http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WJS-521N80B-1&_user=125795&_coverDate=03%2F31%2F2011&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d&_docanchor=&view=c&_searchStrId=1641168037&_rerunOrigin=scholar.google&_acct=C000010182&_version=1&_urlVersion=0&_userid=125795&md5=212f28702472ebc07f4493fd61056ec5&searchtype=a