Govender G.,The Council for Scientific and Industrial Research |
Moller H.,The Council for Scientific and Industrial Research |
Curle U.A.,The Council for Scientific and Industrial Research
Advanced Materials Research | Year: 2014
Semi-solid metal forming is more than 40 years old but its full potential to near net shape form high strength aluminium alloys has been realised only to a limited degree. Alloys developed for traditional manufacturing processes were initially used but it became apparent that alloys specific to SSM forming needed to be developed. The main alloy development criteria revolved around SSM processing temperature, solid fraction (fs) versus temperature sensitivity and age hardening potential. This methodology while sound does not fully address the unique processing behaviour of SSM forming. By its very nature SSM requires the controlled solidification of a part of the melt before forming. From basic solidification fundamentals this results in the enrichment of the remaining liquid with alloying elements. During the forming process segregation of liquid phase essentially produces a component with very different compositions in the regions where the liquid solidifies last. From recent work completed on a wide range of standard alloy systems it has become apparent that this segregation effect has a significant impact on aging behaviour and strength. Low melting point structures formed in the these regions result in localised melting in the grain boundary region and along areas of gross liquid segregation during solution heat treatment, contributing to the poor mechanical properties. Although this behaviour can be addressed using modified heat treatment, this cannot be applied to all current alloy systems. Alloy design for SSM forming must take these phenomena into account in order to develop and or specify aluminium alloys with acceptable mechanical properties. ©(2014) Trans Tech Publications, Switzerland.
Jansen van Rensburg G.J.,The Council for Scientific and Industrial Research |
Kok S.,University of Pretoria |
Wilke D.N.,University of Pretoria
Engineering Optimization IV - Proceedings of the 4th International Conference on Engineering Optimization, ENGOPT 2014 | Year: 2014
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. © 2015 Taylor & Francis Group, London.
Luo H.,The Council for Scientific and Industrial Research |
Vaivars G.,University of Latvia |
Mathe M.,The Council for Scientific and Industrial Research
Journal of Power Sources | Year: 2010
In this paper, the proton exchange membrane prepared by covalent-ionically cross-linking water soluble sulfonated-sulfinated poly(oxa-p-phenylene-3,3-phthalido-p-phenylene-oxa-p-phenylene-oxy-phenylene) (SsPEEK-WC) is reported. Compared with covalent cross-linked PEEK-WC membrane, this covalent-ionically cross-linked PEEK-WC membrane exhibits extremely reduced water uptake and methanol permeability, but just slightly sacrificed proton conductivity. The proton conductivity of the covalent-ionically cross-linked PEEK-WC membrane reaches to 2.1 × 10-2 S cm-1 at room temperature and 4.1 × 10-2 S cm-1 at 80 °C. The methanol permeability is 1.3 × 10-7 cm2 s-1, 10 times lower than that of Nafion® 117 membrane. The results suggest that the covalent-ionically cross-linked PEEK-WC membrane is a promising candidate for direct methanol fuel cell because of low methanol permeability and adequate proton conductivity. © 2010 Elsevier B.V. All rights reserved.
Main R.,Natural Environment Research Council |
Cho M.A.,Natural Environment Research Council |
Mathieu R.,Natural Environment Research Council |
O'Kennedy M.M.,The Council for Scientific and Industrial Research |
And 2 more authors.
ISPRS Journal of Photogrammetry and Remote Sensing | Year: 2011
Quantifying photosynthetic activity at the regional scale can provide important information to resource managers, planners and global ecosystem modelling efforts. With increasing availability of both hyperspectral and narrow band multispectral remote sensing data, new users are faced with a plethora of options when choosing an optical index to relate to their chosen or canopy parameter. The literature base regarding optical indices (particularly chlorophyll indices) is wide ranging and extensive, however it is without much consensus regarding robust indices. The wider spectral community could benefit from studies that apply a variety of published indices to differing sets of species data. The consistency and robustness of 73 published chlorophyll spectral indices have been assessed, using leaf level hyperspectral data collected from three crop species and a variety of savanna tree species. Linear regression between total leaf chlorophyll content and bootstrapping were used to determine the leafpredictive capabilities of the various indices. The indices were then ranked based on the prediction error (the average root mean square error (RMSE)) derived from the bootstrapping process involving 1000 iterative resampling with replacement. The results show two red-edge derivative based indices (red-edge position via linear extrapolation index and the modified red-edge inflection point index) as the most consistent and robust, and that the majority of the top performing indices (in spite of species variability) were simple ratio or normalised difference indices that are based on off-chlorophyll absorption centre wavebands (690-730. nm). © 2011 International Society for Photogrammetry and Remote Sensing, Inc. (ISPRS).
Jansen van Rensburg G.J.,University of Pretoria |
Jansen van Rensburg G.J.,The Council for Scientific and Industrial Research |
Wilke D.N.,University of Pretoria |
Kok S.,The Council for Scientific and Industrial Research
International Journal for Numerical Methods in Biomedical Engineering | Year: 2012
Variation in masticatory induced stress, caused by shape changes in the human skull, is quantified in this article. A comparison on masticatory induced stress is presented subject to a variation in human skull shape. Non-rigid registration is employed to obtain appropriate computational domain representations. This procedure allows the isolation of shape from other variations that could affect the results. An added benefit, revealed through the use of non-rigid registration to acquire appropriate domain representation, is the possibility of direct and objective comparison and manipulation. The effect of mapping uncertainty on the direct comparison is also quantified. As shown in this study, exact difference values are not necessarily obtained, but a non-rigid map between subject shapes and numerical results gives an objective indication on the location of differences. © 2012 John Wiley & Sons, Ltd.
The Council For Scientific And Industrial Research, Korea Institute of Science and Technology | Date: 2013-09-25
A composition for preventing and/or treating dementia and ameliorating memory impairment and/or improving memory, comprising one or more arylnaphthalene lignan derivatives, such as Justicidin A, 5-methoxyjusticidin A, Chinensinaphthol, and a pharmaceutically-acceptable salt thereof, as active ingredient.