Mixing coefficients and their impact in 15 M_⊙ models. Left panel: internal profiles of K, the thermal diffusivity, D_conv, the convective diffusion coefficient, D_shear, the shear diffusion coefficient, D_h, the horizontal turbulence coefficient, and D_eff, the effective diffusivity in the 15 M_⊙ C^* model with internal magnetic fields at solar metallicity. The quantities are plotted when the central mass fraction of hydrogen X_c = 0.35. Middle panel: variation in the H-mass fraction vs. the Lagrangian mass coordinate. Right panel: variation in the angular velocity vs. mass in 15 M_⊙ for the C^* and C models at the end of H burning.