[1] PlasmaPotential Phys Consulting & Res, Canberra, ACT 2601, Australia
[2] Ruhr Univ Bochum, Dept Elect Engn & Informat Sci, D-44780 Bochum, Germany
[3] West Virginia Univ, Dept Phys, Morgantown, WV 26506 USA
[4] Hungarian Acad Sci, Wigner Res Ctr Phys, Inst Solid State Phys & Opt, Konkoly Thege Miklos Str 29-33, H-1121 Budapest, Hungary