A family of integrable differential-difference equations and its Bargmann symmetry constraint

A family of integrable differential-difference equations is constructed through discrete zero curvature equation. The Hamiltonian structures of the resulting differential-difference equations are established by the discrete trace identity. The Bargmann symmetry constraint of the resulting family is presented. Under this symmetry constraint, every differential-difference equation in the resulting family is factored by an integrable symplectic map and a finite-dimensional integrable system in Liouville sense.     

A NEW INTEGRABLE SYMPLECTIC MAP ASSOCIATED WITH A DISCRETE MATRIX SPECTRAL PROBLEM

A hierarchy of lattice soliton equations is derived from a discrete matrix spectral problem. It is shown that the resulting lattice soliton equations are all discrete Liouville integrable systems. A new integrable symplectic map and a family of finite-dimensional integrable systems are given by the binary nonli-nearization method. The binary Bargmann constraint gives rise to a Backlund transformation for the resulting lattice soliton equations.     

S. V. Kovalevskaya system, its generalization and discretization

We consider an integrable three-dimensional system of ordinary differential equations introduced by S. V. Kovalevskaya in a letter to G. Mittag-Leffler. We prove its isomorphism with the three-dimensional Euler top, and propose two integrable discretizations for it. Then we present an integrable generalization of the Kovalevskaya system, and study the problem of integrable discretization for this generalized system.     

The dynamics of nonholonomic systems consisting of a spherical shell with a moving rigid body inside

In this paper we investigate two systems consisting of a spherical shell rolling without slipping on a plane and a moving rigid body fixed inside the shell by means of two different mechanisms. In the former case the rigid body is attached to the center of the ball on a spherical hinge. We show an isomorphism between the equations of motion for the inner body with those for the ball moving on a smooth plane. In the latter case the rigid body is fixed by means of a nonholonomic hinge. Equations of motion for this system have been obtained and new integrable cases found. A special feature of the set of tensor invariants of this system is that it leads to the Euler — Jacobi — Lie theorem, which is a new integration mechanism in nonholonomic mechanics. We also consider the problem of free motion of a bundle of two bodies connected by means of a nonholonomic hinge. For this system, integrable cases and various tensor invariants are found.     

Novikov Algebras and a Classification of Multicomponent Camassa–Holm Equations

A class of multicomponent integrable systems associated with Novikov algebras, which interpolate between Korteweg–de Vries (KdV) and Camassa–Holm‐type equations, is obtained. The construction is based on the classification of low‐dimensional Novikov algebras by Bai and Meng. These multicomponent bi‐Hamiltonian systems obtained by this construction may be interpreted as Euler equations on the centrally extended Lie algebras associated with the Novikov algebras. The related bilinear forms generating cocycles of first, second, and third order are classified. Several examples, including known integrable equations, are presented.     

The integrable case of Adler–van Moerbeke. Discriminant set and bifurcation diagram

The Adler–van Moerbeke integrable case of the Euler equations on the Lie algebra so(4) is investigated. For the L–A pair found by Reyman and Semenov-Tian-Shansky for this system, we explicitly present a spectral curve and construct the corresponding discriminant set. The singularities of the Adler–van Moerbeke integrable case and its bifurcation diagram are discussed. We explicitly describe singular points of rank 0, determine their types, and show that the momentum mapping takes them to self-intersection points of the real part of the discriminant set. In particular, the described structure of singularities of the Adler–van Moerbeke integrable case shows that it is topologically different from the other known integrable cases on so(4).     

一个新的Liouville可积系统及其Lax表示，Bi—Hamilton结构

从一个特征值问题出发,首先推导一族非线性发展方程,其中包括著名MKdV方程做为特殊约化,进一步证明这族方程在Liounille意义下可积并具有Bi-Hamilton结构,而在位执函数和特征函数之间的一定约束下,特征值问题被非线性化为一完全可积的有限维Hamilton系统。     

Study of vortex breakdown in a stratified fluid

An analysis shows that nonsmooth solutions have to be considered. Weak solutions to the Euler equations describing an incompressible stratified fluid under gravity are defined and studied. The study makes use of a wave energy functional proposed for the nonlinear equations. It is shown that the Euler equations are insufficient for stating a well-posed generalized problem. Additional conditions based on physical considerations are proposed. One condition is energy conservation, and the other is a constraint imposed on the density, which is required for stability. A numerical method is developed that is used to analyze how wave breakdown in a stratified fluid depends on stratification. The numerical results are in satisfactory agreement with experiments.     

