1. Laboratory of Mechanics, Materials and Structures, Department of Physics, Faculty of Science, University of Yaounde I, Yaounde, Cameroon
2. Nonlinear Physics and Complex Systems Group, Department of Physics, The Higher Teacher’s Training College, University of Yaoundé 1, Yaoundé, Cameroon
3. Department of Physics, Higher Teacher Training College, University of Yaounde I, Yaounde, Cameroon