A community–wide trophic structure analysis in intertidal ecosystems on the south coast of South Africa
- Authors: Gusha, Molline Natanah C
- Date: 2018
- Subjects: Food chains (Ecology) , Coastal ecology -- South Africa , Intertidal ecology -- South Africa , Marine animals -- Climatic factors -- South Africa , Marine animals -- Food -- South Africa , Marine animals -- Habitat -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/63312 , vital:28392
- Description: Coastal ecosystems are more than microhabitats for marine species. Acting as atmospheric carbon filters, species in coastal environments are directly and/or indirectly associated with transferring organic carbon to species at higher trophic levels. However, the progressing change in global climatic conditions has created the need to assess the consequences of the shifting conditions on both direct and indirect interactions of physical and biological parameters at species and/or community levels. From these perturbations, the effects of biotic homogenization on ecosystem functioning and resilience can also be realised. Herein, I discuss the effects of temperature, nutrients, biotic interactions and habitat characteristics on community dynamics within intertidal rock pool systems on the south coast of South Africa using complementary qualitative and quantitative analytical methods. Seasonality had a significant impact on rock pool species with changes in composition and higher richness in winter than summer. The first two axes of the Canonical Correspondence Analysis (CCA) of the plant and animal communities each explained ~20% of the relationship between physico-chemical parameters and biological variables. The CCA highlighted that seasonal shifts in chlorophyll-a, conductivity, salinity, water depth, surface area and substratum type indirectly influenced species composition. For example, pools with heterogenous substratum comprising a mixture of sand and rock exhibited higher species diversity than homogenously bedded pools. Furthermore, a Bayesian analysis of community structure based on stable isotope ratios was used to assess how trophic pathways of carbon and nitrogen elements reflected community composition and richness. Isotopic biplots showed an increase in food web size, food chain length and the trophic positions of fish and some gastropods in winter compared to summer. There was greater dietary overlap among species in larger pools. In addition, while isotopic nearest neighbour distance and species evenness also showed a positive increase with pool size in summer, the same metrics were almost constant across all pool sizes in winter. These changes in food web packing and species evenness suggest seasonal preferences or migration of species in summer from small pools to larger pools with stable physico-chemical parameters. Furthermore, the presence of fish was seen to promote trophic diversity within some pools. The results from laboratory microcosm grazing experiments demonstrated significant direct and indirect effects of temperature and nutrients within plankton communities. Copepod grazing had an indirect positive influence on phytoplankton biomass and size structure while the interactive effects of temperature and nutrients had contrasting effects on both phytoplankton communities and copepod biomass. Shifts in water chemistry and nutrient treatments were also observed in the presence of copepods. Phosphate addition had a recognisable impact on plankton communities. The presented synthesis of the literature mainly highlighted that positive effects at one trophic level do not always positively cascade into the next trophic level which is evidence of complex interactive biotic, habitat and water chemistry effects within these intertidal ecosystems. Thus, to further understand cascading effects or community structure functioning in general, there may be a need to incorporate and understand species functional traits and how they contribute to trophic diversity, community restructuring and functioning in coastal habitats.
- Full Text:
- Date Issued: 2018
- Authors: Gusha, Molline Natanah C
- Date: 2018
- Subjects: Food chains (Ecology) , Coastal ecology -- South Africa , Intertidal ecology -- South Africa , Marine animals -- Climatic factors -- South Africa , Marine animals -- Food -- South Africa , Marine animals -- Habitat -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/63312 , vital:28392
- Description: Coastal ecosystems are more than microhabitats for marine species. Acting as atmospheric carbon filters, species in coastal environments are directly and/or indirectly associated with transferring organic carbon to species at higher trophic levels. However, the progressing change in global climatic conditions has created the need to assess the consequences of the shifting conditions on both direct and indirect interactions of physical and biological parameters at species and/or community levels. From these perturbations, the effects of biotic homogenization on ecosystem functioning and resilience can also be realised. Herein, I discuss the effects of temperature, nutrients, biotic interactions and habitat characteristics on community dynamics within intertidal rock pool systems on the south coast of South Africa using complementary qualitative and quantitative analytical methods. Seasonality had a significant impact on rock pool species with changes in composition and higher richness in winter than summer. The first two axes of the Canonical Correspondence Analysis (CCA) of the plant and animal communities each explained ~20% of the relationship between physico-chemical parameters and biological variables. The CCA highlighted that seasonal shifts in chlorophyll-a, conductivity, salinity, water depth, surface area and substratum type indirectly influenced species composition. For example, pools with heterogenous substratum comprising a mixture of sand and rock exhibited higher species diversity than homogenously bedded pools. Furthermore, a Bayesian analysis of community structure based on stable isotope ratios was used to assess how trophic pathways of carbon and nitrogen elements reflected community composition and richness. Isotopic biplots showed an increase in food web size, food chain length and the trophic positions of fish and some gastropods in winter compared to summer. There was greater dietary overlap among species in larger pools. In addition, while isotopic nearest neighbour distance and species evenness also showed a positive increase with pool size in summer, the same metrics were almost constant across all pool sizes in winter. These changes in food web packing and species evenness suggest seasonal preferences or migration of species in summer from small pools to larger pools with stable physico-chemical parameters. Furthermore, the presence of fish was seen to promote trophic diversity within some pools. The results from laboratory microcosm grazing experiments demonstrated significant direct and indirect effects of temperature and nutrients within plankton communities. Copepod grazing had an indirect positive influence on phytoplankton biomass and size structure while the interactive effects of temperature and nutrients had contrasting effects on both phytoplankton communities and copepod biomass. Shifts in water chemistry and nutrient treatments were also observed in the presence of copepods. Phosphate addition had a recognisable impact on plankton communities. The presented synthesis of the literature mainly highlighted that positive effects at one trophic level do not always positively cascade into the next trophic level which is evidence of complex interactive biotic, habitat and water chemistry effects within these intertidal ecosystems. Thus, to further understand cascading effects or community structure functioning in general, there may be a need to incorporate and understand species functional traits and how they contribute to trophic diversity, community restructuring and functioning in coastal habitats.
- Full Text:
- Date Issued: 2018
A comparative analysis of environmental policies of South African universities
- Authors: Gyan, Cecilia Adwoa
- Date: 2006
- Subjects: Environmental education -- South Africa , Sustainable development -- Study and teaching , Education, Higher -- South Africa , Universities and colleges -- Environmental aspects , Environmental policy -- South Africa , Campus planning -- Environmental aspects -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4773 , http://hdl.handle.net/10962/d1008067 , Environmental education -- South Africa , Sustainable development -- Study and teaching , Education, Higher -- South Africa , Universities and colleges -- Environmental aspects , Environmental policy -- South Africa , Campus planning -- Environmental aspects -- South Africa
- Description: There has been ongoing global concern on environmental issues and which is supposed to have moved down into smaller institutions and areas through local agenda 2l. Environmental issues are associated not only with care for the environment but also sustainable development. Various universities are beginning to strive for sustainable development and care for the environment. Some universities are therefore integrating care for the environment in their curricula and in their daily operations on campus. The greening of higher educational institutions as models is important as they are the seat for research and training of undergraduates who will become future leaders and policymakers and caretakers of the environment. It is therefore important for undergraduates to be exposed to greening processes in operations, research and curricula whilst still on campus. This study examines the process of formulating a policy and applies that to forming an environmental policy. The study involved a comparative analysis of environmental policies of various tertiary educational institutions from different countries. The study focused on how many universities in South Africa have environmental policies and how the universities which have environmental policies went about their formulation process. The study further examines the duration of the formulation process and the constraints encountered by universities. The study then reviews strategies on how the environmental policy is being implemented and how effective the implementation process is practically and the constraints these institutions face. The findings of the study reveal that few universities ill South Africa have an environmental policy. The universities are making efforts in their implementation process however, not all the principles found in the policies are being implemented effectively as there are no environmental management systems in place and there are no measurable objectives and targets set for proper evaluation of the success or failure of the policy.
- Full Text:
- Date Issued: 2006
- Authors: Gyan, Cecilia Adwoa
- Date: 2006
- Subjects: Environmental education -- South Africa , Sustainable development -- Study and teaching , Education, Higher -- South Africa , Universities and colleges -- Environmental aspects , Environmental policy -- South Africa , Campus planning -- Environmental aspects -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4773 , http://hdl.handle.net/10962/d1008067 , Environmental education -- South Africa , Sustainable development -- Study and teaching , Education, Higher -- South Africa , Universities and colleges -- Environmental aspects , Environmental policy -- South Africa , Campus planning -- Environmental aspects -- South Africa
- Description: There has been ongoing global concern on environmental issues and which is supposed to have moved down into smaller institutions and areas through local agenda 2l. Environmental issues are associated not only with care for the environment but also sustainable development. Various universities are beginning to strive for sustainable development and care for the environment. Some universities are therefore integrating care for the environment in their curricula and in their daily operations on campus. The greening of higher educational institutions as models is important as they are the seat for research and training of undergraduates who will become future leaders and policymakers and caretakers of the environment. It is therefore important for undergraduates to be exposed to greening processes in operations, research and curricula whilst still on campus. This study examines the process of formulating a policy and applies that to forming an environmental policy. The study involved a comparative analysis of environmental policies of various tertiary educational institutions from different countries. The study focused on how many universities in South Africa have environmental policies and how the universities which have environmental policies went about their formulation process. The study further examines the duration of the formulation process and the constraints encountered by universities. The study then reviews strategies on how the environmental policy is being implemented and how effective the implementation process is practically and the constraints these institutions face. The findings of the study reveal that few universities ill South Africa have an environmental policy. The universities are making efforts in their implementation process however, not all the principles found in the policies are being implemented effectively as there are no environmental management systems in place and there are no measurable objectives and targets set for proper evaluation of the success or failure of the policy.
- Full Text:
- Date Issued: 2006
A comparative analysis of Java and .NET mobile development environments for supporting mobile services
- Authors: Zhao, Xiaogeng
- Date: 2003 , 2013-05-23
- Subjects: Microsoft .NET , Java (Computer program language) , Mobile computing , Wireless communication systems
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4578 , http://hdl.handle.net/10962/d1003064 , Microsoft .NET , Java (Computer program language) , Mobile computing , Wireless communication systems
- Description: With the rapid development of wireless technologies, traditional mobile devices, such as pagers and cellular phones, have evolved from a purely communications and messaging-oriented medium to one that supports mobile data communication in general and acts as an application platform. As shown in a recent survey conducted by MDA, easy access to the present-day wireless Internet has resulted in mobile devices gaining more and more attention and popularity. The growth of and demand for mobile Web applications is expected to increase rapidly in the near future, as a range of software companies and mobile device manufacturers release increasingly accessible tools for creating mobile Web application and services. From a variety of possible development environments of this kind, the author has selected and examined two leading contenders, the J2ME and the Microsoft .NET mobile Web application development environments. This document reports the product life cycle of pilot mobile web applications, designed and implemented in each host environment in tum. A feature-by-feature investigation and comparison of the J2ME and .NET environments was carried out, covering the range of issues necessary for a complete mobile Web application development life cycle. The resulting analysis addresses features and efficiencies of the application development environment and the target deployment environment, the degree to which the resultant services are compatible on a variety of platforms, and the ease with which applications can be designed to be extensible. The thesis offers an objective evaluation of the J2ME and the .NET mobile development environments, which highlights their strengths and weaknesses, and suggests guidelines for designing, creating, and deploying high quality mobile Web applications. The research uncovers no clear winner across all categories assessed. J2ME currently favours situations in which bandwidth is limited and client side processing power is relatively sufficient, it exerts the processing power of mobile devices over distributed network environments. .NET requires a less constrained network throughput, but performs adequately on clients with more limited processing power, supports a more diverse target platform range, and offers a more efficient, in terms of development time, development environment. Both technologies are likely to receive significant user support for some time. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
- Date Issued: 2003
- Authors: Zhao, Xiaogeng
- Date: 2003 , 2013-05-23
- Subjects: Microsoft .NET , Java (Computer program language) , Mobile computing , Wireless communication systems
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4578 , http://hdl.handle.net/10962/d1003064 , Microsoft .NET , Java (Computer program language) , Mobile computing , Wireless communication systems
- Description: With the rapid development of wireless technologies, traditional mobile devices, such as pagers and cellular phones, have evolved from a purely communications and messaging-oriented medium to one that supports mobile data communication in general and acts as an application platform. As shown in a recent survey conducted by MDA, easy access to the present-day wireless Internet has resulted in mobile devices gaining more and more attention and popularity. The growth of and demand for mobile Web applications is expected to increase rapidly in the near future, as a range of software companies and mobile device manufacturers release increasingly accessible tools for creating mobile Web application and services. From a variety of possible development environments of this kind, the author has selected and examined two leading contenders, the J2ME and the Microsoft .NET mobile Web application development environments. This document reports the product life cycle of pilot mobile web applications, designed and implemented in each host environment in tum. A feature-by-feature investigation and comparison of the J2ME and .NET environments was carried out, covering the range of issues necessary for a complete mobile Web application development life cycle. The resulting analysis addresses features and efficiencies of the application development environment and the target deployment environment, the degree to which the resultant services are compatible on a variety of platforms, and the ease with which applications can be designed to be extensible. The thesis offers an objective evaluation of the J2ME and the .NET mobile development environments, which highlights their strengths and weaknesses, and suggests guidelines for designing, creating, and deploying high quality mobile Web applications. The research uncovers no clear winner across all categories assessed. J2ME currently favours situations in which bandwidth is limited and client side processing power is relatively sufficient, it exerts the processing power of mobile devices over distributed network environments. .NET requires a less constrained network throughput, but performs adequately on clients with more limited processing power, supports a more diverse target platform range, and offers a more efficient, in terms of development time, development environment. Both technologies are likely to receive significant user support for some time. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
- Date Issued: 2003
A comparative bioinformatic analysis of zinc binuclear cluster proteins
- Authors: Mthombeni, Jabulani S
- Date: 2005
- Subjects: Bioinformatics , Zinc proteins , GABA
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4004 , http://hdl.handle.net/10962/d1004064 , Bioinformatics , Zinc proteins , GABA
- Description: Members of the zinc binuclear cluster family are important fungal transcriptional regulators sharing a common DNA binding domain. Da181p is a pleotropic zinc binuclear cluster protein involved in the induction of the UGA genes required for the γ-aminobutyrate nitrogen catabolic pathway in Saccharomyces cerevisiae. The zinc binuclear cluster domain is indispensable for function in Da181p and little is known about other domains in this protein. The aim of the study was to explore the zinc binuclear cluster protein family using comparative bioinformatics as a complement to biochemical and structural approaches. A database of all zinc binuclear cluster proteins was composed. A total of 118 zinc binuclear proteins are reported in this work. Thirty nine previously unidentified zinc binuclear cluster proteins were found. Four homologues of Da181p were identified by homology searching. Important sequence motifs were identified in the aligned sequences of Da181p and its homologues. The coiled coil motif found in the Ga14p zinc binuclear cluster protein could not be identified in Da181p and its homologues. This suggested that Da181p did not dimerise through this structural motif as other zinc binuclear cluster proteins. Solvent accessible site that could be phosphorylated by protein kinase C or casein kinase II and the role of such sites in the possible regulation of Da181p function were discussed.
