9,979 research outputs found
Computer vision and optimization methods applied to the measurements of in-plane deformations
fi=vertaisarvioitu|en=peerReviewed
Gravitational Wave Tests of General Relativity with the Parameterized Post-Einsteinian Framework
Gravitational wave astronomy has tremendous potential for studying extreme
astrophysical phenomena and exploring fundamental physics. The waves produced
by binary black hole mergers will provide a pristine environment in which to
study strong field, dynamical gravity. Extracting detailed information about
these systems requires accurate theoretical models of the gravitational wave
signals. If gravity is not described by General Relativity, analyses that are
based on waveforms derived from Einstein's field equations could result in
parameter biases and a loss of detection efficiency. A new class of
"parameterized post-Einsteinian" (ppE) waveforms has been proposed to cover
this eventuality. Here we apply the ppE approach to simulated data from a
network of advanced ground based interferometers (aLIGO/aVirgo) and from a
future spaced based interferometer (LISA). Bayesian inference and model
selection are used to investigate parameter biases, and to determine the level
at which departures from general relativity can be detected. We find that in
some cases the parameter biases from assuming the wrong theory can be severe.
We also find that gravitational wave observations will beat the existing bounds
on deviations from general relativity derived from the orbital decay of binary
pulsars by a large margin across a wide swath of parameter space.Comment: 16 pages, 10 figures. Modified in response to referee comment
Future constraints on halo thermodynamics from combined Sunyaev-Zel'dovich measurements
The improving sensitivity of measurements of the kinetic Sunyaev-Zel'dovich
(SZ) effect opens a new window into the thermodynamic properties of the baryons
in halos. We propose a methodology to constrain these thermodynamic properties
by combining the kinetic SZ, which is an unbiased probe of the free electron
density, and the thermal SZ, which probes their thermal pressure. We forecast
that our method constrains the average thermodynamic processes that govern the
energetics of galaxy evolution like energetic feedback across all redshift
ranges where viable halos sample are available. Current Stage-3 cosmic
microwave background (CMB) experiments like AdvACT and SPT-3G can measure the
kSZ and tSZ to greater than 100 if combined with a DESI-like
spectroscopic survey. Such measurements translate into percent-level
constraints on the baryonic density and pressure profiles and on the feedback
and non-thermal pressure support parameters for a given ICM model. This in turn
will provide critical thermodynamic tests for sub-grid models of feedback in
cosmological simulations of galaxy formation. The high fidelity measurements
promised by the next generation CMB experiment, CMB-S4, allow one to further
sub-divide these constraints beyond redshift into other classifications, like
stellar mass or galaxy type.Comment: 11 pages, 3 figures, Accepted to JCA
Observations of Cool-Star Magnetic Fields
Cool stars like the Sun harbor convection zones capable of producing
substantial surface magnetic fields leading to stellar magnetic activity. The
influence of stellar parameters like rotation, radius, and age on cool-star
magnetism, and the importance of the shear layer between a radiative core and
the convective envelope for the generation of magnetic fields are keys for our
understanding of low-mass stellar dynamos, the solar dynamo, and also for other
large-scale and planetary dynamos. Our observational picture of cool-star
magnetic fields has improved tremendously over the last years. Sophisticated
methods were developed to search for the subtle effects of magnetism, which are
difficult to detect particularly in cool stars. With an emphasis on the
assumptions and capabilities of modern methods used to measure magnetism in
cool stars, I review the different techniques available for magnetic field
measurements. I collect the analyses on cool-star magnetic fields and try to
compare results from different methods, and I review empirical evidence that
led to our current picture of magnetic fields and their generation in cool
stars and brown dwarfs.Comment: Published version at http://www.livingreviews.org/lrsp-2012-
The pre-launch Planck Sky Model: a model of sky emission at submillimetre to centimetre wavelengths
We present the Planck Sky Model (PSM), a parametric model for the generation
of all-sky, few arcminute resolution maps of sky emission at submillimetre to
centimetre wavelengths, in both intensity and polarisation. Several options are
implemented to model the cosmic microwave background, Galactic diffuse emission
(synchrotron, free-free, thermal and spinning dust, CO lines), Galactic H-II
regions, extragalactic radio sources, dusty galaxies, and thermal and kinetic
Sunyaev-Zeldovich signals from clusters of galaxies. Each component is
simulated by means of educated interpolations/extrapolations of data sets
available at the time of the launch of the Planck mission, complemented by
state-of-the-art models of the emission. Distinctive features of the
simulations are: spatially varying spectral properties of synchrotron and dust;
different spectral parameters for each point source; modeling of the clustering
properties of extragalactic sources and of the power spectrum of fluctuations
in the cosmic infrared background. The PSM enables the production of random
realizations of the sky emission, constrained to match observational data
within their uncertainties, and is implemented in a software package that is
regularly updated with incoming information from observations. The model is
expected to serve as a useful tool for optimizing planned microwave and
sub-millimetre surveys and to test data processing and analysis pipelines. It
is, in particular, used for the development and validation of data analysis
pipelines within the planck collaboration. A version of the software that can
be used for simulating the observations for a variety of experiments is made
available on a dedicated website.Comment: 35 pages, 31 figure
From Simple to Complex: A Progressive Framework for Document-level Informative Argument Extraction
Document-level Event Argument Extraction (EAE) requires the model to extract
arguments of multiple events from a single document. Considering the underlying
dependencies between these events, recent efforts leverage the idea of
"memory", where the results of already predicted events are cached and can be
retrieved to help the prediction of upcoming events. These methods extract
events according to their appearance order in the document, however, the event
that appears in the first sentence does not mean that it is the easiest to
extract. Existing methods might introduce noise to the extraction of upcoming
events if they rely on an incorrect prediction of previous events. In order to
provide more reliable memory, we propose a simple-to-complex progressive
framework for document-level EAE. Specifically, we first calculate the
difficulty of each event and then, we conduct the extraction following a
simple-to-complex order. In this way, the memory will store the most certain
results, and the model could use these reliable sources to help the prediction
of more difficult events. Experiments on WikiEvents show that our model
outperforms SOTA by 1.4% in F1, indicating the proposed simple-to-complex
framework is useful in the EAE task.Comment: Accepted to the Findings of EMNLP 2023 (Long Paper
Invariant template matching in systems with spatiotemporal coding: a vote for instability
We consider the design of a pattern recognition that matches templates to
images, both of which are spatially sampled and encoded as temporal sequences.
The image is subject to a combination of various perturbations. These include
ones that can be modeled as parameterized uncertainties such as image blur,
luminance, translation, and rotation as well as unmodeled ones. Biological and
neural systems require that these perturbations be processed through a minimal
number of channels by simple adaptation mechanisms. We found that the most
suitable mathematical framework to meet this requirement is that of weakly
attracting sets. This framework provides us with a normative and unifying
solution to the pattern recognition problem. We analyze the consequences of its
explicit implementation in neural systems. Several properties inherent to the
systems designed in accordance with our normative mathematical argument
coincide with known empirical facts. This is illustrated in mental rotation,
visual search and blur/intensity adaptation. We demonstrate how our results can
be applied to a range of practical problems in template matching and pattern
recognition.Comment: 52 pages, 12 figure
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