Magister Scientiae - MSc (Physics)

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https://hdl.handle.net/10566/12433

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Preparation and characterization of tio2-mwcnt hybrid and tio2-fe2o3-mwcnt trihybrid nanofluids
(University of the Western Cape, 2025) Sibiya, Mziwandile
Over the past few decades, numerous studies have been conducted by the research community on the investigation of the cooling properties of nanofluids compared to those of the conventional heat transfer fluids, such as mineral oil, water, engine oil, and ethylene glycol. The literature indicates that many studies have been conducted on mononanofluids and hybrid nanofluids, but studies on trihybrid nanofluids remain limited. Recently, trihybrid nanofluids have emerged as a new class of nanofluids with enhanced thermophysical properties relative to mono and hybrid nanofluids. The aim of this study was to formulate stable hybrid and trihybrid nanofluids and perform a comparative analysis of their stability and thermophysical properties. Prior to nanofluids preparation, the nanoparticles were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS) to study the structural properties, morphology, particle size distribution, and the elemental composition of nanoparticles. Ternary (TiO2-α-Fe2O3-MWCNT) and binary (TiO2-MWCNT) nanoparticles were suspended in deionized water (DIW) at a constant volume concentration of 0.1 vol.% with composition ratios of 15:80:5, 10:80:10, and 5:80:15 for trihybrid and 80:20 and 20:80 for hybrid nanofluids. The stability of THNFs and HNFs was improved by optimizing critical formulation parameters such as nanoparticle composition ratio, dispersion fraction, and sonication time. The stability of nanofluids was assessed via visual inspection, UV-Vis spectroscopy, and pH measurements. The thermophysical properties of THNFs and HNFs(thermal conductivity (κ), viscosity (µ), and electrical conductivity (λ)) were measured using standard instruments. THNFs exhibited enhanced colloidal stability compared to HNFs, indicating improved nanoparticle dispersion and reduced sedimentation. Among THNFs, sample C (TiO2α-Fe2O3-MWCNT) 5:80:15 demonstrated the highest performance, with κ enhanced by 8.97%, λ increased by a factor of 5.2, and µ increased by 37.7%. In the case of HNFs, sample E (TiO2-MWCNT) 20:80 showed the best results, with κ improved by 6.66%, λ enhanced by a factor of 4.83, and µ increased by 34.99%. Conclusively, the κ, λ, and µ values of THNFs were found to be elevated to those of HNFs, showing that hybridization of different nanoparticles enhances the thermophysical performance of nanofluids.
Probing diffuse galactic synchrotron emission using meerkat single dish data
(University of the Western Cape, 2025) Mahlalela, Sifiso
In recent experiments, the 21 cm neutral hydrogen (HI) line has been measured using the intensity mapping (IM) method. Measuring this HI line is a complex process because it is faint and easily contaminated by radio frequency interference (RFI) and the foregrounds. Using the MeerKLASS experiment, from the L-band (900-1670 MHz) data the 21 cm signal was probed using the single dish mode. However, initially the RFI and the most dominant foreground in our Galaxy which is the synchrotron emission had to be investigated, so they could be removed. This process also provided another validation for the existing data pipeline. As synchrotron emission is modeled using a power law, one way to probe said emission is to measure the spectral index of this power law. From the various results available in the literature, the average spectral index for frequencies that are between 0.408 and 3.8 GHz is ∼ −2.7. In this study, the MeerKLASS UHF-data (544-1087 MHz) was used alongside various ancillary experiments to probe the temperature spectral index of the synchrotron emission using the Temperature-Temperature (T-T) analysis method, as well as probing the flux density spectral index using the Spectral Energy Distribution method. From the T-T analysis, the average spectral index calculated between 45 and 923 MHz is −2.71 < β < −2.66; these results are in good agreement (within 1σ) with the existing results from Irfan et al. (2022) and Platania et al. (1998). T-T analysis between MeerKLASS and Haslam data conducted towards the lower end of the UHF-band, however, revealed a sharp and physically unlikely change in the synchrotron spectral index never before seen. This coupled with the Spectral Energy Distribution analysis revealed that further work needs to be conducted on the UHF data reduction pipeline with regards to both calibration and RFI removal. There appears to be a systematic bias in the data at a level of around 15% at the beginning of the UHF-band, decreasing to only around 5% by the end of the UHF-band when comparing these data to MeerKLASS L-Band, Haslam and OVRO-LWA data.
