[1] Univ Politecn Cataluna, FEN, Dept Phys, CSRG, Campus Nord Modul B4, ES-08034 Barcelona, Spain
[2] Max Planck Gesell, Fritz Haber Inst, D-14195 Berlin, Germany
[3] Univ Bristol, Dept Geol, Bristol BS8 1RJ, Avon, England
[4] Santa Fe Inst, Santa Fe, NM 87501 USA
[5] Niels Bohr Inst, DK-2100 Copenhagen, Denmark