792 research outputs found
Test Results of a 1.2 kg/s Centrifugal Liquid Helium Pump for the ATLAS Superconducting Toroid Magnet System
The toroid superconducting magnet of ATLAS-LHC experiment at CERN will be indirectly cooled by means of forced flow of liquid helium at about 4.5 K. A centrifugal pump will be used, providing a mass flow of 1.2 kg/s and a differential pressure of 40 kPa (ca. 400 mbar) at about 4300 rpm. Two pumps are foreseen, one for redundancy, in order to feed in parallel the cooling circuits of the Barrel and the two End-Caps toroid magnets. The paper describes the tests carried out at CERN to measure the characteristic curves, i.e. the head versus the mass flow at different rotational speeds, as well as the pump total efficiency. The pump is of the "fullemission" type, i.e. with curved blades and it is equipped with an exchangeable inducer. A dedicated pump test facility has been constructed at CERN, which includes a Coriolis-type liquid helium mass flow meter. This facility is connected to the helium refrigerator used for the tests at CERN of the racetrack magnets of the Barrel and of the End-Cap toroids
Suspension of the fiber mode-cleaner launcher and measurement of the high extinction-ratio (10^{-9}) ellipsometer for the Q & A experiment
The Q & A experiment, first proposed and started in 1994, provides a feasible
way of exploring the quantum vacuum through the detection of vacuum
birefringence effect generated by QED loop diagram and the detection of the
polarization rotation effect generated by photon-interacting (pseudo-)scalar
particles. Three main parts of the experiment are: (1) Optics System (including
associated Electronic System) based on a suspended 3.5-m high finesse
Fabry-Perot cavity, (2) Ellipsometer using ultra-high extinction-ratio
polarizer and analyzer, and (3) Magnetic Field Modulation System for generating
the birefringence and the polarization rotation effect. In 2002, the Q & A
experiment achieved the Phase I sensitivity goal. During Phase II, we set (i)
to improve the control system of the cavity mirrors for suppressing the
relative motion noise, (ii) to enhance the birefringence signal by setting-up a
60-cm long 2.3 T transverse permanent magnet rotatable to 10 rev/s, (iii) to
reduce geometrical noise by inserting a polarization-maintaining optical fiber
(PM fiber) as a mode cleaner, and (iv) to use ultra-high extinction-ratio
(10^{-9}) polarizer and analyzer for ellipsometry. Here we report on (iii) &
(iv); specifically, we present the properties of the PM-fiber mode-cleaner, the
transfer function of its suspension system, and the result of our measurement
of high extinction-ratio polarizer and analyzer.Comment: 8 pages, 6 figures, presented in the 6th Edoardo Amaldi Conference on
Gravitational Waves, Okinawa, Japan, June 2005, and accepted by "Journal of
Physics: Conference Series". Modifications from version 2 were made based on
the referees' comments on figures. Ref. [31] were update
Ellipsometry noise spectrum, suspension transfer function measurement and closed-loop control of the suspension system in the Q & A experiment
The Q & A experiment, aiming at the detection of vacuum birefringence
predicted by quantum electrodynamics, consists mainly of a suspended 3.5 m
Fabry-Perot cavity, a rotating permanent dipole magnet and an ellipsometer. The
2.3 T magnet can rotate up to 10 rev/s, introducing an ellipticity signal at
twice the rotation frequency. The X-pendulum gives a good isolation ratio for
seismic noise above its main resonant frequency 0.3 Hz. At present, the
ellipsometry noise decreases with frequency, from 1*10^{-5} rad Hz^{-1/2} at 5
Hz, 2*10^{-6} rad Hz^{-1/2} at 20 Hz to 5*10^{-7} rad Hz^{-1/2} at 40 Hz. The
shape of the noise spectrum indicates possible improvement can be made by
further reducing the movement between the cavity mirrors. From the preliminary
result of yaw motion alignment control, it can be seen that some peaks due to
yaw motion of the cavity mirror was suppressed. In this paper, we first give a
schematic view of the Q & A experiment, and then present the measurement of
transfer function of the compound X-pendulum-double pendulum suspension. A
closed-loop control was carried out to verify the validity of the measured
transfer functions. The ellipsometry noise spectra with and without yaw
alignment control and the newest improvement is presented.Comment: 7 pages, 5 figures, presented in 6th Edoardo Amaldi Conference on
Gravitational Waves, June 2005, Okinawa Japan and submitted to Journal of
Physics: Conference Series. Some modifications are made according to the
referee's comments: mainly to explain the relation between the displacement
