731 research outputs found
Near-Infrared Imaging of Early-Type Galaxies III. The Near-Infrared Fundamental Plane
Near-infrared imaging data on 251 early-type galaxies in clusters and groups
are used to construct the near-infrared Fundamental Plane (FP) r_eff ~
sigma_0^1.53 _eff^-0.79. The slope of the FP therefore departs from
the virial expectation of r_eff ~ sigma_0^2 _eff^-1 at all optical and
near-infrared wavelengths, which could be a result of the variation of M/L
along the elliptical galaxy sequence, or a systematic breakdown of homology
among the family of elliptical galaxies. The slope of the near-infrared FP
excludes metallicity variations as the sole cause of the slope of the FP. Age
effects, dynamical deviations from a homology, or any combination of these
(with or without metallicity), however, are not excluded. The scatter of both
the near-infrared and optical FP are nearly identical and substantially larger
than the observational uncertainties, demonstrating small but significant
intrinsic cosmological scatter for the FP at all wavelengths. The lack of a
correlation of the residuals of the near-infrared FP and the residuals from the
Mg_2-sigma relation indicates that the thickness of these relations cannot be
ascribed only to age or metallicity effects. Due to this metallicity
independence, the small scatter of the near-infrared FP excludes a model in
which age and metallicity effects ``conspire'' to keep the optical FP thin. All
of these results suggest that the possible physical origins of the FP relations
are complicated due to combined effects of variations of stellar populations
and structural parameters among elliptical galaxies.Comment: to appear in The Astronomical Journal; 35 pages, including 13
Postscript figures and 1 table; uses AAS LaTeX style file
Composition Mixing during Blue Straggler Formation and Evolution
We use smoothed-particle hydrodynamics to examine differences between direct
collisions of single stars and binary star mergers in their roles as possible
blue straggler star formation mechanisms. We find in all cases that core helium
in the progenitor stars is largely retained in the core of the remnant, almost
independent of the type of interaction or the central concentration of the
progenitor stars.
We have also modelled the subsequent evolution of the hydrostatic remnants,
including mass loss and energy input from the hydrodynamical interaction. The
combination of the hydrodynamical and hydrostatic models enables us to predict
that little mixing will occur during the merger of two globular cluster stars
of equal mass. In contrast to the results of Proctor Sills, Bailyn, & Demarque
(1995), we find that neither completely mixed nor unmixed models can match the
absolute colors of observed blue stragglers in NGC 6397 at all luminosity
levels. We also find that the color distribution is probably the crucial test
for explanations of BSS formation - if stellar collisions or mergers are the
correct mechanisms, a large fraction of the lifetime of the straggler must be
spent away from the main sequence. This constraint appears to rule out the
possibility of completely mixed models. For NGC 6397, unmixed models predict
blue straggler lifetimes ranging from about 0.1 to 4 Gyr, while completely
mixed models predict a range from about 0.6 to 4 Gyr.Comment: AASTeX, 28 pg., accepted for ApJ, also available at
http://ucowww.ucsc.edu/~erics/bspaper.htm
Entanglement and Timing-Based Mechanisms in the Coherent Control of Scattering Processes
The coherent control of scattering processes is considered, with electron
impact dissociation of H used as an example. The physical mechanism
underlying coherently controlled stationary state scattering is exposed by
analyzing a control scenario that relies on previously established entanglement
requirements between the scattering partners. Specifically, initial state
entanglement assures that all collisions in the scattering volume yield the
desirable scattering configuration. Scattering is controlled by preparing the
particular internal state wave function that leads to the favored collisional
configuration in the collision volume. This insight allows coherent control to
be extended to the case of time-dependent scattering. Specifically, we identify
reactive scattering scenarios using incident wave packets of translational
motion where coherent control is operational and initial state entanglement is
unnecessary. Both the stationary and time-dependent scenarios incorporate
extended coherence features, making them physically distinct. From a
theoretical point of view, this work represents a large step forward in the
qualitative understanding of coherently controlled reactive scattering. From an
experimental viewpoint, it offers an alternative to entanglement-based control
schemes. However, both methods present significant challenges to existing
experimental technologies
Corrigendum: Determinants of Non-paid Task Division in Gay-, Lesbian-, and Heterosexual-Parent Families With Infants Conceived Using Artificial Reproductive Techniques.
[This corrects the article DOI: 10.3389/fpsyg.2020.00914.]
SMA Observations of Class 0 Protostars: A High-Angular Resolution Survey of Protostellar Binary Systems
We present high angular resolution 1.3 mm and 850 um dust continuum data
obtained with the Submillimeter Array toward 33 Class 0 protostars in nearby
clouds (distance < 500 pc), which represents so far the largest survey toward
protostellar binary/multiple systems. The median angular resolution in the
survey is 2.5 arcsec, while the median linear resolution is approximately 600
AU. Compact dust continuum emission is observed from all sources in the sample.
Twenty-one sources in the sample show signatures of binarity/multiplicity, with
separations ranging from 50 to 5000 AU. The numbers of singles, binaries,
triples, and quadruples in the sample are 12, 14, 5, and 2, respectively. The
derived multiplicity frequency (MF) and companion star fraction (CSF) for Class
0 protostars are 0.64+/-0.08 and 0.91+/-0.05, respectively, with no correction
for completeness. The derived MF and CSF in this survey are approximately two
times higher than the values found in the binary surveys toward Class I YSOs,
and approximately three (for MF) and four (for CSF) times larger than the
values found among MS stars, with a similar range of separations. Furthermore,
the observed fraction of high order multiple systems to binary systems in Class
0 protostars (0.50+/-0.09) is also larger than the fractions found in Class I
YSOs (0.31+/-0.07) and MS stars (< 0.2). These results suggest that binary
properties evolve as protostars evolve, as predicted by numerical simulations.
