18,633 research outputs found
Lmit and shakedown analysis based on solid shell models
The paper treats the formulation of the shakedown problem and, as special case, of the limit analysis problem, using solid shell models and ES-FEM discratization technology. In this proposal the Discrete shear gap method is applied to alleviate the shear locking phenomenon
Non-linear coupled CNN models for multiscale image analysis
A CNN model of partial differential equations (PDEs) for image multiscale analysis is proposed. The model is based on a polynomial representation of the diffusivity function and defines a paradigm of polynomial CNNs,for approximating a large class of nonlinear isotropic and/or anisotropic PDEs. The global dynamics of spacediscrete polynomial CNN models is analyzed and compared with the dynamic behavior of the corresponding space-continuous PDE models. It is shown that in the isotropic case the two models are not topologically equivalent: in particular discrete CNN models allow one to obtain the output image without stopping the image evolution after a given time (scale). This property represents an advantage with respect to continuous PDE models and could simplify some image preprocessing algorithm
Multiscale Computations on Neural Networks: From the Individual Neuron Interactions to the Macroscopic-Level Analysis
We show how the Equation-Free approach for multi-scale computations can be
exploited to systematically study the dynamics of neural interactions on a
random regular connected graph under a pairwise representation perspective.
Using an individual-based microscopic simulator as a black box coarse-grained
timestepper and with the aid of simulated annealing we compute the
coarse-grained equilibrium bifurcation diagram and analyze the stability of the
stationary states sidestepping the necessity of obtaining explicit closures at
the macroscopic level. We also exploit the scheme to perform a rare-events
analysis by estimating an effective Fokker-Planck describing the evolving
probability density function of the corresponding coarse-grained observables
Aspects of stochastic resonance in reaction-diffusion systems: The nonequilibrium-potential approach
We analyze several aspects of the phenomenon of stochastic resonance in
reaction-diffusion systems, exploiting the nonequilibrium potential's
framework. The generalization of this formalism (sketched in the appendix) to
extended systems is first carried out in the context of a simplified scalar
model, for which stationary patterns can be found analytically. We first show
how system-size stochastic resonance arises naturally in this framework, and
then how the phenomenon of array-enhanced stochastic resonance can be further
enhanced by letting the diffusion coefficient depend on the field. A yet less
trivial generalization is exemplified by a stylized version of the
FitzHugh-Nagumo system, a paradigm of the activator-inhibitor class. After
discussing for this system the second aspect enumerated above, we derive from
it -through an adiabatic-like elimination of the inhibitor field- an effective
scalar model that includes a nonlocal contribution. Studying the role played by
the range of the nonlocal kernel and its effect on stochastic resonance, we
find an optimal range that maximizes the system's response.Comment: 16 pages, 15 figures, uses svjour.cls and svepj-spec.clo. Minireview
to appear in The European Physical Journal Special Topics (issue in memory of
Carlos P\'erez-Garc\'{\i}a, edited by H. Mancini
Study of the 3D Coronal Magnetic Field of Active Region 11117 Around the Time of a Confined Flare Using a Data-Driven CESE--MHD Model
We apply a data-driven MHD model to investigate the three-dimensional (3D)
magnetic field of NOAA active region (AR) 11117 around the time of a C-class
confined flare occurred on 2010 October 25. The MHD model, based on the
spacetime conservation-element and solution-element (CESE) scheme, is designed
to focus on the magnetic-field evolution and to consider a simplified solar
atomsphere with finite plasma . Magnetic vector-field data derived from
the observations at the photoshpere is inputted directly to constrain the
model. Assuming that the dynamic evolution of the coronal magnetic field can be
approximated by successive equilibria, we solve a time sequence of MHD
equilibria basing on a set of vector magnetograms for AR 11117 taken by the
Helioseismic and Magnetic Imager (HMI) on board the {\it Solar Dynamic
Observatory (SDO)} around the time of flare. The model qualitatively reproduces
the basic structures of the 3D magnetic field, as supported by the visual
similarity between the field lines and the coronal loops observed by the
Atmospheric Imaging Assembly (AIA), which shows that the coronal field can
indeed be well characterized by the MHD equilibrium in most time. The magnetic
configuration changes very limited during the studied time interval of two
hours. A topological analysis reveals that the small flare is correlated with a
bald patch (BP, where the magnetic field is tangent to the photoshpere),
suggesting that the energy release of the flare can be understood by magnetic
reconnection associated with the BP separatrices. The total magnetic flux and
energy keep increasing slightly in spite of the flare, while the computed
magnetic free energy drops during the flare with an amount of
erg, which seems to be adequate to provide the energy budget of the minor
C-class confined flare.Comment: 27 pages, 11 figures, Accepted by Ap
Task-based adaptive multiresolution for time-space multi-scale reaction-diffusion systems on multi-core architectures
A new solver featuring time-space adaptation and error control has been
recently introduced to tackle the numerical solution of stiff
reaction-diffusion systems. Based on operator splitting, finite volume adaptive
multiresolution and high order time integrators with specific stability
properties for each operator, this strategy yields high computational
efficiency for large multidimensional computations on standard architectures
such as powerful workstations. However, the data structure of the original
implementation, based on trees of pointers, provides limited opportunities for
efficiency enhancements, while posing serious challenges in terms of parallel
programming and load balancing. The present contribution proposes a new
implementation of the whole set of numerical methods including Radau5 and
ROCK4, relying on a fully different data structure together with the use of a
specific library, TBB, for shared-memory, task-based parallelism with
work-stealing. The performance of our implementation is assessed in a series of
test-cases of increasing difficulty in two and three dimensions on multi-core
and many-core architectures, demonstrating high scalability
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