1. Control & Dynamical Systems and Environmental Science & Engineering, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125
2. Faculté des Sciences Appliquées, Université Libre de Bruxelles, CP 165/11, 50 F. D. Roosevelt Avenue, B-1050 Brussels, Belgium
3. Naval Postgraduate School, Monterey, California 93943
4. Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139
5. Control & Dynamical Systems, California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125