http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6WK2-4G1GFPP-5-1&_cdi=6894&_user=119223&_pii=S0022247X05002647&_origin=&_coverDate=02%2F01%2F2006&_sk=996859998&view=c&wchp=dGLzVzb-zSkWb&md5=f2bf2f0e6fb437171fbeb4949811c637&ie=/sdarticle.pdf