Optimising the polymer solutions and process parameters in the electrospinning of Chitosan
- Authors: Jacobs, Nokwindla Valencia
- Date: 2012
- Subjects: Textile fibers, Synthetic , Nanofibers , Chitosan , Polymer solutions
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: vital:10449 , http://hdl.handle.net/10948/d1010762 , Textile fibers, Synthetic , Nanofibers , Chitosan , Polymer solutions
- Description: Electrospinning is a technique, which can be used to produce nanofibrous materials by introducing electrostatic fields into the polymer solution. Due to their intrinsic properties, such as small fiber diameter, small pore size and large surface area, nanofibres are suitable for use in a variety of applications including wound dressing, filtration, composites and tissue engineering. The study demonstrates the successful and optimised production of Poly(ethylene oxide) (PEO) and chitosan nanofibres by electrospinning. The biocidal effects of chitosan, chitosan-silver nanofibres and silver nanoparticles were successfully investigated. To set up a functional electrospinning apparatus, the PEO solution parameters (concentration, molecular weight, solvent, and addition of polyelectrolyte) and applied potential voltage on the structural morphology and diameter of PEO nanofibres were studied. At lower PEO concentrations, the fibres had morphology with a large variation in fibre diameter, whereas at the higher concentrations, the nanofibres exhibited ordinary morphology with uniform but larger fibre diameters. Higher molecular weight showed larger average diameters when compared to that obtained with the same polymer but of a lower molecular weight. The addition of polyelectrolyte to the polymer solution had an influence on the structural morphology of the PEO. Flow simulation studies of an electrically charged polymer solution showed that an increase in the flow rate was associated with an increase in poly(allylamine hydrochloride) (PAH) concentration for the low molecular weight polymer, the shape and size of the Taylor cone increasing with an increase in PAH concentration for the low molecular weight polymer. During optimization of the PEO nanofibres, based on statistical modelling and using the Box and Behnken factorial design, the interaction effect between PAH concentration and the tip-to-collector distance played the most significant role in obtaining uniform diameter of nanofibres, followed by the interaction between the tip-to-collector distance and the applied voltage and lastly by the applied voltage. The production and optimization of chitosan nanofibres indicated that the interactions between electric field strength and the ratio of trifluoroacetic acid (TFA) and dichloromethane (DCM), TFA/DCM solvents as well as between electric field strength and chitosan concentration had the most significant effect, followed by the concentration of chitosan in terms of producing nanofibres with uniform diameters. Chitosan and chitosan-silver nanofibres could be successfully electrospun by controlling the solution properties, such as surface tension and electrical conductivity with the silver nanoparticles in the chitosan solutions affecting the electrospinnability. The silver nanoparticles in the chitosan solution modified the morphological characteristics of the electrospun nanofibres, while the conductivity and the surface tension were elevated. The fibre diameter of the chitosan and chitosan-silver nanoparticles decreased with an increase in the silver content. The electrospun chitosan nanofibres had a smooth surface and round shape as compared to the silver-chitosan nanofibres with a distorted morphology. The chitosan and chitosan-silver nanofibres as well as the silver nanoparticles exhibited antimicrobial or inhibition activity against S. aureus than against E. coli. S. aureus bacterial culture showed good cell adhesion and spreading inwards into the chitosan nanofibrous membrane. The chitosan-silver nanofibres exhibited a greater minimum inhibitory concentration (MIC), followed by silver nanoparticles and then chitosan nanofibres; suggesting a synergistic effect between the chitosan and silver nanoparticles.
- Full Text:
- Date Issued: 2012
- Authors: Jacobs, Nokwindla Valencia
- Date: 2012
- Subjects: Textile fibers, Synthetic , Nanofibers , Chitosan , Polymer solutions
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: vital:10449 , http://hdl.handle.net/10948/d1010762 , Textile fibers, Synthetic , Nanofibers , Chitosan , Polymer solutions
- Description: Electrospinning is a technique, which can be used to produce nanofibrous materials by introducing electrostatic fields into the polymer solution. Due to their intrinsic properties, such as small fiber diameter, small pore size and large surface area, nanofibres are suitable for use in a variety of applications including wound dressing, filtration, composites and tissue engineering. The study demonstrates the successful and optimised production of Poly(ethylene oxide) (PEO) and chitosan nanofibres by electrospinning. The biocidal effects of chitosan, chitosan-silver nanofibres and silver nanoparticles were successfully investigated. To set up a functional electrospinning apparatus, the PEO solution parameters (concentration, molecular weight, solvent, and addition of polyelectrolyte) and applied potential voltage on the structural morphology and diameter of PEO nanofibres were studied. At lower PEO concentrations, the fibres had morphology with a large variation in fibre diameter, whereas at the higher concentrations, the nanofibres exhibited ordinary morphology with uniform but larger fibre diameters. Higher molecular weight showed larger average diameters when compared to that obtained with the same polymer but of a lower molecular weight. The addition of polyelectrolyte to the polymer solution had an influence on the structural morphology of the PEO. Flow simulation studies of an electrically charged polymer solution showed that an increase in the flow rate was associated with an increase in poly(allylamine hydrochloride) (PAH) concentration for the low molecular weight polymer, the shape and size of the Taylor cone increasing with an increase in PAH concentration for the low molecular weight polymer. During optimization of the PEO nanofibres, based on statistical modelling and using the Box and Behnken factorial design, the interaction effect between PAH concentration and the tip-to-collector distance played the most significant role in obtaining uniform diameter of nanofibres, followed by the interaction between the tip-to-collector distance and the applied voltage and lastly by the applied voltage. The production and optimization of chitosan nanofibres indicated that the interactions between electric field strength and the ratio of trifluoroacetic acid (TFA) and dichloromethane (DCM), TFA/DCM solvents as well as between electric field strength and chitosan concentration had the most significant effect, followed by the concentration of chitosan in terms of producing nanofibres with uniform diameters. Chitosan and chitosan-silver nanofibres could be successfully electrospun by controlling the solution properties, such as surface tension and electrical conductivity with the silver nanoparticles in the chitosan solutions affecting the electrospinnability. The silver nanoparticles in the chitosan solution modified the morphological characteristics of the electrospun nanofibres, while the conductivity and the surface tension were elevated. The fibre diameter of the chitosan and chitosan-silver nanoparticles decreased with an increase in the silver content. The electrospun chitosan nanofibres had a smooth surface and round shape as compared to the silver-chitosan nanofibres with a distorted morphology. The chitosan and chitosan-silver nanofibres as well as the silver nanoparticles exhibited antimicrobial or inhibition activity against S. aureus than against E. coli. S. aureus bacterial culture showed good cell adhesion and spreading inwards into the chitosan nanofibrous membrane. The chitosan-silver nanofibres exhibited a greater minimum inhibitory concentration (MIC), followed by silver nanoparticles and then chitosan nanofibres; suggesting a synergistic effect between the chitosan and silver nanoparticles.
- Full Text:
- Date Issued: 2012
Participation and paradoxes: community control of mineral wealth in South Africa's Royal Bafokeng and Bakgatla Ba Kgafela communities
- Authors: Mnwana, Sonwabile Comfords
- Date: 2012
- Subjects: Political participation -- South Africa , Natural resources -- Co-management -- South Africa , Rural development -- South Africa , Mining corporations -- South Africa , Platinum mines and mining -- South Africa , Sustainable development -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD (Social Sciences)
- Identifier: vital:11952 , http://hdl.handle.net/10353/526 , Political participation -- South Africa , Natural resources -- Co-management -- South Africa , Rural development -- South Africa , Mining corporations -- South Africa , Platinum mines and mining -- South Africa , Sustainable development -- South Africa
- Description: Resource control as a form of community participation in the mineral economy has gained much recognition. One prevailing argument is that direct control of natural resources by local communities is an important precondition for equitable utilisation of the natural resource wealth, peaceful co-existence between mining corporations and indigenous communities, and congenial relations between local communities and the state. Studies have also shown that the absence of direct community control of mineral wealth remains a major factor in the communal resistance and socio-political conflict witnessed in the natural resource-endowed regions of countries such as Nigeria, Ecuador, Sierra Leone and the Democratic Republic of the Congo. However, little is known about mineral resource control at the community level. Does community control necessarily translate to equity? How does local involvement in the mobilisation of mining royalties benefit different segments of the community? Indeed, how do different segments of the community “control” the wealth? What is the specific model adopted to engender broad-based community participation in the utilisation of mineral wealth – and does it matter? These theoretical and practical questions were the impetus for undertaking this study in the Royal Bafokeng and Bakgatla Ba Kgafela – two platinum-rich ‘traditional’ communities in South Africa’s North West Province that have significant control over platinum resources in their territories. Utilising ethnographic data collected in the two study communities in 2008 and 2009, the thesis examines the character of community participation in platinum wealth utilisation; specifically, the conditions under which community participation promotes or hinders sustainable community development. The analysis uses a “three-dimensional participation ladder” conceptual scheme, based in part on Sherry Arnstein’s (1969) “ladder of citizen participation” and subsequent typologies of participation. Among the key findings of the thesis are that despite observed benefits, the interface of resource wealth and community development is fraught with tokenistic participation, elite-targeted grassroots anger, and local tensions – all linked to the contradictory nature of participation. The thesis further reveals that in some instances the challenge of platinum wealth-engendered community development tends to undermine existing customary and democratic spaces for participation, and that this is exacerbated by community-level issues such as poverty and inequality. The findings of the study compel a shift of analytical focus from conflict as an epiphenomenon of collective community exclusion and deprivation (as in the case of many natural-rich countries in Sub-Saharan Africa and elsewhere), to conflict as also resulting from collective community inclusion (in natural resource utilisation). At the policy level, the study generates insights that will, hopefully, assist mineral resource-endowed countries, such as South Africa, in dealing with the challenge of developing appropriate policy frameworks for regulating business and social partnerships between local communities and mining corporations, and within resource-rich communities themselves.
- Full Text:
- Date Issued: 2012
- Authors: Mnwana, Sonwabile Comfords
- Date: 2012
- Subjects: Political participation -- South Africa , Natural resources -- Co-management -- South Africa , Rural development -- South Africa , Mining corporations -- South Africa , Platinum mines and mining -- South Africa , Sustainable development -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD (Social Sciences)
- Identifier: vital:11952 , http://hdl.handle.net/10353/526 , Political participation -- South Africa , Natural resources -- Co-management -- South Africa , Rural development -- South Africa , Mining corporations -- South Africa , Platinum mines and mining -- South Africa , Sustainable development -- South Africa
- Description: Resource control as a form of community participation in the mineral economy has gained much recognition. One prevailing argument is that direct control of natural resources by local communities is an important precondition for equitable utilisation of the natural resource wealth, peaceful co-existence between mining corporations and indigenous communities, and congenial relations between local communities and the state. Studies have also shown that the absence of direct community control of mineral wealth remains a major factor in the communal resistance and socio-political conflict witnessed in the natural resource-endowed regions of countries such as Nigeria, Ecuador, Sierra Leone and the Democratic Republic of the Congo. However, little is known about mineral resource control at the community level. Does community control necessarily translate to equity? How does local involvement in the mobilisation of mining royalties benefit different segments of the community? Indeed, how do different segments of the community “control” the wealth? What is the specific model adopted to engender broad-based community participation in the utilisation of mineral wealth – and does it matter? These theoretical and practical questions were the impetus for undertaking this study in the Royal Bafokeng and Bakgatla Ba Kgafela – two platinum-rich ‘traditional’ communities in South Africa’s North West Province that have significant control over platinum resources in their territories. Utilising ethnographic data collected in the two study communities in 2008 and 2009, the thesis examines the character of community participation in platinum wealth utilisation; specifically, the conditions under which community participation promotes or hinders sustainable community development. The analysis uses a “three-dimensional participation ladder” conceptual scheme, based in part on Sherry Arnstein’s (1969) “ladder of citizen participation” and subsequent typologies of participation. Among the key findings of the thesis are that despite observed benefits, the interface of resource wealth and community development is fraught with tokenistic participation, elite-targeted grassroots anger, and local tensions – all linked to the contradictory nature of participation. The thesis further reveals that in some instances the challenge of platinum wealth-engendered community development tends to undermine existing customary and democratic spaces for participation, and that this is exacerbated by community-level issues such as poverty and inequality. The findings of the study compel a shift of analytical focus from conflict as an epiphenomenon of collective community exclusion and deprivation (as in the case of many natural-rich countries in Sub-Saharan Africa and elsewhere), to conflict as also resulting from collective community inclusion (in natural resource utilisation). At the policy level, the study generates insights that will, hopefully, assist mineral resource-endowed countries, such as South Africa, in dealing with the challenge of developing appropriate policy frameworks for regulating business and social partnerships between local communities and mining corporations, and within resource-rich communities themselves.
- Full Text:
- Date Issued: 2012
Participatory mapping, learning and change in the context of biocultural diversity and resilience
- Authors: Ali, Million Belay
- Date: 2012
- Subjects: Biodiversity conservation -- Research -- Ethiopia Cultural pluralism -- Research -- Ethiopia Ethnopsychology -- Research -- Ethiopia Adult education -- Research -- Ethiopia
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1689 , http://hdl.handle.net/10962/d1003572
- Description: This study set out to investigate the learning and change that emerged in and through participatory mapping in the context of biocultural diversity and resilience in rural Ethiopia. It did this through examining the learning and agency emerging from three participatory mapping practices (Participatory 3 Dimensional Modelling, sketch mapping and eco-cultural calendars) using two case study sites, located in the Bale Mountains and the Foata Mountains in Ethiopia, and honing in on in-depth reflective processes in two community contexts located within the broader case study sites, namely Horo Soba, Dinsho wereda in Bale; and Telecho, in Wolmera wereda, in the Foata Mountain complex. This study tried to answer three research questions related to participatory mapping: its role in mobilizing knowledge related to biocultural landscape, its role in learning and change, and its value in building resilience. The study used qualitative case study research methodology underpinned by critical realist philosophy, and used photographic ‘cues’ to structure the reporting on the cases. It used four categories of analysis: biocultural diversity, educational processes, learning and agency, in the first instance to report on the interactions associated with the participatory mapping practices as they emerged in the two case study sites. This was followed by in-depth analysis and interpretation of participatory mapping and biocultural diversity, as well as participatory mapping and learning, with an emphasis on acquisition, meaning making and identity formation processes. The in-depth analysis drew on social and learning theory, and theory of biocultural diversity and social-ecological resilience. The study also included analysis of broader change processes that were related to and emerged from the social interactions in the mapping activities, and the resultant morphogenesis (change), showing that morphogenesis, while broadly temporal, is not linear, and involves ‘little iterative morphogenic cycles’. These insights were then used to interpret how participatory mapping may contribute to resilience building in a context where social-ecological resilience is increasingly required, such as the two case study sites, where socialecological degradation is highly visible and is occurring rapidly. The study’s contribution to new knowledge lies in relation to the role of participatory mapping in facilitating learning, agency and change which, to date, appears to be under-theorised and under-developed in the participatory mapping and environmental education literature. As such, the study findings provide in-depth insight into how participatory mapping methodologies may ‘work in the world’, in contexts such as those presented in the two cases under study. It has tried to demonstrate how participatory mapping has managed to mobilize knowledge related to biocultural diversity, facilitated the acquisition of knowledge and helped members of the community to engage in meaning making activities relevant to their biocultural landscape and renegotiate their identity within the wider community context. It has also shown that dissonance is an important dynamic in the learning process; and that morphogenesis (or change) occurs over time, but also in smaller cycles that interact at different levels; and that participatory mapping cannot, by itself mobilise significant structural change, at least in the short term. It has also shown, however, that learning and the desire for change can emerge from participatory mapping processes, and that this can be utilized to adapt to the changing socio-ecological environments, potentially contributing to longer term resilience of social-ecological systems.
