Theoretical aspects of the generation of radio noise by the planet Jupiter
- Authors: Deift, Percy A
- Date: 1972
- Subjects: Jupiter (Planet) , Radio astronomy , Radio noise
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5516 , http://hdl.handle.net/10962/d1011051 , Jupiter (Planet) , Radio astronomy , Radio noise
- Description: Decameter radiation was first observed from Jupiter by Burke and Franklin (JGR 60, 213, 1955). In 1964 Bigg (Nature, 203, 1008, (1964)) found that 1o exerted a profound effect on the radiation. The majority of the early theories to explain the origin of the decameter emissions, attributed the radiation to an emission process occurring at or near the electron gyrofrequency or the plasma frequency. Intro., p. 1. The majority of the early theories to explain the origin of the decameter emissions, attributed the radiation to an emission process occurring at or near the electron gyrofrequency or the plasma frequency (for a review see eg. Warwick, Space Sci. Rev. &" 841 (1967)). More recent work centred around the question of how 10 modulates the emission (see the article of Carr and Gulkis (Annual Review of Astronomy and Astrophysics Vol 8 (1970)) for a detailed review).
- Full Text:
- Date Issued: 1972
- Authors: Deift, Percy A
- Date: 1972
- Subjects: Jupiter (Planet) , Radio astronomy , Radio noise
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5516 , http://hdl.handle.net/10962/d1011051 , Jupiter (Planet) , Radio astronomy , Radio noise
- Description: Decameter radiation was first observed from Jupiter by Burke and Franklin (JGR 60, 213, 1955). In 1964 Bigg (Nature, 203, 1008, (1964)) found that 1o exerted a profound effect on the radiation. The majority of the early theories to explain the origin of the decameter emissions, attributed the radiation to an emission process occurring at or near the electron gyrofrequency or the plasma frequency. Intro., p. 1. The majority of the early theories to explain the origin of the decameter emissions, attributed the radiation to an emission process occurring at or near the electron gyrofrequency or the plasma frequency (for a review see eg. Warwick, Space Sci. Rev. &" 841 (1967)). More recent work centred around the question of how 10 modulates the emission (see the article of Carr and Gulkis (Annual Review of Astronomy and Astrophysics Vol 8 (1970)) for a detailed review).
- Full Text:
- Date Issued: 1972
A comparison of attitudes toward intensive competition among high school pupils
- Authors: Potgieter, Justus R
- Date: 1971
- Subjects: Competition (Psychology) in adolescence Competition (Psychology) Interpersonal relations Motivation (Psychology)
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:1930 , http://hdl.handle.net/10962/d1007604
- Description: From Preface: As a teacher with experience in competitive sport, the author became interested in the topic of athletic competition when joining the staff of an all-boys' school. The competitive aspect of sport at such a school can make quite an impression on an inexperienced teacher. The question then arose; Is this competitive atmosphere universal? Is this type of competition acceptable and desirable in our schools? Being a teacher of Physical Education as well as other subjects and also being actively involved in the coaching of senior sports teams the author regarded himself suitably qualified to investigate the matter of athletic competition in our schools.
- Full Text:
- Date Issued: 1971
- Authors: Potgieter, Justus R
- Date: 1971
- Subjects: Competition (Psychology) in adolescence Competition (Psychology) Interpersonal relations Motivation (Psychology)
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:1930 , http://hdl.handle.net/10962/d1007604
- Description: From Preface: As a teacher with experience in competitive sport, the author became interested in the topic of athletic competition when joining the staff of an all-boys' school. The competitive aspect of sport at such a school can make quite an impression on an inexperienced teacher. The question then arose; Is this competitive atmosphere universal? Is this type of competition acceptable and desirable in our schools? Being a teacher of Physical Education as well as other subjects and also being actively involved in the coaching of senior sports teams the author regarded himself suitably qualified to investigate the matter of athletic competition in our schools.
- Full Text:
- Date Issued: 1971
An investigation into religious instruction in state high schools in the Cape Province
- Authors: Penny, Alan Joseph
- Date: 1971
- Subjects: Religious education -- South Africa -- Cape of Good Hope Religious education of teenagers
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:1933 , http://hdl.handle.net/10962/d1007641
- Description: From Preface: The question of religious instruction in Cape Schools first aroused my interest when I was subjected to anything but religious tnstruction during my own high school years. My desire to enquire into the whole position of religious instruction in the high school curriculum grew out of an essay on the role of religion in the education of the child which I wrote whilst reading for the B.Ed. degree. As background, I read Harold Loukes' classic Teenage Religion, and from then onwards, I felt that it was necessary to undertake an investigation of this kind in the Cape Province. My aim was not only prompted out of a desire to expose what I already knew to be an educationally and religiously unsound and unhealthy state of affairs, but more deeply because I, although an ignorant amateur in theology, am aware that too often the traditional religious foundations, poorly built by unintelligent teaching, are shaken, if not destroyed, by scientific discovery and material advancement.
