Some properties of solutions of a scalar Riccati equation with complex coefficients

We give the definition of normal and limit solutions of the Riccati equation with complex coefficients and study some properties of these solutions. We prove the minimality property of a solution of a system of two linear first-order ordinary differential equations.     

Existence and stability of a summable generalized solution to a mathematical model of a catalytic fluidized bed process

For a system of first-order partial differential equations describing a catalytic process in a fluidized bed, we consider a mixed problem in the half-strip 0 ≤ x ≤ h, t ≥ 0. We prove the existence and uniqueness of a bounded summable generalized solution and study its stability. We prove the stabilization as t → ∞ of the values of some physically meaningful functionals of the solution.     

Generalized Solvability of a Parabolic Model Describing Transfer Processes in Domains with Thin Inclusions

Differential Equations - We study a system of first-order partial differential equations with generalized functions as coefficients that describes the heat and mass transfer process in domains with...     

Interaction of weak discontinuities and the hodograph method as applied to electric field fractionation of a two-component mixture

The hodograph method is used to construct a solution describing the interaction of weak discontinuities (rarefaction waves) for the problem of mass transfer by an electric field (zonal electrophoresis). Mathematically, the problem is reduced to the study of a system of two first-order quasilinear hyperbolic partial differential equations with data on characteristics (Goursat problem). The solution is constructed analytically in the form of implicit relations. An efficient numerical algorithm is described that reduces the system of quasilinear partial differential equations to ordinary differential equations. For the zonal electrophoresis equations, the Riemann problem with initial discontinuities specified at two different spatial points is completely solved.     

On the availability of a warm standby system: a numerical approach

We consider a basic duplex system characterized by warm standby and attended by two general heterogeneous repairmen. In order to derive computational results for the point availability of the engineering system, we first employ a stochastic process endowed with time-dependent transition measures satisfying coupled partial differential equations. However, an explicit evaluation of the (exact) solution is in general excluded. Therefore, we also propose a numerical solution of the equations. Our methodology is based on new modification of the first-order upwind scheme applied to a semiinfinite region. As an application, we consider the important case of Weibull–Gnedenko repair and provide an in-depth analysis of some key features of the duplex system.     

Oscillation for a nonlinear dynamic system on time scales

We study the oscillation properties of a system of two first-order nonlinear equations on time scales. This form includes the classical Emden–Fowler differential and difference equations and many of its extensions. We generalize some well-known results of Atkinson, Belohorec, Waltman, Hooker, Patula and others and also describe the relation to solutions of a delay-dynamic system.     

一类二阶线性时变系统的稳定性

本文讨论了一类二阶线性时变系统在临界情况下的稳定性，给出了保证该系统零解稳定的充分条件，这一结果将拓宽控制论中二维线性时变控制系统的研究范围。     

On a Boundary Value Problem of the Biharmonic Equation

In this paper, we study a system of biharmonic equations coupled by the boundary conditions. These boundary conditions contain some combinations of the values, div, curl, and grad. Applications in mathematical physics are possible and the investigations will be done with the help of hypercomplex methods. It is also the aim of the paper to demonstrate the application of Clifford analytic methods to the solution of boundary value problems. The results on a special boundary value problem for the biharmonic equation will be used for the investigation of some first-order systems of partial differential equations. We study a theoretical problem connected with the ∂¯-problem and the solution of a Beltrami system by using a fixed-point iteration. © 1997 B. G. Teubner Stuttgart–John Wiley & Sons Ltd.     

An observation on the periodic solutions to nonlinear physical models by means of the auxiliary equation with a sixth-degree nonlinear term

It is a fact that in auxiliary equation methods, the exact solutions of different types of auxiliary equations may produce new types of exact travelling wave solutions to nonlinear equations. In this manner, various auxiliary equations of first-order nonlinear ordinary differential equation with distinct-degree nonlinear terms are examined and, by means of symbolic computation, the new solutions of original auxiliary equation of first-order nonlinear ordinary differential equation with sixth-degree nonlinear term are presented. Consequently, the novel exact solutions of the generalized Klein–Gordon equation and the active-dissipative dispersive media equation are found out for illustration purposes. They are also applicable, where conventional perturbation method fails to provide any solution of the nonlinear problems under study.     

Finite-difference methods for solving the reaction-diffusion equations of a simple isothermal chemical system

Numerical methods are proposed for the numerical solution of a system of reaction-diffusion equations, which model chemical wave propagation. The reaction terms in this system of partial differential equations contain nonlinear expressions. Nevertheless, it is seen that the numerical solution is obtained by solving a linear algebraic system at each time step, as opposed to solving a nonlinear algebraic system, which is often required when integrating nonlinear partial differential equations. The development of each numerical method is made in the light of experience gained in solving the system of ordinary differential equations, which model the well-stirred analogue of the chemical system. The first-order numerical methods proposed for the solution of this initialvalue problem are characterized to be implicit. However, in each case it is seen that the numerical solution is obtained explicitly. In a series of numerical experiments, in which the ordinary differential equations are solved first of all, it is seen that the proposed methods have superior stability properties to those of the well-known, first-order, Euler method to which they are compared. Incorporating the proposed methods into the numerical solution of the partial differential equations is seen to lead to two economical and reliable methods, one sequential and one parallel, for solving the travelling-wave problem. © 1994 John Wiley & Sons, Inc.     

