Internal structure of a 1.5 M_⊙ stellar model in the main sequence. The hydrogen abundance profile X (black solid line), the adiabatic gradient ∇_ad (red dotted line), the radiative gradient ∇_rad (green dash-dotted line), and the Ledoux gradient ∇_L (blue dashed line) are plotted as functions of the mass fraction. From left to right, tones of gray fill regions of different energy transport processes: convective zone, semiconvective zone, and radiative zone.