4,080 research outputs found
Medium and large-scale variations of dynamo-induced electric fields from AE ion drift measurements
Current models of the low latitude electric field are largely based on data from incoherent scatter radars. These observations are extended through the addition of the rather extensive high quality electric field measurements from the Ion Drift Meter (IDM) aboard the Atmosphere Explorer (AE) spacecraft. Some preliminary results obtained from the Unified Abstract files of satellite AE-E are presented. This satellite was active from the end of 1975 through June 1981 in various elliptical and circular orbits having an inclination near 20 deg. The resulting data can be examined for the variation of ion drift with latitude, longitude, season, solar cycle, altitude, and magnetic activity. The results presented deal primarily with latitudinal variations of the drift features. Diagrams of data are given and briefly interpreted. The preliminary results presented here indicate that IDM data from the AE and the more recent Dynamics Explorer B spacecraft should continue to disclose some interesting and previously unobserved dynamical features of the low latitude F region
The impact of dividend imputation on corporate tax avoidance: The case of shareholder value
© 2017 Elsevier B.V. The objective of this paper is to evaluate whether dividend imputation, whereby tax credits may be passed on to shareholders for corporate tax paid, impacts corporate tax avoidance. This is undertaken with a pooled cross-sectional research design evaluating differences in tax avoidance across firms where there are significant differences in corporate tax avoidance incentives. Specifically, potential differences arise between firms paying dividends with tax credits, paying dividends without tax credits, and not paying dividends. Results suggest that firms paying dividends with tax credits attached are less likely to engage in tax avoidance with an average cash effective tax rate up to 16.9 percentage points higher than firms that pay dividends without tax credits, and up to 14.7 percentage points higher than firms that do not pay dividends at all. Accordingly, this provides insights into the effectiveness of dividend imputation in mitigating corporate tax avoidance, as well as providing support for the continuance of dividend imputation in Australia. Additionally, a positive association is found to exist between outside directors and corporate tax avoidance, extending to firms paying dividends with tax credits where dividend imputation is expected to mitigate such a relation. In combination, these results suggest heterogeneity of costs and benefits of tax avoidance and this is a challenge in evaluating corporate tax aggressiveness generally, and the impact of corporate governance on corporate tax avoidance in particular
Constraints on the distance to SGR 1806-20 from HI absorption
The giant flare detected from the magnetar SGR 1806-20 on 2004 December 27
had a fluence more than 100 times higher than the only two other SGR flares
ever recorded. Whereas the fluence is independent of distance, an estimate for
the luminosity of the burst depends on the source's distance, which has
previously been argued to be ~15 kpc. The burst produced a bright radio
afterglow, against which Cameron et al. (2005) have measured an HI absorption
spectrum. This has been used to propose a revised distance to SGR 1806-20 of
between 6.4 and 9.8 kpc. Here we analyze this absorption spectrum, and compare
it both to HI emission data from the Southern Galactic Plane Survey and to
archival 12-CO survey data. We confirm ~6 kpc, as a likely lower limit on the
distance to SGR 1806-20, but argue that it is difficult to place an upper limit
on the distance to SGR 1806-20 from the HI data currently available. The
previous value of ~15 kpc thus remains the best estimate of the distance to the
source.Comment: 3 pages, 1 embedded EPS figure. Added sentences to end of Abstract
and Conclusion, clarifying that most likely distance is 15 kpc. ApJ Letters,
in pres
GSH23.0-0.7+117, a neutral hydrogen shell in the inner Galaxy
GSH23.0-0.7+117 is a well-defined neutral hydrogen shell discovered in the
VLA Galactic Plane Survey (VGPS). Only the blueshifted side of the shell was
detected. The expansion velocity and systemic velocity were determined through
the systematic behavior of the HI emission with velocity. The center of the
shell is at (l,b,v)=(23.05,-0.77,+117 km/s). The angular radius of the shell is
6.8', or 15 pc at a distance of 7.8 kpc. The HI mass divided by the volume of
the half-shell implies an average density n_H = 11 +/- 4 cm^{-3} for the medium
in which the shell expanded. The estimated age of GSH23.0-0.7+117 is 1 Myr,
with an upper limit of 2 Myr. The modest expansion energy of 2 * 10^{48} erg
can be provided by the stellar wind of a single O4 to O8 star over the age of
the shell. The 3 sigma upper limit to the 1.4 GHz continuum flux density
(S_{1.4} < 248 mJy) is used to derive an upper limit to the Lyman continuum
luminosity generated inside the shell. This upper limit implies a maximum of
one O9 star (O8 to O9.5 taking into account the error in the distance) inside
the HI shell, unless most of the incident ionizing flux leaks through the HI
shell. To allow this, the shell should be fragmented on scales smaller than the
beam (2.3 pc). If the stellar wind bubble is not adiabatic, or the bubble has
burst (as suggested by the HI channel maps), agreement between the energy and
ionization requirements is even less likely. The limit set by the non-detection
in the continuum provides a significant challenge for the interpretation of
GSH23.0-0.7+117 as a stellar wind bubble. A similar analysis may be applicable
to other Galactic HI shells that have not been detected in the continuum.Comment: 18 pages, 6 figures. Figures 1 and 4 separately in GIF format.
