1. Department of Mathematics, Faculty of Science, Beni-Suef University, Beni-Suef, Egypt
2. Department of Mathematics, Faculty of Science, Assiut University, El-Kharja, Egypt
3. Department of Mathematics, Faculty of Science, Cairo University, Giza, Egypt
4. Department of Mathematics, Cankaya University, Ankara, Turkey
5. Institute of Space Sciences, Magurele-Bucharest, Romania