1. Department of Physics Tohoku University Aramaki‐Aza‐Aoba, Aoba‐ku Sendai 980‐8578 Japan
2. Institute of Fluid Science Tohoku University Katahira, Aoba‐ku Sendai 980‐8577 Japan
3. Department of Aerospace Engineering Tohoku University Aramaki‐Aza‐Aoba, Aoba‐ku Sendai 980‐8579 Japan
4. Department of Material Science and Engineering University of Washington Seattle WA 98195 USA