A theoretical study of alkoxyl radical and radical cation mediated cyclisation reactions in unsaturated alkanols
- Authors: Lee, Peter Mattison Clarke
- Date: 2021-04
- Subjects: Gqeberha (South Africa) , Eastern Cape (South Africa) , Density functionals
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/52130 , vital:43430
- Description: A large part of this computational study focussed on selectivity patterns for 4-penten- 1-oxyl radical 1,5- and 1,6-cyclisations and for those of analogous 5-hexenyl, 4- penten-1-aminyl, 4-penten-1-iminyl and 3-phenylpropan-1-oxyl radicals. The study furthermore included cyclisation reactions of the radical cations of 4-penten-1-ol and 3-phenylpropan-1-ol. Calculations were performed for all applicable species involved in the two cyclisation modes studied, i.e. 1,5- and 1,6-cyclisation. These species included radical and radical cation precursors, as well as relevant radical transition state structures and radical adducts. All cyclisation systems investigated used the Density Functional Theory (DFT) functional B3LYP with a combination of eight basis sets. Each basis set used was a progressively higher level of theory than B3LYP/6-31G* which was used as a starting point. Cyclisations for unsubstituted species, e.g. the 4-penten-1-oxyl radical 1,5- and 1,6-cyclisations, were also simulated using the ωB97X-D and ωB97X-V functionals which account for dispersive effects. The same set of eight basis sets were used with these two functionals. , Thesis (PhD) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2021
- Full Text: false
- Date Issued: 2021-04
A trait-based approach to identify indicators for measuring rocky reef ecosystem condition in South Africa
- Authors: Smit, Kaylee
- Date: 2020
- Subjects: Environmental management -- Evaluation , Environmental monitoring -- Methodology Marine ecology -- South Africa
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/49292 , vital:41618
- Description: An important yet challenging task for effective ecosystem-based management of marine ecosystems is the reliable measurement and monitoring of changes in ecosystem condition. In South Africa, the National Biodiversity Assessment (NBA) has relied on cumulative pressure mapping, based on the calculation of cumulative impact scores, as a proxy for measures of marine ecosystem condition. While this method is practical for broad scale assessments where ecological data are lacking, there is a need to groundtruth this approach at local scales using in-situ data. The aim of this thesis was to identify potential indicators that can be used to measure the ecosystem condition of subtidal rocky reefs on the East coast of South Africa to groundtruth national pressure-based condition assessments. This thesis constituted the first attempt to conduct a comprehensive assessment of rocky reef ecosystem condition to validate national pressure-based assessments in South Africa. Based on a comprehensive literature review, a traits-based approach was selected to ensure that ecosystem structure and function were included in condition measurements. Fish and benthic community data were collected using baited remote underwater stereo-video systems (144 video samples) from the Natal Shelf ecoregion. Sampling spanned a gradient of low to high human pressures, which incorporated an effective Marine Protected Area (to define reference conditions), as well as areas exposed to intermediate levels of human pressures and a highly impacted area offshore of a large metropolitan port city. Structural and functional indicators were compared among localities and suitable functional indicators were aggregated into multimetric indices (MMIs) to provide an integrated measurement of ecosystem condition. Approximately 840 benthic biota and 10 400 fish (representing 176 identified fish species) were counted. Results showed that functional indicators, particularly size-based ones, were more effective at detecting changes in ecosystem condition compared with structural indicators based on taxonomy. Reefs in good ecological condition had a higher biomass of target species and a higher proportion of large predatory fish with more adults, compared with impacted areas. Benthic communities, however, appeared less responsive to cumulative pressures. The MMIs, using fish and benthic community data, were used to compare condition categories with those from the NBA. Results showed that the pressure-based assessments provided a reasonable proxy of broad patterns of rocky reef ecosystem condition. However, fine-scale discrepancies between results from the data-driven approach versus the proxy method suggested that broad-scale proxies might overestimate condition in some areas and underestimate it in others. To build on these results, the applicability of structural and functional indicators and MMIs were tested using an independent stereo-BRUVs dataset from the Agulhas Shelf ecoregion. Findings showed that not all MPAs were in good ecological condition compared with adjacent impacted areas, as was estimated by the NBA. However, there is a need to improve the quality of trait data and to test indicators and indices in other ecoregions, ecosystem types and in response to a broader range of improved pressure data. Furthermore, there is a need to apply innovative research to guide the calculation of thresholds for condition categories to advance condition assessments.
- Full Text:
- Date Issued: 2020
A value alignment smart city stakeholder model
- Authors: Van der Hoogen, Anthea Vivian
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/54129 , vital:46309
- Description: The concept of a Smart City has evolved over the last three decades and has attracted the increasing interest of the scientific research community. Unfortunately, many Smart City projects and initiatives do not provide the value expected by all the stakeholders. Many of the reasons for this relate to a lack of data management, data integration, data access and stakeholder participation. People are an integral part of any city’s ecosystem, and the Smart City concept was introduced to address the challenges of an ever-growing global population leading to the risk of depletion of economic, environmental and social resources. The problem addressed in this study is based on the challenges preventing the creation of the value of smart cities or stakeholders. Limited research has been published on the status of Smart City initiatives or on the impact of various success factors on the potential value creation for stakeholders including citizens. Studies on initiatives in developing countries, such as South Africa are even less. Whilst some challenges and constraints related to smart cities in Africa have been reported, there are no studies reporting on initiatives across the data value chain that consider all types of stakeholders, nor the impact of these initiatives. This study addressed this gap in research and designed a theoretical Value Alignment Smart City Stakeholder (VASCS) Model based on a Systematic Literature Review and a review of related theories. The model has important components that should form part of any Smart City project or Smart City initiative. These five main components are: 1) nine Smart City dimensions with related success factors; 2) four stakeholder roles (enablers, providers, utilisers and users); 3) the data value chain; and 4) the five phases of stakeholder benefits/value realisation that can be linked to; 5) stakeholder value alignment. This study applied the VASCS Model to Smart City initiatives in two case studies in the Eastern Cape Province of South Africa, which were the Nelson Mandela Bay and Buffalo City to investigate and understand the status of such initiatives and the alignment of value thereof. The stakeholder interviews were conducted in two rounds with various stakeholders of Smart City initiatives, referred to as cases in the two case studies. An expert review of the VASCS Model was conducted with eight experts in the field of Information Systems and Smart Cities. The findings of this review served to confirm the components of the model, with only minor improvements recommended. It was confirmed that all of the components need to be considered in planning Smart City projects. The first round consisted of six interviews with enablers and providers and the second round consisted of 22 interviews with users, utilisers and citizens. The interviews investigated the value and impact experienced by stakeholders of these initiatives, with a particular focus on the users, utilisers and citizens of the cases. The interview data was transcribed and qualitatively analysed by using Atlas.tiand Excel. The data was analysed according to the Technological, Organisational and Environmental theory constructs and other identified themes. The interview analysis findings revealed several drivers for these initiatives, which were primarily cost reduction, integration and quality assurance. The results also highlighted access to resources, such as technical skills as a challenge. Another challenge identified was connectivity related to access to data and the digital and physical divide that can impact decision making. The main benefits of Smart City initiatives highlighted were the provision of infrastructure, education and training and digitalisation. The theoretical contribution of this study is the VASCS Model, which can assist other researchers and practitioners with knowledge of the factors, drivers, challenges and value obtained in Smart City initiatives. The model has two supplementary components: A Stakeholder Classification Model and a Smart City Success Factor Evaluation Template. The practical contribution of this study is the potential use of the VASCS Model by practitioners, city management, researchers and other stakeholders, who can use the model, with the related model and template for planning and evaluating Smart City initiatives. The model can be used to classify the digital activities according to a Smart City’s success factors while evaluating the value created by these activities. The impact of these initiatives can then be assessed through value realisation and alignment for stakeholders. The scientific contribution is the adoption of the model to the cases in the Eastern Cape. To reveal in depth, rich, interview findings that provide important lessons learnt relating to the value created for the stakeholders and the addition of these findings to the body of knowledge. , Thesis (PhD) -- Faculty of Science, School of Computer Science, Mathematics, Physics and Statistics, 2021
- Full Text:
- Date Issued: 2021-12
A web-based repository for student mobility data in Africa
- Authors: Ferreira, Darren Bradley
- Date: 2016
- Subjects: Student mobility Students, Transfer of -- South Africa -- Psychological aspects , Education, Higher Foreign study
- Language: English
- Type: Thesis , Masters , MCom
- Identifier: http://hdl.handle.net/10948/12605 , vital:27098
- Description: The number of international students studying abroad has doubled since the year 2000 and there are nearly five million students that are enrolled outside their country of origin. Over the past ten years new insights and approaches to the internationalisation of higher education have arisen which has influenced global research and education. Student mobility data is a component of internationalisation data. internationally mobile students are defined as students who have crossed international borders from their countries with the objective to study. Currently, there are several international organisations and projects that manage student mobility data from various Higher Education Institutions (HEIs) across the globe and report on this data. Two of these organisations are the Open Doors Report and Project Atlas. The organisations collect Data for Africa, although it is not as detailed and useful as the data provided about other countries. Since the number of students studying abroad has doubled since the year 2000, the amount of student mobility data kept by data collection agencies and HEIs has also increased. The data collected is not always accurate and this poses a data management problem. This study conducted a survey sent to international offices at various HEIs in South Africa and Africa. The survey investigates the current state of student mobility data management in HEIs. The survey results revealed that the international offices are currently dissatisfied with student mobility data management and will be willing to provide international student data to an African data repository. This study proposes the design and development of a web-based student mobility data repository, known as the African International Portal (AIP). The study identified design guidelines and requirements for a web-based data repository. The requirements, design and design guidelines were used to guide the development of the prototype. Heuristic evaluations were conducted on the prototype in order to identify any major usability problems. Findings revealed that the overall perceptions of the prototype were positive and can be attributed to the design considerations and guidelines used during the development phase. The prototype was evaluated using a full usability evaluation that determined the usefulness, effectiveness and efficiency of the prototype when users are in the process of managing student mobility data. The results indicate that the participants found the AIP to be an effective, efficient and a satisfactory means of managing student mobility data.
- Full Text:
- Date Issued: 2016
Absorptive capacity for responding to environmental: change an assessment of three public-sector agencies
- Authors: Mc Culloch, Samantha
- Date: 2016
- Subjects: Global environmental change Absorptive capacity (Economics)
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/11762 , vital:26966
- Description: In a time of global environmental instability, public-sector organisations that manage and protect natural resources, which are needed for human wellbeing, play an increasingly important role. These organisations frequently have to weigh up the costs and benefits of managing natural resources and their services for the public good. Management of social-ecological systems is commonly characterised by uncertainty, disagreement and trade-offs. In South Africa, these challenges are compounded by the fact that mandated organisations are often inadequately resourced in terms of finances, skilled staff and infrastructure. In order to maintain the resilience and robustness of social-ecological systems, public-sector organisations need to cultivate a set of dynamic capabilities, with strong emphasis on learning from their experiences and adapting their management strategies, to innovate and improve their performances. Absorptive capacity (AC) has been described as the ability of an organisation to recognise the value of new external information, acquire it and assimilate it within the organisation, transforming it by applying it with existing knowledge and exploiting the new knowledge for benefit. Organisations with good AC are able to recognise rapidly changing environments and address them by renewing and building on their levels of skill, knowledge and capability to deal with change. This construct has been extensively researched in industries related to business and technology, where its development has been found to stimulate innovative capabilities. There has, however, been little research into its relevance for public-sector organisations or organisations with environmental mandates. This study used methodological triangulation to assess the perceptions of employees on the current state of AC in three public-sector organisations with environmental mandates. This was done to gain insight into their capacity to absorb information and apply their new knowledge in decision-making, in a manner that navigates through environmental change. The key findings of this research suggest that knowledge transformation and exploitation are enhanced by in-house research capabilities and cross-functional interface between internal departments. These findings also suggest that the acquisition of knowledge is not only determined by the in-house research capacity but also depends on the resources available to these departments in terms of time, finances and skilled staff. There was minimal evidence of knowledge exploitation; however, obstacles that were highlighted as hindering this process included individual responsibility and motivation, as well as general organisation capacities, such as communication hierarchies, funding, time and organisational silos. This research found that the well-studied concept of AC can be used as an institutional mechanism to assess and promote adaptive capacity in public-sector organisations with environmental mandates to navigate and innovate through the Anthropocene.
- Full Text:
- Date Issued: 2016
AC3P: an architecture using cloud computing for the provision of mathematical powerpoint content to feature phones
- Authors: Joubert, Jean-Pierre
- Date: 2012
- Subjects: Cloud computing , Mobile computing , Mathematics -- Study and teaching.
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10474 , http://hdl.handle.net/10948/d1011088 , Cloud computing , Mobile computing , Mathematics -- Study and teaching.
- Description: The Govan Mbeki Mathematics Development Unit (GMMDU) provides additional mathematics content to learners via mathematics workshops and DVDs. Mathematics is presented in PPT format. The prominence of feature phone usage has been confirmed amongst learners in socio-economic disadvantaged schools, specifically those learners participating in the GMMDU mathematics workshops. Feature phones typically contain limited device resources such as memory, battery power, and network resources. Distributed computing provides the potential to facilitate a new class of mobile applications with the provision of off-device resources. The objective of this research was the design of an architecture using Cloud Computing for the provision of mathematics in the form of PPT slides to feature phones. The capabilities of typical feature phones were reviewed as well as various distributed computing architectures that demonstrate potential benefit to the mobile environment. An Architecture using Cloud Computing for Content Provision (AC3P) was subsequently designed and applied as a proof of concept to facilitate the provision of mathematics in the form of PPT slides to feature phones. The application of AC3P was evaluated for efficiency and effectiveness. It was demonstrated that the application of AC3P provided efficient and effective provision of PPT to feature phones. The successful application of AC3P provided evidence that Cloud Computing may be used to facilitate the provision of mathematics content to feature phones. It is evident that AC3P may be applied in domains other than the provision of mathematics.
