1,596 research outputs found
A Robust Parsing Algorithm For Link Grammars
In this paper we present a robust parsing algorithm based on the link grammar
formalism for parsing natural languages. Our algorithm is a natural extension
of the original dynamic programming recognition algorithm which recursively
counts the number of linkages between two words in the input sentence. The
modified algorithm uses the notion of a null link in order to allow a
connection between any pair of adjacent words, regardless of their dictionary
definitions. The algorithm proceeds by making three dynamic programming passes.
In the first pass, the input is parsed using the original algorithm which
enforces the constraints on links to ensure grammaticality. In the second pass,
the total cost of each substring of words is computed, where cost is determined
by the number of null links necessary to parse the substring. The final pass
counts the total number of parses with minimal cost. All of the original
pruning techniques have natural counterparts in the robust algorithm. When used
together with memoization, these techniques enable the algorithm to run
efficiently with cubic worst-case complexity. We have implemented these ideas
and tested them by parsing the Switchboard corpus of conversational English.
This corpus is comprised of approximately three million words of text,
corresponding to more than 150 hours of transcribed speech collected from
telephone conversations restricted to 70 different topics. Although only a
small fraction of the sentences in this corpus are "grammatical" by standard
criteria, the robust link grammar parser is able to extract relevant structure
for a large portion of the sentences. We present the results of our experiments
using this system, including the analyses of selected and random sentences from
the corpus.Comment: 17 pages, compressed postscrip
Lattice Interferometer for Ultra-Cold Atoms
We demonstrate an atomic interferometer based on ultra-cold atoms released
from an optical lattice. This technique yields a large improvement in signal to
noise over a related interferometer previously demonstrated. The interferometer
involves diffraction of the atoms using a pulsed optical lattice. For short
pulses a simple analytical theory predicts the expected signal. We investigate
the interferometer for both short pulses and longer pulses where the analytical
theory break down. Longer pulses can improve the precision and signal size. For
specific pulse lengths we observe a coherent signal at times that differs
greatly from what is expected from the short pulse model. The interferometric
signal also reveals information about the dynamics of the atoms in the lattice.
We investigate the application of the interferometer for a measurement of
that together with other well known constants constitutes a measurement
of the fine structure constant
Direct Imaging of Periodic Sub-wavelength Patterns of Total Atomic Density
Interference fringes of total atomic density with period and
for optical wavelength , have been produced in de Broglie
atom interferometer and directly imaged by means of an ``optical mask''
technique. The imaging technique allowed us to observe sub-wavelength periodic
patterns with a resolution of . The quantum dynamics near the
interference times as a function of the recoil phase and pulse areas has been
investigated.Comment: 4 pages, 4 figures, to be submitted to Phys. Rev. A; order
rearranged, references replaced and added, corrected typo
Proteins: form and function
An overwhelming array of structural variants has evolved from a comparatively small number of protein structural domains; which has in turn facilitated an expanse of functional derivatives. Herein, I review the primary mechanisms which have contributed to the vastness of our existing, and expanding, protein repertoires. Protein function prediction strategies, both sequence and structure based, are also discussed and their associated strengths and weaknesses assessed
Probiotic therapy - recruiting old friends to fight new foes
Against a backdrop of increasing antibiotic resistance, and the emergence of new and evolving pathogens, clinicians are increasingly forced to consider alternative therapies - probiotics are one such alternative
In pursuit of the dynamic optimality conjecture
In 1985, Sleator and Tarjan introduced the splay tree, a self-adjusting
binary search tree algorithm. Splay trees were conjectured to perform within a
constant factor as any offline rotation-based search tree algorithm on every
sufficiently long sequence---any binary search tree algorithm that has this
property is said to be dynamically optimal. However, currently neither splay
trees nor any other tree algorithm is known to be dynamically optimal. Here we
survey the progress that has been made in the almost thirty years since the
conjecture was first formulated, and present a binary search tree algorithm
that is dynamically optimal if any binary search tree algorithm is dynamically
optimal.Comment: Preliminary version of paper to appear in the Conference on Space
Efficient Data Structures, Streams and Algorithms to be held in August 2013
in honor of Ian Munro's 66th birthda
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