4. Electronic Theses and Dissertations (ETDs) - Faculties submissions
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Item Pricing Interest Rate Derivatives Using The Forward Market Model(University of the Witwatersrand, Johannesburg, 2024-10) Konaite, Tshana Tumelo; Mudavanhu, BlessingThe IBOR are due to be discontinued and their replacements have been chosen to be the overnight rates. This change in the risk-free rate comes with challenges of how the new rates will be modelled and how the products will be priced. In this dissertation, we look to explore the classical short-rates and the new generalized Forward Market Model proposed by Andrei Lyanschenko and Fabio Mercurio in 2019. We seek to utilize this model in pricing interest rate derivatives such as caps and swaptions.Item Metagenome sequencing of the lichen species Flavopunctelia flaventior and Parmotrema tinctorum from Gauteng, South Africa(University of the Witwatersrand, Johannesburg, 2024-06) Katane, Malebogo Dimpho; Botes, Angela; De Maayer, PieterLichens are defined as a mutualistic association between fungi (mycobiont) and an algal and/or cyanobacterial photobiont. Increasing evidence suggests that lichens comprise more diverse microorganisms than initially thought, where lichens represent an interaction between archaea, bacteria, filamentous fungi, green algae, yeasts, and viruses. Not many comprehensive studies have been done of South African lichen species. The present study employed metagenome sequencing to investigate the lichen microbiomes of Flavopunctelia flaventior and Parmotrema tinctorum sampled from Bryanston, Gauteng province, South Africa. Furthermore, the roles played by the members of the lichen microbiome within symbioses were also studied by functionally annotating the assembled metagenomes of the two lichen species. This study sets the groundwork for future studies on South African lichen species. In Chapter 1, an extensive literature review on lichens, their ecology, taxonomy and biology is discussed. Furthermore, it delves into the existence and shape of the microbiome beyond the mycobiont and the photobiont. Additionally, possible roles that the lichen microbiome may play in sustaining the lichen symbiosis is also discussed. In Chapter 2, the metagenomes of two lichen species were sequenced, the quality of the reads were assessed, and taxonomic classification was performed to elucidate the composition of microorganisms associated with each lichen species. Both microbiomes were dominated by bacteria, with limited fungi, viruses, and archaea. The majority of the identified phyla and genera were found to be common between the two lichen species. Similarities in the core microbiome was accounted for by the fact that F. flaventior and P. tinctorum were sampled from the same location and they are both members of the Parmeliaceae family. In Chapter 3, the metagenomic reads were assembled and functionally annotated using various bioinformatics tools. We demonstrate that the members of the lichen microbiome are involved in the cycling of nutrients such as carbon and nitrogen. We also found differences in carbon fixation pathways, which were attributed to the accessory microbiome. Finally, a summary highlights key results and recommendations on future work that could be undertaken to further provide insight into biological pathways essential to sustain the lichen symbiosis.Item Fatigue Crack Propagation in AlSi10Mg Additive Manufactured Aeronautical Parts Processed by Laser Shock Peening(University of the Witwatersrand, Johannesburg, 2024) Chinyama, Joel; Polese, ClaudiaAdditive manufacturing (AM) offers advantages for complex aeronautical parts, but inherent defects can reduce fatigue life. Post-processing techniques such as laser shock peening (LSP) can be used to introduce beneficial compressive residual stress that hinders crack propagation. This study investigates LSP as a method to improve fatigue performance in additively manufactured AlSi10Mg aeronautical parts. It examined how varying LSP treatment laser power intensity (1.5 – 4.5 GW/cm2) affects LSP's effectiveness and identified optimal LSP residual stress profiles for peak fatigue performance. The residual stress profiles that were used in this research were adopted from previous experimental work done on AM-manufactured AlSi10Mg alloys within the Wits AM/LSP group. Previous experimental work results on wrought AA2024-T351 (untreated and LSP-treated cases) indicated that LSP-treated samples have a fatigue life of at least four times longer as compared to as-built samples. AFGROW models with similar geometry, material properties and load conditions were used to predict the fatigue life of as-built and LSP-treated cases. An improvement in fatigue life of at least 3.8 times was observed, which was within an acceptable deviation from the experimental results. These results were used