Diffraction of electromagnetic waves by a multielement diffraction grating

A rigorously posed electrodynamical problem of diffraction of a plane wave by a multielement diffraction grating that consists of cylindrical screens with arbitrary curvature is solved by the method of integral equations. We construct an integral representation of the Green function of the problem under consideration which gives a significant increase in the accuracy of calculations and investigate the phenomenon of resonance propagation of an electromagnetic wave along the axis of a two-layer grating irradiated with aE-polarized wave which propagates along the normal to the grating.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 31, No. 2, pp. 87–98, March – April, 1995.     

Diffraction of electromagnetic waves by periodic arrays of rectangular cylinders

Reflection, transmission, and absorption of electromagnetic waves by periodic arrays of conducting or dielectric rectangular cylinders are studied by a finite-difference time-domain technique. Truncated gratings made of lossless and lossy conducting and dielectric elements are considered. Results for surface current density, transmission, and reflection coefficients are calculated and compared with corresponding results in the literature, which are obtained by approximate or rigorous methods applicable only to idealized infinite models. An excellent agreement is observed in all cases, which demonstrates the accuracy and efficacy of our proposed analysis technique. Additionally, this numerical method easily analyzes practical gratings that contain a finite number of elements made of lossless, lossy, or even inhomogeneous materials. The results rapidly approach those for the idealized infinite arrays as the number of elements is increased. The method can also solve nested gratings, stacked gratings, and holographic gratings with little analytical or computational effort.     

Improved algorithm for electromagnetic scattering of plane waves and shaped beams by multilayered spheres

An efficient numerical procedure for computing the scattering coefficients of a multilayered sphere is discussed. The stability of the numerical scheme allows us to extend the feasible range of computations, both in size parameter and in number of layers for a given size, by several orders of magnitude with respect to previously published algorithms. Exemplifying results, such as scattering diagrams and cross-sectional curves, including the case of Gaussian beam illumination, are provided. Particular attention is paid to scattering at the rainbow angle for which approaches based on geometrical optics might fail to provide accurate enough results.     

Multiple scattering of electromagnetic waves by an aggregate of uniaxial anisotropic spheres

An exact analytical solution is obtained for the scattering of electromagnetic waves from a plane wave with arbitrary directions of propagation and polarization by an aggregate of interacting homogeneous uniaxial anisotropic spheres with parallel primary optical axes. The expansion coefficients of a plane wave with arbitrary directions of propagation and polarization, for both TM and TE modes, are derived in terms of spherical vector wave functions. The effects of the incident angle α and the polarization angle β on the radar cross sections (RCSs) of several types of collective uniaxial anisotropic spheres are numerically analyzed in detail. The characteristics of the forward and backward RCSs in relation to the incident wavelength are also numerically studied. Selected results on the forward and backward RCSs of several types of square arrays of SiO? spheres illuminated by a plane wave with different incident angles are described. The accuracy of the expansion coefficients of the incident fields is verified by comparing them with the results obtained from references when the plane wave is degenerated to a z-propagating and x- or y-polarized plane wave. The validity of the theory is also confirmed by comparing the numerical results with those provided by a CST simulation.     

Diffraction of anti-plane shear waves by two moving griffith cracks

The problem of diffraction of anti-plane shear waves by two running Griffith cracks of finite length is investigated by using the Fourier transform method. The mixed boundary value problem is reduced to a pair of triple integral equations having trigonometrical kernels. Using the finite Hilbert transform technique, a solution of the pair of triple integral equations is obtained for the small wave number. Approximate formulae are derived for the stress intensity factors. Numerical results for the stress intensity factors are displayed vs wave number for different crack lengths, velocities and angles of incidence.     

Diffraction of shear waves on cylindrical inclusions and cavities in an elastic half space

Dynamic problems of the steady-state oscillations of a half space with different types of cylindrical homogeneities (cavities, rigid and stiff inclusions) are examined. The boundary of the half space is assumed to be fixed or free of forces. A harmonic shear wave radiating from infinity or a concentrated harmonic source may be radiators of the exciting wave field. Integral representations of displacement amplitudes, which automatically satisfy fixity conditions on the boundary of the half space and radiation conditions at infinity are constructed. The edge problems are reduced to Fredholm integral equations of the second kind and to singular integral equations. Selection of additional conditions for the latter is substantiated. Some computer-generated results are presented.Translated from Problemy Prochnosti, No. 11, pp. 90–94, November, 1990.     

