37,379 research outputs found
4D Seismic History Matching Incorporating Unsupervised Learning
The work discussed and presented in this paper focuses on the history
matching of reservoirs by integrating 4D seismic data into the inversion
process using machine learning techniques. A new integrated scheme for the
reconstruction of petrophysical properties with a modified Ensemble Smoother
with Multiple Data Assimilation (ES-MDA) in a synthetic reservoir is proposed.
The permeability field inside the reservoir is parametrised with an
unsupervised learning approach, namely K-means with Singular Value
Decomposition (K-SVD). This is combined with the Orthogonal Matching Pursuit
(OMP) technique which is very typical for sparsity promoting regularisation
schemes. Moreover, seismic attributes, in particular, acoustic impedance, are
parametrised with the Discrete Cosine Transform (DCT). This novel combination
of techniques from machine learning, sparsity regularisation, seismic imaging
and history matching aims to address the ill-posedness of the inversion of
historical production data efficiently using ES-MDA. In the numerical
experiments provided, I demonstrate that these sparse representations of the
petrophysical properties and the seismic attributes enables to obtain better
production data matches to the true production data and to quantify the
propagating waterfront better compared to more traditional methods that do not
use comparable parametrisation techniques
Integrated structural analysis tool using linear matching method part 2 : Application and verification
In an accompanying paper, a new integrated structural analysis tool using the LMM framework for the assessment of design limits in plasticity including load carrying capacity, shakedown limit, ratchet limit and steady state cyclic response of structures was developed using Abaqus CAE plug-‐ins with graphical user interfaces. In the present paper, a demonstration of the use of this new LMM analysis tool is provided. A header branch pipe in a typical AGR power plant is analysed as a worked example of the current demonstration and verification of the LMM tool within the context of an R5 assessment. The detailed shakedown analysis, steady state cycle and ratchet analysis are carried out for the chosen header branch pipe. The comparisons of the LMM solutions with the results based on the R5 procedure and the step-‐by-‐step elastic-‐plastic FEA verify the accuracy, convenience and efficiency of this new integrated LMM structural analysis tool
Subspace-Based Holistic Registration for Low-Resolution Facial Images
Subspace-based holistic registration is introduced as an alternative to landmark-based face registration, which has a poor performance on low-resolution images, as obtained in camera surveillance applications. The proposed registration method finds the alignment by maximizing the similarity score between a probe and a gallery image. We use a novel probabilistic framework for both user-independent as well as user-specific face registration. The similarity is calculated using the probability that the face image is correctly aligned in a face subspace, but additionally we take the probability into account that the face is misaligned based on the residual error in the dimensions perpendicular to the face subspace. We perform extensive experiments on the FRGCv2 database to evaluate the impact that the face registration methods have on face recognition. Subspace-based holistic registration on low-resolution images can improve face recognition in comparison with landmark-based registration on high-resolution images. The performance of the tested face recognition methods after subspace-based holistic registration on a low-resolution version of the FRGC database is similar to that after manual registration
Controlling solid elastic waves with spherical cloaks
We propose a cloak for coupled shear and pressure waves in solids. Its
elastic properties are deduced from a geometric transform that retains the form
of Navier equations. The spherical shell is made of an anisotropic and
heterogeneous medium described by an elasticity tensor C' (without the minor
symmetries) which has 21 non-zero spatially varying coefficients in spherical
coordinates. Although some entries of C, e.g. some with a radial subscript, and
the density (a scalar radial function) vanish on the inner boundary of the
cloak, this metamaterial exhibits less singularities than its cylindrical
counterpart studied in [M. Brun, S. Guenneau, A.B. Movchan, Appl. Phys. Lett.
94, 061903 (2009).]
In the latter work, C' suffered some infinite entries, unlike in our case.
