72 research outputs found
A young double stellar cluster in a HII region, emerging from its parent molecular cloud
We report the properties of a new young double stellar cluster in the region
towards IRAS 07141-0920 contained in the HII region Sh2-294. High-resolution
optical UBVRI and Halpha images, near-infrared JHKs and H2 filter images were
used to make photometric and morphological studies of the point sources and the
nebula seen towards Sh2-294. The optical images reveal an emission nebula with
very rich morphological details, composed mainly of UV scattered light and of
Halpha emission. Contrasting with the bright parts of the nebula, opaque,
elongated patches are seen. Our optical photometry confirms that the
illuminator of the nebula is likely to be a B0.5V star located at a distance of
about 3.2 kpc. Our near-IR images reveal an embedded cluster, extending for
about 2 pc and exhibiting sub-clustering: a denser, more condensed, sub-cluster
surrounding the optical high-mass B0.5V illuminator star; and a more embedded,
optically invisible, sub-cluster located towards the eastern, dark part of the
nebula and including the luminous MSX source G224.1880+01.2407, a massive
protostellar candidate that could be the origin of jets and extended features
seen at 2.12 micron. The double cluster appears to be clearing the remaining
molecular material of the parent cloud, creating patches of lower extinction
and allowing some of the least reddened members to be detected in the optical
images. We find 12 MS and 143 PMS members using 3 different methods: comparison
with isochrones in optical colour-magnitude diagrams, detection of near-IR
excess, and presence of Halpha emission. The most massive star fits a 4 Myr
post-MS isochrone. The age of the optically selected PMS population is
estimated to be 7-8 Myr. The IR-excess population shows sub-clustering on
scales as small as 0.23 pc and is probably much younger.Comment: 15 pages, 16 figure
A Sample of Intermediate-Mass Star-Forming Regions: Making Stars at Mass Column Densities <1 g/cm^2
In an effort to understand the factors that govern the transition from low-
to high-mass star formation, we identify for the first time a sample of
intermediate-mass star-forming regions (IM SFRs) where stars up to - but not
exceeding - 8 solar masses are being produced. We use IRAS colors and Spitzer
Space Telescope mid-IR images, in conjunction with millimeter continuum and CO
maps, to compile a sample of 50 IM SFRs in the inner Galaxy. These are likely
to be precursors to Herbig AeBe stars and their associated clusters of low-mass
stars. IM SFRs constitute embedded clusters at an early evolutionary stage akin
to compact HII regions, but they lack the massive ionizing central star(s). The
photodissociation regions that demarcate IM SFRs have typical diameters of ~1
pc and luminosities of ~10^4 solar luminosities, making them an order of
magnitude less luminous than (ultra)compact HII regions. IM SFRs coincide with
molecular clumps of mass ~10^3 solar masses which, in turn, lie within larger
molecular clouds spanning the lower end of the giant molecular cloud mass
range, 10^4-10^5 solar masses. The IR luminosity and associated molecular mass
of IM SFRs are correlated, consistent with the known luminosity-mass
relationship of compact HII regions. Peak mass column densities within IM SFRs
are ~0.1-0.5 g/cm^2, a factor of several lower than ultra-compact HII regions,
supporting the proposition that there is a threshold for massive star formation
at ~1 g/cm^2.Comment: 61 pages, 6 tables, 20 figures. Accepted for publication in the
Astronomical Journa
The CCAT-Prime Submillimeter Observatory
The Cerro Chajnantor Atacama Telescope-prime (CCAT-prime) is a new 6-m,
off-axis, low-emissivity, large field-of-view submillimeter telescope scheduled
for first light in the last quarter of 2021. In summary, (a) CCAT-prime
uniquely combines a large field-of-view (up to 8-deg), low emissivity telescope
(< 2%) and excellent atmospheric transmission (5600-m site) to achieve
unprecedented survey capability in the submillimeter. (b) Over five years,
CCAT-prime first generation science will address the physics of star formation,
galaxy evolution, and galaxy cluster formation; probe the re-ionization of the
Universe; improve constraints on new particle species; and provide for improved
removal of dust foregrounds to aid the search for primordial gravitational
waves. (c) The Observatory is being built with non-federal funds (~ \$40M in
private and international investments). Public funding is needed for
instrumentation (~ \$8M) and operations (\$1-2M/yr). In return, the community
will be able to participate in survey planning and gain access to curated data
sets. (d) For second generation science, CCAT-prime will be uniquely positioned
to contribute high-frequency capabilities to the next generation of CMB surveys
in partnership with the CMB-S4 and/or the Simons Observatory projects or
revolutionize wide-field, sub-millimetter line intensity mapping surveys.Comment: Astro2020 APC White Pape
Low and intermediate mass star yields: The evolution of carbon abundances
We present a set of low and intermediate mass star yields based on a modeling
of the TP--AGB phase which affects the production of nitrogen and carbon. These
yields are evaluated by using them in a Galaxy Chemical Evolution model, with
which we analyze the evolution of carbon abundances. By comparing the results
with those obtained with other yield sets, and with a large amount of
observational data, we conclude that the model using these yields combined with
those from Woosley & Weaver (1995) for massive stars properly reproduce all the
data. The model reproduces well the increase of C/O with increasing O/H
abundances. Since these massive star yields do not include winds, it implies
that these stellar winds might have a smoother dependence on metallicity than
usually assumed and that a significant quantity of carbon proceeds from LIM
stars.Comment: 21 pages, 11 figures. To be published in Astronomy and Astrophysic
Accuracy of Capsule Colonoscopy in Detecting Colorectal Polyps in a Screening Population
BACKGROUND & AIMS: Capsule colonoscopy is a minimally invasive imaging method. We measured the accuracy of this technology in detecting polyps 6 mm or larger in an average-risk screening population.
