Corona discharge the electron-liberation is a high-energy photon from an atom within the plasma body relaxing after excitation from an earlier collision. The use of ionized neutral gas as a source of ionization is further diminished in a negative corona by the high-concentration of positive ions clustering around the curved electrode. Under other conditions, the collision of the positive species with the curved electrode can also cause electron liberation. The difference, then, between positive and negative coronas, in the matter of the generation of secondary electron avalanches, is that in a positive corona they are generated by the gas surrounding the plasma
Positive and negative sets union of a sequence of positive or negative sets is also positive or negative; more formally, if ("A") is a sequence of positive sets, then is also a positive set; the same is true if the word "positive" is replaced by "negative". A set which is both positive and negative is a μ-null set, for if "E" is a measurable subset of a positive and negative set "A", then both μ("E") ≥ 0 and μ("E") ≤ 0 must hold, and therefore, μ("E") = 0. The Hahn decomposition theorem states that for every measurable space ("X",Σ) with a signed measure μ,