157 research outputs found
The Spitzer c2d Survey of Nearby Dense Cores: Jet and Molecular Outflow Associated with a YSO in core A of L1251
A long infrared jet has been discovered by the Spitzer c2d legacy program in
core A of L1251. It is associated with a very embedded Class 0 object with an
accretion luminosity of about 0.9 Lsun derived by radiative transfer model
fitting to the observed SED. Comparing the observed IRAC colors along the
infrared jet with those calculated from a model of an admixture of gas with a
power-law temperature distribution indicates that the jet is possibly created
by a paraboloidal bow shock propagating into the ambient medium of n(H_2)=10^5
cm^{-3}. In addition, the variation of the power-law index along the jet
suggests that the portion of hot gas decreases with distance from the jet
engine. The molecular outflow in this region has been mapped for the first time
using CO data. From the calculated outflow momentum flux, a very strong lower
limit to the average accretion luminosity is 3.6 sin i/cos^3 i Lsun, indicative
of a decrease in the accretion rate with time.Comment: To appear in ApJ Letter
The Effects of Culture and Structure on Strategic Flexibility During Business Model Innovation
Herschel observations of the Herbig-Haro objects HH52-54
We are aiming at the observational estimation of the relative contribution to
the cooling by CO and H2O, as this provides decisive information for the
understanding of the oxygen chemistry behind interstellar shock waves. Methods.
The high sensitivity of HIFI, in combination with its high spectral resolution
capability, allows us to trace the H2O outflow wings at unprecedented
signal-to-noise. From the observation of spectrally resolved H2O and CO lines
in the HH52-54 system, both from space and from ground, we arrive at the
spatial and velocity distribution of the molecular outflow gas. Solving the
statistical equilibrium and non-LTE radiative transfer equations provides us
with estimates of the physical parameters of this gas, including the cooling
rate ratios of the species. The radiative transfer is based on an ALI code,
where we use the fact that variable shock strengths, distributed along the
front, are naturally implied by a curved surface. Based on observations of CO
and H2O spectral lines, we conclude that the emission is confined to the HH54
region. The quantitative analysis of our observations favours a ratio of the
CO-to-H2O-cooling-rate >> 1. From the best-fit model to the CO emission, we
arrive at an H2O abundance close to 1e-5. The line profiles exhibit two
components, one of which is triangular and another, which is a superposed,
additional feature. This additional feature likely originates from a region
smaller than the beam where the ortho-water abundance is smaller than in the
quiescent gas. Comparison with recent shock models indicate that a planar shock
can not easily explain the observed line strengths and triangular line
profiles.We conclude that the geometry can play an important role. Although
abundances support a scenario where J-type shocks are present, higher cooling
rate ratios than predicted by these type of shocks are derived.Comment: Accepted for publication in A&
A Chandra Study of the Rosette Star-Forming Complex. II. Clusters in the Rosette Molecular Cloud
We explore here the young stellar populations in the Rosette Molecular Cloud
(RMC) region with high spatial resolution X-ray images from the Chandra X-ray
Observatory, which are effective in locating weak-lined T Tauri stars as well
as disk-bearing young stars. A total of 395 X-ray point sources are detected,
299 of which (76%) have an optical or near-infrared (NIR) counterpart
identified from deep FLAMINGOS images. From X-ray and mass sensitivity limits,
we infer a total population of about 1700 young stars in the survey region.
Based on smoothed stellar surface density maps, we investigate the spatial
distribution of the X-ray sources and define three distinctive structures and
substructures within them. Structures B and C are associated with previously
known embedded IR clusters, while structure A is a new X-ray-identified
unobscured cluster. A high mass protostar RMCX #89 = IRAS 06306+0437 and its
associated sparse cluster is studied. The different subregions are not coeval
but do not show a simple spatial-age pattern. Disk fractions vary between
subregions and are generally 20% of the total stellar population inferred from
the X-ray survey. The data are consistent with speculations that triggered star
formation around the HII region is present in the RMC, but do not support a
simple sequential triggering process through the cloud interior. While a
significant fraction of young stars are located in a distributed population
throughout the RMC region, it is not clear they originated in clustered
environments.Comment: Accepted to the Astrophysical Journal. 49 pages, 12 figures. For a
version with high-quality figures, see
http://www.astro.psu.edu/users/edf/RMC_accepted.pd
The Fourteenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the extended Baryon Oscillation Spectroscopic Survey and from the second phase of the Apache Point Observatory Galactic Evolution Experiment
The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) has been in
operation since July 2014. This paper describes the second data release from
this phase, and the fourteenth from SDSS overall (making this, Data Release
Fourteen or DR14). This release makes public data taken by SDSS-IV in its first
two years of operation (July 2014-2016). Like all previous SDSS releases, DR14
is cumulative, including the most recent reductions and calibrations of all
data taken by SDSS since the first phase began operations in 2000. New in DR14
is the first public release of data from the extended Baryon Oscillation
Spectroscopic Survey (eBOSS); the first data from the second phase of the
Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE-2),
including stellar parameter estimates from an innovative data driven machine
learning algorithm known as "The Cannon"; and almost twice as many data cubes
from the Mapping Nearby Galaxies at APO (MaNGA) survey as were in the previous
release (N = 2812 in total). This paper describes the location and format of
the publicly available data from SDSS-IV surveys. We provide references to the
important technical papers describing how these data have been taken (both
targeting and observation details) and processed for scientific use. The SDSS
website (www.sdss.org) has been updated for this release, and provides links to
data downloads, as well as tutorials and examples of data use. SDSS-IV is
planning to continue to collect astronomical data until 2020, and will be
followed by SDSS-V.Comment: SDSS-IV collaboration alphabetical author data release paper. DR14
happened on 31st July 2017. 19 pages, 5 figures. Accepted by ApJS on 28th Nov
2017 (this is the "post-print" and "post-proofs" version; minor corrections
only from v1, and most of errors found in proofs corrected
Serum 25-hydroxyvitamin D is inversely associated with body mass index in cancer
<p>Abstract</p> <p>Background</p> <p>The association between vitamin D deficiency and obesity in healthy populations and different disease states remains unsettled with studies reporting conflicting findings. Moreover, current dietary recommendations for vitamin D do not take into account a person's body mass index (BMI). We investigated the relationship between serum 25-hydroxy-vitamin D [25(OH)D] and BMI in cancer.</p> <p>Methods</p> <p>A consecutive case series of 738 cancer patients. Serum 25(OH)D was measured at presentation to the hospital. The cohort was divided into 4 BMI groups (underweight: <18.5, normal weight: 18.5-24.9, overweight: 25-29.9, and obese: >30.0 kg/m<sup>2</sup>). Mean 25(OH)D was compared across the 4 BMI groups using ANOVA. Linear regression was used to quantify the relationship between BMI and 25(OH)D.</p> <p>Results</p> <p>303 were males and 435 females. Mean age at diagnosis was 55.6 years. The mean BMI was 27.9 kg/m<sup>2 </sup>and mean serum 25(OH)D was 21.9 ng/ml. Most common cancers were lung (134), breast (131), colorectal (97), pancreas (86) and prostate (45). Obese patients had significantly lower serum 25(OH)D levels (17.9 ng/ml) as compared to normal weight (24.6 ng/ml) and overweight (22.8 ng/ml) patients; p < 0.001. After adjusting for age, every 1 kg/m<sup>2 </sup>increase in BMI was significantly associated with 0.42 ng/ml decline in serum 25(OH)D levels.</p> <p>Conclusions</p> <p>Obese cancer patients (BMI >= 30 kg/m<sup>2</sup>) had significantly lower levels of serum 25(OH)D as compared to non-obese patients (BMI <30 kg/m<sup>2</sup>). BMI should be taken into account when assessing a patient's vitamin D status and more aggressive vitamin D supplementation should be considered in obese cancer patients.</p
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Social Media and Depressive Symptoms in Childhood and Adolescence: A Systematic Review
Concerns are increasingly raised in academic and lay literature about the impact of the internet on young people’s well-being. This systematic review examined empirical research on the relationship between social media use and depressive symptoms in the child and adolescent population. A systematic search of Medline, PsycInfo and Embase databases yielded eleven eligible studies. Relevant results were extracted from each study, with a total sample of 12,646. Analysis revealed a small but statistically significant correlation between social media use and depressive symptoms in young people. However, studies varied widely in methods, sample size and results, making the clinical significance of these findings nuanced. Over half of the studies were cross-sectional, while those of longitudinal design were of limited duration. This review justifies further investigation of this phenomenon, with a need for consensus on variables and measurement
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