- Full Text:
- Date Issued: 2012
- Authors: Ali, Million Belay
- Date: 2012
- Subjects: Biodiversity conservation -- Research -- Ethiopia Cultural pluralism -- Research -- Ethiopia Ethnopsychology -- Research -- Ethiopia Adult education -- Research -- Ethiopia
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1689 , http://hdl.handle.net/10962/d1003572
- Description: This study set out to investigate the learning and change that emerged in and through participatory mapping in the context of biocultural diversity and resilience in rural Ethiopia. It did this through examining the learning and agency emerging from three participatory mapping practices (Participatory 3 Dimensional Modelling, sketch mapping and eco-cultural calendars) using two case study sites, located in the Bale Mountains and the Foata Mountains in Ethiopia, and honing in on in-depth reflective processes in two community contexts located within the broader case study sites, namely Horo Soba, Dinsho wereda in Bale; and Telecho, in Wolmera wereda, in the Foata Mountain complex. This study tried to answer three research questions related to participatory mapping: its role in mobilizing knowledge related to biocultural landscape, its role in learning and change, and its value in building resilience. The study used qualitative case study research methodology underpinned by critical realist philosophy, and used photographic ‘cues’ to structure the reporting on the cases. It used four categories of analysis: biocultural diversity, educational processes, learning and agency, in the first instance to report on the interactions associated with the participatory mapping practices as they emerged in the two case study sites. This was followed by in-depth analysis and interpretation of participatory mapping and biocultural diversity, as well as participatory mapping and learning, with an emphasis on acquisition, meaning making and identity formation processes. The in-depth analysis drew on social and learning theory, and theory of biocultural diversity and social-ecological resilience. The study also included analysis of broader change processes that were related to and emerged from the social interactions in the mapping activities, and the resultant morphogenesis (change), showing that morphogenesis, while broadly temporal, is not linear, and involves ‘little iterative morphogenic cycles’. These insights were then used to interpret how participatory mapping may contribute to resilience building in a context where social-ecological resilience is increasingly required, such as the two case study sites, where socialecological degradation is highly visible and is occurring rapidly. The study’s contribution to new knowledge lies in relation to the role of participatory mapping in facilitating learning, agency and change which, to date, appears to be under-theorised and under-developed in the participatory mapping and environmental education literature. As such, the study findings provide in-depth insight into how participatory mapping methodologies may ‘work in the world’, in contexts such as those presented in the two cases under study. It has tried to demonstrate how participatory mapping has managed to mobilize knowledge related to biocultural diversity, facilitated the acquisition of knowledge and helped members of the community to engage in meaning making activities relevant to their biocultural landscape and renegotiate their identity within the wider community context. It has also shown that dissonance is an important dynamic in the learning process; and that morphogenesis (or change) occurs over time, but also in smaller cycles that interact at different levels; and that participatory mapping cannot, by itself mobilise significant structural change, at least in the short term. It has also shown, however, that learning and the desire for change can emerge from participatory mapping processes, and that this can be utilized to adapt to the changing socio-ecological environments, potentially contributing to longer term resilience of social-ecological systems.
- Full Text:
- Date Issued: 2012
Peri-urban agriculture and population growth : the case of Asmara, Eritrea
- Authors: Fessahaie, Tesfamichael
- Date: 2012
- Subjects: Urban agriculture -- Eritrea -- Asmara , Cities and towns -- Eritrea -- Asmara -- Growth
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10668 , http://hdl.handle.net/10948/d109790
- Description: The aim of this thesis is to provide a differentiated view of peri-urban agriculture in the context of urban population growth in Asmara, Eritrea. Peri-urban agriculture is viewed as a distinct type of broader urban agriculture, and in this case is not as subsistence-orientated as other branches of it. Urban population growth is comprised of three elements, namely, natural population increase, rural-urban migration and outward movement of people to the urban periphery linked to urban expansion. Each receives extensive treatment. Asmara is the capital city of Eritrea and using Weeks (2004:473) phrase can be termed as a “primate city”. As such, it exerts a major influence on the political, economic and cultural life of the country, but has never been subjected to this type of research. The analytical framework that is adopted is that of urban population growth. In order to operationalize it, theoretical insights into each of its three branches were applied. For example, the informalisation of the economy in developing cities was used to explain the operation of peri-urban agriculture in the context of natural population growth. An adaption of the original Harris-Todaro Model by Fields (2004) was used for the migrants, and the Mosaic Model by Bryant and Johnson (1992) for those facing urban encroachment. Primary data were collected in the field by the author with the help of research assistants. This was supplemented by secondary data which involved reports commissioned by the Ministry of Agriculture and the Ministry of Public Works. Focus Group discussions were also held to supplement the data with information, views and insights that do not emerge in one-to-one interviews. This thesis demonstrates that those respondents operating within the context of natural population growth make a viable living from peri-urban agriculture, but that they also recognise that there are considerable challenges to be faced. Three sub-groups of farmers are identified. Of these, poultry farmers are the most vulnerable because of the high costs of the inputs, the uncertainty associated with avian „flu and an undeveloped distribution network. The vegetable producers, on the other hand, have a sophisticated marketing network, but low levels of education, high household numbers and an impending shortage of land and water. The agriculturalists that have migrated to Asmara seem to have created sustainable occupations for themselves over a number of years. However, 75 percent of them felt that migration to Asmara was not worthwhile. This negative view is explained in terms of the struggle it has taken to maintain such a living and the growing shortage of land. This set of farmers achieves lower production levels than its city-reared counterparts, carries considerable expenses and has to hire its land. The farmers who have had to cope with urban encroachment fall into two classes. The first has chosen to remain in peri-urban agriculture despite feeling the pressure to scale down activities and thus have a lower income. The majority of this group are dairy farmers who have to trade off increasing costs of cattle feed against shrinking grazing land. They are unwilling to take the initiative to solve their land problems, but look to the authorities to do so. The second class of respondents in this category have abandoned their agricultural holdings. The majority of these agriculturalists are poultry farmers living in the Eastern side of the city. A shortage of agricultural land, high population densities and high costs of inputs make poultry farming difficult. This thesis, therefore, presents a multifaceted view of peri-urban agriculture. While each set of farmers has to cope with its own particular circumstances, there is a common factor. This is the tension between preserving agricultural land on the urban fringe and the need to expand the city to accommodate its inhabitants.
- Full Text:
- Date Issued: 2012
- Authors: Fessahaie, Tesfamichael
- Date: 2012
- Subjects: Urban agriculture -- Eritrea -- Asmara , Cities and towns -- Eritrea -- Asmara -- Growth
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10668 , http://hdl.handle.net/10948/d109790
- Description: The aim of this thesis is to provide a differentiated view of peri-urban agriculture in the context of urban population growth in Asmara, Eritrea. Peri-urban agriculture is viewed as a distinct type of broader urban agriculture, and in this case is not as subsistence-orientated as other branches of it. Urban population growth is comprised of three elements, namely, natural population increase, rural-urban migration and outward movement of people to the urban periphery linked to urban expansion. Each receives extensive treatment. Asmara is the capital city of Eritrea and using Weeks (2004:473) phrase can be termed as a “primate city”. As such, it exerts a major influence on the political, economic and cultural life of the country, but has never been subjected to this type of research. The analytical framework that is adopted is that of urban population growth. In order to operationalize it, theoretical insights into each of its three branches were applied. For example, the informalisation of the economy in developing cities was used to explain the operation of peri-urban agriculture in the context of natural population growth. An adaption of the original Harris-Todaro Model by Fields (2004) was used for the migrants, and the Mosaic Model by Bryant and Johnson (1992) for those facing urban encroachment. Primary data were collected in the field by the author with the help of research assistants. This was supplemented by secondary data which involved reports commissioned by the Ministry of Agriculture and the Ministry of Public Works. Focus Group discussions were also held to supplement the data with information, views and insights that do not emerge in one-to-one interviews. This thesis demonstrates that those respondents operating within the context of natural population growth make a viable living from peri-urban agriculture, but that they also recognise that there are considerable challenges to be faced. Three sub-groups of farmers are identified. Of these, poultry farmers are the most vulnerable because of the high costs of the inputs, the uncertainty associated with avian „flu and an undeveloped distribution network. The vegetable producers, on the other hand, have a sophisticated marketing network, but low levels of education, high household numbers and an impending shortage of land and water. The agriculturalists that have migrated to Asmara seem to have created sustainable occupations for themselves over a number of years. However, 75 percent of them felt that migration to Asmara was not worthwhile. This negative view is explained in terms of the struggle it has taken to maintain such a living and the growing shortage of land. This set of farmers achieves lower production levels than its city-reared counterparts, carries considerable expenses and has to hire its land. The farmers who have had to cope with urban encroachment fall into two classes. The first has chosen to remain in peri-urban agriculture despite feeling the pressure to scale down activities and thus have a lower income. The majority of this group are dairy farmers who have to trade off increasing costs of cattle feed against shrinking grazing land. They are unwilling to take the initiative to solve their land problems, but look to the authorities to do so. The second class of respondents in this category have abandoned their agricultural holdings. The majority of these agriculturalists are poultry farmers living in the Eastern side of the city. A shortage of agricultural land, high population densities and high costs of inputs make poultry farming difficult. This thesis, therefore, presents a multifaceted view of peri-urban agriculture. While each set of farmers has to cope with its own particular circumstances, there is a common factor. This is the tension between preserving agricultural land on the urban fringe and the need to expand the city to accommodate its inhabitants.
- Full Text:
- Date Issued: 2012
Photoconductive spectroscopy of GaSb thin films
- Authors: Shura, Megersa Wodajo
- Date: 2012
- Subjects: Photoelectron spectroscopy , Photoconductivity
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10549 , http://hdl.handle.net/10948/d1019937
- Description: In this study, we have investigated the photo-response of gallium antimonide (GaSb) by measuring the spectral, injection level, as well as the temperature dependence of the steady-state photoconductivity of epitaxial films. By combining the various photo-response measurements with-galvanometric measurements, the effective excess carrier lifetimes could be calculated and described in terms of the various experimental variables considered. From a comparison of the measured and theoretical carrier lifetimes, a clear discrepancy was found for the injection dependent results. This inconsistency between the expected and measured behaviours was resolved using a two-layer model to describe the photo-conductive response of the thin film. In this model, the generation/recombination processes are considered for the bulk as well as for a depleted near-surface region. By combining these two contributions when calculating the total excess photocurrent, the various experimental results could be successfully described. The photo-response measurements revealed that the main contribution to the photocurrent came from the near-surface region, where the bandto- band and Auger recombination transitions are reduced. From the simulation of the injection level dependence of the excess carrier lifetime, some of the near-surface characteristics, such as the position of the surface Fermi-level and the surface recombination velocity, could be determined. In the case of p-type GaSb, the room temperature surface Fermi-level was found to be pinned (290±20) meV above the valence band maximum, whereas the n-type material had a pinning position of (150±20) meV above the valence band maximum. These pinning positions were shown to be independent of the doping density and relatively insensitive to the surface treatments considered. The presence of a near-surface depletion region, as well as the position of the surface Fermi-level, was corroborated by Raman spectroscopy. From a comparison of the phonon mode and the phonon-hole plasmon coupled mode, a surface Fermi-level position of (300 ± 30) meV was deduced for p-type GaSb. Finally, the effect various surface treatments have on the photo-response, and related surface properties, were investigated. Removal of the native oxide (HCl:H2O) followed by sulphur passivation (Na2S:9H2O) results in a slight decrease in the surface Fermi-level position. Aging studies however revealed that the surface characteristics reverted back to the untreated values following a few days in air. Coating the GaSb surfaces with a thin ZnS layer was found to have little effect on the surface potential, resulting only in a slight increase in the near-surface donor density. The sensitivity of the measured photocurrent to surface treatments and changes in the ambient with cooling, further validate the importance of considering the surface potential and the related space-charge when describing the photoconductive response of GaSb thin films.
- Full Text:
- Date Issued: 2012
- Authors: Shura, Megersa Wodajo
- Date: 2012
- Subjects: Photoelectron spectroscopy , Photoconductivity
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10549 , http://hdl.handle.net/10948/d1019937
- Description: In this study, we have investigated the photo-response of gallium antimonide (GaSb) by measuring the spectral, injection level, as well as the temperature dependence of the steady-state photoconductivity of epitaxial films. By combining the various photo-response measurements with-galvanometric measurements, the effective excess carrier lifetimes could be calculated and described in terms of the various experimental variables considered. From a comparison of the measured and theoretical carrier lifetimes, a clear discrepancy was found for the injection dependent results. This inconsistency between the expected and measured behaviours was resolved using a two-layer model to describe the photo-conductive response of the thin film. In this model, the generation/recombination processes are considered for the bulk as well as for a depleted near-surface region. By combining these two contributions when calculating the total excess photocurrent, the various experimental results could be successfully described. The photo-response measurements revealed that the main contribution to the photocurrent came from the near-surface region, where the bandto- band and Auger recombination transitions are reduced. From the simulation of the injection level dependence of the excess carrier lifetime, some of the near-surface characteristics, such as the position of the surface Fermi-level and the surface recombination velocity, could be determined. In the case of p-type GaSb, the room temperature surface Fermi-level was found to be pinned (290±20) meV above the valence band maximum, whereas the n-type material had a pinning position of (150±20) meV above the valence band maximum. These pinning positions were shown to be independent of the doping density and relatively insensitive to the surface treatments considered. The presence of a near-surface depletion region, as well as the position of the surface Fermi-level, was corroborated by Raman spectroscopy. From a comparison of the phonon mode and the phonon-hole plasmon coupled mode, a surface Fermi-level position of (300 ± 30) meV was deduced for p-type GaSb. Finally, the effect various surface treatments have on the photo-response, and related surface properties, were investigated. Removal of the native oxide (HCl:H2O) followed by sulphur passivation (Na2S:9H2O) results in a slight decrease in the surface Fermi-level position. Aging studies however revealed that the surface characteristics reverted back to the untreated values following a few days in air. Coating the GaSb surfaces with a thin ZnS layer was found to have little effect on the surface potential, resulting only in a slight increase in the near-surface donor density. The sensitivity of the measured photocurrent to surface treatments and changes in the ambient with cooling, further validate the importance of considering the surface potential and the related space-charge when describing the photoconductive response of GaSb thin films.
- Full Text:
- Date Issued: 2012
Photophysicochemical and photodynamic studies of phthalocyanines conjugated to selected drug delivery agents
- Authors: Nombona, Nolwazi
- Date: 2012
- Subjects: Phthalocyanines Photochemistry Photochemotherapy Drug delivery systems Magnesium Zinc Nanoparticles Staphylococcus aureus
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4333 , http://hdl.handle.net/10962/d1004994
- Description: This work reports on the successful synthesis, characterisation and photophysical properties of new asymmetric metal free, magnesium and zinc phthalocyanines. The synthesis of symmetrical phthalocyanines is also reported. A selection of phthalocyanines have been conjugated, covalently linked, encapsulated or mixed with selected of drug delivery agents which include gold or silver nanoparticles, poly-L-lysine, liposomes and folic acid. The influence of delivery agent on the photophysical and photochemical properties of conjugated phthalocyanine is investigated. The studies showed that the Au nanoparticle significantly lowered the fluorescence quantum yield values of the phthalocyanines. The photodynamic activity of Zn phthalocyanine-ε-polylysine conjugates in the presence of nanoparticles towards the inactivation of Staphylococcus aureus showed high photoinactivation in the presence of silver nanoparticles. The presence of silver nanoparticels from the minimal inhibition concentration (MIC₅₀) studies showed remarkable growth inhibition for the tested conjugates even at low concentrations. The conjugate also showed no dark toxicity when evaluated using the chick choriallantoic membrane (CAM) assay. The efficiency of selected zinc phthalocyanine as photodynamic therapy (PDT) agents was investigated. The production of reactive oxygen species (ROS) and phototoxicity of the photosensitizers were assessed. Healthy fibroblast cells and breast cancer (MCF-7) cells were treated with either free phthalocyanine or phthalocyanine bound to either gold nanoparticles or encapsulated in liposomes. Cell viability studies showed the optimum phototoxic effect on non-malignant cells to be 4.5 J.cm⁻². The PDT effect of the liposome bound phthalocyanine showed extensive damage of the breast cancer cells. Gold nanoparticles only showed a modest improvement in PDT activity.
