Diffuse X-ray scattering by ice in the vicinity of the melting point

The X-ray pattern of ice recorded at −10°C reveals, along with the reflexes of a hexagonal phase, intense diffuse X-ray scattering, testifying to the presence of a noncrystalline phase in the sample. Heating of ice to a temperature close to the melting point leads to almost complete decomposition of the crystalline phase. As this takes place, intense diffuse X-ray scattering with a maximum at 2Θ of 23°C appears in the diffraction pattern, which is typical for a metastable amorphous phase. The first maximums of the radial distribution function for the metastable amorphous phase of ice appear to be close in their positions to the first radii of the hexagonal phase coordination spheres.     

On the behavior of indicators of melting: Lennard-Jones system in the vicinity of the phase transition

Various indicators of melting for a system of particles whose pair interaction is described by the Lennard-Jones potential have been considered. The behavior of the radial distribution function g(r) and the associated criteria of melting, modified Lindemann criterion, and criteria based on the properties of short-range orientational order (rotational invariants q _l and w _l of various orders l) has been analyzed in detail in the vicinity of the melting phase transition. A parameter based on the loss of the nearest neighbors of an atom/particle has been proposed to characterize the melting transition. All considered indicators of melting for the Lennard-Jones system have been compared. It has been shown that the indicators of melting derived from the properties of the short-range orientational order are much more sensitive to the melting phase transition and can be used to construct new phenomenological criteria of melting similar to the Lindemann criterion. An additional important advantage of such indicators is the relatively small number of configurations of the system necessary for their calculation.     

Thermodynamics of magnetic alloys in the vicinity of the curie and melting point

The coincidence of two phase transitions of different order is discussed in the case of a liquid ferromagnetic alloy at constant pressure and zero field. Three phases at most are in equilibrium. The experimental data on the Au-Co alloy are briefly mentioned.     

On the possibility of the incommensurate phase near α⇄β transition point in quartz

Explanation of the experimental data on the existance of periodical domain structure near the α?β transition point in quartz reported by G. van Tendeloo et al. is proposed. It is shown that due to the interaction between the soft optical branch and the acoustic one that the soft mode frequency in quartz may correspond to the wave vectors of non-zero value. The specific angular dependence in the soft mode dispersion law provided by such an interaction makes it possible to determine the incommensurate superstructures wave vector's directions. The last coincides with the experimentally observed one. A possible origin of the temperature region narrowness of the incommensurate phase existence is discussed.     

On injection of hydrate-forming gas into a gas-saturated snowy agglomerate while transition through the ice melting point

The paper considers the process of injection of hydrate-forming gas (methane) into a snowy agglomerate (ini-tially saturated with methane). The self-similar problem statement demonstrates that if the warm gas (T_e > 0 °C) is injected under a high pressure (p_e ≥ p_*, where the critical values are found from the initial temperature T₀, pressure p₀, volumetric snow saturation S_i0, and permeability of snow) into the filtration zone with phase transition, this produces four characteristic zones: the nearest zone with all snow transformed into hydrate, therefore, the aggregate filled only with gas and hydrate, the two intermediate zones where gas, snow or water and hydrate are in phase equilibrium state, and the distant zone filled only with gas and snow. The obtained analytical and numerical solutions give an analysis of the influence of key input parameters like initial state of the aggregate, gas injection rate, and its temperature, on the structure and the length of four filtration zones.     

On the possibility of superconductive transition in a strong magnetic field

The possible existence of triplet superconductive transition in metals in a strong magnetic field is shown. In such system in the sufficiently strong magnetic field there are no currents, which can destroy the superconductivity.     

Electrical resistivity anomaly in the vicinity of structural phase transition of p-SnTe

Electrical resistivity of p-SnTe is calculated taking into account the second-order scattering processes through the inter-band electron-phonon interaction based on the Kristoffel-Konsin model. The experimental results can be reasonably explained by our numerical results.     

High-frequency acoustic modes in liquid gallium at the melting point

The microscopic dynamics in liquid gallium at melting has been studied by inelastic x-ray scattering. We demonstrate the existence of acousticlike modes up to wave vectors above one-half of the first maximum of the static structure factor, at variance with earlier results from inelastic neutron scattering [F. J. Bermejo et al., Phys. Rev. E 49, 3133 (1994)]. Despite structural (extremely rich polymorphism) and electronic (mixed valence) peculiarities, the collective dynamics is strikingly similar to the one of van der Waals and metallic fluids. This result speaks in favor of the universality of the short time dynamics in monatomic liquids rather than of system-specific dynamics.     

