A comparison of the aquaculture potential of Clarias gariepinus (Burchell, 1822) and its hybrid with Heterobranchus longifilis valenciennes, 1840 in Southern Africa
- Authors: Oellermann, Lawrence Keith
- Date: 1996
- Subjects: Aquaculture -- South Africa Clarias Clariidae Catfishes -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5246 , http://hdl.handle.net/10962/d1005089
- Description: The aim of this study was to evaluate the aquaculture potential of a hybrid between the two largest African silurid catfish, Heterobranchus longifilis (HL) and Clarias gariepinus (CG) . A morphometric, meristic and karyological study showed that the hybrid shared some of the physical characteristics of both C. gariepinus and H. longifilis, while its chromosome complement and fundamental number (2N = 54, FN = 95), was intermediate between that of H. longifilis (2N = 52, FN = 92) and C. gariepinus (2N = 56, FN = 97). The HLxCG cross could therefore be regarded as a true hybrid. For the characters tested, no morphological or karyological differences were apparent between the HLxCG hybrids produced in West Africa and those produced in southern Africa. In southern Africa, the HL♂xCG♀ cross had higher fertilization and hatching rates than pure strain H. longifilis, C. gariepinus or the reverse cross. There was no difference in the survival of the HL♂xCG♀ hybrid larvae and C. gariepinus larvae up to the onset of exogenous feeding. Pure strain H. longifilis juveniles had a faster growth rate than the H. longifilis ♂ x C. gariepinus ♀ juveniles, but the hybrid always grew at a faster rate than C. gariepinus or the reverse cross. The HL♂xCG♀ cross was consequently chosen as the hybrid with the greatest potential for siluroid aquaculture in southern Africa. The HL♂xCG♀ hybrid showed evidence of partial gonadic, gametic and post-zygotic sterility in both sexes. The hybrid was not completely sterile, as it was artificially induced to spawn, and a small number of viable F₂ hybrid and F₁ hybrid x C. gariepinus larvae were produced. However, in the light of its probable reproductive strategy, it is highly unlikely that the hybrid would pose an ecological risk to the southern African region. The H. longifilis ♂ x C. gariepinus ♀ hybrid was compared to C. gariepinus for selected water quality preferences and tolerances. The hybrid had a wider temperature preference (28 °C to 34 °C) than C. gariepinus (28 °C to 30 °C), but appeared to be more dependent on aerial respiration than C. gariepinus. The air-breathing frequency of hybrid fish began to increase at dissolved oxygen concentrations below 3 .8 mg.ℓ⁻¹, while C. gariepinus only showed an increase in air-breathing frequency at concentrations below 3.0 mg.ℓ¹. The hybrid was more tolerant of un-ionised ammonia (96-hour LC₅₀ = 9.1 mg.ℓ⁻¹) than C. gariepinus (96-hour LC₅₀ = 6.5 mg.ℓ⁻¹), but their 96-hour LC₅₀ salinity tolerances were similar (10.8-11.0 g.ℓ⁻¹). The H. longifilis ♂ x C. gariepinus ♀ hybrid had a higher fillet yield (43.9 %) than C. gariepinus (38.9 %), but the crude protein content and amino acid profile of the two groups were similar. Catfish are traditionally grown in earthen ponds under semi-intensive conditions in southern Africa, at around 4 kg of fish per cubic meter of water (kg.m⁻³). However, the hybrid could tolerate densities of up to 415 kg of fish per cubic metre of water, if the water was exchanged hourly (kg.m⁻³.hr⁻¹), and the density at which yield was optimised was rounded off to 400 kg.m³.hr⁻¹. The high threshold density and water quality tolerances of the H. longifilis ♂ x C. gariepinus ♀ hybrid indicates that it is ideally suited for highly intensive aquaculture. It was concluded that it would be more productive to farm the HL♂xCG♀ hybrid on an intensive basis in southern Africa, than it would be to farm C. gariepinus in the traditional manner.
- Full Text:
- Date Issued: 1996
- Authors: Oellermann, Lawrence Keith
- Date: 1996
- Subjects: Aquaculture -- South Africa Clarias Clariidae Catfishes -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5246 , http://hdl.handle.net/10962/d1005089
- Description: The aim of this study was to evaluate the aquaculture potential of a hybrid between the two largest African silurid catfish, Heterobranchus longifilis (HL) and Clarias gariepinus (CG) . A morphometric, meristic and karyological study showed that the hybrid shared some of the physical characteristics of both C. gariepinus and H. longifilis, while its chromosome complement and fundamental number (2N = 54, FN = 95), was intermediate between that of H. longifilis (2N = 52, FN = 92) and C. gariepinus (2N = 56, FN = 97). The HLxCG cross could therefore be regarded as a true hybrid. For the characters tested, no morphological or karyological differences were apparent between the HLxCG hybrids produced in West Africa and those produced in southern Africa. In southern Africa, the HL♂xCG♀ cross had higher fertilization and hatching rates than pure strain H. longifilis, C. gariepinus or the reverse cross. There was no difference in the survival of the HL♂xCG♀ hybrid larvae and C. gariepinus larvae up to the onset of exogenous feeding. Pure strain H. longifilis juveniles had a faster growth rate than the H. longifilis ♂ x C. gariepinus ♀ juveniles, but the hybrid always grew at a faster rate than C. gariepinus or the reverse cross. The HL♂xCG♀ cross was consequently chosen as the hybrid with the greatest potential for siluroid aquaculture in southern Africa. The HL♂xCG♀ hybrid showed evidence of partial gonadic, gametic and post-zygotic sterility in both sexes. The hybrid was not completely sterile, as it was artificially induced to spawn, and a small number of viable F₂ hybrid and F₁ hybrid x C. gariepinus larvae were produced. However, in the light of its probable reproductive strategy, it is highly unlikely that the hybrid would pose an ecological risk to the southern African region. The H. longifilis ♂ x C. gariepinus ♀ hybrid was compared to C. gariepinus for selected water quality preferences and tolerances. The hybrid had a wider temperature preference (28 °C to 34 °C) than C. gariepinus (28 °C to 30 °C), but appeared to be more dependent on aerial respiration than C. gariepinus. The air-breathing frequency of hybrid fish began to increase at dissolved oxygen concentrations below 3 .8 mg.ℓ⁻¹, while C. gariepinus only showed an increase in air-breathing frequency at concentrations below 3.0 mg.ℓ¹. The hybrid was more tolerant of un-ionised ammonia (96-hour LC₅₀ = 9.1 mg.ℓ⁻¹) than C. gariepinus (96-hour LC₅₀ = 6.5 mg.ℓ⁻¹), but their 96-hour LC₅₀ salinity tolerances were similar (10.8-11.0 g.ℓ⁻¹). The H. longifilis ♂ x C. gariepinus ♀ hybrid had a higher fillet yield (43.9 %) than C. gariepinus (38.9 %), but the crude protein content and amino acid profile of the two groups were similar. Catfish are traditionally grown in earthen ponds under semi-intensive conditions in southern Africa, at around 4 kg of fish per cubic meter of water (kg.m⁻³). However, the hybrid could tolerate densities of up to 415 kg of fish per cubic metre of water, if the water was exchanged hourly (kg.m⁻³.hr⁻¹), and the density at which yield was optimised was rounded off to 400 kg.m³.hr⁻¹. The high threshold density and water quality tolerances of the H. longifilis ♂ x C. gariepinus ♀ hybrid indicates that it is ideally suited for highly intensive aquaculture. It was concluded that it would be more productive to farm the HL♂xCG♀ hybrid on an intensive basis in southern Africa, than it would be to farm C. gariepinus in the traditional manner.
- Full Text:
- Date Issued: 1996
A networking approach to sharing music studio resources
- Authors: Foss, Richard John
- Date: 1996
- Subjects: MIDI (Standard) Computer sound processing Sound -- Recording and reproducing -- Digital techniques
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4659 , http://hdl.handle.net/10962/d1006660
- Description: This thesis investigates the extent to which networking technology can be used to provide remote workstation access to a pool of shared music studio resources. A pilot system is described in which MIDI messages, studio control data, and audio signals flow between the workstations and a studio server. A booking and timing facility avoids contention and allows for accurate reports of studio usage. The operation of the system has been evaluated in terms of its ability to satislY three fundamental goals, namely the remote, shared and centralized access to studio resources. Three essential network configurations have been identified, incorporating a mix of star and bus topologies, and their relative potential for satisfYing the fundamental goals has been highlighted.
- Full Text:
- Date Issued: 1996
- Authors: Foss, Richard John
- Date: 1996
- Subjects: MIDI (Standard) Computer sound processing Sound -- Recording and reproducing -- Digital techniques
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4659 , http://hdl.handle.net/10962/d1006660
- Description: This thesis investigates the extent to which networking technology can be used to provide remote workstation access to a pool of shared music studio resources. A pilot system is described in which MIDI messages, studio control data, and audio signals flow between the workstations and a studio server. A booking and timing facility avoids contention and allows for accurate reports of studio usage. The operation of the system has been evaluated in terms of its ability to satislY three fundamental goals, namely the remote, shared and centralized access to studio resources. Three essential network configurations have been identified, incorporating a mix of star and bus topologies, and their relative potential for satisfYing the fundamental goals has been highlighted.
- Full Text:
- Date Issued: 1996
Ambiguous contagion the discourse of race in South African English writing, 1890-1930
- Cornwell, David Gareth Napier
- Authors: Cornwell, David Gareth Napier
- Date: 1996
- Subjects: South African literature -- History and criticism Race in literature Race relations in literature Social classes in literature Ethnicity in literature Sex role in literature
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:2226 , http://hdl.handle.net/10962/d1002269
- Description: This study explores representations of race and racial difference in the writing of white South Africans in English, between the years, approximately, of 1890 and 1930. The first chapter essays a theoretical and historical investigation of the concept of race and offers a narrative of the rise of Western racialism. Its conclusion, that race has functioned as a vehicle of displacement for other forms of difference in the competition for advantage among social groups, is qualified in Chapter Two by the postulate of an anthropologial absolute, the "ethnic imperative", to help account for the strategic emergence of racialism in specific historical circumstances. The role of the ethnic imperative in the moral economy of colonial South Africa in the years 1890-1930 is examined through the analysis of three representative texts. In Chapter Three, a wide range of primary material is canvassed for prevailing views on the "Native Question", the perceived social threat posed by the half-caste, and the "Black Peril", culminating in the detailed examination of a fictional text. A particular concern in both Chapters Two and Three is the imagery of disease and contagion in terms of which racial contact is typically represented. The following chapter situates the literary works discussed in the study in the context of the South African literary tradition, then uses the example of selected short stories to indicate some narratological problems encountered by the writer with a racialist agenda within the medium of realist fiction. Chapters Five and Six investigate, through the close reading of selected novels, thematic concerns rooted in the intersection of the discourse of race with those of gender and social class. The final chapter reveals how William Plomer's novel, Turbott Wolfe, represents a volatile synthesis of a standard discourse on social class, an acknowledgement of the ethnic imperative, the imagery of contagion, and a principled repudiation of racialism, in a multi-faceted, modernist, and partially self-aware fashion. The more salient conclusions reached by this study concern the inadequacy of purely materialist analysis to account for the phenomenon of racialism, the historically determined link between racial attitudes and sexuality, and the manifest incompatibility of racial ideology with the liberal humanism inscribed in the formal requirements of the realist work of fiction.
- Full Text:
- Date Issued: 1996
- Authors: Cornwell, David Gareth Napier
- Date: 1996
- Subjects: South African literature -- History and criticism Race in literature Race relations in literature Social classes in literature Ethnicity in literature Sex role in literature
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:2226 , http://hdl.handle.net/10962/d1002269
- Description: This study explores representations of race and racial difference in the writing of white South Africans in English, between the years, approximately, of 1890 and 1930. The first chapter essays a theoretical and historical investigation of the concept of race and offers a narrative of the rise of Western racialism. Its conclusion, that race has functioned as a vehicle of displacement for other forms of difference in the competition for advantage among social groups, is qualified in Chapter Two by the postulate of an anthropologial absolute, the "ethnic imperative", to help account for the strategic emergence of racialism in specific historical circumstances. The role of the ethnic imperative in the moral economy of colonial South Africa in the years 1890-1930 is examined through the analysis of three representative texts. In Chapter Three, a wide range of primary material is canvassed for prevailing views on the "Native Question", the perceived social threat posed by the half-caste, and the "Black Peril", culminating in the detailed examination of a fictional text. A particular concern in both Chapters Two and Three is the imagery of disease and contagion in terms of which racial contact is typically represented. The following chapter situates the literary works discussed in the study in the context of the South African literary tradition, then uses the example of selected short stories to indicate some narratological problems encountered by the writer with a racialist agenda within the medium of realist fiction. Chapters Five and Six investigate, through the close reading of selected novels, thematic concerns rooted in the intersection of the discourse of race with those of gender and social class. The final chapter reveals how William Plomer's novel, Turbott Wolfe, represents a volatile synthesis of a standard discourse on social class, an acknowledgement of the ethnic imperative, the imagery of contagion, and a principled repudiation of racialism, in a multi-faceted, modernist, and partially self-aware fashion. The more salient conclusions reached by this study concern the inadequacy of purely materialist analysis to account for the phenomenon of racialism, the historically determined link between racial attitudes and sexuality, and the manifest incompatibility of racial ideology with the liberal humanism inscribed in the formal requirements of the realist work of fiction.
