1. Department of Mathematics (Pure and Applied), Rhodes University, P.O. Box 946140, Grahamstown, South Africa
2. LMFN Mathematics Department, University of Setif, 19000, Algeria
3. Department of Chemical and Materials Engineering, King Abdulaziz University, P.O. Box 80204, Jeddah 21589, Saudi Arabia
4. Department of Mathematics and Computer Sciences, Cankaya University, Balgat 06530, Ankara, Turkey
5. Institute of Space Sciences, P.O. BOX MG-23, 76900 Magurele, Bucharest, Romania