互易定理计算分层半空间上方任意取向偶极子的远区场

利用互易定理推导了考虑直达波和界面反射波时半空间分层界面上任意取向偶极子在上半空间远区辐射场的解析表达式. 进一步考虑电偶极子距离分界面为某一高度情形, 在考虑直达波和反射波程差基础上导出相应辐射场公式. 辐射场解析表达式中分层半空间TM和TE波反射系数可以通过连分数方法或传播矩阵法计算获得. 本文推导过程物理概念清晰, 所得解析结果适于计算观察点远离界面情形下偶极子的远区辐射场. 数值计算结果表明, 利用本文结果可以快速分析半空间上方任意取向偶极子的远区辐射场.     

基于辐射场及遗传算法的矩形波导模式分析法

提出了一种基于辐射场和遗传算法分析矩形波导中工作模式的新方法。这种方法先根据波导口尺寸利用惠更斯原理计算出各模式的辐射场的分布;假设一组模式的复系数,合成总辐射场;将合成的辐射场幅值与测量的辐射场幅值在多点上进行比较,通过遗传算法获得最佳匹配,就可以得到各模式的复系数。计算结果与测量值吻合较好,表明这种方法具有可行性和可靠性,并和基于辐射场的最小二乘法对测量的远场辐射场场强幅值的数据反演进行比较,结果表明遗传算法在测量值有误差时具有容错能力强的优势。     

双光子Jaynes-Cummings模型中初始原子相干性对辐射场压缩的影响

本文研究了任意初态的双光子Jaynes-Cummings模型的一般演化规律,着重于分析初始原子相干性对辐射场压缩行为的影响,作为例子,讨论了一个任意初态的二能级原子与真空态和相干态光场相互作用时辐射场的压缩.数值计算了各种条件下辐射场压缩的时间演化.     

双光子Jaynes—Cummings模型中初始原子相干性对辐射场...

本文研究了任意初态的双光子Jaynes-Cummings模型的一般演化规律,着重于分析初始原子相干性对辐射场压缩行为的影响,作为例子,讨论了一个任意初态的二能级原子与真空态和相干态光场相互作用时辐射场的压缩.数值计算了各种条件下辐射场压缩的时间演化.     

海洋波导中目标声辐射场的计算方法

针对海洋波导中目标声辐射场的计算问题,提出了一种基于波叠加法并在近、远场采用不同水声传播模型的建模方法,可以将近、远场作为一个统一的系统进行高效地分析。该方法通过给定的已知表面振动速度的结构计算出目标内部虚拟点声源的源强,再配合在相应的水声环境中点声源传播模型的Green函数计算出结构外的声辐射场。以Green函数为纽带,在求源强和计算近场声辐射场时采用镜像虚源法,而在计算远场声辐射场时采用简正波法。通过该方法得到的有限水深波导中声速剖面为正梯度、负梯度、负跃层的3种情况下的脉动球、刚体摆动球的声辐射场计算结果与COMSOL的有限元计算结果进行对比,结果表明了该方法在提高计算效率的同时保证了计算精度。      

冲击脉冲辐射天线辐射场计算及应用

根据由张量法得到的任意线天线电场计算公式,利用镜像法推导,得到冲击脉冲辐射天线辐射电场的时域解析表达式。应用该表达式计算冲击脉冲辐射天线应用于辐射波电磁脉冲模拟器的时域辐射场,并与数值计算进行比较,结果表明:解析计算得到的辐射场波形与数值计算结果吻合较好,因此,利用解析表达式可以方便地观察天线结构参数对天线辐射场波形的影响,从而选取合适的参数以产生符合标准要求的天线场波形。     

海面目标红外辐射场的理论模拟和计算软件

对海面舰船的温度场和红外辐射场的理论模型进行研究,得到了计算机模拟的完整方程组.研制了整套进行理论建模的计算机软件,并对某舰的温度场和红外辐射场进行模拟,得到与真实场景吻合的计算结果.     

200MeV电子直线加速器隧道内辐射场测量

对电子直线加速器运行期间隧道内的辐射场进行测量,可以为装置提供重要的参考数据;预测无器件及材料的使用寿命和研究辐射场的开发利用.本文介绍了加速器周围辐射场的特点,论述了丙氨酸(alanine)剂量计的性能和用电子自旋共振测量法进行测量的依据、方法.并分析了用这种方法所得到的结果.     

