Additional physical parameters during the evolution of various 15 M_⊙ models. Left panel: Evolution of the convective core mass during the MS phase as a function of central mass of hydrogen. Center panel: Abundance ratio of nitrogen and hydrogen at the surface normalized to their initial values vs. the surface gravity. Right panel: Profile of the helium mass fraction against the mass coordinate when the central helium fraction Y_c is 0.90. The letters C to F correspond to the models with different prescriptions as described in Table 1.