1. Plasma Research Institute, Science Applications, Incorporated, Boulder, Colorado 80302
2. Laboratory for Extraterrestria Physics, Goddard Space Flight Center, Greenbelt, Maryland 20771
3. Department of Astronomy, University of Florida, Gainesville 32611
4. Jet Propulsion Laboratory, Pasadena, California 91103
5. Observatoire de Paris, Section d'Astrophysique de Meudon, 92190 Meudon, France
6. Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge 02139