First Author:   Anastasios V. Katos University of Macedonia, Greece katos@uom.gr   University of Macedonia, 156 Egnatia Street Thessaloniki, 540 06, Greece   00302310891885(Phone) 00302310891885(Fax) www.uom.gr Second Author: Eleni F. Katsouli University of Macedonia, Greece katsouli@uom.gr   156 Egnatia Street, 156 Egnatia Street Thessaloniki, 540 06, Greece   00302310819883(Phone) 00302310819921(Fax) www.uom.gr