3,874 research outputs found
A Onelab model for the parametric study of mono-dimensional diffraction gratings
This document aims at presenting both theoretical and practical aspects of
the grating_2D Onelab model (available at
http://onelab.info/wiki/Diffraction_grating). This model applies to so-called
mono-dimensional grating, i.e. structures having one direction of invariance.
Various geometries and materials can be handled or easily added. The two
classical polarization cases, denoted here E// and H//, are addressed. The
output consists in a full energy balance of the problem computed from the field
maps. This model is based on free the GNU softwares Gmsh, GetDP and their
interface Onelab.Comment: arXiv admin note: text overlap with arXiv:1302.103
A Fast Algorithm for the Construction of Integrity Bases Associated to Symmetry-Adapted Polynomial Representations. Application to Tetrahedral XY4 Molecules
Invariant theory provides more efficient tools, such as Molien generating
functions and integrity bases, than basic group theory, that relies on
projector techniques for the construction of symmetry--adapted polynomials in
the symmetry coordinates of a molecular system, because it is based on a finer
description of the mathematical structure of the latter. The present article
extends its use to the construction of polynomial bases which span possibly,
non--totally symmetric irreducible representations of a molecular symmetry
group. Electric or magnetic observables can carry such irreducible
representations, a common example is given by the electric dipole moment
surface. The elementary generating functions and their corresponding integrity
bases, where both the initial and the final representations are irreducible,
are the building blocks of the algorithm presented in this article, which is
faster than algorithms based on projection operators only. The generating
functions for the full initial representation of interest are built recursively
from the elementary generating functions. Integrity bases which can be used to
generate in the most economical way symmetry--adapted polynomial bases are
constructed alongside in the same fashion. The method is illustrated in detail
on XY4 type of molecules. Explicit integrity bases for all five possible final
irreducible representations of the tetrahedral group have been calculated and
are given in the supplemental material associated with this paper
Non-Uniform Time Sampling for Multiple-Frequency Harmonic Balance Computations
A time-domain harmonic balance method for the analysis of almost-periodic (multi-harmonics) flows is presented. This method relies on Fourier analysis to derive an efficient alternative to classical time marching schemes for such flows. It has recently received significant attention, especially in the turbomachinery field where the flow spectrum is essentially a combination of the blade passing frequencies. Up to now, harmonic balance methods have used a uniform time sampling of the period of interest, but in the case of several frequencies, non-necessarily multiple of each other, harmonic balance methods can face stability issues due to a bad condition number of the Fourier operator. Two algorithms are derived to find a non-uniform time sampling in order to minimize this condition number. Their behavior is studied on a wide range of frequencies, and a model problem of a 1D flow with pulsating outlet pressure, which enables to prove their efficiency. Finally, the flow in a multi-stage axial compressor is analyzed with different frequency sets. It demonstrates the stability and robustness of the present non-uniform harmonic balance method regardless of the frequency set
How do interactive tabletop systems influence collaboration?
This paper examines some aspects of the usefulness of interactive tabletop systems, if and how these impact collaboration. We chose creative problem solving such as brainstorming as an application framework to test several collaborative media: the use of pen-and-paper tools, the ââaround-the-tableââ form factor, the digital tabletop interface, the attractiveness of interaction styles. Eighty subjects in total (20 groups of four members) participated in the experiments. The evaluation criteria were task performance, collaboration patterns (especially equity of contributions), and usersâ subjective experience. The ââaroundthe-tableââ form factor, which is hypothesized to promote social comparison, increased performance and improved collaboration through an increase of equity. Moreover, the attractiveness of the tabletop device improved subjective experience and increased motivation to engage in the task. However, designing attractiveness seems a highly challenging issue, since overly attractive interfaces may distract users from the task
A finite-element toolbox for the stationary Gross-Pitaevskii equation with rotation
We present a new numerical system using classical finite elements with mesh
adaptivity for computing stationary solutions of the Gross-Pitaevskii equation.
The programs are written as a toolbox for FreeFem++ (www.freefem.org), a free
finite-element software available for all existing operating systems. This
offers the advantage to hide all technical issues related to the implementation
of the finite element method, allowing to easily implement various numerical
algorithms.Two robust and optimised numerical methods were implemented to
minimize the Gross-Pitaevskii energy: a steepest descent method based on
Sobolev gradients and a minimization algorithm based on the state-of-the-art
optimization library Ipopt. For both methods, mesh adaptivity strategies are
implemented to reduce the computational time and increase the local spatial
accuracy when vortices are present. Different run cases are made available for
2D and 3D configurations of Bose-Einstein condensates in rotation. An optional
graphical user interface is also provided, allowing to easily run predefined
cases or with user-defined parameter files. We also provide several
post-processing tools (like the identification of quantized vortices) that
could help in extracting physical features from the simulations. The toolbox is
extremely versatile and can be easily adapted to deal with different physical
models
Checkpointing algorithms and fault prediction
This paper deals with the impact of fault prediction techniques on
checkpointing strategies. We extend the classical first-order analysis of Young
and Daly in the presence of a fault prediction system, characterized by its
recall and its precision. In this framework, we provide an optimal algorithm to
decide when to take predictions into account, and we derive the optimal value
of the checkpointing period. These results allow to analytically assess the key
parameters that impact the performance of fault predictors at very large scale.Comment: Supported in part by ANR Rescue. Published in Journal of Parallel and
Distributed Computing. arXiv admin note: text overlap with arXiv:1207.693
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