- Full Text:
- Date Issued: 2012
Acacia Mearnsii debarking: comparing different debarking technologies in the KwaZulu-Natal and Mpumalanga forestry regions of South Africa
- Authors: Eggers, John Rolf
- Date: 2010
- Subjects: Acacia mearnsii -- South Africa -- KwaZulu-Natal , Acacia mearnsii -- South Africa -- Mpumalanga , Wattles (Plants) -- South Africa -- KwaZulu-Natal , Wattles (Plants) -- South Africa -- Mpumalanga
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10740 , http://hdl.handle.net/10948/1456 , Acacia mearnsii -- South Africa -- KwaZulu-Natal , Acacia mearnsii -- South Africa -- Mpumalanga , Wattles (Plants) -- South Africa -- KwaZulu-Natal , Wattles (Plants) -- South Africa -- Mpumalanga
- Description: Debarking of Acacia mearnsii in South Africa has been conducted using mainly manual systems. Labour shortages and reliability of these systems has caused interest in alternative systems that might be able to debark A. mearnsii. The aim of the research is to compare three mechanised debarking technologies used to debark A. mearnsii. Research trials were conducted on the Demuth, Hyena and Hypro debarkers that would form part of semi-mechanised harvesting systems. The debarking technologies were analysed and compared in terms of productivity per productive machine hour (PMH), debarking quality, system costs and the quality of the bark that was produced. Furthermore, the effect that tree volume, strippability and form have on each of the debarking technologies was determined. The debarking technologies were affected by each of the factors researched. Decreasing tree form had a negative effect on the productivity of each of the technologies. An increase in strippability class (strengthening wood-bark bond strength) caused a decrease in the productivity of each of the machines. An increasing tree volume had a positive effect on the productivity for the three debarking technologies. After the debarking had taken place, samples of bark were analysed at a laboratory to determine if it was acceptable for the processing facilities. Each of the debarking technologies produced bark of varying dimensions, but they were all found to be acceptable. The system costs of the three debarking technologies were compared to a manual system cost at tree volumes of 0.1m³, 0.15m³ and 0.2m³. The Demuth debarker had the best system cost for a tree size of 0.1m³, while the manual system was best for tree volumes 0.15m³ and 0.2m³. The Demuth, Hyena and manual system costs were very similar for each of the tree volumes, with the Hypro being a little higher.
- Full Text:
- Date Issued: 2010
Adaptive user interfaces for mobile map-based visualisation
- Authors: Van Tonder, Bradley Paul
- Date: 2008
- Subjects: Cartography , Maps -- Design , Digital mapping , Geographic information systems , User interfaces (Computer systems) -- Design
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10470 , http://hdl.handle.net/10948/866 , Cartography , Maps -- Design , Digital mapping , Geographic information systems , User interfaces (Computer systems) -- Design
- Description: Mobile devices today frequently serve as platforms for the visualisation of map-based data. Despite the obvious advantages, mobile map-based visualisation (MMV) systems are often difficult to design and use. Limited screen space, resource constraints and awkward interaction mechanisms are among the many problems with which designers and users have to contend. Adaptive user interfaces (AUIs), which adapt to the individual user, represent a possible means of addressing the problems of MMV. Adaptive MMV systems are, however, generally designed in an ad-hoc fashion, making the benefits achieved difficult to replicate. In addition, existing models for adaptive MMV systems are either conceptual in nature or only address a subset of the possible input variables and adaptation effects. The primary objective of this research was to develop and evaluate an adaptive MMV system using a model-based approach. The Proteus Model was proposed to support the design of MMV systems which adapt in terms of information, visualisation and user interface in response to the user‟s behaviour, tasks and context. The Proteus Model describes the architectural, interface, data and algorithm design of an adaptive MMV system. A prototype adaptive MMV system, called MediaMaps, was designed and implemented based on the Proteus Model. MediaMaps allows users to capture, location-tag, organise and visualise multimedia on their mobile phones. Information adaptation is performed through the use of an algorithm to assist users in sorting media items into collections based on time and location. Visualisation adaptation is performed by adapting various parameters of the map-based visualisations according to user preferences. Interface adaptation is performed through the use of adaptive lists. An international field study of MediaMaps was conducted in which participants were required to use MediaMaps on their personal mobile phones for a period of three weeks. The results of the field study showed that high levels of accuracy were achieved by both the information and interface adaptations. High levels of user satisfaction were reported, with participants rating all three forms of adaptation as highly useful. The successful implementation of MediaMaps provides practical evidence that the model-based design of adaptive MMV systems is feasible. The positive results of the field study clearly show that the adaptations implemented were highly accurate and that participants found these adaptations to be useful, usable and easy to understand. This research thus provides empirical evidence that the use of AUIs can provide significant benefits for the visualisation of map-based information on mobile devices.
- Full Text:
- Date Issued: 2008
Adjusting lion diet estimates to assess lion impacts on small prey in Addo Elephant National Park
- Authors: Gerber, Amarein Judith
- Date: 2017
- Subjects: Wildlife conservation -- South Africa -- Addo Elephant National Park , Lion -- Behavior -- South Africa -- Addo Elephant National Park Lion -- Conservation -- South Africa -- Addo Elephant National Park
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/14311 , vital:27542
- Description: Populations of small prey species (< 92 kg) can be regulated by competition, habitat-mediated responses, climate change, disease and predation. Populations of small prey species have declined in the Addo Elephant National Park Main Camp Section since the reintroduction of apex predators (lion and spotted hyaena). One possible explanation is predation by lion and spotted hyaena. However, small prey species are not generally considered preferred prey items of these predators, hence their contribution to predator diets needs to be explored. Global Positioning System (GPS) cluster analysis has emerged as a viable approach to locate lion kills for lion diet estimation in AENP, however this technique is known to bias diet estimates to large prey species. Understanding the impact of lion predation on populations of small prey in Main Camp therefore requires better estimates of lion diets. This study investigated the potential underestimation of small prey species in lion diet estimates by combining the data from scat analysis and carcasses located at GPS clusters. The adjusted lion diets were then used to investigate if the impact of lion predation could explain declines in small prey, by relating lion prey preferences to prey population trends in Nyathi. Using the results from Nyathi, it could then be inferred whether lions could have been responsible for the declines observed in Main Camp. Six GPS-collared lions provided location data used to construct individual movement paths, along which spatio-temporal clusters of GPS locations (n = 4896) were identified for ground investigation. Carcasses (n = 643) were recorded at the GPS clusters and scats (n = 256) were collected at GPS clusters with or without carcasses. Data from the located carcasses and scat collections were then used to create a history of feeding events for each collared lion in Main Camp-Colchester and Nyathi from a) carcasses alone or b) a combination of scats and carcasses, based on an estimated short and long lion throughout period. Relative prey availability was estimated based on camera trapping in Nyathi in high lion, low lion and no lion use areas, as lions may encounter some prey species more than other prey species. Jacobs’ index prey preference was used to investigate the importance of prey species to lion diets at three landscape scales: 1) Nyathi, 2) lion UD and 3) core lion UD. Lastly, prey population trends were investigated in Nyathi to provide an indication of possible changes in prey populations. Large prey species dominated the adjusted diets of lions in Main Camp-Colchester and Nyathi. However, when comparing the GPS carcass-derived lion diet estimate to the combined lion diet estimate, small prey were underestimated more often than large prey in the GPS carcass-derived lion diet estimate. Missed feeding events were therefore a function of prey body size. In addition, missed feeding events were also representative of the lion diets based on carcasses, with the tendency for species more often consumed to be missed more often in the diet record. However, even though small prey species were underestimated, they represented the minority of species consumed by lions and were predominantly avoided by lions in Nyathi. Lion prey preferences thus did not correlate to the declines in small prey species in Naythi, suggesting other potential drivers are important for small population trends in Nyathi. Lion predation cannot be ruled out as a driver of the decline in small prey species in Main Camp, due to different ecological conditions (e.g. vegetation density) in Main Camp compared to Nyathi, during the observed small prey population declines. Lion prey preferences in Nyathi revealed fine-scale variations in species specific preferences by lions, as well as site-specific differences in prey preferences when compared to published lion prey preference meta-analyses. These findings suggest that metaanalysis studies should be used as a guideline from which hypotheses about local predatorprey interactions can be developed rather than as an absolute measure of prey preference.
