Reference:
1. http://www.jped.com.br/conteudo/06-82-S181/ing.pdf
2. http://www3.interscience.wiley.com/cgibin/fulltext/121645452/PDFSTART
3. http://www.mdconsult.com/das/article/body/149795883-2/jorg=journal&source=&sp=22286549&sid=0/N/704113/s0889856109000289.pdf?issn=08898561
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