Boundary element method calculation for coherent electromagnetic scattering from two and three dielectric spheres

A quadratic, isoparametric boundary element formulation has been used to calculate the multiple scattering of electromagnetic waves from systems of two and three dielectric spheres. Extinction efficiency results for the scattering of a plane wave are presented for variations of the separation of the two spheres in three kinds of orientations of the system with respect to the incident wave. These have been verified against analytical calculations based on Mie's theory and calculations by other authors. The results demonstrate a large side scattering resonance (the so-called specular resonance). Agreement between the results establishes the boundary element method as a very powerful tool for solving multiple scattering problems because the method applies to arbitrarily shaped objects having a homogeneous dielectric constant in any configuration. To illustrate the versatility of the method, scattering from three spheres is calculated.     

航天器结构虚拟动态试验技术新进展

随着航天器结构越来越复杂,仅仅用数值分析方法或者仅仅用实尺动态试验方法都不能解决现代航天器结构动力学问题,为了解决这一问题必须采用航天器结构虚拟动态试验技术.其一是虚拟模态试验技术.提出了适用于航天器复杂结构模型修改的子结构试验建模综合技术;介绍了两个实例证明本文介绍的虚拟模态试验技术应用的可靠性:一是CZ-2E运载火箭虚拟模态试验技术,用建议的虚拟模态试验技术成功地预示了CZ-2E运载火箭模态参数.预示的模态参数与随后进行的全箭模态参数一致;另一个是CZ-2F运载火箭虚拟模态试验技术,给出可靠的数学模型与箭船耦合的动态分析数据.其二是虚拟振动试验技术.介绍了振动台虚拟振动试验系统和一个卫星振动台虚拟振动试验实例.卫星振动台虚拟振动试验结果低频响应曲线与试验结果曲线非常一致.     

Application of infra-red surface electromagnetic waves on metals in nondestructive surface testing

The elementary theory of surface electromagnetic waves (SEW), based on a local relation between the induced current density and electric field, is discussed. Based on this theory, typical values of propagation lengths and penetration depths are calculated in the infra-red and visible regions. Experiments using a double-prism configuration have been performed to demonstrate the relative coupling efficiency as a function of prism-gap height and angle of incidence, respectively, for infra-red SEWs. Approximate calculations of propagation lengths for infra-red SEWs on rough surfaces are presented.     

Diffraction of elastic waves by two coplanar Griffith cracks in an infinite transversely-isotropic medium

Summary The problem of diffraction of normally incident longitudinal waves by two parallel and coplanar Griffith cracks embedded in an infinite transversely-isotropic medium is considered. Approximate formulas are derived for stress intensity factors when the wave lengths are large compared, to the distance between the outer edges of the two cracks By taking appropriate limits we derive various interesting and new results.     

Probability of infancy problems for space launch vehicles

This paper addresses the treatment of ‘infancy problems’ in the reliability analysis of space launch systems. To that effect, we analyze the probability of failure of launch vehicles in their first five launches. We present methods and results based on a combination of Bayesian probability and frequentist statistics designed to estimate the system's reliability before the realization of a large number of launches. We show that while both approaches are beneficial, the Bayesian method is particularly useful when the experience base is small (i.e. for a new rocket). We define reliability as the probability of success based on a binary failure/no failure event. We conclude that the mean failure rates appear to be higher in the first and second flights (≈1/3 and 1/4, respectively) than in subsequent ones (third, fourth and fifth), and Bayesian methods do suggest that there is indeed some difference in launch risk over the first five launches. Yet, based on a classical frequentist analysis, we find that for these first few flights, the differences in the mean failure rates over successive launches or over successive generations of vehicles, are not statistically significant (i.e. do not meet a 95% confidence level). This is true because the frequentist analysis is based on a fixed confidence level (here: 95%), whereas the Bayesian one allows more flexibility in the conclusions based on a full probability density distribution of the failure rate and therefore, permits better interpretation of the information contained in a small sample. The approach also gives more insight into the considerable uncertainty in failure rate estimates based on small sample sizes.     

