132 research outputs found
Characterization of Prototype Superfluid Helium Safety Relief Valves for the LHC Magnets
The Large Hadron Collider (LHC) at CERN will use high field superconducting magnets operating in pressurized superfluid helium (He II) at 1.9 K. Cold safety valves, with their inlet in direct contact with the He II bath, will be required to protect the cold masses in case of a magnet resistive transition. In addition to the safety function, the valves must limit their conduction heat load to the He II to below 0.3 W and limit their mass leakage when closed to below 0.01 g/s at 1.9 K with 100 mbar differential pressure. The valves must also have a high tolerance to contaminating particles in the liquid helium. The compliance with the specified performance is of crucial importance for the LHC cryogenic operation. An extensive test program is therefore being carried out on prototype industrial valves produced by four different manufacturers. The behavior of these valves has been investigated at room temperature and at 77 K. Precise heat load and mass leak measurements have been performed on a dedicated test facility at superfluid helium temperature. Results of cold and warm tests performed on as-delivered valves are presented
A Facility for Accurate Heat Load and Mass Leak Measurements on Superfluid Helium Valves
The superconducting magnets of the Large Hadron Collider (LHC) will be protected by safety relief valves operating at 1.9 K in superfluid helium (HeII). A test facility was developed to precisely determine the heat load and the mass leakage of cryogenic valves with HeII at their inlet. The temperature of the valve inlet can be varied from 1.8 K to 2 K for pressures up to 3.5 bar. The valve outlet pipe temperature can be regulated between 5 K and 20 K. The heat flow is measured with high precision using a Kapitza-resistance heatmeter and is also crosschecked by a vaporization measurement. After calibration, a precision of 10 mW for heat flows up to 1.1 W has been achieved. The helium leak can be measured up to 15 mg/s with an accuracy of 0.2 mg/s. We present a detailed description of the test facility and the measurements showing its performances
Atomic step motion during the dewetting of ultra-thin films
We report on three key processes involving atomic step motion during the
dewetting of thin solid films: (i) the growth of an isolated island nucleated
far from a hole, (ii) the spreading of a monolayer rim, and (iii) the zipping
of a monolayer island along a straight dewetting front. Kinetic Monte Carlo
results are in good agreement with simple analytical models assuming
diffusion-limited dynamics.Comment: 7 pages, 5 figure
Elevated soluble Flt1 mediates an anti-angiogenic state in patients with ANCA-associated vasculitis
International audiencen.
Suppression of the near-infrared OH night sky lines with fibre Bragg gratings - first results
The background noise between 1 and 1.8 microns in ground-based instruments is
dominated by atmospheric emission from hydroxyl molecules. We have built and
commissioned a new instrument, GNOSIS, which suppresses 103 OH doublets between
1.47 - 1.7 microns by a factor of ~1000 with a resolving power of ~10,000. We
present the first results from the commissioning of GNOSIS using the IRIS2
spectrograph at the AAT. The combined throughput of the GNOSIS fore-optics,
grating unit and relay optics is ~36 per cent, but this could be improved to
~46 per cent with a more optimal design. We measure strong suppression of the
OH lines, confirming that OH suppression with fibre Bragg gratings will be a
powerful technology for low resolution spectroscopy. The integrated OH
suppressed background between 1.5 and 1.7 microns is reduced by a factor of 9
compared to a control spectrum using the same system without suppression. The
potential of low resolution OH suppressed spectroscopy is illustrated with
example observations.
