7,897 research outputs found
Precise n-gram Probabilities from Stochastic Context-free Grammars
We present an algorithm for computing n-gram probabilities from stochastic
context-free grammars, a procedure that can alleviate some of the standard
problems associated with n-grams (estimation from sparse data, lack of
linguistic structure, among others). The method operates via the computation of
substring expectations, which in turn is accomplished by solving systems of
linear equations derived from the grammar. We discuss efficient implementation
of the algorithm and report our practical experience with it.Comment: 12 pages, to appear in ACL-9
The Fourier extension operator on large spheres and related oscillatory integrals
We obtain new estimates for a class of oscillatory integral operators with
folding canonical relations satisfying a curvature condition. The main lower
bounds showing sharpness are proved using Kakeya set constructions. As a
special case of the upper bounds we deduce optimal estimates for the Fourier extension operator on large spheres in
, which are uniform in the radius . Two appendices are
included, one concerning an application to Lorentz space bounds for averaging
operators along curves in , and one on bilinear estimates
The application of regional-scale geochemical data in defining the extent of aeolian sediments : the Late Pleistocene loess and coversand deposits of East Anglia, UK
The ‘European Coversand Sheet’ is a discontinuous ‘sheet’ of aeolian
(windblown) loess and coversand that extends through eastern and
southern England, across the English Channel into northern France,
Belgium and the Netherlands (Kasse, 1997; Antoine et al., 2003). Whilst
some of the earlier aeolian sediments date from the Middle
Pleistocene, most correspond to the Late Pleistocene Weichselian /
Devensian and earliest Holocene stages. East Anglia contains
considerable accumulations of aeolian sediment. Although several
valuable studies have attempted to determine the spatial extent of
aeolian material (e.g. Catt, 1977, 1985), defining their margins has
proved largely difficult because aeolian material is highly susceptible to
reworking and removal by various natural and anthropogenic agents.
Within this study, we use regional‐scale geochemical data from
soils to reconstruct the extent of aeolian sediments in East Anglia. A
specific geochemical signature, defined by elevated concentrations of
Hafnium (Hf) and Zirconium (Zr), is strongly characteristic of soils
developed on aeolian deposits within the United States, China, Europe
and New Zealand (Taylor et al., 1983). The data suggests that the
approach is sufficiently sensitive to identify a residual aeolian
component within soils even where deposits may be thin and unmappable
by conventional methods, or if the material has been largely
eroded
Quantum network communication -- the butterfly and beyond
We study the k-pair communication problem for quantum information in networks
of quantum channels. We consider the asymptotic rates of high fidelity quantum
communication between specific sender-receiver pairs. Four scenarios of
classical communication assistance (none, forward, backward, and two-way) are
considered. (i) We obtain outer and inner bounds of the achievable rate regions
in the most general directed networks. (ii) For two particular networks
(including the butterfly network) routing is proved optimal, and the free
assisting classical communication can at best be used to modify the directions
of quantum channels in the network. Consequently, the achievable rate regions
are given by counting edge avoiding paths, and precise achievable rate regions
in all four assisting scenarios can be obtained. (iii) Optimality of routing
can also be proved in classes of networks. The first class consists of directed
unassisted networks in which (1) the receivers are information sinks, (2) the
maximum distance from senders to receivers is small, and (3) a certain type of
4-cycles are absent, but without further constraints (such as on the number of
communicating and intermediate parties). The second class consists of arbitrary
backward-assisted networks with 2 sender-receiver pairs. (iv) Beyond the k-pair
communication problem, observations are made on quantum multicasting and a
static version of network communication related to the entanglement of
assistance.Comment: 15 pages, 17 figures. Final versio
Noise and loss of superconducting aluminium resonators at single photon energies
The loss and noise mechanisms of superconducting resonators are useful tools
for understanding decoherence in superconducting circuits. While the loss
mechanisms have been heavily studied, noise in superconducting resonators has
only recently been investigated. In particular, there is an absence of
literature on noise in the single photon limit. Here, we measure the loss and
noise of an aluminium on silicon quarter-wavelength () resonator in
the single photon regime.Comment: LT28 Conference proceeding, to be published in IOP Conference Serie
Truncated Variance Reduction: A Unified Approach to Bayesian Optimization and Level-Set Estimation
We present a new algorithm, truncated variance reduction (TruVaR), that
treats Bayesian optimization (BO) and level-set estimation (LSE) with Gaussian
processes in a unified fashion. The algorithm greedily shrinks a sum of
truncated variances within a set of potential maximizers (BO) or unclassified
points (LSE), which is updated based on confidence bounds. TruVaR is effective
in several important settings that are typically non-trivial to incorporate
into myopic algorithms, including pointwise costs and heteroscedastic noise. We
provide a general theoretical guarantee for TruVaR covering these aspects, and
use it to recover and strengthen existing results on BO and LSE. Moreover, we
provide a new result for a setting where one can select from a number of noise
levels having associated costs. We demonstrate the effectiveness of the
algorithm on both synthetic and real-world data sets.Comment: Accepted to NIPS 201
A perception-action strategy for hummingbirds
Many human and animal tasks are thought to be controlled with the tau informational variable. It is widely accepted that controlling the rate of change of tau during decelerative tasks, such as when braking or landing, is one common perceptual control strategy. However, many tasks require accelerating before decelerating to a goal, such as reaching. An advancement of tau theory shows how a single action formula may be used to control the full action unit from initiation to peak velocity, and to rest at the goal, with the same perceptual tau information as before and accounting for the same decelerative kinematics as before. Here, we test the theory against data from high-speed video of a hummingbird flying to its flower feeder. We find that the theory accounts for 97% of the variance in the data, and thus supports it
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