Experimental observation of disorder-driven hysteresis-loop criticality

We have studied the effect of magnetic disorder on the magnetization reversal process in thin Co/CoO films. The antiferromagnetic CoO layer allows a reversible tuning of the magnetic disorder by simple temperature variation. For temperatures above a critical temperature T(c), we observe a discontinuous magnetization reversal, whereas smooth magnetization loops occur for T相似文献   

Measurement of effective temperatures in an aging colloidal glass

We study the thermal fluctuations of an optically confined probe particle, suspended in an aging colloidal suspension, as the suspension transforms from a viscous liquid into an elastic glass. The micron-sized bead forms a harmonic oscillator. By monitoring the equal-time fluctuations of the tracer, at two different laser powers we determine the temperature of the oscillator, T(o). In the ergodic liquid the temperatures of the oscillator and its environment are equal, while in contrast, in a nonequilibrium glassy phase we find that T(o) substantially exceeds the bath temperature.     

Studies of relaxation processes in organic glasses at low temperatures using the hole-burning spectroscopy technique: Verification of applicability limits of the model of two-level systems

A vitreous state is originally nonequilibrium. Because of this, attempts to classify relaxation processes in glasses as equilibrium and nonequilibrium are, strictly speaking, incorrect. This classification is, however, possible and useful at low temperatures when the model of two-level systems (TLS) appears to be sufficient to describe properties of glasses. Until now, the question of the applicability limits of the TLS model has remained unclear both in the temperature and temporal domains. A number of deviations from the so-called standard TLS model, observed experimentally, can be easily accounted for with allowance for nonequilibrium effects considered as a result of the nonequilibrium state of the TLS ensemble. There are some effects, however, that cannot be consistently explained within the framework of the TLS model. In this paper, we briefly consider the results of studying the relaxation processes in organic glasses at low temperatures in a wide time range using the spectral hole-burning technique. The experimental data are compared with predictions of the TLS model, and spectral criteria for the limits of its applicability are proposed.     

Formation of oriented cadmium telluride films on an amorphous substrate under extremely nonequilibrium conditions

The results of the first experiments related to oriented CdTe film growth on a nonorienting substrate (glass) cooled to negative Celsius temperatures under extremely nonequilibrium conditions are reported. Technological, electron-diffraction, and X-ray investigation results are presented. A condensation diagram characterized by two regions within which the growth rate of films is anomalously low is obtained. The films grown at these rates are shown to possess a nearly perfect crystalline texture. The formation processes of the oriented films on an amorphous substrate under the above conditions are adequately interpreted in the context of a heteroepitaxy soliton model.     

Spectroscopic Mapping of the Nonequilibrium between Electron and Excitation Temperatures in a 1 ATM Helium ARC

The thermostatic states of a 100 amp, 1.016 bar, free-burning helium short arc with a 10 mm electrode gap are mapped from spectroscopic measurements at eight cross sections. The theoretical model used is a multifluids model extended to consider nonequilibrium between electron and excitation temperatures, as well as simple nonequilibrium among excited electronic levels. Seven helium lines are used to determine population densities and upper level excitation temperatures. The electron density is calculated from continuum intensity measurements at C4690. Electron temperatures are found from an astrophysical method suggested by Athay and Menzel. The effective total excitation temperature is obtained by iteration using the multifluids model. The results indicate total excitation temperature values close to the usually calculated "LTE" temperatures, but electron temperatures up to three times larger than the total excitation temperature on the arc centerline near the electrodes. The ratio is approximately 1.5 in the middle of the arc. The heavy particle kinetic temperatures appear to follow the electron temperature, except near the anode, where they drop to values smaller than the total excitation temperatures.     

Bringing entanglement to the high temperature limit

Decoherence due to contact with a hot environment typically restricts quantum phenomena to the low temperature limit, k_{B}T/?ω?1 (?ω is the typical energy of the system). Here we report the existence of a nonequilibrium state for two coupled, parametrically driven, dissipative harmonic oscillators which, contrary to generalized intuition, has stationary entanglement at high temperatures. This clarifies the role of temperature and could lighten the burden on quantum experiments requiring delicate precooling setups.     

Effect of an external action on a pair distribution function in a steady state

An external action that reduces a two-component equilibrium thermodynamic system to a nonequilibrium steady state with scalar fluxes has been studied. A system of integrodifferential equations for pair correlation functions has been obtained. These equations coincide with the second equations of the Bogoliubov-Born-Green-Kirkwood-Yvon hierarchy, but with different effective temperatures. Thus, ordinary integrodifferential equations for a pair correlation function with effective temperatures expressed in terms of the perturbed (nonequilibrium) Maxwellian momentum distribution function can be used to calculate the structural and thermodynamic properties of such a system.     

Negative differential conductance and hot phonons in suspended nanotube molecular wires

Freely suspended metallic single-walled carbon nanotubes (SWNTs) exhibit reduced current carrying ability compared to those lying on substrates, and striking negative differential conductance at low electric fields. Theoretical analysis reveals significant self-heating effects including electron scattering by hot nonequilibrium optical phonons. Electron transport characteristics under strong self-heating are exploited for the first time to probe the thermal conductivity of individual SWNTs (approximately 3600 W m-1 K-1 at T=300 K) up to approximately 700 K, and reveal a 1/T dependence expected for umklapp phonon scattering at high temperatures.     

Large Deviations for the Boundary Driven Symmetric Simple Exclusion Process

The large deviation properties of equilibrium (reversible) lattice gases are mathematically reasonably well understood. Much less is known in nonequilibrium, namely for nonreversible systems. In this paper we consider a simple example of a nonequilibrium situation, the symmetric simple exclusion process in which we let the system exchange particles with the boundaries at two different rates. We prove a dynamical large deviation principle for the empirical density which describes the probability of fluctuations from the solutions of the hydrodynamic equation. The so-called quasi potential, which measures the cost of a fluctuation from the stationary state, is then defined by a variational problem for the dynamical large deviation rate function. By characterizing the optimal path, we prove that the quasi potential can also be obtained from a static variational problem introduced by Derrida, Lebowitz, and Speer.     

高超声速化学非平衡流动MHD效应的数值模拟

对偶极子磁场作用下的三维钝头体高超声速黏性绕流的化学非平衡流动进行了数值模拟.计算结果表明,在偶极子磁场强度为1.353 T时,与无磁场作用时相比,激波的脱体距离增加,增幅约为50%;壁面压力系数下降,局部下降最大达37%;壁面摩擦系数减小,局部最大可减小20%.同时,计算结果与磁场作用下的冻结流进行了比较,结果显示化学非平衡流中激波脱体距离比冻结流中小50%,滞止点温度低一半.     

Stationary nonequilibrium states in the Ising model with locally competing temperatures

We study kinetic one- and two-dimensional Ising models whose transition probabilities occur according to two (or more) locally competing temperatures. The model is solved analytically and studied numerically on different assumptions to reveal a variety of stationary nonequilibrium states and phase transitions; we also investigate the system relaxation in some typical cases.     

Penetration of a low-pressure reflex-discharge plasma into a hollow electrode

It is shown experimentally that the plasma of a hollow-cathode reflex discharge is characterized by a nonequilibrium electron velocity distribution. The parameters of the electron distribution, which is approximated by a superposition of two Maxwellian distributions with different temperatures, are estimated. The penetration of the discharge plasma into the hollow cathode at various cathode potentials and a gas pressure of ∼10^{\t− 2} Pa is studied. It is shown that the plasma parameters in the hollow electrode depend not only on the parameters of the reflex-discharge plasma, but also on the magnitude and configuration of the magnetic and electric fields in the plasma expansion region. It is shown that the plasma penetration can be accompanied by quasineutrality violation and the formation of space-charge double layers. Experiments confirm that the ion current from the nonequilibrium plasma exceeds the Bohm current.     

Nonequilibrium dynamical phase transition of 3D kinetic Ising／Heisenberg spin system

We have studied the nonequilibrium dynamic phase transitions of both three-dimensional (3D) kinetic Ising and Heisenberg spin systems in the presence of a perturbative magnetic field by Monte Carlo simulation. The feature of the phase transition is characterized by studying the distribution of the dynamical order parameter. In the case of anisotropic Ising spin system (ISS), the dynamic transition is discontinuous and continuous under low and high temperatures respectively, which indicates the existence of a tri-critical point (TCP) on the phase boundary separating low-temperature order phase and high-temperature disorder phase. The TCP shifts towards the higher temperature region with the decrease of frequency, i.e. T_{TCP}=1.33×exp(-ω/30.7). In the case of the isotropic Heisenberg spin system (HSS), however, the situation on dynamic phase transition of HSS is quite different from that of ISS in that no stable dynamical phase transition was observed in kinetic HSS after a threshold time. The evolution of magnetization in the HSS driven by a symmetrical external field after a certain duration always tends asymptotically to a disorder state no matter what an initial state the system starts with. The threshold time τ depends upon the amplitude H_{0}, reduced temperature T/T_C and the frequency ω as τ=C·ω^α·H_0^{-β}·(T/T_C)^{-γ}.     

Intriguing heat conduction of a chain with transverse motions

We study heat conduction in a one-dimensional chain of particles with longitudinal as well as transverse motions. The particles are connected by two-dimensional harmonic springs together with bending angle interactions. Using equilibrium and nonequilibrium molecular dynamics, three types of thermal conducting behaviors are found: a logarithmic divergence with system sizes for large transverse coupling, 1/3 power law at intermediate coupling, and 2/5 power law at low temperatures and weak coupling. The results are consistent with a simple mode-coupling analysis of the same model. We suggest that the 1/3 power-law divergence should be a generic feature for models with transverse motions.     

Simple model for active nematics: quasi-long-range order and giant fluctuations

We propose a simple microscopic model for active nematic particles similar in spirit to the Vicsek model for self-propelled polar particles. In two dimensions, we show that this model exhibits a Kosterlitz-Thouless-like transition to quasi-long-range orientational order and that in this nonequilibrium context, the ordered phase is characterized by giant density fluctuations, in agreement with the predictions of Ramaswamy et al.     

Photoinduced superstructure in the low-temperature phase of a Peierls system

This paper is a theoretical study of the properties of the low-temperature phase of a Peierls system when nonequilibrium electron-hole pairs are excited in the phase. A microscopic theory is developed to show that at low temperatures a spatially nonuniform periodic structure with a modulated band gap forms in the thermodynamically nonequilibrium system considered. The critical temperature of formation of such a superstructure, the critical electron-hole pair concentration, the spatial period, and the percentage modulation are calculated. Zh. éksp. Teor. Fiz. 115, 1297–1314 (April 1999)     

Optical properties of nonequilibrium low-dimensional systems

The optical properties of low-dimensional carrier systems ("quantum wire" type) driven away from equilibrium are studied. The frequency and wave-vector-dependent dielectric function of a quasi-one-dimensional electron system under the action of an exciting external pumping source is derived. The optical responses of the system are obtained in terms of its nonequilibrium thermodynamic state, the latter characterized resorting to a nonequilibrium statistical ensemble formalism.     

Fractal dimension of steady nonequilibrium flows

The Kaplan-Yorke information dimension of phase-space attractors for two kinds of steady nonequilibrium many-body flows is evaluated. In both cases a set of Newtonian particles is considered which interacts with boundary particles. Time-averaged boundary temperatures are imposed by Nose-Hoover thermostat forces. For both kinds of nonequilibrium systems, it is demonstrated numerically that external isothermal boundaries can drive the otherwise purely Newtonian flow onto a multifractal attractor with a phase-space information dimension significantly less than that of the corresponding equilibrium flow. Thus the Gibbs' entropy of such nonequilibrium flows can diverge.     

Entropy production in nonequilibrium systems at stationary states

We present a stochastic approach to nonequilibrium thermodynamics based on the expression of the entropy production rate advanced by Schnakenberg for systems described by a master equation. From the microscopic Schnakenberg expression we get the macroscopic bilinear form for the entropy production rate in terms of fluxes and forces. This is performed by placing the system in contact with two reservoirs with distinct sets of thermodynamic fields and by assuming an appropriate form for the transition rate. The approach is applied to an interacting lattice gas model in contact with two heat and particle reservoirs. On a square lattice, a continuous symmetry breaking phase transition takes place such that at the nonequilibrium ordered phase a heat flow sets in even when the temperatures of the reservoirs are the same. The entropy production rate is found to have a singularity at the critical point of the linear-logarithm type.