1. Department of Basic Science, Faculty of Mines and Petroleum Industries, University of Maroua, Maroua, Cameroon
2. National Advanced School of Engineering, University of Yaounde I, Cameroon
3. Laboratory of Mechanics, Materials and Structures, Department of Physics, University of Yaounde I, Cameroon
4. Nord Staße 9 Weimar, Germany
5. Faculty of Engineering Technology, Amol University of Special Modern Technologies, Amol, Iran
6. Neighbourhood of Akcaglan, Imarli Street 28/4, 26030 Eskisehir, Turkey