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Geology of the Elisenheim area, Windhoek district, South West Africa, with special reference to the Matchless amphibolite belt

  • Authors: Finnemore, S H
  • Date: 1976
  • Subjects: Matchless Copper Mine (Namibia) , Geology, Structural -- Namibia , Amphibolite -- Namibia , Geology -- Namibia
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:5053 , http://hdl.handle.net/10962/d1011864
  • Description: The Elisenheim area is situated just north of Windhoek within the Windhoek Formation of the Swakop Subgroup and is underlain by monotonous succession of semi-pelitic schists with intercalations of amphibolite, talc schist, graphitic schist and marble. Petrographic studies on units of the Matchless amphibolite which outcrop in the south of the property, have resulted in the recognition of three different types of amphibolite, namely, epidote amphibolite, porphyroblastic amphibolite and chlorite-amphibole schist. Amphibole porphyroblasts generally display patchy and zonal intergrowths of hornblende and actinolite which are indicative of non-equilibration during prograde metamorphism. Talc schists have been mapped in the north of the property. All lithotypes have undergone three phases of deformation (Fl, FZ, F3) which terminated with the faulting which underlies the Klein Windhoek, Dobra, Tigenschlücht and Kuruma rivers. Medium grade regional metamorphism accompanied F 1, F Z and F 3 and outlasted the latter. Mineral assemblages throughout the area are those of the amphibolite facies and P, T conditions prevailing during metamorphism are estimated to have been at least 5 kb at ~ 550° C. Petrochemical evidence indicates that the Matchless amphibolites are igneous in origin and genetically related to the ultrabasic talc schists. They are similar in composition to oceanic tholeiites and are thought to have been extruded subaqueously.
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  • Date Issued: 1976

Grazing sequence pattern and species selection by cattle in the Dohne sourveld

  • Authors: Daines, Thomas
  • Date: 1976
  • Subjects: Grasses -- Research -- South Africa -- Cape of Good Hope , Grasses -- South Africa -- Cape of Good Hope -- Identification , Grazing -- South Africa
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:4257 , http://hdl.handle.net/10962/d1010955
  • Description: A detailed investigation into the harvesting of the standing grass crop within camps by cattle showed the following: 1. Cattle have a definite order of preference for the components of the Dohne Sourveld grass sward. The most palatable species in order of preference (based on Corrected Species Importance rating) are Themeda triandra, Tristachya hispida, Andropogon appendiculatus, Alloteropsis semialata and Heteropogon contortus. The least preferred species is Elionurus argenteus. 2. The key species, which is defined as the most abundant and productive palatable species, has been identified as Themeda triandra. 3. In harvesting the grass crop, cattle not only have a set preference for species, but also have a set grazing sequence pattern. This can be divided into three main phases. On entering the camp the animals first select the species of their choice, "creaming" these plants (grazed less than 50%) to obtain the most nutritious feed. In their daily search for food they spread their grazing over an increasingly wider area and over a wider range of species. When they can no longer obtain their daily requirements from this "creaming" operation of the more preferred species they return to the most preferred species , which are then heavily grazed (more than 50%) producing the common pattern of area grazing within a camp. These areas increase in size as the cattle graze down the species of their choice, moving to less preferred species as soon as they can no longer obtain their daily intake requirements from the more preferred species. Finally when they have no alternative they graze the least preferred species. 4. Increasing the stocking density does not alter the grazing sequence pattern or change the order of preference for the component species in the sward. It only increases the rate of utilization of the more preferred species and the various phases in the grazing sequence pattern are reached more rapidly. 5. At higher stocking densities the palatable species are more evenly utilized than at lower stocking densities. 6. Cattle graze a greater variety of species when the sward is young and actively growing. As the maturity of the sward increases the cattle concentrate on the more preferred species and are more selective in their grazing. However, their order of preference remains the same. Species that are highly preferred early in the season retain their ranking when the sward is mature. The only exception to this rule is Alloteropsis semialata. Early in the growing season this species is high on the preference list, but as it matures less is taken until when fully mature, it is rejected by cattle. 7. Elionurus argenteus is the least preferred of all the species in the Dohne Sourveld. Cattle will graze this plant as a last resort when grazing a camp early in the season, but reject the plant when it is fully mature. 8. To retain vigour and production of the Dohne Sourveld results of this investigation support the view that grazing management should be based on the principle of controlled selective grazing. Having shown that the more preferred species are over-utilized when attempting to utilize the least preferred species any grazing management that calls for total utilization of all standing vegetation should be rejected. 9. The results of this investigation supports a multicamp system for the Dohne Sourveld where high stocking densities are employed. This will result in the rapid and even utilization of the more preferred species. Management should be based on short period of stay and long period of absence. Cattle should be moved as soon as the key species have been well utilized, but not overgrazed. Cattle should only be returned to the camp when key species have made adequate regrowth following grazing. 10. A method, that is simple to use, is proposed for determining utilization of the veld and key species at different times of the year using the relationship between percentage of ungrazed plants and utilization of the sward and of Themeda triandra, the key grazing species in the sward. 11. Results show that when rested camps are grazed after May, the number of Themeda triandra inflorescences are drastically reduced. Veld that is specifically rested for the production of Themeda triandra seed should be rested from March of the year preceding expected seeding.
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  • Date Issued: 1976

