Ray tracing studies of a complete plane grating monochromator beam line

Optical design of a plane grating monochromator beam line for X-ray spectroscopic studies to be installed on INDUS-1 is studied using ray tracing technique. The main components of the beam line are pre- and post-elliptical mirrors and the plane mirror-grating dispersing system. The ideal positions of the optical components are decided by using our analytical formulation of the Riemer’s kinetic principle for reflecting synchrotron radiation onto the same spot of the dispersing grating. The program is developed indigenously and can be used on a PC. The tangent error and microroughness of the mirrors is explicitly accounted for in the program. The wavelength dependent absorption of radiation at the different reflecting surfaces is also included for calculations of the optical throughput. The dependence of the final image line shape and resolution on various beam line parameters is calculated. The results are useful in deciding the tolerances of the various beam line components and their positions.     

Effect of reflecting modes on combined heat transfer within an anisotropic scattering slab

Under various interface reflecting modes, different transient thermal responses will occur in the media. Combined radiative-conductive heat transfer is investigated within a participating, anisotropic scattering gray planar slab. The two interfaces of the slab are considered to be diffuse and semitransparent. Using the ray tracing method, an anisotropic scattering radiative transfer model for diffuse reflection at boundaries is set up, and with the help of direct radiative transfer coefficients, corresponding radiative transfer coefficients (RTCs) are deduced. RTCs are used to calculate the radiative source term in energy equation. Transient energy equation is solved by the full implicit control-volume method under the external radiative-convective boundary conditions. The influences of two reflecting modes including both specular reflection and diffuse reflection on transient temperature fields and steady heat flux are examined. According to numerical results obtained in this paper, it is found that there exits great difference in thermal behavior between slabs with diffuse interfaces and that with specular interfaces for slabs with big refractive index.     

提升和投射具有伪轨跟踪性质或可扩性的连续流

本文证明了紧度量空间上的连续流经提升或投射后，其伪轨跟踪性质及可扩性是不变的；做为应用给出了不定向闭曲面上具有伪轨跟踪性质的Ｃｒ流的特征。     

地震波传播路径追踪的波动方程方法

在地震勘探的地震波传播研究中,波场传播路径追踪是一项重要研究内容,通常采用射线理论追踪地震波传播路径.提出一种波动方程波场传播路径追踪方法,首先利用窗口Fourier框架展开技术对源点和目标点的波场进行角度分解,并计算它们的方向照明,然后利用角度相干技术获取源点和目标点间的波场传播路径.该方法可以有效考虑地下非均匀介质对地震波场传播的聚焦与散焦作用.     

Nonlinear frequency conversion in coupled ring cavities

The steady-state distribution of circulating power in coupled, unidirectional ring resonators containing a diode-pumped laser crystal and nonlinear optical elements is computed. The full set of transcendental nonlinear equations describing the interactions between the circulating power and the optical elements is solved by a numerical root find function of a commercial mathematics software. The method allows computation of the output of sequential nonlinear processes such as laser gain, second harmonic generation and optical parametric amplification as a function of the input diode pump power. It is also possible to optimize the nonlinear interaction by selecting the optimum interaction cross-section or crystal length. The circulating power may thereby be re-distributed to obtain the lowest possible passive loss.     

Dynamical energy analysis on mesh grids: A new tool for describing the vibro-acoustic response of complex mechanical structures

We present a new approach for modelling noise and vibration in complex mechanical structures in the mid-to-high frequency regime. It is based on a dynamical energy analysis (DEA) formulation which extends standard techniques such as statistical energy analysis (SEA) towards non-diffusive wave fields. DEA takes into account the full directionality of the wave field and makes sub-structuring obsolete. It can thus be implemented on mesh grids commonly used, for example, in the finite element method (FEM). The resulting mesh based formulation of DEA can be implemented very efficiently using discrete flow mapping (DFM) as detailed in Chappell et al. (2013) and described here for applications in vibro-acoustics. A mid-to-high frequency vibro-acoustic response can be obtained over the whole modelled structure. Abrupt changes of material parameter at interfaces are described in terms of reflection/transmission matrices obtained by solving the wave equation locally. Two benchmark model systems are considered: a double-hull structure used in the ship-building industry and a cast aluminium shock tower from a Range Rover. We demonstrate that DEA with DFM implementation can handle multi-mode wave propagation effectively, taking into account mode conversion between shear, pressure and bending waves at interfaces, and on curved surfaces.     

三维LTI射线追踪极小值方程的快速数值解法

线性走时插值（LTI）算法应用于三维射线追踪时,其向前处理过程中的极小值方程是超越方程,无法求出解析解.虽然可以采用网格剖分方式近似求解,网格剖分精度越大,计算结果越精确,但随着剖分精度的提高,向前处理的计算量会以N3的阶次增加,从而导致计算效率的降低.本文将最速下降法引入到LTI射线追踪算法的向前处理,提出了一种求解三维LTI超越方程的快速数值解法,该方法也不是一种精确求解方法,而是沿着负梯度方向不断逼近真实解.计算结果表明,该算法在兼顾射线追踪精度的同时能有效提高计算效率,计算速度快了3倍以上.     

Porosity Imaging in Porous Media Using Synchrotron Tomographic Techniques

This paper describes novel uses of synchrotron radiation in examining porosity distributions within porous media. Tomographic energy dispersive diffraction imaging and Tomographic X-ray fluorescence have been combined within one measurement method and used to highlight the porosity distribution in a typical sample of English Chalk.     

Investigation of Nonuniformity of the Velocity Distribution in the Shear Layer of an Underexpanded Jet by Electric Discharge Tracing of the Flow

Streamwise and radial components of velocity in the shear layer of an underexpanded jet are measured by the method of spark tracing. The nonuniform distribution of gas-dynamic parameters of the flow in this region is caused by streamwise Görtler-type vortex structures.     

基于光路追踪方法的激光交叉束能量转移模型

提出一种基于几何光路追踪方法并可在流体模拟程序中实现在线计算的激光交叉束能量转移(CBET)耦合模型。借助由激光逆轫致吸收公式引入的泵浦激光功率密度在流体网格尺度上的计算公式,该模型可计算探针激光束中每根光线所携带的能量经过与泵浦激光场相互作用带来的损失(或增加),从而实现激光能量在束间的转移。反复迭代的计算方法解决了由于激光束间能量转移与光线历史相关并且束间强耦合带来的方程求解困难。模型很容易推广到多束激光束两两能量交换的情形,也可用于研究逆轫致吸收和激光等离子体相互作用等物理内容。