[1] CNR, IST NEUROBIOL, I-00100 ROME, ITALY
[2] IST NAZL FIS NUCL, FRASCATI NATL LABS, I-00044 FRASCATI, ITALY
[3] UNIV WISCONSIN, DEPT PHYS, MADISON, WI 53706 USA
[4] UNIV WISCONSIN, DEPT ELECT & COMP ENGN, MADISON, WI 53706 USA
[5] UNIV WISCONSIN, CTR SYNCHROTRON RADIAT, MADISON, WI 53706 USA
[6] ECOLE POLYTECH FED LAUSANNE, INST PHYS APPL, CH-1015 LAUSANNE, SWITZERLAND
[7] UNIV CALIF BERKELEY LAWRENCE BERKELEY LAB, GR XRAY OPT, BERKELEY, CA 94720 USA