Pre-release studies on Zophodia Tapiacola (Dyar) (Pyralidae : Lepidoptera) : a biological control agent against jointed cactus, Optuntia Aurantiaca Lindley

  • Authors: Hoffmann, John Hugh
  • Date: 1976
  • Subjects: Pyralidae , Lepidoptera , Cactus , Weeds -- Biological control , Opuntia
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:5857 , http://hdl.handle.net/10962/d1012320 , Pyralidae , Lepidoptera , Cactus , Weeds -- Biological control , Opuntia
  • Description: Jointed Cactus, Opuntia aurantiaca Lindley (see frontispiece), is the most important weed plant in South Africa, infesting approximately, 1,2 X 10¹° M² and costing approximately R240 000 per annum. Tordon herbicide effectively kills jointed cactus bushes to which it is applied. However, apart from being expensive and damaging to beneficial vegetation, spray programmes have not successfully controlled the weed because most small O. aurantiaca plants are impossible to detect in the field. Biological control may provide a solution to the problem. Two insects, the cochineal bug, Dactylopius austrinus De Lotto and the pyralid moth, Cactoblastis cactorum Berg., already exercise a degree of control over the weed. The introduction into South Africa of other natural enemies such as Zophodia tapiacola (Dyar) from Argentina, South America, may reduce the density of jointed cactus to below an acceptable economic threshold. Any insect considered for release should not colonise and destroy beneficial plants of which the culivated spineless cacti are the most vulnerable. Pre-release studies on Z. tapiacola have shown that it can only colonise a few species of low growing cacti and that it will not damage the large spineless cacti or other desirable plants. Further, the moths are relatively fecund and each larva destroys significant amounts of O. aurantiaca during its development. Consequently, Z. tapiacola is not only considered safe for release but it has the potential to act as a successful biological control agent of O. aurantiaca in South Africa.
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  • Date Issued: 1976

Reaction phenomena between Karroo Dolerite and cave sandstone xenoliths in the Bird's River complex

  • Authors: Kenyon, A K
  • Date: 1976
  • Subjects: Volcanic ash, tuff, etc , Igneous rocks -- Inclusions , Sandstone
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:4996 , http://hdl.handle.net/10962/d1005608
  • Description: Mapping of the north-eastern portion of the Bird1s River Complex revealed that two large xenoliths composed of pyroclastic rocks and sandstone of the Cave Sandstone Stage have reacted with the dolerite. All the reaction phenomena normally associated with Karroo Dolerite are encountered. These are: (a) Metasomatism during the stage of iron enrichment of the dolerite with the production of a pyroxene-plagioclase metasomatic granophyre (b) Metasomatism during the stage of alkali enrichment of the dolerite with the production of a potassium feldspar adinole C c) Assimilation 'vi th the production of contaminated doleri tes Cd) Fusion 'vi th the production of glassy rocks including buchi tes (e) The production of rheomorphic veins
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  • Date Issued: 1976

The influence of abiotic factors on the distribution of Biomphalaria pfeifferi (Krauss, 1848) (Planorbidae: Mollusca) and its lifecycle in South-Eastern Africa

