Improvement of an Estimate of the Global Existence Theorem for Solutions of the Bogoliubov Equations

For a one-dimensional system of particles interacting like elastic balls, we improve an estimate of the existence theorem for the global solution of the Cauchy problem for the Bogoliubov equations with initial data from the space of sequences of measurable functions. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 145, No. 3, pp. 420–424, December, 2005.     

Tricomi problem for strongly degenerate equations of parabolic-hyperbolic type

A new integral representation of solutions of a Tricomi problem for a strongly degenerate system of equations of parabolic-hyperbolic type is constructed. Translated fromMatematicheskie Zametki, Vol. 66, No. 3, pp.385–392, September, 1999.     

Asymptotic behavior of nonlinear waves in elastic media with dispersion and dissipation

In the case of nonlinear elastic quasitransverse waves in composite media described by nonlinear hyperbolic equations, we study the nonuniqueness problem for solutions of a standard self-similar problem such as the problem of the decay of an arbitrary discontinuity. The system of equations is supplemented with terms describing dissipation and dispersion whose influence is manifested in small-scale processes. We construct solutions numerically and consider self-similar asymptotic approximations of the obtained solution of the equations with the initial data in the form of a “spreading” discontinuity for large times. We find the regularities for realizing various self-similar asymptotic approximations depending on the choice of the initial conditions including the dependence on the form of the functions determining the small-scale smoothing of the original discontinuity. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 147, No. 2, pp. 240–256, May, 2006.     

The equicontinuity condition for sequences of solution spaces

The verification of an appropriately stated equicontinuity condition for a sequence of solution spaces is one of the two key points in the theory of the Cauchy problem for equations with singular right-hand sides. We obtain a related sufficient condition. Translated fromMatematicheskie Zametki, Vol. 61, No. 3, pp. 416–423, March, 1997. Translated by V. E. Nazaikinskii     

Global regularity estimates for multidimensional equations of compressible non-Newtonian fluids

The present paper is devoted to the problem of global existence of sufficiently regular solutions to two- and three-dimensional equations of a compressible non-Newtonian fluid. In the case of the potential stress tensor, we develop a technique for deriving energy identities that do not contain derivatives of density. On the basis of these identities, in the case of sufficiently rapidly increasing potentials, we obtain an extended system ofa priori estimates for the equations mentioned above. We also study the related problem of estimating solutions to the nonlinear elliptic system generated by the stress tensor. Translated fromMatematicheskie Zametki, Vol. 68, No. 3, pp. 360–376, September, 2000.     

Stability properties of cycles and tori of a simplest nonresonant wave-type equation

For a number of meaningful examples, nonresonant wave-type equations are shown to be characterized by periodic dynamics. Translated fromMatematicheskie Zametki, Vol. 62, No. 5, pp. 744–750, November, 1997. Translated by O. V. Sipacheva     

Some nonlinear equations reducible to diffusion-type equations

The problem of the reducibility of a system of second-order quasi-linear parabolic differential equations to diffusion-type equations is considered. An effective solution algorithm is suggested for this problem in the nondegenerate case. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 123, No. 1, pp. 26–37, April, 2000.     

Optimal method for truncating a chain of equations for two-time Green’s functions

We use an example of a chain of equations describing a system of Bose particles with pairwise interaction to develop a method for decoupling the chain at its second element. We obtain an approximation of the interacting-modes type, which results in a system of nonlinear equations for one-, two-, and three-particle functions. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 147, No. 3, pp. 503–510, June, 2006.     

Impression of a semiinfinite stamp in an elastic strip with regard for friction and adhesion

We consider the problem of contact interaction between a semiinfinite stamp with rectilinear base and an elastic strip with one rigid side. Friction forces in the contact region are taken into account. These forces lead to the division of the contact region into slipping and adhesion zones. With the use of the Wiener–Hopf method, a system of integral equations is reduced to an infinite system of algebraic equations. The computational results of stresses and strains at the boundary and at inner points of the elastic strip are presented. Translated from Matematychni Metody ta Fizyko-Mekhanichni Polya, Vol. 51, No. 1, pp. 138–149, January–March, 2008.     

Summability of series in the root functions of boundary-value problems of Bitsadze-Samarskii type

We investigate the Abel summability of a system of eigenfunctions and associated functions of Bitsadze-Samarskii-type boundary-value problems for elliptic equations in a rectangle. These problems are reduced to a boundary-value problem for elliptic operator differential equations with an operator in boundary conditions in the corresponding spaces and are studied by the method of operator differential equations. __________ Translated from Ukrains’kyi Matematychnyi Zhurnal, Vol. 60, No. 4, pp. 443–452, April, 2008.     

