Before revision: References doi: 10.1016/0038-1101(94)90231-3 doi: 10.1088/0268-1242/17/5/301 doi finder: External Links doi: 10.1088/0268-1242/17/5/3
After revision: References doi: 10.1016/0038-1101(94)90231-3 Lin01 doi finder: External doi: 10.1088/0268-1242/17/5/3