Metastable Region Research Articles

Structural Biology of Calcium Phosphate Nanoclusters Sequestered by Phosphoproteins

Biofluids that contain stable calcium phosphate nanoclusters sequestered by phosphopeptides make it possible for soft and hard tissues to co-exist in the same organism with relative ease. The stability diagram of a solution of nanocluster complexes shows how the minimum concentration of phosphopeptide needed for stability increases with pH. In the stable region, amorphous calcium phosphate cannot precipitate. Nevertheless, if the solution is brought into contact with hydroxyapatite, the crystalline phase will grow at the expense of the nanocluster complexes. The physico-chemical principles governing the formation, composition, size, structure, and stability of the complexes are described. Examples are given of complexes formed by casein, osteopontin, and recombinant phosphopeptides. Application of these principles and properties to blood serum, milk, urine, and resting saliva is described to show that under physiological conditions they are in the stable region of their stability diagram and so cannot cause soft tissue calcification. Stimulated saliva, however, is in the metastable region, consistent with its role in tooth remineralization. Destabilization of biofluids, with consequential ill-effects, can occur when there is a failure of homeostasis, such as an increase in pH without a balancing increase in the concentration of sequestering phosphopeptides.

Distinguishing inert Higgs doublet and inert triplet scenarios

In this article we consider a comparative study between Type-I 2HDM and Y=0, SU(2) triplet extensions having one Z_2-odd doublet and triplet that render the desired dark matter(DM). For the inert doublet model (IDM) either a neutral scalar or pseudoscalar can be the DM, whereas for inert triplet model (ITM) it is a CP-even scalar. The bounds from perturbativity and vacuum stability are studied for both the scenarios by calculating the two-loop beta functions. While the quartic couplings are restricted to 0.1-0.2 for a Planck scale perturbativity for IDM, these are much relaxed (0.8 ) for ITM. The RG-improved potentials by Coleman-Weinberg show the regions of stability, meta-stability and instability of the electroweak vacuum. The constraints coming from DM relic, the direct and indirect experiments like XENON1T, LUX and H.E.S.S., Fermi-LAT allow the DM mass gtrsim 700, ,1176 GeV for IDM, ITM respectively. Though mass-splitting among Z_2-odd particles in IDM is a possibility for ITM we have to rely on loop-corrections. The phenomenological signatures at the LHC show that the mono-lepton plus missing energy with prompt and displaced decays in the case of IDM and ITM can distinguish such scenarios at the LHC along with other complementary modes.

Boundary of Metastable Region within Equations of State by Nigmatulin–Bolotnova

The present paper considers the determination of the two-phase region boundary within a simplified version of the wide-range equations of state of water and steam by Nigmatulin–Bolotnova (EOS NB) in the case the determination is based on the temperature-dependence of the saturated vapor pressure. This version of EOS NB can be used when the temperature and pressure ranges under investigation do not include the area of abnormal features of water at temperatures close to freezing ones (lower than $$10^{o}C$$ ) and when some errors in adiabatic speed of sound in a nearly-critical zone are acceptable. In particular, it is applied to numerically simulating dynamics of cavitation bubbles under their strong collapse. It is shown that in determining the two-phase region boundary within the simplified version of EOS NB on the basis of the temperature-dependencies of the saturated vapor pressure, a number of problems can occur. A simple modification of one of the known temperature-dependencies of the saturated vapor pressure, free of such problems, is presented.

Modification of Equations of State in the Metastable Region for High-speed Vapor Compression

A modification of the well-known wide-range equations of state of Nigmatulin–Bolotnova is proposed for describing the high-speed adiabatic-compression of vapor of tetradecane in the metastable region in physically consistent way. The modification is based on taking into account the effect of delay of vapor condensation processes under high compression rate. It is useful for studying various phenomena associated with high-speed compression of vapor of tetradecane when the compression is close to adiabatic. It can, in particular, be applied to investigating high-speed collapse of cavitation bubbles in tetradecane. The technique of the proposed modification can also be used for a similar correction of other equations of state built on the basis of the generalized Born–Mayer potential.

Optimization of crystallization of biological macromolecules using dialysis combined with temperature control.

A rational way to find the appropriate conditions to grow crystal samples for bio-crystallography is to determine the crystallization phase diagram, which allows precise control of the parameters affecting the crystal growth process. First, the nucleation is induced at supersaturated conditions close to the solubility boundary between the nucleation and metastable regions. Then, crystal growth is further achieved in the metastable zone - which is the optimal location for slow and ordered crystal expansion - by modulation of specific physical parameters. Recently, a prototype of an integrated apparatus for the rational optimization of crystal growth by mapping and manipulating temperature-precipitant-concentration phase diagrams has been constructed. Here, it is demonstrated that a thorough knowledge of the phase diagram is vital in any crystallization experiment. The relevance of the selection of the starting position and the kinetic pathway undertaken in controlling most of the final properties of the synthesized crystals is shown. The rational crystallization optimization strategies developed and presented here allow tailoring of crystal size and diffraction quality, significantly reducing the time, effort and amount of expensive protein material required for structure determination.

Collective in-plane magnetization in a two-dimensional XY macrospin system within the framework of generalized Ott-Antonsen theory.

The problem of magnetic transitions between the low-temperature (macrospin ordered) phases in two-dimensional XY arrays is addressed. The system is modelled as a plane structure of identical single-domain particles arranged in a square lattice and coupled by the magnetic dipole-dipole interaction; all the particles possess a strong easy-plane magnetic anisotropy. The basic state of the system in the considered temperature range is an antiferromagnetic (AF) stripe structure, where the macrospins (particle magnetic moments) are still involved in thermofluctuational motion: the superparamagnetic blocking Tb temperature is lower than that (Taf) of the AF transition. The description is based on the stochastic equations governing the dynamics of individual magnetic moments, where the interparticle interaction is added in the mean-field approximation. With the technique of a generalized Ott-Antonsen theory, the dynamics equations for the order parameters (including the macroscopic magnetization and the AF order parameter) and the partition function of the system are rigorously obtained and analysed. We show that inside the temperature interval of existence of the AF phase, a static external field tilted to the plane of the array is able to induce first-order phase transitions from AF to ferromagnetic state; the phase diagrams displaying stable and metastable regions of the system are presented. This article is part of the theme issue 'Patterns in soft and biological matters'.

Fluctuations, criticality and nonequilibrium effect of the QCD matter

The multiplicity distributions of net-baryon number fluctuation in the first-order chiral phase transition associated with the nonequlibrium effect are investigated within the improved Polyakov–Nambu–Jona–Lasinio model. Compared with the idealized first-order transition in equilibrium, the calculation indicates that the density fluctuations in the metastable and unstable regions are more violent, which possibly affects the statistical distributions of density fluctuation in later stage of an expanding system. Signals induced by the first-order phase transition and those from the nonequilibrium effect are discussed in detail, which could be exploited to identify the first-order phase transition. Besides, the critical exponents of the thermodynamic quantities at both the critical end point and spinodal boundary are investigated.

Effect of Changing Path on Pedestrian Traffic under the Cumulative Effect of Delay Time

In this paper, a lattice hydrodynamic model of two-dimensional bidirectional pedestrian traffic is proposed with consideration of altering path under the cumulative effect of delay time. The stability condition is acquired by linear analysis, and the mKdV equation to describe congestion evolution is derived by reductive perturbation technique. According to the result from the stability analysis, the stability region of pedestrian flow can be divided into stable region, unstable region, and metastable region. On the basis of stable condition, the unstable region is narrowed with the increase of delay time td and the path changing rate γ. It indicates that changing path can effectively improve the stability of the pedestrian flow under the cumulative effect of delay time td. For numerical simulation and analysis of density wave, it is found that the increase of path changing rate γ and the cumulative effect of delay time td are conducive to alleviate pedestrian congestion.

Complex microparticle architectures from stimuli-responsive intrinsically disordered proteins

The controllable production of microparticles with complex geometries is useful for a variety of applications in materials science and bioengineering. The formation of intricate microarchitectures typically requires sophisticated fabrication techniques such as flow lithography or multiple-emulsion microfluidics. By harnessing the molecular interactions of a set of artificial intrinsically disordered proteins (IDPs), we have created complex microparticle geometries, including porous particles, core-shell and hollow shell structures, and a unique ‘fruits-on-a-vine’ arrangement, by exploiting the metastable region of the phase diagram of thermally responsive IDPs within microdroplets. Through multi-site unnatural amino acid (UAA) incorporation, these protein microparticles can also be photo-crosslinked and stably extracted to an all-aqueous environment. This work expands the functional utility of artificial IDPs as well as the available microarchitectures of this class of biocompatible IDPs, with potential applications in drug delivery and tissue engineering.

Low Energy Implantation into Transition-Metal Dichalcogenide Monolayers to Form Janus Structures.

Atomically thin two-dimensional (2D) materials face significant energy barriers for synthesis and processing into functional metastable phases such as Janus structures. Here, the controllable implantation of hyperthermal species from pulsed laser deposition (PLD) plasmas is introduced as a top-down method to compositionally engineer 2D monolayers. The kinetic energies of Se clusters impinging on suspended monolayer WS2 crystals were controlled in the <10 eV/atom range with in situ plasma diagnostics to determine the thresholds for selective top layer replacement of sulfur by selenium for the formation of high quality WSSe Janus monolayers at low (300 °C) temperatures and bottom layer replacement for complete conversion to WSe2. Atomic-resolution electron microscopy and spectroscopy in tilted geometry confirm the WSSe Janus monolayer. Molecular dynamics simulations reveal that Se clusters implant to form disordered metastable alloy regions, which then recrystallize to form highly ordered structures, demonstrating low-energy implantation by PLD for the synthesis of 2D Janus layers and alloys of variable composition.

Electro-Mechanical-Thermal Performance and Stability of Aircraft Energy Networks With Pulse Power Loads

Modern aircraft have an increasing need for pulse power loads which includes new weapon technologies and advanced avionics. These pulse power loads have thermal properties that couple to the electrical system and can lead to nonlinear destabilizing effects at low and high temperatures. These nonlinear electrical stability issues carry through to the mechanical and thermal systems of the aircraft and can damage components. The load is characterized by its duty cycle, period, and power level. For a given pulse load, the system is defined as metastable if there is a nonlinear limit cycle that remains bounded within the defined bus voltage limits. Regions of stability, metastability, marginal metastability, and instability are determined based on bus voltage transient tolerances. In this article a reduced-order nonlinear model of an aircraft's coupled electrical-mechanical-thermal (EMT) system is used to demonstrate the stability, metastability, and performance caused by the pulse load coupled with the EMT system.

Abinitio Determination of the Phase Diagram of CO_{2} at High Pressures and Temperatures.

The experimental study of the CO_{2} phase diagram is hampered by strong kinetic effects leading to wide regions of metastability and to large uncertainties in the location of some phase boundaries. Here, we determine CO_{2}'s thermodynamic phase boundaries by means of abinitio calculations of the Gibbs free energy of several solid phases of CO_{2} up to 50 Gigapascals. Temperature effects are included in the quasiharmonic approximation. Contrary to previous suggestions, we find that the boundary between molecular forms and the nonmolecular phase V has, indeed, a positive slope and starts at 21.5GPa at T=0 K. A triple point between phase IV, V, and the liquid phase is found at 35GPa and 1600K, indicating a broader region of stability for the nonmolecular form than previously thought. The experimentally determined boundary line between CO_{2}-II and CO_{2}-IV phases is reproduced by our calculations, indicating that kinetic effects do not play a major role in that particular transition. Our results also show that CO_{2}-III is stabilized at high temperature and its stability region coincides with the P-T conditions where phase VII has been reported experimentally; instead, phase II is the most stable molecular phase at low temperatures, extending its region of stability to every P-T condition where phase III is reported experimentally.