METHODS: In a prospective study, asymptomatic subjects (n = 884) underwent capsule colonoscopy followed by conventional colonoscopy (the reference) several weeks later, with an endoscopist blinded to capsule results, at 10 centers in the United States and 6 centers in Israel from June 2011 through April 2012. An unblinded colonoscopy was performed on subjects found to have lesions 6 mm or larger by capsule but not conventional colonoscopy.
RESULTS: Among the 884 subjects enrolled, 695 (79%) were included in the analysis of capsule performance for all polyps. There were 77 exclusions (9%) for inadequate cleansing and whole-colon capsule transit time fewer than 40 minutes, 45 exclusions (5%) before capsule ingestion, 15 exclusions (2%) after ingestion and before colonoscopy, and 15 exclusions (2%) for site termination. Capsule colonoscopy identified subjects with 1 or more polyps 6 mm or larger with 81% sensitivity (95% confidence interval [CI], 77%-84%) and 93% specificity (95% CI, 91%-95%), and polyps 10 mm or larger with 80% sensitivity (95% CI, 74%-86%) and 97% specificity (95% CI, 96%-98%). Capsule colonoscopy identified subjects with 1 or more conventional adenomas 6 mm or larger with 88% sensitivity (95% CI, 82%-93) and 82% specificity (95% CI, 80%-83%), and 10 mm or larger with 92% sensitivity (95% CI, 82%-97%) and 95% specificity (95% CI, 94%-95%). Sessile serrated polyps and hyperplastic polyps accounted for 26% and 37%, respectively, of false-negative findings from capsule analyses.
CONCLUSIONS: In an average-risk screening population, technically adequate capsule colonoscopy identified individuals with 1 or more conventional adenomas 6 mm or larger with 88% sensitivity and 82% specificity. Capsule performance seems adequate for patients who cannot undergo colonoscopy or who had incomplete colonoscopies. Additional studies are needed to improve capsule detection of serrated lesions. Clinicaltrials.gov number: NCT01372878
Institutional investors and corporate governance
We provide a comprehensive overview of the role of institutional investors in corporate governance with three main components. First, we establish new stylized facts documenting the evolution and importance of institutional ownership. Second, we provide a detailed characterization of key aspects of the legal and regulatory setting within which institutional investors govern portfolio firms. Third, we synthesize the evolving response of the recent theoretical and empirical academic literature in finance to the emergence of institutional investors in corporate governance. We highlight how the defining aspect of institutional investors – the fact that they are financial intermediaries – differentiates them in their governance role from standard principal blockholders. Further, not all institutional investors are identical, and we pay close attention to heterogeneity amongst institutional investors as blockholders
Comorbidities and Malignancy among NAFLD Patients Compared to the General Population, A Nation-Based Study
(1) Background: Non-alcoholic fatty liver disease (NAFLD) is a common liver disease. Aims: We aimed to investigate the frequency of comorbidities and malignancies among NAFLD patients compared to the general population. (2) Methods: A retrospective study included adult patients with a NAFLD diagnosis. A control group was matched for age and gender. Demographics, comorbidities, malignancies, and mortality were collected and compared. (3) Results: 211,955 NAFLD patients were analyzed in comparison to 452,012 matched general population controls. Significantly higher rates of diabetes mellitus (23.2% vs. 13.3%), obesity (58.8% vs. 27.8%), hypertension (57.2% vs. 39.9%), chronic ischemic heart disease (24.7% vs. 17.3%), and CVA (3.2% vs. 2.8%) were found among NAFLD patients. Patients with NAFLD had significantly higher rates of the following malignancies: prostate cancer (1.6% vs. 1.2%), breast cancer (2.6% vs. 1.9%), colorectal cancer (1.8% vs. 1.4%), uterine cancer (0.4 vs. 0.2%), kidney cancer (0.8% vs. 0.5%), but a lower rate of lung cancer (0.9% vs. 1.2%) and stomach cancer (0.3% vs. 0.4%). The all-cause mortality rate among NAFLD patients was significantly lower in comparison to the general population (10.8% vs. 14.7%, p < 0.001). (4) Conclusions: Higher rates of comorbidities and malignancies among NAFLD patients were observed, but a lower rate of all-cause mortality was found
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