9 research outputs found
Numerical study of a first-order irreversible phase transition in a CO+NO catalyzed reaction model
The first-order irreversible phase transitions (IPT) of the Yaldran-Khan
model (Yaldran-Khan, J. Catal. 131, 369, 1991) for the CO+NO reaction is
studied using the constant coverage (CC) ensemble and performing epidemic
simulations. The CC method allows the study of hysteretic effects close to
coexistence as well as the location of both the upper spinodal point and the
coexistence point. Epidemic studies show that at coexistence the number of
active sites decreases according to a (short-time) power law followed by a
(long-time) exponential decay. It is concluded that first-order IPT's share
many characteristic of their reversible counterparts, such as the development
of short ranged correlations, hysteretic effects, metastabilities, etc.Comment: 17 pages, 10 figure
Power-law persistence and trends in the atmosphere: A detailed study of long temperature records
We use several variants of the detrended fluctuation analysis to study the
appearance of long-term persistence in temperature records, obtained at 95
stations all over the globe. Our results basically confirm earlier studies. We
find that the persistence, characterized by the correlation C(s) of temperature
variations separated by s days, decays for large s as a power law, C(s) ~
s^(-gamma). For continental stations, including stations along the coastlines,
we find that gamma is always close to 0.7. For stations on islands, we find
that gamma ranges between 0.3 and 0.7, with a maximum at gamma = 0.4. This is
consistent with earlier studies of the persistence in sea surface temperature
records where gamma is close to 0.4. In all cases, the exponent gamma does not
depend on the distance of the stations to the continental coastlines. By
varying the degree of detrending in the fluctuation analysis we obtain also
information about trends in the temperature records.Comment: 5 pages, 4 including eps figure
Equilibrium Properties of A Monomer-Monomer Catalytic Reaction on A One-Dimensional Chain
We study the equilibrium properties of a lattice-gas model of an catalytic reaction on a one-dimensional chain in contact with a reservoir
for the particles. The particles of species and are in thermal contact
with their vapor phases acting as reservoirs, i.e., they may adsorb onto empty
lattice sites and may desorb from the lattice. If adsorbed and
particles appear at neighboring lattice sites they instantaneously react and
both desorb. For this model of a catalytic reaction in the
adsorption-controlled limit, we derive analytically the expression of the
pressure and present exact results for the mean densities of particles and for
the compressibilities of the adsorbate as function of the chemical potentials
of the two species.Comment: 19 pages, 5 figures, submitted to Phys. Rev.
Oscillations and dynamics in a two-dimensional prey-predator system
Using Monte Carlo simulations we study two-dimensional prey-predator systems.
Measuring the variance of densities of prey and predators on the triangular
lattice and on the lattice with eight neighbours, we conclude that temporal
oscillations of these densities vanish in the thermodynamic limit. This result
suggests that such oscillations do not exist in two-dimensional models, at
least when driven by local dynamics. Depending on the control parameter, the
model could be either in an active or in an absorbing phase, which are
separated by the critical point. The critical behaviour of this model is
studied using the dynamical Monte Carlo method. This model has two dynamically
nonsymmetric absorbing states. In principle both absorbing states can be used
for the analysis of the critical point. However, dynamical simulations which
start from the unstable absorbing state suffer from metastable-like effects,
which sometimes renders the method inefficient.Comment: 7 eps figures, Phys.Rev.E - in pres