1 Department of Mechanical Engineering, Virginia Polytechnic Institute of Technology and State University, Blacksburg, VA, 24060, USA.
2 Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
3 Department of Physics, University of Wisconsin-Madison, Madison, WI, 53706, USA.
4 Department of Physics, University of Wisconsin-Madison, Madison, WI, 53706, USA; Lawrence Berkeley National Laboratory, Chemical Sciences Division, Berkeley, CA, 94720, USA.
5 Koret School of Veterinary Medicine, The Hebrew University of Jerusalem, Israel.
6 Department of Mechanical Engineering, Virginia Polytechnic Institute of Technology and State University, Blacksburg, VA, 24060, USA. Electronic address: lingl@vt.edu.