1. International Center for Applied MechanicsState Key Laboratory for Strength and Vibration of Mechanical StructuresSchool of Aerospace EngineeringXi'an Jiaotong University Xi'an Shaanxi 710049 P. R. China
2. John A. Paulson School of Engineering and Applied SciencesHarvard University Cambridge MA 02138 USA
3. Kavli Institute for Bionano Science and TechnologyHarvard University Cambridge MA 02138 USA
4. Department of Mechanics and Aerospace EngineeringSouthern University of Science and Technology Shenzhen Guangdong 518055 P. R. China