1. Institute
of Biophysics and Department of Physics, Central China Normal University, Wuhan 430079, P. R. China
2. Key
Laboratory of Magnetic Resonance in Biological Systems, State Key
Laboratory of Magnetic Resonance and Atomic and Molecular Physics,
Wuhan Centre for Magnetic Resonance, Wuhan Institute of Physics and
Mathematics, Chinese Academy of Sciences, Wuhan 430071, P. R. China