共查询到20条相似文献,搜索用时 15 毫秒
1.
S. Franz G. Parisi 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(3):417-422
In this paper we study the critical properties of a finite dimensional generalization of the p-spin model. We find evidence that in dimension three, contrary to its mean field limit, the glass transition is associated
to a diverging susceptibility (and correlation length).
Received 13 May 1998 相似文献
2.
Mixed spin transverse Ising model with longitudinal random crystal field interactions 总被引:1,自引:0,他引:1
N. Benayad R. Zerhouni A. Klümper 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):687-695
The effect of a longitudinal random crystal field interaction on the phase diagrams of the mixed spin transverse Ising model
consisting of spin-1/2 and spin-1 is investigated within the finite cluster approximation based on a single-site cluster theory.
In order to expand a cluster identity of spin-1, we transform the spin-1 to spin-1/2 representation containing Pauli operators.
We derive the state equations applicable to structures with arbitrary coordination number N. The phase diagrams obtained in the case of a honeycomb lattice (N=3) and a simple-cubic lattice (N=6), are qualitatively different and examined in detail. We find that both systems exhibit a variety of interesting features
resulting from the fluctuation of the crystal field interactions.
Received: 13 February 1998 / Accepted: 17 March 1998 相似文献
3.
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
4.
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
5.
T.T. Truong 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):697-703
We point out the existence of an alternative algebraic structure in Yang-Baxter algebra with trigonometric R-matrix, which appears to be the generalization of the Yangian in Yang-Baxter algebras with rational R-matrix and which is described most naturally by q-commutators. Some properties are presented, in particular in the case of the well-known symmetric six-vertex model.
Received: 13 February 1998 / Revised: 16 March 1998 / Accepted: 17 April 1998 相似文献
6.
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
7.
M. Bayindir Z. Gedik 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(2):287-291
We show explicitly that the broad histogram single-spin-flip random walk dynamics does not give correct microcanonical average
even in one dimension. The dynamics violates the detailed balance condition by an amount proportional to the inverse system
size. As a result, in distribution different configurations with the same energy can have different probabilities. We propose
a modified dynamics which ensures detailed balance and the histogram obtained from this dynamics is exactly flat. The broad
histogram equation relating the average number of potential moves to density of states is generally valid.
Received 2 October 1998 and Received in final form 13 October 1998 相似文献
8.
S.G. Magalhães A. Theumann 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(1):5-13
We have examined the role of the BCS pairing mechanism in the formation of the magnetic moment and henceforth a spin glass
(SG) phase by studying a fermionic Sherrington-Kirkpatrick model with a local BCS coupling between the fermions. This model
is obtained by using perturbation theory to trace out the conduction electrons degrees of freedom in conventional superconducting
alloys. The model is formulated in the path integral formalism where the spin operators are represented by bilinear combinations
of Grassmann fields and it reduces to a single site problem that can be solved within the static approximation with a replica
symmetric ansatz. We argue that this is a valid procedure for values of temperature above the de Almeida-Thouless instability
line. The phase diagram in the T-g plane, where g is the strength of the pairing interaction, for fixed variance J
2
/N of the random couplings Jij, exhibits three regions: a normal paramagnetic (NP) phase, a spin glass (SG) phase and a pairing (PAIR) phase where there
is formation of local pairs.The NP and PAIR phases are separated by a second order transition line g=g
c
(T) that ends at a tricritical point T
3
=0.9807J, g
3
=5,8843J, from where it becomes a first order transition line that meets the line of second order transitions at T
c
=0.9570J that separates the NP and the SG phases. For T<T
c
the SG phase is separated from the PAIR phase by a line of first order transitions. These results agree qualitatively with
experimental data in .
Received 14 May 1998 相似文献
9.
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
10.
