28,471 research outputs found
Comprehension of familiar and unfamiliar native accents under adverse listening conditions
This study aimed to determine the relative processing cost associated with comprehension of an unfamiliar native accent under adverse listening conditions. Two sentence verification experiments were conducted in which listeners heard sentences at various signal-to-noise ratios. In Experiment 1, these sentences were spoken in a familiar or an unfamiliar native accent or in two familiar native accents. In Experiment 2, they were spoken in a familiar or unfamiliar native accent or in a nonnative accent. The results indicated that the differences between the native accents influenced the speed of language processing under adverse listening conditions and that this processing speed was modulated by the relative familiarity of the listener with the native accent. Furthermore, the results showed that the processing cost associated with the nonnative accent was larger than for the unfamiliar native accent
Cosmic Variance In the Transparency of the Intergalactic Medium After Reionization
Following the completion of cosmic reionization, the mean-free-path of
ionizing photons was set by a population of Ly-limit absorbers. As the
mean-free-path steadily grew, the intensity of the ionizing background also
grew, thus lowering the residual neutral fraction of hydrogen in ionization
equilibrium throughout the diffuse intergalactic medium (IGM). Ly-alpha photons
provide a sensitive probe for tracing the distribution of this residual
hydrogen at the end of reionization. Here we calculate the cosmic variance
among different lines-of-sight in the distribution of the mean Ly-alpha optical
depths. We find fractional variations in the effective post-reionization
optical depth that are of order unity on a scale of ~100 co-moving Mpc, in
agreement with observations towards high-redshift quasars. Significant
contributions to these variations are provided by the cosmic variance in the
density contrast on the scale of the mean-free-path for ionizing photons, and
by fluctuations in the ionizing background induced by delayed or enhanced
structure formation. Cosmic variance results in a highly asymmetric
distribution of transmission through the IGM, with fractional fluctuations in
Ly-alpha transmission that ar larger than in Ly-beta transmission.Comment: 7 pages 3 figures. Replaced with version accepted for publication in
Ap
Velocity map imaging of the dynamics of reactions of Cl atoms with neopentane and tetramethyl silane
Structure of the regulatory domain of the LysR family regulator NMB2055 (MetR-like protein) from Neisseria meningitidis
Copyright @ 2012 International Union of CrystallographyThe crystal structure of the regulatory domain of NMB2055, a putative MetR regulator from Neisseria meningitidis, is reported at 2.5 Å resolution. The structure revealed that there is a disulfide bond inside the predicted effector-binding pocket of the regulatory domain. Mutation of the cysteines (Cys103 and Cys106) that form the disulfide bond to serines resulted in significant changes to the structure of the effector pocket. Taken together with the high degree of conservation of these cysteine residues within MetR-related transcription factors, it is suggested that the Cys103 and Cys106 residues play an important role in the function of MetR regulators.This study is funded by the Medical
Research Council, with additional finance from the Biotechnology and Biological Science Research Council
Interactions of Jets with Inhomogeneous Cloudy Media
We present two-dimensional slab-jet simulations of jets in inhomogeneous
media consisting of a tenuous hot medium populated with a small filling factor
by warm, dense clouds. The simulations are relevant to the structure and
dynamics of sources such as Gigahertz Peak Spectrum and Compact Steep Spectrum
radio galaxies, High Redshift Radio Galaxies and radio galaxies in cooling
flows. The jets are disrupted to a degree depending upon the filling factor of
the clouds. With a small filling factor, the jet retains some forward momentum
but also forms a halo or bubble around the source. At larger filling factors
channels are formed in the cloud distribution through which the jet plasma
flows and a hierarchical structure consisting of nested lobes and an outer
enclosing bubble results. We suggest that the CSS quasar 3C48 is an example of
a low filling factor jet - interstellar medium interaction whilst M87 may be an
example of the higher filling factor type of interaction. Jet disruption occurs
primarily as a result of Kelvin-Helmholtz instabilities driven by turbulence in
the radio cocoon not through direct jet-cloud interactions, although there are
some examples of these. In all radio galaxies whose morphology may be the
result of jet interactions with an inhomogeneous interstellar medium we expect
that the dense clouds will be optically observable as a result of radiative
shocks driven by the pressure of the radio cocoon. We also expect that the
radio galaxies will possess faint haloes of radio emitting material well beyond
