http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6VBD-4G1WYBW-1-1&_cdi=5924&_user=119223&_pii=S0277539505000063&_origin=&_coverDate=02%2F28%2F2005&_sk=999719998&view=c&wchp=dGLzVlb-zSkzS&md5=ea300759c73cf8b8c7a85e2edee93eba&ie=/sdarticle.pdf