First Author:   José Atilano Pena López University of A Coruña atilano@udc.es   A Coruña, 15071, Spain   34981167000, ext.- 2422(Phone) 34981167000, ext.- 2422(Fax) Second Author: José Manuel Sánchez Santos University of A Coruña santos67@udc.es   A Coruña, 170071, Spain