1. Chief Assistant Professor and Engineer, College of Energy and Electronics, Technical Univ. of Sofia, 8 Kl. Ohridsky Blvd., Sofia 1000, Bulgaria. ORCID: .
2. Associate Professor and Engineer, Dept. of Thermal and Nuclear Power Engineering, Technical Univ. of Sofia, 8 Kl. Ohridsky Blvd., Sofia 1000, Bulgaria (corresponding author). ORCID: .
3. Research Fellow, Institute of Geotechnics, Slovak Academy of Sciences, Kosice, Watsonova 45, Kosice SK-043 53, Slovak Republic.
4. Scientific Secretary, Head of Department of Physical and Physico-chemical Methods of Mineral Processing, and Senior Researcher, Institute of Geotechnics, Slovak Academy of Sciences, Kosice, Watsonova 45, Kosice SK-043 53, Slovak Republic. ORCID: .