Letter to the Editor: Calculation of photoionized plasmas with an average-atom model

We use a simple average-atom model (NIMP) to calculate the distribution of ionization in a photoionization-dominated plasma, for comparison with recent experimental measurements undertaken on the Z-machine at the Sandia National Laboratory. The agreement between theory and experiment is found to be as good for calculations with an average-atom model as for those generated by more detailed models.

Calibration of assessment instruments – classification in mathematics at the Universidad Jorge Tadeo Lozano

Item Response Theory, IRT, is a valuable methodology for analyzing the quality of the instruments utilized in assessment of academic achievement. This article presents an implementation of the mentioned theory, particularly of the Rasch model, in order to calibrate items and the instrument used in the classification test for the Basic Mathematics subject at Universidad Jorge Tadeo Lozano. 509 responses chains of students, obtained in the june 2011 application, were analyzed with a set of 45 items, through eight case studies that are showing progressive steps of calibration. Criteria of validity of items and of whole instrument were defined and utilized, to select groups of responses chains and items that were finally used in the determination of parameters which then allowed the classification of assessed students by the test.