Quasi-equilibrium Behavior Research Articles

Effect of Particle Size on Thermodynamics and Lithium Ion Transport in Ti2Nb2O9 Electrodes Synthesized By Solid State or Sol-Gel Method

Ti2Nb2O9 has been identified as a promising lithium-ion battery anode material with large specific capacity, small cycling degradation, and good capacity retention at large currents. This study aims to gain insight into the charging mechanisms as well as the thermodynamics and ion transport in Ti2Nb2O9 synthesized by the solid state or the sol-gel method and formed by particles of different sizes using potentiometric entropy and operando isothermal calorimetric measurements. First, electrochemical testing showed that Ti2Nb2O9 electrodes made by sol-gel synthesis exhibited larger specific capacity, smaller polarization between lithiation/delithiation, and better capacity retention at large currents compared to those made by solid state synthesis. The measured open-circuit voltage and entropic potential revealed that the same solid solution charging mechanism prevailed and was independent of particle size, as confirmed by in situ XRD measurements. In other words, particle size had no influence on the quasi-equilibrium thermodynamics behavior of Ti2Nb2O9. However, Ti2Nb2O9 electrodes made by sol-gel synthesis featured smaller overpotential and faster lithium diffusion. In fact, operando isothermal calorimetry revealed smaller instantaneous heat generation rates and smaller time-averaged irreversible heat generation rates at Ti2Nb2O9 electrodes made by sol-gel synthesis compared to those made by solid state synthesis at any given C-rate. These observations highlight the smaller resistive losses and the larger electrical conductivity of Ti2Nb2O9 synthesized by the sol-gel method. Furthermore, time-averaged reversible heat generation rates at Ti2Nb2O9 electrodes made by both synthesis methods featured significant contributions from entropic changes, ion adsorption/desorption, and ion solvation/desolvation accompanied by ion-pairing.

Charging processes of Na4Mn9O18 electrode in aqueous electrolyte

Recent trends in electrochemical energy storage –the renewed interest in aqueous electrolytes, the development of nanostructured and/or hybridized materials, the advent of unconventional systems– call for detailed analyses of charging processes. We address this issue in studying a sodium manganese oxide (Na4Mn9O18, NMO) electrode in aqueous environment. Charge storage is examined by cyclic voltammetry (CV) in a wide range of sweep rate (ν) and by equivalent circuit modelling of the electrode impedance response. Voltammetry shows that, with increasing ν, the insertion process evolves from a quasi-equilibrium behavior (ν ≤ 0.1 mV s–1) towards a diffusion controlled regime overlapping with capacitive charging (ν ≥ 0.2 mV s–1), and culminates at even higher rate (ν > 2 mV s–1) in mixed mass transport ohmic control. Impedance analysis permits to discriminate the varying character of charge storage, revealing the low frequency dominance of faradaic insertion and the rising contribution of pseudocapacitive and double layer charging at higher frequency. We show that the frequency decomposition of charging mechanisms obtained by this analysis can be reconciled with the CV analysis. For further clarification of the above analysis in particular, and as a relevant aspect of the NMO behavior in general, we evaluate the chemical diffusion coefficient of Na-ion as a function of potential.

Low-field transport in SiO2

Low-field electronic transport trends in silicon dioxide (SiO2) are usually rationalized in terms of a mobility that is established by the rate of carrier (electron or hole) scattering. However, this perspective leads to a dilemma in which the hole mean free path in SiO2 is inferred to be much less than the interatomic spacing. An alternative picture is proposed herein in which electronic transport in an amorphous insulator such as SiO2 is diffusive (as exemplified by Brownian motion) and primarily involves carrier trapping, rather than scattering. Within this framework, electron transport in SiO2 is found to be a non-equilibrium, diffusive process with negligible trapping, whereas hole transport in SiO2 is dominated by quasi-equilibrium trapping. Non- or quasi-equilibrium behavior are distinguished by the relative magnitude of the carrier drift length compared to the SiO2 thickness, or equivalently, by the transit time compared to the carrier capture (trapping) time.

