http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6WK2-4WH2M7W-8-1&_cdi=6894&_user=119223&_pii=S0022247X09004995&_origin=&_coverDate=11%2F15%2F2009&_sk=996409997&view=c&wchp=dGLzVzz-zSkzS&md5=ad197e29ec04cddec358d53daf6f9283&ie=/sdarticle.pdf