First Author:   Guivis Nkemgha University of Cape Town nkemghazeufackguivis@yahoo.fr   , Cameroon   695754269(Phone) 695754269(Fax) Second Author: Ulrich Kevin Kamwa University of Omar Bongo ulrichkamwa@gmail.com         Third Author: Elsa Tajeussong University of Dschang etajeussong@yahoo.com   , Cameroon