1. Inst. of Logistics, Faculty of Mining, Ecology, Process Control and Geotechnology, Technical Univ. of Košice, Park Komenského 14, 043 84 Košice, Slovakia (Corresponding author), e-mail: lubomir.ambrisko@tuke.sk
2. Dept. of Materials Science, Faculty of Metallurgy, Technical Univ. of Košice, Letná 9, 042 00, Košice, Slovakia