Search

Using experimental data from literature [1], hydrogen density-pressure (ρ-P) and density-temperature (ρ-T) phase diagrams were drawn and evaluated for various pressure and temperature intervals. Solid, liquid, vapor, gas, supercritical liquid, supercritical gas and supercritical fluid regions were identified on the obtained diagrams. There are exact equilibrium boundaries between subcritical phases. On the contrary, it is concluded that there are no such exact boundaries for supercritical phases. Formation of the supercritical fluid between liquid and gas phases explained thermodynamically with first and second order partial derivatives of chemical potential relative to pressure at constant temperature. • Literature values for hydrogen are used for the graphical examination of the supercritical phases on phase diagrams. • Liquid-vapor, superheated steam, overcritical fluid and supercritical fluid regions were determined on the phase diagram. • Supercritical region observed starting at approximately 8 bar pressure between 34-36 K isotherms. • Critical pressure of ionization or decomposition for H 2 molecules was found as 1800 bar. • Supercritical fluid formation explained thermodynamically and a novel p-T phase diagram for hydrogen provided. [ABSTRACT FROM AUTHOR]

[Display omitted] • The amount of dissociation of natural gas hydrates below the quadruple point is non-linearly correlated with the depressurization rate. • The existence of a metastable state could be beneficial for increasing the gas production rate of methane hydrates and for improving the recovery rate of reservoir temperatures. • When hydrates disengagement the metastable region, the gas production rate of hydrates is improved. • The time that the hydrate is in the metastable region needs to be kept at the right time interval. The depressurization method has been proven to be an energy-efficient and relatively feasible production technique for natural gas hydrates. However, during the depressurization process, especially when the hydrates reservoir approaches the quadruple point, it is inevitable to experience phenomena such as freezing and hydrates secondary formation. Therefore, most researchers think that the P-T near the quadruple point may not be suitable for the dissociation of hydrates and a series of depressurization control methods were adopted to avoid this. However, according to other researchers, the effect of depressurization near the quadruple point on the dissociation behavior of hydrates is not inhibitory, but even a promoting effect to a certain extent. In addition, A special region called metastable state appears with the decrease of pressure near the quadruple point, which makes the dissociation behavior of hydrate below the quadruple point different from that above it. Therefore, in this paper, to reveal more clearly the dissociation behavior of natural gas hydrates near the quadruple point and the influence of the existence of metastable state on the depressurization dissociation of hydrate, the dissociation experiment of natural gas hydrates in the porous medium peri -freezing point is investigated in different depressurization rates and amplitudes, peri -freezing point and pressure stabilization times quadruple point. Experimental studies have shown that the amount of dissociation of natural gas hydrates below the quadruple point is non-linearly correlated with the depressurization rate. This correlation is synergistically regulated by the depressurization magnitude per unit of time and the environmental heating efficiency. Compared with the dissociation of hydrates above the freezing point, the metastable region does not show an obvious inhibitory effect on the dissociation of hydrates, and it even effectively shortens the dissociation time of hydrates and improves the heat transfer efficiency of the reservoir. Under the dissociation pressure of 2.5 MPa (metastable state), the reservoir temperature rose from 0 °C to 1 °C in 2.9 h, 3.6 h less than that under 2.6 MPa (above the quadruple point), and 0.7 h more than that under 1.0 MPa (below the metastable state). In addition, the gas production rate of hydrates is improved when hydrates disengagement the metastable region, increasing by 65.12 % compared with those above the quadruple point. However, pressure stabilization times when hydrates are in a metastable state need to be kept within a certain interval, too long or short pressure stabilization time will inhibit the dissociation of hydrates, and reduce the promotion effect on the dissociation of hydrates. [ABSTRACT FROM AUTHOR]

The Fe-Cr-Ni alloy (17-4PH steel) with metastable state was plasma thermochemical treated with and without rare earths (RE) addition. The experimental results show that after plasma thermochemical treatments, the initial coarse-grained structure with 20–40 μm grain size of 17-4PH steel could change into composition gradient nanoscale grains (as small as 5 nm) with random crystallographic orientations in plasma nitrocarburized layer. The hardness, modulus and wear resistance properties of nitrocarburized layer with nanoscale grains could be improved apparently. The present surface nanocrystallizaion method demonstrates the technological significance of metal alloy in improving traditional processing techniques and provides a new approach for surface nanocrystallizing of metal alloys. • Nanocrystalline structures are obtained by plasma treatment of metastable metal. • Grain size of 17-4PH steel is decreased from 20–40 μm to 5 nm by plasma treatment. • Grain nanocrystallization mechanism is mainly due to quasi-spinodal decomposition. [ABSTRACT FROM AUTHOR]

Ionic clathrate hydrates formed from aqueous solutions of tetra- n -butylammonium bromide in the course of rapid cooling (30 K min−1) to −35 °C have been examined. An earlier unknown metastable hydrate of cubic structure I was obtained from the solutions with concentrations from 3.2 to 4.8 mol%. [ABSTRACT FROM AUTHOR]

Abstract Protein aggregation is a multi-step process that requires sequential structural transitions of monomers during their incorporation into oligomers. Such process involves the formation of various intermediate stages in protein structures. Seed-nucleation mediated oligomerization is observed in many aggregation-prone proteins. Understanding of the protein seed's structural features and mechanisms of its transition-state formation are important for knowing the details of post-nucleation aggregation process. We have identified the metastable states in the seeds of the Ubiquitin associated (UBA) domain of Huntingtin Interacting Protein K (HYPK). This is studied by monitoring the events of dynamic transitions of metastable seeds to aggregates or monomers through microscopy, biophysical and computational techniques. HYPK-UBA seeds can exist in specific metastable state(s) that show transition from closed to open conformations, thereby reorienting the helix associated hydrophobic patches to cause its self-aggregation. Metastable seeds show inter-seed exchange of monomers through simultaneous dissociation-association phenomenon. Monomer release from metastable seeds can cause the dissolution of the aggregates. Like metastable monomers, metastable seeds also show reduction in their secondary structure by altering the molecular contacts and solvent accessible hydrophobic surfaces. Induction of metastable seeds from the ground-state is a slow thermodynamic process and it results from excitable perturbations. Conclusively, we propose the concept that the thermodynamic induction of metastable states in HYPK-UBA seed potentiates the molecule to switch its conformations that increases the protein's self-aggregation by the mechanism of hydrophobic patch collapse, while also releasing the monomers from oligomeric seeds due to structural instability. Graphical abstract Unlabelled Image Highlights • The UBA domain of HYPK is an aggregation-prone region that oligomerizes by seed-nucleation mechanism. • HYPK-UBA domain's seeds can exist in metastable states that drive its own aggregation process. • Monomers of HYPK-UBA can exist in metastable states that regulate the process of seed formation. • Formation of metastable states in the seeds and monomer of HYPK-UBA results from the thermodynamic events. [ABSTRACT FROM AUTHOR]

