XiaopingXu∗, ZhouZhou
School of Aeronautics, Northwestern Polytechnical University, Xi’an, 710072, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 11 May 2015
Received in revised form 29 July 2015
Accepted 30 July 2015
Available online 5 August 2015