An investigation of students’ approaches to solving problems using equations of motion
(University of the Western Cape, 2025) Tanci, Sinovuyo
The purpose of this research study is to investigate how to address the under-preparedness of students entering first year physics in South African universities, particularly with regard to their competence in solving kinematics problems. Previous studies show that the best tool for changing and expanding the conceptual understanding of a learner is problem solving; it assists a learner in dealing with new and unfamiliar concepts. These studies have also shown that cooperative learning helps students to share knowledge with each other. This research study thus investigated students’ perceptions of approaches in solving kinematic problems and tasks are examined for the effects of expert problem-solving approaches and cooperative learning on the performance and results obtained by students in first-year mainstream physics at the University of the Western Cape. This process involved profiling students and exploring their problem-solving approaches and performance using prior knowledge and after a teaching and learning focused explicitly on problem-solving. The data was collected by means of surveys and tasks and was analysed using descriptive statistical and qualitative methods. From this study, it can be concluded that cooperative teaching and learning focused on expert problem-solving is necessary in a physics course to address students’ under-preparedness in their first year at university. In addition, it is recommended that lecturers encourage students to use problem solving when tackling any physics problems.
Detecting the turnover of the power spectrum with SKAO and other surveys
(University of the Western Cape, 2025) Dube, Yolanda
Detecting the turnover of the power spectrum with SKAO and other surveys. This thesis explores the potential of next-generation experiments, specifically the Square Kilometre Array and the Dark Energy Spectroscopic Instrument, to detect and constrain the power spectrum turnover, a key feature of the universe’s large-scale structure holding the key for probing ultra-large scales. Employing intensity mapping and galaxy surveys, we utilize Fisher forecasts and Markov Chain Monte Carlo simulations to model and analyze this subtle cosmological signature. Our findings reveal that SKA-MID Band 1 demonstrates the highest detection significance and Figure of Merit, establishing it as the most promising instrument for this endeavor. However, foregrounds introduce a bias on the detected value of the turnover position. While DESI surveys excel at probing small-scale structures, they effectively complement intensity mapping surveys, crucial for a holistic understanding of the universe’s matter distribution. We address significant challenges such as foreground contamination and analyze the effects of the telescope beam, which can obscure the turnover signal for intensity mapping observations. Our study emphasizes the importance of advanced foreground cleaning techniques and beam-induced bias correction for accurate cosmological analysis. This work confirms the feasibility of detecting the power spectrum turnover with observational tools and provides a critical comparative evaluation of current methodologies across various surveys. The insights discussed lay a robust foundation for future research dedicated to refining our understanding of cosmic evolution and its governing parameters as well as addressing the Hubble tension.
Detecting the turnover of the power spectrum with SKAO and other surveys
(University of the Western Cape, 2025) Dube, Yolanda
This thesis explores the potential of next-generation experiments, specifically the Square Kilometre Array and the Dark Energy Spectroscopic Instrument, to detect and constrain the power spectrum turnover, a key feature of the universe’s large-scale structure holding the key for probing ultra-large scales. Employing intensity mapping and galaxy surveys, we utilize Fisher forecasts and Markov Chain Monte Carlo simulations to model and analyze this subtle cosmological signature. Our findings reveal that SKA-MID Band 1 demonstrates the highest detection significance and Figure of Merit, establishing it as the most promising instrument for this endeavor. However, foregrounds introduce a bias on the detected value of the turnover position. While DESI surveys excel at probing small-scale structures, they effectively complement intensity mapping urveys, crucial for a holistic understanding of the universe’s matter distribution. We address significant challenges such as foreground contamination and analyze the effects of the telescope beam, which can obscure the turnover signal for intensity mapping observations. Our study emphasizes the importance of advanced foreground cleaning techniques and beam-induced bias correction for accurate cosmological analysis. This work confirms the feasibility of detecting the power spectrum turnover with observational tools and provides a critical comparative evaluation of current methodologies across various surveys. The insights discussed lay a robust foundation for future research dedicated to refining our understanding of cosmic evolution and its governing parameters as well as addressing the Hubble tension.
Multipoles of the redshift-space power spectrum from SKAO and other surveys
(University of the Western Cape, 2025) Baatjes Ron Ryan
The large-scale distribution of neutral hydrogen in the late universe provides a probe of the underlying distribution of matter, which is a powerful complement to the standard probe delivered by galaxy number counts. Measuring the neutral hydrogen distribution with MeerKAT, SKAO and other radio telescopes through the hydrogen 21 cm line emission has the potential to become a key cosmological probe in the coming years. We investigate the cosmological constraining power of the 21 cm intensity mapping power spectrum in redshift space. To this end, we decompose the power spectrum into multipoles, modelling the effects of foreground avoidance, telescope beam, instrumental noise and the bias of 21 cm intensity fluctuations. Then we use Fisher forecasting methods to estimate the precision that is obtainable by proposed surveys and on the full SKAO. Measurements of the power spectrum multipoles enable measurements of key cosmological parameters and we estimate the precision of such measurements. In particular, the multipoles provide an estimate of the growth rate of large-scale structure, which can deliver tests of the theory of gravity.
Investigation of factors influencing radon release from different materials
(University of the Western Cape, 2024) Ngwadla Xolisani Enkosi
Neutrinoless double beta decays are an exotic decay process that are possible in only a few nuclei. The observation of such decays would establish the Majorana nature of neutrinos (i.e. neutrinos are their own antiparticles). Such experimental validation would indicate new physics, beyond the standard model of electroweak interactions. One promising candidate to observe such decays is the double beta transformation from 136Xe to 136Ba. This is because single beta decays to 136Cs are energetically forbidden. A potential challenge in such experiments are low-activity background from natural radioactivity. Radon is a radioactive, colorless, odorless, and tasteless gas that forms naturally from the radioactive decay of radium, and Thoron is a radioactive isotope of radon with the chemical symbol 220Rn. One such primary background is from the decays of 222Rn and 220Rn in the naturally occurring 238U and 232Th decay chains as shown in Fig. 3.4. This project aims to study the effects of Radon background in a 136Xe double beta decay experiment, with the eventual goal of obtaining solutions to suppress such background to less than 600 radon atoms. We use the Electrostatic Counter (ESC) method to measure the exhalation of 222Rn and 220Rn from the getters, specifically Pure Zirconium R-164 and Scientific and Analytical Equipment Support (SAES) pellets R-159.1. The decay of Radon produces charged Po ions, which are then directed by an electric field onto a solid-state α counter. The presence of Radium (Ra), the parent of radon, in the getters is determined by analyzing the measured decay rates of isotopes 212Po, 214Po, 216Po, and 218Po. In this work, our results show a net 222Rn emanation assay for getters, specifically Pure Zr pellets R-164 and SAES pellets R-159.1, with specific rates of Rnet = (82±23) atoms day.kg , and Rnet = (71±34) atoms day.kg , respectively. The presence of radon in mines (e.g. the Steenkampskraal mine in the Western Cape Province in South Africa) is an important indicator of the health dangers to miners of radon, a known cause of lung cancer. This thesis aims to test the exhalation of radon from rock samples from the mine. The laboratory at UWC contains a vacuum chamber that can be linked to a Radon detector (RAD7) that measures the radon exhalation in a similar way to the ESC, but in this case the radon exhalation is huge compared to the low activity measurements. The radon exhalation was studied using this setup. The Steenkampskraal mine has high natural thorium levels, resulting in high concentrations of thoron activity in the air. At a monazite seam, thoron activity concentrations are larger than 2×104 Bq m−3, with thorium exhalation aligning with these levels. While ventilation can lower thoron concentrations, it cannot completely eliminate them due to the short halflife of thoron.
Silver-magnesium thin film interactions in an oxidzing ambient
(University of the Western Cape, 1999) Malgas, Gerald Franky
Silver has the lowest resistivity of all metals and its good electromigration properties make. it a possible candidate to replace Al in microelectronics circuits. However, silver suffers from several drawbacks. Some of the drawbacks are the difusion of Ag into SiO2, poor adhesion to SiO2, and corrosion of silver when exposed to ambients such as H2S and C}i. To overcome these stability problems, we need diffusion barriers to prevent interdifusion of Ag into SiO2, an adhesion promoter to improve adherence, and a passivation layer to protect the silver against corrosion. Ag(200 nm)/Mg(50 nm) bilayer structure on SiO2 substrates were annealed at temperatures ranging from 300-650°C and times from 30-120 min in a flowing Ar ambient. Upon annealing the Mg segregates to the surface where it reacts with the residual O in the Ar to form a Mg-oxide passivation layer of ~35nm. RBS and AES analysis of the samples indicates that out diffusion of Mg occurs at 350°C, and that reaction is completed at 500°C. Within the detection limits of the analysis techniques used, no interfacial reaction between Mg and SiO2 could be detected. The resistivity of the encapsulated silver films is about 4.3μQ -cm. XRD analysis revealed that no intermetallic compounds could be detected.