On the melting point of amorphous silicon

The entropy and melting point of amorphous silicon cannot be measured in a thermodynamic sense.     

Molecular dynamics of liquid alkaline-earth metals near the melting point

Results of the studies of the properties like binding energy, the pair distribution function g(r), the structure factor S(q), specific heat at constant volume, velocity autocorrelation function (VACF), radial distribution function, self-diffusion coefficient and coordination number of alkaline-earth metals (Be, Mg, Ca, Sr and Ba) near melting point using molecular dynamics (MD) simulation technique using a pseudopotential proposed by us are presented in this article. Good agreement with the experiment is achieved for the binding energy, pair distribution function and structure factor, and these results compare favourably with the results obtained by other such calculations, showing the transferability of the pseudopotential used from solid to liquid environment in the case of alkaline-earth metals.     

On the possibility of corona-discharge ignition in the vicinity of a weakly charged drop executing nonlinear vibrations

An analytic expression for the electric-field strength in the vicinity of a charged drop of an electrically conducting liquid is obtained for the case where the initial shape of the drop executing nonlinear vibrations is specified by a virtual excitation of an arbitrary single mode of capillary vibrations. It turns out that, even at small charges (such that the Rayleigh parameter for the drop is equal to one-tenth of the critical value associated with stability against the intrinsic charge), the electric-field strength at the drop surface in the case of an initial excitation of one of high modes is sufficient for the ignition of a corona discharge.     

On a plausible explanation of the connection of point defect parameters with the melting point

Since a few decades it has been empirically found that the activation enthalpy for the self-diffusion process and the defect formation enthalpy are proportional to the melting temperature. The corresponding proportionality constants have been empirically determined for various categories of solids. An explanation of this empirical fact is suggested on a unified basis that is valid for various classes of solids. By comparing the theoretical values of the proportionality constants with the empirical ones an excellent agreement emerges. Furthermore, for first time, the physical meaning of these proportionality constants is obtained.     

Molecular dynamics of liquid lead near its melting point

The molecular dynamics of liquid lead is simulated at T = 613 K using the following three models of an interparticle interaction potential: the Dzugutov pair potential and two multiparticle potentials (the “glue” potential and the Gupta potential). One of the purposes of this work is to determine the optimal model potential of the interatomic interaction in liquid lead. The calculated structural static and dynamic characteristics are compared with the experimental data on X-ray and neutron scattering. On the whole, all three model potentials adequately reproduce the experimental data. The calculations using the Dzugutov pair potential are found to reproduce the structural properties and dynamics of liquid lead on the nanoscale best of all. The role of a multiparticle contribution to the glue and Gupta potentials is studied, and its effect on the dynamic properties of liquid lead in nanoregions is revealed. In particular, the neglect of this contribution is shown to noticeably decrease the acoustic-mode frequency.     

Resonant magnetoresistance in the vicinity of a phase transition

The change in the electrical conductivity of manganite films upon microwave pumping in the magnetic resonance conditions is investigated. The temperature dependence of the effect correlates with the temperature variation of colossal magnetoresistance (CMR), passing through a maximum at the Curie point. The results are interpreted using a model that assumes a decrease in the absolute value |M| of the magnetic moment of the sample under the action of magnetoresonant saturation, which leads to an increase in resistance in accordance with the CMR mechanism. Theoretical analysis based on the Landau-Lifshitz-Bloch equation confirms the correctness of this model and ensures good agreement with experiment.     

Enhanced decoherence in the vicinity of a phase transition

We study the decoherence of a spin-1/2 induced by an environment which is on the verge of a continuous phase transition. We consider spin environments described by the ferromagnetic and antiferromagnetic Heisenberg models on a square lattice. As is well known, these two-dimensional systems undergo a continuous phase transition at zero temperature, where the spins order spontaneously. For weak coupling of the central spin to these baths, we find that as one approaches the transition temperature, critical fluctuations make the central spin decohere faster. Furthermore, the decoherence is maximal at zero temperature as signaled by the divergence of the Markovian decoherence rate.