http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6VPN-4FN746N-1-5&_cdi=6211&_user=119223&_pii=S1286457905000389&_origin=&_coverDate=03%2F31%2F2005&_sk=999929996&view=c&wchp=dGLbVzW-zSkWz&md5=e6c2a480adcb7a66d0fb8180467212b5&ie=/sdarticle.pdf