1. Research and Modelisation Unit of Mechanical and Physical Systems, University of Dschang 1 , P. O. Box 67, Dschang, Cameroon
2. MoCLiS Research Group 2 , Dschang, Cameroon
3. Research Unit Condensed Matter, Electronics and Signal Processing, University of Dschang 3 , P. O. Box 67, Dschang, Cameroon
4. ICTP South American Institute for Fundamental Research, São Paulo State University (UNESP) 4 , São Paulo, Brazil
5. Instituto de Física Teórica 5 , 01140-070 São Paulo, Brazil