http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6V2W-4VFBYDP-3-H&_cdi=5713&_user=119223&_pii=S0301421508007453&_origin=&_coverDate=04%2F30%2F2009&_sk=999629995&view=c&wchp=dGLzVzb-zSkzV&md5=8596731ec97884449d011d645d5a9ddf&ie=/sdarticle.pdf