Antonio Chella1, Arianna Pipitone2. 1. University of Palermo, Department of Engineering, Viale delle Scienze, Building 6, 90128 Palermo, Italy; ICAR-CNR, Via Ugo La Malfa 153, 90146 Palermo, Italy. Electronic address: antonio.chella@unipa.it. 2. University of Palermo, Department of Engineering, Viale delle Scienze, Building 6, 90128 Palermo, Italy. Electronic address: arianna.pipitone@unipa.it.