the observable jet structure.Comment: 21 pages, 16 figures, submitted to MNRAS. A version with full
resolution figures is available at:
http://www.mssl.ucl.ac.uk/~cjs2/pdf/cloudy_hue.pd
Variational data assimilation using targetted random walks
The variational approach to data assimilation is a widely used methodology for both online prediction and for reanalysis (offline hindcasting). In either of these scenarios it can be important to assess uncertainties in the assimilated state. Ideally it would be desirable to have complete information concerning the Bayesian posterior distribution for unknown state, given data. The purpose of this paper is to show that complete computational probing of this posterior distribution is now within reach in the offline situation. In this paper we will introduce an MCMC method which enables us to directly sample from the Bayesian\ud
posterior distribution on the unknown functions of interest, given observations. Since we are aware that these\ud
methods are currently too computationally expensive to consider using in an online filtering scenario, we frame this in the context of offline reanalysis. Using a simple random walk-type MCMC method, we are able to characterize the posterior distribution using only evaluations of the forward model of the problem, and of the model and data mismatch. No adjoint model is required for the method we use; however more sophisticated MCMC methods are available\ud
which do exploit derivative information. For simplicity of exposition we consider the problem of assimilating data, either Eulerian or Lagrangian, into a low Reynolds number (Stokes flow) scenario in a two dimensional periodic geometry. We will show that in many cases it is possible to recover the initial condition and model error (which we describe as unknown forcing to the model) from data, and that with increasing amounts of informative data, the uncertainty in our estimations reduces
A Function Space HMC Algorithm With Second Order Langevin Diffusion Limit
We describe a new MCMC method optimized for the sampling of probability
measures on Hilbert space which have a density with respect to a Gaussian; such
measures arise in the Bayesian approach to inverse problems, and in conditioned
diffusions. Our algorithm is based on two key design principles: (i) algorithms
which are well-defined in infinite dimensions result in methods which do not
suffer from the curse of dimensionality when they are applied to approximations
of the infinite dimensional target measure on \bbR^N; (ii) non-reversible
algorithms can have better mixing properties compared to their reversible
counterparts. The method we introduce is based on the hybrid Monte Carlo
algorithm, tailored to incorporate these two design principles. The main result
of this paper states that the new algorithm, appropriately rescaled, converges
weakly to a second order Langevin diffusion on Hilbert space; as a consequence
the algorithm explores the approximate target measures on \bbR^N in a number
of steps which is independent of . We also present the underlying theory for
the limiting non-reversible diffusion on Hilbert space, including
characterization of the invariant measure, and we describe numerical
simulations demonstrating that the proposed method has favourable mixing
properties as an MCMC algorithm.Comment: 41 pages, 2 figures. This is the final version, with more comments
and an extra appendix adde
Electrochemical detection of TNT at cobalt phthalocyanine mediated screen-printed electrodes and application to detection of airborne vapours
We describe the use of cobalt phthalocyanine as a mediator to improve the sensitivity for the electrochemical detection of TNT. Commercial screen-printed electrodes containing cobalt phthalocyanine were employed for determination of TNT. Improved sensitivities compared to screen-printed carbon electrodes without phthalocyanine were observed, current response for cyclic voltammetric measurements at modified electrodes being at least double that of unmodified electrodes. A synergistic effect between oxygen and TNT reduction was also observed. Correlation between TNT concentrations and sensor output was observed between 0–200 µM TNT. Initial proof-of-concept experiments combining electrochemical determinations, with the use of an air-sampling cyclone, are also reported
Responding to accents after experiencing interactive or mediated speech
Very little known is about how speakers learn
about and/or respond to speech experienced
without the possibility for interaction. This paper
reports an experiment which considers the effects
of two kinds of exposure to speech (interactive or
non-interactive mediated) on Scottish English
speakers’ responses to another accent (Southern
British English), for two processing tasks,
phonological awareness and speech production.
Only marginal group effects are found according to
exposure type. The main findings show a
difference between subjects according to exposure
type before exposure, and individual shifts in
responses to speech according to exposure type
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