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1.
A new approach to the study of spinodal decomposition for a scalar field is proposed. The approach is based on treating this
process as a relaxation of the one-time correlation function G(q,t)=∫d
r<Φ (0, t)Φ (r,t)>exp(i
q·r), which plays the role of an independent dynamical object (a unique two-point order parameter). The dynamical equation for
G(q,t) (the Langevin equation in correlation-function space) is solved exactly in the one-loop approximation, which is the zeroth
approximation in the approach proposed. This makes it possible to trace the asymptotic behavior of G(q,t) at long and intermediate times t (from the moment of onset of the spinodal decomposition). The values obtained for the power-law growth exponents for the
height and position of the peak in G(q,t) at the intermediate stage is in satisfactory agreement with the data obtained by a number of authors through numerical simulation
of the corresponding stochastic equations describing the relaxation of the local order parameter.
Pis’ma Zh. éksp. Teor. Fiz. 66, No. 6, 432–437 (25 September 1997) 相似文献
2.
B. Hôo K. Boukheddaden F. Varret 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,17(3):449-457
In order to investigate the role of nearest neighbors correlations in the relaxation of the High Spin fraction in spin crossover
compounds, we have developed a two macro-variable dynamical model based on Kubo's treatement of the master equation. This
is compared to the local equilibrium approach, where short-range correlations are assumed to follow adiabatically the long
range-order parameter. The sigmoidal shape of the relaxation, previously associated with the effects of interactions, and
the so-called “tail effect”, i.e. the extra-slowing down at long times due to the correlations are obtained. The accurate comparison to experimental relaxation
data confirms the coexistence of short-range and long-range interactions in spin-crossover solids.
Received 20 April 2000 相似文献
3.
We report on the pressure dependence of the bandgap bowing in the ZnTe 1 m x Se x alloy, in the whole composition range. The bandgap bowing parameter is shown to increase almost linearly with pressure from 1.23 at ambient pressure to 1.6 at 7 GPa. Saturation effects observed in the pressure dependence for x =0.1 and x =0.2 are shown to be related to the direct-to-indirect crossover. Results are discussed and interpreted in the framework of structural relaxation models for gap bowing. A prediction of these models (the negative bowing of the o 15 m ;X 1 transition) is shown to be compatible with the fact that the direct-to-indirect crossover pressure increases with the Se content. 相似文献
4.
Katalin E. Kvr Gyula Batta Jozef Kowalewski Leila Ghalebani Danuta Kruk 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,167(2):239
Conventional relaxation parameters (T1−1, T2−1, and NOE), obtained at different temperatures and magnetic fields, are reported for the hydroxymethyl (C6) carbon in methyl-β-
-glucopyranoside in a D2O/DMSO cryosolvent. These data are interpreted with the Lipari–Szabo model. In addition, two-field measurements of longitudinal and spin-locked relaxation rates related to the cross-correlated carbon–proton dipole–dipole interactions for the same carbon are reported. The complete data set consisting the conventional and cross-correlated relaxation parameters is interpreted using a new “hybrid” approach, in which the Lipari–Szabo model for the auto-correlated spectral densities is combined with the two-site jump model for the cross-correlated spectral densities, with the global correlation time as a common parameter. The two-site jump rates thus obtained are in reasonable agreement with the ultrasonic relaxation measurements, and have reasonable temperature dependence. 相似文献
5.
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
6.
We consider the totally asymmetric simple exclusion process (TASEP) with two-sided Bernoulli initial condition, i.e., with
left density ρ
− and right density ρ
+. We study the associated height function, whose discrete gradient is given by the particle occurrences. Macroscopically one
has a deterministic limit shape with a shock or a rarefaction fan depending on the values of ρ
±. We characterize the large time scaling limit of the multipoint fluctuations as a function of the densities ρ
± and of the different macroscopic regions. Moreover, using a slow decorrelation phenomena, the results are extended from fixed
time to the whole space-time, except along the some directions (the characteristic solutions of the related Burgers equation)
where the problem is still open. 相似文献
7.
S. Risau-Gusman G. Abramson 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,60(4):515-520
We analyze general two-species stochastic models, of the
kind generally used for the study of population dynamics. Although
usually defined a priori, the deterministic version of these
models can be obtained as the infinite volume limit of many
stochastic models (which are necessarily defined by more parameters
than the deterministic one). It is known that damped oscillations in
a deterministic model usually correspond to oscillatory-like
fluctuations in their deterministic counterparts. The quality of
these “oscillations" depends on details of each stochastic model.
We show, however, that the parameters of the deterministic system
are generally enough to obtain very good bounds for the quality of
“oscillations" in any of its stochastic counterparts. These
bounds are shown to depend on only one dimensionless parameter. 相似文献
8.
