16,913 research outputs found
The Best and Brightest Metal-Poor Stars
The chemical abundances of large samples of extremely metal-poor (EMP) stars
can be used to investigate metal-free stellar populations, supernovae, and
nucleosynthesis as well as the formation and galactic chemical evolution of the
Milky Way and its progenitor halos. However, current progress on the study of
EMP stars is being limited by their faint apparent magnitudes. The acquisition
of high signal-to-noise spectra for faint EMP stars requires a major telescope
time commitment, making the construction of large samples of EMP star
abundances prohibitively expensive. We have developed a new, efficient
selection that uses only public, all-sky APASS optical, 2MASS near-infrared,
and WISE mid-infrared photometry to identify bright metal-poor star candidates
through their lack of molecular absorption near 4.6 microns. We have used our
selection to identify 11,916 metal-poor star candidates with V < 14, increasing
the number of publicly-available candidates by more than a factor of five in
this magnitude range. Their bright apparent magnitudes have greatly eased
high-resolution follow-up observations that have identified seven previously
unknown stars with [Fe/H] <~ -3.0. Our follow-up campaign has revealed that
3.8^{+1.3}_{-1.1}% of our candidates have [Fe/H] <~ -3.0 and
32.5^{+3.0}_{-2.9}% have -3.0 <~ [Fe/H] <~ -2.0. The bulge is the most likely
location of any existing Galactic Population III stars, and an infrared-only
variant of our selection is well suited to the identification of metal-poor
stars in the bulge. Indeed, two of our confirmed metal-poor stars with [Fe/H]
<~ -2.7 are within about 2 kpc of the Galactic Center. They are among the most
metal-poor stars known in the bulge.Comment: 28 pages, 6 figures, and 4 tables in emulateapj format; accepted for
publication in Ap
Detection and distribution of Craspedacusta sowerbii: Observations of medusae are not enough
The freshwater cnidarian Craspedacusta sowerbii, native to the Yangtze valley, has invaded lakes and ponds throughout the world. Most distribution records have to date been based on observations of the medusa (jellyfish) stage, including numerous recent publications. We aimed to determine whether polyps are widespread in lakes, and geographical areas, outside of where medusae have been observed, and whether constructed waters are more easily invaded than natural waters. Our results show that C. sowerbii is more common and widespread than is apparent from observations of medusae. We argue that observed occurrences of medusae provide little useful information regarding the distribution of this species, and that published records of new jellyfish occurrences provide unreliable estimates of the timing of introduction, establishment or spread of C. sowerbii in new regions. We found no evidence that constructed waters were more readily invaded than natural waters. Overall, accurate determination of Craspedacusta occurrence and distribution requires systematic surveys of the polyp stages
Chemistry of the Most Metal-poor Stars in the Bulge and the z > 10 Universe
Metal-poor stars in the Milky Way are local relics of the epoch of the first
stars and the first galaxies. However, a low metallicity does not prove that a
star formed in this ancient era, as metal-poor stars form over a range of
redshift in different environments. Theoretical models of Milky Way formation
have shown that at constant metallicity, the oldest stars are those closest to
the center of the Galaxy on the most tightly-bound orbits. For that reason, the
most metal-poor stars in the bulge of the Milky Way provide excellent tracers
of the chemistry of the high-redshift universe. We report the dynamics and
detailed chemical abundances of three stars in the bulge with [Fe/H]
, two of which are the most metal-poor stars in the bulge in the
literature. We find that with the exception of scandium, all three stars follow
the abundance trends identified previously for metal-poor halo stars. These
three stars have the lowest [Sc II/Fe] abundances yet seen in -enhanced
giant stars in the Galaxy. Moreover, all three stars are outliers in the
otherwise tight [Sc II/Fe]-[Ti II/Fe] relation observed among metal-poor halo
stars. Theoretical models predict that there is a 30% chance that at least one
of these stars formed at , while there is a 70% chance that at
least one formed at . These observations imply that
by , the progenitor galaxies of the Milky Way had both reached [Fe/H]
and established the abundance pattern observed in extremely
metal-poor stars.Comment: Submitted to ApJ on 2014 December 23, accepted 2015 May 4th after
minor revisions. ArXiv tarball includes referee report and respons
REST and Linked Data: a match made for domain driven development?
