http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6WGF-4Y34V5F-1-R&_cdi=6821&_user=2744299&_pii=S0019103509004837&_origin=gateway&_coverDate=06%2F30%2F2010&_sk=997929997&view=c&wchp=dGLbVzz-zSkWb&md5=2935f4080221648ba6c94fd60a51b117&ie=/sdarticle.pdf