Grouping in the stock markets of Japan and Korea
  We investigated the temporally evolving network structures of the Japanese and Korean stock markets through the minimum spanning trees composed of listed stocks. We tested the validity of conventional grouping by industrial categories, and found a common trend of decrease for Japan and Korea. This phenomenon supports the increasing external effects on the markets due to the globalization of both countries. At last the Korean market are grouped with the MSCI Korea Index, a good reference for foreigners' trading, in the early 2000s \cite{Jung2006}. In the Japanese market, this tendency is strengthened more and more by burst of the bubble in 1990's. 
Woo-Sung Jung, Okyu Kwon, Taisei Kaizoji, Seungbyung Chae, Hie-Tae   Moon