to validate AFGROW models for exploring different specimens. Fracture mechanics models (AFGROW) were used to compare the fatigue life of as-built and LSP-treated AlSi10Mg samples with different LSP power intensity parameters. The results showed that LSP treatment can significantly extend fatigue life, with the optimal laser power intensity found to be 3.0 GW/cm2. This improvement is attributed to the introduction of compressive residual stresses by LSP, which suppress crack initiation and propagation. The effectiveness of LSP was further explored in the context of the Cessna 172/175 horizontal stabilizer, a part that could benefit from AM for weight reduction and structural integrity. AFGROW models were developed to predict the fatigue life of the centre lightening hole in the forward spar, a critical location for crack initiation. The models incorporated a beta correction factor to account for the specific crack geometry and stress distribution. The beta correction factor was determined by comparing the stress intensity factors from the Finite Element Analysis (FEA) and AFGROW models. The results again demonstrated a significant increase in fatigue life (of at least six times) for LSP-treated parts compared to as-built parts. AFGROW models with a beta correction factor proved valuable for predicting fatigue life in components with complex geometries. This study confirms that LSP is an effective post-processing technique for mitigating fatigue crack propagation in AlSi10Mg AM aeronautical parts.Item Electrocatalytic detection of biomarkers of tuberculosis and cervical cancer(University of the Witwatersrand, Johannesburg, 2024-07) Peteni, Siwaphiwe; Ozoemena, Kenneth IkechukwuThe need for simpler, low cost and efficient diagnostic methods remains a matter of urgency. This has opened numerous streams of research. Electrochemistry is a simple, cost effective and efficient method that has been used for the detection of several diseases such as tuberculosis (TB) and human papilloma virus (HPV). TB has been ranked amongst the most problematic diseases in HIV/AIDS burdened communities, this alone calls for concern. Biomarkers of TB not only indicate mycobacterium infection but can also assist in the early detection of TB which is highly beneficial for the infected person and the health care system. HPV is the causative agent for cervical cancer. Cervical cancer is ranked as the fourth disease that causes mortality amongst women. With that in mind, HPV-16 L1 early detecting means possible early detection of cervical cancer. In this thesis, methyl nicotinate (MN), which is one of TB’s biomarkers was detected in phosphate buffer solution (PBS, pH 6.0) and commercial human serum using cobalt nanoparticles supported on carbon derived from trimesic acid (TMA) (abbreviated as Co-NPs@CTMA) and biphenyldicarboxylic acid (BPDC) abbreviated as Co-NPs@CBPDC) as electrocatalysts. These electrocatalysts were obtained using microwave-assisted metal-organic framework process with TMA and BPDC as ligands. XRD data showed that these electrocatalysts are cobalt nanoparticles with dominant {111} and {200} phase with traces of cobalt oxide (CoO). XPS and Raman data showed that Co-NPs@CBPDC is defect-rich compared to the Co-NPs@CTMA counterpart. BET showed that CoPs@CBPDC has higher surface area and pore size and volume than the Co-NPs@CTMA catalyst. Both electrocatalysts showed reversible cobalt nanoparticle oxidation and reduction reactions, in the absence and in the presence of the MN, thereby allowing for a facile indirect electrochemical detection of this biomarker. The calibration curves showed low limit of detection (LoD) of 0.47 and 0.147 µM for Co-NPs@CTMA and Co-NPs@CBPDC, respectively. The higher performance of the latter is attributed to its enhanced physico-chemical properties compared to the former. Next, HPV-16 L1, which is the conventional high-risk antigen that is present in cervical cancer, was detected using onion-like carbon (OLC) and polyacrylonitrile fibre integrated with OLC (OLC-PAN) as electrode platforms. Two electrode platforms were used; onion-like carbon (OLC) and its polyacrylonitrile (OLC-PAN) composites. Both platforms led to the detection in a wide linear concentration range (1.95 fg/ml to 50 µg/ml), excellent sensitivity (>5.2 µA/log([HPV-16 L1, fg/mL]) and ultra-low detection of ca. 1.0 and 1.4 fg/ml for OLC-PAN and OLC-based immunosensors, respectively. The high specificity of detection was proven by experimenting with an anti-Ovalbumin antibody (anti-Ova) and native Ovalbumin protein (Ova). An immobilized antigenic HPV-16-L1 peptide showed insignificant interaction with anti-OVA in contrast with the excellent interaction with anti-HPV-16 LI antibody. The immunosensors showed satisfactory stability of ~ 3 days of re-usability. The application of the immunosensor as a potential point-of-care diagnostic (PoC) device