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111.
Quantum Ising models in a transverse field are related to continuous-time percolation processes whose oriented percolation versions are contact processes. We study such models in the presence of quasiperiodic disorder and prove localization in the ground state, no percolation, and extinction, respectively, for sufficiently large disorder. 相似文献
112.
The hierarchically constrained kinetic Ising model in one dimension is reviewed, and the results of several analytical approaches to the model are presented. Two standard approximation schemes, an effective-medium approximation and a mode-coupling approximation, are shown to fail. A new class of approximations, termed cluster approximations, is better suited for the model. It yields good results for the spin autocorrelation function, and also elucidates important general properties of the model—its connection with defect-diffusion models and the asymptotic long-time behavior of the autocorrelation function. 相似文献
113.
114.
Ronald Fisch 《Journal of statistical physics》2006,125(3):773-788
For L × L square lattices with L ≤ 20 the 2D Ising spin glass with +1 and −1 bonds is found to have a strong correlation between the energy and the entropy of its ground states. A fit to the data gives the result that each additional broken bond in the ground state of a particular sample of random bonds increases the ground state degeneracy by approximately a factor of 10/3. For x=0.5 (where x is the fraction of negative bonds), over this range of L, the characteristic entropy defined by the energy-entropy correlation scales with size as L
1.78(2). Anomalous scaling is not found for the characteristic energy, which essentially scales as L
2. When x=0.25, a crossover to L
2 scaling of the entropy is seen near L=12. The results found here suggest a natural mechanism for the unusual behavior of the low temperature specific heat of this model, and illustrate the dangers of extrapolating from small L.
PACS numbers: 75.10.Nr, 75.40.Mg, 75.50.Lk 相似文献
115.
The spin-one Ising ferromagnet on a simple cubic lattice is treated in the mean-spherical approximation (MSA) for an exchange
potentialJ(r) parametrized by a Kac-Baker inverse-range parameter γ. The mean-field result is recovered when γ→ 0; in this limit the result is exact. For γ≠ 0, a detailed analysis is given of the phase separation associated with the tricritical point that occurs. The analysis is
made through the relation that gives the internal energy viaJ(r). It shows that the MSA result satisfactorily captures the important thermodynamic features of the tricritical point as long
as γ is not too large. The case of CoulombicJ(r) is also considered; hereJ(r) is antiferromagnetic. An argument is given in support of the expectation that on the simple cubic and body-centered cubic
lattices the CoulombicJ(r) will give rise to a tricritical point at which a λ-line of Néel points meets a paramagnetic-antiferromagnetic coexistence
boundary. 相似文献
116.
Christopher L. Henley 《Journal of statistical physics》1997,89(3-4):483-507
This paper considers the Monte Carlo dynamics of random dimer coverings of the square lattice, which can be mapped to a rough
interface model. Two kinds of slow modes are identified, associated respectively with long-wavelength fluctuations of the
interface height, and with slow drift (in time) of the system-wide mean height. Within a continuum theory, the longest relaxation
time for either kind of mode scales as the system sizeN. For the real, discrete model, an exactlower bound ofO(N) is placed on the relaxation time, using variational eigenfunctions corresponding to the two kinds of continuum modes 相似文献
117.
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
118.
Exact ground states of Ising spin glasses: New experimental results with a branch-and-cut algorithm 总被引:4,自引:0,他引:4
C. De Simone M. Diehl M. Jünger P. Mutzel G. Reinelt G. Rinaldi 《Journal of statistical physics》1995,80(1-2):487-496
In this paper we study two-dimensional Ising spin glasses on a grid with nearest neighbor and periodic boundary interactions, based on a Gaussian bond distribution, and an exterior magnetic field. We show how using a technique called branch and cut, the exact ground states of grids of sizes up to 100×100 can be determined in a moderate amount of computation time, and we report on extensive computational tests. With our method we produce results based on more than 20,000 experiments on the properties of spin glasses whose errors depend only on the assumptions on the model and not on the computational process. This feature is a clear advantage of the method over other, more popular ways to compute the ground state, like Monte Carlo simulation including simulated annealing, evolutionary, and genetic algorithms, that provide only approximate ground states with a degree of accuracy that cannot be determineda priori. Our ground-state energy estimation at zero field is –1.317. 相似文献
119.
120.
The dynamics of spreading of the minority opinion in public debates (a reform proposal, a behavior change, a military retaliation)
is studied using a diffusion reaction model. People move by discrete step on a landscape of random geometry shaped by social
life (offices, houses, bars, and restaurants). A perfect world is considered with no advantage to the minority. A one person-one
argument principle is applied to determine locally individual mind changes. In case of equality, a collective doubt is evoked
which in turn favors the Status Quo. Starting from a large in favor of the proposal initial majority, repeated random size
local discussions are found to drive the majority reversal along the minority hostile view. Total opinion refusal is completed
within few days. Recent national collective issues are revisited. The model may apply to rumor and fear propagation.
Received 23 January 2002 相似文献