[1] Ecole Normale Super, CNRS, Lab Phys Stat, F-75231 Paris, France
[2] Univ Paris 06, F-75231 Paris, France
[3] Univ Paris 07, F-75231 Paris, France
[4] CNRS, UMR 6594, Inst Rech Phenomenes Hors Equilibre, F-13384 Marseille, France
[5] Univ Aix Marseille 1, F-13384 Marseille, France
[6] Univ Aix Marseille 2, F-13384 Marseille, France
[7] Univ Chicago, James Franck Inst, Chicago, IL 60637 USA
[8] Univ Paris 07, Lab Phys Theor Mat Condensee, F-75005 Paris, France
[9] Lab Informat Mecan & Sci Ingn, F-91403 Orsay, France