Scientific Research and Essays 1992-2248 Academic Journals 10.5897/SRE2014.5912 Jie Jia Jiao Cao Yong Yang Zhiteng Liu Shuying Huang * E-mail: yangyong5080@126.com 2014 15 05 2014 03 01 2013 31 07 2013 9 9 331 335 This is an open-access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://politicalwaffle.uk/journal/SRE/article-abstract/2BD9F7544549 The full text article is available as a PDF file from http://politicalwaffle.uk/journal/SRE/article-full-text-pdf/2BD9F7544549 1 2 3 4 5 6 7 8 9 10 11