Showing items 1 - 20 of 375

Your selections:

A framework for price tariffs in the costing structures of South African private hospitals

  • Authors: Botha, Gideon
  • Date: 2020
  • Subjects: Medical care, Cost of -- South Africa , Medical economics -- South Africa Medical care -- South Africa -- Cost control Cost accounting
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/50432 , vital:42167
  • Description: The increase of South African health care costs can be extrapolated into the global healthcare cost challenge, with various factors contributing to this problem. One of the factors viewed as being central to the rising cost of health care is the inability of health care provider organisations to accurately measure unit costs of resources used to treat a patient for their medical condition and patient outcomes. The measurement of an accurate unit cost and patient outcomes is imperative to improving value, which is seen as an improvement in outcomes for every rand spent. The determination of price tariffs and the price tariff payment model used to onward bill the price tariff for medical services have also been identified as having a central role in improving value in health care. In order for price tariffs to improve value, they should be reflective and be based on an accurate unit cost that reflects the cost of resources used to provide efficient and effective care for a patient’s medical condition. For the price tariff payment model to improve value, it needs to reward providers for delivering superior patient outcomes at a lower cost by making price tariffs contingent on achieving specified outcomes as well as incorporating performance payments or holdbacks based on outcomes achieved. This study provides a framework for price tariffs in the costing structures of South African private hospitals. Secondary research was conducted in the form of a comprehensive literature search in order to do an interpretative analysis of the strengths and weaknesses of the various combinations of unit costing models and price tariff payment models used to determine prices in private hospitals. The literature review was followed by primary research that involved three phases, all of which used a qualitative research approach. In Phase 1, primary data were collected using unobtrusive measures that consisted of a data request first, followed by unstructured interviews with representatives of Hospital A and Hospital B to obtain an analysis of the combinations of unit costing model and price tariff payment model used for a laparoscopic appendectomy. In Phase 2, data were collected by means of an unstructured interview with a surgeon describing a laparoscopic appendectomy procedure in detail and based on this process description, the approximate costs for the various resources that were sourced from different suppliers could be calculated. The data analysis and interpretation were done in three phases, with each phase having different research objectives. The data were first coded and then interpreted. In the first primary research phase, the combinations of unit costing models and price tariff payment models used by private Hospital A and Hospital B were evaluated. In the second phase, the recommended combination of unit costing model and price tariff payment model was applied to a hypothetical example and evaluated. In the final phase, based on the outcome of the first and second research phases, a combination of unit costing model and price tariff payment model for private hospitals was recommended. The results showed that the recommended combination of unit costing and price tariff payment model namely time-driven activity-based costing with the global fee price tariff payment model was the most appropriate to determine price tariffs in private hospitals when compared to the unit costing models and price tariff payment models used by Hospital A and Hospital B for a laparoscopic appendectomy. Furthermore, the recommended combination of unit costing model and price tariff payment model was found to be usable for the determination of price tariffs in the costing structures of private hospitals. The time-driven activity-based costing model and global fee price tariff payment model should be adopted or used as guidelines for determining price tariffs in private hospitals in South Africa. Price tariffs would be more transparent as they would reflect the actual resource cost of treating the patient and the resources used and treatment provided could then be assessed against the delivery value chain that charts the principal activities involved in a patient’s care for a medical condition to ensure that patient best-practice protocols are followed. The proposed framework enables the determination of price tariffs based on an accurate unit cost reflecting the actual resources used to provide efficient and effective care and also improve value for the patient.
  • Full Text:
  • Date Issued: 2020

A lean production approach to materials management in the Nigerian construction industry

  • Authors: Albert, Idowu
  • Date: 2020
  • Subjects: Materials management , Lean manufacturing Construction industry -- Nigeria
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/46008 , vital:39408
  • Description: The Nigerian Construction Industry faces a problem of poor materials management that leads to, among other things, materials waste, poor quality of work, poor materials flow, project delay and cost overrun. Overcoming these challenges, requires the rethinking the current modus operandi of the Nigerian construction industry. One such method that has been espoused as having potential to improve materials management, and associated challenges is ‘lean production’. This research aimed at deciphering the lean approach to production management with a view of extracting its utility in enhancing materials management in the construction industry. The qualitative method of research inquiry that is rooted in the phenomenological paradigm was employed. The research activities included a comprehensive review of the related literature and study of selected cases. Abuja, the Federal capital territory of Nigeria was the selected geographical scope of the research. Ten case studies were purposefully selected for the study. The research instrument was a tick box used for direct observation. The study revealed that poor materials management has a negative effect on the materials management plan. Moreover, mixing of waste at the site, negates the effort for identification of materials waste streams, and makes it difficult to account for materials waste, as well as implementing a materials waste management policy on sites. The research also found that poor materials management has a significant effect (high, moderate or low) on materials waste, quality of work, materials flow, productivity, project delay, project profitability and accounting for materials. The research has developed a conceptual model for a lean production approach to materials management based on the results and informed by the theoretical framework. The study has achieved its aim of establishing an understanding of the lean production approach to materials management in the Nigerian construction industry. The study recommends that construction professionals should be well informed on the effects of poor materials management.
  • Full Text:
  • Date Issued: 2020

A management model for human settlements: a case study of Nigeria and South Africa

  • Authors: Adeniran, Adeleye Ayoade
  • Date: 2020
  • Subjects: Human settlements -- Nigeria , Human settlements -- South Africa Sustainable development
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/45985 , vital:39403
  • Description: Persistent depreciating human settlements is a global challenge, particularly in developing countries and this challenge contributes to the continuously increasing housing gap, despite several novel policies and programmes. Although there is a dearth of research-based literature on human settlements management, studies show that property management, Facility Management, housing management and urban management impact the sustainability of all these built environment milieus which form part of the human settlements’ sub-components. This research aimed at altering the afore-said challenge by exploring the management of human settlements in Nigeria and in South Africa. Philosophically, the research is pragmatic, and it rests on positivist deductive reasoning. The methods used for data collection include a review of literature, collection of archival records, and empirical studies of purposively selected professionals and stakeholders involved in human settlements’ management in Nigeria and in South Africa. The findings indicate that existing human settlements in the case studies are “good” and “acceptable” with the majority adopting an outsourced method of management. Furthermore, the lack of maintenance records, the deficiency in policy monitoring and the training of management and maintenance personnel were the three highest ranking factors indicated to be affecting human settlements management. Moreover, an inhabitant’s income, the time available for management, professional expertise and technology employed for management are recognised as the critical sustainability sub-factors affecting human settlement management. The factor analysis established ownership, human resource and capital, social, legal, technology, economic, physical and environmental factors as vital and very significant in achieving sustainable management of human settlements. The study recommends the professionalisation of the field of human settlements as well as a formulation of management policy among others. The study developed a management model for human settlements, and it advocates that human settlements managers, owners and organisations should apply the model in this study, to improve their human settlement management practices, so as to achieve sustainability, and in essence, Sustainable Development Goal 11. It is hoped that the suggested management model will influence human settlement policy development and review, the designing of human settlement management programmes including the framework for their ongoing monitoring and evaluation. The study furthermore contributes to the development of housing and human settlement curricula and evolving human settlement research in both developed and developing countries.
  • Full Text:
  • Date Issued: 2020

