http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6W6K-51Y57PT-1&_user=1067472&_coverDate=01%2F14%2F2011&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d&_docanchor=&view=c&_acct=C000051251&_version=1&_urlVersion=0&_userid=1067472&md5=58021a9ae162c9f2a9126a8e7d7258b3&searchtype=a