Method of perturbations in vector electromagnetic problems of diffraction by a wedge

A vector electromagnetic problem of diffraction by a wedge-shaped region is reduced to a system of coupled functional equations by using Sommerfeld integrals. This system of functional equations is solved by the perturbation method, and the convergence of the related series is analyzed. The system of functional equations is further reduced to linear equations with contracting operators, and the solution is represented in the form of a Neumann series. Reduction to a system with compact operators is also considered. Bibliography: 13 titles. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 230, 1995, pp. 138–156. Translated by M. A. Lyalinov.     

Computation of local symmetries of second-order ordinary differential equations by the Cartan equivalence method

The Cartan equivalence method is used to find out if a given equation has a nontrivial Lie group of point symmetries. In particular, we compute invariants that permit one to recognize equations with a three-dimensional symmetry group. An effective method to transform the Lie system (the system of partial differential equations to be satisfied by the infinitesimal point symmetries) into a formally integrable form is given. For equations with a three-dimensional symmetry group, the formally integrable form of the Lie system is found explicitly. Translated fromMatematicheskie Zametki, Vol. 60, No. 1, pp. 75–91, July, 1996.     

Existence, uniqueness, and dependence on a parameter of solutions of differential-functional equations with ordinary and partial derivatives

For a system of quasilinear hyperbolic equations with a system of differential equations with lag, we prove theorems on the existence and uniqueness of a solution of the Cauchy problem and its continuous dependence on the initial conditions. Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 49, No. 5, pp. 715–719, May, 1997.     

Gauge-invariant discrete models of Yang-Mills equations

Two discrete models of Yang-Mill equations are constructed in the space ℝⁿ for some matrix-valued Lie group. A gauge-invariant discrete model is examined. Translated fromMatematicheskie Zametki, Vol. 61, No. 5, pp. 742–754, May, 1997. Translated by O. V. Sipacheva     

Method of accelerated convergence for the construction of solutions of a Noetherian boundary-value problem

We study the problem of finding conditions for the existence of solutions of weakly nonlinear Noetherian boundary-value problems for systems of ordinary differential equations and the construction of these solutions. A new iterative procedure with accelerated convergence is proposed for the construction of solutions of a weakly nonlinear Noetherian boundary-value problem for a system of ordinary differential equations in the critical case. Translated from Ukrains’kyi Matematychnyi Zhurnal, Vol. 60, No. 12, pp. 1587–1601, December, 2008.     

Lamb's inverse axially symmetric problem

The problem of restoring the velocity of transversal waves in an elastic half-space by a known wave field on the boundary of a medium is studied. The problem is reduced to a system of “integral” equations similar to the Volterra one. Theorems on existence in the small and on uniqueness of the solution are proved. Bibliography: 5 titles. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 203, 1992, pp. 51–67. Translated by T. N. Surkova.     

The Navier-Stokes equations: Asymptotic solutions describing tangential discontinuities

Asymptotic solutions whose weak limit has a jump discontinuity on a two-dimensional surface are studied for the Navier-Stokes equations with small viscosity. The equations describing the leading term of the asymptotics and the correction terms are obtained and analyzed. A recursive procedure for constructing a formal asymptotic series satisfying the corresponding Cauchy problem is described. Translated fromMatermaticheskie Zametki, Vol. 67, No. 6, pp. 938–949, June, 2000.     

Boundary-value problem for a parabolic system of integro-differential equations with integral conditions

Using operators of fractional integration and differentiation, we prove a theorem on the wellposedness of a general parabolic boundary-value problem for a system of integro-differential equations with integral operators in boundary conditions. Translated from Ukrains’kyi Matematychnyi Zhurnal, Vol. 60, No. 12, pp. 1610 – 1618, December, 2008.     

Model Dirac-Maxwell equations with pseudounitary symmetry

We introduce a new system of equations called a model system of Dirac-Maxwell equations, reproducing the main properties of the standard system. At the same time, the model system of equations differs from the standard system in several ways; in particular, it is a tensor system and has a new symmetry with respect to the pseudounitary group. We also propose a version of the model system of Dirac-Maxwell equations with local (gauge) pseudounitary symmetry. We show that any spinor solution of the standard system of Dirac-Maxwell equations can be obtained from the corresponding tensor solution of the model system. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 157, No. 3, pp. 425–435, December, 2008.     

Three-dimensional models of marine magnetotelluric sounding of nonhomogeneous media

We consider the direct problem of three-dimensional modeling of marine magnetotelluric sounding of nonhomogeneous media in the presence of a vertical magnetic field component in the primary field. The problem is reduced to a system of volume integral equations. __________ Translated from Prikladnaya Matematika i Informatika, No. 27, pp. 46–53, 2007.