- Full Text:
- Date Issued: 2005
- Authors: Mthombeni, Jabulani S
- Date: 2005
- Subjects: Bioinformatics , Zinc proteins , GABA
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4004 , http://hdl.handle.net/10962/d1004064 , Bioinformatics , Zinc proteins , GABA
- Description: Members of the zinc binuclear cluster family are important fungal transcriptional regulators sharing a common DNA binding domain. Da181p is a pleotropic zinc binuclear cluster protein involved in the induction of the UGA genes required for the γ-aminobutyrate nitrogen catabolic pathway in Saccharomyces cerevisiae. The zinc binuclear cluster domain is indispensable for function in Da181p and little is known about other domains in this protein. The aim of the study was to explore the zinc binuclear cluster protein family using comparative bioinformatics as a complement to biochemical and structural approaches. A database of all zinc binuclear cluster proteins was composed. A total of 118 zinc binuclear proteins are reported in this work. Thirty nine previously unidentified zinc binuclear cluster proteins were found. Four homologues of Da181p were identified by homology searching. Important sequence motifs were identified in the aligned sequences of Da181p and its homologues. The coiled coil motif found in the Ga14p zinc binuclear cluster protein could not be identified in Da181p and its homologues. This suggested that Da181p did not dimerise through this structural motif as other zinc binuclear cluster proteins. Solvent accessible site that could be phosphorylated by protein kinase C or casein kinase II and the role of such sites in the possible regulation of Da181p function were discussed.
- Full Text:
- Date Issued: 2005
A comparative economic analysis of small scale tobacco production under contract and non-contract farming : the case of Marondera rural district, Mashonaland East province, Zimbabwe
- Authors: Ruzhani, Freddy
- Date: 2015
- Subjects: Farms, Small -- Zimbabwe Tobacco industry -- Zimbabwe Farmers -- Zimbabwe
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/12653 , vital:39296
- Description: Constitutionalism and separation of powers is the most dynamic topic worldwide. Montesquieu, the French philosopher is credited with the doctrine of separation of powers. Various countries adopted the doctrine and modified it, in order to fit their systems of governments. The reason behind is that there is no universally recognized model of separation of powers or one size fit all. Countries apply this doctrine differently in a fashion that fits their domestic laws and constitutional requirements. Montesquieu gave a classic exposition and the rationale for separation of powers in one of his well-celebrated work “The Spirit of Laws”. The concept of separation of powers emerged premised on the theory that the arms of state namely, the judiciary, the legislature and the executive, should operate within their providence without one interfering with the other. From the South African perspective, the Constitution of South Africa of 1996 requires separation of powers even though it is not explicitly so stated in the text. This research examines the unique South African model of separation of powers and how the courts have navigated through it from the time the Constitution was promulgated. It seeks to establish whether or not a South African model of separation of powers has come to the fore. The research further examines the problem of interference amongst the arms of state and mechanism of checks and balances which can be applied to prevent or minimise such interference. In doing so, the study pursued a desktop survey of primary and secondary materials, including scientific literature, legislation, courts’ jurisprudence, and official documents. A comparative perspective was also made in order to learn from the experiences of other jurisdictions where the doctrine is applied. The findings reveal that South Africa has a unique model of separation of powers. The model was learned and enriched from various foreign jurisdictions. The courts have contributed enormously to this model, which contrive to be fluid and living.
- Full Text:
- Date Issued: 2015
- Authors: Ruzhani, Freddy
- Date: 2015
- Subjects: Farms, Small -- Zimbabwe Tobacco industry -- Zimbabwe Farmers -- Zimbabwe
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/12653 , vital:39296
- Description: Constitutionalism and separation of powers is the most dynamic topic worldwide. Montesquieu, the French philosopher is credited with the doctrine of separation of powers. Various countries adopted the doctrine and modified it, in order to fit their systems of governments. The reason behind is that there is no universally recognized model of separation of powers or one size fit all. Countries apply this doctrine differently in a fashion that fits their domestic laws and constitutional requirements. Montesquieu gave a classic exposition and the rationale for separation of powers in one of his well-celebrated work “The Spirit of Laws”. The concept of separation of powers emerged premised on the theory that the arms of state namely, the judiciary, the legislature and the executive, should operate within their providence without one interfering with the other. From the South African perspective, the Constitution of South Africa of 1996 requires separation of powers even though it is not explicitly so stated in the text. This research examines the unique South African model of separation of powers and how the courts have navigated through it from the time the Constitution was promulgated. It seeks to establish whether or not a South African model of separation of powers has come to the fore. The research further examines the problem of interference amongst the arms of state and mechanism of checks and balances which can be applied to prevent or minimise such interference. In doing so, the study pursued a desktop survey of primary and secondary materials, including scientific literature, legislation, courts’ jurisprudence, and official documents. A comparative perspective was also made in order to learn from the experiences of other jurisdictions where the doctrine is applied. The findings reveal that South Africa has a unique model of separation of powers. The model was learned and enriched from various foreign jurisdictions. The courts have contributed enormously to this model, which contrive to be fluid and living.
- Full Text:
- Date Issued: 2015
A comparative kinetic study of the reaction between chromium nitrate solutions and the carboxyl groups of acetate and collage
- Authors: Russell, Allan Edward
- Date: 1962
- Subjects: Chemical kinetics , Chromium , Spectrophotometry , Electrophoresis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4493 , http://hdl.handle.net/10962/d1013101
- Description: The kinetics of the coordination reaction between the carboxyl group of the acetate radical and the trivalent chromium ion has been examined by independent methods at a temperature selected to yield reasonably accurate rate data. The study has been extended to an examination of the rate of chromium "fixation" by the carboxyl groups of hide collagen in a series of miniature tannages carried out under similar conditions for comparative purposes. The effect of olation of the chromium ions in solution on the kinetics of t he coordination reaction has also been examined. The rate of coordination of the acetate radical was followed by solvent extraction and spectrophotometric techniques over a range of concentration and pH levels. The rate data revealed a reaction having typical mass-action characteristics, the rate of reaction depending on the concentration levels of the chromium ion and the ionised acetate radical. An attempt made to distinguish a differential reaction rate in the case of a parallel reaction series using boiled and aged chromium nitrate reactant solutions, failed to reveal any significant differences between the series. The reactant solutions gave absorption spectra characteristic of the trivalent chromium ion with maxima in the 420 mµ and 570 mµ wavelength regions. The changes in optical density occurring in the vicinity of the maxima were followed spectrophotometrically, the height of the 570 mµ being found to increase during the course of reaction, while the height of the 420 mµ peak decreased. The variation in optical density at the 570 mµ peak was found to be directly related to the increase in concentration of the product complex in solution in accordance with the Baer-Bougher law, while the decrease in the height of the 420 mµ peak was related to the properties of unolated OH groups associated with the chromium complex as governed by pH and olation changes during the course of reaction. Boiled and aged chromium nitrate solutions gave reactant solutions having initial optical densities greater than those of the correspending fresh reactant solutions at the 570 mµ peak, and less than those of the fresh solutions at the 420 mµ peak. During the course of reaction, however, the two series converged to the same values. The equilibrium reaction solutions were subjected to paper electrophoretic study which indicated that all tho chromium was present in the form of cationic species. This finding was in accordance with stoicheiometric indications in the solvent extraction studies where coordination in a l : 1 ratio was reflected, giving rise to positively charged complex ions only. Making due allowance for band spreading the numbers of species predicted from the kinetic studies correspond with the electrophoretic patterns found. Application of the classical second order kinetic expression to the solvent extraction rate data, yielded plots having two distinctly linear sections, apparently indicating consecutive second order processes occurring in solution, contrary to the findings of previous workers who assign a first order mechanism to the reaction. This finding was consistent with the view that in the case of both the fresh and aged series, reaction consisted of successive coordination of an acetate radical to each chromium atom of a diol complex. Second order rate "constants" were calculated for each step and their dependency on pH level demonstrated. The findings of Hamm et al that these were first order reactions independent of acetate co'ncentration are believed to be due to their use of a large excess of acetate in their experiments. The kinetic study was further extended to an examination of the rate of "fixation"of trivalent chromium by the carboxyl groups of hide collagen under comparable conditions in a series of miniaturv tanning experiments in which the tannage substrate was provided in each of two physical forms:- (a) As hide powder where surface development was large, and (b) as prepared pelt pieces in which the fibrous weave pattern was retained. In view of the heterogeneity of the tannage systems, remarkable similarity was observed in the reaction course when compared with that of the acetate coordination studies, particularly in the case of the hide powder tannages. The dependency of the tannage rate data upon concentration and pH conditions was also found to be the same as in the case of the pure chemical system. The exact correlation between the rate data for the tannage and pure chemical systems was demonstrated by means of correlation plots. Close correlation was revealed in the case of hide powder tannage while the smaller degree of correlation observed in the case of the pelt tannage systems was attributed to the modifying effects of diffusion, particularly on the initial reaction velocity. The effect of using boiled and aged chromium solutions in the tannages was to increase the initial rate of chroniill!l "fixation" apparently due to tho coordination of a dial species at each coordination site. After the initial reaction period, the two series showed a tendency to converge as in the case of the spectrophotometric studies on the acetate reaction. The convergence trend was regarded as indicative of the tendency for the chromium in fresh solutions to under go rapid olation to the ame level as in the boiled and aged solutions. The experimental observations made on the various systems lead to the following conclusions:- (a) The mechanism of coordination of the acetate radical ttrivalent chromium appears to involve the successive coordination of ligand to each of the chromium atoms of a diol complex, both coordination steps proceeding by second order reaction mechanisms. (b) At the pH levels at which the reaction is carried out, the formation of elated bodios is rapid so that reaction in the case of both fresh and aged solutions essentially occurs between an elated species and the ionised acetate radical. (c) Modificati0ns in the absorption spectrum of the reactant solution at the 570 mµ peak are directly related to coordination, while changes at the 420 mµ peak are related to the formation of loosely-bound hydroxo chromium compounds, the concentrations of which depend on the pH level. (d) The mechanism of chromium fixation in hide is essentially similar to that operating in the case of coordination of the acetate radical to chromium, involving attachment of chromium to the side chain acid r sidues of collagen. (e ) The effect of olation is to enhance the rate of chromium fixation by hide protein during the initial reaction stages and to render possible bridge formation between adjacent side chains by secondary coordination during the latter reaction stages. (f) Where pelt pieces are used instead of hide powder, the initial rate of chromium fixation is dominated by the rate of diffusion of chromium into the fibrous structure. It should be stressed that the observations made on the various reaction systems cannot be regarded as exhaustive and the conclusions are subject to further confirmation. Consequently, the present study is essentially of a preliminary nature, but it is felt that the need for further investigation along similar lines has been demonstrated.
