36,281 research outputs found
The coming robot crime wave
Rapid advances in robotics technology for the battlefield and policing could promote a new breed of copycat "garden shed" robot criminals
H{\alpha} Imaging of Nearby Seyfert Host Galaxies
We used narrowband interference filters with the CCD imaging camera on the
Nickel 1.0 meter telescope at Lick Observatory to observe 31 nearby (z < 0.03)
Seyfert galaxies in the 12 {\mu}m Active Galaxy Sample. We obtained pure
emission line images of each galaxy in order to separate H{\alpha} emission
from the nucleus from that of the host galaxy. The extended H{\alpha} emission
is expected to be powered by newly formed hot stars, and correlates well with
other indicators of current star formation in these galaxies: 7.7 {\mu}m PAH,
far-infrared, and radio luminosity. Relative to what would be expected from
recent star formation, there is a 0.8 dex excess of radio emission in our
Seyfert galaxies. The nuclear H{\alpha} luminosity is dominated by the AGN, and
is correlated with the hard X-ray luminosity. There is an upward offset of 1
dex in this correlation for the Seyfert 1s due to a strong contribution from
the Broad Line Region. We found a correlation between star formation rate and
AGN luminosity. In spite of selection effects, we concluded that the absence of
bright Seyfert nuclei in galaxies with low SFRs is real, albeit only weakly
significant. We used our measured spatial distributions of H{\alpha} emission
to determine what these Seyfert galaxies would look like when observed through
fixed apertures at high redshifts. Although all would be detectable emission
line galaxies at any redshift, most would appear dominated by HII region
emission. Only the most luminous AGN would still be identified at z~0.3.Comment: 13 pages, 11 figures, accepted for publication in Ap
Fast Mesh Refinement in Pseudospectral Optimal Control
Mesh refinement in pseudospectral (PS) optimal control is embarrassingly easy
--- simply increase the order of the Lagrange interpolating polynomial and
the mathematics of convergence automates the distribution of the grid points.
Unfortunately, as increases, the condition number of the resulting linear
algebra increases as ; hence, spectral efficiency and accuracy are lost in
practice. In this paper, we advance Birkhoff interpolation concepts over an
arbitrary grid to generate well-conditioned PS optimal control discretizations.
We show that the condition number increases only as in general, but
is independent of for the special case of one of the boundary points being
fixed. Hence, spectral accuracy and efficiency are maintained as increases.
The effectiveness of the resulting fast mesh refinement strategy is
demonstrated by using \underline{polynomials of over a thousandth order} to
solve a low-thrust, long-duration orbit transfer problem.Comment: 27 pages, 12 figures, JGCD April 201
Effect of disorder studied with ferromagnetic resonance for arrays of tangentially magnetized sub-micron Permalloy discs fabricated by nanosphere lithography
Tangentially magnetized trigonal arrays of sub-micron Permalloy discs are
characterized with ferromagnetic resonance to determine the possible
contributions to frequency and linewidth from array disorder. Each array is
fabricated by a water-surface self-assembly lithographic technique, and
consists of a large trigonal array of 700 nm diameter magnetic discs. Each
array is characterized by a different degree of ordering. Two modes are present
in the ferromagnetic resonance spectra: a large amplitude, `fundamental' mode
and a lower amplitude mode at higher field. Angular dependence of the resonance
field in a very well ordered array is found to be negligible for both modes.
The relationship between resonance frequency and applied magnetic field is
found to be uncorrelated with array disorder. Linewidth is found to increase
with increasing array disorder
Quasiharmonic elastic constants corrected for deviatoric thermal stresses
The quasiharmonic approximation (QHA), in its simplest form also called the
statically constrained (SC) QHA, has been shown to be a straightforward method
to compute thermoelastic properties of crystals. Recently we showed that for
non-cubic solids SC-QHA calculations develop deviatoric thermal stresses at
high temperatures. Relaxation of these stresses leads to a series of
corrections to the free energy that may be taken to any desired order, up to
self-consistency. Here we show how to correct the elastic constants obtained
using the SC-QHA. We exemplify the procedure by correcting to first order the
elastic constants of MgSiO-perovskite and MgSiO-post-perovskite, the
major phases of the Earth's lower mantle. We show that this first order
correction is quite satisfactory for obtaining the aggregated elastic averages
of these minerals and their velocities in the lower mantle. This type of
correction is also shown to be applicable to experimental measurements of
elastic constants in situations where deviatoric stresses can develop, such as
in diamond anvil cells.Comment: 4 figures, 1 table, submitted to Phys. Rev. B, July 200
An Empirical Examination of Compensation of REIT Managers
Principal-agent literature finds that manager and owner incentives can be aligned with performance contingent contracts. We investigate the compensation of Real Estate Investment Trust (REIT) industry executives. The competitive nature of mortgage and equity markets, in conjunction with the corporate tax exemption available when REITs distribute most of their earnings as dividends, is likely to influence the compensation of REIT managers. Executive compensation is modeled as a function of revenues and unexpected profit. After transforming the model to reduce collinearity and heteroskedasticity, we find compensation to be generally positively related to revenue. We also find unexpected profit to be generally insignificantly related to compensation, but positively related in those cases where it is significant.
Mortgage Lenders' Market Response to a Landmark Regulatory Decision Based on Fair Lending Compliance
Regulation of real estate lending has substantially increased in the past decade. Government efforts to improve compliance with Community Reinvestment Act mandates are evidence of increased emphasis on racial equal opportunity in loan origination. To investigate the impact of these efforts, this paper examines the Federal Reserve Bank rejection of Shawmut National Corporation's application to buy New Dartmouth Bank. Rejection was based on Shawmut's poor compliance with fair-lending guidelines. Testing finds significant negative abnormal stock returns for samples of mortgage lenders on the announcement day of Shawmut's application rejection. In addition, cross-sectional analysis reveals an inverse relationship between national banks' cumulative abnormal returns (CARs) and a measure of fair lending.
Geometry of Policy Improvement
We investigate the geometry of optimal memoryless time independent decision
making in relation to the amount of information that the acting agent has about
the state of the system. We show that the expected long term reward, discounted
or per time step, is maximized by policies that randomize among at most
actions whenever at most world states are consistent with the agent's
observation. Moreover, we show that the expected reward per time step can be
studied in terms of the expected discounted reward. Our main tool is a
geometric version of the policy improvement lemma, which identifies a
polyhedral cone of policy changes in which the state value function increases
for all states.Comment: 8 page
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