1. Institute for Autonomous Intelligent Systems, German National Research Center for Information Technology, Schloss Birlinghoven, D-53754 Sankt Augustin, Germany
2. Institute of Physics, Humboldt University of Berlin, Invalidenstr. 110, D-10115 Berlin, Germany
3. Institute for Economics and Traffic, Dresden University of Technology, D-01062 Dresden, Germany
4. Institute for Theoretical Physics, University of Stuttgart, Pfaffenwaldring 57/III, D-70550 Stuttgart, Germany