http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6W8B-4MV0MB9-3-1&_cdi=6650&_user=119223&_pii=S1567134807000056&_origin=&_coverDate=07%2F31%2F2007&_sk=999929995&view=c&wchp=dGLzVzb-zSkWA&md5=caba260e82f69e68d5dc8acde9cc8975&ie=/sdarticle.pdf