- Full Text:
- Date Issued: 1971
- Authors: Penny, Alan Joseph
- Date: 1971
- Subjects: Religious education -- South Africa -- Cape of Good Hope Religious education of teenagers
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:1933 , http://hdl.handle.net/10962/d1007641
- Description: From Preface: The question of religious instruction in Cape Schools first aroused my interest when I was subjected to anything but religious tnstruction during my own high school years. My desire to enquire into the whole position of religious instruction in the high school curriculum grew out of an essay on the role of religion in the education of the child which I wrote whilst reading for the B.Ed. degree. As background, I read Harold Loukes' classic Teenage Religion, and from then onwards, I felt that it was necessary to undertake an investigation of this kind in the Cape Province. My aim was not only prompted out of a desire to expose what I already knew to be an educationally and religiously unsound and unhealthy state of affairs, but more deeply because I, although an ignorant amateur in theology, am aware that too often the traditional religious foundations, poorly built by unintelligent teaching, are shaken, if not destroyed, by scientific discovery and material advancement.
- Full Text:
- Date Issued: 1971
An investigation into the sensory mechanisms underlying the two point threshold, with particular reference to the practice effect
- Authors: Gradwell, Peter Bertram
- Date: 1971
- Subjects: Sensorimotor integration , Perceptual-motor learning
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:3209 , http://hdl.handle.net/10962/d1012085 , Sensorimotor integration , Perceptual-motor learning
- Description: The two point threshold was studied extensively by the psychophysical experimenters of the last century. More recent formulations in signal detection theory have suggested that the statements of these workers about absolute thresholds should be viewed with caution. This study investigates the two point threshold in the light of these formulations, and has two main aims :- (1) To state and deal with the problem of relating a limitation in perceptual ability, such as that which is represented by the two point threshold, to the receptor organisation of the body. (2) To demonstrate a practice effect on the two point threshold, and to consider this in the light of (1) above. To fulfil these two aims, a model of the neural mechanisms underlying the discrimination of two points applied to the skin is proposed, and this is able to accommodate what is known of the two point threshold. Although the model is simple it explicitly accounts for size transfer and the practice effect, and provides some clues as to the type of neural mechanism capable of producing them. The practice effect is demonstrated experimentally, and the results are then referred to the model proposed. The physiology of an organism sets the limits for its behaviour. 'The first aim is thus an important one, in that it considers a specific case of this general problem. And secondly, the practice effect on the two point threshold is typical of a number of fairly simple "learning" phenomena, which are part of the psychologists' study of learning.
- Full Text:
- Date Issued: 1971
- Authors: Gradwell, Peter Bertram
- Date: 1971
- Subjects: Sensorimotor integration , Perceptual-motor learning
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:3209 , http://hdl.handle.net/10962/d1012085 , Sensorimotor integration , Perceptual-motor learning
- Description: The two point threshold was studied extensively by the psychophysical experimenters of the last century. More recent formulations in signal detection theory have suggested that the statements of these workers about absolute thresholds should be viewed with caution. This study investigates the two point threshold in the light of these formulations, and has two main aims :- (1) To state and deal with the problem of relating a limitation in perceptual ability, such as that which is represented by the two point threshold, to the receptor organisation of the body. (2) To demonstrate a practice effect on the two point threshold, and to consider this in the light of (1) above. To fulfil these two aims, a model of the neural mechanisms underlying the discrimination of two points applied to the skin is proposed, and this is able to accommodate what is known of the two point threshold. Although the model is simple it explicitly accounts for size transfer and the practice effect, and provides some clues as to the type of neural mechanism capable of producing them. The practice effect is demonstrated experimentally, and the results are then referred to the model proposed. The physiology of an organism sets the limits for its behaviour. 'The first aim is thus an important one, in that it considers a specific case of this general problem. And secondly, the practice effect on the two point threshold is typical of a number of fairly simple "learning" phenomena, which are part of the psychologists' study of learning.
- Full Text:
- Date Issued: 1971
Ecological studies on the non-parasitic larval stages of some tick species in the Eastern Cape Province of South Africa (Acarina : ixodidae)
- Londt, Jason G. H. (Jason Gilbert Hayden), 1943-
- Authors: Londt, Jason G. H. (Jason Gilbert Hayden), 1943-
- Date: 1971
- Subjects: Ticks -- Ecology -- South Africa -- Eastern Cape , Ixodidae -- Ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5862 , http://hdl.handle.net/10962/d1012777 , Ticks -- Ecology -- South Africa -- Eastern Cape , Ixodidae -- Ecology -- South Africa -- Eastern Cape
- Description: "Ticks have already been studied in our country and abroad. Progress in the field of taxonomy has probably been the most rapid and has culminated in a large number of papers and excellent monographs, but much more remains to be done. To produce an overall picture of the factors influencing the behaviour of the tick under natural conditions, studies have to be conducted on tick ecology and experimental physiology. We still have a lack of knowledge of host specificity, the selection of feeding sites on hosts and the nature of resistance to attacks by ticks. Because of the varied habits of different species of ticks, the first essential prerequisite is an adequate knowledge of their biology." (Jansen 1969). The above words sum up the position of research on ticks in southern Africa at the present time.
- Full Text:
- Date Issued: 1971
- Authors: Londt, Jason G. H. (Jason Gilbert Hayden), 1943-
- Date: 1971
- Subjects: Ticks -- Ecology -- South Africa -- Eastern Cape , Ixodidae -- Ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5862 , http://hdl.handle.net/10962/d1012777 , Ticks -- Ecology -- South Africa -- Eastern Cape , Ixodidae -- Ecology -- South Africa -- Eastern Cape
- Description: "Ticks have already been studied in our country and abroad. Progress in the field of taxonomy has probably been the most rapid and has culminated in a large number of papers and excellent monographs, but much more remains to be done. To produce an overall picture of the factors influencing the behaviour of the tick under natural conditions, studies have to be conducted on tick ecology and experimental physiology. We still have a lack of knowledge of host specificity, the selection of feeding sites on hosts and the nature of resistance to attacks by ticks. Because of the varied habits of different species of ticks, the first essential prerequisite is an adequate knowledge of their biology." (Jansen 1969). The above words sum up the position of research on ticks in southern Africa at the present time.
- Full Text:
- Date Issued: 1971
Effects of vigilance decrement on the recognition of embedded figures
- Authors: Daniel, Robert David
- Date: 1971
- Subjects: Perception -- Testing , Cognitive psychology
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:3202 , http://hdl.handle.net/10962/d1010961
- Description: Field independence was described by Witkin et al (1962) as the ability to separate an item perceived from its context. Here most experiments have used visually presented material where the subject was shown a simple geometrical figure and then a complex one containing the simple figure as part of it: the subject's task was to find and point out where the simple figure was hidden. Recent work has suggested that the skills involved in Witkin's tests might be associated with particular cultural backgrounds. This extension of Witkin's theory of field independence by Wober linked visual phenomena with those of a social and maturational nature: the ability to separate visual items from their context was shown to be aligned with the development of a sense of personal identity ; the person was considered to be an item set in a context or social field, be it family or society around him: an individual, depending on the way he was socialized as a child, may perceive the world analytically, if he did he was labelled field independent, if not he was field dependent. Intro. p.1.
- Full Text:
- Date Issued: 1971
- Authors: Daniel, Robert David
- Date: 1971
- Subjects: Perception -- Testing , Cognitive psychology
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:3202 , http://hdl.handle.net/10962/d1010961
- Description: Field independence was described by Witkin et al (1962) as the ability to separate an item perceived from its context. Here most experiments have used visually presented material where the subject was shown a simple geometrical figure and then a complex one containing the simple figure as part of it: the subject's task was to find and point out where the simple figure was hidden. Recent work has suggested that the skills involved in Witkin's tests might be associated with particular cultural backgrounds. This extension of Witkin's theory of field independence by Wober linked visual phenomena with those of a social and maturational nature: the ability to separate visual items from their context was shown to be aligned with the development of a sense of personal identity ; the person was considered to be an item set in a context or social field, be it family or society around him: an individual, depending on the way he was socialized as a child, may perceive the world analytically, if he did he was labelled field independent, if not he was field dependent. Intro. p.1.
