169 research outputs found
Preconditioning Maximal Center Gauge with Stout Link Smearing in SU(3)
Center vortices are studied in SU(3) gauge theory using Maximal Center Gauge
(MCG) fixing. Stout link smearing and over-improved stout link smearing are
used to construct a preconditioning gauge field transformation, applied to the
original gauge field before fixing to MCG. We find that preconditioning
successfully achieves higher gauge fixing maxima. We observe a reduction in the
number of identified vortices when preconditioning is used, and also a
reduction in the vortex-only string tension.Comment: 9 pages, 4 figure
Charmonium spectral functions in Nf=2 QCD
We report on a study of charmonium at high temperature in 2-flavour QCD. This
is the first such study with dynamical fermions. Using an improved anisotropic
lattice action, spectral functions are extracted from correlators in the vector
and pseudoscalar channels. No signs of medium-induced suppression of the ground
states are seen for temperatures up to 1.5T_c, while at T~2T_c there are clear
signs of modifications. The current systematic and statistical uncertainties in
our data, in particular the relatively coarse lattice and small volume, do not
allow us to draw a firm conclusion at this stage.Comment: 6 pages, talk by JIS at Lattice 2005 (Non-zero temperature and
density
Strong absorption by interstellar hydrogen fluoride: Herschel/HIFI observations of the sight-line to G10.6-0.4 (W31C)
We report the detection of strong absorption by interstellar hydrogen
fluoride along the sight-line to the submillimeter continuum source G10.6-0.4
(W31C). We have used Herschel's HIFI instrument, in dual beam switch mode, to
observe the 1232.4763 GHz J=1-0 HF transition in the upper sideband of the Band
5a receiver. The resultant spectrum shows weak HF emission from G10.6-0.4 at
LSR velocities in the range -10 to -3 km/s, accompanied by strong absorption by
foreground material at LSR velocities in the range 15 to 50 km/s. The spectrum
is similar to that of the 1113.3430 GHz 1(11)-0(00) transition of para-water,
although at some frequencies the HF (hydrogen fluoride) optical depth clearly
exceeds that of para-H2O. The optically-thick HF absorption that we have
observed places a conservative lower limit of 1.6E+14 cm-2 on the HF column
density along the sight-line to G10.6-0.4. Our lower limit on the HF abundance,
6E-9 relative to hydrogen nuclei, implies that hydrogen fluoride accounts for
between ~ 30 and 100% of the fluorine nuclei in the gas phase along this
sight-line. This observation corroborates theoretical predictions that -
because the unique thermochemistry of fluorine permits the exothermic reaction
of F atoms with molecular hydrogen - HF will be the dominant reservoir of
interstellar fluorine under a wide range of conditions.Comment: Accepted for publication in Astronomy and Astrophysics (Herschel
special issue). This revised version corrects a typographic error in the HTML
abstract, in which the lower limit on the HF abundance (should be 6E-9) was
previously misstated. The abstract in the PDF version is correct and the
latter has not been modifie
Nitrogen hydrides in interstellar gas: Herschel/HIFI observations towards G10.6-0.4 (W31C)
The HIFI instrument on board the Herschel Space Observatory has been used to
observe interstellar nitrogen hydrides along the sight-line towards G10.6-0.4
in order to improve our understanding of the interstellar chemistry of
nitrogen. We report observations of absorption in NH N=1-0, J=2-1 and ortho-NH2
1_1,1-0_0,0. We also observed ortho-NH3 1_0-0_0, and 2_0-1_0, para-NH3 2_1-1_1,
and searched unsuccessfully for NH+. All detections show emission and
absorption associated directly with the hot-core source itself as well as
absorption by foreground material over a wide range of velocities. All spectra
show similar, non-saturated, absorption features, which we attribute to diffuse
molecular gas. Total column densities over the velocity range 11-54 km/s are
estimated. The similar profiles suggest fairly uniform abundances relative to
hydrogen, approximately 6*10^-9, 3*10^-9, and 3*10^-9 for NH, NH2, and NH3,
respectively. These abundances are discussed with reference to models of
gas-phase and surface chemistry.Comment: 5 pages, 3 figures, 2 online pages with 2 figures. Accepted for
publication in A&A July 6 (Herschel/HIFI special issue
Ortho-to-para ratio of interstellar heavy water
Despite the low elemental deuterium abundance in the Galaxy, enhanced
molecular D/H ratios have been found in the environments of low-mass star
forming regions, and in particular the Class 0 protostar IRAS 16293-2422. The
CHESS (Chemical HErschel Surveys of Star forming regions) Key Program aims at
studying the molecular complexity of the interstellar medium. The high
sensitivity and spectral resolution of the HIFI instrument provide a unique
opportunity to observe the fundamental 1,1,1 - 0,0,0 transition of the
ortho-D2O molecule, inaccessible from the ground, and to determine the
ortho-to-para D2O ratio. We have detected the fundamental transition of the
ortho-D2O molecule at 607.35 GHz towards IRAS 16293-2422. The line is seen in
absorption with a line opacity of 0.62 +/- 0.11 (1 sigma). From the previous
ground-based observations of the fundamental 1,1,0 - 1,0,1 transition of
para-D2O seen in absorption at 316.80 GHz we estimate a line opacity of 0.26
+/- 0.05 (1 sigma). We show that the observed absorption is caused by the cold
gas in the envelope of the protostar. Using these new observations, we estimate
for the first time the ortho to para D2O ratio to be lower than 2.6 at a 3
sigma level of uncertainty, to be compared with the thermal equilibrium value
of 2:1.Comment: 5 pages, 5 figures, accepted the A&A HIFI Special Issue as a lette
A Large Area Detector proposed for the Large Observatory for X-ray Timing (LOFT)
The Large Observatory for X-ray Timing (LOFT) is one of the four candidate
ESA M3 missions considered for launch in the 2022 time-frame. It is
specifically designed to perform fast X-ray timing and probe the status of the
matter near black holes and neutron stars. The LOFT scientific payload is
composed of a Large Area Detector (LAD) and a Wide Field Monitor (WFM). The LAD
is a 10 m2-class pointed instrument with 20 times the collecting area of the
best past timing missions (such as RXTE) over the 2-30 keV range, which holds
the capability to revolutionize studies of X-ray variability down to the
millisecond time scales. Its ground-breaking characteristic is a low mass per
unit surface, enabling an effective area of ~10 m^2 (@10 keV) at a reasonable
weight. The development of such large but light experiment, with low mass and
power per unit area, is now made possible by the recent advancements in the
field of large-area silicon detectors - able to time tag an X-ray photon with
an accuracy <10 {\mu}s and an energy resolution of ~260 eV at 6 keV - and
capillary-plate X-ray collimators. In this paper, we will summarize the
characteristics of the LAD instrument and give an overview of its capabilities.Comment: Proceedings of SPIE, Vo. 8443, Paper No. 8443-8
Nosocomial outbreak of Pantoea agglomerans bacteraemia associated with contaminated anticoagulant citrate dextrose solution: new name, old bug?
We describe an outbreak investigation of Pantoea agglomerans bacteraemia associated with anticoagulant citrate-dextrose 46% (ACD) solution prepared in-house. A healthy man presented with septic shock during plasmapheresis for granulocyte donation. The solution used for priming and blood samples were sent for culture. Identification of the isolate to species level was performed by gyrB sequencing. Typing was performed by pulsed-field gel electrophoresis (PFGE). In total, eight cases were identified during a three-week period. P. agglomerans was also cultured from six ACD solution bags. Isolates from patients and ACD bags were identical by PFGE. All isolates were susceptible to ampicillin, cephazolin, gentamicin, ciprofloxacin, cefepime and imipenem. (C) 2011 The Healthcare Infection Society. Published by Elsevier Ltd. All rights reserved
The SuperCam Remote Sensing Instrument Suite for Mars 2020
International audienceThe Mars 2020 rover, essentially a structural twin of MSL, is being built to a) characterize the geology and history of a new landing site on Mars, b) find and characterize ancient habitable environments, c) cache samples for eventual return to Earth, and d) demonstrate in-situ production of oxygen needed for human exploration. Remote-sensing instrumentation is needed to support the first three of these goals [1]. The SuperCam instrument meets these needs with a range of instrumentation including the highest-resolution remote imaging on the rover, two different techniques for determining mineralogy , and one technique to provide elemental compositions. All of these techniques are co-boresighted, providing rapid comprehensive characterization. In addition, for targets within 7 meters of the rover the laser shock waves brush away the dust, providing cleaner surfaces for analysis. SuperCam will use an advanced version of the AEGIS robotic target selection software
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