On Exact Multidimensional Solutions of a Nonlinear System of Reaction–Diffusion Equations

We study a nonlinear reaction–diffusion system modeled by a system of two parabolic-type equations with power-law nonlinearities. Such systems describe the processes of nonlinear diffusion in reacting two-component media. We construct multiparameter families of exact solutions and distinguish the cases of blow-up solutions and exact solutions periodic in time and anisotropic in spatial variables that can be represented in elementary functions.     

Exact Solutions for Self-dual Yang–Mills Equations

The (constrained) canonical reduction of four dimensional self-dual Yang–Millstheory to 2, (2+1) dimensional sine-Gordon theory and 2 dimensional Liouvilles theory areconsidered. The Bäcklund transformations (BTs) areimplemented to obtain new classes of exact solutions for the reduced 2 dimensional sine-Gordonand Liouville models. Another transformation is developed and used to obtain exact solution forthe 2+1 and the original 3+1 sine-Gordon models.     

Bäcklund Transformation and Dressing Chains for the Landau–Lifshitz Equation

We use the dressing method for the Landau–Lifshitz equation and the breeding procedure to obtain a modified Landau–Lifshitz equation. We find the Darboux transformation (the dressing) for the integrable Landau–Lifshitz equation of the anisotropic magnet. We find the Bäcklund transformations and dressing chains.     

New Exact Solutions of the Navier–Stokes Equations for Axisymmetric Automodel Flows of Fluids

We investigate self-similar solutions of the Navier–Stokes equations for the axisymmetric flow of a viscous incompressible fluid. The original equations are transformed by the Slezkin method. On the basis of analysis of physical properties of the flow and the Slezkin general equation, we show that, in parallel with the known solutions of this equation, there exist several other solutions with physical meaning. We consider the simplest case of irrotational flows for which current lines may be circles, ellipses, parabolas, and hyperbolas. Unlike the Landau and Squire solutions, these flows are interpreted as nonjet flows of fluid flowing into and out of a homogeneous porous axially symmetric body.     

A One–parameter Family of Bounded Solutions for a System of Nonlinear Integral Equations on the Whole Line

A system of nonlinear integral equations with a convolution type operator arising in the p–adic string theory for the scalar tachyons field is studied. The existence of a one–parameter family of monotone continuous and bounded solutions for this system is proved. The limits of the constructed solutions at ±∞ are calculated.     

Ermakov–Pinney and Emden–Fowler Equations: New Solutions from Novel Bäcklund Transformations

We study the class of nonlinear ordinary differential equations y″ y = F(z, y²), where F is a smooth function. Various ordinary differential equations with a well-known importance for applications belong to this class of nonlinear ordinary differential equations. Indeed, the Emden–Fowler equation, the Ermakov–Pinney equation, and the generalized Ermakov equations are among them. We construct Bäcklund transformations and auto-Bäcklund transformations: starting from a trivial solution, these last transformations induce the construction of a ladder of new solutions admitted by the given differential equations. Notably, the highly nonlinear structure of this class of nonlinear ordinary differential equations implies that numerical methods are very difficult to apply.     

Bäcklund Transformations for the Camassa–Holm Equation

The Bäcklund transformation (BT) for the Camassa–Holm (CH) equation is presented and discussed. Unlike the vast majority of BTs studied in the past, for CH the transformation acts on both the dependent and (one of) the independent variables. Superposition principles are given for the action of double BTs on the variables of the CH and the potential CH equations. Applications of the BT and its superposition principles are presented, specifically the construction of travelling wave solutions, a new method to construct multisoliton, multicuspon and soliton–cuspon solutions, and a derivation of generating functions for the local symmetries and conservation laws of the CH hierarchy.     

Perturbation Method for Particle-like Solutions of the Einstein–Dirac Equations

The aim of this work is to prove by a perturbation method the existence of solutions of the coupled Einstein–Dirac equations for a static, spherically symmetric system of two fermions in a singlet spinor state. We relate the solutions of our equations to those of the nonlinear Choquard equation and we show that the nondegenerate solution of Choquard’s equation generates solutions of the Einstein–Dirac equations.     

Exact Solutions and Integrability of the Duffing – Van der Pol Equation

The force-free Duffing–Van der Pol oscillator is considered. The truncated expansions for finding the solutions are used to look for exact solutions of this nonlinear ordinary differential equation. Conditions on parameter values of the equation are found to have the linearization of the Duffing–Van der Pol equation. The Painlevé test for this equation is used to study the integrability of the model. Exact solutions of this differential equation are found. In the special case the approach is simplified to demonstrate that some well-known methods can be used for finding exact solutions of nonlinear differential equations. The first integral of the Duffing–Van der Pol equation is found and the general solution of the equation is given in the special case for parameters of the equation. We also demonstrate the efficiency of the method for finding the first integral and the general solution for one of nonlinear second-order ordinary differential equations.     

Bäcklund Transformations for the Degasperis-Procesi Equation

Theoretical and Mathematical Physics - We consider the Bäcklund transformation for the Degasperis-Procesi (DP) equation. Using the reciprocal transformation and the associated DP equation, we...     

Solutions for Quasilinear Schrödinger Equations via the Nehari Method

Abstract

For a class of quasilinear Schrödinger equations we establish the existence of both one-sign and nodal ground states of soliton type solutions by the Nehari method.     

On a family of Bäcklund transformations

It is proved that integrals of Abel differential equations can be used in the explicit construction of Bäcklund transformations in mechanics.     

Periodic Solutions for a Class of Forced Lienard-type Equations

By applying the topological degree theory, we establish some sufficient conditions for the existence on T-periodic solutions for the Lienard-type equation Our results extend and improve some known results in the literature.     

Integrable symplectic maps via reduction of Bäcklund transformation

Theoretical and Mathematical Physics - We discuss the stationary potential equations as illustrative examples to explain how to construct integrable symplectic maps via Bäcklund...     

Exact Solutions of Incompressible Navier–Stokes Equations in the Case of Oil and Gas Industrial Problems

Doklady Mathematics - Classes of exact solutions corresponding to vortex and potential flows are presented within the framework of a hydrodynamic model describing flows of a viscous incompressible...     

Existence of Periodic Solutions for Odd Order Ordinary Differential Equations via the Homotopy Method

This paper deals with the problems of finding periodic solutions for the third order ordinary differential equations of the form (1) where T is a fixed positive number and f satisfies some additional conditions which will be stated later.The periodicity problem has been one of main topics in the qualitative theory of ordinary     

Iterative Solutions for a Non-monotone BinaryOperator Equations and Operator System of Equations

By using the theory of the cone and partial ordering. It is studied that the existence and uniqueness of solutions for a non-monotone binary operator equation A(x, x)= x and operator system of equations A(x,x)=x,B(x,x)=x in Banach spaces. Where A and B can be decomposed A=A1+A2, B=B1+B2,A1 and B1 are mixed monotone, A2 and B2 are anti-mixed monotone. The results presented here improve and generalize some corresponding results of mixed monotone operator equations.