1. State Key Laboratory of Mechanical Transmissions, Chongqing University, Chongqing, P. R. China
2. The Second Research Institute of CAAC, Chengdu, P. R. China
3. State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Lanzhou, P.R. China
4. Department of Mechanical Engineering, University of Utah, UT, USA