53 research outputs found
Random Recurrent Neural Networks Dynamics
This paper is a review dealing with the study of large size random recurrent
neural networks. The connection weights are selected according to a probability
law and it is possible to predict the network dynamics at a macroscopic scale
using an averaging principle. After a first introductory section, the section 1
reviews the various models from the points of view of the single neuron
dynamics and of the global network dynamics. A summary of notations is
presented, which is quite helpful for the sequel. In section 2, mean-field
dynamics is developed.
The probability distribution characterizing global dynamics is computed. In
section 3, some applications of mean-field theory to the prediction of chaotic
regime for Analog Formal Random Recurrent Neural Networks (AFRRNN) are
displayed. The case of AFRRNN with an homogeneous population of neurons is
studied in section 4. Then, a two-population model is studied in section 5. The
occurrence of a cyclo-stationary chaos is displayed using the results of
\cite{Dauce01}. In section 6, an insight of the application of mean-field
theory to IF networks is given using the results of \cite{BrunelHakim99}.Comment: Review paper, 36 pages, 5 figure
Hierarchical model for the scale-dependent velocity of seismic waves
Elastic waves of short wavelength propagating through the upper layer of the
Earth appear to move faster at large separations of source and receiver than at
short separations. This scale dependent velocity is a manifestation of Fermat's
principle of least time in a medium with random velocity fluctuations. Existing
perturbation theories predict a linear increase of the velocity shift with
increasing separation, and cannot describe the saturation of the velocity shift
at large separations that is seen in computer simulations. Here we show that
this long-standing problem in seismology can be solved using a model developed
originally in the context of polymer physics. We find that the saturation
velocity scales with the four-third power of the root-mean-square amplitude of
the velocity fluctuations, in good agreement with the computer simulations.Comment: 7 pages including 3 figure
How Gibbs distributions may naturally arise from synaptic adaptation mechanisms. A model-based argumentation
This paper addresses two questions in the context of neuronal networks
dynamics, using methods from dynamical systems theory and statistical physics:
(i) How to characterize the statistical properties of sequences of action
potentials ("spike trains") produced by neuronal networks ? and; (ii) what are
the effects of synaptic plasticity on these statistics ? We introduce a
framework in which spike trains are associated to a coding of membrane
potential trajectories, and actually, constitute a symbolic coding in important
explicit examples (the so-called gIF models). On this basis, we use the
thermodynamic formalism from ergodic theory to show how Gibbs distributions are
natural probability measures to describe the statistics of spike trains, given
the empirical averages of prescribed quantities. As a second result, we show
that Gibbs distributions naturally arise when considering "slow" synaptic
plasticity rules where the characteristic time for synapse adaptation is quite
longer than the characteristic time for neurons dynamics.Comment: 39 pages, 3 figure
A view of Neural Networks as dynamical systems
We consider neural networks from the point of view of dynamical systems
theory. In this spirit we review recent results dealing with the following
questions, adressed in the context of specific models.
1. Characterizing the collective dynamics; 2. Statistical analysis of spikes
trains; 3. Interplay between dynamics and network structure; 4. Effects of
synaptic plasticity.Comment: Review paper, 51 pages, 10 figures. submitte
MARSTRUCT benchmark study on nonlinear FE simulation of an experiment of an indenter impact with a ship side-shell structure
This paper presents a benchmark study on collision simulations that was initiated by the MARSTRUCT Virtual Institute. The objective was to compare assumptions, finite element models, modelling techniques and experiences between established researchers within the field. Fifteen research groups world-wide participated in the study. An experiment involving a rigid indenter penetrating a ship-like side structure was used as the case study. A description of how the experiment was performed, the geometry model of it, and material properties were distributed to the participants prior to their simulations. The paper presents the results obtained from the fifteen FE simulations and the experiment. It presents a comparison of, among other factors, the reaction force versus the indenter displacement, internal energy absorbed by the structure versus the indenter displacement, and analyses of the participants' ability to predict failure modes and events that were observed in the experiment. The outcome of the study is a discussion and recommendations regarding mesh size, failure criteria and damage models, interpretation of material data and how they are used in a constitutive material model, and finally, uncertainties in general
Random recurrent neural networks dynamics
This paper is a review dealing with the study of large
size random recurrent neural networks. The connection weights are
varying according to a probability law and it is possible to predict
the network dynamics at a macroscopic scale using an averaging
principle. After a first introductory section, the
section 2 reviews the various models from the points of
view of the single neuron dynamics and of the global network
dynamics. A summary of notations is presented, which is quite
helpful for the sequel. In section 3, mean-field dynamics
is developed. The probability distribution characterizing global
dynamics is computed. In section 4, some applications
of mean-field theory to the prediction of chaotic regime for Analog
Formal Random Recurrent Neural Networks (AFRRNN) are displayed. The
case of AFRRNN with an homogeneous population of neurons is studied
in section 4.1. Then, a two-population model is studied in
section 4.2. The occurrence of a cyclo-stationary chaos is
displayed using the results of [16]. In
section 5, an insight of the application of mean-field
theory to IF networks is given using the results
of [9]
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