- Full Text:
- Date Issued: 1962
- Authors: Russell, Allan Edward
- Date: 1962
- Subjects: Chemical kinetics , Chromium , Spectrophotometry , Electrophoresis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4493 , http://hdl.handle.net/10962/d1013101
- Description: The kinetics of the coordination reaction between the carboxyl group of the acetate radical and the trivalent chromium ion has been examined by independent methods at a temperature selected to yield reasonably accurate rate data. The study has been extended to an examination of the rate of chromium "fixation" by the carboxyl groups of hide collagen in a series of miniature tannages carried out under similar conditions for comparative purposes. The effect of olation of the chromium ions in solution on the kinetics of t he coordination reaction has also been examined. The rate of coordination of the acetate radical was followed by solvent extraction and spectrophotometric techniques over a range of concentration and pH levels. The rate data revealed a reaction having typical mass-action characteristics, the rate of reaction depending on the concentration levels of the chromium ion and the ionised acetate radical. An attempt made to distinguish a differential reaction rate in the case of a parallel reaction series using boiled and aged chromium nitrate reactant solutions, failed to reveal any significant differences between the series. The reactant solutions gave absorption spectra characteristic of the trivalent chromium ion with maxima in the 420 mµ and 570 mµ wavelength regions. The changes in optical density occurring in the vicinity of the maxima were followed spectrophotometrically, the height of the 570 mµ being found to increase during the course of reaction, while the height of the 420 mµ peak decreased. The variation in optical density at the 570 mµ peak was found to be directly related to the increase in concentration of the product complex in solution in accordance with the Baer-Bougher law, while the decrease in the height of the 420 mµ peak was related to the properties of unolated OH groups associated with the chromium complex as governed by pH and olation changes during the course of reaction. Boiled and aged chromium nitrate solutions gave reactant solutions having initial optical densities greater than those of the correspending fresh reactant solutions at the 570 mµ peak, and less than those of the fresh solutions at the 420 mµ peak. During the course of reaction, however, the two series converged to the same values. The equilibrium reaction solutions were subjected to paper electrophoretic study which indicated that all tho chromium was present in the form of cationic species. This finding was in accordance with stoicheiometric indications in the solvent extraction studies where coordination in a l : 1 ratio was reflected, giving rise to positively charged complex ions only. Making due allowance for band spreading the numbers of species predicted from the kinetic studies correspond with the electrophoretic patterns found. Application of the classical second order kinetic expression to the solvent extraction rate data, yielded plots having two distinctly linear sections, apparently indicating consecutive second order processes occurring in solution, contrary to the findings of previous workers who assign a first order mechanism to the reaction. This finding was consistent with the view that in the case of both the fresh and aged series, reaction consisted of successive coordination of an acetate radical to each chromium atom of a diol complex. Second order rate "constants" were calculated for each step and their dependency on pH level demonstrated. The findings of Hamm et al that these were first order reactions independent of acetate co'ncentration are believed to be due to their use of a large excess of acetate in their experiments. The kinetic study was further extended to an examination of the rate of "fixation"of trivalent chromium by the carboxyl groups of hide collagen under comparable conditions in a series of miniaturv tanning experiments in which the tannage substrate was provided in each of two physical forms:- (a) As hide powder where surface development was large, and (b) as prepared pelt pieces in which the fibrous weave pattern was retained. In view of the heterogeneity of the tannage systems, remarkable similarity was observed in the reaction course when compared with that of the acetate coordination studies, particularly in the case of the hide powder tannages. The dependency of the tannage rate data upon concentration and pH conditions was also found to be the same as in the case of the pure chemical system. The exact correlation between the rate data for the tannage and pure chemical systems was demonstrated by means of correlation plots. Close correlation was revealed in the case of hide powder tannage while the smaller degree of correlation observed in the case of the pelt tannage systems was attributed to the modifying effects of diffusion, particularly on the initial reaction velocity. The effect of using boiled and aged chromium solutions in the tannages was to increase the initial rate of chroniill!l "fixation" apparently due to tho coordination of a dial species at each coordination site. After the initial reaction period, the two series showed a tendency to converge as in the case of the spectrophotometric studies on the acetate reaction. The convergence trend was regarded as indicative of the tendency for the chromium in fresh solutions to under go rapid olation to the ame level as in the boiled and aged solutions. The experimental observations made on the various systems lead to the following conclusions:- (a) The mechanism of coordination of the acetate radical ttrivalent chromium appears to involve the successive coordination of ligand to each of the chromium atoms of a diol complex, both coordination steps proceeding by second order reaction mechanisms. (b) At the pH levels at which the reaction is carried out, the formation of elated bodios is rapid so that reaction in the case of both fresh and aged solutions essentially occurs between an elated species and the ionised acetate radical. (c) Modificati0ns in the absorption spectrum of the reactant solution at the 570 mµ peak are directly related to coordination, while changes at the 420 mµ peak are related to the formation of loosely-bound hydroxo chromium compounds, the concentrations of which depend on the pH level. (d) The mechanism of chromium fixation in hide is essentially similar to that operating in the case of coordination of the acetate radical to chromium, involving attachment of chromium to the side chain acid r sidues of collagen. (e ) The effect of olation is to enhance the rate of chromium fixation by hide protein during the initial reaction stages and to render possible bridge formation between adjacent side chains by secondary coordination during the latter reaction stages. (f) Where pelt pieces are used instead of hide powder, the initial rate of chromium fixation is dominated by the rate of diffusion of chromium into the fibrous structure. It should be stressed that the observations made on the various reaction systems cannot be regarded as exhaustive and the conclusions are subject to further confirmation. Consequently, the present study is essentially of a preliminary nature, but it is felt that the need for further investigation along similar lines has been demonstrated.
- Full Text:
- Date Issued: 1962
A comparative mineralogical and geochemical study of manganese deposits in the Postmasburg Manganese Field, South Africa
- Authors: Thokoa, Mamello
- Date: 2020
- Subjects: Manganese ores -- South Africa -- Postmasburg , Geology -- South Africa -- Postmasburg
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167609 , vital:41496
- Description: The Postmasburg Manganese Field (PMF), located in the Northern Cape Province of South Africa, is host to some of the largest deposits of iron and manganese metal in the world. These deposits are restricted to a geographical area known as the Maremane Dome, an anticlinal structure defined by folded dolostones of the Campbellrand Subgroup and overlying ironformations of the Asbestos Hills Subgroup of the Neoarchaean-Palaeproterozoic Transvaal Supergroup. Manganese ores associated with the Maremane Dome have been divided into two major classes in the literature: the Wolhaarkop breccia-hosted massive ores of the Eastern Belt, as well as the shale-associated ores of the Western Belt. The Eastern Belt ores have been classed as siliceous in nature, while the Western Belt deposits are reported to be typically ferruginous. These divisions were made based on their varying bulk chemical and mineralogical compositions in conjunction with their different stratigraphic sub-settings. Presently, both deposit types are explained as variants of supergene mineralisation that would have formed through a combination of intense ancient lateritic weathering in the presence of oxygen, extreme residual enrichments in Mn (and Fe), and accumulations in karstic depressions at the expense of underlying manganiferous dolostones. This study revisits these deposits and their origins by sampling representative end-member examples of both Eastern Belt and Western Belt manganese ores in both drillcore (localities Khumani, McCarthy and Leeuwfontein), and outcrop sections (locality Bishop). In an attempt to provide new insights into the processes responsible for the genesis of these deposits, the possibility of hydrothermal influences and associated metasomatic replacement processes is explored in this thesis. This was achieved using standard petrographic and mineralogical techniques (transmitted and reflected light microscopy, XRD , SEM-EDS and EMPA), coupled with bulk-rock geochemical analysis of the same samples using a combination of XRF and LAICP- MS analyses. Combination of field observations, petrographic and mineralogical results, and geochemical data allowed for the re-assessment of the different ore types encountered in the field. Comparative considerations made between the bulk geochemistry of the different end-member ore types revealed no clear-cut compositional distinctions and therefore do not support existing classifications between siliceous (Eastern Belt) and ferruginous (Western Belt) ores. This is supported by trace and REE element data as well, when normalised against average shale. The geochemistry reflects the bulk mineralogy of the ores which is broadly comparable, whereby braunite and hematite appear to be dominant co-existing minerals in both Eastern Belt (Khumani) and Western Belt (Bishop) ore. In the case of the McCarthy locality, manganese ore is cryptomelane-rich and appears to have involved recent supergene overprint over Eastern Belt type ore, whereas the Leeuwfontein ores are far more ferruginous than at any other locality studied and therefore represent a more complex, hybrid type of oxide-rich Mn mineralisation (mainly bixbyitic) within massive hematite iron ore. In terms of gangue mineralogy, the ores share some close similarities through the omnipresence of barite, and the abundance of alkalirich silicate minerals. Eastern Belt ores contain abundant albite and serandite whereas the main alkali-rich phase in Western Belt ores is the mineral ephesite. In both cases, Na contents are therefore high at several wt% levels registered in selected samples. The afore-mentioned alkali enrichments have been variously reported for both these deposit types. The occurrence of high alkalis cannot be explained through classic residual or aqueous supergene systems of ore formation, as proposed in prevailing genetic models in the literature. Together with the detection of halogens such as F and Br through SEM-EDS analyses of ore from both belts, the alkali enrichments suggest possible hydrothermal processes of ore formation involving circulation of metalliferous sodic brines. Selected textural evidence from samples from both ore belts lends support to fluid-related models and allow the proposal for a common hydrothermal-replacement model to have been responsible for ore formation across the broader Maremane Dome region.
- Full Text:
- Date Issued: 2020
- Authors: Thokoa, Mamello
- Date: 2020
- Subjects: Manganese ores -- South Africa -- Postmasburg , Geology -- South Africa -- Postmasburg
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167609 , vital:41496
- Description: The Postmasburg Manganese Field (PMF), located in the Northern Cape Province of South Africa, is host to some of the largest deposits of iron and manganese metal in the world. These deposits are restricted to a geographical area known as the Maremane Dome, an anticlinal structure defined by folded dolostones of the Campbellrand Subgroup and overlying ironformations of the Asbestos Hills Subgroup of the Neoarchaean-Palaeproterozoic Transvaal Supergroup. Manganese ores associated with the Maremane Dome have been divided into two major classes in the literature: the Wolhaarkop breccia-hosted massive ores of the Eastern Belt, as well as the shale-associated ores of the Western Belt. The Eastern Belt ores have been classed as siliceous in nature, while the Western Belt deposits are reported to be typically ferruginous. These divisions were made based on their varying bulk chemical and mineralogical compositions in conjunction with their different stratigraphic sub-settings. Presently, both deposit types are explained as variants of supergene mineralisation that would have formed through a combination of intense ancient lateritic weathering in the presence of oxygen, extreme residual enrichments in Mn (and Fe), and accumulations in karstic depressions at the expense of underlying manganiferous dolostones. This study revisits these deposits and their origins by sampling representative end-member examples of both Eastern Belt and Western Belt manganese ores in both drillcore (localities Khumani, McCarthy and Leeuwfontein), and outcrop sections (locality Bishop). In an attempt to provide new insights into the processes responsible for the genesis of these deposits, the possibility of hydrothermal influences and associated metasomatic replacement processes is explored in this thesis. This was achieved using standard petrographic and mineralogical techniques (transmitted and reflected light microscopy, XRD , SEM-EDS and EMPA), coupled with bulk-rock geochemical analysis of the same samples using a combination of XRF and LAICP- MS analyses. Combination of field observations, petrographic and mineralogical results, and geochemical data allowed for the re-assessment of the different ore types encountered in the field. Comparative considerations made between the bulk geochemistry of the different end-member ore types revealed no clear-cut compositional distinctions and therefore do not support existing classifications between siliceous (Eastern Belt) and ferruginous (Western Belt) ores. This is supported by trace and REE element data as well, when normalised against average shale. The geochemistry reflects the bulk mineralogy of the ores which is broadly comparable, whereby braunite and hematite appear to be dominant co-existing minerals in both Eastern Belt (Khumani) and Western Belt (Bishop) ore. In the case of the McCarthy locality, manganese ore is cryptomelane-rich and appears to have involved recent supergene overprint over Eastern Belt type ore, whereas the Leeuwfontein ores are far more ferruginous than at any other locality studied and therefore represent a more complex, hybrid type of oxide-rich Mn mineralisation (mainly bixbyitic) within massive hematite iron ore. In terms of gangue mineralogy, the ores share some close similarities through the omnipresence of barite, and the abundance of alkalirich silicate minerals. Eastern Belt ores contain abundant albite and serandite whereas the main alkali-rich phase in Western Belt ores is the mineral ephesite. In both cases, Na contents are therefore high at several wt% levels registered in selected samples. The afore-mentioned alkali enrichments have been variously reported for both these deposit types. The occurrence of high alkalis cannot be explained through classic residual or aqueous supergene systems of ore formation, as proposed in prevailing genetic models in the literature. Together with the detection of halogens such as F and Br through SEM-EDS analyses of ore from both belts, the alkali enrichments suggest possible hydrothermal processes of ore formation involving circulation of metalliferous sodic brines. Selected textural evidence from samples from both ore belts lends support to fluid-related models and allow the proposal for a common hydrothermal-replacement model to have been responsible for ore formation across the broader Maremane Dome region.
