Nonequilibrium Features Research Articles

Geometry of quantum evolution in a nonequilibrium environment

We theoretically study the geometric effect of quantum dynamical evolution in the presence of a nonequilibrium noisy environment. We derive the expression of the time-dependent geometric phase in terms of the dynamical evolution and the overlap between the time evolved state and initial state. It is shown that the frequency shift induced by the environmental nonequilibrium feature plays a crucial role in the geometric phase and evolution path of the quantum dynamics. The nonequilibrium feature of the environment makes the length of the evolution path become longer and reduces the dynamical decoherence and non-Markovian behavior in the quantum dynamics.

Non-equilibrium spontaneous condensation flow in cryogenic turbo-expander based on mean streamline off-design method

In a modern cryogenic liquefaction system, the turbo-expander is used to operate in the two-phase region so that a high cooling capacity can be provided. Compared with the expansion process in a conventional over-heated turbo-expander, non-equilibrium condensation occurs in the duct when the turbo-expander operates in the two-phase region, which varies the expansion process. In our previous works, the simulation by CFX can predict the nucleation process controlled by gaseous sub-cooling well, and the outlet liquid fraction has a good agreement with our experimental data. As the non-equilibrium condensation simulated by using CFX consumes much time and massive computing resource, it is not feasible to simulate the two-phase expansion in the turbo-expander in a wide off-design range. In this study, we investigate the non-equilibrium spontaneous condensation along the mean streamline of a cryogenic turbo-expander passage by using an off-design computational code compiled by Matlab. The two-phase off-design computational code is developed from our previous overheated off-design code. The calculation function of thermodynamic parameters on the mean streamline and non-equilibrium condensation module are integrated with this code. The variations of thermodynamic parameters on the mean streamline in a non-equilibrium condensation process are simulated. Nucleation onset, droplet growth/vaporization process, liquid fraction distribution are revealed. Droplet developing region is divided according to the droplet critical and mean radius. Simulation results of five two-phase cases are compared and analyzed, and different non-equilibrium condensation features and liquid fraction distributions are found. At last, isentropic efficiency and outlet liquid fraction are used to evaluate two-phase expansion performance, and it is found that the performance results from the simulation in five cases agree with experimental data well.

Plasma-nano-interface in perspective: from plasma-for-nano to nano-plasmas

This article introduces an updated focus of plasma nanoscience after a dozen years of successful international research efforts. The concept of plasma-nano-interface involves two fundamental options: plasmas in contact with nanoscale features and plasmas which have nanoscale dimensions on their own. Non-equilibrium and transient features pertinent to the both cases are discussed in view of the recent progress in the field. Plasma-like phenomena in nanometer-sized materials, the third dimension of plasma nanoscience, also benefit from the insights based on fundamentals of plasma physics. Opportunities for future science discoveries, cross-disciplinary collaborations and translational research and development are highlighted.

Light propagation through one-dimensional interacting open quantum systems

We apply the quantum Langevin equations approach to study nonlinear light propagation through one-dimensional interacting open quantum lattice models. We write a large set of quantum Langevin equations of lattice operators obtained after integrating out the light fields and use them to derive nonequilibrium features of the lattice models. We first consider a Heisenberg like interacting spin-1/2 chain with nearest-neighbor coupling. The transient and steady-state transport properties of an incoming monochromatic laser light are calculated for this model. We find how the local features of the spin chain and the chain length dependence of light transport coefficient evolve with an increasing power of the incident light. The steady-state light transmission coefficient at a higher power depends non-monotonically on the interaction in a finite chain. While the nonlinear light transmission in our studied model seems to be ballistic in the absence of interaction and for a high interaction, it shows an apparent system-size dependence at intermediate interactions. Later, we extend this method to the long-range interaction between spins of the driven-dissipative lattice model and to incorporate various losses typical in many atomic and solid-state systems.

"New Monitoring Geophysical Systems by Oil Deposits Extraction"

The processes of oil deposit development are linked with the movement of multi-phase multi-component media, which are characterized by nonequilibrium and non-linear rheological features. The real behavior of layered systems is defined by the complexity of the rheology of moving fluids and the morphology structure of the porous medium, and also by the great variety of interactions between the fluid and the porous medium [1]. It is necessary to take into account these features in order to informatively describe the filtration processes due to the non-linearity, non-equilibrium and heterogeneity that are features of real systems. In this way, new synergetic events can be revealed (namely, a loss of stability when oscillations occur, and the formation of ordered structures). This allows us to suggest new methods for the control and management of complicated natural systems that are constructed on account of these phenomena. Thus the layered system, from which it is necessary to extract the oil, is a complicated dynamical hierarchical system. To construct the mathematical model of a real object, as a priori information it is necessary to use data from active and passive monitoring, which we can obtain during exploitation of the object. The solution of inverse problems has great significance for the oil industry, because the oil layer refers to a number of natural systems that cannot be observed as a whole by direct measurements. The results of last year’s research showed that in the evolution of dynamic systems, non-stabilities and their origin play a role in the theory of self organization or synergetic studies. Information about their manifestation in the oil reservoir from its extraction can only be obtained using monitoring data, which is sensitive to its hierarchical structure. It should be noted that, to study the thin structure of the discrete hierarchical media, geophysical fields are more sensitive, depending on spatial, time or frequency parameters–namely, electromagnetic and seismic fields. In addition, these fields, excited by local sources due to the geometry of the normal field, have a focusing or localization property that allows the given resolution to be distinguished. For the new methods of wave monitoring is constructed a new theory of distribution wave fields in a medium of hierarchical structure with different physical features.

Thermodynamic Nonequilibrium Features in Binary Diffusion**Supported by the MOST National Key Research and Development Programme under Grant No. 2016YFB0600805, the China Post-doctoral Science Foundation under Grant No. 2017M620757, the Center for Combustion Energy at Tsinghua University, Natural Science Foundation of Hebei Province under Grant Nos. A2017409014, ZD2017001 and A201500111, FJKLMAA, Fujian Normal University, and the UK Engineering and Physical Sciences

Diffusion is a ubiquitous physical phenomenon where thermodynamic nonequilibrium effects (TNEs) are outstanding issues. In this work, we employ the discrete Boltzmann method to investigate the TNEs in the dynamic process of binary diffusion. The main features of the distribution function in velocity space are recovered and discussed. It is found that, with the decreasing gradients of macroscopic quantities (such as density, concentration, velocity, etc.), both the local and global TNEs decrease with the time but increase with the relaxation time in a power law, respectively.

Present status of numerical modeling of hydrogen negative ion source plasmas and its comparison with experiments: Japanese activities and their collaboration with experimental groups

The present status of kinetic modeling of particle dynamics in hydrogen negative ion (H−) source plasmas and their comparisons with experiments are reviewed and discussed with some new results. The main focus is placed on the following topics, which are important for the research and development of H− sources for intense and high-quality H− ion beams: (i) effects of non-equilibrium features of electron energy distribution function on volume and surface H− production, (ii) the origin of the spatial non-uniformity in giant multi-cusp arc-discharge H− sources, (iii) capacitive to inductive (E to H) mode transition in radio frequency-inductively coupled plasma H− sources and (iv) extraction physics of H− ions and beam optics, especially the present understanding of the meniscus formation in strongly electronegative plasmas (so-called ion–ion plasmas) and its effect on beam optics. For these topics, mainly Japanese modeling activities, and their domestic and international collaborations with experimental studies, are introduced with some examples showing how models have been improved and to what extent the modeling studies can presently contribute to improving the source performance. Close collaboration between experimental and modeling activities is indispensable for the validation/improvement of the modeling and its contribution to the source design/development.

Kappa and other nonequilibrium distributions from the Fokker-Planck equation and the relationship to Tsallis entropy.

This paper considers two nonequilibrium model systems described by linear Fokker-Planck equations for the time-dependent velocity distribution functions that yield steady state Kappa distributions for specific system parameters. The first system describes the time evolution of a charged test particle in a constant temperature heat bath of a second charged particle. The time dependence of the distribution function of the test particle is given by a Fokker-Planck equation with drift and diffusion coefficients for Coulomb collisions as well as a diffusion coefficient for wave-particle interactions. A second system involves the Fokker-Planck equation for electrons dilutely dispersed in a constant temperature heat bath of atoms or ions and subject to an external time-independent uniform electric field. The momentum transfer cross section for collisions between the two components is assumed to be a power law in reduced speed. The time-dependent Fokker-Planck equations for both model systems are solved with a numerical finite difference method and the approach to equilibrium is rationalized with the Kullback-Leibler relative entropy. For particular choices of the system parameters for both models, the steady distribution is found to be a Kappa distribution. Kappa distributions were introduced as an empirical fitting function that well describe the nonequilibrium features of the distribution functions of electrons and ions in space science as measured by satellite instruments. The calculation of the Kappa distribution from the Fokker-Planck equations provides a direct physically based dynamical approach in contrast to the nonextensive entropy formalism by Tsallis [J. Stat. Phys. 53, 479 (1988)JSTPBS0022-471510.1007/BF01016429].

The development and application of two-time-scale turbulence models for non-equilibrium flows

This study re-visits the largely overlooked, but highly promising, topic of multi-scale RANS modelling for non-equilibrium turbulent flows. The paper presents the development of RANS models which, at an effective-viscosity level, involve two transport equations for the turbulent kinetic energy; one for the energy of the large scale, energy-producing, eddies and one for that of the smaller eddies, which, through continuous break-up, transfer turbulence energy to the dissipative scales. Two transport equations for the transfer-rate of the turbulent kinetic energy are also necessary, one for the rate of energy transfer from the large to the smaller scales and one for the rate of transfer from the smaller to the dissipative scales, the latter being of course the dissipation rate of turbulence. The two-time-scale model of Hanjalic et al. (1980) has been the starting point of the current developments. The coefficients of the terms which appear in these models have been determined from asymptotic analyses of decaying grid turbulence, homogeneous shear flows and local-equilibrium boundary-layer flows. The models were subsequently further developed to become more responsive to strong non-equilibrium features, such as those caused by strong shear. It has been identified that in general, models which have been optimised to satisfy equilibrium flows (as is usually done) are unable to capture the strong changes the flows are subjected to due to highly non-equilibrium effects, thus needing further development. Within the two-time-scale framework, it has been found possible to overcome this problem, by exploiting the additional information available on the turbulence spectrum. In a further departure from the development of earlier effective-viscosity two-time scale models, here the eddy viscosity expression is made sensitive to the local strain rate, as was also the case in single-scale models developed by Craft et al. (1996).The original contribution of this research is the development of two widely tested two-time-scale linear-eddy-viscosity models, referred to here as NT1 and NT2. The difference between these two models is primarily in the eddy viscosity formulation. The two resulting models have been tested over nine test cases and their performance has been compared to those of the standard high-Reynolds number k−ɛ model, the SSG Reynolds stress transport model and the two-time-scale model of Hanjalic et al. (1980). The test cases comprise of homogeneous shear and normally strained flows, adverse-pressure-gradient, favourable-pressure-gradient and oscillatory boundary layer flows, fully developed oscillatory and ramp up pipe flows and steady and pulsated backward-facing step flows. The models proposed here show considerable promise. They perform well in all cases tested and provide clear improvements over a range of single- and multi-scale models tested in an earlier study (Klein et al., 2015), over a set of test cases which cover a wide range of physical flow phenomena. Moreover, these improvements are achieved without any significant increase in computational requirements in comparison to the computational needs of single-time-scale eddy-viscosity models.

Scale‐dependent nonequilibrium features in a bubbling fluidized bed

We investigate experimentally the nonequilibrium features in a pseudo 2‐D bubbling fluidized bed. Velocities of individual particles are measured by using a particle tracking velocimetry (PTV) method, and void fractions are obtained with the Voronoi tessellation. A bimodal shape of probability density function (PDF) for particle vertical velocity is found in not only time‐averaged but also time‐varying statistics, which is caused by the transition between the dense and dilute phases and breaks the local‐equilibrium assumption in continuum modeling of fluidized beds. The results of time‐varying radial distribution function and voidage distribution also confirm this finding. Moreover, the analysis of voidage, particle velocity, granular temperature and turbulent kinetic energy of particles shows that there is no scale‐independent plateau over the interface, and it seems hard to find a scale‐independent plateau to separate the micro‐ and meso‐scales of fluidized beds, which require sub‐grid meso‐scale modeling for continuum or coarse‐graining methods of gas‐fluidized systems. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2364–2378, 2018

Deciphering hierarchical features in the energy landscape of adenylate kinase folding/unfolding

Hierarchical features of the energy landscape of the folding/unfolding behavior of adenylate kinase, including its dependence on denaturant concentration, are elucidated in terms of single-molecule fluorescence resonance energy transfer (smFRET) measurements in which the proteins are encapsulated in a lipid vesicle. The core in constructing the energy landscape from single-molecule time-series across different denaturant concentrations is the application of rate-distortion theory (RDT), which naturally considers the effects of measurement noise and sampling error, in combination with change-point detection and the quantification of the FRET efficiency-dependent photobleaching behavior. Energy landscapes are constructed as a function of observation time scale, revealing multiple partially folded conformations at small time scales that are situated in a superbasin. As the time scale increases, these denatured states merge into a single basin, demonstrating the coarse-graining of the energy landscape as observation time increases. Because the photobleaching time scale is dependent on the conformational state of the protein, possible nonequilibrium features are discussed, and a statistical test for violation of the detailed balance condition is developed based on the state sequences arising from the RDT framework.

Interpreting the Combustion Process for High-Performance ZrNiSn Thermoelectric Materials.

The ZrNiSn alloy, a member of the half-Heusler family of thermoelectric materials, shows great potential for mid-to-high-temperature power generation applications due to its excellent thermoelectric properties, robust mechanical properties, and good thermal stability. The existing synthesis processes of half-Heusler alloys are, however, rather time and energy intensive. In this study, single-phase ZrNiSn bulk materials were prepared by self-propagating high-temperature synthesis (SHS) combined with spark plasma sintering (SPS) for the first time. The analysis of thermodynamic and kinetic processes shows that the SHS reaction in the ternary ZrNiSn alloy is different from the more usual binary systems. It consists of a series of SHS reactions and mass transfers triggered by the SHS fusion of the binary Ni-Sn system that eventually culminates in the formation of single-phase ternary ZrNiSn in a very short time, which reduced the synthesis period from few days to less than an hour. Moreover, the nonequilibrium feature induces Ni interstitials in the structure, which simultaneously enhances the electrical conductivity and decreases the thermal conductivity, which is favorable for thermoelectric properties. The maximum thermoelectric figure of merit ZT of the SHS + SPS-processed ZrNiSn1-xSbx alloy reached 0.7 at 870 K. This study opens a new avenue for the fast and low-cost fabrication of half-Heusler thermoelectric materials.

Highly excited exciton-polariton condensates

Exciton-polaritons are a coherent electron-hole-photon (e-h-p) system where condensation has been observed in semiconductor microcavities. In contrast to equilibrium Bose-Einstein condensation (BEC) for long lifetime systems, polariton condensates have a dynamical nonequilibrium feature owing to the similar physical structure that they have to semiconductor lasers. One of the distinguishing features of a condensate to a laser is the presence of strong coupling between the matter and photon fields. Irrespective of its equilibrium or nonequilibrium nature, exciton-polariton have been observed to maintain strong coupling. We show that by investigating high density regime of exciton-polariton condensates, the negative branch directly observed in photoluminescence. This is evidence that the present e-h-p system is still in the strong coupling regime, contrary to past results where the system reduced to standard lasing at high density.

Non-Markovian Two-Time Correlation Dynamics and Nonergodicity

The two-time correlation functions of the coordinate and velocity of a non-Markovian harmonic particle are derived analytically. They are decomposed into the components of differences between the initial variances and the equilibrium of the particle; in particular, the dependence of a random force on the initial preparation of the system is included. Using those expressions, we simultaneously investigate nonstationary, nonergodic, and nonequilibrium features of a forced system. It is demonstrated that the result of combining the oscillating relaxation and the initial preparation-dependent noise leads to breakdown of both ergodicity and equilibration of a forced system. The finite-size effect of a coupled-oscillator-chain heat bath is also discussed.

Quantum dynamical speedup in a nonequilibrium environment

We theoretically study the dynamical speedup of a quantum system in a nonequilibrium environment. Based on the trace distance, we derive the generalized Margolus-Levitin and Mandelstam-Tamm types of bounds on the quantum speed limit time of a quantum system evolving from an arbitrary initial state. We demonstrate that the mechanism for the speedup of dynamical evolution is closely associated with both the energy of the system and exchange of information between the system and its environment. It is shown that the nonequilibrium feature of the environment can speed up the quantum evolution in both Markovian and non-Markovian dynamics regions. We emphasize that the non-Markovian effect of the system dynamics is neither necessary nor sufficient to speed up the quantum evolution in a nonequilibrium environment.

Nonequilibrium-induced enhancement of dynamical quantum coherence and entanglement of spin arrays

The random magnetic field produced by nuclear spins has long been viewed as the dominating source of decoherence in the quantum-dot based spins. Here we obtain in both exact and analytical manner the dynamics of spin qubits coupled to nuclear spin environments via the hyperfine interaction, going beyond the weak system-bath interaction and Markovian approximation. We predict that the detailed-balance breaking produced by chemical potential gradient in nuclear baths leads to the rapid oscillations of populations, quantum coherence and entanglement, which are absent in the conventional case (i.e., Overhauser noise). This is attributed to the nonequilibrium feature of the system as shown in the relation between the oscillation period and the chemical potential imbalance. Our results reveal the essentiality of nonequilibriumness with detailed-balance breaking for enhancing the dynamical coherence and entanglement of spin qubits. Moreover, our exact solution explicitly demonstrates that the non-Markovian bath comprised by nuclear spins can preserve the collective quantum state, due to the recovery of coherence. Finally, we propose an experiment using ultracold trapped ions to observe these nonequilibrium and memory effects.

Energy Transfer Dynamics of Formate Decomposition on Cu(110).

Energy transfer dynamics of formate (HCOOa ) decomposition on a Cu(110) surface has been studied by measuring the angle-resolved intensity and translational energy distributions of CO2 emitted from the surface in a steady-state reaction of HCOOH and O2 . The angular distribution of CO2 shows a sharp collimation with the direction perpendicular to the surface, as represented by cosn θ (n=6). The mean translational energy of CO2 is measured to be as low as 100 meV and is independent of the surface temperature (Ts ). These results clearly indicate that the decomposition of formate is a thermal non-equilibrium process in which a large amount of energy released by the decomposition reaction of formate is transformed into the internal energies of CO2 molecules. The thermal non-equilibrium features observed in the dynamics of formate decomposition support the proposed Eley-Rideal (ER)-type mechanism for formate synthesis on copper catalysts.

Molecular dynamics simulation of strong shock waves propagating in dense deuterium, taking into consideration effects of excited electrons.

We present a molecular dynamics simulation of shock waves propagating in dense deuterium with the electron force field method [J. T. Su and W. A. Goddard, Phys. Rev. Lett. 99, 185003 (2007)PRLTAO0031-900710.1103/PhysRevLett.99.185003], which explicitly takes the excitation of electrons into consideration. Nonequilibrium features associated with the excitation of electrons are systematically investigated. We show that chemical bonds in D_{2} molecules lead to a more complicated shock wave structure near the shock front, compared with the results of classical molecular dynamics simulation. Charge separation can bring about accumulation of net charges on large scales, instead of the formation of a localized dipole layer, which might cause extra energy for the shock wave to propagate. In addition, the simulations also display that molecular dissociation at the shock front is the major factor that accounts for the "bump" structure in the principal Hugoniot. These results could help to build a more realistic picture of shock wave propagation in fuel materials commonly used in the inertial confinement fusion.

AC transport and full-counting statistics of molecular junctions in the weak electron-vibration coupling regime

The coupling of the charge carriers passing through a molecule bridging two bulky conductors with local vibrational modes of the molecule gives rise to distinct features in the electronic transport properties on one hand and to nonequilibrium features in the vibrations’ properties, e.g., their population, on the other. Here we explore theoretically a generic model for a molecular junction biased by an arbitrary dc voltage in the weak-coupling regime. We succinctly summarize parts of our past work related to the signature of the electron-vibration interaction on the full-counting statistics of the current fluctuations (i.e., the cumulant generating-function of the current correlations). In addition, we provide a novel account of the response to an ac field exerted on the junction (on top of the dc bias voltage); in particular, we study the nonequilibrium distribution and the displacement fluctuations of the vibrational modes. Remarkably, we find a behavior pattern that cannot be accounted for by classical forced oscillations. The calculations use the technique of nonequilibrium Green’s functions and treat the electron-vibration coupling in perturbation theory, within the random-phase approximation when required.

Effect of the Charge Regulation Behavior of Polyelectrolytes on Their Nonequilibrium Complexation with Oppositely Charged Surfactants.

The nonequilibrium features of oppositely charged macromolecule/surfactant mixtures have been the subject of intensive research recently. Although the nature and extent of polyion charge crucially affect the development of trapped states in these systems, their role in the nonequilibrium association is still poorly understood. In the present study, the impact of mixing on the complexation of hexadecyltrimethylammonium bromide (CTAB) with sodium poly[(vinyl alcohol)-co-(vinyl sulfate)] (PVAS) and poly(acrylic acid) (PAA) samples of similar charge densities has been compared using a variety of experimental methods. The results indicate largely different nonequilibrium behavior depending on the polyions. In the case of the weak polyacid PAA, the binding of CTAB increases its ionization degree, which leads to enhanced equilibrium two-phase concentration range, where kinetically arrested states can be observed upon rapid mixing of the solution components. In contrast, the charge density of the double-hydrophilic PVAS copolymer is fixed, and in addition to the binding of CTAB onto its vinyl sulfate groups, the surfactant molecules also bind onto the vinyl alcohol segments of the copolymer. These factors result in reduced precipitation concentration range and diminishing nonequilibrium effects with decreasing polyion charge density. Our study clearly demonstrates that the charge regulation behavior of various polyelectrolytes can be successfully used to tune the nonequilibrium characteristics of macromolecule/surfactant association.