Z箍缩动态黑腔中泡沫柱的装配精度和误差源分析北大核心CSCD

为了提高Z箍缩动态黑腔中低密度泡沫柱的装配精度,基于辅助移动平台和视觉识别工艺的基础上,对低密度泡沫柱装配的误差源进行了分析与建模。建立设计、加工和装配误差源传递模型和低密度泡沫柱装配同轴度及轴向夹角精度预测模型,获得各误差源对低密度泡沫柱装配精度的影响大小和规律。最后采用某负载进行了模型的有效性验证,当泡沫柱粘接随机位置误差较小时,同轴误差预测值与实测值偏差为0.01-0.03mm,轴向夹角预测值与实测值偏差为0.05°-0.34°。实践表明,该方法可为低密度泡沫柱装配精度的预测和误差源控制提供一定的理论支撑。     

一种含横向圆柱形空腔的声学覆盖层的去耦机理分析

在水下结构表面敷设去耦覆盖层是降低其声辐射的有效途径. 为了深入分析一种含横向无限长空腔的覆盖层的去耦机理, 本文将其等效为均匀介质, 建立了敷设这种覆盖层的单向基体板在线激励下的声辐射模型, 验证了计算模型的有效性, 并利用计算模型对含横向空腔覆盖层的去耦机理进行了分析. 研究结果表明: 基体板-覆盖层接触面的能量流以纵波能量为主, 而横波能量很小, 因而计算覆盖层的去耦特性时可以忽略横波的作用; 和均匀覆盖层相比, 横向空腔型覆盖层在中高频段极大地增强了基体板的力阻抗, 从而更有效地抑制了基体板的振速; 此外, 和均匀覆盖层相比, 横向空腔型覆盖层和水的阻抗失配更大, 使其在中高频具有良好的振动传递损失特性. 因此, 总体而言, 含横向空腔的覆盖层相比均匀覆盖层具有更好的中高频去耦性能.     

The scattering of phonons of arbitrary wavelength at a solid-solid interface: Model calculation and applications

A one-dimensional lattice model of a solid-solid interface is presented within which it is possible to characterize the scattering of phonons at the interface as a function of wavelength. The probability for a phonon to be transmitted across the interface is found generally to decrease with decreasing wavelength, although phenomena such as total reflexion and resonant transmission may occur. Conditions for the existence of a localized interface mode are given. The thermal boundary resistance for heat flow across the interface is expressed in terms of an average temperature-dependent phonon transmission coefficient which generally increases with decreasing temperature and approaches the continuum value at very low temperature. Applications of these results to three-dimensional interfaces in general, and particularly to heat dissipation in catalysts, high-frequency phonon radiators, and Kapitza resistance, are discussed.     

Phoxonic crystals and cavity optomechanics

Phoxonic crystals are dual phononic/photonic crystals exhibiting simultaneously band gaps for both types of excitations. Therefore, they have the ability to confine phonons and photons in the same cavity and in turn allow the enhancement of their interaction. In this paper, we review some of our theoretical works on cavity optomechanical interactions in different types of phoxonic crystals, including two-dimensional, slab, and nanobeam structures. Two mechanisms are behind the phonon–photon interaction, namely the photoelastic and the moving interface effects. Coupling rates of a few MHz are obtained with high-frequency phonons of a few GHz. Finally, we give some preliminary results about the optomechanical interaction when a metallic nanoparticle is introduced into the cavity, giving rise to coupled photon–plasmon modes or, in the case of very small particles, to an enhancement of the electric field at the position of the particle.     

