http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6V0C-4C6KKCV-1-3J&_cdi=5643&_user=119223&_pii=S0020025504001124&_origin=search&_coverDate=12%2F03%2F2004&_sk=998319998&view=c&wchp=dGLbVlW-zSkzV&md5=178a6d562cee85c6f96addc500568a70&ie=/sdarticle.pd