Radioactive source measurements in a liquid xenon time projection chamber
(Universty of the Western Cape, 2024) Tyuka, Odwa Azizipho; Triambak, Smarajit
Double beta decay is a rare nuclear process that can occur in two different modes. The first is known as the two-neutrino double beta decay, which is a second-order weak interaction process and has already been observed in several nuclei. The second one is called neutrino less double beta decay. This is a yet-to-be observed lepton number violating process, which can only be described by new physics, not included in the current standard model that describes elementary particles and their interactions. One attractive case for such studies is the double beta decay of 136Xe to 136Ba. Currently there are several international projects under development that aim to observe 136Xe neutrino less double beta decay. This project aims to contribute to such research with a study of charge-collection energy resolution, with radioactive source measurements in a liquid xenon time projection chamber (TPC).
Mixed lead halide perovskite thin films (X = I, Br) by low pressure chemical vapour deposition
(University of the Western Cape, 2024) Mthimkulu, Mongezi Sean Lucas; Ngqoloda, Siphelo
Three-dimensional (3D) metal halide perovskites (MHPs) have been classified as an emerging semiconductor material since the first report of methyl-ammonium lead tri-bromide (CH3NH3PbBr3) and methyl-ammonium lead tri-iodide (CH3NH3PbI3) were introduced as photosensitisers in dye-sensitised solar cells as reported in 2009 achieving a power conversion efficiency (PCE) of 3.1% and 3.8%, respectively. Owing to the excellent optical and electronic properties and ease of synthesis compared to other semiconductor materials such as crystalline silicon (c-Si), Gallium arsenide (GaAs), and Cadmium telluride (CdTe). 3D MHP have been utilised in other devices such as light emitting diode (LED), field effect transistor (FET), photodetectors, X-ray detectors, and lasers. However 3D MHPs suffer from inherent chemical and structural instabilities over moisture, light, and heat, which are significant challenges and notorious culprits that deteriorate the stability and hinder the commercialisation of perovskite-based devices. Several strategies and techniques have been employed to address these instabilities. Reducing the dimensionality of 3D MHP is a capable and practical approach to addressing the inherent chemical and structural instabilities of 3D MHP, as other methods used to tackle these instabilities, such as compositional mixing and additive engineering tend to be associated with an increased production cost and a reduction in performance. Two-dimensional (2D) and quasi-2D MHP have shown greater stability over moisture, light, and heat, because of these attributes, they have gained substantial interests from researchers recently.
Hybrid two-dimensional perovskite semiconductor layers for electronic applications
(Universty of the Western Cape, 2024) Mercuur, James Winston; Arendse, Christopher
Perovskite materials have emerged as a frontier in advanced functional materials, offering a versatile platform for various applications ranging from solar cells to light-emitting devices. Among the different fabrication techniques, Chemical Vapor Deposition (CVD) stands out for its ability to produce high-quality thin films with precise compositional control. This study delves into synthesising a two-dimensional (2D) hybrid perovskite thin film (PEA)2PbCl4 on diverse substrates, marking a significant advancement in the scalable production of perovskite-based devices. Optimising CVD parameters enabled the deposition of a PbCl2 precursor thin film and its subsequent conversion to the perovskite through an intercalation reaction with PEACl. X-ray diffraction (XRD) analysis, complemented by Rietveld refinement and VESTA simulations, confirmed the hybrid 2D structure of the (PEA)2PbCl4 with an inorganic octahedral layer number (n) equal to one. Scanning electron microscopy revealed a uniform distribution of columnar structures (~120 nm in diameter) for PbCl2 and a woven-like morphology for the perovskite. Optical properties assessed via UV-Vis spectroscopy indicated a band gap of 3.47 eV (Tauc plot) and 3.644 eV (Elliott model) for the perovskite. The perovskite Urbach energy (EU) was estimated at ~236 meV (Urbach method), suggesting significant disorder within the film. However, exciton binding energies were approximately 20 meV, as per the Elliott fit. Photoluminescence spectroscopy showed broadband self-trapped exciton emissions centred at ~532 nm with a full width at half maximum (FWHM) of 140 nm, attributed to intrinsic lattice distortions. These findings contribute to understanding the structural and optical properties of 2D hybrid perovskites and the potential of CVD synthesis, with implications for their application in optoelectronic device fabrication.
