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Originates from ADPAK / average ion model ; Post et al,
ADNDT, 20, (1977), p397.
DOI: 10.1016/0092-640X(77)90026-2
Adjustments by Te-independent factors for W21+ -> W55+ by
Thomas Puetterich.
See Puetterich et al. PPCF 50 (2008), 085016
DOI: 10.1088/0741-3335/50/8/085016
Converted to ADAS adf11 specifications
Martin O'Mullane, 10-11-2011
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