1. Laboratory of Mechanics, Materials and Structures, Research and Postgraduate Training Unit for Physics and Applications, Postgraduate School of Science, Technology and Geosciences, Department of Physics, Faculty of Science, University of Yaoundé 1, P.O. Box 812, Ngoa Ekelle, Yaoundé, Cameroon
2. Department of Mechanical Engineering, Higher Technical Teacher's Training College (ENSET) Ebolowa, University of Ebolowa, P.O. Box 886, Ebolowa, Cameroon