial ratio or a number of financial and non-financial variables which can be used to model corporate failure. The research has met with a certain degree of success although this appears to be confined to the economic environment to which the models have been applied. The models are less successful when applied to other macroenvironments. Limited research has been undertaken into the macroeconomic variables which contribute to business failure or to a combination of the two types of variables. It is appropriate therefore that further consideration be given to the establishment of a model incorporating ALL the variables which could contribute to corporate failure. The purpose of this research is to undertake an investigation of micro- and macroeconomic variables that are freely available to reserachers and which may be used in a failure prediction model. The intention is to obtain a comprehensive, yet simple model which can be used as an overall predictor of PENDING failure.
- Full Text:
- Date Issued: 1994
- Authors: Court, Philip Wathen
- Date: 1994
- Subjects: Bankruptcy -- South Africa Business planning -- South Africa Business failures -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1183 , http://hdl.handle.net/10962/d1002800
- Description: Business failure should be of concern in most industralised countries and the importance of accurately evaluating the phenomenon from a management and investment point of view is enormous. Were it possible to predict failure with a certain degree of confidence, steps could be taken to rectify the situation and the benefit would accrue to all of the stakeholders in the macroenvironment. In essence, the profitability of a business is influenced by two sets of variables. In the first instance, it is influenced by a variety of internal (microeconomic) variables which are firm- specific and which management is generally able to control. A further distinction in this regard may be made between the financial and non-financial variables. In the second instance, it is generally accepted that profitability will be influenced by a number of external (macroeconomic) variables which are generally beyond the control of management. In the main, however, the profitability of the firm is generally determined by a combination of both sets of factors. To date, a great deal of research has been undertaken in an attempt to establish a reliable model which may be used to predict failure. This has mainly been confined to the microeconomic variables which can be used to predict failure and attempts have been made to isolate either a single financial ratio or a number of financial and non-financial variables which can be used to model corporate failure. The research has met with a certain degree of success although this appears to be confined to the economic environment to which the models have been applied. The models are less successful when applied to other macroenvironments. Limited research has been undertaken into the macroeconomic variables which contribute to business failure or to a combination of the two types of variables. It is appropriate therefore that further consideration be given to the establishment of a model incorporating ALL the variables which could contribute to corporate failure. The purpose of this research is to undertake an investigation of micro- and macroeconomic variables that are freely available to reserachers and which may be used in a failure prediction model. The intention is to obtain a comprehensive, yet simple model which can be used as an overall predictor of PENDING failure.
- Full Text:
- Date Issued: 1994
A cultural analysis of Venda guitar songs
- Authors: Kruger, Jaco Hentie
- Date: 1994
- Subjects: Ethnomusicology Venda (African people) -- Music -- Social aspects Songs with guitar Music -- Social aspects Music -- Social aspects -- South Africa -- Venda Symbolism in music
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:2644 , http://hdl.handle.net/10962/d1002309
- Description: This thesis focuses on the articulation in music of human worldviews, and the social contexts in which they emerge. It suggests that people project various forms of social reality through symbolic systems which operate dynamically to maintain and recreate cultural patterns. The symbolic system investigated in support of this suggestion is that constituted by Venda guitar songs. In the performance of these songs, social reality emerges in a combination of symbolic forms: verbal, musical and somatic. The combination of these symbolic forms serves as a medium for individual self-awareness basic to the establishment of social reality and identity, and the drive for social power and legitimacy. A study of these symbolic forms and their performance indicates that musicians invoke the potential of communal music to increase social support for certain principles on which survival strategies in a turbulently changing society might be based. The discourse of Venda guitar songs incorporates modes of popular expression and consciousness, and thus attempts to invoke states of intensified emotion to promote these survival strategies. Performance occasions emerge as a focus for community orientation and the exploration of social networks. They promote stabilizing social and economic interaction, and serve as a basis for moral and cooperative action. Social reality also emerges in musical style, which is treated as the audible articulation of human thought and emotion. Stylistic choices are treated as integral to the conceptualization of contemporary existence. A study of these choices reveals varying degrees of cultural resistance and assimilation, ranging from musical styles which are essentially rooted in traditional social patterns, to styles which integrate traditional and adopted musical elements as articulations of changing self-perceptions, social aspirations, and quests for new social identity.
- Full Text:
- Date Issued: 1994
- Authors: Kruger, Jaco Hentie
- Date: 1994
- Subjects: Ethnomusicology Venda (African people) -- Music -- Social aspects Songs with guitar Music -- Social aspects Music -- Social aspects -- South Africa -- Venda Symbolism in music
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:2644 , http://hdl.handle.net/10962/d1002309
- Description: This thesis focuses on the articulation in music of human worldviews, and the social contexts in which they emerge. It suggests that people project various forms of social reality through symbolic systems which operate dynamically to maintain and recreate cultural patterns. The symbolic system investigated in support of this suggestion is that constituted by Venda guitar songs. In the performance of these songs, social reality emerges in a combination of symbolic forms: verbal, musical and somatic. The combination of these symbolic forms serves as a medium for individual self-awareness basic to the establishment of social reality and identity, and the drive for social power and legitimacy. A study of these symbolic forms and their performance indicates that musicians invoke the potential of communal music to increase social support for certain principles on which survival strategies in a turbulently changing society might be based. The discourse of Venda guitar songs incorporates modes of popular expression and consciousness, and thus attempts to invoke states of intensified emotion to promote these survival strategies. Performance occasions emerge as a focus for community orientation and the exploration of social networks. They promote stabilizing social and economic interaction, and serve as a basis for moral and cooperative action. Social reality also emerges in musical style, which is treated as the audible articulation of human thought and emotion. Stylistic choices are treated as integral to the conceptualization of contemporary existence. A study of these choices reveals varying degrees of cultural resistance and assimilation, ranging from musical styles which are essentially rooted in traditional social patterns, to styles which integrate traditional and adopted musical elements as articulations of changing self-perceptions, social aspirations, and quests for new social identity.
- Full Text:
- Date Issued: 1994
A high school guidance programme aimed at the primary prevention of sexual abuse of children as part of a national strategy for the prevention of child sexual abuse in South Africa
- Authors: McGregor, Dale
- Date: 1994
- Subjects: Child abuse -- South Africa -- Prevention Educational counseling -- Keiskammahoek Educational counseling -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1553 , http://hdl.handle.net/10962/d1003435
- Description: The sexual abuse of children has become recognised as a major problem affecting children in most, if not all, countries of the world. The prevention of such abuse has, in the last decade, become an issue of international significance. In South Africa, prevention efforts are mainly informal ad hoc strategies initiated by individuals or organisations. As such they suffer from being short-lived and often isolated. Prevention efforts fall into the general categories of primary, secondary and tertiary prevention. Primary prevention focuses on preventing abuse from occurring at all. There are two main aspects to this type of prevention. The first aims at teaching children to protect themselves. The second aims at preventing the development of a disposition to abuse. This study set out to suggest and justify the adoption of a national strategy appropriate to the South African situation, including an overview of what can be done through the schooling system. This strategy will provide a framework and context for individual efforts, and hopefully stimulate new programmes. In addition, a detailed prevention programme for implementation in the secondary school, through the medium of the subject Guidance, was developed. This programme addressed itself mainly to that primary aspect of prevention concerned with preventing people from developing a disposition to abuse. The programme consists of lesson plans, teacher's notes and worksheet materials for pupils.
- Full Text:
- Date Issued: 1994
- Authors: McGregor, Dale
- Date: 1994
- Subjects: Child abuse -- South Africa -- Prevention Educational counseling -- Keiskammahoek Educational counseling -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1553 , http://hdl.handle.net/10962/d1003435
- Description: The sexual abuse of children has become recognised as a major problem affecting children in most, if not all, countries of the world. The prevention of such abuse has, in the last decade, become an issue of international significance. In South Africa, prevention efforts are mainly informal ad hoc strategies initiated by individuals or organisations. As such they suffer from being short-lived and often isolated. Prevention efforts fall into the general categories of primary, secondary and tertiary prevention. Primary prevention focuses on preventing abuse from occurring at all. There are two main aspects to this type of prevention. The first aims at teaching children to protect themselves. The second aims at preventing the development of a disposition to abuse. This study set out to suggest and justify the adoption of a national strategy appropriate to the South African situation, including an overview of what can be done through the schooling system. This strategy will provide a framework and context for individual efforts, and hopefully stimulate new programmes. In addition, a detailed prevention programme for implementation in the secondary school, through the medium of the subject Guidance, was developed. This programme addressed itself mainly to that primary aspect of prevention concerned with preventing people from developing a disposition to abuse. The programme consists of lesson plans, teacher's notes and worksheet materials for pupils.
- Full Text:
- Date Issued: 1994
A study of balance and gait following stroke : implications for rehabilitation
- Authors: Turnbull, George Innes
- Date: 1994
- Subjects: Cerebrovascular disease -- Physical therapy , Gait disorders , Equilibrium (Physiology) , People with disabilities -- Rehabilitation
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5168 , http://hdl.handle.net/10962/d1016251
- Description: This study examined: the features and extent of the gait velocity decrement following stroke; the nature of the balance disorder and; investigated relationships between gait and balance. Twenty, fully-ambulant, hemiplegic subjects (12 men and 8 women), with a mean age of 57.2 years (± 10.7), were compared with 20 age- and sex-matched controls. Spatiotemporal gait kinematics were measured at five walking speeds ranging from "very slow" to "very fast". Balance was then measured while subjects maintained a variety of weight shift postures both with feet parallel and then in diagonal positions similar to those assumed during the double support phases of gait. Location and variability of centre of pressure (CP) were measured and the ranges over which CP could be shifted were calculated. Stroke subjects walked very slowly with their "fastest" walking speed (0.5 stat/s ± 0.23) no different from the "slowest" speed (0.38 stat/s ± 0.11) of the controls (p > 0.05). Differences between the other parameters were also found, many of which could be attributed to the differences in walking speeds. However, where the subjects walked at similar velocities, the hemiplegic sample walked with quicker and shoner strides suggesting a "cautious" gait pattern. The single support asymmetry of the strokes decreased with increasing walking speed. The positions of CP in the hemiplegic sample were found to be significantly displaced towards the unaffected leg and deficiencies were found in posterior shifts (p < 0.05). Postural sway was significantly greater in the hemiplegic sample implying less stable balance and the ranges over which the hemiplegic sample shifted weight were significantly less than the controls. The diagonal weight shift tests revealed the difficulty the stroke subjects experienced in shifting CP posterolaterally over the affected leg. Significant correlations were detected confmning the presence of relationships between static balance performance and gait. However, these correlation findings left considerable percentages of variance unexplained. These findings suggest that future rehabilitation should address the poverty of range of walking speed possessed by hemiplegic subjects as well as the reduced ability to weight shift over the hemiplegic limb, particularly posterolaterally. Further study to test these proposals is indicated.
