作者机构:School of Traffic and Transportation, Beijing Jiaotong University, Beijing 100044, China
相关基金:Project supported by the State Key Development Program for Basic Research of China (Grant No 2006CB705500), the National Natural Science Foundation of China (Grant Nos 70631001, 70501004 and 70701004), and Program for New Century Excellent Talents in University (Grant No CET-07-0057).