First Author:   Marina Nunez University of Barcelona mnunez@ub.edu   Barcelona, E-08034, Spain   (34)934021991(Phone) (34)934021991(Fax) Second Author: Francesc Llerena Universitat Rovira i Virgili francisco.llerena@urv.net   Av. de la Universitat, 1 Reus, E-43204, Spain