Highlights • The temperature- and thickness dependence of the lattice parameters of fcc Ti and Al films is investigated. • Metastable fcc Ti films have negative linear coefficients of thermal expansion. • The lattice parameter decreases with increasing temperature according to the «soft mode scenario». • The stable fcc Al (1 1 0) film becomes metastable when reducing the thickness to 8 unit cells. • The metastable Al(1 1 0) film 8 u.c. thick has a negative linear coefficient of thermal expansion. Abstract The molecular dynamics method with many-body potential of interatomic interaction constructed in the embedded atom model is used to study the thermal characteristics of aluminum and metastable fcc titanium nanofilms with (0 0 1) and (1 1 0) surface orientation. It is shown that in Al films the linear coefficients of thermal expansion are positive in all the directions, except for the area close to the melting temperature. For fcc titanium the linear coefficients of thermal expansion in the film plane are negative in a wide temperature range. With increasing temperature, in Ti films the local vibrational densities of states of the surface atomic layers, polarized along the x , y , z axes, shift to the low-energy part of the spectrum only in those directions where a decrease in the lattice parameters is observed. The changes in the interface areas of Al films occurring with increase in temperature, lead to the growth of anharmonicity and a "softening" of the local vibration spectra near the critical temperature. It is shown that the negative coefficient of linear expansion is an indicator of the simulated system being in metastable state. [ABSTRACT FROM AUTHOR]

Abstract The structures of methane hydrate obtained from water emulsions in oils of four types, n -heptane and n -decane were studied. Surfactant Span 80 was used to stabilize emulsions of water in n -heptane and n -decane. Hydrate synthesis was carried out by two methods, namely rapid cooling of a water-in-oil emulsion saturated with methane and long-term isothermal holding of this emulsion. It was shown that different methods of hydrate preparation may result in formation of gas hydrates with different structures. Rapid cooling of three of these emulsions (in two oils and n -heptane) saturated with methane to a temperature below −35 °C leads not only to the formation of the expected methane hydrate of cubic structure I (sI) but also to the cubic structure II (sII) hydrate. In case of oils, the formation of the hydrates in the emulsions seemed to occur at a temperature below the pour point of the corresponding oil. Experiments were carried out with the cooling rate about 14 °C/min at initial methane pressures near 12, 10 and 7 MPa. More detailed investigation showed that in two of these emulsions (in one oil and n -heptane) only sI hydrate is formed during long-term synthesis at 1 °C and methane pressure of 12 MPa. The formed sII hydrate must be metastable. In the case of the emulsion in second oil, the formation of sII hydrate can be related either to the kinetic factor (the formation of metastable hydrate) or to the presence of propane and butanes in the corresponding oil in rather high concentrations. The reason of the metastable phase appearance in the systems under consideration is most likely to be that Span 80 and some kinds of crude oil can inhibit nucleation of sI gas hydrate at the oil – water interface. Thus, some emulsions saturated with methane can be overcooled to a temperature at which the nucleation of sII hydrate is preferable. The data obtained are of interest to understand mechanisms of gas hydrate inhibition/promotion and may provide fresh insight into the influence of crude oils and surfactants on gas hydrate nucleation in water – oil – gas systems. Highlights • Methane hydrate formation in fastly cooled water in an oil emulsion was studied. • sII instead of sI hydrate formation was observed in experiments with two oils and n-heptane. • It was shown that some oils can contain "hidden" C 2 C 4 hydrocarbons. • The "hidden" hydrocarbons are responsible in sII formation in one emulsion. • It was proved that metastable sII methane hydrate can form in another emulsions. [ABSTRACT FROM AUTHOR]

Abstract The temperature and time dependent structure of molten NiP alloy of eutectic composition has been studied by neutron diffraction. Ni particles were found to exist in the melt at temperatures at least up to about 150 degrees above liquidus. The amount varies reversibly as temperature increases but decays slowly with time. Remarkably, particles still exist even after that the melt has been kept more than 30 h at different temperatures in the molten state. The static structure factor and the pair distribution function obtained at 1050 °C are presented. Highlights • Ni particles exist in Ni 81 P 19 melt at temperatures at least up to about 150 degrees above liquidus. • Particles still exist in NiP melt even after it was kept >30 h in the molten state. • The amount of particles in NiP melt increases reversibly with temperature but decays with time. [ABSTRACT FROM AUTHOR]

Optical emission spectroscopy (OES) is an important technique for the diagnostics of plasma parameters in the development of plasma devices and material processing technology. OES depends on the collisional-radiative model which can accurately describe the kinetics of excited species in plasma. Metastable species usually have higher density (2–4 orders of magnitude) and longer lifetime (3–6 orders of magnitude) compared to other excited species, thus play important roles in the reaction kinetics. However, the kinetic of metastable species can be complex due to the transport and self-absorption processes, which may lead to coupling of the plasma reaction kinetics in the adjacent areas. Moreover, the line splitting of some elements make the description of metastable kinetics more complex. This work presents an OES method based on a collisional-radiative model considering the hyperfine splitting of emission lines into metastable levels. The density distribution of metastable state is determined by the self-absorption effect. It is then taken into the rate balance equations of other excited species to make an accurate description of metastable related kinetics. The electron density and temperature are determined based on this model. The OES method is demonstrated on a miniaturized electron-cyclotron-resonance ion thruster. The metastable density, electron density and electron temperature are determined along the radial direction of the ion thruster, which can be useful for revealing the physics of discharge phenomenon and optimizing the performance of the plasma source. This method can be used to determine electron parameters in a large pressure range. [Display omitted] • An OES method utilizing spectral and spatial line-ratios is proposed. • Metastable transport among adjacent areas is considered. • Metastable density is determined by self-absorption considering hyperfine splitting. • Radially-resolved electron density and temperature are determined. • Saturation of electron parameters with operating condition parameters is observed. [ABSTRACT FROM AUTHOR]

