Affiliation: | 1. College of Mathematics and Computer Science, Fuzhou University, Fuzhou 350116, China;2. Department of Mathematics, Beijing Jiaotong University, Beijing 100044, China;3. Department of Mathematics, Embry-Riddle Aeronautical University, Prescott, AZ 86305, United States;4. Department of Mathematics, West Virginia University, Morgantown, WV 26506, United States |