1. Lamont-Doherty Earth Observatory of Columbia University; Palisades New York 10964 USA
2. Daresbury Laboratory; CLRC; Warrington WA4 4AD UK
3. Advanced Light Source, LBNL; MS 80-101, 1 Cyclotron Road, Berkeley California 94720 USA
4. Department of Crystallography, Birkbeck College; University of London; Malet Street, Bloomsbury, London WCIE 7HX UK
5. Department of Geography and Environmental Engineering; United States Military Academy; West Point New York 10996 USA