Vol 50, No 2 (2017)

This article is the third in a series of works devoted to two-dimensional homogeneous cubic systems. It considers the case where the homogeneous polynomial vector on the right-hand side of the system has a quadratic common factor with real zeros. The set of such systems is divided into classes of linear equivalence, in each of which a simplest system being a third-order normal form is distinguished on the basis of appropriately introduced structural and normalization principles. In fact, this normal form is determined by the coefficient matrix of the right-hand side, which is called a canonical form (CF). Each CF is characterized by an arrangement of nonzero elements, their specific normalization, and a canonical set of admissible values of the unnormalized elements, which ensures that the given CF belongs to a certain equivalence class. In addition, for each CF, (a) conditions on the coefficients of the initial system are obtained, (b) nonsingular linear substitutions reducing the right-hand side of a system satisfying these conditions to a given CF are specified, and (c) the values of the unnormalized elements of the CF thus obtained are given.

In this paper, we construct an explicit pairing in Cartier series for formal Lorentz groups of the form (X + Y + XY)/(1 + c²XY), where c is a unit of the ring of integers of the local field. We prove the basic properties of this pairing, namely, bilinearity and invariance, which make it possible to explicitly construct the generalized Hilbert symbol for formal Lorentz groups over rings of integers of local fields with the use of the obtained pairing.

There are many applied problems in which it is necessary to calculate global extrema whose number is large or even infinite. These problems include, for example, some experimental design problems, and the problem of solving large systems of equations. For a single extremum of a function of several variables, one of the commonly used numerical algorithms is the simulated annealing, which is also successfully used in high volume discrete problems (travelling salesman problem). In discrete problems, it is known that the simulated annealing method searches equal global extrema with an equal probability. The continuous case has not been investigated yet. It was assumed that equal extrema are to be found consistently, sharing their neighborhood during the computation. This method is not always effective, especially in the case when multiple extrema fill up a certain region in Rⁿ. The results obtained in this study outline a general approach to the problem. We give computational examples showing the effectiveness of the approach. It can be used to create programs, algorithms indicating the localization of the roots of large equation systems. It can also be noted that many problems of design for regression experiments have an infinite number of solutions.

The paper studies the algorithmic complexity of subproblems for satisfiability in positive integers of simultaneous divisibility of linear polynomials with nonnegative coefficients. In the general case, it is not known whether this problem is in the class NP, but that it is in NEXPTIME is known. The NP-completeness of two series of restricted versions of this problem such that a divisor of a linear polynomial is a number in the first case, and a linear polynomial is a divisor of a number in the second case is proved in the paper. The parameters providing the NP-completeness of these problems have been established. Their membership in the class P has been proven for smaller values of these parameters. For the general problem SIMULTANEOUS DIVISIBILITY OF LINEAR POLYNOMIALS, NP-hardness has been proven for its particular case, when the coefficients of the polynomials are only from the set {1, 2} and constant terms are only from the set {1, 5}.

Loss of stability under uniaxial tension in an infinite plate with a circular inclusion made of another material is analyzed. The influence exerted by the elastic modulus of the inclusion on the critical load is examined. The minimum eigenvalue corresponding to the first critical load is found by applying the variational principle. The computations are performed in Maple and are compared with results obtained with the finite element method in ANSYS 13.1. The computations show that the instability modes are different when the inclusion is softer than the plate and when the inclusion is stiffer than the plate. As the Young’s modulus of the inclusion approaches that of the plate, the critical load increases substantially. When these moduli coincide, stability loss is not possible.

Using the Kovacic algorithm, the nonexistence of liouvillian solutions in the problem of motion of a rotationally symmetric ellipsoid on a perfectly rough horizontal plane for almost all values of parameters of the problem is proven.

In this paper, we study vibrational relaxation of CO molecules with excited electronic states. We consider three electronic terms and account for VV exchanges of vibrational energy within each electronic term, VT transitions of vibrational energy into a translational one, and VE exchange of vibrational energy between electronic terms. The initial vibrational state of the gas is strongly nonequilibrium. The effect of VE exchange on the vibrational relaxation of CO molecules is estimated for different kinds of initial vibrational distributions, in particular, the Treanor and Gordiets ones generalized for gases with electronically excited states. The set of equations of state-to-state vibrational kinetics, together with the gas dynamic equations, is solved numerically in the zero-order approximation of the Chapman–Enskog method for the case of spatially homogeneous relaxation. The following results are obtained: neglecting VE exchanges leads to an incorrect assessment of the number density for each electronic level; however, the error is small for the ground electronic state. It is shown that VE exchanges qualitatively affect the time dependence of the vibrational temperature.