1. Department of Mathematics, Islamic Azad University, Zahedan Branch, Zahedan, Iran
2. Faculty of Sciences and Mathematics, University of Niš, Visegradska 33, 18000 Niš, Serbia
3. Instituto de Matemáticas Multidisciplinar, Universitat Politècnica de València, 46022 Valencia, Spain
4. Department of Applied Mathematics, School of Mathematical Sciences, Ferdowsi University of Mashhad, Mashhad, Iran
5. Department of Mathematics, Kosar University of Bojnord, P. O. Box 9415615458, Bojnord, Iran