1. School of Information and Computer; Hefei University of Technology; No. 193 Tunxi Road Hefei Anhui 230009 China
2. School of Physics and Electronic Engineering; Anqing Normal University; No. 128 Linghunan Road Anqing 246011 China
3. Institute of Technology and Science; The University of Tokushima; 2-1 Minamijyosanjima-cho Tokushima 770-8506 Japan