http://hdl.handle.net/10204/3217 2013-06-18T23:53:52Z http://hdl.handle.net/10204/6704 Title: Cosmological measurements with forthcoming radio continuum surveys Authors: Raccanelli, A; Zhao, G-B; Bacon, DJ; Jarvis, MJ; Percival, WJ; Norris, RP; Rottgering, H; Abdalla, FB; Cress, CM; Kubwimana, J-C; Lindsay, S; Nichol, RC; Santos, MG; Schwarz, DJ Abstract: We present forecasts for constraints on cosmological models that can be obtained using the forthcoming radio continuum surveys: the wide surveys with the Low Frequency Array (LOFAR) for radio astronomy, theAustralian SquareKilometreArray Pathfinder (ASKAP) and theWesterbork Observations of the Deep Apertif Northern Sky (WODAN).We use simulated catalogues that are appropriate to the planned surveys in order to predict measurements obtained with the source autocorrelation, the cross-correlation between radio sources and cosmic microwave background (CMB) maps (the integrated Sachs–Wolfe effect), the crosscorrelation of radio sources with foreground objects resulting from cosmic magnification, and a joint analysis together with the CMB power spectrum and supernovae (SNe). We show that near-future radio surveys will bring complementary measurements to other experiments, probing different cosmological volumes and having different systematics. Our results show that the unprecedented sky coverage of these surveys combined should provide the most significant measurement yet of the integrated Sachs–Wolfe effect. In addition, we show that the use of the integrated Sachs–Wolfe effect will significantly tighten the constraints on modified gravity parameters, while the best measurements of dark energy models will come from galaxy autocorrelation function analyses. Using a combination of the EvolutionaryMap of the Universe (EMU) and WODAN to provide a full-sky survey, it will be possible to measure the dark energy parameters with an uncertainty of {s(w0)=0.05, s(wa)=0.12} and themodified gravity parameters {s( 0) = 0.10, s(µ0) = 0.05}, assuming Planck CMB+SN (current data) priors. Finally, we show that radio surveys would detect a primordial non-Gaussianity of f NL =8 at 1s, and we briefly discuss other promising probes. Description: Copyright: 2012 Royal Astronomical Society. Published in Monthly Notices of the Royal Astronomical Society, vol. 424(2), pp 801-819 2012-08-01T00:00:00Z http://hdl.handle.net/10204/6686 Title: Numerical modelling of defects in rails Authors: Long, CS; Loveday, PW Abstract: The semi-analytical finite element (SAFE) method has become a popular tool for the analysis of elastic waveguides with complex cross-sections. We employ a recently developed hybrid SAFE-3D FE method to study the scattering of guided waves at discontinuities such as welds or cracks in continuous welded train rails. The aim of this particular study is to determine if it is possible to distinguish between scattering from welds and cracks for a given incident mode which is known to propagate long distance in rails. This study represents an initial step in the extension of the current ultrasonic broken rail detector (UBRD) system to detect cracks before complete breaks occur, which will require distinguishing between reflections from cracks and other reflectors such as welds, in order to avoid false alarms. Characterisation of transmission through welds is also useful for predicting the long-range attenuation of transducers in non-destructive evaluation (NDE) and monitoring systems, such as UBRD system developed by the Institute for Maritime Technology (IMT) and the Council for Scientific and Industrial Research (CSIR). Description: 8th South African Conference on Computational and Applied Mechanics (SACAM 2012), Johannesburg, South Africa, 3-5 September 2012 2012-09-01T00:00:00Z http://hdl.handle.net/10204/6655 Title: Spherical stochastic neighbor embedding of hyperspectral data Authors: Lunga, D; Ersoy, O Abstract: In hyperspectral imagery, low-dimensional representations are sought in order to explain well the nonlinear characteristics that are hidden in high-dimensional spectral channels. While many algorithms have been proposed for dimension reduction and manifold learning in Euclidean spaces, very few attempts have focused on non-Euclidean spaces. Here, we propose a novel approach that embeds hyperspectral data, transformed into bilateral probability similarities, onto a nonlinear unit norm coordinate system. By seeking a unit l2-norm nonlinear manifold, we encode similarity representations onto a space in which important regularities in data are easily captured. In its general application, the technique addresses problems related to dimension reduction and visualization of hyperspectral images. Unlike methods such as multidimensional scaling and spherical embeddings, which are based on the notion of pairwise distance computations, our approach is based on a stochastic objective function of spherical coordinates. This allows the use of an Exit probability distribution to discover the nonlinear characteristics that are inherent in hyperspectral data. In addition, the method directly learns the probability distribution over neighboring pixel maps while computing for the optimal embedding coordinates. As part of evaluation, classification experiments were conducted on the manifold spaces for hyperspectral data acquired by multiple sensors at various spatial resolutions over different types of land cover. Various visualization and classification comparisons to five existing techniques demonstrated the strength of the proposed approach while its algorithmic nature is guaranteed to converge to meaningful factors underlying the data. Description: Copyright: 2012 IEEE Xplore. This is an ABSTRACT ONLY. The definitive version is published in IEEE Transactions on Geoscience and Remote Sensing, vol. 51(2), pp 857- 871 2012-07-01T00:00:00Z http://hdl.handle.net/10204/6617 Title: A weakly compressible free-surface flow solver for liquid–gas systems using the volume-of-fluid approach Authors: Heyns, JA; Malan, AG; Harms, TM; Oxtoby, OF Abstract: This paper presents a weakly compressible volume-of-fluid formulation for modelling immiscible high density ratio two-fluid flow under low Mach number conditions. This follows findings of experimental analyses that concluded the compressibility of the gas has a noteworthy effect on predicted pressure loads in liquid–gas flow in certain instances. With the aim of providing a more accurate numerical representation of dynamic two-fluid flow, the solver is subsequently extended to account for variations in gas densities. A set of governing equations is proposed, which accounts for the compressible properties of the gas phase in a manner which allows for a computationally efficient numerical simulation. Furthermore, the governing equations are numerically expressed so that they allow for large variations in the material properties, without introducing notable non-physical oscillations over the interface. For the discretisation of the governing equations an edge-based vertex-centred finite volume approach is followed. The developed solver is applied to various test cases and demonstrated to be efficient and accurate. Description: Copyright: 2012 Elsevier. This is the post print version of the work. The definitive version is published in Journal of Computational Physics, vol. 240, pp 145-157 2013-05-01T00:00:00Z