443 research outputs found
Identification of Showers with Cores Outside the ARGO-YBJ Detector
In any EAS array, the rejection of events with shower cores outside the
detector boundaries is of great importance. A large difference between the true
and the reconstructed shower core positions may lead to a systematic
miscalculation of some shower characteristics. Moreover, an accurate
determination of the shower core position for selected internal events is
important to reconstruct the primary direction using conical fits to the shower
front, improving the detector angular resolution, or to performe an efficient
gamma/hadron discrimination. In this paper we present a procedure able to
identify and reject showers with cores outside the ARGO-YBJ carpet boundaries.
A comparison of the results for gamma and proton induced showers is reported.Comment: 4 pages, to be published in the Proceedings of the 28th International
Cosmic Ray Conference (Tsukuba, Japan 2003
Expected sensitivity of ARGO-YBJ to detect point gamma-ray sources
ARGO-YBJ is a full coverage air shower detector currently under construction
at the Yangbajing Laboratory (4300 m a.s.l., Tibet, China). First data obtained
with a subset of the apparatus will be available in summer 2003 while the full
detector operation is expected in 2005. One of the main aims of ARGO-YBJ is the
observation of gamma-ray sources, at an energy threshold of a few hundreds GeV.
In this paper we present the expected sensitivity to detect point gamma ray
sources, with particular attention to the Crab Nebula. According to our
simulations a Crab-like signal could be detected in one year of operation with
a statistical significance of 10 standard deviations, without any gamma/hadron
discrimination.Comment: 4 pages, 2 Postscript figure
Atorvastatin pretreatment improves outcomes in patients with acute coronary syndromes undergoing early percutaneous coronary intervention: results of the ARMYDA-ACS randomized trial.
This study sought to investigate potential protective effects of atorvastatin in patients with acute coronary syndromes (ACS) undergoing percutaneous coronary intervention (PCI). Background Randomized studies have shown that pretreatment with atorvastatin may reduce periprocedural myocardial infarction in patients with stable angina during elective PCI; however, this therapy has not been tested in patients with ACS. Methods A total of 171 patients with non–ST-segment elevation ACS were randomized to pretreatment with atorvastatin (80 mg 12 h before PCI, with a further 40-mg preprocedure dose [n 86]) or placebo (n 85). All patients were given a clopidogrel 600-mg loading dose. All patients received long-term atorvastatin treatment thereafter (40 mg/day). The main end point of the trial was a 30-day incidence of major adverse cardiac events (death, myocardial infarction, or unplanned revascularization). Results The primary end point occurred in 5% of patients in the atorvastatin arm and in 17% of those in the placebo arm (p 0.01); this difference was mostly driven by reduction of myocardial infarction incidence (5% vs. 15%; p 0.04). Postprocedural elevation of creatine kinase-MB and troponin-I was also significantly lower in the atorvastatin group (7% vs. 27%, p 0.001 and 41% vs. 58%, p 0.039, respectively). At multivariable analysis, pretreatment with atorvastatin conferred an 88% risk reduction of 30-day major adverse cardiac events (odds ratio 0.12, 95% confidence interval 0.05 to 0.50; p 0.004). Conclusions The ARMYDA-ACS trial indicates that even short-term pretreatment with atorvastatin may improve outcomes in patients with ACS undergoing early invasive strategy. These findings may support routine use of high-dose statins before intervention in patients with ACS
Test of candidate light distributors for the muon (g2) laser calibration system
The new muon (g-2) experiment E989 at Fermilab will be equipped with a laser
calibration system for all the 1296 channels of the calorimeters. An
integrating sphere and an alternative system based on an engineered diffuser
have been considered as possible light distributors for the experiment. We
present here a detailed comparison of the two based on temporal response,
spatial uniformity, transmittance and time stability.Comment: accepted to Nucl.Instrum.Meth.
Interrupted versus uninterrupted NOAC peri-implantation of cardiac device: A single-centre randomised prospective pilot trial
BACKGROUND: Many patients requiring cardiac implantable electronic device (CIED) implantation are on long-term oral anticoagulant therapy. While continuation of warfarin has been shown to be safe and reduce bleeding complications compared to interruption of warfarin therapy and heparin bridging, it is not known which novel oral anticoagulants (NOAC) regimen (interrupted vs. uninterrupted) is better in this setting. METHODS: One-hundred and one patients were randomized to receive CIED implantation with either interrupted or uninterrupted/continuous NOAC therapy before surgery. No heparin was used in either treatment arm. The primary end-point was the presence of a clinically significant pocket haematoma after CIED implantation. The secondary end-point was a composite of other major bleeding events, device-related infection, thrombotic events and device-related admission length post device implantation. RESULTS: Both treatment groups were equally balanced for baseline variables and concomitant medications. One clinically significant pocket haematoma occurred in the uninterrupted NOAC group and none in the interrupted group (p = 0.320). There was no difference in other bleeding complications. No thrombotic events were observed in either of the two groups. CONCLUSIONS: Despite the paucity of bleeding events, data from this pilot study suggest that uninterrupted NOAC therapy for CIED implantation appears to be as safe as NOAC interruption and does not increase bleeding complications
Proton-air cross section measurement with the ARGO-YBJ cosmic ray experiment
The proton-air cross section in the energy range 1-100 TeV has been measured
by the ARGO-YBJ cosmic ray experiment. The analysis is based on the flux
attenuation for different atmospheric depths (i.e. zenith angles) and exploits
the detector capabilities of selecting the shower development stage by means of
hit multiplicity, density and lateral profile measurements at ground. The
effects of shower fluctuations, the contribution of heavier primaries and the
uncertainties of the hadronic interaction models, have been taken into account.
