1. Department of Physics and Astronomy; University of Iowa; Iowa City Iowa USA
2. Space Science and Engineering Division; Southwest Research Institute; San Antonio Texas USA
3. The Johns Hopkins University Applied Physics Laboratory; Laurel Maryland USA
4. Goddard Space Flight Center; Greenbelt Maryland USA
5. Space Research Corporation; Annapolis Maryland USA
6. Jet Propulsion Laboratory; Pasadena California USA
7. Department of Astrophysical Science; Princeton University; Princeton New Jersey USA