Manolis K Georgoulis, Academy of Athens, Athens, Greece; Georgia State University, Department of Physics and Astronomy, Atlanta, United States, Spiros Patsourakos, University of Ioannina, Department of Physics, Ioannina, Greece and Evangelia Samara, Observatoire Royal de Belgique, Brussel, Belgium; KU Leuven, Centre for mathematical Plasma-Astrophysics, Leuven, Belgium