A scheduling model for the charging of electric vehicles in photovoltaic powered smart microgrids

  • Authors: Nyumbeka, Dumisani Joshua
  • Date: 2020
  • Subjects: Electric vehicles , Photovoltaic power generation Photovoltaic power generation -- Developing countries
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/49259 , vital:41615
  • Description: Electric vehicles (EVs) have emerged as a viable option to advance sustainable mobility, but adoption is still relatively low. This has been largely due to the limited range one can travel on a single charge, leading to range anxiety, longer charge cycles and long wait times at charging stations. One solution to range anxiety is to erect charging stations on major roads and urban centres. There is also a lack of real-time information regarding the state of charging stations and charging ports in existing charging infrastructure. To increase the benefit of using EVs, using renewable energy sources, such as photovoltaics (PV) to power EVs, can further increase the benefit of reduced carbon footprint. The main research objective was to design a Charge Scheduling Model for charging EVs using a PV-powered smart microgrid (SMG). The model addresses the lack of an integrated platform where EV drivers can schedule when and where to charge their EVs. The model also reduces the negative effects of the adoption of EVs, including range anxiety. The Charge Scheduling Model was developed using the Design Science Research (DSR) methodology and was the main artefact of the study. A literature study was conducted of research related to SMGs, renewable energy, EVs and scheduling, to identify shortcomings that currently exist in EV charge scheduling (EVCS), and to identify the requirements of a potential solution. The literature study also identified the hard and soft constraints that are unique to EVCS, and the available energy in the SMG was identified as one of the hard constraints. Therefore, an Energy Forecasting Model for forecasting energy generated in PV-powered SMGs was required before the Charge Scheduling Model could be designed. During the first iteration of the design and development activities of DSR, four models were designed and implemented to evaluate their effectiveness in forecasting the energy generated in PV-powered SMGs. The models were Support Vector Regression (SVR), K-Nearest Neighbour (KNN), Decision Trees, and Multilayer Perceptron. In the second iteration, the Charge Scheduling Model was designed, consisting of a Four Layered Architecture and the Three-Phase Data Flow Process. The Charge Scheduling Model was then used to design the EVCS prototype. The implementation of the EVCS prototype followed the incremental prototyping approach, which was used to verify the effectiveness of the model. An artificial-summative evaluation was used to evaluate the design of the Charge Scheduling Model, whereas iterative formative evaluations were conducted during the development of the EVCS prototype. The theoretical contribution of this study is the Charge Scheduling Model, and the EVCS prototype is the practical contribution. The results from both evaluations, i.e. the Energy Forecasting Model and the Charge Scheduling Model, also make a contribution to the body of knowledge of EVs.
  • Full Text:
  • Date Issued: 2020

A strategy towards implementing standardised data structures in municipal information systems

  • Authors: Koekemoer, Silma Marguerite
  • Date: 2020
  • Subjects: Data structures (Computer science) , Municipal government -- Data processing Public administration -- Data processing Management information systems
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/46064 , vital:39482
  • Description: The regulation pertaining to a Standard Chart of Accounts (SCOA) for Municipalities was published in 2014 and is applicable to all 257 municipalities and municipal entities in South Africa. The regulation represents a data classification framework or structure and affects all financial management and internal control systems (FMICS) used by municipalities and municipal entities, and affects key business processes within these organisations. Compliance with the SCOA regulation means that the full municipal accountability cycle should accommodate all seven of the SCOA segments, from the budget through transacting and reporting at the transaction level, with all seven of the segments being embedded in the master data table of the municipal FMICS. While the change to technology and systems may be self-evident, the related business change should not be underestimated. This information technology (IT) driven organisational change across the whole municipal environment represents the research topic and key objective of this research study, namely, a strategy towards implementing standard data structures in municipal IT systems. The study followed a pragmatic philosophy using diagnostic reasoning based on an inductive approach, multiple action research methods and a descriptive case study to derive the proposed implementation strategy. The research subjects, which included 25 pilot municipalities, were studied for the duration of the pilot implementation of the strategy with the objective of identifying and utilising the lessons learnt from their experience to fast track the rollout of the strategy to non-pilot municipalities. The study was limited to the local government environment and to South Africa as a geographic area and involved an accidental sample aligned to the implementation project under investigation. The proposed implementation strategy was, however, of a generic nature and is therefore applicable to any other institution or environment engaged in a similar implementation project. The main contribution of the study is an implementation strategy for standard data structures in municipal financial information systems and which consists of seven diagnostics, 17 guiding policies and 48 coherent actions. The strategy was developed and refined during six cycles of data collection, which were conducted at 25 municipalities actively involved in implementing of the standard data structures. The secondary contributions of the research study include three conference papers and one submission to an academic journal.
  • Full Text:
  • Date Issued: 2020

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 transportation management framework for the Polokwane local municipality during Zion Christian Church (ZCC) Easter weekend pilgrimage

  • Authors: Mathebula, Andrew Mabila
  • Date: 2020
  • Subjects: Transportation -- Management , Urban transportation -- Planning Urban transportation -- Management Christian pilgrims and pilgrimages
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/46152 , vital:39509
  • Description: The study investigated the impact of the high volume of vehicular traffic on pilgrims and the community during the Zion Christian Church (ZCC) Easter weekend pilgrimage. The researcher adopted an interpretivist research philosophy, and thus attempted to understand policy, planning, and management of the ZCC Easter pilgrimage through meanings that municipal officials assign to them. The study employed the action research approach by collaborating with the Polokwane Local Municipality (PLM) with a view to evolving lasting solutions to traffic congestion during the Easter weekend. The researchers used the seven-step model proposed by Van Tonder and Dietrichsen (Van Tonder and Dietrichsen, 2008). The justification of the model is that it is aligned with the action research model of Organisational Development (OD). It requires that a diagnosis process should be collaborative and participative towards offering solutions to organisational challenges as opposed to imposing a unilateral theoretical generated solution. This model also fits the ontological stance of the researchers which assumes that reality is co-constructed through engagement with other stakeholders. The researcher conducted semi-structured individual and focus groups discussion (FGD) using openended guides. The data from the informants were collected until a point of saturation. In addition to facilitation FGD discussion, the researcher made his own personal reflection of the participatory action research (PAR). A content analysis method was used to synthesise the qualitative data. The contents were extracted from transcribed interviews. The researcher carefully reviewed the notes several times and coded the notes independently. After that, the researcher coded the codes with each other for any potential contradiction. These codes were converted into themes and sub-themes. The qualitative content analysis process, led by the researcher, was both inductive and deductive. Prior to the inductive process, the researcher listened carefully to the audio recordings transcriptions to get a general understanding of participants’ experiences. The findings indicate that the South African transportation planning approach is ossified and divorced from reality. There is a lacuna to address peak traffic challenges during the Easter weekend and the festive season. It is notable that the government-led seasonal road safety campaigns such as ‘Arrive Alive’ are curiously inadequate to address peak traffic and road accidents challenges in South Africa during the ZCC Easter pilgrimage. The transportation management framework for the PLM as well as a peak traffic standard were developed as part of the study recommendations. These recommendations augur a shift to transport planning in South Africa.
  • Full Text:
  • Date Issued: 2020