- Full Text:
- Date Issued: 2012
- Authors: Nombona, Nolwazi
- Date: 2012
- Subjects: Phthalocyanines Photochemistry Photochemotherapy Drug delivery systems Magnesium Zinc Nanoparticles Staphylococcus aureus
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4333 , http://hdl.handle.net/10962/d1004994
- Description: This work reports on the successful synthesis, characterisation and photophysical properties of new asymmetric metal free, magnesium and zinc phthalocyanines. The synthesis of symmetrical phthalocyanines is also reported. A selection of phthalocyanines have been conjugated, covalently linked, encapsulated or mixed with selected of drug delivery agents which include gold or silver nanoparticles, poly-L-lysine, liposomes and folic acid. The influence of delivery agent on the photophysical and photochemical properties of conjugated phthalocyanine is investigated. The studies showed that the Au nanoparticle significantly lowered the fluorescence quantum yield values of the phthalocyanines. The photodynamic activity of Zn phthalocyanine-ε-polylysine conjugates in the presence of nanoparticles towards the inactivation of Staphylococcus aureus showed high photoinactivation in the presence of silver nanoparticles. The presence of silver nanoparticels from the minimal inhibition concentration (MIC₅₀) studies showed remarkable growth inhibition for the tested conjugates even at low concentrations. The conjugate also showed no dark toxicity when evaluated using the chick choriallantoic membrane (CAM) assay. The efficiency of selected zinc phthalocyanine as photodynamic therapy (PDT) agents was investigated. The production of reactive oxygen species (ROS) and phototoxicity of the photosensitizers were assessed. Healthy fibroblast cells and breast cancer (MCF-7) cells were treated with either free phthalocyanine or phthalocyanine bound to either gold nanoparticles or encapsulated in liposomes. Cell viability studies showed the optimum phototoxic effect on non-malignant cells to be 4.5 J.cm⁻². The PDT effect of the liposome bound phthalocyanine showed extensive damage of the breast cancer cells. Gold nanoparticles only showed a modest improvement in PDT activity.
- Full Text:
- Date Issued: 2012
Pre-concentration of heavy metals in aqueous environments using electrospun polymer nanofiber sorbents
- Authors: Darko, Godfred
- Date: 2012
- Subjects: Heavy metals -- Absorption and adsorption -- Research Nanochemistry -- Research Polystyrene -- Research Polyamides -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4337 , http://hdl.handle.net/10962/d1004998
- Description: This thesis presents an alternative approach for pre-concentrating heavy metals in aqueous environments using electro spun polymer nanofiber sorbents. The conditions for electrospinning polyethersulfone, polystyrene, polysulfone and polyamide-6 were optimized. The morphologies and porosities of the electrospun nanofibers were studied using SEM and BET nitrogen gas adsorptions. The nanofibers had mesoporous morphologies with specific surface areas up to 58 m2/g. The electro spun nanofiber sorbents were characterized in terms of their tunability for both uptake and release of heavy metals. The usability of the sorbent was also assessed. The sorbents showed fast adsorption kinetics for heavy metals « 20 min for As, Cu, Ni and Pb) in different aqueous environments. The adsorption characteristics of the sorbents best fitted the Freundlich isotherm and followed the first order kinetics. The efficiencies of adsorption and desorption of heavy metals on both imidazolyl-functionalized polystyrene and amino-functionalized polysulfone sorbents were more than 95% up to the fifth cycle of usage. Reusability improved dramatically (up to 10 runs of usage) when mechanically stable amino-functionalized nylon-6 electro spun nanofibers were used. The capacity of the amino-functionalized nylon-6 sorbent to pre-concentrate heavy metals compared very favourably with those of aqua regia and HN03+H202 digestions especially in less complex matrices. Due to their highly porous nature, the electro spun nanofibers exhibited high adsorption capacities (up to 50 mg/g) for heavy metal ions. The loading capacities achieved with the imidazolyl-functionalized sorbent were higher than those for amino-functionalized mesoporous silica and biomass-based sorbents. The electro spun nanofiber sorbents presents an efficient and cost effective alternative for preconcentrating heavy metals in aqueous environments.
- Full Text:
- Date Issued: 2012
- Authors: Darko, Godfred
- Date: 2012
- Subjects: Heavy metals -- Absorption and adsorption -- Research Nanochemistry -- Research Polystyrene -- Research Polyamides -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4337 , http://hdl.handle.net/10962/d1004998
- Description: This thesis presents an alternative approach for pre-concentrating heavy metals in aqueous environments using electro spun polymer nanofiber sorbents. The conditions for electrospinning polyethersulfone, polystyrene, polysulfone and polyamide-6 were optimized. The morphologies and porosities of the electrospun nanofibers were studied using SEM and BET nitrogen gas adsorptions. The nanofibers had mesoporous morphologies with specific surface areas up to 58 m2/g. The electro spun nanofiber sorbents were characterized in terms of their tunability for both uptake and release of heavy metals. The usability of the sorbent was also assessed. The sorbents showed fast adsorption kinetics for heavy metals « 20 min for As, Cu, Ni and Pb) in different aqueous environments. The adsorption characteristics of the sorbents best fitted the Freundlich isotherm and followed the first order kinetics. The efficiencies of adsorption and desorption of heavy metals on both imidazolyl-functionalized polystyrene and amino-functionalized polysulfone sorbents were more than 95% up to the fifth cycle of usage. Reusability improved dramatically (up to 10 runs of usage) when mechanically stable amino-functionalized nylon-6 electro spun nanofibers were used. The capacity of the amino-functionalized nylon-6 sorbent to pre-concentrate heavy metals compared very favourably with those of aqua regia and HN03+H202 digestions especially in less complex matrices. Due to their highly porous nature, the electro spun nanofibers exhibited high adsorption capacities (up to 50 mg/g) for heavy metal ions. The loading capacities achieved with the imidazolyl-functionalized sorbent were higher than those for amino-functionalized mesoporous silica and biomass-based sorbents. The electro spun nanofiber sorbents presents an efficient and cost effective alternative for preconcentrating heavy metals in aqueous environments.
- Full Text:
- Date Issued: 2012
Quality of work and work life: understanding the work ethic of medical professionals in selected hospitals in the Eastern Cape region of South Africa
- Authors: Kwizera, Alice Stella
- Date: 2012
- Subjects: Hospitals -- Medical staff -- South Africa -- Eastern Cape Work ethic -- South Africa -- Eastern Cape Medical personnel -- Job satisfaction -- South Africa -- Eastern Cape Protestant work ethic
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3323 , http://hdl.handle.net/10962/d1003111
- Description: This thesis reports a study of work ethic values, beliefs and attitudes held by medical professionals in selected hospitals in the Eastern Cape, South Africa. The study was in response to the public outcry about the declining work ethic and poor service delivery in South Africa’s healthcare sector. Scholarly interest in the work ethic and its role in economic development dates back to Max Weber’s classical work, which was the starting point for my study. The German economic sociologist published his seminal essay on The Protestant Ethic and the Spirit of Capitalism in 1904/1905. Since that time, Weber’s ideas on the Protestant work ethic continue to inform and influence studies of the contemporary work ethic, which is thought to have become secularised. My study was informed by data collected in 2009 through a questionnaire survey and personal interviews. A total of 174 doctors and nurses, working in four urban, periurban and rural hospitals near East London, completed a self-administered questionnaire. The questionnaire replicated the Multi-Dimensional Work Ethic Profile (MWEP) developed by Miller, Woehr and Hudspeth in 2001/2002. The instrument examines seven critical dimensions of the work ethic, namely self-reliance, morality, (foregoing) leisure, hard work, centrality of work in life, not wasting time, and delay of gratification. In addition, I conducted personal interviews in the same four hospitals with 41 hospital managers, doctors, nurses, and patients to discuss their understanding of the work ethic and its practical application. The study found that both doctors’ and nurses’ overall work ethic scores on the MWEP scale were above average. Although there was no significant difference between the overall work ethic scores of the two professions, doctors scored significantly higher than nurses on the ‘hard work’ and ‘self reliance’ dimensions of the work ethic scale. In the qualitative study, the doctors’ work ethic was rated much more highly than the nurses’ by their superiors and patients; and the work ethic of nurses in the urban hospitals was rated much lower than that of their rural colleagues. In contradiction to the idea of the secularization of the contemporary work ethic, religiosity and religious beliefs were influential in the endorsement of work ethic principles. In line with the notion that ‘happy’ workers are more productive, job and life satisfaction were found to be strong correlates of the work ethic of medical professionals.
- Full Text:
- Date Issued: 2012
- Authors: Kwizera, Alice Stella
- Date: 2012
- Subjects: Hospitals -- Medical staff -- South Africa -- Eastern Cape Work ethic -- South Africa -- Eastern Cape Medical personnel -- Job satisfaction -- South Africa -- Eastern Cape Protestant work ethic
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3323 , http://hdl.handle.net/10962/d1003111
- Description: This thesis reports a study of work ethic values, beliefs and attitudes held by medical professionals in selected hospitals in the Eastern Cape, South Africa. The study was in response to the public outcry about the declining work ethic and poor service delivery in South Africa’s healthcare sector. Scholarly interest in the work ethic and its role in economic development dates back to Max Weber’s classical work, which was the starting point for my study. The German economic sociologist published his seminal essay on The Protestant Ethic and the Spirit of Capitalism in 1904/1905. Since that time, Weber’s ideas on the Protestant work ethic continue to inform and influence studies of the contemporary work ethic, which is thought to have become secularised. My study was informed by data collected in 2009 through a questionnaire survey and personal interviews. A total of 174 doctors and nurses, working in four urban, periurban and rural hospitals near East London, completed a self-administered questionnaire. The questionnaire replicated the Multi-Dimensional Work Ethic Profile (MWEP) developed by Miller, Woehr and Hudspeth in 2001/2002. The instrument examines seven critical dimensions of the work ethic, namely self-reliance, morality, (foregoing) leisure, hard work, centrality of work in life, not wasting time, and delay of gratification. In addition, I conducted personal interviews in the same four hospitals with 41 hospital managers, doctors, nurses, and patients to discuss their understanding of the work ethic and its practical application. The study found that both doctors’ and nurses’ overall work ethic scores on the MWEP scale were above average. Although there was no significant difference between the overall work ethic scores of the two professions, doctors scored significantly higher than nurses on the ‘hard work’ and ‘self reliance’ dimensions of the work ethic scale. In the qualitative study, the doctors’ work ethic was rated much more highly than the nurses’ by their superiors and patients; and the work ethic of nurses in the urban hospitals was rated much lower than that of their rural colleagues. In contradiction to the idea of the secularization of the contemporary work ethic, religiosity and religious beliefs were influential in the endorsement of work ethic principles. In line with the notion that ‘happy’ workers are more productive, job and life satisfaction were found to be strong correlates of the work ethic of medical professionals.
- Full Text:
- Date Issued: 2012
Quantification of the cross-sectoral impacts of waterweeds and their control in Ghana
- Authors: Akpabey, Felix Jerry
- Date: 2012
- Subjects: Water hyacinth -- Control -- Environmental aspects -- Ghana Alien plants -- Research -- Ghana Introduced organisms Economic development -- Social aspects -- Research -- Ghana
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5748 , http://hdl.handle.net/10962/d1005435
- Description: The Akosombo Dam on the Volta River in Ghana was built in 1963 to provide cheap energy to fuel industry and to accelerate the economic growth of the country. It provides hydroelectric power, enhanced fishing and water transportation upstream, and improved opportunities for irrigated farming, especially in the lower reaches, and their attendant economic multiplier effects. A few years after the construction of this major dam, a rapid expansion of industrialization took place in Ghana. This brought about an exponential increase in demand for more electrical power. This led to the construction of a smaller dam at Akuse, downstream of the Akosomho Dam in 1981 and the formation of a headpond at Kpong. The impoundment of the river at the two sites (Akosombo and Kpong) caused an alteration in the existing ecological and biophysical processes in the river basin, including a slowing of the flow of the river, upstream and downstream. Changes in the natural processes, such as a reduction in the flow of the river and an increase in nutrient status of the water, resulted in an invasion of aquatic weeds, increasing the density of aquatic snails (intermediate hosts of schistosomiasis), silting and closure of the estuary, as well as other more subtle effects. The invasion of the river's main course and the dams by aquatic plants led to a corresponding reduction of navigable water both upstream and downstream. The aim of this thesis was to quantify the impact and control of waterweeds, especially water hyacinth, Eichhornia crassipes (Mart) Solms-Laubach (Pontederiaceae), in Ghana. A floral survey on the Kpong Headpond recorded 49 emergent, 12 free floating and I submerged aquatic plant species, many of which were indigenous, but the exotic or introduced water hyacinth was recorded at most of the sampling sites, and was the most abundant and had the biggest impact on the utilization of the water resource. Mats of water hyacinth served as substrates for other, indigenous species to grow out into the main channel of the headpond, including the intake point of the Kpong head works of the Ghana Water Company Limited (GWCL) and landing sites for boats. These mats resulted in a reduction of the fish (fin and shell) harvest, reducing the annual production to far below demand. Water hyacinth was also shown to have severe health implications. A survey of the Ministry of Health records showed that the prevalence of both urinary and intestinal schistosomiasis had risen significantly over time as the abundance of waterweeds, most notably water hyacinth, increased, and ranged between 70% and 75% but up to 100% in some lakeside communities. Based on the work done by an NGO on board the medical boat ("Onipa Nua "), losses in terms of money due to the effect on health of the aquatic weed infestations on the Volta River in 2006 amounted to US$ 620,000. Economic losses due to invasive alien aquatic weeds were also calculated on the Oti River Arm of Lake Volta. It was estimated that about US$2.3 million per annum would be lost to the Volta Lake Transport Company and individual boat transport operators if this section of the river were 100% covered by aquatic weeds (water hyacinth and Salvinia molesta D.S. Mitchell (Salviniaceae)). It was also estimated that US$327,038 was spent annually in monitoring and managing the weeds in the Oti River. Control interventions for aquatic weeds have been implemented in river systems in Ghana. The biological control agents Neochetina bruchi Hustache (Coleoptera, Curculionidae) and Neochetina eichhorniae Warner (Coleoptera, Curculionidae) have been used on water hyacinth infestations in the Oti River Arm of Lake Volta, the Tano River and the Lagoon complex in the south-western part of the country. Cyrtobagous salviniae Calder and Sands (Coleoptera: Curculionidae) has been used to control salvinia, and Neohydronomous affinis Hustache (Coleoptera: Curculionidae) to control water lettuce, Pistia stratiotes Lilmaeus (Araceae) in the Tano River and Lagoon complex. Although these projects have been regarded as successful, they have relied on research from elsewhere in the world and no postrelease quantification has been conducted. In evaluating the impact of the biological control agents Neochetina bruchi and Neochetina eichhorniae weevils on water hyacinth infestations in the Tano River, fresh adult feeding scars were recorded as well as the numbers of adult weevils on each water hyacinth plant sampled at six sites. Despite being released in 1994, weevil numbers and resultant damage to plants in the Tano Lagoon was low in comparison to other regions of the world where these agents have been used. The main reason for this is that this lagoon floods seasonally, washing weevil-infested plants out to sea. Water hyacinth then re-infests the lagoon from seed and the weevil populations are low. To resolve this situation, two courses of action are proposed. The first is to mass rear the weevils along the shore of the lagoon and release them when the first seedlings recruit. The second proposal is that additional agents that have shorter lifecycies and are more mobile than the weevils should be released. To this end, the water hyacinth mirid, Eccritotarsus catarinensis (Carvalho) (Hemiptera: Miridae) was imported from South Africa and released onto the Tano Lagoon in 2009. Retrospective laboratory host specificity trials were conducted on Neachetina eichharniae and Neachetina bruchi weevils 15 years after their release into Ghana to see if any variation in their host ranges had occurred. Considerable damage was inflicted on the E. crassipes leaves by the Neachetina weevils, while little feeding damage was recorded on both Heteranthera callifalia Kunth. (Pontederiaceae) and Eichharnia natans (P.Beauv.) Solms (Pontederiaceae). All the weevils introduced on H callifalia and E. natans died after the first week. This study served to confirm the host specificity and thereby the safety of these agents. Invasive alien aquatic macrophytes have negative impacts on the environment and economy of Ghana. The control of these weeds is essential to socioeconomic development and improved human health standards in riparian communities. Biological control offers a safe and sustainable control option, but requires diligent implementation. However, aquatic weed invasion is more typically a result of the anthropogenically induced eutrophication of water bodies, and this is the main issue that has to be addressed.
- Full Text:
- Date Issued: 2012
- Authors: Akpabey, Felix Jerry
- Date: 2012
- Subjects: Water hyacinth -- Control -- Environmental aspects -- Ghana Alien plants -- Research -- Ghana Introduced organisms Economic development -- Social aspects -- Research -- Ghana
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5748 , http://hdl.handle.net/10962/d1005435
- Description: The Akosombo Dam on the Volta River in Ghana was built in 1963 to provide cheap energy to fuel industry and to accelerate the economic growth of the country. It provides hydroelectric power, enhanced fishing and water transportation upstream, and improved opportunities for irrigated farming, especially in the lower reaches, and their attendant economic multiplier effects. A few years after the construction of this major dam, a rapid expansion of industrialization took place in Ghana. This brought about an exponential increase in demand for more electrical power. This led to the construction of a smaller dam at Akuse, downstream of the Akosomho Dam in 1981 and the formation of a headpond at Kpong. The impoundment of the river at the two sites (Akosombo and Kpong) caused an alteration in the existing ecological and biophysical processes in the river basin, including a slowing of the flow of the river, upstream and downstream. Changes in the natural processes, such as a reduction in the flow of the river and an increase in nutrient status of the water, resulted in an invasion of aquatic weeds, increasing the density of aquatic snails (intermediate hosts of schistosomiasis), silting and closure of the estuary, as well as other more subtle effects. The invasion of the river's main course and the dams by aquatic plants led to a corresponding reduction of navigable water both upstream and downstream. The aim of this thesis was to quantify the impact and control of waterweeds, especially water hyacinth, Eichhornia crassipes (Mart) Solms-Laubach (Pontederiaceae), in Ghana. A floral survey on the Kpong Headpond recorded 49 emergent, 12 free floating and I submerged aquatic plant species, many of which were indigenous, but the exotic or introduced water hyacinth was recorded at most of the sampling sites, and was the most abundant and had the biggest impact on the utilization of the water resource. Mats of water hyacinth served as substrates for other, indigenous species to grow out into the main channel of the headpond, including the intake point of the Kpong head works of the Ghana Water Company Limited (GWCL) and landing sites for boats. These mats resulted in a reduction of the fish (fin and shell) harvest, reducing the annual production to far below demand. Water hyacinth was also shown to have severe health implications. A survey of the Ministry of Health records showed that the prevalence of both urinary and intestinal schistosomiasis had risen significantly over time as the abundance of waterweeds, most notably water hyacinth, increased, and ranged between 70% and 75% but up to 100% in some lakeside communities. Based on the work done by an NGO on board the medical boat ("Onipa Nua "), losses in terms of money due to the effect on health of the aquatic weed infestations on the Volta River in 2006 amounted to US$ 620,000. Economic losses due to invasive alien aquatic weeds were also calculated on the Oti River Arm of Lake Volta. It was estimated that about US$2.3 million per annum would be lost to the Volta Lake Transport Company and individual boat transport operators if this section of the river were 100% covered by aquatic weeds (water hyacinth and Salvinia molesta D.S. Mitchell (Salviniaceae)). It was also estimated that US$327,038 was spent annually in monitoring and managing the weeds in the Oti River. Control interventions for aquatic weeds have been implemented in river systems in Ghana. The biological control agents Neochetina bruchi Hustache (Coleoptera, Curculionidae) and Neochetina eichhorniae Warner (Coleoptera, Curculionidae) have been used on water hyacinth infestations in the Oti River Arm of Lake Volta, the Tano River and the Lagoon complex in the south-western part of the country. Cyrtobagous salviniae Calder and Sands (Coleoptera: Curculionidae) has been used to control salvinia, and Neohydronomous affinis Hustache (Coleoptera: Curculionidae) to control water lettuce, Pistia stratiotes Lilmaeus (Araceae) in the Tano River and Lagoon complex. Although these projects have been regarded as successful, they have relied on research from elsewhere in the world and no postrelease quantification has been conducted. In evaluating the impact of the biological control agents Neochetina bruchi and Neochetina eichhorniae weevils on water hyacinth infestations in the Tano River, fresh adult feeding scars were recorded as well as the numbers of adult weevils on each water hyacinth plant sampled at six sites. Despite being released in 1994, weevil numbers and resultant damage to plants in the Tano Lagoon was low in comparison to other regions of the world where these agents have been used. The main reason for this is that this lagoon floods seasonally, washing weevil-infested plants out to sea. Water hyacinth then re-infests the lagoon from seed and the weevil populations are low. To resolve this situation, two courses of action are proposed. The first is to mass rear the weevils along the shore of the lagoon and release them when the first seedlings recruit. The second proposal is that additional agents that have shorter lifecycies and are more mobile than the weevils should be released. To this end, the water hyacinth mirid, Eccritotarsus catarinensis (Carvalho) (Hemiptera: Miridae) was imported from South Africa and released onto the Tano Lagoon in 2009. Retrospective laboratory host specificity trials were conducted on Neachetina eichharniae and Neachetina bruchi weevils 15 years after their release into Ghana to see if any variation in their host ranges had occurred. Considerable damage was inflicted on the E. crassipes leaves by the Neachetina weevils, while little feeding damage was recorded on both Heteranthera callifalia Kunth. (Pontederiaceae) and Eichharnia natans (P.Beauv.) Solms (Pontederiaceae). All the weevils introduced on H callifalia and E. natans died after the first week. This study served to confirm the host specificity and thereby the safety of these agents. Invasive alien aquatic macrophytes have negative impacts on the environment and economy of Ghana. The control of these weeds is essential to socioeconomic development and improved human health standards in riparian communities. Biological control offers a safe and sustainable control option, but requires diligent implementation. However, aquatic weed invasion is more typically a result of the anthropogenically induced eutrophication of water bodies, and this is the main issue that has to be addressed.
- Full Text:
- Date Issued: 2012
Re-tracing representations and identities in twentieth century South African and African photography: Joseph Denfield, regimes of seeing and alternative visual histories
- Authors: Mnyaka, Phindezwa Elizabeth
- Date: 2012
- Subjects: Historical museums -- South Africa -- Eastern Cape , Natural history , Photography -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD (History)
- Identifier: vital:11536 , http://hdl.handle.net/10353/540 , Historical museums -- South Africa -- Eastern Cape , Natural history , Photography -- South Africa
- Description: The thesis examines the photographic collection of Joseph Denfield, an archivist and historian who experimented with photography over a twenty-year period. The study is located within the field of critical visual studies that focuses on historical photography in its depiction of identities and groups in the context of social change. The thesis pays attention to the manner and extent to which Denfield participated in regional visual economies at various moments during his photographic career in order to establish his contribution towards a visual history in Africa and more broadly Southern Africa. It follows Denfield’s career trajectory chronologically. It begins with a study of his photographic work in Nigeria which was oriented around so-called ‘pagan tribes’ and which was framed within the discourse of ethnography. It then pays attention to his growth as an artist in photography that resulted from years of exhibiting in salons. I read these photographs and texts in relation to his earlier work in Nigeria given the extent to which he drew on anthropological discourses. It is through his involvement with photographic art circles that Denfield developed as a historian as a result of his research into the history of photography and regional visual histories. This took the form of both unearthing historical photographs as well as photographing historical sites to construct the past in particular ways through the visual. At each stage he translated these histories into public forms of representation and power thus he figures among a small group of ‘colonial’ photographers that shaped the visual economy of Southern Africa. Through a detailed study of his work, the thesis thus aims to re-think through new dimensions of visual culture.
- Full Text:
- Date Issued: 2012
- Authors: Mnyaka, Phindezwa Elizabeth
- Date: 2012
- Subjects: Historical museums -- South Africa -- Eastern Cape , Natural history , Photography -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD (History)
- Identifier: vital:11536 , http://hdl.handle.net/10353/540 , Historical museums -- South Africa -- Eastern Cape , Natural history , Photography -- South Africa
- Description: The thesis examines the photographic collection of Joseph Denfield, an archivist and historian who experimented with photography over a twenty-year period. The study is located within the field of critical visual studies that focuses on historical photography in its depiction of identities and groups in the context of social change. The thesis pays attention to the manner and extent to which Denfield participated in regional visual economies at various moments during his photographic career in order to establish his contribution towards a visual history in Africa and more broadly Southern Africa. It follows Denfield’s career trajectory chronologically. It begins with a study of his photographic work in Nigeria which was oriented around so-called ‘pagan tribes’ and which was framed within the discourse of ethnography. It then pays attention to his growth as an artist in photography that resulted from years of exhibiting in salons. I read these photographs and texts in relation to his earlier work in Nigeria given the extent to which he drew on anthropological discourses. It is through his involvement with photographic art circles that Denfield developed as a historian as a result of his research into the history of photography and regional visual histories. This took the form of both unearthing historical photographs as well as photographing historical sites to construct the past in particular ways through the visual. At each stage he translated these histories into public forms of representation and power thus he figures among a small group of ‘colonial’ photographers that shaped the visual economy of Southern Africa. Through a detailed study of his work, the thesis thus aims to re-think through new dimensions of visual culture.
- Full Text:
- Date Issued: 2012
Relationships between psychological capital, work engagement and organisational citizenship behaviour in South African automative dealerships
- Authors: Harris, Chantel
- Date: 2012
- Subjects: Work -- Psychological aspects , Employee motivation , Job satisfaction -- South Africa , Organizational behavior , Automobile industry and trade
- Language: English
- Type: Thesis , Doctoral , DCom
- Identifier: vital:9395 , http://hdl.handle.net/10948/d1008059 , Work -- Psychological aspects , Employee motivation , Job satisfaction -- South Africa , Organizational behavior , Automobile industry and trade
- Description: Psychological capital (PsyCap), work engagement (WE) and organisational citizenship behaviour (OCB) are all positive constructs which research has indicated will have a positive impact on the bottom line. In light of Positive Organisational Behaviour, this has become increasingly important, particularly in the service industry where good service leads to satisfied customers and ultimately repeat purchases. This research took on the form of a cross- sectional design, using a composite questionnaire to measure PsyCap, WE and OCB. This was a self-report electronic questionnaire which was distributed via email to customer service representatives (N=276) from a national automotive company with dealerships in Gauteng and the Western Cape. The measurement models were revalidated for the South African sample of customer service representatives through conducting Exploratory Factor Analysis. PsyCap remained a four-factor structure, however lost items in the elimination process. Both the UWES and OCB instruments lost items and became two-factor structures. This makes the notion that these instruments are portable to the South African situation questionable. To confirm these structures, item parcelling was utilised and Confirmatory Factor Analysis was conducted. The results indicated that the new measurement models were better suited to the South African sample. Demographic groups had significant differences in the means for PsyCap, WE and OCB. Further to this, relationships between the constructs were tested through multiple regression and structural equation modeling. The most significant relationship was found between PsyCap and work engagement. Finally, PsyCap (barring optimism) and WE were found to load onto a single factor when testing for factorial independence, while OCB came out as a separate factor.
- Full Text:
- Date Issued: 2012
- Authors: Harris, Chantel
- Date: 2012
- Subjects: Work -- Psychological aspects , Employee motivation , Job satisfaction -- South Africa , Organizational behavior , Automobile industry and trade
- Language: English
- Type: Thesis , Doctoral , DCom
- Identifier: vital:9395 , http://hdl.handle.net/10948/d1008059 , Work -- Psychological aspects , Employee motivation , Job satisfaction -- South Africa , Organizational behavior , Automobile industry and trade
- Description: Psychological capital (PsyCap), work engagement (WE) and organisational citizenship behaviour (OCB) are all positive constructs which research has indicated will have a positive impact on the bottom line. In light of Positive Organisational Behaviour, this has become increasingly important, particularly in the service industry where good service leads to satisfied customers and ultimately repeat purchases. This research took on the form of a cross- sectional design, using a composite questionnaire to measure PsyCap, WE and OCB. This was a self-report electronic questionnaire which was distributed via email to customer service representatives (N=276) from a national automotive company with dealerships in Gauteng and the Western Cape. The measurement models were revalidated for the South African sample of customer service representatives through conducting Exploratory Factor Analysis. PsyCap remained a four-factor structure, however lost items in the elimination process. Both the UWES and OCB instruments lost items and became two-factor structures. This makes the notion that these instruments are portable to the South African situation questionable. To confirm these structures, item parcelling was utilised and Confirmatory Factor Analysis was conducted. The results indicated that the new measurement models were better suited to the South African sample. Demographic groups had significant differences in the means for PsyCap, WE and OCB. Further to this, relationships between the constructs were tested through multiple regression and structural equation modeling. The most significant relationship was found between PsyCap and work engagement. Finally, PsyCap (barring optimism) and WE were found to load onto a single factor when testing for factorial independence, while OCB came out as a separate factor.
- Full Text:
- Date Issued: 2012
Response of mangroves in South Africa to anthropogenic and natural impacts
- Hoppe-Speer, Sabine Clara-Lisa
- Authors: Hoppe-Speer, Sabine Clara-Lisa
- Date: 2012
- Subjects: Mangrove forests , Climatic changes , Forest resilience
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10630 , http://hdl.handle.net/10948/d1012123 , Mangrove forests , Climatic changes , Forest resilience
- Description: The total mangrove area cover in South Africa is 1631.7 ha, with the largest area cover in a few estuaries in the KwaZulu-Natal Province (1391.1 ha) and the remainder recorded in the Eastern Cape Province with 240.6 ha. This represents 0.05 percent of Africa‟s mangrove area cover and although small adds irreplaceable value to the biodiversity of South Africa. Mangroves are threatened by over-utilization through harvesting for firewood and building materials as well as excessive browsing and trampling by livestock. The objective of this study was to investigate the response of mangroves to different stressors from natural change as well as anthropogenic pressures. This was done by identifying pressures, measuring area cover, population structure and environmental parameters such as sediment characteristics. Mangroves in 17 estuaries along the east coast were investigated. Population structure and the area covered by mangroves in 2011/2012 were compared with data from the same area for 1999. Detailed studies were conducted in St. Lucia Estuary to investigate the response of mangroves to reduced tidal flooding; mangrove expansion at a latitudinal limit in a protected area at Nahoon Estuary was studied and the effect of cattle browsing on mangroves was measured at Nxaxo Estuary. The St. Lucia Estuary (28°S; 32°E) represented a unique study site as the mouth has been closed to the sea since 2002 and the mangrove habitats have been non-tidal. St. Lucia Estuary is both a Ramsar and World Heritage site and therefore understanding the response of mangroves to changes in the environment is important. In 2010 sediment characteristics and mangrove population structure were measured at four sites which were chosen to represent different salinity and water level conditions. The site fringing the main channel had the highest density of mangrove seedlings and saplings. The dry site had a lower density of mangroves with mostly only tall adult trees and few saplings. Mangrove tree height and density increased at sites with high sediment moisture and low surface sediment salinity. Few seedlings and saplings were found at sites with dry surface sediment and high salinity. Long term data are needed to assess the influence of mouth closure on recruitment and survival of the mangrove forest at St. Lucia Estuary; however this study has shown that sediment characteristics are unfavourable for mangrove growth at sites now characterized by a lack of tidal flooding. It is not known when exactly the mangroves were planted in Nahoon Estuary (32°S; 27° E), East London, but it is suspected that this was in the early 1970s. Avicennia marina (Forrsk.)Vierh. was planted first, followed a few years later by the planting of Bruguiera gymnorrhiza (L.) Lam. and Rhizophora mucronata (L.) among the larger A. marina trees. Surprisingly the mangrove population appears to be thriving and this study tested the hypothesis that mangroves have expanded and replaced salt marsh over a 33 year period. This study provides important information on mangroves growing at higher latitudes, where they were thought to not occur naturally due to lower annual average temperatures. It further provides insights on future scenarios of possible shifts in vegetation types due to climate change at one of the most southerly distribution sites worldwide. The expansion of mangroves was measured over a 33 year period (1978 - 2011) using past aerial photographs and Esri ArcGIS Desktop 10 software. In addition, field surveys were completed in 2011 to determine the population structure of the present mangrove forest and relate this to environmental conditions. The study showed that mangrove area cover increased linearly at a rate of 0.06 ha-1 expanding over a bare mudflat area, while the salt marsh area cover also increased (0.09 ha-1) but was found to be variable over time. The mangrove area is still small (< 2 ha) and at present no competition between mangroves and salt marsh can be deduced. Instead the area has the ability to maintain high biodiversity and biomass. Avicennia marina was the dominant mangrove species and had high recruitment (seedling density was 33 822 ± 16 364 ha-1) but only a few Bruguiera gymnorrhiza and Rhizophora mucronata individuals were found (< 10 adult trees). The site provides opportunities for studies on mangrove / salt marsh interactions in response to a changing climate at the most southern limit of mangrove distribution in Africa. This research has provided the baseline data, permanent quadrats and tagged trees to be used in future long-term monitoring of population growth and sediment characteristics. At Nxaxo Estuary (32°S; 28°E) the response of mangrove trees (Avicennia marina) to cattle browsing and trampling was investigated by using cattle exclusion plots. Exclusion plots were established by fencing in five 25 m2 quadrats and adjacent to each experimental quadrat a control quadrat (not fenced in, 25 m2) was set-up. Trees were tagged and measured annually from 2010 to 2012. Sediment salinity, pH, moisture, organic content, compaction as well as sediment particle size was also measured in each quadrat. Sediment characteristics did not vary between control and experimental plots but did show changes between the years. The mangrove trees in the cattle exclusion plots grew exponentially over a period of two years. There was a significant increase in mean plant height (5.41 ± 0.53 cm), crown volume (0.54 ± 0.01 m3) and crown diameter (7.09 ± 0.60 cm) from 2010 to 2012. Trees in the control plots had significantly lower growth (p < 0.05). There was a decrease in plant height (-0.07 ± 0.67cm1) and only small increases in crown volume (0.14 ± 0.1 m3) and crown diameter (2.03 ± 2.61 cm). The research showed that browsing on mangroves by cattle stunts growth and causes a shrubby appearance as a result of coppicing. The browsed trees were dwarfed with horizontal spreading of branches and intact foliage close to the ground while the plants in the cattle exclusion plots showed an increase in vertical growth and expansion. In the cattle exclusion plots there was a significantly higher percentage of flowering (67 percent) and fruiting (39 percent) trees in 2012 compared to the control sites where 34 percent of the plants were flowering and 5.4 percent of the plants carried immature propagules. Observations in the field also indicated that cattle had trampled a number of seedlings thus influencing mangrove survival. The study concluded that browsing changes the morphological structure of mangrove trees and reduces growth and seedling establishment. This is an additional stress that the mangroves are exposed to in rural areas where cattle are allowed to roam free. Seventeen permanently open estuaries provide habitat for mangrove forests along the former Transkei coast. This part of the Eastern Cape is mostly undeveloped and difficult to access. Mangrove area cover, species distribution, population structure and health of the mangrove habitat were compared with results from previous studies in 1982 and 1999. The mangrove Bruguiera gymnorrhiza had the densest stands and was widely distributed as it was present in 13 of the 17 estuaries. Avicennia marina was dominant in those estuaries which had the largest area cover of mangroves and was present in 10 estuaries, while Rhizophora mucronata was rare and only present in five estuaries. Anthropogenic and natural impacts were noted within the mangrove habitats in each of these estuaries. Harvesting of mangrove wood, livestock browsing and trampling and footpaths occurred in most of the estuaries (> 70 percent). It was observed that browsing on trees resulted in a clear browse-line and browsing on propagules mainly by goats resulted in reduced seedling establishment in most of the estuaries except those in protected areas. Mangroves had re-established in estuaries where they had been previously lost but mouth closure due to drought and sea storms resulted in the mass die back of mangroves in the Kobonqaba Estuary. There was a total loss of 31.5 ha in mangrove area cover in the last 30 years and this was a total reduction of 10.5 ha (11 percent) for every decade. This is high considering that the present total mangrove area cover is only 240.6 ha for all the Transkei estuaries. In this study it was concluded that the anthropogenic impacts such as livestock browsing and trampling as well as harvesting in these estuaries contributed most to the mangrove degradation as these are continuous pressures occurring over long periods and are expected to increase in future with increasing human population. Natural changes such as sea storms occur less frequently but could result in large scale destruction over shorter periods. Examples of these are mouth closure that result in mangrove mass mortality as well as strong floods which destroy forest by scouring of the banks.