- Full Text:
- Date Issued: 1994
- Authors: Turnbull, George Innes
- Date: 1994
- Subjects: Cerebrovascular disease -- Physical therapy , Gait disorders , Equilibrium (Physiology) , People with disabilities -- Rehabilitation
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5168 , http://hdl.handle.net/10962/d1016251
- Description: This study examined: the features and extent of the gait velocity decrement following stroke; the nature of the balance disorder and; investigated relationships between gait and balance. Twenty, fully-ambulant, hemiplegic subjects (12 men and 8 women), with a mean age of 57.2 years (± 10.7), were compared with 20 age- and sex-matched controls. Spatiotemporal gait kinematics were measured at five walking speeds ranging from "very slow" to "very fast". Balance was then measured while subjects maintained a variety of weight shift postures both with feet parallel and then in diagonal positions similar to those assumed during the double support phases of gait. Location and variability of centre of pressure (CP) were measured and the ranges over which CP could be shifted were calculated. Stroke subjects walked very slowly with their "fastest" walking speed (0.5 stat/s ± 0.23) no different from the "slowest" speed (0.38 stat/s ± 0.11) of the controls (p > 0.05). Differences between the other parameters were also found, many of which could be attributed to the differences in walking speeds. However, where the subjects walked at similar velocities, the hemiplegic sample walked with quicker and shoner strides suggesting a "cautious" gait pattern. The single support asymmetry of the strokes decreased with increasing walking speed. The positions of CP in the hemiplegic sample were found to be significantly displaced towards the unaffected leg and deficiencies were found in posterior shifts (p < 0.05). Postural sway was significantly greater in the hemiplegic sample implying less stable balance and the ranges over which the hemiplegic sample shifted weight were significantly less than the controls. The diagonal weight shift tests revealed the difficulty the stroke subjects experienced in shifting CP posterolaterally over the affected leg. Significant correlations were detected confmning the presence of relationships between static balance performance and gait. However, these correlation findings left considerable percentages of variance unexplained. These findings suggest that future rehabilitation should address the poverty of range of walking speed possessed by hemiplegic subjects as well as the reduced ability to weight shift over the hemiplegic limb, particularly posterolaterally. Further study to test these proposals is indicated.
- Full Text:
- Date Issued: 1994
Behavioural model debugging in Linda
- Authors: Sewry, David Andrew
- Date: 1994
- Subjects: LINDA (Computer system) Debugging in computer science
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4674 , http://hdl.handle.net/10962/d1006697
- Description: This thesis investigates event-based behavioural model debugging in Linda. A study is presented of the Linda parallel programming paradigm, its amenability to debugging, and a model for debugging Linda programs using Milner's CCS. In support of the construction of expected behaviour models, a Linda program specification language is proposed. A behaviour recognition engine that is based on such specifications is also discussed. It is shown that Linda's distinctive characteristics make it amenable to debugging without the usual problems associated with paraUel debuggers. Furthermore, it is shown that a behavioural model debugger, based on the proposed specification language, effectively exploits the debugging opportunity. The ideas developed in the thesis are demonstrated in an experimental Modula-2 Linda system.
- Full Text:
- Date Issued: 1994
- Authors: Sewry, David Andrew
- Date: 1994
- Subjects: LINDA (Computer system) Debugging in computer science
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4674 , http://hdl.handle.net/10962/d1006697
- Description: This thesis investigates event-based behavioural model debugging in Linda. A study is presented of the Linda parallel programming paradigm, its amenability to debugging, and a model for debugging Linda programs using Milner's CCS. In support of the construction of expected behaviour models, a Linda program specification language is proposed. A behaviour recognition engine that is based on such specifications is also discussed. It is shown that Linda's distinctive characteristics make it amenable to debugging without the usual problems associated with paraUel debuggers. Furthermore, it is shown that a behavioural model debugger, based on the proposed specification language, effectively exploits the debugging opportunity. The ideas developed in the thesis are demonstrated in an experimental Modula-2 Linda system.
- Full Text:
- Date Issued: 1994
Biocatalytic and biomimetic studies of polyphenol oxidase
- Authors: Burton, Stephanie Gail
- Date: 1994
- Subjects: Phenol oxidase Polyphenols Oxidases
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4028 , http://hdl.handle.net/10962/d1004088
- Description: Mushroom polyphenol oxidase (EC 1.14.18.1) was investigated to determine its potential for application as a biocatalyst in the synthesis of o-quinones, in organic medium. In order to determine the kinetic properties of the biocatalyst, a system was devised which comprised an immobilised polyphenol oxidase extract, functioning in chloroform. The system was hydrated by the addition of buffer. A simple method for the consistent measurement of reaction rates in this heterogenous system was designed and used to obtain detailed enzyme kinetic data relating to optimisation of reaction conditions and substrate specificity. The aqueous content of the system was optimised using p-cresol as a substrate. A crude, immobilised extract of Agaricus bisporus was used to hydroxylate and oxidise a range of selected p-substituted phenolic substrates, yielding, as the sale products, o-quinones. These products were efficiently reduced to catechols by extracting the reaction mixtures with aqueous ascorbic acid solution. The biocatalytic system was also successfully utilised to produce L-DOPA, the drug used to treat Parkinson's disease, from L-acetyl tyrosine ethyl ester (ATEE). Michaelis-Menten kinetics were used to obtain apparent Km and V values with respect to the selected phenolic substrates, and the kinetic parameters obtained were found to correlate well with the steric requirements of the substrates and with their hydrophobicity. In the course of the investigation, a novel ¹H NMR method was used to facilitate measurement of the UV molar absorption coefficients of the o-quinones in reaction mixtures, thus avoiding the necessity to isolate these unstable, water-sensitive products. The biocatalytic system was extended to a continuous process, in which the immobilised enzyme was shown to function successfully in the chloroform medium for several hours, with high conversion rates. Modifications, involving partial purification and the addition of a surfactant, were investigated to determine their effect on the kinetic parameters. The results obtained using partially purified enzyme indicated that the removal of extraneous protein and/or melanoid material lead to a reduced capacity for conversion of sterically demanding substrates. The addition of the anionic detergent, sodium dodecyl sulphate (SOS), enhanced the ability of the biocatalyst to bind and oxidise sterically demanding substrates. These effects are attributed to changes in the polar state of groups within the protein binding pocket, which result in altered flexibility and hydrophobicity. Computer modelling of several biomimetic dinuclear copper complexes also indicated the importance of flexibility for effective biocatalysis. Novel binuclear copper (II complexes, containing a flexible biphenyl spacer and imidazole or benzimidazole donors, were prepared and analysed using NMR, UV, AA and cyclic voltammetric techniques. The complexes were also shown, in a detailed kinetic study, to mimic the catecholase activity of polyphenol oxidase by oxidising 3,5-di-tertbutylcatechol, and to catalyse the coupling of the phenolic substrate 2,4-di-tert-butylphenol. However, the complexes were apparently too flexible to react with smaller substrates. These biomimetic complexes provided valuable insights into the nature of the dinuclear copper binding site.
- Full Text:
- Date Issued: 1994
- Authors: Burton, Stephanie Gail
- Date: 1994
- Subjects: Phenol oxidase Polyphenols Oxidases
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4028 , http://hdl.handle.net/10962/d1004088
- Description: Mushroom polyphenol oxidase (EC 1.14.18.1) was investigated to determine its potential for application as a biocatalyst in the synthesis of o-quinones, in organic medium. In order to determine the kinetic properties of the biocatalyst, a system was devised which comprised an immobilised polyphenol oxidase extract, functioning in chloroform. The system was hydrated by the addition of buffer. A simple method for the consistent measurement of reaction rates in this heterogenous system was designed and used to obtain detailed enzyme kinetic data relating to optimisation of reaction conditions and substrate specificity. The aqueous content of the system was optimised using p-cresol as a substrate. A crude, immobilised extract of Agaricus bisporus was used to hydroxylate and oxidise a range of selected p-substituted phenolic substrates, yielding, as the sale products, o-quinones. These products were efficiently reduced to catechols by extracting the reaction mixtures with aqueous ascorbic acid solution. The biocatalytic system was also successfully utilised to produce L-DOPA, the drug used to treat Parkinson's disease, from L-acetyl tyrosine ethyl ester (ATEE). Michaelis-Menten kinetics were used to obtain apparent Km and V values with respect to the selected phenolic substrates, and the kinetic parameters obtained were found to correlate well with the steric requirements of the substrates and with their hydrophobicity. In the course of the investigation, a novel ¹H NMR method was used to facilitate measurement of the UV molar absorption coefficients of the o-quinones in reaction mixtures, thus avoiding the necessity to isolate these unstable, water-sensitive products. The biocatalytic system was extended to a continuous process, in which the immobilised enzyme was shown to function successfully in the chloroform medium for several hours, with high conversion rates. Modifications, involving partial purification and the addition of a surfactant, were investigated to determine their effect on the kinetic parameters. The results obtained using partially purified enzyme indicated that the removal of extraneous protein and/or melanoid material lead to a reduced capacity for conversion of sterically demanding substrates. The addition of the anionic detergent, sodium dodecyl sulphate (SOS), enhanced the ability of the biocatalyst to bind and oxidise sterically demanding substrates. These effects are attributed to changes in the polar state of groups within the protein binding pocket, which result in altered flexibility and hydrophobicity. Computer modelling of several biomimetic dinuclear copper complexes also indicated the importance of flexibility for effective biocatalysis. Novel binuclear copper (II complexes, containing a flexible biphenyl spacer and imidazole or benzimidazole donors, were prepared and analysed using NMR, UV, AA and cyclic voltammetric techniques. The complexes were also shown, in a detailed kinetic study, to mimic the catecholase activity of polyphenol oxidase by oxidising 3,5-di-tertbutylcatechol, and to catalyse the coupling of the phenolic substrate 2,4-di-tert-butylphenol. However, the complexes were apparently too flexible to react with smaller substrates. These biomimetic complexes provided valuable insights into the nature of the dinuclear copper binding site.
