1. Department of Mathematics, Faculty of Science, Cairo University
2. Department of Mathematics and Statistics, College of Science, Al-Imam Mohammad Ibn Saud Islamic University, Saudi Arabia; Department of Mathematics, Faculty of Science, Beni-Suef University, Beni-Suef, Egypt
3. Department of Basic Science, Institute of Engineering, Canadian International College, Egypt
4. Department of Mathematics, Cankaya University, Turkey; Institute of Space Sciences, Romania