Showing items 1 - 14 of 14

Your selections:

Understanding biotic interactions in invaded pond communities in the Sundays River irrigation network, South Africa

- Mofu, Lubabalo

  • Authors: Mofu, Lubabalo
  • Date: 2020
  • Subjects: Mozambique tilapia -- South Africa -- Sundays River (Eastern Cape) , Western mosquitofish -- South Africa -- Sundays River (Eastern Cape) , Gobiidae -- South Africa -- Sundays River (Eastern Cape) , Clupeidae -- South Africa -- Sundays River (Eastern Cape) , Reservoirs -- South Africa -- Sundays River (Eastern Cape) , Zooplankton -- South Africa -- Sundays River (Eastern Cape) , Freshwater ecology -- South Africa -- Sundays River (Eastern Cape) , Biotic communities -- South Africa -- Sundays River (Eastern Cape) , Fishes -- Effect of temperature on -- South Africa -- Sundays River (Eastern Cape) , Stable isotopes , Relative Impact Potential
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: http://hdl.handle.net/10962/167089 , vital:41436
  • Description: The Sundays River valley irrigation ponds provide a unique opportunity to investigate biotic interactions within a biological invasions context, as they contain both native and non-native fish species. This study focusses on two native species (Glossogobius callidus and Gilchristella aestuaria) and two non-native species (Oreochromis mossambicus and Gambusia affinis). The ecology of the ponds was driven by physico-chemical variables, mainly temperature, but the interactions between fishes were a complex interplay between temperature, pond community ecology and food web structure. Seasonal changes in temperature and subsequent fluctuations in water levels resulted in changes in zooplankton community. Chlorophyll-a, temperature, G. callidus and G. affinis were the drivers of the seasonal changes in macroinvertebrate composition. Stable isotope analysis identified substantial ontogenetic dietary shifts in all species, corresponding to changes in body size. Stable isotope analysis revealed that the niche space occupied by G. affinis was broad and overlapped with that of the other three focal species. Stable isotope metrics showed that G. affinis and O. mossambicus utilised a wide range of resources compared to G. callidus and G. aestuaria. Stomach content analysis showed that G. callidus, O. mossambicus and G. affinis fed predominantly on benthic resources, while G. aestuaria fed mainly plankton resources. Functional response experiments revealed that G. callidus and G. affinis both displayed Type II functional responses. In single fish trials, G. affinis had significantly higher functional responses than G. callidus. In heterospecific G. callidus-G. affinis combinations the functional response of G. callidus was reduced by the presence of G. affinis, whereas, this combination greatly enhanced G. affinis functional response magnitudes. The functional response of G. callidus, O. mossambicus and G. affinis under two temperature treatments along with fish abundance data was used to determine temporal differences in the ecological impacts of each fish species between seasons. The relative impact potential of O. mossambicus was consistently higher than that of G. callidus and G. affinis. This study demonstrates how seasonal temperature fluctuations affect the relative impact capacities of introduced species. Overall, this thesis showed that high temperature along with life-history traits contributes to the biotic interactions between native and non-native species in novel environments.
  • Full Text:

Nonlinear optical studies of phthalocyanines and their conjugates with nanomaterials

