6,287 research outputs found
The Complexity of Repairing, Adjusting, and Aggregating of Extensions in Abstract Argumentation
We study the computational complexity of problems that arise in abstract
argumentation in the context of dynamic argumentation, minimal change, and
aggregation. In particular, we consider the following problems where always an
argumentation framework F and a small positive integer k are given.
- The Repair problem asks whether a given set of arguments can be modified
into an extension by at most k elementary changes (i.e., the extension is of
distance k from the given set).
- The Adjust problem asks whether a given extension can be modified by at
most k elementary changes into an extension that contains a specified argument.
- The Center problem asks whether, given two extensions of distance k,
whether there is a "center" extension that is a distance at most (k-1) from
both given extensions.
We study these problems in the framework of parameterized complexity, and
take the distance k as the parameter. Our results covers several different
semantics, including admissible, complete, preferred, semi-stable and stable
semantics
Passage of Time in a Planck Scale Rooted Local Inertial Structure
It is argued that the `problem of time' in quantum gravity necessitates a
refinement of the local inertial structure of the world, demanding a
replacement of the usual Minkowski line element by a 4+2n dimensional
pseudo-Euclidean line element, with the extra 2n being the number of internal
phase space dimensions of the observed system. In the refined structure, the
inverse of the Planck time takes over the role of observer-independent
conversion factor usually played by the speed of light, which now emerges as an
invariant but derivative quantity. In the relativistic theory based on the
refined structure, energies and momenta turn out to be invariantly bounded from
above, and lengths and durations similarly bounded from below, by their
respective Planck scale values. Along the external timelike world-lines, the
theory naturally captures the `flow of time' as a genuinely structural
attribute of the world. The theory also predicts expected
deviations--suppressed quadratically by the Planck energy--from the dispersion
relations for free fields in the vacuum. The deviations from the special
relativistic Doppler shifts predicted by the theory are also suppressed
quadratically by the Planck energy. Nonetheless, in order to estimate the
precision required to distinguish the theory from special relativity, an
experiment with a binary pulsar emitting TeV range gamma-rays is considered in
the context of the predicted deviations from the second-order shifts.Comment: 17 pages; Diagram depicting "the objective flow of time" is replaced
with a much-improved diagra
A Gauge-Gravity Relation in the One-loop Effective Action
We identify an unusual new gauge-gravity relation: the one-loop effective
action for a massive spinor in 2n dimensional AdS space is expressed in terms
of precisely the same function [a certain multiple gamma function] as the
one-loop effective action for a massive charged scalar in 4n dimensions in a
maximally symmetric background electromagnetic field [one for which the
eigenvalues of F_{\mu\nu} are maximally degenerate, corresponding in 4
dimensions to a self-dual field, equivalently to a field of definite helicity],
subject to the identification F^2 \Lambda, where \Lambda is the
gravitational curvature. Since these effective actions generate the low energy
limit of all one-loop multi-leg graviton or gauge amplitudes, this implies a
nontrivial gauge-gravity relation at the non-perturbative level and at the
amplitude level.Comment: 6 page
Supersymmetric Euler-Heisenberg effective action: Two-loop results
The two-loop Euler-Heisenberg-type effective action for N = 1 supersymmetric
QED is computed within the background field approach. The background vector
multiplet is chosen to obey the constraints D_\a W_\b = D_{(\a} W_{\b)} =
const, but is otherwise completely arbitrary. Technically, this calculation
proves to be much more laborious as compared with that carried out in
hep-th/0308136 for N = 2 supersymmetric QED, due to a lesser amount of
supersymmetry. Similarly to Ritus' analysis for spinor and scalar QED, the
two-loop renormalisation is carried out using proper-time cut-off
regularisation. A closed-form expression is obtained for the holomorphic sector
of the two-loop effective action, which is singled out by imposing a relaxed
super self-duality condition.Comment: 27 pages, 2 eps figures, LaTeX; V2: typos corrected, comments and
reference adde
QED vacuum fluctuations and induced electric dipole moment of the neutron
Quantum fluctuations in the QED vacuum generate non-linear effects, such as
peculiar induced electromagnetic fields. In particular, we show here that an
electrically neutral particle, possessing a magnetic dipole moment, develops an
induced electric dipole-type moment with unusual angular dependence, when
immersed in a quasistatic, constant external electric field. The calculation of
this effect is done in the framework of the Euler-Heisenberg effective QED
Lagrangian, corresponding to the weak field asymptotic expansion of the
effective action to one-loop order. It is argued that the neutron might be a
good candidate to probe this signal of non-linearity in QED.Comment: A misprint has been corrected, and three new references have been
adde
Chern-Simons Solitons, Toda Theories and the Chiral Model
The two-dimensional self-dual Chern--Simons equations are equivalent to the
conditions for static, zero-energy solutions of the -dimensional gauged
nonlinear Schr\"odinger equation with Chern--Simons matter-gauge dynamics. In
this paper we classify all finite charge solutions by first
transforming the self-dual Chern--Simons equations into the two-dimensional
chiral model (or harmonic map) equations, and then using the Uhlenbeck--Wood
classification of harmonic maps into the unitary groups. This construction also
leads to a new relationship between the Toda and chiral model
solutions
Effect of praziquantel treatment of Schistosoma mansoni during pregnancy on immune responses to schistosome antigens among the offspring: results of a randomised, placebo-controlled trial.
