PhD / Doctoral

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    Neutron star X-ray binaries with MeerKAT
    (2026) Gasealahwe, Kelebogile; Monageng, Itumeleng; Woudt, Patrick
    X-ray binaries make up a large fraction of transient systems. These soucres are categorized into black hole and neutron star systems based on the compact object. The dichotomy between neutron star X-ray binaries and black hole X-ray binaries was well established up to the early 2000s. However, the fundamental differences have come into question since the correlation between the radio continuum and X-ray waveband of an increasing amount of neutron stars systems revealed parallel trends to the black hole counterparts. In this study we make use of a sample set of low-mass neutron star X-ray binary systems to investigate the nature of the disc (X ray) and the jet (radio) activity during outburst events. The sample includes SAX J1808.4-3658 an Accreting millisecond pulsar, two transitional Z/Atoll-sources Cir X-1 and XTE J1701-462 and Z-sources Cyg X-2, GX 340+0, GX 17+2, GX 13+1 and GX 349+2. To investigate the disc and jet activity the sources were observed with radio telescopes MeerKAT and AMI and X-ray telescopes Swift-XRT, MAXI and NICER. SAX J1808.4 3658, Cir X-1 and XTE J1701-462 were observed for the full outbursts in 2019, 2021 and 2022/23 respectively. The group of Z-sources only had single observations made in 2021. The outbursts were analysed through radio imaging and examining the lightcurves. Radio flaring events were identified in the lighcurves and the minimum energy of these flares calculated for XTE J1701-462. On the other hand, for Cir X-1, the minimum energy was calculated for the nebula by measuring the size of the structure directly from the radio image. The Cir X-1 image is a deep field L-band radio image, through which we discovered the jets breaking out of the natal supernova remnant in the structure the nebula revealed. By placing the sources on the radio– X-ray our results suggest that some neutron star X-ray binaries follow a similar trend (slope of the plane) as black hole X-ray binaries. Therefore, the physical nature of the compact object may not play a significant role in the relationship of the jet production and the accretion disc of X-ray binaries.
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    Extended cost effectiveness analysis of interventions for early detection, screening and breast cancer control: case studies of South Africa and Uganda
    (2026) Abewe, Christabell; Sinanovic, Edina; Moodley, Jennifer
    The global statistics for the year 2022 indicate that female breast cancer is the second leading cause of global cancer incidence with an estimated 2.3 million cases and among women, it is the most frequently diagnosed cancer and the leading cause of cancer death among women in 157 countries [1]. In the African region, breast cancer incidence and mortality are on an upward trajectory and predicted to double in Sub-Saharan African by 2050. Given the growing burden of breast cancer in low- and middle-income countries (LMICs), these countries now face the challenge of effectively detecting and treating a disease that was previously considered too uncommon to merit the allocation of finite health care resources. As such, in LMICs there is a need to scale up early detection and screening strategies that can improve on the too common pattern of disease presentation at a stage when prognosis is very poor. We constructed a dynamic state transition model to estimate the cost effectiveness of three breast cancer down-staging interventions in Uganda and South Africa. Our model is premised on a comprehensive mathematical framework that estimates the stage shifts in early versus late stages of breast cancer diagnosis based on proportional performance rates of three early detection and screening interventions (awareness raising, clinical breast examination (CBE) and mammography) spanning 40 years. This study then used the extended cost effectiveness analysis framework to assess the possible distributional impact of utilizing universal public financing as a tool to increase access and coverage of breast cancer early detection interventions in these two countries. This dissertation found that biennial CBE and awareness raising interventions are not only crucial for down-staging breast cancer diagnosis, but they are also economically attractive and viable for options for both Uganda and South Africa. Biennial CBE coupled with treatment interventions for all stages was cost-effective for South Africa with an ICER of $2,708 per healthy life year gained. Awareness raising interventions were also found to be cost effective with an ICER of 3,201 per health life year gained. Mammography screening combined with treatment for all stages was not found to be a cost-effective intervention for South Africa with an ICER of $9,491 per healthy life year gained. For Uganda, we found awareness raising interventions to be the most cost-effective interventions for breast cancer control with a dominant ICER of $-118 per healthy life year gained. Biennial CBE for women aged 40-74 combined with treatment for all stages was also cost effective with an ICER of $416 per healthy life year gained. Biennial MMG screening combined with treatment for all stages was not cost effective with an ICER of $3,110 per healthy life year gained. Further, this thesis demonstrated that publicly financing early detection and screening interventions in LMICs for breast cancer can alleviate a considerable proportion of breast cancer burden and catastrophic health expenditures benefiting the poorest wealth quintiles. In South Africa 44% of the deaths averted are in the wealthiest two quintiles while the poorest two quintiles would account for 34% of the total deaths averted. Regarding financial protection, our analysis shows that publicly financing breast cancer control interventions could avert approximately US $7.89 million over the 40years, this translates to US $197,254 annually. The distribution of catastrophic health expenditures averted is pro-poor, with the poorest wealth quintile accounting for 76% of the averted catastrophic 2 health expenditure cases, on the other hand, the wealthiest two quintiles account for approximately 1.4% of the catastrophic health expenditure cases averted. In Uganda, our analysis shows that 55% of the deaths averted are concentrated in the wealthiest two quintiles while the poorest two quintiles would account for 26% of the total deaths averted. Regarding financial protection, our analysis shows that publicly financing breast cancer control interventions could avert approximately US $29.2 million over the 40-years, this translates to US$729,098 annually. The distribution of catastrophic health expenditures averted is pro-poor, with the lowest three wealth quintiles accounting for 63% of the catastrophic cases averted while the richest two quintiles account for 37% of the cases of catastrophic expenditures averted. The findings from this thesis are notable for breast cancer policy in LMICs as the analysis demonstrated significant down-staging associated with early detection and screening interventions for breast cancer. Implementation of these interventions will require substantial additional financial investments, but our analysis shows that the health benefits will broadly outweigh these requirements for CBE and awareness raising interventions.
