14,686 research outputs found
Expectation-driven interaction: a model based on Luhmann's contingency approach
We introduce an agent-based model of interaction, drawing on the contingency
approach from Luhmann's theory of social systems. The agent interactions are
defined by the exchange of distinct messages. Message selection is based on the
history of the interaction and developed within the confines of the problem of
double contingency. We examine interaction strategies in the light of the
message-exchange description using analytical and computational methods.Comment: 37 pages, 16 Figures, to appear in Journal of Artificial Societies
and Social Simulation
Evidence for O(2) universality at the finite temperature transition for lattice QCD with 2 flavours of massless staggered quarks
We simulate lattice QCD with 2 flavours of massless quarks on lattices of
temporal extent N_t=8, to study the finite temperature transition from hadronic
matter to a quark-gluon plasma. A modified action which incorporates an
irrelevant chiral 4-fermion interaction is used, which allows simulations at
zero quark mass. We obtain excellent fits of the chiral condensates to the
magnetizations of a 3-dimensional O(2) spin model on lattices small enough to
model the finite size effects. This gives predictions for correlation lengths
and chiral susceptibilities from the corresponding spin-model quantities. These
are in good agreement with our measurements over the relevant range of
parameters. Binder cumulants are measured, but the errors are too large to draw
definite conclusions. From the properties of the O(2) spin model on the
relatively small lattices with which we fit our `data', we can see why earlier
attempts to fit staggered lattice data to leading-order infinite-volume scaling
functions, as well as finite size scaling studies, failed and led to erroneous
conclusions.Comment: 27 pages, Latex with 10 postscript figures. Some of the discussions
have been expanded to satisfy a referee. Typographical errors were correcte
Bubble Shape Oscillations and the Onset of Sonoluminescence
An air bubble trapped in water by an oscillating acoustic field undergoes
either radial or nonspherical pulsations depending on the strength of the
forcing pressure. Two different instability mechanisms (the Rayleigh--Taylor
instability and parametric instability) cause deviations from sphericity.
Distinguishing these mechanisms allows explanation of many features of recent
experiments on sonoluminescence, and suggests methods for finding
sonoluminescence in different parameter regimes.Comment: Phys. Rev. Lett., in pres
The Sound of Sonoluminescence
We consider an air bubble in water under conditions of single bubble
sonoluminescence (SBSL) and evaluate the emitted sound field nonperturbatively
for subsonic gas-liquid interface motion. Sound emission being the dominant
damping mechanism, we also implement the nonperturbative sound damping in the
Rayleigh-Plesset equation for the interface motion. We evaluate numerically the
sound pulse emitted during bubble collapse and compare the nonperturbative and
perturbative results, showing that the usual perturbative description leads to
an overestimate of the maximal surface velocity and maximal sound pressure. The
radius vs. time relation for a full SBSL cycle remains deceptively unaffected.Comment: 25 pages; LaTex and 6 attached ps figure files. Accepted for
publication in Physical Review
The Logarithmic Triviality of Compact QED Coupled to a Four Fermi Interaction
This is the completion of an exploratory study of Compact lattice Quantum
Electrodynamics with a weak four-fermi interaction and four species of massless
fermions. In this formulation of Quantum Electrodynamics massless fermions can
be simulated directly and Finite Size Scaling analyses can be performed at the
theory's chiral symmetry breaking critical point. High statistics simulations
on lattices ranging from to yield the equation of state, critical
indices, scaling functions and cumulants. The measurements are well fit with
the orthodox hypothesis that the theory is logarithmically trivial and its
continuum limit suffers from Landau's zero charge problem.Comment: 27 pages, 15 figues and 10 table
Monopole Percolation in the Compact Abelian Higgs Model
We have studied the monopole-percolation phenomenon in the four dimensional
Abelian theory that contains compact U(1) gauge fields coupled to unitary norm
Higgs fields. We have determined the location of the percolation transition
line in the plane . This line overlaps the confined-Coulomb
and the confined-Higgs phase transition lines, originated by a
monopole-condensation mechanism, but continues away from the end-point where
this phase transition line stops. In addition, we have determined the critical
exponents of the monopole percolation transition away from the phase transition
lines. We have performed the finite size scaling in terms of the monopole
density instead of the coupling, because the density seems to be the natural
parameter when dealing with percolation phenomena.Comment: 13 pages. REVTeX. 16 figs. included using eps
Exact clesed form of the return probability on the Bethe lattice
An exact closed form solution for the return probability of a random walk on
the Bethe lattice is given. The long-time asymptotic form confirms a previously
known expression. It is however shown that this exact result reduces to the
proper expression when the Bethe lattice degenerates on a line, unlike the
asymptotic result which is singular. This is shown to be an artefact of the
asymptotic expansion. The density of states is also calculated.Comment: 7 pages, RevTex 3.0, 2 figures available upon request from
[email protected], to be published in J.Phys.A Let
Mechanisms for Stable Sonoluminescence
A gas bubble trapped in water by an oscillating acoustic field is expected to
either shrink or grow on a diffusive timescale, depending on the forcing
strength and the bubble size. At high ambient gas concentration this has long
been observed in experiments. However, recent sonoluminescence experiments show
that in certain circumstances when the ambient gas concentration is low the
bubble can be stable for days. This paper presents mechanisms leading to
stability which predict parameter dependences in agreement with the
sonoluminescence experiments.Comment: 4 pages, 3 figures on request (2 as .ps files
Gauge Theories with Cayley-Klein and Gauge Groups
Gauge theories with the orthogonal Cayley-Klein gauge groups and
are regarded. For nilpotent values of the contraction
parameters these groups are isomorphic to the non-semisimple Euclid,
Newton, Galilei groups and corresponding matter spaces are fiber spaces with
degenerate metrics. It is shown that the contracted gauge field theories
describe the same set of fields and particle mass as gauge
theories, if Lagrangians in the base and in the fibers all are taken into
account. Such theories based on non-semisimple contracted group provide more
simple field interactions as compared with the initial ones.Comment: 14 pages, 5 figure
- …