1. Department of Physics, National Dong Hwa University, 1, Sec 2, Da-Hsueh Rd., Shou-Feng, Hualien 974, Taiwan, R.O.C.
2. Department of Civil Engineering, National Chi-Nan University, Taiwan, R.O.C.
3. Department of Physics, National Taiwan University, Taipei 106, Taiwan, R.O.C.
4. Institute of Physics, Academia Sinica, Taipei 115, Taiwan, R.O.C.