Funding for this research was provided by:
National Natural Science Foundation of China (No.61640210, No.61672447)
CERNET Next Generation Internet Technology Innovation Project (No. NGII20160305)
Science & Education Joint Project of Hunan Natural Science Foundation (No.2017JJ5036)
Upgrading Project of Industry-University- Research of Xiangtan University (No.11KZ|KZ03051)
Received: 18 October 2017
Accepted: 3 April 2018
First Online: 17 April 2018
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