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1.
R. Nassif Y. Boughaleb A. Hekkouri J.F. Gouyet M. Kolb 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(4):453-464
We examine the behaviour of the concentration profiles of particles with repulsive interactions diffusing on a host lattice.
At low temperature, the diffusion process is strongly influenced by the presence of ordered domains. We use mean field equations
and Monte-Carlo simulations to describe the various effects which influence the kinetic behaviour. An effective diffusion
coefficient is determined analytically and is compared with the simulations. Finite gradient effects on the ordered domains
and on the diffusion are discussed. The kinetics studied is relevant for superionic conductors, for intercalation and also
for the diffusion of particles adsorbed on a substrate.
Received: 26 June 1997 / Revised: 18 September 1997 / Accepted: 10 November 1997 相似文献
2.
A. Hader A. Memsouk Y. Boughaleb 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):315-319
We have studied the scaling properties of diffusion fronts by numerical calculations based on the mean field approach in the
context of a lattice gas model, performed in a triangular lattice. We find that the height-height correlation function scales
with time t and length l as C(l, t) ≈l
α
f (t/l
α/β) with α = 0.62±0.01 and β = 0.39±0.02. These exponent values are identical to those characterising the roughness of the diffusion
fronts evolving through a square lattice [1,2], thus confirming their universality.
Received 14 November 2001 / Received in final form 20 April 2002 Published online 31 July 2002 相似文献
3.
M. Casartelli N. Macellari A. Vezzani 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,56(2):149-156
A cylindrical Ising model between thermostats is used to explore the heat conduction for any temperature
interval. The standard Q2R and Creutz dynamics, previously used by Saito, Takesue and Miyashita, fail below the critical temperature,
limiting the analysis to high temperatures intervals. We introduce improved dynamics by removing limitations due to the chessboard-like
refresh, and by supplementing the Q2R rule with Kadanoff-Swift moves. These new dynamics not only prove highly efficient in
recovering old results in their domains of validity, but also allow exploration of steady heat transport between two arbitrary
temperatures, i.e. very far from equilibrium. From an ansatz avoiding references to quasi equilibrium or to local temperature,
and from comparison with numerical simulations, we can consistently define a generalized diffusivity. Its dependence on the
energy density may be evaluated without any recourse to the Green-Kubo formula. 相似文献
4.
A. Chakraborti B.K. Chakrabarti 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(4):677-680
If one places N cities randomly on a lattice of size L, we find that and vary with the city concentration p=N/L
2, where is the average optimal travel distance per city in the Euclidean metric and is the same in the Manhattan metric. We have studied such optimum tours for visiting all the cities using a branch and bound
algorithm, giving the exact optimized tours for small system sizes () and near-optimal tours for bigger system sizes (). Extrapolating the results for , we find that for p=1, and and with as . Although the problem is trivial for p=1, for it certainly reduces to the standard travelling salesman problem on continuum which is NP-hard. We did not observe any irregular
behaviour at any intermediate point. The crossover from the triviality to the NP-hard problem presumably occurs at p=1.
Received 15 April 2000 相似文献
5.
L. Turban 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(2):273-285
We study the influence of an aperiodic extended surface perturbation on the surface critical behaviour of the two-dimensional
Ising model in the extreme anisotropic limit. The perturbation decays as a power of the distance l from the free surface with an oscillating amplitude where follows some aperiodic sequence with an asymptotic density equal to 1/2 so that the mean amplitude vanishes. The relevance
of the perturbation is discussed by combining scaling arguments of Cordery and Burkhardt for the Hilhorst-van Leeuwen model
and Luck for aperiodic perturbations. The relevance-irrelevance criterion involves the decay exponent , the wandering exponent which governs the fluctuation of the sequence and the bulk correlation length exponent . Analytical results are obtained for the surface magnetization which displays a rich variety of critical behaviours in the
-plane. The results are checked through a numerical finite-size-scaling study. They show that second-order effects must be
taken into account in the discussion of the relevance-irrelevance criterion. The scaling behaviours of the first gap and the
surface energy are also discussed.
Received 1 December 1998 相似文献
6.
7.
M. Casartelli L. Dall'Asta A. Vezzani P. Vivo 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(1):91-105
The non-ergodic behavior of the deterministic Fixed Energy Sandpile (DFES), with Bak-Tang-Wiesenfeld (BTW) rule, is explained
by the complete characterization of a class of dynamical invariants (or toppling invariants). The link between such constants
of motion and the discrete Laplacians properties on graphs is algebraically and numerically clarified. In particular, it is
possible to build up an explicit algorithm determining the complete set of independent toppling invariants. The partition
of the configuration space into dynamically invariant sets, and the further refinement of such a partition into basins of
attraction for orbits, are also studied. The total number of invariant sets equals the graphs complexity. In the case of two
dimensional lattices, it is possible to estimate a very regular exponential growth of this number vs. the size. Looking at
other features, the toppling invariants exhibit a highly irregular behavior. The usual constraint on the energy positiveness
introduces a transition in the frozen phase. In correspondence to this transition, a dynamical crossover related to the halting
times is observed. The analysis of the configuration space shows that the DFES has a different structure with respect to dissipative
BTW and stochastic sandpiles models, supporting the conjecture that it lies in a distinct class of universality. 相似文献
8.
