4,909 research outputs found
Spectroscopy of Giant Stars in the Pyxis Globular Cluster
The Pyxis globular cluster is a recently discovered globular cluster that
lies in the outer halo (R_{gc} ~ 40 kpc) of the Milky Way. Pyxis lies along one
of the proposed orbital planes of the Large Magellanic Cloud (LMC), and it has
been proposed to be a detached LMC globular cluster captured by the Milky Way.
We present the first measurement of the radial velocity of the Pyxis globular
cluster based on spectra of six Pyxis giant stars. The mean heliocentric radial
velocity is ~ 36 km/sec, and the corresponding velocity of Pyxis with respect
to a stationary observer at the position of the Sun is ~ -191 km/sec. This
radial velocity is a large enough fraction of the cluster's expected total
space velocity, assuming that it is bound to the Milky Way, that it allows
strict limits to be placed on the range of permissible transverse velocities
that Pyxis could have in the case that it still shares or nearly shares an
orbital pole with the LMC. We can rule out that Pyxis is on a near circular
orbit if it is Magellanic debris, but we cannot rule out an eccentric orbit
associated with the LMC. We have calculated the range of allowed proper motions
for the Pyxis globular cluster that result in the cluster having an orbital
pole within 15 degrees of the present orbital pole of the LMC and that are
consistent with our measured radial velocity, but verification of the tidal
capture hypothesis must await proper motion measurement from the Space
Interferometry Mission or HST. A spectroscopic metallicity estimate of [Fe/H] =
-1.4 +/- 0.1 is determined for Pyxis from several spectra of its brightest
giant; this is consistent with photometric determinations of the cluster
metallicity from isochrone fitting.Comment: 22 pages, 5 figures, aaspp4 style, accepted for publication in
October, 2000 issue of the PAS
Predation by wolves and other large carnivores in northwestern Montana and southeastern British Columbia
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Semi-automatic assessment of I/O behavior by inspecting the individual client-node timelines— an explorative study on 10^6 jobs
HPC applications with suboptimal I/O behavior interfere
with well-behaving applications and lead to increased application runtime. In some cases, this may even lead to unresponsive systems and unfinished jobs. HPC monitoring systems can aid users and support staff to identify problematic behavior and support optimization of problematic applications. The key issue is how to identify relevant applications? A profile of an application doesn’t allow to identify problematic phases during the execution but tracing of each individual I/O is too invasive.
In this work, we split the execution into segments, i.e., windows of fixed size and analyze profiles of them. We develop three I/O metrics to identify three relevant classes of inefficient I/O behaviors, and evaluate them on raw data of 1,000,000 jobs on the supercomputer Mistral. The advantages of our method is that temporal information about I/O activities during job runtime is preserved to some extent and can be used to identify phases of inefficient I/O.
The main contribution of this work is the segmentation of time series and computation of metrics (Job-I/O-Utilization, Job-I/O-Problem-Time, and Job-I/O-Balance) that are effective to identify problematic I/O phases and jobs
Mission Possible: Teachers Serving as Agents of Social Change
A case study was conducted to learn about the formation of social justice teachers, and the methods used by radical educators to engage students in social change. Interviews conducted with eight junior and senior high school social studies teachers identified several types of formative experiences inspiring teachers to become radical educators. Personal and family experiences of oppression during their youth and early adult years, childhood multicultural experiences, social activism, volunteerism, and contact with adult mentors influenced teachers to become social justice educators.
Adopting critical thinking as the cornerstone of their social justice practice, social justice teachers employed strategies to foster critical thinking and moral action as a central feature of social justice pedagogy. These included (1) adopting alternative texts and supplemental resources to focus on social justice issues, (2) emphasizing active learning and 21st century learning skills (Rosefsky, Saavedra, & Opfer, 2012), (3) engaging students in service learning and civic action projects, and (4) integrating the arts within the social studies curriculum to raise cultural awareness and appreciation.
