585 research outputs found
The Century Survey Galactic Halo Project II: Global Properties and the Luminosity Function of Field Blue Horizontal Branch Stars
We discuss a 175 deg^2 spectroscopic survey for blue horizontal branch (BHB)
stars in the Galactic halo. We use the Two Micron All Sky Survey (2MASS) and
the Sloan Digital Sky Survey (SDSS) to select BHB candidates, and find that the
2MASS and SDSS color-selection is 38% and 50% efficient, respectively, for BHB
stars. Our samples include one likely run-away B7 star 6 kpc below the Galactic
plane. The global properties of the BHB samples are consistent with membership
in the halo population: the median metallicity is [Fe/H]=-1.7, the velocity
dispersion is 108 km/s, and the mean Galactic rotation of the BHB stars
3<|z|<15 kpc is -4 +- 30 km/s. We discuss the theoretical basis of the Preston,
Shectman & Beers M_V-color relation for BHB stars, and conclude that intrinsic
shape of the BHB M_V-color relation results from the physics of stars on the
horizontal branch. We calculate the luminosity function for the field BHB star
samples using the Efstathiou, Ellis, & Peterson maximum-likelihood method which
is unbiased by density variations. The field BHB luminosity function exhibits a
steep rise at bright luminosities, a peak between 0.8 < M_V < 1.0, and a tail
at faint luminosities. We compare the field BHB luminosity functions with the
luminosity functions derived from sixteen different globular cluster BHBs.
Kolmogorov-Smirnov tests suggest that field BHB stars and BHB stars in globular
clusters share a common distribution of luminosities, with the exception of
globular clusters with extended BHBs.Comment: 14 pages, including 16 figures, accepted for publication in A
Transport Theory beyond Binary Collisions
Using the Schwinger-Keldysh technique, we derive the transport equations for
a system of quantum scalar fields. We first discuss the general structure of
the equations and then their collision terms. Taking into account up to
three-loop diagrams in \phi^3 model and up to four-loop diagrams in \phi^4
model, we obtain the transport equations which include the contributions of
multi-particle collisions and particle production processes, in addition to
mean-field effects and binary interactions.Comment: 30 pages, 21 figures, minor changes, to appear in Phys. Rev.
Surveying the Inner Halo of the Galaxy with 2MASS-Selected Horizontal Branch Candidates
We use 2MASS photometry to select blue horizontal branch (BHB) candidates
covering the sky |b|>15 deg. A 12.5<J<15.5 sample of BHB stars traces the thick
disk and inner halo to d<9 kpc, with a density comparable to that of M giant
stars. We base our sample selection strategy on the Century Survey Galactic
Halo Project, a survey that provides a complete, spectroscopically-identified
sample of blue stars to a similar depth as the 2MASS catalog. We show that a
-0.20<(J-H)_0<0.10, -0.10<(H-K)_0<0.10 color-selected sample of stars is 65%
complete for BHB stars, and is composed of 47% BHB stars. We apply this
photometric selection to the full 2MASS catalog, and see no spatial
overdensities of BHB candidates at high Galactic latitude |b|>50 deg. We insert
simulated star streams into the data and conclude that the high Galactic
latitude BHB candidates are consistent with having no ~5 deg wide star stream
with density greater than 0.33 objects deg^-2 at the 95% confidence level. The
absence of structure suggests there have been no major accretion events in the
inner halo in the last few Gyr. However, at low Galactic latitudes a two-point
angular correlation analysis reveals structure on angular scales <1 deg. This
structure is apparently associated with stars in the thick disk, and has a
physical scale of 10-100 pc. Interestingly, such structures are expected by
cosmological simulations that predict the majority of the thick disk may arise
from accretion and disruption of satellite mergers.Comment: 11 pages, including figures. Accepted by AJ with minor revision
Conformal Ablative Thermal Protection System for Planetary and Human Exploration Missions: Overview of the Technology Maturation Efforts Funded by NASA's Game Changing Development Program
The Office of Chief Technologist (OCT), NASA has identified the need for research and technology development in part from NASA's Strategic Goal 3.3 of the NASA Strategic Plan to develop and demonstrate the critical technologies that will make NASA's exploration, science, and discovery missions more affordable and more capable. Furthermore, the Game Changing Development Program (GCDP) is a primary avenue to achieve the Agency's 2011 strategic goal to "Create the innovative new space technologies for our exploration, science, and economic future." In addition, recently released "NASA space Technology Roadmaps and Priorities," by the National Research Council (NRC) of the National Academy of Sciences stresses the need for NASA to invest in the very near term in specific EDL technologies. The report points out the following challenges (Page 2-38 of the pre-publication copy released on February 1, 2012): Mass to Surface: Develop the ability to deliver more payload to the destination. NASA's future missions will require ever-greater mass delivery capability in order to place scientifically significant instrument packages on distant bodies of interest, to facilitate sample returns from bodies of interest, and to enable human exploration of planets such as Mars. As the maximum mass that can be delivered to an entry interface is fixed for a given launch system and trajectory design, the mass delivered to the surface will require reduction in spacecraft structural mass; more efficient, lighter thermal protection systems; more efficient lighter propulsion systems; and lighter, more efficient deceleration systems. Surface Access: Increase the ability to land at a variety of planetary locales and at a variety of times. Access to specific sites can be achieved via landing at a specific location (s) or transit from a single designated landing location, but it is currently infeasible to transit long distances and through extremely rugged terrain, requiring landing close to the site of interest. The entry environment is not always guaranteed with a direct entry, and improving the entry system's robustness to a variety of environmental conditions could aid in reaching more varied landing sites.