Finite element computations confirm that elastic waves are smoothly detoured
around a spherical void without reflection.Comment: Version 3: minor typos corrected. Figures captions improved. 5
figures. Key words: 3D elastic cloaking, seismic metamaterials. This paper is
the cover of the 14 July 2014 issue of Applied Physics Letter
Measuring cellular traction forces on non-planar substrates
Animal cells use traction forces to sense the mechanics and geometry of their
environment. Measuring these traction forces requires a workflow combining cell
experiments, image processing and force reconstruction based on elasticity
theory. Such procedures have been established before mainly for planar
substrates, in which case one can use the Green's function formalism. Here we
introduce a worksflow to measure traction forces of cardiac myofibroblasts on
non-planar elastic substrates. Soft elastic substrates with a wave-like
topology were micromolded from polydimethylsiloxane (PDMS) and fluorescent
marker beads were distributed homogeneously in the substrate. Using feature
vector based tracking of these marker beads, we first constructed a hexahedral
mesh for the substrate. We then solved the direct elastic boundary volume
problem on this mesh using the finite element method (FEM). Using data
simulations, we show that the traction forces can be reconstructed from the
substrate deformations by solving the corresponding inverse problem with a
L1-norm for the residue and a L2-norm for 0th order Tikhonov regularization.
Applying this procedure to the experimental data, we find that cardiac
myofibroblast cells tend to align both their shapes and their forces with the
long axis of the deformable wavy substrate.Comment: 34 pages, 9 figure
Acoustic Supercoupling in a Zero-Compressibility Waveguide
Funneling acoustic waves through largely mismatched channels is of
fundamental importance to tailor and transmit sound for a variety of
applications. In electromagnetics, zero-permittivity metamaterials have been
used to enhance the coupling of energy in and out of ultranarrow channels,
based on a phenomenon known as supercoupling. These metamaterial channels can
support total transmission and complete phase uniformity, independent of the
channel length, despite being geometrically mismatched to their input and
output ports. In the field of acoustics, this phenomenon is challenging to
achieve, since it requires zero-density metamaterials, typically realized with
waveguides periodically loaded with membranes or resonators. Compared to
electromagnetics, the additional challenge is due to the fact that conventional
acoustic waveguides do not support a cut-off for the dominant mode of
propagation, and therefore zero-index can be achieved only based on a
collective resonance of the loading elements. Here we propose and
experimentally realize acoustic supercoupling in a dual regime, using a
compressibility-near-zero acoustic channel. Rather than engineering the channel
with subwavelength inclusions, we operate at the cut-off of a higher-order
acoustic mode, demonstrating the realization and efficient excitation of a
zero-compressibility waveguide with effective soft boundaries. We
experimentally verify strong transmission through a largely mismatched channel
and uniform phase distribution, independent of the channel length. Our results
open interesting pathways towards the realization of extreme acoustic
parameters, and their implementation in relevant applications, such as
ultrasound imaging, sonar technology, and sound transmission
Efficient and robust constitutive integrators for single-crystal plasticity modeling
Simulations of the dynamic deformations of metal samples require
elastic-plastic constitutive updates of the material behavior to be performed
over a small time step between updates, as dictated by the Courant condition.
Depending on the deformation conditions, the converged time step becomes short
(~ or less). If an implicit constitutive update is applied to this
class of simulation, the benefit of the implicit update is negated, and the
integration is prohibitively slow. The present work recasts an implicit update
algorithm into an explicit form, for which each update step is five to six
times faster, and the compute time required for a plastic update approaches
that needed for a fully-elastic update. For dynamic loading conditions, the
explicit model is found to perform an entire simulation up to 50 times faster
than the implicit model. The performance of the explicit model is enhanced by
adding a subcycling algorithm to the explicit model, by which the maximum time
step between constitutive updates is increased an order of magnitude. These
model improvements do not significantly change the predictions of the model
from the implicit form, and provide overall computation times significantly
faster than the implicit form over finite-element meshes. These modifications
are also applied to polycrystals via Taylor averaging, where we also see
improved model performance.Comment: 27 pages, 21 figure
Sparse Modeling for Image and Vision Processing
In recent years, a large amount of multi-disciplinary research has been
conducted on sparse models and their applications. In statistics and machine
learning, the sparsity principle is used to perform model selection---that is,
automatically selecting a simple model among a large collection of them. In
signal processing, sparse coding consists of representing data with linear
combinations of a few dictionary elements. Subsequently, the corresponding
tools have been widely adopted by several scientific communities such as
neuroscience, bioinformatics, or computer vision. The goal of this monograph is
to offer a self-contained view of sparse modeling for visual recognition and
image processing. More specifically, we focus on applications where the
dictionary is learned and adapted to data, yielding a compact representation
that has been successful in various contexts.Comment: 205 pages, to appear in Foundations and Trends in Computer Graphics
and Visio
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