3,762 research outputs found
Correlated adaptation of agents in a simple market: a statistical physics perspective
We discuss recent work in the study of a simple model for the collective
behaviour of diverse speculative agents in an idealized stockmarket, considered
from the perspective of the statistical physics of many-body systems. The only
information about other agents available to any one is the total trade at time
steps. Evidence is presented for correlated adaptation and phase
transitions/crossovers in the global volatility of the system as a function of
appropriate information scaling dimension. Stochastically controlled
irrationally of individual agents is shown to be globally advantageous. We
describe the derivation of the underlying effective stochastic differential
equations which govern the dynamics, and make an interpretation of the results
from the point of view of the statistical physics of disordered systems.Comment: 15 Pages. 5 figure
Noise Effects on Synchronized Globally Coupled Oscillators
The synchronized phase of globally coupled nonlinear oscillators subject to
noise fluctuations is studied by means of a new analytical approach able to
tackle general couplings, nonlinearities, and noise temporal correlations. Our
results show that the interplay between coupling and noise modifies the
effective frequency of the system in a non trivial way. Whereas for linear
couplings the effect of noise is always to increase the effective frequency,
for nonlinear couplings the noise influence is shown to be positive or negative
depending on the problem parameters. Possible experimental verification of the
results is discussed.Comment: 6 Pages, 4 EPS figures included (RevTeX and epsfig needed). Submitted
to Phys. Re
Produção animal e meio ambiente: o caso TAC da suinocultura em Santa Catarina.
Projeto/Plano de Ação: 03.06.05.020
Time as a limited resource: Communication Strategy in Mobile Phone Networks
We used a large database of 9 billion calls from 20 million mobile users to
examine the relationships between aggregated time spent on the phone, personal
network size, tie strength and the way in which users distributed their limited
time across their network (disparity). Compared to those with smaller networks,
those with large networks did not devote proportionally more time to
communication and had on average weaker ties (as measured by time spent
communicating). Further, there were not substantially different levels of
disparity between individuals, in that mobile users tend to distribute their
time very unevenly across their network, with a large proportion of calls going
to a small number of individuals. Together, these results suggest that there
are time constraints which limit tie strength in large personal networks, and
that even high levels of mobile communication do not fundamentally alter the
disparity of time allocation across networks.Comment: 10 pages, 3 figures. Accepted for publication in Social Network
Spreading of thin films assisted by thermal fluctuations
We study the spreading of viscous drops on a solid substrate, taking into
account the effects of thermal fluctuations in the fluid momentum. A nonlinear
stochastic lubrication equation is derived, and studied using numerical
simulations and scaling analysis. We show that asymptotically spreading drops
admit self-similar shapes, whose average radii can increase at rates much
faster than these predicted by Tanner's law. We discuss the physical
realizability of our results for thin molecular and complex fluid films, and
predict that such phenomenon can in principal be observed in various flow
geometries.Comment: 5 pages, 3 figure
Effects of Diversity on Multi-agent Systems: Minority Games
We consider a version of large population games whose agents compete for
resources using strategies with adaptable preferences. The games can be used to
model economic markets, ecosystems or distributed control. Diversity of initial
preferences of strategies is introduced by randomly assigning biases to the
strategies of different agents. We find that diversity among the agents reduces
their maladaptive behavior. We find interesting scaling relations with
diversity for the variance and other parameters such as the convergence time,
the fraction of fickle agents, and the variance of wealth, illustrating their
dynamical origin. When diversity increases, the scaling dynamics is modified by
kinetic sampling and waiting effects. Analyses yield excellent agreement with
simulations.Comment: 41 pages, 16 figures; minor improvements in content, added
references; to be published in Physical Review
Aproveitamento de nitrogênio atmosférico em milho, sorgo e milheto no Centro Nacional de Pesquisa de Milho e Sorgo.
Emergence of pulled fronts in fermionic microscopic particle models
We study the emergence and dynamics of pulled fronts described by the
Fisher-Kolmogorov-Petrovsky-Piscounov (FKPP) equation in the microscopic
reaction-diffusion process A + A A$ on the lattice when only a particle is
allowed per site. To this end we identify the parameter that controls the
strength of internal fluctuations in this model, namely, the number of
particles per correlated volume. When internal fluctuations are suppressed, we
explictly see the matching between the deterministic FKPP description and the
microscopic particle model.Comment: 4 pages, 4 figures. Accepted for publication in Phys. Rev. E as a
Rapid Communicatio
Dynamic renormalization group study of a generalized continuum model of crystalline surfaces
We apply the Nozieres-Gallet dynamic renormalization group (RG) scheme to a
continuum equilibrium model of a d-dimensional surface relaxing by linear
surface tension and linear surface diffusion, and which is subject to a lattice
potential favoring discrete values of the height variable. The model thus
interpolates between the overdamped sine-Gordon model and a related continuum
model of crystalline tensionless surfaces. The RG flow predicts the existence
of an equilibrium roughening transition only for d = 2 dimensional surfaces,
between a flat low-temperature phase and a rough high-temperature phase in the
Edwards-Wilkinson (EW) universality class. The surface is always in the flat
phase for any other substrate dimensions d > 2. For any value of d, the linear
surface diffusion mechanism is an irrelevant perturbation of the linear surface
tension mechanism, but may induce long crossovers within which the scaling
properties of the linear molecular-beam epitaxy equation are observed, thus
increasing the value of the sine-Gordon roughening temperature. This phenomenon
originates in the non-linear lattice potential, and is seen to occur even in
the absence of a bare surface tension term. An important consequence of this is
that a crystalline tensionless surface is asymptotically described at high
temperatures by the EW universality class.Comment: 22 pages, 5 figures. Accepted for publication in Physical Review
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