4. Electronic Theses and Dissertations (ETDs) - Faculties submissions
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Item Optimisation of Kick Latency for Enhanced Performance of Robots in the RoboCup Three-Dimensional League through Proximal Policy Optimisation (PPO)(University of the Witwatersrand, Johannesburg, 2024-07) Nekhumbe, Humbulani Colbert; Ranchod, PraveshThis study aimed to enhance the kicking ability of Nao robots in the three-dimensional RoboCup simulation by addressing a crucial challenge observed in the University of Witwatersrand RoboCup team. The focal challenge revolved around a noticeable delay and slow movement manifested by the robot during ball kicks, leading to vulnerabilities in ball possession against opposing teams. To surmount this challenge, the implementation of Proximal Policy Optimisation (PPO), a methodology pioneered by OpenAI, was advocated. The precise objective was to optimise kick parameters, with a primary emphasis on curtailing kick latency. This optimisation aimed to ensure swift and accurate execution across various kicking scenarios, encompassing actions like propelling the ball into the opponent’s territory to bolster ball possession and thwart adversary manoeuvres. Harnessing the iterative advancements embedded in PPO, the successor to Trust Region Policy Optimisation (TRPO), the endeavour was to refine the kicking behaviour of Nao robots. This optimisation process significantly reduced the observed kick delay, and this made the robot more agile and effective at competing in the complex three-dimensional RoboCup simulation environment. The study’s outcomes highlighted substantial progress in reducing kick latency and improving the adaptability of robotic soccer players, opening up possibilities for further exploration in reinforcement learning for autonomous agents.Item Search for high-mass resonances in the Zgamma channel and Quality assurance of Scintillation detector modules of Tile Calorimeter Phase-I Upgrade of the ATLAS detector(University of the Witwatersrand, Johannesburg, 2024-09) Mokgatitswane, Gaogalalwe; Ruan, Xifeng; Solovyanov, Oleg; Mellado, BruceThis thesis presents a search for narrow, high-mass resonances decaying to a Z boson and a photon (Zy) in the final state. The analysis utilizes the full Run 2 dataset collected by the ATLAS experiment at the CERN Large Hadron Collider (LHC), corresponding to an integrated luminosity of 140 fb-1 of proton-proton col- lisions at a center-of-mass energy of ps = 13 TeV. The search focuses on a mass range of 220 GeV and 3400 GeV, aiming to identify deviations from the expected background arising from Standard Model processes. A small excess is observed at 250 GeV within the area of interest, with a combined significance of 2.1 standard deviations, indicating the need for further investigation with more data. Upper limits are set on the production cross-section times branching ratio for resonances decaying to Zy across the investigated mass range. When considering spin-0 resonances produced through gluon-gluon fusion, the observed limits at a 95% confidence level range from 65.5 fb to 0.6 fb. For spin-2 resonances produced via gluon-gluon fusion (with quark-antiquark initial states), the limits vary between 77.4 (76.1) fb and 0.6 (0.5) fb. The thesis also highlights the successful Phase-I upgrade of the Tile Calorimeter in the ATLAS detector, ensuring its continued performance. This involved the replacement of degraded Gap-Crack scintillators and Minimum Bias Trigger Scintillators (MBTS) with non-irradiated ones, along-side optimising their geometry, all in preparation for data taking during LHC Run 3. These upgrade endeavors encompassed the design of new Gap-Crack and MBTS counters, including extensions to higher rapidity, the assembly of these counters, their rigorous qualification, and characterization using radioactive sources (90Sr and 137Cs), along with their seamless integration onto the ATLAS detector.Item Magnetic field strength estimations for the main phases of solar cycles 13-24 using magnetohydrodynamic Rossby waves in the lower tachocline(University of the Witwatersrand, Johannesburg, 2024-09) Morris, Tania Mari; Duba, ThamaThe magnetic field strength (MFS) estimates used by the existing space weather prediction models (SWPMs) are inaccurate. Consequently, it has been indicated that there is a need to find solutions to rectify the wrong assumption that the magnetic field remains constant in strength and location throughout the solar cycle. This study explores a solution to this problem by increasing the granularity and accuracy of the previous MFS estimations by calculating them for the main phases of the solar cycle (solar minimum and maximum) per hemisphere for solar cycles 13-24. A dispersion relation of the fast magnetohydrodynamic (MHD) Rossby wave was derived analytically in spherical coordinates that included a toroidal magnetic field and latitudinal differential rotation, which adequately captures the dynamics of the lower tachocline. Secondly, a change to the methodology of calculating the MFS that utilises the established connection between the observed Rieger-type periodicity (RTP) in solar activity of 150-190 days and the fast MHD Rossby wave in the lower tachocline was proposed. Furthermore, a new magnetic field profile (MFP) of Bφ = B0 sin(6Θ) was introduced to improve the model results. This MFP has a maximum and minimum value at the same latitudes associated with sunspot appearances during these extreme solar cycle phases. Consequently, the MFS values were calculated at a latitude of 29◦ (solar min) and 16◦ (solar max) using the hemispheric RTP data. The average MFS (RTP) for the solar min and solar max in the dominant hemisphere was established to be 8 kG (212 days) and 76 kG (163 days), respectively. For the non-dominant hemisphere, the average MFS was established to be 5 kG (213 days) and 50 kG (183 days) for the