http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6V8X-4TK2P6N-2-1&_cdi=5882&_user=119223&_pii=S016885100800198X&_origin=&_coverDate=04%2F30%2F2009&_sk=999099998&view=c&wchp=dGLzVlb-zSkzk&md5=cc731ba84e11c82d2732c92526306366&ie=/sdarticle.pdf