Accepted for publication in Astrophysical Journa
The Indo-U.S. Library of Coude Feed Stellar Spectra
We have obtained spectra for 1273 stars using the 0.9m Coud\'e Feed telescope
at Kitt Peak National Observatory. This telescope feeds the coud\'e
spectrograph of the 2.1m telescope. The spectra have been obtained with the #5
camera of the coud\'e spectrograph and a Loral 3K X 1K CCD. Two gratings have
been used to provide spectral coverage from 3460 \AA to 9464 \AA, at a
resolution of 1\AA FWHM and at an original dispersion of 0.44 \AA/pixel.
For 885 stars we have complete spectra over the entire 3460 \AA to 9464 \AA
wavelength region (neglecting small gaps of 50 \AA), and partial spectral
coverage for the remaining stars. The 1273 stars have been selected to provide
broad coverage of the atmospheric parameters T, log g, and [Fe/H], as
well as spectral type. The goal of the project is to provide a comprehensive
library of stellar spectra for use in the automated classification of stellar
and galaxy spectra and in galaxy population synthesis. In this paper we discuss
the characteristics of the spectral library, viz., details of the observations,
data reduction procedures, and selection of stars. We also present a few
illustrations of the quality and information available in the spectra. The
first version of the complete spectral library is now publicly available from
the National Optical Astronomy Observatory (NOAO) via FTP and HTTP.Comment: 18 pages, 6 figures, 4 table
The VLA Galactic Plane Survey
The VLA Galactic Plane Survey (VGPS) is a survey of HI and 21-cm continuum
emission in the Galactic plane between longitude 18 degrees 67 degr. with
latitude coverage from |b| < 1.3 degr. to |b| < 2.3 degr. The survey area was
observed with the Very Large Array (VLA) in 990 pointings. Short-spacing
information for the HI line emission was obtained by additional observations
with the Green Bank Telescope (GBT). HI spectral line images are presented with
a resolution of 1 arcmin x 1 arcmin x 1.56 km/s (FWHM) and rms noise of 2 K per
0.824 km/s channel. Continuum images made from channels without HI line
emission have 1 arcmin (FWHM) resolution. VGPS images are compared with images
from the Canadian Galactic Plane Survey (CGPS) and the Southern Galactic Plane
Survey (SGPS). In general, the agreement between these surveys is impressive,
considering the differences in instrumentation and image processing techniques
used for each survey. The differences between VGPS and CGPS images are small, <
6 K (rms) in channels where the mean HI brightness temperature in the field
exceeds 80 K. A similar degree of consistency is found between the VGPS and
SGPS. The agreement we find between arcminute resolution surveys of the
Galactic plane is a crucial step towards combining these surveys into a single
uniform dataset which covers 90% of the Galactic disk: the International
Galactic Plane Survey (IGPS). The VGPS data will be made available on the World
Wide Web through the Canadian Astronomy Data Centre (CADC).Comment: Accepted for publication in The Astronomical Journal. 41 pages, 13
figures. For information on data release, colour images etc. see
http://www.ras.ucalgary.ca/VGP
VICE: Variational Interpretable Concept Embeddings
A central goal in the cognitive sciences is the development of numerical models for mental representations of object concepts. This paper introduces Variational Interpretable Concept Embeddings (VICE), an approximate Bayesian method for embedding object concepts in a vector space using data collected from humans in an odd-one-out triplet task. VICE uses variational inference to obtain sparse, non-negative representations of object concepts with uncertainty estimates for the embedding values. These estimates are used to automatically select the dimensions that best explain the data. We derive a PAC learning bound for VICE that can be used to estimate generalization performance or determine sufficient sample size in experimental design. VICE rivals or outperforms its predecessor, SPoSE, at predicting human behavior in the odd-one-out triplet task. Furthermore, VICE's object representations are more reproducible and consistent across random initializations
First Detection of HCO Absorption in the Magellanic System
We present the first detection of HCO absorption in the Magellanic
System. Using the Australia Telescope Compact Array (ATCA), we observed 9
extragalactic radio continuum sources behind the Magellanic System and detected
HCO absorption towards one source located behind the leading edge of the
Magellanic Bridge. The detection is located at LSR velocity of , with a full width at half maximum of and optical depth of .
Although there is abundant neutral hydrogen (HI) surrounding the sightline in
position-velocity space, at the exact location of the absorber the HI column
density is low, , and there is little evidence for dust
or CO emission from Planck observations. While the origin and survival of
molecules in such a diffuse environment remains unclear, dynamical events such
as HI flows and cloud collisions in this interacting system likely play an
important role.Comment: Accepted for publication in ApJ. 6 pages, 2 figures, 2 table
- âŠ