1. a ETSECCPB, FLUMEN Research Group, DEHMA , Technical University of Catalonia , Jordi Girona 1-3, 08034 , Barcelona , Spain E-mail:
2. b ETSECCPB, FLUMEN Research group, DEHMA , Technical University of Catalonia , Jordi Girona 1-3, 08034 , Barcelona , Spain
3. c ETSECCPB, Department of Applied Mathematics III , Technical University of Catalonia , Jordi Girona 1-3, 08034 , Barcelona , Spain E-mail: