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1.
颗粒介质是复杂的多体相互作用体系, 其弹性源自内部的力链结构, 弹性能量处在亚稳态, 具有复杂的弛豫行为. 在常规作用下, 颗粒介质往往呈现明显的弹性弛豫. 应力松弛是应变恒定时应力的衰减现象, 弹性弛豫是应力松弛的主要原因. 在前期工作基础上, 从弹性势能面和双颗粒温度热力学角度分析了弹性弛豫的机理, 量化了弹性应力演化不可逆过程; 基于双颗粒温度热力学计算得到了弹性能、颗粒温度和应力的演化, 其中应力松弛的计算结果与实验结果基本一致, 讨论了颗粒温度初值和输运系数的影响. 指出, 开展力链结构及其动力学研究是揭示宏观弹性弛豫机理的关键. 相似文献
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本文分析了颗粒流的介观结构及其特征,提出了颗粒流的双颗粒温度概念Tkin和Tconf,表征颗粒无序运动和构型无序演化的程度;进而作为非平衡变量,与经典非平衡热力学(classical irreversible thermodynamics,CIT)变量共同构成颗粒流的热力学状态变量集,确定了颗粒流的能量转换规律和熵产生率等,发展了颗粒流双颗粒温度(two granular temperate,TGT)模型.以体积恒定的简单剪切准静态颗粒流为例,结合离散元模拟(discrete element method,DEM),确定了双颗粒温度模型所需的材料参数,分析了颗粒流发展段的规律和稳恒段的有效摩擦系数. 相似文献
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The spin-dependent tunneling of cobalt clusters embedded in Al2O3 or SiOx has been analyzed as a function of the frequency at room temperature. Two sets of samples, with one or several layers of clusters, have been produced by alternate physical deposition of the metal and the insulator. The impedance versus frequency curves were measured with and without an external magnetic field. The results suggest that when the distance between successive cluster layers is small, some correlations between the cluster positions are present. 相似文献
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We present extensive computational results for the effective temperature,
defined by the fluctuation-dissipation relation between the mean square
displacement and the average displacement of grains, under the action of
a weak, external perturbation, of a sheared, bi-disperse granular packing
of compressible spheres. We study the dependence of this parameter on the
shear rate and volume fractions, the type of particle and the observable
in the fluctuation-dissipation relation. We find the same temperature
for different tracer particles in the system. The temperature becomes
independent on the shear rate for slow enough shear suggesting that it is
the effective temperature of the jammed packing. However, we also show
that the agreement of the effective temperature for different observables
is only approximate, for very long times, suggesting that this defintion
may not capture the full thermodynamics of the system. On the other hand,
we find good agreement between the dynamical effective temperature and a
compactivity calculated assuming that all jammed states are equiprobable.
Therefore, this definition of temperature may capture an instance
of the ergodic hypothesis for granular materials as proposed by theoretical
formalisms for jamming. Finally, our simulations indicate
that the average shear
stress and apparent shear viscosity follow the usual relation with the shear
rate for complex fluids. Our results show that the application of
shear induces jamming in packings whose particles interact
by tangential forces. 相似文献
8.
R. L. Stratonovich 《Journal of statistical physics》1988,53(1-2):5-18
A dynamical system consisting of a subsystem having the variablesz=(q,p) and of another dynamical system (thermostat) is considered in the nonquantum case. Using a dynamical equation, it is shown that the linear and quadratic non-Markov fluctuation-dissipation relations (FDRs) of the first kind are valid in the first nonvanishing approximation in interaction constants. Applying these FDRs, one can determine the statistical properties of the fluctuations when the form of the nonlinear phenomenological equation is known. The non-Markov FDRs of the first kind are the direct generalization (to the inertial case) of the Markov FDRs that are the consequence of detailed balance. 相似文献
9.
Giovanni Gallavotti 《Journal of statistical physics》1996,84(5-6):899-925
It is shown that the chaoticity hypothesis recently introduced in statistical mechanics, which is analogous to Ruelle's principle for turbulence, implies the Onsager reciprocity and the fluctuation-dissipation theorem in various reversible models for coexisting transport phenomena.This paper is dedicated to David Ruelle on the occasion of his 60th birthday. 相似文献
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The paper is devoted to the theory of thermal fluctuations in nonlinear macroscopic systems and to the derivation of variational principles of nonlinear nonequilibrium thermodynamics. In the first part of the paper rigorous universal fluctuation-dissipation relations for nonlinear classical and quantum systems, subjected to dynamic as well as thermodynamic perturbations, are derived and analyzed. General expressions for dissipative fluxes and nonlinear transfer coefficients with the help of fluctuation cumulants are found. The canonical structure of nonlinear evolution equations of macrovariables is derived and the rule of introducing langevinian random forces into these equations, in accordance with fluctuation-dissipation relations. A Markovian theory of fluctuations in a stationary nonequilibrium state is constructed. 相似文献
11.
颗粒介质具有远程无序和近程有序的结构, 是产生动力学不均匀性(dynamical heterogeneity) 和复杂不可逆过程的根源. 本文分析了颗粒介质的结构特征、变形和能量耗散之间的内在关联, 讨论了颗粒介质的弹性, 提出了流变应变增量、耦合应变增量和弹性应变增量的应变增量分解方式. 沿用非平衡热力学框架, 引入表征运动无序的动理学颗粒温度Tk和表征弹性应力涨落的构型温度Tc, 作为非平衡态变量, 建立了双颗粒温度热力学(two-granular-temperature thermodynamics, TGT理论), 注重分析了不可逆过程中的热力学力和流, 并与著名的砂土内变量热力学进行了对比. 相似文献
12.
Yoh-Han Pao 《Journal of Macromolecular Science: Physics》2013,52(2):289-307
Abstract Kubo theory formalism has been used to obtain expressions for shear and dilatational stress relaxation functions in terms of statistical mechanical time-dependent correlation functions. This is equivalent to obtaining expressions for the complex modulus or the complex viscosity for all frequencies. These results provide a basis for calculating the macroscopic consequences of molecular models presently used to provide qualitative understanding of relaxation peaks for solid polymers. The shear and dilatational stress relaxation functions are quite different formally. For a particularly simple model it will be shown that the former is related to the frequency distribution of the kinetic energy and is also closely related to the dielectric relaxation function. The familiar results of the Rouse model are recovered in the results but no friction constant need be assumed in the present approach. 相似文献
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Dependence of effective screening length in granular columns on bead and silo sizes and their ratio 下载免费PDF全文
Apparent mass measurements at the bottom of silos have been carried out. An important parameter in the Janssen model known as the effective screening length has been investigated for different bead and silo diameters as well as of their ratios. It is found that the effective screening length augments with the grain diameter d in addition to the granular column size. It is also revealed that λ exhibits stronger correlation with the bead diameter than that of the silo. This phenomenon is attributed to the reduced-shielding of the vertical stresses to the horizontal ones. 相似文献
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Yoshiki Hidaka Yusaku Hosokawa Koyo Tamura Shoichi Kai 《Physica D: Nonlinear Phenomena》2010,239(11):735-728
Non-thermal Brownian motion of a particle for soft-mode turbulence (SMT) in the electroconvection of a nematic liquid crystal has been experimentally investigated to clarify the statistical and thermodynamical aspects of SMT, using the Lagrangian picture in hydrodynamics. The effective temperature for SMT is obtained in two different ways based on the Einstein relation and the fluctuation theorem from the diffusion due to non-thermal particle fluctuations. The temperatures from the two methods agree well and exhibit a high value of 106 K. They depend on the coarse-graining time, which reflects the anomalous properties of the macroscopic fluctuations for the SMT. 相似文献
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Open systems are very important in science and engineering for their applications and the analysis of the real word. At their steady state, two apparently opposed principles for their rate of entropy production have been proposed: the minimum entropy production rate and the maximum entropy production, useful in the analysis of dissipation and irreversibility of different processes in physics, chemistry, biology and engineering. Both principles involve an extremum of the rate of the entropy production at the steady state under non-equilibrium conditions. On the other hand, in engineering thermodynamics, dissipation and irreversibility are analyzed using the entropy generation, for which there exist two principle of extrema too, the minimum and the maximum principle. Finally, oppositions to the extrema principle have been developed too. In this paper, all these extrema principles will be analyzed in order to point out the relations among them and a synthesis useful in engineering applications, in physical and chemical process analysis and in biology and biotechnology will be proposed. 相似文献
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Gregory L. Eyink 《Journal of statistical physics》1990,61(3-4):533-572
The results of recent work of Kipnis, Olla, and Varadhan on the dynamic large deviations from a hydrodynamic limit for some interacting particle models are formally extended to a general hydrodynamic situation, including non-equilibrium steady states, as a fluctuation-dissipation hypothesis. The basic conjecture is that the exponent of decay in the probability of a large thermodynamic fluctuation is given by the dissipation of the force required to produce the fluctuation. It is shown that this hypothesis leads to a nonlinear version of Onsager-Machlup fluctuation theory that had previously been proposed by Graham. A direct consequence of the theory is a dynamic variational principle for the most probable thermodynamic history subject to imposed constraints (Onsager's principle of least dissipation). Following Graham, the theory leads also to a generalized potential, analogous to an equilibrium free energy, for the nonequilibrium steady state and an associated static variational principle. Finally, a formulation of nonlinear fluctuating hydrodynamics is proposed in which the noise enters multiplicatively so as to reproduce the conjectured large-deviations theory on a formal analogy with the results of Freidlin and Wentzell for finite-dimensional systems. 相似文献
17.
A molecular dynamics simulation of segregation behaviours of horizontally vibrated binary granular mixture 下载免费PDF全文
This paper performs the two-dimensional, soft-sphere
molecular dynamics simulations to study the granular segregation in
a binary granular mixture with the same size but different density
in the container with the sawtooth base under horizontal vibration.
The segregation phase diagram is presented in the
acceleration-frequency space. When the acceleration is high enough
to result in relative motions of the particles, the system can be in
various states (mixed state, vertical and horizontal segregation
state), which depend on both acceleration and frequency. Due to the
sawtooth base there is stratified flow effect besides density
effect. The density effect raises the light particles. The
stratified flow drives the particles in the upper levels to the
right and the particles in the lower particles to the left, those
fact results in the appearance of the left segregation state. The
left segregation state can be changed to the right segregation by
changing the shape of the sawtooth. As the vibration frequency
increases, the stratified flow effect becomes weaker and weaker, so
at high vibration frequencies the vertical segregation state appears
instead of the left segregation state. 相似文献
18.
Creyssels M Dorbolo S Merlen A Laroche C Castaing B Falcon E 《The European physical journal. E, Soft matter》2007,23(3):255-264
We report on measurements of the electrical conductivity in both a 2D triangular lattice of metallic beads and in a chain
of beads. The voltage/current characteristics are qualitatively similar in both experiments. At low applied current, the voltage
is found to increase logarithmically in good agreement with a model of widely distributed resistances in series. At high enough
current, the voltage saturates due to the local welding of microcontacts between beads. The frequency dependence of the saturation
voltage gives an estimate of the size of these welded microcontacts. The DC value of the saturation voltage ( ≃ 0.4 V per
contact) gives an indirect measure of the number of welded contact carrying the current within the 2D lattice. Also, a new
measurement technique provides a map of the current paths within the 2D lattice of beads. For an isotropic compression of
the 2D granular medium, the current paths are localized in few discrete linear paths. This quasi-onedimensional nature of
the electrical conductivity thus explains the similarity between the characteristics in the 1D and 2D systems. 相似文献
19.
《Comptes Rendus Physique》2015,16(3):291-302
We review a few representative examples of granular experiments or models where phase separation, accompanied by domain coarsening, is a relevant phenomenon. We first elucidate the intrinsic non-equilibrium, or athermal, nature of granular media. Thereafter, dilute systems, the so-called “granular gases”, are discussed: idealized kinetic models, such as the gas of inelastic hard spheres in the cooling regime, are the optimal playground to study the slow growth of correlated structures, e.g., shear patterns, vortices, and clusters. In fluidized experiments, liquid–gas or solid–gas separations have been observed. In the case of monolayers of particles, phase coexistence and coarsening appear in several different setups, with mechanical or electrostatic energy input. Phenomenological models describe, even quantitatively, several experimental measures, both for the coarsening dynamics and for the dynamic transition between different granular phases. The origin of the underlying bistability is in general related to negative compressibility from granular hydrodynamics computations, even if the understanding of the mechanism is far from complete. A relevant problem, with important industrial applications, is related to the demixing or segregation of mixtures, for instance in rotating tumblers or on horizontally vibrated plates. Finally, the problem of compaction of highly dense granular materials, which is relevant in many practical situations, is usually described in terms of coarsening dynamics: there, bubbles of misaligned grains evaporate, allowing the coalescence of optimally arranged islands and a progressive reduction of the total occupied volume. 相似文献