Highlighting Thermodynamic Coupling Effects in the Immersion Precipitation Process for Formation of Polymeric Membranes.

In the immersion precipitation process for membrane formation, a polymer casting film is placed in contact with a nonsolvent in a coagulation bath; an essential feature of the membrane formation process is the foray into the metastable region of the ternary phase diagram for the nonsolvent/solvent/polymer system. The primary objective of this article is to trace the origins of such forays. The Maxwell–Stefan diffusion formulation is combined with the Flory–Huggins description of phase equilibrium thermodynamics to set up a model for describing the transient equilibration trajectory that is followed in the polymer casting film. Four different systems are analyzed: water/acetone/CA, water/DMF/PVDF, water/NMP/PSF, and water/NMP/PEI (CA = cellulose acetate; PVDF = poly(vinylidene fluoride); PSF = polysulfone; PEI = polyetherimide, DMF = dimethyl formamide; NMP = N-methyl-2-pyrrolidone). The analysis shows that diffusional forays are mainly engendered due to thermodynamic coupling effects; such effects are quantified by the set of thermodynamic factors , where ai, the activity of species i, is dependent on the volume fractions, ϕi and ϕj, of both nonsolvent (i) and solvent (j). In regions close to phase transitions, the off-diagonal elements Γij(i ≠ j) are often negative and may attain large magnitudes in relation to the diagonal elements Γii. Strong thermodynamic coupling effects cause the transient equilibration trajectories to be strongly curvilinear, causing ingress into the metastable region. If thermodynamic coupling effects are ignored, no such ingress occurs. It is also shown that analogous diffusional forays may lead to emulsion formation in partially miscible liquid mixtures.

Orbital dynamics of 2020 AV2: the first Vatira asteroid

ABSTRACT Vatira-class near-Earth objects (NEOs) have orbits entirely interior to the orbit of Venus with aphelia 0.307 &amp;lt; Q &amp;lt; 0.718 au. Recently discovered asteroid 2020 AV2 by the Zwicky Transient Facility on 2020 January 4 is the first known object on a Vatira orbit. Numerical integrations of 2020 AV2’s nominal orbit show it remaining in the Vatira region for the next few hundred kyr before coupling to Venus and evolving onto an Atira orbit (NEOs entirely interior to Earth’s orbit with 0.718 &amp;lt; Q &amp;lt; 0.983 au) and eventually scattering out to Earth-crossing. The numerical integrations of 9900 clones within 2020 AV2’s orbital uncertainty region show examples of Vatira orbits trapped in the 3:2 mean-motion resonance with Venus at semimajor axis a ≈ 0.552 au that can survive on the order of a few Myr. Possible 2020 AV2 orbits also include those on Vatira orbits between Mercury and Venus that only rarely cross that of a planet. Together, the 3:2 resonance and these rarely-planet-crossing orbits provide a meta-stable region of phase space that is stable on time-scales of several Myr. If 2020 AV2 is currently in this meta-stable region (or was in the past), that may explain its discovery as the first Vatira and may be where more are discovered.

Atomic-Level Characterization of the Distinct Methadone-Induced Conformational Sampling and Activation Kinetics of the µ-Opioid Receptor by Molecular Simulations

Although commonly associated with the treatment of opioid addiction, and structurally different from morphine, methadone is a synthetic opioid agonist of the µ-opioid receptor (MOR) with demonstrated efficiency in the management of chronic pain owing to its unique pharmacokinetics and pharmacodynamics properties. A recent biophysical study suggests that methadone's unique pharmacological features lie in its ability to stabilize distinct MOR active conformations from those induced by classical opioid drugs or G protein-biased agonists. However, the specific effects of methadone on the conformational sampling and activation kinetics of MOR remain largely uncharacterized at the atomic level. To shed light upon this matter, we explored the methadone-induced conformational space of MOR in an explicit lipid-water environment using ∼0.3 ms of enhanced molecular dynamics (MD) simulations, and compared it to the receptor conformational sampling of previously published ∼0.5 ms of high-throughput MD simulations of MOR bound to the classical opioid drug morphine or the G protein-biased ligand TRV-130. Markov State Models (MSMs) built using these large datasets revealed distinct ligand-induced conformational dynamics and activation kinetics of MOR. Predicted equilibrium probabilities from these MSMs suggest that the three explored ligand-bound MOR complexes differentially populate active, inactive, and metastable regions along their respective activation pathways. Finally, transfer entropy estimates based on information theory were used to identify the distinct structural features that most contribute to the activation-induced conformational changes in the three ligand-bound MOR complexes.

Nanostructure in Fe0.65Cr0.35 close to the upper limit of the miscibility gap

The nanostructure of an Fe0.65Cr0.35 alloy has been investigated by atom probe tomography after high-precision thermal treatments close to the upper limit of the miscibility gap (MG). It is found that the wavelength of the decomposed ferrite between Cr- and Fe-rich regions grows exponentially when approaching the upper limit of the MG. Furthermore, the nanostructure change is gradual with temperature indicating a narrow metastable region and a diffuse transition out of the spinodal regime. Atomistic modelling near the limit of instability further supports the experimental observations. The findings are discussed in relation to the Cahn-Hilliard theory.

Chaotic study on a multibody interacting particle system with trajectory of variable curvature radius

Multibody interacting particle system is one of the most important driven-diffusive systems, which can well describe stochastic dynamics of self-driven particles unidirectionally updating along one-dimensional discrete lattices controlled by hard-core exclusions. Such determined nonlinear dynamic system shows the chaos, a complicated motion that is similar to random and can’t determine future states according to given initial conditions. Derived from the study of randomness in the framework of determinism, chaos effectively unifies determinacy and randomness of nonlinear physics, which also embodies the randomness and uncertainty of multi-body particle motions. Besides, chaos often presents complex ordered phenomena like aperiodic ordered motion state etc., which indicates it’s a stable coordination of local random and global mode. Different with previous work, a mesoscopic multibody interacting particle system considering the trajectory of variable curvature radius is proposed, which is more reliable to depict true driven-diffusive systems. Nonlinear dynamical master equations are established. Linear and nonlinear stability analyses are performed to test system robustness, which lead to linear stable region, metastable region, unstable region, triangular wave, solitary wave and kink-antikink wave. Complete numerical simulations under quantitatively changing characteristic order parameters are performed to reveal intrinsic chaotic dynamics mechanisms. By comparing fruitful chaotic patterns, double periodic convergence in stable limit cycles is observed due to attractors folding. System states tend to be limit cycles with the passage of time. The longer time is, the higher density is near attractors. The number of main components of attractors and the shape of them are found to drastically change with these parameters. Hereafter, the chaotic formation mechanism is explained by performing Fourier spectrums analyses. High and low frequency elements are obtained, whose module lengths are found to change periodically with time and nonperiodically with space. Our results show the sensitivity of the chaotic system to initial conditions, which mean slight changes of initial states in one part of system can lead to disproportionate consequences in other parts. The sensitivity is directly related to uncertainty and unpredictability. Moreover, calculations also show that three kinds of attractors (namely, point attractor, limit-cycle attractor and strange attractor) exist in the proposed chaotic system, which control particle motions. The first two attractors are convergence attractors playing a limiting role, which lead to static and balanced features of system. Oppositely, strange attractor makes the system deviate from regions of convergent attractors and creates unpredictability by inducing the vitality of the system and turning it into a non-preset mode. Furthermore, interactions between convergence attractors and strange attractors trigger such locally fruitful modes. This work will be helpful to understand mesoscopic dynamics, stochastic dynamics and non-equilibrium dynamical behaviors of multibody interacting particle systems.

Statistical Properties and Configurational Entropy of a Two-Dimensional Néel Magnetic Skyrmions Population

The study of the thermodynamic properties of topological defects is important not only for understanding their magnetic properties but also for suggesting novel applications. In this paper, the statistical and statistical thermodynamic properties of a population of Néel magnetic skyrmion diameters hosted in an ultrathin cylindrical dot is determined within a two-dimensional analytical approach. The statistical properties such as the skyrmion size are calculated in the region of skyrmion metastability and are compared with the ones obtained using a recent three-dimensional analytical approach based on the analogy with the Maxwell–Boltzmann distribution of dilute gas molecules. The investigation of the statistical thermodynamic properties focus on the calculation of the configurational entropy at thermodynamic equilibrium determined in the continuous limit from the Boltzmann order function. While the statistical properties are quantitatively similar passing from the two-dimensional to the three-dimensional approach, the configurational entropy calculated from the two-dimensional skyrmions distribution is considerably lower than the one obtained from the three-dimensional skyrmions distribution. Because of the strong resemblance between the statistical configurational entropy and Jaynes’s information entropy, it is suggested to use magnetic skyrmions as temperature and external field dependent information entropy carriers for a future potential technological application in the field of low-dimensional magnetic systems and skyrmionics.

Predicting maximally random jammed packing density of non-spherical hard particles via analytical continuation of fluid equation of state.

Dense packings of hard particles are useful models for condensed matters including crystalline and glassy state of solids, simple liquids, granular materials and composites. It is very challenging to devise predictive theories of random packings, due to the intrinsic non-equilibrium and non-local nature of the system. Here, we develop a formalism for accurately predicting the density (i.e., fraction of space covered by the particles) ηMRJ of the maximally random jammed (MRJ) packing state of a wide spectrum of congruent non-spherical hard particles in three-dimensional Euclidean space [Doublestruck R]3, via analytical continuation of the corresponding fluid equation of state (EOS). This formalism is based on the assumption that the fluid branch of the EOS can be analytically extended into the meta-stable region, which leads to a diverging pressure at the jamming point (i.e., the MRJ state). This allows us to estimate ηMRJ as the pole in the EOS, which can be expressed in terms of the virial coefficients encoding intrinsic local n-body packing information of the particles, and depending alone on particle shape. The accuracy of our formalism is verified using the hard sphere system and is subsequently applied to a wide spectrum of non-spherical shapes. The predictions are compared to numerical results whenever possible, and excellent agreements are found.

Clustering of protons as the main factor in increasing the activity of leaching solutions at their electrochemical and photochemical processing

The theoretical substantiation for the proton clustering process during electrochemical and photochemical processing of technological solutions is provided in the paper. This process provides a significant increase in the efficiency of leaching of gold from refractory ores. It was proposed that the chemical processes in aqueous solutions occur not only due to electronic (interelectronic) interactions, but also as a result of proton-electron interactions. The hypothesis is substantiated. Proton-electron interactions play an important role in the destruction and formation of chemical bonds between the solvent and the solute, as well as between dissolved substances. Compounds with a polymer-like structure can be formed during the electrolysis of aqueous solutions of different reagents, containing oxygen dimers (O-O). Hydrated cluster shell of active water molecules is formed around these polymer-like compounds. A metastable region of clustered protons is formed. Water-gas emulsion is formed during electrolysis and irradiatin with UV light. Highly active oxidants such as atomic oxygen, superoxide radical ion, ozone, and hydroxyl radical are synthesized in the gas bubbles. These compounds intensify protonation processes during hydration. The results of experiments on column activation leaching of dispersed gold from large-volume sample of refractory ore from the Pogromnoye deposit prove the validity of the theoretical substantiations.