Third-order constants of motion in quantum mechanics

We investigate the general form of a third-order linear differential operator that is required to commute with the Schrödinger Hamiltonian in two dimensions, and find that the third-order part must be a polynomial of third degree in the generators of the Euclidean group. Partial differential equations that the potentialV must satisfy are derived, and solved for the special cases where the Schrödinger equation separates in polar or Cartesian coordinates. The functionsV thus obtained are nonsingular, but are periodic through elliptic functions. After separation of variables, the Schrödinger equation gives Lame's equation.     

Variational Formulation of Approximate Symmetries and Conservation Laws

We show how the conserved vectors and associated (approximate) Lie symmetry generators of a partial differential equation with a small parameter can be utilized to construct approximate Lagrangians for the equation. We then use the Lagrangian to further determine approximate Noether symmetries and, hence, new associated conservation laws. The theory is applied to a number of perturbations of the wave equation.     

一般完整系统Mei对称性的逆问题

动力学逆问题是星际航行学、火箭动力学、规划运动学理论的基本问题. Mei对称性是力学系统的动力学函数在群的无限小变换下仍然满足系统原来的运动微分方程的一种新的不变性. 本文研究广义坐标下一般完整系统的Mei对称性以及与Mei对称性相关的动力学逆问题. 首先, 给出系统动力学正问题的提法和解法. 引入时间和广义坐标的无限小单参数变换群, 得到无限小生成元向量及其一次扩展. 讨论由n个广义坐标确定的一般完整力学系统的运动微分方程, 将其Lagrange函数和非势广义力作无限小变换, 给出系统运动微分方程的Mei对称性定义, 在忽略无限小变换的高阶小量的情况下得到Mei对称性的确定方程, 借助规范函数满足的结构方程导出系统Mei对称性导致的Noether守恒量. 其次, 研究系统Mei对称性的逆问题. Mei对称性的逆问题的提法是: 由已知守恒量来求相应的Mei对称性. 采取的方法是将已知积分当作由Mei对称性导致的Noether守恒量, 由Noether逆定理得到无限小变换的生成元, 再由确定方程来判断所得生成元是否为Mei对称性的. 然后, 讨论生成元变化对各种对称性的影响. 结果表明, 生成元变化对Noether和Lie对称性没有影响, 对Mei 对称性有影响, 但在调整规范函数时, 若满足一定条件, 生成元变化对Mei对称性也可以没有影响. 最后, 举例说明结果的应用.     

New Symmetries for a Model of Fast Diffusion

The new symmetries for a mathematical model of fast diffusion are determined. A new system method is given to search for new symmetries of differential equations written in a conserved form, several new symmetry generators and exact solutions are presented.     

Lie algebras of classical and stochastic electrodynamics

The Lie algebras associated with infinitesimal symmetry transformations of third-order differential equations of interest to classical electrodynamics and stochastic electrodynamics have been obtained. The structure constants for a general case are presented and the Lie algebra for each particular application is easily achieved. By the method used here it is not necessary to know the explicit expressions of the infinitesimal generators in order to determine the structure constants of the Lie algebra.     

Conformal Invariance and Conserved Quantities of General Holonomic Systems

Conformed invariance and conserved quantities of general holonomic systems are studied. A one-parameter infinitesimal transformation group and its infinitesimal transformation vector of generators are described. The definition of conformal invariance and determining equation for the system are provided. The conformal factor expression is deduced from conformal invariance and Lie symmetry. The necessary and suttlcient condition, that conformal invariance of the system would be Lie symmetry, is obtained under the infinitesimal one-parameter transformation group. The corresponding conserved quantity is derived with the aid of a structure equation. Lastly, an example is given to demonstrate the application of the result.     

The Kac-moody and Virasoro commutation equations

The commutation equation of the Kac-Moody generators realized as functional differential operators is explicitly verified. The anomaly of the loop group generators is briefly discussed and the Virasoro commutation equation is then derived. No use is made of normal ordering in obtaining the central extensions of the above commutation equations.     

Conformal invariance and conserved quantity of third-order Lagrange equations for non-conserved mechanical systems

This paper studies conformal invariance and conserved quantity of third-order Lagrange equations for non-conserved mechanical systems. Third-order Lagrange equations, the definition and a determining equation of conformal invariance of the system are presented. The conformal factor expression is deduced from conformal invariance and Lie symmetry. The necessary and sufficient condition that conformal invariance of the system would have Lie symmetry under single-parameter infinitesimal transformations is obtained. The corresponding conserved quantity of conformal invariance is derived with the aid of a structure equation. Lastly, an example is given to illustrate the application of the results.     

Conformal invariance and integration of first-order differential equations

This paper studies a conformal invariance and an integration of first-order differential equations. It obtains the corresponding infinitesimal generators of conformal invariance by using the symmetry of the differential equations, and expresses the differential equations by the equations of a Birkhoff system or a generalized Birkhoff system. If the infinitesimal generators are those of a Noether symmetry, the conserved quantity can be obtained by using the Noether theory of the Birkhoff system or the generalized Birkhoff system.     

变质量力学系统的三阶拉格朗日方程

本文从变质量力学系统的三阶D’Alember-Lagrange原理出发，导出了变质量力学系统的Lagrange方程。利用该方程可以使我们得到描述变质量力学系统的运动。此外，变质量力学系统的Lagrange方程也可以使三阶运动微分方程理论得到充实。     

Vibrations of a system with memory,non-linear elasticity,friction and relaxation

The solution of a third-order non-linear differential equation with slowly varying coefficients and small time lag is found. This equation governs processes with significant damping, and an application is made to a mechanical vibrating system with non-linear elasticity, internal friction and relaxation.     

Relationship between Symmetries andConservation Laws

The fundamental relation between Lie-Bäcklund symmetry generators andconservation laws of an arbitrary differential equation is derived without regardto a Lagrangian formulation of the differential equation. This relation is used inthe construction of conservation laws for partial differential equations irrespectiveof the knowledge or existence of a Lagrangian. The relation enables one toassociate symmetries to a given conservation law of a differential equation.Applications of these results are illustrated for a range of examples.     

Lie symmetries and conserved quantities for a two-dimensional nonlinear diffusion equation of concentration

The Lie symmetries and conserved quantities of a two-dimensional nonlinear diffusion equation of concentration are considered. Based on the invariance of the two-dimensional nonlinear diffusion equation of concentration under the infinitesimal transformation with respect to the generalized coordinates and time, the determining equations of Lie symmetries are presented. The Lie groups of transformation and infinitesimal generators of this equation are obtained. The conserved quantities associated with the nonlinear diffusion equation of concentration are derived by integrating the characteristic equations. Also, the solutions of the two-dimensional nonlinear diffusion equation of concentration can be obtained.     

The approximate conserved quantity of the weakly nonholonomic mechanical-electrical system

We study the approximate conserved quantity of the weakly nonholonomic mechanical-electrical system.By means of the Lagrange-Maxwell equation,the Noether equality of the weakly nonholonomic mechanical-electrical system is obtained.The multiple powers-series expansion of the parameter of the generators of infinitesimal transformations and the gauge function is put into a generalized Noether identity.Using the Noether theorem,we obtain an approximate conserved quantity.An example is provided to prove the existence of the approximate conserved quantity.     

Chaos in a finite macroscopic system

We study a problem in fluid dynamics that has three competing instabilities and reduce it to a third-order nonlinear ordinary differential equation which exhibits chaotic solutions.     

具有三个任意函数的变系数KdV-MKdV方程的精确类孤子解

利用一个新的变换将变系数KdV-MKdV方程约化为三阶非线性常微分方程(NODE),考虑这个NODE,获得了变系数KdV-MKdV方程的若干精确类孤子解.这种思路也适合于其他的变系数非线性方程,如变系数KP方程、变系数sine-Gordon方程等. 关键词：     

Lie-Bäcklund transformation and ordinary differential equations associated with some nonlinear equations

Lie-Bäcklund-type analysis have been performed for one nonlinear partial differential equation, which is somewhat different from those usually studied. We consider the KdV equation with an explicit x dependence. In this case we show the form of symmetry generators and find the ordinary differential equation connected with them having no movable critical points. This clearly extends the class of equations analysed by Ablowitz.     

Lie Symmetries for a Conformally Flat Radiating Star

We consider a relativistic radiating spherical star in conformally flat spacetimes. In particular we study the junction condition relating the radial pressure to the heat flux at the boundary of the star which is a nonlinear partial differential equation. The Lie symmetry generators that leave the equation invariant are identified and we generate an optimal system. Each element of the optimal system is used to reduce the partial differential equation to an ordinary differential equation which is further analysed. We identify new categories of exact solutions to the boundary conditions. Two classes of solutions are of interest. The first class depends on a self similar variable. The second class is separable in the spacetime variables.     

Interaction between Soliton and Periodic Wave

A truncation for the Laurent series in the Padnleve analysis of the KdV equation is restudied. When the truncation occurs the singular manifold satisfies two compatible fourth-order PDEs, which are homogeneous of degree 3. Both of the PDEs can be factored in the operator sense. The common factor is a third-order PDE, which is homogeneous of degree 2. The first few Invariant manifolds of the third-order PDE are studied. We find that the invariant manifolds of the third-order PDE can be obtained by factoring the invariant manifolds of the KdV equation. A numerical solution of the third-order PDE facts about the third-order PDE. is also presented. The solution reveals some interesting     

增加附加项后广义Hamilton系统的形式不变性与Mei守恒量

研究增加附加项后广义Hamilton系统的形式不变性及其导出的Mei守恒量. 引进无限小变换群及其生成元向量, 给出增加附加项后广义Hamilton系统的形式不变性的定义和判据, 利用规范函数满足的结构方程, 导出与该系统形式不变性相应的Mei守恒量的表达式. 最后, 给出一个算例, 用于说明结果的应用.