  • Authors: Appleton, Christopher Charles
  • Date: 1976
  • Subjects: Schistosomiasis , Mollusks as carriers of disease
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:5835 , http://hdl.handle.net/10962/d1009495 , Schistosomiasis , Mollusks as carriers of disease
  • Description: Previous studies on the influence of abiotic factors on the distribution of bilharzia intermediate host snails of the family Planorbidae are reviewed. Much of this work is basically descriptive and relatively few attempts have been made to examine the effects of these factors on snails in their natural habitats - to identify the factors precisely and to measure their critical levels. An account is given of recent studies on Eiomphalaria pfeifferi (Krauss) in two climatically different regions of southeastern Africa, at 6S5m altitude on the eastern Transvaal escarpment and 19m on the coastal peneplain of northern Zululand. These have shown the species to undergo a similar annual life-cycle of three overlapping generations in both areas. Further, in these areas where the snail has a discontinuous distribution, two abiotic factors, stream geology and water temperature, were found to be important in limiting its distribution. The longitudinal distribution of B. pfeifferi and another host snail Bulinus (Physopsis) globosus (Morelat), extended upstream in a perennial watercourse, the Gladdespruit, on the escarpment only as far as permanently lentic habitats were available. These habitats, usually detached from the channel, characterized the stream's lowest physical zone with its substratum of exposed granite, as opposed to the sandy-bottomed lotic zones upstream. The limit of the snails' occurrence lay close to the junction of these two substratum types. Granite is resistant to erosion but contains soft inclusions which erode more quickly than the hard matrix causing uneven weathering. This results in the formation of depressions in the stream bed (i.e. pools, potholes and backwaters) which provide the permanently lentic conditions necessary for the snails' survival. Temperature recordings made on this plain, upstream of the snails' limit, suggest that the water temperature here exceeded the critical lower levels required for a positive intrinsic rate of natural increase sufficiently often to permit the species to survive here, though not optimally. Above this point however, current velocities are continually in excess of the maximum tolerated (0.3 m/sec.) so that in this situation at least, current velocity is a dominant factor. A contrasting situation exists on the coastal peneplain of northern Zululand where B. pfeifferi occurs in some lentic habitats and not in others. This discontinuous distribution is shown to be related to the prolonged duration of temperatures above the level for optimal increase. The apparently suitable habitats from which B. pfeifferi was absent were found to be both very shallow and to experience these prolonged high temperatures during spring and early summer. This corresponds to the maturation period of the B. pfeifferi 1st generation as defined by Appleton (1974) and causes reduced fecundity probably through impaired gonad development. The density of its filial (2nd) generation is correspondingly reduced. A statistically significant partial-correlation (at a 1% level) was found between the fecundity of the 1st generation and increasing periods of temperatures above the species' optimal limit in the habitats involved during its maturation period (spring). It is interesting to nate here that B. (Ph.) globosus, which is known to be better adapted to high temperatures than B. pfeifferi (Shiff & Husting, 1966) occurred in all the waterbodies concerned. Both these factors therefore play important roles in determining the country-wide distribution pattern of the host snails. This distribution is closely correlated with the availability of permanently lentic habitats. In river systems, which form the main environment for these snails, such stable habitats occur almost entirely in low-gradient reaches over hard bed-rock which is resistant to erosion. Current velocities above 0.3 m/sec. render steeper reaches and those over soft, non-resistant rock and sand (unstable substrata) unsuitable and therefore constitute a most important limiting factor. Temperature however becomes a dominant factor in permanently lentic waterbodies. Biomphalaria pfeifferi is adversely affected by high temperature regimes and where such regimes occur in waterbodies which are too shallow to permit temperature gradient to develop, the species cannot survive whereas B. (Ph.) globosus can do so. This intolerance of high temperature regimes on the part of B. pfeifferi accounts for the species' adoption of a discontinuous distribution over the coastal plain of south-eastern Africa. A comparable pattern has been reported for the species over this plain northwards to approximately 16°S latitude in Mozambique and is probably due to a similar high-temperature effect. Further northwards in equatorial latitudes B. pfeifferi is restricted to the more elevated and cooler areas above an altitude of 500 - 600 m, probably because the very high temperature regimes prevailing in the lowlands there exclude the species altogether.
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  • Date Issued: 1976

The Jesus People : attitude, personal-orientation and life-style changes as a function of non-conformist religious influence

  • Authors: Stones, Christopher R
  • Date: 1976
  • Subjects: Jesus People -- South Africa -- Johannesburg -- Hillbrow -- Attitudes , Youth -- South Africa -- Johannesburg -- Hillbrow -- Religious life , Religious communities -- South Africa
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:3242 , http://hdl.handle.net/10962/d1013312
  • Description: The Jesus People of Hillbrow, Johannesburg, assert that since joining the Jesus movement they have undergone radical changes; from a life of turmoil to a life of relative serenity. Such claims, if valid, have implications for the counter-culture, which is comprised largely of youth alienated from mainstream society and church. The present study then, was an investigation to determine whether the members of the Jesus movement have changed and if so, attempts were made to delineate such changes. The Jesus People investigated were members of the "Invisible Church", who had been residing communally for a period of not less than three months. A battery of questionnaires was administered on two occasions. The first occasion required the subjects to complete the questionnaires as they would have prior to their conversion, while the second administration required that the subjects complete the questionnaires according to their attitudes, values and opinions presently held. To counter any practice effects, the requirements for completion of the questionnaires were reversed for one half of the group randomly chosen. The order of presentation of the questionnaires was kept the same to counter any fatigue-effects. (The control group being matched with the experimental group should experience the same degree of fatigue.) The individuals selected for the control group were recruited from established-church youth clubs. These individuals were matched with the members of the Jesus movement for age, sex, home-language, general intelligence and occupation of father. The procedure of questionnaire administration for the control group was identical to that adopted for the experimental group. Both the experimental and the control group comprised 22 individuals. Incidental to the major design of the present study was the generation of a small (eight) group of Pentecostals, the results of which were analysed separately from those of the experimental and control groups. The finding that this group underwent the least change did not support the a priori expectation that Pentecostals should show changes which are intermediate to those of the experimental and control groups. It is argued however, that this Pentecostal group is not representative of Pentecostals per se. Bearing in mind, that the answers received depend, to a large extent, on the nature of the questions posed, the Jesus People, as a function of conversion (operationally defined as a "Jesus Experience"), underwent significant increases in their degree of perceived security but revealed significant decreases on attributes related to self-actualization. In addition, their predominant life-style orientation changed from personalistic to sociocentric, and there was an increased support for biblicistic fundamentalism. Associated with the above changes were decreases on the majority of the Wilson conservatism-scale dimensions, together with changes on a questionnaire explicitly developed for the present study. It is argued that the changes undergone by the members of the Jesus movement are in a positive direction, the "Invisible Church" serving as a 'half-way house'. Such changes are posited to be a function of an operationally defined "Jesus Experience"; a psycho-sociological experience rather than a theological, ecclesiastical experience.
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  • Date Issued: 1976

