245 research outputs found
Dust-forming molecules in VY Canis Majoris (and Betelgeuse)
The formation of inorganic dust in circumstellar environments of evolved
stars is poorly understood. Spectra of molecules thought to be most important
for the nucleation, i.e. AlO, TiO, and TiO2, have been recently detected in the
red supergiant VY CMa. These molecules are effectively formed in VY CMa and the
observations suggest that non-equilibrium chemistry must be involved in their
formation and nucleation into dust. In addition to exploring the recent
observations of VY CMa, we briefly discuss the possibility of detecting these
molecules in the dust-poor circumstellar environment of Betelgeuse.Comment: contribution to Betelgeuse Workshop 2012: "The physics of Red
Supergiants: recent advances and open questions", 26-29 Nov 2012 Paris
(France
Comparison of maximal myocardial blood flow during adenosine infusion with that of intravenous dipyridamole in normal men
AbstractObjective. This study compared quantitatively the efficacy of intravenous adenosine and dipyridamole for pharmacologic induction of myocardial hyperemia.Background. Pharmacologic vasodilation is used increasingly for induction of myocardial hyperemia in conjunction with radionuclide imaging of myocardial blood flow. Although both intravenous dipyridamole and adenosine have been used, the magnitude of hyperemia induced by these agents and the hyperemia to baseline blood flow ratios have not been quantified and compared.Methods. Twenty normal volunteers were studied with dynamic positron emission tomography (PET) and intravenous nitrogen-13 ammonia. Myocardial blood flow was quantified with a two-compartment tracer kinetic model.Results. Myocardial blood flow at rest averaged 1.1 ± 0.2 ml/min per g and increased significantly to 4.4 ± 0.9 ml/min per g during adenosine and 43 ± 1.3 ml/min per g after dipyridamole administration. Hyperemia to baseline flow ratios averaged 4.3 ± 1.6 for adenosine and 4.0 ± 1.3 for dipyridamole. The average flow ratios and the maximal flows achieved were similar for both agents, but there was considerable variation in the individual response to these agents, as indicated by the range of hyperemia to baseline flow ratios (from 2.0 to 8.4 for adenosine and from 1.5 to 5.8 for dipyridamole). in addition, the hyperemic responses to dipyridamole and to adenosine differed by > 1 ml/min per g in nine subjects.Conclusions. Despite these inter- and istraindividual differences, we conclude that both agents are equally effective in producing myocardial hyperemia
Grazing incidence x ray fluorescence analysis for non destructive determination of In and Ga depth profiles in Cu In,Ga Se2 absorber films
Development of highly efficient thin film solar cells involves band gap engineering by tuning their elemental composition with depth. Here we show that grazing incidence X ray fluorescence GIXRF analysis using monochromatic synchrotron radiation and well characterized instrumentation is suitable for a non destructive and reference free analysis of compositional depth profiles in thin films. Variation of the incidence angle provides quantitative access to the in depth distribution of the elements, which are retrieved from measured fluorescence intensities by modeling parameterized gradients and fitting calculated to measured fluorescence intensities. Our results show that double Ga gradients in Cu In1 x,Gax Se2 can be resolved by GIXR
Sudden stress relaxation in compound semiconductor thin films triggered by secondary phase segregation
A major asymmetric ice trap in a planet-forming disk IV. Nitric oxide gas and a lack of CN tracing sublimating ices and a C/O ratio
[Abridged] Most well-resolved disks observed with ALMA show signs of dust
traps. These dust traps set the chemical composition of the planet forming
material in these disks, as the dust grains with their icy mantles are trapped
at specific radii and could deplete the gas and dust of volatiles at smaller
radii. In this work we analyse the first detection of nitric oxide (NO) in a
protoplanetary disk. We aim to constrain the nitrogen chemistry and the
gas-phase C/O ratio in the highly asymmetric dust trap in the Oph-IRS 48 disk.
We use ALMA observations of NO, CN, CH, and related molecules and model the
effect of the dust trap on the physical and chemical structure using the
thermochemical code DALI. Furthermore, we explore how ice sublimation
contributes to the observed emission lines. NO is only observed at the location
of the dust trap but CN and CH are not detected in the Oph-IRS 48 disk.
This results in an CN/NO column density ratio of and thus a low C/O
ratio at the location of the dust trap. The main gas-phase formation pathways
to NO through OH and NH in the fiducial model predict NO emission that is an
order of magnitude lower than is observed. The gaseous NO column density can be
increased by factors ranging from 2.8 to 10 when the HO and NH gas
abundances are significantly boosted by ice sublimation. However, these models
are inconsistent with the upper limits on the HO and OH column densities
derived from observations. We propose that the NO emission in the Oph-IRS 48
disk is closely related to the nitrogen containing ices sublimating in the dust
trap. The non-detection of CN constrains the C/O ratio both inside and outside
the dust trap to be if all nitrogen initially starts as N and , consistent with the Solar value, if (part of) the nitrogen initially
starts as N or NH.Comment: Accepted for publication in Astronomy and Astrophysic
Exercise-induced QT/R-R-interval hysteresis as a predictor of myocardial ischemia
Abstract: Objectives: Exercise-induced QT/RR hysteresis exists when, for a given R-R interval, the QT interval duration is shorter during recovery after exercise than during exercise. We sought to assess the association between QT/RR hysteresis and imaging evidence of myocardial ischemia. Background: Because ischemia induces cellular disturbances known to decrease membrane action potential duration, we hypothesized a correlation between QT/RR and myocardial ischemia
Detection of HCN Direct l-Type Transitions Probing Hot Molecular Gas in the Proto-Planetary Nebula CRL 618
We report the detection of direct l-type transitions towards the
proto-planetary nebula CRL 618 during a study of vibrationally excited carbon
chains. The J=8,10,11,12,13,14 DJ=0 transitions of HCN in its first excited
bending mode v2=1 were detected in absorption against the continuum of the
central HII region making use of the Effelsberg 100m telescope and the Very
Large Array. Additionally, the J=9 direct l-type transition was detected in
emission presumably indicating a weak maser. All lines are blueshifted with
respect to the systemic velocity of CRL 618 indicating that the lines originate
from a hot, expanding circumstellar envelope. The HCN column density along the
line of sight in front of the continuum is 2E18 cm^-2.Comment: 14 pages, 4 figures, to appear in Ap
Evaluating Added Value of Augmented Reality to Assist Aeronautical Maintenance Workers - Experimentation on On-Field Use Case
Augmented Reality (AR) technology facilitates interactions with information and understanding of complex situations. Aeronautical Maintenance combines complexity induced by the variety of products and constraints associated to aeronautic sector and the environment of maintenance. AR tools seem well indicated to solve constraints of productivity and quality on the aeronautical maintenance activities by simplifying data interactions for the workers. However, few evaluations of AR have been done in real processes due to the difficulty of integrating the technology without proper tools for deployment and assessing the results. This paper proposes a method to select suitable criteria for AR evaluation in industrial environment and to deploy AR solutions suited to assist maintenance workers. These are used to set up on-field experiments that demonstrate benefits of AR on process and user point of view for different profiles of workers. Further work will consist on using these elements to extend results to AR evaluation on the whole aeronautical maintenance process. A classification of maintenance activities linked to workers specific needs will lead to prediction of the value that augmented reality would bring to each activity
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