http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6TJ4-4KSSW7T-7-2K&_cdi=5300&_user=119223&_pii=S0960077906006886&_origin=&_coverDate=04%2F30%2F2007&_sk=999679997&view=c&wchp=dGLbVlW-zSkWW&md5=1e1683a0483c763da9fd3773f71e41d9&ie=/sdarticle.pdf