Instability in a self-modeling crystallization front in a one-component melt

Studies have been made on the stability of planar, cylindrical, and spherical crystallization fronts in a one-compound melt in the presence of small perturbations in the phase-transition surface.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 45, No. 4, pp. 636–639, October, 1983.     

Instability of the background electron multiplication wave front

The initial stage of the development of instability in the front of an ionization wave, which is related to the multiplication of electrons at their small background density, is theoretically described. An analytical expression is obtained for the growth rate of small perturbations as a function (universal for the given gas) of the reduced field strength E/p (where E is the electric field strength and p is the gas pressure). The rate of instability development is calculated for helium, xenon, nitrogen, and sulfur hexafluoride. A new criterion of streamer formation is found.     

Instability development during motion of a metal-insulator phase boundary

Diffusion of a magnetic field into a conductor featuring a metal-insulator phase transition caused by Joule heating is theoretically studied. Development of a thermomagnetic instability at the metal-insulator interphase boundary moving in a fast wave regime is described in the linear stage depending on the wavenumber. Effect of the interphase boundary instability on the operation of a fast-speed electric current breaker based on a (V_1−X Cr_X)₂O₃ solid solution is assessed.     

Nucleation of a non-equilibrium phase in a first order phase transition

We report a newly observed phenomenon of nucleation and first order phase transition, from superfluid helium-four, in which a metastable solid phase nucleates and grows from the overpressured liquid in preference to the stable phase. We discuss these results in terms of the difference in nucleation probabilities that arise from the different interfacial free energies of the phases.     

A new approach to phase retrieval of a wave front

The main thrust of this project was to develop a process including data-gathering and processing techniques that would consistently and without fail discover the phase distribution of a wave front. In the course of the work, new thoughts on data gathering evolved to the point where a novel type of intensity picture bearing little or no resemblance to the wave front or its phase distribution was required for mathematical processing to achieve the phase distribution. For convenience these information images have been dubbed phasorgrams. Phasorgrams are recorded in the diffractive plane or in the image plane of an application device. Additional data, while helpful, are not required, thus eliminating the need for data from two Fourier conjugate planes as in the well-known method of Gerchberg and Saxton. The mathematical processing of these data is carried out by an iterative algorithm which also is new. This algorithm, given good data, has not failed to achieve the phase distribution. Contemporary devices have not been designed to measure the new kinds of data required for the process. Therefore, several novel devices are suggested. The new process could have major implications for the phase problem of X-ray crystallography.     

On the unstable propagation of a phase transition in a solid

To explore a possible mechanism of deep earthquakes, this paper analyzes the unstable propagation of a stress-induced phase transition which is initiated in a homogeneous stress field. This Stephen problem is formulated as an initial-value problem for the phase boundary, and the driving force of the boundary is computed by using the solution of the boundary-value problem for a partially transformed material. The propagation of the phase transition under uniform pressure is numerically simulated. It is shown that (1) under lower pressure, the transition is terminated at a certain size, but it can propagate unstably when an initially transformed region is sufficiently large; and (2) when the pressure attains a critical value, the propagation becomes unstable, and goes in a particular direction depending on the initial shape. These results confirm the possibility of the unstable propagation of phase transition, and provide a theoretical basis for the hypothesis that the phase transition of a mantle material can trigger a deep earthquake.     

About the Coulomb phase transition

High Temperature - The possibility of detecting a gas-liquid Coulomb phase transition in nondegenerate nonideal two-component low-temperature plasma is discussed using the results of calculating...     

Macrokinetic equations for a phase transition of the first sort

Differential equations are derived for phase transition kinetics. Analytic solutions are obtained for linear dependence of new phase growth rate on the degree of completion of the phase transition.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 54, No. 1, pp. 117–121, January, 1988.     

Effect of turbulence of the outer stream on the transition for some classes of self-similar flows

It is shown that in the presence of very low levels of pulsations at the outer limit of the laminar boundary layer the energy of neutral oscillations within the layer itself reaches very high values. This predetermines the transition to turbulent flow.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 30, No. 3, pp. 519–527, March, 1976.     

Additive-induced phase transition of a spin-coated lipid film

We have measured specular neutron reflectivity for dimyristoylphosphatidylcholine (DMPC) films spin-coated on Si substrates with and without NaI. The obtained reflectivity profiles were analyzed using Parratt's equation with taking the distribution of the stacking number of bilayers into consideration, since the bilayer stacking still remains on the film surface and it forms terrace-like islands. The repeat distance of the bilayer stacking for the DMPC/NaI mixture film was drastically decreased at 80 °C, and the evaluated value was consistent with that in an “interdigitated gel” phase. Since this change was not observed for the pure DMPC film, we concluded that the phase transition to an “interdigitated gel” phase was induced by the addition of NaI.     

