1. College of Mathematics and Systems Science, Shandong University of Science and Technology, Qingdao, Shandong, China
2. Department of Mathematical Sciences, Xi’an Jiaotong-Liverpool University, Suzhou, Jiangsu 215123, China
3. College of Electrical Engineering and Automation, Shandong University of Science and Technology, Qingdao, Shandong, China
4. School of Mathematical Sciences, Ocean University of China, Qingdao 266100, China