Chemical transformation and phytochemical studies of bioactive constituents from extract of callistemon citrinus (curtis) skeels
- Authors: Larayetan, Rotimi Abisoye
- Date: 2018
- Subjects: Callistemon Wild flowers
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10353/9122 , vital:34272
- Description: Callistemon citrinus belongs to the family Myrtaceae and exhibits therapeutic activities. The aerial parts of this plant are used to treat different ailments, among them are parasitic infections. The leaves, flowers and stems of Callistemon citrinus were subjected to hydrodistillation. The oils collected were studied by GC-MS analysis for the essential constituents. The overall phenolic content of the leaves oil, radical scavenging, antibacterial action and antioxidant activities of the essential oils of Callistemon citrinus were determined using standard methods, with free radical DPPH or ABTS as reference antioxidants. Chemical transformation of the components was examined for a whole year. A relationship between the chemical change in the volatile oil constituents, antioxidant capacity, percentage yield of the oil of Callistemon citrinus and fluctuation in season has been established. Active phytochemicals present in both ethyl acetate and methanolic extracts of Callistemon citrinus were determined spectrophotometrically. The antimicrobial properties, time of kill, and antioxidant activity of the extracts were explored. The bioactive components were characterized by high level of fatty acids. Squalene, a triterpenoid synthesized in human liver was obtained in the two extracts at varying amounts. The ethyl acetate extract demonstrated strong activity against P. aeruginosa ACC (28.7 ± 1.2 mm), Listeria ACC (26.0 ± 2.0 mm) and Escherichia coli ATCC 35150 (24.0 ± 3.5 mm). Qualitative phytochemical screening revealed the presence of alkaloids, glycosides, saponins, steroids and triterpenoids, fats and oils, flavonoids, phenols and tannins in them. In the quantitative phytochemical determination (total tannin, total flavonoids and flavonols, total phenolic and total antioxidant capacity) were carried out. The minimum time needed to kill the tested bacterial strains totally ranged from 15 to 24 hours. The aqueous extracts used for biosynthesis of nanoparticles were obtained from the fresh aerial parts of the plant. The biosynthesized gold and silver nanoparticles (AuNPs and AgNPs) of the aqueous extracts of the seed, flower and leaf of the plant, which are active as reducing and capping agents, were characterized using UV-VIS spectrophotometry, XRD, SEM, EDS, TEM, and FT IR. The XRD analysis revealed that the AgNPs were crystalline and the TEM showed that the shapes were spherical with an average size of 29 nm. For AuNPs, an average particle size of about 37 nm was confirmed by the TEM while the morphology and composition of the AuNPs were ascertained by SEM and EDS micrographs; uneven spherical shaped nanoparticles were established by the SEM. Both SEM and EDS demonstrated triangular shaped materials made up of silver and oxygen only. Absorption spectra confirmed by UV-VIS signify the dispersed nature of the synthesized nanoparticles with absorption band observed at 280 nm for the leaf AgNPs. FT IR had absorption bands at about 1700 cm-1 establishing the C=O stretching due to the amide bond while the FT IR for the AuNPs showed an absorption peak at 230 cm-1 confirming the presence of gold nanoparticles. The phytochemical investigation, isolation and characterization of the bioactive compounds of various organic crude extracts like hexane, dichloromethane, methanol and ethyl acetate were as well carried out, and the compounds responsible for their medicinal actions were determined. The results from different experiments revealed that the leaves and flowers of Callistemon citrinus possessed phenolic compounds and cyclic ethers with a variety of pharmacological action. The ethyl acetate and methanol crude extracts were found to possess broad spectrum of antimicrobial activities and pharmaceutically essential bioactive components with striking antioxidant capacities that may be used in the synthesis of novel drugs for the management of different ailments. The AuNPs and AgNPs synthesized from the seed, flower and leaf extracts of Callistemon citrinus where found to have prominent antimalarial, antiplasmodial, and antibacterial activities. The biosynthesized nanoparticles inhibit all the bacterial strains used and they were not cytotoxic to Hela cells, confirming their prospect for use as an excellent source for naturally occurring drugs against malaria, cell cytotoxicity, trypanosomes, and microbial infection. Similarly the crude organic extracts and the fractions derived from them exhibited high antimalarial and antitrypanosomal activities, but they were toxic to Hela cells. This is an indication that they will not be safe for use as targeted drugs for mammalian organism.
- Full Text:
- Date Issued: 2018
- Authors: Larayetan, Rotimi Abisoye
- Date: 2018
- Subjects: Callistemon Wild flowers
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10353/9122 , vital:34272
- Description: Callistemon citrinus belongs to the family Myrtaceae and exhibits therapeutic activities. The aerial parts of this plant are used to treat different ailments, among them are parasitic infections. The leaves, flowers and stems of Callistemon citrinus were subjected to hydrodistillation. The oils collected were studied by GC-MS analysis for the essential constituents. The overall phenolic content of the leaves oil, radical scavenging, antibacterial action and antioxidant activities of the essential oils of Callistemon citrinus were determined using standard methods, with free radical DPPH or ABTS as reference antioxidants. Chemical transformation of the components was examined for a whole year. A relationship between the chemical change in the volatile oil constituents, antioxidant capacity, percentage yield of the oil of Callistemon citrinus and fluctuation in season has been established. Active phytochemicals present in both ethyl acetate and methanolic extracts of Callistemon citrinus were determined spectrophotometrically. The antimicrobial properties, time of kill, and antioxidant activity of the extracts were explored. The bioactive components were characterized by high level of fatty acids. Squalene, a triterpenoid synthesized in human liver was obtained in the two extracts at varying amounts. The ethyl acetate extract demonstrated strong activity against P. aeruginosa ACC (28.7 ± 1.2 mm), Listeria ACC (26.0 ± 2.0 mm) and Escherichia coli ATCC 35150 (24.0 ± 3.5 mm). Qualitative phytochemical screening revealed the presence of alkaloids, glycosides, saponins, steroids and triterpenoids, fats and oils, flavonoids, phenols and tannins in them. In the quantitative phytochemical determination (total tannin, total flavonoids and flavonols, total phenolic and total antioxidant capacity) were carried out. The minimum time needed to kill the tested bacterial strains totally ranged from 15 to 24 hours. The aqueous extracts used for biosynthesis of nanoparticles were obtained from the fresh aerial parts of the plant. The biosynthesized gold and silver nanoparticles (AuNPs and AgNPs) of the aqueous extracts of the seed, flower and leaf of the plant, which are active as reducing and capping agents, were characterized using UV-VIS spectrophotometry, XRD, SEM, EDS, TEM, and FT IR. The XRD analysis revealed that the AgNPs were crystalline and the TEM showed that the shapes were spherical with an average size of 29 nm. For AuNPs, an average particle size of about 37 nm was confirmed by the TEM while the morphology and composition of the AuNPs were ascertained by SEM and EDS micrographs; uneven spherical shaped nanoparticles were established by the SEM. Both SEM and EDS demonstrated triangular shaped materials made up of silver and oxygen only. Absorption spectra confirmed by UV-VIS signify the dispersed nature of the synthesized nanoparticles with absorption band observed at 280 nm for the leaf AgNPs. FT IR had absorption bands at about 1700 cm-1 establishing the C=O stretching due to the amide bond while the FT IR for the AuNPs showed an absorption peak at 230 cm-1 confirming the presence of gold nanoparticles. The phytochemical investigation, isolation and characterization of the bioactive compounds of various organic crude extracts like hexane, dichloromethane, methanol and ethyl acetate were as well carried out, and the compounds responsible for their medicinal actions were determined. The results from different experiments revealed that the leaves and flowers of Callistemon citrinus possessed phenolic compounds and cyclic ethers with a variety of pharmacological action. The ethyl acetate and methanol crude extracts were found to possess broad spectrum of antimicrobial activities and pharmaceutically essential bioactive components with striking antioxidant capacities that may be used in the synthesis of novel drugs for the management of different ailments. The AuNPs and AgNPs synthesized from the seed, flower and leaf extracts of Callistemon citrinus where found to have prominent antimalarial, antiplasmodial, and antibacterial activities. The biosynthesized nanoparticles inhibit all the bacterial strains used and they were not cytotoxic to Hela cells, confirming their prospect for use as an excellent source for naturally occurring drugs against malaria, cell cytotoxicity, trypanosomes, and microbial infection. Similarly the crude organic extracts and the fractions derived from them exhibited high antimalarial and antitrypanosomal activities, but they were toxic to Hela cells. This is an indication that they will not be safe for use as targeted drugs for mammalian organism.
