42,952 research outputs found
A massively parallel multi-level approach to a domain decomposition method for the optical flow estimation with varying illumination
We consider a variational method to solve the optical flow problem with
varying illumination. We apply an adaptive control of the regularization
parameter which allows us to preserve the edges and fine features of the
computed flow. To reduce the complexity of the estimation for high resolution
images and the time of computations, we implement a multi-level parallel
approach based on the domain decomposition with the Schwarz overlapping method.
The second level of parallelism uses the massively parallel solver MUMPS. We
perform some numerical simulations to show the efficiency of our approach and
to validate it on classical and real-world image sequences
Cell organization in soft media due to active mechanosensing
Adhering cells actively probe the mechanical properties of their environment
and use the resulting information to position and orient themselves. We show
that a large body of experimental observations can be consistently explained
from one unifying principle, namely that cells strengthen contacts and
cytoskeleton in the direction of large effective stiffness. Using linear
elasticity theory to model the extracellular environment, we calculate optimal
cell organization for several situations of interest and find excellent
agreement with experiments for fibroblasts, both on elastic substrates and in
collagen gels: cells orient in the direction of external tensile strain, they
orient parallel and normal to free and clamped surfaces, respectively, and they
interact elastically to form strings. Our method can be applied for rational
design of tissue equivalents. Moreover our results indicate that the concept of
contact guidance has to be reevaluated. We also suggest that cell-matrix
contacts are upregulated by large effective stiffness in the environment
because in this way, build-up of force is more efficient.Comment: Revtex, 7 pages, 4 Postscript files include
Domain Decomposition Based High Performance Parallel Computing\ud
The study deals with the parallelization of finite element based Navier-Stokes codes using domain decomposition and state-ofart sparse direct solvers. There has been significant improvement in the performance of sparse direct solvers. Parallel sparse direct solvers are not found to exhibit good scalability. Hence, the parallelization of sparse direct solvers is done using domain decomposition techniques. A highly efficient sparse direct solver PARDISO is used in this study. The scalability of both Newton and modified Newton algorithms are tested
Analysis of Schwarz methods for a hybridizable discontinuous Galerkin discretization
Schwarz methods are attractive parallel solvers for large scale linear
systems obtained when partial differential equations are discretized. For
hybridizable discontinuous Galerkin (HDG) methods, this is a relatively new
field of research, because HDG methods impose continuity across elements using
a Robin condition, while classical Schwarz solvers use Dirichlet transmission
conditions. Robin conditions are used in optimized Schwarz methods to get
faster convergence compared to classical Schwarz methods, and this even without
overlap, when the Robin parameter is well chosen. We present in this paper a
rigorous convergence analysis of Schwarz methods for the concrete case of
hybridizable interior penalty (IPH) method. We show that the penalization
parameter needed for convergence of IPH leads to slow convergence of the
classical additive Schwarz method, and propose a modified solver which leads to
much faster convergence. Our analysis is entirely at the discrete level, and
thus holds for arbitrary interfaces between two subdomains. We then generalize
the method to the case of many subdomains, including cross points, and obtain a
new class of preconditioners for Krylov subspace methods which exhibit better
convergence properties than the classical additive Schwarz preconditioner. We
illustrate our results with numerical experiments.Comment: 25 pages, 5 figures, 3 tables, accepted for publication in SINU
Parallel preconditioners for high order discretizations arising from full system modeling for brain microwave imaging
This paper combines the use of high order finite element methods with
parallel preconditioners of domain decomposition type for solving
electromagnetic problems arising from brain microwave imaging. The numerical
algorithms involved in such complex imaging systems are computationally
expensive since they require solving the direct problem of Maxwell's equations
several times. Moreover, wave propagation problems in the high frequency regime
are challenging because a sufficiently high number of unknowns is required to
accurately represent the solution. In order to use these algorithms in practice
for brain stroke diagnosis, running time should be reasonable. The method
presented in this paper, coupling high order finite elements and parallel
preconditioners, makes it possible to reduce the overall computational cost and
simulation time while maintaining accuracy
An efficient nonlinear cardinal B-spline model for high tide forecasts at the Venice Lagoon
An efficient class of nonlinear models, constructed using cardinal B-spline (CBS) basis functions, are proposed for high tide forecasts at the Venice lagoon. Accurate short term predictions of high tides in the lagoon can easily be calculated using the proposed CBS models
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