A test of the nature of cosmic acceleration using galaxy redshift distortions.

Observations of distant supernovae indicate that the Universe is now in a phase of accelerated expansion the physical cause of which is a mystery. Formally, this requires the inclusion of a term acting as a negative pressure in the equations of cosmic expansion, accounting for about 75 per cent of the total energy density in the Universe. The simplest option for this 'dark energy' corresponds to a 'cosmological constant', perhaps related to the quantum vacuum energy. Physically viable alternatives invoke either the presence of a scalar field with an evolving equation of state, or extensions of general relativity involving higher-order curvature terms or extra dimensions. Although they produce similar expansion rates, different models predict measurable differences in the growth rate of large-scale structure with cosmic time. A fingerprint of this growth is provided by coherent galaxy motions, which introduce a radial anisotropy in the clustering pattern reconstructed by galaxy redshift surveys. Here we report a measurement of this effect at a redshift of 0.8. Using a new survey of more than 10,000 faint galaxies, we measure the anisotropy parameter beta = 0.70 +/- 0.26, which corresponds to a growth rate of structure at that time of f = 0.91 +/- 0.36. This is consistent with the standard cosmological-constant model with low matter density and flat geometry, although the error bars are still too large to distinguish among alternative origins for the accelerated expansion. The correct origin could be determined with a further factor-of-ten increase in the sampled volume at similar redshift.

A large population of galaxies 9 to 12 billion years back in the history of the Universe.

To understand the evolution of galaxies, we need to know as accurately as possible how many galaxies were present in the Universe at different epochs. Galaxies in the young Universe have hitherto mainly been identified using their expected optical colours, but this leaves open the possibility that a significant population remains undetected because their colours are the result of a complex mix of stars, gas, dust or active galactic nuclei. Here we report the results of a flux-limited I-band survey of galaxies at look-back times of 9 to 12 billion years. We find 970 galaxies with spectroscopic redshifts between 1.4 and 5. This population is 1.6 to 6.2 times larger than previous estimates, with the difference increasing towards brighter magnitudes. Strong ultraviolet continua (in the rest frame of the galaxies) indicate vigorous star formation rates of more than 10-100 solar masses per year. As a consequence, the cosmic star formation rate representing the volume-averaged production of stars is higher than previously measured at redshifts of 3 to 4.

An Investigation of Procedural Radiation Dose Level Awareness and Personal Training Experience in Communicating Ionizing Radiation Examinations Benefits and Risks to Patients in Two European Cardiac Centers.

PURPOSE: Cardiac interventional practitioners need to be appropriately informed regarding radiation dose quantities and risks. Communicating benefit-risk information to patients requires attention as specified in Basic Safety Standards Directive 2013/59/Eurotom. This study investigated the awareness of procedural radiation dose levels and the impact of personal training experience in communicating ionizing radiation benefit-risks to patients. METHODOLOGY: A questionnaire, consisting of 28 questions, was distributed directly to adult and pediatric interventional cardiology specialists at specialized cardiovascular imaging centers in Dublin, Ireland and Milan, Italy. RESULTS: A total of 18 interventional cardiologists (senior registrar to consultant grades with between 2 y to over 21 y experience in cardiac imaging) participated. The majority of participants (n = 17) stated that parents of pediatric and adult patients should be informed of the potential benefits and risk. All participants indicated they had radiation safety training; however, 50% had not received training in radiation examination benefit-risk communication. Despite this, 77.8% (n = 14) participants indicated a high confidence level in successfully explaining risks and/or benefits of cardiac imaging procedures. When asked to estimate effective dose (ED) values for common cardiac imaging procedures less than 50% identified appropriate dose ranges. All participants underestimated procedural dose values based on recent European data. 50% (n = 9) participants answered all questions correctly for a number of true or false radiation risk statements. CONCLUSION: Benefit-risk communication training deficits and inaccurate understanding of radiation dose levels was identified. Further research and training to support clinicians using radiation on a daily basis is required.