Refractive index and density measurements have been carried out on three nO.m liquid crystalline compounds, namely, 4O.2, 4O.3 and 1O.10 belonging to the N-(p-n-alkoxybenzylidene)-p-n-alkylaniline series. From the data, the orientational order parameter has been estimated using Vuks and Neugebauer local field models. Furthermore, the orientational order parameter has been calculated directly from refractive index data employing the Vuks scaling factor method, Neugebauer f(B) parameter, effective geometry parameter and a method proposed by Kuczyński et al. It is observed that order parameter values estimated from different methods agree well near the nematic–isotropic transition and diverge as the nematic phase attains equilibrium. The temperature gradient of refractive indices and the nematic crossover temperatures have also been estimated for these compounds. The results obtained are compared and discussed. 相似文献
9.
Roberto?Fernández Luiz?R.?Fontes E.?Jord?o?Neves 《Journal of statistical physics》2009,136(5):875-901
We introduce jump processes in ℝ
k
, called density-profile processes, to model biological signaling networks. Our modeling setup describes the macroscopic evolution of a finite-size spin-flip
model with k types of spins with arbitrary number of internal states interacting through a non-reversible stochastic dynamics. We are
mostly interested on the multi-dimensional empirical-magnetization vector in the thermodynamic limit, and prove that, within
arbitrary finite time-intervals, its path converges almost surely to a deterministic trajectory determined by a first-order
(non-linear) differential equation with explicit bounds on the distance between the stochastic and deterministic trajectories.
As parameters of the spin-flip dynamics change, the associated dynamical system may go through bifurcations, associated to
phase transitions in the statistical mechanical setting. We present a simple example of spin-flip stochastic model, associated to a synthetic biology model known as repressilator, which leads to a dynamical system with Hopf and pitchfork bifurcations. Depending on the parameter values, the magnetization random path can either converge to a unique stable fixed
point, converge to one of a pair of stable fixed points, or asymptotically evolve close to a deterministic orbit in ℝ
k
. We also discuss a simple signaling pathway related to cancer research, called p53 module. 相似文献
10.
D.V. Anchishkin A.M. Gavrilik N.Z. Iorgov 《The European Physical Journal A - Hadrons and Nuclei》2000,7(2):229-238
We propose and develop to some extent a novel approach, which allows to effectively describe, for relativistic heavy-ion
collisions, the empirically observed deviation from unity of the intercept λ (i.e. the measured value corresponding to zero
relative momentum p of two registered identical pions or kaons) of the two-particle correlation function C(p,K). The approach is based on the use of two versions of the so-called q-deformed oscillators and the corresponding picture of ideal gases of q-bosons. By these techniques the intercept λ is put into direct correspondence with the deformation parameter q. For fixed deformation strength, the model predicts particular dependence of the intercept λ on the pion pair mean momentum
K.
Received: 2 July 1999 / Revised version: 11 November 1999 相似文献
11.
A. Dıaz-Sánchez L.A. Braunstein R.C. Buceta 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(2):289-294
The roughening of interfaces moving in inhomogeneous media is investigated by numerical integration of the phenomenological
stochastic differential equation proposed by Kardar, Parisi, and Zhang [Phys. Rev. Lett. 56, 889 (1986)] with quenched noise (QKPZ) [Phys. Rev. Lett. 74, 920 (1995)]. We express the evolution equations for the mean height and the roughness into two contributions: the local
and the lateral one in order to compare them with the local and the lateral contributions obtained for the directed percolation
depinning models (DPD) introduced independently by Tang and Leschhorn [Phys. Rev A 45, R8309 (1992)] and Buldyrev et al. [Phys. Rev A 45, R8313 (1992)]. These models are classified in the same universality class of the QKPZ although the mechanisms of growth
are quite different. In the DPD models the lateral contribution is a coupled effect of the competition between the local growth
and the lateral one. In these models the lateral contribution leads to an increasing of the roughness near the criticality
while in the QKPZ equation this contribution always flattens the roughness.
Received 7 April 2000 and Received in final form 7 March 2001 相似文献
12.
We study sandpile models with stochastic toppling rules and having sticky grains so that with a nonzero probability no toppling occurs, even if the local height of pile exceeds the threshold value. Dissipation is introduced by adding a small probability of particle loss at each toppling. Generically for the models with a preferred direction, the avalanche exponents are those of critical directed percolation clusters. For undirected models, avalanche exponents are those of directed percolation clusters in one higher dimension. 相似文献
13.
P. Paci C. Grimaldi L. Pietronero 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(2):235-243
The inclusion of nonadiabatic corrections to the electron-phonon interaction leads to a strong momentum dependence in the
generalized Eliashberg equations beyond Migdal's limit. For a s-wave symmetry of the order parameter, this induced momentum dependence leads to an enhancement of when small momentum transfer is dominant. Here we study how the d-wave symmetry affects the above behavior. We find that the nonadiabatic corrections depend only weakly on the symmetry of
the order parameter provided that only small momentum scatterings are allowed for the electron-phonon interaction. In this
situation, We show that also for a d-wave symmetry of the order parameter, the nonadiabatic corrections enhance . We also discuss the possible interplay and crossover between s- and d-wave depending on the material's parameters.
Received 12 May 2000 相似文献
14.
The evolution of indirect exciton luminescence in AlAs/GaAs coupled quantum wells after excitation by pulsed laser radiation
has been studied in strong magnetic fields (B⩽12 T) at low temperatures (T⩾1.3 K), both in the normal regime and under conditions of anomalously fast exciton transport, which is an indication of the
onset of exciton superfluidity. The energy relaxation rate of indirect excitons measured in the range of relaxation times
between several and several hundreds of nanoseconds is found to be controlled by the properties of the exciton transport,
specifically, this parameter increases with the coefficient of excitonic diffusion. This behavior is qualitatively explained
in terms of migration of excitons between local minima of the random potential in the plane of the quantum well.
Zh. éksp. Teor. Fiz. 114, 1115–1120 (September 1998) 相似文献
15.
We discuss a new general phenomenon pertaining to tiling models of quasicrystal growth. It is known that with Penrose tiles no (deterministic) local matching rules exist which guarantee defect-free tiling for regions of arbitrary large size. We prove that this property holds quite generally: namely, that the emergence of defects in quasicrystal growth is unavoidable for all aperiodic tiling models in the plane with local matching rules, and for many models inR
3 satisfying certain conditions.Research supported in part by NSF Grant No. DMS-9304269 and Texas ARP Grants 003658113 and 003658007. 相似文献
16.
We study the rotor router model and two deterministic sandpile models. For the rotor router model in ℤ
d
, Levine and Peres proved that the limiting shape of the growth cluster is a sphere. For the other two models, only bounds
in dimension 2 are known. A unified approach for these models with a new parameter h (the initial number of particles at each site), allows to prove a number of new limiting shape results in any dimension d≥1.
For the rotor router model, the limiting shape is a sphere for all values of h. For one of the sandpile models, and h=2d−2 (the maximal value), the limiting shape is a cube. For both sandpile models, the limiting shape is a sphere in the limit
h→−∞. Finally, we prove that the rotor router shape contains a diamond. 相似文献
17.
We study the deterministic diffusion coefficient of the two-dimensional periodic Lorentz gas as a function of the density of scatterers. Based on computer simulations, and by applying straightforward analytical arguments, we systematically improve the Machta–Zwanzig random walk approximation [Phys. Rev. Lett.
50:1959 (1983)] by including microscopic correlations. We furthermore, show that, on a fine scale, the diffusion coefficient is a non-trivial function of the density. On a coarse scale and for lower densities, the diffusion coefficient exhibits a Boltzmann-like behavior, whereas for very high densities it crosses over to a regime which can be understood qualitatively by the Machta–Zwanzig approximation. 相似文献
18.
Two cellular automata models with directed mass flow and internal time scales are studied by numerical simulations. Relaxation
rules are a combination of probabilistic critical height (probability of toppling p) and deterministic critical slope processes with internal correlation time tc equal to the avalanche lifetime, in model A, and ,in model B. In both cases nonuniversal scaling properties of avalanche distributions are found for , where is related to directed percolation threshold in d=3. Distributions of avalanche durations for are studied in detail, exhibiting multifractal scaling behavior in model A, and finite size scaling behavior in model B,
and scaling exponents are determined as a function of p. At a phase transition to noncritical steady state occurs. Due to difference in the relaxation mechanisms, avalanche statistics
at approaches the parity conserving universality class in model A, and the mean-field universality class in model B. We also
estimate roughness exponent at the transition.
Received: 29 May 1998 / Revised: 8 September 1998 / Accepted: 10 September 1998 相似文献
19.
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
20.
It is found that the collective effects operating at large distances from the grain surface can produce substantial scattering of the ion flux and create an additional collective drag force dominant for large grain densities. The consideration is restricted to large grain charges β = Zde 2a /TiλDi ? 1 and Ti /Te ? 1 (–eZd being the grain charge in units of electron charge, a being the grain size, λDi being the ion Debye radius and Te,i being electron and ion temperatures, respectively). For present dusty plasma experiments β ≈ 10–50, the large charges of grains are screened non‐linearly and the ion scattering creates non‐linear drag force. The present investigation considers effects of scattering by collective grain fields at large distances from the grains. It is found that the physical reason of the importance of collective drag force, calculated in this paper, is related to presence of weakly screened collective field of grains outside the non‐linear screening distance depending on grain densities. The amplitude of this collective fields of the grains is determined by non‐linear screening at non‐linear screening radius. It is shown that for dust densities of present experiments the collective drag force related to this scattering can be of the order of the non‐linear drag force caused by scattering inside the non‐linear screening radius or even larger. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献