1. School of Engineering and Applied Sciences, Kavli Institute for Nanobio Science and Technology, Harvard University, Cambridge, MA 02138
2. State Key Laboratory for Strength and Vibration of Mechanical Structures, International Center for Applied Mechanics, School of Aerospace Engineering, Xi'an Jiaotong University, Xi’an 710049, China
3. Schlumberger-Doll Research, One Hampshire Street, Cambridge, MA 02139 e-mail:
4. Schlumberger-Rosharon Campus, 14910 Airline Road, Rosharon, TX 77459