- Full Text:
- Date Issued: 2018
Chemical weathering on selected nunataks in western Dronning Maud Land, Antarctica
- Authors: Knox, Jenna Tracy
- Date: 2018
- Subjects: Glacial climates -- Antarctica -- Queen Maud Land , Glaciology -- Antarctica -- Queen Maud Land , Chemical weathering -- Antarctica -- Queen Maud Land , Atmospheric carbon dioxide -- Environmental aspects , Climatic changes -- Antarctica -- Queen Maud Land , Nunataks -- Antarctica -- Queen Maud Land
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/61658 , vital:28046
- Description: High latitude areas are sensitive to the impacts of climate change, and it is expected that the impact of greenhouse warming will be much higher in the polar regions than in any other climatic zones, with the most highly affected area being that of the Antarctic rim (Barsch, 1993). Weathering and pedogenic processes respond to variations in climate, with models predicting that chemical weathering may increase synchronously with global carbon dioxide levels increase, due to dissolution rates and the erosional impact of hydrological cycles in warming climates (Anderson & Anderson, 2010). As liquid water becomes more available in Antarctica the potential for chemical weathering, due to a less moisture-limited environment and increased temperatures, increases (Convey et al., 2009). Weathering processes are important for soil formation and the production of fine-grained material, with chemical weathering being an active constituent of this. Increased rates of soil formation are likely to occur, with global climate changes resulting in greater chemical weathering occurring in Antarctica. Opportunistic sampling was conducted during the Austral summer of 2016/2017, whereby rock, snow and meltwater samples were taken at various sites within the western portion of Dronning Maud Land of Antarctica. Rock samples were placed in resin, and cut with a diamond saw to create thin sections. Optical microscopy and scanning transmission electron microscopy (STEM) were used to analyse mineral weight percentage with depth. Twelve soil samples were dried and weighed, sieved and statistically represented according to particle size. Inductively coupled plasma mass spectrometry (ICP-MS) determined the geochemical analysis for 10 water and snow samples. Rock hardness was inferred through the use of an Equotip, with rebound values recorded for multiple rock faces and samples. Thermal regimes of rock temperature was further recorded using a FLIR infrared camera, and documented for each rock face over a 24 hour period at 2 hourly intervals. The products of increased chemical weathering were evident from particle size analysis; samples were very poorly sorted in nature, and undergo in situ weathering, whereby products were not removed by erosional processes. Weathering rinds were found to be siliceous and ferric, depending on parent lithology. Ferric ratios increased in wt.% from the substrate rock to the external surface, creating the red, iron rich crusts noted on the hand specimens. The observable chemical weathering was found adjacent to intrusions through Precambrian dolerites. Geochemical analysis revealed thin, carbonaceous features, with impurity-rich layers, characteristic of speleothem formation. Carbonaceous layers did not follow underlying substrate features, rather deposited at the external surface, upon which, further precipitation growth could occur, creating karst features. Extensive gypsum coatings (>2mm) under BSE imagery were identified, with the abundance of gypsum salts (below surface level) and rock coatings indicating active sulphuric acid weathering, in western Dronning Maud Land, Antarctica. Were mechanical processes faster than chemical, weathering rinds and solution features on silicate rocks would be uncommon in the Antarctic, periglacial landscape. However, this is not the case as the existence of these landforms implies that chemical weathering may occur faster than mechanical weathering processes (Pope et al., 1995). In a changing world, one needs to monitor these processes at a micro-scale in order to fully understand how periglacial environments react to global climatic changes, and the subsequent impacts on these sensitive environments.
- Full Text:
- Date Issued: 2018
- Authors: Knox, Jenna Tracy
- Date: 2018
- Subjects: Glacial climates -- Antarctica -- Queen Maud Land , Glaciology -- Antarctica -- Queen Maud Land , Chemical weathering -- Antarctica -- Queen Maud Land , Atmospheric carbon dioxide -- Environmental aspects , Climatic changes -- Antarctica -- Queen Maud Land , Nunataks -- Antarctica -- Queen Maud Land
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/61658 , vital:28046
- Description: High latitude areas are sensitive to the impacts of climate change, and it is expected that the impact of greenhouse warming will be much higher in the polar regions than in any other climatic zones, with the most highly affected area being that of the Antarctic rim (Barsch, 1993). Weathering and pedogenic processes respond to variations in climate, with models predicting that chemical weathering may increase synchronously with global carbon dioxide levels increase, due to dissolution rates and the erosional impact of hydrological cycles in warming climates (Anderson & Anderson, 2010). As liquid water becomes more available in Antarctica the potential for chemical weathering, due to a less moisture-limited environment and increased temperatures, increases (Convey et al., 2009). Weathering processes are important for soil formation and the production of fine-grained material, with chemical weathering being an active constituent of this. Increased rates of soil formation are likely to occur, with global climate changes resulting in greater chemical weathering occurring in Antarctica. Opportunistic sampling was conducted during the Austral summer of 2016/2017, whereby rock, snow and meltwater samples were taken at various sites within the western portion of Dronning Maud Land of Antarctica. Rock samples were placed in resin, and cut with a diamond saw to create thin sections. Optical microscopy and scanning transmission electron microscopy (STEM) were used to analyse mineral weight percentage with depth. Twelve soil samples were dried and weighed, sieved and statistically represented according to particle size. Inductively coupled plasma mass spectrometry (ICP-MS) determined the geochemical analysis for 10 water and snow samples. Rock hardness was inferred through the use of an Equotip, with rebound values recorded for multiple rock faces and samples. Thermal regimes of rock temperature was further recorded using a FLIR infrared camera, and documented for each rock face over a 24 hour period at 2 hourly intervals. The products of increased chemical weathering were evident from particle size analysis; samples were very poorly sorted in nature, and undergo in situ weathering, whereby products were not removed by erosional processes. Weathering rinds were found to be siliceous and ferric, depending on parent lithology. Ferric ratios increased in wt.% from the substrate rock to the external surface, creating the red, iron rich crusts noted on the hand specimens. The observable chemical weathering was found adjacent to intrusions through Precambrian dolerites. Geochemical analysis revealed thin, carbonaceous features, with impurity-rich layers, characteristic of speleothem formation. Carbonaceous layers did not follow underlying substrate features, rather deposited at the external surface, upon which, further precipitation growth could occur, creating karst features. Extensive gypsum coatings (>2mm) under BSE imagery were identified, with the abundance of gypsum salts (below surface level) and rock coatings indicating active sulphuric acid weathering, in western Dronning Maud Land, Antarctica. Were mechanical processes faster than chemical, weathering rinds and solution features on silicate rocks would be uncommon in the Antarctic, periglacial landscape. However, this is not the case as the existence of these landforms implies that chemical weathering may occur faster than mechanical weathering processes (Pope et al., 1995). In a changing world, one needs to monitor these processes at a micro-scale in order to fully understand how periglacial environments react to global climatic changes, and the subsequent impacts on these sensitive environments.
- Full Text:
- Date Issued: 2018
Children in conflict with the law - constructions of their family environment
- Mtshutshwane, Anda Sweetgirl, Terblanche, Susan
- Authors: Mtshutshwane, Anda Sweetgirl , Terblanche, Susan
- Date: 2018
- Subjects: Juvenile delinquency -- South Africa -- Eastern Cape , Child development -- South Africa -- Eastern Cape , Problem children -- South Africa -- Eastern Cape , Children -- Legal status, laws, etc. -- South Africa -- Eastern Cape , Crime and age -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10948/32960 , vital:32480
- Description: The studies reviewed for this project indicate that there is an interplay of family and social factors that affect the development of the child. Furthermore, some studies postulate that there is a relationship between children’s engagement in criminal behaviour and their family environment. The present study aimed to explore, describe and interpret how children who have been in conflict with the law construct their family environment. A qualitative research approach that was embedded in an explorative, descriptive and contextual research design was employed in order to achieve the objectives of the study. The research population was constituted of children from a Child and Youth Care Centre. A non-probability purposive sampling technique was employed to select children aged 14 to 17 years who have been in conflict with the law. Individual semi-structured interviews were conducted with the selected children and this data was analyzed using Tesch’s thematic analysis. Ethical considerations that were applicable for the involvement of children and vulnerable groups in research were adhered to. The trustworthiness of the research process, and the findings of the study, were enhanced by employing a variety of data verification strategies. Data was verified using: member checking, peer debriefing, clarifying bias by the researcher, and dense description of the application of the selected methods used in research suggested by Creswell. The major findings of this study include: positive and negative experiences of children prior to involvement to crime in their internal family environment. The external family environment was dominated by gangsterism and crime in the community, police corruption and their interaction with drugs. Furthermore, the study findings revealed positive and negative school experiences and posited several reasons why children break the law. It is hoped that the research will contribute to the knowledge base of Social Work and Practice interventions in the field of child protection services in general and, more specifically, on the criminal justice system.
- Full Text:
- Date Issued: 2018
- Authors: Mtshutshwane, Anda Sweetgirl , Terblanche, Susan
- Date: 2018
- Subjects: Juvenile delinquency -- South Africa -- Eastern Cape , Child development -- South Africa -- Eastern Cape , Problem children -- South Africa -- Eastern Cape , Children -- Legal status, laws, etc. -- South Africa -- Eastern Cape , Crime and age -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10948/32960 , vital:32480
- Description: The studies reviewed for this project indicate that there is an interplay of family and social factors that affect the development of the child. Furthermore, some studies postulate that there is a relationship between children’s engagement in criminal behaviour and their family environment. The present study aimed to explore, describe and interpret how children who have been in conflict with the law construct their family environment. A qualitative research approach that was embedded in an explorative, descriptive and contextual research design was employed in order to achieve the objectives of the study. The research population was constituted of children from a Child and Youth Care Centre. A non-probability purposive sampling technique was employed to select children aged 14 to 17 years who have been in conflict with the law. Individual semi-structured interviews were conducted with the selected children and this data was analyzed using Tesch’s thematic analysis. Ethical considerations that were applicable for the involvement of children and vulnerable groups in research were adhered to. The trustworthiness of the research process, and the findings of the study, were enhanced by employing a variety of data verification strategies. Data was verified using: member checking, peer debriefing, clarifying bias by the researcher, and dense description of the application of the selected methods used in research suggested by Creswell. The major findings of this study include: positive and negative experiences of children prior to involvement to crime in their internal family environment. The external family environment was dominated by gangsterism and crime in the community, police corruption and their interaction with drugs. Furthermore, the study findings revealed positive and negative school experiences and posited several reasons why children break the law. It is hoped that the research will contribute to the knowledge base of Social Work and Practice interventions in the field of child protection services in general and, more specifically, on the criminal justice system.
