129 research outputs found
The mesopancreas is the primary site for R1 resection in pancreatic head cancer: relevance for clinical trials
Evolutionary discriminative confidence estimation for spoken term detection
The final publication is available at Springer via http://dx.doi.org/10.1007/s11042-011-0913-zSpoken term detection (STD) is the task of searching for occurrences
of spoken terms in audio archives. It relies on robust confidence estimation
to make a hit/false alarm (FA) decision. In order to optimize the decision
in terms of the STD evaluation metric, the confidence has to be discriminative.
Multi-layer perceptrons (MLPs) and support vector machines (SVMs) exhibit
good performance in producing discriminative confidence; however they are
severely limited by the continuous objective functions, and are therefore less
capable of dealing with complex decision tasks. This leads to a substantial
performance reduction when measuring detection of out-of-vocabulary (OOV)
terms, where the high diversity in term properties usually leads to a complicated
decision boundary.
In this paper we present a new discriminative confidence estimation approach
based on evolutionary discriminant analysis (EDA). Unlike MLPs and
SVMs, EDA uses the classification error as its objective function, resulting
in a model optimized towards the evaluation metric. In addition, EDA combines
heterogeneous projection functions and classification strategies in decision
making, leading to a highly flexible classifier that is capable of dealing
with complex decision tasks. Finally, the evolutionary strategy of EDA reduces the risk of local minima. We tested the EDA-based confidence with a
state-of-the-art phoneme-based STD system on an English meeting domain
corpus, which employs a phoneme speech recognition system to produce lattices
within which the phoneme sequences corresponding to the enquiry terms
are searched. The test corpora comprise 11 hours of speech data recorded with
individual head-mounted microphones from 30 meetings carried out at several
institutes including ICSI; NIST; ISL; LDC; the Virginia Polytechnic Institute
and State University; and the University of Edinburgh. The experimental results
demonstrate that EDA considerably outperforms MLPs and SVMs on
both classification and confidence measurement in STD, and the advantage
is found to be more significant on OOV terms than on in-vocabulary (INV)
terms. In terms of classification performance, EDA achieved an equal error
rate (EER) of 11% on OOV terms, compared to 34% and 31% with MLPs and
SVMs respectively; for INV terms, an EER of 15% was obtained with EDA
compared to 17% obtained with MLPs and SVMs. In terms of STD performance
for OOV terms, EDA presented a significant relative improvement of
1.4% and 2.5% in terms of average term-weighted value (ATWV) over MLPs
and SVMs respectively.This work was partially supported by the French Ministry of Industry
(Innovative Web call) under contract 09.2.93.0966, âCollaborative Annotation for Video
Accessibilityâ (ACAV) and by âThe Adaptable Ambient Living Assistantâ (ALIAS) project
funded through the joint national Ambient Assisted Living (AAL) programme
Doppler-Free Spectroscopy of Weak Transitions: An Analytical Model Applied to Formaldehyde
Experimental observation of Doppler-free signals for weak transitions can be
greatly facilitated by an estimate for their expected amplitudes. We derive an
analytical model which allows the Doppler-free amplitude to be estimated for
small Doppler-free signals. Application of this model to formaldehyde allows
the amplitude of experimentally observed Doppler-free signals to be reproduced
to within the experimental error.Comment: 7 pages, 7 figures, 1 table, v2: many small improvements + corrected
line assignmen
Space-time evolution of electron cascades in diamond
Here we describe model calculations to follow the spatio-temporal evolution
of secondary electron cascades in diamond. The band structure of the insulator
has been explicitly incorporated into the calculations as it affects
ionizations from the valence band. A Monte-Carlo model was constructed to
describe the path of electrons following the impact of a single electron of
energy E 250 eV. The results show the evolution of the secondary electron
cascades in terms of the number of electrons liberated, the spatial
distribution of these electrons, and the energy distribution among the
electrons as a function of time. The predicted ionization rates (5-13 electrons
in 100 fs) lie within the limits given by experiments and phenomenological
models. Calculation of the local electron density and the corresponding Debye
length shows that the latter is systematically larger than the radius of the
electron cloud. This means that the electron gas generated does not represent a
plasma in a single impact cascade triggered by an electron of E 250 eV energy.
This is important as it justifies the independent-electron approximation used
in the model. At 1 fs, the (average) spatial distribution of secondary
electrons is anisotropic with the electron cloud elongated in the direction of
the primary impact. The maximal radius of the cascade is about 50 A at this
time. As the system cools, energy is distributed more equally, and the spatial
distribution of the electron cloud becomes isotropic. At 90 fs maximal radius
is about 150 A. The Monte-Carlo model described here could be adopted for the
investigation of radiation damage in other insulators and has implications for
planned experiments with intense femtosecond X-ray sources.Comment: 26 pages, latex, 13 figure
Electron detachment from negative ions in bichromatic laser field
Negative ion detachment in two-colour laser field is considered within the
recent modification of Keldysh model which makes it quantitatively reliable.