Wide bandwidth nanomechanical assessment of murine cartilage reveals protection of aggrecan knock-in mice from joint-overuse

Aggrecan loss in human and animal cartilage precedes clinical symptoms of osteoarthritis, suggesting that aggrecan loss is an initiating step in cartilage pathology. Characterizing early stages of cartilage degeneration caused by aging and overuse is important in the search for therapeutics. In this study, atomic force microscopy (AFM)-based force–displacement micromechanics, AFM-based wide bandwidth nanomechanics (nanodynamic), and histologic assessments were used to study changes in distal femur cartilage of wildtype mice and mice in which the aggrecan interglobular domain was mutated to make the cartilage aggrecanase-resistant. Half the animals were subjected to voluntary running-wheel exercise of varying durations. Wildtype mice at three selected age groups were compared. While histological assessment was not sensitive enough to capture any statistically significant changes in these relatively young populations of mice, micromechanical assessment captured changes in the quasi-equilibrium structural-elastic behavior of the cartilage matrix. Additionally, nanodynamic assessment captured changes in the fluid–solid poroelastic behavior and the high frequency stiffness of the tissue, which proved to be the most sensitive assessment of changes in cartilage associated with aging and joint-overuse. In wildtype mice, aging caused softening of the cartilage tissue at the microscale and at the nanoscale. Softening with increased animal age was found at high loading rates (frequencies), suggesting an increase in hydraulic permeability, with implications for loss of function pertinent to running and impact-injury. Running caused substantial changes in fluid–solid interactions in aggrecanase-resistant mice, suggestive of tissue degradation. However, higher nanodynamic stiffness magnitude and lower hydraulic permeability was observed in running aggrecanase-resistant mice compared to running wildtype controls at the same age, thereby suggesting protection from joint-overuse.

Study of In distribution on GaInSb:Al crystals by ion beam techniques

III–V ternary alloys semiconductor materials, in particular Ga1−xInxSb, are ideal candidates for device substrates because of the possibility to define the lattice constant as a function of the third element, indium. Aluminum, an isoelectric dopant for Ga and In, increases the carrier mobility in GaSb crystals and has influence over the concentration of native defects by passivating and/or compensating them. To understand the influence of Al on the distribution of indium in ternary alloys of Ga0.8In0.2Sb, pure and doped ingots were obtained with approximately 1020atoms/cm3 of Al using a vertical Bridgman system. Analysis by scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), X-ray diffraction (XRD), particle induced X-ray emission (PIXE) and particle induced gamma ray emission (PIGE) were used to obtain information on the structure defects and chemical composition of the crystals.The doped ingots showed good structural homogeneity when compared with the undoped alloy, and they were free from cracks and micro cracks. All of the obtained ingots present precipitates, twins and grains with different concentrations of In.The small compositional variation observed in the doped ingots along the radial direction (measured by PIXE), may be related to the solid–liquid interface’s quasi-equilibrium behavior. Regarding to the growth direction, it was observed that the undoped ingots exhibit a higher segregation phenomenon of the third element than the doped ingots.The obtained results indicate that aluminum influences the indium distribution in the ingots, thus ternary ingots with more homogeneous composition can be obtained and consequently electrical properties improved.

Conductance hysteresis in the voltage-dependent anion channel.

Hysteresis in the conductance of voltage-sensitive ion channels is observed when the transmembrane voltage is periodically varied with time. Although this phenomenon has been used in studies of gating of the voltage-dependent anion channel, VDAC, from the outer mitochondrial membrane for nearly four decades, full hysteresis curves have never been reported, because the focus was solely on the channel opening branches of the hysteresis loops. We studied the hysteretic response of a multichannel VDAC system to a triangular voltage ramp the frequency of which was varied over three orders of magnitude, from 0.5mHz to 0.2Hz. We found that in this wide frequency range the area encircled by the hysteresis curves changes by less than a factor of three, suggesting broad distribution of the characteristic times and strongly non-equilibrium behavior. At the same time, quasi-equilibrium two-state behavior is observed for hysteresis branches corresponding to VDAC opening. This enables calculation of the usual equilibrium gating parameters, gating charge and voltage of equipartitioning, which were found to be almost insensitive to the ramp frequency. To rationalize this peculiarity, we hypothesize that during voltage-induced closure and opening the system explores different regions of the complex free energy landscape, and, in the opening branch, follows quasi-equilibrium paths.

