Institution: | 1Department of Physics, Science Laboratories, South Road, Durham DH1 3LE,; 2Department of Physics, Drexel University, 3141 Chestnut Street, Philadelphia, PA 19104, USA,; 3Anglo-Australian Observatory, PO Box 296, Epping, NSW 2121, Australia and; 4Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD |