16918 research outputs found
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Matvis: a matrix-based visibility simulator for fast forward modelling of many-element 21 cm arrays
No full textDetection of the faint 21 cm line emission from the Cosmic Dawn and Epoch of Reionization will require not only exquisite control over instrumental calibration and systematics to achieve the necessary dynamic range of observations but also validation of analysis techniques to demonstrate their statistical properties and signal loss characteristics. A key ingredient in achieving this is the ability to perform high-fidelity simulations of the kinds of data that are produced by the large, many-element, radio interferometric arrays that have been purpose-built for these studies. The large scale of these arrays presents a computational challenge, as one must simulate a detailed sky and instrumental model across many hundreds of frequency channels, thousands of time samples, and tens of thousands of baselines for arrays with hundreds of antennas. In this paper, we present a fast matrix-based method for simulating radio interferometric measurements (visibilities) at the necessary scale. We achieve this through judicious use of primary beam interpolation, fast approximations for coordinate transforms, and a vectorized outer product to expand per-antenna quantities to per-baseline visibilities, coupled with standard parallelization techniques. We validate the results of this method, implemented in the publicly available matvis code, against a high-precision reference simulator, and explore its computational scaling on a variety of problems
Persons with disabilities’ perceptions on self-employment barriers, facilitators and solutions in a rural setting – an exploratory qualitative study
No full textBackground: Self-employment is a prevalent employment or job placement option for persons with disabilities in developing countries like those in Africa. Objective: This research explored perceptions of self-employment barriers, facilitators and solutions among persons with disabilities in a rural South African setting. Methods: This is a qualitative, exploratory, descriptive study design. Purposive sampling was used to recruit ten persons with disabilities in microenterprises in a rural setting of KwaZulu Natal. One-on-one semi-structured interviews were conducted using a piloted question guide in their preferred language. Thematic data analysis was done using the hybrid inductive and deductive approaches. Data was managed using the NVIVO software. Results: Out of ten self-employed participants, nine were male, and one was female. None of the participants had passed grade 12 (a prerequisite for basic jobs and entry into tertiary education), and two had no education. Two themes emerged. Theme one: Participants identified personal, societal and role players related barriers and facilitators in self-employment. Persons with disabilities reported challenges in self-employment. Despite the challenges, they remained resolute in leveraging residual function (functional upper limbs and cognitive abilities) to operate their microenterprise and use their time constructively. Theme two: Persons with disabilities proposed assistance with setting up self-employment in microenterprises as a solution – “What I would need most from a professional…” The proposed solutions involved community-based outreach where key role players engage directly with persons with disabilities in their communities to identify and address their needs. Conclusions: Persons with disabilities in rural KwaZulu Natal seek tailored and transparent services to address barriers to self-employment and ensure the sustainability of their microenterprise
Characterization and cytotoxicity of nanoceria phytosynthesized using Eucalyptus camaldulensis bark extract
No full textCancer, a complex group of diseases characterized by uncontrolled cell growth, poses a significant global health risk. In the context of the high occurrence of breast cancer (BC) in women, conventional chemotherapeutic agents, although effective, frequently bring about challenges such as resistance and recurrence. Nanotechnology is emerging as a promising approach, with attention focused on cerium oxide nanoparticles (CNPs). CNPs possess distinctive characteristics such as antioxidant activity, the ability to transition between Ce3+ and Ce4+ oxidation states, and biocompatibility with living systems. This study introduces a novel phytosynthesis method using Eucalyptus camaldulensis bark extract to synthesize CNPs, emphasizing environmentally friendly methods. Characterization techniques including Fourier transform infrared spectroscopy (FTIR), Powder X-ray diffraction (XRD), Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Transmission electron microscopy (TEM), Diffuse Reflectance (DR) were used to elemental, structural, and morphological properties of synthesized CNPs. Results have shown the successful synthesis of CNPs having cubic fluorite structure with a space group of Fm3m (225) and a crystallite size of 11.2 nm based on XRD characterization. FTIR and EDX have confirmed the elemental analysis of CNPs and the presence of extracted biomolecules during the synthesis process. SEM and TEM images revealed the morphology of the phytosynthesized CNPs as sphere-like, with a size of 2 to 10 nm. Finally, cytotoxicity by MTT assay and uptake of these CNPs on MCF-7 cells demonstrates successful uptake and their potential to inhibit these cancerous cells. The protective effect of CNPs on normal cells was further investigated using a ROS assay on the MCF10A cell line. Furthermore, the catalase-mimic (CAT-mimic) activity of phytosynthesized CNPs was assessed by a commercial CAT-mimic kit assay
Radio continuum spectra of SFGs in the XMM-LSS Field below threshold
No full textThis study investigates the radio spectral properties of KS-selected star-forming galaxies (SFGs) in the XMM-LSS (multimirror mission large-scale structure) field using extensive multiwavelength data. By employing various diagnostics, SFGs are distinguished from quiescent galaxies and AGN across seven redshift bins (0.1 ≤ z ≤ 3.0). The broad-band radio frequency spectral energy distribution is analysed at observer-frame frequencies from 144 to 1500 MHz using median stacking techniques correcting for median flux boosting. We investigate the relationship between the radio spectral index, α (where S ∝ να) and redshift (z). Our analysis reveals no significant inverse correlation between α and z, indicating that the radio spectrum remains independent with varying redshift. We fit the stacked median radio SEDs with a power law (PL), curved power law (CPL), and double power-law (DPL) models. For the DPL and CPL models, we observe a consistent steepening of the low-frequency spectral index across all redshift bins. For the CPL model, the curvature term q is greater than zero in all redshift bins. Model comparisons indicate that spectra are generally well fitted by all the models considered. At 1500 MHz, SFGs display both a steep synchrotron component and a flat free–free emission component, with a thermal fraction consistently around 11 per cent to 18 per cent. Further deep radio observations, with higher resolution to better deal with source blending and confusion noise and wider frequency coverage to better separate non-thermal and thermal radio emission, are required to reveal the detailed physical processes, thus clarifying the nature of radio sources
Biomass-derived carbon-based nanomaterials: current research, trends, and challenges
No full textThe review investigates the use of biomass-derived carbon as precursors for nanomaterials, acknowledging their sustainability and eco-friendliness. It examines various types of biomasses, such as agricultural residues and food byproducts, focussing on their transformation via environmentally friendly methods such as pyrolysis and hydrothermal carbonisation. Innovations in creating porous carbon nanostructures and heteroatom surface functionalisation are identified, enhancing catalytic performance. The study also explores the integration of biomass-derived carbon with nanomaterials for energy storage, catalysis, and other applications, noting the economic and environmental benefits. Despite these advantages, challenges persist in optimising synthesis methods and scaling production. The study also highlights existing research gaps, forms a basis for future studies, and underscores the role of biomass-derived nanomaterials in promoting a circular economy and sustainability
Cosmological multifield emulator
No full textWe present the application of deep networks to learn the distribution of multiple large-scale fields, conditioned exclusively on cosmology while marginalizing over astrophysics. Our approach develops a generalized multifield emulator based purely on theoretical predictions from the state-of-the-art hydrodynamic simulations of the CAMELS project, without incorporating instrumental effects which limit the analysis to specifics of a particular large-scale survey design. To this end, we train a generative adversarial network to generate images composed of three different channels that represent gas density (Mgas), neutral hydrogen density (HI), and magnetic field amplitudes (B). We consider an unconstrained model and another scenario where the model is conditioned on the matter density Ωm and the amplitude of density fluctuations σ8. We find that the generated images exhibit great quality which is on a par with that of data, visually. Quantitatively, we find that our model generates maps whose statistical properties, quantified by probability distribution function (PDF) of pixel values and auto-power spectra, agree reasonably well up to the second moment with those of the real maps. The relative deviation between the PDFs is about 25% in both moments with larger deviations at the tails. The error between the two auto-power spectra is approximately less than 20% on scales larger than k=10h/Mpc, but becomes larger on smaller scales. Moreover, the mean and standard deviation of the cross-correlations between fields in all maps produced by the emulator are in good agreement with those of the real images, which indicates that our model generates instances whose maps in all three channels describe the same physical region. Furthermore, a CNN regressor, which has been trained to extract Ωm and σ8 from CAMELS multifield dataset, recovers the cosmology from the maps generated by our conditional model, achieving coefficient of determination values R2=0.96 and 0.83 corresponding to Ωm and σ8 respectively. This further demonstrates the great capability of the model to mimic CAMELS data. Our model can be useful for generating data, 1000 multiple images in ∼3 seconds as opposed to a simulation which takes days for one realization, that are required to analyze the information from upcoming multi-wavelength cosmological surveys
Investigating the relationship between well-being, engagement and learning experiences among South African publicly funded students in higher education
No full textStudent engagement and positive learning experiences are important determinants of academic performance in higher education. While the role of well-being is also acknowledged, it is not comprehensively addressed as an antecedent for both engagement and learning experience. In fact, interventions to improve academic performance in higher education tend to ignore well-being support. A further problem relates to the dominance of literature from the Global North predicated on relationships between well-being, engagement and learning experience among students with much higher levels of socio-economic status. This stands as a severe limitation in identifying the right kinds of interventions towards ensuring better learning outcomes for African higher education students. Using structural equation modelling, we explored the relationship between psychological and social well-being with student engagement and learning experiences among a sample of 6877 South African higher education students (females = 54.7%; mean age = 23.83; SD = 4.89). Our findings showed that both facets of well-being were positively related to student engagement and learning experiences highlighting psychological and social well-being promotion as a clear responsibility of higher education systems
Women's Rights in a Changing Climate: An Intersectional Analysis of Climate Change and Gender Inequality in Nigeria.