Equilibrium and non-equilibrium charge-state distributions of 2.0 MeV/u carbon ions passing through carbon foils

Both equilibrium and non-equilibrium charge-state distributions were studied experimentally for 2.0MeV/u carbon ions after passing through carbon foils. Measured charge-state distribution established the equilibrium at a target thickness of 10μg/cm2 and this remained unchanged until a maximum target thickness of 98μg/cm2. The equilibrium charge-state distribution, the equilibrium mean charge-state, and the width and skewness of the equilibrium distribution were compared with predictions using existing semi-empirical formulae as well as simulation results, including the ETACHA code. It was found that charge-state distributions, mean charge states, and distribution widths for C2+, C3+, and C4+ incident ions merged into quasi-equilibrium values at a target thickness of 5.7μg/cm2 in the pre-equilibrium region and evolved simultaneously to the ‘real equilibrium’ values for all of the initial charge states, including C5+ and C6+ ions, as previously demonstrated for sulfur projectile ions at the same velocity (Imai et al., 2009). Two kinds of simulation, ETACHA and solution of rate equations taking only single electron transfers into account, were used, and both of them reproduced the measured charge evolution qualitatively. The quasi-equilibrium behavior could be reproduced with the ETACHA code, but not with solution of elementary rate equations.

Equilibrium and Recrossings of the Transition State: What Can Be Learned from Diffusion?

We examine the assumptions and conclusion of (generalized) transition state theory (GTST) by considering the activation process in the diffusion (Langevin) limit. We find the asymptotic structure of the leading eigenfunctions and eigenvalues of the Fokker-Planck operator with a bistable potential and hence the long-time quasi-equilibrium behavior of the phase space probability density function (pdf). Defining reactant and product as small neighborhoods of the stable states, we examine all possible recrossings of the transition state region (TSR) and find their contribution to the mean first passage time (MFPT) from one state to the other. We show that the mean number of recrossings of the TSR is 1, so the MFPT from one state to the other is twice that to the stochastic separatrix, which we use as a generalized transition state (GTS). The activation rate, that is, the rate at which trajectories arrive from one state to the other, is then shown to be one-half of the arrival rate at the GTS and in the limit of a high harrier is independent of the choice of the size of the domains that define the states. We conclude that to obtain the correct rate in (G)TST (i) the quasi-equilibrium density (qepdf) rather than the equilibrium density (epdf) has to be used, (ii) the qepdf contains a boundary layer near the stochastic separatrix, but otherwise the reactant qepdf is nearly equal the epdf, and (iii) all recrossings of the (G)TS are accounted for if the (G)TS is the stochastic separatrix, but not otherwise. We also consider the case of a single metastable state.

Quasi-Equilibrium Evolution in Self-GravitatingN-Body Systems

In this paper, a quantitative characterization of the evolutionary sequences of self-gravitating system is investigated from a thermostatistical point of view. With a particular attention to the pre-collapse stage of long-term dynamical evolution, we focus on the quasi-equilibrium behavior of the N-body systems in the setup of the so-called Antonov problem, i.e., self-gravitating N-body system confined in an adiabatic wall. After addressing the quilibrium properties of self-gravitating systems by means of the generalized entropy, a series of N-body simulation were performed starting with various initial distributions. We found that quasi-equilibrium evolution appears for certain initial conditions away from the thermal equilibrium. The quasi-equilibrium states can be approximately described by the one-parameter family of the stellar models, i.e., stellar polytropic distribution satisfying the effective equation of state P ∝ ρ 1+1/n , which might be regarded as an extremum state of the generalized non-extensive entropy.

Quasi-Equilibrium Volume Changes of Polyaniline Films upon Redox Switching. Formal Potential Distribution and Configurational Modeling

The quasi-equilibrium electrochemomechanical behavior of relatively thick polyaniline films in sulfuric acid is investigated through experimental measurements and theoretical modeling. The leucoemeraldine (LE)-emeraldine (EM) conversion, or redox switching, is studied. The dependence of film volume and electrochemical charge is determined as a function of applied potential. It is observed that the film volume follows the charge, showing an expansion during the second half of the LE-EM oxidation. The model postulates the existence of a stable intermediate, protoemeraldine (PE), with a formal potential distribution for the PE-EM reaction. The volume change is modeled statistically considering contributions from mixing, polymer deformation, and electrostatic charge. The model shows very good agreement with the experiments, indicating that, in the conditions studied, the deformation contribution dominates the volume changes as a result of the conformational modifications undergone by the polymer in the PE-EM oxidation.

