Affiliation: | (1) Department of Mathematics, Faculty of Science, Cairo University, Beni-Suef, Egypt;(2) Department of Mathematics, Faculty of Science, Minia University, Minia, Egypt;(3) Department of Physics, University of Antwerpen, Antwerpen, Belgium;(4) Present address: Mathematics Department, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia |