1. Department of Applied Mechanics, Faculty of Metallurgy and Materials Sciences, University of Chemical Technology and Metallurgy, 8 Kliment Ohridski Blvd., 1756 Sofia, Bulgaria
2. Department of Agrarian Technology, Institute of Engineering and Technology, Korkyt Ata Kyzylorda University, 29A Aiteke Blvd., Kyzylorda, Kazakhstan