- Full Text:
- Date Issued: 2017
Advanced high speed data and clock transmission over optical fibre for square kilometre telescope array
- Authors: Isoe, George Mosoti
- Date: 2018
- Subjects: Very large array telescopes -- South Africa , Semiconductor lasers Optical communications Optical amplifiers
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/30375 , vital:30935
- Description: There is an ever present need from Internet users for more bandwidth. This is manifested by continuous increase in bandwidth demanding applications such as 5G wireless, new end user consumer links like thunderbolt, video conferencing, high definition video-on-demand transmitted over the Internet and massive data transfers required with and within data centres for backup, storage and data processing in cloud computing. Fibre optic communications technologies are playing a pivotal role in communication, being a major enabling technology in our increasingly Internet-centric society. As network services continue to become more dynamic and diverse, Internet service providers are faced with a challenge of cost reduction in the transmission network, power and spectral efficiency as well as scalability of the optical network infrastructure to support incremental expansions and virtual machines. Intelligent design of terrestrial optical networks to allow for simultaneous signal transmission through shared network infrastructure, and the use of low cost, power efficient, high bandwidth transmitters such as vertical surface emitting lasers (VCSELs) as well as exploitation of spectral efficient in-complex advanced modulation formats is a viable approach to this situation. In this study, techniques for spectral efficiency upgrade and simultaneous transmission of data signal, reference frequency (RF) clock signal and pulse-per-second (PPS) over shared infrastructure have experimentally been optimized in a laboratory environment for adoption in next-generation telescope array networks such as the Square Kilometre Array (SKA), time keeping systems such as banking systems, Coordinated Universal Time(UTC) timing and Global Positioning Systems (GPS), as well as high capacity spectral efficient short reach optical fibre networks such as data centres. This work starts by experimentally optimizing VCSEL technology for simultaneous transmission of 10 Gbps data and 1.712 GHz RF clock signal over a single G. 655 optical fibre of length 24.75 Km at different channel spacing and different propagation direction for implementation in a cost effective next-generation telescope array network. The wavelength tuneability property of VCSEL transmitters allows for wavelength adjustment, a key requirement for simultaneous data and RF clock signal transmission over a single optical fibre. A receiver sensitivity of -19.19 dBm was experimentally achieved at back-to-back analysis. A 24.75 Km of simultaneous data and RF clock signal transmission performed at 0.4 nm channel spacing introduced a transmission penalty of 1.07 dB and 1.63 dB for counter and co-propagation scheme respectively. This work mainly utilized direct modulation and direct detection using a positive intrinsic negative (PIN) due to its simplicity and cost effectiveness. A novel modulation technique for simultaneous data and polarization-based pulse-per-second timing clock signal transmission using a single VCSEL carrier is experimentally demonstrated. Two signal types, a directly modulated 10 Gbps data signal and a polarization-based pulse per second (PPS) clock signal are modulated onto a single mode 10 GHz bandwidth VCSEL carrier at 1310 nm. Spectral efficiency is maximized by exploiting the inherent orthogonal polarization switching of the xiv VCSEL with changing bias in transmission of the PPS signal. A 10 Gbps VCSEL transmission with PPS over 11 Km of G.652 fibre introduced a transmission penalty of 0.52 dB. The contribution of PPS clock signal to this penalty was found to be 0.08 dB. A technique for simultaneous directly modulated data and phase modulated reference clock signal transmission over a signal channel in wavelength division multiplexing (WDM) solutions is experimentally demonstrated. This is to prepare solutions to the ever-increasing demand over gigabit/s, terabit/s and gigahertz capacities in WDM-based terrestrial optical fibre transmission systems such as telescope array networks. a total capacity of 30 Gbps (310 Gbps) data and 12 GHz ( 4 3 GHz) reference clock signal are multiplexed at a channel spacing of 100 GHz and simultaneously transmitted over a single mode G.655 fibre of length 24.73 Km. The recovery of the phase modulated RF clock signal using a differential delay line interferometry technique is experimentally demonstrated. A 625 Gbps (2525 Gbps) DWDM data transmission system is further implemented in simulation by multiplexing 25 channels at 25 Gbps per channel using 50 GHz channel spacing. A four level pulse amplitude modulation (4-PAM) data modulation format employing VCSELs is experimentally demonstrated for adoption in high bitrate networks such as big data science projects and data centre networks. 4-PAM offers a good trade-off between complexity, efficiency, reach, and sensitivity. A software defined digital signal processing (DSP) receiver is designed and implemented in MATLAB to recover the transmitted 4-PAM data signal cost effectively without the necessity of costly receiver hardware. A novel technique for maximizing carrier spectral efficiency through simultaneous 20 Gbps 4-PAM data and phase modulated 2 GHz RF clock signal transmission on a single mode 10 GHz bandwidth VCSEL carrier at 1310 nm is experimentally demonstrated for the first time to the best of our knowledge. Data transmission and clock stability performance of the designed high spectral efficient VCSEL-based link network is evaluated through BER curve plots, phase noise measurements and Allan variance analysis respectively. VCSEL-based Raman amplification is experimentally demonstrated as a viable approach for RF clock signal distribution in extended reach astronomical telescope array networks and other extended reach terrestrial optical fibre network application. This is achieved by adopting two pumping techniques namely forward pumping and backward pumping. A maximum on off gain of 5.7 dB and 1.5 dB was experimentally attained for forward pumping and backward pumping at 24 dBm pump power respectively, while a maximum 100.8 Km fibre transmission achieved experimentally. In summary, this study has successfully demonstrated in-complex, spectral efficient, low cost and power efficient simultaneous data signal, reference frequency (RF) clock signal and pulse-per-second (PPS) transmission techniques over shared network infrastructure. Simultaneous transmission of data, RF clock and PPS timing signal is relevant in nextgeneration telescope array networks such as the Square Kilometre Array (SKA), time keeping systems such as banking systems, Coordinated Universal Time (UTC) timing and Global Positioning Systems (GPS), as well as high capacity spectral efficient short reach optical fibre networks such as data centres.
