http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B94T0-4T2GVT8-2-1&_cdi=56452&_user=119223&_pii=S1441352305700358&_origin=&_coverDate=09%2F30%2F2005&_sk=999919997&view=c&wchp=dGLzVlz-zSkWz&md5=ff33d6e358fad78ee76ff9724e9cfea7&ie=/sdarticle.pdf