The GNOSIS background is dominated by detector dark current below 1.67
microns and by thermal emission above 1.67 microns. After subtracting these we
detect an unidentified residual interline component of ~ 860 +/ 210
ph/s/m^2/micron/arcsec^2. This component is equally bright in the suppressed
and control spectra. We have investigated the possible source of the interline
component, but were unable to discriminate between a possible instrumental
artifact and intrinsic atmospheric emission. Resolving the source of this
emission is crucial for the design of fully optimised OH suppression
spectrographs. The next generation OH suppression spectrograph will be focussed
on resolving the source of the interline component, taking advantage of better
optimisation for a FBG feed. We quantify the necessary improvements for an
optimal OH suppressing fibre spectrograph design.Comment: Accepted for publication in MNRAS. 15 pages, 18 figure
Pharmacokinetic and pharmacodynamic study of intranasal and intravenous dexmedetomidine
Background: Intranasal dexmedetomidine produces safe, effective sedation in children and adults. It may be administered by drops from a syringe or by nasal mucosal atomization (MAD NasalTM). / Methods: This prospective, three-period, crossover, double-blind study compared the pharmacokinetic (PK) and pharmacodynamic (PD) profile of i.v. administration with these two different modes of administration. In each session each subject received 1 ÎŒg kgâ1 dexmedetomidine, either i.v., intranasal with the atomizer or intranasal by drops. Dexmedetomidine plasma concentration and Ramsay sedation score were used for PK/PD modelling by NONMEM. / Results: The i.v. route had a significantly faster onset (15 min, 95% CI 15â20 min) compared to intranasal routes by atomizer (47.5 min, 95% CI 25â135 min), and by drops (60 min, 95%CI 30â75 min), (P<0.001). There was no significant difference in sedation duration across the three treatment groups (P=0.88) nor in the median onset time between the two modes of intranasal administration (P=0.94). A 2-compartment disposition model, with transit intranasal absorption and clearance driven by cardiac output using the well-stirred liver model, was the final PK model. Intranasal bioavailability was estimated to be 40.6% (95% CI 34.7â54.4%) and 40.7% (95% CI 36.5â53.2%) for atomization and drops respectively. Sedation score was modelled via a sigmoidal Emax model driven by an effect compartment. The effect compartment had an equilibration half time 3.3 (95% CI 1.8â4.7) minâ1, and the EC50 was estimated to be 903 (95% CI 450â2344) pg mlâ1. / Conclusions: There is no difference in bioavailability with atomization or nasal drops. A similar degree of sedation can be achieved by either method. / Clinical trial registration: HKUCTR-1617
Flow Dominance and Factorization of Transverse Momentum Correlations in Pb-Pb Collisions at the LHC
M31N 2008-12a - the remarkable recurrent nova in M31: Pan-chromatic observations of the 2015 eruption
The Andromeda Galaxy recurrent nova M31N 2008-12a had been observed in eruption ten times, including yearly eruptions from 2008-2014. With a measured recurrence period of days (we believe the true value to be half of this) and a white dwarf very close to the Chandrasekhar limit, M31N 2008-12a has become the leading pre-explosion supernova type Ia progenitor candidate. Following multi-wavelength follow-up observations of the 2013 and 2014 eruptions, we initiated a campaign to ensure early detection of the predicted 2015 eruption, which triggered ambitious ground and space-based follow-up programs. In this paper we present the 2015 detection; visible to near-infrared photometry and visible spectroscopy; and ultraviolet and X-ray observations from the Swift observatory. The LCOGT 2m (Hawaii) discovered the 2015 eruption, estimated to have commenced at Aug. UT. The 2013-2015 eruptions are remarkably similar at all wavelengths. New early spectroscopic observations reveal short-lived emission from material with velocities km s, possibly collimated outflows. Photometric and spectroscopic observations of the eruption provide strong evidence supporting a red giant donor. An apparently stochastic variability during the early super-soft X-ray phase was comparable in amplitude and duration to past eruptions, but the 2013 and 2015 eruptions show evidence of a brief flux dip during this phase. The multi-eruption Swift/XRT spectra show tentative evidence of high-ionization emission lines above a high-temperature continuum. Following Henze et al. (2015a), the updated recurrence period based on all known eruptions is d, and we expect the next eruption of M31N 2008-12a to occur around mid-Sep. 2016
Low incidence of SARS-CoV-2, risk factors of mortality and the course of illness in the French national cohort of dialysis patients
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