230,678 research outputs found
Memory-Based Shallow Parsing
We present memory-based learning approaches to shallow parsing and apply
these to five tasks: base noun phrase identification, arbitrary base phrase
recognition, clause detection, noun phrase parsing and full parsing. We use
feature selection techniques and system combination methods for improving the
performance of the memory-based learner. Our approach is evaluated on standard
data sets and the results are compared with that of other systems. This reveals
that our approach works well for base phrase identification while its
application towards recognizing embedded structures leaves some room for
improvement
Quantum mechanics of spin transfer in coupled electron-spin chains
The manner in which spin-polarized electrons interact with a magnetized thin
film is currently described by a semi-classical approach. This in turn provides
our present understanding of the spin transfer, or spin torque phenomenon.
However, spin is an intrinsically quantum mechanical quantity. Here, we make
the first strides towards a fully quantum mechanical description of spin
transfer through spin currents interacting with a Heisenberg-coupled spin
chain. Because of quantum entanglement, this requires a formalism based on the
density matrix approach. Our description illustrates how individual spins in
the chain time-evolve as a result of spin transfer.Comment: 4 pages, 3 (colour) figure
Introduction to the CoNLL-2002 Shared Task: Language-Independent Named Entity Recognition
We describe the CoNLL-2002 shared task: language-independent named entity
recognition. We give background information on the data sets and the evaluation
method, present a general overview of the systems that have taken part in the
task and discuss their performance.Comment: 4 page
Model study of the sign problem in the mean-field approximation
We argue the sign problem of the fermion determinant at finite density. It is
unavoidable not only in Monte-Carlo simulations on the lattice but in the
mean-field approximation as well. A simple model deriving from Quantum
Chromodynamics (QCD) in the double limit of large quark mass and large quark
chemical potential exemplifies how the sign problem arises in the Polyakov loop
dynamics at finite temperature and density. In the color SU(2) case our
mean-field estimate is in excellent agreement with the lattice simulation. We
combine the mean-field approximation with a simple phase reweighting technique
to circumvent the complex action encountered in the color SU(3) case. We also
investigate the mean-field free energy, from the saddle-point of which we can
estimate the expectation value of the Polyakov loop.Comment: 14 page, 18 figures, typos corrected, references added, some
clarification in sec.I
Wiedemann-Franz violation in the vortex state of a d-wave superconductor
We show that the Wiedemann-Franz law is violated in the vortex state of a
d-wave superconductor at zero temperature. We use a semiclassical approach,
which includes the Doppler shift on the quasiparticles as well as the Andreev
scattering from a random distribution of vortices. We also show that the vertex
corrections to the electrical conductivity due to the anisotropy of impurity
scattering become unimportant in the presence of a sufficiently large magnetic
field.Comment: To be published in Physica C as a proceeding of M2S-HTSC Rio 200
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