A second family of coherent DNP experiments utilizes pulsed µw fields, and modulates the Rabi frequency and the pulse timing. In particular, integral multiples of the sum of these two frequencies, wm = 2p/tm (the modulation frequency) and weff (the effective field), matches an integral multiple of ω !" , and therefore results in polarization transfer. This approach, TOP-DNP, was first implemented with a train of pulses with constant phase and yields an oscillatory nuclear Zeeman polarization frequency profile. More recently, the approach was extended by implementing analogs of the TPPM and XiX H decoupling sequences and (with much higher power) as BEAM-DNP , all of which seek to "recouple" electrons to 1 H.