Characterisation of performance limiting defects in photovoltaic devices using electroluminescence and related techniques
- Authors: Crozier, Jacqueline Louise
- Date: 2015
- Subjects: Photovoltaic cells Solar cells Photovoltaic power systems
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/11004 , vital:26866
- Description: Solar cells allow the energy from the sun to be converted into electrical energy; this makes solar energy an environmentally friendly, sustainable alternative to fossil fuel energy sources. Solar cells are connected together in a photovoltaic (PV) module to provide the higher current, voltage and power outputs necessary for electrical applications. However, the performance of PV modules can limited by the degradation and defects. PV modules can be characterised using various opto-electronic techniques, each providing information about the performance of the module. The current-voltage (I-V) characteristic curve of a module being the most commonly used characterisation technique. The I-V curve is typically measured in outdoor, fully illuminated, conditions. This allows performance parameters such as short circuit current (ISC), open circuit voltage (VOC) and maximum power (PMAX) to be determined. However, it can be difficult to determine the root cause of the performance drop from the I-V curve alone. Electroluminescence (EL) is a module characterisation technique that allows defects and failures in PV modules to be successfully identified. This study investigates the characterisation of solar cells and photovoltaic modules using EL. EL occurs when a solar cell or module is forward biased and the injected electron-hole pairs recombine radiatively. The intensity of the emitted EL is related the applied voltage and the material properties. EL imaging is a useful characterisation technique in identifying module defects and failures. Defects such as micro-cracks, broken contact fingers and fractures are detected in EL images as well as material features such as grain boundaries. The common defects in crystalline silicon are catalogued and the possible causes are discussed. An experimental setup was developed in order to systematically take a high resolution EL image of every cell in the module and record the applied voltage and current. This produces a very detailed, clear, image of each cell with a pixel size in the micrometre range. This process is time consuming to acquire an EL image of an entire module so alternatively a different setup can be used and an EL image of a whole module can be captured in a single frame with an increased pixel size in the millimetre range. For EL imaging a silicon charge-coupled device (CCD) camera was used because it has very good spatial resolution however this sensor is only sensitive to wavelength in the range of 300-1200 nm. There is an overlap in wavelengths from about 900 to 1100 nm allowing the EL emitted from silicon solar cells to be detected. In conjunction with the high-resolution EL system an image processing program was developed to crop, adjust and align the images so only the relevant cell was included. This program also automatically detects certain defects that have a regular shape. Micro-cracks, broken fingers and striation rings are automatically identified. The program has an adjustable sensitivity to identify small or large defects. Defective cells are distinguished from undamaged cells by comparing the binary images to the ideal, undamaged cell. The current-voltage curves and the performance parameters of modules were compared with the EL images in order to discuss and identify power limiting defects. Features that remove significant portions of the cell from electrical contact such as micro-cracks are shown to have a larger effect of the performance of the module. Other features such as broken contact fingers, contact forming failures and striation rings do not significantly lower the performance of the module. Thus an understanding of how different features affect the module performance is important in order to correctly interpret the EL results. The intensity of the luminescence emitted is related to the applied voltage and the quantum efficiency of the cell material. The spectrum of the emitted luminescence was modelled and related to the recombination properties of the cell such as surface recombination velocity and minority carrier diffusion length/lifetime. In this study the emitted spectrum was modelled and the effects of recombination properties of the cell on the emitted spectrum were examined. The spectrum of the detected EL was modelled, dependent on the sensitivity of the camera, the transmission of the filters and the emitted photon flux. The integration of short-pass filters into the experimental setup in order to isolate short-wavelength luminescence was discussed. There is a proportional relationship between the intensity of the emitted EL and the local junction voltage. Resistive losses like series and shunt resistances lower the applied voltage and thus affect the EL image. The voltage dependence was assessed by comparing EL images taken at different applied biases. Analysis of the variation in EL intensity with voltage was successful in determining the origin of certain features in an EL image. Certain defects, those that are related to series resistance or shunting are highly voltage dependent. When a feature has little or no dependence on voltage then the defect could be in the laminate layers and not in the cell material. The results of this study allow for in-depth analysis of the defects found in PV modules using the high resolution EL imaging system and the image processing routine. The development of an image processing routine allows the interpretation of the EL image to be done automatically, resulting in a faster and more efficient process. By understanding the defects visible in the EL image, the test is more meaningful and allows the results to be used to predict module performance and potential failures.