The distribution of separations for Class 0 protostellar binary systems shows a
general trend in which companion star fraction increases with decreasing
companion separation. We find that 67%+/-8% of the protobinary systems have
circumstellar mass ratios below 0.5, implying that unequal-mass systems are
preferred in the process of binary star formation. We suggest an empirical
sequential fragmentation picture for binary star formation.Comment: 71 pages, 23 figures, to be published by Ap
The u'g'r'i'z' Standard Star Network
We present the 158 standard stars that define the u'g'r'i'z' photometric
system. These stars form the basis for the photometric calibration of the Sloan
Digital Sky Survey (SDSS). The defining instrument system and filters, the
observing process, the reduction techniques, and the software used to create
the stellar network are all described. We briefly discuss the history of the
star selection process, the derivation of a set of transformation equations for
the UBVRcIc system, and plans for future work.Comment: References to URLs in paper have been updated to reflect moved
website. Accepted by AJ. 50 pages, including 20 pages of text, 9 tables, and
15 figures. Plain ASCII text versions of Tables 8 and 9 can be found at
http://home.fnal.gov/~dtucker/ugriz/index.html (new URL
Spatially-resolved electronic and vibronic properties of single diamondoid molecules
Diamondoids are a unique form of carbon nanostructure best described as
hydrogen-terminated diamond molecules. Their diamond-cage structures and
tetrahedral sp3 hybrid bonding create new possibilities for tuning electronic
band gaps, optical properties, thermal transport, and mechanical strength at
the nanoscale. The recently-discovered higher diamondoids (each containing more
than three diamond cells) have thus generated much excitement in regards to
their potential versatility as nanoscale devices. Despite this excitement,
however, very little is known about the properties of isolated diamondoids on
metal surfaces, a very relevant system for molecular electronics. Here we
report the first molecular scale study of individual tetramantane diamondoids
on Au(111) using scanning tunneling microscopy and spectroscopy. We find that
both the diamondoid electronic structure and electron-vibrational coupling
exhibit unique spatial distributions characterized by pronounced line nodes
across the molecular surfaces. Ab-initio pseudopotential density functional
calculations reveal that the observed dominant electronic and vibronic
properties of diamondoids are determined by surface hydrogen terminations, a
feature having important implications for designing diamondoid-based molecular
devices.Comment: 16 pages, 4 figures. to appear in Nature Material
Evaluation of the INCREMENT-CPE, Pitt Bacteremia and qPitt Scores in Patients with Carbapenem-Resistant Enterobacteriaceae Infections Treated with Ceftazidime–Avibactam
Background
The aim of this study was to evaluate the predictive performance of the INCREMENT-CPE (ICS), Pitt bacteremia score (PBS) and qPitt for mortality among patients treated with ceftazidime–avibactam for carbapenem-resistant Enterobacteriaceae (CRE) infections.
Methods
Retrospective, multicenter, cohort study of patients with CRE infections treated with ceftazidime–avibactam between 2015 and 2019. The primary outcome was 30-day all-cause mortality. Predictive performance was determined by assessing discrimination, calibration and precision.
Results
In total, 109 patients were included. Thirty-day mortality occurred in 18 (16.5%) patients. There were no significant differences in discrimination of the three scores [area under the curve (AUC) ICS 0.7039, 95% CI 0.5848–0.8230, PBS 0.6893, 95% CI 0.5709–0.8076, and qPitt 0.6847, 95% CI 0.5671–0.8023; P > 0.05 all pairwise comparisons]. All scores showed adequate calibration and precision. When dichotomized at the optimal cut-points of 11, 3, and 2 for the ICS, PBS, and qPitt, respectively, all scores had NPV > 90% at the expense of low PPV. Patients in the high-risk groups had a relative risk for mortality of 3.184 (95% CI 1.35–8.930), 3.068 (95% CI 1.094–8.606), and 2.850 (95% CI 1.016–7.994) for the dichotomized ICS, PBS, and qPitt, scores respectively. Treatment-related variables (early active antibiotic therapy, combination antibiotics and renal ceftazidime–avibactam dose adjustment) were not associated with mortality after controlling for the risk scores.
Conclusions
In patients treated with ceftazidime–avibactam for CRE infections, mortality risk scores demonstrated variable performance. Modifications to scoring systems to more accurately predict outcomes in the era of novel antibiotics are warranted
Sloan Digital Sky Survey Imaging of Low Galactic Latitude Fields: Technical Summary and Data Release
The Sloan Digital Sky Survey (SDSS) mosaic camera and telescope have obtained
five-band optical-wavelength imaging near the Galactic plane outside of the
nominal survey boundaries. These additional data were obtained during
commissioning and subsequent testing of the SDSS observing system, and they
provide unique wide-area imaging data in regions of high obscuration and star
formation, including numerous young stellar objects, Herbig-Haro objects and
young star clusters. Because these data are outside the Survey regions in the
Galactic caps, they are not part of the standard SDSS data releases. This paper
presents imaging data for 832 square degrees of sky (including repeats), in the
star-forming regions of Orion, Taurus, and Cygnus. About 470 square degrees are
now released to the public, with the remainder to follow at the time of SDSS
Data Release 4. The public data in Orion include the star-forming region NGC
2068/NGC 2071/HH24 and a large part of Barnard's loop.Comment: 31 pages, 9 figures (3 missing to save space), accepted by AJ, in
press, see http://photo.astro.princeton.edu/oriondatarelease for data and
paper with all figure
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