link

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WPB-4VT17SN-2&_user=10&_coverDate=05%2F31%2F2009&_alid=1750305892&_rdoc=2&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=6986&_sort=r&_st=13&_docanchor=&view=c&_ct=3755&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=3193de7be8cf2ca7346d706f4ace2021&searchtype=a

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WPB-4Y1WK3S-1&_user=10&_coverDate=02%2F28%2F2010&_alid=1750305892&_rdoc=11&_fmt=high&_orig=search&_origin=search&_zone=rslt_list_item&_cdi=6986&_sort=r&_st=13&_docanchor=&view=c&_ct=3755&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=32439e618a19a146c861c9efa49ee8ca&searchtype=a