- Full Text:
- Date Issued: 1971
Proton conduction in organic solids
- Authors: Chan-Henry, Robert Yatshein
- Date: 1971
- Subjects: Electrolytes -- Conductivity , Protons , Organic conductors , Organic solid state chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4446 , http://hdl.handle.net/10962/d1007729 , Electrolytes -- Conductivity , Protons , Organic conductors , Organic solid state chemistry
- Description: Dielectric, d. c. conductivity and electrolysis measurements have been made principally on solid imidazole and urea. Electrode effects, especially the development of a suitable protode, and techniques for detecting mobile protons in solids were pursued. The dielectric data have been correlated with the d. c. results. A mechanism for extrinsic proton conduction in urea has been proposed.
- Full Text:
- Date Issued: 1971
- Authors: Chan-Henry, Robert Yatshein
- Date: 1971
- Subjects: Electrolytes -- Conductivity , Protons , Organic conductors , Organic solid state chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4446 , http://hdl.handle.net/10962/d1007729 , Electrolytes -- Conductivity , Protons , Organic conductors , Organic solid state chemistry
- Description: Dielectric, d. c. conductivity and electrolysis measurements have been made principally on solid imidazole and urea. Electrode effects, especially the development of a suitable protode, and techniques for detecting mobile protons in solids were pursued. The dielectric data have been correlated with the d. c. results. A mechanism for extrinsic proton conduction in urea has been proposed.
- Full Text:
- Date Issued: 1971
Some aspects of the effect of temperature on the respiratory and cardiac activities of the Cichlid Teleost Tilapia mossambica
- Authors: Josman, V
- Date: 1971
- Subjects: Fishes -- Effect of temperature on , Cichlids
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5859 , http://hdl.handle.net/10962/d1012613
- Description: The importance of the cichlid teleost Tilapia mossambica as a protein source, coupled with its remarkable adaptability, has resulted in its introduction into many water systems throughout the tropical, sub-tropical and even temperate regions of the world. However, its successful exploitation of these waters is dependent very largely upon the value of minimum temperatures and their duration. For e.g. Long et al (1961) has drawn attention to the tremendous mortalities of T. mossambica that occur in shallow water bodies during the precipitous temperature decreases that accompany the winter monsoons in Vietnam and other eastern countries, even at temperatures as high as 14 or 16º C. Coehe (1967) does not recommend stocking with T. mossambica where temperatures are not above 14º C all the time. Ailanson et al (1962) conclude, after an experimental study, that low temperatures (13º C or lower) in South African highveld dams in winter are certainly an important factor in the extensive mortalities of T. mossambica that have been reported from these dams. Jubb (1961) also reports that this species is often killed during a severe winter in Rhodesia. Intro., p.1.
- Full Text:
- Date Issued: 1971
- Authors: Josman, V
- Date: 1971
- Subjects: Fishes -- Effect of temperature on , Cichlids
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5859 , http://hdl.handle.net/10962/d1012613
- Description: The importance of the cichlid teleost Tilapia mossambica as a protein source, coupled with its remarkable adaptability, has resulted in its introduction into many water systems throughout the tropical, sub-tropical and even temperate regions of the world. However, its successful exploitation of these waters is dependent very largely upon the value of minimum temperatures and their duration. For e.g. Long et al (1961) has drawn attention to the tremendous mortalities of T. mossambica that occur in shallow water bodies during the precipitous temperature decreases that accompany the winter monsoons in Vietnam and other eastern countries, even at temperatures as high as 14 or 16º C. Coehe (1967) does not recommend stocking with T. mossambica where temperatures are not above 14º C all the time. Ailanson et al (1962) conclude, after an experimental study, that low temperatures (13º C or lower) in South African highveld dams in winter are certainly an important factor in the extensive mortalities of T. mossambica that have been reported from these dams. Jubb (1961) also reports that this species is often killed during a severe winter in Rhodesia. Intro., p.1.
- Full Text:
- Date Issued: 1971
Some aspects of the mission policy and practice of the Church of the Province of South Africa in Ovamboland, 1924-1960
- Authors: Mallory, Charles Shannon
- Date: 1971
- Subjects: Church of the Province of Southern Africa -- Namibia -- Owambo
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:1232 , http://hdl.handle.net/10962/d1007312 , Church of the Province of Southern Africa -- Namibia -- Owambo
- Description: This thesis is a study that was originally inspired by the question, "What does it mean to be a Christian in rural Africa today?" While the Church needs to ask this question everywhere in the world, from experience the writer believes it is especially germane to the non-Western cultures of Africa and Asia. That experience is drawn from eight years' work among the Kwanyama tribe of Ovambos in the Ovamboland Anglican Mission. Hence, this study is confined to one rural African tribe as it came under 46 years' influence of one Christian denomination.
