http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6TGK-4CYWNBG-2-S&_cdi=5257&_user=119223&_pii=S037673880400403X&_origin=search&_coverDate=10%2F01%2F2004&_sk=997589997&view=c&wchp=dGLbVzz-zSkzk&md5=d3e056097172ea5d1e93ac13b4124f23&ie=/sdarticle.pdf