1. Department of Physics, Faculty of Science, University of Maroua, P. O. Box 814, Maroua, Cameroon
2. Faculty of Engineering Technology, Amol University of Special Modern Technologies, Amol, Iran
3. Neighbourhood of Akcaglan, Imarli Street, No. 28/4, 26030, Eskisehir, Turkey
4. Department of Physics, Faculty of Science, University of Ngaoundere, P. O. Box 454, Cameroon