A 22 GHz water maser radiometer

  • Authors: Nunn, Brian J
  • Date: 1975
  • Subjects: Masers , Radiometers
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:5535 , http://hdl.handle.net/10962/d1012987
  • Description: This thesis describes the properties of interstellar water maser sources, and other sources near 22 GHz. Calculations based on manufacturer's specifications of the 22 GHz mixer, which was to be used in a water radiometer, and on the size antenna aperture of the proposed antenna aperture, show the viability of constructing such a radiometer for spectral line and continuum work. Various sections of the radiometer were constructed, including the Cassegrain feed system and its support, an intermediate frequency amplifier and buffer, a timing control unit, and a data processor. These units are part of the radiometer, which is almost ready for observations of sources.
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  • Date Issued: 1975

A computer analysis of some of the Harrison metrics

  • Authors: Sadler, Christopher John
  • Date: 1975
  • Subjects: Computer science -- Mathematics , Software measurement
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:5427 , http://hdl.handle.net/10962/d1013151
  • Description: In his paper B.K.Harrison concludes with the observation that his "solutions ... are presented as raw material for further research in General Relativity". In the same spirit, the present work started out as an attempt to process that raw material in a production-line powered by a computer. Harrison's solutions uould be fed in at one end, and the finished product, as yet undecided, would appear at the other. In the event, however, the project became more like an exercise in quality control, to continue the analogy. A search was made for algebraic criteria which would distinguish between those solutions which were acceptable for further analysis with particular regard to Gravitational radiation, and those which were not. Regrettably, no criteria could be found which characterised radiative solutions unequivocally, and, at the same time, lent themselves to a computer approach. The result is that the discussion of radiative solutions has had to be relegated to an appendix (Appendix 1), while the main body of the work is concerned with the determination of those quantities (the Newman-Penrose scalars) which would seem to be the foundation of any future computer-based analysis of gravitational radiation. Chapter 1 is an account of the underlying mathematical formulation, defining the terms, concepts and processes involved. In Chapter 2 the transformation of some of the ideas of Chapter 1 into computer software is presented. Chapter 3 is concerned with the specific metrics (the Harrison metrics) and the extent to which they have heen processed. The project has leaned heavily on papers by Harrison for the "raw material", by D' Inverno and Russell Clark, who pioneered the techniques and classified the Harrison metrics, and by Sachs for the treatment of gravitational radiation. However, the analysis of diagonal metrics, the special tetrad of Chapter 2 and the results in Appendix 2 are new.
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  • Date Issued: 1975

Remarks on formalized arithmetic and subsystems thereof

  • Authors: Brink, C
  • Date: 1975
  • Subjects: Gödel, Kurt , Logic, Symbolic and mathematical , Semantics (Philosophy) , Arithmetic -- Foundations , Number theory
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:5424 , http://hdl.handle.net/10962/d1009752 , Gödel, Kurt , Logic, Symbolic and mathematical , Semantics (Philosophy) , Arithmetic -- Foundations , Number theory
  • Description: In a famous paper of 1931, Gödel proved that any formalization of elementary Arithmetic is incomplete, in the sense that it contains statements which are neither provable nor disprovable. Some two years before this, Presburger proved that a mutilated system of Arithmetic, employing only addition but not multiplication, is complete. This essay is partly an exposition of a system such as Presburger's, and partly an attempt to gain insight into the source of the incompleteness of Arithmetic, by linking Presburger's result with Gödel's.
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  • Date Issued: 1975

The agricultural development of the 1820 settlement down to 1846

  • Authors: Webb, Arthur (Arthur C M)
  • Date: 1975
  • Subjects: Agriculture -- South Africa -- Eastern Cape -- History Agricultural colonies -- South Africa -- Eastern Cape British settlers of 1820 (South Africa) Cape of Good Hope (South Africa) -- History -- 1795-1872
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:1060 , http://hdl.handle.net/10962/d1007519
  • Description: Preface: The arrival of the 1820 Settlers in South Africa and their impact on the political and social life of the Cape Colony has been well covered by historical research. This work is an attempt to illuminate yet another area in which their impact was felt. The failure of the settlement scheme under which these people were introduced into the colony has tended to detract from the importance which agriculture played in the early years of their residence in South Africa. The failure of the first crops may well have ended the attempts by many to establish themselves on the land but for others it was the beginning of a process of adaptation to the agricultural conditions of a new country. In this they were remarkably successful and within a decade the English farming community of the eastern frontier was prospering. The theme of this work traces the progress of these farmers through the initial period of crop failures, which condemned the settlement in the eyes of many, and through the ensuing years and later misfortune, the Sixth Frontier war of 1834-35. Both these setbacks were very significant in moulding the development of agriculture as practised by these farmers. In the past, historians have tended to over-estimate the reverse suffered by these farmers during this frontier war. The seemingly paradoxical questions raised by the rapid recovery of this community after the war have been left largely unanswered. Some attempt is made in the pages which follow to shed new light on this issue. In the first three chapters of this work the letters written by Thomas Philipps to his family in Britain form the chief source of information. Much of this correspondence has already found wider publication in a volume edited by Arthur Keppel-Jones, but there are significant omissions, particularly with regard to Philipps' commentary on agricultural matters. Unfortunately, this series of letters ends in 1830, and the chief sources for the latter period of this work are the various entries made) on agricultural matters, in the Graham's Town Journal, together with the farm diary of James Collett, another frontier farmer. From these, and various other works, it has been possible to trace the major developments of this farming community.
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  • Date Issued: 1975

The development of a morphometric model for the estimation of mean annual sediment yield in ungauged catchments of South African river systems

  • Authors: Roberts, Peter J T
  • Date: 1975
  • Subjects: Sedimentation and deposition -- South Africa -- Mathematical models
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:4876 , http://hdl.handle.net/10962/d1013062
  • Description: Hydrologists are regularly faced with the unenviable task of having to predict the magnitude and frequency of phenomena such as floods and droughts; and rates of erosion. If long records are available for analysis the hydrologist is able to base his predictions on the premise that the pattern of variation that has been observed in the past will persist in the future. The confidence that can be placed in any estimate consequently depends to a large extent on the length of time over which the phenomena have been measured at the problem site. Unfortunately the availability of adequate records tends to be the exception rather than the rule and in areas where there is inadequate data, it is necessary to resort to the hazardous procedure of transferring information from the gauged to the ungauged catchments. The transfer of information is accomplished by using empirical methods based on regionalised parameters, but the uncertainties involved together with the economic implications that could arise from a poor estimate, prompt the hydrologist to use as many methods as possible. The need for empirical methods of estimating mean annual sediment yield in ungauged catchments was first appreciated by the author when he was involved in the estimation of design floods and sediment accumulation at sites for proposed reservoirs. Empirical methods of estimating sediment yield are frequently used in an engineering context, but little attention has been given to the catchment surface from which the sediment supply is derived. It is perhaps in this often neglected field of research that the physical geographer can make a contribution. The principal aim of the thesis, more fully discussed in Chapter I, was the development of a morphometric model which could be used to estimate mean annual sediment yield in ungauged catchments in South Africa. The data used in the development of the model were drawn from the catchments, described in Appendix A, that cover a wide range of climate and topography. A description of the approaches adopted by other researchers for the development of empirical models of estimating sediment yield which forms the background to the model has been included as Appendix B. The model was first developed in an elementary form as the focus of a research project which was documented in the form of three reports of research in progress (Roberts, 1973 a, b and c). Analysis of the pattern of variation of suspended sediment yield provided a better understanding of factors affecting sediment yield and supported the selection of the prediction variable (Horton's P ratio) which was used in the model. The concepts of network topology were utilised to gain insight into the environmental factors controlling both the P ratio and sediment yield. Reasons for the high correlation between the P ratio and sediment yield are suggested but it is felt that further research should be focused on this aspect. In order not to break the continuity and development of the steps taken in the derivation of the model details of the calculations are collected in Appendices C, D and E. While many of the figures and tables presented in the thesis appeared in technical notes prepared entirely by the author for the Department of Water Affairs, the views expressed in the thesis do not in any way, either explicitly or by implication, represent any official view or policy of the Department of Water Affairs.
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  • Date Issued: 1975

