24,673 research outputs found
Guiding CTC Posterior Spike Timings for Improved Posterior Fusion and Knowledge Distillation
Conventional automatic speech recognition (ASR) systems trained from
frame-level alignments can easily leverage posterior fusion to improve ASR
accuracy and build a better single model with knowledge distillation.
End-to-end ASR systems trained using the Connectionist Temporal Classification
(CTC) loss do not require frame-level alignment and hence simplify model
training. However, sparse and arbitrary posterior spike timings from CTC models
pose a new set of challenges in posterior fusion from multiple models and
knowledge distillation between CTC models. We propose a method to train a CTC
model so that its spike timings are guided to align with those of a pre-trained
guiding CTC model. As a result, all models that share the same guiding model
have aligned spike timings. We show the advantage of our method in various
scenarios including posterior fusion of CTC models and knowledge distillation
between CTC models with different architectures. With the 300-hour Switchboard
training data, the single word CTC model distilled from multiple models
improved the word error rates to 13.7%/23.1% from 14.9%/24.1% on the Hub5 2000
Switchboard/CallHome test sets without using any data augmentation, language
model, or complex decoder.Comment: Accepted to Interspeech 201
Deep Learning of Atomically Resolved Scanning Transmission Electron Microscopy Images: Chemical Identification and Tracking Local Transformations
Recent advances in scanning transmission electron and scanning probe
microscopies have opened exciting opportunities in probing the materials
structural parameters and various functional properties in real space with
angstrom-level precision. This progress has been accompanied by an exponential
increase in the size and quality of datasets produced by microscopic and
spectroscopic experimental techniques. These developments necessitate adequate
methods for extracting relevant physical and chemical information from the
large datasets, for which a priori information on the structures of various
atomic configurations and lattice defects is limited or absent. Here we
demonstrate an application of deep neural networks to extract information from
atomically resolved images including location of the atomic species and type of
defects. We develop a 'weakly-supervised' approach that uses information on the
coordinates of all atomic species in the image, extracted via a deep neural
network, to identify a rich variety of defects that are not part of an initial
training set. We further apply our approach to interpret complex atomic and
defect transformation, including switching between different coordination of
silicon dopants in graphene as a function of time, formation of peculiar
silicon dimer with mixed 3-fold and 4-fold coordination, and the motion of
molecular 'rotor'. This deep learning based approach resembles logic of a human
operator, but can be scaled leading to significant shift in the way of
extracting and analyzing information from raw experimental data
Initial conditions for cold dark matter particles and General Relativity
We describe the irrotational dust component of the universe in terms of a
relativistic gradient expansion and transform the resulting synchronous metric
to a Newtonian coordinate system. The two metrics are connected via a
space-like displacement field and a time-like perturbation, providing a
relativistic generalization of the transformation from Lagrangian to Eulerian
coordinates. The relativistic part of the displacement field generates already
at initial time a non-local density perturbation at second order. This is a
purely relativistic effect since it originates from space-time mixing. We give
two options, the passive and the active approach, on how to include the
relativistic corrections for example in N-body simulations. In the passive
approach we treat the corrections as a non-Gaussian modification of the initial
Gaussian field (primordial non-Gaussianity could be incorporated as well). The
induced non-Gaussianity depends on scale and the redshift at which initial
conditions are set, with f_NL ~ few for small enough scales and redshifts. In
the active approach we show how to use the relativistic trajectory to obtain
the initial displacement and velocity of particles for N-body simulations
without modifying the initial Gaussian field.Comment: Title adjusted, added a table for clarity, matches published versio
Benchmark calculations for elastic fermion-dimer scattering
We present continuum and lattice calculations for elastic scattering between
a fermion and a bound dimer in the shallow binding limit. For the continuum
calculation we use the Skorniakov-Ter-Martirosian (STM) integral equation to
determine the scattering length and effective range parameter to high
precision. For the lattice calculation we use the finite-volume method of
L\"uscher. We take into account topological finite-volume corrections to the
dimer binding energy which depend on the momentum of the dimer. After
subtracting these effects, we find from the lattice calculation kappa a_fd =
1.174(9) and kappa r_fd = -0.029(13). These results agree well with the
continuum values kappa a_fd = 1.17907(1) and kappa r_fd = -0.0383(3) obtained
from the STM equation. We discuss applications to cold atomic Fermi gases,
deuteron-neutron scattering in the spin-quartet channel, and lattice
calculations of scattering for nuclei and hadronic molecules at finite volume.Comment: 16 pages, 5 figure
Energy resolved STM mapping of C on metal surfaces: A theoretical study
We present a detailed theoretical study of scanning tunneling imaging and
spectroscopy of \Csixty on silver and gold surfaces, motivated by the recent
experiments and discussion by X. Lu et al. [PRL \textbf{90}, 096802 (2003) and
PRB \textbf{70}, 115418 (2004)]. The surface/sample/tip system is described
within a self--consistent DFT based tight--binding model. The topographic and
conductance images are computed at constant current from a full
self--consistent transport theory based on nonequilibrium Green's functions and
compared with those simulated from the local density of states. The molecular
orbitals of \Csixty are clearly identified in the energy resolved maps, in
close correspondence with the experimental results. We show how the tip
structure and orientation can affect the images. In particular, we consider the
effects of truncated tips on the energy resolved maps.Comment: 9 pages, 8 figure
The Effective Energy-Momentum Tensor in Kaluza-Klein Gravity With Large Extra Dimensions and Off-Diagonal Metrics
We consider a version of Kaluza-Klein theory where the cylinder condition is
not imposed. The metric is allowed to have explicit dependence on the "extra"
coordinate(s). This is the usual scenario in brane-world and space-time-matter
theories. We extend the usual discussion by considering five-dimensional
metrics with off-diagonal terms. We replace the condition of cylindricity by
the requirement that physics in four-dimensional space-time should remain
invariant under changes of coordinates in the five-dimensional bulk. This
invariance does not eliminate physical effects from the extra dimension but
separates them from spurious geometrical ones. We use the appropriate splitting
technique to construct the most general induced energy-momentum tensor,
compatible with the required invariance. It generalizes all previous results in
the literature. In addition, we find two four-vectors, J_{m}^{mu} and
J_{e}^{mu}, induced by off-diagonal metrics, that separately satisfy the usual
equation of continuity in 4D. These vectors appear as source-terms in equations
that closely resemble the ones of electromagnetism. These are Maxwell-like
equations for an antisymmetric tensor {F-hat}_{mu nu} that generalizes the
usual electromagnetic one. This generalization is not an assumption, but
follows naturally from the dimensional reduction. Thus, if {F-hat}_{mu nu}
could be identified with the electromagnetic tensor, then the theory would
predict the existence of classical magnetic charge and current. The splitting
formalism used allows us to construct 4D physical quantities from
five-dimensional ones, in a way that is independent on how we choose our
space-time coordinates from those of the bulk.Comment: New title, editorial changes made as to match the version to appear
in International Journal of Modern Physics
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