Lagrange method and boundary conditions for the intensity correlation functions in turbulent media

An exact functional integral representation for the two-point intensity correlation function was previously obtained by the author for a collimated beam wave by solving the moment equation. The variable functions of integration involved therein can be effectively limited to a set of functions determined so that the entire phase term of the integrand becomes stationary against arbitrary variation of the variable functions, exactly according to the Lagrange variational principle in dynamics. The result is free from any expansion and is presented with a set of unperturbed equations of closed form. When making a formal expansion, it leads to the zeroth- and first-order expressions similar to those obtained by an improved two-scale method. With exactly the same procedure, the three-point intensity correlation and the two-frequency intensity correlation were also obtained.The Lagrange method leads to the 'equation of motion' subjected to boundary conditions to continue the phase term from the incident beam wave. The boundary conditions were previously found based on a physical reasoning, while the same conditions are found here purely based an the variational principle. A focused beam wave is assumed for the incident wave, including both spherical and plane waves as special cases.     

Scattering from a Multi-Layered Sphere Located in a High-Order Hermite-Gaussian Beam

Scattering of a high-order Hermite-Gaussian beam by a multi-layered sphere is analyzed. The incident high- order Hermite-Gaussian beam field is expressed by the complex-source-point method and expanded in terms of spherical vector wave functions. The beam shape coefficients of the Hermite-Gaussian beam are obtained. Under electromagnetic field boundary conditions, coefficients in the expressions of scattering fields are derived. Results of the numerical calculation of scattering intensity are presented. The effects of the particle parameters and beam parameters on scattering intensity are discussed in detail.     

A General Spectral-Domain Formulation of the Electromagnetic Scattering by a Perfectly Conducting Circular Cylinder

A full-wave method for the two-dimensional scattering problem by a perfectly conducting circular cylinder is presented, providing an exact solution for the Helmholtz equation in very general cases. The method is based on the Fourier series expression of the boundary conditions (Dirichlet and Neumann) generated by an arbitrary, finite-power, incident beam, and the analysis is performed in the complex plane of the analytic continuation of a space spectral variable. This approach allows us to define an analytic continuation for cylindrical wave expansions, working with lossy propagation media and with a full incident spectrum, including inhomogeneous waves, both in E and in H polarization. Convergence of the modal expansion is investigated, to verify that very weak hypotheses are needed, and no geometrical or paraxial approximation is required. Extact expressions for the expansion coefficients are given, in terms of complex intergrations involving the Fourier spectrum of the incident beam.     

A variational principle for the scattered wave

A Schwinger-type variational principle is presented for the scattered field in the case of scalar wave scattering with an arbitrary field incident on an object of arbitrary shape with homogeneous Dirichlet boundary conditions. The result is variationally invariant at field points ranging from the surface of the scatterer to the farfield and is an important extension of the usual Schwinger variational principle for the scattering amplitude, which is a farfield quantity. Also, a generic procedure, physically motivated by the general principles of boundary conditions and shadowing, is presented for constructing simple trial functions to approximate the fields. The variational principle and the trial function design are tested for the special case of a spherical scatterer and accurate answers are found over the entire frequency range.     

Diffraction of a Plane Electromagnetic Wave by an Infinite Double-Ridge Wedge with a Dielectric Cylinder at the Crest

We reduce the considered problem to solving a matrix equation of the second kind for unknown coefficients of expansion of a diffracted field into a Fourier–Bessel series. This expansion was obtained by imposing boundary conditions on the diffracted field with the subsequent re-expansion of the field function over basis functions in a given interval. The expansion coefficients were determined analytically in the case where the electric diameter of the cylinder is less than unity as well as numerically with a high accuracy by solving the obtained matrix equation using the reduction method. We derived expressions for the pattern of the far-zone field scattered by the studied structure and the backscattering cross section and give exact numerical results for the case of an E-polarized incident wave.     