Decomposing a new nonlinear differential-difference system under a Bargmann implicit symmetry constraint

Firstly, a hierarchy of integrable lattice equations and its bi-Hamilt-onian structures are established by applying the discrete trace identity. Secondly, under an implicit Bargmann symmetry constraint, every lattice equation in the nonlinear differential-difference system is decomposed by an completely integrable symplectic map and a finite-dimensional Hamiltonian system. Finally, the spatial part and the temporal part of the Lax pairs and adjoint Lax pairs are all constrained as finite dimensional Liouville integrable Hamiltonian systems.     

Analysis of the Euler–Poisson equations by methods of power geometry and normal form

New approaches and methods for studying non-linear problems are applied to the classical problem of the motion of a heavy rigid body about a fixed point, i.e., to the system of Euler–Poisson equations. All the asymptotic expansions of the solutions of the Kowalewski equations, to which the Euler–Poisson equations reduce when certain constraints are imposed on the parameters, are found using power geometry. They form 24 families. Then all the exact solutions of the Kowalewski equations of a specific class (which includes almost all the known exact solutions) are found on the basis of these expansions. Five new families of such solutions are found. Instead of the conventional technique of studying the global integrability of the Euler–Poisson equations, studying their local integrability near stationary and periodic solutions is proposed. Normal forms are used for this purpose. Sets of real stationary solutions, in the vicinity of which these equations are locally integrable, are discovered using them. Other real stationary solutions, in the vicinity of which the Euler–Poisson equations are locally non-integrable, are also found. This is established using the theory of resonant normal forms developed and computer calculations of the coefficients of a normal form.     

大位移非线性弹性理论的变分原理和广义变分原理

在前文中[1],作者首次提出了大位移非线性弹性力学的位能原理和余能原理,以及各种完全的和不完全的广义变分原理.但在约束条件和欧拉条件上,证明和叙述都不很明确,有时甚至把原来应该是欧拉方程的误认为是约束条件,如余能驻值原理中,应力位移关系原应是欧拉方程,但把它当作了变分约束条件.这就是说:我们把余能驻值原理约束得超过了必要的要求.还有,在所有变分原理中,应力应变关系式都是不参加变分的约束条件,亦即,他们是从已定应力导出应变或从已定应变导出应力的约束条件.这一点,在文[1](1979)中,并未明确指出.本文并将用高阶拉氏乘子法,导出更一般的广义变分原理(1983)[2].本文使用V.V.Novozhilov的有关非线性弹性力学的成果(1958)[3].     

Confluence of hypergeometric functions and integrable hydrodynamic-type systems

We construct a new class of integrable hydrodynamic-type systems governing the dynamics of the critical points of confluent Lauricella-type functions defined on finite-dimensional Grassmannian Gr(2, n), i.e., on the set of 2×n matrices of rank two. These confluent functions satisfy certain degenerate Euler–Poisson–Darboux equations. We show that in the general case, a hydrodynamic-type system associated with the confluent Lauricella function is an integrable and nondiagonalizable quasilinear system of a Jordan matrix form. We consider the cases of the Grassmannians Gr(2, 5) for two-component systems and Gr(2, 6) for three-component systems in detail.     

Finite-Dimensional Integrable Hamiltonian Systems Related to the Nonlinear Schrödinger Equation

A complete treatment of the binary nonlinearizations of spectral problems of the nonlinear Schrödinger (NLS) equation with the choice of distinct eigenvalue parameters is presented. Two kinds of constraints between the potentials and the eigenfunctions of the NLS equation are considered. From the first constraint, a pair of new finite-dimensional completely integrable Hamiltonian systems which constitute an integrable decomposition of the NLS equation are obtained. From the second constraint, a novel finite-dimensional integrable Hamiltonian system, which includes the system of multiple three-wave interaction as a special case, is obtained. It is found that the eigenvalue parameters real or not can lead to completely different symplectic structures of the restricted NLS flows. In addition, a relationship between the binary restricted Ablowitz–Kaup–Newell–Segur flows and the restricted NLS flows is revealed.     

A HIERARCHY OF INTEGRABLE HAMILTONIAN SYSTEMS WITH NEUMANN TYPE CONSTRAINT

A hierarchy of integrable Hamiltonian systems with Neumann type constraint isobtained by restricting a hierarchy of evolution equations associated with λφ_(xx)+u_iλ~iφ=λ~mφ to aninvariant subspace of their recursion operator.The independentintegrals of motion and Hamiltonian functions for these Hamiltonian systems areconstructed by using relevant reeursion formula and are shown to be in involution.Thusthese Hamiltonian systems are completely integrable and commute with each other.     