On a nonlinear hyperbolic problem arising in two-phase flows in naturally fractured reservoirs

A system of two first-order quasilinear equations consisting of one nonhomogenous hyperbolic conservation law and an ordinary differential equation is investigated in two spatial dimensions. The initial boundary-value problem is solved for the system and existence, uniqueness, and stability theorems are proved. We also obtain a result on the behavior of the solution when time goes to infinity which agrees with practical experience. These results offer mathematical validation to computer models in current usage for the numerical simulation of multiphase flow in naturally fractured reservoirs.     

The application of the differential-constraints method to the two-dimensional equations of gas dynanics

The differential-constraints (DC) method is used to distinguish and construct individual classes of solutions of the two-dimensional equations of gas dynamics with plane and axial symmetry. The solutions (the DP-solutions), which satisfy one, two and three first-order differential constraints are classified. The solution of the Cauchy problem with data on the line of common position in these cases has three, two and one arbitrary functions respectively. In the case of solutions with three- and two-function arbitrariness all the differential constraints compatible with the system considered are indicated. The individual DP-solutions of the gas-dynamics equations are constructed using them. In the case of single-function arbitrariness the differential constraints compatible with the gas-dynamics equations are obtained. This class of solutions includes the well-known generalized Prandtl-Meyer waves. The construction of the DP-solutions of this class reduces to the integration of a system of ordinary differential equations, which is a new representation of this class of solutions.     

Asymptotic analysis of a model of nuclear magnetic autoresonance

We study the system of three first-order differential equations arising when averaging the Bloch equations in the theory of nuclear magnetic resonance. For the averaged system, we construct an asymptotic series for the stable solution with an infinitely increasing amplitude. This result gives a key to understanding the autoresonance in weakly dissipative magnetic systems as a phenomenon of significant growth of the magnetization initiated by a small external pumping.     

On two-parameter spectral problems and their application

We study a spectral problem with two complex parameters for a normal linear system of second-order ordinary differential equations on a closed interval with splitting or nonlocal boundary conditions. The results of this study are used to prove the existence and uniqueness of a generalized solution of a boundary value problem in a cylinder for a class of partial differential equations.     

Analysis of the synchronization model in an anisochronous system

A model system of two first-order differential equations that arises in the synchronization theory of nonlinear oscillations is investigated. Constraints on the parameters of the equations under which the synchronization is realized on every solution are found. A domain of the parameters in which the synchronization occurs only for a part of the solution set is determined.     

Infinite Systems of Hyperbolic Functional Differential Equations

We consider initial-value problems for infinite systems of first-order partial functional differential equations. The unknown function is the functional argument in equations and the partial derivations appear in the classical sense. A theorem on the existence of a solution and its continuous dependence upon initial data is proved. The Cauchy problem is transformed into a system of functional integral equations. The existence of a solution of this system is proved by using integral inequalities and the iterative method. Infinite differential systems with deviated argument and differential integral systems can be derived from the general model by specializing given operators.     

Asymptotics of the solution to a singularly perturbed system of first-order partial differential equations with small nonlinearity in the critical case

A formal asymptotic representation of the solution to an initial-boundary value problem for a singularly perturbed system of first-order partial differential equations with small nonlinearity is constructed.     

A Posterior Estimate of the Particle Method Error for Shallow Water Models

The article examines the application of the particle method to numerical solution of the Cauchy problem for a quasi-linear system of first-order partial differential equations with discontinuous piecewise-constant initial conditions. A posterior estimate of the particle method error is derived for some shallow-water models.     

Exact solution to the periodic boundary value problem for a first-order linear fuzzy differential equation with impulses

Using the expression of the exact solution to a periodic boundary value problem for an impulsive first-order linear differential equation, we consider an extension to the fuzzy case and prove the existence and uniqueness of solution for a first-order linear fuzzy differential equation with impulses subject to boundary value conditions. We obtain the explicit solution by calculating the solutions on each level set and justify that the parametric functions obtained define a proper fuzzy function. Our results prove that the solution of the fuzzy differential equation of interest is determined, under the appropriate conditions, by the same Green’s function obtained for the real case. Thus, the results proved extend some theorems given for ordinary differential equations.     

Version of the elimination method for a system of partial differential equations

For a system of three first-order partial differential equations with three independent variables, we obtain sufficient conditions for one component of the solution to satisfy a third-order Bianchi equation. We also obtain conditions for the solvability of this system by quadratures.