- Full Text:
- Date Issued: 2018
Chipangano: vigilantism and community responses in Mbare District, Zimbabwe, c.2000-2013
- Authors: Munyarari, Tinashe
- Date: 2018
- Subjects: Vigilantism Zimbabwe Mbare , ZANU-PF (Organization : Zimbabwe) , Zimbabwe History 1980- , Vigilantism Zimbabwe Mbare Public opinion , Collective memory Zimbabwe Mbare
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/62126 , vital:28130
- Description: This study examines an aspect of Zimbabwe’s political history, namely the emergence and operations of Chipangano vigilante group in Mbare (2000-2013) and how the community responded to the scourges of this vigilante group. This study shows that Chipangano, which means a pact, was formed with the intention to extend ZANU-PF patronage system, canvassing support and regain control of Mbare district from the MDC. The group consolidated itself as a shadow militia group for ZANU-PF that intimidated the opposition parties and coerced the general populace to attend ZANU-PF functions. It also shows that the vigilante group seized Harare City Council’s duties, such as collecting gate-takings from local and long distance public transport at Mbare Bus Terminal; controlling allocations of market stalls and collecting rents from market stalls, for personal benefits. The group also politicised the access to local state property. Chipangano’s collusion with ZANU-PF and state structures licensed it to engage in criminal activities with impunity, thus this thesis seeks to understand the relationship between the vigilantes, ZANU-PF and state structures. The activities of Chipangano such as abduction, intimidation, beatings, killings and displacement of people resulted in social trauma. This thesis will also explore how this phase of violence is remembered today by the research informants. , Thesis (MA) -- Faculty of Humanities, History, 2018
- Full Text:
- Date Issued: 2018
- Authors: Munyarari, Tinashe
- Date: 2018
- Subjects: Vigilantism Zimbabwe Mbare , ZANU-PF (Organization : Zimbabwe) , Zimbabwe History 1980- , Vigilantism Zimbabwe Mbare Public opinion , Collective memory Zimbabwe Mbare
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/62126 , vital:28130
- Description: This study examines an aspect of Zimbabwe’s political history, namely the emergence and operations of Chipangano vigilante group in Mbare (2000-2013) and how the community responded to the scourges of this vigilante group. This study shows that Chipangano, which means a pact, was formed with the intention to extend ZANU-PF patronage system, canvassing support and regain control of Mbare district from the MDC. The group consolidated itself as a shadow militia group for ZANU-PF that intimidated the opposition parties and coerced the general populace to attend ZANU-PF functions. It also shows that the vigilante group seized Harare City Council’s duties, such as collecting gate-takings from local and long distance public transport at Mbare Bus Terminal; controlling allocations of market stalls and collecting rents from market stalls, for personal benefits. The group also politicised the access to local state property. Chipangano’s collusion with ZANU-PF and state structures licensed it to engage in criminal activities with impunity, thus this thesis seeks to understand the relationship between the vigilantes, ZANU-PF and state structures. The activities of Chipangano such as abduction, intimidation, beatings, killings and displacement of people resulted in social trauma. This thesis will also explore how this phase of violence is remembered today by the research informants. , Thesis (MA) -- Faculty of Humanities, History, 2018
- Full Text:
- Date Issued: 2018
Citizen science, treatment and microbial compliance monitoring in rainwater harvesting in Namibia
- Angala, Hallo Angaleni Nameya
- Authors: Angala, Hallo Angaleni Nameya
- Date: 2018
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/62082 , vital:28105
- Description: Expected release date-April 2020
- Full Text:
- Date Issued: 2018
- Authors: Angala, Hallo Angaleni Nameya
- Date: 2018
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/62082 , vital:28105
- Description: Expected release date-April 2020
- Full Text:
- Date Issued: 2018
Classification of Distinct Fuzzy Subgroups of the Dihedral Group Dp nq for p and q distinct primes and n ∈ N
- Authors: Nxala, Baphumelele Ellen
- Date: 2018
- Subjects: Fuzzy mathematics Fuzzy sets
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/14516 , vital:39997
- Description: In this dissertation, we classify distinct fuzzy subgroups of the dihedral group Dpnq, for p and q distinct primes and n ∈ N, under a natural equivalence relation of fuzzy subgroups and a fuzzy isomorphism. We aim to present formulae for the number of maximal chains and the number of distinct fuzzy subgroups of this group. Our study will include some theory on non-abelian groups since the classification of distinct fuzzy subgroups of this group relies on the crisp characterization of maximal chains. We give the definition of a natural equivalence relation introduced by Murali and Makamba in [67] which we will use in this study. Based on this definition, we introduce two counting techniques that we will use to compute the number of distinct fuzzy subgroups of Dpnq. In this dissertation, we use the criss-cut counting technique as our primary method of enumeration, and the cross-cut method serves as a means of verifying results we obtain from our primary method. To classify distinct fuzzy subgroups of this group, we begin by investigating the dihedral groups Dpnq, for p and q distinct primes and specific values of n = 2 and 3 to observe a trend. We classify the flags of these groups using the characterization of flags introduced in [93]. From this characterization, we then present formulae for the number of distinct fuzzy subgroups attributed to the flags of Dp 2q and Dp 3q . To generalise results for Dpnq, for p and q distinct primes and n ∈ N, we characterize the flags of this group and classify them as either cyclic, mdcyclic for 1 ≤ m ≤ n, or b-cyclic. Finally, we establish a general formula for the number of distinct fuzzy subgroups obtainable from these flags. We conclude by comparing results obtained from using our general formula to those obtained by other researchers for the same group. Based on the results from this study, we give an outline of future research work
- Full Text:
- Date Issued: 2018
- Authors: Nxala, Baphumelele Ellen
- Date: 2018
- Subjects: Fuzzy mathematics Fuzzy sets
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10353/14516 , vital:39997
- Description: In this dissertation, we classify distinct fuzzy subgroups of the dihedral group Dpnq, for p and q distinct primes and n ∈ N, under a natural equivalence relation of fuzzy subgroups and a fuzzy isomorphism. We aim to present formulae for the number of maximal chains and the number of distinct fuzzy subgroups of this group. Our study will include some theory on non-abelian groups since the classification of distinct fuzzy subgroups of this group relies on the crisp characterization of maximal chains. We give the definition of a natural equivalence relation introduced by Murali and Makamba in [67] which we will use in this study. Based on this definition, we introduce two counting techniques that we will use to compute the number of distinct fuzzy subgroups of Dpnq. In this dissertation, we use the criss-cut counting technique as our primary method of enumeration, and the cross-cut method serves as a means of verifying results we obtain from our primary method. To classify distinct fuzzy subgroups of this group, we begin by investigating the dihedral groups Dpnq, for p and q distinct primes and specific values of n = 2 and 3 to observe a trend. We classify the flags of these groups using the characterization of flags introduced in [93]. From this characterization, we then present formulae for the number of distinct fuzzy subgroups attributed to the flags of Dp 2q and Dp 3q . To generalise results for Dpnq, for p and q distinct primes and n ∈ N, we characterize the flags of this group and classify them as either cyclic, mdcyclic for 1 ≤ m ≤ n, or b-cyclic. Finally, we establish a general formula for the number of distinct fuzzy subgroups obtainable from these flags. We conclude by comparing results obtained from using our general formula to those obtained by other researchers for the same group. Based on the results from this study, we give an outline of future research work
- Full Text:
- Date Issued: 2018
Click chemistry electrode modification using 4-ethynylbenzyl substituted cobalt phthalocyanine for applications in electrocatalysis
- Mpeta, Lekhetho S, Fomo, Gertrude, Nyokong, Tebello
- Authors: Mpeta, Lekhetho S , Fomo, Gertrude , Nyokong, Tebello
- Date: 2018
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/187626 , vital:44681 , xlink:href="• https://doi.org/10.1080/00958972.2018.1466118"
- Description: In this work, we report on the synthesis and applications of a new cobalt tetrakis 4-((4-ethynylbenzyl) oxy) phthalocyanine (3) for the detection of hydrazine. The glassy carbon electrode (GCE) was first grafted through diazotization, providing the GCE surface layer with azide groups. Thereafter, the 1,3-dipolar cycloaddition reaction, catalyzed by a copper(I) catalyst was used to “click” complex 3 to the grafted surface of GCE. The new platform was then characterized using cyclic voltammetry (CV), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). This work shows that 3 is an effective sensor with sensitivity of 91.5 μA mM−1 and limit of detection of 3.28 μM which is a great improvement compared to other reported sensors for this analyte.
- Full Text:
- Date Issued: 2018
- Authors: Mpeta, Lekhetho S , Fomo, Gertrude , Nyokong, Tebello
- Date: 2018
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/187626 , vital:44681 , xlink:href="• https://doi.org/10.1080/00958972.2018.1466118"
- Description: In this work, we report on the synthesis and applications of a new cobalt tetrakis 4-((4-ethynylbenzyl) oxy) phthalocyanine (3) for the detection of hydrazine. The glassy carbon electrode (GCE) was first grafted through diazotization, providing the GCE surface layer with azide groups. Thereafter, the 1,3-dipolar cycloaddition reaction, catalyzed by a copper(I) catalyst was used to “click” complex 3 to the grafted surface of GCE. The new platform was then characterized using cyclic voltammetry (CV), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). This work shows that 3 is an effective sensor with sensitivity of 91.5 μA mM−1 and limit of detection of 3.28 μM which is a great improvement compared to other reported sensors for this analyte.
