999 research outputs found
Comment on ``Critical behavior of a two-species reaction-diffusion problem''
In a recent paper, de Freitas et al. [Phys. Rev. E 61, 6330 (2000)] presented
simulational results for the critical exponents of the two-species
reaction-diffusion system A + B -> 2B and B -> A in dimension d = 1. In
particular, the correlation length exponent was found as \nu = 2.21(5) in
contradiction to the exact relation \nu = 2/d. In this Comment, the symmetry
arguments leading to exact critical exponents for the universality class of
this reaction-diffusion system are concisely reconsidered
Multifractality at the spin quantum Hall transition
Statistical properties of critical wave functions at the spin quantum Hall
transition are studied both numerically and analytically (via mapping onto the
classical percolation). It is shown that the index characterizing the
decay of wave function correlations is equal to 1/4, at variance with the
decay of the diffusion propagator. The multifractality spectra of
eigenfunctions and of two-point conductances are found to be
close-to-parabolic, and .Comment: 4 pages, 3 figure
On the tree-transformation power of XSLT
XSLT is a standard rule-based programming language for expressing
transformations of XML data. The language is currently in transition from
version 1.0 to 2.0. In order to understand the computational consequences of
this transition, we restrict XSLT to its pure tree-transformation capabilities.
Under this focus, we observe that XSLT~1.0 was not yet a computationally
complete tree-transformation language: every 1.0 program can be implemented in
exponential time. A crucial new feature of version~2.0, however, which allows
nodesets over temporary trees, yields completeness. We provide a formal
operational semantics for XSLT programs, and establish confluence for this
semantics
Kennisverkenner: van een geo-informatie systeem (GIS) naar een geo-kennis systeem (GKS)
Veel kennis heeft een ruimtelijk aspect en zeker in de agrarische sector zijn activiteiten en bedrijfseigenschappen aan een moment in de tijd en een geografische positie gebonden. Door het gecombineerd ontsluiten van kennis en locatie wordt ruimtelijk zoeken door het kennisnetwerk mogelijk. De Kennisverkenner, een innovatieve manier om (ruimtelijke) kennis te ordenen en te ontsluiten
Unitary chiral dynamics in J/Psi to VPP decays and the role of scalar mesons
We make a theoretical study of the J/Psi decays into \omega\pi\pi,
\phi\pi\pi, \omega K \bar{K} and \phi K\bar{K} using the techniques of the
chiral unitary approach stressing the important role of the scalar resonances
dynamically generated through the final state interaction of the two
pseudoscalar mesons. We also discuss the importance of new mechanisms with
intermediate exchange of vector and axial-vector mesons and the role played by
the OZI rule in the J/\Psi\phi\pi\pi vertex, quantifying its effects. The
results nicely reproduce the experimental data for the invariant mass
distributions in all the channels considered.Comment: 29 pages, 10 figure
Nonequilibrium critical dynamics of the relaxational models C and D
We investigate the critical dynamics of the -component relaxational models
C and D which incorporate the coupling of a nonconserved and conserved order
parameter S, respectively, to the conserved energy density rho, under
nonequilibrium conditions by means of the dynamical renormalization group.
Detailed balance violations can be implemented isotropically by allowing for
different effective temperatures for the heat baths coupling to the slow modes.
In the case of model D with conserved order parameter, the energy density
fluctuations can be integrated out. For model C with scalar order parameter, in
equilibrium governed by strong dynamic scaling (z_S = z_rho), we find no
genuine nonequilibrium fixed point. The nonequilibrium critical dynamics of
model C with n = 1 thus follows the behavior of other systems with nonconserved
order parameter wherein detailed balance becomes effectively restored at the
phase transition. For n >= 4, the energy density decouples from the order
parameter. However, for n = 2 and n = 3, in the weak dynamic scaling regime
(z_S <= z_rho) entire lines of genuine nonequilibrium model C fixed points
emerge to one-loop order, which are characterized by continuously varying
critical exponents. Similarly, the nonequilibrium model C with spatially
anisotropic noise and n < 4 allows for continuously varying exponents, yet with
strong dynamic scaling. Subjecting model D to anisotropic nonequilibrium
perturbations leads to genuinely different critical behavior with softening
only in subsectors of momentum space and correspondingly anisotropic scaling
exponents. Similar to the two-temperature model B the effective theory at
criticality can be cast into an equilibrium model D dynamics, albeit
incorporating long-range interactions of the uniaxial dipolar type.Comment: Revtex, 23 pages, 5 eps figures included (minor additions), to appear
in Phys. Rev.
Critical exponents in Ising spin glasses
We determine accurate values of ordering temperatures and critical exponents
for Ising Spin Glass transitions in dimension 4, using a combination of finite
size scaling and non-equilibrium scaling techniques. We find that the exponents
and vary with the form of the interaction distribution, indicating
non-universality at Ising spin glass transitions. These results confirm
conclusions drawn from numerical data for dimension 3.Comment: 6 pages, RevTeX (or Latex, etc), 10 figures, Submitted to PR
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