- Full Text:
- Date Issued: 2015
Perceptions on the use of social media in the banking industry
- Authors: Cupp, Nicole Leshaan
- Date: 2015
- Subjects: Banks and banking -- Customer services , Banks and banking -- Social aspects , Internet marketing -- South Africa
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: http://hdl.handle.net/10948/5489 , vital:20870
- Description: As banks operate in a competitive environment, it is important for managers and marketers to identify how customer satisfaction and customer retention levels can be can be improved through social media aspects. Although models of customer satisfaction and customer retention have been well researched for client products/services, the literature available on social media as a marketing tool is limited in quantity compared to other more established areas of marketing. This research study reviews existing literature on the banking industry in terms of its characteristics and challenges. Literature on customer satisfaction and customer retention as relevant to the banking industry is reviewed, as well as how social media aspects can improve customer satisfaction and customer retention. Thus the primary objective of this study is to identify the social media aspects (benefits, clients’ trust and content) that influence the intervening variable (customer satisfaction) and dependent variable (customer retention) in the banking industry. An empirical investigation was undertaken to establish whether the independent variables; namely benefits, clients’ trust and content as related to social media can possibly influence customer satisfaction and ultimately customer retention in the banking industry. A positivistic research paradigm was followed for this study. Quantitative data was gathered by distributing questionnaires to a sample of bank clients and managers. The sample size consisted of 150 bank clients and 30 bank managers in the Nelson Mandela Metropolitan area in South Africa. The questionnaires were statistically analysed using the computer programmes Microsoft Excel and Statistica Version 12.0. The validity of the study was measured by utilising Exploratory Factor analysis. Cronbach’s Alpha correlation coefficients were calculated to measure the reliability and internal consistency of the measurement instrument of this study. Data was analysed in four phases. Descriptive statistics concerning the respondents and variables were calculated for this study. The validity of the measuring instrument was tested by performing EFA to consider construct validity. Thereafter, the internal reliability of the data was assessed using Cronbach’s Alpha correlation coefficients. Pearson’s product-moment correlation coefficients and multiple regression analyses were calculated. Through multiple regression calculations, the relationships predicted by the four hypotheses were analysed. Finally, t-tests and analysis of variance (ANOVA) tests were conducted. The empirical investigation revealed that significant positive relationships exist between the independent variables benefits, trustworthy content and the intervening variable customer satisfaction, as well as between these two independent variables and the dependent variable customer retention. From the empirical results it was concluded that if banks offer benefits and trustworthy content to their clients through social media channels, clients are likely to be satisfied with and retained by their bank. This study established and confirmed the significant positive relationship that exists between customer satisfaction and customer retention in the banking industry. All bank managers and marketers will benefit from the empirical results as well as the recommendations of this study on how to improve customer satisfaction and customer retention through social media channels which will ultimately improve the performance of banks.
- Full Text:
- Date Issued: 2015
Text data analysis for a smart city project in a developing nation
- Authors: Currin, Aubrey Jason
- Date: 2015
- Subjects: Natural language processing (Computer science) Human computation Human-computer interaction
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: http://hdl.handle.net/10353/2227 , vital:27709
- Description: Increased urbanisation against the backdrop of limited resources is complicating city planning and management of functions including public safety. The smart city concept can help, but most previous smart city systems have focused on utilising automated sensors and analysing quantitative data. In developing nations, using the ubiquitous mobile phone as an enabler for crowdsourcing of qualitative public safety reports, from the public, is a more viable option due to limited resources and infrastructure limitations. However, there is no specific best method for the analysis of qualitative text reports for a smart city in a developing nation. The aim of this study, therefore, is the development of a model for enabling the analysis of unstructured natural language text for use in a public safety smart city project. Following the guidelines of the design science paradigm, the resulting model was developed through the inductive review of related literature, assessed and refined by observations of a crowdsourcing prototype and conversational analysis with industry experts and academics. The content analysis technique was applied to the public safety reports obtained from the prototype via computer assisted qualitative data analysis software. This has resulted in the development of a hierarchical ontology which forms an additional output of this research project. Thus, this study has shown how municipalities or local government can use CAQDAS and content analysis techniques to prepare large quantities of text data for use in a smart city.
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- Date Issued: 2015
Challenges faced by Teachers in applying reading strategies when teaching English reading in the foundation phase in the Mthatha District
- Authors: Cweba, Vuyokazi
- Date: 2015
- Subjects: Reading(Foundation phase) English language -- Study and teaching -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , D Ed
- Identifier: http://hdl.handle.net/11260/856 , vital:29938
- Description: This study sought to investigate challenges faced by teachers in applying reading strategies when teaching reading in the Foundation Phase in the Mthatha District in South Africa. The study was conducted at Four Junior Secondary Schools. It was prompted by a deep concern about challenges faced by teachers in applying reading strategies required in the Foundation Phase. While studies have been carried out on applying reading strategies in the Foundation Phase, few studies have looked at the factors impacting on reading in South African schools, especially in the Mthatha District where isiXhosa is the mother tongue. The method used in this study involved a qualitative approach. The study addressed the following research questions: What strategies are used in the Foundation Phase? What type of challenges are faced by teachers? To what extent are educators trained to teach reading in the Foundation Phase? Does the lack of resources affect the performance of learners? To what extent does the use of a second language affect the performance of Foundation Phase learners? Do teachers receive enough support from the Department of Education to teach reading? The study is a multiple-case study and data were collected through individual interviews and focus group interviews (sixteen teachers were interviewed). Content analysis guided the data analysis through themes derived from the subsidiary questions. Data reporting took the form of thick description and verbatim quotations in line with the qualitative approach of the study. A pilot study was conducted in two Junior Secondary Schools for the purpose of validity and reliability. ii The study`s findings revealed that: Different reading strategies were used by teachers in the Foundation Phase, teachers faced many challenges in applying reading strategies such as teacher training in the teaching of reading. This suggests that intervention is needed by the Department of Education such as providing relevant resources which are essential in order to address the problem of reading. Improvisation by teachers to improve reading material, insufficient allocation of time, multilingualism, teacher competence, lack of motivation and parental involvement in relation to learner performance in reading all need attention in order to solve problems. Furthermore, lack of resources hinders the reading ability of learners. The use of home language as a medium of instruction in teaching reading is highlighted. There is insufficient support by the Department of Education for Foundation Phase teachers to teach reading. Based on the study findings, the researcher has recommended that teachers should be urged to use reading strategies in a way that benefits learners. The use of reading strategies, therefore, needs more attention. Libraries should be built in these schools to enable learners to develop a culture of reading. Education development officers, subject advisors, lead teachers and parents should work together to improve the reading ability of Foundation Phase learners.
