https://hdl.handle.net/13049/13 Mon, 21 Sep 2026 14:21:32 GMT 2026-09-21T14:21:32Z https://hdl.handle.net/13049/834 The variability and predictability of the IRI B 0 , B 1 parameters over Grahamstown, South Africa McKinnell, Lee-Anne; Chimidza, Oyapo; Cilliers, Pierre The International Reference Ionosphere (IRI) parameters B0 and B1 provide a representation of the thickness and shape, respectively, of the F2 layer of the bottomside ionosphere. These parameters can be derived from electron density profiles that are determined from vertical incidence ionograms. This paper aims to illustrate the variability of these parameters for a single mid latitude station and demonstrate the ability of the Neural Network (NN) modeling technique for developing a predictive model for these parameters. Grahamstown, South Africa (33.3°S, 26.5°E) was chosen as the mid latitude station used in this study and the B0 and B1 parameters for an 11 year period were determined from electron density profiles recorded at that station with a University of Massachusetts Lowell Center for Atmospheric Research (UMLCAR) Digisonde. A preliminary single station NN model was then developed using the Grahamstown data from 1996 to 2005 as a training database, and input parameters known to affect the behaviour of the F2 layer, such as day number, hour, solar and magnetic indices. An analysis of the diurnal, seasonal and solar variations of these parameters was undertaken for the years 2000, 2005 and 2006 using hourly monthly median values. Comparisons between the values derived from measured data and those predicted using the two available IRI-2001 methods (IRI tables and Gulyaeva, T. Progress in ionospheric informatics based on electron density profile analysis of ionograms. Adv. Space Res. 7(6), 39–48, 1987.) and the newly developed NN model are also shown in this paper. The preliminary NN model showed that it is feasible to use the NN technique to develop a prediction tool for the IRI thickness and shape parameters and first results from this model reveal that for the mid latitude location used in this study the NN model provides a more accurate prediction than the current IRI model options. Journal article Tue, 15 Sep 2009 00:00:00 GMT https://hdl.handle.net/13049/834 2009-09-15T00:00:00Z https://hdl.handle.net/13049/833 Implementation of a boundary element method for high frequency scattering by convex polygons with impedance boundary conditions Mokgolele, Mosiamisi Many acoustic and electromagnetic wave scattering problems can be formulated as the Helmholtz equation. Standard finite and boundary element method solution of these problems becomes expensive, as the frequency of incident wave increases. On going research has been devoted to finding methods that do not loose robustness when the wave number increases. Recently, Chandler-Wilde et al. have proposed a novel Galerkin boundary element method to solve the problem of acoustic scattering by a convex polygon with impedance boundary conditions. They applied approximation spaces consisting of piecewise polynomials supported on a graded mesh with smaller elements adjacent to the corners of the polygon and multiplied by plane wave basis functions. They demonstrated via rigorous error analysis that was supported by numerical experiments that the number of degrees of freedom required to achieve a prescribed level of accuracy need only grow logarithmically as frequency increases. In this paper, we discuss issues related to detail implementation of their numerical method. Journal article Fri, 01 Jan 2016 00:00:00 GMT https://hdl.handle.net/13049/833 2016-01-01T00:00:00Z https://hdl.handle.net/13049/832 Effect of hollow centre post in coupled combline resonators Pholele, Thato M.; Chuma, Joseph M.; Ngebani, Ibo The effect of thickness of a hollow post in a combline resonator on the resonant frequency, coupling coefficients and spurious performance are analysed. It is shown that both the electric and magnetic couplings are not significantly affected by the size of the thickness of the hollow post, whereas the resonant frequency and spurious free band both change. When the thickness of the hollow post reduces the spurious free band deteriorates while the resonant frequency increases. Working paper Sun, 01 Jan 2017 00:00:00 GMT https://hdl.handle.net/13049/832 2017-01-01T00:00:00Z https://hdl.handle.net/13049/831 Understanding the Impacts of Rainfall Variability on Natural Forage–Livestock Dynamics in Arid and Semi-Arid Environment Nketsang, Thabo S.; Kassa, Semu Mitiku; Kgosimore, Moatlhodi; Tsidu, Gizaw Mengistu Arid and semi-arid environments are characterized by highly variable and unpredictable rainfall patterns, which significantly affect the structure and function of natural ecosystems. Understanding the interconnected relationship between climate variability, forage availability, and livestock dynamics in these regions is crucial to ensure sustainable management. This study provides novel insights into the effects of rainfall variability on natural forage resources and livestock populations in Botswana. In this arid region, traditional livestock farming remains a key economic and food security pillar. By employing a mathematical model based on plant–herbivore interactions, this article quantitatively evaluates the impact of changes in rainfall timing and intensity on forage biomass and, subsequently, livestock populations. A robust analysis of critical threshold values for ecosystem sustainability is possible when real-world climate data are incorporated. This study examines the effects of harvesting and rainfall variability on livestock dynamics across different locations in Botswana. Delayed rainfall leads to a sharp decline in livestock, while Sehitlwa sees biomass loss without a notable reduction in herd size. In Kgagodi, for example, livestock numbers decline by 37% without harvesting, but they remain stable with controlled harvesting. Conversely, Letlhakeng experiences a 6% increase in livestock numbers despite delayed rainfall, which results in a biomass decline. Both Mabutsane and Letlhakeng maintain stable livestock numbers. The findings confirm that early and intense rainfall enhances livestock productivity, while delayed or reduced rainfall leads to population decline, aligning with observed trends in historical data. Additionally, the study underscores the potential of adaptive livestock harvesting strategies as a viable approach to mitigating climate-related risks in grazing systems. As this work integrates theoretical modeling with empirical climate data, it contributes to understanding arid land dynamics, providing a predictive method for assessing ecosystem responses to climate variability. These insights are invaluable for policymakers, conservationists, and local farmers seeking sustainable livestock management practices in the face of changing climatic conditions. Journal article Wed, 01 Jan 2025 00:00:00 GMT https://hdl.handle.net/13049/831 2025-01-01T00:00:00Z