The results have been used to estimate the total proton-proton cross section at
center of mass energies between 70 and 500 GeV, where no accelerator data are
currently available.Comment: 14 pages, 9 figure
Outcome comparison of 600- and 300-mg loading doses of clopidogrel in patients undergoing primary percutaneous coronary intervention for ST-segment elevation myocardial infarction: results from the ARMYDA-6 MI (Antiplatelet therapy for Reduction of MYocardial Damage during Angioplasty-Myocardial Infarction) randomized study.
Search for Gamma Ray Bursts with the Argo-YBJ Detector in Scaler Mode
We report on the search for Gamma Ray Bursts (GRBs) in the energy range 1-100
GeV in coincidence with the prompt emission detected by satellites using the
Astrophysical Radiation with Ground-based Observatory at YangBaJing (ARGO-YBJ)
air shower detector. Thanks to its mountain location (Yangbajing, Tibet, P.R.
China, 4300 m a.s.l.), active surface (about 6700 m**2 of Resistive Plate
Chambers), and large field of view (about 2 sr, limited only by the atmospheric
absorption), the ARGO-YBJ air shower detector is particularly suitable for the
detection of unpredictable and short duration events such as GRBs. The search
is carried out using the "single particle technique", i.e. counting all the
particles hitting the detector without measurement of the energy and arrival
direction of the primary gamma rays.
Between 2004 December 17 and 2009 April 7, 81 GRBs detected by satellites
occurred within the field of view of ARGO-YBJ (zenith angle < 45 deg). It was
possible to examine 62 of these for >1 GeV counterpart in the ARGO-YBJ data
finding no statistically significant emission. With a lack of detected spectra
in this energy range fluence upper limits are profitable, especially when the
redshift is known and the correction for the extragalactic absorption can be
considered. The obtained fluence upper limits reach values as low as 10**{-5}
erg cm**{-2} in the 1-100 GeV energy region.
Besides this individual search for a higher energy counterpart, a statistical
study of the stack of all the GRBs both in time and in phase was made, looking
for a common feature in the GRB high energy emission. No significant signal has
been detected.Comment: accepted for publication in Ap
Measurement of the cosmic ray antiproton/proton flux ratio at TeV energies with the ARGO-YBJ detector
Cosmic ray antiprotons provide an important probe to study the cosmic ray
propagation in the interstellar space and to investigate the existence of dark
matter. Acting the Earth-Moon system as a magnetic spectrometer, paths of
primary antiprotons are deflected in the opposite sense with respect to those
of the protons in their way to the Earth. This effect allows, in principle, the
search for antiparticles in the direction opposite to the observed deficit of
cosmic rays due to the Moon (the so-called `Moon shadow').
The ARGO-YBJ experiment, located at the Yangbajing Cosmic Ray Laboratory
(Tibet, P.R. China, 4300 m a.s.l., 606 g/cm), is particularly effective in
measuring the cosmic ray antimatter content via the observation of the cosmic
rays shadowing effect due to: (1) good angular resolution, pointing accuracy
and long-term stability; (2) low energy threshold; (3) real sensitivity to the
geomagnetic field.
Based on all the data recorded during the period from July 2006 through
November 2009 and on a full Monte Carlo simulation, we searched for the
existence of the shadow cast by antiprotons in the TeV energy region. No
evidence of the existence of antiprotons is found in this energy region. Upper
limits to the flux ratio are set to 5 % at a median energy of 1.4
TeV and 6 % at 5 TeV with a confidence level of 90%. In the TeV energy range
these limits are the lowest available.Comment: Contact authors: G. Di Sciascio ([email protected]) and R.
Iuppa ([email protected]), INFN Sezione di Roma Tor Vergata, Roma, Ital
Study of the diffuse gamma-ray emission from the Galactic plane with ARGO-YBJ
The events recorded by ARGO-YBJ in more than five years of data collection
have been analyzed to determine the diffuse gamma-ray emission in the Galactic
plane at Galactic longitudes 25{\deg} < l < 100{\deg} and Galactic latitudes .
The energy range covered by this analysis, from ~350 GeV to ~2 TeV, allows the
connection of the region explored by Fermi with the multi-TeV measurements
carried out by Milagro. Our analysis has been focused on two selected regions
of the Galactic plane, i.e., 40{\deg} < l < 100{\deg} and 65{\deg} < l <
85{\deg} (the Cygnus region), where Milagro observed an excess with respect to
the predictions of current models. Great care has been taken in order to mask
the most intense gamma-ray sources, including the TeV counterpart of the Cygnus
cocoon recently identified by ARGO-YBJ, and to remove residual contributions.
The ARGO-YBJ results do not show any excess at sub-TeV energies corresponding
to the excess found by Milagro, and are consistent with the predictions of the
Fermi model for the diffuse Galactic emission. From the measured energy
distribution we derive spectral indices and the differential flux at 1 TeV of
the diffuse gamma-ray emission in the sky regions investigated.Comment: 11 pages, 6 figures, published in AP
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