362 research outputs found
Hypervelocity Star Candidates in the SEGUE G & K Dwarf Sample
We present 20 candidate hypervelocity stars from the Sloan Extension for
Galactic Understanding and Exploration (SEGUE) G and K dwarf samples. Previous
searches for hypervelocity stars have only focused on large radial velocities;
in this study we also use proper motions to select the candidates. We determine
the hypervelocity likelihood of each candidate by means of Monte Carlo
simulations, considering the significant errors often associated with high
proper motion stars. We find that nearly half of the candidates exceed their
escape velocities with at least 98% probability. Every candidate also has less
than a 25% chance of being a high-velocity fluke within the SEGUE sample. Based
on orbits calculated using the observed six-dimensional positions and
velocities, few, if any, of these candidates originate from the Galactic
center. If these candidates are truly hypervelocity stars, they were not
ejected by interactions with the Milky Way's supermassive black hole. This
calls for a more serious examination of alternative hypervelocity-star ejection
scenarios.Comment: 8 pages, 5 figures, published in ApJ, this version includes all
figures as intende
Chemical Cartography with APOGEE: Large-scale Mean Metallicity Maps of the Milky Way
We present Galactic mean metallicity maps derived from the first year of the
SDSS-III APOGEE experiment. Mean abundances in different zones of
Galactocentric radius (0 < R < 15 kpc) at a range of heights above the plane (0
< |z| < 3 kpc), are derived from a sample of nearly 20,000 stars with
unprecedented coverage, including stars in the Galactic mid-plane at large
distances. We also split the sample into subsamples of stars with low and
high-[{\alpha}/M] abundance ratios. We assess possible biases in deriving the
mean abundances, and find they are likely to be small except in the inner
regions of the Galaxy. A negative radial gradient exists over much of the
Galaxy; however, the gradient appears to flatten for R < 6 kpc, in particular
near the Galactic mid-plane and for low-[{\alpha}/M] stars. At R > 6 kpc, the
gradient flattens as one moves off of the plane, and is flatter at all heights
for high-[{\alpha}/M] stars than for low-[{\alpha}/M] stars. Alternatively,
these gradients can be described as vertical gradients that flatten at larger
Galactocentric radius; these vertical gradients are similar for both low and
high-[{\alpha}/M] populations. Stars with higher [{\alpha}/M] appear to have a
flatter radial gradient than stars with lower [{\alpha}/M]. This could suggest
that the metallicity gradient has grown steeper with time or, alternatively,
that gradients are washed out over time by migration of stars.Comment: 16 pages, 12 figures, submitted to A
The Metallicity Distribution Functions of SEGUE G and K dwarfs: Constraints for Disk Chemical Evolution and Formation
We present the metallicity distribution function (MDF) for 24,270 G and
16,847 K dwarfs at distances from 0.2 to 2.3 kpc from the Galactic plane, based
on spectroscopy from the Sloan Extension for Galactic Understanding and
Exploration (SEGUE) survey. This stellar sample is significantly larger in both
number and volume than previous spectroscopic analyses, which were limited to
the solar vicinity, making it ideal for comparison with local volume-limited
samples and Galactic models. For the first time, we have corrected the MDF for
the various observational biases introduced by the SEGUE target selection
strategy. The SEGUE sample is particularly notable for K dwarfs, which are too
faint to examine spectroscopically far from the solar neighborhood. The MDF of
both spectral types becomes more metal-poor with increasing |Z|, which reflects
the transition from a sample with small [alpha/Fe] values at small heights to
one with enhanced [alpha/Fe] above 1 kpc. Comparison of our SEGUE distributions
to those of two different Milky Way models reveals that both are more
metal-rich than our observed distributions at all heights above the plane. Our
unbiased observations of G and K dwarfs provide valuable constraints over the
|Z|-height range of the Milky Way disk for chemical and dynamical Galaxy
evolution models, previously only calibrated to the solar neighborhood, with
particular utility for thin- and thick-disk formation models.Comment: 70 pages, 25 figures, 7 tables. Accepted by The Astrophysical Journa
A Short Scale Length for the \alpha-Enhanced Thick Disk of the Milky Way: Evidence from Low-Latitude SEGUE Data
We examine the \alpha-element abundance ratio, [\alpha/Fe], of 5620 stars,
observed by the Sloan Extension for Galactic Understanding and Exploration
survey in the region 6 kpc < R < 16 kpc, 0.15 kpc < |Z| < 1.5 kpc, as a
function of Galactocentric radius R and distance from the Galactic plane |Z|.
Our results show that the high-\alpha\ thick disk population has a short scale
length (L_thick ~ 1.8 kpc) compared to the low-\alpha population, which is
typically associated with the thin disk. We find that the fraction of
high-\alpha\ stars in the inner disk increases at large |Z|, and that
high-\alpha\ stars lag in rotation compared to low-\alpha\ stars. In contrast,
the fraction of high-\alpha\ stars in the outer disk is low at all |Z|, and
high- and low-\alpha\ stars have similar rotational velocities up to 1.5 kpc
from the plane. We interpret these results to indicate that different processes
were responsible for the high-\alpha\ populations in the inner and outer disk.
