1. Institute of Silicate Engineering, National Academy of Science, Pyongyang, Democratic People's Republic of Korea
2. Pyongyang Transportation University, Pyongyang, Democratic People's Republic of Korea
3. Faculty of Applied Chemical Engineering, Kim Chaek University of Technology, Pyongyang, Democratic People's Republic of Korea
4. Institute of Intelligent Information Technology, National Academy of Science, Pyongyang, Democratic People's Republic of Korea