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1.
A. Bershadskii 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(4):691-693
It is shown that multifractal properties of some random and disordered systems can be simulated using thermodynamics of a
generalized ideal monoatomic gas in a fractal phase space.
Received 25 November 1998 and Received in final form 16 December 1998 相似文献
2.
M. Dugic D. Rakovic 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(4):781-790
We investigate the quantum-mechanical tunneling between the “patterns" of the, so-called, associative neural networks. Being
the relatively stable minima of the “configuration-energy" space of the networks, the “patterns" represent the macroscopically
distinguishable states of the neural nets. Therefore, the tunneling represents a macroscopic quantum effect, but with some
special characteristics. Particularly, we investigate the tunneling between the minima of approximately equal depth, thus
requiring no energy exchange. If there are at least a few such minima, the tunneling represents a sort of the “random walk"
process, which implies the quantum fluctuations in the system, and therefore “malfunctioning" in the information processing
of the nets. Due to the finite number of the minima, the “random walk" reduces to a dynamics modeled by the, so-called, Pauli
master equation. With some plausible assumptions, the set(s) of the Pauli master equations can be analytically solved. This
way comes the main result of this paper: the quantum fluctuations due to the quantum-mechanical tunneling can be “minimized"
if the “pattern"-formation is such that there are mutually “distant" groups of the “patterns", thus providing the “zone" structure
of the “pattern" formation. This qualitative result can be considered as a basis of the efficient deterministic functioning
of the associative neural nets.
Received 15 July 1999 相似文献
3.
N. Vandewalle M. Ausloos Ph. Boveroux A. Minguet 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(2):355-359
We present a method for visualizing the pattern which we believe to be a precursor signature of financial crashes (or ruptures).
The log-periodicity of the pattern is investigated through the envelope function technique. Three periods of the Dow Jones
Industrial Average (DJIA) are investigated: 1982-1987, 1992-1997 and 1993-1998. The presence of a rupture in the end of 1998
is outlined from data taken before the end of August 1998.
Received 15 October 1998 and Received in final form 19 November 1998 相似文献
4.
K. Schenk B. Drossel S. Clar F. Schwabl 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(1):177-185
We study finite-size effects in the self-organized critical forest-fire model by numerically evaluating the tree density and
the fire size distribution. The results show that this model does not display the finite-size scaling seen in conventional
critical systems. Rather, the system is composed of relatively homogeneous patches of different tree densities, leading to
two qualitatively different types of fires: those that span an entire patch and those that do not. As the system size becomes
smaller, the system contains less patches, and finally becomes homogeneous, with large density fluctuations in time.
Received 24 April 1999 and Received in final form 26 October 1999 相似文献
5.
G. Abramson J.L. Vega 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(2):361-364
Multifractal critical phenomena with infinite-temperature critical point and with complex coexistence of the infinite and
finite temperature critical points are considered and it is shown that strange attractors generated by cascades of period-doubling
bifurcations (Feigenbaum scenario) as well as fields of velocity differences in fluid turbulence belong to the former subclass
of the multifractal critical phenomena, while the real traffic processes and real currency exchange processes belong to the
last (complex) subclass of the multifractal critical phenomena. Data obtained by different authors are used for this purpose.
Received 5 February 1999 相似文献
6.
Ying Zhang Gang Hu Shi Gang Chen Yugui Yao 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(1):51-57
A system of coupled master equations simplified from a model of noise-driven globally coupled bistable oscillators under periodic
forcing is investigated. In the thermodynamic limit, the system is reduced to a set of two coupled differential equations.
Rich bifurcations to subharmonics and chaotic motions are found. This behavior can be found only for certain intermediate
noise intensities. Noise with intensities which are too small or too large will certainly spoil the bifurcations. In a system
with large though finite size, the bifurcations to chaos induced by noise can still be detected to a certain degree.
Received 6 April 1999 and Received in final form 1 November 1999 相似文献
7.