- Full Text:
- Date Issued: 2018
Cloud computing adoption: Strategies for Sub-Saharan Africa SMEs for enhancing competitiveness
- Authors: Adane, Martin
- Date: 2018
- Subjects: business intelligence small businesses business planning Article
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/11260/6862 , vital:51101 , xlink:href="https://doi.org/10.1080/20421338.2018.1439288"
- Description: Small and medium-sized enterprises (SMEs) need to design and implement strategies for adopting new technologies as a competitive tool for maintaining their competitive advantage and cloud computing is at its peak. Since its emergence, there has been a surge in the adoption of cloud computing with research into its adoption primarily concentrated on bigger firms. However, a major characteristic of cloud computing is the anticipated possibilities it holds for SMEs. This paper primarily explores cloud computing adoption strategies for SMEs operating in Sub-Saharan Africa. Using a mixed method approach, a sample of 261 respondents and 11 SMEs was respectively used for the quantitative and qualitative stages of the research. The results reveal that, even though SMEs have their unique expectations for adopting cloud computing, they were of the consensus that elements of an adoption strategy should include adoption goals, a roadmap, and considerations. The paper makes specific recommendations to SMEs to develop adoption strategies that meet their specific needs if they expect cloud computing to play a stronger role to support more strategic initiatives to grow their businesses and improve customer experience.
- Full Text:
- Date Issued: 2018
- Authors: Adane, Martin
- Date: 2018
- Subjects: business intelligence small businesses business planning Article
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/11260/6862 , vital:51101 , xlink:href="https://doi.org/10.1080/20421338.2018.1439288"
- Description: Small and medium-sized enterprises (SMEs) need to design and implement strategies for adopting new technologies as a competitive tool for maintaining their competitive advantage and cloud computing is at its peak. Since its emergence, there has been a surge in the adoption of cloud computing with research into its adoption primarily concentrated on bigger firms. However, a major characteristic of cloud computing is the anticipated possibilities it holds for SMEs. This paper primarily explores cloud computing adoption strategies for SMEs operating in Sub-Saharan Africa. Using a mixed method approach, a sample of 261 respondents and 11 SMEs was respectively used for the quantitative and qualitative stages of the research. The results reveal that, even though SMEs have their unique expectations for adopting cloud computing, they were of the consensus that elements of an adoption strategy should include adoption goals, a roadmap, and considerations. The paper makes specific recommendations to SMEs to develop adoption strategies that meet their specific needs if they expect cloud computing to play a stronger role to support more strategic initiatives to grow their businesses and improve customer experience.
- Full Text:
- Date Issued: 2018
Co-Production of trust for effective local Governance: a case study of Nelson Mandela Bay Municipality
- Authors: Salie-Jakoet, Amina
- Date: 2018
- Subjects: Corporate governance--South Africa--Nelson Mandela Bay Municipality Economic development--South Africa--Nelson Mandela Bay Municipality , Municipal officials and employees--South Africa-- Port Elizabeth
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/20308 , vital:29228
- Description: This study acknowledged that while it might be true that protests often turn violent after formal channels have been exhausted, there is an underlying problem of lack of public participation, coproduction and a general lack of trust in and within local government institutions in South Africa. The study therefore proposes that public participation in the municipal governing process is more complex than anticipated. For purposes of data collection, a mixed methods research methodology was adopted and a number of salient recommendations are provided to address the levels of trust within local government. A normative model to enhance coproduction of trust between communities and local government has been proposed. The research is scientifically worthy of distribution to the broader academic community and a number of papers both nationally and internationally have been presented from it.
- Full Text:
- Date Issued: 2018
- Authors: Salie-Jakoet, Amina
- Date: 2018
- Subjects: Corporate governance--South Africa--Nelson Mandela Bay Municipality Economic development--South Africa--Nelson Mandela Bay Municipality , Municipal officials and employees--South Africa-- Port Elizabeth
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/20308 , vital:29228
- Description: This study acknowledged that while it might be true that protests often turn violent after formal channels have been exhausted, there is an underlying problem of lack of public participation, coproduction and a general lack of trust in and within local government institutions in South Africa. The study therefore proposes that public participation in the municipal governing process is more complex than anticipated. For purposes of data collection, a mixed methods research methodology was adopted and a number of salient recommendations are provided to address the levels of trust within local government. A normative model to enhance coproduction of trust between communities and local government has been proposed. The research is scientifically worthy of distribution to the broader academic community and a number of papers both nationally and internationally have been presented from it.
- Full Text:
- Date Issued: 2018
Co-production of trust for effective local governance: a case study of the Nelson Mandela Bay Municipality
- Authors: Jakoet-Salie, Amina
- Date: 2018
- Subjects: Public participation -- South Africa -- Nelson Mandela Bay Local government -- South Africa -- Nelson Mandela Bay
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/20297 , vital:29227
- Description: The primary aim of this study was to establish whether co-production of public services will lead to trust in service delivery and ultimately to trust in government, with specific reference to the Nelson Mandela Bay Municipality (NMBM). Furthermore, this research investigatedthe fundamental reasons for the mistrust in government, in lieu of the ongoing service delivery protests and officials who are at times not held accountable for their actions. This study acknowledges that there is an underlying problem of lack ofpublic participation and co-production at the sphere of local government.This research is solely based on the assumption thatif co-production is non-existent or problematic and if communities lose trust in the performance of municipalities, any attempts by the government to address these challenges relating to effective governance would be ineffective.The studyprovidesan in-depth theoretical review on co-production, public participation, citizen engagement and trust, with reference to both the national and international context. The study employed both quantitative and qualitative research approaches to validate the research questions and authenticate the problem statement. The triangulation approach allowed the researcher to effectively engage the strengths of both research methodologies. The research findings from the empirical survey were statistically analysed using statistical procedures. The data analysis, derived from the qualitative research approach, involved thematic content analysis. The sample populations for the study comprised councillors selected senior officials and ward committee members. For the quantitative approach, questionnaires were employed for the councillors and the officials. Focus group interviews were conducted with ward committee members as the qualitative component of the study. The findings of the study revealed that as a result of communities’ increasing lack of trust and confidence in local government, service delivery protests are increasing.The study further indicated thatcommunities in the NMBM are generally not well informed about the development plans of the municipality and do not adequately participate in local government activities.The findings from the focus group interviewsconcluded that the working relationship between the ward councillors and ward committee members was somewhat strained and this could have a negative impact on service delivery and ultimately trust levels.Recommendations emanating from the empirical survey and focus group interviews are presented to promote public participation and co-production which essentially could lead to an increase in trust in local government. Legislative prescriptions require that communitiesshould actively participate in the decision-making processes at the local sphere of government. In this regard, a normative model is proposed to further enhance this requirement.
- Full Text:
- Date Issued: 2018
- Authors: Jakoet-Salie, Amina
- Date: 2018
- Subjects: Public participation -- South Africa -- Nelson Mandela Bay Local government -- South Africa -- Nelson Mandela Bay
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/20297 , vital:29227
- Description: The primary aim of this study was to establish whether co-production of public services will lead to trust in service delivery and ultimately to trust in government, with specific reference to the Nelson Mandela Bay Municipality (NMBM). Furthermore, this research investigatedthe fundamental reasons for the mistrust in government, in lieu of the ongoing service delivery protests and officials who are at times not held accountable for their actions. This study acknowledges that there is an underlying problem of lack ofpublic participation and co-production at the sphere of local government.This research is solely based on the assumption thatif co-production is non-existent or problematic and if communities lose trust in the performance of municipalities, any attempts by the government to address these challenges relating to effective governance would be ineffective.The studyprovidesan in-depth theoretical review on co-production, public participation, citizen engagement and trust, with reference to both the national and international context. The study employed both quantitative and qualitative research approaches to validate the research questions and authenticate the problem statement. The triangulation approach allowed the researcher to effectively engage the strengths of both research methodologies. The research findings from the empirical survey were statistically analysed using statistical procedures. The data analysis, derived from the qualitative research approach, involved thematic content analysis. The sample populations for the study comprised councillors selected senior officials and ward committee members. For the quantitative approach, questionnaires were employed for the councillors and the officials. Focus group interviews were conducted with ward committee members as the qualitative component of the study. The findings of the study revealed that as a result of communities’ increasing lack of trust and confidence in local government, service delivery protests are increasing.The study further indicated thatcommunities in the NMBM are generally not well informed about the development plans of the municipality and do not adequately participate in local government activities.The findings from the focus group interviewsconcluded that the working relationship between the ward councillors and ward committee members was somewhat strained and this could have a negative impact on service delivery and ultimately trust levels.Recommendations emanating from the empirical survey and focus group interviews are presented to promote public participation and co-production which essentially could lead to an increase in trust in local government. Legislative prescriptions require that communitiesshould actively participate in the decision-making processes at the local sphere of government. In this regard, a normative model is proposed to further enhance this requirement.
- Full Text:
- Date Issued: 2018
Code-switching as a pedagogical strategy in classroom settings: the case of township schools in a South African Metropolitan Municipality
- Authors: Marawu, Sithembele
- Date: 2018
- Subjects: Code switching (Linguistics) , Multilingual education -- South Africa , Education, Bilingual -- South Africa , Language and languages -- Study and teaching -- Bilingual method , English language -- Social aspects -- South Africa , Language and education -- South Africa , Language and education -- Social aspects -- South Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/62406 , vital:28173
- Description: The purpose of this study was to explore the use of code-switching as a pedagogical strategy in bi/multilingual classroom settings. It was prompted by the widespread use of codeswitching (CS) in classrooms, particularly in South African rural and township schools. This study highlighted that learners from disadvantaged backgrounds struggle to learn through the medium of English but aspire to acquire it because of its association with socio-economic advancement. However, poor proficiency in English excludes them from being part of the country's economy. Research studies show that there is a shift from the old orthodoxy which perceived CS as undesirable in classrooms to a new orthodoxy that acknowledges its academic contribution in classrooms. Although more research on classroom CS has been done, this study identified the need for development of new strategies on how to use CS effectively in classrooms as a linguistic and pedagogical resource. In line with critical classroom ethnography, qualitative interpretation of data was used to understand the teachers' discourse behaviour. Additionally, non-probability sampling - specifically purposive sampling - was used to collect data. These methods and approaches assisted in the analysis of the discourse of the three teachers who served as units of analysis in this study. These teachers relied on CS to impart the content of their subjects to the learners. It transpired from data analysis that teachers use CS in classrooms to achieve various functions like social and pedagogical functions. Another finding is that the switches teachers make do not affect the syntactic structure of the matrix language. Moreover, CS enhances understanding of the subject matter. This study concludes by stating that as learners are emergent bilinguals, additive bilingualism would be more ideal in the South African situation than subtractive bilingualism which parents and learners seem to prefer. Lastly, there is a need to harness CS as a communicative and pedagogical resource in classrooms.
