Nonequilibrium Features Research Articles

Centrosomes are autocatalytic droplets of pericentriolar material organized by centrioles.

Centrosomes are highly dynamic, spherical organelles without a membrane. Their physical nature and their assembly are not understood. Using the concept of phase separation, we propose a theoretical description of centrosomes as liquid droplets. In our model, centrosome material occurs in a form soluble in the cytosol and a form that tends to undergo phase separation from the cytosol. We show that an autocatalytic chemical transition between these forms accounts for the temporal evolution observed in experiments. Interestingly, the nucleation of centrosomes can be controlled by an enzymatic activity of the centrioles, which are present at the core of all centrosomes. This nonequilibrium feature also allows for multiple stable centrosomes, a situation that is unstable in equilibrium phase separation. Our theory explains the growth dynamics of centrosomes for all cell sizes down to the eight-cell stage of the Caenorhabditis elegans embryo, and it also accounts for data acquired in experiments with aberrant numbers of centrosomes and altered cell volumes. Furthermore, the model can describe unequal centrosome sizes observed in cells with perturbed centrioles. We also propose an interpretation of the molecular details of the involved proteins in the case of C. elegans. Our example suggests a general picture of the organization of membraneless organelles.

DETAILED AND SIMPLIFIED NONEQUILIBRIUM HELIUM IONIZATION IN THE SOLAR ATMOSPHERE

Helium ionization plays an important role in the energy balance of the upper chromosphere and transition region. Helium spectral lines are also often used as diagnostics of these regions. We carry out 1D radiation-hydrodynamics simulations of the solar atmosphere and find that the helium ionization is mostly set by photoionization and direct collisional ionization, counteracted by radiative recombination cascades. By introducing an additional recombination rate mimicking the recombination cascades, we construct a simplified 3 level helium model atom consisting of only the ground states. This model atom is suitable for modeling non-equilibrium helium ionization in 3D numerical models. We perform a brief investigation of the formation of the He I 10830 and He II 304 spectral lines. Both lines show non-equilibrium features that are not recovered with statistical equilibrium models, and caution should therefore be exercised when such models are used as a basis in the interpretation of observations.

Microstructure, phases morphologies and hardness of a Bi–Ag eutectic alloy for high temperature soldering applications

The conversion to RoHS-compliant lead-free assembly has been a considerable challenge to the electronics industry. Among several alternative solder alloys, Bi–Ag alloys have been highlighted as a potential candidate to replace high Pb solder alloys for applications in oil and gas, automotive and avionics industries. The typical melting temperatures of Bi–Ag near-eutectic alloys are considered acceptable and excellent mechanical properties may be achieved with appropriate microstructures. Such promising alloys for high temperature soldering remain barely understood especially regarding non-equilibrium solidification features. In this study, a directional solidification experiment was carried out with the Bi–2.5wt%Ag eutectic so that a large range of cooling rates (Ṫ) could be obtained under unsteady-state conditions. The experimental investigation include: thermal solidification parameters (growth rate, v and cooling rate, Ṫ), microstructure parameters (eutectic/dendritic spacing, interphase spacings) and phases morphologies analyzed by optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and hardness. Experimental interrelations between hardness and microstructure (scale and morphology) of the eutectic Bi–Ag are reported. Solidification parameters are also associated with each configuration observed along the casting, i.e., coexistence of dendrites and eutectic cells for regions very close to the cooled casting surface, eutectic cells prevailing and eutectic cells together with β-Bi primary phase. The cell spacing, λc, is correlated with hardness by Hall–Petch type equations.

Kinetic modeling of particle dynamics in H− negative ion sources (invited)

Progress in the kinetic modeling of particle dynamics in H(-) negative ion source plasmas and their comparisons with experiments are reviewed, and discussed with some new results. Main focus is placed on the following two topics, which are important for the research and development of large negative ion sources and high power H(-) ion beams: (i) Effects of non-equilibrium features of EEDF (electron energy distribution function) on H(-) production, and (ii) extraction physics of H(-) ions and beam optics.

Numerical analysis of atomic density distribution in arc driven negative ion sources

The purpose of this study is to calculate atomic (H(0)) density distribution in JAEA 10 ampere negative ion source. A collisional radiative model is developed for the calculation of the H(0) density distribution. The non-equilibrium feature of the electron energy distribution function (EEDF), which mainly determines the H(0) production rate, is included by substituting the EEDF calculated from 3D electron transport analysis. In this paper, the H(0) production rate, the ionization rate, and the density distribution in the source chamber are calculated. In the region where high energy electrons exist, the H(0) production and the ionization are enhanced. The calculated H(0) density distribution without the effect of the H(0) transport is relatively small in the upper region. In the next step, the effect should be taken into account to obtain more realistic H(0) distribution.