- Full Text:
- Date Issued: 1994
Comparative aspects of the reproductive biology of seabreams (Pisces: Sparidae)
- Authors: Garratt, Patrick Ashworth
- Date: 1994
- Subjects: Sparidae -- Physiology Sparidae -- Reproduction
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5245 , http://hdl.handle.net/10962/d1005088
- Description: Sexuality in seabreams (Sparidae) is considered to be more complex than in any other family of fishes. Early work indicated five reproductive styles within the family: protandry, protogyny, simultaneous hermaphroditism, rudimentary hermaphroditism and gonochorism. More recently two reproductive styles have been suggested: sex change (protandry and protogyny) and secondary gonochorism (rudimentary hermaphrodites). The need for detailed descriptions of sex differentiation, gonad development and spawning behaviour in this family has been identified by a number of workers in this field. The aims of the present study were: i) to provide accurate, detailed descriptions and comparisons of gonadal development in representatives of each reproductive style, ii) to investigate their spawning strategies, and iii) to relate these findings to current theories on hermaphroditism and sex change in fishes. Four species were investigated. Slinger, Chrysoblephus puniceus, the only known protogynous hermaphrodite in Natal. Santer, Cheimerius nufar, described in the literature as a rudimentary hermaphrodite. Riverbream, Acanthopagrus berda suspected to be a protandrous hermaphrodite. Natal stump nose, Rhabdosargus sarba, reported elsewhere as a protandrous hermaphrodite. Detailed histological analysis showed that morphological and cytological development of all gonads proceeded initially in a female direction, irrespective of reproductive style, but that differentiating gonads of protandrous and protogynous hermaphrodites could easily be distinguished from one another. Early gonadal development was similar in R. sarba and A. berda with gonadal primordia differentiating into distinctly bisexual organs. In C. puniceus and C. nufar gonadal primordia differentiated into ovaries with reduced, inert male elements in the tunica albuginea. Sex differentiation occurred relatively late (100-150mm fork length) in all the species investigated. Few cells conforming to primordial germ cells (PGC's) described in other teleosts were identified. These cells only became evident after the appearance of gonial cells and their identity is questioned. Gonial cells appeared to develop within less-electron-dense cysts of cells. Gonial cells in presumptive male and female elements could not be distinguished from one another morphologically, suggesting the bipotentiality of these cells. All R. sarba and A. berda gonads pass through a predominantly male phase and all fish function first as males, indicating protandrous sex change in both species. All C. puniceus and C. nufar gonads develop initially into ovaries. Sex change thus occurs in both species and protogyny in C. puniceus is confirmed. In C. nufar, sex change may occur before or after sexual maturity and its reproductive style remains uncertain. Investigations into the spawning habits of A. berda have shown that this species spawns inside the Kosi estuary at night. Eggs are released during peak ebb tides. Spawning occurs in large aggregations and several to many males compete to spawn with individual females. This spawning strategy does not conform to predictions made from the size advantage model for protandrous species. Chrysoblephus puniceus appears to have preferential spawning sites on down-current outer reef margins. Spawning was not observed in this species, but changes in behaviour, social structure and colour during the spawning season suggest that it may have a mating system similar to several protogynous labrids and scarids, in which territories are temporary. Cheimerius nufar has a similar mating system. Temporary territories are established by large males during the spawning season, which extends from August to November. Mating is by pair-spawning and dominant territorial males obtain a disproportionate number of matings. 'Streaking' appears to represent an alternative mating strategy for males until they attain a sufficient size to establish and defend territories. The mating pattern of C. nufar suggests that it is either a gonochorist which does not conform to current theoretical predictions; or that it is a protogynous hermaphrodite incorrectly diagnosed as a rudimentary hermaphrodite; or that protogyny in the Sparidae is an ancestral condition and C. nufar is in the process of evolutionary change from a protogynous to a gonochoristic form (or visa versa).
- Full Text:
- Date Issued: 1994
- Authors: Garratt, Patrick Ashworth
- Date: 1994
- Subjects: Sparidae -- Physiology Sparidae -- Reproduction
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5245 , http://hdl.handle.net/10962/d1005088
- Description: Sexuality in seabreams (Sparidae) is considered to be more complex than in any other family of fishes. Early work indicated five reproductive styles within the family: protandry, protogyny, simultaneous hermaphroditism, rudimentary hermaphroditism and gonochorism. More recently two reproductive styles have been suggested: sex change (protandry and protogyny) and secondary gonochorism (rudimentary hermaphrodites). The need for detailed descriptions of sex differentiation, gonad development and spawning behaviour in this family has been identified by a number of workers in this field. The aims of the present study were: i) to provide accurate, detailed descriptions and comparisons of gonadal development in representatives of each reproductive style, ii) to investigate their spawning strategies, and iii) to relate these findings to current theories on hermaphroditism and sex change in fishes. Four species were investigated. Slinger, Chrysoblephus puniceus, the only known protogynous hermaphrodite in Natal. Santer, Cheimerius nufar, described in the literature as a rudimentary hermaphrodite. Riverbream, Acanthopagrus berda suspected to be a protandrous hermaphrodite. Natal stump nose, Rhabdosargus sarba, reported elsewhere as a protandrous hermaphrodite. Detailed histological analysis showed that morphological and cytological development of all gonads proceeded initially in a female direction, irrespective of reproductive style, but that differentiating gonads of protandrous and protogynous hermaphrodites could easily be distinguished from one another. Early gonadal development was similar in R. sarba and A. berda with gonadal primordia differentiating into distinctly bisexual organs. In C. puniceus and C. nufar gonadal primordia differentiated into ovaries with reduced, inert male elements in the tunica albuginea. Sex differentiation occurred relatively late (100-150mm fork length) in all the species investigated. Few cells conforming to primordial germ cells (PGC's) described in other teleosts were identified. These cells only became evident after the appearance of gonial cells and their identity is questioned. Gonial cells appeared to develop within less-electron-dense cysts of cells. Gonial cells in presumptive male and female elements could not be distinguished from one another morphologically, suggesting the bipotentiality of these cells. All R. sarba and A. berda gonads pass through a predominantly male phase and all fish function first as males, indicating protandrous sex change in both species. All C. puniceus and C. nufar gonads develop initially into ovaries. Sex change thus occurs in both species and protogyny in C. puniceus is confirmed. In C. nufar, sex change may occur before or after sexual maturity and its reproductive style remains uncertain. Investigations into the spawning habits of A. berda have shown that this species spawns inside the Kosi estuary at night. Eggs are released during peak ebb tides. Spawning occurs in large aggregations and several to many males compete to spawn with individual females. This spawning strategy does not conform to predictions made from the size advantage model for protandrous species. Chrysoblephus puniceus appears to have preferential spawning sites on down-current outer reef margins. Spawning was not observed in this species, but changes in behaviour, social structure and colour during the spawning season suggest that it may have a mating system similar to several protogynous labrids and scarids, in which territories are temporary. Cheimerius nufar has a similar mating system. Temporary territories are established by large males during the spawning season, which extends from August to November. Mating is by pair-spawning and dominant territorial males obtain a disproportionate number of matings. 'Streaking' appears to represent an alternative mating strategy for males until they attain a sufficient size to establish and defend territories. The mating pattern of C. nufar suggests that it is either a gonochorist which does not conform to current theoretical predictions; or that it is a protogynous hermaphrodite incorrectly diagnosed as a rudimentary hermaphrodite; or that protogyny in the Sparidae is an ancestral condition and C. nufar is in the process of evolutionary change from a protogynous to a gonochoristic form (or visa versa).
- Full Text:
- Date Issued: 1994
Hermeneutics in psychotherapy : a study of interpretation in the context of the psychotherapeutic dialogue
- Authors: Kelly, Kevin John
- Date: 1994
- Subjects: Insight in psychotherapy Psychotherapy -- Methodology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3199 , http://hdl.handle.net/10962/d1009515
- Description: The central aim of this study was to contribute to the understanding of the process of interpretation as it occurs in the context of a dialogue in insight-oriented psychotherapy. The literature review consisted of two parts. Firstly, the philosophical literature on the theory of interpretation was reviewed. A set of central philosophical issues was identified, which pertain to the psychotherapeutic project of interpreting the meaning of a person's experience in the context of a dialogue with that person. Secondly, the psychotherapeutic literature was reviewed. Previous attempts to conceptualise and prescribe processes of interpretation were described. The issues which appeared to be in need of further clarification were identified. A clinical study was conducted to further explore the questions raised in the literature reviews. A methodology was developed which gave access to the direct experience of both clients and therapists during the events of psychotherapeutic interpretation. The methodology yielded a description of the interpretative structure of the psychotherapeutic dialogue for each therapist-client pair. These were then consolidated into a description of general structural features of the psychotherapeutic dialogue. The results consisted of a description of processes and structural features which are intrinsic to the psychotherapeutic interpretation of the meaning of a person's experience in the context of a dialogue. The results were elaborated in an extensive discussion from which the following findings emerged: (l)It is important to distinguish between communicative and interpretative forms of dialogue. (2)Thematisation activity is mediated by a number of dialectically related operations which are intrinsic to the interpretative project of psychotherapy. (3)Insight-oriented psychotherapy relies on the presence of the therapist as a dialogical partner and the therapist is not merely a facilitator of introspection on the part of the client. (4)The character of interpretation in psychotherapy may be understood in certain respects to be an elaboration of functions of the imagination. (5)The process of interpretation can be understood in relational terms and the variations of interpretative experience may be understood as variations of 'an inter-subjective interpretative ideal. (6)Understanding of certain forms of psychopathology is deepened when they are considered as variations of an ideal capacity to engage in interpretative dialogue. (7)It is possible to describe certain ideal conditions which are facilitative of interpretative dialogue and hence of the psychotherapeutic development of self-insight. In conclusion suggestions for further research were made. It was suggested that the perspective of hermeneutic phenomenology provides an appropriate philosophical and methodological foundation for understanding the unique dialogical interpretative situation which is psychotherapy. The study emphasized, both in its content and in the manner of its execution, the need for interpretative efforts to be accompanied by methodological reflection and especially an awareness of how interpretative strategies partially constitute the realities they set out to describe.