- Full Text:
- Date Issued: 2018
- Authors: Marawu, Sithembele
- Date: 2018
- Subjects: Code switching (Linguistics) , Multilingual education -- South Africa , Education, Bilingual -- South Africa , Language and languages -- Study and teaching -- Bilingual method , English language -- Social aspects -- South Africa , Language and education -- South Africa , Language and education -- Social aspects -- South Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/62406 , vital:28173
- Description: The purpose of this study was to explore the use of code-switching as a pedagogical strategy in bi/multilingual classroom settings. It was prompted by the widespread use of codeswitching (CS) in classrooms, particularly in South African rural and township schools. This study highlighted that learners from disadvantaged backgrounds struggle to learn through the medium of English but aspire to acquire it because of its association with socio-economic advancement. However, poor proficiency in English excludes them from being part of the country's economy. Research studies show that there is a shift from the old orthodoxy which perceived CS as undesirable in classrooms to a new orthodoxy that acknowledges its academic contribution in classrooms. Although more research on classroom CS has been done, this study identified the need for development of new strategies on how to use CS effectively in classrooms as a linguistic and pedagogical resource. In line with critical classroom ethnography, qualitative interpretation of data was used to understand the teachers' discourse behaviour. Additionally, non-probability sampling - specifically purposive sampling - was used to collect data. These methods and approaches assisted in the analysis of the discourse of the three teachers who served as units of analysis in this study. These teachers relied on CS to impart the content of their subjects to the learners. It transpired from data analysis that teachers use CS in classrooms to achieve various functions like social and pedagogical functions. Another finding is that the switches teachers make do not affect the syntactic structure of the matrix language. Moreover, CS enhances understanding of the subject matter. This study concludes by stating that as learners are emergent bilinguals, additive bilingualism would be more ideal in the South African situation than subtractive bilingualism which parents and learners seem to prefer. Lastly, there is a need to harness CS as a communicative and pedagogical resource in classrooms.
- Full Text:
- Date Issued: 2018
Coega industrial development zone as a catalyst for development in NMBM
- Authors: Younouss, Sanda Oumarou
- Date: 2018
- Subjects: Industrial development projects -- South Africa -- Port Elizabeth , Industrial development projects -- South Africa Economic development -- South Africa
- Language: English
- Type: Thesis , Masters , MPhil
- Identifier: http://hdl.handle.net/10948/36162 , vital:33901
- Description: It is common for countries to adopt growth-targeted strategies to address poverty and as a result, achieve development. South Africa is not an exception and that is the reason for implementing the industrial development zone (IDZ) programme, intended to achieve growth through exports. As part of this programme, the country established five IDZs, each of which operates in specific investment sectors. The economy of the Eastern Cape is experiencing difficulties in terms of unemployment, low wages and a declining population and the migration out of the Eastern Cape is due to limited job opportunities and low wages. The four largest economic sectors in the province are manufacturing, construction, agriculture and mining. The Coega IDZ (CIDZ) is located in the Eastern Cape Province of South Africa and operates in six investment sectors, namely automotive, agro-processing and aqua farming, chemical manufacturing, business process outsourcing, energy and metals. This research investigated the contribution of the CIDZ as a tool for development in the Eastern Cape and South Africa. It further investigates its contribution to the development of the Eastern Cape in the event of its expansion across three additional investment sectors, namely electronics, clothing and furniture. With the aim of conducting a proper assessment of their contribution, the strengths and weaknesses of these three investment sectors were elucidated. Additionally, the research described the operation of four special economic zones (SEZs), namely the Zarqa Free Zone, the Jebel Ali Free Zone, the East London Industrial Development Zone (ELIDZ) and the Coega Industrial Development Zone (CIDZ). The research methodology used was that of a descriptive study (literature-based). The research revealed that there is a need to add these three investment sectors to the CIDZ in order to develop the Eastern Cape, as they have the potential to meet the challenges that the province is facing. The research led to a number of recommendations inspired by the SEZs presented in the descriptive study, to improve the contribution of the CIDZ to the development of the Eastern Cape.
- Full Text:
- Date Issued: 2018
- Authors: Younouss, Sanda Oumarou
- Date: 2018
- Subjects: Industrial development projects -- South Africa -- Port Elizabeth , Industrial development projects -- South Africa Economic development -- South Africa
- Language: English
- Type: Thesis , Masters , MPhil
- Identifier: http://hdl.handle.net/10948/36162 , vital:33901
- Description: It is common for countries to adopt growth-targeted strategies to address poverty and as a result, achieve development. South Africa is not an exception and that is the reason for implementing the industrial development zone (IDZ) programme, intended to achieve growth through exports. As part of this programme, the country established five IDZs, each of which operates in specific investment sectors. The economy of the Eastern Cape is experiencing difficulties in terms of unemployment, low wages and a declining population and the migration out of the Eastern Cape is due to limited job opportunities and low wages. The four largest economic sectors in the province are manufacturing, construction, agriculture and mining. The Coega IDZ (CIDZ) is located in the Eastern Cape Province of South Africa and operates in six investment sectors, namely automotive, agro-processing and aqua farming, chemical manufacturing, business process outsourcing, energy and metals. This research investigated the contribution of the CIDZ as a tool for development in the Eastern Cape and South Africa. It further investigates its contribution to the development of the Eastern Cape in the event of its expansion across three additional investment sectors, namely electronics, clothing and furniture. With the aim of conducting a proper assessment of their contribution, the strengths and weaknesses of these three investment sectors were elucidated. Additionally, the research described the operation of four special economic zones (SEZs), namely the Zarqa Free Zone, the Jebel Ali Free Zone, the East London Industrial Development Zone (ELIDZ) and the Coega Industrial Development Zone (CIDZ). The research methodology used was that of a descriptive study (literature-based). The research revealed that there is a need to add these three investment sectors to the CIDZ in order to develop the Eastern Cape, as they have the potential to meet the challenges that the province is facing. The research led to a number of recommendations inspired by the SEZs presented in the descriptive study, to improve the contribution of the CIDZ to the development of the Eastern Cape.
- Full Text:
- Date Issued: 2018
Combined spectral and stimulated luminescence study of charge trapping and recombination processes in α-Al2O3:C
- Authors: Nyirenda, Angel Newton
- Date: 2018
- Subjects: Luminescence , Thermoluminescence , Luminescence spectroscopy , Carbon-doped aluminium oxide , Radioluminescence , Time-resolved X-ray excited optical luminescence
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/62683 , vital:28235
- Description: The main objective of this project was to gain a deeper and better understanding of the luminescence processes in a-Al₂O₃:C, a highly-sensitive dosimetric material, using a combined spectral and stimulated luminescence study. The spectral studies concentrated on the emission spectra obtained using X-ray induced radioluminescence (XERL), thermoluminescence (XETL) and time-resolved X-ray excited optical luminescence (TR-XEOL) techniques. The stimulated luminescence studies were based on thermoluminescence (TL), optically stimulated luminescence (OSL) and phototransferred TL (PTTL) methods that were used in the study of the radiation-induced defects at high beta-doses and the deep traps, that is, traps with thermal depths beyond 500°C. The spectral and stimulated luminescence measurements were carried out using a high sensitivity luminescence spectrometer and a Ris0 TL/OSL Model DA-20 Reader, respectively. The XERL emission spectrum measured at room temperature shows seven gaussian peaks associated with F-centres (420 nm), F+-centres (334 nm), F2+-centres (559 nm), Stoke’s vibronic band of Cr3+ (671 nm), Cr3+ R-line emission (694 nm), anti-Stokes vibronic band of Cr3+ (710 nm) and an unidentified emission band (260-300 nm) which we associate with hole recombinations at a luminescence centre. The 694-nm R-line emission from Cr3+ impurity ions is most likely due to recombination of holes at Cr2+ during stimulated luminescence and as a result of an intracentre excitation of Cr3+ in photoluminescence (PL) due to photon absorption. The Cr3+ emission decreases in intensity, whereas the intensity of F-centre emission band is almost constant with repeated XERL measurements. Depending on the amount of X-ray irradiation dose, both holes and/or electrons may take place in the emission processes of peaks I (30-80°C), II (90-250°C) and III (250-320°C) during a TL readout, albeit, electron recombination is dominant regardless of dose. At higher doses, the XETL emission spectra indicate that the dominant band associated with TL peak III (250-320°C) in the material, shifts from F-centre to Cr3+. Using the deep-traps OSL, it has been confirmed that the main TL trap is also the main OSL trap whereas the TL traps lying in the temperature range of 400-550°C constitute the secondary OSL traps. There is evidence of strong retrapping at the main trap during optical stimulation of charges from the secondary OSL traps and the deep traps and that the retrapping occurs via the delocalized bands. At high-irradiation beta-doses, aggregate defect centres which significantly alter the TL and OSL properties, are induced in the material. The induced aggregate centres get completely obliterated by heating a sample to 700°C. The radiation-induced defects cause the main TL peak to shift towards higher temperatures, increase its FWHM, reduce its maximum intensity and cause an underestimation of both the activation energy and order of kinetics of the peak. On the other hand, the OSL response of the material is enhanced following a high-irradiation dose. During sample storage in the dark at ambient temperature, charges do migrate from the deep traps (donors) to the main and intermediate traps (acceptors) and that the major donor traps during this charge transfer phenomenon lie between 500-600°C.
