1. The University Institute of Technology, University of Ngaoundéré (Cameroon), P. O. Box 455 Ngaoundéré, Cameroon
2. UMR6249 Chrono-environment Laboratory, University of Franche-Comté (France), 16 route de Gray, F-25030 Besançon cedex, France
3. The Faculty of Sciences of University, University of Ngaoundéré (Cameroon), P. O. Box 454 Ngaoundéré, Cameroon