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- Date Issued: 2015
The effects of gold coated and uncoated zinc oxide nanohexagons on the photophysicochemical properties of the low symmetry zinc phthalocyanine
- Authors: D'Souza, Sarah , Ogbodu, Rachael , Nyokong, Tebello
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/189077 , vital:44814 , xlink:href="https://doi.org/10.1016/j.molstruc.2015.06.088"
- Description: A new low symmetry, Zn phthalocyanine monosubstituted with diethylaminoethanethiol (mDEAET ZnPc) was synthesized and characterized. This work reports on its photophysical and photochemical properties of mDEAET ZnPc alone and when conjugated to gold coated and uncoated zinc oxide nanohexagons (ZnO NHXs). The photophysicochemical properties generally improved in the presence of the ZnO NHXs. These complexes were also tested for their photodynamic antimicrobial activity against Staphylococcus aureus (S. aureus). The Pc alone showed remarkable growth inhibition even at concentrations as low as 0.05 mg/mL. The conjugates showed a high photoinactivation of S. aureus after 30 min at a fluence of 90 mW cm−2 at a concentration of 0.05 mg/mL. The ZnPc-ZnO NHX conjugates produced the best antimicrobial results.
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- Date Issued: 2015
Enhanced triplet state yields in aqueous media of asymmetric zinc phthalocyanines when conjugated to silver nanoflowers
- Authors: D'Souza, Sarah , George, Reama , Göksel, Meltem , Atilla, Devrim , Durmus, Mahmut , Nyokong, Tebello
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/189099 , vital:44816 , xlink:href="https://doi.org/10.1016/j.poly.2015.08.017"
- Description: Novel low symmetry water-soluble zinc phthalocyanines (ZnPcs, complexes 1 and 2) were synthesized and then mixed with silver nanoflowers. Photophysical and photochemical studies were performed in order to determine the efficiency of complexes 1 and 2 as photosensitizers when alone and when combined with the silver nanoflowers. The Pcs show low fluorescence quantum yields and excellent triplet quantum yields of 0.78 (for 1) and 0.66 (for 2) in aqueous media. The triplet quantum yield values increased to 0.80 and 0.89, respectively, in the presence of silver nanoflowers. Long triplet lifetimes ranging from 180 to 200 μs in DMSO were obtained for complexes 1, 2 and their conjugates with silver nanoflowers.
- Full Text:
- Date Issued: 2015
Effects of differently shaped silver nanoparticles on the photophysics of pyridylsulfanyl-substituted phthalocyanines
- Authors: D'Souza, Sarah , Mashazi, Philani N , Britton, Jonathan , Nyokong, Tebello
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/193564 , vital:45348 , xlink:href="https://doi.org/10.1016/j.poly.2015.06.038"
- Description: This paper reports on the photophysical behavior of (2-pyridylsulfanyl)phthalocyaninato zinc(II) and 2,9(10),16(17),23(24)-tetra-(2-pyridylsulfanyl)phthalocyaninato zinc(II) in the presence of differently shaped silver nanoparticles (nanospheres, nanotriangles and nanoflowers). The presence of shaped nanoparticles increased both triplet quantum yields and lifetimes of the tetra-substituted mercaptopyridine zinc phthalocyanine in DMSO. It is apparent from this work that the shape of the silver nanoparticle used is of little consequence in influencing photophysical behavior of the phthalocyanines.
- Full Text:
- Date Issued: 2015
Effects of ZnO nanohexagons and nanorods on the fluorescence behavior of metallophthalocyanines
- Authors: D'Souza, Sarah , Moeno, Sharon , Nyokong, Tebello
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/189741 , vital:44927 , xlink:href="https://doi.org/10.1016/j.poly.2014.09.012"
- Description: This paper looks at the fluorescence behavior of zinc phthalocyanines: 2,(3),9(10),16(17),23(24)-tetrakis- (mercaptoacetic acid phthalocyaninato) zinc(II) (ZnTMAAPc), 2,(3),9(10),16(17),23(24)-tetrakis-(mercaptopropanoic acid phthalocyaninato) zinc(II) (ZnTMPAPc) and (OH)AlPcSmix (the latter contains a mixture of the di-, tri- and tetra-sulfonated derivatives with an average of three sulfonated groups per molecule) in the presence of ZnO nanoparticles. Fluorescence lifetimes of Pc complexes generally decreased in the presence of ZnO nanoparticles, with generally longer lifetimes for ZnO nanohexagons compared to ZnO nanorods.