was investigated with the screen printed carbon electrode which showed the ability to detect ultra-low (~ 0.7 fg/ml) and high (~ 12 µg/ml) concentrations. This study opens the door of opportunity for further investigation with other electrode platforms and realization of PoC diagnostic devicesfor screening and testing of HPV biomarker for cervical cancer.Item Financial Evaluation of Implementing In-Pit Crushing and Conveying Systems for Waste on Open Pit Mines(University of the Witwatersrand, Johannesburg, 2024) Serepa, Ikaneng; Emwanu, B.The South African mining industry has faced mounting challenges, especially rising expenses that threaten profitability. These escalating costs, driven by various factors including operational expenses such as mining costs, are critical. The distribution of mining costs across activities within the production cycle is crucial, with hauling operations in open pit mines representing a significant portion, as noted by Paricheh et al (2017) at 49%. Due to the substantial economic impact of hauling expenses on mining expenditures, there's a strong incentive to streamline these operations to lower overall costs effectively. Current research highlights a noticeable transition in the mining sector towards embracing in-pit crushing and conveying (IPCC) systems in open pit mines, acclaimed as a cost-effective substitute for conventional truck and shovel (CTS) systems (Awuah-Offei et al, 2009). This research assessed both the integration and financial viability of implementing a waste IPCC system in the loading and hauling operations of an open pit mine. A mixed-methods approach, combining quantitative data from production records and costs with qualitative insights from expert interviews was used. The findings of this research indicate that while the IPCC system can be integrated, there remains a degree of reliance on the CTS system for material transportation from the pit to the IPCC system. For the CTS system, 55 rigid dump trucks (RDTs) are required, constituting 57% of the initial capital expenditure of R1.27 billion. Conversely, the IPCC system requires only 31 RDTs, accounting for 29% of the initial capital costs of R1.37 billion. However, despite the substantial reduction in RDTs, the IPCC system requires significant investment in a crusher and conveyor belt system for waste management, which constitutes 32% of its capital costs. Examination of the operating costs over the life of the mine indicates that there are no cost advantages associated with operating an IPCC system compared to the CTS system. Operating expenses for the IPCC system exceed those of the CTS system by 58%, predominantly driven by the operational costs of the crusher and belt system, contributing to 67% of the IPCC system's costs. The financial assessment results show a positive and acceptable net present value (NPV), internal rate of return (IRR), and payback period for both systems. Nevertheless, the CTS system exhibits superior financial performance, with a NPV of R7.45 billion, an IRR of 83.1%, and a shorter payback period of 1.2 years, and is recommended as a viable option for the mine.Item Measurement of combustion airf low into burners in coal fired plants(University of the Witwatersrand, Johannesburg, 2024) Manqele, Gladwell Sizwe; Schmitz, WalterThis research study is aimed at achieving accurate measurement of mass flow rates in large square industrial square ducts at Eskom’s boiler plants. For safe and efficient operation of Fossil Fuel Firing Boiler Plants, the utility has put in place the Fossil Fuel Firing Regulation Standard which requires that the Total Combustion Air flow be measured at exit from the air heaters, into the ducts. In this study, a sophisticated airflow measuring probe was acquired, herein the current study referred to the 14-hole Omniprobe. The accuracy was found to be within 5% in a free stream flow field. A Five-hole probe was calibrated in the free-stream wind tunnel. The calibration process enabled the derivation of the probe specific polynomials of Pitch, Yaw, Total Pressure, Static Pressure coefficients and velocity components. A prototype air duct was designed for the study to simulate air flow through square ducts with a 90⁰ bend as an abrupt flow disturbance. To achieve the objectives of the study, 6 planes were identified where air flow velocity profiles were generated using the equal area method. The modeling of the velocity profiles was conducted numerically, using CFD (Ansys Fluent), and experimental, using Pitot-static probe, Omniprobe, and a Five-hole probe. The mass flow rates as measured by the Pitot-static tube were found to be consistent at planes 1, 2, 5, and 6. The mass flow rate as calculated from the Pitot-static probe varied by 2.1% through the duct. This justified the selection of the Pitot-static probe as the reference for this study. The velocity profiles