- Full Text:
- Date Issued: 2018
Advances in platinum-amine chemotherapeutic agents : their chemistry and applicationc
- Authors: Jaganath, Yatish
- Date: 2009
- Subjects: Coordination compounds , Antineoplastic antibiotics , Cancer -- Chemotherapy
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10446 , http://hdl.handle.net/10948/d1021222
- Description: The research conducted in this study focussed on advancing the knowledge database of diamineplatinum complexes on two frontiers: 1) the development of novel anticancer complexes, and 2) improvements in their synthetic chemistry. Novel square-planar dichloro and oxalato platinum(II) complexes were synthesized as potential anticancer agents in accordance with a comprehensive set of factors identified as being significant in optimizing such action. The nonleaving ligands consisted of asymmetric chelating chiral diamines of the form 1- (1-R-imidazol-2yl)(R')methanamine (R representing methyl, butyl and R' methyl, phenyl). The complexes were characterized by a host of spectral, thermal and crystallographic techniques. In addition, the stabilities of the complexes were monitored in aqueous and saline solutions. Cytotoxicity screening on three cultured cancer cell lines (MCF-7, HeLa and HT29) indicated the compounds, present as their respective racemates, to have rather modest activities relative to cisplatin; with complexes having the smallest substituents, R,R' = methyl, being most active. In recognition of the limitations of traditional silver-based syntheses of oxalatoplatinum(II) complexes, innovative non-silver methods were developed using the well known cancer drug, oxaliplatin, (trans-R,R-1,2- diaminocyclohexane)oxalatoplatinum(II), as a prototype. These involved direct ligand exchange reactions of the dichloro precursor, (trans-R,R-1,2- diaminocyclohexane)dichloroplatinum(II), with tetrabutylammonium oxalate in essentially non-aqueous solvents. A 90:10 mixture of isoamyl alcohol (3-methyl- 1-butanol):water, proved to be a promising solvent, enabling the recovery of pure oxaliplatin (~98 percent) after 9 hours at 88 °C in yields of up to 86 percent. In light of the perceived unique mode of anticancer action available to mononitroplatinum(IV) complexes (i.e. their STAT3-binding potential), octahedral diamineoxalatoplatinum(IV) complexes containing axially-coordinated nitro and halo co-ligands were synthesized and extensively characterized. Electrochemical studies revealed trends in reduction potential which could be correlated to structural / chemical traits of the coordinated diamine and axial ligands. The similarities of the determined cytotoxicities of the platinum(IV) compounds and their respective platinum(II) analogues, implicated reduction as a means of activation of the platinum(IV) complexes.
- Full Text:
- Date Issued: 2009
Aerial optical fibres in telecommunication systems : SOP and PMD monitoring, and tolerance of modulation formats
- Authors: Ireeta, Winston Tumps
- Date: 2010
- Subjects: Optical communications , Fiber optics
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10542 , http://hdl.handle.net/10948/1478 , http://hdl.handle.net/10948/d1012894 , Optical communications , Fiber optics
- Description: The topic of this thesis is aerial optical fibres in telecommunication systems: state of polarization (SOP) and polarization mode dispersion (PMD) monitoring and tolerance of modulation formats. Errors in optical fibre telecommunication systems are introduced when these polarization effects (SOP and PMD) change. These changes are so intense especially in aerial optical fibres. Part of the backbone of South Africa’s national grid includes long distances of aerial optical fibre between transmission exchange stations. The work in this thesis can be divided into three parts which all deal with the major aspects of PMD in deployed aerial optical fibres: characterization, environmental effects plus other perturbations, and tolerance of different modulation formats. In our work, SOP and PMD field measurements revealed that they both fluctuate more rapidly in deployed aerial optical fibres especially on windy and hot days. The SOP and PMD changes in the aerial optical fibres showed a significant correlation with these environmental parameters. SOP and PMD are stochastic in nature due to changes in the properties of the optical fibres and its positions because of both intrinsic and extrinsic perturbations. In our work, with only 184 PMD values measured and obtained by use of the FTB-5700 single-ended dispersion analyzer, the predicted theoretical Gaussian fit was obtained with a mean of 0.47 ps and standard deviation of 0.08 ps. This small standard deviation was justification for its robustness and accuracy. The statistical distributions for first-order polarization mode dispersion (FO-PMD) and second-order polarization mode dispersion (SO-PMD) for the first time were experimentally confirmed when measured using the FTB-5700 single-ended dispersion analyzer instrument for deployed aerial optical fibres. We were also able to determine the time scale over which to compensate FO-PMD in deployed aerial fibres using the directional time drift autocorrelation function method. It is slightly higher than 390 s for SOP measurements made on a particular windy and hot day. This is due to the fact that the changes of the PMD vector are known to be slower than the SOP changes. vi We also investigated the theoretical statistical distribution that corresponds to output SOP variations. The SOP variations can either be with wavelength (for buried fibre) or with time (for aerial fibre). Our results showed that the statistics of the relative SOP changes approached the distribution proposed by Foschini et al. (2000). Advanced optical modulation formats have become a key ingredient in the design of modern state-of-the-art wavelength-division-multiplexed (WDM) optical transmission systems. In our work, we investigated which of these advanced modulation formats is best suited for the South African network especially on systems that have links of aerial optical fibres. Keywords: aerial optical fibre, polarization mode dispersion (PMD), principal states of polarization (PSP), state of polarization (SOP), first-order PMD, second-order PMD.
