22,323 research outputs found
A bouncing ball model with two nonlinearities: a prototype for Fermi acceleration
Some dynamical properties of a bouncing ball model under the presence of an
external force modeled by two nonlinear terms are studied. The description of
the model is made by use of a two dimensional nonlinear measure preserving map
on the variables velocity of the particle and time. We show that raising the
straight of a control parameter which controls one of the nonlinearities, the
positive Lyapunov exponent decreases in the average and suffers abrupt changes.
We also show that for a specific range of control parameters, the model
exhibits the phenomenon of Fermi acceleration. The explanation of both
behaviours is given in terms of the shape of the external force and due to a
discontinuity of the moving wall's velocity.Comment: A complete list of my papers can be found in:
http://www.rc.unesp.br/igce/demac/denis
Generalized Metropolis dynamics with a generalized master equation: An approach for time-independent and time-dependent Monte Carlo simulations of generalized spin systems
The extension of Boltzmann-Gibbs thermostatistics, proposed by Tsallis,
introduces an additional parameter to the inverse temperature .
Here, we show that a previously introduced generalized Metropolis dynamics to
evolve spin models is not local and does not obey the detailed energy balance.
In this dynamics, locality is only retrieved for , which corresponds to
the standard Metropolis algorithm. Non-locality implies in very time consuming
computer calculations, since the energy of the whole system must be
reevaluated, when a single spin is flipped. To circumvent this costly
calculation, we propose a generalized master equation, which gives rise to a
local generalized Metropolis dynamics that obeys the detailed energy balance.
To compare the different critical values obtained with other generalized
dynamics, we perform Monte Carlo simulations in equilibrium for Ising model. By
using the short time non-equilibrium numerical simulations, we also calculate
for this model: the critical temperature, the static and dynamical critical
exponents as function of . Even for , we show that suitable time
evolving power laws can be found for each initial condition. Our numerical
experiments corroborate the literature results, when we use non-local dynamics,
showing that short time parameter determination works also in this case.
However, the dynamics governed by the new master equation leads to different
results for critical temperatures and also the critical exponents affecting
universality classes. We further propose a simple algorithm to optimize
modeling the time evolution with a power law considering in a log-log plot two
successive refinements.Comment: 10 pages, 5 figures and 5 table
Primitives for Contract-based Synchronization
We investigate how contracts can be used to regulate the interaction between
processes. To do that, we study a variant of the concurrent constraints
calculus presented in [1], featuring primitives for multi-party synchronization
via contracts. We proceed in two directions. First, we exploit our primitives
to model some contract-based interactions. Then, we discuss how several models
for concurrency can be expressed through our primitives. In particular, we
encode the pi-calculus and graph rewriting.Comment: In Proceedings ICE 2010, arXiv:1010.530
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