Author(s):
1. Katarina Maksimović, Serbia
2. Dragi Stamenković, Termoelektro Belgrade, Serbia
3. Slobodanka Boljanović, High School of Mechanical Engineering, Belgrade, Serbia
4. Mirko Maksimović, Waterworks and Sewerage, Serbia
5. Ivana Vasović, Institut Goša, Milana Rakića 35, Beograd, Serbia