In the present, article new methods of exact integration of mixed-type stochastic differential equations with standard Brownian motion, fractional Brownian motion with the Hurst exponent H> 1/2 and the drift term have been constructed. Solutions of these equations are understood in integral sense where, in turn, the standard Brownian motion integral is the Ito integral and the fractional Brownian motion integral is the pathwise Young integral. The constucted integration methods can be attributed to two types. The first-type methods are based on reducing the equations to simpler equations, in particular – to the simplest equations and the linear inhomogeneous equations. In the article, necessary and sufficient conditions of reducing the equations applicable to one-dimensional equations have been obtained and the examples particularly covering the stochastic Bernoulli-type equations have been given. The second-type method is based on going to the Stratonovich equation and is applicable to multidimensional equations. In addition to the mentioned integration methods, the analogues of the differential Kolmogorov equation have been obtained for mathematical expectations and the solution probability density, assuming that coefficients of the mixed-type stochastic differential equation generate commuting flows.

Approximate evaluation of functional integrals containing a centrifugal potential is considered. By a centrifugal potential is understood a potential arising from a centrifugal force. A combination of the method based on expanding into a series of the eigenfunctions of a Hamiltonian generating a functional integral and the Sturm sequence method for the eigenvalue problem is used for approximate evaluation of functional integrals. This combination allows one to significantly reduce a computation time and a used computer memory volume in comparison to other known methods.

This article is devoted to constructing composite approximate formulas for calculation of mathematical expectation of nonlinear functionals of solution of the linear Ito equation in Hilbert space with additive noise. As the leading process, the Wiener process taking values in Hilbert space is examined. The formulas are a sum of the approximations of the nonlinear functionals obtained by expanding the leading random process into a series of independent Gaussian random variables and correcting approximating functional quadrature formulas that ensure an approximate accuracy of compound formulas for third-order polynomials. As a test example, the application of the obtained formulas to the case of a one-dimensional wave equation with a leading Wiener process indexed by spatial and temporal variables is considered. This article continues the research begun in [1].

The problem is motivated by the necessity to calculate the nonlinear functionals of solution of stochastic partial differential equations. Approximate evaluation of mathematical expectation of stochastic equations with a leading random process indexed only by the time variable is considered in [2–11]. Stochastic partial equations in various interpretations are considered [12–16]. The present article uses the approach given in [12].

A graph parameter – a circumference of a graph – and its relationship with the algebraic parameters of a graph – eigenvalues of the adjacency matrix and the unsigned Laplace matrix of a graph – are considered in this article. Earlier we have obtained the lower estimates of the spectral radius of an arbitrary graph and a bipartitebalanced graph for existence of the Hamiltonian cycle in it. Recently the problem of existence of a cycle of length n – 1 in a graph depending on the values of its above-mentioned spectral radii has been investigated. This article studies the problem of existence of a cycle of length n – 2 in a graph depending on the lower estimates of the values of its spectral radius and the spectral radius of its unsigned Laplacian and the spectral conditions of existence of the circumference of a graph (2-connected graph) are obtained.

We consider a linear control system with an almost periodic matrix of coefficients. The control has a form of feedback and is linear in phase variables. It is assumed that the feedback coefficient is almost periodic and its frequency modulus, i.e. the smallest additive group of real numbers, including all Fourier exponents of this coefficient, is contained in the frequency module of the coefficient matrix.

The following problem is formulated: choose such a control from an admissible set so that the closed system has almost periodic solutions, the frequency spectrum (a set of Fourier exponents) of which contains a predetermined subset, and the intersection of the solution frequency modules and the coefficient matrix is trivial. The problem is called the control problem of the spectrum of irregular oscillations (asynchronous spectrum) with a target set of frequencies.

The aim of the work aws to obtain a necessary solvability condition for the control problem of the asynchronous spectrum of linear almost periodic systems with trivial averaging of coefficient matrix The estimate of the power of the asynchronous spectrum was found in the case of trivial averaging of the coefficient matrix.

For real autonomous systems of differential equations with continuously differentiable right-hand sides, the problem of detecting the exact number and localization of the second-kind limit cycles on the cylinder is considered. To solve this problem in the absence of equilibria of the system on the cylinder, we have developed our previously proposed ways consisting in a sequential two-step application of the Dulac – Cherkas test or the Dulac test. Additionally, a new way has been worked out using the generalization of the Dulac – Cherkas or Dulac test at the second step, where the requirement of constant sign for divergence is replaced by the transversality condition of the curves on which the divergence vanishes. With the help of the developed ways, closed transversal curves are found that divide the cylinder into subdomains surrounding it, in each of which the system has exactly one second-kind limit cycle.

The practical efficiency of the mentioned ways is demonstrated by the example of a pendulum-type system, for which, in the absence of equilibria, the existence of exactly three second-kind limit cycles on the entire phase cylinder is proved.

The article proposes a new method for calculating harmonic measures of the boundary components of the finitely connected domain.

One inverse problem of the analytic theory of linear differential equations is considered. Namely, the completely integrable Fuchs equation with four given finite critical points and a given reducible monodromy group of rank 2 on the complex projective line is constructed. Reducibility of the monodromy group of rank 2 means that 2×2-monodromy matrices (the generators of the monodromy group) can be simultaneously reduced by a linear nonsingular transformation to an upper triangular form. In so doing we study the case when the eigenvalue ξ_j of the diagonal matrix of the monodromy formal exponent at a corresponding Fuchs critical point is equal to an integer different from zero (resonance takes place).