Observable dependent quasiequilibrium in slow dynamics

We present examples demonstrating that quasi-equilibrium fluctuation-dissipation behavior at short time differences is not a generic feature of systems with slow nonequilibrium dynamics. We analyze in detail the nonequilibrium fluctuation-dissipation ratio X(t, t(w)) associated with a defect-pair observable in the Glauber-Ising spin chain. It turns out that X not = 1 throughout the short-time regime and in particular X(t(w), t(w)) = 3/4 for t(w) --> infinity. The analysis is extended to observables detecting defects at a finite distance from each other, where similar violations of quasi-equilibrium behavior are found. We discuss our results in the context of metastable states, which suggests that a violation of short-time quasi-equilibrium behavior could occur in general glassy systems for appropriately chosen observables.

Numerical Study on Aging Dynamics in the 3D Ising Spin-Glass Model. II. Quasi-Equilibrium Regime of Spin Auto-Correlation Function

Using Monte Carlo simulations, we have studied isothermal aging of three-dimensional Ising spin-glass model focusing on quasi-equilibrium behavior of the spin auto-correlation function. Weak violation of the time translational invariance in the quasi-equilibrium regime is analyzed in terms of {\it effective stiffness} for droplet excitations in the presence of domain walls. Within the range of computational time window, we have confirmed that the effective stiffness follows the expected scaling behavior with respect to the characteristic length scales associated with droplet excitations and domain walls, whose growth law has been extracted from our simulated data. Implication of the results are discussed in relation to experimental works on ac susceptibilities.

NUMERICAL STUDY ON AGING DYNAMICS IN THE 3D ISING SPIN-GLASS MODEL — QUASI-EQUILIBRIUM BEHAVIOR OF SPIN AUTO-CORRELATION FUNCTIONS

Using Monte Carlo simulations, we have studied aging phenomena in three-dimensional Gaussian Ising spin-glass model focusing on quasi-equilibrium behavior of the spin auto-correlation functions. Weak violation of the time translational invariance in the quasi-equilibrium regime is analyzed in terms of effective stiffness for droplet excitations in the presence of domain walls. The simulation results not only in isothermal aging but also in T-shift aging process. T-shift aging processes exhibit the expected scaling behavior with respect to the characteristic length scales associated with droplet excitations and domain walls in spite of the fact that the growth law for these length scales still shows a pre-asymptotic behavior compared with the asymptotic form proposed by the droplet theory. Implications of our simulational results are also discussed in relation to experimental observations.

Influence of Large-Scale Advective Cooling and Moistening Effects on the Quasi-Equilibrium Behavior of Explicitly Simulated Cumulus Ensembles

Abstract The influence of large-scale advective cooling and/or moistening on the quasi-equilibrium behavior of simulated, tropical oceanic cumulus ensembles is examined in this study. Two sensitivity simulations are performed by imposing time varying/invariant large-scale advective cooling effects and time invariant/varying large-scale advective moistening effects. The results are compared with a control simulation performed with both large-scale advective cooling and moistening effects that are time varying. It is found that the generalized convective available potential energy (GCAPE) tendency is almost one order of magnitude smaller than the GCAPE production in all simulations. This indicates that the quasi-equilibrium assumption of Arakawa and Schubert is well justified. The higher-order behavior of quasi-equilibrium cumulus ensemble is then examined. It is found that the GCAPE variations are nearly equally contributed by temperature and water vapor variations in the control simulation. In the sensiti...

Off-equilibrium dynamics of a (1 + 1)-dimensional directed polymer in random media

The relaxational dynamics of 1+1 dimensional directed polymer in random potential is studied by Monte Carlo simulation. A series of temperature quench experiments is performed changing waiting times. Clear crossover from quasi-equilibrium behavior to off-equilibrium behavior appears in the dynamical overlap function whose scaling properties are very similar to those found in the 3 dimensional spin-glass model. In the off-equilibrium part, the fluctuation dissipation theorem of the 1st kind which relates the response function to the tilt field with the conjugate correlation function, is found broken. These aging effects are brought about by the very slow growth of quasi-equilibrium domain driven by successive loop-excitations of various sizes, which form complex network structures.