Detecting anomalous transients in meertrap data
(Universty of the Western Cape, 2024) Petersen-Charles, Jade Lindsay; Lochner, Michelle
In an era distinguished by significant technological progress, the prevalence of large and complex datasets characterizes the "big data" era across various disciplines. With improved telescopes being built aimed at generating datasets of unprecedented volumes, there is incredible potential for discovery. The MeerKAT radio telescope in South Africa has proven to be an excellent telescope to search for fast radio transients such as pulsars and fast radio bursts (FRBs). MeerTRAP (more TRAnsients and Pulsars), which commensally uses MeerKAT to search for fast radio transients, detects tens of thousands of candidate objects daily (on average), although the vast majority are not of astrophysical origin. Automated techniques such as machine learning are routinely used to identify targeted astrophysical transients. However, an emerging application of machine learning is to aid the detection of unidentified or rare sources, referred to as anomalies.
The effects of ion beams on nonlinear electrostatic waves in space plasmas
(Universty of the Western Cape, 2024) Maxengana, Mihlali; Bharuthram, Ramashwar
The effect of ion beams on linear and nonlinear low frequency electrostatic ion-acoustic waves is examined in multi-species plasma models, which are regularly observed in the terrestrial magnetosphere. These models comprise two thermal (adiabatic) ions and one or two Boltzmann electron species, with different temperatures in the latter case. One or both ions are regarded as drifting (beam) species. The linear study reveals the existence of two linear ion-acoustic modes: slow and fast ion-acoustic modes. The slow ion-acoustic modes emerge in models with at least one beam, while fast modes occur in beam and beamless plasma models. The slow ion-acoustic modes are found to be highly sensitive to variations in ion beam speed, becoming unstable to the ion beam instability for intermediate speeds. In the nonlinear regime, the ion-acoustic modes evolve into nonlinear structures such as solitons and double layers, which are pulse like disturbances in potential, commonly known as electrostatic solitary waves. A critical value of the beam speed must be exceeded for the existence of the slow ion-acoustic solitons of which the one slow mode propagates above and the second below the critical acoustic speed associated with the corresponding linear wave.
Unsupervised machine learning applied to radio data
(Universty of the Western Cape, 2023) Mohale, Koketso; Lochner, Michelle
This thesis presents work motivated by the belief that the next generation of discoveries in the field of astronomy will be made by the marriage of advanced data analysis algorithms in the form of unsupervised learning techniques, and the unprecedented volumes and complexities of data from the next generation of surveys. For several years, computers have been governed by Moore’s law, which posited that computing power would double every two years. The consequence was that computing has also become increasingly cost-effective, which has been a driving force in the ability to generate and analyse large volumes of datasets. These include machine learning advances like the use of deep learning and scalable techniques such as self-supervised learning which have been revolutionising areas of research, for example, natural language processing and computer vision. Similarly, astronomy is also met with a rapid growth in the availability of large datasets. Morden sky observing instruments such as the radio telescope MeerKAT and the optical telescope Blanco (which was used for the Dark Energy Survey) are already producing data volumes at unprecedented scales. The next generation of instruments like the Square Kilometre Array (SKA) and the Vera C. Rubin Observatory are expected to produce orders of magnitude more astronomical data at higher resolution and sensitivity. Ongoing efforts in the form of surveys and data analysis techniques in astronomy are motivated in part by outstanding questions in galaxy evolution and cosmology as well as the potential to discover new unknown phenomena.
Production and evaluation of capacitive deionization electrodes earmarked for the removal of ions from winery wastewater
(University of the Western Cape, 2023) Theron, Cleeve; Bladergroen, Bernard
Membrane capacitive deionization (MCDI) is a desalination technology considered to be cost effective specifically for salt bearing solutions with concentrations below 2000 mg‧L-1, which includes general winery wastewater. To consider winery wastewater to irrigate vineyards, the water needs to be desalinated to some extent. This study aims to establish whether in-house developed electrodes could be applied in MCDI to reduce the concentration of ions contained in winery wastewater model solutions. This would allow wineries to recycle wastewater for irrigation purposes and reduce their reliance on fresh water intake, increasing the winery industry’s drought resilience. Electrode optimization was done by systematically varying electrode production parameters and targeting several specific electrode variables which influence the performance of the electrode in terms of, maximum salt adsorption capacity (mSAC), practical salt adsorption capacity (pSAC), average salt adsorption rate (ASAR), wettability, through-plane electrical conductivity and surface area and pore size distribution with diameters in the mesopore size range.
