1. Hubei Key Laboratory of Optical Information and Pattern RecognitionWuhan Institute of Technology Wuhan 430205 P. R. China
2. Beijing Computational Science Research Center Beijing 100193 P. R. China
3. Department of Gastrointestinal SurgeryXiangya HospitalCentral South University Changsha 410083 P. R. China
4. School of Mathematics and PhysicsChina University of Geosciences (Wuhan) Wuhan 430074 P. R. China