Affiliation: | a Department of Electrical Engineering, Polytechnic School, Aristotle University of Thessaloniki, GR 54124 Thessaloniki, Greece b Division of Mathematics, Polytechnic School, Aristotle University of Thessaloniki, GR 54124 Thessaloniki, Greece c Department of Computer Science, University of Ioannina, P.O. Box 1186, GR 45110 Ioannina, Greece |