1. African Institute for Mathematical Sciences (AIMS-Ghana), East Legon Hills, Accra, Ghana
2. Institute of Mathematics, Brandenburg Technical University, Cottbus-Senftenberg, Germany
3. Department of Physics, Faculty of Science, University of Buea, Laboratory of Research on Advanced Materials and Nonlinear Science (LaRAMaNS), Buea, Cameroon
4. African Institute for Mathematical Sciences (AIMS-Cameroon), Limbe, Cameroon