The radiative lifetimes of Xe 3+ ions in the metastable 5s 2 5p 3 2 P 3/2 and 2 P 1/2 states were measured by using an electrostatic ion beam trap. The lifetimes were obtained by measuring the number of photons emitted during the 2 P 3/2  →  2 D 3/2 (447 nm) and 2 P 1/2  →  4 S 3/2 (357 nm) forbidden transitions of Xe 3+ , as a function of the storage time. The storage lifetime of the Xe 3+ was simultaneously measured by detecting the Xe ions with changed charge escaping from the trap, which yielded information pertaining to the correction of the collision-induced loss of Xe 3+ in the trap. The obtained lifetimes of 7.0 ± 0.2 ms for the 2 P 3/2 state and 16.6 ± 0.8 ms for the 2 P 1/2 state were compared with previously reported theoretical and experimental values. [ABSTRACT FROM AUTHOR]

The previously proposed model for the kinetics of first-order phase transitions (Barsuk et al., 2013) is generalized for r order and m control parameters. Bifurcation and stability analyses of the equilibrium states in thermodynamic systems described by the Landau-type kinetic potential with two order parameters is performed both in the absence of an external field, and in the presence of constant and periodic external fields. Kinetics of thermodynamic systems described by such potential in a small neighborhood of the equilibrium states is also studied. Mean transition time for lysozyme protein in dependence of control parameters is obtained based on the developed model. A detailed bifurcation analysis of the cubic equation solutions is given in Appendix. [ABSTRACT FROM AUTHOR]

Frictional effects on the wave packet dynamics of quantum systems are investigated in the framework of the Schrödinger–Langevin equation. The Schrödinger–Langevin equation is directly solved using the split-operator method. Frictional effects impede the propagation and suppress the spreading of the wave packet. Computational results are presented for an Eckart barrier scattering problem, the decay of a metastable state, and the long-time behavior of a decaying quantum system. Significant features of dissipative Bohmian trajectory dynamics are analyzed for these quantum processes. [ABSTRACT FROM AUTHOR]

The radiative lifetime of the 3s 2 3p 4 1 S 0 metastable state of Ar 2+ was measured using an electrostatic ion beam trap. The lifetime was obtained by measuring the number of photons emitted during the 1 S 0 → 3 P 1 magnetic dipole transition of Ar 2+ as a function of the storage time. The wavelength of the photons was 311 nm. To correct for the collision-induced loss of Ar 2+ ions in the trap, the storage lifetime of the Ar 2+ beam was measured simultaneously by detecting Ar neutrals escaping from the trap. The obtained radiative lifetime was 157 ± 19 ms, which was comparable to previously reported theoretical and experimental values. [ABSTRACT FROM AUTHOR]

In order to research the adaptivity of the capillary tube in the transcritical CO 2 refrigeration system, a separated flow model of a CO 2 capillary in which the metastable phenomenon was taken into consideration was built in the simulation of transcritical CO 2 refrigeration system, and related experiments were carried out by a plant under different gas-cooler outlet temperatures. The performances of the capillary based system were further compared with that of the EEV (electronic expansion valve) based system. The results showed that the relative COP ranged from 82% to 98% when there was a 10 °C deviation between the real gas-cooler outlet temperature and the design value. Thus the capillary based transcritical CO 2 system is promising and could achieve performance close to that of EEV based system in a wide range of gas-cooler outlet temperature. [ABSTRACT FROM AUTHOR]

Layers of amorphous ice were prepared by deposition of supersonic molecular beams of rarefied vapor on a substrate cooled by liquid nitrogen. Molecular beam entered a vacuum chamber through Laval nozzle, which accelerated it to a supersonic speed. An adiabatic expansion of molecular beam leads to a decrease in the temperature at the nozzle outlet and formation of crystalline nanoclusters of water. Under heating of nonequilibrium condensates one could observe a glass transition (softening) and subsequent spontaneous crystallization. The presence of water clusters introduced into nonequilibrium condensates artificially ensured conditions for the initiation of “hot” centers and a transition to an explosive regime of crystallization in an amorphous medium. A theoretical analysis has been made of the role of the thermal conditions in which the crystallization of an amorphous substance proceeds, with allowance for the nonstationary nucleation. [ABSTRACT FROM AUTHOR]

[Display omitted] • The measured phase change pressures of liquid foods were much greater than 210 MPa. • The phase transition point of the solution was affected by the solute type but not by the concentration. • The high pressure metastable phase transition was successfully promoted by implementing perturbation. • Using 20% sodium chloride solution as the perturbation source facilitated the phase transition of apple juice better. • Perturbation induced a decrease in phase transition pressure of apple juice from 305 MPa to 239 MPa. In this study, the distribution of ice Ⅰ - ice III phase transition positions and its influencing factors on various fruit juices and food model solutions under high pressure (HP) were investigated. In addition, the effect of perturbation on induction of phase change in metastable apple juice was also explored. The phase transition positions of fruit juice samples deviated far from the theoretical value (210 MPa/ –21 °C), with pressure in range of 268 ∼ 305 MPa and temperature between –31.09 °C and –37.21 °C, with the most extreme phase transition position of 305 MPa/ –37.21 °C for apple juice. The phase change position was affected by the type of solution but not by the concentration of solutions. The cooling media namely, sodium chloride (5%, 20%) and glucose solution (5%, 20%) were used as perturbation sources to stimulate the metastable apple juice by using instantaneous volume reduction during the ice Ⅰ - ice III phase transition. They successfully promoted the phase transition of apple juice, where 20% sodium chloride solution significantly (p < 0.05) reduced the phase change pressure of apple juice to 239 MPa. The perturbation effect was influenced by the type and concentration of the perturbation source, the composition of the cavity area and the softness of the sample container. [ABSTRACT FROM AUTHOR]