高层大气风场四强度测量法误差分析与计算

利用干涉成像光谱技术和电磁波的多普勒效应,通过测量高层大气(80—300km)中的气辉(极光)辐射线的四个干涉强度值而获知高层大气的速度和温度信息.采用四强度干涉测量法,分别对基于Michelson干涉仪的动镜扫描和基于无动镜四分区镀膜的干涉图获取模式所引起的测量误差进行了深入的理论分析与研究.给出了由于此测量误差所导致的相位误差所引起的高层大气风场速度、温度的误差数值;采用计算机模拟得出了在不同相位误差条件下,两种模式计算得到的风场速度和温度的误差分布图;给出了风速误差、温度误差与相位步进误差的关系曲线 关键词： 高层大气风场测量 四强度测量法 模拟计算     

多导体传输线高频场线耦合模型的研究综述

场线耦合模型的研究是电磁兼容分析和电磁效应评估的重要组成部分。低频时,可以使用基于准TEM波近似的经典场线耦合模型来计算外场激励下的传输线沿线电流电压响应,然而,当入射波频率增加到对应波长与传输线横向尺寸可比拟时,经典模型将产生不可接受的模型误差,因而需要发展高频情况下的场线耦合模型。介绍了国内外多导体传输线高频场线耦合模型的研究进展,详细分析和比较了两个主流分支:TRI模型和TLST模型;之后简要介绍了传输线超理论TLST模型并以算例说明了该模型的准确性和有效性;最后对高频场线耦合模型的研究内容和研究目标进行了总结和展望。     

On asymptotics of the solution of the moving oscillator problem

Asymptotic behavior of the solution of the moving oscillator problem is examined for large and small values of the spring stiffness for the general case of non-zero beam initial conditions. In the limiting case of infinite spring stiffness, it is shown that the moving oscillator problem for a simply supported beam is not equivalent, in a strict sense, to the moving mass problem. The two problems are shown to be equivalent in terms of the beam displacements but are not equivalent in terms of stresses (the higher order derivatives of the two solutions differ). In the general case, the force acting on the beam from the oscillator is shown to contain a high-frequency component , which does not vanish and can even grow when the spring coefficient tends to infinity. The magnitude of this force and its dependence on the oscillator parameters can be estimated by considering the asymptotics of the solution for the initial stage of the oscillator motion. It is shown that, for the case of a simply supported beam, the magnitude of the high-frequency force depends linearly on the oscillator eigenfrequency and velocity. The deficiency of the moving mass model is principally that it fails to predict stresses in the supporting structure. For small values of the spring stiffness, the moving oscillator problem is shown to be equivalent to the moving force problem. The discussion is amply illustrated by results of numerical experiments.     

Study of reflection and transmission on the moving interface of medium

The laws of refection and transimission on a moving interface between two nonvacuum medium are studied and the new method, which can be used for handling reflection and transimission on the moving interfaces between the vacuum-nonvacuum media and between two nonvacuum medium is suggested. The formula of reflection and transmission coefficients that suitable for both cases are derived. The present paper not only enriches electrodynamical theory, but also laies the foundation of optical waveguide modulators and other similar device.     

Effects of contact shape on ballistic phonon transport in semiconductor nanowires

We study the effects of contact shape on ballistic phonon transport in semiconductor nanowires at low temperatures using an approximative scalar model of continuum elasticity. Five different contacts connected to two semiconductor nanowires with different transverse widths are discussed. Numerical results show that the contact shape acts as an ‘acoustic impedance adaptor’, playing a crucial role on the ballistic phonon transmission and thermal conductance. The phonon coupling in the contacts with certain length facilitates ballistic phonon transmission compared to the abrupt interface, in which the phonon scattering is the strongest. It is found that the more the contact is abrupt, the smaller the thermal conductance is. The catenoidal contact rather than the abrupt interface is also the competitive candidate to obtain bigger thermal conductance. These results indicate that choosing an appropriate contact shape is one of the most critical factors to accurately measure the thermal conductance with a very high precision and reliability in different temperature ranges at low temperatures.     

Study of reflection and transmission on the moving interface of medium

The laws of refection and transimission on a moving interface between two nonvacuum medium are studied and the new method, which can be used for handling reflection and transimission on the moving interfaces between the vacuum-nonvacuum media and between two nonvacuum medium is suggested. The formula of reflection and transmission coefficients that suitable for both cases are derived. The present paper not only enriches electrodynamical theory, but also laies the foundation of optical waveguide modulators and other similar device.     