The high-\alpha\ population in the inner disk has a short scale length and
large scale height, consistent with a scenario in which the thick disk forms
during an early gas-rich accretion phase. Stars far from the plane in the outer
disk may have reached their current locations through heating by minor mergers.
The lack of high-\alpha\ stars at large R and |Z| also places strict
constraints on the strength of radial migration via transient spiral structure.Comment: 14 pages, 7 figures, accepted to The Astrophysical Journa
Annual cycles are the most common reproductive strategy in African tropical tree communities
Abstract We present the first crossâcontinental comparison of the flowering and fruiting phenology of tropical forests across Africa. Flowering events of 5446 trees from 196 species across 12 sites and fruiting events of 4595 trees from 191 species across 11 sites were monitored over periods of 6 to 29Â years and analyzed to describe phenology at the continental level. To study phenology, we used Fourier analysis to identify the dominant cycles of flowering and fruiting for each individual tree and we identified the time of year African trees bloom and bear fruit and their relationship to local seasonality. Reproductive strategies were diverse, and no single regular cycle was found in >50% of individuals across all 12 sites. Additionally, we found annual flowering and fruiting cycles to be the most common. Subâannual cycles were the next most common for flowering, whereas supraâannual patterns were the next most common for fruiting. We also identify variation in different subsets of species, with species exhibiting mainly annual cycles most common in West and West Central African tropical forests, while more species at sites in East Central and East African forests showed cycles ranging from subâannual to supraâannual. Despite many trees showing strong seasonality, at most sites some flowering and fruiting occurred all year round. Environmental factors with annual cycles are likely to be important drivers of seasonal periodicity in trees across Africa, but proximate triggers are unlikely to be constant across the continent.Additional co-authors: Roman M. Wittig, Thomas Breuer, Mireille BreuerâNdoundou Hockemba, Crickette M. Sanz, David B. Morgan, Anne E. Pusey, Badru Mugerwa, Baraka Gilagiza, Caroline Tutin, Corneille E. N. Ewango, Douglas Sheil, Edmond Dimoto, FidĂšle Baya, Flort Bujo, Fredrick Ssali, JeanâThoussaint Dikangadissi, Kim Valenta, Michel Masozera, Michael L. Wilson, Robert Bitariho, Sydney T. Ndolo Ebika, Sylvie GourletâFleury, Felix Mulindahabi, Colin M. Beal
Planning for Sustainability in Small Municipalities: The Influence of Interest Groups, Growth Patterns, and Institutional Characteristics
How and why small municipalities promote sustainability through planning efforts is poorly understood. We analyzed ordinances in 451 Maine municipalities and tested theories of policy adoption using regression analysis.We found that smaller communities do adopt programs that contribute to sustainability relevant to their scale and context. In line with the political market theory, we found that municipalities with strong environmental interests, higher growth, and more formal governments were more likely to adopt these policies. Consideration of context and capacity in planning for sustainability will help planners better identify and benefit from collaboration, training, and outreach opportunities
Teriparatide and stress fracture healing in young adults (RETURN â Research on Efficacy of Teriparatide Use in the Return of recruits to Normal duty): study protocol for a randomised controlled trial
Background: Stress fractures are a common and potentially debilitating overuse injury to bone and occur frequently among military recruits and athletes. Recovery from a lower body stress fracture typically requires several weeks of physical rehabilitation. Teriparatide, a recombinant form of the bioactive portion of parathyroid hormone (1â34 amino acids), is used to treat osteoporosis, prevent osteoporotic fractures, and enhance fracture healing due to its net anabolic effect on bone. The study aim is to investigate the effect of teriparatide on stress fracture healing in young, otherwise healthy adults undergoing military training. Methods: In a two-arm, parallel, prospective, randomised controlled, intention-to-treat trial, Army recruits (n = 136 men and women, 18â40 years) with a magnetic resonance imaging (MRI) diagnosed lower body stress fracture (pelvic girdle, sacrum, coccyx, or lower limb) will be randomised to receive either usual Army standard care, or teriparatide and usual Army standard care. Teriparatide will be self-administered by subcutaneous injections (20 ÎŒg/day) for 16 weeks, continuing to 24 weeks where a fracture remains unhealed at week 16. The primary outcome will be the improvement in radiological healing by two grades or more, or reduction to grade zero, 8 weeks after randomisation, assessed using Fredericson grading of MRI by radiologists blind to the randomisation. Secondary outcomes will be time to radiological healing, assessed by MRI at 8, 10, 12, 14, 16, 20 and 24 weeks, until healed; time to clinical healing, assessed using a clinical severity score of injury signs and symptoms; time to discharge from Army physical rehabilitation; pain, assessed by visual analogue scale; health-related quality of life, using the Short Form (36) Health Survey; and adverse events. Exploratory outcomes will include blood and urine biochemistry; bone density and morphology assessed using dual-energy X-ray absorptiometry, peripheral quantitative computed tomography (pQCT), and high-resolution pQCT; physical activity measured using accelerometers; and long-term future fracture rate. Discussion: This study will evaluate whether teriparatide, in addition to standard care, is more effective for stress fracture healing than standard care alone in Army recruits who have sustained a lower body stress fracture. Trial registration: ClinicalTrials.govNCT04196855. Registered on 12 December 2019
Baseline representativeness of patients in clinics enrolled in the PRimary care Opioid Use Disorders treatment (PROUD) trial: comparison of trial and non-trial clinics in the same health systems
BACKGROUND: Pragmatic primary care trials aim to test interventions in real world health care settings, but clinics willing and able to participate in trials may not be representative of typical clinics. This analysis compared patients in participating and non-participating clinics from the same health systems at baseline in the PRimary care Opioid Use Disorders treatment (PROUD) trial.
