1. a Laboratoire de Physique des Solides and LURE , F91405, Orsay, FRANCE
2. b L.C.R. , Thomson CSF, F91401, Orsay, FRANCE
3. c Laboratoire de Chimie du Solide Mineral , F54506, Vandoeuvreles Nancy, FRANCE
4. d Xerox Webster Research Center , Webster, NY, 14580, USA
5. e AT&T Technologies, Engineering Research Center , P.O. Box 900, Princeton, NJ, 08540
6. f SIGNAL UOP Research Center , 50 UOP Plaza, DesPlaines, IL, 60016-6187