2,412 research outputs found
First high-resolution look at the quiet Sun with ALMA at 3 mm
We present an overview of high resolution quiet Sun observations, from disk
center to the limb, obtained with the Atacama Large mm and sub-mm Array (ALMA)
at 3 mm. Seven quiet Sun regions were observed with resolution of up to 2.5" by
4.5". We produced both average and snapshot images by self-calibrating the ALMA
visibilities and combining the interferometric images with full disk solar
images. The images show well the chromospheric network, which, based on the
unique segregation method we used, is brighter than the average over the fields
of view of the observed regions by K while the intranetwork is less
bright by K, with a slight decrease of the network/intranetwork
contrast toward the limb. At 3 mm the network is very similar to the 1600 \AA\
images, with somewhat larger size. We detected for the first time spicular
structures, rising up to 15" above the limb with a width down to the image
resolution and brightness temperature of 1800 K above the local
background. No trace of spicules, either in emission or absorption, was found
on the disk. Our results highlight ALMA's potential for the study of the quiet
chromosphere.Comment: Astronomy and Astrophysics (Letters), in pres
His bundle pacing guided by automated intrinsic morphology matching is feasible in patients with narrow QRS complexes
Pace mapping and visual comparison of the local pacing response with the intrinsic QRS morphology form the mainstay of His bundle pacing (HBP). We evaluated the performance of a surface lead morphology match algorithm for automated classification of the pacing response in patients with narrow intrinsic QRS undergoing electroanatomic mapping (EAM)-guided HBP. HBP was attempted in 43 patients. In 28 cases with narrow QRS, the EnSite AutoMap Module was used for automated assessment of the QRS morphology resulting from pace mapping in the His cloud area with either a diagnostic catheter or the His lead. An intrinsic morphology match score (IMS) was calculated for 1.546 QRS complexes and assessed regarding its accuracy and performance in classifying the individual pacing response as either selective HBP (S-HBP), nonselective HBP (NS-HBP) or right ventricular stimulation. Automated morphology comparison of 354 intrinsic beats with the individual reference determined a test accuracy of 99% (95% CI 98.96–99.04) and a precision of 97.99–99.5%. For His-lead stimulation, an IMS ≥ 89% identified S-HBP with a sensitivity, specificity and positive predictive value of 1.00 (0.99, 1.00) and a negative predictive value of 0.99 (0.98, 1.00). An IMS between 78 and < 89% indicated NS-HBP with a sensitivity and specificity of 1.00 (0.99, 1.00) and 0.99 (0.98, 1.00), respectively. IMS represents a new automated measure for standardized individual morphology classification in patients with normal QRS undergoing EAM-guided HBP. Clinical trial registration: NCT04416958
An analytical description of the disruption of star clusters in tidal fields with an application to Galactic open clusters
We present a simple analytical description of the disruption of star clusters
in a tidal field, which agrees excellently with detailed N-body simulations.
The analytic expression can be used to predict the mass and age histograms of
surviving clusters for any cluster initial mass function and any cluster
formation history. The method is applied to open clusters in the solar
neighbourhood, based on the new cluster sample of Kharchenko et al. From a
comparison between the observed and predicted age distributions in the age
range between 10 Myr to 3 Gyr we find the following results: (1) The disruption
time of a 10^4 M_sun cluster in the solar neighbourhood is about 1.3+/-0.5 Gyr.