- Full Text:
- Date Issued: 2012
- Authors: Hoppe-Speer, Sabine Clara-Lisa
- Date: 2012
- Subjects: Mangrove forests , Climatic changes , Forest resilience
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10630 , http://hdl.handle.net/10948/d1012123 , Mangrove forests , Climatic changes , Forest resilience
- Description: The total mangrove area cover in South Africa is 1631.7 ha, with the largest area cover in a few estuaries in the KwaZulu-Natal Province (1391.1 ha) and the remainder recorded in the Eastern Cape Province with 240.6 ha. This represents 0.05 percent of Africa‟s mangrove area cover and although small adds irreplaceable value to the biodiversity of South Africa. Mangroves are threatened by over-utilization through harvesting for firewood and building materials as well as excessive browsing and trampling by livestock. The objective of this study was to investigate the response of mangroves to different stressors from natural change as well as anthropogenic pressures. This was done by identifying pressures, measuring area cover, population structure and environmental parameters such as sediment characteristics. Mangroves in 17 estuaries along the east coast were investigated. Population structure and the area covered by mangroves in 2011/2012 were compared with data from the same area for 1999. Detailed studies were conducted in St. Lucia Estuary to investigate the response of mangroves to reduced tidal flooding; mangrove expansion at a latitudinal limit in a protected area at Nahoon Estuary was studied and the effect of cattle browsing on mangroves was measured at Nxaxo Estuary. The St. Lucia Estuary (28°S; 32°E) represented a unique study site as the mouth has been closed to the sea since 2002 and the mangrove habitats have been non-tidal. St. Lucia Estuary is both a Ramsar and World Heritage site and therefore understanding the response of mangroves to changes in the environment is important. In 2010 sediment characteristics and mangrove population structure were measured at four sites which were chosen to represent different salinity and water level conditions. The site fringing the main channel had the highest density of mangrove seedlings and saplings. The dry site had a lower density of mangroves with mostly only tall adult trees and few saplings. Mangrove tree height and density increased at sites with high sediment moisture and low surface sediment salinity. Few seedlings and saplings were found at sites with dry surface sediment and high salinity. Long term data are needed to assess the influence of mouth closure on recruitment and survival of the mangrove forest at St. Lucia Estuary; however this study has shown that sediment characteristics are unfavourable for mangrove growth at sites now characterized by a lack of tidal flooding. It is not known when exactly the mangroves were planted in Nahoon Estuary (32°S; 27° E), East London, but it is suspected that this was in the early 1970s. Avicennia marina (Forrsk.)Vierh. was planted first, followed a few years later by the planting of Bruguiera gymnorrhiza (L.) Lam. and Rhizophora mucronata (L.) among the larger A. marina trees. Surprisingly the mangrove population appears to be thriving and this study tested the hypothesis that mangroves have expanded and replaced salt marsh over a 33 year period. This study provides important information on mangroves growing at higher latitudes, where they were thought to not occur naturally due to lower annual average temperatures. It further provides insights on future scenarios of possible shifts in vegetation types due to climate change at one of the most southerly distribution sites worldwide. The expansion of mangroves was measured over a 33 year period (1978 - 2011) using past aerial photographs and Esri ArcGIS Desktop 10 software. In addition, field surveys were completed in 2011 to determine the population structure of the present mangrove forest and relate this to environmental conditions. The study showed that mangrove area cover increased linearly at a rate of 0.06 ha-1 expanding over a bare mudflat area, while the salt marsh area cover also increased (0.09 ha-1) but was found to be variable over time. The mangrove area is still small (< 2 ha) and at present no competition between mangroves and salt marsh can be deduced. Instead the area has the ability to maintain high biodiversity and biomass. Avicennia marina was the dominant mangrove species and had high recruitment (seedling density was 33 822 ± 16 364 ha-1) but only a few Bruguiera gymnorrhiza and Rhizophora mucronata individuals were found (< 10 adult trees). The site provides opportunities for studies on mangrove / salt marsh interactions in response to a changing climate at the most southern limit of mangrove distribution in Africa. This research has provided the baseline data, permanent quadrats and tagged trees to be used in future long-term monitoring of population growth and sediment characteristics. At Nxaxo Estuary (32°S; 28°E) the response of mangrove trees (Avicennia marina) to cattle browsing and trampling was investigated by using cattle exclusion plots. Exclusion plots were established by fencing in five 25 m2 quadrats and adjacent to each experimental quadrat a control quadrat (not fenced in, 25 m2) was set-up. Trees were tagged and measured annually from 2010 to 2012. Sediment salinity, pH, moisture, organic content, compaction as well as sediment particle size was also measured in each quadrat. Sediment characteristics did not vary between control and experimental plots but did show changes between the years. The mangrove trees in the cattle exclusion plots grew exponentially over a period of two years. There was a significant increase in mean plant height (5.41 ± 0.53 cm), crown volume (0.54 ± 0.01 m3) and crown diameter (7.09 ± 0.60 cm) from 2010 to 2012. Trees in the control plots had significantly lower growth (p < 0.05). There was a decrease in plant height (-0.07 ± 0.67cm1) and only small increases in crown volume (0.14 ± 0.1 m3) and crown diameter (2.03 ± 2.61 cm). The research showed that browsing on mangroves by cattle stunts growth and causes a shrubby appearance as a result of coppicing. The browsed trees were dwarfed with horizontal spreading of branches and intact foliage close to the ground while the plants in the cattle exclusion plots showed an increase in vertical growth and expansion. In the cattle exclusion plots there was a significantly higher percentage of flowering (67 percent) and fruiting (39 percent) trees in 2012 compared to the control sites where 34 percent of the plants were flowering and 5.4 percent of the plants carried immature propagules. Observations in the field also indicated that cattle had trampled a number of seedlings thus influencing mangrove survival. The study concluded that browsing changes the morphological structure of mangrove trees and reduces growth and seedling establishment. This is an additional stress that the mangroves are exposed to in rural areas where cattle are allowed to roam free. Seventeen permanently open estuaries provide habitat for mangrove forests along the former Transkei coast. This part of the Eastern Cape is mostly undeveloped and difficult to access. Mangrove area cover, species distribution, population structure and health of the mangrove habitat were compared with results from previous studies in 1982 and 1999. The mangrove Bruguiera gymnorrhiza had the densest stands and was widely distributed as it was present in 13 of the 17 estuaries. Avicennia marina was dominant in those estuaries which had the largest area cover of mangroves and was present in 10 estuaries, while Rhizophora mucronata was rare and only present in five estuaries. Anthropogenic and natural impacts were noted within the mangrove habitats in each of these estuaries. Harvesting of mangrove wood, livestock browsing and trampling and footpaths occurred in most of the estuaries (> 70 percent). It was observed that browsing on trees resulted in a clear browse-line and browsing on propagules mainly by goats resulted in reduced seedling establishment in most of the estuaries except those in protected areas. Mangroves had re-established in estuaries where they had been previously lost but mouth closure due to drought and sea storms resulted in the mass die back of mangroves in the Kobonqaba Estuary. There was a total loss of 31.5 ha in mangrove area cover in the last 30 years and this was a total reduction of 10.5 ha (11 percent) for every decade. This is high considering that the present total mangrove area cover is only 240.6 ha for all the Transkei estuaries. In this study it was concluded that the anthropogenic impacts such as livestock browsing and trampling as well as harvesting in these estuaries contributed most to the mangrove degradation as these are continuous pressures occurring over long periods and are expected to increase in future with increasing human population. Natural changes such as sea storms occur less frequently but could result in large scale destruction over shorter periods. Examples of these are mouth closure that result in mangrove mass mortality as well as strong floods which destroy forest by scouring of the banks.
- Full Text:
- Date Issued: 2012
Rhenium complexes with multidentate benzazoles and related N,X-donor (X = N, O, S) ligands
- Authors: Potgieter, Kim Carey
- Date: 2012
- Subjects: Rhenium , Benzimidazoles , Ligands (Biochemistry)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10438 , http://hdl.handle.net/10948/d1020773
- Description: The coordination behaviour of 4-aminoantipyrine (H2pap) and its Schiff base derivatives with the oxorhenium(V) and tricarbonyl rhenium(I) cores are reported. The reactions of trans-[ReOX3(PPh3)2] (X = Cl, Br) with H2pap were studied, and the complexes cis-[ReX2(pap)(H2pap)(PPh3)](ReO4) were isolated. The ligand pap is coordinated monodentately through the doubly deprotonated amino nitrogen as an imide, and H2pap acts as a neutral bidentate chelate, with coordination through the neutral amino nitrogen and the ketonic oxygen. The reactions of trans-[ReOBr3(PPh3)2] and cis-[ReO2I(PPh3)2] with -(2-aminobenzylideneamino)-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one (H2nap) and 4-(2-hydroxybenzylideneamino)-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one (Hoap) are also reported. The complexes cis-[Re(nap)Br2(PPh3)]Br, [ReO(OEt)(Hnap)(PPh3)]I and [ReO(OMe)(oap)(PPh3)]I were isolated and structurally characterized. The reactions of the Schiff base derivatives 1,2-(diimino-4’-antipyrinyl)ethane (dae) and 2,6-bis(4-amino-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one)pyridine (bap) with [Re(CO)5X] (X = Br or Cl) produced fac-[Re(CO)3(dae)Cl] and fac-[Re(CO)3(bap)Br] respectively. A series of rhenium(I) tricarbonyl complexes containing bidentate derivatives of aniline was synthesized and structurally characterized. With 1,2-diaminobenzene (Hpda) the ‘2+1’ complex salt fac-[Re(CO)3(κ1-Hpda)(κ2-Hpda)]Br was isolated, but with 2-mercaptophenol (Hspo) the bridged dimer [Re2(CO)7(spo)2] was found. The neutral complex [Re(CO)3(ons)(Hno)] was isolated from the reaction of [Re(CO)5Br] with 2-[(2-methylthio)benzylideneimino]phenol (Hons; Hno = 2-aminophenol), with ons coordinated as a bidentate chelate with a free SCH3 group. In the complex [Re(CO)3(Htpn)Br] (Htpn = N-(2-(methylthio)benzylidene)benzene-1,2-diamine) the potentially tridentate ligand Htpn is coordinated via the methylthiol sulfur and imino nitrogen atoms only, with a free amino group. These rhenium(I) complexes, with the exception of [Re2(CO)7(spo)2], revealed broad emissions centred around 535 nm. The reactions of the rhenium(V) complex cis-[ReO2I(PPh3)2] with 2-aminothiophenol (H2atp), benzene-1,2-dithiol (H2tdt) and 2-hydroxybenzenethiol (H2otp) led to the formation of the rhenium(III) compounds [Re(Hatp)(ibsq)2].OPPh3, [Re(sbsq)3].OPPh3 and [Re(obsq)3].OPPh3 (ibsq = 2-iminothiobenzosemiquinonate, sbsq = 1,2-dithiobenzosemiquinonate, obsq = 2-hydroxothiobenzosemiquinonate) respectively. The complexes adopt a trigonal prismatic geometry around the rhenium centre with average twists angles between 3.20-26.10˚. The E1/2 values for the Re(III)/Re(IV) redox couple were found to be 0.022, 0.142 and 0.126 V for [Re(Hatp)(ibsq)2].OPPh3, [Re(sbsq)3].OPPh3 and [Re(obsq)3].OPPh3 respectively. The reactions of the benzoxazole ligands, 3-(benzoxazol-2-yl)pyridin-2-ol (Hbop) and 5-amino-2-(benzoxazol-2-yl)phenol (Habo) with a [ReO]3+ precursor led to the rhenium(III) complex, [ReCl2(bop)(PPh3)2], and the complex salt, [ReO(abo)I(PPh3)2]ReO4, respectively. A variety of benzothiazole and benzimidazole derivatives were reacted with [Re(CO)5Br]. In the case of bis(benzothiazol-2-ylethyl)sulfide (bts), the neutral complex fac-[Re(CO)3(bts)Br] was obtained. The dimeric complexes (μ-dbt)2[Re(CO)3]2 and (μ-mbt)2[Re(CO)3]2 were formed when 1,3-bis(benzothiazol-2-yl)thiourea (Hdbt) and 1-(benzothiazol-2-ylidene)-3-methylthiourea (Hmbt) were used as ligands. The reaction of 2,2’-(oxybis(methylene))bis(benzimidazole) (bmb) with [Re(CO)5Cl] resulted in the rhenium(I) complex salt fac-[Re(CO)3(bmb)]+, with the tri-μ-chlorohexacarbonyl dirhenate [Re2(CO)6Cl3]- as the counter anion. The neutral complex fac-[Re(CO)3(btp)Cl] was isolated from the reaction of the 2,9-bis(benzothiazol-2-yl)-1,10-phenanthroline (btp) ligand and [Re(CO)5Cl]. The reactions of trans-[ReOCl3(PPh3)2] with bis(benzimidazol-2-ylethyl)sulfide (btn) and 1-(benzothiazol-2-ylidene)-3-methylthiourea (Hmbt) led to the formation of the cationic compounds (μ-O)2[Re2O2(btn)2]I2 and [ReCl2(bte)(PPh3)2]Cl (bte = (benzothiazole-2-yl)-N-ethylidenemethanamine) respectively.
