Esterhuizen, H.L.; De Beer, K.J.; Baird, N.(Interim : Interdisciplinary Journal, Vol 7, Issue 2: Central University of Technology Free State Bloemfontein, 2008)
Bezuidenhout, J.; Van der Westhuizen, D.; De Beer, K.J.(Interim : Interdisciplinary Journal, Vol 3, Issue 2: Central University of Technology, Free State, Bloemfontein, 2004)
Bezuidenhout, J.; Van der Westhuizen, D.; De Beer, K.J.(Journal for New Generation Sciences, Vol 3, Issue 2: Central University of Technology, Free State, Bloemfontein, 2005)