• The kinetics of nucleation in a superheated methane–nitrogen solution was investigated. • Measurements has been made at two values of pressure and full range of composition. • The mean life time method has been used. • The results of experiments have been compared with classical nucleation theory. The mean life time method has been used to investigate the kinetics of nucleation in a superheated methane–nitrogen solution. Measurements have been made in the range of nucleation rates J = (1.2·104–1.6·108) m−3s−1. Temperature dependences of the nucleation rate have been obtained for seven compositions of the solution at pressures p = 1.0 and 1.6 MPa. The results of the experiments have been compared with classical nucleation theory (CNT). In contrast to pure methane and hydrogen, where superheating temperatures achieved by experiment are lower than their theoretical values, in methane–nitrogen solutions the opposite behavior is found. Close to the equimolecular composition limiting superheatings of solutions exceed theoretical values by (1.2–1.6) K. Possible reasons for the disagreement between CNT and experiment (size dependence of the surface tension of critical bubbles, bypassing the saddle point of the activation barrier, etc) are analyzed. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Helium atmospheric pressure plasma jet spectra were enhanced by the LIP. • A grounded metallic target extended lifetime of plasma radiation in APPJ. • Population density of He 2 3 S state increased to ∼50 times by LIP. • Relative spatial distribution of the 2 3 S state was deduced along helium flow. • 2 3 S state played a key role in the enhancement of He spectra. A helium (He) atmospheric pressure plasma jet (APPJ) system was constructed, and two guided streamers in He APPJ were produced. The propagation of the guided streamer was observed using ICCD camera when a grounded metallic target was employed. The target extended the lifetime of the plasma radiation of the guided streamer. A ns pulsed laser was irradiated at He APPJ with the target and optical emission spectra were measured. The interaction between the APPJ and pulsed laser enhanced various spectra of He APPJ. The enhancement of the spectra, the line integrated population density of He 2 3 S metastable state, electron temperature, and electron density were measured as the time interval between the pulsed laser and the guided streamer changed. The relative spatial distribution of He 2 3 S metastable state in the guided streamer in the absence of the pulsed laser was deduced along He flow. The role of He metastable state was discussed when the pulsed laser interacted with He APPJ. [ABSTRACT FROM AUTHOR]

W nano-fuzzes have been formed due to the large-flux and low-energy (200eV) He + irradiation at W surface temperature of 1480 °C. Microscopic evolution of W nano-fuzzes during annealing or low-energy (200 eV) He + bombardments has been observed using scanning electron microscopy and thermal desorption spectroscopy. Our measurements show that both annealing and He + bombardments can significantly alter the structure of W nano-fuzzes. W nano-fuzzes are thermally unstable due to the He release during annealing, and they are easily sputtered during He + bombardments. The current study shows that W nano-fuzzes act as a metastable state during low-energy and large-flux He + irradiation at an elevated temperature. [ABSTRACT FROM AUTHOR]

Residual stress has a strong effect on the mechanical performance of coatings. To understand the mechanism of its generation and evolution in metastable alloy coatings, Ni-B alloy coatings with different degrees of crystallinity were prepared on 0.45% carbon steel substrate by an electro-brush plating technique. The amorphous proportion and grain size were investigated by X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). With the help of the Lee model and Suresh model, residual stress in metastable state Ni-B alloy coating was determined from the load-displacement curves obtained by nanoindentation. From XRD and TEM results, the deposition was composed of amorphous and nanocrystalline phases, which contained compressive stress in the as-plated coatings. The compressive level decreased with the increase of annealing temperature. Compared with the Suresh model, Lee model is more suitable to evaluate residual stress in the metastable state materials. The experimental results also revealed that the compressive residual stress level was directly related to the total area of grain boundary. [ABSTRACT FROM AUTHOR]

We report a molecular dynamics (MD) study of homogeneous bubble nucleation in a stretched Lennard-Jones binary mixture at a temperature close to the solvent triple point. The pressure of the limiting stretching p n corresponding to a fixed value of the nucleation rate has been determined. The values of p n achieved in MD simulation are lower than those calculated from classical nucleation theory (CNT). The discrepancy between the data of MD simulation and CNT may be connected with the neglect in the latter of the size dependence of the surface tension of critical bubbles. [ABSTRACT FROM AUTHOR]

We have used photoluminescence (PL) and photomodulation (PM) spectroscopy to investigate the reversible spectral changes of PL in CH 3 NH 3 PbI 3−x Br x films, where x is 1.7. In an as-prepared film, the peak of PL spectra shifts from ∼640 nm near bandedge to ∼750 nm after excitation by a continuous wave (CW) or a pulsed laser with high repetition rate, but keeps at 640 nm excited by same pulsed laser with the repetition rate smaller than 500 Hz. The PM spectroscopy also shows the formation of sub bandgap states after illumination which is responsible for the red shift of PL. The light induced modification of optical properties is reversible after keeping the film out of illumination for several hours at room temperature. We analyze the photoinduced modification to be two-steps processes: the temporary sub bandgap states were first photogenerated in perovskite film, if those states interacting with more coming photons within their lifetimes, light induced metastable states responsible for red-shift of PL will be formed. This instability reduces the electronic bandgap and generates more traps which will degrade the performance of the related photovoltaic devices. [ABSTRACT FROM AUTHOR]

The free energy of the charged drops of water and of light ions inside drop-ionic plasma of clouds and fog was calculated on the basis of the Poisson–Boltzmann equation. It is shown that when the charge is greater than several tens of elementary charge units, the positively and negatively charged drops can have metastable states which are characterized by the space-ordered arrangement of the drops. In general, the drop-ionic plasma has no metastable state. But, in the case that the average charges of positively and negatively charged drops differ in absolute value by less than 10–20%, drop-ionic plasma can have a metastable state as a whole. This state was thought to be responsible for the long confinement of drops in a compact volume and for their subsequent coalescence. It is shown that the electrostatic attraction of drops and their coalescence are capable of explaining the rapid growth of water drops up to rain size inside clouds. [ABSTRACT FROM AUTHOR]