generated from the traverse measurements using the 14-hole Omniprobe showed an error in velocity measurements which are in the proximity of the wall. This can be attributed to the the wall effect. The mass flow rates of air calculated from the Five- hole probe measurements were found to be within 4% of the mass flow rate as calculated from the results of the reference probe in the 1st and 2nd planes upstream of the bend. After the 90⁰ flow disturbance bend, the accuracy drops to 13% at plane 5 and improved slightly at plane 6 to 11.7%. This is attributed to complex flow pattern at these planes. The study concludes that the Pitot-static tube remains the preferred instrument for use in measuring flow rates using the equal area method in large square ducts. The Five-hole probe can be applied where the flow field is not distorted in conjunction with CFD. The Omniprobe’s accuracy in measuring the velocity magnitude, and the angularity of the flow field was verified in an open stream wind tunnel. This study recommends exploring the use of an L-type 14-hole Omniprobe for application in large square industrial ducts.Item Distributed Electric Propulsion on a Joined-Wing Air-Taxi(University of the Witwatersrand, Johannesburg, 2024) Brand, Darren Mark; Schekman, S.Urban Air Mobility (UAM) is a form of aerial transportation within urban areas with the main intention of easing traffic congestion. Electric Vertical Take-off and Landing (EVTOL) air-taxis are currently in development, but no single configuration has been identified as superior for UAM. There is still scope for alternate designs to be explored. A major obstacle to successful UAM operations is the combination of high energy requirements for VTOL and low battery energy densities, thereby affecting operational aircraft range. Aerodynamic efficiency has been identified as a critical factor for achieving maximum flight range while electric battery technology is matured. It is proposed that an air-taxi which combines Distributed Electric Propulsion (DEP) with a joined-wing may achieve superior aerodynamic efficiency compared to other air-taxi designs. A joined-wing air-taxi capable of carrying four passengers and a pilot has been developed with four alternative DEP configurations. These aircraft are herein investigated and compared against one another. A computational approach was followed using STAR- CCM+ to evaluate the flow characteristics and forces around the aircraft for both climb and cruise conditions. It was found that a “Non-DEP” configuration with four proprotors can achieve up to 5% higher aerodynamic efficiency than a DEP variant. However, this configuration suffers with poor lifting capability at high angles of attack. The sensitivity of aerodynamic efficiency to changes in the number of proprotors and their spacing was seen to be negligible according to this investigation.Item Aerodynamic Force Variation on a Trailing MotoGP Motorcycle in a Corner(University of the Witwatersrand, Johannesburg, 2024) Shaw, Craig Byrne; Boer, MichaelMotorcycle racing is a popular form of motor racing. The MotoGP category produces exciting and competitive races due to motorcycles following each other so closely. This has led to significant aerodynamic advancements being made in the MotoGP category over the past decade. Motorcycles and riders often race within the wake of a leading motorcycle as a result of this competitive racing. Racing in the wake provides an advantage on a straight due to the reduced drag force. This allows for greater acceleration and an opportunity to overtake the leading motorcycle. The effect of the wake on a trailing motorcycle in a corner has not been explored in depth. This research was focused on the aerodynamic force variation on a trailing motorcycle in the wake of leading motorcycle. The optimal position for the trailing motorcycle to gain an advantage over the leading motorcycle was determined subsequently. This was achieved using Computational Fluid Dynamics (CFD). The geometry of the motorcycle was obtained using 3D scans of a 1/18th scale model 2018 Repsol Honda RC213V. The geometry of the rider was drawn using CAD. Initial CFD models were created simulating the motorcycle and rider in a straight line to compare to existing published data for validation. The CFD cornering methodology was developed by Queens University in association with Siemens. The method makes use of rotating reference frames. This simulates the motorcycle and rider cornering at a constant velocity around a constant radius corner. Models were created for a singular motorcycle and rider at varying lean angles between 40 and 60 degrees with matched velocities and corner radii. The aerodynamic forces of drag, lift and side force were analysed on the motorcycle and rider for each case. The trends for these forces were determined relative to the changing lean angles. The drag on the