Numerical Solution of a Fluid Filtration Problem in a Fractured Medium by Using the Domain Decomposition Method

Under consideration are the numerical methods for simulation of a fluid flow in fractured porous media. The fractures are taken into account explicitly by using a discrete fracture model. The formulated single-phase filtering problem is approximated by an implicit finite element method on unstructured grids that resolve fractures at the grid level. The systems of linear algebraic equations (SLAE) are solved by the iterative methods of domain decomposition in the Krylov subspaces using the KRYLOVlibrary of parallel algorithms. The results of solving some model problem are presented. A study is conducted of the efficiency of the computational implementation for various values of contrast coefficients which significantly affect the condition number and the number of iterations required for convergence of the method.     

Stable Periodic Solutions of Periodic Systems of Differential Equations

An infinitely differentiable periodic two-dimensional system of differential equations is considered. It is assumed that there is a hyperbolic periodic solution and there exists a homoclinic solution to the periodic solution. It is shown that, for a certain type of tangency of the stable manifold and unstable manifold, any neighborhood of the nontransversal homoclinic solution contains a countable set of stable periodic solutions such that their characteristic exponents are separated from zero.     

Synthesis,Crystal Structure,and Thermal Properties of Substituted Titanates Bi2Pr2Ti3O12 and Bi2Nd2Ti3O12

Physics of the Solid State - Titanates Bi2Pr2Ti3O12 and Bi2Nd2Ti3O12 have been obtained by the solid-phase synthesis using sequential annealing of the Bi2O3, Nd2O3, Pr6O11, and TiO2 stoichiometric...     

Spectral manifestation of the interaction of polyurethane components with oxide groups

The spectral-structural characteristics of polyurethane compositions with antipyrene fillers were investigated by a method of IR spectroscopy. The changes revealed in the vibrational spectra can be caused by intermolecular interaction of oligoether and diphenylmethane diisocyanate with aluminum-, boron-, and phosphor-containing compounds.__________Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 1, pp. 133–135, January–February, 2005.     

Hole-electron mechanism of F-H pair generation in RbCl crystals with impurity electron traps

Production of F, Cl ₃ ⁻ , Ag⁰, and Tl⁰ centers in RbCl:Ag and RbCl:Tl crystals by photons having energies ranging from 5 to 10 eV has been studied at 295 and 180 K. It is shown that creation of near-impurity excitations is accompanied by formation of F centers localized in the vicinity of Ag⁺ and Tl⁺ ions. F centers are produced in direct optical generation of self-trapped excitons. In addition to the well-known mechanism of F-H pair production in nonradiative recombination of electrons with self-trapped holes, a hole-electron process has been revealed for the first time to operate in RbCl:Ag having deep electron traps. By this mechanism, F-H pairs appear in the following sequence of stages: thermally stimulated unfreezing of hopping diffusion of self-trapped holes (V _K centers), tunneling electron transfer from Ag⁰ to the approaching V _K centers, and subsequent nonradiative decay of triplet self-trapped excitons near Ag⁺ ions. Fiz. Tverd. Tela (St. Petersburg) 40, 1238–1245 (July 1998)     

Phase transitions in the ferromagnetic alloys Ni2+x Mn1−x Ga

The phase diagram of the cubic ferromagnetic shape-memory alloy Ni_2+x Mn_1−x Ga is constructed theoretically for the case when the Curie temperature is close to the structural transition temperature. This diagram agrees well with the experimental data obtained from resistance and magnetic susceptibility measurements. It is shown that the transition from the paramagnetic cubic phase to the ferromagnetic tetragonal phase can be second-order or first-order. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 3, 212–216 (10 February 1998)     

On finite groups isospectral to simple symplectic and orthogonal groups

The spectrum of a finite group is the set of its element orders. Two groups are said to be isospectral if their spectra coincide. We deal with the class of finite groups isospectral to simple and orthogonal groups over a field of an arbitrary positive characteristic p. It is known that a group of this class has a unique nonabelian composition factor. We prove that this factor cannot be isomorphic to an alternating or sporadic group. We also consider the case where this factor is isomorphic to a group of Lie type over a field of the same characteristic p.     

Effect of the composition of nickel-containing composites based on stabilised zirconia on catalytic activity in methane steam conversion

A study was carried out on the composition and nature of the stabilizing additive on the activity of nickel-containing composites based on zirconia in the methane steam conversion. The methane conversions were 91–99% on Ni/ZrO₂(Y, Sc, Ce) at 700–800 °C.     

One-pot synthesis of substituted styrenes from vicinal dibromoalkanes and arylboronic acids

Dehydrobromination of vicinal dibromoalkanes in systems comprising 1,2-dimethoxy-ethane, N-butyl-N′-methylimidazolium tetrafluoroborate (or tetrabutylammonium bromide), and a base with subsequent palladium-catalyzed cross-coupling of the thus formed bromoalkenes with arylboronic acids furnished substituted styrenes. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 116–123, January, 2007.