http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6V05-4RGFCV3-2-1&_cdi=5637&_user=119223&_pii=S0165011407005672&_origin=&_coverDate=04%2F16%2F2008&_sk=998409991&view=c&wchp=dGLzVzb-zSkzS&md5=37c3d3a7255cf4b6889993574f3e61b9&ie=/sdarticle.pdf