- Full Text:
- Date Issued: 1994
- Authors: Kelly, Kevin John
- Date: 1994
- Subjects: Insight in psychotherapy Psychotherapy -- Methodology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3199 , http://hdl.handle.net/10962/d1009515
- Description: The central aim of this study was to contribute to the understanding of the process of interpretation as it occurs in the context of a dialogue in insight-oriented psychotherapy. The literature review consisted of two parts. Firstly, the philosophical literature on the theory of interpretation was reviewed. A set of central philosophical issues was identified, which pertain to the psychotherapeutic project of interpreting the meaning of a person's experience in the context of a dialogue with that person. Secondly, the psychotherapeutic literature was reviewed. Previous attempts to conceptualise and prescribe processes of interpretation were described. The issues which appeared to be in need of further clarification were identified. A clinical study was conducted to further explore the questions raised in the literature reviews. A methodology was developed which gave access to the direct experience of both clients and therapists during the events of psychotherapeutic interpretation. The methodology yielded a description of the interpretative structure of the psychotherapeutic dialogue for each therapist-client pair. These were then consolidated into a description of general structural features of the psychotherapeutic dialogue. The results consisted of a description of processes and structural features which are intrinsic to the psychotherapeutic interpretation of the meaning of a person's experience in the context of a dialogue. The results were elaborated in an extensive discussion from which the following findings emerged: (l)It is important to distinguish between communicative and interpretative forms of dialogue. (2)Thematisation activity is mediated by a number of dialectically related operations which are intrinsic to the interpretative project of psychotherapy. (3)Insight-oriented psychotherapy relies on the presence of the therapist as a dialogical partner and the therapist is not merely a facilitator of introspection on the part of the client. (4)The character of interpretation in psychotherapy may be understood in certain respects to be an elaboration of functions of the imagination. (5)The process of interpretation can be understood in relational terms and the variations of interpretative experience may be understood as variations of 'an inter-subjective interpretative ideal. (6)Understanding of certain forms of psychopathology is deepened when they are considered as variations of an ideal capacity to engage in interpretative dialogue. (7)It is possible to describe certain ideal conditions which are facilitative of interpretative dialogue and hence of the psychotherapeutic development of self-insight. In conclusion suggestions for further research were made. It was suggested that the perspective of hermeneutic phenomenology provides an appropriate philosophical and methodological foundation for understanding the unique dialogical interpretative situation which is psychotherapy. The study emphasized, both in its content and in the manner of its execution, the need for interpretative efforts to be accompanied by methodological reflection and especially an awareness of how interpretative strategies partially constitute the realities they set out to describe.
- Full Text:
- Date Issued: 1994
Influence of blue/green versus red and white light sources on human dark adaptation and other selected visual functions
- Authors: Hendrikse, Egbert Johannes
- Date: 1994
- Subjects: Light -- Physiological effect Lighting Vision -- Research Night vision Visual acuity Color -- Physiological effect Color vision
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5146 , http://hdl.handle.net/10962/d1009497
- Description: Red interior lighting used to preserve dark-adaptation needs to be replaced in military applications by blue/green lighting which is not detectable by 3rd-generation image intensifiers. This study investigated the influence of blue/green as compared to red and white light of equal photopic intensity on subsequent visual acuity , contrast sensitivity and dark-adaptation. Male subjects (n = 90) were assigned to one of 15 treatment conditions (n = 6) as determined by the colour (blue/green, red or white) and intensity (0.1; 0.4; 1.6; 6.4 and 25.6 cd/m²) of the pre-adaptation stimuli. A modified Goldmann/Weekers adaptometer was used to present the preadaptation stimuli, test stimuli and record visual (luminance) thresholds of each subject. Blue/green lighting had the same affect on visual (photopic) acuity and contrast sensitivity as white and red lighting. Blue/green affected visual (absolute) threshold at the start and during the process of dark-adaptation in the same manner as white but not the same as red lighting. White and red lighting did not differ significantly (p < 0.01) at low intensities (mesopic range) but did at the higher intensities (photopic range). After exposure to blue/green and white light, it will take longer to reach the same level of dark-adaptation than after exposure to red. These time differences increase with" increased intensities. The brightness ratio between red and white lights to produce the same dark-adaptation increases with an increase in intensity. At the upper mesopic region the differences between the effects of white and red lighting on subsequent dark-adaptation become irregular due to the inability to accurately equate non-monochromatic lights in the mesopic range.
- Full Text:
- Date Issued: 1994
- Authors: Hendrikse, Egbert Johannes
- Date: 1994
- Subjects: Light -- Physiological effect Lighting Vision -- Research Night vision Visual acuity Color -- Physiological effect Color vision
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5146 , http://hdl.handle.net/10962/d1009497
- Description: Red interior lighting used to preserve dark-adaptation needs to be replaced in military applications by blue/green lighting which is not detectable by 3rd-generation image intensifiers. This study investigated the influence of blue/green as compared to red and white light of equal photopic intensity on subsequent visual acuity , contrast sensitivity and dark-adaptation. Male subjects (n = 90) were assigned to one of 15 treatment conditions (n = 6) as determined by the colour (blue/green, red or white) and intensity (0.1; 0.4; 1.6; 6.4 and 25.6 cd/m²) of the pre-adaptation stimuli. A modified Goldmann/Weekers adaptometer was used to present the preadaptation stimuli, test stimuli and record visual (luminance) thresholds of each subject. Blue/green lighting had the same affect on visual (photopic) acuity and contrast sensitivity as white and red lighting. Blue/green affected visual (absolute) threshold at the start and during the process of dark-adaptation in the same manner as white but not the same as red lighting. White and red lighting did not differ significantly (p < 0.01) at low intensities (mesopic range) but did at the higher intensities (photopic range). After exposure to blue/green and white light, it will take longer to reach the same level of dark-adaptation than after exposure to red. These time differences increase with" increased intensities. The brightness ratio between red and white lights to produce the same dark-adaptation increases with an increase in intensity. At the upper mesopic region the differences between the effects of white and red lighting on subsequent dark-adaptation become irregular due to the inability to accurately equate non-monochromatic lights in the mesopic range.
- Full Text:
- Date Issued: 1994
Nutrient supplementation and secondary metaolites in melanoma cells
- Authors: Stoll, Karin Elisabeth
- Date: 1994
- Subjects: Vitamin C -- Therapeutic use Cancer -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4049 , http://hdl.handle.net/10962/d1004110
- Description: Considerable interest exists with regard to the putative therapeutic role of ascorbic acid in various conditions. A condition which has received much attention is cancer, as it is reported that ascorbic acid may be a prophylactic against cancer development. However, the actual involvement of ascorbic acid, an oxidizing/reducing agent, in the development and progression of tumours is presently a subject of much speculation. This study initially addressed the effect of ascorbic acid supplementation over a nutritional concentration range (0 - 100 μg/ml) on the in vitro growth of non-malignant LLCMK and malignant B16 cells. Ascorbic acid supplementation of these two cell types resulted in an overall decrease in the growth of both types of cells. The actual inhibitory mechanism of ascorbic acid on cell growth was not clear. Further study attempted to define and explain a mechanism responsible for this effect. Ascorbic acid has a role in the maintenance of tissue integrity and host defences, thus providing a rational basis for examining its relationship to cancer. Ascorbic acid is lcnown to be essential for the structural integrity of the intercellular matrix of the cells, the latter being a complex aqueous gel containing, amongst other compounds, fats and prostaglandins. Fats and prostaglandins have diverse effects on. membrane stability, enzyme activity and secondary messengers within cells. Hence, this study investigated the effect of ascorbic acid supplementation on certain enzymes and secondary metabolites within the cells, which had the potential to be involved in the control of cell growth. Throughout this study, emphasis was placed on the Bl6 melanoma cells as ascorbic acid supplementation did not significantly affect levels of secondary metabolites within the non-malignant LLCMK cells. Ascorbic acid supplementation of the B16 cells resulted in significant increases in adenylate cyclase activity and cyclic adenosine monophosphate levels, witb a significant decrease in Bl6 cell growth in that particular experiment. As cyclic adenosine monophosphate has a regulatory role in the cell cycle, this study suggested that the inhibitory effect of ascorbic acid supplementation on cell growth was mediated tbrough a final effect provided by the second messenger, cyclic adenosine monophosphate. However, clarification of tbe mechanism of tbe effect of ascorbic acid on adenylate cyclase activity was required. Hence, a further study investigated prostaglandin E₂ levels, as tbese affect adenylate cyclase activity. Prostaglandin E₂ levels were also found to be inversely related to Bl6 cell growth with ascorbic acid supplementation. It thus appeared tbat adenylate cyclase activity was dependent on prostaglandin E₂ levels in the B16 cells, and further study showed that tbis was indeed the case. Here, higher levels of prostaglandin E₂ supplementation of the Bl6 cells inhibited cell growth significantly and also significantly increased adenylate cyclase activity. Arachidonic acid is the precursor of prostaglandin E₂. In the presence of ascorbic acid supplementation, the percentage arachidonic acid composition of the Bl6 cells was inversely correlated with cell growth. Hence, prostaglandin E₂ levels in ascorbic acid supplemented B16 cells appeared dependent on tbe amount of precursor present. This was confirmed when Bl6 cells were supplemented with arachidonic acid. The latter had an inhibitory effect on Bl6 cell growth and also stimulated prostaglandin E₂ production. The cause of tbe inverse relationship between B16 cell growth and arachidonic acid composition with ascorbic acid supplementation was furtber investigated and found to be dependent on tbe uptake of arachidonic acid and other essential fatty acids from tbe medium. The enzymes phospholipase A₂ delta-5 and delta-6-desaturase, and elongase which could influence arachidonic acid levels were not affected to any extent by ascorbic acid supplementation and therefore did not influence the inverse relationship between B16 cell growth and arachidonic acid. Hence, it can be concluded that the effect of ascorbic acid supplementation on the BI6 cells is mediated, in part at least, by cyclic adenosine monophosphate. However, this is not the result of a direct effect of ascorbic acid supplementation. The initial effect of ascorbic acid supplementation concerns fatty acid - in particular arachidonic acid - uptake from the medium, with subsequent cascade effects On secondary metabolites, ultimately affecting the cellular levels of cyclic adenosine monophosphate.
