342 research outputs found
Medical Students\u27 Knowledge of Midwifery Practice After Didactic and Clinical Exposure
Information concerning the student outcomes of interdisciplinary education is limited. The purpose of this study was to identify the knowledge of thirdâyear medical students regarding the practice of certified nurseâmidwives (CNMs). A 1âpage survey instrument was developed and pretested. The instrument was administered as a preâ and posttest at the beginning and end of 7 Obstetrics and Gynecology rotations at 2 medical school clinical campuses of a large Midwestern medical school. Direct interaction with CNMs improved knowledge of collaborative practice arrangements and roles. This was particularly evident in knowledge areas related to CNM prescriptive authority. The medical students who had direct experience with CNMs expressed more interest in working with them in the future than those who lacked the exposure. Collaborative, interdisciplinary education of medical students appeared to promote improved understanding of roles and capabilities
The Albedo of Sea-Ice and Ice Islands in the Arctic Ocean Basin
In spring, when sea-ice is mostly snowcovered, the albedo of the surface is 80-90%, that of melting sea-ice in summer 65-46%, according to the proportion of puddles. Excluding puddles, the albedo of melting shelf-ice is about 77% and that of melting sea-ice about 65%; hence under similar conditions ablation of sea ice is 1.5 times greater than that of shelf ice. Based on airborne and surface measurements, on Ptarmigan flights, T-3, etc
An abundance study of red-giant-branch stars in the Hercules dwarf spheroidal galaxy
Using high-resolution spectroscopy, we provide a determination of [Fe/H] and
[Ca/H] for confirmed red-giant branch member stars of the Hercules dwarf
spheroidal galaxy. Based on this we explore the ages of the prevailing stellar
populations in Hercules, and the enrichment history from supernovae.
Additionally, we provide a new simple metallicity calibration for Stromgren
photometry for metal-poor, red giant branch stars. We find that the red-giant
branch stars of the Hercules dSph galaxy are more metal-poor than estimated in
our previous study that was based on photometry alone. Additionally, we find an
abundance trend such that [Ca/Fe] is higher for more metal-poor stars, and
lower for more metal-rich stars, with a spread of about 0.8 dex. The [Ca/Fe]
trend suggests an early rapid chemical enrichment through supernovae of type
II, followed by a phase of slow star formation dominated by enrichment through
supernovae of type Ia. A comparison with isochrones indicates that the red
giants in Hercules are older than 10 Gyr.Comment: 12 pages, 11 figures. Accepted for publication in A&
Multi-Element Abundance Measurements from Medium-Resolution Spectra. IV. Alpha Element Distributions in Milky Way Dwarf Satellite Galaxies
We derive the star formation histories of eight dwarf spheroidal (dSph) Milky
Way satellite galaxies from their alpha element abundance patterns. Nearly 3000
stars from our previously published catalog (Paper II) comprise our data set.
The average [alpha/Fe] ratios for all dSphs follow roughly the same path with
increasing [Fe/H]. We do not observe the predicted knees in the [alpha/Fe] vs.
[Fe/H] diagram, corresponding to the metallicity at which Type Ia supernovae
begin to explode. Instead, we find that Type Ia supernova ejecta contribute to
the abundances of all but the most metal-poor ([Fe/H] < -2.5) stars. We have
also developed a chemical evolution model that tracks the star formation rate,
Types II and Ia supernova explosions, and supernova feedback. Without metal
enhancement in the supernova blowout, massive amounts of gas loss define the
history of all dSphs except Fornax, the most luminous in our sample. All six of
the best-fit model parameters correlate with dSph luminosity but not with
velocity dispersion, half-light radius, or Galactocentric distance.Comment: 28 pages, 14 figures; accepted for publication in ApJ; very minor
editorial corrections in v
Insight Into the Formation of the Milky Way Through Cold Halo Substructure. II. The Elemental Abundances of ECHOS
We determine the average metallicities of the elements of cold halo
substructure (ECHOS) that we previously identified in the inner halo of the
Milky Way within 17.5 kpc of the Sun. As a population, we find that stars
kinematically associated with ECHOS are chemically distinct from the background
kinematically smooth inner halo stellar population along the same Sloan
Extension for Galactic Understanding and Exploration (SEGUE) line of sight.
ECHOS are systematically more iron-rich, but less alpha-enhanced than the
kinematically-smooth component of the inner halo. ECHOS are also chemically
distinct from other Milky Way components: more iron-poor than typical
thick-disk stars and both more iron-poor and alpha-enhanced than typical
thin-disk stars. In addition, the radial velocity dispersion distribution of
ECHOS extends beyond sigma ~ 20 km s^-1. Globular clusters are unlikely ECHOS
progenitors, as ECHOS have large velocity dispersions and are found in a region
of the Galaxy in which iron-rich globular clusters are very rare. Likewise, the
chemical composition of stars in ECHOS do not match predictions for stars
formed in the Milky Way and subsequently scattered into the inner halo. Dwarf
spheroidal (dSph) galaxies are possible ECHOS progenitors, and if ECHOS are
formed through the tidal disruption of one or more dSph galaxies, the typical
ECHOS [Fe/H] ~ -1.0 and radial velocity dispersion sigma ~ 20 km s^-1 implies a
dSph with M_tot >~ 10^9 M_Sun. Our observations confirm the predictions of
theoretical models of Milky Way halo formation that suggest that prominent
substructures are likely to be metal-rich, and our result implies that the most
likely metallicity for a recently accreted star currently in the inner halo is
[Fe/H] ~ -1.0.Comment: 31 pages and 16 figures, and 3 tables in emulateapj format; accepted
for publication in ApJ. Full tables can be extracted from TeX sourc
All quiet in the outer halo: chemical abundances in the globular cluster Pal 3
Context: Globular clusters (GCs) in the outer halo are important probes of
the composition and origin of the Galactic stellar halo.