This is a factor 5 shorter than derived from N-body simulations of clusters in
the tidal field of the galaxy. (2) The present starformation rate in bound
clusters within 600 pc from the Sun is 5.9+/-0.8 * 10^2 M_sun / Myr, which
corresponds to a surface star formation rate in bound clusters of 5.2+/-0.7
10^(-10) M_sun/yr/pc^2. (3) The age distribution of open clusters shows a bump
between 0.26 and 0.6 Gyr when the cluster formation rate was 2.5 times higher
than before and after. (4) The present star formation rate in bound clusters is
half as small as that derived from the study of embedded clusters. The
difference suggests that half of the clusters in the solar neighbourhood become
unbound within 10 Myr. (5) The most massive clusters within 600 pc had an
initial mass of 3*10^4 M_sun. This is in agreement with the statistically
expected value based on a cluster initial mass function with a slope of -2,
even if the physical upper mass limit is as high as 10^6 M_sun.Comment: 14 pages, 15 figures, to appear in Astronomy & Astrophysic
The VLT-FLAMES Tarantula Survey. VII. A low velocity dispersion for the young massive cluster R136
Detailed studies of resolved young massive star clusters are necessary to
determine their dynamical state and evaluate the importance of gas expulsion
and early cluster evolution. In an effort to gain insight into the dynamical
state of the young massive cluster R136 and obtain the first measurement of its
velocity dispersion, we analyse multi-epoch spectroscopic data of the inner
regions of 30 Doradus in the Large Magellanic Cloud (LMC) obtained as part of
the VLT-FLAMES Tarantula Survey. Following a quantitative assessment of the
variability, we use the radial velocities of non-variable sources to place an
upper limit of 6 km/s on the line-of-sight velocity dispersion of stars within
a projected distance of 5 pc from the centre of the cluster. After accounting
for the contributions of undetected binaries and measurement errors through
Monte Carlo simulations, we conclude that the true velocity dispersion is
likely between 4 and 5 km/s given a range of standard assumptions about the
binary distribution. This result is consistent with what is expected if the
cluster is in virial equilibrium, suggesting that gas expulsion has not altered
its dynamics. We find that the velocity dispersion would be ~25 km/s if
binaries were not identified and rejected, confirming the importance of the
multi-epoch strategy and the risk of interpreting velocity dispersion
measurements of unresolved extragalactic young massive clusters.Comment: 18 pages, 7 figures, accepted by A&
Nurses\u27 Alumnae Association Bulletin - Volume 2 Number 3
The Jefferson Nurse
Letter from the President
Delegates to Biennial Convention
Attention
Blood Transfusion - Plasma Unit
Life in the Army Nurse Corps
Secretary\u27s Report
Elected to New Office
1892-1942
Progress or Alumnae Association 1892-1942
Report of the School of Nursing
Staff News
Please Change My Address
Air Cooled
Red Cross Report
Fingerprinting
Graduates in the U.S. Army and Navy
Degrees Received
Promotions
Jubilee Report
Engagements
Marriages
Births
New Positions - 1941-1942
New Positions on the Nursing Staff of the Hospita
Strange chiral nucleon form factors
We investigate the strange electric and magnetic form factors of the nucleon
in the framework of heavy baryon chiral perturbation theory to third order in
the chiral expansion. All counterterms can be fixed from data. In particular,
the two unknown singlet couplings can be deduced from the parity-violating
electron scattering experiments performed by the SAMPLE and the HAPPEX
collaborations. Within the given uncertainties, our analysis leads to a small
and positive electric strangeness radius, .
We also deduce the consequences for the upcoming MAMI A4 experiment.Comment: 7 pp, REVTeX, uses epsf, minor correction
Combined effect of Zeeman splitting and spin-orbit interaction on the Josephson current in a S-2DEG-S structure
We analyze new spin effects in current-carrying state of superconductor-2D
electron gas-superconductor (S-2DEG-S) device with spin-polarized nuclei in
2DEG region. The hyperfine interaction of 2D electrons with nuclear spins,
described by the effective magnetic field B, produces Zeeman splitting of
Andreev levels without orbital effects, that leads to the interference pattern
of supercurrent oscillations over B. The spin-orbit effects in 2DEG cause
strongly anisotropic dependence of the Josephson current on the direction of B,
which may be used as a probe for the spin-orbit interaction intensity. Under
certain conditions, the system reveals the properties of pi-junction.Comment: 4 pages, 4 figure
Deciphering the trophic interaction between Akkermansia muciniphila and the butyrogenic gut commensal Anaerostipes caccae using a metatranscriptomic approach