强非线性发展方程孤波近似解

研究了一个强非线性发展方程.利用变分原理，首先构造了相应的泛函.选取Lagrange乘子，再用广义变分迭代方法得到了孤波的任意次精度的近似解. 关键词： 发展方程 非线性 孤立子 近似方法     

二维高斯波束对多层球粒子电磁散射的解析解

基于矢量波函数在球和柱坐标系中表达式之间的转换关系,提出了一种求解球坐标系中二维高斯波束波形因子的方法,得到了二维高斯波束波形因子在球坐标系中的解析公式.结合广义米理论推导了在轴二维高斯波束入射多层球粒子的电磁散射的解析解,并对散射强度随散射角的分布进行了数值模拟,结果与平面波入射情况进行了比较. 关键词： 矢量波函数 波形因子 电磁散射 广义米理论     

On Fractional Duffin–Kemmer–Petiau Equation

In this paper we treat a fractional bosonic, scalar and vectorial, time equation namely Duffin–Kemmer–Petiau Equation. The fractional variational principle was used, the fractional Euler–Lagrange equations were presented. The wave functions were determined and expressed in terms of Mittag–Leffler function.     

Gaussian beam scattering by a chiral sphere

Based on the generalized Lorenz–Mie theory that provides the general framework, an analytic solution to Gaussian beam scattering by a chiral sphere is constructed, by expanding the incident Gaussian beam, scattered fields and internal fields in terms of spherical vector wave functions. The unknown expansion coefficients are determined by a system of equations derived from the boundary conditions. For a localized beam model, numerical results of the normalized differential scattering cross section are presented.     

Analytic solution of the Boltzmann-equation for radiative transfer and neutron transport in plane geometry

A power series expansion method for solving the multi-group transport equation in plane-parallel geometry is presented. In this method, the radiation intensity is separated into forward and backward components, which are then expanded in powers of the space variable, while the angular variable is treated exactly. The generalized boundary conditions considered in the analysis allow radiative heat transfer and neutron transport problems to be handled by the same formalism. Analytical expressions are derived for the angular distribution and the angle-integrated intensities by solving a matrix problem in which the matrix elements are integrals over rational functions of the angular variable. Two test problems describing completely different physical situations illustrate the usefulness and generality of the present method.     

A variational treatment of the mixed boundary condition for the equilibrium diffusion equation

We formulate the asymptotic boundary layer analysis which leads to a mixed (Robbin) boundary condition for the equilibrium diffusion equation of radiative transfer. The information required from the nonlinear boundary layer equations to obtain the boundary condition is obtained by deriving and applying an appropriate variational principle. Based upon an examination of certain limiting cases and the good accuracy previously reported in the literature for similar variational treatments, the accuracy of this variational procedure is expected to be quite good over a wide range of conditions.     

Modified (2+1)-dimensional displacement shallow water wave system and its approximate similarity solutions

Recently, a new (2+1)-dimensional shallow water wave system, the (2+1)-dimensional displacement shallow water wave system (2DDSWWS), was constructed by applying the variational principle of the analytic mechanics in the Lagrange coordinates. The disadvantage is that fluid viscidity is not considered in the 2DDSWWS, which is the same as the famous Kadomtsev—Petviashvili equation and Korteweg—de Vries equation. Applying dimensional analysis, we modify the 2DDSWWS and add the term related to the fluid viscidity to the 2DDSWWS. The approximate similarity solutions of the modified 2DDSWWS (M2DDSWWS) is studied and four similarity solutions are obtained. For the perfect fluids, the coefficient of kinematic viscosity is zero, then the M2DDSWWS will degenerate to the 2DDSWWS.     

Fully nonlinear (2+1)-dimensional displacement shallow water wave equation

Recently, a new(2+1)-dimensional displacement shallow water wave equation(2DDSWWE) was constructed by applying the variational principle of analytic mechanics in the Lagrange coordinates. However, the simplification of the nonlinear term related to the incompressibility of the shallow water in the 2DDSWWE is a disadvantage of this approach.Applying the theory of nonlinear continuum mechanics, we add some new nonlinear terms to the 2DDSWWE and construct a new fully nonlinear(2+1)-dimensional displacement shallow water wave equation(FN2DDSWWE). The presented FN2DDSWWE contains all nonlinear terms related to the incompressibility of shallow water. The exact travelling-wave solution of the proposed FN2DDSWWE is also obtained, and the solitary-wave solution can be deduced from the presented travelling-wave solution under a special selection of integral constants.     