Aims: We derive chemical element abundance ratios in red giants belonging to
the remote (R~90 kpc) GC Pal 3 and compare our measurements to those for red
giant stars in both inner and outer halo GCs.
Methods: From high-resolution spectroscopy of four red giants, obtained with
the Magellan/MIKE spectrograph at moderately high S/N, we derive chemical
abundances for 25 alpha-, iron peak-, and neutron-capture elements. These
abundance ratios are confirmed by co-adding low S/N HIRES spectra of 19 stars
along the red giant branch.
Results: Pal 3 shows alpha-enhanced abundance patterns, and also its Fe-peak
and neutron-capture element ratios, are fully compatible with those found in
halo field stars and representative inner halo GCs of the same metallicity
(such as M 13). The heavy elements in Pal 3 appear to be governed by r-process
nucleosyn-thesis. Our limited sample does not show any significant star-to-star
abundance variations in this cluster, although a weak Na-O anti-correlation
cannot be ruled out by the present data.
Conclusions: Pal 3 thus appears as an archetypical GC with abundance ratios
dissimilar to dwarf spheroidal stars, ruling out a direct connection to such
external systems. This conclusion is underscored by the lack of significant
abundance spreads in this GC, in contrast to the broad abundance distributions
seen in the dwarf galaxies. Pal 3 appears to have evolved chemically coeval
with the majority of GCs belonging to Galactic inner and outer halo,
experiencing a similar enrichment history.Comment: 16 pages, 13 figures, accepted for publication in Astronomy and
Astrophysic
Multi-decadal and ontogenetic trophic shifts inferred from stable isotope ratios of pinniped teeth
This work was supported by National Capability funding from the Natural Environment Research Council to the Sea Mammal Research Unit (grant no. SMRU1001).Identifying and characterizing top predatorsâ use of trophic resources provides important information about animal ecology and their response to changing conditions. Information from sources such as stable isotopes can be used to infer changes in resource use as direct observations in the wildare difficult to obtain, particularly in the marine environment. Stable carbon and nitrogen isotope values were recovered from the canine teeth of grey seals collected from haul outs in the central North Sea in the 1970/80s (n = 44) and 2000s (n = 25), spanning a period of marked ecosystem changes in the region. Extracting material deposited during juvenile and adult life-stages, we reconstructed a multi-decadal record ofÎŽ15N and ÎŽ13C variation. Using established correlations between stable isotope ratios and sea bottom temperature we created a proxy for baseline isotopic variability to account for this source of temporal change. We found(1) a significant long-term decline in juvenile grey seal ÎŽ15N values,suggesting trophic position has decreased over time; (2) a decline in adultÎŽ15N values and contraction in stable isotopic niche space after the North Sea regime shift, signifying both a decline in trophic position and change in foraging habits over the 20th century; and (3) evidence for dietary segregation between juvenile and adult animals, showing juvenile individuals feeding at a lower trophic position and in more nearshore areas than adults. Our results demonstrate the efficacy of mining archived biological samples to address ecological questions and imply important ontogenetic and long-term shifts in the feeding ecology of a top predator.Long-term changes in grey seal trophic dynamics may be partly in response to well documented ecosystem changes in the North Sea. Such indirect monitoring of marine predators may have utility when set in the context of ecosystem assessments where paucity of long-term monitoring data is prevalent.Publisher PDFPeer reviewe
Metallicity Evolution of Damped Lyman-alpha Systems out to z~5
We present chemical abundance measurements for 47 damped Lyman-alpha systems
(DLAs), 30 at z>4, observed with the Echellette Spectrograph and Imager and the
High Resolution Echelle Spectrometer on the Keck telescopes. HI column
densities of the DLAs are measured with Voigt profile fits to the Lyman-alpha
profiles, and we find an increased number of false DLA identifications with
SDSS at z>4 due to the increased density of the Lyman-alpha forest. Ionic
column densities are determined using the apparent optical depth method, and we
combine our new metallicity measurements with 195 from previous surveys to
determine the evolution of the cosmic metallicity of neutral gas. We find the
metallicity of DLAs decreases with increasing redshift, improving the
significance of the trend and extending it to higher redshifts, with a linear
fit of -0.22+-0.03 dex per unit redshift from z=0.09-5.06. The metallicity
'floor' of ~1/600 solar continues out to z~5, despite our sensitivity for
finding DLAs with much lower metallicities. However, this floor is not
statistically different from a steep tail to the distribution. We also find
that the intrinsic scatter of metallicity among DLAs of ~0.5 dex continues out
to z~5. In addition, the metallicity distribution and the alpha/Fe ratios of
z>2 DLAs are consistent with being drawn from the same parent population with
those of halo stars. It is therefore possible that the halo stars in the Milky
Way formed out of gas that commonly exhibits DLA absorption at z>2.Comment: Accepted for publication in the Astrophysical Journal. 24 pages, 17
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