1. Max Planck Institute for Dynamics and Self-Organization, Am Faßberg 17, 37077 Göttingen, Germany
2. Institute for the Dynamics of Complex Systems, Georg August Universität, Göttingen, Germany
3. Center for Exploratory Research, R&D group, Hitachi Ltd., Higashi-Koigakubo 1-280, Kokubunji-shi, Tokyo 185-8601, Japan
4. Physics of Fluids Group, Max Planck Center for Complex Fluid Dynamics, MESA+ Institute and J. M. Burgers Center for Fluid Dynamics, University of Twente, PO Box 217, 7500AE Enschede, The Netherlands