http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6VJV-4M7CDW0-1-1&_cdi=6104&_user=119223&_pii=S1386653206003465&_origin=&_coverDate=01%2F31%2F2007&_sk=999619998&view=c&wchp=dGLzVlz-zSkWb&md5=b6e69a579ed3190a0efc37991837ce15&ie=/sdarticle.pdf