http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6VGN-4C2NKS5-1-7&_cdi=6043&_user=119223&_pii=S0969698904000153&_origin=&_coverDate=01%2F31%2F2005&_sk=999879998&view=c&wchp=dGLzVlz-zSkWB&md5=3704c51f2b1867a9762d28efef98dbb9&ie=/sdarticle.pdf