Simulations of the transfer efficiencies between 15N and 13C with various 15N-13C heteronuclear dipolar couplings. A. Conventional 15N/13C CP transfer. B. 15N/13C CP transfer with 1H-irradiation at 59 kHz (solid line) and 43 kHz (dashed line). C. Logarithmic plot of enhancement by 1H-irradiation. D. Mismatched profile of 1H-irradiation. A. - C. the 15N-13Cα dipolar couplings were simulated for 0 (red), 100 (blue), 300 (green), 1000 (black) Hz with all other parameters kept the same. The buildup curves were sampled every 500 ms, and the lines connecting the data points show the trends. D. The simulation was done when 15N-13Cα dipolar coupling equal to zero, and the strength of 1H-irradiation was varied from 0 kHz to 100 kHz.