- Full Text:
- Date Issued: 2010
Agribusiness challenges to effectiveness of contract farming in commercialisation of small-scale vegetable farmers
- Authors: Khapayi, Musa
- Date: 2017
- Subjects: Farms, Small -- South Africa -- Eastern Cape , Agriculture -- Economic aspects -- South Africa -- Eastern Cape , Agricultural industries -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: http://hdl.handle.net/10948/13981 , vital:27363
- Description: The spread of contract farming in South Africa in recent years has provoked an ideological debate in literature. Linking small-scale vegetable farmers with lucrative agricultural markets through agribusiness value chains is seen as one of the foremost emerging agricultural practices to develop the subsistence farming sector into a mainstream economic sector – thereby revitalising the rural economy and alleviating poverty levels in the developing rural areas of South Africa. However, the challenges agribusiness and small-scale farmers experience in contract farming engagement and the prospects for enhancing the inclusion of small-scale farmers into modern value chains remain open to debate – two decades after transition to democracy. Yet the factors and mechanisms influencing the effective application of contract farming in the transition to commercial farming by small-scale farmers have not been thoroughly explored in South African research. Despite the efforts and the substantial investments made and the various policies and initiatives instigated to fast-track the linkages of small-scale farmers into high-value markets, the success stories of previously disadvantaged farmers operating in commercial agri-food chains are rare. Given the millions of small-scale farmers in former homelands alone, the negligible number of small-scale farmers successfully operating in commercial agri-food chains shows that the objectives to enable small-scale farmers to improve their livelihoods through participation in commercial agri-food chains have not yet been met. The broad objectives of the study were therefore to investigate the agribusiness challenges inherent in contract farming and the conditions and incentives required by agribusiness firms to engage small-scale vegetable farmers in contract farming programmes. Furthermore, the study examined the role played by the South African government to reduce the high transaction costs incurred by agribusinesses when engaging small-scale farmers in contractual arrangements. The Amathole and Sarah Baartman (formerly Cacadu) district municipalities in the Eastern Cape Province of South Africa were chosen as the composite survey area for this study. A predominantly qualitative research approach was applied to gather data on the phenomena under study. The following methodologies and research instruments and tools were selected. Firstly – as the secondary component of the research – a systematic review of literature to date was conducted to guide the empirical research and primary methodology. Secondly, the empirical component of the study comprised a questionnaire survey, unstructured interviews and focus group discussions. The questionnaire survey was used to collect data from the agribusiness firms in the area surveyed concerning the following aspects: the significant determinants of contract farming, the incentives required by the agribusiness firms to engage small-scale vegetable farmers in their contract farming programmes and the challenges faced by agribusiness firms in their interaction with small-scale farmers in contractual arrangements. Unstructured interviews were used to gather data from officials at each of the three levels of government – the Department of Rural Development and Land Reform nationally, Department of Agriculture and Land Reform provincially and (at local government level) two district municipalities – on the role played by government to reduce the high transaction costs incurred by agri-firms when procuring agricultural raw materials from small-scale vegetable farmers. Focus group discussions were conducted with small-scale farmers regarding their perspective on working with agribusiness firms and to establish the distinguishing characteristics of small-scale farmers in the area surveyed. Relevant policy documents collected from two of the three representative groups of the study population, i.e. agribusiness personnel and government officials, provided the essential context. The study revealed a limited number of contract farming business linkages between small-scale vegetable farmers and agribusiness firms in the survey area. Those that do exist are problematic to both the agribusiness firms and the small-scale farmers. It emerged that the contract farming environment in the area surveyed is highly polarised and characterised by a fundamental conflict of interest between agribusiness and farmer. Among the divergent key factors inhibiting contract farming engagement were a lack in terms of quality seeds, trust, entrepreneurial skills and formal contract agreements. Asset endowment (both land and non-land assets) was found to be significant pre-selection determinants in the farmer’s capacity to be contracted. Access to innovative technology, as well as government incentives such as production inputs, were found to be critical to agribusiness firms to engage smallscale farmers in their contract farming programmes. Government assistance in terms of high transaction costs to agribusiness firms working with large groups of small-scale farmers was found to be essential but inadequate under current policy. This impacts directly on the effectiveness and promotion of contract farming. Furthermore, the current results corroborate the findings of numerous South African studies in the vast body of worldwide research. Firstly, lack of land and non-land assets continue to be major impediments to the direct participa-tion of small-scale farmers in contract farming programmes and, secondly, the transaction and market information costs incurred by agribusiness prevent the participation of less endowed farmers in contract farming programmes. Conducted within the interpretivist paradigm, the explorative research identified wide-ranging challenges in the relationship between agri-business and small-scale farmers which directly impact the effective-ness of contract farming as a development and agrarian reform strategy. Despite their problematic relationship, however, agribusiness and small-scale contract farmers were in agreement that the government needs to expand its support for agri-firms to incentivise greater numbers of small-scale farmers having the opportunity to achieve commercial status through contract farming. The study therefore recommends a collaborative partnership between private firms and government, with state support through revised policies and development programmes. These amendments are crucial to enhancing the engagement of small-scale vegetable farmers in lucrative agri-food chains.
- Full Text:
- Date Issued: 2017
Algorithms for the solution of the quadratic programming problem
- Authors: Vankova, Martina
- Date: 2004
- Subjects: Quadratic programming , Nonlinear programming , Algorithms
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:11086 , http://hdl.handle.net/10948/348 , Quadratic programming , Nonlinear programming , Algorithms
- Description: The purpose of this dissertation was to provide a review of the theory of Optimization, in particular quadratic programming, and the algorithms suitable for solving both convex and non-convex quadratic programming problems. Optimization problems arise in a wide variety of fields and many can be effectively modeled with linear equations. However, there are problems for which linear models are not sufficient thus creating a need for non-linear systems. This dissertation includes a literature study of the formal theory necessary for understanding optimization and an investigation of the algorithms available for solving a special class of the non-linear programming problem, namely the quadratic programming problem. It was not the intention of this dissertation to discuss all possible algorithms for solving the quadratic programming problem, therefore certain algorithms for convex and non-convex quadratic programming problems were selected for a detailed discussion in the dissertation. Some of the algorithms were selected arbitrarily, because limited information was available comparing the efficiency of the various algorithms. Algorithms available for solving general non-linear programming problems were also included and briefly discussed as they can be used to solve quadratic programming problems. A number of algorithms were then selected for evaluation, depending on the frequency of use in practice and the availability of software implementing these algorithms. The evaluation included a theoretical and quantitative comparison of the algorithms. The quantitative results were analyzed and discussed and it was shown that the results supported the theoretical comparison. It was also shown that it is difficult to conclude that one algorithm is better than another as the efficiency of an algorithm greatly depends on the size of the problem, the complexity of an algorithm and many other implementation issues. Optimization problems arise continuously in a wide range of fields and thus create the need for effective methods of solving them. This dissertation provides the fundamental theory necessary for the understanding of optimization problems, with particular reference to quadratic programming problems and the algorithms that solve such problems. Keywords: Quadratic Programming, Quadratic Programming Algorithms, Optimization, Non-linear Programming, Convex, Non-convex.
- Full Text:
- Date Issued: 2004
Alternative pine species/hybrids for the Cape timber growing regions of South Africa
- Authors: Van der Hoef, André
- Date: 2020
- Subjects: Species -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/47613 , vital:40258
- Description: Pinus radiata has been the preferred commercial sawtimber species for the Cape forestry region for many years. Since the introduction of Fusarium circinatum, and the susceptibility of P. radiata to this disease, the sustainable production of this pine species for the Cape has been negatively impacted due to poor survival in the nursery and in field plantings. For this reason, a number of additional pine species and hybrids have been established in the Cape region of South Africa since 2006 to identify taxa that would perform as well as or better than P. radiata. Three research trials were implemented on contrasting sites that contained eight common species/hybrids treatments that included P. elliottii, P. elliottii x P. caribaea, P. radiata, P. patula x P. greggii var. australis, P. patula x P. oocarpa, P. patula x P. tecunumanii (HE), P. patula x P. tecunumanii (LE) and P. tecunumanii (HE) x P. oocarpa were established at Witelsbos, Kruisfontein and Garcia across diverse soil types, drainage and climate conditions in the Cape. Survival, growth data and tree morphology (forking, foxtails, broken tops and stem form) were assessed at five years of age and individual tree volume was calculated. Five year results indicate that on the waterlogged site at Witelsbos P. elliottii and its hybrid with P. caribaea was best in terms of productivity, at the dry site of Garcia, P. taeda and P. elliottii demonstrated promise, and at Kruisfontein, the most fertile site, P. elliottii x P. caribaea, P. patula x P. tecunumanii (LE) and P. maximinoi were found to be promising alternatives to P. radiata. Wood properties were assessed at Kruisfontein at six-years of age. Basic density and Modulus of Elasticity (MOE) were found to be significantly different for the various species/hybrids. Pinus patula x P. tecunumanii (LE), P. patula x P. greggii (S), P. maximinoi and P. patula x P. tecunumanii (HE) were all significantly better than P. radiata, which would suggest that these taxa would have similar or superior wood strength over P. radiata, the preferred sawtimber species for the Cape region. Only P. tecunumanii (HE) x P. oocarpa had a higher basic density than P. radiata, but not significantly different. Species that had similar basic density were P. patula x P. greggii (S), P. taeda and P. tecunumanii (LE) x P. caribaea. Although P. elliottii x P. caribaea had the highest volume at Witelsbos and Kruisfontein, the timber qualities were the worst, suggesting that some breeding is needed to improve this hybrid to be an acceptable sawtimber species. From this study, several potential alternative species/hybrids have been identified that are tolerant to the F. circinatum pathogen and have acceptable growth and wood properties, compared to P. radiata.