A generalized spin model of financial markets 总被引:1,自引:0,他引:1
D. Chowdhury D. Stauffer 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(3):477-482
We reformulate the Cont-Bouchaud model of financial markets in terms of classical “super-spins” where the spin value is a
measure of the number of individual traders represented by a portfolio manager of an investment agency. We then extend this
simplified model by switching on interactions among the super-spins to model the tendency of agencies getting influenced by the opinion of other managers. We also introduce
a fictitious temperature (to model other random influences), and time-dependent local fields to model a slowly changing optimistic
or pessimistic bias of traders. We point out close similarities between the price variations in our model with N super-spins and total displacements in an N-step Levy flight. We demonstrate the phenomena of natural and artificially created bubbles and subsequent crashes as well
as the occurrence of “fat tails” in the distributions of stock price variations.
Received 13 October 1998 相似文献
11.
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
12.
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
13.
A. Drzewiński A. Ciach A. Maciolek 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):825-833
The two-dimensional Ising films with bulk H and surface H1 fields of opposite sign are studied above and close to bulk criticality by the density matrix renormalization group method.
This technique, applied recently to d=2 Ising films, allows for very accurate results for the adsorption as a function of the reduced deviation from the critical temperature .For strong H1 three distinct classes of shapes of ,determined by the value of the parameter ,where L is the width of the film, are found in agreement with earlier predictions [A. Macioek, A. Ciach, R. Evans, J. Chem. Phys. 108, 9765 (1998)]. For strong and for weak bulk fields is a monotonic function, increasing for strong H and decreasing for weak H, in agreement with scaling analysis and earlier mean-field results. For H between these extreme cases assumes a maximum for and for a depletion occurs, as in recent experiments for critical adsorption in porous materials. For a limited range of H a qualitatively new behavior of is found. In addition to a maximum, a minimum of for appears, which in the mean-field analysis was absent.
Received: 11 February 1998 / Received in final form: 16 February 1998 / Accepted: 17 March 1998 相似文献
14.
S. Galam B. Chopard A. Masselot M. Droz 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(4):529-531
A simple cellular automata model for a two-group war over the same “territory” is presented. It is shown that a qualitative
advantage is not enough for a minority to win. A spatial organization as well a definite degree of aggressiveness are instrumental
to overcome a less fitted majority. The model applies to a large spectrum of competing groups: smoker-non smoker war, epidemic
spreading, opinion formation, competition for industrial standards and species evolution. In the last case, it provides a
new explanation for punctuated equilibria.
Received: 21 April 1998 / Revised and Accepted: 22 April 1998 相似文献
15.
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
16.
E. Agliari M. Casartelli A. Vezzani 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(4):499-506
We study a two dimensional Ising model between
thermostats at different temperatures. By applying the recently
introduced KQ dynamics, we show that the system reaches a steady
state with coexisting phases transversal to the heat flow. The
relevance of such complex states on thermodynamic or geometrical
observables is investigated. In particular, we study energy,
magnetization and metric properties of interfaces and clusters
which, in principle, are sensitive to local features of
configurations. With respect to equilibrium states,
the presence of the heat flow amplifies the fluctuations of both
thermodynamic and geometrical observables in a domain around the
critical energy. The dependence of this phenomenon on various
parameters (size, thermal gradient, interaction) is discussed also
with reference to other possible diffusive models. 相似文献
17.
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
18.
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
19.
G. Parisi F. Ricci-Tersenghi J. J. Ruiz-Lorenzo 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(2):317-325
We show that the numerical method based on the off-equilibrium fluctuation-dissipation relation does work and is very useful
and powerful in the study of disordered systems which show a very slow dynamics. We have verified that it gives the right
information in the known cases (diluted ferromagnets and random field Ising model far from the critical point) and we used
it to obtain more convincing results on the frozen phase of four-dimensional spin glasses. Moreover we used it to study the
Griffiths phase of the diluted and the random field Ising models.
Received 1 December 1998 and Received in final form 17 February 1999 相似文献
20.
D. Stauffer S. Solomon 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(4):473-479
The similarities between phase separation in physics and
residential segregation by preference in the Schelling model of 1971
are reviewed. Also, new computer simulations of asymmetric interactions
different from the usual Ising model are presented, showing spontaneous
magnetisation (=self-organising segregation) and in one case a
sharp phase transition. 相似文献