Department of Physics and Astronomy
http://hdl.handle.net/11394/99
2024-03-29T01:59:51ZSample selection effects in laduma stacking experiments
http://hdl.handle.net/11394/10685
Sample selection effects in laduma stacking experiments
Gwebushe, Lwandile
This study explores the impact of selection effects introduced by input optical cata-logues on high-redshift stacking experiments. Using the Hi stacking technique, the Hi content of LADUMA synthetic data cubes is analyzed within the redshift range of 0.7 < z < 0.758. The focus is on galaxies with stellar masses of M⋆/M⊙ ≥ 108.5. The investigation reveals several key findings. Firstly, the input optical catalogues displays biases towards specific galaxy types, including those with lower stellar masses, lower star-formation rates, lower specific star-formation rates, galaxies in groups, and red galaxies. These biases can lead to higher confusion rates in stacked spectra, emphasizing the need for appropriate correction methods to avoid overestimation in subsequent quantitative analyses. Secondly, the environmental impact on Hi gas properties is examined by comparing group galaxies and non-group galaxies. Non-group galaxies exhibit higher Hi richness and Hi gas fractions compared to group galaxies. Correlations between Hi properties and star-formation/stellar mass properties are observed, indicating that lower mass galaxies are relatively inactive within their environments and are at an earlier stage of evolution. The study also addresses the correction of confusion rates in stacked spectra. While a correction method is implemented, it is found to result in overestimated Hi deple-tion timescales. Criticism is directed towards the use of this method, stressing the importance of employing accurate and robust approaches to correct for confusion rates and ensure precise estimation of galaxy properties.
>Magister Scientiae - MSc
2023-01-01T00:00:00ZExploring poly (2, 5) benzimidazole enhanced with carbon nanotubes for space applications
http://hdl.handle.net/11394/10681
Exploring poly (2, 5) benzimidazole enhanced with carbon nanotubes for space applications
Fourie, Lionel Fabian
This work explores using polymeric materials for space radiation shielding in low-earth orbit. Shielding against radiation is essential on any space mission. Low atomic number materials, such as hydrogen, have shown to be effective in shielding ionising radiation. However, compared to metallic alloys, these materials suer from relatively low mechanical and thermal properties, which limit their application. Aluminium (Al) enjoyed wide use in space applications as a structural and radiation shielding material. However, weight and secondary radiation generation issues have made its use as a shielding material less viable on modern space missions where cost and safety play a crucial role in planning these missions. On modern space missions, conventional shielding materials include Al alloys, high-density polyethylene, and water. The disadvantages include low thermal properties, high atomic numbers, and complex maintenance systems. This lead to exploring other materials that can mitigate some of these drawbacks. A proposed approach to replacing high atomic number metals is deploying hydrogen-rich polymers enhanced with nanofiller materials to form polymer nanocomposites. Poly-mers enhanced with nanofillers can achieve improved physical properties while pro-viding adequate radiation shielding functions at a lower weight with less secondary radiation generation.
Philosophiae Doctor - PhD
2023-01-01T00:00:00ZStructural features of air-processible methyl ammonium lead triiodide (MAPbI3) perovskite thin films grown on Al-doped ZnO Nanowire Arrays
http://hdl.handle.net/11394/10592
Structural features of air-processible methyl ammonium lead triiodide (MAPbI3) perovskite thin films grown on Al-doped ZnO Nanowire Arrays
Phakoe, Mpho
The performance of air stable, mixed halide (MAPbI3-xClx) perovskite based solar cells is highly dependent on the quality and stability of the perovskite thin film, which in turn, is dependent on the substrate on which it is deposited. ZnO presents excellent optoelectronic properties such as high electron mobility and diffusion length, direct band gap with high exciton binding energy. An array of ZnO nanowires (NWs) grown vertically on a conducting substrate, benefits from a large surface area, direct electron transport pathway and reduced recombination rate of carriers when used in a solar cell. These arrays of ZnO NWs may be synthesised by a wide range of methods, with the chemical bath deposition (CBD) method considered to be the most simple and cost-effective.
>Magister Scientiae - MSc
2023-01-01T00:00:00ZChemical pressure-induced transition of the magnetic ground state from ferromagnetic to antiferromagnetic order in CeCuGe and DyCuIn alloys
http://hdl.handle.net/11394/10560
Chemical pressure-induced transition of the magnetic ground state from ferromagnetic to antiferromagnetic order in CeCuGe and DyCuIn alloys
Altayeb, Anas Alamin Hassan
Rare-earth intermetallic compounds continue to attract considerable attention, due to their fundamental importance in understanding physical properties and potential applications based on a variety of phenomena. The ternary intermetallic compounds of the RTX series (R = rare-earth element, T = 3d / 5d transition element, X = p-block element) in particular, were studied extensively for the past two decades. A number of interesting magnetic and electrical properties of practical and fundamental importance, were found in different compounds of the RTX series, including giant and large magnetocaloric effects and magnetoresistivity, antiferromagnetic (AFM) to ferromagnetic (FM) order transitions and rich magnetic transition phase diagrams. Most of these properties are related to the interaction between the R-4f (localized) electronic states and other (itinerant) electronic states in the electronic system. Several experiments have provided evidence for magnetic ground state switching between FM and AFM ordering, driven by pressure or chemical substitution in d and f electron compounds. The methods used to investigate the magnetic phase transitions could be divided into macroscopic and microscopic ones. The macroscopic method relied on the temperature dependences of magnetization, magnetic susceptibility and specific heat measurements while the microscopic method relied on neutron diffraction and Mössbauer effect.
Philosophiae Doctor - PhD
2023-01-01T00:00:00Z