1,845 research outputs found
Constraining angular momentum transport processes in stellar interiors with red-giant stars in the open cluster NGC6819
Clusters are excellent test benches for verification and improvement of
stellar evolution theory. The recent detection of solar-like oscillations in
G-K giants in the open cluster NGC6819 with Kepler provides us with independent
constraints on the masses and radii of stars on the red giant branch, as well
as on the distance to clusters and their ages. We present, for NGC6819,
evolutionary models by considering rotation-induced mixing ; and the
theoretical low-l frequencies of our stellar models.Comment: Submitted to EPJ Web of Conferences, to appear in the Proceedings of
the 3rd CoRoT Symposium, Kepler KASC7 joint meeting; 2 pages, 1 figur
Timing performance of a double layer diamond detector
In order to improve the time precision of detectors based on diamonds sensors we have built a detector with two scCVD layers connected in parallel to the same amplifier. This work describes the design and the first measurements of such a prototype performed on a particle beam at CERN. With this different configuration we have obtained an improvement larger than a factor of 1.6-1.7 for the timing precision of the measurement when compared to a one layer scCVD diamond detector.Peer reviewe
Test of Ultra Fast Silicon Detectors for the TOTEM upgrade project
This paper describes the performance of a prototype timing detector, based on 50 mu m thick Ultra Fast Silicon Detector, as measured in a beam test using a 180 GeV/c momentum pion beam. The dependence of the time precision on the pixel capacitance and bias voltage is investigated in this paper. A timing precision from 30 ps to 100 ps (RMS), depending on the pixel capacitance, has been measured at a bias voltage of 180 V.Peer reviewe
Detection of solar-like oscillations in relics of the Milky Way: asteroseismology of K giants in M4 using data from the NASA K2 mission
Asteroseismic constraints on K giants make it possible to infer radii, masses
and ages of tens of thousands of field stars. Tests against independent
estimates of these properties are however scarce, especially in the metal-poor
regime. Here, we report the detection of solar-like oscillations in 8 stars
belonging to the red-giant branch and red-horizontal branch of the globular
cluster M4. The detections were made in photometric observations from the K2
Mission during its Campaign 2. Making use of independent constraints on the
distance, we estimate masses of the 8 stars by utilising different combinations
of seismic and non-seismic inputs. When introducing a correction to the Delta
nu scaling relation as suggested by stellar models, for RGB stars we find
excellent agreement with the expected masses from isochrone fitting, and with a
distance modulus derived using independent methods. The offset with respect to
independent masses is lower, or comparable with, the uncertainties on the
average RGB mass (4-10%, depending on the combination of constraints used). Our
results lend confidence to asteroseismic masses in the metal poor regime. We
note that a larger sample will be needed to allow more stringent tests to be
made of systematic uncertainties in all the observables (both seismic and
non-seismic), and to explore the properties of RHB stars, and of different
populations in the cluster.Comment: 6 pages, 3 figures, accepted for publication in MNRA
Development of FTK architecture: a fast hardware track trigger for the ATLAS detector
The Fast Tracker (FTK) is a proposed upgrade to the ATLAS trigger system that
will operate at full Level-1 output rates and provide high quality tracks
reconstructed over the entire detector by the start of processing in Level-2.
FTK solves the combinatorial challenge inherent to tracking by exploiting the
massive parallelism of Associative Memories (AM) that can compare inner
detector hits to millions of pre-calculated patterns simultaneously. The
tracking problem within matched patterns is further simplified by using
pre-computed linearized fitting constants and leveraging fast DSP's in modern
commercial FPGA's. Overall, FTK is able to compute the helix parameters for all
tracks in an event and apply quality cuts in approximately one millisecond. By
employing a pipelined architecture, FTK is able to continuously operate at
Level-1 rates without deadtime. The system design is defined and studied using
ATLAS full simulation. Reconstruction quality is evaluated for single muon
events with zero pileup, as well as WH events at the LHC design luminosity. FTK
results are compared with the tracking capability of an offline algorithm.Comment: To be published in the proceedings of DPF-2009, Detroit, MI, July
2009, eConf C09072
The Evolution of FTK, a Real-Time Tracker for Hadron Collider Experiments
We describe the architecture evolution of the highly-parallel dedicated
processor FTK, which is driven by the simulation of LHC events at high
luminosity (1034 cm-2 s-1). FTK is able to provide precise on-line track
reconstruction for future hadronic collider experiments. The processor,
organized in a two-tiered pipelined architecture, execute very fast algorithms
based on the use of a large bank of pre-stored patterns of trajectory points
(first tier) in combination with full resolution track fitting to refine
pattern recognition and to determine off-line quality track parameters. We
describe here how the high luminosity simulation results have produced a new
organization of the hardware inside the FTK processor core.Comment: 11th ICATPP conferenc
A replication study confirms the association of TNFSF4 (OX40L) polymorphisms with systemic sclerosis in a large European cohort
<p><b>Objectives</b> The aim of this study was to confirm the influence of TNFSF4 polymorphisms on systemic sclerosis (SSc) susceptibility and phenotypic features.</p>
<p><b>Methods</b> A total of 8 European populations of Caucasian ancestry were included, comprising 3014 patients with SSc and 3125 healthy controls. Four genetic variants of TNFSF4 gene promoter (rs1234314, rs844644, rs844648 and rs12039904) were selected as genetic markers.</p>
<p><b>Results</b> A pooled analysis revealed the association of rs1234314 and rs12039904 polymorphisms with SSc (OR 1.15, 95% CI 1.02 to 1.31; OR 1.18, 95% CI 1.08 to 1.29, respectively). Significant association of the four tested variants with patients with limited cutaneous SSc (lcSSc) was revealed (rs1234314 OR 1.22, 95% CI 1.07 to 1.38; rs844644 OR 0.91, 95% CI 0.83 to 0.99; rs844648 OR 1.10, 95% CI 1.01 to 1.20 and rs12039904 OR 1.20, 95% CI 1.09 to 1.33). Association of rs1234314, rs844648 and rs12039904 minor alleles with patients positive for anti-centromere antibodies (ACA) remained significant (OR 1.23, 95% CI 1.10 to 1.37; OR 1.12, 95% CI 1.01 to 1.25; OR 1.22, 95% CI 1.07 to 1.38, respectively). Haplotype analysis confirmed a protective haplotype associated with SSc, lcSSc and ACA positive subgroups (OR 0.88, 95% CI 0.82 to 0.96; OR 0.88, 95% CI 0.80 to 0.96; OR 0.86, 95% CI 0.77 to 0.97, respectively) and revealed a new risk haplotype associated with the same groups of patients (OR 1.14, 95% CI 1.03 to 1.26; OR 1.20, 95% CI 1.08 to 1.35; OR 1.23, 95% CI 1.07 to 1.42, respectively).</p>
<p><b>Conclusions</b> The data confirm the influence of TNFSF4 polymorphisms in SSc genetic susceptibility, especially in subsets of patients positive for lcSSc and ACA.</p>
TESS asteroseismology of the known red-giant host stars HD 212771 and HD 203949
International audienc
- …