http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V3B-4B3JKK1-4&_user=10&_coverDate=05%2F31%2F2004&_alid=1623685309&_rdoc=1&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=5726&_st=5&_docanchor=&_ct=10&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=fc42ba133bd56...