An Analytical Model of Radiation-Induced Charge Transfer Inefficiency for CCD Detectors

The European Space Agency's Gaia mission is scheduled for launch in 2013. It will operate at L2 for 5 years, rotating slowly to scan the sky so that its two optical telescopes will repeatedly observe more than one billion stars. The resulting data set will be iteratively reduced to solve for the position, parallax and proper motion of every observed star. The focal plane contains 106 large area silicon CCDs continuously operating in a mode where the line transfer rate and the satellite rotation are in synchronisation. One of the greatest challenges facing the mission is radiation damage to the CCDs which will cause charge deferral and image shape distortion. This is particularly important because of the extreme accuracy requirements of the mission. Despite steps taken at hardware level to minimise the effects of radiation, the residual distortion will need to be calibrated during the pipeline data processing. Due to the volume and inhomogeneity of data involved, this requires a model which describes the effects of the radiation damage which is physically realistic, yet fast enough to implement in the pipeline. The resulting charge distortion model was developed specifically for the Gaia CCD operating mode. However, a generalised version is presented in this paper and this has already been applied in a broader context, for example to investigate the impact of radiation damage on the Euclid dark-energy mission data.Comment: 8 pages, 5 figures, paper accepted for publication in MNRA

TRAJECTORIES: Trajectories in Digital Journalism: Embracing Complexity

When the Journalism Studies Interest Group of the International Communication Association was formed in pre-Katrina New Orleans in 2004, online journalism looked very much like offline journalism. Yes, content was available on a computer screen rather than on a piece of paper or over the airwaves. But otherwise, it was much the same: produced by a news organization, dominated by text, consumed but not created by an audience. By the time the interest group became a division two years later, a hurricane had swept through the media world, and very little was the same as before. Journalism Studies as a distinct scholarly discipline has matured in this age of Web 2.0, a term that came into vogue only in late 2004 as innovators began to engage with the medium as a platform for participation and not just for traditional one-to-many publishing. As the practice of journalism has been transformed over the past decade, so too has the study of that practice. Yet practitioners and scholars both have struggled to adapt to the transformation. Journalists have moved only slowly away from the reification of old practices and toward implementation of new ones. And scholars have only tentatively begun to venture outside the comfort zone of long-standing theories as devices for understanding the nature of change. This essay looks at some of the ways in which an evolving realization of the medium’s distinctiveness has brought fundamental change to the synergistic enterprises of journalism practice and journalism studies

The Na I D resonance lines in main sequence late-type stars

We study the sodium D lines (D1: 5895.92 \AA; D2: 5889.95 \AA) in late-type dwarf stars. The stars have spectral types between F6 and M5.5 (B-V between 0.457 and 1.807) and metallicity between [Fe/H] = -0.82 and 0.6. We obtained medium resolution echelle spectra using the 2.15-m telescope at the argentinian observatory CASLEO. The observations have been performed periodically since 1999. The spectra were calibrated in wavelength and in flux. A definition of the pseudo-continuum level is found for all our observations. We also define a continuum level for calibration purposes. The equivalent width of the D lines is computed in detail for all our spectra and related to the colour index (B-V) of the stars. When possible, we perform a careful comparison with previous studies. Finally, we construct a spectral index (R_D') as the ratio between the flux in the D lines, and the bolometric flux. We find that, once corrected for the photospheric contribution, this index can be used as a chromospheric activity indicator in stars with a high level of activity. Additionally, we find that combining some of our results, we obtain a method to calibrate in flux stars of unknown colour.Comment: 12 pages, including 14 figures and 4 tables. Accepted for publication in MNRA

Baryon fractions in clusters of galaxies: evidence against a preheating model for entropy generation

The Millennium Gas project aims to undertake smoothed-particle hydrodynamic resimulations of the Millennium Simulation, providing many hundred massive galaxy clusters for comparison with X-ray surveys (170 clusters with kTsl > 3 keV). This paper looks at the hot gas and stellar fractions of clusters in simulations with different physical heating mechanisms. These fail to reproduce cool-core systems but are successful in matching the hot gas profiles of non-cool-core clusters. Although there is immense scatter in the observational data, the simulated clusters broadly match the integrated gas fractions within r500 . In line with previous work, however, they fare much less well when compared to the stellar fractions, having a dependence on cluster mass that is much weaker than is observed. The evolution with redshift of the hot gas fraction is much larger in the simulation with early preheating than in one with continual feedback; observations favour the latter model. The strong dependence of hot gas fraction on cluster physics limits its use as a probe of cosmological parameters.Comment: 16 pages, 18 figures, 4 tables. Accepted for publication in MNRA