D.O. Kharchenko S.V. Kokhan 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(1):97-103
Within the power-law approach for noise amplitude dependence on stochastic variables, we present a picture of noise-induced
transitions in systems affected by coloured multiplicative noise. The governed equations for main statistical moments are
obtained and investigated in detail. We show that a reentrant noise-induced transition is realized within a window of the
control parameter.
Received 15 October 2001 / Received in final form 8 July 2002 Published online 17 September 2002 相似文献
8.
L. F. Matin A. Aghamohammadi M. Khorrami 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(3):243-246
The most general reaction-diffusion model on a Cayley
tree with nearest-neighbor interactions is introduced, which can
be solved exactly through the empty-interval method. The
stationary solutions of such models, as well as their dynamics,
are discussed. Concerning the dynamics, the spectrum of the
evolution Hamiltonian is found and shown to be discrete, hence
there is a finite relaxation time in the evolution of the system
towards its stationary state. 相似文献
9.
D. Chowdhury R.C. Desai 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(2):375-384
A Bus Route Model (BRM) can be defined on a one-dimensional lattice, where buses are represented by “particles” that are driven
forward from one site to the next with each site representing a bus stop. We replace the random sequential updating rules
in an earlier BRM by parallel updating rules. In order to elucidate the connection between the BRM with parallel updating
(BRMPU) and the Nagel-Schreckenberg (NaSch) model, we propose two alternative extensions of the NaSch model with space-/time-dependent
hopping rates. Approximating the BRMPU as a generalization of the NaSch model, we calculate analytically the steady-state
distribution of the time headways (TH) which are defined as the time intervals between the departures (or arrivals) of two
successive particles (i.e., buses) recorded by a detector placed at a fixed site (i.e., bus stop) on the model route. We compare these TH distributions with the corresponding results of our computer simulations
of the BRMPU, as well as with the data from the simulation of the two extended NaSch models. We also investigate interesting
kinetic properties exhibited by the BRMPU during its time evolution from random initial states towards its steady-states.
Received 16 December 1999 相似文献
10.
11.
M. Ibañes J. García-Ojalvo R. Toral J.M. Sancho 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(4):663-673
The domain growth processes originating from noise-induced nonequilibrium phase transitions are analyzed, both for non-conserved
and conserved dynamics. The existence of a dynamical scaling regime is established in the two cases, and the corresponding
growth laws are determined. The resulting universal dynamical scaling scenarios are those of Allen-Cahn and Lifshitz-Slyozov,
respectively. Additionally, the effect of noise sources on the behaviour of the pair correlation function at short distances
is studied.
Received 28 June 2000 and Received in final form 29 September 2000 相似文献
12.
B. Schulz S. Trimper M. Schulz 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,15(3):499-505
Random walks in one-dimensional environments with an additional dynamical feedback-coupling is analyzed numerically. The feedback
introduced via a generalized master equation is controlled by a memory kernel of strength the explicit form of which is motivated by arguments used in mode-coupling theories. Introducing several realizations of
the feedback mechanism within the simulations we obtain for a negative memory term, , superdiffusion in the long time limit while a positive memory leads to localization of the particle. The numerical simulations
are in agreement with recent predictions based on renormalization group techniques. A slight modification of the model including
an exponentially decaying memory term and some possible applications for glasses and supercooled liquids are suggested. The
relation to the true self-avoiding is discussed.
Received 16 September 1999 and Received in final form 27 December 1999 相似文献
13.
F. Thalmann 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(4):497-505
A one dimensional trap model for a thermally activated classical particle is introduced to simulate driven dynamics in presence
of “ageing” effects. The depth of each trap increases with the time elapsed since the particle has fallen into it. The consequences
of this dynamical pinning are studied, and velocity-force characteristics are numerically obtained. A special attention is
paid to the situation where the particle is pulled with a spring to ensure a finite average velocity. In the low velocity
regime, the presence of a broad distribution of trapping times leads to suppression of linear response, replaced by a threshold
or by sublinear dynamics. A regime of strong fluctuations is obtained when the particle is driven at intermediate velocities.
