Coherent Averaging: an Alternative to the Average Hamiltonian Theory
  Line-narrowing by periodic modulation of nuclear spin interaction Hamiltonians is the central element of various experimental techniques in NMR spectroscopy. In this study, we present a theoretical formulation of coherent averaging to calculate the heights of narrowed spectral peaks. This concept is experimentally demonstrated using proton spectra of solids obtained under fast magic-angle spinning. 
A. K. Khitrin, Jiadi Xu, Ayyalusamy Ramamoorthy
cond-mat.stat-mech