Our high-level ab initio calculations show that the ZnCl 2+ ground state of 2 Π symmetry is metastable with a bond length of 2.242 Å, an effective dissociation energy of 1.66 eV, and an adiabatic double ionization energy of ZnCl of 26.11 eV. Potential energy curves for 18 Λ + S states and ten Ω states of ZnCl 2+ are presented as well as the associated spectroscopic constants. Tunneling lifetimes, spin–orbit induced predissociation lifetimes and radiative lifetimes for the vibrational levels in the low-lying electronic states of ZnCl 2+ are determined and the metastability of the dication is discussed. [ABSTRACT FROM AUTHOR]

Abstract: The magnetic properties of a cylindrical Ising nanotube with a spin- 1/2 core surrounded by a spin- 3/2 shell system have been studied by means of the effective field theory (EFT). We have investigated the effects of crystal-field coupling at the surface shell and bilinear interactions among the core and surface shells to the order parameters, susceptibility, internal energy, specific heat, and free energy. Some characteristic phenomena are examined in terms of thermal or crystal-field variations when the other system parameters are fixed. Moreover, we have observed first-order and second-order transitions and critical end points in the (D/J, kT/J) plane, where D/J and kT/J are crystal-field and temperature, respectively. [Copyright &y& Elsevier]

Abstract: We numerically study a one-dimensional system of classical localized planar rotators coupled through interactions which decay with distance as ( ). The approach is a first principle one (i.e., based on Newton’s law), and yields the probability distribution of momenta. For large enough and we observe, for longstanding states, the Maxwellian distribution, landmark of Boltzmann–Gibbs thermostatistics. But, for small or comparable to unity, we observe instead robust fat-tailed distributions that are quite well fitted with -Gaussians. These distributions extremize, under appropriate simple constraints, the nonadditive entropy upon which nonextensive statistical mechanics is based. The whole scenario appears to be consistent with nonergodicity and with the thesis of the -generalized Central Limit Theorem. [Copyright &y& Elsevier]

Abstract: A parametric description of phase transitions is done by using general analytical methods involving the bifurcation (branching) of solutions of nonlinear equations in a closed analytical form. The models include an order parameter in the Landau-type kinetic potential, and have been developed to study the impact of both asymmetry and external field on phase transitions in the presence of an intermediate state. General analytical solutions, their stability, and the realization of different transition scenarios in the whole parameter plane divided into three and four regions, respectively, which admit different numbers of distinct physically acceptable solutions, are discussed. The mean transition time between stable liquid and crystalline phases in the region of coexistence of two liquid states is obtained. In particular, the results are analyzed in comparison with generic models of the intrinsic transition dynamics and transition dynamics in the presence of heterogeneity (clusters), when the kinetic potential contains a unitary coefficient of asymmetry. Asymptotic representations of the entire set of parametric dependences are also obtained and analyzed. [Copyright &y& Elsevier]

Abstract: Potential energy curves of low-lying electronic states of the CN2+ dication and of the electronic ground states of CN+ and the neutral CN molecule were calculated using internally contracted multireference CI and the coupled cluster RCCSD(T) methods. Spectroscopic constants and adiabatic excitation energies of 13 quasibound electronic states of the dication were obtained and the energy of charge stripping of CN+ and double ionization energy of CN were predicted. Tunneling and spin–orbit induced predissociation lifetimes for the vibrational levels in the low-lying electronic states are presented and the metastability of the dication is discussed. [Copyright &y& Elsevier]

Abstract: Chitin powder was soaked in concentrated sodium hydroxide solution (45%, w/w), and freezed at −18/−35°C for further modification (the ratio of chitin and sodium hydroxide solution was 1:10, w/v). The degree of deacetylation (DDA) was determined by acid–base titration while the structural changes of the regenerated chitin after alkali-freezing treatment were investigated by X-ray diffraction (XRD), infrared spectroscopy (IR) and differential scanning calorimetry (DSC). The results showed that the formation and growth of ice crystal during the slowly freezing process could break the intra- and inter-molecular hydrogen bonds, disorganize the ordered molecular structure, destruct the compact crystal structure and decline the crystallinity. However, such structural damage was unstable and reversible. Nevertheless, the study explained that the alkali-freezing treatment was beneficial for further modification of chitin, which could significantly promote its solubility and accelerate the chemical reaction rate, while it could also keep its main molecular chains completely. [ABSTRACT FROM AUTHOR]

Abstract: Discovery of the anomalous generation and extinction of crystal nuclei in nonequilibrium supercooled liquids reflects essentially the effects of the real heterogeneous structure and its irreversible relaxation on the stability of the nucleus. The kinetic model involving one order parameter was developed to study the impact of both asymmetry and external field on crystallization, thus allowing looking, in particular, into the heterogeneous structure relaxation in such materials. The role of asymmetry and external field on phase transitions in the presence of an intermediate metastable state is described in comparison with such generic model. We found that the influence of the external field on the system with an intermediate metastable state is to reduce the stability of phases, and, therefore, the crystal nuclei generation could be slowed or even stopped. Meanwhile the role of cubic term in order parameter of the Landau-type potential associated to the asymmetry of the system is to increase the stability of new phase for the suitably varied control parameter. Finally, the cases which allow analytical solution of the problem and the realization of different transition scenarios are discussed. [Copyright &y& Elsevier]

Abstract: Using a previously developed experimental technique, the behavior of small methane and propane hydrate samples formed from water droplets between 0.25 and 2.5mm in size has been studied in the pressure–temperature area between the ice–hydrate–gas equilibrium line and the supercooled water–hydrate–gas metastable equilibrium line, where ice is a stable phase. The unusual persistence of the hydrates within the area bounded by these lines and the isotherms at T=253K for methane hydrate or at T=263K for propane hydrates was observed. This behavior has not previously been reported. For example, in the experiment carried out at 1.9MPa and 268K, the methane hydrates existed in a metastable state (the equilibrium pressure at 268K is 2.17MPa) for 2 weeks, then immediately dissociated into liquid supercooled water and gas after the pressure was isothermally decreased slightly below the supercooled water–hydrate–gas metastable equilibrium pressure. It was found that dissociation of metastable hydrate into supercooled water and gas was reversible. The lateral hydrate film growth rates of metastable methane and propane hydrates on the surface of supercooled water at a pressure below the ice–hydrate–gas equilibrium pressure were measured. The temperature range within which supercooled water formed during hydrate dissociation can exist and a role of supercooled water in hydrate self-preservation is discussed. [Copyright &y& Elsevier]

