21,123 research outputs found
Letter to Sound Rules for Accented Lexicon Compression
This paper presents trainable methods for generating letter to sound rules
from a given lexicon for use in pronouncing out-of-vocabulary words and as a
method for lexicon compression.
As the relationship between a string of letters and a string of phonemes
representing its pronunciation for many languages is not trivial, we discuss
two alignment procedures, one fully automatic and one hand-seeded which produce
reasonable alignments of letters to phones.
Top Down Induction Tree models are trained on the aligned entries. We show
how combined phoneme/stress prediction is better than separate prediction
processes, and still better when including in the model the last phonemes
transcribed and part of speech information. For the lexicons we have tested,
our models have a word accuracy (including stress) of 78% for OALD, 62% for CMU
and 94% for BRULEX. The extremely high scores on the training sets allow
substantial size reductions (more than 1/20).
WWW site: http://tcts.fpms.ac.be/synthesis/mbrdicoComment: 4 pages 1 figur
Computation of epidemic final size distributions
We develop a new methodology for the efficient computation of epidemic final
size distributions for a broad class of Markovian models. We exploit a
particular representation of the stochastic epidemic process to derive a method
which is both computationally efficient and numerically stable. The algorithms
we present are also physically transparent and so allow us to extend this
method from the basic SIR model to a model with a phase-type infectious period
and another with waning immunity. The underlying theory is applicable to many
Markovian models where we wish to efficiently calculate hitting probabilities.Comment: final published versio
Subsurface impurities and vacancies in a three-dimensional topological insulator
Using a three-dimensional microscopic lattice model of a strong topological
insulator (TI) we study potential impurities and vacancies in surface and
subsurface positions. For all impurity locations we find impurity-induced
resonance states with energy proportional to the inverse of the impurity
strength, although the impurity strength needed for a low-energy resonance
state increases with the depth of the impurity. For strong impurities and
vacancies as deep as 15 layers into the material, resonance peaks will appear
at and around the Dirac point in the surface energy spectrum, splitting the
original Dirac point into two nodes located off-center. Furthermore, we study
vacancy clusters buried deep inside the bulk and find zero-energy resonance
states for both single and multiple-site vacancies. Only fully symmetric
multiple-site vacancy clusters show resonance states expelled from the bulk
gap.Comment: 7 pages, 4 figures. Minor changes in v
Strong potential impurities on the surface of a topological insulator
Topological insulators (TIs) are said to be stable against non-magnetic
impurity scattering due to suppressed backscattering in the Dirac surface
states. We solve a lattice model of a three-dimensional TI in the presence of
strong potential impurities and find that both the Dirac point and low-energy
states are significantly modified: low-energy impurity resonances are formed
that produce a peak in the density of states near the Dirac point, which is
destroyed and split into two nodes that move off-center. The impurity-induced
states penetrate up to 10 layers into the bulk of the TI. These findings
demonstrate the importance of bulk states for the stability of TIs and how they
can destroy the topological protection of the surface.Comment: 4+ pages, 3 figures. Published versio
Odd-frequency superconducting pairing in topological insulators
We discuss the appearance of odd-frequency spin-triplet s-wave
superconductivity, first proposed by Berezinskii [{\it JETP} {\bf 20}, 287
(1974)], on the surface of a topological insulator proximity coupled to a
conventional spin-singlet s-wave superconductor. Using both analytical and
numerical methods we show that this disorder robust odd-frequency state is
present whenever there is an in-surface gradient in the proximity induced gap,
including superconductor-normal state (SN) junctions. The time-independent
order parameter for the odd-frequency superconductor is proportional to the
in-surface gap gradient. The induced odd-frequency component does not produce
any low-energy states.Comment: 6 pages, 5 figures. v2 contains minor changes + supplementary
materia
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