NASA:10.1562/0031-8655(1999)069<0203:TEOURA>2.3.CO;2
NASA:10.1562/0031-8655(2001)074<0570:EOAFST>2.0.CO;2
NASA:10.1562/2004-07-06-RA-224.1
NASA:10.1562/2005-04-25-RA-498