Rail package:nlme R Documentation _E_v_a_l_u_a_t_i_o_n _o_f _S_t_r_e_s_s _i_n _R_a_i_l_w_a_y _R_a_i_l_s _D_e_s_c_r_i_p_t_i_o_n: The 'Rail' data frame has 18 rows and 2 columns. _F_o_r_m_a_t: This data frame contains the following columns: _R_a_i_l an ordered factor identifying the rail on which the measurement was made. _t_r_a_v_e_l a numeric vector giving the travel time for ultrasonic head-waves in the rail (nanoseconds). The value given is the original travel time minus 36,100 nanoseconds. _D_e_t_a_i_l_s: Devore (2000, Example 10.10, p. 427) cites data from an article in _Materials Evaluation_ on ``a study of travel time for a certain type of wave that results from longitudinal stress of rails used for railroad track.'' _S_o_u_r_c_e: Pinheiro, J. C. and Bates, D. M. (2000), _Mixed-Effects Models in S and S-PLUS_, Springer, New York. (Appendix A.26) Devore, J. L. (2000), _Probability and Statistics for Engineering and the Sciences (5th ed)_, Duxbury, Boston, MA.