1,038 research outputs found
Performance of the ATLAS Precision Muon Chambers under LHC Operating Conditions
For the muon spectrometer of the ATLAS detector at the large hadron collider
(LHC), large drift chambers consisting of 6 to 8 layers of pressurized drift
tubes are used for precision tracking covering an active area of 5000 m2 in the
toroidal field of superconducting air core magnets. The chambers have to
provide a spatial resolution of 41 microns with Ar:CO2 (93:7) gas mixture at an
absolute pressure of 3 bar and gas gain of 2?104. The environment in which the
chambers will be operated is characterized by high neutron and background with
counting rates of up to 100 per square cm and second. The resolution and
efficiency of a chamber from the serial production for ATLAS has been
investigated in a 100 GeV muon beam at photon irradiation rates as expected
during LHC operation. A silicon strip detector telescope was used as external
reference in the beam. The spatial resolution of a chamber is degraded by 4 ?m
at the highest background rate. The detection efficiency of the drift tubes is
unchanged under irradiation. A tracking efficiency of 98% at the highest rates
has been demonstrated
Performance of the ATLAS Muon Drift-Tube Chambers at High Background Rates and in Magnetic Fields
The ATLAS muon spectrometer uses drift-tube chambers for precision tracking.
The performance of these chambers in the presence of magnetic field and high
radiation fluxes is studied in this article using test-beam data recorded in
the Gamma Irradiation Facility at CERN. The measurements are compared to
detailed predictions provided by the Garfield drift-chamber simulation
programme
Resolution and Efficiency of the ATLAS Muon Drift-Tube Chambers at High Background Rates
The resolution and efficiency of a precision drift-tube chamber for the ATLAS
muon spectrometer with final read-out electronics was tested at the Gamma
Irradiation Facility at CERN in a 100 GeV muon beam and at photon irradiation
rates of up to 990 Hz/square cm which corresponds to twice the highest
background rate expected in ATLAS. A silicon strip detector telescope was used
as external reference in the beam. The pulse-height measurement of the read-out
electronics was used to perform time-slewing corrections which lead to an
improvement of the average drift-tube resolution from 104 microns to 82 microns
without irradiation and from 128 microns to 108 microns at the maximum expected
rate. The measured drift-tube efficiency agrees with the expectation from the
dead time of the read-out electronics up to the maximum expected rate
Construction and Test of MDT Chambers for the ATLAS Muon Spectrometer
The Monitored Drift Tube (MDT) chambers for the muon spectrometer of the AT-
LAS detector at the Large Hadron Collider (LHC) consist of 3-4 layers of
pressurized drift tubes on either side of a space frame carrying an optical
monitoring system to correct for deformations. The full-scale prototype of a
large MDT chamber has been constructed with methods suitable for large-scale
production. X-ray measurements at CERN showed a positioning accuracy of the
sense wires in the chamber of better than the required 20 ?microns (rms). The
performance of the chamber was studied in a muon beam at CERN. Chamber
production for ATLAS now has started
Construction and Test of the Precision Drift Chambers for the ATLAS Muon Spectrometer
The Monitored Drift Tube (MDT) chambers for the muon spectrometer of the
ATLAS detector at the Large Hadron Collider (LHC) consist of 3-4 layers of
pressurised drift tubes on either side of a space frame carrying an optical
deformation monitoring system. The chambers have to provide a track position
resolution of 40 microns with a single-tube resolution of at least 80 microns
and a sense wire positioning accu- racy of 20 ?microns (rms). The feasibility
was demonstrated with the full-scale prototype of one of the largest MDT
chambers with 432 drift tubes of 3.8 m length. For the ATLAS muon spectrometer,
88 chambers of this type have to be built. The first chamber has been completed
with a wire positioning accuracy of 14 microns (rms)
Comments on ``The first detections of the Extragalactic Background Light at 3000, 5500, and 8000 A'' by Bernstein, Freedman and Madore
A critical discussion is presented of the data analysis applied by Bernstein,
Freedman and Madore (2002 ApJ, 571, 56; and ApJ 571, 85) in their measurement
of the Extragalactic Background Light. There are questionable assumptions in
the analysis of the ground-based observations of the Zodiacal Light. The
modeling of the Diffuse Galactic Light is based on an underestimated value of
the dust column density along the line of sight. Comparison with the previously
presented results from the same observations reveals a puzzling situation: in
spite of a large difference in the atmospheric scattered light corrections the
derived Extragalactic Background Light values are exactly the same. The claim
of the paper of a ``detection of the Extragalactic Background Light'' appears
premature.Comment: 6 pages, accepted for Ap