The general approach is illustrated by calculation of angular differential
detachment rates, partial rates for particular ATD (Above Threshold Detachment)
channels and total detachment rates for H ion in bichromatic field with 1:2
frequency ratio. Both perturbative and strong field regimes are examined. Polar
asymmetry and phase effects are quantitatively characterized with some new
features revealed. Phase effects are found to result in a huge anisotropy
factor in the electron angular distribution in the perturbative
regime.Comment: 13 pages, 8 figures in separate files which are not incorporated in
the latex file of the pape
Differential Photoelectron Holography: A New Approach for Three-Dimensional Atomic Imaging
We propose differential holography as a method to overcome the long-standing
forward-scattering problem in photoelectron holography and related techniques
for the three-dimensional imaging of atoms. Atomic images reconstructed from
experimental and theoretical Cu 3p holograms from Cu(001) demonstrate that this
method suppresses strong forward-scattering effects so as to yield more
accurate three-dimensional images of side- and back-scattering atoms.Comment: revtex, 4 pages, 2 figure
LEED Holography applied to a complex superstructure: a direct view of the adatom cluster on SiC(111)-(3x3)
For the example of the SiC(111)-(3x3) reconstruction we show that a
holographic interpretation of discrete Low Energy Electron Diffraction (LEED)
spot intensities arising from ordered, large unit cell superstructures can give
direct access to the local geometry of a cluster around an elevated atom,
provided there is only one such prominent atom per surface unit cell. By
comparing the holographic images obtained from experimental and calculated data
we illuminate validity, current limits and possible shortcomings of the method.
In particular, we show that periodic vacancies such as cornerholes may inhibit
the correct detection of the atomic positions. By contrast, the extra
diffraction intensity due to slight substrate reconstructions, as for example
buckling, seems to have negligible influence on the images. Due to the spatial
information depth of the method the stacking of the cluster can be imaged down
to the fourth layer. Finally, it is demonstrated how this structural knowledge
of the adcluster geometry can be used to guide the dynamical intensity analysis
subsequent to the holographic reconstruction and necessary to retrieve the full
unit cell structure.Comment: 11 pages RevTex, 6 figures, Phys. Rev. B in pres
Spoken term detection ALBAYZIN 2014 evaluation: overview, systems, results, and discussion
The electronic version of this article is the complete one and can be found online at: http://dx.doi.org/10.1186/s13636-015-0063-8Spoken term detection (STD) aims at retrieving data from a speech repository given a textual representation of the search term. Nowadays, it is receiving much interest due to the large volume of multimedia information. STD differs from automatic speech recognition (ASR) in that ASR is interested in all the terms/words that appear in the speech data, whereas STD focuses on a selected list of search terms that must be detected within the speech data. This paper presents the systems submitted to the STD ALBAYZIN 2014 evaluation, held as a part of the ALBAYZIN 2014 evaluation campaign within the context of the IberSPEECH 2014 conference. This is the first STD evaluation that deals with Spanish language. The evaluation consists of retrieving the speech files that contain the search terms, indicating their start and end times within the appropriate speech file, along with a score value that reflects the confidence given to the detection of the search term. The evaluation is conducted on a Spanish spontaneous speech database, which comprises a set of talks from workshops and amounts to about 7 h of speech. We present the database, the evaluation metrics, the systems submitted to the evaluation, the results, and a detailed discussion. Four different research groups took part in the evaluation. Evaluation results show reasonable performance for moderate out-of-vocabulary term rate. This paper compares the systems submitted to the evaluation and makes a deep analysis based on some search term properties (term length, in-vocabulary/out-of-vocabulary terms, single-word/multi-word terms, and in-language/foreign terms).This work has been partly supported by project CMC-V2
(TEC2012-37585-C02-01) from the Spanish Ministry of Economy and
Competitiveness. This research was also funded by the European Regional
Development Fund, the Galician Regional Government (GRC2014/024,
âConsolidation of Research Units: AtlantTIC Projectâ CN2012/160)
Feature analysis for discriminative confidence estimation in spoken term detection
This is the authorâs version of a work that was accepted for publication in Computer Speech & Language. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Computer Speech & Language, 28, 5, (2014) DOI: 10.1016/j.csl.2013.09.008Discriminative confidence based on multi-layer perceptrons (MLPs) and multiple features has shown significant advantage compared to the widely used lattice-based confidence in spoken term detection (STD). Although the MLP-based framework can handle any features derived from a multitude of sources, choosing all possible features may lead to over complex models and hence less generality. In this paper, we design an extensive set of features and analyze their contribution to STD individually and as a group. The main goal is to choose a small set of features that are sufficiently informative while keeping the model simple and generalizable. We employ two established models to conduct the analysis: one is linear regression which targets for the most relevant features and the other is logistic linear regression which targets for the most discriminative features. We find the most informative features are comprised of those derived from diverse sources (ASR decoding, duration and lexical properties) and the two models deliver highly consistent feature ranks. STD experiments on both English and Spanish data demonstrate significant performance gains with the proposed feature sets.This work has been partially supported by project PriorSPEECH (TEC2009-14719-C02-01) from the Spanish Ministry of Science and Innovation and by project MAV2VICMR (S2009/TIC-1542) from the Community of Madrid
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