JOURNAL OF THE KOREAN PHYSICAL SOCIETY, vol. 31, no. 3, page. 384 - 388, 1997-09
JOURNAL OF THE KOREAN PHYSICAL SOCIETY, vol. 31, no. 1, page. 19 - 22, 1997-07
CZECHOSLOVAK JOURNAL OF PHYSICS, vol. 46, page. 1709 - 1710, 1996-01