- Full Text:
- Date Issued: 1996
Cell-free biosynthesis of abscisic acid (ABA) in extracts of flavedo from Citrus sinensis (L.) osbeck
- Richardson, Gaynor Rose-Marie
- Authors: Richardson, Gaynor Rose-Marie
- Date: 1996
- Subjects: Biosynthesis Abscisic acid Citrus fruits
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4221 , http://hdl.handle.net/10962/d1003790
- Description: The biosynthetic origin of the plant growth regulator abscisic acid remains equivocal and almost nothing is known about the enzymes involved in this process. The present research programme describes the development of a cell-free system, capable of synthesizing abscisic acid and attempts to provide further information about the biochemistry and enzymology of this important biosynthetic pathway. Cell-free extracts were prepared either directly from the flavedo (crude) or from an acetone powder derived from flavedo, of mature coloured fruits of Citrus sinensis L. cv. Midknight and incubated with mevalonic acid, isopentenyl pyrophosphate, famesylpyrophosphate, geranylgeranyl pyrophosphate, ß-carotene and 1',4'-trans-abscisic acid diol. The neutral and acidic products formed were purified by thin-layer chromatography and high performance liquid chromatography, and quantified by high performance liquid chromatography, gas chromatography-electron capture and unequivocally identified by combined gas chromatography-mass spectrometry. Abscisic acid, 1',4'-trans-abscisic acid diol and phaseic acid were unequivocally identified as the major acidic products formed in this cell-free system. The acid fraction also contained xanthoxin acid. Labelled and unlabelled ß-carotene was converted into the neutral compounds xanthoxin and xanthoxin alcohol. In addition. high performance liquid chromatography-photodiode array analYSis of the oxy-carotenoid fraction revealed the complete spectrum of ß, ß-carotenoids induding zeaxanthin, antheraxanthin and violaxanthin with accumulation of an oxygenated carotenoid tentatively identified as 9- cis-violaxanthin. Identification of putative C₁₅ intermediates was achieved by either UV spectrophotometry and combined capillary gas chromatography-mass spectrometry or microchemical analYSis and co-chromatography. Refeeding studies using (±)-[2-¹⁴C]_ abscisic acid diol as substrate revealed that abscisic acid was not metabolized to abscisic acid diol, suggesting that it was/is produced as an intermediate rather than as a catabolite of ABA in this system. Stigmasterol, and to a lesser extent cholesterol reduced conversion of ß-carotene to abscisic acid but did not influence transformation of 1',4'-trans-abscisic acid diol to abscisic acid. AM01618 stimulated fonnation of abscisic acid and appeared to exert its effect at the level of conversion of 1' ,4'-trans-abscisic acid diol. Zeatin and the cytokinin analogue, ancymidol inhibited the biosynthesis of abscisic acid whereas dithiothreitol increased incorporation of label from ß-carotene into abscisic acid suggesting involvement of a cytochrome P450-type mixed function oxidase in this reaction sequence. Sodium dodecylsulphate polyacrylamide gel electrophoresis of the enzyme extract derived from Citrus flavedo revealed the presence of a 53 kD protein with peroxidase activity characteristic of a cytochrome P-450. Abscisic acid biosynthesizing activity was always greater in extracts from acetone powder and abscisic acid biosynthesis was enhanced in the presence of AMO 1618, NAD+, NADH, NADPH, MgCI₂ and Molybdate but was inhibited by FAD. Activity was further enhanced by the addition of (R,S)-abscisic acid as a cold-pool trap and by induding 0.1% w/v of either Tween 20 or Triton X 100 in the extraction buffer. When cis-ß-carotene was used as substrate, no abscisic acid was produced. Conversely when either all-trans-ß-carotene or a mixture of the two isomers was used, incorporation into abscisic acid occurred. Upoxygenase activity in cell-free extracts of Citrus flavedo increased with increasing protein concentration. As the ability of lipoxygenase to make xanthoxin from violaxanthin, had been reported, increased activity in the cell-free system implied that carotenoid deavage was being brought about by a non-haem oxygenase with lipoxygenase-like properties. Reports had implicated phoshorylation in the activation of many catalytic enzymes (Hanks et aI., 1985). Phosphorylation of the enzymes in this cell-free system proved unsuccessful. Further, it had been reported that in vitro phosphorylation of several membrane polypeptides and soluble polypeptides from com, had been promoted by the addition of Ca²₊ In this cell-free system Ca + did not have a stimulatory effect on protein phosphorylation. Dioxygenases generally occur as soluble enzymes, where they catalyse many oxygenation reactions in metabolic pathways. The addition of 2-oxo-glutarate, a requirement of most soluble oxidases, did not affect the activity of the cell-free system.
- Full Text:
- Date Issued: 1996
- Authors: Richardson, Gaynor Rose-Marie
- Date: 1996
- Subjects: Biosynthesis Abscisic acid Citrus fruits
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4221 , http://hdl.handle.net/10962/d1003790
- Description: The biosynthetic origin of the plant growth regulator abscisic acid remains equivocal and almost nothing is known about the enzymes involved in this process. The present research programme describes the development of a cell-free system, capable of synthesizing abscisic acid and attempts to provide further information about the biochemistry and enzymology of this important biosynthetic pathway. Cell-free extracts were prepared either directly from the flavedo (crude) or from an acetone powder derived from flavedo, of mature coloured fruits of Citrus sinensis L. cv. Midknight and incubated with mevalonic acid, isopentenyl pyrophosphate, famesylpyrophosphate, geranylgeranyl pyrophosphate, ß-carotene and 1',4'-trans-abscisic acid diol. The neutral and acidic products formed were purified by thin-layer chromatography and high performance liquid chromatography, and quantified by high performance liquid chromatography, gas chromatography-electron capture and unequivocally identified by combined gas chromatography-mass spectrometry. Abscisic acid, 1',4'-trans-abscisic acid diol and phaseic acid were unequivocally identified as the major acidic products formed in this cell-free system. The acid fraction also contained xanthoxin acid. Labelled and unlabelled ß-carotene was converted into the neutral compounds xanthoxin and xanthoxin alcohol. In addition. high performance liquid chromatography-photodiode array analYSis of the oxy-carotenoid fraction revealed the complete spectrum of ß, ß-carotenoids induding zeaxanthin, antheraxanthin and violaxanthin with accumulation of an oxygenated carotenoid tentatively identified as 9- cis-violaxanthin. Identification of putative C₁₅ intermediates was achieved by either UV spectrophotometry and combined capillary gas chromatography-mass spectrometry or microchemical analYSis and co-chromatography. Refeeding studies using (±)-[2-¹⁴C]_ abscisic acid diol as substrate revealed that abscisic acid was not metabolized to abscisic acid diol, suggesting that it was/is produced as an intermediate rather than as a catabolite of ABA in this system. Stigmasterol, and to a lesser extent cholesterol reduced conversion of ß-carotene to abscisic acid but did not influence transformation of 1',4'-trans-abscisic acid diol to abscisic acid. AM01618 stimulated fonnation of abscisic acid and appeared to exert its effect at the level of conversion of 1' ,4'-trans-abscisic acid diol. Zeatin and the cytokinin analogue, ancymidol inhibited the biosynthesis of abscisic acid whereas dithiothreitol increased incorporation of label from ß-carotene into abscisic acid suggesting involvement of a cytochrome P450-type mixed function oxidase in this reaction sequence. Sodium dodecylsulphate polyacrylamide gel electrophoresis of the enzyme extract derived from Citrus flavedo revealed the presence of a 53 kD protein with peroxidase activity characteristic of a cytochrome P-450. Abscisic acid biosynthesizing activity was always greater in extracts from acetone powder and abscisic acid biosynthesis was enhanced in the presence of AMO 1618, NAD+, NADH, NADPH, MgCI₂ and Molybdate but was inhibited by FAD. Activity was further enhanced by the addition of (R,S)-abscisic acid as a cold-pool trap and by induding 0.1% w/v of either Tween 20 or Triton X 100 in the extraction buffer. When cis-ß-carotene was used as substrate, no abscisic acid was produced. Conversely when either all-trans-ß-carotene or a mixture of the two isomers was used, incorporation into abscisic acid occurred. Upoxygenase activity in cell-free extracts of Citrus flavedo increased with increasing protein concentration. As the ability of lipoxygenase to make xanthoxin from violaxanthin, had been reported, increased activity in the cell-free system implied that carotenoid deavage was being brought about by a non-haem oxygenase with lipoxygenase-like properties. Reports had implicated phoshorylation in the activation of many catalytic enzymes (Hanks et aI., 1985). Phosphorylation of the enzymes in this cell-free system proved unsuccessful. Further, it had been reported that in vitro phosphorylation of several membrane polypeptides and soluble polypeptides from com, had been promoted by the addition of Ca²₊ In this cell-free system Ca + did not have a stimulatory effect on protein phosphorylation. Dioxygenases generally occur as soluble enzymes, where they catalyse many oxygenation reactions in metabolic pathways. The addition of 2-oxo-glutarate, a requirement of most soluble oxidases, did not affect the activity of the cell-free system.
- Full Text:
- Date Issued: 1996
Computer modelling of pyrotechnic combustion
- Authors: Taylor, Steven John
- Date: 1996
- Subjects: Combustion -- Computer simulation
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4426 , http://hdl.handle.net/10962/d1006913
- Description: One of the most important industrial uses of pyrotechnic compositions is as delay fuses in electric detonators. Many factors influence the rate of burning of such fuses. These include (a) the primary choice of chemical components, followed by (b) the physical properties of these components, particularly the particle-size and distribution of the fuel, (c) the composition of the system chosen and (d) the presence of additives and/or impurities. A full experimental study of the influences of even a few of these factors, while attempting to hold other potential variables constant, would be extremely time consuming and hence attention has been focused on the possibilities of modelling pyrotechnic combustion. Various approaches to the modelling of pyrotechnic combustion are discussed. These include:- (i) one-dimensional finite-difference models; (ii) two-dimensional finite-element models; (iii) particle-packing considerations; (iv) Monte Carlo models. Predicted behaviour is compared with extensive experimental information for the widely-used antimony/potassium permanganate pyrotechnic system, and the tungsten /potassium dichromate pyrotechnic system. The one-dimensional finite-difference model was investigated to give a simple means of investigating the effects of some parameters on the combustion of a pyrotechnic. The two-dimensional finite-difference model used similar inputs, but at the expense of considerably more computer power, gave more extensive information such as the shape of the burning front and the temperature gradients throughout the column and within the casing material. Both these models gave improved results when allowance was made for autocatalytic kinetics in place of the usual assumption of an "order-of-reaction", n ≤ 1. The particle-packing model investigated the qualitative relationship between the maximum burning rate of a pyrotechnic system and the maximum number of contact points (per 1.00 g composition) calculated for that system. Qualitative agreement was found for those systems which are presumed to burn mainly via solid-solid reactions. The Monte Carlo model investigated the effect of the random packing of fuel and oxidant particles on the variability of the burning rate of a pyrotechnic composition.
- Full Text:
- Date Issued: 1996
- Authors: Taylor, Steven John
- Date: 1996
- Subjects: Combustion -- Computer simulation
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4426 , http://hdl.handle.net/10962/d1006913
- Description: One of the most important industrial uses of pyrotechnic compositions is as delay fuses in electric detonators. Many factors influence the rate of burning of such fuses. These include (a) the primary choice of chemical components, followed by (b) the physical properties of these components, particularly the particle-size and distribution of the fuel, (c) the composition of the system chosen and (d) the presence of additives and/or impurities. A full experimental study of the influences of even a few of these factors, while attempting to hold other potential variables constant, would be extremely time consuming and hence attention has been focused on the possibilities of modelling pyrotechnic combustion. Various approaches to the modelling of pyrotechnic combustion are discussed. These include:- (i) one-dimensional finite-difference models; (ii) two-dimensional finite-element models; (iii) particle-packing considerations; (iv) Monte Carlo models. Predicted behaviour is compared with extensive experimental information for the widely-used antimony/potassium permanganate pyrotechnic system, and the tungsten /potassium dichromate pyrotechnic system. The one-dimensional finite-difference model was investigated to give a simple means of investigating the effects of some parameters on the combustion of a pyrotechnic. The two-dimensional finite-difference model used similar inputs, but at the expense of considerably more computer power, gave more extensive information such as the shape of the burning front and the temperature gradients throughout the column and within the casing material. Both these models gave improved results when allowance was made for autocatalytic kinetics in place of the usual assumption of an "order-of-reaction", n ≤ 1. The particle-packing model investigated the qualitative relationship between the maximum burning rate of a pyrotechnic system and the maximum number of contact points (per 1.00 g composition) calculated for that system. Qualitative agreement was found for those systems which are presumed to burn mainly via solid-solid reactions. The Monte Carlo model investigated the effect of the random packing of fuel and oxidant particles on the variability of the burning rate of a pyrotechnic composition.