- Full Text:
- Date Issued: 2020
Alternative products in the inhibition of te plant pathogen scleroyinia sclerotiorum on potato production
- Authors: Dhliwayo, Tererayi
- Date: 2008
- Subjects: Potatoes -- Diseases and pests
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10587 , http://hdl.handle.net/10948/941 , Potatoes -- Diseases and pests
- Description: White mold caused by Sclerotinia sclerotiorum attacks a wide host range of broad-leafed plants which includes potatoes. Current control is limited to the use of chemicals, but biological control has emerged as an eco-friendly alternative. For the study, 19 bacterial strains and 18 fungal strains obtained from soil samples taken from a potato field naturally infested with the pathogen S. sclerotiorum were tested for the effects on S. sclerotiorum mycelium growth and sclerotia viability in vitro. A total of eight bacterial strains and six fungal strains proved to be effective in the inhibition of S. sclerotiorum mycelium growth on PDA plate using a dual culture technique. These antagonistic microbes were six Bacillus subtilis, Bacillus pumilis, Bacillus marisflavi, Fusarium solani, Fusarium equiseti, Fusarium chlamydosporum, Aspergillus niger, Aspergillus insuetus and Penicillium citrinum. There was a significant difference (p<0.05) in the interaction between S. sclerotiorum mycelium growth and the time after inoculation with a S. sclerotiorum mycelium plug for both bacterial and fungal soil isolates. An additional sclerotia viability test was carried out using four of the eight antagonistic bacteria, and six of the antagonistic fungi. The results showed that two Bacillus species, namely B. pumilis and B. marisflavi can effectively reduce sclerotia viability. The other two bacteria (both B. subtilis), recorded low percentage reduction in sclerotia viability. As for the six antagonistic fungi, the viability test proved to be less effective in determining sclerotia viability. However, the result of this study supports the use of bio-control agents, not only because they are environmentally friendly, but because they are also an effective way of controlling the plant pathogen, S. sclerotiorum.
- Full Text:
- Date Issued: 2008
An adaptive user interface model for contact centres
- Authors: Jason, Bronwin Anastasia
- Date: 2008
- Subjects: Call centers -- Management , Customer services -- Management , Call centers -- Customer services
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10467 , http://hdl.handle.net/10948/989 , Call centers -- Management , Customer services -- Management , Call centers -- Customer services
- Description: Contact centres (CC), are the primary interaction point between a company and its customers and these are rapidly expanding in terms of both workforce and economic scope. An important challenge for today's CC solutions is to increase the speed at which CCAs retrieve information to answer customer queries. CCAs, however, differ in their ability to respond to these queries and do not interact with the computer user interface (UI) in the same way as they each have different capabilities, experience and expertise. Studies have provided empirical support that user performance can be increased when the computer UI characteristics match the user skill level. Adaptive user interfaces (AUIs) are the key to creating personalised systems. Their sole task is to provide an interface most suitable to users' needs whilst facilitating the users' varying skill levels. The aim of this research was to develop an AUI model for CCs to support and improve the expertise level of CCAs. A literature review of CCs, user expertise, AUIs and existing AUI models resulted in the proposal of an AUI model for CCs. The proposed AUI model was described in terms of its architecture, component-level and interface design. An AUI prototype was developed as a proof-of-concept of the proposed AUI model. A literature review on existing AUI evaluation approaches resulted in an evaluation strategy for the proposed AUI model. The AUI prototype was evaluated according to the evaluation strategy that was identified. User testing incorporating eye-tracking and a post-test questionnaire was used to determine the usefulness and usability of the AUI prototype. Significant results were found with regards to user satisfaction ratings, the learnability of the AUI prototype and its effectiveness. This dissertation makes an important contribution in the design of an AUI model that supports and improves the expertise level of CCAs. The model could be used to assist the development of CC applications incorporating AUIs. Future research is however needed to evaluate the effect of the proposed AUI model in a larger CC environment.
- Full Text:
- Date Issued: 2008
An analysis of soil properties associated with badland and gully erosion in rural catchments of the Ngqushwa District, Eastern Cape Province
- Authors: De Jager, Megan Joan
- Date: 2015
- Subjects: Soil mechanics -- South Africa -- Eastern Cape , Soils -- South Africa -- Eastern Cape -- Testing
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/3519 , vital:20438
- Description: Accelerated soil erosion holds strong links to excessive land degradation, socioeconomic problems and accelerated climate change, particularly in developing countries such as South Africa. An analysis of the properties of severely eroded soils is undertaken to determine which characteristic properties influence the erodibility of the soils at several gully and badland sites in three catchments of the Ngqushwa rural municipality, which is tagged as one of the area’s most severely affected by soil erosion and degradation in the Eastern Cape. Physical, biological and chemical properties of the soils were analysed, including aggregate stability, soil texture, organic matter- and carbon content, clay mineralogy, sesquioxide content as Fe2O3 and cation composition. The distribution of a number of these properties was also determined, particularly between erosion sites, along hillslope profiles and with depth. The study area comprises three catchments, namely Mgwalana, Bira and Gqora which share common soil parent materials, land use history, exhibit similar topography and advanced degree of erosion. A total of 63 soil samples were strategically collected from identified erosion zones and site controls devoid of active erosion; where stability was evident by means of vegetation cover and soil surface condition. Surface samples were collected above 30cm depth and subsurface samples at depths greater than 30cm. To determine the fate of carbon additional samples were collected from runon and sink zones at the Mgwalana catchment along a transect from top to bottom slope. Laboratory analyses was performed to determine the soil properties, whereby C content was measured by the dry combustion method, Fe2O3- and cation content by Atomic Absorption (AA) Spectrometer, texture by the separation method described by Schlichting, Blume & Stahr (1995), clay mineralogy by X-Ray Diffraction and organic matter content by conversion of total C. In addition to these properties being used to infer aggregate stability, the wet sieving method was also used for this purpose and for validation of the other soil properties. The results revealed that no one soil property has a greater influence on aggregate stability than the others, but rather that the stability of the soil is dependent on the combinations of these properties in the soil and the interactions that occur between them. Based on this, the results indicated greater stability for runon, sink and control samples, mainly in the topsoil, which were characterised by a relatively higher C- and organic matter content, loam texture and higher concentrations of Ca2+. Furthermore, the less stable eroded samples were characterised by a more clay rich texture particularly in the subsoil, relatively lower C- and organic matter contents and a greater sodicity due to higher concentrations of Na+. The least stable soils belonged to the Gqora catchment, which were found to consist of higher silt content in the topsoil and a higher Fe2O3 content in the subsoil. The clay mineralogy was relatively uniform across all catchments, comprising of primarily illite and secondly kaolinite. The sample with the highest sodicity in terms of ESP contained smectite clay in addition to illite and kaolinite which is assumed to contribute to this increased Na+ concentration. These findings aid in the conclusion that the chemical characteristics of the soils, in association with biological and, to a less extent, physical properties of the soil exacerbate the erosion problem initiated by the extrinsic contributors, such as climate and topography. Investigation into the fate of carbon on eroded lands revealed a topographically driven dynamic whereby the total carbon content was found to be greater at the top and middle slope positions as well as in the sink zone. These hillslope sections were found to have a lower slope gradient and slightly more pronounced concave shape to those sections with lower C values. These topographic variables influence the degree of gully erosion taking place at different hillslope sections, which tends to be greater where slope angle is increased and convexity exists, resulting in the removal of soil C at these positions and its deposition in areas of accumulation, namely the runon and sink zones of low angle concave slope sections. The findings of this research may be used to develop restoration and management strategies with the ultimate goal to reduce the soils vulnerability to erosion by enhancing those soil properties conducive to greater aggregate stability as determined in the present study.
