c1 Refereed Journal Article. Not checked in Sherpa, 03/11/11 RD. Green in Sherpa, author can archive pre-print (ie pre-refereeing), author can archive post-print (ie final draft post-refereeing), email sent to Stephen 15.11.11-MMM. revd, now waiting for signed permission  16.11.11-MMM. revd 17.11.11-MMM. Added from duplicate record: ResPubID23289 and Stephen Gray signed VUIR permission pt.13/6/12, 29.8.12-MMM. Supporting documentation added to dark upload - HD 13/11/17. HERDC documentation added to dark upload - HD 27/7/20