On effective linearly ordered sets of comparison functions

Both the existence and the non-existence of a linearly ordered (by certain natural order relations) effective set of comparison functions (=dense comparison classes) are compatible with the ZFC axioms of set theory.

Effective collision strengths for allowed transitions among the n

Aims.In this paper we report on calculations of collision strengths and effective collision strengths for allowed transitions among the $n \le$ 5 degenerate levels of Al XIII.
Methods.The Dirac atomic R-matrix code (DARC) has been adopted for these calculations.
Results.Collision strengths are reported over a wide energy range below 300 Ryd, and effective collision strengths are provided for electron temperatures of 4.4 $\le$ log $T_{\rm e} \le$ 6.8 K.

Effective collision strengths for transitions in Ni XIX

Aims. In this paper we report electron impact collision strengths and excitation rates for transitions among the lowest 89 levels of Ni XIX.
Methods. The Dirac atomic R-matrix code (DARC) is adopted for the calculations of collision strengths and subsequently the effective collision strengths.
Results. Collision strengths for resonance transitions among 89 levels arising from the (1s2) 2s22p6, 2s22p53$\ell$, 2s2p63$\ell$, 2s22p54$\ell$, and 2s2p64$\ell$ configurations of Ni XIX are reported over a wide energy range below 250 Ryd. Additionally, effective collision strengths for all 3916 transitions among the 89 levels are listed over a wide temperature range below 107 K. Comparisons are made among different calculations and the accuracy of the data is assessed. Finally, comparisons between theoretical and experimental intensity ratios of some prominent lines of Ni XIX are discussed.

Effective collision strengths for inner shell transitions of Fe XVI

Collision strengths for transitions among the energetically lowest 134 levels of the (1s(2)2s(2)) 2p(6)3l, 2p(5)3s(2), 2p(5)3s3p, 2p(5)3s3d, 2p(5)3p3d and 2p(5)3d(2) configurations of Fe XVI are computed, over an electron energy range below 570 Ryd, using the Dirac atomic R-matrix code (DARC) and the flexible atomic code (FAC). All partial waves with J