[1] Department of Electronic Engineering and Physics,
[2] University of Paisley,undefined
[3] Paisley PA1 2BE,undefined
[4] UK,undefined
[5] Department of Physics,undefined
[6] University of Oslo,undefined
[7] N-0316 Oslo,undefined
[8] Norway,undefined
[9] Department of Physics,undefined
[10] University of Lund,undefined
[11] S-223 62 Lund,undefined
[12] Sweden,undefined
[13] Niels Bohr Institute,undefined
[14] University of Copenhagen,undefined
[15] Blegdamsvej 17,undefined
[16] DK-2100 Copenhagen Ø,undefined
[17] Denmark,undefined
[18] Schuster Laboratory,undefined
[19] University of Manchester,undefined
[20] Manchester M13 9PL,undefined
[21] UK,undefined