680 research outputs found
Existence of the Stark-Wannier quantum resonances
In this paper we prove the existence of the Stark-Wannier quantum resonances
for one-dimensional Schrodinger operators with smooth periodic potential and
small external homogeneous electric field. Such a result extends the existence
result previously obtained in the case of periodic potentials with a finite
number of open gaps.Comment: 30 pages, 1 figur
TernausNetV2: Fully Convolutional Network for Instance Segmentation
The most common approaches to instance segmentation are complex and use
two-stage networks with object proposals, conditional random-fields, template
matching or recurrent neural networks. In this work we present TernausNetV2 - a
simple fully convolutional network that allows extracting objects from a
high-resolution satellite imagery on an instance level. The network has popular
encoder-decoder type of architecture with skip connections but has a few
essential modifications that allows using for semantic as well as for instance
segmentation tasks. This approach is universal and allows to extend any network
that has been successfully applied for semantic segmentation to perform
instance segmentation task. In addition, we generalize network encoder that was
pre-trained for RGB images to use additional input channels. It makes possible
to use transfer learning from visual to a wider spectral range. For
DeepGlobe-CVPR 2018 building detection sub-challenge, based on public
leaderboard score, our approach shows superior performance in comparison to
other methods. The source code corresponding pre-trained weights are publicly
available at https://github.com/ternaus/TernausNetV
On spectral stability of solitary waves of nonlinear Dirac equation on a line
We study the spectral stability of solitary wave solutions to the nonlinear
Dirac equation in one dimension. We focus on the Dirac equation with cubic
nonlinearity, known as the Soler model in (1+1) dimensions and also as the
massive Gross-Neveu model. Presented numerical computations of the spectrum of
linearization at a solitary wave show that the solitary waves are spectrally
stable. We corroborate our results by finding explicit expressions for several
of the eigenfunctions. Some of the analytic results hold for the nonlinear
Dirac equation with generic nonlinearity.Comment: 20 pages with figure
Solitary Wave Dynamics in an External Potential
We study the behavior of solitary-wave solutions of some generalized
nonlinear Schr\"odinger equations with an external potential. The equations
have the feature that in the absence of the external potential, they have
solutions describing inertial motions of stable solitary waves.
We construct solutions of the equations with a non-vanishing external
potential corresponding to initial conditions close to one of these solitary
wave solutions and show that, over a large interval of time, they describe a
solitary wave whose center of mass motion is a solution of Newton's equations
of motion for a point particle in the given external potential, up to small
corrections corresponding to radiation damping.Comment: latex2e, 41 pages, 1 figur
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