solar min and max, respectively. The results of this study show a significant difference in the results based on latitude. The findings have also revealed that the periodicity of increased solar activity associated with a specific MFS is affected not only by the solar cycle strength and hemispheric asymmetry but also by the solar cycle phase (or latitude) considered. Additionally, we strongly argue that this study’s MFS results represent reality more closely than previously calculated results. Therefore, we propose that the MFS estimates reported in this study should be considered for the input to various existing space weather prediction models.Item Towards Lifelong Reinforcement Learning through Temporal Logics and Zero-Shot Composition(2024-10) Tasse, Geraud Nangue; Rosman, Benjamin; James, StevenThis thesis addresses the fundamental challenge of creating agents capable of solving a wide range of tasks in their environments, akin to human capabilities. For such agents to be truly useful and be capable of assisting humans in our day-to-day lives, we identify three key abilities that general purpose agents should have: Flexibility, Instructability, and Reliability (FIRe). Flexibility refers to the ability of agents to adapt to various tasks with minimal learning; instructability involves the capacity for agents to understand and execute task specifications provided by humans in a comprehensible manner; and reliability entails agents’ ability to solve tasks safely and effectively with theoretical guarantees on their behavior. To build such agents, reinforcement learning (RL) is the framework of choice given that it is the only one that models the agent-environment interaction. It is also particularly promising since it has shown remarkable success in recent years in various domains—including gaming, scientific research, and robotic control. However, prevailing RL methods often fall short of the FIRe desiderata. They typically exhibit poor sample efficiency, demanding millions of environment interactions to learn optimal behaviors. Task specification relies heavily on hand-designed reward functions, posing challenges for non-experts in defining tasks. Moreover, these methods tend to specialize in single tasks, lacking guarantees on the broader adaptability and behavior robustness desired for lifelong agents that need solve multiple tasks. Clearly, the regular RL framework is not enough, and does not capture important aspects of what makes humans so general—such as the use of language to specify and understand tasks. To address these shortcomings, we propose a principled framework for the logical composition of arbitrary tasks in an environment, and introduce a novel knowledge representation called World Value Functions (WVFs) that will enable agents to solve arbitrary tasks specified using language. The use of logical composition is inspired by the fact that all formal languages are built upon the rules of propositional logics. Hence, if we want agents that understand tasks specified in any formal language, we must define what it means to apply the usual logic operators (conjunction, disjunction, and negation) over tasks. The introduction of WVFs is inspired by the fact that humans seem to always seek general knowledge about how to achieve a variety of goals in their environment, irrespective of the specific task they are learning. Our main contributions include: (i) Instructable agents: We formalize the logical composition of arbitrary tasks in potentially stochastic environments, and ensure that task compositions lead to rewards minimising undesired behaviors. (ii) Flexible agents: We introduce WVFs as a new objective for RL agents, enabling them to solve a variety of tasks in their environment. Additionally, we demonstrate zero-shot skill composition and lifelong sample efficiency. (iii) Reliable agents: We develop methods for agents to understand and execute both natural and formal language instructions, ensuring correctness and safety in task execution, particularly in real-world scenarios. By addressing these challenges, our framework represents a significant step towards achieving the FIRe desiderata in AI agents, thereby enhancing their utility and safety in a lifelong learning setting like the real world.Item Beneath These Saline Stars(University of the Witwatersrand, Johannesburg, 2024) Wilhelm-Solomon, MatthewA plague of drowning strikes an unnamed lakeside city. Hospitals are flooded with patients – primarily Black youth – who have died on soccer pitches, in their homes, and on the streets. A disgraced and divorced white journalist, now working on the arts pages of his newspaper, named Lüderitz Edward Leveza writes a profile on a performing artist and medical doctor, Isiwa: they are tattooed with black lightning, and walk as if on the point of falling. Isiwa is searching for the childhood song stolen from them when police arrested their mother—an activist against the former dictatorship—as a child. They provide Lüderitz information on deaths at the hospital where they work. Lüderitz’s investigation of the drownings takes him deeper into his past, his documentation of torture during the dictatorship, and his entanglement with Isiwa’s life. Together, Isiwa and Lüderitz see inexplicable visions in the city’s sky: men-of-war pass over his apartment block, a shoal of sardines weaves through the tower blocks, and whales arrive to mourn the dead. Isiwa leads an occupation of the city’s Freedom Square in protest against the deaths, but they are increasingly isolated and then arrested. Lüderitz is removed from his job and is mainly alone, punctured by Isiwa’s absence and left longing for them. During this time, he helps a young journalist called Zé in his investigations into the protests and drownings, which lead to a terrifying outcome. Beneath These Saline Stars is an aesthetic reworking of post-colonial journalistic realism and surrealism. It explores moral complicity with violence, loss and queer desire, rebellion and mourning, and the search for healing in a time of concatenated ecological, public health, and political catastrophes. A reflective essay follows the novel, in the form of crônicas – a Brazilian style of fragmentary essay. These explore diverse themes, both theoretical and personal, related to the context, influences and resonances of the novel: transatlantic literature and music; magical realism; créolité and postcolonial thought; Candomblé and climate change. The juxtaposition of these fragments aims to illuminate the personal, literary and political tides from which Beneath these Saline Stars took form.Item Bridging the Gap: Achieving Professionalization Through Memes(University of the Witwatersrand, Johannesburg, 2024) Greaves, Megan; Parkins-Maliko, Natasha‘Bridging the Gap: Achieving Professionalization through Memes’ focuses on how social media is a useful marketing tool that South African Sign Language interpreters can use to promote the professionalism of interpreting. Up to now, there has been little focus on the ways South African Sign Language interpreters can use social media memes/behaviours to promote and advocate for the mainstream recognition of interpreters. This research bridges that gap by conducting a discourse analysis of the various hashtags South African Sign Language interpreters can employ to promote their personal brands as well as the brands of interpreting agencies. It also looks at the various social media strategies individuals and companies use to reach wider audiences. Although social media is a useful tool to promote professionalism, it does not come without its risks and ethical concerns. These risks are discussed in depth, and it is imperative that interpreters keep these risks in mind when using social media.Item Kusengenzeka noma yini: Wakithi singayibiza ngani lendawo?(University of the Witwatersrand, Johannesburg, 2024) Chiliza, Mhlonishwa; Hlasane, RangoatoKusengenzeka noma yini means ‘anything can still happen’, serving as a metaphorical phrase or a saying in isiZulu, which hints at the ambiguities of life within hostels. The phrase is interpretive, and multi-layered, reflecting the beauty, complexities, and systematic violence within the spheres of black social life in South Africa. Wakithi singayibiza ngani lendawo? means ‘what should we call this place?’ This is both a question and a double-sided statement, drawn from the everyday practice of yarning inside the hostel arena. South African hostels are congested and temporal, thus allowing for progress, failure, and the crafting of practices that include exploring life opportunities, self- determination, and recreation of freedom by the dwellers. Wakithi singayibiza ngani lendawo? is a critical question that encapsulate the feeling of yarning and provides a wide range of avenues to negotiate for a new image of hostels. For images that are real or authentic and challenge preconceived portrayal of black migrant residents in South African archives, see the exposé framework between the 1950s -1990s in the documentary series by Ernest Cole, Peter Magubane, Roger Meinjtes and Eli Weinberg. The practice of this resistance group of photographers exposed the injustices of the apartheid regime, while their approach is invasive and shows a violent gaze. It exposes the hostel residents as poor, needy, undignified, bitter and hopeless, and these negative elements overshadow the beautiful experiments that have always been practiced inside the hostel. The purpose of my praxis, through visual arts, is to explore these beautiful experiments inside the hostel by employing a wide range of mediums, such as drawing, sculpture installations, performance (video) and photography. It is a diverse approach that allows for new meanings and ideas to manifest, enabling a new image of hostels to emerge. The work or praxis serve to address the ‘missing narrative’ to reclaim the loss dignity of hostel communities. Inside the hostel engage with intimate objects, and interpreting different types of sounds within the conceptual frame of Wayward Lives, Beautiful Experiments Intimate Histories of Social Upheaval (2019) which is drawn from the work of Saidiya Hartman. The wayward framework and a mode of close narration, influences my philosophical as I navigate hostels to find a newly informed image that is far more human and comprehensive.Item Kwaitoscapes: Reading the historio-graphic narratives in the visual cultures of black youth(University of the Witwatersrand, Johannesburg, 2024) Hlasane, Mphapho Christian; Peterson, BhekizizweThe argument in this thesis is this: The kwaito music video can be an audiovisual disruptor that recasts and sometimes challenges sociopolitical norms. This study examines the optic narratives in kwaito’s visual culture – with a special focus on the music video. The kwaito music video contributes scantly to scholarship about the music video genre on the African continent. As such, in addition to the exploration of kwaito’s aesthetics, this study deepens ‘our’ reading of the kwaito music video’s narration of notions of gender, race and nationalism as they intersect with technological, economic and political imperatives (Emoresele 2022). This study encompasses two interrelated parts: the production two essayistic videos, and a reflective dissertation to advocate and advance what is understood as artistic research from the ‘Global South’. This interdiscursive study is interested in the manner in which kwaito music video grammar is shot through a historio-graphic lens and modality, that requires a reading of kwaito visual culture within a broader constellation of trans-local black cultural practices, visual and otherwise. The kwaito music video reflects and responds to visual motifs found in music videos for South African musical/cultural practices such as ‘bubblegum’, as well as those in Caribbean and