At a first glance there might appear to be an obvious alignment and overlap between the approaches prescribed by REST and Linked Data. On more detailed inspection divergences in scope and applicability present themselves, and for some aspects, incompatibility. In this paper we investigate these similarities and differences and suggest the coupling is worthy of a third look: in combination as a flexible environment in which the developer can focus on domain driven applications
Understanding Hope: A Review of Measurement and Construct Validity Research
Hope has been discussed by philosophers, theologians, educators, and scientists, to name but a few groups of people, over the preceding two millennia. During the last 15 years, C. R. Snyder and his colleagues at the University of Kansas have developed a theory and associated measures of the hope construct that have received extensive, detailed attention both within and outside the field of psychology. In this chapter, we describe Snyder\u27s hope model and some of the research findings that have supported the validity of this construct. Beginning with a conceptual definition of hope, we move to relevant findings about the usefulness of hope in the lives of individuals in various life arenas. We describe measures developed for assessing hope in children and adults, as well as current issues associated with the validity of hope measurement. Finally, we discuss future directions for further investigation of hope
Hydrographic Study of Peirce Island Wastewater Treatment Plant Effluent in the Piscataqua River of Portsmouth, New Hampshire: Report of Findings from the December 10 – 14, 2012 Study Period
In order to assist the New Hampshire Department of Environmental Services (NHDES) evaluate the impact of treated wastewater effluent from Peirce Island Wastewater Treatment Plant (WWTP) to the Lower Piscataqua River and Portsmouth Harbor a hydrographic dye study was conducted in December 2012 in Portsmouth, NH. Eight (8) shellfish cages with American oysters (Crassostrea virginica) and blue mussels (Mytilus edulis) were deployed both upstream and downstream of the Peirce Island WWTP in the Piscataqua River, Little Harbor, and the entrance of Little Bay. Eight (8) mini CTDs that monitor conductivity/salinity, temperature, and depth, and six (6) moored fluorometers, which measure dye tagged effluent from the Peirce Island WWTP were attached to the subsurface cages. A fifty (50) gallon mixture of Rhodamine WT dye and distilled water was injected into WWTP on December 11, 2012 for a half tidal cycle (approximately 12.4 hours). Additionally, boat tracking fluorometers connected with a mobile geographic information system (GIS) were used to measure dye levels on the surface in situ and in real time. Microbiological analyses of fecal coliform (FC), male-specific coliphage (MSC), Norovirus (NoV) genogroup I (GI) and genogroup II (GII), and Adenovirus (AdV) were conducted on WWTP influent and effluent composite samples collected with automated samplers to determine the WWTP efficiency in reducing indicator bacteria and viruses. Microbiological sampling and testing of oysters and mussels from the eight (8) sentinel cages was conducted to assess the impact of WWTP effluent on shellfish growing areas and growing area classifications. Prior to conducting the study, the assumption was that the FDA’s recommended minimum dilution of 1000:1was not applicable in this situation because the recommended dilution is based on a WWTP having at least secondary treatment. The microbiological findings in shellfish samples, wastewater samples from the Peirce Island WWTP, and the results of the dye study, confirm that a minimum of 1,000:1 dilution with respect to Peirce Island WWTP is currently not applicable for this WWTP. The FDA and NHDES recommend continued MSC testing of wastewater samples from the WWTP before and after the WWTP upgrade. The FDA and NHDES recommend a future field study after the WWTP upgrade in order to delineate the 1,000:1 dilution zone
CALENDAR VS. WEEKS TO EXPIRATION LIVESTOCK BASIS FORECASTS: WHICH IS BETTER?
The ability to accurately forecast basis is crucial to risk management strategies employed by many agribusiness firms. Previous research has examined how to effectively use basis forecasts and what factors affect basis, but literature focusing on forecasting basis is sparse. This research evaluates the impact of adopting a time-to-expiration approach, as compared to the more common calendar approach, when forecasting feeder cattle, live cattle, and hog basis. Furthermore, the optimal number of past year's basis levels to include in making basis predictions is evaluated in an out-of-sample framework. Absolute basis forecasts errors are generated for all three commodities and evaluated to determine the signifcance of the two issues mentioned above. Results indicate that basis forecasters should consider using three-year historical averages for feeder cattle and four-year historical averages for live cattle and lean hogs when making basis forecasts. Furthermore, the use of a time-to-expiration method of calculating historical average basis results in very little improvement in basis prediction accuracy compared to the calendar approach.livestock prices, basis, hedging, basis forecasts, Livestock Production/Industries, Marketing,
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