http://www.ftb.hr/files/journals/1/articles/619/public/619-611-1-PB.pdf
http://www.academicjournals.org/AJMR/PDF/pdf2013/26Feb/Zhang%20et%20al.pdf
www.doaj.org/doaj?func=fulltext&aId=1898915
www.scirp.org/journal/PaperDownload.aspx?DOI=10.4236/as.2013.45B025...