106,587 research outputs found
Possible High-Energy Neutrino and Photon Signals from Gravitational Wave Bursts due to Double Neutron Star Mergers
As the technology of gravitational-wave and neutrino detectors becomes
increasingly mature, a multi-messenger era of astronomy is ushered in. Advanced
gravitational wave detectors are close to making a ground-breaking discovery of
gravitational wave bursts (GWBs) associated with mergers of double neutron
stars (NS-NS). It is essential to study the possible electromagnetic (EM) and
neutrino emission counterparts of these GWBs. Recent observations and numerical
simulations suggest that at least a fraction of NS-NS mergers may leave behind
a massive millisecond magnetar as the merger product. Here we show that protons
accelerated in the forward shock powered by a magnetar wind pushing the ejecta
launched during the merger process would interact with photons generated in the
dissipating magnetar wind and emit high energy neutrinos and photons. We
estimate the typical energy and fluence of the neutrinos from such a scenario.
We find that PeV neutrinos could be emitted from the shock front as long
as the ejecta could be accelerated to a relativistic speed. The diffuse
neutrino flux from these events, even under the most optimistic scenarios, is
too low to account for the two events announced by the IceCube Collaboration,
but it is only slightly lower than the diffuse flux of GRBs, making it an
important candidate for the diffuse background of PeV neutrinos. The
neutron-pion decay of these events make them a moderate contributor to the
sub-TeV gamma-ray diffuse background.Comment: Accepted for publication in PRD, minor revisio
Critical phenomena in gravitational collapse of Husain-Martinez-Nunez scalar field
We construct analytical models to study the critical phenomena in
gravitational collapse of the Husain-Martinez-Nunez massless scalar field. We
first use the cut-and-paste technique to match the conformally flat solution
( ) onto an outgoing Vaidya solution. To guarantee the continuity of the
metric and the extrinsic curvature, we prove that the two solutions must be
joined at a null hypersurface and the metric function in Vaidya spacetime must
satisfy some constraints. We find that the mass of the black hole in the
resulting spacetime takes the form , where the
critical exponent is equal to . For the case , we show
that the scalar field must be joined onto two pieces of Vaidya spacetimes to
avoid a naked singularity. We also derive the power-law mass formula with
. Compared with previous analytical models constructed from a
different scalar field with continuous self-similarity, we obtain the same
value of . However, we show that the solution with is not
self-similar. Therefore, we provide a rare example that a scalar field without
self-similarity also possesses the features of critical collapse.Comment: 14 pages, 6 figure
Bernstein type's concentration inequalities for symmetric Markov processes
Using the method of transportation-information inequality introduced in
\cite{GLWY}, we establish Bernstein type's concentration inequalities for
empirical means where is a unbounded
observable of the symmetric Markov process . Three approaches are
proposed : functional inequalities approach ; Lyapunov function method ; and an
approach through the Lipschitzian norm of the solution to the Poisson equation.
Several applications and examples are studied
Uneven illumination surface defects inspection based on convolutional neural network
Surface defect inspection based on machine vision is often affected by uneven
illumination. In order to improve the inspection rate of surface defects
inspection under uneven illumination condition, this paper proposes a method
for detecting surface image defects based on convolutional neural network,
which is based on the adjustment of convolutional neural networks, training
parameters, changing the structure of the network, to achieve the purpose of
accurately identifying various defects. Experimental on defect inspection of
copper strip and steel images shows that the convolutional neural network can
automatically learn features without preprocessing the image, and correct
identification of various types of image defects affected by uneven
illumination, thus overcoming the drawbacks of traditional machine vision
inspection methods under uneven illumination
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