[1] Univ Douala, Fac Sci, Dept Phys, Pure Phys Lab,Grp Nonlinear Phys & Complex Syst, POB 24157, Douala, Cameroon
[2] Univ Douala, Adv Teachers Training Coll Tech Educ, Dept Base Sci Educ, POB 8213, Douala, Cameroon
[3] Univ Ngaoundere, Sch Geol & Min Engn, Dept Phys, POB 115, Meiganga, Cameroon
[4] Univ Douala, Adv Teachers Training Coll Tech Educ, Dept Civil Engn, POB 8213, Douala, Cameroon