1. Faculty of Mechanical Engineering, Wroclaw University of Science and Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland
2. Department of Technical Engineering, Technical University of Varna, Studentska 1, 9010 Varna, Bulgaria
3. Proeko Foundation, Dworcowa 11a/7, 50-456 Wroclaw, Poland