198 research outputs found
A coronal wave and an asymmetric eruptive filament in SUMER, CDS, EIT, and TRACE co-observations
The objectives of the present study is to provide a better physical
understanding of the complex inter-relation and evolution of several solar
coronal features comprising a double-peak flare, a coronal dimming caused by a
CME, a CME-driven compression, and a fast-mode wave. For the first time, the
evolution of an asymmetric eruptive filament is analysed in simultaneous SUMER
spectroscopic and TRACE and EIT imaging data. We use imaging observations from
EIT and TRACE in the 195A channel and spectroscopic observations from the CDS
in a rastering and SUMER in a sit-and-stare observing mode. The SUMER spectra
cover spectral lines with formation temperatures from logT(K) ~ 4.0 to 6.1.
Although the event was already analysed in two previous studies, our analysis
brings a wealth of new information on the dynamics and physical properties of
the observed phenomena. We found that the dynamic event is related to a complex
flare with two distinct impulsive peaks, one according to the GOES
classification as C1.1 and the second - C1.9. The first energy release triggers
a fast-mode wave and a CME with a clear CME driven compression ahead of it.
This activity is related to, or possibly caused, by an asymmetric filament
eruption. The filament is observed to rise with its leading edge moving at a
speed of ~300 km/s detected both in the SUMER and CDS data. The rest of the
filament body moves at only ~150 km/s while untwisting. No signature is found
of the fast-mode wave in the SUMER data, suggesting that the plasma disturbed
by the wave had temperatures above 600 000 K. The erupting filament material is
found to emit only in spectral lines at transition region temperatures. Earlier
identification of a coronal response detected in the Mg X 609.79 A line is
found to be caused by a blend from the O IV 609.83 A line.Comment: 10 pages, 8 figures, A&A, in pres
Hertzsprung-Russell diagram and mass distribution of barium stars
With the availability of parallaxes provided by the Tycho-Gaia Astrometric
Solution, it is possible to construct the Hertzsprung-Russell diagram (HRD) of
barium and related stars with unprecedented accuracy. A direct result from the
derived HRD is that subgiant CH stars occupy the same region as barium dwarfs,
contrary to what their designations imply. By comparing the position of barium
stars in the HRD with STAREVOL evolutionary tracks, it is possible to evaluate
their masses, provided the metallicity is known. We used an average metallicity
[Fe/H] = -0.25 and derived the mass distribution of barium giants. The
distribution peaks around 2.5 Msun with a tail at higher masses up to 4.5 Msun.
This peak is also seen in the mass distribution of a sample of normal K and M
giants used for comparison and is associated with stars located in the red
clump. When we compare these mass distributions, we see a deficit of low-mass
(1 - 2 Msun) barium giants. This is probably because low-mass stars reach large
radii at the tip of the red giant branch, which may have resulted in an early
binary interaction. Among barium giants, the high-mass tail is however
dominated by stars with barium indices of less than unity, based on a visual
inspection of the barium spectral line; that is, these stars have a very
moderate barium line strength. We believe that these stars are not genuine
barium giants, but rather bright giants, or supergiants, where the barium lines
are strengthened because of a positive luminosity effect. Moreover, contrary to
previous claims, we do not see differences between the mass distributions of
mild and strong barium giants.Comment: 14 pages, 17 figure
Barium & related stars and their white-dwarf companions II. Main-sequence and subgiant stars
Barium (Ba) dwarfs and CH subgiants are the less-evolved analogues of Ba and
CH giants. They are F- to G-type main-sequence stars polluted with heavy
elements by a binary companion when the latter was on the Asymptotic Giant
Branch (AGB). This companion is now a white dwarf that in most cases cannot be
directly detected. We present a large systematic study of 60 objects classified
as Ba dwarfs or CH subgiants. Combining radial-velocity measurements from
HERMES and SALT high-resolution spectra with radial-velocity data from CORAVEL
and CORALIE, we determine the orbital parameters of 27 systems. We also derive
their masses by comparing their location in the Hertzsprung-Russell diagram
with evolutionary models. We confirm that Ba dwarfs and CH subgiants are not at
different evolutionary stages and have similar metallicities, despite their
different names. Additionally, Ba giants appear significantly more massive than
their main-sequence analogues. This is likely due to observational biases
against the detection of hotter main-sequence post-mass-transfer objects.