超声与固体中含气泡层的相互作用

本文利用固体层状媒质声反射模型,给出了固体中含气泡层声反射和透射系数的表达式,并由此导出沿固体中含气泡薄层对称和反对称模式界面波的特征方程式。本文还介绍了含气泡固体有效弹性模量的估算方法,文中给出的数值计算具体说明了气泡体积浓度和气泡层厚度对声反射系数、声透射系数以及反对称模式界面波传播速度的影响,本文的研究为根据声反射系数和界面波的传播速度的测量反演固体间气泡层的力学性能提供了理论依据。 关键词：     

Theory of extraordinary optical transmission through subwavelength hole arrays

We present a fully three-dimensional theoretical study of the extraordinary transmission of light through subwavelength hole arrays in optically thick metal films. Good agreement is obtained with experimental data. An analytical minimal model is also developed, which conclusively shows that the enhancement of transmission is due to tunneling through surface plasmons formed on each metal-dielectric interface. Different regimes of tunneling (resonant through a "surface plasmon molecule," or sequential through two isolated surface plasmons) are found depending on the geometrical parameters defining the system.     

太赫兹波大气传输衰减模型

基于修正的Van-Vleck Weisskopf线型、辐射传输色散理论和水汽连续体吸收模型,结合HITRAN数据库,建立了太赫兹波大气传输衰减模型——VVWH,形成了对宽频太赫兹波在真实大气中水平传输衰减的数值模拟能力。同时对太赫兹时域光谱技术(THz-TDS)获取的透射光谱实测数据进行了对比分析。计算结果与实验结果总体变化趋势一致,在吸收谱线处两者吻合良好,但在低频的大气窗口区,实验结果相比计算呈现出更强的传输衰减。考察了相对湿度对太赫兹波大气传输衰减特性的影响变化。     

用分形理论研究低温条件下Al-Al界面间的接触导热现象

界面形貌是固体界面间接触导热的最主要影响因素 ,传统的形貌表征参数与仪器的分辨率和取样长度密切相关 ,因而基于这些参数的常规接触导热模型显然是尺度相关的。分形网络模型利用粗糙表面处处连续却不可微的分形特征 ,采用与尺度无关的分形参数 ,揭示了接触导热的本质 ,为准确预测接触热导开辟了一条新的途径。实验测定了粗糙表面的分形参数和低温条件下 Al50 52 - Al50 52界面间的接触热导 ,将接触热导的实验值与分形网络模型的预测结果进行了比较 ,并就接触热导与压力、分形参数和温度之间的关系进行了分析 ,指出分形网络模型的预测精度与分形参数相关联。     

Capillary filling for multicomponent fluid using the pseudo-potential Lattice Boltzmann method

We present a systematic study of capillary filling for a binary fluid by using mesoscopic a lattice Boltzmann model describing a diffusive interface moving at a given contact angle with respect to the walls. We compare the numerical results at changing the ratio the typical size of the capillary, H, and the wettability of walls. Numerical results yield quantitative agreement with the theoretical Washburn law, provided that the channel height is sufficiently larger than the interface width and variations of the dynamic contact angle with the capillary number are taken into account.     

Theoretical study on the exciton dynamics of coherent excitation energy transfer in the phycoerythrin 545 light-harvesting complex

The experimental observation of long-lived quantum coherence in the excitation energy transfer(EET)process of the several photosynthetic light-harvesting complexes at low and room temperatures has aroused hot debate.It challenges the common perception in the field of complicated pigment molecular systems and evokes considerable theoretical efforts to seek reasonable explanations.In this work,we investigate the coherent exciton dynamics of the phycoerythrin 545(PE545)complex.We use the dissipation equation of motion to theoretically investigate the effect of the local pigment vibrations on the population transfer process.The result indicates that the realistic local pigment vibrations do assist the energy transmission.We demonstrate the coherence between different pigment molecules in the PE545 system is an essential ingredient in the EET process among various sites.The coherence makes the excitation energy delocalized,which leads to the redistribution of the excitation among all the chromophores in the steady state.Furthermore,we investigate the effects of the complex high-frequency spectral density function on the exciton dynamics and find that the high-frequency Brownian oscillator model contributes most to the exciton dynamic process.The discussions on the local pigment vibrations of the Brownian oscillator model suggest that the local heterogeneous protein environments and the effects of active vibration modes play a significant role in coherent energy transport.     

