1. Department of Electrical and Electronics Engineering, University of West Attica, Ancient Olive Grove Campus, GR-12241 Aigaleo, Greece
2. Department of Applied Mathematics and Physics, Graduate School of Informatics, Kyoto University, Sakyo, Kyoto 606-8501, Japan
3. Department of Physics, International Hellenic University, GR-65404 Kavala, Greece
4. Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing, National Observatory of Athens, Metaxa and Vasileos Pavlou, GR-15236 Penteli, Greece