Rectangular Beads from the Final Gravettian Level of the Abri Pataud: Raw Material Identification and its Archaeological Implications
The Final Gravettian level (level 2) of the abri Pataud (Dordogne, France) yielded a large assemblage of body ornaments that consists essentially of 85 quite standardized rectangular beads. Some uncertainty remained about the raw material in which these small beads were made: mammoth ivory, reindeer antler or bone? Non-invasive methods were employed in order to determine the raw material. First chemical analyses using microbeam Proton Induced X-ray Emission analysis (microPIXE) did not enable us to conclude definitively. Therefore, synchrotron and laboratory X-ray microtomography (microCT) were applied on eight beads and allowed us to identify ivory for all of them except for one, which shows slightly different morphological features.Le niveau 2 (Gravettien final) de l’abri Pataud (Dordogne, France) a livré un nombre important d’éléments de parure. L’essentiel (n : 85) correspond à des perles rectangulaires assez standardisées. Certaines incertitudes demeuraient sur leur matière première : ivoire de mammouth, bois de renne ou os ? Des méthodes non-invasives ont alors été employées pour déterminer la nature précise de celles-ci. Les analyses élémentaires par spectrométrie d’émission X induite par particules (PIXE) n’ayant pas été concluantes, la microtomographie de rayons X en laboratoire et au synchrotron a été utilisée sur huit perles et a permis d’identifier le matériau comme étant de l’ivoire, excepté pour l’une d’entre elles qui présente quelques légères différences de structure
Evolution of dust and ice features around FU Orionis objects
(abridged) We present spectroscopy data for a sample of 14 FUors and 2 TTauri
stars observed with the Spitzer Space Telescope or with the Infrared Space
Observatory (ISO). Based on the appearance of the 10 micron silicate feature we
define 2 categories of FUors. Objects showing the silicate feature in
absorption (Category 1) are still embedded in a dusty and icy envelope. The
shape of the 10 micron silicate absorption bands is compared to typical dust
compositions of the interstellar medium and found to be in general agreement.
Only one object (RNO 1B) appears to be too rich in amorphous pyroxene dust, but
a superposed emission feature can explain the observed shape. We derive optical
depths and extinction values from the silicate band and additional ice bands at
6.0, 6.8 and 15.2 micron. In particular the analysis of the CO_2 ice band at
15.2 micron allows us to search for evidence for ice processing and constrains
whether the absorbing material is physically linked to the central object or in
the foreground. For objects showing the silicate feature in emission (Category
2), we argue that the emission comes from the surface layer of accretion disks.
Analyzing the dust composition reveals that significant grain growth has
already taken place within the accretion disks, but no clear indications for
crystallization are present. We discuss how these observational results can be
explained in the picture of a young, and highly active accretion disk. Finally,
a framework is proposed as to how the two categories of FUors can be understood
in a general paradigm of the evolution of young, low-mass stars. Only one
object (Parsamian 21) shows PAH emission features. Their shapes, however, are
often seen toward evolved stars and we question the object's status as a FUor
and discuss other possible classifications.Comment: accepted for publication in ApJ; 63 pages preprint style including 8
tables and 24 figure
Higher-Order Correlations in Non-Stationary Parallel Spike Trains: Statistical Modeling and Inference
The extent to which groups of neurons exhibit higher-order correlations in their spiking activity is a controversial issue in current brain research. A major difficulty is that currently available tools for the analysis of massively parallel spike trains (N >10) for higher-order correlations typically require vast sample sizes. While multiple single-cell recordings become increasingly available, experimental approaches to investigate the role of higher-order correlations suffer from the limitations of available analysis techniques. We have recently presented a novel method for cumulant-based inference of higher-order correlations (CuBIC) that detects correlations of higher order even from relatively short data stretches of length T = 10–100 s. CuBIC employs the compound Poisson process (CPP) as a statistical model for the population spike counts, and assumes spike trains to be stationary in the analyzed data stretch. In the present study, we describe a non-stationary version of the CPP by decoupling the correlation structure from the spiking intensity of the population. This allows us to adapt CuBIC to time-varying firing rates. Numerical simulations reveal that the adaptation corrects for false positive inference of correlations in data with pure rate co-variation, while allowing for temporal variations of the firing rates has a surprisingly small effect on CuBICs sensitivity for correlations
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