653 research outputs found
Generic dialogue modeling for multi-application dialogue systems
We present a novel approach to developing interfaces for multi-application dialogue systems. The targeted interfaces allow transparent switching between a large number of applications within one system. The approach, based on the Rapid Dialogue Prototyping Methodology (RDPM) and the Vector Space model techniques from Information Retrieval, is composed of three main steps: (1) producing finalized dia
logue models for applications using the RDPM, (2) designing an application interaction hierarchy, and (3) navigating between the applications based on the user's application of interest
Nonequilibrium Dynamics in Noncommutative Spacetime
We study the effects of spacetime noncommutativity on the nonequilibrium
dynamics of particles in a thermal bath. We show that the noncommutative
thermal bath does not suffer from any further IR/UV mixing problem in the sense
that all the finite-temperature non-planar quantities are free from infrared
singularities. We also point out that the combined effect of finite temperature
and noncommutative geometry has a distinct effect on the nonequilibrium
dynamics of particles propagating in a thermal bath: depending on the momentum
of the mode of concern, noncommutative geometry may switch on or switch off
their decay and thermalization. This momentum dependent alternation of the
decay and thermalization rates could have significant impacts on the
nonequilibrium phenomena in the early universe at which spacetime
noncommutativity may be present. Our results suggest a re-examination of some
of the important processes in the early universe such as reheating after
inflation, baryogenesis and the freeze-out of superheavy dark matter
candidates.Comment: 24 pages, 2 figure
Non-Commutative Gauge Theories and the Cosmological Constant
We discuss the issue of the cosmological constant in non-commutative
non-supersymmetric gauge theories. In particular, in orbifold field theories
non-commutativity acts as a UV cut-off. We suggest that in these theories
quantum corrections give rise to a vacuum energy \rho, that is controlled by
the non-commutativity parameter \theta, \rho ~ 1/theta^2 (only a soft
logarithmic dependence on the Planck scale survives). We demonstrate our claim
in a two-loop computation in field theory and by certain higher loop examples.
Based on general expressions from string theory, we suggest that the vacuum
energy is controlled by non-commutativity to all orders in perturbation theory.Comment: 11 pages, RevTex. 4 eps figures. v2: Typos corrected. To appear in
Phys.Rev.
Light-cone Superstring Field Theory, pp-wave background and integrability properties
We show that the three strings vertex coefficients in light--cone open string
field theory satisfy the Hirota equations for the dispersionless Toda lattice
hierarchy. We show that Hirota equations allow us to calculate the correlators
of an associated quantum system where the Neumann coefficients represent the
two--point functions. We consider next the three strings vertex coefficients of
the light--cone string field theory on a maximally supersymmetric pp--wave
background. Using the previous results we are able to show that these Neumann
coefficients satisfy the Hirota equations for the full Toda lattice hierarchy
at least up to second order in the 'string mass' .Comment: 23 pages, 3 figures, footnote and references adde
Adiabatic decaying vacuum model for the universe
We study a model that the entropy per particle in the universe is constant.
