1. Department of Engineering Mathematics, Faculty of Engineering, Cairo University, Giza, Egypt
2. Department of Mathematics, Faculty of Science, University of Hail, Hail 2440, Saudi Arabia
3. Department of Mathematics, Faculty of Science, Mansoura University, Mansoura 35516, Egypt
4. School of Mathematical Sciences, University of Jinan, Jinan, Shandong 250022, China
5. Missouri University of Science Technology, 310 Rolla Building, Rolla, MO 65409-0020, USA