North American black music, especially reggae, R & B and hip-hop. Yet, the visual practices within the kwaito music video are not limited to musical genres, but are essential to musicking practices, which are always if not increasingly visual. As such, within a complex set of dynamics in nationalist global popular culture, kwaito visual cultures represent both the positions of black youth, as well as how black youth not only negotiate their place in the so-called global village but also go about claiming their stakes therein (Musila 2022). It is worth thinking about how kwaito visual culture flips the dearth of nationalist grammar as an opportunity to re-map the topographies and visual markers that constitute black cultural work within global popular culture (ibid.: 4). Kwaito visual culture continues to redefine its visual vocabulary to contradict, complicate and reconceive of nationalist visual ideas and identities. It does this through what I term historio- graphic kwaitoscapes – a writing of histories that produce interdiscursive plura-literary texts (Quayson 1997). Historio-graphic kwaitoscapes are a cyclic writing – from the ground, to the lyric, to the screen, and back again.Item Indigenous languages, cultural cognition and public interest in post-apartheid South Africa(University of the Witwatersrand, Johannesburg, 2024) Motsogi, Mphonyana; Mjiyako, LwaziThe South African Language Policy Act was enacted in response to the apartheid system, which systematically marginalised indigenous languages and reduced them to non- official communication tools. The SABC (South African Broadcasting Corporation) and ICASA (Independent Communications Authority of South Africa) have the responsibility of ensuring that all official languages of South Africa, including minority indigenous languages, are equally represented in the broadcasting space. This study examines the extent to which the SABC effectively enforces language quota systems, as mandated by ICASA, to promote and safeguard the development of the Sotho/Tswana language category and other official indigenous languages in the broadcasting space; for instance, Tshivenda. The multilingual program, Motswako is used as a (A case study); the programme was broadcast on SABC 2. The study analysed the South African broadcasting model in conjunction with ICASA's language policy regulation document. The study employed language planning theories and the communication accommodation theory to gain insight into the language context and multilingualism in South Africa. In addition, the study focused on the examination of public interest with the objective to investigate the involvement of the public in policy planning and development. The significance of media practitioners as representatives of the public was understood through the application of the social responsibility theory. This research project employed both qualitative and quantitative research methods, specifically analysing language policy documents from both the SABC and ICASA and other relevant articles on language planning and policy. The quantitative route was taken to quantify within episodes; the number of time hosts code switch/mix to western languages. The data collection process involved the collection of policy documents and articles, and the findings were analysed through thematic analysis. A total of eighteen episodes from the multilingual programme Motswako were selected and evaluated according to the language editorial policy principles of the SABC and the language quota systems established by ICASA. The study revealed that both the SABC and ICASA lack effective mechanisms to monitor and safeguard the development of indigenous languages in locally produced programs.Item Does a social purpose matter to new talent? Understanding the importance of corporate social responsibility to university students(University of the Witwatersrand, Johannesburg, 2024) Humbani, Natasha; Mlilo, SifisoThe current study explored the perceptions of final year undergraduate and postgraduate students on CSR using Social Identity Theory and Signalling Theory. The lack of research in South Africa examining students’ perceptions of CSR and its possible influence on their choice of employer served as the motivation for the investigation. The study was carried out in the South African environment and a qualitative methodology was used to elicit the complex opinions held by these university students about CSR. A sample of 22 final year undergraduate and postgraduate students from diverse academic disciplines participated in this study. Purposive sampling was employed to select participants who possessed specific characteristics that fit the study while snowball sampling facilitated easier access to individuals who would be difficult to reach. The thematic analysis revealed several prominent themes. Themes of giving back to society, social accountability, inclusive work environments, diverse CSR priorities and influence of education and awareness emerged as central factors in students’ decision-making. While further investigations are needed, the study’s findings indicate that a social purpose does in fact appeal to new talent and that students exhibit a higher awareness of external CSR initiatives in comparison to a company’s internal CSR initiatives. The findings also indicated the growing importance of CSR as a determinant factor in students’ choice of an employer. While generalisation is not possible and further research is required the implications of these findings could assist managers and employers to highlight the importance of employer branding messages that emphasize a commitment to social responsibility, thereby fostering a stronger connection with new talent. Additionally, the awareness gap between students’ perceptions of external and internal CSR initiatives underscores an opportunity for organisations to enhance their communication of internal CSR strategies.