http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B82X6-4RWC57P-2-1&_cdi=33022&_user=119223&_pii=S1440244007002010&_origin=&_coverDate=01%2F31%2F2009&_sk=999879998&view=c&wchp=dGLzVlz-zSkzk&md5=3e0cb074f1e448cc2c283d21ac3f43a7&ie=/sdarticle.pdf