- Full Text:
- Date Issued: 2018
- Authors: Nyirenda, Angel Newton
- Date: 2018
- Subjects: Luminescence , Thermoluminescence , Luminescence spectroscopy , Carbon-doped aluminium oxide , Radioluminescence , Time-resolved X-ray excited optical luminescence
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/62683 , vital:28235
- Description: The main objective of this project was to gain a deeper and better understanding of the luminescence processes in a-Al₂O₃:C, a highly-sensitive dosimetric material, using a combined spectral and stimulated luminescence study. The spectral studies concentrated on the emission spectra obtained using X-ray induced radioluminescence (XERL), thermoluminescence (XETL) and time-resolved X-ray excited optical luminescence (TR-XEOL) techniques. The stimulated luminescence studies were based on thermoluminescence (TL), optically stimulated luminescence (OSL) and phototransferred TL (PTTL) methods that were used in the study of the radiation-induced defects at high beta-doses and the deep traps, that is, traps with thermal depths beyond 500°C. The spectral and stimulated luminescence measurements were carried out using a high sensitivity luminescence spectrometer and a Ris0 TL/OSL Model DA-20 Reader, respectively. The XERL emission spectrum measured at room temperature shows seven gaussian peaks associated with F-centres (420 nm), F+-centres (334 nm), F2+-centres (559 nm), Stoke’s vibronic band of Cr3+ (671 nm), Cr3+ R-line emission (694 nm), anti-Stokes vibronic band of Cr3+ (710 nm) and an unidentified emission band (260-300 nm) which we associate with hole recombinations at a luminescence centre. The 694-nm R-line emission from Cr3+ impurity ions is most likely due to recombination of holes at Cr2+ during stimulated luminescence and as a result of an intracentre excitation of Cr3+ in photoluminescence (PL) due to photon absorption. The Cr3+ emission decreases in intensity, whereas the intensity of F-centre emission band is almost constant with repeated XERL measurements. Depending on the amount of X-ray irradiation dose, both holes and/or electrons may take place in the emission processes of peaks I (30-80°C), II (90-250°C) and III (250-320°C) during a TL readout, albeit, electron recombination is dominant regardless of dose. At higher doses, the XETL emission spectra indicate that the dominant band associated with TL peak III (250-320°C) in the material, shifts from F-centre to Cr3+. Using the deep-traps OSL, it has been confirmed that the main TL trap is also the main OSL trap whereas the TL traps lying in the temperature range of 400-550°C constitute the secondary OSL traps. There is evidence of strong retrapping at the main trap during optical stimulation of charges from the secondary OSL traps and the deep traps and that the retrapping occurs via the delocalized bands. At high-irradiation beta-doses, aggregate defect centres which significantly alter the TL and OSL properties, are induced in the material. The induced aggregate centres get completely obliterated by heating a sample to 700°C. The radiation-induced defects cause the main TL peak to shift towards higher temperatures, increase its FWHM, reduce its maximum intensity and cause an underestimation of both the activation energy and order of kinetics of the peak. On the other hand, the OSL response of the material is enhanced following a high-irradiation dose. During sample storage in the dark at ambient temperature, charges do migrate from the deep traps (donors) to the main and intermediate traps (acceptors) and that the major donor traps during this charge transfer phenomenon lie between 500-600°C.
- Full Text:
- Date Issued: 2018
Community education and training colleges as agents of community development in Olievenhoutbosch, Tshwane Municipality
- Authors: Mfenyane, Nozuko Primrose
- Date: 2018
- Subjects: Community education -- South Africa , Community development -- South Africa Vocational education -- South Africa
- Language: English
- Type: Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10948/32762 , vital:32355
- Description: The study investigated how the current Community Education and Training (CET) colleges model, as conceptualized by the Department of Higher Education and Training (DHET), hence the ability of Community Education and Training Colleges to contribute to community development in Olievenbosch community. The findings support the DHET's conceptual model of CET colleges, as a new form of institution that will meet the needs of citizens that may not be able to make it to universities and TVET colleges in South Africa.
- Full Text: false
- Date Issued: 2018
- Authors: Mfenyane, Nozuko Primrose
- Date: 2018
- Subjects: Community education -- South Africa , Community development -- South Africa Vocational education -- South Africa
- Language: English
- Type: Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10948/32762 , vital:32355
- Description: The study investigated how the current Community Education and Training (CET) colleges model, as conceptualized by the Department of Higher Education and Training (DHET), hence the ability of Community Education and Training Colleges to contribute to community development in Olievenbosch community. The findings support the DHET's conceptual model of CET colleges, as a new form of institution that will meet the needs of citizens that may not be able to make it to universities and TVET colleges in South Africa.
- Full Text: false
- Date Issued: 2018
Community participation in urban revitalization in Buffalo City
- Authors: Magwala, Tandiswa
- Date: 2018
- Subjects: Urban renewal -- South Africa -- Buffalo City Municipality , Community development -- South Africa -- Buffalo City Municipality Neighborhoods -- South Africa -- Buffalo City Municipality Sustainable development -- South Africa -- Eastern Cape -- Citizen participation
- Language: English
- Type: Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10948/31521 , vital:31501
- Description: Community participation relates to the process by which community members are involved in the projects that determine pertains to their development needs. It is a means of empowering people by developing their skills and abilities to enable them to negotiate and make appropriate decisions for their development. However, community participation faces many challenges in South Africa and some other countries. For instance, in most, if not all, development projects commenced by local municipalities, community participation is often neglected or becomes an afterthought. In most cases, the communities are consulted after decisions have already been made by government agencies in relation to the kind of development projects that need to be executed. As a result, community participation is a prerequisite in development projects which are meant to improve the livelihoods and standard of living of the majority of communities in South Africa. The Buffalo City Municipality Metro (BCMM) is not an exception to this. The BCMM is located in the Eastern Cape Province, which is one of the poorest provinces in South Africa. In one of the towns in the municipal area, namely Dimbaza in the former Ciskei ‘homeland’, where there are high levels of unemployment and poverty, a prominent feature in the landscape is the many abandoned factory buildings. In recent years, the BCMM has recognized the need to revitalize the nodal areas such as Mdantsane, Dimbaza and Bisho, but due to the fragmented patterns of Bantustan policies the program was negatively affected (BCMM 2014/15/141). As a consequence, the BCMM has supported the implement an urban revitalization project within its area. The aim of this study was to investigate and interrogate whether local communities are involved in urban revitalization in the BCMM. That is, to evaluate community participation in urban revitalization projects in the BCMM, and focusing on Dimbaza community in the Eastern Cape province of South Africa as a case study. The study asks the following questions: Do the BCMM’s urban redevelopment initiatives have community participation component? How can the community be more involved in neighbourhood revitalization? v To what extent do these perceptions and priorities of the people living in neighbourhood of the disused factories match those of the policy makers? What are the perceptions of the people living in the neighbourhood of the disused factories in Dimbaza with regard to redevelopment? What recommendations can emanate from the study to address the current challenges regarding community participation in urban revitalization in BCMM? The study revealed that the majority of the respondents did not participate in the initiation and planning stages of the urban revitalization projects. The study further showed that a considerable proportion of the surveyed Dimbaza residents did not know about the urban revitalization programme, but learnt about it only in the local newspaper. It is therefore recommended that, the BCMM should support the community at all levels of planning to ensure a strong commitment to participation in their urban revitalization or development projects. It is hoped that this study will sensitize the community members of Dimbaza and the roles players involved in the Dimbaza urban revitalization projects including, among others, the Buffalo City Municipality Metropolitan, the Eastern Cape Development Cooperation and the Department of Economic Development, Environmental Affairs and Tourism of the Eastern Cape, to realise the significance and advantages of community participation, and that they will work through the challenges therein in order to increase community participation in development projects.