- Full Text:
- Date Issued: 1971
- Authors: Mallory, Charles Shannon
- Date: 1971
- Subjects: Church of the Province of Southern Africa -- Namibia -- Owambo
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:1232 , http://hdl.handle.net/10962/d1007312 , Church of the Province of Southern Africa -- Namibia -- Owambo
- Description: This thesis is a study that was originally inspired by the question, "What does it mean to be a Christian in rural Africa today?" While the Church needs to ask this question everywhere in the world, from experience the writer believes it is especially germane to the non-Western cultures of Africa and Asia. That experience is drawn from eight years' work among the Kwanyama tribe of Ovambos in the Ovamboland Anglican Mission. Hence, this study is confined to one rural African tribe as it came under 46 years' influence of one Christian denomination.
- Full Text:
- Date Issued: 1971
The Birds' River dolerite complex
- Authors: Booth, P W K
- Date: 1971
- Subjects: Diabase , Diabase -- South Africa -- Cape of Good Hope -- Dordrecht. , Igneous rocks -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5043 , http://hdl.handle.net/10962/d1007664 , Diabase , Diabase -- South Africa -- Cape of Good Hope -- Dordrecht. , Igneous rocks -- South Africa
- Description: A plug-like intrusion of Karroo dolerite, near Dordrecht in the Eastern Cape of the Republic, is described. Field mapping with the, aid of aerial photographs has revealed that the contact of the intrusion, for the most part, dips very steeply outwards. In the south- eastern and eastern areas, however, sheet- or sill-like forms appear to be given off from the main intrusion. In plan view the intrusion is roughly oval shaped, its longer axis being aligned in a north-westerly direction. Its surface area measures approximately 60 square kilometres (24 square miles). A large number of xenoliths composed exclusively of Stormberg sediments, pyroclastic rocks and minor lavas, are to be found cropping out within the dolerite intrusion. These xenoliths, many of which occur in positions far above or below their normal stratigraphic elevation, are extremely variable in size - the largest having an area of approximately 15 square kilometres (6 square miles). The xenoliths represent fragments of the original "roof" of sediments and pyroclastics which have collapsed into and been engulfed by the dolerite magma. This type of dolerite intrusion is known as a "belljar" intrusion. A superficial classification of the dolerites, based chiefly on textural and certain mineralogical features, is presented. In the area surrounding the main intrusion are a number of dolerite dikes and sheets. The youngest phase of igneous activity is represented by the Dragon's Back dike, which cuts across the complex in a north-westerly direction. Several veining phenomena, as well as an interesting variety of metamorphic and metasomatic rocks, are associated with the main dolerite intrusion. Six diatremes are situated in the vicinity of the intrusion. Pyroclastic rocks are represented by a variety of types, and are to be found outside the area of the intrusion, and as xenoliths within it. A tentative interpretation of the mechanism of formation of the intrusion, which appears to be related to volcanic activity and cauldron subsidence, is presented.
- Full Text:
- Date Issued: 1971
- Authors: Booth, P W K
- Date: 1971
- Subjects: Diabase , Diabase -- South Africa -- Cape of Good Hope -- Dordrecht. , Igneous rocks -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5043 , http://hdl.handle.net/10962/d1007664 , Diabase , Diabase -- South Africa -- Cape of Good Hope -- Dordrecht. , Igneous rocks -- South Africa
- Description: A plug-like intrusion of Karroo dolerite, near Dordrecht in the Eastern Cape of the Republic, is described. Field mapping with the, aid of aerial photographs has revealed that the contact of the intrusion, for the most part, dips very steeply outwards. In the south- eastern and eastern areas, however, sheet- or sill-like forms appear to be given off from the main intrusion. In plan view the intrusion is roughly oval shaped, its longer axis being aligned in a north-westerly direction. Its surface area measures approximately 60 square kilometres (24 square miles). A large number of xenoliths composed exclusively of Stormberg sediments, pyroclastic rocks and minor lavas, are to be found cropping out within the dolerite intrusion. These xenoliths, many of which occur in positions far above or below their normal stratigraphic elevation, are extremely variable in size - the largest having an area of approximately 15 square kilometres (6 square miles). The xenoliths represent fragments of the original "roof" of sediments and pyroclastics which have collapsed into and been engulfed by the dolerite magma. This type of dolerite intrusion is known as a "belljar" intrusion. A superficial classification of the dolerites, based chiefly on textural and certain mineralogical features, is presented. In the area surrounding the main intrusion are a number of dolerite dikes and sheets. The youngest phase of igneous activity is represented by the Dragon's Back dike, which cuts across the complex in a north-westerly direction. Several veining phenomena, as well as an interesting variety of metamorphic and metasomatic rocks, are associated with the main dolerite intrusion. Six diatremes are situated in the vicinity of the intrusion. Pyroclastic rocks are represented by a variety of types, and are to be found outside the area of the intrusion, and as xenoliths within it. A tentative interpretation of the mechanism of formation of the intrusion, which appears to be related to volcanic activity and cauldron subsidence, is presented.
