Potgieter, M.; De Jager, J.W.; Van Heerden, C.H.(Journal for New Generation Sciences, Vol 9, Issue 2: Central University of Technology, Free State, Bloemfontein, 2011)
Van Blommenstein, D.; Matope, S.; Van der Merwe, A.F.(Journal for New Generation Sciences, Vol 9, Issue 1: Central University of Technology, Free State, Bloemfontein, 2011)