Commercial maritime higher education needs in South Africa

  • Authors: Allison, Lee-Anne
  • Date: 2020
  • Subjects: Education, Higher -- Curricula , Education, Higher -- Research Merchant marine Shipping -- Economic aspects
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/50350 , vital:42111
  • Description: Seaborne cargo trade accounts for over 80% of the physical volume of global trade. Maritime transport thus fulfils an integral function in the economy of the world. South Africa generates approximately 3.5% of the world’s seaborne trade by value and 1.61% by tonnage; but the business of shipping all that cargo is undertaken by foreign firms. Operation Phakisa, the Comprehensive Maritime Transport Policy and the South African Maritime Road Map, in pursuance of the National Development Plan, aim to revive the commercial maritime sector. In order to meet the demand for the skills and innovative abilities sought at executive and managerial levels in the commercial maritime sector, higher education in the knowledge of maritime business is increasingly becoming a prerequisite. Investment in higher education of quality and relevance in the maritime field would contribute to achieving the goals of the government for harnessing the potential of South Africa’s blue economy. The literature is researched in order to establish an authoritative view that the knowledge and the inspiration for entrepreneurial activity in the maritime sector can be imparted through higher education; and for example, that a viable shipping sector can contribute to the growth of a country’s economy. The South African maritime sector is then described. The commercial maritime higher education available at universities and other institutions of higher learning in South Africa, as well as in other African countries and elsewhere in the world, is examined, in order to be able to identify the degree and diploma courses available. Maritime courses imply not only the content of the educational material, but also the method whereby the knowledge is instilled in learners, and which extends well beyond the classroom. A survey, by way of the personal interviews of leaders in maritime business, maritime government affairs, and academics teaching maritime topics, is then undertaken to ascertain their views on the education required to promote the maritime sector in South Africa, using the list of subjects available for study worldwide, to assist their choice. The literature research and the interview survey by design also enable the secondary aims of the study to be achieved. Those aims include determining how awareness of the maritime domain could be raised and how co-operation between academia, business and government, known as the triple helix could be organised, to promote the growth of the maritime sector. The results of the survey are analysed and tabulated, in order to illustrate the extent of the agreement between those interviewed and the conclusions reached. These conclusions establish: that the commercial maritime education currently available in South Africa, is inadequate to meet the aim of the government to the sector; that a post-graduate degree in the specified maritime studies incorporating a period of internship, and following on a first degree in business subjects, is required; that a triple helix of co-operation between academia, business and the government is essential to grow the commercial maritime sector in which South African entrepreneurs educated in such business will have the advantage; that greater awareness of the maritime domain is essential in South Africa if entrepreneurship in maritime business is to be cultivated; and that such awareness can be cultivated in various ways; but it should start by including more maritime topics in the current school curricula.
  • Full Text:
  • Date Issued: 2020

Data transport over optical fibre for ska using advanced modulation flexible spectrum technology

  • Authors: Dlamini, Phumla Patience
  • Date: 2020
  • Subjects: Fiber optics
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/50666 , vital:42329
  • Description: Flexible Spectrum Dense Wavelength Division Multiplexed (DWDM) optical fibre networks are next-generation technology for handling extremely high data rates of the kind produced by MeerKAT and SKA.We optimise the flexible spectrum for real-time dynamic channel wavelength assignment, to ensure optimum network performance. We needed to identify and develop novel hardware and dynamic algorithms for these networks to function optimally to perform critical tasks. Such tasks include wavelength assignment, signal routing, network restoration and network protection. The antennas of the Square Kilometre Array (SKA) network connect to the correlator and data processor in a simple point-to-point fixed configuration. The connection of the astronomer users to the data processor, however, requires a more complex network architecture. This is because the network has users scattered around South Africa, Africa and the whole world. This calls for upgrade of the classical fixed wavelength spectrum grids, to flexible spectrum grid that has improved capacity, reliable, simple and cost-effectiveness through sharing of network infrastructure. The exponential growth of data traffic in current optical communication networks requires higher capacity for the bandwidth demands at a reduced cost per bit. All-optical signal processing is a promising technique to improve network resource utilisation and resolve wavelength contention associated with the flexible spectrum. Flexible Spectrum Dense Wavelength Division Multiplexed (DWDM) optical fibre networks are next-generation technology for handling extremely high data rates of the kind produced by MeerKAT and SKA. Each DWDM channel is capable of 10 Gbps transmission rate, which is sliceable into finer flexible grid 12.5 GHz granularity to offer the network elastic spectrum and channel spacing capable of signal routing and wavelength switching for the scalability of aggregate bandwidth. The variable-sized portions of the flexible spectrum assignment to end users at different speeds depend on bandwidth demand, allowing efficient utilisation of the spectrum resources. The entire bandwidth of dynamic optical connections must be contiguously allocated. However, there is an introduction of spectrum fragmentation due to spectrum contiguity related to the optical channels having different width. Thus large traffic demands are likely to experience blocking regardless of available bandwidth. To minimise the congestion and cost-effectively obtain high performance, the optical network must be reconfigurable, achievable by adding wavelength as an extra degree of freedom for effectiveness. This can introduce colourless, directionless and contentionless reconfigurability to route individual wavelengths from fibre to fibre across multiple nodes to avoid wavelength blocking/collisions, increasing the flexibility and capacity of a network. For these networks to function optimally, novel hardware and dynamic algorithms identification and development is a critical task. Such tasks include wavelength assignment, signal routing, network restoration and network protection. In this work, we for the first time to our knowledge proposed a spectrum defragmentation technique through reallocation of the central frequency of the optical transmitter, to increase the probability of finding a sufficient continuous spectrum. This is to improve network resource utilisation, capacity and resolve wavelength contention associated with a flexible spectrum in optical communication networks. The following chapter provides details on a flexible spectrum in optical fibre networks utilising DWDM, optimising transmitter-receivers, advanced modulation formats, coherent detection, reconfigurable optical add and drop multiplexer (ROADM) technology to implement hardware and middleware platforms which address growing bandwidth demands for scalability, flexibility and cost-efficiency. A major attribute is tunable lasers, an essential component for future flexible spectrum with application to wavelength switching, routing, wavelength conversion and ROADM for the multi-node optical network through spectrum flexibility and cost-effective sharing of fibre links, transmitters and receivers. Spectrum slicing into fine granular sub-carriers and assigning several frequency slots to accommodate diverse traffic demands is a viable approach. This work experimentally presents a spectral efficient technique for bandwidth variability, wavelength allocation, routing, defragmentation and wavelength selective switches in the nodes of a network, capable of removing the fixed grid spacing using low cost, high bandwidth, power-efficient and wavelength-tunable vertical-cavity surface-emitting laser (VCSEL) transmitter directly modulated with 10 Gbps data. This to ensure that majority of the spectrum utilisation at finer channel spacing, wastage of the spectrum resource as caused by the wavelength continuity constraint reduction and it improves bandwidth utilisation. The technique is flexible in terms of modulation formats and accommodates various formats with spectrally continuous channels, fulfilling the future bandwidth demands with transmissions beyond 100 Gbps per channel while maintaining spectral efficiency.
  • Full Text:
  • Date Issued: 2020