- Full Text:
- Date Issued: 1971
The effects of organic perturbants on the structure of soluble collagen
- Authors: Hart, Geoffrey Joseph
- Date: 1971
- Subjects: Chemistry, Organic , Collagen
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3846 , http://hdl.handle.net/10962/d1012157 , Chemistry, Organic , Collagen
- Description: Organic solvents were used in the present study as a means of investigating the non-covalent interactions involved in the maintenance and pertubation of the three-dimensional structure of the collagen macromolecule in solution. The two main types of non-covalent interaction under consideration are hydrogen bond formation and hydrophobic effects. Elucidation of the relative importance of these factors in the maintenance of the solution structure of proteins is an area of intensive investigation and fundamental significance to biochemistry as a whole. During the past decade, considerable progress has been made towards a clearer understanding of the forces involved, and a number of different theoretical and experimental approaches have emerged. Until about 1960, hydrogen bonding was widely believed to be the dominant non-covalent interaction responsible for the maintenance of secondary and tertiary structure in many proteins. Subsequently, an increasingly important role for apolar (hydrophobic) effects was suggested by a number of authors, and at present there is no satisfactorily definitive interpretation of the available experimental evidence. The current work is based on a comparison of the effects of organic solvents on widely different substrates, namely collagen, cellulose, and the chromatographic reference material, catechin. The chromatographic mobility of catechin on cellulose may be regarded as a phenomenon which is mediated entirely by polar interaction mechanisms. The effects of various organic perturbants and of changing solvent/water ratios are readily interpreted on this basis. In the collagenous systems, however, certain results appear to require the introduction of concepts other than those relating exclusively to polar bonding affinities. The experimental evidence shows that there are cases where the enhancement of the polar interaction potential of solvent/water mixtures, in relation to catechin-cellulose systems, is accompanied by an apparent reduction of polar interaction potential of the same solvent/water mixtures with respect to soluble collagen. The anomaly outlined above will be discussed in terms of two fundamentally different theoretical assumptions. In the first of these, the mechanism of perturbant action in collagenous systems is regarded as essentially similar to that governing catechin-cellulose affinity patterns. Thus, interaction processes are all treated as polar phenomena, in which direct hydrophobic destabilization of the collagen triple helix plays no part. In an attempt to explain the effects of perturbants in both collagen and cellulose-containing systems in terms of the above assumption, two hypotheses are examined involving (1) direct polar interaction between perturbant molecules and functional groups of the protein; (2.) the possibility of an enhanced polar interaction potential of water molecules, due to lowering of the environmental dielectric constant when organic solvents are added to the systems. Within the other broad conceptual division, collagen and cellulose substrates are considered to respond in fundamentally different ways to the action of organic perturbants. As before, cellulose-catechin-solvent interactions are treated as entirely polar phenomena, and perturbant effects interpreted in terms of mechanisms such as direct solvation of the substrate, and the enhanced hydrogen bonding activity of water molecules. In contrast, perturbant lyotropic action with respect to soluble collagen i s viewed as the manifestation of a major contribution by hydrophobic interaction processes to macromolecular stability. Thus, solvents that competitively reduce the assumed entropic contribution to the stability of the collagen triple helix, are seen as potential destabilizers of the native state of the protein and inhibitors of the regeneration of co-operative structures during renaturation. Both of the above approaches are critically assessed in the light of the present work and the dominant trends apparent in the recent literature.
