Scientific Research and Essays 1992-2248 Academic Journals 10.5897/SRE2014.5875 Zhang Chunjian Luo Yuxi Liang Jiuxing Li Lala Li Jiang * E-mail: luoyuc@163.com 2014 15 06 2014 10 03 2014 29 04 2014 9 11 483 494 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/C86E88645219 The full text article is available as a PDF file from http://politicalwaffle.uk/journal/SRE/article-full-text-pdf/C86E88645219 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29