1. Department of Mechanical Engineering, Ohio State University, 201 West 19th Avenue, Columbus, OH 43210, USA.
2. Department of Physics, Ohio State University, 201 West 19th Avenue, Columbus, OH 43210, USA.
3. California Institute of Technology, Pasadena, CA 91125, USA.
4. Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan.