http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6VJV-4FJ5XR2-2-1&_cdi=6104&_user=119223&_pii=S1386653205000363&_origin=&_coverDate=09%2F30%2F2005&_sk=999659998&view=c&wchp=dGLbVzz-zSkWA&md5=b05f11e7d97869f50a1ca2b8463f868e&ie=/sdarticle.pdf