基于变分原理的自适应方法在统一坐标系中的应用

在统一坐标系的基础上引入变分方法,并从自适应网格的正交性、光滑性、疏密程度等角度考虑,获取速度系数h的椭圆方程,从而在边界上可以自由控制h的取值,以适应不同物理问题的需要.算例证明,变分法在统一坐标系中的应用是可行的,在边界上可以满足物理要求.     

修正的变分迭代法在四阶Cahn-Hilliard方程和BBM-Burgers方程中的应用

变分迭代法是一种基于变分原理,具有高数值精度的数值格式,目前已广泛应用于各类强非线性孤立波方程的数值求解中.本文利用修正的变分迭代法对两类非线性方程进行研究.该格式是对原数值方法的一种改进,即在变分项前引入了参数h.通过定义误差函数的离散二范数并在定义域内绘出h-曲线,从而确定出使误差达到最小的h,再返回原迭代过程进行...     

梯度计算的集合变分方案及其在大气Ekman层湍流系数反演中的应用

大气Ekman层湍流系数的准确计算对数值天气预报和污染物扩散计算有着重要的意义. 将集合计算和变分法结合起来, 提出了目标泛函梯度计算的集合变分方案, 并根据正演模式的线性化情况提出了两种计算流程. 利用这种集合变分梯度算法及两种流程对Ekman层湍流系数进行了反演试验, 结果表明这种算法实施简单、方便, 根据观测资料能够比较准确地反演湍流系数值. 关键词： 梯度计算 集合变分 湍流系数 反演     

有耗孤子的最小作用量原理及其在二维光子带隙结构中的应用

采用变分方法对于二维矩形光子带隙结构中X点孤子的耗散以及相干作用进行了动力学分析.通过对由作用量原理得到的孤子参量联立方程组的分析可知，除了耗散作用导致孤子的幅度衰减，并引起孤子横向的展宽以外，同向孤子的相互作用负势函数为耗散作用所减弱，从而使得孤子在x方向的束缚态被削弱.孤子中心间距随x的增加呈现出增幅变化且波动周期增大，当纵向距离增大到一定值后，孤子中心间距将一直增大下去.     

最小作用量原理在电学中的应用实例

依据最小作用量原理,利用Lagrange乘数法分析几个电学问题,得到了一些有意义的结果.     

A novel variational principle in electrostatics and its consequences

We propose a novel variational principle in electrostatics and show that one can derive mirror equation in the context of image problem starting from this principle.     

A new orthogonality relationship for orthotropic thin plate theory and its variational principle

While Hamiltonian system was led to solution of elastic theory a symplectic system-atic methodology for theory of elasticity was established and a symplectic orthogonality relationship was presented[1,2]. For two-dimensional theory of elasticity a new dual vec-tor and a new dual differential matrix were presented by putting the old dual vector[1] in a new order. It was discovered for isotropic materials that the symplectic orthogonality relationship may be decomposed into two independent and s…     

Degenerate perturbation theory and its application to the Hubbard model

Projection operators are incorporated in the canonical transformation to derive an analytical infinite series of a degenerate perturbation expansion. The theory is used to calculate the ground state energy of a half-filled s-band Hubbard model to seventh order.     

Nonperturbative calculations in the framework of variational perturbation theory in QCD

Physics of Atomic Nuclei - We discuss applications of the method based on the variational perturbation theory to perform calculations down to the lowest energy scale. The variational series is...     

共轭线性对称性及其对PT-对称量子理论的应用

传统量子系统的哈密顿是自伴算子,哈密顿的自伴性不仅保证系统遵循酉演化和保持概率守恒,而且也保证了它自身具有实的能量本征值,这类系统称为自伴量子系统.然而,确实存在一些物理系统(如PT-对称量子系统),其哈密顿不是自伴的,这类系统称为非自伴量子系统.为了深入研究PT-对称量子系统,并考虑到算子PT的共轭线性性,首先讨论了共轭线性算子的一些性质,包括它们的矩阵表示和谱结构等;其次,分别研究了具有共轭线性对称性和完整共轭线性对称性的线性算子,通过它们的矩阵表示,给出了共轭线性对称性和完整共轭线性对称性的等价刻画;作为应用,得到了关于PT-对称及完整PT-对称算子的一些有趣性质,并通过一些具体例子,说明了完整PT-对称性对张量积运算不具有封闭性,同时说明了完整PT-对称性既不是哈密顿算子在某个正定内积下自伴的充分条件,也不是必要条件.     

The bogolyubov variational principle in the theory of an anharmonic crystal

The Bogolyubov variational principle for classical systems is used to obtain the variation equation for a self-consistent field. With the help of this equation, various approximations of the self-consistent field method in the theory of a crystal with a multiparticle interaction are studied. The free energy of the crystal is calculated.     

Discrete variational principle and first integrals for Lagrange--Maxwell mechanico-electrical systems

This paper presents a discrete variational principle and a method to build first-integrals for finite dimensional Lagrange--Maxwell mechanico-electrical systems with nonconservative forces and a dissipation function. The discrete variational principle and the corresponding Euler--Lagrange equations are derived from a discrete action associated to these systems. The first-integrals are obtained by introducing the infinitesimal transformation with respect to the generalized coordinates and electric quantities of the systems. This work also extends discrete Noether symmetries to mechanico-electrical dynamical systems. A practical example is presented to illustrate the results.