Database and guide for Lesotho wool and mohair production and quality

  • Authors: Maqalika, Papali Elizabeth
  • Date: 2020
  • Subjects: Mohair -- Dissertations -- Lesotho , Wool -- Dissertations -- Lesotho Textile fabrics -- Lesotho Textile industry -- Lesotho
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/49148 , vital:41605
  • Description: Lesotho produces significant quantities of Merino apparel wool and mohair, both of a quality that allows them to compete on the global market and to make a significant contribution to the economy of the country. Nevertheless, very little production and quality data and trends of these fibres have been documented. This is a serious disadvantage in terms of international trading and benchmarking as well as attempts to improve the production and quality of Lesotho wool and mohair. In the light of the aforementioned, the available production and quality data of the past 10 years have been captured and analysed for trends and also benchmarking, where considered applicable. The main focus is on fibre diameter (fineness), staple length, and yield since they largely determine fibre quality, application and price. Some quality related tests were undertaken to fill certain important gaps in the available data. In addition, prickle and medullation were evaluated on representative wool and mohair samples, respectively, because they represent important quality measures for apparel wool and mohair, respectively. It was found that Lesotho wool and mohair are of a fairly good and internationally competitive quality, with the wool having an average fibre diameter (MFD) of ≈20μm, an average staple length of about 64mm, an average VM level of about 4%, an average yield of about 57%, and the annual production being about 4 million kilograms greasy. The average staple length of the mohair was about 140mm, average MFD about 29μm and the average medullation, which unless otherwise specified, refers to the objectionable medullated fibres (kemp type) including the flat medullated fibre, relatively high at about 5.7%. The latter is certainly an area of concern which needs attention and improvement. It was found that the prickle level (Comfort Factor), of some of the wools tested was of such a level as to make the wool suitable for wearing against the skin. With respect to mohair, there is considerable scope to substantially reduce the level of objectionable medullated (kemp style) fibre level through the appropriate breeding interventions. Production of both wool and mohair has increased slightly over the ten years covered by this study. It also became apparent that Lesotho wool and mohair quality and production are greatly influenced by the farming practices and climatic conditions. Greater adoption of the merino sheep breed, sheds/barns and sheep coats are suggested as ways to reduce mortality rate (due to extremely cold temperatures), improve quality and increase yield and production. Some farming practices such as the lack of barns, supplementary feeding and veterinary care present constraints in terms of production of both wool and mohair. The districts in the Highlands region had the highest production of mostly wool, this being ascribed to better pastures, climatic and other conditions conducive to wool and mohair production. Both wool and mohair are considered to have potential for improved quality and production, which could be affected by appropriate interventions by the Small Agricultural and Development Project (SADP) and others through National Wool and Mohair Growers Association (NWMGA). Nevertheless, since the wool and mohair growers (farmers) do not form part of these and other interventions, they do not readily adopt the various strategies and decisions and do not receive the associated benefits immediately. It is therefore advised that local farmers, relevant educators and researchers be represented in policy and other decision making forums. In this way, educational campaigns will be demand driven with greater chance of adoption and success.
  • Full Text:
  • Date Issued: 2020

Decision analysis to inform invasive alien plant management in the Garden Route Biosphere Reserve

  • Authors: Masunungure, Current
  • Date: 2020
  • Subjects: Invasive plants -- South Africa , Alien plants -- South Africa , Biodiversity -- South Africa -- Management , Ecosystem management -- South Africa
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/49159 , vital:41606
  • Description: Invasive alien plants (IAP) pose significant threats to global economies and biodiversity and are often considered as wicked problems. With an increasing number of IAP and limited resources, their management and decision-making processes are becoming difficult because of uncertainty, multiple and conflicting objectives, and diverse stakeholder views, facts and values. This is particularly challenging given the complex interactions between economic, ecological, and social elements that exist in invaded areas. Consequently, it is important to incorporate new ways of thinking and novel methodologies to improve our understanding of IAP management and the decision-making processes around them, which are currently inadequate. Decision analysis can help with dealing with these challenges and support decision-making under uncertainty. Drawing on the systems thinking approach and the concepts of leverage points, transition management and transformational change, the aim of this thesis was to explore the effectiveness of IAP management and the decision-making process in the Garden Route Biosphere Reserve (GRBR). This was achieved using a mixed methods approach involving: social-ecological inventory (identifying relevant stakeholders); review of literature on the available decision support tools; key informant interviews (stakeholder perspectives on the current decision-making process); and stakeholder workshop and expert consultation (casual loop modelling). The results of this thesis provide evidence that application of the proposed principles of robust decision-making has the potential to overcome the weaknesses of the current decision-making process and as such, enables decision-makers to efficiently allocate resources towards IAS management. A novel causal loop diagram (CLD) was developed to highlight the interconnections between key variables in IAP management and decision-making. This revealed that to transcend ‘policy resistance’ and ‘quickfixes that fail’ archetypes, and improve IAP management, the stakeholders need to consider deep leverage points, for example, fostering trust and shared understanding among different stakeholder groups. These can be realistically maintained over the long-term and can cause a fundamental change in IAP management, rather than focusing on shallow leverage points that are relatively easy to implement but do not result in significant systemic change. The findings of this thesis are flexible and could guide various stakeholder groups at local, national, and international scales in improving the effectiveness of IAP management and decision-making.
  • Full Text:
  • Date Issued: 2020

