17,275 research outputs found
Invisible control of self-organizing agents leaving unknown environments
In this paper we are concerned with multiscale modeling, control, and
simulation of self-organizing agents leaving an unknown area under limited
visibility, with special emphasis on crowds. We first introduce a new
microscopic model characterized by an exploration phase and an evacuation
phase. The main ingredients of the model are an alignment term, accounting for
the herding effect typical of uncertain behavior, and a random walk, accounting
for the need to explore the environment under limited visibility. We consider
both metrical and topological interactions. Moreover, a few special agents, the
leaders, not recognized as such by the crowd, are "hidden" in the crowd with a
special controlled dynamics. Next, relying on a Boltzmann approach, we derive a
mesoscopic model for a continuum density of followers, coupled with a
microscopic description for the leaders' dynamics. Finally, optimal control of
the crowd is studied. It is assumed that leaders exploit the herding effect in
order to steer the crowd towards the exits and reduce clogging. Locally-optimal
behavior of leaders is computed. Numerical simulations show the efficiency of
the optimization methods in both microscopic and mesoscopic settings. We also
perform a real experiment with people to study the feasibility of the proposed
bottom-up crowd control technique.Comment: in SIAM J. Appl. Math, 201
Order out of Randomness : Self-Organization Processes in Astrophysics
Self-organization is a property of dissipative nonlinear processes that are
governed by an internal driver and a positive feedback mechanism, which creates
regular geometric and/or temporal patterns and decreases the entropy, in
contrast to random processes. Here we investigate for the first time a
comprehensive number of 16 self-organization processes that operate in
planetary physics, solar physics, stellar physics, galactic physics, and
cosmology. Self-organizing systems create spontaneous {\sl order out of chaos},
during the evolution from an initially disordered system to an ordered
stationary system, via quasi-periodic limit-cycle dynamics, harmonic mechanical
resonances, or gyromagnetic resonances. The internal driver can be gravity,
rotation, thermal pressure, or acceleration of nonthermal particles, while the
positive feedback mechanism is often an instability, such as the
magneto-rotational instability, the Rayleigh-B\'enard convection instability,
turbulence, vortex attraction, magnetic reconnection, plasma condensation, or
loss-cone instability. Physical models of astrophysical self-organization
processes involve hydrodynamic, MHD, and N-body formulations of Lotka-Volterra
equation systems.Comment: 61 pages, 38 Figure
Recommended from our members
Exact solution of a model for crowding and information transmission in financial markets
An exact solution is presented to a model that mimics the crowding effect in financial markets which arises when groups of agents share information. We show that the size distribution of groups of agents has a power law tail with an exponential cut-off. As the size of these groups determines the supply and demand balance, this implies heavy tails in the distribution of price variation. The moments of the distribution are calculated, as well as the kurtosis. We find that the kurtosis is large for all model parameter values and that the model is not self-organizing
A generalized nonlinear Schr\"odinger equation as model for turbulence, collapse, and inverse cascade
A two-dimensional generalized cubic nonlinear Schr\"odinger equation with
complex coefficients for the group dispersion and nonlinear terms is used to
investigate the evolution of a finite-amplitude localized initial perturbation.
It is found that modulation of the latter can lead to side-band formation, wave
condensation, collapse, turbulence, and inverse cascade, although not all
together nor in that order.Comment: 12 pages, 5 figure
Learning in a Landscape: Simulation-building as Reflexive Intervention
This article makes a dual contribution to scholarship in science and
technology studies (STS) on simulation-building. It both documents a specific
simulation-building project, and demonstrates a concrete contribution to
interdisciplinary work of STS insights. The article analyses the struggles that
arise in the course of determining what counts as theory, as model and even as
a simulation. Such debates are especially decisive when working across
disciplinary boundaries, and their resolution is an important part of the work
involved in building simulations. In particular, we show how ontological
arguments about the value of simulations tend to determine the direction of
simulation-building. This dynamic makes it difficult to maintain an interest in
the heterogeneity of simulations and a view of simulations as unfolding
scientific objects. As an outcome of our analysis of the process and
reflections about interdisciplinary work around simulations, we propose a
chart, as a tool to facilitate discussions about simulations. This chart can be
a means to create common ground among actors in a simulation-building project,
and a support for discussions that address other features of simulations
besides their ontological status. Rather than foregrounding the chart's
classificatory potential, we stress its (past and potential) role in discussing
and reflecting on simulation-building as interdisciplinary endeavor. This chart
is a concrete instance of the kinds of contributions that STS can make to
better, more reflexive practice of simulation-building.Comment: 37 page
Kinetic Exchange Models for Income and Wealth Distributions
Increasingly, a huge amount of statistics have been gathered which clearly
indicates that income and wealth distributions in various countries or
societies follow a robust pattern, close to the Gibbs distribution of energy in
an ideal gas in equilibrium. However, it also deviates in the low income and
more significantly for the high income ranges. Application of physics models
provides illuminating ideas and understanding, complementing the observations.Comment: 15 pages, 20 eps figures, EPJ class; To be published as "Colloquium"
in Eur Phys J
- …