1. State Key Laboratory of Solid Lubrication; Lanzhou Institute of Chemical Physics; Chinese Academy of Sciences; Lanzhou 730000 China
2. Department of Engineering for Innovation; Universitá del Salento; 73100 Monteroni-Lecce Italy
3. Department of Mechanical Engineering; Imperial College London; London SW7 2AZ UK
4. University of the Chinese Academy of Sciences; Beijing 100049 China
5. Department of Functional Morphology and Biomechanics; Zoological Institute; Kiel University; 24118 Kiel Germany