1. School of Mechatronics Engineering, University of Electronic Science and Technology of China, Chengdu, P.R. China
2. State Key Laboratory of Rail Traffic Control and Safety, Beijing Jiaotong University, Beijing, P.R. China
3. State Testing Laboratory of Hangzhou Bearing Test and Research Center, Hangzhou, P.R. China
4. Department of Mechanical Engineering, University of Alberta, Edmonton, Canada