http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6VN5-4T5JP9V-1-5&_cdi=6169&_user=119223&_pii=S0765159708001068&_origin=browse&_coverDate=04%2F30%2F2009&_sk=999759997&view=c&wchp=dGLzVlz-zSkzV&md5=dec3d070718f9585db32291cba35233e&ie=/sdarticle.pdf