- Full Text:
- Date Issued: 1996
Conrad's impressionism : the treatment of space and atmosphere in selected works
- Authors: De Lange, Adriaan Michiel
- Date: 1996
- Subjects: Conrad, Joseph, 1857-1924 -- Criticism and interpretation Conrad, Joseph, 1857-1924 -- Heart of darkness Conrad, Joseph, 1857-1924 -- Nigger of the Narcissus Conrad, Joseph, 1857-1924 -- Nostromo Conrad, Joseph, 1857-1924 -- Lord Jim
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:2229 , http://hdl.handle.net/10962/d1002272
- Description: This thesis focuses on Conrad's representation of space and atmosphere in the "impressionistic" works published between 1897 and 1904, notably The Nigger of the "Narcissus" (1897), "Heart of Darkness" (1899), Lord Jim (1900), and Nostromo (1904). The many conflicting statements regarding the nature of Conrad's impressionism lead one to ask two fundamental questions: What constitutes this strange and elusive phenomenon, and how does it bear upon interpretation? This thesis works towards defining the elusive quality of Conrad's writing by investigating and assessing the contribution of impressionist techniques in the creation of a pervasive space and atmosphere; secondly, it considers how the various constituent elements interact with, and complement one another to form a dominant mode of fictional space in each work; and, thirdly, it indicates the possible impact that these particular Conradian configurations of space and atmosphere might have upon the interpretation of his impressionist works. The thesis argues that the existential condition of isolatio~experienced by Conrad's heroes and narrators is a consequence of epistemological frustration and fragmentation, which, in turn, is a function of impressionist ontology. There is a definite and complementary relationship between each of these notions in Conrad's fiction. The mysterious atmosphere in his works results from the interplay between various configurations of theme, narration and description, and these novelistic elements correspond roughly with the notions of existential isolation (the dominant theme), epistemology (narrating, telling and (re)telling as a method of knowing and understanding the space in which the characters find themselves) and, lastly, the ontological dimensions of the various modes of fictional space (as realized in description). The evocation and invocation of cosmic space in The Nigger of the "Narcissus," the mapping of a dorriinant symbolic space in "Heart of Darkness," the (re)constructions of Jim's psychological space in Lord Jim, and, finally, the "transcription" and "inscription" of a mythical space in Nostromo, indicate a definite development from epistemological to ontological issues. Phrased in more theoretical terms, this development is a movement from asking predominantly epistemological questions like "How can I interpret this world of which I am a part?" "What is there to be known?" "Who knows it ... and with what degree of certainty?", to asking predominantly ontological questions, such as "Which world is this?" "What kinds of worlds are there ... and how are they constituted?". Such questions, categorized by McHale as the dominant characteristics of Modernist and Postmodernist fiction respectively, are already present in Conrad's texts, thus undermining any clear-cut division between these broad categories. Indeed, this thesis suggests that these categories are at best tenuous, and that they should perhaps be used heuristically, rather than definitively
- Full Text:
- Date Issued: 1996
- Authors: De Lange, Adriaan Michiel
- Date: 1996
- Subjects: Conrad, Joseph, 1857-1924 -- Criticism and interpretation Conrad, Joseph, 1857-1924 -- Heart of darkness Conrad, Joseph, 1857-1924 -- Nigger of the Narcissus Conrad, Joseph, 1857-1924 -- Nostromo Conrad, Joseph, 1857-1924 -- Lord Jim
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:2229 , http://hdl.handle.net/10962/d1002272
- Description: This thesis focuses on Conrad's representation of space and atmosphere in the "impressionistic" works published between 1897 and 1904, notably The Nigger of the "Narcissus" (1897), "Heart of Darkness" (1899), Lord Jim (1900), and Nostromo (1904). The many conflicting statements regarding the nature of Conrad's impressionism lead one to ask two fundamental questions: What constitutes this strange and elusive phenomenon, and how does it bear upon interpretation? This thesis works towards defining the elusive quality of Conrad's writing by investigating and assessing the contribution of impressionist techniques in the creation of a pervasive space and atmosphere; secondly, it considers how the various constituent elements interact with, and complement one another to form a dominant mode of fictional space in each work; and, thirdly, it indicates the possible impact that these particular Conradian configurations of space and atmosphere might have upon the interpretation of his impressionist works. The thesis argues that the existential condition of isolatio~experienced by Conrad's heroes and narrators is a consequence of epistemological frustration and fragmentation, which, in turn, is a function of impressionist ontology. There is a definite and complementary relationship between each of these notions in Conrad's fiction. The mysterious atmosphere in his works results from the interplay between various configurations of theme, narration and description, and these novelistic elements correspond roughly with the notions of existential isolation (the dominant theme), epistemology (narrating, telling and (re)telling as a method of knowing and understanding the space in which the characters find themselves) and, lastly, the ontological dimensions of the various modes of fictional space (as realized in description). The evocation and invocation of cosmic space in The Nigger of the "Narcissus," the mapping of a dorriinant symbolic space in "Heart of Darkness," the (re)constructions of Jim's psychological space in Lord Jim, and, finally, the "transcription" and "inscription" of a mythical space in Nostromo, indicate a definite development from epistemological to ontological issues. Phrased in more theoretical terms, this development is a movement from asking predominantly epistemological questions like "How can I interpret this world of which I am a part?" "What is there to be known?" "Who knows it ... and with what degree of certainty?", to asking predominantly ontological questions, such as "Which world is this?" "What kinds of worlds are there ... and how are they constituted?". Such questions, categorized by McHale as the dominant characteristics of Modernist and Postmodernist fiction respectively, are already present in Conrad's texts, thus undermining any clear-cut division between these broad categories. Indeed, this thesis suggests that these categories are at best tenuous, and that they should perhaps be used heuristically, rather than definitively
- Full Text:
- Date Issued: 1996
Death and gnosis: archetypal dream imagery in terminal illness
- Authors: Welman, Mark
- Date: 1996
- Subjects: Jung, C G (Carl Gustav), 1875-1961 Thanatology Death -- Psychological aspects Dreams Dreams Case studies Death in dreams
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3084 , http://hdl.handle.net/10962/d1002593
- Description: The central aim of this study was to explore the meaning of death as both a literal and an imaginative reality, and to elucidate the fundamental tensions between these meanings of death in modern existence. Recognition was given to the need for a poetic rather than a scientific approach to thanatology, and an epistemological foundation for a poetics of death was sought in the tradition of gnosis. Theoretically, the study was grounded in the analytical psychology of C.G. Jung. It was argued that despite Jung's erratic allegiance to a Cartesian ontology and epistemology, his approach to death was nevertheless fundamentally poetic. The poetic parameters of death and dying were explored in the context of Jung's understanding of the dialectical tension between the ego and the self, and it was concluded that while death represents an opening to the imaginative possibilities of existence, these potentialities can come to the fore only when there is a corresponding willingness to die. In these terms, it was concluded that the tension between life and death forms a pivotal dynamic of human existence. These considerations led to the Question of whether the poetic parameters of death and dying are applicable to the encounter with death as a concrete actuality. It was hypothesised that the approach of death would be met at two levels of reality, that of the ego and that of the self. The expectation was that while death would be seen as a literal ending from the perspective of the former, it may represent the fulfilment of Being from the viewpoint of the self. It was also assumed that the tension between these images of death would be mediated by way of archetypal symbols, which represent the bearers of gnosis in modern culture. To address these issues at an empirical level, a hermeneutically grounded thematic analysis of 108 dreams reported by dying persons was undertaken. Twenty initial themes emerged from the data. Each of these themes was in turn elucidated by way of Jung's method of amplification. This exercise yielded five concise themes, these being (a) death, (b) transformation, (c) the self (d) the Feminine, and (e) the Masculine. It was concluded that dreams manifesting during the dying process reveal a fundamental tension between literal and metaphoric possibilities of death. Dream symbols were also found to mediate between this tension, and to orchestrate the individuation process. It was concluded that in the context of dying, dreams may reflect and facilitate the emergence of a meaningful gnosis of death. The clinical implications of these findings were onsidered, and indications for further research were provided.
- Full Text:
- Date Issued: 1996
- Authors: Welman, Mark
- Date: 1996
- Subjects: Jung, C G (Carl Gustav), 1875-1961 Thanatology Death -- Psychological aspects Dreams Dreams Case studies Death in dreams
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3084 , http://hdl.handle.net/10962/d1002593
- Description: The central aim of this study was to explore the meaning of death as both a literal and an imaginative reality, and to elucidate the fundamental tensions between these meanings of death in modern existence. Recognition was given to the need for a poetic rather than a scientific approach to thanatology, and an epistemological foundation for a poetics of death was sought in the tradition of gnosis. Theoretically, the study was grounded in the analytical psychology of C.G. Jung. It was argued that despite Jung's erratic allegiance to a Cartesian ontology and epistemology, his approach to death was nevertheless fundamentally poetic. The poetic parameters of death and dying were explored in the context of Jung's understanding of the dialectical tension between the ego and the self, and it was concluded that while death represents an opening to the imaginative possibilities of existence, these potentialities can come to the fore only when there is a corresponding willingness to die. In these terms, it was concluded that the tension between life and death forms a pivotal dynamic of human existence. These considerations led to the Question of whether the poetic parameters of death and dying are applicable to the encounter with death as a concrete actuality. It was hypothesised that the approach of death would be met at two levels of reality, that of the ego and that of the self. The expectation was that while death would be seen as a literal ending from the perspective of the former, it may represent the fulfilment of Being from the viewpoint of the self. It was also assumed that the tension between these images of death would be mediated by way of archetypal symbols, which represent the bearers of gnosis in modern culture. To address these issues at an empirical level, a hermeneutically grounded thematic analysis of 108 dreams reported by dying persons was undertaken. Twenty initial themes emerged from the data. Each of these themes was in turn elucidated by way of Jung's method of amplification. This exercise yielded five concise themes, these being (a) death, (b) transformation, (c) the self (d) the Feminine, and (e) the Masculine. It was concluded that dreams manifesting during the dying process reveal a fundamental tension between literal and metaphoric possibilities of death. Dream symbols were also found to mediate between this tension, and to orchestrate the individuation process. It was concluded that in the context of dying, dreams may reflect and facilitate the emergence of a meaningful gnosis of death. The clinical implications of these findings were onsidered, and indications for further research were provided.
- Full Text:
- Date Issued: 1996
Domino Servite School: an evaluative case study of a private Christian secondary school in rural Natal
- Authors: Davidson, Michael R
- Date: 1996
- Subjects: Christian education -- South Africa Church schools -- South Africa Education -- South Africa -- Kwazulu Private schools -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1500 , http://hdl.handle.net/10962/d1003382
- Description: Domino Servite School (DSS) is a private school, founded in 1986, and situated on KwaSizabantu (KSB) mission station in the Natal midlands. This research into DSS is a case study which aims to present an illuminative evaluation in the Whole School genre, within that branch of educational research concerned with effective schools. The project aimed to make use of a compatibility paradigm accommodating nomothetic and anthropological data. In attempting triangulation of methodological approaches, it tried to establish the extent to which DSS may be considered an efficient and effective 'New Private' school. It also aimed to understand the school's raison d'ětre. In order to illuminate the relevance and social processes of DSS, evaluation made use of internal and external referents. The internal investigation sought to make judgements in reference to the efficiency of the school as an organisation. On the macro-level, whole school evaluation required extensive curriculum evaluation. On the micro-level, appraisal of teaching and assessment of pupil performance was undertaken. This internal investigation required a critical analysis of the school's formal, informal and hidden curriculum. The external evaluation sought to make judgement in reference to the effectiveness of DSS. On the macro-level, this required evaluation of the findings of the internal investigation in terms of a broader South African context. Implications, for example of the school's 'private' status, and its 'Christian' curriculum in respect of multi-culturalism, education for nationhood , and ethnicity were examined. The analysis of these dimensions paid attention to the school's spatial context in terms of both its 'rural' and missionary setting. Here the focus was on the school's formal curriculum. Analysis of the inter-relational context paid attention to its informal curriculum or the way in which the school deals with the commonality and diversity of its clientele and staff. The inter-relational context of the school examined the hidden curriculum, or the relationship between the school and the broader South African Community. A critical ethnographic account of this institution was therefore possible because of the dual focus on the internal and external evaluation reference points. Internal evaluation made extensive use of direct (non-participant) observation, structured and nonstructured interviews, questionnaires, and documentary analysis. Indirect (participant) observation, in particular Clinical Supervision (CS), was also used. Indirect (non-participant) observation made extensive use of Flanders' Interaction Analysis Categories (FIAC). Teacher self-evaluation was also included, while analysis of pupil performance made use of 'standardised' achievement testing and a tracer study. External evaluation required detailed study of local and international literature on issues relating to private schooling, rural and multi-cultural education, education for nationhood and ethnicity. The research found that much of the school's curriculum path is incongruous with its rural context largely because of its association with the former Department of Education and Training (DET), and because of its missionary heritage. As such the school is presently (1) located within a questionable (formal) curriculum tradition which has little relevance to, nor potential for, the transformational needs of either rural Natal or South Africa in general. However, this does not preclude the possibility of the school making a contribution to education for development in South Africa. (2) The school advocates a mono-cultural Christian value system and modified cultural pluralism which attempts to assimilate pupils from diverse socio-economic and ideologically homogeneous backgrounds. Multi-cultural education, plural values, religious and values democracy are therefore not part of the school's raison d'ětre. (3) The school, through its associated organisation Christians for Truth (CFT), represents a social view espousing either a modified cultural pluralism or multi-nationalism which allows for allegiance to a transcendent value system without compromising group. values and associations. This means that the school aims at assimilating or amalgamating diversity into a mono-cultural unity that transcends group identity. This transcendent culture is defined in Christian terms. The study recommends inter alia, further investigation into the educational implications of_values neutrality and the particularism of secular humanism; a comparative analysis of a random sample of private missionary schools and ordinary state controlled rural schools so that more generalisable results might be obtained; and a more thorough investigation into the parental and pupil contributions to the school, their attitudes and perspectives on missionary education and their feelings about the management styles evident in the organisation.
- Full Text:
- Date Issued: 1996
- Authors: Davidson, Michael R
- Date: 1996
- Subjects: Christian education -- South Africa Church schools -- South Africa Education -- South Africa -- Kwazulu Private schools -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1500 , http://hdl.handle.net/10962/d1003382
- Description: Domino Servite School (DSS) is a private school, founded in 1986, and situated on KwaSizabantu (KSB) mission station in the Natal midlands. This research into DSS is a case study which aims to present an illuminative evaluation in the Whole School genre, within that branch of educational research concerned with effective schools. The project aimed to make use of a compatibility paradigm accommodating nomothetic and anthropological data. In attempting triangulation of methodological approaches, it tried to establish the extent to which DSS may be considered an efficient and effective 'New Private' school. It also aimed to understand the school's raison d'ětre. In order to illuminate the relevance and social processes of DSS, evaluation made use of internal and external referents. The internal investigation sought to make judgements in reference to the efficiency of the school as an organisation. On the macro-level, whole school evaluation required extensive curriculum evaluation. On the micro-level, appraisal of teaching and assessment of pupil performance was undertaken. This internal investigation required a critical analysis of the school's formal, informal and hidden curriculum. The external evaluation sought to make judgement in reference to the effectiveness of DSS. On the macro-level, this required evaluation of the findings of the internal investigation in terms of a broader South African context. Implications, for example of the school's 'private' status, and its 'Christian' curriculum in respect of multi-culturalism, education for nationhood , and ethnicity were examined. The analysis of these dimensions paid attention to the school's spatial context in terms of both its 'rural' and missionary setting. Here the focus was on the school's formal curriculum. Analysis of the inter-relational context paid attention to its informal curriculum or the way in which the school deals with the commonality and diversity of its clientele and staff. The inter-relational context of the school examined the hidden curriculum, or the relationship between the school and the broader South African Community. A critical ethnographic account of this institution was therefore possible because of the dual focus on the internal and external evaluation reference points. Internal evaluation made extensive use of direct (non-participant) observation, structured and nonstructured interviews, questionnaires, and documentary analysis. Indirect (participant) observation, in particular Clinical Supervision (CS), was also used. Indirect (non-participant) observation made extensive use of Flanders' Interaction Analysis Categories (FIAC). Teacher self-evaluation was also included, while analysis of pupil performance made use of 'standardised' achievement testing and a tracer study. External evaluation required detailed study of local and international literature on issues relating to private schooling, rural and multi-cultural education, education for nationhood and ethnicity. The research found that much of the school's curriculum path is incongruous with its rural context largely because of its association with the former Department of Education and Training (DET), and because of its missionary heritage. As such the school is presently (1) located within a questionable (formal) curriculum tradition which has little relevance to, nor potential for, the transformational needs of either rural Natal or South Africa in general. However, this does not preclude the possibility of the school making a contribution to education for development in South Africa. (2) The school advocates a mono-cultural Christian value system and modified cultural pluralism which attempts to assimilate pupils from diverse socio-economic and ideologically homogeneous backgrounds. Multi-cultural education, plural values, religious and values democracy are therefore not part of the school's raison d'ětre. (3) The school, through its associated organisation Christians for Truth (CFT), represents a social view espousing either a modified cultural pluralism or multi-nationalism which allows for allegiance to a transcendent value system without compromising group. values and associations. This means that the school aims at assimilating or amalgamating diversity into a mono-cultural unity that transcends group identity. This transcendent culture is defined in Christian terms. The study recommends inter alia, further investigation into the educational implications of_values neutrality and the particularism of secular humanism; a comparative analysis of a random sample of private missionary schools and ordinary state controlled rural schools so that more generalisable results might be obtained; and a more thorough investigation into the parental and pupil contributions to the school, their attitudes and perspectives on missionary education and their feelings about the management styles evident in the organisation.
