23,536 research outputs found
A control algorithm for autonomous optimization of extracellular recordings
This paper develops a control algorithm that can autonomously position an electrode so as to find and then maintain an optimal extracellular recording position. The algorithm was developed and tested in a two-neuron computational model representative of the cells found in cerebral cortex. The algorithm is based on a stochastic optimization of a suitably defined signal quality metric and is shown capable of finding the optimal recording position along representative sampling directions, as well as maintaining the optimal signal quality in the face of modeled tissue movements. The application of the algorithm to acute neurophysiological recording experiments and its potential implications to chronic recording electrode arrays are discussed
Sound Source Separation
This is the author's accepted pre-print of the article, first published as G. Evangelista, S. Marchand, M. D. Plumbley and E. Vincent. Sound source separation. In U. Zölzer (ed.), DAFX: Digital Audio Effects, 2nd edition, Chapter 14, pp. 551-588. John Wiley & Sons, March 2011. ISBN 9781119991298. DOI: 10.1002/9781119991298.ch14file: Proof:e\EvangelistaMarchandPlumbleyV11-sound.pdf:PDF owner: markp timestamp: 2011.04.26file: Proof:e\EvangelistaMarchandPlumbleyV11-sound.pdf:PDF owner: markp timestamp: 2011.04.2
Position Reconstruction in Drift Chambers operated with Xe, CO2 (15%)
We present measurements of position and angular resolution of drift chambers
operated with a Xe,CO(15%) mixture. The results are compared to Monte Carlo
simulations and important systematic effects, in particular the dispersive
nature of the absorption of transition radiation and non-linearities, are
discussed. The measurements were carried out with prototype drift chambers of
the ALICE Transition Radiation Detector, but our findings can be generalized to
other drift chambers with similar geometry, where the electron drift is
perpendicular to the wire planes.Comment: 30 pages, 18 figure
Measurement of an Elongation of the Pion Source in Z Decays
We measure Bose-Einstein correlations between like-sign charged pion pairs in
hadronic Z decays with the L3 detector at LEP. The analysis is performed in
three dimensions in the longitudinal center-of-mass system. The pion source is
found to be elongated along the thrust axis with a ratio of transverse to
longitudinal radius of
Exploiting correlogram structure for robust speech recognition with multiple speech sources
This paper addresses the problem of separating and recognising speech in a monaural acoustic mixture with the presence of competing speech sources. The proposed system treats sound source separation and speech recognition as
tightly coupled processes. In the first stage sound source separation is performed in the correlogram domain. For periodic sounds, the correlogram exhibits symmetric tree-like structures whose stems are located on the delay
that corresponds to multiple pitch periods. These pitch-related structures are exploited in the study to group spectral components at each time frame. Local
pitch estimates are then computed for each spectral group and are used to form simultaneous pitch tracks for temporal integration. These processes segregate a spectral representation of the acoustic mixture into several time-frequency regions such that the energy in each region is likely to have originated from a single periodic sound source. The identified time-frequency regions, together
with the spectral representation, are employed by a `speech fragment decoder' which employs `missing data' techniques with clean speech models to simultaneously search for the acoustic evidence that best matches model sequences. The paper presents evaluations based on artificially mixed simultaneous speech utterances. A coherence-measuring experiment is first reported which quantifies the consistency of the identified fragments with a single source. The system is then evaluated in a speech recognition task and compared to a conventional fragment generation approach. Results show that the proposed system produces more coherent fragments over different conditions,
which results in significantly better recognition accuracy
Principal Component Analysis and Radiative Transfer modelling of Spitzer IRS Spectra of Ultra Luminous Infrared Galaxies
The mid-infrared spectra of ultraluminous infrared galaxies (ULIRGs) contain
a variety of spectral features that can be used as diagnostics to characterise
the spectra. However, such diagnostics are biased by our prior prejudices on
the origin of the features. Moreover, by using only part of the spectrum they
do not utilise the full information content of the spectra. Blind statistical
techniques such as principal component analysis (PCA) consider the whole
spectrum, find correlated features and separate them out into distinct
components.
We further investigate the principal components (PCs) of ULIRGs derived in
Wang et al.(2011). We quantitatively show that five PCs is optimal for
describing the IRS spectra. These five components (PC1-PC5) and the mean
spectrum provide a template basis set that reproduces spectra of all z<0.35
ULIRGs within the noise. For comparison, the spectra are also modelled with a
combination of radiative transfer models of both starbursts and the dusty torus
surrounding active galactic nuclei. The five PCs typically provide better fits
than the models. We argue that the radiative transfer models require a colder
dust component and have difficulty in modelling strong PAH features.
Aided by the models we also interpret the physical processes that the
principal components represent. The third principal component is shown to
indicate the nature of the dominant power source, while PC1 is related to the
inclination of the AGN torus.
Finally, we use the 5 PCs to define a new classification scheme using 5D
Gaussian mixtures modelling and trained on widely used optical classifications.
The five PCs, average spectra for the four classifications and the code to
classify objects are made available at: http://www.phys.susx.ac.uk/~pdh21/PCA/Comment: 11 pages, 12 figures, accepted for publication in MNRA
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