In this article, we report the optical probing of SnTe (275 nm and 33 nm) and Indium-doped SnTe films (50 nm) which are deposited using thermal evaporation. XRD (X-ray diffraction) and Raman spectroscopy are used to characterize the films. Additionally, the optical characteristics of the material are examined using reflectance and PL (photoluminescence) spectroscopy. Simultaneously, the dynamics of charge carriers are studied using TRUS (Transient reflectance ultrafast spectroscopy). The TRUS probes the thin films in the visible to near-infrared range (400–1600 nm) with a probe latency of a few femtoseconds to 6 ns. The study demonstrates the presence of a resonant state in SnTe, which becomes more prominent and metastable with indium doping. Optical probing of SnTe (275 nm and 33 nm) and indium doped SnTe films (50 nm) which are deposited using thermal evaporation. The films are characterized through XRD (X-ray diffraction) and Raman spectroscopy. Further, the optical properties are investigated through reflectance spectroscopy and PL (photoluminescence) spectroscopy. The emission spectroscopy in the visible regime confirms the presence of 2.1 eV emission. The TRUS measurements confirm the confinement of the charge carriers at 33 nm SnTe film w. r.t 275 nm SnTe. The indium dopant films show the presence of a metastable state which is absent in SnTe. This state resembles the resonant state at 0.82 eV and eventually can be tuned to various optoelectronic applications. [ABSTRACT FROM AUTHOR]

As an important clean energy resource, natural gas hydrates (NGHs) have attracted considerable research interest. Gas recovery efficiency is an important factor affecting the commercial development of NGHs. Owing to the endothermic reaction of NGH dissociation, the temperature of the local hydrate reservoir may be greatly reduced. The dissociation characteristics of NGHs at low temperature may significantly affect the gas production efficiency. More than 90% of the world's NGHs exist in low-permeability fine-grained sediments, and the dissociation behaviors of NGHs in these media below the ice point are not fully understood. In this study, the dissociation characteristics of the hydrate in clayey-silt were tested at negative temperatures. Clayey-silt samples were prepared according to the characteristics of cores recovered in the South China Sea. After methane hydrate formed in the samples, its dissociation rate was tested under different negative temperatures. The results show that the methane hydrate had a low dissociation rate between 243 K and 253 K in the clayey-silt samples. More than 90% of the methane hydrate was preserved within 24 h. The stability of methane hydrate is related not only to dissociation pressure but also to a metastable state. Methane hydrate in clayey-silt has high stability in metastable region. The stability of gas hydrate under negative temperatures has great potential application value in the field of gas storage. [Display omitted] • The self-preservation of methane hydrate in clayey-silt samples has been verified. • Methane hydrate in clayey-silt has high stability in a metastable zone. • In low-permeability porous media, fine-grained methane hydrate exhibited stability below 250 K. [ABSTRACT FROM AUTHOR]

Abstract: The superheated emulsion detector (SED), a well-known detector for neutrons, ions, electrons and photons, contains droplets of superheated liquid held in a viscoelastic gel. It is well known that these droplets are in a metastable state, decaying both spontaneously and when induced by energetic radiation. Here, it is shown that the SED comprises droplets of more than one metastable states nucleating to vapor bubbles at different frequencies. To the best knowledge of the authors the existence of two metastable states of the active liquid in SED has not been reported before. [Copyright &y& Elsevier]

Abstract: A detailed one-dimensional steady and transient numerical simulation of the thermal and fluid-dynamic behavior of capillary tube–suction line heat exchangers has been carried out. The governing equations (continuity, momentum, energy and entropy) for fluid flows, together with the energy equation in solids, are solved iteratively in a segregated manner. The discretized governing equations in the zones with fluid flow are coupled using a fully implicit step-by-step method. An implicit central difference numerical scheme and a line-by-line solver were used in solids. A special treatment has been implemented in order to consider transitions (subcooled liquid region, metastable liquid region, metastable two-phase region and equilibrium two-phase region). All the flow variables (enthalpies, temperatures, pressures, mass fractions, heat fluxes, etc.) together with the thermophysical and transport properties are evaluated at each point of the grid in which the domain is discretized. The numerical model allows analysis of aspects such as geometry, type of fluid, critical or non-critical flow conditions, metastable regions and transient cases. Comparison of the numerical simulation with experimental data presented in the technical literature will be shown in Part II of the present paper. [Copyright &y& Elsevier]

Abstract: A detailed one-dimensional steady and transient numerical simulation of the thermal and fluid-dynamic behavior of capillary tube–suction line heat exchangers considering metastable region and separated flow has been developed in Part I of this paper. The developed numerical model allows analysis of aspects such as geometry, type of fluid, critical or non-critical flow conditions and metastable region. The accuracy of the detailed simulation model is demonstrated in this part (Part II) of the paper by comparing simulation results with a wide range of steady state experimental data from the technical literature, which include the refrigerant mass flow rate, outlet suction line temperature, and temperature profile along concentric and lateral capillary tube–suction line heat exchangers. Of the 196 data points evaluated for mass flow rate 96.4% are within an error of ±15%, 81.1% are within ±10% with a mean deviation of ±6.3%. Of the 143 data points evaluated for outlet suction line temperature 89.5% are within an error of ±2°C, with a mean deviation of ±0.98°C. The numerical results obtained are used to understand the refrigerant flow behavior inside non-adiabatic capillary tubes. Some divergence problems in the numerical solution process is found to be the discontinuity in non-adiabatic capillary tube flow characteristics caused by re-condensation of the refrigerant within the heat exchanger zone; this aspect needs special attention while modeling the non-adiabatic capillary tube flow. Other important parameter to be evaluated experimentally with special care is the capillary tube internal diameter due to its strong influence on the refrigerant flow results (results of any study based on the nominal diameter are to be used with caution). [Copyright &y& Elsevier]