- Full Text:
- Date Issued: 1994
- Authors: Stoll, Karin Elisabeth
- Date: 1994
- Subjects: Vitamin C -- Therapeutic use Cancer -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4049 , http://hdl.handle.net/10962/d1004110
- Description: Considerable interest exists with regard to the putative therapeutic role of ascorbic acid in various conditions. A condition which has received much attention is cancer, as it is reported that ascorbic acid may be a prophylactic against cancer development. However, the actual involvement of ascorbic acid, an oxidizing/reducing agent, in the development and progression of tumours is presently a subject of much speculation. This study initially addressed the effect of ascorbic acid supplementation over a nutritional concentration range (0 - 100 μg/ml) on the in vitro growth of non-malignant LLCMK and malignant B16 cells. Ascorbic acid supplementation of these two cell types resulted in an overall decrease in the growth of both types of cells. The actual inhibitory mechanism of ascorbic acid on cell growth was not clear. Further study attempted to define and explain a mechanism responsible for this effect. Ascorbic acid has a role in the maintenance of tissue integrity and host defences, thus providing a rational basis for examining its relationship to cancer. Ascorbic acid is lcnown to be essential for the structural integrity of the intercellular matrix of the cells, the latter being a complex aqueous gel containing, amongst other compounds, fats and prostaglandins. Fats and prostaglandins have diverse effects on. membrane stability, enzyme activity and secondary messengers within cells. Hence, this study investigated the effect of ascorbic acid supplementation on certain enzymes and secondary metabolites within the cells, which had the potential to be involved in the control of cell growth. Throughout this study, emphasis was placed on the Bl6 melanoma cells as ascorbic acid supplementation did not significantly affect levels of secondary metabolites within the non-malignant LLCMK cells. Ascorbic acid supplementation of the B16 cells resulted in significant increases in adenylate cyclase activity and cyclic adenosine monophosphate levels, witb a significant decrease in Bl6 cell growth in that particular experiment. As cyclic adenosine monophosphate has a regulatory role in the cell cycle, this study suggested that the inhibitory effect of ascorbic acid supplementation on cell growth was mediated tbrough a final effect provided by the second messenger, cyclic adenosine monophosphate. However, clarification of tbe mechanism of tbe effect of ascorbic acid on adenylate cyclase activity was required. Hence, a further study investigated prostaglandin E₂ levels, as tbese affect adenylate cyclase activity. Prostaglandin E₂ levels were also found to be inversely related to Bl6 cell growth with ascorbic acid supplementation. It thus appeared tbat adenylate cyclase activity was dependent on prostaglandin E₂ levels in the B16 cells, and further study showed that tbis was indeed the case. Here, higher levels of prostaglandin E₂ supplementation of the Bl6 cells inhibited cell growth significantly and also significantly increased adenylate cyclase activity. Arachidonic acid is the precursor of prostaglandin E₂. In the presence of ascorbic acid supplementation, the percentage arachidonic acid composition of the Bl6 cells was inversely correlated with cell growth. Hence, prostaglandin E₂ levels in ascorbic acid supplemented B16 cells appeared dependent on tbe amount of precursor present. This was confirmed when Bl6 cells were supplemented with arachidonic acid. The latter had an inhibitory effect on Bl6 cell growth and also stimulated prostaglandin E₂ production. The cause of tbe inverse relationship between B16 cell growth and arachidonic acid composition with ascorbic acid supplementation was furtber investigated and found to be dependent on tbe uptake of arachidonic acid and other essential fatty acids from tbe medium. The enzymes phospholipase A₂ delta-5 and delta-6-desaturase, and elongase which could influence arachidonic acid levels were not affected to any extent by ascorbic acid supplementation and therefore did not influence the inverse relationship between B16 cell growth and arachidonic acid. Hence, it can be concluded that the effect of ascorbic acid supplementation on the BI6 cells is mediated, in part at least, by cyclic adenosine monophosphate. However, this is not the result of a direct effect of ascorbic acid supplementation. The initial effect of ascorbic acid supplementation concerns fatty acid - in particular arachidonic acid - uptake from the medium, with subsequent cascade effects On secondary metabolites, ultimately affecting the cellular levels of cyclic adenosine monophosphate.
- Full Text:
- Date Issued: 1994
Stress manipulation in Dunaliella salina and dual-stage [beta]-carotene production
- Authors: Phillips, Trevor David
- Date: 1994
- Subjects: Dunaliella Carotenes Plants -- Effect of stress on
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4037 , http://hdl.handle.net/10962/d1004097
- Description: The alga Dunaliella salina accumulates large quantities of β-carotene in response to certain environmental and physiological stresses. This hyper-accumulation process has been commercially exploited. However, the currently employed averaging or single-stage process produces β-carotene yields well below the genetic potential of the organism due to the inverse relationship between growth and secondary metabolite production. A dual-stage process, which separates the distinctive growth and secondary metabolite production stages of the alga, has been proposed. The broad aim of the research programme was to evaluate the practicality, scale-up and economic viability of a dual-stage β-carotene production process from D. salina. Preliminary laboratory studies showed that although stress factors such as high salinity and a range of nutrient limitations enhance β-carotene accumulation in D. salina, high light intensity is the single most important factor inducing β-carotene hyper-accumulation in the alga. Furthermore, the preliminary studies indicated that 6-carotene production could be successfully manipulated by the imposition of stress. The stress response of D. salina to high light stress was examined at a fundamental level. The relative partitioning of β-carotene between thylakoid membrane and interthylakoid globular β-carotene has revealed two responses to high light stress. The first is a response in which the alga adapts to the photoinhibitory effects of high light stress by the rapid accumulation and the peripheral localisation of Jl-carotene to the outer extremities of the chloroplast. This is followed by a maintenance response which is characterised by the recovery of the photosynthetic rate and cell growth. A possible interrelationship between the extent of the photo inhibitory response and the amount of β-carotene hyper-accumulation has been noted. An outdoor evaluation of the growth stage of the dual-stage system has demonstrated that D. salina can be grown in a relatively low salinity, nutrient sufficient medium for extended periods without overgrowth by small non-carotenogenic Dunaliella species. In addition, biomass productivities of three times greater than those obtained in the currently employed averaging system were achieved. The role of high light intensity in β-carotene hyper-accumulation was confirmed in outdoor scale-up stress pond studies. The studies demonstrated the feasibility of stress induced ll-carotene production in outdoor cultures of D. salina and β-carotene yields three times greater than those obtained in the currently employed averaging process were achieved. The dual-stage process imposes the specific requirement of viable cell separation on the harvesting system employed. A flocculation-flotation process and an air-displacement crossflow ultrafiltration system were developed and successfully evaluated for the separation of D. salina from the brine solution in a viable form. The extraction of β-carotene from D. salina was evaluated. Supercritical fluid extraction studies showed that the use of a co-solvent mixture of carbon dioxide and propane could effectively reduce the high extraction pressures associated with supercritical carbon dioxide extraction. In addition, a novel hydrophobic membrane assisted hot oil extraction process was developed which separates the complex oil-water emulsions produced during hot oil extraction of 6-carotene from wet D. salina biomass. Process design and economic evaluation studies were undertaken and showed that the economics of the dual-stage process offer significant advantages over the currently employed averaging process.
- Full Text:
- Date Issued: 1994
- Authors: Phillips, Trevor David
- Date: 1994
- Subjects: Dunaliella Carotenes Plants -- Effect of stress on
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4037 , http://hdl.handle.net/10962/d1004097
- Description: The alga Dunaliella salina accumulates large quantities of β-carotene in response to certain environmental and physiological stresses. This hyper-accumulation process has been commercially exploited. However, the currently employed averaging or single-stage process produces β-carotene yields well below the genetic potential of the organism due to the inverse relationship between growth and secondary metabolite production. A dual-stage process, which separates the distinctive growth and secondary metabolite production stages of the alga, has been proposed. The broad aim of the research programme was to evaluate the practicality, scale-up and economic viability of a dual-stage β-carotene production process from D. salina. Preliminary laboratory studies showed that although stress factors such as high salinity and a range of nutrient limitations enhance β-carotene accumulation in D. salina, high light intensity is the single most important factor inducing β-carotene hyper-accumulation in the alga. Furthermore, the preliminary studies indicated that 6-carotene production could be successfully manipulated by the imposition of stress. The stress response of D. salina to high light stress was examined at a fundamental level. The relative partitioning of β-carotene between thylakoid membrane and interthylakoid globular β-carotene has revealed two responses to high light stress. The first is a response in which the alga adapts to the photoinhibitory effects of high light stress by the rapid accumulation and the peripheral localisation of Jl-carotene to the outer extremities of the chloroplast. This is followed by a maintenance response which is characterised by the recovery of the photosynthetic rate and cell growth. A possible interrelationship between the extent of the photo inhibitory response and the amount of β-carotene hyper-accumulation has been noted. An outdoor evaluation of the growth stage of the dual-stage system has demonstrated that D. salina can be grown in a relatively low salinity, nutrient sufficient medium for extended periods without overgrowth by small non-carotenogenic Dunaliella species. In addition, biomass productivities of three times greater than those obtained in the currently employed averaging system were achieved. The role of high light intensity in β-carotene hyper-accumulation was confirmed in outdoor scale-up stress pond studies. The studies demonstrated the feasibility of stress induced ll-carotene production in outdoor cultures of D. salina and β-carotene yields three times greater than those obtained in the currently employed averaging process were achieved. The dual-stage process imposes the specific requirement of viable cell separation on the harvesting system employed. A flocculation-flotation process and an air-displacement crossflow ultrafiltration system were developed and successfully evaluated for the separation of D. salina from the brine solution in a viable form. The extraction of β-carotene from D. salina was evaluated. Supercritical fluid extraction studies showed that the use of a co-solvent mixture of carbon dioxide and propane could effectively reduce the high extraction pressures associated with supercritical carbon dioxide extraction. In addition, a novel hydrophobic membrane assisted hot oil extraction process was developed which separates the complex oil-water emulsions produced during hot oil extraction of 6-carotene from wet D. salina biomass. Process design and economic evaluation studies were undertaken and showed that the economics of the dual-stage process offer significant advantages over the currently employed averaging process.
- Full Text:
- Date Issued: 1994
Structural studies on some enterobacterial capsular antigens
- Authors: Whittaker, Darryl Vanstone
- Date: 1994
- Subjects: Bacterial antigens -- Analysis Antigens Enterobacteriaceae Escherichia coli Klebsiella
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3803 , http://hdl.handle.net/10962/d1003281
- Description: The investigations presented in this thesis form part of a systematic international effort to establish the structures of the capsules produced by the bacterial genera, Escherichia coli and Klebsiella (family enterobacteriaceae). These bacteria are of medical interest as they are opportunistic pathogens and are frequently responsible for serious infections in animals and man. Invasive strains are invariably surrounded by a structurally complex polysaccharide capsule which contributes to the organism's ability to attenuate non-specific host defence mechanisms or, in some instances, to completely prevent an immune response. A knowledge of the chemical composition and structure of the capsule is, therefore, of great value as it provides insight into the mechanisms involved in this process. The E. coli, in particular, have generated considerable interest as their capsules are more structurally diverse and cross-reactivity with other, more pathogenic bacteria has also been demonstrated. Accordingly, the structures of three previously unstudied E. coli K-antigens viz. those produced by serotypes 020:K83:H26, 020:K84:H26, and 09:K48:H9 have been established by chemical and spectroscopic means and are presented in this thesis. In addition, a reinvestigation of the structure of the capsule produced by Klebsiella K15 using a novel enzymatic approach was also undertaken and a revised structure is proposed . The E. coli K48 polysaccharide is of special interest as it was found to contain a new diacetamido trideoxy hexose hitherto unrecorded. A synthesis for this saccharide is also presented. Finally, the application of lithium dissolved in ethylenediamine for the degradation of amino sugar-containing polysaccharides was also investigated using the capsular polysaccharides produced by E. coli serotypes K38 and K84 as model compounds.
