2,945 research outputs found
Local interaction scale controls the existence of a non-trivial optimal critical mass in opinion spreading
We study a model of opinion formation where the collective decision of group
is said to happen if the fraction of agents having the most common opinion
exceeds a threshold value, a \textit{critical mass}. We find that there exists
a unique, non-trivial critical mass giving the most efficient convergence to
consensus. In addition, we observe that for small critical masses, the
characteristic time scale for the relaxation to consensus splits into two. The
shorter time scale corresponds to a direct relaxation and the longer can be
explained by the existence of intermediate, metastable states similar to those
found in [P.\ Chen and S.\ Redner, Phys.\ Rev.\ E \textbf{71}, 036101 (2005)].
This longer time-scale is dependent on the precise condition for
consensus---with a modification of the condition it can go away.Comment: 4 pages, 6 figure
Enhanced Anandamide Plasma Levels in Patients with Complex Regional Pain Syndrome following Traumatic Injury: A Preliminary Report
The complex regional pain syndrome (CRPS) is a disabling neuropathic pain condition that may develop following injuries of the extremities. The pathogenesis of this syndrome is not clear; however, it includes complex interactions between the nervous and the immune system resulting in chronic inflammation, pain and trophic changes. This interaction may be mediated by chronic stress which is thought to activate the endogenous cannabinoid (endocannabinoid) system (ECS). We conducted an open, prospective, comparative clinical study to determine plasma level of the endocannabinoid anandamide by high-performance liquid chromatography and a tandem mass spectrometry system in 10 patients with CRPS type I versus 10 age- and sex-matched healthy controls. As compared to healthy controls, CRPS patients showed significantly higher plasma concentrations of anandamide. These results indicate that the peripheral ECS is activated in CRPS. Further studies are warranted to evaluate the role of the ECS in the limitation of inflammation and pain. Copyright (C) 2009 S. Karger AG, Base
On Spatial Consensus Formation: Is the Sznajd Model Different from a Voter Model?
In this paper, we investigate the so-called ``Sznajd Model'' (SM) in one
dimension, which is a simple cellular automata approach to consensus formation
among two opposite opinions (described by spin up or down). To elucidate the SM
dynamics, we first provide results of computer simulations for the
spatio-temporal evolution of the opinion distribution , the evolution of
magnetization , the distribution of decision times and
relaxation times . In the main part of the paper, it is shown that the
SM can be completely reformulated in terms of a linear VM, where the transition
rates towards a given opinion are directly proportional to frequency of the
respective opinion of the second-nearest neighbors (no matter what the nearest
neighbors are). So, the SM dynamics can be reduced to one rule, ``Just follow
your second-nearest neighbor''. The equivalence is demonstrated by extensive
computer simulations that show the same behavior between SM and VM in terms of
, , , , and the final attractor statistics. The
reformulation of the SM in terms of a VM involves a new parameter , to
bias between anti- and ferromagnetic decisions in the case of frustration. We
show that plays a crucial role in explaining the phase transition
observed in SM. We further explore the role of synchronous versus asynchronous
update rules on the intermediate dynamics and the final attractors. Compared to
the original SM, we find three additional attractors, two of them related to an
asymmetric coexistence between the opposite opinions.Comment: 22 pages, 20 figures. For related publications see
http://www.ais.fraunhofer.de/~fran
Effective Free Energy for Individual Dynamics
Physics and economics are two disciplines that share the common challenge of
linking microscopic and macroscopic behaviors. However, while physics is based
on collective dynamics, economics is based on individual choices. This
conceptual difference is one of the main obstacles one has to overcome in order
to characterize analytically economic models. In this paper, we build both on
statistical mechanics and the game theory notion of Potential Function to
introduce a rigorous generalization of the physicist's free energy, which
includes individual dynamics. Our approach paves the way to analytical
treatments of a wide range of socio-economic models and might bring new
insights into them. As first examples, we derive solutions for a congestion
model and a residential segregation model.Comment: 8 pages, 2 figures, presented at the ECCS'10 conferenc
Role of social environment and social clustering in spread of opinions in co-evolving networks
Taking a pragmatic approach to the processes involved in the phenomena of
collective opinion formation, we investigate two specific modifications to the
co-evolving network voter model of opinion formation, studied by Holme and
Newman [1]. First, we replace the rewiring probability parameter by a
distribution of probability of accepting or rejecting opinions between
individuals, accounting for the asymmetric influences in relationships among
individuals in a social group. Second, we modify the rewiring step by a
path-length-based preference for rewiring that reinforces local clustering. We
have investigated the influences of these modifications on the outcomes of the
simulations of this model. We found that varying the shape of the distribution
of probability of accepting or rejecting opinions can lead to the emergence of
two qualitatively distinct final states, one having several isolated connected
components each in internal consensus leading to the existence of diverse set
of opinions and the other having one single dominant connected component with
each node within it having the same opinion. Furthermore, and more importantly,
we found that the initial clustering in network can also induce similar
transitions. Our investigation also brings forward that these transitions are
governed by a weak and complex dependence on system size. We found that the
networks in the final states of the model have rich structural properties
including the small world property for some parameter regimes. [1] P. Holme and
M. Newman, Phys. Rev. E 74, 056108 (2006)
Quantum Games
In these lecture notes we investigate the implications of the identification
of strategies with quantum operations in game theory beyond the results
presented in [J. Eisert, M. Wilkens, and M. Lewenstein, Phys. Rev. Lett. 83,
3077 (1999)]. After introducing a general framework, we study quantum games
with a classical analogue in order to flesh out the peculiarities of game
theoretical settings in the quantum domain. Special emphasis is given to a
detailed investigation of different sets of quantum strategies.Comment: 13 pages (LaTeX), 3 figure
Statistical physics of the Schelling model of segregation
We investigate the static and dynamic properties of a celebrated model of
social segregation, providing a complete explanation of the mechanisms leading
to segregation both in one- and two-dimensional systems. Standard statistical
physics methods shed light on the rich phenomenology of this simple model,
exhibiting static phase transitions typical of kinetic constrained models,
nontrivial coarsening like in driven-particle systems and percolation-related
phenomena.Comment: 4 pages, 3 figure
Analysis of a threshold model of social contagion on degree-correlated networks
We analytically determine when a range of abstract social contagion models
permit global spreading from a single seed on degree-correlated random
networks. We deduce the expected size of the largest vulnerable component, a
network's tinderbox-like critical mass, as well as the probability that
infecting a randomly chosen individual seed will trigger global spreading. In
the appropriate limits, our results naturally reduce to standard ones for
models of disease spreading and to the condition for the existence of a giant
component. Recent advances in the distributed, infinite seed case allow us to
further determine the final size of global spreading events, when they occur.
To provide support for our results, we derive exact expressions for key
spreading quantities for a simple yet rich family of random networks with
bimodal degree distributions.Comment: 7 Pages, 1 figure, submitted to Phys. Rev.
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