1,644 research outputs found
WISE/NEOWISE Observations of the Jovian Trojans: Preliminary Results
We present the preliminary analysis of over 1739 known and 349 candidate
Jovian Trojans observed by the NEOWISE component of the Wide-field Infrared
Survey Explorer (WISE). With this survey the available diameters, albedos and
beaming parameters for the Jovian Trojans have been increased by more than an
order of magnitude compared to previous surveys. We find that the Jovian Trojan
population is very homogenous for sizes larger than km (close to the
detection limit of WISE for these objects). The observed sample consists almost
exclusively of low albedo objects, having a mean albedo value of .
The beaming parameter was also derived for a large fraction of the observed
sample, and it is also very homogenous with an observed mean value of
. Preliminary debiasing of the survey shows our observed sample is
consistent with the leading cloud containing more objects than the trailing
cloud. We estimate the fraction to be N(leading)/N(trailing) , lower than the value derived by others.Comment: Accepted for publication in Astrophysical Journal. Electronic table
will be available at the publishers websit
Main Belt Asteroids with WISE/NEOWISE I: Preliminary Albedos and Diameters
We present initial results from the Wide-field Infrared Survey Explorer
(WISE), a four-band all-sky thermal infrared survey that produces data well
suited to measuring the physical properties of asteroids, and the NEOWISE
enhancement to the WISE mission allowing for detailed study of Solar system
objects. Using a NEATM thermal model fitting routine we compute diameters for
over 100,000 Main Belt asteroids from their IR thermal flux, with errors better
than 10%. We then incorporate literature values of visible measurements (in the
form of the H absolute magnitude) to determine albedos. Using these data we
investigate the albedo and diameter distributions of the Main Belt. As observed
previously, we find a change in the average albedo when comparing the inner,
middle, and outer portions of the Main Belt. We also confirm that the albedo
distribution of each region is strongly bimodal. We observe groupings of
objects with similar albedos in regions of the Main Belt associated with
dynamical breakup families. Asteroid families typically show a characteristic
albedo for all members, but there are notable exceptions to this. This paper is
the first look at the Main Belt asteroids in the WISE data, and only represents
the preliminary, observed raw size and albedo distributions for the populations
considered. These distributions are subject to survey biases inherent to the
NEOWISE dataset and cannot yet be interpreted as describing the true
populations; the debiased size and albedo distributions will be the subject of
the next paper in this series.Comment: Accepted to ApJ. Online table to also appear on the publisher's
websit
Dynamical Symmetry Breaking in Planar QED
We investigate (2+1)-dimensional QED coupled with Dirac fermions both at zero
and finite temperature. We discuss in details two-components (P-odd) and
four-components (P-even) fermion fields. We focus on P-odd and P-even Dirac
fermions in presence of an external constant magnetic field. In the spontaneous
generation of the magnetic condensate survives even at infinite temperature. We
also discuss the spontaneous generation of fermion mass in presence of an
external magnetic field.Comment: 34 pages, 8 postscript figures, final version to appear on J. Phys.
Inflation-Produced Magnetic Fields in R^n F^2 and I F^2 models
We re-analyze the production of seed magnetic fields during Inflation in
(R/m^2)^n F_{\mu \nu}F^{\mu \nu} and I F_{\mu \nu}F^{\mu \nu} models, where n
is a positive integer, R the Ricci scalar, m a mass parameter, and I \propto
\eta^\alpha a power-law function of the conformal time \eta, with \alpha a
positive real number. If m is the electron mass, the produced fields are
uninterestingly small for all n. Taking m as a free parameter we find that, for
n \geq 2, the produced magnetic fields can be sufficiently strong in order to
seed dynamo mechanism and then to explain galactic magnetism. For \alpha
\gtrsim 2, there is always a window in the parameters defining Inflation such
that the generated magnetic fields are astrophysically interesting. Moreover,
if Inflation is (almost) de Sitter and the produced fields almost
scale-invariant (\alpha \simeq 4), their intensity can be strong enough to
directly explain the presence of microgauss galactic magnetic fields.Comment: 5 pages, 2 figures. Minor revisions. References added. Accepted for
publication in Phys. Rev.
