656 research outputs found
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
Diagnostic Stewardship: A Clinical Decision Rule for Blood Cultures in Community-Onset Methicillin-Resistant Staphylococcus aureus (MRSA) Skin and Soft Tissue Infections
INTRODUCTION: The emergence, spread and persistence of methicillin-resistant Staphylococcus aureus (MRSA) as a causative pathogen in community-onset (CO) skin and soft tissue infections (SSTIs) have resulted in substantial changes in the management of these infections. The indications for obtaining blood cultures in patients with CO-MRSA SSTIs remain poorly defined. The objectives of this study were to derive and validate a clinical decision rule that predicts the probability of MRSA bacteremia in CO-MRSA SSTIs and to identify a low-risk population for whom blood cultures may be safely omitted.
METHODS: This was a retrospective, case-control study with an internal temporal validation cohort conducted at two large urban academic medical centers. Hospitalized adults with CO-MRSA SSTI between 2010 and 2018 were included. Independent predictors of MRSA bacteremia were identified through multivariable logistic regression. A decision rule was derived using weighted coefficient-based scoring. The decision rule was validated in an internal temporal validation cohort.
RESULTS: A total of 307 patients (155 cases and 152 controls) were included in the derivation cohort. A decision rule was created with a major criterion defined as purulent cellulitis and minor criteria defined as abnormal temperature, intravenous drug use, leukocytosis, tachycardia, body mass index \u3câ25 kg/m
CONCLUSION: The decision rule developed and validated in this study provides a standardized, evidenced-based approach to determine the need for blood cultures based on bacteremia risk
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
A Multicenter Evaluation of Vancomycin-Associated Acute Kidney Injury in Hospitalized Patients with Acute Bacterial Skin and Skin Structure Infections
BACKGROUND: We sought to determine the real-world incidence of and risk factors for vancomycin-associated acute kidney injury (V-AKI) in hospitalized adults with acute bacterial skin and skin structure infections (ABSSSI).
METHODS: Retrospective, observational, cohort study at ten U.S. medical centers between 2015 and 2019. Hospitalized patients treated with vancomycin (â„â72 h) for ABSSSI and â„âone baseline AKI risk factor were eligible. Patients with end-stage kidney disease, on renal replacement therapy or AKI at baseline, were excluded. The primary outcome was V-AKI by the vancomycin guidelines criteria.
RESULTS: In total, 415 patients were included. V-AKI occurred in 39 (9.4%) patients. Independent risk factors for V-AKI were: chronic alcohol abuse (aOR 4.710, 95% CI 1.929-11.499), no medical insurance (aOR 3.451, 95% CI 1.310-9.090), ICU residence (aOR 4.398, 95% CI 1.676-11.541), Gram-negative coverage (aOR 2.926, 95% CI 1.158-7.392) and vancomycin duration (aOR 1.143, 95% CI 1.037-1.260). Based on infection severity and comorbidities, 34.7% of patients were candidates for oral antibiotics at baseline and 39.3% had non-purulent cellulitis which could have been more appropriately treated with a beta-lactam. Patients with V-AKI had significantly longer hospital lengths of stay (9 vs. 6 days, pâ=â0.001), higher 30-day readmission rates (30.8 vs. 9.0%, pâ\u3câ0.001) and increased all-cause 30-day mortality (5.1 vs. 0.3%, pâ=â0.024) CONCLUSIONS: V-AKI occurred in approximately one in ten ABSSSI patients and may be largely prevented by preferential use of oral antibiotics whenever possible, using beta-lactams for non-purulent cellulitis and limiting durations of vancomycin therapy
Dirichlet fundamental domains and complex-projective varieties
We prove that for every finitely-presented group G there exists a
2-dimensional irreducible complex-projective variety W with the fundamental
group G, so that all singularities of W are normal crossings and Whitney
umbrellas.Comment: 1 figur
The Fifth Data Release of the Sloan Digital Sky Survey
This paper describes the Fifth Data Release (DR5) of the Sloan Digital Sky
Survey (SDSS). DR5 includes all survey quality data taken through June 2005 and
represents the completion of the SDSS-I project (whose successor, SDSS-II will
