1. Faculty of Forestry Industry, University of Forestry, 10, Kl. Ohridsky Blvd., 1756 Sofia, Bulgaria
2. Faculty of Hydrotechnics, University of Architecture, Civil Engineering and Geodesy, 1, Hristo Smirnenski Blvd., 1046 Sofia, Bulgaria
3. Faculty of Physics, University of Sofia, Blvd. J. Bouchier 5, 1164 Sofia, Bulgaria