H. Niggemann J. Zittartz 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(2):377-379
We present the construction of an optimum ground state for a quantum spin-3/2 antiferromagnet. The spins reside on a decorated
square lattice, in which the basis consists of a plaquette of four sites. By using the vertex state model approach we generate
the ground state from the same vertices as those used for the corresponding ground state on the hexagonal lattice. The properties
of these two ground states are very similar. Particularly there is also a parameter-controlled phase transition from a disordered
to a Néel ordered phase. In the regime of this transition, ground state properties can be obtained from an integrable classical
vertex model.
Received 28 June 1999 相似文献
9.
H. Niggemann A. Klümper J. Zittartz 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(1):15-19
We use the vertex state model approach to construct optimum ground states for a large class of quantum spin-2 antiferromagnets
on the square lattice. Optimum ground states are exact ground states of the model which minimize all local interaction operators.
The ground state contains two continuous parameters and exhibits a second order phase transition from a disordered phase with
exponentially decaying correlation functions to a Néel ordered phase. The behaviour is very similar to that of the corresponding
ground state of a quantum spin-3/2 model on the hexagonal lattice, which has been investigated in an earlier paper.
Received 8 April 1999 相似文献
10.
T. Temesvári C. De Dominicis I. Kondor 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(4):629-634
Replica field theory for the Ising spin glass in zero magnetic field is studied around the upper critical dimension d=6. A scaling theory of the spin glass phase, based on Parisi's ultrametrically organised order parameter, is proposed. We
argue that this infinite step replica symmetry broken (RSB) phase is nonperturbative in the sense that amplitudes of scaling
forms cannot be expanded in term of the coupling constant w2. Infrared divergent integrals inevitably appear when we try to compute amplitudes perturbatively, nevertheless the -expansion of critical exponents seems to be well-behaved. The origin of these problems can be traced back to the unusual
behaviour of the free propagator having two mass scales, the smaller one being proportional to the perturbation parameter
w2 and providing a natural infrared cutoff. Keeping the free propagator unexpanded makes it possible to avoid producing infrared
divergent integrals. The role of Ward-identities and the problem of the lower critical dimension are also discussed.
Received 23 December 1998 and Received in final form 23 March 1999 相似文献
11.
Ya.G. Groda P. Argyrakis G.S. Bokun V.S. Vikhrenko 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(4):527-535
The selfconsistent diagram approximation (SCDA) is generalized for three-dimensional lattice gases with nearest neighbor repulsive
interactions. The free energy is represented in a closed form through elementary functions. Thermodynamical (phase diagrams,
chemical potential and mean square fluctuations), structural (order parameter, distribution functions) as well as diffusional
characteristics are investigated. The calculation results are compared with the Monte Carlo simulation data to demonstrate
high precision of the SCDA in reproducing the equilibrium lattice gas characteristics. It is shown that similarly to two-dimensional
systems the specific statistical memory effects strongly influence the lattice gas diffusion in the ordered states.
Received 7 August 2002 / Received in final form 22 January 2003 Published online 24 April 2003 相似文献
12.
T. Temesvári I. Kondor C. De Dominicis 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(3):493-500
The reparametrization transformation between ultrametrically organised states of replicated disordered systems is explicitly
defined. The invariance of the longitudinal free energy under this transformation, i.e. reparametrization invariance, is shown to be a direct consequence of the higher level symmetry of replica equivalence. The
double limit of infinite step replica symmetry breaking and is needed to derive this continuous gauge-like symmetry from the discrete permutation invariance of the n replicas. Goldstone's theorem and Ward identities can be deduced from the disappearance of the second (and higher order)
variation of the longitudinal free energy. We recall also how these and other exact statements follow from permutation symmetry
after introducing the concept of “infinitesimal" permutations.
Received 21 July 2000 相似文献
13.
M.-C. Chung M. Kaulke I. Peschel M. Pleimling W. Selke 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(4):655-661
The influence of surface defects on the critical properties of magnetic films is studied for Ising models with nearest-neighbour
ferromagnetic couplings. The defects include one or two adjacent lines of additional atoms and a step on the surface. For
the calculations, both density-matrix renormalization group and Monte Carlo techniques are used. By changing the local couplings
at the defects and the film thickness, non-universal features as well as interesting crossover phenomena in the magnetic exponents
are observed.