- Full Text:
- Date Issued: 2020
A comparative photostability study of four propyl piperzine-substituted phenothiazines
- Authors: Drummond, Patricia Mary
- Date: 1997
- Subjects: Phenothiazine
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3756 , http://hdl.handle.net/10962/d1003234 , Phenothiazine
- Description: Four structurally related phenothiazines available in South Africa in a variety of dosage forms and as fine chemicals were investigated to ascertain whether their structural differences in terms of the 2-chloro-/ trifluoromethyl-substituents on the phenothiazine nucleus and the methyl-/ ß-hydroxethyl groups on the piperazine ring accouning for the differences in pharmacological activity can be correlated with their photostability².The four propyl piperazine-substituted derivatives are ranked in the following decreasing order of neuroleptic activity: fluphenazine> trifluoperazine> perphenazine > rochlorperazine. In order to assess their photostability an HPLC method was developed and validated for linearity, accuracy and precision, selectivity, limit of detection and quantitation and ruggedness. Preliminary solution photostudies under controlled light conditions (UV, sunlight, fluorescent light) indicated that the rate of degradation followed first-order kinetics with perphenazine the most susceptible to.photodegradation under all light conditions studied. In vitro and in vivo metabolism yielding the 5-sulphoxide and its reported presence on decomposition of the phenothiazines25 led to the development of a synthetic procedure suitable for the sutphoxides of all four derivatives based on the method proposed by Owens et al. in order to provide standards for comparison in the photostudies⁷. Since ICH regulations require that impurities> 0.1 % are examined and identified⁷⁴ and semi-preparative isolation of photoproducts proved unsuccessful, LC-MS having been well documented for structural.elucidation⁷⁵ ⁷⁵ ⁷⁶ ⁷⁷ was used to characterize solution (UV, sunlight, fluorescent light) and preliminary solid (UV) photostudies. The chloroderivatives underwent dechlorination and sulphoxidation with subsequent photosubstitution in the case of prochlorperazine to yield the 2-hydroxy derivative and sulphoxidation of the dechloro-derivative of perphenazine. The sulphoxides of both trifluoperazine and fluphenazine were formed with further oxidation to the respective sulphones occurring. Preliminary solid state (UV) photostudies showed fluphenazine to be the least stable with 30.71 % degradation as opposed to 7.57% for prochlorperazine, 4.28% for perphenazine and 7.10% for trifluoperazine witn sulphoxidation observed to be. the major degradation pathway. Since in vitro metabolism of perazine derivatives is reported to occur via N-oxidation, N-demethylation, sulphoxidation and aromatic hydroxylation¹⁸ it does appear that there is some correlation between metabolic and photoproducts. However the fact that solution (UV) photostudies indicates trifluoperazine to be the most and perphenazine the least stable does not concur with the proposed order of pharmacological activity.
- Full Text:
- Date Issued: 1997
- Authors: Drummond, Patricia Mary
- Date: 1997
- Subjects: Phenothiazine
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3756 , http://hdl.handle.net/10962/d1003234 , Phenothiazine
- Description: Four structurally related phenothiazines available in South Africa in a variety of dosage forms and as fine chemicals were investigated to ascertain whether their structural differences in terms of the 2-chloro-/ trifluoromethyl-substituents on the phenothiazine nucleus and the methyl-/ ß-hydroxethyl groups on the piperazine ring accouning for the differences in pharmacological activity can be correlated with their photostability².The four propyl piperazine-substituted derivatives are ranked in the following decreasing order of neuroleptic activity: fluphenazine> trifluoperazine> perphenazine > rochlorperazine. In order to assess their photostability an HPLC method was developed and validated for linearity, accuracy and precision, selectivity, limit of detection and quantitation and ruggedness. Preliminary solution photostudies under controlled light conditions (UV, sunlight, fluorescent light) indicated that the rate of degradation followed first-order kinetics with perphenazine the most susceptible to.photodegradation under all light conditions studied. In vitro and in vivo metabolism yielding the 5-sulphoxide and its reported presence on decomposition of the phenothiazines25 led to the development of a synthetic procedure suitable for the sutphoxides of all four derivatives based on the method proposed by Owens et al. in order to provide standards for comparison in the photostudies⁷. Since ICH regulations require that impurities> 0.1 % are examined and identified⁷⁴ and semi-preparative isolation of photoproducts proved unsuccessful, LC-MS having been well documented for structural.elucidation⁷⁵ ⁷⁵ ⁷⁶ ⁷⁷ was used to characterize solution (UV, sunlight, fluorescent light) and preliminary solid (UV) photostudies. The chloroderivatives underwent dechlorination and sulphoxidation with subsequent photosubstitution in the case of prochlorperazine to yield the 2-hydroxy derivative and sulphoxidation of the dechloro-derivative of perphenazine. The sulphoxides of both trifluoperazine and fluphenazine were formed with further oxidation to the respective sulphones occurring. Preliminary solid state (UV) photostudies showed fluphenazine to be the least stable with 30.71 % degradation as opposed to 7.57% for prochlorperazine, 4.28% for perphenazine and 7.10% for trifluoperazine witn sulphoxidation observed to be. the major degradation pathway. Since in vitro metabolism of perazine derivatives is reported to occur via N-oxidation, N-demethylation, sulphoxidation and aromatic hydroxylation¹⁸ it does appear that there is some correlation between metabolic and photoproducts. However the fact that solution (UV) photostudies indicates trifluoperazine to be the most and perphenazine the least stable does not concur with the proposed order of pharmacological activity.
- Full Text:
- Date Issued: 1997
A Comparative Study of Bootstrapping Techniques for Inventory Control
- Authors: Frederick, Lauren
- Date: 2020
- Subjects: Computer bootstrapping -- Inventory control
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/48335 , vital:40849
- Description: Setting correct inventory levels is an important business consideration in order to minimise inventory investment while at the same time ensuring sufficient inventory levels to meet customer demand. Inventory management has a significant impact on both financial and customer service aspects of a business. Selecting appropriate inventory levels requires that products’ lead time demand be accurately estimated in order to calculate the reorder point. The purpose of this study was to empirically determine whether bootstrapping methods used to estimate the lead time demand distribution and reorder point calculation could match or even outperform a standard parametric approach. The two bootstrapping methods compared in this research included variations of those presented by Bookbinder and Lordahl [1989] and do Rego and de Mesquita [2015]. These were compared to the standard parametric approach common in practice which makes use of the Normal distribution for modelling lead time demand. The three reorder point calculation methods were each incorporated into the inventory policy simulations using data supplied by a South African automotive spare parts business. The simulations covered a period of twelve months and were repeated for multiple service levels ranging from 70 to 99 percent. Results of the simulations were compared at a high level as well as for groups of items identified using segmentation techniques which considered different item demand and lead time characteristics. Key findings were that the Normal approximation method was far superior in terms of the service level metric, while the variation of the Bookbinder and Lordahl [1989] method adopted in this study presented possible cost benefits at lower service levels.
- Full Text:
- Date Issued: 2020
- Authors: Frederick, Lauren
- Date: 2020
- Subjects: Computer bootstrapping -- Inventory control
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/48335 , vital:40849
- Description: Setting correct inventory levels is an important business consideration in order to minimise inventory investment while at the same time ensuring sufficient inventory levels to meet customer demand. Inventory management has a significant impact on both financial and customer service aspects of a business. Selecting appropriate inventory levels requires that products’ lead time demand be accurately estimated in order to calculate the reorder point. The purpose of this study was to empirically determine whether bootstrapping methods used to estimate the lead time demand distribution and reorder point calculation could match or even outperform a standard parametric approach. The two bootstrapping methods compared in this research included variations of those presented by Bookbinder and Lordahl [1989] and do Rego and de Mesquita [2015]. These were compared to the standard parametric approach common in practice which makes use of the Normal distribution for modelling lead time demand. The three reorder point calculation methods were each incorporated into the inventory policy simulations using data supplied by a South African automotive spare parts business. The simulations covered a period of twelve months and were repeated for multiple service levels ranging from 70 to 99 percent. Results of the simulations were compared at a high level as well as for groups of items identified using segmentation techniques which considered different item demand and lead time characteristics. Key findings were that the Normal approximation method was far superior in terms of the service level metric, while the variation of the Bookbinder and Lordahl [1989] method adopted in this study presented possible cost benefits at lower service levels.
- Full Text:
- Date Issued: 2020
A comparative study of CERBER, MAKTUB and LOCKY Ransomware using a Hybridised-Malware analysis
- Authors: Schmitt, Veronica
- Date: 2019
- Subjects: Microsoft Windows (Computer file) , Data protection , Computer crimes -- Prevention , Computer security , Computer networks -- Security measures , Computers -- Access control , Malware (Computer software)
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/92313 , vital:30702
- Description: There has been a significant increase in the prevalence of Ransomware attacks in the preceding four years to date. This indicates that the battle has not yet been won defending against this class of malware. This research proposes that by identifying the similarities within the operational framework of Ransomware strains, a better overall understanding of their operation and function can be achieved. This, in turn, will aid in a quicker response to future attacks. With the average Ransomware attack taking two hours to be identified, it shows that there is not yet a clear understanding as to why these attacks are so successful. Research into Ransomware is limited by what is currently known on the topic. Due to the limitations of the research the decision was taken to only examined three samples of Ransomware from different families. This was decided due to the complexities and comprehensive nature of the research. The in depth nature of the research and the time constraints associated with it did not allow for proof of concept of this framework to be tested on more than three families, but the exploratory work was promising and should be further explored in future research. The aim of the research is to follow the Hybrid-Malware analysis framework which consists of both static and the dynamic analysis phases, in addition to the digital forensic examination of the infected system. This allows for signature-based findings, along with behavioural and forensic findings all in one. This information allows for a better understanding of how this malware is designed and how it infects and remains persistent on a system. The operating system which has been chosen is the Microsoft Window 7 operating system which is still utilised by a significant proportion of Windows users especially in the corporate environment. The experiment process was designed to enable the researcher the ability to collect information regarding the Ransomware and every aspect of its behaviour and communication on a target system. The results can be compared across the three strains to identify the commonalities. The initial hypothesis was that Ransomware variants are all much like an instant cake box consists of specific building blocks which remain the same with the flavouring of the cake mix being the unique feature.
- Full Text:
- Date Issued: 2019
- Authors: Schmitt, Veronica
- Date: 2019
- Subjects: Microsoft Windows (Computer file) , Data protection , Computer crimes -- Prevention , Computer security , Computer networks -- Security measures , Computers -- Access control , Malware (Computer software)
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/92313 , vital:30702
- Description: There has been a significant increase in the prevalence of Ransomware attacks in the preceding four years to date. This indicates that the battle has not yet been won defending against this class of malware. This research proposes that by identifying the similarities within the operational framework of Ransomware strains, a better overall understanding of their operation and function can be achieved. This, in turn, will aid in a quicker response to future attacks. With the average Ransomware attack taking two hours to be identified, it shows that there is not yet a clear understanding as to why these attacks are so successful. Research into Ransomware is limited by what is currently known on the topic. Due to the limitations of the research the decision was taken to only examined three samples of Ransomware from different families. This was decided due to the complexities and comprehensive nature of the research. The in depth nature of the research and the time constraints associated with it did not allow for proof of concept of this framework to be tested on more than three families, but the exploratory work was promising and should be further explored in future research. The aim of the research is to follow the Hybrid-Malware analysis framework which consists of both static and the dynamic analysis phases, in addition to the digital forensic examination of the infected system. This allows for signature-based findings, along with behavioural and forensic findings all in one. This information allows for a better understanding of how this malware is designed and how it infects and remains persistent on a system. The operating system which has been chosen is the Microsoft Window 7 operating system which is still utilised by a significant proportion of Windows users especially in the corporate environment. The experiment process was designed to enable the researcher the ability to collect information regarding the Ransomware and every aspect of its behaviour and communication on a target system. The results can be compared across the three strains to identify the commonalities. The initial hypothesis was that Ransomware variants are all much like an instant cake box consists of specific building blocks which remain the same with the flavouring of the cake mix being the unique feature.
