27,662 research outputs found
Adaptation by normal listeners to upward spectral shifts of speech: Implications for cochlear implants
Multi-channel cochlear implants typically present spectral information to the wrong ''place'' in the auditory nerve array, because electrodes can only be inserted partway into the cochlea. Although such spectral shifts are known to cause large immediate decrements in performance in simulations, the extent to which listeners can adapt to such shifts has yet to be investigated. Here, the effects of a four-channel implant in normal listeners have been simulated, and performance tested with unshifted spectral information and with the equivalent of a 6.5-mm basalward shift on the basilar membrane (1.3-2.9 octaves, depending on frequency). As expected, the unshifted simulation led to relatively high levels of mean performance (e;g., 64% of words in sentences correctly identified) whereas the shifted simulation led to very poor results (e.g., 1% of words). However, after just nine 20-min sessions of connected discourse tracking with the shifted simulation, performance improved significantly for the identification of intervocalic consonants, medial vowels in monosyllables, and words in sentences (30% of words). Also, listeners were able to track connected discourse of shifted signals without lipreading at rates up to 40 words per minute. Although we do not know if complete adaptation to the shifted signals is possible, it is clear that short-term experiments seriously exaggerate the long-term consequences of such spectral shifts. (C) 1999 Acoustical Society of America. [S0001-4966(99)02012-3]
Geometrically necessary dislocation densities in olivine obtained using high-angular resolution electron backscatter diffraction
© 2016 The AuthorsDislocations in geological minerals are fundamental to the creep processes that control large-scale geodynamic phenomena. However, techniques to quantify their densities, distributions, and types over critical subgrain to polycrystal length scales are limited. The recent advent of high-angular resolution electron backscatter diffraction (HR-EBSD), based on diffraction pattern cross-correlation, offers a powerful new approach that has been utilised to analyse dislocation densities in the materials sciences. In particular, HR-EBSD yields significantly better angular resolution (<0.01°) than conventional EBSD (~0.5°), allowing very low dislocation densities to be analysed. We develop the application of HR-EBSD to olivine, the dominant mineral in Earths upper mantle by testing (1) different inversion methods for estimating geometrically necessary dislocation (GND) densities, (2) the sensitivity of the method under a range of data acquisition settings, and (3) the ability of the technique to resolve a variety of olivine dislocation structures. The relatively low crystal symmetry (orthorhombic) and few slip systems in olivine result in well constrained GND density estimates. The GND density noise floor is inversely proportional to map step size, such that datasets can be optimised for analysing either short wavelength, high density structures (e.g. subgrain boundaries) or long wavelength, low amplitude orientation gradients. Comparison to conventional images of decorated dislocations demonstrates that HR-EBSD can characterise the dislocation distribution and reveal additional structure not captured by the decoration technique. HR-EBSD therefore provides a highly effective method for analysing dislocations in olivine and determining their role in accommodating macroscopic deformation
Absorption of Energy at a Metallic Surface due to a Normal Electric Field
The effect of an oscillating electric field normal to a metallic surface may
be described by an effective potential. This induced potential is calculated
using semiclassical variants of the random phase approximation (RPA). Results
are obtained for both ballistic and diffusive electron motion, and for two and
three dimensional systems. The potential induced within the surface causes
absorption of energy. The results are applied to the absorption of radiation by
small metal spheres and discs. They improve upon an earlier treatment which
used the Thomas-Fermi approximation for the effective potential.Comment: 19 pages (Plain TeX), 2 figures, 1 table (Postscript
The evolutionary sequence of post-starburst galaxies
© 2017 The Authors. There are multiple ways in which to select post-starburst galaxies in the literature. In this work, we present a study into how two well-used selection techniques have consequences on observable post-starburst galaxy parameters, such as colour, morphology and environment, and how this affects interpretations of their role in the galaxy duty cycle. We identify a master sample of Hδ strong (EWHδ> 3Å) post-starburst galaxies from the value-added catalogue in the seventh data release of the Sloan Digital Sky Survey (SDSS DR7) over a redshift range 0.01 -2.5Å) but one having an additional cut onEWHα (> -3Å).We examine the differences in observables and AGN fractions to see what effect the Hα cut has on the properties of post-starburst galaxies and what these differing samples can tell us about the duty cycle of post-starburst galaxies. We find that Hδ strong galaxies peak in the 'blue cloud', E+As in the 'green valley' and pure E+As in the 'red sequence'.We also find that pure E+As have a more early-type morphology and a higher fraction in denser environments compared with the Hδ strong and E+A galaxies. These results suggest that there is an evolutionary sequence in the post-starburst phase from blue discy galaxies with residual star formation to passive red early-types
Radial Velocities of Newly Discovered Globular Clusters in NGC 5128
We present radial velocity measurements for 74 globular clusters (GCs) in the
nearby giant elliptical NGC 5128, of which 31 are newly discovered clusters.
