13,566 research outputs found
Parallel computing for the finite element method
A finite element method is presented to compute time harmonic microwave
fields in three dimensional configurations. Nodal-based finite elements have
been coupled with an absorbing boundary condition to solve open boundary
problems. This paper describes how the modeling of large devices has been made
possible using parallel computation, New algorithms are then proposed to
implement this formulation on a cluster of workstations (10 DEC ALPHA 300X) and
on a CRAY C98. Analysis of the computation efficiency is performed using simple
problems. The electromagnetic scattering of a plane wave by a perfect electric
conducting airplane is finally given as example
Drichlet forms for Poisson measures and L\'evy processes : the lent particle method
We present a new approach to absolute continuity of laws of Poisson
functionals. The theoretical framework is that of local Dirichlet forms as a
tool to study probability spaces. The method gives rise to a new explicit
calculus that we show first on some simple examples : it consists in adding a
particle and taking it back after computing the gradient. Then we apply it to
SDE's driven by Poisson measure
Impact on floating membranes
When impacted by a rigid object, a thin elastic membrane with negligible
bending rigidity floating on a liquid pool deforms. Two axisymmetric waves
radiating from the impact point propagate. In the first place, a longitudinal
wave front -- associated with in-plane deformation of the membrane and
traveling at constant speed -- separates an outward stress free domain with a
stretched but flat domain. Then, in the stretched domain a dispersive
transverse wave travels at a wave speed that depends on the local stretching
rate. We study the dynamics of this fluid-body system and we show that the wave
dynamics is similar to the capillary waves that propagate at a liquid-gas
interface but with a surface tension coefficient that depends on impact speed.
We emphasize the role of the stretching in the membrane in the wave dynamics
but also in the development of a buckling instability that give rise to radial
wrinkles
Parsing Expression Grammars Made Practical
Parsing Expression Grammars (PEGs) define languages by specifying
recursive-descent parser that recognises them. The PEG formalism exhibits
desirable properties, such as closure under composition, built-in
disambiguation, unification of syntactic and lexical concerns, and closely
matching programmer intuition. Unfortunately, state of the art PEG parsers
struggle with left-recursive grammar rules, which are not supported by the
original definition of the formalism and can lead to infinite recursion under
naive implementations. Likewise, support for associativity and explicit
precedence is spotty. To remedy these issues, we introduce Autumn, a general
purpose PEG library that supports left-recursion, left and right associativity
and precedence rules, and does so efficiently. Furthermore, we identify infix
and postfix operators as a major source of inefficiency in left-recursive PEG
parsers and show how to tackle this problem. We also explore the extensibility
of the PEG paradigm by showing how one can easily introduce new parsing
operators and how our parser accommodates custom memoization and error handling
strategies. We compare our parser to both state of the art and battle-tested
PEG and CFG parsers, such as Rats!, Parboiled and ANTLR.Comment: "Proceedings of the International Conference on Software Language
Engineering (SLE 2015)" - 167-172 (ISBN : 978-1-4503-3686-4
The skeleton of the UIPT, seen from infinity
We prove that geodesic rays in the Uniform Infinite Planar Triangulation
(UIPT) coalesce in a strong sense using the skeleton decomposition of random
triangulations discovered by Krikun. This implies the existence of a unique
horofunction measuring distances from infinity in the UIPT. We then use this
horofunction to define the skeleton "seen from infinity" of the UIPT and relate
it to a simple Galton--Watson tree conditioned to survive, giving a new and
particularly simple construction of the UIPT. Scaling limits of perimeters and
volumes of horohulls within this new decomposition are also derived, as well as
a new proof of the -point function formula for random triangulations in the
scaling limit due to Ambj{\o}rn and Watabiki.Comment: 34 pages, 14 figure
Energy image density property and the lent particle method for Poisson measures
We introduce a new approach to absolute continuity of laws of Poisson
functionals. It is based on the {\it energy image density} property for
Dirichlet forms and on what we call {\it the lent particle method} which
consists in adding a particle and taking it back after some calculation.Comment: 29
Contribution of studies of sub-seismic fracture populations to paleo-hydrological reconstructions (Bighorn Basin, USA)
This work reports on the reconstruction of the paleo-hydrological history of the Bighorn Basin (Wyoming, USA) and illustrates the advantages and drawbacks of using sub-seismic diffuse fracture populations (i.e., micrometric to metric joints and veins forming heterogeneous networks), rather than fault zones, to characterize paleo-fluid systems at both fold and basin scales. Because sub-seismic fractures reliably record the successive steps of deformation of folded rocks, the analysis of the geochemical signatures of fluids that precipitated in these fractures reveals the paleo-fluid history not only during, but also before and after, folding. The present study also points out the need for considering pre-existing fluid systems and basin-scale fluid migrations to reliably constrain the evolution of fluid systems in individual folds
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