Air radon concentration decrease in a waste water treatment plant

Rn-222 is a naturally occurring gas created from the decay of Ra-226. The long-term health risk of breathing radon is lung cancer. One particular place where indoor radon concentrations can exceed national guidelines is in wastewater treatment plants (WWTPs) where treatment processes may contribute to ambient airborne concentrations. The aim of this paper was to study the radon concentration decrease after the application of corrective measures in a Spanish WWTP. According to first measures, air radon concentration exceeded International Commission Radiologica1 Protection (ICRP) normative (recommends intervention between 400 and 1000 Bq m(-3)). Therefore, the WWTP improved mechanical forced ventilation to lower occupational exposure. This measure allowed to increase the administrative controls, since the limitation of workers access to the plant changed from 2 h d(-1) (considering a maximum permissible dose of 20 mSv y(-1) averaged over 5 y) to 7 h d(-1).Juste Vidal, BJ.; Ortiz Moragón, J.; Verdú Martín, GJ.; Martorell Alsina, SS. (2015). Air radon concentration decrease in a waste water treatment plant. Oxford University Press. doi:10.1093/RPD/NCV329

Uncertainty and sensitivity analysis of the effect of the mean energy and FWHM of the initial electron fluence on the Bremsstrahlung photon spectra of linear accelerators

A calculation of the correct dose in radiation therapy requires an accurate description of the radiation source because uncertainties in characterization of the linac photon spectrum are propagated through the dose calculations. Unfortunately, detailed knowledge of the initial electron beam parameters is not readily available, and many researchers adjust the initial electron fluence values by trial-and-error methods. The main goal of this work was to develop a methodology to characterize the fluence of initial electrons before they hit the tungsten target of an Elekta Precise medical linear accelerator. To this end, we used a Monte Carlo technique to analyze the influence of the characteristics of the initial electron beam on the distribution of absorbed dose from a 6 MV linac photon beam in a water phantom. The technique is based on calculations with Software for Uncertainty and Sensitivity Analysis (SUSA) and Monte Carlo simulations with the MCNP5 transport code. The free parameters used in the SUSA calculations were the mean energy and full-width-at-half-maximum (FWHM) of the initial electron distribution. A total of 93 combinations of these parameters gave initial electron fluence configurations. The electron spectra thus obtained were used in a simulation of the electron transport through the target of the linear accelerator, which produced different photon (Bremsstrahlung) spectra. The simulated photon spectra were compared with the 6-MV photon spectrum provided by the linac manufacturer (Elekta). This comparison revealed how the mean energy and FWHM of the initial electron fluence affect the spectrum of the generated photons. This study has made it possible to fine-tune the examined electron beam parameters to obtain the resulted absorbed doses with acceptable accuracy (error < 1%). (C) 2012 Elsevier Ltd. All rights reserved.Juste Vidal, BJ.; Miró Herrero, R.; Verdú Martín, GJ.; Macian, R. (2012). Uncertainty and sensitivity analysis of the effect of the mean energy and FWHM of the initial electron fluence on the Bremsstrahlung photon spectra of linear accelerators. Applied Radiation and Isotopes. 70(7):1267-1271. doi:10.1016/j.apradiso.2012.03.040S1267127170

Probing Electroweak Top Quark Couplings at Hadron Colliders

We consider QCD t\bar{t}\gamma and t\bar{t}Z production at hadron colliders as a tool to measure the tt\gamma and ttZ couplings. At the Tevatron it may be possible to perform a first, albeit not very precise, test of the tt\gamma vector and axial vector couplings in t\bar{t}\gamma production, provided that more than 5 fb^{-1} of integrated luminosity are accumulated. The t\bar{t}Z cross section at the Tevatron is too small to be observable. At the CERN Large Hadron Collider (LHC) it will be possible to probe the tt\gamma couplings at the few percent level, which approaches the precision which one hopes to achieve with a next-generation e^+e^- linear collider. The LHC's capability of associated QCD t\bar{t}V (V=\gamma, Z) production has the added advantage that the tt\gamma and ttZ couplings are not entangled. For an integrated luminosity of 300 fb^{-1}, the ttZ vector (axial vector) coupling can be determined with an uncertainty of 45-85% (15-20%), whereas the dimension-five dipole form factors can be measured with a precision of 50-55%. The achievable limits improve typically by a factor of 2-3 for the luminosity-upgraded (3 ab^{-1}) LHC.Comment: Revtex3, 30 pages, 9 Figures, 6 Table