- Full Text:
- Date Issued: 1996
Multivariate analysis of selected honeybee populations in Africa
- Authors: Radloff, Sarah E
- Date: 1996
- Subjects: Bees -- Africa Bees
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5734 , http://hdl.handle.net/10962/d1005420
- Description: Morphometric characters and sting pheromones of worker honeybees, Apis mellifera Linnaeus were analysed by multivariate methods to characterise selected honeybee populations along five transects in Africa at a meso-scale level of sampling distance resolution. In some, but not all, areas pheromonal clusters were found to be coincident and concordant with the morphometric clusters, thus indicating that different honeybee traits have dispersed variably among populations. All transects were found to contain areas of significantly high variance. High intracolonial variance was taken to indicate localised genetic variation coupled with out-cross matings. Centroids of high intercolonial variance occured at and between cluster boundaries and were typical of transitions between, and rainfall-temperature discontinuities within, ecological-climatological zones, hence areas of ecological instability. Principal component and stepwise discriminant analysis yielded three morphometric clusters corresponding to A. m. sahariensis and A. m. intermissa in Morocco and to A. m. iberica (with three biometric populations) in Spain, but no pheromone clusters. The combined morphometric and pheromonal variance spectra indicated regions of natural hybridisation along a Sahara-Pyrenees transect. In the Horn of Africa, discrete and statistically homogeneous populations were identified: A. m. jemenitica, A. m. bandasii, A. m. sudanensis in Ethiopia and an unclassified group in southwestern Somalia. Areas of high intercolonial variance were interpreted as zones of hybridisation between the populations. Along a transect in west central Africa, three distinct homogeneous populations and two zones of hybridisation were found. These bees were designated as A. m. adansonii whose area of distribution was intruded by an un-named mountain group of bees and a third group, A. m. jemenitica. The delineation of the hybrid zones was supported by intercolonial variance spectra and these significant asymmetries were found to be coincident with transitions between the ecological-climatological zones. In southwestern Africa, two discrete homogeneous populations and a zone of hybridisation between them were identified: A. m. scutellata in northern South Africa and southern Namibia and A. m. adansonii in northern Namibia. Along a transect in the southeastern woodland savanna of Africa, three discrete populations were classified: A. m. litorea in Mozambique, A. m. scutellata in Zimbabwe and A. m. adansonii in northwestern Zambia. A zone of introgression between the last two subspecies occured in south-central Zambia and in the Zambezi valley.
- Full Text:
- Date Issued: 1996
- Authors: Radloff, Sarah E
- Date: 1996
- Subjects: Bees -- Africa Bees
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5734 , http://hdl.handle.net/10962/d1005420
- Description: Morphometric characters and sting pheromones of worker honeybees, Apis mellifera Linnaeus were analysed by multivariate methods to characterise selected honeybee populations along five transects in Africa at a meso-scale level of sampling distance resolution. In some, but not all, areas pheromonal clusters were found to be coincident and concordant with the morphometric clusters, thus indicating that different honeybee traits have dispersed variably among populations. All transects were found to contain areas of significantly high variance. High intracolonial variance was taken to indicate localised genetic variation coupled with out-cross matings. Centroids of high intercolonial variance occured at and between cluster boundaries and were typical of transitions between, and rainfall-temperature discontinuities within, ecological-climatological zones, hence areas of ecological instability. Principal component and stepwise discriminant analysis yielded three morphometric clusters corresponding to A. m. sahariensis and A. m. intermissa in Morocco and to A. m. iberica (with three biometric populations) in Spain, but no pheromone clusters. The combined morphometric and pheromonal variance spectra indicated regions of natural hybridisation along a Sahara-Pyrenees transect. In the Horn of Africa, discrete and statistically homogeneous populations were identified: A. m. jemenitica, A. m. bandasii, A. m. sudanensis in Ethiopia and an unclassified group in southwestern Somalia. Areas of high intercolonial variance were interpreted as zones of hybridisation between the populations. Along a transect in west central Africa, three distinct homogeneous populations and two zones of hybridisation were found. These bees were designated as A. m. adansonii whose area of distribution was intruded by an un-named mountain group of bees and a third group, A. m. jemenitica. The delineation of the hybrid zones was supported by intercolonial variance spectra and these significant asymmetries were found to be coincident with transitions between the ecological-climatological zones. In southwestern Africa, two discrete homogeneous populations and a zone of hybridisation between them were identified: A. m. scutellata in northern South Africa and southern Namibia and A. m. adansonii in northern Namibia. Along a transect in the southeastern woodland savanna of Africa, three discrete populations were classified: A. m. litorea in Mozambique, A. m. scutellata in Zimbabwe and A. m. adansonii in northwestern Zambia. A zone of introgression between the last two subspecies occured in south-central Zambia and in the Zambezi valley.
- Full Text:
- Date Issued: 1996
Observations of glitches in PSR 0833-45 and 1641-45
- Authors: Flanagan, Claire Susan
- Date: 1996
- Subjects: Pulsars Neutron stars
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5480 , http://hdl.handle.net/10962/d1005266
- Description: An eleven-year series of radio timing observations of 0833- 45 (Vela) and PSR 1641- 45 is presented. During this time, five large spin-ups ("glitches") were observed in 0833- 45 and one in 1641-45. The stellar response to these events is investigated, and the three relat ively long complete inter-glitch intervals in 0833-45 are modeled. The results are of relevance to studies of the interiors of neutron stars. The initial aim of the project - to obtain good observational coverage of large glitches in the Vela pulsar - was successfully achieved, and high quality observations of the periods between glitches were obtained as a by-product. The results of the analysis presented here provide support for the existence of both linear and non-linear coupling in the Vela pulsar, and put a limit on the former in PSR 1641- 45. The recently observed existence of a rapidly recovering component of part of a glitch in Vela was verified in the subsequent glitch, although there is now evidence to contradict the suggestion that this component involves a particular region of the star that is implicated in every glitch. Observations of a recent glitch in the same pulsar have resolved a small component of the spin-up; such a component has not been reported for any other large glitch.
- Full Text:
- Date Issued: 1996
- Authors: Flanagan, Claire Susan
- Date: 1996
- Subjects: Pulsars Neutron stars
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5480 , http://hdl.handle.net/10962/d1005266
- Description: An eleven-year series of radio timing observations of 0833- 45 (Vela) and PSR 1641- 45 is presented. During this time, five large spin-ups ("glitches") were observed in 0833- 45 and one in 1641-45. The stellar response to these events is investigated, and the three relat ively long complete inter-glitch intervals in 0833-45 are modeled. The results are of relevance to studies of the interiors of neutron stars. The initial aim of the project - to obtain good observational coverage of large glitches in the Vela pulsar - was successfully achieved, and high quality observations of the periods between glitches were obtained as a by-product. The results of the analysis presented here provide support for the existence of both linear and non-linear coupling in the Vela pulsar, and put a limit on the former in PSR 1641- 45. The recently observed existence of a rapidly recovering component of part of a glitch in Vela was verified in the subsequent glitch, although there is now evidence to contradict the suggestion that this component involves a particular region of the star that is implicated in every glitch. Observations of a recent glitch in the same pulsar have resolved a small component of the spin-up; such a component has not been reported for any other large glitch.
- Full Text:
- Date Issued: 1996
Production ecology of bryophyte vegetation at Marion Island (Sub-Antarctic)
- Authors: Russell, Shaun
- Date: 1996
- Subjects: Bryophytes -- marion island (Prince edward islands) -- Ecology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4224 , http://hdl.handle.net/10962/d1003793
- Description: The world's tundra regions can be considered as the last unexploited terrestrial biome on the earth's surface. Bryophytes contribute significantly to primary production and nutrient cycling in tundra habitats but received considerably less attention than the vascular plants during research for the Tundra Biome Project of the International Biological Programme in the 1970s. The IBP synthesis recognised this and called for more bryophyte production data and improved methodology in future studies. The synthesis also identitied the need for more information on within-site variability, energy/chlorophyll relationships and mineral nutrient studies where tundra bryophyte production patterns are concerned. Marion Island in the sub-Antarctic has an oceanic "tundra" type of vegetation, and the island offers the characteristics of an ideal "natural laboratory" for conducting fundamental ecological research particularly in the field of primary production and energy flow. Studies at Marion Island paralleled those of the IBP but also concentrated on the vascular component of the vegetation. Bryophytes contribute up to 60% of the biomass and 90% of plant cover in the mires that dominate the well-vegetated coastal plain of Marion Island. Following the termination of IBP research therefore it was decided to extend these studies during the 1980s by measuring growth and characterising the major factors influencing growth patterns in Marion Island bryophytes. In this thesis information is given on the physical and biotic environment of Marion Island. Data is presented on the cover, biomass, seasonal and annual production values, and turn-over rates (decomposition) of 15 bryophyte species found across the full range of habit at types at Marion Island. An analysis is also made of growth-associated variables viz. soils, climate, plant energy, chlorophyll. water and mineral nutrient contents. Production was found to be related broadly to moisture-related variables, overlain by nutrient factors in some instances. Higher absolute production figures were obtained than at other tundra sites and interesting phenological data are discussed. The results suggest that decomposition is controlled mainly by tissue degradability factors and that decomposition is more significant than production in controlling biomass accumulation. A model is given for production/decomposition patterns across the range of habitat conditions at Marion Island. Several growth measurement techniques were tested and recommendations are made concerning methodology for future bryophyte production studies. By reference to ecological data collected during the study.
- Full Text:
- Date Issued: 1996
- Authors: Russell, Shaun
- Date: 1996
- Subjects: Bryophytes -- marion island (Prince edward islands) -- Ecology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4224 , http://hdl.handle.net/10962/d1003793
- Description: The world's tundra regions can be considered as the last unexploited terrestrial biome on the earth's surface. Bryophytes contribute significantly to primary production and nutrient cycling in tundra habitats but received considerably less attention than the vascular plants during research for the Tundra Biome Project of the International Biological Programme in the 1970s. The IBP synthesis recognised this and called for more bryophyte production data and improved methodology in future studies. The synthesis also identitied the need for more information on within-site variability, energy/chlorophyll relationships and mineral nutrient studies where tundra bryophyte production patterns are concerned. Marion Island in the sub-Antarctic has an oceanic "tundra" type of vegetation, and the island offers the characteristics of an ideal "natural laboratory" for conducting fundamental ecological research particularly in the field of primary production and energy flow. Studies at Marion Island paralleled those of the IBP but also concentrated on the vascular component of the vegetation. Bryophytes contribute up to 60% of the biomass and 90% of plant cover in the mires that dominate the well-vegetated coastal plain of Marion Island. Following the termination of IBP research therefore it was decided to extend these studies during the 1980s by measuring growth and characterising the major factors influencing growth patterns in Marion Island bryophytes. In this thesis information is given on the physical and biotic environment of Marion Island. Data is presented on the cover, biomass, seasonal and annual production values, and turn-over rates (decomposition) of 15 bryophyte species found across the full range of habit at types at Marion Island. An analysis is also made of growth-associated variables viz. soils, climate, plant energy, chlorophyll. water and mineral nutrient contents. Production was found to be related broadly to moisture-related variables, overlain by nutrient factors in some instances. Higher absolute production figures were obtained than at other tundra sites and interesting phenological data are discussed. The results suggest that decomposition is controlled mainly by tissue degradability factors and that decomposition is more significant than production in controlling biomass accumulation. A model is given for production/decomposition patterns across the range of habitat conditions at Marion Island. Several growth measurement techniques were tested and recommendations are made concerning methodology for future bryophyte production studies. By reference to ecological data collected during the study.
- Full Text:
- Date Issued: 1996
Religion, tradition and custom in a Zulu male vocal idiom
- Ndlovu, Caesar Maxwell Jeffrey
- Authors: Ndlovu, Caesar Maxwell Jeffrey
- Date: 1996
- Subjects: Songs, Zulu Zulu (African people) -- Social life and customs Zionist churches (Africa) -- South Africa -- Transkei Church music -- South Africa African indigenous/independent churches
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:2650 , http://hdl.handle.net/10962/d1002315
- Description: The study is about a Zulu male vocal tradition called isicathamiya performed by 'migrants' in all night competitions called ingomabusuku. This is a performance style popularized by the award winning group Ladysmith Black Mambazo. Isicathamiya, both in its symbolic structure and in the social and culturalpractice of its proponents has much in common with the ritual practices of Zionists. And Zionists are worshippers who integrate traditional beliefs and Christianity. This study will reveal that isicathamiya performance and Zionists are linked in three major areas:in the sqcial bases and practice of its proponents, in the structural properties of their performances and tn the meanings attached to these practices. Firstly, Zionists, who are also called a Separatist or African Independent church, and isicathamiya performers have minimal education and are employed in low income jobs in the cities. Most groups are formed with 'homeboy networks'. Furthermore, performers, unlike their brothers in the city, cling tenaciously to usiko [custom and tradition]. Although they are Christians, they still worship Umvelinqangi [The One Who Came First], by giving oblations and other forms of offerings. Amadlozi [the ancestors] are still believed to be their mediators with God. Also commonplace in this category is the practice of ukuchatha, [cleansing the stomach with some prepared medicine]; and ukuphalaza [taking out bile by spewing, which is also done as a way of warding off evil spirits]. These are rural practices that have meaning in their present domiciles. The second area of similarity consists in the structure of the nocturnal gatherings that form the core of the ritual and performance practices among isicathamiya singers and Zionists. Thus, a core of the ritual of Zionists is umlindelo [night vigil] which takes place every weekend from about 8 at night until the following day. Likewise, isicathamiya performers have competitions every Saturday evening from 8 at night until about 11 am the following day. Although Zionists night vigils are liturgical and isicathamiya competitions secular, the structures of both isicathamiya choreography and Zionists body movements appear the same. These movements are both rooted in a variety of traditional styles called ingoma. Thirdly, the meanings attached to these symbolic correspondences must be looked for in the selective appropriation of practices and beliefs taken to be traditional. Using present day commentaries in song and movement, ingoma and other rural styles performed in competitions and Zionists night vigils reflect a reconstruction of the past. Isicathamiya performers and Zionists see themselves as custodians of Zulu tradition, keeping Zulu ethnicity alive in the urban environment. This is why in this study we are going to see rural styles like ingoma, isifekezeli [war drills], ukusina [solo dancing] that were performed on the fields, now performed, sort of feigned and 'held in' as they are p~rformed in dance halls with wooden stages.
