1. Southwest Research Institute; San Antonio; Texas; USA
2. Rice University; Department of Physics and Astronomy; Houston; Texas; USA
3. Mullard Space Science Lab; University College London; Dorking, Surrey; U. K.
4. Centre d'Etude Spatiale des Rayonnements; Toulouse; France
5. University of Iowa; Department of Physics and Astronomy; Iowa City; Iowa; USA
6. NASA, Goddard Space Flight Center; Greenbelt; Maryland; USA