Capillary filling with pseudo-potential binary Lattice-Boltzmann model

We present a systematic study of capillary filling for a binary fluid by using a mesoscopic lattice Boltzmann model for immiscible fluids describing a diffusive interface moving at a given contact angle with respect to the walls. The phenomenological way to impose a given contact angle is analysed. Particular attention is given to the case of complete wetting, that is contact angle equal to zero. Numerical results yield quantitative agreement with the theoretical Washburn’s law, provided that the correct ratio of the dynamic viscosities between the two fluids is used. Finally, the presence of precursor films is experienced and it is shown that these films advance in time with a square-root law but with a different prefactor with respect to the bulk interface.     

大气环境下激光传输仿真软件的设计与编制

随着激光技术的发展,激光大气传输特性一直是激光领域的研究热点。综合激光大气传输的理论模型,运用科学的软件开发方法设计出了一套仿真系统,用来模拟激光在复杂大气环境中的辐射特性和激光的传输过程。该系统理论模型以Lambert-Beer定律为基础,结合了瑞利散射和米散射等经典理论,当在烟幕环境中模拟激光传输时,采用了多次散射模型。仿真中对大气环境采用逐段细化,每段根据数据库参数变化选取合适的计算模型,以提高仿真精度。绘制出了光斑和等位面随传输距离的演化图形,以演示激光大气的传输过程。     

Frictional vibration transmission from a laterally moving surface to a traveling beam

As the density of information stored in automated magnetic tape libraries continues to increase, greater requirements are placed on the precision of mechanical positioning in order to successfully read and write data bits. The location of the read/write head in the direction across the tape's width (termed the lateral direction) is actively controlled in order to maintain alignment between the head and data tracks, even in the presence of the tape's lateral vibration. However, during repositioning, vibration is undesirably transmitted from the laterally moving head structure to the axially moving tape because of frictional contact between the two adjacent surfaces. As an analog of that interaction, a model is developed here to describe frictional vibration transmission from a surface having prescribed lateral motion to a tensioned beam that travels and slides over it. For a transport speed that is high when compared to the lateral vibration velocity, Coulomb friction between the surface and the beam can be well-approximated by an equivalent form of viscous damping. The beam is divided into contiguous regions corresponding to free spans and the beam's portion that contacts the surface. A critical engagement length between the beam and the surface exists for which vibration transmission at a particular natural frequency can be substantially reduced, and for a given mode, that length depends weakly on the surface's position along the beam's span. By contouring the surface to have portions of differing radii of curvature, the extent of vibration transmission can be reduced over a broad range of frequency.     

Nonlinear surface polaritons in 2D electron system in high magnetic field

The paper deals with the theoretical investigation of nonlinear surface polaritons (NSP) in isolated two-dimensional electron system (2DES) arranged at the interface between linear and nonlinear media and placed into the external quantizing magnetic field directed perpendicularly to 2DES. We consider that nonlinear medium dielectric permeability depends upon the tangential component of electric field only. It is shown that under the integer quantum Hall effect conditions all NSP characteristics are represented by the quantized values. It is found that the NSP spectrum contains two NSP modes - high-frequency and low-frequency ones. It is shown that the NSP can exist only in the case where the value of tangential component of electric field at the interface is less than a certain critical value. It is found that the resonant interaction between the NSP high-frequency mode and surface polariton mode occurs in the vicinity of the cyclotron resonance subharmonic. Received 23 September 2001 / Received in final form 31 January 2002 Published online 2 October 2002 RID="a" ID="a"e-mail: bludov@ire.kharkov.ua