轴对称指向性球面波的界面反射波

无限大平面刚性障板中圆形活塞源的声辐射场可近似为轴对称指向性球面波,前人只给出了活塞面与界面平行时轴对称指向性球面波的界面响应表达式,本文针对活塞面与界面不平行的情况,推导了轴对称指向性球面波的锥面波展开式,并进一步导出了其界面反射波的表达式.在源距远大于声波波长的情况下通过鞍点法将界面反射波的表达式化简为了简化表达式.简化式不仅计算上简洁,而且物理含义清楚:轴对称指向性球面波的界面反射波可视为镜像活塞源激发的轴对称指向性球面波与反射系数的乘积.计算表明,当活塞半径小于声波波长时,反射波对活塞与界面的夹角和接收点的环向方位角不太敏感,反射波的指向性较弱;当活塞半径大于声波波长时,反射波对活塞与界面的夹角和接收点的环向方位角很敏感,反射波的指向性很强.增加活塞与界面的夹角,反射波先增加后减小,反射波的指向性先增强后减弱;当活塞与界面的夹角等于活塞中心镜像点与接收点的连线与界面法线的夹角时,反射波最大,反射波的指向性最强.     

界面尺寸对铜/石墨烯界面热导的影响

采用原子格林函数(AGF)方法研究了界面尺寸对铜/单层石墨烯(SLG)界面热导的影响.建立了有限和无限界面尺寸的AGF计算模型,计算得到的界面热导均在铜的迪拜温度(343 K)附近收敛,但两者计算得到的透射系数和界面热导存在明显差别:有限界面尺寸时计算得到的透射系数在1.5 THz附近达到峰值0.84,而无限界面尺寸时...     

Transport theory for quantum wells with an electric field across the well: a new concept for a transistor

The transport properties of a two-dimensional electron gas in a quantum well with infinite barriers and with an electric field across the well as perturbation is calculated for zero temperature. Background impurity doping, remote impurity doping and interface roughness scattering are considered. The effects which are linear in the electric field are calculated. We suggest an experiment to measure the differences in the interface roughness scattering at the two interfaces of the quantum well by the electric field effect. We also discuss a possible device application of the field effect and describe a transistor working at the metal-insulator transition.     

The near field correlation spectrum of a metallic film

The spatial two-point coherence function of the thermal radiation field at subwave-distance from a metallic film is calculated within fluctuation electrodynamics. Long-range oscillations as a function of lateral separation are seen; we interpret their features by comparing to the dispersion relations of surface plasmon polariton modes on the thin film. The hybridization of the surface modes on the top and bottom interfaces leads to a beatnote in the field correlations, for specific detector setups.     

The oscillatory galvanomagnetic size-effect in multilayered structures

Within the framework of the modified semi-classical Fuchs-Sondheimer model, we investigated theoretically the electrical resistivity of multilayered structures (MLS) consisting of alternating metallic layers (of different purity and different thicknesses) in a transverse magnetic field as functions of the ratio of the adjacent layer thicknesses and the magnetic field value. We have derived both a general formula (valid at arbitrary values of layer thicknesses) and asymptotic expressions that are valid when metallic layers are thick or thin compared with the electron mean free path. We found a non-monotonic behavior in the resistivity vs. the value of an applied magnetic field. As we demonstrated, this behavior is sensitive to the characteristics of the electron scattering in the interlayer interfaces in low magnetic fields. Moreover, the MLS resistivity oscillates in high magnetic fields with the field value (or with the layer thicknesses). The oscillation includes the harmonics that correspond both to the each layer thicknesses and the total thickness. The intensity of the oscillation is determined by the diffusive electron scattering in the interfaces, and the oscillation amplitude is proportional to the coefficient of the electron transmission through the interlayer interfaces. We have calculated numerically the resistivity in a wide range of fields and layer thicknesses at various values of the parameters of the interface and bulk electron scattering.      

Semianalytic treatment for propagation in finite photonic crystal waveguides

We present a semianalytic theory for the properties of two-dimensional photonic crystal waveguides of finite length. For single-mode guides, the transmission spectrum and field intensity can be accurately described by a simple two-parameter model. Analogies are drawn with Fabry-Perot interferometers, and generalized Fresnel coefficients for the interfaces are calculated.     

