1. UNESCO MIRCEN: Microbial, Biochemical and Food Biotechnology, University of the Free State, P.O. Box 339, Bloemfontein, 9300, South Africa.
2. Centre for Microscopy, University of the Free State, P.O. Box 339, Bloemfontein, 9300, South Africa.
3. Department of Physics, University of the Free State, P.O. Box 339, Bloemfontein, 9300, South Africa.
4. Department of Mathematics and Applied Mathematics, University of the Free State, P.O. Box 339, Bloemfontein, 9300, South Africa.