63,406 research outputs found
Migration, trapping, and venting of gas in a soft granular material
Gas migration through a soft granular material involves a strong coupling
between the motion of the gas and the deformation of the material. This process
is relevant to a variety of natural phenomena, such as gas venting from
sediments and gas exsolution from magma. Here, we study this process
experimentally by injecting air into a quasi-2D packing of soft particles and
measuring the morphology of the air as it invades and then rises due to
buoyancy. We systematically increase the confining pre-stress in the packing by
compressing it with a fluid-permeable piston, leading to a gradual transition
in migration regime from fluidization to pathway opening to pore invasion. We
find that mixed migration regimes emerge at intermediate confinement due to the
spontaneous formation of a compaction layer at the top of the flow cell. By
connecting these migration mechanisms with macroscopic invasion, trapping, and
venting, we show that mixed regimes enable a sharp increase in the average
amount of gas trapped within the packing, as well as much larger venting
events. Our results suggest that the relationship between invasion, trapping,
and venting could be controlled by modulating the confining stress
Learning to Skim Text
Recurrent Neural Networks are showing much promise in many sub-areas of
natural language processing, ranging from document classification to machine
translation to automatic question answering. Despite their promise, many
recurrent models have to read the whole text word by word, making it slow to
handle long documents. For example, it is difficult to use a recurrent network
to read a book and answer questions about it. In this paper, we present an
approach of reading text while skipping irrelevant information if needed. The
underlying model is a recurrent network that learns how far to jump after
reading a few words of the input text. We employ a standard policy gradient
method to train the model to make discrete jumping decisions. In our benchmarks
on four different tasks, including number prediction, sentiment analysis, news
article classification and automatic Q\&A, our proposed model, a modified LSTM
with jumping, is up to 6 times faster than the standard sequential LSTM, while
maintaining the same or even better accuracy
Maximum Score Estimation of Preference Parameters for a Binary Choice Model under Uncertainty
This paper develops maximum score estimation of preference parameters in the
binary choice model under uncertainty in which the decision rule is affected by
conditional expectations. The preference parameters are estimated in two
stages: we estimate conditional expectations nonparametrically in the first
stage and then the preference parameters in the second stage based on Manski
(1975, 1985)'s maximum score estimator using the choice data and first stage
estimates. The paper establishes consistency and derives rate of convergence of
the two-stage maximum score estimator. Moreover, the paper also provides
sufficient conditions under which the two-stage estimator is asymptotically
equivalent in distribution to the corresponding single-stage estimator that
assumes the first stage input is known. These results are of independent
interest for maximum score estimation with nonparametrically generated
regressors. The paper also presents some Monte Carlo simulation results for
finite-sample behavior of the two-stage estimator
Energy transfer from baryons to dark matter as a unified solution to small-scale structure issues of the CDM model
Using a semianalytic code, we show how baryon physics in a CDM
cosmology could solve the discrepancy between numerical predictions of dark
matter haloes and observations, ranging from dwarf galaxies to clusters,
without the need of nonstandard dark matter models as advocated, for example,
by [Kaplinghat et al., Phys. Rev. Lett. 116, 041302, (2016)]. Combining well
established results, we show, for the first time, how accounting for baryon
physics, in particular dynamical friction mechanisms, leads to flat
galaxy-cluster profiles and correlations in several of their properties, solves
the so-called `diversity problem' and reproduces very well the challenging,
extremely low-rising rotation curve of IC2574. We therefore suggest treating
baryonic physics properly before introducing new exotic features, albeit
legitimate, in the standard cosmological model.Comment: 10 pages, 4 figures, matching the accepted version on Phys. Rev.
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