Generation of electromagnetic waves by electrons rotating in a radial electrostatic field in free space

A theoretical analysis is made of mechanisms for the generation of electromagnetic waves by electrons rotating in a radial electrostatic field formed by a positively charged filament in free space. A dispersion equation is obtained to describe the interaction between the waves and nonrelativistic electrons. It is shown that electromagnetic fields can be generated by means of Čerenkov resonance. The frequencies and growth rates of the emitted waves are determined and their dependence on the parameters of the problem is investigated. Pis’ma Zh. Tekh. Fiz. 25, 1–4 (November 12, 1999)     

电磁耦合混合动力公交车发动机运行点控制的仿真研究

设计了公交车用电磁耦合双电机(发电机 电动机)混合动力方案,以期在保证功能的同时解决现有方案造价过高的问题.提出了一种基于电磁耦合系统效率最优化的新的发动机运行点控制策略(NECS),以期提高发动机的燃油经济性.利用在Matlab/Simulink/Stateflow环境下构建的电磁耦合混合动力公交车仿真模型,以上海公交车循环工况作为仿真工况,对NECS进行了仿真验证.结果表明,与传统策略相比,该策略的燃油经济性提高了5.6%.     

衍射微透镜在红外单元探测器中的应用

研究了衍射微透镜提高红外探测器探测能力的方法,通过实验将衍射微透镜耦合到红外单元探测器上,使语组合件的响应度提高到３．２倍、比探测率提高到４．２倍。结果表明：采用微透镜作光聚能器后,探测器光敏面面积可减少而光能利用率增加,探测性能提高。衍射微秀镜的结构小,有利于与探测器集成,其研究极具实用价值。     

Introduction. Progress in astronomy: from gravitational waves to space weather

This brief paper introduces and reviews the 'visions of the future' articles prepared by leading young scientists throughout the world for the first of two Christmas 2008 Triennial issues of Phil. Trans. R. Soc. A, devoted, respectively, to astronomy and Earth science. Contributions in astronomy include the very topical gamma-ray bursts, new ideas on stellar collapse and the unusual atmospheres of synchronized planets orbiting nearby stars.     

遥测技术在机动车排气检测中的应用研究

针对机动车保有量快速增长而传统排气监测效果与实际路况排放差异大、检测效率低、社会经济成本高等现状,探讨机动车排气遥测技术的优点,并以实际道路测试数据为例分析筛选高排车、比功率分布区间等实际应用问题。结果表明:遥测技术适用于机动车排气监测技术,对筛选高排车尤其出色。     

Diffraction of torsional waves by a flat annular crack at the interface of two bonded dissimilar elastic solids

The paper deals with the problem of finding the stress distribution near an annular crack located at the interface of two bonded dissimilar elastic solids. The crack is opened by the interaction of a torsional wave incident normally on the annular crack. The problem is reduced to the solution of three simultaneous Fredholm integral equations. The numerical solution of these simultaneous integral equations has been obtained. The solution is used to calculate the stress-intensity factors at the tips of the crack.     

Application of neural networks to the inverse light scattering problem for spheres

A new approach suitable for solving inverse problems in multiangle light scattering is presented. The method takes advantage of multidimensional function approximation capability of radial basis function neural networks. An algorithm for training the networks is described in detail. It is shown that the radius and refractive index of homogeneous spheres can be recovered accurately and quickly, with maximum relative errors of the order of 10(-3) and mean errors as low as 10(-5). The influence of the angular range of available scattering data on the loss of information and inversion accuracy is investigated, and it is shown that more than two thirds of input data can be removed before substantial degradation of accuracy occurs.     

双缝衍射用于CCD响应特性标定的模拟研究

输入输出响应特性是CCD应用中一项重要参数,标定一参数的方法很多。介绍一种新的标定方法－双缝衍射法,即利用双缝衍射图像各亮条纹的衰减关系来产生不同的CCD能量的输入,从而标定CCD的响应。给出了模拟结果。