- Full Text:
- Date Issued: 2019
A comparative study of the comfort related properties of commercial apparel fabrics containing natural and man-made fibres
- Authors: Stoffberg, Marguerite Ester
- Date: 2013
- Subjects: Textile fabrics , Materials -- Thermal properties
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10455 , http://hdl.handle.net/10948/d1020931
- Description: The relationship between the fabric parameters, as independent variables, and the comfort related properties, as dependent variables, of commercial suiting fabrics, containing both natural and man-made fibres, have been studied. The fabric parameters measured in the study were mass, thickness, density, and air permeability. The comfort related properties, tested on a Permetest instrument, included water vapour permeability, water vapour resistance, and thermal resistance, with the moisture permeability index being derived. A total of 26 commercial suiting fabrics, covering a wide range of mass, as well as different fibre types and blends and fabric structures, was tested. The fibres covered, included wool, polyester, viscose, and cotton, while the fabric structures covered were 1x1 plain weave, 2x1 twill and 2x2 twill weave. The objectives of this study were to determine the empirical relationships between the measured fabric properties and the measured comfort related properties, and to determine the role, if any, of fibre type and fabric structure, since many claims are made in practice concerning the relative advantages, in terms of comfort, of a specific fibre type or blend, or fabric structure, over others, some of which being supported by research results. Since the fabrics covered, were commercial and were not engineered so that the different fabric parameters (independent variables) and fibre type and blend, as well as fabric structure could be varied independently of each other, the effects of the various fabric parameters on the fabric comfort related properties were determined and quantified by multiple regression analyses (multi-linear and multi-quadratic), and the best fit regression equations, and contribution of each parameter to the overall fit established. It was found that fabric thickness and fabric mass had the largest effect on the comfort related properties as measured here, fabric mass determining, to a large extent, water vapour permeability, and fabric thickness, thermal resistance. The rest of the fabric parameters included in the study had only a relatively small effect on the measured comfort related properties. The influence of fabric parameters, with particular reference to mass and thickness, on the measured comfort related properties, were much greater than that of fibre type or blend, or fabric structure. It was, therefore, concluded from this study, that the fabric parameters, as opposed to the intrinsic characteristics of a particular fibre, whether natural or man-made, largely determined those fabric comfort related properties measured here.
- Full Text:
- Date Issued: 2013
- Authors: Stoffberg, Marguerite Ester
- Date: 2013
- Subjects: Textile fabrics , Materials -- Thermal properties
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10455 , http://hdl.handle.net/10948/d1020931
- Description: The relationship between the fabric parameters, as independent variables, and the comfort related properties, as dependent variables, of commercial suiting fabrics, containing both natural and man-made fibres, have been studied. The fabric parameters measured in the study were mass, thickness, density, and air permeability. The comfort related properties, tested on a Permetest instrument, included water vapour permeability, water vapour resistance, and thermal resistance, with the moisture permeability index being derived. A total of 26 commercial suiting fabrics, covering a wide range of mass, as well as different fibre types and blends and fabric structures, was tested. The fibres covered, included wool, polyester, viscose, and cotton, while the fabric structures covered were 1x1 plain weave, 2x1 twill and 2x2 twill weave. The objectives of this study were to determine the empirical relationships between the measured fabric properties and the measured comfort related properties, and to determine the role, if any, of fibre type and fabric structure, since many claims are made in practice concerning the relative advantages, in terms of comfort, of a specific fibre type or blend, or fabric structure, over others, some of which being supported by research results. Since the fabrics covered, were commercial and were not engineered so that the different fabric parameters (independent variables) and fibre type and blend, as well as fabric structure could be varied independently of each other, the effects of the various fabric parameters on the fabric comfort related properties were determined and quantified by multiple regression analyses (multi-linear and multi-quadratic), and the best fit regression equations, and contribution of each parameter to the overall fit established. It was found that fabric thickness and fabric mass had the largest effect on the comfort related properties as measured here, fabric mass determining, to a large extent, water vapour permeability, and fabric thickness, thermal resistance. The rest of the fabric parameters included in the study had only a relatively small effect on the measured comfort related properties. The influence of fabric parameters, with particular reference to mass and thickness, on the measured comfort related properties, were much greater than that of fibre type or blend, or fabric structure. It was, therefore, concluded from this study, that the fabric parameters, as opposed to the intrinsic characteristics of a particular fibre, whether natural or man-made, largely determined those fabric comfort related properties measured here.
- Full Text:
- Date Issued: 2013
A comparative study of the Linux and windows device driver architecture with a focus on IEEE1394 (high speed serial bus) drivers
- Authors: Tsegaye, Melekam Asrat
- Date: 2004
- Subjects: Microsoft Windows (Computer file) , Linux , Operating systems (Computers) , DOS device drivers (Computer programs) , Linux device drivers (Computer programs)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4591 , http://hdl.handle.net/10962/d1004829 , Microsoft Windows (Computer file) , Linux , Operating systems (Computers) , DOS device drivers (Computer programs) , Linux device drivers (Computer programs)
- Description: New hardware devices are continually being released to the public by hardware manufactures around the world. For these new devices to be usable under a PC operating system, device drivers that extend the functionality of the target operating system have to be constructed. This work examines and compares the device driver architectures currently in use by two of the most widely used operating systems, Microsoft’s Windows and Linux. The IEEE1394 (high speed serial bus) device driver stacks on each operating system are examined and compared as an example of a major device driver stack implementation, including driver requirements for the upcoming IEEE1394.1 bridging standard.
- Full Text:
- Date Issued: 2004
- Authors: Tsegaye, Melekam Asrat
- Date: 2004
- Subjects: Microsoft Windows (Computer file) , Linux , Operating systems (Computers) , DOS device drivers (Computer programs) , Linux device drivers (Computer programs)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4591 , http://hdl.handle.net/10962/d1004829 , Microsoft Windows (Computer file) , Linux , Operating systems (Computers) , DOS device drivers (Computer programs) , Linux device drivers (Computer programs)
- Description: New hardware devices are continually being released to the public by hardware manufactures around the world. For these new devices to be usable under a PC operating system, device drivers that extend the functionality of the target operating system have to be constructed. This work examines and compares the device driver architectures currently in use by two of the most widely used operating systems, Microsoft’s Windows and Linux. The IEEE1394 (high speed serial bus) device driver stacks on each operating system are examined and compared as an example of a major device driver stack implementation, including driver requirements for the upcoming IEEE1394.1 bridging standard.
- Full Text:
- Date Issued: 2004
A Comparative study of two copper(II) based metal-organic frameworks : Cu2¼(OH)½B4C•8H2O and Cu2Na(OH)B4C•7H2O
- Authors: Coombes, Matthew
- Date: 2013
- Subjects: Copper , Organometallic compounds , Supramolecular organometallic chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4533 , http://hdl.handle.net/10962/d1016245
- Description: This study focussed on two copper(II)-containing metal-organic frameworks (MOFs): Cu2Na(OH)B4C•7H2O and Cu2¼(OH)½B4C•8H2O (B4C = 1,2,4,5- benzenetetracarboxylate). They are both covalent, three-dimensional metalorganic framework polymers containing voids filled with water molecules. Both were characterised by elemental analysis, infrared spectroscopy, X-ray powder diffractometry (both in situ and regular), thermogravimetric analysis, differential scanning calorimetry and X-ray photoelectron spectroscopy. These two MOFs are essentially identical, with the only difference being the substitution of sodium by copper at every 4th site (disordered throughout the crystal). The guest inclusion properties of both MOFs were studied and compared. Although both structures collapse on dehydration, it was observed that Cu2Na(OH)B4C•7H2O is able to take up signifcant amounts of water, methanol and ethanol. All these processes are fully reversible. Car-Parrinello molecular dynamics studies suggest that it is a strong interaction between the oxygen atoms on these molecules with the sodium cation of the MOF that is responsible for this signifcant uptake. In contrast, Cu2¼ (OH)½ B4C•8H2O, the MOF without a sodium cation, did not demonstrate any methanol or ethanol uptake, but was able to take up some water. The uptake of water, however, is not a fully reversible process. The absence of sodium likely results in insuffcient energy to draw methanol and ethanol into the framework, while a subtle rotation of a carboxylate group on dehydration decreases the ability of the framework to form hydrogen bonds, thus reducing the ability to take up water. A series of hydrothermal syntheses were performed in order to develop a method of synthesis superior to the current gel-based synthesis that requires several months and has poor yields. The hydrothermal products were characterized by elemental analysis, infrared spectroscopy, X-ray powder diffractometry, thermogravimetric analysis and differential scanning calorimetry. It was shown that the MOF Cu2Na(OH)B4C•7H2O may be synthesised in almost 100% yield by using a temperature of 120°C over a period of 72 hours. It was not possible to synthesise Cu2¼ (OH)½ B4C•8H2O in a 100% yield - it was only obtained as a minor product.
- Full Text:
- Date Issued: 2013
- Authors: Coombes, Matthew
- Date: 2013
- Subjects: Copper , Organometallic compounds , Supramolecular organometallic chemistry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4533 , http://hdl.handle.net/10962/d1016245
- Description: This study focussed on two copper(II)-containing metal-organic frameworks (MOFs): Cu2Na(OH)B4C•7H2O and Cu2¼(OH)½B4C•8H2O (B4C = 1,2,4,5- benzenetetracarboxylate). They are both covalent, three-dimensional metalorganic framework polymers containing voids filled with water molecules. Both were characterised by elemental analysis, infrared spectroscopy, X-ray powder diffractometry (both in situ and regular), thermogravimetric analysis, differential scanning calorimetry and X-ray photoelectron spectroscopy. These two MOFs are essentially identical, with the only difference being the substitution of sodium by copper at every 4th site (disordered throughout the crystal). The guest inclusion properties of both MOFs were studied and compared. Although both structures collapse on dehydration, it was observed that Cu2Na(OH)B4C•7H2O is able to take up signifcant amounts of water, methanol and ethanol. All these processes are fully reversible. Car-Parrinello molecular dynamics studies suggest that it is a strong interaction between the oxygen atoms on these molecules with the sodium cation of the MOF that is responsible for this signifcant uptake. In contrast, Cu2¼ (OH)½ B4C•8H2O, the MOF without a sodium cation, did not demonstrate any methanol or ethanol uptake, but was able to take up some water. The uptake of water, however, is not a fully reversible process. The absence of sodium likely results in insuffcient energy to draw methanol and ethanol into the framework, while a subtle rotation of a carboxylate group on dehydration decreases the ability of the framework to form hydrogen bonds, thus reducing the ability to take up water. A series of hydrothermal syntheses were performed in order to develop a method of synthesis superior to the current gel-based synthesis that requires several months and has poor yields. The hydrothermal products were characterized by elemental analysis, infrared spectroscopy, X-ray powder diffractometry, thermogravimetric analysis and differential scanning calorimetry. It was shown that the MOF Cu2Na(OH)B4C•7H2O may be synthesised in almost 100% yield by using a temperature of 120°C over a period of 72 hours. It was not possible to synthesise Cu2¼ (OH)½ B4C•8H2O in a 100% yield - it was only obtained as a minor product.