METHODS: This observational analysis relied on secondary electronic health record and administrative claims data in 5 of 6 health systems in the PROUD trial. The sample included patients 16-90âyears at an eligible primary care visit in the 3âyears before randomization. Each system contributed 2 randomized PROUD trial clinics and 4 similarly sized non-trial clinics. We summarized patient characteristics in trial and non-trial clinics in the 2âyears before randomization ( baseline ). Using mixed-effect regression models, we compared trial and non-trial clinics on a baseline measure of the primary trial outcome (clinic-level patient-years of opioid use disorder (OUD) treatment, scaled per 10,000 primary care patients seen) and a baseline measure of the secondary trial outcome (patient-level days of acute care utilization among patients with OUD).
RESULTS: Patients were generally similar between the 10 trial clinics (nâ=â248,436) and 20 non-trial clinics (nâ=â341,130), although trial clinics\u27 patients were slightly younger, more likely to be Hispanic/Latinx, less likely to be white, more likely to have Medicaid/subsidized insurance, and lived in less wealthy neighborhoods. Baseline outcomes did not differ between trial and non-trial clinics: trial clinics had 1.0 more patient-year of OUD treatment per 10,000 patients (95% CI: -â2.9, 5.0) and a 4% higher rate of days of acute care utilization than non-trial clinics (rate ratio: 1.04; 95% CI: 0.76, 1.42).
CONCLUSIONS: trial clinics and non-trial clinics were similar regarding most measured patient characteristics, and no differences were observed in baseline measures of trial primary and secondary outcomes. These findings suggest trial clinics were representative of comparably sized clinics within the same health systems. Although results do not reflect generalizability more broadly, this study illustrates an approach to assess representativeness of clinics in future pragmatic primary care trials
What Do We Know About Contracting Out in the United States? Evidence from Household and Establishment Surveys
A variety of evidence points to significant growth in domestic contracting out over the last two decades, yet the phenomenon is not well documented. In this paper, we pull together data from various sources to shed light on the extent of and trends in domestic outsourcing, the occupations in which it has grown, and the industries engaging in outsourcing for the employment services sector, which has been a particularly important area of domestic outsourcing. In addition, we examine evidence of contracting out of selected occupations to other sectors. We point to many gaps in our knowledge on trends in domestic outsourcing and its implications for employment patterns and to inconsistencies across data sets in the information that is available. We recommend steps to improve data in this area
The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey
The Sloan Digital Sky Survey III (SDSS-III) presents the first spectroscopic
data from the Baryon Oscillation Spectroscopic Survey (BOSS). This ninth data
release (DR9) of the SDSS project includes 535,995 new galaxy spectra (median
z=0.52), 102,100 new quasar spectra (median z=2.32), and 90,897 new stellar
spectra, along with the data presented in previous data releases. These spectra
were obtained with the new BOSS spectrograph and were taken between 2009
December and 2011 July. In addition, the stellar parameters pipeline, which
determines radial velocities, surface temperatures, surface gravities, and
metallicities of stars, has been updated and refined with improvements in
temperature estimates for stars with T_eff<5000 K and in metallicity estimates
for stars with [Fe/H]>-0.5. DR9 includes new stellar parameters for all stars
presented in DR8, including stars from SDSS-I and II, as well as those observed
as part of the SDSS-III Sloan Extension for Galactic Understanding and
Exploration-2 (SEGUE-2).
The astrometry error introduced in the DR8 imaging catalogs has been
corrected in the DR9 data products. The next data release for SDSS-III will be
in Summer 2013, which will present the first data from the Apache Point
Observatory Galactic Evolution Experiment (APOGEE) along with another year of
data from BOSS, followed by the final SDSS-III data release in December 2014.Comment: 9 figures; 2 tables. Submitted to ApJS. DR9 is available at
http://www.sdss3.org/dr
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