- Full Text:
- Date Issued: 1996
- Authors: Ndlovu, Caesar Maxwell Jeffrey
- Date: 1996
- Subjects: Songs, Zulu Zulu (African people) -- Social life and customs Zionist churches (Africa) -- South Africa -- Transkei Church music -- South Africa African indigenous/independent churches
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:2650 , http://hdl.handle.net/10962/d1002315
- Description: The study is about a Zulu male vocal tradition called isicathamiya performed by 'migrants' in all night competitions called ingomabusuku. This is a performance style popularized by the award winning group Ladysmith Black Mambazo. Isicathamiya, both in its symbolic structure and in the social and culturalpractice of its proponents has much in common with the ritual practices of Zionists. And Zionists are worshippers who integrate traditional beliefs and Christianity. This study will reveal that isicathamiya performance and Zionists are linked in three major areas:in the sqcial bases and practice of its proponents, in the structural properties of their performances and tn the meanings attached to these practices. Firstly, Zionists, who are also called a Separatist or African Independent church, and isicathamiya performers have minimal education and are employed in low income jobs in the cities. Most groups are formed with 'homeboy networks'. Furthermore, performers, unlike their brothers in the city, cling tenaciously to usiko [custom and tradition]. Although they are Christians, they still worship Umvelinqangi [The One Who Came First], by giving oblations and other forms of offerings. Amadlozi [the ancestors] are still believed to be their mediators with God. Also commonplace in this category is the practice of ukuchatha, [cleansing the stomach with some prepared medicine]; and ukuphalaza [taking out bile by spewing, which is also done as a way of warding off evil spirits]. These are rural practices that have meaning in their present domiciles. The second area of similarity consists in the structure of the nocturnal gatherings that form the core of the ritual and performance practices among isicathamiya singers and Zionists. Thus, a core of the ritual of Zionists is umlindelo [night vigil] which takes place every weekend from about 8 at night until the following day. Likewise, isicathamiya performers have competitions every Saturday evening from 8 at night until about 11 am the following day. Although Zionists night vigils are liturgical and isicathamiya competitions secular, the structures of both isicathamiya choreography and Zionists body movements appear the same. These movements are both rooted in a variety of traditional styles called ingoma. Thirdly, the meanings attached to these symbolic correspondences must be looked for in the selective appropriation of practices and beliefs taken to be traditional. Using present day commentaries in song and movement, ingoma and other rural styles performed in competitions and Zionists night vigils reflect a reconstruction of the past. Isicathamiya performers and Zionists see themselves as custodians of Zulu tradition, keeping Zulu ethnicity alive in the urban environment. This is why in this study we are going to see rural styles like ingoma, isifekezeli [war drills], ukusina [solo dancing] that were performed on the fields, now performed, sort of feigned and 'held in' as they are p~rformed in dance halls with wooden stages.
- Full Text:
- Date Issued: 1996
The development of the hydraulic biotope concept within a catchment based hierarchical geomorphological model
- Authors: Wadeson, R A (Roy A)
- Date: 1996
- Subjects: Stream ecology -- South Africa Stream measurements -- South Africa Hydrology -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4826 , http://hdl.handle.net/10962/d1005501
- Description: This thesis develops a technique for the identification, classification and quantification of instream flow environments. These features have been traditionally referred to as 'habitats' by lotic ecologists, in this research they are termed 'hydraulic biotopes'. The hydraulic biotope is the lowest of six nested levels of a hierarchical geomorphological model. This model has been developed as a tool to assist river managers, researchers and conservationists to categorise or classify rivers with respect to their geomorphic characteristics. Each level of the model provides data at a different level of resolution. This ranges from the broad scale catchment data to the site specific 'habitat' or hydraulic biotope data. Although this thesis is primarily concerned with the development of the hydraulic biotope, the interaction of all catchment variables needs to be recognised. Detailed analysis of hydraulic biotope data in the Buffalo River are presented within the broader hierarchical model. Consultation with lotic ecologists, together with a review of ecological literature, emphasised the need for a standardised terminology for the classification of ecologically significant instream flow environments. At present a fairly haphazard 'habitat' classification tends to be carried out by most researchers, this often leads to confusion in the identification and naming of different hydraulic biotopes ('habitats'). This confusion is exaggerated by the sharing of terminology between lotic ecology and fluvial geomorphology, usually for the categorisation of different types of features. A review of the ecological literature emphasises the importance of flow hydraulics within a river to describe the distribution of biota. The hydraulic variables considered to be most significant include velocity and depth. As river morphology directly determines the prevailing distribution of depth, velocity and substratum, it is obvious that there are important links to be made between fluvial geomorphology and lotic ecology. This thesis explores the potential of the hydraulic biotope as a tool to help develop those links. This thesis presents a standardised classification matrix for the identification of hydraulic biotopes. The matrix is simply based on water surface characteristics together with channel bed substratum. The validity of this matrix is tested by statistical analysis of hydraulic variables quantifying flow conditions within the various hydraulic biotope classes. Data is presented from four different river systems, each representing a different sedimentological environment. Where possible the influence of discharge has been considered. Results from more than 3000 data points show that hydraulic biotopes have distinct hydraulic characteristics in terms of velocity-depth ratio, Froude number, Reynolds number, 'roughness' Reynolds number and shear velocity. These hydraulic indices represent flow conditions both as an average within the water column, and near the bed. Statistical analysis shows that the hydraulic characteristics of the various hydraulic biotope classes are relatively consistent both within different fluvial environments and at different stages of flow. Unlike the morphological unit in which the hydraulic biotope is nested, in stream flow environments are shown to be temporally dynamic. Using the classification matrix as a tool for identification, hydraulic biotopes identified at one discharge are shown to be transformed from one class to another as a response to change in stage. The pattern of transformation is shown to be consistent within different sedimentological environments. An examination of the associations between hydraulic biotopes and morphological units demonstrates that, although some hydraulic biotopes are common to all morphological units (backwater pools, pools and runs), some features have specific associations. In this study rapids were found to be prevalent in bedrock pavement, bedrock pool and plane bed morphology, while cascades, chutes and riffles were common to plane bed, step and riffle morphology. Results from this research indicate that the hydraulic biotope, within the hierarchical geomorphological model, has the potential to aid the prediction of channel adjustment and associated 'habitat' (hydraulic biotope) transformation in response to changes in flow and sediment yield. These are likely to become increasingly important issues as South Africa strives to maintain a balance between the development of water resources to meet the needs of the rapidly expanding population, whilst at the same time maintaining the fluvial environment for sustainable use.
- Full Text:
- Date Issued: 1996
- Authors: Wadeson, R A (Roy A)
- Date: 1996
- Subjects: Stream ecology -- South Africa Stream measurements -- South Africa Hydrology -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4826 , http://hdl.handle.net/10962/d1005501
- Description: This thesis develops a technique for the identification, classification and quantification of instream flow environments. These features have been traditionally referred to as 'habitats' by lotic ecologists, in this research they are termed 'hydraulic biotopes'. The hydraulic biotope is the lowest of six nested levels of a hierarchical geomorphological model. This model has been developed as a tool to assist river managers, researchers and conservationists to categorise or classify rivers with respect to their geomorphic characteristics. Each level of the model provides data at a different level of resolution. This ranges from the broad scale catchment data to the site specific 'habitat' or hydraulic biotope data. Although this thesis is primarily concerned with the development of the hydraulic biotope, the interaction of all catchment variables needs to be recognised. Detailed analysis of hydraulic biotope data in the Buffalo River are presented within the broader hierarchical model. Consultation with lotic ecologists, together with a review of ecological literature, emphasised the need for a standardised terminology for the classification of ecologically significant instream flow environments. At present a fairly haphazard 'habitat' classification tends to be carried out by most researchers, this often leads to confusion in the identification and naming of different hydraulic biotopes ('habitats'). This confusion is exaggerated by the sharing of terminology between lotic ecology and fluvial geomorphology, usually for the categorisation of different types of features. A review of the ecological literature emphasises the importance of flow hydraulics within a river to describe the distribution of biota. The hydraulic variables considered to be most significant include velocity and depth. As river morphology directly determines the prevailing distribution of depth, velocity and substratum, it is obvious that there are important links to be made between fluvial geomorphology and lotic ecology. This thesis explores the potential of the hydraulic biotope as a tool to help develop those links. This thesis presents a standardised classification matrix for the identification of hydraulic biotopes. The matrix is simply based on water surface characteristics together with channel bed substratum. The validity of this matrix is tested by statistical analysis of hydraulic variables quantifying flow conditions within the various hydraulic biotope classes. Data is presented from four different river systems, each representing a different sedimentological environment. Where possible the influence of discharge has been considered. Results from more than 3000 data points show that hydraulic biotopes have distinct hydraulic characteristics in terms of velocity-depth ratio, Froude number, Reynolds number, 'roughness' Reynolds number and shear velocity. These hydraulic indices represent flow conditions both as an average within the water column, and near the bed. Statistical analysis shows that the hydraulic characteristics of the various hydraulic biotope classes are relatively consistent both within different fluvial environments and at different stages of flow. Unlike the morphological unit in which the hydraulic biotope is nested, in stream flow environments are shown to be temporally dynamic. Using the classification matrix as a tool for identification, hydraulic biotopes identified at one discharge are shown to be transformed from one class to another as a response to change in stage. The pattern of transformation is shown to be consistent within different sedimentological environments. An examination of the associations between hydraulic biotopes and morphological units demonstrates that, although some hydraulic biotopes are common to all morphological units (backwater pools, pools and runs), some features have specific associations. In this study rapids were found to be prevalent in bedrock pavement, bedrock pool and plane bed morphology, while cascades, chutes and riffles were common to plane bed, step and riffle morphology. Results from this research indicate that the hydraulic biotope, within the hierarchical geomorphological model, has the potential to aid the prediction of channel adjustment and associated 'habitat' (hydraulic biotope) transformation in response to changes in flow and sediment yield. These are likely to become increasingly important issues as South Africa strives to maintain a balance between the development of water resources to meet the needs of the rapidly expanding population, whilst at the same time maintaining the fluvial environment for sustainable use.
- Full Text:
- Date Issued: 1996
The dynamics of space use in some Lake Malawi fishes
- Authors: Robinson, Rosanna Lesley
- Date: 1996
- Subjects: Cichlids -- Nyasa, Lake Fishes -- Malawi Fishes -- Nyasa, Lake
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5264 , http://hdl.handle.net/10962/d1005108
- Description: Behaviour and space utilisation of rock-dwelling cichlids were observed at Thumbi East Island, Lake Malawi. 1. Males of five species of the mbuna complex held long-term territories. Pseudotropheus elongatus "aggressive" vigorously defended a feeding area and sometimes a spawning site interspecifically, but did not feed in the peripheral part of their territory. Spawning sites of Pseudotropheus zebra, Pseudotropheus tropheops "orange chest", Labeotropheus fuelleborni, and Petrotilapia nigra were interspecifically-defended, while larger mating territories were defended against conspecific neighbours. Feeding areas were shared with many fish and often extended beyond the defended area. There was considerable variation in behaviour and space use within and between species and between times of day. 2. Non-territorial P. zebra used larger ranges than territorial conspecifics, and fed more on plankton, but individuals had preferred benthic feeding areas, often in conspecific territories. These 'floaters' were often aggressive. Both size and relative brightness independently predicted the outcome of aggressive interactions between floaters, and a site-specific dominance hierarchy was suggested, with some individuals appearing to be semi-territorial. 3. Males and females of 21 and 13 species respectively were found to establish temporary breeding territories. Overall breeding seasonality was bimodal, but reproductive timing and territory characteristics differed among species. Temporary territories had a considerable impact on the behaviour and habitat use of all resident mbuna species, even causing abandonment of territories. 4. Non-breeding Protomelas taeniolatus had limited home ranges, and showed little aggression. During the highly-synchronised reproductive season, males defended spawning sites and females fry-guarding territories. Most chases were directed towards the commonest fish, but predators were chased further and faster. Female behaviour changed over the guarding period. Females generally continued territorial defence after the brood had disappeared. Most broods contained fry of different sizes and species. Significant benefits were found for guarding females with clustered territories, but females did not appear to choose sites adjacent to conspecific parental females. 5. Territoriality in fish is taxonomically widespread and may serve several functions according to species, sex and developmental stage. It also varies according to genotype- and phenotype-limited strategies and short term costs and benefits. Territories may be simultaneously multifunctional.
