[1] Univ Douala, Fac Sci, Dept Phys, Fundamental Phys Lab,Phys Complex Syst Grp, Box 24 157, Douala, Cameroon
[2] Univ Yaounde I, Fac Sci, Lab Modeling & Simulat Engn Biomimet & Prototypes, POB 812, Yaounde, Cameroon
[3] Univ Sannio, Dept Sci & Technol, Via Sanctis, I-82100 Benevento, Italy
[4] Potsdam Inst Climate Impact Res PIK, D-14473 Potsdam, Germany
[5] Humboldt Univ, Dept Phys, D-12489 Berlin, Germany