- Full Text:
- Date Issued: 1994
- Authors: Whittaker, Darryl Vanstone
- Date: 1994
- Subjects: Bacterial antigens -- Analysis Antigens Enterobacteriaceae Escherichia coli Klebsiella
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3803 , http://hdl.handle.net/10962/d1003281
- Description: The investigations presented in this thesis form part of a systematic international effort to establish the structures of the capsules produced by the bacterial genera, Escherichia coli and Klebsiella (family enterobacteriaceae). These bacteria are of medical interest as they are opportunistic pathogens and are frequently responsible for serious infections in animals and man. Invasive strains are invariably surrounded by a structurally complex polysaccharide capsule which contributes to the organism's ability to attenuate non-specific host defence mechanisms or, in some instances, to completely prevent an immune response. A knowledge of the chemical composition and structure of the capsule is, therefore, of great value as it provides insight into the mechanisms involved in this process. The E. coli, in particular, have generated considerable interest as their capsules are more structurally diverse and cross-reactivity with other, more pathogenic bacteria has also been demonstrated. Accordingly, the structures of three previously unstudied E. coli K-antigens viz. those produced by serotypes 020:K83:H26, 020:K84:H26, and 09:K48:H9 have been established by chemical and spectroscopic means and are presented in this thesis. In addition, a reinvestigation of the structure of the capsule produced by Klebsiella K15 using a novel enzymatic approach was also undertaken and a revised structure is proposed . The E. coli K48 polysaccharide is of special interest as it was found to contain a new diacetamido trideoxy hexose hitherto unrecorded. A synthesis for this saccharide is also presented. Finally, the application of lithium dissolved in ethylenediamine for the degradation of amino sugar-containing polysaccharides was also investigated using the capsular polysaccharides produced by E. coli serotypes K38 and K84 as model compounds.
- Full Text:
- Date Issued: 1994
Studies in asymmetric synthesis
- Authors: Ravindran, Swarnam Shanthi
- Date: 1994
- Subjects: Asymmetric synthesis Chirality Organic compounds -- Synthesis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4352 , http://hdl.handle.net/10962/d1005017
- Description: The stereoselectivity of TiCI₄-catalysed Mukaiyama reactions of a camphor acetal-derived chiral silyl enol ether with a range of substituted aromatic aldehydes has been examined. The enantiomeric excess in each of the resulting ß-hydroxy ketones, determined by ¹H NMR spectroscopy using the lanthanide chiral shift reagent Pr(Etcf₃), ranged between 9 and 13%. The stereo-directing potential of the camphor acetal as a chiral auxiliary in the α-benzylation of carboxylate esters has been studied; the acids were chosen to illustrate substituent effects on asymmetric induction. The observed diastereoselectivity increased with increasing steric bulk of the ester group and α-benzylation of the tert-butylacetate derivative proceeded with 48% diastereoselectivity. It is proposed that the enolate adopts an endo-s-trans conformation in the transition state and preferential attack by the electrophile at the somewhat less hindered Si-face is supported by both the optical rotation data and computer modelling studies. Reductive cleavage and hydrolysis of one of the benzylated esters furnished known products from whose optical rotation the configuration of the major diastereomer was established. In order to improve the steric advantage of Si-facial attack, methods of increasing the steric bulk of the blocking group were explored. A novel 2,2-propylenedioxy hydroxycamphor acetal and its 3,3-propylenedioxy analogue were prepared. Selected carboxylate esters of these propylenedioxy acetals were subjected to α-benzylation and the 2,2-(propylenedioxy)-3-exo-tert-butylacetate derivative showed a diastereoselectivity of 57% during a-benzylation. Hydrolysis of the abenzylated phenylacetate analogue offered the known 2,3-diphenylpropanoic acid whose optical rotation indicated the preferred configuration at the new chiral centre to be (R), a result which is consistent with the proposed approach of the electrophile to the less hindered Re-face of theendo-s-trans enolate moiety and reflects an inversion of the configurational bias observed with 2-v exo-carboxylate analogues. Attempts to prepare the monocatechol acetal of the hydroxy camphor derivative although unsuccessful, led to the isolation of two novel dibornyl ethers whose structures were established by 1- and 2-D NMR spectroscopy. A study of novel applications of camphor-derived auxiliaries in the asymmetric synthesis of α-amino acids has been initiated. The several approaches tried led to the preparation of three novel dural glycine derivatives in good yield
- Full Text:
- Date Issued: 1994
- Authors: Ravindran, Swarnam Shanthi
- Date: 1994
- Subjects: Asymmetric synthesis Chirality Organic compounds -- Synthesis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4352 , http://hdl.handle.net/10962/d1005017
- Description: The stereoselectivity of TiCI₄-catalysed Mukaiyama reactions of a camphor acetal-derived chiral silyl enol ether with a range of substituted aromatic aldehydes has been examined. The enantiomeric excess in each of the resulting ß-hydroxy ketones, determined by ¹H NMR spectroscopy using the lanthanide chiral shift reagent Pr(Etcf₃), ranged between 9 and 13%. The stereo-directing potential of the camphor acetal as a chiral auxiliary in the α-benzylation of carboxylate esters has been studied; the acids were chosen to illustrate substituent effects on asymmetric induction. The observed diastereoselectivity increased with increasing steric bulk of the ester group and α-benzylation of the tert-butylacetate derivative proceeded with 48% diastereoselectivity. It is proposed that the enolate adopts an endo-s-trans conformation in the transition state and preferential attack by the electrophile at the somewhat less hindered Si-face is supported by both the optical rotation data and computer modelling studies. Reductive cleavage and hydrolysis of one of the benzylated esters furnished known products from whose optical rotation the configuration of the major diastereomer was established. In order to improve the steric advantage of Si-facial attack, methods of increasing the steric bulk of the blocking group were explored. A novel 2,2-propylenedioxy hydroxycamphor acetal and its 3,3-propylenedioxy analogue were prepared. Selected carboxylate esters of these propylenedioxy acetals were subjected to α-benzylation and the 2,2-(propylenedioxy)-3-exo-tert-butylacetate derivative showed a diastereoselectivity of 57% during a-benzylation. Hydrolysis of the abenzylated phenylacetate analogue offered the known 2,3-diphenylpropanoic acid whose optical rotation indicated the preferred configuration at the new chiral centre to be (R), a result which is consistent with the proposed approach of the electrophile to the less hindered Re-face of theendo-s-trans enolate moiety and reflects an inversion of the configurational bias observed with 2-v exo-carboxylate analogues. Attempts to prepare the monocatechol acetal of the hydroxy camphor derivative although unsuccessful, led to the isolation of two novel dibornyl ethers whose structures were established by 1- and 2-D NMR spectroscopy. A study of novel applications of camphor-derived auxiliaries in the asymmetric synthesis of α-amino acids has been initiated. The several approaches tried led to the preparation of three novel dural glycine derivatives in good yield
- Full Text:
- Date Issued: 1994
Studies related to the process of program development
- Authors: Williams, Morgan Howard
- Date: 1994
- Subjects: Computer programming
- Language: English
- Type: Thesis , Doctoral , DSc
- Identifier: vital:4680 , http://hdl.handle.net/10962/d1007235
- Description: The submitted work consists of a collection of publications arising from research carried out at Rhodes University (1970-1980) and at Heriot-Watt University (1980-1992). The theme of this research is the process of program development, i.e. the process of creating a computer program to solve some particular problem. The papers presented cover a number of different topics which relate to this process, viz. (a) Programming methodology programming. (b) Properties of programming languages. aspects of structured. (c) Formal specification of programming languages. (d) Compiler techniques. (e) Declarative programming languages. (f) Program development aids. (g) Automatic program generation. (h) Databases. (i) Algorithms and applications.
- Full Text:
- Date Issued: 1994
- Authors: Williams, Morgan Howard
- Date: 1994
- Subjects: Computer programming
- Language: English
- Type: Thesis , Doctoral , DSc
- Identifier: vital:4680 , http://hdl.handle.net/10962/d1007235
- Description: The submitted work consists of a collection of publications arising from research carried out at Rhodes University (1970-1980) and at Heriot-Watt University (1980-1992). The theme of this research is the process of program development, i.e. the process of creating a computer program to solve some particular problem. The papers presented cover a number of different topics which relate to this process, viz. (a) Programming methodology programming. (b) Properties of programming languages. aspects of structured. (c) Formal specification of programming languages. (d) Compiler techniques. (e) Declarative programming languages. (f) Program development aids. (g) Automatic program generation. (h) Databases. (i) Algorithms and applications.
- Full Text:
- Date Issued: 1994
Synthetic and spectroscopic studies of 1,4-benzodiazepine analogues
- Authors: Mphahlele, Malose Jack
- Date: 1994
- Subjects: Benzodiazepines Tranquilizing drugs
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4384 , http://hdl.handle.net/10962/d1005049
- Description: In this project, an extensive range of benzodiazepine analogues have been synthesised via Schmidt reaction of specially prepared flavanone, 4-quinolone and l-thioflavanone precursors; nitrogen insertion being effected by use of trimethylsilyl azide in trifluoroacetic acid. In some cases, several of the benzodiazepine analogues have also been prepared by alternative cyclisation routes. A detailed kinetic-mechanistic study of the Schmidt reaction of flavanones has been carried out using 'H NMR spectroscopy to explain the observed regiochemistry of nitrogen insertion. The reaction rates, for the formation of both amide and tetrazolo derivatives have been found to be influenced by the electronic effects of the A- and B-ring substituents. A series of benzodiazepine analogues have been shown to undergo regioselective A-ring chlorination with t-butylhypochlorite; the products being characterised by 'H NMR, IR and mass spectroscopy. The mass spectrometric fragmentation patterns of series of 2-aryl-4-quinolones, and 2-aryl-l ,4-benzodiazepinones and their tetrazolo[l ,5-dl analogues have been elucidated using a combination of low-resolution, high-resolution and metastable-peak analyses. The binding affinities of various benzodiazepine analogues for rat brain benzodiazepine receptors have been evaluated using a radioreceptor assay technique. Structure-activity relationships were investigated to establish the effects of various A-, B- and Coring substituents on binding affinity. The conformational preferences of selected systems have been studied using a combination of multi-pulse 'H NMR spectroscopy, X-ray crystallography and computer modelling techniques with a view to establishing the influence of conformation on binding affinity.