The Century Survey Galactic Halo Project III: A Complete 4300 deg^2 Survey of Blue Horizontal Branch Stars in the Metal-Weak Thick Disk and Inner Halo
We present a complete spectroscopic survey of 2414 2MASS-selected blue
horizontal branch (BHB) candidates selected over 4300 deg^2 of the sky. We
identify 655 BHB stars in this non-kinematically selected sample. We calculate
the luminosity function of field BHB stars and find evidence for very few hot
BHB stars in the field. The BHB stars located at a distance from the Galactic
plane |Z|<4 kpc trace what is clearly a metal-weak thick disk population, with
a mean metallicity of [Fe/H]= -1.7, a rotation velocity gradient of
dv_{rot}/d|Z|= -28+-3.4 km/s in the region |Z|<6 kpc, and a density scale
height of h_Z= 1.26+-0.1 kpc. The BHB stars located at 5<|Z|<9 kpc are a
predominantly inner-halo population, with a mean metallicity of [Fe/H]= -2.0
and a mean Galactic rotation of -4+-31 km/s. We infer the density of halo and
thick disk BHB stars is 104+-37 kpc^-3 near the Sun, and the relative
normalization of halo to thick-disk BHB stars is 4+-1% near the Sun.Comment: 12 pages in emulateapj format, accepted for publication in February
A
Gendered endings: Narratives of male and female suicides in the South African Lowveld
This is the author's accepted manuscript. The final publication is available at Springer via http://dx.doi.org/10.1007/s11013-012-9258-y. Copyright @ Springer Science+Business Media, LLC 2012.Durkheim’s classical theory of suicide rates being a negative index of social solidarity downplays the salience of gendered concerns in suicide. But gendered inequalities have had a negative impact: worldwide significantly more men than women perpetrate fatal suicides. Drawing on narratives of 52 fatal suicides in Bushbuckridge, South Africa, this article suggests that Bourdieu’s concepts of ‘symbolic violence’ and ‘masculine domination’ provide a more appropriate framework for understanding this paradox. I show that the thwarting of investments in dominant masculine positions have been the major precursor to suicides by men. Men tended to take their own lives as a means of escape. By contrast, women perpetrated suicide to protest against the miserable consequences of being dominated by men. However, contra the assumption of Bourdieu’s concept of ‘habitus’, the narrators of suicide stories did reflect critically upon gender constructs
The protein structure initiative structural genomics knowledgebase
The Protein Structure Initiative Structural Genomics Knowledgebase (PSI SGKB, http://kb.psi-structuralgenomics.org) has been created to turn the products of the PSI structural genomics effort into knowledge that can be used by the biological research community to understand living systems and disease. This resource provides central access to structures in the Protein Data Bank (PDB), along with functional annotations, associated homology models, worldwide protein target tracking information, available protocols and the potential to obtain DNA materials for many of the targets. It also offers the ability to search all of the structural and methodological publications and the innovative technologies that were catalyzed by the PSI's high-throughput research efforts. In collaboration with the Nature Publishing Group, the PSI SGKB provides a research library, editorials about new research advances, news and an events calendar to present a broader view of structural biology and structural genomics. By making these resources freely available, the PSI SGKB serves as a bridge to connect the structural biology and the greater biomedical communitie
Drug Adverse Event Detection in Health Plan Data Using the Gamma Poisson Shrinker and Comparison to the Tree-based Scan Statistic
Background: Drug adverse event (AE) signal detection using the Gamma Poisson Shrinker (GPS) is commonly applied in spontaneous reporting. AE signal detection using large observational health plan databases can expand medication safety surveillance. Methods: Using data from nine health plans, we conducted a pilot study to evaluate the implementation and findings of the GPS approach for two antifungal drugs, terbinafine and itraconazole, and two diabetes drugs, pioglitazone and rosiglitazone. We evaluated 1676 diagnosis codes grouped into 183 different clinical concepts and four levels of granularity. Several signaling thresholds were assessed. GPS results were compared to findings from a companion study using the identical analytic dataset but an alternative statistical method—the tree-based scan statistic (TreeScan). Results: We identified 71 statistical signals across two signaling thresholds and two methods, including closely-related signals of overlapping diagnosis definitions. Initial review found that most signals represented known adverse drug reactions or confounding. About 31% of signals met the highest signaling threshold. Conclusions: The GPS method was successfully applied to observational health plan data in a distributed data environment as a drug safety data mining method. There was substantial concordance between the GPS and TreeScan approaches. Key method implementation decisions relate to defining exposures and outcomes and informed choice of signaling thresholds
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