1. School of Mechanical Engineering, Xi'an Jiaotong University and State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi'an 710049, China
2. School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798
3. Institute of Microelectronics, A*STAR (Agency for Science, Technology and Research), Singapore 138634
4. School of Electronics Engineering and Computer Science, Peking University, Beijing 100871, China