http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6W7S-4KPFKNS-2-1&_cdi=6634&_user=119223&_pii=S1468121806000848&_origin=&_coverDate=09%2F30%2F2007&_sk=999919995&view=c&wchp=dGLbVzz-zSkWz&md5=b99cb1e0161c995f6313880ce30764a8&ie=/sdarticle.pdf