- Full Text:
- Date Issued: 2013
A comparison between the responsiveness of selected physiological and subjective mental workload indicators during real-world driving scenarios
- Authors: Schmidtke, Nadia-Jasmine
- Date: 2020
- Subjects: Automobile driving -- Physiological aspects , Automobile driving -- Psychological aspects , Automobile drivers -- Health and hygiene , Mental fatigue , Mental work -- Case studies
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/148115 , vital:38711
- Description: Sub-optimal levels of mental workload in automobile drivers is a risk factor for road accidents. However, mental workload as a construct cannot be directly measured. Common indicators of mental workload include heart rate frequency and variability, eye motion and subjective rating tools. Namely, the National Aeronautics and Space Administration Task Load Index (NASA-TLX), its modified, unweighted version called the Raw-TLX, and the Rating Scale of Mental Effort (RSME). Comparisons between the suitability and responsiveness of these mental workload indicators have been almost exclusively examined in driving simulators. However, real-world driving research is important as even high-fidelity simulators cannot capture the complexity of driving scenarios. Hence, this research aimed to compare the suitability and responsiveness of these mental workload indicators in response to real-world driving scenarios. Six participants drove along a set route for an hour while wearing a heart rate monitor and eye tracker. A dashcam was used to capture footage of the different driving scenarios encountered. The set route comprised of driving through the industrial, residential, provincial main road and Rhodes University campus areas. RSME scores were taken during brief stops after driving though each zone. The NASA-TLX questionnaire was administered on completion of the drive and analysed later as the modified Raw-TLX version. The data collected in response to the encountered driving scenarios were sorted into three meta-groupings. (1) Data was segmented according to the different areas that participants drove through. This was termed Area Events and were long duration scenarios of between five and thirty minutes. These driving scenarios were further segmented into two meta-groups with short duration driving scenarios (< 90 seconds). (2) The Common Events meta-group consisted of driving scenarios that were encountered by all participants. These were scenarios were anticipated by drivers. (3) The All Events meta-group was grouped according to all the driving scenarios that were encountered by participants. It consisted of both anticipated and unanticipated driving scenarios of short durations. Data were further analysed using a method of systematically selecting a threshold value for each mental workload indicator. Responses to driving scenarios which surpassed the threshold were considered indicative of an increase in mental workload. The total frequency of higher mental workload events was used as a determiner responsiveness (or ‘sensitivity’) for each mental workload indicator. Mental workload indicators were evaluated for their responsiveness and suitability for assessing mental workload. Results found blink frequency to be a responsive mental workload indicator for all categories of driving scenarios. Blink frequency and duration were the most responsive short duration mental workload indicators. Furthermore, the indicators were able to distinguish between higher and lower mental workload driving scenarios. However, blink parameters are also sensitive to driver fatigue and drowsiness. Further research on distinguishing mental workload from that of fatigue in response to real-world driving was recommended. Pupil diameter, fixation duration, saccade saccade duration and saccade amplitude were found to be responsive short duration mental workload indicators. However, these measures were not determined to be suitable for real-world driving applications. Pupil diameter was confounded by changing illumination levels. Fixation and saccade responses were confounded by the driving task itself as gaze could not be accounted for. For long duration driving scenarios heart rate frequency, heart rate variability: high-frequency power, blink frequency and RSME were found to be responsive and suitable MWL indicators. The Raw-TLX results could not be assessed for responsiveness as it was administered once. However, it was confirmed as a suitable cumulative mental workload indicator in the application of real-world driving. The moderate levels of workload reported by participants agreed with the experimental protocol that prevented inducing sub-optimal mental workload. Blink frequency shows promise as a responsive and suitable mental workload indicator for different types of driving scenarios. More research is needed regarding the assessment of mental workload during short durations using blink frequency and blink duration. For driving durations between five and thirty minutes long, further research into heart rate frequency, heart rate variability: high frequency power, and the RSME was recommended.
- Full Text:
- Date Issued: 2020
- Authors: Schmidtke, Nadia-Jasmine
- Date: 2020
- Subjects: Automobile driving -- Physiological aspects , Automobile driving -- Psychological aspects , Automobile drivers -- Health and hygiene , Mental fatigue , Mental work -- Case studies
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/148115 , vital:38711
- Description: Sub-optimal levels of mental workload in automobile drivers is a risk factor for road accidents. However, mental workload as a construct cannot be directly measured. Common indicators of mental workload include heart rate frequency and variability, eye motion and subjective rating tools. Namely, the National Aeronautics and Space Administration Task Load Index (NASA-TLX), its modified, unweighted version called the Raw-TLX, and the Rating Scale of Mental Effort (RSME). Comparisons between the suitability and responsiveness of these mental workload indicators have been almost exclusively examined in driving simulators. However, real-world driving research is important as even high-fidelity simulators cannot capture the complexity of driving scenarios. Hence, this research aimed to compare the suitability and responsiveness of these mental workload indicators in response to real-world driving scenarios. Six participants drove along a set route for an hour while wearing a heart rate monitor and eye tracker. A dashcam was used to capture footage of the different driving scenarios encountered. The set route comprised of driving through the industrial, residential, provincial main road and Rhodes University campus areas. RSME scores were taken during brief stops after driving though each zone. The NASA-TLX questionnaire was administered on completion of the drive and analysed later as the modified Raw-TLX version. The data collected in response to the encountered driving scenarios were sorted into three meta-groupings. (1) Data was segmented according to the different areas that participants drove through. This was termed Area Events and were long duration scenarios of between five and thirty minutes. These driving scenarios were further segmented into two meta-groups with short duration driving scenarios (< 90 seconds). (2) The Common Events meta-group consisted of driving scenarios that were encountered by all participants. These were scenarios were anticipated by drivers. (3) The All Events meta-group was grouped according to all the driving scenarios that were encountered by participants. It consisted of both anticipated and unanticipated driving scenarios of short durations. Data were further analysed using a method of systematically selecting a threshold value for each mental workload indicator. Responses to driving scenarios which surpassed the threshold were considered indicative of an increase in mental workload. The total frequency of higher mental workload events was used as a determiner responsiveness (or ‘sensitivity’) for each mental workload indicator. Mental workload indicators were evaluated for their responsiveness and suitability for assessing mental workload. Results found blink frequency to be a responsive mental workload indicator for all categories of driving scenarios. Blink frequency and duration were the most responsive short duration mental workload indicators. Furthermore, the indicators were able to distinguish between higher and lower mental workload driving scenarios. However, blink parameters are also sensitive to driver fatigue and drowsiness. Further research on distinguishing mental workload from that of fatigue in response to real-world driving was recommended. Pupil diameter, fixation duration, saccade saccade duration and saccade amplitude were found to be responsive short duration mental workload indicators. However, these measures were not determined to be suitable for real-world driving applications. Pupil diameter was confounded by changing illumination levels. Fixation and saccade responses were confounded by the driving task itself as gaze could not be accounted for. For long duration driving scenarios heart rate frequency, heart rate variability: high-frequency power, blink frequency and RSME were found to be responsive and suitable MWL indicators. The Raw-TLX results could not be assessed for responsiveness as it was administered once. However, it was confirmed as a suitable cumulative mental workload indicator in the application of real-world driving. The moderate levels of workload reported by participants agreed with the experimental protocol that prevented inducing sub-optimal mental workload. Blink frequency shows promise as a responsive and suitable mental workload indicator for different types of driving scenarios. More research is needed regarding the assessment of mental workload during short durations using blink frequency and blink duration. For driving durations between five and thirty minutes long, further research into heart rate frequency, heart rate variability: high frequency power, and the RSME was recommended.
- Full Text:
- Date Issued: 2020
A comparison framework for server virtualisation systems a case study
- Authors: Van Tonder, Martin Stephen
- Date: 2006
- Subjects: Virtual computer systems -- South Africa Case studies , Virtual storage (Computer science) -- South Africa Case studies
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10481 , http://hdl.handle.net/10948/439 , http://hdl.handle.net/10948/d1012009 , Virtual computer systems -- South Africa Case studies , Virtual storage (Computer science) -- South Africa Case studies
- Description: Recent years have seen a revival of interest in virtualisation research. Although this term has been used to refer to various systems, the focus of this research is on systems which partition a single physical server into multiple virtual servers. It is difficult for researchers and practitioners to get a clear picture of the state of the art in server virtualisation. This is due in part to the large number of systems available. Another reason is that information about virtualisation systems lacks structure, and is dispersed among multiple sources. Practitioners, such as data centre managers and systems administrators, may be familiar with virtualisation systems from a specific vendor, but generally lack a broader view of the field. This makes it difficult to make informed decisions when selecting these systems. Researchers and vendors who are developing virtualisation systems also lack a standard framework for identifying the strengths and weaknesses of their systems, compared to competing systems. It is also time-consuming for researchers who are new to the field to learn about current virtualisation systems. The purpose of this research was to develop a framework to solve these problems. The objectives of the research correspond to the applications of the framework. These include conducting comparative evaluations of server virtualisation systems, identifying strengths and weaknesses of particular virtualisation systems, specifying virtualisation system requirements to facilitate system selection, and gathering information about current virtualisation systems in a structured form. These four objectives were satisfied. The design of this framework was also guided by six framework design principles. These principles, or secondary objectives, were also met. The framework was developed based on an extensive literature study of data centres, virtualisation and current virtualisation systems. Criteria were selected through an inductive process. The feasibility of conducting evaluations using the framework was demonstrated by means of literature-based evaluations, and a practical case study. The use of the framework to facilitate virtualisation system selection was also demonstrated by means of a case study featuring the NMMU Telkom CoE data centre. This framework has a number of practical applications, ranging from the facilitation of decision-making to identifying areas for improvement in current virtualisation systems. The information resulting from evaluations using the framework is also a valuable resource for researchers who are new to the field. The literature study which forms the theoretical foundation of this work is particularly useful in this regard. A future extension to this work would be to develop a decision support system based on the framework. Another possibility is to make the framework, and evaluations, available on-line as a resource for data center managers, vendors and researchers. This would also enable other researchers to provide additional feedback, enabling the framework to be further refined
- Full Text:
- Date Issued: 2006
- Authors: Van Tonder, Martin Stephen
- Date: 2006
- Subjects: Virtual computer systems -- South Africa Case studies , Virtual storage (Computer science) -- South Africa Case studies
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10481 , http://hdl.handle.net/10948/439 , http://hdl.handle.net/10948/d1012009 , Virtual computer systems -- South Africa Case studies , Virtual storage (Computer science) -- South Africa Case studies
- Description: Recent years have seen a revival of interest in virtualisation research. Although this term has been used to refer to various systems, the focus of this research is on systems which partition a single physical server into multiple virtual servers. It is difficult for researchers and practitioners to get a clear picture of the state of the art in server virtualisation. This is due in part to the large number of systems available. Another reason is that information about virtualisation systems lacks structure, and is dispersed among multiple sources. Practitioners, such as data centre managers and systems administrators, may be familiar with virtualisation systems from a specific vendor, but generally lack a broader view of the field. This makes it difficult to make informed decisions when selecting these systems. Researchers and vendors who are developing virtualisation systems also lack a standard framework for identifying the strengths and weaknesses of their systems, compared to competing systems. It is also time-consuming for researchers who are new to the field to learn about current virtualisation systems. The purpose of this research was to develop a framework to solve these problems. The objectives of the research correspond to the applications of the framework. These include conducting comparative evaluations of server virtualisation systems, identifying strengths and weaknesses of particular virtualisation systems, specifying virtualisation system requirements to facilitate system selection, and gathering information about current virtualisation systems in a structured form. These four objectives were satisfied. The design of this framework was also guided by six framework design principles. These principles, or secondary objectives, were also met. The framework was developed based on an extensive literature study of data centres, virtualisation and current virtualisation systems. Criteria were selected through an inductive process. The feasibility of conducting evaluations using the framework was demonstrated by means of literature-based evaluations, and a practical case study. The use of the framework to facilitate virtualisation system selection was also demonstrated by means of a case study featuring the NMMU Telkom CoE data centre. This framework has a number of practical applications, ranging from the facilitation of decision-making to identifying areas for improvement in current virtualisation systems. The information resulting from evaluations using the framework is also a valuable resource for researchers who are new to the field. The literature study which forms the theoretical foundation of this work is particularly useful in this regard. A future extension to this work would be to develop a decision support system based on the framework. Another possibility is to make the framework, and evaluations, available on-line as a resource for data center managers, vendors and researchers. This would also enable other researchers to provide additional feedback, enabling the framework to be further refined
- Full Text:
- Date Issued: 2006
A comparison of conventional and ultrasonic seams in swimwear
- Authors: Tyalana, Nommiselo
- Date: 2018
- Subjects: Textile finishing , Textile finishing agents Seams (Sewing) Textile fabrics Textile fibers Textile design
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/36727 , vital:34048
- Description: Ultrasonic welding technology is a relatively new technology in apparel construction, this research forms part of a study to assess its effectiveness as a joining technology that can be used in ladies swimwear. The ultimate aim was to determine whether the ultrasonic welding joining technique could be successfully used in assembling ladies swimwear garments, comprising only synthetic fibres, namely polyester/Lycra, polyamide/Lycra, polyamide/Lycra power-net and polyamide/Lycra mesh warp knitted fabrics. These specific swimwear fabrics were selected since they comprise 100% thermoplastic synthetic fibres, considered ideal for ultrasonic welding. This study essentially compares and contrasts the performance of two seam joining techniques: namely conventional sewing and ultrasonic welding, in terms of seam strength, when used in the above mentioned four fabrics. Conventionally sewn and ultrasonically welded seams were produced, straight and curved, in both the wale and course directions of the fabrics. The conventionally sewn seams were produced using two sewing machines; namely an overlocker, also known as a mock safety sewing machine, and a cover seam machines. All conventionally sewn seams were stitched and tested under similar conditions. The ultrasonic welded seams were produced using three different wheels, a Medium Male Knurled pattern wheel, a Staggered Triple Stitch pattern wheel and a Single Stitch pattern wheel. The amplitude and speed of the welding machine, during the ultrasonic seaming, were kept constant, except when welding the polyamide/Lycra power-net and the polyamide/Lycra mesh fabrics when the pressure had to be drastically reduced in order to avoid excessively softened seams. The results of the study are presented in the form of line charts, scatter charts and tables. The ultrasonic welded seams, joined with the Medium Male Knurled wheel, exhibited surface waviness, as opposed to those joined with the Staggered Triple Stitch wheel which were smooth. It was found that, in terms of seam strength, the ultrasonic seams produced with the Single Stitch and Medium Male Knurled pattern wheels out performed those produced with the Staggered Triple Stitch wheels. The polyester/Lycra fabric was found easier to handle during the ultrasonic seaming process than the polyamide/Lycra fabric, although the strength of the ultrasonic seams in the polyester/Lycra fabric did not differ consistently from those of the polyamide/Lycra fabric. It was found that the conventional sewn seams were consistently stronger, and had a better appearance, than the ultrasonic welded seams. Although some promising results were obtained, in terms of the strength of the ultrasonic welded seams, the results overall were far too variable, inconsistent and unsatisfactory for this technique of seaming to be recommended at this stage for any of the swimwear fabrics covered. Further, more in depth, studies are required in order to gain a better understating of the effect of the various ultrasonic seaming parameters, as well as fabric parameters on ultrasonic seam strength and consistency.