Abstract: We have developed an apparatus, which can measure heat flux and dielectric constant simultaneously. The heat flux and the dielectric constant of a single crystalline BaTiO3 were simultaneously measured with a temperature resolution of milli-Kelvin to study the detailed behavior of the phase transition. The anomalies are observed between 400 and 402K both in the heat flux and the dielectric measurements with a close correlation between the heat flux and the dielectric constant. A slow increase and a sudden jump in the dielectric constant were observed in the heating process and at least five thermal anomalies were observed between 400.3 and 401.2K in the cooling process. The unstable state was observed in the vicinity of Curie temperature keeping at a constant temperature both in the heating and cooling process. The hysteretic behaviors of the phase transition and the unstable state were discussed in terms of two-phase domains in the transition. [Copyright &y& Elsevier]

Abstract: The formation of skeletal silver–cobalt structures was attempted by means of chemical leaching of Al atoms from various ternary Al–Ag–Co alloys which were prepared by rapid solidification or mechanical alloying. Almost all Al atoms were removed for rapidly solidified alloys and their crystallographic structure was changed from fcc of Al into fcc of Ag during chemical leaching. The microstructures of the leached specimens were observed by transmission electron microscopy. TEM observation showed that the leached specimens had a skeletal structure composed of finely distributed particles and fine pores. The particles were classified into two groups by size. The first one was rather large and about 30nm in size. The other was fine and a few nanometers. No detectable diffraction peaks corresponding to the Co phase were observed but they were detected after annealing at 1073K for 3.6ks. The saturation magnetization of the leached specimens gradually increased with increasing temperature and approached to the maximum. A part of this variation was due to the precipitation of Co from the supersaturated Ag(fcc) phase. The chemical leaching of Al–Co–Ag alloys might open the possibility to form a skeletal material with a metastable state in which a few cobalt atoms dissolved into the silver phase. [Copyright &y& Elsevier]

The problems of escape from metastable state in randomly flipping potential and of diffusion in fast fluctuating periodic potentials are considered. For the overdamped Brownian particle moving in a piecewise linear dichotomously fluctuating metastable potential, we obtain the mean first-passage time as a function of the potential parameters, the noise intensity and the mean rate of switchings of the dichotomous noise. We find noise-enhanced stability phenomenon in the system investigated and the parameter region of the fluctuating potential where the effect can be observed. For the diffusion of the overdamped Brownian particle in a fast fluctuating symmetric periodic potential we obtain that the effective diffusion coefficient depends on the mean first-passage time, as discovered for fixed periodic potential. The effective diffusion coefficients for sawtooth, sinusoidal and piecewise parabolic potentials are calculated in closed analytical form. [Copyright &y& Elsevier]

The kinetics of ordering in fcc alloys during the epitaxial growth is investigated by the kinetic mean field method. There are various evolution behaviors during the growth of the system. The kinetic phase diagrams for the epitaxial alloy of an fcc multilayer are calculated. We have found that there is a kinetic induced oscillatory ordered phase in addition to the equilibrium ordered phase in the kinetic phase diagrams. [Copyright &y& Elsevier]

Light-induced metastable electronic states as observed e.g. in sodium nitroprusside are of fundamental interest for data storage and optical computing. Structural functionality and therefore the light-induced structure itself is of basic interest in such systems. As neutrons are sensitive to the position of the nucleus and non-destructive with respect to the metastable electronic states, neutron photocrystallography provides a useful method to determine light-induced structural changes. A photocrystallographic experimental setup has been built-up at SINQ and has been successfully used at the single-crystal instrument TriCS and the test facility TOPSI (now called MORPHEUS). [Copyright &y& Elsevier]

We investigate the escape of a Brownian particle from fluctuating metastable states. We find the conditions for the noise enhanced stability (NES) effect for periodical driving force. We obtain general equations useful to calculate the average escape time for randomly switching potential profiles. For piece-wise linear potential profile we reveal the noise enhanced stability (NES) effect, when the height of “reverse” potential barrier of metastable state is comparatively small. We obtain analytically the condition for the NES phenomenon and the average escape time as a function of parameters, which characterize the potential and the driving dichotomous noise. [Copyright &y& Elsevier]

We present a study of the noise driven escape of an overdamped Brownian particle moving in a cubic potential profile with a metastable state. We analyze the role of the initial conditions of the particle on the enhancement of the average escape time as a function of the noise intensity for fixed and fluctuating potentials. We observe the noise enhanced stability effect for all the initial unstable states investigated. For a fixed potential we find a peculiar initial condition xc which separates the set of the initial unstable states in two regions: those which give rise to divergences from those which show nonmonotonic behavior of the average escape time. For fluctuating potential at this particular initial condition and for low noise intensity we find large fluctuations of the average escape time. [Copyright &y& Elsevier]

Isochoric heat capacity data of n-C7H16, n-C12H26, and CO2+n-C10H22 in the immediate vicinity of the phase transition points including thermodynamically stable and metastable phases are presented. Measurements were made using a high-temperature, high-pressure, adiabatic, and nearly constant-volume calorimeter in the temperature ranges: for n-heptane—from 323 to 422 K and densities of 657.9, 612.4, and 571.1 kg m−3; for n-dodecane—from 323 to 378 K and densities of 689.2 and 726.8 kg m−3; and for CO2+n-decane mixture—x=0.822 and 0.905 mole fraction of CO2, densities of 347.1 and 287.8 kg m−3, respectively, for temperatures between 471 and 494 K. Some features of the isochoric heat capacity measurements in the immediate vicinity of phase transition temperatures are discussed. This method allowed measurements of CV in the one- and two-phase regions including coexistence curves and metastable phases. Measurements in the stable states were carried out at constant volume by the continuous-heating (dT/dτ>0) method. Measurements near the phase transition points in the stable and metastable states were carried out using continuous-cooling (reverse direction, dT/dτ<0) runs. For each measured liquid isochore during cooling runs we found penetration to the metastable region. The magnitude of the penetration depth varied from 0.03 to 0.41 K depending on measured densities. Our experimental results indicate that the character of the temperature dependence of CV does not change, when moving along an isochore, upon the intersection of the coexistence curve and transition into the metastable state. The results of CV and measurements for n-heptane and n-dodecane in the one-phase region and on the coexistence curve were compared with values calculated from different equations of state (EOS) and previous publications. [Copyright &y& Elsevier]

