http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6T9G-3YS8BV0-11-1&_cdi=5114&_user=6763742&_pii=0309174094000286&_orig=search&_coverDate=12%2F31%2F1995&_sk=999599998&view=c&wchp=dGLbVtz-zSkzS&md5=1eefe48a979d92a851ccccaa907e2c2b&ie=/sdarticle.pdf