45,836 research outputs found
Multifrequency Method for Mapping Active Galactic Nuclei with Allowance for the Frequency-Dependent Image Shift
We consider the problem of multifrequency VLBA image synthesis and
spectral-index mapping for active galactic nuclei related to the necessity of
taking into account the frequency-dependent image shift. We describe our
generalized multifrequency synthesis algorithm with a spectral correction based
on the maximum entropy method. The results of our processing of multifrequency
VLBI data for the radio sources J2202+4216, J0336+3218, and J1419+5423 are
presented.Comment: 12 pages, 2 tables, 6 figure
A Bayesian Variable Selection Approach to Major League Baseball Hitting Metrics
Numerous statistics have been proposed for the measure of offensive ability
in major league baseball. While some of these measures may offer moderate
predictive power in certain situations, it is unclear which simple offensive
metrics are the most reliable or consistent. We address this issue with a
Bayesian hierarchical model for variable selection to capture which offensive
metrics are most predictive within players across time. Our sophisticated
methodology allows for full estimation of the posterior distributions for our
parameters and automatically adjusts for multiple testing, providing a distinct
advantage over alternative approaches. We implement our model on a set of 50
different offensive metrics and discuss our results in the context of
comparison to other variable selection techniques. We find that 33/50 metrics
demonstrate signal. However, these metrics are highly correlated with one
another and related to traditional notions of performance (e.g., plate
discipline, power, and ability to make contact)
Improved Limit on theta_{13} and Implications for Neutrino Masses in Neutrino-less Double Beta Decay and Cosmology
We analyze the impact of a measurement, or of an improved bound, on
theta_{13} for the determination of the effective neutrino mass in
neutrino-less double beta decay and cosmology. In particular, we discuss how an
improved limit on (or a specific value of) theta_{13} can influence the
determination of the neutrino mass spectrum via neutrino-less double beta
decay. We also discuss the interplay with improved cosmological neutrino mass
searches.Comment: 22 pages, 5 figures. Minor corrections, matches version in PR
Magnetoconductivity in the presence of Bychkov-Rashba spin-orbit interaction
A closed-form analytic formula for the magnetoconductivity in the diffusive
regime is derived in the presence of Bychkov-Rashba spin-orbit interaction in
two dimensions. It is shown that at low fields B << B_{so}, where B_{so} is the
characteristic field associated with spin precession, D'yakonov-Perel'
mechanism leads to spin relaxation, while for B >> B_{so} spin relaxation is
suppressed and the resulting spin precession contributes a Berry phase-like
spin phase to the magnetoconductivity. The relative simplicity of the formula
greatly facilitates data fitting, allowing for the strength of the spin-orbit
coupling to be easily extracted
Getting a kick out of the stellar disk(s) in the galactic center
Recent observations of the Galactic center revealed a nuclear disk of young
OB stars, in addition to many similar outlying stars with higher eccentricities
and/or high inclinations relative to the disk (some of them possibly belonging
to a second disk). Binaries in such nuclear disks, if they exist in
non-negligible fractions, could have a major role in the evolution of the disks
through binary heating of this stellar system. We suggest that interactions
with/in binaries may explain some (or all) of the observed outlying young stars
in the Galactic center. Such stars could have been formed in a disk, and later
on kicked out from it through binary related interactions, similar to ejection
of high velocity runaway OB stars in young clusters throughout the galaxy.Comment: 2 pages, 2 figs. To be published in the proceedings of the IAU 246
symposium on "Dynamical evolution of dense stellar systems
Majorana Fermions in Strongly Interacting Helical Liquids
Majorana fermions were proposed to occur at edges and interfaces of gapped
one-dimensional systems where phases with different topological character meet
due to an interplay of spin-orbit coupling, proximity-induced superconductivity
and external magnetic fields. Here we investigate the effect of strong particle
interactions, and show that the helical liquid offers a mechanism that protects
the very existence of Majorana edge states: whereas moderate interactions close
the proximity gap which supports the edge states, in helical liquids the gap
re-opens due to two-particle processes. However, gapless fermionic excitations
occur at spatial proximity to the Majorana states at interfaces and may
jeopardize their long term Majorana coherence.Comment: 7 pages, 4 figure
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