15,667 research outputs found
Atomic-scale representation and statistical learning of tensorial properties
This chapter discusses the importance of incorporating three-dimensional
symmetries in the context of statistical learning models geared towards the
interpolation of the tensorial properties of atomic-scale structures. We focus
on Gaussian process regression, and in particular on the construction of
structural representations, and the associated kernel functions, that are
endowed with the geometric covariance properties compatible with those of the
learning targets. We summarize the general formulation of such a
symmetry-adapted Gaussian process regression model, and how it can be
implemented based on a scheme that generalizes the popular smooth overlap of
atomic positions representation. We give examples of the performance of this
framework when learning the polarizability and the ground-state electron
density of a molecule
Automatic Environmental Sound Recognition: Performance versus Computational Cost
In the context of the Internet of Things (IoT), sound sensing applications
are required to run on embedded platforms where notions of product pricing and
form factor impose hard constraints on the available computing power. Whereas
Automatic Environmental Sound Recognition (AESR) algorithms are most often
developed with limited consideration for computational cost, this article seeks
which AESR algorithm can make the most of a limited amount of computing power
by comparing the sound classification performance em as a function of its
computational cost. Results suggest that Deep Neural Networks yield the best
ratio of sound classification accuracy across a range of computational costs,
while Gaussian Mixture Models offer a reasonable accuracy at a consistently
small cost, and Support Vector Machines stand between both in terms of
compromise between accuracy and computational cost
Estimation Of Reservoir Properties From Seismic Data By Smooth Neural Networks
Traditional joint inversion methods reqnire an a priori prescribed operator that links the reservoir properties to the observed seismic response. The methods also rely on a linearized approach to the solution that makes them heavily dependent on the selection of
the starting model. Neural networks provide a useful alternative that is inherently nonlinear and completely data-driven, but the performance of traditional back-propagation
networks in production settings has been inconsistent due to the extensive parameter
tweaking needed to achieve satisfactory results and to avoid overfitting the data. In
addition, the accuracy of these traditional networks is sensitive to network parameters,
such as the network size and training length. We present an approach to estimate the
point-values of the reservoir rock properties (such as porosity) from seismic and well
log data through the use of regularized back propagation and radial basis networks.
Both types of networks have inherent smoothness characteristics that alleviate the nonmonotonous generalization problem associated with traditional networks and help to
avert overfitting the data. The approach we present therefore avoids the drawbacks of
both the joint inversion methods and traditional back-propagation networks. Specifically,
it is inherently nonlinear, requires no a priori operator or initial model, and is not
prone to overfitting problems, thus requiring no extensive parameter experimentation.Massachusetts Institute of Technology. Borehole Acoustics and Logging ConsortiumMassachusetts Institute of Technology. Earth Resources Laboratory. Reservoir Delineation
ConsortiumSaudi Aramc
Neural networks in geophysical applications
Neural networks are increasingly popular in geophysics.
Because they are universal approximators, these
tools can approximate any continuous function with an
arbitrary precision. Hence, they may yield important
contributions to finding solutions to a variety of geophysical applications.
However, knowledge of many methods and techniques
recently developed to increase the performance
and to facilitate the use of neural networks does not seem
to be widespread in the geophysical community. Therefore,
the power of these tools has not yet been explored to
their full extent. In this paper, techniques are described
for faster training, better overall performance, i.e., generalization,and the automatic estimation of network size
and architecture
Study of noise effects in electrical impedance tomography with resistor networks
We present a study of the numerical solution of the two dimensional
electrical impedance tomography problem, with noisy measurements of the
Dirichlet to Neumann map. The inversion uses parametrizations of the
conductivity on optimal grids. The grids are optimal in the sense that finite
volume discretizations on them give spectrally accurate approximations of the
Dirichlet to Neumann map. The approximations are Dirichlet to Neumann maps of
special resistor networks, that are uniquely recoverable from the measurements.
Inversion on optimal grids has been proposed and analyzed recently, but the
study of noise effects on the inversion has not been carried out. In this paper
we present a numerical study of both the linearized and the nonlinear inverse
problem. We take three different parametrizations of the unknown conductivity,
with the same number of degrees of freedom. We obtain that the parametrization
induced by the inversion on optimal grids is the most efficient of the three,
because it gives the smallest standard deviation of the maximum a posteriori
estimates of the conductivity, uniformly in the domain. For the nonlinear
problem we compute the mean and variance of the maximum a posteriori estimates
of the conductivity, on optimal grids. For small noise, we obtain that the
estimates are unbiased and their variance is very close to the optimal one,
given by the Cramer-Rao bound. For larger noise we use regularization and
quantify the trade-off between reducing the variance and introducing bias in
the solution. Both the full and partial measurement setups are considered.Comment: submitted to Inverse Problems and Imagin
Global Seismology of the Sun
The seismic study of the Sun and other stars offers a unique window into the
interior of these stars. Thanks to helioseismology, we know the structure of
the Sun to admirable precision. In fact, our knowledge is good enough to use
the Sun as a laboratory. We have also been able to study the dynamics of the
Sun in great detail. Helioseismic data also allow us to probe the changes that
take place in the Sun as solar activity waxes and wanes. The seismic study of
stars other than the Sun is a fairly new endeavour, but we are making great
strides in this field. In this review I discuss some of the techniques used in
helioseismic analyses and the results obtained using those techniques. In this
review I focus on results obtained with global helioseismology, i.e., the study
of the Sun using its normal modes of oscillation. I also briefly touch upon
asteroseismology, the seismic study of stars other than the Sun, and discuss
how seismic data of others stars are interpreted.Comment: To appear in Living Reviews of Solar Physic
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