This work was financially supported by theNational Natural Science Foundation of China (No. 21207112), the Natural Science Foundation of Hebei Province (Nos. B2012203060 and B2013203108),the Science Foundation for the Excellent Youth Scholars from Universities and Colleges of Hebei Province (Nos. Y2011113 and YQ2013026), and the Support Program for the TopYoung Talents of Hebei Province.
This work was financially supported by the National Natural Science Foundation of China (grant Nos. 21473153 and 21207112), the Natural Science Foundation of Hebei Province (grant No. B2013203108), the Science Foundation for the Excellent Youth Scholars from Universities and Colleges of Hebei Province (grant No. YQ2013026), and the Support Program for the Top Young Talents of Hebei Province.