Sunyaev-Zel'dovich clusters in millennium gas simulations

Large surveys using the Sunyaev–Zel’dovich (SZ) effect to find clusters of galaxies are now starting to yield large numbers of systems out to high redshift, many of which are new dis- coveries. In order to provide theoretical interpretation for the release of the full SZ cluster samples over the next few years, we have exploited the large-volume Millennium gas cosmo- logical N-body hydrodynamics simulations to study the SZ cluster population at low and high redshift, for three models with varying gas physics. We confirm previous results using smaller samplesthattheintrinsic(spherical)Y500–M500relationhasverylittlescatter(σlog10Y ≃0.04), is insensitive to cluster gas physics and evolves to redshift 1 in accordance with self-similar expectations. Our preheating and feedback models predict scaling relations that are in excel- lent agreement with the recent analysis from combined Planck and XMM–Newton data by the Planck Collaboration. This agreement is largely preserved when r500 and M500 are derived using thehydrostaticmassproxy,YX,500,albeitwithsignificantlyreducedscatter(σlog10Y ≃0.02),a result that is due to the tight correlation between Y500 and YX,500. Interestingly, this assumption also hides any bias in the relation due to dynamical activity. We also assess the importance of projection effects from large-scale structure along the line of sight, by extracting cluster Y500 values from 50 simulated 5 × 5-deg2 sky maps. Once the (model-dependent) mean signal is subtracted from the maps we find that the integrated SZ signal is unbiased with respect to the underlying clusters, although the scatter in the (cylindrical) Y500–M500 relation increases in the preheating case, where a significant amount of energy was injected into the intergalactic medium at high redshift. Finally, we study the hot gas pressure profiles to investigate the origin of the SZ signal and find that the largest contribution comes from radii close to r500 in all cases. The profiles themselves are well described by generalized Navarro, Frenk & White profiles but there is significant cluster-to-cluster scatter. In conclusion, our results support the notion that Y500 is a robust mass proxy for use in cosmological analyses with clusters

Emotional labour and wellbeing: what protects nurses?

Although compassionate care has wide-ranging benefits for patients, it can be emotionally demanding for healthcare staff. This may be a particular problem for those with little experience in a caring role. This study utilises the job demands-resources model to examine links between “emotional labour” and emotional exhaustion in student nurses. In line with the triple-match principle—whereby interactive effects are more likely when job demands, resources, and outcomes are within the same qualitative domain—the protective role of emotional support and emotion-focused coping (i.e., emotional venting) in the relationship between emotional labour and exhaustion is also explored. An online questionnaire was completed by 351 student nurses with experience working in healthcare settings. A strong positive relationship was found between emotional labour and emotional exhaustion, and some support was found for the moderating effects of emotional support and emotion-focused coping. Ways to help student and qualified nurses develop the emotional resilience required to protect their wellbeing, while providing high-quality compassionate care to patients are considered

On the exclusion of intra-cluster plasma from AGN-blown bubbles

Simple arguments suggest that magnetic fields should be aligned tangentially to the surface of an AGN-blown bubble. If this is the case, charged particles from the fully ionised intra-cluster medium (ICM) will be prevented, ordinarily, from crossing the boundary by the Lorentz force. However, recent observations indicate that thermal material may occupy up to 50% of the volume of some bubbles. Given the effect of the Lorentz force, the thermal content must then be attributed to one, or a combination, of the following processes: i) the entrainment of thermal gas into the AGN outflow that inflated the bubble; ii) rapid diffusion across the magnetic field lines at the ICM/bubble interface; iii) magnetic reconnection events which transfer thermal material across the ICM/bubble boundary. Unless the AGN outflow behaves as a magnetic tower jet, entrainment may be significant and could explain the observed thermal content of bubbles. Alternatively, the cross-field diffusion coefficient required for the ICM to fill a typical bubble is roughly 10^16 cm^2 s^-1, which is anomalously high compared to predictions from turbulent diffusion models. Finally, the mass transfer rate due to magnetic reconnection is uncertain, but significant for plausible reconnection rates. We conclude that entrainment into the outflow and mass transfer due to magnetic reconnection events are probably the most significant sources of thermal content in AGN-blown bubbles.Comment: Accepted for publication in MNRAS, 8 pages, 1 figur