We consider the possible manifestations of critical phenomena under pulsed laser ablation (PLA). The mechanism of phase explosion under nanosecond laser ablation is considered and the possibility of estimating the critical temperature from PLA experiments is discussed. A model based on the Euler equations and generalized van der Waals equation is developed to describe rarefaction shock waves (RSW) in near-critical matter. For a near-surface slab of a gold target heated above the critical point and expanding freely in vacuum, the evolution of the RSW has been studied. The possibility of RSW formation in stellar matter is discussed. [Copyright &y& Elsevier]

We present a model of femtosecond laser ablation for a metal target, including three sets of equations for different time scales and ablation conditions: a two-temperature model of laser radiation absorption by conduction electrons and electron–lattice relaxation; the thermal conductivity equation to describe the subsequent temperature evolution; the Euler equations supplemented with generalized van der Waals equation to describe vapor expansion. The solid–liquid interface is followed in the calculations. A metastable state of the molten layer has been shown to occur for regimes both below and above the ablation threshold that may not lead to phase explosion. For phase explosion to be put into effect, an external action has to be applied. For laser fluences below the ablation threshold, a probe laser pulse can play the role of the external action, whereas for high fluences the recoil pressure of the expanding vapor causes explosive boiling. [Copyright &y& Elsevier]

The equilibrium phase diagram of a two-dimensional Ising model with competing exchange and dipolar interactions is analyzed using a Monte Carlo simulation technique. We consider the low temperature region of the (δ,T) phase diagram (δ being the ratio between the strengths of the exchange and dipolar interactions) for the range of values of δ where striped phases with widths h=1 and 2 are present. We show that the transition line between both phases is a first order one. We also show that, associated with the first-order phase transition, there appear metastable states of the phase h=2 in the region where the phase h=1 is the thermodynamically stable one and vice versa. [Copyright &y& Elsevier]

Equiatomic ternary compounds, TbPdIn and DyPdIn, have been studied by means of DC magnetization, AC susceptibility, magnetic relaxation, specific heat and electrical resistivity measurements. The two compounds are ferromagnets below a transition temperature TC=74 K for TbPdIn and TC=38 K for DyPdIn with metastable magnetic properties, behaving as the irreversibility of the temperature dependence of magnetization below a characteristic temperature Tir and the long-time magnetic relaxation behavior below TC when changing the magnetic field at a constant temperature. DyPdIn shows the second phase transition at TN=23 K, caused by the antiferromagnetic coupling. For both compounds, the ground state is not a collinear ferromagnet, but some canted one with antiferromagnetic component. The observed metastable magnetic properties are discussed in terms of domain-wall pinning model. The complex magnetic structures in DyPdIn and TbPdIn are compared with those of isostructural DyNiAl and HoNiAl. [Copyright &y& Elsevier]

• Mn Zn ferrite particles with a size of ≈ 12 nm are prepared by hydrothermal synthesis. • Analysis by Mössbauer spectroscopy and neutron diffraction reveals a metastable state. • Mn 0.6 Zn 0.4 Fe 2 O 4 particles show a non-equilibrium distribution of Zn and Mn. • Superparamagnetism is studied on time scales of Mössbauer and magnetic measurements. • Transition to superparamagnetic state is easily controlled by Zn content. Magnetic behaviour of nanoparticles deviates from their bulk equivalents not only due to finite-size and surface effects but it may be also affected by occurrence of metastable states, such as non-equilibrium cation distribution. The chemical composition along with the specific cation distribution are decisive for magnetic properties of spinel ferrites, the nanoparticles of which can be easily tailored to exhibit peculiar properties suitable for various applications. The present study is devoted to hydrothermally prepared Mn Zn ferrite nanoparticles; namely to five samples with approximate composition Mn 1− x Zn x Fe 2 O 4 , where x = 0.21–0.63, that were prepared by a surfactant-free hydrothermal procedure at a rather low temperature of 180 °C. XRD measurements evidenced the cubic spinel structure and a gradual decrease of the mean crystallite size from 14 to 10 nm with increasing zinc content, which was further confirmed by TEM analysis. 57Fe Mössbauer spectroscopy and temperature-variable magnetic measurements provided valuable insight into the blocking behaviour of particles on two dramatically different time scales and demonstrated that Néel relaxation can be enhanced by increasing the zinc content. Nanoparticles of the selected composition Mn 0.62 Zn 0.41 Fe 1.97 O 4 were subjected to neutron diffraction study at 2 K to determine the ferrimagnetic order and in combination with Mössbauer spectroscopy to analyse the cation distribution. The non-zero occupancy of Zn2+ in octahedral sites evidenced a metastable distribution, and the supplemental DFT study revealed that the distribution of Mn2+ is non-equilibrium as well. [ABSTRACT FROM AUTHOR]

• Methane hydrate formation from aqueous foam under high pressure. • Modified phase-change number for hydrate formation. • Deformation of the foam structure behind the hydrate formation front. • Generation of polycrystalline conical conglomerates (hydrate needles). • Methane hydrate foam melting. This work presents experimental studies of methane hydrate formation from aqueous foam stabilized by surfactants. The experiments were carried out in a high-pressure optical chamber. It is shown that the process of hydrate formation begins near the chamber walls. The front of hydrate formation propagates through the entire volume of a sample at a rate of ∼ 1 mm/s which leads to the hydrate crust formation on the surface of foam cells, while a liquid layer of surfactant solution remains between the hydrate films. The paper discusses the phase transition criterion, which quantifies the fraction of water that converts into hydrate during the adiabatic process. The following phenomena accompanying hydrate formation in foam are described: (1) deformation of the foam structure behind the hydrate formation front due to a decrease in the gas pressure; (2) subsidence of foam associated with capillary suction of solution through the inter-hydrate media; (3) generation of polycrystalline conical conglomerates (hydrate needles) at the foam – solution boundary at the moment, when the front of hydrate formation reaches this boundary. It is noted that these formations have an elongated shape and are oriented along the normal to the surface of the hydrate growth front. Upon melting, the needles retain a transparent hydrate framework, but lose their tightness. As a result, gas is displaced by liquid from their inner volume into foam cells from which these formations have grown. [ABSTRACT FROM AUTHOR]