328,296 research outputs found
Sensitivity analysis of the CREAM method for Human Reliability
This paper reports a sensitivity analysis of the CREAM HRA method. We consider three different aspects: the difference between the outputs of the Basic and Extended methods, on the same HRA scenario; the variability in outputs through the choices made for common performance conditions (CPCs); the variability in outputs through the assignment of choices for cognitive function failures (CFFs). We discuss the problem of interpreting categories when applying the method, and discuss also how dependence is modelled with the approach. We show that the control mode intervals used in the Basic method are too narrow to be consistent with the Extended method. This motivates a new screening method that gives improved accuracy with respect to the Basic method, in the sense that (on average) halves the uncertainty associated with the Basic method
Holographic Imaging of Crowded Fields: High Angular Resolution Imaging with Excellent Quality at Very Low Cost
We present a method for speckle holography that is optimised for crowded
fields. Its two key features are an iterativ improvement of the instantaneous
Point Spread Functions (PSFs) extracted from each speckle frame and the
(optional) simultaneous use of multiple reference stars. In this way, high
signal-to-noise and accuracy can be achieved on the PSF for each short
exposure, which results in sensitive, high-Strehl re- constructed images. We
have tested our method with different instruments, on a range of targets, and
from the N- to the I-band. In terms of PSF cosmetics, stability and Strehl
ratio, holographic imaging can be equal, and even superior, to the capabilities
of currently available Adaptive Optics (AO) systems, particularly at short
near-infrared to optical wavelengths. It outperforms lucky imaging because it
makes use of the entire PSF and reduces the need for frame selection, thus
leading to higher Strehl and improved sensitivity. Image reconstruction a
posteriori, the possibility to use multiple reference stars and the fact that
these reference stars can be rather faint means that holographic imaging offers
a simple way to image large, dense stellar fields near the diffraction limit of
large telescopes, similar to, but much less technologically demanding than, the
capabilities of a multi-conjugate adaptive optics system. The method can be
used with a large range of already existing imaging instruments and can also be
combined with AO imaging when the corrected PSF is unstable.Comment: Accepted for publication in MNRAS on 15 Nov 201
Structural sensitivity analysis: Methods, applications, and needs
Some innovative techniques applicable to sensitivity analysis of discretized structural systems are reviewed. These techniques include a finite-difference step-size selection algorithm, a method for derivatives of iterative solutions, a Green's function technique for derivatives of transient response, a simultaneous calculation of temperatures and their derivatives, derivatives with respect to shape, and derivatives of optimum designs with respect to problem parameters. Computerized implementations of sensitivity analysis and applications of sensitivity derivatives are also discussed. Finally, some of the critical needs in the structural sensitivity area are indicated along with Langley plans for dealing with some of these needs
Progressive Mauve: Multiple alignment of genomes with gene flux and rearrangement
Multiple genome alignment remains a challenging problem. Effects of
recombination including rearrangement, segmental duplication, gain, and loss
can create a mosaic pattern of homology even among closely related organisms.
We describe a method to align two or more genomes that have undergone
large-scale recombination, particularly genomes that have undergone substantial
amounts of gene gain and loss (gene flux). The method utilizes a novel
alignment objective score, referred to as a sum-of-pairs breakpoint score. We
also apply a probabilistic alignment filtering method to remove erroneous
alignments of unrelated sequences, which are commonly observed in other genome
alignment methods. We describe new metrics for quantifying genome alignment
accuracy which measure the quality of rearrangement breakpoint predictions and
indel predictions. The progressive genome alignment algorithm demonstrates
markedly improved accuracy over previous approaches in situations where genomes
have undergone realistic amounts of genome rearrangement, gene gain, loss, and
duplication. We apply the progressive genome alignment algorithm to a set of 23
completely sequenced genomes from the genera Escherichia, Shigella, and
Salmonella. The 23 enterobacteria have an estimated 2.46Mbp of genomic content
conserved among all taxa and total unique content of 15.2Mbp. We document
substantial population-level variability among these organisms driven by
homologous recombination, gene gain, and gene loss. Free, open-source software
implementing the described genome alignment approach is available from
http://gel.ahabs.wisc.edu/mauve .Comment: Revision dated June 19, 200
Improved Perturbation Method and its Application to the IIB Matrix Model
We present a new scheme for extracting approximate values in ``the improved
perturbation method'', which is a sort of resummation technique capable of
evaluating a series outside the radius of convergence. We employ the
distribution profile of the series that is weighted by nth-order derivatives
with respect to the artificially introduced parameters. By those weightings the
distribution becomes more sensitive to the ``plateau'' structure in which the
consistency condition of the method is satisfied. The scheme works effectively
even in such cases that the system involves many parameters. We also propose
that this scheme has to be applied to each observables separately and be
analyzed comprehensively.
We apply this scheme to the analysis of the IIB matrix model by the improved
perturbation method obtained up to eighth order of perturbation in the former
works. We consider here the possibility of spontaneous breakdown of Lorentz
symmetry, and evaluate the free energy and the anisotropy of space-time extent.
In the present analysis, we find an SO(10)-symmetric vacuum besides the SO(4)-
and SO(7)-symmetric vacua that have been observed. It is also found that there
are two distinct SO(4)-symmetric vacua that have almost the same value of free
energy but the extent of space-time is different. From the approximate values
of free energy, we conclude that the SO(4)-symmetric vacua are most preferred
among those three types of vacua.Comment: 52 pages, published versio
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