- Full Text:
- Date Issued: 2012
- Authors: Potgieter, Kim Carey
- Date: 2012
- Subjects: Rhenium , Benzimidazoles , Ligands (Biochemistry)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10438 , http://hdl.handle.net/10948/d1020773
- Description: The coordination behaviour of 4-aminoantipyrine (H2pap) and its Schiff base derivatives with the oxorhenium(V) and tricarbonyl rhenium(I) cores are reported. The reactions of trans-[ReOX3(PPh3)2] (X = Cl, Br) with H2pap were studied, and the complexes cis-[ReX2(pap)(H2pap)(PPh3)](ReO4) were isolated. The ligand pap is coordinated monodentately through the doubly deprotonated amino nitrogen as an imide, and H2pap acts as a neutral bidentate chelate, with coordination through the neutral amino nitrogen and the ketonic oxygen. The reactions of trans-[ReOBr3(PPh3)2] and cis-[ReO2I(PPh3)2] with -(2-aminobenzylideneamino)-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one (H2nap) and 4-(2-hydroxybenzylideneamino)-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one (Hoap) are also reported. The complexes cis-[Re(nap)Br2(PPh3)]Br, [ReO(OEt)(Hnap)(PPh3)]I and [ReO(OMe)(oap)(PPh3)]I were isolated and structurally characterized. The reactions of the Schiff base derivatives 1,2-(diimino-4’-antipyrinyl)ethane (dae) and 2,6-bis(4-amino-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one)pyridine (bap) with [Re(CO)5X] (X = Br or Cl) produced fac-[Re(CO)3(dae)Cl] and fac-[Re(CO)3(bap)Br] respectively. A series of rhenium(I) tricarbonyl complexes containing bidentate derivatives of aniline was synthesized and structurally characterized. With 1,2-diaminobenzene (Hpda) the ‘2+1’ complex salt fac-[Re(CO)3(κ1-Hpda)(κ2-Hpda)]Br was isolated, but with 2-mercaptophenol (Hspo) the bridged dimer [Re2(CO)7(spo)2] was found. The neutral complex [Re(CO)3(ons)(Hno)] was isolated from the reaction of [Re(CO)5Br] with 2-[(2-methylthio)benzylideneimino]phenol (Hons; Hno = 2-aminophenol), with ons coordinated as a bidentate chelate with a free SCH3 group. In the complex [Re(CO)3(Htpn)Br] (Htpn = N-(2-(methylthio)benzylidene)benzene-1,2-diamine) the potentially tridentate ligand Htpn is coordinated via the methylthiol sulfur and imino nitrogen atoms only, with a free amino group. These rhenium(I) complexes, with the exception of [Re2(CO)7(spo)2], revealed broad emissions centred around 535 nm. The reactions of the rhenium(V) complex cis-[ReO2I(PPh3)2] with 2-aminothiophenol (H2atp), benzene-1,2-dithiol (H2tdt) and 2-hydroxybenzenethiol (H2otp) led to the formation of the rhenium(III) compounds [Re(Hatp)(ibsq)2].OPPh3, [Re(sbsq)3].OPPh3 and [Re(obsq)3].OPPh3 (ibsq = 2-iminothiobenzosemiquinonate, sbsq = 1,2-dithiobenzosemiquinonate, obsq = 2-hydroxothiobenzosemiquinonate) respectively. The complexes adopt a trigonal prismatic geometry around the rhenium centre with average twists angles between 3.20-26.10˚. The E1/2 values for the Re(III)/Re(IV) redox couple were found to be 0.022, 0.142 and 0.126 V for [Re(Hatp)(ibsq)2].OPPh3, [Re(sbsq)3].OPPh3 and [Re(obsq)3].OPPh3 respectively. The reactions of the benzoxazole ligands, 3-(benzoxazol-2-yl)pyridin-2-ol (Hbop) and 5-amino-2-(benzoxazol-2-yl)phenol (Habo) with a [ReO]3+ precursor led to the rhenium(III) complex, [ReCl2(bop)(PPh3)2], and the complex salt, [ReO(abo)I(PPh3)2]ReO4, respectively. A variety of benzothiazole and benzimidazole derivatives were reacted with [Re(CO)5Br]. In the case of bis(benzothiazol-2-ylethyl)sulfide (bts), the neutral complex fac-[Re(CO)3(bts)Br] was obtained. The dimeric complexes (μ-dbt)2[Re(CO)3]2 and (μ-mbt)2[Re(CO)3]2 were formed when 1,3-bis(benzothiazol-2-yl)thiourea (Hdbt) and 1-(benzothiazol-2-ylidene)-3-methylthiourea (Hmbt) were used as ligands. The reaction of 2,2’-(oxybis(methylene))bis(benzimidazole) (bmb) with [Re(CO)5Cl] resulted in the rhenium(I) complex salt fac-[Re(CO)3(bmb)]+, with the tri-μ-chlorohexacarbonyl dirhenate [Re2(CO)6Cl3]- as the counter anion. The neutral complex fac-[Re(CO)3(btp)Cl] was isolated from the reaction of the 2,9-bis(benzothiazol-2-yl)-1,10-phenanthroline (btp) ligand and [Re(CO)5Cl]. The reactions of trans-[ReOCl3(PPh3)2] with bis(benzimidazol-2-ylethyl)sulfide (btn) and 1-(benzothiazol-2-ylidene)-3-methylthiourea (Hmbt) led to the formation of the cationic compounds (μ-O)2[Re2O2(btn)2]I2 and [ReCl2(bte)(PPh3)2]Cl (bte = (benzothiazole-2-yl)-N-ethylidenemethanamine) respectively.
- Full Text:
- Date Issued: 2012
Risk preferences and consumption decisions in organic production: the case of Kwazulu-Natal and Eastern Cape provinces of South Africa
- Authors: Kisaka-Lwayo, Maggie
- Date: 2012
- Subjects: Food security -- South Africa , Sustainable development -- South Africa , Organic farming -- South Africa , Natural foods industry -- South Africa , Risk management -- South Africa , Consumers -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD (Agricultural Economics)
- Identifier: vital:11188 , http://hdl.handle.net/10353/492 , Food security -- South Africa , Sustainable development -- South Africa , Organic farming -- South Africa , Natural foods industry -- South Africa , Risk management -- South Africa , Consumers -- South Africa
- Description: Despite phenomenal success of the commercial agricultural sector in South Africa and significant progress in integrating smallholders since democratic reforms, food security concerns remain. Recent global increases in food prices have further exacerbated vulnerabilities and made it imperative to examine alternative food production questions in the country. Organic agriculture is identified as one of the sustainable approaches to farming and offers insights towards a paradigm shift in food and nutritional security. Notwithstanding, consumer awareness, knowledge and consumption of organic foods are significantly lower in developing than developed countries. Risks associated with adoption of organic practices need to be explored to address the supply and demand constraints. Similarly, while consumer awareness of organic foods is the first step in developing demand for organic products, it does not necessarily translate to consumption. Therefore it is important to investigate these issues. The objectives of this study were to: (i) describe the demographic and socio-economic characteristics of organic farmers and consumers; (ii) establish the determinants of farmers‘ decision to participate in organic farming distinguishing between the fully-certified organic, partially-certified organic and non-organic farmers; (iii) elicit farmers risk preferences and empirically analyse farmers sources of risk and risk management strategies; (iv) explore consumer awareness, perceptions and attitudes regarding organic products; and (v) identify the factors that influence consumer‘s preference and consumption of organic products. A total of 400 respondents were surveyed, consisting of 200 smallholder farmers in KwaZulu-Natal and 200 consumers in the Eastern Cape. The KwaZulu-Natal study was conducted earlier and identified the following as major sources of risk, lack of consumer awareness of organic products and lack of information among producers about consumer preferences for organic products. This informed the need to undertake a consumer awareness and preference study, in order to inform producers. The Eastern Cape is a bordering province to KwaZulu-Natal with similar socio economic conditions and a major consumer of produce from KwaZulu-Natal. It was also expected that in the intervening period there could have been awareness about the product. An vii indication of its appeal would not be in the consumption of the product by the people who grow it, but by consumers who reside in bordering regions. Producer and household questionnaires were used to record household activities, socio-economic and institutional data as well as household demographics through personal interviews. The Arrow Pratt Absolute Risk Aversion (APARA) coefficient was used to measure the farmer‘s degree of risk aversion and the experimental gambling approach to establish the risk classification. Consumers were also asked about their awareness and knowledge about organics, attitudes and perceptions towards organics, preference and consumption patterns. The ordered probit results indicate that older farmers, who are less risk averse and reside in the sub-ward Ogagwini, Ezigani, and Hwayi were more likely to be certified organic farmers. Similarly, the propensity to adopt organic farming is positively correlated to household size, livestock ownership, asset base and tenure security. The risk analysis indicates that at higher pay-offs most farmers are intermediate to moderately risk-averse, with little variation according to personal characteristics, and that non-organic farmers tend to be more risk averse than fully-certified and partially-certified farmers. In general, price, production and financial risks were perceived as the most important sources of risk. Using Principal Component Analysis (PCA), seven principal components (PCs) explaining 66.13% of the variation were extracted. Socio economic factors having a significant effect on the various sources of risk are age, gender, education, location, information access and risk taking ability. The most important traditional risk management strategies used by the surveyed farmers are crop diversification, precautionary savings and participating in social networks. There was general awareness of what constituted organic foods with many consumers associating organic foods with health and nutrition, chemical free and produced using indigenous methods of production. However, there was low awareness of organic products among consumers with little or no knowledge of organic certification and standards. According to the logit model the major factors influencing consumer awareness of organic products are: gender, education, employment status, and location of the respondents, person/household member responsible for shopping and the price perception of the decision maker. The discriminant analysis showed that the consumption of organic products is significantly affected by age of the consumer, viii location, person/household member responsible for shopping, consumer awareness of organics, price perception and label trust. The findings from this study provides useful practical insights for policy makers, farm advisers and researchers in the design of effective and efficient policies, programmes and projects which can affect the adoption of organic practices, increase smallholder farmers capacity to manage risk and drive growth in the organic food market.
- Full Text:
- Date Issued: 2012
- Authors: Kisaka-Lwayo, Maggie
- Date: 2012
- Subjects: Food security -- South Africa , Sustainable development -- South Africa , Organic farming -- South Africa , Natural foods industry -- South Africa , Risk management -- South Africa , Consumers -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD (Agricultural Economics)
- Identifier: vital:11188 , http://hdl.handle.net/10353/492 , Food security -- South Africa , Sustainable development -- South Africa , Organic farming -- South Africa , Natural foods industry -- South Africa , Risk management -- South Africa , Consumers -- South Africa
- Description: Despite phenomenal success of the commercial agricultural sector in South Africa and significant progress in integrating smallholders since democratic reforms, food security concerns remain. Recent global increases in food prices have further exacerbated vulnerabilities and made it imperative to examine alternative food production questions in the country. Organic agriculture is identified as one of the sustainable approaches to farming and offers insights towards a paradigm shift in food and nutritional security. Notwithstanding, consumer awareness, knowledge and consumption of organic foods are significantly lower in developing than developed countries. Risks associated with adoption of organic practices need to be explored to address the supply and demand constraints. Similarly, while consumer awareness of organic foods is the first step in developing demand for organic products, it does not necessarily translate to consumption. Therefore it is important to investigate these issues. The objectives of this study were to: (i) describe the demographic and socio-economic characteristics of organic farmers and consumers; (ii) establish the determinants of farmers‘ decision to participate in organic farming distinguishing between the fully-certified organic, partially-certified organic and non-organic farmers; (iii) elicit farmers risk preferences and empirically analyse farmers sources of risk and risk management strategies; (iv) explore consumer awareness, perceptions and attitudes regarding organic products; and (v) identify the factors that influence consumer‘s preference and consumption of organic products. A total of 400 respondents were surveyed, consisting of 200 smallholder farmers in KwaZulu-Natal and 200 consumers in the Eastern Cape. The KwaZulu-Natal study was conducted earlier and identified the following as major sources of risk, lack of consumer awareness of organic products and lack of information among producers about consumer preferences for organic products. This informed the need to undertake a consumer awareness and preference study, in order to inform producers. The Eastern Cape is a bordering province to KwaZulu-Natal with similar socio economic conditions and a major consumer of produce from KwaZulu-Natal. It was also expected that in the intervening period there could have been awareness about the product. An vii indication of its appeal would not be in the consumption of the product by the people who grow it, but by consumers who reside in bordering regions. Producer and household questionnaires were used to record household activities, socio-economic and institutional data as well as household demographics through personal interviews. The Arrow Pratt Absolute Risk Aversion (APARA) coefficient was used to measure the farmer‘s degree of risk aversion and the experimental gambling approach to establish the risk classification. Consumers were also asked about their awareness and knowledge about organics, attitudes and perceptions towards organics, preference and consumption patterns. The ordered probit results indicate that older farmers, who are less risk averse and reside in the sub-ward Ogagwini, Ezigani, and Hwayi were more likely to be certified organic farmers. Similarly, the propensity to adopt organic farming is positively correlated to household size, livestock ownership, asset base and tenure security. The risk analysis indicates that at higher pay-offs most farmers are intermediate to moderately risk-averse, with little variation according to personal characteristics, and that non-organic farmers tend to be more risk averse than fully-certified and partially-certified farmers. In general, price, production and financial risks were perceived as the most important sources of risk. Using Principal Component Analysis (PCA), seven principal components (PCs) explaining 66.13% of the variation were extracted. Socio economic factors having a significant effect on the various sources of risk are age, gender, education, location, information access and risk taking ability. The most important traditional risk management strategies used by the surveyed farmers are crop diversification, precautionary savings and participating in social networks. There was general awareness of what constituted organic foods with many consumers associating organic foods with health and nutrition, chemical free and produced using indigenous methods of production. However, there was low awareness of organic products among consumers with little or no knowledge of organic certification and standards. According to the logit model the major factors influencing consumer awareness of organic products are: gender, education, employment status, and location of the respondents, person/household member responsible for shopping and the price perception of the decision maker. The discriminant analysis showed that the consumption of organic products is significantly affected by age of the consumer, viii location, person/household member responsible for shopping, consumer awareness of organics, price perception and label trust. The findings from this study provides useful practical insights for policy makers, farm advisers and researchers in the design of effective and efficient policies, programmes and projects which can affect the adoption of organic practices, increase smallholder farmers capacity to manage risk and drive growth in the organic food market.