No full textClimate change disproportionately impacts women, particularly in Nigeria where poverty and deep-rooted gender inequalities intersect. This dissertation explores how climate change affects women's socio-economic rights, through an intersectional feminist and human rights lens. This study examines how social identities like gender, class, and ethnicity shape women’s vulnerabilities and coping mechanisms to climate shocks. And how existing gender gaps exacerbate these challenges. Women's limited access to resources, information, and decision- making power hinders their ability to adapt to climate-induced crises such as droughts, floods, and rising sea levels, leading to increased food insecurity, health risks, and gender-based violence. Employing a human rights framework, this research investigates how climate change exacerbates existing gender inequalities, disproportionately affecting women. Through case studies and policy analysis, the study will explore the multifaceted impacts on women's food security, employment, poverty, and health, including reproductive rights. This thesis advocates for the critical inclusion of women in climate change decision-making processes, arguing that their underrepresentation creates a 'value gap' hindering effective solutions. By examining the intersection of climate change and gender inequality in Nigeria, this research investigates the disproportionate impacts on women, including increased vulnerability to food insecurity, health risks, and gender-based violence. It further explores the link between climate-induced displacement and the rise in gender-based violence. Ultimately, this research aims to contribute to building a more just and equitable future for women facing the consequences of climate change
Euclid preparation LXIII. Simulations and non-linearities beyond Lambda cold dark matter. 2. Results from non-standard simulations
No full textThe Euclid mission will measure cosmological parameters with unprecedented precision. To distinguish between cosmological models, it is essential to generate realistic mock observables from cosmological simulations that were run in both the standard Λ-cold-dark-matter (ΛCDM) paradigm and in many non-standard models beyond ΛCDM. We present the scientific results from a suite of cosmological N-body simulations using non-standard models including dynamical dark energy, k-essence, interacting dark energy, modified gravity, massive neutrinos, and primordial non-Gaussianities. We investigate how these models affect the large-scale-structure formation and evolution in addition to providing synthetic observables that can be used to test and constrain these models with Euclid data. We developed a custom pipeline based on the Rockstar halo finder and the nbodykit large-scale structure toolkit to analyse the particle output of non-standard simulations and generate mock observables such as halo and void catalogues, mass density fields, and power spectra in a consistent way. We compare these observables with those from the standard ΛCDM model and quantify the deviations. We find that non-standard cosmological models can leave large imprints on the synthetic observables that we have generated. Our results demonstrate that non-standard cosmological N-body simulations provide valuable insights into the physics of dark energy and dark matter, which is essential to maximising the scientific return of Euclid
Information-seeking behaviour of undergraduate visual communication and design students at the Durban University of Technology
No full textOver the years, quarterly minutes of the Durban University of Technology Library Committee (2022–2023) revealed that students in the Faculty of Arts and Design were not making expected use of library resources. In response, the study adopted a pragmatist research paradigm and conducted mixed methods research, including an online questionnaire, to investigate the information-seeking behaviour, including the information needs and retrieval strategies of undergraduate visual communication and design students. Data were collected from 23 third-year Graphic Design students, fifteen (15) Interior Design students, and fifteen (15) photography students in the Faculty of Arts and Design. Wilson’s (1981) information behaviour model and the Association of College and Research Libraries Competency Standards for Higher Education (2011a), updated by the Companion Document to the Association of College and Research Libraries Framework for Information Literacy for Higher Education: Visual Literacy (2022), formed two components of the study’s theoretical framework. Wilson’s (1981) model and the updated Association of College and Research Libraries standards underpinned the determination of how the selected participants recognised their information needs and located and evaluated information. The framework was applied to solve problems or complete tasks within visual communication and design. The third component of the theoretical framework, McGee’s (1997) model of information literacy integration, supported the evaluation of whether the interaction between the library and undergraduate visual communication and design students was appropriately contextualised, whether the information literacy learning activities were suited to the specific needs of art and design students and whether these practices aligned with visual literacy standards. The study found that the library provided mostly printed books, which did not support the visual, digital, and practice-based nature of visual communication and design studies. Instead, students preferred accessing online images aligning with the curriculum and visual communication and design practices. Students lacked information and visual literacy skills regarding navigating the library shelves and online resources. They preferred to use Google, Google Scholar, and social media platforms as sources for images and artefacts. To improve the frequency of library use, the study recommended that the Durban University of Technology Library market its services and facilities, replace dated sources of information, and provide access to online databases, including patent information, case studies, movies, newsletters, flyers, different types of software, news of current events, and art workshops. The library website and retrieval tools must be adapted to ensure easy navigation and user-friendly interfaces