Low temperature behavior of nonequilibrium multilevel systems

In this paper, we give a low temperature formula for the stationary occupations in Markovian systems away from detailed balance. Two applications are discussed, one to determine the direction of the ratchet current and one on population inversion. Both of these applications can take advantage of low temperatures to improve the gain and typical nonequilibrium features. Our new formula brings to the foreground the importance of kinetic aspects in terms of reactivities for deciding the levels with highest occupation and, thus, gives a detailed quantitative meaning to Landauer's blowtorch theorem at low temperatures.

Numerical study of atomic production rate in hydrogen negative ion sources with the effect of non-equilibrium electron energy distribution function

Spatial non-uniformity of the dissociative hydrogen atom (H0) production has been investigated in a large negative ion source (JAEA 10 A source) with the electron energy distribution function (EEDF) obtained by a Monte-Carlo simulation code for electron transport in 3D3V (three dimensional real and velocity) space. It has been shown that the H0 production rate becomes larger in the upper region (one side in the longitudinal direction) of the source chamber. This spatial non-uniformity of the H0 production profile is mainly explained by the non-equilibrium features of the EEDF in the upper region, i.e., the EEDF consists of thermal electron component with kinetic energy ε < 25 eV and fast electron component with energy ε > 25 eV in the upper region, while the EEDF mainly consists of only thermal electrons in the bottom region. These characteristics for the EEDF and the energy dependence of cross-sections for dissociation and dissociative ionization processes lead to the non-uniform profile of the H0 production. The above numerical results of the spatial H0 non-uniformity are validated and confirmed by comparisons with those by spectroscopic measurement. It has been clarified that the non-equilibrium (fast electron) component of the EEDF has a large contribution to the non-uniformity of the H0 production rate.

Interacting Anderson insulators: The intrinsic electron glass

Abstract The out-of-equilibrium transport properties of Anderson insulators exhibit many glassy features such as slow relaxation, slow approach to a steady state, ageing, and other memory effects. These non-equilibrium features were theoretically anticipated and are believed to result from the interplay between disorder and interactions. Here we review the field-effect experiments that establish the generic nature of electron glasses. It is pointed out that the common feature to all systems that exhibit the characteristic electron-glass properties is their relatively high carrier concentration. Experiments performed as a function of the carrier concentration indicate that below a critical value, the relaxation time becomes very short. It is suggested that this may be the reason why lightly doped semiconductors do not exhibit intrinsic electron-glass effects. The possible connection between the Coulomb gap and the memory dip is discussed.

Temperature Dependence of Highly Excited Exciton Polaritons in Semiconductor Microcavities

Observations of polariton condensation in semiconductor microcavities suggest that polaritons can be exploited as a novel type of laser with low input-power requirements. The low-excitation regime is approximately equivalent to thermal equilibrium, and a higher excitation results in more dominant nonequilibrium features. Although standard photon lasing has been experimentally observed in the high excitation regime, e-h pair binding can still remain even in the high-excitation regime theoretically. Therefore, the photoluminescence with a different photon lasing mechanism is predicted to be different from that with a standard photon lasing. In this paper, we report the temperature dependence of the change in photoluminescence with the excitation density. The second threshold behavior transited to the standard photon lasing is not measured at a low-temperature, high-excitation power regime. Our results suggest that there may still be an electron--hole pair at this regime to give a different photon lasing mechanism.

Nonunitary geometric phases: A qubit coupled to an environment with random noise

We describe the decoherence process induced on a two-level quantum system in direct interaction with a non-equilibrium environment. The non-equilibrium feature is represented by a non-stationary random function corresponding to the fluctuating transition frequency between two quantum states coupled to the surroundings. In this framework, we compute the decoherence factors which have a characteristic "dip" related to the initial phases of the bath modes. We therefore study different types of environments, namely ohmic and supra-ohmic. These environments present different decoherence time-scales than the thermal environment we used to study. As a consequence, we compute analytically and numerically the non-unitary geometric phase for the qubit in a quasi-cyclic evolution under the presence of these particular non-equilibrium environments. We show in which cases decoherence effects could, in principle, be controlled in order to perform a measurement of the geometric phase using standard procedures.

