1. Max Planck Institute for Dynamics and Self-Organization; Am Faßberg 17; Göttingen 37077 Germany
2. Department of Engineering; Universitá Campus Bio-Medico di Roma; Via A. del Portillo 21 Rome 00128 Italy
3. Universitá della Svizzera italiana, Institute of Computational Science; Via Giuseppe Buffi 13 Lugano 9600 Switzerland