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    (En)Gendering the mineral supply chain: women's work and livelihoods in 3T extractivism in Africa's Great Lakes region
    (2026) Furniss, Allison; Ross, Fiona
    This dissertation examines the everyday working context of women along the 3T mineral supply chain in Africa's Great Lakes region. 3T's (tin, tungsten and tantalum) are collectively known as “digital minerals” and classified as critical minerals, central to the production of digital technologies. Using a broad definition of extractivism, this research focuses on women who work in artisanal and small-scale mines (ASM), as well as women in downstream production roles along the supply chain. This includes female mineral traders, transporters, mine owners and women working along the export route. As a multi-sited ethnography, this study uses participant observation, interview and focus group methodologies. The androcentrism of extractivism creates a working context with significant gendered divisions of labour, gendered vulnerabilities and barriers to work. Due to these factors, women experience various extractive violences in gendered ways. These include subtle violences that are material and embodied, premised on disposability. Nevertheless, within the overall working context for women, I argue that women's everyday actions, how they narrate their everyday working context and their “ways of operating” all show that women seek to reframe and insert themselves into dominant narratives, reject victimisation and reappropriate space and place in extractivism. These combined factors contribute to a slow acceptance of their participation. Lastly, I show that as one follows the chain of production, women's participation in extractivism decreases as economic opportunities increase, in an inverse relationship. By focusing on women who put the 3T mineral supply chain in motion and whose labour contributes to the manufacturing of digital technologies, this dissertation (en)genders a global supply chain. This research is based on 13 months of ethnographic fieldwork conducted in 2022-2023 in eastern Democratic Republic of the Congo, Rwanda and Tanzania.
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    Extended theories of gravity: the early universe and stellar interiors
    (2026) Campbell, Mariam; Dunsby, Peter Klaus
    This thesis explores two central themes within extended theories of general relativity: the cosmological dynamics of the early universe and the formulation of mathematical frameworks for modeling relativistic stars, with the overarching aim of testing and constraining model parameters in modified gravity. In the cosmological context, a perturbative analysis of scalar-tensor theories demonstrates that a stable bi-scalar tensor model can yield a cosmic bounce preceding natural inflation. A detailed dynamical systems study of a Dirac–Born–Infeld (DBI) field further shows that initial conditions favorable to a bounce become increasingly likely as the system approaches the ultrarelativistic limit. A key result, derived for the first time in a spatially closed Friedmann-Lemaître-Robertson-Walker (FLRW) spacetime, reveals that the introduction of a negative cosmological constant does not lead to cyclic behavior in the DBI framework, implying that additional exotic degrees of freedom may be necessary to achieve cyclicity. In the study of relativistic stars, this thesis presents two new exact, physically viable solutions to the Tolman–Oppenheimer–Volkoff (TOV) equations within extended gravity models. For theories with a quadratic correction to the Einstein–Hilbert action, the solutions describe (1) a quasi-isotropic stellar configuration with a shell and double-layer structure resembling a dipole distribution, and (2) a configuration characterized by a quartic correction to the Newtonian potential and a smooth boundary matching. These results highlight the effectiveness of analytical methods in capturing the astrophysical behavior of compact objects in modified gravity. Moreover, the structural and compositional differences identified in these stellar models, relative to standard general relativity (GR), suggest potentially observable signatures that could be probed by future astrophysical observations.
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    Constitutionally damaged: moving courageously beyond common law fictions
    (2026) Barns, Shaun; Barnard-Naude, Jaco
    The principle of subsidiarity is used as a device to co-ordinate different bodies or rules which compete to achieve the same goal. It is a principle which can take on many formulations depending on the context of its application. For this study, the focus will be on the principle of subsidiarity as applied to the different arms of government in South Africa and as used in private law remedies as applied in the public sphere, specifically vicarious liability in delict. These formulations of the principle of subsidiarity are known as institutional subsidiarity and substantive subsidiarity, respectively. Currently institutional subsidiarity in South Africa takes a very broad formulation and is seen as implicit in the Constitution of South Africa when applied to the local, provincial and national spheres of government. When discussed in terms of the three arms of government, namely, the legislature; the executive and the judiciary, institutional subsidiarity is discussed under the broad principle of separation of powers. This study seeks to provide a more specific understanding of the separation of powers by translating it into a spectrum between coordination and integrity. It will use examples of tools that courts currently use to co-ordinate and co-operate with other branches. It will also explain when the courts can act without cooperation with the other branches on the other end of the spectrum called integrity. The metaphorical spectrum is useful for the courts as it helps determine what tools are available to them to exercise their constitutional function and provides a link between their institutional purpose and the related rules of substantive subsidiarity. The primary focus of the study will be substantive subsidiarity and specifically the relationship between the common law and the Constitution. The study will use cases involving state vicarious liability in delict, specifically involving the South African Police Service, to show how the previous formulation of substantive subsidiarity has resulted in irreconcilable doctrinal errors in private law. Further, it will analyse recent cases regarding constitutional damages to show that clarity is required from the courts to ensure the future of a robust state liability doctrine in South Africa. A comparative analysis of state liability in England, France and Canada is undertaken to better understand the shortcomings within the South African legal system in this regard. Finally, building on the study of subsidiarity and comparative analysis, a new framework for hard cases within state liability is developed which clearly guides when vicarious liability in delict, direct state delictual liability, constitutional damages and any other damages are appropriate within the South African legal system.