continue through mid-2008). It includes five-band photometric data for 217
million objects selected over 8000 square degrees, and 1,048,960 spectra of
galaxies, quasars, and stars selected from 5713 square degrees of that imaging
data. These numbers represent a roughly 20% increment over those of the Fourth
Data Release; all the data from previous data releases are included in the
present release. In addition to "standard" SDSS observations, DR5 includes
repeat scans of the southern equatorial stripe, imaging scans across M31 and
the core of the Perseus cluster of galaxies, and the first spectroscopic data
from SEGUE, a survey to explore the kinematics and chemical evolution of the
Galaxy. The catalog database incorporates several new features, including
photometric redshifts of galaxies, tables of matched objects in overlap regions
of the imaging survey, and tools that allow precise computations of survey
geometry for statistical investigations.Comment: ApJ Supp, in press, October 2007. This paper describes DR5. The SDSS
Sixth Data Release (DR6) is now public, available from http://www.sdss.or
The Updated Zwicky Catalog (UZC)
The Zwicky Catalog of galaxies (ZC), with m_Zw<=15.5mag, has been the basis
for the Center for Astrophysics (CfA) redshift surveys. To date, analyses of
the ZC and redshift surveys based on it have relied on heterogeneous sets of
galaxy coordinates and redshifts. Here we correct some of the inadequacies of
previous catalogs by providing: (1) coordinates with <~2 arcsec errors for all
of the Nuzc catalog galaxies, (2) homogeneously estimated redshifts for the
majority (98%) of the data taken at the CfA (14,632 spectra), and (3) an
estimate of the remaining "blunder" rate for both the CfA redshifts and for
those compiled from the literature. For the reanalyzed CfA data we include a
calibrated, uniformly determined error and an indication of the presence of
emission lines in each spectrum. We provide redshifts for 7,257 galaxies in the
CfA2 redshift survey not previously published; for another 5,625 CfA redshifts
we list the remeasured or uniformly re-reduced value. Among our new
measurements, Nmul are members of UZC "multiplets" associated with the original
Zwicky catalog position in the coordinate range where the catalog is 98%
complete. These multiplets provide new candidates for examination of tidal
interactions among galaxies. All of the new redshifts correspond to UZC
galaxies with properties recorded in the CfA redshift compilation known as
ZCAT. About 1,000 of our new measurements were motivated either by inadequate
signal-to-noise in the original spectrum or by an ambiguous identification of
the galaxy associated with a ZCAT redshift. The redshift catalog we include
here is ~96% complete to m_Zw<=15.5, and ~98% complete (12,925 galaxies out of
a total of 13,150) for the RA(1950) ranges [20h--4h] and [8h--17h] and
DEC(1950) range [-2.5d--50d]. (abridged)Comment: 34 pp, 7 figs, PASP 1999, 111, 43
The Sloan Digital Sky Survey Quasar Lens Search. III. Constraints on Dark Energy from the Third Data Release Quasar Lens Catalog
We present cosmological results from the statistics of lensed quasars in the
Sloan Digital Sky Survey (SDSS) Quasar Lens Search. By taking proper account of
the selection function, we compute the expected number of quasars lensed by
early-type galaxies and their image separation distribution assuming a flat
universe, which is then compared with 7 lenses found in the SDSS Data Release 3
to derive constraints on dark energy under strictly controlled criteria. For a
cosmological constant model (w=-1) we obtain
\Omega_\Lambda=0.74^{+0.11}_{-0.15}(stat.)^{+0.13}_{-0.06}(syst.). Allowing w
to be a free parameter we find
\Omega_M=0.26^{+0.07}_{-0.06}(stat.)^{+0.03}_{-0.05}(syst.) and
w=-1.1\pm0.6(stat.)^{+0.3}_{-0.5}(syst.) when combined with the constraint from
the measurement of baryon acoustic oscillations in the SDSS luminous red galaxy
sample. Our results are in good agreement with earlier lensing constraints
obtained using radio lenses, and provide additional confirmation of the
presence of dark energy consistent with a cosmological constant, derived
independently of type Ia supernovae.Comment: 9 pages, 3 figures, 2 tables, accepted for publication in A
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