1. Department of Physics and Material Sciences Center, Philipps-Universität Marburg, Renthof 5, 35032 Marburg, Germany
2. NAsPIII/V GmbH, Hans-Meerwein-Straße, 35032 Marburg, Germany
3. Nonlinear Control Strategies, Inc., 7040 N Montecatina Drive, Tucson, Arizona 85704, USA