Time-dependent equation for the intensity in the diffusion limit using a higher-order angular expansion

The first two terms in the spherical-harmonic expansion (the P(1) approximation) of the radiative transfer equation yield the diffusion equation. This approximation applies to multiple scattering and results in a solution for the energy density, the gradient of which is proportional to the light intensity. In this work a higher-order spherical-harmonic expansion of the radiative transfer equation is developed. This equation applies to the radiant intensity rather than the energy density. The equation can be decomposed into two terms: a propagator term obtained from the determinant of the coupled equations describing the individual components of the intensity, and a mixing matrix that describes the cross coupling between different orders of the expansion. Using the Fourier transform, an approximation based on expanding at small wave vectors k leads to an equation similar to the diffusion equation. The equation is expected to predict the intensity for multiple scattering at earlier times and shorter distances than the diffusion equation can. The notion of an equivalent wave field is introduced.     

First passage time problems for a class of master equations with separable kernels

We discuss first passage time problems for a class of one-dimensional master equations with separable kernels. For this class of master equations the integral equation for first passage time moments can be transformed exactly into ordinary differential equations. When the separable kernel has only a single term the equation for the mean first passage time obtained is exactly that for simple diffusion. The boundary conditions, however, differ from those appropriate to simple diffusion. The equations for higher moments differ slightly from those for simple diffusion. Analysis is presented, of a generalization of a model of a random walk with long-range jumps first investigated by Lindenberg and Shuler. Since the equations can be solved exactly one can study the behavior of boundary conditions in the continuum limit. The generalization to a larger number of terms in the separable kernel leads to higher order equations for the first passage time moments. In each case, boundary conditions can be found directly from the original master equation.     

广义非对称Hartmann势Klein-Gordon方程的严格解(英文)

在标量势和矢量势相等的条件下,严格求解了在广义非对称Hartmann势场中粒子运动的Klein Gordon方程;并利用束缚态边界条件,获得了束缚态能谱表达式和由超几何函数表示出的波函数.     

Exact classical and quantum solutions for a covariant oscillator near the black hole horizon in Stueckelberg-Horwitz-Piron theory

We found exact solutions for canonical classical and quantum dynamics for general relativity in Horwitz general covariance theory. These solutions can be obtained by solving the generalized geodesic equation and Schrödinger-Stueckelberg-Horwitz-Piron (SHP) wave equation for a simple harmonic oscillator in the background of a two dimensional dilaton black hole spacetime metric. We proved the existence of an orthonormal basis of eigenfunctions for generalized wave equation. This basis functions form an orthogonal and normalized (orthonormal) basis for an appropriate Hilbert space. The energy spectrum has a mixed spectrum with one conserved momentum p according to a quantum number n. To find the ground state energy we used a variational method with appropriate boundary conditions. A set of mode decomposed wave functions and calculated for the Stueckelberg-Schrodinger equation on a general five dimensional blackhole spacetime in Hamilton gauge.     

光纤模式分析的伽辽金有限元模型

提出了采用二阶吸收边界条件的全矢量平面伽辽金有限元模型,用于分析任意横截面形状和各向异性折射率分布的光纤的传导模式和泄漏模式,能精确求出各模式传输常量的实部和虚部以及模场分布,既不出现伪解,又不漏解.推导了各向异性介质全矢量耦合波动方程及其变分形式,给出了基于结点的二阶三角形单元的离散公式和单元矩阵,成功的将二阶吸收边界条件加入外边界二次线性单元的离散公式.计算表明采用该模型分析光子晶体光纤模式有效折射率与采用多极方法和基于离散函数展开的有限差分法所得结果吻合很好,采用二阶吸收边界条件计算限制损耗比一阶吸收边界条件结果精确.