1. Department of Mathematics, Thiruvalluvar University, Vellore 632115, Tamil Nadu, India
2. MOE-LCSM, School of Mathematics and Statistics, Hunan Normal University, Changsha 410081, China
3. School of Mechanical Engineering, Pusan National University, Busan 46241, Republic of Korea
4. School of Information Science and Engineering, Chengdu University, Chengdu 610106, China