http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6T5H-4BT7D7P-1-V&_cdi=5003&_user=119223&_pii=S0147957104000074&_origin=search&_coverDate=11%2F30%2F2004&_sk=999729993&view=c&wchp=dGLbVzz-zSkWb&md5=013e5d52e7903bc584dfd0080771043b&ie=/sdarticle.pdf