...Hirano,

T. Hirano is with the Institute of Physics, The University of Tokyo, Komaba, Tokyo 153, Japan. E-mail:hirano@phys3.c.u-tokyo.ac.jp .

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...Kuga

T. Kuga is with the Institute of Physics, The University of Tokyo, Komaba, Tokyo 153, Japan. E-mail:kuga@Asone.c.u-tokyo.ac.jp .

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