Sidewall effects on heat transfer in narrow backward facing step in transitional regime

In this work, we study numerically with large eddy simulation, the effects induced by the three-dimensional geometry of the channel on the flow topology that exists when the three-dimensional intrinsic instabilities appear in a backward facing step flow with low aspect ratio for Reynolds in the transitional regime (Re = 1,000–1,600), and its impact on the heat flux in the lower wall. Under the transitional regime, the three-dimensional instabilities begin to appear, but they can be masked by the flows due to the presence of the side walls. The study is carried out with two boundary conditions in the sidewalls, slip, and no-slip, to discriminate between the three-dimensionality induced by the geometry and the intrinsic three-dimensional instabilities. The results obtained are compared between the two boundary conditions, establishing what type of flow prevails and its influence on time-averaged mean Nusselt number for all Reynolds.This work was funded by Ministerio de Ciencia, Innovación y Universidades y fondos FEDER - Proyecto Retos-Colaboración RTC-2017-6137-8

Concealed by darkness: interactions between predatory bats and nocturnally migrating songbirds illuminated by DNA sequencing

Recently, several species of aerial-hawking bats have been found to prey on migrating songbirds, but details on this behaviour and its relevance for bird migration are still unclear. We sequenced avian DNA in feather-containing scats of the bird-feeding bat Nyctalus lasiopterus from Spain collected during bird migration seasons. We found very high prey diversity, with 31 bird species from eight families of Passeriformes, almost all of which were nocturnally flying sub-Saharan migrants. Moreover, species using tree hollows or nest boxes in the study area during migration periods were not present in the bats’ diet, indicating that birds are solely captured on the wing during night-time passage. Additional to a generalist feeding strategy, we found that bats selected medium-sized bird species, thereby assumingly optimizing their energetic cost-benefit balance and injury risk. Surprisingly, bats preyed upon birds half their own body mass. This shows that the 5% prey to predator body mass ratio traditionally assumed for aerial hunting bats does not apply to this hunting strategy or even underestimates these animals’ behavioural and mechanical abilities. Considering the bats’ generalist feeding strategy and their large prey size range, we suggest that nocturnal bat predation may have influenced the evolution of bird migration strategies and behaviour.Peer Reviewe

Oxygen permeation, thermal and chemical expansion of (La, Sr)(Fe, Ga)O3−δ perovskite membranes

International audienceDense ceramic membranes made from mixed conductors are interesting because of their potential applications formethane conversion into syngas (H2 and CO mixture). Such membranes need to present a low differential dimensional variation between the opposite faces submitted to a large gradient of oxygen partial pressure, in order to minimize mechanical stresses generated through the membrane thickness. Besides, high oxygen permeability is required for high methane reforming rate. La(1−x)SrxFe(1−y)GayO3−δ materials fulfil these two main requirements and were retained as membranes in catalytic membrane reactors (CMR). The variations of expansion and oxygen permeation of La(1−x)SrxFe(1−y)GayO3−δ perovskite materials with the partial substitution of lanthanum and iron cations, temperature and oxygen partial pressure, were studied. For low temperatures (800 ◦C), TEC, then dimensional stability of the membrane, and oxygen permeation of La(1−x)SrxFe(1−y)GayO3−δ materials, are significantly affected by Sr content and oxygen partial pressure. Ga has a stabilisation effect on the TEC and has no influence on oxygen permeation flux. A good compromise between dimensional stability and oxygen permeation of materials was found to be La0.7Sr0.3Fe0.7Ga0.3O3−δ compositio