- Full Text:
- Date Issued: 2018
- Authors: Tyalana, Nommiselo
- Date: 2018
- Subjects: Textile finishing , Textile finishing agents Seams (Sewing) Textile fabrics Textile fibers Textile design
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/36727 , vital:34048
- Description: Ultrasonic welding technology is a relatively new technology in apparel construction, this research forms part of a study to assess its effectiveness as a joining technology that can be used in ladies swimwear. The ultimate aim was to determine whether the ultrasonic welding joining technique could be successfully used in assembling ladies swimwear garments, comprising only synthetic fibres, namely polyester/Lycra, polyamide/Lycra, polyamide/Lycra power-net and polyamide/Lycra mesh warp knitted fabrics. These specific swimwear fabrics were selected since they comprise 100% thermoplastic synthetic fibres, considered ideal for ultrasonic welding. This study essentially compares and contrasts the performance of two seam joining techniques: namely conventional sewing and ultrasonic welding, in terms of seam strength, when used in the above mentioned four fabrics. Conventionally sewn and ultrasonically welded seams were produced, straight and curved, in both the wale and course directions of the fabrics. The conventionally sewn seams were produced using two sewing machines; namely an overlocker, also known as a mock safety sewing machine, and a cover seam machines. All conventionally sewn seams were stitched and tested under similar conditions. The ultrasonic welded seams were produced using three different wheels, a Medium Male Knurled pattern wheel, a Staggered Triple Stitch pattern wheel and a Single Stitch pattern wheel. The amplitude and speed of the welding machine, during the ultrasonic seaming, were kept constant, except when welding the polyamide/Lycra power-net and the polyamide/Lycra mesh fabrics when the pressure had to be drastically reduced in order to avoid excessively softened seams. The results of the study are presented in the form of line charts, scatter charts and tables. The ultrasonic welded seams, joined with the Medium Male Knurled wheel, exhibited surface waviness, as opposed to those joined with the Staggered Triple Stitch wheel which were smooth. It was found that, in terms of seam strength, the ultrasonic seams produced with the Single Stitch and Medium Male Knurled pattern wheels out performed those produced with the Staggered Triple Stitch wheels. The polyester/Lycra fabric was found easier to handle during the ultrasonic seaming process than the polyamide/Lycra fabric, although the strength of the ultrasonic seams in the polyester/Lycra fabric did not differ consistently from those of the polyamide/Lycra fabric. It was found that the conventional sewn seams were consistently stronger, and had a better appearance, than the ultrasonic welded seams. Although some promising results were obtained, in terms of the strength of the ultrasonic welded seams, the results overall were far too variable, inconsistent and unsatisfactory for this technique of seaming to be recommended at this stage for any of the swimwear fabrics covered. Further, more in depth, studies are required in order to gain a better understating of the effect of the various ultrasonic seaming parameters, as well as fabric parameters on ultrasonic seam strength and consistency.
- Full Text:
- Date Issued: 2018
A comparison of ecosystem health and services provided by subtropical thicket in and around the Bathurst commonage
- Authors: Stickler, Meredith Mercedes
- Date: 2010
- Subjects: Ecosystem services -- South Africa -- Bathurst , Ecosystem management , Commons -- South Africa -- Bathurst , Natural resources, Communal -- South Africa -- Bathurst , Land use, Rural -- South Africa -- Eastern Cape , Ecosystem health -- South Africa -- Bathurst
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4766 , http://hdl.handle.net/10962/d1007169 , Ecosystem services -- South Africa -- Bathurst , Ecosystem management , Commons -- South Africa -- Bathurst , Natural resources, Communal -- South Africa -- Bathurst , Land use, Rural -- South Africa -- Eastern Cape , Ecosystem health -- South Africa -- Bathurst
- Description: Municipal commonage in South Africa offers previously disadvantaged, landless residents access to both direct ecosystem goods and services (EGS) that provide additional income options and indirect social and cultural services. Given that EGS production is a function of ecosystem health, it is imperative that commonage land be managed to maximize current local benefit streams while ensuring future options through the maintenance of natural ecosystem functions. The payments for ecosystem services (PES) model potentially offers an opportunity for contributing to local economic development while providing fiscal incentives for environmentally sustainable natural resource management. PES depends on the demonstration of quantifiable changes in EGS delivery due to improvement in or maintenance of high ecosystem health that are a verifiable result of modifications in management behavior. This thesis therefore compared spatial variations in (i) ecosystem health and (ii) nine direct and indirect EGS values derived from natural resources on the Bathurst municipal commonage and neighboring Waters Meeting Nature Reserve (NR) to explore how different land use intensities affect ecosystem health and the resulting provision of EGS. The results indicate that the total economic value of annually produced EGS on the study site is nearly R 9.8 million (US$ 1.2 million), with a standing stock of natural capital worth some R 28 million (US$ 3.4 million). Nearly 45% of the total annual production is attributed to Waters Meeting NR, with roughly 34% from the low use zone of the commonage and the remaining 22% from the high use zone. Of the total annual production value on the study site, roughly 59% is derived from indirect (non-consumptive) uses of wildlife for the study site as a whole, though this proportion varies from 25% in the high use zone of the commonage to 94% on Waters Meeting NR. The two largest annual production values on the study site derive from ecotourism (R 3.5 million, US$ 0.4 million) and livestock production (R 2.6 million, US$ 0.3 million), suggesting that while increased production of indirect EGS could generate significant additional revenues, especially on Waters Meeting NR and in the low use zone of the commonage, direct (consumptive) EGS will likely remain an important component of land use on the commonage. A PES project to support the adoption of silvo-pastoral practices could provide positive incentives for improved land use practices on the commonage and potentially be financed by conservation-friendly residents of the Kowie River catchment and/or increased ecotourism revenues from Waters Meeting NR. Allowing carefully designed and monitored local access to natural resources within Waters Meeting NR could also reduce pressure on commonage resources. Together, these approaches could lead to a more sustainable subtropical thicket landscape and ensure that critical natural resources remain available to support local livelihoods in the long-term.
- Full Text:
- Date Issued: 2010
- Authors: Stickler, Meredith Mercedes
- Date: 2010
- Subjects: Ecosystem services -- South Africa -- Bathurst , Ecosystem management , Commons -- South Africa -- Bathurst , Natural resources, Communal -- South Africa -- Bathurst , Land use, Rural -- South Africa -- Eastern Cape , Ecosystem health -- South Africa -- Bathurst
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4766 , http://hdl.handle.net/10962/d1007169 , Ecosystem services -- South Africa -- Bathurst , Ecosystem management , Commons -- South Africa -- Bathurst , Natural resources, Communal -- South Africa -- Bathurst , Land use, Rural -- South Africa -- Eastern Cape , Ecosystem health -- South Africa -- Bathurst
- Description: Municipal commonage in South Africa offers previously disadvantaged, landless residents access to both direct ecosystem goods and services (EGS) that provide additional income options and indirect social and cultural services. Given that EGS production is a function of ecosystem health, it is imperative that commonage land be managed to maximize current local benefit streams while ensuring future options through the maintenance of natural ecosystem functions. The payments for ecosystem services (PES) model potentially offers an opportunity for contributing to local economic development while providing fiscal incentives for environmentally sustainable natural resource management. PES depends on the demonstration of quantifiable changes in EGS delivery due to improvement in or maintenance of high ecosystem health that are a verifiable result of modifications in management behavior. This thesis therefore compared spatial variations in (i) ecosystem health and (ii) nine direct and indirect EGS values derived from natural resources on the Bathurst municipal commonage and neighboring Waters Meeting Nature Reserve (NR) to explore how different land use intensities affect ecosystem health and the resulting provision of EGS. The results indicate that the total economic value of annually produced EGS on the study site is nearly R 9.8 million (US$ 1.2 million), with a standing stock of natural capital worth some R 28 million (US$ 3.4 million). Nearly 45% of the total annual production is attributed to Waters Meeting NR, with roughly 34% from the low use zone of the commonage and the remaining 22% from the high use zone. Of the total annual production value on the study site, roughly 59% is derived from indirect (non-consumptive) uses of wildlife for the study site as a whole, though this proportion varies from 25% in the high use zone of the commonage to 94% on Waters Meeting NR. The two largest annual production values on the study site derive from ecotourism (R 3.5 million, US$ 0.4 million) and livestock production (R 2.6 million, US$ 0.3 million), suggesting that while increased production of indirect EGS could generate significant additional revenues, especially on Waters Meeting NR and in the low use zone of the commonage, direct (consumptive) EGS will likely remain an important component of land use on the commonage. A PES project to support the adoption of silvo-pastoral practices could provide positive incentives for improved land use practices on the commonage and potentially be financed by conservation-friendly residents of the Kowie River catchment and/or increased ecotourism revenues from Waters Meeting NR. Allowing carefully designed and monitored local access to natural resources within Waters Meeting NR could also reduce pressure on commonage resources. Together, these approaches could lead to a more sustainable subtropical thicket landscape and ensure that critical natural resources remain available to support local livelihoods in the long-term.
- Full Text:
- Date Issued: 2010
A comparison of exact string search algorithms for deep packet inspection
- Authors: Hunt, Kieran
- Date: 2018
- Subjects: Algorithms , Firewalls (Computer security) , Computer networks -- Security measures , Intrusion detection systems (Computer security) , Deep Packet Inspection
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/60629 , vital:27807
- Description: Every day, computer networks throughout the world face a constant onslaught of attacks. To combat these, network administrators are forced to employ a multitude of mitigating measures. Devices such as firewalls and Intrusion Detection Systems are prevalent today and employ extensive Deep Packet Inspection to scrutinise each piece of network traffic. Systems such as these usually require specialised hardware to meet the demand imposed by high throughput networks. Hardware like this is extremely expensive and singular in its function. It is with this in mind that the string search algorithms are introduced. These algorithms have been proven to perform well when searching through large volumes of text and may be able to perform equally well in the context of Deep Packet Inspection. String search algorithms are designed to match a single pattern to a substring of a given piece of text. This is not unlike the heuristics employed by traditional Deep Packet Inspection systems. This research compares the performance of a large number of string search algorithms during packet processing. Deep Packet Inspection places stringent restrictions on the reliability and speed of the algorithms due to increased performance pressures. A test system had to be designed in order to properly test the string search algorithms in the context of Deep Packet Inspection. The system allowed for precise and repeatable tests of each algorithm and then for their comparison. Of the algorithms tested, the Horspool and Quick Search algorithms posted the best results for both speed and reliability. The Not So Naive and Rabin-Karp algorithms were slowest overall.
- Full Text:
- Date Issued: 2018
- Authors: Hunt, Kieran
- Date: 2018
- Subjects: Algorithms , Firewalls (Computer security) , Computer networks -- Security measures , Intrusion detection systems (Computer security) , Deep Packet Inspection
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/60629 , vital:27807
- Description: Every day, computer networks throughout the world face a constant onslaught of attacks. To combat these, network administrators are forced to employ a multitude of mitigating measures. Devices such as firewalls and Intrusion Detection Systems are prevalent today and employ extensive Deep Packet Inspection to scrutinise each piece of network traffic. Systems such as these usually require specialised hardware to meet the demand imposed by high throughput networks. Hardware like this is extremely expensive and singular in its function. It is with this in mind that the string search algorithms are introduced. These algorithms have been proven to perform well when searching through large volumes of text and may be able to perform equally well in the context of Deep Packet Inspection. String search algorithms are designed to match a single pattern to a substring of a given piece of text. This is not unlike the heuristics employed by traditional Deep Packet Inspection systems. This research compares the performance of a large number of string search algorithms during packet processing. Deep Packet Inspection places stringent restrictions on the reliability and speed of the algorithms due to increased performance pressures. A test system had to be designed in order to properly test the string search algorithms in the context of Deep Packet Inspection. The system allowed for precise and repeatable tests of each algorithm and then for their comparison. Of the algorithms tested, the Horspool and Quick Search algorithms posted the best results for both speed and reliability. The Not So Naive and Rabin-Karp algorithms were slowest overall.
