40 research outputs found
Influence of temperature on the infrared spectrum of the coronene molecule
Laboratory experiments were performed to study the temperature dependence of the absorption spectrum of the coronene molecule (C24H12), believed to be representative of the polycyclic aromatic hydrocarbon (PAH) molecules present in the interstellar medium. The main results is that both line positions and total intensities are almost unchanged when varying the temperature so that the spectrum is mostly temperature independent in the explored range, supporting the modeling of the IR emission originally made by Leger and Puget where room temperature was used in the calculations. In the structure of the band shape, small temperature correlated changes are observed. Qualitative arguments are given to interpret them
The VLTI / PIONIER near-infrared interferometric survey of southern T Tauri stars. I. First results
Context : The properties of the inner disks of bright Herbig AeBe stars have
been studied with near infrared (NIR) interferometry and high resolution
spectroscopy. The continuum and a few molecular gas species have been studied
close to the central star; however, sensitivity problems limit direct
information about the inner disks of the fainter T Tauri stars.
Aims : Our aim is to measure some of the properties of the inner regions of
disks surrounding southern T Tauri stars.
Methods : We performed a survey with the PIONIER recombiner instrument at
H-band of 21 T Tauri stars. The baselines used ranged from 11 m to 129 m,
corresponding to a maximum resolution of 3mas (0.45 au at 150 pc).
Results : Thirteen disks are resolved well and the visibility curves are
fully sampled as a function of baseline in the range 45-130 m for these 13
objects. A simple qualitative examination of visibility profiles allows us to
identify a rapid drop-off in the visibilities at short baselines in 8 resolved
disks. This is indicative of a significant contribution from an extended
contribution of light from the disk. We demonstrate that this component is
compatible with scattered light, providing strong support to a prediction made
by Pinte et al. (2008). The amplitude of the drop-off and the amount of dust
thermal emission changes from source to source suggesting that each disk is
different. A by-product of the survey is the identification of a new
milli-arcsec separation binary: WW Cha. Spectroscopic and interferometric data
of AK Sco have also been fitted with a binary and disk model.
Conclusions : Visibility data are reproduced well when thermal emission and
scattering form dust are fully considered. The inner radii measured are
consistent with the expected dust sublimation radii. Modelling of AK Sco
suggests a likely coplanarity between the disk and the binary's orbital planeComment: 19 pages, 11 figure
Phase Referencing in Optical Interferometry
One of the aims of next generation optical interferometric instrumentation is
to be able to make use of information contained in the visibility phase to
construct high dynamic range images. Radio and optical interferometry are at
the two extremes of phase corruption by the atmosphere. While in radio it is
possible to obtain calibrated phases for the science objects, in the optical
this is currently not possible. Instead, optical interferometry has relied on
closure phase techniques to produce images. Such techniques allow only to
achieve modest dynamic ranges. However, with high contrast objects, for faint
targets or when structure detail is needed, phase referencing techniques as
used in radio interferometry, should theoretically achieve higher dynamic
ranges for the same number of telescopes. Our approach is not to provide
evidence either for or against the hypothesis that phase referenced imaging
gives better dynamic range than closure phase imaging. Instead we wish to
explore the potential of this technique for future optical interferometry and
also because image reconstruction in the optical using phase referencing
techniques has only been performed with limited success. We have generated
simulated, noisy, complex visibility data, analogous to the signal produced in
radio interferometers, using the VLTI as a template. We proceeded with image
reconstruction using the radio image reconstruction algorithms contained in
AIPS IMAGR (CLEAN algorithm). Our results show that image reconstruction is
successful in most of our science cases, yielding images with a 4
milliarcsecond resolution in K band. (abridged)Comment: 11 pages, 36 figure
Phase Closure Image Reconstruction for Future VLTI Instrumentation
Classically, optical and near-infrared interferometry have relied on closure
phase techniques to produce images. Such techniques allow us to achieve modest
dynamic ranges. In order to test the feasibility of next generation optical
interferometers in the context of the VLTI-spectro-imager (VSI), we have
embarked on a study of image reconstruction and analysis. Our main aim was to
test the influence of the number of telescopes, observing nights and
distribution of the visibility points on the quality of the reconstructed
images. Our results show that observations using six Auxiliary Telescopes (ATs)
during one complete night yield the best results in general and is critical in
most science cases; the number of telescopes is the determining factor in the
image reconstruction outcome. In terms of imaging capabilities, an optical, six
telescope VLTI-type configuration and ~200 meter baseline will achieve 4 mas
spatial resolution, which is comparable to ALMA and almost 50 times better than
JWST will achieve at 2.2 microns. Our results show that such an instrument will
be capable of imaging, with unprecedented detail, a plethora of sources,
ranging from complex stellar surfaces to microlensing events.Comment: 11 pages, 26 figure
Patterns of Alcohol Consumption and Cardiovascular Risk in Northern Ireland and France
Market Liquidity, Investor Participation and Managerial Autonomy: Why Do Firms Go Private?
