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     

真空诱导相干对电磁感应左手效应的影响

研究了具有超精细结构的四能级原子系统在电磁感应下的左手效应.讨论了由交叉耦合自发辐射路径引起的真空诱导相干(VIC)对左手效应的影响.研究表明,在出现左手效应的频率区间VIC效应强弱对介质相对介电常数和相对磁导率实部取值有显著影响,介质的左手效应随VIC效应的增强而增强. 关键词： 量子干涉 真空诱导相干 电磁感应 左手效应     

Role of fluctuational electrodynamics in near-field radiative heat transfer

The objective of this paper is to discuss the role of fluctuational electrodynamics in the context of a generalized radiative heat transfer problem. Near-field effects, including the interference phenomenon and radiation tunneling, are important for applications to nanostructures. The classical theory of radiative transfer cannot be readily applied as the feature size approaches the dominant wavelength of radiative emission. At all length scales, however, propagation of radiative energy is properly represented by the electromagnetic wave approach, which requires the solution of the Maxwell equations. Fluctuational electrodynamics provides a model for thermal emission when solving a near-field radiation heat transfer problem, and the fluctuation-dissipation theorem provides the bridge between the strength of the fluctuations of the charges inside a body and its local temperature. This paper provides a complete and systematic derivation of the near-field radiative heat flux starting from the Maxwell equations. An illustrative example of near-field versus far-field radiation heat transfer is presented, and the length scale for transition from near- to far-field regime is discussed; the results show that this length scale can be as large as three times than predicted from Wien's law.     

First measurements with the neutron decay spectrometer a SPECT

The neutron decay spectrometera SPECT has been built to perform a precise measurement of the proton spectrum shape in the decay of free neutrons. Such a measurement allows a determination of the neutrino electron angular-correlation coefficienta . The present best experiments have an uncertainty of Δa/a = 5% and since the seventies there is no substantial improvement. Witha SPECT, we aim for an uncertainty which is lower by more than an order of magnitude, thus enabling us to perform several precise tests of the Standard Model. In our first beam time at the particle physics beam MEPHISTO at the Forschungsneutronenquelle Heinz Maier-Leibnitz, we studied the properties of the spectrometer. The most serious problem turned out to be the situation- and time-dependent behavior of the background. From the data sets from this beam time in which a background problem was not obvious, we could extract a value ofa = - 0.1151±0.0040^stat , but we could not quantify the background uncertainty. We show ways to deal with the background and other problems for future beam times.     

电感储能加速器运行中电磁辐射的实验研究

发现了一个被普遍忽视的问题, 在电感储能加速器运行中产生很强的电磁辐射. 这种电磁辐射在一定距离范围内可以对测量仪器造成破坏. 通过多次测量, 发现此辐射主频在75MHz左右, 频谱较宽, 是一低频电磁波. 以同轴电缆作为测量仪器的替代物, 测量辐射场对同轴电缆的作用, 罗氏线圈测得电流幅值达217mA. 辐射可能是由回路LC振荡或者加速器中的电爆炸丝开关引起的. 基于LC振荡和电爆炸丝的工作原理, 分别讨论了辐射产生的物理过程. 我们更倾向于认为辐射来源于开关导通引起的回路LC振荡. 此外, 辐射强度受电流的变化率影响, 初级回路电流变化慢, 次级回路变化快, 这样产生了一弱一强的两个辐射信号. 这些为进一步研究电感储能加速器运行中的电磁辐射及防护提供实验支持.     

The spectral-line moment-based (SLMB) modeling of the wide band and global blackbody-weighted transmission function and cumulative distribution function of the absorption coefficient in uniform gaseous media

The spectral-line moment-based (SLMB) modeling is proposed for the calculation of radiative properties of gases on any spectral width. The associated mathematical formulation is obtained by applying several concepts of the k-distribution methods such as the reordering of the wavenumber scale by monotonic variations of the absorption coefficient, together with the application of the k-moment method's principles. This approach gives both a general formula for the BTF and a simple and readily applicable approximation for the blackbody-weighted cumulated k-distribution function of the absorption coefficient. The model is applied for the computation of wide band BTFs and cumulative k-distributions for uniform columns of CO₂ and H₂O in the temperature range (300-2400 K) at atmospheric pressure. Model parameters are deduced from line-by-line (LBL) spectra calculated using the HITEMP database. Comparisons with LBL reference data as well as with contemporary modeling approaches (SLW, FSK, SNB) are performed and discussed.     

Influence of internal radiation on the heat transfer during growth of YAG single crystals by the Czochralski method

Heat and mass transfer taking place during growth of Y₃Al₅O₁₂ (YAG) crystals by the Czochralski method, including inner radiation, is analyzed numerically using a Finite Element Method. For inner radiative heat transfer through the crystal the band approximation model and real transmission characteristics, measured from obtained crystals, are used. The results reveal significant differences in temperature and melt flow for YAG crystals doped with different dopands influencing the optical properties of the crystals. When radiative heat transport through the crystal is taken into account the melt‐crystal interface shape is different from that when the radiative transport is not included. Its deflection remains constant over a wide range of crystal rotation rates until it finally rapidly changes in a narrow range of rotation rates. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Lightweight,Low-Cost Co2SiO4@diatomite Core-Shell Composite Material for High-Efficiency Microwave Absorption

The porous and biomimetic cobalt silicate@diatomite (Co₂SiO₄@diatomite) was successfully synthesized by a two-step method, including the hydrothermal method and calcination to improve the electromagnetic wave absorption property. Different hydrothermal times were well-tuned for Co₂SiO₄@diatomite composites with different loadings of Co₂SiO₄. Interestingly, the Co₂SiO₄@diatomite composites (6 h, 25 wt%) had a smaller minimum reflection loss. Moreover, the minimum reflection loss (RL_min) could reach −12.03 dB at 16.64 GHz and the matched absorber thickness was 10 mm, while the effective absorption bandwidth (EAB, RL ≤ −10 dB) could be 1.92 GHz. In principle, such findings indicate that Co₂SiO₄@diatomite nanocomposites could be a promising candidate for high-efficiency microwave absorption capability.     

c/uA及mi/me取值对于磁重联过程的影响

构造控制电磁场散度误差的有限差分方法,该方法结构简单,可将电磁场散度误差控制在舍入误差量级.该方法应用到GEM,得到的结果与已发表文献类似.研究双流体模型中可调参数光速和离子与电子的质量比对磁重联过程的影响.结果表明：光速增加后,净电荷的积累减少,而重联率几乎不变.离子与电子质量比增加导致电流片变薄,从而使得重联加快.     

悬线式物镜力矩器动态特性的仿真实验研究

悬线式物镜力矩器是目前光学头系统中使用最为广泛的力矩器,其动态特性直接决定了光学头的读写性能。基于ANSYS参数化设计语言(APDL)建立了悬线式光学头物镜力矩器的仿真设计平台。通过仿真平台进行了力矩器一阶共振频率和峰值、二阶共振频率和峰值、扭转共振频率、静态灵敏度、动态灵敏度和相位等动态特性参数的仿真实验,仿真计算的结果与实际测量的结果相比,最大相对误差为4.2%。该仿真平台对于二维乃至三维悬线式物镜力矩器的设计和评价都具有重要的指导意义。