37,563 research outputs found
An upper bound from helioseismology on the stochastic background of gravitational waves
The universe is expected to be permeated by a stochastic background of
gravitational radiation of astrophysical and cosmological origin. This
background is capable of exciting oscillations in solar-like stars. Here we
show that solar-like oscillators can be employed as giant hydrodynamical
detectors for such a background in the muHz to mHz frequency range, which has
remained essentially unexplored until today. We demonstrate this approach by
using high-precision radial velocity data for the Sun to constrain the
normalized energy density of the stochastic gravitational-wave background
around 0.11 mHz. These results open up the possibility for asteroseismic
missions like CoRoT and Kepler to probe fundamental physics.Comment: 6 pages, 2 figures. Updated to match published versio
Generalized decoding, effective channels, and simplified security proofs in quantum key distribution
Prepare and measure quantum key distribution protocols can be decomposed into
two basic steps: delivery of the signals over a quantum channel and
distillation of a secret key from the signal and measurement records by
classical processing and public communication. Here we formalize the
distillation process for a general protocol in a purely quantum-mechanical
framework and demonstrate that it can be viewed as creating an ``effective''
quantum channel between the legitimate users Alice and Bob. The process of
secret key generation can then be viewed as entanglement distribution using
this channel, which enables application of entanglement-based security proofs
to essentially any prepare and measure protocol. To ensure secrecy of the key,
Alice and Bob must be able to estimate the channel noise from errors in the
key, and we further show how symmetries of the distillation process simplify
this task. Applying this method, we prove the security of several key
distribution protocols based on equiangular spherical codes.Comment: 9.1 pages REVTeX. (v3): published version. (v2): revised for improved
presentation; content unchange
Developmental improvement and age-related decline in unfamiliar face matching
Age-related changes have been documented widely in studies of face recognition and eyewitness identification. However, it is not clear whether these changes arise from general developmental differences in memory or occur specifically during the perceptual processing of faces. We report two experiments to track such perceptual changes using a 1-in-10 (Experiment 1) and 1-in-1 (Experiment 2) matching task for unfamiliar faces. Both experiments showed improvements in face matching during childhood and adult-like accuracy levels by adolescence. In addition, face-matching performance declined in adults of the age of 65. These findings indicate that developmental improvements and aging-related differences in face processing arise from changes in the perceptual encoding of faces. A clear face inversion effect was also present in all age groups. This indicates that those age-related changes in face matching reflect a quantitative effect, whereby typical face processes are engaged but do not operate at the best-possible level. These data suggest that part of the problem of eyewitness identification in children and elderly persons might reflect impairments in the perceptual processing of unfamiliar faces
Algebraic Signal Processing Theory: Cooley-Tukey Type Algorithms for DCTs and DSTs
This paper presents a systematic methodology based on the algebraic theory of
signal processing to classify and derive fast algorithms for linear transforms.
Instead of manipulating the entries of transform matrices, our approach derives
the algorithms by stepwise decomposition of the associated signal models, or
polynomial algebras. This decomposition is based on two generic methods or
algebraic principles that generalize the well-known Cooley-Tukey FFT and make
the algorithms' derivations concise and transparent. Application to the 16
discrete cosine and sine transforms yields a large class of fast algorithms,
many of which have not been found before.Comment: 31 pages, more information at http://www.ece.cmu.edu/~smar
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