1. Department of Mathematics, Faculty of Science, Atatürk University, 25240 Erzurum, Turkey
2. Department of Mathematics, Faculty of Mathematics and Computer Science, Transylvania University of Braşov, Iuliu Maniu 50, 50091 Braşov, Romania
3. Department of Mathematical Engineering, Faculty of Chemical and Metallurgical Engineering, Yildiz Technical University, Davutpasa, 34210 Istanbul, Turkey