307 research outputs found
Co-evolutionnary network approach to cultural dynamics controlled by intolerance
Starting from Axelrod's model of cultural dissemination, we introduce a
rewiring probability, enabling agents to cut the links with their unfriendly
neighbors if their cultural similarity is below a tolerance parameter. For low
values of tolerance, rewiring promotes the convergence to a frozen monocultural
state. However, intermediate tolerance values prevent rewiring once the network
is fragmented, resulting in a multicultural society even for values of initial
cultural diversity in which the original Axelrod model reaches globalization
Timing interactions in social simulations: The voter model
The recent availability of huge high resolution datasets on human activities
has revealed the heavy-tailed nature of the interevent time distributions. In
social simulations of interacting agents the standard approach has been to use
Poisson processes to update the state of the agents, which gives rise to very
homogeneous activity patterns with a well defined characteristic interevent
time. As a paradigmatic opinion model we investigate the voter model and review
the standard update rules and propose two new update rules which are able to
account for heterogeneous activity patterns. For the new update rules each node
gets updated with a probability that depends on the time since the last event
of the node, where an event can be an update attempt (exogenous update) or a
change of state (endogenous update). We find that both update rules can give
rise to power law interevent time distributions, although the endogenous one
more robustly. Apart from that for the exogenous update rule and the standard
update rules the voter model does not reach consensus in the infinite size
limit, while for the endogenous update there exist a coarsening process that
drives the system toward consensus configurations.Comment: Book Chapter, 23 pages, 9 figures, 5 table
Efficacy of different antifouling treatments for seawater cooling systems
In an industrial seawater cooling system, the effects of three different antifouling treatments, viz. sodium
hypochlorite (NaClO), aliphatic amines (Mexel1432) and UV radiation, on the characteristics of the fouling formed
were evaluated. For this study a portable pilot plant, as a side-stream monitoring system and seawater cooling
system, was employed. The pilot plant simulated a power plant steam condenser, having four titanium tubes under
different treatment patterns, where fouling progression could be monitored. The nature of the fouling obtained was
chiefly inorganic, showing a clear dependence on the antifouling treatment employed. After 72 days the tubes under
treatment showed a reduction in the heat transfer resistance (R) of around 70% for NaClO, 48% for aliphatic
amines and 55% for UV, with respect to the untreated tube. The use of a logistic model was very useful for
predicting the fouling progression and the maximum asymptotic value of the increment in the heat transfer
resistance (DRmax). The apparent thermal conductivity (l) of the fouling layer showed a direct relationship with the
percentage of organic matter in the collected fouling. The characteristics and mode of action of the different
treatments used led to fouling with diverse physicochemical properties
The Complex Ginzburg-Landau Equation in the Presence of Walls and Corners
We investigate the influence of walls and corners (with Dirichlet and Neumann
boundary conditions) in the evolution of twodimensional autooscillating fields
described by the complex Ginzburg-Landau equation. Analytical solutions are
found, and arguments provided, to show that Dirichlet walls introduce strong
selection mechanisms for the wave pattern. Corners between walls provide
additional synchronization mechanisms and associated selection criteria. The
numerical results fit well with the theoretical predictions in the parameter
range studied.Comment: 10 pages, 9 figures; for related work visit
http://www.nbi.dk/~martine
Fragmentation transition in a coevolving network with link-state dynamics
We study a network model that couples the dynamics of link states with the
evolution of the network topology. The state of each link, either A or B, is
updated according to the majority rule or zero-temperature Glauber dynamics, in
which links adopt the state of the majority of their neighboring links in the
network. Additionally, a link that is in a local minority is rewired to a
randomly chosen node. While large systems evolving under the majority rule
alone always fall into disordered topological traps composed by frustrated
links, any amount of rewiring is able to drive the network to complete order,
by relinking frustrated links and so releasing the system from traps. However,
depending on the relative rate of the majority rule and the rewiring processes,
the system evolves towards different ordered absorbing configurations: either a
one-component network with all links in the same state or a network fragmented
in two components with opposite states. For low rewiring rates and finite size
networks there is a domain of bistability between fragmented and non-fragmented
final states. Finite size scaling indicates that fragmentation is the only
possible scenario for large systems and any nonzero rate of rewiring.Comment: 10 pages, 13 figure
Robustness of cultural communities in an open-ended Axelrod's model
We consider an open-ended set of cultural features in the Axelrod's model of
cultural dissemination. By replacing the features in which a high degree of
consensus is achieved by new ones, we address here an essential ingredient of
societies: the evolution of topics as a result of social dynamics and debate.
Our results show that, once cultural clusters have been formed, the
introduction of new topics into the social debate has little effect on them,
but it does have a significant influence on the cultural overlap. Along with
the Monte-Carlo simulations, we derive and numerically solve an equation for
the stationary cultural overlap based on a mean-field approach. Although the
mean-field analysis reproduces qualitatively the characteristic phase
transition of the Axelrod's model, it underestimates the cultural overlap,
highlighting the role of the local interactions in the Axelrod's dynamics, as
well as the correlations between the different cultural features.Comment: 6 pages and 5 figure
Rank-dependent deactivation in network evolution
A rank-dependent deactivation mechanism is introduced to network evolution.
The growth dynamics of the network is based on a finite memory of individuals,
which is implemented by deactivating one site at each time step. The model
shows striking features of a wide range of real-world networks: power-law
degree distribution, high clustering coefficient, and disassortative degree
correlation.Comment: 5 pages, 5 figures, RevTex
The noisy voter model on complex networks
We propose a new analytical method to study stochastic, binary-state models
on complex networks. Moving beyond the usual mean-field theories, this
alternative approach is based on the introduction of an annealed approximation
for uncorrelated networks, allowing to deal with the network structure as
parametric heterogeneity. As an illustration, we study the noisy voter model, a
modification of the original voter model including random changes of state. The
proposed method is able to unfold the dependence of the model not only on the
mean degree (the mean-field prediction) but also on more complex averages over
the degree distribution. In particular, we find that the degree heterogeneity
---variance of the underlying degree distribution--- has a strong influence on
the location of the critical point of a noise-induced, finite-size transition
occurring in the model, on the local ordering of the system, and on the
functional form of its temporal correlations. Finally, we show how this latter
point opens the possibility of inferring the degree heterogeneity of the
underlying network by observing only the aggregate behavior of the system as a
whole, an issue of interest for systems where only macroscopic, population
level variables can be measured.Comment: 28 pages, 9 figure
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