http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6V0R-4PNF2Y2-1-1&_cdi=5653&_user=119223&_pii=S002437950700331X&_origin=search&_coverDate=12%2F01%2F2007&_sk=995729997&view=c&wchp=dGLbVzW-zSkWB&md5=cd820e800d13e1c818b4d277b4d4e70a&ie=/sdarticle.pdf