Development of MOVPE-grown InAsSb for barrier diode applications

  • Authors: Dobson, Stephen R
  • Date: 2020
  • Subjects: Gallium arsenide semiconductors , Electronics
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/49071 , vital:41598
  • Description: In this study, layers of GaSb, InAs and InAsSb are grown by metalorganic vapour phase epitaxy and characterised. Growth is conducted using the precursors of trimethylgallium, trimethylindium, trimethylantimony and tertiarybutylarsine. Focus is then placed on the characterisation of the materials, carried out by the techniques of X-ray diffraction, photoluminescence spectroscopy, Hall measurements and photocurrent spectroscopy. It is observed that V/III ratio plays a vital role in the growth of the GaSb and InAsSb layers. Epilayers of GaSb showed best crystalline quality when a V/III ratio of 1.2 was used at a growth temperature of 600 °C and a cell pressure of 600 Torr. Resultant Hall measurements indicated p-type GaSb. The Hall carrier concentrations of the p-type GaSb samples were analyzed considering electrical neutrality conditions and found to be highly compensated with evidence of band impurity conduction at low measurement temperatures. Both the donor and acceptor concentrations were determined to be of the order of 1016 cm−3 for all samples. For low temperature (< 150 K) a monovalent acceptor concentration is calculated to have an activation energy at approximately 20 meV. At high temperature (> 150 K) a divalent acceptor is extracted with an activation energy varying between samples based on compensation in a range of 90 meV to 70 meV. Photoluminescence measurements show four peaks with recombination mechanisms linked to the native acceptor identified in literature as either the gallium antisite and/or vacant gallium site. A fifth peak observed is attributed to the longitudinal phonon of the native acceptor. InAs and InAsSb epilayer are all grown at a temperature of 600 °C and cell pressure of 600 Torr. InAs is grown at a V/III ratio of 9.5 on GaAs substrate. Photoluminescence of the InAs layer shows two distinct peaks, one of which is an extrinsic band to band recombination. The other is attributed to free electron to acceptor or a donor-acceptor pair transition. An additional weak peak is also observed which is assigned to the longitudinal phonon of the band to band. InAsSb growth was conducted under a range of V/III ratios of 4.8 to 5, with a vapour phase composition of 0.4 to 0.435. Structural analysis via X-ray diffraction showed a 6 % to 12 % solid antimony content. Photoluminescence exhibited a single broad peak for all samples, with extended band tails. Temperature and power dependant analysis of luminescence indicated a convolution of extrinsic band to tail and band to band recombinations. Hall measurements indicated the InAsSb was n-type material with an apparent measured maximum mobility at 120 K of 9.5 × 103 cm2/V.s. and a room temperature apparent mobility of 7.5 × 103 cm2/V.s. Analysis of hall results using a two-layer model calculated a true bulk mobility of the epilayer at room temperature with an increased value of 15.4 × 103 cm2/V.s. The two-layer model details the effects of the surface conduction. From photoconductivity measurements and further analysis a resultant effective lifetime, at room temperature, was found to be on same order of magnitude as that of InAs materials. Application of a single Einstein oscillator extrapolated 0 K energy gaps for two samples of solid Sb contents of 6 % and 12 %, of 354 meV and 332 meV, respectively. Finally consideration was given to the growth of aluminium containing compounds, particularly AlGaSb. Multiple phases were observed under scanning electron microscope showing growth of GaSb regions surrounded by amorphous solid aluminium and/or aluminium oxide phases. The failure of the aluminium to incorporate into the desired crystal structure is speculated to be due to impure precursor introducing oxygen into the films. Additionally, the effectiveness of the gallium precursor compared to the aluminium precursor in helping the removal of the methyl groups at the growth surface, could also promote a preference for GaSb growth.
  • Full Text:
  • Date Issued: 2020

Development of Tio 2 nanostructure arrays for photonic extraction of hydrogen gas

  • Authors: Suliali, Nyasha Joseph
  • Date: 2020
  • Subjects: Nanostructures , Nanostructured materials Hydrogen
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/49314 , vital:41620
  • Description: Amid the energy crisis of the 21st century, renewable energy is a thriving field of study, light harvesting materials being a central theme due to the abundance of solar energy. Nanostructured TiO2 is the most studied photocatalysis material, since the discovery of its energy harvesting properties by Fujishima and Honda in 1972. Environmentally friendly products such as hydrogen fuel, can be produced using TiO2 due to its non-toxicity, chemical stability and photocatalytic activity. The surprising aspect of this important material is that it can be prepared using cost-effective methods such as hydrothermal synthesis, solution gelation and anodic oxidation. This research focused on the three key elements required to develop TiO2 photoelectrodes i.e. the deposition of Ti films on transparent substrates, a thorough analysis of the chemistry of the anodic oxidation process and the development of the TiO2 thin films. Glass substrates that have Ti films are the base component for TiO2 photoelectrode production. Ti films with thicknesses up to 4 μm, were developed on commercial F-doped SnO2 (FTO) glass substrates using high-power impulse magnetron sputtering (HiPIMS). The sputter deposition experiments were performed in the 1 to 8 kW range at a substrate temperature of 500 °C and Ar pressure of 400 mPa. At higher powers, thicker films were deposited, resulting in increased intensity of Xray-diffraction peaks. However, on comparing the XRD patterns, the (001) peak outgrew the rest regardless of thickness of the film. The deposition process therefore favoured orientation of most of the α-Ti phase crystallites with the [001] axis perpendicular to the substrate surface. Surface roughness results were interesting, showing a non-linear dependence of the surface roughness on HiPIMS pulse energy in the 1 to 8 kW range. The surface roughness is highest at the starting deposition power of 1450 W and reduces to a minimum at 4500 W. From this minimum, it increases to its second highest value at 7900 W. From this data, the parameters required to produce Ti films of lowest surface roughness, for deposition on commercial Technistro® FTO glass, were deduced at the inflection point, where the deposition power was 4500 W. The surface roughness obtained is a critical result for the anodic production of quality TiO2 photoelectrodes, which if high, leads to uneven etching, thus irregular and inefficient photoelectrodes. Direct current magnetron sputtering was also carried out in the 1 to 5 kW range to obtain ratios of power-normalised growth rates of the Ti films. This investigation provided the Ti films on FTO glass, the transparent, conductive substrates which were used to develop TiO2 photoelectrodes. To elucidate the chemistry of anodic oxidation of Ti, a mathematical model of the anodic current density, which had not been reported at the time of its publication, was developed. The technique, a highlight of this research, is a predictive numerical computation of the instantaneous quantities of species that participate in the anodization process. From eleven chemical reactions, 14 first order ordinary differential equations were compiled using the principles of chemical reaction kinetics. The pattern, transient behaviour and response to anodization parameters of the current density signal, were successfully predicted. Strong agreement between the model and measurements was demonstrated in seven experiments. The results confirm that the current density signal is a numerical integral of the kinetics of redox reactions of water. The bulk of this research was on the development of TiO2 nanotubular arrays on Ti foil substrates and Ti films on FTO glass. TiO2 films with well-defined tubular structures were synthesised. The films were developed in anhydrous, polar organic hosts with water and etching agents in the range of 10 V to 70 V. The control of geometrical properties of the tubes such as the length, pore diameter, wall thickness, tube separation and number of nanotubes per unit area was demonstrated. Anatase only and mixed anatase-rutile phase compositions were obtained at different annealing temperatures. Nanotubes with diameters as small as 20 nm and thickness as high as 29 μm were produced. Apart from an increase in nanotube thickness, a decrease in distance between nanotubes grown in diethylene glycol was observed at longer anodization times. Studies of the effects of anodization parameters on the current density measured, morphological and crystallographic properties of the nanotube films were conducted in three main investigations. The first was the study of the effect of anodization parameters on current density. Besides the obvious increase of current density with anodic voltage, the first steady state of the growth process was found to depend on the NH4F concentration. The second investigation focused on the effect of accelerated growth of TiO2 nanotubular films. In the study, 9 μm-thick nanotube films were synthesised at twice the growth rate of a 9 μm-thick control sample. The array obtained by accelerated growth had distinguishable nanotubes, however, the morphological quality was reduced. The third investigation demonstrates the control of the number of nanotubes per unit area. By varying the etchant content, the anodic voltage and the viscosity of the electrolyte host, various distributions were obtained. The research ends with a photoelectrochemical application: measurement on photocurrents generated in a two-electrode setup. The photocurrent densities measured in the off and on conditions were 30 nA/cm2 and 2.57 μA/cm2, respectively, demonstrating photoactivity of the developed films.
  • Full Text:
  • Date Issued: 2020