- Sanusi, Sikiru Olukayode

  • Authors: Sanusi, Sikiru Olukayode
  • Date: 2015
  • Subjects: Phthalocyanines , Nonlinear optics
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: vital:4545 , http://hdl.handle.net/10962/d1017925
  • Description: A number of metallophthalocyanines (MPcs) and metal-free phthalocyanines (H₂Pcs) have been synthesized and characterized using various characterization tools such as ¹H-NMR, TOF mass spectrometry, FT-IR, UV-visible spectrophotometry and CHNS elemental analysis. Some of the MPcs were covalently linked to nanomaterials such as silica nanoparticles (SiNPs), single-walled carbon nanotubes (SWCNTs), magnetite nanoparticles (MNPs) and quantum dots (QDs), or embedded in polymer thin-films using poly(methyl methacrylate) (PMMA) and poly(acrylic acid) (PAA) as the polymer sources. The phthalocyanine-nanomaterial composites (Pc-NMCs) were characterized with FT-IR, UV-visible spectrophotometry, transmission electron microscopy (TEM), thermogravimetry analysis and X-ray diffractometry. The nonlinear optical (NLO) properties (using the open-aperture Z-scan technique) of the MPcs and the Pc-NMCs were investigated. In general, most of the investigated MPcs showed good optical limiting behaviors, except for a few, like the non-peripherally-substituted 2-pyridyloxy phthalocyanines, which showed inhibited NLO response as a result of the ring-strain effects. The absence of a metal center was found to greatly reduce the inherent high nonlinearities expected of some of the phthalocyanine complexes. The octaphenoxy derivatives (61a – 61e) were found to exhibit reverse saturable absorption (RSA) that depends on the singlet-singlet transitions, hence making them less reliable optical limiters. The optical limiting properties of the MPcs were improved in the presence of nanomaterials such as the QDs, MNPs and SWCNTs, with MPc-QDs showing the best optical limiting behavior of the three. SiNPs have no significant effect on the optical limiting behavior of the MPcs. The optical limiting properties of the MPcs were greatly enhanced in the presence of PMMA or PAA polymers. The PAA polymer showed better optical limiting behavior compared to PMMA
  • Full Text:

Copycat

- Thomas, Adèle

Enhancing learner centred education through the eco-schools framework: case studies of eco-schools practice in South Africa and Namibia

- Haingura, Rudolph

  • Authors: Haingura, Rudolph
  • Date: 2009
  • Subjects: Education -- South Africa -- Case studies Education -- Namibia -- Case studies Educational change -- South Africa -- Case studies Educational change -- Namibia -- Case studies Teachers -- Training of -- South Africa -- Case studies Teachers -- Training of -- Namibia -- Case studies Environmental education -- South Africa -- Case studies Environmental education -- Namibia -- Case studies School improvement programs
  • Language: English
  • Type: Thesis , Masters , MEd
  • Identifier: vital:1509 , http://hdl.handle.net/10962/d1003391
  • Description: Since the early 1990’s both South Africa and Namibia have been engaged in educational reform processes to address the discriminatory impacts and orientations of education under Bantu Education which were implemented in both countries prior to independence (Namibia in 1990, and South Africa in 1994). A feature of both educational reform processes is the underpinning theory of learning which draws on social constructivism, and which is articulated as learner centred education. This approach to teaching and learning infuses both policy frameworks. Another common feature is the introduction of environmental education into the formal education systems of both countries, a process which has been championed by development assistance, and which has been supported by programmes such as the Eco-Schools programme which is an international environmental education initiative started after the Rio Earth Summit in 1992, and implemented in a number of countries, including South Africa. The programme has also been piloted in some schools in Namibia. To date no research has been done on the way in which the Eco-Schools framework (its practices, organizing principles, evaluation processes etc.) enhance learner centred education. This study therefore aimed to investigate and understand how the Eco-Schools framework can enhance learner centred education. The study was conducted in 2007 in three Eco-Schools in Namibia and four Eco-Schools in South Africa in the context of the broader national programmes of implementing learner centred education policies, and environmental education histories. The study used a case study methodology, using observation, interviews, and document analysis as the main methods for data generation. The analytical process followed two stages: the first involved an inductive analysis using categories which were organized into a series of analytical memos. The second phase of data analysis involved recontextualising the data drawing on theory and contextual insights to provide insights that address the research question, using analytical statements. The main findings of the study are that the Eco-Schools framework provides numerous opportunities to enhance learner centred education, through contextualization of learning, through strengthening school-community interactions, and through enabling active involvement of learners in decision making and a range of contextually meaningful Eco-Schools practices. The study also showed that the Eco-Schools framework allows for empowerment of learners in relation to diverse needs, and also allows for learner initiated contributions, although this aspect was not well developed in the schools that were included in this study. The study also found that the benefits of Eco-Schools in terms of enhancing learner centred education were limited to only a few learners who were involved in club activities or who were being taught by enthusiastic teachers who were participating in the Eco-Schools programme. The study showed that these benefits can be more widely shared if more teachers were to get involved, and if the Eco-Schools programme were better understood in relation to the curriculum requirements of various subjects and learning areas, and if the Eco-Schools practices could be more successfully integrated across the curriculum. The study also showed that various forms of support were required for implementing the Eco-Schools programme, most notably the support of the Principal, and the Department of Education. The study also identified that parents and other stakeholders in the school were supportive of the Eco-Schools programme since it was perceived to have relevance to learning, as well as the community. The results broadly confirmed that the implementation of Eco-Schools using a whole school, values based and active learning approach promotes a school culture which enhances learner centred education more broadly across the school. The study also found that the Eco-Schools programme added a new dimension to existing discourses on learner centred education, which could be described as a community linked or situated approach to learner centred education.
  • Full Text:

