http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VHT-5119S77-4&_user=1067472&_coverDate=10%2F31%2F2010&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d&_docanchor=&view=c&_acct=C000051251&_version=1&_urlVersion=0&_userid=1067472&md5=571d5fa1b47bb32814c18b0e7e73d611&searchtype=a