Data gathered from interviews, observations, and documents were analyzed using a transformational learning (Mezirow, 2000) and critical thinking theory (Brookfield, 2012). Findings reveal the importance of contact with diverse others and the important role that critical thinking and awareness play in raising social consciousness leading to moral action
Perceptual Discrimination of Phonemic Contrasts in Quebec French: Exposure to Quebec French Does Not Improve Perception in Hexagonal French Native Speakers Living in Quebec
The extent of NGC 6822 revealed by its C stars population
Using the CFH12K camera, we apply the four band photometric technique to
identify 904 carbon stars in an area 28' x 42' centered on NGC 6822. A few C
stars, outside of this area were also discovered with the Las Campanas Swope
Telescope. The NGC 6822 C star population has an average I of 19.26 mag leading
to an average absolute I magnitude of
-4.70 mag, a value essentially identical to the mean magnitude obtained for
the C stars in IC 1613. Contrary to stars highlighting the optical image of NGC
6822, C stars are seen at large radial distances and trace a huge slightly
elliptical halo which do not coincide with the huge HI cloud surrounding
NGC6822. The previously unknown stellar component of NGC 6822 has a exponential
scale length of 3.0' +/- 0.1' and can be traced to five scale lengths. The C/M
ratio of NGC 6822 is evaluated to br 1.0 +/- 0.2.Comment: accepted, to be published in A
A mass spectrometric and quantum chemical study of the vaporisation of lead monoxide in a flow of gaseous arsenic and antimony trioxides
Mass spectrometric studies of the vapours over solid lead oxide in a flow of gaseous arsenic and antimony trioxides were conducted. The following ions of the ternary oxides were detected: Pb3As2O6+, Pb3AsO4+, PbAs2O4+, PbAsO2+, PbSb2O4+, and PbSbO2+. The origin of these species produced by the ionisation and/or fragmentation of ternary gaseous oxides is discussed. The PbAs2O4 species was undoubtedly identified by the determination of the appearance energy. Presumably, the Pb3As2O6 and PbSb2O4 species also existed in the gas phase. Thermodynamic data for the ternary oxides were obtained experimentally by means of a mass spectrometric Knudsen-cell method and were confirmed by quantum chemical calculations
High-Density Genomewide Linkage Analysis of Exceptional Human Longevity Identifies Multiple Novel Loci
Background: Human lifespan is approximately 25 % heritable, and genetic factors may be particularly important for achieving exceptional longevity. Accordingly, siblings of centenarians have a dramatically higher probability of reaching extreme old age than the general population. Methodology/Principal Findings: To map the loci conferring a survival advantage, we performed the second genomewide linkage scan on human longevity and the first using a high-density marker panel of single nucleotide polymorphisms. By systematically testing a range of minimum age cutoffs in 279 families with multiple long-lived siblings, we identified a locus on chromosome 3p24-22 with a genomewide significant allele-sharing LOD score of 4.02 (empirical P = 0.037) and a locus on chromosome 9q31-34 with a highly suggestive LOD score of 3.89 (empirical P = 0.054). The empirical P value for the combined result was 0.002. A third novel locus with a LOD score of 4.05 on chromosome 12q24 was detected in a subset of the data, and we also obtained modest evidence for a previously reported interval on chromosome 4q22-25. Conclusions/Significance: Our linkage data should facilitate the discovery of both common and rare variants tha
Continuous, Semi-discrete, and Fully Discretized Navier-Stokes Equations
The Navier--Stokes equations are commonly used to model and to simulate flow
phenomena. We introduce the basic equations and discuss the standard methods
for the spatial and temporal discretization. We analyse the semi-discrete
equations -- a semi-explicit nonlinear DAE -- in terms of the strangeness index
and quantify the numerical difficulties in the fully discrete schemes, that are
induced by the strangeness of the system. By analyzing the Kronecker index of
the difference-algebraic equations, that represent commonly and successfully
used time stepping schemes for the Navier--Stokes equations, we show that those
time-integration schemes factually remove the strangeness. The theoretical
considerations are backed and illustrated by numerical examples.Comment: 28 pages, 2 figure, code available under DOI: 10.5281/zenodo.998909,
https://doi.org/10.5281/zenodo.99890
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