2,951 research outputs found
Algorithmic Verification of Continuous and Hybrid Systems
We provide a tutorial introduction to reachability computation, a class of
computational techniques that exports verification technology toward continuous
and hybrid systems. For open under-determined systems, this technique can
sometimes replace an infinite number of simulations.Comment: In Proceedings INFINITY 2013, arXiv:1402.661
Suitability of post-Newtonian/numerical-relativity hybrid waveforms for gravitational wave detectors
This article presents a study of the sufficient accuracy of post-Newtonian
and numerical relativity waveforms for the most demanding usage case: parameter
estimation of strong sources in advanced gravitational wave detectors. For
black hole binaries, these detectors require accurate waveform models which can
be constructed by fusing an analytical post-Newtonian inspiral waveform with a
numerical relativity merger-ringdown waveform. We perform a comprehensive
analysis of errors that enter such "hybrid waveforms". We find that the
post-Newtonian waveform must be aligned with the numerical relativity waveform
to exquisite accuracy, about 1/100 of a gravitational wave cycle. Phase errors
in the inspiral phase of the numerical relativity simulation must be controlled
to less than about 0.1rad. (These numbers apply to moderately optimistic
estimates about the number of GW sources; exceptionally strong signals require
even smaller errors.) The dominant source of error arises from the inaccuracy
of the investigated post-Newtonian Taylor-approximants. Using our error
criterium, even at 3.5-th post-Newtonian order, hybridization has to be
performed significantly before the start of the longest currently available
numerical waveforms which cover 30 gravitational wave cycles. The current
investigation is limited to the equal-mass, zero-spin case and does not take
into account calibration errors of the gravitational wave detectors.Comment: 32 pages, 12 figures, submitted to CQG for the NRDA2010 conference
proceedings, added new figure (fig. 5) since last versio
Analysis of parametric biological models with non-linear dynamics
In this paper we present recent results on parametric analysis of biological
models. The underlying method is based on the algorithms for computing
trajectory sets of hybrid systems with polynomial dynamics. The method is then
applied to two case studies of biological systems: one is a cardiac cell model
for studying the conditions for cardiac abnormalities, and the second is a
model of insect nest-site choice.Comment: In Proceedings HSB 2012, arXiv:1208.315
Discontinuous Galerkin approximations in computational mechanics: hybridization, exact geometry and degree adaptivity
Discontinuous Galerkin (DG) discretizations with exact representation of the geometry and local polynomial degree adaptivity are revisited. Hybridization techniques are employed to reduce the computational cost of DG approximations and devise the hybridizable discontinuous Galerkin (HDG) method. Exact geometry described by non-uniform rational B-splines (NURBS) is integrated into HDG using the framework of the NURBS-enhanced finite element method (NEFEM). Moreover, optimal convergence and superconvergence properties of HDG-Voigt formulation in presence of symmetric second-order tensors are exploited to construct inexpensive error indicators and drive degree adaptive procedures. Applications involving the numerical simulation of problems in electrostatics, linear elasticity and incompressible viscous flows are presented. Moreover, this is done for both high-order HDG approximations and the lowest-order framework of face-centered finite volumes (FCFV).Peer ReviewedPostprint (author's final draft
A nested hybridizable discontinuous Galerkin method for computing second-harmonic generation in three-dimensional metallic nanostructures
In this paper, we develop a nested hybridizable discontinuous Galerkin (HDG)
method to numerically solve the Maxwell's equations coupled with the
hydrodynamic model for the conduction-band electrons in metals. By means of a
static condensation to eliminate the degrees of freedom of the approximate
solution defined in the elements, the HDG method yields a linear system in
terms of the degrees of freedom of the approximate trace defined on the element
boundaries. Furthermore, we propose to reorder these degrees of freedom so that
the linear system accommodates a second static condensation to eliminate a
large portion of the degrees of freedom of the approximate trace, thereby
yielding a much smaller linear system. For the particular metallic structures
considered in this paper, the resulting linear system obtained by means of
nested static condensations is a block tridiagonal system, which can be solved
efficiently. We apply the nested HDG method to compute the second harmonic
generation (SHG) on a triangular coaxial periodic nanogap structure. This
nonlinear optics phenomenon features rapid field variations and extreme
boundary-layer structures that span multiple length scales. Numerical results
show that the ability to identify structures which exhibit resonances at
and is paramount to excite the second harmonic response.Comment: 31 pages, 7 figure
Analyzing Binary Black hole Spacetimes
With the first ever detection of gravitational waves from merging black-hole binaries by LIGO (Laser Interferometer GravitationalWave Observatory), a new era of gravitational wave astronomy was started. With its increased sensitivity, LIGO will see many more black-hole binaries in the future. To detect the gravitational waves and elucidate the properties of their sources, one needs theoretical waveform templates. These, in turn, require solving Einstein field equations, at least approximately. Approximate techniques like post-Newtonian theory and black-hole perturbation theory can produce waveforms that are accurate for certain phases of binaries evolution. Numerical relativity, on the other hand, can in principle produce accurate waveforms models for the full binary evolution. However, such simulations are computationally very expensive for the slow inspiral phase. To overcome this issue, we hybridized numerical relativity obtained by solving the Einstein field equations during the late-inspiral, plunge, and ringdown phase and post-Newtonian waveforms for the early-inspiral phase. Here we focus on hybridizing waveforms for precessing black-hole binaries. In this work we also developed a new tool to test the accuracy limits of approximate a binary black-hole spacetimes constructed using analytical approximate techniques. Our method is based on direct comparison to a numerically generated solution to the Einstein field equations
Status of NINJA: the Numerical INJection Analysis project
The 2008 NRDA conference introduced the Numerical INJection Analysis project (NINJA), a new collaborative effort between the numerical relativity community and the data analysis community. NINJA focuses on modeling and searching for gravitational wave signatures from the coalescence of binary system of compact objects. We review the scope of this collaboration and the components of the first NINJA project, where numerical relativity groups shared waveforms and data analysis teams applied various techniques to detect them when embedded in colored Gaussian noise
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