Impact of different chemical synthesis techniques on the structural and photoluminescence properties of Zn4B6O13: RE3+ (where RE3+ = Sm3+, Eu3+, and Dy3+) nanophosphors
(University of the Western Cape, 2023) Siyalo, Athenkosi; Halinditwali, Sylvain
Different chemical synthesizing techniques, such as sol-gel, combustion, and solid-state reaction routes, offer the unique possibility of generating high-purity nanophosphors with different morphologies. In this project, we intend to do a comparative study on the structural and photoluminescence properties of Zn4B6O13:RE3+ (where RE3+ = Sm3+, Eu3+, and Dy3+) nanophosphors using the above-mentioned techniques. Up to now, the comparative study based on the synthesis techniques has not yet been reported. As it will be shown in the literature survey’s section, these methods were found to drastically affect the structural and photoluminescence characteristics of phosphor materials, which directs us to implement such studies on highly crystalline Zn4B6O13: RE3+ (where RE3+ = Sm3+, Eu3+, and Dy3+) nanophosphors. In this work, we intend to use different characterization techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FT-IR), ultraviolet visible spectroscopy (UV-Vis), and photoluminescence (PL) spectroscopy. In this study, we aim to justify the appropriate technique that will produce the best PL properties for Zn4B6O13: RE3+ (where RE3+ = Sm3+, Eu3+, and Dy3+) nanophosphors, which could be used as a benchmark for future researchers in solid-state lighting systems. The incorporation of the Sm3+, Eu3+, and Dy3+ dopants did not change the cubic crystal structure of the Zn4B6O13 host material, as confirmed by the XRD results. However, they caused a slight deviation to higher 2𝜃 values, which confirms the charge exchange between the dopants and the host.
Influence of synthesis method on structural
(Springer, 2023) Noukelag, Sandrine Kamdoum; Noukelag, Sandrine Kamdoum; Ngqoloda, Siphelo; Kotsedi, Lebogang
This contribution reports on the development of two versatile and efcient methods, namely the green and gamma radiolysis for Fe-Ag nanoparticles (NPs) synthesis, characterization, and further their growth inhibition potential on some spoilage microorganisms. Green Ag/Fe2O3 NPs were obtained at Fe-Ag [3:1], annealing temperature of 800 °C for 2 h, and gamma irradiated Ag/Fe3O4 NPs were obtained at Fe-Ag [7:1], a 50 kGy dose. The characterization techniques were performed with these two samples whereby the sizes from crystallographic and microscopic analyses were 39.59 and 20.00 nm for Ag/Fe2O3 NPs, 28.57 and 15.37 nm for Ag/Fe3O4 NPs, respectively. The polycrystallinity nature observed from X-ray diffraction was in accordance with the selected area electron difraction. The vibrational properties confrmed the presence of bimetallic Fe-Ag NPs with the depiction of chemical bonds, Fe–O and Ag–O from attenuated total refection-Fourier transform infrared spectroscopy and elements Ag, Fe, O from energy-dispersive X-ray spectroscopy analyses. The magnetic properties carried out using a vibrating sample magnetometer suggested a superparamagnetic behavior for the Ag/Fe2O3 NPs and a ferromagnetic behavior for the Ag/Fe3O4 NPs. Overall, the green Ag/Fe2O3 NPs successfully inhibited the growth of spoilage yeasts Candida guilliermondii, Zygosaccharomyces fermentati, Zygosaccharomyces forentinus, and spoilage molds Botrytis cinerea, Penicillium expansum, Alternaria alstroemeriae.
Sample selection effects in laduma stacking experiments
(University of the Western Cape, 2023) Gwebushe, Lwandile; Elson, Edward
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.
Structural features of air-processible methyl ammonium lead triiodide (MAPbI3) perovskite thin films grown on Al-doped ZnO Nanowire Arrays
(University of the Western Cape, 2023) Phakoe, Mpho; Cummings, Franscious
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.
Accelerating reionization simulations using machine learning
(University of the Western Cape, 2023) Masipa, Mosima Portia; Sultan, Hassan
Epoch of Reionization (EoR) refers to the time in the history of the universe when the appearance of the first luminous sources reionized the intergalactic medium (IGM). The EoR carries a wealth of information regarding structure formation and evolution. Ongoing and planned 21cm experiments such as the Hydrogen Epoch of Reionization Array (HERA) and the Square Kilometre Array (SKA) are expected to generate huge amounts of high dimensional datasets, and hence a new generation of efficient simulations and tools are required in order to maximize their scientific return. While Convolutional neural networks (CNNs) achieve the state-of-the-art performance to extract information from large scale fields, generating large training datasets and fully exploring the cosmological and astrophysical parameter space require fast simulations.

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