Diffusion coefficients and angular velocity versus mass for a 12 M_⊙ star with υ_ini/υ_crit = 0.4 at the start of hydrogen burning a) when central hydrogen mass fraction is 0.48 b) and 5 × 10^-3c). The area below the convective diffusion coefficient D_conv is grey shaded to depict the convective core. The diffusion coefficient describing meridional circulation D_eff is plotted with two different lines to distinguish between U(r) < 0 (green dotted line) and U(r) > 0 (green dashed line), i.e. the zones transporting angular momentum outwards and inwards respectively.