http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B82X6-4RCW5C8-5-1&_cdi=33022&_user=119223&_pii=S1440244007002575&_origin=&_coverDate=03%2F31%2F2009&_sk=999879997&view=c&wchp=dGLbVlW-zSkWW&md5=bfa84ff14a84380ff84f4d16564c2706&ie=/sdarticle.pdf