http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T0P-51H1DNF-1&_user=10&_coverDate=03%2F01%2F2011&_rdoc=2&_fmt=high&_orig=browse&_origin=browse&_zone=rslt_list_item&_srch=doc-info%28%23toc%234868%232011%23998979996%232788775%23FLA%23display%23Volume%29&_cdi=4868&_sort=d&_docanchor=&_ct=28&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=714b7b0d296f46501c3798933313a0e7&searchtype=a