Erratum to: Scaling up strategies of the chronic respiratory disease programme of the European Innovation Partnership on Active and Healthy Ageing (Action Plan B3: Area 5)
The Science Performance of JWST as Characterized in Commissioning
This paper characterizes the actual science performance of the James Webb
Space Telescope (JWST), as determined from the six month commissioning period.
We summarize the performance of the spacecraft, telescope, science instruments,
and ground system, with an emphasis on differences from pre-launch
expectations. Commissioning has made clear that JWST is fully capable of
achieving the discoveries for which it was built. Moreover, almost across the
board, the science performance of JWST is better than expected; in most cases,
JWST will go deeper faster than expected. The telescope and instrument suite
have demonstrated the sensitivity, stability, image quality, and spectral range
that are necessary to transform our understanding of the cosmos through
observations spanning from near-earth asteroids to the most distant galaxies.Comment: 5th version as accepted to PASP; 31 pages, 18 figures;
https://iopscience.iop.org/article/10.1088/1538-3873/acb29
Effect of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker initiation on organ support-free days in patients hospitalized with COVID-19
IMPORTANCE Overactivation of the renin-angiotensin system (RAS) may contribute to poor clinical outcomes in patients with COVID-19.
Objective To determine whether angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) initiation improves outcomes in patients hospitalized for COVID-19.
DESIGN, SETTING, AND PARTICIPANTS In an ongoing, adaptive platform randomized clinical trial, 721 critically ill and 58 nonâcritically ill hospitalized adults were randomized to receive an RAS inhibitor or control between March 16, 2021, and February 25, 2022, at 69 sites in 7 countries (final follow-up on June 1, 2022).
INTERVENTIONS Patients were randomized to receive open-label initiation of an ACE inhibitor (nâ=â257), ARB (nâ=â248), ARB in combination with DMX-200 (a chemokine receptor-2 inhibitor; nâ=â10), or no RAS inhibitor (control; nâ=â264) for up to 10 days.
MAIN OUTCOMES AND MEASURES The primary outcome was organ supportâfree days, a composite of hospital survival and days alive without cardiovascular or respiratory organ support through 21 days. The primary analysis was a bayesian cumulative logistic model. Odds ratios (ORs) greater than 1 represent improved outcomes.
RESULTS On February 25, 2022, enrollment was discontinued due to safety concerns. Among 679 critically ill patients with available primary outcome data, the median age was 56 years and 239 participants (35.2%) were women. Median (IQR) organ supportâfree days among critically ill patients was 10 (â1 to 16) in the ACE inhibitor group (nâ=â231), 8 (â1 to 17) in the ARB group (nâ=â217), and 12 (0 to 17) in the control group (nâ=â231) (median adjusted odds ratios of 0.77 [95% bayesian credible interval, 0.58-1.06] for improvement for ACE inhibitor and 0.76 [95% credible interval, 0.56-1.05] for ARB compared with control). The posterior probabilities that ACE inhibitors and ARBs worsened organ supportâfree days compared with control were 94.9% and 95.4%, respectively. Hospital survival occurred in 166 of 231 critically ill participants (71.9%) in the ACE inhibitor group, 152 of 217 (70.0%) in the ARB group, and 182 of 231 (78.8%) in the control group (posterior probabilities that ACE inhibitor and ARB worsened hospital survival compared with control were 95.3% and 98.1%, respectively).
CONCLUSIONS AND RELEVANCE In this trial, among critically ill adults with COVID-19, initiation of an ACE inhibitor or ARB did not improve, and likely worsened, clinical outcomes.
TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT0273570