Social learning processes of HIV/AIDS women caregivers on their use of traditional foods and medicinal plants : the case of Raphael Centre and Keiskamma Art and Health Centre communities of practice, Eastern Cape Province, South Africa

- Shonhai, Venencia F

  • Authors: Shonhai, Venencia F
  • Date: 2009
  • Subjects: Keiskamma Art Project (South Africa) , Women caregivers -- South Africa -- Eastern Cape , HIV infections -- Study and teaching -- South Africa , AIDS (Disease) -- Study and teaching -- South Africa , HIV-positive persons -- Care -- South Africa -- Eastern Cape , Medicinal plants -- South Africa , Natural foods -- South Africa
  • Language: English
  • Type: Thesis , Masters , MEd
  • Identifier: vital:1768 , http://hdl.handle.net/10962/d1003653
  • Description: The scale of people being infected by HIV/AIDS (Human Immunodeficiency Virus /Acquired Immune Deficiency Syndrome) has meant that the family and the community have had to become involved in caring for the sick (Van Dyk, 2005). This has inevitably led to the emergence of informal caregivers in the form of family members caring for their relatives (Kipp, Nkosi, Laing & Jhangri, 2006). The research investigated the social learning of women caregivers looking after people living with HIV/AIDS, with emphasis on caregiving practices related to how they use traditional foods and medicinal plants. The research was undertaken in Grahamstown at the Raphael Centre and in Hamburg at Keiskkamma Health Centre and Art Project, Eastern Cape, South Africa. Data was collected using interviews, focus group discussions and diaries written by participants. The data was analyzed in two phases: the first phase involved reading the interview transcripts and collating the responses into analytical memos that were captured into broad categories, while the second phase made use of the community of practice analytical framework to further analyze the data to get better understanding of the social learning processes. This study reveals that participating in a community of practice like Raphael Centre and Keiskamma Health Centre enables caregivers to learn about caregiving. It also reveals that within these communities of practice there are varied learning processes that take place, such as observational and collaborative learning. The research also revealed that caregivers learn from the communities from which they come, for example caregivers learn about traditional food and medicinal plants which they use from their family members, friends, other caregivers as well as non governmental organizations. The research found that caregivers are influenced in their learning and practices by a number of factors which include their own experiences, ambivalent messages from different stakeholders concerned with fighting HIV/AIDS and exposure to new information. The research recommends that diverse learning processes in a community of practice and outside a community of practice should be encouraged and strengthened. It also recommends that HIV/AIDS caregiving options should be strengthened by drawing on experience and knowledge of caregivers. Caregivers should be encouraged to be selfsustaining to improve their caregiving practices. Stakeholders in the field of HIV/AIDS should be alert to and address ambivalence on use of medicinal plants. Existing programmes that enable women to learn about new information on HIV/AIDS should be strengthened.
  • Full Text:

The operation of letters of credit with particular reference to the doctrine of strict compliance, the principle of independence, the fraud exception and conflict of laws

