290 research outputs found
Background studies and shielding effects for the TPC detector of the CAST experiment
Sunset solar axions traversing the intense magnetic field of the CERN Axion
Solar Telescope (CAST) experiment may be detected in a Time Projection Chamber
(TPC) detector, as X-rays signals. These signals could be masked, however, by
the inhomogeneous background of materials in the experimental site. A detailed
analysis, based on the detector characteristics, the background radiation at
the CAST site, simulations and experimental results, has allowed us to design a
shielding which reduces the background level by a factor of ~4 compared to the
detector without shielding, depending on its position, in the energy range
between 1 and 10 keV. Moreover, this shielding has improved the homogeneity of
background measured by the TPC.Comment: 14 pages, 5 figures, accepted in New Journal of Physic
PTGER4 gene variant rs76523431 is a candidate risk factor for radiological joint damage in rheumatoid arthritis patients: a genetic study of six cohorts
[Introduction]
Prostaglandin E receptor 4 (PTGER4) is implicated in immune regulation and bone metabolism. The aim of this study was to analyze its role in radiological joint damage in rheumatoid arthritis (RA).[Methods]
Six independent cohorts of patients with RA of European or North American descent were included, comprising 1789 patients with 5083 sets of X-rays. The Hospital Clínico San Carlos Rheumatoid Arthritis, Princesa Early Arthritis Register Longitudinal study, and Hospital Universitario de La Paz early arthritis (Spain) cohorts were used as discovery cohorts, and the Leiden Early Arthritis Clinic (The Netherlands), Wichita (United States), and National Databank for Rheumatic Diseases (United States and Canada) cohorts as replication cohorts. First, the PTGER4 rs6896969 single-nucleotide polymorphism (SNP) was genotyped using TaqMan assays and available Illumina Immunochip data and studied in the discovery and replication cohorts. Second, the PTGER4 gene and adjacent regions were analyzed using Immunochip genotyping data in the discovery cohorts. On the basis of pooled p values, linkage disequilibrium structure of the region, and location in regions with transcriptional properties, SNPs were selected for replication. The results from discovery, replication, and overall cohorts were pooled using inverse-variance–weighted meta-analysis. Influence of the polymorphisms on the overall radiological damage (constant effect) and on damage progression over time (time-varying effect) was analyzed.[Results]
The rs6896969 polymorphism showed a significant association with radiological damage in the constant effect pooled analysis of the discovery cohorts, although no significant association was observed in the replication cohorts or the overall pooled analysis. Regarding the analysis of the PTGER4 region, 976 variants were analyzed in the discovery cohorts. From the constant and time-varying effect analyses, 12 and 20 SNPs, respectively, were selected for replication. Only the rs76523431 variant showed a significant association with radiographic progression in the time-varying effect pooled analysis of the discovery, replication, and overall cohorts. The overall pooled effect size was 1.10 (95 % confidence interval 1.05–1.14, p = 2.10 × 10−5), meaning that radiographic yearly progression was 10 % greater for each copy of the minor allele.[Conclusions]
The PTGER4 gene is a candidate risk factor for radiological progression in RA.This work was supported by the Instituto de Salud Carlos III (ISCIII), Ministry of Health, Spain [Miguel Servet research contract CP12/03129 (to LRR); Fondo de Investigaciones Sanitarias PI11/02413; and Red de Investigación en Inflamación y Enfermedades Reumáticas RD12/0009/0004, RD12/0009/0011, and RD12/0009/0017]. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewe
On the origin of [Ne II] emission in young stars: mid-infrared and optical observations with the Very Large Telescope
{Abridged version for ArXiv}. We provide direct constraints on the origin of
the [Ne II] emission in 15 young stars using high-spatial and spectral
resolution observations with VISIR at the VLT that allow us to study the
kinematics of the emitting gas. In addition we compare the [Ne II] line with
optical forbidden lines observed for three stars with UVES. The [Ne II] line
was detected in 7 stars, among them the first confirmed detection of [Ne II] in
a Herbig Be star, V892 Tau. In four cases, the large blueshifted lines indicate
an origin in a jet. In two stars, the small shifts and asymmetric profiles
indicate an origin in a photo-evaporative wind. CoKu Tau 1, seen close to
edge-on, shows a spatially unresolved line centered at the stellar rest
velocity, although cross-dispersion centroids move within 10 AU from one side
of the star to the other as a function of wavelength. The line profile is
symmetric with wings extending up to about +-80 km/s. The origin of the [Ne II]
line could either be due to the bipolar jet or to the disk. For the stars with
VLT-UVES observations, in several cases, the optical forbidden line profiles
and shifts are very similar to the profile of the [Ne II] line, suggesting that
the lines are emitted in the same region. A general trend observed with VISIR
is a lower line flux when compared with the fluxes obtained with Spitzer. We
found no correlation between the line full-width at half maximum and the line
peak velocity. The [Ne II] line remains undetected in a large part of the
sample, an indication that the emission detected with Spitzer in those stars is
likely extended.Comment: Accepted for publication in Astronomy & Astrophysics; revised
version: corrected minor typos, corrected center values (col 3) for CoKuTau1
in Table
First Jurassic brittlestar from Neuquén Basin, Argentina
