Systematic effects and mitigation strategies in observations of cosmic re-ionisation with the Hydrogen Epoch of Reionization Array
- Authors: Charles, Ntsikelelo
- Date: 2024
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/432605 , vital:72886 , DOI 10.21504/10962/432605
- Description: The 21 cm transition from neutral Hydrogen promises to be the best observational probe of the Epoch of Reionisation (EoR). It has driven the construction of the new generation of lowfrequency radio interferometric arrays, including the Hydrogen Epoch of Reionization Array (HERA). The main difficulty in measuring the 21 cm signal is the presence of bright foregrounds that require very accurate interferometric calibration. However, the non-smooth instrumental response of the antenna as a result of mutual coupling complicates the calibration process by introducing non-smooth calibration errors. Additionally, incomplete sky models are typically used in calibration due to the limited depth and resolution of current source catalogues. Combined with the instrumental response, the use of incomplete sky models during calibration can result in non-smooth calibration errors. These, overall, impart spectral structure on smooth foregrounds, leading to foreground power leakage into the EoR window. In this thesis we explored the use of fringe rate filters (Parsons et al., 2016) as a mean to mitigate calibration errors resulting from the effects of mutual coupling and the use of an incomplete sky model during calibration. We found that the use of a simple notch filter mitigates calibration errors reducing the foreground power leakage into the EoR window by a factor of ∼ 102. Thyagarajan et al. (2018) proposed the use of closure phase quantities as a means to detect the 21 cm signal, which has the advantage of being independent (to first order) from calibration errors and, therefore, bypasses the need for accurate calibration. In this thesis, we explore the impact of primary beam patterns affected by mutual coupling on the closure phase. We found that primary beams affected by mutual coupling lead to a leakage of foreground power into the EoR window, which can be up to ∼ 104 times and is mainly caused by the unsmooth spectral structure primary of primary beam sidelobes affected by mutual coupling. This power leakage was confined to k < 0.3 pseudo h Mpc−1. Lastly, we also proposed and demonstrated an analysis technique that can be used to derive a flux scale correction in post-calibrated HERA data. We found that after applying flux scale correction to calibrated HERA data, the bandpass error reduces significantly, with an improvement of 6%. The derived flux scale correction was antenna-independent, and it can be applied to fix the overall visibility spectrum scale of H4C data post-calibration in a fashion similar to Jacobs et al. (2013). , Thesis (PhD) -- Faculty of Science, Physics and Electronics, 2024
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- Date Issued: 2024
Anonymous testimony and epistemic responsibility
- Authors: Ajiboro, Aderonke Adeyinka
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/432286 , vital:72858 , DOI 10.21504/10962/432286
- Description: In this thesis, I examine anonymous testimony in both offline (face-to-face) and online (internet and social media) interactions and the epistemic concerns it raises in relation to belief, knowledge, justification, and normative assessments of assertions. I discuss anonymous testimony as involving a relation between the hearer and the content of the testimony in comparison to ordinary cases where the speaker of an assertion is known. In anonymous testimony, the hearer has the burden of epistemic responsibility to arrive at a testimonial belief or arguably acceptance. The hearer is also accountable for the anonymous testimony in the event of re-assertion. I also assess the norms of assertion for anonymous testimony and argue that knowledge, truth, and belief norms that apply in cases where the speaker is known should not be applied to cases of anonymous speakers. Epistemologists have paid little attention to anonymous testimony and its implications on the norms of interaction. This is a study in the epistemology of testimony and it aims at providing further understanding of the epistemic responsibility of hearers of anonymous testimony. In Chapter One, I argue that anonymous testimony can be appropriately described as testimony; where the properties of an assertion to induce belief in the hearer are sufficient to describe the assertion as testimony. I examine the kinds of anonymity and the burden of epistemic responsibility for the hearer. I introduce basically anonymous testimony in offline and online contexts of interaction. A basically anonymous testimony occurs where, at the instance of receiving testimony and making an epistemic decision on it, the speaker is unidentifiable to the hearer. In Chapter Two, I discuss the kinds of epistemic attitudes hearers may have when they receive anonymous testimony. I discuss reductionism, antireductionism, and entitlement theory as accounts of the justification for believing testimony. I argue that acceptance is the appropriate attitude and the entitlement theory provides a basis for accepting anonymous testimony. I also argue that practical reasons are a sufficient to accept anonymous testimony. Also, I discuss the possibility that a hearer of anonymous testimony can make a wrongful presumption by assigning an identity to a person as the speaker of an anonymous testimony. This can cause harm to the ‘person’ of the presumed speaker such as an unwarranted credibility assessment of the person by other people in the community. I also argue that making a credibility assessment of a presumed speaker constitutes harm to a proper epistemic assessment of the content. In Chapter Three, I discuss the possibility of trust relations between an anonymous speaker and a hearer. I argue that the hearer is solely responsible for making an epistemic decision from anonymous testimony. I argue that anonymous testimony can be relevant to a hearer given the value of its content. In Chapter Four, I discuss the applicability of knowledge, truth, belief, reasonable to believe and supportive reasons norms for the re-assertion of anonymous testimony. Hence, I argue that the supportive reasons norm, which acknowledges acceptance of an assertion, the relevance of contexts, and admits both epistemic and practical reasons to make an assertion, should guide the re-assertion of anonymous testimony. I also argue that a hearer should be epistemically conscientiousness for responsible re-assertion of received anonymous testimony. , Thesis (PhD) -- Faculty of Humanities, Philosophy, 2023
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- Date Issued: 2023-10-13
Investigating pedagogical practices of English First Additional Language educators in Grade 12 short stories: a case study
- Authors: Jabe, Sizwe
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424052 , vital:72119
- Description: The focus of this study was to investigate pedagogical practices of English First Additional Language educators in teaching Grade 12 short stories. An interpretive qualitative case study of three educators from three high schools in Chris Hani West district, in Eastern Cape were purposefully selected. Lesson observations, semi-structured interviews, and document analysis (lesson plans) with three English FAL educators were used to collect data. Shulman’s (1986) Pedagogical Content Knowledge was used as the theoretical framework and analytical tool for the study. Data revealed ineffective teaching strategies and on-the-surface subject matter knowledge that hampers the critical teaching of short stories. It also showed that educators have limited knowledge of learners’ learning difficulties and how to address them. The study recommends less teacher talk that was observed in many classes, to be replaced by extended discussions on the part of the learners. Educators should establish a variety of contemporary teaching strategies which put critical thinking and active learning before examination preparation. Lastly, educators, in their teaching of short stories, should consult various resources and attend content workshops to keep subject knowledge up to date. , Thesis (MEd) -- Faculty of Humanities, Study of Englishes of Africa, 2023
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- Date Issued: 2023-10-13