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- Date Issued: 2015
Transformation adaptation: developing a framework for donor organisation support of climate change adaptation in resource poor communities
- Authors: Dada, Rehana
- Date: 2015
- Subjects: Climatic changes , Human beings -- Effect of climate on , Acclimatization
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/4158 , vital:20560
- Description: Poor communities already face severe challenges in meeting their basic needs, whether because of poor income opportunities, inadequate service delivery, or degraded ecosystems that can no longer support the needs of people. Non profit organisations who provide support for development are also challenged by financial restrictions and social and political structures that prevent or limit project development. Climate change is understood to have the most severe impact on the most vulnerable communities and sectors of communities by reducing the availability and accessibility of basic resources such as water, food and energy, impacting severely on human health and wellbeing, and further reducing the capacity of ecosystems to support livelihoods. This will add a layer of significant new complications to the ability of poor communities to maintain or improve standards of living, and further challenge non profit organisations that support such communitiesAnticipatory adaptation to climate change can reduce some of the impacts of climate change, and also address some key development stresses. This thesis aims to provide a framework that is relevant for supporting adaptation to climate change within the context of resource poor communities in a developing country. Non profit organisations and donor agencies could support success and autonomy in adaptation processes by making provision for locally defined understanding of adaptation, and locally determined processes and programmes. This can be taken further into implementation of programming that addresses local short term development priorities alongside, or as part of long term adaptation work. The research followed a number of steps involving a multitude of techniques including literature review, interviews, a survey, consultation with an expert group, further consultation with stakeholders, and a final electronic review. Its outcome is a strategy that can be used to support climate change adaptation in resource poor communities. A definition for adaptation is proposed as an interpretation of adaptation that is relevant in this context. The intended end goal of adaptation as defined in this research is a better form of development that : supports a harmonious and respectful relationship between humans and their natural resource base; averts further destructive global change or at the very least prevents it from becoming unmanageable; and manages the impacts of past and ongoing destructive change so that there is lowest possible loss of natural, human, or cultural resources. The term transformative adaptation emerged from the research processes to describe adaptation to climate change that concurrently addresses development challenges, is grounded in community development aspirations, integrates programming work across multiple thematic areas and approaches, and addresses the causes of climate change within adaptation interventions. The following broad guidelines are used to inform programming within the framework of transformative adaptation : Human communities are faced with an enormous challenge resulting from global change and sociopolitical injustices; Well planned anticipatory adaptation can limit exposure and vulnerability to at least some of the projected impacts of climate change; Adaptation to climate change incorporates a reduction of vulnerability to underlying development stresses, alongside a reduction of vulnerability to specific climate change stresses; Existing development work forms the foundation for adaptation interventions, acknowledging the interdependence of social, natural and economic systems and the need to maintain their health; Adaptation decision making is community based, and acknowledges that resource poor communities are best placed to establish their own development needs, drive implementation of interventions in own spaces, and identify own limits to adaptation; Adaptation work incorporates mitigation objectives so that the causes of climate change are addressed as part of the strategy for coping with climate change; Adaptation programming acknowledges the strong interlinkages between, and integrates work across, the thematic areas of water security, food sovereignty, energy security, land security, human wellbeing and livelihood diversity; Adaptation uses a broad set of approaches that spans research, knowledge sharing, advocacy, and investment in technology and infrastructure; There is flexibility in project design and implementation to allow room for experimentation with new concepts, and also to change design as knowledge, understanding, and geophysical, biophysical and sociopolitical conditions change.
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- Date Issued: 2015
Teachers’ experiences in identifying learners with learning barriers in a Full Service School
- Authors: Dakada, Alinda
- Date: 2015
- Subjects: Inclusive education Learning disabilities -- South Africa -- Eastern Cape Teaching -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: http://hdl.handle.net/10353/6147 , vital:29495
- Description: This study investigates teachers‟ experiences in identifying learners with learning barriers in one primary school in the East London District. It focuses on diversity and inclusive education as well as practices and procedures within the school. This is a phenomenological study conceptualized in terms of social constructivism(Leatherman, 2007), Kurt Lewin‟s Field Theory(Neill, 2004) and ecological systems theory(Maddock, 2000).The literature review encompasses four focal points: conceptualisation of inclusive education, inclusive education in South Africa, policy implementation, and lessons learned from inclusive education implementation both internationally and in South Africa. A qualitative research method is employed in this study through the use of semistructured interviews and observations. The findings are analysed using content analysis. The key findings of this might help the teachers working in full service or mainstream schools to have a good understanding and a sense of what diversity and inclusive education entails. The findings might attempt to examine how educators manage inclusion in the classroom, their competencies and the strategies they need in order to be competent inclusive teachers. Recommendations are developed that point to how practices could be put in place to facilitate an effective implementation strategy for the development of an inclusive education system.
