1. Department of Engineering, Reykjavik University, Menntavegur, 1, IS-102 Reykjavik, Iceland
2. Department of Theoretical Physics, Faculty of Fundamental Problems of Technology, Wroclaw University of Science and Technology, Wybrzeże Wyspiańskiego 27, 50-370 Wroclaw, Poland
3. Science Institute, University of Iceland, Dunhaga 3, IS-107 Reykjavik, Iceland