- Full Text:
- Date Issued: 1971
- Authors: Hart, Geoffrey Joseph
- Date: 1971
- Subjects: Chemistry, Organic , Collagen
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3846 , http://hdl.handle.net/10962/d1012157 , Chemistry, Organic , Collagen
- Description: Organic solvents were used in the present study as a means of investigating the non-covalent interactions involved in the maintenance and pertubation of the three-dimensional structure of the collagen macromolecule in solution. The two main types of non-covalent interaction under consideration are hydrogen bond formation and hydrophobic effects. Elucidation of the relative importance of these factors in the maintenance of the solution structure of proteins is an area of intensive investigation and fundamental significance to biochemistry as a whole. During the past decade, considerable progress has been made towards a clearer understanding of the forces involved, and a number of different theoretical and experimental approaches have emerged. Until about 1960, hydrogen bonding was widely believed to be the dominant non-covalent interaction responsible for the maintenance of secondary and tertiary structure in many proteins. Subsequently, an increasingly important role for apolar (hydrophobic) effects was suggested by a number of authors, and at present there is no satisfactorily definitive interpretation of the available experimental evidence. The current work is based on a comparison of the effects of organic solvents on widely different substrates, namely collagen, cellulose, and the chromatographic reference material, catechin. The chromatographic mobility of catechin on cellulose may be regarded as a phenomenon which is mediated entirely by polar interaction mechanisms. The effects of various organic perturbants and of changing solvent/water ratios are readily interpreted on this basis. In the collagenous systems, however, certain results appear to require the introduction of concepts other than those relating exclusively to polar bonding affinities. The experimental evidence shows that there are cases where the enhancement of the polar interaction potential of solvent/water mixtures, in relation to catechin-cellulose systems, is accompanied by an apparent reduction of polar interaction potential of the same solvent/water mixtures with respect to soluble collagen. The anomaly outlined above will be discussed in terms of two fundamentally different theoretical assumptions. In the first of these, the mechanism of perturbant action in collagenous systems is regarded as essentially similar to that governing catechin-cellulose affinity patterns. Thus, interaction processes are all treated as polar phenomena, in which direct hydrophobic destabilization of the collagen triple helix plays no part. In an attempt to explain the effects of perturbants in both collagen and cellulose-containing systems in terms of the above assumption, two hypotheses are examined involving (1) direct polar interaction between perturbant molecules and functional groups of the protein; (2.) the possibility of an enhanced polar interaction potential of water molecules, due to lowering of the environmental dielectric constant when organic solvents are added to the systems. Within the other broad conceptual division, collagen and cellulose substrates are considered to respond in fundamentally different ways to the action of organic perturbants. As before, cellulose-catechin-solvent interactions are treated as entirely polar phenomena, and perturbant effects interpreted in terms of mechanisms such as direct solvation of the substrate, and the enhanced hydrogen bonding activity of water molecules. In contrast, perturbant lyotropic action with respect to soluble collagen i s viewed as the manifestation of a major contribution by hydrophobic interaction processes to macromolecular stability. Thus, solvents that competitively reduce the assumed entropic contribution to the stability of the collagen triple helix, are seen as potential destabilizers of the native state of the protein and inhibitors of the regeneration of co-operative structures during renaturation. Both of the above approaches are critically assessed in the light of the present work and the dominant trends apparent in the recent literature.
- Full Text:
- Date Issued: 1971
The mode of action of the acyl-diethylamide molluscicides
- Authors: Solomon, Keith Ross
- Date: 1971
- Subjects: Pesticides , Molluscicides
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5821 , http://hdl.handle.net/10962/d1007406
- Description: From Introduction: That bilharziasis an important public health, social and economic problem in the tropical and subtropical countries of the world is well appreciated. (WHO, 1965) Bilharsiasis is the disease caused by parasitic worms of the genus Schistosoma having certain fresh water snails as the intermediate host. In South Africa the more important snails are Bulinus africanus and B. globosus, the secondary hosts of Schistosom haematobium. (WHO, 1965) One method of controling the disease is to reduce the numbers of the intermediate host snails to such a low level that transmission cannot occur (WHO, 1965 and Macdonald, 1965) This has led to a strong interest in those substances that kill snails. The first recorded use of a molluscicide, copper sulphate, was during the first world War in Egypt. (De Villiers, 1965) More recently, the more or less random testing of large numbers of compounds led to the discovery of a large number of molluscicides. These were the heavy metal compounds such as the salts of mercury and arsenic, the substituted phenols such as pentachlorophenol (PCP) and the 2-substituted 4:6-dinitrophenols. (De Villiers, 1965) These compounds are good molluscicides but suffer from a number of disadvantages. The use of copper compounds in hard waters is impractical as the copper precipitates out as the less effective carbonate. The heavy metal salts are expensive and biocidal thus making the treated water unsuitable for human or agricultural use. The phenolic compounds are unpleasant and dangerous to handle and the hydrolysis of PCP is catalysed by sunlight in clear waters. High concentrations of these compounds are required, thus increasing transport and handling costs, particularly in inaccessible areas.
