1. Department of Mathematics, Faculty of Art and Sciencs, Çankaya University, Balgat, 06530 Ankara, Turkey
2. Institute of Space Sciences, P.O. BOX MG-23, 76900 Magurele-Bucharest, Romania
3. Department of Chemical and Materials Engineering, Faculty of Engineering, King Abdulaziz University, P.O. Box 80204, Jeddah 21589, Saudi Arabia
4. Department of Mathematics, Texas A & M University, 700 University Boulevard, Kingsville, TX, USA