1. IEM, UMR 5635 CNRS-ENSCM-UM2, 1919 route de Mende, 34 193 Montpellier cedex 5, France
2. MACS, UMR 5253 Institut Charles Gerhardt, CNRS-ENSCM-UM1-UM2, 8, rue de l'Ecole Normale, 34296 Montpellier cedex 5, France
3. CRMCN, UPR 7251, Campus de Luminy, case 913, 13288 Marseille cedex 09, France