- Full Text:
- Date Issued: 1994
- Authors: Mphahlele, Malose Jack
- Date: 1994
- Subjects: Benzodiazepines Tranquilizing drugs
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4384 , http://hdl.handle.net/10962/d1005049
- Description: In this project, an extensive range of benzodiazepine analogues have been synthesised via Schmidt reaction of specially prepared flavanone, 4-quinolone and l-thioflavanone precursors; nitrogen insertion being effected by use of trimethylsilyl azide in trifluoroacetic acid. In some cases, several of the benzodiazepine analogues have also been prepared by alternative cyclisation routes. A detailed kinetic-mechanistic study of the Schmidt reaction of flavanones has been carried out using 'H NMR spectroscopy to explain the observed regiochemistry of nitrogen insertion. The reaction rates, for the formation of both amide and tetrazolo derivatives have been found to be influenced by the electronic effects of the A- and B-ring substituents. A series of benzodiazepine analogues have been shown to undergo regioselective A-ring chlorination with t-butylhypochlorite; the products being characterised by 'H NMR, IR and mass spectroscopy. The mass spectrometric fragmentation patterns of series of 2-aryl-4-quinolones, and 2-aryl-l ,4-benzodiazepinones and their tetrazolo[l ,5-dl analogues have been elucidated using a combination of low-resolution, high-resolution and metastable-peak analyses. The binding affinities of various benzodiazepine analogues for rat brain benzodiazepine receptors have been evaluated using a radioreceptor assay technique. Structure-activity relationships were investigated to establish the effects of various A-, B- and Coring substituents on binding affinity. The conformational preferences of selected systems have been studied using a combination of multi-pulse 'H NMR spectroscopy, X-ray crystallography and computer modelling techniques with a view to establishing the influence of conformation on binding affinity.
- Full Text:
- Date Issued: 1994
Synthetic and spectroscopic studies of indolizine derivatives
- Authors: Bode, Moira Leanne
- Date: 1994
- Subjects: Indole alkaloids -- Derivatives Spectrum analysis Chemistry, Organic DNA -- Synthesis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4385 , http://hdl.handle.net/10962/d1005050
- Description: The crystalline compound resulting from thermal cyclization of the Baylis-Hillman product, methyl 3-hydroxy-2-methylene-3-(2-pyridyl)propanoate, has been identified as the indolizine derivative, methyl indolizine-2-carboxylate, and this approach involving the reaction of pyridine-2-carboxaldehydes and acrylate analogues has been established as a general route to 2-substituted indolizines. The ease of cyclization the Baylis-Hillman products to indolizines has been shown to increase by converting the hydroxy group to an acetoxy group, and a range of acetylated Baylis-Hillman products were prepared and cyc1ized to the corresponding 2-substituted indolizines, generally in good overall yield. In the reaction of pyridine-2-carboxaldehyde and methyl vinyl ketone, the intermediate cyclized readily and directly to the corresponding indolizine. One- and two-dimensional ¹H and ¹³C NMR analysis of the 2-substituted indolizine products has permitted complete assignment of all ¹H and ¹³C NMR signals, as well as the measurement of all coupling constants for these compounds. A kinetic and mechanistic study has been conducted on the Baylis-Hillman reaction using ¹H NMR spectroscopy. A range of substrates has been examined and the reaction has been found to be third-order overall. A mechanism involving an addition - elimination sequence is proposed, which fits the kinetic data and accounts for observed substituent effects. Reaction of N,N-dimethylacrylamide with pyridine-2-carboxaldehyde in the presence of the tertiary amine catalyst, DABCO, in chloroform, yielded an unexpected product which has been identified by single crystal X-ray diffraction analysis as 1-(2,2,2-trichloro-1-hydroxyethyl)pyridine. Attempted extension of the general indolizine route to the preparation of chromene systems by reacting salicylaldehyde with methyl acrylate in the presence of DABCO, also led to an unexpected, crystalline material, identified by single crystal X-ray diffraction analysis as the coumarin derivative, 3-[(2-formylphenoxy)methyl]coumarin.A series of chloroquine analogues have been prepared from indolizine-2-carboxylic acid, pyrrolo[I,2-a]quinoline-2-carboxylic acid and imidazo[I,2-a]pyridine-2-carboxylic acid by reaction with suitable amines in the presence of the coupling reagent 1, I' -carbonyldiimidazole. This route has been shown to be a vast improvement on earlier procedures and has provided access to both secondary and tertiary indolizine-2-carboxamides. A range of N,N-dialkylindolizine-2-carboxamides have been prepared by this route, and the influence of substituents on their N-CO rotational energy barriers has been determined using variable temperature ¹H and ¹³C NMR techniques. Intercalation with natural DNA by both chloroquine and the synthesized chloroquine analogues has been examined using UV spectrophotometry, and ¹H and ³¹P NMR spectroscopy. The pyrrolo[I,2-a]quinolines have been shown to be DNA intercalators with binding affinities similar to that of the known antimalarial intercalator, chloroquine. In a preliminary study the synthesis of a short oligonucleotide has been undertaken and changes have been observed in the ¹H and ³¹P NMR spectra of the oligonucleotide on addition of the intercalator, chloroquine.
- Full Text:
- Date Issued: 1994
- Authors: Bode, Moira Leanne
- Date: 1994
- Subjects: Indole alkaloids -- Derivatives Spectrum analysis Chemistry, Organic DNA -- Synthesis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4385 , http://hdl.handle.net/10962/d1005050
- Description: The crystalline compound resulting from thermal cyclization of the Baylis-Hillman product, methyl 3-hydroxy-2-methylene-3-(2-pyridyl)propanoate, has been identified as the indolizine derivative, methyl indolizine-2-carboxylate, and this approach involving the reaction of pyridine-2-carboxaldehydes and acrylate analogues has been established as a general route to 2-substituted indolizines. The ease of cyclization the Baylis-Hillman products to indolizines has been shown to increase by converting the hydroxy group to an acetoxy group, and a range of acetylated Baylis-Hillman products were prepared and cyc1ized to the corresponding 2-substituted indolizines, generally in good overall yield. In the reaction of pyridine-2-carboxaldehyde and methyl vinyl ketone, the intermediate cyclized readily and directly to the corresponding indolizine. One- and two-dimensional ¹H and ¹³C NMR analysis of the 2-substituted indolizine products has permitted complete assignment of all ¹H and ¹³C NMR signals, as well as the measurement of all coupling constants for these compounds. A kinetic and mechanistic study has been conducted on the Baylis-Hillman reaction using ¹H NMR spectroscopy. A range of substrates has been examined and the reaction has been found to be third-order overall. A mechanism involving an addition - elimination sequence is proposed, which fits the kinetic data and accounts for observed substituent effects. Reaction of N,N-dimethylacrylamide with pyridine-2-carboxaldehyde in the presence of the tertiary amine catalyst, DABCO, in chloroform, yielded an unexpected product which has been identified by single crystal X-ray diffraction analysis as 1-(2,2,2-trichloro-1-hydroxyethyl)pyridine. Attempted extension of the general indolizine route to the preparation of chromene systems by reacting salicylaldehyde with methyl acrylate in the presence of DABCO, also led to an unexpected, crystalline material, identified by single crystal X-ray diffraction analysis as the coumarin derivative, 3-[(2-formylphenoxy)methyl]coumarin.A series of chloroquine analogues have been prepared from indolizine-2-carboxylic acid, pyrrolo[I,2-a]quinoline-2-carboxylic acid and imidazo[I,2-a]pyridine-2-carboxylic acid by reaction with suitable amines in the presence of the coupling reagent 1, I' -carbonyldiimidazole. This route has been shown to be a vast improvement on earlier procedures and has provided access to both secondary and tertiary indolizine-2-carboxamides. A range of N,N-dialkylindolizine-2-carboxamides have been prepared by this route, and the influence of substituents on their N-CO rotational energy barriers has been determined using variable temperature ¹H and ¹³C NMR techniques. Intercalation with natural DNA by both chloroquine and the synthesized chloroquine analogues has been examined using UV spectrophotometry, and ¹H and ³¹P NMR spectroscopy. The pyrrolo[I,2-a]quinolines have been shown to be DNA intercalators with binding affinities similar to that of the known antimalarial intercalator, chloroquine. In a preliminary study the synthesis of a short oligonucleotide has been undertaken and changes have been observed in the ¹H and ³¹P NMR spectra of the oligonucleotide on addition of the intercalator, chloroquine.
- Full Text:
- Date Issued: 1994
Tangentially symplectic foliations
- Authors: Remsing, Claudiu Cristian
- Date: 1994
- Subjects: Geometry Problems, exercises, etc Geometry, Differential Symplectic manifolds Poisson manifolds Foliations (Mathematics)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5419 , http://hdl.handle.net/10962/d1005233
- Description: This thesis is concerned principally with tangential geometry and the applications of these concepts to tangentially symplectic foliations. The subject of tangential geometry is still at an elementary stage. The author here systematises current concepts and results and extends them, leading to the definition of vertical connections and vertical G-structures. Tangentially symplectic foliations are then characterised in terms of vertical symplectic forms. Some significant particular cases are discussed.
- Full Text:
- Date Issued: 1994
- Authors: Remsing, Claudiu Cristian
- Date: 1994
- Subjects: Geometry Problems, exercises, etc Geometry, Differential Symplectic manifolds Poisson manifolds Foliations (Mathematics)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5419 , http://hdl.handle.net/10962/d1005233
- Description: This thesis is concerned principally with tangential geometry and the applications of these concepts to tangentially symplectic foliations. The subject of tangential geometry is still at an elementary stage. The author here systematises current concepts and results and extends them, leading to the definition of vertical connections and vertical G-structures. Tangentially symplectic foliations are then characterised in terms of vertical symplectic forms. Some significant particular cases are discussed.