BACKGROUND: Offspring of women with schistosomiasis may exhibit immune responsiveness to schistosomes due to in utero sensitisation or trans-placental transfer of antibodies. Praziquantel treatment during pregnancy boosts maternal immune responses to schistosome antigens and reduces worm burden. Effects of praziquantel treatment during pregnancy on responses among offspring are unknown. METHODS: In a trial of anthelminthic treatment during pregnancy in Uganda (ISRCTN32849447; http://www.controlled-trials.com/ISRCTN32849447/elliott), offspring of women with Schistosoma mansoni were examined for cytokine and antibody responses to schistosome worm (SWA) and egg (SEA) antigen, in cord blood and at age one year. Relationships to maternal responses and pre-treatment infection intensities were examined, and responses were compared between the offspring of women who did, or did not receive praziquantel treatment during pregnancy. RESULTS: Of 388 S. mansoni-infected women studied, samples were obtained at age one year from 215 of their infants. Stool examination for S. mansoni eggs was negative for all infants. Cord and infant samples were characterised by very low cytokine production in response to schistosome antigens with the exception of cord IL-10 responses, which were substantial. Cord and infant cytokine responses showed no association with maternal responses. As expected, cord blood levels of immunoglobulin (Ig) G to SWA and SEA were high and correlated with maternal antibodies. However, by age one year IgG levels had waned and were hardly detectable. Praziquantel treatment during pregnancy showed no effect on cytokine responses or antibodies levels to SWA or SEA either in cord blood or at age one year, except for IgG1 to SWA, which was elevated in infants of treated mothers, reflecting maternal levels. There was some evidence that maternal infection intensity was positively associated with cord blood IL-5 and IL-13 responses to SWA, and IL-5 responses to SEA, and that this association was modified by treatment with praziquantel. CONCLUSIONS: Despite strong effects on maternal infection intensity and maternal immune responses, praziquantel treatment of infected women during pregnancy had no effect on anti-schistosome immune responses among offspring by age one year. Whether the treatment will impact upon the offspring's responses on exposure to primary schistosome infection remains to be elucidated. TRIAL REGISTRATION: ISRCTN: ISRCTN32849447
Zero modes, beta functions and IR/UV interplay in higher-loop QED
We analyze the relation between the short-distance behavior of quantum field
theory and the strong-field limit of the background field formalism, for QED
effective Lagrangians in self-dual backgrounds, at both one and two loop. The
self-duality of the background leads to zero modes in the case of spinor QED,
and these zero modes must be taken into account before comparing the
perturbative beta function coefficients and the coefficients of the
strong-field limit of the effective Lagrangian. At one-loop this is familiar
from instanton physics, but we find that at two-loop the role of the zero
modes, and the interplay between IR and UV effects in the renormalization, is
quite different. Our analysis is motivated in part by the remarkable simplicity
of the two-loop QED effective Lagrangians for a self-dual constant background,
and we also present here a new independent derivation of these two-loop
results.Comment: 15 pages, revtex
One-loop quantum cosmological correction to the gravitational constant using the kink solution in de Sitter universe
In this paper, we show the equivalence between a classical static scalar
field theory and the (closed) de Sitter cosmological model whose potential
represents shape invariance property. Based on this equivalence, we calculate
the one-loop quantum cosmological correction to the ground state energy of the
kink-like solution in the (closed) de Sitter cosmological model in which the
fluctuation potential has a shape invariance property. It is
shown that this type of correction, which yields a renormalized mass in the
case of scalar field theory, may be {\it interpreted} as a renormalized
gravitational constant in the case of (closed) de Sitter cosmological model.
Keywords: One-loop correction; kink energy; shape invariance; zeta function
regularization; de Sitter universe.Comment: 18 page
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Climate versus emission drivers of methane lifetime against loss by tropospheric OH from 1860–2100
With a more-than-doubling in the atmospheric abundance of the potent greenhouse gas methane (CH₄) since preindustrial times, and indications of renewed growth following a leveling off in recent years, questions arise as to future trends and resulting climate and public health impacts from continued growth without mitigation. Changes in atmospheric methane lifetime are determined by factors which regulate the abundance of OH, the primary methane removal mechanism, including changes in CH₄ itself. We investigate the role of emissions of short-lived species and climate in determining the evolution of methane lifetime against loss by tropospheric OH, (τCH₄_OH), in a suite of historical (1860–2005) and future Representative Concentration Pathway (RCP) simulations (2006–2100), conducted with the Geophysical Fluid Dynamics Laboratory (GFDL) fully coupled chemistry-climate model (CM3). From preindustrial to present, CM3 simulates an overall 5% increase in τCH₄_OH due to a doubling of the methane burden which offsets coincident increases in nitrogen oxide (NOx emissions. Over the last two decades, however, the τCH₄_OH declines steadily, coinciding with the most rapid climate warming and observed slow-down in CH₄ growth rates, reflecting a possible negative feedback through the CH₄ sink. Sensitivity simulations with CM3 suggest that the aerosol indirect effect (aerosol-cloud interactions) plays a significant role in cooling the CM3 climate. The projected decline in aerosols under all RCPs contributes to climate warming over the 21st century, which influences the future evolution of OH concentration and τCH₄_OH. Projected changes in τCH₄_OH from 2006 to 2100 range from −13% to +4%. The only projected increase occurs in the most extreme warming case (RCP8.5) due to the near-doubling of the CH₄ abundance, reflecting a positive feedback on the climate system. The largest decrease occurs in the RCP4.5 scenario due to changes in short-lived climate forcing agents which reinforce climate warming and enhance OH. This decrease is more-than-halved in a sensitivity simulation in which only well-mixed greenhouse gas radiative forcing changes along the RCP4.5 scenario (5% vs. 13%)
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