光折变材料的带隙结构研究

利用光子晶体的概念和时域有限差分方法计算了当光折变材料的空间折射率呈一维正弦变化时其内部的带隙结构情况,表明在光折变材料中存在极窄的光子带隙。最后讨论了折射率(n)、折射率调制幅度(△n)、周期长度(D)及周期数(N)对光子带隙的影响。     

One-neutron stripping reactions of <Superscript>11</Superscript>Be and <Superscript>19</Superscript>C on light target

We have calculated the one-neutron absorption cross-section and the longitudinal momentum distribution of the core fragment coming out from the breakup of ¹¹Be and ¹⁹C on ⁹Be target at 63 MeV/A and 88 MeV/A beam energies respectively. The reaction mechanism is treated within the framework of the eikonal approximation. The effective range of the nuclear interaction between the core and the valence neutron within the projectile has been determined by comparing the predicted stripping cross-section with the recently measured one. The effective range for ¹⁹C has been found to be smaller than that for ¹¹Be. It qualitatively indicates that ¹⁹C is slightly more halo than ¹¹Be. The smaller width, predicted as well as measured, of the LMD of ¹⁸C than ¹⁰Be also strengthens this fact. The experimental data concerning the LMD of core fragments have been well represented.      

Novel Broadband Reflectarray Antenna with Windmill-Shaped Elements for Millimeter-Wave Application

A novel broadband millimeter-wave reflectarray antenna composed of windmill-shaped elements of variable lengths is proposed. Compared to the conventional single-layer reflectarray elements, the windmill-shaped elements can realize much larger phase variation range (over 600°), leading to broader bandwidth. Using this technique, a 15°-beam-steering reflectarray operating at 30 GHz is designed. The computed results demonstrate the agreement of the main beam steering with the design requirement, and a 1-dB gain bandwidth close to 20% is obtained. The validity of the obtained results is verified by comparing the ones generated by Ansoft High Frequency Structure Simulator (HFSS) with those produced by Ansoft Designer. The antenna is useful for millimeter-wave applications. This work was supported by the National Natural Science Foundation of China (No. 90505001), the High-Tech Research and Development Program of China (No. 2006AA01Z275), and the Creative Research Group Program of UESTC.     

利用偏振度研究混合目标的混合比

提出一种利用偏振度研究混合目标混合比的新方法。通过建立混合目标模型将混合目标散射光的偏振度与混合目标的混合比建立直接的关系,在理论上得到了混合目标混合比分别与混合目标偏振度和归一化偏振度之间的数值关系,并且进一步给出了混合目标混合比由归一化偏振度的反演结果,为研究混合目标提供了新的思路与方法,对偏振度探测混合目标的实验以及工程应用都有重要的理论意义。     

弱磁场中弱相互作用费米气体的有限粒子数效应(英文)

由弱磁场中弱相互作用费米气体的配分函数,导出有限粒子数条件下系统的配分函数G(β,N ).在此基础上,运用统计平均方法求解有限粒子数弱相互作用费米气体热力学量的解析表达式,给出各种温度条件下的热力学性质.研究结果表明,有限粒子数效应使各个热力学量都产生了一个修正项,除温度趋于0外,粒子数对化学势的修正项有直接影响,对内能和热容量的修正项并不产生直接影响.并且有限粒子数效应总是降低化学势,从而使化学势的0点向低温漂移,粒子数增大,会削弱这种效应,粒子间的相互排斥会加强这种效应.     

背部支撑主反射镜的面形分析与支撑点优化

应用有限元方法对背部支撑的主反射镜进行静力学分析.分别对三点支撑和九点支撑进行计算,得到主镜反射面的变形值.以齐次坐标变换法和最小二乘法为理论依据求解反射面变形的PV/RMS值.利用有限元分析软件提供的二次开发功能,编写计算程序,在软件内部调用该程序直接获得PV/RMS值,利用该值作为优化分析的目标函数,寻求背部支撑的最佳支撑点位置.     

双端抽运热容激光器温度特性分析

通过对激光二级管阵列双端抽运热容激光器晶体的分析,建立了热传导模型及边界条件.利用有限元方法模拟了晶体的温度场分布,并分别对抽运光斑直径、抽运持续时间、抽运光强和晶体端面尺寸等因素对温度场分布的影响进行了分析,得到了热容工作模式下的激光器温度特性.结果表明,晶体端面温差随抽运光斑直径的增大先增后减,存在一个极大值,并且在不同抽运光强下,出现端面温差极大点时的抽运光斑直径不变.     

Some theoretical aspects of elastic wave modeling with a recently developed spectral element method

A spectral element method has been recently developed for solving elastodynamic problems. The numerical solutions are obtained by using the weak formulation of the elastodynamic equation for heterogeneous media, based on the Galerkin approach applied to a partition, in small subdomains, of the original physical domain. In this work, some mathematical aspects of the method and the associated algorithm implementation are systematically investigated. Two kinds of orthogonal basis functions, constructed with Legendre and Chebyshev polynomials, and their related Gauss-Lobatto collocation points are introduced. The related integration formulas are obtained. The standard error estimations and expansion convergence are discussed. An element-by-element pre-conditioned conjugate gradient linear solver in the space domain and a staggered predictor/multi-corrector algorithm in the time integration are used for strong heterogeneous elastic media. As a consequence, neither the global matrices nor the effective force vector is assembled. When analytical formulas are used for the element quadrature, there is even no need for forming element matrix in order to further save memory without losing much in computational efficiency. The element-by-element algorithm uses an optimal tensor product scheme which makes this method much more efficient than finite-element methods from the point of view of both memory storage and computational time requirements. This work is divided into two parts. The first part mainly focuses on theoretical studies with a simple numerical result for the Che-byshev spectral element, and the second part, mainly with the Legendre spectral element, will give the algorithm implementation, numerical accuracy and efficiency analyses, and then the detailed modeling example comparisons of the proposed spectral element method with a pseudo-spectral method, which will be seen in another work by Lin, Wang and Zhang.     

LD侧面抽运板条激光器热效应分析

针对板状Nd:YLF激光介质,在高斯光束抽运情况下,用ANSYS有限元软件模拟了激光介质的热效应,对激光介质中各点的温度和应力分布进行了分析和比较.研究发现双侧抽运与单侧抽运相比,更易获得对称的温度分布,随着抽运光斑横截面变大,抽运面中心温度变低.同时得到板条的棱边、端角处存在较大热应力,且引入的机械应力不可忽视,因此,激光器运转时此区域需防止断裂.     

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利用分裂的屏蔽氢不透明度模型计算了Ar、Kr、Xe惰性元素混合物随光子能量变化的不透明度以及Rosseland平均不透明度。研究了温度为100～250eV,密度为0.5～2g·cm-3范围内惰性元素混合物的Rosseland平均不透明度与混合物质、混合比例、温度和密度的密切关系。结果显示,Ar-Xe混合以及Xe-Kr混合后的Rosseland平均不透明度比它们为纯元素时有较大的增加;而Ar-Kr混合后的Rosseland平均不透明度则比纯Kr低。通过对比纯惰性元素随光子能量变化的不透明度峰、谷值,分析了造成混合后不透明度增加或降低的原因,同时给出了获得惰性元素混合物平均不透明度为最大时的混合比例。