The influence of the spectrum of original and preconditioned matrices on a convergence rate of iterative methods for solving systems of finite-difference equations applicable to two-dimensional elliptic equations with mixed derivatives is investigated. It is shown that the efficiency of the bi-conjugate gradient iterative methods for systems with asymmetric matrices significantly depends not only on the matrix spectrum boundaries, but also on the heterogeneity of the distribution of the spectrum components, as well as on the magnitude of the imaginary part of complex eigenvalues. For test matrices with a fixed condition number, three variants of the spectral distribution were studied and the dependences of the number of iterations on the dimension of matrices were estimated. It is shown that the non-uniformity in the eigenvalue distribution within the fixed spectrum boundaries leads to a significant increase in the number of iterations with increasing dimension of the matrices. The increasing imaginary part of the eigenvalues has a similar effect on the convergence rate. Using as an example the model potential distribution problem in a square domain, including anisotropic ring inhomogeneity, a comparative analysis of the matrix structure and the convergence rate of the bi-conjugate gradient method with Fourier – Jacobi and incomplete LU factorization preconditioners is performed. It is shown that the advantages of the Fourier – Jacobi preconditioner are associated with a more uniform distribution of the spectrum of the preconditioned matrix along the real axis and a better suppression of the imaginary part of the spectrum compared to the preconditioner based on the incomplete LU factorization.

In the light of the Howe duality, two different, but isomorphic representations of one algebra as Higgs algebra and Hahn algebra are considered in this article. The first algebra corresponds to the symmetry algebra of a harmonic oscillator on a 2-sphere and a polynomially deformed algebra SU(2), and the second algebra encodes the bispectral properties of corresponding homogeneous orthogonal polynomials and acts as a symmetry algebra for the Hartmann and certain ring-shaped potentials as well as the singular oscillator in two dimensions. The realization of this algebra is shown in explicit form, on the one hand, as the commutant O(4) ⊕ O(4) of subalgebra U(8) in the oscillator representation of universal algebra U (u(8)) and, on the other hand, as the embedding of the discrete version of the Hahn algebra in the double tensor product SU(1,1) ⊗ SU(1,1). These two realizations reflect the fact that SU(1,1) and U(8) form a dual pair in the state space of the harmonic oscillator in eight dimensions. The N-dimensional, N-fold tensor product SU(1,1)^⊗N аnd q-generalizations are briefly discussed.

The light-emitting properties of Si-rich silicon nitride films deposited on the Si (100) substrate by plasma-enhanced (PECVD) and low-pressure chemical vapor deposition (LPCVD) have been investigated. In spite of the similar stoichiometry (SiN_1.1), nitride films fabricated by different techniques emit in different spectral ranges. Photoluminescence (PL) maxima lay in red (640 nm) and blue (470 nm) spectral range for the PECVD and LPCVD SiN_1.1 films, respectively. It has been shown that equilibrium furnace annealing and laser annealing by ruby laser (694 nm, 70 ns) affect PL spectra of PECVD and LPCVD SiN_1.1 in a different way. Furnace annealing at 600 °C results in a significant increase of the PL intensity of the PECVD film, while annealing of LPCVD films result only in PL quenching. It has been concluded that laser annealing is not appropriate for the PECVD film. The dominated red band in the PL spectrum of the PECVD film monotonically decreases with increasing an energy density of laser pulses from 0.45 to 1.4 J/cm². Besides, the ablation of PECVD nitride films is observed after irradiation by laser pulses with an energy density of > 1 J/cm². This effect is accompanied by an increase in blue emission attributed to the formation of a polysilicon layer under the nitride film. In contrast, the LPCVD film demonstrates the high stability to pulsed laser exposure. Besides, an increase in the PL intensity for LPCVD films is observed after irradiation by a double laser pulse (1.4 + 2 J/cm²) which has not been achieved by furnace annealing.

For fullerene matrixes doped by gold nanoparticles we have established experimentally a miss of a red concentration-induced shift of surface plasmon resonance absorption band maximum. Theoretical modeling has been made for spectral characteristics of carbon–bearing nanostructures. Numerical calculations of extinction factors for a spherical metallic particle in an absorbing surrounding medium were based on the Mie theory. Transmission spectra coefficients of densely packed plasmonic nanoparticles monolayers were calculated with the use of the single coherent scattering approximation modified for absorbing matrices. Thin-film Au-air and Au–C₆₀ nanostructures have been fabricated on glass and quartz substrates by thermal evaporation and condensation in vacuum at an air pressure of 2 · 10^–3 Pа. The surface mass density of Au into Au–C₆₀ nanostructures was varied in the range (3.86–7.98) · 10^–6 g/cm². The comparison of theoretical and experimental data allowed making a conclusion that the absorbency in carbon-bearing matrix leads to the attenuation of lateral electrodynamics coupling and blocks collective plasmon resonance in densely packed gold nanostructures.

The results of the discovery of the Periodic law by D. I. Mendeleev are considered, and the actual formulation of this law is given. Some examples of the use of symmetry groups in modern science are given. It is shown that the SO(4,2) group allows presenting the contents of the Periodic system of elements in full coincidence with the experimentally established structure of electronic shells of corresponding atoms without involving any additional quantum numbers characterizing the properties of atoms. adynamic substantiation of the use of representations of the dynamic symmetry group of the quantum system, isovalent to hydrogen, for a mathematical description of the properties of the symmetry of the Periodic system of elements is proposed. Using it, the splitting of the infinite-dimensional unitary representations of the group SO(4,2) into the finite-dimensional multiplets, determined by the quantum numbers describing the states of electrons, was implemented. A problem of inclusion of isotopes of elements in the Periodic system of elements is discussed.