Cosmological Radiative Transfer Codes Comparison Project I: The Static Density Field Tests

Radiative transfer simulations are now at the forefront of numerical astrophysics. They are becoming crucial for an increasing number of astrophysical and cosmological problems; at the same time their computational cost has come to the reach of currently available computational power. Further progress is retarded by the considerable number of different algorithms (including various flavours of ray-tracing and moment schemes) developed, which makes the selection of the most suitable technique for a given problem a non-trivial task. Assessing the validity ranges, accuracy and performances of these schemes is the main aim of this paper, for which we have compared 11 independent RT codes on 5 test problems: (0) basic physics, (1) isothermal H II region expansion and (2) H II region expansion with evolving temperature, (3) I-front trapping and shadowing by a dense clump, (4) multiple sources in a cosmological density field. The outputs of these tests have been compared and differences analyzed. The agreement between the various codes is satisfactory although not perfect. The main source of discrepancy appears to reside in the multi-frequency treatment approach, resulting in different thicknesses of the ionized-neutral transition regions and different temperature structure. The present results and tests represent the most complete benchmark available for the development of new codes and improvement of existing ones. To this aim all test inputs and outputs are made publicly available in digital form.Comment: 32 pages, 39 figures (all color), comments welcom

Learning through contact? The effects on earnings of immigrant exposure to the native population

Factors influencing immigrant labour-market outcomes have received increased scholarly attention lately. A recent research focus has been the effects of residential setting on labour-market outcomes. This study brings a new dimension to this emerging body of research, introducing the role played by workplace composition, in addition to place of residence, in immigrant earnings. Based on Swedish longitudinal register data, ordinary least squares regression is used to examine effects of previous exposure to natives on earnings in three immigrant cohorts (1990, 1995, and 2000) five years after arrival. Besides controlling for individual characteristics and various labour-market attributes, a two-step Heckman correction procedure is applied to take into account the selectivity of entering the Swedish labour market. The main finding of the study is that exposure to the native population at the workplace is more important than residential exposure for predicting immigrant earnings.