[1] Dept. of Pure and Applied Physics, Queen's University of Belfast, Belfast BT7 1NN, United Kingdom
[2] University of California, Lawrence Livermore Natl. Laboratory, Livermore, CA 94551, United States
[3] Department of Physics, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
[4] Department of Physics, University of Kentucky, Lexington, KY 40506, United States
[5] Department of Applied Mathematics, Queen's University of Belfast, Belfast BT7 1NN, United Kingdom
[6] Vilnius University, Res. Inst. of Theor. Phys./Astron., A. Goštauto 12, 01108 Vilnius, Lithuania