共查询到20条相似文献,搜索用时 10 毫秒
1.
Spin-phonon coupling, quadratic in the lattice displacements, is studied assuming that the spin interactions are of infinite range. The magnetic phase transition changes from second to first order for a sufficiently strong coupling. The ferromagnetic spinodal temperature becomes infinite and the paramagnetic spinodal temperature becomes zero for couplings of appropriate signs and strength. Renormalization of the phonon frequencies, within both the Einstein and the Debye schem schemes, is found. 相似文献
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《Physics letters. A》2014,378(30-31):2070-2073
Shallow one-dimensional double-well potentials appear in atomic and molecular physics and other fields. Unlike the “deep” wells of macroscopic quantum coherent systems, shallow double wells need not present low-lying two-level systems. We argue that this feature, the absence of a low-lying two-level system in certain shallow double wells, may allow the finding of new test grounds for quantum mechanics in mesoscopic systems. We illustrate the above ideas with a family of shallow double wells obtained from reflectionless potentials through the Darboux–Bäcklund transform. 相似文献
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The magnetoconductivity tensors of a metal with a weakly anisotropic Fermi surface are determined from analytic solutions to the Boltzmann equation without any restrictions on the magnitude of the cyclotron frequency compared to the collision rate. Results are given for both a two- and a three-dimensional model, the former being analytically simpler to handle. The Hall coefficient and magnetoresistance are obtained as functions of the magnetic field, and we show by explicit calculation how the thermoelectric coefficients at high magnetic fields are determined by the thermodynamic entropy. 相似文献
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The problem of a particle moving in a two-valued random potential occurred in a recent paper by Pomeau. The exact time-dependent solution is here obtained for a quadratic potential by two different methods. The first method treats the problem as a stochastic differential equation and leads to the characteristic function of the probability distribution of the particle coordinate. In the second method the equation for the joint probability density of particle and potential is solved, which leads to the temporal Laplace transform of the distribution. The spectral properties of the evolution operator are examined. 相似文献
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We consider an exclusion process with particles injected with rate at the origin and removed with rate at the right boundary of a one-dimensional chain of sites. The particles are allowed to hop onto unoccupied sites, to the right only. For the special case of = = 1 the model was solved previously by Derridaet al. Here we extend the solution to general , . The phase diagram obtained from our exact solution differs from the one predicted by the mean-field approximation. 相似文献
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A model Boltzmann equation with persistence of state is described and shown to lead to both exact, similarity solutions and general solutions as moment expansions. These, unlike any previously known, are parametrized over the whole range from “small-scattering” to “diffuse-scattering” extremes. 相似文献
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We consider a simple exactly solvable model of an order-disorder transition: noninteracting interfaces moving with constant speed in one dimension. We obtain a linear increase with time of the average domain size and a weak oscillatory behavior of the scattering structure function. 相似文献
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Restricting space to low dimensions can cause deviations from the mean-field behavior in certain statistical systems. We investigate, both numerically and analytically, the behavior of the chemical reaction A+2X3X in one and two dimensions. In one dimension, we produce exact results showing that the trimolecular reaction system stabilizes in a nonequilibrium, locally frozen, asymptotic state in which the ratior of A to X particles is a constant number,r=0.38, quite different from the mean-field ratio,r
MF=1. The same trimolecular model, however, reaches the mean-field limit in two dimensions. In contrast, the bimolecular chemical reaction A+X2X is shown to agree with the mean-field predictions in all dimensions. For both models, we show that the adoption of certain types of transition rules in the laws of evolution can lead to oscillatory steady states. 相似文献
12.
In this paper we study tricritical wetting behaviour in three dimensions. In particular we concentrate on systems with short-ranged
forces and apply linear functional renormalization group techniques to elucidate the effect of fluctuations upon tricriticality.
In comparison with studies of critical wetting we identify an additional fluctuation regime which is relevant for values of
the capillary parameter between 2/9 and 1/2. We demonstrate that this regime essentially provides a crossover from mean-field
like behaviour, in which tricritical exponents are always distinct from their critical counterparts, from intermediate- and
strong-fluctuation behaviour where the critical exponents for tricritical and critical wetting are found to always coincide.
We conclude by discussing briefly the possible relevance of these results for experimental studies of wetting.
Received 4 January 2001 and Received in final form 11 May 2001 相似文献
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An exactly soluble model for the study of projection techniques within the framework of the Hartree-Fock theory is presented. Properties of the exact solutions are analyzed and projections, both before and after variation, are discussed. 相似文献
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Gas-liquid criticality in ionic fluids is studied in exactly soluble spherical models that use interlaced sublattices to represent hard-core multicomponent systems. Short-range attractions in the uncharged fluid drive criticality, but charged ions do not alter the universality class. Debye screening remains exponential at criticality in fully ion-symmetric 1:1 models. However, ionic asymmetry couples charge and density fluctuations in a direct manner: The charge correlation length then diverges precisely as the density correlation length and the Stillinger-Lovett rule is violated at criticality. 相似文献
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《Physics letters. A》1987,122(9):463-466
The nonequilibrium phase diagram of an Ising model in which the evolution of the spins reflects diffusion as well as ordering, is determined via dynamic mean-field theory (pair approximation). There is a first-order transition (in zero field) for sufficiently large diffusion rates. 相似文献
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A. M. W. Verhagen 《Journal of statistical physics》1976,15(3):219-231
An anisotropic triangular Ising model in which the first- and second-order parameters and the field parameters are functionally related is solved exactly by representing the distribution of the atom patterns in terms of a suitably constructed Markov process. The probabilities of patterns, defined as the probabilities generated by this process, are a mathematically tractable alternative to the classical representation of these probabilities in terms of the partition function. The interaction and field parameters of this Ising model, its magnetization, free energy, and its nearest neighbor correlation functions, are expressed in terms of the parameters of this Markov process. Special cases are worked out in detail and numerical examples are given. 相似文献
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Igor N. Karnaukhov 《Zeitschrift für Physik B Condensed Matter》1993,92(3):369-375
We present an integrable model describing the interaction of conduction electrons with an arbitrary number of spin-1/2 impurities in one-dimension. The solution of the model is obtained by means of the Bethe function in the case when the number of particles is not conserved. The impurity magnetization, the Kondo-limit, the specific-heat coefficient are calculated on the basis of the Bethe ansatz solution. 相似文献
20.
A model of a binary mixture, showing a wetting transition, is examined. No prewetting phenomena are found. The scaling functions are obtained for the film thickness and for the correlation lengths. 相似文献