motorcycle and rider increased non-linearly as the lean angle increased with the side force following a similar trend. The lift on the motorcycle and rider also increased non-linearly as the lean angle increased. These same CFD models were recreated with a second motorcycle and rider following a leading motorcycle to determine the effect the wake had on the aerodynamic forces. The second motorcycle and rider were positioned 1 characteristic length behind the leading pair on the same racing line. The drag on the trailing motorcycle and rider decreased as the lean angle increased. The lift on the trailing motorcycle and rider followed a similar trend to the leading pair with it increasing as the lean angle increased and the side force fluctuates as the lean angle increased. This resulted in the trailing motorcycle having a negative allowable change in forward acceleration relative to the leading motorcycle at lean angles lower than 60 degrees. The optimal position for a trailing motorcycle in a corner was determined by positioning the motorcycle and rider on various racing lines and following distances behind the leading motorcycle and rider. This created a grid pattern of the tested trailing positions. Two smaller racing line radii, three larger racing line radii and three different following distances were tested. The optimal trailing position at a 50 degree lean angle was found to be 1 characteristic length behind and on a racing line 1 characteristic width larger than the leading motorcycle. This position resulted in a positive allowable change in forward acceleration relative to the leading motorcycle around a corner radius of 125.86 m at 38.36 m/s. This iii position was tested around another two corner radii of 75 m and 150 m. This resulted in a negative allowable change in forward acceleration of around the 75 m radius corner and a greatly improved positive change in forward acceleration around the 150 m radius corner. From these results it was concluded that this optimal position is only viable around larger radius corners. It was approximated that this optimal position provides the trailing motorcycle an advantage around corner with radii larger than 86.8 m.Item Prediction of Water Hyacinth Coverage on Hartbeespoort Dam(University of the Witwatersrand, Johannesburg, 2024) de Gouveia, Claudia D. Camacho; Bührmann, Doctor JokeWater hyacinth is an invasive weed contributing to Hartbeespoort Dam’s poor water quality. Although biological control is the most effective and sustainable method of controlling water hyacinth, the dam has unfavourable conditions for agents that the weed thrives in. Literature uses mathematical models and remote sensing to theorise growth rates or estimate coverage. However, prediction could prove beneficial as planning biological control is essential to its success. Hence, a model to predict water hyacinth coverage was developed. This research simplified the complex relationships involved in water hyacinth growth to focus on the most influential factors: temperature and nutrients. Missing data were imputed using multiple k-nearest neighbours. Nutrient datasets had limited data, thus five scenarios were developed to extrapolate datasets, using Monte Carlo simulation and seasonal patterns. The features were used to build ensemble, decision tree, artificial neural network and support vector machine models. Ensemble using the bagging method was the best model resulting in a root mean square error of 4.01 for water hyacinth coverage predictions from 1 June 2018 to 1 May 2019.Item e-Commerce adoption in South African SMMEs(University of the Witwatersrand, Johannesburg, 2024) Mathe, Barney; Sunjka, BernadetteIn this research study e-Commerce adoption in Small, Medium and Micro enterprises (SMMEs) in South Africa was studied. The purpose of this study was to determine the factors that constitute for a successful implementation of the e-Commerce strategy and compare this to the adoption of e- Commerce in SMMEs. The study evaluated frameworks/standards for successful e-Commerce implementation and with this evaluation a consolidated conceptual framework for the successful implementation of e-Commerce was developed. Through samples of both SMME and successful/most visited platforms, functionality and performance assessments of the platforms were conducted using the Jaccard similarity method, and time and method study. T-tests and ANOVA were conducted for performance assessments, to assess if there was a significant difference in performance between SMME and successful e-Commerce sites. Through these assessments it was found that there is a clear gap in adoption from both a functionality and performance perspective, 6 out of 7 of the successful sites had advanced to the last stage of adoption while only one SMME platform reached the last stage which is an external integration stage of the developed framework.