Dynamic response of electrons and dispersion force fields near bimetallic interfaces

The induced potential due to an oscillating charge source near the interface of two metals whose electron densities differ slightly, is calculated in the hydrodynamic approximation. Results are given for both planar and spherical interfaces. The potential is used to evaluate the dispersion force field on an atomic system near the interface. It is shown that the force field is divergence-free at very small separation from the planar interface if the electron density profile is diffuse.     

具有非均匀渐变界面DBR的光学特性分析

应用特征矩阵法研究了非均匀渐变界面Al_0.9Ga_0.1As/Al_yGa_1-yAs/GaAs/Al_xGa_1-xAs DBR的光学特性.建立了非均匀渐变界面Al_yGa_1-yAs的折射率模型，并得到了渐变界面特征矩阵的解析解，通过特征矩阵法分别计算了突变GaAs/Al_0.9Ga_0.1As DBR和渐变DBR的反射谱和反射相移，分析了非均匀渐变层对DBR光学特性的影响，对渐变DBR，需要在DBR前面再增加一定厚度的非均匀渐变相位匹配层才能使整个DBR满足中心波长相位匹配条件，并通过光学厚度近似方法求出相位匹配层厚度. 关键词： DBR 反射谱 反射相移 特征矩阵法     

Elliptic nanopores in deformed nanocrystalline and nanocomposite materials

A theoretical model is suggested which describes the nucleation of nanoscale pores (nanopores) of elliptic shape in deformed nanocrystalline and nanocomposite materials. In the framework of the model, elliptic nanopores in nanocrystalline and nanocomposite materials nucleate at interfaces in the stress fields of interfacial edge dislocations with large Burgers vectors. When elliptic nanopores nucleate, they remove the cores of interfacial dislocations. The stress field and energy of such dislocated elliptic nanopores are calculated, and their equilibrium sizes and shape parameters are revealed. It is theoretically shown that the elliptic shape of nanopores is due to the effects of interfaces (grain and interphase boundaries) on fracture processes at the nanoscale level.     

Photodetachment of H-- in an electric field between two parallel interfaces

By using the closed orbit theory, the photodetachment cross section of H- in a static electric field between two parallel elastic interfaces is derived and calculated. It is found that the photodetachment cross section depends on the electric field and the distance between the ion and the elastic interface. The oscillation of the cross section becomes more complicated than in the case of H- near one elastic interface. The results show that near the detachment threshold, the influence of the additional interface can be neglected. But with the increase of the energy, its influence becomes great. At some energies, the cross sections display sharp peaks, contrasting with the staircase structure when only one interface exists. This study provides a new understanding of the photodetachment process of H- in the presence of external field and interfaces.     

Dehydration process in NaCl solutions under various external electric fields

Ionic motions at solid-liquid interface in supersaturated NaCl solutions have been investigated by molecular dynamics (MD) simulation for understanding crystal growth processes. The density profile in the vicinity of the interfaces between NaCl(100) and the supersaturated NaCl solution was calculated. Diffusion coefficients of water molecules in the solution were estimated as a function of distance from the crystal interface. It turned out that the structure and dynamics of the solution in the interfaces was different from those of bulk solution owing to electric fields depending on the surface charge. Therefore, the electric field was applied to the supersaturated solutions and dehydration phenomenon occurring in the process of the crystal growth was discussed. As the electric field increased, it was observed that the Na⁺ keeping strongly hydration structure broke out by the electric force. In supersaturated concentration, the solution structure is significantly different from that of dilution and has a complicated structure with hydration ions and clusters of NaCl. If the electric fields were applied to the solutions, the breakout of hydration structure was not affected with increasing the supersaturated ratio. This reason is that the cluster structures are destroyed by the electric force. The situation depends on the electric field or crystal surface structure.     

The Interfacial Profile in Two-Loop Order

The profile of interfaces separating different phases of statistical systems is investigated in the framework of renormalized field theory. The profile function is calculated analytically in the local potential approximation, using the effective potential to two loops. It can be interpreted as an intrinsic interfacial profile. The loop corrections to the leading tanh-type term turn out to be small. They yield a broadening of the interface.