1. Institute of Mathematics and Physical Sciences (IMSP) University of Abomey-Calavi 01 BP 613 Porto-Novo Benin
2. Faculty of Engineering University of Burundi Bujumbura Burundi
3. College of Science Engineering and Technology University of South Africa P.O. Box 392 UNISA 0003 Pretoria South Africa
4. College of Technology University of Buea P.O. Box 63 Buea Cameroon
5. Department of Physics Shendi University Shendi Sudan
6. The National Institute for Theoretical Physics School of Physics and Mandelstam Institute for Theoretical Physics University of the Witwatersrand Johannesburg Wits 2050 South Africa