1. Institute for Theoretical Physics, University of Cologne, 50937 Köln, Germany
2. Department of Mathematics “Giuseppe Peano,” Università degli Studi di Torino, 10123 Torino, Italy
3. Forschungszentrum Jülich, Institute for Energy and Climate Research (IEK-STE), 52428 Jülich, Germany
4. Max Planck Institute for Dynamics and Self-Organization, Am Faßberg 17, 37077 Göttingen, Germany