DSpace Collection:http://hdl.handle.net/10204/32172015-09-02T13:02:06Z2015-09-02T13:02:06ZA pro-forma design for car-carriers: Low-speed performance-based standardsBenade R, Berman RKienhofer F, Nordengen Phttp://hdl.handle.net/10204/80852015-08-19T21:55:28Z2015-07-01T00:00:00ZTitle: A pro-forma design for car-carriers: Low-speed performance-based standards
Authors: Benade R, Berman R; Kienhofer F, Nordengen P
Abstract: The Australian performance-based standards (PBS) scheme is being evaluated in South Africa as an alternative means of regulating heavy vehicles, allowing for a relaxation of length and mass limits. This has proven to provide economic benefits while improving vehicle safety and emissions. Within the PBS scheme, the vehicle is assessed using twelve performance standards which can be grouped together as low-speed directional, high-speed directional, stability and longitudinal performance measures. Compliance with these standards requires expensive and time-intensive computer simulations; a hurdle to the car-carrier industry in particular. We propose a pro-forma car-carrier design in which limits on the most important car-carrier parameters are defined to ensure compliance with the low-speed PBS. It is proposed that new car-carrier designs complying with this semi-prescriptive pro-forma design be exempted from full PBS assessment in the South African PBS project. In this paper the parametric sensitivity of the low-speed performance standards was assessed, and suitable limits on these parameters were found. Tests were carried out on hypothetical designs within these limits. It was found that each of the 10 000 vehicle configurations generated within the constraints of the pro-forma design met the Level 1 requirements of the low-speed PBS. Future work will ensure compliance with the full set of twelve performance standards. It is estimated that the pro-forma approach as compared to doing full assessments would save the South African car-carrier industry an estimated R1,200,000 in one year.
Description: Proceedings of the 34th Southern African Transport Conference, Pretoria, South Africa, 6-9 July 2015.2015-07-01T00:00:00ZTemporal causality between house prices and output in the U.S.: a bootstrap rolling-window approachNyakabawo, WMiller, SMBalcilar, MDas, SGupta, Rhttp://hdl.handle.net/10204/80212015-08-17T21:55:16Z2015-07-01T00:00:00ZTitle: Temporal causality between house prices and output in the U.S.: a bootstrap rolling-window approach
Authors: Nyakabawo, W; Miller, SM; Balcilar, M; Das, S; Gupta, R
Abstract: This paper examines the causal relationships between the real house price index and real GDP per capita in the US, using the bootstrap Granger (temporal) non-causality test and a fixed-size rolling-window estimation approach. We use quarterly time-series data on the real house price index and real GDP per capita, covering the period 1963:Q1 to 2012:Q2. The full-sample bootstrap non-Granger causality test result suggests the existence of a unidirectional causality running from the real house price index to real GDP per capita. A wide variety of tests of parameter constancy used to examine the stability of the estimated vector autoregressive models indicate short- and long-run instability. This suggests that we cannot rely on the full-sample causality tests and, hence, this warrants a time-varying (bootstrap) rolling-window approach to examine the causal relationship between these two variables. Using a rolling window size of 28 quarters, we find that while causality from the real house price to real GDP per capita occurs frequently, significant, but less frequent, evidence of real GDP per capita causing the real house price also occurs. These results imply that while the real house price leads real GDP per capita, in general (both during expansions and recessions), significant feedbacks also exist from real GDP per capita to the real house price.
Description: Copyright: 2015 Elsevier. This is a post-print version. The definitive version of the work is published in the North American Journal of Economics and Finance, vol. 33, pp 55-732015-07-01T00:00:00ZSimultaneous boundary value and material parameter estimation using imperfect compression dataJansen van Rensburg, GJKok, SWilke, DNhttp://hdl.handle.net/10204/80092015-08-17T21:55:22Z2014-09-01T00:00:00ZTitle: Simultaneous boundary value and material parameter estimation using imperfect compression data
Authors: Jansen van Rensburg, GJ; Kok, S; Wilke, DN
Abstract: Data is available for different hard metal samples tested in compression using a modified tensile test specimen. Three strain gauges were placed 120 degrees apart around the circumference of the centre of the test section. The spread of the strain data obtained from these tests indicate non-uniform compression. In this paper, the benefits of surrogate modelling is investigated using a virtual experiment with parameterised displacement boundary condition that mimics the responses observed in experimental data. The known boundary condition and material parameter values used to perform the finite element analysis in the virtual experiment allows investigation on the accuracy of the parameter identification strategies employed. The unknown material parameters and boundary conditions are first sampled within a reasonable range using a Latin hypercube. Finite element simulations are performed for each sample point and radial basis function interpolation is used to approximate the error function across the design space. A global optimisation algorithm is used to minimise the error function. The associated parameters can then be compared to the known real solution. In another surrogate modelling approach, the interpolation is set up using the full data set obtained from all sample points. Radial basis function interpolations are set up for each of the unknown parameters as output, using the data as input. Now, given the virtual data set as input, each parameter is simply determined by evaluating the associated radial basis function. Sensitivities are also investigated for both strategies by applying 2% random noise to the virtual experiment data. This is done to investigate the effect of noise on the parameter estimation since the real experimental data would contain some noise.
