1. Department of Mechanical Engineering, Pyongyang University of Mechanical Engineering, Pyongyang 999093, Democratic People’s Republic of Korea
2. Department of Resource Development Machinery Engineering, Pyongyang University of Mechanical Engineering, Pyongyang 999093, Democratic People’s Republic of Korea
3. Institute of Nano-Physical Engineering, Kim Chaek University of Technology, Pyongyang 950003, Democratic People’s Republic of Korea
4. Technology College of Ship and Ocean Technology, Kim Chaek University of Technology, Pyongyang 950003, Democratic People’s Republic of Korea