The genus Sisyphus Latr. (coleoptera : scarabaeidae) in Southern Africa

  • Authors: Paschalidis, Karen Margaret
  • Date: 1975
  • Subjects: Beetles -- Africa, Southern , Scarabaeidae -- Africa, Southern
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:5872 , http://hdl.handle.net/10962/d1013000
  • Description: 1. Twenty four species of the genus Sisyphus known in southern Africa are listed with their synonyms and their taxonomy is discussed. 2. A key to the adults of 23 of these species is given. 3. The known distribution of 23 species and seasonal occurrence of 19 species are illustrated and briefly discussed. 4. The general biology of the genus Sisyphus is discussed and the major behavioural and biological differences between the two subgenera Sisyphus and Neosisyphus are given. 5. The laboratory and field investigation into variations in behaviour and biology in eight species occurring in the Mkuzi Game Reserve, with regards to interspecific competition, is presented. 6. The known possible natural enemies of Sisyphus are mentioned and the extent of competition from other genera, based on field and laboratory observations, is outlined. 7. Summary tables of all data with a final tabulated evaluation of the suitability of species for introduction into Australia is given. 8. Nine species have been highly recommended for Australia. Six more species could be considered but most of these still need further investigation. The remaining nine species were found to be unsuitable for transfer to Australia.
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  • Date Issued: 1975

Twistors in curved space

  • Authors: Ward, R S (Richard Samuel), 1951-
  • Date: 1975
  • Subjects: Twistor theory , Space and time
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:5429 , http://hdl.handle.net/10962/d1013472
  • Description: From the Introduction, p. 1. During the past decade, the theory of twistors has been introduced and developed, primarily by Professor Roger Penrose, as part of a long-term program aimed at resolving certain difficulties in present-day physical theory. These difficulties include, firstly, the problem of combining quantum mechanics and general relativity, and, secondly, the question of whether the concept of a continuum is at all relevant to physics. Most models of space-time used in general relativity employ the idea of a manifold consisting of a continuum of points. This feature of the models has often been criticised, on the grounds that physical observations are essentially discrete in nature; for reasons that are mathematical, rather than physical, the gaps between these observations are filled in a continuous fashion (see, for example, Schrodinger (I), pp.26-31). Although analysis (in its generally accepted form) demands that quantities should take on a continuous range of values, physics, as such,does not make such a demand. The situation in quantum mechanics is not all that much better since, although some quantities such as angular momentum can only take on certain discrete values, one still has to deal with the complex continuum of probability amplitudes. From this point of view it would be desirable to have all physical laws expressed in terms of combinatorial mathematics, rather than in terms of (standard) analysis.
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  • Date Issued: 1975

A study of the properties and methods of analysis of high molecular weight N-nitrosamines

  • Authors: Kelly, Felix Thomas
  • Date: 1974 , 2013-10-29
  • Subjects: Nitrosoamines , Chemistry, Physical and theoretical
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:4421 , http://hdl.handle.net/10962/d1006878 , Nitrosoamines , Chemistry, Physical and theoretical
  • Description: Various high molecular weight dialkylnitrosamines were prepared including, for the first time, methyl-n-octadecylnitrosamine and di-n-dodecylnitrosamine. The infrared, ultraviolet and mass spectra of a selection of these compounds were recorded and studied. Gel permeation chromatography was used for the isolation of individual nitrosamines in standard nitrosamine mixtures, while ion-exchange chromatography effected complete clean-up of amine-contaminated nitrosamine solutions. Thin-layer and gas-liquid chromatographic methods were developed for the detection, separation and analysis of nanogram quantities of these lipophilic nitrosamines. In addition the above chromatographic systems were used for the analysis of distillates of spiked wheat flour samples. High recoveries of dicyclopentylnitrosamine, di-n-heptylnitrosamine and di-n-octylnitrosamine, from the spiked wheat flour samples, were achieved using a specially developed freeze-drying/vacuum distillation technique, the distillates obtained being relatively free from major contaminants. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
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  • Date Issued: 1974

Effects of precipitating electrons in the ionosphere

  • Authors: Haschick, Aubrey D
  • Date: 1974
  • Subjects: Electrons , Electron precipitation , Ionosphere , Ionospheric electron density
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:5526 , http://hdl.handle.net/10962/d1012220
  • Description: As early as 1896, around the time of the discovery of the electron by J.J. Thompson, Birkeland was led to propose that aurorae were caused by fast moving electrons or similarly charged particles emitted by the sun and 'sucked in towards' the auroral zones by the geomagnetic field. He later supported this idea by firing electrons at a dipole field surrounding a sphere covered with a fluorescent coating. Extensive ground based observations of auroral features eventually led, in 1950, to the initial direct evidence of the fact that auroral emissions are due to energetic charged particles, consisting partly of protons, entering the earth's atmosphere (Meinel, 1951). However, it was only in 1952 and 1953 that the first measurements of what was later interpreted as bremsstrahlung X- rays from precipitating electrons were made at auroral latitudes. (Meredith et aI, 1955) During the IGY, 1957 - 1958, a number of rockets were fired through and near, visible aurorae and large fluxes of low energy electrons were detected ... Intro., p. 1.
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  • Date Issued: 1974