Instability of second sound under heat flow near the superfluid transition

In heat-carrying superfluids, second sounds become unstable when the difference between the superfluid velocity and the normal fluid velocity exceeds a critical value. We derive a nonlinear evolution equation of the phase of the complex order parameter in this unstable region near the superfluid transition. It indicates emergence of trains of soliton-like heat pulses, which will be nearly periodic in a weakly unstable regime and chaotic in a strongly unstable regime. Experimentally, this instability cannot be observed in usual one-dimensional geometries due to appearance of a normal fluid region at large heat currents. However, we predict that it can be realized in a cell with a constricted part.     

Distribution of the phase front in the freezing of finely-dispersed soils

The process of the freezing of soils is examined with allowance for the migration of moisture in the freezing and thaw zones.Notation , x time and space coordinates - t, W, L dimensionless values of temperature, moisture content, and ice content - c,a, D volumetric heat capacity, diffusivity, and diffusion of moisture - density of the skeleton - W_e equilibrium value of moisture content - enthalpy of phase transformations - _* characteristic time - , gw, , dimensionless values of temperature, moisture content, ice content, and diffusion coefficient of the moisture - Fo Fourier criterion - Ste Stefan number - n empirical constant Indices 0, 1, and 2 pertain to the initial and boundary states Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 56, No. 5, pp. 805–810, May, 1989.     

Fullerenes catalyze the graphite-diamond phase transition

The effect of fullerenes on the graphite-diamond phase transition was experimentally studied. Adding a catalytic amount of fullerenes to graphite during the diamond synthesis at relatively low pressures (4.5–5.5 GPa) and temperatures (about 1200°C) increases the percentage graphite to diamond conversion by a factor of 1.8 as compared to the case of an initial charge containing only graphite or fullerene. Adding fullerene to graphite allows the pressure and temperature of the synthesis to be decreased.     

Photoacoustic spectroscopy of condensed media with a phase transition

The gas-microphone method of recording a photoacoustic (PA) Rosencwaig—Herschow signal is extended theoretically for consideration of material evaporation of a sample. For an excitation source of constant intensity and exponential saturation of vapor concentration, relations are derived to describe the transient dynamics of the PA response. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 70, No. 1, pp. 153–155, January–February, 1997.     

Nonlinear filtration through a porous wedge in the presence of a phase transition

An approximate solution is given for the temperature distribution in a porous body bearing a flow of cooling agent which undergoes a phase transition.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol.21, No. 5, pp.922–928, November, 1971.     

New ferroelastic phase transition induced by impurity tunneling with a structural local transition

We predict a new ferroelastic phase transition in a matrix, which is induced by the tunneling states appearing under the conditions of structural local transitions for impurity ions. This ferroelastic phase transition has been studied in crystals of the proper ferroelastic K₃Na(CrO₄)₂ with impurity molecular ions of MnO₄²⁻ and the dielectric KCl with impurity atoms of Cu⁰. A model of the induced phase transitions of this type is proposed and the related applications are discussed.     

Thermogravitational convection in a square cell involving a phase transition

The processes of freezing and thawing of a liquid in the presence of thermogravitational convection in a square cell with adiabatic vertical and isothermal horizontal walls are considered. The development of convective flow in time depends on the initial conditions, and therefore various scenarios of transition to a stationary solution are possible. The presence of phase transitions in the liquid makes it possible to freeze the transient structure of convective vortices. As a result, depending on the initial conditions, several stationary solutions that differ in both the structure of the convective motion and the magnitude of the heat transfer rate of the medium can exist.Institute of the Mechanics of Multiphase Systems. Russian Academy of Sciences, Tyumen'. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 67, Nos. 1–2, pp. 10–13, July–August, 1994.     

Periodic states in a pressurized flow showing a phase transition

The scope for long-term operation in periodic mode is examined for a pipeline carrying a liquid that can freeze.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 54, No. 6, pp. 938–942, June, 1988.     

Motion of the temperature front and phase transitions of a suspended impurity in flow through a porous medium

Exact solutions are obtained for two problems of nonisothermal percolation flow with phase transitions of the suspended impurity.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 52, No. 2, pp. 248–252, February, 1987.