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