- Makobe, Melanchton Phillip Malepe

  • Authors: Makobe, Melanchton Phillip Malepe
  • Date: 2001
  • Subjects: Letters of credit Conflict of laws Fraud
  • Language: English
  • Type: Thesis , Masters , LLM
  • Identifier: vital:3710 , http://hdl.handle.net/10962/d1007281
  • Description: The thesis covers aspects of the law relating to letters of credit. It deals with the operation of letters of credit with particular reference to the doctrine of strict compliance, the principle of independence, the fraud exception and conflict of laws. According to the principle of independence, banks must make payment in terms of the letter of credit irrespective of any dispute that may exist between the buyer and the seller in an underlying contract or other contracts. Although the principle of independence is clearly established, it is not absolute. An exception occurs in the case of fraud. Thus, if the seller has committed fraud, such as tendering forged documents, the buyer can instruct the bank not to make payment in terms of the credit. If the bank refuses to dishonour the letter of credit, the buyer can apply to a court to interdict the bank from making payment. In South African law the buyer must establish that the seller was party to fraud in relation to the documents presented to the bank for payment before the court can grant an interdict. This thesis also examines the standard of proof of fraud required in letters of credit transactions and proposes a standard of proof which will not unduly favour the seller whose good faith is in dispute. The fast growing technology of computers and telecommunications is rapidly changing the methods of transacting business by paper documentation and letter of credit transactions are no exception. At present the buyer can apply to the bank to issue a letter of credit through the computer and banks also communicate letter of credit transactions through computer networks. However, the beneficiary still has to present documents to the bank for payment in paper form. It is proposed that the Uniform Custom and Practice For Documentary Credits (UCP) be amended to provide for fully computerised letters of credit transactions. Another objective of the thesis is to examine the doctrine of strict compliance. In terms of the doctrine of strict compliance documents presented under the credit must comply strictly with the requirements set out in the credit. If banks are satisfied that the documents presented by the seller strictly conform with the requirements of the credit they are obliged to make payment as required by the credit. It is proposed that the doctrine of strict compliance should not be applied strictly. In other words, the banks should make payment in terms of the credit if the discrepancy in the documents is trivial. The thesis also covers conflict of laws issues. As the UCP does not have rules dealing with conflict of laws, most jurisdictions have developed their own rules to be applied by the courts in cases of conflict of laws. The thesis examines the different rules of conflict of laws as developed and practiced by different jurisdictions.
  • Full Text:

Reduction of tungsten oxides with carbon and hydrogen

- Venables, Dean Stuart

  • Authors: Venables, Dean Stuart
  • Date: 1996
  • Subjects: Oxidation-reduction reaction , Tungsten , Hydrogen , Carbon
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:4342 , http://hdl.handle.net/10962/d1005004 , Oxidation-reduction reaction , Tungsten , Hydrogen , Carbon
  • Description: The reductions of WO₃ with hydrogen, with CO, and with carbon, as well as the reduction of WO₃/graphite mixtures with hydrogen, were studied using thermogravimetry, evolved gas analysis, X-ray powder diffraction, and scanning electron microscopy. The intermediate phases W₂₀O₅₈, W₁₈O₄₉ and WO₂, were observed in the reductions. The final product of the reductions with hydrogen and carbon was tungsten, and we was formed in the reduction with CO. The reaction paths in the overall processes were determined. The reactant/product gas ratio had a considerable influence on which reactions took place. The morphology of the sample was characterised at different stages of the reduction. The shape of the WO₃ particles was retained during the reduction. Particle growth was observed in the reduction with hydrogen and was attributed to the formation of WO₂(OH)₂(g). The kinetics of the reductions were investigated , and the reaction mechanisms determined. The reduction of WO₃ with CO was studied from 650 to 900°C, and occurred at a phase boundary with an activation energy of 40 kJ mol⁻¹ . The reduction of WO₂, was studied under the same conditions. The reaction also occurred at a phase boundary and had an activation energy of 62 kJ mol⁻¹. The reduction of WO₃ with carbon was studied from 935 to 1100°C and took place via CO and CO₂. Two stages were observed in the reduction . The first stage, which corresponded approximately to the formation of WO₂ had an activation energy of 66 kJ mol⁻¹ and was limited by diffusion through the porous reacting particles. The second stage was first order and had an activation energy of 40 kJ mol⁻¹. The reduction of WO₃ and WO₃ graphite mixtures with hydrogen were studied from 575 to 975 °C. The reactions were controlled by mass-transfer under the conditions investigated. The addition of carbon increased the rate of the reduction process , but did not affect the phases formed in the system. CO₂ was evolved mainly at the start, and CO mainly at the end of the process.
  • Full Text:

An investigation into the relationship between kinesthetic sensitivity and balancing ability in pre-school children

- Burger, Laetitia Mary

  • Authors: Burger, Laetitia Mary
  • Date: 1991
  • Subjects: Motor ability in children Perception in children Preschool children
  • Language: English
  • Type: Thesis , Masters , MEd
  • Identifier: vital:1615 , http://hdl.handle.net/10962/d1003497
  • Description: The purpose of this study was to explore the possibility of a linear relationship between kinesthetic sensitivity and balancing ability in pre-school children. Furthermore, the effects of age on kinesthetic sensitivity and balancing ability were investigated. Finally, the role of gender in kinesthetic sensitivity and balancing ability was examined. Fifty-one subjects, between the ages of three and six years, executed five trials on each of two kinesthetic sensitivity tests (an arm abduction test and a hip abduction test); two tests for static balance (on a balance board and on a balance stick) and two tests for dynamic balance (a beam walk test and a stepping stones test). Although the correlations between kinesthetic sensitivity and balancing ability were generally positive, they were very slight. These low correlations are probably an indication that different abilities are required for carrying out the different tasks. Generally, both balancing ability and kinesthetic sensitivity appeared to improve with age. From analysis of individual test results it was obvious that abilities varied from individual to individual (Appendix G). This could have been the result of developmental, motivational or experiential differences. Although the girls generally performed slightly better on most tests than the boys the correlations between test scores for boys were slightly higher than those for girls. At-test indicated that there were no significant differences between the mean scores of the boys and the girls on the balancing or the kinesthetic sensitivity tasks.
  • Full Text:

'n Marxisties-feministiese ondersoek van Wilma Stockenström se roman, Die kremetartekspedisie

- Gardner, Judy Hilary

  • Authors: Gardner, Judy Hilary
  • Date: 1989
  • Subjects: Stockenström, Wilma -- Criticism and interpretation , Stockenström, Wilma. Kremetartekspedisie
  • Language: Afrikaans
  • Type: text , Thesis , Masters , MA
  • Identifier: vital:3568 , http://hdl.handle.net/10962/d1002091
  • Description: Chapter is an exploration of the meanings which may underly the title of this novel. I have tried initially to establish what kind of "expedition" is undertaken, and have come to the conclusion that "expedition" has a multidimensional meaning, that it implies a search, an expedition into different things: an expedition to the city of rose-quartz; the slave woman's expeditions from the baobab tree and back; an inner expedition to gain self-knowledge; an expedition into womanhood; an expedition into the history of Africa, into religion, into language. The second part of the chapter examines the nature of "baobab", since this tree, like the "Tree of Life", is regarded as one growing upside-down. It is this upside-down nature of the tree which led me to believe that many existing stereotypes and myths are turned upside-down in the novel: about slaves, about woman, language, the Afrikaans literary tradition, the "traditional" structure of the novel, culture transcending nature, the slave woman's language. In chapter 2 I have examined only one of these expeditions, viz. the slave woman's inner expeditions consisting of her experiences as a slave and her journeys of reminiscence. These journeys at the same time embrace all the other expeditions. Her inner expeditions are signified by a number of codes, which fulfil literally the function of processes of knowledge, of self- knowledge, as well as of systems in which meaning is contained. By undertaking this inner expedition, the woman gains greater clarity of vision concerning her own existence and the existence of man/woman in general. Chapter 3 deals mainly with the concept of possession/ownership, which results in two diametrically opposed groups: the owner class and the owned class. The peculiar institution of slavery has given rise to these two irreconcilable groups, and therefore a brief history of slavery is included in this chapter. The slave woman is initially one of the owned class, but through indoctrination, she too aspires to become a member of the owner class. In the second half of the chapter, then, the woman is discussed as owner. Her position becomes a reflection of the position of her owners, to illustrate the peculiarity of the capitalist system in which there will always be the rulers and the subjects, the oppressor and the oppressed, the owner and the owned.
  • Full Text:

Life history changes of two reef fish species in exploited and unexploited marine environments in South Africa