Foraging in a dynamic environment: movement and stable isotope ecology of marine top predators breeding at the Prince Edward Archipelago

  • Authors: Carpenter-Kling, Tegan
  • Date: 2020
  • Subjects: Marine ecology , Stable isotope tracers , Estuarine ecology
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/49049 , vital:41596
  • Description: Marine ecosystems are experiencing rapid changes due to climate change. The associated temporal and spatial changes in resource distribution impacts on the foraging behaviour of marine top predators. If these changes negatively affect the ability of marine predators to forage efficiently, there may be dire consequences for their populations. However, evidence of foraging plasticity during adverse conditions, or generalist foraging behaviour, can allow inference about the resilience of species to environmental change and provide essential knowledge towards effective and proactive conservation measures. I examined plasticity in the trophic ecology of 12 marine predator species breeding on Marion Island, southern Indian Ocean, over three years (2015 – 2018), a period characterized by pronounced environmental variability. Firstly, I correlated behavioural states inferred along the GPS tracks of incubating wandering, grey-headed, sooty and light-mantled albatrosses to environmental variables that are indicative of biologically productive oceanographic features. Secondly, I analysed δ13C and δ15N blood values in 12 marine predator species (the afore-mentioned albatrosses as well as king, gentoo, macaroni and eastern rockhopper penguins, northern and southern giant petrels and Antarctic and sub-Antarctic fur seals) over two seasons: summer and autumn. My results revealed that the foraging behaviour of all the species is, to some degree, either plastic (temporally variable isotopic niche) or general (large isotopic niche which remained similar over time), except for the king penguin (small isotopic niche which remained similar over time), a known foraging specialist. Furthermore, despite their dynamic foraging behaviour, resource partitioning among the predators was maintained over time. Due to the ease and relatively low cost of collecting tissues for stable isotope analysis it has the potential to be a powerful tool to monitor the trophic ecology of marine predators. I thus used my simultaneously collected dataset of GPS tracks with the stable isotope blood compositions to investigate some of the assumptions underlying the inferences made from marine predator δ13C and δ15N blood values. I reconstructed species- and guild- specific δ13C and δ15N isoscapes for eight seabird species. Following this, I coupled individual-based movement models of northern giant petrels with global marine isotope models to explore the sensitivity of tissue δ13C values to a range of extrinsic (environmental) and intrinsic (behavioural, physiological) drivers. My results demonstrate the strong influence of reference isoscapes on the inference of stable isotope compositions of marine predators. Furthermore, I show that caution should be used when using non-species-specific or temporally inaccurate isoscapes. I furthermore demonstrate that biological interactions, such as competition for food resources, either past or present, as well as spatio-temporal distribution of food patches strongly influence the foraging behaviour of marine predators. These findings highlight the importance of integrating biological interactions in species distribution models which are used to predict possible distributional shifts of marine predators in the context of global changes. My thesis further developed previously available methods and presents a novel approach to investigate sources of variance in the stable isotopic composition of animals’ tissues.
  • Full Text:
  • Date Issued: 2020

Influence of process energy on stress corrosion susceptibility of a friction hydro pillar repaired steam turbine rotor disc blade locating hole

  • Authors: Pentz, Willem Gerhard
  • Date: 2020
  • Subjects: Friction welding , Mechanical engineering
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/47106 , vital:39810
  • Description: Currently the power generation industry is struggling to keep older coal power plants running efficiently. One of the major hurdles is to keep repair and service cost low. Over time stress corrosion cracking (SCC) occurs in the locating pinholes of tier type rotors which locate the turbine blades. This is where this research aims to assist with an alternative repair technique, Friction Hydro Pillar Processing (FHPP) welding, to have longer service intervals thus saving cost and time. The same material can be used for welding and a new aligned hole can be drilled. FHPP welding is a solid state friction welding process. Four different FHPP axial forces were selected to compare their respective performance in subsequent tensile testing, impact testing and SCC testing. All the tensile samples extracted from preheated welds and post weld heat treated welds fracture in the parent material, which indicates good weld efficiency. The impact crack route from the weld nugget towards the parent material was identified in the energy and force graph. Axial force which promote impact toughness can be selected with this curve. SCC occurs when a tensile stress is applied to a susceptible material when in a conducive environment for cracking. A new SCC W-shape was designed and performed well during initial testing. With the SCC W-shape two specimens can be extracted opposite each other and tested. Both the preheated weld samples and the post weld heat treatment (PWHT) weld samples had improved SCC performance over their respective parent material samples. A high axial force, low process energy, and high process energy rate (low process energy and low weld time) produced a weld with improved SCC resistance. FHPP (with PWHT) is a promising repair technique as it improved on the SCC resistance and impact toughness as well as having 100% bond efficiency. More research is still required to identify the SCC mechanism of the FHPP weld.
  • Full Text:
  • Date Issued: 2020

Integrating sustainability dimensions into construction labour productivity determinants in Zimbabwe