- Full Text:
- Date Issued: 2018
A comparison of muscle fatigue responses between static and quasi-static exertions
- Authors: Nel, Conrad
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3475 , vital:20502
- Description: Background: This study examined localized muscle fatigue responses from sub-maximal quasi-static work protocols and additionally how it compares to purely static work. The goal was to produce research that enhances the understanding of the demands on muscles during manual work to aid in preventing injuries stemming from localized muscle fatigue. Injury rates remain a problem in manual labour sectors, particularly for the lower back and shoulder regions for the manufacturing, service and construction sectors, and for knee and elbow flexors in the sports sector. Few studies have looked at quasi-static work and what the resulting fatigue characteristics are, especially when compared to purely static or purely dynamic work. This comparison is particularly important due to the fact that risk assessment tools that are currently utilized to assess risk in the working environment are based on fatigue studies that focus on purely static or purely dynamic work. This requires attention as many working situations are neither static nor dynamic, but rather quasi-static in nature, with aspects of both dynamic and static muscle components. The scope of this study only encompasses the comparison between purely static and quasi-static work. Objectives: This study had two objectives, firstly, to determine what the fatigue characteristics of quasi-static work are and how it compares to fully static work. Secondly, to determine whether an underlying static component within an otherwise dynamic muscle force affects localized muscle fatigue compared to quasi-static work that has equal amounts of effort but with no underlying static component. Methods: Four experimental conditions were tested, each on four muscles, namely the medial deltoid, bicep brachii, bicep femoris and erector spinae muscles. To test the two objectives of this study, 16 volunteers performed a five minute fatigue protocol, that either entailed a fully static condition which involved: 1) producing a steady force at 25 percent of maximum voluntary force, 2) a quasi-static condition with fully dynamic muscle force that alternates the required force level between zero and 50 percent of maximum force, 3) a quasi-static condition with an underlying static component of five percent of maximum force, or 4) a quasi-static condition with a large underlying static component of 15 percent of maximum force. All the experimental conditions in this study had the same average workload of 25 percent of maximum voluntary force over time and thus total workload. The dependant variables of interest were ratings of perceived exertion, changes in muscle fibre recruitment (% of maximum EMG activity), maximum force and center frequency from a spectral analysis of the surface electromyography. These were measured throughout the protocols at one minute intervals to determine how muscle fatigue progressed, and how the fatigue responses differed between conditions. Results: The data from comparing fully static and quasi-static work showed that of the variables measured, the rating of perceived exertion (RPE) and maximum force data indicated that for bicep brachii and bicep femoris muscles, fully static work is more fatiguing than work that alternates between zero and 50 percent of maximum force. The results for the medial deltoid and erector spinae muscles were inconclusive. The findings regarding the comparison between quasi-static conditions with and without an underlying static component revealed that an underlying static component results in greater fatigue when compared to a quasi-static condition with no static component. The results may also suggest that a larger static component coupled with a smaller peak force results in less fatigue than a condition with a small underlying static component coupled with a higher peak force in some scenarios, provided total work is kept constant. All conditions had to have the same workload in order to be validly compared and thus the condition with a larger underlying static component had a lower peak force compared to the condition with no underlying static component or the condition with a small underlying static component. Conclusions: This study presented evidence that quasi-static work does not induce fatigue when measured by RPE and drop in maximum force in the same way as static work. Additionally, the results indicate that a larger underlying static component does not necessarily fatigue a muscle faster if the overall workload is kept constant. However, the results do suggest that any underlying static component will increase the demand on a muscle when compared to a muscle exertion with no static component. When considering the available literature on how muscles fatigue during low level static contractions, the current understanding is that the larger the force during a static contraction, the faster the onset of fatigue and decrements in performance occur. The results of this study suggest that this same relationship cannot be applied to quasi-static work where an underlying static component is part of an otherwise dynamic muscle force. Thus total workload or peak force may play a larger role than the static muscle exertion in some scenarios.
- Full Text:
- Date Issued: 2016
- Authors: Nel, Conrad
- Date: 2016
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/3475 , vital:20502
- Description: Background: This study examined localized muscle fatigue responses from sub-maximal quasi-static work protocols and additionally how it compares to purely static work. The goal was to produce research that enhances the understanding of the demands on muscles during manual work to aid in preventing injuries stemming from localized muscle fatigue. Injury rates remain a problem in manual labour sectors, particularly for the lower back and shoulder regions for the manufacturing, service and construction sectors, and for knee and elbow flexors in the sports sector. Few studies have looked at quasi-static work and what the resulting fatigue characteristics are, especially when compared to purely static or purely dynamic work. This comparison is particularly important due to the fact that risk assessment tools that are currently utilized to assess risk in the working environment are based on fatigue studies that focus on purely static or purely dynamic work. This requires attention as many working situations are neither static nor dynamic, but rather quasi-static in nature, with aspects of both dynamic and static muscle components. The scope of this study only encompasses the comparison between purely static and quasi-static work. Objectives: This study had two objectives, firstly, to determine what the fatigue characteristics of quasi-static work are and how it compares to fully static work. Secondly, to determine whether an underlying static component within an otherwise dynamic muscle force affects localized muscle fatigue compared to quasi-static work that has equal amounts of effort but with no underlying static component. Methods: Four experimental conditions were tested, each on four muscles, namely the medial deltoid, bicep brachii, bicep femoris and erector spinae muscles. To test the two objectives of this study, 16 volunteers performed a five minute fatigue protocol, that either entailed a fully static condition which involved: 1) producing a steady force at 25 percent of maximum voluntary force, 2) a quasi-static condition with fully dynamic muscle force that alternates the required force level between zero and 50 percent of maximum force, 3) a quasi-static condition with an underlying static component of five percent of maximum force, or 4) a quasi-static condition with a large underlying static component of 15 percent of maximum force. All the experimental conditions in this study had the same average workload of 25 percent of maximum voluntary force over time and thus total workload. The dependant variables of interest were ratings of perceived exertion, changes in muscle fibre recruitment (% of maximum EMG activity), maximum force and center frequency from a spectral analysis of the surface electromyography. These were measured throughout the protocols at one minute intervals to determine how muscle fatigue progressed, and how the fatigue responses differed between conditions. Results: The data from comparing fully static and quasi-static work showed that of the variables measured, the rating of perceived exertion (RPE) and maximum force data indicated that for bicep brachii and bicep femoris muscles, fully static work is more fatiguing than work that alternates between zero and 50 percent of maximum force. The results for the medial deltoid and erector spinae muscles were inconclusive. The findings regarding the comparison between quasi-static conditions with and without an underlying static component revealed that an underlying static component results in greater fatigue when compared to a quasi-static condition with no static component. The results may also suggest that a larger static component coupled with a smaller peak force results in less fatigue than a condition with a small underlying static component coupled with a higher peak force in some scenarios, provided total work is kept constant. All conditions had to have the same workload in order to be validly compared and thus the condition with a larger underlying static component had a lower peak force compared to the condition with no underlying static component or the condition with a small underlying static component. Conclusions: This study presented evidence that quasi-static work does not induce fatigue when measured by RPE and drop in maximum force in the same way as static work. Additionally, the results indicate that a larger underlying static component does not necessarily fatigue a muscle faster if the overall workload is kept constant. However, the results do suggest that any underlying static component will increase the demand on a muscle when compared to a muscle exertion with no static component. When considering the available literature on how muscles fatigue during low level static contractions, the current understanding is that the larger the force during a static contraction, the faster the onset of fatigue and decrements in performance occur. The results of this study suggest that this same relationship cannot be applied to quasi-static work where an underlying static component is part of an otherwise dynamic muscle force. Thus total workload or peak force may play a larger role than the static muscle exertion in some scenarios.
- Full Text:
- Date Issued: 2016
A comparison of nesting behaviour and prey selection in some Southern African species of Ammophila (Hymenoptera : Sphecidae)
- Authors: Weaving, Alan James Shelley
- Date: 1987
- Subjects: Hymenoptera
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5600 , http://hdl.handle.net/10962/d1002050
- Description: Nesting behaviour and prey selection was compared in eight species of Ammophila. The frequent sympatry of these species was a central point of interest in the study. Nest siting differed markedly in several species. A. ferrugineipes, A. dolichodera, A. dolichocephala and, probably, A. conifera nested mostly in open habitats, this being regarded as the most common situation for the majority of Ammophila. A. beniniensis was unusual in nesting in well vegetated habitats, A. vulcania doing so amongst small clumps of vegetation in otherwise open habitats. A. insignis nested in vertical banks or old animal burrows and A. braunsi utilised abandoned burrows of other wasps situated in non-friable clay soils. This is the first time such nest siting has been reported for Ammophila and each of these two species is consequently unique. Many aspects of nest construction behaviour, in particular methods of soil waste disposal, sealing of nests and their final coverage, differed interspecifically, in some cases intraspecifically, but often apparently in response to the habitat. With regard to nest provisioning strategies, all species hunted after digging their nests, except A. dolichodera which is the first Afrotropical Ammophila reported to hunt before excavating its nest. This brings the total number of the world's species of Ammophila showing this behaviour to three. This species, A. beniniensis, A. braunsi and A. vulcania provided one caterpillar per nest; the others supplied several, A. insignis being the only mass provisioner. A. ferrugineipes showed a form of progressive provisioning and maintained several nests at a time; it is the only Afrotropical species known so far to do so. Only two extra-limital species have been reported showing similar behaviour. The observed variations in provisioning strategies can most easily be explained in relation to the habitat. Investigation of prey selection showed that there was very little interspecific overlap in the species of caterpillars used for provisioning nests. This was shown to be due mainly to differing hunting habitat preferences. The various overall patterns of nesting behaviour, and variations in the different components within these patterns, were considered most likely to have resulted from allopatric speciation in different types of vegetation, the more advanced patterns arising in open habitats. The frequent occurrence of sympatry appears to be a reflection of a shifting distribution of mosaic patterns of vegetation types and the post-speciation spread of species. This influence of habitat on behaviour and prey selection has emphasised the need for caution in drawing phylogenetic conclusions from ethology. Further, these considerations provide an alternative to competition in attempting to explain the observed behaviour patterns and distribution of these wasps.
- Full Text:
- Date Issued: 1987
- Authors: Weaving, Alan James Shelley
- Date: 1987
- Subjects: Hymenoptera
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5600 , http://hdl.handle.net/10962/d1002050
- Description: Nesting behaviour and prey selection was compared in eight species of Ammophila. The frequent sympatry of these species was a central point of interest in the study. Nest siting differed markedly in several species. A. ferrugineipes, A. dolichodera, A. dolichocephala and, probably, A. conifera nested mostly in open habitats, this being regarded as the most common situation for the majority of Ammophila. A. beniniensis was unusual in nesting in well vegetated habitats, A. vulcania doing so amongst small clumps of vegetation in otherwise open habitats. A. insignis nested in vertical banks or old animal burrows and A. braunsi utilised abandoned burrows of other wasps situated in non-friable clay soils. This is the first time such nest siting has been reported for Ammophila and each of these two species is consequently unique. Many aspects of nest construction behaviour, in particular methods of soil waste disposal, sealing of nests and their final coverage, differed interspecifically, in some cases intraspecifically, but often apparently in response to the habitat. With regard to nest provisioning strategies, all species hunted after digging their nests, except A. dolichodera which is the first Afrotropical Ammophila reported to hunt before excavating its nest. This brings the total number of the world's species of Ammophila showing this behaviour to three. This species, A. beniniensis, A. braunsi and A. vulcania provided one caterpillar per nest; the others supplied several, A. insignis being the only mass provisioner. A. ferrugineipes showed a form of progressive provisioning and maintained several nests at a time; it is the only Afrotropical species known so far to do so. Only two extra-limital species have been reported showing similar behaviour. The observed variations in provisioning strategies can most easily be explained in relation to the habitat. Investigation of prey selection showed that there was very little interspecific overlap in the species of caterpillars used for provisioning nests. This was shown to be due mainly to differing hunting habitat preferences. The various overall patterns of nesting behaviour, and variations in the different components within these patterns, were considered most likely to have resulted from allopatric speciation in different types of vegetation, the more advanced patterns arising in open habitats. The frequent occurrence of sympatry appears to be a reflection of a shifting distribution of mosaic patterns of vegetation types and the post-speciation spread of species. This influence of habitat on behaviour and prey selection has emphasised the need for caution in drawing phylogenetic conclusions from ethology. Further, these considerations provide an alternative to competition in attempting to explain the observed behaviour patterns and distribution of these wasps.
- Full Text:
- Date Issued: 1987