Compact Clifford–Klein Forms of Homogeneous Spaces of SO(2, n)

A homogeneous space G/H is said to have a compact Clifford–Klein form if there exists a discrete subgroup of G that acts properly discontinuously on G/H, such that the quotient space \G/H is compact. When n is even, we find every closed, connected subgroup H of G = SO(2, n), such that G/H has a compact Clifford–Klein form, but our classification is not quite complete when n is odd. The work reveals new examples of homogeneous spaces of SO(2, n) that have compact Clifford–Klein forms, if n is even. Furthermore, we show that if H is a closed, connected subgroup of G = SL(3, R), and neither H nor G/H is compact, then G/H does not have a compact Clifford–Klein form, and we also study noncompact Clifford–Klein forms of finite volume.     

The Gauss–Bonnet Formula for Hyperbolic Manifolds of Finite Volume

Let M denote an even-dimensional noncompact hyperbolic manifold of finite volume. We show that such manifolds are candidates for minimal volume. Generalizing H. Hopf's ideas around the Curvatura integra for compact Clifford–Klein space forms, we present an elementary combinatorial-metrical proof of the Gauss–Bonnet formula for M. In contrast to former results of G. Harder and M. Gromov, our approach doesn't make use of the arithmetical and differential geometrical machinery.     

The equations of the thermodynamic model of magnetoelasticity of dielectric ferromagnetic bodies

We develop a thermodynamic approach to the mathematical modeling of magnetoelastic processes in dielectric ferromagnetic bodies that are subject to the action of force loading, heating, and an external electromagnetic field. The basis for the construction of the physical relations is the principle of local thermodynamic state. In the computations of the momentum balance equation of the magnetization process account is taken of its tensor character.Translated fromMatematicheskie Metody i Fiziko-Mekhanicheskie Polya, Issue 36, 1992, pp. 30–34.     

Mathematical Modeling of Magnetohydrodynamic Processes in an Aluminum Electrolyzer

We model the electrolysis of aluminum in specific electrolysis baths. A model of the physical process is proposed, allowing for the specific bath design, including the state of the bottom surface. The mathematical model utilizes the information capabilities of the Navier–Stokes equations written for the metal and the electrolyte media. The multidimensional system of equations enables us to consider the magnetohydrodynamic processes in two media and the interaction of the media. The problem is solved numerically. The calculations simulate the interface dynamics and the distribution of velocities and currents in the middle layer in both media. The numerical results are compared with physical experiments.     

Finslerian Fields in the Spacetime Tangent Bundle

Finslerian fields are investigated in the arena of the maximal-acceleration invariantspacetime tangent bundle. A variety of differential-geometric Finslerian fields are exposited. Thestructure of Finslerian quantum fields receives particular emphasis. Also, possible generalizedactions are proposed for Finslerian strings and p-branes. 1999 Elsevier Science Ltd.     

Theory of one-dimensional waves in nonlinear dissipative media

A unified approach is made to the construction of mathematical models describing discontinuous processes, and their analogs in the region of continuous solutions are presented; this makes it possible to distinguish between idealized and actual discontinuities and to classify media on the basis of model equations. The media considered are characterized by physical and geometric nonlinearity and by dissipation due to either viscosity or to the coupling of strain and temperature fields.Institute of Cybernetics, Academy of Sciences of the Estonian SSR, Tallin. Translated from Mekhanika Polimerov, No. 1, pp. 41–48, January–February, 1976.     

Convergence of Finslerian metrics under Ricci flow

In this work,we study the convergence of evolving Finslerian metrics first in a general flow and next under Finslerian Ricci flow.More intuitively it is proved that a family of Finslerian metrics g(t)which are solutions to the Finslerian Ricci flow converges in C~∞ to a smooth limit Finslerian metric as t approaches the finite time T.As a consequence of this result one can show that in a compact Finsler manifold the curvature tensor along the Ricci flow blows up in a short time.     

