1. Department of Mathematics, College of Sciences and Arts, Najran University, 55461 Najran, Saudi Arabia
2. Department of Mathematics, Faculty of Applied Science, Taiz University, Taiz, Yemen
3. Faculty of Natural and Agricultural Sciences, Institute for Groundwater Studies, University of the Free State, 9300 Bloemfontein, South Africa
4. Department of Mathematics, Faculty of Sciences, Cankaya University, 06530 Balgat, Ankara, Turkey
5. Institute of Space Sciences, Magurele-Bucharest, Romania