http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6T0K-52BF9M5-3-1&_cdi=4865&_user=142623&_pii=S0304395911001060&_origin=gateway&_coverDate=05%2F31%2F2011&_sk=998479994&view=c&wchp=dGLzVzz-zSkzV&md5=ef3b4af5022db7bf1eb3c3adaefc15b6&ie=/sdarticle.pdf