http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6T0G-4FF9HF7-7-B&_cdi=4862&_user=119223&_pii=S0304394005000996&_origin=search&_coverDate=06%2F03%2F2005&_sk=996199996&view=c&wchp=dGLbVtb-zSkWb&md5=efd2dd08fc89769fe2b94db165bcd5b7&ie=/sdarticle.pdf