1. Laboratory of Energy Science and Engineering, ETH Zürich, Leonhardstrasse 27, 8092 Zürich, Switzerland.
2. Institute for Biomedical Engineering, University of Zürich and ETH Zürich, Gloriastrasse 35, 8092 Zürich, Switzerland.
3. Department of Mechanical Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.