Callejón-Ferre, Ángel-Jesús, CIMEDES Research Center (CeiA3), Department of Engineering, University of Almería, Ctra. Sacramento, s/n La Cañada, 04120 Almería, Spain. Tel.: +34-950-214-236, Fax.: +34-950-015-491, E-mail: acallejo@ual.es, Spain