Energy transfer from a flat uranium slab to a fine wire via fission fragments

Energy transfer from a flat fissile uranium slab to a fine wire via fission fragments is calculated. The rate of energy transfer versus the thicknesses of the slab and protecting aluminum film, as well as the wire-slab gap, is found. An expression for the absorption coefficient of the wire is derived, and the effect the thickness of the wire has on the energy transfer process is studied. The amount of the edge effect for a finite-size fissioner slab is demonstrated with calculations for vacuum conditions and for argon under a pressure of 0.25 atm.     

Imaging Properties of a Rectangular-Lattice Metallic Photonic-Crystal Slab

We report the imaging properties of a two-dimensional rectangular-lattice photonic crystal （PC） slab consisting of rectangular metallic rods immersed in a dielectric background. By simulating the electromagnetic wave propagation through such a PC slab with the finite-difference time-domain method, we find that a point source placed in the vicinity of the PC slab can form a good-quality image through the slab. The frequency region where a good-quality image is formed can be controlled by choosing the direction along which the PC slab surface normal is placed.     

Radiative heat transfer in a plane-layer mixture of non-gray particulates and molecular gases

The interaction between particulate clouds and molecular gases with respect to radiative heat transfer in a one-dimensional, plane-parallel geometry is investigated. The particulates are assumed to have a non-gray absorption coefficient with a power-law dependence on wavenumber. The absorption coefficient of the molecular gases is described by the popular exponential wide-band model. Heat transfer rates are determined through the evaluation of internal and external slab emissivities of the particulate cloud and through evaluation of slab band absorptances for the molecular gases, modified to account for the interaction with the particles. Simple, closed-form expressions for the slab emissivities and slab absorptances are also introduced, resulting in good accuracy.     

有矩形脉冲内热源的平板中非傅里叶导热研究

 对矩形激光短脉冲能量以内热源形式在有限厚绝热平板内释放所导致的非傅里叶导热过程进行了理论研究，利用格林函数与有限积分变换方法求得了绝热平板内温度分布的解析解,分析了平板内热波传播与反射行为以及温度场的特征。研究结果表明，温度波动频率取决于平板厚度和材料的热弛豫时间，而其幅值则与内热源释放区域的大小和脉冲宽度的长短有关。     

侧面抽运板状激光介质的热汇冷却

高热负荷固体激光介质的热效应已经成为制约激光器功率进一步提高的严重障碍,只有对激光介质进行有效的冷却才能保证其安全运行。以不均匀换热系数模型为基础,研究了具有非均匀内热源的侧面双向抽运板状激光介质在狭窄通道强制对流冷却情况下的耦合换热问题,对热汇冷却方案下介质的温度分布和热应力分布进行了数值模拟和分析,并对复合介质、蓝宝石和金刚石三种热汇材料进行对比。结果表明,忽视换热系数的非均匀性将导致应力计算结果偏低。对于侧面抽运、侧面冷却的激光介质,金刚石热汇冷却方案最佳,蓝宝石热汇方案次之,而复合介质方案不宜采用。     

Asymmetrical guided magnetic polaritons in a ferromagnetic slab

The dispersion relations for guided magnetic polaritons are obtained in an ordered ferromagnetic slab. For this anisotropic system, the guided modes do not have the reflection symmetry with respect to the median plane of the slab which is known to exist for the dielectric polaritons in an ionic crystal slab. The dispersion relations and the phase angles are given for typical values of the parameters.     

The coulomb potential in a finite slab: Orthorhombic symmetry

The vanishing exponential method is used to calculate the electrostatic potential of a rectangular crystalline slab composed of a finite, regular array of similar point charges, each charge occupying a lattice site of an orthorhombic bravais lattice. The results are used to discuss (a) the behaviour of the potential at and near the slab surface, (b) the potential of an electrically neutral crystal, (c) the relationship between the space averaged microscopic potential of (b) and the macroscopic potential and (d) the limiting case of an electrically neutral infinite slab. It is also proved for this slab system, that the limit in the vanishing exponential method does not in general commute with limit used to define an infinite crystal.     

单负介质薄板波导中的表面波模式

 推导了沿单负介质薄板波导传播表面波的特性,根据本征方程运用图解法得到沿介电常数为负的单负介质薄板传播的奇偶对称TM型表面波的色散曲线图和能流分布图。发现表面波在单负介质波导中传播比在双正或双负介质波导中慢,场和能量集中于介质板的上下表面, 一定频率范围内奇偶表面波型能流反向;单片单负介质板能实现功分器和定向耦合器的功能,简化了传统的复杂结构,在发展微波器件的小型化方面有着潜在的应用价值。     

Scattering from a PEC strip buried in non-integer dimensional planar grounded dielectric slab by using Kobayashi potential method

Solution for electromagnetic scattering from a perfect electric conducting strip buried in a planar grounded dielectric slab is determined by using the Kobayashi Potential Method. It is assumed that the dimension of mediums, above and within the slab, is non-integer in the direction normal to interface of the slab. The scattering problem is divided into two parts. In the first part, fields in the absence of strip are determined for plane wave excitation. In the second part, presence of the strip is taken into account. It has been assumed that spacings between the strip and interfaces of the slab are comparatively very larger than the wavelength of monochromatic operating frequency. Due to this assumption, scattered field after reflection from the interfaces has no interaction with the strip. In order to gains more insight, several special cases of the geometry are treated. Using saddle point method, far-zone scattered field for region above the grounded slab is also determined.     

Distribution of the amplitude of the magnetic potential of diffractive beams generated in a ferrite slab by a surface spin wave incident on a slit in an opaque screen

The total magnetic potential generated in the far field of a ferrite slab as a result of a plane noncollinear surface spin wave incident on a slit in an opaque screen is investigated. The dependence of the potential amplitude from the polar angle in the plane of a ferrite slab is calculated for different orientations of the screen with relative to an external magnetic field magnetizing the slab. It is found that two diffractive beams are generated in the slab as a result of spin diffraction on the slit. The angular width of each beam depends largely on the slit’s orientation and can be greater or smaller than value λ _n /D (where D is the slit’s width and λ _n is the length of the spin wave corresponding to each beam).     

Superluminal pulse reflection from a weakly absorbing dielectric slab

Group delay for a reflected light pulse from a weakly absorbing dielectric slab is theoretically investigated, and large negative group delay is found for weak absorption near a resonance of the slab [Re(kd)=mpi]. The group delay for both the reflected and transmitted pulses will be saturated with an increase of the absorption.     

Analysis of Radiation Phenomena in a Wedge Ended Dielectric Slab Waveguide

Radiation phenomena observed in a wedge shape ended dielectric slab waveguide are analyzed using mode matching technique. The case of transverse electric polarization (TE) being parallel to dielectric slab waveguide is assumed. In order to describe the fields in the wedge region, a stack of dielectric plates is assumed and in each layer the fields are expanded in terms of the mixed spectrum of guided and radiated modes. A similar expansion is used in the constant thickness slab waveguide while in free space medium a continuous-radiation mode expansion is used. Then a mode matching approach is applied, incorporating the orthogonality properties of mixed spectrum modes, in order to compute the wave fields inside the dielectric slab waveguide and wedge medium. Mode matching is achieved by discretizing the continuous radiation mode spectrum leading into a numerically stable solution provided a sufficient large number of points are used to convert integrals into finite summations. Numerical computations are carried out for various wedge geometries and shapes including linear and exponential profiles.     

极性半导体膜中的束缚极化子

采用线性组合算符法和幺正变换方法,研究极性晶体膜中束缚极化子的基态能量、自陷能随膜厚d的变化关系.得出束缚极化子的自陷能由两部分组成:第一部分是由于电子-体LO声子相互作用所引起的(E_e-LO^tr)极化子效应;第二部分则是电子-SO声子相互作用引起的.后者又包含两部分,分别是电子与极性膜中两支表面声子相互作用的贡献(E_e-SO^tr(+),E_e-SO^tr(-)).通过对KCl半导体膜的数值计算表明,E_e-LO^tr随膜厚d的增加而增加;但是E_e-SO^tr、极化子的振动频率以及电子-声子相互作用所产生的总自陷能E_e-ph^tr随膜厚d的增加而减少,当膜厚大于5nm时,总自陷能E_e-ph^tr趋于一稳定值.另外,由于束缚势的存在,使极化子的振动频率增大,这主要是由于束缚势的存在,使电子-声子间的相互作用增强,极化子效应增大而引起的.     

Interference simulation in a cold collisionless moving magnetized plasma slab and (free surface of plasma slab)

Abstract

The pattern of intensity due to the interference in a cold collisionless magnetized moving plasma slab is investigated. Theoretically, it is assumed the mentioned layer has been located as a thin layer in an etalon Fabry–Perot interferometer surrounded by vacuum. The direction of external magnetic field is normal to the plasma surface and the plasma slab moves parallel with external constant magnetic field. By taking into account the relativistic considerations, the functions of transmitted intensity are presented coincident with the Airy function form in laboratory and plasma slab frames, respectively. The effects of plasma frequency, cyclotron frequency, thickness of plasma slab, and velocity of the plasma slab on band width, finesse factor, and visibility are simulated. Finally with the assumption that there are two wavelengths near together in incident electromagnetic beam the power resolution for this configuration are analyzed. All studies mentioned above have been done for S-polarized and P-polarized electromagnetic beams separately.     

Long-range surface polaritons in a supported thin metallic slab

It is shown that a thin metallic slab supported by a thick transparent slab may guide infrared surface polaritons (SP) with propagation lengths larger than those of SP in a semi-infinite metals. These long-range SP are “virtual” in the sense that their electromagnetic field is oscillatory across the supporting slab.     

左手材料平板对傍轴高斯光束聚焦特性分析

在傍轴近似下,推导出了左手材料平板聚焦系统的传输矩阵,并利用ABCD定律得到了高斯光束在左手材料中和经过平板透镜聚焦后的传输公式。高斯光束在左手材料内部和像空间的传输公式的研究表明:像高斯光束和物高斯光束束腰大小一致,即左手材料平板透镜实际上对高斯光束没有聚焦作用。研究同时表明左手材料平板对高斯光束的聚焦与几何光学成像规律完全一致,而不存在一般透镜聚焦时的焦移效应。     

单轴各向异性异向介质平板波导中的导模特性

 推导了介电常数张量和磁导率张量中各分量带有不同符号的单轴各向异性异向介质平板波导的导行条件。根据分量符号的正负组合,分情况讨论了导行TE波的偶模特性,画出了平板波导中为实横波数时的布里渊图。结果表明,在特定条件下此平板波导中有无穷多导模,这与传统介质波导及各向同性异向介质平板中只有有限数量模式存在有很大不同。此外,还发现当分量参数满足一定条件时,出现了多个虚横波数的传输模式解,并且该模式存在高频截止。     

The dynamics of a double-dot charge qubit embedded in a suspended phonon cavity

We theoretically investigate the dynamics of a double dot charge qubit that is embedded inside a suspended semiconductor slab in terms of a perturbation treatment based on a unitary transformation. The phonon-induced decoherence is analyzed in detail after a derivation of phonon spectral density. It is shown that a charge qubit of high quality can be obtained due to the inhibition of the electron-phonon coupling in the confined structure of the slab.     

Doppler effects of a light source on a metamaterial slab: a rigorous Green's function approach

We apply a (rigorous) Green's function theory to study the Doppler effects of a light source placed on top of a metamaterial slab. When the receiver is in motion with the source and the slab, we find that, in addition to a conventional Doppler mode, there are several other frequency components that do not obey the standard frequency-shift rule. We show that such new effects are caused by the coupling between the radiated electromagnetic waves and the surface modes of the metamaterial slab, whose dispersion relation varies as a function of velocity in the moving reference frame.     

FDTD study of subwavelength imaging by a photonic crystal slab

The problem of subwavelength imaging via a photonic crystal slab lens made of two-dimensional (2D) square arrays of parallel dielectric cylinders in air is studied and discussed theoretically. The finite-difference time-domain method is employed to investigate the unique features of imaging by such lens. We confirm earlier findings that a photonic crystal slab lens can provide the imaging of a point source. By analysing the transmission properties of the proposed structure, we demonstrate that inside the all-angle negative refraction, there are some favourable directions for waves to travel. We show that the surface termination of the photonic crystal is a key parameter to obtain a good quality image. The super-resolution of two sources separated by a distance less than the wavelength is also considered. It is shown that the achievable resolution is limited by the slab length.