- Full Text:
- Date Issued: 2018
- Authors: Magwala, Tandiswa
- Date: 2018
- Subjects: Urban renewal -- South Africa -- Buffalo City Municipality , Community development -- South Africa -- Buffalo City Municipality Neighborhoods -- South Africa -- Buffalo City Municipality Sustainable development -- South Africa -- Eastern Cape -- Citizen participation
- Language: English
- Type: Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10948/31521 , vital:31501
- Description: Community participation relates to the process by which community members are involved in the projects that determine pertains to their development needs. It is a means of empowering people by developing their skills and abilities to enable them to negotiate and make appropriate decisions for their development. However, community participation faces many challenges in South Africa and some other countries. For instance, in most, if not all, development projects commenced by local municipalities, community participation is often neglected or becomes an afterthought. In most cases, the communities are consulted after decisions have already been made by government agencies in relation to the kind of development projects that need to be executed. As a result, community participation is a prerequisite in development projects which are meant to improve the livelihoods and standard of living of the majority of communities in South Africa. The Buffalo City Municipality Metro (BCMM) is not an exception to this. The BCMM is located in the Eastern Cape Province, which is one of the poorest provinces in South Africa. In one of the towns in the municipal area, namely Dimbaza in the former Ciskei ‘homeland’, where there are high levels of unemployment and poverty, a prominent feature in the landscape is the many abandoned factory buildings. In recent years, the BCMM has recognized the need to revitalize the nodal areas such as Mdantsane, Dimbaza and Bisho, but due to the fragmented patterns of Bantustan policies the program was negatively affected (BCMM 2014/15/141). As a consequence, the BCMM has supported the implement an urban revitalization project within its area. The aim of this study was to investigate and interrogate whether local communities are involved in urban revitalization in the BCMM. That is, to evaluate community participation in urban revitalization projects in the BCMM, and focusing on Dimbaza community in the Eastern Cape province of South Africa as a case study. The study asks the following questions: Do the BCMM’s urban redevelopment initiatives have community participation component? How can the community be more involved in neighbourhood revitalization? v To what extent do these perceptions and priorities of the people living in neighbourhood of the disused factories match those of the policy makers? What are the perceptions of the people living in the neighbourhood of the disused factories in Dimbaza with regard to redevelopment? What recommendations can emanate from the study to address the current challenges regarding community participation in urban revitalization in BCMM? The study revealed that the majority of the respondents did not participate in the initiation and planning stages of the urban revitalization projects. The study further showed that a considerable proportion of the surveyed Dimbaza residents did not know about the urban revitalization programme, but learnt about it only in the local newspaper. It is therefore recommended that, the BCMM should support the community at all levels of planning to ensure a strong commitment to participation in their urban revitalization or development projects. It is hoped that this study will sensitize the community members of Dimbaza and the roles players involved in the Dimbaza urban revitalization projects including, among others, the Buffalo City Municipality Metropolitan, the Eastern Cape Development Cooperation and the Department of Economic Development, Environmental Affairs and Tourism of the Eastern Cape, to realise the significance and advantages of community participation, and that they will work through the challenges therein in order to increase community participation in development projects.
- Full Text:
- Date Issued: 2018
Community radio as a tool for sport development: a case study of Mdantsane FM.
- Authors: Sifingo, Yamkela
- Date: 2018
- Subjects: Community radio--South Africa--Eastern Cape , Radio in community development--South Africa--Eastern Cape , Sport development
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/19650 , vital:43155
- Description: This study focuses on critically examining the role of community radio in sports development, using Mdantsane FM as a case study. To carry out the study, the researcher employed a mixed research methodology as both qualitative and quantitative research approaches were used. In-depth interviews were conducted with key stakeholders and in addition, two focus groups discussions were conducted consisting of eight individuals in each group. The first focus group was held within the radio station and consisted of radio presenters and news readers. The second focus group was held with the external stakeholders who run sports programmes around Mdantsane community, from both the schools and local leagues and competitions. To try and fully represent the studied community and considering the vast population in Mdantsane, a survey/questionnaire study was also carried out. The research findings revealed that Mdantsane FM Community Radio Station listeners and members of the community are of the views that the radio station is playing a crucial role in driving community sport development programs, fixtures, leagues and tournaments. The sport fraternity feels that the radio station promotes local content and it represents the community it serves. Community sport coverage and announcements are said to be always accepted as the sports department operates with an open door policy, where every community member has the equal right to exercise the presence of the radio station accordingly. , Thesis (M Soc Sc) (Communication) -- University of Fort Hare, 2018
- Full Text:
- Date Issued: 2018
- Authors: Sifingo, Yamkela
- Date: 2018
- Subjects: Community radio--South Africa--Eastern Cape , Radio in community development--South Africa--Eastern Cape , Sport development
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/19650 , vital:43155
- Description: This study focuses on critically examining the role of community radio in sports development, using Mdantsane FM as a case study. To carry out the study, the researcher employed a mixed research methodology as both qualitative and quantitative research approaches were used. In-depth interviews were conducted with key stakeholders and in addition, two focus groups discussions were conducted consisting of eight individuals in each group. The first focus group was held within the radio station and consisted of radio presenters and news readers. The second focus group was held with the external stakeholders who run sports programmes around Mdantsane community, from both the schools and local leagues and competitions. To try and fully represent the studied community and considering the vast population in Mdantsane, a survey/questionnaire study was also carried out. The research findings revealed that Mdantsane FM Community Radio Station listeners and members of the community are of the views that the radio station is playing a crucial role in driving community sport development programs, fixtures, leagues and tournaments. The sport fraternity feels that the radio station promotes local content and it represents the community it serves. Community sport coverage and announcements are said to be always accepted as the sports department operates with an open door policy, where every community member has the equal right to exercise the presence of the radio station accordingly. , Thesis (M Soc Sc) (Communication) -- University of Fort Hare, 2018
- Full Text:
- Date Issued: 2018
Comparing sequence and structure of falcipains and human homologs at prodomain and catalytic active site for malarial peptide-based inhibitor design:
- Musyoka, Thommas M, Njuguna, Joyce N, Tastan Bishop, Özlem
- Authors: Musyoka, Thommas M , Njuguna, Joyce N , Tastan Bishop, Özlem
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/148392 , vital:38735 , DOI: 10.1101/381566
- Description: Falcipains are major cysteine proteases of Plasmodium falciparum involved in haemoglobin degradation and remain attractive anti-malarial drug targets. Several inhibitors against these proteases have been identified, yet none of them has been approved for malaria treatment. Other Plasmodium species also possess highly homologous proteins to falcipains. For selective therapeutic targeting, identification of sequence and structure differences with homologous human cathepsins is necessary. The substrate processing activity of these proteins is tightly controlled via a prodomain segment occluding the active site which is chopped under low pH conditions exposing the catalytic site. Current work characterizes these proteases to identify residues mediating the prodomain regulatory function for the design of peptide based anti-malarial inhibitors.
- Full Text:
- Date Issued: 2018
- Authors: Musyoka, Thommas M , Njuguna, Joyce N , Tastan Bishop, Özlem
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/148392 , vital:38735 , DOI: 10.1101/381566
- Description: Falcipains are major cysteine proteases of Plasmodium falciparum involved in haemoglobin degradation and remain attractive anti-malarial drug targets. Several inhibitors against these proteases have been identified, yet none of them has been approved for malaria treatment. Other Plasmodium species also possess highly homologous proteins to falcipains. For selective therapeutic targeting, identification of sequence and structure differences with homologous human cathepsins is necessary. The substrate processing activity of these proteins is tightly controlled via a prodomain segment occluding the active site which is chopped under low pH conditions exposing the catalytic site. Current work characterizes these proteases to identify residues mediating the prodomain regulatory function for the design of peptide based anti-malarial inhibitors.
- Full Text:
- Date Issued: 2018
Comparison of contraceptive discontinuation in users of a copper intrauterine device against depot medroxyprogesterone acetate injectable
- Authors: Dekile-Yonto, Nolusindiso
- Date: 2018
- Subjects: Contraceptives Birth control Women's health services
- Language: English
- Type: Thesis , Masters , Magister of Curationis
- Identifier: http://hdl.handle.net/10353/15520 , vital:40422
- Description: The dynamics of continued contraceptive use, switches to alternatives, or the outright failure of contraception is strong indicators of the effectiveness of health care programmes for women or couples (Ali, Cleland & Shah, 2012:6). Furthermore, unplanned pregnancies often lead to undesirable health, economic, social, and psychological consequences for women (Sedgh, Singh & Hussain., 2014). There is a need to better understand the reasons for discontinuation of contraception to enable health care workers to address the gaps in the provision of family planning services. For this reason, the researcher embarked on a follow-up study of a randomised, controlled trial, which compared the effects on depression and sexual functioning of women after childbirth of a Copper Intrauterine Contraceptive Device (Cu-IUD) with Depot Medroxyprogesterone Acetate (DMPA), (Singata-Madliki, 2014:5). The objectives of the follow-up study was to do a once-off follow-up of the original participants, three years after randomisation.
- Full Text:
- Date Issued: 2018
- Authors: Dekile-Yonto, Nolusindiso
- Date: 2018
- Subjects: Contraceptives Birth control Women's health services
- Language: English
- Type: Thesis , Masters , Magister of Curationis
- Identifier: http://hdl.handle.net/10353/15520 , vital:40422
- Description: The dynamics of continued contraceptive use, switches to alternatives, or the outright failure of contraception is strong indicators of the effectiveness of health care programmes for women or couples (Ali, Cleland & Shah, 2012:6). Furthermore, unplanned pregnancies often lead to undesirable health, economic, social, and psychological consequences for women (Sedgh, Singh & Hussain., 2014). There is a need to better understand the reasons for discontinuation of contraception to enable health care workers to address the gaps in the provision of family planning services. For this reason, the researcher embarked on a follow-up study of a randomised, controlled trial, which compared the effects on depression and sexual functioning of women after childbirth of a Copper Intrauterine Contraceptive Device (Cu-IUD) with Depot Medroxyprogesterone Acetate (DMPA), (Singata-Madliki, 2014:5). The objectives of the follow-up study was to do a once-off follow-up of the original participants, three years after randomisation.