- Full Text:
- Date Issued: 2012
Rural livelihood diversification in semi-arid districts of Zimbabwe : an analysis of Muzarabani, Gokwe and Mwenezi districts
- Authors: Musevenzi, Julius
- Date: 2012
- Subjects: Rural development -- Zimbabwe , Rural poor -- Zimbabwe , Zimbabwe -- Rural conditions
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:9149 , http://hdl.handle.net/10948/d1018922
- Description: This study focuses on rural livelihood diversification and improvement in dry districts of Zimbabwe during the period from 2000 to 2010. It establishes and documents livelihood activities and interventions in three semi-arid districts in Zimbabwe, analyses evidence for rural livelihood diversification and improvement and related challenges, and analyses institutional and policy issues that determine rural livelihood development in the politically charged period from 2000 to 2010. Rural livelihood diversification and improvement is not a recent phenomenon. For years, rural people have diversified their livelihoods for different economic reasons. Despite several studies on rural livelihoods in Zimbabwe, no similar studies have been done to determine the types of livelihood diversification that occur in a politically charged environment and whether they improve people‟s livelihoods. The study was guided by both the sustainable livelihoods framework and the actor oriented approach. Qualitative methodology was used for the overall data collection. Firstly data was collected „from the top‟ through in-depth interviews with officials from government institutions, non-governmental organisations and community leadership structures. Secondly data was collected „from the bottom up‟ through selected participatory methods in study areas. The overall study findings show that despite having increased livelihood interventions in all semi-arid areas, the politically fraught atmosphere constrained livelihood improvement and poverty remained. Although evidence for livelihood diversification is undisputed in the study, the extent to which it contributed to livelihood improvement was limited. The extended period of political constraint reversed some of the livelihood improvement gains recorded by external interventions. As most of the support was targeted at addressing the immediate food needs of the poor in semi-arid districts, this affected the number of long-term interventions targeted at sustainable livelihood development. The study found that the changing policies and institutional arrangements constrained and limited the potential of some of the livelihood strategies adopted during the period under study and as a result most livelihood activities were limited to survival strategies. The study shows that despite a decline in agricultural production during the period under study, it remained the major livelihood activity. Agricultural activities such as cotton and maize production and livestock rearing experienced a decline, but were partially revived through external support from both the government and nongovernmental organisations. Agriculture as a livelihood activity largely benefited from external interventions that rehabilitated irrigation infrastructure and the provision of agricultural inputs during the period. However, despite the dominance of agriculture as a livelihood activity in semi-arid areas non-farm livelihood activities, both locally initiated and externally fostered, played a significant role in supporting rural livelihoods. Poaching and wild fruit harvesting provided food for immediate consumption, whilst gold and diamond panning, wood carving and the commercialisation of non-timber forest products generated cash income for rural livelihoods. Non-farm external livelihood interventions identified resulted in a number of rural livelihood development models important for future rural development. These models were developed around the commercialisation of non-timber forest products for cash income generation, rural human capital development through vocational skills training and rural small livestock asset development. Human capital resulted in the development of rural industry in the form of community based enterprises. Indirectly it also contributed to migrant labour that sent cash and goods back home. The study shows that it is evident that in a politically charged environment livelihood diversification has a range of positive effects. The re-emergence of the barter exchange economy in rural communities contributed to livelihood diversification although sustainability was limited. It is also possible for both barter exchange and the cash market to co-exist in a politically charged environment. The study also shows that traditional leadership and local authorities in study areas became more politicised and militarised and this diverted them from facilitating and supporting rural development and inhibited rural livelihood development efforts by different rural players. The study found that rural livelihoods are not static, and they adapted as best they could in the face of exogenous trends and shocks. Rural areas underwent deep transformations as a result of political dynamics, local livelihood initiatives and external livelihood support. Rural livelihoods changed as rural people devised combined livelihood strategies that went beyond farming. However, in contrast to the widely accepted argument that diversification plays an important role in poverty alleviation, this was clearly not the case in Zimbabwe‟s politically charged environment. This study contributes to the development debate with a case study on the type and extent of livelihood diversification strategies possible in a politically charged environment. Methodologically the study contributes to the possible application of a dual data collection system where data is collected from the top using different methods from those used to collect data from the bottom. This enriched the data at triangulation phase during analysis. The study also contributes to the understanding of the political economy, the type of rural livelihood development possible in politically charged environments, and to how rural people in Zimbabwe react and behave in an endeavour to survive. There was an increased role played by external interventions in livelihood diversification but the extent of their contribution to positive livelihood outcomes was constrained by the politically charged environment that prompted the interventions in the first place. The normal processes of policy development and implementation changed as the role of politicians in planning and implementation became evident and policy aims shifted from rural development to political party self-preservation.
- Full Text:
- Date Issued: 2012
- Authors: Musevenzi, Julius
- Date: 2012
- Subjects: Rural development -- Zimbabwe , Rural poor -- Zimbabwe , Zimbabwe -- Rural conditions
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:9149 , http://hdl.handle.net/10948/d1018922
- Description: This study focuses on rural livelihood diversification and improvement in dry districts of Zimbabwe during the period from 2000 to 2010. It establishes and documents livelihood activities and interventions in three semi-arid districts in Zimbabwe, analyses evidence for rural livelihood diversification and improvement and related challenges, and analyses institutional and policy issues that determine rural livelihood development in the politically charged period from 2000 to 2010. Rural livelihood diversification and improvement is not a recent phenomenon. For years, rural people have diversified their livelihoods for different economic reasons. Despite several studies on rural livelihoods in Zimbabwe, no similar studies have been done to determine the types of livelihood diversification that occur in a politically charged environment and whether they improve people‟s livelihoods. The study was guided by both the sustainable livelihoods framework and the actor oriented approach. Qualitative methodology was used for the overall data collection. Firstly data was collected „from the top‟ through in-depth interviews with officials from government institutions, non-governmental organisations and community leadership structures. Secondly data was collected „from the bottom up‟ through selected participatory methods in study areas. The overall study findings show that despite having increased livelihood interventions in all semi-arid areas, the politically fraught atmosphere constrained livelihood improvement and poverty remained. Although evidence for livelihood diversification is undisputed in the study, the extent to which it contributed to livelihood improvement was limited. The extended period of political constraint reversed some of the livelihood improvement gains recorded by external interventions. As most of the support was targeted at addressing the immediate food needs of the poor in semi-arid districts, this affected the number of long-term interventions targeted at sustainable livelihood development. The study found that the changing policies and institutional arrangements constrained and limited the potential of some of the livelihood strategies adopted during the period under study and as a result most livelihood activities were limited to survival strategies. The study shows that despite a decline in agricultural production during the period under study, it remained the major livelihood activity. Agricultural activities such as cotton and maize production and livestock rearing experienced a decline, but were partially revived through external support from both the government and nongovernmental organisations. Agriculture as a livelihood activity largely benefited from external interventions that rehabilitated irrigation infrastructure and the provision of agricultural inputs during the period. However, despite the dominance of agriculture as a livelihood activity in semi-arid areas non-farm livelihood activities, both locally initiated and externally fostered, played a significant role in supporting rural livelihoods. Poaching and wild fruit harvesting provided food for immediate consumption, whilst gold and diamond panning, wood carving and the commercialisation of non-timber forest products generated cash income for rural livelihoods. Non-farm external livelihood interventions identified resulted in a number of rural livelihood development models important for future rural development. These models were developed around the commercialisation of non-timber forest products for cash income generation, rural human capital development through vocational skills training and rural small livestock asset development. Human capital resulted in the development of rural industry in the form of community based enterprises. Indirectly it also contributed to migrant labour that sent cash and goods back home. The study shows that it is evident that in a politically charged environment livelihood diversification has a range of positive effects. The re-emergence of the barter exchange economy in rural communities contributed to livelihood diversification although sustainability was limited. It is also possible for both barter exchange and the cash market to co-exist in a politically charged environment. The study also shows that traditional leadership and local authorities in study areas became more politicised and militarised and this diverted them from facilitating and supporting rural development and inhibited rural livelihood development efforts by different rural players. The study found that rural livelihoods are not static, and they adapted as best they could in the face of exogenous trends and shocks. Rural areas underwent deep transformations as a result of political dynamics, local livelihood initiatives and external livelihood support. Rural livelihoods changed as rural people devised combined livelihood strategies that went beyond farming. However, in contrast to the widely accepted argument that diversification plays an important role in poverty alleviation, this was clearly not the case in Zimbabwe‟s politically charged environment. This study contributes to the development debate with a case study on the type and extent of livelihood diversification strategies possible in a politically charged environment. Methodologically the study contributes to the possible application of a dual data collection system where data is collected from the top using different methods from those used to collect data from the bottom. This enriched the data at triangulation phase during analysis. The study also contributes to the understanding of the political economy, the type of rural livelihood development possible in politically charged environments, and to how rural people in Zimbabwe react and behave in an endeavour to survive. There was an increased role played by external interventions in livelihood diversification but the extent of their contribution to positive livelihood outcomes was constrained by the politically charged environment that prompted the interventions in the first place. The normal processes of policy development and implementation changed as the role of politicians in planning and implementation became evident and policy aims shifted from rural development to political party self-preservation.
- Full Text:
- Date Issued: 2012
Ruthenium and palladium assisted silver transport in silicon carbide
- Authors: O'Connell, Jacques Herman
- Date: 2012
- Subjects: Gas cooled reactors , Ruthenium , Palladium , Silicon carbide
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10404 , http://hdl.handle.net/10948/d1010960 , Gas cooled reactors , Ruthenium , Palladium , Silicon carbide
- Full Text:
- Date Issued: 2012
- Authors: O'Connell, Jacques Herman
- Date: 2012
- Subjects: Gas cooled reactors , Ruthenium , Palladium , Silicon carbide
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10404 , http://hdl.handle.net/10948/d1010960 , Gas cooled reactors , Ruthenium , Palladium , Silicon carbide
- Full Text:
- Date Issued: 2012
Scientific literacy and education for sustainable development: developing scientific literacy in its fundamental and derived senses
- Authors: Leornard, Samantha Lee
- Date: 2012
- Subjects: Science -- Study and teaching , Science -- Experiments
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:9450 , http://hdl.handle.net/10948/d1010069 , Science -- Study and teaching , Science -- Experiments
- Description: The importance of developing learners’ scientific literacy in both the fundamental and derived senses has been highlighted by Norris & Phillips (2003). Development of the derived sense of science, which is dependent on the development of a sound fundamental sense of science, aims at promoting scientifically literate societies who are able to make informed decisions concerning the natural environment and the promotion of sustainable livelihoods. In turn, response to increasing recognition of environmental degradation, the United Nations’ Decade of Education for Sustainable Development advocated that the principles, values and practices of sustainable development should be integrated into all aspects of education and learning. However, despite these aspirations, the difficulties of insufficient teacher knowledge and a lack of in-service training, both abroad and within South Africa, remain a challenge. In response to this challenge this study investigated the potential of an Integrated Scientific Literacy Strategy (which aimed at increasing in-service teacher knowledge and skills) to contribute to ESD by developing more scientifically literate teachers and learners in primary education. The study was conducted in 2010 in the Port Elizabeth Metropolitan area in the Eastern Cape, South Africa. The study sample comprised seven schools, with a total of nine teachers and 243 learners participating. As the research is situated within the pragmatic paradigm, a mixed methods approach was followed using Creswell and Plano Clark’s (2007) embedded design’s correlational model whereby quantitative data are rooted within a qualitative design to help verify and explain the outcomes. Qualitative measures were generated through teacher interviews and an analysis of their written portfolios. These data were triangulated against quantitative test data gained from an ANCOVA statistical analysis of the learners’ pre- and post-tests, and both the qualitative and quantitative data gleaned from classroom observations and an analysis of the learners’ science notebooks. The data suggest that, when properly implemented, the Integrated Scientific Literacy Strategy can be used to help teachers develop their learners’ scientific literacy by exposing them to open-ended inquiry investigations. Statistically significant differences (p ≤ 0.01; d=0.88) were noted when comparing improvements in learners’ abilities and understandings of scientific investigations (graphs, variables, inquiry and investigable questions) between those learners whose teachers successfully implemented the strategy in their classrooms, and those learners whose teachers were considered to be ‘non-implementers’ of the strategy. Data from this study also suggest that the successful use of the ISLS enables teachers to integrate issues relating to sustainable development into their natural science lessons. In addition, the learner-orientated approach of the strategy also enabled the learners to engage in autonomous learning environments, aspects of which have been identified as being important for meaningfully learning about and internalising important issues related to ESD.
- Full Text:
- Date Issued: 2012
- Authors: Leornard, Samantha Lee
- Date: 2012
- Subjects: Science -- Study and teaching , Science -- Experiments
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:9450 , http://hdl.handle.net/10948/d1010069 , Science -- Study and teaching , Science -- Experiments
- Description: The importance of developing learners’ scientific literacy in both the fundamental and derived senses has been highlighted by Norris & Phillips (2003). Development of the derived sense of science, which is dependent on the development of a sound fundamental sense of science, aims at promoting scientifically literate societies who are able to make informed decisions concerning the natural environment and the promotion of sustainable livelihoods. In turn, response to increasing recognition of environmental degradation, the United Nations’ Decade of Education for Sustainable Development advocated that the principles, values and practices of sustainable development should be integrated into all aspects of education and learning. However, despite these aspirations, the difficulties of insufficient teacher knowledge and a lack of in-service training, both abroad and within South Africa, remain a challenge. In response to this challenge this study investigated the potential of an Integrated Scientific Literacy Strategy (which aimed at increasing in-service teacher knowledge and skills) to contribute to ESD by developing more scientifically literate teachers and learners in primary education. The study was conducted in 2010 in the Port Elizabeth Metropolitan area in the Eastern Cape, South Africa. The study sample comprised seven schools, with a total of nine teachers and 243 learners participating. As the research is situated within the pragmatic paradigm, a mixed methods approach was followed using Creswell and Plano Clark’s (2007) embedded design’s correlational model whereby quantitative data are rooted within a qualitative design to help verify and explain the outcomes. Qualitative measures were generated through teacher interviews and an analysis of their written portfolios. These data were triangulated against quantitative test data gained from an ANCOVA statistical analysis of the learners’ pre- and post-tests, and both the qualitative and quantitative data gleaned from classroom observations and an analysis of the learners’ science notebooks. The data suggest that, when properly implemented, the Integrated Scientific Literacy Strategy can be used to help teachers develop their learners’ scientific literacy by exposing them to open-ended inquiry investigations. Statistically significant differences (p ≤ 0.01; d=0.88) were noted when comparing improvements in learners’ abilities and understandings of scientific investigations (graphs, variables, inquiry and investigable questions) between those learners whose teachers successfully implemented the strategy in their classrooms, and those learners whose teachers were considered to be ‘non-implementers’ of the strategy. Data from this study also suggest that the successful use of the ISLS enables teachers to integrate issues relating to sustainable development into their natural science lessons. In addition, the learner-orientated approach of the strategy also enabled the learners to engage in autonomous learning environments, aspects of which have been identified as being important for meaningfully learning about and internalising important issues related to ESD.
- Full Text:
- Date Issued: 2012
Self-perceived professional identity of pharmacy educators
- Authors: Burton, Susan
- Date: 2012
- Subjects: Academic identity , Communities of practice , Identity (Philosophical concept) , Pharmacy -- Study and teaching , Pharmacy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10139 , http://hdl.handle.net/10948/d1008352 , Academic identity , Communities of practice , Identity (Philosophical concept) , Pharmacy -- Study and teaching , Pharmacy
- Description: The philosophy of pharmaceutical care, which defines a patient-centred approach to practice, has been embraced and upheld by national and international pharmaceutical organisations for two decades. However, pharmacists have been slow to change their practice and implement a pharmaceutical care approach. It has been suggested that amongst other factors, short-comings in pharmaceutical education have contributed to this reluctance of the profession to transform practice. Efforts to address these short-comings in pharmaceutical education have focused on the curriculum and pedagogic practices, and not on the pharmacy educators themselves. Palmer (1998) asserts that “good teaching cannot be reduced to technique; good teaching comes from the identity and integrity of the teacher”. In essence, "we teach who we are" and good teachers have one common trait: “a strong sense of personal identity that infuses their work”. This study identified, described and analysed the self-perceived professional identities of pharmacy educators within the South African context. This included ascertaining factors and contexts which contributed to participants’ self-perception of their professional identity. In an effort to understand the influence the educators have on practice and on changing practice and vice-versa, the attitudes, beliefs and behaviours of participants regarding the philosophy and practice of pharmaceutical care, and pharmaceutical education were also explored. Situated within a constructivist-interpretive, qualitative paradigm and making use of methodological triangulation, this study was conducted in three phases, each employing a different qualitative method to collect data. The first phase made use of narrative analysis to gain an in-depth understanding of pharmacy educators’ perceived professional identities and to explore how their experiences, across various contexts, have formed their professional identities. In-depth individual narrative interviews were used to provide a forum in which the participants could reflect upon and tell their professional life-story. This phase of the study also made use of the exploration of metaphors to further investigate the participants’ professional identity and, more particularly, their images of themselves as “teacher” and role model for students. A maximum variation, purposeful sampling approach was used to recruit eight pharmacy academics - one from each school or faculty of pharmacy in South Africa, as participants in this phase of the study. The second and third phases explored more widely, the insights gained from the first phase and the formation of professional identity, attitudes, beliefs and practices of pharmacy educators in South Africa. Two focus groups were employed during the second phase and the study sample was broadened to include a further ten pharmacy educators. In the third phase, a purpose-designed, qualitative questionnaire was used to extend the study sample to all pharmacy educators in South Africa. A convenience sampling approach was used in both the second and third phases of the study. Thematic analysis and interpretation of the narrative interview and focus group transcripts and the questionnaire responses were conducted using qualitative data analysis software – Atlas.ti®. A multiplicity of self-perceived professional identities was described. However, all of these were multi-faceted and could be situated on a continuum between pharmacist identity on one end and academic identity on the other. In addition, six key determinants were recognised as underpinning the participants’ self-perception of their professional identity. These included three structural determinants: expected role; knowledge base; and practice, and three determinants relating to the emotional dimensions and agency of professional identity: professional status; passions; and satisfiers. The professional identity of the participants had been formed through membership of multiple pharmacy-related communities of practice and continued to be sustained through a nexus of multi-membership. There was extensive support by the participants for the concept of pharmaceutical care; however, it did not impact extensively on their role as pharmacy educators. Furthermore, many expressed concern around the use of the term ‘pharmaceutical care’: its definition; its lack of penetration into, and implementation within the practice environment; and even its relevance to the South African healthcare context. Many of the participants perceived the professional development of future pharmacists to be integral to their role as educators, and was often their source of greatest professional satisfaction. However, concern was also expressed at the dissonance that students were perceived to experience, sometimes, because of the incongruities that they are taught and what they experience in practice. This study has afforded pharmacy educators in South Africa an opportunity to understand better “who” they are as professionals, and to reflect on their role as educators and as role models for future pharmacist. Moreover, the findings contribute to a collective understanding of the professional identity of pharmacy educators and socialisation of pharmacy students into the profession. The insights and recommendations emerging from the study have the potential to make academic pharmacy a more attractive career choice which may have positive implications for the future attraction and retention of pharmacists to academic posts within universities.
