http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6TJ4-4MNYJS6-3-1&_cdi=5300&_user=119223&_pii=S0960077906010320&_origin=&_coverDate=10%2F31%2F2008&_sk=999619998&view=c&wchp=dGLzVlb-zSkzS&md5=94dd243d08cfc998b41bedeebb60b5ca&ie=/sdarticle.pdf