An analytical study on nonequilibrium dissociating gas flow behind a strong bow shockwave under rarefied conditions

In this paper, an explicitly analytical shock mapping relation is approximately deduced based on the theoretical modeling of the chemical nonequilibrium stagnation flow towards a slightly blunted nose. Based on the relation, the complex reacting stagnation flow problem can be discussed under the framework of the simplest normal shockwave flow. Therefore, a quantitatively meaningful criterion for dissociation nonequilibrium flow, that is a specific Damkohler number Dad, is naturally introduced as the ratio of the mapping length of the stagnation streamline and the characteristic nonequilibrium scale. Dad is found to be dependent on the flow’s rarefaction criterion Wr, that is a specific Knudsen number. Then, based on Dad, a normalized analytical formulation is obtained to quantitatively predict the actual degrees of dissociation at the outer edge of the stagnation point boundary layer (SPBL). At last, the direct simulation Monte Carlo (DSMC) method is employed to validate the analytical results, and the related flow mechanism is discussed. The present study not only shows nonequilibrium features of the flow problem, but also provides an indispensable basis for the following study on the nonequilibrium SPBL heat transfer.

Nonequilibrium Features of N2 and Oil System

Nonequilibrium state is a universal phenomenon in gas injection development. However, in previous researches and applications, it tends to be regarded as quasi-equilibrium state, or even equilibrium state. Based on research work by pioneers, a simple model for measuring diffusivity of N2 in oil has been developed. In addition, laboratory experiments were performed in this study. Results indicate that an infinitely thin layer exists between N2 zone and oil zone in the pressure-volume-temperaturacelda (PVT) cell. Gas and oil molecules will slowly diffuse into one another across the sharp interface by convection, dispersion, and diffusion. Viscosity and gas oil ratio (GOR) are two important parameters representing the phase behavior features of the N2 and oil system. These dependent variables are related to parameters like pressure, temperature, and oil viscosity.

Nonequilibrium properties of an atomic quantum dot coupled to a Bose-Einstein condensate

We study nonequilibrium properties of an atomic quantum dot (AQD) coupled to a Bose-Einstein condensate (BEC) within Keldysh-Green's function formalism when the AQD level is varied harmonically in time. Nonequilibrium features in the AQD energy absorption spectrum are the side peaks that develop as an effect of photon absorption and emission. We show that atoms can be efficiently transferred from the BEC into the AQD for the parameter regime of current experiments with cold atoms.

On the Performance of Various Reynolds Stress Models in Resolving Non-equilibrium Features of Turbulent In-cylinder Engine Flows

In highly transient turbulent flows, the energy cascade and related dissipation rate of energy are key factors which must be modeled precisely to obtain the accurate computational predictions. The flow in diesel engines specifically during compression stroke is quite transient, so most commonly used eddy viscosity based turbulence models fail to predict the transitional characteristics of these types of flow. This paper focuses on performance appraisal of three versions of Reynolds stress turbulence models in resolving non-equilibrium features and transitional characteristics of turbulent in-cylinder engine flows. Results indicate that although these turbulence models give the same prediction of averaged quantities of turbulent flows (i.e. mean flow kinetic energy), their results are totally different in calculating non-equilibrium features and the turbulent length scales. According to calculated results, incompressible Launder–Reece–Rodi and Naot second-moment closure models give unreal estimations of the turbulent integral length scale during compression stroke, while the modified Launder–Reece–Rodi model predictions have more similarity with physical trends.

Nonequilibrium phenomena in damaged media and their effects on the elastic properties

Concrete, particularly if damaged, exhibits a peculiar nonlinear elastic behavior, which is mainly due to the coupling between nonequilibrium and nonlinear features, the two of which are intrinsically connected. More specifically, the formulation of a constitutive equation able to properly predict the dynamic behavior of damaged concrete is made difficult by the concomitant presence of two mechanisms: The modification of the microstructure of the medium and the transition to a new elastic state caused by a finite amplitude excitation (conditioning). Memory of that new state is kept when the excitation is removed, before relaxation back to the original elastic state takes place. Indeed, besides accounting for linear and nonlinear parameters, a realistic constitutive equation to be used in reliable prediction models should take into account nonequilibrium effects. Specific parameters, sensitive to finite amplitude excitations, should be introduced to provide information about conditioning effects. In this paper, experimental results indicating that nonlinearity of damaged concrete is memory-dependent will be presented and the implications of such findings in the development of physical models, with relevant outcomes for the characterization of hysteretical features, will be discussed.

Analysis of H atoms in a negative ion source plasma with the non-equilibrium electron energy distribution function

In negative ion sources for the neutral beam injection, it is important to calculate H atom flux onto the plasma grid (PG) surface for the evaluation of H(-) production on the PG surface. We have developed a neutral (H(2) molecules and H atoms) transport code. In the present study, the neutral transport code is applied to the analysis of the H(2) and H transport in a NIFS-R&D ion source in order to calculate the flux onto the PG surface. Taking into account non-equilibrium feature of the electron energy distribution function (EEDF), i.e., the fast electron component, we have done the neutral transport simulation. The results suggest that the precise evaluation of the EEDF, especially in the energy range 15 eV < E < 30 eV is important for the dissociation rate of H(2) molecules by the electron impact collision and the resultant H atom flux on the PG.

Glassy dynamics of crystallite formation: The role of covalent bonds

We examine nonequilibrium features of collapse behavior in model polymers with competing crystallization and glass transitions using extensive molecular dynamics simulations. By comparing to “colloidal” systems with no covalent bonds but the same non-bonded interactions, we find three principal results: (i) Tangent-sphere polymers and colloids, in the equilibrium-crystallite phase, have nearly identical static properties when the temperature T is scaled by the crystallization temperature Tcryst; (ii) Qualitative features of nonequilibrium relaxation below Tcryst, measured by the evolution of local structural properties (such as the number of contacts) toward equilibrium crystallites, are the same for polymers and colloids; and (iii) Significant quantitative differences in rearrangements in polymeric and colloidal crystallites, in both far-from equilibrium and near-equilibrium systems, can be understood in terms of chain connectivity. These results have important implications for understanding slow relaxation processes in collapsed polymers, partially folded, misfolded, and intrinsically disordered proteins.

Analysis of Thomson Scattering from Nonequilibrium Plasmas

We develop the theory for light scattering as a diagnostic method for plasmas in nonequilibrium states. We show how well-known nonequilibrium features, like beam acoustic modes, arise in the spectra. The analysis of an experiment with strongly driven electrons demonstrates the abilities of the new approach; we find qualitatively different scattering spectra for different times and excellent agreement with the experimental data after time integration. Finally, an analysis of data from dense beryllium suggests that an energetic electron component exists in this experiment as well.

Effect of Salt on the Equilibrium and Nonequilibrium Features of Polyelectrolyte/Surfactant Association

The impact of an electrolyte on aqueous mixtures of oppositely charged macromolecules and surfactants is usually explained by assuming an equilibrium association between the components. In this work, it is shown that the nonequilibrium character of polyelectrolyte/surfactant systems plays a crucial role in the interpretation of the effect of salt. Experimental investigations of mixtures of sodium poly(styrenesulfonate) (PSS) and hexadecyltrimethylammonium bromide (CTAB) reveal two distinct effects of added sodium chloride (NaCl). At small and moderate NaCl concentrations, the major impact of the electrolyte is manifested in the reduction of the kinetically stable composition range in which the PSS/CTAB mixtures are trapped in the nonequilibrium colloidal dispersion state. The application of high salt concentrations, however, primarily affects the equilibrium phase properties through considerably decreasing the amount of surfactant bound to the polyelectrolyte.

Equilibrium and Nonequilibrium Features in the Morphology and Structure of Physisorbed Polyelectrolyte Layers

AFM is used to characterize sodium poly(styrene sulfonate) (PSS) layers physisorbed from NaCl solutions with an ionic strength ranging between 0 and 1 M NaCl. Colloidal probe tapping mode imaging shows that domains of PSS salted brushes coexist with flatly adsorbed PSS. The brush area fraction increases with rising degree of polymerization. The surface forces (as measured with colloidal probe technique) are a superposition of steric and electrostatic forces; their respective contribution is determined by the brush area fraction. Unexpectedly, the internal properties of the brush domains (brush thickness and average chain distance) are independent of the deposition salt concentration. Both properties increase with rising polymer length/degree of polymerization, whereas only the brush thickness can be controlled by the surrounding salt concentration (equilibrium feature). Furthermore, we show that the amount of brush-like physisorbed PSS chains leads to an increase in PSS surface coverage, which is also observed with other techniques after addition of salt to the deposition solution (as is extensively described in literature).