All the GC candidates were taken from the list of possible new clusters given
in the Harris, Harris, & Geisler (2004) photometric survey. In addition to the
newly confirmed clusters, we identified 24 definite foreground stars and 31
probable background galaxies. From a combined list of 299 known GCs in NGC 5128
with measured radial velocities and metallicity-sensitive (C - T_1) photometric
indices, we construct a new metallicity distribution function (MDF) for the
cluster system. The MDF shows an approximately bimodal form, with centroids at
[Fe/H] = -1.46 and -0.53, and with nearly equal numbers of metal-poor and
metal-rich clusters in the two modes. However, there are many
intermediate-color clusters in the distribution, and the fainter clusters tend
to have a higher proportion of red clusters. These features of the MDF may
indicate a widespread age range within the cluster system as well as an
intrinsically broad metallicity spread.Comment: 10 pages, 7 figures, 4 tables - accepted in Astronomical Journa
How quickly can you detect it? Power facilitates attentional orienting
This study investigated how power impacts the ability to orient attention across space. Participants were assigned to a high power or control role and then performed a computerised spatial cueing task in which they were required to direct their attention to a target that had been preceded by either a valid or invalid location cue. Compared to participants in the control condition, power-holders were better able to override the misinformation provided by invalid cues. This advantage occurred only at 500 ms stimulus onset asynchrony (SOA), whereas at 1000 ms SOA, when there was more time to prepare a response, no differences were found. These findings are taken to support the growing idea that social power affects cognitive flexibility
Quantum response of weakly chaotic systems
Chaotic systems, that have a small Lyapunov exponent, do not obey the common
random matrix theory predictions within a wide "weak quantum chaos" regime.
This leads to a novel prediction for the rate of heating for cold atoms in
optical billiards with vibrating walls. The Hamiltonian matrix of the driven
system does not look like one from a Gaussian ensemble, but rather it is very
sparse. This sparsity can be characterized by parameters and that
reflect the percentage of large elements, and their connectivity respectively.
For we use a resistor network calculation that has direct relation to the
semi-linear response characteristics of the system.Comment: 7 pages, 5 figures, expanded improved versio
StochKit-FF: Efficient Systems Biology on Multicore Architectures
The stochastic modelling of biological systems is an informative, and in some
cases, very adequate technique, which may however result in being more
expensive than other modelling approaches, such as differential equations. We
present StochKit-FF, a parallel version of StochKit, a reference toolkit for
stochastic simulations. StochKit-FF is based on the FastFlow programming
toolkit for multicores and exploits the novel concept of selective memory. We
experiment StochKit-FF on a model of HIV infection dynamics, with the aim of
extracting information from efficiently run experiments, here in terms of
average and variance and, on a longer term, of more structured data.Comment: 14 pages + cover pag
Super-diffusion in optical realizations of Anderson localization
We discuss the dynamics of particles in one dimension in potentials that are
random both in space and in time. The results are applied to recent optics
experiments on Anderson localization, in which the transverse spreading of a
beam is suppressed by random fluctuations in the refractive index. If the
refractive index fluctuates along the direction of the paraxial propagation of
the beam, the localization is destroyed. We analyze this broken localization,
in terms of the spectral decomposition of the potential. When the potential has
a discrete spectrum, the spread is controlled by the overlap of Chirikov
resonances in phase space. As the number of Fourier components is increased,
the resonances merge into a continuum, which is described by a Fokker-Planck
equation. We express the diffusion coefficient in terms of the spectral
intensity of the potential. For a general class of potentials that are commonly
used in optics, the solutions of the Fokker-Planck equation exhibit anomalous
diffusion in phase space, implying that when Anderson localization is broken by
temporal fluctuations of the potential, the result is transport at a rate
similar to a ballistic one or even faster. For a class of potentials which
arise in some existing realizations of Anderson localization atypical behavior
is found.Comment: 11 pages, 2 figure
Crystallization of YIoQ, a GTPase of unknown function essential for Bacillus subtilis viability
YLoQ is a putative ATP/GTP-binding protein of unknown function identified from the complete sequence of the Bacillus subtilis genome. A gene-knockout programme established that yloQ is one of a set of some 270 indispensable genes for the viability of this organism. Crystals of YloQ have been grown from HEPES-buffered solutions at pH 7.5 containing polyethylene glycol and diffraction data have been collected extending to 2.5 Angstrom spacing
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