1. Ph.D. Student, School of Mathematics and Information Science, Shaanxi Normal Univ., Xi’an, Shaanxi 710019, People’s Republic of China; Lecturer, Faculty of Science, Xi’an Aeronautical Univ., Xi’an, Shaanxi 710077, People’s Republic of China (corresponding author).
2. Supervisor, School of Mathematics and Information Science, Shaanxi Normal Univ., Xi’an, Shaanxi 710019, People’s Republic of China.
3. Ph.D. Student, School of Mathematics and Information Science, Shaanxi Normal Univ., Xi’an, Shaanxi 710019, People’s Republic of China.