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- Date Issued: 2015
A business model for medical subspecialty training in South Africa
- Authors: Dalmeyer, Johannes Paulus Franciscus
- Date: 2015
- Subjects: Health care teams -- Training of -- South Africa , Medical care -- Needs assessment -- South Africa , Evidence-based medicine -- South Africa
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/3508 , vital:20437
- Description: The shortage of healthcare workers and doctors in the developing world compared to the developed world is a problem, and will continue to be so, due to the continual migration of qualified professionals and the inability of the state to remedy these shortfalls. A shortage of healthcare workers and specialist doctors will seriously hamper the Government’s National Health Insurance (NHI) plan, as well as the sustainability of the private health care sector. In addition, the duration of medical training in South Africa is exceptionally long. The three major hospital groups and other private corporates have over the last number of years taken limited initiative to fund education projects in conjunction with the academic institutions. However, these projects have been poorly focused and have been managed in an unstructured and detached manner. There is a desire from the private sector to get involved in these projects on a much larger scale through more formalised structures. Given this background, the primary objective of this research is to develop a business model for medical subspecialty training to complement the current academic subspecialty training in South Africa. A trial model for training subspecialists in reproductive medicine was developed as a first attempt to address the threatening shortages and training duration. This trial programme is the basis of this research. A two-phased process was used in collecting data. In Phase 1 data was collected from stakeholder groups. The results of this survey assisted in generating variables to include in the measuring instrument for the survey in Phase 2. In Phase 2 the perceptions and expectations of sub-specialists (reproductive subspecialists and cardiologists) regarding sub-specialty training was collected. The results of the demographic variables confirm the aging profile of subspecialist and the need to ensure succession. The results further showed that cardiologists and reproductive subspecialist expectations of the training of subspecialists are very similar except for their expectations on the training duration. Reproductive subspecialist respondents agreed more than cardiology subspecialist respondents that the training duration is too long. The biggest gap between perceptions and expectations is also with the factor training. The results showed that the expectations of subspecialists are not met for training. From these results a business model for the training of medical subspecialists is proposed. This proposed business model can play a complementary role to the existing state controlled system and form the bases of Public Private Partnerships (PPP) in medical training. This proposed business model will fit a developing country were the focus is on primary healthcare, with financial and capacity constraints. The proposed model would require role players to bring about change to accommodate a larger scale Public Private Partnership (PPP) to ensure the implementation of the model. The proposed decentralised business model for training subspecialists would allow the trainee subspecialist to practise as a specialist thus maintaining an acceptable income, and enable an expedited completion and lead to a wider dissemination of medical expertise that can be delivered in a wider national foot print. It further will provide for a structured Public Private Partnership.
- Full Text:
- Date Issued: 2015
Spatio-temporal variation in the phytobenthos and phytoplankton community structure and composition of particulate matter along a river-estuary continuum assessed using microscopic and stable isotope analyses
- Authors: Dalu, Tatenda
- Date: 2015
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/54416 , vital:26563
- Description: Phytoplankton and phytobenthos communities play an important role in lotic systems as primary producers providing essential biomolecules to higher trophic oganisms and are important indicators for environmental or ecological change. In this thesis, field studies (observational and experimental) along a river–estuary continuum were conducted to assess the spatio-temporal variation and development of phytobenthos and phytoplankton communities using a combination of stable isotope and community analyses in a temperate southern African system across four study periods: September (early spring) and November/December (late spring) 2012, and February (summer) and May/June (winter) 2013. Additionally, the sources and composition of the particulate organic matter were also analysed using stable isotope (δ15N and δ13C) analysis. The effects of substrate type and flood occurrence were assessed through experimental studies at an up- and downstream site of the river after a major flood event that occurred between October and November 2012. Common household tiles were used as artificial substrates to study the development/succession of phytobenthos communities after the flood disturbance. Distinct diatom communities were observed between upstream and downstream sites and at each site, community structure changed with time indicating succession. In addition to recording diatom characteristics on three natural substrates, namely; macrophytes, rocks and sediment, artificial substrates observations were also made on three different types of artificial substrates, namely; brick, brown clay and grey clay tiles. The natural (species richness 78) and artificial substrates (sp. richness 93) had different communities with the latter having greater species richness. Common phytobenthos taxa were not restricted to a single substrate but preference was generally high for the artificial substrates, especially brown tiles (mean sp. richness 47). Results of the redundancy analysis (RDA) analysis indicated that ammonium, conductivity, total dissolved solids, salinity, pH, oxygen reduction potential, phosphate and water depth were the major determinants of the phytobenthos composition at the two sites. The spatio–temporal variation of phytoplankton and phytobenthos communities and allochthonous organic matter along the river–estuary continuum was assessed at 8 sites using a combination of community and stable isotope analyses. A total of 178 species belonging to 78 genera were recorded with diatoms being predominant, accounting for 81.9 % of the total abundance. The total chl-a concentration along the river-estuary continuum increased from spring to a high in summer before decreasing to a low in winter. Periphyton communities were observed to be significantly different across sites (p < 0.05) in terms of species richness, abundances and isotopically The high periphytic δ15N values (range 7.9–15.2 ‰) recorded at the downstream sites compared to the pristine upstream sites (δ15N values range 4–7 ‰) suggest nutrient enrichment most likely derived from anthropogenic sources. Overall, our results reveal general patterns of periphyton communities and stable isotopes and provide improved information in the use of periphyton δ15N as an excellent indicator of anthropogenic nitrogen pollution. Ecologists are interested in the factors that control, and the variability in, the contributions of different sources to mixed organic materials traveling through lotic systems. We hypothesized that the source matter fuelling mixed organic pools in a river-estuary continuum varies over space and time, with the upper reaches of a system characterized by allochthonous-dominated material and autochthonous contributions becoming more important in the lower reaches. Samples of the mixed organic pools and allochthonous and autochthonous source materials were collected during the four study periods. The C:N ratios of suspended particulate matter (SPM) collected during summer and winter indicated that the lower reaches of the system had similar organic matter contributions from the freshwater and terrestrial sources. Stable isotope analysis in R revealed that the contributions of autochthonous organic matter were high in SPM along the entire continuum, and aquatic macrophytes were significant contributors to SPM specifically in the upper reaches. The terrestrial leaves made major contributions to the SPM in the middle regions of the system (i.e. downstream sites of the river, particularly in early and late spring). Bulk detritus had large allochthonous matter components in the lower reaches (estuary), and the contributions of aquatic macrophytes and benthic algae to bulk detritus were high (> 50 %) in the upper to middle reaches (river), but low (< 20 %) in the lower reaches (estuary). The current investigation represents the first attempt to assess the validity of the River Continuum Concept (RCC) in a southern African temperate river. The phytoplankton and phytobenthos communities, and chl-a concentration followed a trend similar to that proposed for the river continuum concept (RCC). The middle reaches based on the phytobenthos or phytoplankton communities and chl-a concentrations which were employed as proxies for primary production, were the most productive, while the upper reaches were the least primary productive. The evaluation of organic matter contributions to the SPM and detritus along the river–estuary continuum provided a baseline assessment of the nature and sources of potential food for consumers inhabiting different locations during different times of the year. Incorporating such spatio-temporal variations in SPM and detritus into food web studies will improve our understanding of the flow of carbon through aquatic systems.
