1. Research Center for Astronomy and Applied Mathematics, Academy of Athens, Athens 11527, Greece
2. Department of Physics, University of Cincinnati, OH 45269, USA
3. Department of Mechanical Engineering, Technological Educational Institute of Central Macedonia, Serres 62124, Greece
4. Department of Physics, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece
5. Department of Physics, University of Florida, FL 32611-8440, USA