of cavity mirror and the ellipticity noise spectru
Cardiovascular risk factors are major determinants of thrombotic risk in patients with the lupus anticoagulant
QED Effective Action at Finite Temperature: Two-Loop Dominance
We calculate the two-loop effective action of QED for arbitrary constant
electromagnetic fields at finite temperature T in the limit of T much smaller
than the electron mass. It is shown that in this regime the two-loop
contribution always exceeds the influence of the one-loop part due to the
thermal excitation of the internal photon. As an application, we study light
propagation and photon splitting in the presence of a magnetic background field
at low temperature. We furthermore discover a thermally induced contribution to
pair production in electric fields.Comment: 34 pages, 4 figures, LaTe
Endothelial cell apoptosis in chronically obstructed and reperfused pulmonary artery
<p>Abstract</p> <p>Background</p> <p>Endothelial dysfunction is a major complication of pulmonary endarterectomy (PTE) that can lead to pulmonary edema and persistent pulmonary hypertension. We hypothesized that endothelial dysfunction is related to increased endothelial-cell (EC) death.</p> <p>Methods</p> <p>In piglets, the left pulmonary artery (PA) was ligated to induce lung ischemia then reimplanted into the main PA to reperfuse the lung. Animals sacrificed 5 weeks after ligation (n = 5), 2 days after reperfusion (n = 5), or 5 weeks after reperfusion (n = 5) were compared to a sham-operated group (n = 5). PA vasoreactivity was studied and eNOS assayed. EC apoptosis was assessed by TUNEL in the proximal and distal PA and by caspase-3 activity assay in the proximal PA. Gene expression of pro-apoptotic factors (thrombospondin-1 (Thsp-1) and plasminogen activator inhibitor 1 (PAI-1)) and anti-apoptotic factors vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) was investigated by QRT-PCR.</p> <p>Results</p> <p>Endothelium-dependent relaxation was altered 5 weeks after ligation (<it>p </it>= 0.04). The alterations were exacerbated 2 days after reperfusion (p = 0.002) but recovered within 5 weeks after reperfusion. EC apoptosis was increased 5 weeks after PA ligation (<it>p </it>= 0.02), increased further within 2 days after reperfusion (<it>p </it>< 0.0001), and returned to normal within 5 weeks after reperfusion. Whereas VEGF and bFGF expressions remained unchanged, TSP and PAI-1 expressions peaked 5 weeks after ligation (<it>p </it>= 0.001) and returned to normal within 2 days after reperfusion.</p> <p>Conclusion</p> <p>Chronic lung ischemia induces over-expression of pro-apoptotic factors. Lung reperfusion is followed by a dramatic transient increase in EC death that may explain the development of endothelial dysfunction after PE. Anti-apoptotic agents may hold considerable potential for preventing postoperative complications.</p
Single hadron response measurement and calorimeter jet energy scale uncertainty with the ATLAS detector at the LHC
The uncertainty on the calorimeter energy response to jets of particles is
derived for the ATLAS experiment at the Large Hadron Collider (LHC). First, the
calorimeter response to single isolated charged hadrons is measured and
compared to the Monte Carlo simulation using proton-proton collisions at
centre-of-mass energies of sqrt(s) = 900 GeV and 7 TeV collected during 2009
and 2010. Then, using the decay of K_s and Lambda particles, the calorimeter
response to specific types of particles (positively and negatively charged
pions, protons, and anti-protons) is measured and compared to the Monte Carlo
predictions. Finally, the jet energy scale uncertainty is determined by
propagating the response uncertainty for single charged and neutral particles
to jets. The response uncertainty is 2-5% for central isolated hadrons and 1-3%
for the final calorimeter jet energy scale.Comment: 24 pages plus author list (36 pages total), 23 figures, 1 table,
submitted to European Physical Journal
Standalone vertex ďŹnding in the ATLAS muon spectrometer
A dedicated reconstruction algorithm to find decay vertices in the ATLAS muon spectrometer is presented. The algorithm searches the region just upstream of or inside the muon spectrometer volume for multi-particle vertices that originate from the decay of particles with long decay paths. The performance of the algorithm is evaluated using both a sample of simulated Higgs boson events, in which the Higgs boson decays to long-lived neutral particles that in turn decay to bbar b final states, and pp collision data at âs = 7 TeV collected with the ATLAS detector at the LHC during 2011
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