1. Physics of Fluids Group, Department of Science and Technology, Mesa+ Institute for Nanotechnology, Max Planck Center for Complex Fluid Dynamics and J. M. Burgers Centre for Fluid Dynamics, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
2. Department of Mechanical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
3. Océ Technologies B.V., P.O. Box 101, 5900 MA Venlo, The Netherlands
4. Max Planck Institute for Dynamics and Self-Organization, 37077 Göttingen, Germany