1. College of Mathematics and Statistics, Chongqing University, Chongqing, 401331; and Engineering Research Center of Industrial Computed Tomography Nondestructive Testing of the Education Ministry of China, Chongqing University, Chongqing 400044, P. R. China
2. Engineering Research Center of Industrial Computed Tomography Nondestructive Testing of the Education Ministry of China, Chongqing University, Chongqing400044, P. R. China