http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6TY8-4V17CJY-3-3&_cdi=5612&_user=119223&_pii=S0096300308008709&_origin=&_coverDate=02%2F01%2F2009&_sk=997919998&view=c&wchp=dGLzVlz-zSkWW&md5=fd70828a1543651ef3f0e724d050aa8c&ie=/sdarticle.pdf