- Full Text:
- Date Issued: 1971
- Authors: Solomon, Keith Ross
- Date: 1971
- Subjects: Pesticides , Molluscicides
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5821 , http://hdl.handle.net/10962/d1007406
- Description: From Introduction: That bilharziasis an important public health, social and economic problem in the tropical and subtropical countries of the world is well appreciated. (WHO, 1965) Bilharsiasis is the disease caused by parasitic worms of the genus Schistosoma having certain fresh water snails as the intermediate host. In South Africa the more important snails are Bulinus africanus and B. globosus, the secondary hosts of Schistosom haematobium. (WHO, 1965) One method of controling the disease is to reduce the numbers of the intermediate host snails to such a low level that transmission cannot occur (WHO, 1965 and Macdonald, 1965) This has led to a strong interest in those substances that kill snails. The first recorded use of a molluscicide, copper sulphate, was during the first world War in Egypt. (De Villiers, 1965) More recently, the more or less random testing of large numbers of compounds led to the discovery of a large number of molluscicides. These were the heavy metal compounds such as the salts of mercury and arsenic, the substituted phenols such as pentachlorophenol (PCP) and the 2-substituted 4:6-dinitrophenols. (De Villiers, 1965) These compounds are good molluscicides but suffer from a number of disadvantages. The use of copper compounds in hard waters is impractical as the copper precipitates out as the less effective carbonate. The heavy metal salts are expensive and biocidal thus making the treated water unsuitable for human or agricultural use. The phenolic compounds are unpleasant and dangerous to handle and the hydrolysis of PCP is catalysed by sunlight in clear waters. High concentrations of these compounds are required, thus increasing transport and handling costs, particularly in inaccessible areas.
- Full Text:
- Date Issued: 1971
The parasite complex of the citrus psylla, trioza erytreae (Del Guercio) (Homoptera)
- Authors: McDaniel, J. R.
- Date: 1971
- Subjects: Psylla -- Regulation , Citrus , Biological control systems , Parasites
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5865 , http://hdl.handle.net/10962/d1012866
- Description: 1. Fifteen parasite species comprising the T. erytreae complex in Salisbury are listed. 2. Detailed, illustrated accounts are given of the biology of two primary parasites, Tetrastichus Pradiatus Waterston and Psyllaephagus pulvinatus (Waterston ), and their main hyperparasite, Aphidencyrtus cassatus Annecke. 3. The biology of the remaining twelve less important hyperparasites is briefly described and illustrated. 4. Keys are given to the adults, pupae and pupal remains of the parasites. 5 . The population fluctuations of T. erytreae and its parasites, as determined from field studies in the Salisbury area, are reported . 6. The interrelationships between T. erytreae and its parasites are summarised and discussed. Summary, p. 89.
- Full Text:
- Date Issued: 1971
- Authors: McDaniel, J. R.
- Date: 1971
- Subjects: Psylla -- Regulation , Citrus , Biological control systems , Parasites
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5865 , http://hdl.handle.net/10962/d1012866
- Description: 1. Fifteen parasite species comprising the T. erytreae complex in Salisbury are listed. 2. Detailed, illustrated accounts are given of the biology of two primary parasites, Tetrastichus Pradiatus Waterston and Psyllaephagus pulvinatus (Waterston ), and their main hyperparasite, Aphidencyrtus cassatus Annecke. 3. The biology of the remaining twelve less important hyperparasites is briefly described and illustrated. 4. Keys are given to the adults, pupae and pupal remains of the parasites. 5 . The population fluctuations of T. erytreae and its parasites, as determined from field studies in the Salisbury area, are reported . 6. The interrelationships between T. erytreae and its parasites are summarised and discussed. Summary, p. 89.
- Full Text:
- Date Issued: 1971
- «
- ‹
- 1
- ›
- »