7,360 research outputs found
Static-test results from exhaust nozzles with novel features for supersonic-aircraft applications
Unions and Managerial Pay
Unions compress the wage distribution among workers covered by union contracts. We ask whether unions also have an effect on the managers of unionized firms. To this end we collected and assembled data on unionization and managerial pay within firms and industries in the U.S. and across countries. Generally, we find a negative correlation between executive compensation and unionization in our cross-section data, but no relationship of changes in unionization on the growth of compensation of executives over time. Using NLRB elections data, we find that a loss of union members due to decertification elections is associated with higher CEO pay, although our estimates are imprecise. With CPS data we consistently find that where unions are stronger, fewer managers are employed
Lithium abundance and 6Li/7Li ratio in the active giant HD123351 I. A comparative analysis of 3D and 1D NLTE line-profile fits
Current three-dimensional (3D) hydrodynamical model atmospheres together with
NLTE spectrum synthesis, permit to derive reliable atomic and isotopic chemical
abundances from high-resolution stellar spectra. Not much is known about the
presence of the fragile 6Li isotope in evolved solar-metallicity RGB stars, not
to mention its production in magnetically active targets like HD123351. From
fits of the observed CFHT spectrum with synthetic line profiles based on 1D and
3D model atmospheres, we seek to estimate the abundance of the 6Li isotope and
to place constraints on its origin. We derive A(Li) and the 6Li/7Li isotopic
ratio by fitting different synthetic spectra to the Li-line region of a
high-resolution CFHT spectrum (R=120 000, S/R=400). The synthetic spectra are
computed with four different line lists, using in parallel 3D hydrodynamical
CO5BOLD and 1D LHD model atmospheres and treating the line formation of the
lithium components in non-LTE (NLTE). We find A(Li)=1.69+/-0.11 dex and
6Li/7Li=8.0+/-4.4 % in 3D-NLTE, using the line list of Mel\'endez et al.
(2012), updated with new atomic data for V I, which results in the best fit of
the lithium line profile of HD123351. Two other line lists lead to similar
results but with inferior fit qualities. Our 2-sigma detection of the 6Li
isotope is the result of a careful statistical analysis and the visual
inspection of each achieved fit. Since the presence of a significant amount of
6Li in the atmosphere of a cool evolved star is not expected in the framework
of standard stellar evolution theory, non-standard, external lithium production
mechanisms, possibly related to stellar activity or a recent accretion of rocky
material, need to be invoked to explain the detection of 6Li in HD123351.Comment: 16 pages, 11 figures. Accepted for publication in A&
Activity and Diversity of Collembola (Insecta) and Mites (Acari) in Litter of a Degraded Midwestern Oak Woodland
Litter-inhabiting Collembola and mites were sampled using pitfall traps over a twelve-month period from four sub-communities within a 100-acre (40-ha) oak-woodland complex in northern Cook County, Illinois. Sampled locations included four areas where future ecological restoration was planned (mesic woodland, dry-mesic woodland, mesic upland forest, and buckthorn-dominated savanna) and a mesic woodland control that would not be restored. Fifty-eight mite and 30 Collembola taxa were identified out of 5,308 and 190,402 individuals trapped, respectively. There was a significant positive relationship between litter mass and both mite diversity and the ratio of Oribatida to Prostigmata and a significant negative relationship between Collembola diversity and litter. Based on multivariate analysis, Collembola and mite composition differed by sub-community and season interaction
Quantum Phase Transition of Ground-state Entanglement in a Heisenberg Spin Chain Simulated in an NMR Quantum Computer
Using an NMR quantum computer, we experimentally simulate the quantum phase
transition of a Heisenberg spin chain. The Hamiltonian is generated by a
multiple pulse sequence, the nuclear spin system is prepared in its
(pseudo-pure) ground state and the effective Hamiltonian varied in such a way
that the Heisenberg chain is taken from a product state to an entangled state
and finally to a different product state.Comment: 5 pages, 5 eps figures. Accepted in Phys. Rev.
Tangential Motions and Spectroscopy within NGC 6720, the Ring Nebula
We have combined recent Hubble Space Telescope WFPC2 images in the [O III]
5007 and [N II] 6583 lines with similar images made 9.557 years earlier to
determine the motion of the Ring Nebula within the plane of the sky. Scaled
ratio images argue for homologous expansion, that is, larger velocities scale
with increasing distance from the central star. The rather noisy pattern of
motion of individual features argues for the same conclusion and that the
silhouetted knots move at the same rate as the surrounding gas. These
tangential velocities are combined with information from a recent high
resolution radial velocity study to determine a dynamic distance, which is in
basic agreement with the distance determined from the parallax of the central
star. We have also obtained very high signal to noise ratio moderate resolution
spectra (9.4 Angstrom) along the major and minor axes of the nebula and from
this determined the electron temperatures and density in the multiple
ionization zones present. These results confirm the status of the Ring Nebula
as one of the older planetary nebulae, with a central star transitioning to the
white dwarf cooling curve. (Based on observations with the NASA/ESA Hubble
Space Telescope, obtained at the Space Telescope Science Institute, which is
operated by the Association of Universities for Research in Astronomy, Inc.,
under NASA Contract No. NAS 5-26555 and the San Pedro Martir Observatory
operated by the Universidad Nacional Autonoma de Mexico.)Comment: Astronomical Journal, in pres
Interacting Binaries with Eccentric Orbits. III. Orbital Evolution due to Direct Impact and Self-Accretion
The rapid circularization and synchronization of the stellar components in an
eccentric binary system at the onset of Roche lobe overflow (RLO) is a
fundamental assumption common to all binary stellar evolution and population
synthesis codes, even though the validity of this assumption is questionable
both theoretically and observationally. Here we calculate the evolution of the
orbital elements of an eccentric binary through the direct three-body
integration of a massive particle ejected through the inner Lagrangian point of
the donor star at periastron. The trajectory of this particle leads to three
possible outcomes: direct accretion (DA) onto the companion star within a
single orbit, self-accretion (SA) back onto the donor star within a single
orbit, or a quasi-periodic orbit around the companion star. We calculate the
secular evolution of the binary orbit in the first two cases and conclude that
DA can increase or decrease the orbital semi-major axis and eccentricity, while
SA always decreases the orbital both orbital elements. In cases where mass
overflow contributes to circularizing the orbit, circularization can set in on
timescales as short as a few per cent of the mass transfer timescale. In cases
where mass overflow increases the eccentricity, the orbital evolution is
governed by competition between mass overflow and tidal torques. In the absence
of tidal torques, mass overflow resulting in DI can lead to substantially
subsynchronously rotating donor stars. Contrary to common assumptions, DI
furthermore does not always provide a strong sink of orbital angular momentum
in close mass-transferring binaries; in fact we instead find that a significant
part can be returned to the orbit during the particle orbit. The formulation
presented here can be combined with stellar and binary evolution codes to
generate a better picture of the evolution of eccentric, RLO binary star
systems.Comment: 15 pages, 10 figures, Accepted for publication in Ap
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