Articulated fossil ophiuroids from South America were reported for the Devonian, Cretaceous, Eocene, and Miocene. Here
we report the first Jurassic record of an articulated ophiuroid from the Sierra Chacaicó Formation (early Pliensbachian–
Sinemurian) in Neuquén Basin, Argentina, and discuss the taphonomic processes that allowed its preservation. The Sierra
Chacaicó Formation represents the onset of the Early Jurassic extensive marine transgression in the basin. The basal
section comprises shoreface and offshore Gilbert-type delta system, which was affected by hyperpycnal discharges. The
middle and upper sections are represented by offshore deposits, affected by storms and eroded by hyperpycnal channel-levee
systems. The ophiuroid specimen was found in levels of massive, fine, tuffaceous sandstone beds and covered
by coarse sandstone containing a large amount of plant debris and organic matter. It was preserved articulated, with a
complete disc and almost complete arms. Based on the microstructure of the spine-bearing lateral arm plates, the ophiuroid
is assigned to Sinosura, an extinct genus of the family Ophioleucidae, widespread in the Lower Jurassic deposits
of Europe but previously unknown from other parts of the world. The posture of the ophiuroid, with one arm curved
distally and extended in one direction and the other four arms symmetrically oriented in the opposite direction, suggests
a walking or escape movement frozen in time. This implies that the ophiuroid was buried alive by sediment thick enough
to prevent successful escape. The taphonomic and sedimentologic evidence indicates that the fossil material was found in
hyperpycnal deposits accumulated in offshore positions, which carried a high concentration of sediment in suspension
The emissivity of foam-covered water surface at L-band: theoretical modeling and experimental results from the FROG 2003 field experiment
Sea surface salinity can be measured by microwave
radiometry at L-band (1400–1427 MHz). This frequency is a
compromise between sensitivity to the salinity, small atmospheric
perturbation, and reasonable pixel resolution. The description
of the ocean emission depends on two main factors: 1) the sea
water permittivity, which is a function of salinity, temperature,
and frequency, and 2) the sea surface state, which depends on the
wind-induced wave spectrum, swell, and rain-induced roughness
spectrum, and by the foam coverage and its emissivity. This study
presents a simplified two-layer emission model for foam-covered
water and the results of a controlled experiment to measure the
foam emissivity as a function of salinity, foam thickness, incidence
angle, and polarization. Experimental results are presented, and
then compared to the two-layer foam emission model with the
measured foam parameters used as input model parameters. At
37 psu salt water the foam-induced emissivity increase is 0.007
per millimeter of foam thickness (extrapolated to nadir), increasing
with increasing incidence angles at vertical polarization,
and decreasing withPostprint (published version
Search for solar axion emission from 7Li and D(p,gamma)3He nuclear decays with the CAST gamma-ray calorimeter
We present the results of a search for a high-energy axion emission signal
from 7Li (0.478 MeV) and D(p,gamma)3He (5.5 MeV) nuclear transitions using a
low-background gamma-ray calorimeter during Phase I of the CAST experiment.
These so-called "hadronic axions" could provide a solution to the long-standing
strong-CP problem and can be emitted from the solar core from nuclear M1
transitions. This is the first such search for high-energy pseudoscalar bosons
with couplings to nucleons conducted using a helioscope approach. No excess
signal above background was found.Comment: 20 pages, 8 figures, final version to be published in JCA
Solar axion search with the CAST experiment
The CAST (CERN Axion Solar Telescope) experiment is searching for solar
axions by their conversion into photons inside the magnet pipe of an LHC
dipole. The analysis of the data recorded during the first phase of the
experiment with vacuum in the magnet pipes has resulted in the most restrictive
experimental limit on the coupling constant of axions to photons. In the second
phase, CAST is operating with a buffer gas inside the magnet pipes in order to
extent the sensitivity of the experiment to higher axion masses. We will
present the first results on the data taking as well as the
system upgrades that have been operated in the last year in order to adapt the
experiment for the data taking. Expected sensitivities on the
coupling constant of axions to photons will be given for the recent run just started in March 2008.Comment: Proceedings of the ICHEP 2008 conferenc
Search for low Energy solar Axions with CAST
We have started the development of a detector system, sensitive to single
photons in the eV energy range, to be suitably coupled to one of the CAST
magnet ports. This system should open to CAST a window on possible detection of
low energy Axion Like Particles emitted by the sun. Preliminary tests have
involved a cooled photomultiplier tube coupled to the CAST magnet via a
Galileian telescope and a switched 40 m long optical fiber. This system has
reached the limit background level of the detector alone in ideal conditions,
and two solar tracking runs have been performed with it at CAST. Such a
measurement has never been done before with an axion helioscope. We will
present results from these runs and briefly discuss future detector
developments.Comment: Paper submitted to the proceedings of the "4th Patras Workshop on
Axions, WIMPs and WISPs", DESY, Hamburg Site - Germany, 18-21 June 2008.
Author affiliations are reported on the title page of the paper. In version
2: 1 affiliation change, 3 references adde
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