Description: Proceedings of the 4th International Engineering Optimization Conference 2014 (EngOpt2014), Instituto Superior Tecnico, Lisbon, Portugal, 8-11 September 2014. . Due to copyright restrictions, the attached PDF file only contains the abstract of the full text item. For access to the full text item, please consult the publisher's website2014-09-01T00:00:00ZReconstructing the velocity field beyond the local universeJohnston, RBacon, DTeodoro, LFANichol, RCWarren, MSCress, Chttp://hdl.handle.net/10204/79932015-05-25T21:55:26Z2014-10-01T00:00:00ZTitle: Reconstructing the velocity field beyond the local universe
Authors: Johnston, R; Bacon, D; Teodoro, LFA; Nichol, RC; Warren, MS; Cress, C
Abstract: We present a maximum probability approach to reconstructing spatial maps of the peculiar velocity field at redshifts z ~ 0.1, where the velocities have been measured from distance indicators (DI) such as D(sub n) - s relations or Tully–Fisher. With the large statistical uncertainties associated with DIs, our reconstruction method aims to recover the underlying true peculiar velocity field by reducing these errors with the use of two physically motivated filtering prior terms. The first constructs an estimate of the velocity field derived from the galaxy over-density d(sub g) and the second makes use of the matter linear density power spectrum P(sub k). Using N-body simulations we find, with an SDSS-like sample (N(sub gal) 33 per deg(sup 2)), an average correlation coefficient value of r = 0.55 ± 0.02 between our reconstructed velocity field and that of the true velocity field from the simulation. However, with a suitably high number density of galaxies from the next generation surveys (e.g. N(sub gal) 140 per deg(sup 2)) we can achieve an average r = 0.70±0.02 out to moderate redshifts z ~ 0.1. This will prove useful for future tests of gravity, as these relatively deep maps are complementary to weak lensing maps at the same redshift.
Description: Copyright: 2010 Springer Verlag. This is the pre-print/post-print version of the work. The definitive version is published in the Journal of General Relativity and Gravitation, vol. 46, pp 1-182014-10-01T00:00:00ZRam pressure statistics for bent tail radio galaxiesMguda, ZFaltenbacher, AVan der Heyden, KGottlöber, SCress, CVaisanen, PYepes, Ghttp://hdl.handle.net/10204/79832015-05-25T21:55:16Z2015-01-01T00:00:00ZTitle: Ram pressure statistics for bent tail radio galaxies
Authors: Mguda, Z; Faltenbacher, A; Van der Heyden, K; Gottlöber, S; Cress, C; Vaisanen, P; Yepes, G
Abstract: In this paper we use the MareNostrum Universe Simulation, a large scale, hydrodynamic, non-radiative simulation in combination with a simple abundance matching approach to determine the ram pressure statistics for bent radio sources (BRSs). The abundance matching approach allows us to determine the locations of all galaxies with stellar masses >10(sup11)MSol in the simulation volume. Assuming ram pressure exceeding a critical value causes bent morphology, we compute the ratio of all galaxies exceeding the ram pressure limit (RPEX galaxies) relative to all galaxies in our sample. According to our model 50% of the RPEX galaxies at z=0 are found in clusters with masses larger than 10(sup14.5)MSol the other half resides in lower mass clusters. Therefore, the appearance of bent tail morphology alone does not put tight constraints on the host cluster mass. In low mass clusters, M<10(sup14)MSol, RPEX galaxies are confined to the central 500 kpc whereas in clusters of >10(sup15)Msol they can be found at distances up to 1.5Mpc. Only clusters with masses >10(sup15)MSol are likely to host more than one BRS. Both criteria may prove useful in the search for distant, high mass clusters.
Description: Copyright: 2015 Oxford University Press2015-01-01T00:00:00ZCosmological measurements with forthcoming radio continuum surveysRaccanelli, AZhao, G-BBacon, DJJarvis, MJPercival, WJNorris, RPRottgering, HAbdalla, FBCress, CMKubwimana, J-CLindsay, SNichol, RCSantos, MGSchwarz, DJhttp://hdl.handle.net/10204/79712015-05-25T21:55:17Z2012-08-01T00:00:00ZTitle: 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 Oxford University Press2012-08-01T00:00:00Z