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- Date Issued: 2015
An Assessment of the Effect of Rotenone on Selected Non-Target Aquatic Fauna: Reflections on Henri Lefebre, Urban Theory and the Politics of Scale
- Authors: Dalu, Tatenda , Wasserman, Ryan J , Jordaan, Martine , Froneman, Pierre William
- Date: 2015
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/70425 , vital:29654 , https://doi.org/10.1371/journal.pone.0142140
- Description: Rotenone, a naturally occurring ketone, is widely employed for the management of invasive fish species. The use of rotenone poses serious challenges to conservation practitioners due to its impacts on non-target organisms including amphibians and macroinvertebrates. Using laboratory studies, we investigated the effects of different rotenone concentrations (0,12.5, 25, 37.5, 50, 100 μg L-1) on selected invertebrate groups; Aeshnidae, Belostomatids, Decapods, Ephemeroptera, Pulmonata and zooplankton over a period of 18 hours. Based on field observations and body size, we hypothesized that Ephemeropterans and zooplankton would be more susceptible to rotenone than Decapods, Belostomatids and snails. Experimental results supported this hypothesis and mortality and behaviour effects varied considerably between taxa, ranging from no effect (crab Potamonuates sidneyi) to 100% mortality (Daphnia pulex and Paradiaptomus lamellatus). Planktonic invertebrates were particularly sensitive to rotenone even at very low concentrations. Future research should investigate the recovery time of invertebrate communities after the application of rotenone and conduct field assessments assessing the longer term effects of rotenone exposure on the population dynamics of those less sensitive organisms.
- Full Text:
- Date Issued: 2015
An assessment of the effect of rotenone on selected non-target aquatic fauna:
- Authors: Dalu, Tatenda , Wasserman, Ryan J , Jordaan, Martine , Froneman, P William , Weyl, Olaf L F
- Date: 2015
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/143247 , vital:38214 , https://doi.org/10.1371/journal.pone.0142140
- Description: Rotenone, a naturally occurring ketone, is widely employed for the management of invasive fish species. The use of rotenone poses serious challenges to conservation practitioners due to its impacts on non-target organisms including amphibians and macroinvertebrates. Using laboratory studies, we investigated the effects of different rotenone concentrations (0, 12.5, 25, 37.5, 50, 100 μg L-1) on selected invertebrate groups; Aeshnidae, Belostomatids, Decapods, Ephemeroptera, Pulmonata and zooplankton over a period of 18 hours. Based on field observations and body size, we hypothesized that Ephemeropterans and zooplankton would be more susceptible to rotenone than Decapods, Belostomatids and snails.
- Full Text:
- Date Issued: 2015
Assessment of the spatial and temporal variations in periphyton communities along a small temperate river system: A multimetric and stable isotope analysis approach
- Authors: Dalu, Tatenda , Bere, Taurai , Richoux, Nicole B , Froneman, P William
- Date: 2015
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124249 , vital:35580 , https://doi.org/10.1016/j.sajb.2015.05.028
- Description: Periphyton community structure and stable isotope values have been identified as potential indicators of anthropogenic nitrogen pollution, an increasingly important challenge in aquatic systems. The aim of the study was to assess the spatio-temporal changes in periphyton characteristics to identify potential anthropogenic nitrogen pollution sources such as agricultural and sewage discharge within the Kowie River catchment, South Africa. Periphyton was collected once a season from five sites between September 2012 and May 2013. Diversity indices, multimetric and stable isotope analyses were employed for describing the spatial and temporal dynamics of periphyton community assemblages. Water depth, salinity, resistivity, oxygen reduction potential, nitrates, water velocity and conductivity were the major factors affecting periphyton community structure. Eighty-seven periphyton taxa belonging to 43 genera were recorded throughout the study sites and periods. Periphyton species richness, abundance and stable isotope signatures differed significantly among sites but not among seasons. The lower sections of the Kowie River were polluted by anthropogenic sources as indicated by the high periphytic isotopic nitrogen values (7.9–15.2‰) compared to the pristine upstream sites (4–8‰). We recommend that researchers use a combination of community structure and stable isotope measurements to monitor the periphyton in lotic systems.