Combining our spectroscopic orbits with the Hipparcos astrometric data, we
derive the orbital inclinations and the mass of the WD companion for four
systems. Since this cannot be done for all systems in our sample yet (but
should be with upcoming Gaia data releases), we also analyse the mass-function
distribution of our binaries. We can model this distribution with very narrow
mass distributions for the two components and random orbital orientation on the
sky. Finally, based on BINSTAR evolutionary models, we suggest that the orbital
evolution of low-mass Ba systems can be affected by a second phase of
interaction along the Red Giant Branch of the Ba star, impacting on the
eccentricities and periods of the giants.Comment: Accepted for publication in A&A on the 5th of April, 201
Application of Large-Scale Synthetic Power System Models for Energy Economic Studies
Due to information confidentiality issues, there is limited access to actual power system models that represent features of actual power grids for teaching, training, and research purposes. The authors\u27 previous work describes the process of creating synthetic transmission networks, with statistics similar to those of actual power grids. Thus, this paper outlines a systematic methodology to augment the synthetic network base case for energy economic studies. The key step is to determine generator cost models by fuel type and capacity. Based on statistics summarized from the actual grids, two approaches are proposed to assign coefficients to generator cost models. To illustrate the proposed creation procedure, we describe the construction of a synthetic model for Electric Reliability Council of Texas footprint. Simulation results are presented to verify that the created test system is able to represent the behavior of actual power systems
Medical Data Architecture Platform and Recommended Requirements for A Medical Data System for Exploration Missions
Minimize or reduce the risk of adverse health outcomes and decrements in performance due to in-flight medical capabilities on human exploration missions. To mitigate this risk, the ExMC MDA project addresses the technical limitations identified in ExMC Gap Med 07: We do not have the capability to comprehensively process medically relevant information to support medical operations during exploration missions. This gap identifies that the current in-flight medical data management includes a combination of data collection and distribution methods that are minimally integrated with on-board medical devices and systems. Furthermore, there are a variety of data sources and methods of data collection. For an exploration mission, the seamless management of such data will enable a more medically autonomous crew than the current paradigm of medical data management on the International Space Station. ExMC has recognized that in order to make informed decisions about a medical data architecture framework, current methods for medical data management must not only be understood, but an architecture must also be identified that provides the crew with actionable insight to medical conditions. This medical data architecture will provide the necessary functionality to address the challenges of executing a self-contained medical system that approaches crew health care delivery without assistance from ground support. Hence, the products derived from the third MDA prototype development will directly inform exploration medical system requirements for Level of Care IV in Gateway missions.In fiscal year 2019, the MDA project developed Test Bed 3, the third iteration in a series of prototypes, that featured integrations with cognition tool data, ultrasound image analytics and core Flight Software (cFS). Maintaining a layered architecture design, the framework implemented a plug-in, modular approach in the integration of these external data sources. An early version of MDA Test Bed 3 software was deployed and operated in a simulated analog environment that was part of the Next Space Technologies for Exploration Partnerships (NextSTEP) Gateway tests of multiple habitat prototypes. In addition, the MDA team participated in the Gateway Test and Verification Demonstration, where the MDA cFS applications was integrated with Gateway-in-a-Box software to send and receive medically relevant data over a simulated vehicle network. This software demonstration was given to ExMC and Gateway Program stakeholders at the NASA Johnson Space Center Integrated Power, Avionics and Software (iPAS) facility. Also, the integrated prototypes served as a vehicle to provide Level 5 requirements for the Crew Health and Performance Habitat Data System for Gateway Missions (Medical Level of Care IV). In the upcoming fiscal year, the MDA project will continue to provide systems engineering and vertical prototypes to refine requirements for medical Level of Care IV and inform requirements for Level of Care V
Does stress perfusion imaging improve the diagnostic accuracy of late gadolinium enhanced cardiac magnetic resonance for establishing the etiology of heart failure?
Background
Late gadolinium enhanced cardiovascular magnetic resonance (LGE-CMR) has excellent specificity, sensitivity and diagnostic accuracy for differentiating between ischemic cardiomyopathy (ICM) and non-ischemic dilated cardiomyopathy (NICM). CMR first-pass myocardial perfusion imaging (perfusion-CMR) may also play role in distinguishing heart failure of ischemic and non-ischemic origins, although the utility of additional of stress perfusion imaging in such patients is unclear. The aim of this retrospective study was to assess whether the addition of adenosine stress perfusion imaging to LGE-CMR is of incremental value for differentiating ICM and NICM in patients with severe left ventricular systolic dysfunction (LVSD) of uncertain etiology.
Methods
We retrospectively identified 100 consecutive adult patients (median age 69 years (IQR 59â73)) with severe LVSD (mean LV EF 26.6 ± 7.0%) referred for perfusion-CMR to establish the underlying etiology of heart failure. The cause of heart failure was first determined on examination of CMR cine and LGE images in isolation. Subsequent examination of complete adenosine stress perfusion-CMR studies (cine, LGE and perfusion images) was performed to identify whether this altered the initial diagnosis.
Results
On LGE-CMR, 38 patients were diagnosed with ICM, 46 with NICM and 16 with dual pathology. With perfusion-CMR, there were 39 ICM, 44 NICM and 17 dual pathology diagnoses. There was excellent agreement in diagnoses between LGE-CMR and perfusion-CMR (Îș 0.968, p<0.001). The addition of adenosine stress perfusion images to LGE-CMR altered the diagnosis in only two of the 100 patients.
Conclusion
The addition of adenosine stress perfusion-CMR to cine and LGE-CMR provides minimal incremental diagnostic yield for determining the etiology of heart failure in patients with severe LVSD
NOEMA maps the CO environment of the red supergiant Cep
Red supergiant stars are surrounded by a gaseous and dusty circumstellar
environment created by their mass loss which spreads heavy elements into the
interstellar medium. The structure and the dynamics of this envelope are
crucial to understand the processes driving the red supergiant mass loss and
the shaping of the pre-supernova ejecta. We have observed the emission from the
CO line from the red supergiant star ~Cep with the NOEMA
interferometer. In the line the synthesized beam was ~arcsec
(~au at 641~pc). The continuum map shows only the unresolved
contribution of the free-free emission of the star chromosphere. The
continuum-subtracted channel maps reveal a very inhomogeneous and clumpy
circumstellar environment. In particular, we detected a bright CO clump, as
bright as the central source in the line, at 1.80~arcsec south-west from the
star, in the blue channel maps. After a deprojection of the radial velocity
assuming two different constant wind velocities, the observations were modelled
using the 3D radiative transfer code \textsc{lime} to derive the
characteristics of the different structures. We determine that the gaseous
clumps observed around ~Cep are responsible for a mass loss rate of , in addition to a
spatially unresolved wind component with an estimated mass-loss rate of . Therefore, the clumps have a
significant role in ~Cep's mass loss (). We cannot exclude that
the unresolved central outflow may be made of smaller unresolved clumps.Comment: 15 pages, 4 tables, 9 figures. 2nd version : one co-author removed
and acknowledgement updated (consistent with erratum
https://doi.org/10.1093/mnras/stz1006
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