1. Department of Physics, Chemistry and Mathematics, Alabama A&M University, Normal, AL 35762, USA
2. Department of Mathematics and Statistics, College of Science, Al-Imam Mohammad Ibn Saud Islamic University, Riyadh-13318, Saudi Arabia
3. Department of Mathematics and Statistics, Tshwane University of Technology, Pretoria 0008, South Africa
4. Department of Engineering Mathematics and Physics, Higher Institute of Engineering, El Shorouk, Cairo, Egypt
5. Department of Mathematics, Faculty of Science and Arts, Bozok University, 66100 Yozgat, Turkey
6. Mathematics Department, Faculty of Science and Arts, Taibah University, Al-Ula, Saudi Arabia
7. Mathematics Department, Faculty of Science, Beni-Suef University, Egypt
8. School of Electronics and Information Engineering, Wuhan Donghu University, Wuhan 430212, P. R. China
9. Department of Mathematics, Howard University, Washington, DC-20059, USA
10. Science Program, Texas A & M University at Qatar, P. O. Box 23874, Doha, Qatar