Received: 12 December 1997 / Accepted: 25 February 1998 相似文献
14.
15.
G. Parisi F. Slanina 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(4):603-611
We present a variational approach for directed polymers in D transversal dimensions which is used to compute the correction to the mean field theory predictions with broken replica symmetry.
The trial function is taken to be a symmetrized version of the mean-field solution, which is known to be exact for . We compute the free energy corresponding to that function and show that the finite-D corrections behave like D
-4/3
. It means that the expansion in powers of 1/D should be used with great care here. We hope that the techniques developed in this note will be useful also in the study
of spin glasses.
Receveid 19 May 1998 相似文献
16.
M. Khorrami A. Aghamohammadi 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(3):223-227
A system of particles is studied in which the stochastic
processes are one-particle type-change (or one-particle diffusion)
and multi-particle annihilation. It is shown that, if the
annihilation rate tends to zero but the initial values of the
average number of the particles tend to infinity, so that the
annihilation rate times a certain power of the initial values of
the average number of the particles remain constant (the double
scaling) then if the initial state of the system is a
multi-Poisson distribution, the system always remains in a state
of multi-Poisson distribution, but with evolving parameters. The
large time behavior of the system is also investigated. The system
exhibits a dynamical phase transition. It is seen that for a
k-particle annihilation, if k is larger than a critical value
kc, which is determined by the type-change rates,
then annihilation does not enter the relaxation exponent of the
system; while for k < kc, it is the annihilation (in
fact k itself) which determines the relaxation exponent. 相似文献
17.
S. Lübeck N. Rajewsky D.E. Wolf 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(4):715-721
The Bak-Tang-Wiesenfeld (BTW) sandpile model is a cellular automaton which has been intensively studied during the last years
as a paradigm for self-organized criticality. In this paper, we reconsider a deterministic version of the BTW model introduced
by Wiesenfeld, Theiler and McNamara, where sand grains are added always to one fixed site on the square lattice. Using the
Abelian sandpile formalism we discuss the static properties of the system. We present numerical evidence that the deterministic model is only
in the BTW universality class if the initial conditions and the geometric form of the boundaries do not respect the full symmetry
of the square lattice.
Received 19 August 1999 相似文献
18.
We show that the emergence of criticality in the locally-defined Bak-Sneppen model corresponds to separation over a hierarchy
of timescales. Near to the critical point the model obeys scaling relations, with exponents which we derive numerically for
a one-dimensional system. We further describe how the model can be related to the glass model of Bouchaud (J. Phys. I France
2, 1705 (1992)), and we use this insight to comment on the usual assumption of stationarity in the Bak-Sneppen model. Finally,
we propose a general definition of self-organised criticality which is in partial agreement with other recent definitions.
Received 14 January 2000 and Received in final form 18 April 2000 相似文献
19.
M. Grifoni E. Paladino U. Weiss 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(4):719-729
The dynamics of the reduced density matrix of the driven dissipative two-state system is studied for a general diagonal/off-diagonal
initial state. We derive exact formal series expressions for the populations and coherences and show that they can be cast
into the form of coupled nonconvolutive exact master equations and integral relations. We show that neither the asymptotic
distributions, nor the transition temperature between coherent and incoherent motion, nor the dephasing rate and relaxation
rate towards the equilibrium state depend on the particular initial state chosen. However, in the underdamped regime, effects
of the particular initial preparation, e.g. in an off-diagonal state of the density matrix, strongly affect the transient dynamics. We find that an appropriately tuned external ac-field
can slow down decoherence and thus allow preparation effects to persist for longer times than in the absence of driving.
Received 23 October 1998 and Received in final form 26 February 1999 相似文献