1,266 research outputs found
Divergent Time Scale in Axelrod Model Dynamics
We study the evolution of the Axelrod model for cultural diversity. We
consider a simple version of the model in which each individual is
characterized by two features, each of which can assume q possibilities. Within
a mean-field description, we find a transition at a critical value q_c between
an active state of diversity and a frozen state. For q just below q_c, the
density of active links between interaction partners is non-monotonic in time
and the asymptotic approach to the steady state is controlled by a time scale
that diverges as (q-q_c)^{-1/2}.Comment: 4 pages, 5 figures, 2-column revtex4 forma
Information feedback and mass media effects in cultural dynamics
We study the effects of different forms of information feedback associated
with mass media on an agent-agent based model of the dynamics of cultural
dissemination. In addition to some processes previously considered, we also
examine a model of local mass media influence in cultural dynamics. Two
mechanisms of information feedback are investigated: (i) direct mass media
influence, where local or global mass media act as an additional element in the
network of interactions of each agent, and (ii) indirect mass media influence,
where global media acts as a filter of the influence of the existing network of
interactions of each agent. Our results generalize previous findings showing
that cultural diversity builds-up by increasing the strength of the mass media
influence. We find that this occurs independently of the mechanisms of action
(direct or indirect) of the mass media message. However, through an analysis of
the full range of parameters measuring cultural diversity, we establish that
the enhancement of cultural diversity produced by interaction with mass media
only occurs for strong enough mass media messages. In comparison with previous
studies a main different result is that weak mass media messages, in
combination with agent-agent interaction, are efficient in producing cultural
homogeneity. Moreover, the homogenizing effect of weak mass media messages are
more efficient for direct local mass media messages than for global mass media
messages or indirect global mass media influences.Comment: 20n pages, 10 figure
Conservation laws for the voter model in complex networks
We consider the voter model dynamics in random networks with an arbitrary
distribution of the degree of the nodes. We find that for the usual node-update
dynamics the average magnetization is not conserved, while an average
magnetization weighted by the degree of the node is conserved. However, for a
link-update dynamics the average magnetization is still conserved. For the
particular case of a Barabasi-Albert scale-free network the voter model
dynamics leads to a partially ordered metastable state with a finite size
survival time. This characteristic time scales linearly with system size only
when the updating rule respects the conservation law of the average
magnetization. This scaling identifies a universal or generic property of the
voter model dynamics associated with the conservation law of the magnetization.Comment: 5 pages, 4 figures; for related material please visit
http://www.imedea.uib.e
Selfsimilar Domain Growth, Localized Structures and Labyrinthine Patterns in Vectorial Kerr Resonators
We study domain growth in a nonlinear optical system useful to explore
different scenarios that might occur in systems which do not relax to
thermodynamic equilibrium. Domains correspond to equivalent states of different
circular polarization of light. We describe three dynamical regimes: a
coarsening regime in which dynamical scaling holds with a growth law dictated
by curvature effects, a regime in which localized structures form, and a regime
in which polarization domain walls are modulationally unstable and the system
freezes in a labyrinthine pattern.Comment: 13 pages, 6 figure
Navy Acquisition via leasing: policy, politics, and polemics with the Maritime Prepositioned Ships
In recent months, leasing has been prominent in the press in connection with the Air Force's ill-fated attempt to obtain the use of Boeing re-fueling tankers without buying them. Gone from memory is the early 1980's controversial Navy leasing program of Maritime Pre-positioned Ships that had a different result. This paper presents an analysis of the various issues and parties to the very creative and innovative financing on behalf of the Navy's Military Sealift Command. Still in existence today, the 1983 contracts for thirteen TAKX ships were valued at approximately $2.6 billion. While the decision is often framed as a lease versus purchase choice, the facts indicate that the option to purchase was not seen as viable at the time. In hindsight, the TAKX leasing program was successful and cost effective, despite the whirlwind of political commentary and intrigue and the dueling quantitative analyses surrounding it. However, as an unintended (or, perhaps, intended) consequence, laws and policies have since been changed so that leasing is no longer viable for financing military assets. The case presented here considers altering existing laws and regulations to once again permit leasing of military resources.Approved for public release; distribution is unlimited
Importance of single nodes in dynamics on networks
Identifying key players in collective dynamics remains a challenge in several research
fields, from the efficient dissemination of ideas to drug target discovery in biomedical problems. The
difficulty lies at several levels: how to single out the role of individual elements in such intermingled
systems, or which is the best way to quantify their importance. Centrality measures describe a node's
importance by its position in a network. The key issue obviated is that the contribution of a node to
the collective behavior is not uniquely determined by the structure of the system but it is a result of the
interplay between dynamics and network structure
Nonlinear oscillator with parametric colored noise: some analytical results
The asymptotic behavior of a nonlinear oscillator subject to a multiplicative
Ornstein-Uhlenbeck noise is investigated. When the dynamics is expressed in
terms of energy-angle coordinates, it is observed that the angle is a fast
variable as compared to the energy. Thus, an effective stochastic dynamics for
the energy can be derived if the angular variable is averaged out. However, the
standard elimination procedure, performed earlier for a Gaussian white noise,
fails when the noise is colored because of correlations between the noise and
the fast angular variable. We develop here a specific averaging scheme that
retains these correlations. This allows us to calculate the probability
distribution function (P.D.F.) of the system and to derive the behavior of
physical observables in the long time limit
Importance of single nodes in dynamics on networks
Identifying key players in collective dynamics remains a challenge in several research
fields, from the efficient dissemination of ideas to drug target discovery in biomedical problems. The
difficulty lies at several levels: how to single out the role of individual elements in such intermingled
systems, or which is the best way to quantify their importance. Centrality measures describe a node's
importance by its position in a network. The key issue obviated is that the contribution of a node to
the collective behavior is not uniquely determined by the structure of the system but it is a result of the
interplay between dynamics and network structure
Ordering and finite-size effects in the dynamics of one-dimensional transient patterns
We introduce and analyze a general one-dimensional model for the description
of transient patterns which occur in the evolution between two spatially
homogeneous states. This phenomenon occurs, for example, during the
Freedericksz transition in nematic liquid crystals.The dynamics leads to the
emergence of finite domains which are locally periodic and independent of each
other. This picture is substantiated by a finite-size scaling law for the
structure factor. The mechanism of evolution towards the final homogeneous
state is by local roll destruction and associated reduction of local
wavenumber. The scaling law breaks down for systems of size comparable to the
size of the locally periodic domains. For systems of this size or smaller, an
apparent nonlinear selection of a global wavelength holds, giving rise to long
lived periodic configurations which do not occur for large systems. We also
make explicit the unsuitability of a description of transient pattern dynamics
in terms of a few Fourier mode amplitudes, even for small systems with a few
linearly unstable modes.Comment: 18 pages (REVTEX) + 10 postscript figures appende
Anomalous lifetime distributions and topological traps in ordering dynamics
We address the role of community structure of an interaction network in
ordering dynamics, as well as associated forms of metastability. We consider
the voter and AB model dynamics in a network model which mimics social
interactions. The AB model includes an intermediate state between the two
excluding options of the voter model. For the voter model we find dynamical
metastable disordered states with a characteristic mean lifetime. However, for
the AB dynamics we find a power law distribution of the lifetime of metastable
states, so that the mean lifetime is not representative of the dynamics. These
trapped metastable states, which can order at all time scales, originate in the
mesoscopic network structure.Comment: 7 pages; 6 figure
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