1 Center for Systems Engineering and Applied Mechanics (CESAME), Department of Mathematical Engineering, Université catholique de Louvain, 4, Avenue G. Lemaître, 1348 Louvain-la-Neuve
2 Department of Civil and Environmental Engineering, 711 Davis Hall, University of California, Berkeley, CA 94720-1710
3 Dipartimento di Ingegneria dell'Informazione e Matematica Applicata, via Ponte Don Melillo, 84084 Fisciano (SA)
4 Cemagref, UMR G-EAU, 361 rue JF Breton, F-34196 Montpellier Cedex 5
5 Istituto per le Applicazioni del Calcolo, Viale del Policlinico 137, 00161 Rome