- Buxton, Colin David

  • Authors: Buxton, Colin David
  • Date: 1988
  • Subjects: Reef fishes -- Africa, Southern Chrysoblephus laticeps Chrysoblephus cristiceps
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: vital:5189 , http://hdl.handle.net/10962/d1001965
  • Description: A detailed investigation into the life histories of Chrysoblephus laticeps and c. cristiceps in exploited and unexploited marine environments on the south-east coast of southern Africa is presented. The study provided information necessary for the evaluation of marine reserves as a management option for these and similar reef species. Visual underwater assessments showed a clear spatial separation between adults and juveniles of both species, suggesting a recruitment of juveniles into shallow water followed by a gradual outward migration into deeper water with age. Denslty estlmates of C. laticeps in the Noordhoek (0.0064 fish/m²) and Tsitslkamma (0.0254 fish/m²) areas were significantly different and were attributed to exploitation. Within area differences in density were also significantly correlated with temperature) depth and substratum relief. Similar comparisons for C. cristiceps were not possible because these fish shied away from divers. Habitat preferences were mirrored in the diets of both species which fed on a wide variety of reef associated benthic animals. Size of prey appeared to be gape limited, only larger fish being able to manipulate prey. Quantitative differences between the diets of fish sampled in different areas were a reflection of differences in available prey and not related to the relative density of predators. The dietary characteristics recorded in these fish were typical of search hunters. An age and growth study based on the examination of sectioned otoliths showed that both species were slow growing and long lived. Maximum recorded ages were 18 and 22 years for C. laticeps and C. cristiceps respectively. Growth rates in exploited and unexploited areas were not significantly different although there was an indication that growth was slower in the exploited areas for C. cristiceps. Several inconsistencies in otolith interpretation and terminology were evaluated. Contrary to other South African studies the results suggested that somatic growth was fastest just after spawning. This coincided with the winter months and was reflected by the deposition of a hyaline zone in the otolith. Two independent estimates, the Pauli derivation and visually assessed length frequency analysis, produced the same value for total mortality of C. laticeps in the Tsitsikamma area (0.2). This result, together with a significant difference in the rate of fishing mortality at different areas along the coast suggested that the populations sampled were discrete and supported the postulate that both species were sedentary. Further support was obtained from a mark-recapture study. Although sample numbers were low the results showed no evidence of large scale migratory patterns in these fish. An investigation of the reproductive biology of both fish showed that they were protogynous hermaphrodites, all males being derived from females with no evidence for polyandry. Males were shown to be capable of mating with a number of females and this, together with monandry, monochromatism and a small testis size, suggested a polygynous mating system in both species. Observations of the courtship behaviour in captive c. laticeps also supported polygyny. A significant difference in the mean size at sex reversal between unexploited and exploited populations supported the postulate that sex reversal was independent of the size or age of the animal. The size at which sex reversal occurred appeared to be dependent on sex ratio. A detailed yield per recruit analysis of the response of the population to different levels of fishing mortality and size at recruitment (t [subscript]r), showed that sex reversing species were particularly vulnerable to over fishing. This was due to a dramatic decline in the number of surviving individuals past t[subscript]r which resulted in a skewing of the sex ratio towards females. Evidence is presented to show that current legislation is inadequately protecting the spawner stock of both species. In conclusion it is shown that longevity, sex reversal, restricted movements and the occupation of a demersal habitat make these species particularly vulnerable to over exploitation in a size- selective fishery. The sustained yield in the linefishery is suggested to be a result of distant recruitment from relatively unexploited populations rather than the adequacy of current conservation measures. The need to protect the spawner stock is emphasised and the use of marine reserves as an additional protection for sedentary reef-dwelling species is therefore advocated.
  • Full Text:

Die metaroman : dekonstruksie-ondersoek

- Hambidge, Joan, 1956-

Synthesis of flavan-3, 4-diols, stereochemistry of novel biflavanols and new non-tannins from Acacia Mearnsii