- Full Text:
- Date Issued: 2018
Compensation for distribution of timing and reference signals over optical fibre networks for telescope arrays
- Authors: Wassin, Shukree
- Date: 2018
- Subjects: Fiber optics , Optical communications Very large array telescopes Optical fiber detectors
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/36425 , vital:33941
- Description: Significant advancements and developments have been made in optical frequency standards, in recent years. In order to verify the accuracy and preciseness of the disseminated RF signal, it is essential to compare its stability with the standards provided in literature as well as by metrology institutes. However, conventional frequency comparison techniques via satellites have extremely inferior stability qualities. As a result, the need for an alternative ultra-high precision RF transfer method presented itself. Highly accurate and precise frequency dissemination across optical fiber has proved a leading contender and a possible solution. When compared to conventional data transfer media, optical fiber has proven to be more superior and yields lower transmission errors and is immune to radio frequency interference. A further quality of optical fibre is that its transmission distance can be extended to greater degree than the traditional coaxial cable due to its low loss property. This thesis deals with the compensation of phase noise in single mode optical fibre. Phase noise degrades the performance and stability of the RF signal as well as the optical carrier frequency across long-haul optical networks. This work begins by experimentally demonstrating a unique and novel way for measuring the round-trip optical fibre latency times. The technique is based on all optical wavelength conversion using a stable PPS injection signal. The result highlighted the importance for active phase error compensation along a fibre link. Various computer simulations were used to study the influence of temperature fluctuation on the optical fibre. The first ever error signals generated at NMU was experimentally demonstrated. Results illustrated that, by minimizing the error voltage the phase difference between the transmitted and reference signals were reduced to zero. Performance analysis testing of the VCSEL phase correction actuator showed that majority of the dither iterations that induced the phase compensation took approximately 0.15 s. Residual frequency instabilities of 3.39791 x 10-12 at 1 s and 8.14848 x 10-12 at 103 s was measured when the 26 km G.655 fibre link was running freely. Experimental results further showed that the relative frequency stabilities measured at 1 s and 103 s were 4.43902 x 10-12 and 1.62055 x 10-13 during active compensation, respectively. The novel work presented in this thesis is exciting since the VCSEL is used as the optical source as well as the phase correction actuator. The benefits of such a device is that is reduces system costs and complexities.
- Full Text:
- Date Issued: 2018
- Authors: Wassin, Shukree
- Date: 2018
- Subjects: Fiber optics , Optical communications Very large array telescopes Optical fiber detectors
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/36425 , vital:33941
- Description: Significant advancements and developments have been made in optical frequency standards, in recent years. In order to verify the accuracy and preciseness of the disseminated RF signal, it is essential to compare its stability with the standards provided in literature as well as by metrology institutes. However, conventional frequency comparison techniques via satellites have extremely inferior stability qualities. As a result, the need for an alternative ultra-high precision RF transfer method presented itself. Highly accurate and precise frequency dissemination across optical fiber has proved a leading contender and a possible solution. When compared to conventional data transfer media, optical fiber has proven to be more superior and yields lower transmission errors and is immune to radio frequency interference. A further quality of optical fibre is that its transmission distance can be extended to greater degree than the traditional coaxial cable due to its low loss property. This thesis deals with the compensation of phase noise in single mode optical fibre. Phase noise degrades the performance and stability of the RF signal as well as the optical carrier frequency across long-haul optical networks. This work begins by experimentally demonstrating a unique and novel way for measuring the round-trip optical fibre latency times. The technique is based on all optical wavelength conversion using a stable PPS injection signal. The result highlighted the importance for active phase error compensation along a fibre link. Various computer simulations were used to study the influence of temperature fluctuation on the optical fibre. The first ever error signals generated at NMU was experimentally demonstrated. Results illustrated that, by minimizing the error voltage the phase difference between the transmitted and reference signals were reduced to zero. Performance analysis testing of the VCSEL phase correction actuator showed that majority of the dither iterations that induced the phase compensation took approximately 0.15 s. Residual frequency instabilities of 3.39791 x 10-12 at 1 s and 8.14848 x 10-12 at 103 s was measured when the 26 km G.655 fibre link was running freely. Experimental results further showed that the relative frequency stabilities measured at 1 s and 103 s were 4.43902 x 10-12 and 1.62055 x 10-13 during active compensation, respectively. The novel work presented in this thesis is exciting since the VCSEL is used as the optical source as well as the phase correction actuator. The benefits of such a device is that is reduces system costs and complexities.
- Full Text:
- Date Issued: 2018
Computational analysis and cavity optimisation to achieve directional solidification in a cast aluminium alloy [Al7SiMg] component
- Authors: Nohanyaza, Melikhaya
- Date: 2018
- Subjects: Metal castings , Automobiles -- Materials , Alloys , Light metal alloys
- Language: English
- Type: Thesis , Masters , MEng
- Identifier: http://hdl.handle.net/10948/22913 , vital:30141
- Description: The study at hand focussed on A356.0 industrial and high production die casting alloy. Since the birth of metal casting, numerous researchers have addressed the multiple phenomena that influence the casting quality and mechanical properties of castable alloys. This study harnessed research findings on A356.0 alloy and the aluminium family as a whole, to improve the casting soundness of the component already in the production process. The local foundry showed interest in understanding solidification and quality of A356.0 alloy fluxed with NaCl+KCl melt cleaning flux plus 4 of TiB2 5:1 master alloy grain refining rods and A356.0 alloy processed with KCl+Ti (presumably KCl+TiB2) grain refining flux plus 4 of TiB2 5:1 master alloy rods. Numerical analysis was used to define the progressive nature and directional solidification of the alloy using MAGMA5. MAGMA5.3 virtual optimisation capabilities were used for development of future component casting methods and procedures to solve macro- and microporosity evident on the casting. To find a direct link between the virtual and foundry environment, a preliminary study was conducted on a simple foundry stage of cone billet casting for both alloys with and without mould/casting interface coating. The findings indicated that A356.0 maintained its shrinkage volume percentage at mould temperatures above 300 °C, but progressively increased at temperatures below. Furthermore, thermal insulation coat (also used on Right Hand Side [RHS] mould of the foundry component) influenced the shrinkage distribution on the casting while localised at the centre on non-coated mould/casting interfaces for both KCl+Ti and NaCl+KCl melt fluxed A356.0 at similar percentage shrinkage for mould temperatures greater or equal to 300 °C. Near thin foundry castings for both flux treatments indicated similar mechanical properties at similar casting stages. The mechanical properties of both conditions seemed to degrade as a function of die casting period. Secondary dendrite arm spacing microstructure parameter for NaCl+KCl and KCl+Ti fluxed alloy averaged 40 μm and 35 μm respectively across all test zones. However, individual SDAS definitions per test zone indicated possible micro segregation on NaCl+KCl fluxed alloy and instantaneous solidification as a result of constitutional supercooling on alloys fluxed with KCl+Ti alloy. The growth rate solidification parameter was symmetrical about the centre of the component, where the centre of the component experienced an exponential drop from the top (away from the filling gate) to the bottom (near the filling gate) of the component. A virtual approach to tooling geometrical design indicated a weak influence on both micro- and macroporosity. However, the introduction of low thermal capacity, high heat transfer at Left Hand Side [LHS] tooling and a new cooling system arrangement indicated a higher influence in achieving sound casting. Knowledge gained in this study will improve local foundry competitiveness and introduce cost effective virtual approach foundry developments. The study will also introduce new methods for industrial research and position Nelson Mandela University as a leader in this field.
- Full Text:
- Date Issued: 2018
- Authors: Nohanyaza, Melikhaya
- Date: 2018
- Subjects: Metal castings , Automobiles -- Materials , Alloys , Light metal alloys
- Language: English
- Type: Thesis , Masters , MEng
- Identifier: http://hdl.handle.net/10948/22913 , vital:30141
- Description: The study at hand focussed on A356.0 industrial and high production die casting alloy. Since the birth of metal casting, numerous researchers have addressed the multiple phenomena that influence the casting quality and mechanical properties of castable alloys. This study harnessed research findings on A356.0 alloy and the aluminium family as a whole, to improve the casting soundness of the component already in the production process. The local foundry showed interest in understanding solidification and quality of A356.0 alloy fluxed with NaCl+KCl melt cleaning flux plus 4 of TiB2 5:1 master alloy grain refining rods and A356.0 alloy processed with KCl+Ti (presumably KCl+TiB2) grain refining flux plus 4 of TiB2 5:1 master alloy rods. Numerical analysis was used to define the progressive nature and directional solidification of the alloy using MAGMA5. MAGMA5.3 virtual optimisation capabilities were used for development of future component casting methods and procedures to solve macro- and microporosity evident on the casting. To find a direct link between the virtual and foundry environment, a preliminary study was conducted on a simple foundry stage of cone billet casting for both alloys with and without mould/casting interface coating. The findings indicated that A356.0 maintained its shrinkage volume percentage at mould temperatures above 300 °C, but progressively increased at temperatures below. Furthermore, thermal insulation coat (also used on Right Hand Side [RHS] mould of the foundry component) influenced the shrinkage distribution on the casting while localised at the centre on non-coated mould/casting interfaces for both KCl+Ti and NaCl+KCl melt fluxed A356.0 at similar percentage shrinkage for mould temperatures greater or equal to 300 °C. Near thin foundry castings for both flux treatments indicated similar mechanical properties at similar casting stages. The mechanical properties of both conditions seemed to degrade as a function of die casting period. Secondary dendrite arm spacing microstructure parameter for NaCl+KCl and KCl+Ti fluxed alloy averaged 40 μm and 35 μm respectively across all test zones. However, individual SDAS definitions per test zone indicated possible micro segregation on NaCl+KCl fluxed alloy and instantaneous solidification as a result of constitutional supercooling on alloys fluxed with KCl+Ti alloy. The growth rate solidification parameter was symmetrical about the centre of the component, where the centre of the component experienced an exponential drop from the top (away from the filling gate) to the bottom (near the filling gate) of the component. A virtual approach to tooling geometrical design indicated a weak influence on both micro- and macroporosity. However, the introduction of low thermal capacity, high heat transfer at Left Hand Side [LHS] tooling and a new cooling system arrangement indicated a higher influence in achieving sound casting. Knowledge gained in this study will improve local foundry competitiveness and introduce cost effective virtual approach foundry developments. The study will also introduce new methods for industrial research and position Nelson Mandela University as a leader in this field.
- Full Text:
- Date Issued: 2018