http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6V7S-4D3WJKD-1-1&_cdi=5850&_user=119223&_pii=S0148296304001079&_origin=search&_coverDate=10%2F31%2F2005&_sk=999419989&view=c&wchp=dGLzVzz-zSkzV&md5=dfcd46fb967a87eb488cfa98e4c2ad0b&ie=/sdarticle.pdf