http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6WWS-4C6KS8N-1-5&_cdi=7138&_user=119223&_pii=S0954611104000423&_origin=search&_coverDate=08%2F31%2F2004&_sk=999019991&view=c&wchp=dGLzVtz-zSkWb&md5=8c19092ff8b18b4a161eb72787ff9e2c&ie=/sdarticle.pdf