http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T24-42696KF-1&_user=1760270&_coverDate=04%2F30%2F2001&_rdoc=1&_fmt=high&_orig=browse&_srch=doc-info(%23toc%234908%232001%23999209998%23225229%23FLA%23display%23Volume)&_cdi=4908&_sort=d&_docanchor=&_ct=8&_acct=C000037419&_version=1&_urlVersion=0&_userid=1760270&md5=d4ed25378af3ff6b7e35e339be98da2e