Physico-chemical and substructural studies on Nudaurelia capensis β virus

  • Authors: Struthers, J Keith
  • Date: 1974
  • Subjects: Imbrasia cytherea , Insects -- Viruses , RNA viruses , DNA
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:4075 , http://hdl.handle.net/10962/d1007327 , Imbrasia cytherea , Insects -- Viruses , RNA viruses , DNA
  • Description: From Introduction: The pine emperor moth, Nudaurelia cytherea capensis Stoll is an insect which, during the larval stage, causes extensive defoliation of the pine tree, Pinus radiata in the Cape province. These insects are susceptible to a virus disease, which on occasions causes large scale mortality. Five nonoccluded viruses have been shown to infect the pine emperor moth, and of these, one found in the greatest concentration, Nudaurelia capensis β virus (NβV) has been characterised to the greatest extent. This virus has been shown to contain RNA, to be isometric with a diameter of 36 mm, and to have a molecular weight of 16 million. The virus occurs in all stages of the insect's development, and by fluorescent antibody staining has been shown to develop in the cytoplasm of the host's cells. There have in recent years been a number of reports describing nonoccluded RNA viruses which appear to be similar to NβV. These are the viruses isolated from the moths Gonometa podocarpi and Antheraea eucalypti, and the one from the citrus red mite, Panonychus citri. These viruses have not been as extensively characterised as NβV, so the extent of the similarity between them and NβV is not known. However it would appear as if their discovery collectively heralds the emergence of a distinct new grouping within the nonoccluded RNA viruses of insects. This work reports the isolation and further characterisation of N. capensis β virus, its protein and nucleic acid.
  • Full Text:
  • Date Issued: 1974

Studies on anaerobic R factor transfer in facultative and anaerobic enteric bacteria

  • Authors: Moodie, Hildegard Laura
  • Date: 1974
  • Subjects: Anaerobic bacteria , R factors
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:4252 , http://hdl.handle.net/10962/d1007684 , Anaerobic bacteria , R factors
  • Description: Introduction: R factor mediated transfer of antibiotic resistance between Enterobacteriaceae has been reported to occur in the mammalian gastrointestinal tract (Farrar et al, 1972; Guinée, 1970; Kasuya, 1964; Reed et al, 1969; Wiedemann et al, 1970). In vivo conjugal transfer of genetic material has also been demonstrated with F¹, F⁺ and Hfr Escherichia coli strains (Jones & Curtiss, 1970). The environment in the lower gastrointestinal tract, where bacteria are abundant, is mainly anaerobic. This is demonstrated by the dominance of obligately anaerobic bacteria such as Bacteroides species (Finegold, 1969; Moore et al, 1969) and direct studies of intestinal gas composition (Askevold, 1956). However, most laboratory investigations of the incidence of R factors and their transfer frequencies have been performed under aerobic conditions using faecal facultative strains. The only investigation of resistance transfer under anaerobic conditions in vitro is that of Mitsuhashi (1965), who reported complete inhibition of transfer of an R factor from a Shigella flexneri donor to an Escherichia coli recipient. In addition, Fisher (1957) reported restriction of chromosomal transfer by an E. coli Hfr strain under anaerobic conditions in various media. On the basis of these results, it could be questioned whether in vivo R factor transfer is in fact possible (Chabbert et al, 1969). The contradictory situation prompted a reexamination of conjugation in facultative strains under anaerobic conditions. Both Fisher (1957) and Mitsuhashi (1965) obtained anaerobic conditions by evacuation. In this investigation, both mating and selection of recombinants were performed under stringent anaerobic conditions using methods developed for the isolation of obligate anaerobes (Hungate, 1969) to obtain a degree of anaerobiosis similar to that found in vivo.
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  • Date Issued: 1974

The Aapiesboomen magnesite deposit, Burgersfort, Transvaal

  • Authors: Taylor, N C
  • Date: 1974
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:21130 , http://hdl.handle.net/10962/6505
  • Description: The published literature on magnesite is extensively reviewed as regards the properties, uses, production, occurrence and genesis of the mineral. Despite opposition from the producers of sea water magnesia in recent years, magnesite still finds a ready market for the manufacture of refractory materials, particularly in the steel industry. Less important uses include the manufacture of magnesium metal, carbonic acid gas, Sorel cement, paper, pharmaceuticals and fertilizers. Large bodies of cryptocrystalline magnesite occur in Greece, Yugoslavia, Turkey and India, while the deposits in Austria, Czechoslovakia, Russia and China produce most of the world supply of crystalline material. Four types of magnesite bodies may be distinguished: quartz-magnesite deposits, talc-magnesite occurrences, magnesite associated with sedimentary rocks and sagvandite, a magnesite-bronzite rock. Most South African deposits, including the Aapiesboomen body, belong to the first type. Experimental, field and textural evidence indicates that the quartz-magnesite deposits may form from serpentine under a wide range of hydrothermal and supergene conditions below about 400°C and between very low and very high concentrations of co2 in the fluid phase. Above 400°C talc is produced at the expense of quartz. Sedimentary magnesite has been observed t o form in present day saline lakes, but the large size of the older crystalline deposits associated with limestones and dolomites has been used as an argument against the use of the same principle to explain the genesis of the latter bodies : much controversy still surrounds the sedimentary-hydrothermal debate concerning their origin. It seems probable thet sagvandites are produced by a process of CO2- metasomatism.
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  • Date Issued: 1974

