Humphreys, P.; Erfort, E.; Fester, V.; Chhiba, M.; Kotze, R.; Philander, O.; Sam, M.(Journal for New Generation Sciences, Vol 8, Issue 2: Central University of Technology, Free State, Bloemfontein, 2010)
Dimitrov, D.; Hugo, P.A.; Deez, B.(Journal for New Generation Sciences, Vol 8, Issue 2: Central University of Technology, Free State, Bloemfontein, 2010)