http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6WKB-4VWB1FB-1-C&_cdi=6902&_user=74021&_orig=search&_coverDate=09%2F30%2F2009&_sk=999679994&view=c&wchp=dGLbVlW-zSkzk&md5=a04161d945ae58c82653c4838d09229f&ie=/sdarticle.pdf