- Full Text:
- Date Issued: 2015
An analysis of the influence of phosphorus poisoning on the exhaust emission after treatement systems of light-duty diesel vehicles
- Authors: Toral del Rio, Maria Isabel
- Date: 2007
- Subjects: Diesel motor -- Alternative fuels , Automobiles -- Pollution control devices , Automobiles -- Motors -- Exhaust gas , Motor fuels
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10405 , http://hdl.handle.net/10948/697 , Diesel motor -- Alternative fuels , Automobiles -- Pollution control devices , Automobiles -- Motors -- Exhaust gas , Motor fuels
- Description: Climate change has become a discussion topic of exponentially increasing urgency and importance amoung world leaders of all disciplines. These changes are brought about by the emission of so-called Greenhouse gases from various human activities. The primary cause of CO2 emissions is the burning of the Earth’s supply of nonrenewable natural fossil fuels like coal, oil and natural gas. The world first agreed on the prevention of “dangerous” climatic changes at the Earth Summit in 1992. The Kyoto Protocol of 1997 was the first step toward protection of the atmosphere and prescribes restrictions on emission pollutants. Since then the vehicle gas emissions are being controlled by means of different gas emissions norms, like the European Union Norm in Europe. The automotive manufacturers and suppliers are collectively working on reducing overall vehicle emissions. They are focusing on several different emission limiting possibilities, for example improved engine design, special fuel development and exhaust gas treatment systems. The exhaust gas treatment process requires continuous controlling and management of the exhaust gas emissions while driving a vehicle. Certain factors such as high emission temperatures have a negative influence on the life span of these systems. Their functionality and durability is also known to be reduced by the presence of chemical poisoning species like sulphur, phosphorus, zinc and calcium. The chemical poisoning species are produced during combustion of fuel and engine oil. They are therefore contained in the exhaust emissions and can poison the catalyst when passing over it. Phosphorous poisoning is particularly problematic and should be reduced considerably. This study involves the investigation of the phosphorous poisoning process and aims to provide clarity regarding the influences of different fuel and oil compositions on the severity of the process. Engine oil and biodiesel are two major sources of phosphorous poisoning. The phosphorus contained in biodiesel fuel is a natural component and can be minimized during the refining procedure. In contrast to others studies, the biodiesel fuel used during this project was SME (Soya Methyl Ester) with a 20% biodiesel content. This choice of fuel was made because of the increasingly important role that this type of biodiesel is playing in the European market and the future tendency to increase the percentage of biodiesel in the mixture with standard diesel fuel. The phosphorus contained in engine oil is a necessary additive to retain the antioxidant and anti-wear properties of the oil. This study examined the poisoning influences from the most commonly used phosphorus containing oil additive, Zinc Dithiophosphates (ZDDP), as well as a Zn-free, phosphorus containing anti-wear oil additive. This formulation provides information about the phosphorus poisoning process as caused by the engine oil in the absence of Zn in the oil additives. The results show how the phosphorus content in biodiesel fuel affects the functionality of the exhaust gas treatment systems and the importance of reducing the permitted content of phosphorus contained in the fuel. Reducing the phosphorus content in the fuel will conserve the functionality of the exhaust gas treatment systems during their operational life and thereby protect the environmental from emission pollutants. It also provides insight into the differences in the poisoning processes when the phosphorus deposited on the catalyst comes from biodiesel fuel and when it comes from the engine oil. Finally the results also illustrate the influence of different phosphorous forms contained in engine oil additives on the catalyst poisoning process. This information could be used for the development of new oil additive formulations.
- Full Text:
- Date Issued: 2007
An appraisal of warm temperate mangrove estuaries as food patches using zooplankton and RNA: DNA ratios of Gilchristella aestuaria larvae as indicators
- Authors: Bornman, Eugin
- Date: 2018
- Subjects: Mangrove swamps Fishes -- Larvae , Mangrove ecology , Zooplankton
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/17908 , vital:28481
- Description: Mangrove habitats are considered as the ideal fish nursery as they are known to increase the growth and survival of juvenile fishes by providing enhanced food availability and protection. However, most studies have focused on tropical mangroves with a few recent warm temperate studies finding conflicting results. Furthermore, the nursery value of South African mangroves to fishes remain understudied in subtropical areas, while warm temperate mangroves are yet to be evaluated. This study aimed to assess whether mangrove presence leads to any advantage to the larvae of an important estuarine resident fish species, Gilchristella aestuaria, by comparing the food patch quality of South African warm temperate mangrove and non-mangrove estuaries. Results indicate that larvae fed primarily on the dominant prey species, Pseudodiaptomus hessei, Paracrtia longipatella, and Acartiella natalensis. However, postflexion larvae consumed more of the larger species, P. hessei, within the two mangrove estuaries (16.09 %V in Nahoon and 13.79 %V in Xhora) than the two nonmangrove estuaries (12.20 %V in Gonubie and 7.05 %V in Qora), despite other prey species occurring at similar densities. Results indicate that mangrove habitats acted as sediment sinks, slightly reducing the turbidity of these estuaries which resulted in postflexion larvae actively selecting larger, more nutritious prey, which in turn, significantly increased their individual instantaneous growth rates (0.11 ± 0.21 Gi) when compared to postflexion larvae in non-mangrove estuaries (0.09 ± 0.12 Gi). This study found that mangrove presence was significantly related to postflexion larval densities when coupled with abiotic (such as temperature and turbidity) and biotic factors (such as predator-prey interactions). Understanding the spatial and temporal dynamics, predator-prey interactions as well as the growth and survival of G. aestuaria is particularly important as they are key zooplanktivores that are prey to other species in estuarine food webs.
- Full Text:
- Date Issued: 2018