http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6WK2-4H2PJYD-2-K&_cdi=6894&_user=119223&_pii=S0022247X05007754&_origin=&_coverDate=01%2F15%2F2006&_sk=996869997&view=c&wchp=dGLbVlW-zSkzk&md5=c62420a5bc02696ea4f6c5ce72b6eecf&ie=/sdarticle.pdf