1. School of Mathematics and Physics, Nanjing Institute of Technology, Jianging, Nanjing, P.R. China
2. Department of Mathematics, College of Science, Qassim University, Burayadah, Saudi Arabia
3. Department of Mathematics, Faculty of Education, Ain Shams University, Roxy, Cairo, Egypt
4. Department of Computational Sciences, School of Sciences, CHRIST University, Delhi NCR, Ghaziabad, India
5. Department of Mathematics, Babeş-Bolyai University, Cluj-Napoca, Romania