Metastable Region Research Articles

Strain engineering of electronic, elastic, and piezoelectric responses in oxygen-decorated phosphorene

The electronic, elastic, and piezoelectric properties of semi-oxidized phosphorene subjected to uniaxial strains were studied using first-principles calculations based on the density functional theory. Both zigzag and armchair uniaxial loads caused significant changes in partial charges and band gaps as a semiconductor–metal transition occurs outside the metastable regions. The bridge structures exhibited great flexibility along the armchair direction resulting from the high buckling parameter in these structures. The calculations confirmed the linear response of polarization. The in plane and out of plane stress piezoelectric coefficients were comparable to 2D materials. The results demonstrated that both the uniaxial strain and the oxygen atom arrangement can be used to tune the anisotropic properties of phosphorene making the new derivatives ideal for flexible devices and energy conversion applications.

Thermodynamics of supersaturated steam: Towards an equation of state

Thermodynamics of supersaturated (supercooled) steam at conditions occurring in steam turbines, and inaccessible thus to experiments, has been studied by a number of theoretical and semi-theoretical methods with the goal to assess available theoretical tools for developing an equation of state. Extended virial expansions with different reference systems have been used along with two, qualitatively different equations of state. According to the proposed strategy, all equations were first used for the vapor-liquid coexistence curve and then extended to the metastable region and tested against computer simulation data. Despite the fact that no specificities of supersaturated steam have been accounted for, all the considered methods provide results with deviations from (pseudo)experimental data up to about 5% over the entire range of thermodynamic conditions except the critical region. It turns out that the perturbed virial expansion with a suitably chosen reference system outperforms other methods, including equations of state originally developed for liquid water.

METAPUF: A challenge response pair generator

Physically unclonable function (PUF) is a hardware security module preferred for hardware feature based random number and secret key generation. Security of a cryptographic system relies on the quality of the challenge-response pair, it is necessary that the key generation mechanism must unpredictable and its response should constant under different operating condition. Metastable state in CMOS latch is undesirable since it response becomes unpredictable, this feature used in this work to generate a unique response. A feedback mechanism is developed which forces the latch into the metastable region; after metastable state, latch settle to high or state depends on circuit internal condition and noise which cannot be predicted. Obtained inter hamming variation for 8 PUF is 51% and average intra hamming distance is 99.76% with supply voltage variation and 96.22% with temperature variation.

Perspective: Identification of collective variables and metastable states of protein dynamics.

The statistical analysis of molecular dynamics simulations requires dimensionality reduction techniques, which yield a low-dimensional set of collective variables (CVs) {x i } = x that in some sense describe the essential dynamics of the system. Considering the distribution P( x ) of the CVs, the primal goal of a statistical analysis is to detect the characteristic features of P( x ), in particular, its maxima and their connection paths. This is because these features characterize the low-energy regions and the energy barriers of the corresponding free energy landscape ΔG( x ) = -k B T ln P( x ), and therefore amount to the metastable states and transition regions of the system. In this perspective, we outline a systematic strategy to identify CVs and metastable states, which subsequently can be employed to construct a Langevin or a Markov state model of the dynamics. In particular, we account for the still limited sampling typically achieved by molecular dynamics simulations, which in practice seriously limits the applicability of theories (e.g., assuming ergodicity) and black-box software tools (e.g., using redundant input coordinates). We show that it is essential to use internal (rather than Cartesian) input coordinates, employ dimensionality reduction methods that avoid rescaling errors (such as principal component analysis), and perform density based (rather than k-means-type) clustering. Finally, we briefly discuss a machine learning approach to dimensionality reduction, which highlights the essential internal coordinates of a system and may reveal hidden reaction mechanisms.

Stabilization by dissipation and stochastic resonant activation in quantum metastable systems

In this tutorial paper we present a comprehensive review of the escape dynamics from quantum metastable states in dissipative systems and related noise-induced effects. We analyze the role of dissipation and driving in the escape process from quantum metastable states with and without an external driving force, starting from a nonequilibrium initial condition. We use the Caldeira–Leggett model and a non-perturbative theoretical technique within the Feynman–Vernon influence functional approach in strong dissipation regime. In the absence of driving, we find that the escape time from the metastable region has a nonmonotonic behavior versus the system-bath coupling and the temperature, producing a stabilizing effect in the quantum metastable system. In the presence of an external driving, the escape time from the metastable region has a nonmonotonic behavior as a function of the frequency of the driving, the thermal-bath coupling and the temperature. The quantum noise enhanced stability phenomenon is observed in both systems investigated. Finally, we analyze the resonantly activated escape from a quantum metastable state in the spin-boson model. We find quantum stochastic resonant activation, that is the presence of a minimum in the escape time as a function of the driving frequency. Background and introductory material has been added in the first three sections of the paper to make this tutorial review reasonably self-contained and readable for graduate students and non-specialists from related areas.

Determination of limit of stability profiles for liquefied natural gas: a thermodynamic approach

Efficient design, operation, handling, and transportation of natural gas as liquefied natural gas (LNG) are controlled by its phase behavior. A phase, in a non-reacting system, is known to be stable when it is at its lowest Gibbs energy; an alternative criterion to the minimization of the Gibbs energy is presented for phase stability status determination of pure systems and mixtures. On this premise, the stability limit determination method by the Helmholtz stability criterion was employed for the determination of stability limits which were used to successfully generate stability limit profiles for LNG and its constituents. To further investigate the metastable region, a new and robust model was developed and successfully used to produce vapor and liquid spinodals as well as binodal curves for the LNG constituents. The model accurately predicted the critical points and was shown to be in very close agreement with the available predicted and experimental results.

EXPERIMENTAL AND NUMERICAL INVESTIGATION OF METASTABLE FLOW OF REFRIGERANT R-22 THROUGH CAPILLARY TUBE

This study presents an experimental investigation of metastable region take place forrefrigerant flow through adiabatic and non-adiabatic capillary tube of window type airconditioner. Large numbers of experiments are carried out to explain the effect of length ofstraight and helical capillary tube on metastable region under adiabatic and non-adiabaticconditions. for the case of adiabatic capillary tube, three different length are selected(70,100 and 150) cm and two helical capillary tube, the length of each tube is 100 cm withtwo coil diameters (2 and 6) cm. For the non-adiabatic capillary tube, the straight capillarytube suction line is 150 cm while the length of non-adiabatic helical capillary tube is 200 cmwith 8 cm coil diameter. The results show that the length is the most influence parameterson beginning of metastable region. In addition the helical coil tube effect on the beginningof metastable region. As well as for the adiabatic and non-adiabatic capillary tube it isconcluded that mass flow rate is the main parameters on beginning of metastable region.Also effect of length and coiling on both pressure drop and mass flow rate are discussed.The CFD commercial code, ANSYS CFX 16.1 based on finite volume method using Kturbulencemodel considering the homogeneous flow between phases applied to straightcapillary tube. The present numerical data has been validated with the present workexperimental data and with other researchers. A good agreement is obtained which can belead to use ANSYS CFX 16.1 in the design and optimization of capillary tube in airconditioner.

Understanding Processes Following Resonant Electron Attachment: Minimum-Energy Crossing Points between Anionic and Neutral Potential Energy Surfaces.

The equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) method with and without a complex absorbing potential (CAP) is applied for the study of the complex potential energy surfaces (CPES) of temporary anions and their parent neutral molecules. Crossings between the anionic state and the neutral state can be connected to the emission of nearly zero-energy electrons, which is demonstrated by the examples of acrylonitrile and methacrylonitrile. We show that the location of the minimum-energy crossing point (MECP) relative to the equilibrium structures of the neutral molecule and the anion can explain experimentally observed peaks on the threshold line of two-dimensional electron-energy loss spectra. The location and energy of the MECP is also crucial in dissociative electron attachment as we illustrate for chloro-substituted ethylenes. It is demonstrated that both the metastable region of the anionic CPES and the crossing with the neutral PES need to be considered to explain trends in the chloride ion formation cross sections of dichloroethylenes.

Metastability at the Loss of the Morphological Stability of the Moving Boundary of a Fluid

The morphological stability of the interface between two fluids has been analyzed for the case where one of them displaces the other in a radial Hele-Shaw cell. The numerical calculation has shown for the first time that the critical size of instability decreases with an increase in the perturbation amplitudes of the interface and reaches a value previously determined from independent analytical calculations of the thermodynamic entropy production and the maximum entropy production principle. This reason is important evidence for the hypothesis that the entropy production makes it possible to predict nonequilibrium phase transitions in hydrodynamic systems (i.e., it is an analog of the thermodynamic potential). In other words, the entropy production determines a kinetic binodal, i.e., the interface of a metastable region in the case of perturbations with arbitrary amplitude.

Concentration fluctuations in the early stages of LLPS and partial dissolution of melt-memory in broadly distributed ethylene copolymers

The mechanism of liquid-liquid phase separation (LLPS) is investigated in a random ethylene 1-hexene copolymer (E/H) with a broad comonomer content distribution. SANS measurements were first carried out using the original resin with deuterium added via direct isotope exchange to preserve the original branching distribution. Upon lowering the melt temperature, the upshift of SANS profile observed only below a critical scattering vector is consistent with the signature of nucleation and growth during LLPS in the metastable region. Differences in branching distribution between the original broad resin and a broad multi-components blend of narrow E/H copolymers studied previously, result in slower LLPS dynamics in the former that has a more continuous change of comonomer content between molecules. Time-resolved light scattering and light transmittance measurements in the metastable region of the broad resin, reveal the nucleation and growth stages of LLPS. Dissolution of crystalline melt-memory, associated with an inversion of the crystallization rate with decreasing the temperature of the initial melt, is found to occur mainly within the LLPS induction period and is associated with concentration fluctuations prior to the LLPS nucleation step. The typical sea-island morphology associated with LLPS via nucleation and growth is observed under bright-field optical microscopy after one-day annealing in the metastable region.

On the tuning in the (mh,mt) plane: Standard Model criticality vs. high-scale SUSY

We analyse the predictions of both Higgs and top masses in a generic MSSM satisfying gauge-coupling unification, radiative electroweak symmetry breaking, with a natural (non-splitted) spectrum of soft-breaking terms, and an arbitrary soft-breaking scale (above a few TeV). This procedure allows us to identify a relatively narrow SUSY-allowed region in the (mh,mt) plane. We argue that the compatibility of the measured values of Higgs and top masses with this SUSY-allowed region is not less surprising than the corresponding compatibility with the narrow SM metastability region. As such, it provides a non-trivial signal of the compatibility of present data with a supersymmetric completion of the SM.

Strain-engineering of Janus SiC monolayer functionalized with H and F atoms

Based on ab initio density functional theory calculations, the structural, electronic, mechanical, acoustic, thermodynamic, and piezoelectric properties of (F,H) Janus SiC monolayers are studied. The new set of derivatives shows buckled structures and different band gap values. Under strain, the buckling changes and the structures pass from semiconducting to metallic. The elastic limits and the metastable regions are determined. The Young's modulus and Poisson ratio reveal stronger behavior for the modified conformers with respect to graphene. The values of the Debye temperature make the new materials suitable for thermal application. Moreover, all the conformers show in-plane and out-of-plane piezoelectric responses comparable with known two-dimensional materials. If engineered, such piezoelectric Janus structures may be promising materials for various nanoelectromechanical applications.

Fick’s law in non-local evolution equations

We study the stationary non-local equation which corresponds to the energy functional of a one-dimensional Ising spin system, in which particles interact via a Kac potential. In particular, following some of the techniques developed in the work of De Masi et al. [Arch. Ration. Mech. Anal. 201(2), 681–725 (2011)], we construct a time invariant profile for the model proposed in the work of Giacomin and Lebowitz [J. Stat. Phys. 87(1), 37–61 (1997)]. The boundary conditions share the same sign and both lie above the value m*β=1−1/β, which divides the metastable region from the unstable one, the inverse temperature being fixed and larger than the critical value βc = 1. Due to the non-equilibrium setting, a non-zero magnetization current, which scales with the inverse of the size of the volume ε−1, does flow in the system [M. Colangeli et al., J. Stat. Phys. 167(5), 1081–1111 (2017)]. Here ε−1 also represents the ratio of macroscopic and mesoscopic length. We show that for ε > 0 small enough, the stationary profile has no discontinuities so that no phase transition occurs; although expected when the magnetizations are larger than mβ, this turns out to be non-trivial in the metastable region. Moreover, when ε−1 → ∞, the solution converges to the macroscopic profile which solves the local diffusion equation. The validity of Fick’s law in this context is then established.

Distinct magnetic field dependence of N\xe9el skyrmion sizes in ultrathin nanodots

We investigate the dependence of the Néel skyrmion size and stability on perpendicular magnetic field in ultrathin circular magnetic dots with out-of-plane anisotropy and interfacial Dzyaloshinskii-Moriya exchange interaction. Our results show the existence of two distinct dependencies of the skyrmion radius on the applied field and dot size. In the case of skyrmions stable at zero field, their radius strongly increases with the field applied parallel to the skyrmion core until skyrmion reaches the metastability region and this dependence slows down. More common metastable skyrmions demonstrate a weaker increase of their size as a function of the field until some critical field value at which these skyrmions drastically increase in size showing a hysteretic behavior with coexistence of small and large radius skyrmions and small energy barriers between them. The first case is also characterized by a strong dependence of the skyrmion radius on the dot diameter, while in the second case this dependence is very weak.

Solution properties and salt-solution equilibria in the H-Li-Na-K-Ca-Mg-Cl-H2O system at 25 °C: A new thermodynamic model based on Pitzer's equations

A large part of Li production comes from the exploitation of saline lakes and salars. Industrial processes for Li recovery from such resources have to deal with highly saline waters. It is therefore necessary to develop the knowledge of Li chemistry adapted to these contexts. The present work aims to present a new set of Pitzer interaction parameters able to describe the chemical behavior of the H-Li-Na-K-Ca-Mg-Cl-H2O system up to salt solubility, at 25 °C. In a previous work, the model was limited to the H-Li-Na-K-Cl-H2O system. It is extended here by including Ca and Mg, taking into account recently revised parameters allowing the thermal properties of the binary CaCl2-H2O and MgCl2-H2O systems to be represented. The consistent extension of the thermodynamic database was made possible by the study of the binary CaCl2-H2O system up to the supersaturated metastable region and of nine ternary systems, namely X-Ca-Cl, X-Mg-Cl and Ca-Mg-Cl (where X = H, Li, Na, K). The model was finally tested on five quaternary systems.

Enhancing Metastability by Dissipation and Driving in an Asymmetric Bistable Quantum System.

The stabilizing effect of quantum fluctuations on the escape process and the relaxation dynamics from a quantum metastable state are investigated. Specifically, the quantum dynamics of a multilevel bistable system coupled to a bosonic Ohmic thermal bath in strong dissipation regime is analyzed. The study is performed by a non-perturbative method based on the real-time path integral approach of the Feynman-Vernon influence functional. We consider a strongly asymmetric double well potential with and without a monochromatic external driving, and with an out-of-equilibrium initial condition. In the absence of driving we observe a nonmonotonic behavior of the escape time from the metastable region, as a function both of the system-bath coupling coefficient and the temperature. This indicates a stabilizing effect of the quantum fluctuations. In the presence of driving our findings indicate that, as the coupling coefficient increases, the escape time, initially controlled by the external driving, shows resonant peaks and dips, becoming frequency-independent for higher values. Moreover, the escape time from the metastable state displays a nonmonotonic behavior as a function of the temperature, the frequency of the driving, and the thermal-bath coupling, which indicates the presence of a quantum noise enhanced stability phenomenon. Finally, we investigate the role of different spectral densities, both in sub-Ohmic and super-Ohmic dissipation regime and for different cutoff frequencies, on the relaxation dynamics from the quantum metastable state. The results obtained indicate that, in the crossover dynamical regime characterized by damped intrawell oscillations and incoherent tunneling, the spectral properties of the thermal bath influence non-trivially the short time behavior and the time scales of the relaxation dynamics from the metastable state.

Equation of state for the Lennard-Jones truncated and shifted fluid with a cut-off radius of 2.5 σ based on perturbation theory and its applications to interfacial thermodynamics

ABSTRACTAn equation of state is presented for describing thermodynamic properties of the Lennard-Jones truncated and shifted (LJTS) potential with a cut-off radius of 2.5 σ. It is developed using perturbation theory with a hard-sphere reference term and labelled with the acronym PeTS (perturbed truncated and shifted). The PeTS equation of state describes the properties of the bulk liquid and vapour and the corresponding equilibrium of the LJTS fluid well. Furthermore, it is developed so that it can be used safely in the entire metastable and unstable region, which is an advantage compared to existing LJTS equations of state. This makes the PeTS equation of state an interesting candidate for studies of interfacial properties. The PeTS equation of state is applied here in two theories of interfaces, namely density gradient theory (DGT) and density functional theory (DFT). The influence parameter of DGT as well as the interaction averaging diameter of DFT are fitted to data of the surface tension of the LJTS fluid obtained from molecular simulation. The results from both theories agree very well with those from the molecular simulations.

Effect of applied strain on phase separation of Fe–28 at.% Cr alloy: 3D phase-field simulation

A quantitative simulation of the separation of the α′ phase in Fe–28 at.% Cr alloy under the effects of applied strain is performed by utilizing a three-dimensional phase-field model. The elongation of the Cr-enriched α′ phase becomes obvious with the influence of applied uniaxial strain for the phase separation transforms from spinodal decomposition of 700 K to nucleation and growth of 773 K. The applied strain shows a significant influence on the early stage phase separation, and the influence is enlarged with the elevated temperature. The steady-state coarsening with the mechanism of spinodal decomposition is substantially affected by the applied strain for low-temperature aging, while the influence is reduced as the temperature increases and as the phase separation mechanism changes to nucleation and growth. The peak value of particle size distribution decreases, and the PSD for 773 K becomes more widely influenced by the applied strain. The simulation results of separation of the Cr-enriched α′ phase with the applied strain provide a further understanding of the strain effect on the phase separation of Fe–Cr alloys from the metastable region to spinodal regions.

Stability analysis and wave dynamics of an extended hybrid traffic flow model

The stability analysis and wave dynamic properties of an extended hybrid traffic flow model, WZY model, are intensively studied in this paper. The linear stable condition obtained by the linear stability analysis is presented. Besides, by means of analyzing Korteweg–de Vries equation, we present soliton waves in the metastable region. Moreover, the multiscale perturbation technique is applied to derive the traveling wave solution of the model. Furthermore, by means of performing Darboux transformation, the first-order and second-order doubly-periodic solutions and rational solutions are presented. It can be found that analytical solutions match well with numerical simulations.

Metastability in the formation of Condon domains

Metastability effects in the formation of Condon non-spin magnetic domains are considered. A possibility for the first-order phase transition occurrence in a three-dimensional electron gas is described in the case of two-frequency de-Haas-van Alphen magnetization oscillations originating from two extremal cross sections of the Fermi surface. The appearance of two additional domains is shown in the metastable region in aluminum. The phase diagram temperature-magnetic field exhibits the presence of second-order and first- order phase transitions in the two-frequency case.