13,291 research outputs found
Scalable Approach to Uncertainty Quantification and Robust Design of Interconnected Dynamical Systems
Development of robust dynamical systems and networks such as autonomous
aircraft systems capable of accomplishing complex missions faces challenges due
to the dynamically evolving uncertainties coming from model uncertainties,
necessity to operate in a hostile cluttered urban environment, and the
distributed and dynamic nature of the communication and computation resources.
Model-based robust design is difficult because of the complexity of the hybrid
dynamic models including continuous vehicle dynamics, the discrete models of
computations and communications, and the size of the problem. We will overview
recent advances in methodology and tools to model, analyze, and design robust
autonomous aerospace systems operating in uncertain environment, with stress on
efficient uncertainty quantification and robust design using the case studies
of the mission including model-based target tracking and search, and trajectory
planning in uncertain urban environment. To show that the methodology is
generally applicable to uncertain dynamical systems, we will also show examples
of application of the new methods to efficient uncertainty quantification of
energy usage in buildings, and stability assessment of interconnected power
networks
Shrinkage Estimation of the Power Spectrum Covariance Matrix
We seek to improve estimates of the power spectrum covariance matrix from a
limited number of simulations by employing a novel statistical technique known
as shrinkage estimation. The shrinkage technique optimally combines an
empirical estimate of the covariance with a model (the target) to minimize the
total mean squared error compared to the true underlying covariance. We test
this technique on N-body simulations and evaluate its performance by estimating
cosmological parameters. Using a simple diagonal target, we show that the
shrinkage estimator significantly outperforms both the empirical covariance and
the target individually when using a small number of simulations. We find that
reducing noise in the covariance estimate is essential for properly estimating
the values of cosmological parameters as well as their confidence intervals. We
extend our method to the jackknife covariance estimator and again find
significant improvement, though simulations give better results. Even for
thousands of simulations we still find evidence that our method improves
estimation of the covariance matrix. Because our method is simple, requires
negligible additional numerical effort, and produces superior results, we
always advocate shrinkage estimation for the covariance of the power spectrum
and other large-scale structure measurements when purely theoretical modeling
of the covariance is insufficient.Comment: 9 pages, 7 figures (1 new), MNRAS, accepted. Changes to match
accepted version, including an additional explanatory section with 1 figur
One-point fluctuation analysis of the high-energy neutrino sky
We perform the first one-point fluctuation analysis of the high-energy
neutrino sky. This method reveals itself to be especially suited to
contemporary neutrino data, as it allows to study the properties of the
astrophysical components of the high-energy flux detected by the IceCube
telescope, even with low statistics and in the absence of point source
detection. Besides the veto-passing atmospheric foregrounds, we adopt a simple
model of the high-energy neutrino background by assuming two main
extra-galactic components: star-forming galaxies and blazars. By leveraging
multi-wavelength data from Herschel and Fermi, we predict the spectral and
anisotropic probability distributions for their expected neutrino counts in
IceCube. We find that star-forming galaxies are likely to remain a diffuse
background due to the poor angular resolution of IceCube, and we determine an
upper limit on the number of shower events that can reasonably be associated to
blazars. We also find that upper limits on the contribution of blazars to the
measured flux are unfavourably affected by the skewness of the blazar flux
distribution. One-point event clustering and likelihood analyses of the IceCube
HESE data suggest that this method has the potential to dramatically improve
over more conventional model-based analyses, especially for the next generation
of neutrino telescopes.Comment: 41 pages, 6 figures, 2 tables; different blazar model than v1 but
same result
Screening and metamodeling of computer experiments with functional outputs. Application to thermal-hydraulic computations
To perform uncertainty, sensitivity or optimization analysis on scalar
variables calculated by a cpu time expensive computer code, a widely accepted
methodology consists in first identifying the most influential uncertain inputs
(by screening techniques), and then in replacing the cpu time expensive model
by a cpu inexpensive mathematical function, called a metamodel. This paper
extends this methodology to the functional output case, for instance when the
model output variables are curves. The screening approach is based on the
analysis of variance and principal component analysis of output curves. The
functional metamodeling consists in a curve classification step, a dimension
reduction step, then a classical metamodeling step. An industrial nuclear
reactor application (dealing with uncertainties in the pressurized thermal
shock analysis) illustrates all these steps
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