Received 27 July 2000 and Received in final form 5 October 2000 相似文献
14.
F.W.S. Lima J.E. Moreira J.S. Andrade Jr. U.M.S. Costa 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(1):107-110
We investigate the two-dimensional eight-states ferromagnetic Potts model in the Voronoi-Delaunay tessellation. In this study,
we assume that the coupling factor J varies with the distance r between the first neighbors as , with . The disordered system is simulated applying the single-cluster Monte-Carlo update algorithm and the reweighting technique.
We find that this model displays a first-order phase transition if , in agreement with previous recent studies. For and 1.0, a typical second order transition is observed and the critical exponents for magnetization and susceptibility are
calculated.
Received 19 May 1999 and Received in final form 2 June 1999 相似文献
15.
D. Stauffer P.M.C. de Oliveira 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(4):587-592
The density of never changed opinions during the Sznajd consensus-finding process decays with time t as 1/t
θ. We find θ ≃ 3/8 for a chain, compatible with the exact Ising result of Derrida et al. In higher dimensions, however, the exponent differs from the Ising θ. With simultaneous updating of sublattices instead of
the usual random sequential updating, the number of persistent opinions decays roughly exponentially. Some of the simulations
used multi-spin coding.
Received 22 August 2002 / Received in final form 12 November 2002 Published online 31 December 2002 相似文献
16.
J.L. Meunier A. Morel 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(2):341-352
For the first order transition of the Ising model below , Isakov has proven that the free energy possesses an essential singularity in the applied field. Such a singularity in the
control parameter, anticipated by condensation theory, is believed to be a generic feature of first order transitions, but
too weak to be observable. We study these issues for the temperature driven transition of the q states 2D Potts model at . Adapting the droplet model to this case, we relate its parameters to the critical properties at and confront the free energy to the many informations brought by previous works. The essential singularity predicted at the
transition temperature leads to observable effects in numerical data. On a finite lattice, a metastability domain of temperatures
is identified, which shrinks to zero in the thermodynamical limit.
Received 30 March 1999 相似文献
17.
The fourth-order cumulant of the magnetization, the Binder cumulant,
is determined at the phase transition of
Ising models on square and triangular lattices, using Monte
Carlo techniques. Its value at
criticality depends sensitively on
boundary conditions, details of the
clusters used in calculating the cumulant, and symmetry of the
interactions or, here, lattice structure. Possibilities to
identify generic critical cumulants are discussed. 相似文献
18.
E. Brézin C. De Dominicis 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):467-471
The replicated field theory of the random field Ising model involves the couplings of replicas of different indices. The resulting
correlation functions involve a superposition of different types of long distance behaviours. However the n = 0 limit allows one to discuss the renormalization group properties in spite of this phenomenon. The attraction of pairs
of replicas is enhanced under renormalization flow and no stable fixed point is found. Consequently, an instability occurs
in the paramagnetic region, before one reaches the Curie line, signalling the onset of replica symmetry breaking.
Received 28 July 2000 相似文献
19.
J. Török S. Krishnamurthy J. Kertész S. Roux 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(4):697-701
We introduce a model for the slow relaxation of an energy landscape caused by its local interaction with a random walker whose
motion is dictated by the landscape itself. By choosing relevant measures of time and potential this self-quenched dynamics can be mapped on to the “True” Self-Avoiding Walk model. This correspondence reveals that the average distance of
the walker at time t from its starting point is , where for one dimension and 1/2 for all higher dimensions. Furthermore, the evolution of the landscape is similar to that in growth
models with extremal dynamics.
Received 8 August 2000 相似文献
20.
M. Acharyya D. Stauffer 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):571-575
We have studied the nucleation in the nearest neighbour ferromagnetic Ising model, in different (d) dimensions, by extensive Monte-Carlo simulation using the heat-bath dynamics. The nucleation time () has been studied as a function of the magnetic field (h) for various system sizes in different dimensions (d=2,3,4). The logarithm of the nucleation time is found to be proportional to the power (-(d-1)) of the magnetic field (h) in d dimensions. The size dependent crossover from coalescence to nucleation regime is observed in all dimensions. The distribution
of metastable lifetimes are studied in both regions. The numerical results are compared and found to be consistent with the
classical theoretical predictions. In two dimensions, we have also studied the dynamical response to a sinusoidally oscillating
magnetic field. The reversal time is studied as a function of the inverse of the coercive field. The applicability of the
classical nucleation theory to study the hysteresis and coercivity has been discussed.
Received: 21 January 1998 / Accepted: 17 March 1998 相似文献