Revising the age for the Baptistina asteroid family using WISE/NEOWISE data
We have used numerical routines to model the evolution of a simulated
Baptistina family to constrain its age in light of new measurements of the
diameters and albedos of family members from the Wide-field Infrared Survey
Explorer. We also investigate the effect of varying the assumed physical and
orbital parameters on the best-fitting age. We find that the physically allowed
range of assumed values for the density and thermal conductivity induces a
large uncertainty in the rate of evolution. When realistic uncertainties in the
family members' physical parameters are taken into account we find the
best-fitting age can fall anywhere in the range of 140-320 Myr. Without more
information on the physical properties of the family members it is difficult to
place a more firm constraint on Baptistina's age.Comment: 27 pages, 16 figures, accepted to Ap
Polarization selection rules for inter-Landau level transitions in epitaxial graphene revealed by infrared optical Hall effect
We report on polarization selection rules of inter-Landau level transitions
using reflection-type optical Hall effect measurements from 600 to 4000 cm-1 on
epitaxial graphene grown by thermal decomposition of silicon carbide. We
observe symmetric and anti-symmetric signatures in our data due to polarization
preserving and polarization mixing inter-Landau level transitions,
respectively. From field-dependent measurements we identify that transitions in
decoupled graphene mono-layers are governed by polarization mixing selection
rules, whereas transitions in coupled graphene mono-layers are governed by
polarization preserving selection rules. The selection rules may find
explanation by different coupling mechanisms of inter-Landau level transitions
with free charge carrier magneto-optic plasma oscillations
WISE/NEOWISE observations of Active Bodies in the Main Belt
We report results based on mid-infrared photometry of 5 active main belt
objects (AMBOs) detected by the Wide-field Infrared Survey Explorer (WISE)
spacecraft. Four of these bodies, P/2010 R2 (La Sagra), 133P/Elst-Pizarro,
(596) Scheila, and 176P/LINEAR, showed no signs of activity at the time of the
observations, allowing the WISE detections to place firm constraints on their
diameters and albedos. Geometric albedos were in the range of a few percent,
and on the order of other measured comet nuclei. P/2010 A2 was observed on
April 2-3, 2010, three months after its peak activity. Photometry of the coma
at 12 and 22 {\mu}m combined with ground-based visible-wavelength measurements
provides constraints on the dust particle mass distribution (PMD), dlogn/dlogm,
yielding power-law slope values of {\alpha} = -0.5 +/- 0.1. This PMD is
considerably more shallow than that found for other comets, in particular
inbound particle fluence during the Stardust encounter of comet 81P/Wild 2. It
is similar to the PMD seen for 9P/Tempel 1 in the immediate aftermath of the
Deep Impact experiment. Upper limits for CO2 & CO production are also provided
for each AMBO and compared with revised production numbers for WISE
observations of 103P/Hartley 2.Comment: 32 Pages, including 5 Figure
Inflation-Produced Magnetic Fields in Nonlinear Electrodynamics
We study the generation of primeval magnetic fields during inflation era in
nonlinear theories of electrodynamics. Although the intensity of the produced
fields strongly depends on characteristics of inflation and on the form of
electromagnetic Lagrangian, our results do not exclude the possibility that
these fields could be astrophysically interesting.Comment: 6 page
Evolving Spatially Aggregated Features from Satellite Imagery for Regional Modeling
Satellite imagery and remote sensing provide explanatory variables at
relatively high resolutions for modeling geospatial phenomena, yet regional
summaries are often desirable for analysis and actionable insight. In this
paper, we propose a novel method of inducing spatial aggregations as a
component of the machine learning process, yielding regional model features
whose construction is driven by model prediction performance rather than prior
assumptions. Our results demonstrate that Genetic Programming is particularly
well suited to this type of feature construction because it can automatically
synthesize appropriate aggregations, as well as better incorporate them into
predictive models compared to other regression methods we tested. In our
experiments we consider a specific problem instance and real-world dataset
relevant to predicting snow properties in high-mountain Asia
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