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- Date Issued: 2015
An Assessment of the Effect of Rotenone on Selected Non-Target Aquatic Fauna
- Authors: Dalu, Tatenda , Wasserman, Ryan J , Jordaan, Martine , Froneman, P William , Froneman, Pierre William , Weyl, Olaf L F
- Date: 2015
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124240 , vital:35579 , https://doi.org/10.1371/journal.pone.0142140.g001
- Description: Rotenone, a naturally occurring ketone, is widely employed for the management of invasive fish species. The use of rotenone poses serious challenges to conservation practitioners due to its impacts on non-target organisms including amphibians and macroinvertebrates. Using laboratory studies, we investigated the effects of different rotenone concentrations (0, 12.5, 25, 37.5, 50, 100 μg L-1) on selected invertebrate groups; Aeshnidae, Belostomatids, Decapods, Ephemeroptera, Pulmonata and zooplankton over a period of 18 hours. Based on field observations and body size, we hypothesized that Ephemeropterans and zooplank- ton would be more susceptible to rote none than Decapods, Belostomatids and snails. Experimental results supported this hypothesis and mortality and behaviour effects varied considerably between taxa, ranging from no effect (crab Potamonuates sidneyi) to 100% mortality (Daphnia pulex and Paradiaptomus lamellatus). Planktonic invertebrates were par- ticularly sensitive to rotenone even at very low concentrations. Future research should investigate the recovery time of invertebrate communities after the application of rotenone and conduct field assessments assessing the longer term effects of rotenone exposure on the population dynamics of those less sensitive organisms.
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- Date Issued: 2015
Feeding ecology, residency patterns and migration dynamics of bull sharks (Carcharhinus leucas) in the southwest Indian Ocean
- Authors: Daly, Ryan
- Date: 2015
- Subjects: Bull shark -- Ecology , Bull shark -- Feeding and feeds
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5924 , http://hdl.handle.net/10962/d1017802
- Description: Bull sharks (Carcharhinus leucas) are globally distributed top predators that play an important ecological role within coastal marine communities. However, little is known about how the spatial and temporal scales of their habitat use are associated with their ecological role. In this study, a population of sub-adult and adult bull sharks were investigated within a remote subtropical marine community in the southwest Indian Ocean off the coast of southern Mozambique. The main objectives of the study were to test a minimally invasive remote biopsy sampling method; to investigate the feeding ecology of bull sharks; and to investigate the temporal and spatial scales of bull shark residency patterns and migration dynamics. Biopsy tests on free-swimming bull sharks showed that the devised sampling technique provided a minimally invasive and consistent method (biopsy retention rate = 87%) to obtain muscle tissue samples sufficiently large enough (310±78mg, mean ± SD) for stable isotope analysis. Results from the stable isotope analysis showed that adult bull sharks appeared to exhibit a shift towards consistentlyhigher trophic level prey from an expanded foraging range compared to sub-adults, possibly due to increased mobility linked with size. Additionally, bull sharks had significantly broader niche widths compared to top predatory teleost assemblages with a wide and enriched range of δ13C values relative to the local marine community, suggesting that they forage over broad spatial scales along the east coast of southern Africa. Results from the passive acoustic telemetry investigation, conducted over a period between 10 and 22 months, supported these findings showing that the majority of tagged adult sharksexhibited temporally and spatially variable residency patterns interspersed with migration events. Ten individuals undertook coastal migrations that ranged between 433 and 709km (mean = 533km) with eight of these sharks returning to the study site. During migration, individuals exhibited rates of movement between 2 and 59km.d-1 (mean = 17.58km.d-1) and were recorded travelling annual distances of between 450 and 3760km (mean = 1163km). These findings suggest that adult bull sharks are not the sedentary species once thought to be but rather, consistently move over broad spatial scales on the east coast of southern Africa and play an important predatory role shaping and linking ecological processes within the southwest Indian Ocean.
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- Date Issued: 2015
The challenges of the child support grant as a poverty alleviation strategy
- Authors: Damba, Ntombethemba
- Date: 2015
- Subjects: Economic assistance, Domestic -- South Africa -- Uitenhage , Income maintenance programs -- South Africa -- Uitenhage , Social security -- South Africa -- Uitenhage
- Language: English
- Type: Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10948/6193 , vital:21048
- Description: South Africa is a democratic country since 1994 and transformation brought policies that aimed to address the inequalities and poverty situation countrywide. During apartheid era the existence of social assistance was more focused on minority group. Hence the eroded social inequality cannot be ignored as poverty takes its toll in our communities. It was the previously termed state maintenance grant that was phased out with the introduction of Child support grant (CSG). The purpose of CSG was to reduce child poverty; however a long list of challenges regarding the aims and objectives of the CSG surfaced. This study was about the challenges of child support grant as poverty alleviation strategy in waNobuhle community in Uitenhage. The purpose of the study was also to investigate the value CSG adds in the beneficiaries’ lives in terms of poverty alleviation and what is mostly hindering the CSG from alleviating poverty. The research design for the study could be classified as mixed designs which include qualitative and quantitative approach, taking a form of action research. A sample of 30 participants was drawn from SASSA beneficiaries. The sampling method for the study was purposive, which is a non-probability sampling. Semi structured questionnaires and semi structured interviews were utilized to collect data and the data collected was analysed thematically and descriptive statistics analysis was undertaken as well. Questionnaires to collect data from the thirty (30) CSG beneficiaries’ from KwaNobuhle community and semi structured interviews was undertaken. The most important findings that emerged from the study were that participants appeared to have a clear understanding of the fact that CSG represented a government strategy to support children, fight poverty and uplift the standard of living for the poor. However, majority of the participants were not satisfied with CSG as poverty alleviation strategy, participant’s wants government to increase the amount of CSG and to create employment opportunities. The CSG was pointed as inadequate due to the fact that all family members of the beneficiaries are dependent on the CSG. The conclusion drawn was that CSG paid to KwaNobuhle beneficiaries seemed to be achieving their aims even though the CSG is announced to be inadequate, employment is a necessity and the gap between departments serving the community. The findings of the study are discussed as suggestions to SASSA and the Department of Social development.