Host glycans are paramount in regulating the symbiotic relationship between humans and their gut bacteria. The constant flux of host-secreted mucin at the mucosal layer creates a steady niche for bacterial colonization. Mucin degradation by keystone species subsequently shapes the microbial community. This study investigated the transcriptional response during mucin-driven trophic interaction between the specialised mucin-degrader Akkermansia muciniphila and a butyrogenic gut commensal Anaerostipes caccae. A. muciniphila monocultures and co-cultures with non-mucolytic A. caccae from the Lachnospiraceae family were grown anaerobically in minimal media supplemented with mucin. We analysed for growth, metabolites (HPLC analysis), microbial composition (quantitative reverse transcription PCR), and transcriptional response (RNA-seq). Mucin degradation by A. muciniphila supported the growth of A. caccae and concomitant butyrate production predominantly via the acetyl-CoA pathway. Differential expression analysis (DESeq 2) showed the presence of A. caccae induced changes in the A. muciniphila transcriptional response with increased expression of mucin degradation genes and reduced expression of ribosomal genes. Two putative operons that encode for uncharacterised proteins and an efflux system, and several two-component systems were also differentially regulated. This indicated A. muciniphila changed its transcriptional regulation in response to A. caccae. This study provides insight to understand the mucin-driven microbial ecology using metatranscriptomics. Our findings show that the expression of mucolytic enzymes by A. muciniphila increases upon the presence of a community member. This could indicate its role as a keystone species that supports the microbial community in the mucosal environment by increasing the availability of mucin sugars.Peer reviewe
The VLT-FLAMES Tarantula Survey IV: Candidates for isolated high-mass star formation in 30 Doradus
Whether massive stars can occasionally form in relative isolation or if they
require a large cluster of lower-mass stars around them is a key test in the
differentiation of star formation theories as well as how the initial mass
function of stars is sampled. Previous attempts to find O-type stars that
formed in isolation were hindered by the possibility that such stars are merely
runaways from clusters, i.e., their current isolation does not reflect their
birth conditions. We introduce a new method to find O-type stars that are not
affected by such a degeneracy. Using the VLT-FLAMES Tarantula Survey and
additional high resolution imaging we have identified stars that satisfy the
following constraints: 1) they are O-type stars that are not detected to be
part of a binary system based on RV time series analysis; 2) they are
designated spectral type O7 or earlier ; 3) their velocities are within 1\sigma
of the mean of OB-type stars in the 30 Doradus region, i.e. they are not
runaways along our line-of-sight; 4) the projected surface density of stars
does not increase within 3 pc towards the O-star (no evidence for clusters); 5)
their sight lines are associated with gaseous and/or dusty filaments in the
ISM, and 6) if a second candidate is found in the direction of the same
filament with which the target is associated, both are required to have similar
velocities. With these criteria, we have identified 15 stars in the 30 Doradus
region, which are strong candidates for being high-mass stars that have formed
in isolation. Additionally, we employed extensive MC stellar cluster
simulations to confirm that our results rule out the presence of clusters
around the candidates. Eleven of these are classified as Vz stars, possibly
associated with the zero-age main sequence. We include a newly discovered W-R
star as a candidate, although it does not meet all of the above criteria.Comment: 14 pages, 13 figures, 5 tables; Accepted for publication by A&
Systematic uncertainties in the analysis of star cluster parameters based on broad-band imaging observations
High-resolution Hubble Space Telescope (HST) imaging observations of star cluster systems provide a very interesting and useful alternative to spectroscopic studies for stellar population analyses with 8-m class telescopes. Here, we assess the systematic uncertainties in (young) cluster age, mass and (to a lesser extent) extinction and metallicity determinations, based on broad-band imaging observations with the HST. Our aim here is to intercompare the results obtained using a variety of commonly used modelling techniques, specifically with respect to our own extensively tested multidimensional approach. Any significant differences among the resulting parameters are due to the details of the various, independently developed, modelling techniques used, rather than to the stellar population models themselves. Despite the model uncertainties and the selection effects inherent to most methods used, we find that the peaks in the relative age and mass distributions of a given young (≲109 yr) cluster system can be derived relatively robustly and consistently, to accuracies of σt≡Δ〈log(age/yr)〉≤ 0.35 and σM≡Δ〈log(Mcl/M⊙)〉≤ 0.14, respectively, assuming Gaussian distributions in cluster ages and masses for reasons of simplicity. The peaks in the relative mass distributions can be obtained with a higher degree of confidence than those in the relative age distributions, as exemplified by the smaller spread among the peak values of the mass distributions derived. This implies that mass determinations are mostly insensitive to the approach adopted. We reiterate that as extensive a wavelength coverage as possible is required to obtain robust and internally consistent age and mass estimates for the individual objects, with reasonable uncertainties. Finally, we conclude that the actual filter systems used for the observations should be used for constructing model colours, instead of using conversion equations, to achieve more accurate derivations of ages and masse
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