- Saayman, Henry Martin

  • Authors: Saayman, Henry Martin
  • Date: 1967
  • Subjects: Tannins Acacia mearnsii Stereochemistry Wattles (Plants) Chemistry, Analytic
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: vital:4444 , http://hdl.handle.net/10962/d1007704
  • Description: From Summary: The structural elucidation of condensed tannins, which are considered to consist of C₁₅-flavan units, presents certain difficulties. These tannins occur in extremely complex mixtures, and their isolation is complicated by their susceptibility to oxidative denaturation. Limitations in the formation of significant degradation products add to these problems. Since condensed tannins of black wattle bark yield anthocyanidins on treatment with mineral acids, they are considered to be proanthocyanidin in character. For this reason the initial approach to the investigation of the structures of condensed tannins was by way of the synthesis of novel 7-hydroxyflavan-3,4-diols having a low degree of hydroxyl substitution. Submission of these to modern physical techniques such as nuclear magnetic resonance (n.m.r.) spectroscopy would yield valuable data regarding the chemical shifts and coupling constants of heterocyclic and benzenoid protons which may be used for subsequent work on more highly hydroxylated diols, biflavanols and finally the condensed tannins themselves.
  • Full Text:

Investigation leading to a process for the synthesis of hydrogen sulphide from sulphur and certain lubricating oils derived from petroleum

- Schauder, H

  • Authors: Schauder, H
  • Date: 1952
  • Subjects: Hydrogen sulfide
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:4499 , http://hdl.handle.net/10962/d1013160
  • Description: The primary object of the present study was to provide a process adaptable to prevailing South African conditions, for the manufacture of hydrogen sulphide. Such a process would also be suitable for use in other countries where the gas is not obtainable naturally or from refinery operations or as a by-product from other industries. Early in the study it was found that the literature embodying prior work was very scattered in character and had to be sought in many different fields of research. It was therefore decided to make the record of prior work as comprehensive as possible so as to provide, at the same time, a starting point tor future workers on related subjects. Intro., p. 1.
  • Full Text:

The preservation and standardisation of South African hides and skins

- Kritzinger, Carl Cronje

  • Authors: Kritzinger, Carl Cronje
  • Date: 1946
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: vital:21052 , http://hdl.handle.net/10962/6157
  • Description: During the past fifty years the problems of the leather industry have been tackled from various aspects by scientific research workers all over the world, and "works control" today forms one of .the important foundation stones of efficiently run tanneries and footwear factories. The raw materials of the tanning industry, hides and skins, constitute the largest proportion of the cost of production, and it is ' only natural that the improvement of these valuable raw materials should be given primary attention by any leather scientist. Until only a few years ago, however, the South African hide and skin industry was at a serious ·disadvantage in that it had to base recommendations for improved production methods almost exclusively on overseas experience and practice. The importance of the differences existing between South Africa and European or American countries with regard to climate, slaughtering, hide and skin production in general, transport and sale, however, necessitates a different approach to our specific problems. The overseas hide and skin industry has had, since the beginning of this century, the support and particularly the guidance of scientific research; but it was not until 1935, when, through the support of the Hide and Skin advisory Board, Prof. W. F. Barker founded the original Tanning, Hides and Skins Research Department at Rhodes University College, Grahamstown, that science actively entered the field of hide and skin production in this country. Much of the work done had of course to be based on the results obtained by overseas research institutions, and the adaptation of such results to suit our own problems for some time formed a considerable part of the investigations undertaken. This thesis embodies the results of work undertaken by the writer since 1943 on specific problems of the South African hide and skin industry. Much of the work has already received publication through the Circulars and Journals of this Institute, but it is embodied here again in order to maintain the continuity. The attitude throughout has been to evolve methods of production suited to our own conditions, and the adoption of the recommendations contained in this thesis should lead to improvement in the quality of our hides and skins. Much still remains to be done, and it is the sincere hope of the writer that this work will stimulate and form the basis for subsequent investigations. For that reason more or less detailed descriptions are given of all experiments conducted, and the theory of curing in its relation to tanning is briefly discussed . The literature in each of the four Parts has been attached at the end of that Part to facilitate reference work. At the same time, however, the writer kept in mind the requirements of the trade itself, therefore much of the work is discussed in popular terms. It is hoped that the correct balance between the two extremes has been arrived at.
  • Full Text:
  • 1
  • Disclaimer
  • Privacy
  • Copyright
  • Contact