1. Department of Applied Mathematics and Informatics, Faculty of Mechanical Engineering, Technical University Košice, Letná 1, 042 00 Košice, Slovakia
2. Institute of Physics, Faculty of Sciences, P.J. Šafárik University, Park Angelinum 9, 041 54 Košice, Slovakia
3. Institute of Materials Research, Slovak Academy of Sciences, Watsonova 47, 040 01 Košice, Slovak Republic