2,748 research outputs found
Super-Brownian motion with extra birth at one point
A super-Brownian motion in two and three dimensions is constructed where
"particles" give birth at a higher rate, if they approach the origin. Via a
log-Laplace approach, the construction is based on Albeverio et al. (1995) who
calculated the fundamental solutions of the heat equation with one-point
potential in dimensions less than four
On the large scale behavior of super-Brownian motion in three dimensions with a single point source
In a recent work, Fleischmann and Mueller (2004) showed the existence of a
super-Brownian motion in R^d, d=2,3, with extra birth at the origin. Their
construction made use of an analytical approach based on the fundamental
solution of the heat equation with a one point potential worked out by
Albeverio et al. (1995). The present note addresses two properties of this
measure-valued process in the three-dimensional case, namely the scaling of the
process and the large scale behavior of its mean
Force Statistics and Correlations in Dense Granular Packings
In dense, static, polydisperse granular media under isotropic pressure, the
probability density and the correlations of particle-wall contact forces are
studied. Furthermore, the probability density functions of the populations of
pressures measured with different sized circular pressure cells is examined.
The questions answered are: (i) What is the number of contacts that has to be
considered so that the measured pressure lies within a certain error margin
from its expectation value? (ii) What is the statistics of the pressure
probability density as function of the size of the pressure cell? Astonishing
non-random correlations between contact forces are evidenced, which range at
least 10 to 15 particle diameter. Finally, an experiment is proposed to tackle
and better understand this issue.Comment: 10 pages, 12 figure
Two interacting particles in a random potential: mapping onto one parameter localization theories without interaction
We consider two models for a pair of interacting particles in a random
potential: (i) two particles with a Hubbard interaction in arbitrary dimensions
and (ii) a strongly bound pair in one dimension. Establishing suitable
correpondences we demonstrate that both cases can be described in terms
familiar from theories of noninteracting particles. In particular, these two
cases are shown to be controlled by a single scaling variable, namely the pair
conductance . For an attractive or repulsive Hubbard interaction and
starting from a certain effective Hamiltonian we derive a supersymmetric
nonlinear model. Its action turns out to be closely related to the one
found by Efetov for noninteracting electrons in disordered metals. This enables
us to describe the diffusive motion of the particle pair on scales exceeding
the one-particle localization length and to discuss the corresponding
level statistics. For tightly bound pairs in one dimension, on the other hand,
we follow early work by Dorokhov and exploit the analogy with the transfer
matrix approach to quasi 1d conductors. Extending our study to M particles we
obtain a M-particle localization length scaling like the Mth power of the
one-particle localization length.Comment: 29 pages, Revtex, no figure
Beyond saliency: understanding convolutional neural networks from saliency prediction on layer-wise relevance propagation
Despite the tremendous achievements of deep convolutional neural networks
(CNNs) in many computer vision tasks, understanding how they actually work
remains a significant challenge. In this paper, we propose a novel two-step
understanding method, namely Salient Relevance (SR) map, which aims to shed
light on how deep CNNs recognize images and learn features from areas, referred
to as attention areas, therein. Our proposed method starts out with a
layer-wise relevance propagation (LRP) step which estimates a pixel-wise
relevance map over the input image. Following, we construct a context-aware
saliency map, SR map, from the LRP-generated map which predicts areas close to
the foci of attention instead of isolated pixels that LRP reveals. In human
visual system, information of regions is more important than of pixels in
recognition. Consequently, our proposed approach closely simulates human
recognition. Experimental results using the ILSVRC2012 validation dataset in
conjunction with two well-established deep CNN models, AlexNet and VGG-16,
clearly demonstrate that our proposed approach concisely identifies not only
key pixels but also attention areas that contribute to the underlying neural
network's comprehension of the given images. As such, our proposed SR map
constitutes a convenient visual interface which unveils the visual attention of
the network and reveals which type of objects the model has learned to
recognize after training. The source code is available at
https://github.com/Hey1Li/Salient-Relevance-Propagation.Comment: 35 pages, 15 figure
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