Modification of special relativity and local structures of gravity-free space and time

Besides two fundamental postulates, (i) the principle of relativity and (ii) the constancy of the one-way speed of light in all inertial frames of reference, the special theory of relativity uses the assumption about the Euclidean structure of gravity-free space and the homogeneity of gravity-free time in the usual inertial coordinate system. Introducing the so-called primed inertial coordinate system, in addition to the usual inertial coordinate system, for each inertial frame of reference, we assume the flat structures of gravity-free space and time in the primed inertial coordinate system and their generalized Finslerian structures in the usual inertial coordinate system. We combine this assumption with the two postulates (i) and (ii) to modify the special theory of relativity. The modified special relativity theory involves two versions of the light speed, infinite speed c^′ in the primed inertial coordinate system and finite speed c in the usual inertial coordinate system. It also involves the c^′-type Galilean transformation between any two primed inertial coordinate systems and the localized Lorentz transformation between any two usual inertial coordinate systems. The physical principle is: the c^′-type Galilean invariance in the primed inertial coordinate system plus the transformation from the primed to the usual inertial coordinate systems. Evidently, the modified special relativity theory and the quantum mechanics theory together found a convergent and invariant quantum field theory.     

Study of wave processes in shells and plates with regard to transverse normal and shear deformation

A variant of the theory of orthotropic plates and cylindrical shells taking account of transverse normal and shear deformation was examined. Independent approximations were adopted for distribution of displacements and stresses over the thickness of the shell. One of the requirements for constructing the theory is physical correctness, which is achieved by utilizing variational methods for formulating the mathematical model. The Reissner principle for dynamic processes was used for derivation of the equations. The elliptical part of the starting differential operator was shown to be symmetrical and positive in the space of the integrate of square functions. We examined the problem of the propagation of axially symmetric harmonic waves in the cylinder using the starting differential equations. These results were compared with those obtained equations derived in elasticity theory. Analysis of induced vibration was carried out for the case of a square plate upon the action of a suddenly applied load.Presented at the Ninth International Conference on the Mechanics of Composite Materials, Riga, Latvia, October, 1995.Translated from Mekhanika Kompozitnykh Materialov, Vol. 31, No. 6. pp. 816–823, November–December, 1995.     

Model of a layered plate considering nonideal contact between layers

We propose a mathematical model for doing calculations for layered plates, allowing for both rigid and sliding contact in the presence of frictional forces between the sliding layers. The model takes into account the distribution of tangential and normal displacements across the thickness of the sliding layered stack, and also the distribution of transverse normal stresses. The strain tensor is obtained using the Cauchy relations; the stress tensor is obtained based on Hooke's law. Tne Lagrange variational principle allows us to obtain the resolvent system of differential equations and the corresponding boundary conditions. The spatial model for deformation of a layered plate has a number of special features compared with familiar models. The system of differential equations has operators no higher than second order. It is described relative to displacements on the faces of the stack. This is convenient in solving problems involving sliding of layers with and without friction.Translated from Mekhanika Kompozitnykh Materialov, Vol. 31, No. 5, pp. 671–676, September–October 1995.     

Percolation theory and some applications

The goal of the survey is to present mathematically rigorous results obtained in the recent years in the new mathematical discipline: percolation theory, which is on the border between the theory of random fields, stochastic geometry, and mathematical physics. Here not only classical percolation schemes are considered (bond and site problems on lattices) but also various generalizations that arose in connection with actual physical applications.Translated from Itogi Nauki i Tekhniki, Teoriya Veroyatnostei, Matematicheskaya Statistika, Teoreticheskaya Kibernetika, Vol. 24, pp. 53–110, 1986.     

Mathematical Modeling and Simulation of a Flexible Shaft-Flexible Link System With End Mass

In this study, the equation of motion of a single link flexible robotic arm with end mass, which is driven by a flexible shaft, is obtained by using Hamilton's principle. The physical system is considered as a continuous system. As a first step, the kinetic energy and the potential energy terms and the term for work done by the nonconservative forces are established. Applying Hamilton's principle the variations are calculated and the time integral is constructed. After a series of mathematical manipulations the coupled equations of motion of the physical system and the related boundary conditions are obtained. Numerical solutions of equations of motion are obtained and discussed for verification of the model used.     

