Institute of Fluid Dynamics, ETH Zurich, Zurich, Switzerland.|Department of Physics, University of California at San Diego, La Jolla, California, United States of America.|Department of Physics, University of California at San Diego, La Jolla, California, United States of America.|Institute of Fluid Dynamics, ETH Zurich, Zurich, Switzerland.|Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland.