Computation Center, Wuhan University, Wuhan, China 430072;Faculty of Computer Science, China University of Geosciences, Wuhan, Hubei, P.R. China 430074;School of Computer Science, China University of Geosciences, Wu-Han, 430074, China Research Center for Space Science and Technology, China University of Geosciences, Wu-Han, China 430074;The University of Aizu, Aizu-Wakamatsu City Fukushima, Japan 965-8580