基金Acknowledgments We thank Ms Mekie Takahashi, Ms Ritsuko Kanda (Nagaya University, Japan), Dr Changliang Fu and Dr Shouqing Lu (Institute of Mechanics, Chinese Academy of Sciences) for technical assistance. This work was partly supported by research grants from the National Natural Science Foundation of China (10602031) and Grants-in-aid for Scientific Research on Priority Areas (#15086270 to M.S.) and Creative Research (# 16GS0308 to M.S.) from the Ministry of Education Science Sports and Culture, Japan.