Electron-cyclotron maser emission, however, does not involve population inversions of atomic energy levels. The term maser was adopted here as an analogy is somewhat of a misnomer. In ECME, the injection of nonthermal, semi-relativistic electrons into a plasma produces a population inversion analogous to that of a maser in the sense that a high-energy population was added to an equilibrium distribution. This is very similar to the beginning of the plasma emission process described in the previous section, but when the plasma density is low and/or the magnetic field strength is high such that f B > f p (Equations 1 and 2), energy from the nonthermal electrons cannot efficiently be converted into Langmuir waves. This leads instead to direct emission at f B through a plasma instability that is expressed analytically as a negative absorption coefficient (i.e. positive growth rate) for a particular particle distribution, most famously the loss-cone distribution. ECME is the accepted mechanism for microwave spike bursts from the chromosphere and is sometimes invoked to explain features of coronal radio bursts that cannot be explained by plasma emission or gyrosynchrotron emission.