The sources for the entropy are the particle creation and a lambda decaying
term. We find exact solutions for the Einstein field equations and show the
compatibilty of the model with respect to the age and the acceleration of the
universe.Comment: 10 pages, 2 figure
Phenomenology of Particle Production and Propagation in String-Motivated Canonical Noncommutative Spacetime
We outline a phenomenological programme for the search of effects induced by
(string-motivated) canonical noncommutative spacetime. The tests we propose are
based, in analogy with a corresponding programme developed over the last few
years for the study of Lie-algebra noncommutative spacetimes, on the role of
the noncommutativity parameters in the dispersion relation. We focus on
the role of deformed dispersion relations in particle-production collision
processes, where the noncommutativity parameters would affect the threshold
equation, and in the dispersion of gamma rays observed from distant
astrophysical sources. We emphasize that the studies here proposed have the
advantage of involving particles of relatively high energies, and may therefore
be less sensitive to "contamination" (through IR/UV mixing) from the UV sector
of the theory. We also explore the possibility that the relevant deformation of
the dispersion relations could be responsible for the experimentally-observed
violations of the GZK cutoff for cosmic rays and could have a role in the
observation of hard photons from distant astrophysical sources.Comment: With respect to the experimental information available at the time of
writing version 1 of this manuscript (hep-th/0109191v1) the situation has
evolved significantly. Our remarks on the benefits of high-energy
observations found additional encouragement from the results reported in
hep-th/020925
The association of lesion eccentricity with plaque morphology and components in the superficial femoral artery: a high-spatial-resolution, multi-contrast weighted CMR study
<p>Abstract</p> <p>Background</p> <p>Atherosclerotic plaque morphology and components are predictors of subsequent cardiovascular events. However, associations of plaque eccentricity with plaque morphology and plaque composition are unclear. This study investigated associations of plaque eccentricity with plaque components and morphology in the proximal superficial femoral artery using cardiovascular magnetic resonance (CMR).</p> <p>Methods</p> <p>Twenty-eight subjects with an ankle-brachial index less than 1.00 were examined with 1.5T high-spatial-resolution, multi-contrast weighted CMR. One hundred and eighty diseased locations of the proximal superficial femoral artery (about 40 mm) were analyzed. The eccentric lesion was defined as [(Maximum wall thickness- Minimum wall thickness)/Maximum wall thickness] ≥ 0.5. The arterial morphology and plaque components were measured using semi-automatic image analysis software.</p> <p>Results</p> <p>One hundred and fifteen locations were identified as eccentric lesions and sixty-five as concentric lesions. The eccentric lesions had larger wall but similar lumen areas, larger mean and maximum wall thicknesses, and more calcification and lipid rich necrotic core, compared to concentric lesions. For lesions with the same lumen area, the degree of eccentricity was associated with an increased wall area. Eccentricity (dichotomous as eccentric or concentric) was independently correlated with the prevalence of calcification (odds ratio 3.78, 95% CI 1.47-9.70) after adjustment for atherosclerotic risk factors and wall area.</p> <p>Conclusions</p> <p>Plaque eccentricity is associated with preserved lumen size and advanced plaque features such as larger plaque burden, more lipid content, and increased calcification in the superficial femoral artery.</p
Have we already detected astrophysical symptoms of space-time noncommutativity ?
We discuss astrophysical implications of -Minkowski space-time, in
which there appears space-time noncommutativity. We first derive a velocity
formula for particles based on the motion of a wave packet. The result is that
a massless particle moves at a constant speed as in the usual Minkowski
space-time, which implies that an arrival time analysis by -rays from
Markarian (Mk) 421 does not exclude space-time noncommutativity. Based on this
observation, we analyze reaction processes in -Minkowski space-time
which are related to the puzzling detections of extremely high-energy cosmic
rays above the Greisen-Zatsepin-Kuzmin cutoff and of high-energy (20 TeV)
-rays from Mk 501.Comment: 10 pages, 6 figures, submitted to PRD, corrected some mistake
Effective Potential and Spontaneous Symmetry Breaking in the Noncommutative phi^6 Model
We study the conditions for spontaneous symmetry breaking of the
(2+1)-dimensional noncommutative phi^6 model in the small-theta limit. In this
regime, considering the model as a cutoff theory, it is reasonable to assume
translational invariance as a property of the vacuum state and study the
conditions for spontaneous symmetry breaking by an effective potential
analysis. An investigation of up to the two loop level reveals that
noncommutative effects can modify drastically the shape of the effective
potential. Under reasonable conditions, the nonplanar sector of the theory can
become dominant and induce symmetry breaking for values of the mass and
coupling constants not reached by the commutative counterpart.Comment: 11 pages, 2 figures, corrected to match with the PRD versio
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