- Full Text:
- Date Issued: 1996
- Authors: Robinson, Rosanna Lesley
- Date: 1996
- Subjects: Cichlids -- Nyasa, Lake Fishes -- Malawi Fishes -- Nyasa, Lake
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5264 , http://hdl.handle.net/10962/d1005108
- Description: Behaviour and space utilisation of rock-dwelling cichlids were observed at Thumbi East Island, Lake Malawi. 1. Males of five species of the mbuna complex held long-term territories. Pseudotropheus elongatus "aggressive" vigorously defended a feeding area and sometimes a spawning site interspecifically, but did not feed in the peripheral part of their territory. Spawning sites of Pseudotropheus zebra, Pseudotropheus tropheops "orange chest", Labeotropheus fuelleborni, and Petrotilapia nigra were interspecifically-defended, while larger mating territories were defended against conspecific neighbours. Feeding areas were shared with many fish and often extended beyond the defended area. There was considerable variation in behaviour and space use within and between species and between times of day. 2. Non-territorial P. zebra used larger ranges than territorial conspecifics, and fed more on plankton, but individuals had preferred benthic feeding areas, often in conspecific territories. These 'floaters' were often aggressive. Both size and relative brightness independently predicted the outcome of aggressive interactions between floaters, and a site-specific dominance hierarchy was suggested, with some individuals appearing to be semi-territorial. 3. Males and females of 21 and 13 species respectively were found to establish temporary breeding territories. Overall breeding seasonality was bimodal, but reproductive timing and territory characteristics differed among species. Temporary territories had a considerable impact on the behaviour and habitat use of all resident mbuna species, even causing abandonment of territories. 4. Non-breeding Protomelas taeniolatus had limited home ranges, and showed little aggression. During the highly-synchronised reproductive season, males defended spawning sites and females fry-guarding territories. Most chases were directed towards the commonest fish, but predators were chased further and faster. Female behaviour changed over the guarding period. Females generally continued territorial defence after the brood had disappeared. Most broods contained fry of different sizes and species. Significant benefits were found for guarding females with clustered territories, but females did not appear to choose sites adjacent to conspecific parental females. 5. Territoriality in fish is taxonomically widespread and may serve several functions according to species, sex and developmental stage. It also varies according to genotype- and phenotype-limited strategies and short term costs and benefits. Territories may be simultaneously multifunctional.
- Full Text:
- Date Issued: 1996
The inner image: an examination of the life of Helen Elizabeth Martins leading to her creation The Owl House and A Camel Yard as outsider art
- Authors: Ross, Susan Imrie
- Date: 1996
- Subjects: Sculptors -- South Africa -- Biography Martins, Helen Elizabeth, 1897-1976 Owl House (Nieu Bethesda, South Africa) Art brut Women artists -- South Africa Nieu bethesda (South africa) -- Description and travel Primitivism in art Creation (Literary, artistic, etc.) Artists -- Psychology Symbolism in art
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:2430 , http://hdl.handle.net/10962/d1002227
- Description: The Owl House is situated in the Karoo village of Nieu Bethesda, and the person responsible for its creation, Helen Elizabeth Martins (1897-1976), is South Africa's best known Outsider artist. A number of newspaper and magazine articles, television programmes, radio interviews, play, films, short stories, theses and art works have resulted directly from her work. Interest in The Owl House continues to grow, with visitors coming from all over South Africa, and various parts of the world,to visit it. The Owl House was Helen Martins' home for most of her 78 years. During the last 30 or so years of her life she devoted all her time and energy to transforming the interior of her house into a glistening fantasy world of colour and light, using crushed glass stuck to almost every surface, coloured glass pane inserts in the walls, mirrors of many sizes and shapes, and countless paraffin lamps and candles. She called her garden' A Camel Yard', and filled it with over 500 cement statues, structures and bas reliefs. All the labour involved, apart from crushing and sorting the coloured glass, was provided by at least four different men, who assisted her over the years, Johannes Hattingh, Jonas Adams, Piet van der Merwe and Koos Malgas, though Helen Martins was the inspiration and director behind it all. Through a study of Helen Martins' background and life, and their effects upon her psyche, a rigorous attempt has been made to reach some understanding of why she became a recluse, and what caused her to create this unique body of work comprising her entire domestic environment. She became increasingly asocial as her life progressed, and ultimately ended it by committing suicide in 1976. Through the universality of symbolism, the meanings of the subjects, themes and concerns which she chose to depict are studied. Then, together with some knowledge of her life and personal influences, an attempt has been made to deduce what it was that Helen Martins was trying to express and work through in her creations. This study also led to an awareness of the fact that, although each one is unique, there are many examples of Outsider Art throughout the world. Fundamentally, creators of Outsider Art remain asocial in relation to their cultural milieu and cultural context. Some other examples of Outsider Art, both in South Africa as well as in Europe and India, were visited, and are described and compared with The Owl House as well as with one another. The way in which society reacts or responds to Outsider Art and its creators is studied through the comprehensive records of one specific case which caused great controversy in Johannesburg during the 1970s. Ultimately, working alone or with assistance, it is the Outsider artist who is the driving force behind these unique works, and whose indefinable inner fire of passion alone makes it possible to bring them into being. It would seem that the fascination with Outsider Art is that through their work, creators allow others a glimpse into a different sense of reality which is both mysterious and inexplicable.
- Full Text:
- Date Issued: 1996
- Authors: Ross, Susan Imrie
- Date: 1996
- Subjects: Sculptors -- South Africa -- Biography Martins, Helen Elizabeth, 1897-1976 Owl House (Nieu Bethesda, South Africa) Art brut Women artists -- South Africa Nieu bethesda (South africa) -- Description and travel Primitivism in art Creation (Literary, artistic, etc.) Artists -- Psychology Symbolism in art
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:2430 , http://hdl.handle.net/10962/d1002227
- Description: The Owl House is situated in the Karoo village of Nieu Bethesda, and the person responsible for its creation, Helen Elizabeth Martins (1897-1976), is South Africa's best known Outsider artist. A number of newspaper and magazine articles, television programmes, radio interviews, play, films, short stories, theses and art works have resulted directly from her work. Interest in The Owl House continues to grow, with visitors coming from all over South Africa, and various parts of the world,to visit it. The Owl House was Helen Martins' home for most of her 78 years. During the last 30 or so years of her life she devoted all her time and energy to transforming the interior of her house into a glistening fantasy world of colour and light, using crushed glass stuck to almost every surface, coloured glass pane inserts in the walls, mirrors of many sizes and shapes, and countless paraffin lamps and candles. She called her garden' A Camel Yard', and filled it with over 500 cement statues, structures and bas reliefs. All the labour involved, apart from crushing and sorting the coloured glass, was provided by at least four different men, who assisted her over the years, Johannes Hattingh, Jonas Adams, Piet van der Merwe and Koos Malgas, though Helen Martins was the inspiration and director behind it all. Through a study of Helen Martins' background and life, and their effects upon her psyche, a rigorous attempt has been made to reach some understanding of why she became a recluse, and what caused her to create this unique body of work comprising her entire domestic environment. She became increasingly asocial as her life progressed, and ultimately ended it by committing suicide in 1976. Through the universality of symbolism, the meanings of the subjects, themes and concerns which she chose to depict are studied. Then, together with some knowledge of her life and personal influences, an attempt has been made to deduce what it was that Helen Martins was trying to express and work through in her creations. This study also led to an awareness of the fact that, although each one is unique, there are many examples of Outsider Art throughout the world. Fundamentally, creators of Outsider Art remain asocial in relation to their cultural milieu and cultural context. Some other examples of Outsider Art, both in South Africa as well as in Europe and India, were visited, and are described and compared with The Owl House as well as with one another. The way in which society reacts or responds to Outsider Art and its creators is studied through the comprehensive records of one specific case which caused great controversy in Johannesburg during the 1970s. Ultimately, working alone or with assistance, it is the Outsider artist who is the driving force behind these unique works, and whose indefinable inner fire of passion alone makes it possible to bring them into being. It would seem that the fascination with Outsider Art is that through their work, creators allow others a glimpse into a different sense of reality which is both mysterious and inexplicable.
- Full Text:
- Date Issued: 1996
The nutritional requirements of Haliotis midae and development of a practical diet for abalone aquaculture
- Authors: Britz, Peter Jacobus
- Date: 1996
- Subjects: Abalones -- Nutrition Abalone culture
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5307 , http://hdl.handle.net/10962/d1005152
- Description: The available literature on abalone nutrition was synthesised and the prospects for developing a complete pelleted dry feed for Haliotis midae evaluated. The similar body compositions, digestive structures, enzyme activity, acceptance of a wide variety of feed ingredients and comparable growth performance on formulated diets of various abalone species suggests that they have similar nutritional requirements. Abalone also appear to be similar to other farmed monogastric animals in that digestion is primarily extracelluar and they possess a large, muscular crop and stomach. Abalone energy metabolism is carbohydrate based. They are capable of digesting high levels of dietary protein but their ability to utilise fat is limited. Abalone have been shown to consume predictable amounts of dry feed which is efficiently converted into body weight. Efficiency indices of utilisation of formulated feeds, such as feed conversion ratio, protein efficiency ratio, net protein utilisation and apparent digestibility have been successfully applied to abalone. It was concluded that the prospects for developing complete diets for H. midae using a conventional animal feed science model were good. The ability of H. midae to utilise a range of proteins which had potential for inclusion in practical diets was investigated. Five protein rich ingredients, namely, casein, fishmeal, soya oil cake, Spirulina, and torula yeast, were fed to H. midae in semi-purified diets. Two algal diets, fresh Plocamium corallorhiza and dried Ecklonia maxima were fed as controls. Abalone fed on fishmeal and Spirulina based diets displayed significantly higher growth rates than diets containing soya oil cake, torula yeast, casein and E. maxima. Growth rates of abalone fed with P. corallorhiza were significantly lower than all other diets. All artificial diets yield lower feed conversion ratios (0.7-1.8) and higher protein efficiency ratios (3.3-6.5) ratios than the seaweed control diets (FCR = 2.8-3.4; PER = 2.2-3.0). The results indicated that fishmeal and Spirulina were the most suitable proteins for inclusion in practical diets for H. midae. The effect of protein level on growth rate and nutritional indices was evaluated by feeding starch bound, fishmeal based diets containing 27, 32, 37, 42 and 47% protein to juvenile H. midae. Weight gain was positively related to the level of dietary protein, increasing by 18% between 27% and 47% protein. Protein efficiency ratio declining from 3.2 to 2.3 with an increasing dietary protein content. Feed consumption rate was approximately 1% of body weight per day for all diets. Post-weaning abalone (ca. lOmm shell length, 0.2g) differed from larger juveniles (ca. 35mm, 8g) in their response to varying proportions of dietary protein and energy. The smaller animals appeared to have a lower protein requirement and poorer ability to utilise lipid than the larger juveniles. Proximate analyses revealed that the levels of protein, lipid and carbohydrate in abalone soft tissue increased with increasing dietary levels of these nutrients. Larger juveniles contained significantly higher levels of protein and carbohydrate, but lower levels of lipid, ash and moisture, than the smaller post-weaning abalone. The assimilation efficiency of [U-¹⁴C]-arginine by H. midae fed diets enriched with [U-¹⁴C]-arginine was only 0.45%. Furthennore, supplementation of diets with graded levels of crystalline arginine did not have any effect on growth rates. It was concluded that the prospects for defining the quantitative amino acid requirements of H. midae using crystalline amino acids are not promising. Rates of gastric evacuation and enzyme secretion were monitored in juvenile H. midae fed an extruded, fishmeal based dry feed. Gut fullness peaked 6h after feed was offered and the bulk of feed consumed was digested within 24 h. Enzyme secretion appeared to begin with the onset of feeding and continued for at least 6h after peak gut fullness was attained. Protease activity increased significantly following ingestion but amylase activity was maintained at a more or less constant level. A low level of lipase activity was observed suggesting that the ability of H. midae to digest fat is limited. The growth rate of H. midae fed an extruded, fishmeal based feed increased with increasing temperature between 12°C and 20°C. Between 20°C and 24°C a marked decline in growth rate accompanied by a deterioration in feed conversion and increased mortality was observed. Consumption of a dry pelleted feed was shown to be a function of body size and temperature. Based on these data a model which predicts a daily ration for H. midae was developed. The present study showed that H. midae efficiently utilises extruded dry feeds containing conventional feed ingredients. Although technical difficulties were encountered in measuring apparent digestibility, it was concluded that the prospects for developing practical diets according to established nutritional principles are promising.
- Full Text:
- Date Issued: 1996
- Authors: Britz, Peter Jacobus
- Date: 1996
- Subjects: Abalones -- Nutrition Abalone culture
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5307 , http://hdl.handle.net/10962/d1005152
- Description: The available literature on abalone nutrition was synthesised and the prospects for developing a complete pelleted dry feed for Haliotis midae evaluated. The similar body compositions, digestive structures, enzyme activity, acceptance of a wide variety of feed ingredients and comparable growth performance on formulated diets of various abalone species suggests that they have similar nutritional requirements. Abalone also appear to be similar to other farmed monogastric animals in that digestion is primarily extracelluar and they possess a large, muscular crop and stomach. Abalone energy metabolism is carbohydrate based. They are capable of digesting high levels of dietary protein but their ability to utilise fat is limited. Abalone have been shown to consume predictable amounts of dry feed which is efficiently converted into body weight. Efficiency indices of utilisation of formulated feeds, such as feed conversion ratio, protein efficiency ratio, net protein utilisation and apparent digestibility have been successfully applied to abalone. It was concluded that the prospects for developing complete diets for H. midae using a conventional animal feed science model were good. The ability of H. midae to utilise a range of proteins which had potential for inclusion in practical diets was investigated. Five protein rich ingredients, namely, casein, fishmeal, soya oil cake, Spirulina, and torula yeast, were fed to H. midae in semi-purified diets. Two algal diets, fresh Plocamium corallorhiza and dried Ecklonia maxima were fed as controls. Abalone fed on fishmeal and Spirulina based diets displayed significantly higher growth rates than diets containing soya oil cake, torula yeast, casein and E. maxima. Growth rates of abalone fed with P. corallorhiza were significantly lower than all other diets. All artificial diets yield lower feed conversion ratios (0.7-1.8) and higher protein efficiency ratios (3.3-6.5) ratios than the seaweed control diets (FCR = 2.8-3.4; PER = 2.2-3.0). The results indicated that fishmeal and Spirulina were the most suitable proteins for inclusion in practical diets for H. midae. The effect of protein level on growth rate and nutritional indices was evaluated by feeding starch bound, fishmeal based diets containing 27, 32, 37, 42 and 47% protein to juvenile H. midae. Weight gain was positively related to the level of dietary protein, increasing by 18% between 27% and 47% protein. Protein efficiency ratio declining from 3.2 to 2.3 with an increasing dietary protein content. Feed consumption rate was approximately 1% of body weight per day for all diets. Post-weaning abalone (ca. lOmm shell length, 0.2g) differed from larger juveniles (ca. 35mm, 8g) in their response to varying proportions of dietary protein and energy. The smaller animals appeared to have a lower protein requirement and poorer ability to utilise lipid than the larger juveniles. Proximate analyses revealed that the levels of protein, lipid and carbohydrate in abalone soft tissue increased with increasing dietary levels of these nutrients. Larger juveniles contained significantly higher levels of protein and carbohydrate, but lower levels of lipid, ash and moisture, than the smaller post-weaning abalone. The assimilation efficiency of [U-¹⁴C]-arginine by H. midae fed diets enriched with [U-¹⁴C]-arginine was only 0.45%. Furthennore, supplementation of diets with graded levels of crystalline arginine did not have any effect on growth rates. It was concluded that the prospects for defining the quantitative amino acid requirements of H. midae using crystalline amino acids are not promising. Rates of gastric evacuation and enzyme secretion were monitored in juvenile H. midae fed an extruded, fishmeal based dry feed. Gut fullness peaked 6h after feed was offered and the bulk of feed consumed was digested within 24 h. Enzyme secretion appeared to begin with the onset of feeding and continued for at least 6h after peak gut fullness was attained. Protease activity increased significantly following ingestion but amylase activity was maintained at a more or less constant level. A low level of lipase activity was observed suggesting that the ability of H. midae to digest fat is limited. The growth rate of H. midae fed an extruded, fishmeal based feed increased with increasing temperature between 12°C and 20°C. Between 20°C and 24°C a marked decline in growth rate accompanied by a deterioration in feed conversion and increased mortality was observed. Consumption of a dry pelleted feed was shown to be a function of body size and temperature. Based on these data a model which predicts a daily ration for H. midae was developed. The present study showed that H. midae efficiently utilises extruded dry feeds containing conventional feed ingredients. Although technical difficulties were encountered in measuring apparent digestibility, it was concluded that the prospects for developing practical diets according to established nutritional principles are promising.