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- Date Issued: 2015
The trophic ecology of the endangered endemic Barau's Petrel (Pterodroma baraui) from Reunion Island, south-western Indian Ocean
- Authors: Danckwerts, Daniel Keith
- Date: 2015
- Subjects: Petrels -- Réunion , Pterodroma baraui , Ecology -- Réunion
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5925 , http://hdl.handle.net/10962/d1017803
- Description: Réunion is the only tropical island that supports two endemic gadfly petrels. Population modelling has indicated that the current threats to the Barau’s Petrel (Pterodroma baraui) may drive it to extinction; this fate is almost definite for the Mascarene Petrel (Pseudobulweria aterrima). Management interventions have therefore been implemented, but conservation potential is handicapped since virtually nothing is known about the former species’ at-sea biology. Thus, following numerous recommendations, this study aimed to combine stomach content, stable isotope, and fatty acid analyses so to provide new information on the at-sea ecology of Barau’s Petrel. Breeding colonies were repeatedly visited over the same season and samples gathered from adults, fledglings, and downy chicks. Stomach contents consisted mostly of accumulated cephalopod beaks whereas structures from fishes, molluscs, arthropods, and crustaceans were less frequently encountered. Fatty acid profiles of blood varied greatly among individuals and the lowincidences of monounsaturated and n-3 fatty acids discounted fish as an important dietary component. δ¹⁵N of blood indicated a niche between the fourth and fifth trophic levels, which proposes that these birds scavenge to a greater degree than other sympatric seabirds and suggests that adults are also reliant on their endogenous reserves during breeding. δ¹³C values confirmed the migratory behaviour of adults since birds returning from the non-breeding grounds were enriched relative to individuals sampled through the breeding period. Significant intra-breeding season variations in δ13C were also observed, which matched this species’ patterns of habitat use as have recently described. These results collectively indicate an opportunistic behaviour, which implies some degree of resilience against shifts in prey availability/accessibility, and suggest that this species’ reproduction isdependent on distant foraging areas. This breeding strategy is synonymous with great vulnerability as over-investing into a single breeding episode may jeopardize future survival and fecundity. Thus, in light of environmental conditions that are becoming increasingly more susceptible to dramatic changes, the birds could rather be prioritising adult survival, over reproductive output. Further work is obviously necessary and should benefit from databases of fatty acid profiles and isotope signatures of potential prey species.
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- Date Issued: 2015
Views of HIV and AIDS amongst rural secondary school youth: an exploratory study
- Authors: Daniels, Brendon Mara Laurence
- Date: 2015
- Subjects: Sexually transmitted diseases -- Study and teaching Communicable diseases -- Prevention High school students
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: http://hdl.handle.net/10948/11460 , vital:26928
- Description: The HIV and AIDS epidemic continues to affect communities worldwide particularly so in South Africa. Youth, also the so-called Coloured youth, continue to remain at risk of infection, in spite of having been exposed to information about HIV and AIDS. This study explores the views of Coloured secondary school youth in a rural town in the Eastern Cape, on HIV and AIDS. Fifteen secondary school learners, both boys and girls, from Grades 10 to 12 were purposively selected. This qualitative study, framed within an interpretivist paradigm, draws on a phenomenological methodology. The data was generated from using drawing and focus group interviews and analysed using thematic analysis. The research adhered to ethical principles and trustworthiness was ensured. Constructivism and Bronfenbrenner’s bio-ecological systems theory were used to frame the study and to make meaning of the findings. In response to the primary research question, What views do Coloured youth attending a secondary school in a rural town have of HIV and AIDS?, five themes emerged, namely: individuals spread HIV, impoverished family life increases youth vulnerability to HIV, youth under pressure from peers knowingly engage in risky behaviour, misconceptions fuel the epidemic, and HIV and AIDS “captures the community in its net”. Drawing on the findings and in response to the secondary research question, What guidelines can be developed to assist educators to facilitate learners taking action against the spread of HIV and AIDS?, several guidelines were developed. They suggest that teachers should use participatory pedagogies to engage secondary school learners when teaching HIV and AIDS, build self-esteem in their learners, assist learners in dealing with peer pressure, engage learners in erasing misconceptions, and enable learners to break free from being “caught in the net” of HIV and AIDS. Collectively these guidelines could enable learners to take action in protecting themselves and their community against the spread of the HI virus. The study concludes that the views that Coloured secondary school learners from a rural town have about HIV and AIDS show their awareness of the realities of the epidemic affecting the individual, the family, the school and their community. They have constructed their views of HIV and AIDS in a way which shows their understanding of the complexities of the epidemic.
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- Date Issued: 2015