http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6T16-4G54CRT-1-3&_cdi=4882&_user=119223&_pii=S0167527305002603&_origin=search&_coverDate=11%2F02%2F2005&_sk=998949997&view=c&wchp=dGLbVtz-zSkzV&md5=e58116df3c07ce7bcce9004867b14445&ie=/sdarticle.pdf