882 research outputs found
MagAO: Status and on-sky performance of the Magellan adaptive optics system
MagAO is the new adaptive optics system with visible-light and infrared
science cameras, located on the 6.5-m Magellan "Clay" telescope at Las Campanas
Observatory, Chile. The instrument locks on natural guide stars (NGS) from
0 to 16 -band magnitude, measures turbulence
with a modulating pyramid wavefront sensor binnable from 28x28 to 7x7
subapertures, and uses a 585-actuator adaptive secondary mirror (ASM) to
provide flat wavefronts to the two science cameras. MagAO is a mutated clone of
the similar AO systems at the Large Binocular Telescope (LBT) at Mt. Graham,
Arizona. The high-level AO loop controls up to 378 modes and operates at frame
rates up to 1000 Hz. The instrument has two science cameras: VisAO operating
from 0.5-1 m and Clio2 operating from 1-5 m. MagAO was installed in
2012 and successfully completed two commissioning runs in 2012-2013. In April
2014 we had our first science run that was open to the general Magellan
community. Observers from Arizona, Carnegie, Australia, Harvard, MIT, Michigan,
and Chile took observations in collaboration with the MagAO instrument team.
Here we describe the MagAO instrument, describe our on-sky performance, and
report our status as of summer 2014.Comment: 13 pages, 11 figures, to appear in Proc. SPIE 9148-
Dynamics of hadron strong production and decay
We generalize results of lattice QCD to determine the spin-dependent
symmetries and factorization properties of meson production in OZI allowed
processes. This explains some conjectures previously made in the literature
about axial meson decays and gives predictions for exclusive decays of vector
charmonia, including ways of establishing the structure of Y(4260) and Y(4325)
from their S-wave decays. Factorization gives a selection rule which forbids
near threshold with the tensor meson in helicity 2. The
relations among amplitudes for double charmonia production \e^+e^-\to
\psi\chi_{0,1,2} are expected to differ from the analagous relations among
light flavour production such as \e^+e^-\to \omega f_{0,1,2}.Comment: 13 pages; journal versio
Looking for a gift of Nature: Hadron loops and hybrid mixing
We investigate how coupling of valence q qbar to meson pairs can modify the
properties of conventional q qbar and hybrid mesons. In a symmetry limit the
mixing between hybrids and conventional q qbar with the same J^PC is shown to
vanish. Flavor mixing between heavy and light q qbar due to meson loops is
shown to be dual to the results of gluon mediated pQCD, and qualitatively
different from mixing involving light flavors alone. The validity of the OZI
rule for conventional q qbar and hybrid mesons is discussed.Comment: v2: added important references and discussion of previous literature;
results and conclusions unchanged. 8 pages, 2 figure
The nucleon's octet axial-charge g_A^8 with chiral corrections
The value of the nucleon's flavour-singlet axial-charge extracted from
polarised deep inelastic scattering is sensitive to the value of the octet
axial-charge g_A^8 which is usually taken from an analysis of hyperon
beta-decays within the framework of SU(3) symmetry, namely 0.58 \pm 0.03. Using
the Cloudy Bag model we find that the value of g_A^8 is reduced by as much as
20% below the usual phenomenological value. This increases the value of the
flavour singlet axial charge (g_A^0|_inv) derived from deep inelastic data and
significantly reduces the difference between it and g_A^8.Comment: 12 page
Confinement and the Pion Nucleon Sigma Term
Gribov's theory of confinement offers a simple explanaton of the value of the
pion nucleon sigma term. There is no need to invoke a large strange quark
component in the nucleon.Comment: 4 pages, Cavendish HEP 93/
MetricGAN+/-: Increasing Robustness of Noise Reduction on Unseen Data
Training of speech enhancement systems often does not incorporate knowledge
of human perception and thus can lead to unnatural sounding results.
Incorporating psychoacoustically motivated speech perception metrics as part of
model training via a predictor network has recently gained interest. However,
the performance of such predictors is limited by the distribution of metric
scores that appear in the training data. In this work, we propose MetricGAN+/-
(an extension of MetricGAN+, one such metric-motivated system) which introduces
an additional network - a "de-generator" which attempts to improve the
robustness of the prediction network (and by extension of the generator) by
ensuring observation of a wider range of metric scores in training.
Experimental results on the VoiceBank-DEMAND dataset show relative improvement
in PESQ score of 3.8% (3.05 vs 3.22 PESQ score), as well as better
generalisation to unseen noise and speech.Comment: 5 pages, 4 figures, Submitted to EUSIPCO 202
Non Intrusive Intelligibility Predictor for Hearing Impaired Individuals using Self Supervised Speech Representations
Self-supervised speech representations (SSSRs) have been successfully applied
to a number of speech-processing tasks, e.g. as feature extractor for speech
quality (SQ) prediction, which is, in turn, relevant for assessment and
training speech enhancement systems for users with normal or impaired hearing.
However, exact knowledge of why and how quality-related information is encoded
well in such representations remains poorly understood. In this work,
techniques for non-intrusive prediction of SQ ratings are extended to the
prediction of intelligibility for hearing-impaired users. It is found that
self-supervised representations are useful as input features to non-intrusive
prediction models, achieving competitive performance to more complex systems. A
detailed analysis of the performance depending on Clarity Prediction Challenge
1 listeners and enhancement systems indicates that more data might be needed to
allow generalisation to unknown systems and (hearing-impaired) individualsComment: Accepted @ ASRU 2023 SPARKS worksho
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