99,539 research outputs found
Devaney's chaos revisited
In this note, we give several equivalent definitions of Devaney's chao
Order-Preservation for Multidimensional Stochastic Functional Differential Equations with Jump
Sufficient and necessary conditions are presented for the order-preservation
of stochastic functional differential equations on with non-Lipschitzian
coefficients driven by the Brownian motion and Poisson processes. The
sufficiency of the conditions extends and improves some known comparison
theorems derived recently for one-dimesional equations and multidimensional
equations without delay, and the necessity is new even in these special
situations.Comment: 18page
Distribution Dependent SDEs with Singular Coefficients
Under integrability conditions on distribution dependent coefficients,
existence and uniqueness are proved for McKean-Vlasov type SDEs with
non-degenerate noise. When the coefficients are Dini continuous in the space
variable, gradient estimates and Harnack type inequalities are derived. These
generalize the corresponding results derived for classical SDEs, and are new in
the distribution dependent setting.Comment: 28page
Early soft X-ray to UV emission from double neutron star mergers: implications from the long-term radio and X-ray emissions of GW 170817
Recent long-term radio follow-up observations of GW 170817 reveals a simple
power-law rising light curve, with a slope of , up to 93 days after
the merger. The latest X-ray detection at 109 days is also consistent with such
a temporal slope. Such a shallow rise behavior requires a mildly relativistic
outflow with a steep velocity gradient profile, so that slower material with
larger energy catches up with the decelerating ejecta and re-energizes it. It
has been suggested that this mildly relativistic outflow may represent a cocoon
of material. We suggest that the velocity gradient profile may form during the
stage that the cocoon is breaking out of the merger ejecta, resulted from shock
propagation down a density gradient. The cooling of the hot relativistic cocoon
material immediately after it breaks out should have produced soft X-ray to UV
radiation at tens of seconds to hours after the merger. The soft X-ray emission
has a luminosity of over a period of
tens of seconds for a merger event like GW 170817. The UV emission shows a rise
initially and peaks at about a few hours with a luminosity of . The soft X-ray transients could be detected by
future wide-angle X-ray detectors, such as the Chinese mission Einstein Probe.
This soft X-ray/UV emission would serve as one of the earliest electromagnetic
counterparts of gravitation waves from double neutron star mergers and could
provide the earliest localization of the sources.Comment: 5 pages, 2 figures, ApJL in press, discussions on the reverse shock
emission in the refreshed shock scenario for the long-term radio and X-ray
emissions are adde
Non-Gaussian Parameter in k-Dimensional Euclidean Space
We generalize the non-Gaussian parameter, which is utilized to characterize
the distinction of dynamics between realistic and Gaussian Brownian diffusions,
in k-dimensional Euclidean space
On the regular-convexity of Ricci shrinker limit spaces
In this paper, we study the structure of the pointed-Gromov-Hausdorff limits
of sequences of Ricci shrinkers. We define a regular-singular decomposition
following the work of Cheeger-Colding for manifolds with a uniform Ricci
curvature lower bound, and prove that the regular part of any Ricci shrinker
limit space is convex, inspired by Colding-Naber's original idea of parabolic
smoothing of the distance functions.Comment: revised version, to appear in J. Reine Angew. Mat
A numerical simulation of the backward Raman amplifying in plasma
This paper describe a numerical simulation method for the interaction between
laser pulses and low density plasmas based on hydrodynamic approximation. We
investigate Backward Raman Amplifying (BRA) experiments and their variants. The
numerical results are in good agreement with experiments.Comment: 11 pages, 4 figur
Order Preservation for Path-Distribution Dependent SDEs
Sufficient and necessary conditions are presented for the order preservation
of path-distribution dependent SDEs. Differently from the corresponding study
of distribution independent SDEs, to investigate the necessity of order
preservation for the present model we need to construct a family of probability
spaces in terms of the ordered pair of initial distributions.Comment: 12 page
Generative Dual Adversarial Network for Generalized Zero-shot Learning
This paper studies the problem of generalized zero-shot learning which
requires the model to train on image-label pairs from some seen classes and
test on the task of classifying new images from both seen and unseen classes.
Most previous models try to learn a fixed one-directional mapping between
visual and semantic space, while some recently proposed generative methods try
to generate image features for unseen classes so that the zero-shot learning
problem becomes a traditional fully-supervised classification problem. In this
paper, we propose a novel model that provides a unified framework for three
different approaches: visual-> semantic mapping, semantic->visual mapping, and
metric learning. Specifically, our proposed model consists of a feature
generator that can generate various visual features given class embeddings as
input, a regressor that maps each visual feature back to its corresponding
class embedding, and a discriminator that learns to evaluate the closeness of
an image feature and a class embedding. All three components are trained under
the combination of cyclic consistency loss and dual adversarial loss.
Experimental results show that our model not only preserves higher accuracy in
classifying images from seen classes, but also performs better than existing
state-of-the-art models in in classifying images from unseen classes
Inefficient cosmic ray diffusion around Vela X : constraints from H.E.S.S. observations of very high-energy electrons
Vela X is a nearby pulsar wind nebula (PWN) powered by a year old
pulsar. Modeling of the spectral energy distribution of the Vela X PWN has
shown that accelerated electrons have largely escaped from the confinement,
which is likely due to the disruption of the initially confined PWN by the SNR
reverse shock. The escaped electrons propagate to the earth and contribute to
the measured local cosmic-ray (CR) electron spectrum. We find that the escaped
CR electrons from Vela X would hugely exceed the measured flux by HESS at TeV if the standard diffusion coefficient for the interstellar medium is
used. We propose that the diffusion may be highly inefficient around Vela X and
find that a spatially-dependent diffusion can lead to CR flux consistent with
the HESS measurement. Using a two-zone model for the diffusion around Vela X,
we find that the diffusion coefficient in the inner region of a few tens of
parsecs should be for TeV CR electrons,
which is about two orders of magnitude lower than the standard value for ISM.
Such inefficient diffusion around PWN resembles the case of the Geminga and
Monogem PWNe, suggesting that inefficient diffusion may be common in the
vicinity of PWNe spanning a wide range of ages.Comment: Accepted by ApJ, more discussions added, conclusions unchanged, 9
pages, 9 figure
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