A contribution to the biology of Tilapia mossambica Peters in Lake Sibaya, South Africa

  • Authors: Bruton, Michael N
  • Date: 1973
  • Subjects: Cichlids , Tilapia , Mozambique tilapia
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:5839 , http://hdl.handle.net/10962/d1009950 , Cichlids , Tilapia , Mozambique tilapia
  • Description: An account is given of some aspects of the biology of Tilapia mossambica Peters in Lake Sibaya, South Africa. Previous work on Tilapia in Lake Sibaya is reviewed. Apart from brief gillnet surveys, which recorded the species' presence, no research on T. mossambica had been performed at Lake Sibaya before the two-year study of Minshull who collected data on food preferences, depth distribution of juveniles and breeding biology of adults. The main physiographical features of the lake are outlined. Lake Sibaya is a warm shallow coastal lake with extensive shallow terraces in the littoral which shelve abruptly into underwater valleys. The substrate is predominantly sandy. Aquatic macrophytes are generally restricted to water 1-7 m deep. Adult fishes (over 8 cm SL) are usually absent from water deeper than 12 m and shallower than 0.5 m, whereas juveniles may occur at all depths, and fry only in very shallow water. T. mossambica inhabits the littoral in the warm and transition periods (August to April) but moves into deep water in the cool season (May to July). Exposed and sheltered shallow areas are utilised for different purposes by adult fishes, the former for nesting, and the latter for feeding and mouth-brooding. Habitat selection by males was governed by nest site selection. Habitat Nests were most common in sheltered, sparsely vegetated littoral and sublittoral areas, but also present in well-vegetated sheltered areas. Breeding females preferred sheltered littoral areas but ventured onto the terrace to release the young. Juvenile and fry T. mossambica inhabited shallow exposed shores with a temperature gradient which reversed diurnally. The breeding, shoaling and feeding behaviour of T. mossambica is described, and integrated with data on T. mossambica from other systems. The breeding season spans seven months. Shoaling takes place in shallow water probably as a means of protection. T. mossambica is an omnivorous feeder relying largely on diatoms. The main predator is probably the barbel Clarias gariepinus, but avian predators may be more important. A method whereby the time of formation of rings on the scales of T. mossambica is described. The fishes were found to reach maturity after one year at a length of about 8 cm in females, and after two years at 10 cm in males. The breeding population had a standard length mode of 14 cm (females) and 17 cm (males). The maximum final size was about 24 cm SL. An estimate of the standing crop for fishes in the littoral and subiittoral areas of the eastern and southern shores of the south basin is given. The data were derived from a mark and recapture The biology of T. mossambica in Lake Sibaya as revealed by the present study is discussed with reference to data on the same and similar species in other systems. The utilis ation of the available resources in the lake by T. mossambica is commented upon, and reference is made to the significance of stunting, and the import ance of the retention of generalised characters for the successful habitation of the cyclically-renewed habitat of the littoral. Precocious breeding in T. mossambica is regarded as a functional adaptation which increases the proportion of fishes small enough to utilise the rich food resources in shallow water.
  • Full Text:
  • Date Issued: 1973

Atmospheric ionization by precipitated electrons

  • Authors: Wulff, Annemarie
  • Date: 1973 , 2013-10-31
  • Subjects: Ionization , Electrons
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:5503 , http://hdl.handle.net/10962/d1007229 , Ionization , Electrons
  • Description: From Introduction: Precipitation of energetic particl es into the upper atmosphere is known to cause aurora at high latitudes. Sanae is situated in the vicinity of the South Atlantic Geomagnetic Anomaly (Gledhill and Van Rooyen (1963)) where the magnetic field intensity is very low and it is felt that this phenomenon may enhance the loss of particles from the trapping zone into the upper atmosphere. Previous work at Rhodes has shown that it is extremely likely that particle precipitation could be the cause of some ionospheric effects at Sanae. Gledhill and Torr (1966) found that a "disturbed" ionosphere at Sanae was linked with "high" fluxes of precipitated electrons in the area conjugate to Sanae. Later papers by Gledhill, Torr and Torr (1967), and Torr and Torr (1967a, 1968a) established that electrons are precipitated over a large part of the earth's surface and this phenomenon is probably responsible for an average of about 30% of F-layer disturbances. The frequency of precipitation and corresponding disturbances is most pronounced in the South Atlantic Geomagnetic Anomaly . , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
  • Full Text:
  • Date Issued: 1973
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