  • Authors: Moyo, Tirivavi
  • Date: 2020
  • Subjects: Construction industry -- Labor productivity -- Zimbabwe , Construction workers -- Zimbabwe Construction industry -- Employees -- Zimbabwe Construction industry -- Management
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/46207 , vital:39514
  • Description: Low construction labour productivity and inadequate welfare of construction workers is a compound challenge in Zimbabwe. This challenge is due to shortcomings situated in the Decent Work Agenda. Whilst a plethora of contributory factors exists, those that affect the Zimbabwean construction industry were identified for interrogation. Therefore, the study aimed to improve and sustain construction labour productivity in Zimbabwe through fulfilling significant decent work substantive elements, in consideration of demographic variables of stakeholders. A cross-sectional survey research strategy was utilised with quantitative data being collected from selected respondents through the use of questionnaires. The population for the study consisted of randomly selected construction companies registered with the Construction Industry Federation of Zimbabwe and based in Harare, Bulawayo and Shurugwi where site managers’/project managers’ participated. Construction skilled and semi-skilled workers on thirteen (13) construction sites, situated within the same study area, participated in the study. Educators from technical and vocational training institutions and respondents from relevant regulatory bodies were also selected to participate in the study. Quantitative data analysis methods which included Pearson chi-squared tests, Mann-Whitney U tests; Kruskal-Wallis tests, Pearson bivariate correlation method and Regression analysis were utilised. Demographic variables (age, gender, designation, educational levels and experience) were utilised to determine the existence of statistically significant differences in respondents’ perceptions. Construction companies are encouraged to implement corporate social responsibility strategies through equipping workers of different educational levels with knowledge and skills that can be transferred to and benefit themselves and their communities. Adequately trained construction workers best serve their communities through improving their livelihoods, improved safety and health consciousness and quality workmanship. People centred management aspects were found to be fundamental within construction sites as they promote the welfare of workers and should precede any productivity improvement drives. Technical and vocational training institutions need to inculcate sustainability learning objectives within their curricula if any meaning strides in enhancing welfare and productivity of workers is to be achieved. Also, establishing structured on-the-job training that incorporates sustainability learning objectives to achieve workers’ safety on sites is essential. There was a consensus that working conditions must ensure the welfare of workers first before any productivity gains can be realised. Provision of acceptable decent working conditions for different designations and educational levels was encouraged. A comprehensive model was developed for sustaining construction labour productivity that included statistically significant regression models and derived statistically significant demographics from construction labour productivity determinants under study. Validation of the regression models was undertaken through cross-validation and comparison with existing theory. Tenable labour productivity performance measurement and reporting must be inclusive of decent work accomplishments. Short-term interventions that include awareness campaigns and provision of adequate working conditions are required for project-based resolutions whilst, long-term interventions are required where structural reforms within the training of skilled, semi-skilled workers and managers are required, for continuous improvement.
  • Full Text:
  • Date Issued: 2020

Managing the corporate reputation of a transforming organisation: a study of multimedia University of Kenya

  • Authors: Mtange, Margaret Mulekani
  • Date: 2020
  • Subjects: Organizational change -- Management , Universities and colleges -- Kenya -- Sociological aspects -- Case studies , Universities and colleges -- Research -- Economic aspects -- Kenya -- Case studies
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/50837 , vital:42873
  • Description: Universities, like other organisations, are challenged to manage corporate identity and reputation to maintain a competitive edge. Few studies in Africa focus on the impact of internal communication on corporate identity and reputation management during organisational transformation. Thus, this study interrogated how a transforming and complex university in Kenya managed the corporate identity, image and reputation for competitive advantage. The purpose of the study was to establish how Multimedia University of Kenya (MMU) management communicated with its employees to nurture the corporate identity, image and reputation during a ten-year period of transformation. The study draws insights from in-depth interviews with 23 university management members, 178 self-administered questionnaires through random stratification of MMU employees, and content review of two MMU strategic plans ranging from 2011 to 2021. The findings suggest that MMU management used formal and interactive channels to create awareness of organisational transformation. These channels included face-to-face engagements, formal meetings and mediated communication through telephone conversations and intranet that facilitated record keeping. The management engaged in top-down and bottom-up communication to build employee trust, while employees expressed reservations of bottom-up information accuracy, suggesting information exclusion. On the contrary, the employees preferred digital and interpersonal channels for internal communication, which included telephone conversations, social media, personal visits by MMU management, and university events. Publicity activities were to disseminate information to prospective students and sponsors through selected private television, vernacular radio, and MMU radio stations, traditional print media, and the MMU website to communicate the MMU brand and image. Employees acknowledged that MMU brands itself as a leader in telecommunication, technology, mechanical, manufacturing, and media training through state-of-the-art equipment, robust faculty, and problem-solving ventures through research. The current study proposes stronger employee involvement, executive packaging and positioning, coaching successful faculty members as brand ambassadors, retraining employees, and employee participation in policy formulation to enhance new culture. In addition, these opositions will enhance the corporate identity, brand, as well as university performance, product quality, policy and processes to enrich the corporate reputation during transformation. The findings challenge university management to actively engage the corporate communication function, emphasise employee participation, and focus on the continual improvement of corporate identity and reputation management practices for competitive advantage. The current study proposes a participative, multi-layered and multi-dimensional communication model for efficient and excellent internal communication. The current study recommends that corporate communication practitioner be strategically positioned to coordinate employee engagement, utilise appropriate communication channels and counsel university management on corporate identity, image and reputation management during organisational transformation.
  • Full Text:
  • Date Issued: 2020

Mechatronics based highspeed rotational piezo actuator

  • Authors: Raffler, Oliver
  • Date: 2020
  • Subjects: Piezoelectric materials , Piezoelectric devices Mechatronics
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/${Handle} , vital:39811
  • Description: The aim of this thesis is the development of a novel mechatronics-based high speed piezo actuator for rotational and linear motion. Mainly, the thesis deals with the development of a system for mechanical coupling of any number of piezostacks. This mechanical coupling allows the actuator to achieve a significantly increased deflection compared to current approaches. The developed concept offers the possibility of a linear or rotary motion. It is also possible to combine the two types of movement. In the first step, in order to gain a better understanding of the topic, the piezo technology and especially the existing piezo actuators and -motors are examined. Currently, the force generated by the piezo actuators is mainly transmitted by friction. The only exception is the PAD-Actuator, which transmits force by means of form locking. The concept developed here also transmits its force by means of form locking and, in addition to that, offers a novel and unique drive concept in the field of piezo actuators. In the course of this thesis a new concept for the mechanical coupling of piezo actuators was developed, simulated and subsequently manufactured. Thus the system could be examined under real conditions. The investigations carried out mainly dealt with quasi-static and dynamic investigations. In addition to that, the emission of the airborne and structure-borne noise of the system was analysed.
  • Full Text:
  • Date Issued: 2020

