[1] Univ Bologna, Dept Phys & Astron, Viale Berti Pichat 6-2, I-40127 Bologna, Italy
[2] Univ Trieste, Dept Engn & Architecture, Via Alfonso Valerio 10, I-34127 Trieste, Italy
[3] Elettra Sincrotrone Trieste SCpA SS 14, Km 163-5, I-341499 Basovizza, TS, Italy
[4] Lawrence Livermore Natl Lab, 7000 East Ave, Livermore, CA 94550 USA