PT Journal AU Yu, B Zeng, F Yang, Y Xing, Q Chechin, A Xin, X Zeylikovich, I Alfano R. R. TI Torsional vibrational modes of tryptophan studied by terahertz time-domain spectroscopy SO Biophys. J. PY 2004 BP 1649 EP 1654 VL 86 IS 3 DE THz applications ER