1. School of Life and Environmental Sciences, Guilin University of Electronic Technology, Guilin 541004, P. R. China, http://rsc.guet.edu.cn/RSC/public/show.aspx?par2=0014&par=864
2. Department of Physical and Environmental Sciences, University of Toronto Scarborough, Toronto, Ontario M1C 1A4, Canada, http://www.utsc.utoronto.ca/~bkraatz/