Sustained masers -the "cross-talk" situation We also performed numerical studies of model (A), which was introduced to mimics the magnetization dynamics of the 1 H nuclear spins in the presence of a 2 H reservoir. The presence of this additional nuclear spin reservoir allows for the repolarization of the former, both with and without µw irradiation, by an indirect "cross-talk" mechanism through the electron non Zeemann reservoir. In this case, only the 1 H spins are coupled to the detection circuit of the spectrometer, to which they lose energy, whereas the likewise hyperpolarized 2 H only exchange energy with other spins. As detailed in ref. and explained above, this process leads to partial repolarization, i.e., re-cooling, from deuterium spins, together with a loss of polarization, therefore heating, of the 1 H nuclei. Thus, model (A) introduces a simplified description of this process, where the z magnetization m z (r, t) tends to the value m th 0z (r, t) that corresponds to the deuterium spin temperature, whilst deuterium spins itself relaxe to thermal equilibrium, in the absence of µw irradiation (see Eqs. 5 and 6). In our simulations, the equilibrium magnetization m st o was set to m st o = -0.05 × m mw oz , where m mw oz represents the 1 H stationary (negative) magnetization upon microwave irradiation, and the initial state of the magnetization. Figure shows simulations performed on an disk-shaped model sample. The model parameters were assigned the following values m o = 200 A/m, γ 2 = 650 Hz, γ rd = 2 kHz, so that γ rd /γ 2 = 3.1 and ω dip /γ rd = 22.22. In this model, the rates of return to the lattice temperature of the 2 H reservoir is set to γ st = 0.030 Hz and the 1 H/ 2 H equilibration rate of spin temperatures is γ n,ee = 20 Hz (see Eq; 6. During the early stage of the dynamics, the in-plane magnetization envelope exhibits a succession of a few (∼ 7 -8) maser bursts of decaying intensities with time, until it reaches a long-term evolution of monotonous decay. Due to the presence of the dipolar field the asymmetry and the "bursts within burst" profiles are also reproduced. At longer evolution times the amplitude of the in-plane magnetization decays monotonously, whereas the z component of the magnetization returns to its thermal equilibrium value, in the absence of µw irradiation, with the γ st time constant. These simulations thus reproduce satisfactorily the basic features of the experimental observations described in Reference , i.e., asymmetric masers at short times and long lasting monotonous decay at long times.