http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WKM-529C3JS-1&_user=1067472&_coverDate=03%2F03%2F2011&_rdoc=1&_fmt=high&_orig=gateway&_origin=gateway&_sort=d&_docanchor=&view=c&_acct=C000051251&_version=1&_urlVersion=0&_userid=1067472&md5=5f342f65a05cd4a51f1e69d4bd0d32b5&searchtype=a