1. Department of Engineering Science, Kermanshah University of Technology, Kermanshah, Iran
2. Department of Mathematics, Faculty of Science, Cairo University, Giza, Egypt
3. Department of Mathematics, Duba University College, University of Tabuk, Saudi Arabia
4. Department of Mathematics, Faculty of Arts and Sciences, Cankaya University, Ankara 06530, Turkey
5. Institute of Space Sciences, Magurele-Bucharest, P. O. Box MG-23, R 76900, Romania