44,775 research outputs found
Systematic and random errors in rotating-analyzer, ellipsometry
Errors and error sources occurring in rotating-analyzer ellipsometry are discussed. From general considerations it is shown that a rotating-analyzer ellipsometer is inaccurate if applied at P = 0° and in cases when π = 0° or where Δ is near 0° or 180°. Window errors, component imperfections, azimuth errors and all other errors may, to first order, be treated independently and can subsequently be added. Explicit first-order expressions for the errors δΔ and δπ caused by windows, component imperfections, and azimuth errors are derived, showing that all of them, except the window errors, are eliminated in a two-zone measurement. Higher-order errors that are due to azimuth errors are studied numerically, revealing that they are in general less than 0.1°. Statistical errors are also discussed. Errors caused by noise and by correlated perturbations, i.e., periodic fluctuations of the light source, are also considered. Such periodic perturbations do cause random errors, especially when they have frequencies near 2ωA and 4ωA
Efficiently decoding Reed-Muller codes from random errors
Reed-Muller codes encode an -variate polynomial of degree by
evaluating it on all points in . We denote this code by .
The minimal distance of is and so it cannot correct more
than half that number of errors in the worst case. For random errors one may
hope for a better result.
In this work we give an efficient algorithm (in the block length ) for
decoding random errors in Reed-Muller codes far beyond the minimal distance.
Specifically, for low rate codes (of degree ) we can correct a
random set of errors with high probability. For high rate codes
(of degree for ), we can correct roughly
errors.
More generally, for any integer , our algorithm can correct any error
pattern in for which the same erasure pattern can be corrected
in . The results above are obtained by applying recent results
of Abbe, Shpilka and Wigderson (STOC, 2015), Kumar and Pfister (2015) and
Kudekar et al. (2015) regarding the ability of Reed-Muller codes to correct
random erasures.
The algorithm is based on solving a carefully defined set of linear equations
and thus it is significantly different than other algorithms for decoding
Reed-Muller codes that are based on the recursive structure of the code. It can
be seen as a more explicit proof of a result of Abbe et al. that shows a
reduction from correcting erasures to correcting errors, and it also bares some
similarities with the famous Berlekamp-Welch algorithm for decoding
Reed-Solomon codes.Comment: 18 pages, 2 figure
Sequential bifurcation for observations with random errors
Simulation;Bifurcation;analyse
Redundancy Allocation of Partitioned Linear Block Codes
Most memories suffer from both permanent defects and intermittent random
errors. The partitioned linear block codes (PLBC) were proposed by Heegard to
efficiently mask stuck-at defects and correct random errors. The PLBC have two
separate redundancy parts for defects and random errors. In this paper, we
investigate the allocation of redundancy between these two parts. The optimal
redundancy allocation will be investigated using simulations and the simulation
results show that the PLBC can significantly reduce the probability of decoding
failure in memory with defects. In addition, we will derive the upper bound on
the probability of decoding failure of PLBC and estimate the optimal redundancy
allocation using this upper bound. The estimated redundancy allocation matches
the optimal redundancy allocation well.Comment: 5 pages, 2 figures, to appear in IEEE International Symposium on
Information Theory (ISIT), Jul. 201
The consistency of estimator under fixed design regression model with NQD errors
In this article, basing on NQD samples, we investigate the fixed design
nonparametric regression model, where the errors are pairwise NQD random
errors, with fixed design points, and an unknown function. Nonparametric
weighted estimator will be introduced and its consistency is studied. As
special case, the consistency result for weighted kernel estimators of the
model is obtained. This extends the earlier work on independent random and
dependent random errors to NQD case
Two Theorems in List Decoding
We prove the following results concerning the list decoding of
error-correcting codes:
(i) We show that for \textit{any} code with a relative distance of
(over a large enough alphabet), the following result holds for \textit{random
errors}: With high probability, for a \rho\le \delta -\eps fraction of random
errors (for any \eps>0), the received word will have only the transmitted
codeword in a Hamming ball of radius around it. Thus, for random errors,
one can correct twice the number of errors uniquely correctable from worst-case
errors for any code. A variant of our result also gives a simple algorithm to
decode Reed-Solomon codes from random errors that, to the best of our
knowledge, runs faster than known algorithms for certain ranges of parameters.
(ii) We show that concatenated codes can achieve the list decoding capacity
for erasures. A similar result for worst-case errors was proven by Guruswami
and Rudra (SODA 08), although their result does not directly imply our result.
Our results show that a subset of the random ensemble of codes considered by
Guruswami and Rudra also achieve the list decoding capacity for erasures.
Our proofs employ simple counting and probabilistic arguments.Comment: 19 pages, 0 figure
On the effect of random errors in gridded bathymetric compilations
We address the problem of compiling bathymetric data sets with heterogeneous coverage and a range of data measurement accuracies. To generate a regularly spaced grid, we are obliged to interpolate sparse data; our objective here is to augment this product with an estimate of confidence in the interpolated bathymetry based on our knowledge of the component of random error in the bathymetric source data. Using a direct simulation Monte Carlo method, we utilize data from the International Bathymetric Chart of the Arctic Ocean database to develop a suitable methodology for assessment of the standard deviations of depths in the interpolated grid. Our assessment of random errors in each data set are heuristic but realistic and are based on available metadata from the data providers. We show that a confidence grid can be built using this method and that this product can be used to assess reliability of the final compilation. The methodology as developed here is applied to bathymetric data but is equally applicable to other interpolated data sets, such as gravity and magnetic data
Random Errors in Superconducting Dipoles
The magnetic field in a superconducting magnet is mainly determined by the position of the conductors. Hence, the main contribution to the random field errors comes from random displacement of the coil with respect to its nominal position. Using a Monte-Carlo method, we analyze the measured random field errors of the main dipoles of the LHC, Tevatron, RHIC and HERA projects in order to estimate the precision of the conductor positioning reached during the production. The method can be used to obtain more refined estimates of the random components for future projects
Distances and absolute magnitudes from trigonometric parallaxes
We first review the current knowledge of Hipparcos systematic and random
errors, in particular small-scale correlations. Then, assuming Gaussian
parallax errors and using examples from the recent Hipparcos literature, we
show how random errors may be misinterpreted as systematic errors, or
transformed into systematic errors.
Finally we summarise how to get unbiased estimates of absolute magnitudes and
distances, using either Bayesian or non-parametrical methods. These methods may
be applied to get either mean quantities or individual estimates. In
particular, we underline the notion of astrometry-based luminosity, which
avoids the truncation biases and allows a full use of Hipparcos samples.Comment: 20 pages, 8 figures, Invited paper in Haguenau Colloquium
"Harmonizing Cosmic Distance Scales in a Post-Hipparcos Era", 14-16/09/98, to
appear in ASP Conf. Series, D. Egret and A. Heck ed
- …