Ocean dynamics of the shelf and bays of the eastern Agulhas bank: a process-oriented numerical modelling study

  • Authors: Bailey, Dylan Francis
  • Date: 2020
  • Subjects: Oceanography -- Research , Marine biology , Marine meteorology , Hydrography
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/49038 , vital:41595
  • Description: There is a general need for a broader base of information on the finer detail of ocean processes in the Eastern Agulhas Bank region. In this thesis, the Regional Ocean Modelling System (ROMS) was applied to resolve high resolution (~1km) bay and shelf scale ocean processes along the south eastern coastline of South Africa using an offline multi-nested approach. Experimental and reference ocean model runs were used with in situ instrument mooring data to investigate how currents and temperature in the bays and the adjacent shelf are affected by the bathymetry, Agulhas Current (AC), regional winds, and coastal trapped waves (CTW). Focus was given to temperature, circulation, and coastal trapped waves, given the abundance of hourly in situ mooring data for these variables, making them suitable for comparison with the ocean model. SST variability trends were seasonally and spatially predictable, being greatest in the summer months and smallest in the winter months. A region of high SST variability extended from Port Alfred toward the south-west, indicating entrainment of nearshore upwelled water and instabilities in the inshore front of the AC. Shelf bottom temperature variability had a more spatially diverse seasonal trend, with coastal variability the highest (lowest) and offshore variability the lowest (highest) during the summer (winter) months. A distinct asymmetry in mean seasonal shelf bottom temperatures evident to the south of Algoa Bay and St Francis Bay was shown to be dependent on the profile of the shelf margin in relation to the inshore front of the AC using an experimental model run. Bay-scale anti-cyclonic circulation patterns dominate the bays throughout the year, with regions of strong mean surface currents occurring south of Cape Recife and Cape St Francis. General circulation patterns over the shelf are strongly governed by regional wind regimes, with the strongest flows being south-westward occurring during north-easterly wind events. Shelf bottom flows typically follow the expected Ekman-veering response, apart from near coastal flows that are topographically steered. A region of consistently strong south-westward shelf bottom flow extends from the east of Port Alfred to the shelf margin south of Bird Island. This flow is predominantly driven by the AC, although its velocity is strongly governed by regional winds. Circulation patterns during powerful eastward moving wind systems are strongly governed by the passage of associated CTW. Comparisons with an experimental model run where surface winds were removed revealed that the shelf wave was responsible for 61% of water volume displacement during a CTW event, and that the coastal shear turbulence caused by this displacement has a direct effect on the mixed layer depth. The links made between the complex shelf and bay ocean processes indicate that subtle changes to the ocean state will have far reaching effects on the regional ocean environment and its biota. Given the challenges of climate change, this is of paramount importance if we are to quantify these effects and mitigate their impacts, particularly with respect to the socio-economic dependency of those who rely on the ocean for its living resources.
  • Full Text:
  • Date Issued: 2020

Plankton dynamics in response to algal blooms in a highly eutrophic estuary in South Africa

  • Authors: Smit, Taryn
  • Date: 2020
  • Subjects: Algal blooms -- South Africa , Estuaries -- South Africa
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/49303 , vital:41619
  • Description: The global rise in the incidence of harmful algal blooms in estuaries is a major concern given their importance as a nursery area for a variety of invertebrates and fishes. On the warm-temperate, south-east coast of South Africa, the Sundays Estuary experiences persistent, seasonal HABs due to stable eutrophic conditions. Spring blooms of the dinoflagellate, Heterosigma akashiwo, were recorded for several years in the estuary. This Raphidophyte is known for its consequences in fish and shellfish aquaculture and exhibits harmful properties such as mucilage and reactive oxygen species production. Subsequently, the dissertation investigated larval fish assemblage dynamics, larval prey and predator dynamics and body condition in association with H. akashiwo blooms. HABs mainly altered the water quality within the mesohaline zone in terms of microalgal biomass and dissolved oxygen. Hypereutrophic blooms of H. akashiwo reached 24 996 cells∙mL-1 during the study period. Supersaturated dissolved oxygen concentrations (up to ~13 mg∙L-1 at night and ~21 mg∙L-1 during the day) were recorded during hypereutrophic blooms (> 80 μg∙L-1, ≥ 2781 H. akashiwo cells∙mL-1). Dissolved oxygen differed significantly by bloom state, with the highest dissolved oxygen concentrations. Larval fish density, diversity and community structure variability were lower during hypereutrophic blooms compared to standard blooms and bloom absence, albeit statistically insignificant. Estuarine resident larval density was negatively correlated with dissolved oxygen concentration (P < 0.001). Dominant prey copepod of G. aestuaria larvae, P. hessei, was less abundant and variable during hypereutrophic blooms (mean: 664, range: 4-4301 individuals per m3) compared to standard blooms (mean: 950, range: 2-5237 individuals per m3) and bloom absence (mean: 1182, range: 23-7259 individuals per m3). Although HABs did not appear to drive a mismatch between prey and G. aestuaria larvae, early juvenile larvae made only a small contribution to the assemblage (0.2-1.8%). In terms of predator effects, yolk sac larvae were negatively related to R. terranatalis (P < 0.05). A significant positive relationship was found between prey, P. hessei and G. aestuaria preflexion (P < 0.001), flexion (P < 0.001) and postflexion (P < 0.05) larvae. In a world first, the effects of HABs were investigated on a larval fish species, Gilchristella aestuaria, using biochemical body condition analyses. During severe bloom conditions, G. aestuaria larvae were smaller and the assemblage consisted of mainly early developmental stages (stats). Body condition (RNA per dry weight) was poorest in the presence of hypereutrophic blooms (P < 0.001). A bell-curved relationship between RNA/DW and dissolved oxygen concentration was also produced in a 3-day time-lagged GAM (P < 0.001). In conclusion, hypereutrophic bloom conditions appeared to trigger adult G. aestuaria spawning in the upper mesohaline zone of the estuary in response to heightened primary productivity which occurs during the early bloom stage. However, reductions in copepod abundance (P. hessei) and unfavourable oxygen concentrations interfered with grow-out of G. aestuaria larvae. This research showed that HABs can alter nursery properties to the detriment of G. aestuaria larvae can have serious knock-on effects up the food chain. The loss in abundance of adult, juvenile and larval G. aestuaria, a key forage fish in South African estuaries, has major implications for estuarine food webs, especially in reduced prey availability to juvenile fishes and birds. There is still much to learn about the effects of HABs on the physiological and behavioural aspects on plankton communities worldwide.
  • Full Text:
  • Date Issued: 2020
  • Disclaimer
  • Privacy
  • Copyright
  • Contact