2,472 research outputs found
Local stability of a gravitating filament: a dispersion relation
Filamentary structures are ubiquitous in astrophysics and are observed at
various scales. On a cosmological scale, matter is usually distributed along
filaments, and filaments are also typical features of the interstellar medium.
Within a cosmic filament, matter can contract and form galaxies, whereas an
interstellar gas filament can clump into a series of bead-like structures which
can then turn into stars. To investigate the growth of such instabilities, we
derive a local dispersion relation for an idealized self-gravitating filament,
and study some of its properties. Our idealized picture consists of an infinite
self-gravitating and rotating cylinder with pressure and density related by a
polytropic equation of state. We assume no specific density distribution, treat
matter as a fluid, and use hydrodynamics to derive the linearized equations
that govern the local perturbations. We obtain a dispersion relation for
axisymmetric perturbations and study its properties in the (k_R, k_z) phase
space, where k_R and k_z are respectively the radial and longitudinal
wavenumbers. While the boundary between the stable and unstable regimes is
symmetrical in k_R and k_z and analogous to the Jeans criterion, the most
unstable mode displays an asymmetry that could constrain the shape of the
structures that form within the filament. Here the results are applied to a
fiducial interstellar filament, but could be extended for more astrophysical
systems such as cosmological filaments and tidal tails.Comment: 8 pages, 1 figure, published in A&
Post-Permanency: An Assessment for Familiesâ Needs for Services and Supports
This article reports the results of a qualitative study that sought the perspectives of birth parents and adoptive parents following reunification or adoption of children from foster care. Using a participatory action design that actively involved young adults formerly in foster care and parents in the design and implementation of the study, the study focused on the consumersâ perspectives on several issues related to permanency. The article reports findings from interviews with a subset of 27 birth and adoptive families in New York City who were asked about their post-permanency experiences and from interviews with 38 child welfare professionals who were asked to respond to the parentsâ perspectives. The article offers directions for child welfare practice and program development
Towards a resolved Kennicutt-Schmidt law at high redshift
Massive galaxies in the distant Universe form stars at much higher rates than
today. Although direct resolution of the star forming regions of these galaxies
is still a challenge, recent molecular gas observations at the IRAM Plateau de
Bure interferometer enable us to study the star formation efficiency on
subgalactic scales around redshift z = 1.2. We present a method for obtaining
the gas and star formation rate (SFR) surface densities of ensembles of clumps
composing galaxies at this redshift, even though the corresponding scales are
not resolved. This method is based on identifying these structures in
position-velocity diagrams corresponding to slices within the galaxies. We use
unique IRAM observations of the CO(3-2) rotational line and DEEP2 spectra of
four massive star forming distant galaxies - EGS13003805, EGS13004291,
EGS12007881, and EGS13019128 in the AEGIS terminology - to determine the gas
and SFR surface densities of the identifiable ensembles of clumps that
constitute them. The integrated CO line luminosity is assumed to be directly
proportional to the total gas mass, and the SFR is deduced from the [OII] line.
We identify the ensembles of clumps with the angular resolution available in
both CO and [OII] spectroscopy; i.e., 1-1.5". SFR and gas surface densities are
averaged in areas of this size, which is also the thickness of the DEEP2 slits
and of the extracted IRAM slices, and we derive a spatially resolved
Kennicutt-Schmidt (KS) relation on a scale of ~8 kpc. The data generally
indicates an average depletion time of 1.9 Gyr, but with significant variations
from point to point within the galaxies.Comment: 6 pages, 4 figures, 2 tables, accepted by Astronomy and Astrophysic
Dark Matter Fraction in Disk-Like Galaxies Over the Past 10 Gyr
We present an observational study of the dark matter fraction in star-forming
disk-like galaxies up to redshift , selected from publicly
available integral field spectroscropic surveys, namely KMOS3D}, KGES, and
KROSS. We provide novel observational evidence, showing that at a fixed
redshift, the dark matter fraction gradually increases with radius, indicating
that the outskirts of galaxies are dark matter dominated, similarly to local
star-forming disk galaxies. This observed dark matter fraction exhibits a
decreasing trend with increasing redshift. However, on average, the fraction
within the effective radius (upto outskirts) remains above 50\%, similar to
locals. Furthermore, we investigated the relationships between the dark matter,
baryon surface density, and circular velocity of galaxies. We observe a
decreasing trend in the dark matter fraction as baryon surface densities
increase, which is consistent across all stellar masses, redshift ranges, and
radii, with a scatter of 0.13 dex. On the other hand, the correlation between
the circular velocity at the outermost radius and the dark matter fraction
within this radius has a relatively low scatter (0.11 dex), but its slope
varies with stellar mass and with redshift, providing observational evidence of
the dynamical evolution of the interplay between the baryonic and dark matter
distributions with cosmic time. We observe that low stellar mass galaxies
() undergo a higher degree of
evolution, which may be attributed to the hierarchical merging of galaxies.Comment: Comments are welcom
Scandinavian clinical practice guideline on fluid and drug therapy in adults with acute respiratory distress syndrome.
To access publisher's full text version of this article, please click on the hyperlink in Additional Links field or click on the hyperlink at the top of the page marked Files.
