21,751 research outputs found
Anisotropic KPZ growth in 2+1 dimensions: fluctuations and covariance structure
In [arXiv:0804.3035] we studied an interacting particle system which can be
also interpreted as a stochastic growth model. This model belongs to the
anisotropic KPZ class in 2+1 dimensions. In this paper we present the results
that are relevant from the perspective of stochastic growth models, in
particular: (a) the surface fluctuations are asymptotically Gaussian on a
sqrt(ln(t)) scale and (b) the correlation structure of the surface is
asymptotically given by the massless field.Comment: 13 pages, 4 figure
Model checking usage policies
We study usage automata, a formal model for specifying policies on the usage of resources. Usage automata extend finite state automata with some additional features, parameters and guards, that improve their expressivity. We show that usage automata are expressive enough to model policies of real-world applications. We discuss their expressive power, and we prove that the problem of telling whether a computation complies with a usage policy is decidable. The main contribution of this paper is a model checking technique for usage automata. The model is that of usages, i.e. basic processes that describe the possible patterns of resource access and creation. In spite of the model having infinite states, because of recursion and resource creation, we devise a polynomial-time model checking technique for deciding when a usage complies with a usage policy
Two-dimensional Poisson Trees converge to the Brownian web
The Brownian web can be roughly described as a family of coalescing
one-dimensional Brownian motions starting at all times in and at all
points of . It was introduced by Arratia; a variant was then studied by
Toth and Werner; another variant was analyzed recently by Fontes, Isopi, Newman
and Ravishankar. The two-dimensional \emph{Poisson tree} is a family of
continuous time one-dimensional random walks with uniform jumps in a bounded
interval. The walks start at the space-time points of a homogeneous Poisson
process in and are in fact constructed as a function of the point
process. This tree was introduced by Ferrari, Landim and Thorisson. By
verifying criteria derived by Fontes, Isopi, Newman and Ravishankar, we show
that, when properly rescaled, and under the topology introduced by those
authors, Poisson trees converge weakly to the Brownian web.Comment: 22 pages, 1 figure. This version corrects an error in the previous
proof. The results are the sam
Mean Field Voter Model of Election to the House of Representatives in Japan
In this study, we propose a mechanical model of a plurality election based on
a mean field voter model. We assume that there are three candidates in each
electoral district, i.e., one from the ruling party, one from the main
opposition party, and one from other political parties. The voters are
classified as fixed supporters and herding (floating) voters with ratios of
and , respectively. Fixed supporters make decisions based on their
information and herding voters make the same choice as another randomly
selected voter. The equilibrium vote-share probability density of herding
voters follows a Dirichlet distribution. We estimate the composition of fixed
supporters in each electoral district and using data from elections to the
House of Representatives in Japan (43rd to 47th). The spatial inhomogeneity of
fixed supporters explains the long-range spatial and temporal correlations. The
estimated values of are close to the estimates obtained from a survey.Comment: 11 pages, 7 figure
ATCA observations of the galaxy cluster Abell 3921 - I. Radio emission from the central merging sub-clusters
We present the analysis of our 13 and 22 cm ATCA observations of the central
region of the merging galaxy cluster A3921 (z=0.094). We investigated the
effects of the major merger between two sub-clusters on the star formation (SF)
and radio emission properties of the confirmed cluster members. The origin of
SF and the nature of radio emission in cluster galaxies was investigated by
comparing their radio, optical and X-ray properties. We also compared the radio
source counts and the percentage of detected radio galaxies with literature
data. We detected 17 radio sources above the flux density limit of 0.25
mJy/beam in the central field of A3921, among which 7 are cluster members. 9
galaxies with star-forming optical spectra were observed in the collision
region of the merging sub-clusters. They were not detected at radio
wavelengths, giving upper limits for their star formation rate significantly
lower than those typically found in late-type, field galaxies. Most of these
star-forming objects are therefore really located in the high density part of
the cluster, and they are not infalling field objects seen in projection at the
cluster centre. Their SF episode is probably related to the cluster collision
that we observe in its very central phase. None of the galaxies with
post-starburst optical spectra was detected down our 2 flux density
limit, confirming that they are post-starburst and not dusty star-forming
objects. We finally detected a narrow-angle tail (NAT) source associated with
the second brightest cluster galaxy (BG2), whose diffuse component is a partly
detached pair of tails from an earlier period of activity of the BG2 galaxy.Comment: 17 pages, 9 figures, accepted for publication in A&A, date of
acceptance 29/06/2006. A version of the paper with higher resolution images
can be downloaded at:
http://astro.uibk.ac.at/~c.ferrari/ATCA_Paper/A3921_ATCA.pd
From interacting particle systems to random matrices
In this contribution we consider stochastic growth models in the
Kardar-Parisi-Zhang universality class in 1+1 dimension. We discuss the large
time distribution and processes and their dependence on the class on initial
condition. This means that the scaling exponents do not uniquely determine the
large time surface statistics, but one has to further divide into subclasses.
Some of the fluctuation laws were first discovered in random matrix models.
Moreover, the limit process for curved limit shape turned out to show up in a
dynamical version of hermitian random matrices, but this analogy does not
extend to the case of symmetric matrices. Therefore the connections between
growth models and random matrices is only partial.Comment: 18 pages, 8 figures; Contribution to StatPhys24 special issue; minor
corrections in scaling of section 2.
Phase synchronization of coupled bursting neurons and the generalized Kuramoto model
Bursting neurons fire rapid sequences of action potential spikes followed by
a quiescent period. The basic dynamical mechanism of bursting is the slow
currents that modulate a fast spiking activity caused by rapid ionic currents.
Minimal models of bursting neurons must include both effects. We considered one
of these models and its relation with a generalized Kuramoto model, thanks to
the definition of a geometrical phase for bursting and a corresponding
frequency. We considered neuronal networks with different connection topologies
and investigated the transition from a non-synchronized to a partially
phase-synchronized state as the coupling strength is varied. The numerically
determined critical coupling strength value for this transition to occur is
compared with theoretical results valid for the generalized Kuramoto model.Comment: 31 pages, 5 figure
Bosonic Field Propagators on Algebraic Curves
In this paper we investigate massless scalar field theory on non-degenerate
algebraic curves. The propagator is written in terms of the parameters
appearing in the polynomial defining the curve. This provides an alternative to
the language of theta functions. The main result is a derivation of the third
kind differential normalized in such a way that its periods around the homology
cycles are purely imaginary. All the physical correlation functions of the
scalar fields can be expressed in terms of this object. This paper contains a
detailed analysis of the techniques necessary to study field theories on
algebraic curves. A simple expression of the scalar field propagator is found
in a particular case in which the algebraic curves have internal symmetry
and one of the fields is located at a branch point.Comment: 26 pages, TeX + harvma
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