- Full Text:
- Date Issued: 2012
- Authors: Burton, Susan
- Date: 2012
- Subjects: Academic identity , Communities of practice , Identity (Philosophical concept) , Pharmacy -- Study and teaching , Pharmacy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10139 , http://hdl.handle.net/10948/d1008352 , Academic identity , Communities of practice , Identity (Philosophical concept) , Pharmacy -- Study and teaching , Pharmacy
- Description: The philosophy of pharmaceutical care, which defines a patient-centred approach to practice, has been embraced and upheld by national and international pharmaceutical organisations for two decades. However, pharmacists have been slow to change their practice and implement a pharmaceutical care approach. It has been suggested that amongst other factors, short-comings in pharmaceutical education have contributed to this reluctance of the profession to transform practice. Efforts to address these short-comings in pharmaceutical education have focused on the curriculum and pedagogic practices, and not on the pharmacy educators themselves. Palmer (1998) asserts that “good teaching cannot be reduced to technique; good teaching comes from the identity and integrity of the teacher”. In essence, "we teach who we are" and good teachers have one common trait: “a strong sense of personal identity that infuses their work”. This study identified, described and analysed the self-perceived professional identities of pharmacy educators within the South African context. This included ascertaining factors and contexts which contributed to participants’ self-perception of their professional identity. In an effort to understand the influence the educators have on practice and on changing practice and vice-versa, the attitudes, beliefs and behaviours of participants regarding the philosophy and practice of pharmaceutical care, and pharmaceutical education were also explored. Situated within a constructivist-interpretive, qualitative paradigm and making use of methodological triangulation, this study was conducted in three phases, each employing a different qualitative method to collect data. The first phase made use of narrative analysis to gain an in-depth understanding of pharmacy educators’ perceived professional identities and to explore how their experiences, across various contexts, have formed their professional identities. In-depth individual narrative interviews were used to provide a forum in which the participants could reflect upon and tell their professional life-story. This phase of the study also made use of the exploration of metaphors to further investigate the participants’ professional identity and, more particularly, their images of themselves as “teacher” and role model for students. A maximum variation, purposeful sampling approach was used to recruit eight pharmacy academics - one from each school or faculty of pharmacy in South Africa, as participants in this phase of the study. The second and third phases explored more widely, the insights gained from the first phase and the formation of professional identity, attitudes, beliefs and practices of pharmacy educators in South Africa. Two focus groups were employed during the second phase and the study sample was broadened to include a further ten pharmacy educators. In the third phase, a purpose-designed, qualitative questionnaire was used to extend the study sample to all pharmacy educators in South Africa. A convenience sampling approach was used in both the second and third phases of the study. Thematic analysis and interpretation of the narrative interview and focus group transcripts and the questionnaire responses were conducted using qualitative data analysis software – Atlas.ti®. A multiplicity of self-perceived professional identities was described. However, all of these were multi-faceted and could be situated on a continuum between pharmacist identity on one end and academic identity on the other. In addition, six key determinants were recognised as underpinning the participants’ self-perception of their professional identity. These included three structural determinants: expected role; knowledge base; and practice, and three determinants relating to the emotional dimensions and agency of professional identity: professional status; passions; and satisfiers. The professional identity of the participants had been formed through membership of multiple pharmacy-related communities of practice and continued to be sustained through a nexus of multi-membership. There was extensive support by the participants for the concept of pharmaceutical care; however, it did not impact extensively on their role as pharmacy educators. Furthermore, many expressed concern around the use of the term ‘pharmaceutical care’: its definition; its lack of penetration into, and implementation within the practice environment; and even its relevance to the South African healthcare context. Many of the participants perceived the professional development of future pharmacists to be integral to their role as educators, and was often their source of greatest professional satisfaction. However, concern was also expressed at the dissonance that students were perceived to experience, sometimes, because of the incongruities that they are taught and what they experience in practice. This study has afforded pharmacy educators in South Africa an opportunity to understand better “who” they are as professionals, and to reflect on their role as educators and as role models for future pharmacist. Moreover, the findings contribute to a collective understanding of the professional identity of pharmacy educators and socialisation of pharmacy students into the profession. The insights and recommendations emerging from the study have the potential to make academic pharmacy a more attractive career choice which may have positive implications for the future attraction and retention of pharmacists to academic posts within universities.
- Full Text:
- Date Issued: 2012
Soil erosion and sediment source dynamics of a catchment in the Eastern Cape province, South Africa: an approach using remote sensing and sediment source fingerprinting techniques
- Authors: Manjoro, Munyaradzi
- Date: 2012
- Subjects: Soil erosion -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10663 , http://hdl.handle.net/10948/d1015038
- Description: This study originated from an evaluation of the performance of a commercially available high concentration point focus concentrator PV system. The effect of module design flaws was studied by using current-voltage (I-V) curves obtained from each module in the array. The position of reverse bias steps revealed the severity of mismatch in a string of series-connected cells. By understanding the effects of the various types of mismatch, power losses and damage to the solar cells resulting from hot spot formation can be minimized and several recommendations for improving the basic performance of similar systems were made. Concern over the extent and type of defect failure of the concentrator photovoltaic (CPV) cells prompted an investigation into the use of a light beam induced current (LBIC) technique to investigate the spatial distribution of defects. An overview of current and developing LBIC techniques revealed that the original standard LBIC techniques have found widespread application, and that far-reaching and important developments of the technique have taken place over the years. These developments are driven by natural progression as well as the availability of newly developed advanced measurement equipment. Several techniques such as Lock-in Thermography and the use of infrared cameras have developed as complementary techniques to advanced LBIC techniques. As an accurate contactless evaluation tool that is able to image spatially distributed defects in cell material, the basis of this method seemed promising for the evaluation of concentrator cells.
- Full Text:
- Date Issued: 2012
- Authors: Manjoro, Munyaradzi
- Date: 2012
- Subjects: Soil erosion -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10663 , http://hdl.handle.net/10948/d1015038
- Description: This study originated from an evaluation of the performance of a commercially available high concentration point focus concentrator PV system. The effect of module design flaws was studied by using current-voltage (I-V) curves obtained from each module in the array. The position of reverse bias steps revealed the severity of mismatch in a string of series-connected cells. By understanding the effects of the various types of mismatch, power losses and damage to the solar cells resulting from hot spot formation can be minimized and several recommendations for improving the basic performance of similar systems were made. Concern over the extent and type of defect failure of the concentrator photovoltaic (CPV) cells prompted an investigation into the use of a light beam induced current (LBIC) technique to investigate the spatial distribution of defects. An overview of current and developing LBIC techniques revealed that the original standard LBIC techniques have found widespread application, and that far-reaching and important developments of the technique have taken place over the years. These developments are driven by natural progression as well as the availability of newly developed advanced measurement equipment. Several techniques such as Lock-in Thermography and the use of infrared cameras have developed as complementary techniques to advanced LBIC techniques. As an accurate contactless evaluation tool that is able to image spatially distributed defects in cell material, the basis of this method seemed promising for the evaluation of concentrator cells.
- Full Text:
- Date Issued: 2012
Soil fertility enhancement through appropriate fertilizer management on winter cover crops in a conservation agriculture system
- Authors: Dube, Ernest
- Date: 2012
- Subjects: Fertilizers , Soil fertility , Crops -- Nutrition , Soil productivity , Range management , Grazing -- Management , Forage plants , Humus
- Language: English
- Type: Thesis , Doctoral , PhD (Crop Science)
- Identifier: vital:11239 , http://hdl.handle.net/10353/d1001044 , Fertilizers , Soil fertility , Crops -- Nutrition , Soil productivity , Range management , Grazing -- Management , Forage plants , Humus
- Description: A study was carried out to determine the effects of oat (Avena sativa) and grazing vetch (Vicia darsycapa) winter cover crops and fertilizer application on SOM, phosphorus (P) pools, nutrient availability, nutrient uptake, maize yield and seedbanks of problematic weeds in an irrigated maize-based conservation agriculture (CA) system. A separate experiment was carried out to investigate the effects of the winter cover crops on nitrogen (N) management, N use efficiency and profitability. After four years of continuous rotation, the winter cover crops significantly (p<0.05) increased particulate SOM and hot water soluble carbon in the 0 – 5 and 5 – 20 cm soil depths. When fertilized, oat was better able to support SOM sequestration in water stable aggregates at 0 – 20 cm whilst grazing vetch was more effective at 20 – 50 cm. Where no fertilizer was invested, there were significant (p<0.01) reductions in biomass input and SOM on oat-maize and weedy fallow-maize rotations whereas vetch-maize rotations did not respond, both at 0 – 5 and 5 – 20 cm. Targeting fertilizer to the winter cover crop required less fertilizer, and yet gave a similar SOM response as targeting the fertilizer to the maize crop. In addition to increasing SOM in the surface soil (0 – 5 cm), the winter cover crops significantly (p<0.05) increased labile pools of P, including microbial P. The cover crops also significantly (p<0.05) increased maize P concentration during early growth, extractable soil P, Cu, Mn, and Zn but had no effect on Ca and K. Grazing vetch increased soil mineral N but reduced extractable soil Mg. Without fertilizer, there were sharp declines in maize grain yield on oat and weedy fallow rotations over the four year period, but less so, on the grazing vetch. Grazing vetch increased maize growth, grain yield response to N fertilizer, nitrogen use efficiency (NUE) and profitability for fertilizer rates below 180 kg N ha-1. Oat effects however on maize yield and NUE were generally similar to weedy fallow. Based on the partial factor productivity of N, the highest efficiencies in utilization of fertilizer N for maize yield improvement under grazing vetch and oat are obtained at 60 kg N ha-1 and would decline thereafter with any increases in fertilizer application rate. Grazing vetch gave N fertilizer replacement values of up to 120 kg N ha-1 as well as the highest marginal rates of return to increasing N fertilizer rate. The cover crops were more effective than the weedy fallow in reducing seedbank density of Digitaria sanguinalis, Eleusine indica, Amaranthus retroflexus and Datura stramonium at 0 – 5 cm soil depth, causing weed seed reductions of 30 - 70%. The winter cover crops however, selectively allowed emergence of the narrow leafed weeds; Cyperus esculentus and Digitaria sanguinalis in the maize crop. The findings of this study suggested that grazing vetch is suited for SOM improvement in low fertilizer input systems and that fertilizer is better invested on winter cover crops as opposed to maize crops. Oat, on the other hand, when fertilized, would be ideal for C sequestration in water stable aggregates of the surface soil. Grazing vetch is ideal for resource poor farmers who cannot afford mineral fertilizers as it gives grain yield improvement and high fertilizer replacement value. Grazing vetch can produce enough maize yield response to pay its way in the maize-based systems and oat may not require additional N than that applied to the weedy fallow. Phosphorus and Zn are some of the major limiting essential plant nutrients on South African soils and the winter cover crops could make a contribution. The cover crops also hasten depletion of some problematic weeds from seedbanks, leading to reduced weed pressure during maize growth.
- Full Text:
- Date Issued: 2012
- Authors: Dube, Ernest
- Date: 2012
- Subjects: Fertilizers , Soil fertility , Crops -- Nutrition , Soil productivity , Range management , Grazing -- Management , Forage plants , Humus
- Language: English
- Type: Thesis , Doctoral , PhD (Crop Science)
- Identifier: vital:11239 , http://hdl.handle.net/10353/d1001044 , Fertilizers , Soil fertility , Crops -- Nutrition , Soil productivity , Range management , Grazing -- Management , Forage plants , Humus
- Description: A study was carried out to determine the effects of oat (Avena sativa) and grazing vetch (Vicia darsycapa) winter cover crops and fertilizer application on SOM, phosphorus (P) pools, nutrient availability, nutrient uptake, maize yield and seedbanks of problematic weeds in an irrigated maize-based conservation agriculture (CA) system. A separate experiment was carried out to investigate the effects of the winter cover crops on nitrogen (N) management, N use efficiency and profitability. After four years of continuous rotation, the winter cover crops significantly (p<0.05) increased particulate SOM and hot water soluble carbon in the 0 – 5 and 5 – 20 cm soil depths. When fertilized, oat was better able to support SOM sequestration in water stable aggregates at 0 – 20 cm whilst grazing vetch was more effective at 20 – 50 cm. Where no fertilizer was invested, there were significant (p<0.01) reductions in biomass input and SOM on oat-maize and weedy fallow-maize rotations whereas vetch-maize rotations did not respond, both at 0 – 5 and 5 – 20 cm. Targeting fertilizer to the winter cover crop required less fertilizer, and yet gave a similar SOM response as targeting the fertilizer to the maize crop. In addition to increasing SOM in the surface soil (0 – 5 cm), the winter cover crops significantly (p<0.05) increased labile pools of P, including microbial P. The cover crops also significantly (p<0.05) increased maize P concentration during early growth, extractable soil P, Cu, Mn, and Zn but had no effect on Ca and K. Grazing vetch increased soil mineral N but reduced extractable soil Mg. Without fertilizer, there were sharp declines in maize grain yield on oat and weedy fallow rotations over the four year period, but less so, on the grazing vetch. Grazing vetch increased maize growth, grain yield response to N fertilizer, nitrogen use efficiency (NUE) and profitability for fertilizer rates below 180 kg N ha-1. Oat effects however on maize yield and NUE were generally similar to weedy fallow. Based on the partial factor productivity of N, the highest efficiencies in utilization of fertilizer N for maize yield improvement under grazing vetch and oat are obtained at 60 kg N ha-1 and would decline thereafter with any increases in fertilizer application rate. Grazing vetch gave N fertilizer replacement values of up to 120 kg N ha-1 as well as the highest marginal rates of return to increasing N fertilizer rate. The cover crops were more effective than the weedy fallow in reducing seedbank density of Digitaria sanguinalis, Eleusine indica, Amaranthus retroflexus and Datura stramonium at 0 – 5 cm soil depth, causing weed seed reductions of 30 - 70%. The winter cover crops however, selectively allowed emergence of the narrow leafed weeds; Cyperus esculentus and Digitaria sanguinalis in the maize crop. The findings of this study suggested that grazing vetch is suited for SOM improvement in low fertilizer input systems and that fertilizer is better invested on winter cover crops as opposed to maize crops. Oat, on the other hand, when fertilized, would be ideal for C sequestration in water stable aggregates of the surface soil. Grazing vetch is ideal for resource poor farmers who cannot afford mineral fertilizers as it gives grain yield improvement and high fertilizer replacement value. Grazing vetch can produce enough maize yield response to pay its way in the maize-based systems and oat may not require additional N than that applied to the weedy fallow. Phosphorus and Zn are some of the major limiting essential plant nutrients on South African soils and the winter cover crops could make a contribution. The cover crops also hasten depletion of some problematic weeds from seedbanks, leading to reduced weed pressure during maize growth.
- Full Text:
- Date Issued: 2012