http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6TYH-4GSTS2Y-3-C&_cdi=5619&_user=119223&_pii=S0377042705004206&_origin=&_coverDate=09%2F01%2F2006&_sk=998069997&view=c&wchp=dGLzVzb-zSkWb&md5=6976dd31eb30b33ba2ee7921deb3e4d2&ie=/sdarticle.pdf