Theory of heterogeneous decay of a gas-supersaturated solution on passive gas bubbles

St Petersburg State University. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 95, No. 1, pp. 111–126, April, 1993.     

Forces and torques exerted on bodies sliding in a fluid

The motion of a system of bodies along a plane in a viscous fluid in the presence of flow shear is considered. It is demonstrated that a main torque, linearly proportional to the velocities of the bodies, is exerted by the fluid on the system of the bodies and the plane. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 89–96, January–February, 1997.     

Soliton relaxation in antiferromagnets

We study the relaxation two-parameter one-dimensional solitons in antiferromagnets using the phenomenological theory. Allowing for relaxation terms of a relativistic and exchange nature, we set up a system of evolution equations for the constants of the motion of a soliton and calculate the corresponding integral curves, which describe the variation of the soliton parameters in the relaxation process. Zh. éksp. Teor. Fiz. 111, 1633–1650 (May 1997)     

Elementary acts of crystallization in an environment with high supersaturation

A whole complex of phenomena occurring upon crystallization of substances from solutions and vapors has been considered. A generalized conception of crystallization has been developed. According to this conception the kinetics of the process and the properties of the crystallization product are determined not only by nucleation and molecular growth of crystals, but also by their directed aggregation. The role of the thermal and hydrodynamic selection of regular shaped aggregates in the course of their transformation into pseudo single crystals has been discussed. A relation between the properties of the crystals and their reactivity has been found.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1710–1717, October, 1994.     

Morphological Memory of Dispersed Solid Phases

A formalism of the morphological memory of disperse systems was formulated. Using CsI as an example, it was established that a dispersed solid phase formed by vapor condensation stores information on the nucleation, growth, and aggregation of its particles for a long time. Therefore, the determination of distribution functions of properties and the texture of particles at the end of the condensation allows us to qualitatively describe the genesis of the phase. Basic equations and conditions relating properties of crystals of the dispersed phase, which are necessary for the extraction of information on the genesis from data on final distribution functions of crystal states, were considered.     

A kinetic model for formation of nanodisperse matter in the gas phase

Taking CsI aerosol as an example, it was shown that growth of primary aerosol particles can be described in terms of both discrete and continuum models. This conclusion is based on the results of experiments carried out using a method that makes it possible to distinguish primary particles against the background of their aggregates, to provide a complete transfer of the primary particles from aerosol bulk to a collector, and to determine the particle sizes by transmission electron microscopy. Under the conditions studied, the size distribution of the primary particles is described by a Fokker—Planck type equation.     

Isotopic Realization of Continuous Mappings

In the metastable range, a class of mappings yielding a negative solution of the isotopic realization problem (posed by E. V. Shchepin in 1993) and satisfying an additional technical condition is described in algebraic terms. Namely, one constructs an obstruction to isotopic realization of a discretely realizable continuous mapping f of an n-polyhedron to an orientable PL m-manifold; the completeness of this obstruction is established for in the case where f is discretely realizable by skeleta. Also, for , a series of mappings (with singular set consisting of a p-adic solenoid, , and a point) is presented for which the problem is solved in the negative. Furthermore, it is shown that the problem is solved in the affirmative in the metastable range if stabilization with codimension one is allowed, as well as in the case of a mapping , under the condition that f is discretely realizable by skeleta and the configuration singular set is acyclic in dimension (in the sense of the SteenrodSitnikov homology). Bibliography: 31 titles.     

Electron microscopy of biomaterials based on hydroxyapatite

Three types of biomaterials based on hydroxyapatite are synthesized and investigated. Hydroxyapatite nanocrystals or microcrystals precipitated from low-temperature aqueous solutions serve as the initial material used for preparing spherical porous granules approximately 300–500 μm in diameter. Sintering of hydroxyapatite crystals at a temperature of 870°C for 2 h or at 1000°C (for 3 h) + 1200°C (for 2 h) brings about the formation of solid ceramics with different internal structures. According to the electron microscopic data, the ceramic material prepared at 870°C is formed by agglomerated hydroxyapatite nanocrystals, whereas the ceramics sintered at 1200°C (with a bending strength of the order of 100 MPa) are composed of crystal blocks as large as 2 μm. It is established that all the biomaterials have a single-phase composition and consist of the hydroxyapatite with a structure retained up to a temperature of 1200°C.