http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6TYH-4KTVP0D-2-59&_cdi=5619&_user=119223&_pii=S0377042706004742&_origin=&_coverDate=09%2F01%2F2007&_sk=997939998&view=c&wchp=dGLbVlz-zSkWA&md5=f8777e6ca2f24392a771011fe9434597&ie=/sdarticle.pdf