- Full Text:
- Date Issued: 1996
The pyrrolizidine alkaloids of Senecio chrysocoma and Senecio paniculatus
- Authors: Logie, Catherine Gwynedd
- Date: 1996
- Subjects: Senecio -- Analysis Pyrrolizidines Botanical chemistry
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4339 , http://hdl.handle.net/10962/d1005000
- Description: In order to compare the pyrrolizidine alkaloid content of two closely related species, Senecio chrysocoma and S. paniculatus, nine populations of plants distributed between the two species, were examined. Three novel pyrrolizidine alkaloids, 7ß-angelyl-l-methylene-8∝-pyrrolizidine, 7ß-angelyl-l-methylene-8∝-pyrrolizidine and 7ß-angelyl-l-methyleneSO!-pyrrolizidine-4-oxide, as well as eight known pyrrolizidine alkaloids, 7-angelylhastanecine, 9-angelylhastanecine, 7-angelylplatynecine, 9-angelylplatynecine, 9-angelylplatynecine-4-oxide, sarracine, neosarracine and retrorsine, were isolated and identified by NMR and GC-MS techniques. Traces of five tiglyl isomers, 9-tiglylplatynecine, 9-tigl ylplatynecine-4-oxide, 7ß-tiglyl-l-methylene-8∝-pyrrolizidine, sarranicine and neosarranicine, were also isolated and tentatively identified; however, these compounds could have been artefacts of the extraction and analytical procedures. While both species of plant investigated, S. chrysocoma and S. paniculatus, were found to be morphologically different, their pyrrolizidine alkaloid content was, in fact, very similar. The presence of retrorsine in S. paniculatus plant extracts, but not in those from S. chrysocoma plants, was the only major chemical difference observed. It is perhaps significant that retrorsine was the only macrocyclic pyrrolizidine to be identified. A comprehensive, computerised database of physical data for pyrrolizidine alkaloids has been compiled, which has facilitated the identification of new pyrrolizidines and the examination of trends in proton and carbon-13 NMR data for pyrrolizidine alkaloids. A stereospecific synthesis of 7ß-angelyl-l-methylene-8∝-pyrrolizidine was undertaken toconfirm the absolute stereochemistry of the product isolated from S. chrysocoma and S. paniculatus. An inseparable 5:2 mixture of 7ß-angelyl-l-methylene-8∝-pyrrolizidine and 7ß-angelyl-l,2-didehydro-l-methyl-8∝-pyrrolizidine, together with a small amount of tiglyl isomer, was finally synthesised. The application of various chiral differentiating chromatographic and spectroscopic techniques confirmed that both the natural and synthetic products had the same stereochemistry, permitting the natural alkaloid to be identified as 7ß-angelyl-methylene-8∝-pyrrol izidine
- Full Text:
- Date Issued: 1996
- Authors: Logie, Catherine Gwynedd
- Date: 1996
- Subjects: Senecio -- Analysis Pyrrolizidines Botanical chemistry
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4339 , http://hdl.handle.net/10962/d1005000
- Description: In order to compare the pyrrolizidine alkaloid content of two closely related species, Senecio chrysocoma and S. paniculatus, nine populations of plants distributed between the two species, were examined. Three novel pyrrolizidine alkaloids, 7ß-angelyl-l-methylene-8∝-pyrrolizidine, 7ß-angelyl-l-methylene-8∝-pyrrolizidine and 7ß-angelyl-l-methyleneSO!-pyrrolizidine-4-oxide, as well as eight known pyrrolizidine alkaloids, 7-angelylhastanecine, 9-angelylhastanecine, 7-angelylplatynecine, 9-angelylplatynecine, 9-angelylplatynecine-4-oxide, sarracine, neosarracine and retrorsine, were isolated and identified by NMR and GC-MS techniques. Traces of five tiglyl isomers, 9-tiglylplatynecine, 9-tigl ylplatynecine-4-oxide, 7ß-tiglyl-l-methylene-8∝-pyrrolizidine, sarranicine and neosarranicine, were also isolated and tentatively identified; however, these compounds could have been artefacts of the extraction and analytical procedures. While both species of plant investigated, S. chrysocoma and S. paniculatus, were found to be morphologically different, their pyrrolizidine alkaloid content was, in fact, very similar. The presence of retrorsine in S. paniculatus plant extracts, but not in those from S. chrysocoma plants, was the only major chemical difference observed. It is perhaps significant that retrorsine was the only macrocyclic pyrrolizidine to be identified. A comprehensive, computerised database of physical data for pyrrolizidine alkaloids has been compiled, which has facilitated the identification of new pyrrolizidines and the examination of trends in proton and carbon-13 NMR data for pyrrolizidine alkaloids. A stereospecific synthesis of 7ß-angelyl-l-methylene-8∝-pyrrolizidine was undertaken toconfirm the absolute stereochemistry of the product isolated from S. chrysocoma and S. paniculatus. An inseparable 5:2 mixture of 7ß-angelyl-l-methylene-8∝-pyrrolizidine and 7ß-angelyl-l,2-didehydro-l-methyl-8∝-pyrrolizidine, together with a small amount of tiglyl isomer, was finally synthesised. The application of various chiral differentiating chromatographic and spectroscopic techniques confirmed that both the natural and synthetic products had the same stereochemistry, permitting the natural alkaloid to be identified as 7ß-angelyl-methylene-8∝-pyrrol izidine
- Full Text:
- Date Issued: 1996
The role of microzooplankton in carbon cycling in the Southern Ocean
- Authors: Froneman, Pierre William
- Date: 1996
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:21066 , http://hdl.handle.net/10962/6234
- Description: A 3-year study was carried out on the role of microzooplankton in carbon cycling in the south Atlantic and the Atlantic sector of the Southern Ocean. Microzooplankton grazing impact on phytoplankton was estimated during austral summer and winter employing the dilution technique. Carnivory by larger zooplankton on microzooplankton during summer was estimated using in vitro incubations. Microzooplankton assemblages were always dominated by protozoans comprising ciliates and dinoflagellates. In the ( 20 um chlorophyll fraction, microzooplankton grazing was sufficient to control the growth of the nano- and picophytoplankton suggesting that, where larger microphytoplankton cells dominate, micro zooplankton maintain the background concentrations of the nano- and picophytoplankton. During winter, when small nano- and picophytoplankton cells dominate total chlorophyll concentrations, the microzooplankton grazing impact on phytoplankton is dramatically increased. Microzooplankton removed on average 37% of the initial phytoplankton stock or 70% of the daily phytoplankton production. These results suggest that in winter, micro zooplankton are the main sink for phytoplankton production. Carnivory experiments conducted with selected meso- (copepods) and macro zooplankton (euphausiids and tunicates) showed that all species examined consumed micro zooplankton in the presence of substantial chlorophyll concentrations. Microzooplankton can, therefore, be regarded as trophic intermediates between bacterioplankton, small phytoplankton cells and larger zooplankton species in the Southern Ocean. The results of this investigation suggest a spatiotemporal shift in efficiency of the biological pump mediated by changes in the size composition of the phytoplankton assemblages. South of the Antarctic Polar Front (APF) large IV microphytoplankton cells dominate the summer chlorophyll biomass, suggesting that larger zooplankton grazers represent the main sink for phytoplankton production. Under these conditions, carbon flux to the interior of the ocean will be high due to diel vertical migrations by grazers and the production of large, fast sinking faecal pellets. The sedimentation of large phytoplankton cells also contributes to flux. In the permanently open waters south of the APF and throughout the Southern Ocean during winter, small phytoplankton cells dominate total chlorophyll, resulting in the microbial loop being the main sink for phytoplankton production. The close coupling between the micro zooplankton and the microbial loop dramatically reduces the transfer of organic carbon from the surface layers to depth. Carnivory by metazoans on microzooplankton may reduce the high grazing impact of micro zooplankton and, may also represent an important source of carbon flux originating from the microbial loop.
- Full Text:
- Date Issued: 1996
- Authors: Froneman, Pierre William
- Date: 1996
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:21066 , http://hdl.handle.net/10962/6234
- Description: A 3-year study was carried out on the role of microzooplankton in carbon cycling in the south Atlantic and the Atlantic sector of the Southern Ocean. Microzooplankton grazing impact on phytoplankton was estimated during austral summer and winter employing the dilution technique. Carnivory by larger zooplankton on microzooplankton during summer was estimated using in vitro incubations. Microzooplankton assemblages were always dominated by protozoans comprising ciliates and dinoflagellates. In the ( 20 um chlorophyll fraction, microzooplankton grazing was sufficient to control the growth of the nano- and picophytoplankton suggesting that, where larger microphytoplankton cells dominate, micro zooplankton maintain the background concentrations of the nano- and picophytoplankton. During winter, when small nano- and picophytoplankton cells dominate total chlorophyll concentrations, the microzooplankton grazing impact on phytoplankton is dramatically increased. Microzooplankton removed on average 37% of the initial phytoplankton stock or 70% of the daily phytoplankton production. These results suggest that in winter, micro zooplankton are the main sink for phytoplankton production. Carnivory experiments conducted with selected meso- (copepods) and macro zooplankton (euphausiids and tunicates) showed that all species examined consumed micro zooplankton in the presence of substantial chlorophyll concentrations. Microzooplankton can, therefore, be regarded as trophic intermediates between bacterioplankton, small phytoplankton cells and larger zooplankton species in the Southern Ocean. The results of this investigation suggest a spatiotemporal shift in efficiency of the biological pump mediated by changes in the size composition of the phytoplankton assemblages. South of the Antarctic Polar Front (APF) large IV microphytoplankton cells dominate the summer chlorophyll biomass, suggesting that larger zooplankton grazers represent the main sink for phytoplankton production. Under these conditions, carbon flux to the interior of the ocean will be high due to diel vertical migrations by grazers and the production of large, fast sinking faecal pellets. The sedimentation of large phytoplankton cells also contributes to flux. In the permanently open waters south of the APF and throughout the Southern Ocean during winter, small phytoplankton cells dominate total chlorophyll, resulting in the microbial loop being the main sink for phytoplankton production. The close coupling between the micro zooplankton and the microbial loop dramatically reduces the transfer of organic carbon from the surface layers to depth. Carnivory by metazoans on microzooplankton may reduce the high grazing impact of micro zooplankton and, may also represent an important source of carbon flux originating from the microbial loop.
