1. Member of the technical staff at Bell Laboratories, Murray Hill, New Jersey 07974 and is a user of the synchrotron radiation facilities at the University of Wisconsin-Madison and the Brookhaven National Synchrotron Light Source
2. Lecturer in the Department of Physics, University of Warwick, Coventry CV4 7AL, United Kingdom, and is a user at the Daresbury Synchrotron Radiation Source