http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6VCT-4TCR1PN-5-C&_cdi=5963&_user=119223&_pii=S0377221708007364&_origin=&_coverDate=10%2F01%2F2009&_sk=998019998&view=c&wchp=dGLbVzW-zSkzk&md5=f4d6a899085cf42639deb76e6ca607e6&ie=/sdarticle.pdf