External url http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235139%232008%23999269997%23699030%23FLA%23&_cdi=5139&_pubType=J&_auth=y&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=b3f2ba3b4c5ce2eb0228d493132f37dd Cover photo 55674-file.image.jpg
