1. School of Engineering and Applied Science, The George Washington University, Washington D. C., 20052, USA
2. School of Mechanical Engineering and Automation, Beihang University, Beijing 100191, China
3. Art College, Jilin University, Changchun, 130025, China
4. School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue 639798, Singapore