A nonlinear Hamiltonian structure for the Euler equations

The Euler equations for inviscid incompressible fluid flow have a Hamiltonian structure in Eulerian coordinates, the Hamiltonian operator, though, depending on the vorticity. Conservation laws arise from two sources. One parameter symmetry groups, which are completely classified, yield the invariance of energy and linear and angular momenta. Degeneracies of the Hamiltonian operator lead in three dimensions to the total helicity invariant and in two dimensions to the area integrals reflecting the point-wise conservation of vorticity. It is conjectured that no further conservation laws exist, indicating that the Euler equations are not completely integrable, in particular, do not have soliton-like solutions.     

On Discretization of the Euler Top

The application of intersection theory to construction of n-point finite-difference equations associated with classical integrable systems is discussed. As an example, we present a few new discretizations of motion of the Euler top sharing the integrals of motion with the continuous time system and the Poisson bracket up to the integer scaling factor.     

Multiexponential models of (1+1)-dimensional dilaton gravity and Toda-Liouville integrable models

We study general properties of a class of two-dimensional dilaton gravity (DG) theories with potentials containing several exponential terms. We isolate and thoroughly study a subclass of such theories in which the equations of motion reduce to Toda and Liouville equations. We show that the equation parameters must satisfy a certain constraint, which we find and solve for the most general multiexponential model. It follows from the constraint that integrable Toda equations in DG theories generally cannot appear without accompanying Liouville equations. The most difficult problem in the two-dimensional Toda-Liouville (TL) DG is to solve the energy and momentum constraints. We discuss this problem using the simplest examples and identify the main obstacles to solving it analytically. We then consider a subclass of integrable two-dimensional theories where scalar matter fields satisfy the Toda equations and the two-dimensional metric is trivial. We consider the simplest case in some detail. In this example, we show how to obtain the general solution. We also show how to simply derive wavelike solutions of general TL systems. In the DG theory, these solutions describe nonlinear waves coupled to gravity and also static states and cosmologies. For static states and cosmologies, we propose and study a more general one-dimensional TL model typically emerging in one-dimensional reductions of higher-dimensional gravity and supergravity theories. We especially attend to making the analytic structure of the solutions of the Toda equations as simple and transparent as possible.     

Five constructions of integrable dynamical systems connected with the Korteweg-de Vries equation

Two countable sets of integrable dynamical systems which turn into the Korteweg-de Vries equation in a continous limit are constructed. The integrability of the dynamics of the scattering matrix entries for these systems is proved and an integrable reduction in the finitedimensional case is pointed out. A construction of the integrable dynamical systems connected with the simple Lie algebras and generalizing the discrete kdV equation is presented. Two general constructions of differential and integro-differential equations (with respect to time t) possessing a countable set of first integrals are found. These equations admit the Lax representation in some infinite-dimensional subalgebras of the Lie algebra of integral operators on an arbitrary manifold M ⁿ with measure . A construction of matrix equations having a set of attractors in the space of all matrix entries is given.     

The generation,propagation, and extinction of multiphases in the KdV zero‐dispersion limit

We study the multiphases in the KdV zero‐dispersion limit. These phases are governed by the Whitham equations, which are 2g + 1 quasi‐linear hyperbolic equations where g is the number of phases. We are interested in both the interaction of two single phases and the breaking of a single phase for general initial data. We analyze in detail how a double phase is generated from the interaction or breaking, how it propagates in space‐time, and how it collapses to a single phase in a finite time. The Whitham equations are known to be integrable via a hodograph transform. The crucial step in our approach is to formulate the hodograph transform in terms of the Euler‐Poisson‐Darboux solutions. Under our scheme, the zeros of the Jacobian of the transform are given by the zeros of the Euler‐Poisson‐Darboux solution. Hence, the problem of inverting the hodograph transform to give the Whitham solution reduces to that of counting the zeros of the Euler‐Poisson‐Darboux solution. © 2002 Wiley Periodicals, Inc.     

SYMMETRY CONSTRAINT OF THE LEVI EQUATIONS BY BINARY NONLINEARIZATION

In this paper, the translation of the Lax pairs of the Levi equations is presented. Then a symmetry constraint for the Levi equations is given by means of binary nonlinearization method. The spatial part and the temporal parts of the translated Lax pairs and its adjoint Lax pairs of the Levi equations are all constrainted as finite dimensional Liouville integrable Hamiltonian systems. Finally, the involutive solutions of the Levi equations are presented.