1. Laboratory of Biophysics, University of Yaounde I, B.P. 812 Yaounde, Cameroon
2. Department of Physics, Higher Teacher Training College of Bertoua, B.P. 652 Bertoua, Cameroon
3. Botswana International University of Science and Technology, Private Bag 16 Palapye, Botswana
4. Department of Physics, Faculty of Science, University of Maroua, B.P. 814 Maroua, Cameroon
5. Laboratory of Mechanics, University of Yaounde I, B.P. 812 Yaounde, Cameroon