1. Department of Mathematics, Cankaya University, Öğretmenler Cad. 14, 06530 Ankara, Turkey
2. Institute of Space Sciences, Magurele, Bucharest, Romania
3. Science Faculty, Department of Mathematics, Firat University, 23119 Elaziğ, Turkey
4. Science Faculty, Department of Mathematics, Federal University Dutse, 7156 Jigawa, Nigeria