1. Department of Materials Science and Engineering; University of Ioannina; Ioannina 45110 Greece
2. Institute of Computational Science; Università della Svizzera italiana; Lugano CH-6904 Switzerland
3. Department of Informatics and Computer Technology; Technological Education Institute of Western Macedonia; Kastoria 52100 Greece
4. Department of Mathematics, School of Applied Mathematics & Physical Sciences; National Technical University of Athens; Athens 15780 Greece