Shaban Sedghi
Department of Mathematics, Islamic Azad University-Ghaemshahr Branch, Ghaemshahr P.O. Box 163, Iran
Nabi Shobe
Department of Mathematics, Islamic Azad University-Babol Branch, Iran
Shahram Sedghi
Department of Mechanical Engineering, Iran and University of Science and Technology, Narmak, Tehran 16844, Iran