31,026 research outputs found
Women at work in NASA
Photographs and brief descriptions summarize the diversity of the female work force at NASA. Jobs are classified as: (1) technical support positions; (2) clerical and nonprofessional administrative; (3) professional administrative; and (4) professional scientific and engineering
A new deformation mechanism in pyrolytic carbon at high temperatures
Creep deformation mechanism of pyrolytic graphite at high temperatures in response to stres
SPECIES I: Spectroscopic Parameters and atmosphEric ChemIstriEs of Stars
The detection and subsequent characterisation of exoplanets are intimately
linked to the characteristics of their host star. Therefore, it is necessary to
study the star in detail in order to understand the formation history and
characteristics of their companion(s). Our aims were to develop a community
tool that allows the automated calculation of stellar parameters for a large
number of stars, using high resolution echelle spectra and minimal photometric
magnitudes, and introduce the first results in this work. We measured the
equivalent widths of several iron lines and used them to solve the radiative
transfer equation assuming local thermodynamic equilibrium to obtain the
atmospheric parameters (, [Fe/H], logg and ). We used
these values to derive the abundance of 11 chemical elements in the stellar
photosphere (Na, Mg, Al, Si, Ca, Ti, Cr, Mn, Ni, Cu and Zn). Rotation and
macroturbulent velocity were obtained using temperature calibrators and
synthetic line profiles to match the observed spectra of five absorption lines.
Finally, by interpolating in a grid of MIST isochrones, we derived the mass,
radius and age using a Bayesian approach. SPECIES obtains bulk parameters that
are in good agreement with measured values from different existing catalogues,
including when different methods are used to derive them. We find excellent
agreement with previous works that used similar methodologies. We find
discrepancies in the chemical abundances for some elements with respect to
other works, which could be produced by differences in , or in
the line list or the atomic line data used to derive them. We also obtained
analytic relations to describe the correlations between different parameters,
and we implemented new methods to better handle these correlations, which
provides a better description of the uncertainties associated with the
measurements.Comment: 28 pages, 26 figures, resubmitted to A&
Baryon magnetic moments in chiral perturbation theory
We consider the chiral expansion of the octet baryon magnetic moments in
heavy baryon chiral perturbation theory including all terms which are of order
. These terms are formally of quadratic order in the quark masses. We show
that despite the large non-analytic quark mass corrections to the
Coleman-Glashow relations at order , including all analytic and
non-analytic corrections at order , which in total are of moderate size,
allows for a fit to the measured magnetic moments due to the appearance of
counter terms with free coupling constants of natural size. In this scheme, the
transition moment is predicted to be .Comment: 20 pp, LaTeX file, 2 figures (uses epsf), corrected versio
An investigation into the archaeological application of carbon stable isotope analysis used to establish crop water availability: solutions and ways forward
Carbon stable isotope analysis of charred cereal remains
is a relatively new method employed by archaeological
scientists to investigate ancient climate and irrigation
regimes. The aim of this study was to assess the effect of
environmental variables on carbon isotope
discrimination (D) in multiple environments to develop
the technique and its archaeological application, using
crops grown at three experimental stations in Jordan.
There are two key results: (1) as expected, there was a
strong positive relationship between water availability
and D; (2) site, not water input, was the most important
factor in determining D. Future work should concentrate
on establishing ways of correcting D for the influence of
site specific environmental variables and on assessing
how well carbon isotope discrimination values are
preserved within the archaeological record
Long-term variations in abundance and distribution of sulfuric acid vapor in the Venus atmosphere inferred from Pioneer Venus and Magellan radio occultation studies
Radio occultation experiments have been used to study various properties of planetary atmospheres, including pressure and temperature profiles, and the abundance profiles of absorbing constituents in those planetary atmospheres. However, the reduction of amplitude data from such experiments to determine abundance profiles requires the application of the inverse Abel transform (IAT) and numerical differentiation of experimental data. These two operations preferentially amplify measurement errors above the true signal underlying the data. A new technique for processing radio occultation data has been developed that greatly reduces the errors in the derived absorptivity and abundance profiles. This technique has been applied to datasets acquired from Pioneer Venus Orbiter radio occultation studies and more recently to experiments conducted with the Magellan spacecraft. While primarily designed for radar studies of the Venus surface, the high radiated power (EIRP) from the Magellan spacecraft makes it an ideal transmitter for measuring the refractivity and absorptivity of the Venus atmosphere by such experiments. The longevity of the Pioneer Venus Orbiter has made it possible to study long-term changes in the abundance and distribution of sulfuric acid vapor, H2SO4(g), in the Venus atmosphere between 1979 and 1992. The abundance of H2SO4(g) can be inferred from vertical profiles of 13-cm absorptivity profiles retrieved from radio occultation experiments. Data from 1979 and 1986-87 suggest that the abundance of H2SO4(g) at latitudes northward of 70 deg decreased over this time period. This change may be due to a period of active volcanism in the late 1970s followed by a relative quiescent period, or some other dynamic process in the Venus atmosphere. While the cause is not certain, such changes must be incorporated into dynamic models of the Venus atmosphere. Potentially, the Magellan spacecraft will extend the results of Pioneer Venus Orbiter and allow the continued monitoring of the abundance of distribution of H2SO4(g) in the Venus atmosphere, as well as other interesting atmospheric properties. Without such measurements it will be difficult to address other issues such as the short-term spatial variability of the abundance of H2SO4(g) at similar latitudes in Venus atmosphere, and the identities of particles responsible for large-scale variations observed in NIR images
Spin-Flavor Structure of Large N Baryons
The spin-flavor structure of large N baryons is described in the 1/N
expansion of QCD using quark operators. The complete set of quark operator
identities is obtained, and used to derive an operator reduction rule which
simplifies the 1/N expansion. The operator reduction rule is applied to the
axial currents, masses, magnetic moments and hyperon non-leptonic decay
amplitudes in the limit, to first order in breaking, and
without assuming symmetry. The connection between the Skyrme and quark
representations is discussed. An explicit formula is given for the quark model
operators in terms of the Skyrme model operators to all orders in for
the two flavor case.Comment: 36 pages, 2 eps figures, uses revte
Chiral corrections in hadron spectroscopy
We show that the implementation of chiral symmetry in recent studies of the
hadron spectrum in the context of the constituent quark model is inconsistent
with chiral perturbation theory. In particular, we show that the leading
nonanalytic (LNA) contributions to the hadron masses are incorrect in such
approaches. The failure to implement the correct chiral behaviour of QCD
results in incorrect systematics for the corrections to the masses.Comment: 7 pages, latex, 1 eps figure, version to appear in Phys. Lett.
Bosonic Operator Methods for the Quark Model
Quark model matrix elements can be computed using bosonic operators and the
holomorphic representation for the harmonic oscillator. The technique is
illustrated for normal and exotic baryons for an arbitrary number of colors.
The computations are much simpler than those using conventional quark model
wavefunctions
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