leads to longer nuclear relaxation times and this may partially compensate for the line broadening reduction. In practice, in a glassy sample, the probability of having two dipolarly coupled electrons separated by the Larmor frequency is very scarce. Nonetheless, this mechanism is so efficient that it can be experimentally observed alone or in addition to the Solid-Effect. Magic Angle Spinning case As in the static case, the MAS-DNP mechanism of Cross effect is deeply modified due to the time dependent energy level. By taking a simple three spin system, it has been demonstrated that the Cross-Effect mechanism is different in the Static and MAS case. The Cross Effect is the result of very fast multi-step process involving EPR single quantum transition, electron dipolar anti-crossing and Cross Effect degeneracy conditions. In the most simple case the MAS-DNP mechanism can be explained by the combination of a single quantum transition followed by the Cross-Effect degeneracy condition, or by the electron-dipolar anti-crossing followed by the Cross-Effect degeneracy condition. This in turn change dramatically the CE dependence over the static magnetic field which doesn't scale like B0−1 and makes it much more efficient than the solid effect. Thermal mixing Thermal mixing is an energy exchange phenomenon between the electron spin ensemble and the nuclear spin, which can be thought of as using multiple electron spins to provide hyper-nuclear polarization. Note that the electron spin ensemble acts as a whole because of stronger inter-electron interactions. The strong interactions lead to a homogeneously broadened EPR lineshape of the involved paramagnetic species. The linewidth is optimized for polarization transfer from electrons to nuclei, when it is close to the nuclear Larmor frequency. The optimization is related to an embedded three-spin (electron-electron-nucleus) process that mutually flips the coupled three spins under the energy conservation (mainly) of the Zeeman interactions. Due to the inhomogeneous component of the associated EPR lineshape, the DNP enhancement by this mechanism also scales as B0−1. DNP-NMR Enhancement Curves Many types of solid materials can exhibit more than one mechanism for DNP. Some examples are carbonaceous materials such bituminous coal and charcoal (wood or cellulose heated at high temperatures above their decomposition point which leaves a residual solid char). To separate out the mechanisms of DNP and to characterize the electron-nuclear interactions occurring in such solids a DNP enhancement curve can be made. A typical enhancement curve is obtained by measuring the maximum intensity of