1. School of Mathematics and Statistics, Central South University, Changsha, China
2. Department of Mathematics, Yusuf Maitama Sule University, Kano, Nigeria
3. Department of Mathematics, Guangdong University of Petrochemical Technology, Maoming, China
4. Department of Mathematics, College of Science, Qassim University, Buraydah, Saudi Arabia
5. Department of Mathematics, Faculty of Science, Tanta University, Tanta, Egypt