1. Associate Professor, Dept. of Mechanics of Materials, Kim Chaek Univ. of Technology, Pyongyang, Democratic People’s Republic of Korea (corresponding author).
2. Associate Professor, Laboratory of Power-Driven Machine, Kim Chaek Univ. of Technology, Pyongyang, Democratic People’s Republic of Korea.
3. Professor, Dept. of Scientific Research, Kim Chaek Univ. of Technology, Pyongyang, Democratic People’s Republic of Korea.