- Full Text:
- Date Issued: 1996
The taxonomy and life-history of Argyrosomus japonicus and A. inodorus, two important sciaenids off the South African coast
- Authors: Griffiths, Marc H
- Date: 1996
- Subjects: Argyrosomus Sciaenidae -- South Africa Sciaenidae -- Namibia
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5323 , http://hdl.handle.net/10962/d1005169
- Description: A study of the biology, anatomy and taxonomy of the sciaenid fishes of the genus Argyrosomus from South Africa and Namibia revealed that three species were confused under the name "Argyrosomus Izololepidotus (Lacepède 1801)". Comparison of morphometric and meristic data, otoliths, swim-bladders, drumming muscles, and other morphological features of specimens from southern Africa, Madagascar, the Mediterranean, the eastern Atlantic Ocean, Japan and Australia, revealed that "A. hololepidotus" is a complex of four species: A. japonicus (Temminck & Schlegel 1843), which occurs off southern Africa, Japan and Australia; A. inodorus sp. nov., which is known from Namibia to the Kei River (32°40'S) on the east coast of South Africa; A. coronus sp. nov., which is known from central and northern Namibia and Angola, and A. hololepidotus, which appears to be endemic to Madagascar. Both A. japonicus and A. inodorus are important recreational and commercial linefish species in South Africa. Although A. inodorus occurs on the east and west coasts of South Africa, and A. japonicus is found between Cape Point and Mozambique, the former species is abundant only between Cape Point and the Kei River, and the latter species from Cape Agulhas to northern KwaZulu/Natal. The life-histories of Argyrosomus japonicus and A. inodorus, within these respective ranges, were elucidated using length-at-age, reproductive, catch and effort, size composition, otolith dimension/fish length and tagging data. Median sizes at maturity (L₅₀) for A. japonicus were 920 mm TL (5 years) for males and 1070 mm TL (6 years) for females. All males >1100 mm TL (7 years) and all females >1200 mm TL (8 years) were mature. Females grew faster than males, but in both sexes growth slowed dramatically after maturity. Maximum age recorded was 42 years, but fish older than 27 years were rare. Adult A. japonicus were predominantly found in the nearshore marine environment, but also occurred in estuaries and in the surf zone. Spawning takes place in the nearshore environment, from August to November in Natal, and from October to January in the Southern and South-Eastern Cape regions. A large proportion of the adult population migrate to Natal to spawn, although spawning may continue once they return to the Cape. Early juveniles of 20-30 mm TL recruit into turbid estuaries along the entire east coast, possibly aided by olfactory cues. They appear to remain in the upper reaches of the estuaries where they find suitable food and refuge from predators until they grow to about 150 mm TL. Juveniles larger than this size were found in the middle and lower reaches of estuaries and also in the surf zone. Juvenile A. japonicus (<1000 mm TL) generally did not migrate long distances, but remained as separate sub-stocks until they reached maturity. A. inodorus grows more slowly than A. japonicus, and attains a lower maximum age (25 years) and a smaller maximum size (34 vs 75 kg). There was no significant difference between the growth rates of male and female A. inodorus. Those in the South-Westem Cape initially grew faster than those on the east coast, but growth slowed sooner in the former region with the result that these fish attained a smaller maximum size. Although ripe A. inodorus were sampled throughout the year, there was a distinct spawning season from August to December, with a peak in spring (Sept-Nov). Spawning occurred throughout the study area for this species, in <50 m depth. Size at sexual maturity for A. inodorus was smaller in the South-Eastern Cape than in the Southern Cape. Median size at maturity for females was attained at 310 mm TL (1.3 years) in the former and at 375 mm TL (2.4 years) in the latter region, and the length at which all females were mature was 400 mm (3.5 years) and 550 mm (4.7 years) respectively. For males the estimates of Lso and total maturity were 200 mm (1 year) and 400 mm (2.8 years) for the SouthEastern Cape and 250 mm (1.5 years) and 450 mm (3.4 years) in the Southern Cape. East of Cape Agulhas, A. inodorus was found from just beyond the surf zone to depths of 120 m. Adults occurred predominantly on reef (>20 m) while juveniles were found mainly over soft substrata of sand/mud (5-120 m depth). Early juveniles do not enter estuaries, but apparently recruit to nursery areas immediately beyond the backline of breakers (5-10 m depth), and then move seawards with growth. No juveniles were obtained from the area west of Cape Agulhas as substrates <200 m depth were unsuitable for trawling. Due to lower water temperatures, the adults in this area were found from within the surf zone to depths of only 20 m. East and west of Cape Agulhas there was evidence of offshore dispersal in winter, in response to oceanographic changes. Based upon otolith morphology, juvenile and adult distribution patterns, sizes at sexual maturity and on tagging data, A. inodorus between Cape Point and the Kei River apparently exist as three separate stocks, one in the South-Eastern Cape, one in the Southern Cape and one in the South-Western Cape, with limited exchange. The life-histories of A. japonicus and A. inodorus are discussed in terms of their management. The large size at maturity of A. japonicus together with evidence for considerable human impact on the early juvenile, juvenile, and the adult phases of the life-cycle indicate that estuarine nursery habitats need to be conserved, that the minimum size limit should be increased, and that current bag limits for this species should be reviewed. Although the current minimum size limit provides protection for A. illodorus until maturity, evidence is presented which indicates that at least one and possibly all of the stocks of this species are currently over-exploited. Stock assessment of the South African A. japonicus and A. inodorus resources, and the implementation of effective management strategies, are therefore a matter of urgency.
- Full Text:
- Date Issued: 1996
- Authors: Griffiths, Marc H
- Date: 1996
- Subjects: Argyrosomus Sciaenidae -- South Africa Sciaenidae -- Namibia
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5323 , http://hdl.handle.net/10962/d1005169
- Description: A study of the biology, anatomy and taxonomy of the sciaenid fishes of the genus Argyrosomus from South Africa and Namibia revealed that three species were confused under the name "Argyrosomus Izololepidotus (Lacepède 1801)". Comparison of morphometric and meristic data, otoliths, swim-bladders, drumming muscles, and other morphological features of specimens from southern Africa, Madagascar, the Mediterranean, the eastern Atlantic Ocean, Japan and Australia, revealed that "A. hololepidotus" is a complex of four species: A. japonicus (Temminck & Schlegel 1843), which occurs off southern Africa, Japan and Australia; A. inodorus sp. nov., which is known from Namibia to the Kei River (32°40'S) on the east coast of South Africa; A. coronus sp. nov., which is known from central and northern Namibia and Angola, and A. hololepidotus, which appears to be endemic to Madagascar. Both A. japonicus and A. inodorus are important recreational and commercial linefish species in South Africa. Although A. inodorus occurs on the east and west coasts of South Africa, and A. japonicus is found between Cape Point and Mozambique, the former species is abundant only between Cape Point and the Kei River, and the latter species from Cape Agulhas to northern KwaZulu/Natal. The life-histories of Argyrosomus japonicus and A. inodorus, within these respective ranges, were elucidated using length-at-age, reproductive, catch and effort, size composition, otolith dimension/fish length and tagging data. Median sizes at maturity (L₅₀) for A. japonicus were 920 mm TL (5 years) for males and 1070 mm TL (6 years) for females. All males >1100 mm TL (7 years) and all females >1200 mm TL (8 years) were mature. Females grew faster than males, but in both sexes growth slowed dramatically after maturity. Maximum age recorded was 42 years, but fish older than 27 years were rare. Adult A. japonicus were predominantly found in the nearshore marine environment, but also occurred in estuaries and in the surf zone. Spawning takes place in the nearshore environment, from August to November in Natal, and from October to January in the Southern and South-Eastern Cape regions. A large proportion of the adult population migrate to Natal to spawn, although spawning may continue once they return to the Cape. Early juveniles of 20-30 mm TL recruit into turbid estuaries along the entire east coast, possibly aided by olfactory cues. They appear to remain in the upper reaches of the estuaries where they find suitable food and refuge from predators until they grow to about 150 mm TL. Juveniles larger than this size were found in the middle and lower reaches of estuaries and also in the surf zone. Juvenile A. japonicus (<1000 mm TL) generally did not migrate long distances, but remained as separate sub-stocks until they reached maturity. A. inodorus grows more slowly than A. japonicus, and attains a lower maximum age (25 years) and a smaller maximum size (34 vs 75 kg). There was no significant difference between the growth rates of male and female A. inodorus. Those in the South-Westem Cape initially grew faster than those on the east coast, but growth slowed sooner in the former region with the result that these fish attained a smaller maximum size. Although ripe A. inodorus were sampled throughout the year, there was a distinct spawning season from August to December, with a peak in spring (Sept-Nov). Spawning occurred throughout the study area for this species, in <50 m depth. Size at sexual maturity for A. inodorus was smaller in the South-Eastern Cape than in the Southern Cape. Median size at maturity for females was attained at 310 mm TL (1.3 years) in the former and at 375 mm TL (2.4 years) in the latter region, and the length at which all females were mature was 400 mm (3.5 years) and 550 mm (4.7 years) respectively. For males the estimates of Lso and total maturity were 200 mm (1 year) and 400 mm (2.8 years) for the SouthEastern Cape and 250 mm (1.5 years) and 450 mm (3.4 years) in the Southern Cape. East of Cape Agulhas, A. inodorus was found from just beyond the surf zone to depths of 120 m. Adults occurred predominantly on reef (>20 m) while juveniles were found mainly over soft substrata of sand/mud (5-120 m depth). Early juveniles do not enter estuaries, but apparently recruit to nursery areas immediately beyond the backline of breakers (5-10 m depth), and then move seawards with growth. No juveniles were obtained from the area west of Cape Agulhas as substrates <200 m depth were unsuitable for trawling. Due to lower water temperatures, the adults in this area were found from within the surf zone to depths of only 20 m. East and west of Cape Agulhas there was evidence of offshore dispersal in winter, in response to oceanographic changes. Based upon otolith morphology, juvenile and adult distribution patterns, sizes at sexual maturity and on tagging data, A. inodorus between Cape Point and the Kei River apparently exist as three separate stocks, one in the South-Eastern Cape, one in the Southern Cape and one in the South-Western Cape, with limited exchange. The life-histories of A. japonicus and A. inodorus are discussed in terms of their management. The large size at maturity of A. japonicus together with evidence for considerable human impact on the early juvenile, juvenile, and the adult phases of the life-cycle indicate that estuarine nursery habitats need to be conserved, that the minimum size limit should be increased, and that current bag limits for this species should be reviewed. Although the current minimum size limit provides protection for A. illodorus until maturity, evidence is presented which indicates that at least one and possibly all of the stocks of this species are currently over-exploited. Stock assessment of the South African A. japonicus and A. inodorus resources, and the implementation of effective management strategies, are therefore a matter of urgency.
- Full Text:
- Date Issued: 1996
Three dimensional kinetic analysis of asymmetrical lifting
- Authors: Li, Jian-Chuan
- Date: 1996
- Subjects: Lifting and carrying , Human engineering , Materials handling , Manual work
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5174 , http://hdl.handle.net/10962/d1018240
- Description: Manual lifting is dynamic in nature and involves asymmetrical loading of the human body. This study investigated kinematic and kinetic characteristics of asymmetrical lifting in three dimensions, and then constructed a 3-D biomechanical force model of the lower back which is capable of quantifying torsional stress on the human spine. Eleven healthy adult male manual workers were recruited as subjects and lifted a 1 Okg load placed at the sagittal plane (0°) and at 30°, 60° and 90° lateral planes to the right, from 150mm and 500mm initial lift heights, respectively, to an 800mm high bench in the sagittal plane. Subjects' spinal motions and the trajectorial movements of the load in three-dimensional space were monitored simultaneously by a Lumbar Motion Monitor and a V-scope Motion Analyzer. Generally, the spinal motion factors increased as a function of increasing task asymmetry and differed (p < 0.05) between the lower (150mm) and higher (500mm) levels in the sagittal plane. In all asymmetrical conditions the motion factors showed a dramatic increase at the 500mm level compared to the increase at the 150mm level. The rates of increase in the horizontal and frontal planes were greater than those in the sagittal plane. Task asymmetry had a significant effect on the spinal kinematic parameters in the frontal plane at the two lift heights, and only at the high level (500mm) in the horizontal plane, with exception of average acceleration . Initial lift height exerted a significant effect on peak velocity and acceleration in both frontal and horizontal planes and on range of motion in the horizontal plane. Kinetic characteristics of the object being lifted in three-dimensions increased with an increase in task asymmetry. The increase was more dramatic in the lateral direction in the horizontal plane. However, motion factors in the vertical direction dominated the full range of the lift, irrespective of task asymmetry and lift height. The kinetic measures differed (p < 0.05) between the lower ( 1 50mm) and the higher (500mm) levels in the vertical direction except for average force. Task asymmetry had a significant effect on dynamic measures in the anterior-posterior direction. Both task asymmetry and lift height had a significant effect on dynamic motion factors in the lateral direction. From insights gained in the empirical study a three-dimensional biomechanical force model of the lower back was constructed based on a mechanism of muscle force re-orientation in the lumbar region. Acknowledging that the lower back is designed to be able to rotate around its longitudinal axis, the proposed model accounts for compression and shear forces and a torsional moment. The model has similar predictability to Schultz and Andersson's (1981) model when the human trunk exerts only a flexion-extension moment in the sagittal plane, but additionally predicts dramatic increases in shear forces, oblique muscle forces and torsional moment under asymmetrical lifting conditions which the Schultz-Andersson model does not. The increase rates in these forces and moment are not linearly related over task asymmetric angle.
- Full Text:
- Date Issued: 1996
- Authors: Li, Jian-Chuan
- Date: 1996
- Subjects: Lifting and carrying , Human engineering , Materials handling , Manual work
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5174 , http://hdl.handle.net/10962/d1018240
- Description: Manual lifting is dynamic in nature and involves asymmetrical loading of the human body. This study investigated kinematic and kinetic characteristics of asymmetrical lifting in three dimensions, and then constructed a 3-D biomechanical force model of the lower back which is capable of quantifying torsional stress on the human spine. Eleven healthy adult male manual workers were recruited as subjects and lifted a 1 Okg load placed at the sagittal plane (0°) and at 30°, 60° and 90° lateral planes to the right, from 150mm and 500mm initial lift heights, respectively, to an 800mm high bench in the sagittal plane. Subjects' spinal motions and the trajectorial movements of the load in three-dimensional space were monitored simultaneously by a Lumbar Motion Monitor and a V-scope Motion Analyzer. Generally, the spinal motion factors increased as a function of increasing task asymmetry and differed (p < 0.05) between the lower (150mm) and higher (500mm) levels in the sagittal plane. In all asymmetrical conditions the motion factors showed a dramatic increase at the 500mm level compared to the increase at the 150mm level. The rates of increase in the horizontal and frontal planes were greater than those in the sagittal plane. Task asymmetry had a significant effect on the spinal kinematic parameters in the frontal plane at the two lift heights, and only at the high level (500mm) in the horizontal plane, with exception of average acceleration . Initial lift height exerted a significant effect on peak velocity and acceleration in both frontal and horizontal planes and on range of motion in the horizontal plane. Kinetic characteristics of the object being lifted in three-dimensions increased with an increase in task asymmetry. The increase was more dramatic in the lateral direction in the horizontal plane. However, motion factors in the vertical direction dominated the full range of the lift, irrespective of task asymmetry and lift height. The kinetic measures differed (p < 0.05) between the lower ( 1 50mm) and the higher (500mm) levels in the vertical direction except for average force. Task asymmetry had a significant effect on dynamic measures in the anterior-posterior direction. Both task asymmetry and lift height had a significant effect on dynamic motion factors in the lateral direction. From insights gained in the empirical study a three-dimensional biomechanical force model of the lower back was constructed based on a mechanism of muscle force re-orientation in the lumbar region. Acknowledging that the lower back is designed to be able to rotate around its longitudinal axis, the proposed model accounts for compression and shear forces and a torsional moment. The model has similar predictability to Schultz and Andersson's (1981) model when the human trunk exerts only a flexion-extension moment in the sagittal plane, but additionally predicts dramatic increases in shear forces, oblique muscle forces and torsional moment under asymmetrical lifting conditions which the Schultz-Andersson model does not. The increase rates in these forces and moment are not linearly related over task asymmetric angle.
- Full Text:
- Date Issued: 1996