热辐射输运问题的隐式蒙特卡罗方法求解

热辐射与物质相互作用及辐射光子在物质中的传输是惯性约束聚变研究中的重要课题. 介绍了基于隐式蒙特卡罗方法的辐射输运方程,在该方程的积分-微分形式基础上,推导了利于蒙特卡罗方法模拟的等价的积分输运方程;基于积分方程设计数值模拟流程,编写三维蒙特卡罗数值模拟程序;针对热辐射输运典型问题及benchmark问题开展了数值实验,计算结果验证了方法的适应性及程序的正确性. 关键词： 热辐射 惯性约束聚变 输运方程 隐式蒙特卡罗     

Asymptotic preserving numerical schemes for a non‐classical radiation transport model for atmospheric clouds

We present numerical schemes for the P1‐moment and M1‐moment approximations of a non‐classical transport equation modeling radiative transfer in atmospheric clouds. In contrast to classical radiative transfer, the photon path‐length is introduced as an additional variable and serves as pseudo‐time in this model. Because clouds may have optically thick regions, we introduce a diffusive scaling and show that the diffusion limits of the moment models and the original equations agree. Furthermore, we show that the numerical schemes also preserve the diffusion asymptotics as well as the set of admissible and realizable states, both for the explicit and the implicit discretization of the pseudo‐time variable. A source iteration‐like method is proposed, and we observe that it converges slowly in the optical thick case, but a suitable initialization can help to overcome this problem. We validate our method in 1D and present simulation results in the 2D‐case for real cloud data. Copyright © 2013 John Wiley & Sons, Ltd.     

Multi-coupled single scattering method of solving vector radiative transfer equations

<正>A new method of multi-coupled single scattering(MCSS) for solving a vector radiative transfer equation is developed and made public on Internet.Recent solutions from Chandrasekhar’s X-Y method is used to validate the MCSS’s result,which shows high precision.The MCSS method is theoretically simple and clear,so it can be easily and credibly extended to the simulation of aerosol/cloud atmosphere’s radiative properties,which provides effective support for research into polarized remote sensing.     

Photon diffusion in a relativistically expanding sphere

A relativistically expanding sphere exists ill many explosive astrophysical systelns, including gamma ray bursts, neutron star mergers, and some supernovae. In this paper we investigate the photon diffusion process in a relativistically expanding sphere, which is important for understanding the energetic and radiative characters of the above inentioned explosive systenls. The following contents are discussed in the frame work of special relativity： random walks of photons by scattering witti electrons, photospheres, photon diffusion, and the energy flux density emerging from the surface of the expanding sphere. Some of the results are also applicable to the Universe since the Universe is also a spherical expanding system.     

High-Precision Direct Method for the Radiative Transfer Problems

It is the main aim of this paper to investigate the numerical methods of the radiative transfer equation.Using the five-point formula to approximate the differential part and the Simpson formula to substitute for integral part respectively, a new high-precision numerical scheme, which has 4-order local truncation error, is obtained. Subsequently,a numerical example for radiative transfer equation is carried out, and the calculation results show that the new numerical scheme is more accurate.     

基于角系数跟踪反射能量研究太空中空心圆柱体温度分布

利用角系数跟踪反射能量求得辐射传递因子,探讨太空中太阳入射下、热控涂层对空心圆柱体温度分布的影响.使用有限差分法离散圆柱坐标系下三维稳态导热方程,考虑辐射-导热边界条件,用Patankar线性化方法将边界条件线性化,用点迭代法来求解名义上的线性化方程组从而得到空心圆柱体的温度分布.热控涂层表面的辐射特性用一组矩形谱带来近似.本文的研究方法对太空航天器件温度分布的精确数值求解具有参考价值.     

Influence of Mg Composition on Optical Properties of Exciton Confinement in Strained Wurtzite ZnO/MgxZn1-xO Cylindrical Quantum Dots

Based on the effective-mass approximation and variational approach, excitonic optical properties are investigated theoretically in strained wurtzite (WZ) ZnO/Mg_xZn_1-xO cylindrical quantum dots (QDs) for four different Mg compositions: x=0.08, 0.14, 0.25, and 0.33, with considering a three-dimensional carrier confinement in QDs and a strong built-in electric field effect due to the piezoelectricity and spontaneous polarization. The ground-state exciton binding energy, the interband emission wavelength, and the radiative lifetime as functions of the QD structural parameters (height and radius) are calculated in detail. The computations are performed in the case of finite band offset. Numerical results elucidate that Mg composition has a significant influence on the exciton states and optical properties of ZnO/Mg_xZn_1-xO QDs. The ground-state exciton binding energy increases with increasing Mg composition and the increment tendency is more prominent for small height QDs. As Mg composition increases, the interband emission wavelength has a blue-shift if the dot height L<3.5 nm, but the interband emission wavelength has a red-shift when L>3.5 nm. Furthermore, the radiative lifetime increases rapidly with increasing Mg composition if the dot height L>3 nm and the increment tendency is more prominent for large height QDs. The physical reason has been analyzed in depth.     

A new approach to optimizing pigmented coatings considering both thermal and aesthetic effects

Pigmented coatings with high reflectivity against solar irradiation can be used to control unwanted thermal heating that occurs as materials absorb sunlight such as heat in buildings that increases cooling loads. However, these surfaces produce glare that is unpleasant to the eye, and the coatings themselves can damage the appearance of the coated object. We introduce a new optimization method that embraces both thermal and aesthetic requirements. Our proposed coatings maximize the reflectivity of the near infrared (NIR) region to reduce thermal heating, while for aesthetic appeal they also minimize the visible (VIS) reflected energy received by human eyes, especially at wavelengths where eye sensitivity is high. The optimization parameter is defined as the ratio of the total reflected energy in the NIR region to that in the VIS region weighted by human eye sensitivity. Titanium dioxide is used as the pigment, and databases of its radiative properties are constructed using the Mie theory. To compute reflectivity, nongray radiative heat transfer in an anisotropic scattering monosized pigmented layer, with independent scattering, including direct and diffuse solar irradiations, is analyzed using radiation element method by ray emission model (REM²). Colors are calculated and optimization parameter is evaluated by using spectral reflectivity. Finally, the optimum values of particle size, volume fraction of pigment, and coating thickness are obtained.     

HgII离子精细结构能级和辐射寿命

用全相对论多组态自洽场方法,计算了HgII离子的5d10nl、5d96s2、5d9nsnp、5d96p2和5d86s26p等组态的3840个精细结构能级和辐射寿命以及各种跃迁参数.能级的计算值和实验值符合得较好.同时,我们还发现了一些长寿命亚稳态能级.     

辐射传输中的一个伪极限问题及其数学物理原理

当太阳入射角度和观测角都趋向于水平时,由平面平行大气辐射传输方程计算得到的大气顶的反射辐射值不唯一,其值依赖于太阳和观测角的趋近于水平方向的路径曲线,即从数学角度称为出现极限的不唯一或极限不连续.事实上这违背了辐射场物理原理,这种不连续是由于常规算法中忽略了大气辐射传输中一个隐含的物理原理而导出的.在极限条件下必须引入满足Snell光学定律的界面边界条件,否则会导致错误的结论. 关键词： 辐射传输 局地热力学平衡 大气光学 Snell定律