- Full Text:
- Date Issued: 1994
The dissociation of ammonium salts and their effect on the physiology and biochemistry of L-lysine synthesis by Corynebacterium glutamicum FP6
- Authors: Kenyon, Colin Peter
- Date: 1994
- Subjects: Ammonium salts Lysine -- Synthesis Corynebacterium Dissociation -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4034 , http://hdl.handle.net/10962/d1004094
- Description: The availability and assimilation of NH₄⁺ plays an integral role in the growth of microorganisms and the production of amino acids by these organisms. This study investigated the dissociation of NH₄⁺in aqueous solution, its availability and effect on the enzymes of NH₄⁺ assimilation and its influence on lysine production by Corynebacterium glutamicum.In aqueous solution the extent of dissociation of NH₄C1, {NH₄)₂S0₄ and (NH₄)₂HP0₄ increases with decreasing concentration. A model is proposed for the dissociation of these molecules. It is believed that at very low concentrations, dissociation to NH₃ plus the respective counter-ions occurs. At these low concentrations the NH₃ acts as the substrate for glutamine synthetase. At the higher concentrations dissociation is to NH₄⁺ which is the substrate for glutamate dehydrogenase. At these higher concentrations the enzyme activities obtained for glutamate dehydrogenase, at equivalent concentrations of the above ammonium salts, were different when based on the total concentration of NH₄⁺, and similar when based on the concentration of free NH₄⁺. L-Iysine occurs in the +1 ionic form, at pH 7,2. The lysine which is produced during fermentation associates with the anionic counter-ion of the ammonium salt used. The concentration of the free NH₄⁺ in the media appears to affect both the rate of lysine synthesis as well as the yield. The lysine fermentation occurs in two stages; a growth (or replicative) phase, during which very little lysine is produced, and a lysine synthesis (or maturation) phase. During the lysine synthesis phase there is no cell replication, however an increase in the mass of the biomass produced is apparent. Evidence is provided for the possible concomitant synthesis of the the cell wall polymer, glycerol teichoic acid, and lysine. On the basis of this evidence, a nucleotide balance is proposed for lysine and teichoic acid synthesis. The replicative phase and the maturation phase have to be effectively separated to obtain optimal lysine yields and titres. It is believed that teichoic acid synthesis during the replicative phase must be kept to a minimum for optimal yields and titres to be obtained, and on completion of the cell wall and therefore teichoic acid synthesis, lysine synthesis ceases. As the production of lysine appears to be affected by the NH₄⁺ concentration in the culture media, it is proposed that a futile cycle may exist around the transport and assimilation of the NH₄⁺. If the fermentations are run at low free NH₄⁺ concentrations, it was shown that lysine yields of 0,66, on the glucose utilised, are attainable during the fermentation.
- Full Text:
- Date Issued: 1994
- Authors: Kenyon, Colin Peter
- Date: 1994
- Subjects: Ammonium salts Lysine -- Synthesis Corynebacterium Dissociation -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4034 , http://hdl.handle.net/10962/d1004094
- Description: The availability and assimilation of NH₄⁺ plays an integral role in the growth of microorganisms and the production of amino acids by these organisms. This study investigated the dissociation of NH₄⁺in aqueous solution, its availability and effect on the enzymes of NH₄⁺ assimilation and its influence on lysine production by Corynebacterium glutamicum.In aqueous solution the extent of dissociation of NH₄C1, {NH₄)₂S0₄ and (NH₄)₂HP0₄ increases with decreasing concentration. A model is proposed for the dissociation of these molecules. It is believed that at very low concentrations, dissociation to NH₃ plus the respective counter-ions occurs. At these low concentrations the NH₃ acts as the substrate for glutamine synthetase. At the higher concentrations dissociation is to NH₄⁺ which is the substrate for glutamate dehydrogenase. At these higher concentrations the enzyme activities obtained for glutamate dehydrogenase, at equivalent concentrations of the above ammonium salts, were different when based on the total concentration of NH₄⁺, and similar when based on the concentration of free NH₄⁺. L-Iysine occurs in the +1 ionic form, at pH 7,2. The lysine which is produced during fermentation associates with the anionic counter-ion of the ammonium salt used. The concentration of the free NH₄⁺ in the media appears to affect both the rate of lysine synthesis as well as the yield. The lysine fermentation occurs in two stages; a growth (or replicative) phase, during which very little lysine is produced, and a lysine synthesis (or maturation) phase. During the lysine synthesis phase there is no cell replication, however an increase in the mass of the biomass produced is apparent. Evidence is provided for the possible concomitant synthesis of the the cell wall polymer, glycerol teichoic acid, and lysine. On the basis of this evidence, a nucleotide balance is proposed for lysine and teichoic acid synthesis. The replicative phase and the maturation phase have to be effectively separated to obtain optimal lysine yields and titres. It is believed that teichoic acid synthesis during the replicative phase must be kept to a minimum for optimal yields and titres to be obtained, and on completion of the cell wall and therefore teichoic acid synthesis, lysine synthesis ceases. As the production of lysine appears to be affected by the NH₄⁺ concentration in the culture media, it is proposed that a futile cycle may exist around the transport and assimilation of the NH₄⁺. If the fermentations are run at low free NH₄⁺ concentrations, it was shown that lysine yields of 0,66, on the glucose utilised, are attainable during the fermentation.
- Full Text:
- Date Issued: 1994
The effects of particle precipitation on the ionosphere in the South Atlantic Anomaly Region
- Authors: Haggard, Raymond
- Date: 1994
- Subjects: Precipitation (Chemistry) Ionosphere Ionospheric electron density
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5463 , http://hdl.handle.net/10962/d1005248
- Description: The first ground based observations of aeronomic phenomena in the South Atlantic Anomaly Region are presented. These data show that enhancements in foF2 and foE can be directly attributed to precipitated electron energy fluxes in the Anomaly Region. The regular occurrence of particle induced sporadic-E ionization is also presented together with the first measurable 391.4 nm airglow radiation of about 16 R. The first comprehensive survey of energy fluxes carried by energetic particles using satellites is also presented for both daytime and nighttime as well as the seasonal fluctuations. We found that the nocturnally precipitated electron energy fluxes varied between 1 x 10⁻⁴ and 38 x 10⁻⁴ erg cm²s⁻¹, depending upon magnetic activity and season, whereas the daytime precipitated electron energy fluxes tended to vary between 1 x 10⁻³ and 8 x 10⁻³ erg cm⁻²s⁻¹, with a tendency to decrease during magnetically active periods. Electron density and temperature contours as well as NO⁺ and 0⁺ ions contours for nighttime are also presented. The main conclusion of the study is that precipitating electrons provide a significant and sometimes dominant source of ionization in the ionosphere over the South Atlantic Anomaly Region.
- Full Text:
- Date Issued: 1994
- Authors: Haggard, Raymond
- Date: 1994
- Subjects: Precipitation (Chemistry) Ionosphere Ionospheric electron density
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5463 , http://hdl.handle.net/10962/d1005248
- Description: The first ground based observations of aeronomic phenomena in the South Atlantic Anomaly Region are presented. These data show that enhancements in foF2 and foE can be directly attributed to precipitated electron energy fluxes in the Anomaly Region. The regular occurrence of particle induced sporadic-E ionization is also presented together with the first measurable 391.4 nm airglow radiation of about 16 R. The first comprehensive survey of energy fluxes carried by energetic particles using satellites is also presented for both daytime and nighttime as well as the seasonal fluctuations. We found that the nocturnally precipitated electron energy fluxes varied between 1 x 10⁻⁴ and 38 x 10⁻⁴ erg cm²s⁻¹, depending upon magnetic activity and season, whereas the daytime precipitated electron energy fluxes tended to vary between 1 x 10⁻³ and 8 x 10⁻³ erg cm⁻²s⁻¹, with a tendency to decrease during magnetically active periods. Electron density and temperature contours as well as NO⁺ and 0⁺ ions contours for nighttime are also presented. The main conclusion of the study is that precipitating electrons provide a significant and sometimes dominant source of ionization in the ionosphere over the South Atlantic Anomaly Region.
- Full Text:
- Date Issued: 1994
The meaning of work in a developing society a rural South African study
- Authors: Sully, Preis Max
- Date: 1994
- Subjects: Work -- Psychological aspects Ciskei (South Africa) -- Rural conditions Keiskammahoek (South Africa) -- Social conditions
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3066 , http://hdl.handle.net/10962/d1002575
- Description: The primary aim of this thesis is to explore, at a psychological level, the meaning of work in a rural developing society context. Additional aims comprise: the examination of distinctions in the meaning of work between different occupational niches; and the development of an appropriate conceptual and methodological approach for understanding meaning of work issues in developing society contexts. The research was conducted in the Keiskammahoek district situated in Ciskei, a South African homeland area. Demographically, the area comprises farms, small rural villages and one small town. It has traditionally fulfilled the role of a labour reserve, and the local economy largely depends on income generated through migrant labour. The population predominantly comprises indigenous Xhosa speakers, although a few whites, individuals of mixed racial origin and other ethnic groups are represented. In order to accommodate the diversity of work experience in rural society, an approach was adopted which relied on the participants' subjective definition of work. A conscious attempt was made to avoid defining work exclusively as remunerated employment. At a metatheoretical level, the meaning of work model used is grounded in Kelly's (1955) Personal Construct Theory. It comprises three facets, namely process, context and content. A multiple case study analysis was carried design was used, through to a in which nomothetic idiographic level of understanding. The primary' research instrument comprised an interview, in which data was derived from life-history material, a repertory grid, and focused interview questions. In the development of case studies, a process of triangulation was used to link the three sources of data. The thesis explores the relationship between participants and their work in several ways. First, it looks at how work and non-work are constituted and related to one another, and at how personally valuable work is contrasted to less valuable work. Second, it explores the relationship between the individual's orientation to work and their life and occupational context. Finally, it discusses the proposal that work meanings change and evolve with the development of the individual, and with shifts in social and historical circumstance.
- Full Text:
- Date Issued: 1994
- Authors: Sully, Preis Max
- Date: 1994
- Subjects: Work -- Psychological aspects Ciskei (South Africa) -- Rural conditions Keiskammahoek (South Africa) -- Social conditions
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3066 , http://hdl.handle.net/10962/d1002575
- Description: The primary aim of this thesis is to explore, at a psychological level, the meaning of work in a rural developing society context. Additional aims comprise: the examination of distinctions in the meaning of work between different occupational niches; and the development of an appropriate conceptual and methodological approach for understanding meaning of work issues in developing society contexts. The research was conducted in the Keiskammahoek district situated in Ciskei, a South African homeland area. Demographically, the area comprises farms, small rural villages and one small town. It has traditionally fulfilled the role of a labour reserve, and the local economy largely depends on income generated through migrant labour. The population predominantly comprises indigenous Xhosa speakers, although a few whites, individuals of mixed racial origin and other ethnic groups are represented. In order to accommodate the diversity of work experience in rural society, an approach was adopted which relied on the participants' subjective definition of work. A conscious attempt was made to avoid defining work exclusively as remunerated employment. At a metatheoretical level, the meaning of work model used is grounded in Kelly's (1955) Personal Construct Theory. It comprises three facets, namely process, context and content. A multiple case study analysis was carried design was used, through to a in which nomothetic idiographic level of understanding. The primary' research instrument comprised an interview, in which data was derived from life-history material, a repertory grid, and focused interview questions. In the development of case studies, a process of triangulation was used to link the three sources of data. The thesis explores the relationship between participants and their work in several ways. First, it looks at how work and non-work are constituted and related to one another, and at how personally valuable work is contrasted to less valuable work. Second, it explores the relationship between the individual's orientation to work and their life and occupational context. Finally, it discusses the proposal that work meanings change and evolve with the development of the individual, and with shifts in social and historical circumstance.
- Full Text:
- Date Issued: 1994