Quasistatic anti-plane motion in the simplest theory of nonlinear viscoelasticity

We consider a very simple model in the framework of differential viscoelastic materials which are isotropic and incompressible. In this model the Cauchy stress tensor is split in an elastic part and a dissipative part. The elastic part is derived from a strain-energy density function only of the first invariant of the Cauchy–Green strain tensor. The dissipative part is like the Navier–Stokes equations: linear in the stretching tensor with a constant viscosity parameter. For this model we provide some time and spatial estimates in the quasistatic approximations for the equations governing anti-plane shear motions. Several explicit examples for specific form of the strain energy are produced. Our results impose analytical restrictions on the mathematical properties of the strain energy to ensure a physical behavior in the creep and recovery experiments. Moreover, we show polynomial decay for the spatial behavior in the class of stress-hardening (or strain-stiffening) materials. For stress-softening materials a Phragmen–Lindelof alternative is proved.     

Über die Finslerschen Räume mit Verallgemeinerter Metrik

Finsler spaces with generalized metric are defined as C — manifolds, endowed with a Finslerian connection and a Finslerian tensor field of type (O,2). For this field, both the symmetric and the antisymmetric parts are non-degenerate, and the covariant h- and v-derivations vanish.For these spaces the Eisenhart problem is solved, i.e. necessary and sufficient conditions for the existence, as well as the most general form of such a connection are determined.     

Isometries,submetries and distance coordinates on Finsler manifolds

This paper considers fundamental issues related to Finslerian isometries, submetries, distance and geodesics. It is shown that at each point of a Finsler manifold there is a distance coordinate system. Using distance coordinates, a simple proof is given for the Finslerian version of the Myers–Steenrod theorem and for the differentiability of Finslerian submetries.     

On tropical Clifford’s Theorem

We prove an analogue of Clifford’s inequality for tropical curves. Next we focus on the hyperelliptic case and we characterize divisors attaining equality. Finally we speculate whether inequality in tropical Clifford’s Theorem does imply hyperellipticity, in analogy with the classical case.     

On solving discontinuous extremal problems

An approach to solving discontinuous problems of optimization and control is described. The approach is based on the concept of approximate gradient introduced in Ref. 1. Generalizations of the theorems of Kuhn-Tucker and Dubovitsky-Milyutin and the maximum principle of Pontryagin are proved. The mathematical constructions described allow one to solve a wide variety of applied problems of optimization and control within the class of nonsmooth (including discontinuous) functions. The paper continues the investigations of Refs. 1–2.     

Transient control in nuclear power reactors

Linear and nonlinear problems of transient control in reactors are considered. Controllability of distributed systems is analyzed for mathematical models described by the reactor dynamics system. Sufficient conditions of transient controllability are derived for these reactor models.Translated from Nelineinye Dinamicheskie Sistemy: Kachestvennyi Analiz i Upravlenie — Sbornik Trudov, No. 3, pp. 39–45, 1993.     

Exp-function method for constructing exact solutions of Sharma–Tasso–Olver equation

In this paper we use the Exp-function method for the analytic treatment of Sharma–Tasso–Olver equation. New solitonary solutions are formally derived. Change of parameters, which drastically changes the characteristics of the equations, is examined. It is shown that the Exp-function method provides a powerful mathematical tool for solving high-dimensional nonlinear evolutions in mathematical physics. The proposed schemes are reliable and manageable.     

Finslerian 3-spinors and the generalized Duffin�CKemmer equation

The main facts of the geometry of Finslerian 3-spinors are formulated. The close connection between Finslerian 3-spinors and vectors of the 9-dimensional linear Finslerian space is established. The isometry group of this space is described. The procedure of dimensional reduction to 4-dimensional quantities is formulated. The generalized Duffin?CKemmer equation for a Finslerian 3-spinor wave function of a free particle in the momentum representation is obtained. From the viewpoint of a 4-dimensional observer, this 9-dimensional equation splits into the standard Dirac and Klein?CGordon equations.