This article is open access.The objective of the Scandinavian Society of Anaesthesiology and Intensive Care Medicine (SSAI) task force on fluid and drug therapy in adults with acute respiratory distress syndrome (ARDS) was to provide clinically relevant, evidence-based treatment recommendations according to standards for trustworthy guidelines.The guideline was developed according to standards for trustworthy guidelines, including a systematic review of the literature and use of the GRADE methodology for assessment of the quality of evidence and for moving from evidence to recommendations.A total of seven ARDS interventions were assessed. We suggest fluid restriction in patients with ARDS (weak recommendation, moderate quality evidence). Also, we suggest early use of neuromuscular blocking agents (NMBAs) in patients with severe ARDS (weak recommendation, moderate quality evidence). We recommend against the routine use of other drugs, including corticosteroids, beta2 agonists, statins, and inhaled nitric oxide (iNO) or prostanoids in adults with ARDS (strong recommendations: low- to high-quality evidence). These recommendations do not preclude the use of any drug or combination of drugs targeting underlying or co-existing disorders.This guideline emphasizes the paucity of evidence of benefit - and potential for harm - of common interventions in adults with ARDS and highlights the need for prudence when considering use of non-licensed interventions in this patient population.Scandinavian Society of Anaesthesiology and Intensive Care Medicine (SSAI
Molecular gas in Low Luminosity Radio Galaxies in (proto-)clusters at z~0.4-2.6
We investigate the role of the environment in processing molecular gas in radio galaxies (RGs). We observed five RGs at z=0.4-2.6 in dense Mpc-scale environment with the IRAM-30m telescope. We set four upper-limits and report a tentative CO(7-6) detection at signal-to-noise ratio SNR>~2 for COSMOS-FRI~70, at z=2.63. If the detection will be confirmed at higher SNR, COSMOS-FRI~70 will become the most distant brightest cluster galaxy (BCG) candidate detected in CO. We speculate that the cluster environment might have played a role in preventing the refueling via environmental mechanisms such as galaxy harassment, strangulation, ram-pressure, or tidal stripping. The RGs of this work are excellent targets for ALMA as well as next generation telescopes such as the James Webb Space Telescope
A Revised Design for Microarray Experiments to Account for Experimental Noise and Uncertainty of Probe Response
Background
Although microarrays are analysis tools in biomedical research, they are known to yield noisy output that usually requires experimental confirmation. To tackle this problem, many studies have developed rules for optimizing probe design and devised complex statistical tools to analyze the output. However, less emphasis has been placed on systematically identifying the noise component as part of the experimental procedure. One source of noise is the variance in probe binding, which can be assessed by replicating array probes. The second source is poor probe performance, which can be assessed by calibrating the array based on a dilution series of target molecules. Using model experiments for copy number variation and gene expression measurements, we investigate here a revised design for microarray experiments that addresses both of these sources of variance.
Results
Two custom arrays were used to evaluate the revised design: one based on 25 mer probes from an Affymetrix design and the other based on 60 mer probes from an Agilent design. To assess experimental variance in probe binding, all probes were replicated ten times. To assess probe performance, the probes were calibrated using a dilution series of target molecules and the signal response was fitted to an adsorption model. We found that significant variance of the signal could be controlled by averaging across probes and removing probes that are nonresponsive or poorly responsive in the calibration experiment. Taking this into account, one can obtain a more reliable signal with the added option of obtaining absolute rather than relative measurements.
Conclusion
The assessment of technical variance within the experiments, combined with the calibration of probes allows to remove poorly responding probes and yields more reliable signals for the remaining ones. Once an array is properly calibrated, absolute quantification of signals becomes straight forward, alleviating the need for normalization and reference hybridizations
Combined CO & Dust Scaling Relations of Depletion Time and Molecular Gas Fractions with Cosmic Time, Specific Star Formation Rate and Stellar Mass
We combine molecular gas masses inferred from CO emission in 500 star forming
galaxies (SFGs) between z=0 and 3, from the IRAM-COLDGASS, PHIBSS1/2 and other
surveys, with gas masses derived from Herschel far-IR dust measurements in 512
galaxy stacks over the same stellar mass/redshift range. We constrain the
scaling relations of molecular gas depletion time scale (tdepl) and gas to
stellar mass ratio (Mmolgas/M*) of SFGs near the star formation main-sequence
with redshift, specific star formation rate (sSFR) and stellar mass (M*). The
CO- and dust-based scaling relations agree remarkably well. This suggests that
the CO-H2 mass conversion factor varies little within 0.6dex of the main
sequence (sSFR(ms,z,M*)), and less than 0.3dex throughout this redshift range.
This study builds on and strengthens the results of earlier work. We find that
tdepl scales as (1+z)^-0.3 *(sSFR/sSFR(ms,z,M*))^-0.5, with little dependence
on M*. The resulting steep redshift dependence of Mmolgas/M* ~(1+z)^3 mirrors
that of the sSFR and probably reflects the gas supply rate. The decreasing gas
fractions at high M* are driven by the flattening of the SFR-M* relation.
Throughout the redshift range probed a larger sSFR at constant M* is due to a
combination of an increasing gas fraction and a decreasing depletion time
scale. As a result galaxy integrated samples of the Mmolgas-SFR rate relation
exhibit a super-linear slope, which increases with the range of sSFR. With
these new relations it is now possible to determine Mmolgas with an accuracy of
0.1dex in relative terms, and 0.2dex including systematic uncertainties.Comment: ApJ accepte
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