UWCScholar

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Now showing 1 - 5 of 11

Recent Submissions

Primordial non-Gaussianity — the effects of relativistic and wide-angle corrections to the power spectrum
(Institute of Physics, 2025) Guedezounme, Sêcloka; Jolicoeur, Sheean; Maartens, Roy
Wide-angle and relativistic corrections to the Newtonian and flat-sky approximations are important for accurate modeling of the galaxy power spectrum of next-generation galaxy surveys. In addition to Doppler and Sachs-Wolfe relativistic corrections, we include the effects of lensing convergence, time delay and integrated Sachs-Wolfe. We investigate the impact of these corrections on measurements of the local primordial non-Gaussianity parameter fNL, using two futuristic spectroscopic galaxy surveys, planned for SKAO2 and MegaMapper. In addition to the monopole, we include the quadrupole of the galaxy Fourier power spectrum. The quadrupole is much more sensitive to the corrections than the monopole. The combination with the quadrupole improves the precision on fNL by ∼ 45% and ∼ 63% for SKAO2 and MegaMapper respectively. Neglecting the wide-angle and relativistic corrections produces a shift in fNL which is very sensitive to the magnification bias and the redshift evolution of the comoving number density. In the case of SKAO2, the shift in fNL is negligible — since the contributions to the shift from integrated and non-integrated effects nearly cancel. For MegaMapper, there is only partial cancellation of integrated and non-integrated effects and the shift is ∼ 0.6 σ. We point out that some of the approximations made in the wide-angle and relativistic corrections may artificially suppress the shift in fNL.
Context matters: Why we must consider resources and context when implementing artificial intelligence tools in the teaching and learning of mathematics in South Africa
(AOSIS (pty) Ltd, 2025) Govender Rajendran
South African schools face stark inequalities in infrastructure, connectivity, language, and teacher preparedness. These contextual factors profoundly shape what artificial intelligence (AI) can and cannot do for mathematics teaching and learning. This article synthesizes recent peer-reviewed scholarship, policy texts, and book chapters to argue that AI adoption must be context-responsive: aligned to local resource constraints, multilingual realities, professional development ecosystems, and regulatory frameworks (notably POPIA). This article emphasizes that without attention to connectivity, electricity, devices, teacher TPACK, multilingual pedagogy, and data protection, AI may amplify—rather than reduce—existing inequities. In mitigation, this article provides practical, evidence-based principles for context-aware AI implementation in South African mathematics education.
The LOFAR two-metre sky survey: vii. third data release
(EDP Sciences, 2026) Jarvis, MJ; Vaccari, Mattia; Shimwell, TW
We present the third data release of the LOFAR Two-metre Sky Survey (LoTSS-DR3). The survey images cover 88% of the northern sky and were created from 12 950 h of data (18.6 PB) accumulated over 10.5 years. Producing the images took 20 million core hours of processing through direction-independent and direction-dependent calibration pipelines that correct for instrumental effects as well as spatially and temporally varying ionospheric distortions. In our 120–168 MHz continuum mosaic images with an angular resolution of 600 (900 below declination 10◦) we catalogue 13 667 877 sources, formed from 16 943 656 Gaussian components. The scatter in the astrometric precision approximately follows the expected noise-like behaviour but with an additional systematic component of at least 0.2400 that is likely due to calibration imperfections. The random flux density scale error is 6%, while the systematic offset was previously shown to be within 2%. The median sensitivity of our mosaics is 92 µJy beam−1, improving to 68 µJy beam−1 at high observing elevations, but degrading to 183 µJy beam−1 at the celestial equator due to station area projection effects. Completeness simulations, accounting for realistic source models, time- and bandwidth-smearing effects, and astrometric errors, indicate that we detect more than 95% of compact sources with integrated flux densities exceeding 9 times the local root mean square (RMS) noise. However, the recovered source counts in a particular integrated flux density bin do not match the injected counts until flux densities exceed 45 times the local RMS noise. The Euclidean-normalised differential source counts derived from the survey constrain the radio source population over five orders of magnitude and are in good agreement with previous deep and wide-area surveys. All data products are publicly available, including catalogues, individual-field Stokes I, Q, U, and V images, mosaicked Stokes I images, and uv data with associated direction-dependent calibration solutions.
Beyond the grid: navigating water supply and sanitation service ecosystems in informal settlements
(Public Library of Science, 2026) Anciano, Fiona; Dube, Mmeli; Casas, Ana
Hundreds of millions of people living in urban informal settlements rely on irregular and unsafe water supply and sanitation services. To meet their needs, they must navigate fragmented service delivery environments and use multiple different water and sanitation facilities. Using high-frequency longitudinal survey data from three informal settlements in Kenya, Peru and South Africa, we document the variability in water supply and sanitation service access. Across the year-long study period, 62–73% of respondents across all contexts changed their primary toilet, with 10–27% reporting five or more different primary facilities, with similar variability in water access. High levels of disruption were reported, with issues related to crowding/queuing, breakdowns, and physical barriers disrupting accessibility all contributing to the churn of services. To explain the results, we develop the concept of a “service ecosystem” to describe how people living in urban informal settlements rely on multiple water supply and sanitation services simultaneously and how these patterns of access shift over time. Using James C Scott’s theory of legibility, we argue that this irregularity means these service ecosystems are largely illegible within formal monitoring frameworks, that typically categorise households by a primary service. This leads to an information deficit for policymakers and practitioners who have a mandate to improve services in these environments. We further develop the implications of service ecosystems by calling for policymakers and service providers to recognise and support a diversity of service systems which have sufficient redundancy between them to meet the needs of populations, at least until broader structural reforms can address the underlying challenges in these settings.
Immunosensor enhanced with silver nanocrystals for on-chip prostate-specific antigen detection
(Multidisciplinary Digital Publishing Institute (MDPI), 2025) Mokwebo, Kefilwe; Oranzie, Marlon; Okhai, Timothy
An electrochemical immunosensor for the quantification of prostate-specific antigens (PSAs) using silver nanocrystals (AgNCs) is reported. The silver nanocrystals were synthesized using a conventional citrate reduction protocol. The silver nanocrystals were characterized using scanning electron microscopy (SEM) and field effect scanning electron microscopy (FESEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Fourier-transform infrared spectroscopy (FTIR), UV-Vis spectroscopy, and small-angle X-ray scattering (SAXS). The proposed immunosensor was fabricated on a glassy carbon electrode (GCE), sequentially, by drop-coating AgNCs, the electro-deposition of EDC-NHS, the immobilization of anti-PSA antibody (Ab), and dropping of bovine serum albumin (BSA) to prevent non-specific binding sites. Each stage of the fabrication process was characterized by cyclic voltammetry (CV). Using square wave voltammetry (SWV), the proposed immunosensor displayed high sensitivity in detecting PSA over a concentration range of 1 to 10 ng/mL with a detection limit of 1.14 ng/mL and R2 of 0.99%. The immunosensor was selective in the presence of interfering substances like glucose, urea, L-cysteine, and alpha-methylacyl-CoA racemase (AMACR) and it showed good stability and repeatability. These results compare favourably with some previously reported results on similar or related technologies for PSA detection.