Effect of Vertical Wind Shear on Numerically Simulated Multicell Storm Structure

Abstract A strictly two-dimensional cloud model was used to gauge the effect of vertical wind shear on the mature phase behavior of model-simulated multicellular storms, extending the previous work of the authors. We specifically examined the propagation speed, quasi-equilibrium behavior, storm scale and updraft orientation of the model storms as a function of shear intensity. We also considered the precipitation efficiencies of our. model storms and applied density current and Rotunno–Klemp–Weisman theories to our results. Our previous work revealed that model storms could achieve a mature phase consisting of repetitive multicellular development when certain numerical obstacles were overcome. This was referred to as a “quasi-equilibrium state.” We found herein that this state was also reached by model storms even when subjected to a very wide range of low-level wind shear intensities, although the temporal behavior during this stage was clearly dependent on the shear. We also found a very systematic rela...

Effects of Cumulus Entrainment and Multiple Cloud Types on a January Global Climate Model Simulation

An improved version of the GISS Model II cumulus parameterization designed for long-term climate integrations is used to study the effects of entrainment and multiple cloud types on the January climate simulation. Instead of prescribing convective mass as a fixed fraction of the cloud base grid-box mass, it is calculated based on the closure assumption that the cumulus convection restores 0the atmosphere to a neutral most convective state at cloud base. This change alone significantly improves the distribution of precipitation, convective mass exchanges and frequencies in the January climate. The vertical structure of the tropical atmosphere exhibits quasi-equilibrium behavior when this closure is used, even though there is no explicit constraint applied above cloud base. Global aspects of the simulation using the neutral buoyancy closure are almost identical to those obtained in a previous study with a closure relating cumulus mass flux explicitly to large-scale forcing. A prescription of 0.2 km−1 for the fractional rate of entrainment lower the peak of the convective heating profile, reduces equatorial specific humidifies in the upper atmosphere to more realistic values, and greatly increases eddy kinetic energy at the equator due to reduced momentum mixing. With two cloud types per convective event, each cloud type having a prescribed size and entrainment rate, a clear bimodal distribution of convective mass flux is obtained in strong convective events. At the same time, many of the desirable climate features produced by the neutral buoyancy and entrainment experiments are preserved.

Non-equilibrium C-V and I-V characteristics of metal-insulator-semiconductor capacitors

The C-V characteristics of metal-insulator-semiconductor (MIS) structures exhibit considerable departure from their quasi-equilibrium behavior under the application of large depleting voltages. The deviation is the result of d.c. current flowing through the insulator, so that steady state non-equilibrium conditions exist in the semiconductor. The primary effects are a lowering of the high frequency capacitance below its quasi-equilibrium minimum value C ∞, a deviation of the I-V characteristics of the structure from those of the insulator and the development of a large voltage drop across the semiconductor. The low and high frequency capacitances coincide in this non-equilibrium range. The non-equilibrium properties have been observed for deposited films of Si 3N 4, SiO 2, and Al 2O 3. Experimental data are presented for films of pyrolytically deposited Si 3N 4 on p- and n-type silicon substrates, in the dark and for various levels of illumination. A model is developed in which current in the semiconductor occurs through the generation of carriers in the depletion region, and bulk diffusion of carriers in the case of illumination, and where the insulator current proceeds through the Poole-Frenkel mechanism. Agreement between theory and experiment is obtained, and the possible use of the non-equilibrium effect in determining the minority carrier lifetime of the substrate is indicated.

Kinetic Theory of Adsorption of Intermediates in Electrochemical Catalysis

The behavior of adsorbed intermediates in consecutive electrochemical reactions is discussed in terms of the steady-state rate equations, and a comparison with results obtained using the quasiequilibrium assumption is made. The adsorption pseudocapacitance vs potential plot is shown to be symmetrical only when the quasiequilibrium assumption is made, namely when the ratio of specific rate constants for the desorption step (which is rate determining) and initial ion-discharge step, is exceedingly small. The C—V relationship is calculated for three types of mechanism: (i) discharge followed by atom—atom recombination, (ii) discharge followed by first-order decomposition, (iii) discharge followed by ion—atom desorption; cases for activated and nonactivated adsorption conditions are distinguished. Deviations from the symmetrical quasiequilibrium behavior are shown to depend on the kinetic pathway and, for a particular mechanism, are larger the larger is the value of the Temkin parameter r (defined by the rate of change of apparent standard free energy of adsorption of the intermediate with coverage). For a given value of r, these deviations are shown to be largest for the pathway when discharge is followed by ion—atom desorption, and smallest for the case when discharge is followed by a first-order decomposition step. Further, for any one mechanism, conditions of nonactivated adsorption lead to larger deviations than for the case when activated adsorption occurs.