1. Faculty of Energy Science, Kim Il Sung University 1 , Pyongyang 999093, Democratic People’s Republic of Korea
2. School of Water Resources and Environment and Research Center of Environmental Science and Engineering, China University of Geosciences 2 , Beijing 100083, People’s Republic of China
3. Faculty of Physics, Kim Il Sung University 3 , Pyongyang 999093, Democratic People’s Republic of Korea