Several statistical methods exist to extract from a multiple sequence alignment such coupled residue pairs : observed versus expected frequencies of residue pairs ( OMES ); the McLachlan Based Substitution correlation ( McBASC ); statistical coupling analysis; Mutual Information ( MI ) based methods; and, most recently, direct coupling analysis ( DCA)
32.
Helium ionization is important because it is a critical part of the formation of the corona : when solar material is cool enough that the helium within it is only partially ionized ( i . e . retains one of its two electrons ), the material cools by radiation very effectively via both black body radiation and direct coupling to the helium Lyman continuum.
